Recycled aggregate concrete acoustic barrier · RECYCLED AGGREGATE CONCRETE ACOUSTIC BARRIER Zbigniew Adam Krezel Thesis submitted in partial fulfillment of the requirements for the

RECYCLED AGGREGATE CONCRETE ACOUSTIC BARRIER

Zbigniew Adam Krezel

Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Civil Engineering

Swinburne University of Technology Melbourne Australia

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EXECUTIVE SUMMARY This document reports on a research project aimed at developing a concrete acoustic barrier

made from Recycled Aggregate (RA) Concrete. The research project was undertaken in

response to the needs expressed by the Victorian concrete recycling industry. The industry,

the scientific community conducting research into relevant disciplines, and the community

at large, represented by Victorian government agencies, are of the opinion that there is a

need to devise a higher value utilisation application for selected concrete recycling

products.

This document outlines the rationale and objectives of the research project which involves

the examination of Recycled Concrete (RC) Aggregate, the design and examination of RA

Concrete, and finally the development of an acoustic barrier made from RA Concrete.

The literature review presented in this report examines aspects of concrete recycling and

concrete technology pertaining to traditional and alternative constituent materials for

concrete production. Firstly, the importance and influence of fine and coarse aggregate on

basic properties of concrete is introduced. Secondly, an account on the use of alternative

materials in concrete technology, especially of coarse recycled aggregates and

supplementary cementitious materials (SCM) is described. Thirdly, some of the physical

and mechanical properties and how the use of RC Aggregate and SCM changes these

properties are discussed. Fourthly, a number of commonly used techniques and neutron

scattering techniques to investigate aggregate and concrete properties are introduced and

discussed. Fifthly, the porosity of aggregate and concrete including durability are

specifically discussed and testing methods are reasoned. The literature review also

discusses the use of no-fines concrete; its physical, mechanical and acoustic properties.

Finally it presents an account of the use of concrete in transportation traffic noise

attenuation devices.

This document continues with an outline of a methodology that was adopted in this

research project. It outlines experimental work aimed at examining the properties of RC

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Aggregate which amongst other properties includes porosity, particle size distribution,

water absorption, shape and density. It continues examining RA Concrete properties and

includes, among other properties, compressive strength, porosity and durability as well as

sound absorption of acoustic barrier. The methodology introduces standard and purposely

modified test procedures used in the examination of aggregates, concrete and acoustic

barrier. An account of various research techniques is presented, spanning from simple

visual observations to more sophisticated neutron scattering techniques. The summary of

test procedures follows a description of test specimen composition and their sizes, and a

suite of tested specimens. It also introduces statistical methods used to analyse test results.

After a detailed description of the aggregate, concrete and RA Concrete acoustic barrier,

the document outlines a summary of data generated through the experimental program of

this research project. The data on fine aggregate, on selected 14/10mm coarse RC

Aggregate, on concrete made from natural and recycled aggregate and on acoustic barrier

are presented and discussed. Test results of various physical, mechanical and acoustic

properties of aggregate, concrete and barrier are reported, analysed and discussed. The data

from observations, visual assessment and scientific experimentation of specific properties

are then crossed analysed in a search for relationships between properties of fine and coarse

aggregates and properties of concrete made from such aggregates. A cross analysis of data

on ‘less-fines’ RA Concrete and on the acoustic performance of barrier is examined, and

the relationship between the volume of interconnected voids in a porous part of ‘less-fines’

concrete, and the sound absorption of acoustic barrier is discussed and reported.

The document then presents a synthesis of the literature review results, project aims

adopted within the experimental program and test results in the three main areas of this

research project. These areas include recycled concrete aggregate, recycled aggregate

concrete and acoustic barrier made from RA Concrete.

Finally, conclusions reached through the course of this investigation are summarised and

recommendations are proposed in relation to the RA Concrete acoustic barrier. The main

conclusion is that selected RC Aggregate can be used in the production of concrete of a

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compressive strength of 25MPa, if the moisture content and water absorption in the

aggregate are closely monitored, and the foreign material content is kept below 1.5%. The

author concludes that acoustic barrier made from selected RC Aggregate has unique sound

absorption characteristics that can easily be tunable by a selection of appropriate aggregate

and by specific concrete mix designs. Recommendations for further research are also

proposed.

ACKNOWLEDGEMENTS

The author wishes to express his gratitude and appreciation to Associate Professor Kerry

McManus, AM for his guidance and support.

The author would like to thank the Australian Institute of Nuclear Science and Engineering

(AINSE) for the grant that enabled the use of the Australian Nuclear Science and

Technology Organisation (ANSTO) research facilities at Lucas Heights. The author would

also like to express his gratitude to: Ecorecycle Victoria for the market development grant

which has allowed this research project to be undertaken; Recycling Industries Pty Ltd, for

supplying the aggregate and covering some of the testing costs; Westkon Precast Concrete

Pty Ltd, for manufacturing and transportation of the barrier panels; and Boral Resources

(Vic) Pty Ltd, for supplying of ready-mixed RA Concrete.

The author would like to acknowledge the help he received in conducting some tests, and

the discussions and advice of many engineering professionals and scientists from various

institutions including; ANSTO, AINSE, Commonwealth Scientific and Research

Organisation (CSIRO), RMIT University, Ecorecycle Victoria, VicRoads, Recycling

Industries Pty Ltd, Hollow Core Concrete Pty Ltd, Unicrete Concrete Pty Ltd, Westkon

Precast Concrete Pty Ltd, Boral Concrete Laboratories Pty Ltd, Graeme Harding and

Associates Pty Ltd, and Swinburne University of Technology. The author would like to

thank in particular, David Bell, David Lewis, Hans Brinkies, Dr Robert Knot, Dr Laurie

Aldridge, Peter Dale, Peter Southorn, and Mario Tabone.

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The author would also like to acknowledge the occasional assistance of many

undergraduate and postgraduate civil engineering students from the Faculty of Engineering

and Industrial Sciences at Swinburne University of Technology, in the sampling and testing

of aggregate, making and testing of concrete, and assistance in manufacturing a prototype

and commercially produced RA Concrete acoustic barrier.

But most of all I would like to thank my wife Joanna and my daughters Patricia and

Stephanie for their support.

DECLARATION

• The thesis contains no material which has been accepted for the award of any other

degree or diploma;

• To the best of my knowledge this thesis contains no material previously published or

written by another person except where due reference is made in the text of the thesis;

and

• Where the work is based on joint research or publications, disclosures of the relative

contributions of the relative workers or authors are made.

Zbigniew Adam Krezel

Table of Contents ABSTRACT ………………………………………………...……………………….ii - v List of FIGURES List of TABLES CHAPTER 1 - INTRODUCTION..............................................................................1-1

1.1 IMPORTANCE of the WORK ......................................................................1-31.2 RELEVANCE to OTHER RESEARCH .......................................................1-41.3 HYPOTHESIS and OBJECTIVES................................................................1-61.4 PROJECT OUTLINE ....................................................................................1-71.5 PROJECT AIMS............................................................................................1-8

CHAPTER 2 – LITERATURE REVIEW.................................................................2-1

2.1 INTRODUCTION .........................................................................................2-12.2 CONCRETE CONSTITUENT MATERIALS..............................................2-2

2.2.1 Coarse Aggregate...................................................................................2-42.3 ALTERNATIVE CONSTITUENT MATERIALS in CONCRETE .............2-62.4 CONCRETE WASTE and CONCRETE RECYCLING...............................2-9

2.4.1 Alternative Sources of Coarse Aggregate............................................2-102.4.2 Current Applications for Recycled Concrete Products ........................2-132.4.3 Under-utilisation of Recycled Concrete Aggregate.............................2-13

2.5 COMPARISON between NATURAL and RECYCLED CONCRETE AGGREGATE .........................................................................................................2-15

2.5.1 Shape and Surface Texture ..................................................................2-162.5.2 Particle Size Distribution .....................................................................2-172.5.3 Water Absorption.................................................................................2-202.5.4 Particle Density and Bulk Density.......................................................2-212.5.5 Impurities and Foreign Materials in RC Aggregate.............................2-222.5.6 Aggregate Porosity...............................................................................2-232.5.7 Other Properties ...................................................................................2-24

2.6 NORMAL DENSITY and NO-FINES CONCRETE..................................2-242.7 COMPARISON between STANDARD and RECYCLED AGGREGATE (RA) CONCRETE ...................................................................................................2-27

2.7.1 Physical and Mechanical Properties ....................................................2-272.7.2 Acoustic Properties ..............................................................................2-322.7.3 Porosity and Fractal Dimensions .........................................................2-33

2.8 USE of CONVENTIONAL and NEUTRON SCATTERING TECHNIQUES in TESTING of CONCRETE PROPERTIES..........................................................2-38

2.8.1 Conventional Techniques.....................................................................2-402.8.2 Small Angle Neutron Scattering ..........................................................2-47

2.9 USE of CONCRETE in ACOUSTIC BARRIERS......................................2-502.9.1 Road Traffic Noise and Noise Mitigation Methods.............................2-502.9.2 Sound Absorbing Barriers....................................................................2-52

2.10 SUMMARY.................................................................................................2-58

CHAPTER 3 – METHODOLOGY and EXPERIMENTAL DESIGN ..................3-1

3.1 INTRODUCTION .........................................................................................3-13.2 EXPERIMENTAL and DEVELOPMENTAL PROGRAM - OVERVIEW.3-33.3 FINE AGGREGATE ...................................................................................3-12

3.3.1 Particle Size Distribution .....................................................................3-133.4 NATURAL (N) COARSE AGGREGATE..................................................3-13

3.4.1 Particle Size Distribution .....................................................................3-143.4.2 Elemental Composition........................................................................3-14

3.5 RECYCLED CONCRETE (RC) AGGREGATE........................................3-143.5.1 Cement Paste Residue (cpr) Content ...................................................3-153.5.2 Impurities and Foreign Materials Content ...........................................3-163.5.3 Cement Content in RC Aggregate Fines..............................................3-173.5.4 Microstructure and Elemental Composition ........................................3-183.5.5 Particle Density....................................................................................3-193.5.6 Bulk Density ........................................................................................3-193.5.7 Particle Size Distribution .....................................................................3-203.5.8 Water Absorption.................................................................................3-203.5.9 BET Porosity........................................................................................3-203.5.10 SANS Porosity.....................................................................................3-21

3.6 NATURAL AGGREGATE (NA) CONCRETE .........................................3-223.6.1 Workability and Consistency...............................................................3-233.6.2 Compressive Strength ..........................................................................3-233.6.3 Mass per Volume .................................................................................3-233.6.4 Apparent Volume of Permeable Voids ................................................3-243.6.5 Water Absorption.................................................................................3-243.6.6 BET Porosity........................................................................................3-243.6.7 SANS Porosity.....................................................................................3-253.6.8 Interconnected Air Void Content in No-Fines NA Concrete...............3-25

3.7 RECYCLED AGGREGATE (RA) CONCRETE........................................3-263.7.1 Workability and Consistency...............................................................3-263.7.2 Microstructure Development ...............................................................3-273.7.3 Mass per Volume .................................................................................3-273.7.4 Compressive Strength ..........................................................................3-283.7.5 Apparent Volume of Permeable Voids ................................................3-283.7.6 BET Porosity........................................................................................3-293.7.7 SANS Porosity.....................................................................................3-293.7.8 Fractal Mass .........................................................................................3-323.7.9 Interconnected Air Void Content in No-Fines RA Concrete...............3-33

3.8 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE .......................3-333.8.1 Interconnected Air Void Content.........................................................3-343.8.2 Sound Absorption – Impedance Tube Method ....................................3-34

3.9 PROTOTYPE and COMMERCIALLY PRODUCED BARRIER .............3-353.9.1 Sound Absorption – Reverberation Room Method .............................3-35

3.10 CONCRETE MIX DESIGN........................................................................3-373.11 PROTOTYPE BARRIER DESIGN ............................................................3-373.12 LIMITATIONS and OMISSIONS ..............................................................3-383.13 SUMMARY.................................................................................................3-39

CHAPTER 4 – RESULTS and DISCUSSION..........................................................4-1

4.1 INTRODUCTION .........................................................................................4-14.2 METHODS of ANALYSIS ...........................................................................4-2

4.3 FINE AGGREGATE ..................................................................................4.3-14.3.1 Introduction.........................................................................................4.3-14.3.2 Particle Size Distribution and Fineness Modulus ...............................4.3-14.3.3 Discussion of the Results ....................................................................4.3-6

4.4 RECYCLED CONCRETE (RC) AGGREGATE.......................................4.4-14.4.1 Introduction.........................................................................................4.4-14.4.2 Composition – Cement Paste Residue Content ..................................4.4-24.4.3 Content of Physical Contaminants......................................................4.4-54.4.4 Cement Content and Elemental Composition Aggregate Fines .......4.4-114.4.5 Particle Density.................................................................................4.4-194.4.6 Bulk Density .....................................................................................4.4-234.4.7 Particle Size Distribution ..................................................................4.4-244.4.8 Water Absorption..............................................................................4.4-274.4.9 Porosity .............................................................................................4.4-294.4.10 Discussion of the Results ..................................................................4.4-44

4.5 RECYCLED AGGREGATE (RA) CONCRETE.......................................4.5-14.5.1 Introduction.........................................................................................4.5-14.5.2 Microstructure Development ..............................................................4.5-24.5.3 Mass per Volume ................................................................................4.5-84.5.4 Compressive Strength .......................................................................4.5-104.5.5 Water Absorption..............................................................................4.5-114.5.6 Apparent Volume of Permeable Voids (VPV) .................................4.5-124.5.7 Porosity .............................................................................................4.5-144.5.8 Fractal Dimensions ...........................................................................4.5-274.5.9 No-fines Recycled Aggregate Concrete............................................4.5-294.5.10 Discussion of the Results ..................................................................4.5-31

4.6 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE ......................4.6-14.6.1 Introduction.........................................................................................4.6-14.6.2 Porosity and Interconnected Air Voids...............................................4.6-24.6.3 Sound Absorption ...............................................................................4.6-34.6.4 Discussion of the Results ....................................................................4.6-7

4.7 PROTOTYPE BARRIER ...........................................................................4.7-14.7.1 Introduction.........................................................................................4.7-14.7.2 Laboratory prototype ..........................................................................4.7-14.7.3 Commercial prototype ........................................................................4.7-74.7.2 Summary and Discussion..................................................................4.7-144.7.3 Discussion of the Results ..................................................................4.7-18

4.8 DISCUSSION OF THE RESULTS............................................................4.8-1

CHAPTER 5 - SUMMARY, CONCLUSIONS and RECOMMENDATIONS......5-1

5.1 SUMMARY...................................................................................................5-15.2 CONCLUSIONS............................................................................................5-35.3 RECOMMENDATIONS...............................................................................5-4

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List of FIGURES Figure 1.1 Project major stages......................................................................................1-7Figure 1.2 Detailed outline of the project major stages .................................................1-7 Figure 2.1 Concrete recycling plant setup (courtesy Recycling Industries Pty. Ltd.) .2-12Figure 2.2 Schematic representation of aggregate grading in an assembly of aggregate

particles: (a) uniform size, (b) continuous grading, (c) replacement of small sizes by large sizes, (d) gap-graded aggregate, (e) no-fines grading (Mindess, 1981).2-19

Table 2.9 Porosity a 15-year-in-service concrete (Eighmy, 2003) ..............................2-35Table 2.10 Porosity of neat cement paste (Hansen, 1987)...........................................2-36Table 2.12 Porosity of hardened cement paste with added various elements contained in

concrete waste (Chandra, 1997)...........................................................................2-38Figure 2.3 Six types of adsorption isotherms (Gregg, 1982).......................................2-42Figure 2.4 Adsorption and desorption isotherms for a porous solid (Gregg, 1982) ....2-42Figure 2.5 Adsorption and desorption isotherms for a solid with limited pore size

(Gregg, 1982).......................................................................................................2-43Figure 2.6 Type A hysteresis loop and possible pore structures (Thomas, 1997) .......2-43Figure 2.7 Type B hysteresis loop and possible pore structures (Thomas, 1997) .......2-44Figure 2.8 Type C hysteresis loop and possible pore structures (Thomas, 1997) .......2-44Figure 2.9 Noise spectra for heavy and light vehicles traffic (Nelson, 1987) .............2-51Figure 2.10 Cross-section of typical absorptive-type barrier (GRC, 1990).................2-53Figure 2.11 Granular concrete barrier (Kotzen, 1999) ................................................2-54 Figure 4.3.1 Apparent VPV of N40 Concrete and FM of fine aggregate...................4.3-3Figure 4.3.2 Apparent VPV of N25 Concrete and FM of fine aggregate...................4.3-4Figure 4.3.3 Apparent VPV in bottom layer of N40 Concrete ...................................4.3-5Figure 4.3.4 Apparent VPV in bottom layer of N25 Concrete ...................................4.3-5Figure 4.3.5 Comparison between apparent VPV in N25 and N40 Concrete ............4.3-7

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Figure 4.4.1 Stockpile of RC Aggregate.....................................................................4.4-1Figure 4.4.2 Particles of RC Aggregate (A – cement paste residue only, B and C –

natural aggregate coated with cpr) ......................................................................4.4-3Figure 4.4.3 Relative composition of 14/10mm RC Aggregate (sample

RCA_11_00_s1&s2)...........................................................................................4.4-3Figure 4.4.4 Composition of 14/10mm RC Aggregate (after additional segregation)4.4-4Figure 4.4.5 Sample of 14/10mm RC Aggregate with segregated foreign materials .4.4-5Figure 4.4.6 Average content of foreign materials in 14/10mm RC Aggregate.........4.4-6Figure 4.4.7 Average content of low density (<1,000kg/m3) particles in 14/10mm RC

Aggregate............................................................................................................4.4-7Figure 4.4.8 Average number of foreign materials in 14/10mm RC Aggregate ........4.4-8Figure 4.4.9 Occurrence frequency of foreign materials in 14/10mm RC Aggregate4.4-9Figure 4.4.10 Average weight [g] of various foreign materials per typical, 4kg samples

of 14/10mm RC Aggregate.................................................................................4.4-9Figure 4.4.11 Examples of foreign materials in 14/10mm RC Aggregate ...............4.4-10Figure 4.4.12 Foreign materials in 14/10mm RC Aggregate....................................4.4-11Figure 4.4.13 Equivalent GB cement content in 14/10mm RC Aggregate ..............4.4-12Figure 4.4.14 Powder samples of RA Concrete – SEM examination.......................4.4-13Figure 4.4.15 BSE image of RC Aggregate fines.....................................................4.4-14Figure 4.4.16 ED X-ray analysis of RC Aggregate fines .........................................4.4-14Figure 4.4.17 BSE image of natural aggregate (basalt) fines ...................................4.4-15Figure 4.4.18 ED X-ray analysis of natural aggregate (basalt) fines........................4.4-16Figure 4.4.19 BSE image of GB cement...................................................................4.4-17Figure 4.4.20 ED X-ray analysis of GB cement .......................................................4.4-17Figure 4.4.21 BSE image of cement paste residue ...................................................4.4-18Figure 4.5.22 Elemental composition of natural and 14/10mm RC Aggregates -

summary............................................................................................................4.4-18Figure 4.4.23 Saturated surface dry density of 14/10mm RC Aggregate.................4.4-19Figure 4.4.24 Relationship between cpr content and saturated surface dry density of

14/10mm RC Aggregate ...................................................................................4.4-20Figure 4.4.25 Dry particle density of 14/10mm RC Aggregate................................4.4-20Figure 4.4.26 Relationship between cpr content and dry particle density in 14/10mm RC

Aggregate..........................................................................................................4.4-21Figure 4.4.27 Relationship between cpr content and apparent density in 14/10mm RC

Aggregate..........................................................................................................4.4-22Figure 4.4.28 Bulk density of the 14/10mm natural and RC Aggregates.................4.4-24Figure 4.4.29 Particles of 14/10mm RC Aggregate retained on 13.2mm, 9.5mm, 6.7mm,

4.75mm, 2.36mm and 75μm sieves (from right to left)...................................4.4-25Figure 4.4.30 Particle size distribution of 14/10mm RC Aggregate – average of 1999 –

2003 samples.....................................................................................................4.4-26Figure 4.4.31 Comparison of particle size distribution of natural aggregate and

14/10mm RC Aggregate ...................................................................................4.4-27Figure 4.4.32 Water absorption of 14/10mm RC Aggregate measured by the weigh-in-

water method.....................................................................................................4.4-28Figure 4.4.33 Relationship between cement paste residue (cpr) content and water

absorption in 14/10mm RC Aggregate .............................................................4.4-29Figure 4.4.34 Example of powder (<150μm) samples of neat cement pastes of various

cement/water ratios (0.2w/c, 0.4w/c and 0.8w/c) .............................................4.4-30Figure 4.4.35 Example of solid sample of cement paste residue of RC Aggregate

obtained from concrete of known w/c ration of 0.4..........................................4.4-30

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Figure 4.5.1 Sample of RA Concrete..........................................................................4.5-2Figure 4.5.2 Carbon coated samples of RA Concrete– SEM examination.................4.5-2Figure 4.5.3 BSE image of RA Concrete....................................................................4.5-3Figure 4.5.4 Example of semi-quantitative ED X-ray analysis of RA Concrete........4.5-4Figure 4.5.5 Interface zone in RA Concrete ...............................................................4.5-5Figure 4.5.6 BSE image of microcracks in the interface zone in RA Concrete .........4.5-6Figure 4.5.7 BSE image microcracks in the interface zone in RA Concrete..............4.5-7Figure 4.5.8 BSE image microcracks in the interface zone in RA Concrete and in the cpr

of RC Aggregate .................................................................................................4.5-7Figure 4.5.9 Apparent specific gravity of RA25 Concrete .........................................4.5-9Figure 4.5.10 Mass per volume of RA25 Concrete ....................................................4.5-9Figure 4.5.11 Compressive strength of RA25 Concrete ...........................................4.5-11Figure 4.5.12 Water absorption of RA25 Concrete after immersion (72h) ..............4.5-12Figure 4.5.13 Samples of RA25 Concrete – VPV investigation...............................4.5-13Figure 4.5.14 Apparent volume of permeable voids in RA25 Concrete ..................4.5-13Figure 4.5.15 BET total pore volume of RA Concrete (old cpr+na & na+old cpr)..4.5-15Figure 4.5.16 BET micropores total volume of RA Concrete (old cpr+na & na+old cpr)

...........................................................................................................................4.5-16Figure 4.5.17 BET micropore surface area of RA Concrete (old cpr+na & na+old cpr)16Figure 4.5.18 BET total pore surface area of RA Concrete (old cpr+na & na+old cpr) 17Figure 4.5.19 BET average pore diameter of pores in RA Concrete (old cpr+na &

na+old cpr) ........................................................................................................4.5-18Figure 4.5.20 Powder sample used in SANS examination .......................................4.5-19Figure 4.5.21 Solid samples used in SANS examination .........................................4.5-19Figure 4.5.22 SANS samples (2001), porosity accessible to H2O............................4.5-20Figure 4.5.23 SANS samples (2001), porosity accessible to D2O............................4.5-20Figure 4.5.24 SANS samples (2001), porosity accessible to 50%H2O & 50% D2O 4.5-21Figure 4.5.25 SANS samples (2002), porosity accessible to H2O............................4.5-22Figure 4.5.26 SANS samples (2002), porosity accessible to D2O............................4.5-23Figure 4.5.27 SANS samples (2002), porosity accessible to 50%H2O & 50%D2O.4.5-23Figure 4.5.28 RCA9 series (powder samples) _ Scattering intensity I(Q) vs. Scattering

length Q.............................................................................................................4.5-24Figure 4.5.29 RCA11 series (D2O made solid samples) _ Scattering intensity I(Q) vs.

Scattering length Q ...........................................................................................4.5-25Figure 4.5.30 Fractal mass (2001 samples) at different moisture conditions ...........4.5-28Figure 4.5.31 Fractal mass (2002 samples) at different moisture conditions ...........4.5-28Figure 4.5.32 Samples of no-fines RA Concrete ......................................................4.5-29Figure 4.5.33 Compressive strength of no-fines RA Concrete.................................4.5-30Figure 4.5.34 Mass per volume of no-fines RA Concrete ........................................4.5-31 Figure 4.6.1 Samples of ’no-fines’ concrete made from RC Aggregate ....................4.6-2Figure 4.6.2 Interconnected air voids ratio in ‘less-fines’ NA and RA Concrete.......4.6-3Figure 4.6.3 Impedance tube and ‘less-fines’ RA Concrete samples .........................4.6-4Figure 4.6.4 Sound absorption coefficient of ‘less-fines’ RA Concrete.....................4.6-4Figure 4.6.5 Sound absorption coefficient of ‘less-fines’ RA Concrete samples of

porous layer thickness of 100mm .......................................................................4.6-5

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Figure 4.7.1 Compressive strength of RA Concrete used in laboratory prototype barrier

.............................................................................................................................4.7-2Figure 4.7.2 Formwork, steel reinforcement and lifting inserts of laboratory prototype . 3Figure 4.7.3 Laboratory prototype of the ‘less-fines’ RA Concrete acoustic barrier .4.7-4Figure 4.7.4 ‘Less-fines’ RA Concrete panels assembled as a retaining wall ............4.7-5Figure 4.7.5 Laboratory prototype panels in reverberation room...............................4.7-6Figure 4.7.6 Sound absorption coefficient of laboratory prototype acoustic barrier ..4.7-6Figure 4.7.7 Alternative aggregate (reclaimed and washed) considered for concrete to

manufacture commercial barrier prototype.........................................................4.7-8Figure 4.7.8 Particle size distribution of aggregate considered to be used in the

production of commercial barrier prototype .......................................................4.7-8Figure 4.7.9 Compressive strength development of normal density concrete used in

commercially manufactured prototype .............................................................4.7-10Figure 4.7.10 Samples of no-fines 14/10mm RA Concrete......................................4.7-10Figure 4.7.11 Compressive strength development of no-fines concrete used in

commercially manufactured prototype .............................................................4.7-11Figure 4.7.12 Placing normal density and screeding no-fines RA Concrete in

commercially manufactured prototype .............................................................4.7-12Figure 4.7.13 Shop drawing of commercial prototype barrier..................................4.7-12Figure 4.7.14 Commercial prototype of the ‘less-fines’ RA Concrete acoustic barrier . 13Figure 4.7.15 Commercial prototype panels in reverberation room.........................4.7-13Figure 4.7.16 Sound absorption coefficient of commercial prototype acoustic barrier.. 14Figure 4.7.17 Reverberation test results ...................................................................4.7-16

List of TABLES Table 2.1 Comparison between natural and RC Aggregate.........................................2-16 Table 2.2 Particle size distribution of coarse aggregate – AS2758.1-1998 .................2-18 Table 2.3 Particle size distribution of coarse RC Aggregate (Sagoe-Crentsil 1999; Sautner

1999) ....................................................................................................................2-19 Table 2.4 Comparison of particle size distribution of the 14mm RC Aggregate and locally

manufactured basaltic aggregate..........................................................................2-20 Table 2.5 Porosity of some common rock (Neville, 1999)..........................................2-23 Table 2.6 Porosity comparison between natural and RC Aggregate ...........................2-23 Table 2.7 Porosity classification (Nawy 1997; Ramachandran 2001).........................2-34 Table 2.8 Porosity of cement paste (Bagel, 1997) .......................................................2-35 Table 2.9 Porosity a 15-year-in-service concrete (Eighmy, 2003) ..............................2-35 Table 2.10 Porosity of neat cement paste (Hansen, 1987)...........................................2-36 Table 2.11 Porosity and apparent VPV of various cement pastes (Nawy, 1997)........2-36 Table 2.12 Porosity of hardened cement paste with added various elements contained in

concrete waste (Chandra, 1997)...........................................................................2-38 Table 2.13 Comparison between SEM and other microscopes ...................................2-45 Table 2.14 Range of porosity related parameters measured by conventional and neutron

scattering techniques............................................................................................2-48 Table2. 15 Sound absorption coefficient (α) and NRC of commercial barriers..........2-55 Table 2.16 Sound absorption coefficient (α) – Vicroads requirements.......................2-55 Table 2.16 Sound absorption coefficient (α) of no-fines concrete barrier (Vicroads, 2001)

..............................................................................................................................2-57 Table 2.17 Buffer zone width for reflective and absorptive barriers ...........................2-57 Table 3.2.1 Experimental design program - major stages .............................................3-3 Table 3.2.2 Project stages and properties tested ............................................................3-5 Table 3.2.3 RC Aggregate and Natural Aggregate examination – summary ................3-7 Table 3.2.4 RA and NA Concrete development and examination – summary..............3-9 Table 3.2.5 Prototype and commercially manufactured acoustic barrier examination –

summary 3-10 Table 3.2.6 AUSANS sample suite.........................................................................3-11 Table 3.2.7 BET nitrogen adsorption test program.................................................3-11 Table 3.3.1 Fine aggregate sources .........................................................................3-12 Table 3.5.1 SANS experiments (1999 and 2000 - sample suite ..................................3-22 Table 3.7.1 Curing regime of concrete test specimens ................................................3-26 Table 3.7.1 AUSANS - May 2001 experiments - sample suite ...................................3-30 Table 3.7.3 AUSANS - May 2001 experiments - sample moisture conditions...........3-30 Table 3.7.4 AUSANS - January 2002 experiments - sample suite..............................3-31 Table 3.7.5 AUSANS - January 2002 experiments - sample moisture conditions......3-32 Table 3.9.1 Sound absorption examination of ‘less-fines’ RA Concrete acoustic barrier

using reverberation room method ........................................................................3-36

Table 4.3.1 Fine aggregate sources.............................................................................4.3-2 Table 4.3.2 Particle size distribution of fine aggregate, average percentage passing.4.3-2 Table 4.3.3 Fineness modulus and moisture content of fine aggregate ......................4.3-2 Table 4.3.4 Fineness modulus of fine aggregate and Apparent VPV - N40 Concrete4.3-3 Table 4.3.5 Mix suitability factors (MSF) of N40 Concrete.......................................4.3-6 Table 4.4.1 Particle density of 14/10mm RC Aggregate – results summary............4.4-22 Table 4.4.2 Particle size distribution of 14/10 mm RC Aggregate – percentage passing25 Table 4.4.3 Particle size distribution of 14/10 mm Natural Aggregate – percentage passing

...........................................................................................................................4.4-26 Table 4.4.4 RC Aggregate samples examined by the BET nitrogen adsorption ......4.4-31 Table 4.4.5 RC Aggregate samples examined by the BET nitrogen adsorption –

classification by degree of weathering..............................................................4.4-31 Table 4.4.6 Porosity of 14/10mm RC Aggregate – summary results .......................4.4-44 Table 4.4.7 Average engineering properties of 14/10mm RC Aggregate, summary4.4-45 Table 4.5.1 RA Concrete – compressive strength reduction ....................................4.5-10 Table 4.5.2 SANS porosity of RA Concrete (2001 samples) ...................................4.5-25 Table 4.5.3 SANS porosity of RA Concrete (2002 samples) ...................................4.5-26 Table 4.5.4 Average properties of RA25 Concrete – summary................................4.5-32 Table 4.6.1 Mix proportions of ’less-fines’ concrete..................................................4.6-2 Table 4.6.2 Peak resonant frequency simulation ........................................................4.6-6 Table 4.7.1 Mix proportions of concrete used for commercial prototype ..................4.7-9 Table 4.7.2 Weight of panels made from RA Concrete............................................4.7-15 Table 4.7.3 Simulation of barrier height reduction – barrier 18m from noise source .... 17 Table 4.7.4 Simulation of barrier height reduction – barrier 8m from noise source 4.7-17

1-1

CHAPTER 1 - INTRODUCTION

The construction industry and concrete manufacturers have realised that they will need

to use available aggregate rather than search for the perfect aggregate to make an ideal

concrete suitable for all purposes (Day, 1999). Simultaneously, significant increases in

concrete recycling result in hundreds of tonnes of Recycled Concrete (RC) Aggregate

that could be used in the production of concrete for specific purposes (Nolan, 1998;

Ecorecycle, 2004).

Currently, RC Aggregate is mainly being used as a substitute material for natural

aggregate in unbound sub-base and base pavement layers in road construction.

However, the perception amongst Victorian concrete recyclers, the scientific

community and concrete manufacturers, is that selected RC Aggregate can be used in

the production of concrete of compressive strengths of up to 40MPa (Recycling

Industries Pty Ltd; CSIRO; Boral Concrete Services Pty Ltd, 1998 – 2005).

One of the most significant steps in promoting the use of recycled concrete aggregate in

new concrete, was the 1994 publication by the RILEM Technical Committee of 121

titled ‘Specification for Concrete with Recycled Aggregate’ (RILEM, 1994). The

specification supplemented numerous research efforts from researchers around the

world, especially from the US, Europe and Japan. In Australia, research efforts have

been oriented towards two principal aims; firstly at increasing the understanding of

basic engineering properties of locally manufactured recycled concrete aggregate; and

secondly at the utilisation of the aggregate as concrete aggregate. A significant

achievement of the Victorian concrete recycling industry and scientific community is

the publication ‘Guidance on the Preparation of Non-structural Concrete Made from RC

Aggregate, (CSIRO, 1998). The guide became a valuable resource and tool for concrete

technologists, concrete manufacturers and clients specifying concrete. The guide was

superseded by the publication of the HB 155-2002 ‘Guide to the use of recycled

concrete and masonry materials’ (SA, 2002).

Although there are current technical specifications for recycled concrete aggregate for

the use as a sub-base material in road construction, there is an urgent need to establish

technical and performance standards for RC Aggregate for the use in concrete

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production (VicRoads, 1997; CSIRO, 1998). The technical standard specifications for

RC Aggregate for concrete production would allow concrete recyclers to produce

aggregate that meets such standard specifications and subsequently could be the most

effective way of promoting RC Aggregate to the concrete and construction industry as a

quality alternative material for concrete production (Recycling Industries Pty Ltd;

CSIRO; Boral Concrete Services Pty Ltd, 1998 – 2005). The standard specifications

could be supplemented by policies, strategies and education programs in construction

and demolition waste minimisation, leading to a wider acceptance of RC Aggregate as a

viable alternative aggregate for concrete manufacturing (EcoRecycle, 2004).

The development of technical specifications would need to be supplemented by a

change in attitude and business practice in the construction and demolition industry.

Segregation, at the source of demolition waste, is considered as a necessary and

extremely important change in the handling of concrete debris. However, it has to be

emphasised that all other steps involved in the production of RC Aggregate are almost

the same as in the production of standard concrete aggregate. Selective demolition and

segregation of waste could significantly improve the quality and visual appearance of

the aggregate, and therefore lead to change in perception and attitude towards RC

Aggregate, and consequently contribute to a greater acceptance of it as concrete

aggregate (Recycling Industries Pty Ltd; CSIRO; Boral Concrete Services Pty Ltd, 1998

– 2005).

Eminent examples of a positive, environmentally responsible attitude of Victorian

government agencies, consultants, contractors and concrete recycling industry are two

projects in Melbourne; the 60L ‘green’ building in Carlton; and the CH2 new council

house for the City of Melbourne in Little Collins Street. In both projects the ‘green’

concrete was requested by the clients, specified by the consultants, designed by concrete

technologies and produced by local ready-mix concrete manufacturers (Melbourne,

2004). The concrete used in these projects was made from reclaimed and recycled

concrete aggregate and recycled water, with a significant content of supplementary

cementitiuos materials replacing Portland cement. The total replacement materials in

the 25MPa concrete accounted for 94%; and in the 32MPa and 40MPa concrete,

replacement materials accounted for 35% of the total weight of constituent materials

(Boral, 2004).

1-3

This document reports on the research project aimed at an examination of selected RC

Aggregate, and the influence of its inherent properties, especially of the porosity of

aggregate on physical, mechanical and acoustic properties of concrete made from this

aggregate. The document also reports on the development of the RA Concrete acoustic

barrier, which is one of the many possible applications for RC Aggregate. This

application seems to best utilise the inherent properties of the aggregate, and offers a

low cost alternative to commercially available sound reflective and absorptive barriers.

1.1 IMPORTANCE of the WORK

The significance of this work is threefold; it presents an example of a novel use of RC

Aggregate in modern concrete technology; it provides further contribution to knowledge

on RC Aggregate and RA Concrete; and it proposes a ready to use alternative product, a

concrete acoustic barrier made from selected RC Aggregate.

This research project demonstrates that it is feasible to use alternative construction

materials such as reprocessed concrete waste, in modern concrete technology, to

manufacture a commercial product that can compete with similar products produced

with standard concrete aggregate. It demonstrates that using concrete waste deriving

from demolition and construction sites, the construction industry and concrete

manufacturers could significantly contribute to sustainability in construction. The

report proposes that, pre-cast concrete acoustic barriers made from selected RC

Aggregate can significantly contribute to an increase in concrete recycling, and the

reuse of concrete recycling products in infrastructure projects. Consequently, it can

contribute to a diversion of hundreds of tonnes of concrete waste from landfill sites to

recycling plants, as well as reducing raw material extraction and use.

From a concrete technology viewpoint, the significance of this work arises from an

innovative approach in the use of RC Aggregate in the production of concrete. Amid

other contributions, the report presents a practical account and contributes to the

knowledge of the design of concrete mixes using RC Aggregate, as well as on the

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production, placement and curing of RA Concrete and pre-cast products made from

such concrete.

The scientific significance of this work results from a contribution that provides an

understanding of the basic engineering properties of RC Aggregate, particularly of

porosity, and its influence on the physical, mechanical and acoustic properties of RA

Concrete. In addition, the scientific importance is evident in the use of the Small Angle

Neutron Scattering (SANS) technique, to determine the pore structure of RA Concrete

used as a supplement to conventional techniques including BET nitrogen adsorption.

From a commercial viewpoint, the importance of this work results from a development

of a RA Concrete product designed to mitigate transportation traffic noise. The

concrete acoustic barrier made from selected RC Aggregate has an acoustic

performance superior to those of conventional concrete barriers, which are of a

reflective nature. The benefit of the advantageous sound absorbing properties of RA

Concrete acoustic barriers is enhanced by a cost efficiency arising from lower

manufacturing costs and an effective use of constituent concrete materials, and ease of

manufacturing.

1.2 RELEVANCE to OTHER RESEARCH

To some extent, a major part of this research project is an extension of numerous

research studies undertaken by European, American, Japanese and Australian scientists

over the years on the use of RC Aggregate as coarse aggregate in new concrete (Lahner,

1993; Eighmy, 2003; Otsuki, 2003; Sagoe-Crentsil, 1999).

Research studies undertaken by Australian scientists from numerous research

organisations including the Commonwealth Scientific and Industrial Research

Ogranisation (CSIRO) Division of Building, Construction and Engineering and the

Australian Road Research Board (ARRB) in addition to various Australian universities,

have concluded that it is feasible to use selected RC Aggregate for production of

concrete of a compressive strength of up to 40MPa (CSIRO, 1998).

1-5

Most of these studies concentrated on the compressive strength of RA Concrete and

aggregate properties including density, crushing value, amount of foreign material and

water absorption of RC Aggregate (Sagoe-Crentsil, 1999; Sautner, 1999). However,

there is limited knowledge on the porosity of the aggregate and its influence on plastic

and hardened properties of concrete made from material of varying pore characteristics

and pore connectivity.

The CSIRO’s study also pointed out that the porosity of aggregate along with potential

chemical contamination need closer examination (CSIRO, 1998). This research project

investigates the porosity of commercial 14/10 mm RC Aggregate and its influence on

physical, mechanical and acoustic properties of RA Concrete.

Amongst other objectives, the main aim of this project was to expend the body of

knowledge on properties of RC Aggregate and the performance of concrete made from

this aggregate, along with proposing areas for further research related to RC Aggregate,

RA Concrete and concrete acoustic barrier.

1-6

1.3 HYPOTHESIS and OBJECTIVES

The hypothesis is:

That the inherent properties of RC Aggregate, porosity in particular, can augment the

performance of proposed composite absorbent and reflective acoustic barrier.

The main objectives of the project are to:

• Investigate basic engineering properties of selected RC Aggregate with a particular

emphasis on porosity of cement paste residue of the aggregate

• Investigate and model RA Concrete’s physical, mechanical and acoustic properties

that could be best utilised in concrete acoustic barrier

• Develop a pre-cast concrete sound barrier made from RA Concrete

1-7

1.4 PROJECT OUTLINE

The research project consisted of two major phases; experimental and developmental,

which were further divided into four stages; examination of fine aggregate and its effect

on durability of concrete; examination of coarse aggregate; development of concrete;

and development of a concrete acoustic barrier. Figure 1.1 summarises the four major

stages of this research project, and Figure 1.2 further outlines the research project’s

major stages.

Figure 1.1 Project major stages

Figure 1.2 Detailed outline of the project major stages

Fine Aggregate

Coarse Aggregate

Concrete

Acoustic Barrier

Fine Aggregate

Natural (N) Aggregate

Normal -density Natural Aggregate (NA) Concrete

‘Less-fines’ RA Concrete

RA Concrete Acoustic Barrier

Recycled Concrete (RC) Aggregate

No-fines NA Concrete

Normal -density Recycled Aggregate (RA) Concrete

No-fines RA Concrete

1-8

1.5 PROJECT AIMS

A. FINE AGGREGATE

The aim for the examination of a range of fine aggregate from various suppliers in the

Melbourne metropolitan area was to find the fine aggregate that would produce the most

durable concrete i.e. concrete with the lowest volume of permeable voids. It was

deemed necessary to find concrete sand that will produce cement paste of the highest

possible quality to compensate presumed inferior properties of coarse RC Aggregate.

B. COARSE AGGREGATE

Two types of coarse aggregate were investigated; local basalt, a natural (N) Aggregate

and recycled concrete (RC) Aggregate. The overall aim of the coarse aggregate

examination was to differentiate between these two types of aggregate in a range of

physical and mechanical properties. The investigation of RC Aggregate aimed at a

thorough characterisation of the aggregate in order to expand the body of knowledge on

selected RC Aggregate as well as to provide necessary data for accurate concrete mix

proportioning of recycled aggregate (RA) Concrete. The aim for the examination of N

Aggregate, with similar physical characteristics, specifically shape and particle size

distribution to those of the 14/10 mm RC Aggregate, was to generate a control set of

data.

B.1 Recycled Concrete (RC) Aggregate

The aim of the RC Aggregate examination was to investigate and characterise physical

and mechanical properties of the aggregate with a special focus on the determination of:

Relative composition of 14/10mm RC Aggregate, especially the content of

cement paste residue (cpr)

Particle size distribution

Re-cementing properties of RC Aggregate fines

Type and amount of any foreign material in the aggregate

Water absorption of the aggregate

Particle density

1-9

Elemental and mineral composition of cpr of RC Aggregate

Porosity of cpr of RCA using BET nitrogen adsorption in terms of:

BET total porosity

BET total volume of pores

BET volume of micropores

BET total surface area

BET pore size distribution

Porosity of cpr of RC Aggregate using SANS technique in terms of:

SANS total porosity

SANS fractal mass

B.2 Natural (N) Aggregate

The aim of the examination of N Aggregate was to produce a set of control data on

coarse aggregate of the particle size distribution and particle shape similar to those of

14/10mm RC Aggregate.

C CONCRETE

From a coarse aggregate point of view, two types of concrete were investigated;

concrete made from natural aggregate, (NA) Concrete, and concrete made from

recycled concrete aggregate, (RA) Concrete. The NA Concrete was manufactured from

locally available basalt, whereas the RA Concrete was manufactured from selected


C.1 NATURAL AGGREGATE (NA) CONCRETE

Two types of NA Concrete were investigated, normal density and no-fines concrete.

The aim of the investigation of NA Concrete was to derive a set of data that could be

used to compare with the data obtained from the RA Concrete examination.

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C.1.a Normal density NA Concrete

The aim of the examination of normal density 14/10mm, 25MPa NA Concrete (N25)

was to provide a reference N25 concrete of well-defined physical and mechanical

properties for the purpose of comparison with properties of normal density RA

Concrete. The focus of the N25 concrete examination was to determine:

• Compressive strength at 28 days

• Mass per volume of N25 concrete

• Volume of permeable voids in hardened N25 concrete

• Water absorption after immersion of N25 concrete

• Porosity of new cement paste of N25 surrounding natural aggregate in terms of:

o BET total porosity

o BET surface area

o BET total pore volume

o BET volume of micropores

o BET pore size distribution

• Porosity of new cement paste of N25 surrounding natural aggregate in terms of:

o SANS total porosity

o SANS fractal mass.

C.1.b No-fines NA Concrete

The aim of examining physical and mechanical properties of no-fines concrete made

from N Aggregate was to determine:

• Compressive strength of no-fines NA Concrete at 28 days

• Mass per volume of no-fines NA Concrete

• Volume of permeable voids in hardened no-fines NA Concrete

• Water absorption after immersion

• Volume of interconnected air voids and channels

as well as to provide no-fines NA Concrete with a well defined set of physical and

mechanical properties for the purpose of comparison with no-fines RA Concrete.

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C.2 RECYCLED AGGREGATE (RA) CONCRETE

Three types of RA Concrete were investigated viz. normal density, no-fines and ‘less-

fines’ concrete. The aim of the investigation was to develop RA Concrete with an

ultimate balance between compressive strength, durability and acoustic performance of

new concrete, as well as to characterise physical, mechanical and acoustic properties of

concrete made from selected RC Aggregate.

C2.a Normal density RA Concrete

The aim of examining physical and mechanical properties of the 14/10mm, 25MPa RA

Concrete (RA25) made from selected RC Aggregate was to investigate the effect of the

aggregate on:

• Compressive strength of normal density RA Concrete at 28 days

• Mass per volume of RA25 Concrete

• Volume of permeable voids in hardened RA25 Concrete

• Water absorption after immersion of RA25 Concrete

• Porosity of new cement paste of RA25 Concrete surrounding cpr of RC

Aggregate in terms of:

o BET total porosity

• BET surface area

• BET total pore volume

• BET volume of micro-pores

• BET pore size distribution

as well as porosity of new cement paste of RA25 concrete with a surrounding cpr of

RC Aggregate in terms of:

• SANS total porosity

• SANS fractal mass

C.2.b No-fines concrete

The aim of examination of physical, mechanical and acoustic properties of no-fines RA

Concrete was to investigate the effects of RC Aggregate on:

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• Compressive strength of no-fines RA Concrete at 28 days

• Mass per volume of no-fines RA Concrete

• Volume of permeable voids in hardened no-fines RA Concrete

• Water absorption after immersion

• Volume of interconnected air voids and channels in the concrete matrix

C.2.c ‘Less-fines’ RA Concrete

The ‘less-fines’ RA Concrete consists of two distinctive layers, the solid and porous

layer. The purpose of developing ‘less-fines’ RA Concrete was to create a composite

concrete of adequate physical and mechanical characteristics from a structural integrity

perspective, which simultaneously will be able to absorb sound energy in a frequency

range between 63Hz and 2,000Hz. The examination included the determination of:

• Mass per volume of ‘less-fine’ RA Concrete

• Volume of interconnected air voids and channels in ‘less-fine’ RA Concrete, and

• Sound absorption of ‘less-fines’ RA Concrete of various relative thickness of

porous and solid layers in the concrete.

D. ACOUSTIC BARRIER

A ‘less-fines’ RA Concrete acoustic barrier was developed to test the merit of newly

devised ‘less-fines’ RA Concrete in terms of its structural integrity and ability to absorb

sound energy in a frequency range similar to that of transportation traffic noise. The

reason behind the use of RC Aggregate for the production of barriers was to

demonstrate the value- added application for reprocessed concrete waste.

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CHAPTER 1 - INTRODUCTION.................................................................................1-1 1.1 IMPORTANCE of the WORK ......................................................................1-3 1.2 RELEVANCE to OTHER RESEARCH........................................................1-4 1.3 HYPOTHESIS and OBJECTIVES................................................................1-6 1.4 PROJECT OUTLINE ....................................................................................1-7 1.5 PROJECT AIMS............................................................................................1-8

Figure 1.1 Project major stages......................................................................................1-7 Figure 1.2 Detailed outline of the project major stages .................................................1-7

2-1

CHAPTER 2 – LITERATURE REVIEW

2.1 INTRODUCTION

The literature review provides the necessary background information on concrete

technology in general, along with materials used for concrete manufacturing with a

strong focus on concrete aggregate. The fine and coarse concrete aggregates are

reviewed in terms of their properties, and the testing techniques used in the

characterisation of concrete aggregate are also reviewed. In addition, background

information on the basic engineering properties of conventional concrete is presented

including its acoustic characteristics. With reference to coarse aggregate and

conventional concrete, porosity has been identified as one of the most decisive

properties affecting the physical, mechanical, and acoustic characteristics of concrete,

subsequently, literature on porosity of coarse aggregate and concrete is reviewed.

The literature review presents the current state of knowledge and examples of successful

uses of alternative materials in concrete technology, and in particular the use of

Recycled Concrete (RC) Aggregate as a coarse aggregate fraction in non-structural

concrete. It also presents a review of available literature on RC Aggregate properties

including particle size distribution, density and water absorption, and identifies the need

to investigate porosity and possible chemical contamination of the aggregate.

A comparison between conventionally used aggregate in concrete technology and RC

Aggregate is made based on basic engineering properties. Furthermore, accounts of

data, opinions and experience gained from successful applications of RC Aggregate as

coarse aggregate in concrete production are presented, and characteristics of RA

Concrete are compared with those of concrete made from natural aggregate. An

analysis of differences between NA Concrete and RA Concrete is presented in a range

of physical, mechanical and acoustic properties.

A review of conventional research techniques used in the examination of concrete

aggregate and concrete is presented. This is followed by a review of non-destructive

methods to investigate the microstructure of bulk materials which includes the Small

Angle Neutron Scattering (SANS) technique. A comparison based on typical

2-2

measurements derived by different methods of pore size distribution, of the total volume

of pores and of the pore surface area of concrete is presented.

The literature review also presents background information on road traffic noise, on the

use of concrete as a material for road sound barriers and on the acoustic performance of

commercially available concrete sound barriers.

The background information reviewed in this chapter formed the basis for a formulation

of the hypothesis and objectives of this research project. The aim of the research project

is aimed at the characterisation of locally produced selected RC Aggregate and its

differentiation from natural basalt aggregate, as well as at developing a concrete product

that best utilises the inherent properties of RC Aggregate.

2.2 CONCRETE CONSTITUENT MATERIALS

Modern concrete is a sophisticated composite material which is constantly undergoing

improvements and modifications. However, the basic constituents of conventional,

ordinary Portland cement (OPC) concrete such as fine and coarse aggregate, cement,

and water, remain the same. There are other materials such as chemical admixtures

including superplasticisers, water reducers, and air entrainers that can be used to modify

the characteristics of OPC concrete. There is also an increase in the use of pozzolanic

materials including fly ash, granulated blast-furnace slag and silica fume (Neville,

1999). Over the last few decades, the uses of various alternative fine and coarse

aggregates in the production of concrete have been investigated, including the use of RC

Aggregate.

Hydraulic cements produced in Australia fall into two broad categories; General

Purpose (GP) which includes ordinary Portland cements and blended cements (GB); and

special purpose cements (CCAA&AS, 2004). In standard concrete where there is no

need for special characteristics such as resistance to sulphates, development of high

early strength, or reduction in heat of cement hydration, the GP cement is used.

2-3

In Australia, the most commonly used fine and coarse aggregates in concrete

technology are natural gravels, sands, and crushed rock. In the Melbourne metropolitan

area, crushed basalt as coarse aggregate, and natural quarry sand as fine aggregate are

readily available and most commonly used (Day, 1999).

Although the fine and coarse aggregate in concrete matrix provide inert filler, the

aggregates’ petrographical, physical and mechanical properties can significantly affect

concrete plastic and hardened characteristics. Nawy (1997) defines the most important

properties of aggregate for ordinary concrete being the particle size distribution,

aggregate shape, porosity and possible reactivity with cement. Nawy (1997) also states

that surface texture has significant influence on concrete strength, since cubically

shaped crushed stones with a rough surface appear to produce higher strength concrete

than smoother faced uncrushed gravel, as bonding between aggregate and cement paste

is increased. Other properties that characterise concrete aggregate include: strength and

rigidity expressed as a crushing value, soundness which defines aggregate resistance to

normal weathering conditions, abrasion resistance, dimensional stability, alkali

reactivity, density, and water absorption.

Fine aggregate occupies approximately 30% of the total volume of conventional

concrete, and the quality of fine aggregate affects the properties of concrete

(CCAA&AS 2004). The recommended amount of fine aggregate in workable concrete

depends on the grading of the aggregate, cement content, particle shape and grading of

the coarse aggregate and intended use of concrete.

Ryan (1992) reports that river, pit, and quarry sands are most commonly used for fine

aggregate in metropolitan Melbourne. Fine aggregate from those sources consists of a

high proportion of silica in various forms, which is advantageous for the bonding

between aggregate and cement, consequently leading to more durable concrete. Day

(1999) identifies seven features affecting suitability of fine aggregate as concrete

aggregate. These include particle size distribution, particle shape and surface texture,

clay, silt and dust content, chemical impurities, presence of mechanically weak

particles, water absorption and mica content. Grading is singled out as the most

important property, followed by particle shape and presence of impurities that

determines acceptance of fine aggregate as suitable for concrete manufacture.

2-4

According to Day (1999), local fine aggregate is of an acceptable quality with the

exception of You Yang granitic sand, which is highly absorptive.

The particle size distribution of fine aggregate can be and often are represented by the

fineness modulus (FM). The FM is calculated from the sum of cumulative percentages

retained on standard sieves ranging from 4.75mm to 150μm (Neville, 1999). Mindess

(1981) states that although the FM is a crude depiction of aggregate grading it can be

used to check uniformity of grading if small changes are expected. It is possible that

aggregate of very different particle size distribution can have the same fineness

modulus. The FM of fine aggregate is used in mix proportioning as a convenient

parameter describing aggregate grading which has a significant effect on the workability

of concrete.

Mindess (1981), states that the fineness modulus should be in a range between 2.3 and

3.2, where lower numbers represent a fine grading and higher numbers are

representative of coarse grading of concrete sands. Nawy (1997) argues that fine

aggregate with a fineness modulus of 2.5 and lower produces concrete with a sticky

consistency, less workability and lower compressive strength, and that fine aggregate

with the fineness modulus of 2.75 to 3.2 produces concrete of higher compressive

strength and durability.

Use of sub-standard fine aggregate in concrete can retard settings, increase bleeding and

results in poor workability and increased water demand. Consequently it produces

porous, highly permeable and less durable concrete (Neville, 1999).

2.2.1 Coarse Aggregate

In Australia, the properties of coarse aggregate should comply with the requirements of

the Australian Standard AS2758.1 - 1998 ‘Aggregates and rock for engineering

purposes, Part1: Concrete aggregates’ (SAA, 1998). The standard identifies basalt,

diorite and granite as the most commonly used coarse aggregate in Australia

(CCAA&AS 2002). In metropolitan Melbourne Ryan (1992) identifies crushed basalt

as the most commonly used coarse aggregate for concrete production followed by

2-5

hornfels, toscanite and to a lesser extent, river gravel as other sources for concrete

aggregate. In the Sydney district, Pienmunne (2001) states that igneous rocks such as

basalt, dolerite and granite, and metamorphic rocks such as hornfel and quartzite, are

used in concrete production. There is an increase in the use of river gravel as an

aggregate for ready-mixed concrete. The round shape and a smooth surface texture of

river gravel allow the pumping of concrete to be relatively easy. The use of river gravel

is dictated by a reduced availability of other aggregate.

Crushed igneous rocks are preferred as coarse aggregate for concrete, as they have

higher strength and are less reactive than metamorphic or sedimentary rocks. However,

the production of aggregate from igneous rocks has declined from 4.8 million tonnes per

annum (tpa) (65% of the total aggregate market) in the 1970s, to 2.7 millions tpa (35%)

in 2000. As the deposits of suitable igneous rock close to major metropolitan cities in

Australia are becoming scarce, especially in the Sydney region, there is an increase in

the production of river gravel and lower quality sedimentary rocks. There is also a

sharp increase in coarse aggregate produced from concrete waste, from practically

nothing in the 1970s to 1.2 million tpa in 2000 in Sydney, and 0.7 millions tpa in

Melbourne, which accounts for approximately 10% of the total aggregate market in

Australia. Some of the RC Aggregate is used in the production of concrete (Pienmunne,

2001).

The coarse aggregate for concrete can be characterised by its shape, surface texture,

grading, particle and bulk density, water absorption, and content of impurities and other

potentially harmful materials such as silt, clay, or organic matter. Mindess (1981) states

that to proportion workable, of adequate strength and durable concrete, at least the

following properties of coarse aggregate must be known: shape, texture, grading,

moisture content, specific gravity, and bulk density.

The Australian Standard AS 2758.1-1998 ‘Concrete aggregates’ expands on those

requirements and identifies the following aggregate properties to be known to the

concrete technologists to design suitable concrete mixes: particle density, bulk density,

water absorption, particle size distribution, alkali aggregate reactivity, and soluble salts

content (SAA, 1998).

2-6

Sagoe-Crentsil (1999) confirms that the most common coarse aggregate used for

concrete in Melbourne is crushed basalt. He defines the basic properties of this

aggregate including water absorption of 1.0%, crushing value of 15%, and particle

density of 2,890kg/m3. No foreign material content in locally produced basalt was

reported. Neville (1999), states that the crushing strength of basalt is approximately

200MPa, the crushing value is about 12%, and specific gravity is 2.85 on average.

As a response to the growing demand for coarse concrete aggregate and the growing

volume of quality recycled aggregate, the Australian Standard AS 2758.1-1998

‘Concrete aggregates’, since its last update in 1998, also allows the use of crushed

concrete as coarse concrete aggregate. However, the use of such aggregate should be

authorised after additional testing is conducted, or previous experience justifies its use

as coarse concrete aggregate (SAA, 1998).

2.3 ALTERNATIVE CONSTITUENT MATERIALS in CONCRETE

Although the basic concepts governing concrete technology remain unchallenged,

concrete has undergone many changes. Cement and aggregate manufacturers constantly

strive for higher quality products leading to a better, more economic concrete, so a wide

range of chemical admixtures have been developed in order to alter concrete

characteristics. Concrete technologists have also observed many advantages which

result from the use of industrial by-products such as fly ash, and materials from

alternative sources such as reclaimed and recycled aggregate (Tabone, 1999).

An excellent example of concrete made from alternative constituent materials is the

concrete used in two projects in Melbourne, the 60L office building in Carlton, and the

City of Melbourne new Council House (CH2) in Collins Street. The concrete used in

those two projects was made from alternative constituent materials such as reclaimed

and recycled aggregate, recycled water, and supplementary cementitious materials. The

total replacement materials in the 25MPa concrete accounted for 94%, and in the

32MPa and 40MPa concrete accounted for 35% of total weight of materials (Bowie,

2004).

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Recycled water, usually in the form of water-cement slurry, is a by-product of

reclaiming of plastic state concrete waste. An over-specified or rejected plastic state

concrete is reclaimed at concrete batching plants where water-cement slurry and

reclaimed aggregate are separated, and then used for immediate application, or stored

for further use. It is now common practice that any other standard concrete produced at

batching plants that have reclaim facilities, consists of approximately 4% of water-

cement slurry as a water replacement. Slurry is also extensively use in special purpose

‘green’ concrete (Bowie, 2004).

Blended cements are another example of the use of alternative materials in concrete

manufacturing in Australia. The GB cements are defined by Australian Standard

AS3972-1997 ‘Portland and blended cements’, as consisting of Portland cement and

more than 5% of mineral additions (SAA, 1997). The ground granulated blast furnace

(GGBF) slag, and pozzolanic materials, such as fly ash, and silica fume, are the most

common blending minerals in Type GB cements. Those silicous, or silicous and

alumminous materials, are by-products generated during iron production or coal

burning.

Cement replacement materials, also known as supplementary cementitious materials

(SCMs) which include GGBF slag, fly ash, and silica fume, are now being promoted for

use in concrete as they can improve the characteristics of concrete, reduce cost, and are

an example of environmentally responsible practice in the concrete industry. They aim

to reduce the negative impact on the natural environment caused by the production of

Portland cement. Pozzolanas and GGBF slag have either none, or have very few

cementing properties. However, the silica in those minerals reacts with the calcium

hydroxide Ca(OH)2, or hydraulic properties in the case of GGBF slag, being activated

by Ca(OH)2, produced during hydration of Portland cement to form calcium silicate

hydrates (C-S-H). The beneficial effects of using SCMs in concrete include lower heat

of hydration, lower thermal shrinkage and reduced permeability, however, these

materials tend to alter setting time and rate of strength gain.

Australian government agencies and professional associations, including the Concrete

Institute of Australia, promote and support the use of SCMs in concrete. A prominent

example is the Vicroads Specification for Structural Concrete Section 610, which

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provides scope for utilisation of SCMs as replacement for Portland cement (Vicroads,

1997). It is now at the client’s and concrete manufacturer’s discretion to specify SCMs

in ordinary concrete and it is mandatory to use SCMs for concrete in marine or sulphate

aggressive environments (Vicroads, 1997).

The use of alternative aggregate in concrete has been initiated not only because there is

an increased amount of concrete waste that can be converted into concrete aggregate but

also because the quality of the natural aggregate deposits, the size of those deposits, and

access and distance over which transport is economical, make the availability of high

quality concrete aggregate often unobtainable or uneconomic in many parts of the

world, including Australia. In Melbourne, the remote locations of aggregate sources

have prompted warnings that an over-reliance on existing business practices, and over-

reliance on natural aggregate as the only source of aggregate for concrete production,

are now considered uneconomical practices and are considered unsustainable and

uneconomical uses of natural resources (Day, 1999).

Apart from the increased transportation cost of concrete aggregate from distant

locations, and the impact of waste, another reason to consider alternative aggregate, as

Day (1999) claims, is that it is more and more difficult to obtain aggregate, both fine

and coarse, conforming to typical specifications, which tend to specify ideal properties

of aggregate. Day (1999) suggests that alternative concrete mix design procedures, and

approaches to satisfy concrete purchaser requirements, need to be devised. The use of

what would typically be defined as substandard aggregate should be at the discretion of

the concrete manufacturer as long as the final product satisfies purchaser specifications

(Day, 1999). Those opinions have been confirmed and expressed by many other

concrete practitioners in Melbourne (Brand, 1999 – 2004; Tabone, 1999 -2004).

A positive step towards economic and ecological sustainability is the provision in the

current standards for the use of alternative materials, such as crushed concrete waste in

concrete products, as long as the alternative aggregate satisfies requirements set for

natural aggregate (SAA, 1998). However, there is a need to set technical standards for

selected recycled aggregate products against target applications. These specifications

could define product characteristics that must be met for specific construction

application.

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Pienmunne (2001) states that although the supply of recycled concrete aggregate can be

erratic, as it is linked with intensity of activities in demolition and construction, the RC

Aggregate is a significant source of alternative aggregate.

In Victoria, a positive step in promotion of RC Aggregate for concrete manufacture was

the publication of the ‘Guide for Specification of Recycled Concrete Aggregate (RCA)

for Concrete Production’ in September 1998, by the Commonwealth Scientific and

Industrial Research Organisation (CSIRO) Building, Construction and Engineering

Division (CSIRO, 1998).

2.4 CONCRETE WASTE and CONCRETE RECYCLING

Concrete waste, which falls into the construction and demolition (C&D) waste category,

is generated when creation of new, or modifications to existing urban infrastructure

such as transport systems, communication networks and buildings are made. With the

increased urbanisation of the world’s growing population there is also an increase in

C&D waste generation. This prompts a realisation that built-in urban infrastructure

along with C&D waste (unless dumped at the landfill) contains a large stock of

materials, and that efficient management of concrete, steel, bricks, or their waste, is

necessary to sustain the future growth and increased demand for construction materials

(Lahner, 1994).

In developed countries there is an increased societal demand on government agencies

and industries to search for alternative materials and reduce waste to achieve

ecologically sustainable development. A report prepared by the US Department of

Transportation on ‘Recycled Materials in European Highway Environments’ in 2000,

concludes that in most European Union countries (especially Denmark, The

Netherlands, and Germany) recycling and reuse of C&D waste is very well established

(FHWA, 2000). A notable example presented in this report is of recycling and the use

of recycled products in The Netherlands. It is interesting to note that 1.2 million tonnes

of recycled asphalt rubble is used as concrete aggregate and that hundreds of tonnes of

bottom ash are used as lightweight aggregate in the production of concrete blocks. It is

an impressive achievement that 100% of municipal waste incinerator fly ash generated

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by the municipal solid waste to energy conversion, as well as GGBF slag and electric

coal fly ash, are used in cement production or used in concrete as supplementary

cementitiuos materials. Further to that, almost 100% of building and demolition waste

is also recycled and used. The report states that 2 million tonnes (about 20% of all

concrete waste) of crushed concrete is used as concrete aggregate (FHWA, 2000).

Lauritzen (1994) presents numerous examples of reuse, recycling and successful use of

recycled C&D waste, especially concrete waste recycling products, in new

infrastructure. The American Concrete Pavement Association states that approximately

2.6 million tonnes of concrete pavement alone is recycled each year (Nash, 2003).

In Victoria, since 1986, there has been a constant increase in public and business

awareness of the negative social and environmental impacts of C&D waste.

Consequently, the recycling of concrete waste has increased. Currently more than 50%

of concrete waste is recycled (Ecorecycle, 2002). Nolan (1998) reports that in Victoria,

0.7 million tonnes of concrete waste was recycled in 1997/98. The majority of RC

Aggregate is used in road construction as a substitute for natural aggregate, mainly in

the sub-base layer. However, higher value utilisation of selected RC Aggregate has

been postulated by local aggregate manufacturers. This view is supported by findings

published by CSIRO in 1998, and personal communication with Recycling Industries

Pty Ltd (CSIRO, 1998).

2.4.1 Alternative Sources of Coarse Aggregate

In Australia over the last decade, generation of C&D waste has steadily increased. This

necessitated changes in the concrete waste stream and resulted in a change of attitude

towards waste within the demolition and construction industries (Ecorecycle, 2004).

The environmentally responsible approach of the government and industry to C&D

waste has resulted in an increased rate of recycling, and reuse of concrete waste. It

seems that there is a common understanding and consensus that depletion of natural

resources is a real threat, landfill space is becoming scarce, and that waste disposal

causes significant environmental and social impact. There is also a general consensus

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that recycled C&D waste including RC Aggregate can be used for construction

purposes.

The main source of raw material for recycling of concrete waste comes from demolition

of concrete structures. The quality and purity of the raw material affect the quality of

recycling products and ultimately commercial acceptance of concrete recycling

products. The process of manufacturing concrete recycling products is relatively

simple. To produce high quality concrete recycling products that satisfy commercial

and technical specifications it is crucial to segregate concrete waste at source

eliminating any low and high density and friable contaminants (Bell, 1998). Recycling

process and plant setup depends on desired grading and quality of the final product. In

situations when crushed concrete waste is to be used as fill material, the use of a mobile

crusher is usually sufficient. However, when crushed concrete waste is used to produce

RC Aggregate for road sub-base or as a concrete aggregate, a proper plant with at least

two crushers, vibrating screens, magnets and conveyor belts has to be established. Once

concrete rubble has been deposited at a recycling plant it is then broken by a pulveriser

mounted on an excavator. Pieces of concrete waste broken to a suitable size are then

crushed in a primary jaw crusher and then passed via conveyor belts into a cone crusher.

The crushed material is passed through a set of vibrating screens and sieved on the way

to a stockpile. After each crusher, the rotating magnets remove remains of steel

reinforcement whereas pickers manually remove other contaminants. Manufacturers of

recycled concrete products claim that any desired grading of recycled concrete

aggregate can be achieved with appropriate modifications to the plant (Curmi, 1998).

Currently in the Melbourne metropolitan area, there are a number of companies

recycling concrete waste. These include Delta Demolition Pty Ltd, Boral Resources

(Vic) Pty Ltd, although Recycling Industries Pty Ltd at Laverton North produces the

largest quantities of selected RC Aggregate of adequate quality that can be used as

concrete aggregate. Figure 2.1 shows the concrete crushing plant at Laverton North.

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Figure 2.1 Concrete recycling plant setup (courtesy Recycling Industries Pty. Ltd.) Over the past 20 years, concrete recycling and the use of its products in infrastructure

projects has increased significantly in Victoria. The range of applications for concrete

recycling products has expanded from the use of aggregate in the unbound sub-base

layer in road construction to the use of coarse RC Aggregate in new concrete.

Concrete recycling in Victoria was initiated in 1986 by a local recycling company,

Recycling Industries Pty Ltd, of the Alex Fraser Group of Companies. Initially the

company produced relatively low value materials in order to get market acceptance, as

well as to gain necessary experience and expertise in crushing concrete waste. Even

though at the beginning, recycled concrete products were treated with suspicion, they

gradually gained the attention of the construction industry, local government, and the

Victorian road authority, Vicroads (Bell, 1998). Joint efforts among the Alex Fraser

Group, CSIRO, Division of Building, Construction and Engineering, and Vicroads

resulted in the development of the first specification for crushed concrete in Australia

known as the 820 Specification for Crushed Concrete for Pavement Sub-base (Vicroads,

1992). In 1995 the specification was revised by Vicroads. Currently the 820Q

specification encompasses Class3 and Class4 of various nominal sizes of Crushed

Concrete for Pavement Sub-base (Vicroads, 1997).

Another step in the promotion of the use of alternative construction materials and in the

development of specifications for crushed concrete was the introduction in July 1997 of

Vicroads 821 Specification for 20 mm nominal size Class3 Cement Treated Crushed

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Concrete for Pavement Sub-base (Vicroads, 1997). In the meantime the Alex Fraser

Group of Companies adopted a quality management system and introduced its own

commercial specifications for 20 mm Class2 Crushed Concrete, and 14/10 mm Class1

Recycled Concrete Aggregate - RCA (Bell, 1998).

2.4.2 Current Applications for Recycled Concrete Products

In recent years, companies such as the Delta Group (Concrete Recycling Division),

Boral Resources Pty Ltd and others, have also made a significant impact in the

minimisation and recycling of concrete waste. Some of the metropolitan Melbourne

councils and the Melbourne Water Authority have contributed to the increased use of

recycled concrete waste by requesting and specifying the use of RC Aggregate in their

projects. There are already many examples of successful applications of this material in

some of the major projects in Victoria. One such project was the Western Ring Road in

Melbourne, where 75,000 tonnes of recycled concrete was used as a sub-base material

in road pavements. Another successful application of recycled concrete products was a

sub-base for the New Formula 1 Grand Prix racetrack at Albert Park in Melbourne,

where a total of 100,000 tonnes of RC Aggregate was used for its construction (Bell,

1998).

A survey conducted by Richardson (1994) revealed a growing interest in concrete

recycling, and reported that 60% of municipal councils in Melbourne were engaged and

committed to concrete recycling. The survey also revealed that 13% of concrete

recycling products were used as a fill material, 16% as a sub-base material in footpath

construction, 19% as trench base material, 43% as sub-base in road construction, and

8% as aggregate for concrete production. The survey forecasts an annual estimated

demand for concrete recycling products used by municipal councils in Australia of

about 750,000 tonnes per year.

2.4.3 Under-utilisation of Recycled Concrete Aggregate

Mindess (1981) indicates that the escalating problem of solid waste disposal has

prompted consideration of waste as a source of aggregate for concrete. Mindess (1981)

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indicates that using solid waste as concrete aggregate provides ‘the only real potential’,

however, he identifies three factors to be taken into account when waste products are

under consideration for use as concrete aggregate: economy (mainly the amount of

transportation required), compatibility with other materials, and required properties of

concrete. Mindess (1981) points out that the shape and reactivity of recycled solid

waste aggregate (glass waste in particular), might affect concrete properties, and

anticipation and assessment of potential problems must be carried out. In the US, in

1980, a total of 25 million tonnes of building waste such as bricks, concrete, and

reinforcing steel from demolition, was considered as aggregate for concrete (Mindess,

1981).

In Japan, Kasai (1994) reports that 25.4 million tonnes of concrete waste was generated

in 1990 with a recycling rate of 48%. He also states that since 1991, government

policies promoting concrete recycling are in place together with an ambitious plan to

recycle and reuse 100% of concrete waste. In Japan the utilisation of recycled concrete

aggregate as a road base material began in 1978. The technical guidelines were first

published in 1992, and the draft guideline for utilization of RC Aggregate in concrete

production was presented in 1994 (Kasai, 1994). In Germany, Schulz (1994) reports

that 23 million tonnes of C&D waste were generated and used in 1989/1990, to meet the

increased demand for concrete aggregate.

In Victoria, there has been a growing acceptance of the use of RC Aggregate as a sub-

base material in road construction. This is also due to the improved quality of the

concrete recycling products produced to satisfy the requirements of the 820 Vicroads

specification. It therefore seemed logical to continue to investigate the use of selected

aggregate in the production of new concrete. The CSIRO (1998) reports that

commercially available selected RC Aggregate has properties which make it a suitable

substitute for natural coarse aggregate in concrete of compressive strength of 25MPa

(N25).

Curmi (1999) points out that in Australia the manufacturing process of RC Aggregate is

now well understood, and aggregate of various grading can be produced, and that the

crushing process is easily adaptable.

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The high quality recycled aggregate that is suitable for use in new concrete is the

selected 14/10mm Class1 RC Aggregate. It consists of natural aggregate, with cement

paste residue adhered to it, and less than 2% of impurities of various nature. The

minimum particle density of the aggregate exceeds 2,100kg/m3 and the grading

complies with industry specifications. The manufacturer of 14/10mm RC Aggregate

advises that although the density of the new aggregate is lower than commonly used

natural aggregates which have significant impact on the yield and the unit mass of

concrete, the aggregate is suitable for concrete (Bell 1998; Brand 1998).

2.5 COMPARISON between NATURAL and RECYCLED CONCRETE AGGREGATE

The basic engineering properties of coarse and fine aggregate, besides many other

factors, determine the quality of concrete. Most rocks and stones can be used as

concrete aggregate as long as they are sound, durable and resistant to volume changes.

The suitability of the coarse aggregate for concrete manufacturing is dependent also on

its shape, surface texture, grading, particle, and bulk density, water absorption, and

content of impurities and potentially harmful materials such as silt, clay or organic

matter. Mindess (1981) states that to design workable concrete, of adequate strength

and durability, a range of properties of coarse aggregate must be known, such as shape

and texture, grading, moisture content, specific gravity and bulk density.

Raw materials for production of the natural aggregate and RC Aggregate contribute to

some differences and variations of aggregate properties. The igneous, metamorphic or

sedimentary rocks used in the production of natural coarse concrete aggregate are

relatively homogenous. This results in considerable consistency of natural aggregate

coming from a particular rock source. The concrete waste which often consists of waste

material other than concrete debris, such as timber waste, steel reinforcement, bricks,

plastic, etc., can result in an aggregate containing some impurities. As RC Aggregate is

produced from composite material, its particles vary in composition and irregular

distribution of cement paste residue and rock material.

Recycled concrete aggregate consists of natural aggregate coated with cement paste

residue, pieces of natural aggregate, or just cement paste and some impurities. Relative

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amounts of those components, as well as grading, affect aggregate properties, and

classify the aggregate as suitable for production of concrete. There is a general

consensus that the amount of cement paste residue has a significant influence on the

quality, and the physical, mechanical and chemical properties of the aggregate, and as

such has potential influence on the properties of RA Concrete. Table 2.1 presents a

comparison between natural aggregate and RC Aggregate (Gomez-Soberon, 2003).

Table 2.1 Comparison between natural and RC Aggregate

Property Unit N Aggregate RC Aggregate Dry specific density kg/m3 2,570 – 2,640 2,260 – 2,280 Specific density (surface dry) kg/m3 2,590 – 2,670 2,410 – 2,420 Water absorption % 0.88 – 1.13 5.83 – 6.81 Total porosity % 2.70 – 2.82 13.42 – 14.86

2.5.1 Shape and Surface Texture

In particular, the shape of the coarse aggregate is an important characteristic that can

affect the mechanical properties of concrete. The shape and surface texture of the

coarse aggregate influence the strength of concrete by providing an adequate surface

area for bonding with the paste or creating unfavourable high internal stresses (Mindess,

1981). The Australian Standard AS 2758.1 - 1998 ‘Concrete Aggregate’, classifies

shapes of aggregate into two categories, desirable and less desirable (SAA, 1998). The

desirable shapes include rounded, irregular and angular, whereas less desirable shapes

include flaky, elongated, and flaky and elongated. Neville (1999), states that a cube-

shaped aggregate (as long as it is ideally graded) interlocks much better than an

aggregate of elongated or flaky shape, consequently leading to stronger concrete.

Concrete made from elongated or flaky aggregate is less workable and prone to develop

higher amounts of entrapped air pockets.

Further, the shape of an aggregate can be classified by an index known as the angularity

number, which defines the amount of voids in aggregate after compaction. For

example, the highest amount of voids created by aggregate of approximately 45% has

the angularity number 12 (SAA, 1995). The coarse aggregate used in the majority of

concrete manufactured in the Melbourne metropolitan area is mostly angular, (Bowie,

2002). The difference in water requirements for concrete using angular, and rounded

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coarse aggregate, is approximately 10 liters per cubic meter of additional water for

concrete made from angular aggregate (CCAA&AS, 2004).

The surface texture of aggregate contributes significantly to the development of a

physical bond between aggregate and cement paste. It also affects the water/cement

(w/c) ratio, workability, and strength. The surface texture of aggregate is classified as

glassy, smooth, granular, rough, crystalline, and honeycombed (SAA, 1998). Local

basalt used as concrete aggregate has a rough surface (Curmi, 1998). For best

workability, a smooth surface is most desirable, however, for the best bond between

aggregate and cement paste, and also for optimum strength, the rough-textured particles

are preferred (CCAA&AS, 2004). Tasong (1998) identifies the rough surface texture of

aggregate as contributing to a better bonding between aggregate and cement paste in

concrete.

The optimum workability of concrete can be achieved with the use of rounded particles

(CCAA&AS, 2004). Mindess (1981) states that well rounded and compact aggregate

particles close to spherical shape with a relatively smooth surface, are the ideal

aggregate for concrete.

Despite the lack of formal study on the surface texture and shape of RC Aggregate

produced in Melbourne, there is a universal consensus that locally manufactured

aggregate has a rough texture and round shape (Curmi 1999; Bell 1999; Brand 1999).

2.5.2 Particle Size Distribution

Mindess (1981) states that particle size distribution determines the cement paste

requirement in concrete, and that it is more economic to use well graded aggregate as it

requires less cement paste. In general, aggregate can be well (continuously) graded or

gap graded. Continuously-graded aggregate is predominantly specified in concrete

technology although less common gap-graded aggregate is also being used. However,

above average care has to be exercised.

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Particle size distribution has a direct influence on the water demand of concrete,

workability, and durability of concrete. Combined, continuous grading of fine and

coarse aggregate produces cohesive, workable, and durable concrete with fewer voids

between aggregate particles (CCAA&AS, 2004). Combined grading which is coarser

(deficient in fine aggregate) than stipulated by the Australian Standard AS2758.1-1998

‘Concrete aggregate’, however, produces harsh, difficult to place and finish concrete,

with insufficient amount of cement paste to fill voids between coarse aggregate (SAA,

1998). A combined grading with excess of fine aggregate, or with excessively fine

sand, produces uneconomical concrete as the water demand of the concrete is high,

hence requiring more cement (CCAA&AS, 2004).

Although the continuously graded aggregate as specified by the Australian Standard AS

2758.1-1998 ‘Concrete aggregate’, leads to ideal packing of different size fractions in

concrete matrix, Neville (1999), claims that from an economic view point, the use of

gap-graded aggregate for concrete is an increasingly more common practice. The gap-

graded aggregate is the aggregate where one or more intermediate size fractions are

omitted. Table 2.2 presents the particle size distribution of gap-graded (single-size) and

continuously graded aggregate.

Table 2.2 Particle size distribution of coarse aggregate – AS2758.1-1998

Sieve aperture [mm] 19 13.5 9.5 6.7 4.75 2.36 0.75 % passing; nominal size 14mm continuously graded

100 85-100 25 -55 0-10 0-2

% passing; single-size 14mm 100 85-100 0-20 0-5 0-2 % passing; single-size 10mm 100 85-100 0-20 0-5 0-2

The combined grading of fine and coarse aggregate affects the water and cement paste

amount per cubic meter of concrete. It also affects the packing of aggregate in concrete

which can further be related to the amount of air voids in no-fines concrete. Figure 2.2

presents a schematic demonstration of different combined grading of aggregate in

concrete matrix.

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Figure 2.2 Schematic representation of aggregate grading in an assembly of

aggregate particles: (a) uniform size, (b) continuous grading, (c) replacement of small sizes by large sizes, (d) gap-graded aggregate, (e) no-fines grading (Mindess,

1981)

Figure 2.2a shows that one-sized aggregate creates a higher volume of voids between

aggregate particles consequently requiring a higher amount of cement paste to fill

completely the space between aggregate. When continuously graded aggregate is used

(see Figure 2.2b) the smaller particles pack between larger particles reducing the

amount of voids between aggregate particles consequently requiring less cement paste.

Sagoe-Crentsil (1999) and Sautner (1999), report on the use of RC Aggregate in

concrete of compressive strength of 25MPa. The grading of the aggregate used in their

studies is shown in Table 2.3.

Table 2.3 Particle size distribution of coarse RC Aggregate (Sagoe-Crentsil 1999; Sautner 1999)

Sieve aperture [mm] 19 13.5 9.5 6.7 4.75 2.36 0.15 % passing; Sagoe-Crentsil 100 91.4 28.7 7.6 5.4 4.2 0.5 % passing; Sautner 98 60 31 31 10 4 0.1

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It is worth noting that although there were significant differences in grading reported by

Sautner (1999), and Sagoe-Crentsil (1999), the difference in reduction in the

compressive strength of RA Concrete of 9% and 10% respectively, in comparison with

the control concrete, was relatively small. Although there was reduction in compressive

strength, the plastic state properties of concrete did not differ from those of natural

aggregate.

Table 2.4 presents grading of both the RC Aggregate, and locally produced basalt used

by Sagoe-Crentsil (1999) for RA25 Concrete and controlled N25 Concrete.

Table 2.4 Comparison of particle size distribution of the 14mm RC Aggregate and locally manufactured basaltic aggregate

Sieve aperture [mm] 19 13.5 9.5 6.7 4.75 2.36 0.15 % passing; RC Aggregate 100 91.4 28.7 7.6 5.4 4.2 0.5 % passing; Basalt 100 84 43.7 5.6 2.1 1.0 0.2

Grading variations of concrete aggregate are controlled by concrete technologists and

taken into account in the concrete mix design process. The difference in grading

between natural and RC Aggregate will be analysed in terms of a combined grading of

coarse and fine aggregate (Tabone, 2000).

2.5.3 Water Absorption

An aggregate for concrete can be in various moisture states such as oven-dry, air-dry,

saturated-surface-dry, and wet. Water absorption of the aggregate is related to its

porosity and is the amount of moisture absorbed by the minute pores present in the

aggregate from its air-dry state to its saturated-surface-dry state. Knowledge of this

property is necessary for determining the amount of water per cubic meter of concrete

or for maintaining a desirable water/cement ratio. Any deviations in water absorption of

aggregate can significantly alter fresh concrete characteristics. In the case of highly

absorptive aggregate, additional water might be required to provide adequate

workability. This as a consequence, introduces free water in concrete mix and results in

concrete bleeding, increase drying shrinkage and affects creep characteristics (Neville,

1999). Ramachandran (2001) indicates that because water absorption of the aggregate

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has the potential to increase drying shrinkage of concrete, aggregate absorbing more

than 3% of water should not be used as coarse concrete aggregate.

Tasong (1998) reports on an investigation on the influence of aggregate properties, and

the aggregate-cement paste interface on concrete properties and, amongst various

properties identifies water absorption and aggregate surface roughness as those

contributing to the development of a strong bond between paste and aggregate. Mindess

(1981), states that normal weight coarse aggregate used for concrete has water

absorption between 1% and 2%, and that water absorption higher than that indicates

higher porosity of the aggregate. In Melbourne, local crushed basalt has water

absorption of 1.0% (CSIRO, 1998) whereas Tasong (1998) reports water absorption of

basalt of 1.4%,

Etxeberria (2004) reports on water absorption of coarse recycled aggregate of 4.3%.

The CSIRO (1998), reports that the average water absorption of RC Aggregate is 5%

which is much higher than commonly used natural aggregates in concrete technology.

The variability of water absorption of RC Aggregate can be overcome by pre-wetting of

the aggregate. This is followed by consequent adjustment of water content per cubic

meter of concrete when designing mix proportions.

2.5.4 Particle Density and Bulk Density

One of the basic properties used to classify aggregate, particle or bulk density is closely

related to mineral composition and porosity. The Australian Standard AS 2578.1-1998

‘Concrete aggregates’ defines particle density as the mass of a quantity of oven dried

particles divided by their saturated surface dried volume, and the bulk density, as the

mass of a unit volume of oven dried aggregate. Bulk density is determined either as

compacted or un-compacted. Particle density of aggregate is directly related to porosity

which indirectly influences the strength of the aggregate. Aggregate density is used

mainly in concrete mix proportioning as aggregates of different density influence the

yield and mass per volume of concrete (CCAA&SA, 2004).

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The particle density of natural aggregate ranges between 2,100kg/m3 and 2,700kg/m3.

The particle density of locally manufactured RC Aggregate exceeds 2,100kg/m3

(CSIRO, 1998). Ravindrarajah (1985) and Hansen (1992) report on the particle density

of coarse recycled concrete aggregate of 2,200kg/m3.

The bulk density, besides depending on mineral composition and porosity of aggregate

particles, also depends on particle size distribution. Mindess (1981) states that

maximum bulk density can be achieved when the fine aggregate content in combined

aggregate is between 35% and 40%, and such aggregate is most economical as

minimum cement paste is required. The bulk density of normal density coarse

aggregate ranges between 1,450kg/m3 to 1,750kg/m3 (Mindess, 1981).

2.5.5 Impurities and Foreign Materials in RC Aggregate

The quality of an aggregate and its suitability as concrete aggregate is also determined

by the presence of reactive minerals and impurities (foreign materials), which include

organic matter, sugar, silt, clay and dust. Excessive amounts of fine particles of silt,

clay, and dust increase the demand for water in concrete. This results in a loss of

strength, and increases concrete permeability. It may also form a coating on the

aggregate decreasing the bond between the aggregate and the cement paste

(CCAA&AS, 2002). The amount of impurities in any aggregate can be expressed as

both weak particle, and low-density particle content. The content of weak particles

should be less than 0.5% and that of the low density particles should not exceed 1%

(SAA, 1998). The low density particles, which mainly include wood and other organic

matter, tend to rise to the surface of a plastic concrete which consequently produces

pop-outs and staining of finishes in the hardened concrete. Natural aggregate which is

produced from a raw material occurring in large outcrops of relatively homogeneous

igneous or metamorphic rock has very few foreign materials.

In contrast, raw material for production of RC aggregate is prone to impurities and

foreign materials. Depending on its origin, impurities in RC Aggregate can include

low-density materials such as plastic, wood or organic matter, rubber, plaster and friable

materials. It can also include asphalt, clay, as well as steel reinforcement. Sautner

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(1999) reports that the total amount of foreign material in RC Aggregate used for

concrete for footpath construction was less than 0.1%, Sagoe-Crentsil (1999) reports a

total amount of impurities of 1.2%.

2.5.6 Aggregate Porosity

Neville (1999), states that the porosity of aggregate not only affects other properties of

the aggregate, such as water absorption and density, but also has significant effects on

concrete properties, especially permeability and durability. Commonly used in concrete

manufacturing coarse aggregates have a porosity of up to 5%. Etxeberria (2004) reports

on coarse natural aggregate of average porosity of 2.3%. Table 2.5 shows the porosity

of common rocks used in concrete technology (Neville, 1999).

Table 2.5 Porosity of some common rock (Neville, 1999)

Rock group Porosity [%] Basalt 0.5 –1.5 Quartzite 1.9 -15.1 Limestone 0.0 – 37.6 Granite 0.4 – 3.8

The porosity of RC Aggregate is more complex than that of natural aggregate, and is a

function of porosity of the natural aggregate used in manufacturing of original concrete,

porosity of cement paste of the original concrete, and of the in-service conditions of

concrete used to produce RC Aggregate. The porosity of RC Aggregate also depends

on the amount of cement paste residue present in the aggregate. A comparison between

total porosity of natural and recycled concrete aggregate, is presented in Table 2.6

(Gomez-Soberon 2003; Etxeberria 2004).

Table 2.6 Porosity comparison between natural and RC Aggregate

Property Unit Natural Aggregate RC Aggregate Total porosity (Gomez-Soberon 2003)

% 2.70 – 2.82 13.42 – 14.86

Total porosity (Etxeberria 2004)

% 1.86 – 2.81 9.13 – 10.94

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2.5.7 Other Properties

The crushing value of concrete aggregate specified by the Australian Standard AS

2758.1-1998 ‘Concrete aggregate’ for conditions of the most severe exposure is limited

to 30% (SAA, 1998). RC Aggregate used in Australia satisfy the specified limit. As an

example, the RC Aggregate used by Sautner (1999) had an average crushing value of

19%, while aggregate used by Sagoe-Crentsil (1999) had 23% on average.

Otsuki (2003) argues that the quantity and quality of cement paste residue adhered to

natural aggregate in RC Aggregate affect the strength of recycled aggregate concrete

especially RA Concrete with low water/cement ratio. The effect is less significant with

higher w/c ratios, which could indicate that cpr has similar properties to highly porous

cement pastes.

The content of fines in RC Aggregate influences its suitability as concrete aggregate.

Snyder (1995) reports on various studies on densely graded crushed concrete in the

State of Minnesota and states that the presence of significant amount of fines in crushed

concrete appears to re-cement the RC Aggregate. This is due to the presence of some

content of cementitious particles in the fines. He suggests removal of cementitious fines

and substitution of inert fines to reduce the ability of the RC Aggregate to re-cement.

2.6 NORMAL DENSITY and NO-FINES CONCRETE

Most of the concrete produced nowadays is made from well-graded aggregate, however,

for special purposes such as reduced density concrete, the gap-graded aggregate is often

used. Neville (1999) suggests three main means of reducing density of concrete. The

most common is to use a lightweight aggregate which results in a lightweight aggregate

concrete. The other ways include increasing air content in cement paste, which results

in cellular concrete, and creating air voids between coarse aggregate particles as in the

case of no-fines concrete.

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The no-fines concrete is a special concrete which is made from the gap-graded

aggregate, where aggregate smaller than 4.75mm is omitted. The omission of fine

aggregate in concrete mix creates voids between coarse aggregate particles.

Neville (1999) defines no-fines concrete as an agglomeration of coarse aggregate

particles, each surrounded by a coating of cement paste of up to 1.3mm thick. The

density of no-fines concrete depends primarily on the size and grading of the aggregate.

Well-graded aggregate should be avoided as it compacts to higher density no-fines

concrete. Single sized aggregate between 10mm and 20mm is preferred with 5%

oversize and 10% undersize particles allowed (Neville, 1999). However, CCAA (1999)

reports that blended aggregate, a combination of 10mm and 7mm, as well as 20mm and

14mm has been found to perform satisfactorily. Neville (1999) states that no particles

smaller than 5mm should be present, and that flaky, elongated or sharp edged crushed

aggregate should be avoided. A pre-wetting of the aggregate in order to facilitate

uniform coating by the cement paste is suggested.

The workability of no-fines concrete is difficult to specify and measure; consequently

there is no workability test except a visual inspection to check the consistency of

concrete batches, and to assess uniformity of the cement paste coating the aggregate. It

is recommended that the no-fines concrete should be placed relatively very rapidly

because the thin layer of cement paste can dry out, which consequently results in a

reduced strength (Brook, 1982). No-fines concrete compacts very little, therefore

compaction of no-fines concrete is not recommended except for rodding in the corners

of a formwork or vibrating for a very short time to prevent the cement paste from

running off. The thin layer of cement paste makes curing very important, and so moist

curing is recommended. Steel reinforcing of no-fines concrete is not recommended

unless it is covered with a protective layer of cement paste.

Mix proportions by volume are usually specified, of the cement/aggregate ratio and

water/cement ratio. Typically w/c ratios are between 0.38 and 0.52 (Malhotra, 1976).

Although in Australia CCAA (1999) suggests a relatively low w/c ratio, in the range of

between 0.4 and 0.45. The cement/aggregate ratio, which typically controls the

compressive strength of no-fines concrete, varies between 1:6 and 1:10. CCAA (1999)

reports on a no-fines concrete of a w/c ratio of 0.4, cement/aggregate ratio of 1:8

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resulting in concrete of compressive strength of 7.5MPa and density of 1,850kg/m3. It

has been reported by McIntosh (1956) that the aggregate/cement ratio of 1:6 and the w/c

ratio of 0.38 produce no-fines concrete of the compressive strength at 28 days of 14MPa

and a density of 2,020kg/ m3.

Neville, (1999) reports that the density of no-fines concrete using normal weight

aggregate ranges from 1,600kg/m3 to 2,000kg/m3 with corresponding compressive

strengths of between 1.5MPa and 14MPa. Malhotra (1976) reports that the flexural

strength is typically 30% of the compressive strength which is relatively higher than for

ordinary, normal density concrete and that shrinkage is significantly lower, ranging

from 120x10-6 to 200x10-6. However, CCAA (1999) reports that the drying shrinkage

of no-fines concrete can be up to 300 microstrain and that it has higher permeability

than standard concrete. The density and compressive strength of no-fines concrete is

dependent on the cement content, aggregate/cement ratio by volume and water/cement

ratio by mass. The water/cement ratio also depends on water absorption of the

aggregate, however, if the w/c ratio is higher than optimum the cement paste is not

adhesive.

Neville, (1999) states that because no-fines concrete has large pores and that it is subject

to limited capillary suction, the capillary pores are not fully saturated, which makes this

type of concrete frost resistant. However, even limited absorption of water makes no-

fines concrete unsuitable for use in foundations and in situations where it may become

saturated with water. Neville (1999), claims that maximum absorption can be as high as

12.5%, but under normal conditions the absorbed water does not exceed 5% by mass.

To reduce air permeability Neville (1999) suggests that external walls would need to be

rendered on both sides. The open texture of no-fines concrete makes it very suitable for

rendering. Rendering and painting on both sides increases sound transmission loss but

at the same time reduces sound absorption. In situations where acoustic properties are

considered to be of paramount importance, one side of the wall should not be rendered.

Although Neville (1999) suggests that the main application for no-fines concrete is as

the pre-cast in-fill panels in framed structures, Meininger (1988) reports on the use of

no-fines concrete in domestic car parks overlaying a permeable sub-grade, and as

pavement around trees which allows easy drainage. In Australia, CCAA (1999) reports

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on the use of no-fines concrete in external and internal walls of low-rise and multi-

storey units, in free-draining pavements for light traffic car parks, as well as in tennis

courts, drainage layers and levelling courses.

2.7 COMPARISON between STANDARD and RECYCLED AGGREGATE (RA) CONCRETE

Concrete is a two-phase composite material. For the first few hours, after the

constituent materials are mixed together in a production process, concrete remains in a

plastic state. In this state concrete is transported, placed, compacted and finished.

Proper placing techniques and adequate compaction of plastic state concrete are

necessary to expel trapped air from the concrete matrix, which can adversely influence

the properties of hardened concrete. Concrete starts to harden after several hours when

the chemical reaction between water and mineral compounds in cement start to

accelerate. It is absolutely crucial to cure concrete during the hydration process i.e.

maintain the required amount of water necessary to hydrate cement to obtain the desired

concrete microstructure. All the steps and processes involved in proportioning of

concrete constituent materials, mixing them, placing, compacting, finishing and curing

of concrete have the potential to impact on the microstructural development of concrete

and its physical and mechanical properties. Regardless of the type of aggregate used in

concrete, the same care has to be exercised to both concrete made from natural

aggregate, and that made from recycled concrete aggregate.

2.7.1 Physical and Mechanical Properties

According to Australian Standard AS1379-1997 ‘Specification and supply of concrete’

there are basic plastic state and hardened properties that have to be specified such as

slump (measure of concrete rheology), compressive strength (at 7 and 28 days), and

durability and shrinkage (SAA, 1997).

The rheological properties of concrete describe the flow behaviour of fresh concrete.

The flow behaviour (plastic flow) is characterised by two parameters, yield stress and

plastic viscosity, however, a slump of fresh concrete is the most practical measure and

the most widely accepted approximation of the rheological behaviours of concrete. The

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slump of plastic state concrete is not only indicative of flow behaviour, which includes

the workability and finishability of fresh concrete, but also is used to control

consistency of concrete mixes.

Variations in slump of concrete can be caused by factors related to concrete mix design,

especially to the amount of water per cubic metre of concrete and by factors related to

the aggregate, especially to combined grading, shape, and water absorption.

CSIRO (1998) reports on an 80mm slump of 25MPa RA Concrete and a 70mm slump

of control NA Concrete of identical mix proportion, with the same w/c ratio of 0.45.

The ‘Guide for Specification of Recycled Concrete Aggregate for Concrete Production’

identifies a set of properties that are equally achievable in both the RA Concrete and

NA Concrete of the same amount of cementitious binder (CSIRO, 1998). Mix

proportioning, batching, placing and finishing of concrete made from RC Aggregate

require similar procedures and equipment as for conventional concrete. The optimal

ratio of the coarse to fine aggregate in RA Concrete required for desired cohesiveness is

the same as in NA Concrete, and cohesiveness and workability of fresh concrete are

comparable providing the grading and shape of aggregates are similar. However,

additional pre-wetting is suggested to control water demand in RA Concrete. Otsuki,

(2003) proposes a double-mixing method for improving strength, chloride penetration,

and carbonation resistance of RA Concrete.

Although Lauritzen (1994) reports on a reduction in compressive strength in RA

Concrete by up to 20%, the CSIRO Guide shows that it is possible for RA Concrete to

achieve the same compressive strength as the (N25 grade) NA Concrete, providing

commercially available RC Aggregate has adequate quality. There is a presumption

that the presence of significant volumes of the cement paste residue in the aggregate

might have some effect on elastic properties such as drying shrinkage, and creep.

However, the measured drying shrinkage of RA Concrete with a compressive strength

of 25MPa did not exceed the specified 700 microstrains (CSIRO, 1998).

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Trial mixes are recommended to optimise fresh and hardened properties of RA

Concrete, and the use of fly ash is desirable to minimise or eliminate possible alkali-

silica reactivity of the aggregate (Bowie 1999; Brand 1999).

Sagoe-Crentsil (1999), states that the predominant mode of failure, when RA Concrete

is subjected to compressive force, is either due to the aggregate or the cement paste and

depends on the target compressive strength. RA Concrete of a compressive strength of

25MPa and below predominantly fails in the cement paste due to the lower binder

content, whereas in RA Concrete of compressive strength higher than 25MPA, failure

occurs in the aggregate. This might suggest that the compressive strength of 25MPa at

28 days is the optimum for RA Concrete.

Compressive Strength

The compressive strength of concrete is affected by both the aggregate properties, and

the characteristics of the new cement paste that is developed during the maturing of

concrete. The potential strength of concrete is partially a function of aspects related to

mix proportioning such as cement content, water/cement ratio and choice of suitable

aggregate but also a function of proper curing when chemical bonding develops. The

w/c ratio, proper compaction and adequate curing, affect the development of concrete

microstructure, and also affect the amount, distribution and size of pores. Mindess

(1981) states that porosity is the primary factor governing the strength of concrete.

The bond that is developed when concrete hardens is the aggregate-paste bond, which is

both physical and chemical. Ryan (1992) suggests that to maintain the most

advantageous aggregate-paste bond some chemical activity between some reactive

elements of the aggregate and hydration products in cement paste has to develop. The

presumption is that RC Aggregate might develop an even stronger chemical bond with

cement paste, as the chemical composition of the aggregate is different from those of

commonly used natural aggregates and the re-bonding of some elements in cement paste

residue can take place (Brand, 1999; Tabone, 2001). The most important parameters of

the aggregate affecting compressive strength are its shape, texture and maximum size.

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Although the strength of the coarse aggregate is one of the dominant factors in

classification of concrete aggregate, Mindess (1981) states that to some extent it is of

less importance as most of the aggregates are stronger than cement paste. Despite the

presumption of a probable stronger bond between fresh cement paste and RC Aggregate

in low grade concrete, Sagoe-Crentsil (1999) reports on a reduction of compressive

strength gain at 28 days of 10% in comparison to control (N25) natural aggregate

concrete. Sautner (1999) indicates that the reduction in compressive strength

development in N20 concrete at 3 days was 29%, at 7 days was 20%, and at 28 days

was 11.5%.

Durability

As the compressive strength of concrete remains the most recognisable and desirable

property, an understanding of various transport mechanisms and deterioration processes

in concrete matrix becomes equally important. As Andrews-Phaedonos (2001) states,

durability is now regarded as an integral part in the design of concrete structures, and

that durability enhancing parameters are explicitly built into design specifications.

Durability of concrete is a function of many design and production aspects which

include the choice of an optimum w/c ratio at the mix design phase, as well as proper

compaction and curing. Further, the durability of concrete can be enhanced by

inclusion of pozzolana such as fly ash, GGBF slag and silica fume.

A selection of low w/c ratios of approximately 0.4 reduces bleeding of concrete and

does not result in an excess of free water in concrete, and can consequently contribute to

ultimate microstructure development of relatively impermeable concrete, as the amount

of capillary voids is reduced and the voids are disconnected. Whereas the selection of

higher w/c ratios results in a higher volume of interconnected capillary pores which

contribute to high permeability and reduced durability of the concrete.

Compaction of concrete also has a significant effect on concrete durability. Lack of, or

inadequate compaction contributes to low durability of concrete, as the trapped air in

fresh concrete is not expelled from the material. Although the entrapped air voids are

not interconnected they can also cause durability problems (Neville, 1999).

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The use of the optimum curing method and its duration of properly proportioned and

compacted concrete results in durable concrete. The maintenance of continuous moist

curing in particular, contributes to a higher degree of hydration which reduces the

amount of capillary pores as un-hydrated cement contributes to capillary porosity

(Andrews-Phaedonos, 2001).

Apart from factors related to the quality of cement paste (microstructure development,

capillary porosity) and its effects on durability of concrete, there is a potential for

aggregate to influence durability of concrete. Aggregate containing certain siliceous

minerals might undergo a reaction with soluble alkalis in concrete known as the alkali-

silica reaction (ASR). Reactive forms of silica in aggregate react with alkalies such as

potassium and the sodium hydroxides present in cement to produce alkali-silica gel.

Moisture transporting through the concrete matrix, then alkali-silica gel swells inducing

pressure, expansion, and cracking. It has been widely accepted that inclusion of silica

fume or fly ash reduces suspected aggregate alkali-silica reactivity (Neville, 1999; Day

1999; Nawy, 1997).

There are numerous indirect tests to assess durability of concrete. Those indirect tests

measure either permeability or absorption of concrete and include:

• Water Permeability (this test takes one to several weeks to complete)

• Gas Permeability – nitrogen adsorption (which is relatively quick test)

• Rapid Chloride Permeability Test (RCPT) (which takes only up to four days to

complete although a 90-day chloride pounding is necessary to properly correlate the

data)

• Initial Surface Absorption Test (ISAT)

• Porosity Tests – Mercury Intrusion Porosimetry (MIP)

• Sorptivity Tests – (which requires a 21day preparation and conditioning period)

Andrews-Phaedonos (2001) argues that those tests have to be undertaken by experts in

specialised laboratories and that there is a need for more user friendly and simpler tests

to assess permeability or absorption characteristics of concrete relatively quickly.

Currently in Victoria, the Apparent Volume of Permeable Voids (VPV) test in

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accordance with the Australian Standard AS 1012.21-1999 is most commonly used

(SAA, 1999).

CSIRO (1998) suggests that long term durability of RA Concrete has to be closely

investigated as besides adequate compressive strength, the resistance to deteriorating

mechanisms is of paramount importance in concrete structures. Several areas of

concern are identified: possibility of chemical contamination including chloride and

sulphur based deposits affecting rheology, setting characteristics and durability, and

porosity of the cement paste residue component of RC Aggregate affecting concrete

permeability.

2.7.2 Acoustic Properties

As concrete undoubtedly has become the most dominant material in noisy urban

environments, its acoustic properties have become very important design and

performance criteria. In standard construction and buildings, concrete is recognised for

its good sound insulating properties as it contributes to the provision of acoustically

comfortable living environments expected by modern society (CCAA, 1999).

There are two parameters describing acoustic properties of concrete, the sound

transmission loss or class (STC) and sound absorbency. Sound absorption depends on

the porosity of concrete whereas sound transmission loss depends on density of

materials per unit area. The high-density concrete has higher STC and does not absorb

sound energy whereas low density concrete is a good sound insulator and can have

some sound absorption capacities. To increase the STC of concrete, structural and non-

structural elements such as partitions or external walls and sandwich panels are often

used (Mindess, 1981).

Lightweight concrete which is less dense and more porous absorbs sound energy better

than normal density concrete. However, the total porosity of concrete not only

contributes to sound absorption, but to a greater connectivity of pores. For example,

concrete made from lightweight aggregate which has irregular interconnected pores,

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absorbs sound energy better than more porous foamed or aerated concrete which has

discrete, unconnected air entrained bubbles (Mindess, 1981).

In terms of sound absorption there are two commonly used testing methods to examine

acoustic properties of acoustic materials, these are the reverberation chamber method

(SAA, 1988) and the impedance tube method (SAA, 1999).

2.7.3 Porosity and Fractal Dimensions

Porosity

Porosity of concrete is a function of the combined porosities of aggregates and hardened

cement paste (HCP). Section 2.5.6 of this document reviews the porosity of coarse

aggregate whereas this section reviews porosity of cement paste and the combined

porosity of concrete.

Primarily, the porosity in HCP can be in the form of gel pores, capillary pores, or

entrapped air voids. In cement pastes, the intrinsic gel porosity results from a chemical

reaction between elements and compounds present in the cementitious binder and water.

This type of porosity depends on the degree of hydration and maturity of the paste. The

formation of gel pores is complete as long as there is sufficient water to hydrate cement,

and w/c ratio is above 0.4 in concrete without water-reducing admixtures. Another type

of porosity, capillary porosity, is caused by the movement of free water in hardening

cement paste, which usually results from excessive (free) water if the w/c ratio is above

0.4. The presence of entrapped air voids in concrete is mainly due to insufficient

compaction of concrete and also to the shape and grading of aggregate (Mindess, 1981).

Although, fundamentally there are mainly three types of pores in concrete: gel,

capillary, and entrapped air, different authors tend to expand the basic classifications

and in some instances do not agree on the pore size range (Mindess 1981;

Ramachandran 2001; Mehta 1986; Nawy 1997).

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Ramachandran (2001) classifies pores in hardened cement paste into three main types:

interlayer space in C-S-H (previously termed as gel pores), capillary pores, and air

voids, and states that the size of the capillary pores is dependent on w/c ratio and degree

of hydration. Well hydrated, low w/c ratio cement pastes have smaller pores, in ranges

between 100Å and 500Å, whereas cement pastes of higher w/c ratio can have capillary

voids up to 5,000Å.

Mindess (1981), states that gel pores mainly affect shrinkage and creep of the cement

paste whereas large capillary pores in pore sizes ranging between 50nm and 10μm

affect the strength and permeability of cement paste; and medium capillaries, in a pore

size range between 10nm and 50nm also affect shrinkage at high humidity. Nawy

(1997) alternatively classifies pores in cement pastes by the size of pores into three

groups: micropores, mesopores, and macropores. Table 2.7 presents an alternative

classification of pores in concrete and the size range of each type of pores.

Table 2.7 Porosity classification (Nawy 1997; Ramachandran 2001)

Pore Type Size Range [nm]

Micropores (Gel pores) - Interparticle spacing between C-S-H < 2.5 Small capillaries 2.5 - 10 Mesopores Medium capillaries 10 - 50 Large capillaries 50 – 10,000 Macropores Entrapped air bubbles or voids 1,000 – 1x106

Porosity is a physical property that influences mechanical properties of concrete such as

its strength, durability, shrinkage, creep, permeability, and ionic diffusion. Total

porosity of properly proportioned, placed and cured hardened concrete depends on pores

developed in a cement paste, entrained or entrapped air voids, and voids in the pieces of

aggregate particles. Porosity in the form of continuous channels, or micro-cracks can

also develop as a result of curing and environment conditions (Mehta, 1986). The total

porosity of poor quality concrete can be as high as 15%. This is derived on the

assumption that the average quality hardened cement paste contains approximately 50%

of air or water filled voids, and that natural aggregate commonly used in concrete

technology has porosity of up to 5%.

Parameters defining porosity include pore size distribution, pore size (commonly

expressed as pore diameter) pore surface area, and volume of pores. Any of the

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parameters or any combination of them influence in different ways various properties of

hardened concrete. Frias (2000) argues that the pore size distribution of pore system in

concrete, rather than the total porosity is the critical factor affecting the performance

and durability of concrete. Bagel (1997) presents results of porosity measured by the

Mercury Intrusion Porosimetry (MIP) method of cement pastes of different

water/cement ratios of 0.4, 0.5, 0.6, and 0.7 hydrated for 28 days. Table 2.8 summarises

the results.

Table 2.8 Porosity of cement paste (Bagel, 1997)

Water/cement ratio Parameter Unit 0.4 0.5 0.6 0.7

Pore volume mm3/g 43.9 48.7 75.9 66.8 Pore radius nm 71.1 68.1 74.4 78.1 Surface area m2/g 3.27 3.54 3.45 2.77 Total porosity % 12.1 11.4 16.5 14.6

Neville (1999) further relates the quantity and characteristics of various pores and voids

to concrete strength, elasticity, shrinkage, and permeability. In relation to concrete

strength, the total volume of pores not their size or continuity, has a dominant influence.

Drying shrinkage of concrete is influenced heavily by the total surface of the pore

system, whereas permeability is reported to be affected by the volume as well as size

and continuity of the pores.

Eighmy (2003) also reports on the examination of a 15-year-in-service concrete

pavement (mean compressive strength of 35MPa) and prediction of future behaviour of

concrete made from recycled materials of the same composition, and mix proportions of

concrete compressive strength of 40MPa. Table 2.9 presents total porosity and surface

area of pores in RA Concrete.

Table 2.9 Porosity a 15-year-in-service concrete (Eighmy, 2003)

Property Unit 40MPa laboratory made concrete

35MPa field-aged concrete

Porosity % 8.2 – 10.2 10.0 – 13.4 Effective surface area m2/g 2.3 – 11.5 1.4 – 2.9

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Hansen (1987) investigated porosity of cement pastes of 0.4, 0.6 and 0.75 water/cement

ratios. Surface area and pore volume of various neat cement pastes are presented in

Table 2.10.

Table 2.10 Porosity of neat cement paste (Hansen, 1987)

Water/cement ratio Parameter Unit 0.4 0.6 0.75

Total surface area m2/g - 84 96 Capillary pores (2.6nm - 70nm) surface area m2/g - 84.7 92 Cumulative pore volume (at p/po =0.965 corresponding to a pore diameter ~70nm)

cm3/g - 0.158 0.188

Cumulative capillary pore volume cm3/g - 0.153 0.193 Pore volume of pore diameters <4nm cm3/g 0. 052 0.035 0.038 Total pore volume cm3/g 0.127 0.263 0.325 Bulk density g /cm3 1.99 1.83 1.76

Kriechbaum (1994) reports that the specific surface area of various Portland cement

pastes measured by the BET method ranges from 40m2/g to 70m2/g.

Nawy (1997) indicates that the development of the physical microstructure of a cement

paste is related to the hydration process of cement influenced also by total water content

per cubic meter of concrete which sometimes results in concrete bleeding. Excessive

water causing concrete bleeding, contributes to a higher capillary porosity, the

connectivity of which can be expressed as the apparent volume of permeable voids

(VPV) in the cement paste of hardened concrete. Table 2.11 presents total porosity on

cement pastes of various w/c ratios. A good correlation between total porosity and

apparent volume of permeable voids validates the VPV methods as a compelling

indicator of total porosity.

Table 2.11 Porosity and apparent VPV of various cement pastes (Nawy, 1997)

Water/cement ratio Parameter 0.26 0.28 0.4 0.5 0.6 0.75

Total porosity [%] 7.5 8.8 11.3 12.5 12.7 13 Apparent VPV [%] 6.2 8.0 12.2 12.7 12.5 13.3

It is understandable that the microstructure development and porosity of concrete have

direct impact on many physical and mechanical properties of concrete, such as density,

which consequently might have effects on the acoustic characteristics of concrete.

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However, Diamond (1999) points out that the fundamental microstructural

characteristics of concrete are still not perfectly understood. He also states that

geometrical characterisation including that of fractal geometry, has not been addressed

adequately by researchers.

Fractal Types and Dimensions

Furthermore, in addition to the usual characterisation of porosity expressed in terms of

pore size distribution, total pore volume, the description of the geometry of pores would

complete the picture. Diamond’s (1999) study on concrete porosity using backscatter

SEM revealed that pores in concrete are fractal in nature. A geometry of the capillary

pores, which are formed at the time when concrete sets and are remnants of space that

existed between cement grains in the fresh concrete is far from the assumed model of

regular and spherical model approximation. Diamond (1999), states that the majority of

capillary pores are elongated and irregular, and highly convoluted in outline with only

some of the more regular triangular or ovoid shapes. Larger pores and voids including

entrapped air of typical diameter of about 50μm are assumed to be nearly spherical.

Accidental air pockets which form much larger bubbles are assumed to be of an

irregular shape (Neville, 1999).

The fractal nature of the concrete microstructure described by Russ (1992) is

approximated to a dense object within which exists a distribution of pores, which are of

a fractal nature. The boundaries between the solid and pore elements in concrete even

in spherical pores, appear to be rough and highly convoluted, all of which affects

porosity measurements. In three-dimensional space a topological dimension is 2 and

the fractal dimension of a boundary surface is between 2 and 3 consisting of a fractional

component between 0 and 1. Russ (1992) states that the higher the fractional

component of the fractal dimension, the greater the visual appearance of the roughness

of the boundary. Mixed fractals reported by Diamond (1999) indicate the occurrence of

two different classes of pore geometry where higher fractal dimension represents the

more convoluted capillary pores, and lower fractal dimension describes a less rough

pore system.

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Waste influence on porosity

The nature of cement and the formation of four major minerals in hardened cement

paste also affect porosity of concrete. Chandra (1997) states that some elements

contained in waste have an influence not only on hydration reactivity, strength, setting

time and durability, but also on microstructure of hardened cement paste. Even small

amounts, as low as 0.1% of some elements on top of expected standard amounts

included in cement can influence microstructure development of HCP. Increasing the

content of some elements such as: addition of 0.7% of phosphorus results in a slight

increase of large pores; addition of 0.5% of fluorine results in an increase of total

volume of pores and of volume of larger pores; addition of chlorine results in an

increase of small capillary pores; addition of 1% of chromium results in an increased

amount of large capillary pores. Whereas increased amounts of manganese, and/or

magnesium does not affect pore volume and pore size distribution in hardened cement

paste. Table 2.12 presents the pore structure of HCP containing various added elements

that might be present in concrete waste.

Table 2.12 Porosity of hardened cement paste with added various elements contained in concrete waste (Chandra, 1997)

Added element

P F Cl Cr Mn Amount added

0.7% 0.5% 2.0% 0.1% 0.1%

Pore size Control porosity [%]

Pore volume [%] 3-5nm 0.75 1.25 1.5 0.75 0.75 1 5-50nm 4 5 4 2 6.5 2.5 50-500nm 8.5 12 11 4.5 7 7 500nm-5μm 21.5 16 20 25.5 22.5 23.5 5-30μm 4.5 5.5 6 7 5.5 5 Total volume

39.25

39.75

42.5

39.75

42.25

39

2.8 USE of CONVENTIONAL and NEUTRON SCATTERING TECHNIQUES in TESTING of CONCRETE PROPERTIES

The microstractural characteristic of concrete depends on many factors including total

porosity, pore volume, pore size distribution, pore surface area, interfacial features, etc.

An adequate understanding of these factors is crucial in devising durable concrete.

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Determination of concrete properties also necessitates application of diverse techniques

to examine those properties. Besides gaining information on a specific characteristic of

concrete, Day (1999) identifies three other main purposes for concrete testing: to

establish whether the concrete attained sufficient maturity for stripping, stressing, etc.;

to establish whether the concrete is satisfactory for the intended purpose; and to detect

quality variations in supplied concrete to a given specification.

In practice, over 90% of tests on concrete are to test its compressive strength and slump

(Day, 1999). Some other tests, apart from the slump test to assess fresh concrete

properties include: various workability tests other than slump test; bleeding, air content,

setting time, segregation time, unit weight, wet analysis, temperature, and heat

generation.

Some tests measuring hardened concrete properties include: compressive strength,

tensile strength (direct tension, modulus of rupture and indirect/splitting tensile

strength) density, shrinkage, creep, modulus of elasticity, absorption, permeability,

freeze/thaw resistance, resistance to aggressive chemicals, resistance to abrasion, bond

to reinforcement, etc.

In assessment of the porosity of concrete there are numerous methods measuring

various aspects and parameters of concrete porosity. Diamond (1989) states that the

following methods can be used: optical microscope, liquid displacement techniques,

Mercury Intrusion Porosimetry (MIP), Brunauer-Emmett-Teller (BET) nitrogen or

water vapour adsorption, helium inflow, image analysis, Low Angle X-ray Scattering

and Nuclear Magnetic Resonance (NMR).

It appears that there is a wide range of standard research techniques used to characterise

physical and mechanical properties of concrete. However, in examination of concrete

porosity where the range of pore sizes typically spanning six to seven orders of

magnitude, from a fraction of a nanometer (~0.35nm) to a hundred microns (~350μm)

there is no single technique to measure this range and different techniques yield

different values (Sereda, 1980). Commonly, Mercury Intrusion Porosimetry and BET

gas adsorption are used to determine pore size distribution, pore volume and specific

surface area of pores in concrete. In terms of non-distractive methods Bhattachrja,

2-40

(1993) suggests the Nuclear Magnetic Resonance for measuring total pore volume and

surface area of cementitious materials: and Allen (1999) reports on the use of Small

Angle X-ray and Neutron Scattering (SAXS and SANS) in the examination of

microstructures of cementitious materials. The use of non-destructive methods has

increased as they provide supplementary data to those customarily used in concrete

research (MIP and BET).

2.8.1 Conventional Techniques

Conventional techniques to measure microstructure of cementitious materials include

Mercury Intrusion Porosimetry, BET nitrogen (or other gases used as sorbents)

adsorption, and various permeability measurement techniques. Analysis of optical

microscope, TEM or SEM images, can also be used in the determination of pore size

distribution, and specific surface area in cementitious materials. However, all those

conventional techniques require special sample preparation which also includes

complete drying of the samples. This can damage pore structure in cementitious

materials leading to erroneous results.

The two most commonly used volumetric experimental methods of estimating pore

volume and diameter are the gas adsorption method (also known as the Brenauer-

Emmett-Teller method BET) and the mercury porosimeter method (MIP) which

measures a wide range of pore sizes. The range of pore size measured with BET is

between 0.35nm and 70nm, and measured with MIP between 3.5nm and 200μm

(Hansen, 1987) whereas Thomas (1997) reports that the range of pore size measured by

BET nitrogen adsorption is from 15Å to 200Å, and the range measured by MIP is

between 100Å and 100μm.

Although MIP is commonly used, Diamond (1999) argues that MIP does not provide an

adequate approximation to the true size distribution of pores in hydrated cement

systems, as the microstructure is damaged by the sample preparation regime, and is

further damaged during examination, as the mercury is forced under significant

pressure. In the MIP method, mercury is forced into the pore system of a porous

material and absorbed volume is directly measured. Although the mercury

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porosimetery method is used to estimate pore volume and pore size distribution of pores

as small as 35Å in diameter, Thomas (1997) states that it is impractical to force mercury

into pores of diameter lower than 100Å.

Despite a widespread acceptance of the MIP method in examination of porosity of

hydrated cementitious materials, Cook (1999) gives an account of the destructive nature

of this technique. The pressure of mercury generated during an experiment is

approximately 300MPa, which in case of a non-continuous pore system enforces

mercury penetration by breaking through pore walls. MIP is said to give smaller than

actual porosity as mercury cannot penetrate either pores smaller than 10nm, or isolated

pores whose walls cannot be broken by high pressure.

Brenauer-Emmett-Teller (BET) Method

The gas adsorption method is based on the phenomenon of gas condensation in narrow

pores at pressures lower than saturated vapour pressure of the examined material.

Classically, volumes of gas progressively adsorpted by the material, and those of gas

progressively desorpted, are represented by the isotherms (plot of relative pressure p/p0

versus pore volume) (Gregg, 1982). There are six principal types of adsorption

isotherms that are indicative of the porosity of tested material and pore nature. As an

example: Type-1 isotherms are characteristic of microporous adsorbents with pore size

below 20Å; Type-2 and Type-3 isotherms are indicative of non-porous solids; Type-4

and Type-5 isotherms are characteristic of a mesoporous solid with pore size range

between 20Å and 500Å. Figure 2.3 presents the six main types of adsorption isotherms.

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Figure 2.3 Six types of adsorption isotherms (Gregg, 1982)

The non-porous solids subjected to BET nitrogen examination produce isotherms where

the path of the adsorption line on a plot of relative pressure (p/p0) versus amount of gas

adsorbed is the same as the desorption line.

The desorption isotherms produced by porous solids produce a hysteresis loop formed

by path difference between adsorption and desorption of gas in the pore structure of

tested material. Figure 2.4 presents the adsorption and desorption isotherms

characteristic to porous solids of microstructure of continuously graded pores.

Figure 2.4 Adsorption and desorption isotherms for a porous solid (Gregg, 1982)

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When the pore size distribution of solid material microstructure has limited pore size (is

not continuously graded) the adsorption and desorption isotherms tend to create a

hysteresis loop above (0.0 < p/p0 < 0.5) and below (~0.8 < p/p0 < 1) reversible regions

of the isotherms. Figure 2.5 shows the adsorption and desorption isotherms of solids

with limited pore size.

Figure 2.5 Adsorption and desorption isotherms for a solid with limited pore size

(Gregg, 1982)

Thomas (1997) states that the shape of the hysteresis in the adsorption-desorption

isotherm is related to the pore geometry of tested porous material. The isotherms can

form five types (Type A, B, C, D and E) of hysteresis loops. Figures 2.6, 2.7 and 2.8

present possible hysteresis loops and possible pore structure.

Figure 2.6 Type A hysteresis loop and possible pore structures (Thomas, 1997)

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The Type A hysteresis is indicative of capillary pores of the ink-bottle shape where the

body of the pore has a radius much higher that the pore entrance. The width between

the adsorption branch and the desorption branch of the isotherm indicates the difference

in diameter of the neck and body of the ink-bottle-shaped capillary pores (Thomas,

1997).

Figure 2.7 Type B hysteresis loop and possible pore structures (Thomas, 1997) Type B hysteresis is produced when in the desorption cycle, the pores are emptied at

relative pressure corresponding to the width of the pore and the adsorption branch has a

step at relative pressure of unity. Type B hysteresis is characteristic of pores formed by

parallel plates or ink-bottle-shaped pores with body diameter of 1,000Å.

Figure 2.8 Type C hysteresis loop and possible pore structures (Thomas, 1997)

Type C hysteresis is characteristic of spheroidal pores with circular cavity radius having

various-sized entrances.

2-45

Scanning Electron Microscopy

Scanning Electron Microscopy (SEM) is one of many tools to view microscopic objects

which also include the Optical Microscope (OP) and the Transmission Electron

Microscope (TEM). These tools are used to investigate topographical properties of the

surface of materials and to quantitatively analyse elemental composition of materials

(Brinkies, 1995). Table 2.13 presents a comparison between OP, TEM and SEM.

Table 2.13 Comparison between SEM and other microscopes

OM TEM SEM Specimen shape Thin film Thin film Bulk Specimen state Solid, liquid in the

atmosphere Solid in vacuum Solid in vacuum

Magnification x 2000 x 50 – 1,500,000 x 10 – 1,000,000 Ultimate resolution 200nm 1Å 5Å

Some of the advantages and important features the SEM offers are the ease of changing

magnifications and stereographic image display. SEM is fully computerised and images

can be photographed and analysed using image analysis techniques. Specimens in sizes

of 50nm to 1cm can be viewed using SEM at a range of magnifications of up to

1,000,000 times, whereas, TEM can be used to view objects in size between 1Å and

50nm (JEOL, n.d.).

The SEM can operate in various modes generating various kinds of signals including X-

ray, secondary electrons (SEI) imaging, and backscattered electron (BEI) imaging

which provide different types of information. The SEI mode is used in investigation of

surface topography of bulk materials whereas in the BEI mode compositional

observations of a deeper layer of specimen surface can also be achieved. The

backscatter electron image and data on elemental composition are a function of the

average atomic number of the substances composing the specimen surface. In the X-ray

mode of operation of SEM, an elemental analysis of specimen can be examined. When

an incident electron beam irradiates a surface of a specimen, characteristic X-rays are

emitted and then are detected on a signal detector. Analysis using the energy dispersive

X-ray spectrometer (EDS) determines elements and their atomic weight concentration in

2-46

an examined area of specimen. To identify elements in unknown specimens, the multi-

channel analyser has to be calibrated using known standard specimens (JEOL, n.d.).

The function of a common SEM is based on the operating principle of a cathode ray

tube (CRT). In the CRT, heating of a tungsten filament generates electrons at a

potential of several thousand volts. A generated electron beam is then focussed and

directed by electromagnetic coils, also known as condenser lenses, onto examined

specimens. A beam of 10nm diameter continually scans the surface of a specimen

where electrons are scattered and emitted from the specimen’s surface. Scattered and

emitted electrons produce images of the topographical or composition features of the

sample’s surface which are detected by secondary electron or backscattered electron

detectors (JEOL, 1998).

One of the limitations of SEM is that only very small area of the sample can be

examined (Brinkies, 1995). Although the X-ray Diffraction (XRD) is considered as a

more appropriate method to determine compound composition, when the objectives of

the project were taken into account, the SEM was deemed as an adequate method as it

contributes to SANS experimentation, and porosity and microcracks can be

investigated.

Apparent Volume of Permeable Voids Test

A whole range of tests to indirectly measure durability of concrete is available.

Although the apparent volume of permeable voids (VPV) test, which is relatively

simple and quick, is preferred in Victoria (Vicroads, 1997). The VPV test allows

relatively quick measurement of the amount of space occupied by interconnected,

permeable voids, which is regarded as a compelling indication of durability of concrete.

Some of the advantages of the VPV test is that simple laboratory equipment including

standard drying oven, heated water bath, water tank and balance are required to carry

out the test, and that it can be completed in 5 days.

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Day (1999) indicates that concrete specified for major projects in Melbourne has 100

year durability requirements and adequate indication of such durability is an equivalent

measure of apparent volume of permeable voids in hardened concrete of 9%.

2.8.2 Small Angle Neutron Scattering

Despite the lack of a rigorous approach to data interpretation and availability of

equipment the neutron scattering techniques have a potential to be very attractive

research methods allowing non-destructive examination of bulk materials in their

natural saturated state. The non-distractive nature of these techniques combined with

the lack of special preparation or pre-treatment of tested samples, are the main

advantages of neutron or x-ray scattering over conventional techniques. The lower

accessible pore size with the use of SAXS is of 30nm and by SANS is of 1Å, which

extends the accessibility of conventional techniques such as MIP and BET gas

adsorption by an order of magnitude. Livingston (1995) states that because SANS can

access porosity not accessible to those examined by BET or MIP, the microstructure

characteristics including pore size distribution and inner surface area will not be

commensurate.

In neutron scattering, the microstructure information is in the form of a scattering

profile where the intensity of the scattering follows the scattering vector. The scattering

is dominated by the interface between solid and empty, or filled with water (D2O or

H2O) pores in concrete matrix. The scattering profile is a kind of modified Fourier

transform of the solid-pore structure over many length-scales ranging from nanometer

to micrometer, which at high scattering angles directly follows Porod’s law.

Determination of quantitative microstructural parameters of cementitious materials is

only possible if the composition and density of the solid are accurate. One way of

determining possible composition and density of hydrated cements and concrete is by

contrast variation studies where there is a strong difference between scattering from

D2O bound solid (C-S-H particles) and H2O bound C-S-H (Allen, 1987). Radlinski and

Hilde (2003) state that elemental composition measured with SEM can be used to

calculate density of solid part of concrete matrix. Table 2.14 presents a comparison of

2-48

parameters determined by conventional and neutron or X-ray scattering techniques

related to microstructure of cementitious materials (Livingston, 1995).

Table 2.14 Range of porosity related parameters measured by conventional and neutron scattering techniques

Conventional Methods SANS/SAXS Parameter Method Parameter Symbol Total surface area BET gas adsorption Total surface area Si - - Porod surface area Sv - - Fractally rough surface area Sf - - Surface fractal dimension Dv Total porosity MIP Total porosity ΦN Capillary porosity MIP Capillary porosity - Gel porosity MIP Gel porosity - - - C-S-H volume ΦC-S-H - - Gel volume + fractal porosity ΦGEL - - Volume fractal dimension Dv - - Volume fractal correlation length Eν - - C-S-H globule radius Rg

It can be seen that neutron scattering techniques seem to be a very versatile tool that

offer wider than conventional techniques, possibility of examining a broader range of

parameters, and as such have the ability to provide more precise characterisations of

microstructure of cementitious materials including RA Concrete, and cement paste

residue of RC Aggregate.

Despite pioneering work done by Winslow, Allen, Hansen, Livingston and others,

Sabine (1995) points out that interpretation of SANS profiles from hydrated cement is

not simple and is also a function of scattered particle shape, which can be quasi-spheres,

quasi-spheres plus disks, or characterised by fractal parameters.

Small Angle Neutron Scattering

Livingston (1995), states that the materials science of hydrated Portland cement

products is still not completely worked out. This is partially due to the fact that

conventional methods have certain limitations and are destructive to a certain extent.

Inner porosity examinations by either MIP or BET gas adsorption methods, or outer

porosity examinations with Scanning Electron Microscopy require sample preparation

2-49

that has the potential to disturb its microstructure, or the techniques themselves can be

destructive. Various neutron scattering techniques including the Ultra Small Angle

Neutron Scattering (USANS), Small Angle Neutron Scattering (SANS), Small Angle

X-ray Scattering (SAXS), and Small Angle Light Scattering (SALS) provide non-

destructive alternatives to MIP, BET nitrogen adsorption, or SEM. They provide

information on the statistical average structure over the whole sample (Allen, 1987).

In each of these techniques radiation is elastically scattered by a sample and the

resulting scattering pattern is analysed to provide information about the size, shape and

orientation of some component of the sample as well as fractal dimensions of the

concrete microstructure. Aldridge (1995) states that the gel pores (5Å – 100Å) and

medium capillary pores (100Å – 500Å) can be investigated with the use of SANS.

The Australian SANS instrument emits the incident flux of neutron radiation of

wavelengths from 0.06nm to 10nm, which allows a range of pores from 6Å to 10nm in

diameter to be probed. The incident flux of neutron radiation is collimated and directed

at a sample. Some of incident radiation is transmitted by the sample, some neutrons are

absorbed and some are scattered. The scattered neutrons are detected by a detector

which is positioned at some distance and scattering angle.

As the scattering from H2O and D2O is very different, the SANS technique, other than

its non-destructive nature for examining bulk material, offers a possibility of

undertaking the isotopic contrast variation experiments yielding information on the

permeation and diffusion of different types of water into porous systems (Allen, 1987).

However, the hydrogen present in light water (H2O) contributes to a multiple scattering.

Livingston (1995) proposes that to avoid the possibility of multiple scattering the

thickness of samples of cementitious materials should not exceed 1mm if the samples

are prepared with H2O. Concrete specimens prepared with D2O can be thicker.

Aldridge (1995) relates multiple scattering with the wavelength of the neutron beam and

sample thickness and proposes sample thickness of 2mm for wavelengths greater than

4Å.

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Although it is recommended that samples for SANS examination do not require oven

drying at 1050C, if the results are to be compared with those porosity data derived from

conventional methods, the samples can be oven dried. Livingston (1995) also suggests

that representative specimens of cement paste including aggregate should be examined,

as the microstructure development of concrete greatly depends on the amount of

aggregate and its characteristics.

Livingston (1995) indicates that neat cement paste and concrete specimens should be

prepared, cured and stored in a CO2 free atmosphere as carbonation can rapidly take

place in such thin samples.

Aldridge (1995) concludes that although the volumes of capillary pores of cement

pastes of 0.25 and 0.8 water/cement ratio should differ significantly the SANS

scattering profiles obtained in his experiment were not different. He speculates that

scattering was from amorphous globules of C-S-H for data obtained at the scattering

wave vector (Q) of 0.0056 to 0.05Å-1and from the gel pores in the C-S-H at Q range

between 0.05 and 0.21Å-1. He calculated the average radii of globular entities

producing scattering profile to be 350Å and gel pores to be 50Å.

2.9 USE of CONCRETE in ACOUSTIC BARRIERS

2.9.1 Road Traffic Noise and Noise Mitigation Methods

Kotzen (1999) states that an urban population in modern cities is constantly exposed to

excessive noise due to an increase in large-scale transport facilities including

motorways and railways. Noise levels generated in urban transport infrastructure

depend mainly on type, volume, and speed of the transportation noise source.

Road traffic noise is characterised by two parameters; sound pressure level (SPL) and

frequency spectrum of the sound. Intensity of road traffic noise is predominantly a

function of the volume of traffic as well as type and proportion of vehicle types (heavy

and light vehicle) in the traffic flow. The sound pressure level generated by vehicles is

mainly a function of engine and exhaust emitted noise, which is further amplified by the

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noise from a tyre-surface interaction. The tyre-surface interaction noise contribution is

predominant at frequencies above 1,000Hz. The dominant noise of transportation

traffic lies between frequencies of 100Hz and 1,000Hz. Figure 2.9 illustrates the noise

spectra of a typical road traffic noise caused by heavy and light vehicle traffic (Nelson,

1987).

Figure 2.9 Noise spectra for heavy and light vehicles traffic (Nelson, 1987)

Average road traffic noise generated by heavy vehicles exceeds 76dB(A) (which

corresponds to no-weighted SPL of 85dB) in the low frequency range (up to 200Hz) and

in the mid-frequency range (between 200Hz and 500Hz). In the high frequency range

between 500Hz and 2kHz it exceeds 73dB(A) (which corresponds to absolute measure

of noise of 80dB). Light vehicle road traffic noise is generally lower than heavy vehicle

noise by approximately 9dB at the corresponding frequencies.

Human response and effects on health and effects on day and night activities to

excessive transportation noise vary, and are dependent on many social and

environmental aspects. Although Nelson (1987) identifies the SPL of 65dB(A) as the

absolute upper tolerated acceptable limit by the community, the noise generated by

transportation infrastructure is much higher than the acceptable limit of 65dB(A).

To mitigate excessive transportation noise in urban environments, the noise levels of

newly constructed transportation infrastructure must now comply with the specified

limits. The most stringent requirements on transportation noise reaching residents

2-52

alongside transport infrastructure are in countries such as the Netherlands and Denmark

where the day noise level is limited to 55dB(A) (Kotzen, 1999). In Australia, the

Victorian State Road Authority, Vicroads sets the 63dB(A) as the limit for newly

constructed roads and 68dB(A) for existing roads (Vicroads, 1994).

There are various measures that can be employed to mitigate road traffic noise which

include increasing the distance between noise source and affected residential areas, the

use of tunnels, false cuttings and earth mounds, employment of quieter road surfaces,

provision of better noise insulation of residential dwellings, and installation of acoustic

barriers.

Currently acoustic barriers seem to be the most practical way of mitigating

transportation noise. Despite that, Hemond (1983) questions the effectiveness of

highway sound reflective barriers to reduce low frequency noise generated by heavy

vehicles, due to diffraction (bending of waves around barriers) of long wavelength

noise. Kotzen (1999) states that in urban environments the most feasible option in

reducing the annoyance of transportation noise is to erect vertical, cantilevered or bio-

barriers. In terms of acoustic performance there are three types of barriers; reflective,

dispersive, and sound absorptive.

Kotzen (1999), states that in Europe there is a tendency to use absorptive barriers that

acoustically soften the environment because the height of the barrier can be reduced

and/or to reduce the buffer zone width to achieve required noise reduction. Day (2004)

proposes a general guide to illustrate the benefits of using absorptive barriers over

reflective type barriers. For example, to reduce noise level to 60dB(A) a 3-meter high

absorptive barrier or 4-meter high reflective barrier would be required. Day (2004)

indicates that the buffer zone reduction of approximately 50 meters can be achieved by

substituting a 4-meter high reflective barrier with an absorptive barrier of the same

height.

2.9.2 Sound Absorbing Barriers

In Victoria, reflective barriers made from concrete, timber or plastic are usually

installed alongside busy arterial roads with lesser use of sound absorptive barriers.

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Noise attenuation of reflective barriers generally depends on their location, height and

mass per unit area. This type of barrier is effective in situations when a noise source is

close to a residential area and the opposite side is an open space. Materials used for

reflective barriers include timber, pre-cast concrete, fibreglass reinforced concrete,

metal, and plastic. The life span of reflective barriers depends on material used, and

ranges from 15 years in the case of timber, to 40 years for concrete barriers (Schubert,

1988).

The main difference between reflective and dispersive barriers is the added benefit of

the dispersion of sound waves in any desired direction, usually upwards or downwards,

which prevents the noise build-up, which is likely to occur in the case of classic vertical

reflective barriers. The same type of materials as for reflective barriers can be used to

manufacture dispersive barriers.

The acoustic effectiveness of sound absorptive barriers depends on the internal structure

of the material used for the barrier, which must allow incident sound waves to enter the

matrix of the barrier. Part of the energy of the sound waves can then be dissipated and

the energy is converted into a combination of mechanical vibration and heat. The

remaining sound energy is reflected back into the noise source (Kotzen, 1999). Figure

2.10 presents a cross-section of an absorptive barrier.

Figure 2.10 Cross-section of typical absorptive-type barrier (GRC, 1990)

2-54

A subcategory of sound absorptive barriers is a reactive barrier, which according to

Kotzen (1999) incorporates a certain amount of cavities or resonators per area. The

reactive barrier is designed to attenuate specific frequencies of noise. In this type of

barrier, sound waves enter the cavities through the openings in the barrier surface.

A variety of materials can be used to manufacture any type of acoustic barrier with the

inclusion of concrete. In general, concrete barriers are designed and used as reflective

or dispersive barriers, however, Kotzen (1999) reports on the concrete reactive New

Jersey ‘Laghi’ barrier, and absorptive woodfibre concrete, and granular concrete

barriers. Granular and woodfibre concrete absorptive barriers comprise ‘either wood

fibres or small cementaceuos balls that are used as the aggregate’ Kotzen, (1999).

Figure 2.11 presents a granular concrete barrier.

Figure 2.11 Granular concrete barrier (Kotzen, 1999)

The acoustic performance of sound absorbing barriers is represented by two parameters,

sound absorption coefficient (α), and also calculated average known as noise reduction

coefficient (NRC). Table 2.15 presents a summary of the acoustic performance of

commercially available sound absorbing barriers used in Melbourne (Schubert 1988;

Hollow Core 2000; Unicrete Concrete 2000; GRC Composites 1990)

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Table2. 15 Sound absorption coefficient (α) and NRC of commercial barriers Frequency

1/3 Octave Band [Hz]

Rocla Sound-trap

Boral Durisol Kruss-crete

Anti Sound

Unibloc-5060

GRC

100 0.91 0.29 0.5 0.1 0.2 0.13 0.9 125 1.05 0.23 0.75 0.15 0.25 0.21 0.15 1.05 160 1.07 0.25 0.85 0.2 0.25 0.28 1.06 200 1.18 0.48 0.95 0.25 0.4 0.49 1.14 250 1.07 0.68 0.95 0.35 0.5 0.74 0.25 1.1 315 1.02 0.81 0.9 0.45 0.7 0.91 1.05 400 1.08 1.02 0.5 0.6 0.95 0.96 1.06 500 1.08 1.17 0.45 0.8 0.95 0.99 0.7 1.08 630 1.04 1.2 0.4 1 0.9 1 0.95 800 1.02 1.13 0.3 1.1 0.75 1 0.94 1000 0.93 0.97 0.28 1 0.7 0.99 0.95 0.91 1250 0.86 0.85 0.25 0.85 0.6 0.96 0.88 1600 0.77 0.82 0.25 0.8 0.4 0.99 0.8 2000 0.75 0.92 0.25 0.9 0.4 0.92 0.75 0.75

Noise reduction coefficient 0.96 0.94 0.48 0.76 0.64 0.91 0.66 0.96

In Victoria, the Victorian Road Authority, Vicroads sets the requirements for sound

absorbency of the noise attenuation barriers in its standard specifications for road and

bridge works (Vicroads, 1997). Section DC270A.05 specifies acoustic performance and

structural requirements related to sound absorptive noise barriers. It states that;

• the minimum mass density of surface area shall not be less than 15kg/m2

• the minimum area of wall tested for sound absorption in a reverberation room shall

be 12m2

• appropriate structural design standards should be used

• barriers should be designed such that any panel or fragments of the panels will not

fall on roadway if vehicles impact them

• barriers should not have holes or gaps allowing noise to pass through them

• materials used must be corrosion and ultraviolet radiation resistant

• the sound absorption coefficient should not be less than specified in Table

DC270A.051 (please refer to Table 2.16)

Table 2.16 Sound absorption coefficient (α) – Vicroads requirements

Frequency [Hz] 125 250 500 1000 2000 Sound absorption coefficient 0.70 0.80 0.90 0.90 0.80

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Calculated Noise Reduction Coefficient of barriers satisfying Vicroads requirements is

NRC 0.82.

There are numerous factors related to the choice of a type of sound barrier and material

used for its manufacture, including engineering, environmental and cost considerations.

Kotzen, (1999) identifies the following engineering and environmental considerations:

structural strength including wind, self-weight, static and dynamic loading

impact effects from stones and vehicles

safety of vehicles on collision with a barrier

durability of barrier materials including resistance to chemical agents, heat, and

ultra-violate light

maintenance requirements

Increasingly, ecological sustainability aspects are also considered when materials for

barrier design are chosen. Considerations include: the minimal energy used to transport

raw materials; manufacture and erection of the barrier; the maximum use of locally

available materials, preferably from renewable sources (Kotzen, 1999).

Visual integration and landscape integrity are also very important factors in devising

transportation infrastructure and although they are often given greater weight than cost

of the barrier in a cost-benefit analysis, in most situations, cost remains a dominant

factor in choosing the type and material for acoustic barriers. The cost of the barrier is

influenced by: design and materials of the barrier; support structure and foundation;

method of installation; maintenance requirements such as frequency inspections, repair,

cleaning, and treatment. Kotzen (1999) identifies maintenance cost as a significant

factor in selection of barrier and states that the cost of maintenance of concrete barriers

is relatively low when compared with other barrier types and materials.

Schubert (1988) specifies costs for the supply and erection of a range of different types

of acoustic barriers in Victoria. Although the prices are outdated, the relativity of cost

between different types of barrier has not changed. In general, the cost of supply and

installation of an absorptive barrier is on average twice that of the dispersive barrier and

three times as much as for the reflective.

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Apart from noise attenuation performance, structural properties, cost and aesthetics,

Schubert (1988) identifies the service life of acoustic barrier as an important criterion in

selecting material for the barrier. Commonly used reflective timber barrier has a

lifespan of up to 15 years whereas pre-cast concrete is up to 40 years.

Limited studies on sound absorbency of no-fines concrete were undertaken by the Road

Construction Authority however, as Schubert (1988) reports, it has been found that the

barrier produced of no-fines concrete made from a single size 20mm aggregate,

performed poorly in the 100Hz – 1000Hz frequency range. Table 2.16 presents sound

absorption capabilities of no-fines concrete in a frequency range between 63Hz and

500Hz (Vicroads, 2001).

Table 2.16 Sound absorption coefficient (α) of no-fines concrete barrier (Vicroads, 2001)

Frequency [Hz] 63 80 100 125 160 200 250 315 400 500 α coefficient 0.17 0.16 0.15 0.12 0.1 0.08 0.07 0.09 0.1 0.1

Day (2004) argues that using sound absorptive barriers instead of purely reflective

barriers has two main benefits; it reduces the height of the barrier to achieve required

sound pressure levels at the receiver or reduces a buffer zone between the barrier and

the receiver. Table 2.17 presents the benefits of using sound absorbing barriers (Day,

2004).

Table 2.17 Buffer zone width for reflective and absorptive barriers

Barrier type and buffer zone width [m] Barrier height [m] Reflective Absorptive None 500 500 3 180 90 6 35 20

Reduction of the height of the barrier leads to various benefits such as a reduction of the

amount of material used to manufacture a barrier, reduction of transportation and

installation requirements, resulting in the overall benefit of reduced use of resources and

energy. The use of sound absorbing barrier also results in lessening of visual

obstruction, which is due to the lower height of the barrier. Alternatively, if the same

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height of sound absorbing barrier remains, the buffer zone can be reduced. The

application of sound absorptive barriers results in more urban land being made available

for residential development, or for quieter urban environments adjacent to transportation

routes.

2.10 SUMMARY

The literature review outlined the current state of knowledge on aggregate for concrete,

especially on alternative coarse aggregate produced from concrete waste. The rationale

for concrete recycling and the use of alternative aggregate in concrete technology is

examined. It is supported with examples of the successful use of concrete made from

recycled concrete aggregate. The literature review also introduces transportation noise

pollution and the means of mitigating it in urban environments. Sound reflecting and

absorptive barriers have been reviewed and concrete barriers evaluated.

A number of conclusions have been reached based on available literature, discussions

and consultations with professionals from relevant engineering, research and scientific

disciplines, and the three main issues identified.

Firstly, there is growing evidence of the feasibility of substituting RC Aggregate for

natural aggregate in concrete manufacturing and also an increased use of selected RC

Aggregate in concrete production.

Secondly, there is evidence that some properties of RC Aggregate such as porosity,

shape and surface texture of the aggregate could have some positive impacts on the

mechanical and acoustic properties of concrete made from such aggregate.

And thirdly, the inherent and purposely introduced porosity of RA Concrete leads to

increased sound absorption of acoustic barriers made from such concrete.

This thesis reports upon the use of RC aggregate in a high value product, an absorptive

barrier for sound to replace reflective barriers. This new device utilises the properties of

RC Aggregate and enhances the performance of the acoustic barrier.

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The following chapter outlines methodology, and experimental and developmental

programs devised to increase the understanding of properties of locally produced

selected RC Aggregate, differentiate the aggregate from commonly used natural

aggregate, and characterises concrete and acoustic barrier made from the 14/10mm RC

Aggregate.

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CHAPTER 2 – LITERATURE REVIEW ........................................................................1 2.1 INTRODUCTION ............................................................................................1 2.2 CONCRETE CONSTITUENT MATERIALS .................................................2

2.2.1 Coarse Aggregate ......................................................................................4 2.3 ALTERNATIVE CONSTITUENT MATERIALS in CONCRETE ................6 2.4 CONCRETE WASTE and CONCRETE RECYCLING ..................................9

2.4.1 Alternative Sources of Coarse Aggregate ...............................................10 2.4.2 Current Applications for Recycled Concrete Products ...........................13 2.4.3 Under-utilisation of Recycled Concrete Aggregate ................................13

2.5 COMPARISON between NATURAL and RECYCLED CONCRETE AGGREGATE ............................................................................................................15

2.5.1 Shape and Surface Texture......................................................................16 2.5.2 Particle Size Distribution ........................................................................17 2.5.3 Water Absorption....................................................................................20 2.5.4 Particle Density and Bulk Density ..........................................................21 2.5.5 Impurities and Foreign Materials in RC Aggregate................................22 2.5.6 Aggregate Porosity..................................................................................23 2.5.7 Other Properties ......................................................................................24

2.6 NORMAL DENSITY and NO-FINES CONCRETE .....................................24 2.7 COMPARISON between STANDARD and RECYCLED AGGREGATE (RA) CONCRETE ......................................................................................................27

2.7.1 Physical and Mechanical Properties........................................................27 2.7.2 Acoustic Properties .................................................................................32 2.7.3 Porosity and Fractal Dimensions ............................................................33

2.8 USE of CONVENTIONAL and NEUTRON SCATTERING TECHNIQUES in TESTING of CONCRETE PROPERTIES.............................................................38

2.8.1 Conventional Techniques........................................................................40 2.8.2 Small Angle Neutron Scattering .............................................................47

2.9 USE of CONCRETE in ACOUSTIC BARRIERS .........................................50 2.9.1 Road Traffic Noise and Noise Mitigation Methods................................50 2.9.2 Sound Absorbing Barriers.......................................................................52

2.10 SUMMARY ....................................................................................................58 Figure 2.1 Concrete recycling plant setup (courtesy Recycling Industries Pty. Ltd.) ....12 Figure 2.2 Schematic representation of aggregate grading in an assembly of aggregate

particles: (a) uniform size, (b) continuous grading, (c) replacement of small sizes by large sizes, (d) gap-graded aggregate, (e) no-fines grading (Mindess, 1981)....19

Table 2.9 Porosity a 15-year-in-service concrete (Eighmy, 2003) .................................35 Table 2.10 Porosity of neat cement paste (Hansen, 1987)..............................................36 Table 2.12 Porosity of hardened cement paste with added various elements contained in

concrete waste (Chandra, 1997)..............................................................................38 Figure 2.3 Six types of adsorption isotherms (Gregg, 1982) ..........................................42 Figure 2.4 Adsorption and desorption isotherms for a porous solid (Gregg, 1982) .......42 Figure 2.5 Adsorption and desorption isotherms for a solid with limited pore size

(Gregg, 1982) ..........................................................................................................43 Figure 2.6 Type A hysteresis loop and possible pore structures (Thomas, 1997) ..........43

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Figure 2.7 Type B hysteresis loop and possible pore structures (Thomas, 1997) ..........44 Figure 2.8 Type C hysteresis loop and possible pore structures (Thomas, 1997) ..........44 Figure 2.9 Noise spectra for heavy and light vehicles traffic (Nelson, 1987) ................51 Figure 2.10 Cross-section of typical absorptive-type barrier (GRC, 1990)....................53 Figure 2.11 Granular concrete barrier (Kotzen, 1999)....................................................54 Table 2.1 Comparison between natural and RC Aggregate............................................16 Table 2.2 Particle size distribution of coarse aggregate – AS2758.1-1998 ....................18 Table 2.3 Particle size distribution of coarse RC Aggregate (Sagoe-Crentsil 1999;

Sautner 1999) ..........................................................................................................19 Table 2.4 Comparison of particle size distribution of the 14mm RC Aggregate and

locally manufactured basaltic aggregate .................................................................20 Table 2.5 Porosity of some common rock (Neville, 1999) .............................................23 Table 2.6 Porosity comparison between natural and RC Aggregate ..............................23 Table 2.7 Porosity classification (Nawy 1997; Ramachandran 2001)............................34 Table 2.8 Porosity of cement paste (Bagel, 1997) ..........................................................35 Table 2.9 Porosity a 15-year-in-service concrete (Eighmy, 2003) .................................35 Table 2.10 Porosity of neat cement paste (Hansen, 1987)..............................................36 Table 2.11 Porosity and apparent VPV of various cement pastes (Nawy, 1997) ...........36 Table 2.12 Porosity of hardened cement paste with added various elements contained in

concrete waste (Chandra, 1997)..............................................................................38 Table 2.13 Comparison between SEM and other microscopes ......................................45 Table 2.14 Range of porosity related parameters measured by conventional and neutron

scattering techniques ...............................................................................................48 Table2. 15 Sound absorption coefficient (α) and NRC of commercial barriers.............55 Table 2.16 Sound absorption coefficient (α) – Vicroads requirements..........................55 Frequency [Hz] ...............................................................................................................55 Table 2.16 Sound absorption coefficient (α) of no-fines concrete barrier (Vicroads,

2001) .......................................................................................................................57 Frequency [Hz] ...............................................................................................................57 Table 2.17 Buffer zone width for reflective and absorptive barriers ..............................57

3-1

CHAPTER 3 – METHODOLOGY and EXPERIMENTAL DESIGN

3.1 INTRODUCTION

The previous chapter summarised the literature review on aggregate for concrete

manufacturing, concrete in general, and the use of concrete in acoustic barriers. The

specific focus of the literature review was an evaluation of:

• recycling of concrete waste

• usage and properties of RC Aggregate

• concrete technology issues resulting from the use of RC Aggregate in new concrete

• testing and research techniques used in concrete technology and material science to

examine the basic physical and mechanical properties, especially those related to

porosity of aggregate and concrete

• use of non-destructive techniques including neutron scattering in the examination of

microstructure of cementitious materials

• use of concrete in acoustic products specifically in acoustic barriers for urban

freeways; and

• acoustic properties and acoustic testing of concrete barriers

The review of literature has been authenticated through ongoing personal contact with

professionals representing the concrete industry. They include concrete recyclers,

concrete product manufacturers as well as researchers in the relevant research fields that

include technical staff operating scientific instruments. Consulted professionals

included members of the following organisations:

Division of Building, Construction and Engineering, Commonwealth Scientific

Industrial and Research Organisation (CSIRO), Melbourne

Physics Department and Waste Management Group, Australian Nuclear Science

Technical Organisation (ANSTO), Lucas Heights, Sydney

Acoustic Laboratories, RMIT University, Melbourne

Concrete Institute of Australia (CIA), Victorian Branch, Melbourne

Cement and Concrete Association of Australia, Melbourne

Recycling Industries Pty. Ltd., Alex Fraser Group, Laverton North, Melbourne

Westkon Precast Concrete Pty. Ltd, Sunshine, Melbourne

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Hollow Core Concrete Pty. Ltd., Laverton North, Melbourne

Unicrete Industries Pty. Ltd., Braybrook, Melbourne

Boral Testing Services (Concrete Laboratories), Boral Resources Pty Ltd, Thornbury,

Melbourne

Vicroads, Environmental Services, Kew, Melbourne

Geoscience Australia, Symonston, Canberra

University of Melbourne

Monash University, Melbourne

New York City Transit Authority, New York

The following chapter outlines the experimental and developmental program that was

devised for this research project. The experimental program was aimed at examining

and gaining an understanding of the engineering properties of RC Aggregate and RA

Concrete and differentiating these alternative materials from commonly used natural

aggregate and standard concrete. The experimental program also included an

examination of physical properties of fine aggregate, and the effect on durability of

concrete. The developmental program aimed at utilizing inherent properties of RC

Aggregate in the development of ‘less-fines’ RA Concrete and the use of such concrete

in acoustic barriers. The research gained from the experimental and developmental

programs that have been devised, was the result of literature surveys, guidance from

standard test procedures and consultations with professionals in related fields.

The experimental and developmental components of this research project were divided

into four distinctive stages:

EXPERIMENTAL

An examination of physical properties and the effect of fine aggregate grading on

durability of concrete

An examination of RC Aggregate physical and mechanical properties

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DEVELOPMENTAL

The development of RA Concrete and examination of its physical, mechanical and

acoustic properties

The development of a pre-cast RA Concrete acoustic barrier and examination of its

acoustic properties

3.2 EXPERIMENTAL and DEVELOPMENTAL PROGRAM - OVERVIEW

The experimental design and developmental program was divided into four stages. The

first two stages were associated with an assessment of existing materials and

differentiating between commonly used natural aggregate for concrete and alternative

recycled concrete aggregate, whereas the final two stages were associated with the

development of new products made from selected RC Aggregate. Table 3.2.1 presents

definitions of the four major stages of the experimental and developmental programs

whereas Figure 3.2.1 further outlines the project stages by introducing major phases of

the project.

Table 3.2.1 Experimental design program - major stages Stages Stage definition EXPERIMENTAL Stage 1 Investigation of impact of fine aggregate grading on durability of concrete Stage 2 Examination of RC Aggregate and limited investigation of quarry sourced local

basalt (Natural Aggregate) DEVELOPMENTAL Stage 3 Development and examination of RA Concrete and limited examination of NA

Concrete (control concrete) Stage 4 Development and examination of RA Concrete acoustic barrier

The initial stages of the experimental program of this research project aimed at

examining RC Aggregate properties in order to obtain necessary data, enabling the

design of RA Concrete mixes, and allowing a thorough characterisation of the concrete.

Furthermore, it also included testing of an acoustic barrier that was developed to utilise

some inherent or purposely modified properties of RC Aggregate and RA Concrete.

3-4

( + )

( + )

Stage 1 Stage 2 Stage 3 Stage 4

Figure 3.2.1 Outline of the experimental and developmental program

The four main stages of the experimental and developmental programs were further

divided into a number of phases where each phase dealt with a specific property of

either; the aggregate, concrete, or acoustic barrier. In some instances, control samples

of natural aggregate (local basalt) and concrete made from such aggregate were deemed

as necessary for comparison purposes. Table 3.2.2 outlines all stages of the

experimental program; properties examined at each stage; and testing methods or

procedures used.

Fine Aggregate

Natural (N) Aggregate

Normal density NA Concrete

‘Less-fines’ RA Concrete

Acoustic Barrier

RC Aggregate

No-fines NA Concrete

Normal density RA Concrete

No-fines RA Concrete

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Table 3.2.2 Project stages and properties tested

Stages Stage

definition Properties & research techniques Test

procedures EXPERIMENTAL Stage 1 Fine Aggregate Particle size distribution - PSD AS1141.11

Composition (cpr content) Procedure #1 Elemental composition – SEM SEM Cement content in aggregate fines AS1141.72 Impurities and foreign material Procedure #2 Particle size distribution – PSD AS1141.11 Particle density AS1141.6.1 Bulk density AS1141.4 Water absorption AS1114.6.1 Porosity – SANS SANS

RC Aggregate and/or N Aggregate

Porosity – BET BET Consistency and workability – slump test AS1012.3.1 Microstructure development – SEM SEM Mass per Volume AS1012.12.1 Compressive strength AS1012.9 Durability – VPV AS1012.21 Porosity / micro-cracks – SEM SEM Porosity – SANS SANS Porosity – BET BET

DEVELOPMENTAL Interconnected air voids content Procedure #3

Stage 2 Stage 3

RA Concrete and/or NA Concrete

Sound absorption – impedance tube AS1935 Acoustic Barrier

Design and manufacture AS3600 Stage 4

Sound absorption – reverberation room AS1045

In the first two stages, the fine and coarse aggregates were examined from a strength,

durability, and acoustics requirements perspective to provide data for further use in the

development of an optimum concrete mix design. The decision to use the 14/10mm

RC Aggregate as a coarse fraction necessitated the use of a well graded fine aggregate.

As a consequence, it was necessary to examine locally available fine aggregate from

major suppliers of concrete sand in the Melbourne metropolitan area. The particle size

distribution of concrete sands from six different sources were examined in order to

derive the fineness modulus (FM), often used as a supplementary parameter

characterising fine aggregate.

Furthermore, RC Aggregate was examined to quantify foreign materials such as bricks,

wood, plastic, metal, etc in the aggregate. An excessive amount of contaminants was

3-6

perceived to have a potentially deleterious effect on the strength and durability of

concrete made from RC Aggregate.

Basic engineering properties of RC Aggregate such as particle size distribution, water

absorption and particle density were investigated in order to assist in the concrete mix

design, as well as to expand the existing body of knowledge on this material. This was

followed by a more detailed examination of porosity of the aggregate which was

deemed to influence physical and mechanical properties of RC Aggregate.

The 14/10mm RC Aggregate was tested for its paste/aggregate composition i.e. the

relative amounts of cement paste residue (cpr) and natural rock in the aggregate. The

relative amount and quality of cpr was perceived to influence particle density,

aggregate’s overall porosity and water absorption. The paste/aggregate composition of

the aggregate was examined in accordance with an in-house method developed by the

author (see Appendix 1), that included a combination of mechanical separation, visual

inspection and subsequent mass measurements of each constituent. Relative amounts of

cement paste residue and natural aggregate were also examined by mapping images

obtained from a Scanning Electron Microscopy (SEM) examination. Within SEM and

micro-cracks examinations’, backscatter images were taken at very low magnifications

(15 to 30 times). Photographs of concrete specimens that were cut and used for other

tests were also examined.

Apart from the investigation of paste/aggregate composition of RC Aggregate, an

elemental and compound composition examination of cement paste residue of the

aggregate was also carried out. Although the area examined by the SEM is relatively

small and could perceived to be less representative, it was recognised that this test could

give a valid indication of elemental and compound composition along with evidence of

any chemical contaminants present in cement paste residue of RC Aggregate.

Crushed cement paste residue and fines of RC Aggregate were also examined for

elemental composition using the Scanning Electron Microscopy examination. The fines

were also examined to investigate re-cementing properties of the aggregate.

Following basic characterisation, more detailed tests were then employed to examine

the porosity of cement paste residue of RC Aggregate. A non-destructive neutron

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scattering method, the Small Angle Neutron Scattering (SANS) was used to examine

total porosity and fractal dimensions of pore structure. This was followed by Brenauer-

Emmett-Teller’s (BET) nitrogen adsorption method to determine the volume, size and

surface area of pores. Table 3.2.3 summarises the properties that were tested, along

with the number and size of test samples of natural and RC Aggregate.

Table 3.2.3 RC Aggregate and Natural Aggregate examination – summary

Aggregate type and property examined

Test procedures

Number of samples per test

Frequency of tests / total number of tests

Sample size

Fine aggregate PSD AS1141.11 3 ∑ 6 500g Coarse aggregate Aggregate composition

Procedure #1 (Appendix 1)

3 1 in 4 months, 12 lots, ∑ 35

1.5kg

Elemental composition

SEM 2 - 3

1 in 6 months ∑ 18

Slabs 2 x 20 x 20mm Powder ~2g

Cement content AS1141.72 1 ∑ 4 Powder ~ 80g Foreign materials and impurities


1 Every month ∑ 32

5kg

PSD AS1141.11 2 Every month ∑(64+6)70

2kg

Particle density AS1141.6.1 2 ∑ 24 2kg Bulk density AS1141.4 2 ∑ 24 ~ 15kg Water absorption AS1141.6 2 ∑ 24 2kg Porosity BET 5 – 10 ∑ 21 ~ Ø 5mm Porosity SANS 7 ∑7 6 x 6 x 6mm

The third stage of the project dealt with the development and characterisation of RA

Concrete, with a specific focus on the investigation into an optimum relationship

between porosity of RC Aggregate and physical and mechanical properties of RA

Concrete. Initially the development of RA Concrete included devising concrete mix

designs of normal density concrete of various compressive strengths ranging from

15MPa to 40MPa, which later was limited to a compressive strength of RA Concrete of

25MPa. In addition, mix designs of no-fines RA Concrete were devised, and properties

investigated. Control samples of concrete made from natural aggregate (local basalt)

for both normal density and no-fines concrete were also prepared and examined. A

concept of ‘less-fines’ concrete emerged, resulting in the development of a two-layered

concrete viz. solid and porous. Methods of mix proportioning of ‘less-fines’ RA

3-8

Concrete were devised, and samples with various relative thickness of solid and porous

layers were investigated.

The scope of the RA Concrete examination and adopted procedures related to a type of

concrete classified as; normal density, no-fines or ‘less-fines’. Plastic properties of

‘less-fines’ and no-fines RA Concrete were assessed by a visual inspection, whereas in

the case of normal density concrete, consistency and workability of fresh concrete were

tested by a standard slump test. Properties of hardened concrete, such as mass per

volume, compressive strengths and apparent volume of permeable voids (VPV) were

tested in the Concrete and Fluid Mechanics laboratories at Swinburne University of

Technology (SUT) using standard equipment.

Samples used for examining the microstructure development in RA Concrete using

SEM were cut from test specimens using a concrete saw. Samples were examined for

the presence of micro-cracks and microstructure development with a specific focus on

the boundary zone between new cement paste and cement paste residue of the

aggregate. Some of the slab-like specimens used in SANS experiments were also

examined by SEM to determine elemental composition.

Porosity characteristics of RA Concrete including total volume of pores in concrete

matrix, volume of micropores, pore size distribution and specific surface area were

determined using the BET nitrogen adsorption method. A supplementary non-

destructive SANS method was also used to examine pore structure and to determine the

fractal mass, a parameter describing roughness of pores in RA Concrete. The

Australian Nuclear Science and Technology Ogranisation (ANSTO) facilities at Lucas

Heights were used to prepare and test concrete specimens over the period of 1999 to

2002.

A ‘less-fines” RA Concrete of various relative thicknesses of solid and porous layers

was then examined to gauge concrete durability using the VPV method. The amount of

partly interconnected air voids in porous layers was measured using the water

displacement method. Sound absorption of ‘less-fines’ RA Concrete was then

determined through the impedance tube method.

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Although a 28-day continuous moist curing regime was adopted in the case of all test

specimens of NA and RA Concrete, an allowance for alternative curing by PE sheet

wrapping was made. A limited number of the slab-like specimens prepared with D2O

were cured for 56 days in deuterium oxide. Table 3.2.4 presents an outline of the

testing program for the concrete examination, the frequency of tests, and number and

size of test specimens.

Table 3.2.4 RA and NA Concrete development and examination – summary

Concrete type & property examined

Testing procedures

Number of samples per test


Sample size

Normal density Consistency AS1012.3 1 Every batch ~ 0.025m3 Microstructure development

SEM

2 - 3 1 in 4 months ∑ 11

3 x 20 x 20mm

Mass per volume AS1012.12.1 3 Every batch / mix design ∑ 40

Ø 150 x 300mm

Compressive strength (f’c)

AS1012.9 3 Every batch / mix design ∑ 40

Ø 150 x 300mm

Durability - VPV AS1012.21 2 or 3 (sliced into 4)

Selected mixes ∑ 12

Ø 100 x 200mm

Porosity / microcracks

SEM

2 - 3 1 in 4 months ∑ 11

3 x 20 x 20mm

Porosity SANS

10 1 per year ∑ 20

Powder ~2g 5 x 5 x 5mm 2 x 20 x 20mm

Porosity BET 5-10 particles 1 in 4 months ∑ 34 ~ Ø 5mm No-fines Consistency Visual Every batch ~ 0.025m3 Microstructure SEM 2 - 3 1 in 4 months 2 x 20 x 20mm Mass per Volume AS1012.12.1 3 Every batch / mix

design Ø 150 x 300mm

Compressive strength

AS1012.9 3 Every batch / mix design

Ø 150 x 300mm

Durability - VPV AS1012.21 2 (sliced in 4) Selected mixes ∑ 10 Ø 100 x 200mm ‘Less-fines’ Consistency Visual 1 Every batch ~ 0.025m3 Mass per volume AS1012.12.1 3 ∑ 12 Ø 83 x 150mm Interconnected air voids


1 ∑ 34 Ø 83 x 150mm Ø 100 x 200mm

Sound absorption AS1935 1 ∑ 9 Ø 83 x 150mm

The final stage of the project consisted of the design, development and testing of a

prototype and commercially manufactured acoustic barrier made from the 14/10mm RC

Aggregate. The requirements set for acoustic barrier design were to best utilize the

3-10

physical and mechanical characteristics of the ‘less-fines’ RA Concrete and its ability to

absorb and reflect sound energy. A total of approximately 11m2 of the barrier prototype

was manufactured in pre-cast panels, in the Concrete and Heavy Structures laboratories

at Swinburne University of Technology. Panels were air cured for 28 days, before

being transported and tested at the Acoustic Laboratory at RMIT University in

Melbourne. The same design and similar production procedures were applied to

commercially manufactured barriers at Westkon Precast Concrete Pty Ltd. Panels sized

1 x 4 metres were manufactured, air cured, and cut into three parts to enable their

placement in the reverberation chamber. The reverberation room method was used to

measure the sound absorption coefficient of the prototype, and of commercially

manufactured barriers (SAA, 1988). Table 3.2.5 summarises the final stage of the

project experimental and developmental program.

Table 3.2.5 Prototype and commercially manufactured acoustic barrier examination – summary

Property Testing

procedure Number of samples per test


Sample size

Sound absorption AS1045 12 ∑ 1 150 x 850 x 1250mm Sound absorption AS1045 9 ∑ 1 150 x 1000 x 1300mm

The experimental program of the project also included the use of the Australian Small

Angle Neutron Scattering (AUSANS) facilities at ANSTO, Lucas Heights. The SANS

technique was used to determine the pore structure of the RC Aggregate’s cement paste

residue, and microstructure of RA Concrete in a range of pore sizes ranging between

10Å and 100Å. The SANS experimental program was employed to supplement the

BET nitrogen adsorption examination of microstructure of the aggregate and concrete

which can measure porosity in the range of pore sizes between 17Å and 3mµ. Apart

from the standard specimen preparation for SANS testing, some specimens were

prepared and cured with deuterium oxide (D2O). The curing regime for samples

prepared with H2O was a 28-day continuous curing in light water, whereas specimens

prepared with D2O were continuously cured for 56 days in deuterium oxide.

The SANS experimentation was carried out in four rounds: September 1999, March

2000, May 2001, and January 2002. Initially, irregularly shaped samples of RC

Aggregate particles were investigated, then cubic samples 6 x 6 x 6mm were cut from

3-11

the aggregate, and finally two lots of the slab-like 2 x 25 x 25mm samples of RA

Concrete were prepared and examined. Table 3.2.6 shows the AUSANS testing

program.

Table 3.2.6 AUSANS sample suite

Round Shape and size of samples

No. of samples

Moisture conditions

1999 Irregular aggregate 4 Oven dry 2000 Cubic 6 x 6 x 6mm 7 Oven dry, H2O, D2O May 2001 Slabs 2 x 25 x 25mm 10 Oven dry, H2O, D2O May 2001 <150µm powder 6 Oven dry January 2002 Slabs 2 x 25 x 25mm

(H2O made) 4 Oven dry, H2O, D2O,

50% H2O + 50% D2O January 2002 Slabs 2 x 25 x 25mm

(D2O made) 6 D2O, oven dry, H2O,

50% H2O + 50% D2O

Concurrently with the AUSANS experimentation, the pore structure of RC Aggregate

and RA Concrete was examined using the Brunauer-Emmett-Teller (BET) nitrogen

adsorption technique, which was chosen to measure pore size distribution in a range

partially overlapping with SANS. Controlled standards were created for natural

aggregate (local basalt), and of the cement pastes of water/cement ratios of 0.2, 0.4, and

0.8. These standards were used as the benchmark porosity for subsequent

characterization of the aggregate and concrete. The pore structure of the cement paste

residue of RC Aggregate, and those of RA Concrete were then compared with control

standards. Six lots of test specimens were prepared and examined at the Micromeretics

Laboratory at Swinburne University of Technology. Some tested specimens were

previously examined by the non-destructive SANS technique. Table 3.2.7 shows an

experimental design program of the BET nitrogen adsorption experiments.

Table 3.2.7 BET nitrogen adsorption test program

Examination date & number of samples Samples May Oct April May June Dec Jan

Natural aggregate (na), 0.2 cp 2 2 0.8 w/c new cement paste (0.8 cp) 1 0.4 w/c new cement paste (0.4 cp) 2 RC Aggregate cement paste residue (rca-cpr), old cp +na, na + old cp

10 6 1

0.8 cp + rca-cpr 3 0.4 cp + rca-cpr 3 3

3-12

The following sections present details of research methods and test procedures adopted

in the experimental and developmental programs of the project. Account or reference is

given to experimental setup, laboratory equipment, detailed procedures, and laboratory

reports requirements.

3.3 FINE AGGREGATE

The quality and properties of fine aggregate including aggregate grading amongst other

factors have an influence on the durability of concrete. In Victoria, it is preferred to

express the durability of hardened concrete as the apparent volume of permeable voids.

To formulate durable concrete made from alternative coarse aggregate, the cement paste

surrounding RC Aggregate has to be of the highest possible quality. The purpose of

examining the grading of fine aggregate was to select an aggregate that would yield the

highest quality of cement paste in new concrete. Subsequently, properties of the six

different concrete sands used in the Melbourne metropolitan area were investigated.

The particle size distribution (PSD) was examined and one single parameter known as

the fineness modulus (FM) was derived for each of the fine aggregate. Table 3.3.1

presents the sources of fine aggregate.

Table 3.3.1 Fine aggregate sources

Source 1 Source 2 Source 3 Source 4 Source 5 Source 6 Pronto Langwarrin

Pioneer Heatherton

CSR Lyndhurst

Pronto Yea

Boral Langwarrin

Boral Bacchus Marsh

Representative samples were obtained directly from a stopped conveyor belt at various

concrete production plants. A sampling frame was used and procedures described in the

Australian Standard AS1141.3.1-1996 Methods for sampling and testing aggregate,

Method 3.1: Sampling aggregates were followed. Three samples of 5kg each, per

every supplier, were obtained in five equal increments. Samples were bagged and

labeled. In addition, an adequate amount of fine aggregate to produce nine (9) concrete

test specimens was obtained.

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The Australian Standard AS 1141.11 – 1996 Methods for sampling and testing

aggregates, Method 11: Particle size distribution by sieving procedures was followed

to determine the grading of fine aggregate. A standard sieve set ranging between the

4.75mm sieve to 0.075mm was used. Test portions of 500g were used and the sieve set

was hand agitated. Tests were performed at the Geotechnical Laboratory at SUT.

A parameter known as fineness modulus (FM) of sand was then estimated using the

particle size distribution data. The FM is a sum of cumulative percentages retained on

the standard sieves (0.150, 0.300, 0.600, 1.18, 2.36 and 4.75mm) divided by 100

(Nawy, 1997).

3.4 NATURAL (N) COARSE AGGREGATE

Any natural aggregate chosen for this research project had to bear a resemblance to

grading characteristics of the 14/10mm RC Aggregate, of which the examination was

the main purpose of this research. Ideally, shape and surface texture of N Aggregate

should also be similar to those of RC Aggregate, although differences in raw materials

used for the production of the aggregates made it difficult to match those characteristics.

Local basalt supplied by the Boral Quarry Pty Ltd was deemed suitable on the basis of

similar particle size distribution.

Sampling of N Aggregate was in accordance with the Australian Standard AS1141.3.1-

1996 Methods for sampling and testing aggregate, Method 3.1: Sampling aggregates.

Representative samples were obtained directly from a stopped conveyor belt at concrete

production plants. A sampling frame was used to obtain the 15kg representative

samples in five equal increments. To obtain the required grading, some single sized

aggregate had to be added to the aggregate supplied by Boral Quarry Pty Ltd. Test

portions for specific tests were derived using a sampler divider.

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The Australian Standard procedures described in AS1141.11-1996 Methods for

sampling and testing aggregates, Method 11: Particle size distribution by sieving was

followed to determine the grading of N Aggregate. Test portions of 2kg were used. A

standard sieve set, and hand agitation was used. Particle size distribution tests were

performed when comparison data to those of RC Aggregate had to be generated. In

total, six samples were tested over a period of three (3) years. Tests were conducted at

the Geotechnical Laboratory at SUT.

3.4.2 Elemental Composition

A semi-quantitative analysis of the natural aggregate in slab-like samples prepared for

SANS or other SEM samples where micro-cracks were examined was performed. The

data was used to establish standards for an elemental and compound composition of

natural aggregate.

The SEM examination was performed using a JEOL JSM840 Scanning Electron

Microscope equipped with EDS (Energy Dispersive X-ray Analysis), under the

guidance and assistance of Mr. Hans Brinkies at the Electron Microscopy Laboratory at

Swinburne University of Technology, (SEM, 1999). The same equipment and technical

support was used in other experiments involving SEM. Section 3.5.4 outlines the

testing procedures and sample preparation regime.

3.5 RECYCLED CONCRETE (RC) AGGREGATE

The coarse aggregate used in this research project is a commercially available product

known as 14/10mm RCA. The aggregate is manufactured by Recycling Industries Pty

Ltd at the Alex Fraser Group of Companies. At present, the 14/10mm RC Aggregate is

being used as a partial substitute for coarse aggregate in various types of concrete,

including low strength concrete for footpaths or construction of residential slabs

manufactured by Hi-tech Concrete Pty Ltd in Melbourne. The choice of this aggregate

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was based on results of previous investigations into concrete recycling by the author,

and also instigated by the request of the industrial partner of the project. It has been

decided that this aggregate would be the most suitable for the production of concrete

acoustic barriers.

Representative samples of RC Aggregate were obtained by the author or supplied by the

company from its stockpiles at the concrete recycling plant at Laverton North, Victoria.

Sampling from the side of the stockpile was carried out with the use of a board and

shovel, and samples were placed in sealed plastic bags. Procedures described in the

Australian Standard AS1141.3.1-1996 Methods for sampling and testing aggregate,

Method 3.1: Sampling aggregates were followed. The 20kg samples were obtained in

five equal increments. Sample portions for specific tests were reduced using a sample

divider. The frequency of specific tests was accordingly adjusted to the relative

importance of examined property to the overall objectives of the project.

3.5.1 Cement Paste Residue (cpr) Content

Determination of the content of cement paste residue in RC Aggregate was carried out

in accordance with procedures devised by the author (see Appendix 1). Initially,

particles of clean natural aggregate, aggregate coated with cement paste, and fragments

of cement paste residue were segregated. Particles of aggregate coated with more than

approximately 10% of cement paste residue were then broken to smaller pieces until

natural aggregate and cpr were separated. Test portions of 1.5kg were used. Test

portions were reduced from combined samples collected over a three month period

between January 1999 and October 2001. A total of thirty two (32) representative

samples of RC Aggregate were reduced to twelve (12) test portions. The tests were

carried out at the Concrete Laboratory at Swinburne University of Technology.

RC Aggregate composition was also determined from area mapping of RA Concrete

samples, which were cut for some other tests, mainly in the VPV and SANS

examinations.

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3.5.2 Impurities and Foreign Materials Content

Occurrence of any other materials other than natural aggregate and cement paste residue

in RC Aggregate may adversely affect compressive and tensile strength, abrasion

resistance, surface finish, and durability of new concrete. The content of foreign

materials in RC Aggregate was assessed by a method devised by the author (see

Appendix 1). The classification of foreign materials in RC Aggregate is listed as

follows:

A. Brick particles

B. Plasterboard pieces (gypsum)

C. Mortar (cement-lime)

D. Wood pieces

E. Other organic matter such as grass, paper, etc

F. Clay particles

G. Bitumen

H. Plastic

I. Steel fibre-reinforcement

J. Glass

K. Pebbles or other aggregate coated with paint or other protective coating

L. Miscellaneous (paint, foam, etc)

Foreign materials were then further classified as lighter or as heavier than 1,000kg/m3.

Light impurities such as wood, other organic matter and plastic, tend to adversely affect

the durability and surface finish of concrete. A simple test was devised to determine the

weight of particles and isolate particles lighter than 1,000kg/m3. All foreign material

was submerged in water, separated, oven dried and weighed.

The frequency of occurrence of each class of foreign material in 14/10mm RC

Aggregate was recorded and, along with other information on the quality of the

aggregate, shared with the industry partner.

A total of thirty two (32) samples of the 14/10mm RC Aggregate were examined

between January 1999 and August 2001. The visual assessment of RC Aggregate,

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classification of foreign materials, and determination of their content by weight was

carried out at the Geotechnical Laboratory at SUT.

3.5.3 Cement Content in RC Aggregate Fines

One of the assumptions developed during the early stages of the project was that

particles smaller than 75µm might contain traces of unhydrated cement, as some of the

RC Aggregate is produced from relatively fresh concrete waste. A modified method

was adopted to determine any content of cement in aggregate fines. The method

described in the Australian Standard AS1141.72-1996 Methods for sampling and

testing aggregate, Method 72: Cement content of cement stabilised materials was

modified by the author. The modification included removal of the fines, and subsequent

substitution of the stabilised cement with RC Aggregate’s fines.

Fine particles smaller than 75µm were removed from the RC Aggregate through

sieving. A total of eight (8) samples were prepared where three (3) samples were used to

derive a calibration curve, and five (5) to determine the amount of unhydrated cement in

the aggregate. The calibration curve was derived using 14/10mm RC Aggregate

without particles smaller than 75µm and GB cement. A portion of 20g of cement was

used, which is equivalent to 0.5% of cement content. The GB cement was chosen as it

has a relatively high content of pozzolanas and exhibits a mineral composition that is

closer to the elemental and compound distinctiveness of RC Aggregate’s fines, as the

SEM examination had indicated.

The test portions consisted of 4kg of 14/10mm RC Aggregate, plus 80g of particles of

75µm or below. The 80g portion size was derived from an average content of 2% in all

of the RC Aggregate samples. There were no other deviations from the standard

procedures. Tests were conducted at the Chemistry Laboratory at SUT.

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3.5.4 Microstructure and Elemental Composition

The Scanning Electron Microscopy was used to examine elemental (based on assumed

compound) composition of cement paste residue of RC Aggregate, and to examine the

aggregate’s microstructure (SEM, 1999). The SEM was predominantly used to identify

micro-cracks in the aggregate itself, and in the transition zone between new paste and

RC Aggregate.

Solid slab-like samples and powder samples were examined. The solid samples, 3mm

thick, 20 x 20mm, were cut from larger RC Aggregate particles, collected at the

Laverton North concrete recycling plant during the crushing process of concrete waste,

or alternatively, cut from the concrete made from 14/10mm RC Aggregate. Powder

samples were grinded to particles below 150µm with the use of a laboratory grinder.

The instrument used was the JEOL JSM840, which is a conventional type of Scanning

Electron Microscope, equipped with EDS (Energy Dispersive X-ray Analysis). This

conventional type of SEM requires nonconductive samples to be made conductive. A

carbon coater was used to coat solid samples of RC Aggregate with evaporated high

purity carbon. Carbon coated solid samples were mounted on aluminum disks. Some of

the aggregate were immersed in resin. Powder samples were attached to a double-sided

carbon tape, and mounted on aluminum pin type SEM mounts.

A total of 24 solid and 6 powder samples were examined. To assure the best

representation of the population of RC Aggregate cement paste residue in these

samples, a number of specific areas of up to 50mm2 were selected. A total of forty (40)

areas of different sizes were examined. The SEM examination of each sample started

with an analysis of Back-scatter Electron (BSE) images of RC Aggregate cement paste

residue surface at low magnifications (15 times), which followed by an EDS of the

selected areas.

The Backscatter Electron images were obtained with an atomic number contrast. At

low magnifications (e.g. 15 times), areas of approximately 48mm2 (8mm x 6mm) were

analysed, whereas at higher magnifications (e.g. 500 times), areas of approximately

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0.0005mm2 (25µm x 20µm) were assessed. Dark areas on the BSE images are

representative of elements with a low mean atomic number, such as calcium, whereas

lighter areas are representative of elements with a high mean atomic number, such as

iron. Elemental spectra were produced, which quantified elements present in the

analyzed areas. Subsequently, a semi-quantitative analysis of elements in their assumed

compound composition was performed, and results obtained. Although the analysis was

semi-quantitative, as the examined samples were not compared against known

standards, the method was assumed as adequate for comparative purposes. To ensure a

high standard and validity of data, the operational conditions of the instrument were

kept constant.

Observations on micro-cracks using BSE images at low magnifications were recorded.

Chosen areas were further analyzed, and some of the BSE images stored as TIFF files.

Elemental spectra and qualitative analysis results were copied as pictures on Microsoft

Word documents.

3.5.5 Particle Density

Standard procedures in accordance with the Australian Standard AS 1141.6.1 – 2000

Methods for sampling and testing aggregates, Method 6.1: Particle density and water

absorption – weighing-in-water method were followed in order to determine the

particle density of RC Aggregate. This method also allows the determination of

apparent particle density (ρA), particle density on a dry basis (ρD), and on a saturated-

surface-dry basis (ρS). 2kg test portions were examined.

Each test portion was reduced from the combined samples of the three monthly

sampling periods. A total of twelve (12) samples were examined at the Geotechnical

Laboratory at SUT.

3.5.6 Bulk Density

The compacted bulk density of oven dried RC Aggregate was examined. The

procedures of the Australian Standard AS1141.4-2000 Methods for sampling and

testing aggregates, Method 4: Bulk density of aggregate was followed. A ten (10)

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litre cylindrical watertight measure was used to determine the compacted bulk density.

A total of fifteen (15) samples were examined between January 1999 and August 2003

at the Geotechnical Laboratory at SUT.


Determination of RC Aggregate grading followed procedures of the Australian Standard

AS1141.11-1996 Methods for sampling and testing aggregates, Method 11: Particle

size distribution by sieving. The standard sieve set was hand agitated. Two test

portions of approximately 2kg were obtained from monthly samples over a period from

January 1999 to August 2001, and in late 2003. A total of sixty four (64) tests were

examined at the Geotechnical Laboratory at SUT.


Water absorption of RC Aggregate was determined in accordance with the Australian

Standard AS 1141.6.1 – 2000 Methods for sampling and testing aggregates, Method

6.1: Particle density and water absorption – weighing-in-water method. The 2kg test

portions, obtained from combined three monthly samples over a three (3) year period

were tested. A total of twelve (12) samples were examined. Water absorption was

examined at the Geotechnical Laboratory at SUT.

Water absorption of the aggregate was also determined during the SANS experimental

program. RC Aggregate absorption of light water (H2O) and heavy water (D2O) was

investigated. Although the size of the SANS specimens (6 x 6 x 6mm) was relatively

small and could be less representative, the results that were obtained as a by-product in

the SANS examination were used for comparative purposes. A total of seven (7)

samples were examined at ANSTO laboratories at Lucas Heights.

3.5.9 BET Porosity

Porosity of RC Aggregate in terms of specific surface area, pore size distribution, and

pore volume, was examined using the Brenauer-Emmett-Teller BET nitrogen adsorption

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method (SUT, 1999). Porosity in pore size, ranging between 17Å and 3μm, was

examined.

The ASAP 2000 instrument was used with two independent vacuum pump systems; one

for degassing; and one for analysis. The range of pressure measurements varied from 0

up to 950mmHg. Powder and solid samples were placed in sample tubes and examined.

Each solid sample consisted of approximately ten (10) pieces of aggregate and powder

sample weight was approximately four (4) grams. Control standards were established

for cement pastes of 0.2, 0.4, and 0.8 water/cement ratios, either from purposely

prepared pastes or by using the known standards. Samples of RC Aggregate for the

porosity examination using the BET nitrogen adsorption method were selected on a

visual basis. The cement paste residue samples were classified as either; highly,

moderately, or slightly weathered.

The BET nitrogen adsorption examination of RC Aggregate and then of RA Concrete

was performed under the guidance and assistance of Mr. David Lewis, at the

Micromeretics Laboratory at SUT.

3.5.10 SANS Porosity

The Small Angle Neutron Scattering technique was used to examine the porosity in pore

sizes ranging between 10Å and 100Å. The Australian Small Angle Neutron Scattering

(AUSANS) facilities at the Australian Nuclear Science Technical Organisation

(ANSTO) at Lucas Heights were used to prepare and test RA Concrete samples

(ANSTO, 1999). The SANS results were also used to determine the fractal mass of

pore structure of RC Aggregate’s cement paste residue. The SANS experimental

program was chosen to complement the BET nitrogen adsorption method, in order to

obtain corresponding data on microstructure of the aggregate.

Examination of RC Aggregate porosity using the SANS technique was carried out in

September 1999 and March 2000. Initially, irregularly shaped samples of RC

Aggregate particles were investigated, followed by cubic 6 x 6 x 6mm samples. RC

Aggregate cubes were cut out of cement paste residue. All samples were tested in oven

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dried conditions. Table 3.5.1 presents the SANS testing program of RC Aggregate,

cement paste residue.

Table 3.5.1 SANS experiments (1999 and 2000 - sample suite

Month & year Shape and size of samples No. of samples Moisture conditions Sep 1999 Irregular aggregate 4 Oven dry March 2000 Cubic 6 x 6 x 6mm 7 Oven dry, H2O, D2O

The SANS investigation was carried out in accordance with ANSTO procedures under

the guidance and assistance of Dr Robert Knot, from the Australian Nuclear Science

Technical Organisation. The same procedures and facilities were also used in the

examination of concrete as outlined in Section 3.6.7 and Section 3.7.7 of this document.

3.6 NATURAL AGGREGATE (NA) CONCRETE

Two types of NA Concrete; normal density, and no-fines concrete were investigated. In

the investigation of compressive strength and volume of permeable voids, concrete

samples were prepared in accordance with the Australian Standard AS1012.8.1-2000

Methods of testing concrete, Method 8.1: Method for making and curing concrete –

Compression and indirect tensile test specimens.

All of the NA Concrete samples were prepared at the Concrete Laboratory at Swinburne

University of Technology. Concrete was placed in layers in cylindrical moulds, which

were clamped securely to a vibrating table. Concrete was compacted through the use of

a laboratory vibrating table at a frequency of 50Hz. After initial storage and subsequent

demoulding, specimens were continuously cured in lime-saturated water at a

temperature of 23±2°C for a period of 28 days. Representative concrete specimens for

BET and SANS porosity examinations were cut out of the compressive strength

samples, or cast in specially prepared moulds.

The frequency of preparing and testing of NA Concrete samples was dependent on the

project’s overall objectives and availability of the BET and AUSANS facilities. Plastic

and hardened properties of NA Concrete were investigated.

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3.6.1 Workability and Consistency

Workability and consistency of fresh concrete was examined using a slump test in

accordance with the Australian Standard AS1012.3.1-1998 Methods of testing concrete,

Method 3.1: Determination of properties related to the consistency of concrete –

Slump test. In the case of normal density NA Concrete, the slump test was performed

on every batch of concrete made using standard procedures and equipment. With

reference to the no-fines NA Concrete, a slump test by observation was deemed to be

valid.

3.6.2 Compressive Strength

The compressive strength of normal density and no-fines NA Concrete was determined

following procedures of the Australian Standard AS1012.9-1999 Methods of testing

concrete, Method 9: Determination of the compressive strength of concrete

specimens. Portland cement mortar capping was adopted for normal density concrete,

and restrained natural rubber capping for no-fines concrete was used to ensure a high

standard of test specimens, and integrity of compression strength test results. Three

specimens per concrete batch were cast, cured and crushed. Cylinders of 150mm in

diameter and 300mm in height were used. All specimens were tested after the 28 day

period of continuous moist curing in the lime-saturated water.

3.6.3 Mass per Volume

All of the NA Concrete specimens prepared for compression strength (three per test)

test, and the VPV (two per test) investigation, were measured and weighed in

accordance with the Australian Standard AS1012.12.1 – 1998 Methods of testing

concrete, Method 12.1: Determination of mass per unit volume of hardened concrete

– rapid measuring method to determine the mass per volume. A total of twelve (12)

samples (representing 36 specimens) of N40, and eight (8) samples (representing 24

specimens) of N25 were examined at the Concrete Laboratory at SUT.

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3.6.4 Apparent Volume of Permeable Voids

The Australian Standard AS1012.21 – 1999 Methods of testing concrete, Method 21:

Determination of water absorption and apparent volume of permeable voids in

hardened concrete procedures were followed to determine the volume of

interconnected void space in hardened NA Concrete. Specimens of 100mm in diameter

were cut into four equal slices, oven dried to a constant mass, immersed, and boiled in

water. The VPV of 40MPa natural aggregate concrete was examined when the fine

aggregate for this research project was investigated. Six (6) samples; two specimens

each, were examined at that stage. In addition, the VPV of N25 Concrete was

investigated, to derive a control set of data on volume of interconnected void space in

concrete of a comparable mix design to those of RA25 Concrete. A total of twelve (12)

samples were examined.

The VPV examination of NA Concrete was performed at the Concrete and Fluid

Mechanics laboratories at SUT.


Water absorption of NA Concrete was determined to create a standard set of data for

comparison purposes. Water absorption was examined in accordance with Australian

Standard AS1012.21 – 1999 Methods of testing concrete, Method 21: Determination

of water absorption and apparent volume of permeable voids in hardened concrete.

Water absorption of NA Concrete was examined using the same samples as in the

apparent VPV examination.

3.6.6 BET Porosity

Specific surface area, pore size distribution and pore volume of NA Concrete was

examined using the Brenauer-Emmett-Teller BET nitrogen adsorption method (SUT,

1999). Porosity ranging between 17Å and 3μm was examined in order to establish a

control standard for concrete porosity to be compared with porosity of recycled concrete

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aggregate, and recycled aggregate concrete. The BET measurements were also used to

supplement and compare SANS results of porosity on the same specimens. Samples of

cement pastes of water/cement ratios of 0.4 and 0.8 were prepared, and BET porosity

determined to establish control samples of porosity for comparison purposes.

Instrumentation, sample preparation and test parameters as described in section 3.5.9 of

this document, also apply to the NA examination using BET nitrogen adsorption.

3.6.7 SANS Porosity

The AUSANS instrument at Lucas Heights was used to examine porosity of NA

Concrete. Sample preparation and testing procedure outlined in the AUSANS

procedures were followed (ANSTO, 1999). Samples of new cement paste were

prepared. A number of pastes of w/c ratios of 0.2, 0.4, and 0.8 were investigated. Two

cement paste samples per every water cement ratio were prepared. The 0.2 w/c ratio

samples were prepared using a superplasticiser (Type HWR). The data obtained from

the SANS investigation of cement paste formed a benchmark for future porosity

comparison purposes, between SANS porosity data obtained from RA Concrete and RC

Aggregate examinations.

3.6.8 Interconnected Air Void Content in No-Fines NA Concrete

Interconnected air void ratios in no-fines NA Concrete were examined using a water

displacement method developed by the author (see Appendix 1). A glass dish with

marked increments of volume was used. Samples of no-fines concrete were slowly

submerged into a known volume of water to a specified porous layer thickness. The

volume of displaced water due to the presence of concrete was recorded. Ratio of voids

and aggregate for a specific thickness of the no-fines concrete was calculated. The

Fluid Mechanics Laboratory at SUT was used.

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3.7 RECYCLED AGGREGATE (RA) CONCRETE

Batches of RA Concrete were prepared either at the Concrete Laboratory at Swinburne

University of Technology, or at the Boral Concrete Laboratory at Thornbury. Methods

described in the Australian Standard AS1012.8.1-2000 Methods of testing concrete,

Method 8.1: Method for making and curing concrete – Compression and indirect

tensile test specimens were followed in preparing, sampling, and curing of concrete

specimens. Standard cylinder moulds; 100mm and/or 150mm in diameter were used.

Concrete was placed in layers in the moulds, which were attached to a vibrating table,

and compacted at a frequency of 50Hz. After the initial 24 hour period of storage and

demoulding, RA Concrete samples for compressive and VPV testing were cured under

standard moist curing conditions (100% RH and 23±2°C) in lime-saturated water.

Laboratory curing tanks were used, and all specimens were cured for 28 days with the

exception of specimens used for acoustic tests. Samples for the impedance tube test,

and the SANS test were wrapped in two polyethylene plastic bags, and stored in the

laboratory at a controlled temperature of 23±2°C. Table 3.7.1 summarises the curing

regimes employed in the RA Concrete experimental program (also applicable to any

other concrete made from natural aggregate in this research project).

Table 3.7.1 Curing regime of concrete test specimens

Tests / Curing Bath-cured Sealed-cured Air-cured Compressive strength Yes - - Volume of permeable voids Yes - - Impedance tube - Yes - Reverberation chamber - - Yes

3.7.1 Workability and Consistency

Workability and consistency of fresh RA Concrete was examined by the means of a

slump test in accordance with the Australian Standard AS1012.3.1-1998 Methods of

testing concrete, Method 3.1: Determination of properties related to the consistency of

concrete – Slump test. In the case of normal density RA Concrete, the slump test was

performed on every batch of concrete made using standard procedures and equipment.

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However, due to the workability and consistency of the ‘less-fines’ and no-fines RA

Concrete, the slump test was conducted by visual observation.

3.7.2 Microstructure Development

Examination of the microstructure of RA Concrete was conducted with the use of a

Scanning Electron Microscopy complying with standard SEM procedures (SUT, 1999).

There was a specific focus on the detection of micro-cracks in the transition zone

between new cement paste and RC Aggregate. Solid slab-like 20mm x 20mm samples

3mm thick were examined. The samples were cut from larger RA Concrete specimens

made from 14/10mm RC Aggregate. Solid samples were coated with purified carbon

and mounted on sample holders.

A total of six (6) solid samples were examined. In these samples, specific areas of

approximately 1mm2 were selected, which were assumed to best represent the interface

zone in RA Concrete. A total of twenty five (25) areas were examined. Visual

assessments and observations of micro-cracks on studied images at low magnifications

were recorded.


Mass per volume of RA Concrete was determined using procedures in accordance with

the Australian Standard AS1012.12.1 – 1998 Methods of testing concrete, Method

12.1: Determination of mass per unit volume of hardened concrete – rapid measuring

method. All of the concrete specimens that were used for testing compressive strength

and VPV were used to record and calculate mass per volume of hardened concrete. The

measurements were taken on saturated surface-dry specimens. Three (3) specimens per

concrete batch, a total of forty two (42) were examined.

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To determine the compressive strength of RA Concrete, The test specimens were

prepared and cured in accordance with the Australian Standard AS1012.8 – 2000

Methods of testing concrete, Method 8: Method for making and curing concrete

compression, indirect tensile and flexure test specimens, in the laboratory or in the

field.

Three (3) specimens for every batch or for every concrete mix design were prepared.

Two sizes of standard cylinder specimens were used, depending on availability of

moulds. When compressive strength tests were performed at the commercial laboratory,

cylinders of 100mm in diameter and 200mm in height were used. Cylinders of 300mm

in diameter and 300mm in height were used for tests conducted at Swinburne University

of Technology.

Compressive strength of RA25 concrete was determined in accordance with a testing

method described in Australian Standard AS1012.9 – 1999 Methods of testing concrete,

Method 9: Determination of the compressive strength of concrete specimens.

3.7.5 Apparent Volume of Permeable Voids

The apparent volume of permeable voids in RA Concrete was determined using a

testing method set out in the Australian Standard AS1012.21 – 1999 Methods of testing

concrete, Method 21: Determination of water absorption and apparent volume of

permeable voids in hardened concrete. This method allows determining the volume of

interconnected void space of concrete which is emptied during oven drying and filled

with water during subsequent immersion and boiling.

For selected batches of concrete, two test cylinders 100mm in diameter were prepared.

After a required curing period, each 200mm high sample was cut into four equal slices

(approximately 50 mm thick) with a concrete saw. A laboratory water bath with a

heater was used to boil portions of concrete specimens.

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The VPV examination was performed at the Concrete and Fluid Mechanics laboratories

at Swinburne University of Technology and at the Boral Concrete Laboratory at

Thombury.

3.7.6 BET Porosity

Specific surface area, pore size distribution, and pore volume of RA Concrete was

examined using the Brenauer-Emmett-Teller nitrogen adsorption method in accordance

with standard BET Procedures (SUT, 1999). Porosity in the pore diameter range

between 17Å and 3μm was examined. In some cases, the BET measurements were

intended to supplement and compare the SANS results of porosity of the same

specimens. Selected SANS specimens which underwent a non-distractive examination

using neutron scattering were then used to examine the porosity in an extended range

using BET nitrogen adsorption.

Samples were sourced from broken pieces of RC25 Concrete used in compressive

strength tests. They were further crushed in a laboratory crusher to obtain particles of

approximately 4 to 5mm in diameter. The RA Concrete samples were then segregated

and classified as either containing more than 50% of cement paste residue and new

cement paste (samples designation; old cpr + na), or samples containing less than 50%

of cement paste residue with visible traces of concrete sand or pieces of fresh cement

paste, or traces of natural coarse aggregate (samples designation; na + old cpr). Solid

samples consisting of small aggregate pieces were placed in testing tubes, degassed, and

tested using the ASAP 2000 instrument. Generated standards of RC Aggregate were

used for comparison and analysis.

3.7.7 SANS Porosity

Following an examination of irregularly shaped and cubed samples of RC Aggregate

porosity using the SANS technique, the third lot of samples were prepared and

examined in May 2001. A total of ten (10) solid samples of RA Concrete were

prepared. The sample suite included: specimens of neat cement paste of different w/c

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ratios and a mixture of cement paste residue of RC Aggregate and fresh cement pastes

of various w/c ratios (see Table 3.7.1).

Table 3.7.1 AUSANS - May 2001 experiments - sample suite

Samples group Sample Sample designation and description

1 neat 0.2 cement paste (cp) 2 neat 0.4 cp 3 neat 0.8 cp 4 0.2 cp + 1g of recycled concrete aggregate (rca) 5 0.4 cp + 1g of rca

RCA1 – (6) samples prepared using H2O and cured in H2O

6 0.8 cp + 1g of rca 1 neat 0.4 cp 2 neat 0.8 cp 3 0.4 cp + 1g of rca


4 0.8 cp + 1g of rca RCA9 5 Powder cpr1-1&2, cpr2-1&2, cpr3-1&2

All samples were prepared and cured with H2O. Samples were tested at various

moisture conditions, oven dried, saturated in H2O, saturated in D2O, and saturated in a

mixture of 50% of D2O and 50% of H2O. Samples of powdered RC Aggregate were

also tested. Table 3.7.3 demonstrates designations and the moisture conditions of the

samples of the May 2001 testing round.

Table 3.7.3 AUSANS - May 2001 experiments - sample moisture conditions

AUSANS Sample designation

Samples moisture conditions

RCA1 oven dried samples (six samples) RCA2 oven dried samples (four samples + Al + background) RCA3 RCA1 saturated in H2O RCA4 RCA2 saturated in H2O RCA5 RCA1 saturated in D2O RCA6 RCA2 saturated in D2O RCA7 RCA1 saturated in 50%D2O & 50%H2O RCA8 RCA2 saturated in 50%D2O & 50%H2O RCA9 Powder

The first lot of samples designated as RCA1 were wrapped in aluminium foil and placed

in sample holders of the UASANS instrument. Initially, the neutron beam transmission

was measured for 300 seconds, then each sample was subjected to radiation of an

intensive beam of neutrons for two periods of 3,600 seconds each, and scattered neutron

were detected using the AUSANS detector. After the first lot of samples were scattered,

they were soaked in light water for 12 hours and scattered as RCA3, then dried and

3-31

subsequently soaked in heavy water, and scattered as RCA5, and then oven dried for 12

hours and soaked in a 50/50 mixture of light and heavy water before being subjected to

radiation of an intensive beam of neutrons for 2 hours per sample, as RCA7. A similar

sequence of radiation, soaking and drying was employed to examine the second lot of

the SANS samples RCA2, RCA4, RCA6 and RCA8 respectively. As part of the SANS

experimentation, the absorption of light and heavy water was investigated. The testing

schedule of the May 2001 SANS round of experiments is presented in Appendix 2.

The fourth round of the SANS experiment also included the preparation and curing of

some of the samples using D2O. All samples were solid slabs, which included neat

cement paste samples of w/c ratios of 0.4 and 0.8. Other samples consisted of known

amount of cement paste residue of RC Aggregate of previously determined elemental

composition embedded in fresh cement paste. Table 3.7.4 presents RA Concrete

samples examined in January 2002.

Table 3.7.4 AUSANS - January 2002 experiments - sample suite

Samples group Sample Sample description

1 neat 0.4 cement paste (cp) 2 0.4 cp+ 1g of natural aggregate (na) 3 0.4 cp + 1g of recycled concrete aggregate (rca) 4 0.4 cp + 0.5g of (rca) 5 0.8 cp

RCA11 – (6) samples prepared using D2O and cured in D2O

6 0.8 cp + 0.5g of (rca) 1 neat 0.4 cp 2 neat 0.8 cp 3 0.4 + 1g of (rca)


4 0.8 + 1g of (rca) 1 neat 0.8 cp RCA19 – (2) samples 2 0.8 + natural aggregate (na)

The SANS samples were examined at various moisture conditions in order to

investigate the influence of light, heavy, and 50/50 mixture of light and heavy water on

the scattering profile of the same samples. Table 3.7.5 presents moisture conditions of

the SANS sample suite of the January 2002 testing round.

3-32

Table 3.7.5 AUSANS - January 2002 experiments - sample moisture conditions

Samples group Samples moisture conditions RCA11 saturated D2O (five samples) RCA12 oven dried samples (four samples + Al foil) RCA13 RCA11 dry (after 11h) RCA14 RCA12 saturated in D2O (after 11h) RCA15 RCA11 saturated in H2O RCA16 RCA12 saturated in H2O RCA17 RCA11 saturated in 50%D2O & 50%H2O RCA18 RCA12 saturated in 50%D2O & 50%H2O

As in the third round of SANS experiments, a group of samples was subjected to

radiation of an intensive neutron beam under various moisture conditions such as; oven

dried, soaked in D2O, H2O or 50/50 solution of light and heavy water. The testing

schedule and sample preparation for the January 2002 SANS experiments is presented

in Appendix 2.

Neutron scattering experimentation using the SANS technique was performed in

accordance with the AUSANS procedures (ANSTO, 1999). Total porosity was

estimated with the use of a program developed at Geoscience Australia in Canberra.

The program called ‘PRINSAS’ allows estimating total porosity of examined concrete

specimens (Hinde and Radlinski, 1999 – 2003).

The SANS data was analyzed with the help of Dr Alan Hinde and Dr Andrzej Radlinski,

using computer facilities at GeoScience Australia in Canberra, and with the help of Dr

Laurie Aldridge of ANSTO at Lucas Heights.

3.7.8 Fractal Mass

Fractal mass, a measure of the roughness of pores in two-phase material, was estimated

from SANS data using Microsoft Excel and Origin software. The fractal mass was

calculated from a SANS scattering profile on a log-log scale. Fractal mass is a slope of

the line of best fit in a plot of scattering intensity log (I), versus scattering wave vector

log (I(Q)).

3-33

3.7.9 Interconnected Air Void Content in No-Fines RA Concrete

A water displacement method (see Appendix 1) was used to examine interconnected air

voids in all of the no-fines and ‘less-fines’ RA Concrete samples. The procedures

described in section 3.6.8 apply.

3.8 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE

The experimental program described above, aimed at differentiating natural aggregate

and RC Aggregate and increasing the understanding of differences between NA

Concrete and RA Concrete of compressive strengths of 25MPa and 40MPa.

The next phase in this research project aimed at taking advantages of these differences

and developing a product that best utilizes the inherent properties of RC Aggregate.

The developmental program outlined below aimed at:

1. Material (‘less-fines’ RA Concrete) development using the impedance tube method,

2. Product (acoustic barrier) development which involved

a. Research testing of a prototype barrier developed at Swinburne University of

Technology, and

b. Commercial product manufactured at Westkon Precast Concrete Pty Ltd

3. Simulation of acoustic character of barrier installation (Harding, 2004)

The development of the ‘less-fines’ RA Concrete followed an investigation of the

performance of 14/10mm RC Aggregate in normal density, and in no-fines concrete. A

good understanding of RA Concrete, especially of the potential of no-fines concrete to

entrap and dissipate energy of sound waves, led to an investigation of a two-layered

concrete. The no-fines layer would allow sound waves to enter into the concrete matrix,

whereas the solid layer would provide structural strength of the two-layer ‘less-fines’

RA Concrete, and also provide a reflective surface to allow sound waves to resonate.

This structure was further employed in acoustic barriers.

The normal density and no-fines RA Concrete was prepared and examined in

accordance with various Australian Standards as described in sections 3.6 and 3.7 of

3-34

this document, with the only exception being the compaction of no-fines RA Concrete,

where special plates were used to compact each layer of concrete in a cylindrical mould.

Two methods of achieving two-layered ‘less-fines’ concrete were investigated. In the

first method, the concrete mix design has a deficiency of fine aggregate and the two

layered structure is developed by over-vibration of such concrete. In the second

method, the normal density concrete is placed first and compacted, followed by the

placement of no-fines concrete in the porous layer, concluding with screeding with a

plank of timber.

The mix designs of ‘less-fine’ RA Concrete were based on the required relative

thickness of porous and solid layers. The amount of cement paste had to be sufficient to

coat coarse aggregate in the porous layer and to fill available space between coarse

aggregate in the solid layer.

3.8.1 Interconnected Air Void Content

The method introduced in Section 3.6.8, and described in Appendix 1 applies.

Interconnected air void content was examined on all impedance tube samples, with

porous layer thicknesses ranging between 40 and 90 millimeters.

3.8.2 Sound Absorption – Impedance Tube Method

Sound absorption capacities of the ‘less-fines’ RA Concrete were determined in

accordance with the Australian Standard AS1935-1999 Method for the measurement of

normal incidence sound absorption coefficient and specific normal acoustic

impedance of acoustic materials by the tube method.

The size of cylindrical test specimens was; 83mm in diameter, and 150mm in overall

height. The specimens were of varying relative thickness of porous and solid layers. A

total of 10 samples were tested at the Applied Physics Acoustic Laboratory at RMIT

University in Melbourne.

3-35

3.9 PROTOTYPE and COMMERCIALLY PRODUCED BARRIER

The ultimate purpose of this research project, other than a thorough examination of

commercially manufactured 14/10mm RC Aggregate, was to develop and manufacture

a concrete acoustic barrier with the use of such aggregate. On the basis of preliminary

results, it was concluded that the ‘less-fines’ RA Concrete with solid layer compressive

strength of 25MPa is adequate to manufacture an acoustic barrier. Based on sound

absorption characteristics of the ‘less-fines’ concrete samples of different thicknesses of

porous layers obtained by the impedance tube method, it was decided that the prototype

barrier consists of a combination of panels of different porous layer thicknesses. The

prototype acoustic barrier (acoustic system) had been designed to have three sets of

panels of different porous layer thicknesses: 40mm, 60mm, and 80mm. The one-pour

method of the fines deficient concrete was used to manufacture twelve (12) panels.

Concrete used for the prototype was classified as ‘less-fine’ and over-vibration was

required to allow the development of two distinctive layers viz. solid and porous.

Further to the development of the barrier prototype, a commercial acoustic barrier was

developed. The commercially manufactured barrier consisted of three (3) panels. The

size of each panel was 1 meter by 4 meters. The designed thickness of porous layer was

40 mm. The two-pour method was used to manufacture panels of the acoustic barrier.

The solid layer was produced from the normal density RA Concrete using reclaimed

aggregate supplied by Boral Resources Pty Ltd, and the porous layer was made from the

no-fines RA Concrete using the 14/10mm RC Aggregate.

In both the prototype and commercially manufactured barriers, the major objectives

were to test production methods and to investigate acoustic performance of the barrier

using the reverberation room method.

3.9.1 Sound Absorption – Reverberation Room Method

Procedures, instrumentation, and requirements with reference to test specimens for the

measurement of sound absorption of the ‘less-fines’ RA Concrete acoustic barrier in a

3-36

reverberation room are described in the Australian Standard AS1045 – 1988 Acoustics –

Measurement of sound absorption in a reverberation room.

According to the standard, the barrier had to have an area ranging between 10m2 and

12m2 if the barrier is tested in reverberation rooms with a volume less than 250m3. The

samples (panels) shall be of rectangular shape, with the ratio of width to length between

0.7 and 1. Table 3.9.1 presents the acoustic barrier panels used in the determination of

sound absorption coefficient using the reverberation room method.

Table 3.9.1 Sound absorption examination of ‘less-fines’ RA Concrete acoustic barrier using reverberation room method

Acoustic Barrier Number

of panels Panel size Date of test

Prototype 12 150 x 850 x 1250mm October 2002 Commercially manufactured 3 cut in

3 parts 150 x 1000 x 1300mm November 2003

Panels of the barrier were placed directly on the floor of the reverberation room, and

care was taken to ensure a distance between the boundary of the panels and the room

did not exceed 1 meter, and that the edges of the panels adjacent to the room boundaries

were parallel.

The instrumentation including signal generator, source filter, loudspeakers,

microphones, measuring filter, amplifiers, and recording equipment complied with

standard requirements. The test signal was generated in a bandwidth of one-third

octave, and the source and measuring filters were used to maintain the one-third octave

bandwidth in a desired range of frequencies between 63Hz and 2,000Hz.

The acoustic testing of barriers was performed at a constant temperature of 25°C, and

relative humidity of 55%.

The measurements of reverberation times as a function of time in a reverberation

chamber with the barrier, and without the barrier, were recorded and followed by the

calculation of equivalent sound absorption area (As). Sound absorption coefficient is

obtained by dividing As by the surface area of the barrier. Two measurements of

3-37

reverberation time were obtained; the first with the barrier and the second one of an

empty room.

Reverberation room tests were conducted by Mr. Peter Dale and Mr. John Watson at the

Acoustic Laboratories at RMIT University, which is the NATA Registered laboratory

No 1421.

3.10 CONCRETE MIX DESIGN

Special concrete mix design procedures were considered unnecessary and proportioning

of RA Concrete was based on similar principles as for ordinary Portland cement

concrete. The initial mix designs were based on a mixture of different approaches such

as gap grading (Stewart, 1951), so-called British method (DOE, 1988), the CONAD

method (Day, 1999), and trial mix method. The author sought advice on final concrete

mix designs from a local concrete manufacturer, (Boral, 1999). Some corrections to

concrete mix proportions were based on the differences in specific gravity (particle

densities) of the natural coarse aggregate and RC Aggregate 2.7 and 2.2 respectively.

To overcome a potential influence of variable water absorption of RC Aggregate on

plastic and hardened properties of RA Concrete, a pre-wetting of the aggregate was

employed.

3.11 PROTOTYPE BARRIER DESIGN

The prototype and commercially manufactured acoustic barriers made from selected RC

Aggregate were developed to provide an optimum balance between sound absorption

capabilities and structural integrity. The two layered barrier panels were design to

withstand design loading, in accordance with the Australian Standard AS 1170.1-2002

Structural design actions, Part 1: Permanent, impose and other actions and AS

1170.2-2002 Structural design actions, Part 2: Wind actions.

The formwork for the manufacturing of precast panels was designed in accordance with

the Australian Standard AS3610-1995 Formwork for concrete.

3-38

The design of reinforcement, cover to reinforcement, and concrete strength followed

procedures of the Australian Standard AS3600-2001Concrete Structures. Concrete was

specified and delivered in accordance with the Australian Standard AS1379-1997

Specification and supply of concrete.

In the production of concrete panels, two methods were employed. The prototype

barrier (12 panels of approximately 1m2) was manufactured in laboratories at

Swinburne University of Technology. A small laboratory drum mixer was used to

produce concrete for the prototype barrier. The formwork and steel reinforcement were

prepared at the Heavy Structure Laboratory. The ‘less-fines’ RA25 Concrete mix was

used, and the one-pour method was employed to place concrete. Over-vibration was

employed to allow control segregation of concrete and development of two distinctive

layers. Air curing of concrete panels was employed.

The commercially manufactured acoustic barrier consisted of three precast panels, each

4m2 in area. A standard steel formwork used in the precast concrete industry was used.

Standard procedures were used to fix steel reinforcements and place lifting points. The

two-pour technique was employed to place RA40 Concrete in the formwork. Firstly, a

layer of the normal density concrete was placed and compacted, which followed

placement of a layer of the no-fines RA Concrete made from 14/10mm RC Aggregate.

The normal density concrete made from reclaimed 20mm graded aggregate, and no-

fines concrete used in the production of commercially manufactured barriers was

delivered by Boral Resources (Concrete) Pty Ltd.

3.12 LIMITATIONS and OMISSIONS

The experimental and developmental program presented in this chapter reflects the core

experimental work of the project. The author is aware that the program could include

other tests to characterise RC Aggregate such as:

• alkali reactivity of the material to assess the potential of a silica-alkali reaction in

RA Concrete

• permeability tests to complement porosity assessment of the aggregate, and to better

estimate the durability of RA Concrete

3-39

• weak particles content including clay lumps, soft and friable particles in RC

Aggregate

• aggregate soundness and evaluation by exposure to a sodium sulfate solution

• a complete knowledge of the original concrete used to make the RC Aggregate

including its strength, cement content, water/cement ratio, air content, density, type

of aggregate, etc,.

However, laboratory space availability along with time, precluded the inclusion of such

tests in this project’s experimental program.

The experimental program of RA Concrete would ideally include tests to examine

properties of concrete such as: indirect tensile strength (‘Brazil’ or splitting test),

flexural strength, shrinkage to complete mechanical properties characterisation of RA

Concrete and permeability to further contribute to durability characteristics.

There are also properties of the acoustic barrier that the author would like to examine in

more detail; such as impact resistance of the porous layer, compressive strength of core

concrete specimens obtained from the barrier and volume of permeable voids of core

concrete specimens obtained from acoustic barrier panels. The author would also like to

manufacture another set of barriers, test it in the reverberation room, install a

demonstration barrier, and perform field durability and acoustic effectiveness tests.

3.13 SUMMARY

This chapter presented the research methodology and the experimental design program

adopted in order to fulfill the main objectives of the project. The chapter outlined the

four major stages and the main phases of the experimental program, which was devised

with the help of professionals in related engineering disciplines from various

commercial, educational and scientific organizations.

The brief overview of the project methodology followed a more detailed description of

rationale of each of the research techniques employed, methods used at each phase,

sampling procedures, sample sizes and locations of where the tests were performed.

3-40

The methodology described investigations into fine aggregate, natural and recycled

concrete coarse aggregates, concrete made from these aggregate, and an investigation of

the final product, the ‘less-fines’ RA Concrete acoustic barrier.

The following chapter presents a summary of results along with a data analysis based on

the methodology and experimental design program described in this chapter.

3-41

CHAPTER 3 – METHODOLOGY and EXPERIMENTAL DESIGN ............................1

3.1 INTRODUCTION ............................................................................................1 3.2 EXPERIMENTAL and DEVELOPMENTAL PROGRAM - OVERVIEW....3 3.3 FINE AGGREGATE ......................................................................................12

3.3.1 Particle Size Distribution ........................................................................13 3.4 NATURAL (N) COARSE AGGREGATE.....................................................13

3.4.1 Particle Size Distribution ........................................................................14 3.4.2 Elemental Composition...........................................................................14

3.5 RECYCLED CONCRETE (RC) AGGREGATE ...........................................14 3.5.1 Cement Paste Residue (cpr) Content.......................................................15 3.5.2 Impurities and Foreign Materials Content ..............................................16 3.5.3 Cement Content in RC Aggregate Fines.................................................17 3.5.4 Microstructure and Elemental Composition ...........................................18 3.5.5 Particle Density .......................................................................................19 3.5.6 Bulk Density ...........................................................................................19 3.5.7 Particle Size Distribution ........................................................................20 3.5.8 Water Absorption....................................................................................20 3.5.9 BET Porosity...........................................................................................20 3.5.10 SANS Porosity ........................................................................................21

3.6 NATURAL AGGREGATE (NA) CONCRETE.............................................22 3.6.1 Workability and Consistency ..................................................................23 3.6.2 Compressive Strength .............................................................................23 3.6.3 Mass per Volume ....................................................................................23 3.6.4 Apparent Volume of Permeable Voids ...................................................24 3.6.5 Water Absorption....................................................................................24 3.6.6 BET Porosity...........................................................................................24 3.6.7 SANS Porosity ........................................................................................25 3.6.8 Interconnected Air Void Content in No-Fines NA Concrete..................25

3.7 RECYCLED AGGREGATE (RA) CONCRETE...........................................26 3.7.1 Workability and Consistency ..................................................................26 3.7.2 Microstructure Development ..................................................................27 3.7.3 Mass per Volume ....................................................................................27 3.7.4 Compressive Strength .............................................................................28 3.7.5 Apparent Volume of Permeable Voids ...................................................28 3.7.6 BET Porosity...........................................................................................29 3.7.7 SANS Porosity ........................................................................................29 3.7.8 Fractal Mass ............................................................................................32 3.7.9 Interconnected Air Void Content in No-Fines RA Concrete ..................33

3.8 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE...........................33 3.8.1 Interconnected Air Void Content ............................................................34 3.8.2 Sound Absorption – Impedance Tube Method .......................................34

3.9 PROTOTYPE and COMMERCIALLY PRODUCED BARRIER ................35 3.9.1 Sound Absorption – Reverberation Room Method.................................35

3.10 CONCRETE MIX DESIGN ...........................................................................37 3.11 PROTOTYPE BARRIER DESIGN................................................................37 3.12 LIMITATIONS and OMISSIONS..................................................................38 3.13 SUMMARY ....................................................................................................39

3-42

Figure 3.2.1 Outline of the experimental and developmental program ............................4 Table 3.2.1 Experimental design program - major stages.................................................3 Table 3.2.2 Project stages and properties tested ...............................................................5 Table 3.2.3 RC Aggregate and Natural Aggregate examination – summary....................7 Table 3.2.4 RA and NA Concrete development and examination – summary .................9 Table 3.2.5 Prototype and commercially manufactured acoustic barrier examination

– summary...............................................................................................................10 Table 3.2.6 AUSANS sample suite............................................................................11 Table 3.2.7 BET nitrogen adsorption test program....................................................11 Table 3.3.1 Fine aggregate sources ............................................................................12 Table 3.5.1 SANS experiments (1999 and 2000 - sample suite......................................22 Table 3.7.1 Curing regime of concrete test specimens ...................................................26 Table 3.7.1 AUSANS - May 2001 experiments - sample suite ......................................30 Table 3.7.3 AUSANS - May 2001 experiments - sample moisture conditions ..............30 Table 3.7.4 AUSANS - January 2002 experiments - sample suite .................................31 Table 3.7.5 AUSANS - January 2002 experiments - sample moisture conditions .........32 Table 3.9.1 Sound absorption examination of ‘less-fines’ RA Concrete acoustic barrier

using reverberation room method ...........................................................................36

4.1-1

CHAPTER 4 – RESULTS and DISCUSSION

4.1 INTRODUCTION

The previous chapter outlined the experimental program of this research project

concerned with two main aspects, firstly with gaining a better understanding of the

differences between commonly used coarse aggregate in the concrete industry and the

aggregate made from concrete waste, and secondly with developing an application

where those differences could be best utilised e.g. concrete acoustic barrier. An account

of testing procedures, sample suits for each test and rationale for examining specific

properties were presented.

This chapter summarises results of the tests conducted as part of the experimental and

developmental program of this research project, which differentiate between natural and

RC Aggregate and characterise the acoustic barrier.

The results of fine aggregate testing are first presented and a rationale for choosing the

concrete sand from Bacchus March Quarry is discussed. Some of the results generated

at that stage of the project also formed a set of control data of NA Concrete that was

further used in the analysis and comparison with RA Concrete.

Furthermore, this chapter presents results of a series of tests that aimed at characterising

commercially available 14/10mm RC Aggregate, and test results of comparable natural

coarse aggregate. The testing program and test results of coarse aggregate mainly

focused on the composition of RC Aggregate, its grading, particle and bulk densities

and on the aggregate porosity. The discussions on the differences between those

properties of natural and of recycled coarse aggregate follow.

This chapter then presents results of a testing program of concrete made from the

14/10mm RC Aggregate. Although the results form a set of data characterising basic

engineering properties of concrete made from both natural and recycled coarse

aggregate, the bulk of the data presents porosity related properties of N25 and RA25

Concrete including apparent volume of permeable voids in hardened concrete, water

absorption, BET and SANS porosity. The results characterise three types of concrete;

4.1-2

normal density, ‘no-fines’ and ‘less-fines’ concrete. A comparison between natural

aggregate concrete and RA Concrete of a compressive strength of 25MPa is made and

results discussed.

Further to the characterisation of RC Aggregate and RA Concrete, and differentiation

with standard aggregate and concrete, the results of the developmental program of

acoustic barriers are presented. Initially, results of acoustic testing using an impedance

tube of ‘less-fines’ RA Concrete are presented, followed by a complete acoustic

characterisation of a barrier prototype made at Swinburne University of Technology,

concluding with the commercially produced barrier by Westkon Precast Concrete Pty

Ltd.

This chapter presents only a summary of the results. The full set of results on specific

properties of aggregate, concrete and barrier can be found in appropriate appendices.

4.2 METHODS of ANALYSIS

Standard statistical methods in data collection and data analyses were employed.

Random sampling of the aggregate and concrete was predominantly used with the

exception of the SEM examination, where discriminatory selection of an examined area

was employed.

The author believes that although a limited number of samples were collected and

prepared for testing, they were sufficiently representative of the population of aggregate

and concrete. The sampling procedures were designed in such a way that each sample

was representative of the material tested. Consistency in sampling procedures was

ensured; the sample preparation and experimental environment was maintained and

controlled, as to reduce deviations and to obtain data of desired quality.

Although limited, the number of experiments and amount of data obtained from those

experiments were carefully chosen to enable establishing relationships and correlations

between different factors or parameters representing material’s properties; such as

between porosity and compressive strength, VPV and compressive strength, etc.

4.1-3

Great care was taken in collecting data. Well designed spreadsheets and/or

experimental reports were prepared in order to make the data collection efficient and to

simplify data analysis (see Appendix 3 for examples of test reports). Each report or

spreadsheet contained standard information including date, time, environmental test

conditions, operator, testing machine, etc to make data identification, recording and

analysis more efficient.

Statistical calculations allowed extracting maximum information from a set of test

results generated through the experimental program. All possible attempts were made

to thoroughly understand the nature of collected data and any variations.

In regards to data presentation, Microsoft Excel was used for the preparation of

spreadsheets as well as for most of the statistical analysis and plotting quantitative data.

To allow a better visualization of the data and data analysis results; tables, plots and

graphs were selected as a preferred way of displaying trends, patterns, changes, relative

sizes and variability.

All possible attempts were taken to avoid any misrepresentations or to knowingly

mislead the reader by the data presented in the tables, graphs and plots. Data from most

experiments has been rounded off, usually to two or three significant numbers in order

to allow better conceptualisation and reading of numerical data. Despite that, in a few

isolated cases, quantitative data from some experiments showed a wide variation, in

which case variable standard for rounding has not been used. Sampling errors were

estimated and analysed in order to obtain an appreciation of the magnitude of error, to

understand it, and to prevent a misuse of the extreme data. In a few isolated cases,

judgment was exercised when extreme values had the potential to affect the set of data.

In these cases, extreme values were excluded from the set.

Regression analysis was used to investigate relationships between variables such as

porosity and compressive strength, VPV and compressive strength, etc. Simple linear

regression of two quantitative variables was used to find the best straight line fit as the

data plotted on scatter plots indicated linear relationships between variables. A use of

several statistical programs was investigated including SPSS and Origin, although

Microsoft Excel was deemed most satisfactory and consequently used to perform the

4.1-4

regression analysis and to fit data to a linear regression model. The R2, which is a

measure of the strength of the linear relationship, was determined and recorded to

demonstrate efficacy of the linear regression model in explaining variations.

It is the author’s believe that although the results are only indicative of the true

situation, they truly reflect properties and parameters of examined aggregate, concrete

and the barrier

4.1-5

CHAPTER 4 – RESULTS and DISCUSSION.................................................................1

4.1 INTRODUCTION ............................................................................................1 4.2 METHODS of ANALYSIS ..............................................................................2

CHAPTER 4 – RESULTS and DISCUSSION.................................................................1

4.1 INTRODUCTION ............................................................................................1 4.2 METHODS of ANALYSIS ..............................................................................2

4.2-1

4.2 METHODS of ANALYSIS

Standard statistical methods in data collection and data analyses were employed. Random

sampling of the aggregate and concrete was predominantly used with the exception of the

SEM examination, where discriminatory selection of an examined area was employed.

The author believes that although a limited number of samples were collected and prepared

for testing, they were sufficiently representative of the population of aggregate and

concrete. The sampling procedures were designed in such a way that each sample was

representative of the material tested. Consistency in sampling procedures was ensured; the

sample preparation and experimental environment was maintained and controlled, as to

reduce deviations and to obtain data of desired quality.

Although limited, the number of experiments and amount of data obtained from those

experiments were carefully chosen to enable establishing relationships and correlations

between different factors or parameters representing material’s properties; such as between

porosity and compressive strength, VPV and compressive strength, etc.

Great care was taken in collecting data. Well designed spreadsheets and/or experimental

reports were prepared in order to make the data collection efficient and to simplify data

analysis (see Appendix 3 for examples of test reports). Each report or spreadsheet

contained standard information including date, time, environmental test conditions,

operator, testing machine, etc to make data identification, recording and analysis more

efficient.

Statistical calculations allowed extracting maximum information from a set of test results

generated through the experimental program. All possible attempts were made to

thoroughly understand the nature of collected data and any variations.

In regards to data presentation, Microsoft Excel was used for the preparation of

spreadsheets as well as for most of the statistical analysis and plotting quantitative data. To

allow a better visualization of the data and data analysis results; tables, plots and graphs

4.2-2

were selected as a preferred way of displaying trends, patterns, changes, relative sizes and

variability.

All possible attempts were taken to avoid any misrepresentations or to knowingly mislead

the reader by the data presented in the tables, graphs and plots. Data from most

experiments has been rounded off, usually to two or three significant numbers in order to

allow better conceptualisation and reading of numerical data. Despite that, in a few isolated

cases, quantitative data from some experiments showed a wide variation, in which case

variable standard for rounding has not been used. Sampling errors were estimated and

analysed in order to obtain an appreciation of the magnitude of error, to understand it, and

to prevent a misuse of the extreme data. In a few isolated cases, judgment was exercised

when extreme values had the potential to affect the set of data. In these cases, extreme

values were excluded from the set.

Regression analysis was used to investigate relationships between variables such as

porosity and compressive strength, VPV and compressive strength, etc. Simple linear

regression of two quantitative variables was used to find the best straight line fit as the data

plotted on scatter plots indicated linear relationships between variables. A use of several

statistical programs was investigated including SPSS and Origin, although Microsoft Excel

was deemed most satisfactory and consequently used to perform the regression analysis and

to fit data to a linear regression model. The R2, which is a measure of the strength of the

linear relationship, was determined and recorded to demonstrate efficacy of the linear

regression model in explaining variations.

It is the author’s believe that although the results are only indicative of the true situation,

they truly reflect properties and parameters of examined aggregate, concrete and the barrier.

4.2-3

4.2 METHODS of ANALYSIS ................................................................................... 1

4.3-1

4.3 FINE AGGREGATE

4.3.1 Introduction

Amongst various direct effects of coarse aggregate and cement paste microstructure on

quality and durability of concrete, the particle size distribution of fine aggregate can

also significantly affect durability.

Six different sources of fine aggregate were investigated to choose the most suitable

concrete sand for this research project. The decision to choose particular concrete sand

was made on the basis of the quality of cement paste produced from six different fine

aggregate. The decisive property of cement paste was the apparent volume of

permeable voids which is widely used and accepted in Victoria as a valid indicator of

durability of concrete.

Grading of coarse aggregate and mix proportion of each concrete type remained

constant; the only variable was particle size distribution of fine aggregate which was

examined, and fineness modulus (FM) calculated. Moisture content was also measured

to accurately adjust concrete mix designs.

A number of test specimens of N25 and N40 Concrete were prepared from each fine

aggregate, continuously cured, cut into four equal parts, and apparent VPV determined.

Computer simulation of concrete mix designs was carried out to determine a mix

suitability factor where the only variable was the grading of fine aggregate.

4.3.2 Particle Size Distribution and Fineness Modulus

Samples of concrete sand were obtained from six locations in the greater metropolitan

Melbourne area (see Table 4.3.1) and examined to determine moisture content, particle

size distribution and to calculate fineness modulus. The knowledge of these basic

properties is required to correctly proportion concrete mix, especially to derive the

optimum water content per cubic meter of concrete.

4.3-2

Table 4.3.1 Fine aggregate sources

Sample 1 2 3 4 5 6 Supplier Pronto Pioneer CSR Pronto Boral Boral Location Langwarrin Heatherton Lyndhurst Yea Langwarrin Bacchus

Marsh

Firstly, the moisture content of each sample was determined by placing samples in the

oven and drying them for 48 hours at a temperature of 106ºC and then weighing the

moisture loss. Representative samples of equal mass, of approximately 500g from each

source, were selected and a sieve analysis conducted. Table 4.3.2 presents PSD

percentage passing of fine aggregate from six locations that were used to calculate the

FM of tested samples.

Table 4.3.2 Particle size distribution of fine aggregate – average percentage passing

Samples 1 2 3 4 5 6 Sieve apertures [mm] PSD – average percentage passing 4.75 100.0 100.0 98.2 98.1 99.1 99.1 2.36 99.6 99.1 92.3 87.0 91.9 91.3 1.18 98.2 95.4 76.8 71.4 80.6 80.8 0.600 80.9 78.7 57.0 53.5 62.9 62.3 0.425 61.3 64.1 47.7 41.6 50.2 44.5 0.300 33.2 37.5 38.3 25.4 34.9 23.4 0.150 0.0 0.0 10.7 6.6 9.8 0.0 0.075 0.0 0.0 0.0 0.0 0.0 0.0

Based on the cumulative percentage retained on sieve sizes ranging from 0.150mm to

4.75mm, the FM of sand was calculated. Table 4.3.3 presents fineness modulus and

moisture content of tested samples.

Table 4.3.3 Fineness modulus and moisture content of fine aggregate

Sample 1 2 3 4 5 6 Moisture content [%] 6.0 2.3 5.2 6.6 6.2 7.1 Fineness modulus 2.28 2.25 2.79 3.16 2.72 2.99

Furthermore, a relationship between aggregate grading and apparent volume of

permeable voids in concrete made from those aggregate was sought. Concrete samples

using different fine aggregates were prepared and tested. Table 4.3.4 presents the

4.3-3

average VPV of N40 Concrete that was made from various fine aggregate and

associated fineness modulus.

Table 4.3.4 Fineness modulus of fine aggregate and Apparent VPV of N40 Concrete

Sample 1 2 3 4 5 6 Fineness modulus 2.28 2.25 2.79 3.16 2.72 2.99 VPV [%] 8.85 9.15 8.96 8.87 9.06 8.90

Figure 4.3.1 shows the volume of permeable voids in N40 Concrete, made from a

selection of fine aggregate, associated with that particular aggregate fineness modulus,

whereas Figure 4.3.2 presents a similar relationship in N25 Concrete.

8.90 8.85 9.15 8.96 9.06 8.87

7.24 7.50 7.74 7.75 7.758.15

2.992.28 2.25

2.79 2.723.16

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

Boral_BM Pronto_L Pioneer_H CSR_L Boral_L Pronto_Y

Fine aggregate supplier

VPV

& F

M

VPV sample VPV bottom layer FM

Linear (VPV bottom layer) Linear (VPV sample)

Figure 4.3.1 Apparent VPV of N40 Concrete and FM of fine aggregate

4.3-4

13.97 14.39 14.46 14.52 14.50 14.81

2.99 3.16 2.792.25 2.28 2.72

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

Boral_B_M Pronto_Y CSR_L Pioneer_H Pronto_L Boral_L

Fine aggregate supplier

VPV

[%] &

FM

Total VPV Bottom layer VPV FM of fine aggregateLinear (Bottom layer VPV) Linear (Total VPV)

Figure 4.3.2 Apparent VPV of N25 Concrete and FM of fine aggregate

In both N25 and N40 Concrete, the fine aggregate from Bacchus March Quarry

produced concrete of the lowest average amount of apparent volume of permeable

voids. Consequently, it can be concluded that cement paste made from this aggregate is

less permeable, contributing to a more durable concrete. The results also support the

motion that the fine aggregate of FM between 2.75 and 3.2 produces the most durable

concrete (Nawy, 1997).

In addition to the analysis of the average apparent VPV in N40 Concrete, a comparison

between the apparent volumes of permeable voids in bottom layers of concrete samples

was carried out. It was deemed necessary to analyse the bottom layers of concrete

samples, as the acoustic barrier’s structural backing consists of a relatively thin (60mm

to 110mm) layer of concrete with embedded steel reinforcement. The results indicated

that the Bacchus March sand produces the most durable bottom layer. Figures 4.3.3 and

4.3.4 present apparent VPV results of the bottom layers of N25 and N40 Concrete.

4.3-5

7.24

7.50

7.74 7.75 7.75

8.15

6.60

6.80

7.00

7.20

7.40

7.60

7.80

8.00

8.20

8.40

Bor

al_B

M

Pron

to_L

Pion

eer_

H

CSR

_L

Bor

al_L

Pron

to_Y

Fine aggregate suppliers

VPV

- av

erag

e

Figure 4.3.3 Apparent VPV in bottom layer of N40 Concrete

13.11

13.52

13.63 13.65 13.67

13.78

12.60

12.80

13.00

13.20

13.40

13.60

13.80

14.00

Bor

al_B

_M

Pron

to_Y

CSR

_L

Pion

eer_

H

Pron

to_L

Bor

al_L

Fine aggregate suppliers

VPV

- av

erag

e

Figure 4.3.4 Apparent VPV in bottom layer of N25 Concrete

Further to the experimental work previously described, a concrete mix design

simulation was performed using the CONAD demonstration program, to investigate the

influence of particle size distribution on mix suitability factor (MSF). All of the N40

Concrete mix design parameters, such as specific gravity of fine and coarse aggregates,

mix proportions and coarse aggregate grading were kept constant. The only variable

was the fine aggregate grading. Table 4.3.5 presents the specific surface area (SSA) of

4.3-6

fine aggregate and MSF of N40 Concrete resulting from different grading of fine

aggregate.

Table 4.3.5 Mix suitability factors (MSF) of N40 Concrete

Sample 1 2 3 4 5 6 SSA – specific surface area of fine aggregate [m2]

62.38 63.96 57.71 51.29 53.84 57.49

MSF – mix suitability factor

31.4 32.0 24.6 27.0 28.0 29.5

The results of the computer simulation show that mix suitability factor of N40 concrete

made from different fine aggregate are high and indicate good quality concrete. The

concrete made from Bacchus March Quarry fine aggregate has a MSF of 29.5 which

according to Day (1999, p. 52), indicates structural concrete of a very good quality.

As a consequence of the data analysis and computer simulation, concrete sand supplied

by Boral Resources Pty Ltd from Bacchus Marsh Quarry was chosen for the research

project.

Section 4.4.6 of this document further discusses other aspects of apparent volume of

permeable voids in concrete. The influence of coarse aggregate on apparent VPV in

NA Concrete and RA Concrete of a compressive strength of 25MPa will be discussed.

4.3.3 Discussion of the Results

The aim of the study of fine aggregate sourced from Melbourne’s major aggregate

suppliers, included an examination of particle size distribution, determination of the

fineness modulus and an investigation of the effect of grading on the amount of

apparent volume of permeable voids in concrete made from a variety of fine aggregate,

was to select the fine aggregate that will yield the most durable concrete.

It has been found that although there are some grading variations of the fine aggregate

supplied by quarries around Melbourne, the particle size distribution of all of the fine

aggregate is within the limits of the grading envelope set in Table 3 of the Australian

Standard AS 2758.1 – 1998 ‘Concrete Aggregate’ (SAA, 1998).

4.3-7

The test results of apparent VPV in hardened N25 and N40 are below the limits set by

VicRoads in its specifications for standard concrete (Vicroads, 1997). Figure 4.3.5

presents a comparison between the average apparent VPV of N25 and N40 Concrete

and the specified limits.

17

1413.6

9.0

0

2

4

6

8

10

12

14

16

18

N25 N40

NA Concrete type

VPV

[%]

VicRoads LimitAverage of 12 samples

Figure 4.3.5 Comparison between apparent VPV in N25 and N40 Concrete

The investigation of the influence of fine aggregate grading on the apparent volume of

permeable voids in concrete has fulfilled its objective, enabling the author to select fine

aggregate for the project. The decision to choose concrete sand supplied by Boral

Resources Pty. Ltd. from the Bacchus March Quarry was well supported by the motion

proposed by Nawy, (1997) that fine aggregate, with a fineness modulus of 2.75 to 3.2,

produces the most workable concrete of higher compressive strength and durability.

The computer simulation also supported the experimental results.

The test results of compressive strength and VPV of concrete made from the various

fine aggregate and natural coarse aggregate were also used as control sample data.

4.3-8

4.3 FINE AGGREGATE ........................................................................................1

4.3.1 Introduction...............................................................................................1 4.3.2 Particle Size Distribution and Fineness Modulus .....................................1 4.3.3 Discussion of the Results ..........................................................................6

Figure 4.3.1 Apparent VPV of N40 Concrete and FM of fine aggregate .........................3 Figure 4.3.2 Apparent VPV of N25 Concrete and FM of fine aggregate .........................4 Figure 4.3.3 Apparent VPV in bottom layer of N40 Concrete .........................................5 Figure 4.3.4 Apparent VPV in bottom layer of N25 Concrete .........................................5 Figure 4.3.5 Comparison between apparent VPV in N25 and N40 Concrete...................7

Table 4.3.1 Fine aggregate sources ...................................................................................2 Table 4.3.2 Particle size distribution of fine aggregate – average percentage passing.....2 Table 4.3.3 Fineness modulus and moisture content of fine aggregate ............................2 Table 4.3.4 Fineness modulus of fine aggregate and Apparent VPV of N40 Concrete ...3 Table 4.3.5 Mix suitability factors (MSF) of N40 Concrete.............................................6

4.4-1

4.4 RECYCLED CONCRETE (RC) AGGREGATE

4.4.1 Introduction

The coarse aggregates chosen for this research project included:

• 14/10mm RC Aggregate manufactured by Recycling Industries Pty Ltd at the

Laverton North recycling plant and;

• 14/10mm N (natural) Aggregate, a locally available basalt supplied by Boral

Resources Pty Ltd and used as a control aggregate

Both aggregates are commercially available products. The Class1, 14/10mm RC

Aggregate is a ready to use concrete aggregate of a fixed grading. However, in the case

of the 14/10mm N Aggregate, in order to keep the grading as a constant parameter in

both aggregate, two single size aggregates; the 14mm and 10mm basalt aggregate were

mixed to a required particle size distribution. In standard industry operations, similar or

any other desired grading, is produced from a single sized aggregate, which is dozed

and combined in the concrete batching process. Figure 4.4.1 presents the 14/10mm RC

Aggregate in a stockpile at the Laverton North recycling plant.

Figure 4.4.1 Stockpile of RC Aggregate

As a general rule, the suitability of coarse aggregate as a material for concrete

production is decided mainly due to its physical and mechanical properties. The

Australian Standard AS2758.1-1998 ‘Aggregates and rock for engineering purposes,

Part 1: Concrete aggregates’ specifies these properties and refers to testing procedures

800mm

4.4-2

for a specific property. Thorough knowledge of the basic engineering properties of

coarse aggregate is fundamental, as it allows concrete technologists to design concrete

mixes.

This section of the report presents outcomes of the characterisation of selected recycled

concrete aggregate and differentiates the aggregate from comparable natural coarse

aggregate in a range of properties including: composition of aggregate particles, content

of foreign materials, particle and bulk densities, water absorption, and porosity. In

addition, the re-cementing potential of RC Aggregate is reported.

4.4.2 Composition – Cement Paste Residue Content

Pertinent to its composition, commonly used coarse aggregate (including basalt) used in

the production of concrete can be seen as a homogeneous material. However, the

composition of RC Aggregate is not so uniform, as the feedstock material used in its

production is already a composite in nature; cement paste and aggregate, and it may

consist of other waste.

To optimise the effectiveness of waste recovery and to minimise the variations of

recycled products, the concrete waste is separated at source from other C&D waste, and,

preferably delivered to recycling plants with minimal content of other waste materials.

The bulk of the concrete waste is crushed into smaller particles of specified size and in

the process, during particular stages, electromagnets or manual pickers remove any

foreign material including steel reinforcement. In general, variability of the raw

material does not affect the aggregate’s grading, however, the content of foreign

material in recycling products (RC Aggregate) depends strongly on the degree of

contamination of the feedstock material, and on the effectiveness of segregation of those

materials at various stages of the production process.

Uncontaminated, 14/10mm RC Aggregate consists of some particles of natural

aggregate (fine and coarse fraction), of particles of natural aggregate coated with some

cement paste residue (cpr), and of particles of pure cpr. The size of these particles

ranges from sporadic 19mm aggregate pieces, though majority of them are of 14 and

4.4-3

10mm in size, to an insignificant percentage of particles smaller than 75 microns. In the

uncontaminated particles, the relative content of natural aggregate and cpr particles has

considerable bearing on the basic engineering properties of RC Aggregate. The

differences between natural aggregate and cpr in crushing value, water absorption, and

porosity, might be quite substantial, therefore, the relative content of those components

in RC Aggregate has potential to significantly impact the aggregate properties.

Various types of coarse particles of uncontaminated RC Aggregate are presented in

Figure 4.4.2. The A particle is of a pure cement paste residue, the B particle is of

natural aggregate (basalt) coated with less than 10% of cpr, and the C particle is of

natural aggregate (vesicular basalt) coated with more than 10% of cpr.

Figure 4.4.2 Particles of RC Aggregate (A – cement paste residue only, B and C – natural aggregate coated with cpr)

A representative number of samples of the 14/10mm RC Aggregate were examined in

order to determine typical composition of the aggregate, particularly the amount of

cement paste residue in the aggregate. Figure 4.4.3 presents an example of relative

composition of the 14/10mm RC Aggregate.

43.8 %

2.5 %

30.4 %

23.3 %

cpr (cement paste residue) only

NA (natural aggregate) only

NA coated with up to 10% of cpr

foreign material

Figure 4.4.3 Relative composition of 14/10mm RC Aggregate (sample

RCA_11_00_s1&s2)

A CB

4.4-4

Test results indicated that about 70% of the aggregate consists of natural aggregate

particles, and up to 30% of cement paste residue. The amount of foreign materials

shown in Figure 4.4.3 of 2.5% is an example of extremely high content, considering that

on average, foreign material accounts for approximately 1.18% by weight.

Figure 4.4.4 presents data on composition of the 14/10mm RC Aggregate over a period

of three years. The composition of cement paste residue content in the aggregate seems

to be in a well defined range with a standard deviation (STDEV) of 2.8% in 1999, 1.7%

in 2000, and 3.0% in 2001.

1.5

44.2

22.2

32.1

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

cpr (cement pasteresidue) only

NA (natural aggregate)only

NA coated with up to10% of cpr

foreign material

RC Aggregate constituents

Con

tent

[%]

199920002001

Figure 4.4.4 Composition of 14/10mm RC Aggregate (after additional segregation)

In the course of mechanical segregation of cpr from natural aggregate, it has been

observed that other than a small number of particles, the majority of natural aggregate

within RC Aggregate has not been crushed during the manufacturing process. The less

common cases of broken natural aggregate part were associated with a very high

compressive strength of original concrete (Recycling Industries, 1999). This confirms

the presumption that the majority of cement paste residue in currently produced RC

Aggregate has a lower strength in comparison to that of natural aggregate.

4.4-5

4.4.3 Content of Physical Contaminants

The Australian Standard AS 2758.1-1998 ‘Part 1. Concrete aggregates’ sets the content

limits for some impurities in aggregate, which include sugars, soluble salts, organic

mater and clay minerals. The content limits in both fine and coarse aggregate set

control measures to eliminate any adverse effects of these impurities on the strength,

abrasion resistance, surface finish and durability of concrete. Organic matter, sugar, or

any other carbohydrates influence setting time by delaying or suspending the set of

cement in concrete. A higher than permitted level of soluble salts in aggregate can

cause disintegration of concrete and corrosion of steel reinforcement, whereas, clay

minerals in aggregate cause strength reduction and volume changes.

The content of impurities in alternative concrete aggregate also has its limitations.

Commercial specifications for 14/10mm RC Aggregate set the maximum content of all

foreign materials of 1% by mass in Class 1A, and 2% in Class 1B aggregate. The

specifications do not take into account soluble salts or sugar content, but rather high

density materials such as steel reinforcement; and low density materials such as wood

and other organic matter. Figure 4.4.5 presents a breakdown by standard particle sizes

of a sample of the 14/10mm RC Aggregate into foreign materials and uncontaminated

aggregate.

Figure 4.4.5 Sample of 14/10mm RC Aggregate with segregated foreign materials

Pure 14/10mm RC Aggregate

Segregated foreign material

4.4-6

The amount of foreign materials in the 14/10mm RC Aggregate was determined from a

number of representative samples weighing 5kg that were randomly selected from

monthly batches of the aggregate. The RC Aggregate was dried in a laboratory oven at

a temperature of 103 ±2°C, sieved, then any organic and inorganic materials other than

clean pieces of the aggregate were isolated and their mass determined. Figure 4.4.6

presents the average percentages of all foreign materials in Class1, 14/10mm RC

Aggregate determined over a period of three years.

1.23

1.51

0.81

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Jan-Dec 1999 Jan-Dec 2000 Jan-Aug 2001

Period of time

Perc

enta

ge b

y w

eigh

t

Figure 4.4.6 Average content of foreign materials in 14/10mm RC Aggregate

The results show that the average total content of all physical contaminants in RC

Aggregate range between 0.81% and 1.51% with a few extreme cases where the highest

content of 5% in sample RCA_08_00 was noted. In general, the total level of foreign

material in the aggregate is below the limit indicated in the manufacturer’s

specification.

Furthermore, the amount of low density particles within RC Aggregate was determined.

After the segregation of uncontaminated particles and any foreign materials in RC

Aggregate, the aggregate was immersed in water to identify low density particles. The

low density particles were then dried and weighed. The test results show an average

content of 0.025%, which is considered as insignificant. It was observed that in

majority of tested aggregate, low density particles were not present. Figure 4.4.7

4.4-7

presents the average content of particles lighter that 1,000kg/m3 in 14/10mm RC

Aggregate measured over a period of three years.

0.04

0.01

0.03

0.00

0.01

0.01

0.02

0.02

0.03

0.03

0.04

0.04

0.05

0.05


Period of time

Perc

enta

ge b

y w

eigh

t

Figure 4.4.7 Average content of low density (<1,000kg/m3) particles in 14/10mm

RC Aggregate

The number and amount of different types of foreign materials in RC Aggregate is

highly dependent on the concrete waste stream, which is instigated by the choice of

demolition method and whether significant separation of concrete waste from other

C&D debris is employed. The content of foreign materials also depends on the

handling of feedstock at the recycling plant and on the effectiveness of their removal

during the crushing process.

The production of 14/10mm RC Aggregate at the Laverton North recycling plant is

governed by quality assured (QA) procedures. The manufacturer makes every effort to

minimise the amount of different categories of foreign materials in the aggregate,

especially those which contribute to volume instability such as; bricks, gypsum, wood,

clay lumps, and plate glass. Figure 4.4.8 presents the average number of different types

of physical contaminants in the aggregate.

4.4-8

7.5

4.9

5.6

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0


Period of time

Perc

enta

ge b

y w

eigh

t

Figure 4.4.8 Average number of foreign materials in 14/10mm RC Aggregate

It is interesting to note that over the three year testing period, the number of different

categories of foreign materials has decreased from an average of 7.5 to just below 5.

This illustrates the effectiveness of the QA procedures, and demonstrates improvements

in the quality of 14/10mm RC Aggregate.

Although the presence of some inert physical contaminants such as plastics and metals

can have a lesser impact on new concrete, the degradable organic matter or reactive

C&D waste such as gypsum in plasterboard, plate glass, and to some extend bricks, can

lead to deleterious reactions. The rate of recurrence of different types of foreign

materials in the aggregate was examined to identify the most frequently present physical

contaminants. Figure 4.4.9 presents data on the rate occurrence of different types of

impurities in 14/10mm RC Aggregate.

It has been noticed that in the majority of examined samples; bricks, wood, other

organic matter (leaves, grass, twigs, etc), plastics and glass were present. These

materials have a potential to activate localised internal expansion or impair the surface

finish of concrete, consequently reducing its strength and/or durability. Reoccurrence,

and an above the limit content of plate glass and brick particles can lead to an alkali

silica reaction or the slaking of some types of bricks.

4.4-9

13%

22%28%

31% 31%

78%

91%84%

75%

66%

44%

16%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

stee

lre

info

rcem

ent

coat

ed p

ebbl

e or

aggr

egat

e

pain

t or f

oam

clay

plas

ter

bitu

men

mor

tar

glas

s

plas

tic

othe

r org

anic

mat

ter woo

d

bick

Perc

enta

ge o

f ocu

renc

e

Figure 4.4.9 Occurrence frequency of foreign materials in 14/10mm RC Aggregate

Other physical contaminants such as bitumen, foam, paint, etc can also have an effect

on concrete performance. Figure 4.4.10 presents the average weight of each foreign

material in a specific quantity of aggregate.

28.10

102.23

0.78 0.99 0.697.67

0.96 0.18 0.16 0.43

23.17

11.25

0.00

20.00

40.00

60.00

80.00

100.00

120.00

stee

lre

info

rcem

ent

coat

ed p

ebbl

e or

aggr

egat

e

pain

t or f

oam

clay

plas

ter

bitu

men

mor

tar

glas

s

plas

tic

othe

r org

anic

mat

ter woo

d

bick

Ave

rage

wei

ght o

f for

eign

mat

eria

l [g]

Figure 4.4.10 Average weight [g] of various foreign materials per typical, 4kg samples of 14/10mm RC Aggregate

4.4-10

The data presented in Figure 4.4.3.10 indicates that by weight, the most significant

contributor of foreign materials in 14/10mm RC Aggregate are pebbles coated with

water based paint, pieces of steel reinforcement and bricks. Considering the variable

nature of source material for the production of RC Aggregate, the presence of paint-

coated pebbles was considered an extreme case (16% occurrence, see Figure 4.4.8).

Although, rightly so, the paint-coated pebbles were classified as foreign materials, their

characteristics indicated that their impact on new concrete would be insignificant. The

decision to include this type of impurity in the aggregate was made by the production

manager based on an engineering assessment. Alternatively, presence of the paint-

coated pebbles also demonstrates the possibility of the aggregate being contaminated

with a variety of unconventional materials, in some cases, unrelated to standard

demolition and construction waste. Figure 4.4.11 and Figure 4.4.12 present images of

different foreign materials (wood, paint-coated pebbles and brick particles),

demonstrating physical contaminants segregated by particle size.

Figure 4.4.11 Examples of foreign materials in 14/10mm RC Aggregate

Brick particle Paint coated pebbles

Wood

4.4-11

Figure 4.4.12 Foreign materials in 14/10mm RC Aggregate

An investigation into the composition and presence of physical contaminants revealed

that the presence of cement paste residue and foreign materials is intrinsic to RC

Aggregate. It also became apparent that although both the cpr and physical

contaminants are kept in a well defined range, they have a significant bearing on the

basic engineering properties of RC Aggregate.

The total cement paste residue content in the 14/10mm RC Aggregate was found to be

27%, which can be affixed to pieces of natural aggregate or be found in pure cement

paste form.

The foreign material content in 14/10mm RC Aggregate is on average 1.18%. The most

frequently present foreign materials in the aggregate include brick and wood particles.

During the testing period it was observed that the number and amount of physical

contaminants declined; a result of improvements in the production process of the

aggregate.

4.4.4 Cement Content and Elemental Composition of RC Aggregate Fines

A grading analysis of 14/10mm RC Aggregate showed that the content of very fine

particles is quite considerable, although consistent with the limits set by the

Brick particle

Plastic

Bitumen particle

4.4-12

manufacturer. The nature of the raw material and processes involved in the production

of the aggregate make the fines an integral part of the aggregate. The average content of

particles smaller than 75μm in the aggregate was found to be 2%. This was determined

by dry (see section 4.4.7) and wet sieve processes.

Observations made during the examination of elemental composition of the solid

particles of cement paste residue of RC Aggregate’s prompted further investigation into

the aggregate’s fines. Studies on the elemental and mineral composition of the fines

were conducted in addition to an assessment of re-cementing characteristic of the fines.

The re-cementing value of the fines was expressed as an equivalent of GB cement in the

aggregate. A calibration curve was devised based on the increase in temperature of

accelerated hydration of 0.5% to 1.5% of cement in the aggregate. In addition, the GB

cement was substituted with fines of the 14/10mm RC Aggregate and rise in

temperature was recorded. Figure 4.4.13 shows the calibration curve and an increase in

temperature due to accelerated hydration of some of the aggregate’s fines.

6

7

8

9

10

11

12

13

14

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Cement content [%]

Tem

pera

ture

rise

[0 C]

Figure 4.4.13 Equivalent GB cement content in 14/10mm RC Aggregate

The results indicate that a 2% inclusion of cement paste residue particles smaller than

75μm, causes a temperature rise, which is characteristic of the hydration of cements.

Based on the temperature rise and SEM results that indicate a high calcium content in

4.4-13

the fines, it can be concluded that a 2% content of particles smaller than 75μm in

14/10mm RC Aggregate, could have an equivalent cementing potential of

approximately 0.57% of GB cement.

More extensive studies using XRD and methodology similar to that described in this

section are currently being undertaken to further investigate the influence of cement

paste residue on chemical bonding in concrete made from RC Aggregate.

The Scanning Electron Microscopy was used to investigate the differences in elemental

(oxide) composition between natural and RC Aggregate, and to analyse mechanically

induced cracks in recycled aggregate.

Examination of the elemental composition aimed at supplementing the study of the re-

cementing potential of the fines and of cement paste residue of 14/10mm RC

Aggregate. Representative powder samples, mainly derived from the aggregate’s fines

(some powder samples were obtained from crushed cpr) and solid samples purposely

prepared or cut from RA Concrete were used. Areas as large as possible of powder and

solid samples were analysed using Energy Dispersive X-ray facilities to determine

elemental (oxide) composition. Figure 4.4.14 presents SEM powder samples of RC

Aggregate and sample holders, whereas Figure 4.4.15 presents a Backscatter electron

(BSE) image of RC Aggregate fines.

Figure 4.4.14 Powder samples of RA Concrete – SEM examination

4.4-14

Figure 4.4.15 BSE image of RC Aggregate fines

In each powder sample that was examined by the use of SEM, a number of

representative areas were selected to perform an elemental composition analysis. Figure

4.4.16 presents a plot of the Energy Dispersive X-ray analysis results of one of the areas

representing RC Aggregate fines.

Figure 4.4.16 ED X-ray analysis of RC Aggregate fines

The analysis of the BSE images of the RC Aggregate fines indicate relatively well-

distributed particles of various sizes smaller then 75µm, which could indicate presence

of partially hydrated cement particles or particles of pozzolanic materials. An

apparently equal distribution of lighter grey and darker grey areas indicates presence of

calcium and silica elements respectively. The results of the ED X-ray analysis (Figure

4.4-15

4.4.16) indicate that two equally dominant elements present in RC Aggregate fines are

silica and calcium. Apart from that, there are also traces of other elements present

including; aluminium, iron, potassium, sulphate, magnesium, chloride, titanium and

sodium. When compared with a standard natural aggregate which does not contain

those elements to such an extent; the elements could be considered as contaminants, and

their influence on hydration of cement should be investigated and taken into account

(section 2.7.3 Table 12 in this document).

In order to gain a thorough understanding of basic characteristics of RC Aggregate

fines, two similar materials were chosen to provide the basis for comparison; fines of

basaltic aggregate and GB cement. Figure 4.4.17 shows an example of a BSE image of

fines of natural aggregate (basalt), and Figure 4.4.18 shows the Energy Dispersive X-

ray analysis of the basalt fines passing through a 75µm sieve.

Figure 4.4.17 BSE image of natural aggregate (basalt) fines

4.4-16

Figure 4.4.18 ED X-ray analysis of natural aggregate (basalt) fines

The particular shape of basaltic fines is more elongated and angular than those of RC

Aggregate fines, which is attributed to less handling and to the structural makeup of

natural aggregate. The fines of basalt aggregate are less round and have relatively high

content of very fine particles. In comparison, the fines of RC Aggregate, which are

made from cement paste residue (relatively softer and structurally weaker material),

have more rounded particles.

Observations based on numerous visual inspections revealed that the basalt fines

contain approximately 50% of 75µm particles and 50% of particles smaller than 75µm.

Observations based on colour differentiation indicate that in most samples

approximately 70% of particles are of silica (darker grey) and that there is a relatively

high content of metallic elements (brighter colours).

Samples of the GB cement particles were also investigated using the BSE and EDX

analysis. Figure 4.4.19 presents an example of typical BSE images and Figure 4.4.20

shows the EDX of GB cement.

4.4-17

Figure 4.4.19 BSE image of GB cement

Figure 4.4.20 ED X-ray analysis of GB cement

An analysis of BSE images reveals that approximately 95% of GB cement particles are

significantly smaller than 75µm, and that the predominant particle size is approximately

15µm. The slightly lighter colour of the cement particles seen on the BSE images is

indicative of calcareous elements. The ED X-ray analysis plot of the GB shows that

approximately 75% of the total content of the cement is calcium, in one of its oxide

forms.

Solid samples of RC Aggregate were analysed using the same procedures and testing

environment. Figure 4.4.21 shows a typical example of a Backscatter Electron image of

highly weathered cement paste residue.

4.4-18

Figure 4.4.21 BSE image of cement paste residue

The darker grey areas represent sand particles, lighter coloured areas represent HCP,

whereas areas very bright, almost white, are representative of metallic elements

(typically minor inclusions of sulphate, aluminium, potassium, iron, titanium, iron and

magnesium). Figure 4.4.22 shows a summary of an elemental composition of N

Aggregate (basalt) and RC Aggregate (cpr powder and cpr solid).

0.00 0.00 0.72 2.25 0.00 0.00 0.00 1.25 0.00 0.00 0.00 0.00

95.77

18.78

34.85 35.36

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

Na2O MgO Al2O3 SiO2 P2O3 SO3 Cl K2O CaO TiO2 Cr2O3 MnO Fe2O3Compound

Con

tent

[%]

N Aggregate RC Aggregate solid RC Aggregate powder

Figure 4.5.22 Elemental composition of natural and 14/10mm RC Aggregates -

summary

4.4-19

4.4.5 Particle Density

The saturated surface dry (SSD), apparent and dry particle densities of the 14/10mm RC

Aggregate were examined to enable the author to make a comparison with the natural

reference aggregate and to allow accurate concrete mix design. A representative (36

reduced to 12) number of samples were examined over a period of three years. The

total number of samples and testing frequency was decided on the basis of low

variability of the tested aggregate. Figures 4.4.23 present surface dry particle density of

the 14/10mm RC Aggregate.

2.25

2.30

2.35

2.40

2.45

2.50

2.55

2.60

1 2 3 4 5 6 7 8 9 10 11 12

Sample group

Satu

rate

d dr

y su

rfac

e de

nsity

[t/m

3]

Figure 4.4.23 Saturated surface dry density of 14/10mm RC Aggregate

The average SSD particle density of 14/10mm RC Aggregate is well above the limit

specified by both the Australian Standard (AS 2758.1-1998) and the aggregate

manufacturer. The average of 2,450kg/m3 exceeds the specified minimum of

2,100kg/m3. The relatively small variation (STDEV of 40kg/m3) which, combined with

a relatively high density of the aggregate, makes it a suitable concrete aggregate. This

in turn increases the confidence of concrete technologists that basic properties such as

SSD particle density of aggregate are in a well defined range, which subsequently

assists in accurate concrete mix design.

2,450kg/m3

4.4-20

A relationship between SSD particle density and cement paste content was also

investigated. Figure 4.4.24 presents a linear correlation between SSD and cpr content.

2.44 2.44 2.55 2.44 2.45 2.49 2.44 2.47 2.46 2.40 2.38 2.47 y = -0.004x + 2.4788

0.00

5.00

10.00

15.00

20.00

25.00

RCA

_08&

09&

10_9

9

RCA

_05&

06&

07_0

1

RCA

_02&

03&

04_0

1

RCA

_05&

06&

07_0

0

RCA

_11&

12&

01_0

1

RCA

_08&

09&

10_0

0

RCA

_02&

03&

04_0

0

RCA

_05&

06&

07_9

9

RCA

_02&

03&

04_9

9

RCA

_11&

12&

01_0

0

RCA

_08&

09&

10_0

1

RCA

_01_

99

cpr [

%] &

satu

rate

d su

rfac

e dr

y de

nsity

[t/m

3 ]

cpr [%]SSD [t/m3]Linear (cpr [%])Linear (SSD [t/m3])

Figure 4.4.24 Relationship between cpr content and saturated surface dry density

of 14/10mm RC Aggregate

It is evident that the SSD particle density of 14/10mm RC Aggregate is dependent on

the content of cement paste residue as would be expected. An increased amount of cpr

in the aggregate results in a lower SSD particle density.

2.15

2.20

2.25

2.30

2.35

2.40

2.45

2.50

1 2 3 4 5 6 7 8 9 10 11 12

Sample group

Dry

den

sity

[t/m

3]

Figure 4.4.25 Dry particle density of 14/10mm RC Aggregate

4.4-21

Experimental procedures of the Australian Standard 1141.6.1 were also used to

determine dry particle and apparent densities. Figure 4.4.25 presents the dry particle

density of 14/10mm RC Aggregate.

The dry particle density of 14/10mm RC Aggregate ranges from 2,270kg/m3 to

2,450kg/m3 with a standard deviation of STDEV 45kg/m3. The results are consistent

with those reported in various publications. For example, Soutos et al (2004) reports on

the dry particle density of coarse RC Aggregate of 2,220kg/m3 and on SSD particle

density of 2,410kg/ m3. The aggregate was produced from precast concrete elements of

demolished high-rise buildings. In comparison, conventional, natural aggregates used

in concrete technology typically have a particle density ranging from 2,100kg/ m3 to

2,700kg/ m3.

A relationship between the content of cement paste residue and dry particle density was

also investigated. As in the other types of particle density, the results indicate that the

dry particle density of the aggregate decreases as the cpr content increases (see Figure

4.4.26).

2.34 2.34 2.45 2.33 2.35 2.37 2.33 2.36 2.35 2.28 2.27 2.35 y = -0.0055x + 2.3793

0.00

5.00

10.00

15.00

20.00

25.00

RC

A_0

8&09

&10

_99

RC

A_0

5&06

&07

_01

RC

A_0

2&03

&04

_01

RC

A_0

5&06

&07

_00

RC

A_1

1&12

&01

_01

RC

A_0

8&09

&10

_00

RC

A_0

2&03

&04

_00

RC

A_0

5&06

&07

_99

RC

A_0

2&03

&04

_99

RC

A_1

1&12

&01

_00

RC

A_0

8&09

&10

_01

RC

A_0

1_99

cpr [

%] &

par

ticle

den

sity

[t/m

3 ]

cpr [%]Particle density [t/m3]Linear (Particle density [t/m3])Linear (cpr [%])

Figure 4.4.26 Relationship between cpr content and dry particle density in

14/10mm RC Aggregate

4.4-22

A similar trend was observed in the apparent particle density within 14/10mm RC

Aggregate, which is on average 2,630kg/m3. Figure 4.4.27 presents a negative linear

correlation between cpr content and apparent particle density.

2.61 2.59 2.72 2.62 2.62 2.69 2.62 2.65 2.65 2.59 2.55 2.67y = -0.0017x + 2.6428

0.00

5.00

10.00

15.00

20.00

25.00R

CA

_08&

09&

10_9

9

RC

A_0

5&06

&07

_01

RC

A_0

2&03

&04

_01

RC

A_0

5&06

&07

_00

RC

A_1

1&12

&01

_01

RC

A_0

8&09

&10

_00

RC

A_0

2&03

&04

_00

RC

A_0

5&06

&07

_99

RC

A_0

2&03

&04

_99

RC

A_1

1&12

&01

_00

RC

A_0

8&09

&10

_01

RC

A_0

1_99

cpr[

%] &

app

aren

t par

ticle

den

dsity

[t/m

3]

cpr [%]Apparent density [t/m3]Linear (cpr [%])Linear (Apparent density [t/m3])

Figure 4.4.27 Relationship between cpr content and apparent density in 14/10mm RC Aggregate

With reference to the particle density of RC Aggregate expressed either as; saturated-

surface-dry, dry or apparent particle density, it has been found that the particle density

exceeds the specified minimums of 2,100kg/m3. Table 4.4.1 presents a summary of

results of the particle density investigation of 14/10mm RC Aggregate.

Table 4.4.1 Particle density of 14/10mm RC Aggregate – results summary

Particle density [kg/ m3] 14/10mm RC Aggregate Natural aggregate Range 2,380 – 2,550 Average 2,450 2,690

SSD

Variation 40 Range 2,270 – 2,450 Average 2,340 2,670

Dry

Variation 45 Range 2,550 – 2,720 Average 2.63 2,700

Apparent

Variation 48

4.4-23

An investigation into the particle density of 14/10mm RC Aggregate, one of the basic

engineering properties, allowed the generation of accurate input data to design concrete

mixes. Although the minimum value of particle density of 2,100kg/m3 specified by the

aggregate manufacturer is correct, it has been found that it is quite conservative and not

specific enough.

The variation in particle density of 14/10mm RC Aggregate is relatively low, indicating

that the feedstock used to manufacture the aggregate is of a relatively consistent

composition. In the course of the three year investigation period, it was found that

particle density is not affected by any seasonal variations or a continuously improving

production process of the aggregate.

Further to a fundamental determination of basic engineering properties such as SSD, dry

and apparent particle density, the influence of cement paste residue on the particle

density was also examined. A relationship has been established that density is inversely

affected by the content of cement paste residue as was expected. The increase in cpr

content in the aggregate lowers its density.

4.4.6 Bulk Density

The bulk of the density of 14/10mm RC Aggregate and basalt aggregate was examined

in their compacted state. Figure 4.4.28 presents the average bulk densities of recycled

and controlled natural aggregate.

4.4-24

1,430

1,700

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

14/10mm RC Aggregate 14/10mm N Aggregate

Bul

k de

nsity

[kg/

m3]

Year 1999Year 2000Year 2001Year 2003

Figure 4.4.28 Bulk density of the 14/10mm natural and RC Aggregates

The compacted bulk density of the aggregate is influenced by particle size distribution

and density of the aggregate particles. The average compacted bulk density of the

14/10mm RC Aggregate is 1,420kg/m3, which is approximately 15–20% lower than the

control basalt aggregate, however, it is still well above the minimum (1,200kg/m3)

specified by the manufacturer. The variability of bulk density expressed as the average

STDEV of 31kg/m3 is very low, which indicates that particle density and particle size

distribution were very consistent.


Particle size distribution (PSD) was identified as one of the most noticeable and

important properties in this research project, as it is directly linked with a development

of void networks in acoustic barriers. Figure 4.4.29 shows a sample of the 14/10mm RC

Aggregate segregated by various sizes corresponding to standard sieve apertures.

4.4-25

Figure 4.4.29 Particles of 14/10mm RC Aggregate retained on 13.2mm, 9.5mm, 6.7mm, 4.75mm, 2.36mm and 75μm sieves (from right to left)

Table 4.4.2 shows the yearly average PSD of 14/10mm RC Aggregate determined over

the four (4) year period.

Table 4.4.2 Particle size distribution of 14/10 mm RC Aggregate – percentage passing

Sieve aperture [mm]

19.0 13.2 9.5 6.7 4.75 2.36 pan Testing period

Percentage passing sieve aperture [%] Year 1999 100 72.9 25.3 10.1 2.3 1.0 1.0 Year 2000 100 87.3 30 9.8 2.4 0.8 0.8 Year 2001 100 81.9 25.1 7.4 2.7 0.8 0.8 Year 2003 100 79.5 34.4 12.6 7.1 4.1 0.5

The majority of the aggregate remained on the 10mm sieve, and only 1% of the particles

have particles smaller than 75 micrometers when determined by dry sieving. The

amount of fines (<75μm) determined by the wet sieve analysis is on average 2%.

Variations in the aggregate grading were within the limits specified by the

manufacturer. Figure 4.4.30 presents a comparison between upper and lower limits

specified in the Australian Standard 2758.1-1998 for concrete aggregate and the average

yearly PSD of 14/10mm RC Aggregate.

4.4-26

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Sieve aperture [mm]

Perc

enta

ge p

assi

ng

Lower limitUpper limitYear 1999Year 2000Year 2001Year 2003

Figure 4.4.30 Particle size distribution of 14/10mm RC Aggregate – average of 1999 – 2003 samples

Control samples were prepared from single-size aggregates; 10mm and 14mm. Firstly,

volumes of RC Aggregate of a particular size were measured. Test portions of natural

aggregates were determined using identical volumes of comparable RC Aggregate.

This was consistent with the approach that is taken when concrete mixes are designed;

however, it also resulted in a very small deviation in the grading of the natural aggregate

compared with those of the 14/10mm RC Aggregate. The difference in the particle size

distribution of the two aggregates was deemed as negligible, therefore not requiring any

adjustments. Table 4.4.3 presents the grading of some of the basalt samples used as a

control aggregate.

Table 4.4.3 Particle size distribution of 14/10 mm Natural Aggregate – percentage passing

Sieve aperture [mm]

19.0 13.2 9.5 6.7 4.75 2.36 pan Sample Percentage passing sieve aperture [%] NA-99-04 100 89 33.5 5.8 0.6 0.1 0.1 NA-00-03 100 92 48.6 14 2.6 0.3 0.3 NA-01-07 100 91.6 42.9 5.8 0.6 0.1 0.1

4.4-27

Figure 4.4.31 presents a comparison between the 14/10mm natural aggregate and RC

Aggregate. It can be noticed that natural aggregate has a lower amount of aggregate

fraction retaining on the 4.75mm and 2.36mm sieves.

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Sieve aperture [mm]

Perc

enta

ge p

assi

ng

Lower limitUpper limitRC AggregateNatural aggregate

Figure 4.4.31 Comparison of particle size distribution of natural aggregate and

14/10mm RC Aggregate Although there was some dissimilarity in particle size distribution between the

14/10mm RC Aggregate and those of the natural aggregate, the difference was within an

acceptable limit. The difference resulted from the variations in aggregate shape and

aggregate bulk density.

4.4.8 Water Absorption If not accounted for, highly absorptive aggregate can significantly alter the hydration

process by reducing the amount of available water for the chemical reaction,

subsequently leading to presence of un-hydrated cement in concrete matrix. This has

potential to reduce strength of concrete and makes it less durable. Water absorption in

coarse RC Aggregate can be as high as 8.5%, and in the natural coarse aggregate is

typically about 1% (Soutsos, 2004; CSIRO, 2002). A representative number of test

4.4-28

portions of the aggregate were reduced to thirty six (36) samples. Figure 4.4.32

presents the results of water absorption of 14/10mm RC Aggregate.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

1 2 3 4 5 6 7 8 9 10 11 12

Sample group

Wat

er a

bsor

ptio

n [%

]

Figure 4.4.32 Water absorption of 14/10mm RC Aggregate measured by the weigh-

in-water method

The water absorption in tested aggregate was relatively low when compared with

reports in available literature. It ranged between 4% and 5.2% with an average of

4.67%. Appropriate adjustments to the water content per cubic meter of concrete can

be made on the basis of these results.

Furthermore, a relationship between the cement paste residue content in the aggregate

and its water absorption was investigated. Figure 4.4.33 presents the relationship

between water absorption and cpr content in 14/10mm RC Aggregate.

4.4-29

y = 0.0751x + 4.1806

0.00

5.00

10.00

15.00

20.00

25.00

RC

A_0

8&09

&10

_99

RC

A_0

5&06

&07

_01

RC

A_0

2&03

&04

_01

RC

A_0

5&06

&07

_00

RC

A_1

1&12

&01

_01

RC

A_0

8&09

&10

_00

RC

A_0

2&03

&04

_00

RC

A_0

5&06

&07

_99

RC

A_0

2&03

&04

_99

RC

A_1

1&12

&01

_00

RC

A_0

8&09

&10

_01

RC

A_0

1_99

cpr [

%] &

wat

er a

bsor

ptio

n [%

]cpr [%]WA [%]Linear (WA [%])Linear (cpr [%])

Figure 4.4.33 Relationship between cement paste residue (cpr) content and water

absorption in 14/10mm RC Aggregate

It has been observed that a positive correlation exists between cpr content and water

absorption. A relative increase of cement paste residue leads to increased water

absorption of the aggregate.

4.4.9 Porosity

The basic engineering properties of RC Aggregate including particle and bulk density,

and water absorption, are also dependent on the porosity of cement paste residue of the

aggregate. Various testing techniques were used to examine the porosity of 14/10mm

RC Aggregate ranging from absorption of water, adsorption of nitrogen to a neutron

scattering method. Control samples were first established to allow a subsequent

comparison of results of the aggregate porosity. Figures 4.4.34 and 4.4.35 present

examples of the BET porosity standards.

4.4-30

Figure 4.4.34 Example of powder (<150μm) samples of neat cement pastes of various cement/water ratios (0.2w/c, 0.4w/c and 0.8w/c)

Figure 4.4.35 Example of solid sample of cement paste residue of RC Aggregate obtained from concrete of known w/c ration of 0.4

A representative number of cement paste residue test portions of the 14/10mm RC

Aggregate were selected. The sample suite of the cpr collected and examined

corresponds to a testing period of four (4) years. The test portions were selected from

aggregate samples that were mechanically broken at the compositional examination of

14/10mm RC Aggregate. According to a degree of possible carbonation, the cement

paste residues were classified into three categories; LOW (slightly weathered cpr, and

of or corresponding to, a good quality, very low w/c ratio of approximately 0.2 or to

natural aggregate), MODERATELY (reasonably weathered cpr, and of or

corresponding to, an average quality cement paste w/c ratios of approximately 0.4 to

0.6) and HIGHLY (distinctly weathered cpr, and of, or corresponding to a poor quality

of cement paste, of w/c ration of approximately 0.8). Tables 4.4.4 and 4.4.5 present the

4.4-31

sample suite, control standard, and classification of the BET nitrogen adsorption

porosity examination.

Table 4.4.4 RC Aggregate samples examined by the BET nitrogen adsorption

RC Aggregate samples – BET designation

Assumed control standards 0.2w/c paste -natural aggregate

0.4w/c paste

0.8w/c paste

s_142 to s_149 & s_171, to s_173 & s_201, to s_209, s_213 & s_216 & s_224 to s_232 S_174 s_214 s_215

Table 4.4.5 RC Aggregate samples examined by the BET nitrogen adsorption – classification by degree of weathering

HIGHLY weathered samples of cpr

MODERATELY weathered samples of cpr

Slightly (LOW) weathered samples of cpr

s_142, s_144, s_147, s_149, s_201, s_228, s_231,

s_146, s_148, s_172, s_207, s_208, s_209, s_213, s_216, s_225, s_227, s_230, s_229, s_232

s_143, s_145, s_171, s_173, s_202, s_203, s_204, s_205, s_206, s_224, s_226

BET porosity is expressed in terms of total pore volume, pore size distribution, pore

surface area, and pore diameter. Figure 4.4.36 shows an adsorption isotherm of the

reference 0.4 w/c ratio paste. The isotherm is characteristic of porous solids and the

hysteresis loop created by the adsorption and desorption branches indicate a uniform

distribution of pores of different sizes in the pore size range ranging between 17Å and

3μm. A similar pattern and shape of isotherms in all samples of the cement paste

residue have been observed. This confirms that the microstructure of cement paste

consists of a reasonably evenly distributed network of pores as was expected.

4.4-32

0.4 neat cement paste (sample s_214) - adsorption isotherm

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Relative pressure [p/po]

Vol

ume

adso

rbed

[cc/

g]

Figure 4.4.36 BET isotherm – 0.4 w/c ratio, neat cement paste

Figure 4.4.37 presents an adsorption-desorption isotherm of the porosity reference

created for highly weathered cement paste residue. The reference standard was

developed using neat new cement paste of w/c with a ratio of 0.8.

0.8 neat cement paste (sample s_215) - adsorption isotherm

0

10

20

30

40

50

60

70

80

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


Vol

ume

adso

rbed

[cc/

g]

Figure 4.4.37 BET isotherm – 0.8w/c ratio, neat cement paste

4.4-33

Figure 4.4.38 presents an example of an isotherm of one of the cement paste residue

samples, which has been classified as highly weathered.

HIGHLY weathered sample of cpr (s_147) , adsorption isotherm

0

5

10

15

20

25

30

35

40

45

50

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


Vol

ume

adso

rbed

[cc/

g]

Figure 4.4.38 BET isotherm of HIGHLY weathered cpr (s_147)

The highly weathered cement paste residues of 14/10mm RC Aggregate have pore size

distribution spread relatively evenly over the whole porosity range measured by BET

nitrogen adsorption. It could also be concluded that the shape of the isotherm is similar

to the isotherms produced by other referenced samples or of the cpr samples.

Figure 4.4.39 shows the BET isotherm of one of the moderately weathered cement paste

residue samples, which has a porosity characteristic of standard concrete with a design

water/cement ratio of between 0.4 and 0.6. Prior to the BET nitrogen adsorption

examination, this sample (s_229) was subjected to a non-destructive SANS porosity

investigation.

4.4-34

MODERATELY weathered cpr (d2o-cp-0.4 + cpr), (sample s_229), adsorption isotherms

0

5

10

15

20

25

30

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


Vol

ume

adso

rbed

[cc/

g]

Figure 4.4.39 Example of MODERATELY weathered cpr (BET sample s_229) Cement paste residue samples obtained from concrete of a relatively short in-service life

were classified as slightly (LOW) weathered cpr. Predominantly, the identification and

classification of samples was based on the information provided by the aggregate

manufacturer on the source material, and classification was based on a visual

assessment (colour and hardness). A number of the samples were first examined using

the SANS method before being subjected to the BET examination. Figure 4.4.40

presents the adsorption-desorption isotherm of the LOW weathered sample of cement

paste residue of the 14/10mm RC Aggregate.

Slightly (LOW) weathered cpr (d2o-cp-0.4), (sample s_226), adsorption isotherm

0

5

10

15

20

25

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1


Vol

ume

adso

rbed

[cc/

g]

Figure 4.4.40 Example of LOW weathered cpr (BET sample s_226)

4.4-35

The analysis of the BET isotherms and hysteresis produced by the adsorption and

desorption branches prompted the following major conclusions.

• The shape of the isotherm confirms that cement pastes are porous solids and that the

pores are distributed consistently over the entire pore size range, between 17Å and

3μm.

• The hysteresis loops indicate that the shape of pores is either in the form of parallel

plates, ink-bottle-shaped pores or the pores are spheroidal.

Apart from the capability to classify porous solids and characterise pore structure in

solids, the BET nitrogen adsorption allows the measurement of the total porosity, total

pore volume, volume of micropores, pore surface area, and an average pore diameter.

Initially, the reference porosity parameters of the three different categories of cement

paste residue were established. A total porosity standard of 17.5% for the highly

weathered paste was determined. Figure 4.4.41 presents the BET total porosity.

17.5

7.3

9.9

15.3

19.8

27.9

14.413.5

0.00

5.00

10.00

15.00

20.00

25.00

30.00

control 0.8 cp*[s_215]

HW cpr[s_228]

HW cpr[s_231]

HW cpr[s_201]

HW cpr[s_149]

HW cpr[s_142]

HW cpr[s_144]

HW cpr[s_147]

BET

por

osity

[%]

Figure 4.4.41 BET porosity of HIGHLY weathered cement paste residue of 14/10mm RC Aggregate

4.4-36

Test results of the BET nitrogen adsorption examination of the total porosity of highly

weathered cpr of 14/10mm RC Aggregate defined a range of porosity from 7.3% to

27.9%. The total porosity in majority of the samples is below the reference porosity of

17.5%. The average total porosity of significantly weathered cpr is 15.4%.

The total porosity reference standard established for moderately weathered cpr was

8.1%. Figure 4.4.42 presents results of the BET examination of total porosity of

moderately weathered cpr of the 14/10mm RC Aggregate.

8.1

4.2

7.1

8.2

6.8

4.8

8.4

6.5

5.75.55.55.4

5.34.7

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

cont

rol 0

.4 c

p*[s

_214

]

MW

cpr

[s_1

72]

MW

cpr

[s_2

25]

MW

cpr

[s_2

27]

MW

cpr

[s_2

13]

MW

cpr

[s_2

30]

rca_

04_1

*[s

_207

]

MW

cpr

[s_2

32]

MW

cpr

[s_1

48]

rca_

04_3

*[s

_208

]

MW

cpr

[s_1

46]

rca_

04_2

*[s

_216

]

MW

cpr

[s_2

29]

rca_

04_4

*[s

_209

]

BET

por

osity

[%]

Figure 4.4.42 BET porosity of MODERATELY weathered cement paste residue of

14/10mm RC Aggregate

The results indicate that the majority of samples have a total porosity lower than the

reference porosity of 8.1% and that the average total porosity of moderately weathered

cpr is 6%.

In order to assume a classification system, cement pastes that required a much higher

energy input in segregating cpr from natural aggregate were classified as slightly

weathered even though the weathering was not measured . Some of the samples (s_145,

s_171, s_173) also had pieces of natural aggregate, which were difficult to isolate. A

4.4-37

porosity standard of 0.9% was established for the LOW weathered cpr (sample s_174).

Figure 4.4.43 presents total porosity of slightly weathered cement paste residues.

0.9

2.31.9

1.4

2.9 3.03.5

5.85.7

3.93.73.7

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

cont

rol c

p +

na[s

_174

]

cont

rol c

p +

na[s

_145

]

cont

rol c

p +

na[s

_171

]

LW c

pr [s

_173

]

LW c

pr [s

_206

]

LW c

pr [s

_143

]

LW c

pr [s

_203

]

LW c

pr [s

_205

]

LW c

pr [s

_224

]

LW c

pr [s

_204

]

LW c

pr [s

_202

]

LW c

pr [s

_226

]

BET

por

osity

[%]

Figure 4.4.43 BET porosity of slightly (LOW) weathered cement paste residue of 14/10mm RC Aggregate

Test results show that the total porosity in all of the cement paste residue samples

exceeded the reference porosity. The average BET porosity in slightly weathered cpr of

14/10mm RC Aggregate is 4% and of cement paste residue containing some natural

aggregate is 1.87%.

Furthermore, the pore volume was analysed in terms of the total pore volume (BET

range from 17Å to 3μm) and volume of micropores. All samples of the cement paste

residue of 14/10mm RC Aggregate were categorised as ‘old cpr’ and an average of all

the data is presented in the following figures. Figure 4.4.44 shows an average total pore

volume in cpr and compares it against the three reference standards (e.g. ‘0.2w/c cp’ -

0.2 water/cement ratio new cement paste)

An average total volume of pores in the cement paste residue of 0.036cm3/g is

characteristic of slightly weathered pastes. A relatively low total volume of pores in the

4.4-38

BET porosity range (17Å to 3μm) could indicate that pores in weathered cpr are bigger

than 3μm, and that the volume of such pores was not measured.

0.032

0.058

0.093

0.036

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

old cpr 0.2w/c cp 0.4w/c cp 0.8w/c cp

Sample group

Tota

l por

e vo

lum

e [c

m3 /g]

Figure 4.4.44 BET - Total pore volume of cement paste residue (old cpr) -

comparison with porosity standards However, the volume of micropores is higher than those of the reference standards,

which indicates that through the weathering process or other in-service mechanisms,

minute pores are created or access to already existing pores is made possible. Figure

4.4.45 presents an average volume of micropores in the cpr of 14/10mm RC Aggregate.

0.00023

0.00087

0.00136

0.00200

0

0.0005

0.001

0.0015

0.002

0.0025

old cpr 0.2w/c cp 0.4w/c cp 0.8w/c cpSample group

Mic

ropo

res v

olum

e [c

m3 /g]

Figure 4.4.45 BET – Micro-pore volume of cement paste residue (old cpr) –

comparison with porosity standards

4.4-39

Further to the total porosity and volume examinations, the surface area of pores in the

cpr was analysed and compared with established standards. A relatively high total pore

surface area of 15.73m2/g, which is characteristic of moderately to highly weathered

pastes, is caused by a high content of micropores in tested samples. A large amount of

very small pores increases surface area. Figure 4.4.46 presents the BET total surface

area of pores in a range between 17Å and 3μm, whereas Figure 4.4.47 shows the surface

area of micropores.

15.73

6.41

12.03

19.61

0

5

10

15

20

25


Sample group

Tota

l por

e su

rfac

e ar

ea [m

2 /g]

Figure 4.4.46 BET – Total pore surface area of cement paste residue (old cpr) – comparison with porosity standards

4.4-40

0.40

1.85

4.73

2.89

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5


Sample group

Mic

ropo

res s

urfa

ce a

rea

[m2 /g

]

Figure 4.4.47 BET – Micropore surface area of cement paste residue (old cpr) –

comparison with porosity standards A relatively high content of micropores in cement paste residue decreases the average

pore diameter. The average diameter of pores in the cpr is 94Å whereas in the reference

porosity standards is in the vicinity of 195Å. Figure 4.4.48 presents the pore diameter

of reference samples and the average pore diameter of cement paste residue of the


200

94

189194

0

50

100

150

200

250


Sample group

Ave

rage

por

e di

amet

er [Å

]

Figure 4.4.48 BET – Average pore diameter of pores in cement paste residue (old

cpr) – comparison with porosity standards

4.4-41

A simple regression analysis of the BET nitrogen adsorption porosity results was

performed. Relationships between various parameters of the BET porosity such as total

porosity, total pore volume, volume of micropores, pore surface area, and pore average

diameter were investigated. Figure 4.4.49, Figure 4.4.50 and Figure 4.4.51 present

examples of the relationship between total porosity, total surface, and micropores area

in three categories of cement paste residue; highly weathered, moderately weathered,

and slightly weathered.

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

HW cpr[s_228]

HW cpr[s_231]

HW cpr[s_201]

HW cpr[s_149]

HW cpr[s_142]

HW cpr[s_144]

HW cpr[s_147]

poro

sity

[%],

SSA

[m2/

g]

porosity SSA [17-3,000A] SSA microporesLinear (porosity) Linear (SSA [17-3,000A]) Linear (SSA micropores)

Figure 4.4.49 BET porosity of HIGHLY weathered RC Aggregate

In the highly weathered RC Aggregate, an increase in the surface area of micropores is

positively correlated with the increase in total porosity of the cement paste residue.

There is also a positive correlation between the surface area of micropores and the

surface area of all pores in the 17Å and 3μm range.

4.4-42

0.00

5.00

10.00

15.00

20.00

25.00

MW

cpr

[s_1

72]

MW

cpr

[s_2

25]

MW

cpr

[s_2

27]

MW

cpr

[s_2

13]

MW

cpr

[s_2

30]

rca_

04_1

*[s

_207

]

MW

cpr

[s_2

32]

MW

cpr

[s_1

48]

rca_

04_3

*[s

_208

]

MW

cpr

[s_1

46]

rca_

04_2

*[s

_216

]

MW

cpr

[s_2

29]

rca_

04_4

*[s

_209

]

poro

sity

[%],

SSA

[m2/

g]

porosity SSA [17-3,000A] SSA microporesLinear (SSA [17-3,000A]) Linear (SSA micropores) Linear (porosity)

Figure 4.4.50 BET porosity of MODERATLY weathered RC Aggregate

The moderately weathered cement paste residue that is present in most of the RC

Aggregate has shown the strongest relationship between various porosity parameters

including total porosity and surface area of pores. The increase in porosity correlates

strongly with the increase of micropores, which subsequently contributes to the increase

of surface area of micropores and pores in a BET range of 17Å and 3μm as was

expected.

On the other hand, the slightly weathered RC Aggregate, which has a relatively small

volume of micropores, or where there is a possibility that nitrogen molecules cannot

access the micropores, exhibit different relationships. The increase in total porosity is

only slightly affected by the increase in amount of micropores. The contribution to the

overall surface area of all pores by the micropores is negligible.

4.4-43

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

LW cpr[s_173]

LW cpr[s_206]

LW cpr[s_143]

LW cpr[s_203]

LW cpr[s_205]

LW cpr[s_224]

LW cpr[s_204]

LW cpr[s_202]

LW cpr[s_226]

poro

sity

[%],

SSA

[m2/

g]

porosity SSA [17-3,000A] SSA microporesLinear (porosity) Linear (SSA [17-3,000A]) Linear (SSA micropores)

Figure 4.4.51 BET porosity of LOW weathered RC Aggregate

Further to the BET nitrogen adsorption investigation of cement paste residue of the

14/10mm RC Aggregate, the SANS examination was used to extend and supplement

porosity range accessible to the BET method. Initially, irregularly shaped samples of

cpr, similar to those used in the BET investigation were analysed, which were followed

by cubic 6 x 6 x 6mm samples.

At that stage, the analysis of cement paste residue using the SANS results was non

conclusive due to multiple and incoherent scattering from samples that were thicker

than 3mm.

Investigation of the porosity of cement paste residue of 14/10mm RC Aggregate

identified that the pores are either in the form of parallel plates, ink-bottle-shaped pores

or are spheroidal in shape. The total porosity and other porosity parameters depend on

the quality of cpr and on the in-service life of concrete used in the production of RC

Aggregate. Table 4.4.6 presents a summary of the porosity parameters of the 14/10mm

RC Aggregate.

4.4-44

Table 4.4.6 Porosity of 14/10mm RC Aggregate – summary results

Porosity parameter Unit cpr of 14/10mm RC Aggregate

Reference

Range % 1.36 – 27.91 Average % 7.22 0.86

Total porosity

Variation % 5.67 Range cm3/g 0.0037 – 0.07 Average cm3/g 0.03 0.032

Total pore volume

Variation cm3/g 0.019 Range cm3/g 0.00011 – 0.0057 Average cm3/g 0.0012 0.00023

Volume of micropores

Variation cm3/g 0.0012 Range m2/g 2.99 – 34.72 Average m2/g 10.45 6.41

Total surface area

Variation m2/g 7.29 Range m2/g 0.17 – 13.58 Average m2/g 2.79 0.4

Micropores surface area

Variation m2/g 2.99 Range Å 46 – 984 Average Å 142.19 200

Average pore diameter Variation Å 165.28


This section presented results of the examination of 14/10mm RC Aggregate. The

properties examined included; cement paste residue content, physical contaminants

content, content and re-cementing qualities of fines, particle size distribution, particle

and bulk density, water absorption, and porosity.

The results indicate that the selected 14/10mm RC Aggregate has a specific set of well

defined unique properties. Some of the physical properties of the aggregate are specific

to the material. For example, content of cement paste residue and content of various

remnants of other waste material in the aggregate are intrinsic to the waste material used

in production, and to RC Aggregate.

A relatively high content of fine particles smaller than 75μm in 14/10mm RC Aggregate

is another unique property of the material. The fines appear to have some re-cementing

potential, which can contribute to hydration of cement in concrete made from RC

4.4-45

Aggregate. Another property of the aggregate that has potential to be beneficial from a

concrete technology view point is its shape.

However, some of the aggregate’s properties including inconsistent water absorption

and higher porosity have to be closely monitored and controlled if the aggregate is used

in concrete.

Table 4.4.7 presents a summary of the basic engineering properties of 14/10mm RC

Aggregate.

Table 4.4.7 Average engineering properties of 14/10mm RC Aggregate – summary

Property Unit 14/10mm RC Aggregate

Reference / basalt

Cement paste residue content % 27 0 Foreign material content % 1.18 0 Fines (<75μm) content % 2 0 Re-cementing potential % of GB 0.5 0 Particle density (SSD) kg/m3 2,450 2,750 Bulk density (compacted) kg/m3 1,420 1,700 Water absorption % 4.67 0.5 Total porosity (range 17Å - 3μm) % 7.22 0.86 Total pore volume(range 17Å - 3μm) cm3/g 0.036 0.32 Total volume of micropores cm3/g 0.002 0.00023 Total surface area(range 17Å - 3μm) m2/g 10.73 6.41 Total surface area of micropores m2/g 2.79 0.4 Pore average diameter (range 17Å - 3μm) Å 142.2 200 Particle size distribution 14/10mm 14/10mm Elemental composition Calcium rich Silica rich

The test results generated at this stage of the experimental program defined the basic

engineering properties of 14/10mm RC Aggregate. The majority of the data was

subsequently used in other stages of the experimental and developmental program of

this research project. The next section reports on an examination of concrete made from


4.4-46

4.4 RECYCLED CONCRETE (RC) AGGREGATE .............................................1 4.4.1 Introduction...............................................................................................1 4.4.2 Composition – Cement Paste Residue Content.........................................2 4.4.3 Content of Physical Contaminants ............................................................5 4.4.4 Cement Content and Elemental Composition of RC Aggregate Fines ...11 4.4.5 Particle Density .......................................................................................19 4.4.6 Bulk Density ...........................................................................................23 4.4.7 Particle Size Distribution ........................................................................24 4.4.8 Water Absorption....................................................................................27 4.4.9 Porosity ...................................................................................................29 4.4.10 Discussion of the Results ........................................................................44

Figure 4.4.1 Stockpile of RC Aggregate...........................................................................1 Figure 4.4.2 Particles of RC Aggregate (A – cement paste residue only, B and C –

natural aggregate coated with cpr) ............................................................................3 Figure 4.4.3 Relative composition of 14/10mm RC Aggregate (sample

RCA_11_00_s1&s2) .................................................................................................3 Figure 4.4.4 Composition of 14/10mm RC Aggregate (after additional segregation)......4 Figure 4.4.5 Sample of 14/10mm RC Aggregate with segregated foreign materials .......5 Figure 4.4.6 Average content of foreign materials in 14/10mm RC Aggregate ...............6 Figure 4.4.7 Average content of low density (<1,000kg/m3) particles in 14/10mm RC

Aggregate ..................................................................................................................7 Figure 4.4.8 Average number of foreign materials in 14/10mm RC Aggregate...............8 Figure 4.4.9 Occurrence frequency of foreign materials in 14/10mm RC Aggregate......9 Figure 4.4.10 Average weight [g] of various foreign materials per typical, 4kg samples

of 14/10mm RC Aggregate .......................................................................................9 Figure 4.4.11 Examples of foreign materials in 14/10mm RC Aggregate......................10 Figure 4.4.12 Foreign materials in 14/10mm RC Aggregate..........................................11 Figure 4.4.13 Equivalent GB cement content in 14/10mm RC Aggregate.....................12 Figure 4.4.14 Powder samples of RA Concrete – SEM examination.............................13 Figure 4.4.15 BSE image of RC Aggregate fines ...........................................................14 Figure 4.4.16 ED X-ray analysis of RC Aggregate fines................................................14 Figure 4.4.17 BSE image of natural aggregate (basalt) fines .........................................15 Figure 4.4.18 ED X-ray analysis of natural aggregate (basalt) fines ..............................16 Figure 4.4.19 BSE image of GB cement.........................................................................17 Figure 4.4.20 ED X-ray analysis of GB cement .............................................................17 Figure 4.4.21 BSE image of cement paste residue .........................................................18 Figure 4.5.22 Elemental composition of natural and 14/10mm RC Aggregates -

summary..................................................................................................................18 Figure 4.4.23 Saturated surface dry density of 14/10mm RC Aggregate .......................19 Figure 4.4.24 Relationship between cpr content and saturated surface dry density of

14/10mm RC Aggregate .........................................................................................20 Figure 4.4.25 Dry particle density of 14/10mm RC Aggregate......................................20 Figure 4.4.26 Relationship between cpr content and dry particle density in 14/10mm RC

Aggregate ................................................................................................................21 Figure 4.4.27 Relationship between cpr content and apparent density in 14/10mm RC

Aggregate ................................................................................................................22 Figure 4.4.28 Bulk density of the 14/10mm natural and RC Aggregates .......................24

4.4-47

Figure 4.4.29 Particles of 14/10mm RC Aggregate retained on 13.2mm, 9.5mm, 6.7mm, 4.75mm, 2.36mm and 75μm sieves (from right to left) .........................................25

Figure 4.4.30 Particle size distribution of 14/10mm RC Aggregate – average of 1999 – 2003 samples...........................................................................................................26

Figure 4.4.31 Comparison of particle size distribution of natural aggregate and 14/10mm RC Aggregate .........................................................................................27

Figure 4.4.32 Water absorption of 14/10mm RC Aggregate measured by the weigh-in-water method...........................................................................................................28

Figure 4.4.33 Relationship between cement paste residue (cpr) content and water absorption in 14/10mm RC Aggregate ...................................................................29

Figure 4.4.34 Example of powder (<150μm) samples of neat cement pastes of various cement/water ratios (0.2w/c, 0.4w/c and 0.8w/c) ...................................................30

Figure 4.4.35 Example of solid sample of cement paste residue of RC Aggregate obtained from concrete of known w/c ration of 0.4 ................................................30

Figure 4.4.36 BET isotherm – 0.4 w/c ratio, neat cement paste .....................................32 Figure 4.4.37 BET isotherm – 0.8w/c ratio, neat cement paste ......................................32 Figure 4.4.38 BET isotherm of HIGHLY weathered cpr (s_147) ..................................33 Figure 4.4.39 Example of MODERATELY weathered cpr (BET sample s_229)..........34 Figure 4.4.40 Example of LOW weathered cpr (BET sample s_226) ............................34 Figure 4.4.41 BET porosity of HIGHLY weathered cement paste residue of 14/10mm

RC Aggregate..........................................................................................................35 Figure 4.4.42 BET porosity of MODERATELY weathered cement paste residue of

14/10mm RC Aggregate .........................................................................................36 Figure 4.4.43 BET porosity of slightly (LOW) weathered cement paste residue of

14/10mm RC Aggregate .........................................................................................37 Figure 4.4.44 BET - Total pore volume of cement paste residue (old cpr) - comparison

with porosity standards ...........................................................................................38 Figure 4.4.45 BET – Micro-pore volume of cement paste residue (old cpr) – comparison

with porosity standards ...........................................................................................38 Figure 4.4.46 BET – Total pore surface area of cement paste residue (old cpr) –

comparison with porosity standards........................................................................39 Figure 4.4.47 BET – Micropore surface area of cement paste residue (old cpr) –

comparison with porosity standards........................................................................40 Figure 4.4.48 BET – Average pore diameter of pores in cement paste residue (old cpr) –

comparison with porosity standards........................................................................40 Figure 4.4.49 BET porosity of HIGHLY weathered RC Aggregate...............................41 Figure 4.4.50 BET porosity of MODERATLY weathered RC Aggregate.....................42 Figure 4.4.51 BET porosity of LOW weathered RC Aggregate.....................................43

4.4-48

Table 4.4.1 Particle density of 14/10mm RC Aggregate – results summary..................22 Table 4.4.2 Particle size distribution of 14/10 mm RC Aggregate – percentage passing

.................................................................................................................................25 Table 4.4.3 Particle size distribution of 14/10 mm Natural Aggregate – percentage

passing.....................................................................................................................26 Table 4.4.4 RC Aggregate samples examined by the BET nitrogen adsorption.............31 Table 4.4.5 RC Aggregate samples examined by the BET nitrogen adsorption –

classification by degree of weathering....................................................................31 Table 4.4.6 Porosity of 14/10mm RC Aggregate – summary results .............................44 Table 4.4.7 Average engineering properties of 14/10mm RC Aggregate – summary....45

4.5-1

4.5 RECYCLED AGGREGATE (RA) CONCRETE

4.5.1 Introduction

A thorough understanding of the basic engineering properties of 14/10mm RC

Aggregate allows its full utilisation and correct application as the coarse aggregate in

concrete. RA Concrete samples were prepared and used in the investigation of various

properties including; compressive strength, volume of permeable voids, microstructural

development, porosity, and sound absorption.

Apart from a normal density RA Concrete, there were two other types of concrete made

from RC Aggregate; the no-fines and ‘less fines’ concrete. An open pan mixer with a

50L capacity was used. Constituents of concrete mix were weighed and placed in

plastic bags, then charged into the mixer in the following order: coarse aggregate, fine

aggregate, cement, fly ash (if required). Concrete constituents were dry mixed for

approximately 2 minutes before water was steadily added at a very low rate. The mix

stayed agitated for approximately five minutes, before a standard slump test was

performed. In the case of the no-fines and ‘less-fines’ concrete, a visual assessment of

slump was deemed sufficient.

Test cylinders were cast in two layers with subsequent compaction of each layer on a

vibrating table with the exception of samples for the impedance tube testing, where only

one layer of 150 mm was placed and compacted. Concrete samples were covered with a

plastic bag for a period of about 24 hours between casting and demoulding. Finally, the

test specimens were placed in a curing tank for 28-day continuos curing. Figure 4.5.1

presents a cross-section of normal density concrete made from the 14/10mm RC

Aggregate. The three different forms of coarse aggregate that can be seen are; pieces of

natural aggregate, pieces of natural aggregate coated with cement paste residue, and

pieces of cpr only.

4.5-2

Figure 4.5.1 Sample of RA Concrete

4.5.2 Microstructure Development

An examination of the microstructure of RA Concrete was performed with the use of a

Scanning Electron Microscope (SEM). The SEM investigation included; study of

porosity of concrete, study of an interface zone between aggregate and cement paste,

and the determination of elemental composition.

The aim of the study of the interface zone in RC Aggregate was to investigate the

development of microcracks, whose presence influences concrete durability and

compressive strength. The SEM study also assisted in the examination of mechanical

cracks in RC Aggregate. The elemental composition determination provided the

necessary information to calculate the density of concrete samples subjected to SANS

and subsequently to determine SANS porosity. Figure 4.5.2 presents carbon coated

samples of RA Concrete that were used in the SEM Backscatter Electron (BSE) image

analysis (microcracks) and Energy Dispersive (ED) X-ray analysis (elemental

composition).

Figure 4.5.2 Carbon coated samples of RA Concrete– SEM examination

New cement paste RC Aggregate particles

4.5-3

Figure 4.5.3 presents an example of a BSE image of RC Aggregate. Dark areas in the

BSE images indicate elements of lower atomic numbers such as silica and calcium,

whereas lighter areas indicate elements of higher atomic numbers such as titanium and

iron.

Figure 4.5.3 BSE image of RA Concrete

The BSE images show (example in Figure 4.5.3) that the cement paste residue of RC

Aggregate consists of particles of fine aggregate (quartzite, silica mineral) and hydrated

cement paste residue (calcium rich minerals). The new cement paste (with visible light

colour spots) contains significant amounts of Alumina (Al2O3), Iron Oxide (Fe2O3) in

the mineral form of either tricalcium aluminate (C3A) or as tetracalcium alumino-ferrite

(C4AF), Magnesia (MgO) and Titania (TiO2). Figure 4.5.4 presents the quantitative ED

X-ray analysis results of RA Concrete of an area occupied by both the RC Aggregate

(~70%) and new cement paste (~30%).

New cement paste of RA Concrete

Cement paste residue of RC Aggregate

New cement paste of RA Concrete

Fine aggregate particles in RC Aggregate

4.5-4

Figure 4.5.4 Example of semi-quantitative ED X-ray analysis of RA Concrete

Two intrinsic features of the recycled concrete aggregate; the water absorption and

surface texture, can significantly affect the interface zone, and subsequently reduce

compressive strength and durability of concrete. High water absorption can cause either

shrinkage cracking (dry aggregate absorbing water from fresh cement paste), or can

cause bleeding on the aggregate’s surface (saturated aggregate).

The BSE images were used to investigate the interface zone between new cement paste

and particles of RC Aggregate. Two aspects were investigated; the first one of the

4.5-5

aggregate surface and packing of the new cement paste against the surface, and the

second aspect of cracking in the surface of the aggregate, and cracking in the new

cement paste. Figure 4.5.5 shows an interface zone in RA Concrete.

Figure 4.5.5 Interface zone in RA Concrete

Analysis of the BSE images reveals that there is a significant difference between bulk

cement paste and the interface zone in RA Concrete. The amount of cracks present in

the interface zone tends to be higher that the microcracks in the bulk of the new cement

paste. Figure 4.5.6 shows an interface zone with longitudinal microcrack.

cpr of RC Aggregate

New cement paste

Interface zone

4.5-6

Figure 4.5.6 BSE image of microcracks in the interface zone in RA Concrete

These types of cracks are characteristic of RA Concrete made from RC Aggregate at its

natural moisture conditions, which was not pre-wetted in the bathing process. The new

cement pastes in the interface zone of such concrete develop shrinkage cracks reducing

the contact surface and packing between aggregate and cement paste. This

subsequently introduces areas of high tensile stress, which reduce concrete strength and

increase its permeability.

The cracks in the interface zone can also be due to cracks on the surface of the

aggregate. Figure 4.5.7 presents a perpendicular crack on the surface of the cement

paste residue of RC Aggregate.

New cement paste

cpr of RC Aggregate

300μm long crack in the interface zone – along the face of cpr

4.5-7

Figure 4.5.7 BSE image microcracks in the interface zone in RA Concrete

Figure 4.5.8 shows 300μm of space into the aggregate from the interface zone in RA

Concrete. This type of microcracking (mechanically introduced) is quite common in the

outer layer of cement paste residue of the RC Aggregate which extends the interface

zone in new concrete.

Figure 4.5.8 BSE image microcracks in the interface zone in RA Concrete and in the cpr of RC Aggregate

New cement paste

Sand particle in the cpr of RC Aggregate

70μm crack in the cpr – perpendicular to the interface zone

cpr of RC Aggregate

New cement paste

cpr of RC Aggregate

300μm

4.5-8

The results of the analysis of BSE images lead to a conclusion that the interface zone in

RA Concrete is very different to the one in standard concrete. The zone is affected by

the intrinsic nature of the aggregate, which tends to contain high amount of microcracks

caused by the handling and production process of RC Aggregate. Shrinkage cracks can

also be present in the interface zone due to high water absorption of the aggregate. This

microstructure of the interface zone in concrete made from RC Aggregate is very likely

to cause a reduction in compressive strength and increase permeability.


Any variations in density of concrete are good early stage indicators of the quality of

concrete in general. The density of concrete is directly related to various properties

including porosity, and affects its compressive strength and durability. The reduced

density or significant variations of mass per volume of standard concrete (made from

natural aggregate) are results of either; inadequate compaction, variation of RC

Aggregate, or an excessive amount of free water. The mass per volume of normal

density concrete (2,400kg/m3) reduced by a lack of compaction can cause a reduction in

compressive strength (e.g. by up to 5% when a content of air is increased by 1%). An

increase of approximately 20 liters of free water content can result in a 1% reduction in

density.

Apart from free water content and lack of compaction, the mass per volume of RA25

Concrete is affected mainly by the particle density of aggregate and its porosity. Any

variability of aggregate properties contributes to variations in concrete density. Figure

4.5.9 presents apparent specific gravity and Figure 4.5.10 shows mass per volume of

RA25 Concrete.

4.5-9

1.95

2

2.05

2.1

2.15

2.2

2.25

RA

C25

_10_

99_s

1

RA

C25

_10_

99_s

2

RA

C25

_10_

99_s

3

RA

C25

_03_

00_s

2

RA

C25

_03_

00_s

1

RA

C25

_03_

00_s

3

RA

C25

_08_

00_s

2

RA

C25

_08_

00_s

1

RA

C25

_11_

00_s

2

RA

C25

_11_

00_s

1

RA

C25

_04_

01_s

2

RA

C25

_04_

01_s

1

RA

C25

_10_

01_s

3

RA

C25

_10_

01_s

2

RA

C25

_10_

01_s

1

Sample group

App

aren

t Spe

cific

Gra

vity

Figure 4.5.9 Apparent specific gravity of RA25 Concrete

2100

2150

2200

2250

2300

2350

2400

RA

C25

_11_

00_s

2

RA

C25

_11_

00_s

1

RA

C25

_10_

99_s

2

RA

C25

_10_

99_s

1

RA

C25

_08_

00_s

2

RA

C25

_08_

00_s

1

RA

C25

_06_

01_s

2

RA

C25

_06_

01_s

1

RA

C25

_04_

01_s

2

RA

C25

_04_

01_s

1

RA

C25

_03_

00_s

2

RA

C25

_03_

00_s

1

Sample group

Mas

s per

vol

ume

[kg/

m3]

Figure 4.5.10 Mass per volume of RA25 Concrete

The specific gravity of RA25 Concrete is in a range between 2.05 and 2.22 with a

standard deviation of 0.15. The average mass per volume of RA25 is 2,270kg/m3 with a

STDEV of 75kg/m3. A standard deviation of 2.5% is relatively high, which indicates

that either the process of producing concrete needs to be controlled, or the aggregate’s

variability closely monitored and adjusted.

4.5-10


Intrinsic variability in concrete’s properties is related to many factors including;

inherent inconsistency of the aggregate as well as factors related to production of

concrete. In order to control variability of concrete properties and to guarantee required

characteristic compressive strength, it is necessary to design concrete mixes for a target

compressive strength, which has an inbuilt appropriate standard deviation and a

constant (k) that regulates the proportion of results permitted to fall below the specified

strength. The ‘k’ value of 1.65 (which is accepted in Australia) and STDEV of 2MPa

were adopted in deriving the target compressive strength of 28MPa.

Three concrete test cylinders for each mix design or batch of aggregate were prepared.

The samples were rubber capped at the top end and tested in accordance with standard

procedures. The compressive strength tests were performed at the 28-day concrete

maturity. Some samples were prepared and tested in a commercial laboratory.

Appendix 4 presents tests results of the compressive strength of RA Concrete performed

at the Boral Concrete Laboratory. Table 4.5.1 shows an average compressive strength

of RA Concrete of all test specimens in a compressive strength ranging between 15MPa

and 40MPa.

Table 4.5.1 RA Concrete – compressive strength reduction

Average compressive strength @ 28 days 15MPa 20MPa 25MPa 28MPa 32MPa 40MPa

Control concrete 15.4 20.3 27.0 29.5 33.7 42.7 RA Concrete 14.7 19.1 24.7 26.6 30.4 38.2 Reduction in strength [MPa] 0.7 1.2 2.3 2.9 3.3 4.5 Reduction in strength [%] 4.55% 5.91% 8.52% 9.83% 9.79% 10.54%

Test results show that concrete made from RC Aggregate does not develop the same

compressive strength at 28 days as concrete made from natural crushed rock such as

basalt, where the same amount of cementitious binder is used. It can be noticed that the

reduction in compressive strength of RA Concrete ranges on average from 4.6% to

10.6% in comparison to NA Concrete. The reduction is lower in concrete of low

compressive strengths (15MPa and 20MPa), and the reduction is slightly higher in

concrete of grades 25MPa and above. Figure 4.5.11 shows the compressive strength of

RA25 Concrete.

4.5-11

22

23

24

25

26

27

28

RA

C25

_10_

99_s

1

RA

C25

_03_

00_s

2

RA

C25

_03_

00_s

1

RA

C25

_11_

00_s

2

RA

C25

_10_

99_s

2

RA

C25

_11_

00_s

1

RA

C25

_08_

00_s

2

RA

C25

_04_

01_s

2

RA

C25

_04_

01_s

1

RA

C25

_06_

01_s

2

RA

C25

_06_

01_s

1

RA

C25

_08_

00_s

1

Sample group

Com

pres

sive

stre

ngth

[MPa

]

Figure 4.5.11 Compressive strength of RA25 Concrete

Although the target strength of 28MPa was not achieved in RA25 Concrete, the test

results indicate that the characteristic compressive strength of 25MPa is exceeded by

approximately 60% in tested specimens. In the case of N25 Concrete, all the samples

exceeded the characteristic compressive strength of 25MPa at 28 days. The

compressive strength reduction in RA25 Concrete is 8.5%, where the same amount of

cementitious binder is used.


Apart from compressive strength and mass/volume examination, another straight

forward test used to examine the quality of concrete is determination of its water

absorption. The water absorption of concrete is also a crude measure of its porosity.

Figure 4.5.12 presents water absorption levels after immersion of RA25 Concrete.

4.5-12

0

2

4

6

8

10

12

RA

C25

_10_

99_s

1

RA

C25

_10_

99_s

2

RA

C25

_10_

99_s

3

RA

C25

_03_

00_s

1

RA

C25

_03_

00_s

2

RA

C25

_03_

00_s

3

RA

C25

_08_

00_s

1

RA

C25

_08_

00_s

2

RA

C25

_11_

00_s

1

RA

C25

_11_

00_s

2

RA

C25

_04_

01_s

1

RA

C25

_04_

01_s

2

RA

C25

_10_

01_s

1

RA

C25

_10_

01_s

2

RA

C25

_10_

01_s

3

Sample group

Wat

er a

bsor

ptio

n [%

]

Figure 4.5.12 Water absorption of RA25 Concrete after immersion (72h)

It can be seen that although RA25 Concrete is made of recycled concrete aggregate,

which is highly water-absorbing (section 4.4), the standard deviation of 1% is relatively

low. The average water absorption of RA25 Concrete is 9.2%.

4.5.6 Apparent Volume of Permeable Voids (VPV)

Durability is equally the most imperative quality of concrete. Durability of concrete

can be expressed in a number of different ways and parameters. In Victoria, apparent

volume of permeable voids is widely accepted by the authorities and the industry. The

VPV method of testing durability measures the volume of water absorbed by voids in

hardened concrete after submersion and boiling. The hardened cement paste in concrete

of typically characteristic compressive strengths has specific water permeability,

expressed as a maximum characteristic percentage of VPV. In Victoria, apart from

industry standards, the most rigorous limits are specified by Vicroads. For example,

standard concrete of a compressive strength of 25MPa has a maximum VPV of 17%

(Vicroads, 1994).

While the VPV in concrete made from natural aggregate is detailed in section 4.2 of this

document, this section only presents outcomes of the investigation of apparent VPV in

RA25 Concrete made from 14/10mm RC Aggregate. In the experimental stages of this

4.5-13

project, fifteen (15) samples were tested. Figure 4.5.13 presents examples of test

specimens cut into four parts as required by the Australian Standard, AS1012.21-1999

and the water tank used to boil the specimens (SAA, 1999). Figure 4.5.14 presents the

VPV results of RA25 Concrete.

Figure 4.5.13 Samples of RA25 Concrete – VPV investigation

15

15.5

16

16.5

17

17.5

18

18.5

19

19.5

20

RA

C25

_10_

99_s

1

RA

C25

_10_

99_s

2

RA

C25

_10_

99_s

3

RA

C25

_03_

00_s

1

RA

C25

_03_

00_s

2

RA

C25

_03_

00_s

3

RA

C25

_08_

00_s

1

RA

C25

_08_

00_s

2

RA

C25

_11_

00_s

1

RA

C25

_11_

00_s

2

RA

C25

_04_

01_s

1

RA

C25

_04_

01_s

2

RA

C25

_10_

01_s

1

RA

C25

_10_

01_s

2

RA

C25

_10_

01_s

3

Sample group

App

aren

t Vol

ume

of P

erm

eabl

e V

oids

[%]

Figure 4.5.14 Apparent volume of permeable voids in RA25 Concrete

Test results indicate that in majority of cases, the VPV in concrete made from RC

Aggregate exceeds the recommended maximum of 17%. The average VPV in RA25

Concrete is 17.98%, with a relatively low standard deviation (STDEV) of 0.81%. The

maximum measured VPV was 19.32%, whereas the minimum was 16.58%.

4.5-14

The VPV of comparable N25 Concrete made from natural aggregate was 13.6%. The

results indicate that an inherent permeability in new cement paste (13.6%) is augmented

by the porosity in coarse RC Aggregate.

It has to be noted that both the N25 and RA25 were made using GB cement only.

Further study needs to be conducted in order to investigate the possibility of lowering

the VPV in concrete, by the inclusion of fly ash or silica fume in the concrete mixes.

Based on the outcomes of investigation of the VPV content in RA25 Concrete,

corrective measures were employed when concrete for the laboratory and commercial

prototypes was designed in which fly ash was used.

4.5.7 Porosity

Apart from water absorption and the apparent volume of permeable voids which are

measures of the porosity of concrete (or aggregate) accessible to water under normal

saturation or after boiling in water for 5 hours; porosity accessible to other media can be

examined. Porosity accessible to gases (nitrogen) and neutrons was examined as part

of this research project and is reported in this section.

BET porosity

The BET porosity of aggregate was described in section 4.4 of this document. The

following section reports only on the BET porosity of RA25 Concrete made from the

14/10mm RC Aggregate. The control standards created at previous stages of the

experimental program (cement pastes of w/c ratios of 0.2, 0.4 and 0.8) were used as

references to compare various porosity parameters such as; total volume of pores, total

porosity, microporosity, and pore diameter.

The RA Concrete samples were grouped into two categories; concrete made from coarse

aggregate with 70% of cpr and 30% of natural aggregate (old cpr + na) and concrete

made from coarse aggregate made up of 30% of cpr and 70% of natural aggregate (na +

old cpr).

4.5-15

The total BET volume of pores accessible to nitrogen in RA25 concrete was examined

and a comparative study undertaken. Figure 4.5.15 presents a comparison between the

reference standards and concrete samples.

0.013

0.032

0.058

0.093

0.026

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

old cpr+na na+old cpr 0.2w/c cp 0.4w/c cp 0.8w/c cp

Sample group

Tota

l por

e vo

lum

e [c

m3 /g]

Figure 4.5.15 BET total pore volume of RA Concrete (old cpr+na & na+old cpr)

The total volume of pores in concrete samples in a BET range between 17Å and 3μm is

lower than the reference porosity standards. The results support the notion that a

relative content of natural aggregate component in RC Aggregate contributes to the

quality of the aggregate and can lower its porosity, subsequently producing concrete of

lower porosity. Although the total volume of pores is lower than the reference porosity

standards, the volume of micropores is higher than the control standard. Figure 4.5.16

presents the volume of micropores in RA Concrete.

4.5-16

0.00023 0.00023

0.00136

0.00087

0.00042

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

old cpr+na na+old cpr 0.2w/c cp 0.4w/c cp 0.8w/c cpSample group

Mic

ropo

res v

olum

e [c

m3/

g]

Figure 4.5.16 BET micropores total volume of RA Concrete (old cpr+na & na+old

cpr)

The total volume of micropores in RA25 concrete is comparable with the volume of the

reference standard of a good quality (with water reducing admixture) cement paste

(0.2w/c cp) and of the basalt aggregate. This is an indicator that the new cement paste

in RA25 Concrete has low capillary porosity and that the contribution of RC Aggregate

is not significant. Figure 4.5.17 presents surface area of micropores.

0.93

0.40

2.89

1.85

0.52

0

0.5

1

1.5

2

2.5

3

3.5


Sample group

Mic

ropo

res s

urfa

ce a

rea

[m2 /g

]

Figure 4.5.17 BET micropore surface area of RA Concrete (old cpr+na & na+old

cpr)

4.5-17

A higher volume of relatively smaller pores (see Figure 4.5.16) should result in a higher

surface of micropores in RA25 Concrete. However, the micropore surface area is

relatively low, which can indicate that the pore size distribution is dominated by large

micropores. Figure 4.5.18 presents total pore surface area in RA25 Concrete.

5.286.41

12.03

19.61

3.67

0

5

10

15

20

25


Sample group

Tota

l por

e su

rfac

e ar

ea [m

2 /g]

Figure 4.5.18 BET total pore surface area of RA Concrete (old cpr+na & na+old

cpr)

The higher content of micropores in RA25 concrete (old cpr+na) and their lower

average diameter (100Å), contribute to a higher pore surface area whereas the opposite

is valid in concrete with a predominant content of natural aggregate. In both RA25

concrete the total pore surface area is lower than that of the reference porosity.

Figure 4.5.19 presents a comparison between average pore diameter in RA25 concrete

and the reference porosity.

4.5-18

100

309

200 189194

0

50

100

150

200

250

300

350


Sample group

Ave

rage

por

e di

amet

er [Å

]

Figure 4.5.19 BET average pore diameter of pores in RA Concrete (old cpr+na &

na+old cpr)

The average pore diameter in concrete with a higher content of natural aggregate in the

mix is above the reference diameter of 195Å, whereas the diameter of pores in concrete

containing predominantly cpr, is below the control porosity. This can be attributed to

differences in the volume of micropores. The RA25 concrete (old cpr+na) has a higher

content of micropores which lowers the average pore diameter. In the case of RA25

Concrete (na+old cpr), the uniformity of natural aggregate microstructure and higher

pore diameter elevate the average diameter of pores.

SANS porosity

A non-destructive porosity examination of RA Concrete involved the use of Australian

Small Angle Neutron Scattering (AUSANS) facilities. Porosity of solid and powder

samples were examined in a pore size range between 17Å and 100Å. Powder samples

of particle sizes of 150μm and solid slabs (2mm x 20mm x 20mm) were to be examined

in their natural state, without any preparation including saturation or drying. However,

in order to explore the SANS technique further, and to explore its capabilities in the

examination of cementitious materials, it was decided that dry and saturated samples

will also be investigated. Therefore, apart from porosity measured by neutron radiation,

porosity accessible to a light (H2O), heavy (D2O) and mixture of 50% of light water and

4.5-19

50% of heavy water was also determined during the SANS experiments. Figure 4.5.20

presents an example of a powder sample used in the SANS investigation.

Figure 4.5.20 Powder sample used in SANS examination

Solid samples which were prepared by using either; H2O or D2O were kept wrapped to

prevent carbonation. The solid samples were in two forms; one of a neat cement paste

(reference SANS porosity), and the second form of RA Concrete slabs. Figure 4.5.21

presents solid samples wrapped in aluminium foil ready for the SANS examination

(numbered by a sample port number of the AUSANS instrument).

Figure 4.5.21 Solid samples used in SANS examination

A decision to include contrast variation studies using SANS, i.e. to scatter concrete

samples at different moisture conditions and to use two types of water, presented itself

with an opportunity to measure water absorption of thin slabs of cement pastes and RA

Concrete. Samples were saturated for 24 hours in either; H2O, D2O or 50/50 mixture of

heavy and light water, before being subjected to neutron radiation. Figure 4.5.22

presents porosity accessible to light water in samples tested in May 2001.

4.5-20

0

2

4

6

8

10

12

0.2 cp+ rca

0.4 cp+ rca

0.4 cp+ rca

0.8 cp+ rca

0.8 cp+ rca

0.2 cp 0.4 cp 0.4 cp 0.8 cp 0.8 cp

Samples

Poro

sity

[%]

Figure 4.5.22 SANS samples (2001), porosity accessible to H2O

The results clearly indicate that RA Concrete is more porous than neat cement pastes,

which is attributed to a higher porosity of RC Aggregate. The porosity also increases

with an increase of the water/cement ratio, which can be explained by the principal that

a higher w/c ratio increases the amount of capillary pores in cement pastes. In all RA

Concrete samples, the porosity accessible to light water is higher than those of neat

cement paste of comparable w/c ratios (0.2, 0.4 and 0.8). Figure 4.5.23 presents the

porosity of cement pastes and RA Concrete accessible to D2O.

0

2

4

6

8

10

12

14

0.2 cp+ rca

0.4 cp+ rca

0.4 cp+ rca

0.8 cp+ rca

0.8 cp+ rca

0.2 cp 0.4 cp 0.4 cp 0.8 cp 0.8 cp

Samples

Poro

sity

[%]

Figure 4.5.23 SANS samples (2001), porosity accessible to D2O

4.5-21

A similar trend was observed when the SANS samples were submerged in heavy water.

It can be noticed that generally, the porosity accessible to D2O is approximately 10%

higher (when differences in density between heavy and light water are taken into

account) than the porosity accessible to H2O. For example, the porosity of the 0.2cp

sample accessible to light water is 4.9%, whereas the porosity of the same sample

accessible to heavy water is 6.1% (as D2O) or 5.6% (as H2O equivalent; after correction

due to density differences of heavy and light water at 20oC of 1.1056g/mL versus

0.9982g/mL respectively). Similarly, RA Concrete (0.2cpr+rca) has the porosity

accessible to H2O of 5.7% and to D2O of 6.8%.

As an integral part of the SANS contrast variation experimentation, the samples were

also saturated in a mixture of 50% of light water and 50% of heavy water. Figure

4.5.24 presents porosity accessible to 50%H2O and 50%D2O solutions.

0

2

4

6

8

10

12

14

0.2 cp+ rca

0.4 cp+ rca

0.4 cp+ rca

0.8 cp+ rca

0.8 cp+ rca

0.2 cp 0.4 cp 0.4 cp 0.8 cp 0.8 cp

Samples

Poro

sity

[%]

Figure 4.5.24 SANS samples (2001), porosity accessible to 50%H2O & 50% D2O

In the case of porosity accessible to 50%H2O and 50%D2O solutions, a familiar trend

was observed; firstly, an inclusion of RC Aggregate increases porosity, and secondly, an

increase of water/cement ratio increases porosity of cement pastes and RA Concrete.

The experimental investigation of porosity using the AUSANS instrument at Lucas

Heights was repeated in January 2002. The SANS samples were prepared in the same

4.5-22

laboratory environment and under identical conditions to those in the previous run; with

the only deviation being the use of heavy water to prepare and cure one lot of the neat

cement pastes and RA Concrete. The methodology of the SANS experimentation

required samples to be saturated in various forms of water. Figure 4.5.25 presents

porosity accessible to light water of the January 2002 SANS samples.

8.57.7

10.59.39.5

0.0

2.0

4.0

6.0

8.0

10.0

12.0

0.4 cp 0.4 cp + na[1g]

0.4 cp+rca[0.5g]

0.4 cp+rca[1g]

0.8 cp+rca[0.5g]

Poro

sity

[%]

Figure 4.5.25 SANS samples (2002), porosity accessible to H2O

The H2O accessible porosity of neat cement paste (0.4cp) is 8.4%, which is slightly

higher than the comparable porosity of the SANS samples tested in May 2001.

However, similar observations and trends can be noticed, which confirms that the

inclusion of RC Aggregate results in an increase of the porosity of concrete. On the

other hand, the inclusion of natural aggregate in one of the samples (0.4cp+na[1g]),

results in less porous concrete than the reference cement paste (0.4cp). The results also

confirm that an increase in the cement/water ratio results in increased capillary porosity

e.g. RA Concrete of a water/cement ratio of 0.4 (sample 0.4cp+rca[0.5g]) has porosity

of 9.4% (10.5% of D2O) whereas RA Concrete of water/cement ratio of 0.8 (sample

0.8cp+[0.5g]) has a higher porosity of 10.4% (11.6% of D2O).

Figures 4.5.26 and 4.5.27 present porosity of reference cement pastes and RA Concrete

accessible to heavy water, and a solution of 50%H2O and 50%D2O.

4.5-23

The analysis of differences between porosity accessible to heavy water and to light

water in the same samples can be partially explained by different densities and the

variation might be due to different viscosity of the two types of water (1.25centipoise of

D2O and 1.005centipoise of H2O). It appears that the surface tension, which is almost

identical in the two types of water, has no bearing to the differences.

10.59.8 9.7

12.0 12.4

11.012.0

14.1

12.8

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

0.4

cp

0.4

cp

0.4

cp +

na

[1g]

0.4

cp +

rca[

0.5g

]

0.4

cp +

rca[

1g]

0.4

cp +

rca[

1g]

0.8

cp

0.8

cp +

rca[

0.5g

]

0.8

cp +

rca[

1g]

Poro

sity

[%]

Figure 4.5.26 SANS samples (2002), porosity accessible to D2O

9.79.0 8.7

10.6 10.311.0

13.0

11.711.4

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0.4

cp

0.4

cp

0.4

cp +

na

[1g]

0.4

cp+r

ca[0

.5g]

0.4

cp +

rca[

1g]

0.4

cp +

rca[

1g]

0.8

cp

0.8

cp+r

ca[0

.5g]

0.8

cp +

rca[

1g]

Poro

sity

[%]

Figure 4.5.27 SANS samples (2002), porosity accessible to 50%H2O & 50%D2O

4.5-24

The core aspect of the SANS experimentation was to gauge the bulk of cement pastes

and RA Concrete samples using neutron radiation, and to detect a neutron scattering

pattern produced by cementitious materials. The intensity of the neutron beam and the

length of the scattering vectors used can estimate total porosity of tested materials and

geometry of the pores.

Figure 4.5.28 presents the log-log plots of the RCA9 series of powder samples of

cement paste residue (~70%) and new cement paste (~30%) isolated from RA Concrete

solid samples and grinded to 150μm particles. Figure 4.5.29 presents the log-log plot of

neutron scattering profiles of solid samples prepared with D2O and cured in D2O.

I(Q) for all RCA9

1E-1

1E+0

1E+1

1E+2

1E+3

1E+4

1E-2 1E-1 1E+0

Q (A-1)

I(Q) (

cm- 1)

RCA9_1

RCA9_2

RCA9_3

RCA9_4

RCA9_5

RCA9_6

Figure 4.5.28 RCA9 series (powder samples) _ Scattering intensity I(Q) vs. Scattering length Q

Scattering intensity I(Q) and scattering vector length (Q) data can be used for the

determination of a number of microstructural parameters of cementitious materials

including total porosity and fractal mass. The raw data was first reduced to account for

instrumental errors and environmental conditions, and analysed using the ‘PRINSAS’

program developed at Geoscience Australia.

4.5-25

I(Q) for all RCA11

1E-2

1E-1

1E+0

1E+1

1E+2

1E+3

1E-2 1E-1 1E+0

Q (A-1)

I(Q) (

cm- 1)

RCA11_1

RCA11_2

RCA11_3

RCA11_4

RCA11_5

Figure 4.5.29 RCA11 series (D2O made solid samples) _ Scattering intensity I(Q) vs. Scattering length Q

Tables 4.5.2 presents SANS porosity of neat cement pastes and of RA Concrete

determined in May 2001.

Table 4.5.2 SANS porosity of RA Concrete (2001 samples)

Samples Porosity [%] RCA1_1 (SANS) neat 0.2 cement paste (cp) 17.8RCA1_2 (SANS) neat 0.4 cp 19.7RCA1_3 (SANS) neat 0.8 cp 19.8RCA1_4 (SANS) 0.2 cp + 1g of recycled concrete aggregate (rca) 16.5RCA1_5 (SANS) 0.4 cp + 1g of rca 14.3RCA1_6 (SANS) 0.8 cp + 1g of rca 15.8RCA2_1 (SANS) neat 0.4 cp 17.9RCA2_2 (SANS) neat 0.8 cp 20.3RCA2_3 (SANS) 0.4 cp + 1g of rca 14.5RCA2_4 (SANS) 0.8 cp + 1g of rca 16.0RCA9_1 (SANS) Cement paste residue cpr_2_1 5.4RCA9_2 (SANS) Cement paste residue cpr_3_2 5.4RCA9_3 (SANS) Cement paste residue cpr_1_2 7.5RCA9_4 (SANS) Cement paste residue cpr_1_1 6.6RCA9_5 (SANS) Cement paste residue cpr_2_2 6.7RCA9_6 (SANS) Cement paste residue cpr_3_1 7.1

4.5-26

It can be seen that the SANS porosity in pore sizes ranging between 17Å and 100Å is

higher than the total porosity measured by the BET method or various water absorption

methods. For example, porosity of solid samples of neat cement pastes range from

17.8% (water/cement ratio of 0.2) to 20.3% (water/cement ratio of 0.8). The

relationship between an increase of water/cement ratio with an increase in porosity is

noticeable, although less evident than in porosity accessible to water. The less evident

difference can be attributed to a relatively narrow range of pores subjected to the SANS

method, which mainly detects the gel and small capillary pores.

In all previous cases, an inclusion of RC Aggregate particles in cement paste increased

the total porosity of RA Concrete, as the aggregate’s cpr is highly porous. This

relationship however does not apply to SANS porosity. An inclusion of RC Aggregate

reduces the total porosity in the SANS pore size range. For example, cement paste of a

water/cement ratio of 0.4 has a SANS porosity of 18.8%, whereas the same paste with

imbedded particles of RC Aggregate has the porosity of 14.4%. A similar relationship

applies to all SANS samples, which leads to a conclusion that there is a very

insignificant amount of micropores and small mesopores in RC Aggregate.

Table 4.5.3 presents SANS porosity of samples examined in January 2002. Some of the

samples were prepared and cured in heavy water (RCA11)

Table 4.5.3 SANS porosity of RA Concrete (2002 samples)

Samples Porosity [%] RCA11_1 (SANS) neat 0.4 cement paste (cp) 6.9RCA11_2 (SANS) 0.4 cp+ 1g of natural aggregate (na) 5.0RCA11_3 (SANS) 0.4 cp + 1g of recycled concrete aggregate (rca) 4.7RCA11_4 (SANS) 0.4 cp + 0.5g of (rca) 5.7RCA11_5 (SANS) 0.8 cp + 0.5g of (rca) 2.8RCA12_1 (SANS) neat 0.4 cp 22.3RCA12_2 (SANS) neat 0.8 cp 18.4RCA12_3 (SANS) 0.4 + 1g of (rca) 16.2RCA12_4 (SANS) 0.8 + 1g of (rca) 16.5RCA13_1 (SANS) neat 0.4 cp 37.4RCA13_2 (SANS) 0.4 cp+ 1g of (na) 29.0RCA13_3 (SANS) 0.4 cp + 1g (rca) -RCA13_4 (SANS) 0.4 cp + 0.5g of (rca) 33.0RCA13_5 (SANS) 0.8 cp + 0.5g of (rca) 17.5

4.5-27

In the macroporosity and upper band of the mesoporosity; as it has been shown

previously, the inclusion of RC Aggregate contributes to an increased total porosity of

RA Concrete; however, at the same time the aggregate reduces the micro and

mesoporosity of such concrete.

Although water absorption (porosity accessible to heavy and light water) measured as

part of the SANS experimental program indicates a slight increase in porosity accessible

to water in the January 2002 samples when compared with the porosity of the 2001

samples, the increase in SANS porosity is more evident.

Total porosity of cement paste samples prepared with light water with a w/c ratio of 0.4

ranges from 22.3% to 37.4%. The relationships observed in the previous run (May

2001 SANS investigation) linked the inclusion of RC Aggregate in cement paste with a

reduction in the micro and mesoporosity. The SANS porosity of RA Concrete is in a

wide range of 16.2% to 33%. The same relationship; reduction in porosity in pore sizes

ranging between 10Å and 100Å, is also valid with cement paste and RA Concrete of a

w/c ratio of 0.8.

In the case of the SANS samples prepared and cured with heavy water, the total

porosity is cooperatively low, which can be related to different microstructural

developments of the concrete matrix and/or to different scattering profiles from D2O

made material. The total porosity of the 0.4 w/c ratio cement paste is 6.9%, whereas the

porosity of the same w/c ratio RA Concrete samples is reduced to 5.1% on average.

4.5.8 Fractal Dimensions

The SANS intensity-scattering profile can also be used to estimate fractal mass, which

is a measure of the roughness and shape of pores in the concrete matrix. The fractal

mass is represented by a slope of the line of best fit of the plot of scattering intensity,

log (I) versus scattering wave vector, log (I(Q)). Figures 4.5.30 and 4.5.31 present a

summary of the fractal mass of the 2001 and 2002 SANS samples at various moisture

states.

4.5-28

-3

-2.9

-2.8

-2.7

-2.6

-2.5

-2.4

-2.3

-2.2

-2.1

-2

DR

Y

0.2

cp

0.4

cp s1

0.4

cp s2

0.8

cp s1

0.8

cp s2

H2O

0.2

cp

0.4

cp s1

0.4

cp s2

0.8

cp s1

0.8

cp s2

D2O

0.2

cp

0.4

cp s1

0.4

cp s2

0.8

cp s1

0.8

cp s2

H2O

/D2O

0.2

cp

0.4

cp s1

0.4

cp s2

0.8

cp s1

0.8

cp s2

Moisture conditions & samples

Frac

tal m

ass,

Dm

Figure 4.5.30 Fractal mass (2001 samples) at different moisture conditions

-3

-2.9

-2.8

-2.7

-2.6

-2.5

-2.4

-2.3

-2.2

-2.1

-2

DR

Y

0.4

cp

0.4

cp .5

g rc

a

D2O

0.4

cp

0.4

cp .5

g rc

a

H2O

0.4

cp

0.4

cp .5

g rc

a

D20

/H20

0.4

cp

0.4

cp .5

g rc

a

Moisture conditions & samples

Frac

tal m

ass,

Dm

Figure 4.5.31 Fractal mass (2002 samples) at different moisture conditions

Considering that the neutron scattering of the two-phase materials; solid and air/water,

is less prone to multiple or incoherent scattering when heavy water is used to saturate

pores, an assumption was made that the D2O saturated samples will most likely

represent the true geometry of pores in concrete. In such a case, a fractal mass of

4.5-29

approximately 2.8 indicates that the pores in pore sizes ranging between 17Å and 100Å

are convoluted and have a very rough surface.

4.5.9 No-fines Recycled Aggregate Concrete

The design concept of the RA Concrete acoustic barrier, which consists of two layers,

one of them of no-fines concrete structure, necessitated the application of 14/10mm RC

Aggregate in such concrete. Investigation into no-fines concrete was primarily limited

to compressive strength and mass/volume determinations. Some visual assessments in

relation to the consistency of concrete were mainly conducted to examine workability

and how the new paste flows in the aggregate’s matrix, and to assess uniformity of

coating of the aggregate. Figure 4.5.32 presents two samples of no-fines RA Concrete

of a characteristic compressive strength of 10MPa. It was observed that when a

compressive force was applied to crush samples of no-fines concrete, most failures

occurred in the cement paste. This observation leads to a conclusion that differences

between basalt aggregate and RC Aggregate have no significant bearing on the

compressive strength of no-fines concrete.

Figure 4.5.32 Samples of no-fines RA Concrete

Figure 4.5.33 presents a summary of results of a compressive strength examination of

no-fines concrete made from the 14/10mm natural aggregate and RC Aggregate.

4.5-30

7.7

9.8 9.9 9.6

7.2

12.9

0

2

4

6

8

10

12

14

NF_

N(2

5)_1

0_99

_s2

NF_

N(2

5)_1

0_99

_s1

NF_

RA

C(2

5)_1

0_99

_s2

NF_

RA

C(2

5)_1

0_99

_s1

NF_

RA

C(2

5)_0

8_00

_s1

NF_

barr

ier_

pane

ls

Com

pres

sive

stre

ngth

[MPa

]

Figure 4.5.33 Compressive strength of no-fines RA Concrete

It can be noted that there are minor differences in test results between no-fines concrete

made from natural aggregate and RC Aggregate, and that the characteristic compressive

strength of 10MPa has not been attained. However, the concrete mix design used in the

production of the laboratory and commercial prototypes has been adjusted, and the

required compressive strength was achieved.

Although the differences in terms of compressive strength between NA Concrete and

RA Concrete are insignificant; the RC Aggregate has a noticeable influence on the mass

per volume of no-fines concrete. Figure 4.5.34 presents mass per volume of no-fines

concrete. The results indicate that there is a 10% reduction in mass per volume in the

no-fines concrete made from 14/10mm RC Aggregate, in comparison to similar

concrete made from natural aggregate.

4.5-31

1600

1650

1700

1750

1800

1850

1900

1950

2000

NF_

N(2

5)_1

0_99

_s2

NF_

N(2

5)_1

0_99

_s1

NF_

RAC(

25)_

08_0

0_s1

NF_

RAC(

25)_

10_9

9_s2

NF_

RAC(

25)_

10_9

9_s1

NF_

barr

ier_

pane

ls

Mas

s / V

olum

e [k

g/m3 ]

Figure 4.5.34 Mass per volume of no-fines RA Concrete


The investigation into RA Concrete of a characteristic compressive strength of 25MPa

made from selected 14/10mm RC Aggregate fulfilled its aim of the characterisation of

basic engineering properties. The concrete physical, mechanical and microstructural

properties are reported. The general conclusion derived from the investigation is that

RA25 Concrete has different characteristics than those of concrete made from

comparable natural aggregate with the same amount of cementitious binder. The plastic

state properties do not differ as long as the RC Aggregate is pre-wetted. The NA

Concrete and RA Concrete were designed for an 80mm slump and there was little

variation between both types of concrete.

The compressive strength and durability of RA25 Concrete are well defined, although

there is approximately an 8.5% reduction of compressive strength in RA25 Concrete

partially due to weaker mortar residue fraction attached to original natural aggregate.

Durability of RA25 Concrete can be reduced as there is an increase of approximately

30% in the volume of permeable voids in RA25 Concrete.

4.5-32

The reduction in strength and durability results from inherent porosity of the cement

paste residue, and due to mechanical cracks induced by the handling and manufacturing

process of the RC Aggregate. Table 4.5.4 presents a summary of some engineering

properties of RA25 Concrete.

Table 4.5.4 Average properties of RA25 Concrete – summary

Property Unit RA25 Concrete

NA25 Concrete

Apparent specific density kg/m3 2,100 2,650 Mass/volume kg/m3 2,270 2,700 Characteristic compressive strength MPa 24.7 27 Water absorption, AS1012.21 % 8.8 5.1 Apparent VPV % 17.98 13.6 Porosity accessible to H2O % 6.7 – 10.8 5.1 Porosity accessible to D2O % 8.2 – 13.8 6.1 Porosity accessible to 50%H2O -50%D2O % 8.3 – 12.6 5.6 BET pore volume (range 10Å -100Å) cm3/g 0.0195 0.013 BET volume of micropores (10Å -100Å) cm3/g 0.000375 0.00023 BET surface area (range 10Å -100Å) m2/g 4.475 3.67 BET surface area of micropores m2/g 0.725 0.52 BET average diameter (10Å -100Å) Å 204 100 SANS total porosity % 15.2 - 25 29

No-fines concrete Mass/volume kg/m3 1,780 1,930 Characteristic compressive strength MPa 8.9 8.7

4.5-33

4.5 RECYCLED AGGREGATE (RA) CONCRETE.............................................1 4.5.1 Introduction...............................................................................................1 4.5.2 Microstructure Development ....................................................................2 4.5.3 Mass per Volume ......................................................................................8 4.5.4 Compressive Strength .............................................................................10 4.5.5 Water Absorption....................................................................................11 4.5.6 Apparent Volume of Permeable Voids (VPV)........................................12 4.5.7 Porosity ...................................................................................................14 4.5.8 Fractal Dimensions .................................................................................27 4.5.9 No-fines Recycled Aggregate Concrete..................................................29 4.5.10 Discussion of the Results ........................................................................31

Table 4.5.1 RA Concrete – compressive strength reduction...........................................10 Table 4.5.2 SANS porosity of RA Concrete (2001 samples) .........................................25 Table 4.5.3 SANS porosity of RA Concrete (2002 samples) .........................................26 Table 4.5.4 Average properties of RA25 Concrete – summary......................................32 Figure 4.5.1 Sample of RA Concrete .............................................................................2 Figure 4.5.2 Carbon coated samples of RA Concrete– SEM examination ................2 Figure 4.5.3 BSE image of RA Concrete .......................................................................3 Figure 4.5.4 Example of semi-quantitative ED X-ray analysis of RA Concrete .......4 Figure 4.5.5 Interface zone in RA Concrete .................................................................5 Figure 4.5.6 BSE image of microcracks in the interface zone in RA Concrete .........6 Figure 4.5.7 BSE image microcracks in the interface zone in RA Concrete .............7 Figure 4.5.8 BSE image microcracks in the interface zone in RA Concrete and in

the cpr of RC Aggregate .........................................................................................7 Figure 4.5.9 Apparent specific gravity of RA25 Concrete ..........................................9 Figure 4.5.10 Mass per volume of RA25 Concrete.......................................................9 Figure 4.5.11 Compressive strength of RA25 Concrete.............................................11 Figure 4.5.12 Water absorption of RA25 Concrete after immersion (72h) .............12 Figure 4.5.13 Samples of RA25 Concrete – VPV investigation.................................13 Figure 4.5.14 Apparent volume of permeable voids in RA25 Concrete...................13 Figure 4.5.15 BET total pore volume of RA Concrete (old cpr+na & na+old cpr).15 Figure 4.5.16 BET micropores total volume of RA Concrete (old cpr+na & na+old

cpr)..........................................................................................................................16 Figure 4.5.17 BET micropore surface area of RA Concrete (old cpr+na & na+old

cpr)..........................................................................................................................16 Figure 4.5.18 BET total pore surface area of RA Concrete (old cpr+na & na+old

cpr)..........................................................................................................................17 Figure 4.5.19 BET average pore diameter of pores in RA Concrete (old cpr+na &

na+old cpr).............................................................................................................18 Figure 4.5.20 Powder sample used in SANS examination .........................................19 Figure 4.5.21 Solid samples used in SANS examination............................................19 Figure 4.5.22 SANS samples (2001), porosity accessible to H2O ..............................20

4.5-34

Figure 4.5.23 SANS samples (2001), porosity accessible to D2O...............................20 Figure 4.5.24 SANS samples (2001), porosity accessible to 50%H2O & 50% D2O.21 Figure 4.5.25 SANS samples (2002), porosity accessible to H2O ..............................22 Figure 4.5.26 SANS samples (2002), porosity accessible to D2O...............................23 Figure 4.5.27 SANS samples (2002), porosity accessible to 50%H2O & 50%D2O..23 Figure 4.5.28 RCA9 series (powder samples) _ Scattering intensity I(Q) vs.

Scattering length Q ...............................................................................................24 Figure 4.5.29 RCA11 series (D2O made solid samples) _ Scattering intensity I(Q)

vs. Scattering length Q ..........................................................................................25 Figure 4.5.30 Fractal mass (2001 samples) at different moisture conditions ..........28 Figure 4.5.31 Fractal mass (2002 samples) at different moisture conditions ..........28 Figure 4.5.32 Samples of no-fines RA Concrete .........................................................29 Figure 4.5.33 Compressive strength of no-fines RA Concrete ..................................30 Figure 4.5.34 Mass per volume of no-fines RA Concrete ..........................................31

4.6-1

4.6 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE

4.6.1 Introduction

Following the experimental investigation into the practicality and properties of no-fines

concrete made from 14/10mm RC Aggregate, a concept of a ‘less-fines’ concrete has

emerged. The concept of ‘less-fines’ concrete has been developed by the author as a

result of attempts to improve the visual appearance of the no-fines RA Concrete. It

became evident that the amount of render could be calculated for a specific render

thickness by calculating voids between aggregate particles. Furthermore, it became

apparent that a thicker coat of the render creates a layer of a normal density concrete,

which can increase its compressive strength.

Based on mix designs for normal density and no-fines concrete, concrete mix designs

with a deficiency of fine aggregate in the mixes were developed. The consistency of the

plastic state concrete was assessed visually. The flow of cement paste between coarse

aggregate, and the capacity of the plastic concrete to form two distinctive layers was

observed. In the top layer of no-fines concrete, the distribution of coarse aggregate and

its coating by cement paste was inspected. In the bottom layer, the capacity of the

cement paste to consolidate under vibration and, to fill voids between coarse aggregate

particles was visually assessed.

In hardened ‘less-fines’ concrete, the volume of interconnected voids and sound

absorbency were examined. The compressive strength and VPV of concrete were

analysed separately for each layer and are discussed in other sections (section 4.5.6 and

4.5.9), of this document.

Various shapes of test specimens, including round and rectangular were investigated.

Different sizes and thickness of the samples were analysed, capability to develop two

distinctive layers examined, and concrete mixes adjusted. Figure 4.6.1 presents samples

of ‘less-fines’ RA Concrete prepared for an impedance tube examination.

4.6-2

Figure 4.6.1 Samples of ’no-fines’ concrete made from RC Aggregate

Table 4.6.1 presents an example of mix proportions of the ‘less-fines’ RA Concrete.

Table 4.6.1 Mix proportions of ’less-fines’ concrete

RA Concrete NA Concrete Constituent material Quantity [kg/m3]

GB cement 200 200 Fly ash 60 60 Water 100 100 14/10mm RC Aggregate 1,000 - 14/10mm basalt - 1,000 Concrete sand 300 300 Additives - -

4.6.2 Porosity and Interconnected Air Voids

A structural robustness of the ‘less-fines’ concrete is provided by an adequate

compressive strength of both layers, and a strong bond between the layers. The acoustic

functioning of the ‘less-fines’ concrete depends on its density, porosity and

characteristics of the porous layer. The thickness of the porous layer and amount of

interconnected air voids accessible to sound waves are two main factors contributing to

sound absorption.

Porosity and density of normal density and no-fines concrete was discussed in other

sections of this document. This section reports only on the voids in the porous layer of

the ‘less-fines’ RA Concrete created by empty spaces between coarse aggregate.

4.6-3

Based on test results and observations made in other phases of the experimental

program of this research project, a conclusion was drawn that differences in the shape of

coarse aggregate contribute to differences in the bulk density and specific packing of the

aggregate. Concrete specimens made from natural and RC Aggregate were prepared in

order to analyse interconnected voids developed in the porous layer. Figure 4.6.2

presents a relative amount of empty interconnected space in the porous layer of the

14/10mm ‘less-fines’ RA Concrete and comparable 14/10mm ‘less-fines’ NA Concrete.

0

5

10

15

20

25

30

35

40

45

50

60mm 75mm 90mm 105mm 150mm

Porous layer thickness [mm]

% A

ir vo

ids

less-fines NA Concreteless-fines RA ConcreteLinear (less-fines RA Concrete)Linear (less-fines NA Concrete)

Figure 4.6.2 Interconnected air voids ratio in ‘less-fines’ NA and RA Concrete

The average proportion of empty space in concrete made from natural aggregate,

between the aggregate coated with cement paste in the porous layer is 34%, and in

concrete made from a similar grading, RC Aggregate, is 41.5%. The ratio of voids

drops with an increase of thickness of the porous layer, as the accumulation of cement

paste in the concrete matrix grows proportionally to increased surface area, and

interconnectivity decreases with an increase of thickness of the porous layer.

4.6.3 Sound Absorption A number of specimens were prepared to measure the sound absorption coefficient of

‘less-fines’ concrete with varying thickness of the porous layer. An impedance tube

4.6-4

instrument at RMIT University (see Figure 4.6.3) was used to determine sound

absorption within a frequency range of 63Hz and 2,000Hz.

Figure 4.6.3 Impedance tube and ‘less-fines’ RA Concrete samples

The impedance tube method provides a capable diagnostic tool in the investigation of

acoustic materials, which measures normal and statistic sound absorption coefficients.

Figure 4.6.4 presents test results of some of the ‘less-fines’ RA Concrete samples with

porous layer thickness ranging from approximately 20mm to 130mm.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 400 800 1200 1600 2000

Frequency [Hz]

Soun

d ab

sorp

tion

coef

ficie

nt

~15mm~30mm~40mm~100mm~130mm

Figure 4.6.4 Sound absorption coefficient of ‘less-fines’ RA Concrete

Samples

Impedance tube

4.6-5

It is evident that even a very thin (15/20mm) layer of porous concrete contributes to

sound absorption. It is also evident that with an increase of the thickness of the layer,

sound absorption increases, as well as changes in its characteristics. In thicker layers,

where channels of interconnected voids can form, the sound absorption shows the

characteristics of resonant absorbency. It can be noticed that there is a peak at the

principal resonant frequency (approximately 400Hz) of the material, which follows a

trough and another peak at the second resonant frequency of approximately 1,000Hz.

Although the test results validate the concept and clearly identify a dominant pattern; it

was decided that apart from basic investigation into a relationship between thickness of

porous layer and sound absorption, the 100mm thick layer is to be examined more

thoroughly. Three samples were prepared and sound absorption measured (see Figure

4.6.5)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Frequency [Hz]

Soun

d ab

sorp

tion

coef

ficie

nt

Figure 4.6.5 Sound absorption coefficient of ‘less-fines’ RA Concrete samples of porous layer thickness of 100mm

Similar to previously presented data (Figure 4.6.4), a pattern demonstrating resonant

absorbency has been observed. The interconnected air voids in the porous concrete

matrix form and act as the resonators (Helmholtz resonators). The principal peak

frequency in all samples occurs approximately at a frequency range between 350Hz and

450Hz. The magnitude of the peak resonant frequency expressed as sound absorption

coefficient varies from 0.45 to 0.92. The peak at approximately 400Hz is attributed to a

4.6-6

concrete matrix created by the coarse aggregate of the same size in all tested samples,

and therefore similar spacing between the openings of interconnected air channels on

the surface of the porous layer.

A preliminary conclusion has been hypothesised that although the thickness of the

porous layer has a bearing on the peak resonant frequency and sound absorbency, the

limited number of tests does not allow the proposition of a definite relationship.

Considering the possibility of using other grading of aggregate, i.e. substituting the

14/10mm RC Aggregate with a single size aggregate (e.g. 20mm, 14mm, 10mm, 6.3mm

or 4.75mm) or with double sized aggregate (20/6.3mm 10/4.75mm, etc), the distribution

of voids within the porous layer would change. A change in aggregate size would

therefore change the distance between the opening, the cross-section and length of the

channels. This would consequently lead to different sound absorption characteristics

including peak resonant frequency. To predict a dominant frequency and to investigate

the tuneability of the ’less-fines’ concrete, a computer simulation using size of the

aggregate as the main variable was performed.

The simulation investigated the effects of the thickness and composition of the porous

layer on the peak resonant frequency. The spacing (centres) of the entrances to the

voids; their diameter (DIA), the length (L) and the thickness (Thickness) of the layer

formed a set of variables and input data for the simulation.

Table 4.6.2 presents simulation results and demonstrates tuneability aspect of the

acoustic performance of the barrier.

Table 4.6.2 Peak resonant frequency simulation Centres 0.020 [m] Centres 0.020 [m] Centres 0.030 [m] Thickness 0.070 [m] Thickness 0.070 [m] Thickness 0.100 [m] DIA 0.008 [m] DIA 0.010 [m] DIA 0.005 [m] C 340.0 [m/s] C 340.0 [m/s] C 340.0 [m/s] L 0.050 [m] L 0.050 [m] L 0.050 [m] L1 0.056 L1 0.058 L1 0.054 s 5.03E-05 s 7.85E-05 s 1.96E-05 v 0.000028 v 0.000028 v 0.00009 Frequency 306 Hz Frequency 378 Hz Frequency 109 Hz

4.6-7

The simulation is based on the following equation;

Frequency(peak) =(C/2PI)*SQR(A/LV)

Where;

V - volume of chamber A – cross-section area of the neck L – length of the chamber C – speed of sound

It can be seen that the peak frequency of approximately 400Hz, obtained from

experiments conducted with the use of an impedance tube is explained by the simulation

results presented in the middle segment of Table 4.6.2. The simulation confirmed that,

in the porous layer of an average thickness of 70mm; the centres of the openings created

by the 14/10mm aggregate are 20mm apart; the length of the air channels is

approximately 50mm; the diameter of the openings and the channels is approximately

10mm, the peak resonant frequency is approximately 380Hz.


The ‘less-fines’ concrete appears to be a feasible alternative to two separate types of

concrete; the normal density and no-fines concrete. It is possible to devise a mix

design, which results in concrete with a structure where two distinctive layers can

develop. The ‘less-fines’ concrete applied in acoustic barriers provides the required

structural integrity whilst simultaneously absorbing sound energy.

The acoustic performance of the ‘less-fines’ concrete shows the characteristics of

resonant absorbency, which allows to target certain frequencies of sound. The

principal, peak resonant frequency relates to a configuration of resonant chambers,

which are created in the porous layer of the ‘less-fine’ concrete by the aggregate

arrangement. The 14/10mm ‘less-fines’ RA Concrete has a sound absorption

coefficient of approximately 0.8 at a peak frequency of approximately 400Hz.

4.6-8

4.6 ‘LESS-FINES’ RECYCLED AGGREGATE CONCRETE.............................1

4.6.1 Introduction...............................................................................................1 4.6.2 Porosity and Interconnected Air Voids .....................................................2 4.6.3 Sound Absorption .....................................................................................3 4.6.4 Discussion of the Results ..........................................................................7

Figure 4.6.1 Samples of ’no-fines’ concrete made from RC Aggregate...........................2 Figure 4.6.2 Interconnected air voids ratio in ‘less-fines’ NA and RA Concrete.............3 Figure 4.6.3 Impedance tube and ‘less-fines’ RA Concrete samples ...............................4 Figure 4.6.4 Sound absorption coefficient of ‘less-fines’ RA Concrete ...........................4 Figure 4.6.5 Sound absorption coefficient of ‘less-fines’ RA Concrete samples of

porous layer thickness of 100mm .............................................................................5 Table 4.6.1 Mix proportions of ’less-fines’ concrete........................................................2 Table 4.6.2 Peak resonant frequency simulation ..............................................................6

4.7-1

4.7 PROTOTYPE BARRIER

4.7.1 Introduction

Following promising outcomes of developmental program and examination of the ‘less-

fines’ RA Concrete, the concept of sound absorbing concrete barrier was finalised. It

was decided that two prototypes of acoustic barrier would be developed; laboratory

prototype and commercially produced prototype. In the developmental process and at

the production stage, a number of variables were to be considered and tested such as;

various concrete mix designs, a range of RC Aggregate, different structural

configurations and a variety of production aspects.

The primary aims of developing laboratory and commercially manufactured prototypes

of acoustic barrier were to further investigate and subsequently establish the optimum

balance between sound absorption capabilities and structural integrity in the barrier.

The optimum utilisation of inherent properties of the 14/10mm RC Aggregate was also

to be achieved. As a result, the barrier consisting of two distinctive layers; solid and

porous, was also designed in accordance with relevant standards to withstand the design

and in-service loading. The manufacturing process was to follow closely industry codes

of practice, which allowed efficient production of pre-cast RA Concrete panels.

4.7.2 Laboratory prototype

The laboratory prototype barrier was manufactured in twelve (12) panels of

approximately 1m2 each. The concrete used to produce the prototype was the ‘less-

fines’ RA25 concrete made from the 14/10mm RC Aggregate. The panels were cast

using the one-concrete-pour method. An over-vibration of panels on a horizontal

casting bed was employed to allow segregation of concrete and subsequently

development of two distinctive layers. The prototype barrier panels were air cured.

Aggregate

The coarse aggregate used in concrete for the production of the laboratory prototype

was the 14/10mm RC Aggregate. The basic engineering properties of the aggregate

4.7-2

were consistent with those described in section 4.4 of this document. The coarse

aggregate was pre-wetted. The fine aggregate used in the production of laboratory

prototype was the concrete sand from Bacchus Marsh Quarry as described in section 4.3

of this document.

Concrete

The ‘less-fines’ RA Concrete with the target compressive strength of 25MPa was used

in the structural backing layer. Two concrete mixes were considered; the first one with

only GB cement as the cementitious binder (280kg per 1m3 of concrete), and the second

mix of the GB cement with addition of fly ash as partial replacement and supplementary

additive (220g of GB cement and 60kg of fly ash per 1m3 of concrete). Both concrete

mixes were employed to make panels. It was observed that the ‘less-fines’ RA

Concrete with fly ash was more workable and contributed better to the development of

desired two layered structure in the barrier. Figure 4.7.1 presents test results of the

compressive strength examination of concrete use in the production of the laboratory

prototype acoustic barrier.

0

5

10

15

20

25

30

35

Target - 25MPa RA Concrete - panel RA Concrete (+pfa) - panel No-fines RA Concrete(+pfa)

Act

ual c

ompr

essi

ve st

reng

th [M

Pa]

Figure 4.7.1 Compressive strength of RA Concrete used in laboratory prototype

barrier

As a result of fines deficiency in the ‘less-fine’ RA Concrete and over-vibration, two

distinctive layers formed. The compressive strength of consolidated (normal density)

concrete, in the structural backing layer exceeded the 25MPa characteristic strength.

The concrete (of the no-fines concrete consistency) which formed itself in the porous

4.7-3

layer of the panel also exceeded target compressive strength of 10MPa. Test samples of

concrete used in the laboratory prototype were sealed in plastic bags, whereas the

barrier panels were air cured. It is recommended that a curing compound or water

spraying of panels for at least seven (7) days be implemented to achieve required

compressive strength.

Process: making panels

The formwork preparation, fixing of steel reinforcement and casting of concrete for the

laboratory prototype took place in the Heavy Structures and Concrete laboratories at

Swinburne University of Technology. Concrete was mixed in laboratory concrete

mixer. Concrete for the bottom and middle levels was made from ‘less-fines’ RA

Concrete with the GB cement content of 280kg per 1m3 of concrete. Concrete for

panels in the top level, with a design thickness of porous layer of 90mm was made with

the fly ash supplement (60kg per 1m3 of concrete). The one-concrete-pour method of

placing concrete in the formwork was employed. A laboratory vibrating table was used

to consolidate concrete and to cause the development of two distinctive layers. The top

surface of the panels was screeded and the panels left to cure in the air. Figure 4.7.2

presents the formwork with reinforcement and lifting inserts of the laboratory prototype

panels.

Figure 4.7.2 Formwork, steel reinforcement and lifting inserts of laboratory prototype

4.7-4

Barrier structure

The acoustic barrier consists of two layers; a structural backing (normal density

concrete) and sound absorbing layer (no-fines concrete). The overall thickness of the

barrier was 150mm. The relative thickness of both layers can vary, and depends on

required sound absorption and on the structural constraints e.g. the height and

consequent increase in self-weight and wind loading. The minimum cover to steel

reinforcement was 25mm.

The structural backing layer in the laboratory prototype varied from 60mm to 110mm,

and the thickness of porous layer varied from 40mm to 90mm. The barrier system

comprised of three levels of panels. The bottom level with the structural backing layer

thickness of 110mm, the middle level with the solid layer of 80mm and the top level

with the structural backing layer of approximately 60mm. Figure 4.7.3 shows the

laboratory prototype assembled into an acoustic system.

Figure 4.7.3 Laboratory prototype of the ‘less-fines’ RA Concrete acoustic barrier

The panels underwent an extensive handling with the use of hoists and forklifts

including numerous loading and unloading from transportation equipment. The panels

were produced at Swinburne University of Technology, transported to a reverberation

room at the RMIT University for acoustic testing and brought back to the SUT to be

assembled into an acoustic system shown in Figure 4.7.3. Despite relatively low

4.7-5

characteristic compressive strength of 25MPa of concrete in the structural backing layer

and 10MPa in the porous layer, the structural integrity of the barrier was intact. Figure

4.7.4 shows the final installation of the barrier as a retaining wall in the Hawthorn

campus of the University. Field durability studies are to be conducted.

Figure 4.7.4 ‘Less-fines’ RA Concrete panels assembled as a retaining wall

Sound absorption

A reverberation room method was used to measure sound absorption coefficient in a

frequency range between 100Hz and 5,000Hz. Two sound absorption coefficients were

determined; one of the panels treated as an absorption area and the other one of the

panels as a discrete object. Figure 4.7.5 shows laboratory prototype panels in the

reverberation room and Figure 4.7.6 presents a plot of sound absorption characteristics

of ‘less-fines’ RA Concrete acoustic barrier.

4.7-6

Figure 4.7.5 Laboratory prototype panels in reverberation room

0

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0.9

1

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Frequency [Hz]

Soun

d ab

sorp

tion

coef

ficie

nt

as absorptionareaas discreteobject

Figure 4.7.6 Sound absorption coefficient of laboratory prototype acoustic barrier

The results indicate that the porous layer in the laboratory prototype acoustic barrier

made from the 14/10mm RC Aggregate contributes to significant sound absorption. For

comparison, the standard concrete or timber barriers purely reflect sound energy and

have zero sound absorbency.

4.7-7

4.7.3 Commercial prototype

The commercially produced acoustic barrier was manufactured in three (3) precast

panels, each 4m2 in area. The structural and acoustic design of the barrier and the

design of the manufacturing process aimed at maximum utilisation of standard

components such as; steel formwork, steel reinforcement and lifting inserts, and

employment of standard procedures of making concrete, placing it in formwork, etc.

Two types of aggregate were used; 20mm reclaimed (washed) aggregate (see Figure

4.7.7) in the structural backing layer, and 14/10mm RC Aggregate in the porous layer.

The two-concrete-pour method was used to place two types of concrete in the

formwork. As the first step, a designated layer of normal density concrete (20mm

RA40 concrete) made from reclaimed/washed 20mm graded aggregate was placed and

compacted. This followed by a placement of the no-fines, 14/10mm RA15 concrete and

screeding it in a porous layer. A commercial concrete manufacturer delivered the

20mm RA40 concrete, and the no-fines 14/10mm RA15 to the precast concrete yard in

a standard concrete agitator track. The commercial prototype was air cured and the

formwork stripped after 20 hours.

Aggregate

Apart from the 14/10mm RC Aggregate used at experimental stages of the project and

for the production of laboratory prototype, the two other types of commercially

available aggregate were considered as alternative aggregate to make concrete for

structural backing of the barrier. The first alternative aggregate, known as a 20mm

graded ‘reclaimed’ aggregate (denoted as D20R), which is an equivalent of the Class3

Crushed Concrete aggregate, which meets the requirements of the 820Vicroads

specification (Vicroads, 1994). The second alternative aggregate is known as 20mm

graded ‘washed’ aggregate (B20W), which is an aggregate derived from a plastic

concrete waste, washed at the concrete batching plants, to a grading which resembles a

combined grading of standard coarse and fine natural aggregates. Figure 4.7.7 presents

the reclaimed and washed aggregates in laboratory trays.

4.7-8

Figure 4.7.7 Alternative aggregate (reclaimed and washed) considered for concrete

to manufacture commercial barrier prototype

For concrete in the porous layer also two types of aggregate were also considered; the

14/10mm RC Aggregate (described in section 4.4 of this document) and 14/10mm

Scoria aggregate. Figure 4.7.8 presents the grading envelop set by the Australian

Standard, AS2758 – 1998 ‘Part2. Concrete Aggregate’ and PSD of some of the

aggregate considered as alternatives in concrete for the production of commercial

prototype barrier (SAA, 1998).

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Sieve aperture [mm]

Perc

enta

ge p

assi

ng

Lower limitUpper limit14/10 RC AggregateD20RD14/10R14/10 N Aggregate

Figure 4.7.8 Particle size distribution of aggregate considered to be used in the

production of commercial barrier prototype

4.7-9

The differences between basic engineering properties, including particle size

distribution of various aggregate were investigated and considered in the concrete mix

designs.

Concrete

The decision to use the two-concrete-pour method of placing concrete, necessitated

development of two types of concrete; normal density and no-fines concrete. In order to

incorporate industry standard procedures, the concrete mixes were designed by the

Boral Concrete Services Pty Ltd. Trial mixes were then prepared and tested in

commercial concrete laboratory in Thornbury. Table 4.7.1 presents summary of mix

designs for a normal density 20mm RA40 concrete and for no-fines RA Concrete.

Table 4.7.1 Mix proportions of concrete used for commercial prototype

20mm RA Concrete

14/10mm no-fines RA Concrete

Constituent material

Quantity [kg/m3] GB cement 200 200 Fly ash 80 80 Water 164 164 14/10mm RC Aggregate - 1,500 20mm washed reclaimed 1,680 - Concrete sand - - Additives 13 7

The normal density, RA Concrete samples were cured in a lime saturated water and

compressive strength determined at 3-days, 7-days and 28-days of concrete maturity.

Figure 4.7.9 presents compressive strength development of RA Concrete made from the

20mm washed (B20Washed) and reclaimed (D20Reclaimed) aggregate.

4.7-10

28.4

45.3

43

0

10

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30

40

50

0 5 10 15 20 25 30Maturity [Days]

Com

pres

sive

stre

ngth

[MPa

]

D20Reclaimed

B20Washed

Standard

Figure 4.7.9 Compressive strength development of normal density concrete used in

commercially manufactured prototype

Based on the test results it was decided that the structural layer can be made from

normal density RA Concrete using 20mm washed aggregate instead of the 14/10mm RC

Aggregate. The no-fines concrete for the porous layer was made from the 14/10mm RC

Aggregate. Figure 4.7.10 presents samples of the 10MPa no-fines RA Concrete on

vibrating table.

Figure 4.7.10 Samples of no-fines 14/10mm RA Concrete

Figure 4.7.11 presents the results of the compressive strength development of no-fines

RA Concrete. The concrete mix design was considered as adequate and subsequently

used in commercially produced concrete.

4.7-11

10.6

7.4

0

2

4

6

8

10

12

0 5 10 15 20 25 30Maturity [Days]

Com

pres

sive

Stre

ngth

[Mpa

]

D14/10R

S14/10

Figure 4.7.11 Compressive strength development of no-fines concrete used in

commercially manufactured prototype

The use of a lightweight aggregate, 14/10mm scoria was also investigated as it could

further reduce the weight of the panel; however, the strength reduction of more than

30% compared with RC Aggregate excluded it as a viable alternative.

Process: making panels

Commercial facilities were used to prepare the formwork, to fix steel reinforcement, to

attach lifting inserts, and to cast the normal density and no-fines concrete. The normal

density concrete was poured first, followed by a standard compaction. Then, practically

with no delay, the no-fines RA Concrete was poured and screed using a timber plank.

The panels were air cured, stripped and lifted to a storage space after approximately 20

hours. Figure 4.7.12 shows two stages of the manufacturing of commercial prototype;

placing normal density RA Concrete in structural backing layer and screeding of the no-

fines RA Concrete of the porous layer.

4.7-12

Figure 4.7.12 Placing normal density and screeding no-fines RA Concrete in commercially manufactured prototype

Barrier structure

Apart from specific aspects related to different production method, all other features of

laboratory prototype panels were implemented also in the commercial prototype. The

designed thickness of porous layer in all three panels was 40mm. Figure 4.7.13 presents

a shop drawing of the commercial prototype and Figure 4.7.14 presents panels in

storage.

Figure 4.7.13 Shop drawing of commercial prototype barrier

4.7-13

Figure 4.7.14 Commercial prototype of the ‘less-fines’ RA Concrete acoustic barrier

Sound absorption

The 4m x 1m panels were cut into three equal parts and transported to the Acoustic

Laboratories at the RMIT University. The sound absorption coefficient was determined

in the frequency range between 100Hz and 2,000Hz. Figure 4.7.15 shows panels of the

commercial prototype in the reverberation room and Figure 4.7.16 presents sound

absorption characteristics of the commercial prototype barrier.

Figure 4.7.15 Commercial prototype panels in reverberation room

4.7-14

0

0.1

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0.3

0.4

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0.6

0.7

0.8

0.9

1

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Frequency [Hz]

Soun

d ab

sorp

tion

coef

ficie

nt

Figure 4.7.16 Sound absorption coefficient of commercial prototype acoustic

barrier

4.7.2 Summary and Discussion

This section reported on one of the value added applications for the RC Aggregate; the

precast concrete panels of sound absorbing barrier. Environmental benefits of the ‘less-

fines’ RA Concrete acoustic barriers fall into two broad areas; firstly to the usage of

alternative coarse aggregate in new concrete and secondly to the potential of reducing

transportation noise impacts in urban environments.

The use of RC Aggregate in production of concrete barrier relates to the following

aspects:

• Reduction in the use of and reliance on natural resources

• Value added application for recycled concrete waste with the use of existing

technologies, standard processes and existing facilities

• Reduction in weight of the barrier panels, which results in smaller support structure,

and more efficient use of transportation and erection equipment.

The reduction in weight is one of the benefits of using RC Aggregate in the production

of acoustic barriers panels, which subsequently reduces design loading. A typical

barrier (150mm thick) made from normal density concrete would weigh 360kg per 1m2,

4.7-15

whereas comparable barrier made from RC Aggregate weights 40kg per 1m2 less.

Furthermore, if the barrier is partially made of the ‘less-fines’ RA Concrete with the

40mm porous layer, the weigh per 1m2 is reduced by 55kg. Such decrease in the self-

weight of the barrier’s panels reduces design loading, and therefore results in smaller

footing and support system. Table 4.7.2 presents the weight of the barrier made from


Table 4.7.2 Weight of panels made from RA Concrete

Panel Structural backing Porous layer 1 m2 4 m2 Thickness Density Weight/m2 Thickness Density Weight/m2 Weight Weight [mm] [kg/m3] [kg] [mm] [kg/m3] [kg] [kg] [kg] 0 2140 0 150 1740 261 261 1044 60 2140 128 90 1740 157 285 1140 80 2140 171 70 1740 122 293 1172 110 2140 235 40 1740 70 305 1220 150 2140 321 0 1740 0 321 1284

The benefits resulting from barrier’s acoustic performance and capacity to absorb sound

include:

• Reduction of a height of the barrier to achieve desired sound pressure level at the

receiver

• Reduction of a buffer zone between the barrier and the receiver to maintain desired

sound pressure level at the receiver

The acoustic performance of the laboratory and commercial prototypes can be

visualised in Figure 4.7.17. The sound absorption performance of the prototypes is

compared with those of commonly used concrete/timber reflective barrier and the

recommended by the Vicroads standard for purely sound absorbing barriers (Vicroads,

1994).

4.7-16

0

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0 400 800 1200 1600 2000

Frequency [Hz]

Soun

d ab

sorp

tion

coef

ficie

nt

Vicroads DC270A.51Laboratory prototypeCommercial prototypeReflective barrier

Figure 4.7.17 Reverberation test results

It is evident that the prototype barrier’s acoustic capabilities in absorbing sound

outperform the commonly used, concrete/timber reflective barrier. The comparison

shows also, that although significant sound absorption capabilities, the barrier does not

meet the limits set by the authorities. However, if the prototype is classified as the

sound absorbing barrier, all other requirements of the standard are satisfied. On the

other hand, if the prototype is classified as a reflective barrier; it conforms to all

requirements of Australian and State Authorities.

It is the author’s intention to conduct a field studies on the acoustic attenuation

capabilities of the barrier and durability of ‘less-fines’ RA Concrete, however at this

stage computer modeling was perceived sufficient. Acoustic simulation was performed

to assess performance of the ‘less-fines’ RA Concrete acoustic barrier in a scenario

where the noise source of a specific characteristics (55dB at frequency of 125Hz to the

maximum of 90dB at the peak frequency of 1,000Hz) is located at a distance of 88m

from a residential dwelling (Harding, 2004). Two scenarios were investigated; one with

the barrier very close to the noise source (8m) and the second scenario when the barrier

is placed at 18 meters from the noise source. Table 4.7.3 and Table 4.7.4 present

summary of the modeling in terms of two variables; barrier height and sound pressure

level at the receiver.

4.7-17

Table 4.7.3 Simulation of barrier height reduction – barrier 18m from noise source

Barrier height [m] 0 1 2 3 4 5 6 Sound pressure level dB(A) Concrete reflective barrier 63 62 59 56 54 52 50 Commercial prototype 63 61 57 54 51 48 46

Acoustic simulation results indicate that in the first scenario when a barrier is erected

18m apart from the noise source a reflective barrier of 3.5m in height would need to be

installed in order to not exceed recommended by the international standards, the day

exposure limit of 55dB(A). However, the same limit will not be exceeded if 2.7 meter

high commercial prototype ‘less-fines’ RA Concrete barrier would be installed.

Table 4.7.4 Simulation of barrier height reduction – barrier 8m from noise source

Barrier height [m] 0 1 2 3 4 5 6 Sound pressure level dB(A) Concrete reflective barrier 63 63 59 56 54 52 50 Commercial prototype 63 62 56 52 49 47 45

In the second scenario when a barrier is placed closer, eight (8) meters to the source of

transportation noise; to achieve the SPL of 55dB(A), a 3.5m timber or standard concrete

barrier would need to be installed. However, if commercial prototype of ‘less-fines’ RA

Concrete acoustic barrier would be employed, the added benefit of sound absorption

leads to a reduction in the height of 1.25 metres. Such reduction consequently leads a

significant reduction in material and installation cost, and reduction in visual

obstruction.

While it is apparent that the presence of porous layer in the barrier leads to sound

absorption, the structure of the layer and its influence on acoustic characteristics of the

barrier can easily be manipulated. Both the thickness of the layer and relative amount

of air voids in the layer influence sound absorption characteristics. The layer thickness

and voids distribution can be altered by various concrete mix designs and by variations

in coarse aggregate grading. The grading and packing of the aggregate in the porous

layer result in development of interconnected air voids. Different thickness of porous

layer contributes to the lengths of the interconnected air voids and aggregate size

contributes to spacing between the voids (as discussed in section 4.6 of this document).

4.7-18


The laboratory and commercial prototypes made from 14/10mm RC Aggregate and

reclaimed aggregate demonstrated a value added application for recycled concrete

products available in Victoria.

The pre-cast panels of barrier prototypes were used as a testing ground for a commercial

concrete made from RC Aggregate and as a testing ground for investigation of

manufacturing of an alternative product made from RA Concrete.

The outcomes of the developmental program of the barrier demonstrate feasibility and

practicability of applying selected RC Aggregate in ‘less-fines’ concrete which

contributes to significant sound absorption of the barrier.

The structural and acoustic robustness of ‘less-fines’ RA Concrete were also discussed

in other sections of this report, which in conjunction with the test results of acoustic

barrier’s prototypes in commercial laboratories, confirmed the benefits of such

application for selected RC Aggregate.

The results of acoustic testing of the prototypes in reverberation room indicate

significant sound absorption capabilities in the frequency range similar to transportation

noise. The sound absorption of the barrier is up to 80% of incident noise at various

frequencies. The test results and computer simulation indicate that such absorption

characteristics of the barrier can lead to tangible benefits of a height or/and buffer zone

reduction when the ‘less-fines’ RA Concrete acoustic barrier is applied as a noise

barrier in urban environments.

4.7-19

4.7 PROTOTYPE BARRIER .................................................................................1 4.7.1 Introduction...............................................................................................1 4.7.2 Laboratory prototype.................................................................................1 4.7.3 Commercial prototype...............................................................................7 4.7.2 Summary and Discussion........................................................................14 4.7.3 Discussion of the Results ........................................................................18

4.7 PROTOTYPE BARRIER .................................................................................1 4.7.1 Introduction...............................................................................................1 4.7.2 Laboratory prototype.................................................................................1 4.7.3 Commercial prototype...............................................................................7 4.7.2 Summary and Discussion........................................................................14 4.7.3 Discussion of the Results ........................................................................18

Figure 4.7.1 Compressive strength of RA Concrete used in laboratory prototype barrier2 Figure 4.7.2 Formwork, steel reinforcement and lifting inserts of laboratory prototype..3 Figure 4.7.3 Laboratory prototype of the ‘less-fines’ RA Concrete acoustic barrier .......4 Figure 4.7.4 ‘Less-fines’ RA Concrete panels assembled as a retaining wall ..................5 Figure 4.7.5 Laboratory prototype panels in reverberation room .....................................6 Figure 4.7.6 Sound absorption coefficient of laboratory prototype acoustic barrier ........6 Figure 4.7.7 Alternative aggregate (reclaimed and washed) considered for concrete to

manufacture commercial barrier prototype...............................................................8 Figure 4.7.8 Particle size distribution of aggregate considered to be used in the

production of commercial barrier prototype .............................................................8 Figure 4.7.9 Compressive strength development of normal density concrete used in

commercially manufactured prototype ...................................................................10 Figure 4.7.10 Samples of no-fines 14/10mm RA Concrete ............................................10 Figure 4.7.11 Compressive strength development of no-fines concrete used in

commercially manufactured prototype ...................................................................11 Figure 4.7.12 Placing normal density and screeding no-fines RA Concrete in

commercially manufactured prototype ...................................................................12 Figure 4.7.13 Shop drawing of commercial prototype barrier........................................12 Figure 4.7.14 Commercial prototype of the ‘less-fines’ RA Concrete acoustic barrier .13 Figure 4.7.15 Commercial prototype panels in reverberation room ...............................13 Figure 4.7.16 Sound absorption coefficient of commercial prototype acoustic barrier..14 Figure 4.7.17 Reverberation test results..........................................................................16

Table 4.7.1 Mix proportions of concrete used for commercial prototype ........................9 Table 4.7.2 Weight of panels made from RA Concrete..................................................15 Table 4.7.3 Simulation of barrier height reduction – barrier 18m from noise source.....17 Table 4.7.4 Simulation of barrier height reduction – barrier 8m from noise source.......17

4.8-1

4.8 DISCUSSION OF THE RESULTS

The project’s experimental phase started with an investigation of fine aggregate sourced

from Melbourne’s major aggregate suppliers with an aim of selecting concrete sand

which will yield the most durable concrete. Based on a volume of permeable voids test

results, fine aggregate from Bacchus Marsh Quarry was chosen. The particle size

distribution of this aggregate expressed as a fineness modulus of 2.9 contributes to

concrete of a characteristic compressive strength of 25MPa that has good workability,

meets the strength target, and has hardened cement paste of a VPV of 13.6%, which

indicates durable concrete.

The 14/10mm RC Aggregate investigated in this research project is one of a variety of

commercially available concrete recycling products in Victoria. A wide selection of

engineering properties was examined. The properties included; cement paste residue

content, physical contaminants content, content and re-cementing qualities of fines,

particle size distribution, particle and bulk density, water absorption, and porosity.

An examination of the selected 14/10mm RC Aggregate revealed that the aggregate has

a specific set of well defined although unique properties, which differentiate it from

comparable natural aggregate. The most distinguishable properties of RC Aggregate are

the content of cement paste residue and the content of various foreign materials in the

aggregate. These are intrinsic to the waste material and to aggregate components

affecting other physical and mechanical properties such as aggregate’s porosity, density,

water absorption and content of very fine particles.

A 2% content of particles smaller than 75μm in 14/10mm RC Aggregate appears to

have some re-cementing potential, which can be a factor in the hydration of cement in

concrete made from RC Aggregate.

Apart from inconsistent and high water absorption, high porosity, and content of some

foreign material, the aggregate has a specific microstructure containing a high amount

of microcracks. These mechanically induced microcracks, together with a specific

4.8-2

porosity of cement paste component of the aggregate, have the potential to affect

concrete strength and durability.

All of these properties make the aggregate very unique, however, if the properties are

monitored and the variability controlled, the aggregate can be used in concrete. An

extensive investigation into some basic properties including particle size distribution,

saturated surface dry density and physical contaminants content, indicate that the

produced aggregate consistently meets specified requirements.

The application for selected 14/10mm RC Aggregate investigated in this research

project was as a coarse aggregate in concrete of a characteristic compressive strength of

25MPa. The standard industry approach practiced in Victoria to mix design and

production of concrete was adopted. A straight substitution of coarse aggregate in

concrete was aimed for, with some adjustments to the water/cement ratio resulting from

differences in water absorption of the aggregate. Pre-wetting of the aggregate was

deemed necessary in order to control the plastic state properties of RA25 Concrete and

self desication cracking.

A wide range of physical, mechanical and microstructural properties of hardened

concrete were examined as part of this research project. The compressive strength and

durability of RA25 Concrete is well defined, although the concrete has different

characteristics to a comparable concrete made from natural aggregate of the same

amount of cementitious binder.

An 8.5% reduction of compressive strength and decreased durability (VPV of 0.81%

above recommended limit) of RA25 Concrete results from inherent porosity of the

cement paste residue and mechanically induced cracks in the handling and

manufacturing process of the RC Aggregate.

Another commercially realistic application for selected 14/10mm RC Aggregate

investigated as part of this project was as coarse aggregate in no fines and ‘less-fines’

concrete.

4.8-3

The ‘less-fines’ RA Concrete is a fusion of two separate types of concrete; the normal

density and no-fines concrete. The ‘less-fines’ concrete has a unique structure where

two distinctive layers are present; solid and porous. Apart from adequate physical and

mechanical properties, the ‘less-fines’ concrete showed unique acoustic performance

characteristics of resonant absorbents. The structure of porous layers and presence of

solid layers allowed the formation of interconnected air channels, which reflect back

some of the sound energy and absorb some in a specific range of frequencies. The

principal peak resonant frequency relates to a configuration of resonant chambers,

which are created in the porous layer of the ‘less-fine’ concrete by the aggregate

arrangement. The 14/10mm ‘less-fines’ RA Concrete has a sound absorption

coefficient of approximately 0.8 at a peak frequency of approximately 400Hz. It has

also been demonstrated by results of impedance tube testing and computer simulation

that the peak frequency can be modeled to target a range of dominant noise frequencies.

It has also been demonstrated that when the ‘less-fines’ concrete is applied in an

acoustic barrier it provides the required structural integrity whilst simultaneously

absorbing sound energy. The laboratory and commercial prototypes made from ‘less-

fines’ RC Aggregate and reclaimed aggregate demonstrated a value added application

for recycled concrete products available in Victoria.

The pre-cast panels of barrier prototypes provided a testing ground for a commercial

concrete made from RC Aggregate and a testing ground for a trial production in a

commercial setting of an alternative product made from RA Concrete.

The outcomes of the developmental program of the barrier demonstrate feasibility and

practicability of applying selected RC Aggregate in ‘less-fines’ concrete which

contributes to significant sound absorption of the barrier. The structural and acoustic

robustness of ‘less-fines’ RA Concrete which were discussed in other sections of this

report, and the test results of acoustic barrier’s prototypes in commercial laboratories,

confirmed the benefits of this particular application of selected 14/10mm RC

Aggregate.

The results of acoustic testing of the prototypes in a reverberation room indicate

significant sound absorption capabilities in a frequency range similar to transportation

4.8-4

noise. The sound absorption of the barrier is up to 80% of incident noise at various

frequencies. The test results and computer simulation indicate that such absorption

characteristics of the barrier can lead to tangible benefits of a height and/or buffer zone

reduction when the ‘less-fines’ RA Concrete acoustic barrier is applied as a noise

barrier in urban environments.

4.8-5

4.8 DISCUSSION OF THE RESULTS..................................................................1

5-1

CHAPTER 5 - SUMMARY, CONCLUSIONS and RECOMMENDATIONS

5.1 SUMMARY

In Victoria, there is a steady increase of C&D waste generation including concrete

waste. Currently the waste stream allows concrete waste to be disposed at landfill sites

however available landfill space to dispose waste is becoming scarce in urban

environments. In response to such a situation, numerous research on recycling and use

of recycled concrete is undertaken and practical applications have been proposed to the

industry, which is now aware of alternative ways of disposing C&D waste, and is aware

of alternative construction materials including selected 14/10mm RC Aggregate.

Subsequently, concrete recycling is expanding and is now well established in Victoria.

The process of crushing concrete waste is well understood and can easily be adjusted to

produce concrete recycling products of desirable characteristics. Concrete recycling

products are currently used as a substitute for natural aggregate in sub-base layers in

road construction however research communities and the industry in Victoria are of the

opinion that a locally produced selected RC Aggregate can be used as alternative

aggregate in concrete.

Significant efforts of concrete recyclers, research community, concrete technologists

and precast concrete product manufacturers are directed in searching for high value

utilisation for selected RC Aggregate. There are numerous examples of successful use

of recycled concrete aggregate as a partial or total substitute for natural coarse aggregate

in new concrete and significant research efforts to fully understand RC Aggregate and

concrete made from such aggregate.

However, despite a growing awareness and positive steps towards sustainability in

construction, there are still possible alterations to be implemented in the current

construction and demolition practice, along with some reservation and uncertainty that

needs to be overcome among the concrete industry and concrete buyers.

5-2

Apart from waste problems, industrialised nations face transportation noise pollution

problems. Noise pollution due to excessive transportation noise has a negative social

and environmental impact and is being addressed in a number of ways. The limits for

noise exposure are set and practical ways to reduce impacts are implemented.

Currently, the most practical and cost effective way of reducing transportation noise

affecting residents is to install sound barriers. In Victoria at present, timber reflective

barriers are preferred and widely used.

However, the need to reduce transportation noise imprint on urban environments

prompts the use of sound absorbing barriers and more durable materials.

The ‘less-fines’ RA Concrete barrier proposed by this research seems to address the

need for finding an added value application for concrete waste whilst addressing

transportation noise pollution.

The precast concrete barrier made from selected RC Aggregate proposed by this

research has adequate physical, mechanical and acoustic properties. The barrier

concept, manufacturing processes of making concrete and producing precast concrete

panels, have been tested in commercial settings and accepted by the industry.

The ‘less-fines’ RA Concrete acoustic barrier provides a viable alternative to

commercially available acoustic barrier.

5-3

5.2 CONCLUSIONS

A number of conclusions have been drawn on the basis of the literature review,

consultations with researchers and practitioners in relevant professional areas. The

main conclusions are as follow;

RC Aggregate is underutilised and there is a need for finding an added value application

for selected aggregate.

The RC Aggregate has a unique set of well defined engineering properties, although the

aggregate is different form standard coarse aggregate used in concrete technology.

The manufacturing process is well adjusted to current needs, although it is easily

adjustable and concrete recyclers can produce selected aggregate that meets desired

specifications and the needs of the concrete industry.

Selected RC Aggregate can be used as a coarse aggregate substitute in concrete of

characteristic compressive strength of 25MPa; however, strength reduction of

approximately 8.5% can be expected.

The reduction of compressive strength and durability expressed as volume of permeable

voids are due to mechanically induced microcracks and the presence of physical

impurities such as wood, plastic, organic matter, etc.

Although the cement aste residue of RC Aggregate generally reduces strength of the

aggregate and concrete, the mineralogcal composition of solid or powder cement paste

residue can contribute to strength development due to its re-cementing properties.

The most appropriate applications for concrete made from RC Aggregate are pre-mix

concrete and precast concrete elements, as the design parameters and manufacturing

process can be closely controlled.

5-4

The ‘less-fines’ concrete, which is an alternative to normal density and to no fines

concrete, develops a structure that absorbs sound energy.

The ‘less-fines’ concrete made from selected RC Aggregate provides better structural

and acoustic characteristics due to the shape and porosity of the aggregate.

5.3 RECOMMENDATIONS

The author is aware of the limitations of the experimental and developmental program

adopted in this research and that a number of other properties of RC Aggregate, RA

Concrete and ‘less-fines’ acoustic barriers could be investigated.

To fully understand the aggregate and to more comprehensively differentiate it from

natural aggregate the following study is recommended;

• alkali reactivity of the aggregate to assess the potential of a silica-alkali reaction in

RA Concrete

• permeability tests to complement porosity assessment of the aggregate, and to better

estimate the durability of RA Concrete

• weak particles content including clay lumps, soft and friable particles in RC

Aggregate

• aggregate soundness and evaluation by exposure to a sodium sulfate solution

• chemical contamination of the aggregate and its influence on hydration of cement in

RA Concrete

The author would also like to recommend further study of ‘less-fines’ RA Concrete

durability by coring sample from the prototypes and to assess impact resistance of the

barrier.

A demonstration project is recommended to examine aspects related to the installation

of barriers and to allow for field durability and acoustic effectiveness tests.

5-5

CHAPTER 5 - SUMMARY, CONCLUSIONS and RECOMMENDATIONS ...............1 5.1 SUMMARY ......................................................................................................1 5.2 CONCLUSIONS...............................................................................................3 5.3 RECOMMENDATIONS ..................................................................................4

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Publications-1

PUBLICATIONS and INVITED PRESENTATIONS Patent application • Swinburne University of Technology, Krezel, Z.A. and McManus (2002),

Australian and the USA application AU&US patent # 200247534 A1, Swinburne Acoustic Barrier, Melbourne.

Conference papers (refereed) • Krezel, Z.A., Ilijoski, T., and Otto, L., (2005), Handling of recycled concrete

aggregate in overhead bins concrete batching plants, 5rd International Congress Valorisation and Recycling of Industrial Waste VARIREI 2005, 28-30 June, L’Aquila, Italy.

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• Krezel, Z.A., and McManus, K.J., (2003), Sound absorbing concrete barrier, 3th International Conference on Modelling and Experimental Measurements Acoustics 2003, 16-18 June, Cadiz, Spain.

• Krezel, Z.A., and McManus, K.J., (2003), Development and Commercialisation of Recycled Aggregate Acoustic Barrier, 4rd International Congress and Exposition “Added Value and Recycling of Industrial Waste VARIREI 2003”, 24-27 June, L’Aquila, Italy.

• McManus, K.J., Evans, R.P., Krezel, Z.A., and Alabaster, P., (1999), Sound Barriers for Urban Freeways using Recycled Concrete Aggregate, Civil and Environmental Engineering Conference, Asian Institute of Technology, November, Bangkok, Thailand.

• Krezel, Z.A. and McManus, K.J., (2001), Ecologically Sustainable Acoustic Barriers, 20th Australian Road Research Board Conference, 19-21March, Melbourne.

• Krezel, Z.A., and McManus, K.J., (2001), New Products made from Concrete Waste, 3rd International Congress “Added Value and Recycling of Industrial Waste”, L’Aquila, 25-29 June, Italy.

• Krezel, Z.A., and McManus, K.J., (2000), Recycled Aggregate Concrete Sound Barriers for Urban Freeways, 4th International Conference on the Environmental and Technical Implications of Construction with Alternative Material, WASCON 2000, May, Leeds/Harrogate, UK.

• Krezel, Z.A., and McManus, K.J., (2000), Use of Recycled Concrete Aggregate in Road Infrastructure, 10th Road Engineering Association of Asia and Australasia Conference, 4-9 September, Tokyo.

Publications-2

• Krezel, Z.A. and McManus, K.J., (2000), Recycling Demolition Waste to Fight Noise Pollution, 4th Annual Australian Environmental Engineering Research Event, 21-24 November, Victor Harbor.

• Krezel, Z.A., and McManus, K.J., (1999), Recycled Concrete Products in the Production of Concrete Sound Barriers, 3rd Environmental Engineering Research Event, ’99, November, Castlemaine, Victoria.

Extended abstracts (refereed) • Krezel, Z. A., Knott, R., Aldridge, L., McManus K. J., (2000), Examining Porosity

of Recycled Concrete Aggregate and Recycled Aggregate Concrete using Small Angle Neutron Scattering, 3rd ANU Australian Small Angle and Surface Scattering Meeting, 11-13 October, Canberra ACT.

Professional reports • Krezel, Z.A., McManus, K.J., (2002), Recycled Aggregate Concrete Sound

Absorbing Barriers for Urban Freeways, Ecorecycle Victoria, Melbourne. Invited presentations • Krezel, Z.A., (2000), Recycled Concrete Aggregate in Pre-cast Concrete Noise

Panels, Concrete Institute of Australia Technical Evening, Melbourne, 5 September. Posters • McManus, K.J., and Krezel, Z.A., (2003), Acoustic properties of Swinburne

Acoustic Barrier, Transportation Research Board Summer Workshop 2003 Beneficial Use, Sustainability and Pollution Prevention in Transportation Infrastructure, 29 June – 1 July 2003, Portsmouth, New Hampshire, USA.

• McManus, K.J., and Krezel, Z.A., (2003), Durability of Recycled Aggregate Concrete used in Swinburne Acoustic Barrier, Transportation Research Board Summer Workshop 2003 Beneficial Use, Sustainability and Pollution Prevention in Transportation infrastructure, 29 June – 1 July 2003, Portsmouth, New Hampshire, USA.

• Krezel, Z.A., Alabaster, P., Bakshi, E., and McManus, K.J., (1999), Neutron Scattering Techniques in the Examination of Recycled Aggregate Concrete, Joint AINSE-ANU Symposium on Small Angle Scattering and Reflectometry, Lucas Heights, Sydney, 30 September.

Documents

Recycled aggregate concrete acoustic barrier · RECYCLED AGGREGATE CONCRETE ACOUSTIC BARRIER Zbigniew Adam Krezel Thesis submitted in partial fulfillment of the requirements for the