m 2010 Ceet 26 Manirafasha Amos Gs20050571

8/13/2019 m 2010 Ceet 26 Manirafasha Amos Gs20050571

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KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY

INSTITUT DES SCIENCES ET TECHNOLOGIE DE KIGALI

Avenue de lArme, BP3900 Kigali- Rwanda

FACULTY OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL

TECHNOLOGY

A PROJECT REPORT

ON

Submitted by:

MANIRAFASHA Amos (REG. NO: GS20050571)

Under the guidance of

Mr.And NGARAMBE

Submitted in partial fulfillment of requirements for the award of

BACHELOR OF SCIENCE DEGREE IN CIVIL ENGINEERING AND

ENVIRONMENT TECHNOLOGY

SEPTEMBER, 2009

ANALYSIS OF THE USES OF LIGHT CONCRETE, NORMAL COCRETE

AND HEAVY CONCRETE IN RWANDA

PROJECT ID: CEET/O9/02


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KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY

INSTITUT DES SCIENCES ET DE TECHNOLOGIE DE KIGALI

Avenue de l'Arme, B.P. 3900 Kigali, Rwanda

FACULTY OF ENGENEERING

DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL

TECHNOLOGY

C E R T I F I C A T E

This is to certify that the Project Work entitled ANALYSIS OF THE USES OF

LIGHT CONCRETE, NORMAL COCRETE AND HEAVY CONCRETE IN

RWANDA is a record of the original work done by MANIRAFASHA Amos

(REG.No: GS20050571) in partial fulfillment of the requirement for the award of

Bachelor of Science Degree in Civil Engineering and Environmental Technology of

Kigali Institute of Science and Technology during the Academic Year 2008.

..

Andr NGARAME G. Senthil KUMARAN

Project Supervisor HEAD, Dept. of CE&ET

Submitted for the Project Examination held at KIST on September 2009


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DECLARATION

I,MANIRAFASHA Amos hereby declare that this research ANALYSIS OF THE

USES OF LIGHT CONCRETE, NORMAL COCRETE AND HEAVY

CONCRETE IN RWANDA for the award of Bachelor of Science Degree in Civil

Engineering and Environmental Technology is my original work and has never been

presented anywhere else for the same purpose. All sources I have used and quoted have

been acknowledged as complete references.

.. ..

MANIRAFASHA Amos Andr NGARAME

REG NO 20050571 Project Supervisor


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DEDICATION

This research project is dedicated to:

Almighty God,

My beloved father KANYANZIRA Flicien,

My beloved mather MUKARUZIMA Spciose

My Brothers and sisters,

All my Colleagues,

All my friends.


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ACKNOWLEDGEMENT

I am deeply intended to almighty God who has guided me through the whole period of

my studies. My sincere thanks are due all friends and colleagues who helped me in one-

way or another. I am very grateful to all members of my family for their support and

advice.

My special thanks are addressed to the Government of Rwanda for its appreciable policy

of promoting education at all levels.

Again my sincere acknowledgements go to entire administration of KIST and the whole

academic staff.

My sincere gratitude goes to my supervisor, Mr. Andr NGARAMBE for his technical

and wise advice, suggestions and corrections that made this research project fruitful.

Finally I express my gratitude to each one who directly and indirectly contributed to

make my studies successful today.


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ABSTRACT

Ttis project is the study of the light concrete, normal concrete and heavy concrete which

are used in different construction in RWANDA. The uses of lightweight aggregate and

heavy concrete in concreting are possible in construction to day in RWANDA.

A systematic imvestigation was undertaken to determe the availability of lightweight

aggregate, normal weight aggregate and heavy weight aggregate; their application and the

advantages of uses light concrete, normal concrete and heavy concrete.

To identify the characteristics of lightweight aggregate, normal weight aggregate and

heavy aggregate; and to know why normal concrete is more popular compare to other

types of concrete.

After, characterize the lightweight aggregate, normal weight aggregate and heavy

aggregate; then compare the uses of light concrete, normal concrete and heavy concrete

in RWANDA.

Therefore the results show that the normal concrete is more useful because of more

frequent of normal weight aggregate.


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TABLE OF CONTENTS

C E R T I F I C A T E .......................................................................................................... i

DECLARATION ................................................................................................................ ii

DEDICATION ................................................................................................................... iii

ACKNOWLEDGEMENT ................................................................................................. iv

ABSTRACT ........................................................................................................................ v

TABLE OF CONTENTS ................................................................................................... vi

LIST OF ABBREVIATIONS ............................................................................................ ix

NOMENCLATURES AND SYMBOLS LIST .................................................................. x

LIST OF TABLES ............................................................................................................. xi

LIST OF FIGURES ........................................................................................................... xi

Chapter1. GENERAL INTRODUCTION .......................................................................... 1

1.1 Introduction ............................................................................................................... 1

1.2Problem statement ..................................................................................................... 1

1.3 Objectives of the project ........................................................................................... 2

1.4 Scope of the project .................................................................................................. 2

1.5 Justification of the project ......................................................................................... 2

1.6 Methodology ............................................................................................................. 3

Chapter 2. LITERATURE RIVIEW ................................................................................... 4

2.1 History of concrete .................................................................................................... 4

2.2 Properties of Concrete............................................................................................... 5

2.3 Applications of Concrete .......................................................................................... 7

2.4 Types of cement ........................................................................................................ 8

2.5 Admixtures ................................................................................................................ 9

2.6 Types of aggregate .................................................................................................. 11

2.6.1 Lightweight aggregate ..................................................................................... 11

2.6.2 Normal weight aggregate ................................................................................. 12

2.6.3 Heavyweight aggregate .................................................................................... 12

2.6.3.1 Characteristics of heavy aggregate ............................................................... 13

2.7 Fresh concrete ......................................................................................................... 14

2.7.1 Introduction ...................................................................................................... 14


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2.7.2 Workability ...................................................................................................... 14

2.7.3 Shrinkage ......................................................................................................... 15

2.7.4 Creep ................................................................................................................ 16

2.7.5 Advantages and disadvantages of concrete ...................................................... 16

2.8 Behavior of hardened concrete ............................................................................... 17

2.8.1 Strength ............................................................................................................ 17

2.9 Light concrete ......................................................................................................... 21

2.9.1 Definition ......................................................................................................... 21

2.9.2 Quality control ................................................................................................. 22

2.9.3 Concrete Strength............................................................................................. 22

2.9.4 Moisture Contents ............................................................................................ 23

2.9.5 Production considerations ................................................................................ 23

2.10 Normal concrete .................................................................................................... 24

2.10.1 Characteristics of normal concrete ................................................................. 24

2.10.2 Advantages & the disadvantages of normal concrete .................................... 25

2.11 Heavy concrete ...................................................................................................... 25

2.11.1 Characteristics of heavy concrete .................................................................. 25

2.11.2 Compressive strength ..................................................................................... 26

2.11.3 Mixing and curing .......................................................................................... 26

2.12 Concrete in road pavements ...................................................................................... 27

Chapter 3. MATERIALS AND ANALYSIS.................................................................... 28

3.1 Materials ............................................................................................................... 28

3.1.1 Ordinary Portland cement ................................................................................ 28

3.1.2 Aggregate ......................................................................................................... 28

3.1.4 Water ................................................................................................................ 29

3.1.5 Admixture ........................................................................................................ 30

3.2 ANALYSIS ............................................................................................................. 31

3.2.1 Ligh concrete ................................................................................................... 31

3.2.2 Normal concrete ............................................................................................... 33

3.2.3 Heavy concrete................................................................................................. 33

3.2.4 Comparison of light , narmal and heavy concrete ........................................... 34


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Chapter 4. RESULTS AND DISCUSSION ..................................................................... 36

4.1 Comparison of uses of lightweight concrete, normal concrete and ........................ 38

heavy concrete in RWANDA ................................................................................. 38

4.2 Discussion ............................................................................................................... 38

Chapiter. CONCLUSION AND RECOMMENDATION ................................................ 39

CONCLUSION ............................................................................................................. 39

RECOMMENDATION ................................................................................................ 40

REFERENCES ................................................................................................................. 41

APPANDICES .................................................................................................................. 42


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LIST OF ABBREVIATIONS

ASTM: American Society for Testing and Materials

PCC: Portiland Cement Concrete

BS: British Standard

CA: Coarse Aggregate

FA: Fine Aggregate

CIMERWA: Cimenterie du Rwanda

ELECTROGA: Etablissement Public de Production de Transport et de Distribution

dEau et de Gaz

KIST: Kigali Institute of Science and Technology

OPC: Ordinary Portland Cement

RWF: Rwandan franc

SFAR: Student Financing Agency in Rwanda

W/C: Water Cement ratio

L.C: Light concrete

N.C: Normal concrete

H.V: Heavy concrete

Aggr.:Aggregate

SCC: Self-consolidating concrete

Fe3O4: Magnetite

BaSO4: Barites

AASHO:

V : volume

P : maximum load applied on a single aggregate

h : distance


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NOMENCLATURES AND SYMBOLS LIST

kg: kilogram

g: gram

m3: cubic meter

MPa: Mega Pascal

KN: kilo Newton

Me: Fineness Modulus

22: mean compressive strength of aggregate

W/B: Water binder ratio

E :Modulus of Elasticity

&: and

%: percentage

t: Temperature

OC: Degree celcius

mm: millimeter

mm2: millimeter square


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LIST OF TABLES

Table2.1 Common types of concrete admixtures ............................................................. 10

Table 3.1 Quality of aggregate ......................................................................................... 29

Table.3.1 Comparison of light , normal and heavy concrete ............................................ 35

Table 4.1 Availability of aggregate in Rwanda ................................................................ 36

Table 4.2 Availability of concrete in RWANDA ............................................................. 37

LIST OF FIGURES

Figure 2.1 The effect of the aggregate type on compressive strength .............................. 19

Figure. 2.2 Stress-strain relationship for concrete ........................................................... 20

Figure 2.3 Different modulus of alacticity ........................................................................ 20


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do the analysis of the uses of all three types of concrete in RWANDA, and to know why

some types of concrete are not used.

Also, another problem is that may be in RWANDA we use normal concrete only because

the other types of concrete are not known, this analysis will discover why.

1.3 Objectives of the project

Main objectives

The main objective of this project is to do the analysis of the normal concrete, light

concrete, and heavy concrete used in RWANDA.

Specific objectives

To know the uses of normal concrete. To know the uses of light concrete. To know the uses of heavy concrete. To compare the availability of normal, light and heavy concrete.

1.4 Scope of the project

My project is based on the analysis of the uses of normal, light and heavy concrete.

The contents required for each type of concrete:

Cement

Aggregate

Water and

Admixture.

1.5 Justification of the project

This project will be helpful to the Government of RWANDA through the authorities in

charge of infrastructure to improve the uses of concrete in construction.

Also to conduct another research regarding any other type of concrete used in

RWANDA.

And helpful to any other who want to use any type of concrete.


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Finally this project is very helpful in such a way that it helps me to increase my

knowledge in concrete.

1.6 Methodology

The methodologies used to achieve the intended objectives of this work are:

Documentation: Library and internet Field investigation and Questionnaire.


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Chapter 2. LITERATURE RIVIEW

2.1 History of concrete

Concrete is a material used in building construction, consisting of a hard, chemically inert

particulate substance, known as an aggregate (usually made from different types of sand

and gravel), that is bonded together by cement and water.

The Assyrians and Babylonians used clay as the bonding substance or cement. The

Egyptians used lime and gypsum cement. In 1756, British engineer, John Smeaton made

the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate and

mixing powered brick into the cement. In 1824, English inventor, Joseph Aspdin

invented Portland Cement, which has remained the dominant cement used in concrete

production. Joseph Aspdin created the first true artificial cement by burning ground

limestone and clay together. The burning process changed the chemical properties of the

materials and Joseph Aspdin created a stronger cement than what using plain crushed

limestone would produce.

The other major part of concrete besides the cement is the aggregate. Aggregates include

sand, crushed stone, gravel, slag, ashes, burned shale, and burned clay. Fine aggregate

(fine refers to the size of aggregate) is used in making concrete slabs and smooth

surfaces. Coarse aggregate is used for massive structures or sections of cement.

Concrete that includes imbedded metal (usually steel) is called reinforced concrete or

ferroconcrete. Reinforced concrete was invented (1849) by Joseph Monier, who received

a patent in 1867. Joseph Monier was a Parisian gardener who made garden pots and tubs

of concrete reinforced with an iron mesh. Reinforced concrete combines the tensile or

bendable strength of metal and the compressional strength of concrete to withstand heavy

loads. Joseph Monier exhibited his invention at the Paris Exposition of 1867. Besides his

pots and tubs, Joseph Monier promoted reinforced concrete for use in railway ties, pipes,

floors, arches, and bridges. [7]

The use of concrete dates to many ancient civilizations. The Romans, in particular, used

concrete for everything from buildings to the cores of aqueducts. The Romans were also

among the first to experiment with mixing additives into their concrete. They understood


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that mixing it with certain things would make it more water-resistant and less likely to

crack under pressure.

Self-consolidating concrete (SCC) has arrived, but vibration still prevails and still follows

principles described in a two-part series from March-April 1959. Explaining the

fundamentals is never outmoded; the subject of this "primer" was reprised in a June 2002

Concrete Basics column titled "To Improve Placement, Understanding Vibration Is Key."

Concrete is still known today for its durability and longevity. As with any building

material, it does have its share of completely acceptable alternatives. Wood is often

designed to be load-bearing, particularly in foundations, and can be treated to

withstand the negative effects of moisture and termites. Steel is both sturdy and cost-

effective, and can be ideal in areas infested by insects. Insulated steel panels are also

often used instead of concrete in the construction of walls. [4]

2.2 Properties of Concrete

After learning briefly about the history of concrete, let us focus upon the properties of

concrete. Concrete is an artificial building material whose production differs from

application to application. Amongst general properties of concrete, we must understand

that concrete should possess certain physical and chemical properties, tensile strength,

low-level of permeability to avoid moisture and retain chemical and volume stability.

Concrete essentially has a high level of compress ional strength, while the tensile strength

of concrete is relatively very weak. As concrete can crack under its own weight, it needs

to be reinforced. It is generally reinforced using steel bars or fibre and iron mesh. To

reduce the tensile strength of concrete, it is also pre-stressed with the use of steel cables.

The deciding factor for strength is also inherently related to the proportion and ratio of

water and cement, the type of cement used and the strength of used aggregate.

Generally, concrete made using lower water-cement ratio makes a stronger concrete than

when higher ratios are used. It is noticed that concrete made out of rough broken rock

pieces is much stronger than concrete made using smooth pebbles. The reason is that the

material should not result into more surface bondage area as this will increase the


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quantity of bondage, which is cement, resulting in weaker concrete. It is known that

limestone possesses higher bonding properties than conventionally used gravel.

Normally, a 28-day compressive strength testing is done to achieve desired workability.

The 28-day test for compressive strength is achieved by determining the right quantity of

cement required in water cement ratio. In structures like arches, vaults where shapes and

structures with internal forces require concrete.

Workability of concrete means the ability of a concrete to fill the mould appropriately,

producing the desired work without plummeting the quality of concrete. Concrete

workability is achieved with the water ratio, shape and size of aggregate and the level of

hydration. It is observed that workability can be considerably improved by increasing the

quantity of water, or with usage of plasticizer.

More water content can lead to bleeding and segregation, which can result in poor quality

concrete formation.

Curing is a process that keeps the concrete intact by providing an appropriate

environment. It is considered that good curing ensures a moist environment for hydration.

This steady hydration results in low level of permeability, thus increasing concrete

strength and quality. Concrete also needs to be protected from shrinkage. As concrete has

low thermal expansion co-efficient, this means that it cannot handle repetitive expansion

and shrinkage.

If there is no external force used for expansion, it can result in sizeable force acting

against it, resulting in shrinkage and cracking of structure. As concrete grows older, it

goes on shrinking due to internal forces caused within the material.

Cracking of concrete begins at micro level. Normally, concrete is kept in a wet state to

allow easy moulding when required. Hydration and hardening of concrete can lead to

shrinkage and cracking when it has not yet developed the tensile strength. It is important

to reduce stress before curing. Freezing of concrete before the curing is complete can

seriously hamper the process of hydration. This can also decrease the concrete strength

and weaken and damage the concrete.


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Creeping is described as constant deformation of a material owing to internal stress

taking place in the material. The amount of reinforcement of concrete structures ensures

minimal shrinkage, creep and cracking.

These general concrete properties of concrete are taken care of during building of

concrete. Depending upon the end application, concrete is accordingly treated for

maximum strength and durability.

Good concrete has to satisfy performance requirement in plastic or green state and also

the hardened state.

The concrete should be workable and free segregation and bleeding.

In its hardened state concrete should be strong, durable, and impermeable.

It should have minimum dimensional changes.

The properties and performance of concrete are dependent to a large extend on the

characteristics and properties of the aggregates themselves. In general, an aggregate to be

used in concrete must be clean, hard, strong, properly shaped and well graded.

The aggregate must possess chemical stability, resistance to be abrasion, and to freezing

and thawing. They should not contain deterious material which may cause physical or

chemical change, such as cracking, swelling, softening or leaching.

One of the most popular concrete used is Portland cement, mineral aggregates and water.

Concrete often solidifies as the cement hydrates and glues all the other components

together. It has a high compressive strength and general uses of concrete include

pavements, fences, gates, walls and more. In old times, concrete was often referred to as

liquid stone. Sometimes external stabilizers are included to concrete to give it desired

characteristics. [6]

2.3 Applications of Concrete

Concrete has been used for construction since ancient times. Modern day concrete

application include dams, bridges, swimming pools, homes, streets, patios, basements,

balustrades, plain cement tiles, mosaic tiles, pavement blocks, kerbs, lamp-posts, drain

covers, benches and so on?. It is interesting to note that over six billion tons of concrete is


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produced each year, and is the second most widely used substance. Concrete is specific to

different applications like rebuilding, mending and construction. Concrete building

components in different sizes and shapes are also made before hand and later applied.

They include wall panels, doorsills, beams, pillars and more. Post-tensioned slabs is a

preferred method for industrial, commercial and residential floor slab construction. Ready

mixed concrete is durable and hard wearing and is used for variety of applications owing

to its crack-resistance and durability. Situ concrete is cast in place, on site. Precast

concrete finds application in concrete certain walls, exterior cladding and structural walls,

as it monolithic and can be easily used for two-way structural systems. It is also

adjustable to post tensioning and easily adapts to any building shape.

Controlled-density fill is used as structural fill, foundation pillar, pavement base an pipe

bedding. It is also known as flowable mortar.

The life expectancy of concrete flooring materials is much more than other flooring

material. It is used to enhance concrete applications and to add colour and texture to

interiors, driveways, pathways and patios.

Fiber cement is made using a mixture of sand, cellulose fibers and cement. It has a wood-

like appearance, is durable and used for decorative shapes and trim application.

Vegetative roofs are used in residential societies, office buildings, hospitals, schools,

recreational facilities, shopping centers and airports.

Concrete is used to provide prolonged building benefits by functioning as thermal mass,

acoustical barrier and durable structure.

Other Applications

Beams, drain tiles, piers, steps, Post, Beam and Deck ,Pilasters and round column forms

Brickledge application, High Performance Admixtures ,Masonry ,Soil solidification. [9]

2.4 Types of cement

1. Ordinary Portland cement Ordinary Portland cement 33 Grade-Is 269: 1989 Ordinary Portland cement 43 Grade-Is 8112: 1989 Ordinary Portland cement 53 Grade-Is 12269: 1987


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2. Rapid Hardening Cement -Is 8041: 19903. Extra Rapid hardening Cement - _4. Sulphate Resisting Cement -Is 12330: 19885. Portland Slag Cement -Is 455: 19896. Quick Setting Cement -Is _7. Super Sulphated Cement -Is 6909: 19908. Low Heat Cement -Is 12600: 19899. Portland Pozzolana Cement -Is 1489 (Part I) 1991 (fly ash based)

-Is 1489 (part II) 1991 (Calcined Clay

based)

10.Air Entraining Cement - _11.coloured Cement: White Cement -Is 8042: 198912.Hydrophobic Cement -Is 8043: 199113.Masonry Cement -Is 3466: 198814.Expansive Cement - _15.Oil Well Cement -Is 3466: 198816.Rediset Cement - _17.Concrete Sleeper grade Cement -IRS-T 40: 198518. High Alumina Cement -Is 6452: 198919.Very High Strength Cement [1]2.5 AdmixturesAdmixture are the materials other than the basic ingredients of concrete cement,water,

and aggregate; added to the concrete mix immediately before or during mixing to modify

one or more of the specific properties of concrete in the fresh or hardened state. [2]


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Table2.1 Common types of concrete admixtures

Admixture Function Typical compound Applications Disadvantages

Accelerator i. More rapid

gain of strength

ii. More rapid

stting

Calicium chloride

Sodium sulphate

Sodium aluminate

Sodium silicate

Sodium carbonate

Potassium hydroxide

i. Normal rate of

strength at low t

ii. Shorter

stripping times.

iii. Plugging of

pressure leaks

iv. sprayed

concreting

i. possible

cracking due to

heat evolution.

ii. Possibility of

corrosion of

embedded

reinforcement

Set-retarders Detalyed setting Hydroxylatedcarboxylic

acids, sugers

i. Maintain

workability at

high tii. Reduce rate of

heat evolution

iii.Extend placing

times

May promote

bleeding

Water-reducing

accelerator

Increased

workability with

faster gain of

strength

Mixture of calcium

chloride and

lignosulphonate

Water-reducers

with faster

strength

development

Risk of

corrosion

Water-reducing

Retarders

Increased

workability and

delayed setting

Mixture of sugers or

Hydroxylatedcarboxylic

acids and

lignosulphonate

Water-reducers

with slower loss

of workability.

Air-entraining

agents

Entrainment of

air into concrete

Wood resins, fasts,

lignosulphonate

Increase

durability of frost

without

increasing cement

content, cellular

concrete

Carefull contol of

air content and

mixing time

necessary

Water-proofers i. prevention of

water from

entering

capillaries of

concrete

Potash soaps,

butylstearate petroleum

waxes

Reduce

permeability,

Reduce surface

staining,

Watertighteness


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ii. Reduced

permeability of

concrete

of structures

without using

very low w/c ratio

plasticizers

(Water-reducing)

Increased

workability

Calcium and sodium

lignosulphonate

i. Higher

workability withstrength

unchanged

ii. Higher strength

with workability

unchanged

iii.Less cement

for same strength

and workability

Retardation at

high dosagesTendency to

segregate

Premature

stiffening under

certain conditions

Super plasticizers

Super-water-

redusers

Geatly

increseased

workability

Sulphonate

malamineformaldehyde

resin, Sulphonated

naphthalene-

formaldelyde resin,

Mixtures of saccharates

and acid amides

i. Water-reducers,

but over a wide

range

ii. Facilitae

production of

flowing concrete

Tendency to

segregate

May increase rate

of loss of

workability

2.6 Types of aggregate

2.6.1 Lightweight aggregate

The lightweight aggregates having unit weight up to 12KN/m3

are used to manufacture

the structural concrete and masonry blocks for reduction of self-weight of structure.

Light weight aggregate can be classified into two categories namely natural light weight

aggregates and artificial light weight aggregates. [2]

Natural lightweight aggregate:

Pumice

Datomice

Scoria


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Volcanic cinders

Sawdust

Rice husk

Artificial light weight aggregate:

Artificial cinders

Coke breeze

Foamed slag

Bloated clay

Expanded shale and slate

Sintered fly ash

Exfoliated vermiculite

Expanded partite

Thermo Cole beads

2.6.2 Normal weight aggregateThe commonly used aggregates; sand and gravels, crushed stone which have specific

gravities between 2.5 to 2.7 produced concrete with unit weight ranging from 23 to 26

KN/m3 and crushing strength at 28 days between 15 to 40 Mpa. [2]

2.6.3 Heavyweight aggregate

Some heavyweight aggregate having specific gravities ranging from 2.8 to 2.9 and unity

weights from 28 to29 KN/m3 such as magnetite (Fe3O4), and barites(BaSO4) and scarp

iron are used in the manufacture of heavy weight concrete which is more effective as

radiation shield. Concrete having unit weight of about 30KN/m3, 36KN/m3

and56KN/m3 can be produced by using magnetite, barites and scarp iron, respectively.

The compressive strength of these concrete is of the order of 20 to25 Mpa. The cement-aggregate ratio varies 1:5 to 1:9 with a water-cement ratio between 0.5 to 0.6. The

produce dense and crack-free concrete. The main drawback with these aggregates is that

they are not suitably graded and hence it is difficult to have adequate workability without

segregation.


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2.6.3.1Characteristics of heavy aggregate Structural properties like strength and stiffness Resist to abrasion With the aggregate react with the hydrated Portland cement paste. The thermal conductivity of the aggregate might be an issue in lightweight

concrete used for insulation, and the coefficient of thermal expansion of the

aggregate also is issue of the pcc will be subjected to a large range of service

temperature.

The roughness or smoothness of the aggregate plays a role in the workability offresh pcc.

The gradation of the aggregate is also of some importance.

According to size of aggregate are divided into two types as follows:

a. Fine aggregate

It is the aggregate most of which passes through a 4.5 mm IS sieve and contains only so

much coarse material as is permited by the specifications. Sand considered to have a

lower size limit of about 0.07mm. For increased workability and for economy as

reflected by use of less cement, the fine aggregate should have a rounded shape. The

purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a

workability agent. .

b. Coarse aggregate

The aggregate most of which are retained on the 4.75 mm IS sieve and contain only so

much of fine materials ar is permitted by the the specifications are termed coarse

aggregates. As with fine aggregate, for increased workability and economy as reflected

by the use of less cement, the coarse aggregate should have a rounded shape. Even

though the definition seems to limit the size of coarse aggregate, other considerationsmust be accounted for. When properly proportioned and mixed with cement, these two

groups yield an almost voidless stone that is strong and durable. In strength and

durability, aggregate must be equal to or better than the hardened cement to withstand the

designed loads and the effects of weathering. It can be readily seen that the coarser the

aggregate, the more economical the mix. [2]


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2.7 Fresh concrete

2.7.1 Introduction

The performance requirements of hardened concrete are more or less well defined with

respect to shape and strength. To achieve these objectives economically, the fresh

concrete, in addition to have suitable composition in terms of quality and quantity of

cement, aggregate and admixtures, should satisfy a number of requirement form the

mixing stage till is transported, placed in formwork and compacted. The requirement may

be summarized as follows.

(i) The mix should be able to produce a homogeneous fresh concrete from theconstituent materials of the batch under the action of the mixing forces.

(ii) The mix should be stable, in that it should not segregate duringtransportation and placing when it is subjected to forces during handling

operations limited nature

(iii) The mix should be cohesive and sufficiently mobile to be placed in theform around the reinforcement and should be able to cast into require

shape without losing continuity or homogeneity under the available

techniques of placing the concrete at a particular job.

(iv) The mix should be amenable to proper and thorough compaction into adense, compact concrete with minimum voids under the existing facilities

of compaction at the site.

2.7.2 Workability

The diverse requirements of mixability, stability, transportability, placeability and

compactibility of fresh concrete are referred to as workability. The workability of fresh

concrete is thus a composite property. We can define workability as that property of

freshly mixed concrete or mortar which determines the homogeneity with which it can be

mixed, placed, and compacted. Every job requires a particular workability. The concrete

which is considered workable for mass concrete foundation is not workable for concrete

to be used in roof construction and vice-versa.


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Sometimes the terms consistency and plasticity are used to denote the workability of a

concrete mix. The consistency of the mix really means the wetness of the mix, and a

wetter mix need not have all the above desired properties.

Factor affecting workability:

Water content: Water content in a given volume of concrete, will significant influences

on the workability. The higher the water content per cubic meter of concrete, the higher

will be the fluidity of concrete, which is one of the important factors affecting

workability.

Mixing proportion: Aggregate/cement ratio is an important factor influencing

workability. The higher agg/cement ratio, the leaner is the concrete.

Size af aggregate: The bigger the size of the aggregate, the less in the surface area and

hence less amount of water is required for wetting the surface and less matrix or paste is

required for lubricanting the surface to reduce internal friction.

Shape of aggregate: The shape of aggregates influences workability in good mesure.

Surface texture: The influence of surface texture on workability is again due to the fact

that the total surface area of rough textured aggregate is more than the surface area of

smoof rounded aggregate of same volume.

Grading of aggregate: This is one of the factors which will have maximum influence on

workability. A well graded aggregate is the one which has least amount of voids in a

given volume.

Use of admixtures: Of all the factor mentioned above, the most important fact which

affects the workability is the use of admixture.[1]

2.7.3 Shrinkage

The concrete is always subjected to changes in volume which affect long-term strengthand durability, this change in volume cause cracks in concrete. One of the important

factors that contribute to the cracks in concrete is that due to shrinkage.

Two types of shrinkage are recognized, namely plastic and drying shrinkage.


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-Plastic Shrinkage: the hydration of cement causes a reduction in the volume of system of

cement plus water to an extent of about 1 per cent of volume of dry cement. This

contraction is plastic shrinkage

-Drying Shrinkage: the shrinkage that takes place after the concrete has set and hardened

is called drying shrinkage and most of it takes place in the first few months.

2.7.4 Creep

The increase in strain in concrete with time under sustained stress is termed creep. The

shrinkage and creep occur simultaneously and they are assumed to be additive for

simplicity. When the sustained load is removed, the strain decreases immediately by an

amount equal to elastic strain at the given age. This instantaneous recovery is then

followed by gradual decrease in strain, called creep recovery which is a part of total creep

strain suffered by the concrete.

The rate of creep decreases with time and time the creep strains attained at a period of

five years are usually taken as terminal values. While 80 to 85 per cent shrinkage strains

occur in six months, only about 75 per cent of creep strains occur in twelve months. All

the factors which influence shrinkage influence creep also in similar way.

2.7.5 Advantages and disadvantages of concrete

a. advantages:

Concrete is economical in the long run as compare to other engineering materials.

Concrete possess a high compressive strength, and the corrosive and the weathering

effects are minimal.

Concrete can even be sprayed on and filled into fine cracks for repairs by the granting

process.The concrete can be pumped and hence it can be laid in the difficult positions

also. It is durable and fire resistant and requires very little maintenance.b.Disadvantages:

Concrete has low tensile strength and hence cracks easily. Therefore concrete is to be

reinforced with steel or meshes.

Fresh concrete shrinks on drying and hardened concrete expands on wetting.


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Concrete under sustained loading undergoes creep resulting in the reduction of prestress

in the prestressed concrete construction.

Concrete expands and contracts with the change in temperature.

Concrete is not entirely impervious to moisture and contains soluble salts which may

cause efflorescence.

Concrete is liable to disintegrate by alkali and sulphate attack.

Lack of ductility inherent in concrete as material is disadvantageous with respect to

earthquake resistant design. [2]

2.8 Behavior of hardened concrete

The behavior of hardened concrete can be characterized in terms of its short-term

(essentially instantaneous) and long-term properties. Short-term properties include

strength in compression, tension, bond, and modulus of elasticity. The long-term

properties include creep, shrinkage, behavior under fatigue, and durability characteristics

such as porosity, permeability, freeze-thaw resistance, and abrasion resistance

2.8.1 Strength

The strength of concrete depends on a number of factors including the properties and

proportions of the constituent materials, degree of hydration, rate of loading, method of

testing and specimen geometry.

The properties of the constituent materials which affect the strength are the quality of fine

and coarse aggregate, the cement paste and the paste-aggregate bond characteristics

(properties of the interfacial, or transition, zone). These, in turn, depend on the macro-

and microscopic structural features including total porosity, pore size and shape, pore

distribution and morphology of the hydration products, plus the bond between individual

solid components. Concrete composition limits the ultimate strength that can be obtained

and significantly affects the levels of strength attained at early ages. Two dominant

constituent materials that are considered to control maximum concrete strength are coarse

aggregate and paste characteristics. The important parameters of coarse aggregate are its

shape, texture and the maximum size. Since the aggregate is generally stronger than the

paste, its strength is not a major factor for normal strength concrete; However, the


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aggregate strength becomes important in the case of higher-strength concrete or

lightweight aggregate concrete. Surface texture and mineralogy affect the bond between

the aggregates and the paste as well as the stress level at which microcracking begins.

The surface texture, therefore, may also affect the modulus of elasticity, the shape of the

stressstrain curve and, to a lesser degree, the compressive strength of concrete. Since

bond strength increases at a slower rate than compressive strength. Tensile strengths may

be very sensitive to differences in aggregate surface texture and surface area per unit

volume. Using the aggregates for the mix proportions of high strength concretes, they

also found close correlations between the mean compressive strengths of the aggregates

and the compressive strength of the concretes, ranging from 35 to 75 MPa (5,000 to

10,700 psi), at both 7 days and 28 days of age. The mean compressive strength of the

aggregate is calculated as:

22is the mean compressive strength of aggregate

V is the volume of a single aggregate determined using Archimedes's principle after the

over dried weight is measured

Pis the maximum load applied on a single aggregate

his the distance between the two opposite load points of P

In a study by Lindgard and Smeplass [1993] six aggregate types with different strength

and rigidity were tested: dehydrated bauxite, quartzite, quartz-diorite (as reference),

gneiss/granite, basalt and limestone. All the aggregates except gneiss/granite were

crushed. Fig. 2.1. shows the effect of the aggregate type on compressive strength. The

difference between the highest and the lowest strengths is approximately 40%. The

authors noted, however, that the bauxite and the basalt aggregates were porous and

capable of absorbing significant amounts of mixing water, thus reducing the effective

W/CM from 0.30 to 0.24 and 0.27 respectively.


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Figure. 2.2 Stress-strain relationship for concrete

An equation representing the stress and stain curve completely should satisify the

following conditions:

i. at=0, =0 iii.at=f, =uii.at=o, =o

Figure 2.3 Different modulus of alacticity

Strain

Initial

tangent

A Tangent

B

Secant

strain

o o

fo

ff

Stress

Stress


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2.9 Light concrete

2.9.1 Definition

There are differing definitions for concretes that can be produced with lightweight

aggregates. Low-density concrete generally is produced with partite or vermiculite

aggregates, rarely exceeds (800 kg/m3). Structural lightweight concretes are typically

produced with expanded shales, clays, slates and slag. They can also be made with

pumice or scoria, which are naturally occurring volcanic aggregates. By definition,

structural lightweight concretes have a minimum compressive strength of (17.2 Mpa) and

an air-dried unit weight of (1,440 to 1,850 kg/m3). Moderate strength concretes fall

somewhere in between low-density and structural lightweight concrete. For comparison,

normal-weight concretes have a typical dry unit weight of (2,300 to 2,400 kg/m3).

Advantages of using lightweight aggregates

The primary advantage of using lightweight aggregates to precasters is the reduction of

product weight. Reduction in weight can lead to improved economy of structural

components because there will be less dead load for the structure to support.

Also, as mentioned previously, this may significantly affect the way in which products

can be shipped..

Another reason to consider using lightweight aggregates is that sometimes the dead load

of a product is near or above the capacity of the crane being used at a plant.

With lightweight aggregates, it may be possible to reduce the weight of the product so

that special cranes would not be necessary, or to produce larger sections than would be

possible with normal-weight concrete. Also, a reduction in crane movements may be

realized since longer reaches are possible with lighter loads.

Lightweight aggregates can also provide unique and potentially useful properties to

concrete besides reduced weight.

Lightweight concrete is thermally efficient. With warmer walls, there is less risk of

condensation. Lightweight concrete is fire-resistant. Because lightweight aggregates have

already been pre-fired, they are stable and do not decompose in high temperatures. This is

ideal for building components or refractory products.


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Lightweight concrete absorbs energy well. With the addition of fiber reinforcement and

even foaming agents, an extremely lightweight concrete could be produced and used for

such products as highway impact attenuators or sacrificial blast-resistant barriers.

With reduced weight, lightweight concrete will have a correspondingly reduced

hydrostatic pressure on formwork. This is useful when casting large, custom products.

Also, water that has been absorbed into the porous structure of lightweight aggregates is

said to provide additional water for internal curing. [5]

2.9.2 Quality control

To assure uniform quality, manufacturers should ensure that gradations and dry, loose

unit weight of the lightweight aggregates are consistent. Reports including this data can

usually be obtained from the aggregate supplier. If this is not the case, plant personnel

should do the tests themselves. Variation in either the aggregate gradations or the dry,

loose unit weight generally requires adjustments to the mix proportions in order to

produce uniform concrete. In addition, both unit weight and slump testing of the fresh

concrete should be performed frequently in order to verify consistency of the mix

constituents and the concrete itself. Slumps should be as low as possible while remaining

sufficiently easy to place, consolidate and finish. [5]

2.9.3 Concrete Strength

Lightweight concretes generally have what is called a strength ceiling. This is the

maximum compressive or tensile strength a certain mix can obtain despite improvements

to the cementations materials. This limiting strength is dependent on the strength of the

lightweight coarse aggregate and/or the quality of the contact zone and bond between the

aggregate and the surrounding cement paste. It is possible to achieve a slight increase in

strength by reducing the maximum size of coarse aggregates. Given that these limits

exist, it should be noted that structural lightweight concrete strengths compare favorably

with that of normal-weight concretes in the 3,000 to 5,000 psi-range. [5]


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2.9.4 Moisture Contents

Highly absorptive lightweight aggregate should be wetted at least 24 hours prior to use,

allowing time for the porous aggregate to become fully saturated. Wetting aggregate may

be a logistical challenge depending on the weather, with freezing a possibility in cold

weather and moisture loss in the hot weather. However, one benefit of wetting is that it

helps keep the aggregate particles from segregating during handling.

It is not recommended that dry lightweight aggregate be directly batched and mixed

because the aggregate particles can continue to absorb water from the mix. This can

cause the mix to segregate or stiffen before it can be placed.

Because of the high variability of aggregate moisture contents, water-cement ratios are

generally not specified for lightweight concretes. Calculation of water-cement ratios is

hampered by the uncertainty of the total amount of water contained in the aggregates. [5]

2.9.5 Production considerations

It may be necessary to extend mix times for lightweight concrete compared with

conventional concrete to ensure that all of the mix constituents are properly mixed.

Greater variations in workability should be expected, compared with conventional

concrete with the same slump. Along those same lines, the amount of air-entraining

admixture necessary to produce a constant amount of air content could also vary widely.

Consult your admixture supplier for more information.

Depending on the porosity and the degree of the aggregate angularity, the concrete could

be more difficult to place and finish. In some cases it is possible for the aggregate and the

other mix constituents to separate, allowing the lightweight aggregate particles to float

toward the concrete surface. Overworking the concrete can also cause the mix to

segregate. This situation can be remedied by adjusting the aggregate gradation to reduce

the size of the larger aggregates, adding natural sand or other filler materials. Although

this is the opposite problem encountered with self-consolidating concrete, where the goal

is to keep aggregates suspended in the mix, it is likely that similar rheological mix

enhancements can help stabilize the mix.


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As with other conventional concrete mixes, ease of placement can be enhanced by

including air entrainment if not already a part of the mix design. Air entrainment also

reduces bleeding and segregation and improves durability.

Finally, lightweight concretes may have an increased tendency to experience drying

shrinkage and creep (strain increase over long periods of time with a constant load).

Steam curing effectively reduces the likelihood of both drying shrinkage and creep.

The decision to use lightweight aggregates in order to economize transportation costs is

one that requires you to take into account many variables. Although not every project is a

good candidate for the use of lightweight aggregate, some projects definitely are. In

addition, some of the more unique properties that lightweight aggregates offer could

enhance specialized products, whether they are fire-resistant, blast-resistant or other

insulating products. Its good to keep your options open and be ready to take advantage

of opportunities that allow you to boost your plants income. Ultimately, only you can

decide if your products should lose some weight. As with our own diet, if you wish to

lose weight, you must be patient and should expect some trial-and-error in finding the

right combination of what works best. [5]

2.10 Normal concrete

2.10.1 Characteristics of normal concrete

Normal concrete or ordinary concrete is a mixture of fine aggregate, water, cement and

coarse aggregate. All components of ordinary concrete are mixed together until they

become a paste, which surrounds the voids in aggregate during its fresh concrete.

Compressive strength depends upon water, the cement ratio and the quality of the cure

cycle. According to the ACI code, the compressive strength of the concrete is obtained

from the standard test cylinder 6-in(150mm) diameter by 12-in(300mm) high measured at

7,14 and 28 days of age before testing. After 28 days of water curried or placed in aconstant temperature room to obtain 100% of humidity.

For normal weight concrete, the value of shrinkage is 0.003 when the specimen after

casting is submerged in water not less than 7 days. To avoid high shrinkage in the

concrete, we have to consider proportional size of aggregate, water-cement ratio and

humidity.[4]


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2.10.2 Advantages & the disadvantages of normal concrete

As a construction material Concrete has the following advantages:

1. Concrete can handle the compression stresses 10 times more than the tension and the

most of loads in our life is compression.

2. Concrete is a brittle material which gives the advantage to make a rigid structure.

3. Easy to handle over specially now there is plants that give you ready mix concrete.

Disadvantages:

1. Concrete is weak in handling tension.

2. Because concrete is a brittle material the strength upon shear must be checked.

3. Needs another material to reinforce it against excessive shear and tension. [5]

2.11 Heavy concrete

2.11.1 Characteristics of heavy concrete

A heavy material such as concrete is capable of buffering a large part of the free heat

gains, such as solar radiation and heat. Concrete can therefore decrease energy

consumption as well as improve thermal comfort. A taskforce of three principal

organisations related to concrete construction has investigated and documented the

advantages of heavy buildings. Energy balance calculations were undertaken for

buildings of heavy and lightweight construction in various European climates, for both

residential and office circumstances. The results show that a solid residential building

requires 2-7% less bought energy for heating compared to a building of lightweight

construction. This has significant economical and environmental impacts. Where cooling

is required, the energy savings are even larger and cooling facilities can be avoided

altogether in many heavy buildings. The advantages are further increased if the effect of

thermal mass is actively taken into account in the building design. An information

database of the role of concrete in energy efficient buildings including a portfolio of

energy efficient concrete buildings has been compiled. [9]


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2.11.2 Compressive strength

The inclusion of heavy aggregate in concrete does not increase the concrete strength as

previously expected to reflect their characteristics of higher strength and density. This

can attribute to the cracking types, which takes place as the crack propagating in the

paste. This can observed by testing results of compressive strengths that an increase of

iron ore and iron shot amount makes a little growth in concrete strength. In fact an

inclusion of 40% of heavy aggregate in volume only raises the compressive strength up to

5% higher than the strength of regular concrete.

To investigate the effect of metallic aggregate on the mechanical properties of heavy

concrete, the mixture of concrete are designed with a unique water to cement ratio W/C

equal to 0.48, and 0%,1o%, 20%, 40% and 48.8% of metallic aggregate in volume in the

testing program. The latest mixture has been used in same nuclear power plants. It is

noted that the amount of iron shot is fixed at 9.2% for all mixture while the iron ore is

varied, therefore the unity weight of concrete increase with the increase of metallic

aggregate content. And it is noted that some admixtures such as water reducers and

superplastizer and not advisable in the mixture of heavy concrete in order to ascertain to

the minimum requirement of water which supplies sufficient amount of hydrogen atoms.

[9]

2.11.3 Mixing and curing

The procedure for mixing heavy concrete is similar to ordinary concrete. In a typical

mixing procedure, iron shot are mixed first, followed by cement and then water, as some

as mixing of regular concrete. However due to higher specific gravities of both iron ore

and iron shot, too much compacting vibration that can lead to segregation has to be

avoided. Trial mix for each mixture has been engaged until a good workability and

sufficient strength gain achieved. In the mean time air content for each mix, which could

provide useful data to figure out the amount of voids. All concrete specimens were cast in

molds for one day and then placed in water for 28 days prior to testing; the specimens for

cracking analysis were placed in air for another three days before the process of pre-

cracking and dying. [10]


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2.12 Concrete in road pavements

Some pavement designers assume "average concrete" properties in their calculations

without any information about which aggregates, cement, pozzolans, or mixture

proportions that the con- tractor will use later on the job. Concrete properties of particular

importance to pavement design are: E (Modulus of Elasticity), strength, thermal

expansion, shrinkage, creep, heat generation, and durability (physical and chemical

reactivity). A good pavement designer should also be a concrete expert.

At the AASHO Road Test, there were two distinctive failure modes. The very thin

pavements failed with continuous edge pumping that caused edge cracking that coalesced

into a longitudinal edge crack. The thicker pavements failed by joint pumping that caused

transverse cracking starting particularly in the traffic leave side of the joints. The data

from both were averaged together in the road test analysis to develop a performance

equation. Even so, of the 84 pavement test sections greater than 8 in (200 mm) in

thickness, only seven sections had a serviceability index of less than 4.0 at the end of the

testing. In fact, only three sections could actually be considered as having failed. Hence,

one can conclude that even though the AASHO data is the best that we have, it hardly

predicts failure of the thicknesses of pavement that are now being built. [10]


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Chapter 3. MATERIALS AND ANALYSIS

3.1 Materials

3.1.1 Ordinary Portland cement

The OPC used in this project was manufactured at MASHYUZA in CEMERWA factory,

BAMBURI in KENYA and HIMA in UGANDA. This kind of cement from

MASHYUZA made with three basic raw materials such as: lime stone, quartz and clay.

The two first are found at MASHYUZA quarry, the raw pulps concentration is: 70% of

lime stone; 155 of quartz and 5% of clay soil.

The cement samples produced was tested in national laboratory to determine its physical

properties such us fineness, setting time, standard consistency, soundness, density and

compressive strenght. The role of Ordinary Portland Cement is to bind materials together.

3.1.2 Aggregate

The aggregates are used primarily for the purpose of providing bulk to concrete, to

increase the density of the resulting mix. The aggregate is frequently used in two or more

sizes. The most important function of the fine aggregate is to assist the mixture, in

producing workability and uniformity to fresh concrete. It also assists the cement paste to

hold the coarse aggregate, particles in suspension.

The source of aggregate is not difficult in this country. That sand was free from deterious

materials.

Take a sample of different aggregate from different area in RWANDA and results from

national laboratory are: GIHARA, BUGESERA, GITI CYINYONI, KARONGI,

MUKUNGWA, GATUMBA, MUSANZE and RUSINE River.


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Table 3.1 Quality of aggregate

Aggregate Specific gravity Water

absorption (%)

bulk density

(g/m3)

uncompacted

bulk density

(g/m3

)GIHARA 2.71 0.4 1.64 1.48

BUGESERA 2.67 0.14 1.62 1.48

GITI

CYINYONI

2.64 0.32 1.61 1.45

KARONGI 2.92 0.52 1.71 1.51

MUKUNGWA 2.70 1.62 1.57 1.4

GATUMBA 2.89 0.3 1.64 1.52

MUSANZE 2.97 0.2 1.75 1.52

According to their unit weight are classified flowing:

Normal weight aggregate, Lightweight aggregate and Heavy weight aggregate.

AndAccording to size of aggregate are divided into two types as follows:

fine aggregate and coarse aggragate.

3.1.4 Water

Water is used in concrete to react with cement and thus causing it to set and harden, also

facilitates mixing, placing and compacting of fresh concrete. It is also used for washing

the aggregates and for curing purposes. Water used for both mixing and curing should be

free from injurious amount of deterious materials. The quality of water is important

because impurities in it may interface with setting of the cement may adversely affect the

strength of concrete or cause staining of its surface. And the quality of water is covered

by clause saying that water should be fit for drinking. The source of that water used in

this project was water distributed by ELECTROGAZ


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3.1.5 Admixture

3.1.5 1.Definition

Admixture are the materials other than the basic ingredients of concrete, cement, water

and added to the concrete mix immediately before or during mixing one or more of the

specific properties of concrete in the flesh or hardened state. [2]

3.1.5 2 Sika latex

Sika latex is generally added to the clean mixing water within the range 1:1-1:4. for all

application a part from sprayed on renders a bonding coat of sika latex: water(1:1) mixed

with fresh cement and sand (1:1) should be brushed into the prepared surface. Sub

sequent mortar application must be carried out whilst the bonding coat is still wet.

Application and limitation

Rendering, floor toppings should be allowed to cure correctly. Protect the appliedmortar from frost exposure.

Avoid excessive air-entrainment through over mixing. Do not use neat sika latex or sika latex with water as bonding agent. Especially

always add cement and sand.

Minimum application temperature is +5 C Clean all tools and application equipment with water immediately after use.

3.1.5 3. Sikatop

Designed for use on concrete, mortar, and masonry substates. Easily applied by brush,

roller, or spray equipment. This fine textured, abrasion-resistant coating is used for

protection against deicing salts and for damp proofing/water proofing.


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3.2 ANALYSIS

3.2.1 Ligh concrete

3.2.1.1 Properties of structural

Concrete can be produced with density which are 25 to 40 percent lower but with

strengths equal to the maximum normally achieved by ordinary concrete.

Characteristics of lightweight concrete

Low density: the density of the concrete varies from 300 to 1200 kg/m3.

High strength: cellular concrete has high compressive strength in relation to its density.

The strength of aerated cellular concrete is about 15 to 20 percent of its compressive

strength. Due to much higher strength to mass ratio, the cellular concrete floor and roof

slabs are approximately one quarter the weight of normal reinforced concrete slabs.

Thermal insulation: the insulation value of light weight concrete is about 3 to 6 times that

of bricks and about 10 times that of other concrete. A 200 mm thick and wall of aerated

concrete of density 800kg/m3has the same degree of insulation as a 400 mm thick brick

wall of density 1600kg/m3.

Fire resistance: light weight has excellent fire resisting properties. Its thermal

conductivity makes its suitable for protecting other structures from the effects of fire.

Shrinkage: light weight concrete is subjected to shrinkage but to a limited extend.

Sound insulation: sound insulation in cellular concrete is normal not as good as in dense

concrete.

Repairability: light weight products can be easily sown, cut drilled or nailed. This makes

construction easier.Speed of construction: with the adoption of prefabrication is possible to design the

structure on the concept of molecular which ensure of faster rate of construction.

Economy: due to light weight and high strength to mass ratio of cellular concrete

products, their use results in lesser consumption of steel.


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Quality control: a better quality control is exercised in construction of structure with light

weight concrete products owning to the use of factory made units.

3.2.1.2 Applications of lightweight concrete

Different uses of light weight concrete can summarized as follows:

As load bearing masonry wall using cellular concrete blocks As precast floor and roof panels in all types of buildings As a filler wall in the form of precast reinforced wall panels in multistoried

building.

As partition walls in residential, institutional and industrial building. As in situ composite roof or floor slabs with reinforced concrete grid beams. As precast composite wall or floor panels, and As insulation cladding to exterior walls of all types of buildings, particularly in

office and industrial building.

These are many advantages of having low density.

-It helps in reduction of dead load

-It increases the progress of building and lowers haulage and handling costs.

-It will result in considerable economy.

-Lower thermal conductivity

And one of the disadvantages of conventional concrete is the high self weight of

concrete.

Basically there is only one method for making concrete light.

This is achieved in actual practice by 3 different ways.

By replacing the usual mineral aggregate by cellular porous or light weightaggregate.

By introducing gas or air bubbles in mortar. This known as aerated concrete. By omitting sand fraction from aggregate. This is called no-fines concrete.


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3.2.2 Normal concrete

Normal concrete or ordinary concrete is a mixture of fine aggregate, water, cement and

coarse aggregate. Density of normal concrete is in the order of 22 to 26 KN/m3.

Application of normal concrete

As load bearing masonry wall using concrete blocks As precast floor and roof panels in all types of buildings As a filler wall in the form of precast reinforced wall panels in multistoried

building.

As partition walls in residential, institutional and industrial building. As in situ composite roof or floor slabs with reinforced concrete grid beams. As precast composite wall or floor panels.

3.2.3 Heavy concrete

Heavy concrete having unit weight of about 30KN/m3

to 57KN/m3

and produced by using

heavy weight aggregate.

Application of heavy concrete


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The most common use of high-strength concrete is for construction of high-rise

buildings. At 969 ft (295 m), Chicago's 311 South Wacker Drive uses concrete with

compressive strengths up to 12,000 psi (83 MPa) and is the tallest concrete building in

the United States. [7]

Heavy aggregate is some times desired when structure such as pcc walls and floor are

constructed and radiation shielding is important. One common example is in hospitals

where X-Ray facilities might be enclosed in heavy weight pcc walls so that the radiation

used there in does not escape and pose a threat to other building occupants. A few

examples of heavy weight aggregate are iron slugs and steel bar bearings.

3.2.4 Comparison of light , narmal and heavy concrete

By definition lightweight concrete is lighter ther normal-weight concrete. This 25 to 35%

weight reduction affords architects and engineers considerable design flexibility and

substantial cost savings to the owner. The reduction in unit weight provides less dead

load, resulting in improved seismic structural response and permits the use of longer

spans, thinner sections, and smaller size structural members, less reinforcing steel and

less costly foundations. Because lightweight concrete has greater tire resistance than

normal-weight concrete, required tire ratings are achieved with thinner floor sections,

further reducing the dead load and enhancing the advantages. All of this adds up to more

efficient structural systems with less material being used, which in turn improves the

long-term sustainability of the concrete industry and the environment.

Concrete is made lighter primarily by replacing the "heavy" normal weight aggregate

with lightweight aggregate and by maintaining air entrainment at about 6%.

The primary difference between high-strength concrete and normal-strength concrete

relates to the compressive strength that refers to the maximum resistance of a concrete

sample to applied pressure. Although there is no precise point of separation between

high-strength concrete and normal-strength concrete, the American Concrete Institute

defines high-strength concrete as concrete with a compressive strength greater than 6000

psi (41 MPa)


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Table.3.1 Comparison of light , normal and heavy concrete

Light concrete Normal concrete Heavy concrete

Compressive

strength N/mm2on cubic samples

9 to 88 10 to 60 Greater than

60 up to 115

Density(KN/m3) 14.40 to 18.4 22.4-24.0 Greater than 25

Cost Cheap Medium Expensive

Aggreagate Lightweight aggr. Normal weight aggr. Heavy weight aggr.

Transport Easly (low weight) Difficult Difficult

Some reasons of

use

Insulation, and

reduction of the dead

load of structure

Normal use Protection against

eradiation, rigid

pavement of roads.


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Chapter 4: RESULTS AND DISCUSSION

Table 4.1 Availability of aggregate in Rwanda

Types of aggregates Quantity Examples Sources

Lightweight

aggregate

Medium Volcanic cinders,

Sawdust and

Rice husk

Northern province,

Western province,

carpentry workshop,

southern province

and eastern province

Normal weight

Aggregate

High Sand, gravel,

crushed stone,

coarse aggregate,

In all province

In all rivers

Heavy weight

aggregate

Low Crushed rock with

high density.

All province


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Table 4.2 Availability of concrete in RWANDA

Types of

concrete

availability Compressive

strength

Aggregates

used

Observation

Lightweight

concrete

Low - Volcanic

cinders

Some dont know

the different of

L.C and N.C and

they confuse plain

concrete& L.C.

Normal weight

concrete

More 99% 16.5 -25 Mpa Sand, Gravel,

crushed stone,

coarse

aggregate.

It has observed

that normal

concrete are more

used in all

province.

Heavy weight

concrete

low - crushed stone

(dolerite)

We need other

cement for

making heavy

concrete.


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4.1 Comparison of uses of lightweight concrete, normal concrete and

heavy concrete in RWANDA

I found that 99% of concrete used in RWANDA are normal concrete because of

availability of normal aggregate in all region of country, and is known by many people,

and are not very expansive. And other concrete are not known by many people and they

confuse plain concrete and light concrete. By example lightweight aggregate are available

in RWANDA but are not used in all construction use only in construction of road. But

they are an absence of cement used in heavy concrete in RWANDA. When you want to

use them there is one way of getting that cement, is to import in other countries have

successful for production of that cement or CIMERWA should produce cement that have

strength grade more than 32.5 especially for highter grade concretes, it means the use of

heavy concrete are very expensive.

4.2 Discussion

Data received from different companies show that they dont know the difference

between Lightweight concrete, Normal weight concrete and Heavy concrete. They name

concrete according to the quantity of cement used in mixing ratio of cement and

aggregate; when they use low quantity of cement in cement/aggregate ratio the concrete

produced is Lightweight concrete. And when they use more quantity of cement means

that concrete produced is Heavy concrete.

By example:

Lightweight concrete 1:3:5 Normal concrete 1:2:4 Heavy concrete 1:1:2

But all types of concrete used are Normal concrete, because they use normal weight

aggregate with at different mixing ratio and differents size;


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Chapiter 5 CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION

The research conducted during this work has increasing our understanding in several

areas related to the lightweight concrete, normal concrete and heavy concrete .

The conclusions that could be made from the results are:

Some site dont know the difference between light concrete, normal concrete and heavy

conrete.

They know that the type of concrete depends on the mixing ratio of cement and

aggregates; when use more quantity of cement means that heavy concrete, and when use

low quantity is lightweight concrete.

Lightweight concrete should be used in different areas in our contry because of

availability of lightweight aggregate in all area of RWANDA and are not expensive and

the compressive strength is not as great as ordinary concrete, but it weathers just as well.

Among its advantages are less need for structural steel reinforcement, smaller foundation

requirements, better fire resistance and most importantly, the fact that it can serve as an

insulation material!

Als heavy concrete should be used in our contry because of their advantages by example

some time they dont need to be reinforced,


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5.2 RECOMMENDATION

Analysis of light concrete, normal concrete and heavy concrete it helps different clients

to differenciate these three types of concrete and facilitate the selection of type of

concrete used.

It is recommended the Ministry of education to encourage the final year students by

helping them executing what they have discovered in order to improve our technology in

Rwanda.

It is recommended to the government authorities to sensitive the population on the use of

Light concrete as new building material for making walling blocks on the market

industry, since it might be cheap and easily made in the country.

In view of the following on some special concrete its recommended to be used in

development contries like RWANDA such us heavy concrete in order to reduce the

damaged roads cause damage to vehicles, reduce their fuel efficiency and lead to

passenger discomfort. The rigid pavements or the concrete roads, on the other hand,

provide smooth drive consistently over long period of time The bitumen roads, although

incur lower initial cost, end up costing more in comparison with concrete roads, on

account of higher maintenance requirements. The concrete roads offer special

advantages in city in terms of their capacity to withstand heavy traffic loads, long service

life and minimum maintenance costs.


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REFERENCES

[1]M.S SHETTY and S.CHAND(2005), Concrete Technology Theory and

Practice, Technical Advisor, MC Bauchemie Pvt Ltd

[2]ML GAMBHIR (1995),Concrete Technology, Second edition

[3]Neville A.M. (1963), Properties of Concrete Technology, Sir Isaac and Pitman sons

Ltd London.

[4]www.wikipedia.org/wiki/compressive strength (2007)

[5]e- mail [email protected]

[6]htt:/// www.cement.org/bosic/concrete products_histrenght.asp

[7]http://cr4.globalspec.com/thread/42583/Concrete-beams-for-ceiling

[8]http://www.tfhrc.gov/structur/hpc/hpc2/ack.htm[9]http://www.tfhrc.gov/pubrds/julaug98/concrete.htm

[10]http://www.spancrete.com/products.php


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APPANDICES


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m 2010 Ceet 26 Manirafasha Amos Gs20050571