CRITICAL STATE OF FLY ASH-BOTTOM ASH MIXTURE

MARWA A RAHMAN

A project report submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Civil – Geotechnics)

Faculty of Civil Engineering

Universiti Technologi Malaysia

DECEMBER 2010

iii

To my beloved father and mother

To my beloved husband and his family

To my dear brother

For their never ending care and support

Thank you for everything

iv

ACKNOWLEDGEMENT

Praise to Allah, the Most Gracious and Most Merciful, Who has created the

mankind with knowledge, wisdom and power.

Special thanks go to Professor Dr. Aminaton Marto for giving this

opportunity to work under her supervision and for sharing her great knowledge and

experience with me.

I would like to convey my deepest gratitude to all the staff of Geotechnical

Laboratory, Faculty of Civil Engineering, UTM. Appreciation is also extended to all

people who gave me heartfelt corporation and shared their knowledge and for giving

some of their valuable time.

.

Finally, I am deeply and forever indebted to my husband, parents, and my

brother for their love, spiritual support, and encouragement throughout my entire life.

Without them I would never come up to this stage.

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ABSTRACT

The burning of coal in the process of generating electricity, leads to the

production of solid waste such as the fly ash and bottom ash. Numerous studies had

been carried out to determine the mechanical properties of fly ash and also bottom

ash. An extension of these studies is necessary in order to explore further usage of

these ashes, in particular when mixed together in optimum percentage. The critical

state boundary surface of the soil or material is important to identify the limit of

stress imposed from various stress level and stress history. Hence, this study aimed at

developing the critical state boundary surface of a mixture of 60% fly ash and 40%

bottom ash by weight, is vital. The results obtained could be used as a guideline

when working in the future with coal ash mixture of the same mix ratio. The samples

used in this study were collected from Tanjung Bin power station in Johor, Malaysia.

The fly ash-bottom ash mixture used in this study had a liquid limit of about 22%

and behaved as non-plastic material. The mixture is classified as well-graded sandy

silt with specific gravity of about 2.36. From the compaction test it showed that the

maximum dry unit weight of this mixture is 14.54 kN/m3, achieved at 8.5% optimum

water content. The critical state parameters of the mixture obtained in this study are

λ= 0.032, κ = 0.013, ζ=0.035, N=1.85 and M=1.152. From the critical state

parameters obtained, the critical state boundary surface of fly ash- bottom ash

mixture (60:40% by weight) had been established.

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ABSTRAK

Pembakaran arang batu yang digunakan di dalam proses penjanaan kuasa

elektrik telah menyebabkan penghasilan sisa pepejal seperti abu terbang dan abu

dasar. Pelbagai kajian telah dijalankan untuk menentukan sifat mekanikal abu

terbang dan abu dasar ini. Lanjutan kepada kajian ini perlu dijalankan bagi mengkaji

dengan lebih mendalam kegunaan sisa-sisa abu ini terutamanya apabila di

campurkan bersama dalam peratus yang optimum. Sempadan permukaan keadaan

genting bagi tanah atau bahan adalah penting bagi menentukan had kepada tegasan

yang boleh dikenakan, yang mungkin bermula pada tahap dan sejarah tegasan

tertentu. Oleh itu, kajian ini yang dijalankan bertujuan untuk menghasilkan

sempadan permukaan keadaan genting bagi campuran abu terbang dan abu dasar

pada nisbah berat 60% abu terbang dan 40% abu dasar, adalah sangat penting. Hasil

keputusan daripada kajian ini boleh dijadikan sebagai panduan kepada kerja-kerja

yang melibatkan campuran abu arang batu dengan nisbah campuran yang sama pada

masa hadapan. Sampel kajian telah diambil dari stesen janakuasa Tanjung Bin di

Johor, Malaysia. Campuran abu terbang - abu dasar yang telah digunakan didalam

kajian ini mengandungi had cecair sebanyak 22% dan berkeadaan tidak plastik.

Campuran ini juga diklasifikasikan sebagai kelodak berpasir bergred baik dengan

nilai graviti tentu sebanyak 2.36. Hasil keputusan daripada ujian pemadatan pula

menunjukkan berat unit kering maksimum bagi campuran ini adalah sebanyak

14.54 kN/m3 yang telah terhasil pada nilai kandungan air optimum sebanyak 8.5%.

Parameter keadaan genting yang telah diperolehi dalam kajian ini adalah λ= 0.032,

κ = 0.013, ζ=0.035, N=1.85 dan M=1.152. Daripada parameter-parameter keadaan

genting yang diperolehi ini, sempadan permukaan keadaan genting bagi campuran

abu terbang - abu dasar (60:40% timbangan berat) telah dapat dihasilkan.

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TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Background of Studies 1

1.2 Problem Statement 4

1.3 Objectives of the Study 4

1.4 Scope of Study 5

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2 LITERATURE REVIEW 6

2.1 Introduction 6

2.2 Coal Ash 7

2.2.1 Fly Ash 8

2.2.1.1Class C Fly Ash 9

2.2.1.2 Class F Fly Ash 9

2.2.2 Use of fly ash in Highway Construction 10

2.2.2.1Fly Ash in Concrete Mixture 10

2.2.2.2 Fly Ash in Asphalt Pavements 11

2.2.2.3 Fly Ash in Embankment 11

2.2.3 Bottom Ash 13

2.2.3.1Bottom ash in Concrete Mixture 13

2.2.3.2Bottom Ash in Embankment 14

2.3 Fly Ash Bottom - Ash Mixture 14

2.3.1 Physical Properties of Fly Ash-Bottom Ash 15

Mixture

2.3.1.1 Grain Size Distribution 15

2.3.1.2 Atterberg Limit 16

2.3.1.3 Specific Gravity 16

2.3.2 Compaction 17

2.3.3 Shear Strength 18

2.4 Use of Fly Ash - Bottom Ash Mixtures 19

in Highway Construction

2.5 Critical State theory 20

2.5.1 Definition of state parameters 21

2.5.2 The state boundary surface 22

2.5.3 Critical Void Ratio 24

2.5.4 Critical State Parameters of Some Types 25

of Soil

2.5.5 Critical State of Fly Ash 27

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3 METHODOLOGY 30

3.1 Introduction 30

3.2 Testing Materials 32

3.3 Fly Ash –Bottom Ash Mixture Physical Tests 32

3.3.1 Grain Size Distribution 32

3.3.1.1 Sieve Analysis 33

3.3.2.2 Hydrometer Test 33

3.3.2 Atterberg Limit Test 34

3.3.2.1 Liquid Limit Test-Cone 35

Penetration Method

3.3.2.2 Plastic Limit Test 36

3.3.3 Specific Gravity Test 36

3.4 Compaction Test 37

3.5 Triaxial Test 38

3.5.1 Isotropic Consolidation Test 42

3.5.2 Consolidated–Undrained Triaxial 43

Compression (CU) Test

3.6 Data Analysis 44

4 RESULT AND DISCUSSION 45

4.1 Introduction 45

4.2 Physical Properties Tests 46

4.2.1 Particle Size Distribution 46

4.2.2 Atterberg Limits 47

4.2.2.1 Liquid Limit 47

4.2.2.2 Plastic Limit 48

4.2.3 Specific Gravity 48

4.2.4 Summary of Physical Tests Results 49

4.3 Compaction Test 50

4.4 Isotropic Consolidation Test 51

4.5 Triaxial compression Test 54

4.5.1 Stress Path and Critical State Line 57

4.5.2 Critical Void Ratio 62

x

4.5.3 Critical State Boundary Surface 64

5 CONCLUSIONS AND RECOMMENDATIONS 66

5.1 Conclusions 66

5.2 Recommendations 67

REFERENCES 69

Appendices A-J 72-113

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Critical state parameters of some soil types 27

3.1 Isotropic consolidation test series 42

3.2 Testing program for normally consolidated samples 43

3.3 Testing program for overconsolidated samples 44

4.1 Particle size distribution test results 46

4.2 Specific Gravity Values 49

4.3 Summary of physical tests results and soil classification 49

4.4 Results from standard (proctor) compaction test 51

4.5 The final critical state parameters 64

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 The Graphical Diagram of Coal Ash Generation 2

2.1 The top uses of CCPs in 2008 8

2.2 Grain size distribution curves of fly and 16

bottom ash mixtures

2.3 Compaction curves of ash mixtures 18

2.4 Critical state line and stress paths for undrained loading 21

on normally consolidated clay

2.5 Plots of triaxial tests results of CU and CD 23

2.6 The critical state boundary surface 24

2.7 Loading and unloading of fly-ash specimen 28

in Oedometer test

2.8 Stress path of normally consolidated fly-ash 29

3.1 Flow chart of Methodology 31

3.2 The sieves on the mechanical shaker 33

3.3 Cylinders for hydrometer test 34

3.4 Liquid limit test apparatus 36

3.5 Pycnometer were put in vacuum to remove the air 37

3.6 Standard compaction test apparatus 38

3.7 Triaxial Compression test on progress 39

4.1 Particle size distribution curve 47

4.2 Liquid limit test result 48

4.3 Compaction Curve for standered (proctor) test 50

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4.4 Specific volumes versus mean normal effective stress 52

from isotropic consolidation tests

4.5 Normal consolidation line 52

4.6 Swelling line 53

4.7 Recompression line from isotropic consolidation tests 54

4.8 Consolidated undrained compression test results 55

for normally consolidated sample

4.9 Consolidated undrained compression test results 56

for over consolidated sample

4.10 Failure points for CU compression tests on isotropically 57

consolidated specimens of all stress histories in 𝑞 − 𝑝′ space

4.11 Failure points for CU compression tests on isotropically 59

consolidated specimens of all stress histories in 𝑣 − 𝑝′ space

4.12 The critical state line in 𝑣 − 𝑙𝑛 𝑝′ space 59

4.13 Effective stress paths from CU test 60

of normally consolidated samples in 𝑞 − 𝑝′ space

4.14 Effective stress paths from CU test of over consolidated 61

samples in ee 'p/'p'p/q space

4.15 Effective stress paths from CU test of NC and OC 62

samples in ee 'p/'p'p/q space

4.16 Critical voids ratio line from undrained triaxial tests 63

on Tanjung Bin fly ash: bottom ash mixture

4.17 Critical state boundary surfaces from CU test 64

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LIST OF SYMBOLS

BS - British Standard

C.V.R - Critical Void Ratio

CCPs - Coal Combustion Products

CSL Critical State Line

CU - Consolidated Undrain

Gs - Specific Gravity

LL - Liquid Limit

MCC - Modified Cam Clay

NCL - Normal Consolidation Line

OCR - Over Consolidation Ratio

PI - Plasticity Index

PL - Plastic Limit

RL - Recompression Line

SL - Swelling Line

USCS - Unified Soil Classification System

wopt - Optimum Moisture Content

γd max - Maximum Dry Unit Weight

∆u - Change of Pore Water Pressure

σ3′ - Effective minor principal stresses

σ1′ - Effective major principal stresse

q - Deviator Stress

p′ - Mean Normal Effective Stress

M - The Slope of Critical State Line on The p'-q' Plane

𝑣 - Specific volume

- Intercept of Critical State Line with the 𝑣 − axis

xv

λ - The slope of normal consolidation line in 𝑣 − p′ space

ϕ’c - Critical Internal Friction Angle

ζ - The Slope of Recompression Line on The q-p'-Plane

N - Intercept of Normal State Line with the 𝑣 − axis

k - The Slope of Swelling Line on The q-p'-Plane

𝑒 - Void Ratio

H - The Slope of The Hvorslev Surface on The p'-q' Plane

% - Percentage

p′c - Effective Consolidation Stress

p′e - Equivalent Consolidation Pressure

B - Pore Pressure Coefficient

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Sieve Analysis Test 72

B Hydrometer Test 75

C Liquid Limit Test 81

D Specific Gravity Test 85

E Standard Compaction Test 87

F Apparatus of Triaxial Compression Test 90

G Sample Preparation 92

H Isotropic Consolidation Test 94

I Triaxial Compression Test 96

J Stress Path 108

CHAPTER 1

INTRODUCTION

1.1 Background

Coal-burning in the process of generating electricity, leads to the production

of solid waste such as fly ash, bottom ash, boiler slag and flue gas desulphurization

(FGD) materials (Vom Berg, 1998). During combustion in an electric power plant,

the first step is crushed the coal, then injected into the boiler furnaces, where the coal

is burned. The organic matter in the coal is burned off at once, whereas the

incombustible material melting and tends to fuse together to form ash. The coarse

particles of the ash is the bottom ash and boiler slag, settles at the bottom of the

boiler furnace. Fine particles, is fly ash, remain suspended in the flue gas stream

(Kim et al., 2006). Figure 1.1 shows the procedure of generating coal ash in power

plants. Electricity is one of the basic inputs required for the development of any

country. In India nearly 73% of installed power generation capacity is thermal, of

which about 90% is coal-based generation (Singh, 2005). In United States; over one-

half of the electricity is generated by burning coal. The large consumption of coal

generates a large volume of coal ash. In the US, the coal-burning power produced

last year about 70 million tons of coal more (ACAA, 2008).

2

Figure 1.1 The Graphical Diagram of Coal Ash Generation (EPA, 2005)

Such wastes are of the major concern for the electric power plants, because

they constantly need to expand the areas of solid waste disposal and this leads to

increased costs. This problem fast becomes a social problem since the expansion in

disposal area may become another environmental problem. EPA(2005) mentioned

that the solid wastes include (fly ash, bottom ash, boiler slag and flue gas

desulfurization (FGD) have been used in civil engineering applications as structural

fills, sheetrock, replacement for Portland cement and as agricultural fertilizer.

3

Fly ash is a fine part of the coal combustion products (CCPs). It has particle

sizes ranging between fine silts and fine sands. It is a light weight and self draining

material compared to natural soil. Therefore, fly ash has been successfully used as a

structural fill material for constructing highway embankments (Chand and Subbarao,

2007).

Bottom ash and boiler slag, are coarse with sizes varying from sand to gravel.

They are composed of non-combustible particles and unburned carbon, similar to fly

ash. They fall to the bottom of the furnace and are removed as non molten particles

(clinkers). The type of by product produced depends on the type of furnace used to

burn the coal.

There are many investigations about the properties of separated single types

of ash (fly ash or bottom ash), but there are a few studies about the fly ash-bottom

ash mixtures with high fly ash contents. Commonly both the production and disposal

ratio of fly ash and bottom ash are approximately 80:20 by weight. Therefore, in

most cases uses the same percentage of disposed ash with its high content of fly ash

to increase the benefit, with less cost and time to finish the project (ACAA, 2001).

However Kim et al. (2005) tried to analyse the mechanical properties such as

compressibility, stiffness, strength, permeability and compaction to samples with

different mixture ratios of fly ash and bottom ash (50%, 75%, and 100% fly ash by

weight) collected from two power plants in Indiana. They found the coal ash mixture

compare favourably with the granular materials. Yoon et al. (2009) described the

construction and the instrumentation of a demonstration embankment built with an

ash mixture (60:40 by weight of fly ash-bottom ash) on State Road 641, Terre Haute,

Indiana, USA. They found that this ash mixture can be considered an acceptable

embankment construction material.

4

1.2 Problem Statement

A number of studies had been carried out to determine the engineering

properties of the coal ash mixture. An extension of this work is necessary in order to

explore further usage of coal ash particularly when mixed together in optimum

percentage. The critical state boundary surface of the soil or material is important to

identify the limit of stress imposed from various stress level and stress history.

Hence, the study aiming at developing a critical state boundary surface for a mixture

of 60% by weight of fly ash and 40% of bottom ash is vital. The results could be

used as a guideline when working with this coal ash mixture in civil engineering

work.

1.3 Objective of the Study

This study is aimed at developing a critical state boundary surface of 60:40

(% by weight) of fly ash–bottom ash mixture. Hence the followings objectives had

been formulated:

1. To determine the basic characteristics of the coal ash mixture.

2. To evaluate the compaction characteristics of coal ash mixture.

3. To determine the shear strength parameters for the compacted coal ash

mixture of various over consolidation ratio at the critical state condition.

4. To produce a critical state boundary surface of coal ash mixture.

5

1.4 Scope of the Study

This study focuses on the critical state boundary surface of fly ash-bottom ash

mixture for the materials taken from Tanjung Bin power plant station, Johor,

Malaysia. The mixture used in this study is 60:40 % by weight of fly ash to bottom

ash. This study includes determination of the basic characteristics for the coal ash

mixture (particle size distribution, specific gravity and Atterberg limit), evaluation of

the compaction characteristics (maximum dry density and optimum water content),

and the determination of the shear strength parameters for the compacted coal ash

mixture of various over consolidation ratio (OCR=1, 2.5, 4, 10) at the critical state

condition.

REFERENCES

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American coal ash association.

ACAA, (2001). CCP Survey Results. published ,FHWA- 2001.Va:American Coal

Ash Association

ACAA, (2003). Fly Ash Facts for Highway Engineers. FHWA-, 2003.Va :American

Coal Ash Association.

Braja, M.D. (2008).Advaced Soil Mechanics. Third Edition. Taylor and Francis.

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Butalia,T.S., and Wolfe, W.E. (2009). Beneficial Use of Coal Combustion By-

products in the Rehabilitation of Failed Asphalt Pavements. International

Journal of Environmental Science and Engineering 1:2 2009.

Casagrande,A.(1938). Compaction tests and critical density investigations of

cohesionless materials for erankan Falls dam. U.S. Engineer corbs. Boston

Distric

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Chand, S. K. and Subbarao, (2007). Strength and slake durability of lime stabilized

pond ash: Journal of Materials in Civil Engineering, ASCE 19 (7) (2007), pp.

601–608.

Chun,L.B.,Sung,K.J., Sang ,K.T., and Tea,C.S. (2008) .A Study on the Fundamental

Properties of Concrete Incorporating Pond-Ash in Korea, Korea Institute of

Construction Materials.

Cross, D., Stephens, J. and Vollmer, J. (2006 )..Structures Applications of 100

percent Fly Ash Concrete. Montana State University

EPA (2005) .Using coal ash in highway construction: A guide to benefits and

impacts, United State Environmental Protection Agency, EPA-530 –k-05-002,

April 2005.

Kim, B., Balunaini, U. Prezzi, M. and Salgado, R (2005) . Geotechnical Properties of

Fly Ash Bottom Ash Mixture for use in Highway Embankments. DOI 10.1061/

(ASCE) 1090-0241(2005)131: 7(914),PP 914.

Kim, B., Balunaini, U. Prezzi, M., and Salgado, R (2006). Determination of Ash

Mixture Properties and Construction of Test Embankment. Part A”

FHWA/IN/JTRP-2006/24, November 2006.

Lindon, K. A. (2008). Using Coal Fly Ash in Road Construction. UK Quality Ash

Association.pp 173-183

Marto,. A. (1996). Critical State Of Keuper Marl Silt. Jurnal Kej.Awam Jil.9 Bil.2

RMRC.(2008). User guidelines for byproducts and secondary use materials in

pavement constructions. Coal fly ash.

Schofield, A. and Worth,P. (1968).Critical State Soil Mechanics. First Edition. Mc

Graw –Hill Publishing Company Limited.

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Singh, R.N. (2005). Need for fly ash management concern and achievement of NLC

in fly ash management. Journal of Coal Ash Institute of India, VII, 12–22.

Smith, I. (2006). Elements of Soil Mechanics. 8th edition. Blackwell Publishing.

Taylor, D.W. (1948).”Fundamental of soil mechanics” Wiley, new yourk.

Vom Berg, W.(1998). Utilization of fly ash in Europe. Proc. of Int. Conf. on Fly

ash Disposal and Utilization ,vol. I, Central Board of Irrigation and Power, New

Delhi, India (1998), pp. 8–14.

Waseem, M., Prashant A., Chandra, S. (2004). Single Element Test Predictions for

Stress-Strain Behavior Of Panki Fly-ASH. Department of Civil Engineering,

Indian Institute of Technology Kanpur, India-208016

Whitlow,R.(2001). Basic Soil Mechanics. Fourth edition. pearson Education Ltd.

Yoon, S., Balunaini, U., Yildirim, I .Z. , Prezzi, M., and Siddiki, N. Z (2009).

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Materials in Civil Engineering : DOI 10.1061/ (ASCE) 0899-

1561(2009)21:6(271)