STRENGTH AND COMPRESSIBILITY CHARACTRISITCS OF...

STRENGTH AND COMPRESSIBILITY CHARACTRISITCS OF KAOLIN

MIXED WITH BOTTOM ASH

MOHAMMAD EHSAN JORAT

A report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Civil - Geotechnics Engineering

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JULY 2010

iii

To my beloved father and mother, Mohammad Amin Jorat and Mehran Kiani

Haghighi and my sister, Yasamin Jorat for their never ending support.

Thank you for everything.

iv

ACKNOWLEDGEMENT

To complete this Master Degree Project report, I had received a lot of

information and valuable guidance from my supervisor, Prof. Dr. Aminaton Binti

Marto. Her knowledge and research on coal ash related subjects are particularly

helpful to provide me the insights and understanding needed to complete this report.

Thus, I wish to express my deepest gratitude and appreciation to her for her

generosity, critics, and intellectual support.

Sincere gratitude goes to all the laboratory technicians in the Department of

Geotechnics and Transportation, Faculty of Civil Engineering, Universiti Teknologi

Malaysia who assisted me in doing my laboratory testing.

The moral supports and concerns I constantly received from my family and

friends are well acknowledged. I am thankful to have them supporting me all the way

to finish this report.

v

ABSTRACT

Coal is one of the world’s most important sources of energy, fuelling almost

40% of electricity worldwide. The burning of coal produced coal ash that mostly

consists of Fly Ash and Bottom Ash. Bottom Ash (normally recognized as coal

combustion residues from pulverized fuel power stations) has been categorized as

solid garbage. However, the utilization of Bottom Ash in construction-related

applications has received some attention within the last decade. This project aimed at

determining the strength and compressibility of Kaolin, mixed with 25 %, 50% and

60% of bottom ash. Kaolin, in powdered forms, was mixed with Bottom Ash and

compacted at optimum moisture content. The strength and compressibility of the

compacted samples were determined from direct shear test, unconsolidated

undrained triaxial tests, and one-dimensional consolidation test, besides the

California Bearing Ratio and permeability tests. It was observed that the granular

nature of Bottom Ash increased the friction angle of Kaolin, increased the

permeability and expedite the consolidation rate. However, the addition of 25%

Bottom Ash gives the highest shear strength of Kaolin while the addition of 60%

Bottom Ash gives the highest permeability and coefficient of consolidation. This

results show that Bottom Ash can be used to increase the strength of soil, in

particular the soft soil and also could expedite the consolidation of the soil. This is

due to the granular nature of the materials that could increase the voids in the

mixtures and also contribute to increase in friction angles.

vi

ABSTRAK

Arang batu merupakan salah satu sumber tenaga dunia yang paling penting

yang dapat memberikan hampir 40% dari kuasa elektrik seluruh dunia. Pembakaran

arang batu yang dihasilkan oleh abu batubara adalah sebahagian besarnya terdiri

daripada abu terbang dan abu bawah. Abu bawah (biasanya dikenali sebagai residu

pembakaran arang batu dari loji kuasa bahan api serbuk) telah dikategorikan sebagai

sampah padat. Namun, penggunaan abu bawah dalam aplikasi yang berkaitan

dengan pembinaan telah mendapat beberapa perhatian sejak sedekad yang lalu.

Projek ini bertujuan untuk menentukan kekuatan dan kebolehmampatan Kaolin,

dicampur dengan 25%, 50% dan 60% dari arang batu. Kaolin, dalam bentuk serbuk,

dicampur dengan abu bawah dan dipadat pada kandungan lembapan optimum.

Kekuatan dan kebolehmampatan sampel terpadat ditentukan dari ujian ricih terus,

ujian tiga paksi tak terkukuh tak tersalir dan ujian pengukuhan satu dimensi, selain

“California Bearing Ratio” dan ujian kebolehtelapan. Didapati bahawa sifat berbijian

abu bawah meningkatkan sudut geseran Kaolin, meningkatkan kebolehtelapan dan

mempercepatkan kadar pengukuhan. Namun, penambahan abu bawah sebanyak 25%

memberikan kekuatan ricih Kaolin yang tertinggi sedangkan penambahan abu bawah

sebanyak 60% memberikan nilai pekali kebolehtelapan dan pekali pengukuhan

Kaolin yang paling tinggi. Keputusan ini menunjukan bahawa abu bawah boleh

digunakan untuk meningkatkan kekuatan tanah, khususnya tanah lembut dan dapat

mempercepatkan pengukuhan tanah. Ini disebabkan oleh sifat berbijian bahan yang

dapat meningkatkan rongga dalam campuran dan juga menyumbang terhadap

peningkatan sudut geseran.

vii

TABLE OF CONTENTS

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 ABBREVIATIONS xiv

LIST OF SYMBOLS xv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Problem Statement 3

1.3 Objectives 4

1.4 Scope of Study 5

1.5 Importance of study 7

2 LITERATURE REVIEW 8

viii

2.1 Introduction 8

2.2 Bottom Ash 9

2.2.1 Properties of bottom ash 10

2.2.1.1 Physical Characteristics 10

2.2.1.1.1 Physical Appearance 10

2.2.1.1.2 Specific Gravity and Water

Adsorption 11

2.2.1.1.3 Gradation 11

2.2.1.2 Mechanical Properties 13

2.2.1.2.1 Compaction 13

2.2.1.2.2 Shear Strength 16

2.2.1.2.3 Compressibility 17

2.2.1.2.4 Permeability 19

2.2.2 Coal Combustion Residues 21

2.2.3 Utilization of Bottom Ash 21

2.3 Soft Clay 24

2.3.1 Physical and chemical properties 25

2.3.2 Shear Strength 25

2.3.3 Compressibility Characteristics 26

2.4 Experimental works on Bottom Ash as an

admixture 27

2.4.1 Physical Charactristics 28

2.4.1.1 Specific Gravity and Water

Adsorption 28

2.4.1.2 Gradation 28

2.4.2 Mechanical Characteristics 31

2.4.2.1 Compaction 31

2.4.2.2 Shear Strength 35

2.4.2.3 Permeability 38

2.4.2.4 Compressibility 39

2.4.2.5 Strength 43

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3 METHODOLOGY 48

3.1 Introduction 48

3.2 Collecting Literature Reviews 49

3.3 Collection Of Sample 49

3.4 Laboratory Works 52

3.5 Physical Properties 52

3.5.1 Grain Size Analysis Test 52

3.5.2 Specific Gravity Test 53

3.6 Mechanical Properties 53

3.6.1 Compaction Test 53

3.6.2 Direct Shear Test 54

3.6.3 1-Dimentional Consolidation Test 54

3.6.4 Permeability Test 55

3.6.5 California Bearing Ratio (CBR) Test 55

3.6.6 Triaxial Test 56

4 RESULTS AND DISCUSSION 58

4.1 Introduction 58

4.2 Physical Properties 58

4.2.1 Grain Size Distribution 58

4.2.2 Specific Gravity 61

4.3 Mechanical Properties 62

4.3.1 Compaction Test 62

4.3.2 Permeability Test 66

4.3.3 California Bearing Ratio (CBR) Test 66

4.3.4 Direct Shear Test 71

4.3.5 Unconsolidation Undrained Test Triaxial

Test 77

4.3.6 1-Dimentional Consolidation Test 80

x

5 CONCLUSIONS 84

5.1 Conclusions 84

5.2 Recommendations 86

REFERENCES 87

APPENDIX 94

xi

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Indiana grading requirements for base and sub-base

materials

13

2.2 Result of direct shear tests on Indiana bottom ash 16

2.3 Typical of permeability coefficient 20

2.4 Hydraulic Conductivity of Ash Mixtures 21

2.5 Total coal combustion product production and use 23

2.6 The physical and chemical properties of the natural

White Kaolin

25

2.7 Typical values of coefficient of Volume

Compressibility

27

2.8 Grain Size Distribution of Natural Lateritic Soil with

Addition of Kiln Ash Wastes

29

2.9 Basic Grain Size Indices and Unified Soil

Classification System Framing of the Investigated Ash

30

2.1O Standard Proctor Compaction, Permeability,

Unconfined Compressive Strength and Soil Solution

pH Test Results

32

2.11 Hydraulic Conductivity of Ash Mixtures 38

4.1 Magnitudes of Cu and Cc in different mixtures 60

4.2 Samples classified by Unified System 61

4.3 Specific gravity values 62

4.4 Optimum Moisture Content – Maximum Dry Density 65

4.5 Swelling values for compacted specimens of 15

blows per layer

68

xii


blows per layer

68


blows per layer

69

4.8 Details for penetration resistance 70

4.9 Allowable CBR values 71

4.1O Results of direct shear tests of different materials. 72

4.11 Peak Strength carried out by Direct Shear Test 76

4.12 Summary of Unconsolidation Undrained Test 78

4.13 Coefficient of consolidation of bottom ash+ kaolin

mixtures

82

4.14 Coefficient of volume compressibility of bottom

ash–residual soil mixtures

83

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

1.1 Salahuddin Abdul Aziz power plant 6

2.1 Salahuddin Abdul Aziz power plant 6

2.1 Typical gradation ranges of coal ash 12

2.2 Typical compaction curve for cohensionless soils 14

2.3 Compaction curve for bottom ash from Gallagher

Power Plant, Indiana

15

2.4 One-Dimensional compression curves of West Virginia

Bottom Ash

18

2.5 One-dimensional compression curves for bottom ash

and a medium sand

19

2.6 Utilization of fly ash, bottom ash, boiler slag and flue

gas desulfurization

22

2.7 Leading Bottom Ash Uses 24

2.8 Grain-size distribution of the fly and bottom ash mixture

used in the construction of the demonstration

embankment

27

2.9 Particle size distributions of fly, bottom, and fly/Bottom

Ash mixtures from (a) Wabash River plant; and

(b) A. B. Brown plant

29

2.1O Compaction curve for the 60% of fly and 40% of

Bottom Ash mixture

31

2.11 Compaction curves of ash mixtures 33

2.12 Variation of MDD with pulverised coal Bottom Ash

content for soilcement- PCBA mixtures

34

2.13 Variation of OMC with pulverised coal Bottom Ash

content for soil (cement) PCBA mixtures

35

xiv

2.14 Stress-strain and volume change results from

consolidated-drained triaxial tests completed on ash

mixtures from (a) and (b) Wabash River plant;

and (c) and (d) A. B. Brown plant

37

2.15 Volume change behaviour from CID triaxial test

performed at different confining stresses on ash

mixtures from (a) Wabash River plant; and (b) A. B.

Brown plant

37

2.16 Consolidation test results for natural red soil, natural

red soil with 5% kiln ash after 1 day, and after 62 days

39

2.17 Consolidation results of natural red soil, natural soil

with

10% kiln ash after 7 days, after 62 days, and after 177

days

40

2.18 Consolidation results of natural red soil, natural red soil

with 20% kiln ash after 1 day, and natural red soil after

180 days

40

2.19 Tangent constrained moduli of ash mixtures and sands 42

2.2O One-dimensional compression curves of ash mixtures

from (a) Wabash River plant; and (b) A. B. Brown plant

43

2.21 Unconfined compression strength versus dry unit weight

of mixtures with different bentonite content

44

2.22 Variation of soaked CBR with pulverised coal bottom

ash content for soil (cement) PCBA mixtures

45

2.23 Variation of UCS (7 days curing) with pulverised coal

bottom ash content for soil-cement-PCBA mixtures

46

2.24 Variation of UCS (7days cured + 7 days soaked) with

pulverised coal bottom ash content for

soil-cement-PCBA mixtures

46

2.25 Variation of UCS (14 days curing) with pulverized coal

bottom ash content for soil-cement- PCBA mixture

47

2.26 Variation of UCS (28 days curing) with pulverized coal

bottom ash content for soil-cement- PCBA mixture

47

xv

3.1 Flow chart of the activities in the study 48

3.2 Kapar Power Plant 50

3.3 Ash disposed area 51

3.4 Collection of bottom ash 51

4.1 Grain size distributions for 75% Kaolin + 25% Bottom

ash

59


ash

59


ash

60

4.4 Compaction curve for 75% Kaolin + 25% Bottom ash 63



4.7 Combined Compaction Curves 64

4.8 Samples swelling curve for 15 blows per each layer 67

4.9 Samples swelling curve for 35 blows per each layer 67

4.1O Samples swelling curve for 62 blows per each layer 68

4.11 Shear stress-displacement for 40% kaolin + 60%

bottom ash

73


bottom ash

74


bottom ash

74

4.14 Results of direct shear tests (40% Kaolin + 60%

Bottom ash)

75


Bottom ash)

75


Bottom ash)

76

4.17 The Mohr Circle from UU test (40% Kaolin + 60%

Botttom ash)

79


Botttom ash)

79

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Botttom ash)

80

4.2O The Void Ratio Vs pressure for 60% Bottom Ash +

40% Kaolin

81

4.21 The Void Ratio Vs pressure for 50% Bottom Ash +

50% Kaolin

81

4.22 The Void Ratio Vs pressure for 25% Bottom Ash +

75% Kaolin

82

xvii

LIST OF ABBREVIATIONS

AASHTO- - American Association of State Highway and

Transportation Officials

ACAA - American Coal Ash Association

ASTM - American Society of Testing and Materials

BS - British Standard

CBR - California bearing ratio

CCRs - Coal combustion residues

CD - Consolidated drained

CU - Consolidated undrained

FGD - Flue gas desulfurization

USCS - Unified Soil Classification System

xviii

LIST OF SYMBOLS

dρ Dry density

ρ Bulk density

w Moisture content of soil

sG Specified gravity

D Diameter

S Shear strength

c Cohesion intercept

φ Angle of internal friction

1σ Major principle stress

2σ Intermediate principle stress

3σ Minor principle stress

λ Wavelength

d Inter planner spacing

θ Angle of incidence of X-ray to the Cu target element

uC Coefficient of uniformity

cC Coefficient of curvature

dγ Compacted dry density

nγ Normalized density

wγ Water density

dσ Deviator stress

vε Volumetric strain

aε Axial strain

CC Compression index

xix

e Void ratio

σ ′ Effective pressure

xx

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Specific gravity 94

B Compaction 95

C Grain size distribution 97

D Permeability 100

E Soaked CBR 103

F Direct shear 115

G Triaxial UU 121

H 1- Dimensional Consilidation 123

CHAPTER I

INTRODUCTION

1.1 Introduction

Soft clays are widely found throughout the coastal plains of Malaysia, central

plain of Thailand and East of Sumatra, Indonesia. Soft or poor unstable ground

generally means subsoil, which has shear strength of less than 40 kPa. Soft soil can

be physically moulded by light finger pressure. For very soft soil, the shear strength

is less than 20 kPa and the soil can be extruded between fingers when squeezed. Soft

soils are also generally referred to as weak compressible soils such as coastal alluvial

soil or marine clay, and slime in examining pond areas (Neoh, 2000).

Besides the common use of surcharge with vertical drains, there are many

others methods to stabilize soft soil, such as the use of floating piles, stone columns,

replacement method, etc. (Broms, 1977; Raju, 2000). However, cost is the main

concern for considering these stabilization methods. Generally the stabilization of

soft clay usually involves expensive soil improvement methods to enhance stability

and reduce uneven settlement. In construction of road structures, especially road

embankments, bridge approaches and slopes, they require an extensive stabilization

of wider foundation base. Consequently, requirement for land area is increasing. In

2

most cases, imported backfill materials are also required and will further increase the

overall cost of the project (Loke, 2000).

The solutions of many geotechnical issues for construction are very much

directly or indirectly related to the understanding of the problematic soils. Soft clay

is one of the problematic soils which are commonly found along the coastal areas at

West Malaysia. In Klang area, the thickness of the soft marine clay may vary from

20 to 40m (Cheung, 2008).

Coal is one of the world’s most important sources of energy, fuelling almost

40% of electricity worldwide. In many countries this figures much higher: Poland

relies on coal for over 97% of its electricity; South Africa for 92%; China for 77%;

and Australia for 76% (Joseph, 2005). Coal was introduced as a raw material for

power generation since 1988 in Malaysia. The existing coal-fired power plants in

Malaysia are Kapar (1,600 MW) commissioned in 1988, TNB Janamanjung (2,100

MW) commissioned in 2003 and Tanjung Bin (2,100 MW) commissioned in 2004.

Looking at the electricity generation mix, the percentage of coal remains stable at an

average of 8.6 percent from 1993-2000 and increased slightly to 12 and 14.1 percent

in 2001 and 2002 respectively. However, in 2003, the percentage increased

tremendously from 14.1 percent to 24.6 percent of coal in the electricity generation

mix due to the commissioning of Janamanjung power plant. According to Joseph

(2005), with the two more new constructed coal-fired power plants, Jimah and

Tanjung Bin, coal consumption is expected to increase from 10 million ton to 19

million ton in year 2010. Malaysia imports about 70 percent of its total coal

requirements from Indonesia, other will be imported through bulk carriers from

mines in China, Australia, South Africa, and elsewhere as the need arises.

Coal ash mostly consists of fly ash and bottom ash, according to the

American Coal Ash Association (ACAA, 2003), in the US, the general production

ration of fly ash and Bottom Ash is approximately 80:20. The heavier ash that drops

through the bottom of the furnace where it is collected in a funnel is called as bottom

3

ash. It is classified as wet or dry Bottom Ash depending on the type of furnace used

and relatively coarse material. The lighter fly ash is carried through the boiler with

the exhaust gases and is collected by ash precipitators (Huang, 1990). Fly ash

accounts for 70 to 80 percent of the coal ash produced by most electric power plants

while Bottom Ash constitutes about 10% - 18% of the overall ash.

Bottom Ash [normally recognized as coal combustion residues (CCRs) from

pulverized fuel power stations] has been categorized as solid garbage. But, CCRs are

increasingly being regarded as a useful substitute material resource. They had an

appearance similar to dark grey coarse sand, and its particles are clusters of micron

sized granules, up to 10 mm in diameter (60% - 70% smaller than 2mm. 10% - 20%

smaller than 75 microns) (ACAA, 1998).

1.2 Problem Statement

The growing demand for electricity resulted in the construction of many coal

fired power plants. As the consumption of coal by power plants increases, so does

the production of coal ash. While the use of coal increases, waste issues associated

with coal production are tempted more and more thoughtfulness (Joseph, 2005).

Even though there is no report about the producing of coal ash annually in Malaysia,

but basically about 10% of total weight of the coal burned produces ash (Huang,

1990). Disposal of unused coal ash is costly and places a considerable burden on the

power industry and finally transferred to the electricity consumer. In addition, the

disposing of ash contributes to the ongoing problem of diminishing landfill space

pose an environmental hazard. Previously, most researches had been focussing on the

properties of fly ash (ACAA, 1998).

4

Nevertheless, some of the studies showed that the engineering properties of

most Bottom Ash were more favourable than those of traditional highway material

and has the capability to improve asphalt pavement performance when used to

substitute a portion of the aggregate in asphalt mixes. Changeability of coal Bottom

Ash is a latency problem because of the variability in type and origin of coal burned,

boiler types, degree of coal pulverization, firing conditions in the furnace and ash

handling practice (Huang, 1990). There is a requirement for a systematic manner to

estimate locally available bottom ashes for potential construction utilization because

even Bottom Ash produced from unitary source can be entirely difference depending

on the operating conditions and procedures.

Kapar power plant consumed enormous quantities of coal each year. This

produces a substantial amount of unused coal ash. The majority of ash is disposed in

mines prior to their reclamation. Besides, there are many areas of the Malaysia faced

with a shortage of conventional construction materials. In city areas where demands

of construction materials are high, deficiency in the supply of conventional materials

aggregates. In addition, zoning restrictions and environmental regulations often

remove accept Table materials from availability. Normally these same city areas are

served by power stations that produce large quantities of ash. Obviously, a

favourable combination of circumstances is created for utilization of power plant ash

as a partial or full substitute for conventional aggregates in various applications. The

successful use of Bottom Ash in civil engineering construction would provide

significant economic savings.

The advancement of works in bearing capacity studies have led to further

works on the use of reinforcement in soft soils or clays. Soft clays have been known

to cover vast coastal areas of Malaysia (Neoh, 2000). As development progresses,

more construction areas have occupied these compounds. The problem with soft clay

is large settlement and low bearing capacity. With more research being conducted,

various techniques are available to reduce the settlement and increase the bearing

capacity of soft clays.

5

1.3 Objectives

This master project is aimed at improvement in the strength and

compressibility characteristics of Kaolin, representing as soft clay, by mixing with

Bottom Ash so that Bottom Ash as waste material could be used in improvement of

soft soils. Hence, the objectives of this project are as follow:

i. To determine changes in basic properties of Kaolin mixed with various

percentage of Bottom Ash. These percentages are 25%, 50% and 60% by

weight of bottom ash.

ii. To evaluate the strength characteristics of Kaolin mixed with bottom ash

at maximum compaction.

iii. To determine the compressibility characteristics of Kaolin mixed with

bottom ash at maximum compaction.

1.4 Scope of Study

In this project, only the Bottom Ash from Sultan Salahuddin Abdul Aziz

Shah power plant (Kapar, Selangor) is concerned (Figure 1.1, Figure 1.2). Sultan

Salahuddin Abdul Aziz Shah power plant is located at the west coast of Peninsular

Malaysia, approximately 50 km to the west of capital city of Malaysia, Kuala

Lumpur. It is normally known as Kapar Power Station. The power station lies

between the mouths of the Kapar Besar and the Serdang Kecil Rivers. Totalling 2420

6

MW, this station consists of steam plants firing oil, gas and coal as well as open

cycle Frame 9 gas turbines.

Kapar Energy Ventures Sdn. Bhd owns, operates and maintains Sultan Salahuddin

Abdul Aziz Power Station since 9th July 2004, after successful acquisition of the

power plant from Tenaga Nasional Berhad.

Figure 1.1: The Location of Sultan Salahuddin Abdul Aziz power plant

(www.maps.google.com, 2010).

Figure 1.2: Salahuddin Abdul Aziz Shah power plant in Kapar Selangor.

7

The study focuses on the strength and compressibility of Kaolin mixed with

Bottom Ash. Kaolin had been used to represent the clay soil. The engineering

properties of the materials had been tested using the standard method such as the

British Standard 1377, 1996 or the American Society for Testing and Materials

(ASTM), depending upon the suitability or the availability of the equipment in the

laboratory within Universiti Teknologi Malaysia (UTM).

1.5 Importance of study

Since construction is inevitable in many areas of Malaysia and of course

some other parts of the world that have the problem in strength and compressibility

of soft clay, basic knowledge and understanding of soft clay and Bottom Ash

properties are of great importance to improve the strength and compressibility of soft

clay mixed with Bottom Ash. Using this mixture, increase in strength that leads to

increase in ultimate bearing capacity of soil, decrease in coefficient of volume

compressibility and decrease in coefficient of consolidation that lead to smaller

settlement are expected. Relatively, smaller settlement cause better compressibility.

This allows the engineers to use the results obtained for preliminary design

purposes involving construction of the soft soil that could be improved by adding

certain percentages of Bottom Ash.

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