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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
ix
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
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
4.6 Swelling values for compacted specimens of 35
blows per layer
68
4.7 Swelling values for compacted specimens of 62
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
xiii
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
4.2 Grain size distributions for 50% Kaolin + 50% Bottom
ash
59
4.3 Grain size distributions for 40% Kaolin + 60% Bottom
ash
60
4.4 Compaction curve for 75% Kaolin + 25% Bottom ash 63
4.5 Compaction curve for 50% Kaolin + 50% Bottom ash 63
4.6 Compaction curve for 40% Kaolin + 60% Bottom ash 64
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
4.12 Shear stress-displacement for 50% kaolin + 50%
bottom ash
74
4.13 Shear stress-displacement for 75% kaolin + 25%
bottom ash
74
4.14 Results of direct shear tests (40% Kaolin + 60%
Bottom ash)
75
4.15 Results of direct shear tests (50% Kaolin + 50%
Bottom ash)
75
4.16 Results of direct shear tests (75% Kaolin + 25%
Bottom ash)
76
4.17 The Mohr Circle from UU test (40% Kaolin + 60%
Botttom ash)
79
4.18 The Mohr Circle from UU test (50% Kaolin + 50%
Botttom ash)
79
xvi
4.19 The Mohr Circle from UU test (75% Kaolin + 25%
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
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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