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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.
v
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.
vi
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.
vii
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
viii
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
ix
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
xiii
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
xiv
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
ACAA, (2008) .Coal Combustion Product (CCP), published, Alexander, Va:
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
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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)