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EVALUATION OF FLOW AND IN-PLACE STRENGTH
CHARACTERISTICS OF FLY ASH COMPOSITE
MATERIALS
Hrushikesh Naik
Department of Mining Engineering
National Institute of Technology, Rourkela
~i~
EVALUATION OF FLOW AND IN-PLACE
S T R E N G TH CH AR A CT E R IS T IC S OF
FLY ASH COMPOSITE MATERIALS
A thesis submitted in partial fulfilment of the requirements
for the degree of
Doctor of Philosophy
in
Mining Engineering
by
Hrushikesh Naik
Under the supervision of
Dr. M.K. Mishra (N.I.T Rourkela)
&
Dr. K.U.M. Rao (I.I.T Kharagpur)
Department of Mining Engineering
National Institute of Technology
Rourkela - 769 008, India
September, 2013
DEPARTMENT OF MINING ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, ROURKELA
ODISHA, INDIA – 769 008
CERTIFICATE
This is to certify that the thesis entitled “Evaluation of flow and in-place strength
characteristics of fly ash composite materials”, being submitted by Hrushikesh Naik, Roll
No. 50605001 to the National Institute of Technology, Rourkela for the award of the degree of
Doctor of Philosophy in Mining Engineering, is a bona fide record of research work carried
out by him under our supervision and guidance.
The candidate has fulfilled all the prescribed requirements for award of the degree.
The thesis, which is based on candidate’s own work, has not been submitted elsewhere for
the award of a degree.
In our opinion, the thesis is of the standard required for the award of Doctor of Philosophy
in Mining Engineering.
To the best of our knowledge, he bears a good moral character and decent behaviour.
Supervisors
Dr. M.K. Mishra
Dr. K.U.M.Rao
(Supervisor)
(Co-supervisor)
Department of Mining Engineering
Department of Mining Engineering
NATIONAL INSTITUTE OF TECHNOLOGY
INDIAN INSTITUTE OF TECHNOLOGY
Rourkela-769 008 (INDIA)
Kharagpur-721302 (INDIA)
~i~
Acknowledgement
This report is a result of my efforts as a research scholar towards my Ph. D. at
Geomechanics Laboratory of the Department of Mining Engineering, National Institute of
Technology Rourkela. During this time, I have been supported by various people to whom I
wish to express my gratitude.
I would first like to express my deep sense of respect and gratitude towards my
supervisors Prof. M.K. Mishra and Prof. K.U.M. Rao, for their inspiration, motivation,
guidance, and generous support throughout this research work. I am greatly indebted to them
for their constant encouragement and valuable advice at every phase of the doctoral
programme. The dissertation work would not have been possible without their elaborate
guidance and full encouragement. What I learned from them will be an invaluable asset for
the rest of my life.
I would like to extend my special thanks to the Management of Thermal Power Plants
from where the fly ash samples were collected for carrying out this research work especially
to the Head, Ennore Thermal Power Plant and Captive Thermal Power Plant II of Rourkela
Steel Plant and all other power plants for providing fly ash which is used in this research.
My special thanks go to Prof. B.K. Pal, Prof. D.P. Tripathy, and Prof. S. Jayanthu
(former Heads of the Department of Mining Engineering) and all other faculty and staff
members of the department for their help in completion of this work.
~ ii ~
I also express my thanks to Heads and staff members of Chemical Engineering, Civil
Engineering, Metallurgical and Materials Engineering, Mechanical Engineering, and Ceramic
Engineering Department for their help and cooperation in sample testing and instrumental
analysis in their departmental laboratories.
I want to extend my sincere gratitude to members of my doctoral scrutiny committee
for their comments and suggestions throughout this research work, especially to Prof.
C.R.Patra for his invaluable help during the course of this study.
I am also thankful to Fly Ash Unit, Department of Science and Technology; Govt. of
India for their financial assistance in sponsoring a research project titled “Evaluation of flow
and in-place strength characteristics of fly ash composite materials” vides sanction order no.
FAU/DST/600(19) Dated: 30th March 2009 to meet some of the expenditure incurred to carry
out this research work.
Finally, I would like to express my deepest gratitude to my beloved parents, my wife
Suprava and two daughters (Madhusmita and Poornima) who made all these possible, for
their endless encouragement, support, love, and patience throughout the research period.
(Hrushikesh Naik)
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ABSTRACT
Of the seven hundred and fifty millions of metric tons of fly ash that are produced annually
worldwide, only a small portion e.g., 20% to 50% of the fly ash is used for productive
purposes, such as an additive or stabilizer in cement, bricks, embankments, etc. The
remaining amount of fly ash produced annually must either be disposed off in controlled
landfills/ mine fills or waste containment facilities, or stockpiled for future use or disposal. As
a result of the cost associated with disposing these vast quantities of fly ash, a significant
economical incentive exists for developing new and innovative, yet environmentally safe
applications for the utilization of fly ash. The main aim of the present investigation was
designed to develop an engineered backfill material to be placed in mine voids using fly ash
as the major component. Experimental set up was designed and fly ash samples from seven
numbers of thermal power plants situated at different parts of the country were collected.
Investigation
into
detail
physical,
chemical,
morphological,
and
mineralogical
characterizations have been carried out to choose the most favorable fly ash source for slurry
transportation.
Flow parameters such as viscosity, shear stress, shear rate (25s-1 to 1000s-1),
temperature (200C to 400C), and solid concentration (20% to 60%), etc. were determined.
Flow behavior was influenced with addition of additives as cationic surfactant cetyltrimethyl
ammonium bromide (CTAB) and a counter-ion sodium salicylate (NaSal). As the fly ash
concentration in the slurry increased an increase in viscosity was observed. Addition of
surfactants (0.1% to 0.5%) modified the flowing attributes from shear thickening to shear
thinning/Newtonian pattern and eliminated yield stress completely/partially compared to that
of untreated fly ash slurry. Temperature of the slurry environment was also observed to
~ iv ~
influence the flowing behavior. An operating temperature varying from 300C to 400C was
found to be ideal for improving the flowing attributes. Surfactants used in this study also
reduced the surface tension of water by adsorbing at the solid-liquid interface. The addition of
the surfactant resulted in reduced surface tension by 53 to 56% and facilitated floating of fly
ash particles for smooth flow in pipelines. The zeta potential value of the fly ash slurry was
negative (-27mV) without any additive, but changed to positive value (> +30mV) when
surfactant was added to the slurry. Addition of the surfactant modified the surface properties
of the fly ash particles keeping the suspension in the stable condition. The settling
characteristic of the slurry was studied to know the settling behavior of the fly ash particles.
The treated fly ash slurry exhibited better suspension attributes as compared to that of
untreated fly ash.
Lime was selected to enhance the strength characteristics of fly ash composite
materials. Lime pH optimization study was carried out to find the optimum quantity of lime
which was added to the fly ash to increase the in-place strength of fly ash composite
materials. Unconfined compressive strength, Brazilian Tensile strength, and triaxial tests were
conducted at varying curing periods i.e. at 0 day, 7 days, 14 days, 28 days, and 56 days.
Ultrasonic pulse velocity was measured and microstructural analysis was carried out to
examine the strength behavior of the developed composite materials. Fourier Transfom
Infrared Spectroscopy (FTIR) study was carried out to find the effect of lime addition on
strength parameters. The SEM images were also obtained to study the ettringite formation in
the fly ash composite materials. From the results of this study it is inferred that there is
substantial strength gain with curing period. Empirical equations are developed to predict the
flow and strength behavior of the selected and optimized fly ash material.
~v~
CONTENTS
CERTIFICATE
i
ACKNOWLEDGMENT
ii
ABSTRACT
iv
CONTENTS
vi
LIST OF FIGURES
xiii
LIST OF TABLES
xix
CHAPTER 1: INTRODUCTION
1
1.1
Introduction
1
1.1.1
The Background
1
1.1.2
Needs statement and motivation for the present work
2
1.1.3
Objectives and scope of the study
4
1.1.3.1
Objectives
4
1.1.3.2
Scope of the study
4
1.1.3.3
Approach/ Methodology
5
1.1.4
Outline and organization of thesis
7
CHAPTER 2: LITERATURE REVIEW
8
2.1
Introduction
8
2.2
General properties of fly ash
9
2.2.1
Physical properties
9
2.2.2
Chemical properties
10
Fly ash as mine void filling material
14
2.3.1
Suitability of fly ash as mine void filling material
14
2.3.2
Settling characteristics, leachates, and heavy metals in fly ash
18
2.3.3
Paste backfill system
19
2.3
2.4. High concentration hydraulic slurry pipeline system
22
2.5. Drag reduction technology
34
2.5.1
Drag reduction by using surfactants
36
2.5.2
Polymeric drag reduction research
41
2.6. Surfactants
43
~ vi ~
2.6.1
Classification of surfactants
43
2.6.2
Micelles
44
2.6.3
Drag reduction with surfactant solutions
48
2.6.4
Anionic surfactants
49
2.6.5
Cationic surfactants
49
2.6.6
Non-ionic surfactants
49
2.7.
Engineering uses of fly ash
50
2.8
Colloidal stability
54
2.8.1
55
2.9
Rheology, fluid behaviours, and constitutive models
56
2.9.1
Newtonian fluids
57
2.9.2
Non-Newtonian fluids
57
2.9.3
Time dependent fluids
58
2.9.3.1
Thixotropic fluids
58
2.9.3.2
Rheopectic fluids
58
2.9.4
2.10
Interparticle forces
Time independent fluids
59
2.9.4.1
Pseudoplastic or shear thinning fluids
59
2.9.4.2
Shear thickening fluids
59
2.9.4.3
Yield shear thickening
60
2.9.4.4
Yield stress
60
Rheological models
62
2.10.1
Bingham Plastic model
62
2.10.2
Cross model
63
2.10.3
Power law model
64
2.10.4
Casson model
65
2.10.5
Herschel-Bulkley model
65
2.11 Independent characterization by measuring zeta potential
67
2.12 Viscosity and viscosity-temperature models
68
2.12.1
Arrhenius equation
69
2.12.2
Frenkel equation
70
2.13 Rheometry
70
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2.13.1
2.13.2
Rotaional type rheological instruments
71
2.13.1.1
72
Plate type
2.13.1.1.1
Parallel plate
72
2.13.1.1.2
Cone and plate
72
2.13.1.1.3
Concentric cylinders (cup and bob)
73
2.13.1.1.4
Vane geometry
73
Tube type rheometer
CHAPTER 3:
74
75
METHODOLOGY
3.0
Materials and methods
75
3.1
Introduction
75
3.2
Materials
76
3.2.1
Fly ash
76
3.2.2
Additives
76
3.2.2.1
Surfactant
76
3.2.2.2
Counter-ion
78
3.2.2.3
78
3.2.3
Water
79
3.2.4
Millipore water
79
3.2.5
3.3
Lime
Mobil oil (Tranself type B 85W140)
79
Laboratory investigation and characterization of materials
79
3.3.1
X-ray diffraction (XRD) analysis
79
3.3.2
Scanning Electron Microscopy (SEM) studies
80
3.3.3
Chemical characterization
80
3.3.3.1
Energy-dispersive X-ray spectroscopy (EDX) studies
80
3.3.3.2
Energy dispersive X-ray fluorescence (ED-XRF) studies
81
3.3.4
Physical characterization
81
3.3.4.1
Specific gravity
81
3.3.4.2
Specific surface area
82
3.3.4.3
Particle size analysis
82
3.3.4.4
3.3.5
pH (ASTM D 4972)
Surface Tension
82
83
~ viii ~
3.3.6
Zeta Potential
83
3.3.7
Settling study of fly ash slurry
85
3.3.7.1
3.3.8
3.4
3.5
3.6
3.7
Static settling tests
FTIR Spectroscopy study of fly ash slurry
85
86
Experimental apparatus used for rheology study
86
3.4.1
Description of the instrument
89
3.4.2
Experimental steps for rheology measurement
90
Characterization of fly ash slurry at 20% solid concentration
91
3.5.1
Experimental procedure and range of parameters
91
3.5.2
Sample preparation
92
3.5.3
Range of parameters
92
Characterization of fly ash slurry at 30% solid concentration
93
3.6.1
93
Sample preparation and measurement techniques followed
Characterization of fly ash slurry at 40% solid concentration
93
3.7.1
Parametric variations and sample preparation
93
3.8
Characterization of fly ash slurry at 50% solid concentration
94
3.9
Characterization of fly ash slurry at 60% solid concentration
95
3.10 Methods of sample preparation for strength study
95
3.10.1 Sample preparation
95
3.10.2 OMC-MDD study
95
3.10.3 Sample preparation for UCS study
97
3.10.4 Sample preparation for tensile strength study
97
3.10.5 Sample preparation for Ultrasonic Pulse Velocity test
98
3.10.6 Methods of testing
100
3.10.6.1
Triaxial compression test
100
3.10.6.2
Compaction test
100
3.10.6.3
Unconfined compressive strength test
100
3.10.6.4
Brazilian tensile strength test
102
3.10.6.5
Ultrasonic pulse velocity test
102
3.11 Experimental size
3.11.1
103
Characterization study
103
~ ix ~
3.11.2
Rheological study
104
3.11.3
Strength study
107
CHAPTER 4: RESULTS AND DISCUSSION
109
4.1
Introduction
109
4.2
Section I
111
4.2.1
Characterization of ingredients
111
4.2.1.1
Physical properties
111
4.2.1.1.1
Specific gravity
111
4.2.1.1.2
Specific surface area and bulk density
112
4.2.1.1.3
Porosity and moisture content
112
4.2.1.1.4
Grain size analysis
113
4.2.1.1.5
Co-efficient of uniformity
113
4.2.2
4.3
4.2.1.2
Morphological properties
115
4.2.1.3
Chemical and mineralogical properties
117
Summary
120
Section II
121
4.3.1
Results of 20% solid concentration (lean slurry concentration)
122
4.3.1.1
Effect of surfactants on fly ash slurry rheology
122
4.3.1.2
Rheological behavior of fly ash slurry
124
4.3.1.2.1 Shear viscosity
124
4.3.1.2.2 Effect of temperature on fly ash slurry rheology 128
4.3.2
4.3.1.3
Surface tension
131
4.3.1.4
Zeta potential
131
4.3.1.5
Summary of observations at 20% solid concentration
132
Results of 30% solid concentration (low slurry concentration)
133
4.3.2.1
Rheology
133
4.3.2.1.1 Effect of surfactants on fly ash slurry rheology
134
4.3.2.1.2 Shear viscosity
136
4.3.2.1.3 Effect of temperature on fly ash slurry rheology 139
4.3.2.2
Surface tension
141
4.3.2.3
Zeta potential
142
~x~
4.3.2.4
4.3.3
4.3.4
4.3.5
4.4
Summary of observations at 30% solid concentration
142
Results of 40% solid concentration (low slurry concentration)
143
4.3.3.1
Influence of surfactant on fly ash-slurry rheology
143
4.3.3.2
Influence of surfactant on shear viscosity
148
4.3.3.3
Surface tension
149
4.3.3.4
Zeta potential
149
4.3.3.5
Summary of observations at 40% solid concentration
150
Results of 50% solid concentration (medium slurry conc.)
150
4.3.4.1
Effect of surfactants on fly ash slurry rheology
150
4.3.4.2
Effect of surfactant on shear viscosity
154
4.3.4.3
Effect of temperature on fly ash-slurry viscosity
157
4.3.4.4
Yield stress
160
4.3.4.5
Summary of observations at 50% solid concentration
160
Results of 60% solid concentration (medium slurry conc.)
161
4.3.5.1
Influence of surfactant on fly ash-slurry rheology
161
4.3.5.2
Effect of surfactant on shear viscosity
164
4.3.5.3
Effect of temperature on fly ash-slurry viscosity
167
4.3.5.4
Yield stress behaviour
169
4.3.5.5
Summary of observations at 60% solid concentration
172
4.3.6
Effect of pH on fly ash-slurry rheology
172
4.3.7
Effect of solid concentration on fly ash slurry rheology
174
4.3.8
Settling rate of fly ash slurry
177
Section III
179
4.4.1
Results of geotechnical investigation of the selected fly ash slurry
179
4.4.1.1
Geotechnical properties of developed fly ash composites
179
4.4.1.1.1
Compaction characteristics
179
4.4.1.1.2
Unconfined compressive strength
180
4.4.1.1.3
Brazilian tensile strength characteristics
182
4.4.1.1.4
Shear strength parameters
183
4.4.1.1.5
Ultrasonic pulse velocity
183
4.4.2
Micro-structural analysis of developed composite materials
~ xi ~
187
4.4.3
X-ray diffraction analysis of developed composite materials
190
4.4.4
FTIR analysis of developed composite materials
192
4.4.5
Development of empirical models
197
4.4.5.1
197
4.4.6
4.5
Relationship between UCS, BTS and P-wave velocity
Development of empirical equations from rheology study
Summary
200
200
CHAPTER 5: CONCLUSIONS
201
5.1
Conclusions
201
5.1.1
Section-I (Material Characterization)
202
5.1.2
Section-II (Rheology study)
203
5.1.2.1
Part-A (Untreated fly ash slurry)
203
5.1.2.2
Part-B (Treated fly ash slurry)
203
5.1.3
Section-III (Strength characterization)
205
5.2
Scope for Future Work
207
5.3
Strength and weaknesses of the thesis
208
5.3.1
Strength
208
5.3.2
Weaknesses
208
REFERENCES
209
LIST OF PUBLICATIONS
233
CURRICULUM VITAE
236
~ xii ~
LIST OF FIGURES
Figure
Page
No.
No.
1.1
Schematic diagram showing the detailed scheme of investigation
6
2.1
Structure of a surfactant
45
2.2
Different types of fluids
58
2.3
Rheograms of various continuum fluid models
60
2.4
Flow curves for yield stress fluids
61
2.5
Plots of shear stress vs. shear rate (flow curves)
63
2.6
Schematic diagram of particle electric double layer
68
2.7
Mechanism of flocculation
68
3.1
Location map of India from where the fly ash samples were collected
77
3.2
Molecular structural diagram of CTAB
77
3.3
Molecular structural diagram of the counter-ion
78
3.4
Scanning Electron Microscope
80
3.5
Schematic diagram of Malvern Particle Size Analyzer
83
3.6
Relation between Zeta Potential and Suspension Stability
84
3.7
Settling study of fly ash slurry
85
3.8
Schematic diagram of the rotational rheometer with coaxial concentric
88
cylinder measuring system (Standard: ISO 3219) (δ≤1.2)
3.9
Schematic diagram of the Rheometer
90
3.10
Lime-pH relationship diagram
96
3.11
UCS mould for sample preparation
97
3.12
Sample inside mould for UCS test
98
3.13
Sample of UCS specimens prepared (undergoing curing)
98
3.14
Schematic representation of ultrasonic pulse velocity measurement
99
3.15
Sample preparation for proctor compaction test
101
3.16
Unconfined compressive strength test set up (make: Instron K600, UK)
101
3.17
Test set up for Brazilian tensile strength test (make: HEICO, India)
102
3.18
Ultrasonic pulse velocity test instrument and view of test in progress
103
3.19
A typical P-wave velocity signal plot of fly ash composite material
103
~ xiii ~
3.20
Parametric variations and scheme of experimental investigations for
106
rheology study
4.1
Particle size distribution curve of fly ash sample F1
114
4.2
Particle size distribution of F1 fly ash sample
114
4.3
Particle size distribution curve of fly ash samples F3, F6, F4 and F2
114
4.4
Particle size distribution curve of fly ash samples F5 and F7
116
4.5
SEM Photomicrographs of F1, F2, F3 and F4 fly ash samples at 5000x
116
4.6
SEM Photomicrographs of F5, F6, and F7 fly ash samples at 5000x and
117
1000x
4.7
XRD Pattern of F1 fly ash sample
119
4.8
XRD Pattern of F2 & F3 fly ash samples
119
4.9
XRD Pattern of F4 and F5 fly ash samples
120
4.10
Rheogram of fly ash slurry without any additive
122
4.11
Rheogram of fly ash slurry with additive concentration 0.1%
123
4.12
Rheogram of fly ash slurry with additive concentration 0.2%
124
4.13
Rheogram of fly ash slurry with additive concentration 0.3%
124
4.14
Rheogram of fly ash slurry with additive concentration 0.4%
124
4.15
Rheogram of fly ash slurry with additive concentration 0.5%
125
4.16
Flow curve of fly ash slurry without any additive
126
4.17
Flow curve of fly ash slurry with additive concentration 0.1%
126
4.18
Flow curve of fly ash slurry with additive concentration 0.2%
126
4.19
Flow curve of fly ash slurry with additive concentration 0.3%
127
4.20
Flow curve of fly ash slurry with additive concentration 0.4%
127
4.21
Flow curve of fly ash slurry with additive concentration 0.5%
127
4.22
Viscosity vs. temperature plot of fly ash slurry without any additive
128
4.23
Viscosity vs. temperature plot of fly ash slurry with additive
129
concentration 0.1%
4.24
Viscosity vs. temperature plot of fly ash slurry with additive
129
concentration 0.2%
4.25
Viscosity vs. temperature plot of fly ash slurry with additive
concentration 0.3%
~ xiv ~
130
4.26
Viscosity vs. temperature plot of fly ash slurry with additive
130
concentration 0.4%
4.27
Viscosity vs. temperature plot of fly ash slurry with additive
130
concentration 0.5%
4.28
Plot of surface tension vs. additive concentration
131
4.29
Plot of zeta potential vs. surfactant concentration
132
4.30
Settling results of fly ash slurry
133
4.31
Rheogram of untreated fly ash slurry
134
4.32
Rheogram of fly ash slurry at additive concentration 0.1%
135
4.33
Rheogram of fly ash slurry at additive concentration 0.2%
135
4.34
Rheogram of fly ash slurry at additive concentration 0.3%
135
4.35
Rheogram of fly ash slurry at additive concentration 0.4%
136
4.36
Rheogram of fly ash slurry at additive concentration 0.5%
136
4.37
Flow curve of untreated fly ash slurry
137
4.38
Flow curve of fly ash slurry with additive concentration 0.1%
137
4.39
Flow curve of fly ash slurry with additive concentration 0.2%
137
4.40
Flow curve of fly ash slurry with additive concentration 0.3%
138
4.41
Flow curve of fly ash slurry with additive concentration 0.4%
138
4.42
Flow curve of fly ash slurry with additive concentration 0.5%
138
4.43
Viscosity vs. temperature plot of untreated fly ash slurry without additive
139
4.44
Viscosity vs. temperature plot of fly ash slurry with additive
139
concentration 0.1%
4.45
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.2%
140
4.46
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.3%
140
4.47
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.4%
140
4.48
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.5%
141
4.49
Rheogram of fly ash slurry without additive
144
4.50
Rheogram of fly ash slurry with 0.1% additive
145
4.51
Rheogram of fly ash slurry with (a) 0.2%, (b) 0.3%, (c) 0.4%, and (d)
145
0.5% additive
4.52
Yield stress vs. Temperature plot of fly ash slurry without additive
~ xv ~
146
4.53
Flow curve of fly ash slurry without additive
146
4.54
Viscosity vs. Temperature plot of fly ash slurry without additive
147
4.55
Viscosity vs. Temperature plot of fly ash slurry with 0.1% additive
147
4.56
Viscosity vs. Temperature plot of fly ash slurry with additive
148
4.57
Flow curve of fly ash slurry with additive concentration 0.1%
149
4.58
Flow curve of fly ash slurry with additive
149
4.59
Rheogram of fly ash slurry without additive
151
4.60
Rheogram of fly ash slurry with additive concentration 0.1%
152
4.61
Rheogram of fly ash slurry with additive concentration 0.2%
152
4.62
Rheogram of fly ash slurry with additive concentration 0.3%
153
4.63
Rheogram of fly ash slurry with additive concentration 0.4%
153
4.64
Rheogram of fly ash slurry with additive concentration 0.5%
154
4.65
Flow curve of fly ash slurry without additive
155
4.66
Flow curve of fly ash slurry with additive concentration 0.1%
156
4.67
Flow curve of fly ash slurry with additive concentration 0.2%
156
4.68
Flow curve of fly ash slurry with additive concentration 0.3%
156
4.69
Flow curve of fly ash slurry with additive concentration 0.4%
157
4.70
Flow curve of fly ash slurry with additive concentration 0.5%
157
4.71
Viscosity vs. temperature plot of fly ash slurry without additive
158
4.72
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.1%
158
4.73
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.2%
158
4.74
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.3%
159
4.75
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.4%
159
4.76
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.5%
159
4.77
Yield stress vs. temperature plot of fly ash slurry without additive
160
4.78
Rheogram of fly ash slurry without additive
161
4.79
Rheogram of fly ash slurry with additive concentration 0.1%
162
4.80
Rheogram of fly ash slurry with additive concentration 0.2%
162
4.81
Rheogram of fly ash slurry with additive concentration 0.3%
163
4.82
Rheogram of fly ash slurry with additive concentration 0.4%
163
4.83
Rheogram of fly ash slurry with additive concentration 0.5%
164
~ xvi ~
4.84
Flow curve of fly ash slurry without additive
164
4.85
Flow curve of fly ash slurry with additive concentration 0.1%
165
4.86
Flow curve of fly ash slurry with additive concentration 0.2%
165
4.87
Flow curve of fly ash slurry with additive concentration 0.3%
165
4.88
Flow curve of fly ash slurry with additive concentration 0.4%
166
4.89
Flow curve of fly ash slurry with additive concentration 0.5%
166
4.90
Viscosity vs. temperature plot of fly ash slurry without additive
167
4.91
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.1%
167
4.92
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.2%
168
4.93
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.3%
168
4.94
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.4%
168
4.95
Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.5%
169
4.96
Yield stress vs. temperature plot of fly ash slurry without additive
170
4.97
Yield stress vs. temp. plot of fly ash slurry with additive conc. 0.1%
170
4.98
Yield stress vs. temp. plot of fly ash slurry with additive conc. 0.2%
170
4.99
Yield stress vs. temp. plot of fly ash slurry with additive conc. 0.3%
171
4.100
Yield stress vs. temp. plot of fly ash slurry with additive conc. 0.4%
171
4.101
Yield stress vs. temp. plot of fly ash slurry with additive conc. 0.5%
171
4.102
Viscosity vs. solid concentration at shear rate 100 and 200 s-1
175
4.103
Viscosity vs. solid concentration at 200C and 300C
176
4.104
Settling study cylinder set up
177
4.105
Settling study cylinders at various doses of additives
177
4.106
Settlement vs. time plot at 20% solid concentration
178
4.107
Settlement vs. time plot at 0.1% additive concentration
178
4.108
Compaction curve of fly ash composite material
180
4.109
UCS values of fly ash composite material at different curing periods
181
4.110
Post failure profiles of few UCS samples
181
4.111
Post failure profiles of few Brazilian tensile test samples
182
4.112
Tensile strength values of developed composites at different curing
183
periods
4.113
Relationship between curing period and cohesion
~ xvii ~
184
4.114
Post failure profile of a triaxial test specimen
184
4.115
Relationship between curing period and angle of internal friction
185
4.116
P-wave velocities of developed composites at different curing periods
186
4.117
Relationship between curing period and Poisson’s ratio
186
4.118
Relationship between curing period and density
187
4.119
SEM image of untreated fly ash at 5000x
188
4.120
SEM image of 07 days curing at 5000 x
188
4.121
SEM image of 14 days curing at 5000 x
189
4.122
SEM image of 28 days curing at 5000 x
189
4.123
SEM image of 56 days curing at 5000 x
190
4.124
XRD peak of fly ash composite material at 7 days curing
191
4.125
XRD peak of fly ash composite material at 14 days curing
191
4.126
XRD peak of fly ash composite material at 28 days curing
191
4.127
XRD peak of fly ash composite material at 56 days curing
192
4.128
FTIR results of untreated fly ash
193
4.129
FTIR spectra of treated fly ash (FA 48w50S.1N.1L1.8)
193
4.130
FTIR spectra of treated fly ash (FA 48w50S.2N.2L1.6)
194
4.131
FTIR spectra of treated fly ash (FA 49.8w50S.1N.1L0)
194
4.132
FTIR spectra of treated fly ash (FA 49.6w50S.2N.2L0)
195
4.133
FTIR results of treated fly ash composites at 7 days curing period
195
4.134
FTIR results of treated fly ash composites at 14 days curing period
196
4.135
FTIR results of treated fly ash composites at 28 days curingperiod
196
4.136
FTIR results of treated fly ash composites at 56 days curing period
197
4.137
Correlation between cohesion and angle of internal friction
198
4.138
Correlation between P-wave velocity and Poisson's ratio
198
4.139
Relationship between BTS and UCS
199
4.140
Relationship between density and P-wave velocity
199
4.141
Correlation between density and curing period
199
~ xviii ~
LIST OF TABLES
Table
Page
No.
No.
2.0
Range of chemical composition of Indian coal ashes and soils
12
2.1
Drag reducing polymer solutions
41
2.2
Common types of surfactants
45
2.3
List of commercially available surfactants which are used by various
46
researchers
2.4
List of surfactants, counter-ions, and polymers used by different
47
researchers
2.5
Different types of rheological fluid models
62
3.1
Sample ID and their source of collection
76
3.2
Physical and chemical properties of the surfactant (CTAB)
77
3.3
Physical and chemical properties of the counter-ion (NaSal)
78
3.4
Chemical composition of the lime
79
3.5
Relation between zeta potential and suspension stability
84
3.6
Physical parameters of the measuring tools and sensor system
89
3.7
Sample ID, Parametric variations and suspension characteristic features at
92
solid concentration 20%
3.8
Sample ID, Parametric variations and suspension characteristic features at
94
solid concentration 30%
3.9
Sample ID, Parametric variations and suspension characteristic features at
94
solid concentration 40%
3.10
Sample ID, Parametric variations and suspension characteristic features at
94
solid concentration 50%
3.11
Sample ID, Parametric variations and suspension characteristic features at
95
solid concentration 60%
3.12
Lime – pH relationship
96
3.13
Various proportions of fly ash, surfactant (CTAB), NaSal, and Lime
96
3.14
Experimental size for characterization study
104
3.15
Detailed parametric variations and scheme of experimental design for
104
~ xix ~
rheology study
3.16
Various proportion of fly ash, CTAB, NaSal, Lime and Water for different
107
curing periods
3.17
Total number of tests conducted
108
3.18
Total number of samples tested
108
3.19
Experimental design chart
108
4.1
Physical properties of fly ash samples
112
4.2
Results of particle size analysis of fly ash samples
115
4.3
Chemical composition of fly ashes obtained from EDX study
117
4.4
Elemental composition of fly ashes obtained from XRF study
118
4.5
pH value of fly ash slurry at 20% solid concentration
173
4.6
pH value of fly ash slurry at 30% solid concentration
173
4.7
pH value of fly ash slurry at 40% solid concentration
174
4.8
pH value of fly ash slurry at 50% solid concentration
174
4.9
pH value of fly ash slurry at 60% solid concentration
174
4.10
Engineering properties of fly ash composite materials (FCM)
180
4.11
UCS values of FCM at different curing periods
181
4.12
Relationship between curing period and Brazilian tensile strength
182
4.13
Shear strength parameters of fly ash composite materials
184
4.14
Relationship between curing period and Poisson’s ratio
185
4.15
P-wave velocities of developed composite matrials at different curing
186
periods
4.16
Relationship between curing period and density
186
4.17
Ultrasonic test parameters
187
4.18
The developed correlation among various parameters of fly ash composite
198
materials
4.19
The developed correlation among various parameters of FCM
~ xx ~
200
Chapter 1: Introduction
CHAPTER 1
1.1. Introduction
This chapter gives backgrounds, motivations, and objectives for conducting research
in the fields of fly ash utilization and management, a brief overview of the problem to be
tackled, and its application domains. A brief summary of the structure of thesis in the form of
a series of short chapter abstracts can be found at the end of this introductory chapter.
1.1.1. The background
The problem of fly ash generation and utilization has been extensively studied over the
last three decades. With the increasing demand of coal consumption in turn generates huge
amount of fly ash as a by-product of coal combustion. At present, approximately 290 million
tons of coal is being consumed per annum and produces 170 million tons of fly ash per annum
(Senapati and Mishra, 2012). The generation of fly ash is projected to exceed 300 million tons
per annum by 2017 and 1000 million tons by 2032 A.D (Kumar, 2010). This large volume of
fly ash would occupy huge land area (presently about 65,000 acres of valuable land is
occupied by ash ponds in India) and will pose a serious threat to the environment. Therefore,
there is an urgent need to adopt technologies for gainful utilization and safe management of
fly ash on sustainable basis. Though efforts have been made to utilize the fly ash, yet it is very
meagre as compared to its generation. Presently, India’s fly ash utilization level is only about
85 million tons per year i.e. 50% (Kumar, 2010) and rest 50% is accumulating in the ash
ponds every year. So there is a pressing need of finding higher utilization percentage of fly
ash to address the ever decreasing availability of land area.
Fly ash finds its uses in applications such as in Cement/Concrete/Brick making, in
highways, and embankments constructions, agriculture, hydro power, and irrigation, value
added products like composites/wood substitutes/light weight aggregates/insulating, and
abrasion resistant materials, and as effluent treatment agent etc. But none of these applications
can consume huge volume that India produces. One area where large amount of fly ash can be
used is mine void filling. Nearly one third of our thermal power plants are pit-head power
1
Chapter 1: Introduction
stations. Most of these mines cart sand for backfilling from river beds, which are normally 5080 kms away from the mines. Apart from the royalty, huge amount of expenditure is also
incurred on transportation of sand. In addition, sand is in great demand for many construction
projects and is in short supply in many areas. The availability of river bed sand as a void
filling material is decreasing. So finding an alternative to this is highly desirable. At the same
time mine voids has strong potential to absorb fly ash in bulk without compromising the roof
stability (Kumar, 2003). With the application of current level of technology the percentage of
extraction in the underground coal mines is about 40-50% only, which can be increased
significantly with change in implementation of higher level of technologies. Increased
production through new technologies would also demand higher rates of restoration of mined
out areas to ensure safety and ecological balance. The filling of mine cavities would also
release millions of tons of coal blocked in support pillars.
Keeping the above fact in mind, an attempt is made in this investigation to develop an
engineered backfill fly ash composite material which can replace river bed sand to be used for
filling underground mine voids. However there exists no commercially established technology
or mechanism to transport fly ash to underground void filling areas. The major impediment in
fly ash transportation through water medium is its relative heavy particles. The efficiency of
any transportation system would depend on the flow behaviour of the fly ash particles. In this
investigation the flow characteristics of fly ash slurry was studied with and without an
additive at varying temperature environment. There are many successful case histories of
modifying the flow behavior of mineral slurries and liquids with additives. The problem with
fly ash transportation is its specific gravity. Majority of the particles tend to settle down in
water (sp. gr. 1) flow pipe lines due to its higher specific gravity (average > 2.0). In this
investigation the influence of additives on flow behaviour has been evaluated.
1.1.2. Needs statement and motivation for the present work
The availability of land area to the growing population of India is becoming dearer
day by day. It also adversely reflects in agricultural output. In India there are more than 85
coal based thermal power plants which are continuously producing fly ash and dumping the
fly ash-water slurry in the ash ponds situated nearby the plant. Out of the 170 million tons of
produced fly ash about 50% is utilized and 50% rest is dumped in the ash ponds. At present
2
Chapter 1: Introduction
about 65,000 acres of valuable cultivable land is occupied with fly ash. The problem is
attributed to the fact that high concentration of fly ash or pond ash is difficult to be
transported due to its higher specific gravity. In the lean slurry transportation system huge
amount of water energy also goes to the ash pond area which not only occupies large area but
also contaminates the surface and ground water regime. The other disadvantage of this system
is that energy consumption to pump the slurry increases because of large volume of water
involved in transportation of fly ash. This is because of the quick settling tendency of the fly
ash particles in the pipe bottom during transportation which may lead to pipe jam if enough
water is not flushed along with fly ash. Hence lean slurry transportation is adopted in all the
power plants in India. Therefore to address the twin problem of quick settling nature of fly ash
and to reduce the water requirement, the flow properties has been evaluated by selecting an
additive which will modify the surface properties of the fly ash significantly as a result we can
go for adopting high concentration slurry disposal system. The developed slurry can be
transported in pipelines to mine void filling areas for stowing purposes to replace the ever
depleting river bed sand.
The developed fly ash slurry can be constituted as a composite suspension of fly ash
and chemical reagents in water. A number of available additives can be used to alter the
chemical and physical properties of the fly ash slurry as required for better flowability and
stability of the slurry. There is still a lack of information in the open literature regarding the
effects of various chemical reagents such as surface active agents (surfactants) on the
rheological properties of fly ash slurries at varying temperature environment. Hence, this
research investigates the effects of chemical reagents on the rheology of fly ash slurries.
Mineral and chemical reagents play an important role in controlling the physical and chemical
properties of fly ash slurries. However, not all chemical reagents influence in the same way on
the rheological properties, primarily because of their different physical and chemical
properties. There is still a lack of information regarding the coupled effects of chemical
reagents and temperature on the rheology of fly ash slurries. Therefore, in this investigation
an attempt is made to develop a better understanding of the important mechanisms that
controls the rheology of fly ash slurry subjected to varying temperature environment and to
3
Chapter 1: Introduction
investigate the performance of chemical reagents in controlling the rheological behavior of fly
ash slurries.
The present study also undertakes in-place strength development investigation using
another reagent i.e. lime to develop a backfill material to be placed in mine voids for filling
purposes. The knowledge thus gained could ultimately allow the optimization of fly ash slurry
rheology parameters to enhance flowing attributes and at the same time strength gain of the
developed material would lead both to ecological and economic benefits. The details have
been briefly described in the succeeding sections.
1.1.3. Objectives and scope of the work
1.1.3.1. Objectives
The primary objective of the present investigation was to develop an engineering material
based on fly ash to be placed in underground coal mine voids. The specific objectives to meet
the aim were the following:
i.
To characterize the typical fly ash from several sources
ii.
To select the most favourable fly ash for its potential to flow in hydraulic pipelines
iii.
To select and characterize the additives to modify the fly ash material
iv.
To determine the flow behavior with the selected additive and optimize the same
v.
To determine the strength characteristics of the in-place fly ash composite materials
after mixing with lime.
vi.
Analysis of the experimental results to predict the behavior of fly ash composite
material
1.1.3.2. Scope of the study
The investigation was undertaken with fly ash procured from seven number of thermal
power plants located at various parts of the country listed elsewhere. The following works in
addition to others were undertaken for all the seven fly ashes to determine their suitability for
use as a stowing material.
a.
Mineralogical characterization such as
X-ray diffraction (XRD) analysis
Scanning Electron Microscopy (SEM) studies
4
Chapter 1: Introduction
b. Chemical Characterization such as :
Energy-dispersive X-ray spectroscopy (EDX) studies
Energy-dispersive X-ray Fluorescence (XRF) studies
c.
Physical characterization such as:
Specific surface area
Particle size analysis
Moisture content
Specific gravity
Bulk density
Porosity
pH
Out of the seven fly ashes studied only one fly ash was selected based on the above properties
to further investigate the rheological behavior and in-place strength characteristics with and
without an additive.
1.1.3.3. Approach/methodology
The objective of the investigation was to develop an alternate engineering material to be
placed in underground coal mine voids. One of the major impediments in placing the fly ash
in underground coal mines is its high specific gravity. It adversely affects the flowing
behavior. So surface acting agents (surfactants) has been chosen and added to change the
rheological parameters. Its in-place strength behavior was also tried to be enhanced with
addition of another additive e.g. lime. The methodology followed is shown in the flow chart
(Figure 1.1). The aim and objectives are achieved by:
i)
Characterization of seven fly ashes and selection of the best one for further analysis
ii) Selection of additives and their characterization
iii) Development and characterization of fly ash based composite materials with additives
iv) Evaluation of rheological properties of the developed materials at varying conditions
such as shear stress, shear rate, temperature, and concentration
v) Optimization of the fly ash composite material with respect to above for strength
enhancement
5
Chapter 1: Introduction
vi)
Selection, characterization and optimization of strength enhancing materials
vii)
Determination of the mechanical behaviour of the developed fly ash composite
materials
viii)
Analysis of results to assist in deciding the influence of different parametric
variations.
Fly ash from different sources collected
Evaluation for suitability to fill mine voids
Surfactant
Development of fly ash composite material for flowability
Counter-ion
Determination of rheological parameters at different solid concentration
Optimization of surface influencing ingredients
Lime
Determination of geotechnical properties of FCM
Analysis of the results
Figure 1.1: Schematic diagram showing the detailed scheme of the investigation
6
Chapter 1: Introduction
1.1.4. Outline and organization of thesis
The aim and specific objectives have been addressed through well designed and regulated
approaches. The details of the investigation carried out as well as the results are reported in
different sections. The thesis is structured as follows:

Chapter 1 introduced problem statement, background of the work, goal to reflect the
long term objectives and specific objectives to meet the goal. It also introduced the
methodology adoted with a flow chart to show the different steps involved in carrying
out the research and parametric variations that were experimented.

Chapter 2 is devoted to a detailed literature survey on fly ash utilization trends in
mining sector and its economical and environment friendly transportation to mine
filling site. Also the basic concepts involved in fly ash slurry transportation, the
physical and chemical properties of fly ash and the role of chemical additives to
reduce drag friction in pipelines are discussed. A brief introduction to rheology and
constitutive rheological models are also reviewed.

Chapter 3 introduced the materials which were used to carry out the research, their
sourcing and collection methods. In this chapter the material characterization and
methods are discussed as per the National and International standards available in the
literature. This chapter also discussed about sample preparation, testing process,
machines used, and their brief specifications. I also highlight the sample size and
number of tests carried out to meet the goal.

Chapter 4 described and presented the results of this investigation in three different
sections. Section I deals with the material characterization results, section II deals with
results of the rheology study, and section III deals with the results of strength
characteristics study.

Chapter 5 deals with the summary of observations and important conclusions drawn
on the basis of analysis and experimental results. A few recommendations for future
research work have also been formulated here. Strength and weaknesses of the thesis
is also highlighted.
7
Chapter 2: Literature Review
CHAPTER 2
2. Literature Review
This chapter provides information about the relevant work and the state-of-the-art
related to the area of fly ash utilization and drag reduction phenomena in pipe line
transportation system. The incremental development for rheology modification in slurry flow
pipelines from past decades to the recent has been addressed here.
2.1. Introduction
There is a substantial amount of literature that focuses specifically on fly ash utilization
and management. The ash ponds are typically near to the site of power plants as long distance
transportation of large quantities is very uneconomical in terms of water consumption and
power consumption. So, prospects of transporting increasing quantities of fly ash
economically should be explored. Mine filling is one such option where large scale utilization
is possible. But its transportation to mine filling site is not yet economically established. This
investigation is an attempt to address a few aspects of this issue. A major problem in large
scale transportation of fly ash is the high specific weight or settlement characteristics of the
slurry.
The rheological behavior of the fly ash slurries must be optimized to achieve effective
suspension properties for smooth flow in the pipe lines. Modification of surface properties of
fly ash particles through additions of chemically active materials (additives) is one such
option. A number of additives such as polymers and surfactants are available that alter the
chemical and physical properties of the fly ash slurries as required for the flowability as well
as stability of the slurry transportation. The various aspects such as rheology, additives, drag
reduction; settlements etc. have been discussed in detail. The literature review part of the
current investigation is divided into eight parts i.e.
i.
General properties of fly ash
ii.
Suitability of fly ash as a mine filling material
8
Chapter 2: Literature Review
iii.
Hydraulic pipeline transportation with and without an additive
iv.
Drag reduction technology
v.
Drag reducing surfactants
vi.
Polymeric drag reduction research
vii.
Engineering uses of fly ash, specifically the strength development of fly ash composite
materials.
viii.
Rheology and constitutive rheological models
2.2. General properties of fly ash
2.2.1. Physical Properties
Physical properties of fly ash help in classifying the fly ashes for engineering
purposes. Rehsi and Garg (1988) have made a critical assessment of the different physical
properties of Indian fly ashes. The particles of the fly ashes were angular as well as irregular
in shape. The shape of particles were affected the different physical properties of fly ash.
The specific gravity (sp. gr.) of fly ash is generally low compared to that of soil (Ghosh, 1996;
Sridharan and Prakash, 2007). Pandian et al., (1998) reported that the range of sp. gr. varies
from 1.46 to 2.66 for Indian fly ashes. Sp. gr. of Indian fly ashes varies in the range of 1.66 to
2.55 as reported by Sridharan and Prakash (2007). Gray and Lin (1972) reported that the
variation of sp. gr. of the fly ash is the result of a combination of many factors such as
gradation, particle shape, and chemical composition. The low sp. gr. of the fly ash is mainly
attributed due to the presence of large number of hollow cenospheres from which the
entrapped air cannot be removed, or the variation in the chemical composition, in particular
iron content, or both are attributable to these facts (Ghosh, 1996; Pandian et al., 1998;
Pandian, 2004; Sridharan and Prakash, 2007).
Grain size distribution indicates if a material is well graded, poorly graded, fine or
coarse, etc. and also helps in classifying the coal ashes. Coal ashes are predominantly silt
sized with some sand-size fraction. Leonards and Bailey (1982) have reported the range of
gradation for fly ashes and bottom ashes which can be classified as silty sands or sandy silts.
The pond ashes consist of silt-size fraction with some sand-size fraction. The bottom ashes are
coarser particles consisting predominantly of sand-size fraction with some silt-size fraction.
Based on the grain-size distribution, the coal ashes can be classified as sandy silt to silty sand.
They are poorly graded with coefficient of curvature ranging between 0.61 and 3.70. The
9
Chapter 2: Literature Review
coefficient of uniformity is in the range of 1.59–14.0. Pandian et al., (1998) carried out
experimental investigation on Indian coal ashes and reported that fly ashes are fine grained
substances consisting of mainly silt-size particles with some clay-size particles of uniform
gradation. Consistency limits namely liquid limit, plastic limit, and shrinkage limit are
extensively used in the field of geotechnical engineering. Pandian (2004) reported that fly
ashes have liquid limit ranging from 26 to 51%. He observed from the experimental study
that fly ashes are non-plastic and hence plastic limit could not be determined. It was also not
possible to carry out shrinkage limit tests since the ash pats crumbled upon drying. Free swell
index has been developed in the field of geotechnical engineering to differentiate between the
swelling and non-swelling soils (Sridharan and Prakash, 2007). Nearly 70% of Indian coal
ashes exhibit negative free swell index which is due to flocculation, low sp. gr., and less
quantity of clay size particles (Pandian, 2004; Sridharan and Prakash, 2007). Investigations
carried out by Pandian et al., (1998) show that the coal ash particles are generally
cenospheres, leading to low values of specific gravity.
The classification of coal ashes from geotechnical engineering point of view is
important for an effective and efficient use in geotechnical engineering practices (Pandian,
2004). The fly ashes are classified as fine grained ashes as they comprise of predominantly
silt sized particles. They can belong to one of the five subgroups, namely MLN, MLN-MIN,
MIN, MIN-MHN and MHN as reported by Sridharan and Prakash (2007). If more than 50%
of fines belongs to either the coarse silt size (20 μm < particle size ≤ 75 μm) category, or the
medium silt size (7.5 μm < particle size ≤ 20 μm) category or fine silt plus clay size (particle
size ≤ 7.5 μm) category, then the ash is accordingly represented as MLN, MIN and MHN. If
the coarse and medium silt size fractions comprise more than 50% fines and more than the
percentage of combined medium silt and fine silt plus clay size fractions, then the ash is
designated as MLN-MIN group. If the medium and fine silt plus clay silt size fractions
comprise more than 50% fines and also more than the percentage of combined coarse silt and
medium silt size fractions, then the ash is designated as MIN-MHN group.
2.2.2. Chemical Properties
Sridharan and Prakash (2007) stated that the chemical properties of fly ash depends
upon many factors such as geological factors related with coal deposits deciding its quality,
10
Chapter 2: Literature Review
the composition of the parent coal, the combustion conditions like the method of burning and
control of combustion process, the additives used for flame stabilization, corrosion control
additives used, hopper position, flow dynamics of the precipitators, and the removal
efficiency of pollution control devices. In particular, fly ashes that are produced from the
same source with similar chemical composition can have significantly different mineralogy
depending upon the coal combustion technology used, which in turn affect the ash hydration
properties. The mineral groups present in coal such as hydrated silicates, carbonates, silicates,
sulphates, sulphides, phosphates, and their varying proportions normally play a dominant role
in deciding the chemical composition of the fly ash. When the pulverized coal is subjected to
combustion, the clay minerals undergo complex thermo-chemical transformations. During
this process, sillimanite and mullite are crystallized as slender needles along with glass
formation.
Pyrites and other iron bearing minerals form iron oxides and calcite gets
transformed into CaO. The glassy phase formed renders pozzolanity to the fly ash. In almost
all geotechnical engineering applications, the pozzolanic property of fly ash plays an
important role.
Krishna, (2001) stated that the term pozzolana is used to designate a siliceous or a
siliceous and aluminous material which by itself, possesses no cementitious value but in the
presence of water, chemically reacts with calcium hydroxide to form the compounds
possessing cementitious properties. Based on pozzolanic property, fly ashes can be classified
as self pozzolanic, pozzolanic, and non-pozzolanic. Fly ashes can also be classified as
reactive and non reactive fly ashes. Reactive fly ashes are those, which react with lime to
give sufficient amount of strength. Non-reactive fly ashes are those, which do not give
sufficient strength even on addition of lime. Self pozzolanic and pozzolanic fly ashes are
reactive fly ashes where as non-pozzolanic fly ashes are nothing but non reactive fly ashes.
According to the American Society for Testing Materials (ASTM C618 – 08) the ash
containing more than 70 wt% SiO2 + Al2O3+ Fe2O3 and being low in lime are defined as class
F, while those with a SiO2 + Al2O3+ Fe2O3 content between 50 and 70 wt% and high in lime
are defined as class C. The low-calcium Class F fly ash is commonly produced from the
burning of higher-rank coals (bituminous or anthracite coals) that are pozzolanic in nature.
The high-calcium Class C fly ash is normally produced from the burning of low-rank coals
11
Chapter 2: Literature Review
(lignite or sub-bituminous coals) and is self pozzolanic in nature. Ahmaruzzaman (2010)
stated that the chief difference between Class F and Class C fly ash is in the amount of
calcium and the silica, alumina, and iron content in the ash. In Class F fly ash, total calcium
typically ranges from 1 to 12%, mostly in the form of calcium hydroxide, calcium sulphate,
and glassy components, in combination with silica and alumina. In contrast, Class C fly ash
may have reported calcium oxide contents as high as 30 - 40%. Another difference between
Class F and Class C fly ash is that the amount of alkalis (combined sodium and potassium),
and sulphates (SO4), are generally higher in the Class C fly ash than in the Class F fly ash.
The range of chemical composition of Indian coal ashes together with that for soil (for
comparison purposes) is reported in Table 2.0.
Table 2.0.Range of chemical composition of Indian coal ashes and soils (Pandian, 2004)
Compounds Fly ash
SiO2
38–63
Al2O3
27–44
TiO2
0.4–1.8
Fe2O3
3.3–6.4
MnO
0–0.5
MgO
0.01–0.5
CaO
0.2–8
K2O
0.04–0.9
Na2O
0.07–0.43
LOI
0.2–3.4
Roode (1987) reported that loss on ignition is
Soils
43–61
12–39
0.2–2
1–14
0–0.1
0.2–3.0
0–7
0.3–2
0.2–3
5–16
generally equal to the carbon content.
Throne and Watt (1965) observed that the amount of SiO2 or SiO2 + Al2O3 in fly ash
influences the pozzolanic activity. Minnick (1959) reported that a relatively high percentage
of carbon content decreases the pozzolanic activity. The silica content in fly ashes ranges
between 38 to 63%, the alumina content ranges between 27 and 44%, the calcium oxide
content is in the range of 0 to 8%. It has been found that all the Indian coal ashes satisfy the
chemical requirements for use as a pozzolana. According to ASTM 618 classification,
typically fly ash originated from lignite coal as from Neyveli lignite mines can be termed as
Class ‘C’ and the rest can be termed as Class ‘F’. Torrey (1978) reported that fly ash
collected by electrostatic precipitators (ESP) has 38% more CaO and 58% less carbon content
than ash collected by mechanical collectors. Moreover the former is finer than the latter.
12
Chapter 2: Literature Review
Davis (1949) has stated that finer the fly ash, higher is its pozzolanic reactivity.The
investigations carried out on Indian fly ashes show that all the fly ashes contain silica,
alumina, iron oxide, and calcium oxide (Pandian and Balasubramonian, 2000).
The
mineralogical composition of fly ash, which depends on the geological factors related to the
formation and deposition of coal, its combustion conditions, can be established by X-ray
diffraction (XRD) analysis. Quartz and mullite are the major crystalline constituents of lowcalcium fly ash (CaO < 5%), whereas high-calcium fly ash (CaO > 15%) consists of quartz,
C3A, CS, and C4AS (Sengupta, 1991; Erol et al., 2000; Singh and Kolay, 2002; Pandian,
2004; Sridharan and Prakash, 2007; Ahmaruzzaman, 2010).
The morphological studies
through Scanning Electron Microscope (SEM) indicate that the coal ash contains glassy solid
spheres (plerospheres), hollow spheres called cenospheres, sub rounded porous grains,
irregular agglomerates, and irregular porous grains of unburned carbon (Senol et al., 2003;
Sridharan and Prakash, 2007).
When water or any aqueous medium comes in contact with fly ash iron, aluminum,
and manganese oxides sink which determines the release of the trace elements associated with
them into the aqueous medium. The degree of solubility of these oxides in turn depends upon
the pH of the aqueous medium (Sridharan and Prakash, 2007). The fly ash with higher free
lime and alkaline oxides exhibits higher pH values (Pandian, 2004; Sridharan and Prakash,
2007). Sridharan and Prakash (2007) reported that about 50% of Indian fly ashes are alkaline
in nature.
Formation of cementitious materials by the reaction of lime with the pozzolans in
presence of water is called hydration. The hydrated calcium silicate or calcium aluminate,
join the inert materials together to give strength to fly ash material. The pozzolanic reactions
for stabilisation are given by the following equations.
CaO + H2O → Ca (OH)2 + Heat
Ca (OH)2 → Ca++ + 2(OH)
Ca++ + 2(OH) + SiO2 → CSH (Calcium Silicate Hydrate)
(Gel)
Ca++ + 2(OH) + Al2O3 → CAH (Calcium Aluminate Hydrate)
(Fibrous)
Class C type fly ash does not need addition of lime where as class F does (Senol et al., 2002).
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Chapter 2: Literature Review
2.3. Fly ash as mine void filling material
This section provides information about the relevant work and the state-of-the-art
related to the area of fly ash utilization in mining sector focusing its suitability and detailed
review of fly ash utilization trends in underground and opencast coal mining sectors. More
literature on this topic can be found elsewhere (Chugh et al., 2001; Kumar, et al., 2003;
Kumar and Mathur, 2005; Rao et al., 2005; Paul et al., 1994; Rahman, 2005; Ram et al.,
2007; Arora and Aydilek, 2005).
2.3.1. Suitability of fly ash as mine filling material
Recently Ahmaruzzaman (2010) published a critical review article on the utilization of
fly ash. In his paper he discussed about current and potential applications of coal fly ash,
including its utilization in cement and concrete, adsorbent for the removal of organic
compounds, waste water treatment, light weight aggregates, zeolite synthesis, mine backfill,
and road construction. However, no reference is given to its rheological parameters to
transport fly ash hydraulically to mine filling areas.
Jirina and Jan (2010) studied the possibility of filling empty underground void spaces
with fly ash and cement fly ash mixes, for the purpose of reducing the impact of deep mining
activities on the surface. The method of physical modelling was used to study the behaviour
of fly ash mixes deposited in extracted mine spaces. The physical model experiment proved
that fly ash mixes could be used as a filling material in underground cavities that was created
as a result of deep mining, without serious difficulties of strata movement. Due to its small
angle of slope (30-350), fly ash material spread out to the sides. The fly ash settled not only in
the lower parts of the mine working, but also penetrated beyond the caving falls created, e.g.
due to seismic events. Due to its higher cohesion (C=9.5 KPa for dry fly ash), the fly ash did
not behave as loose material, but blocks are formed that gradually become submerged in
water.
Bulusu et al., (2005 & 2007) investigated the success of coal combustion by-product
based grout mixtures in reducing acid mine drainage problems in mines. Laboratory
experiments conducted for grouts with different proportions of class F fly ash, flue gas
desulfurization by-product, and quicklime, for slump, modified flow, bleed, and strength. The
14
Chapter 2: Literature Review
selected optimal grout mixture was injected into the Frazee mine, located in Western
Maryland. Pre- and post-injection water quality data were collected to assess the long-term
success of the grouting operation by analysing mine water, surface water, and ground water.
The tests indicated that the four mechanical properties of grout mixtures, slump, modified
flow, bleed, and strength, are related to the fly ash and free lime content of the mixture. Eight
years of post-injection water quality monitoring showed that there was significant decrease in
acidity, concentration of major ions, and trace elements in the mine water. The grout cores
showed that the hardened grout retained its strength and low hydraulic conductivity with no
evidence of in-situ weathering.
Mishra and Das (2010) examined the suitability of Talcher coal fly ash for stowing in
the nearby underground coal mines based on their physico-chemical and mineralogical
properties. The SEM images revealed spherical particle morphology of the ash samples which
would create lubricating action due to the well known “ball-bearing” effect which would
result in frictionless flow in the stowing range causing less wear and tear on the pipelines.
Due to improved rheology, it would also help in reducing the energy cost in pipeline
transportation during hydraulic stowing operations. The presence of SiO2 in abundance would
increase the strength and the presence of CaO would give cementing properties after stowing.
The ash samples also contain very negligible amount of unburned carbon and hence there is
no risk of spontaneous heating if utilized as a stowing material in underground coal mines.
Ozerskii and Ozerskii (2003) reported the results of a study of the mineral, chemical,
and radionuclide compositions of coal ash and slag waste of the Berezovsk state regional
power plant and the capping of the Berezovskii-1 coal mine suggested disposal of the waste
into the mined-out space. The use of the ash for reclamation of refuse soils have a positive
ecological effect due to the chemical amelioration, strengthening, and lower settlement of the
refuse soils and compensation of the rock mass deficit in the mined-out space.
Ward et al., (1999) described a power station fly ash transportation system, from a bag
house to a mine rehabilitation site, at a distance of 12 Km. Ash was mixed with water and
pumped to the mine rehabilitation site. The concentration of the ash / water mixture was kept
at Cw ≈ 70%. Physical tests demonstrated that it is possible to leave the pipeline full of slurry
15
Chapter 2: Literature Review
at Cw = 65% for up to 24 hours and still successfully restart the plant. The deposited ash also
exhibited a relative fast strength gain which allowed rehabilitation to be commenced in 1-2
weeks of cessation of ash deposition.
Kumar (2000) studied the leaching behaviour of trace elements of the ashes of a
Captive Thermal Power Station and the following conclusions were drawn from his study:
 In the study period of 274 days there was practically no leaching of elements namely
chromium, selenium, aluminium, silver, arsenic, boron, barium, vanadium, antimony,
and molybdenum from all the fly ash samples reported.
 Out of the nine elements found in the leachates only calcium and magnesium were
found to be leaching in the entire period. The other seven elements namely iron, lead,
copper, zinc, manganese, sodium, and potassium leaching was sometimes intermittent.
The leaching of sodium and potassium practically stopped after 35 days and 40 days
respectively.
 The concentration of elements in the leachates was below the permissible limits for
discharge of effluents as per IS: 2490 and also for drinking water standards IS: 10500.
On the basis of the above observations it is found that fly ash is environmentally
benign material and can be engineered for their bulk utilization for reclamation of mined out
areas and for soil amendment for good vegetation.
Jain and Sastry (2001) reported that the acid mine drainage (AMD) problem can be
mitigated in the coal mining areas with the use of fly ash and slurry transportation system can
be conveniently adopted. Size modification can improve its flow properties. Pelletization of
fly ash is one such option to improve size and shape of fly ash.
Vories (2003) reported that the placement of fly ash materials on the mine site resulted
in a beneficial impact to human health and the environment. He opined that the beneficial
uses of fly ash in mining sector include:
a. A seal to contain acid forming materials and prevent the formation of AMD;
b. An agricultural supplement to create productive artificial soils on abandoned surface mine
lands where native soils are not available;
16
Chapter 2: Literature Review
c. A flowable fill that seals and stabilizes abandoned underground coal mines to prevent from
subsidence and strata movement;
d. A non-toxic, earth like filling material for final pits ad within the spoil area.
Kumar & Mathur (2005) reported that about 10,000 m3 of pond ash was stowed in an
underground coal mine successfully. About 13,000 m3 pond ashes were also stowed in
Durgapur Rayatwari Colliery of Western Coalfields Ltd. (Singh & Goel, 2006). The results of
both the demonstration were quite encouraging and it is observed that fly ash stowed bed has
good stability. The leachate was also found to have no adverse impact due to the use of these
additives (Kumar et al., 2003).
Ghosh (2005) demonstrated through laboratory tests that pond ash with additives
could be safely used as a stowing material for underground coal mines. He reported that the
water percolation rate was 16.235 cm/h without any additive and 18.97 cm/h with additive.
This shows that use of an additive has a positive impact on the percolation rate. The results of
spontaneous heating tests showed that the proportion of total combustible material is very
low, i.e. 2.244%.
So the ash sample did not attain crossing point and ignition point
temperature even at a bath temperature of 2000C.
Panday and Kumar (2005) reported the feasibility of filling about 150 lakh MT of fly
ash in 10 years time in one of the underground coal mine by adopting lean slurry
transportation system. Prashant (2005) reported that the present share of mine filling
application is about 3% only which can increase many folds by proper utilization in filling of
abandoned and active coal mines.
Rao et al., (2005) reported that the overall cost of stowing was less than that of sand
stowing. They also observed that the system of ash stowing was advantageous over sand
stowing and estimated that the overall ash stowing cost was nearly Rs.24 less than that of sand
stowing.
Roy Choudhry (2005) reported successful dumping of 100 lac m3 of ash in
underground collieries which were very close to thermal power plants. The attributes of fly
ash such as silt-size particles, low bulk density, high water holding capacity, favourable pH,
17
Chapter 2: Literature Review
presence of many nutrients such as N, P, S, etc. are favourable properties for mine spoil
reclamation as well (Ram amd Masto, 2010).
Ghosh et al., (2006) reported that fly ash has no affinity towards spontaneous heating
and hence can be safely used as underground filling material for stowing purposes.They also
reported that the sp. gr. of the ash was 2.0, about 25% lighter than river bed sand (average sp.
gr. 2.65). These characteristics favour hydraulic transportation during filling as it would cause
less head loss during transportation through pipelines reducing energy cost and cost of
hydraulic transportation as compared to sand. The ash was also having low bulk density i.e.
1.08 t/m3, which is 37% less than that of sand (with average bulk density of 1.67 t/m3).
2.3.2. Settling characteristics, leachates, and heavy metals in fly ash
Colloidal solids normally carry charges on their surface which lead to the stabilization
of the suspension by addition of some chemical reagents. The surface property of such
colloidal particles can be changed or the dissolved material can be precipitated to facilitate the
separation by gravity or by filtration.
Dutta et al., (2009) reported the leaching of ten elements-namely, Fe, Mn, Ca, Na, K,
Cu, Cr, Zn, Arsenic, and Pb. The leaching conditions were selected to broadly simulate that of
surface coal mines in order to estimate the usefulness of the materials for back-filling of
abandoned coal mines and assess the possibility of contamination of the sites by release of
heavy metal ions. A much higher mobility of the elements had been observed at a low pH.
Less leaching was found at a high pH except for arsenic. The mobility of toxic elements from
fly ash was negligible where the final pH of the leachate was alkaline or nearly neutral.
Prasad et al., (2003) found that pond ash and weathered ash leach heavy metals in
alarming concentration when pH value was beyond 6.0.
Hwang and Lattore (2011) conducted a statistical screening test to obtain information
on the factors governing groundwater quality after open pit restoration using manufactured
coal ash aggregates (MAs) as a sub-soil substitute. MA application rate was (2:1 or 1:2
topsoil/MA volume ratio), rainfall intensity (high or low), and aggregate size (2.36-4.75 mm
or 4.75- 9.53 mm). Among the water quality parameters examined (pH, turbidity, heavy metal
18
Chapter 2: Literature Review
content, conductivity, and hardness), the last two parameters were significantly higher (p <
0.05) in soil amended with MAs than in a control reactor using sand. Based on the statistical
analysis, the results depicted that the pH, turbidity, and heavy metal (Pb and Cd)
concentration were not a problem in mine restoration operation.
Kumar et al., (2006) reported that faster rate of settlement is desirable for quicker
drainage of water during hydraulic stowing with fly ash. Faster settlement of solids avoids
clogging of pores of barricades and also it would not cause building up of any hydrostatic
pressure inside the barricades leading to its damage. On the other hand if the solids are left in
suspension for a longer period of time, there is a likelihood of escape of fines through the
barricades. It is found that the settlement rate can be increased by increasing the slurry
concentration by using a suitable additive (Jain and Sastry 2003).
Jain et al., (2006) observed that elements from acidic ash leach readily than from
alkaline ash. Fly ashes are generally disposed at pH 7.0-8.5. They confirmed that the leaching
in alkaline medium was much lower as compared to acidic medium and opined that fly ash
can be used safely for mine filling purposes in alkaline medium without having any adverse
impact on the environment.
2.3.3. Paste backfill system
It is basically high solids concentration slurry. The term “paste” generally implies
mixes containing over 70% solids concentration with less than 4% bleed.
Bunn (1989) observed that at a concentration of less than 60% with a maximum flow
rate of 0.03 m3/s resulted in 1.7 m/s velocity, enough to facilitate pipe line transportation
smoothly. Approximately 900 tonnes of fly ash paste with Cw<64% was transferred to the
disposal site in a period of 21 pumping days with an average of paste mass flow rate of 30 t/h.
The angle of inclination of the deposited material was 2 to 3 degrees. Even the heavy rainfall
during monsoon has produced no erosion at the observed site.
Bunn et al., (1990) examined the maximum amount of water that is available for
recycling from a range of dense phase fly ash slurries. It was found that in a dense phase
slurry system that disposed 1000 tons of slurry, with a Cw of 73% required 730 tons of fly ash
19
Chapter 2: Literature Review
with 270 tons of water. When this 1000 tons of slurry was deposited at the disposal site 120
tons of water was available for recycling. Therefore, 150 tons of water was captured in the
deposited ash. From this study it was found that the percentage of water available for
recycling varied depending on the concentration Cw and the particle size distribution of the fly
ash. The volume of return water varied from 12.4% to 59.8%. It was also observed that the
deposited slurry placement density showed an increase when the slurry pumped was above Cw
of 65%.
Bunn et al., (1991) examined the relationship between the packing density of slurry
obtained by assisted compaction and the pumpability as determined by rheology testing. The
results indicated that the differences between the Cw’s from the rheology tests and the
compacted fly ash slurries varied from 12.5% to 14.94%. The variation in the d 50 of the fly
ash samples tested ranged from 8µm to 45µm.
Rudzinski (2005) described a study of the behaviour of fresh cement pastes under
shear in a rotational viscometer. It was observed that an addition of fly ash to Portland chinker
influenced the change of flow behaviour of cement pastes from thixotropic flow to
thixotropic-dilatant flow. Addition of fly ashes without decreasing the amount of cement
brought about an increase in the basic rheological characteristics of cement pastes, growth
intensity being dependent on volume fraction of solid and percentage of addition.
Chugh et al., (1999) developed paste backfill mixes consisting of 70% Coal
Combustion By-products (CCBs) to reduce movement and acid mine drainage (AMD) and
opined that the mix could increase production by 5-8% more. They also successfully
demonstrated that backfill material with 65-70% CCBs, gob and fine coal processing waste
provided lateral containment and strengthened coal pillars.
Jorgenson and Crooke (2001) indicated that placement of fly ash paste under saturated
and unsaturated conditions would not impact ambient water quality. The fly ash paste
exhibited good engineering characteristics when compared to the native soils and mine spoils
currently used for reclamation. Strengths obtained from the fly ash and water mixtures were
generally higher than those found in the natural soils.
20
Chapter 2: Literature Review
Nagataki et al., (1984) found that the rate of adsorption of superplasticizer on fly ash
was higher than that in cement. It was also observed that amount of superplasticizer had
positive influence on coefficient of viscosity of fly ash and there was a correlation between
bulk sp. gr. of fly ash and fluidity of paste. The higher the bulk sp. gr., the lower is the
coefficient of viscosity.
Mahlaba et al., (2011) compared the behaviour of pastes by varying brine composition
mixed with two types of fly ashes. The results showed that fly ash played a more prominent
role in the behavior of pastes than brines. Therefore they concluded that the constituent of
paste play a major role in the development of an environmentally sound paste backfill
practice.
Turkel (2007) studied a mixture of high volume fly ash, crushed limestone powder,
and low percentage of pozzolana cement in different compositions. The amount of pozzolana
cement was kept constant as 5% of fly ash weight. The amount of mixing water was chosen in
order to provide optimum pumpability by determining the spreading ratio of the mixture using
flow table method. The test results indicated that the mixtures had superior shear strength
properties compared to that of compacted soils.
Corners (2001) reported that cement was the largest cost component in the backfill
system and recommended that partial replacement of cement with type “C” fly ash as 50%. It
was observed that compressive strengths equal or greater than the compressive strengths of
type “F” fly ash mixture at only 20% cement replacement.
McLoren et al., (2001) evaluated the use of admixtures in reducing backfill binder
concentrations and demonstrated a 20% reduction of cement is possible while maintaining
critical strength and flowability criteria. The addition of an admixture (in two variations i.e.
0.25g per kg and 0.50g per kg) - a foaming agent, had several effects on the backfill
including slower water drainage from the backfill resulting in a reduction of total bleed water,
reduced sensitivity of the flow properties to variations in the moisture content, increased
compaction rate of the backfill at high solids contents, a higher dispersion with the addition of
the cement than that of the tailings alone, enhanced flowability of the backfill material, and an
overall reduction in the compressive strength of the backfill. The treated mixture had better
21
Chapter 2: Literature Review
flow properties and hold particles in suspension more effectively than untreated backfill. The
reduced shrinkage of the material allowed better adhesion of the mass to the stope walls. The
reduction in uniaxial compressive strength in three-day tests made it impractical for use in
backfill. The addition of other alternative admixtures resulted in an increase in compressive
strength and substantial binder content reduction. Additionally, the admixture enhanced
flowability of the backfill to an extent that further strength gains may be possible by reducing
the water content of the backfill while still maintaining minimum flowability criteria.
Deb and Chugh (2005) developed eco-friendly paste backfill mixes using coarse coal
processing wastes (gob) and CCBs and placed 9,293 tons in an abandoned underground panel.
The developed grouts flowed laterally to a distance greater than the depth of the mine.
Prashant et al., (2005) observed in laboratory testing that pond ash could be used as a
paste backfill material up to a concentration of 58% by wt.
2.4. High concentration hydraulic slurry pipeline system
Conventionally fly ash is mixed with large amount of water and transported by
pipelines to nearby ash ponds which involve little economic evaluation and other aspects. But
for long distance transportation of high volume fly ash, there exist no established criteria.
Problems faced in this system are friction loss, head loss, high energy consumption, high
settlement rate at the pipeline itself, very less volume/concentration etc. There have been
many attempts by researchers for high concentration slurry transportation world over. But the
mechanism has not yet been commercially established. In this literature review details of flow
behavior of fly ash and high concentration slurry with and without an additive have been
presented. There are many published articles or literatures on pipeline transportation with
addition of polymers and surfactants to alter the rheological behavior (Durand, 1951; Horsely,
1982; Wasp et al., 1977). One of the major impediments in pipeline transportation is the
velocity of flow that depends on many factors (Wood and Kao, 1966). Some of the important
parameters are:
(i)
Carrier fluid properties like viscosity, density, etc.
(ii)
Properties of solid particles like sp. gr., size, shape, terminal settling velocity etc.
22
Chapter 2: Literature Review
(iii)
Properties of the slurry, solid concentration, viscosity, and particle size
distribution, percentage of sub-sieve particles etc.
(iv)
Pipe diameter, pipe surface condition etc.
The presence of fine particles increases the viscosity of the slurry and they offer increased
resistance to settling behaviour of larger particles. The various design parameters that are
required to be established for the design of the pipeline system can be classified under the
following three categories:
(i)
Hydraulic parameters
(ii)
Parameters affecting corrosion-erosion characteristics
(iii)
Parameters affecting the operational stability of the system.
Newtonian state of motion is preferable to non-Newtonian state as the former uses less
energy due to reduced head loss (Hanks, 1982).
Panda et al., (1996) have established the pressure loss in horizontal pipes for
transportation of fly ash up to 60% solid concentration (by weight) by correlating it with the
rheological behaviour of the slurry. They estimated pressure loss using pressure loss models
developed for Newtonian fluids in the range of 20-25% concentration by weight.
Chandel et al., (2010) evaluated the performance of fly ash slurry in terms of pressure
drop, specific energy consumption etc. for Cw of 50-70%. They observed that with increase in
flow velocity, the pressure drop in the pipeline increased with minimum value for 60% solid
concentration and maximum value for 70.2%. The relative pressure drop decreased for
increase in flow velocity for a flow velocity range of 1 to 2m/s and specific energy
consumption increased steeply when the concentration value was more than 65%. They found
the flow behavior to be non-Newtonian for fly ash and bottom ash slurry. Gahlot et al., (1992)
investigated the performance of centrifugal slurry pumps with coal and zinc tailings slurries in
the concentration ranges of 0-57 % by weight. They observed that the head and the efficiency
of the pump decreased with increase in solid concentration, particle size, and sp. gr. of solids,
but independent of the pump flow rate. They observed higher reduction in the head compared
to the efficiency and had shown linear decrease in the head and the efficiency ratios with
increase in solid concentration up to 50% by weight.
23
Chapter 2: Literature Review
Seshadri and Singh (2000) found that relative viscosity of fly ash slurry increased
sharply as the solid concentration exceeded 40% by weight. For bottom ash slurry the relative
viscosity increased sharply beyond 30% by weight. The yield stress of the fly ash slurry also
increased sharply beyond 40% by weight. Total head of slurry column decreased almost
linearly as the discharge rate increased from 3 lps to 18 lps and pump input power increased
linearly as the discharge rate increased from 3 lps to 18 lps. The pump efficiency increased
from 10% to 45% as the discharge rate increased from 2 lps to 18 lps. The specific energy
consumption decreased from 1.4 kWh to almost 0.2 kWh as the solid concentration is
increased from 15% to 53% by weight. From the above results it was concluded that it is
possible to subsequently increase the concentration of solids and affect savings in water and
energy consumption.
Knezevic and Kolonja (2008) conducted experiments at a concentration of solid and
liquid components: 1:1.92 (mass concentration Cw = 34.2%, Volume concentration Cv =
19.8%), 1:1.485 (Cw = 40.2%, Cv = 24.2%), 1:1.015 (Cw = 49.6%, Cv = 31.9%) and 1:0.9 (Cw
= 54.6%, Cv = 36.4%). The authors accomplished the transport of ash and bottom ash slurry at
mass concentrations between 40% and 50%. The test of the pressure decrease showed that the
energy losses were the highest when the concentration was more than 50% solids.
Verkerk (1982) concluded that the mass concentration of 45% was the boundary value
for the substitution of the centrifugal slurry pumps with the piston pumps. The test ascertained
that the slurry with lower ash and bottom ash concentration acted as fluid, while as the
concentration increased it became more like a ‘sliding panel’. The boundary value for this
change was set at 69±1% of mass concentration.
Sive and Lazarus (1986) have concluded that the centrifugal slurry pumps were
applicable when the mass concentration was kept below 48%, based on their tests in the
closed test circuit with varying flow rate (up to 100 dm3/s) and with different velocities (up to
6.4 m/s).
Vlasak and Chara (2007) presented the results of an experimental study of flow
behavior of fine-grained highly concentrated slurries consisting of a mixture of water, kaolin,
and fly ash in horizontal straight pipes. Kaolin slurry showed time-independent, yield pseudo24
Chapter 2: Literature Review
plastic response for volume concentrations higher than about 60%. However the fluidic fly
ash- gypsum water mixture showed time dependent and substantial decrease of flow
resistance due to the effect of shearing during the initial period of pumping. An intensive
shearing of concentrated fluidic fly ash-gypsum slurry resulted in a substantial reduction of
the hydraulic gradient in the laminar region and in a marked shift of the laminar/ turbulent
transition point towards a lower velocity value. After shearing in a turbulent regime a
reduction in the hydraulic gradient at the transition point reached about 50% of its original
value.
Sadisun et al., (2006) observed that unconfined compressive strength (UCS) increased
with curing time as well as fly ash content. The higher the fly ash content the more was the
strength. Slaking index also decreased with increase in fly ash content as well as cement
content in the mixture. They opined that fly ash content had a direct bearing on viscosity of
mixture, its stability, reduced clogging, etc. They proposed optimum constituents of 8%
cement with 42% fly ash for lining materials.
Bournonville and Nzihou (2002) investigated two different water-washed municipal
solid waste incinerator fly ashes at 23 C with concentration 35% to 50%. The rheological
behavior of these fly ashes in aqueous suspensions was studied using a parallel plate
rheometer. Shear-thinning behavior was observed in one sample whereas thixotropic behavior
was found in the other. The viscosity is found to be dependent on both the volume fraction of
solids in the suspension and on the yield stress. Viscosity decreased with increase in
concentration as well as the shear rate which was due to breakdown of the structures of the
suspension.
Senapati et al., (2010) investigated the rheological behavior of 5 different fly ash
slurry samples with varying median particle size. Shear thinning behavior was observed for
all the samples at higher solids volume fractions in the range of 0.32-0.49. It was also found
from the study that the relative viscosity is very much sensitive to the concentration of solids,
particle size, and particle size distribution.
Revati et al., (2009) experimented with different composition of fly ash, gypsum and
quarry waste for both flow behavior as well as UCS value. It was found that quarry waste
25
Chapter 2: Literature Review
content influenced the water requirement more than that due to fly ash. It was also found that
150±50mm flow was not readily flowable as compared to other flow ranges.
Tsai and Knell (1986) found that the rheological behavior of coal water slurry
followed the Ostwald-de Waele power law model for the entire shear rate range (0-10000 s-1).
The flow behavior index was found to increase from 0.6 to 1.0 (i.e. from pseudoplastic to
Newtonian), as shear rate exceeded a threshold value (i.e. 400s-1) that depended on coal
content and coal particle size and size distribution. The 70 wt% utility grind coal water slurry
(average particle diameter of 38
m) became less pseudoplastic with flow behavior index
increasing from 0.70 to 0.82 at shear rates above 400s-1.
Chen et al., (2009) obsreved that 65.3 wt% exhibited a Newtonian fluid behavior and
the slurry flow was free from wall-slip effects. But at 67.1 wt % and 68.2 wt% solid contents,
the slurry flows were strongly affected by wall-slip and with the increase of wall shear stress,
the slurries exhibited their true rheological behaviors firstly as a shear-thinning fluid and then
as a shear thickening fluid. The existence of a minimum value of slippage contribution
indicated the transition of flow behavior from shear thinning to shear thickening.
Lu et al., (1998) discussed the flow pattern and pressure drop in highly concentrated
slurry transportation pipelines. They observed that the particles tend to settle down to the
bottom of pipes due to the action of gravity force forming different flow patterns which can
be indicated by particle concentration profile. Three distinct flow patterns were observed for
different particle size distribution at different velocities; such as fully stratified, partially
stratified, and fully suspended flow patterns. Pressure drop in slurry flows are strongly
dependent on the flow pattern developed in pipelines. Fine particles suspended in water make
the water more viscous, and increase the friction. The mixture of particles of different sizes is
helpful to reduce pressure drop in pipeline flow slurries.
Chandel et al., (2011) observed that for a fly ash slurry concentration Cw = 60% at
25 C with relative slurry viscosity of 16.27, the centrifugal pump efficiency was 32% at a
discharge rate of 40m3/hr. It was also observed that as the relative slurry viscosity increased
the pump efficiency decreased.
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Chapter 2: Literature Review
Fly ash slurries exhibited time dependent and non-Newtonian flow behavior for Cw >
60% (Bunn et al., 1990). They observed that Bingham model fitted well for Cw < 0.6% and
Bingham plastic model for Cw > 60%. It was also found that Cw is sensitive to source of ash,
temperature, pH, and the total mass flow rate of slurry, pipe diameter, and pump pressure and
power requirement.
Hellsten and Harwigsson (1999) found out that a combination of Betaine surfactant
and an anionic surfactant reduced the flow resistance between a flowing water-based liquid
system and a solid surface.
Bunn et al., (1999) conducted experiments on fly ash slurries in the concentration
range of 65% to 74 % in a 120mm diameter pipe loop having a length of 125m. Rise in
pressure loss was accompanied by a change in the flow properties of slurry which changed
from a liquid like mixture to one that tends to form sliding paste at the concentration of
around 69% ± 1% by weight.
Kuganathan (2001) developed the tailings paste fill composition from blended tailings
paste fill using 3-3.5% port land cement and found out that the cost of paste fill was much
lower than the total tailings paste fill that could be produced from the same tailings. He
observed that there was an optimum range of particle size distribution associated with any
particular tailings, which would result in the most economical paste fill for those tailings.
Usui et al., (2001) carried out experimental studies on rheology and pipeline
transportation of dense fly ash slurry. Simha’s model was used to predict the maximum
packing volume fraction for non-spherical particles suspension and successfully used to
predict the slurry viscosity under completely dispersed conditions. The model resulted in the
estimation of inter particle bonding force between primary particles in a cluster and the power
consumption and flow rate relationship in hydraulic slurry pipeline transportation system. A
possible way to reduce the cost of slurry pipeline system by means of periodical addition of a
stabilizer was proposed. Vlasak et al., (2002) highlighted the use of peptizing agent to
decrease the viscosity and yield stress depressing the strong non-Newtonian flow behaviour of
the slurry due to the presence of colloidal particles.
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Chapter 2: Literature Review
Lei et al., (2002) studied rheological characteristics and sedimentation stability of the
slurry with the addition of four kinds of stabilizing additives. Additives used in their study
were rhamsan gums, carboxymethyl cellulose, xanthan gum, and naphthalene-sulfonate
formaldehyde condensate (NSF). They observed that viscosity of the fly ash-water slurry
increased as the concentration of stabilizer increased. Therefore NSF was used as a dispersing
additive to reduce the viscosity of the fly ash water slurry. The concentration of dispersing
additive (NSF) was 0.3 weight % /slurry. The long molecular branches of the additive were
effective for building up network structures necessary to prevent the sedimentation of fly ash
particles. They suggested the use of an additive as a stabilizing agent at a concentration of 0.2
weight % for preparation of stable fly ash-water slurry.
Parida et al., (1996) reported that ash slurry consisting of fly ash or fly ash-bottom ash
mixture exhibit non-Newtonian pseudo-plastic flow behaviour at high concentrations in the
range of 60-65% by weight. Presence of bottom ash having larger particles in the ash slurry
affected slurry rheology and head loss in pipeline flow positively.
Singh and Singh (2003) reported that when filling material is sent through pipelines in
the form of slurry, frictional head loss was an important factor to be computed. Jain and
Sastry (2004) found that more the concentration of fly ash more the loss in pressure.
Simultaneously higher the velocity of slurry flow higher the pressure loss. The pressure loss
was minimized by adding an additive to the slurry. They also observed the maximum fly ash
concentration possible for slurry transportation was 50%.
Thissen and Kuy (2005) found out to dispose 1000 ton of fly ash about 5667 m3 of
water was required at 15% solid concentration whereas only 667 m3 of water was required to
dispose same amount of fly ash at 65% solid concentration saving about 88% of water energy
which in turn reduced the pumping cost. From this study it was concluded that the
conventional lean slurry disposal system is plagued with transporting large quantities of water
with only small amount of ash loading.
The rheological behaviour of fly ash slurry having particle size 0.3mm - 75 m was
studied by Seshadri et al., (2005) at different concentrations with and without an additive i.e.
sodium hexametaphosphate of 0.1 % concentration. The computations of pressure drop
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Chapter 2: Literature Review
showed substantial saving in energy consumption when the additive was added into the fly
ash slurry at higher concentrations as it modified the rheological properties of the fly ash
slurry significantly. They reported that slurries above solid concentration of 60% by weight
were non-Newtonian and Bigham plastic model fitted the data over the range of shear rates
investigated. Sodium hexametaphosphate at 0.1 % concentration as an additive reduced both
Bigham viscosity and yield stress of the fly ash slurry significantly.
Addition of certain kinds of surfactants, as well as polymers, to a Newtonian fluid
causes considerable drag reduction in the turbulent pipe flow. Surfactants used by Aguilar et
al., (2006) were Tris (2-hydroxys-ethyl) tallowalkyl ammonium acetate (tallowalkyl N-(C2H4)
OH)3 AC, from AKZO Chemicals. This solution consists of 2,000 ppm of surfactant, plus
1740 ppm of sodium salicylate (NaSal) used as counterion, and 3.75 mM/l of copper
hydroxide (Cu (OH)2), which is a compound that helps reduce the fluid viscosity to a water –
like value, without diminishing its drag-reducing ability.
Knezevic et al., (2008) observed marginal drop in flow rate and pressure when the ash
concentration was beyond 40 to 50% compared to quantity of fly ash and bottom ash
transported during the time limit. Senapati et al., (2008) studied the modelling of viscosity for
power plant ash slurry at higher concentrations and effect of solid volume fraction, particle
size, and hydrodynamic forces in a non-Newtonian laminar flow regime. A model
incorporating maximum solids fraction, power law index, median particle size, co-efficient of
uniformity, shear rate is developed to predict the viscosity.
Chandel et al., (2009) described the effect of additives on pressure drop and
rheological characteristics of fly ash slurry at high concentration (above C w = 60% by
weight). There was reduction in pressure drop when soap solution (0.1 to 1.5%) was added to
the fly ash slurry at higher concentrations. Slurries of fly ash at these concentrations showed a
Bingham fluid behaviour. The Bingham viscosity and yield shear stress values increased with
increase in concentrations, the increase being more pronounced at higher concentrations. The
addition of soap solution as an additive to the fly ash slurry reduced the rheological
parameters and resulted in substantial decrease in energy consumption. Steward and Slatter
(2009) tested the pipe flow behaviour of fly ash and water mixtures in a closed loop pipe
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Chapter 2: Literature Review
system at solids concentrations ranging from 51% to 74% by mass. They used the HerschelBulkley rheological model to evaluate pipe flow.
Nigle and Neil (2003) observed that friction reduction in non-settling pipe flow
occurred when viscosity was changed with chemical reagents and additives. They studied the
effects of different chemical reagents on drilling mud slurries (using sodium acid
pyrophosphate and sodium hexametaphosphate), phosphate rock slurries (using caustic soda),
and limestone cement feed slurries (using a combination of sodium tripolyphosphate and
sodium carbonates).
Slaczka and Piszczynski (2008) tested four nonionic surfactants as additives to
enhance flowability of coal-water slurries. The flow properties were measured by means of a
coaxial rotating rheometer for 55 wt% coal concentration. From the study it was found that
such a mixture without any additive has a consistency of dense pulp and not indicated any
flowability. The addition of the surfactant made the mixture flowable. Increasing the
hydrophobicity of coal grains improved flowability of coal-water slurry and allowed to get
slurries of higher concentrations. It was also observed that removing the air from the surface
of coal grains, by heating slurries up to the boiling point, exposed the larger part of their
surface and consequently increased the adsorption of surfactant, that led to increase in
hydrophobicity of the coal grains surface and finally decreased the viscosity of the slurry. For
the most effective additive, after heating slurry to boiling point before introducing the
chemical agent (surfactant), for the lowest tested shear rates the apparent viscosities were
decreased by 11.8%, 9.7% and 0% for the additive dosages of 250g/t, 500g/t, and 750 g/t,
respectively in comparison with those not degassed. Vlasak et al., (2010) tested three different
kaolin-water mixtures with an overpressure capillary viscometer, rotational viscometer, and
experimental pipeline loop. The effect of peptizing agents and their concentration was
investigated. It was demonstrated that even very low concentration of peptizing agent resulted
in a significant reduction in the apparent viscosity and in the yield stress. Sodium carbonate
and soda water-glass were used as peptizing agent in the mass concentration varying from
Ca=0.02 to 2%. The original value of yield stress of the kaolin slurry with concentration Cm =
0.55 could be reduced from τy= 134 Pa to 6 Pa for Ca = 0.15% and from τy=34.1 Pa to 0.5 Pa
for Ca = 0.1% respectively.
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Chapter 2: Literature Review
Boylu et al., (2005) studied the effect of caboxymethyl cellulose (CMC) on the
stability of coal-water slurry. The results depicted that polymeric anionic CMC agent had
higher effect on the stability of coal-water slurry.
Shimada et al., (2008) concluded that addition of 3% surfactant controlled the
bleeding of fly ash-water slurry that also improved its fluidity.
Cassasa et al., (1984), studying the rheological behaviour, sedimentation stability, and
electrophoretic mobility of four bituminous coals in water and in solutions of simple wellcharacterized surfactants, observed that slurry rheology and stability depended on coal
particle surface charge and recommended the use of the additives to improve rheological
parameters.
Huynh et al., (2000) measured the rheological properties of chalcopyrite slurry with
chemical treatments, showing that there was an increase in repulsive electrostatic forces
between particles which, in turn, reduced the slurry viscosity and the solid content of the
slurry was increased by over 10 wt. % for the same pumping energy input. He et al., (2004),
using a cationic surfactant selected to modify fly ash particle behaviour recommended that the
dispersing agents influence viscosity, pH, and be non-toxic, and biodegradable.
Elizabet et al., (2011) treated fly ash under variety of conditions with an anionic
surfactant. The properties of the modified products were compared to those of the untreated
samples. The surfactant dosage was 0.1%, 05% and 0.2% wt and temperature varied from
50 C to 80 C. It was found from the study that the surface of the modified fly ash became
more hydrophobic in comparison to that of the untreated fly ash. The degree of agglomeration
reduced significantly in the modified samples.
Chandel et al., (2009) reported the effect of a mixture of sodium carbonate and Henko
detergent in the ratio of 5:1 (0.2% by wt) as an additive on pressure drop and rheological
characteristics of fly ash slurry at high concentration (above C w
60% by weight). They
found a reduction in pressure drop when the above additive was added to the fly ash slurry at
higher concentrations. They observed a marked decrease in viscosity of the fly ash slurry from
14.50 Pa.s to 7.75 Pa.s at Cw = 60% and at 70% solid concentration, plastic viscosity reduced
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Chapter 2: Literature Review
from 245.30 Pa.s to 150.2 Pa.s. Data also showed that the additive decreased the yield shear
stress of fly ash slurry from 0.36 Pa to 0.1 Pa at Cw =60% and at 70% solid concentration
yield stress reduced from 1.945 Pa to 1.20Pa.
Vlasak and Chara (2009) investigated the effect of slurry composition and volumetric
concentration on the flow behaviour of fluidic fly and bottom ash and sand slurries containing
fine-grained and coarse-grained particles. Kaolin slurries with and without a peptizing agent
were used as the carrier liquid for the sand slurries to compare the effect of Newtonian and
non-Newtonian carriers. The study revealed a time-dependent yield pseudo-plastic behavior
of fluidic fly and bottom ash slurries. The highly concentrated sand-kaolin slurries showed
non-Newtonian behavior. When the carrier kaolin slurry is peptized, the hydraulic gradient in
the laminar region markedly lowered and the addition of small amounts of kaolin favorably
affected the flow behavior of the sand slurry. To compare the effect of Newtonian and nonNewtonian carriers on the slurry flow behavior, a chemical agent with a peptizing effect (a
sodium carbonate, which supplied the slurry with Na+ ions for the compensation of the Kaolin
particle surface charge) was used to change the physical- chemical environment of the slurry
and to depress the attractive interparticle forces, which evoke non-Newtonian behavior of the
slurry. Due to the peptizing agent the slurry flow behavior changed from non-Newtonian to
nearly Newtonian.
Tsutsumi and Yoshida (1987) found that at a constant shear rate the apparent viscosity
of the suspension with agglomerates decreased with temperature while the relative viscosity
increased. The change was caused by the growth of agglomeration, because hydrodynamic
forces decrease with temperature.
Lee and Sakai (2003) investigated the influence of the character of fly ash on the
fluidity of cement paste with a polycarboxylic acid type superplasticizer in connection with
the particle size distribution, unburned carbon content, specific surface area and shape of the
fly ash. The fluidity of the fly ash cement paste with an added 20 vol% fly ash increased with
an increasing roundness of the fly ash and they also found that there was a linear correlation
between the roundness and the fluidity of fly ash cement paste. It was also reported that the
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Chapter 2: Literature Review
improvement of fluidity from mixing with fly ash typically came from the ball bearing effect
of fly ash that have spherical particles.
Mosa et al., (2008) investigated the effect of chemical additives on rheological
characteristics of coal water slurry. The power-law model was applied to determine the nonNewtonian properties of coal slurries. Three types of dispersants, namely sulphonic acid,
sodium tri-polyphosphate, and sodium carbonate were studied and tested at different
concentrations ranging from 0.5 to 1.5% by weight from total solids, out of which sulphonic
acid was recorded the best performance in modification and reducing slurry viscosity. Sodium
salt of carboxymethyl cellulose and xanthan gum were tested as stabilizers at concentrations
in the range of 0.05 to 0.25 % by weight from total solids. It was found that apparent viscosity
and flow properties of coal water slurries are sensitive to the use of chemical additives. The
best dosage of all tested dispersants was found to be as 0.75% by wt of solids and the best
dosage of stabilizers was found to be 0.1% by weight of total solids.
Karmakar et al., (2011) studied the effectiveness of flocculants as anioninc, non-ionic,
and cationic and observed that settling rate was fastest with anionic polymers (39.8 cm/min),
and slowest with cationic polymers (3.8 cm/min). It was also observed that for cationic
polymers the residual turbidity was very less (46 NTU) as compared to anionic (262 NTU)
and non-ionic (716 NTU). The size of flocs was very small in case of cationic, moderate in
case of non-ionic and much larger in case of anionic. The interface appeared very late in case
of cationic but it appeared instantly in case of anionic polymers.
Seshadri et al., (2008) used sodium hexametaphosphate at 0.1% concentration (by
weight) as an additive to study the rheological behaviour of fly ash slurries and observed that
Bingham plastic model represented the variation of shear stress with shear rate reasonably
well. For sample number 1 at 60% solid concentration the slurry yield stress was 0.3541 Pa
which is reduced to 0.0194 Pa by addition of the additive. Similarly the slurry viscosity was
13.1 Pa without any additive and it is reduced to 8.6 Pa by addition of the additive. This trend
was observed for all the five samples tested.
Mishra et al., (2002) investigated the rheological behavior of some Indian coal-water
slurries using a HAAKE RV30 viscometer. It was found that coal-water slurry exhibited
33
Chapter 2: Literature Review
pseudoplastic flow behavior. The apparent viscosity varied with the amount of coal in the
slurry, pH, and temperature, which was the highest around pH 6 and the lowest near pH 8.
Coal – water slurries showed non-Newtonian behavior at low pH. The change in apparent
viscosity with the temperature of coal-water slurry could be described by a simple Arrheniustype equation. The values of apparent activation energy were found to be relatively
independent of the rate of shear and solid concentration.
Huynh et al., (2000) found that the magnitude of the yield stress reduced when either
hydrochloric, nitric or sulfuric acid was used to decrease the pH of chalcopyrite slurry. With
hydrochloric and nitric acids, the viscosity of the slurry also reduced with decreasing pH- a
behavior which was attributed to changes in the surface chemistry of the particles with pH.
Addition of phosphates to the slurry also reduced the yield stress as well as the viscosity as
absorbed phosphate produced an enhanced repulsive force between particles due to the
presence of long-range electrostatic and short-range steric interactions. The use of either acids
or phosphates permitted the solid content of the slurry to be increased by over 10 wt. % for
the same pumping energy input. It was also observed that the yield stress of the chalcopyrite
slurry decreased from a value of 75 Pa to 10 Pa as the pH of the slurry was decreased from 11
to 3.5. The magnitude of the yield stress decreased as the pH is reduced for all the acids used.
Viscosity is decreased when pH of the slurry is increased with addition of H2SO4 but the trend
was reversed in the case of HCl and HNO3 as pH modifiers. It will support the addition of
lime for our case. The influence of phosphates on slurry rheology revealed that the yield stress
decreased from a value of 70 Pa to 25 Pa as the concentration of polyphosphate increased
from 0 to 9mg/kg for slurry concentration of 69 wt%. The pumping energy requirement for
the chalcopyrite slurry reduced from a value of 175000 kWh to 45000 kWh when the pH was
reduced from a value of 11.5 to 7.5. Similarly the pumping energy requirement was found to
increase as the solid concentration of the slurry was increased from 50 wt% to 70 wt% for
various doses phosphate addition.
2.5. Drag reduction technology
Drag reduction is a phenomenon in which the friction of a fluid flowing in a pipeline
in turbulent flow is decreased by using a small amount of an additive. Drag reduction occurs
34
Chapter 2: Literature Review
when a small amount of an additive such as a surfactant or polymer causes a reduction in the
turbulent friction. This reduction in friction causes the pressure drop in the pipe flow to be
less than that of the pure fluid leading to decrease in the pumping energy requirements of such
systems. Several types of additives have been studied which cause this drag reduction
phenomenon to occur. These include:
i.
Surfactants
ii.
Polymers
iii. Aluminium disoaps and
iv. Fibres
Surfactants are very useful due to its ability to self- repair upon mechanical
degradation due to high shear. Degradation occurs when a molecule undergoes a region of
high shear in hydraulic pipeline transport systems because these systems use multiple pumps.
Surfactants are efficient drag reducers. Surfactants are able to repair themselves in a matter of
few seconds upon degradation from shear. This characteristic makes surfactants a good
additive for pipeline transport system. Now-a-days biodegradable surfactants are available as
drag reducing additives. These surfactants are less susceptible to mechanical degradation. The
influence of these surfactants on turbulent flow characteristics is appreciable with only few
parts per million of surfactant solution, added to the solvent (Ohlendorf et al., 1986). The
effect of surfactants to reduce drag has been studied and reported in many literatures (e.g.
Lumley, 1969; Virk, 1971; Sellin et al., 1982; Hoyt, 1986; Morgan & McCormick, 1994;
Tiederman, 1985; Matthys, 1991; Gyr and Bewersdorf, 1995).
The main purpose of drag reduction is to delay the onset of turbulent flows. In other
words, a drag reducer will shift the transition from a laminar flow to a turbulent flow to higher
flow velocity. Guar gum, a natural polymer (polysaccharide) also showed effective influence
on drag reduction. Hoyt (1990) used 10 ppm polymer concentration in the pipeline
transportation system which not only reduced the drag, but also reduced the heat transfer that
maintained low oil viscosity. Similar observations were also reported by Beaty et al., (1984).
Also, in sewerage pipes and storm-water drains polymers have been used to increase the flow
rates so that the peak loads do not result in over flowing; if only relatively infrequent use is
required, this can be much cheaper than constructing new pipelines (Sellin, 1982).
35
Chapter 2: Literature Review
2.5.1. Drag reduction by using surfactants
Surfactants are molecules which contain a hydrophobic tail and a hydrophilic head
groups. Surfactants can be further classified by their hydrophilic group. The different types of
surfactants are anionic, nonionic, zwitterionic, and cationic. Surfactants behave in a
characteristic manner in aqueous solution. In these solutions the hydrophobic groups avoid
contact with water by forming micelles. In micelles the hydrophilic parts, which are polar,
contacts the water allowing the non-polar, hydrophobic, parts to concentrate in the centre of
the micelle. The micelles form different structures in aqueous solutions including spherical,
rod-like, lamellar, and vesicles. The types of surfactant as well as the structure of the micelle
both contribute to the drag reducing properties of the molecule.The principal uses of
surfactants and related compounds are the dispersion of fly ash particles in water for smooth
flow in hydraulic pipelines. Hydrophilic fly ash particles can be rendered more hydrophobic,
which is a necessary requirement for the floatability of fly ash particles, by addition of
surfactants. The use of aqueous surfactant solutions to improve wetting properties of fly ash
particles has important practical consequences for its transportation in pipelines. Cationic
surfactants and others are used in this application.
Chandel el al., (2011) investigated the effect of drag reducing additives on the
characteristics of two different types of pumps with fly ash slurries and found that the head
and efficiency of the centrifugal slurry pump decreased with increase in solid concentration
and slurry viscosity whereas pump input power increased with increased solid concentration.
The addition of drag reducing additive improved the performance of the centrifugal slurry
pump in terms of head and efficiency.
Roh et al., (1995) observed that surfactants improved the slurriability of coal with
shear thinning behavior. The addition of surfactants also enhanced the resistance of coal-water
slurry to sedimentation. It was also found that the slurriability at a constant apparent viscosity
of 2000 mPa.s could be increased by ~11 wt% when an anionic surfactant (CWM 1002) was
added together with a small amount of electrolyte (NaOH). The amounts of CWM 1002 and
electrolyte (NaOH) as the dispersing materials were 0.4 and 0.1% wt% on the dry coal basis
respectively.
36
Chapter 2: Literature Review
Granville et al., (1977) observed that molecular structure of surfactant had profound
effect on the wetting rates of fly ash particles. Wetting rates increased in roughly linear
fashion in the temperature range from 200C to 400C.
Dodge and Metzner (1959), and Shaver and Merrill (1959) noticed unusually low
friction factors for certain non-Newtonian solutions like those of sodium carboxy
methylcellulose in water. Drag reduction has also been reported for several suspensions of
insoluble particles such as fine grains or fibres and for micro bubbles. Ohlendorf et al. 1986;
Rose and Foster, 1989; and Chou, 1991 investigated a number of alkyltrimethyl ammonium
cationic surfactants with excess sodium salicylate drag reducers with alkyl groups ranging
from C12 to C22 (even – numbered carbon atoms).
Shikata et al., (1988, 1997) indicated that counterions played a role as break down and
reformation of the entanglement points. They also pointed out that, there were three kinds of
motions in a rod-like surfactant solution. The first and second motions are the entanglement
release motion and the motion of bending parts of rod-like micelles, respectively. These kinds
of motions strongly affect the rheological properties of the surfactant solution. The last one is
the rotational and translational motion of surfactants and counterions in rod like micelle. This
kind of motion does not strongly affect the rheological properties of the rod like surfactant
solution.
Barret et al., (1993) showed a steep increase of viscosity of cetylpyridinium salt
(CPy)-sodium salicylate mixture when the concentration increased, at a constant brine
concentration. Surfactants: tris (2-hydroxyethyl) – tallow ammonium acetate (TTAA,
Ethoquad T/13-50) (10 m mol/lit) with NaSal (10 m mol /litre) as counterion was investigated
by Bottenhagen et al. (1997) in a couette cell under shear.
Stress-induced precipitation and microstructure change were studied by Lu et al.,
(1998). They examined a solution of Arquad 16-50 (commercial cetyl trimethyl ammonium
chloride, CTAC) (5m mol/l) with 3-chlorobenzoate (12.5 m mol /l) counterion under shear
and extensional flow at 200C, shear rates of 1000s-1 and 1500s-1, and observed an abrupt
decrease in shear viscosity after about 200s of shear.
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Chapter 2: Literature Review
Alkyltrimethyl ammonium surfactants were found to be effective drag reducers when
combined with different counterions in the dilute concentration range (Zakin et al., 1998).
The experimental results conducted by various researchers showed that the drag reduction
occurs only in turbulent flow when a certain wall shear stress is exceeded (Fontaine et al.,
1999; Zakin et al., 1983).
Zwitterionic surfactants named SPE 98330 was added into the district heating system
with the aim to decrease the flow resistance in the tubes and thus to decrease the energy
consumption (Myska and Mik, 2003). Myska and Chara (2001) obtained the effectiveness in
drag reduction as high as over 90% with this agent.
Roi Gurka et al., (2004) used Agnique PG 264-U surfactant at 20ppm, biodegradable
type, and found that the flow exhibited less floctuations. Munekata et al., (2006) studied the
surfactant solution with drag reduction in a swirling flow of vortex motion. The surfactant
solution used 500 ppm of Cetyl-trimethyl Ammonium Bromide (CTAB) with water
containing Sodium Salicylate (NaSal) at the same molar concentration as CTAB. They found
that the maximum drag reduction reached up to 80% when the inclination angle of the vane
was 450.
Feng-Chen et al., (2008) tested cationic surfactant, Cetyltrimethyl Ammonium
Chloride (CTAC) in a closed circuit water flow. Local tap water was used as the solvent.
Sodium Salicylate (NaSal) was added to the solution with the same weight concentration as
that of CTAC for providing counterions. 25 ppm and 75 ppm CTAC solutions at 300 C were
used as the drag-reducing fluid. The rheology measurement indicated that only 75 ppm CTAC
solution showed distinct rheological properties whereas the measured properties of 25 ppm
CTAC solution were almost the same as those of water at the same temperature.
Piotrowski (2008) studied the polymer surfactant complex formation and its effect on
drag reduction. For a mixture the following substrates were used: poly (ethylene oxide) (PEO)
and cetyl trimethyl ammonium bromide (CTAB) with sodium salicylate (NaSal). The drag
reduction behaviours of PEO, CTAB with salt and their mixtures in dilute aqueous solution
were compared.
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Chapter 2: Literature Review
Flow regimes depend on many factors: such as the individual magnitudes of the liquid
and gas flow rate; the physical properties such as density, viscosity, and surface tension. Very
large pressure drops occur with the high viscosity fluids (Duangprasert et al., 2008).
Surfactants used by them was SDS (C12 H25 NaO4S) solutions at 0.5,1, and 2 CMC (Critical
micelle concentration), 1 CMC = 2.75 g/ liter (1 CMC ≈2750 ppm).
A type of cationic surfactant CTAC (C16 H33 N (CH3)3 Cl) cetyltrimethyl ammonium
chloride mixed with same weight percent of counterion material NaSal (HOC6H4 COONa)
was used (Kawaguchi and Feng, 2007) as a drag – reducing additive to water at a mass
concentration of 40 ppm. The CTAC was dissolved in tap water. Cationic surfactants were
less affected by calcium or sodium ions naturally found in tap water. This is the reason why
cationic surfactants combined with a counterion such as sodium salicylate (NaSal) are
frequently used in the basic studies or applications to district heating and cooling systems. At
concentrations of 30 ppm and 100ppm, the shear viscosity of the solution at a shear rate of
200s-1 in 250C was 0.82 and 0.97 m Pa s respectively, showed no stress thinning in the range
of 10s-1 to 300 s-1. For the surfactant drag-reducing additives, the rod-like micelle structures
are thought to be the key to give complicated rheological fluid properties including
viscoelasticity. NaSal acts to reduce ion radius of CTAC to deform micellar shape from
globular to rod-like. In their experiment, same weight concentration of NaSal was always
included in the CTAC solution.
Candau et al., (1994) showed a constant viscosity of a solution of dodecyl methyl
ammonium bromide but when NaCl was added, viscosity decreased. Ethoquad T/13-50 and
Arquad 16-50, products of Akzo Chemie, in mixtures with sodium salicylate were tested in
hydronic systems of buildings. Metaupon was used in 300 mm pipes of a cooling system in
mines.
Cationic surfactants mostly create an effective drag reduction when used in
combination with organic salts such as sodium salicylate. Sodium salicylate ions are known to
bind strongly to the micelle surface and facilitate the formation of large semi-flexible
wormlike aggregates, at very low concentration (around 1 mM), which form an entangled
network. These solutions are characterized by a striking onset of viscoelasticity. In recent
years, drag reducing aqueous surfactants has drawn much attention as a class of additives
which are self-repairable after degradation. That feature makes them suitable for potential
39
Chapter 2: Literature Review
applications in recirculation systems. Usually, as a drag reducer, poly (ethylene oxide) PEO is
used. However, drag reducing polymers are sensitive to mechanical and thermal degradation.
Water-soluble polymers like PEO form complexes with cationic and anionic
surfactants, in which polymer film was formed around micelle. The addition of salt
facilitateed a formation of surfactant – polymer aggregates. The critical aggregation
concentration (CAC), the concentration at which the surfactant started to bind to the polymer
was lowered; the size of the surfactant micelles increased and the number of micellar
aggregates attached to a polymer chain also increased with the ionic strength.
Certain surfactants, such as CTAB and CTAC, with addition of appropriate
counterions such as sodium salicylate, form network microstructures at very low
concentrations (a few hundred ppm to 4000 ppm) are very effective in reducing friction
factors in turbulent flow. Cationic drag reducing surfactant solution have been the most
extensively studied because of their broad drag reduction temperatures (unlike nonionic
surfactants, which have narrow temperature ranges) and insensitive to the presence of calcium
or magnesium ions in water, which cause the precipitation of some anionic surfactants. They
are also much less expensive than zwitterionic surfactants. Many drag reducing cationic
surfactants are quaternary ammonium salts with one long alkyl chain with typical chemical
structures of the form CnH2n+1 N+(CH3)3Cl (n=12-18) (Hu and Matthys, 1997).
Some aqueous solutions of cationic surfactants cause very effective drag reduction
phenomena in turbulent flow even at very dilute concentration. These aqueous solutions can
reduce 80% of the drag in a turbulent straight pipe flow in a wide range of temperature. Dragreducing cationic surfactant molecules form rod-like micelles in an aqueous solution under
the presence of a counterion. These rod-like micelles entangle together to make a certain
network structure. Rod-like micelles are formed with not so strong intermolecular interaction,
so two rod-like micelles can cross and pass through each other at the entangle point.
Polymers were initially used as drag reducing additives for turbulent water flow to
reduce the frictional drag by up to 80%. However, polymer solutions are strongly affected by
mechanical degradation, which may result in shorter life time of drag reduction effectiveness.
Surfactants are emerging as approaches to reduce the frictional drag by 70% to 80% but to be
40
Chapter 2: Literature Review
less affected by mechanical degradation. Therefore, surfactants are now being considered as
practical drag reducing additives.
Hu and Matthys (1997) reported a shear thickening behavior of the system tetradecyl
dimethyl aminoxide with sodium dodecylsulfate plus added NaCl with a peak of the viscosity
curve around 60s-1 for a fixed concentration ratio of all three components.
Cates (1993) suggested that salt concentration and specific counterion effects are
important in determining the dependence of average micellar size on concentration, and that
the size of micelles influences the viscosity curve. They found that NaBr is able to promote a
large increase of the size of micelles while NaCl has no noticeable effect.
2.5.2. Polymeric drag reduction research
In a number of practical situations of fluid flow, turbulence occurs near solid surfaces
that results in high magnitude of energy losses due to turbulent friction. There are basically
two types of additives which can alter the turbulent flow and cause a reduction in the pressure
loss, namely macromolecules like polymers or surfactants, and simple solids like sand grains
or fibres. The non-ionic surfactant Lubrol 17A10 in the presence of the electrolyte K2SO4 has
been found to be an effective drag reducer at temperatures near its cloud point (ICI). Among
the drag-reducers, poly oxyethylene alcohol non-ionic surfactants alone seem to be
mechanically stable.
Polymer solutions are the most widely studied and most often employed for the drag
reducing systems. Several typical polymer drag reducing solutions listed (Table 2.1).
Table 2.1: Drag reducing polymer solutions
Water – Soluble polymers Solvent – soluble polymers
Poly (ethylene oxide)
Polyisobutylene
Polyacrylamide
Polystyrene
Guar gum
Poly (methyl methacrylate)
Xanthan gum
Polydimethylsiloxane
Carboxymethly cellulose
Poly (cis-isoprene)
Hydroxyethyl Cellulose
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Chapter 2: Literature Review
The higher the molecular weight (MW) the more effective a given polymer as a drag
reducer (Shenoy, 1976). Polymers with a MW below 1, 00,000 seem to be ineffective (Hoyt
and Fabula 1963). As the average MW of poly (ethylene oxide) (PEO) is increased from
2x105 to above 5x106, the solution concentration to achieve about 70% drag reduction on a
rotating disk is reduced from 600 to 100 ppm. The higher the MW the greater is the drag
reduction for a given concentration and Re number. The longer polymer chain provides more
chance for entanglement and interaction with the flow. The extension of the polymer chain is
critical for drag reduction. The most effective drag reducing polymers are essentially in linear
structure, with maximum extensivity for a given molecular weight. Poly (ethylene oxide),
Polyisobutylene and Polyacrylamide are typical examples of linear polymers. Polymers
lacking linear structure, such as Gum Arabic and the Dextrans, are ineffective for drag
reduction.
Phukan et al., (2000) studied two types of polymers at various concentrations. The
concentrations of 100, 250, 300 and 450 ppm of commercial guargum and 50, 100, and 150
ppm of purified guargum were used for homogeneous injection. The maximum power
reduction of 28% was obtained in case of 300 ppm commercial guargum and approximately
the same percentage was obtained in case of 100 ppm purified guargum. The maximum drag
reduction was 35.5% at 300 ppm of commercial guargum and 38% at 100 ppm of purified
guargum. The study revealed great potential of using drag reducing polymers for irrigation
water management. There was reduction in power consumption, increase in radius of
coverage and net drag reduction when polymer was added with the water used in sprinkler
irrigation system.
A drag reduction occurs at very low concentrations in the ppm region. Increasing the
concentration beyond 30-40 ppm lowers drag reduction for PEO in a small tube owing to
increase of the viscosity with increasing concentration. Drag reduction was observed in
concentration as low as 0.02 ppm (Oliver and Bakhtiyarov, 1983). Using a rotating disk
apparatus (Choi and John, 1993) or a rotating cylinder (Bilgen and Boulos, 1972), drag
reduction induced by water-soluble polymers (PEO and Guar gum) and solvent–soluble
polymers (Polyisobutylene) showed similar results to the experiments performed with a small
tube.
42
Chapter 2: Literature Review
McCormick et al., (1986) concluded that water soluble polymers as hydrophobically
modified
Polyacrylamide
polymers,
anionic,
and
cationic
polyelectrolytes
and
polyampholytes were effective drag reducers. All copolymers were found to confirm a
universal curve for drag reduction, when normalized for hydrodynamic volume fraction
polymer in solution.
Biopolymers such as high molecular weight polysaccharides produced by living
organisms can provide effective drag reduction (Shenoy, 1984). Polysaccharides of several
fresh water and marine algae, fish slimes, sea water slime and other fresh water biological
growths have been found to be good drag reducers also. Kim and Sirviente (2007) found out
that Salt (Sodium chloride) enhanced the drag reduction efficiency of poly acrylic acid diluted
solution because the salt molecules prevented the aggregation of PAA chains.
2.6. Surfactants
The term surfactant came from the contraction of “surface active agent”. This
contraction describes surfactants because a predominant characteristic of surfactants is their
ability to lower the surface tension of liquids. Surfactants are amphiphilic compounds i.e.
hydrophilic head group and a hydrophobic tail group. The hydrophilic head group is a polar
group which usually ionizable and capable of forming hydrogen bonds. The hydrophobic tail
group is a non-polar group which is typically a long chain alkyl group (Zakin et al., 1998).
Due to this unique structure, surfactants show characteristic behaviours when in an aqueous
solution. The hydrophobic group repels water in solution while the hydrophilic group is
attracted to the polar water molecules. This causes the hydrophobic groups to cluster together
in hydrocarbon phase in order to avoid contact with the water while the hydrophilic polar
groups surround them and are in contact with the water. The aggregates formed are called
micelles.
2.6.1. Classification of surfactants
There are several types of surfactants which include anionic, cationic, zwitterionic,
and nonionic surfactants. Anionic soap surfactants are water soluble and have a negative
charge when in aqueous solutions. They exhibit good drag reduction results when the shear
stress is not too high, i.e. lower flow rates. They are, however, very sensitive to hard water
43
Chapter 2: Literature Review
metal ions such as Ca2+ and Mg2+ which make them insoluble in water. Anionic surfactants
also form foam. This results in complications in many systems that do not have the ability to
handle foam formation. Hence they have not been considered good surfactants to be drag
reducing agents. Cationic surfacetants have a positive charge when immersed in aqueous
solutions. These surfactants are not affected by the metal ions in tap water as the anionic
surfactants. Cationic surfactants produce good drag reduction results over a wide temperature
range, and are relatively stable and offer self-repairability.
Zwitterionic surfactants have both negative and positive charges on the head group of
the molecule. Since these surfactants contain both types of charges, it may cause the
surfactant molecule to be sensitive to the ions present in water or solutions which may
decrease in the stability of these types of surfactants. One beneficial characteristic of
zwitterionic surfactants is that they are readily biodegradable and less toxic than some other
surfactants. This makes that environment friendly.
Nonionic surfactants have no charge on their head groups. These types of surfactants
are stable and are able to self-repair quickly after degradation from high shear. Similar to
zwitterionic surfactants, nonionic surfactants are also less toxic than most and are rapidly
biodegradable. However, they are generally only effective as drag reducing agents over a
relatively narrow temperature range near their upper consolute or cloud point temperature.
2.6.2. Micelles
Surfactants have the ability to group themselves in consistent patterns due to the
hydrophobic and hydrophilic components of the molecules. The hydrophobic ends of the
surfactants group themselves together when in aqueous solutions because these ends are nonpolar and repel the polar water molecules. Conversely, the hydrophilic or polar ends of
surfactants are attracted to the water molecules. This causes the surfactants to form clusters
called micelles. Micelles form into several different shapes including spherical, rod-like,
lamellar, and vesicles. Typically, at low concentrations micelles are spherical. When the
concentration of the surfactant is increased or the temperature of the solution is decreased the
micelles may form into rod-like micelles. Drag reducing surfactant systems are typically
composed of long rod-like micelles. Surfactants are essentially “Schizophrenic” molecules
44
Chapter 2: Literature Review
that have a distinct hydrophilic (water loving) head and a non-polar hydrophobic (wateravoiding) tail and can absorb at an interface to modify its properties (Figure 2.1).
Figure 2.1: Structure of a surfactant
Tail
Head
Surfactants are mostly complex mixtures of different variants generated during the
manufacturing process, the commonest and simplest being the mix of oligomers that
constitute a typical nonylphenol 9-mole ethoxylate. Interaction of various surfactants with
solids and liquids can produce a wide range of effects such as wetting (lubrication),
emulsifications, dispersions, anti-deposition, foaming, and anti-foaming. Surfactants reduce
the surface tension of water by adsorbing at the solid-liquid interface. They also reduce the
interfacial tension between solid and water by adsorbing at the solid-liquid interface. Some
commonly encountered surfactants of each type are presented in Table 2.2.
Table 2.2: Some common types of surfactants
Surfactants
Types
Ionic
1) Anionic (based on sulphate, Sulfonate or Carboxylate anions)
a.
Sodium dodecyl sulphate (SDS), ammonium lauryl sulphate,
and other alkyl sulphate salts
b.
Sodium laureth sulphate, also known as Sodium lauryl ether
sulphate (SLES)
2)
c.
Alkyl benzene sulfonate
d.
Soaps, or fatty acid salts
Cationic (based on quaternary ammonium cations)
i)
Cetyl trimethyl ammonium bromide (CTAB) a.k.a hexadecyl
trimethyl ammonium bromide, and other alkyltrimethyl ammonium
salts
ii)
Cetylpyridinium chloride (CPC)
iii) Polyethoxylated tallow amine (POEA)
45
Chapter 2: Literature Review
iv) Benzalkonium chloride (BAC)
v)
3)
Non-ionic
Benzethonium chloride (BZT)
Zwitterionic (Amphoteric)
a.
Dodecyl betaine
b.
Dodecyl dimethylamine oxide
c.
Cocamidopropyl betaine
d.
Coco ampho glycinate
a)
Alkyl Poly(ethylene oxide)
b)
Co-polymers of poly(ethylene oxide) and poly(propylene oxide)commercially called Poloxamers or poloxamines
c)
Alkyl polyglucosides, including
Octyl glucoside
Decyl maltoside
d)
Fatty alcohols ( such as Cetyl alcohol and Oleyl alcohol)
e)
Cocamide MEA, Cocamide DEA, Cocamide TEA
Surfactants which are used by different researchers are listed in Table 2.3. The advantage
of incorporating a surfactant into the fly ash slurry is to reduce drag friction and improve upon
flowing behaviour of the material. Different researchers have used different types of
surfactants. Some of the commonly used surfactants are given in Table 2.4.
Table 2.3: List of commercially available surfactants which are already used by various
researchers (Usui et al., 2001, Lei et al., 2002, and Seshadri et al., 2005)
Sl.No. Surfactants
1
Polystyrene sulphuric acid as dispersing additive
2
Sodium Hexametaphosphate of 0.1% concentration has been used as an additive
3
Rhamsan gums (S-194, S-130 obtained from Alcaligenes
4
Caboxymethyl Cellulose (CMC)
5
Xanthan gum (Vanzan)
6
Bio-polysaccharides
7
Naphthalene-sulfonate-formaldehyde condensate (NSF)
8
Pine oil
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Chapter 2: Literature Review
9
Glecerol (Natural oils & fats)
10
Any anionic detergent having good dispersing properties e.g. Sodium lauryl
sulphate (SLS)
11
Polyelectrolites
Table 2.4: List of surfactants, counter ions and polymers used by different researchers
Name of the Surfactants
Researchers used for investigation
Cetyltrimethyl Ammonium Bromide (CTAB)
Hu and Matthys, 1997,
It is a quaternary ammonium halide
Munekata et al., (2006),
Chemical Formula: C19H42BrN
Kaushal et al., (2005)
Type of surfactant: Cationic
Cetyltrimethyl Ammonium Chloride (CTAC),
Qi and Zakin (2002),
Trade names: Arquad 16-50 &
Kawaguchi et al., 1997,
Ethoquad T/13-50, Arquad 18,
Rose et al., (1984),
Ethoquad O-12, C16H33N(CH3)3Cl
Myska and Stern, (1998),
Habon G which is hexadecyl-dimethyl-
Lu et al., (1998)
hydroxyethyl ammonium, 3-hydroxy-2naphtoate, Type of surfactant: Cationic
Alkyltrimethylammonium
Aguilar et al., (2006),
Tris (2-hydroxyethyl)-tallow ammonium acetate, Boltenhagen et al., (1997)
Type of surfactant: Cationic
SDS, Chemical formula: C12H25NaO4S
Duangprasert et al., (2008)
SPE 98330, Type of surfactant: Zwitterionic
Myska and Mik, (2003)
SPE 9;8300 (It’s basic components are Betaines)
Oleyl Betaine Oleyl trimethylaminimide
Dodecyl methyl ammonium Bromide
Candau et al., 1994
Lubrol 17A10- Condensate of Oleyl/ Cetyl
Shenoy, A.V. (1976)
Alcohol, Type of surfactant: Non-ionic
Lubrol 12A9- Condensate of dodecyl alcohol
Lubrol N13- Condensate of nonyl phenol with
13 mols of ethylene oxide
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Chapter 2: Literature Review
Agnique PG 264-U (Alkyl Polyglycosides) also
Roi Gurka et al., (2004)
known as Agrimul PG 2062
Sodium Oleate and Sodium Dodecyl
Severson, K. (2005)
Benzenesulfonate, Type of surfactant: An-ionic
surfactant
Aerosol OT
Fontaine, et al., (1999)
List of counter ions
1. Sodium Salicylate (NaSal),
Aguilar et al., (2006)
HOC6H4COONa
2. Sodium 2-hydroxy benzoate (Nasal)
Severson et al., (2005)
3. Sodium Bromide (NaBr)
Barret et al., (1993)
4. 3-Chlorobenzoate
Boltenhagen et al., (1997)
List of polymers
1.
Poly (ethylene oxide) (PEO)
2.
Polyacrylamide 1822S and 1340S, MW=1.3X106 Da and 2.0X106 Da, Jayme
Pinto et al., (2006)
3.
Guargum
4.
Xanthan Gum
5.
Carboxymethyl Cellulose
6.
Hydroxyethyl Cellulose
7.
Superfloc A110 (Hydrolysed Polyacrylamide), den Toonder et al., (1995)
2.6.3. Drag reduction with surfactant solutions
When the concentration of a surfactant solution exceeds a critical value, the surfactant
molecules start to form aggregates, i.e. micelles. The association of the molecules to micelles
is reversible, i.e. when the concentration is below the critical value the micelles will dissociate
into molecules again. The micelles are always in thermodynamic equilibrium with the
molecules, and are of the size of about 20 to 1000 surfactant molecules. Depending on the
molecular structure, concentration, type of solvent, three geometrical types of micelles can be
distinguished: spheres, rods and discs. The drag reducing ability of a surfactant solution
depends strongly on the shape of these micelles.
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Chapter 2: Literature Review
2.6.4. Anionic surfactants
Savins (1994) observed that the addition of an electrolyte (e.g. KCl) helped to increase
the drag reduction. KCl helped in the enhancement of the association of the soap molecules
and that the soap micelles, which were initially spherical in the aqueous solution, were
rearranged under the influence of the electrolyte into cylindrical shapes, which in turn formed
a network of interlaced rod-like elements. The soap concentrations involved were of the order
of 0.1%, which are considerably higher than the polymer concentrations. The researcher also
observed stress controlled drag reduction effect in the soap solutions. The drag reduction
increased with increasing shear stress up to a critical value. Beyond the critical value, the drag
reduction of the soap solution became indistinguishable from that of the soap-free solution.
This indicates that the network of micelles collapses if the shear stress exceeds a critical shear
stress. This occurs because of a temporary disentanglement of the network induced by
turbulent vortices and eddies in fully developed flow. If the wall shear stress is reduced from
above to below the critical value, then the network bond reform and the reducing ability of the
solution is restored. In contrast, once the polymer chains are broken by high shear stress, the
drag reducing ability of the polymer solution is permanently lost.
2.6.5. Cationic surfactants
Gadd (1966) suggested the possibility of using the CTAB-naphthol mixture to reduce
turbulent friction, because the mixture showed shear-thinning characteristics. Similar to
anionic surfactant solutions, the drag reducing ability of the CTAB-naphthol solution
terminated at some upper Reynolds number corresponding to a critical shear stress where
there was a scission of the micelles. One marked advantage of cationic surfactants over the
anionic ones is that these complex soaps do not precipitate in the presence of calcium ions.
2.6.6. Non ionic surfactants
Zakin and Lui (1983) investigated the effect of temperature, electrolyte concentration,
surfactant concentration and the effect of mechanical shear on three nonionic surfactants
formed from linear alcohols and ethylene oxide moieties. They found that 1% solutions of the
commercial surfactants like Alfonic 1214 were more effective than the 0.5% solutions. The
critical shear stress for mechanical degradation in the case of nonionic surfactant was
dependent on the surfactant concentration, electrolyte type and concentration, and on the
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Chapter 2: Literature Review
temperature. The molecular structure of the surfactant has an important effect on its micelle
size and shape which in turn profoundly influence the drag reducing ability. Nonionic
surfactants have an advantage over the anionic and cationic counter parts because they are
both mechanically and chemically stable. They do not precipitate out in the presence of
calcium ions and therefore can be used in impure waters, seawater or concentrated brine
solutions.
2.7. Engineering uses of fly ash
There are numerous case histories available on the utilization of fly ash either alone or
mixed with lime, gypsum or both. Typically fly ash has been used for soil stabilization (Chu
et al., 1955), as embankment material (Rymond, 1961), Structural fill (Digioia and Nuzzo,
1972), for injection grouting (Joshi et al., 1987), as a replacement to cement (Gopalan and
Haque, 1986; Xu and Sarcar, 1994), in coastal land reclamation (Kim and Chun, 1994) and in
roads and embankments (Kumar, 2003).
Many successful applications have involved mixing fly ash with additional lime and
gypsum for strength gain purposes. Two types of reactions occur when lime, fly ash, and
water are mixed. The first is the self-hardening of fly ash itself as it reacts with calcium ion in
solution to form C-S-H gel. It is called pozzolanic reaction. The other reaction is due to
presence of lime that produces various hydration products. Studies conducted by different
researchers have concluded that the pozzolanic activity of the fly ash is influenced by its
phase composition, chemical composition, fineness, morphology and loss on ignition. The
reactions of fly ash with lime and/or gypsum are well documented and described in detail
elsewhere (Sivapillaih et al., 1995; Ramesh et al., 1998; Ghosh and Subbarao, 2001;
Sridharan et al., 1999).
Maser et al., (1975) reported successful case studies on fly ash –cement mixture for
subsidence control. Fauconnier and Kersten (1982) reported that the use of pulverized fly ash
filling had effectively stabilized the coal pillars reducing the risk of pillar failure in areas of
low safety factor.
Galvin and Waner (1982) opined that ash fill improved the model pillar strength
significantly at 200 days. The strength increased by 50% and 40% for width to height ratio of
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Chapter 2: Literature Review
1.0 and 2.0 respectively. They also opined that the use of ash fill could improve extraction
volume of 35%.
Yu and Counter (1988) reported the results of the use of class “C” type fly ash as a
binder for consolidated backfill at a sulphide ore mine. The fly ash so used replaced about
60% of Portland cement with considerable cost savings. A mix proportion of 40% cement and
60% fly ash resulted in compressive strength of 2.4 MPa in 28 days.
Petulanans (1988) also reported the use of high volume fly ash for subsidence control.
Palarski (1993) reported the use of fly ash, mill tailings, rock, and binding agents to make
consolidated backfill material to improve extraction percentage in coal mines.
Ghosh (1996) achieved a tensile strength of 1.08 MPa and compressive strength of
1.32 MPa by adding lime of 10% and gypsum of 1% of fly ash to class F type fly ash.
Tannant and Kumar (2000) mixed fly ash, kiln dust, and mine spoil to obtain
unconfined compressive strength of 1 MPa and moduli of 350 MPa in 28 days and found the
composite suitable for haul road design.
Chugh et al., (2001) successfully demonstrated that extraction ratio in a room- andpillar mine can be increased by about 14% with paste backfill that included coal processing
waste and coal combustion by products (fly ash). Sear (2001) identified the fill potential of fly
ash with minimal adverse effect to environment.
Ziemkiewick and Bluck (2002) have reported that the use of grout consisting of 20%
flue gas de-sulfurization (FGD) sludge, 20% class “F” type fly ash and 60% FBC ash. The
final mixture showed an unconfined compressive strength of about 3.6 MPa in 28 days.
Kumar et al., (2003) has reported the use of pond ash (a mixture of fly ash and bottom
ash) of grain size between -75 to +20 meshes with equal percentage of water (by weight) for
underground stowing of a coal mine. The pond ash water mixture with additives exhibited
100% settlement of solids within 30minutes of placement. The settlement time further
reduced with an increase in additive concentration. The additives also improved the
percolation rate of the mixture with little adverse effect on mine water. The barricades placed
51
Chapter 2: Literature Review
to arrest the fill material showed negligible load due to the placement signifying self-standing
behaviour of the mixture.
Narasimha et al., (2003) in laboratory experiments have used gypsum to activate high
calcium fly ash and obtained a compressive strength of about 6.9 MPa.
Mishra and Rao (2006) developed a fly ash composite material of uniaxial
compressive strength of about 12 MPa over a curing period of 56 days with more than 85%
fly ash mixed with lime and gypsum.
Another technique aimed at increasing or maintaining the stability of soil mass is
chemical soil stabilization by adding some specific organic compounds such as surfactants. In
a molecule of surfactant, one portion has great affinity for solvent, where as the remaining
portion, with almost negligible affinity for the solvent, tends to concentrate on interface. This
portion of surfactant rejected by solvent has a long hydrocarbon chain. The adsorption of this
chain on the surfaces of soil particles helps in interlinking them. A relatively small quantity of
these stabilizers may give optimum results in attaining better water proofing and strength
properties.
Kaushal et al., (2005) studied the different percentages of a cationic surfactant CTAB
along with 0.2% non-woven geo-fibers and 1% lime by weight of dry fly ash with 0.095%,
0.190%, 0.285%, and 0.380% CTAB by dry weight of fly ash to treat and reinforce micro fine
fly ash. The results showed that the CBR and shear strength values for fly ash mixed with 1%
lime, 0.2% non-woven geo-fibers, and 0.19% of surfactant increased in comparison to that of
untreated and un-reinforced fly ash by 3.36 and 2.04 times respectively.
Laboratory tests conducted by Raju et al., (1996) have shown that at solid
concentrations above 40% by weight, fly ash slurries more or less behave like pseudo
homogenous suspensions. They opined that laminar flow can be obtained for concentration
more than 50% when solid concentration approach static settled levels (maximum achievable
concentration under gravity settling process). However, at these high concentrations, the fly
ash slurries behave like non-Newtonian fluids with rheological equations showing either
Bingham or yield pseudo-plastic behaviour.
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Chapter 2: Literature Review
The optimum transport concentration of slurry (Parida et al., 2005) flow is determined
with respect to the specific energy consumption (SEC) which is defined as the hydraulic
energy in KWh, required to transport 1 ton of material through a distance of 1 km.
Accordingly, SEC is given by the ratio Ph / Ws, Where Ph is the hydraulic power in Kw
required to transport the slurry through 1 km at the minimum design velocity and W s is the
solids flow rate in tones / hr. Substituting the relevant terms for Ph and Ws, the equation for
SEC in KWh / tone per km is given by:
SEC = 2.724 * 103 H / (ρm C w)
(2.1)
Where ρm=slurry density (kg/m3), Cw=slurry concentration, and H is the hydraulic head.
It was observed by them that the SEC reaches the minimum value between concentrations 3040 % by weight. From the point of commercial consideration, the higher limit of 40% by
weight, where SEC value is reasonably low can be adopted as the optimum concentration for
the mixture slurry. For a particular mass throughput there is an optimum pipeline diameter
and density that will result in the lowest specific energy consumption. Alternatively, it is
calculated from:
SEC (KWh/t/km) = g*im/3.6 Ss Cv
(2.2)
Where, g = acceleration due to gravity (m/s2), im = mixture head loss (m water/m),
Ss = Solid’s relative density, Cv = Solid’s concentration by volume
The SEC is determined for a constant tonnage in a given pipe diameter as density or
solid’s concentration varies. For each pipeline diameter the minimum SEC occur at the
transition, from laminar to turbulent flow. In this instance, it is not possible to operate at these
velocities, as the solids will settle on the pipeline invert. The maximum density that can be
achieved without significantly increasing the specific power consumption is approximately
1.75-1.80 t/m3 in a 225mm pipeline. At higher densities, the flow becomes laminar and SEC
increases dramatically.
While simplifying transport, the use of large amounts of water causes many problems.
The fill must be dewatered after it is placed so that it will consolidate- a process which causes
entrained fine material and cement to be flushed out along with the large volumes of excess
water. This reduces the strength of the placed fill and deposits fines and cement in the lower
53
Chapter 2: Literature Review
horizons, creating hazards for workers, and increasing the need for maintenance of workings
and equipments. These factors limit the structural strength that can be obtained at low costs,
since load-bearing capacity of the fill depends on cement content and void ratio (Landriault, et
al., 2000 & 2001). The term course and fine are arbitrary and relative to the tailings grinds
being compared. The percentage of material passing sizes of 0.074, 0.044, and 0.020mm
(0.0029, 0.0017 and 0.00146 in.) is also used as a reference point, because materials of these
sizes are missing from traditional classified sand-type tailings (Vickyery and Boltd, 1989).
Materials of minus 0.074mm (200-mesh) are referred to as fines; materials of minus 0.044mm
(325-mesh) are referred to as slimes.
There are also additional costs associated with pumping excess water to the surface,
such as maintaining clogged bulkheads, ditches, and sumps; and repairing wear on pump
components caused by the flushed cement. In recent years, low-water-content, highconcentration paste backfills have been developed to reduce the problems associated with
high-water-content slurry backfills. This type of fill provides better support and a safer
working environment than does slurry sand fill because the excess water is eliminated, which
allows greater strength to be achieved and minimizes maintenance costs.
2.8. Colloidal stability
Most knowledge on the dense slurry flow in a pipe has been concerned with slurries
consisting of either coarse particles with settling tendencies or very fine particles creating
homogeneous, often non-Newtonian slurry. During the slurry flow, shear-induced translation
and rotational motions of the particles cause hydrodynamic interactions, which result in
particle-particle collisions and formation of temporary multiples. Such interactions lead to an
increase in the rate of viscous energy dissipation and slurry bulk density. If the attractive
forces acting in the slurry prevail, the process of coagulation and sedimentation is initiated.
However, the simultaneous existence of the repulsive forces stabilizes the slurry and keeps
individual particles separated. When the solid particles are mixed with water, attractive and
repulsive forces between colloidal particles initiate the process of coagulation, and the
particles tend to bunch into voluminous aggregates with a loose structure since coagulation
decreases the total energy of the system. During the slurry flow a great deal of energy is
consumed by the aggregates deformation. In the voluminous aggregates a great deal of water
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Chapter 2: Literature Review
is trapped, contributing to an increase in the yield stress and apparent viscosity of the slurry as
well as decreasing the maximum slurry concentration.
Forces acting on particles: These arise from interaction between particles and result in the
overall repulsion or attraction between particles.
Repulsive forces are:
Electrostatic charges
Entropic repulsion of polymeric or surfactant material on the surface of the particle.
Net repulsive forces cause particles to remain separated.
Attractive forces are:
London - Van der Walls attraction between particles
Electrostatic attraction between unlike charges on different parts of a particle.
Net attractive forces causes the particles to flocculate
Dispersion stability: There are generally two ways to modify the surface properties of a
particle to maintain a stable dispersion. Those are Electrostatic forces and steric forces.
Electro-statically: The existence of a net charge which causes particles to repel one
another.
Sterically: By absorption of polymer molecules on the particles and film of absorbed
surfactant which prevents the particles from adhering to one another which may be
sufficient to keep the dispersed particles in suspension.
2.8.1. Interparticle forces
When two colloidal particles approach each other, two types of interaction can occur:
DLVO interactions and non-DLVO interactions (Verwey and Overbeek, 1947). The DLVO
theory assumes that as two particles approach each other, repulsive and attractive forces act
upon them. The total interaction energy between each pair of particles can be described by
Equation 2.3.
VDLVO = VR + VA
(2.3)
Where VDLVO is the total DLVO interaction potential, VR is the total repulsive potential and
VA is the total attractive component.
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Chapter 2: Literature Review
The repulsive and attractive forces mainly involve the electrical forces, due to the
overlap of the electrical double layers, and van der Waals forces, respectively. As two
colloidal particles approach from a large separation to distances around 10 nm, the electrical
repulsion rises to a maximum and the interaction energy is repulsive. While, at smaller
separation distance the van der Waals attraction is dominant resulting in a deep minimum in
the total interactions. At interparticle distances less than about 1 nm, repulsion exists due to
the overlap of the electron clouds of the atoms; however, there are a number of other forces
that come into play at such a short distance, such as solvent structural forces and electron
overlap repulsion. Thus, a colloidal dispersion exhibiting DLVO interactions may be
thermodynamically unstable due to the depth of the minimum, but kinetically stable due to the
presence of the electrostatic barrier. Therefore, the ionic strength and pH of the medium, and
consequently, the zeta potential of the particles are critical to particle stability if only DLVO
interactions are considered. In colloidal suspensions that include either free or adsorbed or
anchored polymer chains, an additional component to the interparticle interaction may be
included, commonly referred to as non-DLVO interactions. Non-DLVO interactions can
include hydrophobic, hydration, steric, and acid-base forces. Hydrophobic forces are longrange attractive forces having been shown to operate over distances of hundreds of
nanometers, thus, they can dramatically affect interparticle forces. Hydration forces are the
result of a gel-like layer formed around colloidal particles which is well known to be present
on metal oxide surfaces (Hunter and Nicol, 1968).
2.9. Rheology, Fluid Behaviors, and Constitutive Models
It is appropriate to introduce the science of rheology at this point, since it does appear
in various forms in a number of references visited in the literature review. Rheology is the
discipline of fluid dynamics that studies the relationship between fluid deformation and stress.
It is nothing but the science of deformation and flow of matter. It is also described as the
study of flowing matter, such as liquids, slurries, emulsions, and melts. Rheology describes
the deformation of such matter when it is subjected to external shear forces. Laboratory
instruments called rheometers are available to experimentally investigate the deformation of
such matter under measured rates of shears. Some fluids, such as water, exhibit Newtonian
flow behavior, in which case the shear stress in the fluid is uniformly proportional to the
applied rate of shear, Equation (2.4).
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Chapter 2: Literature Review
τ=ηγ
(2.4)
Where τ is the shear stress, η is referred to as the Newtonian viscosity and γ is the applied
shear rate. When the shear stress is plotted against the applied shear rate, the resultant graph is
known as rheogram. In terms of fluid flow, materials may be classified as either Newtonian or
Non-Newtonian fluids.
2.9.1. Newtonian Fluids
By definition Newtonian behavior is when the viscosity is independent of shear rate
and does not depend on the shear history. Most simple liquids like water, acetone, or oils are
Newtonian. Liquids showing any variation from this behavior are referred to as nonNewtonian. In pipeline transportation, concentrated suspensions showing non-Newtonian
behavior are frequently encountered. Figure 2.2 illustrates the different types of rheological
response by plots of shear stress vs. shear rate; these are also known as flow curves. In simple
shear, the response of a Newtonian fluid is characterized by a linear relationship between the
applied shear stress and the rate of shear. Newtonian fluids appear as straight lines that
intersect the origin of a rheogram, the slope of which gives the viscosity of the fluid.
Newtonian behavior is typically only observed in suspensions and slurries when the particles
can be considered non-interacting or fully dispersed. Under these conditions particle
collisions are assumed to occur in a relatively insignificant number of cases. Thus the
movement of particles in the flow field results in only an increase in the viscous energy
dissipation.
2.9.2. Non-Newtonian Fluids
Fluids for which the viscosity varies with shear rate are known as Non-Newtonian
fluids. For non-Newtonian fluids the viscosity is often called the apparent viscosity to
emphasize the distinction from Newtonian behavior. Non-Newtonian fluids will either exhibit
a yield stress, non-linear viscosity characteristics, or both. The nature of the non-Newtonian
behavior depends on the solids concentration, the particle shape, the particle size, the particle
size distribution, and suspending liquid rheological properties. The suspension/slurry may
develop a yield stress and/or become time dependent in nature as structures develop within
the fluid at higher solids concentrations (Barnes, 1989).
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Chapter 2: Literature Review
Figure 2.2: Different types of fluids
2.9.3. Time-Dependent Fluids
Two typical types of time-dependent fluid behaviors are possible i.e., thixotropy,
where the fluid thins with shear and time and the opposite is the rheopexy, where the fluid
thickens with shear and time.
2.9.3.1. Thixotropic Fluids
A fluid which exhibits a drop in viscosity with time under a constant shear strain rate
is said to be thixotropic. The viscosity undergoes a gradual recovery when the shear stress is
removed. A truly thixotropic fluid will exhibit a completely reversible behavior. If the flow
curve of such a fluid is measured in a single experiment in which the value of shear rate is
steadily increased at a constant rate from zero to some maximum value and then decreased at
the same rate, a hysteresis loop is obtained. The larger the enclosed area in the loop, more
severe is the time-dependent behavior of the material. The enclosed area would be zero for a
purely viscous fluid, i.e. no hysteresis effect is expected for time-independent fluids. A
pseudo thixotropic fluid does not completely return to its original state of yield stress.
2.9.3.2. Rheopectic Fluids
In this case an increase in apparent viscosity with time under constant shear rate or
shear stress, followed by a gradual recovery when the stress or shear rate is removed. It is also
called anti-thixotropy or negative thixotropy. Relatively few fluids which show the negative
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Chapter 2: Literature Review
thixotropy, i.e., their apparent viscosity increases with time of shearing. In this case, the
hysteresis loop is obviously inverted. As opposed to thixotropic fluids, external shear fosters
the buildup of structures in this case. It is not uncommon for the same fluid to display both
thixotropy as well as rheopexy under appropriate combination of solid concentration and
shear rate.
The present study however, is primarily focused on the measurement of the
rheological properties of settling fly ash slurries where it is necessary to continuously shear
the slurries to keep them water borne. Under these conditions it is assumed that the fluid will
be fully sheared and that the rheological properties will be unlikely to change further with
time. Thus time-dependent effects will not be investigated further and the discussion will
focus only on time independent behavior.
2.9.4. Time-Independent Fluids
2.9.4.1. Pseudoplastic or Shear Thinning Fluids
Most common colloidal suspensions are shear thinning (also referred to as
pseuodoplasticity) because the viscosity decreases as the shear rate increases (Figure 2.3).
This is perhaps the most widely encountered type of time-independent non-Newtonian fluid
behavior in engineering practices. Shear-thinning fluids are those for which the slope of the
rheogram decreases with increasing shear rate (He et al., 2004). The shear thinning nature of
industrial slurries is attributed to the alignment of particles and / or flocs in the flow field. An
increase in the shear rate from rest results in instantaneous alignment of particles in the
direction of shear, thus providing a lower resistance to flow. As such, the suspension will
show a decreasing viscosity with increasing shear rate. Pseudoplastic fluids are typically
suspensions of solids or dissolved long chain polymer strands. As the shear increases the
structure of the fluid becomes more ordered, which steadily reduces the apparent viscosity.
2.9.4.2. Shear Thickening Fluids
Shear thickening behavior should not be confused with dilatancy, which is a change in
volume on deformation, though dilatancy is often used to describe shear thickening behavior
over certain ranges of shear rates. Such fluids exhibit an increase in viscosity with an increase
in the shear strain rate (Figure 2.3). The degree of shear thickening and its onset is a function
of the solids concentration, particle shape and size distribution. At rest the particles are
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Chapter 2: Literature Review
assumed to be situated in such a way that the void space between particles is at a minimum,
but as the shear rate increases the particles become more disordered and there may be
insufficient liquid to fill the space between the particles leading to direct particle-particle
contact which causes an increase in the apparent viscosity of the fluid or shear thickening
behavior. In the case of dilatancy the viscosity increases with shear rate. Although this
behavior has received little attention in the test books on rheology, it has important
consequences in pipeline transportation. For example, clay-based slips exhibit shear
thickening behavior at high shear conditions (>1000s-1), which is typical of mixing, pumping,
spraying, bushing, and injection.
Figure 2.3: Rheograms of various continuum fluid models
2.9.4.3. Yield Shear Thickening
Yield shear thickening behavior is not common but over a certain range of shear rates,
slurries and suspensions depending on the properties of the solid particles and the suspending
liquid can exhibit shear thickening behavior (Figure 2.4). In the case of yield shear thickening
behavior, Herschel-Bulkely model, Equation (2.11), outlined for yield-pseudoplastic fluids
can be used to describe the fluids rheological behavior, except that pre-exponential parameter
n must be greater than one.
2.9.4.4. Yield Stress
The yield stress of a fluid is commonly defined as the stress that is required to initiate
flow of the material. It is an internal property that enables a fluid to resist deformation up to a
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Chapter 2: Literature Review
certain point, effectively enabling it to behave as a solid while it is subjected to stresses that
are less than the yield stress. It is believed that the material responds similar to an elastic solid
until the yield stress is reached, at which point the fluid starts to flow. The yield stress is
usually explained as the fluid which contains an internal structure that is able to resist a
certain amount of stress before flow commences. Yield stress has got its practical usefulness
in engineering design and operation of processes where handling and transport of industrial
suspensions are involved. The minimum pump pressure required to start a slurry pipeline and
the entrapment of air in thick pastes are typical problems where the knowledge of the yield
stress is essential. Some of the more simple types of flow curves associated with yield stress
behavior in fluids are presented in Figure 2.4.
Figure 2.4: Flow curves for yield stress fluids
The two most common types of tests to determine the yield stress are direct measurement and
extrapolation. Numerous techniques have been developed for the direct determination of the
yield stress, but one of the more simple methods uses a generic rotational rheometer and vane
geometry. If a direct measurement is not possible then rheological data must be obtained at
shear rates as low as possible and then an extrapolation procedure must be used to obtain an
estimated value for the yield stress. Indirect methods simply involve the extrapolation of shear
stress-shear rate data to zero shear rate with or without the help of a rheological model. The
value obtained by the extrapolation of a flow curve is known as “extrapolated” or “apparent”
yield stress, whereas yield stress measured directly, usually under a near static condition, is
termed “static” or “true” yield stress value. Direct measurements generally rely on some
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Chapter 2: Literature Review
independent assessment of yield stress as the critical shear stress at which the fluid yields or
starts to flow. Indirect determination of the yield stress simply involves the extrapolation of
experimental shear stress-shear rate data at zero shear rates.
2.10. Rheological Models
Numerous rheological models are available for the purpose of mathematically
describing the rheological characteristics of a fluid (Table 2.5). Such models provide a means
by which various aspects of a fluid’s rheological behavior can be taken into account in the
mathematical modeling of various fluid dynamics related processes, and many such examples
can be found in the literature review.
Table 2.5.Different types of rheological fluid models
Newtonian
Pseudoplastic
n
K
Dilatant
(n
n
K
1)
( n
Bingham
1)
n
y
Casson
1
1
2
1
2
0
Herschel-Bulkley
y
1
2
2
c
K
n
η = ηs (1-Φ/Φm)-[η]Φm
Krieger-Dougherty equation
Three commonly used rheological models are the Bingham plastic model, power law model,
and Herschel-Bulkley models. Each of these three empirical rheological models along with
Cross model and Casson model is presented below.
2.10.1. Bingham Plastic Model
Concentrated suspensions usually cannot flow until a minimum yield stress (τ y) is
exceeded. It corresponds to Bingham plastic flow which means the linear flow curve is
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Chapter 2: Literature Review
independent of the shear rate above τy. The simplest type of yield stress fluid model is the
Bingham plastic model (Bingham, 1919), shown in Equation (2.5). This model is timeindependent, two parameter rheological model.
τ = τy + ηp
(2.5)
Where τ is the shear stress (Pa), τy is the Bingham model yield parameter, ηp is the Bingham
plastic viscosity (Pa.s) and
is the shear rate applied to the fluid (1/s). This model suits a
fluid with a yield stress and linear viscous behavior. For this model once the yield stress is
exceeded it is assumed that the fluid behaves like a Newtonian fluid, where the shear stress
increases proportionally with increases in shear rate. However, there are few suspensions and
slurries for which the Bingham model can be used to describe the rheological behavior over a
wide range of shear rates. But over a small range of low values of shear rate the Bingham
model may be more applicable for a wider range of suspensions and slurries. This is
illustrated by the flow curves in Figure 2.5 which depicts the various fluid models.
Flow
Bingham (Newtonian with yield stress)
Shear Stress,
Bingham Plastic
(Shear-thinning with yield stress)
Shear Thinning (Pseudoplastic)
Newtonian
y
Shear Thickening
(Dilatant)
Deformation
Shear Rate,
Figure 2.5.Plots of shear stress vs. shear rate (flow curves)
2.10.2. Cross Model
To predict the shape of the general flow curve it is necessary to differentiate well both
the low and the high shear rate regions so that four parameter models are established. One
such equation is given by the Cross model:
(ηo – η)/(η-η∞
)m
or (η-η∞)/(ηo-η∞) = 1/(1 + K )m
63
(2.6)
Chapter 2: Literature Review
Where ηo and η∞ refers to asymptotic values of viscosity at very low and very high shear
rates, K is a constant with dimensions of time and m is a dimensionless constant. It has
essentially the same parameters, but can be broken down into sub-models to fit partial data.
2.10.3. Power Law Model
There are many rheological models available to study the flow behaviour of
concentrated particulate slurries. Among them, the power law model is well accepted for
various applications (Chhabra & Richardson, 1999; George et al., 1984). Shear-thinning
fluids without yield stress typically obey a power law model over a range of shear rates
(Figure 2.5). The power law model also referred to as the Ostwald-de Waale model, Equation
(2.7), may be used to model the rheological behavior of pseudoplastic fluids. The model is
expressed as:
τ=K
n
(2.7)
Where, K is defined as the pre-exponential factor or consistency index or power law index
(Pa.sn) and n as the exponential factor or the flow-behavior index and also called power law
exponent (dimensionless). The relative value of K refers to the viscous behavior of the fluid,
while the value of n describes the deviation of the fluid behavior from Newtonian behavior.
The power law describes three flow behaviours (Lester, 1994). For pseudoplastic fluids n
must be less than unity. If n is equal to one then Equation (2.7) reduces to the Newtonian
model and K becomes the Newtonian viscosity, η. A value of n greater than one is used to
describe the behavior of a shear thickening fluid. The apparent viscosity (ηa) is estimated from
the power-law model as:
ηa = τ/ =K
n-1
(2.8)
Which is also known as the power-law model, where ηa is known as the apparent
shear rate (s-1), K consistency coefficient
viscosity (Pascal se
of fluid (Pa/s) (the higher the value of K the more viscous the fluid), and n is the flow
behaviour index also called the power law index, which is a measure of the degree of
departure from the Newtonian fluid flow. This model suits a fluid without yield stress that
exhibits non-linear flow behavior. The power law model typically provides a good fit over a
range of one to two orders of magnitude in shear rate.
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Chapter 2: Literature Review
The data generated from the present study were fitted to a linear equation using
ordinary least squares regression to determine a slope (plastic viscosity) and an intercept
(yield stress), according to Bingham model as below:
τ = τy + ηp
Where τ is the measured
(2.9)
, τy is the yield stress, and ηp is
the plastic viscosity. The apparent viscosity, ηa, is typically reported as the ratio of the
measured shear stress to the applied shear rate (τ/ ) at a specific shear rate (Hackley and
Ferraris, 2001).
2.10.4. Casson Model
Generally most suspensions and slurries can be described as yield-pseudoplastic
fluids; once the yield stress is exceeded the fluid can be expected to act similar to a non-yield
stress shear thinning fluid. Two of the more simple models that exist for yield pseudoplastic
fluids are the Casson and Herschel-Bulkely model. Initially developed to describe the
properties of printing inks but latter shown to be suitable for some yield stress fluids, the
Casson model is shown in Equation (2.10).
√τ = √τy +√ (η )
(2.10)
This model is also time-independent two parameter rheological models can often be
used to characterize non-settling fine particle slurries. These slurries are considered to be
viscoplastic, which means that they behave like solids below a critical stress (the yield stress).
2.10.5. Herschel-Bulkley Model
Shear-thinning power law fluids with yield stress are sometimes called HerschelBulkley fluids. In most cases the flow curve above τy is shear dependent. Several models have
been proposed to describe this behavior, one such model is called Herschel-Bulkley model.
This model suits a fluid with a yield stress that exhibits non-linear viscous behavior. The
Herschel-Bulkely model (Herschel and Bulkley, 1926) is a three parameter model that is quite
similar to the power law model, with an additional yield stress term, τ y, shown in Equation
(2.11).
τ = τy
65
n
(2.11)
Chapter 2: Literature Review
Where τ is the shear stress (Pa), τy is the yield stress (Pa), K is the Herschel-Bulkley
consistency index (Pa.sn),
is the shear rate applied to the fluid (1/s) and n is a power. This
model is essentially the combination of the previous two. It carries an extra empirical
parameter compared to each of the other two, but has the advantage of combining non-linear
viscous behavior with a yield stress, which neither of the other two models can do. The
Herschel-Bulkely model is more widely used than the Casson model because the extra term
increases the range of fluid behavior that can be described by this model. In the case of either
the Casson or Herschel-Bulkely model the fluids yield stress must either be obtained from an
experimental measurement, such as vane method or by extrapolation from measured
rheological data; shear stress and shear rate.
Typically fly ash slurry will exhibit both yield stress and varying viscosity at different
shear rates, which firmly places it in the realms of a non-Newtonian fluid. Therefore,
knowledge of rheological behavior is essential in numerous industrial operations that involve
pipeline transportation of slurries or pastes, including (i) beneficiation (e.g., wet mixing and
milling, atomization, and filtration), (ii) shape forming, and (iii) coating/deposition.
Rheological properties are extremely useful in the structural characterization of particle-liquid
systems, and the determination of how particle-particle interactions affect the stability of the
slurry. A major objective in any slurry transportation system is to improve the homogeneity
by reducing the number and size of defects. Accurate control of the slurry colloid chemistry
leads to more uniform, denser, and favorable characteristics that result in engineered materials
with the designed properties. The colloidal approach to slurry transportation allows control of
the interaction forces between particles that determine the physical behavior at all stages of
processing and transportation. The main goal of suspension transportation is to maintain
stable particle dispersion since attractive forces (namely London-van der Waals forces)
develop as particles approach each other. Colloid science offers different possibilities for
maintaining a stable dispersion.
Repulsive forces between particles can be achieved by adding different kinds of
deflocculants, which stabilize the suspension by electrostatic and/ or polymeric mechanisms.
The flow properties of a suspension are influenced on the one hand by the quantity, shape,
and size of particles, and on the other by the nature and strength of the inter-particle forces.
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Chapter 2: Literature Review
Particulate suspensions play key roles in hydraulic pipeline transportation systems. In general,
suspended fly ash particles are smaller than approximately 100 microns in size. The most
distinguishing feature of industrial suspensions is its polydispersity. The particle size
distribution of industrial suspensions has a broad range, from several hundred micrometers to
several nanometers, but, usually, the major part of the particles has a size range,
approximately from 100-50 to 0.1-0.05µm. Thus, the industrial suspensions are essentially the
mixed colloidal-noncolloidal suspensions. Accordingly, rheology is a suitable tool to correlate
the colloidal properties with the desired characteristics while the slurry is being transported.
2.11. Independent Characterization by Measuring Zeta Potential (ζ)
The indirect characterization of slurry rheology by measuring ζ is feasible because the
relationship between ζ and apparent viscosity ( a) is valid for a lot of solid/liquid systems
(He et al., 2004). The state of dispersion in the slurry, namely, the rheological behaviour, is
closely related to the ζ of the particles (Greenwood and Kendall, 1999), which represents the
potential difference between the surface of the particles and the external plane of Helmholtz,
illustrated by use of a model for the electric double layer as depicted in Figure 2.6. The ζ of a
suspension is an indication of the magnitude of the repulsive force between the particles. The
higher the ζ with the identical polarity is, the more predominant the electrostatic repulsion
between the particles. On the contrary, when the ζ is close to the iso-electric point (ζ =0), the
particles tend to flocculate, as illustrated in Figure 2.7 (He et al., 2004). The electric double
layer develops when a particle is immersed in the continuous fluid (i.e. water). Once the
immersion occurs, charged species will start to migrate across the solid/liquid interface until
equilibrium is reached. Ions that directly increase the charge on the particle surface are called
as potential determining ions which are unique to each type of the particle system. With many
types of solid particle suspensions, especially oxides and sulfide mineral slurries, the potential
determining ions are H+ or OH-. In this case, the change in the pH of a liquid can cause a
change in the particle surface charge. Hence, for given mineral slurry, ζ is directly dependent
on the pH value. The relationship between ζ and pH value in slurries can characterize
rheological behaviours of slurries that confirms well to the results obtained using rheometers
or viscometers.
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Chapter 2: Literature Review
Figure 2.6: Schematic diagram of particle electric double layer
.
Figure 2.7: Mechanism of flocculation (He et al., 2004)
2.12. Viscosity and Viscosity-Temperature Models
When a stress (σ) is applied to a solid it deforms elastically according to Hooke’s law:
σ=Gγ
(2.12)
Where G is the elastic modulus (Young’s modulus) and γ is the strain. When the strain falls to
zero the sample recovers its original shape. This is commonly illustrated by a spring. If the
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Chapter 2: Literature Review
shear is large then the structure of the sample can break and hence it not only deforms but
starts to flow. In the simplest case the response follows Newton’s law:
(2.13)
Where τ is the shear stress,
is the velocity gradient (also known as the shear rate) and η is a
coefficient of viscosity (or simply the viscosity). Viscosity, also called internal friction, is one
of the most important physical properties of a fluid system. Viscosity changes with shear rate,
temperature, pressure, moisture, and solid concentration; all these changes can be modeled by
using well known equations (Arrhenius and Frenkel). There are two kinds of viscosity:
dynamic viscosity with a unit of Pa.s or P (poise) and kinematic viscosity expressed in m2/s or
S (stokes). The kinematic viscosity is a ratio of dynamic viscosity of a given liquid and its
density at the same temperature. Plots of viscosity as a function of shear rate are known as
viscosity curves.
2.12.1. Arrhenius Equation
The obtained viscosity values can be described by means of the most commonly
applied Arrhenius equation. The effect of temperature is normally fitted with the Arrheniustype relationship which is shown in Equation 2.14 (Choi et al., 2000). According to this
equation, the viscosity values (η) obtained at a constant shear rate can be correlated with
temperature:
η = A exp Ea/TR
(2.14)
Where η is the dynamic viscosity (Pa.s), A is the pre-exponential factor (Pa.s) and a constant
related to the molecular motion and the frequency of particle collisions in the collision theory,
Ea is the exponential constant that is also known as flow activation energy for viscous flow at
a constant shear rate (J/mol). It is referred by Arrhenius as representing the energy difference
between the reactants and an activated species. The term Ea is therefore called the activation
energy. The activation energy is the energy barrier that the reactants must surmount in order
to react. Therefore, the activation energy is viewed as an energetic threshold for a fruitful
reaction. R is the universal gas constant (J/mol/K) and T is the absolute temperature (Kelvin).
According to this equation, viscosity decreases as temperature increases i.e. there is an inverse
relationship between viscosity and temperature. The value of A can be approximated as the
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Chapter 2: Literature Review
infinite-temperature viscosity (η∞), which is exact in the limit of infinite temperature. Hence,
equation (2.14) can be rewritten in the following form:
η = η∞ exp Ea/RT
(2.15)
Although equation (2.14) normally appears in the literature, equation (2.15) gives a more
accurate representation of the fluid since the pre-exponential value is better defined here. It is
widely accepted that natural logarithmic viscosity is directly proportional to the reciprocal
value of the temperature. To increase the flexibility of this equation, constants a and b are
introduced into equation (2.16) as shown below:
ln (η) + a = b/T
(2.16)
By knowing that viscosity decreases with increasing temperature and has a curve concave
upward when a viscosity vs. temperature graph is plotted, η ≈ ηT∞ when temperature is
approximately infinity. Similarly, a decreasing temperature would increase the viscosity of a
fluid body and thus, temperature at T0 would give η ≈ ηTo in which ηTo > ηT∞. Based on the
above mentioned conditions, equation (2.16) can be rearranged into the following form:
η = ηT∞ (ηTo/ηT∞)To/T
(2.17)
The Ea can be obtained as the following after comparing equations (2.15) and (2.17):
Ea = T0 R ln (ηTo/η∞)
(2.18)
R is the universal gas constant which is equal to 8.314 J/mol/K. ηTo is the viscosity at
temperature T0 which, has been taken as the zero-temperature viscosity.
2.12.2. Frenkel Equation
The obtained viscosity values can also be described by means of the most commonly
applied Frenkel Equation:
η = CT exp D/T
(2.19)
Where A, B, C, D are constants and T is the temperature.
2.13. Rheometry
The term “rheometry” is usually used to refer to a group of standard experimental
techniques for investigating the rheological behavior of materials (fluid or solid). It is of great
importance in determining the constitutive equation of a fluid or in assessing the relevance of
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Chapter 2: Literature Review
any proposed constitutive law. Rheometry aims at determining the fluid characteristics from
measurements performed in simple and controlled flows. In these tests, the fluid is stressed in
a simple manner, such that few components from its stress tensor differ from zero. Thus, from
the components of shear stress and shear rate, one can obtain a characteristic equation. In
practice, in order to measure a fluid’s viscosity, the fluid should be confined between some
devices, with determined conditions (one fixed and another with fixed speed). The fluid
should be confined in a tube, between concentric cylinders. This device is defined as a
rheometer. A rheometer is usually an engine, which can exert a torque / force on a material
and accurately measures its response with time (or conversely, it can impose a strain and
measure the resulting torque). The correct determination of the rheological properties of
different fluids including suspensions and slurries is important to many research and industrial
applications. To achieve this, the choice of the correct instrument for this application is
essential, as many different methods and instruments exist for determining the rheological
properties of fluids. Whatever the design of the instrument is two essential components are
required to correctly measure the rheological flow properties of non-elastic fluids; these are an
ability to apply a measured shear stress or shear rate to the fluid and to measure the fluids
response to the applied shear stress or shear rate. All of those relying on a small gap between
the shearing surfaces, like a cone and plate geometry or parallel plate geometry, generally are
not used and are not applicable in the industry. The most common instrument used is that
which relies on Couette flow, involving confinement of the sample between a rotating cup and
a stationary bob, or (vice versa) a rotating bob and stationary cup. Here the torque is measured
as a function of rotational speed and can be interpreted to determine the shear stress as a
function of shear rate. Most common laboratory type instruments can be separated into two
categories; rotational type and tube type.
2.13.1. Rotational Type Rheological Instruments
Of the two basic types of rheometers previously mentioned the rotational type is the
most common and includes cones and plate, parallel plate, concentric cylinder, and vane
geometries. In the rotational type rheological instruments, the fluid sample is sheared as a
result of the rotation of a cylinder or cone. The shearing occurs in a narrow gap between two
surfaces, usually one rotating and the other stationary. A significant advantage of the
71
Chapter 2: Literature Review
rotational type rheometer is that only a small sample volume is usually required, which also
means that control of temperature and pressure of the sample can be more readily achieved.
Accuracy, reliability, and ease of use make these instruments extremely common, though they
are more expensive compared to other types of rheometers.
2.13.1.1. Plate Type
2.13.1.1.1. Parallel Plate
The parallel plate geometry consists of two parallel disks separated by a defined
distance, with the space between two disks filled with the sample liquid. One of the two disks
rotates at a defined speed and the resistance of the fluid to the motion is recorded as a torque.
Measurements of slurries and suspensions with the parallel plate geometry can be affected by
slip and settling particles. As particles settle a concentration gradient will develop lending to
incorrect values of measured torque and incorrectly determined rheological properties. A
further problem with the parallel plate geometry is that there is often quite a low upper limit
on the shear rates that can be examined, particularly with low viscosity fluids that can be
ejected from the geometry due to centripetal forces at higher values of shear rate. The main
disadvantage of parallel plates comes from the fact that the shear rate produced varies across
the sample. In most cases the software takes an average value for the shear rate. Wider the
gap, there is more chance of forming a temperature gradient across the sample and so it is
important to surround the measuring system and sample with some form of thermal cover or
oven.
2.13.1.1.2. Cone and Plate
The common feature of a cone-and-plate geometry is that the fluid is sheared between
a flat plate and a cone with a low angle. In the case of cone and plate geometry either the cone
or the plate can rotate at a set speed and the resistance of the fluid to motion, the torque, is
measured. The calculations to determine the shear stress and shear rate require that the tip of
the cone touch the plate, but because this is often impractical a truncated cone can be used
instead. In a truncated cone a small portion of the tip of the cone is removed but the cone is
positioned as if the cone was complete. The small clearance between the cone (whether
truncated or not) and the stationary plate means that particles can become easily trapped.
Trapped particles significantly increase the measured resistance (the torque) and this can lead
72
Chapter 2: Literature Review
to significant errors in the calculated shear stress. Thus the size of particles in suspensions that
can be measured with the cone and plate geometry is quite limited. Settling and slip may also
affect the measurements from a cone and plate geometry, in same way that the parallel plate
geometry is affected and test samples can also be ejected from this geometry at higher
rotational speeds. For particulate material the cone and plate geometry is not recommended.
Because, if the mean particle diameter is not some five to ten times smaller than the gap; the
particles can jam at the cone apex resulting in noisy data. Materials with a high concentration
of solids are also prone to being expelled from the gap under high shear rates, another reason
to avoid the use of cone.
2.13.1.1.3. Concentric Cylinders (Cup and Bob)
The cup and bob type measuring systems come in various forms such as coaxial
cylinder, double gap, Mooney cell, etc. The coaxial-concentric cylinder system consists of a
bob or inner cylinder and a cup or outer cylinder, with the fluid placed in the annular region
between the two cylinders. Usually the inner cylinder is rotated and the resistance of the fluid
to the motion measured as a torque. Their advantage comes from being able to work with low
viscosity materials and suspensions. Their large surface area gives them a greater sensitivity
and so they will produce good data at low shear rates and viscosities. The shear rate is
determined by geometrical dimensions and the speed of rotation. The shear stress is calculated
from the torque and the geometrical dimensions. For concentric cylinder geometry, it is easier
to calculate the shear stress compared to the shear rate, as the calculations are not dependent
on the dimensions of the geometry or the rheological properties of the fluid being examined.
Thus from the measured torque, the shear stress may be determined as shown in Equation
(2.20).
τ = M / [2π (к R) 2 L]
(2.20)
Where, к represents the ratio between the radius of the two cylinders (inner/outer), L the
length of the cylinders and R the radius of the outer cylinder.
2.13.1.1.4. Vane Geometry
“Vane-in-a-cup” geometry can be used to eliminate the problem of slip. This
configuration, which consists of four blades connected to a spindle, is simply used as an
73
Chapter 2: Literature Review
attachment that can be made to fit an existing rheometer. However, the vane geometry cannot
prevent particles settling and so it is generally restricted to those systems where particles
either do not settle or settle very slowly. Another important use of the vane geometry is in the
direct determination of the yield stress of a fluid.
2.13.2. Tube type rheometer
A tube rheometer primarily consists of a pressurized reservoir and a capillary tube.
Fluid is filled in the reservoir and forced out through the tube under a certain pressure and the
flow rate is recorded. Usually the tube is placed in a vertical position though measurements
with horizontal tubes are possible. It is usual when determining the pressure drop across a
tube rheometer to assume that the fluid has no (or a minimal) velocity when it exits the end of
the tube. This assumption will not always be valid and under certain conditions can lead to
significant errors that are referred to as “kinetic effects”. End effects, which are the
combination of entrance and exit effects, may influence the results from a tube rheometer.
2.14. Krieger-Dougherty model
This equation shows that there is an increase in the viscosity of the medium when
particles are added. This increase depends on the concentration of the particles (Struble and
Sun, 1995):
η = ηs (1-Φ/Φm)-[η]Φm
(2.21)
where [ ], the intrinsic viscosity, is equal to 2.5 for spheres, is the volume concentration of
particles,
m
the maximum packing, the viscosity of the suspension and
0
is the viscosity
of the medium. Therefore, if the viscosity of the cement paste and the concentration of the
aggregates are known, and the maximum packing of the particles is determined, then the
viscosity of the concrete can be calculated.
Keeping the above literature in mind, it is decided to investigate the flow behaviour of
surfactant admixtured fly ash slurry to reduce drag friction during hydraulic transportation in
pipelines for filling mine voids, which constitutes the application I am most interested in.
74
Chapter 3:Methodology
CHAPTER 3
METHODOLOGY
3. Materials and methods
This chapter introduces the various materials used for this investigation and
laboratory characterization techniques followed as per the prescribed standards and
procedures in context of fly ash transportation and utilization.
3.1. Introduction
The objective of the investigation was to study the flow behavior of the fly ash slurry
and to determine its in-place strength characteristics to achieve bulk utilization in filling mine
voids. The major ingredients used were fly ash, surfactant, sodium salycilate, and lime.
Sample preparation, various methods followed for characterization of ingredients, rheology
study, strength study, and development of different composite materials are reported.
The coal ash, which includes both fly ash and the bottom ash (or boiler slag), and is
better known as the pulverized fuel ash, is a by-product produced at thermal power plants due
to the combustion of pulverized coal, with low calorific value and with high ash content. It is
a pozzolana (a siliceous and aluminous material which in itself possesses little or no
cementitious value but will, in finely divided form and in the presence of moisture, reacts
chemically with calcium hydroxide, at normal temperatures, to form compounds possessing
cementitious properties). The quality of the ash produced mainly depends on the quality of
coal, its pulverization method, combustion technique, ash handling, and collection techniques.
Physical properties help in classifying the coal ashes for various engineering purposes and
some are related to engineering properties.
The properties investigated are specific gravity, grain size distribution, specific surface
area, wet density, moisture content, porosity, chemical composition, morphological
characteristics, turbidity, pH, rheology, settling characteristics, FTIR studies, optimum
moisture content-maximum dry density relationships, unconfined compressive strength,
Brazilian tensile strength, shear strength parameters, ultrasonic pulse velocity, poisson’s ratio,
Young’s modulus, etc.
75
Chapter 3:Methodology
3.2. Materials
3.2.1. Fly ash
Fly ash samples used in the investigation were procured from seven numbers of coalfired thermal power plants situated in India (Figure 3.1). They are class F fly ashes which
were collected in dry state directly from hoppers attached to electrostatic precipitators in
gunny bags made of strong poly-coated cotton with 50 kg capacity. The chute of hoppers was
slowly opened and bags were filled. The mouth of each bag was sealed immediately after
collection and the same was again inserted in another polypack to prevent atmospheric
influences and transported with care from the plant to the place of experimentation and kept in
a controlled environment. The sample ID and their source of collection are given in Table 3.1.
Sample ID
Table-3.1: Sample ID and their source of collection
Source of collection of samples
Sample Code
F1
Ennore Thermal Power Plant, Ennore
F2
National Aluminium Company, Angul
F3
State
(ETPS)
Tamilnadu
(NALCO)
Odisha
IB Thermal Power Plant, Jharsuguda
(OPGC)
Odisha
F4
Patratu Thermal Power Plant, Ranchi
(PTPS)
Jharkhand
F5
Rourkela Steel Plant, CPP-II, Rourkela
(RSPII)
Odisha
F6
Super Thermal Power Plant, NTPC, Angul
(STPP)
Odisha
F7
Talcher Thermal Power Plant, Talcher
(TTPS)
Odisha
3.2.2. Additives
3.2.2.1. Surfactant
The surfactant used in this study was Cetyltrimethyl Ammonium Bromide (CTAB). Its
chemical formula is C19H42BrN. This was chosen due to its relative inertness with calcium or
sodium ions present in tap water. The surfactant was procured from LOBA Chemie Pvt. Ltd.,
Mumbai, India. The molecular weight of the surfactant is 364.46. CTAB is a cationic
surfactant that is known to be very effective for drag reduction when accompanied with
suitable counter-ions. The hydrophobic head group which is a long chain hydrocarbon with 19
carbons in the structure of the surfactant is attached to the fly ash particle, converting it from
hydrophilic to hydrophobic property. The physical and chemical properties of the surfactant
are shown in Table 3.2. The molecular structural diagram is shown in Figure 3.2.
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Chapter 3:Methodology
7
2
6
4
5
3
1
Figure 3.1: Location map of India from where the samples were collected
Table 3.2.Physical and chemical properties of the surfactant (CTAB)
Sl. No.
Parameters
% Value
1
Minimum Assay value
99
2
Heavy metals (as Pb)
0.001
3
Iron (Fe)
0.001
4
Sulphated ash
0.1
5
Loss on drying
1.0
Figure 3.2.Molecular structural diagram of CTAB
77
Chapter 3:Methodology
3.2.2.2. Counter-ion
The counter-ion used was Sodium Salicylate (NaSal) (HOC6H4COONa). Its molecular
weight is 160.10. This was added to the slurry at the same weight concentration as that of the
surfactant. It was suggested that for the surfactant drag-reducing additives, the rod-like
micelle structures are the key to give complicated rheological fluid properties including
viscoelasticity. The counter-ion reduces ion radius of the surfactant to deform micellar shape
from globular to rod-like micelles. These rod-like micelles entangle together to make a certain
network structure (Rehage and Hoffmann, 1991). Nguyen et al. (2006) opined that counterions also play a role as catalysts for the breakdown and reformation of the entanglement
points. The physical and chemical properties of the counter-ion used are given in Table 3.3.
The molecular structural diagram of the counter-ion is presented in Figure 3.3.
Table 3.3.Physical and chemical properties of the counter-ion (NaSal)
Sl. No. Parameters
% Value
1
Minimum assay (calculated to dried material)
99
Maximum limits of impurities
2
Loss on drying at 1050 C
0.5
3
Chloride (Cl)
0.02
4
Sulphate (SO4)
0.05
5
Heavy metals (as Pb)
0.002
Figure 3.3.Molecular structural diagram of the counter-ion
3.2.2.3. Lime
Commercially available chemically pure lime (CaCO3) (make: Merck Company
Limited, Mumbai) has been used in this investigation. Table 3.4 gives the constituents of lime
used.
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Chapter 3:Methodology
3.2.3. Water
Since the fly ash is to be transported through ordinary water medium in pipelines, so
ordinary tap water of pH 7.0 was chosen for preparation of the fly ash slurry in this study.
3.2.4. Millipore water
Millipore water was used for standardization of rheometer and surface tensiometer. It
is ultra pure ion free water. Its electrical resistivity is 18.2MΩ, surface tension 71.5 mN/m and
pH varies from 6.5 to 7.
3.2.5. Mobil oil (Tranself type B 85W140)
Elf Tranself type B 85 W 140 was used for standardization of rheometer readings. It is
multi-grade transmission oil developed especially for the rear axles of many heavy earth
moving machineries (HEMMs). It is known for its excellent thermal and oxidation stability
(Net at 29.50C).
Table 3.4.Chemical composition of the lime
Minimum Assay (Acidimetric)
98.5 %
Maximum
limits
of
impurities
content
expressed in percentages
Substances insoluble in hydrochloric acid
0.050 %
Chloride (Cl) content
0.050 %
Sulphate (SO4) content
0.500 %
Heavy metals (as Pb) content
0.005 %
Iron (Fe) content
0.050 %
3.3. Laboratory investigation and characterization of materials
The following tests were conducted for the seven fly ash samples in the laboratory
following the prescribed standards and procedures by using the various instruments discussed
below:
3.3.1. X-ray diffraction (XRD) analysis
The raw materials after oven dried were taken for X-ray diffraction analysis. The Xray diffraction was carried out by XRD Spectrometer (make: Philips Analytical X-ray B.V.,
UK) studies, using a graphite monochromator and Cu Kα radiation. The ash samples were
79
Chapter 3:Methodology
scanned for 2θ angle ranging from 5 to 800. These studies are carried out primarily to identify
the mineral phases.
3.3.2. Scanning Electron Microscopy (SEM) studies
The raw materials after oven dried were also taken for Scanning Electron Microscope
(SEM) study. SEM provides a means of imaging micro surfaces, particle size analysis, grain
boundaries, etc. In this investigation a SEM (make: JEOL JSM 6480 LV, Japan) was used to
conduct these studies. Figure 3.4 shows the Scanning Electron Microscope set up in the
laboratory where the investigation was carried out.
Figure 3.4.Scanning Electron Microscope
3.3.3. Chemical characterization
The chemical properties of the coal ashes influence the environmental impacts that
may arise out of their use/disposal. The adverse impacts include contamination of surface and
subsurface water with toxic heavy metals present in the coal ashes, loss of soil fertility around
the plant sites, etc. Thus a detailed study of the chemical composition, morphological studies,
pH, total soluble solids etc. is necessary. Chemical composition also suggests the possible
areas of application of coal ash.
3.3.3.1. Energy-dispersive X-ray spectroscopy (EDX) studies
The chemical composition, calculated as major oxides, of the ash samples are obtained
with the help of an EDX set-up (make: JEOL JSM 6480 LV, Japan). EDX is a technique used
80
Chapter 3:Methodology
for identifying the elemental composition of the specimen. The EDX analysis system works
as an integral feature of a SEM and cannot operate on its own without the latter. It is an
analytical tool predominantly used for chemical characterization. Being a type of
spectroscopy, it relies on the investigation of a sample through interactions between light and
matter, analyzing X-rays in its particular case. Its characterization capabilities are due in large
part to the fundamental principle that each element of the periodic table has a unique
electronic structure and, thus, a unique response to electromagnetic waves. Spectroscopy data
is often portrayed as a graph plotting counts vs. energy. The peaks correspond to
characteristic elemental emissions. The release of X-rays creates spectral lines that are highly
specific to individual elements; thus, the X-ray emission data can be analyzed to characterize
the sample in question.
3.3.3.2. Energy dispersive X-ray fluorescence (ED-XRF) studies
XRF analysis (make: Philips PW2400 X-ray, Japan) was conducted to determine the
chemical constituents of the samples. ED-XRF technology provides one of the simplest, most
accurate and most economic analytical methods for the determination of the chemical
composition of many types of materials. It is non-destructive and reliable, requires no, or very
little, sample preparation and is suitable for solid, liquid and powdered samples. It can be used
for a wide range of elements, from sodium (11) to uranium (92), and provides detection limits
at the sub-ppm level; it can also measure concentrations of up to 100% easily and
simultaneously.
3.3.4. Physical characterization
The physical properties such as grain size analysis, particle size distribution, specific
gravity, and specific surface area were determined following the standard procedures.
3.3.4.1. Specific gravity (sp. gr.)
This is an important parameter and affects the flow characteristics of fly ash slurry.
Sp. gr. is the density of a substance divided by the density of water. It is calculated as:
Specific gravity, S =
(W4
(W2 W1 )
W2 ) (W3 W1 )
81
(3.1)
Chapter 3:Methodology
Where, W1 = Weight of dry sp. gr. bottle with lid,
W2 = Weight of dry sp. gr. bottle with
rd
lid + 1/3 vol. of ash sample, W3 = W2 + distilled water, W4 = Weight of dry sp. gr. bottle
with lid + Distilled water. The sp. gr. of the fly ash samples were determined in the
laboratory by using a stoppered bottle having a capacity of 50 ml as per the guidelines
provided by the American Society of Testing Materials (ASTM D 854).
3.3.4.2. Specific surface area
The specific surface area of the ash samples were determined by using a Blaine’s
apparatus (ASTM C 204) with Portland cement as a standard reference material. For
calculating the specific surface area of the ash samples, the following equation given by Singh
and Kolay (2002) was used: Specific surface area (cm2/g),
A = {Ss (1-es) √e3√T} / {√ es3√Ts (1-e)}
(3.2)
Where A is the specific surface area of the ash sample, Ss the specific surface area of the
Portland cement (3460 cm2/g), e the void ratio of the ash sample, es the void ratio of the
cement (=0.5), Ts the measured time interval of manometer drop, for cement (77.18s) and T is
the measured time interval of manometer drop for ash sample.
3.3.4.3. Particle size analysis
The grain size analysis of the untreated fly ash sample was carried out by Malvern
particle size analyzer (U.K) laser diffraction apparatus. In this investigation the gradational
properties of the ash samples are obtained by using photo-sedimentation method, which
measures the change of concentration by passing a beam of light through the suspension. Soft
imaging system has also been used to determine the grain-size distribution characteristics of
the ash samples by using Mastersizer 2000 version 5.22. A schematic layout of the instrument
has been shown in Figure 3.5.
3.3.4.4. pH (ASTM D 4972)
The pH value was determined to identify the acidic or alkaline characteristic of fly ash
samples. The pH value denotes the hydrogen ion concentration on the liquid and it is the
measure of acidity and alkalinity of the liquid. According to the law of mass action, in any
liquid, (Concentration of H+ ions * concentration of OH- ions) / (concentration of un-dissolved
82
Chapter 3:Methodology
HOH Molecules) = 10-14. The pH is determined by the electrolysis and dissociation of H+ and
OH- ions
in a liquid and the milli volts generated gives the reading on scale either by
movement of analog pointer or digital recording. In this study the measurement of pH was
carried out using digital pH meter model 111 (make: Systronics, India) with accuracy up to
0.02 units as per the procedure suggested by Jackson (1958).
The instrument was
standardized with three standard buffer solutions of pH 7.00, 4.00 and 10.00 at 250C. The
suspension was stirred well and allowed to come to room temperature (25 1°C) before taking
the pH measurement.
Figure 3.5 Shematic diagram of Malvern Particle Size Analyzer
3.3.5. Surface Tension
Surface tension is a property of the surface of a liquid that allows it to resist an
external force. Surface tension of the fly ash slurry was measured by Surface Tensiometer
(make: DCAT 11 EC, Dataphysics, Germany) a dynamic contact angle meter using the
Wilhelmy plate with an accuracy of ±0.01 mNm-1 at room temperature 250C.
3.3.6. Zeta Potential (ζ)
The ζ of all the slurries was measured by using electrophoretic technique by zeta sizer
(make: ZS Nano-Series, Malvern Instruments, U.K). This instrument automatically calculates
the electrophoretic mobility of the colloidal fly ash particles and converts it into ζ. The ζ
values are at least an average of five measurements. All measurements were made at the
ambient temperature. Colloidal particles dispersed in a solution are electrically charged due to
their ionic characteristics and dipolar attributes. Each particle dispersed in a solution is
83
Chapter 3:Methodology
surrounded by oppositely charged ions called the fixed layer. Outside the fixed layer, there are
varying compositions of ions of opposite polarities, forming a cloud-like area. This area is
called the diffuse double layer, and the whole area is electrically neutral. When a voltage is
applied to the solution in which particles are dispersed, particles are attracted to the electrode
of the opposite polarity, accompanied by the fixed layer and part of the diffuse double layer,
or internal side of the "sliding surface".
The significance of ζ is that its value can be related to the stability of colloidal
dispersions. The ζ indicates the degree of repulsion between adjacent, similarly charged
particles in dispersion. For molecules and particles that are small enough, a high ζ will confer
stability, i.e. the solution or dispersion will resist aggregation. When the potential is low,
attraction exceeds repulsion and the dispersion will break and flocculate. So, colloids with
high ζ (negative or positive) are electrically stabilized while colloids with low ζ tend to
coagulate or flocculate as outlined in the Table 3.5 and Figure 3.6 (Vallar et al., 1999).
Table 3.5: Relation between ζ and suspension stability
ζ [mV]
from 0 to ±5
from ±5 to ±10
from ±10 to ±30
from ±30 to ±40
from ±40 to ±60
more than ±61
Stability behavior of the colloid
Rapid coagulation or flocculation
Instable dispersion
Incipient instability
Moderate stability
Good stability
Excellent stability
Figure 3.6: Relation between ζ and Suspension Stability
84
Chapter 3:Methodology
3.3.7. Settling study of fly ash slurry
3.3.7.1. Static settling tests
A series of experiments were conducted, which monitored the settling of fly ash slurry
under static conditions for 24 hours (Figure 3.7). After this time, an obvious division between
the settled material and the clear decant water could be seen. The depth of this section was
measured and corresponding volume calculated. One of the objectives of this investigation
was to provide a detailed study of the settling characteristics of fly ash slurry at different
concentration levels. In this investigation settling study was carried out by using test tubes of
100 ml capacity as per prescribed standards. The maximum settled concentration of slurry is
an indicator of the limiting concentration beyond which the flowability of fly ash slurry
ceases to occur. The maximum settled concentration is found after allowing a slurry of given
concentration to settle for a long period of time (>24 hours) until the equilibrium condition is
reached. Studies were conducted by Senapati et al., (2005) on fly ash slurry at weight
concentrations varying from 50 – 67%. The slurry prepared at these concentrations settled in a
graduated glass cylinder for 72 hours after which no further settling occurred. The maximum
settled concentrations at different weight concentrations are determined from the readings of
the settled volume and water volume using the following relationship.
Cwmax = Ws/ (Ws + Ww)
(3.3)
Where Ws = weight of solids in the settled mass, Ww = weight of water present in the settled
mass. The study conducted by them revealed that the maximum settled concentration of fly
ash slurry is 58%.
Figure 3.7: Settling study of fly ash slurry
85
Chapter 3:Methodology
3.3.8. FTIR Spectroscopy study of fly ash
Fourier Transform Infrared (FTIR) IR Prestige-21 model was used for this
investigation. FTIR spectroscopy bases its functionality on the principle that almost all
molecules absorb infrared light. Most FTIR spectroscopy uses a Michelson interferometer to
spread a sample with the infrared light spectrum and measure the intensity of the infrared light
spectrum not absorbed by the sample. FTIR spectroscopy is a multiplexing technique, where
all optical frequencies from the source are observed simultaneously over a period of time
known as scan time. The spectrometer measures the intensity of a specially-encoded infrared
beam after it has passed through a sample. The resulting signal, which is a time domain digital
signal, is called an Interferogram and contains intensity information about all frequencies
present in the infrared beam. This information can be extracted by switching this signal from
a time domain digital signal to a frequency domain digital signal, which is accomplished by
applying a Fourier transform over the interferogram and producing what is called a single
beam spectrum. Fly ash samples both raw and modified by additives were analysed in the
laboratory by preparing samples by using a hydraulic press. The results are reported and
discussed in the respective sections.
3.4. Experimental apparatus used for rheology study
The various flow related properties as shear stress, shear rate, viscosity, torque, etc.
were determined with a rheometer (make: Physica MCR 101, Germany). It employs
concentric cylinder geometry with a rotating inner cylinder and a stationary outer cylinder.
The torque developed on the inner cylinder due to a sample is directly related to the sample
viscosity. In this study, all samples were measured by the use of CC 27 tool master system (as
per DIN 6129 standard). A thermal jacket allows the use of an external fluid circulator to
control or regulate the temperature of the sample measured. The laminar flow of a liquid in
the space between coaxial cylinders is known as” Couette Flow”. In this case, the outer
cylinder, with a radius re remains stationary. The inner cylinder with a radius ri and height L is
rotated at constant speed (Ω rad/s). It is assumed that the flow of the fluid between the
cylinders is steady and laminar and that the end effects are negligible. Consider a volume of
fluid between the inner cylinder and an arbitrary radius r. Let ω be the angular velocity of the
fluid at this radius r. The torque exerted on the fluid at this radius is:
86
Chapter 3:Methodology
M = τr (2πrh) r
(3.4)
Where τr is the shear stress: The torque M measured at the surface of the inner
cylinder must be the same as the torque at any arbitrary radius r since the motion is steady.
Rewriting in terms of the shear stress we get
τr =
(3.5)
It can be observed from the equation 3.5 that the shearing stress is inversely
proportional to the square of the distance from the axis of rotation. It is interesting to note that
by using an annular gap that is small compared to the cylinder radii, the shearing stress on the
fluid will be almost constant throughout the volume of the testing fluid. The tangential
velocity of the fluid at the radius r is:
V=rώ
(3.6)
The gradient of velocity is given by:
dv/dr = r (dώ/dr)+ώ
(3.7)
In equation 3.7, the first term represents the rate of shear and the second term represents the
radial velocity gradient of rigid body rotation. For a Newtonian fluid, τr= µ , or
M/ (2πr2h) =µr (dώ/dr)
(3.8)
dώ/dr= M/ (2πhµr3)
(3.9)
=r (dώ/dr), µ the viscosity and thus:
Integrating the equation 3.9 with appropriate boundary conditions, results in the expression:
M= (4πµhR12R22ώ)/ (R22 - R12 )
(3.10)
or M = cµ ώ, where c is the instrument constant and R outer radius.
In Figure 3.8 the abbreviated numbers and legends may be read as: 1–inner cylinder
connected with measuring scale; 2–fly ash slurry; 3–outer cylinder (measuring cup); 4–outer
temperature controlling jacket connected to the circulator bath to control the temperature with
an accuracy of
0.50C. Positioning length (DIN position) =72.5 mm; approximate sample
volume = 19.0 ml, active length (check length) = 120.2 mm. The shear rate, for different
rotating speed of the bob (1), is calculated using the equation:
87
Chapter 3:Methodology
= (π*n/30)*[(1+δ2)/ (δ2-1)];
= (2 π*n)/60
(3.11)
The shear strain γ is calculated using the equation:
γ = (1/10)*[(1+δ2)/ (δ2-1)]*φ; where δ= re/ri
(3.12)
Shear stress τ in fly ash slurry, are calculated using the equation:
τ = [(1+δ2)/ (200*δ2)]*[M/ (2πLri2CL]
(3.13)
αcyl. cone = 1200; (rshaft/ri) ≥ 0.3; L/ri≥ 3
Where, τ = shear stress (Pa),
= torque or moment (mNm), = strain or deformation (%),
φ = deflection angle (m rad), = shear rate (s-1), n= speed (min-1), ri/re = internal / external
cylinder radius (m), = angular velocity (s-1) = (2π/60)*n.
CL = end effect correction factor = 1.10. Empirical values for: CL=1.1 for Newtonian fluids,
and up to 1.2 recommended for standard measurements according to ISO 3219 for shear
thinning fluids. For pseudoplastic fluids at low shear rates CL is up to 1.28.
Figure 3.8: Schematic diagram of the rotational rheometer with coaxial concentric cylinder measuring
system (Standard: ISO 3219) (δ≤1.2)
Rheological properties of tested slurries were obtained by measuring shear stress at
specific shear rates ranging from 25-1000 s-1. Physical parameters of the measuring tools and
88
Chapter 3:Methodology
sensor system are presented in Table 3.6. In this instrument, the stationary cup, which houses
the slurry, and into which the rotating bob, mounted vertically, was inserted. The shear rate
was linearly increased from 25-1000 s-1. The temperature was varied from 200C to 400C by a
water bath circulator. The above temperature range was selected based on the average
temperature variation during the various seasons of a year in India during which the fly ash
slurry is to be transported. Shear viscosity was measured by a shear rate sweep experiment.
The minimum waiting time was set at 20 s at each shear rate. First, the equipment was tested
for its reliability by use of standard Mobil oil (type B 85W140 multi-grade transmission oil
meeting API GL-5, and MIL-L-2105D levels of specifications), distilled water, Millipore
water (ultra pure and ion free water having pH 6.5 to 7, surface tension 71.5 mN/m) and
ordinary tap water. The measured data matched favorably with their standard values. The
rheological properties such as viscosity, shear stress, and torque were determined at a fixed
shear rate for each sample and the reported values were the average of five measurements for
each parameter.
Table 3.6: Physical parameters of the measuring tools and sensor system
Instrument Make
Anton Paar Rheometer, Germany
Model No.
Physica MCR 101 (air bearing system)
Sensor System
CC 27
Description
Co-axial cylinder measuring system
Standard
ISO 3219 (≤ 1.2)
Cone angle
αcyl. cone = 1200, L/ri ≥ 3
Measuring range
Shear rate 0-1000 s-1
Physical Dimensions
Measuring Bob, Diameter, Di = 26.664 mm, Measuring Cup, Diameter,
De = 28.922 mm, Ratio of Radii, δ = 1.085; Gap Length = 40.014 mm
Measuring Gap = 1.129 mm
3.4.1. Description of the Instrument
A temperature controlled couette rheometer with accurate independent temperature
control device for measuring the viscosity of the fly ah slurry was used. The schematic
diagram of the rheometer is presented in Figure 3.8. Both cup and bob are made up of 304
stainless steel coated with zirconia. The slurry was poured into the outer cylinder. When the
89
Chapter 3:Methodology
inner cylinder was placed concentrically, the slurry resided in the annular space between the
cylinders. The inner cylinder was rotated by a drag cup motor which gives torque applied (M)
to the inner cylinder (accuracy ~ 0.0001 µNm) and the outer cylinder is stationary. As the
inner cylinder was rotated, the slurry was sheared continuously at the set temperature
environment. Circulator bath was kept on all the time to maintain a constant set temperature
of the slurry. During shearing, the rotational speed of the inner cylinder was measured by an
inductive position sensor which gives the strain rate with accuracy ~ 0.008 µrad.
Figure 3.9: Schematic diagram of the Rheometer
3.4.2. Experimental steps for rheology measurement
For the rheometric test the F1 fly ash sample was selected out of seven fly ash samples
investigated due its favorable properties as a mine filling material (Table 4.1). The active
dispersive agent used was CTAB. Couterion selected for this study was NaSal. The fly ash
slurry was mixed thoroughly by a magnetic stirrer. The additive was mixed with water, used
for slurry preparation. The simplified scheme of the rheometer is displayed on Figure 3.9. The
fly ash slurry was poured into the container (3) i.e. the external cylinder which is fixed nonmovably into the equipment stand. Inside the external cylinder the internal cylinder called the
bob (1) can be rotated. Because of the intrinsic friction of the layers of the fly ash slurry (2)
appearing between the rotating internal cylinder and the external cylinder torque developed is
measured. The internal cylinder is connected to a measuring scale which makes a turn and the
90
Chapter 3:Methodology
data displayed on the measuring scale changes. The procedure followed in the rheometric
tests was repetitive, and is summarized as follows:
i.
First, the entire apparatus was connected (Rheometer, circulator bath, computer and
the air compressor) and power supply was made on.
ii.
Next, the circulator bath temperature was set up. The working principle of this
equipment was to maintain the temperature of the circulating fluid by means of
heating and cooling fins. This fluid circulates through the “heat jacket” (accessory
coupled to the rheometer in Figure 3.9), which envelops the spindle, maintaining the
sample temperature constant. Depending on the temperature range at which it is
working, a type of circulating fluid is to be used. For temperatures varying between
50C and 800C, the fluid is water.
iii.
In the rheoplus software, the entire test procedure was configured: the option for shear
stress or shear rate controlled test was made, the spindle used was indicated, the test
time and shear rate or shear stress imposed was defined (for gathering shear stress or
shear rate data, respectively).
iv.
Next the rheometer was activated from the software, and the test started.
Test results were obtained by conducting close to 60 experimental tests for a particular
concentration of solids.
3.5. Characterization of Fly Ash Slurry at 20% Solid Concentration
3.5.1. Experimental Procedure and Range of Parameters
The Rheometer confirms to ISO 3219 (DIN EN ISO 3219, 1993). It consists of a
motor with attached gear box system for varying the speed in steps of equal ratio. The
cylindrical measuring bob is attached to a torsion bar and the concentric measuring cup can be
rotated at the desired speed. Temperature was controlled by a fluid bath circulator with an
accuracy of ±0.50 C of the desired temperature. Shear viscosity was measured by the constant
shear rate sweep test experiment. The minimum waiting time set is at 20 seconds at each shear
rate to allow the viscosity value to reach equilibrium at each shear rate. Viscosity at each
shear rate was calculated as the average of ten measurements.
91
Chapter 3:Methodology
3.5.2. Sample Preparation
The rheometric test needed 100ml of slurry suspension. It was prepared with 20 gram
of fly ash and 80ml of ordinary tap water. Surfactant and counter-ion was added to water first
and mixed thoroughly. Then the fly ash was added to it kept in a glass beaker. Stirring was
done with a glass rod gently so as to avoid attrition of the particles. The container was then
covered with aluminium foil tightly to avoid evaporation of water to the atmosphere as well as
to enable uniform mixing of fly ash particles in the liquid medium. Tests were carried out
after one hour of sample preparation. For rheometric tests, about 19 ml of the slurry sample
was poured into the cup and the bob was lowered into the cup so that the free surface touches
the top of the bob. The tests were conducted at shear rates varying from 100, 200, 300, 400,
and 500 sec-1. The recommended maximum shear stress is at a shear rate of about 511 sec-1
and exposing cement slurry to shear rates above 511 sec-1 has been reported to generate
inconsistent results (Shah and Jeong, 2003).
3.5.3. Range of Parameters
Experiments were carried out for a total of six solid liquid mixtures at varying
temperature environment. The concentration of additives used was 0, 0.1, 0.2, 0.3, 0.4, and
0.5% (by weight). This range of additive concentration was selected based on literature
review (Seshadri et al., 2005 and Li et al., 2002). Table 3.7 shows the different fly ash
composite slurries used in this investigation for 20% solid concentration.
Table 3.7.Sample ID, Parametric variations and suspension characteristic features at 20% solid conc
Sample
No.
Fly ash
(gram)
Surfactant
(gm)
Water
(ml)
Solid Conc.
C w (by wt.)
0.5
Counterion
(gm)
0.5
Zeta
Potential
(mV)
+49.300
pH at
27±10C
20
Surface
Tension
(mNm)
31.636
20.1
19.0
80
20.2
19.2
0.4
0.4
80
20
31.758
+37.500
7.59
20.3
19.4
0.3
0.3
80
20
31.224
+45.800
7.47
20.4
19.6
0.2
0.2
80
20
31.335
+36.900
7.97
20.5
19.8
0.1
0.1
80
20
32.897
+40.800
7.25
20.6
20.0
0.0
0.0
80
20
70.684
-27.000
7.74
92
7.30
Chapter 3:Methodology
The rates of shear during the measurements were varied from 100 to 500s-1 with a step
of 100 each. These ranges correspond to the magnitudes of shear rates usually expected in low
concentration fly ash slurry pipeline transportation systems. The lower shear rate range from 2
s-1 to 20 s-1 was used by Seshadri et al., 2005 for highly concentrated slurries i.e. Cw≈68% (by
weight). They also used shear rates ranging from 20 to 120 per second for high concentration
slurry of Cw (60 to 65 %) for their rheological investigation.
3.6. Rheological characterization at 30% solid concentration
The cationic surfactant CTAB was selected for its eco-friendly nature. It is less
susceptible to mechanical degradation (Zakin & Lui, 1983) and also known potential to
positively influence turbulent flow with very small amount (Ohlendorf et al., 1986). It is also
least affected by the presence of calcium and sodium ions in tap water (Kawaguchi et al.,
1997; Feng-Chen et al., 2008). The counter-ion acts as a reagent to reduce ion radius of the
surfactant to deform micellar shape from globular to rod-like micelles.
3.6.1. Sample preparation and measurement techniques followed
30% solids concentrations of slurries were prepared by using fly ash with ordinary tap
water. For each temperature, the shear rates investigated varied from 25 to 500s-1. On the
basis of literature review, five different surfactant concentrations i.e. 0.1%, 0.2%, 0.3%, 0.4%,
and 0.5% of the total weight of the slurry were selected (Seshadri et al., 2005; Verma et al.,
2008; Biswas et al., 2000; Li et al., 2002; Usui et al., 2001). An equal amount of a counterion same as that of the surfactant concentration was also added to the slurry to take care of the
calcium and sodium ions naturally present in tap water (Kawaguchi et al., 1997; Feng-Chen et
al., 2008; Munekata et al., 2006). The samples were prepared by first adding the required
amount of surfactant and the counter-ion to the required quantity of tap water. The prepared
solution was mixed thoroughly using a magnetic stirrer, and fly ash was added to it. Table 3.8
presents the different composition of fly ash slurry and corresponding measured values of zeta
potential and surface tension from the laboratory study for 30% solid concentration.
3.7. Characterization of fly ash slurries at 40% solid concentration
3.7.1. Parametric variations and sample preparation
Slurry samples were prepared with 40 wt. % of fly ash with ordinary tap water. The
shear rates investigated varied from 25-1000 s-1 for each temperature. An equal amount of a
93
Chapter 3:Methodology
counter-ion equal to the surfactant concentration was also added to the slurry to prevent
precipitation of surfactants due to the presence of Ca and Na ions in tap water (Munekata et
al., 2006; Li et al., 2008). The counter-ion acts to reduce ion radius of the surfactant to
deform micellar shape from globular to rod-like (Kawaguchi et al., 1997). The samples were
prepared by adding the required amount of surfactant and the counter-ion to the required
quantity of tap water and mixing thoroughly by a magnetic stirrer. Measurements were carried
out as per standards (DIN EN ISO: 3219, 1993). Table 3.9 presents the different composition
of fly ash slurry and corresponding measured values of zeta potential and surface tension from
the laboratory study for 40% solid concentration.
Table 3.8.Sample ID, Parametric variations and suspension characteristic features at 30% solid conc
Sampl Fly
Surfacta Counter Wate Solid Conc. Surface
Zeta
pH at
e No. ash
nt (gm)
-ion
r
Cw (by wt.) Tension
Potential 250C
(gm)
(gm)
(ml)
(mN/m)
(mV)
30.1 29.0
0.5
0.5
70
30
32.178
+35.200
7.73
30.2 29.2
0.4
0.4
70
30
32.249
+34.534
7.63
30.3 29.4
0.3
0.3
70
30
31.830
+33.800
7.24
30.4 29.6
0.2
0.2
70
30
31.902
+32.100
7.64
30.5 29.8
0.1
0.1
70
30
33.305
+31.700
7.66
30.6 30.0
0.0
0.0
70
30
57.900
-25.000
7.30
Table 3.9.Sample ID, Parametric variations and suspension characteristic features at 40% solid conc
Sampl Fly
Surfacta CounterWate Solid Conc. Surface
Zeta
pH
e ID
ash
nt (gm)
ion
r
Cw (by wt.) Tension
Potential
at
(gm)
(gm)
(ml)
(mN/m)
(mV)
250C
40.1 39.0
0.5
0.5
60
40
33.119
+36.511
7.23
40.2 39.2
0.4
0.4
60
40
32.225
+35.679
7.33
40.3 39.4
0.3
0.3
60
40
31.645
+33.796
7.14
40.4 39.6
0.2
0.2
60
40
31.231
+32.678
7.34
40.5 39.8
0.1
0.1
60
40
33.265
+31.689
7.56
40.6 40.0
0.0
0.0
60
40
58.543
-25.000
7.40
3.8. Rheological characterization at 50% solid concentration
Rheological characterization at 50% solid concentration was carried out at parametric
variations listed in Table 3.10.
Table 3.10.Sample ID, Parametric variations and suspension characteristic features at 50% solid conc
Sample
No.
50.1
50.2
50.3
50.4
50.5
50.6
Fly ash
(gram)
49.0
49.2
49.4
49.6
49.8
50.0
Surfactant
(gm)
0.5
0.4
0.3
0.2
0.1
0.0
Counter-ion
(gm)
0.5
0.4
0.3
0.2
0.1
0.0
94
Water (ml)
50
50
50
50
50
50
Solid Conc. C w
(by wt.)
50
50
50
50
50
50
Chapter 3:Methodology
3.9. Rheological characterization at 60% solid concentration
Table 3.11 presents the different composition of fly ash slurry at 60% solid concentration.
Table 3.11.Sample ID, Parametric variations and suspension characteristic features at 60% solid conc
Sample No.
60.1
60.2
60.3
60.4
60.5
60.6
Fly ash
(gram)
59.0
59.2
59.4
59.6
59.8
60.0
Surfactant
(gm)
0.5
0.4
0.3
0.2
0.1
0.0
Counter-ion
(gm)
0.5
0.4
0.3
0.2
0.1
0.0
Water
(ml)
40
40
40
40
40
40
Solid Conc.
C w (by wt.)
60
60
60
60
60
60
3.10. Methods of sample preparation for strength study
3.10.1. Sample preparation
Availability of free lime enhances the pozzolanic reaction of materials. Silica lime
reaction is pH dependent. The solubility of silica and its reaction with lime is directly related
to the pH value. pH of the medium increases when the lime content exceeds the optimum lime
content necessary for the silica to react. But pH reaches a constant value when the solution is
saturated with lime (Sivapullaiah et al., 1995). It reflects the saturation of the silica-lime
reaction a pozzolanic activity. In this investigation quick lime - a commercially available
additive was chosen for this study.
The pH of the raw fly ash and fly ash-surfactant-NaSal mixture were determined as
suggested by IS: 2720-Part 26 (1987) at room temperature in a pH meter to identify the acidic
or alkaline characteristic of fly ash. The suspension was stirred well and allowed to come to
room temperature (25 1°C) before taking the pH measurement. The pH of raw fly ash and
fly ash-surfactant-NaSal-lime were obtained, which varied within 6.67 to 12.5 (Table 3.12).
The pH value increased by more than 50% at 5% lime content which remained almost
constant after that (Figure 3.10). Therefore, on the basis of pH study (Figure 3.10), a fixed
percentage of quick lime i.e. 5% was used in preparing the fly ash composites along with
0.2% CTAB and 0.2% NaSal (Table 3.13) for evaluation of strength properties.
3.10.2. OMC-MDD Study
Moisture content and dry unit weight have direct bearing on the compaction of
particles. There exists an optimum quantity of moisture content at which the dry unit weight is
maximum. Modified proctor compaction test was carried out as per IS: 2720 – Part (1983) to
determine the maximum dry density and optimum moisture content of the fly ash- lime95
Chapter 3:Methodology
surfactant-NaSal mixes for preparation of specimen samples. The samples were prepared at
their respective OMC and MDD. The ingredients such as fly ash, lime, surfactant, and NaSal
were blended in the required proportion in dry condition. The dry mixed ingredients were put
in a poly pack, covered, and left for about an hour for homogenization. Then required amount
of water was added to the mixture and mixed thoroughly. The mixture was left in a closed
container for uniform mixing and to prevent loss of moisture to atmosphere. The wet mixture
was compacted in the proctor mould.
Table 3.12: Lime – pH relationship
Lime %
pH
0
6.77
2
9.2
5
12.5
7
12.4
10
11.9
12
11.6
15
11.4
Figure 3.10: Lime-pH relationship diagram
Table 3.13: Various proportions of fly ash, surfactant (CTAB), NaSal, and Lime
Sl.No.
Ingredients
Percentage (%)
1.
Fly Ash
94.6%
2.
Lime
5.0%
3.
CTAB
0.2%
4.
NaSal
0.2%
96
Chapter 3:Methodology
3.10.3. Sample preparation for UCS test
A Mould of 38 mm diameter and 76 mm length was used for preparation of the
unconfined compressive strength (UCS) test samples as per IS: 2720-part 10 (1991). Samples
were prepared with uniform tamping. Two circular metal spacer discs of height 5 mm and
diameter 37.5 mm each with base (7 mm height, 50 mm diameter) were used at top and
bottom ends of the mould to compact the sample such that the length of the specimen was
maintained at 76 mm (Figure 3.11). Then the discs were removed and another spacer disc of
height 100 mm and diameter 37.5 mm with a base (height 7 mm, 50 mm diameter) was used
to remove the sample from the mould. The final prepared specimen had length to diameter
ratio of 2 (Figures 3.12 and 3.13).
Figure 3.11: UCS mould for sample preparation
3.10.4. Sample Preparation for Tensile Strength Test
The determination of direct tensile strength of soil or rock material is difficult. So,
indirect way (Brazilian tensile strength) of its determination is practiced. The Brazilian
tensile test make the sample fail under tension though the loading pattern is compressive in
nature. The tensile strength was determined as per ASTM D 3967. The sample for Brazilian
tensile strength test was prepared using the same mould of UCS test samples. For this
purpose, two circular metal spacer discs of 5 mm and 62 mm heights and 37.5 mm diameters
with base (height 7 mm, 50 mm diameter) were used. The final prepared specimen had length
97
Chapter 3:Methodology
to diameter ratio of 0.5. The specimens prepared for tensile strength test were of 38 mm
diameter and 19 mm thick. The specimens were placed diametrically during test. The sample
fails diametrically in tension by application of load.
Sample
Figure 3.12: Sample inside mould for UCS test
Figure 3.13: Sample of UCS specimens prepared (undergoing curing)
3.10.5. Sample preparation for ultrasonic pulse velocity test
Ultrasonic pulse velocity test is a nondestructive testing technique typically used to
determine the dynamic properties of materials. The accuracy of it is influenced by many
factors such as direction, material composition, dampness, weaknesses present, travel
98
Chapter 3:Methodology
distance, and diameter of transducer. This test was carried out as per IS: 10782 (1983). The
specimen used for the uniaxial compression tests were used for it. The ultrasonic pulse
velocity test is a measurement of the transit time of a longitudinal vibration pulse through a
sample of known path length.
It is carried out with two transducers (transmitting and
receiving) placed at the opposite ends of the samples (Figure 3.14).
Figure 3.14: Schematic representation of ultrasonic velocity measurement
The electrical impulses of a specified frequency are generated by pulse generator that
is converted into elastic waves which propagate through the sample by the transmitter. The
mechanical energy of the propagating waves that propagate through the sample are received
by the transducer (receiver) placed at the opposite end and then turns into electrical energy of
the same frequency.
The signal travel time through the specimen is registered in the
oscilloscope.
The relationship between various parameters on pulse velocity, density, elastic
constants, modulus values are given by the following equations.
………………………………………… (3.14)
…………………………………… (3.15)
99
Chapter 3:Methodology
……………………………………… (3.16)
……………………………………………… (3.17)
Where,
= compression P wave velocity, m/s,
= shear S wave velocity, m/s, = density,
kg/m3, = Poisson’s ratio, E= Young’s Modulus, Pa, K= Bulk Modulus, Pa and G= Shear
(Rigidity) Modulus, Pa.
3.10.6. Methods of Testing
3.10.6.1. Tri-axial Compression Test
Material properties as cohesion and angle of internal friction of the fly ash-SurfactantNaSal-Lime composite material were determined from triaxial tests. The un-drained, tri-axial
compression test was carried out as per IS: 2720 – Part 11 (1993). Three identical samples of
38 mm diameter and 76 mm length were prepared at optimum moisture content and maximum
dry density of the materials obtained from the modified proctor compaction test. The samples
were tested by giving confining pressures of 1 kg/cm2, 2 kg/cm2 and 3 kg/cm2 respectively.
Average values of three tests for each type were considered for analysis. Mohr-Coulomb
relation between two normal stresses (τ = C + бn tan ) was used to determine cohesion and
angle of internal friction of the materials.
3.10.6.2. Compaction test
Modified proctor compaction test is typically used to give a higher standard of
compaction. It was performed to determine the maximum dry density and optimum moisture
content of the materials. The sample was compacted in the mould in five layers using a
rammer of 4.9 kg mass with a fall of 450 mm by giving 25 blows per layer (Das and Yudhbir,
2006). The compacted energy value given was 2674 kJ/m3. Figure 3.15 depicts the
arrangements made for sample preparation.
3.10.6.3. Unconfined Compressive Strength Test
Unconfined compressive strength test was carried out to determine the resistance of
material to any external loading. The availability of free lime and reactive silica and
aluminum etc. play a vital role in strength gain. Moisture content has direct effect on
100
Chapter 3:Methodology
reactivity. Hence it is preserved by curing the sample in a controlled chamber with
humidity at 30
95%
20C. The unconfined compressive strength tests were conducted at a strain
rate of 1.2 mm/min load and deformation data were recorded till failure of the specimen. The
experimental set up and prepared samples for unconfined compression test are shown in
Figure 3.16.
Figure 3.15: Sample preparation for proctor compaction test
Sample
Figure 3.16: Unconfined Compressive Strength Test (make: Instron K600, UK)
101
Chapter 3:Methodology
3.10.6.4. Brazilian tensile strength test
Determination of direct tensile strength of soil or rock mass is difficult so indirect test
i.e. Brazilian tensile test is practiced in real life situations. The Brazilian tensile test make the
sample fail under tension though the loading pattern is compressive in nature. The samples
were placed diametrically on the disc during testing (Figure 3.17). The sample fails
diametrically in tension by application of load. The indirect tensile strength is calculated as:
бt =
(3.18)
Where бt = Brazilian Tensile Strength, P = Failure load, D = Diameter of the sample,
t =thickness of the sample.
Sample
Figure 3.17: Test set up for Brazilian tensile strength test (make: HEICO, India)
3.10.6.5. Ultrasonic Pulse Velocity Test
P-wave velocity values of developed composites were determined using an ultrasonic
velocity measurement system (make: GCTS, USA; Figure 3.14). This system includes 10
MHz bandwidth receiver with pulse raise time less than 5 nano-seconds, 20 MHz acquisition
rate with 12 bit resolution digitizing board, transducer platens with 200 kHz compression
mode and 20 kHz shears mode. The test was carried out by applying two sensors to opposite
surface of the specimen. Sufficient surface contact between the sensors and the specimen was
102
Chapter 3:Methodology
maintained by a couplet such as honey. Figure 3.18 depicts the Ultrasonic pulse velocity test
instrument and a view of test in progress. Figure 3.19 shows a typical P-wave velocity signal
plot of fly ash composites.
Sample
Figure 3.18: Ultrasonic pulse velocity test instrument and view of test in progress
Figure 3.19: A typical P-wave velocity signal plot of fly ash composite
3.11. Experimental Size
3.11.1. Characterization
Seven number of fly ash samples were characterized with a view to select the best
material for flow and in-place strength study. The various tests conducted and number of
samples tested is presented in Table 3.14.
103
Chapter 3:Methodology
Table 3.14: Experimental size for characterization study
Sl. No.
Type of test
No. of samples tested
1
XRD
21
2
SEM
21
3
EDX
21
4
XRF
7
5
Specific gravity
21
6
Specific surface area
21
7
Particle size analysis
21
8
Turbidity
21
9
pH
21
10
Surface tension
18
11
Zeta potential
18
12
Settling study
21
13
FTIR
21
Total number of tests conducted= 253
3.11.2. Rheology
The surface nature of fly ash particles is an important factor in the high solid/ liquid
ratio (fly ash-water) suspensions behavior. With a view to modify the surface properties of the
fly ash particles in this investigation, a cationic surfactant CTAB was used along with a
counter-ion NaSal to study the rheological properties of chemically treated fly ash slurry.
Solid concentrations varying from 20% to 60% by weight of fly ash-water suspensions was
treated with surfactant and counter-ion and analyzed experimentally at varying temperature
environment (200C to 400C). Table 3.15 and Figure 3.20 present the detailed parametric
variations and scheme of experimental studies designed for this investigation.
Table 3.15.Detailed parametric variations and scheme of experimental design for rheology study
FA
(g)
20.0
CTAB
(g)
0.0
NaSal
(g)
0.0
WATER
(ml)
80
TEMPERATURE
(0 C)
20, 25, 30, 35, 40
SHEAR RATES
(1/s)
100, 200, 300, 400, 500
19.8
0.1
0.1
80
20, 25, 30, 35, 40
100, 200, 300, 400, 500
19.6
0.2
0.2
80
20, 25, 30, 35, 40
100, 200, 300, 400, 500
104
Chapter 3:Methodology
19.4
0.3
0.3
80
20, 25, 30, 35, 40
100, 200, 300, 400, 500
19.2
0.4
0.4
80
20, 25, 30, 35, 40
100, 200, 300, 400, 500
19.0
0.5
0.5
80
20, 25, 30, 35, 40
100, 200, 300, 400, 500
30.0
0.0
0.0
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
29.8
0.1
0.1
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
29.6
0.2
0.2
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
29.4
0.3
0.3
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
29.2
0.4
0.4
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
29.0
0.5
0.5
70
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500
40.0
0.0
0.0
60
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
39.8
0.1
0.1
60
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
39.6
0.2
0.2
60
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
39.4
0.3
0.3
60
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
39.2
0.4
0.4
60
20, 25, 30, 35, 40
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
39.0
0.5
0.5
60
20, 25, 30, 35, 40
50.0
0.0
0.0
50
20, 25, 30, 35, 40
49.8
0.1
0.1
50
20, 25, 30, 35, 40
49.6
0.2
0.2
50
20, 25, 30, 35, 40
49.4
0.3
0.3
50
20, 25, 30, 35, 40
49.2
0.4
0.4
50
20, 25, 30, 35, 40
49.0
0.5
0.5
50
20, 25, 30, 35, 40
60.0
0.0
0.0
40
20, 25, 30, 35, 40
59.8
0.1
0.1
40
20, 25, 30, 35, 40
59.6
0.2
0.2
40
20, 25, 30, 35, 40
59.4
0.3
0.3
40
20, 25, 30, 35, 40
59.2
0.4
0.4
40
20, 25, 30, 35, 40
59.0
0.5
0.5
40
20, 25, 30, 35, 40
105
25, 50, 100, 200, 300, 400, 500, 600,
700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
25, 50, 100, 150, 200, 250, 300, 350,
400, 500, 600, 700, 800, 900, 1000
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
10, 20, 25, 30, 40, 50, 60, 70, 80, 90,
100, 200
Chapter 3:Methodology
Figure 3.20: Parametric variations and scheme of experimental investigations for rheology study
106
Chapter 3:Methodology
3.11.3. Strength
The investigation included many characterization studies including major laboratory
tests such as compaction, unconfined compressive strength (UCS), Brazilian tensile strength
(BTS), Ultrasonic pulse velocity tests. The reported results represent average values of three
to four samples for each test type except that for compaction to determine MDD and OMC.
The test results that were not within 4% to 7% of each other were discarded and fresh samples
were prepared and tested. The total numbers of tests conducted were 21 with about 65
samples (Tables 3.16 – 3.18).
Table 3.16: Various proportion of fly ash, CTAB, NaSal, Lime and Water for different curing periods
Sample
FA (g)
CTAB
NaSal (g) Lime
Water
Curing
Type of test No. of
No.
(g)
(g)
(ml)
Period
samples
(days)
tested
1
29.32
0.062
0.062
1.55
3.8 0
UTS
3
2
117.58
0.248
0.248
6.2
15.53 0
UCS
3
3
117.58
0.248
0.248
6.2
15.53 0
Triaxial
3
4
117.58
0.248
0.248
6.2
15.53 0
Ultrasonic
3
5
29.32
0.062
0.062
1.55
3.8 7
UTS
3
6
117.58
0.248
0.248
6.2
15.53 7
UCS
3
7
117.58
0.248
0.248
6.2
15.53 7
Triaxial
3
8
117.58
0.248
0.248
6.2
15.53 7
Ultrasonic
3
9
29.32
0.062
0.062
1.55
3.8 14
UTS
3
10
117.58
0.248
0.248
6.2
15.53 14
UCS
3
11
117.58
0.248
0.248
6.2
15.53 14
Triaxial
3
12
117.58
0.248
0.248
6.2
15.53 14
Ultrasonic
3
13
29.32
0.062
0.062
1.55
3.8 28
UTS
3
14
117.58
0.248
0.248
6.2
15.53 28
UCS
3
15
117.58
0.248
0.248
6.2
15.53 28
Triaxial
3
16
117.58
0.248
0.248
6.2
15.53 28
Ultrasonic
3
17
29.32
0.062
0.062
1.55
3.8 56
UTS
3
18
117.58
0.248
0.248
6.2
15.53 56
UCS
3
19
117.58
0.248
0.248
6.2
15.53 56
Triaxial
3
20
117.58
0.248
0.248
6.2
15.53 56
Ultrasonic
3
Total number of samples tested =
107
60
Chapter 3:Methodology
Table 3.17: Total number of tests conducted
UCS
BTS
Triaxial
Proctor
compaction
1
5
5
P-Wave velocity
5
5
Total = 1+5+5+5+5 = 21
Table 3.18: Total number of samples tested
UCS
BTS
Triaxial
Proctor compaction
1x3
5x3=15
5x3=15
P-Wave
velocity
5x3=15
5x3=15
Total = 3+15+15+15+15=63
(Excluding tests for material characterization and rheology = 200 samples)
Table 3.19: Experimental Design Chart
Compositions
Sl.
Compa
UCS
UTS
Triaxial
P-wave velocity
ction
No.
7
14
28
56
ᶘ
56
+6.2+15.53)
28
(117.58+0.248+0.248
14
3
7
+6.2+15.53)
56
ᶘ
28
(117.58+0.248+0.248
14
2
7
1.55+3.8)
56
ᶘ
28
(29.32+0.062+0.062+
14
Lime+Water)
1
7
(FA+CTAB+NaSal+
*
*
*
*
+
+
+
+
¨
¨
¨
¨
-
-
-
-
*
*
*
*
+
+
+
+
¨
¨
¨
¨
-
-
-
-
*
*
*
*
+
+
+
+
¨
¨
¨
¨
-
-
-
-
108
Chapter 4:Results and discussion
CHAPTER 4
4. Results and Discussion
This chapter describes the results obtained from laboratory studies in three different
sections. First section discusses the results obtained from material characterization study to
select the best material out of seven different samples studied. Second section describes the
results obtained from rheology tests for the selected best material at varying shear rates and
temperature environment. Third section deals with the results obtained from strength study of
the optimized fly ash slurry material at varying curing periods i.e., 0, 7, 14, 28, and 56 days.
4.1. Introduction
Slurries commonly refer to mixture of settling particles and some certain liquid such as
water. The transport of slurries by hydraulic pipelines is widespread in the minerals,
metallurgy, water, and some other industrial applications to carry the raw materials and their
products to the designated places. Similarly, fly ash can be transported most economically
over great distances using a hydraulic slurry pipeline. Notwithstanding the good technical
results achieved by fly ash slurry technologies, technical areas, which deserve further
development work, still exist. Design data for slurry pipeline systems are usually obtained
using pilot plant studies. The high correlations obtained between pilot plant data and
rheometer data suggests that it is possible to use a simple co-axial concentric rotational
rheometer instead of a specially designed pilot plant in the design of slurry pipelines (Blissett
and Rowson, 2013). The primary objective of this work was to investigate the rheological
properties of concentrated fly ash slurries by using rheological instruments with a view to
transport the material smoothly and economically (by reducing drag friction) to mine site area
to fill worked out empty void spaces. Fine fly ash slurry may be described as a colloidal
system in which the solids are dispersed through the liquid. Because of the high surface
charge to mass ratio of fly ashes, van der Waals attractive forces and electrostatic repulsive
forces dominate particle-particle interactions. It is the sum total of these two forces between
109
Chapter 4: Results and discussion
particles that determine the nature of the slurry rheology. The net particle interactions can be
strongly repulsive, where the particles remain dispersed, so that the fluid exhibits Newtonian
flow characteristics. The rheological properties of fine fly ash slurries can be manipulated by
altering the concentration of solids and by controlling the electrostatic repulsive forces
between the particles. The electrostatic repulsive forces can be increased or decreased by
manipulating the pH and the ionic content in the suspending medium. Increasing the repulsive
forces with the addition of a dispersing agent may break down the structure and reduce or
eliminate non-Newtonian flow behaviour. Alternatively, the net interaction between particles
can be strongly attractive so that a floc structure will be created. Flocs can form networks
which cause the slurry to exhibit non-Newtonian flow characteristics. This structure can resist
shear distortion giving the fluid a yield stress. With the addition of small amounts of specific
chemical reagents it is possible to manipulate particle-particle interactions between fly ash
particles in the slurry. Variations in flow behaviour including elimination of yield stress are
associated with these changes. Almost all pipelines in the world today are transporting
material in the turbulent flow regime using a critical velocity to keep the particles in
suspension (Ihle and Tamburrino, 2012). Laminar flow attracts sedimentation and blockage of
the pipelines. Therefore, rheological characterization is essential before designing any
pipeline system. The engineering properties of a material are dependent to a large extent on
the composition of material. There exists wide variation in the composition of fly ash
depending on coal types, types of furnace, temperature, collection technique, etc. The
geotechnical properties of the developed composite materials were also determined as per
established methods. All the results of the current investigation and their corresponding
analysis have been presented in different sections as mentioned below:
a.
Characterization of ingredients (fly ash) from seven different sources
b. Selection of best fly ash material for rheology study
c.
Rheological investigation of the selected material
d. Selection of best composite material with respect to its flow characteristics
e.
Geotechnical properties of developed composite materials
f.
Analysis of the results at different parametric variations
110
Chapter 4: Results and discussion
4.2. Section-I
4.2.1. Characterization of ingredients
The primary aim of this investigation was to develop fly ash based composite
materials suitable for mine filling applications. So a detailed analysis of the constituent
materials was first carried out to select the best material out of seven different sources for
further study with respect to its flow and in-place strength characteristics. The results of the
material characterization study are reported here as given below.
4.2.1.1. Physical properties
Physical properties help in classifying the coal ashes for engineering purposes and
some are related to engineering properties. The fly ash was collected in dry state and was in
loose stage. Its average water content was less than 1%. The fly ash used had a powdery
structure with medium to dark grey colour indicating low lime content (Meyers et al., 1976).
The measured physical properties of seven fly ash samples are reported in Table 4.1.
4.2.1.1.1. Specific gravity (G)
Sp. gr. is an important physical property for evaluating geotechnical applications. A
series of tests were conducted to determine the sp. gr. (G) values of the fly ash samples, and
the average values of G are reported in Table 4.1. These values ranged from 2.20 to 2.27,
indicating some variation among ash sources. The sp. gr. of F1 is lower as compared to other
ash sources i.e. 2.20 which are due to high percentage of fine particles. As reported by Kim
and Chun (1994), the variation in G values is attributable to two factors: (1) chemical
composition, and (2) presence of hollow fly ash particles or particles with porous or vesicular
textures.
Different amounts of hollow particles present in fly ash caused a variation in apparent
sp. gr. The apparent sp. gr. is also affected by the porosity of its particles. This variation may
also be due to trapped micro bubbles of air in ash particles (Trivedi and Singh, 2004). Guo et
al., (1996) examined the chemical compositions of hollow and solid fly ash particles
separately, and the data revealed that hollow-particle fly ash had significantly lower iron
content (4.5%) than solid particle fly ash (25%).
111
Chapter 4: Results and discussion
4.2.1.1.2. Specific surface area and bulk density
The specific surface area of the fly ash samples varies between 0.187 m 2/g and 1.24
m2/g and the bulk density of the fly ash samples ranged between 1.60 g/cm3 and 1.99 g/cm3
(Table 4.1). Though there is little difference in values, comparatively, the average sp. gr. and
bulk density of fly ashes were found to be less than that of river bed sand. The F1 fly ash is
having less sp. gr. and more specific surface area compared to others which would also
facilitate possible surface modification by chemical additives for smooth flow in the pipelines.
A larger specific surface area of fly ash will make the fly ash particles more easily grafted by
the surfactant, making it more suitable to be modified. The high specific surface area of fly
ash will also result in a strong adsorptive capacity of fly ash to surfactant suspensions.
4.2.1.1.3. Porosity and moisture content
The porosity of the bulk fly ash samples varied between 9.135% and 34.2% and the
moisture content varied between 0.15 % - 0.8% (Table 4.1). The presence of pores in fly ash
may influence the eventual chemical state of the adsorbed vapour by shielding material
contained in pores from photochemical degradation (Schure et al., 1985).
Table 4.1.Physical properties of fly ash samples
Parameters
F1
F2
F3
F4
F5
F6
F7
Colour
Grey
Grey
Grey
Specific gravity (G)
2.20
2.23
2.27
Dark
grey
2.25
Light
grey
2.26
Light
grey
2.24
Light
grey
2.21
Bulk density (ρ), g/cm3
1.75
1.6
1.67
1.89
1.95
1.99
1.80
Porosity (φ), %
20.5
34.2
15.7
19.6
20.732
9.135
18.55
Moisture content, %
0.20
0.8
0.25
0.15
0.398
0.22
0.401
Specific surface area, m2/g
1.24
0.185
0.458
0.187
0.408
0.428
0.395
D(4,3), µm
171.61
14.27
48.204
91.26
48.214
59.79
65.608
D(3,2), µm
8.5
5.04
13.105
32.05
13.115
14.003
15.175
D90
988.5
30.831
113.727
187.61
113.757
144.133
158.144
D50
11.2
8.367
29.972
74.573
29.871
39.375
43.47
D10
3.81
2.649
7.184
18.013
7.173
7.248
7.966
Coefficient of uniformity,
Cu
6.3
1.15
1.12
0.70
1.13
1.09
1.07
Particle size analysis
112
Chapter 4: Results and discussion
4.2.1.1.4. Grain size analysis
The grain size distribution of fly ashes is very important factor for their use as
pozzolans as it influences the strength behaviour. It provides information related to particle
size- whether coarse grained or fine grained and their gradation, etc. The particle sizes of
seven fly ash samples exhibit wide variations (Figures 4.1- 4.4), with F4 being the coarsest and
F2 the finest fly ash. The results of particle size analysis of the fly ash samples are also
summarized in Table 4.2. The grain size distributions for the fly ash samples indicated that the
fly ash samples consist of sand-sized (<4.75 mm), silt-sized (0.075-0.002 mm), and clay-sized
(<0.002 mm) particles. The sample from F1 (ETPS) exhibits a near normal distribution of
fines and coarse fractions. Almost 90% of the particles are less than 50 µm which confirms to
the ASTM (D 2487-06, 2006). Fly ashes from other six sources though possess fine sizes; the
percentage is less than that of F1.
4.2.1.1.5. Coefficient of uniformity
The coefficientt of uniformity (Cu=D60/D10), defined as the ratio of the 60% passing
size to 10% passing size affects the workability of the fly ash grains. Backfill materials with a
Cu ranging from 4 to 6 would show improved packing density, reduced porosity, and
generally high friction angle (Sargeant, 2008; Eromoto et al., 2006). The higher the
coefficient of uniformity, the better is its adaptability to compaction and hence strength. The
coefficient of uniformity of the seven samples varies from 0.70 to 6.3. The minimum value
belongs to PTPS (F4) which has highest fraction of coarsest particles. The maximum value 6.3
was exhibited by ETPS (F1). This value is more than 6, thus the fly ash particles can be
regarded as well graded (Sridharan and Prakash, 2007). Other fly ash specimens show C u
value less than 6. Hence the fly ash sample F1 is well graded compared with the other fly ash
samples as per the classification and gradation of soils (ASTM International D 2487-06,
2006).
Also, only the F1 fly ash sample depicted bi-modal particle size distribution thought to
be the sum of two normal distributions. These materials are known to favour high densities of
the consolidated mass because of their enhanced packing characteristics (Oberacker et al.,
2001).
113
Chapter 4: Results and discussion
Figure 4.1.Particle size distribution curve of fly ash sample F1
Figure 4.2.Particle size distribution of F1 fly ash sample
F6
F3
F4
F2
Figure 4.3.Particle size distribution curve of fly ash samples F3, F6, F4 and F2
114
Chapter 4: Results and discussion
4.2.1.2. Morphological properties
The SEM photomicrographs depicted the presence of particles with different shapes
namely, glassy solid spheres, hollow sphere (cenospheres), broken, sphere within another
sphere (plerosphere), tubular, smooth porous grains, and some other irregularly shaped
particles (Figures 4.5 and 4.6). These particles affect the compaction behaviour (Leonards and
Bailey, 1982). The micrographs depict without any formation of cementitious compounds. It
confirms that the fly ash used in this investigation has low calcium content. It compares
favourably well to those observed elsewhere (Baker and Laguros, 1984).
Table 4.2.Results of particle size analysis of fly ash samples
Sample
Size range (%)
ID
‹ 1 µm
1 µm - 50 µm
› 50 µm
F1
3.66
87.80
08.54
F2
2.77
92.73
04.50
F3
1.02
68.20
30.78
F4
0.10
34.37
65.53
F5
1.02
68.40
30.58
F6
0.97
58.07
40.96
F7
0.90
55.16
43.94
The fly ash investigated is predominantly fine grained and mostly composed of compact or
hollow spheres of different sizes. Some other vitreous unshaped fragments also can be seen in
the F7 fly ash sample. SEMs also show that the spheres in the F2 fly ash sample are more
closely packed than those in the other samples; thus, F2 exhibits the lowest surface area and
pore volume. Unlike other samples, F4 has many unshaped fragments that are ascribed to
unburned char (Trivedi and Singh, 2004; Wang et al., 2008). Spherical particles make up
most of the fly ash, especially in the finer fractions. These spheres are glassy and mostly
transparent (Figure 4.5: F1, F2; and Figure: 4.6, F6), indicating complete melting of silicate
minerals. The few opaque spheres (Figure 4.6, F7) are mostly composed of magnetite or other
iron oxide particles (Fisher et al., 1978). The fly ash particles in F1 sample are similar in
shape and form- distinctly spherical shape which is considered to be ideal material for mine
115
Chapter 4: Results and discussion
filling purposes (Canty and Everett, 2001). It is apparent that F1 fly ash has much superior
particle morphology than the other fly ashes. Comparatively, it has more spherical particles
compared with the other fly ash samples, and this feature would create a lubricating effect,
known as the ball-bearing phenomena, resulting in a frictionless flow in stowing pipelines.
F5
F7
Figure 4.4.Particle size distribution curve of fly ash samples F5 and F7
F2
F1
F3
F4
Figure 4.5.SEM Photomicrographs of F1, F2, F3 and F4 fly ash samples at 5000x
116
Chapter 4: Results and discussion
F6
F5
F7
F7
Figure 4.6.SEM Photomicrographs of F5, F6, and F7 fly ash samples at 5000x and 1000x
4.2.1.3. Chemical and mineralogical properties
The chemical properties of the coal ashes greatly influence the environmental impacts
that may arise out of their use/disposal as well as their engineering properties and also the
chemical composition of fly ash is important indicators of suitability of a material for
geotechnical applications. Hence, this calls for a detailed study of their chemical composition.
The major constituents of these samples are silica (SiO2), alumina (Al2O3), and iron oxide
(Fe2O3). Minor quantities of calcium oxide (CaO), magnesium oxide (MgO), sodium oxide
(Na2O), potassium oxide (K2O), titanium oxide (TiO2), and other compounds are also
observed to be present in lesser quantity (Table 4.3).
Sample
ID
Table 4.3.Chemical composition of fly ashes obtained from EDX study
Elements (weight %)
SiO2
Al2O3
Fe2O3
CaO
K2O
TiO2
Na2O
MgO
F1
56.77
31.83
1.82
0.98
1.96
2.77
0.68
2.39
F2
59.15
34.80
3.52
0.76
2.62
1.14
0.05
0.05
F3
59.64
35.60
2.86
0.85
1.86
0.91
0.06
0.67
F4
68.48
22.90
3.15
0.36
0.91
1.46
0.03
0.06
F5
62.41
31.65
3.17
0.89
2.63
0.00
3.42
0.08
F6
62.25
30.47
2.48
0.92
1.39
0.58
0.02
1.90
F7
61.46
36.95
2.59
0.82
2.01
0.31
0.07
0.26
117
Chapter 4: Results and discussion
The abundance of SiO2 (≈ 62% of the total composition) in all the fly ash samples
would help in increasing the strength of the filling material and offer better load-bearing
capacity in taking the load of the overlying strata after filling the mine voids. Because of a
small amount of free lime (CaO) content (< 1%), the fly ash samples possess negligible
pozzolanic or cementing properties. Because the sum total of SiO2, Al2O3, and Fe2O3 is >
70% and CaO content is < 6% in all the fly ash samples tested, they are classified as class F
fly ash (ASTM C 618-94, 1995). F1 fly ash sample contains little higher calcium oxide
content compared to other fly ash samples which would help in strength gain.
The elemental composition of fly ash samples is shown in Table 4.4, as obtained from
XRF, a bulk technique that can determine average chemical composition of bulk fly ash and
identify differences in matrix composition between individual particles (Hansen and Fisher,
1980). The results show that all the fly ash samples are abundant in Si and Al, and possess
minor concentrations of Fe, Ca, Mg, K, Ti, and P. In the ash samples, the elements present in
decreasing order of abundance are O, Si, Al, Fe, Ti, K, Ca, P, and Mg.
Table 4.4.Elemental composition of fly ashes obtained from XRF study
Elements (weight %)
Elements/
F1
F2
F3
F4
F5
F6
F7
F8
ETPS
NALCO
OPGC
PTPS
RSPII
STPS
TTPS
ZPS
Ca
0.58
0.479
0.416
0.456
0.476
0.548
0.497
0.263
Fe
3.84
3.73
3.26
4.41
4.84
4.46
3.47
3.15
K
0.76
0.685
0.78
1.07
0.918
1.13
0.62
0.92
Mg
0.314
0.309
0.274
0.228
0.347
0.464
0.203
0.327
Na
0.086
0.070
0.056
0.064
0.075
0.082
0.058
0.067
P
0.157
0.142
0.062
0.116
0.137
0.210
0.123
0.112
S
0.044
0.072
0.025
0.033
0.124
0.040
0.029
0.055
Si
21.56
19.97
20.31
19.98
18.48
20.96
20.73
20.89
Ti
1.145
1.286
1.099
1.087
0.989
1.01
1.195
1.239
Al
16.14
17.70
15.29
13.95
13.418
15.79
15.58
17.516
Sample ID
Low calcium/class F fly ash has a relatively simple mineralogy consisting of
aluminosilicate glass and varying amounts of the crystalline phase assemblage: quartz,
118
Chapter 4: Results and discussion
mullite, hematite, and ferrite spinel (McCarthy et al., 1981). The XRD patterns of the various
fly ash samples are presented in Figures (4.7 - 4.9).
Figure 4.7.XRD Pattern of F1 fly ash sample
The X-ray diffraction profiles of the fly ash samples indicate the presence of
crystalline phases. The major mineral constituents of fly ashes are Quartz (SiO2) and Mullite
(Al6Si2O13).
Figure 4.8.XRD Pattern of F2 & F3 fly ash samples
119
Chapter 4: Results and discussion
The other mineralogical fraction of the fly ash indicated the presence of hematite (Fe2O3),
magnetite (Fe3O4), and rutile (TiO2) (White & Case, 1990, Singh and Kolay, 2002). The
diffractograms show that they have similar diffraction patterns. Crystalline phase quartz may
be considered as the primary mineral present in all the fly ash samples, indicated by sharp
peaks in the diffraction patterns (Trivedi and Singh, 2004). The peak near 2θ=25.500 are
identified as mullite. The peaks which occur near 2θ=16.50 are identified as refractory mullite
(Sarkar et al., 2006). Along with the alumino-silicate mineral, the occurrence of strong peaks
close to 2θ=26.490 indicates quartz. The presence of heavy minerals such as magnetite and
hematite are identified by their respective peaks near 2θ=21.40 and 2θ=26.20.
Figure 4.9.XRD Pattern of F4 and F5 fly ash sample
4.2.2. Summary
The primary objective of this study was to select the best mine filling material out of the
seven fly ashes studied. On the basis of the results reported in this study, the following
conclusions are made:
1. F1 fly ash has good particle size distribution (Cu > 6) as compared to that of the other
fly ashes, thereby fulfilling the requirements as a good grading material.
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Chapter 4: Results and discussion
2. It has got greater amount of fine particles which favors for effective cover of
surfactant on the surface of particles in the wet-modification process.
3. F1 fly ash has a higher specific surface area compared with the other F class fly
ashes, facilitating possible surface modification by chemical additives for smooth
flow in the pipelines.
4. F1 fly ash has much superior particle morphology compared with the other F class
fly ashes. Comparatively, F1 has more spherical particles, a feature that would create
a lubricating effect due to the ball-bearing phenomena, resulting in a frictionless
flow in stowing pipelines.
5. The F1 sample has relatively high CaO content that would assist in strength
enhancement without sacrificing its flow attributes.
6. The abundance of silica (SiO2) would increase strength and CaO would enhance
cementing properties.
7. F1 fly ash sample has also lower sp. gr. value compared to other samples which
would help in keeping the particles floated in pipelines during its hydraulic
transportation.
Overall results have indicated that the F1 fly ash have several superior desirable
properties that would make it attractive to fill mine voids. Therefore, this fly ash material was
selected for further study with respect to its flow and in-place strength characteristics.
4.3. Section II
The correct determination of the rheological properties of different fluids including
suspensions and slurries is important to many research and industrial applications. To achieve
this, the rheology investigation of the best fly ash material (F1) was carried out at varying
shear rates i.e. from 25 to 1000 1/s at varying temperature environment (200C to 400C). The
study was carried out starting from 20% solid concentration (lean slurry) and went up to 60%
solid concentration (high density slurry) at an incremental value of 10% each. The results of
the study are presented in five different sub-sections i.e. for 20% solid concentration, for 30%
solid concentration, for 40% solid concentration, for 50% solid concentration, and for 60%
solid concentration and suitable conclusions are drawn at the end of each sub-section.
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Chapter 4: Results and discussion
4.3.1. Results of 20% solid concentration (lean slurry concentration)
4.3.1.1. Effect of surfactants on fly ash slurry rheology
The aim of this investigation was to evaluate the rheological properties of fly ash
composite materials after addition of surfactant and the counter-ion to reduce drag friction.
The results are discussed with respect to varying temperature environment and additive
concentration. It is observed that the variation of the shear stresses with shear rates at all
slurry combinations for fly ash samples at varying temperature environment almost follows
straight line behaviour with a zero yield stress (τy) (Figures 4.12 to 4.15). The slurry depicted
shear thickening behaviour without any additive (Figure 4.10) that confirms to the observation
made elsewhere (Whittingstall, 2001). The shear stress exhibited increasing trend as the shear
rate increased from 100s-1 to 500s-1. The behavior did not change with higher temperature
(Figure 4.10). This trend confirms to that of mineral suspended slurry (Boger, 2002). The
governing relation for that slurry is given by Ostwald- De Waele model as below:
τ = K γn
(4.1)
Figure 4.10.Rheogram of fly ash slurry without any additive
This shear thickening or dilatant behavior is an undesirable feature for any pipeline
transportation system. Hence fly ash slurry flow behaviour was evaluated with additives. The
additive was added at a concentration varying from 0.1%, 0.2%, 0.3%, 0.4%, and 0.5%. At
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Chapter 4: Results and discussion
0.2% additive concentration, the shear stress value was minimum at 300 C at each shear rate.
The trend was almost linear implying Newtonian flow behavior (Figure 4.12). Similar pattern
were also observed for other additive concentration up to 0.5% with the shear stress values
varied between 5 Pa to 12 Pa. The minimum shear stress observed was at 0.2% additive
concentration at a temperature of 300 C at a shear rate value of 500s-1 reflecting the near
Newtonian flow behaviour. However at a concentration of 0.4% at 310 C the slurry exhibited
linear trend i.e. Newtonian behaviour. The slurry behaviour changed to non-Newtonian at
0.5% additive concentration. It reflects that addition of additive has positive impacts on slurry
transportation system. The observation that the viscosity and shear stress decreased for all the
cases with increase in temperature confirms that the slurry followed the fundamental
properties of viscous materials. At 0.1% additive concentration the flow behaviour was erratic
and uneven which is attributed to insufficient availability of additive concentration to modify
the flow properties (Figure 4.11).
Orange 350C, Purple 290C, Blue 320C
Figure 4.11.Rheogram of fly ash slurry with additive concentration 0.1%
The shear stress of the slurries decreased with increasing temperature (Figures 4.12 to 4.15).
The slurry exhibited almost Newtonian flow pattern with a zero yield stress (Figures 4.12 to
4.15) when the concentration of the additive solution increased gradually with an incremental
value of 0.1% (by weight).
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Chapter 4: Results and discussion
Figure 4.12.Rheogram of fly ash slurry with additive concentration 0.2%
Figure 4.13.Rheogram of fly ash slurry with additive concentration 0.3%
Figure 4.14.Rheogram of fly ash slurry with additive concentration 0.4%
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Chapter 4: Results and discussion
Figure 4.15.Rheogram of fly ash slurry with additive concentration 0.5%
4.3.1.2. Rheological behavior of fly ash slurry
4.3.1.2.1 Shear viscosity
Shear viscosity of fly ash slurries with and without an additive at varying temperature
environment were also studied. The shear viscosity increased sharply from 1mPas to 3mPas
with the shear rates varying from 100 to 500 per second for all the temperature ranges tested
without any additive (Figure 4.16). This phenomenon confirms to that reported by Barnes et
al., (1989). At additive concentration 0.1% the flow pattern was erratic and uneven depicting
insufficient particle modification (Figure 4.17). When the temperature was maintained at 350C
the flow behavior was shear thickening, but at 320C the viscosity increased linearly with shear
rate. At additive concentration 0.2% and 0.3% (by weight) the slurry exhibited near
Newtonian flow behaviour (Figure 4.18- 4.19). At 200C and 230C the slurry depicted shear
thinning behavior. The shear thinning nature of the slurry is due to the alignment of particles
in the flow field. The increasing rate of stress results in instantaneous alignment of particles in
the direction of shear which in turn provides lower resistance to flow. This confirms to
observations elsewhere (Boger, 2002).
Shear thinning behaviour was distinctly observed at 200 C at 0.3% additive
concentration also (Figure 4.19). It is a desirable feature for any hydraulic pipeline transport
system. Shear thinning pattern was observed from 290 C to 310 C though at a reduced rate at
additive concentration of 0.4% (Figure 4.20). At concentration of 0.5% of the additive near
Newtonian behaviour was observed except at 200 C (Figure 4.21). Addition of 0.5% (by
weight) of additive concentration to the slurry has produced some undesirable results
125
Chapter 4: Results and discussion
compared to other additive concentrations, because of the high concentration of the additive
which was added to the slurry. However at 0.2% and 0.3% (by weight) of additive
concentration the slurry suspension showed good rheological behaviour at around 200 C. The
effective additive concentration range was found to be from 0.2% to 0.3% (by weight).
Light blue 320C, Purple 290C, and Blue 200C
Figure 4.16.Flow curve of fly ash slurry without any additive
Figure 4.17.Flow curve of fly ash slurry with additive concentration 0.1%
Figure 4.18.Flow curve of fly ash slurry with additive concentration 0.2%
126
Chapter 4: Results and discussion
Figure 4.19.Flow curve of fly ash slurry with additive concentration 0.3%
Figure 4.20.Flow curve of fly ash slurry with additive concentration 0.4%
Figure 4.21.Flow curve of fly ash slurry with additive concentration 0.5%
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Chapter 4: Results and discussion
4.3.1.2.2. Effect of temperature on fly ash slurry rheology
Temperature affects the modification of the fly ash particles by decreasing the
viscosities as the temperature rises. This is due to the enhanced dissolving activity of the
surfactant at higher temperatures. However, an elevated temperature would weaken the
surface grafting modification. The viscosity of untreated fly ash slurry did not show any
variation with higher temperatures as well as shear rates. The viscosity values varied from 1.2
- 3 mPa.s at shear rates 100s-1 to 500s-1 respectively (Figure 4.22).
Figure 4.22.Viscosity vs. temperature plot of fly ash slurry without any additive
It shows the higher the shear rate the more is the viscosity. When surfactant additive at
0.1% was added, changes in viscosity values were observed without any established trend
(Figure 4.23). This phenomenon is due to insufficient interaction between fly ash and
surfactant at 0.1% additive concentration. At 0.2% additive concentration high slurry
viscosity values were obtained at shear rate value of 100s-1. Minimum values between 6 to 9
mPa.s were obtained at 300C (Figure 4.24). When the surfactant concentration increased from
0.3 to 0.5% the slurry viscosity exhibited higher values i.e more than 15 mPa.s (Figures 4.25
to 4.27). The optimum modification temperatures for treated fly ash slurries were found to be
300C-350C.
The values of both shear stress and shear viscosity decreased with increase in
temperature which confirms to the fundamental properties of any viscous material (Shenoy,
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Chapter 4: Results and discussion
1976). It is attributed to the increase in the consistency of the slurries, which decreased the
resistance to shear. A comparatively larger value of initial stress is required to start the
process of shearing when relatively larger numbers of solid particles are present. The yield
stress was almost zero as fly ash used in this investigation was very fine in nature. This
decrease is due to decrease in the number of particles and the surface area of the solids per
unit volume of the slurry with reduction in solid concentration. The viscosity of the fly ash
slurry showed a decreasing trend with increase in temperature at 0.3%, 0.4% and 0.5%
additive concentration (Figures 4.25 to 4.27). It confirms to the conclusion elsewhere
(Shenoy, 1976).
Figure 4.23.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.1%
Figure 4.24.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.2%
129
Chapter 4: Results and discussion
Figure 4.25.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.3%
Figure 4.26.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.4%
Figure 4.27.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.5%
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Chapter 4: Results and discussion
4.3.1.3. Surface Tension
Surfactants are also known as tensides, which are wetting agents and can lower the
surface tension of a liquid, allowing easier spreading leading to lower the interfacial tension
between solid particles and the liquid. Surfactants reduced the surface tension of water by
adsorbing at the solid-liquid interface. The addition of surfactant resulted in reduced surface
tension by 53 to 56% as compared to that without any additive (Figure 4.28).
Figure 4.28.Plot of surface tension vs. additive concentration
4.3.1.4. Zeta Potential (ζ)
The ζ of fine powder fly ash particles and the amount adsorption of the slurry were
investigated as well. The viscosity of the fly ash slurry without any additive was found to be
varied from 1mPas to 3mPas during test measurements. This low value was because of the
rapid settling tendencies of the fly ash particles at the bottom of the measuring cup during the
test due to flocculation activity of the colloidal fly ash particles in the suspension. The ζ value
of the fly ash slurry was negative (-27mV) without any additive, but changed to positive value
(> +30mV) when surfactant was added to the slurry (Figure 4.29). This is due to electrostatic
bonding between the negative sites of the fly ash particles and the cationic head groups of the
surfactants. This mechanism is expected to result in higher positive ζ values. As a result,
negatively charged fly ash particles would repel each other, and therefore, flocculation was
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Chapter 4: Results and discussion
prevented and dispersion achieved. Addition of the surfactant modified the surface properties
of the fly ash particles keeping the suspension in the stable condition. This observation is in
agreement with the desirable features of any electrically stabilized colloids described
elsewhere (Greenwood & Kendall. 1999).
Figure 4.29.Plot of zeta potential vs. surfactant concentration
4.3.1.5. Summary of observations at 20% solid concentration
Rheological behaviour improved significantly when surfactant at 0.2% and 0.3%
concentration were added to the fly ash slurry. It was also observed that the addition of the
surfactant to the slurry suspension reduced the surface tension of the liquid considerably
which would aid for better wetting of the fly ash particles and reduce the drag friction. The
surfactant reduced the surface tension value of the liquid significantly from a value of 71
mNm-1 to 31 mNm-1 confirming better wetting properties. It would facilitate reduced
resistance to flow. The zeta potential value for the fly ash slurry with addition of surfactant
exceeded +30 mV. It confirms that the suspension was stable during the test measurements. It
was also observed that the slurry suspension settled down leaving the water medium at the top
after about three to four hours of the measurement (Figure 4.30). It would help in draining out
excess water which is a desirable feature of the pipeline transport in any fly ash disposal
system.
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Chapter 4: Results and discussion
Figure 4.30: Settling results of fly ash slurry
4.3.2. Results of 30% solid concentration (low slurry concentration)
4.3.2.1. Rheology
Rheological parameters as viscosity, shear stress, surface tension, and zeta potential
were studied for 30% concentration of fly ash with different percentage of surfactant and
counter-ions. The results such as the rheograms and flow curves of fly ash slurries are
presented in graphical form. The untreated suspensions of fly ash slurries exhibited
heterogeneous flow behaviour (Seshadri and Singh, 2000) which is evident from Figures
(4.31, 4.37, and 4.43) compared to the treated fly ash slurries. Addition of the surfactant to the
fly ash slurries produced almost Newtonian behaviour and shear thinning effects. The
majority of non-Newtonian fluids are infact shear-thinning, in that their viscosities decrease
with increasing shear rate. As depicted by Whittingstall (2001), the structure of most fluids
lends itself to this behavior because their components do one of the following: (1) Anisotropic
particles align with the flow streamlines to reduce their hydrodynamic cross-section. (2)
Aggregates of particles tend to break apart under shear forces, again minimizing
hydrodynamic disturbance. (3) Surfactant molecules existing as random coils elongate in the
streamlines. (4) Particles arrange themselves in formations to reduce energy, much like racing
133
Chapter 4: Results and discussion
cars line up behind each other to take advantage of the leading car. The effect of the additive
is thus to reduce or eliminate the yield stress of the slurries rather than the viscosity which
compares favourably well with the results obtained by Jones and Chandler (1989).
4.3.2.1.1. Effect of surfactants on fly ash slurry rheology
Figures (4.31 - 4.36) shows the rheograms of the fly ash slurries at different
temperatures and effect of surfactant additive (0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight)
on the flow behaviour at varying shear rates. It is observed from the results that the untreated
fly ash slurry showed turbulent flow behaviour (Figure 4.31) compared to treated fly ash
slurries (Figures 4.32- 4.36). In the case of treated fly ash slurries shear stress decreased with
increasing temperature at a fixed shear rate for all the surfactant dosages tested. The fly ash
slurries showed shear thinning behaviour at 200C and 250C which is a desirable feature for
any hydraulic transport system (Wei et al., 2009; Roh et al., 1995). At 300C, 350C, and 400C
the slurries almost showed straight line (Newtonian) behaviour with a zero yield stress. At
0.1% additive concentration (Figure 4.32) the slurry followed Newtonian behaviour at 200 C,
but changed to shear thickening behavior as temperature increased which is an undesirable
property for pipeline transport system. Many of these rheograms exhibit a turbulent vortice
artifact, where the measured shear stress was seen to climb dramatically from a certain shear
rate value, in an apparent display of shear thickening. The rheogram presented at 300C, 350C
and 400C (Figure 4.32) provides a good example of this artifact, where the shear stress data
suddenly climbed away from the fitted curve at a shear rate of about 200s-1.
Figure 4.31.Rheogram of untreated fly ash slurry
134
Chapter 4: Results and discussion
Figure 4.32.Rheogram of fly ash slurry at additive concentration 0.1%
Figure 4.33.Rheogram of fly ash slurry with additive concentration 0.2%
Figure 4.34.Rheogram of fly ash slurry with additive concentration 0.3%
135
Chapter 4: Results and discussion
Figure 4.35.Rheogram of fly ash slurry with additive concentration 0.4%
Figure 4.36.Rheogram of fly ash slurry at additive concentration 0.5%
4.3.2.1.2. Shear viscosity
Figures (4.37 - 4.42) shows the shear viscosity of fly ash slurries with additive
concentration of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% (by weight) at varying temperatures. It is
observed that the shear viscosity decreased sharply from 200C to 400C reaching a minimum
value (4.8mPa.s) at 400C with the shear rates varying from 25s-1 to 500 s-1 for all the additive
ranges tested (Figures 4.38 - 4.42). Shear thinning behaviour was also observed at 200C and
250C for all the slurries tested. At 300C, 350C, and 400C the viscosities of the slurries almost
remained unchanged for the shear rates varying from 25s-1 to 500s-1 confirming that the slurry
showed Newtonian flow behaviour. Best results are obtained at 350C and 400C for an additive
concentration varying from 0.2% to 0.4%. In this case also the untreated fly ash slurry showed
136
Chapter 4: Results and discussion
turbulent flow behaviour without depicting any definite trend (Figure 4.37) as compared to
treated fly ash slurries.
Figure 4.37. Flow curve of untreated fly ash slurry
Figure 4.38. Flow curve of fly ash slurry with additive concentration 0.1%
Figure 4.39. Flow curve of fly ash slurry with additive concentration 0.2%
137
Chapter 4: Results and discussion
Figure 4.40. Flow curve of fly ash slurry with additive concentration 0.3%
Figure 4.41. Flow curve of fly ash slurry with additive concentration 0.4%
Figure 4.42. Flow curve of fly ash slurry with additive concentration 0.5%
138
Chapter 4: Results and discussion
4.3.2.1.3. Effect of temperature on fly ash slurry rheology
In this sub-section the results are analyzed with respect to viscosity variation with
varying temperatures. It is observed that the values of both shear stress and viscosity
decreased with increase in temperature (Figures 4.44 - 4.48) which confirms to fundamental
properties of any viscous material as for all normal liquids (Topallar and Bayrak, 1998). This
is due to the enhanced dissolving activity of the surfactant at higher temperatures. This result
also compares favourably with the observations made by Shenoy (1976). This is due to
decrease in number of particles and the surface area of the solids per unit volume of the slurry
with reduction in solid concentration.
Figure 4.43. Viscosity vs. temperature plot of untreated fly ash slurry without additive
Figure 4.44. Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.1%
139
Chapter 4: Results and discussion
Figure 4.45. Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.2%
Figure 4.46. Viscosity vs. temperature plot of fly ash slurry additive concentration 0.3%
Figure 4.47. Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.4%
140
Chapter 4: Results and discussion
Figure 4.48. Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.5%
Addition of surfactant caused a considerable decrease in viscosity. The decrease in
viscosity with increasing temperature was steep from 200C to 300C and after that the viscosity
decrease was marginal till 400C for all the shear rates studied. This is due to the formation of
spherical micelles which grow continually in size with the increase of temperature until at the
cloud point when they can no longer grow and phase separation occurs and it exists only in
relatively dilute surfactant solutions (Shenoy, 1976). However, from Figure 4.43 (untreated
fly ash slurry) it is observed that the flow behaviour did not show any definite trend compared
to the treated fly ash slurries. In this case the flow behaviour is erratic and irregular compared
to chemically treated fly ash slurries. At 0.1% additive concentration (Figure 4.44) the slurry
behaviour was better at low shear rates i.e., 25s-1, 50s-1, and 100s-1 compared to higher shear
rates.
4.3.2.2. Surface Tension (ST)
Surface tensions of the six fly ash slurries with and without an additive are presented
in Table 3.8. Because of the addition of surfactant to the slurries, ST reduced by 43% to 46%
compared to that of untreated slurries, and reduced by 51% to 54% as compared to ST of tap
water (68.9mN/m). The surfactants facilitated easier spreading leading to lower the interfacial
tension between solid particles and the liquid. This phenomenon is due to the hydrophobic
group which is a long chain hydrocarbon with 12 carbons in the structure of surfactant, is
141
Chapter 4: Results and discussion
attached to the fly ash particle, converting it from hydrophilic to hydrophobic property (Xiao
and Zho, 2002).
4.3.2.3. Zeta potential (ζ)
The zeta potential values of all the slurries are reported in Table 3.8. It was observed
that the ζ value of the untreated fly ash slurry was -25mV at pH 7.30. However, in the
presence of surfactants, the zeta potentials are dramatically shifted towards more positive
values (>+31mV). This is an important observation since at ζ values exceeding +30 mV
adequate dispersion of the fly ash particles seems to be sustained (He et al., 2004). This is due
to electrostatic bonding between the negative sites of fly ash particles and the cationic head
groups of the surfactants. This mechanism was expected to result in higher positive zeta
potentials. As a result, negatively charged fly ash particles would repel each other and,
therefore flocculation was prevented and dispersion achieved.
4.3.2.4. Summary of observations at 30% solid concentration
The following conclusions are made with respect to 30% solid concentration:
 All the treated fly ash slurries exhibited shear-thinning and/ or Newtonian flow
properties with zero yield stress.
 Minimum viscosity and shear stress at 4.8mPa.s and 2Pa respectively were obtained
with 0.2% additive concentration at 400 C.
 The surfactant additive has also modified the surface properties of the fly ash particles
from negative ζ values to positive values and suspension stability of the slurry was
improved.
 Surface tension of the fly ash slurries is reduced by 43% to 46% compared to that of
untreated slurries, and it is reduced by 51% to 54% as compared to ST of tap water
(68.9mN/m). It exhibits the positive characteristics of fly ash slurry for pipeline
transportation with the addition of a cationic surfactant (CTAB) and a counter-ion
(NaSal) which would reduce specific energy consumption and water requirements.
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Chapter 4: Results and discussion
4.3.3. Results of 40% solid concentration (medium slurry concentration)
4.3.3.1. Influence of surfactant on slurry rheology
Data from rheometer are presented as a linear plot of shear stress versus shear rate
(Rheograms). This type of plot allows the viewer to see directly if there is Newtonian
behavior because the plot will take the form of a straight line through the origin. A nonNewtonian response is non-linear and may or may not pass through the origin. If the sample
has an apparent yield stress, then the line or curve will have some positive y-axis intercept.
Fly ash slurries exhibited strong flocculation behaviour in absence of chemical additives
(Struble and Sun, 1995; Bentz, 2007). A yield stress is needed to break down this flocculated
structure into smaller flocs or individual particles to induce flow. The yield stress value of 0.3
Pa to 4 Pa was obtained for 40% solid concentration without any additive (Figure 4.49.b).
This Figure clearly depicted Bingham plastic model as given below:
τ = τy + η
(4.2)
This is a straight-line fit shifted up the y-axis to accommodate a yield stress (τy).
Bingham plastic materials do not flow until a critical yield stress is exceeded; thereafter a
linear relationship is shown between the shear stress and shear rate. Thus, Bingham plastic
materials behave as solids below the yield stress and flow like a viscous liquid when the yield
stress is exceeded. The rheological parameters, namely yield stress and plastic viscosity, were
calculated from the measured shear stress- shear rate curves for each of the mixtures from the
above model. To know the flow behaviour of the untreated fly ash slurry, experiments were
carried out for a wide range of shear rates varying from as low as 25s -1to as high as 1000s-1 at
400C for fly ash slurry at 40% solid concentration to draw a complete rheogram. The result of
the study is presented in Figure 4.49(a) which shows the relationship between shear stress and
shear rate rheogram. Maximum shear rate observed was 611 s-1, confirming observations
reported by Shah and Jeong (2003). Beyond the shear rate value of 600 s-1 shear stress
decreased almost linearly reaching to a minimum value of about 10 Pa. Figure 4.49(b) shows
the shear stress-shear rate relationship without any additive at varying temperature
environment (200C to 400C).
143
Chapter 4: Results and discussion
40
35
Temperature-40 degree centigrade
(a)
Shear Stress, Pa
30
Without additive
25
20
15
10
5
0
0
100
200
300
400
500
600
700
800
900
1000
Shear Rate, 1/s
30
T-20
T-25
T-30
T-35
T-40
Shear Stress, Pa
25
20
(b)
Without additive
15
10
5
0
0
50
100
150
200
250
300
350
400
450
500
Shear Rate, 1/s
Figure 4.49. Rheogram of fly ash slurry without additive
(Note: T-Temperature in degree centigrade)
Slurry rheological parameters fitted well to Bingham plastic model with positive
values of yield stress (0.3 Pa to 4 Pa). At 400C the yield stress value was maximum (4 Pa) and
at 200C the yield stress value was minimum (0.3 Pa). However, addition of the surfactant to
fly ash slurry completely eliminated the yield stress (Figures 4.50- 4.51 a, b, c, d). Therefore,
the influence of the surfactant eliminated the yield stress of the slurries rather than the
viscosity which compares favourably well with the results obtained by Jones & Chandler
(1989). The yield stress increased almost exponentially as the temperature increased from
200C to 400C for the fly ash slurry without any additive (Figure 4.52). At 0.1% additive
concentartion the slurry behaviour was shear thickening at 400C which is not a desirable
property for pipeline transport systems (Figure 4.50). But the slurry behavour was shear
thinning between 200 C and 350 C temperature range. Here again it is seen that the flow curves
cross each other when the shear rate increased beyond 611 s-1 confirming to the results of
Shah and Jeong (2003). It is established that shear rate beyond 600 s-1 would not facilitate
reduced energy consumption.
144
Chapter 4: Results and discussion
Figure 4.50. Rheogram of fly ash slurry with 0.1% additive
(Note: T-Temperature in degree centigrade)
(a)
160
Additive concentration 0.2%
T-20
T-25
T-30
T-35
(b)
200
T-40
T-20
180
140
T-25
Additive concentration 0.3%
T-30
T-35
T-40
160
140
Shear Stress, Pa
Shear Stress, Pa
120
100
80
60
120
100
80
60
40
40
20
20
0
0
0
200
400
600
800
0
1000
200
400
Shear Rate, 1/s
180
(c)
160
T-20
Additive concentration 0.4%
T-25
T-30
600
800
1000
Shear Rate, 1/s
T-35
(d)
160
T-40
Additive concentration 0.5%
T-20
140
T-25
T-30
T-35
T-40
140
Shear Stress, Pa
Shear Stress, Pa
120
120
100
80
60
100
80
60
40
40
20
20
0
0
0
100
200
300
400
500
0
100
Shear Rate, 1/s
200
300
400
500
Shear Rate, 1/s
Figure 4.51. Rheogram of fly ash slurry with (a) 0.2%, (b) 0.3%, (c) 0.4%, and (d) 0.5% additive
(Note: T-Temperature in degree centigrade)
145
Chapter 4: Results and discussion
Figure 4.52. Yield stress vs. Temperature plot of fly ash slurry without additive
Figure 4.53(a) presents a complete flow curve for a time-independent non-Newtonian
fluid. Region (1) corresponds to viscosities relative to low shear rates, region (2) corresponds
to viscosities relative to the medium shear rates and region (3) corresponds to viscosities
relative to high shear rates. Viscosity decreased as the shear rate increased for slurry without
any additive as the shear rate is increased from 25 s-1 to 1000 s-1 (Figure 4.53.a). Lower
temperature ranges (200C, 250C, and 300C) depicted good results (Figure 4.53.b) compared to
higher temperature ranges (350C and 400).
180
Without additive
160
a
Temperature-40 degree centigrade
Viscosity, mPa.s
140
1
120
100
2
80
60
3
40
20
0
25
125
225
325
425
525
625
725
825
925
1025
Shear Rate, 1/s
180
Without additive
T-20
160
T-25
T-30
T-35
T-40
b
Viscosity, mPa.s
140
120
100
80
60
40
20
0
25
75
125
175
225
275
325
375
425
Shear Rate, 1/s
Figure 4.53. Flow curve of fly ash slurry without additive
(Note: T-Temperature in degree centigrade)
146
475
525
Chapter 4: Results and discussion
The viscosity increased as the temperature was increased from 200C to 400C for slurry without any
additive (Figure 4.54). It showed shear thickening behavior.
Figure 4.54. Viscosity vs. Temperature plot of fly ash slurry without additive
(Note: SR-Shear Rate)
Figure 4.55. Viscosity vs. Temperature plot of fly ash slurry with 0.1% additive
(Note: SR-Shear Rate)
When surfactant was added to the slurry the rheological properties changed drastically
(Figure 4.55). The viscosity decreasing substantially as the temperature was increased from
200C to 400C. These results compare favourably well as with the observations made by
Shenoy (1976). This phenomenon is due to the formation of spherical micelles which grow
continually in size with the increase of temperature until at the cloud point when they can no
longer grow and phase separation occurs; which occurs only in relatively dilute surfactant
solutions (Shenoy, 1976). At 0.1% additive concentration the slurry behaviour depicted erratic
147
Chapter 4: Results and discussion
results at lower temperature ranges and behaved reasonably well beyond 300C range (Figure
4.55).
600
Additive concentration 0.2%
450
SR-25
SR-50
SR-100
400
SR-200
SR-300
SR-400
350
SR-500
SR-600
SR-700
300
SR-800
SR-900
SR-1000
Additive concentration 0.3%
500
Viscosity, mPa.s
Viscosity, mPa.s
500
250
200
150
100
400
SR-25
SR-50
SR-100
SR-200
SR-300
SR-400
SR-500
SR-600
SR-700
SR-800
SR-900
SR-1000
300
200
100
50
0
0
20
25
30
35
40
20
25
Temperature, 0C
600
Additive concentration 0.4%
35
40
Additive concentration 0.5%
400
SR-25
SR-50
SR-100
SR-300
SR-400
SR-500
SR-200
500
350
300
Viscosity, mPa.s
400
Viscosit, mPa.s
30
Temperature, 0C
300
200
SR-25
SR-50
SR-100
SR-200
SR-300
SR-400
SR-500
250
200
150
100
100
50
0
0
20
25
30
35
40
20
25
Temperature, 0C
30
Temperature,0C
35
40
Figure 4.56. Viscosity vs. Temperature plot of fly ash slurry with additive
(Note: SR-Shear Rate)
4.3.3.2. Influence of surfactant on shear viscosity
At very low shear rates, from 25 - 50 s-1, the slurry exhibited inconsistent results,
because a minimum value of shear rate is required to start the flow to take place (Figure 4.57).
Figure 4.58 shows the shear viscosity of fly ash slurries with additive concentration ranging
from 0.2% to 0.5% (by weight) at varying temperatures. Shear viscosity decreased sharply
from 200C to 400C, with the shear rates varying from 25 to 1000 s-1 for the entire additive
ranges tested. Shear thinning behaviour, a favourable property for pipeline transport, was
observed at 200C and 250C for all the slurries tested (Senapati and Mishra, 2012). The
viscosity values of the slurries were nearly constant for the shear rates varying from 50 - 500
s-1 at 400C, confirming that the slurry showed Newtonian flow behavior i.e. the material
would flow smoothly in pipelines. The results obtained at 350C and 400C with additive
concentration of 0.4% and 0.5% (Figure 4.58) were favourable.
148
Chapter 4: Results and discussion
Figure 4.57. Flow curve of fly ash slurry with additive concentration 0.1%
(Note: T-Temperature in degree centigrade)
500
600
Additive concentration 0.2%
Additive concentration 0.3%
450
Viscosity, mPa.s
350
T-20
T-25
T-35
T-40
T-30
Viscosity, mPa.s
400
300
250
200
T-20
500
150
100
T-25
T-30
T-35
T-40
400
300
200
100
50
0
0
25
225
425
625
825
1025
25
225
425
Shear Rate, 1/s
500
450
Additive concentration 0.4%
T0-20
T-30
T-40
450
400
T-25
T-35
825
1025
Additive concentration 0.5%
400
T-20
T-25
T-30
T-35
T-40
350
Viscosity, mP.s
350
Viscosity, mPa.s
625
Shear Rate, 1/s
300
250
200
150
300
250
200
150
100
100
50
50
0
0
25
125
225
325
425
525
25
125
Shear Rate, 1/s
225
325
425
525
Shear Rate, 1/s
Figure 4.58. Flow curve of fly ash slurry with additive
(Note: T-Temperature in degree centigrade)
4.3.3.3. Surface Tension
The addition of surfactant reduced surface tension of fly ash slurries by 43% to 47%
compared to untreated slurry and by 52% to 55% compared to plain tap water (Table 3.9).
The surfactants facilitated easier spreading, leading to lower the interfacial tension between
solid particles and the liquid.
4.3.3.4. Zeta potential (ζ)
Surfactants comprised of hydrophilic and hydrophobic groups, by which they act as a
bond combining mineral particles and host polymers (Zana, 2002). It is advantageous to have
a single chemical agent such as a surfactant that can accomplish both surface modification
and stabilization of heavy metals. The ζ of the untreated fly ash slurry was -25 mV at pH 7.4,
149
Chapter 4: Results and discussion
increasing (> +31 mV) when the surfactant was added to the slurry (Table 3.9). From these
results, it is confirmed that the fly ash slurry suspension is stable and the fly ash particles
would repel each other and, therefore, flocculation would be prevented and dispersion
achieved, facilitating smooth flow and reduced clogging of pipelines. Both yield stress and
viscosity (apparent or plastic) strongly depends on the particle characteristics of the powders
employed in preparing fly ash slurry with a constant volume fraction of water. As the yield
stress is dominated by the characteristics of the fly ash particles, the additive acted as diluents,
effectively decreasing the fly ash particle number density.
4.3.3.5. Summary of observations at 40% solid concentration
 The test results clearly indicated that the fly ash-water slurry rheology is strongly
influenced by the chemical additives. The presence of elements such as iron oxide,
aluminium oxide, and other alkaline earth materials in the fly ash slurry gave rise to
adverse rheological properties, and these effects were negated by the addition of a
surfactant (CTAB) that formed charged complexes with the fly ash particles.
 All the treated slurries exhibited shear-thinning and Newtonian properties. The
surfactant modified the surface properties of the fly ash particles and improved its
suspension stability.
 The surface tension of the treated fly ash slurry is reduced compared to untreated fly
ash slurry and that of the suspending medium (water). This implies that this fly ash has
greater potential to be transported in pipelines with the addition of a cationic surfactant
and a counter-ion which will reduce specific energy consumption and water
requirements.
 The flow properties and viscosity of the fly ash water suspensions were sensitive to
the use of chemical additives.
4.3.4. Results of 50% solid concentration (medium slurry concentration)
4.3.4.1. Effect of surfactants on fly ash slurry rheology
Figure 4.59 shows the rheogram of fly ash-water slurries (at 200C to 400C) without
any additive. The slurry without any additive exhibited shear thickening behavior with yield
stress values of varying magnitude which is not a desirable feature for any slurry pipeline
150
Chapter 4: Results and discussion
transportation system. At 250C the behavior is closer to Bingham (yield-constant viscosity)
non-Newtonian fluid. The value of the yield stress was found to be 2 Pa. At 350C and 400C
also the slurry behaviour was same but the yield stress was reduced to 1.5 Pa. At 200C the
flow behavior is shear thickening (i.e. dilatants). The rheological data suggests that shear
thickening is occurring in the slurry at a shear rate of 300s-1 because of the increase in slope
of the rheometric data beyond these shear rates. This is not the case however, as this increase
in slope is actually an artifact that is caused by turbulent vortices forming at the bob surface,
which occurs with low viscosity fluids being sheared at high shear rates (Chryss and Pullum,
2007). The governing relation for this behavior is given by Herschel-Bulkley model:
τ = τy
n
(4.3)
Figure 4.59.Rheogram of fly ash slurry without additive
At 50% solid concentration yield stress is completely or nearly eliminated in case of
all surfactant treated slurries. Overall at 0.1% additive concentration the slurry depicted shear
thinning behavior; this is a desirable feature for any hydraulic slurry pipeline transport system
(Figure 4.60). Because, shear thinning materials display a decrease in viscosity with
increasing shear rate, i.e. the material appears to flow more easily with increasing shear rate
(Senapati and Mishra, 2012). Shear thickening materials, on the otherhand display an opposite
behavior, i.e. the viscosity increases with increased shear rate. This behavior is seen in highly
concentrated suspensions (Seshadri et al., 2005).
151
Chapter 4: Results and discussion
Figure 4.60.Rheogram of fly ash slurry with additive concentration 0.1%
When the additive concentration was 0.1% at the slurry temperature of 350C,
Newtonian fluid behaviour without any yield stress was observed. When the additive
concentration was increased to 0.2%, the slurry depicted shear thinning behaviour except at
400C which depicted shear thickening behaviour (Figure 4.61). Similar behaviour of coal
water slurry was also obtained and attributed to the breaking of agglomerates at a higher shear
rates (Swain and Panda, 1996).
Figure 4.61.Rheogram of fly ash slurry with additive concentration 0.2%
At 0.3% additive concentration slurry behaviour was shear thinning except at 400C
(Figure 4.62). Similar trend was observed at 0.4% and 0.5% additive concentration (Figures
152
Chapter 4: Results and discussion
4.63 and 4.64). However here also the slurry behaviour was shear thickening at 400C and
350C. Results obtained at 0.2% and 0.3% additive concentration between 300 C to 350C
produced the most favourable flow properties. The flow curves of fly ash-water slurry
presented in Figure 4.62 show pseudoplastic flow behaviour. As the shear rate increased the
structure of the fluid became more ordered, which steadily reduced the apparent viscosity.
The power law model also referred to as the Ostwald-de Waale model was used to fit the
rheological data of pseudoplastic fluids.
Figure 4.62.Rheogram of fly ash slurry with additive concentration 0.3%
Figure 4.63.Rheogram of fly ash slurry with additive concentration 0.4%
153
Chapter 4: Results and discussion
The flow properties of fly ash slurry at 50% solid concentration with surfactant exhibit
minimum or near non-exist yield stress which is a favourable attribute for smooth flow. The
primary purpose of adding surfactant to fly ash slurry was to disperse flocculated fly ash
particles. Due to the dispersion effect, the fluidity of the slurry is increased, i.e. the yield
stress and plastic viscosity reduced. The surfactant is believed to adsorb onto the fly ash
particles and altered the degree of flocculation in one of these three ways: (1) Increasing the
zeta potential and, thus, the repulsive forces between the fly ash particles (electrostatic double
layer repulsion), (2) Increasing solid-liquid affinity, (3) Introducing a physical barrier against
flocculation, steric hindrance i.e., the importance of steric forces in dispersing fly ash
suspensions through increasing the electrostatic double layer forces (Yoshioka et al. 1997).
Figure 4.64.Rheogram of fly ash slurry with additive concentration 0.5%
4.3.4.2. Effect of surfactant on shear viscosity
The viscosity of untreated fly ash slurry was more than 60mPa.s at a shear rate value
of 25s
-1
that became asymptotic when shear rates increased to 200s-1 and beyond (Figure
4.65). But when the additive was added, the slurry behaved differently. At 0.1% additive
concentration the slurry behaviour was Newtonian at 300C. At 200C and 250C the slurry
behaviour was shear thinning and at 350C and 400C the behaviour was shear thickening
(4.66). As the additive concentration was increased to 0.2%, 0.3%, 0.4%, and 0.5% (Figures
4.67-4.70) there was some noise in the data at low shear rates (25s-1 to 50s-1). Beyond shear
154
Chapter 4: Results and discussion
rate values of 100s-1 the slurry behaviour was shear thinning except at 350C and 400C. At 50%
fly ash concentration with 0.1% additive at 300 C the slurry exhibited Newtonian flow
behavior even at lower shear rates. The behavior again became Newtonian for all
concentration of surfactant irrespective of temperature ranges when the applied shear rate was
200s-1 or more. It confirms to that observed elsewhere (Seshadri et al., 2006).
Figure 4.65.Flow curve of fly ash slurry without additive
Wide range of shear rate values varying from 25s-1 to 1000s-1 with additive concentration
varying from 0.1% to 0.5% was investigated in order to draw a complete flow curve for this
time-independent non-Newtonian fluid to clearly demarcate three flow regions i.e., region (1)
corresponding to viscosities relative to low shear rates, region (2) corresponding to viscosities
relative to the medium shear rates and region (3) corresponding to viscosities relative to
higher shear rates (Whittingstall, 2001). This wide range of shear rates starting from 25s-1 to
1000s-1 was also investigated because for pumping of slurries common shear rate range varies
from 1-103s-1 (Carrington and Langridge, 2005). With 50% solid concentration and additive
presence from 0.2% to 0.5%, the viscosity values decreased with increasing shear rates upto
1000s-1 (Figures 4.67-4.70). Thus the additive (surfactant) influenced the rheological behavior
of the treated slurries. Because the rheological behavior of a particle suspension is dependent
on the balance between a range of different forces, i.e., van der Waals, electrical double layer
forces, steric forces, acting between colloidal particles. If the summation of these forces
results in an overall attractive inter-particle force, flocculation will be promoted. In
concentrated suspensions these flocs create a continuous three-dimensional inter-particle
155
Chapter 4: Results and discussion
network which can display a considerable resistance to both flow and consolidation. On the
otherhand, if the overall forces are repulsive the particles will be dispersed and suspension
will flow readily (Marmy et al., 2012).
Figure 4.66.Flow curve of fly ash slurry with additive concentration 0.1%
Figure 4.67.Flow curve of fly ash slurry with additive concentration 0.2%
Figure 4.68.Flow curve of fly ash slurry with additive concentration 0.3%
156
Chapter 4: Results and discussion
Figure 4.69.Flow curve of fly ash slurry with additive concentration 0.4%
Figure 4.70.Flow curve of fly ash slurry with additive concentration 0.5%
4.3.4.3. Effect of temperature on fly ash-slurry viscosity
The untreated fly ash slurry depicted erratic and uneven flow behaviour as the
temperature was increased from 200C to 400C and produced minimum visocity values at 300 C
(Figure 4.71). Addition of surfactant changed the behavior of fly ash slurry to smooth pattern
though with varying viscosity values. At 200C the viscosity values were between 60 mPa.s to
1000 mPa.s which reduced to about 2 to 100 mPa.s at 400C at different shear rates though the
rate of decrease beyond 300C is minimum (Figures 4.72 - 4.76). When the additive
concentration was 0.1% at 300C there is culmination of all the curves at varying shear rates
demarketing two viscosity regions (Figure 4.72). When the additive concentration was
157
Chapter 4: Results and discussion
increased to 0.2% best results are obtained at 300C, 350C, and 400C at low shear rate values
i.e., at 25s-1, 50s-1, and 100s-1 (Figure 4.73). Minimum viscosity values obtained at 0.2%
additive concentration at above shear rates at 400C due to the enhanced dissolving activity of
the surfactant at higher temperatures. Similar trend was observed when the additive
concentration was increased to 0.3%, 0.4%, and 0.5% (Figures 4.74 - 4.76).
Figure 4.71.Viscosity vs. temperature plot of fly ash slurry without additive
Figure 4.72.Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.1%
Figure 4.73.Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.2%
158
Chapter 4: Results and discussion
Figure 4.74.Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.3%
Figure 4.75.Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.4%
Figure 4.76.Viscosity vs. temperature plot of fly ash slurry with additive conc. 0.5%
159
Chapter 4: Results and discussion
4.3.4.4. Yield stress
The untreated 50% solid concentration fly ash slurry showed high yield stress values
at varying temperatures. The minimum value obtained was at 300C (Figure 4.77). This
phenomenon is due to the formation of spherical micelles which grow continually in size with
the increase of temperature until at the cloud point when they can no longer grow and phase
separation occurs (Shenoy, 1976). The optimum temperature was found to be 300C when no
additive was added to the slurry. When surfactant of different concentration was added there
was no yield stress value and hence not produced here.
Figure 4.77.Yield stress vs. temperature plot of fly ash slurry without additive
4.3.4.5. Summary of observations at 50% solid concentration
 The test results clearly indicated that the fly ash-water slurry rheology depended on
chemical additives. It was found that the flow properties and the apparent viscosity of
the fly ash-water slurries are very sensitive to these reagents. Yield stress was
completely eliminated in the presence of these reagents.
 The decrease in viscosity with increasing temperature is attributed to the increase of
the kinetic energy of the fly ash particle and rapid movement of the dangled chains of
the surfactant units at the fly ash – water interface.
 It is found that the optimum temperature is 300C and optimum surfactant
concentration is found to be 0.2% taking into all the observations together.
160
Chapter 4: Results and discussion
4.3.5. Results of 60% solid concentration (high concentration slurry)
4.3.5.1. Influence of surfactant on fly ash-slurry rheology
The flow curve for fly ash slurry has been reported to fit several different
mathematical forms (Mishra et al., 2002). The common denominator of all these functions is
that all of them indicate the existence of a yield stress, i.e. flocculated fly ash slurry is a
viscoplastic material. Rheograms were drawn for 60% solid concentration with and without
an additive in the temperature range of 200C-400C. The untreated fly ash slurry (Figure 4.78)
behaviour was Bingham yield plastic. The yield stress observed varied between 0.2 - 0.5 Pa.
But when the slurry was treated with the additive the slurry depicted Newtonian flow
behaviour without yield stress at 0.1% additive concentration except at 250C where shear
thinning behavior was observed (Figure 4.79). Fly ash slurry at 60% solid concentration was
evaluated for shear stress values at higher shear rates i.e. upto 1000s-1. But the shear stress
values obtained were very random for shear rates of more than 200s-1 and hence those data
were not reported here. This observation confirms to that published elsewhere (Seshadri et al.
2006). Since 60% solid concentration is high density slurry, so the shear rates varied from
25s-1 to 200s-1 only.
Figure 4.78.Rheogram of fly ash slurry without additive
161
Chapter 4: Results and discussion
Figure 4.79.Rheogram of fly ash slurry with additive concentration 0.1%
From Figures 4.80 and 4.81 at 0.2% and 0.3% additive concentrations, best results
were observed at 300 C and 400 C clearly depicting Newtonian flow behavior. All the 60% fly
ash slurry types with varying additive concentration produced almost zero yield stress except
at 200C and 250C. For high concentration slurry disposal system, 200 C temperatures with an
additive concentration of 0.2% is found to be ineffective which may be due to the temperature
is too low to start the reactions to take place. Here also, best results were obtained at 300 C
which is the optimum temperature value for complete reaction to take place. No yield stress
values were obtained at 0.1% additive concentration. Best results were again obtained at 0.4%
additive concentration except at 200 C which depicted little amount of higher shear stress
values compared to other temperature ranges investigated. Here the slurry behaved like a
Newtonian fluid without any yield stress. The results were very much encouraging which
confirms to the results obtained by Seshadri and co-workers (2006) where they concluded that
as the solid concentration increases the specific energy consumption decreases which is true
for this set of observations also. Compared to 0.4% additive concentration 0.5% additive
concentration is found to be having some noise in the observational data. This is because of
the high dose of additive concentration which produced some noise in the flow curves and
rheograms. At 0.2% additive concentration and at 400C temperature produced best results.
Again at 0.3% additive concentration best results are obtained at 400C.
162
Chapter 4: Results and discussion
Figure 4.80.Rheogram of fly ash slurry with additive concentration 0.2%
Figure 4.81.Rheogram of fly ash slurry with additive concentration 0.3%
Figure 4.82.Rheogram of fly ash slurry with additive concentration 0.4%
163
Chapter 4: Results and discussion
Figure 4.83.Rheogram of fly ash slurry with additive concentration 0.5%
4.3.5.2. Effect of surfactant on shear viscosity
Viscosity was found to be more in case of fly ash slurry without any additive
(maximum 0.8 Pa.s) at 200 C that reduced to 0.3Pa.s at 200s-1 shear rate (Figure 4.84). When
the additive was added, the viscosity values reduced to as low as 0.04 Pa.s. Reduction in
viscosity was due to reduction in interparticle friction in the turbulent flow regime. In the
laminar flow regime, this effect can be attributed to the reduction of surface tension and zeta
potential of the fine particles due to the presence of additive (Chandel et al., 2009). At 0.1%
additive concentration maximum viscosity observed was 0.25 Pa.s at 400 C (Figure 4.85).
Best results were obtained when additive concentration was increased to 0.2% and 0.3% at
400 C (Figures 4.86 and 4.87).
Figure 4.84.Flow curve of fly ash slurry without additive
164
Chapter 4: Results and discussion
Figure 4.85.Flow curve of fly ash slurry with additive concentration 0.1%
Figure 4.86.Flow curve of fly ash slurry with additive concentration 0.2%
Figure 4.87.Flow curve of fly ash slurry with additive concentration 0.3%
165
Chapter 4: Results and discussion
Figure 4.88.Flow curve of fly ash slurry with additive concentration 0.4%
Figure 4.89.Flow curve of fly ash slurry with additive concentration 0.5%
At 0.2% additive concentration slurry behaved like a Newtonian fluid with viscosity
values as low as 0.05 Pa.s and viscosity values remained constant in the shear rate range of
10s-1 to 200s-1 depicting laminar flow behaviour. Again at 0.3% additive concentration at 400
C temperature viscosity values were as low as 0.1 Pa.s (4.87). At 0.4% additive concentration
at 400 C the viscosity values were more than 0.2 Pa.s (Figure 4.88). At 0.5% additive
concentration at 400 C, viscosity values were more than 0.25 Pa.s (Figure 4.89).The variation
in the rheological behaviour due to the changes in colloid interactions among fly ash particles
is clearly seen in the plots of apparent viscosity against shear rate curves in Figure 4.87.The
optimum condition obtained was at 0.2% additive concentration when the slurry temperature
was maintained at 400C (Figure 4.86). Therefore, this slurry combination was selected for
166
Chapter 4: Results and discussion
studying the strength characteristics of the composite material by adding another reagent
which can impart some strength to sustain the filled mass.
4.3.5.3. Effect of temperature on fly ash-slurry viscosity
An increase in the temperature of the system leads to an increase in the kinetic energy
of the particles, which results in a decrease in the viscosity of the fly ash-water slurry. The
slurry without any additive did not exhibit any established flow pattern and depicted irregular
flow behaviours and shear thickening trends were observed (Figure 4.90). At additive
concentration 0.1% also the slurry behaved erratically which was due to insufficient surfactant
concentration to fully modify the fly ash surface properties (Figure 4.91). But as the surfactant
concentration increased to 0.2% the slurry flow behavior improved (Figure 4.92) and at 0.3%
additive concentration the slurry flow parameters further smoothened (Figure 4.93). The
Slurry viscosities reduced from 1.6 Pa.s to 0.2 Pa.s when the temperature increased from 200C
to 400C.
Figure 4.90.Viscosity vs. temperature plot of fly ash slurry without additive
Figure 4.91.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.1%
167
Chapter 4: Results and discussion
Best results were obtained at 0.2% and 0.3% additive concentration as there was less noise in
the data as depicted in Figure (4.92 and 4.93).
Figure 4.92.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.2%
Figure 4.93.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.3%
Figure 4.94.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.4%
168
Chapter 4: Results and discussion
Figure 4.95.Viscosity vs. temperature plot of fly ash slurry with additive concentration 0.5%
4.3.5.4. Yield stress behavior
Maximum value of yield stress was observed (11 Pa) when the fly ash slurry was not
treated with any additive which reduced to 6Pa at 400 C (Figure 4.96). The yield stress
reduced drastically with addition of additive (Figures 4.97 to 4.101). When the additive
concentration was 0.1% maximum yield stress observed was 1.43 Pa at 200 C and zero at
350C and 400C. Similarly at 0.2% additive concentration maximum yield stress was observed
at 200 C which reduced to zero value at 300 C, 350 C, and 400 C. Similar observations were
also made with 0.3% and 0.4% additive concentration (Figures 4.99 and 4.100). When the
additive concentration was 0.5% maximum value of yield stress observed was 23 Pa which
reduced to zero value at 400 C only (Figure 4.101). Similar observation was made with 0.5%
additive concentrations at 400 C. Surfactant solutions form spherical micelles above a certain
concentration called the critical micelle concentration (CMC). At appropriate conditions such
as by addition of counterions, spherical micelles transform and rod-like micelles or even
threadlike micelles are formed in the surfactant solutions (Qi et al., 2003). These rod-like or
thread-like micelles can align along the flow direction in a pipeline like polymer chains and
are the cause of the drag reduction ability of surfactant solutions.
169
Chapter 4: Results and discussion
Figure 4.96.Yield stress vs. temperature plot of fly ash slurry without additive
Figure 4.97.Yield stress vs. temperature plot of fly ash slurry with additive concentration 0.1%
Figure 4.98.Yield stress vs. temperature plot of fly ash slurry with additive concentration 0.2%
170
Chapter 4: Results and discussion
Figure 4.99.Yield stress vs. temperature plot of fly ash slurry with additive concentration 0.3%
Figure 4.100.Yield stress vs. temperature plot of fly ash slurry with additive concentration 0.4%
Figure 4.101.Yield stress vs. temperature plot of fly ash slurry with additive concentration 0.5%
171
Chapter 4: Results and discussion
4.3.5.5. Summary of observations at 60% solid concentration
The conclusions made here are:
 With 60% fly ash concentration at 400C with 0.2% surfactant the viscosity and
shear stress values were minimum.
 The slurries prepared exhibited pseudoplastic behaviour. The slurry became more
viscous with increases in solid content.
 0.2% additive concentration produced best results. Therefore, 0.2% additive
concentration was chosen for further study with respect to its in-place strength
characteristics.
 The composite followed the Newtonian behavior and the relation obtained is
approximately τ =
. The corresponding value of viscosity is found to be
0.045 Pa.s.
 Untreated 60% concentration fly ash slurry exhibited high yield stress values from
11 Pa to 6 Pa at different temperature environment.
 The rheological properties of fly ash-water slurry depend significantly on the solid
concentration and temperature of the slurry.
4.3.6. Effect of pH on fly ash-slurry rheology
The surface properties of fly ash particles and the ionic strength of the supernatant
solution strongly influence the rheology of fly ash-water slurry. Supernatant composition and
ionic strength can vary with pH since comparatively large amounts of metal ions are dissolved
at low pH and at pH greater than about 8 the dissolution of the same decreases to trace
amounts (Kaji et al., 1985). The resulting ionic strength has a significant effect on the stability
of fly ash-water slurry stabilized by electric charge on the particles against flocculation
(Heimenz, 1986). The oxygen-containing functional groups along with the inorganic minerals
contribute to particle surface charge. The oxygen-containing functional groups with
exchangeable cations play a very crucial role in influencing changes in yield stress and
apparent viscosity (Boger et al., 1987). The surface charge is low at low pH, as the functional
172
Chapter 4: Results and discussion
groups are hydrogen exchanged. The net attractive interaction between the particles results in
flocculation. Hence at low pH the apparent viscosity of fly ash slurry is high. Kaji et al.,
(1987) reported the influence of pH on the apparent viscosity of coal-water slurry in the pH
range of 7 to 8.5 only. According to them, viscosity of coal-water slurry increases with
decreasing pH, i.e., with increasing hydrogen ion concentration in the supernatant solution.
Keeping the above theory in mind the pH was measured for fly ash slurries and the results are
reported below. The pH test carried out with the selected fly ash slurry concentration (i.e.
20% to 40%) with varying surfactant and counter-ion exhibited favourable attributes (Tables
4.5 - 4.9). pH values of all the fly ash-additive slurry varied between 7.14 to 7.63 at room
temperature i.e. 270 ± 30C. The pH of ordinary tap water is 7. Hence the additive used for this
study has no influence on pH of the slurry. All the tested slurries were alkaline in nature
which is a favourable trait without any adverse environmental impact.
Table 4.5.pH value of fly ash slurry at 20% solid concentration
Sample Fly ash Surfactant Counter- Water
Solid
pH at
No.
(gram)
(gm)
ion
(ml)
Conc.
27±10C
(gm)
C w (by
temp.
wt.)
20.1
19.0
0.5
0.5
80
20
7.30
20.2
19.2
0.4
0.4
80
20
7.59
20.3
19.4
0.3
0.3
80
20
7.47
20.4
19.6
0.2
0.2
80
20
7.57
20.5
19.8
0.1
0.1
80
20
7.25
20.6
20.0
0.0
0.0
80
20
7.74
Table 4.6.pH value of fly ash slurry at 30% solid concentration
Sample Fly
Surfacta CounterWater Solid
pH at 250C
No.
ash
nt (gm)
ion
(ml)
Conc.
(gm)
(gm)
Cw (by wt.)
30.1
29.0
0.5
0.5
70
30
7.73
30.2
29.2
0.4
0.4
70
30
7.63
30.3
29.4
0.3
0.3
70
30
7.24
30.4
29.6
0.2
0.2
70
30
7.64
30.5
29.8
0.1
0.1
70
30
7.66
30.6
30.0
0.0
0.0
70
30
7.30
173
Chapter 4: Results and discussion
Table 4.7.pH value of fly ash slurry at 40% solid concentration
Sample Fly
Surfacta CounterWater Solid Conc. pH at 250C
No.
ash
nt (gm)
ion
(ml)
Cw (by wt.)
(gm)
(gm)
40.1
39.0
0.5
0.5
60
40
7.23
40.2
39.2
0.4
0.4
60
40
7.33
40.3
39.4
0.3
0.3
60
40
7.14
40.4
39.6
0.2
0.2
60
40
7.34
40.5
39.8
0.1
0.1
60
40
7.56
40.6
40.0
0.0
0.0
60
40
7.40
Table 4.8.pH value of fly ash slurry at 50% solid concentration
Sample
Fly
Surfactant Counter- Water
Solid
pH at
No.
ash
(gm)
ion
(ml)
Conc.
27±10C
(gram)
(gm)
C w (by
wt.)
50.1
49.0
0.5
0.5
50
50
7.20
50.2
49.2
0.4
0.4
50
50
7.39
50.3
49.4
0.3
0.3
50
50
7.27
50.4
49.6
0.2
0.2
50
50
7.37
50.5
49.8
0.1
0.1
50
50
7.25
50.6
50.0
0.0
0.0
50
50
7.24
Sampl
e No.
60.1
60.2
60.3
60.4
60.5
60.6
Table 4.9.pH value of fly ash slurry at 60% solid concentration
Fly
Surfacta CounterWater Solid Conc.
pH at 250C
ash
nt (gm)
ion
(ml)
Cw (by wt.)
(gm)
(gm)
59.0
0.5
0.5
40
60
7.23
59.2
0.4
0.4
40
60
7.23
59.4
0.3
0.3
40
60
7.24
59.6
0.2
0.2
40
60
7.25
59.8
0.1
0.1
40
60
7.26
60.0
0.0
0.0
40
60
7.30
4.3.7. Effect of solids concentration on fly ash slurry rheology
The rheological properties of particle suspensions are controlled by factors of both
physical and chemical origin. Some general factors are: Concentration of particles, specific
surface of the particles, particle shape, and state of flocculation. In fly ash-water suspensions
the hydration is also a contributing factor.
174
Chapter 4: Results and discussion
Figure 4.102.Viscosity vs. solid concentration at shear rate 100 and 200 s-1
The effect of concentration on the viscosity of a suspension is described by the
Krieger-Dougherty equation as given below (Struble and Sun, 1995):
η = ηs (1-Φ/Φm)-[η]Φm
(4.4)
Where ηs is the viscosity of the suspending medium (the liquid phase), Φ is the volume
fraction of particles, Φm is the maximum volume fraction of particles, and [η] is the intrinsic
viscosity. The maximum concentration is very sensitive to the particle size distribution and
particle shape. Furthermore, the flocculation of particles may lower Φm since the flocs
themselves are not closely packed. The intrinsic viscosity is a measure of the effect of
individual particles on the viscosity. Figure 4.102 illustrates the effect of concentration and
175
Chapter 4: Results and discussion
shape of particles, according to the Krieger-Dougherty equation, on the viscosity of a
suspension. Apparent viscosity of the fly ash slurry increased with increase in solid
concentration (Figures 4.102 and 4.103). This is due to the fact that hydrophilicity of fly ash
surface increases with increase in solid concentration and the frictional forces between the
particles become significant with corresponding increase in resistance. The inner surface of
hydrophilic fly ash is not penetrated by water and hence more of it is available in the
interparticular spaces. Availability of less water outside the hydrophilic fly ash particles
decreases the fluidity or increases the viscosity of the slurry (Liang and Jiang, 1986; Liang
and Jiang, 1987; Chong et al., 1971; Ting and Luebbers, 1957).
180
600
Viscosity, mPa.s
Viscosity, mPa.s
160
140
120
Additive conc. 0.1%
100
80
R2=0.840
60
40
R2=0.643
500
Additive conc. 0.2%
400
300
200
100
20
0
0
20
30
40
Solid conc. (wt. %)
50
20
60
25
1200
Temp. 200C, Shear Rate, 200 1/s
800
30
35
40
45
Solid conc. (wt. %)
50
55
60
Temp. 200C, Shear Rate, 200 1/s
1000
600
Viscosity, mPa.s
700
Viscosity, mPa.s
Temp. 300C, Shear Rate, 100 1/s
700
Temp. 300C, Shear Rate, 100 1/s
200
Additive conc. 0.2%
500
400
300
200
800
Additive conc.…
600
400
R2=0.879
200
R2=0.987
100
0
0
20
25
30
35
40
45
Solid conc. (wt. %)
50
55
60
20
25
30
35
40
45
Solid conc. (wt. %)
Figure 4.103.Viscosity vs. solid concentration at 200C and 300C
176
50
55
60
Chapter 4: Results and discussion
4.3.8. Settling rate of fly ash slurry
The settling rates of particles in the fly ash slurries used in this study were determined
using a 100ml glass measuring cylinder (Figure 4.104-105). A quantity of 75ml of the slurry
was placed in the measuring cylinder (where the solid volume fraction was the same as that
used in the rheological tests) and thoroughly mixed by up-turning the cylinder multiple times.
The settling velocity of the clear zone interface was then observed.
Figure 4.104: Settling study cylinder set up
Figure 4.105: Settling study cylinders at varying doses of additives
177
Chapter 4: Results and discussion
The settling rate varied dramatically between different additive concentrations, usually
due to the existence of inter-particle forces and the fastest settling rate is observed without any
additive (Figures 4.106 and 4.107). The fly ash particles settle down very quickly without any
additive but with the use of the additive the particles remain floated during test experiments.
Similar observations were also made with flocculant elsewhere (Jain, 2004). Therefore the
shear stress- shear rate plots give a clear picture of the rheological behaviour of the fly ash
water slurry under consideration.
Figure 4.106: Settlement vs. time plot at 20% solid concentration
Figure 4.107: Settlement vs. time plot at 0.1% additive concentration
178
Chapter 4: Results and discussion
4.4. Section III
4.4.1. Results of geotechnical investigation of the selected material
The engineering properties of a material depend largely on the composition of the
material. There exists wide variation in the composition of fly ash depending on coal types,
types of furnace, temperature, collection technique adopted, etc. (Pandian et al., 1995). The
geotechnical properties of the developed composite materials were determined as per
established methods. All the results of the current investigation and their corresponding
analyses have been presented in different sections as mentioned below. The engineering
properties of a material such as unconfined compressive strength, Brazilian tensile strength
etc. is dependent on the moisture content and dry density. Typically the higher the compaction
the better is its geotechnical characteristics. Hence it is necessary to achieve the desired
degree of compaction to meet the expected properties (Nicholson et al., 1994). Compaction is
the process of increasing the density of material by the application of mechanical energy such
as tamping, rolling, and vibration. It is achieved by forcing the particles closer with a
reduction in air voids. Optimum moisture content (OMC) is the moisture content at which
compacted material reaches the maximum dry density of solid particles.
4.4.1.1. Geotechnical properties of developed fly ash composite materials (FCMs)
The developed composite materials were subjected to various engineering tests such as
Compaction behaviours, Unconfined Compressive Strength Test, Brazilian Tensile Strength
Test, Ultrasonic Pulse Velocity Test, Micro Structural Analyses, and X-Ray Diffraction
(XRD) Analysis, the results of which are presented in the following sub-sections.
4.4.1.1.1. Compaction Characteristics
The compaction characteristics of the developed fly ash composite materials were
carried out to determine the optimum moisture content and maximum dry density the results
of which are presented in Figure 4.108. As the water content was increased, the dry density of
the specimen increased. The optimum MDD of the developed composite materials was found
to be 1443 Kg/m3 (Table 4.10) and the corresponding value for OMC was 12.51%.
179
Chapter 4: Results and discussion
Table 4.10 Engineering properties of FCM
Moisture Content (%)
Dry Density (Kg/m3)
7.37
1260
9.97
1346
12.51
1443
16.11
1341
20.85
1254
Figure 4.108: Compaction curve of fly ash composite material
4.4.1.1.2. Unconfined compressive strength
The unconfined compressive strength (UCS) of a material is its resistance to any
externally applied load. It reflects inter granular cohesion as well as strength of cementing
material holding those grains. The samples were tested both with and without lime addition.
The sample without lime addition did not exhibit any significant strength value. It was only
297 kPa. There was no appreciable change in the strength value at different curing periods as
well and hence those data are not reported here. However lime addition changed the strength
behavior significantly. At 7 days of curing period the uniaxial compressive strength of the
composite increased manifold. It failed at 1.215 MPa thus achieved a 305% increase (Table
4.11). Then the increase rate reduced to 10% exhibiting 1.330 MPa at 14 days. But the rate of
increase increased to 54% at 28 days curing to exhibit 2.85 MPa. The specimen continued
exhibiting increased strength value at 56 days though with much reduced rate (Figure 4.109).
All the samples exhibited shear type of failures thus confirming to the development of
cohesion between particles (Figure 4.110).
180
Chapter 4: Results and discussion
Table 4.11: UCS values of FCM at different curing periods
Curing Period (days)
Compressive Strength (MPa)
0
0.297
7
1.215
14
1.450
28
2.850
56
2.950
Figure 4.109.UCS values of fly ash composite material at different curing periods
Figure 4.110: Post failure profiles of UCS samples
181
Chapter 4: Results and discussion
4.4.1.1.3. Brazilian tensile strength characteristics
Tensile strength is an important property to predict the cracking behaviour of the filled
mass and is a vital parameter to evaluate the suitability of fly ash as a filling material in mine
voids. In the present study tensile test was conducted on developed composites to evaluate the
tensile strength as well as the cracking behaviour of the material. The tensile strength of the
fly ash composite material showed significant improvement with curing periods. At 28 days
curing the tensile strength values increased at 100% and 200% to that of at 7 and 14 days
respectively (Table 4.12). Marginal increase was also observed at 56 days curing period
(Figure 4.112). All the specimens failed more or less at the middle through an induced force
which is tensile in nature (Figure 4.111). The failure occurred within 70 to 110 seconds thus
confirming to that suggested in ASTM D3967.
Figure 4.111.Post failure profiles of Brazilian tensile test samples
Table 4.12: Relationship between curing period and Brazilian tensile strength
Curing period (days)
0
7
14
28
56
Brazilian tensile strength (kPa)
057
150
180
300
335
182
Chapter 4: Results and discussion
Figure 4.112: Tensile strength values of developed composites at different curing periods
4.4.1.1.4. Shear strength parameters
The post failure profile of a triaxial test specimen is presented in Figure 4.114. The
shear strength parameters of compacted fly ash composite materials are presented in Table
4.13. There is little change in cohesion and angle of internal friction values at 7 and 14 days
curing (Figure 4.113 and 4.115). Both cohesion and angle of internal friction increased with
curing period. At 28 days curing the friction angle is about 350 which are typical of any
medium hard rock (Vutukuri et al., 1978). This confirms that the developed composite
material would be suitable to support roof load and would also resist putting pressure on
barricades.
4.4.1.1.5 Ultrasonic Pulse velocity
The P-wave velocity depends on the quality of transmission, cohesiveness of
constituent materials, dampness, presence of weaknesses such as cracks, voids, etc. Its
accuracy also depends on the homogeneity of the specimen. The ultrasonic pulse velocities
varied between 1410 m/s to 2158 m/s at varying curing periods from 7 days to 56 days (Table
4.15). Maximum values were obtained at 56 days curing period, thus confirming the increased
conductivity in the sample. But it increased by 12% at 28 days thus reflecting improved
transmissivity of the wave due to enhanced pozzolanic activity. The rise is marginal between
7 and 14 days of curing.
183
Chapter 4: Results and discussion
Table 4.13: Shear strength parameters of fly ash composite materials
Curing period
Cohesion (kPa) Angle of internal friction (degrees)
7
53
27.85
14
54
28.35
28
71
34.60
56
78
36.52
Figure 4.113: Relationship between curing period and cohesion
Figure 4.114: Post failure profile of a triaxial test specimen
184
Chapter 4: Results and discussion
Figure 4.115: Relationship between curing period and angle of internal friction
The P-wave velocity at 56 days of curing period was 2158 kPa and least values were
obtained for 7 days of curing period which confirms to the results obtained in UCS and BTS
tests. The Poisson’s ratio is also an important parameter of a material under loading. The
Poisson’s ratio values were obtained from ultrasonic pulse velocity test as well. The Poisson’s
ratio values of each composite decreased with increase in curing period. The Poisson’s ratio
values varied between 0.28 and 0.44 of all developed composites cured at 7, 14, 28 and 56
days (Table 4.14). The Poisson’s ratio values of each composite did not change significantly
with longer curing periods which are the typical characteristics of any material. Young’s
modulus (E) values were also obtained from nondestructive testing (Table 4.17). The Young’s
modulus (E) values increased with curing period confirming to enhance pozzolanic activities
resulting in higher stiffness of the composites. The velocity of propagation increases with
increased stiffness of the material (Yesiller et al., 2000). The density of the material also
increased with curing period (Table 4.16) confirming to strength gain.
Table 4.14: Relationship between curing period and Poisson’s ratio
No. of days cured
Poisson’s ratio
07
0.44
14
0.41
28
0.40
56
0.22
185
Chapter 4: Results and discussion
Figure 4.116: P-wave velocities of developed composites at different curing periods
Table 4.15: P-wave velocities of developed composites at different curing periods
Curing period (days)
P-wave velocities (m/s)
Poisson’s Ratio
7
1410
0.44
14
1414
0.41
28
1577
0.40
56
2158
0.28
Table 4.16: Relationship between curing period and density
Curing period (days)
Density (Kg/m3)
7
1460
14
1470
28
1520
56
1700
Figure 4.117: Relationship between curing period and Poisson’s ratio
186
Chapter 4: Results and discussion
Figure 4.118: Relationship between curing period and density
Table 4.17: Ultrasonic test parameters
Ultrasonic test parameters
Curing Period (days)
7
14
28
Young’s modulus (kPa)
950337
1196933
1764446
Bulk modulus (kPa)
1038263
2146938
3377293
Shear (Rigidity) modulus
133268
425325
661389
(kPa)
S-wave velocity (m/s)
235
560
580
56
5750525
4795166
2211523
697
4.4.2. Micro-structural analysis
The SEM images show development of gel at different stages of pozzolanic reaction.
It confirms to the observation that during early stages, the reactive particles in the fly ash
composite served as nucleation sites for hydration and pozzolanic reaction products as (C-SH,C-A-H,C-A-S-H) [Lav et al., 2000]. Cementitious compounds are formed around fly ash
particles (Figures 4.119-4.123). The composite at 56 days of curing period exhibited densegel-like mass covering all reactive particles completely and filling up the inter-particle space
with blurred grain boundaries (Figures 4.123). It appears like a massive unit compared to the
other composites. The dense gel acted as a binding substance and appears to be evenly
distributed to form compact structure, thus creating more contact and higher cohesion that in
turn reflects in greater strength values. It was observed from static laboratory tests that all
samples exhibited maximum strength values at 56 days. So its SEM analysis was carried out
to understand the micro-structural aspects. The strength values of the developed fly ash
187
Chapter 4: Results and discussion
composites increased with increasing curing period due to the formation of calcium silicate
hydrate (CSH) and calcium aluminate silicate hydrate gels (CASH) around fly ash particles
(Cetin et al., 2010).
Figure 4.119: SEM image of untreated fly ash at 5000x
Figure 4.120.SEM image of 7 days curing at 5000 x
188
Chapter 4: Results and discussion
Figure 4.121.SEM image of 14 days curing at 5000 x
Figure 4.122.SEM image of 28 days curing at 5000 x
189
Chapter 4: Results and discussion
Figure 4.123.SEM image of 56 days curing at 5000 x
4.4.3. X-ray diffraction analysis of FCM
The mineralogical analyses of the composites are very important to determine the
changes in the mineralogical phases due to pozzolanic reactions. Cementing compounds such
as CSH, CAH and CASH were indentified in 3% cement stabilized fly ash only and fly ash –
black cotton soil mixes at 28 days curing by XRD analysis (Krishna, 2001). The strength
development is also dependent on the amount of hydration products as well as their
interlocking mechanisms (Lav and Lav, 2000). The formation of reaction products such as
calcium silicate hydrates CSH; Calcium aluminates hydrates (CAH) and Calcium aluminates
silicate hydrates (CASH) were confirmed from x-ray diffraction analysis (Figures 4.1244.127). These new cementitious compounds induce aggregation effect in fly ash and bind the
particles together to form fly ash clusters and resulted in overall enhanced strength behaviours
of composites. Quartz the primary mineral present in fly ash indicated by sharp peaks at 27 0
(approximately).
190
Chapter 4: Results and discussion
600
Q: Quartz
H: Hematite
CSH: Calcium silicate hydrate
CAH: Calcium aluminate hydrate
500
Intensity, counts
400
Q
300
200
Q
100
CSH
CAH
CSH CAH
CAH
CSH
CSH
Q
Q
H
Q
0
5
10
15
20
25
30
35
40
Diffraction angle, 2
45
50
55
60
65
70
(degrees)
Figure 4.124.XRD peak of fly ash composite material at 7 days curing
Q
600
Q: Quartz
H: Hematite
CSH: Calcium silicate hydrate
CAH: Calcium aluminate hydrate
CASH: Calcium aluminate silicate hydrate
500
Intensity, counts
400
300
200
Q
CSH
100
CSH
CAH
CSH
Q
CAH
CAH
CSH
CSH
CASH
CSH
Q
H
Q
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Diffraction angle, 2 (degrees)
Figure 4.125.XRD peak of fly ash composite material at 14 days curing
600
Q
Q: Quartz
H: Hematite
CSH: Calcium silicate hydrate
CAH: Calcium aluminate hydrate
CASH: Calcium aluminate silicate hydrate
500
Intensity, counts
400
300
200
Q
CSH
CSH
100
CASH
CAH
CSHCAH CAH
CSH
Q
CSH
CSH
Q
H
Q
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Diffraction angle, 2 (degrees)
Figure 4.126.XRD peak of fly ash composite material at 28 days curing
191
Chapter 4: Results and discussion
700
Q: Quartz
H: Hematite
CSH: Calcium silicate hydrate
CAH: Calcium aluminate hydrate
Q
600
Intensity, counts
500
400
300
200
Q
CSH
100
CSH
CAH
CSH
CAH
CAH
CSH
Q
CSH
CSH
Q
H
Q
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Diffraction angle, 2 (degrees)
Figure 4.127.XRD peak of fly ash composite material at 56 days curing
4.4.4. FTIR Analysis
FTIR (Fourier Transform Infrared Spectrometry) investigation has been carried out to
obtain information regarding functional groups of materials/compounds.
The quality or
consistencies of the fly ash-additive mixture after treatement have been significantly depicted.
The FTIR monograph in Figure 4.128 shows that the untreated fly ash has peaks at 1089.78
cm-1, 796.60 cm-1, and 462.92 cm-1. These peaks attribute to T-O-Si (internal linkage; T = Si
or Al); Si-O-Si (external linkage); Si-O-Si or O-Si-O groups of fly ash that are mainly
responsible for strength behavior of the material. When the fly ash was mixed with lime,
surfactant and NaSal, a doublet (two peaks) was observed at ~ 790 cm-1 and a peak at ~ 1400
cm-1 region that reflects the presence of O-C-O group (Figures 4.129 - 4.130) i.e. no
geolitesation even in presence of surfactant and counter-ion (Ojha et al., 2004). As the curing
period progressed to 7 and 14 days the peaks were observed at ~ 3400 cm-1, 1400 cm-1, 16001650 cm-1. The peaks depict OH stretching to OH bonding (Figures 4.132 – 4.134). These
peaks depict the presence of O-C-O, H-O-H groups. At 28 days curing period 3300 – 3600,
1350 – 1450,
1600-1650 and ~ 950 cm-1 peaks with OH, O-C-O, H-O-H and O-C-O
stretching and H-O-H and H-O-H internal Ti-O-Si group bonding were observed (Figure
4.135). This reflects higher bonding i.e. effective goelitesation (Park & Kang, 2008). The
peaks were broader after 56 days of curing (Fig 4.136).
192
Chapter 4: Results and discussion
Figure 4.128: FTIR results of untreated fly ash
Figure 4.129.FTIR spectra of treated fly ash (FA 48w50S.1N.1L1.8)
193
Chapter 4: Results and discussion
Figure 4.130: FTIR spectra of treated fly ash (FA 48w50S.2N.2L1.6)
Figure 4.131: FTIR spectra of treated fly ash (FA 49.8w50S.1N.1L0)
194
Chapter 4: Results and discussion
Figure 4.132: FTIR spectra of treated fly ash (FA 49.6w50S.2N.2L0)
120
%T
105
90
75
60
45
30
15
0
4000
7 days
3500
3000
2500
2000
1750
1500
1250
1000
750
Figure 4.133.FTIR results of treated fly ash composites at 7 days curing period
195
500
1/cm
Chapter 4: Results and discussion
70
%T
60
50
40
30
20
10
0
4000
3500
14 days
3000
2500
2000
1750
1500
1250
1000
750
500
1/cm
Figure 4.134: FTIR results of treated fly ash composites at 14 days curing period
35
%T
30
25
20
15
10
5
0
4000
28days
3500
3000
2500
2000
1750
1500
1250
1000
750
500
1/cm
Figure 4.135: FTIR results of treated fly ash composites at 28 days curing period
196
Chapter 4: Results and discussion
70
%T
60
50
40
30
20
10
4000
56days
3500
3000
2500
2000
1750
1500
1250
1000
750
500
1/cm
Figure 4.136: FTIR results of treated fly ash composites at 56 days curing period
4.4.5. Development of Empirical models
A part of the objectives was to develop model equations for the investigation with the
parameters like UCS, BTS, and P-wave velocity. Those are reported here for the best fit
coefficient of determination.
4.4.5.1. Relationship between UCS, BTS and P-wave velocity
The investigation involved samples for various parametric determinations. Each
parameter has been discussed separately earlier. A few empirical models have been developed
to establish mutual coefficient of determination between UCS and P-wave velocity, BTS and
P-wave velocity etc. The data are analyzed using multiple regression models by the method of
least squares (Figures 4.137-143). There exists relation between compressive strength of fly
ash-lime and fly ash-lime-gypsum mixes with chemical composition, loss on ignition, CBR
and tensile strength using power model (Ghosh and Dey, 2009). It confirms that the
relationship between compressive strength and P-wave velocity become stronger with
increasing curing period. The results of regression model between unconfined compressive
strength, Brazilian tensile strength and P-wave velocity at different curing period are reported
(Table 4.18).
197
Chapter 4: Results and discussion
Table 4.18: The developed correlation among various parameters of fly ash composite materials
Parameters
Best fit relation
R2 value
UCS - BTS
y = 94.599x + 43.892
0.9790
Cohesion and angle of internal friction
y = 0.3511x + 9.3572
0.9972
Density and curing period
y = 5.0559x + 1404.8
0.9661
Density and P-wave velocity
y = 0.3146x + 1021.7
0.9988
P-wave velocity and poisson’s ratio
y = -0.0002x + 0.7034
0.9688
Figure 4.137: Correlation between cohesion and angle of internal friction
Figure 4.138: Correlation between P-wave velocity and Poisson's ratio
198
Chapter 4: Results and discussion
Figure 4.139: Relationship between BTS and UCS
Figure 4.140.Correlation between density and P-wave velocity
Figure 4.141.Correlation between density and curing period
199
Chapter 4: Results and discussion
4.4.6. Development of empirical equations from rheology study
Model equations for the investigation with the parameters like Shear Stress (SS),
Shear Rate (SR), Viscosity (V), Yield Stress (YS), and Temperature (T). Those are reported
here for some of the best fit correlations (Table 4.19).
Table 4.19.The developed correlation among various parameters of FCM
Equation
R2 Value
20
y=0.0088x-0.1626
0.9939
0.3
20
y=0.0282x+0.1048
0.9996
SS-SR
0.2
30
y=0.0387x-1.4852
0.9926
4.
SS-SR
0.3
30
y=0.0106x-0.1304
0.9927
5.
SS-SR
0.5
40
y=0.2097x-3.9578
0.9935
6.
SS-SR
0.2
60
y=0.7299x-14.529
0.9932
7.
SS-SR
0.2
60
y=0.0456x-0.8206
0.9307
8.
SS-SR
0.3
60
y=0.588x-6.5426
0.9957
9.
SS-SR
0.4
60
y=0.5824x-2.5752
0.9992
Sl.No.
Correlation
Additive conc.
Solid conc.
between
(%)
(%)
1.
SS-SR
0.2
2.
SS-SR
3.
4.5. Summary
In this study, the prime objective was to select an alternate backfill material to fill
mine voids. To achive the objectives seven number of fly ash samples were collected from
seven different sources. The seven number of fly ash samples were tested in the laboratory to
study their suitability for mine filling purposes. Out of the seven fly ashes studied the best
suitable one was selected for further study with respect to its flow and in-place strength
characteristics. A surface active agent (surfactant) was added to the selected fly ash to modify
the flow behaviour of the slurry in pipelines during its transportation to fill mine voids. Flow
study was conducted at different additive concentration to optimize the same. The secondary
objective was to measure the in-place strength characteristics of developed fly ash composite
materials. The in-place strength characteristics of developed composite materials were
measured by using another reagent called lime. The results of all the investigation were
reported in this section.
200
Chapter 5: Conclusions
___________________________________________________________________________
CHAPTER 5
CONCLUSIONS
5.1. CONCLUSIONS
The primary objective of this study was to develop a suitable mine filling material and
to evaluate its flow and in-place strength characteristics for the selected material. The reported
results reflect some of the characteristics of fly ash samples from seven numbers of thermal
power plants situated in various parts of the country. The potential of surfactant modified fly
ash slurry was evaluated for its smooth flow in pipelines to be transported to mine sites for
filling purposes. The modified slurry improved the flow properties by reducing drag friction
in hydraulic pipelines. Besides flow, strength characteristics of any backfill material are vital
parameters to judge its suitability for underground applications. Strength characteristics of
the fly ash composites were studied through different methods such as unconfined
compressive strength, Brazilian tensile strength, cohesion, angle of internal friction, Young’s
modulus, Poisson’s ratio, bulk modulus, shear modulus, and ultrasonic pulse velocity useful
for mine filling applications and to understand the engineering behavior of composite
materials.
Micro-structural analysis was carried out to gain better understanding of the
mechanism of lime, fly ash, and surfactant interaction. The change in surface morphology
and variation in chemical composition due to formation of hydration products were also
analyzed through scanning electron micrographs and energy dispersive X-ray results. X-ray
diffraction analyses were also carried out to identify the hydration production phases.
The results are concluded in three different sections i.e. I, II, and III. The investigation
focused on analyzing and evaluating fly ash from seven different sources of India for their
suitability for flowing in hydraulic pipelines (Section-I). The fly ash with most favorable flow
properties has been further analyzed with respect to the surface behavior and its modification
attributes (Section-II). The modified fly ash has been developed with strength enhancing
agent and evaluated (Section-III).
201
Chapter 5: Conclusions
5.1.1. Section-I (Material characterization)
From the material characterization study the following conclusions are made.
1. The coefficient of uniformity (Cu) of the seven fly ash samples varied from 0.70 to
6.3. The maximum value 6.3 was exhibited by ETPS (F1) fly ash. This value is more
than 6, thus this fly ash sample can be regarded as well graded compared with the
other fly ash samples as per the classification and gradation of soils. Other fly ash
specimens show Cu value less than 6.
2. The F1 fly ash sample depicted bi-modal particle size distribution thought to be the
sum total of two normal distributions. These materials are known to favor high
densities of the consolidated mass because of their enhanced packing characteristics.
3. The specific surface area of the fly ash samples tested varied between 0.187 m2/g and
1.24 m2/g and the bulk density ranged between 1.60 g/cm3 and 1.99 g/cm3. Though
there is little difference in values, comparatively, the average specific gravity and bulk
density of fly ashes were found to be less than that of river bed sand.
4. The F1 fly ash has low specific gravity (2.20) and more specific surface area (1.24
m2/g) as compared to that of others which would facilitate improved surface
modification by chemical additives for smooth flow in pipelines.
5. The fly ash particles in F1 sample are similar in shape and form- distinctly spherical in
shape and have much superior particle morphology that would create a lubricating
effect resulting in a frictionless flow.
6. The F1 fly ash sample has relatively high CaO content to assist in strength
enhancement without sacrificing its flow attributes.
7. The porosity of the bulk fly ash samples varied between 9.135% and 34.2% and the
moisture content varied between 0.15 % - 0.8%.
8. Overall results have indicated that the F1 fly ash has several superior desirable
properties that would make it attractive to fill mine voids. Therefore, F1 fly ash sample
was selected to undertake further study with respect to its flow and in-place strength
characteristics.
202
Chapter 5: Conclusions
5.1.2. Section-II (Rheology study)
This section gives the flow parameters results of both untreated fly ash slurry as well
as surfactant modified fly ash slurry (treated) in two parts i.e. Part-A and Part-B.
5.1.2.1. Part-A (Untreated fly ash slurry)
1.
The slurry without any additive exhibited shear thickening behavior with yield stress
values of varying magnitude. Maximum value of yield stress observed was 11 Pa.
2.
The untreated suspensions of fly ash slurries exhibited heterogeneous flow behavior.
3.
The viscosity increased as the temperature was increased from 200C to 400C.
4.
Fly ash slurries exhibited strong flocculation behavior in absence of chemical
additives and the yield stress value of 0.3 Pa to 4 Pa was obtained for 40% solid
concentration.
5.
The untreated fly ash slurry showed turbulent flow behavior without depicting any
definite trend. The ζ value of the fly ash slurry was negative (-27mV) without any
additive, but changed to positive value (> +30mV) when surfactant was added to the
slurry.
6.
The addition of surfactant resulted in reduced surface tension by 53% to 56% as
compared to that without any additive.
7.
The shear viscosity increased sharply from 1mPas to 3mPas with the shear rates
varying from 100 to 500 per second for all the temperature ranges tested.
5.1.2.2. Part-B (Treated fly ash slurry)
The conclusions derived from the treated fly ash slurry are the following.
1. Rheological behavior improved significantly when surfactant at 0.2% and 0.3%
concentration were added to the fly ash slurry.
2. The surface tension (ST) of the treated fly ash slurry is reduced compared to untreated
fly ash slurry and that of the suspending medium (water). The surfactants reduced the
ST of the liquid significantly from a value of 71 mNm-1 to 31 mNm-1 confirming
better wetting properties. It reduced by 51% to 54% as compared to that of tap water
(68.9mN/m).
203
Chapter 5: Conclusions
3. The zeta potential value (ζ) for the fly ash slurry with addition of surfactant exceeded
+30 mV. It is a favorable attribute for the particles to remain floated that in the
suspending medium so that no pipe jam takes place and hence requirement of water
will be minimized.
4. The decrease in viscosity with increasing temperature is spectacular from 200C to
300C and after that the viscosity decrease is marginal till 400C for all the shear rates
studied.
5. Minimum viscosity and shear stress at 4.8mPa.s and 2Pa respectively were obtained
with 0.2% additive concentration at 400 C i.e. the slurry followed the fundamental
properties of viscous materials.
6. At 0.1% additive concentration the flow behavior was erratic and uneven which is
attributed to insufficient availability of additive concentration to modify the flow
properties.
7. At 0.2% additive concentration, the shear stress value was minimum at 30 0 C at each
shear rate.
8. It is found that the optimum temperature is 300C and optimum surfactant
concentration is found to be 0.2% taking into all the observations together.
9. With 60% fly ash concentration at 400C with 0.2% surfactant the viscosity and shear
stress values were minimum.
10. It is observed that the shear viscosity decreased sharply from 200C to 400C reaching a
minimum value (4.8mPa.s) at 400C with shear rates varying from 25s-1 to 500s-1 for all
the additive ranges tested.
11. 0.2% surfactant concentration produced best results. Therefore, 0.2% surfactant
concentration was chosen for further study with respect to its in-place strength
characteristics. The composite followed the Newtonian behavior and the relation
lue of viscosity is found
to be 0.045 Pa.s.
5.1.3. Section-III (Strength characterization)
The strength behavior of selected fly ash samples were also investigated with and without
additives. The following conclusions are drawn with respect to strength behavior.
204
Chapter 5: Conclusions
1. The fly ash sample used has less than 1% moisture content.
2. The sample without lime addition did not exhibit any significant strength value. It was
only 297 kPa. There was no appreciable change in the strength value at different curing
periods as well. Therefore, fly ash alone is not amenable to be used as a backfill
material without any additive.
3. Addition of lime changed the strength behavior significantly. At 7 days of curing
period the uniaxial compressive strength of the composite increased manifold. It failed
at 1.215 MPa thus achieved a 305% increase. Then the increase rate reduced to 10%
exhibiting 1.330 MPa at 14 days. But the rate of increase increased to 54% at 28 days
curing to exhibit 2.85 MPa. The specimen continued exhibiting increased strength
value at 56 days though with much reduced rate. All the samples exhibited shear type
of failures thus confirming to the development of cohesion between particles.
4. The optimum MDD of the developed composite materials was found to be 1443 Kg/m3
and the corresponding value for OMC was 12.51%.
5. Unconfined compressive strengths increased from 0.71 to 3.14 MPa with curing period.
The FCM exhibited maximum compressive strength value of 3.14 MPa at 56 days
curing.
6. Brazilian tensile strengths increased from 55.7 to 357 kPa with curing period.
7. The ultrasonic pulse velocities varied in the range of 797 m/s to 1699 m/s for varying
curing periods, reaching a maximum value at 56 days curing.
8. The morphology of all the mixes showed the formation of hydrated gel at 56 days
curing. The voids between the particles were filled by growing hydrates with curing
time.
9. Microanalysis and compositional analysis confirmed the formation of new cementitious
compounds such as calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH),
and calcium aluminate silicate hydrate (CASH) which leads to increase in strength of
the material over time.
10. XRD patterns indicate CAH is the most dominant formation followed by CSH and
CASH.
11. As the fly ash was mixed with lime, surfactant and NaSal, doublet (two peaks) were
observed at 792.74 cm-1 with another at 1400 cm-1 region in FTIR monographs. It
205
Chapter 5: Conclusions
reflects the presence of calcium, hence attribute of a good geolite. Without lime no
geolitesation even in presence of surfactant and counter-ion was observed.
12. As the curing period progressed to 7 and 14 days the peaks went up to 3400 cm -1, 1400
cm-1, 1600-1650 cm-1. The peaks depict OH stretching to OH bonding. At 28 days
curing period broader peaks with O-C-O stretching and H-O-H bonding were observed.
These reflect higher capacity of adsorption. The peaks were broader at 56 days of
curing with silica-alumina bonding with extra at 950 cm-1. These peaks with curing
periods reflect that good geolite has been formed.
13. The tensile strength of the fly ash composite material showed significant improvement
with curing periods. At 28 days curing the tensile strength values increased at 100%
and 200% to that of at 7 and 14 days respectively. Marginal increase was also observed
at 56 days curing period.
14. Both cohesion and angle of internal friction increased with curing period. At 28 days
curing period the friction angle was about 350 which are typical of any medium hard
rock. This confirms that the developed composite material would be suitable to support
roof load and would also resist putting pressure on barricades.
15. The ultrasonic pulse velocities varied between 1410 m/s to 2158 m/s at varying curing
periods from 7 days to 56 days. Maximum values were obtained at 56 days curing
period, thus confirming the increased conductivity in the sample. But it increased by
12% at 28 days thus reflecting improved transmissivity of the wave due to enhanced
pozzolanic activity. The rise is marginal between 7 and 14 days of curing.
16. The P-wave velocity at 56 days of curing period was 2158 kPa and least values were
obtained for 7 days of curing period which confirms to the results obtained in UCS and
BTS tests.
17. The Poisson’s ratio values of each composite decreased with increase in curing period.
The Poisson’s ratio values varied between 0.28 and 0.44 of all developed composites
cured at 7, 14, 28, and 56 days. The Poisson’s ratio values of each composite did not
change significantly with longer curing periods which are the typical characteristics of
any material.
206
Chapter 5: Conclusions
18. The Young’s modulus (E) values increased with curing period confirming to enhance
pozzolanic activities resulting in higher stiffness of the composites. The velocity of
propagation increases with increased stiffness of the material.
19. The density of the material also increased with curing period confirming to strength
gain.
20. The SEM images show development of gel at different stages of pozzolanic reaction. It
confirms to the observation that during early stages, the reactive particles in the fly ash
composite served as nucleation sites for hydration and pozzolanic reaction products as
(C-S-H, C-A-H, C-A-S-H). Cementitious compounds are formed around fly ash
particles.
21. The composite at 56 days of curing period exhibited dense-gel-like mass covering all
reactive particles completely and filling up the inter-particle space with blurred grain
boundaries. It appears like a massive unit compared to the other composites. The dense
gel acted as a binding substance and appears to be evenly distributed to form compact
structure, thus creating more contact and higher cohesion that in turn reflects in greater
strength values.
22. The formation of reaction products such as calcium silicate hydrates CSH; Calcium
aluminate hydrates (CAH), and Calcium aluminates silicate hydrates (CASH) were
confirmed from X-ray diffraction analysis. These new cementitious compounds induce
aggregation effect in fly ash and bind the particles together to form fly ash clusters and
resulted in overall enhanced strength behaviors of composites.
23. The model equations governing the relationship between Brazilian tensile strength and
unconfined compressive strength and unconfined compressive strength and ultrasonic
pulse velocity values were developed having correlation coefficient (R2) values varying
from 70% to 90%.
5.2. Scope for future work
The investigation has certain limitations and hence all the factors that contribute to the
smooth flow in pipelines could not be addressed in time. So the future research work should
incorporate the following aspects in detail.
207
Chapter 5: Conclusions
i.
A study of the surface chemistry of the slurry by X-ray photoelectron spectroscopy
(XPS) under considered chemical treatments is recommended in future work to
describe the observed changes in the rheological properties.
ii.
Drag reduction experiments can be conducted with laboratory scale pipe loop
setups to verify the percentage drag reduction by surfactant modified fly ash
slurries and that with untreated slurries.
iii.
Pipe loop tests can be carried out to measure the pressure loss and head loss
parameters both in horizontal pipelines and vertical pipelines.
iv.
Numerical modeling can be carried out to verify the experimental data and predict
the flow behaviors and pressure loss parameters.
v.
Performance of developed composites was evaluated experimentally. Same should
be carried out in field conditions and correlated.
5.3. Strength and weaknesses of thesis
5.3.1. Strengths
(a) The research work undertaken involved a very extensive laboratory experiments in
three phases, viz. the determination of material characteristics and particle size
analysis, geo-technical characteristics and enhancement of strength properties and
lastly the experiments related to flow parameters such as viscosity, shear stress, shear
rate and solid-water concentrations. Further the flow behavior was also determined
with additives.
(b) Substantial literature survey was undertaken
(c) The thesis is made in greater detail and meticulously prepared.
(d) A good number of publications, both in international and national journals as well as
conferences from the work undertaken.
(e) The influence of surfactants on fly ash flow parameters explained.
5.3.2. Weaknesses
Investigation was limited to seven numbers of samples. The same should be carried
out for more number of samples with more variations not limited by time.
208
References
___________________________________________________________________________
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List of publications
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LIST OF PUBLICATIONS
A. Journal Articles
1. Naik, H.K., Mishra, M.K., Rao, K.U.M., and Dey, D., 2009, Evaluation of the role of a
cationic surfactant on the flow characteristics of fly ash slurry, Elsevier Journal of
Hazardous Materials, Vol. 169, pp. 1134-1140.
2. Naik, H.K., Mishra, M.K., and Rao, K.U.M., 2009, The effect of drag-reducing
additives on the rheological properties of fly ash-water suspensions at varying
temperature environment, International Peer-reviewed on-line Journal of Coal
Combustion and Gasification Products, Vol. 1, pp. 25-31.
3. Naik, H.K., Mishra, M.K., and Rao, K.U.M., 2011, Influence of chemical reagents on
rheological properties of fly ash slurry at varying temperature environment, International
Peer-reviewed on-line Journal of Coal Combustion and Gasification Products, Vol. 3, pp.
83-93.
4. Naik, H.K., Mishra, M.K., and Rao, K.U.M., 2011, Parametric Evaluation of Some
Indian Fly ashes for Filling Underground Coal Mine Voids, International Peer-reviewed
on-line Journal of Coal Combustion and Gasification Products, Allen Press Publ., USA,
CCGP-D-12-00002.1, Vol. 4, pp. 28-36..
5. Naik, H.K., Mishra, M.K., and Rao, K.U.M., 2011, Potential of fly ash utilization in
mining sector-a review, Indian Mining and Engineering Journal, Vol. 50, No. 03, pp. 0722.
6. Naik, H.K., 2006, Environment friendly large volume utilization of coal combustion byproducts by the mining and other Industries- the present scenario, The Indian Mineral
Industry Journal, pp. 126-131.
B. Conference Presentations (International)
7. Naik, H.K., Mishra, M.K., and Rao, K.U.M., (2009), Rheological characteristics of fly
ash slurry at varying temperature environment with and without an additive, Proceedings
of the International Conference on “World of Coal Ash (WOCA) 2009” held at the
University of Kentucky, Lexington, USA, can be viewed online at
http://www.flyash.info/, pp.1-12.
8. Naik, H.K., Mishra, M.K., and Rao, K.U.M., (2011), Evaluation of Flow
Characteristics of Fly Ash Slurry at 40% Solid Concentration with and without an
Additive, Proceedings of the International Conference on “World of Coal Ash (WOCA)
2011” held at Denver, Colorado, USA, can be viewed online at http://www.flyash.info/,
pp.1-15.
9. Naik, H.K., Mishra, M.K., and Behera, B. (2007): “Laboratory Investigation and
Characterization of Some Coal Combustion Byproducts for their Effective Utilization”,
Proc. of the 1st International Conference on Managing the Social and Environmental
233
List of publications
_____________________________________________________________________________________
Consequences of Coal Mining in India, 19-21 Nov. 2007, jointly organized by the I.S.M.
University, University of New South Wales and Australian National University. pp: 763770.
10. Naik, H.K., Mishra, M.K., Das, M.P.S., and Sahu, V. (2007): “Large volume coal
combustion by-product (CCB) utilization in mine void filling: a preliminary laboratory
study”, Proceedings of the Indian Mining Congress on “Emerging Trends in Mineral
Industry”, Udaipur, Rajasthan, India, pp: 257-264.
11. Naik, H.K., Mishra, M.K., Nayak, P.K., and Srikrishnan, V. (2007): “Strength
Development of Fly Ash by Lime and Gypsum Addition for its Effective Utilization-a
Laboratory Investigation”, Proc. of the Indian Chemical Engineering Congress,
Chemcon-2007, organized by Indian Institute of Chemical Engineers, Kolkata, West
Bengal, pp. 402.
C. Conference Presentations (National)
12. Naik, H.K., and Mishra, M.K. (2007): “Environmental Issues Concerning to Thermal
Power Plants – A Critical Review”, Proceedings of the National Seminar on “Energy,
Environment and Economics”, Electrical Engineering Department, N.I.T. Rourkela,
Odisha, pp: TP12 (1-7).
13. Naik, H.K., Mishra, M.K., Das, M.P.S., and Sahu, V. (2007): “Flow characteristics
study of fly ash slurry for underground mine void filling by Fluent-a Computational Fluid
Dynamics Software”, Proc. of the National Seminar on “Mining Technology-Present and
Future”, Bhubaneswar, Odisha, pp: 27-34.
14. H.K.Naik, M.K.Mishra, and K.U.M. Rao, (2011), Evaluation of Some Indian Fly ashes
for Filling Underground Coal Mine Voids, National conference on Fly Ash, Hotel ITC
Kakatiya, Hyderabad, conducted by Centre for fly Ash Research and Management (CFARM), New Delhi during 5th to 7th Dec. 2011.
15. Naik, H.K. and Mishra, M.K. (2007): “Fly ash: A resource material for multifarious
utilization”, Proceedings of the National Environment Awareness Campaign-2006,
Rourkela, Odisha, pp: 01-14.
16. Behera, B., Mishra, M.K., and Naik, H.K., (2008), Critical review of Fly Ash
Utilization in Mines, Proc. of National Conference on “Emerging Trends in the Mining
and Allied Industries”, Department if Mining engineering, NIT, Rourkela, pp. 277-283.
17. Naik, H.K. (2007): “Environmental Impact of power plant coal combustion byproducts”, Proc. of the National Seminar on Industrial Waste Management, NIT,
Rourkela, pp: 38-43.
18. Naik, H.K. (2007): “Coal Combustion By-products utilization and management- The
Current Scenario”, Proc. of the All India Seminar on Catalyzing Vision 2020: Challenges
of Indian Chemical Engineers, NIT Rourkela, Odisha, pp. 146-153.
234
List of publications
_____________________________________________________________________________________
19. Naik, H.K. (2007): “Environmental and Ecological Concerns of Thermal Power Plants
vis-à-vis non-conventional energy sources”, Proc. of the National Conference on
Technological Advances and Emerging Societal Implications, N.I.T. Rourkela, pp: 266277.
20. Naik, H.K. (2007): “Environment friendly utilization of fly ash – a review of recent
practices”, Proc. of the National seminar on Environmental Management, Asansol, West
Bengal, pp: 18
21. Naik, H.K. (2007): “Environmental impact of fly ash and its utilization trends in India –
a review of current practices”, Proc. of the National Conference on Technology for
Sustainable Utilization of Natural Resources ‘TechSUNR 2007’, Paralakhemundi,
Odisha, pp: 39
22. Naik, H.K. (2006): “Possible Areas of Large Volume Utilization of Thermal Power
Wastes in Mines – an overview” Proc. of all India Seminar on Minerals & Metallurgical
Industries Wastes & By- Products, Bhubaneswar, Odisha, pp: 22-32.
23. Naik, H.K. (2006): “Fly ash: Its Material Characteristics, Environmental Implications
and Utilization Strategies in India – A Review”, Proc. of the 3rd Annual workshop on fly
ash and its application, Paralakhemundi, Odisha, pp: 34-37.
24. Naik, H.K. (2006): “Fly ash: A resource Material for large volume Utilization in mines –
A Review”, Proceedings of the National Seminar on “Mining Technology and
Environmental Issues”, Udaipur, Rajasthan, pp: 81-87.
25. Naik, H.K. (2006): “The Origin and Multifarious Utilization of Coal ash-An overview”,
Proc. of the National Workshop on Modern Management on Mine Production, Safety and
Environment, Bengal Engineering and Science University, Shibpur, Howrah, West
Bengal, pp: 123-129.
5. Details of completed sponsored research projects during Ph.D. study period
Title of the Project
Funding agency/client
Evaluation of flow and in
place strength
characteristics of fly ash
composite materials
Department of Science
and Technology, GOI
235
Total financial
outlay (Lakhs)
Rs.14.25 lakhs
Year of start &
total period
2009, 2 years
Curriculum Vitae
__________________________________________________________________________________
Curriculum Vitae
1. Name
HRUSHIKESH NAIK
2. Father’s Name
Birabara Naik
3. Mother’s Name
Bachana Naik
4. Date of birth
19th February, 1959
5. Designation
Associate Professor and Head, Mining Engineering Dept.
6. Professional Degrees Obtained
UNIVERSITY
Regional Engineering
College,
Rourkela
(Presently
N.I.T,
Rourkela)
Indian School of
Mines
University,
Dhanbad
DEGREE
B. Sc. Engg. (Mining)
YEAR
1984
M. Tech.
1990
7. Employment Record
UNIVERSITY/
INSTITUTION
National
Institute
of
Technology, Rourkela, Odisha
National
Institute
of
Technology, Rourkela, Odisha
Regional
Engineering
College, Rourkela, Odisha
Regional
Engineering
College, Rourkela, Odisha
Regional
Engineering
College, Rourkela, Odisha
FIELD OF SPECIALISATION
Mining Engineering
Opencast Mining
DESIGNATION
PERIOD
Associate Professor
(Mining Engineering
Department)
Assistant Professor
(Mining Engineering
Department)
Project officer and Head of
the Nodal Centre for Odisha
(NTMIS)
Lecturer (Senior Scale)
01.01.2006 - Till Date
Lecturer
8. Other Related Experience- Research/ Industrial
Industry
Designation
Coal India Limited
Junior Executive Trainee
236
09.12.1995 - 31.12.2005
30.12.1991- 08.12.1995
19.08.1991- 29.12.1991
19.08.1985 - 18.08.1991
PERIOD
05.09.1984-17.08.1985
Curriculum Vitae
__________________________________________________________________________________
9. Professional Development Courses Completed during the Ph.D. Study Period relating
to the chosen field of research
Department
a
Two weeks training
Sponsored by Technical
16th to 27th
of Mining
program on “Advanced
Education Quality
July 2006
and Mineral
Improvement Program
Mining Research
(two weeks) Resources
(TEQIP), NIT Rourkela
Laboratory
Engg.,
Equipments”
Southern
b
Short term course on
“The Science of Coal
Ash Utilization”
c
Short term course on
“The Science of Coal
Ash Utilization”
d
Short term course on
“Transportation and
Storage of Fly Ash”
e
Advanced short term
course with extended
program on “ASH DYKE
Organized by: University of
Kentucky, Centre for
Applied Energy Research,
USA, in collaboration with
American Coal Ash
Association
Organized by: University of
Kentucky, Centre for
Applied Energy Research,
USA, in collaboration with
American Coal Ash
Association
Industrial Tribology,
Machine Dynamics and
Maintenance Engineering
Centre
Dept. of Civil Engineering,
National Institute of
Technology, Rourkela
4th to 7th
May, 2009
MANAGEMENT AND
ITS DESIGN”
9th to 10th
May, 2011
Illinois
University,
Carbondale,
USA
Lexington
Convention
Centre,
Kentucky,
USA
Marrion
Tech Centre,
Denver,
Colorado,
USA
3rd to 5th
December
2008
Indian
Institute of
Technology,
New Delhi
8th February Civil Engg.
to 12th
Dept. N.I.T,
February
Rourkela
2007
f
One week short term
course on “ MATLAB,
SIMULINK AND
LABVIEW FOR
ENGINEERING
APPLICATIONS”
Department of Electrical
Engineering, National
Institute of Technology,
Rourkela
19th
February to
23rd
February
2007
Electrical
Engg. Dept.
N.I.T.,
Rourkela
g
Short term course on
“Advanced Ceramics
Processing &
Characterization”
Department of Ceramic
Engineering, National
Institute of Technology,
Rourkela
1st July to
4th July
2008
Ceramic
Engg. Dept.
NIT
Rourkela
237
Curriculum Vitae
__________________________________________________________________________________
h
Conference on
“Open Access to Science
Publications: Policy
Perspective, Opportunities and
Challenges”
Council of Scientific &
Industrial Research, PUSA,
New Delhi-110012
i
Short term course on
“Materials Technology:
Advanced Processes and
Characterizations”
Department of Metallurgical 7th -11th
and Materials Engineering,
December
National Institute of
2009
Technology, Rourkela
24th March
2009
India
Habitat
Centre, New
Delhi
Metallurgical
and Materials
Engg. Dept.,
NIT Rourkela
11. Fellowship of Academic bodies and Professional Societies: Fellow of Institution of
Engineers (India) awarded in the year 2009
10. Membership of Scientific and Professional Societies
Sl.No. Name of the Institution / Society/Forum
Membership No.
i
Mining, Geological and Metallurgical Institute of India
MMGI-6115
ii
Mining Engineers Association of India
LMMEA-2756
iii
Institution of Engineers ( India )
Life membership No.115538/5
iv
Mining and Engineering Journal Readers Forum
LMJRF-416
v
Indian Society for Technical Education (ISTE)
Life membership No. 7895
vi
Indian Institute of Chemical Engineers (IIChE)
Life membership
Residential Address:
Hrushikesh Naik
Q. No. B-11, Third Street,
N.I.T, Campus, Rourkela-769 008
Dist- Sundargarh, Odisha, India
Email: [email protected],
[email protected]
Phone: 09937115419 (M)
238

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