CHACTERIZATION AND CLASSIFICATION OF A thesis Submitted by

CHACTERIZATION AND CLASSIFICATION OF
SOME LOCAL FLY ASHES
A thesis
Submitted by
Alok Patel
(211CE1230)
In partial fulfillment of the requirements
for the award of the degree of
Master of Technology
In
Civil Engineering
(Geotechnical Engineering)
Department of Civil Engineering
National Institute of Technology Rourkela
Odisha -769008, India
May 2013
CHACTERIZATION AND CLASSIFICATION
OF SOME LOCAL FLY ASHES
A thesis
Submitted by
Alok Patel
(211CE1230)
In partial fulfillment of the requirements
for the award of the degree of
Master of Technology
In
Civil Engineering
(Geotechnical Engineering)
Under the Guidance of
Prof. S.K Das
Department of Civil Engineering
National Institute of Technology Rourkela
Odisha -769008, India
May 2013
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY
ROURKELA, ODISHA-769008
CERTIFICATE
This is to certify that the thesis entitled, “CHARACTERIZATION
AND CLASSIFICATION OF SOME LOCAL FLY ASHES”
submitted by ALOK PATEL bearing Roll No. 211CE1230 in partial
fulfillment of the requirements for the award of Master of Technology
degree in Civil Engineering with specialization in “Geotechnical
Engineering” during 2011-2013 session at the National Institute of
Technology, Rourkela is an authentic work carried out by him under my
supervision and guidance.
To the best of my knowledge, the matter embodied in the thesis has not
been submitted to any other University/Institute for the award of any
degree or Diploma.
Date: 29-May-13
Place: Rourkela
Prof. S.K Das
Department of Civil Engineering
National Institute of Technology, Rourkela
Odisha
ACKNOWLEDGEMENTS
First and foremost, praise and thanks goes to God for the blessing that
has bestowed upon me in all my endeavors.
I am deeply indebted to Prof. S.K Das, Associate Professor of
Geotechnical Engineering Division, my advisor and guide, for the
motivation, guidance, tutelage and patience throughout the research
work. I appreciate his broad range of expertise and attention to detail, as
well as the constant encouragement he has given me over the years.
There is no need to mention that a big part of this thesis is the result of
joint work with him, without which the completion of the work would
have been impossible.
I am grateful to Prof. N Roy, Head, Department of Civil Engineering for
his valuable suggestions during the synopsis meeting and necessary
facilities for the research work.
I extend my sincere thanks to administrative staff of Geotechnical
Engineering Division for their timely help and encouragement for this
work.
I would like to thank my parents and sisters. Without their love, patience
and support, I could not have completed this work.
Alok Patel
Roll No: 211CE1230
Department of Civil Engineering
N.I.T Rourkela
i|Page
ABSTRACT
Excavation of soil to use the top soil for road construction, earth dam construction, soil
stabilization, backfill material, is a great matter of concern as it takes thousands of years to
form the natural top soil. Due to soil excavation, deforestation occurs, which affects the biodiversity. Industrial waste such as fly-ash, slag etc can be effectively used as alternate soil
material. Utilization of fly ash is also a major challenge to the sustainability of thermal power
stations and large scale utilization of fly ash in geotechnical constructions will reduce the
problems of its disposal. As the properties of fly ashes vary from place to place; there is a
need to check the variability of properties to for its effective utilization. Hence, before the
utilization of fly ash as a construction material, it is necessary to study properties of fly ash
from different sources, so that it can be used beneficially. In this present study, four fly ashes
form local thermal power plants are considered. Several Geo engineering laboratory
experiments were performed on these fly ashes to determine its properties. The experimental
results of present fly ashes were compared with that available in the literature. The optimum
lime content is found out in terms of unconfined compressive strength and is found to depend
upon the source of fly ash. Using the classification scheme available in literature it was
observed that all the four fly ashes considered here belong to the same class, but a wide
variation in their properties is observed. Experimental results also showed strength, cohesion
and friction are increased by stabilizing fly ash with lime. But the strength value and increase
in stabilized value are also distinctly different for these four fly ashes. Hence, there is a need
to consider an alternate classification scheme for fly ash for its effective utilization as a fill
and embankment material.
ii | P a g e
TABLE OF CONTENTS
Title
ACKNOWLEDGEMENTS
i
ABSTRACT
ii
TABLES OF CONTENTS
iii
LIST OF TABLES
vii
LIST OF FIGURES
ix
CHAPTER 1
INTRODUCTION
1.1
Overview
2
1.2
Fly ash production and disposal
2
1.3
How Fly ash is hazaradous
4
1.4
Variation of fly ash properties
5
1.5
Fly ash utilization
7
CHAPTER 2
LITERATURE SURVEY
2.1
Introduction
10
2.2
Classification of fly ash
10
2.3
Literature based on fly ash study
12
2.4
Literature based on fly ash properties
13
CHAPTER 3
3.1
MATERIALS & METHODS
Introduction
3.2 Materials used
17
17
3.2.1 Fly ash
17
3.2.2 Lime
18
3.3 Experimental setup & procedure
iii | P a g e
18
3.4 Chemical properties
18
3.4.1 Chemical composition
19
3.4.2 X-ray diffraction
19
3.4.3 Scanning electron Microscope
19
3.4.4 pH
20
3.4.5 Lime reactivity
20
3.5 Physical properties
20
3.5.1 Specific gravity
21
3.5.2 Grain size distribution
21
3.5.3 Free swell index
21
3.5.4 Specific surface
22
3.5.5 Geotechnical classification system for fly ash.
22
3.6 Engineering properties
23
3.6.1 Compaction characteristics
23
3.6.2 Permeability characteristics
24
3.6.3 Unconfined compressive strength
24
3.6.4 Lime fixation
25
3.6.5 Shear strength from Direct shear box test
25
3.6.6 Shear strength from Triaxial shear test
25
3.6.7 CBR
26
3.6.8 Dispersiveness
26
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3.6.9 Angle of repose
CHAPTER 4
27
RESULT & DISCUSSION
4.1 Introduction
29
4.2 Chemical properties
29
4.2.1 Chemical composition
29
4.2.2 X-ray diffraction spectra
30
4.2.3 Morphology
30
4.2.4 pH
33
4.2.5 Lime reactivity
33
4.3 Physical properties
34
4.3.1 Specific gravity
34
4.3.2 Grain size distribution
35
4.3.3 Free swell index
36
4.3.4 Specific surface
37
4.3.5 Geotechnical classification system for fly ash.
38
4.4 Engineering properties
39
4.4.1 Compaction characteristics
39
4.4.2 Permeability characteristics
41
4.4.3 Unconfined compressive strength
42
4.4.3.1 Lime fixation
v|Page
42
4.4.3.2 Variation of UCS with MC
42
4.4.4 Shear strength from Direct shear box test
44
4.4.5 Shear strength from Triaxial shear test
45
4.4.5.1 Maximum deviator stress vs CaO curve
50
4.4.6 CBR
52
4.4.7 Dispersiveness
54
4.4.8 Void ratio
55
4.4.9 Liquid limit test
55
CHAPTER 5
CONCLUSION
5.1 Concluding remarks
57
5.2 Scope for further study
58
REFERENCES
59
vi | P a g e
LIST OF TABLES
Table1.1 Production & Utilization of fly ashes in different country
8
Table2.1 Utilization of fly ash for different purpose
10
Table2.2 Chemical requirement of class C and class F fly ashes
11
Table3.1 Fly ash classification system
23
Table3.2 classification of dispersive soils based on double hydrometer test
26
Table4.1 Chemical composition of fly ashes of present study and some of Indian fly ashes
29
Table4.2 pH values of fly ashes for present study and some of Indian fly ashes
33
Table4.3 Lime reactivity of fly ashes for present study and some of Indian fly ashes
33
Table4.4 Specific gravity of fly ashes with water and kerosene as pore medium, present study 34
Table4.5 Specific gravity of some of Indian fly ashes with water as pore medium
34
Table4.6 Grain size distribution of fly ashes for present study & some of Indian fly ashes
35
Table4.7 Free swell ratio of fly ashes for present study and some of Indian fly ashes
37
Table4.8 Specific surface area of fly ashes for present study
37
Table4.9 Fly ash classification system of fly ashes and Indian fly ashes
38
Table4.10 Compaction characteristics of fly ashes for present study and some Indian fly ash 40
Table4.11 Permeability values of fly ashes ,present study and Indian fly ashes
41
Table4.12 Variation of UCS with MC, present study
43
Table4.13 Shear strength parameters by Direct shear box Test, present study
and Indian fly ashes
Table4.14 Variation of undrained shear strength parameters of fly ashes
vii | P a g e
44
with curing period,present study
48
Table4.15 Variation of Maximum Deviator stress value with change in curing
period, present study
50
Table4.16 Variation of Maximum Deviator stress value with change in CaO value and
curing period, present study
52
Table4.17 CBR values of fly ashes under unsoaked and soaked condition and some
Indian fly ashes
53
Table4.18 Classification of dispersive soils based on double hydrometer test results
54
Table4.19 emax and emin values of fly ashes, present study
55
Table4.20 Liquid limit values of fly ashes, present study
55
viii | P a g e
LIST OF FIGURES
Fig1.1 Schematic view of a typical coal based thermal power plant
4
Fig1.2 Variation of OMC with MDD over different time period over different sources
7
Fig4.1 X-ray diffraction spectra of fly ashes, present study
30
Fig4.2 Surface morphology of NALCO fly ash sample
31
Fig4.3 Surface morphology of TTPS fly ash sample
31
Fig4.4 Surface morphology of NTPC fly ash sample
32
Fig4.5 Surface morphology of KALUNGA fly ash sample
32
Fig4.6 Vaiation of SG of fly ashes wth water and kerosene as pore medium
35
Fig 4.7 Grain size distribution of fly ashes for present study
36
Fig4.8 Compaction curves of fly ashes , present study
39
Fig4.9 Normalized compaction curves of fly ashes, present study
39
Fig4.10 Effect of lime addition on UCS strength of fly ashes
42
Fig4.11 Effect of UCS with change in MC
43
Fig4.12 Failure envelopes from direct shear box tests on fly ashes as in compacted state
45
Fig4.13 Strain-stress curve of Kalunga fly ash with no curing
46
Fig4.14 Strain-stress curve of Kalunga fly ash with 7 days curing
46
Fig4.15 Strain-stress curve of NALCO fly ash with no curing
46
Fig4.16 Strain-stress curve of NALCO fly ash with 7 days curing
46
Fig4.17 Strain-stress curve of NTPC fly ash with no curing
47
Fig4.18 Strain-stress curve of NTPC fly ash with 7 days curing
47
ix | P a g e
Fig4.19 Strain-stress curve of TTPS fly ash with no curing
47
Fig4.20 Strain-stress curve of TTPS fly ash with 7 days curing
47
Fig4.21 Strain-stress curve of KALUNGA fly ash after 3,5,7 days of curing
49
Fig4.22 Strain-stress curve of NALCO fly ash after 3,5,7 days of curing
49
Fig4.23 Strain-stress curve of NTPC fly ash after 3,5,7 days of curing
49
Fig4.24 Strain-stress curve of TTPS fly ash after 3,5,7 days of curing
49
Fig4.25 Kalunga fly ash CaO vs Deviator stress curve
50
Fig4.26 NALCO fly ash CaO vs Deviator stress curve
50
Fig4.27 NTPC fly ash CaO vs Deviator stress curve
51
Fig4.28 TTPS fly ash CaO vs Deviator stress curve
51
Fig4.29 CBR curves of fly ashes under unsoaked condition
53
Fig4.30 CBR curves of fly ashes under soaked condition
54
x|Page
CHAPTER 1
Introduction
1|Page
1.1 Overview
Fly ashes have close resemblance with the volcanic ashes. In early age volcanic ashes
were used as hydraulic cements, which were made near the small Italian town Pozzuoli.
Hence the term “pozzolan” was coined. That was one of best pozzolans used in the
world.
Now-a-days, fly ashes are generated from coal fired electricity generating plant. With
rapid industrialization, there has been an increase in production of fly ash. The power
plants grind the coal mass to make it fine powder form, before it is burnt. The mineral
residue left by burning coal is collected from exhaust gases by electro static precipitator
and collected for use. The major problem of the whole process, of production of fly ash is
their safe disposal and management. The waste generated from industries are complex
characteristics and composition, hence it is necessary to safely dispose the wastes
otherwise it will have a negative impact on environment and social life, which will
ultimately disturb the ecological system. Proper treatment has to be made before the
disposal and storage of the industrial wastes, otherwise it makes the soil and water
contaminate.
The micro sized fly ash mainly consists of silica, alumina and iron. The fly ash particles
are generally spherical in size, which makes them easy to blend and to flow, to make a
suitable mixture. The capillarity is one of the best properties for fly ashes to add as
admixture for concrete. The fly ash contains amorphous and crystalline nature of
minerals. The properties of fly ashes vary timely, with complex variation in all chemical,
physical and geotechnical properties, and for this it is necessary are need to study the
properties of fly ash from different soureces.
1.2 Fly Ash Production And Disposal
Coal is used as a fuel, in thermal power plant for generation of steam. In past coal was
used generated from the furnaces of boilers in the form of lumps. The old boiler proved
to be non energy efficient, hence to optimize the energy efficient from coal mass, the
thermal power plants used pulverized coal mass. The pulverized coal mass is injected into
2|Page
combustion chamber, where it burns instantly and efficiently. The output ash is known as
fly ash, which consists of molten minerals. When the coal ash moves along with the flue
gases, the air stream around the molten mass makes the fly ash particle spherical in
shape. The economizer is subjected, which recovers the heat from fly ash and stream
gases. During this process, the temperature of fly ashes reduced suddenly. If the
temperature falls rapidly, the fly ashes are resulting amorphous or glassy material and if
the cooling process occurs gradually, the hot fly ashes becomes more crystalline in
nature. It shows that the implements of economizer, improves its reactivity process.
When fly ash is not subjected to economizer, it forms 4.3% soluble matter and pozzolanic
activity index becomes 94% [23] .When it subjected to economizer, it forms 8.8% soluble
matter and pozzolanic activity index becomes 103% [23] .Finally, the fly ashes are
removed from the flue gases by mechanical dust collector, commonly referred to
electrostatic precipitator (ESPs) or scrubbers. The flue gases which are almost free from
fly ashes are subjected to chimney into the atmosphere.
The ESPs have the more efficiency about 90%-98% for the removal of lighter and finer
fly ash particles. Generally ESPs consists of four to six hoppers, which are known as field
and the fineness of fly ash particles are proportional to number of fields available. Hence,
if fly ashes are collected from first hopper, the specific surface area found to be 2800
cm2/gm, where the collection is from last hopper, it is high about 8200cm2/gm[23]. The
pulverized coal being burnt, 80% of coal ashes are removed from flue gases and it
recovers as fly ashes, next 20% of coal ashes, if coarser in size, and then collected from
bottom of the furnace. This material is called as bottom ash. This can be removed in dry
form or it can be collected from water filled hopper, from the bottom of the furnace.
When sufficient amount of bottom ash filled the hopper, it can transferred by water jets or
water sluice to a disposal pond, where it is called as pond ash. Fig1.1 gives the idea of
systematically idea of disposal of coal ash, in a coal base thermal power plant.
3|Page
Fig1.1 Schematic view of a typical coal based thermal power plant
(data source Prakash and Sridharan 2007)
Disposal of coal is major environmental issue, because it pollutes the atmosphere and
contaminate the ground water. The two way of disposal system are :
If the fly ash quality is good, then it is collected by ESPs and packed in moisture proof
bags and finally transferred to other locations for other geotechnical use in embankments,
cement industry like. If the quality is not good, then it adds to requisite moisture, to
prevent the fly ash from the atmosphere. This process is called Dry disposal system.
Fly ash is subjected to water, and pumped to disposal site called as dyke. Dykes are
constructed around the site or lagoon. The lagoons are filled with slurry, before switch to
next slurry. Once the ash particles are settle, the water above is removed by natural ways.
This process is called Wet disposal system.
1.3 How Fly Ash Is Hazaradous
Fly ash is hazardous due to its disposal problem. The method of disposed of fly ash and
bottom ash in the form of slurry, in the ash pond is a long term method. The several
problems occur during this process are:
4|Page
When the ash ponds are full, then it requires several construction materials, so wastage of
resources. When lagoons are full, then transferring of fly ashes from one site to another is
difficult one. Raising the fly ash dyke by using construction material or excavate the fly
ash dyke is problematic. The construction of ash pond requires huge amount of land,
which deplete the valuable amount of agricultural land. When one fly ash dyke filled up,
then construction of another dyke is not economical and wastage of valuable agriculture
land. Large quantity of water requires making it in the form of slurry. During rainy
seasons the salt and metallic content with the fly ash, leach to ground water and make it
contaminated. Fly ash contains maximum amount of heavy metals and also unwanted
substances, which cause health problem. Potentially toxic elements present in fly ashes
are chromium, arsenic, cadmium, lead, nickel, zinc like this. If these materials go into
human internal system, it causes toxic to cancer and damage of nervous system, like
cognitive deficits, behavior problem and developmental delays. The fly ashes can also
damage heart, respiratory distress, lung disease, reproductive problems and impaired
bone development in children. If someone lives near unlined wet ash pond, then chances
of getting cancer by arsenic contaminated water, if arsenic is one of the trace element in
fly ash.
When coal ash come contact with ground water, the harmful elements leach and dissolve
with water. The coal ash contains heavy elements leachate that seeps through ground
water ways through streams, river and wetlands and also into the aquifers, which supply
drinking water. This causes the people, to supply new drinking water. The fly ashes toxic
elements also travel to the environment, by runoff and erosion and through the air
medium. Another way fly ash is fine powder material and travel in air, if not properly
disposed; it pollutes the air and water, which cause respiratory problem. It also settles in
crops and leaves, which cause lower yield. Hence, it is necessary to check the fly ash
properties, for its utilization.
1.4 Variability Of Fly Ash Properties
The variability of fly ashes depends on many factors like coal deposits geology, methods
of control and burning of combustion process, additive use for flame stabilization, hopper
position, number of hoppers, corrosion control additives used, dynamic flow of
5|Page
precipitator, and efficiency of pollution control instrument. But mainly the characteristic
of fly ash is affected by the type of coal from which it is derived. Coal is formed by
carbonaceous rock deposit, accumulated vegetable matter, which changes its composition
under the influence of temperature, pressure and time over millions of year past. Hence,
coal varies widely in its chemical composition. Based upon origin of formation of coal,
different source of coal supply varies with different grade. General grade of coal are
Grade A, Grade B, Grade C, Grade D, Grade E, Grade F are available. Coal supply to
power plants Kalunga, NTPC, TTPS and NALCO are categorize under grade E or F type
of coal.
Each grade of coal is different from each other with respect to their method of supply
and chemical composition. Hence, according to that, fly ash properties are also varying
with different sources. Exposure to atmosphere the properties of fly ashes are also
different from the same source with a different time period. The fly ashes which are
produced from same sources, with one type of chemical composition have different
mineralogical structure with another, depends upon coal combustion technique.
Subsequently it, affects the hydration properties of fly ashes. The fly ashes, which are
encounter in field by engineers in the field, are widely varied in their properties and
response to external nature. The physio-chemical behavior controls their nature. In the
present time, the geo environmental factors are more complex and engineers are forced to
face such situation. Like soil, the fly ashes have also unfavorable situations in field, so fly
ashes are also need to check its variation of properties, before its applications in the field.
The behavior and composition are so much different that, all of fly ashes are doing not
meet all requirement in all conditions. Hence properties characterizations of fly ashes are
necessary for, any fly ash consideration for geotechnical applications. Many ways the
unfavorable conditions are suit to modify, the fly ash properties for suitable performance
in the field. From the following Fig1.2, the results of variation of optimum moisture
content (OMC) and maximum dry density (MDD) for different fly ashes collected from
the different plant over different time period are varying from 3 days to 2 years.
6|Page
Fig1.2 Variation of OMC with MDD over different time period over different sources Reference[12]
Compared to other fly ashes, the variations in Panki fly ash found to be less. This has
implication in terms of quality control specification of dry density and water content in
the field compaction of fly ash. There are many factors like gradation, carbon content,
iron content, and fineness etc., which control compaction characteristics of fly ashes.
Like soils, the fly ashes are also some particulates and heterogeneous matters, so no two
fly ashes obtained from different sources are alike. Even though, the fly ashes obtained
from same plant with different time are also different in nature.
1.5 Fly Ash Utilization
Utilization of fly ash in particular, can be broadly grouped into three categories.
The Low Value Utilizations includes, Road construction, Embankment and dam
construction, back filling, Mine filling, Structural fills, Soil stabilization, Ash dykes etc.
The Medium Value Utilizations includes Pozzolana cement, Cellular cement,
Bricks/Blocks, Grouting, Fly ash concrete, Prefabricated building blocks, Light weight
aggregate, Grouting, Soil amendment agents etc.
The High Value Utilizations includes Metal recovery, Extraction of magnetite, Acid
refractory bricks, Ceramic industry, Floor and wall tiles, Fly ash Paints and distempers
etc.
Instead of these, there is large wastage of fly ash material, so large number of
technologies developed for well management of fly ashes. This utilization of fly ash
7|Page
increased to 73 MT upto the year 2012. Fly ash has gained acceptance from the year
2010-12. The present production of fly ashes in the country India are about 130 MT per
year and expected to increase by 400MT by year 2016-17 by 2nd annual international
summit for FLYASH Utilization 2012 scheduled on 17th & 18th January 2013 at NDCC
II Convention Centre, NDMC Complex, New Delhi.
Table1.1 Production & Utilization of fly ashes in different country
Ref: Alam and Akhtar , Int Jr of emerging trends in engineering and development , Vol.1 [2] ,
(2011)
Country
India
China
Germany
Australia
France
Italy
USA
UK
Canada
Denmark
Netherland
Annual ash
production, MT
131
100
40
10
3
2
75
15
6
2
2
Ash utilization
in %
56
45
85
85
85
100
65
50
75
100
100
From the above Table1.1, the fly ash utilization in India is 56% for the country during the
year 2010-12, hence rest of the fly ashes are waste material. Now, it’s necessary to use all
of fly ash, considering its adverse effect on environment. Lots of effort has been made to
utilize the fly ash upto 100%. For this mission, energy foundation announces 2nd
international summit on 2013 for fly ash utilization. The mission is also gathering some
knowledge, information about solution for development of suitable utilization of fly ash.
The well planned coal utilization, concentrated on its bulk utilization. This is possible
only when, we make geotechnical applications such as back filling, embankment
construction, and pavement construction like this. We can utilize more than 60% fly ash
for low value applications, if execution is proper. For this a thorough analysis be require
for check the physical, chemical and geotechnical properties, for suitability of fly ashes.
8|Page
CHAPTER 2
Literature Survey
9|Page
2.1 Introduction
Since 1970’s various effort have been made in utilization of fly ash in geotechnical
engineering field. This chapter deals with literature on fly ash production and its
utilization in real field, types of fly ashes, variation on properties of fly ashes from
different sources and the literature based on experiment methodology to check fly ash
properties.
From, present scenario, India depend 65-70% production of electricity with coal based
power plant, in which the fly ash production in India is, 110 MT/year. So, from Table2.1
now the current ash utilization in India are:
Table2.1 Utilization of fly ash for different purpose Data source: Ministry of Environment & Forests
Mode of Fly Ash Applications
% Utilization
Dykes
35
Cement
30
Land Development
15
Building
15
Others
5
2.2 Classification Of Fly Ash
After Pulverizations, the fuel ash extract from flue gases, by electrostatic precipitator is
called fly ash. It is finest particles among Pond ash, Bottom ash and Fly ash. The fly
ashes are extracted from, high stack chimney.
Fly ash contains non combustible
particulate matter, with some of unburned carbon. Fly ashes are generally contains silt
size particles. Based on lime reactivity test, fly ashes are classified in four different types,
as follows:
10 | P a g e
I
Cementitious fly ash
I
Cementitious and pozzolanic fly
I
Pozzolanic fly ash
I
Non-pozzolanic fly ash
The fly is called cementitious, when it has free lime and negligible reactive silica. A
pozzolanic fly ash is one which has reactive silica and negligible free lime content. The
cementitious and pozzolanic fly ash contains, both free lime and reactive silica
predominantly. Non-pozzolanic fly ash contains neither of free lime nor of reactive silica.
The non pozzolanic fly ash do not take part in self cementing or pozzolanic reactions.
Main difference is that, cementitious material hardens, when come in contact with water
and pozzolanic fly ash hardens only after , get in contact with activated lime with water.
The second and third category of fly ashes found widely.
Another way of classification of fly ash is that, class C and class F category of fly ashes,
based upon chemical composition. Class C category of fly ashes obtained from burning
lignite and sub-bituminous type of coal, which contains more than 10% of calcium oxide.
Class F category of fly ashes obtained from, burning bituminous and anthracite type of
coal, which contains less than 10% of calcium oxide.
The chemical compositions of any fly ashes, which are categorize into class C or class F
fly ashes are as follows in Table2.2:
Table2.2 Chemical requirement of class C and class F fly ashes (data source: ASTM C618-94a)
Fly ash
Particulars
Class F
Class C
SiO2+Al2O3+Fe2O3
:% minimum
70.0
50.0
SO3
:% maximum
5.0
5.0
MC
:% maximum
3.0
3.0
LOI
:% maximum
6.0
6.0
Many of fly ashes, in India are basically class F fly ash, since majority of coal are
bituminous.
11 | P a g e
2.3 Literature Based On Fly Ash Study
Sherwood and Ryley(1970) studied that, the fraction of lime present in fly ash , behaves
the self hardening properties of fly ash, in the form of calcium oxide.
Gray and Lin(1972) studied , the variation of specific gravity of fly ashes and is due to the
particle shape & size , gradation and chemical composition.
Mclaren and Digioia(1987) studied that the fly ashes have low values of specific gravity as
comparsion to soil, so it can use as backfill material for embankment, weak foundation
soil. Since, earth pressure exerted by fly ashes are small.
Martinet al(1990) , stated that fly ash in moist and partial saturate conditions, shows
apparent cohesion values, due to capillary rise and it is not to be use as long term stability
of fly ash. For shear criteria shear strength is the major one.
Yudbir and Honjo(1991) found that lime content of fly ash behaves as self hardening
properties, depends upon availability of free lime & carbon content in the samples.
Wesche(1991) studied that ,the loss of ignition percentage on fly ash , determine the
presence of unburnt carbon on fly ash.
Rajasekhar(1995) found that fly ashes are mainly consists of cenosphere and paleosphere
.The low values of specific gravity are due to spherical particle present in which the
entrapped air bind within it.
Singh(1996) studied that the unconfined compressive strength is a function of free lime
content and apparent cohesion.
Singh and Panda(1996), shows that shear strength of a sample of freshly compacted fly
ash is a function of and of internal friction angle, which in turn depends upon the
maximum dry density of fly ash sample.
N.S Pandian(1998) The low specific gravity ,good draining nature ,ease way of
compaction , good frictional properties etc, can easily gain the use of any geotechnical
engineering applications.
12 | P a g e
Pandian and Balasubramonian(1999) The co-efficient of permeability of fly ash depends
upon degree of compaction, grain size distribution and pozzolanic activity of fly ashes.
Erdal Cokca(2001) Fly ash consists of hollow spherical cells of silicon, aluminium and
iron oxide, so it provides a array of bivalent and trivalent cation like Ca+2, Al+3 anf Fe+3
in ionized state, which can promotes the disperse clay minerals.
Das and Yudhbir(2005) They said that the lime content, iron content, loss on iginition ,
morphology and mineralogy structure affects the geotechnical properties of fly ashes.
2.4 Literature Based On Variability Of Fly Ash Properties
Gray and Lin (1972) Many factors are responsible for large variation in values of specific
gravity of fly ashes such as gradation, particle shape and size and chemical composition.
The shear strength parameters , using triaxial shear test, the fly ash as-compacted state for
partially saturated condition is due to apparent cohesion and curing period(for pozzolanic
fly ash).
Lambe and Whiteman (1979) For dry sand the angle of repose is approximately equal to
angle of shearing resistance in loose state.
Leonards and Bailey (1982) Fly ashes are fine grained substances consisting of mainly silt
sized particles of uniform gradation
Hart et al., (1991) The X-ray diffraction study indicates that fly ashes predominantly
contain quartz and feldspar minerals.
Ranjan et al., (1998) study that quartz , mullite may be present as crystalline compounds
consists of 10-15% by weight of fly ash.
Sridharan et al., (1998) For direct shear box test under as compacted condition, fly ashes
exhibits apparent cohesion, due to capillary stresses as a consequence of partial
saturation.
Prasad and Bai (1999) studied that due to high reactive silica present in fly ash, fly ash
exhibit greater lime reactivity than bottom ash or pond ash.
13 | P a g e
Sridharan and Prakash (2000) Fly ashes show negative free swell indices due to , low
values of specific gravity and due to flocculation and as a consequence of their free lime
content.
Sridharan et al., (2001) found that the principal constituents of fly ashes are silica(SiO2),
alumina(Al2O3) and ferric oxide(Fe2O3).Oxides of calcium, magnesium and sodium are
also present in fly ashes. If carbon particles do not burn in furnace of boiler, then unburnt
carbon particles are also present in fly ashes, and this can be determined from loss on
ignition test.He also studied that the pH of fly ashes vary in the range of low value 3 to
high value about 12. About 50% of Indian fly ashes are alkaline in nature.
Sridharan et al., (2001) study that the morphology through SEM indicates fly ash contains
glassy solid spheres, hollow spheres, sub rounded porous grains, irregular agglomerates
and irregular porous grains of unburned carbon(black in colour). If iron particles are
present , they can be spotted as angular grains of magnetite (dark gray in colour). The low
reactivity of fresh sample indicates low reactive silica or free lime content or high
unburned carbon content in fly ash. The particle size distribution and grain characteristics
of fly ashes, determine the constitutive behavior and other physical and engineering
properties of fly ashes. As fly ashes are predominantly silt size particles, specific surfaces
of fly ashes are quite low as compared to kaolinite. The range of specific surface of
indian fly ashes are 130-530 m2/kg
Sridharan and Pandian (2001) Compacted fly ash tested in unsoaked condition , have
higher CBR values ,then soaked condition of most of the fine grained soils. Such higher
CBR value is due to capillary force, that exist in the partly saturated state.
Das and Kalidas (2002) The specific surfaces of fly ashes , subjected to grain size in ESP
hoppers may vary considerably.
Trivedi and Sud (2004) The specific gravity increases, with increase in fineness and finest
fly ash has maximum specific gravity. Table
shows that, some of variation in specific
gravities.
Prakash and Sridharan(2006) If more than 50% of fines (i.e., fraction of size finer than
75m) belongs to either the coarse silt size category or the medium silt size category or
14 | P a g e
(fine silt+clay) size category , then the ash is represented as MLN or MIN or MHN
respectively.
Prakash and Sridharan(2007) The fly ashes exhibit lower dmax and higher OMC. This is
due to their low specific gravity, poorly graded particles and presence of more
cenospheres. The coarser fly ashes higher OMC and lower dmax , while finer fly ashes
exhibits a lower OMC and higher dmax. The coefficient of permeability is a function of
grain size distribution, degree of compaction and pozzolanic property of fly ashes. For
compacted ashes, k decreases with the degree of compaction increases. Fly ashes falls in
the range of k of silts. For partially saturated compacted fly ash , exhibits some UCC
strength due to capillary stress induced some apparent cohesion and pozzolanic action.
Fly ash has been classified in two classes class C and class F fly ashes. Class C fly ash is
produced from burning lignite and sub-bituminous coal. Class F fly ash is produced from
burning bituminous and anthracite coal as per ASTM C618-94a.
15 | P a g e
CHAPTER 3
Materials and Methods
16 | P a g e
3.1 Introduction
This chapter discuss the materials use and the methods applied for determine chemical,
physical and engineering properties of fly ash materials. Large scale utilization of fly ash
reduces the problem faced by thermal power plants, which reduce the deforestation and
reduce the natural earth material. Assessment of behavior of fly ash is essential, before
use it as a construction material. Even, though the adequate support of full scale field test
are not available, laboratory test control the adequate support of variables encounter in
real engineering practice. The behavior & trend observed in laboratory test experiment,
practically realized the understanding of performance of material in structural field and
may be use as mathematically relationship to predict the behavior of field structures. The
details of material use, sample preparation and experimental procedures have been
outline in this chapter.
3.2 Material Used
3.2.1 Fly Ash
The fly ash is light weight coal combustion by product, which result from the combustion
of ground or powdered bituminous coal, sub-bituminous coal or lignite coal. Fly ash is
generally separated from the exhaust gases by electrostatic precipitator before the flue
gases reach the chimneys of coal-fired power plants. Generally this is together with
bottom ash removed from the bottom of the furnace is jointly known as coal ash. The fly
ash is highly heterogeneous material where particles of similar size may have different
chemistry and mineralogy. There is variation of fly ash properties from different sources,
from same source but with time and with collection point (Das and Yudhbir, 2005). Fly
ash contains some un-burnt carbon and its main constituents are silica, aluminium oxide
and ferrous oxide. In dry disposal system, the fly ash collected at the bottom of the
mechanical dust collectors and ESPs. From the dry storage silos also fly ashes are
collected in closed wagons or moisture proof bags or metallic bins, if the quality of the
fly ash is good. The dry fly ash so collected is then transported to the required locations
where it is subjected to further processing before its use in many non-geotechnical
applications such as cement industry, brick manufacturing and the like. In the present
study fly ashes were collected from four different sources of power plants from the
17 | P a g e
hopper. The fly ashes were collected from captive power plant of Mahavir ferro alloy pvt
ltd IDC Kalunga, National Thermal Power Corporation Kaniha, Talchir Thermal Power
Station Talchir and captive power plant of National Aluminium Company Ltd, Anugul.
Before going to test, the samples were screened through 2 mm sieve , to separate out the
vegetative and foreign material. To get a clear homogeneity, the samples are mixed
thoroughly and get into the oven nearly about 105-110 0C. The materials are stored in air
tight container, for subsequent use.
3.2.2. Lime
Lime produced from mines from different types of lime kiln. It is extracted from stone
product by calcinations process at about 10000C.
Hence the process is CaCO3+heat CaO+CO2
When quicklime hydrated with water formed slacked lime i.e, CaO+H2OCa(OH)2.
Calcium oxide, CaO was used in this project work, to sieve through 150 sieve, which
kept in a air tight container for subsequent use.
3.3 Experimental Setup And Procedure
The present study consists of experimental methods for characterization of fly ash. The
experimental methods refer to investigation of fly ash in terms of morphological,
chemical, physical and geotechnical properties. The thorough understanding of the
chemical, physical and geotechnical engineering properties of coal ashes and their
engineering behavior, as the property characterization of coal ashes governs their
suitability for various geotechnical end uses. The experimental methods in the present
study are elaborated as follows:
3.4 Chemical Properties Mineralogy
Chemical properties of fly ashes are mostly influence by the environmental factors
composition, which arise their general use as well as engineering properties. Hence, the
detail study of chemical properties governs with chemical composition, pH, X-ray
diffraction, Lime reactivity etc.
18 | P a g e
3.4.1 Chemical Composition
Chemical composition suggests the best possible applications of fly ashes. It has seen
that, the presence of calcium silicate and aluminium silicate affects the pozzolanic
activity of fly ash. Relatively high percentage of carbon decreases the pozzolonic activity.
The chemical composition adversely influence the index and engineering properties of fly
ash like presence of alumina, silica, iron and unburnt carbon. If more iron content is
available, then it gives more specific gravity. Unburned carbon in coal ashes also affects
their pozzolanic reactivity, composition and strength characteristics. Pozzolanic
characteristics and reactive silica content make the coal ashes different from soils. For
knowing the chemical composition, the Energy Dispersive X-ray (EDX) micro analyser
fitted with SEM. From the weight percentage of individual element present, the weight
percentage of oxides of elements can be calculated.
3.4.2 X-Ray Diffraction
The X-ray diffraction technique gives the idea about the crystalline element present in it,
carried out primarily to identify the mineral phases. The process of ash formation controls
or retards the morphology and crystal growth of minerals. Even though fly ash is
regarded as an amorphous ferro alumino silicate material, the X-ray diffraction spectra of
fly ashes indicate that they contain both crystalline and amorphous phases of materials.
The samples were dried at 1050C and mainly taken into powered form for X-ray
diffraction analysis. X-ray powder diffraction was initially carried out on the powders for
qualitative identification of mineral phases. The sample is analyzed by passing through a
Philips diffractometer with a Cu K radiation source and a single crystal graphite
monochromator. An angular range of 10-600 of 2value in 0.10 increments was used
throughout. The test has been carried out at NIT Rkl (Metallurgical & Materials
Engineering Dept).
3.4.3 Scanning Electron Microscope Studies
Scanning electron microscope , study shows that the clear and close view of individual
particles of fly ashes , which further signify that fly ashes are finer than bottom ash.
Investigations show that the fly ash particles are generally cenospheres and plerospheres
leading to low values for specific gravity. The chemical and mineralogical
19 | P a g e
characterization of fly ash is not only beneficial for knowing its composition, but also
helps in its classification for its possible utilization as an engineering material. The
particle morphology of fly ash is analyzed using Scanning Electron Microscope
(SEM).The particle shape is quantified by using image analysis. The SEM used in the
present study is JEOL-JSM-6480 LV model.SEM used to scan a finely focused beam of
kilovolt energy. An image is formed by scanning electrode ray tube in synchronism with
the beam and modulating the brightness of this tube with beam excited signals. The
samples are prepared with carbon coating before being putting in the SEM.
3.4.4 pH Of Coal Ashes
If fly ash contains more free lime and alkali, it exhibits more pH value. Since, maximum
fly ashes tested in laboratory are alkali in nature. The degree of solubility of the oxides in
turn depends upon the pH of the aqueous medium. Direct reading type conforming to pH
test conforming to IS 2720 (part 26) – 1987 with glass electrode and a calomal reference
electrode or any other suitable electrode can be used. pH values of coal ashes mainly
depend upon their alkaline oxide content and free lime content. pH of coal ashes can vary
over a wide range from , extremely low of the order of about 3 to a value as high as 12.
About 50% of Indian fly ashes are alkaline in nature. The acidic or alkaline
characteristics of fly ash can be quantitatively expressed by means of hydrogen ion
concentration i.e, -log[H+]= pH ,where H+ is expressed in moles/litre.
3.4.5 Lime Reactivity
The silicious material reacts with calcium present in fly ash and with moisture forms a
cementitious compound. The reaction goes on to form water insoluble calcium silicates
and aluminium silicates. This property is called as lime reactivity. Lime reactivity of fly
ash depends upon free lime, reactive silica, iron and unburned carbon content. Silica in
form of amorphous or as aluminate in crystalline form is called as reactive silica.It is
tested under specified conditions, by compressive strength of standard mortar cubes of fly
ashes as specify in (IS: 1727, 1967)
3.5 Physical Properties:
The Bulk utilization of fly ash is mainly in areas such as backfill, construction of
embankment and backfill. These application needs to check the physical properties of fly
ashes.
20 | P a g e
Basically, physical properties are classifying the fly ashes for engineering purpose and
use in engineering field also. The properties discussed are specific gravity, grain size
distribution, free swell index and specific surface, geotechnical classification system for
fly ashes.
3.5.1 Specific Gravity
For all normal calculation relative density, void ratio, hydrometer analysis, specific
gravity are important tool for geotechnical applications. In general, the specific gravity of
coal ashes lies around 2.0 but can vary to a large extent (1.6 to 3.1). Because of the
generally low value for the specific gravity of coal ash compared to soils, ash fills tend to
result in low dry densities. The low values of specific gravity is a advantage for use fly
ash as a backfill material, which exert low pressure in earth retaining wall or any
foundation structure. The specific gravity of fly ash can be done accordance with IS:
2720(part III/Sec.I) 1980.
3.5.2 Grain Size Distribution
The grain size distribution curve gives the idea about fine or coarse grain type of particle
present, according to that it classify the fly ashes. Most sizes of particles present in fly
ashes are silt size particles. Before going for hydrometer analysis, fly ash to need for wet
sieve analysis through 75sieve size. Wet Sieve analysis was conducted for coarser
particles greater than 75µ and hydrometer analysis was conducted for finer particles less
than 75µ as per IS: 2720 (part IV)-1985. Coefficient of uniformity (Cu) and coefficient of
curvature (Cc) for fly ash was also to be found out. As per specification, the hydrometer
analysis shall be done using the dispersion agent sodium hexameta phosphate.
3.5.3 Free Swell Index (FSI)
Free swell is the increase in volume of a soil, without any external constraints, on
submergence in water. The possibility of damage to structures due to swelling of
expansive clays need be identified, by an investigation of those soils likely to possess
undesirable expansion characteristics. The level of the soil in the kerosene graduated
cylinder shall be read as the original volume of the soil samples, kerosene being a nonpolar liquid does not cause swelling of the soil. The level of the soil in the distilled water
cylinder shall be read as the free swell level. The free swell index of the soil shall be
calculated as follows:
21 | P a g e
Free swell index, percent =( Vd – Vk)/Vk *100
Where
Vd= the volume of soil specimen read from the graduated cylinder containing distilled
water
Vk = the volume of soil specimen read from the graduated cylinder containing kerosene.
This part IS: 2720 (Part XL)-1977 deals with the method of test for the determination of
free swell index of soils.
3.5.4 Specific Surface
This theory is based on, Brunauer Emmett Teller, (BET) which explain the physical
attraction of gas molecules on its solid surfaces, which is based on important analysis for
measurement for specific surface area of material. The concept of this theory is the
extension of Langmuir theory, which says that, gases molecule monolayer adsorption to
multilayer adsorption. This hypotheses is based on (i) The gas molecules physically
adsorbed the solid surfaces infinite no of process. (ii) There is no interaction between
each layer of adsorption. (iii) After, that Langmuir theory can be applied to each layer.
According to IS: 11578-1986 determination of specific surface of powder or powder
porous material, quantity of nitrogen which completely covers the surface of solid area is
calculated independently. Number of such gas molecule, multiplied with area of each
molecule of contact surface gives the total area per unit material.
3.5.5 Geotechnical Classification System For Coal Ashes
As per USCS, soils are broadly classified into coarse grained and fine grained, depending
upon percentage passing through 75 micron sieve. The fly ashes are also classified in
geotechnical engineering view point based on particle size distribution and gradation,
using geotechnical engineering classification system (Prakash and Sridharan, 2006).
Further classification is based on hydrometer analysis by IS:2720(Part4)-1985 for check
the plasticity character of fly ashes. Gradation of fly ashes is similar to USCS
classification system, except it has no plasticity chart. Hence L, I and H are used to
indicate the Coarse silt size fraction (20 micron< particle size < 75 micron), Medium silt
size fraction(7.5 micron< particle size < 20 micron) and fine silt+clay size fraction
respectively.
22 | P a g e
If more than 50% of fines (i.e., fraction of size finer than 75m) belongs to either the
coarse silt size category or the medium silt size category or (fine silt+clay) size category,
then the ash is represented as MLN or MIN or MHN respectively.
Table3.1 Fly ash classification system (data source Prakash and Sridharan 2007)
Use of dual symbols:
Non-Plastic
More than 50% of fines is in the
particle
MLN
size range
inorganic coarse silt
sized fractions
If more than 50% of
fines is in the range
7.m<particle
size<m, which is
(m<particle size<m)
also more than the
percentage of
combined medium silt
More than 50% of fines is in the
MIN
particle size range (7.m<particle
Non-Plastic
and (fine silt+clay)
inorganic medium
size fractions, then
silt sized fractions
use MLN-MIN
size<m)
If more than 50% of
fines is in the range
Non-Plastic
More than 50% of fines is in the
MHN
inorganic(fine
particle size range , particle
silt+clay)sized
size<7.m
fraction
particle size
<m,which is also
more than the
percentage of
combined coarse silt
and medium silt size
fractions,then use
MIN-MHN
The typical chart Table3.1 have shown the classification of fly ashes passing through
more than half of the material through 0.075 mm sieve size.
3.6 Engineering Properties
The bulk utilization of coal ashes in geotechnical applications such as construction of
embankments, back filling, construction of roads and the like. A clear idea of all
engineering properties of fly ashes is essential for any planning and execution of civil
engineering project.
3.6.1 Compaction Characteristics
From compaction curve, the maximum value of dry density is important parameters for
strength, permeability and compressibility calculation. The engineering properties
improve only due to densification of fly ash. The maximum unit weight of material
depends upon the method of energy applications, plasticity characteristics, grain size
23 | P a g e
variation, and moisture content at compaction state. The variation of dry density with
moisture content is less as compared to well graded soil. For wide variation of change in
specific gravity of fly ashes with those of soils, it needs to compare the normalized values
of moisture content and normalized values of dry unit weight, of fly ash with those of
soils
Normalized dry unit weight= dn=dm[Gstd/Gm]
Normalized water content = wn=wm[Gm/Gstd]
With knowledge of the water density relation as determined by this test, better control of
the field compaction of soil fill is possible. This standard IS: 2720 (Part VII) – 1980 lays
down the method for the determination of the relation between the water content and the
dry density of soils using light compaction, in which a rammer of 2.6 kg mass with fall of
310 mm is used to compact the soil in the mould in three layers, each layer being
subjected to 25 blows of the rammer.
3.6.2 Permeability Characteristics
The use of this test is to determine the permeability (hydraulic Conductivity) of fly ash by
the variable head permeability test. The coefficient of permeability (or hydraulic
conductivity) refers to the ease with which water can flow through a soil. The coefficient
of permeability of fly ashes falls in the range of ‘k’ of silts. This property is essential for
the calculation of seepage through earth dams or under sheet pile walls, the calculation of
the seepage rate from waste storage facilities (landfills, ponds, etc.). The Permeability of
fly ash depends upon grain size, degree of compaction, pozzolanic activity etc. The codal
provision follows for this experiment is IS: 2720 ( Part 17 ) – 1986 . Calculate the
permeability, using the following equation:
K=[(a*L)* loge(h1/h2)]/(A*t)
The variable head test is preferred, because of permeability of most of fly ashes falls in
the range of ‘k’ of silts. The particles are able to densely pack during compaction,
resulting in comparatively low values of permeability and minimum seepage of water
through fly ash embankment.
3.6.3 Unconfined Compressive Strength
Unconfined compressive test can exist for clays by virtue of their cohesion component of
the shear strength, which arises due to capillary stress and also it is the strength obtained
24 | P a g e
by testing the material specimen of standard diameter i.e., L/D=2 and height having a
known dry density and water content under a gradually increasing axial compressive
load. This is used to calculate the differential settlement calculation of fly ash embedded
structure. The UCS test were performed according to IS: 2720 (Part X)-1991.
3.6.4 Lime Fixation
Due to low shear strength of fly ash various studies have been made to stabilize using
lime. Variation of the strength of fly ash due to the addition of lime is controlled by
following mechanism, formation of cementitious compounds due to pozzolanic reactions,
which increases the strength. Most of the fly ashes are characterized by the low free lime
content, in spite of having appreciable reactive silica in them. However, the most
important point is the finding of the optimum lime percentage. In the present study, the
optimum amount of lime, known as lime fixation point, it is defined in terms of the lime
content with maximum unconfined compressive strength (UCS), beyond which the UCS
either remains constant or decreases. The UCS strength is performed for lime fixation.
The UCS test were performed according to IS: 2720 (Part X)-1991.
3.6.5 Shear Strength From Direct Shear Box Test
The purpose of this test was to calculate cohesion (cu) and angle of friction (ɸu) of fly ash.
As fly ash is non-cohesive at un-disturbed state, sample was made at its OMC. Fly ash
specimen was made at OMC, and then it is prepared by pushing a cutting square size of
plate. The lower part of shear box which bear against the load jack was set along the
upper part of the box to bear against the proving ring. Dial of the proving ring was set to
zero. The shear parameters samples at their corresponding MDD and OMC were
determined according to IS: 2720 (Part XIII) 1986.These samples were of size
60mm×60mm×25mm.
3.6.6 Shear Strength From Triaxial Shear Tests
The useful laboratory test conducted to determine the shear strength of soils is the triaxial
shear test. Shear tests, namely unconsolidated undrained shear test, consolidated
undrained shear test with or without pore pressure and consolidated drained shear test,
can be conducted with ease using the standard triaxial shear test set up. For fly ashes, the
effective friction angle is relatively high. For pozzolanic fly ash, another factor that
affects the shear strength parameters is the curing period. For immediate fly ash testing,
25 | P a g e
the shear parameters depends upon apparent cohesion, which is due to capillary stress
arise. Upto this part the undrained shear strength parameters of typical fly ashes
compacted to their dmax has been carried out according to IS 2720 ( Part 11) : 1993
3.6.7 California Bearing Ratio (CBR)
In geotechnical engineering practice, the ratio of the force per unit area required to
penetrate a specimen of soil with a circular plunger of standard size at a standard rate to
that required for the corresponding penetration of a standard material is known as
California Bearing Ratio (CBR). IS: 2720-Part 16(1979) specifies the diameter of the
plunger as 50 mm and the rate of penetration as 1.25 mm/minute. For low lying area
drainage is poor, so that submergence of road occurs, then soaked CBR values are useful.
3.6.8 Dispersiveness
The ability of any particulate matter such as soils and coal ashes to get dispersed in water
and washed away is known as its dispersiveness. The non-plastic nature of the material
contributes to dispersiveness. Non-dispersive materials are best suited for bulky
structures like embankment, dyke and all kinds of water retaining structures. The
laboratory test, double hydrometer test has been performed for dispersiveness. According
to this method:
Table3.2 classification of dispersive soils based on double hydrameter test (data source Prakash and
Sridharan 2007)
Degrees of Dispersion: %
Classification
<35
Non-dispersive
35-50
Moderately dispersive
50-75
Highly dispersive
>75
Extremely dispersive
In double hydrometer test, based on hydrometer analysis IS:2720(Part4)-1985 the
dispersion ratio is defined as the ratio of the percentage finer than 0.005mm diameter
measured without any dispersion agents in a hydrometer test to that measured with
dispersion agents, which is expressed in percentage. The percentage of dispersion is an
indicator of the ability of soils to erode due to their dispersiveness as shown in Table3.2.
26 | P a g e
3.6.9 Angle of Repose
The angle of repose is the steepest angle of the slope relative to the horizontal plane when
material on the slope face is on the verge of sliding. In general it refers to the maximum
angle at which an object can rest on an inclined plane without sliding down. The internal
angle between the inclined surface of the material and the horizontal surface is known as
the angle of repose and is depends mainly upon to the density, surface area and shape of
the particles and the coefficient of friction of the material. The angle is in the range of 0o
to 90o.The dry fly ash is poured into a cylindrical pipe on a level surface and made it full.
Using the ruler top of the surface of fly ash leveled and then cylindrical mould was lifted
up. The fly ash mound was placed like a conical shape. The height of the tip of the
conical shaped fly ash and the diameter of the spread is measured in terms of height and
radius of spread.
27 | P a g e
CHAPTER 4
Result & Discussion
28 | P a g e
4.1 Introduction
The following test to characterize the chemical properties of fly ashes has been
elaborated as follows. The following tests have been conducted to characterize the
sample of fly ash which has been collected from kalunga, NTPC, TTPS and NALCO
thermal power plant.
4.2 Chemical Properties
4.2.1 Chemical Composition
From, the present study Table4.1 it shows, that the alumina contain is less than, that
of silicon dioxide and calcium oxide contain is less than 10%. Hence, these are the
type of class F fly ash. The formation of calcium silicate and aluminium silicate is
more in case of NALCO fly ash, which accelerates the lime reactivity process. More
iron content in Kalunga fly ash leads to other fly ashes, cause more compressive
strength than others.
Table4.1 Chemical composition of fly ashes of present study and some of Indian fly ashes
*(data source Prakash and Sridharan 2007)
SOURCE
SiO2
Al2O3
Fe2O3
MgO
CaO
K2O
Na2O
LOI
MC
TTPS
40.01
26.82
14.09
4.4
4.74
4.81
3.95
0.63
0.55
Kalunga
29.49
19.46
26.82
3.26
6.59
5.46
-
7.68
1.24
NTPC
37.06
29.02
13.97
4.24
5.23
4.99
4.31
0.70
0.48
NALCO
41.65
22.38
15.04
4.76
4.75
5.82
4.72
0.50
0.38
Source
SiO2
Al2O3
Fe2O3
MgO
CaO
K2O
Na2O
LOI
MC
Neyveli*
38.78
44.24
4.13
0.02
7.87
0.05
0.44
3.47
1.05
Ghaziabad*
53.22
38.14
3.44
0.24
1.01
0.67
0.14
3.04
0.10
Badarpur*
58.45
32.38
4.71
0.23
0.63
0.61
0.23
2.71
0.05
Rihand*
57.94
34.28
5.86
0.40
0.20
0.51
0.30
0.51
-
Raebareli*
60.57
31.10
4.27
0.41
0.91
0.71
0.20
-
1.83
The loss on ignition of Kalunga fly ash is more than other fly ashes. With respect to present
study, there is large variation in weight percentage, studied by sridharan(2007). The quartz and
mullite percentage are less as compared to previous study, while the oxides of magnesium,
29 | P a g e
potassium and sodium are more for present study. The iron percentage is also more for the
present study specially to Kalunga fly ash.
4.2.2 X-Ray Diffraction Spectra
A=Kalunga fly ash
B=NALCO fly ash
C=NTPC fly ash
D=TTPS fly ash
Fig4.1 X-ray diffraction spectra of fly ashes, present study
The XRD spectra Fig4.1 of four fly ashes named as A (Kalunga fly ash), B
(NALCO fly ash), C (NTPC fly ash) and D (TTPS fly ash) are follows. In all
cases approximately, same number of peaks are shown with little bit different
amount of peaks. The maximum no of peaks in crystalline nature is find out for
quartz and mullite. Instead of these calcium and hematite are also present in
crystalline state. The fly ash contains both amorphous and crystalline phases of
minerals. Besides major elements, it also contains oxides of magnesium,
potassium or sodium with little amount. If the fly ashes contain presence of
unburnt carbon, there will be loss on ignition.
4.2.3 Morphology
The morphological study through SEM indicates that, the NALCO fly ash
Fig4.2 contains cenospheres with small agglomerates, while that of TTPS fly
ash Fig4.3 contain cenospheres without agglomerates and contains single cells.
30 | P a g e
In both the cases, fly ash contains glassy solid spheres. In case of NTPC fly
ash, Fig4.4 with addition cenospheres, some hollow spheres called as
plerospheres are also present with maximum of single grained cells.
Fig4.2 Surface morphology of NALCO fly ash sample
Fig4.3 Surface morphology of TTPS fly ash sample
31 | P a g e
Fig4.4 Surface morphology of NTPC fly ash sample
Fig4.5 Surface morphology of KALUNGA fly ash sample
In case of kalunga fly ash Fig4.5 which shows that, it is different from other fly ashes
from the surface morphology. It indicates the presence of sub rounded porous grains,
irregular agglomerates and irregular porous grains of unburned carbon. The kalunga fly ash
looks like spotted as opaque spheres and angular grains, which indicates the presence of
magnetite, which is dark gray in color.
32 | P a g e
4.2.4 pH of Fly Ashes
Table4.2 pH values of fly ashes for present study and some of Indian fly ashes (*data source Prakash and Sridharan 2007)
Present study
Source
pH
Kalunga
NTPC
7.50
7.30
Sridharan (2007)
TTPS NALCO
6.00
Raebareli*
Korba*
Vijayawada*
Badarpur*
Ghaziabad*
7.36
5.13
7.61
6.07
5.52
6.61
It shows that from Table4.2, approximately 50% of Indian fly ashes are alkaline and other 50% are acidic in nature. It depends
upon the presence of alkaline oxide content and free lime available. As more percentage of CaO available with Kalunga and
NTPC fly ash, it shows alkaline in nature.
4.2.5 Lime Reactivity
The lime reactivity of fly ash primarily depends on presence of reactive silica and formation of aluminium silicate and calcium
silicate gel. For the present study, it shows that there is more values of lime reactivity for TTPS and NALCO fly ash. This is may
be due to presence of more reactive silica present in TTPS and NALCO fly ash, which leads to further formation of aluminium
and calcium silicate gel. The present result also, very much match with the experimental result by Sridharan(2007)
Table4.3 Lime reactivity of fly ashes for present study and some of Indian fly ashes (*data source Prakash and Sridharan 2007)
Present study
Source
Lime reactivity:
kPa
Sridharan (2007)
Kalunga
NTPC
TTPS
NALCO
Raebareli*
Korba*
Neyveli*
Vindayanagar*
Ghaziabad*
2786
3120
3276
3306
3060
2558
2143
3580
3269
As per present study, Table4.3 the lime reactivity of Indian fly ashes are also lies within same range. Hence, the decreasing order
of Lime reactivity is NALCO, TTPS, NTPC and Kalunga fly ashes respectively.
33 | P a g e
4.3 Physical Properties
4.3.1 Specific Gravity
The low values of specific gravity of fly ashes can be mainly attributed to the presence of
more number of cenospheres present. Practically, for Indian fly ashes the range of
specific gravity lies between 1.66-2.55. The following Table4.4 of present study shows
that, the values of specific gravity with respect to distilled water and with kerosene.
Table4.4 Specific gravity of fly ashes with water and kerosene as pore medium, present study
Source
Specific gravity
(water as pore medium)
Specific gravity
(Kerosene as pore medium)
Range
(data
source:Prakash
and Sridharan 2007)
Kalunga
2.41
2.67
NTPC
2.04
2.31
TTPS
2.13
2.58
NALCO
2.21
2.49
1.66-2.55
The increase in specific gravity value with respect to kerosene with that of distilled water
is due to easy expulsion of air from the voids of spherical grain particles. From the study ,
it also shows that there is more value of specific gravity of Kalunga fly ash and it is due
to the presence of more iron particles for Kalunga fly ash, from the chemical composition
chart. Table4.5 shows the range of specific gravity values of Indian fly ashes.
Table4.5 Specific gravity of some of Indian fly ash with water as pore medium
(*data source Prakash and Sridharan 2007)
Source
Specific gravity
(water as pore medium)
34 | P a g e
Korba*
2.04-2.10
Vijayawada*
2.03-2.11
Ghaziabad*
2.12-2.13
Ramagundam*
1.98-2.23
Neyveli*
2.01-2.55
Specific gravity with kerosene as pore medium
3.0
2.5
KALUNGA fly ash
NTPC fly ash
TTPS fly ash
NALCO fly ash
2.0
2.0
2.5
3.0
Specific gravity with water as pore medium
Fig4.6 Vaiation of SG of fly ashes wth water and kerosene
as pore medium, present study
From the equality curve, Fig4.6 it shows that if any non-polar liquid like kerosene is used
as the pore medium instead of water, the removal of air is more effective and higher
specific gravity values are obtained. The ranges of Indian fly ashes, as per experimental
study by Sridharan(2001) are also lies within the values in between 1.66-2.55
4.3.2 Grain Size Distribution
Table4.6 Grain size distribution of fly ashes for present study & some of Indian fly ashes (data source
Prakash and Sridharan( 2007)
Source
Silt size
fraction: %
71.94
Sand size
fraction: %
25.56
Cu
Cc
Kalunga
Clay size
fraction: %
2.50
7.67
1.04
NTPC
2.98
68.67
28.35
9.63
0.61
TTPS
2.76
74.72
22.52
6.83
0.88
NALCO
3.70
79.63
16.67
5.53
1.08
Raebareli*
2.0
70.0
28.0
5.88
0.75
Korba*
1.0
71.0
28.0
6.00
1.14
Vijayawada*
4.5
70.5
25.0
5.70
0.61
Kahalgoan*
6.0
72.0
22.0
4.00
1.50
Rihand*
14.7
78.2
07.0
4.30
1.70
35 | P a g e
From the grain size distribution Table4.6 fly ashes are fine grained substances, consisting
of mainly silt size particles with uniform gradation. From the Table it shows that, fly ash
becomes finer if Cu reduces. The grain size distribution of fly ash have same resemblance
with that of grain size distribution of fly ashes studied by Sridharan(2007).
100
% age finer
80
60
KALUNGA fly ash
NTPC fly ash
NALCO FLY ASH
TTPS fly ash
40
20
0
0.01
0.1
1
Particle size in mm
Fig 4.7 Grain size distribution of fly ashes
for present study
(data source Prakash and Sridharan 2007)
The Fig4.7 shows the grain size distribution curve for fly ashes for present study, which
shows similar nature with gradation of Indian fly ashes. Particle size finess, primarily
depends upon the no of hopper from which sample collected and according to which
grain size gradation changes.
4.3.3 Free Swell Index
Fly ashes exhibits negative free swell indices, it is due to presence of clay particles
present in flocculated structure. More the clay particles, more is flocculation and more is
the swelling. Hence the swelling, in case of kerosene is more, than that of distilled water.
It is due to, more or easy expulsion of air from the voids, as kerosene is a polar liquid. If
more swelling in kerosene, than that of water, fly ash exhibits negative free swell ratio.
36 | P a g e
Table4.7 Free swell ratio of fly ashes for present study and some of Indian fly ashes (data source
Prakash and Sridharan 2007)
Source
Free swell index (%)
Remarks
NTPC
-31.34
NALCO
-35.53
Kalunga
-25.00
TTPS
-30.88
Due to
Raebareli*
-30.10
flocculation
Vijayawada*
-34.40
Badarpur*
-14.30
Ghaziabad*
-35.00
Kahalgoan*
-30.80
From the Table4.7 the present experimental study of fly ashes, resemblances with the
experimental investigation by Sridharan (2007)
4.3.4 Specific Surface
As the fly ashes primarily contain silt size particles, there specific surface area is quite
low as compared to kaolinite which is coarsest clay mineral. The specific surface area of
fly ash is influenced by gradation of fly ash particles. If more than 50% of fines are silty,
then it depends upon silt size particles present with it. Primarily, it also depends upon
ESP hoppers from which fly ash are collected. If more no of hoppers are present, finer the
fly ash particles.
Table4.8 Specific surface area of fly ashes for present study
Source
Specific surface: m2/kg
Kalunga
297.3
TTPS
138.5
NALCO
192.1
NTPC
106.5
If more is the specific gravity value, finer the ash particles and more is the specific
surface area. Range of specific surface of Indian fly ashes (data source: Sridharan et al.,
2001e) are 130-530 m2/kg. Present study Table4.8 also lies between the specified ranges
37 | P a g e
of Indian fly ashes. The more value of specific surface for Kalunga fly ash is due to
presence of more pore spaces available with it.
4.3.5 Geotechnical Classification System For Fly Ash
The fly ashes are satisfactorily classified based upon particle size distribution and
gradation characteristics. The present study shows that, there is more percentage of
coarse silt size fractions among all others. But, from the experimental investigation by
Sridharan (2007), it shows that there is all most equal proportion of sand size and coarse
silt size fraction. However, from present study and by Sridharan (2007) Table4.9 study all
sources of fly ash particles are categorize under MLN-MIN.
Table4.9 Fly ash classification system of fly ashes and Indian fly ashes (data source *Prakash and
Sridharan 2007)
Particle size distribution:
%
Source
G
Clay
size
Silt
size
Sand
size
Distribution of fines as a
percentage of total fraction
passing 75m size
Fine
Medium Coarse
silt
silt
silt
Kalunga
NTPC
TTPS
NALCO
2.41
2.04
2.13
2.21
2.50
2.98
2.76
3.70
71.94
68.67
74.72
79.63
25.56
28.35
22.52
16.67
6.29
5.52
5.05
4.73
Particle size distribution:
%
9.63
11.56
8.19
5.91
56.02
51.59
61.48
68.98
Source
G
Clay
size
Silt
size
Sand
size
Distribution of fines as a
percentage of total fraction
passing 75m size
Fine
Medium Coarse
silt
silt
silt
Raebareli*
Korba*
Vijayawada*
Kahalgoan*
2.05
1.98
1.95
2.21
2.55
2.00
1.00
4.50
6.00
9.50
70.00
71.00
70.50
72.00
63.90
28.00
28.00
25.00
22.00
26.60
3.9
9.1
8.9
4.8
5.5
Neyveli*
38 | P a g e
18.6
14.5
19.8
23.0
34.5
27.3
27.3
23.0
30.0
12.0
Classification
MLN-MIN
MLN-MIN
MLN-MIN
MLN-MIN
Classification
MLN-MIN
MLN-MIN
MLN-MIN
MLN-MIN
MLN-MIN
4.4 Engineering Properties
4.4.1 Compaction Characteristics
From the Fig4.8 shows that compaction curves of fly ashes are relatively flatter due to lower specific gravity, uniformly graded
particles, presence of more cenospheres which are dominating factors controlling the compaction behavior of fly ashes. Since,
the actual compaction curve of fly ashes not possible to compare with those of soils, it is essential to replot the actual value
with normalized values.
KALUNGA fly ash
NTPC fly ash
TTPS fly ash
NALCO fly ash
13.0
12.8
KALUNGA fly ash
NTPC fly ash
TTPS fly ash
NALCO fly ash
17
16
Normalized Dry unit weight kN/m
3
12.6
Dry unit weight kN/m
3
12.4
12.2
12.0
11.8
11.6
11.4
11.2
11.0
10.8
10.6
15
14
13
12
10.4
10.2
11
16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46
Moisture content %
Fig4.8 Compaction curves of fly ashes, present study
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
Normalized Moisture content %
Fig4.9 Normalized compaction curves of fly ashes, present study
The second Fig4.9 is the normalized value of the compaction curve, which facilitates the comparison between compaction
characteristics of fly ashes with that of soils. From the present study, the fly ashes are relatively flatter indicating the water
insensitive (i.e., low dmax and more OMC) and this is due to increased resistance offered by pozzolanic reaction. More void
spaces and pore spaces are present in Kalunga fly ash, for which water content is more and giving low value of dry density as
39 | P a g e
comparison to other fly ashes. In general for fly ashes for compactive effort, if u value is more, it gives more d value. Further
it showed that, OMC is directly and MDD is inversely proportional to LOI. Compared to soil with organic content fly ash
exhibit lower dmax and higher OMC due to presence of hollow and solid spheres. The following Table4.10 shows the MDD and OMC
values of experimental result and some of Indian fly ashes.
Table4.10 Compaction characteristics of fly ashes for present study and some Indian fly ashes *(data source Prakash and Sridharan 2007)
sources
Maximum dry
Optimum
density(MDD)
moisture
3
in kn/m
content(OMC)
Normalized
Maximum dry
density(MDD)
in kn/m3
Normalized
Optimum
moisture
content(OMC)
in %
in %
Indian fly
ashes range
NTPC
12.65
23.9
16.44
18.40
NALCO
13.05
20.1
15.64
16.76
Kalunga
11.48
37.3
12.62
33.92
TTPS
12.95
22.4
16.11
18.00
OMC:%
17.9-62.3
d:kN/m38.9-
Badarpurl*
11.0
36.9
13.8
29.5
13.8
Ramagundam*
13.8
24.2
16.4
20.4
Ghaziabad*
12.2
33.2
15.2
26.7
From the experimental study by Sridharan (2007), the present studies are more correlates. The present study of MDD and
OMC lies in the range between the values of Indian fly ashes.
40 | P a g e
4.4.2 Permeability Characteristics
The self cementing and pozzolanic fly ashes tend to have low permeability than the non
pozzolanic fly ashes, due to the formation of pozzolanic compounds that reduce the
permeability appreciably with time in the field. The low values of permeability of fly
ashes can be considered as additives in the construction of seepage cutoffs like
impervious blankets and cores in earth water retaining structures and also lessen the
probability of ground water pollution. The permeability values of Table4.11 present study
and some of Indian fly ashes are as shown:
Table4.11 Permeability values of fly ashes, present study and Indian fly ashes data source (data
source Prakash and Sridharan 2007)
Coefficient of
Source
permeability
(-*10^-3): mm/s
NTPC
0.393
Kalunga
0.440
NALCO
0.360
TTPS
0.386
Vijayawada*
0.340
Ghaziabad*
0.190
Neyveli*
0.320
Korba*
0.919
From the present study, we can say that if more void ratio or more pore spaces are present
it leads to more permeable. More d value, fly ash exhibits less permeable. Less
pozzolanic effect contributes to, more permeability. The table shows that, the permeable
values of some of Indian fly ashes, which are approximately close to experimental result.
The co-efficient of permeability is defined as the velocity of flow (v) through the porous
material per unit hydraulic gradient (i).
41 | P a g e
4.4.3 Unconfined Compressive Strength
4.4.3.1 Lime Fixation Curve
For the present study all are categorize with low calcium fly ash i.e, class F fly ash.
Fig4.10 shows the variation of UCS value with lime content of fly ashes for the present
study and it can be seen that UCS value increase with lime content upto lime fixation
point .
900
850
800
TTPS fly ash
NTPC fly ash
NALCO fly ash
KALUNGA fly ash
750
700
UCS kPa
650
600
550
500
450
400
350
300
250
200
0
1
2
3
4
5
6
7
8
9
CaO %
Fig4.10 Effect of lime addition on UCS strength of fly ashes
With additional increase in lime the UCS value appreciable constant for all the fly ashes.
Lime fixation point depends upon lime reactivity. Since, availability of reactive silica is
restricted for Kalunga and NTPC fly ash; it shows low values of lime fixation i.e., both
are 6% respectively. But, the lime reactivity of NALCO and TTPS fly ash has
appreciable more than Kalunga and NTPC fly ash, hence more lime i.e, 7% require for
lime fixation for both the fly ashes. If present of reactive silica is unavailable, addition of
any amount of lime will not effective.
4.4.3.2 Variation Of UCS Value With MC
For the present study with respect to MC, the UCS values of fly ash samples were tested.
For the optimization result the starting water content was first water content attained from
the standard proctor compaction test. The unconfined compressive strengths of specimens
were determined from strain-stress curves plots for different water content for all the fly
42 | P a g e
ashes. Partly saturated compacted fly ash exhibits some unconfined compressive strength
when tested in an unsoaked condition. This can be attributed to the capillary stresses and
pozzolanic action, induced shear strength or apparent cohesion.
500
450
400
NALCO fly ash
TTPS fly ash
NTPC fly ash
KALUNGA fly ash
UCS in kPa
350
300
250
200
150
100
50
15
20
25
30
35
40
MC %
Fig4.11 Effect of UCS with change in MC
For all the fly ashes shown in Fig4.11, there is variation of UCS values with change in
moisture content. The curve shows similar nature, that of fine sand. Same observations
have also made by Das and Yudhbir (2005) for MC and UCS relationship.
Table4.12 Variation of UCS with MC, present study
NALCO
Moisture
UCS kPa
content (%)
16.3
151.55
18.0
154.84*
20.1 OMC*
108.72
21.6
68.83
NTPC
Moisture
UCS kPa
content (%)
18.3
239.03
19.9
297.27
21.7
280.03*
23.9 OMC*
251.67
25.4
230.62
TTPS
Moisture
UCS kPa
content (%)
14.7
223.57
17.8
261.60
20.2
272.23*
22.4 OMC*
244.42
Kalunga
Moisture
UCS kPa
content (%)
27.3
377.50
30.6
407.47
34.2
478.53*
37.3OMC*
476.48
40.5
450.19
From the above Table4.12 ,the unconfined compressive strength for as compacted test
samples both on dry and wet of optimum for NALCO, NTPC, TTPS, Kalunga fly ashes
have given. The dry side of optimum value gives more strength, then wet side of
optimum .The variation of unconfined compressive strength with water content is similar
to that of very fine sand. The result shows that for a given dry density, the apparent
43 | P a g e
cohesion increases with degree of saturation and reaches a maximum. Additional
saturation decreases the apparent cohesion.
4.4.4 Shear Strength From Direct Shear Box Test
For Direct shear Box test, the existence of cu in compacted state is due to presence of
capillary stresses for partial saturation. Under compacted condition, fly ash exhibits
apparent cohesion. The values of u reduced upon saturation with moisture content
available. Fig4.12 indicate the failure envelops of fly ashes under as compacted
conditions and Table4.13 lists the shear strength parameters of fly ashes from direct shear
box test.
Table4.13 Shear strength parameters by Direct shear box Test, present study and Indian fly ashes
*(data source Prakash and Sridharan 2007)
Source
As-compacted condition
Cu: kPa
44 | P a g e
u: degrees
Kalunga
24.39
35.06
NTPC
23.27
34.93
TTPS
22.48
34.69
NALCO
21.69
33.18
Raibareli*
23
34
Korba*
22
34
Badarpur*
26
32
Ramagundam*
23
33
Kalunga fly ash
NTPC fly ash
TTPS fly ash
NALCO fly ash
130
120
Shear stress kPa
110
100
90
80
70
60
50
40
60
80
100
120
140
160
Normal stress kPa
Fig4.12 Failure envelopes from direct shear box tests on fly ashes as in compacted state
From the present study, it found that the cohesion component is due to the capillary stress
arises, which induced apparent cohesion. With increase in water content the frictional
value decreases.
4.4.5 Shear Strength From Triaxial Shear Test
The most useful laboratory test conducted to determine the shear strength parameters of
fly ash is the triaxial shear test. In this study an effort was also made to find out the effect
of curing on the shear strength parameters of stabilized fly ash. At the optimum lime
content the strength increases with days of curing.
45 | P a g e
confining stress 98.1kPa
confining stress 196.2kPa
confining stress 294.3kPa
1000
confining stress 98.1 kPa
confining stress 196.2 kPa
confining stress 294.3 kPa
1400
900
1200
800
Deviator stress kPa
Deviator stress kPa
700
600
500
400
300
1000
800
600
400
200
200
100
0
0
0
1
2
3
4
5
6
7
8
0
9
1
2
3
4
5
Fig4.13 Strain-stress curve of Kalunga fly ash with no curing
7
8
Fig4.14 Strain-stress curve of Kalunga fly ash with 7 days curin
confining stress 98.1 kPa
confining stress 196.2kPa
confining stress 294.3kPa
2
confining stress 98.1kN/m
2
confining stress 196.2 kN/m
2
confining stress 294.3 kN/m
1000
6
Axial strain %
Axial strain %
1400
1300
1200
1100
1000
Deviator stress kPa
Deviator stress kPa
800
600
400
900
800
700
600
500
400
300
200
200
100
0
0
0
2
4
6
8
10
Axial strain %
Fig4.15 Strain-stress curve of NALCO fly ash with no curing
46 | P a g e
0
1
2
3
4
5
6
7
8
Axial strain %
Fig4.16 Strain-stress curve of NALCO fly ash with 7 days curing
confining stress 98.1kPa
confining stress 196.2 kPa
confining stress 294.3 kPa
850
900
800
750
800
700
650
700
600
Deviator stress kPa
Deviator stress kPa
confining stress 98.1 kPa
confining stress 196.2 kPa
confining stress 294.3 kPa
550
500
450
400
350
300
250
200
600
500
400
300
200
150
100
100
50
0
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
0
1
2
3
4
Axial strain %
5
6
7
8
9
Axial strain %
Fig4.17 Strain-stress curve of NTPC fly ash with no curing
Fig4.18 Strain-stress curve of NTPC fly ash with 7 days curing
confining stress 98.1 kPa
confining stress 196.2 kPa
confining stress 294.3 kPa
1000
confining stress 98.1 kPa
confining stress 196.2 kPa
confining stress 294.3 kPa
1000
900
800
Deviator stress kPa
Deviator stress kPa
800
600
400
200
700
600
500
400
300
200
100
0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
Axial strain %
Fig4.19 Strain-stress curve of TTPS fly ash with no curing
47 | P a g e
0
2
4
6
8
Axial strain %
Fig4.20 Strain-stress curve of TTPS fly ash with 7 days curing
The above curves Fig4.13-Fig4.20 show the variation of deviator stress with change in
axial strain for the Kalunga, NALCO, NTPC and TTPS fly ash respectively.
Table4.14 Variation of undrained shear strength parameters of fly ashes with curing period,present
study
Source
Fresh sample
7 days curing
Cu: kPa
u: degrees
Cu: kPa
u: degrees
NALCO
24.68
36.45
70.06
42.15
TTPS
25.39
35.31
71.61
40.87
NTPC
26.63
33.94
72.37
39.12
Kalunga
82.19
30.03
140.74
46.92
The shear parameters of the stabilized fly ash samples for immediate and after
seven days of curing have shown in Table4.14. From the Table and curve
shown above, shear parameters of NALCO fly ash has better values than TTPS
fly ash, which is better than NTPC fly ash. After seven days curing the increase
shear parameters had also same trend as it was before. Hence, it shows better
lime reactivity or reactive silica present in NALCO fly ash than the other two
fly ashes.
From the present study which gives the accurate values of shear parameters,
gives the idea about apparent cohesion and pozzolanic effect. The fly ash study,
for fresh fly ash sample the cohesion component is due to capillary stress and the
angle of internal friction is due to both combined effect of pozzolanic effect and
maximum dry density of fly ash achieve.
After seven days curing, the pozzolanic effect of fly ash plays important role for
cohesion and angle of internal friction, which increases with addition of lime.
Further the angle of internal friction is the main strength criteria for fly ashes,
which is proportional to increase dry density.
Further the curve Fig4.21-Fig4.24 shown below the variation of deviator stress
with change in axial strain with different days of curing. The increase in deviator
stress value with curing for different fly ashes is due to its lime reactivity value.
48 | P a g e
fly ash 3 days of curing
fly ash 5 days of curing
fly ash 7 days of curing
1000
700
600
Deviator stress kPa
800
Deviator stress kPa
fly ash 3 days of curing
fly ash 5 days of curing
fly ash 7 days of curing
800
600
400
500
400
300
200
200
100
0
0
0
1
2
3
4
5
6
0
1
2
3
Axial strain %
Fig4.21 Strain-stress curve of KALUNGA fly ash after 3,5,7 days of curing
550
5
6
7
8
Fig4.22 Strain-stress curve of NALCO fly ash after 3,5,7 days of curing
fly ash 3 days curing
fly ash 5 days curing
fly ash 7 days curing
fly ash 3 days curing
fly ash 5 days curing
fly ash 7 days curing
600
4
Axial strain %
600
500
500
Deviator stress kPa
Deviator stress kPa
450
400
350
300
250
200
400
300
200
150
100
100
50
0
0
0
1
2
3
4
5
6
7
8
Axial strain %
Fig4.23 Strain-stress curve of NTPC fly ash after 3,5,7 days of curing
49 | P a g e
0
1
2
3
4
5
6
7
8
9
Axial strain %
Fig4.24 Strain-stress curve of TTPS fly ash after 3,5,7 days of curing
Table4.15 Variation of Maximum Deviator stress value with change in curing period, present study
Source
NALCO
3 days curing:Deviator
stress kPa
633.30
5 days curing: Deviator
stress kPa
660.45
7 days curing: Deviator
stress kPa
728.43
TTPS
564.77
573.71
588.04
NTPC
352.24
411.15
550.10
Kalunga
863.66
977.80
1011.42
Maximum Deviator Stress Vs Lime Content Curve
3 days curing
7 days curing
1700
750
1600
700
Deviator stress kPa
Deviator stress kPa
1800
1500
1400
1300
1200
1100
1000
3 days curing
7 days curing
800
650
600
550
500
450
900
400
800
0
1
2
3
4
5
6
7
8
CaO %
Fig4.25 Kalunga fly ash CaO vs Deviator stress curve
50 | P a g e
0
1
2
3
4
5
6
7
8
CaO %
Fig4.26 NALCO fly ash CaO vs Deviator stress curve
3 days curing
7 days curing
3 days curing
7 days curing
565
480
560
475
555
470
550
545
Deviator stress kPa
Deviator stress kPa
465
460
455
450
445
440
540
535
530
525
520
515
435
510
430
505
500
425
495
420
0
2
4
6
8
0
CaO %
Fig4.27 NTPC fly ash CaO vs Deviator stress curve
2
4
6
8
CaO %
Fig4.28 TTPS fly ash CaO vs Deviator stress curve
From the above graph shown Fig4.25-Fig4.26, there is significant amount of increase in maximum deviator stress with
increase in curing period. The increase deviator stress with increase curing period is more significant for 28 days curing, but
however the increase in strength from three to seven days curing is due to pozzolanic effect of fly ash which depends upon the
lime reactivity of fly ash with addition of lime. With the effects of curing and lime addition the maximum stress values
increase considerably. The maximum value of deviator stress increased with curing period and with addition of lime mix. The
above Fig4.25 shows Kalunga fly ash sample and Fig4.26 shows fly ash for NALCO sample for maximum deviator stress with
lime addition whereas the NTPC and TTPS fly ashes are in between.
51 | P a g e
The above two Fig4.27 and Fig4.28 shows the variation of maximum deviator stress with
lime for NTPC and TTPS fly ash respectively.
A considerable strength increases with increase of lime and curing period, drawn from
triaxial compression test. Increase in curing period of lime treated fly ash specimen show
improvement in the deviator stress value. However the gain in strength with curing period
is more in initial days of curing which tends to decreases with increase in curing period.
Table4.16 Variation of Maximum Deviator stress value with change in CaO value and curing
period,present study
Source NALCO
Kalunga
NTPC
TTPS
CaO:
3 days
7 days
3 days
7 days
3 days
7 days
3 days
7 days
%
curing
curing
curing
curing
curing
curing
curing
curing
448.13
474.62
496.14
552.05
0
2
390.02
599.43
865.36
1019.47
453.04
478.54
527.53
563.26
4
540.17
627.67
1290.36
1316.98
441.26
480.50
519.68
558.41
6
545.08
779.63
1521.11
1764.26
422.62
481.48
507.91
555.13
8
519.12
730.08
1414.81
1710.07
423.61
475.60
502.02
539.30
From the Table4.16 above shown that, the increase trend in deviator stress value is more
incase of NALCO fly ash followed by TTPS and NTPC fly ashes, which further
illustrates the pozzolanic activity order.
4.4.6 CBR
The fly ashes, a fine-grained material, when placed at of Proctor maximum dry density
and corresponding water content, exhibits capillary forces, in addition to friction resisting
the penetration of the plunger and thus high values of CBR are obtained.
52 | P a g e
Table4.17 CBR values of fly ashes under unsoaked and soaked condition and some Indian fly
ashes(data source Prakash and Sridharan 2007)
Source
CBR:%
Un soaked condition
Soaked condition
NTPC
6.94
0.66
NALCO
12.26
0.74
TTPS
5.29
0.86
Kalunga
22.49
5.73
Korba*
13.8
0.2
Vijayawada*
20.6
0.2
Ghatiabad*
18.9
0.2
From the Table4.17 it shows that the fly ash having more CBR values, this is because of
more silt size particles and more fine sand size particles present from grain size
distribution curve. The load- penetration curves for fly ash compacted at Proctor’s
maximum dry densities both unsoaked Fig4.29 and soaked Fig4.30 condition are as:
KALUNGA fly ash
NTPC fly ash
NALCO fly ash
TTPS fly ash
8
Load in kN
6
4
2
0
0
2
4
6
8
10
12
Penetration in mm
Fig4.29 CBR curves of fly ashes under unsoaked condition
53 | P a g e
3.5
3.0
Load in kN
2.5
2.0
NTPC fly ash
KALUNGA fly ash
NALCO fly ash
TTPS fly ash
1.5
1.0
0.5
0.0
0
2
4
6
8
10
12
Penetration in mm
Fig4.30 CBR curves of fly ashes under soaked condition
On the contrary, when fly ash samples for four days soaked condition, under some
placement condition, they exhibit low values of CBR. This can be attributed to further
destruction of capillary forces under soaked condition.
4.4.7 Dispersiveness
According to double hydrometer test, the degrees of dispersion of four different fly ashes
are as follows:
Table4.18 Classification of dispersive soils based on double hydrometer test results (data source
Prakash and Sridharan 2007)
Source
Degree of Diepersion: %
Classification
TTPS
57.17
Highly dispersive
NTPC
83.33
Extremely dispersive
NALCO
38.33
Moderately
dispersive
Kalunga
22.31
Non dispersive
From the Table4.18, it shows that the NTPC fly ashes are extremely dispersive due to,
more percentage of fine particles are present followed by TTPS fly ash and NALCO fly
54 | P a g e
ash. Hence this property plays vital role for mass application such as retaining wall
structure, embankment and dykes. The Non dispersiveness of Kalunga fly ash particles is
may be due to present of heavy metals.
4.4.8 Void Ratio
Table4.19 emax and emin values of fly ashes, present study
Source
emax
emin
Kalunga
2.391
1.130
NTPC
1.211
0.457
TTPS
1.380
0.545
NALCO
1.502
0.599
The relative emax and emin values of fly ash are as above Table4.19. The above values are
like that, more pore spaces are present in Kalunga fly ash, which exhibits more emax and
emin value. The other fly ashes are, varies according to their coarse silt size fraction.
Table4.19 shows the present study of different fly ashes having different void ratio in
maximum and minimum condition.
4.4.9 Liquid Limit Test
The experimental result of present, fly ashes Table4.20 have significant amount of water
content at liquid limit. This variation is due to more silt size fraction present. If more silt
size is present less will be liquid limit value. This is because, if some silt are added to the
clay, the liquid limit value decreases
Table4.20 Liquid limit values of fly ashes, present study
Source
Water content:%
NTPC
32.86
NALCO
24.56
TTPS
28.44
Kalunga
47.01
Table4.20 shows the different liquid limit values of fly ashes for present study.
55 | P a g e
CHAPTER 5
Conclusion
56 | P a g e
5.1 Concluding Remark
Based on the present project work, the following conclusions can be made:
1. Fly ashes considered in the present study are of Class F fly ash with CaO containt
less than 10%.
2. The NALCO fly ash contains cenospheres with small agglomerates whereas
TTPS fly ash contains cenospheres with single cells without agglomerates, NTPC
fly ash both contains cenospheres and plerospheres. Kalunga fly ash contains subrounded porous grains, irregular agglomerates and irregular porous grains of
unburnt carbon.
3. The samples in the decreasing order of lime reactivities of fly ashes are NALCO,
TTPS, NTPC and Kalunga samples respectively. Lime reactivity depends upon
the presence of reactive silica.
4. Specific gravity found in present study are 2.41, 2.21, 2.13 and 2.04 for Kalunga ,
NALCO, TTPS , NTPC fly ash respectively. If more iron particles are present ,
specific gravity is more as in Kalunga fly ash but however specific gravity of fly
ashes are small due to more number of cenospheres are present.
5. From the present study, the grain size distribution of fly ashes are uniformly
graded silty particles and Cu value reduces with increase in finess of fly ash.
6. The free swell ratio for NALCO, NTPC, TTPS and Kalunga fly ash are -35.53%,
-31.34%, -30.88% and -25.00% respectively.
7. The samples in the decreasing order of specific surface area are Kalunga,
NALCO, TTPS and NTPC fly ashes respectively.
8. The fly ashes considered for the present study belong to the category of MLNMIN.
9. The lime fixation point of Kalunga & NTPC fly ashes are 6% whereas NALCO
& TTPS fly ashes are 7% respectively. UCS value increased when lime increased
upto lime fixation point.
10. From the present study fly ashes compacted dry side of optimum give more
strength than wet side of optimum.
57 | P a g e
11. From triaxial shear test, samples with shear parameter values in decreasing order
are Kalunga, NTPC, TTPS and NALCO fly ash samples. Fly ash exhibits, more
of its shear strength from internal friction and exhibits some amount of apparent
cohesion.
12. The decreasing order of CBR values for the
present study are in order of
Kalunga, NALCO, NTPC and TTPS fly ash samples respectively. Low value of
CBR under soaked condition is due to destruction of capillary forces under soaked
condition. This indicates that CBR value of compacted fly ash is very susceptible
to degree of saturation.
13. The decreasing order of degree of dispersions are in order of NTPC, TTPS ,
NALCO and Kalunga fly ash samples .
14. Its low specific gravity, freely draining nature, ease of compaction, good frictional
properties, pozzolanic activity etc can be gainfully used for construction of
embankment, roads and fill behind a retaining structure.
5.2 Scope for Further Study
Though fly ashes are being used in different geotechnical engineering application, but there is not
a standard classification scheme for the same and the present classification scheme does not show
the true difference between the properties.
Hence, there is a need to characterize fly ashes from different sources and at different conditions
of the plant.
A better classification scheme should be framed considering chemical, mineralogical along with
the particle size consideration of the fly ash.
58 | P a g e
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