BAHIR DAR UNIVERSITY
BAHIR DAR INSTITUTE OF TECHNOLOGY
SCHOOL OF RESEARCH AND POST GRADUATE STUDIES
FACULTY OF CIVIL AND WATER RESOURCE ENGINEERING
MSc Thesis on
STABLIZATION OF BLACK COTTON SOILWITHCEMENT,
STONE DUST AND RICE HUSK ASH IN CASE OF WORETA
TOWN
BY
BANCH DAGNEW ALEMU
Advisor: Dr. YebeltalZeri
January, 2021
Bahir Dar, Ethiopia
BAHIR DAR UNIVERSITY
BAHIR DAR INSTITUTE OF TECHNOLOGY
FACULTY OF CIVIL AND WATER RESOURCE ENGINEERING
STABLIZATION OF BLACK COTTON SOIL WITH CEMENT, STONE
DUST AND RICE HUSK ASH IN CASE OF WORETA TOWN
BY
BANCH DAGNEW ALEMU
A thesis submitted to the school of Research and Graduate Studies of Bahir
Dar Institute of Technology
BDU in partial fulfillment of the requirements
For the Degree of
Master of Science in Geotechnical Engineering
Advisor: Yebeltal Zeri (Ph.D.)
January, 2021
Bahir Dar, Ethiopia
DECLARATION
I, the undersigned, declare that the thesis comprises my own work. In compliance with
internationally accepted practices, I have acknowledged and refereed all materials used in this
work. I understand that non-adherence to the principles of academic honesty and integrity,
misrepresentation/ fabrication of any idea/data/fact/source will constitute sufficient ground for
disciplinary action by the University and can also evoke penal action from the sources which have
not been properly cited or acknowledged.
Name of the student Banch Dagnew Alemu
Signature _____________
Date of submission: ________________
Place: Bahir Dar
This thesis has been submitted for examination with my approval as a university advisor.
Advisor Name: Yebeltal Zerie (Ph.D.)
Advisor‘s Signature: ______________________________
i
ACKNOWLEDGEMENTS
Firstly, I express my heartfelt gratitude to my advisor, Dr, Yebeltal Zerie for his supervision and
guidance throughout this research work. I would also like to thank Bahir Dar University soil
laboratory staffs for their continuous assistant throughout the laboratory tests that I have
performed. A special gratitude and love goes to my family and my friends for their unfailing
support.
ii
ABSTRACT
Expansive soils, such as black cotton soils, are basically susceptible to detrimental volumetric
changes, with change in moisture content. The cyclic wetting and drying process causes vertical
movements in expansive soils and these movements lead to failure of structures. There have been
many methods available to control expansiveness of these soils. The removal of expansive soils
and replacement with suitable material has been widely practiced all over the world where there is
suitable material within economic distances. Stabilization is another alternative being used
worldwide. The main objective of this study is to test and analyzes the effectiveness of the mix of
cement, stone dust and rice husk ash as a stabilizer on the geotechnical Properties of black cotton
soils (BCS) in woreta; due to the reason that black cotton soil s become an alarming worldwide
problem.
This study presents the variation of some index and Engineering properties of black cotton soil
when it is mixed with different percentages (cement percentage of 4 and 8, and stone dust and rice
husk ash percentage of 5, 10, 15 and 10, 15, 20 respectively) of cement, stone dust and rice husk
ash and the results were found that up to the addition of these stabilizing materials there is an
increase in strength parameters. A cycle of tests such as atterberg limit test, California bearing
ratio (CBR), specific gravity, sieve analysis, and unconfined compressive strength test were
carried out on black cotton soil samples with different percentages of cement, stone dust, rice
husk ash and their mixes. The test results show that cement, stone dust and rice husk ashcan be
effectively utilized as stabilization material for black cotton soils with optimum cement, stone
dust, and rice husk ash content up to 8%, 15%, and 20% respectively for expansive soils of high
to marginal swelling potential. It is recommended based on the results of this research that these
three stabilizing materials can be suited as a viable option for stabilization of foundation bases
and subgrade founded on black cotton soil. The preliminary investigation of this soil shows that it
belongs to A-7-5class of soil according to the AASHTO and CH as per the USCS soil
classification system.
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Keywords: Black Cotton soil, Stabilization, California Bearing Ratio, and Atterberg limit test
iv
Table of Contents
DECLARATION ............................................................................................................................... i
ACKNOWLEDGEMENTS .............................................................................................................. ii
ABSTRACT .....................................................................................................................................iii
LIST OF ABBREVIATIONS .......................................................................................................... ix
LIST OF SYMBOLS ........................................................................................................................ x
LIST OF FIGURES ......................................................................................................................... xi
LIST OF TABLES .......................................................................................................................... xii
CHAPTER 1 ..................................................................................................................................... 1
INTRODUCTION ............................................................................................................................ 1
1.1 BACK GROUND OF THE STUDY ................................................................................................... 1
1.2 STATEMENT OF THE PROBLEM .................................................................................................. 3
1.3 OBJECTIVES OF THE STUDY ................................................................................................................. 3
1.4 SCOP OF THE STUDY ..................................................................................................................... 4
1.5 SIGNIFICANCE OF THE STUDY .................................................................................................... 5
1.6 ORGANIZATION OF THE STUDY ................................................................................................. 5
CHAPTER 2 ..................................................................................................................................... 6
LITERATURE REVIEW ................................................................................................................. 6
2.1 REVIEW OF EXPANSIVE SOIL ...................................................................................................... 6
2.1.1. Characteristics of Expansive Soils .............................................................................................. 6
2.1.2 Identification and classification .................................................................................................... 7
2.1.3. Source of expansive Soils ........................................................................................................... 8
2.1.4 Mineralogy of Expansive Soils .................................................................................................... 9
2.1.5 Properties of Expansive Soils ..................................................................................................... 11
2.1.6 Engineering Problems due to Expansive Soils ........................................................................... 12
2.1.7 Design and Construction Considerations in Expansive Soils ..................................................... 13
2.1.8 Mitigation and Measures on Expansive Soils ............................................................................. 13
2.2. METHODS OF SOIL STABLIZATION ......................................................................................... 14
2.2.1. Introduction ............................................................................................................................... 14
2.2.2 Objectives of Soil Stabilization .................................................................................................. 15
v
2.2.3 Methods of Soil Stabilization ..................................................................................................... 15
2.2.4 Type of stabilizers ...................................................................................................................... 16
2.2.5 Choice of Soil Stabilization Methods ......................................................................................... 18
2.2.6Soil Stabilization Techniques ...................................................................................................... 18
2.2.7 Previous Similar Works ............................................................................................................. 20
CHAPTER 3 ................................................................................................................................... 29
MATERIALS AND METHODS .................................................................................................... 29
3.1 INTRODUCTION ............................................................................................................................ 29
3.2 MATERIALS.................................................................................................................................... 29
3.2.1 Black Cotton Soil ....................................................................................................................... 29
3.2.2 Cement ....................................................................................................................................... 30
3.2.3 Stone dust ................................................................................................................................... 30
3.2.4 Rice husk ash ............................................................................................................................. 31
3.3 METHODS ....................................................................................................................................... 32
3.3.1. Soil Investigation and Description ............................................................................................ 32
3.3.2. Laboratory Testing and Analysis of Samples ............................................................................ 32
3.3.3 Soil Classification ...................................................................................................................... 33
3.3.4 Soil Index Property Tests ........................................................................................................... 34
3.3.5Mixing Ratios.............................................................................................................................. 45
CHAPTER 4 ................................................................................................................................... 46
RESULTS AND DISCUSSION ..................................................................................................... 46
4.1INTRODUCTION ............................................................................................................................. 46
4.2 PROPERTIES OF NATURAL SOIL USED FOR THE STUDY ..................................................... 46
4.3 GEOTECHNICAL CHARACTERSTICS OF STONE DUST .......................................................................... 48
4.4 GEOTECHNICAL CHARACTERSTICS OF RICE HUSK ASH .................................................... 49
4.5 CHARACTERSTICS OF CEMENT ................................................................................................ 50
4.6 FREE SWELL TEST (CONTROLLING TEST) .............................................................................. 51
4.7ATTERBERG LIMIT ........................................................................................................................ 53
4. 7. 1 Atterberg Limits of Soil Treated with Cement ......................................................................... 53
4.7.2 Atterberg Limit of Soil Treated with Stone Dust ....................................................................... 54
4.7.3 Atterberg Limit of Soil Treated with Rice Husk Ash ................................................................. 55
vi
4.7.4 Atterberg Limit of Soil Treated with Cement, Stone Dust and Rice Husk Ash Mixture ............ 56
4.8 LINEAR SHRINKAGE CHARACTERSTICS ................................................................................ 59
4.9 SPECIFIC GRAVITY....................................................................................................................... 61
4.9 COMPACTION CHARACTERSTICS (DRY DENSITY AND MOISTURE CONTENT) ............. 62
4.9.1 Compaction Characteristics of Soil treated with Cement ........................................................... 62
4.9.2. Compaction Characteristics of Soil treated with Stone Dust ..................................................... 63
4.9.3. Compaction Characteristics of Soil treated with Rice huskash .................................................. 64
4.10 CALIFORNIYA BEARING RATIO .............................................................................................. 67
4.10.1. CBR values of Soil treated with Cement ................................................................................. 67
4.10.2 CBR values of Soil treated with Stone Dust ............................................................................. 68
4.10.3. CBR values of Soil treated with Rice Husk Ash ..................................................................... 69
4.10.2. CBR values of Soil treated with Cement, Stone Dust and Rice Husk Ash Mixture................. 70
4.11 UNCONFINED COMPRESSIVE STRENGTH (UCS) .................................................................. 71
4.11.1 Unconfined Compressive Strength of Soil treated with cement ............................................... 72
4.11.2 Unconfined Compressive Strength of Soil treated with Stone Dust ......................................... 72
4.11.3. Unconfined Compressive Strength of Soil treated with Rice Husk Ash .................................. 73
4.11.4. Unconfined Compressive Strength of Soil treated with Mixture of Cement, Stone Dust and
Rice Husk Ash .................................................................................................................................... 74
CHAPTER 5 ................................................................................................................................... 76
CONCLUSION AND RECOMMENDATIONS ........................................................................... 76
5.1 CONCLUSION ................................................................................................................................. 76
5.2 RECOMMENDATIONS .................................................................................................................. 77
REFERENCES ............................................................................................................................... 78
APPENDIX ..................................................................................................................................... 84
Appendix A. Natural Moisture Content Test Results .............................................................................. 84
Appendix B: Specific Gravity Test Results ............................................................................................. 85
Appendix C. Grain Size Analysis (Wet Sieve) for Untreated Soil .......................................................... 94
Appendix D: Free Swell Test Results (Controlling Test) ........................................................................ 95
Appendix E: Linear Shrinkage Limit Test .............................................................................................. 98
Appendix F: Atterberg Limit Test Result ................................................................................................ 99
Appendix G: Moisture Density Relation and CBR test ........................................................................... 115
Appendix H: Unconfined Compressive strength Test (UCS) .................................................................. 133
vii
Appendix I Chemical Composition of Rice Husk Ash Stone Dust ....................................................... 151
Appendix J Photos taken during testing and site visit ........................................................................... 152
viii
LIST OF ABBREVIATIONS
Symbols
Descriptions
units
AASHTO
American Association of State High Way transport officials
CBR
California Bearing Ratio
LL
Liquid Limit
%
PL
Plastic Limit
%
PI
Plastic Index
MDD
Maximum Dry Density
OMC
Optimum Moisture Content
CS
Clayey Sand
ERA
Ethiopian Roads Authority
%
kg/m³
FA
Fulvic Acid
HA
Humic Acid
MDD
Maximum Dry Density
PTE
Potentially Toxic Element
QD
Quarry Dust
RHA
Rice Husk Ash
RLT
Repeated Load Triaxial
SCMs
Supplementary Cementation Materials
SD
Stone Dust
UCS
Unconfined Compressive Strength
USCS
Unified soil classification system
ix
LIST OF SYMBOLS
Designation
Description
ρ
wet density
GS
specific gravity
Units
gm/cm²
ρd
dry density
e
Axial strain
%
L
Specimen Deformation,
mm
Lo
Length of Sample,
mm
Qu
Cu
Unconfined Compressive Strength
Undrained Shear Strength
x
KPa
KPa
LIST OF FIGURES
Figure 1 Expansive soil distribution in Ethiopia (Bantayehu) ....................................................................... 9
Figure 2 Mineralogy of Expansive Soil ...................................................................................................... 11
Figure 3 overview of the area where the sample was taken. ....................................................................... 30
Figure 4 the sample of stone dust material .................................................................................................. 31
Figure 5 the sample of Rice husk ash material ............................................................................................ 31
Figure 6 location of test pits ........................................................................................................................ 32
Figure 7 Specific Gravity Test sample ........................................................................................................ 35
Figure 8 Casagrande Cup and Cone Penetrometer apparatus ...................................................................... 37
Figure 9 soil specimens at plastic limit ....................................................................................................... 38
Figure 10 the linear shrinkage soil specimen in its mold. ........................................................................... 40
Figure 11 free swell index of expansive soil treated with cement, stone dust and rice husk ash ................. 52
Figure 12 Variation of atterberg limit values of the treated soil with different cement content at 7 days and
14 days curing time ..................................................................................................................................... 53
Figure 13 Variation of Atterberg limit values of the treated soil with different stone dust content at 7 days
and 14 days curing time .............................................................................................................................. 55
Figure 14 Variation of Atterberg limit values of the treated soil with different rice husk ash content at 7
days and 14 days curing time ...................................................................................................................... 56
Figure 15 variation of plasticity index values of the soil treated with cement, stone dust and rice husk ash
mix .............................................................................................................................................................. 59
Figure 16 linear shrinkage of expansive soil treated with cement, stone dust and rice husk ash ................. 61
Figure 17 Specific gravity of expansive soil treated with cement, stone dust and rice husk ash ................. 62
Figure 18 dry density vs. moisture content for the soil treated with cement ............................................... 63
Figure 19dry density vs. moisture content for the soil treated with stone dust ............................................ 64
Figure 20 dry density vs. moisture content for the soil treated with rice husk ash ...................................... 65
Figure 21Comparison of MDD and OMC of soil treated with mixture of cement, stone dust, & rice husk
ash............................................................................................................................................................... 66
Figure 22 distribution of soaked CBR values for the soil treated with cement ............................................ 67
Figure 23 Distribution of Soaked CBR values for the soil treated with stone dust ...................................... 69
Figure 24 Distribution of soaked CBR values for the soil treated with rice husk ash.................................. 70
Figure 25 Distribution of CBR values for the soil treated with cement, stone dust and rice husk ash mixture
.................................................................................................................................................................... 71
Figure 26 Variation of UCS for cement treated soil for no curing and 7 day curing .................................. 72
Figure 27 Variation of UCS for uncured and with 7 days cured stone dust treated soil .............................. 73
Figure 28 Variation of UCS f treated soil by rice husk ash for no curing and 7 day curing ........................ 74
Figure 29 Variation of UCS f treated soil by cement, stone dust and rice husk ash mixture for without
curing and 7 day curing............................................................................................................................... 75
xi
LIST OF TABLES
Table 1Mineral composition of clayey soils ............................................................................................... 10
Table 2Chemical Properties of Expansive soils and their range .................................................................. 12
Table 3summary of literature Review ......................................................................................................... 25
Table 4 standards of tests ............................................................................................................................ 33
Table 5 Standard Specific Gravity .............................................................................................................. 36
Table 6 Relative CBR values for sub base and sub grade soils (Desalegn, June 2012). .............................. 43
Table 7 Mix Ratio of Sample ...................................................................................................................... 45
Table 8 Rating of materials based on their CBR value (ERA, 2002) .......................................................... 47
Table 9 Subgrade strength classes (Pavement Design Manual Volume1 Flexible Pavement – 2013)......... 47
Table 10 geotechnical properties of soil...................................................................................................... 48
Table 11 chemical and geotechnical characteristics of the stone dust ......................................................... 49
Table 12 Chemical composition and Geotechnical Characteristics of Rice husk ash .................................. 50
Table 13 Oxide composition of Mugher PC (Awol A. 2011)...................................................................... 51
Table 14 Effect of different percentage of additives on Free swell index of natural soil ............................. 52
Table 15 Effect of 4% and 8 % of cement on stone dust and rice husk ash mixture on Free swell index of
natural soil .................................................................................................................................................. 52
Table 16 Atterberg limit values for soil treated with 4% Cement with stone dust and rice husk ash mixture.
.................................................................................................................................................................... 57
Table 17 Atterberg Limit values for soil treated with 8% Cement with stone dust and rice husk ash
mixture. ...................................................................................................................................................... 57
Table 18 Soil classification according to degree of shrinkage (V.N.S Murthy) .......................................... 60
Table 19 Linear shrinkage value of expansive soil treated with cement, stone dust and rice husk ash ....... 60
xii
CHAPTER 1
INTRODUCTION
1.1 BACK GROUND OF THE STUDY
Soil stabilization is defined as chemical or physical treatments which increase or maintain the
stability of a soil or improve its engineering properties. There are three broad types of soil
stabilization: biological, physical and chemical. Soil stabilization aims at improving soil strength
and increasing resistance to softening by water through bonding the soil particles together, water
proofing the particles or combination of the two.
Stabilization can increase the shear strength of a soil and control the shrink-swell properties of a
soil, thus improving the load bearing of a sub grade to support pavements and foundations. For
the past several years, researchers have recognizing the use of locally available materials which
are cost-effective and abundantly available as by products from industrial and agricultural
activities to improve the properties of expansive soil with an aim to reduce stabilization costs.
The poorest soil among all is Black cotton soil (BC soil). In Rajkot area, this BC soil is spread
over southern part of district. A Rich proportion of montmorillonit is found in BC soil from
mineralogical analysis. High percentage of montomorillonit renders a high degree of
expansiveness. This property results in cracks in soil without any warning. Thus, cracks have
sometimes extend sever limit like ½'' to 12'' deep (Oza and Gundaliya, 2013).
Expansive soil is one of the most abundant problematic soils in Ethiopia, over the past 13 years,
40% of the total road sector development expenditure in Ethiopia was allocated to rehabilitation
and upgrading of truck roads with an additional 11% utilized and maintenance works alone. This
problem urges the need for wider application of coo-effective and environmentally friendly
technologies of improving soil properties, such as chemical stabilization, to be customized and
adapted to be current road construction trend in the country (ERA, 2011). It is estimated that
about 40% of the country of Ethiopia is covered with expansive clay, pausing economical and
construction challenges to the sector (Molenaar, 2005).
1
Expansive soils are a type of soils which has the ability to swell and soften when their moisture
content increased and shoes the tendency to shrink and dry cracked when the moisture content is
decreased. This volume change causes widespread damage to building and road, necessitating
stabilization of such soil prior to the construction. Soils containing the clay mineral
montmorilonite generally exhibit such properties.
Soil sample were collected from in Amhara region S/Gonder zone woreta town in order to relative
effectiveness, and arrive at appropriate proportion of stabilizing. The geological characteristics of
woreta district are almost all portions are covered by expansive soil. One influential method to
control of the volume changes of black cotton soils is stabilized it with mineral and chemical
admixtures that prevent the changes or isolate the changes. Soil stabilization is the alteration
preservation of one or more soil properties to improve the engineering characteristics and
performance of a soil. Soil stabilization aims at improving soil strength and increasing resistance
to softening by water through bonding the soil particles together, water proofing the particles or
combination of the two.
Traditionally and widely accepted types of soil stabilization techniques use products such as
bitumen emulsions which can be used as bending agents for producing a road base. And also,
Portland cement has been used as an alternative to soil stabilization.
Some renewable technologies are: enzymes, surfactants, biopolymers, and scientific polymers,
co-polymer-based products, cross-linking styrene acrylic polymers, tree resins, ionic stabilizers,
fiber reinforcement, calcium chloride, calcite, sodium chloride, magnesium chloride and more.
Some of these new stabilizing techniques create hydrophobic surfaces and mass that prevent road
failure from water penetration of heavy frosts by inhabiting the ingress of water into the treated
layer. Soil stabilization is also done by various methods by adding fly ash, rice husk ash,
chemicals, fibers, by different geo materials like geo synthetic, geo grid and geo form.
The mineralogical properties of the black cotton soils basically fall under montomrilonite group,
having more swelling and shrinking characteristics. It is highly sensitive to moisture changes,
compressive sub grade material.
Hence, sub grade, and it is undesirable characteristics to be modified using a suitable stabilization
technique. Here cement, stone dust and rice husk ash are used as stabilizer.
2
1.2 STATEMENT OF THE PROBLEM
Failure of structures built on expansive soils is phenomena, which take place mainly due to
moisture content fluctuation. In Ethiopia where these problems are significantly visible, measures
should be taken considering the quality, cost and time consumption of the remedial action which
appears to be stabilization.
The need to address the alarmingly increasing cost of soil stabilizers has led to intense research
towards cost-effective utilization of wastes for engineering purposes. This Project is to investigate
the best ways to make problematic (expansive) soils useful (better) for geotechnical engineering
purposes and requirements for engineering needs.
The basic problems which enforce to do this paper are:
 Foundation failure of the structure‘s due presence of expansive soils
 Cost savings, because stone dust and rice husk ash are by far cheaper than traditional
stabilizers such as cement and lime
 Low bearing capacity of expansive clays
 High cost of replacement with selected materials of the expansive soils.
 The production of traditional stabilizers, such as cement, is environmental unfriendly
processes;
 Waste management can be done economically;
There for, this study is an attempt to investigate the properties of locally produce stone dust,
cement and rice husk ash as soil stabilizer and evaluate the effect of its application.
1.3 OBJECTIVES OF THE STUDY
General Objective
The general objective of this study is to evaluate the best choice in quality, cost and time as a
stabilizing agent for expansive soil between cement, stone dust, and rice husk ash stabilization
technique.
3
The specific objectives of this study are:
 To study the strength characteristics of the black cotton soil for different blends with
cement, stone dust, and rice husk ash with different percentage combinations (4%, and
8%cement; 5%, 10%, 15% stone dust and 10%, 20%, 30% rice husk ash).
 To study the suitable blend that can be used in the stabilization of black cotton soil.
 To study the engineering properties of black cotton soil before and after stabilization with
cement.
 To study the engineering properties of black cotton soil before and after stabilization with
stone dust.
 To study the engineering properties of black cotton soil before and after stabilization with
rice husk ash.
 To study the engineering properties of black cotton soil after stabilization with mixing of
cement, stone dust and rice husk ash.
 To improve the strength, reduce the swelling index and to increase the bearing capacity of
the black cotton soil, it is stabilized using different materials like cement, stone dust, and
rice husk ash.
 To determine the optimum dose of the stabilizer, which improves the strength and bearing
capacity of soil which is suitable for structures
1.4 SCOP OF THE STUDY
This study is basically concerning with the characteristics study on black cotton soil admixed with
cement, stone dust, and rice husk ash for woreta district. The characteristics of the soil of the site
will be studied. The geomorphologic and hydrological history of the environment in which the
route passes will be discussed.
In the geotechnical engineering, soil characterization and stabilization is the primary task for
further design and construction of structures in that area or specific place.
This study has been supported by secondary resources and a series of laboratory experiments.
However, the findings of the research are limited to soil samples considered in the research which
are expansive clay soil only. The results are also specific to the type of chemical additives used
and test procedures that have been adopted in the experimental work. Therefore, findings should
be considered indicative rather than definitive for filed applications.
4
1.5 SIGNIFICANCE OF THE STUDY
This research will be helpful in showing an alternate and locally available material for soil
stabilization by reducing cost and by protecting the environment. It will also be helpful in
reduction of waste materials.
The main purpose of soil stabilization in many engineering applications is to contribute to
the structure of safety and its cost analysis. The study provides as an input for further geotechnical
researchers to fill the gap in the soil study in the construction industry.
The research also helps me to conduct other researches in different thematic areas and to
determine the magnitude of the soil stabilization and focus on the factors on which it depends for
preliminary foundation design of constructions implemented at different areas.
To make black cotton soils suitable as a good sub-stratum for a construction usage, improvement
in existing properties is necessary.
1.6 ORGANIZATION OF THE STUDY
The thesis is organized and presented in five chapters. The first chapter introduces about the study
area and research background. Chapter two assesses review of different literatures about
expansive soils, black cotton soils and their stabilization mechanisms. In chapter three, the
materials used, sample collection methods, soil laboratory testing and the testing methods are
discussed. In chapter four, discussions on the obtained test results analysis and evaluations are
made. On the fifth chapter, the conclusions and recommendations are presented. Next to this
chapter, all the different materials referenced in this study are presented for the means of
acknowledgment. At the end, details of the laboratory test results sited under appendix section.
5
CHAPTER 2
LITERATURE REVIEW
2.1 REVIEW OF EXPANSIVE SOIL
2.1.1. Characteristics of Expansive Soils
Soils to be used as road sub grade material may have different characteristics such as soils with
good load bearing capacity which is suitable for the use of sub grade material and on the other
hand soils which are unsuitable to be used as subgrade material such as highly expansive soils.
Thus, detailed investigation has to be conducted on the subgrade material to evaluate its
suitability to be used as load carrying section of a pavement prior to going to the other steps of
pavement design. The physical properties of expansive clays and most clay soils are often poorer
than may be required for a particular project because of their instability due to shrink-swell
characteristics with the variation of their engineering properties.
According to Shiara and Prakash (2004) expansive soils absorb water heavily, swell, become soft
and lose strength. These soils are easily compressible when wet and possesses a tendency to
heave during wet condition and shrink in volume and develop cracks during dry seasons of a year,
and they show extreme hardness and cracks when they are in dry condition. The seasonal change
in volume of expansive soils is manifested by both horizontal and vertical movements, the
horizontal movement leads to fissure opening during dry seasons and closing during wet seasons
whereas the vertical movement leads to cyclic changes in levels. The magnitude of these
movements decreases with depth, where there are no seasonal moisture changes.
According to Muni Budhu (2011), about 40 to 60% of expansive soils have grain sizes less than
0.001 mm. These soils generally have higher liquid limit and plasticity index and extremely low
CBR values. At their liquid limit, the volume change is of the order of 200 to 300% and results in
swelling pressure as high as 8kg/cm² to 10kg/cm². Soaked laboratory CBR values of expansive
soils are mostly found to be in the range of 2 to 4%. Due to very low CBR values, highly
exaggerated pavement thickness is required for designing flexible pavement which leads to
extremely high project cost estimates
6
2.1.2 Identification and classification
Expansive soil can be identifying by soil laboratory test and also field identification. Some
peculiar characteristics associated with these problematic geo-materials from literature are
unstable mineralogical composition (commonly, montmorillonite, allophone, halloysite etc.), high
insitu moisture contents, unstable soil structure and fabric, high water absorption capacity, low
insitu density, variable degree of desiccation with depth, variable density-moisture relationships
with pre-test sample preparation methods, liquefaction prone, erodible/dispersive, collapse
phenomena, shrinkage and expansiveness, difficulty to stabilize in terms of controlling volume,
strength, water absorption capacity, durability and post construction problems (Gidigasu, 1987).
In the field, expansive soils can be identified by applying several identification techniques. Some
of the important field identification methods used to indicate potential of expansiveness of soils
includes (Miller, J. N. 1992)
• Surface cracks during dry season.
• When wet sticky and difficult to clean the soil from hand and when dry very hard like rock
• They usually have black or grey color
• Cracks are observed on nearby light weight structures such as houses and fences
As with any site investigation field observations and reconnaissance can provide valuable data of
the extent and nature of expansive soils and their associated problems. Some key features are
observed locally and important observations include:
Soil Characteristics:
• Spacing and width of wide or deep shrinkage cracks
• High dry strength and low wet strength – high plasticity soil
• Stickiness and low traffic ability when wet
• Shear surfaces have glazed or shiny appearance
Geology and topography:
• Undulating topography
• Evidence of low permeability evidence by surface drainage and infiltration features
Environmental conditions:
• Vegetation type
7
2.1.3. Source of expansive Soils
The constituents of the parent material during the early and intermediate stages of the weathering
process determine the type of clay formed. The nature of the parent material is much more
important during initial stages than after intense weathering for long periods of time. The parent
materials that can be associated with expansive soils are classified into two groups. The first
group comprises the basic igneous rocks and the second group comprises the sedimentary rocks
that contain montomorillinite as a constituent. The basic igneous rocks are comparatively low in
silica, generally about 45% to 52% (Chen, 1988). Rocks those are rich in metallic base such as the
pyroxenes, amphiboles, biotic and olivine fall within this category. Such rocks include the gabbro,
basalt and volcanic glass. Shale and clay stone are one of sedimentary rocks that contain
montmorillonite as a constituent. These constituents of clay stones subsequently weathered to
montmorillonite.
In Ethiopia, expansive soils covered nearly 40% surface area of the country (Molenaar, 2005).
Expansive soils are observed in area such as central Ethiopia, following the major trunk road like
Addis Ababa - Ambo, Addis Ababa - Weliso, Addis Ababa –DebereBerehan, Addis AbabaGohatsion, and Addis Ababa - Mojo. It also covers the area like Mekelle, Bahirdar, Gambela,
Arbaminch and the most Southern, South-west and southeast part of the capital Addis Ababa area
in which the most major recent construction are being carried out. The quantity and distribution of
expansive soil in Ethiopia, presented below in figure 1.
8
Figure 1Expansive soil distribution in Ethiopia (Bantayehu)
2.1.4 Mineralogy of Expansive Soils
Expansive soils have very high clay content. There are three common types of clay minerals.
Clays are silicates built of two basic building blocks, silicate tetrahedron and aluminum or
magnesium octahedron. Clay particles are less than 2 microns (0.002 mm) in diameter. Clay
minerals are formed by sandwiching tetrahedral and octahedral layer sand sheets together. The
tetrahedron sheet can be considered as a layer of silicon ions between a layer of oxygen and a
layer of hydroxyl ions.
On the basis of their crystalline arrangement, clay minerals can be categorized into three general
groups, namely:
 Kaolinite group
 Illite group
 Montmorillonite group
It is a known fact that the three most important groups of clay minerals are montmorillonite, illite,
and kaolinite, which are crystalline hydrous Alumino silicates (Daniel 2004). Mineral
composition of clayey soils presented below in table 1.
9
Table 1Mineral composition of clayey soils
2.1.4.1Kaolinite
Kaolinite has a structural unit made up of alumina sheet jointed to silica sheet, with many layers
staked together. The bond between layers is tight and difficult to separate them. Kaolinite is very
stable and water is unable to penetrate between the layers. It shows little swelling during wetting.
2.1.4.2 Montmorrilonite
Montmorrilonite is the most common of all clay minerals. Its basic structure consists of an
alumina sheet sandwiched between two silica sheets. The basic montmorrilonite units are stacked
with one on top of the other but the bond between individual units‘ is10relatively week, so water
can easily penetrate between the sheets and separation of them produces swelling. It is extremely
active, and its activity decreases as the adsorbed cation exchanges in the order of Sodium,
Lithium, Potassium, Calcium, Magnesium and Hydroxyl.
2.1.4.2 Illite
Illite has a basic structure similar to montomorilite but the basic units are bonded together by
potassium ion which is un exchangeable. The illite units are reasonably stable, with swelling
much less than montmorrilonite. Mineralogical structure of expansive soil presented below in
figure 2 below.
10
Figure 2Mineralogy of Expansive Soil
2.1.5 Properties of Expansive Soils
2.1.5.1 Physical Characteristics of Expansive Soils
Dry expansive soils have a very hard consistence; wet expansive soils are very plastic and sticky.
It is generally true that expansive soils are friable only over a narrow moisture range, but their
physical properties are greatly influenced by soluble salts and/or adsorbed water and sodium.
The water holding capacity of expansive soils differs widely, which is attributed to their complex
pore space dynamics; water is absorbed in the clay surface and retained between crystal lattice
layers. Expansive soils can be classified on the basis of certain inherent characteristics of the soil.
2.1.5.2 Chemical Characteristics of Expansive Soils in Ethiopia
Most expansive soils have high cation exchange capacity (CEC) and high base saturation
percentage (BSP) and also, they have high PH value (Fkerte, 2006). In table 2 below, chemical
properties of expansive soils and their range were presented.
11
Table 2 Chemical Properties of Expansive soils and their range
Characteristics
Range
CEC
30-80 cmol(+) of dry soil
Ca/Mg Ratio
3:1
PH
6-8 for acidic
8-9.5 for high exchangeable
sodium
2.1.6 Engineering Problems due to Expansive Soils
Expansive soils are known to cause severe problems on the present construction industry; which
can lead to expensive design and construction cost, mitigation measures like expense for
stabilization materials and repeated and costly maintenance works.
The following are the major engineering difficulties that are caused by the adverse properties
(large changes in their volume with variation in moisture content, which are related to the
periodic cycle of drying and wetting) of the expansive soils.
2.1.6.1 Differential settlement
This can cause cracking, rutting and deformations in general distresses on road and runway
pavements, failure of drainage structures like bridges, culverts etc. similar cracking and
deformation difficulties occurs on foundation slabs and walls of small buildings, pipelines and
sewerage systems and other similar lightweight structures.
2.1.6.2 Instability of cut slops
Cut slops on these soils are prone to instabilities and slope movements due to erosion, heaving
and slumping. In place where they are overlain by stiff material, the stiffness contrast can lead to
even larger issue(Fkerte,2006).
2.1.6.3 Gully formation
Gully formation is associated with the poor permeability and erosion susceptibility nature of
expansive soils. This causes serious economic as well as environmental difficulties. Scouring of
12
drainage structures seriously affects the overall performance of road infrastructure in many
localities.
2.1.6.4. Difficult ground operations
Workability of expansive soils is poor due to their sticky and slippery character when saturated
with water. This attributes to the difficulty of earth work on expansive soils (Fkerte,2006). In
general, engineering problems of expansive soils is one of the biggest challenges in the
construction industry. Even if there is no statics available on the cost consequences and the
amount of damage caused by the difficulties of these soils, there is a serious economic loss and
substantial increase in cost of construction projects. Therefore, the presence and problem of
expansive soils should have to overlook during site investigation for certain project and should
properly address in the design stage.
2.1.7 Design and Construction Considerations in Expansive Soils
In road projects, if expansive soils are encountered, the measures proposed to deal with them
should be economically reasonable and proportionate to the risks of potential pavement damages
and increased maintenance costs. The commonly practiced measures to deal with expansive soils
during design phase include (ERA, 2002);
• Avoid expansive soil area by realignment,
• Excavate the expansive soil and replace it with suitable material,
• Treat/stabilize the expansive soil using Lime, cement, Bitumen,
• Minimize moisture changes and potential swelling in the expansive soils.
2.1.8 Mitigation and Measures on Expansive Soils
Expansive soils do not meet the specification requirements of many standards, including the
Ethiopian Roads Authority Standard Technical Specifications (ERA, 2002). Thus, expansive sub
grade soils may need improvement to their engineering properties to be used as construction
materials by physical or chemical stabilization or modification of their problematic nature.
According to ERA Site Investigation Manual-2002 (Special Investigation), whenever expansive
soils are encountered during the design or construction phase of a road project, the following
mitigation measures are recommended.
13
2.1.8.1. Realignment
Realignment is recommended and possible if the areas covered with expansive soils is of limited
extent. When the coverage of the expansive soil is of limited extent, rather than going for
treatment or removal of the problematic section, realignment can be effective and economical.
2.1.8.2. Excavation and Replacement
This is mostly recommended measure as the problematic soils are completely removed and
replaced by selected suitable material. However, these measures are only economically viable if
the selected borrow material is found in the project vicinity. It is commonly estimated that it is
sufficient to excavate the expansive soil to a depth of about1m, even if some expansive soil
remains under the selected material, it will be confined and protected from moisture changes. The
backfill materials should have CBR values similar to that of the over laying embankment
materials (CBR >5%, i.e., sub grade strength class S3) and should not previous in order not act as
drain.
2.1.8.3 Soil Treatment/Modification
The problematic nature of expansive soils can be improved by applying several treatment
measures. Some treatment methods developed and being applied in road construction projects
include stabilizing by using stabilizing agents such as lime, cement, bitumen and chemicals. The
other treatment method is covering the whole stretch of the subgrade section of expansive soil by
protective layers such as geotextile.
2.2. METHODS OF SOIL STABLIZATION
2.2.1. Introduction
Soil stabilization is the process of improving the engineering properties of weak soil and thus
making it more stable for specific purpose. It is required when the soil available for construction
is not suitable for the intended purpose. In its broadest senses, the term stabilization includes
compaction, pre-consolidation, drainage and many others. A cementing material or a chemical is
added to a natural soil for the purpose of stabilization.
The principles of soil stabilization are used for controlling the grading of soils and aggregates in
the construction of bases and sub-bases of the highways and airfields. Sometimes, soil
stabilization is used for city and suburban streets to make them more noise-absorbing (Arora,
2003/4; Ehitabezahu, 2011).
14
Geotechnical properties of problematic soils such as soft fine-grained and expansive soils are
improved by various methods. The problematic soil is removed and replaced by a good quality
material or treated using mechanical and/or chemical stabilization (Ismaiel, 2006).
Due to their mineralogical composition, soils may be rather complex materials. Stabilization is
therefore not a straight forward application of a given stabilizing agent. A number of aspects
should be taken into account in the selection of the proper stabilization technique. The factors that
should be considered include physical and chemical composition of the soil to be stabilized,
availability and economic feasibility of stabilizing agents, ease of application, site constraints,
climate, curing time, and safety. Such factors should be taken into account in order to select the
proper type of stabilization.
2.2.2 Objectives of Soil Stabilization
The application of stabilizing agents can improve (Dr. Chitrain & Shahidnoor):• Strength (stability and bearing capacity) of the soil
• Durability and resistance to the effect of water
• Volume stability
• Permeability
• Wet soils can be dry out
• The workability of clay soils
• Load spreading capacity of pavement layers
Soil stabilization is defined as making major developments to the engineering properties of soils
by adjusting the natural soil features with an additive. These additives may contain other soils or
materials such as lime, fly ash, cement, asphalt polymers, and fibers (Warren.k and Kirby.T
2004). Traditionally, additives such as cement, bitumen, and lime have achieved widespread use.
Bitumen is typically used as a soil surface treatment to limit dust and loss of fines. Cement is used
to provide strength to soil. Lime is often used in clay soils to control plasticity.
2.2.3 Methods of Soil Stabilization
Basically, two methods of soil stabilization are commonly practiced in construction.
2.2.3.1 Mechanical Stabilization
Mechanical stabilization can be defined as a process of improving the stability and shear strength
characteristics of the soil without altering the chemical properties of the soil. It is common to use
15
both mechanical and chemical means to achieve specified stabilization. The main methods of
mechanical stabilization can be categorized in to compaction, mixing or blending of two or more
gradations, applying geo-reinforcement and mechanical remediation (Molenaar, 2005).
2.2.3.2 Chemical Stabilization
Chemical stabilization is a method of improving the engineering properties of a material by
adding chemical substances. Chemical stabilization is used for a wide range of purposes
including: improving the bearing capacity and strength of pavement layers, dry temporary
bypasses during rainy periods, delay certain chemical reactions that are detrimental to road soils
or aggregates, dry out soil where the moisture content is too high for successful compaction, make
soil less permeable where necessary, reduce the plasticity of soils used in road construction and
thereby reducing the effect of moisture variations, changing clay to a more granular and workable
material and reducing swelling and shrinkage properties (Gautrans, 2004).
2.2.4 Type of stabilizers
There are two types of stabilizers
1. Traditional soil stabilizer:
 Lime
 Portland cement
 Fly ash
2. Nontraditional soil stabilizer
Currently, an increasing number of non-traditional additives have been developed for soil
stabilization purposes. Non-traditional stabilizers can be generally classified into major
categories, including, salts, acids, enzymes, lingo sulfonates, emulsions, polymers, tree resin,
molasses and geo-fibers.
•Stabilization using Salt (NaCl, MgCl2, CaCl2),
•Stabilization Using Polymers,
•Stabilization using Molasses
1. Lime
Lime is a chemical additive that has been utilized as a stabilization agent in soils for centuries.
Lime will react well with medium, moderately fine, and fine-grained clay soils. In clay soils, the
16
main benefit from lime stabilization is the reduction of soil‘s plasticity and improvement of the
strength by reducing the soil‘s swell and increasing its degree of compaction. It also increases the
strength and workability of the soil (US army, 1994).
2. Portland cement
It is one of a chemical additive that can be used to stabilize the expansive soils to improve soil
engineering properties as well as the mechanical characteristics of the soil like degree of
compaction. Generally, Cement Stabilization is ideally suited for well graded aggregates with a
sufficient number of fines to effectively fill the available voids space and float the coarse
aggregate particles (US army, 1994).
3. Fly ash
Fly ash is a by-product of coal combustion in power plants. Fly ash contains silica, alumina, and
calcium oxides, iron oxide and alkalis in its composition, and is considered as a pozzolanic
material. Color is one of the important physical properties of fly ash in terms of estimating the
lime content qualitatively. Lighter color of fly ash indicates the presence of high calcium oxide,
and darker colors of fly ash represent high organic content.
Fly ash can be used to improve the engineering properties of soil. However, it must be wellknown that fly ash properties are highly variable and depend on chemical composition of coal and
combustion technology (Nath & Sarker, 2018).
Fly ash has little cementation properties compared to lime and cement. Most of the fly ashes
belong to secondary binders; these binders cannot produce the desired effect on their own.
However, in the presence of a small amount of activator, it can react chemically to form
cementation compound that contributes to improved strength of soft soil. Fly ashes are readily
available and cheaper.
There are two main classes of fly ashes;
• Class C
• Class F
Class C fly ashes are produced from burning sub bituminous coal; it has high cementing
properties because of high content of free CaO. Class C from lignite has the highest CaO (above
30%) resulting in self-cementing characteristics. F class fly ashes are produced by burning
anthracite and bituminous coal; it has low self-cementing properties due to limited amount of free
17
CaO available for flocculation of clay minerals and thus requires addition of activators such as
lime or cement (Shahidnoor& Dr. Chitrain).
2.2.5 Choice of Soil Stabilization Methods
2.2.5.1 Soil Type
This primarily refers to the particle size distribution and chemical composition. Compaction is not
recommended for fine-grained soils as they are easily powdered and could be blown off.
Treatment of some soils that has a lot of sulfates with calcium base stabilizers such as lime and
cement can cause extreme swelling of soil (Nyakarura, 2009).
2.2.5.2 Moisture Content
In very dry soils, dust may form when the soil is compacted while high moisture content could
cause soil particles segregation hence loss of soil stability which may result the soil to become
plastic (Nyakarura, 2009).
2.2.5.3 Site Conditions
Physical conditions such as space have to be considered. Stationary continuous method, which
requires space where a central unit is to be installed, will not be applicable where there is space
limitation (Nyakarura, 2009).
2.2.5.4. Cost
The method of stabilization chosen must be cheaper than other available techniques (Nyakarura,
2009).
2.2.6Soil Stabilization Techniques
Soil stabilization techniques may be grouped under two main categories. The first one is;
improvement of soil property of the existing soil without using any admixture, such as
compaction and drainage which improve the inherent shear strength of soil and the second
improvements of soil property with the help of admixtures such as cement, lime, fly ash, bitumen
and chemicals (Nyakarura, 2009).
Several practices on expansive soil stabilization are described here below.
1. Stabilization by Compaction
18
Loose materials can be made more stable simply by application of compaction. Though,
compaction cannot be considered as stabilization process, it plays a fundamental role in the
Properties of stabilized materials.
This is the process of increasing the density of soil by packing the particles together with
reduction in volume but does not involve removal of water. The reduction of air content results in
the reduction of pores which act as conduits of water and consequently reduces permeability of
the soil.
2. Deep Foundation Techniques
The foundation is made to rest at a depth below the zone within which volume changes in the soil
occur due to seasonal moisture changes. This includes the installation of piles, piers and caisson
(Nyakarura, 2009).
3. Stabilization by Industrial Waste
Industrial waste is the waste produced by industrial activity. Stalin et.al suggested that utilization
of industrial waste in the geotechnical engineering field can solve the problem of disposal of
industrial waste such as Copper slag, Ground granulated blast furnace slag.
4. Stabilization by Reinforcement
Using fibers like rubber tire chips, waste plastics, synthetic fibers can successfully stabilize the
expansive soils. Geo-synthetics (sheet polymeric material) have been used since 1970s in
geotechnical structures for functions such as separation, reinforcement, drainage, filtration and
liquid containment and as gas barriers (Nyakarura, 2009).
5. Soil-Cement Stabilization
The principal advantages with soil-cement are that almost all soils are amenable to this technique.
It is a scientifically designed engineering material, and cement itself is a standard material whose
quality is tested and assured. Because of its very high flexural strength, it has a very high load
spreading property. Thus, soil cement is able to spread the load over a wider area and bridge over
locally weak spots of the underlying sub-grade or sub-base. The durability of soil cement is of a
high order, and its strength is known to increase with age.
The main disadvantages are the higher cost than lime-soil and the need for a high degree of
quality control. Because of volumetric changes that take place when cement hydrates, early
shrinkage cracks are formed in soil-cement layers (Nyakarura, 2009).
19
2.2.7 Previous Similar Works
2.2.7.1 Stone dust as a Stabilizer
Kumarwat et al. (2014) studied the effect of calcium carbide residue (CCR) and stone dust
particle as a stabilized material on the property of black cotton soil. They have mixed stone dust
and CCR in different percentages with black cotton soil and conducted various tests UCS, OMS
& MDD, CBR, etc. on the prepared soil samples. From the tests results, they have demonstrated
that when stone dust and CCR mixed in equal amount (10% -10%) gives the better results on the
improvement of engineering properties of soil.
Tiwariet et al.(2016)this paper deals with a feasibility study carried out to find the suitability of
using waste material i.e., stone dust and polypropylene fibers as stabilizing material for improving
the engineering properties of black cotton soil. Various tests like CBR, UCS were performed on
the soil samples prepared by using stone dust and Polypropylene fibers mixed with black cotton
soil at different percentages. On the basis of the results obtained from these tests, it concluded that
the strength of black cotton soil can be substantially improved by mixing with stone dust and
polypropylene fibers as stabilized materials.
Singh et al. (2016) studied the effect of moisture content, degree of compaction, etc. on various
geotechnical properties of soil. A series of tests such as heavyweight compaction and CBR test
are done to estimate the strength characteristics of compacted soil using fly ash and stone dusts as
well as tests like specific gravity test, grain size distribution test by mechanical sieve analysis etc.
are performed to obtain some physical properties of soil. These results will be very much helpful
for the successful utilization of fly ash and stone dust in different fields such as embankment
construction, road base and sub-base construction, designing of retaining walls etc. in an ecofriendly manner.
2.2.7.2 Cement as a Stabilizer
Cement is a binder, a substance used in construction that sets, hardens and adheres to other
materials, binding them together. An increase in cement content generally causes an increase in
strength and durability. Both normal and air entraining cement give almost the same results of
stabilization (Solihu, 2020; Zhang and Tao, 2008).
20
Portland pozzolanic cement is composed of calcium silicates and calcium-aluminates that hydrate
to form cementation products and has been successfully used for binding soil particles together,
thereby forming a hard stable mass (Mishra, 2014).
The strength development of stabilized clay is controlled by the hydration of cement and the
reaction. Test results show that from the viewpoint of plasticity, compaction and strength
characteristics, and economy, addition of 6–8% cement and 10–15% rice husk ash is
recommended as an optimum amount (Basha et al., 2005).
Several factors associated with the cement amendment process including operating variables such
as cement and water contents, water/cement ratio (specifically for cement paste), pH and curing
time, etc. have been studied for their influence on soil strength or metal stabilizing respectively,
resulting in general findings (e.g., soil strength increases with curing time, higher cement
concentrations) results in higher strength (Saride et al., 2013).
Okafora and Egbeb(2013)explore the potentials of utilizing cement kiln dust in improving the
properties of soil for use as base course material in pavement construction. The paper examined
the material used for the construction of Sankwala- Busi Road in Obanliku, Cross River State,
Nigeria, with a view of stabilizing it to obtain a sub base and base course material. Cement kiln
dust (CKD) can be used as an alternative to lime, Portland cement and fly ash, which is
sometimes used in roads construction. Utilization of CKD is not only effective for improving the
soils‘ strength, but also helps in minimizing the cost (Ismail and Belal, 2015). The CKD sample
consists mainly of calcite (74%) and quartz (23%). The dust sample consists mainly of carbonates
(about 70–75% share) (Bochenczyk, 2019).
Research about cement treated soil has examined various characteristics of strengthened and
stabilized soil, but has mainly focused on either the unconfined compressive strength or
potentially toxic element (PTE) stabilizing results respectively in response to cement dosing(Pan,
et al.2018).
Al-Rawas et al.(2005) study the effect of lime, cement, combinations of lime and cement, Sarooj
(artificial pozzolan) and heat treatment on the swelling potential of Al-Khod expansive soil. The
samples treated with 3% cement, 3% lime and 3% lime, and 3% Sarooj showed an initial increase
in plasticity index.
21
The fiber used has a high tensile strength, which explains why the cement-fiber-improved
specimens could tolerate high shear stresses even after peak strength is reached. The existence of
fiber in the cement-soil mixture does not significantly change the unconfined compressive
strength. The stiffness of the mixture can be significantly increased when the mixture is cured
under vertical curing stress, compared with the mixture without curing stress (Starcher, 2013).
Use of the type of black cotton soil land may suffer severe damage to the construction with the
change in atmospheric conditions (Oza and Gundaliya, 2013).In this paper, the effects of three
variable parameters on shrinkage property and strength are studied of the initial water content,
curing period, cement content and lime content based on shrinkage experiments and strength
experiments, the main content is early curing time influence (Zhe et al., 2011).
Soil cement is an intimate mix of soil, cement and water which is well compacted and cured to
form a strong base course. The terms ―Cement treated soil‖ and ―Cement modified soil‖ refer to
the compacted mixes when cement is used in small proportions to impart some strength or to
modify the properties of the soil and these mixes do not fulfill the mix design requirements
specified for soil-cement (Akanbi and Job, 2014).
Portland cement is generally used as a chemical additive in stabilization of soils. A lot of soils,
devoid of organic matter and capable of being pulverized, can be stabilized with cement
(Komolafe and Osinubi, 2019).
The soil sample taken for the study is clay with high plasticity (CH) which truly requires to be
strengthened. The soil is stabilized with different percentages of rice husk ash and a small amount
of cement (Roy, 2014).
The maximum percentage strength gain is achieved in the third stage of curing, which is between
14 and 28 days of curing. In contrast to 2% cement stabilized soil combinations, the strength
gains in stage two was less than 900% for all combinations for 6% cement stabilized soil (James,
2019).
Compressed Stabilized Earth Blocks (CSEBs) are manufactured using stabilizers to provide
adequate compressive strength and durability, so, as to make them suitable as building blocks.
Though cement is a popular stabilizer used in manufacture of CSEBs, no study has been reported
22
utilizing lime in combination of cement. This experimental study on CSEBs prepared using lime
as a replacement to cement (Nagaraj et al., 2014)
The pavement thicknesses are drawn, and it was found that with increase in the percentage of
cement, quarry dust and lime, the strength increases, therefore the thickness of the pavement
decreases (Satish et al., 2018).
The soil specimens compacted at low water/stabilizer ratio showed better performance than those
compacted at high water/stabilizer ratio having identical unconfined compressive strength (UCS)
(Dhakal, 2012).
Since the moisture contents selected in this study for the laboratory tests were way beyond the
optimum moisture content of raw soils, it was very difficult to compact the soil/stabilizer mixture
in the mold manually, i.e., by dropping the hammer. So, in order to achieve a uniform
compaction, it is recommended to use automatic compactors (Wang, 2002)
Recycle materials from the agricultural waste coconut shell and husk into useable engineering
material as an admixture to stabilize poor lateritic soil from Olokoro, Umuahia, Nigeria to
improve the characteristic strength, durability and volume stability for civil engineering
construction works (Onyelowe, 2016).
Cement and cement-sawdust ash (CSDA) application to the clayey soil led to the exchange of
hydrated covalent cations in the contaminated soil with the divalent cations (such as Ca 2+ and
Mg2+) in the cement (Owamah et al., 2017).
Sodium silicate is not a suitable stabilizer for expansive soils, but it relatively gives encouraging
results on coarse grained materials. Good drainage system is highly recommended for sodium
silicate stabilization (Ehitabezahu, 2011).
2.2.7.3 Rice Husk Ash as a Stabilizer
The covering present over a grain of rice to protect it is called rice husk. India is the secondlargest rice producing country after China. Rice is one of the basic and main crops grown in India.
It is observed that 108.86 million tons of rice was produced in India during year 2016–17 and
104.32 million tons during year 2015–16. During parboiling process at rice mill, rice husk is
23
burned which give waste as rice husk ash. For about 1000 kg of rice or paddy milling, about 55 kg
of rice husk ash is obtained after burning 220 kg of rice husk (Yadav et al., 2017).
Roy, 2014 studied the effect of rice husk ash (RHA) along with cement on the sub grade clayey
soil characteristics. It was found that with increase in the proportion of rice husk ash and cement,
optimum moisture content and CBR increases whereas maximum dry density decreases. The
behavior of clayey soil mixed with rice husk ash and lime, and it was observed that the maximum
improvement in CBR value is with combination of 6% lime + 10% RHA (Kumar & Preethi,
2014).
Basha et al.(2005) replaced the soil with various proportions of rice husk ash and cement. It was
found that 6–8% of cement and 15–20% RHA shows the optimum value. Addition of rice husk
ash to the cement stabilized soil shows the significant result in CBR.
In another study, Alhassan (2008) investigated permeability of lateritic soil treated with lime and
RHA, using A-7-6 lateritic soil and compacted at BSL compaction energy with up to 8% lime
content (by dry weight of the soil) at 2% variations. Each of the soil-lime mixture was admixed
with up to 8% RHA at 2% variations. Effects of the ash on the soil-lime mixtures were
investigated with respect to UCS and coefficient of permeability.
In a related study, Okafor and Okonkwo (2009) investigated the effects of rice husk ash on some
geotechnical properties of lateritic soil, using lateritic soil classified as an A-2-6 (0) according to
AASHTO classification system for sub-grade purposes. The investigation included evaluation of
properties such as compaction, consistency limits and strength of the soil with RHA content of 5,
7.5, 10 and 12.5% by weight of the dry soil.
Mtallib and Bankole(2011) used lime and RHA to experimentally study improvement of index
properties and compaction characteristics of tropical lateritic clays. The two A-7-6 soils, studied,
showed significant improvement in properties. Performance of the treated soil as road bases was
considered, while its performance under other geotechnical structures other than road bases was
not taken into consideration. Literature review summary presented below in table 3.
24
Table 3summary of literature Review
Researcher
Materials used
Test method
Major finding
Saride et al., Cementand lime
 Sieve analysis
The strength of the soil is dependent
2013
 Atterberg limits
on soil type and constituents
 UCS
including clay mineralogy.
 Compaction test
Uzomaka et
cement, lime,
 Sieve analysis
Quarry dust is the best suitable when
al., 2010
quarry dust and rice
 Atterberg limits
compared with cement, lime, and rice
husk
 Specific gravity
husk for the stabilization of road
 Compaction and
bases.
 CBR test
Mudgal et
Stone dust and lime
al., 2014
 Sieve analysis
UCS & CBR the strength increases
 Atterberg limits
up to 20% addition of stone dust in
 Specific gravity
lime stabilized soil.
 Compaction and
 CBR test
 UCS
 Free swell
Basha et al.,
rice husk ash and
 Atterberg limit
Addition of 6–8% cement and 10–
2005
cement
 Compaction
15% rice husk ash is recommended
 UCS and
as an optimum amount.
 CBR test
Solihu, 2020 cement
 UCS, and
For any silty sand with some clayey
 Atterberg limits
contents, cement is effective as a
stabilizing agent.
25
Tiwari et al
stone dust and
 Atterberg limit
The black cotton soil can be used as a
(2016)
polypropylene
 UCS
sub grade soil for road construction
fibers
 CBR, &
after stabilizing using stone dust
 Standard proctor test
andpolypropylene fibers
Khemiss and cement and lime
 Compaction
The best performances are obtained
Mahamedi,
 CBR and
for a mix treatment corresponding to
2014
 Undrained direct shear
8% cement and 4% lime contents.
tests
Gundaliya,
cement waste dust
 Atterberglimit
Cement dust provides substantial and
2013
and lime
 UCS test
durable
benefits
when
used
as
stabilizing agent for BC Soil.
Singhe et.
stone dust and fly
 UCS and
Because of increase of the proportion
al.,2016
ash
 CBR test
of stone dust theunconfined
compressive strengthincreases.
Zhe et al.,
cement and lime
2011
 Shrinkage and
Shrinkage increases with initial
 UCS test
moisture content and curing period,
decreases with the increase of the
cement content.
Ehitabezahu
cement, lime and
 Atterberg limit
Sodium silicate is not suitable
, 2011
sodium silicate
 Compaction, and
additive expansive soil stabilization.
 CBR tests
Bochenczyk,
2019
cement kiln dust
 X-ray spectrometer
(XRS), and
 X-ray diffraction (XRD)
test
The dustsdue to their composition
and, the significant concentration of
chlorides, could be problematic to
recover.
26
Okafora and
cement kiln dust
 Atterberg limits,
CBR, UCS were greatly improved by
Egbeb, 2013
(CKD)
 Compaction test,
the addition of 24% CKD to the soil.
 CBR and
 UCS test.
Roy, 2014
cement and rice
 Compaction test
Soil stabilization using 10% RHA
husk ash
 CBR and
content with 6% cement is
 UCS test,
recommended as optimum amount
for practical purposes.
James, 2019 cement and sawdust
ash (SDA)
 Atterberg limit,
The SDA amendment results in a
 Specific gravity and
minimum increase of 8% in early
 UCS test
strength at 7 days of curing and 19%
increase in delayed strength at 28
days of curing.
Jenifer and
cement, brick
 UCS
The compressive, flexural strength
Rani, 2016
powder
 Tensile strength and
and split tensile strength increases up
 Flexural strength tests
to 10%, 20% replacement of
cementation material.
Wang, 2002
Alhassan,
rock soil and
 Compaction
Increase of cement content from
cement
 UCS and
5%to 9% doubled the expansion
 Linear expansion test
magnitude.
rice husk ash, and
 UCS,
Not more than 6% RHA can be used
lime
 Permeability, and
to increase UCS and reduce
 Compaction test
permeability of lateritic soil.
 CBR and
Increase in RHA content increased
 Compaction test
the OMC and volume stability but
2008
Okafor and
Okonkw,
rice husk ash
2009
decreased the MDD and plasticity.
27
Mtallib and
rice husk ash and
 Compaction,
Plasticity of the soils significantly
Bankole,
lime
 Atterberg limit, and
reduced with addition of lime and the
 CBR test
ash.
2011
Kumar and
rice husk ash &
 UCS, and
Addition of industrial waste (RHA)
Preethi,
lime
 CBR test
alone gave an average improvement
2014
of 60% when compared with virgin
sample.
28
CHAPTER 3
MATERIALS AND METHODS
3.1 INTRODUCTION
In this section, description and classification of materials used for the research, testing procedures
and results are presented. Soil tests were done in the Geotechnical Engineering Laboratories of
Bahir Dar University. Relevant data of material characterization obtained from secondary
resources were acknowledged.
The research method used in this study is experimental. The preliminary task is visiting different
places of Woreta town at which the soil at the site is black cotton soils and gathered information
about these soils. Three places were selected and explored using test pitting and representative
black cotton soil samples were collected from these places and the collected soil samples were
transported to Bahir Dare university soil laboratory for testing and experimenting to ascertain the
geotechnical characteristics of these soils under investigation.
3.2 MATERIALS
3.2.1 Black Cotton Soil
The black cotton soil sample used for this research is collected from woreta town. The soil is dark
gray. This soil type is identified by field investigation by its color and physical properties. A
sufficient amount of disturbed sample is collected at three test pits at a depth around 1.5m and 3m
from around Health office, Hospital, and poli technique school.
During pitting of the sample test pits, the top surface of the soil was first cleared with all the
organic wastes and other waste materials. This soil samples are carefully packed and transported
to the laboratory, the soils air dried for 2 weeks before testing. The physical properties of
expansive soils vary from place to place. In general, these soils have very low load carrying
capacity and high swelling and shrinkage characteristics. Figure 3 below shows an overview of
the area where the sample was taken.
29
Figure 3 overview of the area where the sample was taken.
3.2.2 Cement
Cement is a binder, a substance used in construction that sets, hardens and adheres to other
materials, binding them together. An increase in cement content generally causes an increase in
strength and durability. Portland pozzolana cement (PPC) was used for this study.
3.2.3 Stone dust
Stone dust is the by-Product containing minerals and trace elements, obtained from the crushing
operation of stones, usually processed by natural or mechanical means. For this research, stone
dust properly packed in sacks and transported to the laboratory and then sieves by sieve size of
0.425mm. The sample of stone dust material used in this study is presented in figure 4 below.
30
Figure 4the sample of stone dust material
3.2.4 Rice husk ash
Rice husk ash, basically a waste material, is produce from woreta rice - mill industry while
processing rice from paddy. The ashes used in this study are obtained from burning of rice husk in
the incinerator. About 20 – 22% rice husk is generated from paddy, and about 25% of this total
husk becomes ash when burned. It is non – plastic in nature. RHA has a good pozzolanic
property. The sample of rice husk ash material used in this study is presented in figure 5 below.
Figure 5the sample of Rice husk ash material
31
Figure 6location of test pits
3.3 METHODS
3.3.1. Soil Investigation and Description
Field investigations of the soil included field description of the soil and collection of
representative soil samples for laboratory tests. Sampling of the soil was conducted at three
different places of woreta town such as around health office, poli technique college and woreta
hospital. The terrain of the land feature is flat and extensively covered by expansive soil. The
sample was taken at a depth of about 1.5m - 3m.
3.3.2. Laboratory Testing and Analysis of Samples
To evaluate the effect of cement, stone dust and rice husk ash as stabilizing additives in expansive
soils, the following tests were conducted with the addition of these materials to expansive soils
with varying proportions by dry weight of the total quantity.
32
Table 4 standards of tests
Type of test
Standard
Standard Compaction
ASTM-D1883
California bearing ratio (CBR)
ASTM-D1883
Liquid & Plastic limit test
ASTM D 4318
Specific gravity
ASTM D 854
Sieve analysis
ASTM D 422
This thesis presents laboratory test results to evaluate the effect of addition of Cement, stone dust,
and rice husk ash on the Geotechnical behavior of the expansive soil in terms of grain size
distribution, atterberg limits, specific gravity, compaction characteristics, free swell, CBR and
unconfined compressive strength. The amount of cement was varied from 0 to 8% by dry weight
of soil. The soil used in this study was expansive soil and the materials collected from Woreta
town. The expansive soil was treated in addition of stone dust ranging 0, 5, 10, and 15
percentages and rice husk ash ranging 0, 10, 15, and 20 percentages by dry weight of the soil.
3.3.3 Soil Classification
The most widely used soil classification systems for engineering purposes are American
Association of State Highway and Transportation Officials (AASHTO) and Unified soil
classification system (USCS). The AASHTO system of soil classification comprises seven groups
of inorganic soils from A-1 to A-7, with 12 subgroups in all. The system is based on particle-size
distribution, liquid limit and plasticity index. On the other hand, the Unified Soil classification
system is based on the recognition of the type and predominance of the constituents considering
grain size, gradation, plasticity and compressibility. It divides soil in to three major divisions:
coarse grained soils, fine-grained soils and highly organic soils. Field identification is
33
accomplished by visual examination for the coarse-grained soils and a few simple hand tests for
the fine-grained soils. In the laboratory, the grain-size curve and the atterberg limits test are used.
3.3.4 Soil Index Property Tests
3.3.4.1 Moisture Content
The test is conducted in accordance with ASTM D 2216 a small representative sample of the
natural soil specimens are obtained and oven-dried at 105°C for at least 24hours. The samples
were then reweighed, and the difference in weight was assumed to be the weight of the water
driven off during drying. The difference in weight was divided by the weight of the dry soil,
giving the water content of the soil a dry weight basis. The water content is also used in
expressing the phase relationships of air, water, and solids in a given volume of soils.
The full steps of determining of the moisture content
(a) Determine the mass of soil solids.
MS = MCDS – MSC
[3.1]
(b) Determine the mass of pore water.
MW = MCMS –MCDS
[3.2]
(c) Determine the water content.
W=Mw/Ms x100
[3.3]
Where:
MS = mass of soil solids
Mw = mass of pore water
MCDS = mass of can, lid and dry soils
MCMS=mass of can, lid and moist soils
W=water content in %
3.3.4.2 Specific Gravity
Specific gravity which is the measure of heaviness of the soil particles is determined by the
method of pycnometer method using a soil sample passing No. 10 sieve and oven dried at 105
degrees centigrade.
This test is conducted based on ASTM D 854-00 – Standard methods for Specific Gravity testing
of Soil Solids. Specific gravity is the ratio of the mass of a unit volume of soil at a stated
temperature to the mass of the same volume of gas-free distilled water at a stated temperature.
34
The test includes the determination of the specific gravity for the natural soil and mixes. The
pycnometer used in the testing of specific gravity is indicated in figure 7 below.
Figure 7 Specific Gravity Test sample
Data Analysis:
Calculate the specific gravity of the soil solids using the following formula:
Specific Gravity
GS= (WO÷ (WO+ (WA-WB)[3.4]
Where:
W0 = weight of sample of oven-dry soil, g = WPS - WP
WA = weight of pycnometer filled with water
WB = weight of pycnometer filled with water and soil.
The general ranges for specific gravity of soil can be categorized are as shown in the table 5
below.
35
Table 5 Standard Specific Gravity
Type of soil
Specific gravity
sand
2.63 to2.67
silt
2.65 to2.7
Clay and silt soil
2.67 to 2.9
Organic soil
1 to 2.6
3.3.4.3 Atterberg Limits Test
Atterberg limits are expressed in terms of the moisture content of the soil. The plastic limit is the
moisture content that defines where the soil changes from a semisolid to a plastic (flexible) state.
The liquid limit is the moisture content that defines the limit that the soil changes from a plastic to
a viscous fluid state. The test includes the determination of the liquid limits, plastic limits, and the
shrinkage limit for the natural soil and the expansive soil stabilizer with cement, stone dust and
rice husk ash mixtures. The tests are conducted for both treated and untreated soil samples in
accordance withASTMD4318 testing procedures.
3.3.4.3.1 Liquid Limit Test (LL)
Liquid Limit (LL) is defined as the arbitrary limit of water content at which the soil is just about
to pass from the plastic state into the liquid state. At this limit, the soil possesses a small value of
shear strength, losing its ability to flow as a liquid. In other words, the liquid limit is the minimum
moisture content at which the soil tends to flow as a liquid. The soil sample for liquid limit is air
dried and contains the material passing through a sieve size No. 40 (425μm aperture). This soil
obtained thoroughly mixed with water to form a homogeneous paste on a flat glass plate.
Liquid Limit can be determined either by casagrande cup method or cone penetration method.
Casagrande Cup method is an apparatus that consists of a semispherical brass cup that is
repeatedly dropped onto a hard rubber base from a height of 10 mm by a cam operated
mechanism to determine the liquid limit. The water content corresponding to 25 numbers of
blows on the semi-log graph of moisture content versus number of blows defines the liquid limit.
36
A Fall Cone (Cone Penetrometer) method, on the other hand is popular in Europe and Asia,
appears to offer a more accurate (less prone to operator‘s errors) method of determining both the
liquid and plastic limits (Budhu, 2011). In the fall cone test, a cone with an apex angle of 30°and
total mass of 80 grams is suspended above, but just in contact with, the soil paste.
Therefore, in this thesis work, casagrande cup testing method is used to determine the liquid limit.
The test soil sample waited for soaking was obtained and thoroughly mixed with water to form a
homogeneous paste on a flat glass plate or using porcelain evaporating dish. The casagrande cup
and cone penetrometer apparatus presented below in figure 8.
Figure 8Casagrande Cup and Cone Penetrometer apparatus
3.3.4.3.2 Plastic Limit Test (PL)
Plastic Limit (PL) is the arbitrary limit of water content at which the soil tends to pass from the
plastic state to the semi-solid state of consistency. Thus, this is the minimum content, at which the
change in shape of the soil is accompanied by visible cracks, i.e., when worked upon, the soil
crumbles (the mixes is molded between the fingers and rolled between the palms of the hand until
it dried (Venkatramaiah, 2006).
A portion of the homogeneous natural soil-water paste and the mixes used previously for the
liquid limit test is left out for the determination of plastic limit. A ball of the natural soil and
sufficiently, even though the soil is already relatively drier than the ones used for liquid limit. The
37
sample is then divided in to approximately two equal parts. Each of the parts is rolled into a
thread between the first finger and the thumb. The thread is then rolled between the tip of the
fingers of one hand and the glass. This is continued until the diameter of the thread is reduced to
about3mm. The movement continued until the thread shears both longitudinally and transversely.
The crumbled natural soil a mix is then put in the moisture container and the moisture content is
determined. The same procedure is also carried out for the treated soil with increment of stone
dust content. In the figure 8 below showed a photo of the crumbled soil specimen during Plastic
Limit determination.
To determine the Plastic Limit, the following calculations are used; - therefore:
a) Calculate the water content of each of the soils placed moisture cans
b) Compute the average of the water contents to determine the plastic limit, PL.
Plastic Limit (PL) = Average W % [3.5]
The soil specimens at plastic limit test in laboratory presented below in figure 9 below.
.
Figure 9soil specimens at plastic limit
3.3.4.3.3 Plasticity Index (PI)
Plasticity index (PI) is the range of water content within which the soil exhibits plastic properties.
It is the difference between the liquid limits and their corresponding plastic limits. The plasticity
indexes of the samples are calculated as:
PI =LL – PL[3.6]
Where is
PI=plastic index
38
LL=liquid limit
PL=plastic limit
3.3.4.4 Free Swell Test (FS) and Linear Shrinkage Test
Black cotton soil is well known for its swelling properties. It usually consists of an alumina sheet
sandwiched between silica sheets. An example of such soil is montmorillonite clay. The bond
between individual units is weak that water can easily penetrate between the sheets and separates
the particle, which leads to swelling. If water saturated clay is allowed to stand freely for two to
three days, it will increase in volume. The increase in volume of the soil is called free swell.
This test has not been standardized by ASTM. The method was suggested, in 1956, by Holtz and
Gibbs to measure the expansive potential of cohesive soils, and it gives a fair approximation of
the degree of expansiveness of the soil sample. The procedure consists of pouring very slowly of
10 cubic centimeters of oven dry soil passing No.40 sieve in to 100 cubic centimeters, full of
Water, graduated measuring cylinder and letting the content stand for approximately 24Hrs. Until
all the soil completely settles on the bottom of the graduating cylinder.
The free swell values of soil are calculated using the following formula.
Free Swell (%) =
Final volume- Initial volume×100%
[3.7]
Initial volume
Soils having free swell less than 50% are not expansive, if the free swell is in the range 50% and
100%; it is considered to be margin and when the free swell is greater than 100% the soil is
considered expansive.
Linear shrinkage test follows ASTM D 427 and covers the determination of total linear shrinkage
from linear measurement on a standard bar of length 140 mm with a semicircular section of
diameter 25 mm, the grove filled by a soil of the fraction passing 0.425 mm test sieve, originally
having the moisture content of the liquid limit.
Shrinkage Limit (SL) is the water content at which the soil tends to pass from the semisolid to the
solid state. It is that water content at which a soil, regardless, of further drying, remains constant
in volume. In other words, it is the maximum water content at which further reduction in water
39
content will not cause a decrease in volume of the soil mass, the loss in moisture being mostly
compensated by entry of air into the void space. In fact, it is the lowest water content at which the
soil can still be completely saturated.
The thoroughly mixed soil-water paste and the soil-water-quarry dust mixture used previously for
the liquid limit test at approximately 20mm penetration value were placed in a standard shrinkage
mold. Then the mold with the soil paste was dried in the oven maintained at a temperature of 105
to 1100C for about 24hours. After complete drying, the mold and soil were cooled and the mean
length of the soil bar was measured. The photo presented in figure 10 below showed the linear
shrinkage soil specimen in its mold.
Figure 10the linear shrinkage soil specimen in its mold.
[3.8]
3.3.4.5 Grain size Analysis and Soil Classification
3.3.4.5.1 General
The grain-size analysis was carried out to determine the relative proportions of different grain
sizes which makes up a given soil mass. It is not actually possible to determine the individual soil
sizes, as the test only brackets various ranges of sizes.
40
A classification scheme provides a method of identifying soils in a particular group that would
likely exhibit similar characteristics. Soil classification is used to specify a certain soil type that is
best suited for a given application. It can be used to establish a soil profile along a desired crosssection of a soil mass. There are several classification schemes available. Each was devised for a
specific use. For example, the American Association of State Highway and Transportation
Officials (AASHTO) developed one scheme that classifies soils according to their usefulness in
roads and highways, while the Unified Soil Classification System (USCS) was originally
developed for use in airfield construction but was later modified for general use (Budhu, 2011).
3.3.4.5.2Unified Soil Classification System (ASTM D 2487)
The USCS is neither too elaborate nor too simplistic. The USCS uses symbols for the particle size
groups. These symbols and their representations are G-gravel, S-sand, M-silt, and C-clay. These
are combined with other symbols expressing gradation characteristics—W for well graded and P
for poorly graded—and plasticity characteristics—H for high and L for low, and a symbol, O,
indicating the presence of organic material. A typical classification of CL means a clay soil with
low plasticity, while SP means poorly graded sand (Budhu, 2011).
3.3.4.5.3AASHTO Soil Classification System (AASHTO M 145)
The AASHTO soil classification system is used to determine the suitability of soils for
earthworks, embankments, and road bed materials. According to AASHTO, granular soils are
soils in which 35% or less are finer than the No. 200 sieve (0.075 mm). Silt-clay soils are soils in
which more than 35% are finer than the No. 200 sieve (Budhu, 2011).
3.3.4.6Compaction
The test includes the determination of the maximum dry density and the optimum moisture
content for the natural soil and the treated soil. The tests are conducted for uncured stabilized soil
samples in accordance of the ASTM D 698 Standard test Methods for Laboratory Compaction
testing procedures. The mold is filled with five equal layers of soil, and each layer is subjected to
25 drops of the hammer.
3.3.4.6.1 Maximum Dry Density
The maximum dry density is conducted for both the natural and treated soil, by varying the
moisture content. The sample is then compacted into the 944 cubic centimeters (of mass m 1); in
41
five layers of approximately equal mass, with each layer receiving 25 blows. The blows are
uniformly distributed over the surface of each layer. The collar is then removed, and the
compacted sample leveled off at the top of the mold with a straight edge. One small representative
sample is then taken from the compacted soil for the determination of moisture content. The same
procedure is repeated until a minimum of five sets of samples are taken for moisture content
determination. The bulk density is then calculated for each compacted specimen using:
ρ= (m1-m2)
944
[3.9]
The dry density is also calculated using the following equation:
ρd= ρ
1+w
[3.10]
Where;
W=moisture content in percent divided by 100
ρ = wet density in grams per cm²
The values of the dry densities as obtained from the equation above are plotted against their
respective moisture contents and the dry densities; MDD is deduced as the maximum point on the
resulting curves.
3.3.4.6.2 Optimum Moisture Content
The corresponding value of moisture contents at maximum dry densities, which is deduced from
the graph of dry density against moisture content, gives the optimum moisture content.
3.3.4.7 California Bearing Ratio (CBR) Test
The California Bearing Ratio test is a simple penetration test developed to evaluate the strength of
road sub grades (soil below the pavement) and makes no attempt to determine any of the standard
soil properties such as density. It is merely a value, and it is integral to the process of road design.
It is however by far the most commonly used in pavement design. Furthermore, it is also used as a
means of classifying the suitability of a soil for use as sub grade or base course material in
highway construction.
The CBR test (ASTM terms the test simply as a bearing ratio test) measures the shearing
resistance of a soil under controlled moisture and density conditions. The CBR number is
obtained as the ratio of the unit load (in KN/m²) required effecting a certain depth of penetration
42
of the penetration piston (with an area of 19.4cm ²) in to a compacted specimen of soil at some
water content and density to the standard unit load required to obtain the same depth of
penetration on a standard sample of crushed stone.
In equation form
CBR % =
Test unit load
*100[3.11]
Standard Unit Load
The CBR value for a given soil will depend upon its density, molding moisture content, and
moisture content after soaking. Since the product of laboratory compaction should closely
represent the results of field compaction, the first two of these variables must be carefully
controlled during the preparation of laboratory samples for testing. Unless it can be ascertained
that the soil being tested will not accumulate moisture and be affected by it in the field after
construction, the CBR tests should be performed on soaked samples. In addition, the result of a
CBR test also depends on the resistance to the penetration of the piston. Therefore, the CBR
indirectly estimates the shear strength of the material being tested (Desalegn, June 2012). Relative
CBR values for sub base and sub grade soils presented below in table 6 according to Desalegn,
June 2012.
Table 6 Relative CBR values for sub base and sub grade soils (Desalegn, June 2012).
CBR (%)
> 80
50 to 80
30 to 50
Material
Sub base
Sub base
Rating
Excellent Very Good
Sub base
Very
Good
20 to 30
Sub
grade
Good
10 to 20
Sub
grade
Fair to
Good
5 to 10
Sub
grade
poor to
Fair
<5
Sub grade
Very
Poor
In this research, three point CBR Tests on soil samples with a compaction effort of 10 blows, 30
blows and 65 blows for each layer (5 layers) is made. The density versus CBR is plotted and the
CBR corresponding to maximum dry density is determined from the graph for evaluating the 95%
maximum dry density.
Swell readings are taken before and after soaking of the specimens to obtain the swelling or
expansion ration. At the end of the soaking period, the CBR penetration test is made to obtain a
CBR value for the soil in saturated condition. For the three penetration tests for the CBR values, a
surcharge of the same magnitude as for the swell test is placed on the soil sample. The test on
soaked gives information concerning the expected soil expansion.
43
3.3.4.8 Unconfined Compressive Strength (UCS)
The purpose of this test was to determine the unconfined compressive strength, which was then
used to calculate the unconsolidated undrained shear strength of the clay under unconfined
conditions.
According to the ASTM standard, the unconfined compressive strength (qu) is defined as the
compressive stress at which an unconfined cylindrical specimen of soil will fail in a simple
compression test. In addition, in this test method, the unconfined compressive strength is taken as
the maximum load attained per unit area, or the load per unit area at 15% axial strain, whichever
occurs first during the performance of a test. The unconfined compressive strength test is
applicable only in cohesive soils. In this test the soil goes to failure by axial load only with no
confining stresses. The unconfined compressive strength tests were conducted for both natural
and treated samples. The tests are conducted for uncured and stabilized soil samples in
accordance ASTM D 2166 - Modified test methods for laboratory UCS testing procedures.
e (%)= ∆L *100
Lo
[3.12]
Where is
e (%) =axial strain
L = Specimen Deformation, [mm]
Lo = Length of Sample, Lo (mm)
Stress=P/A
[3.13]
Where is
P= Applied Load, [KN]
A= Corrected Area, [mm2]
Cu = qu
2
[3.14]
Where i
qu = Unconfined Compressive Strength (KPa)
Cu=Undrained Shear Strength (KPa)
44
3.3.5Mixing Ratios
The amount of cement added to the soil sample was varied by a percentage of 4 and 8%. The
amount of stone dust added to the mixture of soil was 5%, 10% and 15% and also rice husk ash
was 10%, 15%, &20%. Mixing ratios used for, and this study are summarized in the table below.
Each mixing ratios were tested for atterberg limits, free swell, compaction, CBR and UCS tests.
The mix ratio of the sample designation presented below in table 7.
Table 7 Mix Ratio of Sample
Natural Soil
Soil
Soil + 4% C
Soil + Cement
Soil + 8% C
Soil + 5% SD
Soil + 10% SD
Soil + Stone Dust
Soil + 15% SD
Soil + 10% RHA
Soil + 15% RHA
Soil + Rice husk ash
Soil + 20% RHA
Soil+ Cement + Stone Dust+ Rice husk Ash
10%RHA
15%RHA
Soil+4%C+5%SD+
20%RHA
10%RHA
15%RHA
Soil+4%C+10%SD+
20%RHA
10%RHA
15%RHA
Soil+4%C+15%SD+
20%RHA
Soil+8%C+5%SD+
10%RHA
15%RHA
Soil+8%C+10%SD+
Soil+8%C+15%SD+
45
20%RHA
10%RHA
15%RHA
20%RHA
10%RHA
15%RHA
20%RHA
CHAPTER 4
RESULTS AND DISCUSSION
4.1INTRODUCTION
In this chapter, the final output of the tests which are conducted in the laboratory are briefly
discussed and presented. The relevant geotechnical properties of the soil are investigated both for
natural and stabilized soil samples. The laboratory tests which are conducted for soils and soils
treated with cement, stone dust, and rice husk ash are the moisture content, atterberg limit (LL
and Pl),compaction test (MDD,OMC), CBR test, unconfined compression test (UCS) and free
swell test. These results are also compared to each other.
4.2 PROPERTIES OF NATURAL SOIL USED FOR THE STUDY
According to the laboratory test results of the natural soil sample obtained during the present
study liquid limit of 93.63%, plastic limit of 51.81%, plastic index of 41.82%, MDD of
1.35g/cm³, and OMC of41%. The soil has dark gray color. The colors of the soils were identified
using visual site identification. The soil is classified as A-7-5 as per the AASHTO and CH as per
the USCS classification system. As far as the engineering performance of soils of this class is
concerned, such soils are expansive soils which have volume changing properties with variation
in moisture content (Chen, 1988).
The liquid limit and plasticity index values for subgrade materials are very much greater than the
requirements set in ERA 2002 standard specifications, which requires the liquid limit to be less
than 60% and the plasticity index to be less than 30%.Hence, the soil under investigated sample
shows higher values in each parameter has a very high expansive potential. The free swell index
of 130% also revealed that the soil was very expansive soil, since its value is greater than 100%.
Furthermore, the CBR value of 1.4%, indicate that the soil has a very low load bearing capacity
and subgrade strength class of S1. Thus, it clearly shows that the soil doesn‘t comply with the
ERA specification 2002 requirement, which requires CBR value greater than 5% for subgrade
soil. Shortly speaking, since the subgrade materials are weak in bearing loads and has expansive
46
nature, it needs treatment. According to ERA 2002, based on their CBR values, earth materials to
be used as different pavement layers are categorized as follows in table 8below.
Table 8Rating of materials based on their CBR value (ERA, 2002)
CBR value (%)
Quality of subgrade
0-3
Very poor
3-7
poor to faire
7-20
Faire
20-50
Good
>50
Excellent
According to pavement design manual volume1 flexible pavement – 2013 the sub grade strength
classes also presented below in table 9 below.
Table 9 Subgrade strength classes (Pavement Design Manual Volume1 Flexible Pavement –
2013)
CBR Class
CBR value in %
S1
<3
S2
3, 4
S3
5, 6, 7
S4
8 – 14
S5
15 – 30
S6
> 30
For most geotechnical construction works, especially highway construction, the untreated
expansive soil requires initial modification and/or stabilization to improve its workability and
engineering property. Test result of black cotton soil sample is presented in table10 below.
47
Table 10 geotechnical properties ofsoil
Soil Property
Result
Natural moisture content
37.8
Specific gravity
2.69
Liquid limit (%)
93.63
Plastic limit (%)
51.81
Plastic index (%)
41.82
Optimum moisture content (%)
41
Maximum dry density (g/cm³)
1.35
4 days soaked CBR (%)
1.4
UCS (KPa)
148.5
Color
Dark gray
Linear shrinkage (%)
16.43
Specific gravity
2.69
AASHTO
A-7-5
USCS
CH
From the above table, the soil sample laboratory result need improvement before use any type of
infrastructure. This improvement treats by cement, stone dust, and rice husk ash as soil stabilizer
materials.
4.3 GEOTECHNICAL CHARACTERSTICS OF STONE DUST
The geotechnical characteristics of the stone dust material specifically taken from Woreta stone
crashing industry used in this study is tested at Bahir Dar university soil laboratory and the results
are presented in table 11 below.
48
Table 11chemical and geotechnical characteristics of the stone dust
Constituent
Percentage
1 Chemical properties
SiO2
79.1
Al2O3
2.4
Fe2O3
1.12
CaO
0.88
MgO
0.78
Na2O
0.16
K2O
2.34
MnO
<0.01
P2O5
0.65
TiO2
<0.01
H2O
1.71
LOI
11.4
2 Physical Properties
Specific gravity
2.87
LL
Nil
PL
Non-plastic
PI
Non-plastic
LS
Nil
FS
Nil
4.4 GEOTECHNICAL CHARACTERSTICS OF RICE HUSK ASH
From the chemical analysis test, the chemical composition of the RHA used in this study was
obtained as shown in table 12 below (As analyzed by Geological Survey of Ethiopia, Central
Laboratory).
According to ASTM C618 pozzolanic material is a siliceous or siliceous and aluminous material
which, in itself, possesses little or no cementation value but which will, in finely divided form in
the presence of moisture, react chemically with calcium hydroxide at ordinary temperature to
form compounds possessing cementation properties.
49
Table 12 Chemical composition and Geotechnical Characteristics of Rice husk ash
Parameters
Test Values
1 Chemical properties
SiO2
47.74
Al2O3
16.9
Fe2O3
13.9
CaO
7.32
MgO
4.58
Na2O
2.36
K2O
0.84
MnO
0.16
P2O5
0.75
TiO2
1.72
H2O
1.67
LOL
2.5
2 Physical Properties
Specific gravity
2.3
LL
Nil
PL
Non-plastic
PI
Non-plastic
LS
Nil
FS
Nil
Based on ASTM C618 the result showed that the RHA fulfilled the requirements to N &F class of
pozzolana where the SiO2+Al2O3+Fe2O3= 78.54% (>70% and 50%, SO3=0 (<4% and 5%)) and
LOI = 0.08 %(< 10%).
4.5 CHARACTERSTICS OF CEMENT
Mugher ordinary Portland cement (OPC) was used for this study.The oxide composition of the
cement is presented in the table 13below(Awol A.2011).
50
Table 13Oxide composition of Mugher PC (Awol A. 2011)
Constituent
Total Percentage
CaO
66.31
SiO2
20.03
Al2O3
5.94
Fe2O3
3.73
SO3
1.14
MgO
1.07
Insoluble residue
0.12
Loss on ignition
0.08
4.6 FREE SWELL TEST (CONTROLLING TEST)
The Free swell index of the expansive soil is found to be high due to its cyclic swelling shrinkage
behavior. Free swell index value decreased with increase in percentage of cement, stone dust and
rice husk ash added.
The maximum reduction of free swell index was 15% occurred at the mix of 8%cement+15%
stone dust+20% rice husk ash. When the soil was treated with cement the maximum reduction in
free swell was 32.5% occurred at 12% addition of cement but when we see the value of free swell
index at 8% and 12%of cement.
In case of stone dust maximum reduction of free swell index was 42.5% occurred at 20% and at
15% stone dust the value is 45%, therefore we use 15% stone dust as a maximum dosage and for
the rice husk ash 20% ash used. The value of free swell index at 20% rice husk ash is reducing to
32.5%. In all cases, free swell had a consistent reducing nature. Results are presented below in
table 14 and 15 and graphically in the figure11.
51
Table 14Effect of different percentage of additives on Free swell index of natural soil
Cement
Percentage
Free swell index
(%)
0%
2%
130 122.5
Reduced by (%)
0.0
5.8
Stone Dust
4%
8%
12%
5%
10%
15%
70
37.5
32.5
113
87.5
45
46.2 70.8
75.0
13.5
32.7
65.4
Rice Husk Ash
20% 10% 15% 20%
25%
42.5
52.5 32.5
27.5
67.3 38.5 59.6 75.0
71.2
80
Table 15 Effect of 4% and 8 % of cement on stone dust and rice husk ash mixture on Free
swell index of natural soil
4% cement
8% cement
Rice Husk Ash
Rice Husk Ash
Stone
Stone
Dust
10% 15% 20%
Dust
10% 15% 20%
5%
92.5 62.5
5%
57.5
10%
15%
42.5 35 27.5
35 22.5 15
10%
15%
65
45
55
47.5 32.5
30 22.5
35
27.5
Free swell index (%)
0
2C
4C
8C
12c
5SD
10SD
15SD
20SD
10RHA
15RHA
20RHA
25RHA
4C5SD10RHA
4C5SD15RHA
4C5SD20RHA
4C10SD10RHA
4C10SD15RHA
4C10SD20RHA
4C15SD10RHA
4C15SD15RHA
4C15SD20RHA
8C5SD10RHA
8C5SD15RHA
8C5SD20RHA
8C10SD10RHA
8C10SD15RHA
8C10SD20RHA
8C15SD10RHA
8C15SD15RHA
8C15SD20RHA
140
120
100
80
60
40
20
0
Figure 11free swell index of expansive soil treated with cement, stone dust and rice husk ash
52
4.7ATTERBERG LIMIT
In this subsection, atterberg limits i.e. liquid limit (LL), plastic limit (PL) and plasticity index (PI)
test results for the treated black cotton soil with cement, stone dust, and rice husk ash is discussed
here under.
4. 7. 1 Atterberg Limits of Soil Treated with Cement
For the black cotton soil treated with cement only, the tests were carried out for the mixes that
were prepared at 4% and 8% of cement by dry weight of the soil and for the samples cured for 7
and 14 days.
Hence, the addition of cement in varying proportions with the soil and the effect of the same on
the atterberg limit values of the mix and the changes made on the respective properties as
compared to the native black cotton soil are discussed in here under. Variation of liquid & plastic
limits and the plasticity index for 7 day and 14 day for different cement content of treated black
cotton soil is shown in figure12 below.
100
90
80
70
60
50
40
30
20
10
0
0
4c
8c
LL
PL
PI
LL
0 days
PL
PI
7 days
LL
PL
PI
14 days
Curing Duration
Figure 12Variation of atterberg limit values of the treated soil with different cement content
at 7 days and 14 days curing time
53
The liquid limit (LL) of the native/untreated black cotton soil is determined as 93.63% whereas
after the addition of Portland cement up to 8%, the liquid limit decreased to 44.63% at 14 days
curing time. From the figure above, it can be seen that the liquid limit (LL) decreased with
increasing of cement content and curing time.
The plastic limit (PL) of the native black cotton soil was found to be 51.8 % and when cement is
added, the plastic limit of the cement-treated soil decreased to 34.03% with the addition of cement
up to 8%.
Consequently, the Plasticity Index (PI) of the cement treated black cotton soil decreases with the
increase in cement content. The PI of the untreated soil (41.82%) is decreased to 10.6% with the
addition of 8% cement at 14 days curing. The decrease in Plasticity Index (PI) of the cement
treated soil is due to the cement hydration that is accompanied by an increase in PH of the pore
fluid and Ca++ ion concentration on the clay surface. The permeability of the cement treated clay
reduces with the increase of cement content and curing time. This reduction could be due to the
Pozzolanic cement substances, which block the pores in the soil cement matrix.
4.7.2 Atterberg Limit of Soil Treated with Stone Dust
The atterberg limit tests for black cotton soil treated with stone dust only were carried out by
preparing mixes by varying the stone dust content by 5% (i.e. 5%, 10% and 15%) by dry weight
of the soil cured for 7 and 14 days.
Variation of liquid limits, plastic limits and the plasticity index for the treated black cotton soil
with different proportion of stone dust is shown in figure 13 below. Even though there is no
significant effect on the plastic Index (PI) of soil treated with stone dust, there was a slight
reduction in atterberg limits with increasing stone dust content.
54
0
5SD
10SD
15SD
LL
PL
0 days
PI
LL
PL
PI
7 days
LL
PL
PI
14 days
Figure 13 Variation of Atterberg limit values of the treated soil with different stone dust
content at 7 days and 14 days curing time
The addition of stone dust to the native black cotton soil did not cause practical significant
improvement on the Plasticity Index (PI) of the treated soil when compared with cement and rice
husk ash. This is due to the fact that the natural soil had very high clay content so that the addition
of stone dust only reinforced the sand size content of the soil-dust mixture with no textural and no
chemical change of the clay particles of the black cotton soil.
The Plasticity Index (PI) of the treated black cotton soil decreases with the increase in stone dust
content. The PI of the untreated soil (41.82%) is decreased to 26.3% with the addition of stone
dust up to 15%.
4.7.3 Atterberg Limit of Soil Treated with Rice Husk Ash
The atterberg limit tests for black cotton soil treated with rice husk ash only were carried out by
preparing mixes by varying the rice husk ash content by 10%, (i.e.10%, 15% and 20%) by dry
weight of the soil.
The liquid limit of black cotton soil alone was 93.63%. Adding various proportion of rice husk
ash has substantial effects on the liquid limit of the black cotton soil; the liquid limit goes on
decreases rapidly with increasing of percentage of rice husk ash content. The plastic limit of black
cotton soil alone was 51.81%. Addition of various fraction of rice husk ash has significant effects
on the plastic limit of the RHA stabilized black cotton soil; the plastic limit goes on decreases.
55
100
80
60
0
40
10RHA
20
15RHA
0
20RHA
LL
PL
0 days
PI
LL
PL
PI
7 days
LL
PL
PI
14 days
Figure 14 Variation of atterberg limit values of the treated soil with different rice husk ash
content at 7 days and 14 days curing time
The Plasticity Index (PI) of the treated black cotton soil decreases with the increase in rice husk
ash. The PI of the untreated soil (41.82%) is decreased rapidly to 9.9% with the addition of rice
husk ash, up to 20%.
4.7.4 Atterberg Limit of Soil Treated with Cement, Stone Dust and Rice Husk Ash Mixture
Atterberg limit tests for black cotton soil treated with cement, stone dust and rice husk ash
mixture were carried by varying the cement content by 4 and 8% for 5, 10 and 15% stone dust
and 10, 15 and 20% rice husk ash content (i.e. 4%C+5%SD+10%RHA, 4%C+5%SD+15%RHA,
etc.) and for each group of mixes, the samples were cured for 7 and 14 days.
It is noted that the liquid limit (LL) and plastic limit (PL) of the mix of the 3 stabilizing materials
treated black cotton soil slightly decreased with increase of the content and curing time. The stone
dust content increased; there were an accompanied reduction in the liquid limit (LL) of the treated
soil due to the reduction in clay content of the soils as the non-plastic stone dust increased.
56
Stone
dust
5%
10%
15%
Table 16Atterberg limit values for soil treated with 4% Cement with stone dust and rice
husk ash mixture.
Curing Time
0 day
7 day
14 day
Rice husk ash
Atterberg
limit
10%
15%
20% 10% 15%
20%
10%
15%
20%
LL (%)
81.7
76.4
67
75.8 72.3
65.5
66.1
64.8
59
PL (%)
46.3
44.6
42.7
43.8 44.2
41.7
41.4
40.7
39.9
PI (%)
35.4
31.8
24.3
32
28.1
23.8
24.7
24.1
19.1
LL (%)
80
75.4
69.4
75.1 73.1
67.3
61.8
59.2
56.8
PL (%)
46.2
45
43.4
43.6
43
42.4
37.6
37.1
36.4
PI
33.8
30.4
26
31.5 30.1
24.9
24.2
22.1
20.4
LL
78.4
74.2
70.4
76.1 72.6
68.4
68.4
63.1
61
PL
45.1
44.3
42.7
44.7 43.8
42
43.3
42.3
40.8
PI
33.3
29.9
27.7
31.4 28.8
26.4
25.1
20.8
20.2
Table 17Atterberg Limit values for soil treated with 8% Cement with stone dust and
rice husk ash mixture.
Curing Time
0 day
7 day
14 day
Rice husk ash
Stone
Atterberg
dust
limit
10%
15%
20%
10%
15%
20%
10%
15%
20%
LL
75.4
67.3
62 72.4
64.7
57.3
61.5
58
53
PL
43.7
42.3
40.1
43
40
39.4
38 37.5
37.6
5%
PI
31.7
25
21.9
29.4
24.7
17.9
23.5
20.5
15.4
LL
75.4
67.3
62
72.3
64.7
57.3
61.5
58
53
PL
43.7
42.3
40.2
43
40
39.4
38
37.5
37.5
10%
PI
31.7
25
21.8
29.3
24.7
17.9
23.5
20.5
15.5
LL
72.1
66.1
59.2
64.2
59
55.3
58.6
53.2
49.8
PL
42
41.6
41
41.9
41
40.6
41.1
40.6
40.1
15%
PI
30.1
24.5
18.2
22.3
18
14.7
17.5
12.6
9.7
The Plasticity Index (PI) of the cement, stone dust and rice husk ash mixture treated black cotton
soil decreases substantial with the increase in the stabilizer content. The PI of the untreated soil
(40.6%) is decreased to 9.7% with the addition of 8% cement+15% stone dust + 20% rice husk
ash.
57
58
Plastic Index
40
35
30
25
20
15
10
5
0
0 day
7 day
14 day
Figure 15variation of plasticity index values of the soil treated with cement, stone dust and
rice husk ash mix
The Plasticity Index of the black cotton soil treated with cement, stone dust and rice husk ash
mixture reduces further as compared to soil treated with cement, stone dust and rice husk ash
alone.
The addition of 4 and 8% cement alone reduces the PI of the untreated soil by 60.8%, and 74.6%
respectively. Whereas, with the addition of 5, 10, 15% stone dust; and 10, 15, 20% rice husk ash
alone reduces the PI of the untreated soil by 16.8, 27, 37, 39.7, 62.9 and 73 % respectively. When
we see the mixed treated soil, the addition of 8%C+15%SD+10%RHA, 8%C+15%SD+15%RHA,
and 8%C+15%SD+20%RHA the PI of the untreated soil
reduces by 58.1, 70, and76.8%
respectively.
This is due to the fact that when the cement, stone dust and rice husk ash are mixed together, the
mixes acts as a ‗Cement-Mortar‘ which further reduces the plasticity characteristics of the treated
soil than the soil treated with cement alone. However, the observed reduction with increasing the
stone dust content is not that much significant as compared to the effect of the cement and rice
husk ash does in improving the plastic index of the treated soil.
4.8 LINEAR SHRINKAGE CHARACTERSTICS
Linear shrinkage value of the sampled soil shows decrement as the percentage of cement, stone
dust and rice husk ash increased. The reduction was visible at mix ratio of
59
8%C+15%SD+20%RHA. The maximum reduction of shrinkage limit was 74.3% found at this
mix ratio and the minimum was found at 5% stone dust, the value of shrinkage limit is 14.3%.
According to Murthy (Table 18 below) the quality of treated soil at mix ratio of
8%C+15%SD+20%RHA was to fall under good quality of soil because the shrinkage limit at this
ratio is <5%. The addition of non-shrinking and cohesion less material in sample soils decreased
the tendency of the samples to shrink. The value of linear shrinkage of expansive soil treated with
cement, stone dust and rice husk ash was described in table19 below and also graphically in figure
16 below.
Table 18 Soil classification according to degree of shrinkage (V.N.S Murthy)
Sr (%)
<5
5─10
10─15
>15
Quality of
soil
Good
Medium
good
Poor
Very poor
Table 19Linear shrinkage value of expansive soil treated with cement, stone dust and rice
husk ash
Sample
Designation
0
4C
8C
5SD
10SD
15SD
10RHA
15RHA
20RHA
4C5SD10RHA
4C5SD15RHA
4C5SD20RHA
4C10SD10RHA
4C10SD15RHA
Shrinkage limit
value (%)
16.4
13.2
9.0
14.3
13.2
10.0
13.6
11.1
8.9
12.6
11.8
10.0
11.7
11.1
Reduced
by (%)
0.0
19.6
45.2
13.0
19.6
39.1
17.4
32.6
45.7
23.5
28.3
39.1
28.7
32.6
Sample
Designation
4C10SD20RHA
4C15SD10RHA
4C15SD15RHA
4C15SD20RHA
8C5SD10RHA
8C5SD15RHA
8C5SD20RHA
8C10SD10RHA
8C10SD15RHA
8C10SD20RHA
8C15SD10RHA
8C15SD15RHA
8C15SD20RHA
60
Shrinkage limit
value (%)
10.2
11.9
10.9
9.7
10.4
8.9
8.6
10.1
8.9
5.7
9.6
6.1
4.2
Reduced
by (%)
37.8
27.8
33.9
40.9
37.0
45.7
47.4
38.7
46.1
65.2
41.3
63.0
74.3
Shrinkage limit value (%)
0
4C
8C
5SD
10SD
15SD
10RHA
15RHA
20RHA
4C5SD10RHA
4C5SD15RHA
4C5SD20RHA
4C10SD10RHA
4C10SD15RHA
4C10SD20RHA
4C15SD10RHA
4C15SD15RHA
4C15SD20RHA
8C5SD10RHA
8C5SD15RHA
8C5SD20RHA
8C10SD10RHA
8C10SD15RHA
8C10SD20RHA
8C15SD10RHA
8C15SD15RHA
8C15SD20RHA
18.0
16.0
14.0
12.0
10.0
8.0
6.0
4.0
2.0
0.0
Figure 16linear shrinkage of expansive soil treated with cement, stone dust and rice husk
ash
4.9SPECIFIC GRAVITY
Adding of cement, stone dust and rice husk ash in different percentage had changed the specific
gravity of the soil. The Specific Gravity of the rice husk ash material used in this study is 2.3.
Increasing of rice husk ash decreased the specific gravity. Because of fly ash particles are hollow,
thin walled, having low weight than conventional to soil, so in mixed samples the overall weight
become less. The value of untreated soil reduced from 2.69to 2.22 at the mix of 20% rice husk
ash.
The Specific Gravity of the stone dust material used in this study is 2.87. The laboratory test
result shows that, there is a dramatic increase in specific gravity of the untreated black cotton soil
with addition of stone dust and cement. This increase in specific gravity of the soil-stone dust
mixtures is due to the higher value of specific gravity of stone dust. The higher value,3.33 record
at mixing of 8%C+15%SD+10%RHA. The specific gravity test results of the black cotton soils
are presented in figure17 below.
61
Specific gravity
3.5
3
2.5
2
1.5
1
0.5
0
Figure 17 Specific gravity of expansive soil treated with cement, stone dust and rice husk
ash
4.9 COMPACTION CHARACTERSTICS (DRY DENSITY AND MOISTURE
CONTENT)
For determining the relationships between compacted dry density and soil moisture content,
modified proctor tests were done and accordingly the maximum dry density (MDD) and optimum
moisture content (OMC) of the treated soil were determined according to AASHTO T-180. The
compaction characteristics for the treated black cotton soil with cement only, stone dust only, rice
husk ash only and with the combination of the three is discussed hereunder.
4.9.1 Compaction Characteristics of Soil treated with Cement
For the black cotton soil treated with Portland cement at 4% and 8% of cement by dry weight of
the soil, the respective compaction curves that shows the relationship between the dry density and
moisture content were plotted against the ‗dry densitymoisture content‘ curve of the native black
cotton soil and the comparison of the same with the untreated soil is presented in figure below.
62
Dry Density
1.42
1.40
1.38
1.36
1.34
1.32
1.30
1.28
1.26
1.24
1.22
20.00
Natural Soil
4% Cement
8% Cement
25.00
30.00
35.00
40.00
45.00
50.00
55.00
Moisture Content(%)
Figure 18dry density vs. moisture content for the soil treated with cement
From the figure 18above, it shows that addition of cement to natural soil in the cause of this study
lead to increase in the maximum dry density (MDD) and the optimum moisture content (OMC).
Increases in the optimum moisture content (OMC) with increase in the quantity of cement could
possibly be due to increase in the surface area needed to coat as the quantity of cement increases,
which makes the mix to require more water for the hydration of cement. The OMC of the treated
soil increased slightly from 41% to 43.5% at 8% cement content. The observed increase in the
optimum water content (OMC) of the cement treated soil is due to the hydration of cement, in
which the cement by itself utilizes the added water for the hydration reaction. After the addition
of cement, the MDD of the treated soil increase from 1.35g/cm³ to 1.4g/cm³ with increasing the
cement content. Since cement with higher specific gravity value is added to natural soil, which in
turn gives rise to an increase in the maximum dry density (MDD) of the entire mixture.
4.9.2. Compaction Characteristics of Soil treated with Stone Dust
For the sample soil treated with stone dust, the maximum dry density (MDD) were determined to
be 1.39gm/cm³, 1.42gm/cm³, and 1.44gm/cm³ with the addition of 5%, 10%, and 15% of stone
dust by dry unit weight of the soil respectively.
Accordingly, with the addition of stone dust up to 15%, the Optimum Moisture Content (OMC) of
the treated black cotton soil is decreased to 36% from 38.8% of the untreated soil. Here also, the
OMC of the treated soil decreases continuously as the proportion of stone dust increases.
63
Dry Density (g/cm³)
1.45
1.40
1.35
Natural Soil
5SD
1.30
10SD
15SD
1.25
1.20
20.00
25.00
30.00
35.00
40.00
45.00
Moisture Content (%)
50.00
55.00
Figure 19dry density vs. moisture content for the soil treated with stone dust
It is noted that as stone dust content is increased, there is an increase in the maximum dry density
(MDD) and a reduction in the optimum moisture content, as demonstrated in figure19 above.
The increase in MDD and reduction in the OMC could be attributed to the fact that, as the low
density particle black cotton soilsare replaced by a relatively high density stone dust (specific
gravity of 2.87), an increase in the density of the composite material is expected.
The reduction in the OMC could also be due to the reduction in the clay content, which causes a
reduction in the water absorptive capacity of the composite material and subsequent increase in
dry density (dry density is inversely proportional to moisture content).
4.9.3. Compaction Characteristics of Soil treated with Rice huskash
For the black cotton soil treated with rice husk ash at 10%, 15% and 20% of RHA by dry weight
of the soil, the respective compaction curves that shows the relationship between the dry density
and moisture content were presented in figure 20 below.
64
Dry Density (g/cm³)
1.36
1.34
1.32
1.30
1.28
1.26
1.24
1.22
1.20
20.00
Natural Soil
10RHA
15RHA
20RHA
25.00
30.00
35.00
40.00
45.00
50.00
55.00
Moisture Content (%)
Figure 20dry density vs. moisture content for the soil treated with rice husk ash
Figure20 above shows the effect of the addition of rice husk ash on the compaction characteristics
of the soils tested. The figure show that adding rice husk ash increased the OMC and decrease
amount of the MDD correspond to increasing of rice husk ash percentage. For the sample soil
treated with rice husk ash, the maximum dry density (MDD) were determined to be 1.34g/cm³,
1.29g/cm³, and 1.27g/cm³ with the addition of 10%, 15%, and 20% of rice husk ash by dry unit
weight of the soil respectively.
Principally, increase in dry density is an indicator of improvement. But, unfortunately rice husk
ash (RHA), instead, reduce the dry density. The decrease in density occurs because of both the
particles size and specific gravity of the soil and stabilizer. Decreasing dry density indicates that it
needs low compactive energy to attain its MDD.
Accordingly, with the addition of rice husk ash up to 20%, the Optimum Moisture Content
(OMC) of the treated black cotton soil is increased to 48.2% from 41% of the untreated soil. The
reason for the increase in OMC is exceeding water absorption by rice husk ash (RHA) as a result
of its porous properties.
Generally the maximum dry density of soil decreases with an increase of RHA content. This is
due to comparatively low specific gravity value of RHA than that of replaced soil, i.e. RHA (with
lower specific gravity) fills the soil voids, and it contributes to a decrease in density. The OMC
65
increased due to reduction of free silt and free clay fraction in the soil forming a coarser material,
aprocess requiring water to takes place, thus more water is absorbed as RHA content increases.
4.9.4. Compaction Characteristics of Soil treated with Cement Stone Dust and Rice Husk
Ash Mixture
Soil treated with cement stone dust and rice husk ash mixture has exhibited an increase in the dry
density of the soil, accompanied by a reduction in the optimum moisture content. The maximum
dry density was recorded to be 1.471gm/cm³ at 39% moisture content for the soil treated with
8%cement+15% stone dust+10%rice husk ash it can be seen in figure21 below.
MDD
OMC
8C15SD20RHA
8C15SD15RHA
8C15SD10RHA
8C10SD20RHA
8C10SD15RHA
8C10SD10RHA
8C5SD20RHA
MDD
8C5SD15RHA
8C5SD10RHA
8C5SD15RHA
8C5SD20RHA
8C10SD10RHA
8C10SD15RHA
8C10SD20RHA
8C15SD10RHA
8C15SD15RHA
8C15SD20RHA
OMC
1.48
1.46
1.44
1.42
1.4
1.38
1.36
8C5SD10RHA
41.5
41
40.5
40
39.5
39
38.5
38
37.5
Figure 21Comparison of MDD and OMC of soil treated with mixture of cement, stone dust,
& rice husk ash
Though, the addition of cement cause an increasing in the dry density of the soil, the observed
increase in the MDD of the treated soil with cement, stone dust, and rice husk ash mixture may be
associated with the increase in the size of the clay particles as the fine-grained soil particles turned
to a coarser one with the addition of cement and due to the addition of stone dust; the sand size
content of the treated soil increased and accordingly the cement, stone dust, and rice husk ash
mixture resulted in an increase in the skeleton of soil grains which in turn allows higher
compaction. The observed reduction in the OMC of the treated soil could be attributed to the
reduction in the clay content of the soil, which causes a reduction in the water absorptive capacity
of the composite material.
66
4.10CALIFORNIYA BEARING RATIO
The california bearing ratio (CBR) values are considered as the very important strength
parameters in the selection of construction materials in terms of the load bearing capacity, and it
is a familiar indicator test used to evaluate the strength of soils. CBR tests were carried out for the
untreated/native black cotton soil as well as for the treated black cotton soil with cement only,
stone dust only, and rice husk ash only and with the combination of cement, stone dust rice husk
ash with different proportions.
4.10.1. CBR values of Soil treated with Cement
For the black cotton soil treated with Portland cement, sample specimens were prepared at 4%
and 8% of cement by dry weight of the soil. The CBR values for the soil treated with cement were
determined on soil samples compacted at OMC and soaked in water for 96 hours (4 days) by
placing a 4.5 kg surcharge load.
40
35
CBR (%)
30
25
20
15
10
5
0
0
4C
cement content
8C
Figure 22 distribution of soaked CBR values for the soil treated with cement
The CBR values of the native/untreated black cotton soil is determined as 1.4% after 4days
soaking, which indicate a total loss of strength of the untreated black cotton soil on soaking.
Whereas after the addition of cement, the CBR values of the treated soil increased with increasing
the cement content and reach a maximum CBR value of 33.5% with 8% cement content.
67
From the figure above, it can be concluded that the CBR values of cement treated soil increased
with increasing cement content. The reason for the improvement of the CBR values of the cement
treated soil could be because of the cementing pozzolanic reaction between the soils and cement
materials. The chemical hydration during the reaction, regarded as calcium hydroxide, or
Ca(OH)2, formed additional cementation material that bound particles together and enhanced the
strength of the soil. The recorded CBR values of 15% for soil treated with 4% cement is
categorized as subgrade strength class S-5, whereas the CBR value of 33.5% with 8% cement
content is grouped as S-6 subgrade strength class according to (ERA, 2002). Hence, it is
concluded that soil treated with cement content of 4% and higher, fulfills the subgrade strength
requirement stipulated in ERA 2002 Manual.
4.10.2 CBR values of Soil treated with Stone Dust
For the black cotton soil treated with stone dust only, sample specimens were prepared at 5%,
10%, and15% of stone dust by dry weight of the soil. The CBR values for the soil treated with
stone dust were determined on soil samples compacted at OMC and soaked in water for 4-days
under a 4.5kg surcharge load. Then the CBR values were recorded after 4 days soaking. The
respective soaked CBR values for the soil treated with different proportion of stone dust are
summarized in figure below. The soaked CBR values of the treated soil increases slightly with
increasing stone dust contents. The maximum CBR value recorded to be 19% for the soil treated
with15% stone dust content. The slight increase in CBR values may be attributed because of the
reason that the grains of the stone dust form an interlocking system with the soil grains, which
results in an increase in resistance to penetration.
68
20
18
16
CBR (%)
14
12
10
8
CBR (%)
6
4
2
0
0
5SD
10SD
15SD
Stone dust content
Figure 23 Distribution of Soaked CBR values for the soil treated with stone dust
The CBR values of soil treated with stone dust increased with increasing the stone dust content.
However, the addition of stone dust to the native black cotton soil has not brought significant
improvement on the strength (CBR values) of the treated soil. This is due to the fact that the
natural soil had very high clay content so that the addition of stone dust only reinforced the sand
size content of the soil-dust mixture and form an interlocking system with no chemical change of
the clay particles of the black cotton soil. The recorded CBR value of 6.8% for soil with 5% stone
dust is fall under subgrade strength class S-3. On the other hand, recorded CBR values of 9.9%
for soil treated with 10%, and 19% for soil treated with15% stone dust categorized as subgrade
strength class S-4 and S-5respectively according to (ERA, 2002b).
4.10.3. CBR values of Soil treated with Rice Husk Ash
The variations of California Bearing Ratio (CBR) with different percentage of soil and rice
husk ash combinations are shown in figure below for 4 days soaked conditions. The maximum
California Bearing Ratio (CBR) value of 10.7% is found to occur with the 20% Rice Husk Ash
(RHA) contents under soaked condition.
69
12
CBR (%)
10
8
6
CBR (%)
4
2
0
0
10RHA
15RHA
Rice husk ash content
20RHA
Figure 24 Distribution of soaked CBR values for the soil treated with rice husk ash
In the above figure, values of CBR showed an increasing trend with increasing percentages of RHA
content. Slightly rate of increment observed up to 20% RHA content. The increment in the CBR
value is due to the gradual formationof cementations compounds between the RHA and CaOH
contained in the soil.
4.10.2. CBR values of Soil treated with Cement, Stone Dust and Rice Husk Ash Mixture
CBR tests for black cotton soil treated with cement, stone dust and rice husk ash mixture were
carried out by varying the stone dust content by 5% (i.e. 5%, 10%, and 15%) and rice husk ash
content by 10%( i.e. 10%, 15%, and 20%) while keeping 8% cement content constant. The CBR
values of the treated soil increased when the cement, stone dust and rice husk ash proportion
increased as it is shown in figure below. But this increment is at a smaller rate.
70
90
80
70
60
50
40
30
20
10
0
CBR (%)
Figure 25 Distribution of CBR values for the soil treated with cement, stone dust and rice
husk ash mixture
Higher CBR values were recorded for the soil treated by cement, stone dust and rice husk ash
mixture than the soil treated with cement alone. For the soil treated with 8%C + 5% SD+20%
RHA, 8%C+ 10% SD+20RHA, and 8%C+ 15% SD+20%RHAthe recorded CBR values are
56.7%, 63% and 76.7% higher than the CBR values of the soil treated with cement only.
The observed higher CBR values for the soil treated by a mixture of cement, stone dust and rice
husk ash mixture than the soil treated with cement alone could be attributed to the fact that when
cement and stone dust are mixed together, the mixes of additives acts as a ‗cement-mortar‘ which
resulted in the formation of strong bond between the soil particles which in turn increases the
resistance to penetration during the CBR tester than the soil treated with cement alone.
Hence, it is concluded that soil treated with the mixture of cement, stone dust and rice husk ash
for all the mix proportion even at the smaller stabilizer content (8%OPC+5%SD+10RHA)
categorized as subgrade strength class S-6 (CBR>30%) according to ERA (2002) and fulfills the
subgrade strength requirement stipulated in ERA 2002 Site Investigation Manual.
4.11 UNCONFINED COMPRESSIVE STRENGTH (UCS)
Unconfined compression test is used to determine the unconsolidated, un-drained strength of a
cohesive soil for a cylinder of soil without lateral support, which demonstrates evaluation of soils
without later support like road embankment materials.
The unconfined compression strength is often used as an index to quantify the improvement of
soils due to treatment. For example, ASTM D-4609 (Standard guide for evaluating effectiveness
71
of admixture for soil stabilization) states that an increase in unconfined compressive strength of
345 KPa (50 psi) or more must be achieved for a treatment to be considered effective. UCS tests
were carried out for the untreated/native black cotton soil as well as for the treated black cotton
soil with cement only, stone dust only, and rice husk ash only and with the combination of
mixtures with different proportions and different curing periods.
4.11.1 Unconfined Compressive Strength of Soil treated with cement
The UCS values for the soil treated with cement were carried out on soil sample specimens
prepared at 4%, and 8% of cement by dry weight of the soil. Soil sample compacted and tested
immediately after compaction (No curing) and soil sample compacted and tested after 7 days
curing is done. The UCS value of the native/untreated black cotton soil is determined as
148.58Kpa indicating that the untreated black cotton soil has poor strength and shear resistance.
Whereas after the addition of cement, the UCS values of the treated soil increased with increasing
the cement content. UCS values for the soil treated with different proportion of Cement with no
curing and after 7 days curing of the soil sample are summarized in figure 26 below.
400
UCS (KPa)
300
200
0
100
4C
8C
0
0 day
7 day
Curing day
Figure 26 Variation of UCS for cement treated soil for no curing and 7 day curing
As it can be shown on figure above, it is observed that soil samples treated with cement and cured
for 7 Days shows significant improvement on UCS values than soil treated with the same amount
of cement content with no curing applied (i.e. test immediately after compaction).
4.11.2 Unconfined Compressive Strength of Soil treated with Stone Dust
The UCS tests for black cotton soil treated with stone dust only, were carried out by preparing
remolded specimens for the mixes with varying stone dust content by 5% (i.e. 5%, 10%, and15%)
72
by dry weight of the soil. However, the addition of stone dust to the native black cotton soil has
insignificant improvement on the UCS values of the treated soil.
300
UCS (%)
250
200
150
0 day
100
7 day
50
0
0
5SD
10SD
stone dust content
15SD
Figure 27 Variation of UCS for uncured and with 7 days cured stone dust treated soil
The observed slight increment on UCS values is because it is thought that the grains of the stone
dust form an interlocking system with the soil grains which results in an increase in shear
resistance of the treated soil which in turn increase the unconfined compressive strength.
However, the UCS value of the black cotton soil treated with stone dust alone doesn‘t have
practical significant improvement. This is due to the fact that the natural soil had very high clay
content so that the addition of stone dust only reinforced the soil grains and create an interlocking
system with no chemical change of the clay particles of the black cotton soil.
4.11.3. Unconfined Compressive Strength of Soil treated with Rice Husk Ash
The UCS tests for black cotton soil treated with rice husk ash only, were carried out by preparing
remolded specimens for the mixes with varying rice husk ash content by 10% (i.e. 10%, 15%, and
20%) by dry weight of the soil. However, the addition of rice husk ash to the native black cotton
soil has insignificant improvement on the UCS values of the treated soil. The value of rice husk
ash treated soil increased from 148Kpa to226.59 Kpa and 255.16Kpa at 20% rice husk ash
content for uncured state and 7 day cured day respectively.
73
300
250
UCS (kpa)
200
150
0 day
100
7 day
50
0
0
10RHA
15RHA
20RHA
Rice husk ash content
Figure 28 Variation of UCS f treated soil by rice husk ash for no curing and 7 day curing
4.11.4. Unconfined Compressive Strength of Soil treated with Mixture of Cement, Stone
Dust and Rice Husk Ash
UCS tests for black cotton soil treated with cement, stone dust and rice husk ash mixture were
carried out by varying the stone dust content by 5% (i.e. 5%, 10%, and 15%) and RHA content by
10%(i.e. 10%, 15%, and 20%) while keeping 8% cement content constant. UCS test results for
the treated black cotton soil with cement, stone dust and rice husk ash mixture for different
proportion of the added stabilizers is presented in figure 29 below.
74
ucs (Kpa)
450
400
350
300
250
200
150
100
50
0
0 day
7 day
Mix Ratio
Figure 29 Variation of UCS f treated soil by cement, stone dust and rice husk ash mixture
for without curing and 7 day curing
Generally, the Unconfined Compressive Strength (UCS) values of the treated soil increased when
the cement, stone dust and rice husk ash proportion increased as it is shown in figure above. The
maximum value of UCS record at 8%C+10SD+20RHA mix proportion are 345.59 and 421.6 for
uncured and cured mix respectively.
75
CHAPTER 5
CONCLUSION AND RECOMMENDATIONS
5.1 CONCLUSION
Based on the study and results of the investigation, the following conclusions are drawn:
 The studied black cotton soil is classified as A-7-5 soil according to AASHTO
classification system. Furthermore, the plasticity index, CBR, and linear shrinkage results
of the native soil revealed that the soil has a very low bearing capacity, high swelling
potential and susceptible to volume change which makes it unsuitable to use it as a
subgrade soil unless it is treated with suitable stabilizer.
 Soils treated with cement alone by 4% and 8% dry weight of the soil showed significant
improvement in strength and reduces the swelling property of the native soil significantly
and also improve the plasticity characteristics of the soil. Generally it was observed that
with increasing the cement content, strength of the treated soil improved, plasticity and
swelling potential of the soil getting decreased.
 Soil treated with only stone dust (SD), by 5%, 10%, and 15% by dry weight of the soil
showed slight/nominal improvement in the strength and plasticity characteristics of the
soil.
 Treating expansive soils with stone dust only and rice husk ash only has not brought
significant improvement on the plasticity of the treated soil. And it is concluded that stone
dust and rice husk ash by itself is not an effective stabilizer for treating expansive soils
when compared with soil treated with cement only.
 Whereas, soil treated with cement, stone dust and rice husk ash mixture significantly
improve the strength and profoundly reduce the plasticity characteristics of the treated
soil.
 Proper curing is important in strength development for all proportion cases. A curing
period of 7days was observed to yield maximum compressive strength of stabilized
expansive soil.
 When cement, stone dust and rice husk ash mixtures, the mixes of the additives acts like a
‗Cement-Mortar‘. Hence, holistic and significant improvements were recorded for the soil
76
treated by cement, stone dust and rice husk ash mixtures than the soil treated with cement
alone.
 According to ERA (2002d), the material forming the road subgrade shall have a minimum
soaked Californian Bearing Ratio (CBR) of greater than 5%. Furthermore, according to
ASTM D-4609 (Standard guide for evaluating effectiveness of admixture for soil
stabilization) an increase in unconfined compressive strength of 345 KPa or more must be
achieved after seven days curing for a treatment to be considered effective and as
benchmark for long-term stabilization.
 Soil treated with the mix proportion of (8%C + 5%SD+20%RHA) resulted in soaked CBR
of 56.7%, Plasticity Index of 23 and UCS value 365.23kPa after 7 days curing.
 Therefore (8%C + 5%SD+20%RHA) was found to be the optimum stabilizer content for
the studied soil to utilize it as a road subgrade soil and fulfills all the requirements
stipulated for a road subgrade material according to ERA (2002d) and ASTM D-4609
(Standard guide for evaluating effectiveness of admixture for soil stabilization)
requirements.
5.2 RECOMMENDATIONS
 The present work has attempted to evaluate and characterize the engineering properties of
black cotton soil material collected only from 3 areas. However, as the country is endowed
with widely distributed black cotton soil deposit, it is recommendable to carry out
investigation from samples collected from other areas in order to develop a guide-line.
 The effect of curing time (longer curing periods) on the engineering properties of the
cement, stone dust and rice husk ash stabilized black cotton soils shall be evaluated since
hydration and pozzolanic reactions of cement are time bound.
 This research study was conducted on black cotton soils treated with cement alone, stone
dust alone, rice husk ash alone, and cement, stone dust and rice husk ash combination, but
researches can be made to mix cement and stone dust, cement and rice husk ash, and stone
dust and rice husk ash with a trial proportions at this study area.
 Research studies shown that physical and chemical properties of RHA are dependent on
the soil chemistry, paddy varieties and climatic conditions. Therefore, it‘s mandatory to
assess the stabilizing potential of RHA from different sources.
77
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Cement or Lime Solidified Soil. International Conference on Future Energy.
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APPENDIX
Appendix A. Natural Moisture Content Test Results
Table A. 1: Natural moisture content test results of untreated soil
Can No
Mass of can (g),
M1
Mass of can+ wet
soil (g), M2
Mass of can+ dry
soil (g), M3
Moisture content,
W (%)
1
35.47
115.56
93.22
38.7
2
36.82
143.25
115.15
35.9
3
35.72
134.21
106.59
39.0
Average %
37.8
Mass of water, Mw =M2-M3
Mass of dry soil, Ms =M3-M1
Moisture content, w%= Mw/ Ms*100%
84
Appendix B: Specific Gravity Test Results
85
86
87
88
89
90
91
92
93
Appendix C. Grain Size Analysis (Wet Sieve) for Untreated Soil
Particle larger than 2mm % =
Sand( 2mm-0.075mm )% =
silt (0.075mm-0.002mm) % =
clay (less than 0.002mm) % =
2
2.7
41.3
54
94
Appendix D: Free Swell Test Results (Controlling Test)
95
96
97
Appendix E: Linear Shrinkage Limit Test
98
Appendix F: Atterberg Limit Test Result
1. Umtreated Soil
Without curing
7day curing
14 day curing
2. Soil treated with Cement
99
Without curing
7day curing
14 day curing
100
3. Soil treated with Stone Dust Only
Without curing
7 Day curing
101
14 Day curing
102
4. Soil treated with Rice Husk ASH Only
Without curing
103
7 Day curing
104
14 Day curing
105
4 Soil treated with Cement, Stone dust andRice Husk ASH mixture
Without curing
106
107
108
7 Day curing
109
110
111
14 days curing
112
113
114
Appendix G: Moisture Density Relation and CBR test
1. Untreated Soil
115
2. Soil treated by Cement
4% cement (4C)
116
8% Cement (8C)
3.Soiltreated by Stone Dust
117
5% stone dust (5SD)
10% Stone Dust (10SD)
118
15% Stone Dust (15SD)
119
4
Soil treated by Rice Husk Ash
120
10% Rice Husk Ash (10RHA)
15% Rice Husk Ash
121
20% Rice Husk Ash (20RHA)
122
5. Soil treated by cement, Stone Duse, and rice husk ash mixture
8C5SD10RHA Mixes
123
8C5SD15RHA Mix
124
8C5SD20RHA Mixes
125
8C10SD10RHA Mixes
126
8C10SD15RHA Mixes
127
128
8C10SD20RHA Mixes
8C15SD10RHA Mixes
129
8C15SD15RHA Mixes
130
131
8C15SD20RHA Mixes
132
Appendix H: Unconfined Compressive strength Test (UCS)
1 Untreated Soil with out and with 7 days curing
2 Soil treated with Cement (Without and with 7 days curing)
133
134
135
3 Soil treated with Stone Dust
136
137
138
4 Soil treated with Rice Husk Ash
139
140
141
4 Soil treated with Cement, Stone Dust and Rice Husk Ash Mixtures
142
143
144
145
146
147
148
149
150
Appendix I Chemical Composition of Rice Husk Ash Stone Dust
151
Appendix J Photos taken during testing and site visit
Photo C. 1: Liquid limit test in laboratory
152
Photo C. 2: Free swell test in laboratory
153
Photo C. 3: UCS test reading in laboratory
154
Photo C. 4: CBR reading in laboratory
155