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NWANKWOR, NWACHUKWU AZU
PG/PhD/02/33841
OPTIMIZATION OF RICE-HUSK-ASH AND STRAW AS STABILIZERS
FOR EARTH MATERIAL [MUD] FOR BUILDING CONSTRUCTION
Education
A THESIS SUBMITTED TO THE DEPARTMENT OF VOCATIONAL TEACHER EDUCATION
(INDUSTRIAL TECHNICAL EDUCATION SECTION), FACULTY OF EDUCATION,
UNIVERSITY OF NIGERIA, NSUKKA
Webmaster
Digitally Signed by Webmaster‟s Name
DN : CN = Webmaster‟s name O= University of Nigeria, Nsukka
OU = Innovation Centre
2010
UNIVERSITY OF NIGERIA
ii
OPTIMIZATION OF RICE-HUSK-ASH AND STRAW AS
STABILIZERS FOR EARTH MATERIAL [MUD] FOR
BUILDING CONSTRUCTION
by
NWANKWOR, NWACHUKWU AZU
PG/PhD/02/33841
DEPARTMENT OF VOCATIONAL TEACHER EDUCATION
(INDUSTRIAL TECHNICAL EDUCATION SECTION)
UNIVERSITY OF NIGERIA, NSUKKA
NOVEMBER, 2010
OPTIMIZATION OF RICE-HUSK-ASH AND STRAW AS STABILIZERS
FOR EARTH MATERIALS[MUD] FOR BUILDING CONSTRUCTION
by
NWANKWOR, NWACHUKWU AZU
PG/PhD/02/33841
A THESIS SUBMITTED TO THE
DEPARTMENT OF VOCATIONAL TEACHER EDUCATION
(INDUSTRIAL TECHNICAL EDUCATION SECTION)
UNIVERSITY OF NIGERIA, NSUKKA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE AWARD OF THE DOCTOR OF PHILOSOPHY (Ph.D.) DEGREE IN
INDUSTRIAL TECHNICAL EDUCATION (BUILDING TECHNOLOGY)
SUPERVISOR; SIR, PROF. S. C.O.A. EZEJI
NOVEMBER, 2010
i
ii
APPROVAL PAGE
THIS THESIS HAS BEEN APPROVED FOR THE
DEPARTMENT OF VOCATIONAL TEACHER EDUCATION
(INDUSTRIAL TECHNICAL EDUCATION SECTION)
UNIVERSITY OF NIGERIA, NSUKKA
by
_____________________________ ____________________________
SIR, PROF. S. C. O. A. EZEJI Internal Examiner
Supervisor
____________________________ _______________________
PROF. O. T. IBENEME PROF. E. E. AGOMUO
External Examiner Head of Department
_____________________
PROF. S. A. EZEUDU
Dean of Faculty
iii
CERTIFICATION
NWANKWOR, NWACHUKWU AZU, a postgraduate student of the Department of Vocational
Teacher Education (Industrial Technical Education - Building Technology), with Registration
Number PG/PhD/02/33841, has satisfactorily completed the requirements for the award of the
Degree of Doctor of Philosophy (Ph.D.) in Industrial Technical Education – Building
Technology. The work embedded in this Thesis is original and has not been submitted in part or
full for any Degree of this University or any other University.
_________________________ ________________________________
N. A. NWANKWOR SIR, PROF. S. C. O. A. EZEJI
Student Supervisor
iv
DEDICATION
This work is dedicated to:
The Almighty God, the Creator of the universe, who taught our first parents how to build with
earth (mud), and to the entire family of Late Evangelist and Elder Mrs. Azu Nwankwo.
v
ACKNOWLEDGEMENTS
The researcher is sincerely grateful to all the individuals and corporate persons who
contributed in one way or the other to make this project a success. The researcher is grateful to his
supervisor, Sir, Prof. S. C. O. A. Ezeji, whose eagle‟s eye corrections, commitment, personal counsel
and guidance brought out quality in this research, and to his wife (Lady Dr. H. Ezeji), special thanks
for putting in words of encouragement when they mattered most.
The researcher wishes to acknowledge with gratitude the counsel, advice, suggestions and
painstaking time spent by Prof. O. M. Okoro and Dr E. O. Ede to read and correct this report during
and after the proposal defense. My appreciation goes to Prof. Mrs. E. U. Anyakoha for her counsel
and advice during the re-presentation of the proposal defense, and to Dr Mrs. T. C. Ogbuanya for her
encouragements in the face of frustrating situations during the course of this research. The researcher
is grateful to Prof. N. J. Ogbazi for always keeping an open door to attend to this “Yola Man” and to
Prof. F. A. Okwo whose encouraging words kept this researcher, when every hope of successfully
completion of this work was at lowest ebb. May God bless them all. The researcher is also grateful to
all the staff of the Department of Vocational Teacher Education, University of Nigeria, Nsukka.
Especially Dr A. E. A. Anene, Mrs. Theresa Idika, Elder Mrs. C. K. Uta and Mr. Emmanuel Onah for
all their assistance in material and information location within this university and to other Lecturers in
the Department of Vocational Teacher Education for their various assistance and encouragement.
The researcher is gratefully indebted to Ven. Prof. Chinedu O. Nebo, the Vice Chancellor,
whose tenor in the University of Nigeria, Nsukka restored security and safety to the campus; and for
providing a convenient internet service that made it possible for the researcher to gain quick access to
other international researchers and research centers for materials in earth building development and
conservation. The researcher‟s gratitude also goes to the Federal University of Technology, Yola, for
granting him the study fellowship to pursue this programme. To all my colleagues at Federal
University of Technology, Yola, especially my neighbor Mr. and Mrs. Hassan Nicodemus and Mr.
John Dogari, for attending to my family during my periods of long absence. I appreciate you so much.
I say may God bless you all abundantly. The researcher sincerely appreciate with gratitude all the
Laboratory Technologist and their assistants who conducted the tests and analysis with the researcher,
especially my cousin Mr. Yuel O. Kalu (Civil Engineering Dept., UNN); Mr. Cletus Nwokorie (Dept.
of Soil Science), Mal. Raji (Dept. of Biochemistry) and Mr. Thomas Pambi(Dept. of Civil
Engineering) all of the Federal University of Technology, Yola. Thank you all immensely. This
researcher is also grateful to all whose works were made direct or indirect references to, during the
course of this research. The researcher is thankful to the Statisticians - Prof. F. A. Ogbu, Mr. Julius
Ugonna, Dr A. A. Abdulkadir and Dr. D. Eze for the data analysis.
The researcher fondly acknowledges the unquantifiable contributions and sacrifices of my
family members and friends, especially my beloved wife Mrs. Cecilia E. A. Nwankwor (Cecy Baby),
my wonderful, lovely children Simon, Blessed, Favour and Precious Oluebubechukwu, my dear Sister
Ada Ajike; and my Cousins John and Immanuel Nwankwo who had to go through difficult times
during the course of this research. And to my Sister and Brothers - Elder Mrs. E. O. Nkere, Elders I.
A. Nwankwor, C. A. Nwankwor, O. S. Azu, Revd. John Azu and their families; and all of the Azu
Nwankwo extraction, for their encouragement, moral and financial assistance while this programme
lasted. I say God bless you all.
The researcher‟s special thanks goes to Mr. and Mrs. K. O. Uka and Mr. and Mrs. Ukpai
Okonkwo and their entire families for their willingness, without pre-notice, to render every assistance
all through this programme. To Rev Williams I. Njoku, Elder Candid E. Umazi and Messer Nelson I.
Mba, K. K. Agwu, O. A. Ndukwe, Joseph Mecha, Abianya Okoro, Obinna Ojeh, and all others too
numerous to mention, the researcher prays for God‟s favour and blessings on you all for your prayer
support and encouragement during this research. Finally and very importantly, the researcher is most
grateful to the Almighty God for His sustenance, favour, blessings and protection from several
accidents and attacks while this research lasted.
vi
TABLE OF CONTENTS
page no
ACKNOWLEDGEMENTS v
TABLE OF CONTENT vi
LIST OF TABLES ix
LIST OF FIGURES xi
ABSTRACT xii
CHAPTER I: INTRODUCTION 1
Background of the Study 1
Statement of the Problem 6
Purpose of the Study 7
Significance of the Study 8
Research Questions 9
Hypotheses 10
Scope of the Study 11
Assumptions and Limitations 12
CHAPTER II: REVIEW OF RELATED LITERATURE 13
Conceptual Framework 13
Building with the Earth-Material: History and Practices 16
Soil Properties and Factors Affecting its Choice as a Building Material 18
Earth Material(Soil) Stabilization for Earth Building Purposes 21
Types of Stabilizer(Additive) Used to Stabilize the Earth Material 23
Factors Affecting the Stability of the Earth Material(Mud/Soil) 26
Socio-Economic and Environmental Reasons for Alternative Building Materials 27
Government Initiatives on Earth Building in Nigeria 29
Building Standards/Codes (Benchmarks) Related to Compressive Strength
and Erosion Resistance Qualities of Earth Buildings 32
Review of Related Researches on the Stabilization of the Earth Material(Mud/Soil) 38
Optimization and Standardization of Products/Processes 44
Material and Specimen Testing Method 48
Summary of Review of Related Literature 49
CHAPTER III: METHODOLOGY 52
Research Design 52
Area of Study 53
Study Location 53
Sampling Technique 53
Sample Size 54
Research Equipment/Instrument for Data Collection 55
Validation of the Instrument/Equipment 55
Reliability of the Instrument/Equipment 57
Research Specimen 58
Experimental Procedure 59
i. Selection /Collation of Research Materials 59
ii. Soil Preparation 60
iii. Stabilizer Preparation 60
vii
iv. Field and laboratory Testing of Base Materials 61
v. Batching of Materials 62
vi. Specimen Production 63
vii. Laboratory Testing of the Samples 65
Method of Data Analysis 67
CHAPTER IV: PRESENTATION AND ANALYSIS OF DATA 68
Chemical/Material Composition of the Research Materials 68
i. Particles Distribution of the Soil Samples 68
ii. Chemical Composition of the Three Soil Samples 69
iii. Chemical Composition of the RHA Compared with that of Cement 74
iv. Analysis of the Chemical Composition of the Straw 76
Data Analysis Based on the Research Questions 77
Test of the Hypotheses 104
Major Findings 132
Discussions 135
CHAPTER V: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 138
Re-statement of the Problem of the Study 138
Summary of Procedure Adopted 139
Major Findings 140
Implications of the Study 142
Conclusions 142
Recommendations 143
Limitations of the Study 144
Suggestion for Further Study 144
REFERENCES 146
APPENDIXES 156
APPENDIX A: Soil Classification Based on Particles Size 156
APPENDIX B: Basic Data on Cement Stabilized Earth Blocks(CSEBs) 158
APPENDIX C: Formulae for Calculating the Compressive Strength
and the Erosion Resistance Of The Stabilized Earth Blocks 160
APPENDIX D: Comprehensive Schedule of the Mean Values of the
Twenty-seven Experimental Groups 162
APPENDIX E: Schedule of the Raw Values and the Calculated Means
of the Compressive Strength and Erosion Resistance Ratios
of the Twenty-seven Experimental Groups of the Stabilized
Earth Blocks 164
APPENDIX F: Schedule of The Univariate Analysis of Variance (UANOVA)
of the Compressive Strength Data Incorporating the Descriptive
Statistics, Test of Between-Subjects Effects, Post-Hoc Tests
and the Homogeneous Sub-Sets Tests 168
viii
APPENDIX G: Schedule of The Univariate Analysis of Variance (UANOVA)
of the Erosion Resistance Ratios Data Incorporating the
Descriptive Statistics, Test of Between-Subjects Effects,
Post-Hoc Tests and the Homogeneous Sub-Sets Tests 177
APPENDIX H: Case-Processing Summary for the Compressive Strength
and Erosion Resistance and Stabilizer Means 186
APPENDIX I Case-Processing Summary: If Stabilizer = 1 189
APPENDIX J Case-Processing Summary: If Soil Type = 1 193
APPENDIX K Case-Processing Summary: If Mix Proportion = 1 197
ix
LIST OF TABLES
Tables page
1 Differences in Compressive Strength Between Established and Pilot Blocks 57
2 Erosion Resistance Ratios from Laboratory and Field-based Tested and
Pilot Blocks 58
3 Compressive Strength of the Pilot Study Blocks Compared with Main
Experimental Results 59
4 Erosion Resistance Ratios of the Pilot Blocks Compared with the Main
Experimental Blocks 59
5 Schedule of Specimen Grouping by Stabilizer, Mix Proportion and Soil Types 66
6 Particles Distribution of the Three Earth Building Soil Samples 70
7 Chemical Composition of the Three Soil Samples 71
8 Chemical Composition of Rice Husk Ash (RHA) and Ordinary Portland Cement 76
9 Chemical Composition of Straw 77
10 Detailed Schedule of the Compressive Strength for Experiments I, II and III 85
11 Comparison of Mean Values of Compressive Strength Based on Stabilizer Type 86
12 Comparison of Mean Values of Compressive Strength Based on Soil Type 89
13 Comparison of Mean Value of Compressive Strength Based on Mix Proportions 92
14 Schedule of the Erosion Resistance Ratios from Experiments I, II and III 93
15 Comparison of Mean Values of Erosion Resistance Ratios Based on Stabilizer Type 95
16 Comparison of the Mean Values of Erosion Resistance Ratios Based on Soil Type 97
17 Comparison of the Mean Value of Erosion Resistance Ratios Based on Mix
Proportions 100
18 Schedule of Mean Compressive Strength and Erosion Resistance Ratios 101
19 Test of Between-Subjects Effects (Dependent Variable: Compressive Strength) 105
20 Pairwise Comparisons Based on Stabilizer Type(Dependent Variable: Compressive
Strength) 106
21 Multiple Comparisons Based on Stabilizer Type (Dependent Variable:
x
Compressive Strength) 107
22 Test of Between-Subjects Effects (Dependent Variable: Compressive Strength) 109
23 Pairwise Comparisons Based on Soil Type (Dependent Variable: Compressive
Strength) 110
24 Multiple Comparisons Based on Soil Type (Dependent Variable: Compressive
Strength) 113
25 Test of Between-Subjects Effects (Dependent Variable: Compressive Strength) 111
26 Pairwise Comparisons Based on Mix Proportions (Dependent Variable: Compressive
Strength) 114
27 Multiple Comparisons Based on Mix Proportions (Dependent Variable: Compressive
Strength) 115
28 Schedule of Comprehensive Data on Mean Erosion Resistance Ratios 116
29 Test of Between-Subjects Effects (Dependent Variable: Erosion Resistance) 117
30 Pairwise Comparisons Based on Stabilizer Type (Dependent Variable: Erosion
Resistance) 118
31 Multiple Comparisons Based on Stabilizer Type(Dependent Variable: Erosion
Resistance) 119
32 Test of Between-Subjects Effects (Dependent Variable: Erosion Resistance) 121
33 Pairwise Comparisons Based on Soil Type (Dependent Variable: Erosion Resistance)123
34 Multiple Comparisons Based on Soil Type (Dependent Variable: Erosion Resistance)123
35 Test of Between-Subjects Effects (Dependent Variable: Erosion Resistance) 124
36 Pairwise Comparisons Based on Mix Proportions (Dependent Variable: Erosion
Resistance) 125
37 Multiple Comparisons Based on Mix Proportions (Dependent Variable:
Erosion Resistance) 126
38 Test of Between-Subjects Effects (Dependent Variable: Compressive Strength) 128
39 Test of Between-Subjects Effects (Dependent Variable: Erosion Resistance) 129
40 Descriptive Statistics on RHA+Straw (Dependent Variable: Compressive Strength)131
41 Descriptive Statistics on RHA+Straw (Dependent Variable: Erosion Resistance) 132
xi
xii
LIST OF FIGURES
Figures page
1 Illustration of Experimental Groupings 59
2 The Researcher Batching out Materials with the Local Earth Builder 63
3 The Researcher Mixing the Materials after Batching 64
4 Specimen Compressed Stabilized Earth Block 64
5 One of the Research Assistants (Immanuel) with the Local Earth Builder 64
6 Samples of the Stabilized earth Block Specimen after Demoulding 64
7 A Comparism of the Compressive Strength of Earth Materials Stabilized with
RHA, Straw and RHA-Straw 86
8 A Comparism of the Erosion Resistance Ratios of Earth Materials Stabilized with
RHA, Straw and RHA-Straw 95
xiii
Abstract
This project was primarily a material research and development endeavour centered on
optimizing the use of two local stabilizers - straw and rice-husk-ash – in stabilizing the earth
material for quality earth building construction. The research sought to find out the most efficient
and cost effective way of using rice-husk-ash and/or straw for earth material stabilization; what
mix proportion of the these stabilizers and with what type of soil will give an optimal
compressive strength and erosion resistance of the stabilized earth material. To achieve this, a 3
x 3 x 3 experimental model was adopted - 3 stabilizer groups (RHA, Straw and RHA-Straw), on
3 earth building soil samples (Clayey, Red and Laterite soil types), at 3 mix proportions (11%,
14.5% and 20%). A laboratory analysis was conducted to identify the particles distribution and
chemical composition of the soil samples and the major chemical elements of the stabilizers that
could affect the structural properties of the stabilized earth material. Nine research questions and
eight null hypotheses were developed to guide this research. A total of 270 compressed,
stabilized earth block specimen were produced, 10 for each of the 27 experimental groups. Out of
these 10 blocks, 5 blocks were randomly selected and assigned to the 27 different experimental
groups. The Rockwell Universal Medium Strength Cube Crushing Machine was used to test the
compressive strengths, while the University of Technology, Sydney(UTS) type Spray Test
Instrument was used to test the erosion resistance capacity of the earth material. Frequency count,
Mean and Ratio were used for the primary analysis of the data to answer the research questions,
while an Analysis of Variance (ANOVA) statistical model employing a univariate approach was
used to test the hypotheses and validate the primary findings. The findings of this study showed
that all the soil samples had their particles distributions within the acceptable range (25 – 40%) of
clay for earth building works; all the three soil samples contained Iron, Potassium, Magnesium,
Calcium, Zinc, Nitrates, Phosphorous at varying percentages, while the red soil and clayey soil
contained Cadmium at 0.10% and 0.36% respectively. Only the clayey soil contained 1.53% of
Sodium. The RHA was found to be basically a Silicon Dioxide fine powder(25µ), containing
Silicon Dioxide(89.75%), Calcium Oxide(2.19%), Potasium Oxide(2.08%), Aluminium
Oxide(0.48%), Ferric Oxide(0.89%), Manganese Oxide(0.43), Phosphorous Oxide (0.67%),
Titanium Oxide(0.16%) and traces of Magnesium Oxide and Sodium Oxide. The Straw was
composed of Silicon Oxide (31.50%), Holocellulose (26.20%), Alpha Cellulose(14.6%),
Hemicellulose (10.60%0, Alcohol-Benzene solubility(7.50%), and Lignin(9.60%). Differences in
the stabilizer type was found to have significant effect (P < 0.05) on the mean compressive
strength (F = 2473.157) and (F = 7239.684) on the erosion resistance capacity of the stabilized
earth material. Changes in the soil types had significant effect (P < 0.05) on the mean
compressive strength (F = 2554.283) and (F = 728.616) on the erosion resistance capacity of the
stabilized earth material. Variations in the mix proportion had significant effect (P < 0.05) on the
compressive strength (F = 279.3.88) and on the erosion resistance capacity (F = 89.128) of the
stabilized earth material. The interaction between stabilizer type, soil type and mix proportion
significantly affected the compressive strength (F = 14.136) and the erosion resistance capacity(F
= 95.435) of the stabilized earth material. Red soil stabilized with a combination of RHA-Straw
at a mix proportion of 20 per cent (1:1:8) produced an optimal compressive strength( χ = 4.82
±0.023) and erosion resistance capacity (χ = 6.82 ± 0.02) of the stabilized earth material. Through
the investigation of the structural behaviour characteristics of the stabilized earth material based
on different stabilizer types, changes in soil types and variations in the mix proportion, the study
ended with a quality stabilized earth material product that optimized the use of these locally
available additives – RHA and Straw – for earth material stabilization.
1
CHAPTER I
INTRODUCTION
Background of the Study
The use of earth (kneaded mud or clay), which is commonly called earth material in
international research documents, as a building material dates back thousands of years as
recorded in history books including The Holy Bible, (Genesis 11 & Exodus 1). Some of the first
man-made structures inhabited by man were made of earth materials. Until date the use of this
earth material for construction of buildings remains common in many parts of the world where
specific climate or economic conditions dictate, and where the sun-dried earth block –
international referred to as adobe, construction know-how is commonplace.
Earth has been used for the construction of buildings since the most ancient times, and the
traditional housing that exist in many parts of our planet bear witness to this fact. In several parts
of the world, earth material has been widely used and is still being used as a construction
material, especially for building walls, flooring and for roofing. Historical records show that the
use of earth as a building material dates back to ancient times in Mesopotamia (5000 – 4000 BC),
(Pollock, 1999). Easton (1996), estimated that, at least, 50 per cent of the world‟s population still
live in homes built of earth, while Little and Morton (2001) projected that one-third of the
world‟s population live in buildings made of earth materials across most climate zones of the
world. To date there are still pieces of evidence in several parts of Nigeria, of earth walls and
buildings that have survived more than a century within Sokoto caliphate, in Kano City, the
Fombina prison walls in Yola, the Missionary‟s houses/churches at Badagry in Lagos state and
several palace walls (obi) and shrines within the eastern parts of Nigeria. Presently one of the
oldest unprotected earth structures, the Pueblo of Taos, reported to be about 900 years old is still
standing tall in New Mexico, USA, (Heathcole & Ravindrajah, 2006).
2
Earth building is widely considered as a common method for providing cheap
accommodation since earth is readily available almost everywhere on the planet (Martinson,
2005). Earth or soil is available universally and there is a large variability in the properties of the
soil to meet different needs. Today, earth building production techniques range from the most
rudimentary, manual and craft-based to the most sophisticated, mechanized and industrial method
(Houben, Rigassi & Garnier, 1994). The compressed earth block is the modern descendant of the
sun-dried earth block, more commonly known as the adobe block. In most climate zones of
Nigeria, earth is cheap and available, and has been in use since ancient times, as a functional
building material.
Abandoned and forgotten with the advent of industrial building materials, particularly
cement and steel, earth as a building material is today the subject of renewed interest in
developing countries as well as in industrialized countries. Often criticized for its sensitivity to
water and its lack of durability, this building material, according to Arumala, Gondal, and
Bennett (2004), has in its natural form many advantages for the construction of durable,
comfortable and low-cost housing. Arumala, Gondal, and Bennett further argued that, if logic and
modern methods are applied to the use of earth, it can be all of the following - efficient and
durable; cheaply available locally; economical in energy and in foreign currency for developing
countries; an encouragement for the development of building trade skills; job creation; capital
gains generating; a dynamic for the building sector; ideal for small and medium scale industries.
The use of earth for building construction in Nigeria, started a free slide into unpopularity,
from the middle of the twentieth century, when Portland cement was introduced into the
construction industry. The introduction of Portland cement as a major building material
notwithstanding, the use of the earth material has continued to compete favourably with Portland
cement-based houses, especially in most rural and semi-urban Nigeria. As the cost of cement-
and steel-based building materials continues to increase in the face of a dwindling real value of
3
personal income in the last two to four decades, coupled with the Federal Government‟s reform
programme, interests in earth building have reawakened, especially among low-income
Nigerians. There is also a growing global concern for the development of socially and
environmentally friendly quality building materials. This growing global concern has in turn
heightened the need to develop alternative sustainable building materials to augment current
supplies of building materials. The primary focus of the concerns raised and the efforts being
made are all geared towards the production of environmentally friendly, low-cost, quality and
affordable human shelter.
To build these affordable, low-cost, decent and quality houses for Nigerians, as reinforced
by the Federal Government‟s National Economic Empowerment and Development Strategies
(NEEDS) programme and the current Federal Governments Seven-Point Agenda as they affect
quality human shelter, suggests a need to build durable houses at the lowest cost possible.
Building such low-cost houses is not possible with the current cost of building materials, which
has remained high and continues to increase day by day, with no significant increase in the real
value of the personal income of a larger percentage of Nigerians. As researches began to discover
some health problems associated with the use of many of the building materials classified as
standard, there is need for developing other alternative, cheaper, renewable sources of building
materials to realize this target of building quality, low-cost and affordable decent shelter for
Nigerians, (The Nigerian “Country Profile” to the United Nations, 1997; NEEDS
Documentations, 2004). Such other alternative sources of cheaply available quality building
materials must also take into account sustainability and environmental friendliness of such
products without compromising quality and standards of modern construction. One such
approach is the use of the earth material for building houses. To use this earth material as a viable
alternative sustainable building material, measures must be taken to overcome known weaknesses
of the earth material (Niazi, 1998). There is therefore every need for a concerted effort to
4
overcome the identified weaknesses associated with the stability, waterproofing quality and
resistance to erosion by water of the earth material. One method to achieve this is through earth
material stabilization - a technique involving the addition of natural or processed binders to earth
such as straw, cement, and rice-husk-ash and lime to improve certain properties of earth, (Stulz &
Mukerji 1988). Generally, even the best of earth material and water mixture to produce sun-dried
mud blocks (adobe) can develop cracks. It is important therefore to add some other materials to
the mixture to overcome such and other weaknesses of the earth material, (Sidibe 1985).
In traditional and advanced earth building technology systems, earthbuilders have used
some additives, technically referred to as stabilizers, to stabilize and improve the quality of the
earth material for building purposes. These stabilizers are substances, which are added to a base
material, to improve certain properties; these include benign additives such as plant oils, dung,
urine, which have minor effect and the more powerful stabilizers such as cement and lime,
(Minke, 2000). As Oraedu (1984) discovered, the functions of any earth stabilizer include to
cement the particles together so that the walls would be stronger, and to improve its “water-
proving” characteristics, so that water absorption is at an acceptable minimum. Internationally,
advanced studies and technological changes in stabilizing the earth material with known
additives, such as cement and lime have already revolutionalized earth building practices and
produced high quality standard earth buildings of compressive strengths of between 13 to
24.5Mpa[Mega-pascal] (Christensen, 2001).
Straw (one of the local stabilizers), is a collection of dry needle leaved grasses
(Wikipedia, 2006). Straw, the stalks remaining after the harvest of grains, is a renewable
resource, grown annually. It is tough and fibrous; lasts far longer than hay, which is leafy. The
combination of chemical elements in the straw distinguishes it from other organic materials that
would have decayed when in contact with water, thereby making the straw an excellent stabilizer
for earth building material (see p.77 for detailed analysis of the chemical composition of straw).
5
In the Biblical times, straw was used by the Jews, mixed straw into mud/clay for the construction
of the different magnificent structures in Egypt, the construction of the walls of Jericho, the
Tower of Babel and the walls of the City of King David (The Holy Bible, Genesis 14 & Exodus:
1–18). Among the traditional earth building zones of Nigeria, (running from the upper south-east
and the upper south-west through the middle belt up to the far north within the Sokoto caliphate
and the Borno emirate of Maiduguri), straw has been added to the earth material in different
forms of earth building techniques as a stabilizer. These earth-building techniques include the
wattle-and-daub, adobe and rammed earth construction, (Lasisi & Osunde, 1985; Lawson, 1991).
Rice-husk-ash(RHA), one of the new additions to the list of earth material stabilizers, is
produced from burning the rice husk - the surrounding of the paddy rice. This rice-husk, a by-
product of the rice milling process, is rich in silica about 85 per cent to 95 per cent by weight
(Ou, Xi & Corotis, 2006). During the milling of the paddy rice, about 75 per cent is received as
rice, broken rice, and bran. Twenty-two (22) per cent is received as rice-husk. According to
Bronzeok Ltd (2003), rice-husk-ash is a general term describing all types of ash produced from
burning rice husk. This rice-husk according to Singhania (2004) contains about 75 per cent
organic volatile matter, leaving 25 per cent to be converted into ash during the burning process. It
is usually higher in ash than other biomass fuels – close to 20 per cent. Rice-husk-ash (RHA) is
82–95 per cent silica, highly porous and lightweight, with a very high external surface area
(Oliver, 2007). Its absorbent and insulation properties are useful to many industrial applications,
(Bronzeoak Ltd, 2003). It is these qualities of the RHA that have made it handy to experiment in
the stabilization of earth materials for earth building construction.
The interest for low-cost, quality houses, to meet critical needs for quality housing
shortages in Nigeria and standard against trial-and-error in improving the functional requirements
of the earth material, challenged the interest of this researcher for this project. The researcher was
interested in optimizing [i.e. enhancing the effectiveness of these stabilizers, or a way of making
6
them function at their best or most effective, or use these stabilizers to their best advantage,
(Singer,2006)], the use of these local stabilizers for earth building purposes. This optimization
involved series of experiments with the two stabilizers (RHA and Straw) to achieve an optimal
compressive strength and erosion resistance performance of the stabilized earth material. In this
project the researcher also accepts that optimization also implies the use of specific techniques to
determine the most cost effective and efficient solution to a problem or design for a process, a
technique which stands out as one of the major quantitative tools in industrial decision making,
(Wikitionary, 2007)
Statement of the Problem
In the traditional earth building techniques in Nigeria, local additives have been used to
stabilize earth materials and some traditional earth-builders have achieved quality improvement
through choice of soil type (e.g. between red and clayey soils). The type of additives used under
the traditional earth building practices depends on the expertise of the earth-builder and
availability of the additives. No attempt is made at developing uniform mix proportions for
universal applicability of the known local additives such as straw and cow dung. It is also
believed locally that while some additives improve the quality of the earth material, some react
negatively with other additives when combined in a particular mix.
The degree of quality improvement under this traditional practice is mostly through trial-
and-error and a reflection of the expertise of the builder and the type of additives available within
the locality. There is, therefore, need to determine which of the additives, at what proportion and
with which type of soil that gives optimal functional quality of the earth material. This will make
for wider use of identified efficient techniques for improving the quality of the earth as a building
material.
7
The problem of this research was to find out the most efficient and cost effective way of
using rice-husk-ash and/or straw for earth material stabilization; what mix proportion of the these
stabilizers with what type of soil will give an optimal compressive strength and erosion resistance
for the stabilized earth material. The study investigated the structural behaviour characteristics of
stabilized earth materials as a result of differences in the stabilizer type, changes in the soil type
and variations in the mix proportion. In this process, the study ended with a quality stabilized
earth material product that optimized the use of these locally available additives – RHA and
Straw – for earth material stabilization.
Purpose of the Study
The purpose of this study was to optimize the use of RHA(rice-husk-ash) and straw as
stabilizers for earth materials for earth building construction. To achieve this, the researcher
employ several field experiments to identify differences in the compressive strength and erosion
resistance characteristics of the earth material as a result of changing the stabilizer types,
variations in the mix proportions and differences in the soil type. In the process of this study the
researcher investigated the effect(s) of changing the stabilizer type as well as the interactive
effect(s) of variations in the mix proportions and the differences in the soil types on the optimal
compressive strength and erosion resistance capacity of the stabilized earth material. The final
product of this study resulted in a curriculum component for the teaching of earth building
construction in Nigerian colleges. Specifically, the purpose of this research was to:
i. Identify particles distribution and chemical characteristics of the soil types that
can affect the quality of stabilized earth material for earth building purposes;
ii. Determine the chemical composition of the two stabilizers(additives), RHA and
Straw, used in stabilizing the earth material;
8
iii. Determine the differences in the mean compressive strength of earth materials
stabilized with RHA(rice-husk-ash) or Straw and that stabilized with a composite
of RHA-Straw as of differences in stabilizer type .
iv. Determine the effect(s) of differences in soil type on the mean compressive
strength the earth material stabilized with RHA(rice-husk-ash) or Straw and that
stabilized with a composite of RHA-Straw.
v. Determine the interaction effect(s) of variations in the mix proportions on the
mean compressive strength of the earth material stabilized with RHA(rice-husk-
ash) or Straw or that stabilized with a composite of RHA-Straw across three
different soil types.
vi. Determine the differences in the mean erosion resistance quality of earth
materials stabilized with RHA(rice-husk-ash) or Straw and that stabilized with a
composite of RHA-Straw as of differences in stabilizer type.
vii. Determine the effect(s) of differences in the soil types on the mean erosion
resistance capacity of the earth material stabilized with RHA(rice-husk-ash) or
Straw or that stabilized with a composite of RHA-Straw.
viii. Determine the interaction effect(s) of variations in the mix proportions on the
mean erosion resistance capacity of the earth material stabilized with RHA(rice-
husk-ash) or Straw or that stabilized with a composite of RHA-Straw across three
different soil types and;
ix. Establish an optimal mix proportion of the stabilizers (RHA, Straw and RHA
with Straw) and identify particular soil type (red, clayey and laterite soil) that
results to an optimal compressive strength and erosion resistance of the stabilized
earth material.
9
x. Finally, provide a curriculum component for the teaching/learning of earth
building construction in Nigerian technical colleges/colleges of technology and
earth building industry.
Significance of the Study
This research is significant to the earth builder, prospective earth building owner,
researchers and students and teachers in earth building technologies. This is because the research
has succeeded in optimizing the use of two locally available earth material stabilizers(RHA and
Straw) for improved structural qualities of the earth material for overall safety of earth buildings.
Specifically this research is significant, as its findings has removed the technical lapses that
usually accompany “chance” and trial-and-error approach in the determination of the mix
proportions of earth material stabilizers, thereby removing undue human influences which would
normally affect the structural quality of earth buildings for general application in earth building
projects. This research is specifically significant as the outcome has provided builders with a
databased guideline to rationally decide on the merits or otherwise of combining rice-husk-ash
and straw in stabilizing the earth material for optimal structural performance. This study is
significant as the findings provide earth builders and their clients building construction teachers
and students with valid data on the effect(s) of soil types on the structural performance of the
earth material stabilized with either rice-husk-ash and/or straw.
The findings of this research has also provided earth-builders and earth building
researchers with an authentic data to work with, in the ongoing efforts to develop alternative
sustainable, environmentally friendly, low-cost building materials. This study is significant in the
earth building industry as a valuable addition to the development of a standard earth building
technology curriculum for colleges and an eventual National Earth Building Code for Nigeria.
Finally, this study is significant in providing teachers and learners with statistically established
10
mix proportions (curriculum component) for the teaching/learning and practice of earth building
construction in Nigerian colleges and building industry.
Research Questions
To guide the conduct of this study nine, research questions were generated as follows:
1. What are the major chemical elements and particles distribution found in the three
common earth building soil types(red, clayey and laterite soils) that can affect the
structural qualities of the stabilized earth material?
2. What are the major chemical elements found in the two locally available
stabilizers(RHA and Straw) that can affect their efficacy as earth material
stabilizers?
3. What is the effect of differences in stabilizer type on the mean compressive strength
of earth material stabilized with RHA, Straw or RHA-Straw?
4. What is the effect of differences in the soil type on the mean compressive strength
of earth material stabilized with RHA, Straw or RHA-Straw?
5. What is the effect of variations in mix proportions on the mean compressive
strength of earth material stabilized with RHA, Straw or RHA-Straw?
6. What is the effect of differences in stabilizer type on the mean erosion resistance
capacity of earth material stabilized with RHA, Straw or RHA-Straw?
7. What is the effect of differences in the soil type on the mean erosion resistance
capacity of earth material stabilized with RHA, Straw or RHA-Straw?
8. What is the effect of variations in mix proportions on the mean erosion resistance
capacity of earth material stabilized with RHA, Straw or RHA-Straw?
11
9. Which combination of stabilizer(s) and soil type and at what mix proportion will
produce optimal compressive strength and erosion resistance capacity of earth
material stabilized with RHA, Straw or RHA-Straw?
Hypotheses
Eight null hypotheses formulated to direct this study were tested at 0.05 levels of
significance respectively:
Ho 1 There is no significant difference in the mean compressive strength of stabilized
earth material as a result of difference in the stabilizer type.
Ho 2 There is no significant difference in the mean compressive strength of stabilized
earth material as a result of the effect(s) of changes in the soil type.
Ho 3 There is no significant difference in the mean compressive strength of stabilized
earth material as a result of the interaction effect(s) of variations in the mix
proportions on three different soil types.
Ho 4 There is no significant difference in the mean erosion resistance capacity of
stabilized earth material as a result of the difference in the stabilizer type.
Ho 5 There is no significant difference in the mean erosion resistance capacity of
stabilized earth material as a result of the effect(s) of changes in the soil type.
Ho 6 There is no significant difference in the mean erosion resistance capacity of
stabilized earth material as a result of the interaction effect of variations in the
mix proportions on three different soil types.
Ho 7 There is no significant interaction effect of stabilizer type, soil type and mix
proportion on the mean compressive strength and erosion resistance capacity of
stabilized earth material.
Ho 8 There is no significant combination of stabilizers, soil type and mix proportion
that will optimize the use of RHA, Straw or RHA-Straw for earth material
12
stabilization, with respect to their compressive strength and erosion resistance
qualities.
Scope of the Study
This research was focused on establishing, through experimentation, an optimal mix
proportion for the singular use and/or a combination of two local earth material stabilizers
(additives) - rice-husk-ash(RHA) and straw, in stabilizing the earth material for optimal
compressive strength and erosion resistance. The specimen for this study was made-up of
compressed stabilized earth blocks(CSEBs). Two local stabilizers(additives) – RHA and Straw,
were used as the treatment variables at three different mix proportions across three different earth
building soil types. This allowed for a detailed study of these variables without losing sight of
cost management and sustainability of the outcome of the research. However, equipment
availability, such as some relevant photometric x-ray diffraction equipments, limited the number
of parameters/variables studied in this research.
Assumptions
This research operated on the assumption that soil as a major component of the earth‟s
crust, is a chemically stable compound, because it has been formed over a long time,
(Montgomery, 1998), and that changes within a geographical location like Nigeria (in the
tropics), will be minimal. The study also assumed that machineries and equipment used in the
experiments including those used in the statistical analysis are standard, valid and reliable.
13
CHAPTER II
REVIEW OF RELATED LITERATURE
In this chapter several related literature materials reviewed as the basis and springboard
for this research are presented, under 13 sub-titles, namely,
- Conceptual Framework;
- Building with the Earth Material(Mud): History and Practices;
- Soil Properties and Factors Affecting Its Choice as a Building Material;
- Earth Material (Soil) Stabilization for Earth Building Purposes;
- Types of Stabilizers (Additives) Used in Stabilizing the Earth Material;
- Factors Affecting the Stability of the Earth Material;
- Socio-Economic and Environmental Reasons for Alternative Building Materials;
- Government Initiatives on Earth Building in Nigeria;
- Building Standards/Codes(Benchmarks) Related to Compressive Strength and
Erosion Resistance Qualities of Earth Buildings:
- Review of Related Research on the Stabilization of the Earth Material(Soil/Mud);
- Optimization and Standardization of Product/Processes;
- Materials and Specimen Testing Methods; and the
- Summary of Review of Related Literature.
Conceptual Framework
As the world populations grow and interactions improve, and as aspirations to higher
living standards rise, so do the demands for quality housing grow even more rapidly, (Oruwari,
Jev and Owei, 2002). As this human population continues to grow with a widening level of
quality housing poverty, especially among the developing countries, the resultant effect include
increases in the prices of basic building materials. In Nigeria today, locally sourced and
14
developed building materials show evidence of viable alternatives for effective urban
regeneration and production of decent low-cost houses (Ajayi, 2004). Earth material, one of such
viable alternative building materials has been used since ancient times as a functional quality
building material and remains a major building material to date. Recently, developments within
the earth building industry have also shown evidence of improvements in the use of the earth
material for quality modern housing and as a viable alternative for low-cost quality housing
especially in the developing world. This is the primary concept upon which this project is hinged.
The strength of materials and their environmental friendliness upon which most modern
designs are based is concerned with the strength, below which construction failures are likely to
occur with its accompanying environmental effect, (Angus, 1998; Mosely, Bungney & Hulse,
1999). For building materials such as blocks and concrete, it is assumed that the strength
distribution would be approximately normal. Within the construction industry, two principal limit
states are of concern, namely:
i. Ultimate limit state, that is, the limit at which the structure must be able to withstand
with adequate factor of safety against collapse, the load for which it was designed.
ii. Serviceability limit, that is, the limit at which the structure can comfortably withstand
deflection, cracks, durability, excessive vibration, fatigue, and fire resistance without
any appreciable damage to the structure (Mosely, Bungney & Hulse, 1999).
The importance of each of these limit states differ according to the nature of the structure and its
purpose. Load bearing capacity, material strength, and constructional methods are important
parameters in assessing the importance of each of these limit states for any particular structure.
In the building construction industry, quality control measures require that construction
methods, materials and processes comply with laid down standards and codes of practice. This
ensures quality of the products and safety to the life-long users of the product. As Craven (2006)
puts it, building codes are there for your protection. In the traditional earth building practices in
15
Nigeria, earth builders achieved some measure of quality improvement of the structural qualities
of the earth material through choices between soil types and addition of local stabilizers such as
straw, animal dung, juice from different trees and shrubs, (Lawson, 1991). The degree of this
quality improvement was mostly through trial and error, depending on the expertise and
experience of the earth builder and the availability of the necessary stabilizers (additives). There
is therefore every need to develop some standards for the various aspects of the earth building
practice in order to optimize their quality, flexibility in use, capacity utilization and taste within
the context of modern housing requirements. The area of major interest in this research was on
the renewed interest in the later part of the last century on various ways of improving the quality
of the earth material through earth material stabilization which has rekindled research interest
into the various aspects of earth material stabilization, (McHenry, Jnr., 1997; Kennedy, 2002;
Maini, 2002). Thus, the concept of optimization in the production and use of products formed the
central focus of this research.
In a broad sense the technological capacity and capability to optimize the use of local
additives (stabilizers) in stabilizing the earth materials for building construction in Nigeria may
be defined in two ways; first, the capacity to identify suitable soils and their limit states. Second
is the capability to work on the natural characteristic weaknesses of the earth material; to improve
the structural qualities of the earth material so as to incorporate such improved earth material into
modern housing designs and programmes, without losing their desirable natural characteristics. It
is therefore important to develop an optimal mix proportion of the local additives(stabilizer) on a
given soil type that will result to an optimal compressive strength and erosion resistance quality
for the stabilized earth material as a standard for general application in earth building
construction. This is the horizon that this project has explored.
16
Building with the Earth Material: History and Practices
Earth, also referred to as mud or soil, is an ancient building material that is still in use in
many different forms across different climate zones of the world. About 30 percent of the world‟s
population and 50 percent of the rural population in the developing world live in earth houses
(North, 1998; Houben & Guilland, 1994; McHenry Jnr., 1997). This high percentage of earth
house dwellers in developing countries, notwithstanding, earth building, according to Norton
(1997) is not a phenomenon of the third world.
Building with earth draws from vernacular or folk traditions in building that have been
refined through experimentation over the centuries, (North, 1998; McHenry Jr., 1997). Earth
buildings are extremely varied. Technically speaking, the variety of earth buildings depends on
the type of soil available, the use and, the function to which the buildings are applied, (Norton,
1997). Over the past several decades, numerous vernacular building methods have been
investigated, and in some cases reviewed and improved upon by a new-breed of visionary
designer-builders (Kennedy, 2002). According to North (1998) a great variety of earth building
technologies have evolved in different parts of the world in response to local soil, weather, and
earthquake conditions. These techniques and processes include:
1. Rammed Earth - an ancient technique that dates back to at least, 7000BC in Pakistan.
2. Cob - used extremely in tropical Africa where suitable soils are obtainable over a
wide area.
3. Adobe (sun dried mud blocks) - used centuries back in traditional earth building
areas such as North Africa, the Middle East, South America and the south western
United States, where in all cases this building method is still in widespread use. It
dates back to, at least, 8300BC in Jericho.
17
4. Wattle and daub (or technique of weaving sticks (wattle) into rectangular spaces as
support for mud in-filling) - it is perhaps the oldest technique and is still used in many
parts of the world, (including the South Eastern parts of Nigeria).
5. Compressed earth blocks – one of the more modern additions to earth building; it is
similar to adobe, but differs in water/earth ratio, density, and significantly more
uniform, (King, 1989; North 1998; Kennedy, 2002; Little & Morton, 2000; Jurina &
Righeth, 2004).
Earth is the oldest and most widely used building material in the world today. It is
abundant, inexpensive and energy efficient (McHenry, Jnr., 1997). Buildings made of earth can
be durable and beautiful, (Norton, 1997). This earth material(mud) remains one of the oldest
materials used for building construction in rural areas, with several advantages including fire
resistance, being cheaper than most other alternative building materials, good noise absorption,
easy to work, using simple tools and skills and is readily available on site, (Bengtsson &
Whitaker, 1998; Ifeka, 2004). Earth buildings according to Howe (1992), blend well with the
environment, have high thermal mass and an excellent acoustic property. In addition to walling,
earth can be used to make excellent floors and ceilings. There is hardly any continent or country,
which does not have numerous examples of earth construction (Maini, 2002).
New developments in earth construction according to Maini (2002) really started in the
1950s with the technology of compressed stabilized earth blocks. Since the 1960s and 1970s,
Africa has seen the widest world development of compressed stabilized earth blocks - CSEB -
(Maini, 2002). In building with earth, simplicity of materials needs not be an excuse for poor
planning, (McHenry Jnr, 1997). The builder needs to consider which building process will be
used - whether the walls are to be built in-situ or made into bricks first, whether to employ a
contractor or build-it-yourself (North, 1998).
18
Earth construction is an ancient technique, which has been refined until date. It involves
some knowledge of soil science, engineering and building construction, (Burrough, 2002b). This
research therefore needed to identify the characteristics of the different soil types that will affect
the quality of the stabilized earth material.
Soil Properties and Factors Affecting its Choice as a Building Material
The earth material used for building works come from the soil and forms a major
component of the stabilized earth blocks. Some authors refer to it as laterite, others call it
soilcrete, (Ola, 1985; Lasisi & Osunde, 1985; Florex & Ezetah, 1985). According to Fletcher &
Hodges (2002), any definition of soil will depend on the context of the question. The important
thing to understand about soil is that rock, sand, gravel and silt make-up what is known as the
skeleton of the soil. These materials are inert and are not altered by moisture, and do not expand
or contract. The clay portion is known as the binder. It changes with the presence of moisture
(Bengtsson & Whitaker, 1998). In simple terms, soil used for buildings is referred to as mud,
earth or earth material.
Soil and earth are synonymous when used in relation to building works. The term refers to
the sub-soil and should not be confused with other definitions of soil, which includes weathered
organic materials on the topsoil (Little and Morton, 2001; Bengtsson & Whitaker, 1998).
According to Montgomery (1999), soil generally consists of solid, liquid and gas. These are
commonly referred to as soil particles. Soil also contains water and air.
Soil is an important part of the geological cycle and, the parent material, climate,
topography, weathering and the amount of time a particular soil has developed influence its
characteristics. Soil is affected by variations in climate, parent materials, type of weathering and
time and these produce distinct soils that express these variations (Fletcher & Hodges, 2002).
19
The properties of any soil type to be used in building are of great importance to the earth
builder (King, 1989). It is, therefore essential to identify the properties of soil as a building
material in order to create a good quality product. According to Maini (2002) and Howe (1992),
whereas soils for making earth blocks are widespread, those with large amount of organic matter,
concentration of salts or highly unstable clay must be excluded.
Soils used for building construction undergo detrimental physical changes when they
become wet; the majority of these changes are due to the presence of small particles called clay
(Montgomery, 1998). Clay plays a valuable function in the production of building blocks, but
they can have a detrimental effect on the stability of the material, if they get wet. Soils that are to
be used as building materials must not contain unwanted organic materials, or include made-up
soils and it can be a natural selection of particles, or a mixture of different soils to attain a more
suitable particles distribution (Montgomery & Thomas, 2000).
Soils are classified in several different ways, namely, by their geological origin, mineral
content (chemical composition), by particles size or by consistency which is mainly related to its
moisture content (Ezeji, 1984; Bengtsson and Whitaker, 1998). There are different soil
classification systems in use, such as the United Soil Classification System (USCS), the
American Association of State Highway and Transport Official System (AASHTOS) and the
British Soil Classification System for Engineering Purposes (BSCSEP). Although there are
variations in the test methods adopted by each of these systems, they all use soil particles size,
distribution and Atterberg limits. In general the systems assume that coarse materials are better
than fines, low liquid limit is better than high liquid limit, a well-graded soil is better than poorly
graded soil. All the systems accept that a well-graded soil refers to soil with lots of particles sizes
mixed together; and that this allows small soil particles to fill the pores between larger materials
and therefore give denser mix than uniformly sized materials. (Mckinley, 1996; Nyle & Ray,
1999).
20
According to Montgomery (1998), some of the physical characteristics that could be used
to define soil particles are colour, size, shape, surface texture, density and specific surface area.
Soils used for earth building are commonly grouped and named according to their particle size
distribution. Locally earth building soils are classified mainly according to their physical
characteristics of colour, mineral content and particles size, (Development Alternatives, DA,
2002). Thus, we have three common earth building soils of red, clayey and gravel/lateritic soil
types. It should also be noted that soil materials seldom occur separately and this necessitates a
further classification according to the percentage of each particle size, which the soil contains as
shown in Appendix A (Ezeji, 1984; Bengtsson & Whitaker, 1998)
The clay fraction of the soil is of major importance in earth building construction, because
it binds the other particles together. The presence of clay in soil is necessary to achieve sufficient
green strength in freshly formed blocks, to enable demoulding and handling without excessive
breakage (Montgomery 1998; Bengtsson & Whitaker, 1998). On the other hand, the main
weakness of the soil as a building material has to do with the presence of clay, resulting from its
low resistance to water absorption. Because of this clay fraction, which is necessary for cohesion,
walls built of unstabilized soil will swell on absorbing water and shrink on drying (Nyle and Ray
1989; Bengtsson & Whitaker, 1998).
Some soils are considered unsuitable for manufacturing stabilized earth blocks and need
to be modified or discarded; while some soils have certain physical characteristics that can be
generally accepted for building works. Due to varying geochemistry around the world, care must
be taken in selecting soil types for the building of earth structures. An approach that works well
in the Middle East may not be suitable in Africa (Burrough, 2002(b)). Nevertheless, the quality of
nearly any inorganic soil as a building material can be improved remarkably with the addition of
common stabilizers (Montgomery, 1998; Kerali, 2001; Bengtsson & Whitaker, 1998). This
research in identifying the characteristics of the different soil types had to first identify the
21
particles distribution of the different soil types and the major chemical elements contained in
them.
Earth Material Stabilization for Earth Building Purposes
A normal building concrete is made up of coarse and fine aggregates with cement as a
binding agent (Ezeji, 1984); while earth used for building works contain gravel, sand and silt
with clay as the binding agent. But unlike cement, silt and clay are unstable under water,
(Fletcher & Hodges, 2002). It is, therefore, of interest to the earth builder to identify the
constituent elements in any given soil, the approximate percentage in quantity and their
characteristics in order to evaluate same for earth building. It is also important to know the
characteristics of the clay content, whether it is expansive, stable or unstable (Burrough, 2002a).
This information is necessary to determine the nature/type of stabilization to adopt. The
stabilization technique, according to Houben (1994) can be broken down into three categories,
namely, mechanical, physical and chemical. Mechanical stabilization compacts the soil, changing
its density, mechanical strength, compressibility, permeability and porosity. Physical stabilization
changes the properties of the soil by acting on its texture - this can be done by controlling the
mixture of different grains fractions, heat treatment, drying or freezing and chemical treatment.
Chemical stabilization changes the properties of the soil by adding other materials or chemicals.
New developments in earth building worldwide have generally taken the traditional
methods, extracted the good aspects and added new methods to develop new techniques. This
new techniques can give earth buildings with far increased performance than the old techniques
(Dobson, 2004). Moor & Heathcole (2002) in their study of Australian earth buildings noted that
earth in an unstabilised form has limited durability. According to Sidibe (1985) even the best of
soil and water mixture to produce adobe (sun-dried mud blocks) can develop cracks. Therefore it
is important to add other materials to the mix to prevent water from penetrating into the dry
22
blocks. Stabilization of the soil (earth material) increases its resistance to destructive weather
condition in one or more of the following ways:
- by cementing the particles of the soil together leading to increased strength and
cohesion.
- by reducing movement (shrinkage and swelling) of the soil when its moisture content
varies due to weather conditions.
- by making the soil waterproof or at least less permeable to moisture (Bengtsson &
Whitaker, 1998).
The primary aim of soil stabilization is to increase the soil‟s resistance to destructive
weather conditions. High clay soils require very high proportion of stabilization or a combination
of stabilizers to achieve results (Kerali, 2001). Making various important changes to the
traditional manufacture of mud blocks and to incorporate them into modern buildings can
enormously improve their performance, while keeping their desirable characteristics (Howe,
1992). These include improved mixing and moulding technique, design improvement,
incorporation of damp-proofing membranes, raising the blocks above the foundation, stabilizing
the earth blocks to make them totally waterproof and waterproofing the external walls (Lawson,
1991; Burrough, 2002a). According to Heathcole and Ravindrajah (2003), to improve the
durability, compressed earth bricks are generally stabilized with from five per cent to 12 per cent
cement, with around eight per cent being generally suitable for most soils.
In spite of all the advantages of soil stabilization for earth buildings, it is important to note
that because of many different kinds of soil and many types of stabilizers, there is no single
answer for all cases (Kennedy, 2002; Bengtsson & Whitaker, 1998). In a study of strength
characteristics of stabilized earth materials, Adeagbo (1999) and Anibogu (1999), cautioned that
in the process of developing earth or laterite based materials, the curing procedure and strength
testing more often than not, follow the standards set for cement based materials or cement mixes,
23
whereas the hardening process of materials other than cement, require a different approach to
curing to achieve high strength that would be retained for a considerable time. It is therefore
important to develop a mix proportion of the local additives(stabilizer) that will give the earth
material optimal compressive strength and erosion resistance as a standard for general application
in earth building construction. This is a principal horizon, as mentioned in the introduction of this
report, that this project has worked on.
Types of Stabilizer(Additive) Used to Stabilize the Earth Material
There are several types of additives used as stabilizers, in earth building technologies the
world over. Some stabilizers are chemical compounds, while others are natural materials. These
include sand/clay, Portland cement, lime, bitumen, pozzolana, natural fibers, sodium silicate
(water-glass), commercial stabilizers (for roads), resins, whey, molasses, gypsum, and cow dung
(Bengtsson & Whitaker, 1998). Some of the stabilizers that would be encountered in this
research are given more detailed mention below.
a) Sand/Clay: Sand and clay occur in their natural states as the skeleton and binding
components of the soil. Sand or clay is added to improve the grading of soil. Sand is
added to soils, which are too clayey, while clay is added to soils which are too sandy
(Kerali, 2001). This method improves the strength and cohesion of the soil, while moisture
movement of a clayey soil is reduced. The earth builder must note, however, that this
improvement in the grading of the soil material does not stabilize the soil to a high degree
but will increase the effect of and reduce the required amount of other stabilizer(s),
(Montgomrey, 1998; Bengtsson & Whitaker, 1998; Nelson, 2002).
b) Ordinary Portland cement: This is the binding agent in mortar and concrete. It is a
combination of limestone or chalk with clay mixed in a proportion, which depends on the
type of cement desired (Ezeji, 1984). Portland cement greatly improves the compressive
24
strength and imperviousness and may also reduce moisture movement, especially when
used with sandy soils (Kerali 2001; Bengtsson & Whitaker, 1998). Portland cement is an
important ingredient in compressed stabilized earth blocks. Without its inclusion
compressed blocks would be no different from common sun dried mud blocks(adobe) and
would simply disintegrate on contact with water or when subjected to moderate loading
impact (Kerali, 2001).
In stabilized blocks, variations in Portland cement quality and quantity can drastically
affect its properties and behaviour more than any other input variable (Gooding, 1994). As
a rough guide, sandy soils need five to 10 per cent cement for stabilization, silty soil 10 - 12
percent and clayey soil 12.5 - 15.0 percent. Soil-cement blocks should be cured for at least
seven days under moist and damp conditions (Gooding, 1994; Kerali, 2001).
c) Pozzolana (e.g. fly-ash, volcanic-ash, rice-husk-ash): The ASTM Code (1992) defines
pozzolana as a siliceous or siliceous-aluminous material which in itself possesses little or
no cementing value but will, in finely divided form and in the presence of moisture
chemically react with calcium hydroxide at ordinary temperature to form compounds
possessing cementing properties [American Society for Testing Materials (ASTM),
Definitions p. 618 – 78]. It is a natural or artificial material containing silica in a reactive
form (Neville, 1991; Neville & Brooks, 1993).
Pozzolana also refers to a volcanic ash, first collected at Pozzuoli, Italy and used for
making hydraulic cement. Pozzolanas can be produced artificially from rice-husk-ash
(Dictionary of Scientific and Technological Terminologies). According to Oraedu (1985),
rice-husk-ash is considered as one of the artificial pozzolanas containing high percentage of
silica. This high percentage silica enables the ash to react with calcium hydroxide to form
cementeous compound. Thus when used as a soil stabilizer, it reduces sulphate attack on
mud blocks since there would be little or no calcium hydroxide remaining to warrant
25
sulphate attacks, (Neville, 1995). The main reason for using pozzolana as a stabilizer is
that it easily combines with the alkaline content of the cement and soil, thus effectively
lowering the alkaline content (Glaville & Neveille, 1997). According to Neville & Brooks
(1993), natural pozzolanas improve their activity by calcinations in the range of 550oC to
1110oC, depending on the material. Neville and Brooks also confirmed that rice-husk-ash
burnt at 450oC has been found to produce pozzolanas conforming to the requirements of
earlier American Standards for Testing Materials (ASTM Standards C618).
(d) Natural Fiber (e.g. Grass, Straw, Sisal, Saw Dust): Many types of straw can be used for
soil stabilization, but it must not include legumes and be of good quality, needle leafed and
dried (Bengtsson & Whitaker, 1998; McHenry, Jnr, 1997). This makes it easier to stabilize
soils with natural fiber during the dry season within the tropics. According to Baggs(1996),
using natural nontoxic building materials such as clay and straw reduces exposure to out-
gassing toxic chemicals and provides us with safe and comfortable buildings, while easing
the environmental impact of the construction industry at the same time. The technique of
building walls with clay/straw has been highly developed in China, where grains storage
bins of up to eight meters diameter, 8.5meters height and 250tones holding capacity, have
been constructed with this earth material (Bengtsson & Whitaker, 1998).
(e) Other Local Stabilizers: Cow dung - this is an animal waste, which is commonly used in
mortar for rendering wall surfaces and roof soffits. Lawson (1991) in a study of low-cost
materials for building in north-east Nigeria discovered that at Kaski and Yin in the north-
east arid zone, the building mortar and rendering which are much more durable than the
blocks are made from the same soil with cow dung added to it. Another local stabilization
technique Lawson also discovered was the use of shells of the fruit (kuba) of the dorawa
tree, soaked in water and the water used to mix the earth material to make an earth block
protective coating.
26
As many types of earth material stabilizers are being identified and developed, the import of
material economy cannot be simply compromised if low-cost housing is of primary concern. This
research has therefore chosen between traditionally known stabilizers and emerging new ones
that are locally cheaply availably for development and quality usage.
Factors Affecting the Stability of the Earth Material(Mud/Soil)
Soil is generally a (chemically) stable compound because it has been formed over a long
period of time and any chemical changes would have taken place within its environment. For
majority of cases, scientists can assume that soil will be chemically unaffected(stable) by the
environment (Montgomery, 1998). The fundamental problem of building with soil is that it will
lose compressive strength when it becomes wet. Consequently, it is the responsibility of the
designer to ensure that either the weakening effect that moisture has on soil is greatly reduced or
the possibility of the soil getting wet is removed (Gooding & Thomas, 1995).
Many types of stabilizer are in use, but cement and lime appear to be the most common
types of stabilizer used in earth building works globally, (Development Alternatives (DA), 2001).
It has also been suggested in literature on stabilized (earth) blocks that the durability of the blocks
is closely related to the block‟s properties, which in turn are not constant during the lifetime of
the blocks (Ingles & Metcalf, 1972; Spence, 1975). The strength of an earth block, according to
Maini (2002), is related to the press quality, the compressive force and to the quality of the
stabilizer.
Earth needs to be stabilized because the earth as found in its natural state is not durable
for long term use in buildings (North, 1997; Kerali, 2001). By modifying the properties of soil,
its long-term performance can be significantly improved, (Dunlap, 1975). Soil stabilization
focuses on altering the soil‟s phase structure, namely, the soil-water-air interphase. The general
goal is to reduce the volume of interstitial voids, fill empty voids and improve bonding between
27
the soil grains. In this way better mechanical properties, reduced porosity, limited dimensional
changes and enhanced resistance to normal and severe exposure conditions can be achieved,
(Gooding & Thomas 1995). Considering the various factors affecting the degree of improvement
in the structural qualities of the earth material, this research adopted to identify the major
chemical composition of the soil types and the stabilizers and to treat the three different common
types of earth building soils with these two locally available stabilizers at varying mix
proportions. This is to ensure valid and reliable end product(s). The research also took into
cognizance that it is locally believed that some additives(stabilizers) improve the quality of the
stabilized earth material while some react with other stabilizers to adversely affect the stabilized
material
Socio-Economic and Environmental Reasons for Alternative Building Materials
The last two to three decades have witnessed an upsurge of renewed interest in the use of
earth materials for buildings (Norton, 1997). Today in many parts of the world, improvements in
earth building technologies have made it begin to regain technical and social acceptance among
the rich and the poor, (Maini, 2002). Earth can be used in several different ways in buildings,
including load-bearing walls, thermal and acoustic insulation to walls and roofs. Earth materials
are particularly beneficial for natural air quality, (Little & Morton, 2002). The use of earth can
have significant environmental benefits, in particular, reducing carbon emission and waste
production. Among the many reasons for the use of earth as a building material, (Kennedy,
2002), is that it gives an excellent, suitable characteristic product that gives low carbon emission,
efficient use of finite resources, minimizing pollution and waste, use of benign materials, local
sourcing and bio-degradability (Maini, 2002).
Earth building is one of the modern building techniques commonly grouped under the
label “natural building”. Natural building itself is a philosophy that relies on materials and
28
techniques which are ecologically sound, culturally sensitive, reliant on local resources and skills
and are within the economic reach of local inhabitants, many of whom cannot currently afford
shelter (Bengtsson & Whitaker, 1998). Those who recognize the environmental, social and
economic cost of current ways of construction believe that earth building provides part of the
solutions to the complex worldwide problem of sustainable living (Kennedy, 2002).
Cost, often the deciding factor in many projects is where earth building technologies
benefits are most felt. Apart from the issue of reducing unemployment and creating micro-
industries, the direct cost saving in construction is between 8 and 18 per cent (Burrough, 2002a;
Howe, 1992). According to Fathy (1973), housing should be based on traditional forms of
architecture, not those forms imported from the west. The people themselves should be
immediately involved with the design, building and ownership of their own house. When the
government or private contractors step in, Fathy (1973) further argues, the result is often housing
and planning which is vastly out of touch with local socio-cultural, economic and environmental
conditions. Earth building is in every aspect collaborative and as such can form the hub of other
self-help initiatives within communities providing both capital and methodology, (Ifeka, 2004).
According to Robson in Burrough (2002b), earth homes are economical to build and no
other building material can match the relationship of earth buildings to the environment. There is
no smell of synthetics, no sound of mechanical systems and no rattling when the wind roars. A
home of earth is simply a constructed environment that grows from the earth, yet remains as a
natural sustainable environment (Burrough, 2002a). Building with earth material can be a way of
helping with sustainable management of earth‟s resources. Earth buildings can be put in place
using simple machineries and human energy (North, 1998). Building with earth presents a
symbiotic way of using the resources of the environment to meet human needs and using these
human needs to manage the environment.
29
It is important to note here that the success of housing development programmes
(anywhere) hinges not solely on technical issues but include efficient management of existing
resources and effective communication between communities and funders, (Oruwari, Jev and
Owei, 2002). Being sensitive to the need of community is not only ethical but also imperative
from a delivery perspective, (Burrough, 2002a). According to Howe (1992), the cost of housing
must be kept within the limits of the ability of the owners to pay.
The ambition of all people to own or have access to a decent shelter is not a luxury but a
necessity. As Howe (1992) stated, housing can be simplified so that all can take part – the young
and the old. This concept of self-help with guidance is the motivation and basis for the formation
of organizations such as Habitat for Humanity (Howe, 1992, Ifeka, 2004).
At present, in Nigeria, regulations, materials and consumer interests make housing
expensive and struggling to get government mortgage, with harsh strings attached over a period
of 30 years cannot be defined as producing affordable housing for all. Money saved on materials
and labour cost in earth building may be small, but this is a considerable saving when less money
has to be borrowed, (Howe, 1992). Furthermore, Howe stated that if we cannot limit borrowing
to curtail interest payment, provide labour to curtail wages and use earth to manufacture building
components, then we have greatly empowered the prospective homebuilder with his own solution
to shelter. Ifeka (2004), agreed with Howe‟s (1992) argument based on her women empowerment
project in Anambra State of Nigeria as sponsored by the Ford Foundations in 2004. The
conclusion of this matter is that low-cost housing must assume that the prospective owner has
substantial if not total, equity in the building (Howe, 1992; Ifeka 2004; Oruwari, Jev & Owei,
2002). This research is therefore not interested in this material development project for only
academic exercise but as a major contribution to ongoing search for alternative quality renewable
building/housing material for the teaming populations of Nigeria and the developing worlds.
30
Government Initiatives on Earth Building in Nigeria
Throughout the world, developing countries are facing severe problems with regards to
the supply of building materials, the core of the construction sector, (Oruwari, Jev & Owei,
2002). The countries of Africa are facing severe problems with the supply of building materials
(UNCHS, 2001). In most cases, building materials consume about 70 per cent of the total cost of
a building. It must therefore, be realized that meeting the shelter requirements in any nation, will
depend, to a great extent, on the availability of basic building materials at affordable prices,
(Howe, 1992; Kennedy, 2002). Crucial to this would be the strengthening of domestic technology
capability to produce quality indigenous building materials such as stabilized earth materials for
earth building purposes.
Nigerian governments since independence in 1960 have pursued various housing policies
and programmes. Yet paucity of decent housing remains unabated. According to Ifeka (2004),
housing poverty is linked to other forms of poverty and is very often seen as an urban
phenomenon; while the rural area is associated with lack of other basic amenities. It appears that
most government housing efforts in Nigeria have concentrated more on housing policy
formulation for urban dwellers. In the second republic, the various levels of government,
(Federal, State and Local) came up with housing policies and programmes that also concentrated
at the urban and semi-urban areas. These include the Shagari housing programmes, the Jakande
housing project, etc. In the 1980s, the Military government pursued a policy of local production
of building materials to reduce the cost of house production in Nigeria (Okpala, 1989). The quest
for the production of alternative local building materials led to the establishment of several Burnt
Brick factories across the country and the revival of other building materials factories including
the AT & P Sapele; Serom Woods Calabar, Woods (Nig.) Ltd, Port Harcourt, Emenite (Nig.) Ltd,
Enugu and several others. Most of these industries, according to Oruwari, Jev & Owei (2002),
have either “died” or are operating below 50 percent installed capacity. Within the same 1980s
31
the Nigerian Building and Roads Research Institute (NBRRI) effectively commenced the
production of cement-stabilized clay blocks of normal sand-crete block size, with a locally made
block moulding machine. Yet more than 20 years later, this feat of producing cement stabilized
clay blocks is yet to be commercialized (Oruwari, Jev & Owei, 2002).
While these government industries and factories are ailing, local production and use of
sun-dried mud blocks and wattle-and-daub structures are still thriving within the rural areas of the
country. This is a clear indication of continued patronage of earth building techniques yearning
for technological improvement in methods and processes to give high quality products. Although
Nigeria suffers scarcity and is import dependent, she is endowed with abundant building
materials that have the lowest gross energy requirement. These materials are often traditional
building materials such as timber, soil, stone, bricks, fiber etc. (Oruwari, Jev & Owei, 2002).
In the last one-and-a-half decades Nigerian governments have once again been making
renewed efforts to encourage private participation in housing provision and to encourage efforts
at reducing the cost of house production in Nigeria through the production and use of local
building materials (Isoung, 2004; Adegboye, October 19, 2004; NEEDS, 2005). These materials
include burnt bricks, mud-blocks, and fiber impregnated roofing sheets. However, these
government efforts appear to be poorly coordinated or haphazardly implemented. An NGO in
Abia State – Abia Civil Societies Group – noted that the Abia State Economic Empowerment and
Development Strategies‟ (ABSEEDS) policy on housing does not take into consideration the
housing needs of the rural communities. This NGO went further to canvas the need for
governments to popularize the use of local building materials, which are cheaper and can create
employment and income for the local population, in the state housing programme (Njoku, 2005).
In Ebonyi State, there is a gigantic signpost at Mgbo – 15km to Abakaliki – conspicuously
announcing the state government‟s Building Materials Research Factory and another close-by
boldly inscribed, “Championing Development in Indigenous Technology through Research in
32
Cement–Earth Works”. Both the Research Centre and Factory are presently safe-havens for
reptiles under bulks of idle, expensive factory and research equipment.
Currently, the government in Nigeria has a housing policy that encourages research and
development into local building materials development and utilization under the National
Economic Empowerment and Development Strategies (NEEDS). So far, research efforts at the
Nigerian Building and Roads Research Institute (NBRRI) are skewed in favour of design and
production of tools and equipment for the extraction/production of local building materials
(Isoung, 2004). Research into earth building materials appears to remain more of an academic
pursuit waiting to be harnessed and translated into concrete technological improvement for earth
building practice in Nigeria. This researcher deliberately decided to use experienced local earth
builders and engineering students as the research assistants so that they will be able to incorporate
the findings of this research into their own techniques for an overall quality improvement of earth
building practices.
Building Standards/Codes (Benchmarks) Related to Structural Strength and Erosion Resistance
of Earth Buildings
Performance based clauses for structures recognize all the likely loads to be imposed on
the structure, while the strength of the structure(building) can be demonstrated by recognizable
methods of calculations (Benge, 1999). The performance criteria of any building structure consist
of a list of likely loads and other factors that must be considered when assessing the stability of
the building. By this reason, the functional requirements of many building standards/codes
clauses on structure require buildings to withstand the combination of loads that they are likely to
experience during construction or alteration and throughout their lifetime.
In Nigeria today, after over a century of the introduction of industrialized building
materials, we have just celebrated the introduction, in February 2007 and the signing into law of
33
the first ever-Nigerian Building Code. This code is primarily concerned with the same
industrialized building materials also regarded as standard, with no clear mention of earth (mud)
building practices in Nigeria. This is not totally strange as Webster (2003) puts it, model building
codes, such as the American Uniform Building Code (UBC), the Basic Building Code (BBC),
and the Standard Building Code (SBC) always lag behind current knowledge of materials and
construction practices. For example, even within the zones of the world where earth-building
technologies are well advanced, standards for compressed earth blocks are not addressed in any
of the American National Adobe Codes. Thus, while the quality control of adobe blocks is
reasonably well known, since the manufacturing process has been around for thousands of years,
that of compressed stabilized earth block (CSEB) technology is comparatively at infancy having
been around for just about 40 years (Webster, 2003). This lagging behind of national building
codes‟ development, usually lead to the development of some localized common standards of
practice within a given locality. There is therefore need to establish ways and means of making
the most efficient use of these local stabilizers, at what proportions and with which soil type to
produce optimal functional quality of the stabilized earth material in Nigeria. This would
guarantee quality in the products and ensure safety of the users, if the quest/ambition for
alternative, sustainable, low-cost, environmentally friendly housing is to be taken seriously. It
will also ensure uniformity in the material manufacture and usage.
At present, there are no readily available, official building standards specific on earth
building in Nigeria. The story is the same in many other developing countries including some of
the advanced countries of the world. As a result of these, a number of other reference documents
are being used. These include description of historic techniques provided by various bodies,
foreign standards and codes of practice and documents written by researchers and practitioners
(Benge, 1999).
34
Until May 2007, Nigeria did not have any building code/standards of her own (Daily Sun,
May 2007). For all the past years the Nigerian construction industry had officially used three
main foreign codes – the British Standards (BS., now BSI – EN) codes, the American Uniform
Building Codes (UBC) and the American Society for Testing and Measurements (ASTM) codes.
It is also important to note that at present copies of even the newly approved, ever indigenous
building codes, are yet to reach most of the practitioners, researchers and other related institutions
to date. Even in the newly approve/adopted Nigerian Building Code only a passing mention is
made of standards related to earth building regulations within its sections, (NIOB, 2007).
Currently the few complete National Building Codes dealing specifically with compressed earth
materials include the New Zealand Building Standards, New Mexico Earth Building Code,
Building Code of Germany (written in German) and the Australian Earth Building regulations
(Benge, 1999).
In France a non-profit organization, CRATerre, specializing in earth construction has
developed a compressed earth block (CEB) code for the government. In this CRATerre document
it is specifically stated that the ratio of wet to dry compressive strength of earth block should be
not more than 0.5. In the United States of America the Uniform Building Codes (UBC) and the
American Society for Testing and Measurement (ASTM) standards originally made for adobe
(sun-dried mud blocks) applying to “low strength masonry” are used as guide for earth building
construction. Until recently standards for pressed earth blocks are not addressed in any of the
“adobe codes” in the United States of America, (Webster, 2003). In some of the states in
America the relevant sections of these codes are being modified to meet specific requirements for
compressed earth block (CEB) practices. These states include Texas, New Mexico, Arizona,
Utah, California and Colorado, (Environmental Construction Technology, ECT, 2004).
In Africa, only a few countries have any semblance of any national building standards,
specifically addressing compressed earth blocks (CEB). In South Africa, the South Africa Bureau
35
of Standards code specifies a minimum compressive strength for compressed earth blocks of
435psi(pounds per square inch) equivalent of 3Mpa(Mega-pascal), (Bengtsson & Whitaker,
1998). Others include the Building and Public Works Laboratory of Cote-de-ivory (1980),
“Recommendations for Design and Construction of Low-cost Buildings in Soil Cement” and the
Indian Standards Institute (1994) Specifications on Stabilized earth blocks first published in
1960, (Environmental Construction Technology, ECT, 2004).
The British Standards (BS 1924:1990 – Part 1 and 2) dealing with stabilized earth
materials for civil engineering purposes requires that stabilized earth materials for civil
engineering purposes must have a cured compressive strength of not less than 1.85Mpa(Mega
pascal) [268.25psi (pound per square inch)]. Four sections of this British Standards were adopted
to guide the experiments as follows - CSI 04200 [Masonry]; CSI 04210 [Masonry Bricks]; CSI
04212 [Adobe Masonry] and CSI 04220 [Concrete Unit Masonry] which requires that the
ultimate compressive strength of rammed earth walls should be between 450 – 800psi (3.103 –
5.517Mpa), that stabilized earth blocks should be above 700psi (4.828Mpa) depending on the
type of stabilizer and production process. For cement stabilized earth blocks (CEB) the American
Uniform Building Code specifies a bearing capacity of 17.241 – 26.897Mpa (2500 – 3900psi).
The British Building Regulation 2004 specifies a minimum characteristic of unconfined
compressive strength (f’cu) = > 3.5 N/mm2 for stabilized rammed earth walls with a typical
range of f’cu ≈ 3.5 N/mm2 to 12 N/mm2.
The New Mexico building code on compressed earth blocks (NMAC 14.7.8.23J) states as
follows;
“Compressive Strength: cured units shall have a minimum compressive strength of three
hundred (300) pounds per square inch (i.e. 2.06Mpa) when tested, (Arumala, Gondal and
Bennett, 2004). The compressed earth block shall be tested on the flat position. The
36
length of the tested unit must be a minimum of twice the width…The compressive
strength is defined as P/A, where P = load and A = area of compression face”.
The New Zealand earth building code which is more of a performance based code is not very
specific about the strength of earth building materials. Three main aspects of this code address
earth building regulations – i.e. NZS 4297 – Engineering Design of Earth Building; NZS 4298 –
Materials and Workmanship for Earth Building and NZS 4299 – Earth Buildings Not Requiring
Specific Design. The New Zealand code specifies that the compressive strength of compressed
earth blocks for standard grade construction with design strength of 0.5Mpa requires that test
results of the least of 5 individual results is set as follows:
- compressive strength for samples with height/thickness ratio of 1 = 1.3Mpa(188.5psi);
- compressive strength for samples with height/thickness ratio of 0.4 = 1.8Mpa(261psi);
- flexural tensile test – 0.25Mpa(36.5psi).
According to the 1987 ILO Report, a 1.0Mpa (145psi) 28-day minimum wet compressive
strength value for earth blocks are recommended for dry arid zones, while a 2.8Mpa (406psi)
minimum 28-day wet compressive strength values are recommended for the wet rainy zones,
(Kerali, 2000).
In the New Zealand Earth Building Standard, keeping water out of buildings is dealt with
under NZBC clauses E1 – Surface Water; E2 – Penetration of the Building Envelop and Floor
Structure; E3 – Internal Moisture. The Development Alternative (2003) provides a table of basic
data on the compressive strength specifications for cement stabilized earth blocks as shown in
Table 2. Taking an average of the various compressive strength specifications will give a
minimum compressive strength requirement for compressed earth blocks at 2.608Mpa
(378.208psi). See Appendix B.
According to Porteous (1992), the majority of failures in building elements are caused by
water. It follows therefore, that compliance with the New Zealand‟s clause for external and
37
internal moisture penetration and control can greatly improve the durability of earth walls. Under
the clause E2‟s Functional Requirements of the New Zealand‟s Earth Building Code, earth
buildings are required to be constructed to provide adequate resistance to penetration by and the
accumulation of, moisture from outside. By implication, the ability of any construction to keep
water out is therefore vital to the assessment of the performance of the building elements, (ECT,
2007).
According to Cytrn (1957), any earth block that is placed under a water spraying machine
at 250kpa water pressure for 33 minutes without more than two of its corners deteriorating and
surface erosion not more than 10% would be considered good for earth building purposes. The
Australian Spray test which involves water sprayed horizontally from a 35 holes nozzle at 50kpa
pressure from a distance of 470mm for 1hour requires that maximum erosion is 60mm per hour.
In another development a spray test developed by Wolfskill (1970) was adapted by Jagadish and
Reddy (1987) to test pressed soil blocks in India. In this study by Jagadish and Reddy, a shower
rose approximately 100mm in diameter was held a distance of 175mm over the specimens. Water
was sprayed vertically onto the specimens at a pressure of 100kPa(kilo-pascal) and at a rate of
0.94 l/sec. The specimens were sprayed for between 5 and 20 minutes. The depth of erosion
following the spray was divided by the total precipitation to produce an Erosion Ratio (ER).
From the findings of their study, Jagadish and Reddy who carried out their test both in the
laboratory and at field testing on a particular soil to compare the severity of the test,
recommended after three years of exposure, that a field sample with an ER of 0.012 compared to
a laboratory value of 0.039 was acceptable. On the other hand the New Zealand‟s performance
based earth building codes requires the limiting of the erosion depth depending upon local factors
such as wind speed, annual rainfall and the orientation of the wall with respect to the prevailing
wind driven rain direction.
38
This research recognizing the existence of the various standards/codes and regulations
related to earth building practices have therefore adopted as the guiding benchmarks for the
minimum compressive strength requirement for compressed earth blocks at 3.00Mpa (435psi)
and allowable erosion resistance ratio as 10 per cent.
Review of Related Research on the Stabilization of the Earth Material
Several studies have been conducted in different parts of the world on earth building
traditions and techniques. Some of these studies have been specific on soil stabilization while
others are generalized on earth buildings. Little and Morton (2001) conducted a study on
building with earth in Scotland and discovered that:
- Scottish traditional earth building technologies have evolved to take advantage of
local skills and materials and respond to local conditions.
- There is sufficient and easy access to earth as a resource for building in a significant
number of regions and locations in Scotland.
- Several projects show that earth has the potentials to be used to produce high quality
building products.
- The high profile of many new earth buildings is encouraging a wider acceptance.
Howe (1992) in an earlier study, concluded among other things, that earth can be used in a
number of ways to construct dwellings and that by making several important changes to the
traditional manufacture of mud-blocks and to their incorporation into modern buildings, their
performance can be enormously improved, while keeping their desirable characteristics. Based
on the findings from this study, Howe cautioned that discarding such a plentiful resource as earth
was never a good idea and people are beginning to see it. Ifeka (2004) in a Ford Foundation
Sponsored work on “Nigeria Building Better Lives Brick-by-Brick”, discovered that earth is the
39
most immediate and locally available material that provides the cheapest and lowest impact on
construction material; that in many areas the earth material can be extracted from the building site
itself and that earth buildings tend to be more comfortable and energy efficient than many other
contemporary houses made of other materials. These studies clearly present the earth material as
a possible source of alternative quality low-cost building material.
Some of the pioneering studies on soil stabilization in Nigeria include that of
Chukwudebe (1966) where cement was used to stabilize laterite for block moulding. In 1977,
Agarwal did another study in which groundnut husk-ash (GHA) mixed with cement and soil was
used to produce earth panels of 300 x 300 x 25mm sizes. Osayere (1984) and Oraedu (1985)
studied the effects of modifying concrete and stabilizing earth blocks with rice-husk-ash (RHA)
respectively, and discovered that the chemical composition of rice-husk-ash was comparable to
that of ordinary Portland cement, and completely different from that of unburnt rice husk. In
three other separate studies Florex and Ezetah (1985), Owoeleye (1985) and Mbata (1989)
investigated the strength and durability of cement-stabilized earth bricks (CSEB) and discovered
that 5-8 per cent cement stabilization provided bricks with good compressive strength and
durability properties. Their results, using mean compressive strength, showed that there was an
appreciable increase in compressive strength of the earth blocks as the percentage of cement and
compatibility pressure increased. These studies give credence to the efficacy of the various
additives in earth material stabilization and also provided a guide for determining possible mix
proportions in this present research.
In 1993, Mbata further investigated the effects of some chemical degradation process on
the durability of compressed soil-cement bricks using both high and low concentration of
magnesium and potassium aluminum sulphate solutions. From the study, Mbata (1993)
discovered that all the blocks lost their initial compressive strength after being soaked in 0.5
40
percent and 5.0 percent sulphate solutions. Mbata, therefore, concluded from this study that
cement stabilized soil bricks are not capable of withstanding sulphate attacks without protection.
James and Rao (1984), and Neville (1991), in two independent studies on RHA stabilized
soil blocks discovered that the quality of the rice-husk-ash (RHA) depends on four parameters,
namely: burning time and temperature, cooling time and grinding conditions. In 1986 Madu
conducted an investigation on soil amelioration with rice-husk-ash. The study reported that rice-
husk-ash can be used as a pozzolana in partial replacement of cement for soil stabilization. Madu
(1986), in this study discovered that rice-husk-ash has the advantage of increasing the resistance
of cement-stabilized soil to sulphate attacks. Also, the study revealed that rice-husk-ash reduces
the rate of hardening of the concrete elements. Madu added that low strength development at the
early ages including high shrinkage effects were observed. The results of these preceding studies
indicate the advantages achievable with rice-husk-ash and the necessary precautions to note
during their production as an earth material stabilizer. But none of these studies reported any tests
in relation to the permeability of the concrete elements. This is one of the major areas this
research has investigated.
In 1989 Ojosu examined the acoustic properties of building materials for building design
and revealed that rice husk can be used with cement to produce acoustic materials. In the said
study, Ojosu (1989) investigated some local materials such as rice husk, palm fiber, coconut fiber
and polystyrene foam for producing acoustic building products. The study revealed that rice husk
can effectively be used in the production of ceiling boards and surface boards. While Ojosu
concluded that rice husk can be used to produce ceiling boards, the study did not state whether
the rice husk was converted to ash or used in its natural state. Besides, the study was not directed
towards earth stabilization for building construction. Secondly the study was silent on the type of
tests carried out on the ceiling board.
41
In a study of partial replacement of cement with rice-husk-ash in concrete element,
Ukpong (1991) discovered that rice husk ash could be used in the production of concrete
elements with some degree of success. In the said study, Ukpong (1991) mixed cement, sand and
the burnt rice husk with water to produce concrete cubes. The cubes were subjected to tests
including compressive strength test, the result of the test revealed that the concrete cubes
recorded adequate compressive strength. The permeability test showed that the rate of penetration
of water into the concrete was low. Ukpong also discovered that there was reduction in the
weight of the concrete when the cube was compared with similar cubes produced from the
mixture of cement and sand without rice-husk-ash. The study also noted that the rice husk does
not burn with flame and the rate of burning was very slow indicating that rice husk is fire
resistant to some extent. In this study, Ukpong did not give reasons why the rice husk was burnt
into ashes before use. Nevertheless, Ukpong‟s research stands among earlier studies on the use of
rice-husk-ash to replace cement in stabilizing earth-based products in Nigeria with significant
success.
In another study “Replacement of Cement with Rice Husk in Concrete Construction”,
Emenari,(1987) used rice-husk-ash with sand and cement to produce concrete cubes. At the end
of the study, Emenari concluded that the use of rice-husk-ash in concrete construction reduced
the cost of concrete elements. In his cost analysis, Emenari stated that if a concrete industry uses
about 220,000 bags of cement each year at the cost of N11.00/bag, the cost is N2,420,000.00 but
with 15 per cent replacement of cement with rice-husk-ash, the cost reduces to N2,057,000.
Emenari‟s study also revealed that rice-husk-ash reduces hydration on concrete and improves its
resistance to attack by sulphate soil. In 1994 Onyemachi took the research further in an
investigation of the utility of rice husk and its derivative in the building industry. In this study,
Onyemachi (1994) subjected rice husk to various tests to determine its chemical composition and
properties. In the process of determining the physical properties, the liquid limit device was used
42
to determine the liquid limit content of the rice husk ash. Compressive strength machine was
used to determine the strength of rice husk concrete. Diffusibility test was also carried out to
determine the thermal conductivity of the rice-husk. The study discovered that rice husk has some
organic substances, which make it difficult to bind effectively with cement. For this reason,
Onyemachi converted the rice husk into inorganic material by burning it into ashes. A mixture of
cement:sand:rice-husk-ash was used in the study. The study revealed that rice-husk-ash, can be
used in construction as a weight saving material. It was also discovered from this study that the
mixture of rice-husk-ash, cement and sand has the same comparative strength with a mixture of
cement and sand for rendering purposes. The study effectively succeeded in confirming that rice-
husk-ash can be used in building construction. These two studies - Emenari,(1987) and
Onyemachi(1994) - did not test the concrete cubes for moisture permeability, but further give
credibility to the efficacy of rice-husk-ash as an earth material stabilizer.
Fashoba (1994) also carried out a research on the use of rice-husk-ash in concrete
elements. In the said study, Fashoba adopted the method of partial replacement of cement with
rice-husk-ash. The concrete cubes for this was made from a mixture of cement, sand and rice-
husk-ash. The concrete was cured by autoclave. While the quantity of cement in the mixture was
kept constant, the rice-husk-ash was repeatedly increased to produce samples with different mix
ratios. A comparison of the compressive strength test result revealed that there were no
significant differences between the concrete produced from cement, sand and rice-husk-ash and
the concrete produced from cement and sand. In all these studies so far rice-husk-ash was used in
combination with an internationally known chemical stabilizer - cement. This present research
was not only interested in the stabilizer combination aspect but the combination of two locally
cheaply available stabilizers – RHA and Straw. This present research on optimizing the use of
two locally available stabilizers has not only studied the two stabilizers – RHA and Straw,
43
without any addition of cement but also went further to investigate their efficacy in improving the
erosion resistance capacity of the stabilized earth material.
Montgomery (1998) and Kerali (2001) are among those that have done comprehensive
work on compressed cement stabilized soil bricks (CCSSB). Montgomery (1998), based on the
findings of the study concluded among others that the difficulty of defining soil with any degree
of accuracy for all the different soil types in the world, poses a difficult task to the stabilized soil
brick manufacturer to ensure that the soil chosen is suitable for the intended purpose. Kerali‟s
(2001) study which was primarily focused on durability of compressed cement stabilized blocks,
examined the inter-play between three variables in stabilized blocks; constituent materials,
processing methods and the effects of exposure conditions. Kerali among other things concluded
that it is possible to significantly raise the strength, improve the dimensional stability and wear
resistance of cement-stabilized soil blocks to the level that they can be safely used in building
unrendered walls in the humid tropics. These two studies introduced three other interesting
elements of earth material quality and usage – effects of soil type, production processes and
constituent materials. These three additional factors affecting the quality of stabilized earth
material products further inspired this researcher to also investigate the major chemical elements
in the soil types and the stabilizers in the course of this research.
Awari and Elinwa (2001) used groundnut-husk-ash at different replacement levels with
cement to produce concrete. Awari and Elinwa (2001) discovered that the properties of the
groundnut-husk-ash (GHA) after passing through a 212m sieve have predominantly silicates
and aluminates compounds. They also discovered that at 5-10 per cent replacement levels, the
concrete produced higher compressive strength in the range of 18.40 - 19.91 Mpa, while an
increase of the Groundnut-Husk-Ash (GHA) above 10 percent lowered the strength development
of the concrete. In 2002, Zubairu and Okoli researched into the properties of compressed earth
blocks stabilized with rice-husk-ash (RHA) burnt in an open air and discovered that there were
44
significant variations in the compressive strength of the blocks stabilized with rice-husk-ash (5%)
and those stabilized with cement (5%) respectively. All the blocks in Zubairu and Okoli‟s (2002)
study were wet-cured for seven days and sun dried for 14 days. The findings of these last two
studies served as a guide to the determination of the mix proportions and also kindled the interest
of this present research on the importance of the fineness of the rice-husk-ash. From findings of
Zubairu and Okoli‟s study, this current research noted the need for caution in the burning process
for the rice-husk-ash and ensured that the burning kiln was covered to avoid contamination by
other elements.
Optimization and Standardization of a Process/Product
Optimization in simple English usage means the process of making the way something is
done or used as efficient as possible, (Summers, Gadsby & Rundell(eds), 2000). Optimization
also refers to the use of specific techniques to determine the most cost effective and efficient
solution to a problem or design for a process. This technique is one of the major quantitative
tools in industrial decision making, (Wikitionary, 2007).Singer (2006), defined optimization as a
process of enhancing the effectiveness of something, or a way of making something function at
its best or most effective, or use something to its best advantage. According to Wikipedia (2007)
the process of optimization as related to business and engineering refers to methodologies for
improving the efficiency of a production process; the practice of making changes or adjustments
to a process, to get results. When we talk about optimizing a process, we are usually trying to
maximize one or more of the process specifications, while keeping all others within their range.
According to Oracle (2007), optimization is a process that finds a best, or optimal,
solution for a model. For example, somebody wants to know the maximum possible return on an
investment portfolio, but he/she is not sure how much money to put into each separate
45
investment. Or, you are a project manager with budget constraints, and you need to figure out
which combination of seven possible projects will result in the highest profit. Or, you are a
petroleum engineer, and you must determine the optimal number of oil wells to drill given a
certain reservoir size and specified production rates.
Optimization is primarily concerned with three basic ingredients of a problem:
An objective function (output/product) which needs to be minimized or maximized. For
instance, in a manufacturing process, one might want to maximize the profit or minimize
the cost. In fitting experimental data to a user-defined model, we might minimize the total
deviation of observed data from predictions based on the model. In designing a building
wall, we might want to maximize the strength.
A set of variables (treatments) which affect the value of the objective function. In the
manufacturing problem, the variables might include the amounts of different resources
used or the time spent on each activity. In fitting-the-data problem, the unknowns are the
parameters that define the model. In the building wall design problem, the variables used
define the strength qualities, shape and dimensions of the wall.
A set of constraints (standards specifications/code of practice) that allow the variables to
take on certain values but exclude others. For the manufacturing problem, it does not
make sense to spend a negative amount of time on any activity, so we constrain all the
"time" variables to be non-negative. In the earth material improvement problem, we
would probably want to limit ourselves to the minimum strength specification for
building walls and to constrain its shape, weight and quantity of component materials
(Wikipedia, 2007 and Singer, 2006)
46
The optimization problem in this research was to determine the values of the variables
(treatments) that maximize the objective function (compressive strength and erosion resistance
capacity of the earth material) while satisfying the constraints (standards of practice within the
building construction industry) in order to incorporate quality earth buildings into modern
building designs. It therefore follows that optimizing the use of rice-husk-ash and straw in earth
material stabilization will also involve the generation of a mix proportion that gives optimal
compressive strength and erosion resistance of the earth material.
Standardization on the other hand means a process of setting or establishing standards of
practice or procedure. In this sense, standards simply implies that, it is a universally agreed upon
set of guidelines for interoperateability. According to Hopper (2005), the wonderful thing about
standards is that there are so many of them to choose from. In the words of the Wikipedia (2005),
standardization in the context of technology and industry is the process of establishing a technical
standard among competing entities in the market, where there will bring benefits without hurting
competition. It can also be viewed as a mechanism for optimizing economic use of scarce
resources, such as forest, which are threatened by paper manufacture. According to the Malta
Standards Authority(MSA, 2006), standards are documents defining characteristics, for example,
dimensions, safety aspects, performance requirements, of a product, process, or service in line
with the technical/ technological state-of-the-art standards. The Malta Standards
Authority(MSA,2006), further explains that standards are developed by experts representing the
interests of the economic and social parties “stakeholders” (producers, service providers,
suppliers, users, consumers, public authorities, scientists/professional institutions, educational
authorities). It therefore follows that a single research/individual research work cannot correctly
be said to be capable of standardizing a product or process. This research was therefore set out to
47
provide a databased result than will contribute to the standardization of earth materials stabilized
with rice-husk-ash and/or straw.
Thorndike and Hagen (1997), defined standardization in terms of educational testing, as
meaning that all the students in a test answered the same questions and a large number of
questions under uniform direction, under the same time limit and that there is a uniform or
standard reference group to the performance of which a student‟s performance can be compared.
Another definition of standardization in the context of testing said, it simply implies uniformity
in administering and scoring the test, (Anastasi, 1976).
Within the field of products and services, Wikitionary (2007) defines standardization as
the process of establishing a standard or the process of making standard, of adapting so all are
similar. Similarity here implies uniformity of the products/services being standardized just as in
educational testing, except that the procedures to achieve these standards are relatively different.
In Wikipedia (2006), standardization in the context of social sciences is often about establishing
standards of various kinds and improving efficiency to handle people, their interactions, cases
and so forth. Voluntary consensus standards bodies develop these standards.
Some of the key objectives of standardization, according to the Malta Standardization
Authority (MSA, 2004), include defining performances of products processes and services, so
intervening in all life phases of a product from its design to its use and tertiary activities.
Moreover, standardization involves establishing products safety characteristics, so as to protect
people coming in contact with it. Quality and safety are therefore two very important aspects that
guide the standardization activity (MSA, 2006). The European Union Council (Vardakas, 2003)
explains that standards deal with the technical aspects of almost any product, service or process.
They are nearly always voluntary but play a very crucial role in the design, manufacturing,
packaging and end-of-life stages when used. They can also deal with efficient use of natural
resources (such as earth materials in this research).
48
Recently, according to Gudmundsson, Corso and Boer (1997), the use of product
architecture as the basis for standardizing parts, modules, and interfaces has emerged as a new
approach to increase the effectiveness and efficiency of products development and indeed the
whole value adding chain (Mayer & Lehnerd, 1997; Sanchez, 1999; Cusumano & Nobeoka,
1998). However, Bessant and Francis (2005), has quickly countered this claim, stating that as
widely as this product architecture concept has been discussed in literature, there is still a lack of
empirically grounded theory supporting its successful implementation. This researcher did not
therefore consider the product architecture concept but focused on following a standard
procedure in determining a mix proportion of these two local additives (stabilizers) that
optimized their use in earth material stabilization. It is hoped that this mix proportion will
according to MSA (2006) assure compatibility and interchangeability, reduce unnecessary variety
and increase the cost-effectiveness of the process and procedure for the manufacture of stabilized
earth materials for earth building construction, thereby optimizing the use of this additives.
This aspect of the literature review became necessary to explain that this project was an
optimization exercise and not that of product standardization as an individual do not normally
standardize a product or process alone. It has been included to clarify any possible confusion
between what is common practice in survey studies as standardization and what really is
standardization in product and process development.
Material and Specimen Testing Methods
Two common standards exist within the Nigerian construction industry – the British
Standards and the American Standards for Building and Engineering Works. (There is, however,
a recently approved Nigerian Building Code 2007, which deals mainly with industrialized
building materials, also classified as standard materials). There are no approved standards
specific on earth building construction in Nigeria for now. Specifically, the British Standard BS
49
1924 Part l on stabilized material testing and BS 3921 Part II on Clay Bricks; Strength, Water,
Absorption and Dimensions, was therefore adopted and applied in all the laboratory tests and
field experiments of this research.
Other standards on earth building include those of New Zealand, where three standards
have been developed – NZS 4297 - Engineering Design for Earth Buildings; NZS 4298 -
Materials and Workmanship for Earth Buildings and NZS - 4299 Earth Buildings not Requiring
Specific Designs (Walker & Morris, 2004), and the 2003 New Mexico Earth Building Materials
Code. These other standards were also made reference to for guidance during the field and
laboratory experiments.
Soils for building purpose according to Seeley (1981) may be subjected to a number of
tests to establish their identity and classify them. Some of the important tests include particles
size distribution test, liquid limit test and plastic limit test. The particles size distribution test is a
laboratory-based analysis to identify the soil characteristics. It may be a simple sedimentary test
to identify the percentage distribution of the main soil elements of fine gravel, sand, clay and silt,
(Smith, 1999). According to Seeley(1981), the British Code of Practice (CP1014) provides the
basis for field identification of soil particles and the strength features, which have important
influence on the foundation (building) behaviour. In spite of all the rigors of soil classification,
simple soil identification can be performed by anybody with a sensitive analysis and people can
learn this technique with a short training. The main points to examine are grain sizes
distribution, plasticity characteristics, compressibility and cohesion and to know how the binders
bind the inert grains (Ezeji 1984; Stulz, 1998; MaKinley 1999; Maini, 2002). A more elaborate
laboratory tests involving the chemical/elemental photometric analysis of the base materials may
also be conducted as it became necessary to identify the soil characteristics and chemical
composition, (Smith, 1999: Craig, 1998).
50
Summary of Review of Related Literature
The literature materials so far reviewed in this chapter has shown that the use of earth
materials for building construction is a very ancient tradition that is still surviving today in spite
of several negative influences brought on it by the introduction of cement- and steel-based
building materials. The review has also established that if logic and modern construction
technologies are applied to earth building, it will provide a viable alternative quality low-cost,
environmentally friendly housing for the teaming populations in developing countries. It has also
been demonstrated from the literature reviewed that as the world population levels grow,
especially within developing countries, so has the need for quality housing far outstretched its
availability. It was also shown from this review that with the increasing cost of major (standard)
building materials, it is becoming more and more difficult for the average income earner to build
or own his/her own house.
This literature review has shown that our traditional earth builders had always taken some
precautions through trial-and-error to improve the structural qualities of the earth material in their
earth building practices. This review has also established that, although the earth material has the
potential of being an effective alternative source of quality building material, Nigerian
governments‟ efforts to encourage earth building practices has been more of paper work and
academic rhetoric‟s than practice.
Documents reviewed in this chapter indicate, that improvements in the structural qualities
of the earth materials suggest a marriage of traditional practices and modern methods of
construction to produce widely acceptable quality products for earth building purposes. The
literature review also indicates that there is every need to optimize such and other possible
improvements. It has also been established from the documentations in this literature review that,
the mix proportions of the base materials - earth and stabilizers, production processes and
51
material quality and selection are major contributors to the quality of the end product and safety
to the life-long user of the improved earth materials.
The literature materials reviewed in this chapter indicates that it is possible to optimize a
product or processes from an individual/given project while standardizing a product or processes
is a collective/collaborative effort of different experts. The documents reviewed in this chapter
shows that standardization would involve comparing results from different experts and
practitioners (stakeholders) in a given area/discipline and reaching a consensus on the key
material content before a product can be said to have been standardized.
In all the related studies so far reviewed, there is ample evidence that the use of stabilizers
(additives) - local and universal - in stabilizing the earth material can improve their functional
qualities. Most of the studies reviewed in this chapter shows that most of the concluded/available
researches are skewed in favour of universally well known stabilizers and in a single independent
dose treatment except for that of lime:cement and cement:rice-husks-ash stabilizers. None of the
documents the researcher came across during this review was specifically interested in the
erosion resistance capacity and/or in establishing optimal mix proportions of the materials
in order to make most efficient use of these local stabilizers in terms of structural qualities. In
addition, a close examination of most of these studies showed that the study samples/specimens
have mainly been of purely cylindrical laboratory samples, which cannot be easily replicated for
field use. These are the gaps this research intends to fill by adopting a field-based approach to
optimize the use of these locally available stabilizers as earth material stabilizers.
The reviewed literature have also identified the need for comparing whatever optimal
results obtained from this research with the bench-marks as specified in the relevant building
codes/regulations.
52
CHAPTER III
METHODOLOGY
This chapter is concerned with the method, procedures and materials adopted in the
conduct of this research. The research design and the research instrument, validity and reliability
of the research equipment are described in this chapter together with the sample size and
sampling techniques. The research specimen, the experimental procedure - incorporating the
seven major steps in the conduct of the experiments, and the method of data analysis adopted
form the concluding parts of this chapter.
Research Design
The researcher adopted a material research and development design to investigated the
interaction effects of three stabilizer groupings (RHA, Straw and RHA-Straw), on three earth
building soil types (Clayey, Red and Laterite soil types), at three levels of mix proportions (11%,
14.5% and 20%) on the compressive strength and erosion resistance capacity of earth material.
This resulted in a 3 x 3 x 3 factorial experimental model at the field/laboratory level.
(Mckinley,1996). The study while researching into the interactions between the primary and
secondary operators and their effect on the dependent variables ended with the development of a
product out of the material study. This design was considered appropriate in line with Cooper‟s
(1995) and Bessant and Francis (2005) guideline on new products development and Uzoagulu‟s
(1998) illustration of factor based experimental design.
This experimental design took into account the effects of other factors such as types of
soil and variations in the mix proportions, while investigating the effects and interactive effects
of changes in the stabilizer type on the optimal strength and erosion resistance capacity of
stabilized earth material. This design allowed the researcher a comprehensive treatment of the
variables, providing both control and practical results that can easily be replicated and used by
prospective earth builders, researchers, and earth building owners.
53
Area of the Study
This study was primarily a developmental research endeavor centered on the optimization
of two earth material stabilizers – RHA and Straw, to improve the compressive strength and
erosion resistance capacity of the stabilized earth materials. The earth samples and the stabilizers
were collected from two local government areas within Adamawa State (i.e. Yola North within
Yola Metropolis and Girei Local Government Area). The study area is bounded by latitudes 8o
and 9o and longitudes 7.5
o and 9
o in Adamawa State, Nigeria. Both the material collection and the
experiments were conducted within the Sahel Savannah region of Nigeria, where earth-building
practices have been popular and is still common-place among the middle and low income
earners. This made sense for the study and also relevant to the locality.
Selection of Research Specimen
The selection and collation of the two base materials – earth and stabilizer, for the
production of the specimen were guided by three experimental techniques of convenience,
stratification and simple random sampling techniques, (Lenth, 2001; Walker & Morris, 2002).
i. Convenience Technique: Yola and Girei Local Government Areas of Adamawa
state were selected for convenience and secondly they belong to the Sahel Savannah
region, where earth building has been practiced since ancient times and is still
relatively popular, (Lenth, 2001).
ii. Specimen Stratification: The soil samples were stratified into the three local,
common classifications of earth building soil types namely, red soil, clayey soil,
and laterite soil, (Montgomery, 1998; Development Alternatives, DA, 2002)
iii. Simple Random Sampling: Simple random sampling technique is a common
research approach to improve reliability and minimize bias(Uzoagulu,1998). Out of
the ten stabilized specimen blocks from each experimental group, eight sample
54
blocks were randomly selected through a simple drop-test. Out of the number that
passed the drop-test, five sample blocks were randomly selected for the actual
laboratory test for the experiments in this research.
Specimen Size and Selection Procedure
A total of 135 stabilized specimen blocks were selected from the 270 experimental blocks
produced by the researcher. These 135 specimen blocks formed the experimental samples for the
two different laboratory tests and measurements. The selection of these 135 sample blocks were
based on both stratified and random sampling techniques. The specimen blocks were first
stratified according to the 27 experimental mix groups, while the five sample blocks for the
laboratory tests were randomly selected from the eight blocks that passed the drop-test.
To select the study samples, eight stabilized earth block specimen were first selected
through a drop-test from the ten specimen blocks produced from each of the 27 finite mix batches
for the experiments. From these eight specimen blocks five sample stabilized earth block were
randomly selected (in line with standard codes, see note below). These five block samples were
used for each of the 27 pairs of experiments – i.e. 27 experimental tests on compressive strength
and 27 erosion resistance ratios tests respectively.
[NB In choosing the specimen size(quantity) the researcher took into cognizance, that no
fixed number and no fixed percentage is ideal, rather it is the circumstance of the study
situation that determines what number or percentage of the population that should be
studied (Nwanna, 1985; Uzoagulu, 1998; Lenth, 2001; Walker & Morris, 2002; Osuala,
2003; Oracle, 2007). Secondly, in the absence of any readily available specific Earth
Building Code in Nigeria for now, the few foreign standards - British Standard BS 1924
Part l on stabilized material testing and BS 3921 Part II on clay Bricks; Strength, Water,
Absorption and Dimensions; BS 6073 parts l and 2, (1981) and BS 3921,(1985) on
55
sample size for material testing and the New Zealand Earth Building Standards- NZS
4297 - Engineering Design for Earth Buildings; NZS 4298 - Materials and Workmanship
for Earth Buildings and NZS 4299 - Earth Buildings not Requiring Specific Designs
(Walker and Morris, 2004), and the 2003 New Mexico Earth Building Materials Code,
were adopted in determining this sample size from the specimen blocks produced].
Research Equipment/Instrument for Data Collection
Two standard engineering measuring equipments were used for the experiments – the
Medium Strength Cube-crushing Machine for test of compressive strength of the stabilized earth
material. The Spray Test Apparatus using a 4.4mm nozzle at a pressure of 100kPa for testing the
erosion resistance of the stabilized earth materials was the second instrument.
Validity of the Instruments/Equipment
The Rockwell Universal Cube Crushing Machine for mild strength test was used
throughout the experiment to test the compressive strength of the samples. This machine is a
universally accepted quality, compressive strength testing equipment. This machine is equipped
with a privately branded version of digital indicators to measure cube crushing (compressive)
strength. The equipment is simple to use and gives more accurate readings than other analog
gauges such as the Michelettee Cube Crushing Machine, (Admet, 2008).
According to Admet (2008), material testing for construction is a major business with the
responsibility to certify that the materials used in construction projects are as specified by the
designers and meet set standards. To further validate this equipment, the researcher carried
repeated pilot tests with an experienced Laboratory Technologist with the Department of Civil
Engineering, Federal University of Technology, Yola, on five blocks whose compressive
strengths were already established from other machines to verify the validity of the machine
before being used in this research.
56
Table 1
Differences in Compressive Strength Between Established and Pilot Blocks
Type of Block Block 1 Block 2 Block 3 Block 4 Block 5
Compressive Strength of Pilot Test Blocks 3.65 3.61 3.65 3.64 3.63
Compressive Strength of Existing Blocks 3.66 3.63 3.64 3.64 3.61
Differences in Reading -0.01 -0.02 0.01 0.00 0.02
Ratio of Means 1:1 Correlation between Blocks 0.59
The results as presented in Table 1 returns a mean ratio of 1:1 when the results from the
two sets of data are compared, while the correlation coefficient is positively high at 0.59
indicating a high degree of similarity between the sets of data. These results clearly validated the
equipment for this research.
The Spray Test Instrument used for this study incorporated the Crytrn(1957)
specifications as modified by the University of Technology, Technology Development Unit
(DTU), Sydney Australia (Heartcote, 2001). Repeated pilot tests were conducted with this spray
test instrument by the researcher and the chief technologist, Department of Civil Engineering,
Federal University of Technology, Yola, on two groups of five randomly selected stabilized
blocks from the specimen. The results from the two sets of pilot tests were further compared with
the results from a field test by two field practicing Engineers/Lecturers at the Departments of
Civil Engineering and Building, Federal University of Technology, Yola. This was done to
clearly establish the validity of the Spray Test Instrument. These results are presented in Table 2.
The relationship between the three sets of blocks was compared using
Table 2
Erosion Resistance Ratios from Laboratory and Field-based Tested and Pilot Blocks
Type of Block Block 1 Block 2 Block 3 Block 4 Block 5 Mean
1st Set of Lab-based Pilot Blocks 8.03 8.01 7.65 7.45 7.66 7.76
2nd
Set of Lab-based Pilot Blocks 7.57 7.83 8.02 7.51 7.65 7.72
Field-based Pilot Blocks 7.76 8.04 7.65 7.58 7.79 7.76
Grand Mean of all Readings 7.75
Ratio of Mean 105:100:105
57
their Standard Deviation and the ratio scale. The result as presented in Table 2 justifies the
researcher‟s conclusion that the instrument was produced to precision and valid for the tests in
this research.
Reliability of the Instruments/Equipment
The Rockwell Cube Crushing Machine is a universal industrial/research strength testing
equipment manufactured by an internationally reputed industry/laboratory equipment
manufacturer. The home made Spray Test Instrument was produced by an expert laboratory
technologist following the DTU specifications under the guidance of the researcher. Both the
Rockwell compressive strength test machine and the spray test instrument were used in the pilot
survey with ten randomly selected stabilized blocks from the specimen for this research. The
results of these pilot tests, as shown on Table 3, compared favourably with the readings from the
main experiments to establish the reliability of these two equipments.
Table 3
Compressive Strength of the Pilot Study Blocks Compared with Main Experimental Ressults
Type of Block Block 1 Block 2 Block 3 Block 4 Block 5
Readings from Pilot Blocks 2.49 3.23 3.57 3.31 4.70
Mean Values from Main Experiment 2.49 3.24 3.56 3.34 4.69
Differences in Reading 0.00 -0.01 0.01 -0.03 0.01
Correlation Co efficient 0.9998
The correlation coefficient of the two sets of tested blocks returned a perfect correlation at 0.9998
coefficient level. This result does not need any further examination to accept that the equipment
was standard and reliable. In Table 4 the result of the tests on the erosion resistance ratios of the
pilot blocks are presented.
58
Table 4
Erosion Resistance Ratios of the Pilot Blocks Compared with the Main Experimental Blocks
Type of Block Block 1 Block 2 Block 3 Block 4 Block 5
Readings from Pilot Blocks 8.29 8.29 3.54 2.69 4.68
Mean Values from Main Exp. 8.27 8.31 3.56 2.71 4.69
Differences in Reading -0.01 0.06 -0.02 -0.02 -0.01
Mean Correlation 0.9992
Research Specimen
The specimen for this research was made-up of 270 compressed stabilized earth
blocks(CSEBs) produced from the 27 experimental sets (batches/groups) based on the type of
stabilizer, mix proportion and soil types. There were three primary experimental sets/groups
based on the three different stabilizer(additive) combinations of rice-husk-ash, straw and rice-
husk-ash combined with straw. These three primary experimental sets were separated into three
sub-sets/groups according to the soil type - red earth, clayey and laterite soil. The stabilizer-soil
type subsets/groupings were further stratified into three batch groupings depending on the mix
proportions/percentage of stabilizer added (11%, 14.5 % and 20%) as illustrated in the chart on
figure 1. This arrangement gave a 3 x 3 x 3 factorial experimental design.
Experimental Procedure
The 27 different sets of experiment for this research were carried out under seven major
steps, namely, selection/collation of research materials, soil preparation, stabilizer(additive)
preparation, field and laboratory testing of the base materials, batching of materials, specimen
production, and laboratory testing of the samples.
1. Selection/Collation of Research Materials
The selection and collation of the two base research materials – earth and stabilizers, used
in this research followed a guided step-by-step procedure as follows:
59
(a) Soil Selection: Two of the soil samples – red soil and laterite soil, used in this
research were extracted from existing earth builder‟s soil pits at depths not less than
750mm below ground level. The clayey soil was extracted from a dead ant-hill, (as is also
the local practice). The criteria for the selection of the sample soil types were based on
literature and field tests, (Das, 1994; Honben and Guillard, 1994; Craig, 1998). These
criteria included the grain size distribution, chemical composition, moisture content and
depth for soil extraction.
(b) Stabilizers (Additives) Collation: The two local stabilizers(additives) – rice-husk-
ash and straw, were collated as follows;
i. Rice-Husk-Ash (RHA): The rice husk was collected clean in „bacco‟
bags, directly from available rice-mills at Sangirei and Jambutu areas
EXPERIMENTAL SET-UP
Rice-Husk-Ash Group Straw Group RHA & Straw Group
Rice-Husk-Ash-Red
Soil
Rice-Husk-Ash-Clay
Soil
Rice-Husk-Ash-Laterite
Soil
Straw-Red Soil
Straw-Clay Soil
Straw-Laterite Soil
Rice-Husk-Ash & Straw –Red Soil
Rice-Husk-Ash & Straw –Clay Soil
Rice-Husk-Ash & Straw –
Laterite Soil
Rice-Husk-
Ash-Red Soil
[11%]
Rice-Husk-
Ash-Red Soil
[14.5%]
Rice-Husk-
Ash-Red Soil
[20%]
Rice-Husk-
Ash-clay Soil
[11%]
Rice-Husk-
Ash-Clay Soil
[14.5%]
Rice-Husk-
Ash-Clay Soil
[20%]
Rice-Husk-Ash-
Laterite Soil
[11%]
Rice-Husk-Ash-
Laterite Soil
[14.5%]
Rice-Husk-Ash-
Laterite Soil
[20%]
Straw-Red Soil [11%]
Straw-Red Soil [14.5%]
Straw-Red Soil [20%]
Straw-Clay Soil [11%]
Straw-Clay Soil [14.5%]
Straw-Clay Soil [20%]
Straw-Laterite
Soil [11%]
Straw-Laterite
Soil [14.5%]
Straw-Laterite
Soil [20%]
Rice-Husk-Ash & Straw –Red Soil
[11%]
Rice-Husk-Ash & Straw –Red Soil [14.5%]
Rice-Husk-Ash & Straw –Red Soil
[20%]
Rice-Husk-Ash & Straw –Clay Soil
[11%]
Rice-Husk-Ash & Straw –Clay Soil
[14.5%]
Rice-Husk-Ash & Straw –Clay Soil
[20%]
Rice-Husk-Ash & Straw –Laterite
Soil [11%]
Rice-Husk-Ash & Straw –Laterite
Soil [14.5%]
Rice-Husk-Ash & Straw –Laterite
Soil [20%]
Fig. 1: ILLUSTRATION OF EXPERIMENTAL GROUPS
60
of Girei Local Government Area and Yola metropolis all within the
study area.
ii. Straw Collation: The straw was collected with the help of one of the
research assistant (a local earth builder) from the field in a dry
condition. All forms of broad-leafed grasses including legumes were
not included in the straw.
2. Soil Preparation: The soil samples were extracted from the three different locations,
around the university campus and at Jambutu area of Yola metropolis. The three soil types
were separately sun-dried on an abandoned concrete platform used during the construction
of the School of Science Annex at Federal University of Technology, Yola. The researcher
swept and washed the platform to keep it clean during the drying of the soil samples. These
drying samples were turned daily until a uniform soil colour was obtained from top to
bottom indicating uniform moisture content. The soil samples were separately labeled and
stored accordingly.
3. Stabilizers Preparation: The two stabilizers – rice-husk-ash and straw – were separately
prepared before use as follows:
i. Rice-Husk-Ash: The collated rice husk was burnt to ashes using a locally
constructed kiln made from sealed empty drums with appropriate air inlet
openings and an ash collection outlet at the bottom level. This precaution ensured
that only rice-husk was burnt not rice-husk and sand or other mixture of
impurities. The burning and cooling time and temperature were kept constant all
through the burning process. The burnt rice-husk-ash was ground into a fine
powder and sieved turning it into a quality pozzolana (a siliceous or siliceous-
aluminous material which in itself possesses little or no cementing value but will,
in finely divided form and in the presence of moisture chemically react with
61
calcium hydroxide at ordinary temperature to form compounds possessing
cementing properties) [N.B. The burning time, temperature, cooling time and
cooling conditions of the rice-husk-ash were carefully checked, and as much as
possible kept constant all through the burning process, by the researcher. The
burning kiln was always covered to avoid the introduction of any foreign element
that could contaminate the ash. This was to ensure that the experiments were not
unduly affected by other extraneous variables]. After the burning, the ash was
ground and sieved with a BS 245 gauge to attain a fineness of 25µ. The grinding
machine and the sieve used in this research were washed with detergents water,
rinsed with clean water and allowed to dry before being used.
ii. Straw: The dry screened straw was manually cut into smaller lengths about 4cm
for easy storage and mixing during the block moulding. The stored straw was
spread out once again on the experimental platform for at least two days to allow
it loose any accumulated moisture during storage, and kept in this dry state until
the time of batching with the sample soils.
4. Field and Laboratory Testing of the Base Materials: A simple sight and sedimentation
tests were conducted at the field to select the soil types for this research. Further
laboratory tests were conducted on all the three soil samples in the Department of Soil
Science Laboratory, Federal University of Technology, Yola to determine their particles
size distribution. A chemical analysis of the same sample soils were carried out in the
Department of Biochemistry Laboratory to determine their chemical composition.
The two stabilizers (locally available additives) were laboratory tested to identify
the major active ingredients/chemical composition at the Department of Biochemistry
Laboratory and validated at the Department of Geology, Material Science Laboratory, all
at Federal University of Technology, Yola. A simple test for good drinking water was
62
used to select the water for mixing the materials to avoid contamination from
unsuspected chemicals or any other organic impurity.
5. Batching of Materials (Measuring out of materials in proportions for mixing): The
different soil samples were batched out first. The stabilizers were then batched and added
to each soil sample separately at replacement level of 11, 14.5 and 20 per cents
respectively (approximately 1:8, 1:6 and 1:4 mix proportions). All measurements were by
volume in all the mix batches, (British Standard - BS EN, 206, 2002). The researcher‟s
previous field experience in the construction industry was also brought to bear in these
experiments to ensure quality of end-products. Each of the specimen groups, based on the
stabilizer and soil types were worked-on on a separate day to avoid complication in the
specimen identification.
6. Specimen Production: The batched materials (earth and stabilizers) were first dry-mixed.
Water was then added until a workability state was attained for each batch. As a result of
the microscopic behavior of the straw in earth building works, all the batches incorporating
straw were mixed with water for a minimum of 24 hours to allow for natural impregnation
of the straw and earth mix through adequate moisturization of the straw element before
moulding. These straw incorporating mixes were covered with tarpaulin during the periods
of moisturization to keep away any possible infiltrations. The concrete platform beside the
The Researcher with the Local Builder Collating and Batching the Earth Materials.
Fig 2
63
School of Technology and Science Education Block, Federal University of Technology,
Yola, Adamawa State was used for the mixing of all the batches. This platform was first
washed, allowed to dry and then thoroughly swept to avoid any form of contamination
from the environment. Each of the specimen blocks were wet cured within the laboratory
floor for seven days and sun-dried for a minimum of 21days before being used for the
experiments. The normal block-press moulding machine was used throughout the
production process.
A total of 27 experimental groups (sets/batches), based on the type of stabilizer,
soil types and mix proportion were developed in this research. Ten(10) specimen
compressed stabilized earth blocks (CSEBs) were produced from each of these 27 finite
mix groups. This gave a total of 10 blocks each out of the 3 different stabilizer types x 3
soil types x 3 variations in the mix proportions.
Each of the specimen blocks measured 100 x 150 x 350mm (see figure 4). Table 5
gives a summary of the experimental groupings based on the type of stabilizer, the soil type
and variations in the mix proportions as earlier illustrated in figure 1. A total of 270
specimen compressed stabilized earth blocks (CSEBs) were produced for this research.
7 Laboratory Testing of the Samples: Five sample blocks randomly selected from the eight
blocks that passed the drop-test, from each of the 27 mix groups were used for the entire
The Researcher Mixing the Batched Materials
for the Block Moulding
Specimen Stabilized Earth
Block
350mm
150mm
100mm
Fig 4 Fig 3
64
experiment (i.e. 27 sets of 5 sample blocks). Each set of the five (100 x 150 x 350mm)
stabilized earth block samples, representing each of the 27 mix groupings, were cut into
two equal cubes across the length giving two cubes of approximately 100 x 150 x 175
mm. A total of 10 sample block cubes were therefore produced, by this block cutting,
giving a total of 270 sample earth block cubes for the entire experiment. From each set of
the 10 sample cubes, five were used to test for the compressive strengths and the other
five for the erosions resistance capacity respectively (i.e. five sample blocks for a
particular laboratory test and measurement) This gave a total of 27 sets of five sample
earth block cubes for compressive strength and erosion resistance ratios respectively.
a. Compressive Strength Test: Each of the 135 sample block cubes (a set of five
cubes from a particular mix group for each test) was subjected to a standard cube-
crushing test in turns, using a medium strength cube-crushing machine. The cubes
were sandwiched in-between two smooth hardwood surfaces to avoid direct
contact of the samples with the metallic surface of the machine, thereby avoiding
unwanted surface breakdown of the samples. The crushing weight was applied
gradually until each of the cubes crumbled/disintegrated under load. The readings
were recorded accordingly, (See Appendix D and E, page 163 and 167).
One of the Engineering Students (Immanuel)
Operating the Block Moulding Machine
Fig 5
Some of the Cured Earth Blocks Being
Sun-dried at the Open Field
Fig 6
65
Table 5
Schedule of Specimen Grouping by Stabilizer, Mix Proportion and Soil Types
Key: Soil Sample A – Clayey soil; x- Rice-Husk-Ash and
Soil Sample B – Laterite Soil and y - Straw;
Soil Sample C – Red Soil;
N.B. Only one stabilizer mix batch was worked-on each day (e.g. xA1, xA2, xA3). All the
specimens produced each day were wet-cured for seven days and open dried for 21 one days
respectively before the laboratory tests and measurements.
Compressive Strength(α) - is expressed as total load at crushing moment per square
area of contact or N/mm2 (see Appendix C for the formula for the calculations).
b. Erosion Resistance Ratio: Each of the second set of the 135 sample block cubes
(a set of five cubes from a particular mix group for each test) was placed on a
clean platform in the bathtub of the spray instrument in turns for the erosion
resistance test. One face of each of the sample cubes was placed under a vertically
Specimen Grouping Based on Stabilizer Type, Soil and Mix Proportion Soil Samples Percentage of Stabilizer Soil Samples
Clayey Soil(A) Laterite Soil(B) Red Soil(C)
RH
A(x
)
[EX
PE
RIM
EN
T I
] 11% xA1 xB4 xC7
14.5% xA2 xB5 xC8
20% xA3 xB6 xC9
ST
RA
W(y
)
[EX
PE
RIM
EN
T I
I] 11% yA1 yB4 yC7
14.5% yA2 yB5 yC8
20% yA3 yB6 yC9
RH
A &
ST
RA
W(x
y)
[EX
PE
RIM
EN
T I
II] 11% xyA1 xyB4 xyC7
14.5% xyA2 xyB5 xyC8
20% xyA3 xyB6 xyC9
66
inclined spray at 70kPa for 120minutes delivering a total of 7500 mm spray on the
surface of the sample cube, (an equivalent of the strongest driving rain for 5 years
in Nigeria, Nigerian Airports Authority (NAA), Yola, May 2008). The sample
cube was then removed, dried and measured to ascertain the depth of wear. The
dried sample was also weighed to check the difference in precipitation. The second
face of each sample cube was subjected to a horizontal spray test for another 120
minutes in turns, dried and readings taken of the mass loss and depth of erosion
respectively. This tests and measurements were carried out for all the 27 sets of the
sample cubes. A summary of the erosion resistance ratios for the five sample cubes
for each batch are presented Appendix C and D, page 156 and 160. Erosion
Resistance Ratio (ERR) - represents a ratio of the rate at which the earth blocks
precipitates (mass loss) under the water spray (simulated rainfall) over time (see
Appendix E for the formula for the calculations).
Method of Data Analysis
Frequency count, the Mean and Ratios statistics were used for the primary analyses and
interpretations of the relevant data to answer the research questions. The Analysis of Variance
(ANOVA) statistical model, employing a computer-based univariate analysis approach was used
to test the hypotheses and validate the primary findings. The univariate statistics was accepted
for the analysis, because it could analyze both the effects of the stabilizers and the interactive
effects of the different soil types and variations in the mix proportions on the compressive
strength and erosion resistance qualities of the stabilized earth material. The data generated from
the different experimental tests were used for the analysis. The researcher believes that through
this approach the findings of this research are both valid and reliable.
67
CHAPTER IV
PRESENTATION AND ANALYSIS OF DATA
The data for this research is presented and analyzed in this chapter under four major sub-
headings, viz, chemical/material composition of the research materials, data analysis based on the
research questions, test of hypotheses, major findings and finally the discussion.
Chemical/Material Composition of the Research Materials
Three different local earth building soil types (red, clayey and laterite soils - see page 19
and 20, for guide on local classification) and two types of stabilizers, rice-husk-ash(RHA) and
Straw, were involved in this research. The presentation under this heading is sub-divided into
four, namely, particles distribution of the soil material, chemical composition and analysis of the
sample soil, chemical composition and analysis of the RHA as compared with ordinary portland
cement and the chemical composition and analysis of Straw. Data on the material composition of
the stabilizers and soil types are presented in Tables 6 to 9. Each table is followed with an
analysis of the data contained therein.
1. Particles Distribution of the Soil Samples: The particles distribution of the three soil
samples as presented in Table 6 shows that each of the soil types contain some amount
of clay that falls within manageable percentages for earth building purposes [red soil –
24.50 per cent; clayey soil – 36.20 per cent; laterite soil – 18.60 per cent], (California
Uniform Building Code(UBC), 2005 and Houben, Rigassi and Garnier, 1994). The
percentage of the sand content range between 59.30 per cent for the red soil, 47.50 per
cent for the clayey soil and 52.50 per cent for laterite soil which were also considered
adequate for making stabilized earth blocks, (Homes, 1998).
The grading balance between the sand and clay contents of these natural soil types
justifies the need for their chemical stabilization (addition of additives to improve their
68
inert properties of permeability and porosity) and to also mechanically stabilize the soils
(application of adequate compression during block production) to improve on the density,
mechanical strength and compressibility of the earth blocks.
Table 6
Particles Distribution of the Three Earth Building Soil Samples
The variations in the percentages of the constituent materials giving the soil its
texture and properties are not enough to threaten the quality of the earth blocks, thus
giving no cause for any physical stabilization (i.e. to affect the properties and texture) of
the soil types, as these would have little or no effect on the erosion resistance and
compressive strength of the earth material. All the soil samples contained impurities
below 5 per cent which is acceptable in earth building construction, (MacHenry, Jnr,
1997; Bentgtsson and Whitaker, 1998; and Kerali, 2001). The presence of these other
impurities however, prompted a further chemical analysis of the soil contents to identify
what these and other chemical elements make-up the soils and what possible effect(s)
they could have on the earth material stabilization, (see Table 7).
2. Chemical Composition of the Three Soil Samples: The data presented in Table 7,
demonstrates some of the distinct chemical characteristics of the three soil types. From
the result of the laboratory analysis, seven out of the nine different chemical elements
Soil material Percentage of the Material Content(%)
Red Earth Clayey Soil Laterite Soil
Gravel 8.24 4.25 19.75
Sand 59.30 47.50 52.50
Clay 24.50 36.20 18.60
Silt 5.23 7.60 5.85
Other Impurities 2.73 4.45 3.30
69
are present in all the three different soil types at varying percentages. Only the clay soil
contains all the nine elements identified, while the laterite soil contains eight of the
elements.
Table 7
Chemical Composition of the Three Soil Samples
S/N0 Chemical Element Percentage of Element Contained(%) Red Earth Clayey Soil Laterite Soil
1 Iron(Fe) 35.14 14.57 29.63
2 Potassium(K) 29.34 37.30 26.08
3 Magnesium(Mg) 12.72 11.20 9.16
4 Calcium(Ca) 16.01 14.16 13.85
5 Zinc(Zn) 3.80 17.89 14.86
6 Nitrates 1.44 1.60 3.84
7 Phosphorous(P) 1.45 1.39 2.58
8 Cadmium(Cd) 0.10 0.36 -
9 Sodium(Na) - 1.53 -
The red and clayey soils contain Cadmium(Cd), a slow combusting element, at
very low percentages of 0.10 and 0.36. Cadmium is used to lower the melting
temperature of other metals alloyed with it. Cadmium and solutions of its compounds are
highly toxic, with cumulative effects similar to those of mercury poisoning.
Cadmium Sulphate (3CdSO4·8H2O) is used as an astringent. Its presence in the clayey
and red soils play no major significant role in earth block manufacture, except that it
combines easily with zinc to form low combustible compounds and burns in the air to
form Cadmium Oxides (CdO), (Microsoft Encarta, 2006).
The second element found only in the clayey soil, Sodium (Na), is a highly reactive
and extremely soft metallic element grouped under alkaline earth metals. It reacts
violently with water forming Sodium Hydroxide and Sodium Hydrogen. It is found
naturally, as in this clayey soil, in the compound state as Sodium Carbonate. The Sodium
70
content of the clayey soil naturally combines with other compounds in the earth material
matrix to form salts, which dissolve when in contact with water and crystallizes when dry
resulting in efflorescence. This made the presence of this Sodium a concern in this
research, which required special attention.
According to Microsoft Encarta (2006), most common soil hues are in the red to
yellow range, getting their colour from iron oxide minerals coating the soil particles. The
presence of the Iron(Fe) element in the three soils in varying percentages clearly affected
their colour texture. The presence of Iron(Fe) and Zinc(Zn) in all the soil types is also
important as they are known to combined with Ferric Oxide as found in the rice-husk-ash
and reacts with Silicon Dioxide to improve the structural strength of the rice-husk-ash
stabilized earth blocks. Ferric Oxide and Zinc are also known to chemically react with
Magnesium Oxide and Silica as contained in a pozzolana.
Three alkaline earth metals of Calcium, Magnesium and Potassium were also
found in the three soil samples. Calcium is one of the earth's most abundant elements,
found in compounds as diverse as marble, gypsum, and chalk was found in all the three
soil samples in the order of laterite soil - 13.85 per cent; clayey soil - 14.16 per cent and
red soil – 16.01 per cent. The durability of the Calcium element also makes it an
important component of industrial products such as cement. Calcium is probably best
known for its contributions to the health of our own teeth and bones. Calcium is
commonly found in a chemically combined state in lime (calcium hydroxide), cement and
mortar (as calcium hydroxide or a variety of silicates of calcium). Silica as found in the
rice-husk-ash is known to react with the Calcium hydrate compounds to form Calcium
Silicate Hydrates, which lowers the alkalinity of straw, (Shafiq, 1988). Through this
interaction the dangers of alkaline composite pore water effect in fiber (straw) stabilized
71
earth blocks can be reduced. The presence of Calcium in the soil samples was therefore, a
plus in the development of the structural quality of the earth material.
Potassium is found in nature in large quantities, ranking eighth in the order of
abundance as one of the elements of Earth‟s crust. Potassium in the earth‟s crust is found
in various minerals such as carnallite, feldspar, saltpeter, greensand, and sylvite.
Potassium is a constituent of all plant and animal tissue as well as a vital constituent of
the fertile soil, Microsoft Encarta (2006). Potassium forms many compounds resembling
corresponding sodium compounds, based on a valence of 1. Some of the most important
of these compounds include - Potassium bromide (KBr), a white solid formed by the
reaction of potassium hydroxide and bromine, is used in photography, engraving, and
lithography, and in medicine as a sedative, Potassium chromate (K2CrO4), a yellow
crystalline solid, and Potassium bichromate, or Potassium dichromate (K2Cr2O7), a red
crystalline solid, which are powerful oxidizing agents used in matches and fireworks, in
textile dyeing, and in leather tanning. Others include Potassium nitrate (KNO3), a white
solid prepared by fractional crystallization of Sodium nitrate and Potassium chloride
solutions, is used in matches, explosives, and fireworks, and in pickling meat. Occurring
naturally as saltpeter, Potassium permanganate (KMnO4), a purple crystalline solid, is
used as a disinfectant and germicide and as an oxidizing agent in many important
chemical reactions. Potassium sulfate (K2SO4), a white crystalline solid, is an important
potassium fertilizer and is also used in the preparation of potassium alum. Potassium
hydrogen tartrate (KHC4H4O6), commonly known as cream of tartar, is a white solid used
in baking powder and in medicine.
Among all these Potassium compounds only Potassium iodide (KI), a white
crystalline compound that is very soluble in water, and is used in photography for
preparing gelatin emulsions and in medicine for the treatment of rheumatism and
72
overactivity of the thyroid gland. Potassium iodide does not occur naturally in the Earth‟s
crust, (Microsoft Encarta, 2006), this made this researcher not to worry about its possible
presence in the soil samples. The high presence of Potassium(K) among the soil samples,
was only of interest to this researcher as it reflected on the degree of the strength
development of the earth materials and possibly on the durability of the earth material
depending on the type of stabilizer(additives) used, [red soil – 29.34 per cent; clayey soil
– 37.30 per cent and laterite soil – 26.08 per cent].
The presence of the third alkaline earth metal, Magnesium (laterite soil - 9.16 per
cent; red soil - 12.72 per cent; and clayey soil - 11.20 per cent) is also of interest in this
earth building research. According to Simsung (2003), the Magnesium as contained in the
three soil samples reacts with Zinc-Oxide to form a chemical bond that is resistant to
Sulphuric Acid attack in earth building. The presence of Zinc, in the three soil types is
therefore an added advantage for the RHA and the RHA with Straw stabilized earth
blocks, (Mbata, 1993 and Madu, 1986).
All of these three alkaline earth metals are cation (positive ions) chemical
elements. The varying percentages of their occurrence in these three soil samples is seen
to reflect on the proportionate clay(anion compound) content of the soil samples, - anions
attracting the cations through the natural cation exchange process.
The three soil samples contain varying quantities of Nitrates (red soil – 1.44 per
cent; clayey soil – 1.60 per cent; laterite – 3.84 per cent), which naturally combines with
lime (Calcium Hydroxide the natural compound of Calcium) to form a strong chemical
bond which is good for the strength development of stabilized earth material. The
reaction of these Nitrates with lime was demonstrated in the strength improvement of the
stabilized earth materials containing the RHA as the Nitrates react on the Calcium-oxide
in the pozzolana.
73
Phosphorous(P), a non metallic element, insoluble in water is also found in all the soil
types. This Phosphorous(P) reacts with Calcium(Ca) to form Calcium Phosphate (Ca3(PO4)2),
which combines under high temperatures with Silicon Dioxide to produce Red Phosphorous
(Microsoft Encarta 2006). Red Phosphorous is a non poisonous microcrystalline powder.
This Red Phosphorous powder does not occur naturally in a free state but as a Phosphate
which also combines with oxygen to form Phosphorous Oxide (P2O3), a delinquent reducing
agent, which combines with other mineral elements to increase soil fertility. This behaviour
of soil Phosphorous makes earth building a good biodegradable natural building material.
3. Chemical Composition and Analysis of the Rice Husk Ash as Compared with that
of Ordinary Portland Cement: The result of the laboratory analysis of the chemical
composition of the rice-husk-ash compared with that of Ordinary Portland Cement(OPC) is
presented in Table 8. The data show that Ordinary Portland Cement is predominantly a
Calcium Oxide substance while the RHA is primarily an Amorphous Silica substance. Both
the RHA and Ordinary Portland Cement contain very low percentages of Titanium Oxide
with the RHA containing approximately half the quantity contained in Ordinary Portland
Cement.
The table also shows that while Ordinary Portland Cement contains up to 5.35 per cent
of Aluminum Oxide with very low Potassium Oxide content (0.62 per cent), RHA contains
more of Potassium Oxide (2.08 per cent) and almost a negligible amount of Aluminum Oxide
(0.48 per cent) with 2.19 per cent of free Calcium-Oxide, (see Table 8). The free Calcium
Oxide is known to naturally combine with the Nitrates found in the soil samples and
Hydrogen when water is added to the mix for hydration and workability, to form a strong
chemical bond which is good for the strength development of stabilized earth materials.
Ordinary Portland cement is also shown to be of 75microns and 2.65 specific gravity,
74
Table 8
Chemical Composition of Rice Husk Ash(RHA) and Ordinary Portland Cement.
Constituent Elements Percentage of the Constituent Elements
Rice husk ash Ordinary
Portland Cement
Silicon dioxide (SiO2)
[Silica activity index (SA)
71.3%]
89.75 22.35
Aluminum oxide )Al2O3) 0.48 5.35
Ferric oxide (Fe2O3) 0.89 3.49
Calcium oxide (CaO) 2.19 65.8
Potassium oxide (K2O) 2.08 0.62
Magnesium oxide (MgO) Traces 1.37
Sodium oxide (Na2O) Traces 0.21
Manganese oxide (Mn2O3) 0.43 0.29
Phosphorous oxide (P 2O5) 0.67 0.19
Titanium oxide (TiO2) 0.16 0.33
Microns 25µ 75µ
Specific Gravity 2.13 2.65
while RHA presents a finer powder at 25microns and 2.13 specific gravity. This gives the
RHA an advantage of being able to fill-in finer pores in the earth material mixes, thereby
producing earth blocks of higher density than those of Ordinary Portland Cement under
the same production conditions. This finer powder of RHA was seen to positively
contribute to the compressive strength quality of the stabilized earth material. On the
other hand, this high degree of fineness of the RHA makes it require much more water for
workability in RHA stabilized earth blocks. The Potassium-oxide in the RHA, a
compound of Potassium is also known to combine with other Nitrate compounds in the
soil to form Potassium Nitrate (KNO3), a white solid normally prepared by fractional
crystallization of Sodium nitrate and Potassium chloride solutions thereby reducing the
explosive tendencies of this white solid while improving the health quality of the earth
material. The reaction between the Magnesium Oxide(MgO) and Manganese
Oxide(Mn2O3) in the RHA and the Potassium found in the soil samples increased the
75
quantity of Potassium Permanganate (KMnO4), compound thereby increasing the
disinfectant and germicide (health) potential of the earth material.
The presence of Phosphorous oxide in this RHA was seen to increase the effect of
the Red Phosphorous powder in the soil samples that occur naturally in a free state as a
Phosphate which combines with oxygen to form Phosphorous Oxide (P2O3), a delinquent
reducing agent, with the possibility of combining with other mineral elements to increase
soil fertility.
4. Analysis of the Chemical Composition of the Straw: In Table 9 the chemical composition
of Straw shows that this fibrous tubular stem, whose chemical structure is yet to be fully
elucidated, (Charoenvai, Khedari, Hirunlabh, Daguenet and Quenard, 2005) is an
amorphous substance containing Phenolic, Methoxyl, Hydroxyl and other constitute
groups as presented. The Straw like the RHA contains a reasonable percentage of Silicon
Oxide (31.50 per cent).
Table 9
Chemical Composition of Straw
S/N0 Chemical Element Contained Percentage of Constituent
Elements
1 Cellulose – C5H10O5 – (polymer of glucose)
i. Holocellulose
ii. Alpha Cellulose
26.20
14.60
2 Hemicellulose
(a polymer of xylemn bonded by B – 1, 4
10.60
3 Alcohol-Benzene solubility 7.50
4 Lignin – C7H10O3 (a polymer phenol) 9.60
5 Silicon oxide (SiO2) 31.5
The four major chemical elements include Holocellulose (26.2 per cent) and Alpha
Cellulose (14.6 per cent), Lignin (9.60 per cent) and Silicon Oxide (31.5 per cent). The
presence of the Lignin and Hemicelluloses in the Straw is of interest in this research. This
fibrous stem disintegrates in the presence of alkaline pore water, thus breaking the link
76
between the individual fiber cells. This uncommon combination of chemical elements in
the Straw distinguishes it from other organic materials that would have decayed when in
contact with water, thereby making the Straw an excellent stabilizer for earth building
material. On the other hand the fibrous/tubular nature of the straw is responsible for the
rough texture of Straw stabilized earth blocks (see figure 6, page 61).
Data Analysis Based on the Research Questions
The data collected from the various experimental tests and measurements are presented in
Tables 8 to 14 followed with relevant graphic illustration of the data presented in figures 7 - 14.
[NB: Higher arithmetic values in the compressive strength translate to higher strength
characteristic for the compressive strengths, while higher arithmetic values for the erosion
resistance ratios translate to weaker resistance capacity].
Research Question 1
What are the major chemical elements found in the three common earth building soil types (red,
clayey and laterite soils) that can affect the structural qualities of the stabilized earth material?
The result of the laboratory analysis of the three soil types as presented in Table 7
followed with an elaborate discussion of the various chemical elements demonstrates some
measure of distinction in the chemical characteristics of the three soil types. The laboratory
analysis shows that seven out of the nine different chemical elements were present in all the three
different soil types at varying percentages. These include Iron(Fe), Potassium(K),
Magnesium(Mg), Calcium(Ca), Zinc(Zn), Nitrates, and Phosphorous(P). The red and clayey soils
contain Cadmium(Cd), a slow combusting element at very low percentages of 0.10 and 0.36
respectively. As indicated in the discussion that followed Table 7, Cadmium and solutions of its
compounds are highly toxic, with cumulative effects similar to those of mercury poisoning. Its
presence in the clayey and red soils play no significant role in earth block manufacture, except
77
that it combines easily with Zinc to form low combustible compounds and burns in the air to
form Cadmium Oxides (CdO), (Microsoft Encarta, 2006).
The ninth chemical element – Sodium(Na) an alkaline earth metal was found only in the
clay soil. Sodium (Na), is a highly reactive and extremely soft metallic element, and reacts
violently with water to form Sodium Hydroxide and Sodium Hydrogen. It is found naturally, as in
this clayey soil, in a compound state as Sodium Carbonate. The Sodium content of the clayey soil
naturally combines with other compounds in the earth material matrix to form salts which
dissolves when in contact with water and crystallizes when dry resulting in efflorescence. The
presence of Sodium in the clay soil even at this low percentage of 1.53 per cent required that
special attention be given to it, to avoid the negative effects of the Sodium Chloride formed when
Sodium compounds react with water. In this research it was discovered that the soaking of the
stabilized earth blocks during the first seven days of wet curing lowered the anticipated
efflorescent action of the Sodium Chloride and the Carbonates formed out of the reaction
between the Sodium compounds and other materials of the matrix. The soaking of the blocks
during the wet curing appears to have washed/soaked away most of the sodium salts. The
Magnesium Oxide and Zinc Oxide in the RHA also reacted with the Sodium Carbonates to
further neutralize the anticipated negative effects of this Sodium compounds.
The effect of the Sodium content in the clayey soil was noticed slightly in the Straw
stabilized earth blocks, as it was suspected to have weakened the cell walls of the lignin and
reacted negatively with the cellulose content of the Straw to increase the rate of water absorption
of the Straw stabilized earth blocks. This researcher suspects that the presence of this Sodium
only in the clayey soil may have been because the clayey soil samples were collected from a dead
ant-hill that is currently being used by the local earth builders.
The other two alkaline earth metals found in all the soil samples are Magnesium (9.16 per
cent; 12.92 per cent; and 11.20 per cent) and Calcium (13.00 per cent; 14.16 per cent and 15.27
78
per cent) is also of interest in this earth building research. During the experiments it was
discovered that the reactive Silica in the RHA reacted with the Calcium hydrate compounds to
form Calcium Silicate Hydrates which lowered the alkalinity in the composite material of Straw
with RHA matrix, (Shafiq, 1988). Through this interaction the dangers of alkaline composite
pore water effect in fiber (straw) stabilized earth blocks was reduced. This researcher believes
that this type of interaction will slow down the embitterment process of natural fiber composites
(Charoenvai, S., Khedari, J., Hirunlabh, J., Daguenet, M. & Quenard, D. 2005), thereby giving
the RHA with Straw(composite) stabilized earth blocks an added advantage. The durability of the
Calcium element is also a plus in the use of this earth material.
The interaction between the Calcium content in the soils with the pozzolana was good for
improved density and erosion resistance of the RHA and RHA with Straw stabilized earth
material. The Magnesium content in the soil reacting with Zinc-Oxide in the RHA formed a
chemical bond that is resistant to Sulphuric Acid attack in the stabilized earth material, (Simsung,
2003 and Madu, 1986). The presence of Zinc, in the different soil types was therefore an added
advantage for the RHA and the RHA with Straw stabilized earth blocks.
All the three soil types contain different percentages of Iron(Fe) whose most pronounced
effect on soil types in their colour texture (Microsoft Encarta 2006). This was clearly reflected in
the soil samples used in this research. Another major chemical element found in the three soil
types Zinc(Zn), was of advantage for the RHA and the RHA with Straw stabilized earth blocks.
The Iron(Fe) and Zinc(Zn) contents in the soils also played important roles in the block quality as
they combined with the Ferric Oxide in the RHA and reacted with the Silicon Dioxide in the
RHA(pozzolana) to improve the structural strength of the RHA stabilized earth blocks over that
of Straw stabilized earth material.
The three soil samples contain varying quantities of Nitrates (red soil – 1.44 per cent,
clayey soil – 1.60, laterite soil – 3.83 per cent), which naturally combine with lime to form a
79
strong chemical bond which is good for the strength development of stabilized earth blocks.
Potassium(K) another chemical element of interest in earth material quality was found in high
quantities in all the three soil types as red soil - 29.34 per cent, clayey soil – 37.30 per cent, and
laterite soil – 26.08 per cent. The presence of Potassium, a chemically very reactive and
extremely soft metallic element in these soil types is interesting because Potassium forms many
compounds resembling corresponding sodium compounds, based on a valence of 1 as stated
under analysis of the chemical elements of the soil samples above. Of all the mentioned chemical
compounds of Potassium, only Potassium iodide (KI), a white crystalline compound that is
clearly very soluble in water. But Potassium iodide does not occur naturally in the Earth‟s crust,
(Microsoft Encarta, 2006).The important aspect of the Potassium content of the soils is its very
reactive nature that contributed to the easy combination of the different stabilizers to affect both
the strength and durability of the earth block at varying degrees depending on the type of
stabilizer(additives) used. As noted earlier Potassium being a constituent of all plant and animal
tissue as well, is a vital constituent of soil fertility. Potassium Sulphate (K2SO4), a white
crystalline solid, is also an important Potassium fertilizer also used in the preparation of
potassium alum. These qualities of Potassium add to give the earth material its a excellent
biodegradability quality that it easy to recycle as a building material.
The last of the chemical elements common to the three soil samples Phosphorous(P), is a
non metallic element and insoluble in water. This Phosphorous(P) reacts with Calcium(Ca) to
form Calcium Phosphate (Ca3(PO4)2), which combines under high temperatures with Silicon
Dioxide(sand) to produce Red Phosphorous (Microsoft Encarta 2006). This Red Phosphorous
powder does not occur naturally in a free state but as a Phosphate which also combines with
oxygen to form Phosphorous Oxide (P2O3), a delinquent reducing agent, which combines with
other mineral elements to increase soil fertility. This Red Phosphorous, a non poisonous
microcrystalline powder adds to make the earth material a health friendly building material. This
80
behaviour of soil Phosphorous adds to make earth material a good biodegradable natural building
material.
The analysis so far has shown that the particles distribution and chemical composition of
the three soil types fall within acceptable range for earth building purposes. The analysis of all
the chemical elements of the soil types shows that the chemical composition of the three soil
types did not require any major physical stabilization before it can be used. The analysis has also
identified some of the chemical element such as the Potassium and Phosphorous as contributing
positively to make the earth material an excellent biodegradable building material, while the earth
alkaline earth materials like Calcium and Magnesium, and others such as the Iron and Zinc
positively interacted with the chemical elements of the stabilizers to improve the strength
development of the stabilized earth material.
Research Question 2
What are the major the chemical elements found in the two locally available stabilizers (RHA
and Straw) that can affect their efficacy as earth material stabilizers?
The relevant data for this research question are presented in Tables 8 and 9 on pages 75
and 76 of this report. The data on the two tables clearly show that there is a wide range of
distinction between the two stabilizers. Table 8 shows the chemical composition of RHA as
compared with that of ordinary Portland cement. In this Table 8, the data show that while RHA is
basically a Silicon Dioxide fine powder, the Ordinary Portland Cement is a highly Calcium Oxide
based fine powder [Silicon Oxide: RHA – 89.75 OPC – 22.35 per cent and Calcium Oxide: RHA
- 2.19 per cent, OPC – 65.80 per cent.
Table 8 also shows that while Ordinary Portland Cement contains up to 5.35 per cent of
Aluminum Oxide with very low Potassium Oxide content (0.62 per cent), RHA contains more of
Potassium Oxide (2.08 per cent) and almost a negligible amount of Aluminum Oxide (0.48 per
81
cent) with only of traces of Magnesium Oxide and Sodium Oxide. RHA also present a finer
powder at 25 microns and 2.13 specific gravity, while ordinary Portland cement is shown to be of
75microns and 2.65 specific gravity. This fineness gives the RHA an advantage of being able to
fill-in finer pores in the earth material mixes. This finer powder of RHA positively contributes to
the density and compressive strength quality of the stabilized earth material. On the other hand
this high degree of fineness of the RHA makes it require much more water for workability in
RHA stabilized earth material. It was discovered that the combined presence of the Iron and
Calcium ions in the soil samples reacting with the Aluminium-oxide and Calcium-oxides in the
RHA produced a crystallization of Aluminoferrite(Ca6Al2Fe) and Tatracalcium aluminate
hydrate(Ca4Al13) which is believed to have contributed to the significant difference in
compressive strength between the RHA based stabilizer and the Straw only stabilized earth
material, (Cook and Lim, 2007). The researcher also believes that the reactive Calcium and
Magnesium cations as found in the soil samples will react with the Ferrosilicate ions and other
siliceous materials in the RHA and the Straw to form insoluble crystalline materials which bind
the matrix to produce a quality building material.
The chemical structure of the Straw as presented in Table 9 and the discussion that
followed it, show that the chemical composition of this fibrous tubular stem, is yet to be
completely elucidated, (Charoenvai, Khedari, Hirunlabh, Daguenet and Quenard, 2005). The best
identified chemical structure of the straw is that it is an amorphous substance containing
Phenolic, Methoxyl, Hydroxyl with a few other constitute groups as presented in Table 9. The
Straw contains a reasonable percentage of Silicon Oxide (31.50 per cent). The presence of
Lignin(9.60 per cent) and Hemicelluloses(26.2 per cent) as one of the four major chemical
elements found in the Straw was of interest in this research. It was identified in this study that the
Magnesium, an alkaline earth metal, in the soil reacting with the Holocellulose and the Alpha
Cellulose brought about a microscopic behavior in the straw stabilized earth material. There was
82
therefore need for a natural impregnation of the Straw-earth mix to allow for adequate
moisturization of the Straw element before moulding. This was taken care of in this research by
allowing the Straw-earth wet mix for at least 24 hours, under a tarpaulin covering to avoid
contamination before moulding.
The action of the other alkaline earth metal of Calcium in the soil types was also noticed
on the chemical characteristics of the Straw. The Silicon Oxide element in the Straw reacted with
the Calcium hydrate compounds developed in the mixes to form Calcium Silicate Hydrates which
lowers the alkalinity of the Straw, (Shafiq, 1988). Through this interaction the dangers of alkaline
composite pore water effect in fiber(straw) stabilized earth material was reduced. The effect of
this interaction is believed will also slow down the embitterment process of this natural fiber
composite, (Charoenvai, Khedari, Hirunlabh, Daguenet and Quenard, 2005).
This uncommon combination of chemical elements in the Straw distinguishes it from
other organic materials that would have decayed when in contact with water, thereby making the
Straw an excellent stabilizer for the earth material. On the other hand the fibrous/tubular nature
of the straw is responsible for the rough texture of straw stabilized earth blocks (see Fig. 6, page
64). It is therefore safe to conclude that the peculiar chemical composition of the Straw makes it
remain a reliable stabilizer for the earth material.
Research Question 3
What is the effect of differences in stabilizer type on the mean compressive strength of earth
material stabilized with RHA, Straw or RHA-Straw?
This research question was interested in finding out what happens when the two
stabilizers are used separately and in combination to stabilize the earth material. To investigate
their effect(s) three sets of experiments were conducted. The RHA and the Straw were used
separately and in combination of RHA-Straw to stabilize the earth material at three different mix
proportions based on three soil types. In Table 12 a comprehensive set of the results from the
83
three Experimental Groups (I, II and III) pooled together is presented. From the data presented in
this Table 12, the effects and interactive effects of the stabilizer types on the compressive
strength of the stabilized earth material were examined. The data genrally shows that earth
material stabilised with RHA produce blocks of higher compressive strength than those stabilized
Table 10
Detailed Schedule of the Compressive Strength for Experiments I, II and III
SS,N
0/N0
Experimental
Group
Type of
Stabilizer
Mix
Proportion
[%]
Soil Type Compressive
Strength
Group
Mean
1 EXPERIMENT [I]1 RHA 20%[1:1:8] Clayey Soil 2.72
Gro
up
Mea
n f
or
Ex
per
imen
t I
– 3
.15
Mp
a
2 EXPERIMENT [I]2 RHA 14.5%[1:6] Clayey Soil 2.49
3 EXPERIMENT [I]3 RHA 11%[1:8} Clayey Soil 2.41
4 EXPERIMENT [I]4 RHA 20%[1:1:8] Laterite Soil 3.51
5 EXPERIMENT [I]5 RHA 14.5%[1:6] Laterite Soil 3.24
6 EXPERIMENT [I]6 RHA 11%[1:8} Laterite Soil 2.81
7 EXPERIMENT [I]7 RHA 20%[1:1:8] Red Soil 4.20
8 EXPERIMENT [I]8 RHA 14.5%[1:6] Red Soil 3.56
9 EXPERIMENT [I]9 RHA 11%[1:8} Red Soil 3.37
10 EXPERIMENT [II]1 STRAW 20%[1:1:8] Clayey Soil 1.97
Gro
up
Mea
n f
or
Ex
per
imen
t II
– 2
.62
Mp
a
11 EXPERIMENT [II]2 STRAW 14.5%[1:6] Clayey Soil 2.13
12 EXPERIMENT [II]3 STRAW 11%[1:8} Clayey Soil 1.99
13 EXPERIMENT [II]4 STRAW 20%[1:1:8] Laterite Soil 2.44
14 EXPERIMENT [II]5 STRAW 14.5%[1:6] Laterite Soil 2.67
15 EXPERIMENT [II]6 STRAW 11%[1:8} Laterite Soil 2.34
16 EXPERIMENT [II]7 STRAW 20%[1:1:8] Red Soil 3.69
17 EXPERIMENT [II]8 STRAW 14.5%[1:6] Red Soil 3.34
18 EXPERIMENT [II]9 STRAW 11%[1:8} Red Soil 3.03
19 EXPERIMENT[III]1 RHA+STRAW 20%[1:1:8] Clayey Soil 3.32 G
rou
p M
ean
fo
r
Ex
per
imen
t II
I –
3.9
1M
pa
20 EXPERIMENT[III]2 RHA+STRAW 14.5%[1:6] Clayey Soil 3.04
21 EXPERIMENT[III]3 RHA+STRAW 11%[1:8} Clayey Soil 2.89
22 EXPERIMENT[III]4 RHA+STRAW 20%[1:1:8] Lateriteoil 4.15
23 EXPERIMENT[III]5 RHA+STRAW 14.5%[1:6] Laterite Soil 4.05
24 EXPERIMENT[III]6 RHA+STRAW 11%[1:8} Laterite Soil 3.68
25 EXPERIMENT[III]7 RHA+STRAW 20%[1:1:8] Red Soil 4.82
26 EXPERIMENT[III]8 RHA+STRAW 14.5%[1:6] Red Soil 4.69
27 EXPERIMENT III]9 RHA+STRAW 11%[1:8} Red Soil 4.52
with Straw at 3.15Mpa to 2.62Mpa, while a combination of RHA-Straw also produced earth
materials of higher compressive strength than earth material stabilised with only RHA or Straw
with group compressive strengths at a ratio of 3.91Mpa:3.15Mpa:2.62Mpa in favour of RHA-
Straw stabilized material. This gives a ratio of 149:120:100 for better comparism. This
84
comparism is demonstrated more clearly for the three stabilizer groups on Table 13 with a more
elaborate presentation of the ratio scales.
Table 11
Comparison of Mean Values of Compressive Strength Based on Stabilizer Type
Type of Stabilizer Percentage of Stabilizer Mean Compressive Strength (Mpa)
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 2.41 2.81 3.37
14.5%[1:6] 2.49 3.24 3.56
20%[1:1:8] 2.72 3.51 4.20
Group Mean Compressive Strength for RHA Mix – 3.15Mpa
ST
RA
W
11%[1:8] 1.99 2.34 3.03
14.5%[1:6] 2.13 2.67 3.34
20%[1:1:8] 1.97 2.44 3.69
Group Mean Compressive Strength for Straw Mix – 2.62Mpa
RH
A-S
TR
AW
11%[1:8] 2.89 3.68 4.52
14.5%[1:6] 3.04 4.05 4.69
20%[1:1:8] 3.32 4.15 4.82
Group Mean Compressive Strength for RHA-Straw Mix – 3.91Mpa
Ratio of Mean Compressive Strength “Between”
RHA:Straw:RHA-Straw Stabilizer Groups - 120:100:149
On this Table 13 the mean compressive strength values within the three experimental
groups indicate that there are measureble differences in the structural qualities between the earth
material stabilized with RHA or Straw and those stabilised with RHA-Straw. The ratio of the
group means help to better demonstrate the implications of these values. The ratio returns the
value of (Compressive Strength - 3.15Mpa:2.62Mpa:3.91Mpa) = 120:100:149. The simple
interpretation of these ratios is that the combined RHA-Straw stabilised earth material is 49 per
cent stronger in compressive strength than earth materials stabilised with Straw and 29 per cent
stronger than those stabilized with RHA only, whereas earth material stabilized with RHA is 20
per cent stronger than those stabilized with Straw. These ratios clearly demonstrate the degree of
differences between these three stabilizer groups under two conditions of soil difference and
variations in mix proportion.
85
These differences in the behaviour of the three stabilizer groups is further illustrated
graphically in Figure 8. In this Figure 8, the variations in the compressive strengths demonstrate a
close association in behaviour pattern between the RHA stabilized earth material with that of
combined RHA-Straw stabilized material on the clayey and laterite soils, with clear shift in
behaviuor parttern on the red soil.
A Comparison of Compressive Strengths of Earth Material Stabilized with
RHA, Straw and RHA-Straw
0
1
2
3
4
5
6
Exp.
[I,II&III]1
Exp.
[I,II&III]2
Exp.
[I,II&III]3
ExP.
[I,II&III]4
Exp.
[I,II&III]5
ExP.
[I,II&II]6
Exp.
[I,II&III]7
Exp.
[I,II&III]8
Exp.
[I,II&III]9
Experimental Groups
Com
pr.
Str
ength
Valu
es(M
pa)
RHA Straw RHA & Straw
The data so far presented and analysed evidently show that there is clear difference in
compressive strength development between these three stabilizer groups. The researcher therefore
concludes, based on all the pieces of evidence so far analysed, that there is a measurable
difference in the compressive strength quality of stabilized earth material as a result of the
different stabilizer types. To further varify whether these differences are real or just mere chance
differences or resulting from other research errors, the data was further analysed with the
Analysis of Variance(ANOVA) statistics under Hypothesis 2 of this research.
Research Question 4
What is the effect of differences in the soil types on the mean compressive strength of earth
material stabilized with RHA, Straw or RHA-Straw?
Fig. 7
86
The data collected from the 27 experiments as presented on Tables 10 and 11, are re-
presented here as Table 12. In this Table 12 columns 5, 10 and 15 are included to show the values
of the pooled mean compressive strength values for the stabilizer type groups based on the soil
types. The ratio of the pooled mean values “within” the stabilizer groups are presented in rows 6,
11 and 16 and the ratio “between” the groups is presented at the bottom row.
Table 12
Comparison of Mean Values of Compressive Strength Based on Soil Type
Type of Stabilizer Percentage of Stabilizer Mean Compressive Strength (Mpa)
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 2.41 2.81 3.37
14.5%[1:6] 2.49 3.24 3.56
20%[1:1:8] 2.72 3.51 4.20
Pooled Mean 2.54 3.19 3.71
Ratio of Pooled Mean “Within” Based on Soil Type – 100:126:146
ST
RA
W
11%[1:8] 1.99 2.34 3.03
14.5%[1:6] 2.13 2.67 3.34
20%[1:1:8] 1.97 2.44 3.69
Pooled Mean 2.04 2.48 3.35
Ratio of Pooled Mean “Within” based on Soil Type – 100:122:164
RH
A-S
TR
AW
11%[1:8] 2.89 3.68 4.52
14.5%[1:6] 3.04 4.05 4.69
20%[1:1:8] 3.32 4.15 4.82
Pooled Mean 3.08 3.96 4.68
Ratio of Pooled Mean “Within” based on Soil Type – 100:129:152
Ratio of Weighted Mean of Compressive Strength “Between” Experimental Groups:
Clayey Soil -120:100:151; Laterite Soil -129:100160; Red Soil – 111:100:140
The data as presented on this Table 12 clearly show that there are differences in the
compressive strengths based on the soil types “within” and “between” the groups. The ratios
within each of the three stabilizer groups demonstrate the degree of difference in the compressive
87
strengths of stabilized earth material based on soil types. The results of the ratios are as follows:
RHA - Clayey soil - 100:Laterite soil - 126:Red soil - 146;
Straw - Clayey soil - 100:Laterite soil - 122:Red soil - 164 and
RHA-Straw - Clayey soil - 100:Laterite soil - 129:Red soil - 152.
These ratios illustrates that irrespective of stabilizer type, there are differences in the compressive
strength of stabilized earth material based on soil type. The differences are higher between the
clayey and red soils – at approximately 50 per cent difference for the RHA and RHA-Straw
stabilizer groups and 64 per cent for the Straw stabilized earth material. The differences are
closer between the clayey and laterite soils where the RHA and RHA-Straw stabilizers show a
slightly above 25 per cent and the Straw group at 22 per cent difference. The ratios also support
an earlier finding under Research Question 3, that the compressive strength behaviour pattern of
the RHA and RHA-Straw groups are more closely associated than the Straw stabilizer group
The last row on Table 12 contains the ratios of the groups‟ mean compressive strength
between the three stabilizer groups to demonstrate the degree of differences based on soil type.
The ratios returned the following values based soil type between the stabilizer groups:
Clayey Soil - RHA-120:Straw-100:RHA-Straw - 151
Laterite Soil - RHA-129:Straw-100:RHA-Straw -160 and
Red Soil – RHA-111:Straw-100:RHA-Straw - 140
The implication of these ratios is that there are differences in the compressive strength of
stabilized earth material based on soil type. The simple interpretation of these statistics shows
that the RHA-Straw stabilized material is approximately 30 per cent stronger in compressive
strength over that of RHA stabilized material on the all three soil types. The same RHA-Straw
stabilized material is 51 per cent stronger than the Straw stabilized material on clayey soil, 60 per
cent stronger on laterite soil and 40 per cent on red soil. These ratios also demonstrate the degree
of variability between the different stabilizer groups based on the soil types. The degree of
88
variability is most significant on the clayey and laterite soils than on the red soil and higher
between Straw and RHA-Straw stabilizer groups.
The data presented on this Tables 12 demonstrates the interactive effects of combining
RHA-Straw in stabilizing the earth material. This is clearly noticed in the attendant
improvements in the compressive strength as compared to that of RHA and Straw stabilized earth
material. The summary of the ratios between the groups evidently show a clearer difference along
the axis of stabilizer groups, as the soil type changed. The data also demonstrates that the
compressive strength quality of the RHA stabilized earth material and that of combined RHA-
Straw stabilized earth material share some degree of close association in the pattern of
proportionate improvement as the soil type change. The data on Table 14 indicates that the
effects of combining the two stabilizers showed in higher compressive strength. The researcher
therefore concludes based on the pieces of evidence from the data presented and analyzed so far,
that there are significant differences in the compressive strength quality of earth materials
stabilized with RHA, Straw and that stabilized with RHA-Straw as a result of differences in the
soil type.
Research Question 5
What is the effect of variations in mix proportions on the mean compressive strength of earth
material stabilized with RHA, Straw or RHA-Straw?
In response to this Research Question 5, the data from the three experimental groups were
pooled together according to their stabilizer groups and mix proportions. The data presented on
Table 13 also contains the pooled mean compressive strength for each mix group under column 6
for a clearer understanding and analysis. On Table 13, the ratios of the pooled mean values of the
compressive strength based on the mix proportions are included to compare the degree of
variability in the compressive strength of the differently stabilized earth materials. The pooled
89
mean values presented in column 6 of Table 13 represents the degree of compressive strength
attainment based on variations in the mix proportions across three earth building soils.
Table 13
Comparison of the Mean Value of Compressive Strength Based on Mix Proportions
Type of Stabilizer Percentage of Stabilizer Mean Compressive Strength (Mpa) Pooled Mean
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 2.41 2.81 3.37 2.86
14.5%[1:6] 2.49 3.24 3.56 3.10
20%[1:1:8] 2.72 3.51 4.20 3.48
Ratio of Pooled Mean “Within” Based on Mix Proportion – 100:108:122
ST
RA
W 11%[1:8] 1.99 2.34 3.03 2.45
14.5%[1:6] 2.13 2.67 3.34 2.71
20%[1:1:8] 1.97 2.44 3.69 2.70
Ratio of Pooled Mean “Within” Based on Mix Proportion – 100:111:111
RH
A-S
TR
AW
11%[1:8] 2.89 3.68 4.52 3.71
14.5%[1:6] 3.04 4.05 4.69 3.93
20%[1:1:8] 3.32 4.15 4.82 4.10
Ratio of Pooled Mean “Within” Based on Mix Proportion – 100:106:111
Ratio of Weighted Mean of Compressive Strength “Between” Experimental Groups:
11%[1:8] -117:100:151; 14.5%[1:6] - 114:100:145; and 20%[1:1:8] - 129:100:152
The comparative ratios of the pooled mean values are presented in rows 5, 10 and 15 of
Table 13. These ratios compare the differences in the compressive strengths within each stabilizer
groups based on the mix proportions. The ratio under the RHA shows the highest variability
based on mix proportions occurring between 11% and 20% mixes. The Straw and RHA-Straw
group indicate minimal differences based on mix proportions with 11% and 20% varying most at
11 per cent.
90
The overall compressive strength behaviour of the material is demonstrated with the ratio
of the weighted mean compressive strength “between” the stabilizer groups presented in the last
column of Table 13. The ratios gave the following values:
11% [1:8] mix - RHA - 117:Straw - 100:RHA-Straw - 151;
14.5% [1:6] mix - RHA - 114:Straw - 100:RHA-Straw - 145; and
20% [1:1:8] mix - RHA - 129:Straw - 100:RHA-Straw - 152.
The general interpretation of all these ratio statistics is that while the differences in
compressive strengths “within” the stabilizer groups as shown earlier are minimal, the differences
“between” the groups are significant. The ratios show that the RHA-Straw group has the highest
difference of approximately 49.33 per cent above the Straw stabilizer under the three different
mix proportions. The RHA-Straw group also show higher strength attainment of approximately
32.5 per cent above the RHA stabilizer group under the 11% and 14.5% mixes and 23 per cent
difference under the 20% mix proportion.
Generally, the data presented and analyzed so far demonstrates that variation in mix
proportions have effect on the compressive strength of stabilized earth materials. Based on the all
the information presented so far the researcher safely concludes that there are significant
differences in the compressive strength characteristics of earth material stabilized with different
stabilizer types as a result of variations in the mix proportions.
Research Question 6
What is the effect of differences in stabilizer type on the mean erosion resistance capacity of
earth material stabilized with RHA, Straw or RHA-Straw?
This research question was interested in the second component of the structural qualities
of building which has to do with erosion resistance capacity. The question was set out to find out
91
the effect(s) of stabilizing the earth material with the two local stabilizers as single stabilizers and
in combination. To investigate the effect(s) of these three groups of stabilizer – RHA, Straw and
Table 14
Schedule of the Erosion Resistance Ratios from Experiments I, II and III
0/N0 Experimental Group Type of
Stabilizer
Mix
Proportion
[%]
Soil Type Erosion
Resistance
Ratios[%]
Group
Mean
1 EXPERIMENT [I]1 RHA 20%[1:1: 4] Clayey Soil 7.45
Gro
up
Mea
n f
or
Ex
per
imen
t I
–
8.0
2%
2 EXPERIMENT [I]2 RHA 14.5%[1:6] Clayey Soil 8.27
3 EXPERIMENT [I]3 RHA 11%[1:8} Clayey Soil 8.42
4 EXPERIMENT [I]4 RHA 20%[1:1: 4] Laterite Soil 7.80
5 EXPERIMENT [I]5 RHA 14.5%[1:6] Laterite Soil 8.31
6 EXPERIMENT [I]6 RHA 11%[1:8} Laterite Soil 8.79
7 EXPERIMENT [I]7 RHA 20%1:1: 4] Red Soil 7.48
8 EXPERIMENT [I]8 RHA 14.5%[1:6] Red Soil 7.56
9 EXPERIMENT [I]9 RHA 11%[1:8} Red Soil 8.09
10 EXPERIMENT [II]1 STRAW 20%[1:1: 4] Clayey Soil 10.60
Gro
up
Mea
n f
or
Ex
per
imen
t II
–
9.5
0%
11 EXPERIMENT [II]2 STRAW 14.5%[1:6] Clayey Soil 8.95
12 EXPERIMENT [II]3 STRAW 11%[1:8} Clayey Soil 9.16
13 EXPERIMENT [II]4 STRAW 20%[1:1: 4] Laterite Soil 10.81
14 EXPERIMENT [II]5 STRAW 14.5%[1:6] Laterite Soil 9.26
15 EXPERIMENT [II]6 STRAW 11%[1:8} Laterite Soil 9.45
16 EXPERIMENT [II]7 STRAW 20%1:1: 4] Red Soil 9.18
17 EXPERIMENT [II]8 STRAW 14.5%[1:6] Red Soil 9.03
18 EXPERIMENT [II]9 STRAW 11%[1:8} Red Soil 9.08
19 EXPERIMENT[III]1 RHA+STRAW 20%[1:1: 4] Clayey Soil 7.12
Gro
up
Mea
n f
or
Ex
per
imen
t II
–
7.3
8%
20 EXPERIMENT[III]2 RHA+STRAW 14.5%[1:6] Clayey Soil 7.39
21 EXPERIMENT[III]3 RHA+STRAW 11%[1:8} Clayey Soil 7.89
22 EXPERIMENT[III]4 RHA+STRAW 20%[1:1: 4] Laterite Soil 7.20
23 EXPERIMENT[III]5 RHA+STRAW 14.5%[1:6] Laterite Soil 7.86
24 EXPERIMENT[III]6 RHA+STRAW 11%[1:8} Laterite Soil 8.03
25 EXPERIMENT[III]7 RHA+STRAW 20%1:1: 4] Red Soil 6.81
26 EXPERIMENT[III]8 RHA+STRAW 14.5%[1:6] Red Soil 7.01
27 EXPERIMENT III]9 RHA+STRAW 11%[1:8} Red Soil 7.14
RHA-Straw - three sets of experiments were conducted. The RHA and the Straw were used
separately and in combination of RHA-Straw to stabilize the earth material at three different mix
92
proportions based on three soil types. In this Table 14 a comprehensive set of the results from the
three Experimental Groups (I, II and III) are pooled together and presented. From the data
presented on this Table 14, the effects and interactive effects of the stabilizer types on the erosion
resistance capacity of the stabilized earth material were examined.
The data genrally shows that earth material stabilised with RHA produce better erosion
resistance capacity (8.02% resistance ratio) than those stabilized with Straw with 9.50%
resistance ratio, while a combination of RHA-Straw also produced earth materials of even better
erosion resistance capacity at 7.38% resistance ratio than earth material stabilised with only RHA
or Straw. The ratio for the three groups‟ mean erosion resistance capacities returned a value of
109:129:100 for better comparism. This comparism is demonstrated more clearly for the three
stabilizer groups on Table 15 with a more elaborate presentation of the ratio scales.
Table 15
Comparison of Mean Values of Erosion Resistance Ratios Based on Stabilizer Type
Type of Stabilizer Percentage of Stabilizer Erosion Resistance Ratio (%)
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 8.42 8.79 8.09
14.5%[1:6] 8.27 8.31 7.56
20%[1:1:8] 7.45 7.80 7.48
Group Mean Erosion Resistance Ratio Stabilizer Type – 8.02%
ST
RA
W
11%[1:8] 9.16 9.45 9.08
14.5%[1:6] 8.95 9.26 9.03
20%[1:1:8] 10.60 10.81 9.18
Group Mean Erosion Resistance Ratio Stabilizer Type – 9.50%
RH
A-S
TR
AW
11%[1:8] 7.89 8.03 7.14
14.5%[1:6] 7.39 7.86 7.01
20%[1:1:8] 7.12 7.20 6.81
Group Mean Erosion Resistance Ratio Stabilizer Type – 7.38%
Ratio of Mean Erosion Resistance Ratio “Between”
RHA:Straw:RHA-Straw Stabilizer Groups - 109:129:100
On this Table 15 the mean erosion resistance ratio between the three experimental groups
indicate that there are measureble differences in erosion resistance capacities of earth material
93
stabilized with RHA or Straw and those stabilised with RHA-Straw. The ratio of the group means
help to better demonstrate the implications of these values. The ratio returns the value of (Erosion
Resistance Ratio – 8.02%:9.50%:7.38%) = 109:129:100. The simple interpretation of these ratios
is that the RHA stabilized earth material is 9 per cent weaker than the combined RHA-Straw
stabilised earth material but 20 per cent better than the Straw stabilized earth materiel. The ratio
also says that RHA-Straw stabilized earth material is 29 per cent better in erosion resistance
capacity than the Straw stabilized earth material. These ratios clearly demonstrate the degree of
differences in erosion resistance capacities between these three stabilizer groups under two
conditions of soil difference and variations in mix proportion.
These differences in the erosion resistance behaviour of the three stabilizer groups is
further illustrated graphically in Figure 9. In this Figure 9, the variations in the graph illustrates a
close association in behaviour pattern between the RHA stabilized earth material with that of
combined RHA-Straw stabilized material all through the experiment.
Comparism of Erosion Resistance Ratios of Earth Material Stabilized with
RHA, Straw and RHA-Straw
0
2
4
6
8
10
12
Exp.
[I,II&III]1
Exp.
[I,II&III]2
Exp.
[I,II&III]3
ExP.
[I,II&III]4
Exp.
[I,II&III]5
ExP.
[I,II&II]6
Exp.
[I,II&III]7
Exp.
[I,II&III]8
Exp.
[I,II&III]9
Experimental Groups
Ero
sio
n R
esis
tance R
atios(%
)
RHA Straw RHA & Straw
The data so far presented and analysed evidently show that there is measurable
difference in erosion resistance capacities between these three stabilizer groups. The researcher
therefore feels comfortable to conclude, based on all the pieces of evidence so far analysed, that
Fig. 8
94
there is a difference in the erosion resistance capacity of stabilized earth material as a result of the
interaction of the different stabilizer types. To further varify extent of the significance of these
differences, these data were further analysed with the Analysis of Variance(ANOVA) Statistics
under Hypothesis 6 of this research.
Research Question 7
What is the effect of differences in the soil type on the mean erosion resistance capacity of earth
material stabilized with RHA, Straw or RHA-Straw?
The data from the 27 experiments was pooled together an studied to answer this Research
Question 7. This data is presented here as Table 16 incorporating three different columns
(columns 5, 10 and 15) showing the pooled mean compressive strength values for the three
stabilizer groups in accordance with the different soil types. The ratio of the pooled mean values
“within” the stabilizer groups are displayed in rows 6, 11 and 16 and the ratio “between” the
groups is presented at the bottom in row 17.
The pooled mean values of the erosion resistance ratios of the various stabilizer groups
based on the soil type are reduced to ratio scales on this Table 16. These ratios were used to
compare the relationship between the erosion resistance capacities of these differently stabilized
earth material. The ratios “within” groups demonstrate the degree of difference in the erosion
resistance capacity of stabilized earth material based on soil types for each stabilizer group. The
results of the ratios are as follows:
RHA - Clayey soil – 104:Laterite soil - 108:Red soil - 100;
Straw - Clayey soil - 105:Laterite soil - 108:Red soil - 100 and
RHA-Straw - Clayey soil - 106:Laterite soil - 110:Red soil - 100.
These ratios demonstrate that irrespective of stabilizer type, there are some measure of
differences in the erosion resistance capacity of stabilized earth material based on soil type.
95
Table 16
Comparison of the Mean Values of Erosion Resistance Ratios Based on Soil Type
Type of Stabilizer Percentage of Stabilizer Erosion Resistance Ratio (%)
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 8.42 8.79 8.09
14.5%[1:6] 8.27 8.31 7.56
20%[1:1:8] 7.45 7.80 7.48
Pooled Mean 8.05 8.30 7.71
Ratio of Pooled Mean “Within” Based on Soil Type – 104:108:100
ST
RA
W
11%[1:8] 9.16 9.45 9.08
14.5%[1:6] 8.95 9.26 9.03
20%[1:1:8] 10.60 10.81 9.18
Pooled Mean 9.57 9.84 9.10
Ratio of Pooled Mean “Within” based on Soil Type – 105:108:100
RH
A-S
TR
AW
11%[1:8] 7.89 8.03 7.14
14.5%[1:6] 7.39 7.86 7.01
20%[1:1:8] 7.12 7.20 6.81
Pooled Mean 7.47 7.70 6.99
Ratio of Pooled Mean “Within” based on Soil Type – 106:110:100
Ratio of Weighted Mean of Compressive Strength “Between” Experimental Groups:
Clayey Soil -108:128:100; Laterite Soil -108:128:100; Red Soil – 110:130:100
These ratios show that while the differences between the groups are closely proportionate for the
RHA and Straw groups, the interaction effect of combining the two stabilizers in a mix increased
the differences in the erosion resistance capacity of the stabilized earth material based soil types
under the RHA-Straw stabilized group. The implication of these ratios is that there is a closer
association in the behaviour pattern of erosion resistance capacities of earth material stabilized
with RHA and that stabilized with Straw than the RHA-Straw group. This a near opposite pattern
from the compressive strength behaviour under Research Question 3 where the compressive
strength behaviour pattern of the RHA and RHA-Straw groups were more closely associated than
the Straw stabilizer group.
96
To investigate the effect of differences in the soil type on the erosion resistance capacity
of the three differently stabilized earth material, the pooled mean values for each group based on
soil type were compared using a ratio scale. These comparative ratios are shown in column 17 of
Table 18. The ratios returned the following values between the stabilizer groups based on soil
type: Clayey Soil - RHA-108:Straw-128:RHA-Straw – 100
Laterite Soil - RHA-108:Straw-128:RHA-Straw -100 and
Red Soil – RHA-110:Straw-130:RHA-Straw - 100
The implication of these ratios is that the differences in the erosion resistance capacity of
stabilized earth material for the three stabilizer types are closer under the clayey and laterite soils,
while the differences are more pronounced under the red soil. The overall interpretation of this
ratio statistics shows that, based on soil type, the RHA-Straw stabilized material is approximately
28.7 per cent better in erosion resistance capacity than the Straw stabilized material and
approximately 8.7 per cent better than the RHA stabilized earth material. On the other hand, the
RHA stabilized material is exactly 20 per cent better in erosion resistance capacity than the Straw
stabilized earth material as a result of differences in the soil type. From all the information and
analysis produced so far the researcher confidently concludes that there are measureable
differences in the erosion resistance capacities of earth materials stabilized with RHA, Straw and
that stabilized with RHA-Straw as a result of differences in the soil type.
Research Question 8
What is the effect of variations in mix proportions on the mean erosion resistance capacity of
earth material stabilized with RHA, Straw or RHA-Straw?
To respond to this Research Question 8, the data from the three experimental groups were
pooled together and presented on Table 17 based on stabilizer groups and mix proportions. Table
19 contains the pooled mean erosion resistance ratios for each mix group under column 6 for a
97
clearer understanding and analysis. The pooled mean values presented in column 6 represents the
degree of erosion resistance capacity of the various experimental groups based on variations in
Table 17
Comparison of the Mean Value of Erosion Resistance Ratios Based on Mix Proportions
Type of Stabilizer Percentage of Stabilizer Mean Compressive Strength (Mpa) Pooled Mean
Clayey Soil Laterite Soil Red Soil
RH
A
11%[1:8] 8.42 8.79 8.09 8.43
14.5%[1:6] 8.27 8.31 7.56 8.05
20%[1:1:8] 7.45 7.80 7.48 7.58
Ratio of Pooled Mean “Within” Based on Mix Proportion – 111:106:100
ST
RA
W 11%[1:8] 9.16 9.45 9.08 9.23
14.5%[1:6] 8.95 9.26 9.03 9.08
20%[1:1:8] 10.60 10.81 9.18 10.20
Ratio of Pooled Mean “Within” Based on Mix Proportion – 102:100:113
RH
A-S
TR
AW
11%[1:8] 7.89 8.03 7.14 7.69
14.5%[1:6] 7.39 7.86 7.01 7.42
20%[1:1:8] 7.12 7.20 6.81 7.04
Ratio of Pooled Mean “Within” Based on Mix Proportion – 109:105:100
Ratio of Weighted Mean of Erosion Resistance Ratios “Between” Groups:
11%[1:8] - 110:120:100; 14.5%[1:6] - 108:122:100; 20%[1:1:8] - 108:145:100
the mix proportions across three soil types. These pooled mean erosion resistance ratios based on
the mix proportions were converted to ratio scales and presented on this Table 17. The ratios
were used to compare the degree of variability in the erosion resistance capacity of the three
differently stabilized earth materials. These comparative ratios are presented in rows 5, 10 and 15
of Table 17. The ratio of the pooled mean values within each groups returned the following
values: RHA - 11%[1:8] - 111: 14.5%[1:6] - 106: 20%[1:1:8] – 100
Straw - 11%[1:8] - 102: 14.5%[1:6] -100: 20%[1:1:8] - 113
RHA-Straw - 11%[1:8] - 109: 14.5%[1:6] - 105: 20%[1:1:8] – 100
98
The ratios under the RHA display the highest degree of variability based on mix
proportions between 11% and 20% mixes. The Straw and RHA-Straw group indicate minimal
differences based on mix proportions with the highest difference of only 11 per cent between
11% and 20% mixes. The overall erosion resistance capacity behaviour of the stabilized material
is demonstrated with the ratio of the weighted mean erosion resistance ratios “between” the
stabilizer groups presented in the column 17 of Table 19. The ratios gave the following values:
11% [1:8] mix - RHA - 110:Straw - 120:RHA-Straw - 100;
14.5% [1:6] mix - RHA - 108:Straw - 122:RHA-Straw - 100; and
20% [1:1:8] mix - RHA - 108:Straw - 145:RHA-Straw - 100.
The simple interpretation of all these ratio statistics is that there are minimal difference in the
erosion resistance capacity between the differently stabilized earth materials as a result of
variations in the mix proportions. The ratio of the weighted mean erosion resistance ratios
between the stabilizer groups demonstrates that there are differences in erosion resistance
capacities between the groups with the highest between the RHA-Straw and Straw groups at 45
per cent under the 20% mix proportion. These ratios also show that the RHA-Straw and Straw
stabilizer groups maintained an average variability of 21 per cent between the 11% and 14.5%
mix proportions. The RHA-Straw and RHA stabilizer groups show a consistent 8 per cent
difference between the 14.5% and 20% mix proportions.
Generally, the data presented and analyzed so far demonstrates that variation in mix
proportions have effect on the erosion resistance capacity of stabilized earth material. Based on
the all the information presented so far the researcher safely concludes that there are some
measurable differences in the erosion resistance capacity of earth material stabilized with
different types of stabilizer as a result of variations in the mix proportions.
99
Research Question 9
Which combination of stabilizer(s) and soil type and at what mix proportion will produce optimal
compressive strength and erosion resistance capacity of earth material stabilized with RHA,
Straw or RHA-Straw?
This Research Question 9 represents the central focus of this project, which, seeks to
optimize the use of two local stabilizers (additives) for earth material stabilization. Investigations
on this research question by implication is the final stage of this research since it has already been
established under Research Questions 3 to 8, that there are differences in the dependent variables
(compressive strength and erosion resistance capacity), as the stabilizer types differ. And that
interactions between the soil types and variations in the mix proportions effect these variables.
The central focus of this research question was to identify, if possible, what stabilizer type, at
what mix proportion and with which soil type can produce an optimal (best possible within the
given parameters) compressive strength and erosion resistance capacity among these three
differently stabilized earth material.
To achieve this, a comprehensive presentation of the mean values from the entire 27 pairs
(compressive strength and erosion resistance values) of experiment became inevitable. This
information is presented on Table 18. The Table also contains an additional symbol [.] to indicate
which experimental group produced what result. A close study of the data presented on this Table
18 show that, under the RHA stabilized earth material, Experiment [I]7 (column 5, row 3) has the
highest compressive strength of 4.20Mpa and the best erosion resistance capacity at 7.45 per cent
based on red soil. This result clearly present Experiment [I]7 as the group with the optimal
compressive strength and erosion resistance capacity for the RHA stabilizer group (i.e. RHA at
20% mix based on red soil).
The outcome of Experiment [II] based the Straw stabilizer is different. The Straw
stabilized group has its highest compressive strength of 3.69Mpa from Experiment [II]7 based on
100
Table 18
Schedule of Mean Values of the Compressive Strength and Erosion Resistance Ratios
Type of
Stabilizer
%age of
Stabilizer
Mean Compressive Strength (Mpa) Mean Erosion Resistance (%)
Clayey
Soil
Laterite
Soil
Red
Soil
Pooled
Mean
Clayey
Soil
Laterite
Soil
Red
Soil
Pooled
Mean
RH
A
[EX
PE
RIM
EN
T
I]
11%[1:8] 2.41
[3]
2.81
[6]
3.37
[9]
2.86 8.42
[3]
8.79
[6]
8.09
[9]
8.43
14.5%[1:6] 2.49
[2]
3.24
[5]
3.56
[8]
3.10 8.27
[2]
8.31
[5]
7.56
[8]
8.05
20%[1:4] 2.72
[1]
3.51
[4]
4.20
[7]
3.48 7.45
[1]
7.80
[4]
7.48
[7]
7.58
Weighted Mean within Group 3.15 8.02
ST
RA
W
[EX
PE
RIM
EN
T
II]
11%[1:8] 1.99
[3]
2.34
[6]
3.03
[9]
2.47 9.16
[3]
9.45
[6]
9.08
[9]
9.23
14.5%[1:6] 2.13
[2]
2.67
[5]
3.34
[8]
2.71 8.95
[2]
9.26
[5]
9.03
[8]
9.19
20%[1:4] 1.97
[1]
2.44
[4]
3.69
[7]
2.37
10.60
[1]
10.81
[4]
9.18
[7]
10.20
Weighted Mean within Group 2.52 9.54
RH
A-S
TR
AW
[EX
PE
RIM
EN
T
III]
11%[1:8] 2.89
[3]
3.68
[6]
4.52
[9]
3.52 7.89
[3]
8.03
[6]
7.14
[9]
8.01
14.5%[1:6] 3.04
[2]
4.05
[5]
4.69
[8]
3.83 7.39
[2]
7.86
[5]
7.01
[8]
7.52
20%[1:4] 3.32
[1]
4.15
[4]
4.82
[7]
4.06 7.12
[1]
7.20
[4]
6.81
[7]
7.05
Weighted Mean within Group 3.80 7.54
Ratio of Weighted Mean
Between Groups
Compressive Strength
125:100:151
Erosion Resistance Ratio
106:127:100
Key. The Arabic numeral [1], [2]……[8], [9] identifies mix groups based on percentage of
additive and soil type as shown within the cells..
red soil, but its erosion resistance ratio of 9.18 per cent is not the best within the Straw group.
The best erosion resistance ratio from this group is 8.95 per cent under Experiment [II]2. The
data under Experiment [II] indicates that although Experiment [II]7 is of higher compressive
strength, it is weaker in erosion resistance than Experiments [II]2, [II]3, [II]8 and [II]9
101
respectively. The best possible option from the data presented under the Straw stabilized earth
material, is that of Experiment [II]8 with a mix proportion of 14.5%[1:6] on the red soil, which
gives 3.34Mpa of compressive strength and 9.03 per cent erosion resistance ratio. This is because
even when this is not the highest compressive strength attained within this group, the
compressive strength of 3.34Mpa is comfortably above the allowed minimum standard of
2.07Mpa with a relatively better erosion resistance value than that of Experiments [II]7 and [II]9.
The conclusion for Experiment II based on the data presented is that there is no optimal
mix proportion for this Straw stabilized earth material. The guiding principle in this case would
depend on the primary structural quality on emphasis.
The result of Experiment [III] as presented in this Table 20, shows clearly that
Experiment [III]7 has the highest compressive strength of 4.82Mpa and the best erosion
resistance capacity of 6.97 per cent for the RHA-Straw stabilized earth material. From this result
it clear that the mix proportion of 20%[1:1:8] based on red soil produced the optimal
compressive strength and the best erosion resistance capacity among the entire 9 experimental
sets of this group.
Comparing the entire data presented and analyzed under this Table 20, it is evidently clear
that the 20% [1:1:8] mix proportion under the combined RHA-Straw group based on red soil is
the overall optimal mix proportion for these differently stabilized earth material. Applying the
principles of performance based criteria for earth building works which sees erosion
resistance/moisture penetration and compressive strength development as vital ingredients of
building wall durability (Benge,2005), the researcher concludes that:
- an optimal mix proportion is possible from this experiment;
- the optimal mix proportion is 20%[1:1:8] mix proportion based on red soil using
RHA-Straw;
102
- this mix proportion produced the optimal compressive strength (4.82Mpa) and
erosion resistance capacity (6.97%) from the entire experiments;
- this result optimized the use of these three stabilizer groups for earth material
stabilization.
These conclusions are further tested with a higher statistical model to establish whether the
findings under this research question is statistically significant or a result of measurement error or
chance occurrence. The decision on the possible optimal mix proportion for this locally stabilized
earth material forms the focus of Hypothesis 8 of this research, (see page 129).
Test of the Hypotheses
Eight null hypotheses generated for this research, as presented under the first chapter of
this research report, are tested below to affirm or reject any of them, and to validate or discard,
the findings from the analyses under the nine research questions above. An Analysis of Variance
(ANOVA) statistical model employing a Univariate Analysis of Variance was adopted in which
an F-value (P < 0.05 level) indicates that the very variable being tested is significant and the null
hypothesis is rejected in favour of the alternate hypothesis.
[NB: - Higher arithmetic values in the compressive strength translate to higher strength
characteristic for the compressive strengths, while higher arithmetic values for the erosion
resistance ratios translate to weaker erosion resistance capacity.
- Schedules of the comprehensive Analysis of Variance(ANOVA) adopting a
univariate approach for the entire research data, to test the hypotheses are presented as
Appendixes C, D, E, F and G, page ].
Hypothesis 1: There is no significant difference in the mean compressive strength of stabilized
earth material as a result of the differences in the stabilizer type.
103
The data generated from the nine different experiments under Experimental Groups I, II
and II, as presented on Table 10, page 84 was used to test this hypothesis. The thrust of this
hypothesis was to investigate the effect of differences in stabilizer type on the mean compressive
strength of earth material stabilized with RHA, Straw or RHA-Straw. The data collected from the
9 x 3 experimental groups of this research on the compressive strength of stabilized earth
material presented on Table 10 on page 84 was used for the statistical analysis to accept or reject
this hypothesis.
The analysis used an Analysis of Variance (ANOVA) statistics adopting a Univariate
approach. The details of the Univaraite Analysis based on the data generated from the test of the
compressive strength values collected from the experimental groups is contained in Appendix E
on pages 160 – 164. The analysis started with the Descriptive Statistics resulting to a Test of
Between-Subjects Effects schedule presented on Table 19. The data on this Table 19 provided
general information about the level of significance of the effects the variables on the compressive
strength of the differently stabilized earth material. The data shows that there are significant
differences in the compressive strength of stabilized earth material as a result of differences in the
stabilizer.
Table 19
Tests of Between-Subjects Effects (Dependent Variable: Compressive Strength)
Source
Type III Sum of Squares
df
Mean Square
F
Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
87.078a
1398.833
38.902
4.395
40.178
.677
1.118
.919
.889
.849
1486.760
87.928
26
1
2
2
2
4
4
4
8
108
135
134
3.349
1398.833
19.451
2.197
20.089
.169
.280
.230
.111
.008
425.842
177859.57
2473.157
279.388
2554.283
21.522
35.549
29.218
14.136
.000
.000
.000
.000
.000
.000
.000
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
104
From these data presented on Table 19, the effect of differences in the stabilizer type on
the compressive strength of the stabilized earth material returned an F (2473.157) at .000 level of
significance. This result clearly shows that differences in the stabilizer types have significant
effect on the compressive strength of differently stabilized earth material. The simple
interpretation is that differences in stabilizer type significantly affect the mean compressive
strength of stabilized earth material.
The investigation went further from this result to study the extent of these effects between
the three stabilizer groups in order to possibly, identify which stabilizer type had most effect on
the compressive strength of the material. This further investigation used both the estimated
marginal means and the observed means generated from the experiments of this research. The
estimated marginal means of the compressive strength values were used to conduct a “Pairwise
Comparison” for the three different stabilizer groups. The result of the Pairwise Comparison
based on the estimated marginal means analysis as presented on Table 20 confirmed that there are
significant differences in the mean compressive strength of stabilized earth material as a result of
the differences in the stabilizer type.
Table 20
Pairwise Comparisons Based on Stabilizer Type (Dependent Variable: Compressive Strength)
(I) Stabilizer
(J) Sabilizer
Mean Difference
(I –J)
Std. Error Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
RHA
Straw
RHA+Straw
.544*
-.765*
.019
.019
.000
.000
.506
-.802
.581
-.728
Straw
RHA
RHA+Straw
-.544*
-1.309*
.019
.019
.000
.000
-.581
-1.346
-.506
-1.272
RHA+Straw RHA
Straw
.765*
1.309*
.019
.019
.000
.000
.782
1.272
.802
1.346
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent tp no adjustments).
The information presented on this Table 20 demonstrates that when the mean
compressive strengths of these three differently stabilized earth materials are compared against
105
each other, the differences are positively significant in favour of the RHA-Straw material against
those of RHA and Straw stabilized materials. The difference between the RHA and Straw
stabilized material also returned a positively significant difference in favour of the RHA material.
The Straw stabilized earth material compared with the RHA-Straw and Straw Stabilized material
shows a negatively significant difference against the RHA material. The result of this comparison
demonstrates that irrespective of the stabilizer type there are significant differences in the
compressive strength of stabilized earth material as a result of differences in the stabilizer type.
This result demonstrates that between the stabilizer types there are significant differences in the
compressive strength of the stabilized earth material. This comparison also showed that when any
of the stabilizers is compared against the other two (P < 0.05) all had significant difference in
their effect on the compressive strength of the stabilized earth material.
Based on the result of this Pairwise Comparison the researcher decided to conduct a post-
hoc analysis to indentify the individual contributions of the different stabilizer groups on this
significant difference in compressive strength of the stabilized earth material. The post-hoc
analysis resulted in a multiple comparison of this stabilizer type subset based on the observed
Table 21
Multiple Comparisons Based on Stabilizer Type(Dependent Variable: Compressive Strength)
(I) Stabilizer (J) Stabilizer
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe RHA Straw
RHA-Straw
.5436*
-.7651*
.01870
.01870
.000
.000
.4971
-.8115
.5900
-.7187
Straw RHA
RHA-Straw
-.5436*
-1.3087*
.01870
.01870
.000
.000
-.5900
-1.3551
-.4971
-1.2623
RHA-Straw RHA-Straw
Straw
.7651*
1.3087*
.01870
.01870
.000
.000
.7181
1.2623
.8115
1.3551
LSD
RHA Straw
RHA-Straw
.5436*
-.7651*
.01870
.01870
.000
.000
..5065
-.8022
.5806
-.7281
Straw RHA
RHA-Straw
-.5436*
-1.3087*
.01870
.01870
.000
.000
-.5806
-1.3457
-.5065
-1.2716
RHA-Straw RHA-Straw
Straw
.7651*
1.3087*
.01870
.01870
.000
.000
.7281
1.2716
.8022
1.3457
Based on observed means
*The mean difference is significant at the .05 level
106
means. The schedule of this multiple comparison is presented on Table 21. The result of this
homogeneous subset analysis further illustrates that there are significant differences in the
compressive strength of stabilized earth material as a result of changes in the stabilizer types.
The results of the Scheffe‟s and LSD analysis on this Table 21 shows that the interaction
effect of the three stabilizer groups are significantly different from each other. The RHA-Straw
group showed highest strength differential over that of the Straw group at ±1.3087 mean
difference and at ±0.7651 against the RHA stabilizer group. The RHA also shows a significantly
moderate strength difference over the Straw stabilizer group at, ±0.5436 mean difference, (P <
0.000).
From the pieces of evidence so far presented and analyzed the results clearly demonstrate
that there are significant differences in the compressive strength quality of differently stabilized
earth material as a result of the differences in the stabilizer type. The result of this analysis further
confirms the findings under Research Question 3 as authentic with additional statistically based
information that these differences are significant within and between the different Stabilizer
groups.
In summary, the interpretation of these pieces of information resulting from all the
analysis is that:
- differences in stabilizer type significantly affect the compressive strength attainable
by stabilized earth material;
- RHA-Straw stabilized earth material has the most positively significant difference
when compared with those of RHA or Straw stabilized earth material;
- RHA stabilized earth material has higher positive significant effect on the
compressive strength of stabilized earth material than that of Straw stabilized
material;
107
Based on these statistically supported confirmations, the researcher safely concludes that
there are significant differences in the mean compressive strength qualities of earth material
stabilized with RHA, Straw and RHA-Straw as a result of differences in the stabilizer type. The
null Hypothesis 1is therefore rejected. The alternate that there are significant differences in the
mean compressive strength of stabilized earth material as a result of differences in the stabilizer
type is accepted.
Hypothesis 2
There is no significant difference in the mean compressive strength of stabilized earth material
as a result of changes in the soil type.
The second hypothesis of this research was to investigate further the interaction effect of
soil type on the compressive strength of earth material stabilized with RHA, Straw or RHA-
Straw. The comprehensive data of one set of the 27 experiments of the research to study this
interaction effect(s) on the compressive strength of stabilized earth material presented on Table
10 on page 84 was used for the statistical analysis.
Employing a univariate based Analysis of Variance (ANOVA), the data was analyzed as
presented in Appendix F on pages 165 – 174. The analysis started with the Descriptive Statistics
leading to a Test of Between-Subjects Effects earlier presented on Table 19. This result of the
Test of Between-Subject Effects presented on Table 19 was also used for investigating this
hypothesis and is re-presented here for convenience as Table 22. The data on Table 22 gave
general information about the significance of the entire operator variables. The data demonstrates
that differences in the compressive strength of stabilized earth material based on interactions with
different soil types are significant, (P < 0.000). The result of the Test of Between-Subject Effects
returned an F(2554.283) value at 0.000 level of significance for the interaction effect of changes
in soil types on earth material stabilized with different types of stabilizer.
108
Table 22
Tests of Between-Subjects Effects (Dependent Variable: Compressive Strength)
Source
Type III Sum of Squares
Df
Mean Square
F
Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
87.078a
1398.833
38.902
4.395
40.178
.677
1.118
.919
.889
.849
1486.760
87.928
26
1
2
2
2
4
4
4
8
108
135
134
3.349
1398.833
19.451
2.197
20.089
.169
.280
.230
.111
.008
425.842
177859.57
2473.157
279.388
2554.283
21.522
35.549
29.218
14.136
.000
.000
.000
.000
.000
.000
.000
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
This result clearly shows that differences in the soil type have significant effect on the
compressive strength of differently stabilized earth material. The investigation went further from
this result to study the extent of this effects between the three different soil types.
To investigate the extent of these effects the analysis compared the interaction effects
between the three different soil types. Using the Estimated Marginal Means of the research data
the researcher conducted a pairwise comparison for the different soil types as presented on Table
23. The data on Table 23 confirmed that there are significant differences in the compressive
Table 23
Pairwise Comparisons Based on Soil Type (Dependent Variable: Compressive Strength)
(I)Soiltype
(J)Soiltype
Mean Difference
(I –J)
Std. Error Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Clay soil Laterite
Red soil
-.656*
-1.336*
.019
.019
.000
.000
.-.693
-1.373
-.619
-1.299
Laterite Clay soil
Red soil
.656*
-.680*
.019
.019
.000
.000
.619
-.717
-.693
-.643
Red soil Clay soil
Laterite
1.336*
680*
.019
.019
.000
.000
1.299
.643
1.373
.717
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent to no adjustments).
109
strength of earth materials stabilized with RHA, Straw or a composite of RHA-Straw as a result
of changes in the soil type. This result demonstrates that irrespective of the soil type there are
significant differences in the compressive strength of the earth material stabilized with different
types of stabilizers.
A close study of the second column of Table 23 shows that when the three soil types are
compared, using the Mean Difference(I-J), the red soil returned positive significantly differences
against the clayey and laterite soils, while the laterite soil is also positively significant against the
clayey soil. The clayey soil shows negative significant differences against the red and laterite
soils. This analysis indicates that red soil has more effect on the differences in the compressive
strength of the stabilized earth material. On the other hand the laterite soil was also of higher
significant effect than the clayey soil.
To further confirm the individual contributions of the different soil types on the
significant difference in compressive strength of the stabilized earth material, a multiple
comparison of this homogeneous subset (soil type) based on the observed means was conducted.
The result of this multiple comparison is presented on Table 24.
Table 24
Multiple Comparisons Based on Soil Type (Dependent Variable: Compressive Strength)
(I) Soiltype (J) Soiltype
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe Clay soil Laterite
Red soil
-.6560*
-1.3362*
.01870
.01870
.000
.000
.-.7024
-1.3826
-.6096
-1.2896
Laterite Clay soil
Red soil
.6560*
-.6802*
.01870
.01870
.000
.000
.6096
-.7266
-.7024
-.6338
Red soil Clay soil
Laterite
1.3362*
6802*
.01870
.01870
.000
.000
1.2898
.6338
1.3826
.7266
LSD
Clay soil Laterite
Red soil
-.6560*
-1.3362*
.01870
.01870
.000
.000
.-.6931
-1.3733
-.6189
-1.2992
Laterite Clay soil
Red soil
.6560*
-.6802*
.01870
.01870
.000
.000
.6189
-.7173
-.6931
-.6432
Red soil Clay soil
Laterite
1.3362*
6802*
.01870
.01870
.000
.000
1.2992
.6432
1.3733
.7173
Based on observed means
*The mean difference is significant at the .05 level
110
The result of this homogeneous subset analysis further illustrates that there are significant
differences in the compressive strength of earth material stabilized with different stabilizers as a
result of the interaction effects of the different soil types. From the Scheffe‟s and LSD results the
analysis further demonstrates that the red soil displayed highest strength differential over that of
clayey soil at ±1.3362 mean difference and a moderately significant strength differential at ±0.
6802 mean difference against the laterite soil. The laterite soil shows a moderately significant
compressive strength differential of ± 0.6560 mean difference against the clayey soil group, (P <
0.000).
The simple interpretation resulting from all the pieces of evidence so far presented is that
there is a significant difference in the compressive strength quality of stabilized earth material as
a result of the interaction effects of changes in soil types. The result of this analysis further
confirms the findings under Research Question 4 as authentic with additional clarification that
these differences are significant with respect to all the soil types. This researcher feels
comfortable, based on this detailed analysis, to conclude that there are significant differences in
the compressive strength qualities of earth material stabilized with RHA, Straw and RHA-Straw
as a result of the interaction effect of the different soil types. The null Hypothesis 2 of this
research is therefore rejected in favour of the alternate hypothesis that changes in soil type
significantly affect the differences in the compressive strength of earth material stabilized with
different stabilizers.
Hypothesis 3
There is no significant difference in the mean compressive strength of stabilized earth material
as a result of the interaction effect of variations in the mix proportions.
Hypothesis 3 of this research was to investigate the interaction effect of variation in mix
proportions on the mean compressive strength of earth material stabilized with RHA, Straw or
111
RHA-Straw. The data collected from the 27 experimental groups of this research on the
compressive strength of stabilized earth material presented on Table 10 on page 84 was used for
the statistical analysis to accept or reject this hypothesis.
The analysis was based on a Univariate Analysis of Variance (UNOVA) of the
compressive strength values collected from the experimental groups, as contained in Appendix E
on pages 160 – 164. The analysis started with the Descriptive Statistics leading to a Test of
Between-Subjects Effects earlier presented on Table 19. This result of the Test of Between-
Subject Effects presented on Table 19 was also used for investigating this hypothesis and is re-
presented here for convenience as Table 25. The data on this Table 25 provided a general
information about the significance of the interaction variables demonstrating. The data also
demonstrates that differences in the compressive strength of stabilized earth material as a result
of variation in mix proportions are significant.
Table 25
Tests of Between-Subjects Effects (Dependent Variable: Compressive Strength)
Source
Type III Sum of Squares
df
Mean Square
F
Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
87.078a
1398.833
38.902
4.395
40.178
.677
1.118
.919
.889
.849
1486.760
87.928
26
1
2
2
2
4
4
4
8
108
135
134
3.349
1398.833
19.451
2.197
20.089
.169
.280
.230
.111
.008
425.842
177859.57
2473.157
279.388
2554.283
21.522
35.549
29.218
14.136
.000
.000
.000
.000
.000
.000
.000
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
From the data presented on Table 25 an F(279.388)value at P < 0.000 was returned from
the result of the Test of Between-Subject Effects for the interaction effect of variations in mix
proportion for the earth material stabilized with different types of stabilizer. This result clearly
shows that variations in the mix proportions have significant effect on the compressive strength
112
of differently stabilized earth material. The researcher went further from this result to study the
extent of these effects between the various mix proportions.
The Estimated Marginal Means of the research data were used to conducted a pairwise
comparison for the three different mix proportions (11%; 14.5% and 20%) as presented on Table
26. The data on Table 26 confirmed that there are significant differences in the compressive
strength of earth material stabilized with RHA, Straw or RHA-Straw as a result of the interaction
effect of variations in the mix proportion. This result demonstrates that between the variations in
mix proportions there are significant differences in the compressive strength of the earth material
stabilized with different types of stabilizer.
Table 26
Pairwise Comparisons for the Mix Proportions (Dependent Variable: Compressive Strength)
(I)mix proportion
(J)mix proportion
Mean Difference
(I –J)
Std. Error
Sig a
95% Confidence Interval for Differencesa
Lower
Boundary
Upper
Boundary
20% 14.5%
11%
.182*
.440*
.019
.019
.000
.000
..145
.403
.219
.477
14.5% 20%
11%
-.182*
.258*
.019
.019
.000
.000
-.219
.221
-.145
.295
11% 20%
14.5%
-.440*
-.258*
.019
.019
.000
.000
-.477
-.295
-.403
-.221
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent to no adjustments).
A close study of the column on Mean Difference (I – J) of Table 26 shows that when the mix
proportions are compared, 20%[1:1:8] mix proportion returned positively significant differences
against the 14.5%[1:6] and 11%[1:8] mix proportions. The 11%[1:8] mix proportion resulted in
negatively significant difference against the 20% [1:1:8] and 14.5%[1:6] mix proportions. The
14.5%[1:6] mix proportion returned a positively significant difference against only the 11%[1:8]
mix proportion. This analysis demonstrates that 20% mix showed higher effect on the significant
113
differences in the compressive strength of the stabilized earth material. The 14.5%[1:6] mix was
also of higher significant effect over the 11%[1:8] mix.
Based on the outcome of this analysis the researcher decided to conduct a third level
analysis to indentify accurately the individual contributions of the various mix proportions on the
significant differences in compressive strength of the stabilized earth material. A multiple
comparison of this homogeneous subset (mix proportion) based on the observed means was
conducted. The result of this multiple comparison is presented on Table 27. The result of this
homogeneous subset analysis further illustrates that there are significant differences in the
compressive strength of earth material stabilized with different stabilizers as a result of the
interaction of the different mix proportions.
Table 27
Multiple Comparisons Based on Mix Proportions (Dependent Variable: Compressive Strength)
(I) mixprop (J) mixprop
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe 20% 14.5%
11%
.1820*
.4398*
.01870
.01870
.000
.000
.1356
.3934
.2284
.4862
14.5% 20%
11%
-.1820*
.2578*
.01870
.01870
.000
.000
-.2284
.2114
-.1356
.3042
11% 20%
14.5%
-.4398*
-.2578*
.01870
.01870
.000
.000
-.4862
-.3042
-.3934
-2114
LSD
20% 14.5%
11%
.1820*
.4398*
.01870
.01870
.000
.000
.1449
.4027
.2191
.4768
14.5% 20%
11%
-.1820*
.2578*
.01870
.01870
.000
.000
-.2191
.2207
-.1449
.2948
11% 20%
14.5%
-.4398*
-.2578*
.01870
.01870
.000
.000
-.4768
-.2948
-.4027
-.2207
Based on observed means
*The mean difference is significant at the .05 level
From the results of the Scheffe‟s and LSD analysis the 20% mix displayed low but significant
strength differentials of±0.1820 mean difference over that of 14.5% and ±0.4398 mean difference
over that of 11% mix proportions. The 14.5% mix showed a ±0.2578 mean difference against
that of 11% mix proportion, (P < 0.000).
114
The pieces of evidence as analyzed so far clearly demonstrate that there are significant
differences in the compressive strength quality of differently stabilized earth material as a result
of the interactions with the varying mix proportions. The result of this analysis further confirms
the findings under Research Question 5 as authentic with additional clarification that these
differences are significant within and between the different mix proportions. Based on these
statistically supported confirmations from this detailed analysis, the researcher safely concludes
that there are significant differences in the compressive strength qualities of earth material
stabilized with RHA, Straw and RHA-Straw as a result of the interaction with different mix
proportions. The null Hypothesis 3 of this research is therefore rejected in favour of the alternate
hypothesis that the interactions with variations in mix proportions significantly affect the
differences in the mean compressive strength of earth material stabilized with differently
stabilizers.
Hypothesis 4
There is no significant difference in the mean erosion resistance capacity of stabilized earth
material as a result of the difference in the stabilizer type.
This fourth hypothesis of the research was to investigate the effect of differences in
stabilizer type on the mean erosion resistance capacity of stabilized earth material. The
comprehensive data from the second set of the 27 experiments of the research to study the
interaction effect(s) of the variables on the erosion resistance capacity of stabilized earth material
presented on Table 28was used for the statistical analysis.
The Analysis of Variance (ANOVA) for this data employing a univariate approach is
presented in Appendix F on pages 165 – 174. The analysis started with the Descriptive Statistics
resulting in a Test of Between-Subjects Effects presented on Table 29. The data on Table 29 gave
115
Table 28
Schedule of Comprehensive Data of the Mean Erosion Resistance Ratios
0/N0 Experimental Group Type of
Stabilizer
Mix
Proportion
[%]
Soil Type Erosion
Resistance
Ratios[%]
1 EXPERIMENT [I]1 RHA 20%[1:1:4] Clayey Soil 7.45
2 EXPERIMENT [I]2 RHA 14.5%[1:6] Clayey Soil 8.27
3 EXPERIMENT [I]3 RHA 11%[1:8] Clayey Soil 8.42
4 EXPERIMENT [I]4 RHA 20%[1:1:4] Laterite Soil 7.80
5 EXPERIMENT [I]5 RHA 14.5%[1:6] Laterite Soil 8.31
6 EXPERIMENT [I]6 RHA 11%[1:8] Laterite Soil 8.79
7 EXPERIMENT [I]7 RHA 20%1:1:4] Red Soil 7.48
8 EXPERIMENT [I]8 RHA 14.5%[1:6] Red Soil 7.56
9 EXPERIMENT [I]9 RHA 11%[1:8] Red Soil 8.09
10 EXPERIMENT [II]1 STRAW 20%[1:1:4] Clayey Soil 10.60
11 EXPERIMENT [II]2 STRAW 14.5%[1:6] Clayey Soil 8.95
12 EXPERIMENT [II]3 STRAW 11%[1:8} Clayey Soil 9.16
13 EXPERIMENT [II]4 STRAW 20%[1:1:4] Laterite Soil 10.81
14 EXPERIMENT [II]5 STRAW 14.5%[1:6] Laterite Soil 9.26
15 EXPERIMENT [II]6 STRAW 11%[1:8] Laterite Soil 9.45
16 EXPERIMENT [II]7 STRAW 20%1:1:4] Red Soil 9.18
17 EXPERIMENT [II]8 STRAW 14.5%[1:6] Red Soil 9.03
18 EXPERIMENT [II]9 STRAW 11%[1:8] Red Soil 9.08
19 EXPERIMENT[III]1 RHA+STRAW 20%[1:1:4] Clayey Soil 7.12
20 EXPERIMENT[III]2 RHA+STRAW 14.5%[1:6] Clayey Soil 7.39
21 EXPERIMENT[III]3 RHA+STRAW 11%[1:8] Clayey Soil 7.89
22 EXPERIMENT[III]4 RHA+STRAW 20%[1:1:4] Laterite Soil 7.20
23 EXPERIMENT[III]5 RHA+STRAW 14.5%[1:6] Laterite Soil 7.86
24 EXPERIMENT[III]6 RHA+STRAW 11%[1:8] Laterite Soil 8.03
25 EXPERIMENT[III]7 RHA+STRAW 20%1:1:4] Red Soil 6.81
26 EXPERIMENT[III]8 RHA+STRAW 14.5%[1:6] Red Soil 7.01
27 EXPERIMENT III]9 RHA+STRAW 11%[1:8] Red Soil 7.14
a general information about the significance of the entire operator variables. This data on Table
29 demonstrates that generally there are significant differences in the erosion resistance capacity
of stabilized earth material as a result of the interaction effects of the variables including
differences in the stabilizer types, (P < 0.000).
The result of the Test of Between-Subject Effects returned an F(7239.684) value at 0.000 level of
significance for the effect of differences in stabilizer type on the erosion resistance capacity of
stabilized earth material. This result clearly shows that differences in stabilizer type have
significant effect on the erosion resistance capacity stabilized earth material.
116
Table 29
Tests of Between-Subjects Effects (Dependent Variable: Erosion Resistance )
Source
Type III Sum of Squares
Df
Mean Square
F
Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
142.627a
9307.455
106.536
1.312
10.722
18.006
.143
.291
5.618
.795
9450.877
143.421
26
1
2
2
2
4
4
4
8
108
135
134
5.486
9307.455
53.268
.656
5.361
4.502
.036
.073
.702
.007
745.557
1264981.9
7239.684
89.128
728.616
611.807
4.855
9.875
95.435
.000
.000
.000
.000
.000
.000
.001
.000
.000
a. R Squared = .990 (Adjusted R Squared = .993)
The investigation went further from this result to study the extent of these effects between the
three different stabilizer types.
At this second level of the investigation using the Estimated Marginal Means of the
research data the researcher conducted a pairwise comparison for the different stabilizer types as
presented on Table 30. The data on Table 30 re-affirmed that there are significant differences in
the mean erosion resistance capacity of earth materials stabilized with RHA, Straw or a
composite of RHA-Straw as a result of differences in the stabilizer type. This result demonstrates
that irrespective of the type of stabilizer there are significant differences in the erosion resistance
Table 30
Pairwise Comparisons Based on Stabilizer Type(Dependent Variable: Erosion Resistance)
(I) Stabilizer (J) Stabilizer
Mean Difference
(I –J)
Std. Error Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
RHA Straw
RHA-Straw
-1.487*
.632*
.018
.018
.000
.000
-1.523
.597
-1.451
.668
Straw RHA
RHA-Straw
1.487*
2.119*
.018
.018
.000
.000
1.451
2.083
1.523
2.155
RHA-Straw RHA
Straw
-.632*
-2.119*
.018
.018
.000
.000
-.668
-2.155
-.597
-2083
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent to no adjustments).
117
capacity of the earth material stabilized with different types of stabilizers.
From the information in the second column of Table 30 it is clear that when the three
stabilizer types are compared, using the Mean Difference(I-J), the Straw group returned positive
significant differences in favour of the RHA-Straw and RHA groups, while the RHA is also
positively significant against the RHA-Straw. The RHA-Straw group shows negatively
significant differences against the RHA and Straw groups. Since higher percentage in erosion
resistance ratios implies greater weakness in the erosion resistance capacity of the stabilized
material this analysis indicates that RHA-Straw stabilizer group has better quality effect on the
differences in the erosion resistance capacity of the stabilized earth material. On the other hand
the RHA stabilizer group was also of better significant effect than the Straw stabilizer.
To further confirm the individual contributions of the different stabilizer types on the
significant difference in erosion resistance capacity of the stabilized earth material, a post-hoc
test based on the observed means was conducted. This test resulted to a table of multiple
comparisons of the interaction effects of the stabilizer type sub-set as presented on Table 31.
Table 31
Multiple Comparisons Based on Stabilizer Type (Dependent Variable: Erosion Resistance)
(I) Stabilizer (J) Stabilizer
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe RHA Straw
RHA-Straw
-1.4869*
-.6324*
.01808
.01808
.000
.000
-1.5318
.5896
-1.4420
.6773
Straw RHA
RHA-Straw
1.4869*
2.1193*
.01808
.01808
.000
.000
1.4420
2.0744
1.5318
2.1642
RHA-Straw RHA
Straw
-.6324*
-2.1193*
.01808
.01808
.000
.000
-.6773
-2.1642
-.5876
-2.0744
LSD
RHA Straw
RHA-Straw
-1.4869*
-.6324*
.01808
.01808
.000
.000
.-1.5227
.5966
-1.4510
.6683
Straw RHA
RHA-Straw
1.4869*
2.1193*
.01808
.01808
.000
.000
1.4510
2.0835
1.5227
2.1552
RHA-Straw RHA
Straw
-.6324*
-2.1193*
.01808
.01808
.000
.000
-.6683
-2.1552
-.5966
-2.0835
Based on observed means
*The mean difference is significant at the .05 level
118
The result of this homogeneous subset analysis further illustrates that there are significant
differences in the erosion resistance capacity of earth material stabilized as a result of the
differences in stabilizer type. From the Scheffe‟s and LSD results the analysis further
demonstrates that RHA-Straw stabilized earth material displayed significantly high erosion
resistance capacity differential of ±2.1193 mean difference against the Straw stabilized group.
The results on Table 31 also show that the RHA stabilized material has high erosion resistance
capacity difference of ±1.4869 over the Straw stabilized material. The difference in erosion
resistance capacity between the RHA-Straw and RHA stabilized material showed a moderate but
significant differential at ±0.6324 mean difference, (P < 0.000).
The interpretation resulting from all the pieces of evidence so far presented is that there is
a significant difference in the compressive strength quality of stabilized earth material as a result
of interactions with different earth building soil types. The result of this analysis further confirms
the findings under Research Question 4 as authentic with additional clarification that these
differences are significant with respect to all the soil types. This researcher feels comfortable,
based on the confirmations from this detailed analysis, to conclude that there are significant
differences in the compressive strength qualities of earth material stabilized with RHA, Straw
and RHA-Straw as a result of the interaction with different soil types. The null Hypothesis 2 of
this research is therefore rejected in favour of the alternate hypothesis that changes in soil type
significantly affect differences in the compressive strength of earth material stabilized with
differently stabilizers.
Hypothesis 5
There is no significant difference in the mean erosion resistance capacity of stabilized earth
material as a result of changes in the soil type.
This hypothesis was set out to investigate the interaction effect of soil type on the erosion
resistance capacity of earth material stabilized with RHA, Straw or RHA-Straw. The
119
comprehensive data of one set of the 27 experiments dealing with the interaction effect(s) of
changes in soil type on the erosion resistance capacity of stabilized earth material presented on
Table 27, page 116 was used for the statistical analysis of the data for this hypothesis.
The Analysis of Variance (ANOVA) for the data adopting a univariate approach is
presented as Appendix F on pages 165 – 174. The analysis of the data started with the
Descriptive Statistics resulting to a Test of Between-Subjects Effects presented on Table 32. The
data on Table 32 gave generalized information about the significance of the entire operator
variables. The data demonstrates that there are differences in the erosion resistance capacity of
stabilized earth material based on the interactions with different soil types, (P < 0.000).
Table 32
Tests of Between-Subjects Effects (Dependent Variable: Erosion Resistance Ratio)
Source
Type III Sum of Squares
Df
Mean Square
F
Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
142.627a
9307.455
106.536
1.312
10.722
18.006
.143
.291
5.618
.795
9450.877
143.421
26
1
2
2
2
4
4
4
8
108
135
134
5.486
9307.455
53.268
.656
5.361
4.502
.036
.073
.702
.007
745.557
1264981.9
7239.684
89.128
728.616
611.807
4.855
9.875
95.435
.000
.000
.000
.000
.000
.000
.001
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
The result of the Test of Between-Subject Effects returned an F(728.616) value at 0.000
level of significance for the interaction effect of changes in soil types on earth material stabilized
with different types of stabilizer. This result clearly shows that differences in the soil type have
significant effect on the erosion resistance capacity of differently stabilized earth material. The
investigation went further from this result to study the extent of these effects between the three
different soil types. At this point, the analysis used the estimated marginal means of the research
data to conduct a pairwise comparison of the different soil types as presented on Table 33. The
120
data on Table 33 re-affirmed that there are significant differences in the erosion resistance
capacity of earth materials stabilized with RHA, Straw or a composite of RHA-Straw as a result
of changes in the soil type.
Table 33
Pairwise Comparisons Based on Soil Type(Dependent Variable: Erosion Resistance)
(I) Soiltype (J) Soiltype
Mean Difference
(I –J)
Std. Error Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Clay soil Laterite
Red soil
-.254*
.429*
.018
.018
.000
.000
.-.290
.393
-.218
.465
Laterite Clay soil
Red soil
.254*
.683*
.018
.018
.000
.000
.218
.647
.290
.719
Red soil Clay soil
Laterite
-.429*
683*
.018
.018
.000
.000
-.465
-.719
-.393
-.647
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent tp no adjustments).
This result demonstrates that there are significant differences in the erosion resistance capacity of
the earth material stabilized with different types of stabilizers depending on the soil type. This is
illustrated under the second column of Table 33 which shows that when the three soil types are
compared, using the Mean Difference(I-J), the red soil returned negative significant differences
against the clayey and laterite soils, whereas the laterite soil returned positively significant
against the clayey soil and red soils. The clayey soil shows negative significant difference against
the laterite soil and a positive one against the red soils. Noting that higher arithmetic values in the
erosion resistance ratios indicates higher capacity weakness, the interpretation of these data is
that the red soil has higher effect on the differences in the erosion resistance capacity of the
stabilized earth material followed by the laterite soil which is of higher significant effect than the
clayey soil.
To further confirm the individual contributions of the different soil types on the
significant difference in erosion resistance capacity of the stabilized earth material, a multiple
121
comparison of this homogeneous subset (soil type) based on the observed means was conducted.
The result of this multiple comparison is presented on Table 34.
The result of this homogeneous subset analysis further illustrates that there are significant
differences in the erosion resistance capacity of earth material stabilized with different stabilizers
as a result of the interaction with different soil types. From the Scheffe‟s and LSD results the
analysis further demonstrates that the red soil displayed moderately significant erosion resistance
capacity differential of ±0.6829 mean difference over that of laterite soil and at ±0.4289 mean
difference against the clayey soil group. The laterite and clayey soils demonstrates a low but
significant differential in their erosion resistance capacity at ±2549 mean difference, (P < 0.000).
Table 34
Multiple Comparisons Based on Soil Type (Dependent Variable: Erosion Resistance)
(I) Soiltype (J) Soiltype
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe Clay soil Laterite
Red soil
-.2549*
.4289*
.01808
.01808
.000
.000
.-.2989
.3840
-.2091
.4738
Laterite Clay soil
Red soil
.2540*
.6829*
.01808
.01808
.000
.000
.2091
.6380
.2989
.7278
Red soil Clay soil
Laterite
-.4289*
-.6829*
.01808
.01808
.000
.000
-.4738
-.7278
-.3840
-.6380
LSD
Clay soil Laterite
Red soil
-.2549*
.4289*
.01808
.01808
.000
.000
.-.2898
.3930
-.2182
.4647
Laterite Clay soil
Red soil
.2540*
.6829*
.01808
.01808
.000
.000
.2182
.6470
.2898
.7187
Red soil Clay soil
Laterite
-.4289*
-.6829*
.01808
.01808
.000
.000
-.4647
-.7178
-.3930
-.6470
Based on observed means
*The mean difference is significant at the .05 level
The result of all the analysis clearly shows that there is enough pieces of evidence to
prove that there is a significant difference in the erosion resistance capacity of differently
stabilized earth material as a result of interaction effects of differences in the soil types. The
result of these analyses validates the findings under Research Question 7 as authentic with
additional clarification that these differences are significant with respect to all the soil types.
Based on this detailed analysis, the researcher confidently concluded that there are significant
122
differences in the erosion resistance capacity of earth material stabilized with RHA, Straw and
RHA-Straw resulting from the interaction effect of the different soil types. The null Hypothesis 5
of this research is therefore rejected, in favour of the alternate hypothesis that changes in soil type
significantly affect differences in the compressive strength of earth material stabilized with
different types of stabilizer.
Hypothesis 6
There is no significant difference in the mean erosion resistance capacity of stabilized earth
material as a result of the interaction effect of variations in the mix proportions.
This is the sixth hypothesis of this research set out to study the interaction effect of
variation in mix proportions on the erosion resistance capacity of earth material stabilized with
RHA, Straw or RHA-Straw. The data collected from the second set of the 27 experimental
groups of this research to study the factors affecting the erosion resistance capacity of stabilized
earth material as presented on Table 27, page 116 was used for the statistical analysis to accept or
reject this hypothesis. The analysis, once again, employed the Analysis of Variance(ANOVA)
statistics adopting a univariate approach as contained in Appendix E on pages 160 – 164.
Starting with the Descriptive Statistics the analysis tested the interaction effect(s) of variations in
Table 35
Tests of Between-Subjects Effects (Dependent Variable: Erosion Resistance)
Source
Type III Sum of Squares
Df Mean Square
F Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
142.627a
9307.455
106.536
1.312
10.722
18.006
.143
.291
5.618
.795
9450.877
143.421
26
1
2
2
2
4
4
4
8
108
135
134
5.486
9307.455
53.268
.656
5.361
4.502
.036
.073
.702
.007
745.557
1264981.9
7239.684
89.128
728.616
611.807
4.855
9.875
95.435
.000
.000
.000
.000
.000
.000
.001
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
123
mix proportions on the erosion resistance capacity of stabilized earth material. This initial
analysis resulted in the Test of Between-Subjects Effects schedule presented as Table 35.
The data on Table 35, once again, demonstrates that generally there are significant
differences in the erosion resistance capacity of stabilized earth material as a result of the
interaction effect of the variables including variations in the mix proportions. The analysis
returned an F(89.128)value at P < 0.000 from the result of the Test of Between-Subject Effects
for the interaction effect of variations in mix proportion on the erosion resistance capacity of the
earth material stabilized with different types of stabilizer. This result clearly shows that variations
in the mix proportions have significant effect on the erosion resistance capacity of differently
stabilized earth material. From the result of this analysis the researcher went further to study the
extent of these effects between the various mix proportions using the estimated marginal means
of the research data.
The estimated marginal means were used to conduct a pairwise comparison of the three
different mix proportions (11%; 14.5% and 20%) as presented on Table 36. The data on Table 36
demonstrated the levels of significance between the three mix proportions. The data on this Table
36 shows that there are significant differences in the erosion resistance capacity of earth material
Table 36
Pairwise Comparisons for Mix Proportions (Dependent Variable: Erosion Resistance Capacity)
(I) Mix prop. (J)mix prop.
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
20% 14.5%
11%
.075*
-.161*
.018
.018
.000
.000
.039
-.197
.111
-.125
14.5% 20%
11%
-.075*
-.236*
.018
.018
.000
.000
-.111
.272
-.039
-.200
11% 20%
14.5%
.161*
.236*
.018
.018
.000
.000
.125
.200
.197
.272
Based on estimated marginal means
*The mean difference is significant at the .05 level
a. Adjusted for multiple comparisons: Least significant Difference(equivalent to no adjustments).
124
stabilized with RHA, Straw or RHA-Straw as a result of the interaction effect of variations in the
mix proportion. The data under the third column on Mean Difference (I – J) of Table 36 shows
that when the mix proportions are compared, 20%[1:1:8] mix proportion soil returned positively
significant differences against the 14.5%[1:6] and a negatively significant difference against the
11%[1:8] mix proportions. The 11%[1:8] mix proportion resulted in positively significant
differences against the 20% [1:1:8] and 14.5%[1:6] mix proportions. The 14.5%[1:6] mix
proportion returned positively significant differences against the 11%[1:8] and 20%[1:1:8] mix
proportion. Considering that higher arithmetic values of the erosion resistance ratios used in this
analysis connotes weaker capacity, this analysis demonstrates that 20% mix showed better
significant effect on the differences in the erosion resistance capacity of the stabilized earth
material. The 14.5%[1:6] mix was also of better significant effect over that of 11%[1:8] mix.
Based on the outcome of this analysis the researcher also decided to conduct another
round of analysis to indentify accurately the degree of individual mix group contributions to these
significant differences in erosion resistance capacity of the stabilized earth material. A multiple
comparison of this homogeneous subset (mix proportion) based on the observed means
Table 37
Multiple Comparisons Based on Mix Proportions (Dependent Variable: Compressive Strength)
(I) mixprop (J) mixprop
Mean Difference
(I –J)
Std. Error
Sig a 95% Confidence Interval for Differencesa
Lower Boundary Upper Boundary
Scheffe 20% 14.5%
11%
.0749*
-.1613*
.01808
.01808
.000
.000
.0300
-.2062
.1198
-.1164
14.5% 20%
11%
-.0749*
-.2362*
.01808
.01808
.000
.000
-.1198
.2811
-.0300
-.1913
11% 20%
14.5%
.1613*
.2362*
.01808
.01808
.000
.000
.1164
.1913
.2062
.2811
LSD
20% 14.5%
11%
.0749*
-.1613*
.01808
.01808
.000
.000
.0390
-.1972
.1107
-.1255
14.5% 20%
11%
-.0749*
-.2362*
.01808
.01808
.000
.000
-.1107
-.2721
-.0390
-.2004
11% 20%
14.5%
.1613*
.2362*
.01808
.01808
.000
.000
.1255
.2004
.1972
.2721
Based on observed means
*The mean difference is significant at the .05 level
125
was conducted. The result of this multiple comparison is presented on Table 37.
The result of this homogeneous subset analysis further illustrates that there are significant
differences in the erosion resistance capacity of earth material stabilized with different stabilizers
as a result of the interaction with the different mix proportions. The data presented on Table 37
on the Scheffe‟s and LSD analysis results shows that there are generally low but significant
differences in erosion resistance capacity between the different mix proportions. The 20% mix
proportion displayed lowest differential of ±0.0749 mean difference over that of 14.5% mix and
±0.1613 against the 11% mix proportion. The 14.5% mix showed higher significant differential
against the 11% mix at ±0.2362 mean difference, (P < 0.000).
The researcher has gone through this analysis to provide every necessary pieces of
evidence to clearly demonstrate that there are significant differences in the erosion resistance
capacity of differently stabilized earth material as a result of the interactions effect of variation in
mix proportions. The result of this analysis further confirms the findings under Research
Question 8 as authentic with additional clarification that these differences are significant within
and between the different mix proportions. Based on these statistically supported detailed
analyses, the researcher safely concludes that there are significant differences in the erosion
resistance capacity of earth material stabilized with RHA, Straw and RHA-Straw as a result of
the interaction effect of the different mix proportions. The null Hypothesis 6 of this research is
therefore rejected in favour of the alternate hypothesis, that interaction effect of variations in mix
proportions significantly affect the differences in the mean erosion resistance capacity of earth
material stabilized with differently stabilizers.
Hypothesis 7
There is no significant interaction effect of stabilizer type, soil type and mix proportion on the
mean compressive strength and erosion resistance capacity of stabilized earth material.
126
From Hypothesis 1 to 6, this research has been able to clearly establish that there are
significant differences in the compressive strength qualities and erosion resistance capacity of
earth material stabilized with either RHA or Straw or a composite of RHA-Straw. Hypothesis 7
was set out to investigate the interactive effect of the different soil types and variations in the mix
proportions on the structural characteristics (compressive strength and erosion resistance
capacity) of the stabilized earth material. To test this, hypothesis the data generated from the
entire experiments of this research formed the primary instrument. The result of the Test of
Between-Subjects Effects for both the compressive strength and erosion resistance qualities are
here re-presented as Tables 38 and 39.
Table 38
Tests of Between-Subjects Effects (Dependent Variable: Compressive Strength)
Source
Type III Sum of Squares
df Mean Square
F Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
87.078a
1398.833
38.902
4.395
40.178
.677
1.118
.919
.889
.849
1486.760
87.928
26
1
2
2
2
4
4
4
8
108
135
134
3.349
1398.833
19.451
2.197
20.089
.169
.280
.230
.111
.008
425.842
177859.57
2473.157
279.388
2554.283
21.522
35.549
29.218
14.136
.000
.000
.000
.000
.000
.000
.000
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
The data presented on Table 38 shows that the interaction (P < .000) between the
stabilizer type and mix proportions returned an F(21.522), for the interaction between the
stabilizer and soil type the analysis returned an F(35.549) and F(29.218) for the interaction
between the mix proportions and soil type. An analysis of the combined interaction between the
three variables – stabilizer type, mix proportion and soil type returned an F(14.136) at 0.000
significant level. The result of this different analysis displayed on Table 38 clearly demonstrates
that there are significant differences in the mean compressive strength of stabilized earth material
127
as a result of the interaction between the different stabilizer types, changes in soil type and
variations in the mix proportion.
The second segment of this hypothesis was on the effect of the interactions between the
same variables on the erosion resistance capacity of the stabilized earth material. The Test of
Between-Subjects Effects based on the erosion resistance capacity was used to study these
effects. The result is presented on Table 39.
The result of the Test Between-Subject Effects based on the erosion resistance capacity of
the stabilized earth material on this Table 39 clearly shows that there are significant differences in
the erosion resistance capacities as a result of the effects of the interactions between the three
Table 39
Tests of Between-Subjects Effects (Dependent Variable: Erosion Resistance)
Source
Type III Sum of Squares
Df Mean Square
F Sig.
Corrected Model
Intercept
Stabilizer
mixprop
soiltype
stabilizer * mixprop
stabilizer * soiltype
mixprop * soiltype
Stabilizer * mixprop * soiltype
Error
Total
Corrected Total
142.627a
9307.455
106.536
1.312
10.722
18.006
.143
.291
5.618
.795
9450.877
143.421
26
1
2
2
2
4
4
4
8
108
135
134
5.486
9307.455
53.268
.656
5.361
4.502
.036
.073
.702
.007
745.557
1264981.9
7239.684
89.128
728.616
611.807
4.855
9.875
95.435
.000
.000
.000
.000
.000
.000
.001
.000
.000
a. R Squared = .990 (Adjusted R Squared = .988)
independent variables. The interaction (P < .000) between the stabilizer type and the mix
proportions was significant at F(611.807), the interaction between the stabilizer shows a
significant difference in the erosion resistance capacity of F(4.855) at 0.001 level of significance,
while the interaction effect of variations in mix proportions and soil type returned an F(9.875) at
P < .000. The interaction effect of the three variables – stabilizer, mix proportion and soil type,
combined showed a significant difference of F(95.435) at 0,000 level of significance. The result
of this combined interaction effects summarizes the argument that there are significant
128
differences in the erosion resistance capacity of stabilized earth material due to the interaction
between the different stabilizer types, variations in mix proportions and changes in the soil type.
The clarity of the results of the analyses presented on Tables 38 and 39 left the researcher
in no doubt that Hypothesis 7 is completely reject. The alternate hypothesis that there are
significant differences in the compressive strength and erosion resistance qualities of the
stabilized earth material as a result of the interaction effects of differences in stabilizer type, soil
type and variation in mix proportions is upheld.
Hypothesis 8
There is no significant combination of stabilizers, soil type and mix proportion that will optimize
the use of RHA, Straw or RHA-Straw for earth material stabilization, with respect to their
compressive strength and erosion resistance qualities.
The concern of this Hypothesis forms the central focus of this research and by implication
the last segment of the investigations in this research. The primary attention of the presentations
and analysis under this hypothesis is to identify through statistically based investigation, any
possible combinations of the independent variables of stabilizer type, mix proportion and soil
type that can produce optimal(best possible within the given parameters) structural qualities -
compressive strength and erosion resistance capacity - for stabilized earth material.
The univariate approach of the ANOVA statistics was employed to analyze the data
generated from the 27 pairs of experiment conducted in this research in response to this
hypothesis. Since the concern of this hypothesis is that of identifying the relevant parameters, the
descriptive statistics of the ANOVA schedule was found handy for the investigation. To avoid an
unwieldy table presentation, only the third segment of the ANOVA “Descriptive Statistics
Schedule” containing the variables combination with the highest compressive strength value is
presented here as Table 40(culled from Appendix F, page 168) and that on the best erosion
resistance capacity is presented as Table 41(Appendix G, page177) .
129
Table 40
Descriptive Statistics on RHA+Straw (Dependent Variable: Compressive Strength)
Stabilizer Mix Proportion Soil Type Mean Std Deviation
N
RHA+Straw 20% Clayey Soil 3.3320 .01643 5
Laterite Soil 4.1500 .01000 5
Red Soil 4.8200 .02345 5
Total 4.1007 .63004 15
14.5% Clayey Soil 3.0400 .06745 5
Laterite Soil 4.0500 .05244 5
Red Soil 4.6880 .00837 5
Total 3.9260 .70379 15
11% Clayey Soil 2.9100 .03240 5
Laterite Soil 3.6820 .02168 5
Red Soil 4.5200 .01000 5
Total 3.7040 .68088 15
Total Clayey Soil 3.0940 .18719 5
Laterite Soil 3.9607 .21068 5
Red Soil 4.6760 .12788 5
Total 3.9102 .67702 15
From the data presented on Table 40, RHA-Straw at 20% mix proportion based on red
soil (emboldened by the researcher for easy identification by readers), produced the highest
compressive strength(4.8200Mpa) from the entire experimental groups. This gives the optimal
compressive strength for the earth material stabilized with RHA, Straw or a composite RHA-
Straw. Under the compressive group a combination of RHA-Straw at 20% mix proportion on red
soil significant stands out as the optimal mix proportion for the group.
The data for the identification of the optimal mix combination for the erosion resistance
capacity group, is also a section of the entire ANOVA Descriptive Statistics schedule on
Appendix G, page 177. For convenience, only the third section of this ANOVA schedule is
presented here for the analysis as Table 41. From this Table 41 the ANOVA Descriptive
Statistics analysis presented on Table 41 it is not difficult to identify the variables combination
with the best erosion resistance capacity. The RHA-Straw stabilizer at 20% mix proportion based
on red soil produced the lowest mean resistance ratio of 6.8200 per cent. This mix combination
produced an optimal erosion resistance capacity from the entire experiment. RHA-Straw at 20%
130
mix proportion on red soil significant stands out as the optimal mix proportion for the erosion
resistance experimental group.
Table 41
Descriptive Statistics (Dependent Variable: Erosion Resistance Capacity)
Stabilizer Mix Proportion Soil Type Mean Std Deviation N
RHA+Straw 20% Clayey Soil 7.1200 .01000 5
Laterite Soil 7.2000 .01414 5
Red Soil 6.8200 .02000 5
Total 7.0467 .16990 15
14.5% Clayey Soil 7.3900 .01225 5
Laterite Soil 7.8680 .01789 5
Red Soil 7.1420 .01924 5
Total 7.4667 .31227 15
11% Clayey Soil 7.8940 .01517 5
Laterite Soil 8.0300 .01000 5
Red Soil 7.0100 .43652 5
Total 7.6447 .52309 15
Total Clayey Soil 7.4680 .33223 5
Laterite Soil 7.6993 .37207 5
Red Soil 6.9907 .27088 5
Total 7.3860 .43767 15
Based on the analysis presented so far, it evidently follows that red soil stabilized with a
composite of RHA-Straw stabilizer at a mix proportion of 20% [1:1:8] produced the optimal
compressive strength( χ = 4.82 ±0.023) and erosion resistance capacity (χ = 6.82 ± 0.02) from
the stabilized earth material. The outcome of this analysis confirms the researcher‟s conclusion
under Research Question 9, that Experiment III]7, stands out as the optimal mix group for earth
material stabilized with these three different stabilizer (additive) types under investigation.
Hypothesis 8 of this research is therefore evidently rejected in favour of the alternative
hypothesis.
Findings
Based on the data generated from this research and the detailed analysis of the data, the
following findings were made.
131
1. The particles distribution of the three earth building soil samples used in this research
fall within the acceptable range (25 – 40%) of clay for quality earth stabilization and
impacted positively on the stabilization and biodegradability characteristics of the earth
materials.
2. The three soil samples contained Iron(Fe), Potassium(K), Magnesium(Mg), Calcium(Ca),
Zinc(Zn), Nitrates, Phosphorous(P) at varying percentages, while the red soil and clayey
soil contained Cadmium(Cd) at 0.10% and 0.36% respectively. Only the clayey soil
contained Sodium(Na) of 1.35%.
3. The chemical composition of the three earth building soil types all fall within the
acceptable range for quality earth building soil types and impacted positively on the
stabilization and biodegradability characteristics of the earth materials.
4. The soaking of the Sodium containing soil-based earth material during the first seven
days of wet curing appears to have wiped/neutralized the efflorescence action of the
Sodium content.
5. The RHA was found to be basically Silicon Dioxide fine powder(25µ), containing
89.75% Silicon Dioxide(SiO2), Calcium Oxide(CaO) 2.19%, Potasium Oxide(K2O)
2.08%, with Aluminium Oxide(Al2O3), Ferric Oxide(Fe 2O3), Manganese Oxide(Mn2O3),
Phosphorous Oxide (P2O5), Titanium Oxide(TiO2) at less than 0.9% each and traces of
Magnesium Oxide and Sodium Oxide.
6. The Straw whose chemical structure is yet to be fully elucidated (Charoenvai, Khedari,
Hirunlabh, Daguenet and Quenard,2005) was found to be composed mainly of Silicon
Oxide(31.50%), Holocellulose(26.20%), Alpha Cellulose(14.6%),
Hemicellulose(10.60%0, Alcohol-Benzene solubility(7.50%), and Lignin(9.60%).
7. The chemical structure of the Straw, which distinguishes it from other organic materials
makes it a good earth material stabilizer.
132
8. The Straw-based stabilized earth materials required a minimum of 24 hours of
moisturization to take care of the microscopic behavior of the Straw in earth material
stabilization.
9. Differences in the stabilizer type contributed significantly to the differences in the mean
compressive strength (F = 2473.157; P < .000) of the stabilized earth material.
10. The interaction effect of changes in the soil type significant effected the mean
compressive strength (F = 2554.283; P < .000) of earth material stabilized with different
types of stabilizer.
11. The interaction effect of variations in mix proportions significant effected the mean
compressive strength (F = 279.388; P < .000) of earth material stabilized with different
types of stabilizer.
12. Differences in the stabilizer type contributed significantly to the differences in the mean
erosion resistance capacity (F = 7239.684; P < .000) of the stabilized earth material.
13. The interaction effects of changes in the soil type significant effected the mean erosion
resistance capacity (F = 728.616; P < .000) of earth material stabilized with different types
of stabilizer.
14. The interaction effects of variations in mix proportions significant effected the mean
erosion resistance capacity (F = 89.128; P < .000) of earth material stabilized with different
types of stabilizer.
15. The combined interaction effects of differences in the stabilizer type and variations in
mix proportions significant effected the mean compressive strength (F =21.522; P < .000)
of stabilized earth material.
16. The combined interaction effects of differences in the stabilizer type and changes in the
soil type significant effected the mean compressive strength (F =35.549; P < .001) of
stabilized earth material stabilized.
133
17. The combined interaction effects of variations in the mix proportions and changes in the
soil type significant effected the mean compressive strength (F =29.218; P < .000) of earth
material stabilized with different types of stabilizer.
18. The overall interaction effects of differences in the stabilizer type, changes in the soil type
significant and variation in the mix proportion effected the mean compressive strength (F
= 14.136; P < .000) of stabilized earth material.
19. The combined interaction effects of differences in the stabilizer type and variations in
mix proportions significant effected the mean erosion resistance capacity (F =611.807; P <
.000) of stabilized earth material.
20. The combined interaction effects of differences in the stabilizer type and changes in the
soil type significant effected the mean erosion resistance capacity (F =4.855; P < .001) of
stabilized earth material.
21. The combined interaction effects of variations in the mix proportions and changes in the
soil type significant effected the mean erosion resistance capacity (F =9.875; P < .000) of
earth material stabilized with different types of stabilizer.
22. The overall interaction effects of differences in the stabilizer type, changes in the soil type
significant and variation in the mix proportion effected the mean erosion resistance
capacity (F = 95.435; P < .001) of stabilized earth material.
23. Red soil stabilized with a combination of RHA-Straw at a mix proportion of 20 per cent
(1:1:8) produced an optimal compressive strength( χ = 4.82 ±0.023) and erosion
resistance capacity (χ = 6.82 ± 0.02) of the stabilized earth material.
24. A mix proportion of 20 per cent (1:1:8) with a composite RHA-Straw stabilizer based on
red soil optimizes the use of RHA and Straw as stabilizing agents for earth building
construction.
134
Discussion
The outcome of this research confirms that earth material stabilization is a very ancient
tradition/technique developed through practice and experience (North, 1998; Bengtsson &
Whitaker, 1998 and Maini, 2002). The researcher also established, as noted by Houben (1994),
Kennedy, (2002), and Heathcole and Ravindrajah (2003) that different stabilization methods have
been adopted to meet different construction needs. This research through its several literature
reviews established that in many of stabilization techniques, straw has remained one of the most
ancient additives used to stabilize the earth material for better strength attainment; that advances
in science and technology within the building construction industry have introduced more
scientific approaches to earth material stabilization as stated by Dobson, (2004). These
developments in earth material stabilization have made it possible to use several other types of
additives such as RHA in earth material stabilization based on the discovery that burnt under
controlled conditions RHA produces a fine amorphous silicon pozzolana of a chemical
composition comparable to that of ordinary Portland cement, (Oraedu, 1985; Naville & Brooks ,
1993).
The laboratory analysis shows that the three soil samples were natural soil types. The
implication is that the outcome of this research can be practiced once natural soil is available for
house production, Montgomery, 1998). The effect of differences in the soil type on the structural
quality of the stabilized earth material demonstrates the importance of quality soil identification
and selection as cautioned by Bengtsson & Whitaker(1998) and Kennedy, (2002). On the other
hand, the findings of this research have clearly shown that changes in additive type and variations
in the mix proportions significantly affect the structural qualities of the stabilized earth material.
The laboratory tests of the stabilized earth material clearly established that the chemical
composition of the soil samples contributed in one way or the other in the direction and degree of
the structural improvements of the stabilized earth material, (Gooding, 1994; Kerali, 2001 &
135
Burrough, 2002a). The experiments in this research have shown that there is need to take every
necessary precaution during the production and curing of the stabilized material to avoid
contamination.
The results from this research clearly demonstrate the efficacy of locally available
additive materials for earth material stabilization, and that significant differences exist in the
structural qualities of the stabilized earth material as the type and proportion of stabilizer changes
in line with the soil type used. This finding justifies earlier claims by Spence (1974), Howe
(1992) and Gooding (1994) that the properties of the base material, type of fertilizer and
proportion affect the degree of stabilization possible.
The outcome of this research also clearly demonstrates that the effects and interactiion
effects of both the primary and secondary operator variables of stabilizer type, soil type and
variations in the mix proportions affect and to a large extent determine the degree and direction
of the quality improvement and their differences, (Ingles &Metcalf, 1972; Maini, 2002). The
statistical analysis further demonstrates that this study through the several experiments was able
to establish that an optimal mix proportion and material combination was possible in order to
optimize the use of these local stabilizers (additives).
Through this study, the researcher has produced a teaching component that would form a
major curriculum component for teaching in building construction based courses. The researcher
has also demonstrated that students/teachers of technology-based programmes can conduct pure
laboratory based researches with high degree of success. Finally, the end-product of this research
is an encouraging development demonstrating that the heaps of wasting rice husks in many rice-
producing communities can be turned into a utilitarian product, employing very simple
technologies. The findings of this research lay support to the need to look inwards within our
environment to find alternative ways to produce quality low cost houses for the teaming
population of our society and by the same reason create jobs for the increasing jobless population.
136
CHAPTER V
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
In this chapter, the statement of the problem for this research is re-stated with an abridged
version of the methodology adopted for this research and the conclusions drawn based on the
findings. Recommendations resulting from the conclusions and the implications of the findings
along with the suggestions based on the outcome of this research are also presented in this
chapter.
Re-statement of the Problem
Earth material(mud) is one of the most ancient natural building materials used to build the
earliest man-made shelters. The use of earth (kneaded mud or clay), which is commonly called
earth material in international research documents, as a building material dates back thousands
of years. Some of the first man-made structures inhabited by man were made of earth materials.
The use of this earth material for building construction suffered a major setback since the
discovery of cement- and steel-based construction materials with better structural qualities.
Interesting, however, as the cost of house production with cement- and steel-based construction
materials has continued to rise daily. Researchers have also started to discover some health
implication in the use of many of the building materials classified as standard. These
developments have brought with it a resurgence of interest in earth building construction. This
resurgence of interest in earth building construction also recognizes that known weaknesses of
the earth materials must be worked-on for the material to meet modern construction standards
and acceptance. To deal with these key weaknesses related to its structural strength and erosion
resistance, several methods of stabilizing the material have been developed. The most popular
one is the compressed cement stabilized earth blocks (CCSEB) technology. This technology has
137
taken advantage of the binding qualities of cement and the environmental and health friendliness
of the earth material to produce a technically improved type of earth building blocks.
The popularity and growing wide acceptance of this compressed cement stabilized earth
block technology have also began to impact on the cost of buildings made from this compressed
cement stabilized earth block technology. There is therefore need to continue to research into and
develop other alternative, cheaper, sustainable, environmentally and health friendly ways of
producing quality low-cost houses for the teaming populations, especially within the developing
countries like Nigeria. Some of the ways already being worked-on combines traditional practices
and advances in science and technology within the building construction industry.
The problem of this was to find out “the most efficient and cost effective way of using
rice-husk-ash and/or straw for earth material stabilization?” Specifically, the research sought to
identify the particles distribution and chemical characteristics of the soil samples, and the
chemical composition of the different stabilizers that effect earth material stabilization. The study
investigated the structural behaviour characteristics of stabilized earth materials as a result of
differences in the stabilizer type, changes in the soil type and variations in the mix proportion. By
implication the researcher was interested in discovering what mix combinations of these
stabilizers with what type of soil will produce an optimal compressive strength and erosion
resistance capacity for the stabilized earth material. In this process, the study ended with a
stabilized earth material product that optimized the use of these locally available additives –
RHA and Straw – for earth material stabilization.
Summary of Procedures Adopted
The study adopted a material research and development design employing a 3 x 3 x 3
factorial experimental model to determine the effects of the three different factors on the
compressive strength and erosion resistance capacity of the stabilized earth material. The factors
138
were three stabilizer types (RHA, Straw and RHA-Straw), three earth building soil type (Clayey,
Red and Laterite), and three levels of mix proportions (11%, 14.5% and 20%). A laboratory
analysis was conducted to identify the particles distribution and chemical composition of the soil
samples and the major chemical elements of the stabilizers that could affect the structural
properties of the stabilized earth material. A total of 270 compressed, stabilized earth block
specimen were produced. Ten specimen blocks were produced from each of the 27 experimental
groups. Out of these 10 blocks, five blocks were randomly selected and assigned to the 27
different experimental groups. The Rockwell Universal Medium Strength Cube Crushing
Machine was used to test the compressive strengths, while the University of Technology,
Sydney(UTS) type Spray Test Instrument was used to test the erosion resistance capacity of the
earth material. Frequency count, Mean and Ratio were used to answer the research questions.
Analysis of Variance was used to test the hypotheses at probability level of 0.05.
The results obtain from the laboratory tests were first presented in a tabular form. A simple
frequency count, the mean statistical and the ratio scale were used for the primary analysis to
answer the six research questions, while an Analysis of Variance (ANOVA) statistical model
employing the univariate analysis was used to test the eight null hypotheses and validate the
findings under the nine research questions.
Major Findings
1. The particles distribution of the three earth building soil samples used in this research
fall within the acceptable range (25 – 40%) of clay for quality earth stabilization and
impacted positively on the stabilization and biodegradability characteristics of the earth
materials.
2. The chemical composition of the three soil samples contained Iron(Fe), Potassium(K),
Magnesium(Mg), Calcium(Ca), Zinc(Zn), Nitrates, Phosphorous(P) at varying
139
percentages, while the red soil and clayey soil contained Cadmium(Cd) at 0.10% and
0.36% respectively. Only the clayey soil contained Sodium(Na) of 1.35%.
3. The RHA was found to be basically Silicon Dioxide fine powder(25µ), containing
89.75% Silicon Dioxide(SiO2), Calcium Oxide(CaO) 2.19%, Potasium Oxide(K2O)
2.08%, with Aluminium Oxide(Al2O3), Ferric Oxide(Fe 2O3), Manganese Oxide(Mn2O3),
Phosphorous Oxide (P2O5), Titanium Oxide(TiO2) at less than 0.9% each and traces of
Magnesium Oxide and Sodium Oxide.
4. The Straw whose chemical structure is yet to be fully elucidated according to Charoenvai,
Khedari, Hirunlabh, Daguenet and Quenard, (2005) was found to be composed of Silicon
Oxide (31.50%), Holocellulose (26.20%), Alpha Cellulose(14.6%),
Hemicellulose(10.60%0, Alcohol-Benzene solubility(7.50%), and Lignin(9.60%).
5. The chemical structure of the Straw, which distinguishes it from other organic materials
makes the Straw a good earth material stabilizer.
6. Differences in the stabilizer type contributed significantly to the differences in the mean
compressive strength (F = 2473.157; P < .000) and erosion resistance capacity (F =
7239.684; P <.000) of the stabilized earth material.
7. The combined interaction effects of differences in the stabilizer type, changes in the soil
type and variation in the mix proportion significantly effects the mean compressive
strength (F = 14.136; P < .000) the mean erosion resistance capacity (F = 95.435; P < .001)
of stabilized earth material.
8. Red soil stabilized with a combination of RHA-Straw at a mix proportion of 20 per cent
(1:1:8) produced the optimal compressive strength( χ = 4.82 ±0.023) and erosion
resistance capacity (χ = 6.82 ± 0.02) of the stabilized earth material.
140
9. A mix proportion of 20 per cent (1:1:8) with a composite RHA-Straw stabilizer based on
red soil optimizes the use of RHA and Straw as stabilizing agents for earth building
construction.
10. Earth material stabilization improves the structural qualities of the earth material in terms
of its compressive strength and erosion resistance capacity, reflecting the interactions
effects of differences in the type of stabilizer, variations in mix proportions and changes
in soil type.
11. The outcome of this research has produced a curriculum material for teaching/learning of
earth material construction technology in colleges.
Implications of the Study
The findings of this research represent an important contribution to other ongoing efforts to
develop alternative, cheaper and sustainable sources of building materials for producing quality
low-cost houses for Nigerians. The result of this study has produced a quality material for
incorporation in Nigerian school curriculum for teaching earth building construction in Nigerian
colleges. As the cost of major building materials continues to rise, without a proportionate
increase in the real-income of the average Nigerian, the findings of this research represents some
relief for the prospective house owner who cannot afford the cost of some building materials
classified as standard. The findings of this research will create an open door for actualizing one of
the key objectives of the Nigerian government‟s NEEDS programme and the 7-Point agenda,
focused towards provision of quality shelter for all Nigerians.
The outcome of this research will also challenge the expertise of both practitioners and
researchers in earth building practices to look inwards in their search for ways and means of
developing alternative cheaper sources of quality building materials. The commercialization of
the major findings of this research will translate waste (rice husk and straw) into wealth and
create avenues for self-help approach to providing quality low-cost houses for Nigerians.
141
Conclusions
Concerted efforts have been made in this research to re-establish the efficacy of these two
locally available earth materials stabilizers(additive) – RHA and Straw. This researcher has also
been able to establish that the interactions between the internal composition of the different
stabilizers with that of the soil types and the variations in the mix proportions impact and reflect
on the degree and extent of the compressive strength and erosion resistance capacity
development/improvement. This research generated quality data from the various experiments
followed with elaborate analysis that lead to definite conclusions. From the analysis this
researcher has been able to establish that interaction effects of differences in stabilizer type,
changes in the soil types and variations in the mix proportions reflect significantly on the
compressive strength and erosion resistance capacity development/improvement of stabilized
earth material.
The outcome of this study has established that the earth material stabilized with a
composite RHA-Straw stabilizer behave significantly different and better in their compressive
strength and erosion resistance qualities from those stabilized with RHA or Straw only. This
researcher through this detailed statistically based experimental investigation has succeeded in
developing an optimal mix proportion for the stabilizer and soil type based on varying mix
proportions that produces an optimal structural quality of the stabilized earth material for quality
low-cost buildings. Very importantly also the outcome of this study has produced a curriculum
material for teaching of earth building construction in colleges and industry. Having gone this far,
this researcher is evidently convinced that the objective of optimizing the use of RHA and Straw
for earth material stabilization has been achieved with red soil stabilized with RHA-Straw at 20%
[1:1:8] mix.
142
Recommendations
Based on the findings of this research, the researcher wishes to recommend that –
1. The outcome of this research be expanded through practical field/community
demonstrations in real life earth building practices beginning with simple building
structures to standard houses.
2. Nigerian earth building heritage, should be improved upon and accepted as one of the
most viable options to meet our countries yawning gap in the provision of quality human
shelter for the ever-growing human population.
3. Local methods of our earth material stabilization should be improved upon so that in turn
these improvements will reflect in the qualities of the Nigerian modern earth building
designs and construction.
4. Nigerian governments should create avenues through their NEEDS schemes, the 7-Point
Agenda and their millennium development goal programmes for wider community-based
demonstration of the efficacy of the products of this research in providing quality earth
building materials for quality earth building construction.
5. The various levels of the Nigerian government should practically begin to back-up their
policies of looking inwards to reduce the cost of house production in Nigeria by
incorporating quality earth building designs into the nation‟s housing schemes.
6. Researches into Nigerian earth-building heritage, preservation and development should
be given the right impetus in order to contribute effectively in the realization of the
country‟s millennium development goals.
7. The Nigerian Educational Research and Curriculum Development Council should
consider the result of the research as an important component of instruction in Nigerian
colleges.
143
Suggestions for Further Study
As a result of some of the limitations mentioned above and for the reason that action
researches such as this one is usually a progressive one, this researcher recommends that –
1. There should be a replication of this study at purely field-based demonstration and
analysis level under a government or agency sponsorship, to remove the inconveniences
of funding faced in this research and to give the findings greater impetus for durable
quality low-cost housing for Nigerians.
2. There should be a replication of this study based on the forest savannah region of Nigeria
where traditional wattle-and-daub earth building designs is the common practice, unlike
the rammed earth or adobe designs commonly found around the sahel savannah region –
the base-area of this research.
3. A further research on the other variables such as effects of water-cement ratio,
compaction method, effects of curing methods, bullet proofing quality of the stabilized
earth material and other durability factors should be undertaken on a detailed study as this
one.
144
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154
APPENDIX A
SOIL CLASSIFICATION BASED ON PARTICLES SIZES
155
Material Sizes of Particles Means of Field Identification
Gravel 6.00 - 2.00mm Coarse pieces of rock which are round, net or
angular
Sand 2.00 - 0.06mm Sand breaks down completely when dry. The
particles are visible to the naked eyes…
Silt 0.06mm - 0.002mm Particles are not visible to the naked eyes, but
slightly gritting to the fingers. Most lumps can be
molded but not rolled into threads
Clay Smaller than
0.002mm
Smooth and greasy to touch. Holds together when
dry and is sticky wet
Organic
matters
Up to 1cm long Spongy or stiggy in appearance. Has odour of
decayed wood.
(Culled from Bengtsson and Whitaker, 1998)
156
APPENDIX B
BASIC DATA ON CEMENT STABILIZED EARTH BLOCKS(CSEB)
157
Block characteristics Performance characteristics
Dry Compressive Strength at 28 days
(+10% after 1 year and +20% after 2 years)
4 to 6 Mpa = 40 to 60 kg/cm2
Wet Compressive Strength at 28 days ( 3 days
immersion)
2 to 3 MPA = 20 to 30 kg/cm2
Dry Bending Strength (at 28 days) 0.5 to 1 Mpa = 5 to 10 kg/cm2
Dry Shear Strength (at 28 days) 0.4 to 0.6 Mpa = 4 t0 6 kg/cm2
Water Absorption at 28 days ( after 3 days
immersion)
8 to 12% (by weight)
Apparent Bulk Density 1700 to 2000kg/m3
Energy Consumption (To be compared with kiln
fired (wire cut) bricks = 539 MJ and country
fired bricks = 1657MJ)
110MJ
(culled from DA Series #12, 2003)
158
APPENDIX C
FORMULAE FOR CALCULATING THE COMPRESSIVE STRENGTH AND THE
EROSION RESISTANCE OF THE STABILIZED EARTH BLOCKS
159
[CACULATIONS]
Formula 1. Compressive Strength (α) expressed as total load at crushing moment per square
area of contact or N/mm2.
Calculation: Compressive Strength(α) = Mpa
[where: Crushing Load(N) = load at which the block crumbles/crushes.
Effective Surface Area(mm) = the surface area of the block in direct
contact with the hardwood surfaces on the crushing machine].
Formula 2. Erosion Resistance Ratio (ERR) - represents a ratio of the rate at which the earth
blocks precipitates (mass loss) under the water spray (simulated rainfall) over time.
Calculation: Erosion Resistance Ratio [ERR] (χ) =
[where: Ed (Depth of Erosion) = Vb – Vc ; Vb = volume of block before the
water spray; Vc = volume of block after the water spray; T = total time of
water spray(simulated rain].
Effective Surface Area(mm)
mm)
Crushing Load (N)
Ed
T
160
APPENDIX D:
COMPREHENSIVE RECORD OF THE MEAN VALUES RESULTING FROM
THE 27 EXPERIMENTAL GROUP
161
S/N0 Experiment Group
Type of Stabilizer
Mix Proportion
Soil Type
Compressive Strength
(Mpa)
Erosion Resistance
Ratio(%)
1 EXPERIMENT [I]1 RHA 20% [1:4] Clayey Soil 2.72 7.45
2 EXPERIMENT [I]2 RHA 14.5% [1:6] Clayey Soil 2.49 8.27
3 EXPERIMENT [I]3 RHA 11% [1:8] Clayey Soil 2.41 8.42
4 EXPERIMENT [I]4 RHA 20% [1:4] Laterite Soil 3.51 7.80
5 EXPERIMENT [I]5 RHA 14.5% [1:6] Laterite Soil 3.24 8.31
6 EXPERIMENT [I]6 RHA 11% [1:8] Laterite Soil 2.81 8.79
7 EXPERIMENT [I]7 RHA 20% [1:4] Red Soil 4.20 7.48
8 EXPERIMENT [I]8 RHA 14.5% [1:6] Red Soil 3.56 7.56
9 EXPERIMENT [I]9 RHA 11% [1:8] Red Soil 3.37 8.09
10 EXPERIMENT [II]1 STRAW 20% [1:4] Clayey Soil 1.97 10.60
11 EXPERIMENT [II]2 STRAW 14.5% [1:6] Clayey Soil 2.13 8.95
12 EXPERIMENT [II]3 STRAW 11% [1:8] Clayey Soil 1.99 9.16
13 EXPERIMENT [II]4 STRAW 20% [1:4] Laterite Soil 2.44 10.81
14 EXPERIMENT [II]5 STRAW 14.5% [1:6] Laterite Soil 2.67 9.26
15 EXPERIMENT [II]6 STRAW 11% [1:8] Laterite Soil 2.34 9.45
16 EXPERIMENT [II]7 STRAW 20% [1:4] Red Soil 3.69 9.18
17 EXPERIMENT [II]8 STRAW 14.5% [1:6] Red Soil 3.34 9.03
18 EXPERIMENT [II]9 STRAW 11% [1:8] Red Soil 3.03 9.08
19 EXPERIMENT [III]1 RHA+STRAW 20% [1:1:8] Clayey Soil 3.32 7.12
20 EXPERIMENT [III]2 RHA+STRAW 14.5% [1:1:12] Clayey Soil 3.04 7.39
21 EXPERIMENT [III]3 RHA+STRAW 11% [1:1:16] Clayey Soil 2.89 7.89
22 EXPERIMENT [III]4 RHA+STRAW 20% [1:1:8] Laterite Soil 4.15 7.20
23 EXPERIMENT [III]5 RHA+STRAW 14.5% [1:1:12] Laterite Soil 4.05 7.86
24 EXPERIMENT [III]6 RHA+STRAW 11% [1:1:16] Laterite Soil 3.68 8.03
25 EXPERIMENT [III]7 RHA+STRAW 20% [1:1:8] Red Soil 4.82 6.81
26 EXPERIMENT [III]8 RHA+STRAW 14.5% [1:1:12] Red Soil 4.69 7.01
27 EXPERIMENT [III]9 RHA+STRAW 11% [1:1:16] Red Soil 4.52 7.14
162
APPENDIX E SCHEDULE OF THE RAW VALUES AND THE CALCULATED MEAN OF THE
COMPRESSIVE STRENGTH AND EROSION RESISTANCE RATIOS FROM THE
27 EXPERIMENTAL GROUPS OF THE STABILIZED EARTH BLOCKS
163
S/N0 Experimental Group
Type of Stabilizer
Mix Proportion
[%]
Soil Type Measured Parameters
Compressive
Strength (Mpa)
Erosion
Resistance Ratio(%)
Raw
Value
Mean
Value
Raw
Value
Mean
Value 1 EXPER.[I]1 RHA 20 [1:4] Clayey Soil 2.72 2.72 7.44 7.45
2.70 7.43
2.71 7.46
2.72 7.50
2.75 7.40 2 EXPER.[I]2 RHA 14.5 [1:6] Clayey Soil 2.43 2.49 8.26 8.27
2.52 8.26
2.49 8.29
2.53 8.28
2.49 8.26 3 EXPER.[I]3 RHA 11 [1:8} Clayey Soil 2.44 2.41 8.44 8.42
2.41 8.40
2.40 8.44
2.41 8.41
2.39 8.41 4 EXPER.[I]4 RHA 20 [1:4] Laterite Soil 3.52 3.51 7.79 7.80
3.48 7.80
3.52 7.79
3.52 7.82
3.53 7.80 5 EXPER.[I]5 RHA 14.5 [1:6] Laterite Soil 3.19 3.24 8.34 8.31
3.24 8.30
3.30 8.29
3.23 8.30
3.24 8.32 6 EXPER.[I]6 RHA 11 [1:8} Laterite Soil 2.81 2.81 8.80 8.79
2.78 8.78
2.85 8.78
2.81 8.80
2.80 8.78 7 EXPER.[I]7 RHA 20 [1:4] Red Soil 4.22 4.20 7.48 7.48
4.18 7.47
4.21 7.50
4.19 7.48
4.21 7.50 8 EXPER.[I]8 RHA 14.5 [1:6] Red Soil 3.56 3.56 7.55 7.56
3.56 7.55
3.55 7.56
3.54 7.55
3.55 7.58 9 EXPER.[I]9 RHA 11 [1:8} Red Soil 3.37 3.37 8.06 8.09
3.34 8.10
3.38 8.09
3.37 8.11
3.39 8.08 10 EXPER.[II]1 STRAW 20 [1:4] Clayey Soil 1.87 1.97 10.57 10.60
2.06 10.61
1.97 10.58
1.98 10.62
1.97 10.62 11 EXPER.[II]2 STRAW 14.5 [1:6] Clayey Soil 2.08 2.13 8.96 8.95
2.19 8.95
164
2.13 8.95
2.13 8.96
2.12 8.93 12 EXPER.[II]3 STRAW 11 [1:8} Clayey Soil 1.95 1.99 9.18 9.16
2.03 9.17
1.95 9.15
2.03 9.17
1.99 9.15 13 EXPER.[II]4 STRAW 20 [1:4] Laterite Soil 2.42 2.44 10.79 10.81
2.47 10.82
2.44 10.80
2.43 10.82
2.44 10.82 14 EXPER.[II]5 STRAW 14.5 [1:6] Laterite Soil 2.63 2.67 9.28 9.26
2.70 9.25
2.67 9.28
2.67 9.25
2.68 9.23 15 EXPER.[II]6 STRAW 11 [1:8} Laterite Soil 2.34 2.34 9.44 9.45
2.35 9.47
2.33 9.44
2.35 9.46
2.33 9.44 16 EXPER.[II]7 STRAW 20 [1:4] Red Soil 3.71 3.69 9.18 9.18
3.68 9.18
3.70 9.16
3.67 9.20
3.68 9.19 17 EXPER.[II]8 STRAW 14.5 [1:6] Red Soil 3.31 3.34 9.05 9.03
3.29 9.01
3.36 9.05
3.35 9.01
3.36 9.03 18 EXPER.[II]9 STRAW 11 [1:8} Red Soil 3.00 3.03 9.09 9.08
3.03 9.07
3.11 9.08
3.03 9.07
2.98 9.08 19 EXPER.[III]1 RHA & STRAW 20 [1:4] Clayey Soil 3.32 3.32 7.11 7.12
3.34 7.13
3.34 7.11
3.35 7.13
3.31 7.12
20 EXPER.[III]2 RHA & STRAW 14.5 [1:6] Clayey Soil 2.99 3.04 7.40 7.39
3.04 7.37
3.04 7,39
2.98 7.40
3.15 7.39
21 EXPER.[III]3 RHA & STRAW 11 [1:8} Clayey Soil 2.86 2.89 7.90 7.89
2.87 7.91
2.91 7.87
2.90 7.89
2.91 7.90
22 EXPER.[III]4 RHA & STRAW 20 [1:4] Laterite Soil 4.14 4.15 7.21 7.20
4.15 7.18
4.14 7.21
4.16 7.19
165
4.16 7.21
23 EXPER.[III]5 RHA & STRAW 14.5 [1:6] Laterite Soil 4.07 4.05 7.87 7.86
4.05 7.88
4.08 7.85
3.96 7.89
4.09 7.85
24 EXPER.[III]6 RHA & STRAW 11 [1:8} Laterite Soil 3.68 3.68 8.04 8.03
3.69 8.02
3.68 8.04
3.71 8.02
3.65 8.03
25 EXPER.[III]7 RHA & STRAW 20 [1:4] Red Soil 4.85 4.82 6.80 6.81
4.81 6.85
4.80 6.83
4.84 6.81
4.80 6.81
26 EXPER.[III]8 RHA & STRAW 14.5 [1:6] Red Soil 4.68 4.69 7.16 7.14
4.69 7.14
4.70 7.15
4.68 7.11
4.69 7.15 27 EXPER.[III]9 RHA & STRAW 11 [1:8} Red Soil 4.53 4.52 7.18 7.21
4.51 7.23
4.53 7.22
4.51 6.23
4.52 7.19
166
APPENDIX F
SCHEDULE OF THE UNIVARIATE ANALYSIS OF VARIANCE (UANOVA) OF
THE COMPRESSIVE STRENGTH DATA INCORPORATING THE DESCRIPTIVE
STATISTICS, TEST OF BETWEEN-SUBJECTS EFFECTS, POST-HOC TESTS AND
THE HOMGENEOUS SUB-SETS TESTS
167
APPENDIX G
SCHEDULE OF THE UNIVARIATE ANALYSIS OF VARIANCE (UANOVA) OF
THE EROSION RESISTANCE RATIOS INCORPORATING THE DESCRIPTIVE
STATISTICS, TEST OF BETWEEN-SUBJECTS EFFECTS, POST-HOC TESTS AND
THE HOMGENEOUS SUB-SETS TESTS
168
APPENDIX H:
CASE PROCESSING SUMMARY OF THE COMPRESSIVE STRENGTH AND
EROSION RESISTANCE AND STABILIZER MEANS
169
APPENDIX I
CROSS PROCESSING SUMMARY OF THE MEANS: IF STABILIZER = 1
170
APPENDIX J:
CROSS PROCESSING SUMMARY OF THE MEANS: IF SOIL TYPE = 1
171
APPENDIX K
CROSS PROCESSING SUMMARY OF THE MEANS: IF MIX PROPORTION = 1