Descriptives - University of Nigeria

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


PG/PhD/02/33841

DEPARTMENT OF VOCATIONAL TEACHER EDUCATION

(INDUSTRIAL TECHNICAL EDUCATION SECTION)


NOVEMBER, 2010

OPTIMIZATION OF RICE-HUSK-ASH AND STRAW AS STABILIZERS

FOR EARTH MATERIALS[MUD] FOR BUILDING CONSTRUCTION

by


PG/PhD/02/33841

A THESIS SUBMITTED TO THE




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




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

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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

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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.

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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.

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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

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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

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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

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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


23 Pairwise Comparisons Based on Soil Type (Dependent Variable: Compressive

Strength) 110

24 Multiple Comparisons Based on Soil Type (Dependent Variable: Compressive

Strength) 113


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


33 Pairwise Comparisons Based on Soil Type (Dependent Variable: Erosion Resistance)123

34 Multiple Comparisons Based on Soil Type (Dependent Variable: Erosion Resistance)123


36 Pairwise Comparisons Based on Mix Proportions (Dependent Variable: Erosion

Resistance) 125

37 Multiple Comparisons Based on Mix Proportions (Dependent Variable:

Erosion Resistance) 126



40 Descriptive Statistics on RHA+Straw (Dependent Variable: Compressive Strength)131

41 Descriptive Statistics on RHA+Straw (Dependent Variable: Erosion Resistance) 132

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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.

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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).

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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

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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

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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.

http://en.wikipedia.org/wiki/Cost

http://en.wikipedia.org/wiki/Quantitative

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


8. What is the effect of variations in mix proportions on the mean erosion resistance


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.


earth material as a result of the effect(s) of changes in the soil type.


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.


stabilized earth material as a result of the effect(s) of changes in the soil type.


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

http://en.wikipedia.org/wiki/Cost

http://en.wikipedia.org/wiki/Quantitative

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).

http://en.wiktionary.org/wiki/standard

http://en.wiktionary.org/wiki/standard

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


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


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%]


[11%]

Rice-Husk-Ash & Straw –Red Soil [14.5%]


[20%]


[11%]


[14.5%]


[20%]

Rice-Husk-Ash & Straw –Laterite

Soil [11%]


Soil [14.5%]


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


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


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)


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 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


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


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


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



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%


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


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


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%



13 EXPERIMENT [II]4 STRAW 20%[1:1: 4] Laterite Soil 10.81


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


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%


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


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


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 (%)


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


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


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


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 (%)


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


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



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


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


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


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 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


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


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


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


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


Source


Df

Mean Square

F

Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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)



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



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



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



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


Source


df

Mean Square

F

Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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




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



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



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


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


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


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



13 EXPERIMENT [II]4 STRAW 20%[1:1:4] Laterite Soil 10.81


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


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


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


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


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


Df

Mean Square

F

Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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)


Mean Difference

(I –J)



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




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)


Mean Difference

(I –J)

Std. Error



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



118


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


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


Df

Mean Square

F

Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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)


Mean Difference

(I –J)



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



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.


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)


Mean Difference

(I –J)

Std. Error



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



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


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


Df Mean Square

F Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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



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




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



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



125

was conducted. The result of this multiple comparison is presented on Table 37.


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


Source


df Mean Square

F Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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


Df Mean Square

F Sig.

Corrected Model

Intercept

Stabilizer

mixprop

soiltype



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


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


Red Soil 4.6880 .00837 5

Total 3.9260 .70379 15

11% Clayey Soil 2.9100 .03240 5


Red Soil 4.5200 .01000 5

Total 3.7040 .68088 15

Total Clayey Soil 3.0940 .18719 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


Red Soil 6.8200 .02000 5

Total 7.0467 .16990 15

14.5% Clayey Soil 7.3900 .01225 5


Red Soil 7.1420 .01924 5

Total 7.4667 .31227 15

11% Clayey Soil 7.8940 .01517 5


Red Soil 7.0100 .43652 5

Total 7.6447 .52309 15

Total Clayey Soil 7.4680 .33223 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



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


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.


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