Stabilization of Compressed Earth Blocks Using Different Additives

1

STABILIZATION OF COMPRESSED EARTH BLOCKS

USING DIFFERENT ADDITIVES

PROJECT REPORT

Submitted in partial fulfilment of the

Requirements for the award of the

Degree of Bachelor of Technology in Civil Engineering

of the University of Kerala

Submitted By

ARYA N.

ATHIRA RENCHEN

BLESS ANN VARGHESE

DIVYA VARKEY

SUMIN NATH MUKUNDAN K. K.

Guided By

Dr. BINDU J.

DEPARTMENT OF CIVIL ENGINEERING

COLLEGE OF ENGINEERING TRIVANDRUM

TRIVANDRUM - 16

2012-2013

2

DEPARTMENT OF CIVIL ENGINEERING

COLLEGE OF ENGINEERING TRIVANDRUM

TRIVANDRUM - 16

CERTIFICATE

This is to certify that this Project Report on Stabilization of compressed earth blocks using

different additives is a bonafide record of the work done by ARYA N., ATHIRA

RENCHEN, BLESS ANN VARGHESE, DIVYA VARKEY, SUMIN NATH MUKUNDAN

K. K. students of Civil Engineering, College of Engineering Trivandrum, in the partial

fulfilment of the requirements for the award for BTech Degree in Civil Engineering of the

University of Kerala.

Guided by Head of the Department

Dr. Bindu J. Prof. Jyothis Thomas Assistant Professor Professor

Department of Civil Engineering Department of Civil Engineering

College of Engineering College of Engineering

Trivandrum Trivandrum

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ACKNOWLEDGEMENT

We express our gratitude to our guide Dr. BINDU J., Asst. Professor, Department of Civil

Engineering, College of Engineering Thiruvananthapuram, for the expert guidance and

advice in completing the project.

We express our sincere thanks to Mrs. JYOTHIS THOMAS, Professor and Head,

Department of Civil Engineering, Prof. M. B. Joisy, U.G. Professor, Mrs. JAYA V., Staff

Advisor, Department of Civil Engineering Thiruvananthapuram, for their kind co-operation,

encouragement and help.

We would also wish to record our gratefulness to all our friends and classmates for

their help and support in carrying out this work successfully.

We thank God Almighty for blessing us in completing this report.

ARYA N.

ATHIRA RENCHEN

BLESS ANN VARGHESE

DIVYA VARKEY

SUMIN NATH MUKUNDAN K. K.

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CONTENTS

1. Introduction 1

1.1. Historical background 2

2. Literature review 3

3. Methodology 5

4. CSEBs 6

5. Raw materials 7

5.1. Soil 7

5.2. Stabilisers 8

5.2.1. Cement 8

5.2.2. China clay 9

5.2.3. Fly ash 9

5.2.4. Coir fibre 10

5.2.5. Charcoal 11

5.2.6. Cow dung 11

6. Preliminary investigations 11

6.1. Soil investigation 11

6.1.1. Field tests 11

6.1.1.1. Smell test 11

6.1.1.2. Touch test 12

6.1.2. Laboratory tests 12

6.1.2.1. Grain size analysis 12

6.1.2.2. Atterberg limits 12

6.1.2.3. Specific gravity determinations 13

6.1.2.4. Shear parameters 13

6.1.2.5. Optimum moisture content 14

6.2. China clay 14

6.3. Coir fibre 15

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6.4. Fly ash 15

6.4.1. Grain size distribution 15

6.4.2. Specific gravity 16

6.5. Cement

6.5.1. Standard consistency 16

6.5.2. Setting time 16

6.5.3. Compressive strength 17

7. Preparation of CSEBs 17

7.1. General 17

7.1.1. Soil 17

7.1.2. Water 17

7.1.3. Stabilisers 17

7.2. Methods of preparation 17

7.2.1. Quantity of constituents per block 18

7.2.2. List of stabilisers used 18

7.3. Procedure 19

7.3.1. Mixing 19

7.3.2. Compaction 19

7.3.3. Curing 19

7.3.4. Testing 19

7.3.4.1. Compressive strength test 19

7.3.4.2. Water absorption test 20

8. Observations 20

9. Analysis and interpretations of result 23

10. Conclusions 31

11. Limitations and scope for future study 31

12. References 32

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LIST OF FIGURES

1. Test moulds 6

2. China clay 9

3. Fly ash 10

4. Coir fiber 10

5. Charcoal 11

6. Grain size distribution curve for soil 12

7. Flow curve of soil 13

8. Graph for finding out the shear parameters of soil 14

9. Compaction curve of soil 14

10. Grain size distribution curve for china clay 15

11. Hydrometer analysis of fly ash 15

12. Grain size distribution curve for fly ash 16

13. CSEB test cubes 19

14. Compressive strength testing machine 19

15. Water absorption test 20

16. Compressive strength of CSEB with varying composition of soil, cement, china clay

and coir fiber 23

17. Compressive strength of CSEB with varying composition of oil, cement and fly ash

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18. Compressive strength of CSEB with varying composition of soil, cement, charcoal

and cow dung 24

19. Compressive strength of CSEB for the best combination of set c, f and d 24

20. Comparison of best combination of CSEB obtained with commercial CSEB brick 25

21. Percentage increase from 7th

day compressive strength for CSEB with varying

composition of soil, cement, china clay and coir fiber 25



composition of soil, cement and fly ash 26



composition of soil, cement, charcoal and cow dung 26


day compressive strength for best combination of CSEB

in terms of durability 27

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25. Compressive strength analysis of set C CSEB with varying cement content and

constant china clay content 27

26. Compressive strength analysis of set C CSEB with varying china clay content and

constant cement content 28

27. Compressive strength analysis of set F CSEB with varying cement content and

constant fly ash content 28

28. Compressive strength analysis of set F CSEB with varying fly ash content and

constant cement content 29

29. Compressive strength analysis of set D CSEB with varying cement content and

constant charcoal and cow dung content 29

30. Compressive strength analysis of set D CSEB with varying charcoal content and

constant cement and cow dung content 30

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LIST OF TABLES

1. Basic data on CSEB 6

2. Quantity of constituents per block for each set of block prepared 18

3. 7 day compressive strength test results of CSEB 20

4. Test results of durability test of CSEB 21

5. Test results of water absorption of CSEB 21

6. Test results of hand compacted form of commercial CSEB 21

7. Standard rates of items used 22

8. Rates of prepared CSEB 22

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ABSTRACT

Soil as a construction material has been used for thousands of years by civilizations all over the world.

Since the compressive strength of soil blocks is limited, additives were also used along with raw soil

to improve its properties. In recent years Compressed Stabilized Earth Blocks (CSEB) have emerged as

an alternative solution for the improvement of soil as a construction material. CSEB is compressed

hydraulically or manually using an earth block press. The present study is intended to analyse the

feasibility of improving the properties of CSEB using low cost additives which are locally available and

also ecofriendly. The main objective of the present study was to determine the optimum percentage

of stabilizers that could be used as an additive for the preparation of CSEBs with regard to strength,

durability, economy and availability of materials. The soil chosen for making compressed blocks was

the lateritic soil available locally. Stabilisers used for the study include china clay, coir fibre, fly ash,

charcoal and cow dung along with a small percentage of cement. Additives were added in different

percentages for the preparation of compressed blocks of 10cm x 10cm x 10cm size. Hand compaction

technique was adopted for the preparation of CSEBs using a standard proctor hammer. The soil was

mixed with 16% water, 4-6% cement and 4-6% stabiliser. The various stabiliser combinations used

were coir fibre – china clay, fly ash and charcoal-cow dung. The prepared cubes were cured for 2 days

in shade and were exposed to sun for 3 days. The cubes were tested at the end of 7th, 14th and 28th

day of casting to analyse their durability and 28th day compressive strengths. These cubes were also

checked for their percentage water absorption after 24 hours of immersion in water. After

conducting tests on compressed blocks with different additives it was found that the best proportion

in terms of strength, durability, water absorption and economy was the one which contained 88%

soil, 6% cement and 6% fly ash along with 16% of water. The compressive strength of hand

compacted blocks may be less than that of hydraulically compacted blocks. In order to examine the

variation in compressive strength due to method of compaction, two sets of cubes were also

prepared with composition as in the commercial standards. One set was compacted hydraulically and

the second set was hand compacted. It was found that the compressive strength of machine

compacted blocks is 1.72 times greater than that of hand compacted blocks. The above combination

also gave an average compressive strength of 4.81MPa at the end of 28th day, which is yet higher

than the 28th day strength of a commercial CSEB. The total cost incurred for the preparation of the

above combination was almost comparable to that of a commercial CSEB. Though the conclusion

arrived at is based on limited experimental work, the results are promising for the preparation of

CSEB on a large scale using fly ash which is a waste material generated in huge quantities from

thermal power plants. The recommendation of production of CSEB on a large scale using fly ash can

also address the waste disposal problem to a great extent.

Submitted by, Guided by,

Arya N. Dr. Bindu J.

Athira Renchen

Bless Ann Varghese

Divya Varkey

Sumin Nath Mukundan K. K.

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1. INTRODUCTION

Earth as a construction material has been used for thousands of years by civilizations

all over the world. Some of the oldest buildings on the planet were made of earth. Currently

it is estimated that one half of the world's population (approximately three billion people on

six continents) lives or works in buildings constructed of earth. Earth is a 100% eco-friendly

building material.

The practice of using cement as a construction material creates environmental hazards.

The limestone mining and different stages of cement manufacture cause hazardous

environmental impacts on air, water, soil and vegetation.

In recent years, earth is now backing in fashion as its ecological and aesthetic benefits

attract the attention of an increasing number of contemporary architects and eco-builders.

Industrial sectors devoted to earthen building are currently emerging as this sustainable

material wins over.

Compressed Stabilized Earth Blocks (CSEB) offer a great stride towards the

improvement of earth construction. CSEB is the raw earth stabilized and compressed

hydraulically or manually using an earth block press .The advantages of CSEB are in the

wait time for material, the elimination of shipping cost, the low moisture content, and the

uniformity of the block thereby minimizing, if not eliminating the use of mortar and

decreasing both the labour and materials costs.

This project report strives to prepare CSEBs with different stabilizers in different soil

compositions with different curing periods and suggest an optimum composition for CSEBs

with regard to durability, economy and availability of materials. It also offers a comparative

analysis with the prevailing block type.

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1.1 HISTORICAL BACKGROUND

Earth as a construction material has been used for thousands of years by civilizations

all over the world. Many different techniques have been developed; the methods used vary

according to the local climate and environment as well as local traditions and customs. As a

modest estimate it is thought that as many as 30% of the world’s population lives in a home

constructed in earth (Houben & Guillaud, 1994).

The first attempts for compressed earth blocks were tried in the early days of the 19th

century in Europe. The architect Francois Cointereaux precast small blocks of rammed earth

and he used hand rammers to compress the humid soil into a small wooden mould held with

the feet.

The first steel manual press which has been produced in the world in the 1950’s was

the CINVA-RAM press designed by engineer Raul Ramirez at the CINVA centre in Bogota,

Columbia. It was the result of a research programme for a social housing in Colombia to

improve the hand molded & sun dried brick (adobe). This press could get regular blocks in

shape and size, denser, stronger and more water resistant than the common adobe. Since

then many more types of machines were designed and many laboratories got specialized and

skilled to identify the soils for buildings. Many countries in Africa as well as South

America, India and South Asia have been using a lot this technique.

The soil, raw or stabilized, for a compressed earth block is slightly moistened, poured

into a steel press (with or without stabilizer) and then compressed either with a manual or

motorized press. CEB can be compressed in many different shapes and sizes. For example,

the Auram press 3000 proposes 18 types of moulds for producing about 70 different blocks.

Compressed earth blocks can be stabilized or not. But most of the times, they are stabilized

with cement or lime. Therefore, we prefer today to call them Compressed Stabilized Earth

Blocks (CSEB).

The input of soil stabilization allowed people to build higher with thinner walls, which

have a much better compressive strength and water resistance. With cement stabilization,

the blocks must be cured for four weeks after manufacturing. After this, they can dry freely

and be used like common bricks with a soil cement stabilized mortar.

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2. LITERATURE REVIEW

Compressed Stabilized Earth Blocks (CSEB) gives an option of energy efficient, cost

efficient and environmental friendly building material in the growing concern regarding

sustainable building materials and related environmental issues. Extensive studies have been

carried out to determine its performance for various applications. Stabilized earth blocks

(sometimes called rammed earth blocks) are made from soil mixed with stabilizing material

such as Portland cement, formed into blocks under high pressure, and cured in the shade.

Researchers have showed that compressed earth bricks demonstrate many advantages

compared to conventional burnt bricks. This study focuses on the comparative performances

of earth blocks using different stabilizers like Portland cement, fly ash, china clay, coir fiber,

charcoal and cow dung.

Dr. Robert M Brooks (2009) conducted strength tests on remoulded clay blended

with rice husk ash (rha) and fly ash. Cost comparison, stress strain behaviour,

unconfined compressive strength was studied. Brooks suggested a rha content of

12% and a fly ash content of 25% were recommended for strengthening the

expansive subgrade soil.

S. A. Naeini and S. M. Sadjadi (2009) conducted studies on unsaturated clayey

soils reinforced with randomly included waste polymer fibre. The samples were

subjected to direct shear. He observed significant improvement in the shear strength

parameters (C and φ) of soil. The reinforcement benefit increased with an increase in

fibre content.

Oluwole fakunle bamisaye (2011) studied the suitability and lime stabilization

requirement of some selected lateritic soil samples as pavement construction

materials. The samples were subjected to strength tests. He observed that the

plasticity indices were reduced; the compressive and shear strengths were improved.

Behzad kalantari and Bujang B. K. Huat (2009) conducted a laboratory study on

stabilizing peat soil using Ordinary Portland cement (OPC) as binding agent and

polypropylene fibres as additive. The result of strength tests show significant

strength improvement of stabilized peat soil through curing period.

Billong (2008) conducted experimental tests on earth blocks using calcined kaolinite

clay, and industrial slaked lime as stabilizer and laterite soil. He found that

increasing the percentage of lime increases the compressive strength of earth blocks.

Also increasing laterite-binder ratio decreases compressive strength and water

absorption.

Guettala et al (2002) describes the durability of lime stabilized earth blocks. They

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conducted durability test and freeze-thaw test on earth blocks using clay soil and

sand and lime as stabilizer. They concluded that by increasing the compacting stress

from 5 to 20 MPa, it will improve the compressive strength up to 70%. They also

found that water absorption and weight loss decrease with increasing of compacting

stress and lime content.

Mesbah et al (2004) studied about the development of a direct tensile test for

compacted earth blocks using sisal fibres as stabilizer and sandy slit soil. They used

direct tensile test to determine the tensile strength of compacted earth blocks. They

found that the use of natural fibre reinforcement can improve ductility in tension,

inhibition of tensile crack propagation after initial formation, and inhibition of

shrinkage cracking.

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3. METHODOLOGY

The main objective of the project was the preparation of CSEBs that are efficient in

terms of strength, durability and economy. The initial stage involved a brief analysis of

locally available stabilizers to assess their availability, performance and cost to help the

selection of appropriate ones for the study. Soil that has been used for block construction

was collected from CSEB factory. A sample of the raw soil was tested in the laboratory for

identifying various soil properties. Further the collected soil was filtered to two portions for

attaining a standard gradation of the mix.

Preparation of CSEBs was done utilizing hand compaction in metal moulds of size

10cm X 10cm X 10cm made for this particular purpose. The soil was mixed with water and

stabilizer in a particular proportion that was adopted from a commercial manufacturer and

the mix was pressed to the defined shapes compacted in three layer with 25 blows per layer,

using standard proctor hammer of 2.5kg and 45cm free fall. The concentration and

combination of stabilizers were then varied. Durability of these mud blocks was checked at

7days, 14 days and 28 days. Also these cubes were checked for their percentage water

absorption after keeping them immersed in water for 24 hours.

All the CSEB blocks were given an adequate curing by water and air for a period of

minimum five days. Results of the tests were studied to understand the effect of various

stabilizers, their combinations and concentrations on the properties of CSEBs.

The compressive strength of hand compacted blocks may be less than that of

hydraulically compacted blocks. In order to examine the variations in compressive strength

due to method of compaction, two sets of cube were also prepared with composition as in

the commercial standards. One set was compacted hydraulically and the second was hand

compacted. Their test results were compared with the CSEBs made with different

compositions.

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4. CSEBs

Compressed Stabilized Earth Block often referred to simply as CSEB, is a type of

manufactured construction material formed in a mechanical press that forms an appropriate

mix of clay, aggregate, stabilizer and water into a compressed block. Compaction of soil

using a press improves the quality of the material. Builders appreciate the regular shape and

sharp edges of the compressed earth block. Also the production of CSEB required moderate

to low skilled labour, since the CSEB manufacture is very simple.

The compressive strength of the blocks is improved by compaction. Due to the ease in

construction and low cost, CSEBs can be used in rural and urban contexts and can meet very

widely differing needs, means and objectives.

Its advantages include energy efficiency and eco-friendliness, cost efficiency,

management of resources etc.

These comparative studies reveal that CSEB deserve the same or better acceptance as

the common walling materials used. But to extend the use of CSEBs even to low-cost

housing even in rural areas, production techniques need to be further improved. This can be

achieved by considering the following carefully:

Optimising the proportions of soil and stabiliser, considering the characteristics of

soil.

Compactive effort to be applied to produce blocks that are dense and strong with

regular surfaces and edges.

Fig 1: Test moulds

Table 1: Basic data on CSEB [source: auroville earth institute]

PROPERTIES SYMBOL UNIT CLASS A

CLASS B

28 day dry compressive strength

(+20% after 1 year)

σ d 28 MPa 5-7 2-5

28 day wet compressive strength

(after 24 hours immersion)

σ w 28 MPa 2-3 1-2

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28 day dry tensile strength (on a

core)

τ 28 MPa 1-2 0.5-1

28 day dry bending strength β 28 MPa 1-2 0.5-1

28 day dry shear strength S 28 MPa 1-2 0.5-1

Poisson’s ratio µ - 0.15-0.35 0.35-0.50

Young’s Modulus E MPa 700-1000 -

Apparent bulk density Γ Kg/m3 1900-2200 1700-2000

Coefficient of thermal expansion - mm/ºC 0.010-0.015 -

Swell after saturation (24 hours

immersion)

- mm/m 0.5 – 1 1 - 2

Shrinkage (due to natural air

drying)

- mm/m 0.2 – 1 1 - 2

Permeability - mm/sec 1.10-5 -

Total water absorption - % weight 5 – 10 10 - 20

Specific heat C KJ/Kg ~ 0.85 0.65 - 0.85

Coefficient of conductivity Λ W/mºC 0.46 – 0.81 0.81 – 0.93

Damping coefficient µ % 5 - 10 10 - 30

Lag time (for 40 cm thick wall)

D H 10-12 5-10

Coefficient of acoustic

attenuation (for 40 cm thick wall

at 500 Hz)

- dB 50 40

Fire resistance * - - Good Average

Flammability * - - Poor Average

5. RAW MATERIALS

5.1. SOIL

The soil required to manufacture CSEBs is a soil consisting of minimum quantity of silt and

clay so as to facilitate cohesion. A few laboratory experiments can identify the soil required

for this purpose. The main properties to be examined are:

Grain size distribution, to know quantity of each grain size,

Plasticity characteristics, to know the plasticity of clays and silts,

Compressibility, to know the optimum moisture content, which will require the

minimum of compaction energy for the maximum density,

Cohesion, to know how the binders bind the inert grains.

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5.2. STABILISERS

Soils that do not possess the desired characteristics for a particular construction can be

improved by adding one or more stabilizers. Each stabilizer can fulfil one (or at the most

two) of the following functions:

Increase the compressive strength and impact resistance of the soil construction, and

also reduce its tendency to swell and shrink, by binding the particles of soil together.

Reduce or completely exclude water absorption (causing swelling, shrinking and

abrasion) by sealing all voids and pores, and covering the clay particles with a

waterproofing film.

Reduce cracking by imparting flexibility which allows the soil to expand and

contract to some extent.

Reduce excessive expansion and contraction by reinforcing the soil with fibrous

material.

The effect of stabilization is usually increased when the soil is compacted. Sometimes

compaction alone is sufficient to stabilize the soil, however, without an appropriate

stabilizer, the effect may not be permanent, particularly in the case of increased exposure to

water.

The stabilizers for the CSEBs were selected based on their efficiency (as obtained from

earlier studies), availability, economy etc. The selected stabilizers along with a brief

description are given below:

5.2.1. CEMENT

Soils with low clay contents are best stabilized with Portland cement, which binds

the sand particles and gravel in the same way as in concrete, that is, it reacts with the

water in the soil mixture to produce a substance which fills the voids, forming a

continuous film around each particle, binding them all together.

The reaction of cement and water (known as hydration) liberates calcium hydroxide

(slaked lime) which reacts with the clay particles to form a kind of pozzolanic

binder. If the clay content is too low the lime remains free. This can be remedied by

replacing a proportion (15 to 40 % by weighs) of the cement with a pozzolana,

which is usually cheaper than cement.

Just as in cement-sand mortars, soil-cement mixes become more workable by adding

lime. If the clay content is high, the additional lime reacts with it to further stabilize

the soil.

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The appropriate cement content will vary according to the aspects mentioned above.

A minimum of 5 % is recommended, while cement contents exceeding 10 % are

considered unsuitable, because of the high cost of cement.

Soil and cement must be mixed dry, and the water added and thoroughly mixed just

before use, as the cement begins to react with water immediately.

Once the cement has begun to harden, it becomes useless. Soil cement cannot be

recycled.

The more thoroughly the soil is mixed, the higher the ultimate strength, which is

obtained by compaction.

Portland cement is the stabilizer that provides the greatest strength as well as

resistance to water penetration, swelling and shrinkage.

5.2.2. CHINA CLAY

Fig 2: China clay

China Clay is also known as hydrated Aluminium Silicate. It is one of the purest of the

clays and it is composed mainly of the mineral kaolinite usually formed when granite is

changed by hydrothermal metamorphism. The soil has constant viscosity as well as low bulk

density and low moisture absorption. China clays have long been used in the ceramic

industry, especially in fine porcelains, because they can be easily moulded, have a fine

texture, and are white when fired. As far as the availability is not a problem, china clay can

be economic if it can impart sufficient strength.

5.2.3. FLY ASH

Fly ash usually refers to ash produced during combustion of coal and it comprises of fine

particles that rise with flue gases. Primary reason for using fly ash in soil stabilization is to

improve compressive strength and shear strength of soil.

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Fig 3: Fly ash

Other benefits of usage of fly ash in soil stabilization include higher resistance values,

reduction in plasticity, lower permeability, reduction of pavement thickness, elimination of

excavation –material hauling/handling, and base importation, aid compaction, provide “all-

weather” access onto and within project sites. Class C fly ash and Class F product blends

can be used in many geotechnical applications associated with highway construction such as

enhancing strength properties, stabilizing embankments, controlling shrink well properties

of expansive soils, acting as a drying agent to reduce soil moisture control to enhance

compaction etc. Class C fly ash is a very effective dying agent and is very capable of

reducing soil moisture content by 30 % or more. Moreover, the problem of safe disposal and

beneficial utilization of large quantities of fly ash by-products can be solved to a great

extend by using it as a soil stabilizer.

5.2.4. COIR FIBRE

Fig 4: Coir fiber

Coir is a versatile vegetable fiber which is found between the hard, internal shell and

the outer coat of coconut. As the natural fibers are generally cheap, locally available,

biodegradable and eco-friendly, use of this is recommended in civil engineering

construction practice. Coir fiber is produced in large quantities in South Asian countries

such as India, Sri Lanka, Indonesia, Philippines, etc. Coir fibers have got better mechanical

properties such as tensile strength and toughness. It is resistant to fungal and bacterial

decomposition. In spite of low cellulose content, coir fiber has a very close fiber structure

which account for its better durability compared to other natural fibers. Experiments

20

revealed that addition of coir as random reinforcing material increases strength and stiffness

of the soil.

5.2.5. CHARCOAL

Fig 5: Charcoal

Soil when mixed with charcoal has found to attain strength and stiffness. Soil

stabilization using charcoal is desirable considering the factors such as availability,

economy and eco-friendliness.

5.2.6. COW DUNG

Using cow dung for plastering and flooring of structures was an ancient practice in

South India. Cow dung is generally used as a soil stabilizer because it has been observed

that the addition of cow dung in soil will improve the compressive strength, permeability,

erosion resistance, resistance to water penetration and cracking of soil.

Cow dung improves the plasticity of clays and acts as a reinforcing agent reducing

concentrated cracks that can lead to breakage within the raw bricks.

6. PRELIMINARY INVESTIGATIONS

The purpose of preliminary investigation is to determine various properties of raw

materials which are necessary for the production of Compressed Stabilized Earth Blocks.

6.1. SOIL INVESTIGATION

Field tests as well as laboratory tests are adopted for finding out the properties. For

small scale works, finding out the properties by field tests is enough. But for large scale

production of Compressed Stabilized Earth Blocks laboratory analysis is always necessary.

6.1.1. FIELD TESTS

6.1.1.1. SMELL TEST

This test is performed to find out the presence of organic matters in the soil. For this,

the soil was smelled immediately after the sampling. If it smells musty it contains organic

21

matters. The soil sample didn’t have any musty smell, which indicated that the soil is

suitable for the production of Compressed Stabilized Earth Blocks.

6.1.1.2 TOUCH TEST

Remove the largest grains and crumble the soil by rubbing the sample between the

fingers and the palm of the hand. If it feels rough and has no cohesion when moist the soil is

sandy. If it feels slightly rough and is moderately cohesive when moistened the soil is silt.

If, when dry, it contains lumps or concretions which resist crushing and if it becomes plastic

and sticky when moistened the soil is clayey (Houben & Guillaud, 1994).

6.1.2. LABORATORY TESTS

6.1.2.1. GRAIN SIZE ANALYSIS

Grain size analysis was done to determine the size of grains which constitute the soil

and percentage of total weight represented by the grains in various size ranges. It was done

according to the IS 2720(part 4):1985. For analyzing the grain sizes mechanical analysis

was adopted which consists of two stages. Sieve analysis for the analysis of coarse grained

soil (particle size greater than 75 micron) and sedimentation analysis for fine grained soil

(particle size lesser than 75 micron). Hydrometer method was used for sedimentation

analysis. Finally a grain size distribution curve was drawn.

Fig 6: Grain size distribution for soil

Percentage of clay =2%

Percentage of silt =2%

Percentage of sand =86%

Percentage of gravel =10%

6.1.2.2. ATTERBERG LIMITS

Atterberg Limit tests were performed based on IS 2720(part 5):1985. These tests

were used for finding out the consistency limits of the fine grained soil such as liquid limit

0

20

40

60

80

100

0.001 0.01 0.1 1 10

% F

INER

SIEVE SIZE(mm)

GRAIN SIZE DISTRIBUTION CURVE

22

and plastic limit. The liquid limit is the water content in percentage, at which the soil has a

shear strength that it flows to close a groove of standard width for 1.25cm length when

jarred 25 times using standard liquid limit apparatus such as Casagrande’s apparatus. Plastic

limit is the water content at which the soil can be rolled into a thread of approximately 3mm

in diameter without crumbling.

Fig 7: Flow curve of soil

• Liquid Limit =40.9%

• Plastic Limit =25%

6.1.2.3. SPECIFIC GRAVITY DETERMINATION

Specific gravity determination test was performed based on the IS 2720(Part 3/Sec 2):

1980. Specific gravity is the ratio of the weight in air of a given volume of dry soil solids to

the weight of an equal volume off distilled water at 40C. It was determined using a

pycnometer.

Specific gravity of the soil =2.67

6.1.2.4. SHEAR PARAMETERS

Direct shear test was used to find out the shear parameters such as cohesion and angle

of internal friction. The shear stress at failure when plotted against the normal stress on the

sample results in a graph which can be very closely represented by a straight line. The

cohesion and the angle of internal friction of the soil are as follows.

39.5

40

40.5

41

41.5

42

42.5

43

1 10 100

Wat

er

con

ten

t (%

)

No. of blows

FLOW CURVE

23

Fig 8: Graph for finding out the shear parameters of soil

• Cohesion of the soil =0.075 kg/cm2

• Angle of internal friction of the soil =43.490

6.1.2.5. OPTIMUM MOISTURE CONTENT

Optimum moisture content is determined by conducting compaction test. For a given

soil and compaction process there exist optimum values of the moisture content which will

give the maximum value of the dry density.

Fig 9: Compaction curve of soil

• Optimum moisture content (OMC) =16.4%

• Maximum dry density =1.88 g/cc

6.2. CHINA CLAY

Selected china clay is having a plastic limit of the 25.5% and specific gravity 2.65.

Hydrometer analysis was also conducted to study the grain size distribution of the particle.

0

0.1

0.2

0.3

0.4

0.5

0.6

0 0.1 0.2 0.3 0.4 0.5

She

ar s

tre

ss (

kg/m

2)

Normal stress (kg/m2)

GRAPH FOR FINDING OUT THE SHEAR PARAMETERS

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

10 12 14 16 18

wat

er

con

ten

t (%

)

Dry density (g/cc)

COMPACTION CURVE

24

Fig 10: grain size distribution curve for china clay

• Percentage of silt =26%

• Percentage of clay =74%

6.3. COIR FIBRE

The selected fibers are having aspect ratio 131.11 with average length 118mm and

diameter 0.9mm.

6.4. FLY ASH

6.4.1. GRAIN SIZE DISTRIBUTION

Fig 11: hydrometer analysis of fly ash

0

20

40

60

80

100

120

0.001 0.01 0.1 1

% F

INER

SIZE OF SIEVE OPENING(mm)

HYDROMETER ANALYSIS

25

Fig 12: Grain size distribution curve for fly ash

• Percentage of silt= 100%

• Percentage of clay=0%

6.4.2. SPECIFIC GRAVITY

• Specific gravity of fly ash= 2.25

6.5. CEMENT

6.5.1. STANDARD CONSISTENCY

Standard consistency of cement paste is defined as the consistency which will permit the

Vicat plunger to penetrate to a point 5 to 7 mm from the bottom of the Vicat mould when the plunger

is lowered to touch the surface of the test block. The consistency of cement paste is standardized

by varying the water content until the paste has a specific resistance to penetration. Standard

consistency test was performed according to IS: 4031(Part-4)-1988

• Standard consistency of the cement= 35%

6.5.2. SETTING TIME

In the beginning of the process of hydration of cement, the paste loses the fluidity

and within a few hours, noticeable stiffening results. This is called initial setting. Further

build up of hydration process is followed by commencement of the hardening process,

responsible for the strength concrete which is known as the final set. Initial setting time is

the time required by which needle of standard dimensions fails to pierce the block beyond 5

mm measured from the bottom of the Vicat mould. Final setting time is the time required by

which needle of standard dimensions makes an impression while annular attachment fails to

do so in a Vicat mould. Setting time of the cement was performed according to IS 4031(Part

5)-1988

• Initial setting time of the cement= 45 minutes

• Final setting time of cement= 9 hours

0

20

40

60

80

0.001 0.01 0.1 1

% F

INER

SIZE OF SIEVE OPENING(mm)

HYDROMETER ANALYSIS

26

6.5.3. COMPRESSIVE STRENGTH

The compressive strength of cement is the main property of the material needed in

the structural design. Strength of cement is usually determined by conducting compression

test on cement mortar cubes. Compressive strength testing was according to IS: 4031 (Part

6)-1988

• Average compressive strength= 15 N/mm2

7. PREPARATION OF CSEBs

7.1. GENERAL

The constituents of CSEB are:-

1. Soil

2. Water

3. Stabiliser

7.1.1. SOIL

The soil used for the preparation of CSEBs was obtained from an earth block

manufacturing unit at Kollankonam, Thiruvananthapuram. The soil obtained was lateritic.

This soil sample was first passed through a 15mm sieve. The soil particles retained were

then ground and passed through 6mm sieve. Thus two sets of soil, one between the size

ranges 15mm-6mm and the other less than 6mm.

7.1.2. WATER

The addition of water served in the hydration of cement in the blocks and also to

obtain a mix of desired workability.

The amount of water required to be added was found out by calculating the Optimum

Moisture Content (OMC) of the soil.

7.1.3. STABILISERS

Based on the standards used in the commercial manufacturing unit and from the

references in the journals, the amount of stabilizer used per block was fixed between 4%-6%

of the total weight of each block. The variation in the concentration of the stabilizer was

made to study the effect of this variation in the strength amongst the blocks. Various

combinations of stabilizers were used; the details of which are explained in the later

sections.

7.2. METHOD OF PREPARATION

The CSEBs were prepared by hand compaction using a standard proctor hammer of

2.5kg weight with a free fall of 45cm.

27

7.2.1. QUANTITY OF CONSTITUENTS PER BLOCK

The percentages by weight of various components used were:-

Soil - 90%

Of the total soil used:

Coarse soil (6-15mm) - 33%

Fine soil (<6mm) - 67%

Stabilisers - 4-6%

Cement - 6-4%

Table 2: Quantity of constituents per block for each set of block prepared

7.2.2. LIST OF STABILISERS USED

China clay

Coir fibre

Fly ash

Charcoal

Cow dung

S.

No

SET SOIL CEMENT ADDITIVES

Weight

(g)

% Weight

(g)

% Name of additive Weight

(g)

%

1. C C1 2200 88 150 6 China Clay 150 6

Coir Fibre 5.3

C2 2250 90 100 4 China Clay 150 6

Coir Fibre 5.3

C3 2300 92 100 4 China Clay 100 4

Coir Fibre 5.3

2. F F1 2200 88 150 6 Fly ash 150 6

F2 2250 90 100 4 Fly ash 150 6

F3 2300 92 100 4 Fly ash 100 4

3. D D1 2200 85.28 150 5.81 Charcoal 150 5.81

Cow dung 80 3.10

D2 2250 87.21 100 3.88 Charcoal 150 5.81

Cow dung 80 3.10

D3 2300 89.15 100 3.875 Charcoal 100 3.875

Cow dung 80 3.10

28

Fig 13: CSEB test cubes

7.3. PROCEDURE

7.3.1. Mixing

The coarse and finely ground soil sample along with stabiliser and cement were

thoroughly mixed manually at first. Water was then added to this and was then mixed again.

7.3.2. Compaction

This mix was then filled in the mould in 3 equal layers with each layer being

compacted 25 times with the standard proctor hammer to achieve a density of 0.025kg/cm3.

7.3.3. Curing

The prepared blocks were sprinkled with water for 3 days and then were kept under

shade for 2 days.

7.3.4. Testing

7.3.4.1 Compression strength test

Fig 14: compressive strength testing machine

29

The blocks thus prepared and cured were then tested for compressive

strength in the compression testing machine of capacity 3000kN at a rate of loading

140kgf/cm2/min. The specimen was placed between two plywood sheets and centred

carefully between the plates of the testing machine. The maximum load at failure was noted

from which the compressive strength was calculated.

7.3.4.2 Water absorption test

Casted cubes were cured properly, weighed and immersed in water for 24

hrs. Wet weight is taken and percentage water absorption is determined.

Fig 15: water absorption test

8. OBSERVATIONS

The results obtained are

Table 3: 7 day compressive strength test results of CSEB

COMPRESSIVE STRENGTH

RESULTS

Set 7 day compressive

strength (MPa)

C

C1 2.06

C2 1.197

C3 0.608

F

F1 1.99

F2 0.795

F3 1.226

D

D1 1.158

D2 1.02

D3 0.991

30

Table 4: Test results of durability test of CSEB

DURABILITY RESULTS

Set 7 day compressive

strength(MPa)

14 day compressive

strength(MPa)

28 day compressive

strength(MPa)

C

C1 2.06 2.158 2.354

C2 1.197 1.472 1.687

C3 0.608 0.657 1.246

F

F1 1.99 2.55 2.796

F2 0.795 1.668 1.766

F3 1.226 1.275 1.226

D

D1 1.158 1.324 1.373

D2 1.02 1.128 1.158

D3 0.991 1.094 1.192

Table 5: Test results of water absorption test of CSEB

SET % Water Absorbed

C C1 21.2

C2 21.4

C3 21.58

F F1 18.5

F2 20.52

F3 18.79

D D1 19.8

D2 18.81

D3 20.1

Table 6: Test results of hand compacted form of commercial CSEB

TEST RESULTS OF HAND COMPACTED

FORM OF COMMERCIAL CSEB

7th day compressive strength 1.525



Water absorption 13.5

28th

day compressive strength result of machine compacted commercial block =

4.361 MPa

Hence a factor of 4.361/2.534=1.72 is applied on 28th

day compressive strength

on other sets of blocks

Cost of one commercial block= Rs 16.

31

Table 7: Standard rate of items used

Sl. No Item Rate (Rs)

1. Cement 325/ 50kg

2. Coir Fibre 17.50/ kg

3. China Clay 4/ kg

4. Fly ash 5/ kg

5. Cow dung 1.56/ kg

6. Charcoal available as free waste

7 Soil 0.85/kg

8 Labour cost 1.77/brick

Table 8: Rates of prepared CSEB

SET Constituent per block Cost (Rs) Total Cost per

Block including

labour

charges(Rs)

Cost per brick

as per size

22.5X12.5X10

cm3 Material Weight (kg)

C C1 Soil 2.2 1.87 5.308 14.86

Cement 0.150 0.975

Coir Fibre 0.0053 0.093

China Clay 0.150 0.6

C2 Soil 2.25 1.9125 5.025 14.07

Cement 0.100 0.65

Coir Fibre 0.0053 0.093


C3 Soil 2.3 1.95 4.863 13.61

Cement 0.100 0.65

Coir Fibre 0.0053 0.093


F F1 Soil 2.2 1.87 5.365 15.02

Cement 0.150 0.975

Fly Ash 0.150 0.75

F2 Soil 2.25 1.9125 5.0825 14.23

Cement 0.100 0.65

Fly Ash 0.150 0.75

F3 Soil 2.3 1.95 4.870 13.63

Cement 0.100 0.65

Fly Ash 0.100 0.5

D D1 Soil 2.2 1.87 4.74 13.27

Cement 0.150 0.975

Charcoal 0.150 Free

Cow dung 0.08 0.125

D2 Soil 2.25 1.9125 4.4574 12.48

Cement 0.100 0.65

Charcoal 0.150 Free

Cow dung 0.08 0.125

D3 Soil 2.3 1.95 4.495 12.58

Cement 0.100 0.65

Charcoal 0.100 Free

Cow dung 0.08 0.125

32

9. ANALYSIS AND INTERPRETATION OF RESULTS

Fig 16: Compressive strength of CSEB with varying composition of soil, cement, china clay and coir

fiber

Among the set C CSEB, C1 composition has the highest compressive strength of 2.354

MN/m2.

Coir fibre added will act as a reinforcement between the soil particles

Fig 17: Compressive strength of CSEB with varying

Composition of soil, cement and fly ash

Among the set F CSEB, F1 has the highest compressive strength of 2.796 MN/m2.

0

0.5

1

1.5

2

2.5

0 7 14 21 28

CO

MP

. ST

R(M

N/m

2

NO OF DAYS

COMPRESSIVE STRENGTH OF SET C

c1

c2

c3

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30

CO

MP

STR

(MN

/m2 )

NO. OF DAYS

COMPRESSIVE STRENGTH OF SET F

F1

F2

F3

33

Fig 18: Compressive strength of CSEB with varying composition of soil, cement, charcoal and cow

dung

Among the set D CSEB, D1 has the highest compressive strength of 1.373 MN/m2.

Cow-dung when added to CSEB improves plasticity of clays, reduces green

breakage but higher the cow-dung content in bricks, the lower is their strength and

density, and higher is the water absorption.

Fig 19: Compressive strength of CSEB for the best combination of set C, F and D

Comparing the compressive strength of CSEB for the best combination of set C, F and D, F1

has the maximum compressive strength of 2.796 MN/m2.

0.5

0.8

1.1

1.4

1.7

2

2.3

2.6

2.9

3.2

0 5 10 15 20 25 30

CO

MP

STR

(MN

/m2)

NO.OF DAYS

MAXIMUM COMPRESSIVE STRENGTH

C1

F1

D1

0.7

0.9

1.1

1.3

1.5

1.7

0 5 10 15 20 25 30

CO

MP

STR

(MN

/m2 )

NO OF DAYS

COMPRESSIVE STRENGTH OF SET D

D1

D2

D3

34

Fig 20: Comparison of best combination of CSEB obtained with commercial CSEB brick.

F1 block gives better results than commercial blocks in terms of compressive strength

Fig 21: Percentage increase from 7th day compressive strength for CSEB with varying composition

of soil, cement, china clay and coir fiber

On comparing the percentage increase of compressive strength for set C, we can infer that

C3 has the highest percentage increase of compressive strength.

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30

CO

MP

STR

(N

/mm

2)

NO OF DAYS

COMPARISON OF COMPRESSIVE STRENGTH

C1

F1

test brick

0

20

40

60

80

100

120

10 15 20 25 30

% IN

CEA

SE F

RO

M 7

th D

AY

CO

MP

ST

REN

GTH

NO OF DAYS

% INCREASE FROM 7th DAY COMPRESSIVE STRENGTH FOR SET C

C1

C2

C3

35


of soil, cement and fly ash

On comparing the percentage increase of compressive strength for set F, we can infer that F2

has the highest percentage increase of compressive strength


of soil, cement, charcoal and cow dung

On comparing the percentage increase of compressive strength for set D, we can infer that

D3 has the maximum percentage increase of compressive strength

When the charcoal composition is decreased, a steep increase in durability is observed.

0

20

40

60

80

100

120

140

10 15 20 25 30

% IN

CEA

SE F

RO

M 7

th D

AY

CO

MP

ST

REN

GTH

NO. OF DAYS

% INCREASE FROM 7th DAY COMPRESSIVE STRENGTH FOR SET F

F1

F2

F3

0

5

10

15

20

25

10 15 20 25 30

% IN

CEA

SE F

RO

M 7

th D

AY

CO

MP

ST

REN

GTH

NO OF DAYS

% INCREASE FROM 7th DAY COMPRESSIVE STRENGTH FOR SET D

D1

D2

D3

36

Fig 24: Percentage increase from 7th day compressive strength for best combination of CSEB in

terms of durability

On comparing the percentage increase from 7th day compressive strength for best

combination of CSEB in terms of durability, F2 is more durable

Charcoal does not contribute much to compressive strength of the blocks.

Fig 25: Compressive strength analysis of set C CSEB with varying cement content and

constant china clay content

From the graph, we can infer that on increasing the amount of cement with constant

amount of china clay, compressive strength increases. This implies that cement

imparts more compressive strength.

0

50

100

150

10 15 20 25 30

% IN

CEA

SE F

RO

M 7

th D

AY

CO

MP

ST

REN

GTH

NO OF DAYS

MAXIMUM % INCREASE FROM 7th DAY COMPRESSIVE STRENGTH

C3

F2

D3

0

0.5

1

1.5

2

2.5

0 5 10 15 20 25 30

CO

MP

R S

TR (

N/m

m2

)

NO OF DAYS

CONSTANT CHINA CLAY VARYING CEMENT

C1

C2

37

Fig 26: compressive strength analysis of set C CSEB with varying china clay content and

constant cement content

On increasing the percentage of china clay composition with constant cement

content, compressive strength increases abruptly

Fig 27: compressive strength analysis of set F CSEB with varying cement content and

constant fly ash content

Compressive strength varies directly with the cement content.

0

0.5

1

1.5

2

0 5 10 15 20 25 30

CO

MP

R S

TR (

N/m

m2)

NO OF DAYS

CONSTANT CEMENT VARYING CHINA CLAY

C2

C3

0

0.5

1

1.5

2

2.5

3

0 5 10 15 20 25 30CO

MP

R S

TR (

N/m

m2)

NO OF DAYS

CONSTANT FLY ASH VARYING CEMENT

F1

F2

38

Fig 28: compressive strength analysis of set F CSEB with varying fly ash content and

constant cement content

From the graph we can infer that the compressive strength of F3 remains almost

constant

In F2, even though initial 7day compressive strength is comparatively low, yet

attains a higher value in 28day compressive strength.

This implies that fly ash contributes more to compressive strength but the attainment

of compressive strength is slow compared to cement.

Fig 29: Compressive strength analysis of set D CSEB with varying cement content and

constant charcoal and cow dung content

Compressive strength varies proportionally with the variation of cement content.

0

0.5

1

1.5

2

0 5 10 15 20 25 30

CO

MP

R S

TR (

N/m

m2)

NO OF DAYS

CONSTANT CEMENT VARYING FLY ASH

F3

F2

0

0.5

1

1.5

0 5 10 15 20 25 30

CO

MP

R S

TR (

N/m

m2)

NO OF DAYS

CONSTANT CHARCOAL VARYING CEMENT

D1

D2

39

Fig 30: Compressive strength analysis of set D CSEB with varying charcoal content and

constant cement and cow dung content

Keeping all other constituents constant, by changing the amount of charcoal there is

no significant change in compressive strength.

That is, charcoal does not impart much to compressive strength properties but it can

be used as filling material, reducing the amount of soil used per block.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 5 10 15 20 25 30

CO

MP

R S

TR (

N/m

m2)

NO OF DAYS

CONSTANT CEMENT VARYING CHARCOAL

D2

D3

40

10. CONCLUSIONS

Of the best combinations of each set, F1 has highest compressive strength,

satisfactory durability and least water absorption.

Comparing with the compressive strength of commercial bricks, F1 has highest

compressive strength than commercial CSEB and then comes the C1.

Cost of F1 is Rs 15/- while that of commercial block is Rs 16/-.

On addition of china clay and fly ash, compressive strength increases considerably.

Even though fly ash gives best results, attainment of compressive strength in fly

ash bricks is a slow process.

11. LIMITATIONS AND SCOPE FOR FUTURE STUDY

Since manual compaction was given, there was a chance of non uniformity in the

compaction efforts.

Since round bottom hammers were used, there is a chance of non uniformity at the

edges as the mould had straight edges.

In the case of set C blocks, strength could be varied by varying the curing period.

Hence there is scope for further study in variation of strength with curing time.

Since the actual size of blocks is scaled down to 10x10x10cm, there are chances of

variations in the results from the actual values.

41

12. REFERENCES

1. Behzad Kalantari, Bujang B.K. Huat, 2009, Effect of Fly Ash on the Strength values

of Air Cured Stabilized Tropical Peat with Cement, Electronic Journal of

Geotechnical Engineering, V14N, Scopus.

2. Guettala A., A. Abibsi and H. Houari, 2006. Durability study of stabilized earth

concrete under both laboratory and climatic conditions exposure. Construction and

Building Materials, 20(3): 119-127.

3. Mesbah A., J. C. Morel P. Walker, K. Ghavami, 2004. Development of a Direct

Tensile Test for Compacted Earth Blocks Reinforced with Natural Fibres. Journal of

Materials in Civil Engineering, 16(1): 95-98.

4. Naeini S. A., S. M. Sadjadi, 2009. ” Effect of Waste Polymer Materials on Shear

Strength of Unsaturated Clays”, EJGE Journal, Vol 13: 1-12.

5. Oluwole fakunle bamisaye, 2011, “The Suitability and Lime Stabilization

Requirement of Some Lateritic Soil Samples as Pavement”, International Journal for

Pure and Applied Science and Technology, 2(1), pp. 29-46.

6. Robert M. Brooks.,2009.International Journal of Research and Reviews in Applied

Sciences ISSN: 2076-734X, EISSN: 2076-7366 Volume 1, Issue 3

7. IS: 4031(Part-4)- 1988

8. IS: 4031(Part-5)- 1988

9. IS: 4031(Part-6)- 1988

10. http://www.lime.org, 2001, “Using lime for soil stabilisation and modification”,

National lime association.

11. http://www.wikipedia.org

http://www.lime.org/

http://www.wikipedia.org/

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