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THE UNIVERSITY OF NAIROBIDEPARTMENT OF CIVIL AND CONSTUCTION ENGINEERING

AN INVESTIGATION INTO THE STRENGTH, DURABILITY AND COST PROPERTIES OF INTERLOCKING SOIL STABILIZED

BLOCKS (ISSBs)

DONE BY: F16/1340/2010

MUTINDA JOSEPH KIVUVA

A project submitted as a partial fulfilment for the award ofBACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015

ABSTRACTThe interlocking soil stabilized block technology has in the recent past been gaining momentum in the East African community, mostly in Uganda and Tanzania.

This project was aimed at investigating on the strength and durability properties of the straight rectangular double interlocking stabilized soil block. Apart from these two properties, this research project also aimed at looking into the cost of building using interlocking soil stabilized blocks as opposed to the conventional construction methods.

The results obtained in this research indicated that the ISSB has a 28 day compressive strength of about 2.0N/mm2 at 12% cement stabilization. The recommended strength at 28 days is 2.5N/mm2. The durability tests indicated that the ISSB absorbs about 4.9% of water at 28 days (at 12% cement stabilization) therefore meeting the limit which is set at 15%. The abrasion test gives an abrasion of 1.785% of material abraded at 28 days with 12% stabilization. A cost analysis indicated that the ISSB technology is way cheaper than the conventional block technology.

The recommendations given in order to improve the use of this technology are more government involvement, standardization of the ISSB building and testing methods and the inclusion of the ISSB technology in education curricula.

DEDICATION

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I dedicate this project to my mum Ms. Ruth Mutinda, my auntie Ms. Jemimah Mumo and to the beautiful twins Helen and Wambui, my lovely nieces.

ACKNOWLEDGEMENTS

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I would like to acknowledge my project supervisor, Eng. S K Mutua for the invaluable guidance and mentoring he took me through the entire period of the project. I would also like to thank Prof. Esther Obonyo of the University of Florida for introducing me into the area of low cost housing and interlocking block design, and her constant encouragement.

Special thanks to the entire team at the National Housing and Building Research Agency (NHBRA), Dar es Salaam, Tanzania for their invaluable lessons on Interlocking Soil Stabilized Block production and building design lessons.

Last but not least I would like to greatly appreciate the team at the University of Nairobi Civil Engineering Lab for their guidance and assistance.

TABLE OF CONTENTS

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CONTENTS.................................................................................................6LIST OF ACRONYMS................................................................................8LIST OF TABLES......................................................................................8LIST OF FIGURES....................................................................................91. INTRODUCTION............................................................................10

1.1 BACKGROUND INFORMATION...........................................................101.2 PROBLEM STATEMENT..............................................................111.3 OBJECTIVES..................................................................................111.4 METHODOLOGY........................................................................12X1.5 PROJECT SIGNIFICANCE....................................................................121.6 LIST OF FACILITIES/MATERIALS..........................................................13

FACILITIES..........................................................................................13MATERIALS.........................................................................................13

2 LITERATURE REVIEW......................................................................142.1 HISTORICAL BACKGROUND...............................................................142.2 OPERATING PRINCIPLES...................................................................142.3 TYPES OF INTERLOCKING SOIL STABILIZED BLOCKS..............................15

CLASSIFICATION ACCORDING TO MATERIAL COMPOSITION............................15CLASSIFICATION ACCORDING TO SHAPES AND SIZES....................................16

2.4 PRODUCTION................................................................................172.5 WALL CONSTRUCTION....................................................................172.6 BUILDING DESIGN..........................................................................182.7 ADVANTAGES OF ISSB...................................................................182.8 DISADVANTAGES OF ISSB...............................................................202.9 SOIL STABILIZATION.......................................................................202.11 LABORATORY TESTS....................................................................21

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TESTS ON THE SOIL SAMPLE...................................................................21TESTS ON THE ISSB............................................................................21

3 EXPERIMENTATION...............................................................................223.1 SAMPLE COLLECTION......................................................................223.2 PREPARATION................................................................................22

PREPARATION OF THE SOIL SAMPLE...............................................223.1 FIELD TESTS...................................................................................223.3 PREPARATION OF TEST BATCHES.............................................24

3.3.1 PREPARATION OF THE SOIL BLOCKS..............................................253.3.2 PREPARATION OF THE CONCRETE BLOCKS.....................................26

3.2 LAB TESTS...................................................................................26COMPRESSIVE STENGTH TEST........................................................26WATER ABSORPTION TEST.....................................................................27ABRASION TEST..............................................................................27

4.0 RESULTS, ANALYSIS AND DISCUSSION..............................................294.1 FIELD TEST RESULTS...................................................................29

4.1.1 HAND MOULDING TEST................................................................294.1.2 THREAD TEST............................................................................294.1.3 GLASS – JAR TEST......................................................................294.1.4 SHRINKAGE TEST.....................................................................31

4.2 LABORATORY TEST RESULTS...........................................................31BLOCK CRUSHING RESULTS...........................................................31WATER ABSORPTION TEST RESULTS..............................................42ABRASION TEST RESULTS...............................................................44

4.3 COST ANALYSIS.........................................................................455.0 CONCLUSION...................................................................................46

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LIST OF ACRONYMSISSB-Interlocking soil stabilized block

UN-United Nations

HSD-AIT-Human Settlements Division of the Asian Institute of Technology

TITR - Thailand Institute and Technological Research

RHA - Rice Husk Ash

OPC – Ordinary Portland Cement

NHBRA- National Housing and Building Research Agency

LIST OF TABLESTable 3.1 Mix Proportions for ISSB test batch................................................25

Table 4.1 Test results for the glass jar sedimentation test............................30

Table 4.2 Test results for the shrinkage test.................................................31

Table 4.1 Crushing results for 8% ISSB..........................................................32

Table 4.2 Crushing results for 10% ISSB........................................................34


Table 4.4 Crushing results for cement control...............................................38

Table 4.5 Water absorption test results.........................................................42

Table 4.6 Abrasion test results......................................................................44

LIST OF FIGURES

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Table 3.1 Mix Design for ISSB test batch.......................................................18

Table 4.1 Test results for the glass jar sedimentation test............................24

Table 4.2 Test results for the shrinkage test.................................................25

Table 4.1 Crushing results for 8% ISSB..........................................................26

Figure 4.1 Plot of Compressive Strength of ISSB against Age at 8% Stabilization...................................................................................................27





Table 4.4 Crushing results for cement control...............................................32

Figure 4.4 Plot of Compressive Strength against Age for Control..................33

Figure 4.5 Comparison of strengths of ISSBs at different stabilizations........34

Figure 4.6 Comparison of strengths of ISSBs to that of the cement control. .35

Table 4.5 Water absorption test results.........................................................36

Figure 4.7 Comparison of percentage of water absorbed to the percentage stabilization...................................................................................................37

Table 4.6 Abrasion test results......................................................................38

Figure 4.8 Percentage of material abraded against percentage of cement stabilization...................................................................................................39

Table 4.7 Cost Analysis..................................................................................40

LIST OF PLATES

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Plate 3.1: Sedimentation Bottle Setup

Plate 3.2 Shrinkage Limit setup.

Plate 3.2 Dimensions and general profile of the rectangular double interlocking block.

Plate 3.3 Rectangular type double interlocking ISSBs curing

Chapter 1

1. INTRODUCTION1.1 BACKGROUND INFORMATION

The UN Committee on Economic, Social and Cultural Rights recognizes everyone’s right to an adequate standard of living, including adequate housing. However, millions around the world live in life and health-threatening conditions, in overcrowded slums and informal settlements. These conditions do not uphold their human rights and their dignity. The epitome of the adequate housing problem is the African continent. Approximately 31% of adults from the sub-Saharan Africa didn’t have enough money to provide adequate housing for themselves and their families in the recent past (2010) [1].

Inadequate housing has been one of the biggest challenges faced by developing and middle-income economies all over the world. Due to the financial burden of providing adequate housing to the people, the low-income countries have been most hit by this problem. This coupled with the lack of technical know-how, an unfavorable political climate and even socio-economic setbacks have meant that the problem of inadequate housing has been unresolved to date.

Kenya, for instance, has 26% of its adult inhabitants unable to provide adequate housing for themselves and their families[2]. This percentage is much higher, however, in the urban areas. This has led to the mushrooming

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of slums in the outskirts of the city. Nairobi, for instance, is home to the largest slum in Africa-Kibera. Many other slums have also cropped up in the city.

The question that any stakeholder in the housing sector needs to address is ‘Is there anything that can be done to alleviate this problem?’ In order to address this question, however, one needs to appreciate the fact that the inadequate housing problem is one multi-dimensional aspect which needs to be looked at as so. The problem is technical,financial and socio-political.

The use of appropriate and readily available technology may be the solution to this problem. This project focused on the use of the interlocking soil stabilized soil block to solve the inadequate housing problem in Kenya.

1.2 PROBLEM STATEMENT

Many people in the country are unable to provide shelter for themselves and their families. The biggest challenge that these people face is that of the lack of sufficient funds.

The design of affordable and high quality houses is therefore important in alleviating the housing problem in the country. This project was aimed at investigating on the suitability of the interlocking soil stabilized block as a low cost material in the construction of these houses. The use of these blocks translates into the overall reduction of the cost of constructing a typical house significantly.

1.3 OBJECTIVES

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The objectives of this project were:

i) To investigate on the strength of the interlocking block.ii) To investigate on the durability of the interlocking block.iii) To compare the cost of construction of the ISSB to traditional

construction methods.

1.4 METHODOLOGY

In order to investigate into the properties of the ISSB the following was done:

i) Appropriate soil samples were collected. In this case red coffee soil.ii) Relevant soil tests were done to determine the applicability of this

soil in the production of the interlocking block. iii) Several interlocking blocks were produced using the manually-

operated interlocking machine.iv) In order to determine the strength of the blocks they were

subjected to compressive testing.v) In order to determine the relative durability of the block adverse

weather conditions were simulated in the lab with the block being introduced to water repeatedly to test on its resistance to corrosion in case of rain. The strength of the block was then determined after every exposure.

vi) In order to determine the cost of production of the interlocking block a comparison was done between the prices of materials used to make a unit of this block to that of materials used to make an equal size of the concrete block.

1.5 PROJECT SIGNIFICANCE

The impact of the use of the interlocking block is that many people across the country and even around the world will be able to access affordable and

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high quality structures for their shelter. The design of low cost housing units means that more families will be adequately housed.

This project also further encouraged the use of appropriate technology in order to solve the inadequate housing problem. This research is only a simple step towards the paradigm shift in the construction industry. This project is supposed to encourage potential home owners to embrace the idea of appropriate technology and use the readily available materials to provide shelter for themselves and their families.

1.6 LIST OF FACILITIES/MATERIALS

FACILITIES

The following facilities were needed:

i) Soil grading apparatusii) Soil shear strength determination apparatusiii) Soil shrinkage limit determination apparatusiv) Plastic limit determination apparatusv) Manually operated interlocking block press machine

MATERIALS

A list of the required materials is as below:

i) 80kg red coffee soil samplesii) 20kg grade 32.5 Ordinary Portland Cement

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iii) 30kg sand

Chapter 2

2 LITERATURE REVIEW2.1 HISTORICAL BACKGROUND

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Research activities in the area of the interlocking block technology date back to the 1960’s in Thailand, Malaysia and Philippines. This was in an attempt to solve the inadequate housing problem in their rural areas. Initially the Thailand Institute of Technological Research (TITR) made solid soil-cement blocks using the CINVA – Ram manual block press (developed in Colombia in 1956).

However, the soil-cement blocks developed then had a few disadvantages which were:

i) They were relatively heavy.ii) During construction certain masonry skills were requirediii) A lot of mortar was required for the joints and this increased the

cost of construction and also lengthened the time of construction significantly.

In order to take care of these problems, the Human Settlements Division of the Asian Institute of Technology (HSD-AIT) in Bangkok in co-operation with TITR developed the interlocking block technique in the early 1980s. The first demonstration house was constructed in 1984 in Thailand and between 1986 to 1992 the Post Graduate Centre for Human Settlements (PGHS) of Belgium assisted them to optimize the interlocking technique reaching a high degree of maturity.[4]

2.2 OPERATING PRINCIPLESThe blocks are shaped with projecting parts, which fits exactly into depressions in the blocks placed above, such that they are automatically aligned horizontally and vertically. The significance of this is that blocks can be dry stacked without the need for any mortar. However, it is advisable to have the blocks on the first few courses immediately after the substructure

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bound with mortar. The same is also recommended for the last few courses before the installation of the ring beam.

The fact that these blocks can be dry-stacked and their shape is such that they exactly fit on each other means that no special masonry skills is needed to lay these blocks.

Some blocks have vertical holes for:i) Reducing the unit weight of the block.ii) Inserting reinforcement such as steel rods or even bamboo.iii) Pouring liquid mortar (grout) for additional stability of the structure.

It is also important to note that the length of these blocks is usually exactly double its width. This is in order to achieve alignment of the blocks which are placed at right angles.

2.3 TYPES OF INTERLOCKING SOIL STABILIZED BLOCKS

There are many types of soil stabilized blocks depending on:

i) Material compositionii) Shapeiii) Size

The choice of which ISSB to use is influenced by the required use and also by the required strengths.

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CLASSIFICATION ACCORDING TO MATERIAL COMPOSITION.

The most common ones are the soil-cement blocks, the Rice Husk Ash (RHA) cement blocks and the concrete block.

The Soil-Cement Block

In the production of the soil-cement blocks, the cement : soil ratio ranges between 1:6 and 1:10[3]. Laboratory tests are therefore essential for the determination of the actual cement: soil ratio to be used for a particular type of soil.

The Rice Husk Ash Block

These blocks are produced by pressing a mixture of rice husk ash and cement. For the RHA cement blocks, the cement to RHA ratio is generally 1:4[4].

The Concrete Block

Typical cement to sand to gravel ratio is 1:5:3.

Lime is a good stabilizer for clays for it reacts to form strong bonds between the particles. Reaction is accelerated by other additives. At high curing temperature the cementing of the molecules is stronger. Lime also breaks the soil lumps making it easier to mix. Lime content to be used is between 4 to 8% of dry weight of soil.

Combined lime and cement used when the soil has too much clay and lime alone will not react enough to water proof it or make it strong. Lime makes the soil easy to work with and cement helps in strength gain.

Combination of lime with pozzolana (Rice Husk Ashes) – normally the lime will react with pozzolana (high content of silica) to make cement (almost as good as) Portland cement – OPC) but reaction is slow. This can be used for sandy and clayey soils.

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Combination of lime with pozzolana (Rice Husk Ashes) leads to the formation of cement as the lime reacts with the pozzolana(high silica content). The cement so formed is as good as Ordinary Portland Cement (OPC) but the reaction is slow. This procedure can be used for sandy and clayey soils.

CLASSIFICATION ACCORDING TO SHAPES AND SIZES

For all standard walls a size of 300 x 150 x 100 mm block is used. With this block one can do either a single brick or double brick thick wall.

Half blocks (150 x 150 x100mm) can either be moulded to size or made from cutting freshly moulded full blocks into three quarters.

Channels blocks are also available. They are of the same size as full, half and three quarters blocks, but a channel along the long axis into which reinforcements and concrete can be placed to form lintels or ring beams is available.

2.4 PRODUCTION

ISSB can be produced by compaction by hand or mechanically, depending on the shape, type of block, material used, required quality and available resources. They can be made at the building site or on a larger scale block yard. Soil cement blocks are commonly manufactured in manually operated block presses (modification of CINVA Rams).

Normally, two workers prepare the soil mix, shovel it into the mould and close the lid. Compaction is done by a third worker, who pulls down a long steel handle (lever arm), which pushes up the base plate. After opening the lid and ejecting the block, it is removed by a fourth worker and stacked under a shade for curing and hardening.

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In case of other materials, blocks need tamping and even vibrations for proper compaction. Manual tamping is done by jabbing the mix with a piece of wood or dropping the filled mould several times on a hard surface. After demoulding the blocks are carried away on pallets for curing.

2.5 WALL CONSTRUCTION

The first course is placed in a mortar bed, but before that, the blocks are laid dry on the foundation around the entire building in order to ensure that they fit exactly next to each other (leaving no gaps) and that an exact number of blocks is used. When laying the first course in the mortar bed, care must be taken that the blocks are perfectly horizontal and in a straight line or at right angles at corners.

Once the base course is hardened, the blocks are dry-stacked, with the help of a wooden or rubber hammer to knock the blocks gently in place. Up to 10 layers can be placed at a time before the grout holes are filled with liquid mortar (A cement to sand ratio of 1:3 is recommended, with 1 part water).

It is advisable to place channel blocks around the building at window sill height to install a ring beam. They should also be placed directly above door and window to install lintels and directly below the roof to finish the walls with a ring beam. In case of earthquake regions and in order to increase structural stability it advisable to insert steel rods or bamboo reinforcement in the vertical holes especially at corners, wall junctions and on either side of openings.

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The interlocking blocks are ideally suitable for load-bearing wall construction even for 2 or more storeyed building provided the height of the wall does not exceed 20 times its thickness and wall sections without buttresses or cross walls do not exceed 4.5m length (to prevent buckling).

Though less economic, non-load bearing constructions are more common, where the walls are infills between framed reinforced concrete (columns and beams) structure which supports the roof. Here care must be taken to achieve a good bond between the wall and framework.

2.6 BUILDING DESIGN

Any type of building can be constructed using the interlocking blocks. The main constraints being that the plan should be rectangular and all wall dimensions and opening must be multiples of the length of the block type used. The rest are the same as other standard building type.

However, there are new machines that can produce curved blocks hence solving the problem of always using rectangular dimensions.

2.7 ADVANTAGES OF ISSB

The stabilized soil blocks present the following advantages over conventional building materials:

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i) The material required for block production and building construction are usually locally available in most regions, therefore in areas in which timber is scarce and expensive, construction with interlocking blocks has environmental advantage (no deforestation, low energy requirement for block production and transportation).

ii) Unlike the case of timber constructions, termites cannot cause damage to the structure.

iii) Compared to the conventional masonry the dry assembly of the interlocking blocks saves construction time and a large amount of mortar, which would otherwise be required for horizontal and vertical joints.

iv) Without the need for high waged skilled masons (except for the base course) by saving cement (less mortar) and with the speed of construction the building costs are lower than for standard masonry

v) construction. Additional costs are saved by building load bearing walls instead of infill walls between a structural frame.

vi) The structural stability and durability of interlocking block construction can be far greater than for comparable timber constructions. Grout holes and channel blocks provide means of inserting steel reinforcement in vulnerable parts of a building for increased wind and earthquake resistance.

vii) Interlocking blocks can be produced on a small scale on the building site (for self-construction) or on a large scale in centralized production units.

viii) The interlocking block technique is suitable for the construction of multi-storeyed building in the same way as for standard masonry constructions.

ix) Interlocking cement stabilized blocks need less water for production and treatment.

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x) Very little cement is used in the production of a unit interlocking block. A 50kg bag of cement can produce between 100 to 150 blocks whereas it can only produce approximately 25 conventional concrete blocks.

2.8 DISADVANTAGES OF ISSB

Some of the disadvantages of stabilized soil blocks is as listed below

i) The technology is relatively new. People are therefore reluctant to apply it. Hence a well-coordinated dissemination strategy to introduce it to potential builders is vital.

ii) Although skilled masons are not needed for construction, a certain amount of training is required to ensure that the walls are properly aligned and no gaps are left.

iii) In the production of the blocks training is needed not only in determining the correct type of soil, correct mix proportion and moisture contents, but also in producing uniform sized blocks (that is, avoiding under or over-filling the block moulds before compaction)

iv) Even with the greatest care in assembling the walls, the joints are not entirely resistant to wind and rain penetration, therefore, plastering the interior wall surface is usually necessary.

2.9 SOIL STABILIZATION

Soil stabilization may be defined as any process aimed at improving the performance of a soil as a construction material.

All kinds of soil may be suitable for cement stabilization if they satisfy the following condition:-

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i) The combined percentage of clay and silt should not be less than 10% and not more than 40%.The recommended optimum fraction of silt and clay by United Nations is 25% of which the clay content should be more than 10% for an optimum results.

The clay is necessary to achieve sufficient green strength in a fresh formed block to enable de-moulding and handling without excessive breakage. The maximum size of soil grain is 5mm (rectangular sieve trough).

The physical properties of the used soil sample determine its ease of mixing, forming, demoulding, permeability, shrinkage, dry strength and apparent bulk density.

Chapter 3

3 EXPERIMENTATION3.1 SAMPLE COLLECTION

The samples needed for the project were grade 32.5 Normal Setting OPC, red coffee soil and sand.

The samples were obtained from the civil engineering materials lab.

3.2 PREPARATION

PREPARATION OF THE SOIL SAMPLE

The soil sample, as received from the field, was air-dried. The clods were broken with wooden mallet to hasten drying. Tree roots and pieces of bark were removed from the sample.

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Sieving was then done to remove over size materials from the soil samples using a wire mesh screen with aperture of about 6mm in diameter.

3.1 FIELD TESTS

These tests were conducted on the field. Some of them are described below:

i) Smell Test

This test was done to determine the presence of organic matter in the soil sample.

Organic matter usually hinders hydration of cement.

Organic materials are normally found at the top layer and therefore the top layer of the excavation site was scraped off before the sample was collected.

ii) Colour Appearance

Dark-brown crumby humus found in the soil (organic matter)was discarded.

Light brown to black colour indicated the presence of at least a small proportion of organic matter but can be suitable for stabilizing.

A reddish to dark brown colour indicated the presence of iron oxide which is acceptablefor soil stabilization purposes.

White to yellow colouring indicated the predominance of lime based compounds or sand and this can be stabilized.

Pale colouring is characteristic of the presence of clay which can be stabilized using lime or cement.

iii) Hand Moulding Test

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A soil sample with a maximum particle size of 6mm was moistened and formed into a cube with an edge of about 2.3cm.

If a cube is formed easily, a high clay content is present.

The moulded cube was allowed to dry out in the sun for one day.

iv) Thread Test

This is similar to the plastic limit test. The soil was formed into a thread upon the addition of some water to increase its plasticity.

v) Glass – Jar Test/ Sedimentation Bottle Test

This test gives a rough idea of the percentage of each fraction present – the test was done as follows:

- A clear glass bottle was used for this test- Particles greater than 10mm were removed from the sample- The bottle was filled to aquarter full with soil - Aquarter teaspoon of table salt was then mixed with water. Once the salt

was dissolved the mixture was emptied into the bottle.

- Water was added until the bottle was 2/3 full.

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- The contents of the bottle were then shaken thoroughly

- The contents were left to settle for 8 hours.- After eight hours the contents were again thoroughly shaken and left to

settle for another eight hours.

vi) Linear Shrinkage Test

A mould of dimensions 40 x 40 x 600mm was filled with soil near its liquid limit .The mould walls were greased so as to allow free movement of soil as it shrinks in size.

The difference between the final and initial length is the linear shrinkage. It is normally represented as a percentage of the original length.

Plate 3.1: Sedimentation Bottle Setup

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Plate 3.2 Shrinkage Limit setup.

3.3 PREPARATION OF TEST BATCHES

The ISSB test batches used for this research were the straight double interlocking block whose dimensions and general shape is as shown below:

Plate 3.2 Dimensions and general profile of the rectangular double interlocking block.

TheISSB test blocks were prepared in the following ratios:

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Table 3.1 Mix Design for ISSB test batch

Block Type Ratios

ISSB With 40% River Sand Cement: Soil: River Sand(1:5:3)Cement: Soil: River Sand(1:6:4)Cement: Soil: River Sand(1:7:5)

ISSB Without River Sand Cement: Soil(1:8)Cement: Soil(1:10)Cement: Soil(1:12)

The cement control block was prepared in the following ratio:

Cement:Sand(1:1.5)

The procedure for the preparation of the samples was done as follows:

3.3.1 PREPARATION OF THE SOIL BLOCKS

The clods within the soil sample were broken down using a wooden hammer in order to reduce their sizes. Care was taken not break the individual soil particles.

The soil sample was sieved using a sand screen in order to ensure a smooth finish as well as a uniform product which minimizes on the possibility of cracks on the block.

The soil sample was then mixed with the cement and the river sand in the appropriate ratios.

For the stabilized soil blocks the ratios of the various constituents was as tabulated on Table 3.1.

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The cement: water ratio for all the samples was at OMC which was generally determined through the gradual addition of water to the sample until it was easily workable.

The constituents of the above mixture were then thoroughly mixed to the extent that a uniform color was observed for the entire mixture.

The mixture was then fully compressed using the manual press machine to produce the interlocking blocks.

The so produced blocks were then left to cure in the open for 28 days. The strength of the blocks was monitored regularly on the 7th, 14th and 28th day and the results recorded.

Plate 3.3 Rectangular type double interlocking ISSBs curing.

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3.3.2 PREPARATION OF THE CONCRETE BLOCKS

The mix proportion for the concrete blocks was at Cement: Sand (1:1.5). The sand and the cement were thoroughly mixed, a little water added to make the mix workable.

The mix was then compressed using the manual press machine. The obtained block was then cured under water for 28 days. The strength of the blocks was constantly monitored regularly. The blocks were crushed on the 7th, 14th and 28th day and the results recorded.

3.2 LAB TESTS

These tests were carried out in the laboratory in order to compliment the field tests. They were necessary in order to provide accurate results on the suitability of the soil sample as well as the strength and durability of the ISSB.

Some of the lab tests carried out on the ISSB are:

i) Compressive strength testii) Durability Tests

COMPRESSIVE STENGTH TEST

This test was done to determine the compressive strength of the interlocking soil block.

The test was done by crushing the block using the cube crusher to determine its 7-day, 14-day and 28-day strength.

The results from this test gave a rough idea of the amount of loading that the block can withstand under working conditions before failure.

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A cement control block was also crushed in order to do a comparison of their strengths.

The results obtained for these tests are recorded for analysis purposes. These results are recorded in tables 4.1 through 4.4

WATER ABSORPTION TEST

One of the biggest enemy to ISSB is water. ISSBs are vulnerable to weather especially during rainy season as soil material can expand and loose cohesiveness, particularly with cement plaster.

Walls constructed out of ISSBs should have adequate compressive strength under dry conditions; however they will lose their strength under adverse moisture content. The amount of water absorption by an ISSB is thus of particular importance in this case.

The procedure for the determination of the water absorption by the ISSB is described below:

Two blocks were randomly selected from each group at 28 days and then weighed on a balance. These blocks were then immersed completely in water for 24 hours, after which they wereremoved and weighed again. The percentage of water absorbed by the blocks was estimated as follows:

W m=Ww−WdW d

×100

Where Wm=percentage moisture absorption

Ww=Weight of soaked ISSB

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Wd=Weight of dry ISSB

The results obtained from the water absorption test were tabulated for analysis purposes and are recorded in table 4.5.

ABRASION TEST

The abrasion test is one of the methods used to determine on the durability of the ISSB. A good quality ISSB should be able to resist abrasion as much as possible. The more an ISSB is abraded, the poorer is its quality and hence the less durable it is.

The procedure used for determining the abrasion of the ISSBs is as described below:

After the interlocking blocks had attained the age of 28 days, two blocks were selected at random and weighed in the laboratory and their weight recorded.The blocks were placed on a smooth and firm surface and then wire-brushed to and fro on all the surfaces for 50 times. One stroke for this case is considered as a combination of a to and fro motion on each surface.

After brushing, the blocks were weighed again to determine the amount of material or particles abraded. This procedure was then repeated for different cement contents.

The amount of material abraded was calculated as shown below:

Ma=Mi−MfMi

×100

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Where Ma= percentage of material abraded

Mi= initial mass of block

Mf=final mass of block

The values obtained from this experiment were then tabulated for analysis purposes.

Chapter 4

4 RESULTS, ANALYSIS AND DISCUSSION4.1 FIELD TEST RESULTS

4.1.1 HAND MOULDING TEST

The cube was easily formed in the hand moulding test.

A few surface cracks occurred on the surface of the cube. This was an indication of a high clay content fraction which may give similar cracking problems in the blocks.

In order to prevent such cracks occurring on the interlocking blocks, it was necessary to add 40% river sand to the soil sample used to make the test batch.

4.1.2 THREAD TEST

The rolled thread started breaking up at a diameterof less than 3mm.

This indicated that the fine content was too high. Too much fine content means that the block may start cracking due to the bulking and shrinking of clay as it gains and loses water respectively.

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In order to make the soil useful in making the interlocking blocks therefore, some river sand was added to increase the amount of silt in the sample. Too much sand however may lead to the splitting of the ISSB once produced. Therefore just the right amount of sand should be added. In this case about 40% sand was added to the soil sample.

After the addition of the sand the thread started breaking up at about 4mm diameter.

4.1.3 GLASS – JAR TEST

From the above test, the larger particles settled to the bottom whereas the fines settled at the top immediately after the larger particles with a clear distinction.

The fractions of each settled fraction were obtained as follows:

Table 4.1 Test results for the glass jar sedimentation test

SECTION LENGTH

Total Length of settled soil 11cm

Length of top layer 7.5cm

Length of bottom layer 3.5cm

Percentage of fines = Lengthof toplayerTotal lenght of settled soil×100

= 7.511 ×100

=68.18%

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Percentage of silt = Lengthof bottomlayerTotal lenght of settled soil×100

= 3.511 ×100

=31.82%

ANALYSIS

The above soil sample contained too much fines.

DISCUSSION

If silt and clay content > 40% then the soil sample is unsuitable for ISSB. This is because too much clay content leads to periodic bulking and shrinkage as water is introduced and as it evaporates respectively. This leads to the cracking of the block. Too much silt content on the other hand leads to the splitting of the block.

On the other hand, for the silt and clay content < 10% then the soil samples not suitable for ISSB. This soil, however, is good for foundations and floors.

If the silt and clay content is between 10% and 40% the soil is good for ISSB, foundations, floors and walls.

The above soil sample contained too much fines. Therefore for the above results it was necessary to add some sand to the sample in order to balance out the sand: clay ratio.

27

4.1.4 SHRINKAGE TEST

Table 4.2 Test results for the shrinkage test

Initial Length of Specimen Final Length of Specimen

600mm 555mm

The reduction in length of the specimen was:

600mm-555mm=45mm

ANALYSIS

Therefore the percentage expected shrinkage of the ISSB blocks upon drying can be estimated as:

Percentage Shrinkage of Block =Change∈lengthof specimenInitial Length of Specimen ×100

= 45mm600mm×100

= 7.5%

DISCUSSION

Too much shrinkage on the soil blocks may lead to cracks and even permanent deformations on walls and fittings once walls are constructed.

28

Therefore shrinkage on the ISSBs should be kept to a minimum to avoid any of these adverse effects.

The shrinkage obtained above was 7.5%. This amount of shrinkage is allowed for the blocks as they are not bound by mortar and hence they are free to move and give an allowance for any deformations.

4.2 LABORATORY TEST RESULTS

BLOCK CRUSHING RESULTS

The block crushing results are tabulated in the tables 4.1 to 4.3 below. It can be observed that the compressive strength of the ISSBs increases with an increase in the percentage of cement used for stabilization. The compressive strength of the ISSB ranges from 0.7 on the seventh day to 2.0 on the 28th day.

ISSB

8% StabilizationTable 4.1 Crushing results for 8% ISSB

Age

(Days)

Dry Mass(kg)

Crushing Force(KN)

Avarage Crushing Force(KN)

Avarage Compressive Stregth(N/mm2)

75.45.35.5

222031

24.3 0.7

145.45.35.4

383537

36.7 1.1

285.35.25.3

423743

40.6 1.2

29

From the tabulation on table 4.1 above and the plot of compressive strength against age at 8% cement stabilization, the following can be observed:

The compressive strength of the ISSB increases with age. The curve generally tends to flatten out as the days progress.

5 10 15 20 25 300.600000000000001

0.700000000000001

0.800000000000001

0.900000000000001

1

1.1

1.2

1.3

Strength against age at 8% Stabilization

Age(Days)

Com

pres

sive

Stre

ngth

(N/m

m2)

Figure 4.1 Plot of Compressive Strength of ISSB against Age at 8% Stabilization

The curve above shows a general increase in the compressive strength of the ISSB as time progresses.

A comparison of the strengths of 8% stabilization to 10% stabilization however indicate that an increase in the cement content leads to a general increase in the strength of the ISSB.

30


Age

(Days)

Dry Mass(kg)

Crushing Force(KN)



75.25.45.4

333033

32 0.9

145.35.35.1

586062

60 1.7

285.15.15.3

657569

70 2.0

The table above shows the results for the crushing tests of ISSBs at 10% stabilization.

As the case with 8% stabilization, the strength generally increases with time. At 28 days the ISSB achieves a strength of 2.0N/mm2.

31

6 11 16 21 26 310.600000000000001

0.800000000000001

1

1.2

1.4

1.6

1.8

2

2.2


Age(Days)

Com

pres

sive

Stre

ngth

(N/m

m2)


Figure 4.2 shows a plot of the compressive strength of the blocks with age. As observed in the table, it is clear that the strength of the block increases with time.

32


Age

(Days)

Dry Mass(kg)

Crushing Force(KN)



75.05.15.3

453739

40 1.1

144.85.05.4

586962

63 1.8

285.45.25.3

726569

69 2.0

At 12% stabilization, a repetition of the trend at 8% and 10% is observed. The 28 day strength of the block however does not vary from that at 10% stabilization.

33

6 11 16 21 26 310.600000000000001

0.800000000000001

1

1.2

1.4

1.6

1.8

2

2.2


Age(Days)

Com

pres

sive

Stre

ngth

(N/m

m2)


Figure 4.3 is a graphical representation of the variation of the compressive strength of the soil block with time. It is clear that the strength increases with time.

DISCUSSION

The recommended 28day strength for interlocking soil stabilized blocks is over 2.5N/mm2. The highest strength recorded for the ISSB samples tested above was at 2.0N/mm2. The blocks therefore failed to attain the required compressive strength.

The main reasons why these blocks did not attain the required strength may be improper compaction of the stabilized soil in the press machine, improperly graded soil and poor soil samples.

34

The more the cement content, the stronger the block becomes with time. This is the reason why the blocks having 12% stabilization are generally stronger than that with 8% and 10% stabilization.

THE CONTROL (CONCRETE BLOCK)Table 4.4 Crushing results for cement control

Age

(Days)

Crushing Force(KN)



74537

240 6.8

145869

440 12.5

287265

490 13.9

Table 4.4 shows the results for the crushing test of the concrete block. As for the soil blocks, the strength of this block increases with time.

A comparison of the strengths of the soil blocks to that of the concrete block is shown in figure 4.6.

35

6 11 16 21 26 316

7

8

9

10

11

12

13

14

15

Strength against age for concrete block

Age(Days)

Com

pres

sive

Stre

ngth

(N/m

m2

)

Figure 4.4 Plot of Compressive Strength against AgeforControl

A graphical representation of the variation of compressive strength of the cement control with time is shown in figure 4.4 above.

36

5 10 15 20 25 300.5

0.7

0.9

1.1

1.3

1.5

1.7

1.9

2.1

Comparison of ISSB strenghts at different stabilizations

8% 10% 12%

Age(days)

Com

pres

sive

Stre

ngth

(N/m

m2

)

Figure 4.5 Comparison of strengths of ISSBs at different stabilizations

A composite plot of the variation of the compressive strengths of the soil blocks at different stabilizations is shown in figure 4.5.

It is clear that the strength of the blocks increases with an increase in the stabilization up to a certain point. This is so because the 28day strength of the 10% stabilized block is equal to that at 12% stabilization.

37

6 11 16 21 26 310

2

4

6

8

10

12

14

16

Comparison of ISSB Strength to Cement Block Strength

8% 10% 12% Control

Age(Days)

Com

pres

sive

Stre

ngth

(N/m

m2)

Figure 4.6 Comparison of strengths of ISSBs to that of the cement control

Figure 4.6 above shows a comparison of the strengths of the ISSSBs to that of the cement control. It can be estimated that the strength of the mortar block is about 14 times that of the soil blocks.

DISCUSSION

The results above show a general increase in the strength of the ISSB with time. A comparison of the strengths of the ISSBs indicate an increase in strength with an increase in cement content.

This is expected because generally more cement content means more bonding of the soil particles. However it should be noted that excessive cement may lead to a loss of strength of the block after some time. The

38

strength of the mortar block alone however was very low, at 13.9N/mm2 due to the fact that no coarse aggregates were included in the mix design. The reason why coarse aggregates were excluded from the mix is because the sample could not be fully compressed.

A comparison of the strength of the ISSB to that of the concrete block indicates that the concrete block is stronger than that of the ISSB.

WATER ABSORPTION TEST RESULTS

The water absorption test results are tabulated below.

Table 4.5 Water absorption test results

Cement (%)

Dry Mass,Wd(Kg)

Wet Mass,Ww(kg)

Water Absorbed(%)

Average Water Absorbed,Wm(%)

85.25.1

5.85.5

11.57.8

9.7

105.15.3

5.55.7

7.87.5

7.7

125.44.8

5.75.0

5.64.2

4.9

From table 4.50 it can be observed that the amount of water absorbed decreases with an increase in cement content.

39

8 8.5 9 9.5 10 10.5 11 11.5 12 12.54

5

6

7

8

9

10

Comparison of percentage of water absorbed to percentage of the cement stabilized

Percentage of Cement Stabilization

Wat

er A

bsor

bed(

%)

Figure 4.7 Comparison of percentage of water absorbed to the percentage stabilization

Figure 4.7 shows a plot of the percentage of water absorbed to the percentage of cement stabilization.

The graphical plot gives a clear picture of the fact that the amount of water absorbed decreases with an increase in the cement stabilization.

DISCUSSION

The amount of water absorbed by the ISSBs reduces with an increase in cement content as the tiny cement particles, as they bond the soil particles together, cover more pores within the soil particles which would otherwise have been filled with water. Therefore the higher the cement content, the higher the number of pores covered hence the less the water absorbed by the blocks.

40

The maximum water absorption after 28 days expected for the blocks is 15%. The maximum water absorption observed in this experiment was 9.7%. Therefore these blocks met the water absorption specifictions.

ABRASION TEST RESULTS

The abrasion test results were tabulated as shown in table 4.6 belowTable 4.6 Abrasion test results

Cement Stabilizatio

n (%)

Mass Before Abrasion,Mi(kg)

Mass After Abrasion,Mf(kg)

Abraded away (%)

Average Abraded Away, Ma (%)

85.34.9

5.14.8

3.772.04

2.905

105.45.7

5.35.6

1.852.13

1.990

125.55.7

5.45.6

1.821.75

1.785

Table 4.6 gives the results for the abrasion test on the blocks at the different cement stabilization at 28 days in dry condition.

The percentage of material abraded decreased with an increase in the cement stabilization.

41

8 8.5 9 9.5 10 10.5 11 11.5 12 12.51.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

3.1

Percentage abraded vs Cement content

Cement Stabilization(%)

Perc

enta

ge A

brad

ed(%

)

Figure 4.8 Percentage of material abraded against percentage of cement stabilization

Figure 4.8 gives a graphical representation of the decrease in abrasion with an increase in cement stabilization.

DISCUSSION

The higher the cement content, the lower the abrasion observed in the blocks. This is so because as the amount of cement increases, so does the bonding between the soil particles hence making it harder for them to be broken away from the block.

4.3 COST ANALYSIS

42

In order to perform the cost analysis, a comparison of the construction of 1m2 of wall was done for:

i) ISSBii) Soil Masonry Walliii) Concrete block

Table 4.7 Cost Analysis

Type of Block Price Per Block(Ksh.)

No. Needed per Sq. Meter

Price per Sq. Meter(Ksh.)

ISSB 14 35 490

Concrete block 120 10 1200

Soil Masonry Block(Baked)

6 30 180

From the table 4.7 above, it is clear that the ISSB costs less than the cement block per square meter. The cost of building a square meter of cement wall is more than twice that of building a square meter of wall using the ISSB block.

Furthermore, the cement block requires mortar for its joints, which leads to additional costs. The ISSB on the other hand is dry stacked and thus does not require any mortar for its joints, hence making it even cheaper.

The soil masonry block, however cheap, has the disadvantage of forming weak structures. The aesthetic quality of walls made out of these blocks however is low.

43

DISCUSSION

When a comparison between the cost of constructing a square meter of wall using the concrete block and that of the ISSB is done, it is observed that it is cheaper to construct using the ISSB. The cost considered in this case is only the production cost of the block. If other costs like the cost of mortar and the opportunity cost of time are considered, building using the interlocking soil block is far much cheaper.

Chapter 5

44

5 CONCLUSION AND RECOMMENDATIONS5.1 CONCLUSION

Based on the tests carried out and the cost analysis done in this research, it can be concluded that the ISSB technology is superior to the traditional construction methods like the waffle and daub or the baked brick. At 2.0N/mm2, the block is much stronger than the baked brick. However, the blocks produced in this research did not meet the minimum strength standards for ISSBs which is 2.5N/mm2 at 28 days. The possible cause of this may be the fact that the blocks were not sprayed with water in the cause of their curing to aid in cement hydration.

The durability tests conducted in this research also indicated that the blocks durability is acceptable as the water absorption and abrasion test results met the set standards.

It can also be concluded that the ISSB technology is less costly compared to the traditional construction methods. This is based on the cost analysis carried out during the research.

45

5.2 RECOMMENDATIONS

In as much as the ISSB technology has been found to be more superior than most of the traditional construction methods, still much can be done to improve on it. Some of the recommendations on improvements are as discussed below:

5.2.1 STANDARDIZATION

The interlocking stabilized soil technology is relatively new in the region and therefore not much information exists on this technology.

Firstly, standard quality tests are not properly documented. Some tests therefore have to perform on a relative scale which is not very objective. A good example is the drop test and the abrasion test. Standard quality tests thus need to be developed.

Secondly, there no clear building standards in place to control the construction using this technology. Most clients and even building industry professionals are thus unable to adopt this technology due to this shortcoming.

Standard mix designs also do not exist. This may be due to the fact the soil samples in the region differ quite significantly from one area to another. Nevertheless, with the right quality tests on the soils, charts can be developed to aid in mix design.

5.2.2 EDUCATION

Most people within the East African community are still skeptical about this technology. In order to ensure the full adoption of this technology in this community, therefore, there is need for awareness creation to the people on the advantages that this technology has.

5.2.3 GOVERNEMENT INVOLVEMENT

It is commendable that the government of the United Republic of Tanzania has totally adopted this technology and is on the forefront in promoting the use of ISSBs.

46

Other East African governments should follow suit and ensure the full adoption of this technology in their respective countries.

Chapter 6

6 REFERENCESBOOKS AND PUBLICATIONSDan Lewis, (2004). Human Settlements in Crisis, pp 6, pp 34-41, UNHABITAT, Nairobi, Kenya

Andabati, D. (2009). Construction Manual. Double Interlocking Rectangular Blocks for House Construction pp 4

Ahmad SH et al,(2002). Agenda 21 for Sustainable Construction in Developing CountriesCountries,Pretoria

Rigassi, V. (1995).Compressed Earth Blocks :Manual of Production. CRATerre-EAG, Aus der Arbeit von GATE. Germany:Braunschweig Vieweg.

ONLINE

Gallup World Poll, http://www.gallup.com/services/170945/world-poll.aspxhttp://www.nhbra.go.tz/

http://www.nhbra.go.tz/

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