THE UNIVERSITY OF NAIROBI
DEPARTMENT 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 of
BACHELOR OF SCIENCE IN CIVIL ENGINEERING
2015
ABSTRACT
The 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
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.
ii
ACKNOWLEDGEMENTS
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.
iii
TABLE OF CONTENTS
CONTENTS .................................................................................... IV
LIST OF ACRONYMS ..................................................................... VI
LIST OF TABLES .......................................................................... VI
LIST OF FIGURES ........................................................................ VII
1.
INTRODUCTION ................................................................... 1
1.1
2
BACKGROUND INFORMATION .....................................................
1
1.2
PROBLEM STATEMENT ........................................................ 2
1.3
OBJECTIVES .........................................................................
1.4
METHODOLOGY ................................................................. 3
X1.5
PROJECT SIGNIFICANCE............................................................
1.6
LIST OF FACILITIES/MATERIALS
3
4
.................................................. 4
FACILITIES ...............................................................................
4
MATERIALS ...............................................................................
5
LITERATURE REVIEW .............................................................. 6
2.1
HISTORICAL BACKGROUND ........................................................
6
2.2
OPERATING PRINCIPLES
2.3
TYPES OF INTERLOCKING SOIL STABILIZED BLOCKS .......................... 8
........................................................... 7
CLASSIFICATION ACCORDING TO MATERIAL COMPOSITION. ........................ 8
CLASSIFICATION ACCORDING TO SHAPES AND SIZES
............................... 9
2.4
PRODUCTION.......................................................................10
2.5
WALL CONSTRUCTION ............................................................10
2.6
BUILDING DESIGN ................................................................12
2.7
ADVANTAGES OF ISSB...........................................................12
iv
2.8
DISADVANTAGES OF
ISSB ......................................................13
2.9
SOIL STABILIZATION .............................................................14
2.11 LABORATORY TESTS .................. ERROR! BOOKMARK NOT DEFINED.
TESTS ON THE SOIL SAMPLE.................. ERROR!
TESTS ON THE
3
BOOKMARK NOT DEFINED.
ISSB .......................... ERROR! BOOKMARK NOT DEFINED.
EXPERIMENTATION
.....................................................................15
3.1
SAMPLE COLLECTION ..............................................................15
3.2
PREPARATION ......................................................................15
PREPARATION OF THE SOIL SAMPLE ........................................15
3.1 FIELD TESTS .........................................................................15
3.3
PREPARATION OF TEST BATCHES .......................................18
3.3.1
PREPARATION OF THE SOIL BLOCKS ........................................19
3.3.2
PREPARATION OF THE CONCRETE BLOCKS
.................................21
3.2 LAB TESTS .........................................................................22
COMPRESSIVE STENGTH TEST ................................................22
WATER ABSORPTION TEST ............................................................23
ABRASION TEST ....................................................................24
4.0
RESULTS, ANALYSIS AND DISCUSSION .......................................25
4.1
FIELD TEST RESULTS...........................................................25
4.1.1 HAND MOULDING TEST ........................................................25
4.1.2 THREAD TEST ...................................................................25
4.1.3 GLASS – JAR TEST .............................................................26
4.1.4
SHRINKAGE TEST ............................................................28
4.2 LABORATORY TEST RESULTS ....................................................28
BLOCK CRUSHING RESULTS....................................................29
WATER ABSORPTION TEST RESULTS ........................................39
v
ABRASION TEST RESULTS ......................................................41
4.3
5.0
COST ANALYSIS ...............................................................42
CONCLUSION .........................................................................45
LIST OF ACRONYMS
ISSB-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 TABLES
Table 3.1 Mix Proportions for ISSB test batch ......................................... 19
Table 4.1 Test results for the glass jar sedimentation test ....................... 26
Table 4.2 Test results for the shrinkage test .......................................... 28
Table 4.1 Crushing results for 8% ISSB ................................................. 29
Table 4.2 Crushing results for 10% ISSB ............................................... 31
Table 4.3 Crushing results for 12% ISSB ............................................... 33
Table 4.4 Crushing results for cement control ........................................ 35
Table 4.5 Water absorption test results ................................................. 39
Table 4.6 Abrasion test results ............................................................. 41
vi
LIST OF FIGURES
Table 3.1 Mix Design for ISSB test batch ............................................... 19
Table 4.1 Test results for the glass jar sedimentation test ....................... 26
Table 4.2 Test results for the shrinkage test .......................................... 28
Table 4.1 Crushing results for 8% ISSB ................................................. 29
Figure 4.1 Plot of Compressive Strength of ISSB against Age at 8%
Stabilization ....................................................................................... 30
Table 4.2 Crushing results for 10% ISSB ............................................... 31
Figure 4.2 Plot of Compressive Strength of ISSB against Age at 10%
Stabilization ....................................................................................... 32
Table 4.3 Crushing results for 12% ISSB ............................................... 33
Figure 4.3 Plot of Compressive Strength of ISSB against Age at 12%
Stabilization ....................................................................................... 34
Table 4.4 Crushing results for cement control ........................................ 35
Figure 4.4 Plot of Compressive Strength against Age for Control ............... 36
Figure 4.5 Comparison of strengths of ISSBs at different stabilizations ...... 37
Figure 4.6 Comparison of strengths of ISSBs to that of the cement control 38
Table 4.5 Water absorption test results ................................................. 39
Figure 4.7 Comparison of percentage of water absorbed to the percentage
stabilization ....................................................................................... 40
Table 4.6 Abrasion test results ............................................................. 41
vii
Figure 4.8 Percentage of material abraded against percentage of cement
stabilization ....................................................................................... 42
Table 4.7 Cost Analysis ....................................................................... 43
LIST OF PLATES
Plate 3.1: Sedimentation Bottle Setup ................................................... 17
Plate 3.2 Shrinkage Limit setup. ........................................................... 18
Plate 3.2 Dimensions and general profile of the rectangular double
interlocking block. .............................................................................. 19
Plate 3.3 Rectangular type double interlocking ISSBs curing .................... 21
vii
i
Chapter 1
1.
INTRODUCTION
1.1 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 healththreatening 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 lowincome countries have been most hit by this problem. This coupled with the
lack of technical know-how, an unfavorable political climate and even socioeconomic 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
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.
2
1.3 OBJECTIVES
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 manuallyoperated 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.
3
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
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 apparatus
ii)
Soil shear strength determination apparatus
iii)
Soil shrinkage limit determination apparatus
iv)
Plastic limit determination apparatus
v)
Manually operated interlocking block press machine
4
MATERIALS
A list of the required materials is as below:
i)
80kg red coffee soil samples
ii)
20kg grade 32.5 Ordinary Portland Cement
iii)
30kg sand
5
Chapter 2
2
LITERATURE REVIEW
2.1 HISTORICAL BACKGROUND
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 required
iii)
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 cooperation 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]
6
2.2 OPERATING PRINCIPLES
The 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
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.
7
2.3 TYPES OF INTERLOCKING SOIL STABILIZED BLOCKS
There are many types of soil stabilized blocks depending on:
i)
Material composition
ii)
Shape
iii)
Size
The choice of which ISSB to use is influenced by the required use and also
by the required strengths.
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
8
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.
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.
9
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.
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
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.
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.
11
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:
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
12
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.
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.
13
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: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.
14
Chapter 3
3
EXPERIMENTATION
3.1 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.
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.
15
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
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:
16
-
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.
- 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.
Plate 3.1: Sedimentation Bottle Setup
17
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 3.2 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:
18
Plate 3.2 Dimensions and general profile of the rectangular double interlocking block.
TheISSB test blocks were prepared in the following ratios:
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.
19
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.
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.
20
Plate 3.3 Rectangular type double interlocking ISSBs curing.
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.
21
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 test
ii)
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.
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
22
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:
Wm =
Where
 − 
× 100
W
Wm=percentage moisture absorption
Ww=Weight of soaked ISSB
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.
23
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 =
Where
 − 
× 100
Mi
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.
24
Chapter 4
4
RESULTS, ANALYSIS AND DISCUSSION
4.1 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.
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.
25
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
ℎ   
Percentage of fines =
 ℎ   
=
×100
7.5
11
×100
=68.18%
Percentage of silt =
ℎ   
 ℎ   
=
×100
3.5
11
×100
=31.82%
26
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 =
ℎ  ℎ  
 ℎ  
=
45
600
×100
×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.
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
28
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% Stabilization
Table 4.1 Crushing results for 8% ISSB
Age Dry
Mass(kg)
(Days)
Crushing
Force(KN)
5.4
22
7 5.3
20
5.5
31
5.4
38
14 5.3
35
5.4
37
5.3
42
28 5.2
37
5.3
43
Avarage
Crushing
Force(KN)
Avarage
Compressive
Stregth(N/mm2)
24.3
0.7
36.7
1.1
40.6
1.2
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.
29
Strength against age at 8% Stabilization
1.3
Compressive Strength(N/mm2)
1.2
1.1
1
0.9
0.8
0.7
0.6
5
10
15
20
25
30
Age(Days)
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
10% Stabilization
Table 4.2 Crushing results for 10% ISSB
Age Dry
Mass(kg)
(Days)
Crushing
Force(KN)
5.2
33
7 5.4
30
5.4
33
5.3
58
14 5.3
60
5.1
62
5.1
65
28 5.1
75
5.3
69
Avarage
Crushing
Force(KN)
Avarage
Compressive
Stregth(N/mm2)
32
0.9
60
1.7
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
Strength against age at 10% Stabilization
2.2
Compressive Strength(N/mm2)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
6
11
16
21
26
31
Age(Days)
Figure 4.2 Plot of Compressive Strength of ISSB against Age at 10% Stabilization
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
12% Stabilization
Table 4.3 Crushing results for 12% ISSB
Age Dry
Mass(kg)
(Days)
Crushing
Force(KN)
5.0
45
7 5.1
37
5.3
39
4.8
58
14 5.0
69
5.4
62
5.4
72
28 5.2
65
5.3
69
Avarage
Crushing
Force(KN)
Avarage
Compressive
Stregth(N/mm2)
40
1.1
63
1.8
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
Strength against age at 12% Stabilization
2.2
Compressive Strength(N/mm2)
2
1.8
1.6
1.4
1.2
1
0.8
0.6
6
11
16
21
26
31
Age(Days)
Figure 4.3 Plot of Compressive Strength of ISSB against Age at 12% Stabilization
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 Crushing
Force(KN)
(Days)
7
14
28
45
37
58
69
72
65
Avarage
Crushing
Force(KN)
Avarage
Compressive
Stregth(N/mm2)
240
6.8
440
12.5
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
Strength against age for concrete block
15
14
Compressive Strength(N/mm2 )
13
12
11
10
9
8
7
6
6
11
16
21
26
31
Age(Days)
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
Comparison of ISSB strenghts at different stabilizations
2.1
Compressive Strength(N/mm2 )
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
5
10
15
20
25
30
Age(days)
8%
10%
12%
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
Comparison of ISSB Strength to Cement Block Strength
16
Compressive Strength(N/mm2)
14
12
10
8
6
4
2
0
6
11
16
21
26
31
Age(Days)
8%
10%
12%
Control
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
Wet
(%) Mass,Wd(Kg) Mass,Ww(kg
)
8
10
12
Water
Absorbe
d(%)
5.2
5.8
11.5
5.1
5.5
7.8
5.1
5.5
7.8
5.3
5.7
7.5
5.4
5.7
5.6
4.8
5.0
4.2
Average
Water
Absorbed,Wm
(%)
9.7
7.7
4.9
From table 4.50 it can be observed that the amount of water absorbed
decreases with an increase in cement content.
39
Comparison of percentage of water absorbed to
percentage of the cement stabilized
10
Water Absorbed(%)
9
8
7
6
5
4
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
Percentage of Cement Stabilization
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 below
Table 4.6 Abrasion test results
Cement Mass Before
Mass After
Abrade
Stabilizatio Abrasion,Mi(kg Abrasion,Mf(kg d away
n (%) )
)
(%)
8
10
12
5.3
5.1
3.77
4.9
4.8
2.04
5.4
5.3
1.85
5.7
5.6
2.13
5.5
5.4
1.82
5.7
5.6
1.75
Averag
e
Abrade
d
Away,
Ma (%)
2.905
1.990
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
Percentage abraded vs Cement content
3.1
2.9
Percentage Abraded(%)
2.7
2.5
2.3
2.1
1.9
1.7
1.5
8
8.5
9
9.5
10
10.5
11
11.5
12
12.5
Cement Stabilization(%)
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)
ISSB
ii)
Soil Masonry Wall
iii)
Concrete block
Table 4.7 Cost Analysis
Type of Block Price Per
Block(Ksh.)
No. Needed
per Sq. Meter
Price per Sq.
Meter(Ksh.)
35
490
Concrete block 120
10
1200
Soil Masonry 6
Block(Baked)
30
180
ISSB 14
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.
44
Chapter 5
5
CONCLUSION AND RECOMMENDATIONS
5.1 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
46
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.
Other East African governments should follow suit and ensure the full
adoption of this technology in their respective countries.
Chapter 6
6
REFERENCES
BOOKS AND PUBLICATIONS
Dan 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
Countries
Countries,Pretoria
Rigassi, V. (1995).Compressed Earth Blocks :Manual of Production. CRATerre-EAG,
Aus der Arbeit von GATE. Germany:Braunschweig Vieweg.
47
ONLINE
Gallup World Poll, http://www.gallup.com/services/170945/world-poll.aspx
http://www.nhbra.go.tz/
48