NSF IRES 2009 Summer Research

Investigation of Sustainability of SSBs and Burnt Bricks for Sand Dam Construction

Ryan Clark

Willems Leveille

Acknowledgement:

This Program is Supported by the National Science Foundation

NSF Award No. 0755959

Principal Investigator: Dr. Esther Obonyo, University of Florida

Co. Principal investigator: Dr. Robert Ries, University of Florida

NSF Program Manager: Prof. Wayne Patterson

Table of Contents

List of Plates .............................................................................................................................................................4

List of Figures..........................................................................................................................................................5

List of Appendices ....................................................................................................................................................6

1.Introduction ..........................................................................................................................................................7

1.1Background ........................................................................................................................................................7

1.2Methodology .......................................................................................................................................................8

1.2.1Aim ...................................................................................................................................................................8

1.2.2Objectives ........................................................................................................................................................8

1.2.2.1Kenya Segment .............................................................................................................................................8

1.2.2.2United States Segment .................................................................................................................................8

1.2.3Research Tasks ................................................................................................................................................8

2.Procedures ............................................................................................................................................................9

2.1Soil Testing .........................................................................................................................................................9

2.2SSB Construction ...............................................................................................................................................9

2.3Testing of the SSBs and Burnt Bricks ........................................................................................................... 12

3.Findings ............................................................................................................................................................. 13

3.1Soil Testing ...................................................................................................................................................... 13

3.2Testing of the SSBs and burnt bricks ............................................................................................................ 15

4.Discussion .......................................................................................................................................................... 16

4.1Soil .................................................................................................................................................................... 16

4.2SSB & Burnt Brick ......................................................................................................................................... 17

5.Research Implications ...................................................................................................................................... 19

5.1Possibilities for Errors .................................................................................................................................... 19

5.1.1Soil Testing ................................................................................................................................................... 19

5.1.2SSBs and Burnt Bricks ................................................................................................................................ 19

5.2Recommendations for United States Segment ............................................................................................. 20

5.2.1Soil and SSBs ................................................................................................................................................ 20

5.2.2Design ............................................................................................................................................................ 21

5.3Other Recommendations ................................................................................................................................ 21

6.Outcomes ........................................................................................................................................................... 22

6.1Kenya Segment ................................................................................................................................................ 22

6.2Focus Audience ............................................................................................................................................... 22

References ............................................................................................................................................................. 23

1. Manual for selection, Testing and production of SSB-University of Nairobi and Housing

Department (MORPW&H) – Stabilised Soil Blocks (SSB) 2003.

2. Low-cost cements (Pozzolanas) – Intermediate Technology Development Group Ltd.

i. Reg. No.871954 0121.92.07

ii. Reg. No.871954 0126.92.03

iii. Reg. No.871954 0125.92.07

iv. Reg. No.871954 0122.92.07

v. Reg. No.871954 91/102.11

3. Earth Construction – A COMPREHENSIVE GUIDE – Hugo Houben and Hubert

Guillaud (Intermediate Technology Publications 1994)

4. SECOND INTERIM REPORT ON POZZOLAN HOUSING PROJECT (UGANDA) FOR

INTERNATIONAL DEVELOPMENT RESEARCH CENTRE, EAST AND CENTRAL

AFRICAN REGIONAL OFFICE – W. BALU TABAARO –ENTEBE UGANDA 22ND APRIL,

1991

List of Plates

Plate 1: Mixing 9 parts soil ½ part cement using bowl 3 Plate 2: Mixing in water and testing consistency of mix 4 Plate 3: Filling mould with mix while compressing with fingers and leveling top 4 Plate 4: Preparing mould for compression 4 Plate 5: Compressing and ejecting 4 Plate 6: Improper loading of the mould and improper lifting lead to SSB failure 5

List of Figures

Figure 1:) Atterberg Limits Test4

Figure 2: Particle Size Distribution 5

Figure 3: Water absorption Test 6

Figure 4: Compressive Strengths of Post-Immersed SSBs 7

Figure 5: Compressive Strengths vs Percent Absorption 8

List of Appendices

1. Introduction

1.1 Background

Water has been called the defining crisis of the twenty-first century. No one knows this better than the water-

starved countries of East Africa. Arid and Semi-Arid land (ASAL) covers almost eighty percent of the East-

African country of Kenya (Ominde), and between thirty-five and forty percent of Kenyans reside in these

seasonally dry areas (SASOL). This presents the Kenyan government, that normally considers water shortage, a

serious problem: The question to be answered is how the government can provide enough water to sustain the

lives and livelihoods of the millions of Kenyans living in the ASALs? The answer is two-fold and has been

answered by different groups in similar ways. First, small communities in these areas must provide their own

water through rain water harvesting, and the second solution by construction of sand dams.

Because the East-African country of Kenya straddles the equator, it experiences a short and long rainy seasons

with intervening short and long dry seasons. The seasonal riverbeds created by these seasons provide water for a

few months out of the year, but the water is full of sand and mud from upstream and quickly empties or dries out.

Sand dams make use of the rainy seasons and the sandy water by creating artificial aquifers in the seasonal

riverbeds. The sand washed down the river accumulates over two or three rainy seasons behind the concrete dam

and actually retains up to forty percent of its’ volume in water (Brahic). This shallow aquifer can provide water

to a community for many months after the rainy season has ended.

Excellent Development is a London based charity founded by Simon Maddrell and Joshua Mukusia which

focuses on the development of Kenyan water sources. Practical Action is also a UK based charity which focuses

on Kenyan water sources with a foundation built on studies done by Sahelian Solutions Foundation (SASOL)

and Maji na Ufanisi. Both organizations use the construction of sand dams to improve the reliability of water to

communities in the ASAL areas of Kenya, and consider the project’s life-line the community that the sand dam

will benefit. SASOL states, “The local community has to take the initiative, to identify the stretch of river where

water storage would be most useful, and has to agree to provide the labor needed” (SASOL 36). Excellent

Development corroborates that a successful project must be community both owned and meet design

requirements.

Seasonal riverbeds provide the best location for the dam, whose foundation must be based on an impermeable

sub-layer of bedrock which generally occurs at some depth below riverbed (SASOL 37). The dam itself is then

constructed of materials mostly found in the local community such as timber, sand and stones, and water with

the exception a binder such as cement and binding wire (Practical). Portland cement can be a very costly

material for the communities, costing around Ksh 1000 per 50 kg bag in Nairobi. This has led to research into

alternative materials for the construction of sand dams.

One proposed alternative new material to be used in the construction of a sand dam is stabilized soil blocks

(SSBs). In order to make SSBs, an appropriate soil must be chosen. Murum, an abundant soil found around

Kenya and other parts of East Africa, has been found to be suitable. Because Mokena is one of the most

populous regions of the Arid and Semi-Arid Lands (ASALs) in south eastern Kenya and can greatly benefit from

the use of sand dams, the team decided to use murum from this region for investigations. The murum is readily

available and is readily obtained at minimum cost from a location close to a proposed site for a sand dam.

SSBs constructed out of murum usually require a plasticizer and stabilizer to achieve sufficient workability and

eventual strength after curing. The former Housing and Building Research Institute (HABRI) of the University

of Nairobi has issued guidelines for different ratios of soil to stabilizers in its’ Manuel for the Selection Testing

and Production of SSB. The team decided to use a ratio of 1 part cement to 18 part soil as this has been

determined by HABRI to be the lowest proportion of cement to soil suitable for the use in SSBs. After tweaking

this Kenyan standard the team decided to also use a ratio of 0.5 part cement to 0.5 part hydrating lime to 18 parts

soil as this further reduces the cost and need of cement. To completely eliminate the need of cement, blocks were

also made with 0.5 part rice husk ash to 0.5 part lime to 18 part soil.

Burnt bricks are another proposed option to use in the construction of a sand dam. These can be found around

many villages in the ASALs and are relatively inexpensive to buy at around Ksh 3 per brick. Usually the

villagers are equipped to create their own burnt bricks with the only cost being the time spent collecting the

materials. Again, as Mokena is the focused region, the team decided to collect burnt bricks from this region.

1.2 Methodology

1.2.1 Aim

To investigate an alternative material to concrete to use in the construction of sand dams in the Arid and Semi-

Arid Lands of East Africa. The team will test building materials commonly used in Kenya and other East African

countries to determine their suitability in the construction of a sand dam. If none can be used, the team will

investigate alterations, which will allow for the materials effective use or will recommend other materials and

further research.

1.2.2 Objectives

1.2.2.1 Kenya Segment

a. To determine which region can benefit from the use of sand dams

b. To use the soil from identified region in the production of SSBs of differing stabilizers and soil to

stabilizer ratios

c. To test the capacity of burnt bricks and compressed SSBs to determine which, one of them can be most

viable in the construction of a sand dam.

d. If SSBs are the most promising, the aim is to determine which ratio of stabilizer to soil produces the most

effective block and to suggest ways to improve on their production.

1.2.2.2 United States Segment

a. To determine whether or not the soil in the Mokena district has sufficient deposit that can sustain the

production of SSBs

b. If soil is inadequate, to find ways to improve the properties of the soil by mixing with other available soil

types from the area

c. To produce and test SSBs made with the improved soil

d. To identify alternative procedures for the production of improved alternative materials and to carry out

local capacity building with a view to empowering them to be able to construct sand dams.

1.2.3 Research Tasks

a. To make SSBs of 1:18 cement-soil ratio (mix proportions).

b. To make SSBs with a ½:½:18 lime-cement-soil ratio.

c. To make SSBs with a ½:½:18 rice husk ash-lime-soil ratio.

d. To determine the gradation and plasticity of the soil used in the production of the SSBs.

e. To test the permeability and absorption of the constructed SSBs and burnt bricks.

f. To classify the compressive and tensile strengths of the burnt bricks and SSBs.

g. To construct a demonstration unit which can be utilized by the University of Nairobi to better understand

and test the use of alternative materials in the construction of a sand dam.

2. Procedures

2.1 Soil Testing

Sand dams are typically used in Arid and Semi-Arid environments in Kenya. Being aware that they are widely

used in the Kitui District, the team had interest to examine other areas in Kenya that could benefit from the use

of sand dams. Using digital topographic maps to locate seasonal riverbeds and then checking the population

densities around these rivers, the team was able to decide on a location in the Mokena District of south-east

Kenya.

In order to best evaluate the possibilities of using SSBs in the construction of sand dams in Mokena, the team

required samples of soil which are readily available in this district. This soil, contemporarily called murum

(laterite), would be used to produce the SSBs used in this research and plays heavily into the final capacity of the

SSBs. Therefore the team needed to be able to classify the soil along with identifying several of its’ properties.

The team began testing the soil by using soil which passed a 0.425mm or 425 micron sieve to determine the

Atterburg Limits: shrinkage limit, plastic limit, liquid limit, and plasticity index. These values can be easily used

to determine other soil properties such as compressibility, permeability, strength, flow index, liquidity index, and

toughness index. Determining these properties allow the given soil to be easily compared to soils with similar

qualities.

Because the gradation of the soil used in the production of SSBs is so critical to the final capacity of the SSB, the

team found it necessary to determine the gradation of the soil from gravels to clay. To begin classifying the soil,

200 grams of soil was wet sieved using a number 200 BS (0.075mm) sieve to eliminate silts and clays. The

remaining soil was dried over night and then dry sieved to determine the gradation of particles ranging from fine

sands to gravel. 50 grams of soil passing a number 200 sieve was used to perform a hydrometer analysis. This

test allowed the team to determine the percent fines in the overall soil sample.

2.2 SSB Production

Because Portland cement can be such a costly and highly sought after building material in Kenya, selling for

around Ksh 1000 per 50 kg bag, it is necessary for communities to find an alternative building material to

eliminate the need for financial assistance. Stabilized soil blocks are becoming an increasingly popular building

material in many construction projects and have also been the focus of much research at the former Housing and

Building Research Institute (HABRI) of the University of Nairobi. Because SSBs constructed out of murum

usually require a plasticizer and stabilizer to achieve a sufficient strength, HABRI has issued guidelines for

different ratios of soil to stabilizers in its’ Manuel for the Selection Testing and Production of SSB.

The team decided to use a ratio of 1 part cement to 18 part soil as this has been determined by HABRI to be the

lowest proportion of cement to soil suitable for the use in SSBs. After adopting this Kenyan standard the team

decided to also use a ratio of .5 part cement to .5 part hydrating lime to 18 parts soil as this further reduces the

cost and need of cement. To completely eliminate the need of cement, blocks were also made with .5 part rice

husk ash to .5 part lime to 18 part soil. Although SSBs have never been tested for their use in sand dams,

research on this application could lead to a cheap alternative to the contemporary Portland cement. When

producing the SSBs, the team took note of many different aspects of the process.

Primarily the team found that the process is not very standardized or technical. The mixes used to make the SSBs

usually consist of soil, a stabilizer, and water with the soil and stabilizer being mixed at a set ratio. The team did

not use a container of a specific volume to mix at the appropriate ratio but rather used a bowl (in the absence of a

gauge box) to scoop the necessary amount of material. In the 1:18 cement to soil mix one half bowl of Portland

cement was mixed with 9 whole bowls of soil to achieve the appropriate ratio. This process held for the ½:½:18

lime-cement-soil mix and the ½:½:18 lime-pozzolan-soil mix. HABRI’s Manuel for the Selection Testing and

Production of SSB suggests using a batching box to ensure identical mixes.

Plate 1: Mixing 9 parts soil ½ part cement using bowl

Even with the use of a batch box, however, the amount of water added to the mix is purely based on visual

observation and experience. The team followed the customary approach of sprinkling water until the mix reached

a satisfactory consistency. While sprinkling the water the team continued turning the mix with a spade and broke

apart any large lumps of soil. To check whether or not the mix has reached the correct water content HABRI

instructs, “Squeeze a handful of the dampened soil into a ball and drop it onto a hard surface….if the sample

breaks into four or five pieces then the mix has the right amount of water.” A more conventional method is to

simply compress a sample of the mix in ones hand. If the mix remains together after tossing it into the air, the

mix has the right amount of water. However, if water is released from the mix upon compression in the palm, too

much water has been added.

Plate 2: Mixing in water and testing consistency of mix

The team also found that the way the mix is placed in the mould can drastically affect the outcome of the final

SSB. If the mix is lightly compressed with the fingertips as the mix is being placed in the mould the SSB will be

difficult to compress but will be very solid and will hold together well upon ejection from the mould. The soil

should always be made flush with the top of the mould (when loosely hand compacted) and while HABRI

recommends oiling the mould after every SSB conventionally it is only oiled after every three to four bricks

depending on the type of mix.

Plate 3: Filling mould with mix while compressing with fingers and leveling top

Plate 4: Preparing mould for compression

Plate 5: Compressing and ejecting

In addition to improper water content in the mix other factors which may affect the outcome of the SSB should

be given due consideration. For instance the mix is placed in the mould without any initial compaction, the team

found the SSB will normally break apart upon being lifted away from the press. Another factor that leads to

failure is how the SSB is lifted away from the mould. The block should be lifted from the longer, middle portion

as opposed to the square ends. Also, if the mould is not oiled after at least every two bricks the SSB will have a

tendency to break apart upon ejection.

Plate 6: Improper loading of the mould and improper lifting lead to SSB failure

SSBs are often made using Portland cement as a plasticizer according to HABRI who suggests cement to soil

ratios ranging from 1:20 to 1:10. The team’s 1:18 cement to soil ratio falls in this suggested range and requires

very little cement. However, to further reduce the amount of needed cement, contemporaries use hydrating lime

as an additive at a lime to cement to soil ratio of ½:½:18. To completely eliminate the need for cement the team

used the same ratio but with a rice husk ash as a pozzolanic material. As research is ongoing by HABRI using a

rice husk ash mix, this proved to be a readily available material that can be low cost and easy to produce.

2.3 Testing of the SSBs and Burnt Bricks

The main focus of this research is to find alternative materials that can be incorporated in sand dams. Because

of this, the team decided to test the capacity of the blocks after immersion in water. The absorption of the

different blocks along with their compressive strengths were tested in labs while their permeability and

seepage would be evaluated with the use of a demonstration unit. The absorption and compressive strengths

after saturation, at 28-days, and at 7-weeks tests were performed by the team.

The absorption test was the first to be carried out. The team began testing the blocks by first weighing each

block to record the initial weight. After weighing them, the team put each block in a plastic bag to catch any

large parts or particles that have fallen off from the original block and to aid in removing the blocks from the

water. These blocks are then left in the water for 24 hours. When 24 hours have passed the SSBs and burnt

brick are taken out for observation and weighed. This allows for the determination of the percent absorption.

With this data, the team can estimate how each block will perform in damp conditions for long amounts of

time.

To get an idea of how strong each SSB and burnt brick is after being absorbed in water, the team conducted a

post-immersion compressive test. This test was performed immediately after concluding the absorption test to

ensure each block was totally saturated with water. This process is repeated on each of the SSBs and burnt

bricks.

The compressive strength test was performed after the SSBs cured for a period of at least 28 days. Although

contemporarily the 28 day strength is taken as the ultimate strength of the SSB, Hugo Houben and Hubert

Guillard say that a cement stabilized block will only reach 60-70% of its’ ultimate strength in this time and a

lime stabilized block can take up to 7 weeks (Houben). Therefore the 7-week ultimate strength test was

performed. According to Houben and Guillard the ultimate strength should be reached at 7 weeks instead of

28 days.

3. Findings

3.1 Soil Testing

After examining the soil taken from Mokena the team observed that it appeared to be a coarse, sandy soil. The

team then began testing the soil by determining the Atterburg Limits: shrinkage limit, plastic limit, liquid limit,

and plasticity index. The liquid limit and plastic limit tests were performed following ASTM testing procedures.

A graph of the flow curve shows liquid limit of 49.2% and the plastic limit was determined to be 24.5%.

Figure 1

The liquid limit and the plastic limit allowed the team to find that the soil has a plasticity index of 24.67%. The

liquidity index was then found to be -0.8 and the toughness index was found to be 1.5. Based on the flow index

and the toughness index the team was able to compare the murum from Mokena to soils with similar properties

and found that the soil has relative shear strength of _value not indicated????__. The team also determined the

shrinkage limit which was found to be 12.4%.

The team also performed a sieve and hydrometer analysis to determine the gradation of the soil. A sample of soil

with a mass of 50 grams was used to perform the hydrometer analysis, while 200 grams of soil was wet-sieved

using # 200 (75 micrometer) sieve and dried for 24 hours for the sieve analysis.

Figure 2

Silt Sand Gravel

Clay Fine Medium Coarse Fine Medium Coarse Fine

% 0 1 9 19 11 7 22 26

Total % 0 29 40 26

Figure 3

The sieve analysis showed that the largest particles found in the soil sample is a fine gravel constituting 26% of

the total sample. It also showed that the murum was made up of 22% coarse sand, 7% medium sand, and 11%

fine sand. Therefore sand made up about 40% of the total sample confirming the observation that the sample was

a coarse, sandy soil. Because only particles larger than the number 200 BS sieve were used for the sieve analysis,

a hydrometer analysis allowed the team to be able to evaluate the fines in the soil sample. The hydrometer

analysis allowed the team to conclude that there was no presence or very little clays in the soil sample. The

sample was found to be made up of 29% silts with 19% being coarse silts, 9% being medium silts, and 1% being

fine silts.

3.2 Testing of the SSBs and burnt bricks

Figure 4

As shown on the graph in Figure 4, the burnt brick absorbed the least with a percent absorption of only

17.27%. The 1/18 cement-soil SSB absorbed the second least amount of water with an absorption percent of

18.27%. The ½:½:18 lime-cement-soil SSB appeared to absorb the second highest amount of water as its’

final weight constituted 56.31% water, while the ½:½:18 lime-pozzolan-soil SSB disintegrated immediately

upon immersion. This hindered the team from being able to re-weigh the lime-pozzolan-soil SSB.

After re-weighing the post-immersed blocks, the team tested the compressive strength. This allowed the team

to be able to estimate the strengths of blocks after being exposed to moisture for long periods of time and to

allow for comparison to be made on the ultimate strengths after curing. Due to the extreme amount of

absorption and eventual disintegration of the ½:½:18 lime-pozzolan-soil SSB the team was not able to test the

compressive strength of the block post-exposure to moisture.

Figure 5

Observing the graph of Figure 5, the burnt brick appears to have the highest compressive strength reaching

about 60.85 pounds per square inch before failure while the ½:½:18 lime-cement-soil SSB only reached a

compressive strength of (0.126 N/mm2) 17.68 pounds per square inch before failure. The 1:18 cement-soil

SSB was found to have a post-immersed compressive strength of (0.4077 N/mm2) 57.15 pounds per square

inch, which was close to the strength of the burnt brick. Again, the ½:½:18 lime-pozzolan-soil SSB was not

tested due to the total disintegration in the presence of water.

Figure 6

As shown in Figure 6, the cement-soil block appears to have the highest compressive strength with that of (1.4

N/mm2) 196.48 pounds per square inch while the lime-pozzolan-soil had the lowest with ( 0.607 N/mm2) 85.13

pounds per square inch. The burnt brick had a compressive strength very close to the cement-soil which was (

1.348 N/mm2)188.95 pounds per square inch and lime-cement block had a strength of ( 0.849 N/mm2)119.06

pounds per square inch.

4. Discussion

4.1 Soil

The soil used by the team in the construction of SSBs plays a major role in the final strength and capacity of the

SSB. Even when a stabilizer is added, many of the soils properties can have a significant impact on the success

or failure of the SSB. While the digital topographic maps indicate many seasonal riverbeds in an ASAL

environment, and population densities show that approximately _?????__ people per square kilometer live in this

region, upon reviewing the findings of the analysis of the soil the team can form many conclusions about the

choice of the area in Mokena for the use of sand dams constructed of SSBs or burnt bricks.

The team initiated investigation into the soil by testing the Atterberg limits. After determining the liquid limit

and the plastic limit the team found that the soil has a plasticity index of 24.67%. Such a low plasticity index

indicates a soil with a high percentage of silt. Although The Auroville Building Center (AVBC) recommends

using a soil with around 15% silt, it recommends using a more sandy soil than clayey or silty. A Plasticity index

of 24.67% could mean that the soil has a percentage of silt comparable to the percentage of sand. The soil also

had a very low shrinkage limit of only around 12.4% indicating that the sample has very low percentage clay.

The liquidity index was also found to be -.8. A negative liquidity index such as this indicates a desiccated or

dried, hard soil.

The team then followed the Atterberg limits by determining the gradation of the soil and performing a

hydrometer analysis. Although the sieve analysis indicated the soil used in the production of the SSBs was a

fairly well graded soil from fine gravel to fine sand, the hydrometer analysis indicated the murum collected from

Mokena had a high percentage of silt at 29% and lacked any presence of clay. This corroborates the assumptions

made from the plasticity index. Clay is an essential material in the production of SSBs and compressed earth

blocks. The Auroville Building Center (AVBC) recommends using a soil consisting of at least 20% clayey

material, 15% silt, 50% sand, and 15% gravel. In this case because the soil used in the construction of SSBs

lacks clay, AVBC recommends there would be need in adding clay or an average of 5% cement and only using

lime as a stabilizer for clayey soils. Although the team did not add clay to the soil, the 1:18 cement-soil SSBs

constitute about 5.5% cement. When considering these findings, the assumption can be made that the 1:18

cement-soil SSBs will perform better than ½:½:18 lime-cement-soil SSBs and the ½:½:18 rice husk ash-lime-

soil SSBs. Another conclusion can be made that the murum collected in Mokena is not suitable for the use in

SSBs without considerable altering and stabilizers. SSBs made with this soil will likely not perform well without

the addition of clays or cement. Any SSBs stabilized with lime or lime and pozzolan will likely perform worse

than those which use Portland cement do to the high percentage of silts present in the soil.

4.2 SSB & Burnt Brick

After conducting a series of tests on the SSBs and the burnt bricks, the team was able to get a general idea of

what block or brick can be used in the construction of a sand dam. All the information that was gathered

allowed the team to make concrete conclusions on the research. The absorption, saturated compressive, 28-

day, and 7-week tests were all the analyses that were done by the team.

As the graph of Figure 3 portrays, the burnt brick performed the best having absorbed a little below 20% of

water. The cement-soil block perform the second best giving a result almost having an identical percentage

with the burnt brick while the lime-cement block posted the second worst results with a reading of more than

50%. Having disintegrated within minutes of being fully immersed, the lime-pozzolan-soil block performed

the worst having 100% absorption. This revealed to the team that the lime-pozzolan-soil block cannot be used

in the presence of water without some form of plastering to prevent the SSBs from contact with any moisture.

But as soon as the plastering erodes away then the block will fail because of the exposure to moisture.

The saturated compressive strength test was done on the SSBs after completing the absorption test. Shown in

Figure 4, the burnt brick came out with the best results. The burnt brick failed after a load of little more than

60 pounds per square inch. The cement-soil block performed very well as expected; having failed after a load

of about 57 pounds per square inch was applied. Besides the lime-pozzolan-soil block, the lime-cement block

did not perform too well compared to the burnt brick and cement block having a maximum load of about 17

pounds per square inch.

When comparing the percent absorption to the compressive strength post-immersion, the team was able to

determine which blocks appear to perform best in the presence of moisture while an external load is being

applied.

Figure 7

The 1:18 cement-soil SSB and the burnt brick appear to be almost identical with the burnt brick having the

higher compressive strength and lower absorption percentage of the two, as the graph of Figure 7 portrays.

Both absorption percentages appear close to 20% while their compressive strengths are very close to 60

pounds per square inch. With the high compressive strength post-immersion, the burnt brick doesn’t seem to

be affected by the increase in moisture. With the exception of the ½:½:18 lime-pozzolan-soil SSB, the

½:½:18 lime-cement-soil SSB performed worst with a 56.31% absorption and a compressive strength of only

(0.126N/mm2)17.86 pounds per square inch. After examining the performance of the lime-pozzolan-soil SSB

during the absorption and compressive tests, the team concluded that this ratio cannot be used in any sand

dam design or any other structure. The team concurred that the overall compressive strength of each block

will depend on how well each did in the absorption test. So it was no surprise that the burnt brick and cement

block performed the best while the lime-cement and lime-pozzolan-soil blocks did not.

The next procedure, the 28-day strength test, was performed on all of the blocks after 28 days of curing. The

cement block as revealed by Figure 6, came out with the best results with a maximum load of

(1.4N/mm2)196.5 pounds per square inch while the lime-pozzolan-soil block performed the worst as expected

with a maximum load close to 90 pounds per square inch. The burnt posted the second best results with a

maximum load of about 190 pounds per square inch. But the burnt brick was produced before the other SSBs

which the team predicted would contribute to the better overall readings in each test. The lime-cement did

fairly well, but had the third best reading which was about 120 pounds per square inch.

The difference in strengths for each block after 28 days and post-immersion also aided the team in making

final decisions on which material would be most suitable. For the burnt brick was 42.34% which was the

highest while the lime-pozzolan-soil block had the lowest with 0%. The cement block turned out to be very

low with a percentage of 4.54% and the lime-cement had the second highest with 30%.

5. Research Implications

5.1 Possibilities for Errors

5.1.1 Soil Testing

5.1.2 SSBs and Burnt Bricks

While performing the many tests and producing the SSBs, the team encountered a good amount of mistakes that

may have a large or small impact on the data gathered up and also the conclusions of this research. While

producing these SSBs, the team ran into faults that may have hindered the SSBs performance on each test as well

as the information gathered. Also while performing the tests the team noticed some mistakes that may have a

significant impact on the data. Some of these mistakes include, not enough samples tested, not all the SSBs were

made from the same batch, SSBs not all loaded into mold the same, differences in depth of SSB and burnt bricks,

tested only after 21 days of curing, and also the burnt bricks having a smaller volume than the SSBs.

Failure to test sufficient number of samples has a high possibility of causing error in the information because

unless the information is clearly accurate then it will not present enough data on each SSB’s strength and

durability characteristics. The team realized that if they had tested more specimens, they would have obtained

more data which would represent accurate results. Another error that may have an impact is the way the team

loaded the soil into the mould. After making a few SSBs, the team realized that patting down the soil while in the

mould will decrease the chances of it collapsing on extrusion from mould. As a result, the blocks that were

compressed after being patted down will stay compacted better than those that were not. This could affect the

overall strength during testing.

Some of the SSBs were made from different batches on different days which meant they took various curing

time. So when the team began testing, the blocks of different ages were tested at the same time. This would

impact the data because some of the SSBs had not attained the required age needed for testing. Another issue that

may have a significant impact on the information obtained is the differences in the depth of the SSB with that of

the burnt bricks. The difference in depth especially with the burnt bricks would cause it to fail more easily

because of the different heights of load application in comparison to that of a whole brick. The data collected

from values of these tests would provide in consisted information relating to the strength.

These are just a few of the descriptions as to why these errors in our research may cause some of this information

to be inaccurate.

5.2 Recommendations for United States Segment

5.2.1 Soil and SSBs

The testing that has been performed on the soil from the Mokena district in south-east Kenya, the SSBs produced

using stabilized soil, and the burnt bricks collected from the Mokena district has led the team to be able to make

several recommendations for further research during the program segment in the United States. Testing has

revealed many characteristics of the sample soil which affect the outcome of the SSBs along with many qualities

of the burnt bricks already in use by the rural communities in the ASALs of Kenya. The Unites States segment of

the research program can allow the team to build on the completed research to test ways to improve the soil,

SSBs, and burnt bricks.

Experiments performed on the murum samples taken from the Mokena district have proved that the soil,

unmodified, is not suitable for the use in the construction of SSBs. However, many modifications can be made to

the soil which should allow for its’ successful use in the construction of SSBs. Although the team will not be

using soil taken directly from the Mokena district in the research undertaken in the United States, it will be able

to recreate a soil of the same composition of gravels, sands, and fines to simulate that which would be found in

Mokena. The team can then make modifications to this model soil that will represent modifications that could be

made to the actual soil from Mokena.

One major alteration that could be made to the soil would be the increase in the percentage of clays and clayey

materials present in the Mokena soil samples. Because clays and silts are the naturally occurring cementitious

materials found in most soils, improvements on the fines can be made in the composition of the murum sample.

The soil was shown to have no presence of clays, therefore the team suggests bringing the percentage of clays in

the soil to around 20% to meet standards stated by AVBC before the soils use in the production of SSBs. The

team could also use this alteration to decrease the percentage silt from the current 29% to the recommended 15%

and to increase the sand content of 10% to reach the suggested 50%. The gravel should also be reduced to 15%

before SSBs are made out of this soil.

After obtaining the desired particle distribution of soil types, the team could then use the soil to create new 1:18

cement-soil SSBs. These should perform better than the ones created during the Kenya Segment due to the

higher percentage of sand present and the existence of clays. However, because the specified soil would still be

considered a sandy soil due to the high percentage of sand, new ½:½:18 lime-cement-soil SSBs and ½:½:18 rice

husk ash-lime-soil SSBs should not be constructed unless further alterations are made to the soil. SSBs made of

these ratios with the current modified soil would likely perform poorly due to the lower percentage of fines.

The team could experiment with different contents of cement to see if the modified soil could handle lower

percentages of cement in the construction of the SSBs. This would further reduce the production costs associated

with the price of Portland cement. SSBs could be produced with a cement-soil ratio of 1:20 and 1:22 and tested

along with the 1:18 cement-soil SSBs. The team could then further alter the soil to raise the percentage of fines

which would allow for the use of lime or lime and pozzolan as a stabilizer in the production of SSBs. The soil

would need to be modified until the sample could be classified as a clayey soil to justify the use of lime or lime

and pozzolan as a stabilizer. The soil could be made to be representative of the black cotton soil found

throughout Kenya instead of the murum collected in Mokena. However, the cost of transporting large amounts of

a different soil into Mokena should be evaluated before this option is considered.

SSBs produced of the two different batches of modified soil could be left to cure for a longer period to further

test the increase in ultimate strength after the contemporary time of 28 days. Compressive and tensile strengths

could be taken at 14, 21, and 28 days along with periods of up to 7 or 8 weeks to allow for the comparison

between the curing times commonly used of 28 days and those suggested by Houben and Guillaud. Because the

Kenya segment did not allow for the testing of tensile strengths of the SSBs or burnt bricks, the United States

segment could give the team the opportunity to test this and would also give a better understanding of the

capacity of the SSBs.

Tests could be conducted on the SSBs constructed out of the modified soil similar to those conducted during the

Kenya segment. The absorption of all of the new SSBs should be tested along with their compressive and tensile

strengths post-immersion. A period of 24 hours should still be used for the absorption test as during the Kenya

segment. This test could also be performed at different intervals during the curing period allowing the team to

determine at what time the SSBs could be satisfactorily used in the presence of water. The team could also

perform abrasion tests on the SSBs to simulate deterioration of the SSBs due to the flow of water.

5.2.2 Design

The team could further use the United States segment to research on suitable design for a sand dam constructed

of SSBs or burnt bricks. This could include experimenting with alternative designs and building practices. The

compressive and tensile strengths could be used to help decide on the orientation of the SSBs. Contemporary

designs could be modified to better suit the use of SSB or burnt bricks instead of the usual mass concrete.

Foundation design could come into consideration to possibly eliminate the need of any concrete. Contemporary

practices such as wall thickness increment of the sand dam from top to bottom could still be considered and

improved on. The team would also need to consider and research possibilities for mortar as this greatly affects

the strength and durability of completed structure. Plasters could also be considered if the SSBs appear to

perform poorly in the presence of water.

5.3 Other Recommendations

Further research should be conducted on the capacity of the burnt bricks to allow for the comparison of all

parameters to those of the new SSBs. The team will likely not be able to successfully replicate the burnt bricks in

the United States. Therefore, ongoing research on burnt bricks should be performed in Kenya with bricks made

from areas in the district of interest. Tests that were made on the SSBs constructed in the United States should be

performed on the burnt bricks to allow researchers to fully compare all properties with those of the SSBs.

To expand the research teams’ horizon in data collection soil samples should be collected from different districts

of Kenya and create SSBs specifically from the sample of each district. Then run all of the necessary tests on

each specific SSB as well as the soil to conclude which of the group is suitable for the construction of any

structure, with particular to sand dams. Also to compare each of the results for the tests of each SSB and soil

sample from the different districts, to distinguish which are superior both in strength while also being cost-

effective (create a data bank).

Another way to continue this research is to build a demonstration unit that will simulate the exact force exerted

on the dam by the river. This will give a small-scale replica of an actual sand dam which will help the researcher

visually see how the SSBs react to a simulation of an actual river flow.

6. Outcomes

6.1 Kenya Segment

The Kenya segment of the research resulted in many findings that can be useful in areas such as materials, water

resources, and construction in the East African region. Many conclusions can be drawn about the location of

Mokena, the murum soil found in Mokena, the burnt bricks produced in Mokena, and the SSBs made from the

soil from Mokena. The team was also able to identify many areas such as Baringo, Samburu, Moyale, Isiolo etc.

for further research.

Primarily the team was able to conclude that the murum found in Mokena is not suitable for the use in SSBs

without significant alterations. The soil lacks the presence of any clays or clayey materials and has 29% silts

which are inadequate for the use in SSBs. There is also too little sand at only 40% and too much gravel at 26%.

The soil could be modified to make it sufficient for the use in this form of construction material, but must have

its’ basic composition altered or use a large amount of a stabilizer like Portland cement which is not a very cost

effective material.

Because of its poor performance in almost each of the tests that were conducted, the team concluded that lime-

pozzolan-soil SSB constructed out of the soil in Mokena cannot be used in any sand dam design. As previously

stated, SSBs of this compostion, when exposed to moisture of any sorts, will fail completely. The cement and

lime-cement SSBs performed the best of the SSBs. Although the lime-cement SSB performed fairly well, it still

did not perform better than the burnt brick which is a more cost-effective material. Since the burnt brick

performed exceptionally well with only the cement-soil SSB giving it the best challenge of all the SSBs, the team

has concurred that the burnt brick can be used as material in the construction of the sand dam as well as the

cement-soil SSB. Being that cement is very costly and the aim is to choose an alternative and cost-effective

material, through this research the team confirmed that the burnt brick is the best possible solution.

6.2 Focus Audience

This research should be brought to the attention of the National Science Foundation (NSF), the University of

Nairobi, Non-Governmental Agencies (NGOs) that specialize in sand dams, and any organizations who are

working with materials. This research should be brought to the attention of the NSF because they are the

organization funding this research. Because many if not all of the mentors, professors, and lab technicians

giving advice and helping with the testing during this research come from the University of Nairobi, this

research should be brought to all their attention. There are a number of NGOs in Kenya and around the world

who specialize in or are doing work with materials specifically stabilized soil blocks and earth blocks which can

also be related to sand dams. To get the knowledge of stabilized soil blocks and the research being done with

them around the world, then it posting this research in journals or any science/engineering magazines will be a

skillful way of achieving this.

References

Brahic, Catherine. 11/16/2006 Sand dams: low-tech weapons against climate change. www.newscientist.com. 4/19/2009 Excellent Development. Sand Dams. www.excellentdevelopement.com 4/18/09 Practical Action. Sand Dams. www.practicalaction.com. 9/6/2006. 4/18/2009 SASOL & Maji na Ufanisi. 1999. Where theer is no water. Majestic Printing Works Ltd. 9966-9642-0-7 Ominde, S.H., 1968. Land and Population Movement in Kenya. Pub. Heinemann Publishing Company, London, 202 pp.

Earth Construction: Houben, Hugo and Hubert Guillaud. 1989. A Comprehensive Guide.. Intermediate Technology

Publications, London. 1-85339-193-X

Nissen-Petersen, Erik for Danish International Development Assistance (DANIDA). 2006. Water from Dry Riverbeds. ASAL

Consultants Ltd.

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