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Page 1: Fundamental Studies on Ecological Housing Materials

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The Eighteenth KKCNN Symposium on Civil Engineering

 December 19-21, 2005, Taiwan

FUNDAMENTAL STUDIES ON ECOLOGICAL HOUSING MATERIALSIN KENYA

Kazuhito Sakata1, Yoshinobu Oshima

2, and Kunitomo Sugiura

 Department of Urban and Environmental Engineering, Kyoto University, Japan

[email protected] , [email protected] , [email protected]

ABSTRACT

This paper reports on the fundamental property of Stabilized Soil Block (SSB) and field

investigation of pozzolan in Kenya, which can reduce the cost of SSB by replacing cement.

First of all, compressive tests were carried out on SSB specimens using local soils. As a result,

it is found that SSB using Murram has enough strength for single story housing, but others do

not have enough strength. Next, we investigated pozzolan distribution around Nairobi area. InGreat Rift Valley, enormous amount of pozzolan is found by radar exploration, which opens

to the economical supply of pozzolan for SSB. We also investigated Nyumbani Village, where

SSBs are applied to housing materials, to find out the feasibility of SSB. Finally we can say

that SSBs can reduce the housing cost, especially using pozzolan admixture, which also leads

to poverty reduction in Kenya.

INTRODUCTION

In Kenya, due to its housing standard legislated by the colonial authorities, who protected

settlers’ environment, excessive high quality-materials for housing construction are required

even up to now, which restricts new constructions for low income people. Thus in the urbanand the peri-urban areas of Kenya, illegally constructed houses are widely spread to create

slums. The capital city, Nairobi with a population of three million has about 60% of its

residents living in slums, which occupy just 5% of the total residential land area. The terrible

unhygienic dwelling condition in the slums causes epidemic diseases and crimes.

Furthermore high cost of cement results in the sluggish housing provision. The ratio of a 50kg

cement bag cost to average daily wage exceeds five in Kenya. Cement is manufactured by

three companies: Bamburi Cement Ltd., Blue Triangle, and Athi River Mining Ltd. These

companies operate a cartel to maintain artificially high prices. The severe shortage of

1  Graduate Student2  Professor3 

Assistant Professor

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appropriate housing cannot be improved unless serious measures are taken.

Stabilized Soil Block, SSB, has been proposed as an alternative material for low cost

housing. SSB is a mix of water and soil with cement, and generally used as building materials.

SSB is regarded as an ecological material because there is no burning process during

manufacture and the price is affordable for low income people. In recent years, the use of SSB

as ecological building material has been increasingly expanding not only in developingcountries but also in New Mexico of the United States, France, and Australia.

Furthermore the cost and the strength of SSB can be improved by using pozzolan which is

a finely-divided material that reacts with calcium hydroxide and alkalis to form compounds

 possessing cementitious properties, and enormous amount of pozzolan is recognized in Great

Rift Valley in Kenya.

Therefore in this study, fundamental property of SSB using local soils is evaluated, and

investigation of pozzolan distribution in Great Rift Valley is also carried out. We also

investigated Nyumbani Village as a case study, where SSB is applied to build economical

houses. These simple building technologies now have the potential to transform lives in

Kenya’s cities and could help build affordable houses. But until recently the adoption of this

technology was being held back because such houses would not be legally recognized.

Fig. 1 Slum area in Nairobi

COMPRESSIVE TEST FOR SSB

Test set up

Compressive test was conducted on three types of SSB specimens, all of which include

3% of cement and appropriate amount of water. Red Coffee Soil, Murram, and Quarry Dust

respectively were used for main components. Red Coffee Soil and Quarry Dust were tested

once respectively, and Murram was tested twice. The specimens were made by using manual

machine for SSB showed in Fig 2. Dimensions of the specimens are shown in Table 1. A

universal testing machine in Fig 3 was used to measure the compressive strength of the

specimens.

Result

Murram showed compressive strength of about 1.6MPa. Red Coffee Soil showedcompressive strength of only 0.60 MPa. Quarry Dust showed almost no compressive strength.

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Table 1 shows the summary of the results of the compressive test.

Thus Murram, which is a type of hard soil containing small stones found in East Africa, is

the best component of SSB. It should be noticed that the material cost of this SSB is only four

to five Ksh per unit block.

Table 1 compressive test results of SSB

Main component of SSB Red Coffee Soil Murram Quarry Dust

Sample number 1 2 3 4

Size

length (cm)

width (cm)

height (cm)

28.7

14.0

11.0

28.6

14.0

11.5

29.0

14.15

11.4

29.0

14.4

13.8

Compressive stress (MPa) 0.60 1.62 1.32 0.22

Fig. 2 Manual machine for SSB Fig. 3 Compressive test

POZZOLAN DISTRIBUTION IN KENYA

Pozzolan

A Pozzolan is a finely-divided material that reacts with calcium hydroxide and alkalies to

form compounds possessing cementitious properties. Pozzolans such as diatomaceous earth,

volcanic ash, opaline shale, pumicite, and tuff exist near the ground surface. These materials

require further processing such as calcining, grinding, drying, etc. Natural pozzolans have

 been used in dams and bridges to lower the heat of hydration and increase resistance of

concrete to sulfate attack and control the alkali-silica reaction. Usually the pozzolanic deposit

must be in the vicinity of the project to support mining and processing costs.

Investigation for Pozzolan distribution

At the Great Rift Valley which is a rift of the earth running from West Asia to East Africa,

there was huge volcanic activity in the remote past, and now abundant amount of volcanic ash

and rocks are recognized. We made an investigation tour to Great Rift Valley in the vicinity of

 Naivasha City to find out the distribution of pozzolan by radar exploration. Three places wereselected to be exploration sites and were situated at lat. 0°32′25″S and long 36°32′25″E, lat.

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00°54’49’’S and long 36°31’1’’E, and lat. 00°27’03’’S and long 36°16’31’’E respectively.

Investigation Result

Fig.4 shows the radar test in the filed. Fig.5 and Fig.6 show the surface of volcanic ash at

Great Rift Valley. It was found that volcanic ash was accumulated at least over ten meters

underground at these three points. Chemical analysis is planned to be conducted to find outtheir chemical components and what kind of pozzolan is the most appropriate admixture for

SSB.

Fig. 4 Underground detection 

Fig. 5 Volcanic ash at Great Rift Valley Fig. 6 Volcanic ash at Great Rift Valley

Diatomite factory

A tour to a diatomite factory in the vicinity of Naivasha was also organized. The diatomite

 produced at this factory contains 86% of SiO2  and 0.7% of AlO2. It can be said that those

components have good potential to be used as pozzolan material. Moreover it should be

noticed that during production process great amount of diatomite dust is disposed without

recycle or reuse, and the amount reaches about 50% of whole production amount. If this

disposed diatomite dust is used and transported to Nairobi and other cities, a pozzolan

material with good quality can be obtained easily.

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CASE STUDY

 Nyumbani village

 Nyumbani village in the Kitui district, which is about 100km from Nairobi, has been

developed by NGO. This village is a self-sustaining community to assist AIDS-affected

seniors and children by providing housing as well as medical, educational, and counselingstructures and services in an environment conducive to the spiritual and cultural development

of the residents.

SSB for low cost housing

In this village, SSB is employed to make 160 houses which can accommodate around

1,000 children, young adults and elderly, most of whom are HIV affected. The main

component of the SSB made in this village is Red Coffee Soil. Quarry dust and cement are

used as admixture. Especially, they use interlock SSB as shown in Fig. 7, which can be piled

without mortar because of its interlock shape.

Fig.7 SSB in Nyumbani village Fig. 8 House made with SSB in

Nyumbani village

Cost comparison

Two types of houses are built in this village. Fig.8 shows the typical house in this village.

Table 2 shows their areas and cost. Cost of the house made with concrete blocks is also

compared in Table 2. The difference of material cost between SSB and concrete block and the

fee for transporting concrete blocks from Nairobi are taken into account.

The machine to make SSB is imported from a South African company called Hydrofoam.

Table 3 shows the cost of the machine, the number of SSB which can be produced per day, the

number of necessary laborer, and the cost of one SSB.Seven percents of cement is mixed into each SSB, and the amount of cement per each

SSB seems to be too much. If we replace the cement by pozzolan, the cost can be reduced

effectively.

Table 2 Cost of SSB house and of Concrete Block house

SSB Concrete Block

Type 1 120 mm2  720,000 Ksh 2,226,000 Ksh

Type 2 77 mm2  490,000 Ksh 1,520,000 Ksh

(Labor cost included)

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Table 3 Cost and laborer summary

Machine Machine cost

(Ksh)

 Number of

SSB /day

 Number of

laborer

Cost of one

SSB

Hydrofoam machine 2,500,000 2,400 11 14

Manual machine 50,000 500 6 12

CONCLUSIONS

We evaluate SSB for low cost material experimentally and also investigate the pozzolan

distribution to apply it for the admixture of SSB. The following conclusions can be drawn:

1)  From the experiment the Murram SSB showed compressive strength of about 1.6MPa.Material cost of this SSB is only four to five Ksh per unit block. It was also found that

Red Coffee Soil SSB showed compressive strength of only 0.60 MPa. Quarry Dust SSB

showed almost no compressive strength. Thus we can say that Murram is appropriate for

SSB.

2)  In Great Valley Rift, an enormous amount of volcanic ash, which can be used as

admixture for SSB to reduce the cost, was accumulated at least over ten meters

underground.

3)  At Nyumbani village in the Kitui district, where SSB is employed to make 160 houses for

those who are HIV affected, it was found that the cost of the houses can be reduced by

applying pozzolan as admixture for SSB.

ACKNOWLEDGEMENT

This study was funded by science research funds, No.16404009, from the Education

Bureau of Japan. The experiment was conducted at the laboratory of Civil Engineering

Department in Jomo Kenyatta University in Kenya. I would like to express sincere thanks to

the technical staffs of the department for this assistance.

REFERENCES

Walter O. Oyawa. (2005), “Development of local cementitious materials for low cost housing – phaseⅡ”