fundamental studies on ecological housing materials
TRANSCRIPT
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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
3
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”