Lateritic soil—cement bricks for rural housing

The International Journal of Cement Composites and Lightweight Concrete, Volume 6, Number 3

Lateritic s o i l c e m e n t bricks for rural housing J. O. A k i n m u s u r u *

SYNOPSIS The need to utilise local materials for the building industry in developing countries cannot be overemphasised. Lateritic soils are abundantly available in the tropics and can be used for the manufacture of durable bricks. This paper reports on improvement of the strength of these bricks by addition of cement. Results show that to achieve optimal strength conditions, the soil-cement bricks require much less hard firing than plain bricks. Depending on the firing temperature and amount of cement used, the addition of cement could result in brick strengths of up to four times those with no cement added at the same temperature and at least two and a half times the maximum strength with plain bricks at any firing temperature.

KEYWORDS Bricks, soil-cement, laterities, low cost thermal degradation, materials, strength of

* Senior Lecturer, Department of Civil Engineering, University of Ife, Ile-lfe, Nigeria @ Construction Press 1984 0262-5075/84/06360185/$02.00

August 1984

housing, compressive strength, construction, cement content, firing temperature, construction materials.

INTRODUCTION A major factor affecting the construction industry in developing countries is the cost of building materials most of which have to be imported. As prices increase sharply, there is a growing awareness to relate research to local materials as alternatives for the construction of functional but low-cost dwellings. Some efforts have been made in this direction [1-5] with promising results. These efforts have been justified by the particular case of the construction of the Institute of Strategic Studies in the Plateau Region of Jos in Northern Nigeria [6] which was built of single-storey earth walls complete with all modern equipments and facilities. Apart from low cost, the reddish natural colour of the walls, coupled with their low-rise nature, gave the natural architecture an aesthetic blend with the landscape of the area without interrupting with the native dwelling and constructions nearby. There is also the added cooling effect of such walls in a hot climate. In an earlier work [3], the crushing strength of mud blocks at ambient temperatures made from a lateritic soil and reinforced with pieces of a rope material, also locally available, was investigated. An optimum strength condition was achieved with 2.5% by weight of fibres and compressive strength was improved by up to 50% over that of unreinforced blocks. Rope fibre-reinforced blocks were, however, found to be unsuitable in the manufacture of bricks but the use of single-sized pebbles in place of the fibres significantly improved brick strengths, the optimum strength being achieved with 12.5% by weight of pebbles. The bricks were found best produced by firing in a furnace at temperatures that were increased in stages, and optimum conditions were achieved at about 900°C. This paper is a follow-up of the above investigation with ordinary portland cement added on to cylindrical mud blocks and burnt bricks for added strength.

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Lateritic soil - - c e m e n t bricks for rural housing

Akinmusuru

LATERITIC SOILS The use of lateritic soils is dictated by their cheapness, natural abundance and widespread use for the construction of mud walls for rural dwellings. Studies of laterites have been reported by Maignien [7] and Gidigasu [8], and their use in highway construction in Nigeria has also been reported [9,10,11]. For burnt bricks made of different types of laterite, Mesida [12] has shown that the chemical composition of the soil significantly affects the stress-strain relationships and the crushing strengths of the bricks especially at the high temperatures involved in the firing process.

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'- 6 TEXT MATERIALS AND PROCEDURE The soil used was a reddish browh laterite; the specific gravity of the grains was 2.47 and the liquid and plastic limits were respectively 45% and 20%. A geochemical breakdown showed that it was composed of 55% silica, 18% ferrous oxide, 15% alumina and lesser proportions of the oxides of titanium, potassium, sodium, magnesium, manganese and calcium. A compaction mould, cross-section 7.24 x 103 mm 2 and height 110 mm was used to make cylindrical specimens of the soil at the optimum moisture content of 20% which corresponded to the maximum dry density of 1600 kg/m 3. This cylindrical specimen size was used in all the tests. Ordinary portland cement was used to improve the strength and, in tests in which pebbles were included, only material between 2 mm and 4 mm average size was used. Curing was achieved by air drying at the ambient temperature of 25°C for eight days, which was earlier found to result in optimum strength [3]. For brick making, a large furnace capable of heating a chamber up to 1500°C was used for firing the cylindrical bricks up to 1000°C. Controlled firing was necessary if caking of the bricks was to be avoided (that is, brick developing a hard shell while inside was not adequately affected by the firing process). Firing was thus executed by raising the temperature in steps of 250°C every two hours. At each required brick temperature, specimens were allowed to cool before being subjected to unconfined compression test. For each set of data, three specimens were crushed. The aim of the experiments was to determine the effects of firing temperature, percentage cement content and presence of pebble addition on the crushing strength of the blocks and bricks.

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TEST RESULTS AND DISCUSSION Effect of firing temperature The effect of firing temperature on the crushing strength of cement-stabilised brick is shown in Figures 1 and 2 respectively for plain and pebble-reinforced bricks at different percentage cement contents. The trend was the same in both cases: for all cement contents, maximum strength was achieved at a firing temperature of about 500°C. Also, the crushing strength increased sharply for increasing temperatures less than about 500°C because of the progressive fusion of the cement and soil grains. The intergranular bond after the fusion was irreversible as

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Akinmusuru

Lateritic soil - - c e m e n t bricks for rural h o u s i n g

the cement would alter the material properties of the soil. It was observed on examination of the crushed bricks that the cement-soil combination at temperatures above 500°C broke up in the form of clinkers which bore no resemblance to the original cement and soil; nor did they have any material properties similar to those of the constituent materials. The clinkers broke easily at the slightest disturbance thus explaining the sharp drop in crushing strength at temperatures above 500°C. Irrespective of the cement content, at 900°C, the crushing strengths of the cement stabilised bricks with no pebble addition were about the same as for plain bricks with no cement or pebble edition. With the pebble-reinforced bricks, the strength of those without cement was higher at 900'°C than those with cement addition. It appears then that at 900°C, the presence of pebbles does not help the soil-cement bricks.

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Effect of c e m e n t content Figures 3 and 4 show the

influence of cement content at different temperatures on the strength of bricks without and with pebbles. In general, at all temperatures up to 500°C, the crushing strengths increased up to 7.5% cement content. For bricks with no pebbles, this trend was also the same at 750°C but, with pebbles added, the strength at 750°C practically remained constant. Beyond 750°C, the trend was erratic, showing a decreasing trend in the strengthcement content relationship. The graphs indicate that at cement contents in excess of 7.5% the trend was not easily predictable, strengths mainly increasing for temperatures up to 500°C. In any case, at higher cement contents, the bricks would have become too expensive. At 500°C, the strength obtainable at 7.5% cement content is four times that with no cement for bricks with no pebbles added and nearly thrice with pebbles added. At 500°C. even 5% cement content would still make strength improvement factors to be as high as 3.5 for plain bricks and nearly 2.5 with pebbles added. The brick strength with 7.5% cement added and at 500°C is about 2.5 times the maximum strength achievable with plain bricks fired to 900°C (no pebbles added). Effect of pebble addition In Figure 5, the crushing strength values obtained with pebbles reinforcing the bricks have been plotted against those without pebbles for all proportions of cement contents used. For each cement content, a linear relationship was established. It is evident that, on average, there is no significant change in crushing strengths brought about by the addition of pebbles, although some improvement can be achieved with the addition of pebbles when there is no cement [3].

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CONCLUSIONS

The influence of firing temperatures and of cement and pebble additions on the crushing strength of bricks made from a lateritic soil have been investigated. While maximum crushing strength is achievable for bricks with no cement addition at about 900°C, a much lower

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Lateritic soil - - cement bricks for rural housing

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Figure 5 Relationship between crushing strengths of soil-cement bricks with and without pebbles added firing temperature of about 500°C is adequate to achieve maximum strength if cement is added to the soil mix. At temperatures higher than 500°C, the soilcement composite forms brittle clinkers which can take very little load: the higher the firing temperature beyond 500°C, the sharper is the drop in strength of the bricks. The presence of pebbles would only hasten the disintegration of the clinkers. The effect of cement addition to the bricks is generally characterised by increased strengths for temperatures up to 500°C and for cement contents up to 7.5%. The strength of the bricks could be increased fourfold by the addition of 7.5% cement. Even lower cement contents increase strength considerably. Cement contents in excess of 7.5% appear to be uneconomical. It is also shown that no appreciable strength improvement could be obtained by the addition of pebbles in the formation of soil-cement bricks to sufficiently justify the efforts of obtaining pebbles of one particular size. Thus, in the use of lateritic soil-cement mixes for the production of bricks, the best mix combination appears to be 7.5% cement content with no pebbles added and fired in stages up to 500°C.

ACKNOWLEDGEMENTS The author wishes to thank Professor A. A. Afonja, Head, Department of Metallurgical and Materials

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Engineering of the University of Ife, for permission to use oven facilities in that department. Mr. David A. Fadare assisted in the testing and to him also many thanks are due.

REFERENCES 1. Akinmusuru, J. O. 'Application of engineering geology to rural needs in developing countries', Bulletin of the International Association of Engineering Geology, No. 22, Dec., 1980, pp. 279-82. 2. Akinmusuru, J. O. and Akinbolade, J. A. 'Stability of loaded footings on reinforced soil', Journal of the Geotechnical Engineering Division, Proceedings of the American Society of Civil Engineers, Vol. 107, No. G T 6 , Proc. Paper 16320, June, 1981, pp. 819-27. 3. Akinmusuru, J. O. and Adebayo, t. O. 'Fibre reinforced earth blocks', Journal of the Construction Division, Proceedings, American Society of Civil Engineers, Vol, 107, No. CO3, Proc. Paper 16517, Sept. 1981, pp. 487-96. 4. Akinmusuru, J. O., Akinbolade, J. A. and Odigie, D. O. 'Bearing capacity tests on fiber-reinforced soil', Proceedings, Second International Conference on Geotextiles, Las Vegas, USA, Aug. 1982. 5. Lasisi, F. 'Masonry units for low-income housing from cement stabilised lateritic soils', Proceedings, International Conference on Low Income Housing - - Technology and Policy, Bangkok, Thailand, June 1977, pp. 1037-46. 6. Giwa, D. 'Return of Mother Earth in Jos', Daily Times Newspaper, Times Publications Ltd., Lagos, Nigeria, No. 2205, June 18, 1979, p. 7 7. Maignien, R. 'Review of research on laterites', UNESCO publication, Paris, 1966. 8. Gidigasu, M. D. 'Lateritic Soil Engineering', Elsevier Scientific Publications Co., New York, 1976. 9. Ola, S. A. 'Need for estimated cement requirements for stabilising lateritic soil', Journal of the Transportation Engineering Division, Proceedings of the American Society of Civil Engineers, Vol. 100, No. TE2, Proc. Paper 10534, May 1974, pp. 379-88. 10. Ola, S. A. 'Geotechnical properties and behaviour of some stabilised Nigerian lateritic soils', Quarterly Journal of Engineering Geology, Vol. II, No. 2, 1978, pp. 145-60. 11. Akinmusuru, J. O., Omotosho, P. O. and Omotosho, T. O. Y. 'Behaviour of soils subjected to multicyclic compaction', Proceedings, 8th African Regional Conference, International Society of Soil Mechanics and Foundation Engineering, Harare, Zimbabwe, June, 1984. 12. Mesida, E. A. 'On the utilisation of lateritic clays for rural bricks', M.Sc. Thesis, University of Ife, lie-Ire, Nigeria, 1976,