The Internatlona/ Journal of Cement Composites and Lightweight Concrete, Volume 9, Number 2
Properties of clay-sand-rice husk ash mixed bricks M. A. R a h m a n ~
Synopsis Bricks were made from clay-sand mixes with different percentages of rice husk ash and burnt in a furnace for different firing times. The firing durations at 1000°C were 2 hours, 4 hours and'6 hours. The effects of rice husk ash contents on workable mixing water content, Atterberg limits, linear shrinkage, density, compressive strength and water absorption of the bricks were investigated. Test results indicated that lightweight bricks could be manufactured with rice husk ash without any deterioration in the quality of bricks. Further, the compressive strength of the bricks was higher with rice husk ash contents. The optimum firing duration was found to be 4 hours at 1000°C. It is shown that bricks made of clay-sand-rice husk ash mixes can be used in load bearing walls. Keywords Bricks, clays, sands, rice husk ash, construction materials, firing temperature, shrinkage, compressive strength, density, water absorption, strength of materials, walls.
INTRODUCTION Most third world countries suffer from an acute housing shortage principally because of the increasing need for new housing units created by the growing population. Although in a developing country like Nigeria where the cost of a unit block of concrete or sandcrete (mixture of cement and sand) is relatively high, at present these materials serve as the backbone of building construction. The use of concrete for low cost housing and roads in rural areas of the country is not often necessary. There are large clay deposits in some parts of Nigeria. High quality firing woods are also available and are very cheap. The increasing cost of building materials such as concrete or sandcrete block, and the ready availability of clay deposits and firing woods dictate the need to examine the potential for utilising local clay deposits in the building construction industry. Clays are the raw materials for burnt bricks. Bricks are adequately strong and durable for construction purposes. If production is carried out under reasonable and economic conditions, burnt bricks should be much cheaper than concrete blocks. Some efforts have been made in this direction with promising results [1-31 Mesida [1} has shown that burnt bricks made of different types of Nigerian lateritic clays are satisfactory for normal housing purposes, especially for the construction of bungalows and one storey buildings. Akinmusuru " Lecturer, Department of Civil Engineering, University of Ire, Ile-lfe, Nigena. Recewed 8 August 1986 Accepted 17 January 1987 © Longman Group UK Ltd 1987 0262-5076/87/09206105/$02.00
and Adebayo  investigated the crushing strength of mud blocks at ambient temperatures made from a lateritic soil and reinforced with pieces of a rope material. Akinmusuru [31 also investigated the effects of cement on compressive strength and the optimum firing temperature of bricks made from lateritic soil. Aderibigbe et al.  investigated two clay deposits from Lagos in Nigeria for the development of cement-stabilised blocks. Rice husk is a waste product, generated from the accumulation of the outer covering of rice grains during the milling process; it constitutes about 20% of 300 million matric tonnes of rice produced annually in the world . Use or disposal of rice husk has frequently proved difficult. On the other hand, its use in construction protects the environment. The idea of combining carbonaceous materials with clay in brickmaking is well established. The motives for inclusion of these waste materials in brickmaking are various. Rai  used industrial and agricultural wastes for the production of low cost building materials. Pepplinkhouse [7} utilised rice husks in brickmaking. AI-Taie and AI-Rawi [8} also utilised agricultural wastes such as bagasse, rice husks and straw in the production of lightweight clay bricks. They were particularly concerned to produce bricks with low thermal conductivities. Tauber et al. [91 noted that most of the organic material volatilises and escapes when the green bricks are fired. The brick becomes lighter, cheaper and easier to handle and transport. Murray et al.  noted that the green bricks incorporating added waste materials showed higher strength than normal ones. These would reduce losses through breakage and rate of drying could be also faster. The consistency and workability of clays could be improved on the addition of waste materials. Carter et al.  investigated the properties of bricks
Properties o f clay-sand-nce husk ash mb~ed bricks
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incorporating unground rice husk for low-cost housing. The aim of this paper is to find the effects of rice husk ash on the various properties of bricks made from clay-sand mixes and also to examine the suitability of these bricks for both load and non-load bearing walls.
TEST MATERIALS The materials used in this investigation were clay soil, fine sand and rice husk ash.
Clay soil The clay soil was collected from Ilesha, Nigeria. The plastic properties and chemical composition of the soil are given in Table 1. Table 1 Properties of original clay soil sample Properties SiO2 AI20:,, Fe203 Loss on ignition Undetermined Natural water content Liquid limit Plastic limit Plasticity index
~!,58.32 20.74 545 8.35 7 ;4 16.86 69.70 36.20 33.50
Sand The sand passing through 0.60 mm sieve size only was used: It was collected from pits. The colour of the sand was light brown.
Rice husk ash In this study burning of rice husks was carried out as follows: Rice husk ash (RHA) was prepared in a furnace by burning the husks at 500°C for 2 hours. RHA was whitish grey in cOIour. RHA passing through 0.075mm sieve size was used. A geochemical breakdown showed that it was composed of mainly silica (89.50%), and lesser proportions of the oxides of various elements such as potassium, sodium, calcium and magnesium Loss on ignition of rice husk ash was 3.59%.
Atterberg limit tests were performed on vanous clay-sand-RHA mixes. Water was added to clay-sandRHA mixes until it gave a consistency suitable for thorough and proper mixing in the preparation of cia7 bricks. Different workable mixing water contents were obtained for different percentages of RHA contents. The workable mixing water content increased with RHA contents, since RHA had more affinity for w a t e r The procedure used in the preparation, drying al;,:i firing of bricks was as follows: (1) Clay-sand-RHA mixes and predetermined workable water content were mixed in a large tray by hand unti! a uniform mixture was obtained. (2) The mixture was stored in a cool and humid room for about 24 hours. During this period, the water content could be uniformly distributed throughout the mixture. (3) The clay-sand-RHA mixture was then moulded. Hand moulding was used. A roughly shaped (slightly longer and thicker than the required size) clot of tempered clay-sand-RHA mixture was thrown forcely into ~ mould of sizes 5cm x 5cm x 5 c m The excess material on the top of the mould was trimmed and removed by a thin wire. Before filling the mould with clay, the mould was dipped in water to prevent the clay sticking to it (known as siop-moutding). (4) Next, the moulded brick was demoulded immediately and dried in the sun for 8 days at ambient, temperature of 30°C. The bricks were oven dried at 105°C for 24 hours prior to firing. (5) tn this study, a furnace capable of heating a chamber up to 1200°C was used for ~iring the bricks up to 1000°C. To avoid caking of the bricks (brick developing a hard shell while inside not being adequately affected by the firing process), controlled firing was used. Firing was executed continuously in four steps (250 ° , 500 °, 750 ° and 1000°C) and firing duration at each step was 2 hours except for the last step. Three series of bricks were fired, receiwng 2-hour, 4-hour and 6-hour soak at I000°C respectively. The measured properties of the bricks were linear shrinkage, density, compressive strength, 24-hour ,mmersion water absorption and 5-hour boiling water absorption-properties considered to be important to evaluate the suitability of bricks for use. For each set of data, three specimens were used. 90 bricks were burnt out of 105 green bricks ..... 45 bricks were used for compressive strength test:~ and the remaining -45 were used in water absorption t e s t s
EXPERIMENTAL PROCEDURE The clay soil used in this investigation was highly plastic. In order to improve the consistency and workability of the clay, 30% (by weight of dry soil) Of fine sand was mixed with it. Sand decreased plasticity, linear shrinkage and warping. Clay soil was pulverised and spread out in a large tray. Then sand was added on top of the clay and mixed thoroughly until uniform colour was obtained. Different percentages of rice husk ash were then added to the clay-sand mixes. Percentages of rice husk ash were 5, 10, 15 and 20 (by weight of dry clay-sand mixes)
TEST RESULTS AND DISCUSSION Atterberg limits and workable mixing water contents The results of Atterberg lit-nit tests and workable mixing water contents are shown in Table 2. It can be seen that both liquid and plastic limits increase, whilst plasticit'f index decreases with RHA contents Workable mixing water content also increases with increase in RFIA.
Properties ot clay-sand-nce husk ash mixed bricks
Table 2 Effects of rice husk ash (RHA) on Atterberg limits and workable mixing water content of clay-sand mixes Rice h u s k ash (% weight)
Liquid limit (%)
Plastic limit (%)
0 5 10 15 20
52.55 54.05 56.10 58.30 61.80
34.50 37.02 40.12 44.13 49.50
Plasticity index (%)
Mixing water content (%)
18.05 17.03 16.98 14.17 12.30
38.10 44.30 48.70 50.50 52.10
Water absorption Table 5 shows 24-hour immersion and 5-hour boiling water absorption. Both values increase with rice husk ash contents, the increase in water absorption being non-linear. The 5-hour boiling water absorption is higher than the 24-hour water absorption, the maximum values being 20% and 25% respectively. All bricks meet generally accepted absorption criteria [11 ]. The results show that, from considerations of economy, compressive strength and water absorption, the optimum duration of firing is 4 hours at 1000°C. The compressive strengths of all bricks made from clay-sand-RHA mixes also satisfy the minimum compressive strength requirements of 10.00 N/ram 2 and 2.75 N/mm 2 for load and non-load bearing wails [1 2].
I_inear shrinkage and density The summary of the results of linear shrinkage, and dry and firing densities are shown in Table 3. All these properties decrease with RHA contents. The decrease in dry density with 20% RHA is about 14%, indicating that by adding RHA it would be possible to produce light weight bricks.
Table3 Effects of rice husk ash(RHA) on linear shrinkage, dry density and firing density of clay-sand bricks Rice husk ash (% weight) 0 5 10 15 20
Linear Dry s h r i n k a g e density (%) (kg/m 3) 7.53 7.27 7.13 7.01 6.80
1600 1500 1440 1400 1370
Table 5 Effect of rice husk ash (RHA) on water absorption Rice husk ash (% weight) 0 5 10 15 20
Water absorption (%) 5-hour boiling 24-hour absorption absorption 2h 4h 6h 2h 4h 6h 16.16 17.37 17.77 17.28 18.15
17.59 18.00 20.55 19.91 20.0t
15.37 16.84 19.69 20.88 20.20
21.40 21.99 22.85 2453 24.61
22.48 23.47 24.95 25.00 25.20
19.70 21.64 23.80 25.41 25.50
Firingdensity (kg/m3) 2h 4h 6h 1540 1480 1460 1420 1380
1540 1470 1430 1420 1380
1590 1530 1460 1440 1420
CONCLUSIONS On the basis of test results, the following conclusions can be drawn: 1. Workable mixing water content, liquid limit and plastic limit increase with RHA contents while plasticity index decreases. Rice husk ash improves the consistency and workability of the clay to produce clay bricks.
Compressive strength The results of compressive strength are shown in Table 4. The compressive strengths of both burnt and unburnt bricks are seen to increase with RHA contents. The increase in strength is almost linear, the bricks which received 4-hour soak at 1000°C, giving maximum compressive strength.
2. The density of brick decreases with increase in RHA contents. Light weight bricks can thus be produced without any deterioration in the quality of the bricks.
Table4 Effect of rice husk ash (RHA) on compressive strength
4. The optimum firing duration at 1000°C is 4 hours. RHA tends to decrease the firing duration required to produce well burnt bricks.
Rice husk ash (% weight) 0 5 10 15 20
Compressive strength (Nimm 2) Burnt brick Green brick 2h 4h 6h 2.61 2.74 2.85 2.94 3.08
8.83 9.05 9.23 9.55 9.70
12.13 12.80 14.32 14.52 14.60
12.01 12.30 12.50 12.63 12.65
3. RHA decreases the linear shrinkage of the brick. Compressive strength and water absorption, on the other hand, increase with the addition of RHA. The water absorption is, however, within allowable limits.
5. Bricks made of clay-sand-RHA mixes can be used for load bearing wails.
ACKNOWLEDGEMENTS The author acknowledges with thanks the assistance of Mr I. O. Odeyemi in testing, and that of Dr G. Thorbecke for the geochemical analysis of clay and rice husk ash.
Properties o f clay-sand-rice husk ash m i x e d bricks
REFERENCES 1. Mesida, E. A. 'Utilisation of some lateritic clays for burnt bricks', Journal of Mining and Geology, Vol. 15, No. 2, 1978, pp. 108-14. 2. Akinmusuru, J. O. and Adebayo, I. O. 'Fibre re inforced earth blocks', Journal of the Construction Division, Proceedings, American Society of Civil Engineers, Vol. 107, No. CO3, September 1981, pp 487-96. 3. Akinmusuru, J. O. 'Lateritic soil-cement bricks for rural housing', The International Journal of Cement Composites and Lightweight Concrete', Vol. 6, No 3, August 1984, pp. 185-8. 4. Aderibigbe, D. A., Akeju, T. A. I. and Orangun, C. O. 'Optimal water/cement ratios and strength characteristics of some local clay soils stabilised with cement', RILEM, Materials and Structures, Vol. ! 8, March-April 1985, pp. 103-8. 5. Cook, D. J., Pama, R. P. and Darner, S. A. 'The behaviour of concrete and cement paste containing rice husk ash', Proceedings, Conference of Hydraulic Cement Pastes, Their Structures and Properties, University of Sheffield, April 1976, pp 268-83.
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Rai, M. 'Low cost building materials using industrial and agricultural wastes', international Journal of Housing Science, Vol. 2, 1978, pp 213-21 Pepptinkhouse, H J. Utilisation of rice nulls Jn brickmaking --. an industrial trial', Journal of Australian Ceramic Society, Vol 16. 1980, pp 26-8. AI-Taie, M. H. and AbRawi, S. A. 'Manufacture of lightweight clay bricks from local materials ~, Paper presented at Second Scientific conference, Bagh dad, December 1975 Tauber, E., Pepptinkhouse, H J. and Crook, D i-i 'Lightweight ceramics', Journal of Austral;at,, Ceramic Society, Vol 10 !974, pp. 12-5. Murray, M. J., Pepplinkho~Jse, H. J. and Liversidge, R M 'Production of lightweight bricks and blocks utilising sawdust wastes', Division of Building Research Report, C.S.I R O, Australia, 1981 Carter, G. W., Cannor, M A and Mansell, D S 'Properties of bricks incorporating unground nce husks', Building and Environment, Vol. !7, No 4, 1982, pp. 285-91 Everett, A., Materials, Published by B.T Batsford Ltd, t978, Ed., p 125