UTILIZATION OF RICE HUSK ASH BLENEDED CEMENT IN LATERITIC BRICK AND CONCRETE PRODUCTION

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1 UTILIZATION OF RICE HUSK ASH BLENEDED CEMENT IN LATERITIC BRICK AND CONCRETE PRODUCTION ABSTRACT Umoh, A. A. and Ujene, A. O. Department of Building, Faculty of Environmental Studies. University of Uyo, Uyo, Nigeria. Phone: The study was aimed at finding an adequate amount of rice husk ash (RHA) that could replaced Ordinary Portland Cement (OPC) in the production of Laterite Stabilized Bricks and Concrete for building purpose. Sixteen mixes consisting of various percentages of OPC by the volume of dry laterite, and the OPC being partially replaced with,, and % RHA were used in bricks production; while two mix ratios of 1:1:2 and 1:2:3 (OPC :Fine laterite: Coarse laterite) with OPC replaced with,, and % RHA, were adopted for laterite concrete production. The water absorption test on the bricks were between 8.26% and 18.90% with OPC/RHA stabilized bricks having higher values, while the compressive strength at 28 days range within 4.01 Nmm -2 and 2.14 Nmm -2 for OPC bricks, and 1.08 Nmm -2 to 3.84 Nmm -2 for bricks incorporating RHA. The compressive strength of laterite cubes tested at 28 days had values of 9. Nmm -2 to 18 Nmm -2 for mixes using 1:1:2, and 6. Nmm -2 to Nmm -2 for mixes that have 1:2:3 mix ratio. % RHA in 8% and 12% OPC of the volume of dry laterite were adequate for bungalows and load-bearing wall construction, respectively. A mix ratio of 1:1:2 containing % RHA, and % RHA in the mix ratio of 1:2:3 are recommended for masonry and insulating concrete, respectively. Keywords: Compressive Strength; Laterite; Rice husk ash; Stabilization; Water absorption INTRODUCTION The high cost of building materials has been one major hindrance to housing ownership. One way of bringing down the cost is by finding alternative construction materials to conventional ones. Such alternative materials are laterite and rice husk ash (RHA). Laterite is a soil formed as a result of weathering of igneous rock under conditions of high temperature and high rainfall, where the decomposition process result in a soil leached of silica and calcium carbonate but retaining high concentration of iron and aluminum sesquioxides (McCarthy, 2000). Laterite can be found in hard or cemented state. It is in cemented form in areas that have sparse vegetation like in the arid zone. The cementation, which is cause by free iron oxide in the soil, is such that the hard laterite can be processed and used as coarse aggregate in concrete production. The stabilization of laterite using cement, lime and bitumen has been reported to be effective in overcoming inherent problems such as low compressive strength and high permeability associated with unstabilized soil blocks. Ola (1983) reported that soil blocks stabilized with 10-12% cement content produces blocks that can be used for load-bearing wall construction. The compressive strength of stabilized laterite blocks has been reported to be comparable with cement-sand mix, and that the compressive strength increases with the curing age (Okunnu, 1980) Rice husk ash is obtained by the burning of rice husk. The temperature being kept between 0 0 and c will produce a reactive ash rich in silica content. The burning process can either be done in a purposely-made incinerator or in open heaps of quantity not more than 20Kg (Chinde-Prasirt, 1983). The use of RHA as partial replacement of cement in sandcrete block production is reported by Okpala (1987). He found out that cement replaced with RHA up to % produces sandcrete blocks that meet the requirement for load-bearing walls up to 3- storey height. Rice husk ash has been used as constituent in concrete production. Ikpong (1993), Umoh (1997) and Sakr (2006) used RHA as partial replacement of cement. The results revealed that optimal replacement levels of -% of cement with RHA produced a concrete of compressive strength in the range of N mm -2. The use of RHA as partial replacement of cement in the stabilization of soil-block and laterite concrete production is scarce in literature; therefore, this study intends to look into some mechanical properties of lateritic block and concrete with a view to establishing the optimal replacement levels that will meet stated standard requirements for housing need. MATERIALS AND METHOD Materials The laterite used was obtained from a village in Ini local Government Area of Akwa Ibom State. The lumps were broken using club hammer, and the coarser particles separated from the fine ones using 5mm sieve size. The coarser particles were used as coarse aggregate and the fine particles as fine aggregate. Sieve analysis, liquid and NJAFE VOL. 9 No. 3,

2 plastic limit tests were conducted on the laterite. The rice husk ash was collected from a local mill in Odoro-ikpe, Ini local Government Area of Akwa Ibom State. Burning was done in a dug pit of diameter 625mm and of depth 2mm. This was done to prevent the ash from being carried away by wind. The ash was initially sieved through a 212 micron mesh wire. Particles retained on the wire were manually ground and sieved again. A sieve analysis was conducted on the ash. Commercially available Ordinary Portland Cement (Dangote brand) was used. Initial and final setting times were carried out on the cement to ascertain conformity with relevant standards. The Water used for mixing and curing of specimens was potable drinking water from the tap in the Building Soil and Concrete laboratory, University of Uyo,Uyo, Nigeria. Method Bricks: Two sets of bricks were produced. The first set consisted of four (4) mixes containing laterite (as fine aggregate) added with 6, 8, 10, and 12% of cement by volume of the dry laterite respectively. The second set had twelve (12) mixes consisting of laterite and various percentages of Ordinary Portland Cement (OPC) as in the first set and each percentage being replaced with,, and % RHA by volume. Each mix was done manually. The cement and RHA were first mixed until a uniform colour was attained. The blended material was then added to the laterite and mixed thoroughly. Water was carefully sprinkled on it and mixed. The amount of water added to mix was 14% by the volume of the laterite. This was determined through a plot of density-moisture contents. The wet mixture was then moulded using a manually operated Cinva ram, which produces four (4) bricks of 210mm by 100mm by 70mm, at a time. A total of 192 bricks were produced. The green bricks were spread inside the workshop with the pallets for two (2) days. Water was sprinkled on the bricks every evening for five (5) days after which they were allowed to dry under the prevailing weather condition for test at 14 and 28 days. The compressive strength test was conducted on four specimens of every mix and a mean value computed; water absorption test using immersion method was carried out at 28 days. Concrete cubes: Two mix proportions 1:1:2 and 1:2:3 (OPC: fine laterite: coarse laterite) by volume were adopted. In each mix ratio cement was replaced with,, and % RHA by volume. Volume replacement was used due to differences in specific gravities of the two materials. In each mix, water was gradually added until it attained a medium workability level monitored with slump and compacting factor apparatuses. Compaction was done manually and as specified by BS EN 12390: part 2 (2009). A total of 72 cubes of 1mm were cast. The fully compacted concrete in the moulds were covered with wet jute bags for 24 hours to prevent flash set. The cubes were removed and cured in curing tank until they were ready for compressive strength test at 7, 14, and 28 days hydration period. RESULTS AND DISCUSION Materials Laterite: The results of sieve analysis and atterberg test conducted on the lateritic soil are presented in Tables 1 and 2. It shows that the percentage of particles passing 75 micron sieve is below 5%, which is the minimum recommended for a very good laterite soil (Kamang, 1988). The liquid and plastic limit values were 25% and 21% respectively, giving a plasticity index value of 4%. This value did not exceed the maximum plasticity index of 35% specified by BS 1377 (1990) for soil to be considered for design purpose. Table 1: Sieve analysis of Lateritic soil Sieve sizes (mm) Material Retained % passing Grammes (g) Percentage (%) Pan Source: Authors Experimental Work NJAFE VOL. 9 No. 3,

3 Table 2: Atterberg limits for lateritic soil Container Liquid limit Plastic limit Weight of wet sample + container Weight of dry sample + container Weight of container Loss of water Weight of dry sample Moisture content Number of blows Ave. 21% Source: Authors Experimental Work Rice husk ash: The sieve analysis on the RHA is presented in Table 3. It shows that the RHA can be ground to fineness close to that of the OPC which it replaces. The setting times of OPC and OPC/RHA blended paste is presented in Table 4. The pastes containing RHA were slow in setting than OPC pastes. The slow setting has been attributed to low generation of heat-induced evaporation of water from the pastes as a result of lower cement content (Ikpong, 1993); and also because the reaction between cement and water is exothermic, the plain cement paste because of higher content evolves a greater amount of heat. However, in all the pastes, the initial and final setting times met the recommended time limit of BS EN (2009). Table 3: Sieve analysis of rice husk ash Sieve sizes (micron) % passing (RHA) % passing (OPC) Tray - - Table 4: Setting times of OPC and OPC/RHA pastes Paste (%): OPC-RHA Initial setting time (Hr+Min.) Final setting time (Hr+Min.) BS EN 197-1(2009) requirement Min. 45 minutes >10Hrs. The chemical analysis of the RHA is presented in Table 5. It shows that the percentage summation of acidic oxides of silica, alumina and iron is 76.22%, which meets the requirement of American Standard for Testing and Materials (ASTM) C 618 (2008) for pozzolans. The loss of ignition was 9.24%, which is still within the stipulated range by the standard. Therefore, the RHA processed and used in this investigation having met the conditions can be classified as a pozzolan. The specific gravity of the RHA was 2.12 while that of OPC was 3.1. This informed the blending of the two materials by volume. Table 5: Chemical composition of rice husk ash Oxide % content SiO Al2O Fe2O CaO 4.20 MgO 1.42 Na2O 0.13 P2O 0.67 K2O 3.23 LOI 9.24 NJAFE VOL. 9 No. 3,

4 Bricks Water absorption The results of water absorption test on brick specimens at 28 days are shown in Table 6. Bricks stabilized with cement only (that is 0% RHA) have less absorptive capacity than bricks incorporating RHA. It was equally observed that the rate of absorption increases with increase in the percentage of RHA replacement with cement except for mixes of 12% cement that did not follow the trend. This increase in water absorption can be related to the fact that the release of calcium hydroxide [Ca (OH)]2 from cement hydration is not sufficient for complete pozzolanic reaction between it and the silica in the RHA thereby leaving some RHA paste un-reacted and thereby forming spots for ingress of moisture. Furthermore, the bricks made from mixes of 12% cement show that there must have been release of sufficient calcium hydroxide due to increase in the quantity of the cement used for the silica in the RHA to undergo complete pozzolanic reaction and therefore less water absorption. Table 6: Water absorption of laterite bricks stabilizes with OPC and OPC/RHA OPC by volume of Laterite (%) RHA replacing OPC (%) Weight of specimen Water absorption (%) Dry (Kg) Wet (Kg) Compressive strength The compressive strength of bricks stabilized with OPC and OPC/RHA blended are presented in Table 7. It is observed that compressive strength decreases with increased in the percentage of RHA content replacing OPC; and that OPC stabilized bricks recorded higher values than OPC/RHA stabilized bricks at the same day however, the compressive strength show a remarkable improvement at 28 days than at 14 days in all cases. This later development portray the fact that the release of Ca (OH) 2 by the cement hydration is being used by the silica and that it is time dependent. In the % and % RHA in 6% cement, and -% RHA in 8% cement; the compressive strength values have met the minimum requirement of 1.4 Nmm -2 for the construction of bungalow. Similarly, % RHA in 10% cement, -% RHA in 12% cement are above Nmm -2 stipulated by Building regulation (1976) IN: Lasisi and Ogunjide (1984) for the construction of load-bearing walls of up to two-storey building. For optimal utilization, mix containing % RHA in 8% and 12% cement are recommended for use in bungalow and load-bearing wall construction, respectively. Concrete Workability The result of the workability test on the fresh concrete is presented in Table 8. Slumps of between 26 and 48mm, and compacting factor of 0.90 to were recorded. All values fell within medium workability range. Compressive strength The value of the compressive strength of the laterite concrete at 7, 14 and 28 days are shown in Table 9. The compressive strength of mix ratio 1;1:2 and its associated RHA contents is between 9.Nmm -2 and 18Nmm -2 at 28 days hydration, while a mix ratio of 1:2:3 with the same RHA contents varies between 6.66 Nmm -2 and Nmm -2. Generally, the compressive strength decreases with increase in the percentage of RHA but increased with hydration period up to 28 days tested. Mixes of ratio 1:1:2 have higher compressive strength than mixes of ratio 1:2:3. This could be attributed to less quantity of aggregate required to be lubricated by the binder (OPC/RHA) in NJAFE VOL. 9 No. 3,

5 mixes of ratio 1:1:2 than those in mixes 1:2:3. The replacement of cement with -% RHA in the mix ratio of 1:1:2 have attained a compressive strength of 6.9 Nmm Nmm -2 recommended for masonry concrete, and mix ratio 1:2:3 with -% RHA contents have met the strength requirement for insulating concrete which is stipulated between 0.7 Nmm -2 and 7 Nmm -2 (ASTMC3, 1990). An optimal mix containing % RHA in the mix ratio of 1:1:2, and % RHA in the mix ratio of 1:2:3 for masonry and insulating concrete, respectively is recommended. Table 7: Compressive strength of laterite bricks stabilized with OPC and OPC/RHA OPC by volume of Laterite (%) RHA replacing OPC (%) Compressive strength (Nmm -2 ) 14 days 28 days Table 8: slump and compacting factor values of lateritic concrete having various %RHA contents Mix ratio RHA replacing OPC (%) Slump (mm) Compacting factor 1:1: :2: Table 9: Compressive strength of laterite concrete 0.90 Mix ratio RHA Content (%) Compressive strength (Nmm -2 ) 7 days 14 days 28 days 1:1:2 0 1:2:3 0 Source: Authors Experimental Work CONCLUSION AND RECOMMENDATION The study which aimed at determining the suitability of RHA as a substitute material for OPC in the production of laterite bricks and concrete has proven that RHA can be an alternative source. In the investigation it was observed that bricks stabilized with OPC/RHA have higher water absorption rate than those stabilized with OPC, and that NJAFE VOL. 9 No. 3,

6 with a higher % of cement, say 12% and above, the reverse could be the case. The compressive strength of bricks decreases with increase in the quantity of RHA but increases with time up to the 28 days tested. Although most of the bricks met various standard requirements, bricks made with % RHA in 8 and 12% OPC by volume of laterite are considered adequate for wall construction of bungalows, and load-bearing wall construction, respectively. It was also observed that the compressive strength of laterite concrete tested, a mix ratio of 1:1:2 with various percentages of RHA replacing OPC recorded higher values than mixes of ratio 1:2:3. Therefore, for proper utilization of RHA in laterite concrete production, a mix ratio of 1:1:2 with % RHA, and % RHA in mix ratio 1:2:3 is suitable and recommended for masonry and insulating concrete production, respectively. REFERENCES American Society for Testing and Materials ASTMC3-99: Standard Specification for Structural Lightweigth Concrete (ASTMC3-99), West Conshohocken, PA. American Society for Testing and Materials ASTMC618-08: Standard Specification for Coal fly ash and raw or Calcined Natural Pozzolan for use in Concrete (ASTMC618-08), West Conshohocken, PA. British Standard Institution BSI 1377 Part 2: Methods of Test for Soils for Civil Engineering Purposes, London: BSI. BS EN Cement Composition, Specification and Conformity Criteria for Common Cements, London: BSI. BS EN Testing hardened Concrete: Making and Curing Specimens for Strength Tests, London: BSI. Chide-prasirt, P. C Low cost cement for rural area, report No. 2/1983, Office of Technology for Rural Development, Faculty of Engineering, Khon Kaen University. Ikpong, A. A The Relationship between Strength and Non-destructive Parameters of Rice Husk Ash Concrete, Building and Environment 23, Kamang, E. E. J Effect of Water-Cement Ratio on the Strength Properties of Stabilized Laterite Soils, Nigeria Journal of Construction and Management 1 (1), Lasisi, F. and Ogunjide, A. M Effect of Grain Size on the Strength Characteristics of Cement-Stabilized Laterite Soils, Building and Environment 19 (1), McCarthy, D. F Essentials of Soil Mechanics and Foundation, 4 th edition Okpala, D. C Some Engineering Properties of Sandcrete Blocks Containing Rice Husk Ash, Building and Environment 28 (3), Okunnu, K. O Studies of Sandcrete and Lancrete Blocks in Building Technology, Student Independent Study Project, Department of Agricultural Engineering, Ile-Ife, Nig. Ola, S. A Geotechnical Properties and Behaviour of some Nigerian Lateritic Soils, Lagos, Balkema Publishers. Sakr, K Effects of Silica fume and rice husk ash on the Properties of Heavy weight concrete, Journal of Materials in Civil Engineering 18 (3), Umoh, A. A The Effect of Rice Husk Ash on Strength of Low Workability Concrete, Gombe Technical Education Journal 1, NJAFE VOL. 9 No. 3,