Investigation of the Effects of Rice Husk and Rice Straw on the Properties of Lightweight Fibrecrete Blocks

Abstract

Uganda’s progress towards achieving sustainable growth is curtailed by poor and limited infrastructure, over 60% of the urban population live in slums with poor quality housing and hygiene, 44% of the households sleep in one room, the situation is more critical in Kampala where about 70% sleep in one room. About 67% of Ugandans live in dwellings with brick walls while 28% live in dwellings of mud walls reinforced with timber poles. Over 90% of framed structure in Uganda are built from reinforced concrete structures with bricks or block infill walls that are heavy thus influencing the type and size of structural members hence its cost. This research focused on use of Rice Husks (RH) and Rice Straws (RS) in lightweight fibrecrete blocks for benefit of their reduced weight, reducing environmental pollution, low processing energy, and availability at modest cost. In this research, the fibres were alkali-treated using sodium hydroxide solution prepared by dissolving 15g of sodium hydroxide pellets in 1 liter of water heated at 100°C for 60 minutes. This was aimed at increasing surface roughness, expose cellulose to fibre surface, improve fibre/matrix adhesion, eliminate weak boundary layers and remove superficial lignin layer. The alkali treated fibres were used to prepare one hundred twenty one (121) fibrecrete blocks of RH and RS with varying proportions of 0%, 10%, 20%, 30%, 40%, and 50% fibre and tested for their density, compressive strength, water absorption, thermal conductivity, fire resistances and microstructure. The densities of lightweight fibrecrete blocks ranged between 1947-1485kg/m³ with a reduction of 7.9 - 30.5% compared to aggregate blocks of 2138kg/m³ density. Compressive strength of the blocks varied between 1.53 - 5.36 N/mm² and 1.28 - 3.48 N/mm² for RH and RS blocks respectively with control block having compressive strength of 7.2N/mm² at 28 days. Compressive strength loss in the lightweight fibrecrete blocks tested for fire resistance ranged between 10.7- 34.3% and 6.8-73.7% for RH and RS-blocks respectively while the water absorption ranged between 5.8-7.8% for RH and 6.4-11.3% for RS blocks and 3.6% for aggregate blocks. Thermal conductivity was improved by 13.4-64.8%. The researcher concluded that, RH-40 and RS-20 blocks have the most appropriate proportions for lightweight fibrecrete blocks. This would reduce Environmental degradation, utilize agricultural waste, increase the income of the farmers, reduce construction cost due to reduced density of fibrecrete blocks, and increase thermal insulation hence thermal comfort of the occupants.