Investigation into the Cementitious Properties of a Mixture of Rice Husks Ash with Building Lime

Abstract

The aim of this study was to investigate the cementitious properties of the product resulting from a mixture of rice husk ash (RHA) and building lime. Chemical analyses were done using Gravimetric and Atomic Absorption Spectroscopy, while particle size distribution of RHA carried out using hydrometer analysis. Concrete mixes containing different proportions of lime:RHA binder were cast. The binder was made by replacing lime with RHA at intervals of 20% and reducing the interval to 10% closer to the optimum. The same binder: sand: ballast mix proportions of 1:2:4 respectively at a constant 0.5 w/c ratio was used in all concrete mixes and subjected to air and water curing at room temperature. Workability tests were performed on all the concrete mixes. Standard consistency, initial and final setting times, and mortar compressive strength of the optimal blend were established. Characteristic compressive and tensile strength of optimal lime:RHA concrete were determined and the results compared with those of Portland Pozzolana Cement (PPC) concrete and cost analysis carried out. Results show that RHA has high silica content (more than 70%). Workability was found to reduce with increase in RHA content in the mix as indicated by reduction in slump values from 10mm to 2mm and reduction in compaction factor values from 0.78 to 0.69. For concrete samples cured in air the optimal blend was at 50% lime with 50% RHA while for water cured samples was at 30% Lime and 70%RHA. Initial and final setting time of the optimal lime:RHA binder was found to be 285 and 1485 minutes respectively, its 28 day mortar compressive strength was 7.07 N/mm2. Mean compressive and tensile strengths of optimal lime:RHA concrete were found to be 10.83N/mm2 and 1.49 N/mm2 respectively while that of PPC concrete was 20.08 N/mm2. The overall cost of the lime:RHA binder and hence the concrete was found to be less than half compared with an equivalent concrete grade made of PPC.