Effect of water/cement ratio on the compressive strength of groundnut husk ash (GHA) concrete

The study examined the potentials of Groundnut Husk Ash (GHA) as a partial replacement to ordinary Portland cement (OPC) in concrete production. Chemical analysis conducted on GHA reveals that it satisfies the ASTM (1978) minimum requirement of 70% composition of the three oxides (i.e. SiO2, Al2O3 and Fe2O3). The pozzolanicity of GHA was further confirmed from the minimum Pozzolana activity index (PAI) value of 86.05. Specifically, GHA at step concentration of 0%, 2 %, 4%, 6% and 8 % respectively, were blended with coarse and fine aggregates using water cement ratios of 0.5, 0.6, and 0.7, respectively in order to achieve a target mean strength of 20 N/mm2 for the GHA concrete specimens. Compressive strength of the concrete specimens increased with increase in age of curing and decreased with increase in GHA content as well as water cement ratio. The workability of the concrete was quite reasonable and the initial and final setting times were within the range stipulated by conventional specifications. In view of the time dependent gain in strength of materials that are pozzolanic in nature, GHA content up to 8% is adjudged suitable for concrete production