The Impact of Guinea Corn Husk Ash as an Admixture for Crack Control in Concrete

Abstract

Guinea corn husk, a post-harvest agricultural waste common in Northern Nigeria is often heaped up constituting environmental nuisance. Guinea Corn Husk Ash (GCHA) is an incinerated by-product of it. In this experimental investigation, it was used to replace cement in concrete at levels of 0%, 5%, 10%, 20%, 30% and 40% by weight. The sample cubes were casted and cured for 3, 14, 28 and 56 days before crushing. Before then, the chemical constituents of the GCHA were determined from an X-Ray diffraction analyzer. The oxides found in the ash included SiO2 (85.4%), K2O (4.01%), Fe2O3 (0.64%), CaO (2.04%) and NaO2 (0.98%). SO3 and AI2O3 were not detected. The combined percent of SiO2, Al2O3 and Fe2O3 of 86.04% is above the 70% benchmark for a pozzolana material. Also, SO3 and NaO2 fell below the maximum allowable values of 4% and 1.5% respectively. The fresh concrete had slump values that ranged from 11mm for 0% cement replacement to 3.6mm for 40% replacement. The hard concrete had the highest compressive strength value of 23.67 N/mm2 for plain concrete and 49.3 N/mm2 at 5% GCHA replacement level. All were at 56 days of curing, satisfying quality for heavy load bearing. Beam samples cured for 3, 14, 28 and 56 days were subjected to flexural tests until they developed cracks. The cracks were measured for lengths (CRL) and width (CRW) for different replacement levels and curing days with a crack measuring microscope. The results show that, at 14days curing, there is a trend in the crack values’ reduction for the hardened GCHA concrete. This trend is also marginally seen for the 28 day cured samples, particularly at up to 20% replacement levels. The decrease in crack values were up to 17.2% and 2091% for CRL and CRW respectively. However, there were no significant crack controls with samples of higher replacement levels and those cured for 3 and 56 days. GCHA concrete can therefore be used to for heavy load bearing structures and for crack control at 5 – 20% replacement levels when cured for 14 days and 38 days.