Early-age effect of corn cob ash as a partial replacement for Portland cement in concrete

School of Civil and Environmental Engineering, University of the Witwatersrand, Johannesburg, South Africa

^* Corresponding author: Damilola4fa4@gmail.com

Abstract

One of the effects of supplementary cementitious materials (SCMs) in concrete is the dilution effect which is as a result of partially replacing Portland cement with SCMs. The dilution effect of corn cob ash (CCA) with respect to strength gain and transport properties of concrete is the focus of this study. 100 mm concrete cubes were prepared with corn cob ash partially replacing Portland cement at 15% and 30% using w/b ratio of 0.4 and 0.6. The effect of CCA replacement level on the compressive strength development between 3 and 28 days, and transport properties at 28 days of curing was done. This was compared to the effect of fly ash at the same replacement level and 100% Portland cement content. The results showed that compressive strength decreases with increasing ash content and increases with increasing curing age. The dilution effect of CCA was more pronounced at the two replacement levels than fly ash with a marginal gain or strength loss compared to w/c ratio corresponding to each w/b ratio. The oxygen permeability index obtained for CCA concrete were lower compared to that of fly ash concrete at the same replacement levels and PC concrete at the same w/b ratio. Also, the water sorptivity index and chloride conductivity index for CCA concrete were higher than that of fly ash and PC concrete at the same w/b ratio.