Compressive Strength and Optimization of Concrete Produced by Replacing Cement with Coconut Shell Ash (CSA) and Groundnut Shell Ash (GSA)

Abstract

The compressive strength and optimization of concrete produced by replacing cement with CSA and GSA was conducted in this study. The materials used were cement, water, fine aggregate, coarse aggregate, CSA, and GSA. The CSA and GSA replaced cement at 5, 10, 15, 20, and 25% in combination, with a total of seventy two (72) cubes cast, while the concrete compressive strength was determined after curing by complete immersion in water at 7, 14, 21, and 28 days. The modeling and optimization was done with the aid of design expert (version 13) software, while the Analysis of Variance (ANOVA) was done using SPSS (Statistical Package for Social Sciences) version 23 and adopting the Least Square Difference (LSD) method. Results from the findings showed that the CSA used in the study is a good reactive pozzolana, and the GSA is not a reactive pozzolana. Also, the increase in CSA and GSA content in concrete reduces its workability, and concrete compressive strength. However, cement replaced with 5%CSA-0%GSA gave the optimum 28 days compressive strength which is not statistically significantly from the control concrete and can be used to produce concrete of compressive strength close to the control. Further findings from the regression model showed that CSA-GSA concrete compressive strength significantly fits a linear model and can be used to predict the 7, 14, 21, and 28 days compressive strength of CSA-GSA concrete, while the optimized result showed that CSA and GSA replacement of cement at 3.29% and 4.45% respectively yielded an optimum compressive strength of approximately 22.31N/mm2.