­Response Surface Methodology-Based Optimisation of Cost and Compressive Strength of Rubberised Concrete Incorporating Burnt Clay Brick Powder

Abstract

Modified concrete is increasingly being produced by substituting concrete constituents with waste materials. Among waste materials are powder from waste clay bricks replacing Ordinary Portland Cement and Waste Tire Rubber (WTR) replacing natural coarse aggregate. However, the use of modified concrete is controlled by its cost-performance balance. This paper summarises the cost advantages of using rubberised concrete incorporated with Burnt Clay Brick Powder (BCBP) where findings are evaluated in comparison with conventional concrete. In this study, compressive strength of concrete containing BCBP was investigated using mixes generated by Response Surface Methodology (RSM). Desirability analysis was employed to optimise BCBP and WTR contents yielding maximum compressive strength at lower cost. Production cost of concrete containing these waste materials reduced compared to conventional concrete. RSM evaluation demonstrated that empirical findings were well suited into linear and quadratic models for cost and compressive strength responses respectively. The coefficients of determination of greater than 0.85 for all responses established that the models were capable of explaining variability in the responses. 5% BCBP and 6.875% WTR contents established maximum 7-days compressive strength at lower cost. Optimisation of cost and 28-days compressive strength from desirability analysis gave 5% BCBP and 5.844% WTR contents as optimum values. Verification of the model findings indicated considerable agreement with the verified values. From the findings, it was confirmed that a reasonable cost-performance balance for modified concrete can be achieved using BCBP and WTR.