Modeling and Optimization of High-Volume Fly Ash Self-Compacting Concrete Containing Crumb Rubber and Calcium Carbide Residue Using Response Surface Methodology

In this research, the fresh and hardened properties of high-volume fly ash self-compacting rubbercrete containing calcium carbide waste were optimized using response surface methodology (RSM). The variables used were crumb rubber (CR) as a partial substitute by volume of fine aggregate at 0% to 40%, fly ash (FA) as a partial substitute to cement at 0% to 80%, and calcium carbide residue (CCR) as an additive by weight of cementitious materials at 0% to 20% levels at increment rate of 5%. The fresh properties of the self-compacting concrete (SCC) considered were passing ability, slump flow, and segregation resistance, while the hardened properties examined were compressive strength, flexural strength, splitting tensile strength, and microstructural properties. The experimental results showed that the incorporation of FA and CCR improved the passing ability and slump flow. However, increasing the CR content retarded it, although the segregation resistance was improved with the increase in proportion of the replacement materials. Similarly, CR, CCR, and FA improved the strength of the SCC; however, the reverse was the case at higher proportion replacement beyond 10% CR, 10% CCR, and 40% FA. The proposed models were found to be relevant for all P-value reactions of less than 5%. Results of the multi-objective optimization indicated that the optimum mixture could be achieved by replacing, by volume, the fine aggregate with 11.29% of CR, cement with 39.08% FA by weight, and total cementitious material by 5% CCR by weight of cementitious materials.