Optimization of Clinker Factor for Low-Carbon Penta-Blended Cement Mortar via Box–Behnken Design of Response Surface Methodology

Abstract

Utilization of calcined limestone as supplementary cementing materials (SCMs) along with other additional SCMs (fly ash, silica fume, uncalcined limestone) can effectively influence the fresh and hardened properties of low clinker cement mortar. In this research work, response surface methodology was performed to investigate the better mix results and reduce the number of trials. Fly ash (FA), silica fume (SF), uncalcined limestone (UCLS), calcined limestone (CLS) and superplasticizer (SP) were the independent variables. Consistency, initial setting time, final setting time, fineness and compressive strength were target functions. A five-factor six-level Box–Behnken design (BBD) was used to optimize the clinker factor. The independent variables were used at replacement ratio of 0%, 20%, 35% (FA); 3%, 6%, 9% (SF); 0%, 10%, 15% (UCLS); 0%, 10%, 15% (CLS); 0.5%, 1%, 1.5% (SP). In total, 46 mixes were cast and tested after 28 days of curing. Results revealed that the mix containing 5% FA, 5% UCLS, 15% CLS, 9% SF and 0.5% SP increased compressive strength and consistency, which was quite better than the other mixes. Statistical analysis revealed that R2 ranges from 0.83 to 0.99, which is desirable for a perfect model. Finally, the clinker factor was optimized at factor of 0.66 with 34% replacement of clinker with mineral admixtures.