Optimization of Bentocrete parameters using Response Surface Methodology (RSM)

The present study aims at the influence of water/cement (W/C) ratio on workability, compressive strength, and durability, and microstructure of concrete by partial replacement of cement with bentonite (Bentocrete). The model development with the help of the matrix design was carried out using Response Surface Methodology (RSM). Scanning Electron Microscope (SEM) and X-ray diffraction used for assessment of bentonite microstructure. The variables in this research were water/cement (W/C) ratio and percentage of bentonite replacement. The W/C ratio was varied between 0.60 and 0.70; 0%, 10%, 20% and 30% of cement were substituted with bentonite. The responses (slump value, compaction factor, compressive strength (28 d), split tensile strength, flexural strength and charge passed through concrete (28 d) were assayed for all mixes. Design Expert 11.0 version was utilized for optimization using RSM. Bentonite' s high-water absorption capacity decreased the workability as the OPC percentage decreased in the Bentocrete. The result has shown that the compressive strength, split tensile strength, and flexural strength of Bentocrete has decreased to 80% replacement of bentonite with OPC, increasing beyond that. This decrease is due to bentonite' s pozzolanic reactivity. The durability of Bentocrete improved up to 20% replacement of OPC with bentonite. The increase is might be due to the pore filling effect, bentonite particles occupy the voids created by OPC since the particles of bentonite were finer than OPC. The models generated from RSM are valid with statistical significance in all the factors considered. 9.91% of the cost can be cut down at 80% cement substitution. The optimum solution with a desirability of 0.881 was obtained with 3.92% of bentonite substitution and 0.62 W/C ratio. The intended Bentocrete can be utilized in low-cost concrete production.