Strength Prediction and Optimisation of Velvet Tamarind Pod Ash Cement Blends via Response Surface Methodology

This paper tries to provide a predictive model for determining the mortar compressive strength of Portland limestone cement blended with Velvet Tamarind Pod ash (VTPA) and eggshell powder (ESP). The mortar compressive strength of VTPA-ESP cement blends was determined according to experimental runs from Design Expert 13 using response surface methodology via Central Composite and Box-Benkhen designs, respectively. The factors considered include a blending ratio of 0.25–0.75, cement replacement of 2–6 wt.%, and curing age of 3 and 60 days, respectively. Model equations obtained using response surface methodology via CCD adequately predicted the mortar compressive strength for VTPA-ESP cement blends. The design comparison indicated that CCD produced a better prediction of the mortar strength of the ternary cement blends, which satisfied second-order polynomial regression. When researchers held the curing age and blending ratio constant and increased the cement replacement from 2 to 6 wt.%, they observed a slight increase in the mortar strength followed by a decrease. A similar trend was observed at various blending ratios as the curing age progressed from 3-60 days while the cement replacement and blending ratio was held constant, increasing the mortar strengths. When researchers held the curing age and cement replacement constant, they observed increased blending ratios. Results revealed that despite the diminution of the cement with either VTPA or ESP, the strength experienced either similar or better values than control, proving that pozzolanic activity was experienced. The mortar strength prediction was significantly influenced by the curing age for both CCD and BBD, with high F values for the curing age of 246.23 and 49.62, respectively. Researchers obtained the optimal conditions for predicting the mortar strength of VTPA-ESP-cement blends: blending ratio of 0.258, cement replacement of 3.20 wt.% and curing age of 59.23 days with a mortar strength of 44.93 N/mm2 and desirability of 1.000 for CCD while the blending ratio of 0.283, cement replacement of 2.083 wt.%, curing age of 59.513 days and mortar compressive strength of 45.330 N/mm2 and desirability of 1.000 BBD respectively.