The engineering properties and pozzolanic reaction kinetics of quaternary blended binder high strength mortars optimized by the Taguchi method

Abstract

The Taguchi method has been applied for the experimental design of the mixture proportions of quaternary blended cement mortars on the basis of four factors. The design of experiment derived mixture proportions have been examined on four levels, comprising supplementary cementitious materials (SCMs) viz: ultra-fine treated palm oil fuel ash (u-TPOFA; at 4 levels of 30, 35, 40, and 45%), ground granulated blast furnace slag (GGBFS; at 4 levels of 12.5, 15, 17.5, and 20%), metakaolin (MK; at 4 levels of 7.5, 10, 12.5, and 15%) as partial replacement of ordinary Portland cement (OPC), and water to binder ratio (W/B; at 4 levels of 25, 26, 27, and 28%), in order to achieve an optimum mixture. The response factors employed were compressive strength (CS), porosity (P%), and water absorption (Abs%) at the ages of 3, 7, 14, and 28 days. By utilizing the L16 array as proposed by the Taguchi method, the specimens prepared were analyzed using 16 experiments. The results obtained showed that the response values of the optimized mixture using the Taguchi method were much better than the plain cement mortar mix and those proposed in the initial 16 series. The workability of the optimum mix increased by about 6% over the plain cement mortar mix. The relative CS results of the optimum mix was 116.92% at 28 days of curing. Likewise, the relative P% and Abs% results of the optimum mix exhibited notable reductions at 28 days of about 40.0% and 45%, respectively. Further analyses were carried out using thermogravimetric (TG) and x-ray diffraction (XRD) analyses to quantify the contribution of the SCMs and their chemical reaction which was reflected by the remaining amount of the unreacted portlandite in the mix. According to the results, the optimum quaternary blended binders mortar mix which utilized only 37.5% of cement by volume (i.e., a reduction from 882.22 to 330.83 kg/m3) portrayed improved physical properties, chemical reaction, enhanced workability, better CS, as well as lower P% and Abs% compared to the plain cement mortar.