The synergistic effect of adding a blend of deflocculants and microsilica on the properties of high temperature resistant lightweight concrete with cenospheres

Abstract This paper presents the effects of deflocculants (sodium tripolyphosphate, polycarboxylate ether) and their blend with microsilica (MS) on the rheological, hydration and physical-mechanical properties of lightweight concretes with cenospheres (CS) designed for using in high temperatures. Blending deflocculants reduces the viscosity of cement paste (CAC) up to 6 times compared to the same paste with only one deflocculant. Increasing MS in the concrete mix to 10% extends the time of the exothermic effect by 57.7% and reduces the temperature of the exothermic effect by 21%. The synergistic effect of using MS and a blend of deflocculants contributes to strength development in lightweight concrete samples at all treatment temperatures. The addition of 2.5–7.5% MS into concrete mixes containing CS results in increased sample strength and shrinkage from 1.45 to 2.6 times and from 0.14% to 0.41%, respectively, and a decrease in sample density from 1210 to 1140 kg/m3 after firing at 1200 °C.