Influence of low-dose chemicals on the early strength of Portland cement: statistical and calorimetric evidence

Abstract

The effectiveness of 15 chemical admixtures (including alkanolamines, alcohols, chloride/non-corrosive accelerators and retarders) on the early strength development of a P.II 52·5R cement was determined using statistical methods. The results showed that, under low dose conditions (≤ 0·05 wt%), sodium thiocyanate, calcium chloride, sodium hydroxide, triethanolamine and glucose contributed to the 1-d strength enhancement of the cement and that only sodium thiocyanate, triethanolamine, triisopropanolamine and calcium chloride were effective up to 3 d. In addition to the strength test proposed by the statistical model, a calorimeter was used for a supplementary measurement to identify interactions among the chemicals. The calorimetric test results revealed that the interaction between triethanolamine and sodium thiocyanate was more pronounced for the amount of heat released before 72 h due to the accelerating effects on both the C3S and C3A phases. Furthermore, a statistical test showed that even at a higher dose (0·1 wt%), the effect of calcium nitrate was far less efficient than the effect of calcium chloride, which did not significantly improve the overall early strength of cement.