Effect of calcium sulfoaluminate cement prehydration on hydration and strength gain of calcium sulfoaluminate cement-ordinary portland cement mixtures

Abstract

In this work, the negative impacts of calcium sulfoaluminate (CSA) cement prehydration on hydration and strength gain are investigated. CSA cement in three different states – virgin, prehydrated, and prehydrated and sieved were tested. Cement paste mixtures were made with three levels of ordinary portland cement (OPC) – 0%, 30%, and 70% (indicating the percentage of OPC in total cementitious material) at a water-to-cementitious materials ratio of 0.40. CSA cement prehydration causes an increase in the particle size measured by laser diffraction, the presence of elongated particles in the electron micrograph, and the detection of hydrated and carbonated phases using thermogravimetric analysis. Prehydration of CSA cement has detrimental effects on hydration and strength gain on CSA-OPC mixtures, with exact effects depending strongly on the OPC level in the cement paste. In mixtures with 70% OPC, the effect of prehydration is pronounced – heat release of the mixture with virgin CSA cement at seven days is 33% higher than in the mixture with prehydrated CSA cement and the corresponding strength at 28 days is 196% higher. Relationships between heat release, bound water, and compressive strength and the effect of prehydration on these relationships were also explored. Sieving the prehydrated CSA cement before use presents some limited benefits in the reducing the detrimental effects of prehydration.