Effect of sulfate content on cement mixtures

Portland cement, calcium aluminate cement and calcium sulfate mixtures were investigated to determine the influence of sulfates and the effect of curing conditions on durability. This study focused on the richest mix of Portland cement. The PC/CAC ratio was kept constant at 5.67, and different proportions of calcium sulfate were added (0%, 1%, 3%, 5% and 10%). Samples were kept at 20 °C and 97% relative humidity or immersed in water. The dimensional change and mineralogical composition of samples were evaluated. The results showed that the dimensional change of samples in the PC/CAC and PC/CAC/CS¯ systems depended on the amount of sulfate added and on the curing conditions. The dimensional change was associated not only with amorphous ettringite formation, but also with the subsequent formation of a C-S-H gel.