Influence of mineral admixtures on early-age behavior of calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements were developed for shrinkage compensation of concrete. This study investigates the expansion characteristics of CSA-portland cement (CSA-OPC) systems in the presence of mineral admixtures (MA). Unrestrained expansion of CSA-based cement pastes incorporating Class C fly ash (FA), Class F FA, and silica fume (SF) were monitored at water-cementitious material ratios (w/cm) of 0.34 and 0.44. Despite the same amount of expansive component, CSA-OPC-MA mixtures exhibited noticeable difference in expansion. The Class F FA increased the unrestrained expansion at early age for both w/cm, which was attributed to lower material resistance (that is, stiffness) due to the presence of Class F FA. Furthermore, the expansion of the Class C FA-based mixture ceased at 2 days at both w/cm due to faster consumption of ye'elimite. A calorimetric study of Class C FA-based mixture revealed early depletion of sulfates, which correlated well with the completion time of expansion. Additionally, the presence of SF lowered the expansion, which was attributed to the lower alkalinity of pore solution, incomplete hydration of ye'elimite, and increased material stiffness.