Influence of exposure conditions on expansion characteristics of lime-rich calcium sulfoaluminate-belite blended cement

Expansive characteristics of calcium sulfoaluminate-belite (CSAB) cement can be harnessed for making shrinkage-compensating concrete. The level of expansion is dependent on several factors, such as the amounts of ye'elimite and calcium sulfate available in CSAB cement. Moreover, calcium sulfate from an external source can also influence the expansion characteristics by increasing the supersaturation with respect to ettringite. In this study, the influence of externally available calcium sulfate was investigated by curing a blend of Portland cement (PC) and CSAB cement to different concentrations (1 g/l and 5 g/l) of gypsum solutions. Expansion of the PC-CSAB blended cement was found to be directly affected by the ye'elimite content (CSAB dosage) and the gypsum concentration in exposure solution. The presence of external calcium sulfate during the hydration of ye'elimite was found to affect the hydrate phase assemblage, the pore structure, and the morphology of ettringite. Furthermore, the level of expansion depended on the age at which the specimens were exposed to the gypsum solution, indicating the influence of matrix stiffness on resultant expansion.