Effect of steel slag on the hydration and strength development of calcium sulfoaluminate cement

In this study, effects of steel slag on the hydration and strength development of calcium sulfoaluminate (CSA) cement were investigated. Pastes with 0%, 10%, 20%, and 40% (by mass) of steel slag replacements for CSA cement were tested for setting time, chemical shrinkage, electrical resistivity, and compressive strength. The hydration products, bound water content, pore structure, and pH value of the pore solutions of these pastes were also analyzed. The results indicate that at early ages (from 2 h to 28 d), steel slag worked like a filler and had a dilution effect on CSA cement hydration. Therefore, setting time increased and chemical shrinkage, electrical resistivity, chemically bound water content, and compressive strength of the pastes reduced with increase of steel slag replacements. But, at late ages (90 days), these properties in pastes with steel slag replacements surpassed those of the plain CSA cement paste due to hydration of steel slag, which increased pH values of pore solutions and subsequently stabilized ettringite in the pastes. Steel slag replacement for CSA cement also accelerated strätlingite formation. Both ettringite stabilization and strätlingite formation appeared to be the primary mechanisms for strength compensation.