Effect of seawater as mixing water on the hydration behaviour of tricalcium aluminate

Abstract

This study explored the mechanism of the effect of seawater on tricalcium aluminate (C3A) hydration. The results showed that seawater retarded C3A hydration and reduced the reaction degree of C3A. The co-existence or ion pairing of Ca2+ and SO42− onto the surface of C3A poisoning the reactive sites is the main reason for this retardation. Besides, the precipitation of Mg(OH)2 on the surface of C3A would prolong the induction period for another 30 min and then consequently decrease the dissolution rate of C3A hydration. Trace amounts of MgSO40 and Mg2+ present in the alkaline solution had little retardation effect. It was also found that Cl− would preferentially react with C3A to form Friedel's salt, rather than forming hydroxy-AFm as that in the C3A-deionized water paste. The direct formation of Friedel's salt resulted in an accumulation of Al3+ in solution, which would also hinder the subsequent dissolution of C3A.