Influence of addition of calcite on growth of ettringite crystals

Abstract

It has been well-known that calcite accelerates growth of ettringite crystals. In-situ observation of growing ettringite crystals was carried out to clear this origin. Only needle-like ettringite crystals were observed without addition of calcite, whereas both needle-like crystals and spherulites were observed in the presence of calcite powder. Spherulite, consisting of many acicular ettringite crystals and including calcite in its core, is formed first followed by generation of needle-like crystals. It may be considered that the cause of the acceleration of ettringite crystal growth due to calcite results from the rapid generation of spherulites and the growth of needle-like crystals with the high density by the secondary nucleation.