Optimization of hydration kinetics, phase development and mechanical properties of CAC in mix with calcite by addition of sodium hydroxide and citric acid

The influence of sodium hydroxide and citric acid on the hydration of a calcium aluminate cement – calcite mixture was investigated. Both the effect of the two additives individually and in combination were analysed. Sodium hydroxide accelerates the reaction, leads to dominant monocarbonate formation and higher inner strength. However, the workability is reduced. Citric acid retards the reaction, lowers the inner strength but has a positive influence on the workability. Furthermore, the main reaction with citric acid only begins when the concentration of citric acid in the pore solution drops below 125–115 mmol/l. In combination of both additives, NaOH improves the inner strength, whereas higher doses of citric acid improve the workability, whereby the dominant hydrate phase composition changes from monocarbonate to CAH 10 . In addition, it was observed that a higher degree of hydration within the first 24 h is associated with increased inner strength after 28 d.