The role of sulfate mineralogy and cure temperature in delayed ettringite formation

Warm-cured cement pastes tend to become expansive during service at normal ambient temperatures. Evidence that delayed ettringite formation is responsible is critically reviewed and it is concluded that ettringite is partially or completely destabilised during thermal cure. These features are corroborated and quantified by thermodynamic calculations. Reformation of ettringite at ambient temperature has potential for expansion but other associated reactions could also contribute. The relevant chemical and mineralogical balances are reviewed. Some tentative suggestions are given to avoid or minimise delayed ettringite formation but it is emphasised that further focused research is required to quantify the causes of expansion and formulate suitable protocols to avoid dimensional instability. (C) 1996 Elsevier Science Limited.