Hydration reactions and stages of clinker composed mainly of stoichiometric ye'elimite

Ye'climitc (Ca4Al6O12SO4 or C(4)A(3)(S) over bar) is the main hydraulic mineral present in calcium sulfoaluminate cement (CSA). The hydration of ye'elimite is responsible for the early age cement properties. We identify 5 stages in the hydration of neat stoichiometric ye'elimite in suspensions with water to binder ratio 40 and 100. During stage I (initial period) there is a rapid rise of the solution concentration appears followed by a fast slowdown. Stage 11 (dormant period) shows a slow but steady fall of the concentrations. The rate of reaction increases again during stage III (acceleration period) as indicated by the rising pH and solution concentrations. This leads to stage IV (main hydration period) during which the rapid and massive dissolution of anhydrous phases and precipitation of hydrates occurs. With that stage V (final period) is reached during which the recrystallization of formed hydrates continues. The duration of each stage is directly linked to the evolution of the solution concentrations and the type hydration reaction. In particular, the crystallinity of aluminium hydroxide seems to play an important role. The findings obtained in suspension were successfully linked to experiments on paste.