A new view on the kinetics of tricalcium silicate hydration

C3S hydration is an interesting example of chemical coupling between C3S dissolution, C–S–H and portlandite precipitation. It occurs because Ca2 +, OH− and silicate ions are present in C3S, in both hydration products and in the surrounding solution. Various experimental data sets reveal that the undersaturation with respect to C3S always increases when C3S hydration enters into the deceleratory phase, leading to the conclusion that C3S dissolution is at the origin of this deceleration, not C–S–H growth. In addition, as soon as portlandite precipitates, the dissolution limits the hydration already in the acceleratory hydration step. The evolution of the undersaturation cannot account for the hydration peak. Rather, it results from an extension and subsequently a decrease of the C3S reactive surface area. The formation and coalescence of dissolution etch-pits can provide a reasonable explanation for the C3S hydration kinetics.