Implications for C 3 S kinetics from combined C 3 S/ CA hydration

This study was performed to understand the influence of a critical amount of CA on the kinetics of C 3 S hydration. For this purpose, monoclinic C 3 S was blended with 15 wt.% CA and investigated by heat flow calorimetry and in situ XRD at 23°C at a water to cement ratio of 0.5. The binary mixture shows 3 distinct heat flow maxima where the underlying C 3 S dissolution is proceeding stepwise. The C 3 S dissolution rates during the 3 steps are varying strongly, depending on the hydrate phase precipitated during the respective reaction step. Comparison of these dissolution rates with a pure C 3 S reference sample allows the conclusion that the dissolution rate of pure C 3 S after the heat flow maximum might be governed by either the remaining available reactive surface of C 3 S or a diffusion‐controlled process, which would both be influenced by the respective hydrate phase precipitating on the C 3 S surface.