Impact of KOH on the interfacial precipitation rates of C-S-H during the early hydration of C3S

In this work we investigated the influence of alkalis on the hydration of two triclinic samples of C₃S. One pure C₃S and one Al-doped C₃S (0.5 wt.‐% Al₂O₃). We added differently concentrated KOH solutions representing alkalis in the pore solution, which lead to an increase of the interfacial precipitation rates of C-S-H during the hydration of C₃S compared to the hydration without KOH. Isothermal calorimetry was conducted for the determination of the rates of reaction during the hydration process and ICP-OES measurements for the determination of the pore solution composition at certain times of hydration. The increasing effect of KOH solution on the calculated interfacial precipitation rates from pore solution data can explain the enhancement of the rates of reaction recorded by heat flow calorimetry during the early hydration. Therefore, the interfacial precipitation rates of C-S-H can accurately describe the acceleration effect of alkalis on the early hydration of C₃S.