Influence of gypsum and KOH on the hydration of pure triclinic C3S

This work focuses on the isolated and combined influence of gypsum and KOH on the hydration of pure triclinic C 3 S. The addition of gypsum shows a prolonged induction period and increased maximum reaction rates during C 3 S hydration. These effects are further enhanced when KOH is added. Pore solution composition from ICP-OES measurements of suspension experiments show pore solutions dominated by an equilibrium with gypsum. Resulting changes in C-S-H interfacial precipitation rates are qualitatively correlated with either a prolonged or shortened induction period. A comparison of C 3 S reaction rates calculated based on C-S-H interfacial precipitation rate model and C 3 S reaction rates observed by XRD and TGA show an accurate quantitative description of the C 3 S hydration in the presence of gypsum and KOH. In the combined presence of KOH and gypsum, higher C-S-H surface areas quantitatively explain the increase in C 3 S reaction rates regarding the decreased interfacial precipitation rates. • Decreased C-S-H interfacial precipitation rate by gypsum addition prolongs C 3 S induction period. • Increased C-S-H surface area by gypsum addition leads to increased C 3 S maximum reaction rates. • Additional KOH enhances both effects in the presence of gypsum.