Investigations on the effect of alkalis on C-S-H growth rates and their impact on early C3S hydration rates

Abstract

In this work, we investigated the influence of alkalis on C-S-H precipitation and growth rates in solutions supersaturated with respect to C-S-H. Therefore, we used an experimental setup that leads to C-S-H precipitation and growth in solutions with a known KOH concentration. The results show that the KOH concentration in solution generally leads to an increase of the C-S-H growth rates at lower supersaturation levels. Based on these findings, we calculated theoretical reaction rates of C3S hydration using the precipitation rates of C-S-H. The comparison between these calculated rates and measured reaction rates from hydration experiments shows good agreement, allowing us to present a quantitative model for the effect of alkalis in combination with aluminum. Furthermore, we provide a quantitative analysis of how alkalis and aluminum modify reaction rates during the acceleration period of C3S hydration, which can be explained by different behaviors in the nucleation and growth of C-S-H.