Influence of aluminium on the hydration of triclinic C3S with addition of KOH solution

In this work we studied two samples of triclinic C3S. Namely pure triclinic C3S with no addition of foreign ions and triclinic C3S doped with 0.5 wt.-% Al2O3 to investigate the influence of aluminium on the hydration of C3S in the first 24 h and additionally the effect of KOH solution. During hydration Al-doped C3S shows lower reaction rates in the acceleration period compared to pure C3S. Al ions lead to precipitation of C-A-S-H phase and reduces the overall reactive surface area of C-S-H. Furthermore, Al ions in solution decrease the supersaturation of C-S-H during hydration and therefore the precipitation rates are lower for the Al-doped C3S. The addition of KOH solution leads to a general acceleration of reaction for both C3S samples, but at a concentration of 0.3 mol/L KOH both samples show comparable reaction rates during the main hydration event and the effect of Al is reversed.