The coupling effect of calcium concentration and pH on early hydration of cement

The results suggest that simultaneous removal of calcium and hydroxyl ions can significantly increase the length of induction period and reduce the height of the silicate reaction peak in the calorimetric curves, whereas the removal of hydroxyl or calcium ions alone cannot. The calculation of saturation index of alite, CH, and C-S-H indicates that undersaturation degree of alite during induction period is well related to the length of induction period and simultaneous removal of calcium and hydroxyl ions is likely to cause lower undersaturation degree of alite, longer induction period, and postponed time of silicate peak. The increase of pH could result in a higher sulfate concentration and subsequently a higher aluminate peak, and a shorter time interval between silicate and aluminate peak.