Influence of silanes on the hydration of cement by separating the cement into its individual phases

Cementitious materials can be treated with organosilicon compounds (silanes) to achieve a water‐repellent effect. However, the influence of silanes on cement hydration is still not fully understood. For this reason, we studied the hydration of the main Portland cement phase (C₃S ‐ tricalcium silicate) and the interaction with iBTES (isobutyltriethoxysilane), iOTES (isooctyltriethxysilane) and nOTES (n‐octyltriethoxysilane) by isothermal calorimetry and in‐situ X‐ray diffraction (XRD). The results show that C₃S hydration is initially retarded and subsequently accelerated by iBTES and iOTES. In addition to the hydration process, the crystal growth of the portlandites (calcium hydroxide) is also affected by the silanes. The XRD results indicate that the portlandites grow significantly more plate‐like. In this context, the influence of the silanes on the portlandite crystallization was therefore also recorded in a special experimental setup. From the scanning electron microscope images it can be shown that all portlandite crystals grown in the presence of silanes have a platelike morphology. This is due to the fact that the hexagonal surfaces of the portlandite are covered by silanes and thus the growth direction of the crystals is affected. The modified portlandite crystals indicate that silanes also influence the microstructure of the cement paste and therefore its chemical and mechanical properties.