Hydration of C3S thin films

Thin films of C3S of a few tens of nanometers were produced by electron beam evaporation. After verification that the chemical composition of the bulk material remained unchanged, the samples were hydrated with water vapor in a reaction chamber under saturated pressure and temperature conditions, and were kept isolated from atmospheric exposure throughout the whole duration of the experiment. Analyses by X-ray photoelectron spectroscopy at different stages of hydration evidence a shift of the Si peaks to higher energies and a subsequent decrease of the Ca–Si binding energy distance, indicating silicate polymerization expected upon formation of C–S–H. The measured molar Ca/Si ratio evolves from that of a jennite-like material, of about 1.55, at the beginning of the experiment (attributed to pre-hydration of the thin films), to a tobermorite-like ratio of 0.85 after 3 h of hydration.