Adsorption mechanism of multiple water molecules on tricalcium silicate (001) surface: a DFT study

An in-depth understanding of the hydration mechanism of tricalcium silicate is an important basis for optimizing cement strength development. In this study, the adsorption of water molecules onto the M3-C3S(001) surface at different water coverage levels (θ = 1/5, 2/5, 3/5, 4/5, and 1) was investigated using first-principles calculations. We find that the conclusions for single water molecule adsorption cannot be fully applied to multiple water molecule adsorption. The total adsorption energies became more negative with increasing water coverage, while the average adsorption energy of each water molecule became more positive with increasing water coverage. The water–water interactions reduced the water–surface interactions and were responsible for the anti-cooperative adsorption of multiple water molecules onto M3-C3S(001). The formation of Ca–OH (–Ca) bonds favors the detachment of Ca from covalent oxygen, which reveals the significant role of dissociative adsorption. This work aims to extend the water adsorption study on M3-C3S(001) from single water adsorption to multiple water adsorptions, providing a more detailed understanding about the initial water reaction on the C3S surface.