Monte Carlo Molecular Modeling of Temperature and Pressure Effects on the Interactions between Crystalline Calcium Silicate Hydrate Layers.

The interactions of calcium silicate hydrates with water are at the heart of critical features of cement-based materials behavior such as drying and autogenous shrinkage, hysteresis, creep and thermal expansion. In this article, the interactions between nanocrystalline layers of calcium silicate hydrates are computed from Grand Canonical Monte Carlo (GCMC) molecular simulations. The effects of temperature, chemical potential and pressure on these interactions are studied. The results are confronted with simulation and experimental data found in the literature concerning surface energy, cohesive pressure and out-of-plane elastic properties. The disjoining pressure isotherms of calcium silicate hydrates are negligibly affected by changes in water pressure under saturated conditions. The surface energy decreases with the temperature, the chemical potential of water and the water pressure. Coarse-grained simulations are performed using the potential of mean force obtained at the molecular level. The mesostructure presents hysteresis with respect to mechanical and thermal loads. The anharmonicity of the interactions identified at the molecular scale translate in an asymmetry tension/compression and thermal expansion that are also observed at the mesoscale. These results leave room to a better understanding of the multiscale origin of physical properties of calcium silicate hydrates.