Temperature Dependence of Nanoconfined Water Properties: Application to Cementitious Materials

Nanoconfined water exhibits peculiar properties with respect to the bulk that plays a crucial role in damage processes affecting concrete sustainability. We employed molecular simulation techniques to investigate water physical properties in calcium-silicate-hydrate nanopores and compare them with bulk water. We considered systems opened to and isolated from the environment to characterize the effect of the density and the fluid order, respectively. Under freezing conditions, we found that the most disruptive effect in nanopores of cement paste arises from the hydraulic pressure. Upon heating, the water expansion in the closed porosity is the most disruptive process. Combining thermodynamic, structural, and dynamical data, we found liquid-liquid transitions in the temperature range 180-195 K. Further lowering the temperature, we found from translational mean-square displacements glass transitions at ∼170 K for all systems, except for bulk water in the open system, where the transition was located at ∼155 K. Confinement effects on diffusion coefficients in our molecular models are also in very good agreement with experimental data. These findings underscore the importance of accounting for the molecular nature of water to investigate temperature-induced damage mechanisms in cement and concrete.