The interactions between water molecules and C-S-H surfaces in loads-induced nanopores: A molecular dynamics study

Molecular dynamics simulations are used to investigate the interactions between water molecules and C-S-H surfaces and transport properties of water confined in the nanopore. Firstly, a C-S-H model based on experimental results is constructed, then a nanopore induced by tensile loading is taken into account for the first time. Structural and dynamical properties of confined water and interactions between water solution and C-S-H surface are further investigated at the molecular level. Water molecules gathering in the vicinity of C-S-H surfaces perpendicular to Z direction present peculiar structural and dynamic characteristic: layer structure, high density, obvious orientation preference, and low diffusion coefficient. The silicate chains are connected with water molecules by the high-strength hydrogen bonds formed among water and non-bridge oxygen atoms (O_NB), bridge oxygen atoms (O_B) in silicate chains, while surface calcium ions sheets are prone to attract oxygen atoms in water molecules. The special structural and dynamic features are mainly determined by the interactions among water, silicate chains, and surface calcium ions sheets. Due to the lack of strong constraint from the C-S-H substrates and driven by water molecules in the nanopore, the surface calcium ions diffuse more rapidly than those constrained inside of the C-S-H gel and could diffuse into the nanopore full of water molecules.