Diffusion and physicochemical behavior of chloride and sodium ions in C-S-H gel pores : A molecular dynamics investigation

Overview & Synopsis

Calcium silicate hydrate (C-S-H) gel is an amorphous material with a complex, disordered structure that complicates the understanding of its atomic-scale properties. While many studies have investigated ionic diffusion in C-S-H pores, the behavior of sodium (Na + ) and chloride (Cl -) ions, particularly in relation to the Ca/Si ratio, is not well understood. In this study, atomistic models of C-S-H were developed with varying Ca/Si ratios, pore sizes, and NaCl concentrations. Molecular dynamics simulations were used to calculate the self-diffusion profiles of Na + and Cl -ions. Results indicate that pore size strongly affects diffusivity and adsorption through confinement and electrical double layer effects. The solid surface influences ionic mobility up to approximately 1.2 nm. The Ca/Si ratio has minimal impact on the diffusion profiles of nonadsorbed ions, but its rise enhances Cl -mobility near the surface and increases chloride binding capacity, consistent with prior studies.