Estimation of Calcium Ion Diffusion Coefficient in Cement Hydrated Silicate Gel (C-S-H) under Different Compressive Stresses by Molecular Dynamics Simulation

The transfer of water and ions in the hydrate of cement determines the durability of cementitious materials. Due to its structural similarity, tobermorite which is an important mineral analog of the main phase of cement hydrate was used to investigate the transfer behavior at the molecular level. In this study, the diffusion coefficient of calcium ions in hydrated cement paste was investigated by the Molecular Dynamics (MD) simulation method. There are pores with a width of 59.82 A° between two substrates made of tobermorite crystals. The thickness of the tobermorite layer on each side was considered to be 27.98 A°. Initially, no ions were added to the two layer structure of tobermorite and modeled water between the two layers, but after obtaining the results in another step to bond calcium ion and chloride ion and evaluate the diffusion process, 24 chloride ions were randomly added to the tobermorite structure on both sides. For this modeling, BIOVIA materials studio 2017 software was used to perform MD simulations.