Structure and properties of thaumasite and its aqueous interfaces revealed by molecular dynamics simulations

Thaumasite, along with ettringite, is responsible for sulfate attack in concrete based on Portland cement. We use classical molecular dynamics (MD) computer simulation technique together with the ClayFF-MOH force field to quantitatively investigate the structural, vibrational, mechanical and thermodynamic properties of thaumasite. Additionally, path integral MD technique is applied for a more detailed examination of the structure and dynamics of intracrystalline hydrogen bonds in this material. The results of classical MD simulations are in good agreement with available experimental data and DFT calculations. Mineral-water interfaces for the (1 0 0) and (0 0 1) surfaces of thaumasite and ettringite are also simulated and compared. The solid-water interfacial energies for (1 0 0) and (0 0 1) thaumasite and ettringite surfaces provide new insights on the atomistic scale solubility mechanisms of these minerals. The simulations also confirm the possibility of thaumasite epitaxial growth on the surface of ettringite.