Stepwise modeling approach to explore the interfacial behavior of Ca(OH)2/Sulfate

Concrete infrastructure within the salt spray zone is subject to corrosion triggered by sulfate, resulting in the deterioration of durability. Nevertheless, the atomic interface of Ca(OH)₂/sulfate remains incompletely understood. In the present study, the adsorption behavior (chemical or physical) of gas sulfate was firstly determined by density functional theory approach, followed by a deep investigation on physical adsorption mechanism of Ca(OH)₂/sulfate interface through classical molecular dynamics (MD) simulations, and presenting detailed conformations of sulfate hydration layer via quantum chemistry (QC) calculations. Results suggested: The chemical adsorption activity between sulfur gas and Ca(OH)₂ surface is negligible, with the primary role of SO₂/SO₃ being to act as a donor of sulfate ions in the corrosion process. Large-scale MD simulations reveal that the diffusion of sulfate ions to the CH surface requires the formation of a complete first hydration layer. Therefore, in high-concentration droplets, the competitive effect between sulfate ions and water molecules leads to agglomeration. The conformations of the three most probable types of hydrated layers of sulfate ions at room temperature were determined using the Boltzmann distribution calculated via QC methods, and corresponding strength of hydrogen bonding within these hydrated layers was evaluated.