Computational Molecular Analysis of Chloride Transport in Hydrated Cement Paste

Concrete in transportation infrastructure is constantly subjected to the ingress of chloride, which could cause reinforcement corrosion and significant deterioration of concrete structures if not well controlled. Major types of reinforcement corrosion, such as pitting corrosion and concentration-cell corrosion, are usually initiated with localized chloride concentrations whose behavior is closely related to the transport characteristics of chloride ions in hydrated cement paste. However, unless studied at the molecular level, chloride transport behavior cannot be properly understood and controlled in view of the high heterogeneity of cement paste. The findings are presented from a research study recently conducted with a molecular dynamics (MD) approach to investigate the physicochemical nature of the various interactions between chloride ions and cement hydration products, which might significantly influence chloride transport in cement paste. Six hydrated compounds including portlandite, C-S-H phases (tobermorite and jennite), AFm phases (hydrocalumite and kuzelite), and the AFt phase (ettringite) were modeled and then validated by using the Cl-35 nuclear magnetic resonance spectroscopy technique. On the basis of the MD-generated ionic trajectory, the macroscopic transport phenomenon of chloride species was evaluated in the vicinity of each different hydration product in terms of a computed effective diffusion coefficient.