Concrete in transportation infrastructure is constantly subjected to the ingress of chloride from traffic operations, infrastructure maintenance activities and the natural environment. Chloride ingress could cause reinforcement corrosion and lead to significant deterioration of concrete structures if not well attended. Major types of reinforcement corrosion, such as the pitting corrosion and concentration-cell corrosion, are usually initiated with localized chloride concentration that is closely related to the transport characteristics of chloride ions in hydrated cement paste. However, unless studied at the molecular level the chloride transport behavior cannot be properly understood and controlled considering the high heterogeneity of cement paste. This paper presents the findings from a research study recently conducted using a molecular dynamics (MD) approach to investigate the physicochemical nature of the various interactions between chloride ions and cement hydration products that might significantly influence chloride transport in cement paste. Six hydrated compounds including the Portlandite, C-S-H phases – Tobermorite and Jennite, AFm phases – Hydrocalumite and Kuzelite, and the AFt phase – Ettringite, each with a known crystalline structure, were modeled to represent the hydration products of ordinary calcium silicate and calcium aluminate cement systems. Using the 35Cl-NMR spectroscopy technique, the MD models were validated and then used to study the dynamic behavior of chloride ions at the water–solid interfaces. Based on the MD-generated ionic trajectory, the macroscopic transport phenomenon of chloride species was evaluated in the vicinity of each differenthydration product in terms of a computed effective diffusion coefficient.
Samenvatting