Chloride binding to calcium silicate hydrates (C-S-H) in cement paste: a molecular dynamics analysis

A research study was recently conducted using the molecular dynamics approach to investigate the physico-chemical nature of interactions between chloride ions and various hydration products of cement that could lead to chloride accumulation in concrete. This paper presents the findings of one primary focus of the study, i.e. studying the transport behaviour of chloride ions in the calcium silicate hydrate (C-S-H) phases of cement paste. Based on a comprehensive review, three reprehensive hydrated compounds, i.e. the portlandite, tobermorite and jennite, were modelled to evaluate the transport property of generic C-S-H phases in cement paste. Using the 35Cl nuclear magnetic resonance spectroscopy technique, the MD models were validated and used to study the binding capacity of C-S-H phases towards the migrating chloride ions at the water–solid interfaces. The macroscopic transport phenomenon of chloride in C-S-H phases was studied in terms of the effective diffusion coefficient computed using a mean-square displacement approach.