Modelling of chloride transport in marine concrete structures

Abstract

The detrimental effects related to chloride-induced corrosion in reinforced concrete structures highlight the need for development of a comprehensive models for predicting the chloride penetration in concrete in order to secure the corrosion-free life under chloride laden environments. The main purpose of this thesis is to develop a mathematical model for predicting chloride transport in marine concrete structures exposed to corrosive environments. The factors to the chloride transport in concrete were defined as pore structure and chloride binding, which are applicable to the case of chloride diffusion for submerged condition and chloride diffusion-convection for tidal zone of concrete bridge. The pore structure in concrete was quantified by obtaining the main parameters in transport process such as pore size distribution, tortuosity, and thus chloride diffusion coefficient, which was largely dependent on the concrete mix conditions, ranging from 1.12 to 7.29 m2/s. Based on this, chloride diffusion was modelled by taking into account of chloride binding capacity, consisting of non-equilibrium sate of chloride mass transfer and non-linear chloride binding isotherm to relate equilibrium concentration of chlorides. From the simulation results, chloride diffusion rates at initial period were mainly controlled by the effective diffusion coefficients, and then reduced by about one order of magnitude due to increased chloride binding capacity. From the modelling of chloride diffusion-convection, considering the coupled action of moisture and chloride transports, drying humidity condition at concrete surface was a decisive factor to service life estimation. In particular, humidity conditions between 60 – 70% at drying cycles imposed higher amount of chloride accumulations near the surface and increased the rate of chloride convection through concrete depth as compared with the case of over 80% humidity levels. The objective of this study is to provide a mathematical approach for determination of serviceability in reinforced concrete structures.