Modelling of water and chloride transport in concrete during yearly wetting/drying cycles

The simultaneous transport of water and chloride in concrete has been modelled. The water transport is described with a concentration dependent diffusion coefficient. The chloride transport is modelled with a convective part, caused by the water transport, and a diffusive part, caused by the chloride concentration gradient in the pore water. Because the water velocity depends on the pore radius, the chloride transport is a complex pore radius dependent process. Modelling this process leads to an expression for the dispersion coefficient, for the chloride diffusion. The model equations are applied on concrete with a yearly variation of the surface water concentration. A few different boundary conditions for the chloride transport are described. The water distribution is almost homogeneous over the samples. The chloride concentration at the surface can rise considerably, when water leaves the concrete sample, while chloride stays behind. Crystallization and a few other possible model extensions are discussed.

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