Origin of chloride diffusivity of cement pastes - a scale transition analysis

For estimation of the durability of structures, it is highly desirable to quantify and simulate the chloride diffusion process in concrete. To this end, diffusion-cell experiments delivering the chloride diffusivity of cement pastes with different water-cement ratios (related to different microporosities) are evaluated in a scale-transition analysis. For prediction of the apparent chloride diffusivity, cement paste can be modelled by means of a differential scheme involving non-diffusive spherical inclusions in a diffusive matrix. As a result, chloride diffusivity of cement paste is obtained as a function of the microporosity and the chloride diffusivity in the micropore solution. Remarkably, the latter turns out to be one order of magnitude smaller than the chloride diffusivity in a pure salt solution system. The smaller diffusivity is probably caused by structuring of water molecu les along the pore surface of cement paste