Chloride ingress into concrete is a major cause for material degradation, such as cracking due to corrosion-induced steel reinforcement swelling. Corresponding transport processes encom- pass diffusion, convection, and migration, and their mathematical quantification as function of the concrete composition remains…
Chloride ingress into concrete is a major cause for material degradation, such as cracking due to corrosion-induced steel reinforcement swelling. Corresponding transport processes encom- pass diffusion, convection, and migration, and their mathematical quantification as function of the concrete composition remains an unrevealed enigma. Approaching the problem step by step, we here concentrate on the diffusivity of cement paste, and how it emerges from the microstructural features of the materials, and the chloride diffusivity in the capillary pore spaces. We employ advanced self- consistent homogenizationtheoryas recentlyused forpermeabilityupscaling,basedon theresolution of the pore space as pore channels being oriented in all space directions. This results in a surprisingly simple analytical (yet implicit) relation between porosity, pore diffusivity and the overall diffusivity of the cement paste. This relation is supported by experiments, and re-confirms the pivotal role that layered water most probably plays in pore diffusivity reduction with respect to that found under the chemical condition of a bulk solution.