Mesoscale Modelling of the Chloride Diffusion in Cracks and Cracked Concrete

In service, cracks or microcracks are usually present in concrete as a result of several mechanisms, for example the drying shrinkage, thermal gradients, freezing-thawing cycles, alkali-aggregate reaction and external loading. It has been realized that cracking can significantly accelerate the ingress of chlorides into concrete since it provides preferential flow channels and allow more chlorides to penetrate. But it is also believed that cracking plays an important role on the penetration speed of chloride. The objective of this paper is to quantify the diffusion coefficient of chloride through cracks of concrete with different crack widths by means of the mesoscale modelling method based on the available experimental results from literatures. In the numerical models, the position and opening width of cracks are artificially prescribed based on geometrical layout of the samples used in test. Additionally, the Voronoi diagram technique is adopted to discrete the domain of a specimen in order to reduce the mesh bias. On the Voronoi diagram, a randomly distributed lattice network is constructed to represent the transport process of chlorides. The range of investigated crack width is from 20 to 600 μm covering the data in experimental program. The diffusion coefficients of chloride through cracks of different width, Dcr, are numerically determined by the trial and error method. It is concluded that chloride can penetrate into cracks with a much higher speed than that in free water. When the crack width is lager than a critical value, Dcr is determined as 10000 mm2/h and independent of the crack width.