Effect of cracks on concrete diffusivity: A meso-scale numerical study

Concrete cover is often cracked due to e.g. shrinkage, thermal and mechanical loadings, making the service life of concrete structures severely reduced. The diffusivity are strongly dependent on the micro-/meso-structure of concrete. Considering the concrete heterogeneities, cracked concrete at meso-scale is treated as a four-phase composite composed of aggregate particles, cement paste matrix, the interfacial transition zone (ITZ) and crack phase. A meso-scale simulation model for the investigation on the chloride diffusivity into heterogeneous cracked concrete is proposed. In the model, each phase has its own mechanical and diffusion properties. The aggregate is set as impermeable, and the diffusion properties of the cement paste and the ITZs are determined by water-to-cement ratio. For the crack phase, the diffusion coefficient is obtained by fitting the available test data. The accuracy of the developed meso-scale simulation method is verified and discussed. The effect of artificial crack and tortuous crack on the chloride diffusivity is explored. The simulation results indicate that the developed meso-scale model can successfully describe the chloride diffusivity into cracked concrete. Moreover, it is found that the apparent chloride diffusivity in cracked concrete depends on not only the crack width but also the crack depth.