Quantifying permeability, electrical conductivity, and diffusion coefficient of rough parallel plates simulating cracks in concrete

Cracks in concrete accelerate mass transport and shorten the service life of structures. In this study, cracks were physically simulated using a Plexiglas parallel-plate setup with adjustable distance between the plates (to achieve various crack widths) and with two distinct crack wall roughness values. Transport properties of such simulated cracks were measured and linked to crack geometry. Saturated permeability and ion diffusion coefficient of cracks were measured using constant head permeability test, electrical migration test, and electrical impedance spectroscopy. The results showed that the permeability coefficient of a crack is highly dependent on the crack width square, and to a lesser extent, on the crack tortuosity and wall surface roughness. The result of migration and impedance tests showed that crack diffusivity is only slightly affected by crack width and only for cracks tighter than 90 μm. Generally, crack diffusivity was found to be similar to the pore solution diffusivity, multiplied by a crack connectivity coefficient (β_cr); the latter can be measured from an electrical conductivity test.