The efficiency of Darcy and two-dimensional diffusion flow models to estimate water penetration into concrete

Abstract

Darcy's equation which governs the one-dimensional flow of fluids through porous media, is widely used to as­sess the per­me­abil­ity of con­crete, while water penetrating into concrete spreads in all directions. For this reason, this paper deals with the validity of Darcy flow model, regarding water penetration into concrete. In addition, two-dimensional diffusion flow model was employed to predict water penetration into concrete. For this purpose, “Cylindrical chamber” method was used to measure the permeability of the 28-day concrete specimens with water to cement ratios of 0.4, 0.5 and 0.6. The results obtained indicated that water penetration into the studied concrete specimens did not follow a Darcy flow model, although water flow through the specimens was laminar. It was also observed that water penetration indices, including average and maximum penetrated water depth, wet surface by water (water penetration profile) and the area of the wet surface were predicted with acceptable accuracy using the optimum diffusion coefficients. In addition, direct relationships were observed between the optimum diffusion coefficients, applied water pressure and water to cement ratio, while optimum diffusion coefficients decreased with increasing the test duration. The results obtained also showed that the optimum diffusion coefficient was higher in vertical direction than that of the radial direction. Finally, strong correlations were seen to exist between the permeability parameters (optimum diffusion coefficients, maximum and average penetrated water depth, area of wet surface and penetrated water volume), test duration and applied water pressure, while there were weak correlations between the optimum diffusion coefficients and penetrated water volume.