Numerical simulation on diffusion–reaction behavior of concrete under sulfate–chloride coupled attack

Abstract

The transport of sulfate–chloride salts in concrete is the main cause of its structural deterioration. Traditional numerical simulation assumes that the diffusion coefficients of sulfate ions and chloride ions are both constant leading to large deviations in the predicted results. Based on the mass conservation law, Fick’s second law, and the theory of porous media, a variable coefficient transport model of sulfate–chloride salts in concrete is established in this paper. The model fully reflects the adsorption and desorption of chloride ions in the transport process, the reaction-filling process of sulfate ions and hydration products, as well as the most important porosity and tortuosity affecting ion transport. Results show that the prediction results of the two-dimensional variable coefficient model are consistent with experimental and literature results, with maximum error of 23.49%. The analysis of influencing factors shows that the interaction between sulfate ions and chloride ions does not change the transport law of ions in concrete, but delays the rate of ion corrosion within about 700 days. The ability of chloride ions to be adsorbed decreases by about 20% when sulfate ions are present, and the desorption rate is about 40% to 60%. The tortuosity decreases with the increase of water-binder ratio, and increasing the initial porosity from 5% to 12% leads to an early appearance of cracks by about 1400 days.