Experimental and numerical investigation of cast-in-situ concrete under external sulfate attack and drying-wetting cycles

In this paper, a numerical model was proposed to simulate the diffusion of sulfate and the strength degradation of cast-in-situ concrete under sulfate attack and drying-wetting cycles. The hysteresis of moisture transport was used to illustrate the moisture transport mechanisms during the wetting and drying process. The ion transport model was proposed according to Fick's second law, and moisture transport, chemical reactions, advection and damage were taken into account. The cast-in-situ concrete cylinder specimens exposed to sulfate and drying-wetting conditions were conducted by the indoor experiments. The concentration of the sodium sulfate solutions varied at 0%, 3%, 5% and 10%, showing that the ingress of sulfate and strength degradation were significantly accelerated by the increase in the sulfate concentration. The compressive strength of the specimens exposed to sulfate increased before 6 months and then decreased. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were performed to observe and identify the corrosion products of concrete exposed to sulfates. The effectiveness of the proposed method was analyzed through a comparison between the numerical and experimental results for the sulfate distribution and the compressive strength loss. Numerical studies were performed to present the response of concrete to sulfate diffusion under different drying-wetting cycles and boundary conditions. The results were approximately close to the experimental data and indicated that advection accelerated the diffusion process. The loss of compressive strength could be predicted at the period of damage initially induced by sulfate attack, and the comparatively longer drying period and lower environmental moisture level could promote the diffusion of sulfate. In general, the proposed diffusion model coupled with moisture transfer could be capable of simulating sulfate diffusion and strength degradation due to external sulfate attack and drying-wetting cycles. (C) 2020 Elsevier Ltd. All rights reserved.