Durability investigation of fractured coal-gasified ash slag concrete eroded by sulfate and chlorine salts

The combined action of sulfate and chlorine salts erodes concrete structures in coastal and saline-alkali zones. The induced fractures under load also accelerate the deterioration of concrete. In this study, ion erosion tests of fractured coal-gasified ash slag (FC-GAS) concrete under dry-wet cyclic conditions were performed using ordinary concrete as the reference. The mass loss rates, the relative dynamic moduli of elasticity, and the distribution patterns of chlorine and sulfate ions of specimens in erosive environments of single sulfate salt, single chlorine salt, and mixed sulfate and chlorine salts were measured. The deterioration mechanism of FC-GAS concrete under coupled erosion by sulfate and chlorine salts was explored with SEM and XRD techniques. By introducing the influence coefficient and deterioration coefficient of the fracture width of FC-GAS concrete, a modified model describing the diffusion behavior of chlorine ions in FC-GAS concrete was established. The results show that for the concrete specimens after erosion in sulfate salt and the mixture of sulfate and chlorine salts, the mass and the relative dynamic modulus of elasticity first increased and then dropped. The deterioration of the concrete performance after soaking in the mixed solution was significantly lower than that of the specimen after dry-wet cycles in the single solution. The formation of fractures accelerated ion erosion. Chlorine and sulfate ions in the mixed solution could inhibit the diffusion of other ions. The diffraction peak strengths of the erosion products of the specimen after dry-wet cycles in the mixed solution were significantly reduced. The results calculated by the proposed modified model on the diffusion of chlorine ions in FC-GAS concrete agreed with the experimental results.