Damage mechanism and interfacial transition zone characteristics of concrete under sulfate erosion and Dry-Wet cycles

The durability of concrete structures under sulfate attack is of paramount importance to the structural safety and serviceability. Previous relevant researches have considered concrete as a single phase and homogeneous material in experiments without analyzing its multi-phase and heterogeneous properties. In addition, the damage mechanism of concrete under sulfate attack at the microscopic level, i.e., interfacial transition zone (ITZ), was not fully explored in literature. Therefore, this paper provided a comprehensive investigation on the damage mechanism and ITZ characteristics of concrete under sulfate attack and dry-wet cycles. Two typical sulfate attack conditions were examined in an experimental study, which includes 10% Na2SO4 and 10% MgSO4 solutions (by mass), respectively. The deterioration process of concrete was investigated by inspecting the visual change, corrosion resistance coefficient, and ions transportation. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Atomic Force Microscopy (AFM) were also utilized to analyze the micro-topography change and corrosion products of concrete. The results indicate that the porosity of ITZ increases with the dry-wet cycles in tap water, and the concrete microstructure can be compensated by sulfate solutions, in which cases the compensation of C30 concrete is more remarkable than that of C60. 10% Na2SO4 solution is found to exhibit a stronger compensation effect than 10% MgSO4 solution. However, such compensation effect cannot offset the sulfate erosion damage on the microstructure of concrete. As a result, the porosity and initial cracks of ITZ continue to expand, and finally accelerate the cracking process and deterioration of concrete. It is also found that that under the combined effect of sulfate corrosion and dry-wet cycles, the roughness of ITZ increases with exposure time together with the largest increase in tap water. This study provides new insights and deeper understanding into the deterioration process and ITZ-link characteristics of concrete under sulfate erosion, the results of which serve as a decision basis for more durable concrete structure design. (C) 2020 Elsevier Ltd. All rights reserved.