Mechanical Property Analysis and Sulfate Ion Concentration Prediction of Mortar and Concrete Exposed to Dry–Wet Sulfate Erosion Under Continuous Bending Loads

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The objective of this study is to examine the variations in the properties of cementitious materials subjected to bending loads in conjunction with dry and wet cycles of sulfate exposure. This investigation involved applying continuous bending loads at 0%, 20%, and 40% of the ultimate bending capacity to cementitious material specimens. Furthermore, three sets of mortars and concretes with differing water–cement ratios were formulated and analyzed using X-ray diffraction, scanning electron microscopy, and compressive strength tests. The findings indicated that while the flexural strength, compressive strength, and porosity of the specimens initially increased, they ultimately declined as the cementitious materials degraded over time within the sulfate solution. Additionally, it was observed that an increase in bending load corresponded with a decrease in flexural strength, alongside a rise in the internal sulfate ion concentration. By integrating an enhanced form of Fick’s second law with chemical reaction kinetics, a transport model for sulfate ions in cement-based materials was developed under the coupling effect of bending load and sulfate exposure, utilizing Comsol Multiphysics. The simulation results, which align well with the experimental observations, exhibit an error of approximately 5% at a depth of 5 mm.