Concrete surfaces in the evaporation zone above sulfate-rich soils are subject to severe damage from scaling. Such a physical sulfate attack (PSA) on concrete is a consequence of a cyclic regime between hot-dry and cold-wet environments, during which sodium sulfate crystals expand within the porous media (binder matrix or aggregate) and exert high pressure on the pore walls. Currently, no accepted standard exists for evaluating the resistance of concrete to the PSA phenomenon. In this study, an accelerated physical sulfate attack test protocol was used to determine the effect of blended cement and water-to-binder ratio on concrete resistance to PSA. The testing included a preconditioning protocol for presaturating concrete specimens in a 10% sodium sulfate solution for 15 days, with heat-drying specimens at 50 degrees C before and after immersion. Specimens were then partially immersed in a 10% sodium sulfate solution and subjected to a cyclic regime composed of hot-dry [40 degrees C, 30% RH] and cold-wet [8 degrees C, 85% RH] conditions for 19 h each, separated by a 4-h transition at room temperature. Silica fume (GUb-SF), limestone (GUL), and slag (GUb-S) blended cements were used and compared with general use (GU) cement. A fifth binder (GUL-GP) contained 20% glass powder as a partial replacement of the limestone-portland cement was also used. Three different water-to-binder ratios were used for each binder: 0.35, 0.45, and 0.55. As expected, mixes with lower water-to-binder ratios showed the best performance against PSA, i.e., the lowest mass loss after 15 cycles of exposure (30 days). GUb-SF cement improved the resistance of mixtures with a high water-to-binder ratio compared to GU mixtures. Contrary to silica fume and slag, limestone reduced the resistance of concrete to PSA and showed the highest rate of visual damage for all water-to-binder ratios.
Concrete structures in saline soil regions are prone to degradation due to chloride and sulfate erosion, compounded by the concurrent infiuences of drying, high and low temperatures, and freeze-thaw cycles. This study establishes a simulation test system for complex saline soil environments, integrating findings from real-world environmental investigations. The investigation focused on the degradation mechanism of concrete under the combined impacts of dry-wet and high-low temperature cycles, coupled with composite salt erosion. Additionally, the impacts of water-cement ratio, fiy ash content, and basalt fiber content on concrete's mechanical properties and ion erosion resistance were analyzed. The alterations in the internal pore structure of corroded concrete were examined through nuclear magnetic resonance (NMR) technology. Utilizing the XGBoost algorithm, a predictive model for chloride and sulfate ion concentrations in concrete, under the combined infiuence of dry-wet and high-low temperature cycles, coupled with composite salt erosion, was developed. The findings reveal that the rate of concrete deterioration is gradually accelerating under the combined erosion to dry-wet cycles, high-low temperature cycles, and composite salt. Optimal fiy ash and basalt fiber dosages for corrosion resistance are determined to be 10% and 0.10%, respectively. During advanced erosion stages, concrete porosity, capillary and macropore volume fractions increase, while gel pore volume fraction declines significantly. The XGBoost-based chloride and sulfate concentration prediction model demonstrates strong agreement with experimental measurements, yielding correlation indices of R2 = 0.98 and 0.97, respectively. Interpretation results obtained using SHAP from the machine learning model align with experimental outcomes.