Model of Mechanical Properties of Concrete in Western Saline Soil Regions Based on Grey Theory

Concrete structures in western saline soil regions are subjected to extreme environments with coupled dry-wet cycles and high concentrations of erosive ions such as Cl−, SO42−, and Mg2+, leading to severe degradation of mechanical properties. This study employed a simulated accelerated, high-concentration solution (Solution A, ~8× seawater salinity) similar to the composition of actual saline soil to perform accelerated dry-wet cycling corrosion tests on ordinary C40 concrete specimens for six corrosion ages (0, 5, 8, 10, 15, and 20 months). For each age, three replicate cube specimens were tested per property. The changes in cube compressive strength, splitting tensile strength, prism stress–strain full curves, and microstructure were systematically investigated. Results show that in the initial corrosion stage (0–5 months), strength exhibits a brief increase (compressive strength by 11.87%, splitting tensile strength by 9.23%) due to pore filling by corrosion products such as ettringite, gypsum, and Friedel’s salt. It then enters a slow deterioration stage (5–15 months), with significant strength decline by 20 months, where splitting tensile strength is most sensitive to corrosion. Long-term prediction models for key parameters such as compressive strength, splitting tensile strength, elastic modulus, peak stress, and peak strain were established based on grey GM(1,1) theory using the measured data from 0 to 20 months, achieving “excellent” accuracy (C ≤ 0.1221, p = 1). A segmented compressive constitutive model that considers the effect of corrosion time was proposed by combining continuous damage mechanics and the Weibull distribution. The ascending branch showed high consistency with the experimental curves. Life prediction indicates that under natural dry-wet cycling conditions, the service life of ordinary concrete in this region is only about 7.5 years when splitting tensile strength drops to 50% of initial value as the failure criterion, far below the 50-year design benchmark period. This study provides reliable theoretical models and a quantitative basis for durability design and life assessment of concrete structures in western saline soil regions.