Damage Evolution and Pore Structure-Strength Model of Concrete under Plateau Environmental Curing and Hydraulic Pressure

• Combined effects of plateau curing and hydraulic pressure on concrete were studied. • Low-humidity and variable-temperature curing caused initial micro-damage. • Splitting tensile strength exhibited notably higher damage sensitivity ( D t > 0.4). • X-ray CT revealed water pressure triggers pore coalescence and sphericity drop. • Model linking porosity, diameter, sphericity to strength proposed ( R 2 > 0.81). To address the dual challenges of "early-age low-humidity variable-temperature curing" and "late-age high hydraulic pressure" faced by hydraulic concrete in plateau regions, this study investigated their combined effects on performance evolution. By integrating simulated environmental experiments (RH 40%, -10∼40°C; 0∼2 MPa) with X-ray CT three-dimensional reconstruction, the correlation between macroscopic mechanical properties and microscopic pore structure evolution was quantitatively analyzed. The results indicated that the low-humidity plateau curing environment significantly determined the initial microstructure. Specifically, frost heave damage caused by low temperatures (-10°C) severely weakened the matrix, whereas high-temperature curing (40°C), despite promoting hydration and enhancing early strength, induced drying shrinkage effects that generated numerous interconnected pores, thereby markedly increasing sensitivity to subsequent hydraulic pressure damage. The application of hydraulic pressure led to significant strength degradation, with splitting tensile strength exhibiting notably higher damage sensitivity ( D t > 0.4) than compressive strength. The underlying mechanism involves physical softening of the matrix and the "hydraulic splitting" effect driven by pore hydraulic pressure at micro-crack tips. CT reconstruction further revealed that high hydraulic pressure triggered pore coalescence, leading to a surge in meso-pore volume and a significant decline in sphericity. Consequently, a multi-factor pore structure-strength prediction model ( R 2 > 0.81) was established by incorporating porosity, equivalent diameter, and sphericity. This model effectively corrects the bias of single-factor analysis, revealing that compressive strength decay is governed by the increase in pore diameter, while tensile strength deterioration depends critically on the reduction in pore sphericity.