Damage evolution mechanism of hydraulic concrete under low-pressure curing and varying freezing temperatures

This study explores the effect of early-age low-pressure curing on freeze–thaw damage evolution of concrete in plateau environments with low pressure and large temperature differentials. Freeze–thaw tests were performed at curing pressures of 63, 74, and 101 kPa and minimum temperatures of −10, −20, and −30 °C, using macroscopic evaluation, nuclear magnetic resonance, and a Thermal-Hydraulic-Mechanics mesoscopic model. Results show that low-pressure curing significantly coarsens the initial pore structure. Decreasing temperature narrows the freezing front transition zone, leading to severe deformation gradients and stress concentrations at specimen boundaries and in the Interfacial Transition Zone. Damage-mechanism transitions: at ∼−10 °C, frost-heave stress from pore-water phase change dominates; below −20 °C, freezable-water depletion shifts dominance to thermal-incompatibility stress from differential aggregate–mortar thermal expansion. This reveals the intrinsic correlation between low-pressure curing and extreme low-temperature service, providing theoretical support for frost-resistance optimization and reliability evaluation of plateau hydraulic structures.