Effect of early-age salt exposure on the long-term durability of concrete

Due to tight construction schedules, environmental constraints, and construction organization requirements, many engineering structures are unavoidably exposed to salt-containing environments at an early age. During this period, concrete hydration and pore structure are still undergoing rapid development, and the premature ingress of salts may amplify the risk of long-term performance deterioration. However, a systematic understanding of this issue remains limited. In this study, long-term exposure tests were conducted on concrete specimens subjected to different early-age curing conditions in single-salt and composite salt-attack environments, under both full immersion and wet–dry cycling regimes. The evolution of macroscopic performance degradation and ion transport behaviour was systematically investigated, and the damage and failure mechanisms of early-age cured concrete under multi-ion coupled salt attack were elucidated through multiple microstructural characterisation techniques. The results indicate that early-age exposure to magnesium-containing salts significantly impairs the long-term durability of concrete. Under composite salt action, the chemical attack induced by magnesium ions is dominant; wet–dry cycling further accelerates the salt-attack process compared with full immersion; and under insufficient curing and wet-dry cycling, concretes with lower water-cement ratios may exhibit greater sensitivity to early-age salt attack. These findings provide mechanistic insights and experimental support for the performance-oriented design and curing strategies of concrete materials in complex environments such as saline soils and coastal regions.