Mechanical and damage characteristics study of concrete under repeated sulfate erosion

The mechanical properties of concrete structures change under repeated sulfate salt erosion, a transformation observable through the evolving energy characteristics during compression. This study conducts uniaxial compression tests on ordinary concrete under repeated sulfate solution and pure water erosion, referencing uniaxial compression tests on concrete with admixtures under sulfate solution erosion, comparing and analyzing their mechanical properties and energy conversion characteristics. Findings indicate: (1) Repeated sulfate erosion increases the nonlinearity of the concrete's stress-strain curve, especially during the initial compaction phase. Regardless of peak strength, both the energy dissipation curve and damage variables defined by dissipated energy show consistent trends. This suggests that sulfate salts react within the concrete, generating new substances that fill pores, temporarily increasing the elastic modulus while degrading the original structure, ultimately leading to brittle failure. (2) Considering repair effectiveness, protection of repair products, and the evolution of dissipated energy, peak strength variations, and SEM images of internal microcracks, the optimal timing for self-healing in ordinary concrete is suggested to be after 14 wet-dry cycles. (3) Under repeated sulfate salt erosion, the stress-strain relationship of ordinary concrete significantly deviates from traditional damage constitutive models, especially during initial compaction phase. Constitutive models based on damage variable evolution and dissipated energy show better agreement with experimental results in this phase.