Damage mechanism and mechanical behavior of recycled aggregate concrete under the coupled compressive loading and sulfate erosion

Sulfate attack poses a significant threat to the durability of concrete structures, particularly in marine and salt lake environments. This study systematically examines the effects of sustained compressive loading and sulfate exposure on recycled aggregate concrete (RAC). Hollow prismatic specimens were prepared with varying recycled coarse aggregate replacement ratios (0 %, 50 %, 100 %), sustained compressive stress levels (0, 0.25fc, 0.5fc), and dry-wet cycles (0, 60, 120). The results indicate that compressive stress below 0.5fc effectively mitigates the durability damage of RAC, evidenced by a slower mass increase and a reduced decline in the relative dynamic modulus of elasticity. Microscopic analysis reveals ettringite and gypsum as primary sulfate attack products, with a higher concentration in RAC without sustained loading. Sustained loading delays the formation of these internal erosion products, reduces overall porosity and lowers the proportion of harmful pores. Furthermore, sustained compressive loading significantly reduces the loss of compressive strength and modulus of elasticity, though its impact on plastic deformation capacity is limited. A predictive model for axial compressive strength was developed, along with a biphasic constitutive model that accurately describes the compressive behavior of RAC under combined sustained loading and sulfate attack. These findings provide valuable insights for the design and evaluation of RAC structures in aggressive sulfate environments.