Multiphysical damage characteristics of concrete exposed to external sulfate attack: Elucidating effect of drying–wetting cycles

Drying–wetting cycles (DWC) are suspected of influencing the performance of concrete under sulfate attack, but the nature and extent of this influence are still unclear. Therefore, this research concerns understanding the effects of drying–wetting regimes. To this end, pastes, mortars, and concretes were subjected to cyclic drying–wetting with an interval of 12, 24, or 48 h prior to various physical and microstructural analyses. Additionally, drastic drying–wetting conditions with forced drying at 60 °C to reduce relative humidity from 100% to 55% and field-like drying–wetting conditions with gentle stepwise drying in the natural environment were adopted to examine the relationship between the laboratory and field testing. The results indicate that the conditioning regime with a dry–wet ratio of 3:1 and a dry–wet interval of 48 h can be considered a means to accelerate external sulfate attack (ESA) in a short duration and take both reliability and reproducibility into account without overly sacrificing the anticipated filed conditions. The results confirm that the drying–wetting cycle length and the drying mode affect the transport and reaction mechanisms of sulfate ions and the degradation kinetics of sulfate attack. The implications of these findings inform the design of drying–wetting regime for aggressive aqueous environments.