Chloride Ion Ingress in Concrete Exposed to a Cyclic Wetting and Drying Environment

摘要

Concrete agricultural buildings are subjected to severe corrosion of their reinforcing steel by moisture and aggressive ions. Several accidents have indicated that corrosion is more severe in areas subjected to cyclic exposure to corrosive fluids than those submerged in the fluids. Laboratory experiments were conducted to study the effect of cyclic wetting-drying on the ingress of moisture and chloride ions in concrete. Expedited experiments were conducted using 10% NaCl solution and infrared lights for drying. The wetting and drying durations were 1 h and 7 h, respectively. Results show that chloride concentrations in the surface layers (0 to 5 mm) of the concrete samples that were subjected to cyclic wetting and drying were much higher than those in the saturated samples; the differences became greater as the experimental time continued from 14 to 45 to 90 days. In addition, the difference in Cl concentration decreased with the depth in the concrete samples. Overall, the rate of chloride transport in concrete under cyclic wetting and drying was quicker than that in immersed concrete. This indicates a potential for faster damage to concrete structures under cyclic wetting and drying conditions