New insights for modeling chloride ingress under freeze-thaw loading

Realistic assessment of concrete durability must consider complex interactions when multiple mechanisms combine to degrade reinforced concrete structures under field conditions. Recent research has drawn attent ion to the interaction of degradation mechanisms occurring in the harsh environmental conditions of the Nordic countries (frost attack/chloride penetration). Frost attack of concrete affects the chloride penetration by reducing the concrete cover, and more importantly, by changing the characteristics of the surface and internal concrete due to cracking. Literature tells us that a long period of freezing conditions will slow chloride ingress. These new results, however, show that the rate of chloride ingress remains about the same regardless of whether the tests are exposed to daily freeze-thaw cycling. This suggests that the interaction between the various transport mechanism (capillary water uptake, water and vapour diffusion and micro ice lens pumping) is complex, and that no single mechanism consistently explains the test results. Even if freezing slows bulk transport, other mechanisms counteract the slowdown. Their combined interactions result in profil es identical to those of pure panding under constant ambient temperature In the current work, a numerical simulation method based on the dominating transport mechanism, is proposed to analyse the ingress of chloride into concrete under freeze-thaw action. Unsaturated flow theory for capillary water uptake and chloride ingress is considered for simulating water and chloride ingress into concrete next.