The size effect in corrosion greatly influences the predicted life span of concrete infrastructures

Chloride-induced corrosion of reinforcing steel in concrete is the main cause for premature degradation of concrete infrastructures worldwide. Since mid of the last century, the conceptual approach to tackle this challenge in science and engineering is based on a threshold chloride concentration (Ccrit) for corrosion initiation. Here, we present an experiment that shows that Ccrit depends strongly on the exposed steel surface area. The smaller the tested specimen, the higher and the more variable becomes Ccrit. This size effect can be explained by the local conditions at the steel-concrete interface, which exhibit pronounced spatial variability. The size effect has major implications for the future use of the concept of Ccrit. It questions the reproducibility of typically small-scale laboratory testing and the applicability of laboratory results to engineering structures. We show that the weakest link theory is suitable to transform Ccrit from small to large dimensions, which lays the basis for taking into account the size effect in science and engineering of corrosion of infrastructures.