Towards understanding corrosion initiation in concrete – influence of local concrete properties in the steel-concrete interfacial zone

Chloride-induced corrosion is the most common deterioration process for reinforced infrastructure objects. Improving the understanding of the conditions for initiation of localized corrosion is urgently needed. Research is focused on the influence of “defects” at the steel-concrete interface (SCI), as these weak points might be responsible for corrosion initiation. In contrast to numerous studies with “lab concrete”, this study reports results from reinforced concrete cores drilled from old infrastructure objects containing a non-corroding rebar. In contrast to laboratory studies, this guarantees real conditions at the SCI comprising also irregularities such as air voids, plastic settlement voids, cracks, etc. This allows to study chloride-induced corrosion in real conditions and to determine the so-called “critical chloride content” Ccrit. Visual inspection of the SCI enables to establish (or not) influences of the local conditions at the SCI and Ccrit. It was found that Ccrit strongly decreased with the carbonation depth, even if the carbonation front had not reached the steel. Moreover, coarse air voids and cracks were in this study not particularly susceptible sites for corrosion initiation