Modeling the kinetics of corrosion in concrete patch repairs and identification of governing parameters

Patch repair is a commonly used method for rectifying localized corrosion damage in reinforced concrete members. However, the ring-anode effect, which is corrosion at the intersection between the substrate and the repaired concrete, is a commonly observed failure mechanism after patch repairs. In this study, the kinetics of the corrosion in the ring-anode zones of repaired concrete structures is investigated by numerical modeling. All simulations, in agreement with the existing experimental and in situ observations, have demonstrated the formation of a ring-anode zone in the 2–5 cm portion of the substrate from the interface between the substrate and the repaired concrete. Furthermore, the anodic current density in the ring-anode zone is found to have a peak near the repaired concrete and to asymptotically approach to the corrosion current density observed in the substrate before the patch repair. More importantly, the simulations demonstrate quantitatively how various parameters affect the ring-anode corrosion. It was found that the resistivities of substrate and repair concretes are the most significant factors that influence the magnitude of macrocell corrosion, followed by the availability of oxygen in the patch. It was observed that the ring-anode effect is a localized problem that occurs in the substrate near the repair bond line, and the size of the patch and the cover thickness are not significant factors affecting the phenomenon.