Characterizing mechanisms controlling pit growth of steel in concrete

Chloride-induced corrosion damage of steel in concrete typically initiates as localized pitting, which may either repassivate or continue to grow and evolve into more widespread forms of damage. However, models developed to forecast corrosion damage generally neglect the early stages of pitting corrosion. This omission stems in part from the assumption that traditional carbon steel reinforcement rapidly transitions to more general corrosion, as well as from the limited understanding of the fundamental mechanisms governing pitting corrosion in concrete. Most durability forecasting models therefore rely on a chloride threshold to distinguish between the period before and after corrosion initiation, implicitly assuming that exceeding a critical chloride content leads to widespread corrosion activation. In contrast, this paper explores an alternative framework grounded in established concepts of pit stability that are commonly applied to immersed and atmospheric corrosion systems.

This work seeks to elucidate the mechanisms controlling pit growth of steel in concrete through a combination of experimental methods and physics-based computational modeling, with the goal of identifying conditions under which repassivation may occur. Artificial pit experiments are employed to investigate the influence of concrete configuration on pit stability and repassivation behavior. The steel–concrete interface is highly complex and heterogeneous, and two key concrete properties are expected to play dominant roles in pitting corrosion: its ability to act as a diffusion barrier and its capacity to buffer pH. The former is anticipated to promote stable pit growth, whereas the latter is expected to favor repassivation.