Atomistic Chloride-Induced Depassivation and Corrosion Initiation of Reinforcing Steel A Coupled Electrochemical–Transport–Stochastic Framework

Chloride-induced corrosion of reinforcing steel cannot generally be described as a direct electron transfer from an iron atom to a chloride ion. Chloride is an anion and is not normally the principal electron acceptor in the corrosion reaction.Instead, chloride may adsorb at, penetrate, or destabilize defects in the passivefilm. Iron oxidation supplies electrons, while dissolved oxygen or, under oxygenpoor conditions, another cathodic process consumes them. Corrosion initiationconsequently depends on coupled processes including chloride transport throughconcrete, interfacial adsorption, passive-film defect generation and repair, chargetransfer, ionic transport, and local solution chemistry.This paper presents a proposed multiscale framework that combines establishedelectrochemical and transport relations with phenomenological equations for passivefilm degradation and probabilistic corrosion initiation. The framework coupleschloride activity at the steel surface, a passive-film defect-state variable, anodic irondissolution, cathodic oxygen reduction, local acidification, and a time-dependentinitiation hazard. The proposed constitutive relations are hypotheses for testing, notexperimentally established universal laws. Their parameters must be determined forthe steel composition, concrete pore solution, temperature, moisture condition, andelectrochemical potential. The paper also outlines an experimental and computationalprogram for connecting atomistic calculations to concrete-scale prediction.