Propagation of pitting corrosion of steel in concrete

Abstract

Where exposed to an aggressive environment, concrete structures will develop reinforcement corrosion at some point in their life. Chloride ions from de-icing salt or sea water induce pitting corrosion. Local cross section reduction may occur relatively quickly and expansion due to corrosion products precipitating may crack and spall concrete cover and reduce steel-concrete bond. With the aging of the existing stock, questions arise about the effects of corrosion on their structural behaviour, safety and reliability.TNOhas started a four-year programme to investigate this subject. One project concerns modelling of pitting corrosion from electrochemical principles, aimed at prediction of cross section loss with time and, in a next stage, corrosion product formation. Existing models for pitting corrosion are highly simplified and essentially two-dimensional, while pitting is clearly a three-dimensional phenomenon. The difference may have serious consequences for structural safety. New approaches are needed, including new conceptual models and addressing uncertainties on several levels. The paper presents some conceptual models for pitting corrosion and reports preliminary results of numerical (finite element) modelling of pitting corrosion, based on solving potential and current distributions and resulting in cross section loss as a function of time. Further work including experimental validation is foreseen.