Corrosion Processes of Carbonated Chloride-Contaminated Reinforced Concrete and Electrochemical Chloride Extraction (ECE) Efficiency

Abstract

Civil engineering structures and historical buildings can suffer from corrosion of the embedded reinforcing steel once the concrete cover is totally carbonated and/or when chloride ions have reached the steel/concrete interface. In practice, these two types of contamination can be encountered separately or combined requiring implementation of proper repair methods. In this research, carbonated and chloride-contaminated reinforced concrete specimens were studied by three main analysis means: electrochemical characterizations, Raman microspectrometry and scanning electron microscopy (SEM). The specimens were contaminated in a two-step process involving addition of chlorides followed by carbonation of the complete cover. Electrochemical chloride extraction (ECE) was then performed as a repair treatment (1 A/m² of steel surface during 8 weeks). The efficiency of the treatment and its impact on the steel/concrete interface and cement matrix were studied during the treatment, after steel depolarization and on the long term (several months) in order to evaluate the durability of the treatment. Electrochemical characterizations showed an increase of corrosion rates comparing the specimens after fabrication and after carbonation (from a negligible level of 0.1 µA/cm² to values in excess of 10 µA/cm²). SEM observations confirmed this significant increase with the identification of a corrosion layer on most of the steel/concrete interface after carbonation. The ECE efficiency was evidenced by a decrease of chloride content below the practical threshold value of 0.4% by weight of cement after a two weeks treatment. Simultaneously a realkalisation ring was observed around the reinforcement bar having a diameter of about 1 cm after four weeks. Results obtained after depolarization showed that a two weeks ECE treatment allowed the stabilization of the corrosion state of the rebar.