Long-Term Electrochemical Evaluation of Commercial Surface-Applied Corrosion Inhibitors for Chloride-Contaminated Reinforced Mortar

The corrosion of reinforcing steel induced by chloride ingress is one of the main causes of premature deterioration in reinforced concrete structures. Among the available mitigation strategies, surface-applied corrosion inhibitors are attractive as a repair option because they are inexpensive and easy to apply to existing structures. However, comparative data on commercial surface-applied inhibitors of different chemical bases, tested on already-contaminated concrete under identical conditions, remain limited. This study evaluates the effectiveness of three commercial inhibitors (an alkoxysilane base, an alkylsilane mixture and an aqueous organo-mineral formulation) applied as surface rehabilitation treatments on mortar specimens contaminated with 2% Cl− by cement weight. The electrochemical behaviour of the embedded carbon steel was monitored over 370 days by means of linear polarisation resistance (LPR) and electrochemical impedance spectroscopy (EIS). The results showed that all three treatments reduced the corrosion rate relative to the untreated reference, with inhibition efficiencies of up to 90%, the alkoxysilane-based treatment giving the lowest corrosion rates. EIS revealed differences in the charge transfer resistance and pore solution response associated with each product. Nevertheless, none of the treatments achieved negligible corrosion conditions, indicating that surface-applied inhibitors mitigate but do not fully arrest chloride-induced corrosion under the conditions studied.