Hybrid corrosion protection of chloride-contaminated concrete

Abstract

This paper examines steel corrosion initiation and arrest in chloride-contaminated concrete. Corrosion damage is, at least in part, attributed to the production of acid at sites of corrosion initiation. Solid phase inhibitors provide a reservoir of hydroxyl ions to inhibit damage. Pit re-alkalisation is identified as an important protective effect in electrochemical treatments used to arrest corrosion. An acidification–pit-re-alkalisation model is used to explain the lateral spread of chloride-induced corrosion across a steel surface, the time required to arrest corrosion in cathodic protection and the potential shifts observed as protection is achieved. The process of pit re-alkalisation may be achieved using a relatively small electric charge that is readily impressed off sacrificial anodes using a power supply. A simple but powerful electrochemical treatment comprises a hybrid of a brief pit-re-alkalisation process to arrest corrosion followed by low maintenance galvanic protection to prevent local acidification. Methods of monitoring the steel corrosion rate in electrochemically treated concrete have been developed and used to assess corrosion risk. The brief pit-re-alkalisation process may be applied at any time using the existing anode system to manage future corrosion risk.