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This study was the first of its kind which looked at long term performance of hybrid anode systems in reinforced concrete while also using a holistic approach to corrosion risk assessment. An independent appraisal of the site performance of DuoGuard™ Hybrid Anode™ systems was conducted on six bridges structures between 2013 and 2014. The hybrid systems had been installed on six reinforced concrete bridge structures in the UK between 2006 and 2013. The aim of the study was to investigate the efficiency of current design approach to meet the residual service life when the anodes are operating in the galvanic phase. This was achieved by analysing data on the general condition of the structures, the ongoing performance of the installed hybrid anodes, and assessing the overall corrosion risk of the structures. It was found that the six structures were generally in good condition, with low associated corrosion risks. More specifically, the areas protected by the hybrid anode systems had no associated defects or evidence of corrosion. This is a positive finding for the wider implementation of hybrid anode systems as an alternative corrosion management technique. The reinforcement in the protected areas remained predominately in a passive condition, with calculated corrosion rates below the ISO 12696:2012 recommended threshold of 2mA/m². On some occasions the corrosion rates exceeded the recommended threshold; in these instances, corrosion risk was assessed by analysing the trends of long term monitoring data (e.g. open steel circuit potentials) for signs of corrosion initiation. This study also makes recommendations on aspects of design approach in order to improve redundancy, functionality and robustness of hybrid anode systems.

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