Abstract
The long-term performance of hybrid anode corrosion protection systems (UK invention disclosed in Patent GB2426008B) was investigated on six bridge structures as part of a holistic approach to corrosion risk management, using the performance criteria in ISO BS EN 12696:2016. The aim of the study was to review the effectiveness of current design approaches 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 subsequent corrosion risk. It was found that the six structures were generally in good condition, 1 to 8 years after refurbishment works, with low associated corrosion risk in areas protected by the hybrid anode systems. 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 12696:2016 recommended threshold of 2mA/m2.
Highlights
1.1 Hybrid corrosion protection technologyCathodic protection (CP) of reinforced concrete structures is a well-established method of preventing the initiation of, and arresting ongoing, corrosion
The aim of this study was to analyse the effectiveness of hybrid anode systems at preventing corrosion initiation of the reinforcing steel using the holistic approach of a condition and corrosion risk assessment
The results of the visual inspections indicated that the areas protected by the hybrid anode systems were found to have no visual defects, and the structures were generally in a good condition
Summary
1.1 Hybrid corrosion protection technologyCathodic protection (CP) of reinforced concrete structures is a well-established method of preventing the initiation of, and arresting ongoing, corrosion. The hybrid corrosion protection system is a discrete zinc anode system that is installed into pre-drilled cavities within reinforced concrete (Figure 1) Hybrid technology combines both an impressed and galvanic system to arrest ongoing corrosion and prevent future initiation. The system is connected to a temporary, constant 9V DC power supply, typically for a period of at least one week, depending on the type of reinforcement (e.g. mild steel or prestressed), to deliver a charge to the reinforcing steel [1,2,3,4,5] This initial impressed treatment phase re-passivates the reinforcement by means of generating a reservoir of alkali at the steel concrete interface and is achieved by passing a minimum of 50kC of charge per metre squared of steel surface area [5,6,7,8,9]. This latter treatment phase continues for the remainder of the anodes’ working life and provides a relatively low current to the steel reinforcement to maintain steel passivity [3, 10,11,12,13]
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