Monitoring results of galvanic anodes in steel reinforced concrete over 20 years

Abstract

Sacrificial anodes have been used in reinforced concrete structures for up to 20 years. This paper reviews the performance of the oldest set of anodes. It demonstrates, from results of current output and steel depolarisation levels, that the repair system is still functioning adequately overall but with signs of deterioration beyond 15 years. These prototype anodes designed for a 10-year life continue to deliver a reduced but significant current complying with currently accepted criteria. The current output of the anodes was shown to experience two events which caused a reduction in performance at 6 and 14 years likely to be related to a reduction in capillary porosity from the build-up of zinc corrosion products and the drop of the pH below that of saturated lithium hydroxide respectively. Nonetheless, the overall reduction in current was found to be adequately described by an anode aging model where the current delivered is halved over constant time intervals, enabling determination of an ‘aging-factor’. For these prototype anodes the ‘aging-factor’ was estimated to be around 7 years with a potential of extending this period if measures are taken to delay or eliminate the two current reduction events. Use of this anode aging model will enable better design of galvanic corrosion control systems and will allow the approximate current output of the system to be predicted at any particular time in its design life.