Long-term performance of galvanic anodes used for the protection of steel reinforced concrete and the understanding of anode aging

Galvanic anodes have been widely used for corrosion protection in steel-reinforced concrete, initiallyin patch repair applications and more recently in new construction projects. Over time, these anodes were further developed to provide medium-term corrosion control. However, their aging behaviour has not been fully understood, limiting the ability to design systems withreliable service lives of 20–30 years. This article identifies a multi-regime aging pattern that appears to be consistent across different types ofanodes.

Several field trials were monitored over periods of up to 26 years. Analysis of the results revealed a distinct aging patternprimarily influenced by the type of anode activator, anode geometry, and the spacing of the anodes relative to the steel density. This pattern wasfurther validated through geometrical modelling, laboratory testing, and review of published literature.

The observed agingbehaviour follows an approximately exponential decline in current output, enabling the definition of an Aging Factor — the period over whichthe anode current output reduces by half. Two overlapping aging regimes were identified. Regime 1 is associated with the gradual reduction inthe zinc core surface area as the anode is consumed. Regime 2 results from pore blocking within the surrounding mortar caused by theaccumulation of corrosion products, which progressively restrict ionic pathways. Continued pore blocking eventually leads to near-completerestriction of ionic movement and the development of a residual-current-controlled regime that no longer follows an exponential decay trend.When applied within its intended parameters, the Aging Factor offers a practical and physically meaningful approach for the durability design ofgalvanic anode systems in reinforced concrete. It enables prediction of minimum end-of-life current output appropriate to the level of corrosionrisk. Recognising the regime-dependent nature of anode aging also helps reconcile previously differing long-term observations and supports themore reliable use of galvanic corrosion prevention and protection systems in construction practice.