ABSTRACT

Galvanic anodes have been used to provide various levels of corrosion protection to reinforced concrete structures for many years. Some installations have met expectations and others have not performed as desired. Failures have been associated with lack of understanding of the performance of anodes with time. Long-term monitoring of galvanic anodes has allowed detailed analysis of their performance and aided in the understanding of the way performance diminishes with time and how temperature affects current delivery. The aging effect of the anode is described by an Aging Factor which was found to be specific to each anode type. Knowledge of the Aging Factor and the mean annual temperature has permitted performance expectations and duration of protection to be defined prior to final design. Successful designs are designs which meet the specified performance expectations for the design service life and are based on the actual performance of the specified galvanic anode in the service environment. The temperature and corrosivity of the environment must be considered. Long-term galvanic anode performance data has been used to validate the proposed design approach.

Background

Corrosion of reinforcing steel in concrete is the leading cause of deterioration of concrete infrastructure in the U.S and worldwide [1]. Reinforced concrete structures can be designed and maintained to achieve long service lives but unfortunately, some bridges, piers, and other structures show signs of active corrosion such as rust staining and concrete spalling, during their intended service life. Left unchecked, chloride induced corrosion can lead to major structural problems. Many severely corroded structures have been replaced at great expense and with significant disruption to the public.

Galvanic anodes have been shown to control reinforcement corrosion for periods beyond 20 years, but their long-term performance behavior was not documented until recent analysis of long-term monitoring results of some early field trials [1, 2]. Careful analysis of long-term performance data and analysis of anodes removed from structures has established a mechanism of anode aging that can be predicted. A term defined as an Aging-Factor was found to allow reasonable prediction of the long-term behavior of the anodes. The Aging-Factor describes how current output diminishes with time in such a way as to be halved at constant time intervals.

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