Corrosion is the primary cause of repairs to reinforced concrete bridges and other civil structures.
Galvanic corrosion protection systems have been developed to provide long-term corrosion protection to existing concrete structures suffering from corrosion. Through the partnership and support of structure owners such as Ohio Department of Transportation, Ontario Ministry of Transportation, Florida Department of Transportation and Transport New South Wales these systems have been installed and monitored on bridge decks and substructures for many years. Some of these structures have been monitored for over 20 years. This paper presents the development, installation and 20-year field performance of these galvanic corrosion protection systems and how this real-world performance data can be used to design long-life galvanic corrosion protection systems to extend the service life of reinforced concrete structures.
Chloride induced corrosion of steel reinforcement in concrete structural elements is a major worldwide problem [1]. Chlorides can be introduced into the concrete via de-icing salts, seawater, high salinity groundwater or sabkha soils [1.2]. This leads to localised breakdown of the normally passive steel reinforcement in the form of pitting corrosion [2].
Enhanced concrete repairs, where galvanic anodes are attached to the steel around the perimeter of the repair, have now become common practice and the process is fast being accepted as an essential part of repair works worldwide, and included in most concrete repair standards including EN 1504 and ACI Repair Application 8 and Australian repair code SA HB 84. The anodes are necessary to deal with the phenomenon of incipient anode formation or ring effect [2,3,4,5,6,7], where corrosion is transferred to the periphery of the repair. The anodes act as an essential form of intentional ‘cathodic prevention’ so that the adjacent steel remains cathodic and corrosion initiation is prevented.
The galvanic anodes described in this paper were developed in the late 1990's and are produced from zinc metal encased in a specially formulated porous cementitious mortar saturated with lithium hydroxide (pH >14.5). Such an environment, with a reservoir of excess lithium hydroxide maintaining a constantly high pH, was shown to sustain the zinc in an active condition producing soluble zinc corrosion products that do not stifle the corrosion process of the metal [7,13].
