This report describes the application of four sacrificial zinc anode cathodic protection systems to a reinforced concrete highway bridge deck. Two system designs were found to be the most promising in terms of polarized potentials and protective current densities achieved during the 3-year monitoring program. One design uses commercially available zinc ribbon anodes spaced at 5-in. (127-mm) centers; the other, custom-fabricated perforated zinc sheets. Both systems are overlaid with an open-graded asphalt friction course. The systems yield maximum current density and polarized potentials under warm and moist environmental conditions. Under these conditions average potentials (relative to copper/copper sulfate) are shifted by approximately -130 mV on the ribbon span having 5-in. (127 mm) spacing and nearly -380 mV for the span utilizing the perforated zinc sheet. Current densities for both systems range from about 3 to 4 mA/sq. ft. (32 to 43 mA/m sq.) of rebar surface area under these conditions. Drier or cooler conditions result in decreased current output and some loss in polarization. The final two designs having ribbon anodes spaced at 12-in. (305-mm) and 18-in. (456-mm) centers were much less promising in view of the low current densities and small polarization shifts detected on these systems.
Abstract