Cathodic Protection Field Trials on Prestressed Concrete Components
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1995-11-01
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Abstract:This is the Interim Report in a study to demonstrate the feasibility of using cathodic protection (CP) on concrete bridge structures containing prestressed steel. Past laboratory and test yard studies had indicated that overprotection could result in the evolution of atomic hydrogen and the embrittlement of prestressing steel. Systems utilizing catalyzed titanium mesh, conductive rubber, and arc-sprayed zinc anodes were installed on prestressed pilings and girders of the Howard Frankland Bridge in Tampa, Florida, and systems using flame-sprayed zinc and conductive paint anodes were installed on the soffit of prestressed box beams of the Abbey Road and West 130th Street bridges near Cleveland, Ohio. The installation of all systems went well, with two exceptions. A strong October storm caused damage to the substructure and CP systems installed on the Howard Frankland Bridge, and leaking joints on the Ohio bridges caused construction delays and additional work. The three zones using zinc anodes were all started up in sacrificial mode, but after a few months on-line, polarization of the steel in these zones was inadequate, and operation will be switched to impressed current in the near future. The conductive rubber anode used on seawater pilings initially leaked a large amount of current to the seawater, but this has moderated as steel below water has become polarized. The conductive paint anode is showing signs of early disbondment, and may not be well suited for service in this environment. A review of literature and early data indicate that constant voltage, with a current limit, may be the optimal mode of control for structures containing prestressed steel and this will be studied in the monitoring phase of this contract. Following two and a half years of monitoring the CP systems, components will be evaluated and tests will be conducted to determine effects on the bond and structural properties of the steel.
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