High levels of chloride were found in cross head beams on a motorway bridge in the northwest of England. The design made access for testing repair and protection difficult as steel buried up to 800mm deep within the cross head was exposed to high levels of chloride. Tests and trials were carried out to see to what extent the inaccessible steel could be cathodically protected from a surface applied anode.

After successful trials, a full impressed current cathodic protection system was installed using a mixed metal oxide titanium mesh anode with a shotcrete overlay. Detailed calculations of steel surface areas and current requirements were carried out. After nine months of monitoring, it is apparent that the system could have been designed assuming a maximum current density requirement of less than 10mA/m2 of steel surface area rather than the 20mA/m2 used in the design.

Embedded reference electrodes 700mm deep in concrete measured polarization of steel 800mm from the anode on the surface. This showed that embedded probe anodes were not required to protect the highly congested steel deep inside the cross head.

Subject
Depolarization, Electric current, Steel surfaces, Cathodic protection, Probes, Reference electrodes, Anode surfaces, Current densities, Steel, Polarization, Chlorides, Concrete, Anodes
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2004
Association for Materials Protection and Performance (AMPP)
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