Cathodic Protection of Reinforced Concrete Structure Using Discrete Anode Strips—Case History

Abstract

A condition assessment performed on a substructure of a balance bridge revealed reinforcement corrosion had been initiated by chloride penetration and carbonation. For the east wall, cathodic protection with impressed current was proposed to protect the reinforcing steel. A cathodic protection system was designed based on discrete titanium anode strips, inserted perpendicular to the concrete surface. An average of 10 strips per sq. meter of concrete surface was placed in holes drilled to a depth of 35 cm in order to achieve a uniform distribution of protective current to the steel. The substructure was divided into 2 independently controlled anode zones. During installation several problems were revealed regarding electrical continuity within the reinforcement network and electrical contact between the reinforcing steel and the anode system. Results of additional monitoring of the performance of the cathodic protection system revealed a pronounced non-uniform current distribution over the concrete surface and a high current demand in 1 of the zones. Eventually, this resulted in an anodic current density exceeding the FHWA limit. Frequent monitoring is needed to verify if this high current output will decrease with time. This research shows there is a strong need for quantitative information regarding anodic and cathodic current distribution as affected by local condition of the embedded steel, concrete resistivity, and cover thickness.