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


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

Author(s): J. Gulikers

Publication: Special Publication

Volume: 192


Appears on pages(s): 873-886

Keywords: carbonation; cathodic protection; chlorides; corrosion

Date: 4/1/2000

A condition assessment performed on a substructure of a balance bridge revealed that reinforcement corrosion had been initiated by chloride penetration and carbonation. For the eastward wall, cathodic protection with impressed current was proposed to protect the reinforcing steel. In view of the average thickness of the concrete cover of 60 mm together with the extensive delamination covering approximately 50% of the surface area, a cathodic protection system was designed based on discrete titanium anode strips, inserted perpendicular to the concrete surface. In order to achieve a uniform distribution of protective current to the steel, an average of 10 strips per square meter of concrete surface was placed in holes drilled to a depth of 35cm. The substructure was subdivided into two independently controlled anode zones. During the installation several problems were encountered regarding electrical continuity within the reinforcement network and electrical contact between the reinforcing steel and the anode system. In view of the innovative nature of the design and the increased risk of non-uniform current distribution provisions were made for additional monitoring of the performance of the cathodic protection system. Measurements included concrete resistance, current distribution over the concrete surface and frequent depolarization. The results revealed a pronounced non-uniform current distribution over the concrete surface and a high current demand in one of the zones. Eventually, this resulted in an anodic current density exceeding the FHWA limit. Frequent monitoring is performed to verify if this high current output will decrease with time. There is a strong need for quantitative information regarding anodic and cathodic current distribution as affective by local condition of the embedded steel, concrete resistivity and cover thickness. This information will be of benefit for the design of cathodic protection installations.