Half Cell Potential Survey Mapping

Birmingham City Laboratories

Reinforced concrete can be subjected to corrosion processes that can lead to damage and failure. Undertaking an accurate half-cell potential survey aids in detecting corrosion in reinforcement. Corrosion of steel in concrete is an electrochemical process. A potential field can be measured on the concrete surface by the use of an electrode, known as a half-cell and a high-impedance voltmeter. 

Birmingham City Laboratories are now using the The Canin + Corrosion Analyzing Instrument. Reinforcement condition is evaluated by measuring cover depth, carbonation depth, reinforcement condition, concrete surface resistivity and using the half-cell potential survey method

      

The Canin+ is reported as the fastest instrument for corrosion analysis, offering a practical, cost-effective approach to the investigation of reinforced concrete. Corrosion analysis with the Canin+ allows a rapid, comprehensive test of the site and provides a fast assessment of locations where corrosion is likely to take place. Corrosion analysis with the half-cell potential method: accurate field potential measurements aid in detecting active corrosion in rebars.






Half cell survey

When reinforcement steel comes into contact with the highly alkaline water solution in the pores of the concrete, a passive film of hydrated iron oxide with a thickness of a few atomic layers is created on the steel surface, which protects the reinforcement from corrosion. This passive film is decomposed due to the reaction of the concrete with atmospheric carbon dioxide (CO2) (carbonation), or by the penetration of substances aggressive to steel, above a critical concentration, in particular chlorides from de-icing salt or salt water. The chemical reaction creates an anode at the point where corrosion is taking place and a cathode where there is no rust. Corrosion of steel in concrete occurs following the destruction of the passive film of hydrated iron oxide, above all by chlorides, but also due to carbonation. The potential difference between a corroding reinforcement area (anode) and a passive reinforcement (cathode) can be detected by means of potential field measurements allowing the position where active corrosion is taking place to be localized.