Short-term benefits of cathodic protection of steel in concrete

Abstract

In 1998, concrete specimens were cast and exposed to either chlorides (salt/dry cycles or mixed-in during casting) or accelerated carbonation, which resulted in different corrosion conditions for embedded steel bars. The behavior of electrochemical parameters (corrosion potential, concrete resistivity, corrosion rate and chloride content) was studied over a period of 2.5 years1 INTRODUCTIONAn oxide film known as ‘passive’ layer protects reinforcing steel embedded in concrete. This layer is produced by the action of the pore solution (pH ≈ 13) and oxygen, remaining thermodynamically stable under certain conditions. However, passivation is destroyed when the chloride concentration is high enough or when the pH of the pore solution is reduced to near-neutral values. Under chloride attack, localized corrosion deterioration, in the form of pitting corrosion, takes place. Furthermore, the effect of reduced pH dissolves the passive layer over the whole surface of the steel bars. When pitting corrosion is affecting the reinforcing steel, the pH inside such pits is believed to be acidic (Arup 1983), even to significantly low values if enough oxygen is availabletesting (Polder 2002). In 2010, four specimens were selected and subjected to CP current.