03294 The Ministry of Transportation of Ontario's Experience With Electrochemical Chloride Extraction (ECE) 1989 - 2002

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Product Number: 51300-03294-SG

ISBN: 03294 2003 CP

Author: F. Pianca, H. Schell, D. Lai, R. Raven

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The corrosion of steel reinforcement in concrete highway structures involves electrochemical reactions and as such can be arrested by electrochemical means such as cathodic protection or electrochemical chloride extraction (ECE). The ECE method is typically similar to cathodic protection in that it involves application of current. It requires the installation of a temporary anode (5 - 8 weeks) on the surface of the concrete and the passage of direct current between the anode and the steel reinforcement which serves as the cathode. The current density of the ECE process is approximately 100 times the current density used in conventional cathodic protection. The Ministry of Transportation of Ontario (MTO) first used ECE on an experimental basis in 1989. More recently, the Ministry has specified ECE on conventional contractor-bid contracts to mitigate the effect of corrosion distress on 5 piers and 1 abutment at the Burlington Bay Skyway in Burlington and 12 bridge abutments in North Bay, Ontario. Evaluation of ECE by the Ministry has indicated variable performance. Performance as expected, meeting the -250 mV static potential criterion specified by the Ministry has been documented on some structures but not on others. The reason for this variable performance is not yet well understood. The paper will review variables such as total ampere hours passed, depth of concrete cover, depth of chloride corrosion threshold relative to the reinforcement, steel current density compared to concrete current density and corrosion potentials prior to and after treatment. Rate of corrosion measurements by the linear polarization technique will also be presented as well as concrete resistivity readings prior to and after treatment. The paper will attempt to identify parameters that predict the probability of success of the ECE treatment. Typical costs experienced on the Ministry's ECE contracts to date will also be reported.