Pilot Applications of Electrochemical Chloride Extraction on Concrete Bridge Decks in Virginia

About the report:

A recent SHRP study confirmed that applying an electrical field between the surface of a concrete structure and the rebars (like cathodic protection, except with 50 to 500 times more current) can expel the chloride ions from salt-contaminated reinforced concrete and mitigate rebar corrosion. This new rehabilitation method was tried on two whole deck spans, as part of pilot trials in Virginia to demonstrate the practicality of this electrochemical chloride extraction (ECE) process on full-sized bridge elements and to help refine the technique. The total concrete area treated was approximately 720 m 2 (7,750 ft2). To avoid traffic interruption, half of the deck was treated at a time (for 8 weeks, though a shorter time would likely suffice). The treatment used a very simple installation and procedure, involving placement of a temporary electrolyte-soaked anode system (of inert catalyzed titanium mesh sandwiched between two layers of felt) on the surface of the deck, and the application of total charges that varied between 741 to 1,077 A-hr./m 2 (68.8 to 100.1 A-hr./ft 2) in 57 to 58 days between the anode and the rebars. Approximately 72.2 to 82.1% of the initial chloride ions were removed from the concrete in various depths. These magnitudes surpassed the removal rate of 40 to 50% that was suggested for very heavy treatment by one SHRP report. A minor rectifiable difficulty was encountered in neutralizing the acidity generated in the electrolyte, especially during the first several days of each treatment phase. Lithium was used in the electrolyte for two portions of the deck and was observed to migrate readily into the concrete. However, a similar attempt to simultaneously inject a cationic corrosion inhibitor (tetraphenylphosphonium) into the concrete, which represented a first attempt ever on a concrete deck, yielded uncertain results. It is uncertain whether the corrosion inhibitor had migrated into the concrete; if it had, it was in quantities less than the minimum detection level of 25 ppm, by the capillary electrophoresis method used. Overall, the pilot treatment of the deck was judged to be very simple to perform and more than reasonably successful.

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