Norcure® Electrochemical Chloride Extraction and Galvashield® XP embedded galvanic anodes extend service life of I-480 Bridge Substructure
Synopsis of article published in the July-August, 2004 issue of Bridge Builder magazine

Constructed in the early 1970's, the mainline structure of the I-480 viaduct through downtown Omaha, Nebraska to the Missouri River consists of 1.5 miles of concrete deck and steel box girders supported by 66 large conventionally reinforced concrete piers. By the mid-1990s, the 30 year-old structure was experiencing deterioration of the concrete deck and concrete substructure. This deterioration was due to chloride-induced corrosion of the reinforcing steel.

The corrosion damage to the concrete deck had progressed to the point that a complete deck replacement was required. While the concrete piers had also become chloride contaminated through failed expansion joints and plugged deck drains, it was desirable to implement a repair strategy instead of replacing the existing piers. The rehabilitated piers were to have a similar service life expectation as the newly replaced deck. To meet the 40+ year design service life for the rehabilitated viaduct structure, an evaluation of corrosion mitigation options for the piers was performed.

To start, a detailed understanding of the current state of corrosion was obtained through a corrosion evaluation. The evaluation consisted of core testing, petrographic analysis, delamination survey, chloride ion profile, depth of carbonation and a half cell corrosion potential survey. This evaluation indicated that the conditions varied throughout the structure.

With this information in hand, the corrosion mitigation strategy selected to meet the design objectives for the I-480 Viaduct was to perform Norcure Electrochemical Chloride Extraction on twenty-six of the piers with the highest chloride contamination levels, and to install Galvashield XP embedded galvanic anodes in the patch repairs on the remaining piers. All piers were then coated to prevent future chloride contamination. The substructure repair project was completed in 2002.

Over 16,000 ft2 of concrete surface area was electrochemically treated using the Norcure system on the I-480 piers. The typical treatment time for the ECE process was approximately 60 days. During the treatment process, hydroxyl ions are being generated at the reinforcing steel. The increase in hydroxyl ions and decrease in chloride ions lowers the Cl-/OH- ratio leaves the reinforcing steel in a passive condition and effectively raises the chloride threshold for initiation of future corrosion.

For the piers with lower chloride concentrations, a localized corrosion mitigation approach was employed by using embedded galvanic anodes to prevent the initiation of new corrosion activity around the concrete patches, thereby extending the service life of the repairs. All piers were coated with a pigmented sealer to prevent future chloride contamination and improve the overall aesthetics of the structure.

For additional information regarding the Norcure Chloride Extraction, Galvashield XP or other products and services for corrosion mitigation, please contact Vector Corrosion Technologies.

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