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In this project, researchers investigated methods for mitigating corrosion in reinforced concrete structures on the substructure of a bridge in Minneapolis, Minnesota. They treated several corrosion-damaged columns and pier caps with electrochemical chloride extraction (ECE). Then selected ECE-treated and untreated structures were wrapped with fiber reinforced polymer (FRP) wraps or sealed with concrete sealers to prevent future chloride ingression. They installed embeddable corrosion monitoring instrumentation in the field structures to evaluate the effectiveness of ECE treatment. Although the ECE process reduced average chloride levels in the treated structures by approximately 50%, several locations still had chloride concentrations in excess of the established corrosion threshold following ECE treatment. Resistivity probe failures that occurred at some of these locations indicated corrosion within the treated structures still could occur, despite re-passivation of the reinforcing steel following ECE treatment. Continued monitoring of the installed instrumentation is required to evaluate the long-term effectiveness of ECE treatment and concrete wrapping/sealing as a corrosion mitigation technique. In laboratory testing of the three FRP wrap types, the Mbrace CFRP and GFRP reported higher peeling loads and lower diffusion rates than the AMOCO CRFP, and thus were considered more effective sealant systems. However, concrete sealers are recommended to prevent future chloride ion ingress, instead of FRP wraps, because the use of sealers does not prevent visual inspection of the concrete for corrosion damage.

Grout materials and grouting practices used in post-tensioned (PT) bridge construction prior to 2003 frequently resulted in the formation of air- or water-filled pockets; termed grout voids; inside PT tendons. Grout voids have been identified as conditions that can promote a corrosive environment within PT tendons. This report details the second phase of a two-phase project that was commissioned by MnDOT to identify best practices for the investigation of PT tendon conditions in bridge structures constructed prior to 2003. This report presents information and recommendations that will assist MnDOT in selecting and developing a project approach; work plan; and budget for future inspection and repair contracts for their pre-2003 era PT bridge inventory.

Reinforced concrete bridge substructures in Minnesota and other northern climates possess an elevated risk for chloride induced corrosion damage; which can reduce capacity and shorten service life. Research was performed in 1997 to investigate new strategies for corrosion mitigation; including electrochemical chloride extraction (ECE) and installation of fiber reinforced polymer (FRP) wrap; which were applied on several corrosion-damaged piers on a 30-year-old bridge in Minneapolis. This report presents the results of follow-up research performed to assess the condition of the treated piers after 20 additional years of service; in order to understand the long-term effectiveness of the strategies implemented. The combination of ECE treatment and FRP wrap installation was found to be very effective; with no concrete distress or probable corrosion activity identified in the treated elements. Poor or mixed performance was observed with all other strategies; including both ECE treatment followed by application of a penetrating sealer and FRP wrap installation that was not accompanied with ECE. In addition; significant chloride contamination occurred in all of the subject piers within the 20 years since the initial study; indicating that neither FRP wrap nor concrete sealers prevented the ingress of new chlorides in the manner in which these systems were installed in the initial study. The findings indicated that performing ECE treatment; or installing FRP wraps; did not alone eliminate the risk of future corrosion activity. The most effective corrosion mitigation strategy to extend the service life of reinforced concrete bridge substructures was to minimize water and chloride exposure.