Corrosion Performance of Epoxy-Coated Reinforcing Bars in a Bridge Substructure in Marine Environment

Abstract To evaluate the corrosion performance of epoxy-coated reinforcing bars in concrete in marine environments, a condition survey of a Georgia concrete bridge substructure constructed in 1984 and reinforced with epoxy-coated steel bars was conducted. The field survey of this structure included visual physical condition inspection, concrete cover measurement, half-cell potential measurement, concrete coring, and epoxy-coated bar sampling. Concrete cores taken from the structure were sectioned for chloride analysis, and sampled bar segments were inspected for coating adhesion, coating thickness, extent of damage and corrosion. No concrete distress induced by corrosion of epoxy-coated bars was observed. Low coating adhesion was observed on all sampled bars as well as various levels of coating damage. The average coating thickness was 155 μm (6.1 mils), and 18% of the measurements were smaller than 125 μm (5 mils). The coating apparently did not meet the thickness requirements of either ASTM A775-81 Standard Specification for Epoxy-Coated Steel Reinforcing Bars (valid at the time of the bridge construction) or the current version of this specification, ASTM A775-06. The extracted bars did not show active corrosion despite the presence of chloride concentrations at the bar depth of up to 0.079 percent by weight of concrete (wt%). One bar sample showing corrosion staining was taken from the tidal zone and the bar-level chloride concentration at that location was 0.251 wt%. An established statistical model was adapted to estimate the remaining service life of the substructure. Using a conservative assumption that epoxy-coated bars have a chloride corrosion threshold of 0.079 wt%, calculations suggest that the substructure would have already developed significant distress if uncoated bars had been used and that epoxy-coated bars may extend service life for 7 years in tidal zone and 20 years in splash zone areas. Future inspections are suggested to refine this model.