Performance Evaluation Of Iowa Bridge Decks Constructed With Epoxy-Coated Reinforcing Bars, RB06-011, 2011

(2011) Performance Evaluation Of Iowa Bridge Decks Constructed With Epoxy-Coated Reinforcing Bars, RB06-011, 2011. Transportation, Department of

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Abstract

Epoxy coatings have been used on the embedded reinforcing bars of bridge decks since the mid-1970s to mitigate deterioration caused by chloride-induced corrosion. The use of chloride-based deicers became common in the early 1960s and caused corrosion of conventional uncoated bars in bridge decks within 5 to 10 years of commencement of deicer applications. In response to this rapid deterioration, the National Bureau of Standards researched coatings to protect the reinforcement (National Bureau of Standards, 1975), resulting in the development of epoxy-coated reinforcing bars, which were used in bridge decks beginning in 1973. While corrosion-related deterioration has been prevalent on bridge decks with uncoated reinforcing bars in northern climates where the use of deicing salts is common, bridge decks constructed after 1973 with epoxy-coated reinforcing have shown good corrosion resistance with only limited exceptions. On the whole, previous laboratory and field studies regarding the performance of epoxy-coated reinforcing bars are very promising; however, some laboratory and field studies have yielded differing results. In recent years, maintenance personnel for the Iowa Department of Transportation (Iowa DOT) have reportedly performed patch repairs to some bridge decks reinforced with epoxy-coated bars. At one such bridge, the southbound US 65 bridge (Bridge No. 7788.5L065) over the Union Pacific Railroad near Bondurant in Polk County, Iowa, deck repairs were performed by Iowa DOT maintenance personnel in the Spring of 2010, based on our communications regarding this topic with Mr. Gordon Port of the Iowa DOT. These repairs were observed by engineers from the Iowa DOT Office of Bridges and Structures, who reported that significant corrosion was found at a number of epoxy-coated reinforcing bars uncovered during this patch work. These repairs were reportedly performed at spalls and delaminated areas corresponding to cracks over transverse reinforcing bars, and involved careful removal of the concrete from over the bars. Figures 1 through 4 contain photographs provided by Iowa DOT personnel showing the removal process (Figure 1), the conditions encountered (Figures 2 and 3), and close-up views of the corroded reinforcing (Figure 4). As a result of these observations, the Iowa Department of Transportation has requested this study to gain further understanding of the long-term performance of bridge decks reinforced with epoxy-coated bars. The two main objectives of this study are to determine the long-term effectiveness of the epoxy coatings and to determine the potential causes for the deterioration at locations where corrosion has occurred. Wiss, Janney, Elstner Associates, Inc. (WJE) and the Iowa DOT identified eight different bridge decks across Iowa for this study that were constructed using epoxy-coated reinforcing bars. A field investigation consisting of visual inspections, a delamination survey, a concrete cover survey, electrical testing for susceptibility to corrosion, and concrete sampling was conducted within a survey area deemed to be representative of the condition of each bridge deck. Laboratory testing, including chloride ion content testing, characterization of the extracted bars, petrographic examination of the concrete, and carbonation testing, was conducted on the core samples taken from each bridge deck.