Deterioration of Mixed Rebar and Fiber-Reinforced Concrete Bridge Decks

Between 1973 and 1989, approximately 600 bridge decks were constructed in Minnesota with a top layer of epoxy-coated rebar and a bottom layer of uncoated rebar (i.e., mixed rebar deck) to potentially reduce corrosion in the top layer of rebar. In the last five years, at least 20 bridge decks were constructed with polypropylene fibers in the concrete mix to reduce the width and amount of cracking. This project investigated how mixed rebar or polypropylene fibers affected the rate of deterioration in bridge decks (e.g., spalling of underside of deck concrete or unsound concrete on the top wearing surface) compared to control structure decks of approximately the same age. Visual inspections were conducted on certain bridges to compare the visual degradation of the mixed rebar and fiber-reinforced decks with their control structure decks. The results were subdivided to indicate how the superstructure type, average daily traffic, route type, and wearing surface crack density affected the condition ratings and rate of deterioration. The mixed rebar decks reached worse condition states than the control structures when comparing the condition of the underside of the deck; steel superstructures had the largest negative affect on the deterioration. Recommendations included: create an inspection rating element for mixed rebar decks that quantifies the underside of deck crack density, use a robust crack sealing method on mixed rebar decks when they have been at NBE Element #12 CS2 for approximately 7 years, and continue comparing fiber-reinforced decks to control structure decks to analyze the deterioration over time.