Behavior of Epoxy-Coated Textured Reinforcing Bars

Cracking in bridge decks is a common but difficult problem to control. Both research and experience show that the use of epoxy-coated reinforcement, which is mandated by most state departments of transportation (DOT’s) for bridge decks, increases cracking. Although the epoxy coating protects the steel from corrosion, bond strength is compromised and the increased cracking exacerbates durability issues in concrete. As a means to improve bond and reduce the formation of cracks, the Illinois Department of Transportation (IDOT) proposed texturizing the surface of epoxy-coated bars. IDOT developed a prototype textured epoxy coating and this report details a preliminary study on the bond strength of reinforcing bars with the new coating. Direct pull-out tests were performed on uncoated, standard epoxy-coated, and textured epoxy-coated No. 5 and No. 8 reinforcing bars to compare the bond characteristics. Standard epoxy-coated bars clearly demonstrated an increased tendency to slip and split the concrete. Initially, bars with the textured epoxy coating showed good force-slip behavior similar to black steel, but a rapid degradation of slip resistance was observed. On average, the peak nominal bond stress developed in the textured epoxy-coated No. 5 bars was approximately 17% lower than the uncoated bars. Pull-out specimens with No. 8 bars were confined using steel and shape memory alloy (SMA) wires to prevent concrete splitting. The confined No.8 bar specimens demonstrated behavior similar to the No. 5 bar specimens. In addition to the direct pull-out tests, three beam specimens were fabricated using No. 5 bars as a preliminary means to compare the bond behavior of the bars flexure. Overall, in both the direct pull-out and flexural testing—the added frictional resistance of the textured epoxy-coating showed promise as an effective way to improve slip resistance and reduce concrete cracking. However, further research is needed to optimize the coating and characterize its behavior.IDOT-R27-SP35Ope