Bond Strength of Epoxy-Coated Reinforcement to Concrete

Beam-end specimens were used to determine the effects of coating thickness (3 to 17 mils), bar size (No. 5 - No . 11), bar position (top- cast and bottom- cast), deformation pattern (3 patterns), and cover (1, 2 and 3 bar diameters) on the bond strength between de - formed reinforcement and concrete . The reduction of bond strength by epoxy coating is a function of deformation pattern, bar size, and coating thickness. The bond strength of small bars is more sensitive to coating thickness than the bond strength of larger bars. Large bars are affected more by the presence of epoxy coating than small bars. Bars with relatively larger rib bearing areas are affected less by the coating than bars with smaller bearing areas. Epoxy-coated top cast bars are affected less by the coating than bottomcast bars. Designs based on these observations will be less conservative than those based on the development length provisions in the 1989 ACI Building Code. Nonlinear finite element analysis was conducted to study the role played by epoxy coatings. The model includes representations for deformed steel bar, concrete, and the interfacial material. The interface is represented by special link elements. The longitudinal splitting crack is modeled using a nonlinear fracture mechanics scheme. The interfacial properties, mainly friction, govern bond performance. The finite element studies reveal close agreement between observed laboratory behavior and the computer results