Bond strength of black and epoxy-coated reinforcement - a theoretical approach

This paper analyzes the mechanics of bond strength of ribbed reinforcing bars in lapped joints under splitting modes of failure. Two failure types are identified, and analytical expressions to relate the bond strength developed by ribbed bars to the bursting forces generated by bond action are derived. Accuracy of the analysis is confirmed against test data. The resulting formulations are used to assess the bond strength reduction attributable to epoxy coating of reinforcement, and to examine the factors that influence the magnitude of that reduction. The analysis shows that relative rib area and confining pressure exert a significant influence on the reduction in bond strength of coated reinforcement, but that the reduction is not greatly influenced by rib face angle or by concrete strength.