Bond of Epoxy-Coated Reinforcement to Concrete: Bar Parameters

The effects of coating thickness, deformation pattern, and bar size on the reduction in bond strength between reinforcing bars and concrete caused by epoxy coating are described. Tests include beam-end and splice specimens containing No. 5, No. 6, No. 8, and No. 11 bars with average coating thicknesses ranging from 3 to 17 mils. Three deformation patterns are evaluated. All bars are bottom-cast. Beam-end specimens have covers of 2 bar diameters, while splice specimens have covers that depend on bar size and are less than 2 bar diameters. The results are compared with the splice tests that were used to establish the epoxy-coated bar provisions in the 1989 ACI Building Code and 1989 AASHTO Bridge Specifications. Epoxy coatings are found to significantly reduce bond strength, but the extent of the reduction is less than used to select the development length modification factors in the ACI Building Code and AASHTO Bridge Specifications. Coating thickness has little effect on the amount of bond strength reduction for No. 6 bars and larger. However, the thicker the coating, the greater the reduction in bond strength for No. 5 bars and smaller. In general, the reduction in bond strength caused by an epoxy coating increases with bar size. The magnitude of the reduction depends on the deformation pattern: bars with relatively larger ribbearing areas are affected less by the coating than bars with smaller bearing areas. This is the first in a series of reports. Subsequent reports will address the effects of concrete cover, bar position, concrete strength, and transverse reinforcement.