Bond Behavior of Uncoated and Epoxy-Coated Reinforcement in Concrete

This report summarizes an experimental program conducted to investigate the bond behavior of epoxy-coated and uncoated reinforcement in concrete. The objectives were to investigate the effect of bar surface (epoxy, uncoated), concrete strength (6, 10, 12, 14 ksi), addition of micro silica to concrete (6, 10, 12 and 14 ksi concrete with micro silica and 6 and 10 ksi concrete without micro silica), and bar size (No. 6, No. 8, No. 11). Undisturbed rebar strain distribution along the development length was determined for epoxy-coated and uncoated bars using strain gages embedded inside the rebar. This was the first time the strain distribution of epoxycoated rebar had been measured.

Ninety-six inverted half-beam specimens were tested while monitoring load, initial cracking load, free-end slip, and loaded-end slip. Four of the 96 specimens (2 uncoated, 2 epoxy-coated) had test bars with internally embedded strain gages. All of the specimens were designed to fail in bond by splitting of the concrete. All of the bars were cast with at least 12 in. of concrete above the bar (bottom cast). The reinforcement of a particular size was from the same heat of steel with the N type deformation pattern.

A bond failure hypothesis for epoxy-coated bars is presented. The results were evaluated and compared to current design codes and previous research.