Effects of Epoxy-Coating on the Bond of Reinforcing Steel to Concrete

Abstract

The effects of deformation pattern! bar size, concrete cover, casting position, concrete slump 1 consolidation, transverse reinforcement, and concrete strength 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. A preliminary investigation of the behavior of epoxy-coated hooks is also described. Epoxy coatings reduce bond strength. In general, this reduction increases with bar size and changes with deformation pattern: bars with a relatively large rib-bearing area are affected less by the coating than bars with a smaller bearing area. The bond strength of both uncoated and coated bars increases as concrete cover increases. The bottom to top-cast bar strength ratio, B/T, increases for uncoated bars and decreases for coated bars as concrete slump increases. Transverse steel increases bond strength; coated confined bars had virtually the same bond strength as uncoated unconfined bars. Design recommendations are made. Analytical studies are conducted on a statical model, consisting of two rigid bodies (steel and concrete) in contact, and a finite element model, representing onehalf of a beam-end specimen. Statical model analyses indicate that 0.35 and 0.10 can be adopted as representative coefficient~ of friction for uncoated and coated bars, respectively. Finite element analyses indicate an increase in bond force will occur with an increase in cover, lead length, or bar size.