Title: Fundamental Tests on the Effect of an Epoxy Coating on Bond Strength

Author(s): John Cairns and Ramli Abdullah

Publication: Materials Journal

Volume: 91

Issue: 4

Appears on pages(s): 331-338

Keywords: bond (concrete to reinforcement); concretes; epoxy resins; friction; pullout tests; reinforcing steels; Materials Research

DOI: 10.14359/4040

Date: 7/1/1994

Abstract:
A survey of the rules in various national codes for detailing of concrete structures reveals wide variations in the bond strength reduction specified for fusion-bonded epoxy-coated reinforcing bars. Investigation of the background to code rules reveals that the differing test methods and bar rib patterns used in research reports consulted by the code drafters have led to the adoption of differing requirements. The paper reports two sets of tests carried out to investigate the effect of a fusion-bonded epoxy coating on bond. Fundamental tests of friction characteristics show that coating reduces friction between steel and concrete by around 40 to 50 percent when stress normal to the interface is low, but that the difference in behavior reduces as normal stress increases. Results of friction tests are related to results of pullout-type bond tests on bars with short embedment length. Bond tests demonstrate that the bond reduction due to a fusion-bonded epoxy coating depends on the bar-concrete slip at which the comparison is made, the reduction being greatest at a small slip, and on the inclination of the face of the bar ribs. It is suggested that the difference in development length requirements could be reduced if restrictions were placed on rib geometry of bars selected for coating. However, it is concluded that it would not be feasible to raise performance of coated bars to that of currently acceptable uncoated bars by specifying a minimum rib face angle for coated bars.