Effect of Reinforcing Bar Contamination on Steel-Concrete Bond During Concrete Construction

Synopsis: During concrete construction, form oil, bond breaker, concrete splatter and other types of contaminants often contaminate reinforcement. Current specifications and quality control measures require the removal and clean up of these contaminants before the placement of concrete due to a concern of a reduction in bonding capacity. This is costly, labor intensive, and may not be necessary. Currently, there is limited research on the effect of reinforcing bar contamination on the bond between the deformed steel reinforcing bar and concrete. Because of this lack of data, specifications are conservative and require the removal of the contaminant. Inspectors often cite ACI 301-96, Standard Specifications for Structural Concrete, which states, “When concrete is placed, all reinforcement shall be free of materials deleterious to bond.” If it could be conclusively proven that this level of care is unnecessary, the construction industry would benefit greatly. To address the effects of contaminants on bond characteristics of deformed steel reinforcing bars, a preliminary study was completed at the University of Missouri-Rolla. The research program focused on three contaminants often seen during construction: form oil, bond breaker and concrete splatter. Other variables included size of reinforcing bar, strength of concrete and epoxy versus uncoated reinforcing bar. This paper will provide the experimental program and test procedures as well as the test results and observations. The results reveal that in the majority of situations tested, the ultimate bond stress was not significantly affected by the three contaminants tested. In some cases, the bond breaker and form oil affected the smaller epoxy coated bars, while the effect of concrete splatter was insignificant.