Form-release agents, bond breakers and cement splatter sometimes contaminate reinforcing steel before concrete is placed. However ACI 301-96, "Standard Specifications for Structural Concrete," says: "When concrete is placed, all reinforcement shall be free of materials deleterious to bond." Inspectors often cite this sentence when requiring contractors to remove form-release or bond-breaker overspray and cement splatter from contaminated rebar. But is this work really necessary?
The Aberdeen Group ran a series of bond pull-out tests to assess the effect of contaminants on bond strength. Pull-out tests measure the bond force acting parallel to the bar on the interface between the bar and concrete. Clean, black Grade-60 steel bars and bars with form-release agents, curing compound/bond breakers, cement splatter, motor oil and rust on their surfaces were tested. The form release and curing compound/bond breaker were sprayed on 100% of the rebar surface to duplicate the worst case of contaminant coverage possible during construction. The used motor oil was applied to the entire bar length with a rag, and a cement paste was mixed and applied to various areas of the rebar. To produce rusted rebar, bars were dipped in hydrochloric acid then stored in a moist curing room. The results, based on 27 tests of bars with nine different surface conditions, show that the contaminants didn't adversely affect bond.