Form Oil and Rebar - More on the Controversy
This July 10, 2017, article in PRECAST, INC. "Bond, Reinforcement Bond" concludes with more on the chemistry and physics of form oil and rebar (reinforcing bar) preparation.
"FORM OIL Like rust, the question of how much detrimental effect form oil has on reinforcing bars is now the subject of research. The current code provisions within ACI 301, "Specifications for Structural Concrete;' section 18.104.22.168, state, "Do not allow formwork release agent to contact reinforcement;' The NPCA Quality Control Manual for Precast Concrete Plants, section 4.3.2, also states, "Reinforcement and other items to be embedded in concrete shall be free of form release agent."
However, recent research (5) casts doubt on this intuitive school of thought and current code language. Until additional data verifies results, form oil should be removed from reinforcing elements, particularly on epoxy-coated and smooth FRP bars.
(5) Belarbi, A, Richardson, NO., Swenty, MK and Taber, L.H, (2010), Effect of Combination on Reinforcing Bar-Concrete Bond, Journal of Performance of Constructed Facilities, ASCE, Vol. 24, No. 3, May -June "
This June 01, 1998 article in CONCRETE CONSTRUCTION references another report that found no significant difference in nine different rebar surface conditions tested in three different ways.
HOW CLEAN MUST REBAR BE?
Most specifications require reinforcement to be free of deleterious materials. But do common construction contaminants have a harmful effect on bond?
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."