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Concrete Casting News from the Hill and Griffith Company

Form Oil on Concrete Rebar

Posted by Hill and Griffith Company on Jan 28, 2021 12:55:40 PM

Article excerpt from the August 2013 issue of Concrete Contractor magazine by James R. Baty II

The Concrete Foundations Association explains the code reference and common misconceptions regarding oil on rebar for residential concrete.

Question

On several of our most recent residential projects, the inspector in our area has been complicating our pour schedule when finding form oil over-sprayed on the rebar in our walls. Is it our misunderstanding that form oil on rebar shouldn’t pose a problem to the wall performance or the acceptance of our pre-pour inspection? – Concrete Contractor (Ohio)

Concrete Release Agent and Rebar

Answer

Your question addresses a common problem across the construction industry that is created as codes are modified over time. Regardless of the comparison of residential to commercial work, code edition after code edition presents challenges to professionals throughout the industry to remain current with the latest acceptable practices and minimum requirements. In the specific case of the acceptability of form oil sprayed on rebar for residential applications, this is both a question of appropriate code reference applying more properly to the residential concrete code — ACI 332 — rather than ACI 318, and of referencing the most recent version, ACI 332-10, instead of older versions -04 or -08.

Appropriately referencing ACI 332-10, your inspector and you can develop a common understanding of this issue based on the presented reference. Stated in section 4.2.4 of ACI 332-10, the code provides:

4.2.4 Surface conditions of reinforcement—At the time concrete is placed, deformed bar and welded wire reinforcement shall be free of materials deleterious to development of bond strength between the reinforcement and the concrete.

R4.2.4 Common surface contaminants such as concrete splatter, rust, form oil, or other release agents have been found not to be deleterious to bond.

This version of the residential concrete code presents two issues that are significant to this topic and to the successful resolution of the argument. The first is that during construction, nothing should be found on the reinforcement that would adversely affect the bond strength of the reinforcement in the concrete. The inspector on your project is rightly wanting to make sure the purpose for the steel present in the concrete is successfully achieved, or at the very least, not voided by preventing such a bond. However, the second issue is equally as important even though it occurs in the commentary. Referencing significant industry research, the explanation is given as to what common site conditions found on rebar are not to be considered deleterious to bond. As you might expect, form oil is one such surface contaminant that is not to be considered deleterious to bond.

The obvious next question in your discussion might be why such a surface contaminant is not deleterious to bond. This is the purpose of the reference to the type of reinforcement found in the code section. Deformed bar and welded wire are both designed to achieve a mechanical bond with the concrete rather than a chemical or adhesive bond. The mechanical bond relies on a keying action with the deformations along the length of the reinforcement bar. Therefore, as long as the surface contaminants do not effectively eliminate the presence of those deformations, they would not be considered deleterious to bond.

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