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Coatings that Affect Bond to Reinforcement

ASCC Position Statement #3

ACI 318-02, “Building Code Requirements for Structural Concrete,” Section 7.4.1 states: “At the time concrete is placed, reinforcement shall be free from mud, oil, or other nonmetallic coatings that decrease bond.” The Commentary does not indicate which nonmetallic coatings decrease bond. It does however, indicate that research has shown that a normal amount of rust increases bond, and further states that: “Specific limits on rust are based on tests, plus a review of earlier tests and recommendations.”

ACI 301-99, “Specifications for Structural Concrete,” Section, states: “When concrete is placed, reinforcement shall be free of materials deleterious to bond.” No guidance is provided on which materials affect bond, but section on Formwork states “Do not allow formwork release agent to contact reinforcing steel…” This provision was introduced in ACI 301-1996. 

Engineers or inspectors typically direct concrete contactors to clean bars that are coated with materials believed to decrease bond. Formrelease agents, bond breakers and cement splatter sometimes come in contact with reinforcing steel before concrete is placed. In the absence of data concerning the types of materials that decrease bond, cautious engineers and inspectors usually require all such materials to be cleaned from the reinforcing. However, two recent studies have provided test data showing that some of these materials don’t decrease bond.

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