Q.: If reinforcing bars have been stored outside and have a coating of rust, how much rust is acceptable?
A.: Section 12 of ASTM A 615-96a, "Standard Specification for Deformed and Plain Billet Steel Bars for Concrete Reinforcement," says that rust shall not be cause for rejection provided the weight, dimensions, cross-sectional area, and tensile properties of a hand-wire-brushed test specimen aren't less than the ASTM specification requires.
Section 7.4.2 of ACI 318-95, "Building Code Requirements for Structural Concrete," has a similar statement indicating that reinforcement with rust shall be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen aren't less than applicable ASTM specification requirements.
Q: The project inspector is requiring us to wire-brush mill scale and rust off all our rebar. Although the rebar has been at the site for a couple of weeks, we don't think the rust is that heavy or will interfere with the bond between the concrete and steel. Any suggestion? We're tired of brushing rebar.
A: Fortunately, there are a couple of standards to assist you. The ASTM standard specification for deformed steel reinforcement and the Concrete Reinforcing Steel Institute (CRSI) Manual of Standard Practice both give the same information: Reinforcing bars with rust, mill scale, or a combination of both should be considered as satisfactory, provided the minimum dimensions, weight, and height of deformation of a hand-wire-brushed test specimen are not less than the applicable ASTM specification requirements. This inspection criteria recognizes studies that have shown mill scale and rust enhance the bond between concrete and steel. for document Concrete Reinforcing Steel Institute (CRSI) Manual of Standard Practice PDF download.
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