|Q||There is some question on our project whether rust on the reinforcing steel is acceptable. I’ve been told that rust was not a reason for rejection. Do you know of some authoritative document that takes account of cleanliness of the bar?
|A||1/17/07 – Response prepared by Terry Egland, Principal, Registered Engineer, Testing Engineers, Inc., San Leandro
According to the Concrete Reinforcing Steel Institute (CRSI) in a similar FAQ, they state “Rust actually improves bond because it increases the roughness of the surface. However – and this is the exception – if there is so much rust that the weight of the bar is reduced or the height of the deformation is reduced, then the rust is considered harmful.”
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As noted in documents issued by ASTM, ACI, CRSI, and Caltrans, some rusting of the reinforcing steel is acceptable and advantageous. The difficulty in addressing this issue is the subjectivity of a visual evaluation as suggested by CRSI (“A light surface coating…”) and Caltrans (“…free of …excessive mill scale and scabby rust and other coatings of any character…’). Common sense and fabrication tolerances should be used. Where there is readily visible pitting or scale associated with rust (not mill scale) and where the engineer or inspector have cause for concern that the deformations and/or cross sectional area of the bar have been reduced, the degree of rusting may need to be determined by laboratory testing. As always, the project specifications, where more stringent than the published standards, shall prevail over all else.
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