10.016  Some Rust on Rebar is Acceptable

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?

-- Anonymous

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."

Check out the following references:

CRSI Engineering Data Report #54 Field Inspection of Reinforcing Bars Page 3 Surface Conditions of Bars, "A light surface coating of rust on reinforcing steel should not be a cause for rejection by the inspector"

ACI 318 Building Code and Commentary - Section 7.4.2, "Except for prestressing steel, steel reinforcement with rust and mill scale, or a combination of both, shall be considered satisfactory, provided the minimum dimensions and weight of a hand-wire-brushed test specimen comply with applicable ASTM specifications." Section 7.4.3, "Prestressing steel shall be clean and free of oil, dirt, scale, pitting and excessive rust. A light coating of rust shall be permitted."

ASTM A615 Standard Specification for Deformed and Plain Carbon Steel Bars for Concrete Reinforcement - Section 12.2, "Rust, seams, surface irregularities, or mill scale shall not be cause for rejection, provided the weight, dimensions, cross-sectional area and tensile properties of a hand wire brushed test specimen are not less that the requirements of this specification."

ASTM A706 Standard Specification for Low-Alloy Deformed and Plain Bars for Concrete Reinforcement - Section 11.2, "Rust, seams, surface irregularities, or mill scale shall not be cause for rejection, provided the weight, dimensions, cross-sectional area and tensile properties of a hand wire brushed test specimen are not less that the requirements of this specification."

CALTRANS - Standard Specifications M ay 2006 Section 52-1.05 CLEANING, "Before concrete is placed, the reinforcement to be embedded shall be free of mortar, oil, dirt, excessive mill scale and scabby rust and other coatings of any character that would destroy or reduce the bond."

Conclusion

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.