Rust on Rebar: Required Surface Condition of Reinforcing Steel

Pool Engineering, Inc. is frequently asked about the required surface condition of reinforcing steel with regards to rust. It is a common misconception that reinforcing steel must be free of rust.

The 2014 Edition of ACI 318, Building Code Requirements for Structural Concrete, in section, 26.6 states:

26.6 Reinforcement materials and construction requirements – Nonprestressed reinforcement with rust, mill scale, or a combination of both shall be considered satisfactory, provided a hand-wire-brushed representative test specimen of the reinforcement complies with the applicable ASTM specification for the minimum dimensions (including height of deformations) and weight per unit length.

Further to the above cited code language, the ACI 318R commentary to this section states the following:

R26.6.1.2(b) – Research has shown that a normal amount of rust increases bond. Normal rough handling generally removes rust that is loose enough to impair the bond between the concrete and reinforcement.

Hopefully, this clarifies the issue of rust on reinforcing steel.