Do we need to remove corrosion or rust from reinforcing steel prior to placing concrete?
Not if certain conditions are met as described and codified below.
Corrosion or rust does not need to be removed from reinforcing steel prior to placing concrete as long as the reinforcing steel complies with the following:
- Cross-sectional area of steel reinforcement complies with ASTM A615 (in other words, the corrosion has not compromised the strength of the steel)
- Minimum dimensions, including the height of deformations, complies with ASTM A615 (in other words, the corrosion has not compromised the ability for the concrete to grip the deformations)
- Minimum weight per unit length complies with ASTM A615
- Corrosion or rust is not loose or flaky
Importantly, rust is allowed by the relevant building codes referenced below with particular emphasis on the underlined section of the code's Commentary.
American Concrete Institute (ACI)
ACI CODE-318-25 Building Code for Structural Concrete—Code Requirements and Commentary
Part 9: Construction
Chapter 26—Construction Documents and Inspection
26.6—Reinforcement materials and construction requirements
26.6.1.2 Compliance requirements:
26.6.1.2(f) 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. [ACI 318 Commentary: (f) Specific limits on rust are based on tests (Kemp et al. 1968) plus a review of earlier tests and recommendations. Kemp et al. (1968) provides guidance with regard to the effects of rust and mill scale on bond characteristics of deformed reinforcing bars. Research has shown that a normal amount of rust increases bond. Handling during construction activities generally removes any loosely adhering rust on the reinforcing bars that may otherwise impair the bond of the bars with the surrounding concrete.]
26.6.1.2(g) Prestressing reinforcement shall be free of mill scale, pitting, and excessive rust. A light coating of rust shall be permitted. [ACI 318 Commentary: (g) Guidance for evaluating the degree of rusting on strand is given in Sason (1992).]
26.6.1.2(h) At the time concrete is placed, reinforcement to be bonded shall be clean of ice, mud, oil, or other deleterious coatings that decrease bond. [ACI 318 Commentary: (h) The use of epoxy coating in accordance with 20.5.2 is permitted. Materials used for the protection of prestressed reinforcement against corrosion in unbonded tendons are not considered to be contaminants as described in this provision.]