Q: Is rust OK?

Free CRSI Video
Is Rust OK?
Learn about the effects of rust on rebar. 

A: There are a number of things that can get onto the surface of rebar and affect the bond strength between the rebar and concrete. Oil and grease need to be wiped off with a solvent. Dirt and mud can be washed off or cleaned off using a wire brush.

However, rust, mill scale, and surface irregularities actually increase the bond because they increase the roughness of the rebar. So yes, rust is OK... except if there is so much rust that the weight, dimensions, or cross-sectional area of the rebar have reduced to below the minimum specified by the material standard.

Q: Is it okay to bend or to re-bend reinforcing bars in the field?

A: The bending or rebending of steel reinforcing bars in the field is one of the most common and one of the most controversial procedures that frequently come into question related to cast-in-place reinforced concrete construction.

These situations may arise as the result of unplanned occurrences (when rebar is accidentally run over by a vehicle, for example), because of on-site corrections and adjustments, or as intentional building changes.

The best advice for dealing with these situations is to always involve the architect/engineer and to follow the guidelines presented in the ACI 318 Building Code (Section 7.3.2), and the ACI 301 Specification (Section 3.3.2.8).

Q: Will bending or rebending reinforcing bars in the field weaken them?

A: Basically, no. Those concerned about the resulting mechanical properties should consult the test results summarized in the accompanying table (see below).

K. Babei and N.M. Hawkins, "Field Bending and Straightening of Reinforced Steel,"
Concrete International, 1992.

Q: What about cutting reinforcing bars in the field? Is that okay?

A: Field cutting may be required when design changes or errors in detailing, fabrication, or placement create extra length in bars that are either stockpiled or already embedded in concrete.

Smaller-sized reinforcing bars, #10, #13, and #16, for example, may be cut with bolt cutters. Bar sizes #19 and larger may be cut with either an abrasive saw or, more often, with an oxy-acetylene torch.

Q: Will flame cutting affect uncoated reinforcing bars?

A: Recent tests have demonstrated that oxy-acetylene flame cutting of reinforcing bars has virtually no effect on the material properties of the bar, affecting only 3/16 inch from the cut end. Flame cutting of epoxy-coated bars, however, is not recommended.

Q: Can epoxy-coated bars be flame-cut?

A: No, using this procedure on epoxy-coated bars is not recommended. Use flame cutting on uncoated reinforcing bars only.

Also, the ends of epoxy-coated bars that are cut with either bolt cutters or an abrasive saw should always be treated with coating material provided to repair damaged coating.

Q: Is it all right to use unspecified lap splices in the field?

A: According to the ACI 318 Building Code, design drawings are to specify location and length of lap splices. The ACI 315 Standard further instructs that both placing drawings and structural drawings contain the same details.

However, with the architect/enginner's approval, dowel-bar mechanical splices and lap-splice connector systems may be used to replace prebent or other types of dowels in connecting two separate pours of a reinforced concrete structure.

In all cases, procedures specified by both the splice manufacturer and project specifications should always be followed closely.

Q: When is it appropriate to use welded splices in the field?

A: The ACI 318 Building Code requires the architect/engineer to indicate the type and location of welded splices of reinforcing bars on the project drawings or in the project specifications.

The ACI 318 Building Code further requires that all welded splices should conform to the Structural Welding Code for Reinforcing Steel published by the American Welding Society, which requires the project contractor to prepare written welding procedure specifications (WPS) for all welded splices.

These will depend heavily on the assessment of carbon-equivalent (CE) and other rebar properties as determined by the mill test reports that accompany each shipment.

For more information about welding reinforcing steel, see the American Welding Society's (AWS)
Structural Welding Code for Reinforcing Steel.

Q: Can tack welding be used to hold reinforcing bars during assembly?

A: Field tack welding should never be used as a substitute for tying in assembling and securing reinforcing bars. Rare exceptions are specified in the International Building Code.