Acceptable Level of Rebar Corrosion Before Concrete Pouring Based on International Standards
According to international standards such as ACI 301 ("Specifications for Structural Concrete"), ACI 318 ("Building Code Requirements for Structural Concrete"), and the EN 13670 (Execution of Concrete Structures):
Minor rust or mill scale on the surface of rebars is generally permissible, provided that the rust is tightly adhering and does not significantly reduce the cross-sectional area of the steel or affect the bond with the concrete.
Loose or flaky rust, dirt, oil, ice, or other foreign materials must be removed before concrete placement, as these can negatively impact the bond between the steel and the concrete.
Specifics from International Codes:
ACI 301-20, Section 3.3.2.5:
"Reinforcement with rust, mill scale, or a combination of both will be considered satisfactory, provided the minimum dimensions (including height of deformations) and weight of a hand-wire-brushed test specimen are not less than applicable ASTM specifications."
EN 13670:2009, Section 8.6.4:
"Surface contamination and loose rust shall be removed. Permanent, tightly adherent rust is not considered harmful to the bond with concrete."
Commentary from Both Standards:
If pitting or measurable loss of section occurs such that the rebar diameter or weight falls below specified dimensional tolerances (per ASTM A615, A706, A775, etc.), such rebars must be rejected or replaced.
There is no specified percentage of rust or corrosion by area in most codes; the key criteria are the absence of loose corrosion products and no reduction of rebar diameter/weight below standard requirements.
Practical Guideline:
Light, firm rusting (orange-brown in color and difficult to remove by hand brushing) is typically acceptable.
Heavy, flaky rust or surface scaling must be removed, and if the steel is pitted or dimensionally reduced, the bar should not be used.
Summary Table
| Condition | Acceptable | Action Required |
|----------------------------------------|------------|-----------------------------------|
| Tightly adherent, light rust/mill scale| Yes | None (if size is within standard) |
| Loose/flaky rust or contamination | No | Clean or replace the rebar |
| Pitted/reduced cross-section | No | Reject or replace the rebar |
References:
ACI 301-20, Section 3.3.2.5
ACI 318-19, Section 20.2.2.2
EN 13670:2009, Section 8.6.4
Note:
If you require project-specific recommendations or additional evaluations, consulting with a qualified structural engineer and referring to local standards is recommended.
For professional waterproofing, repair, and strengthening of concrete structures, you may contact RBS-CONTECH or Iran Concrete Clinic at www.clinicbeton.com and www.rbs-contech.com.