Technical Questions

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Epoxy-coated reinforcement and cover depth against ground

Q. Table of ACI 318-19 requires that concrete cast against and permanently in contact with ground has 3-in. (76 mm) specified cover over reinforcement. Can this cover be reduced if the reinforcement is epoxy coated?


A. The 3-in. minimum cover requirement for concrete cast against and permanently in contact with ground is partially a corrosion issue, but mainly concerns constructability issues for these elements. Footings, retaining walls, grade beams, and uncased caissons (drilled shafts) are examples of elements where this cover requirement is likely applicable. From a historical perspective, the 3-in. cover requirement was added to the 1920 concrete building code, and this respondent believes it has several subtle conditions contained in this cover dimension.

There is no explicit provision in the Code addressing a cover depth reduction over epoxy-coated reinforcement. Commentary Provision R20.5.1.1 of ACI 318-19 states: “Alternative methods of protecting the reinforcement from weather may be provided if they are equivalent to the additional concrete cover required by the Code. When approved by the building official under the provisions of 1.10, reinforcement with alternative protection from weather may not have concrete cover less than the cover required for reinforcement not exposed to weather.”

Therefore, a reduction in cover depth to “not less than that required for reinforcement not exposed to weather” may be approved by the building official following Section 1.10.1. This means the building official will likely want to see some documentation to support a reduction in depth of cover. Methods of achieving this waiver usually consist of a sealer or membrane on the concrete surface (not applicable for a soil cast surface), using reinforcement with corrosion resistance better than uncoated, carbon-steel bars, using less permeable concrete, or some combination of these.


References:  ACI 318-19; 318 Historical ACI Building Code Requirements (1908-2005)

Topics in Concrete:  318 Building Code; Corrosion; Durability

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