What is the minimum concrete cover required for #6 rebar in a concrete footing that will be in direct contact with earth?
Correct Answer
B) 3 inches
According to ACI 318, reinforcing steel in concrete cast against and permanently exposed to earth requires a minimum cover of 3 inches. This protects the rebar from corrosion and ensures proper bond with the concrete.
Why This Is the Correct Answer
ACI 318 Building Code Requirements for Structural Concrete specifically requires 3 inches of concrete cover for reinforcing steel in concrete that is cast against and permanently exposed to earth. This requirement ensures adequate protection of the rebar from moisture, soil chemicals, and other corrosive elements that could compromise the structural integrity. The 3-inch cover also provides sufficient concrete thickness to develop proper bond between the rebar and concrete while maintaining the steel's structural capacity over the building's design life.
Why the Other Options Are Wrong
Option A: 4 inches
2 inches of cover is typically required for concrete exposed to weather or outdoor air, but not sufficient for direct earth contact where additional protection from soil moisture and chemicals is needed.
Option D: 1.5 inches
1.5 inches is insufficient cover for earth-contact applications and would only be appropriate for interior concrete members not exposed to weather or earth contact, where corrosion risk is minimal.
Memory Technique
Think 'Dirt = 3' - when concrete touches dirt/earth, you need 3 inches of cover to protect the rebar from the harsh underground environment.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 - Concrete Cover Requirements, Table 20.6.1.3.1
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