What is the minimum concrete cover required for #5 rebar in a concrete footing that will be in direct contact with earth?
Correct Answer
C) 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 mandates a minimum 3-inch concrete cover for reinforcing steel in concrete that is cast against and permanently exposed to earth. This requirement exists because soil contact creates a corrosive environment that can damage rebar over time. The 3-inch cover provides adequate protection against moisture infiltration, chemical attack from soil, and ensures proper concrete-to-steel bond development. This standard applies regardless of the rebar size when the concrete is in direct earth contact.
Why the Other Options Are Wrong
Option A: 4 inches
4 inches exceeds the minimum requirement and would be unnecessarily conservative for standard footing applications, though it might be specified for special exposure conditions or by specific project requirements.
Option B: 1.5 inches
2 inches of cover is typically used for concrete exposed to weather but not in direct earth contact, such as exterior walls, or for concrete in contact with water but not soil.
Option D: 2 inches
1.5 inches is insufficient cover for earth-contact applications and would only be appropriate for interior concrete elements not exposed to weather or earth, such as beams and columns in controlled environments.
Memory Technique
Use the phrase 'Three for Thee Earth' - when concrete touches earth, you need 3 inches of cover to protect the rebar from the corrosive soil environment.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 (Concrete Cover Requirements) or Table 20.6.1.3.1 for minimum cover requirements
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