What is the minimum concrete cover required for #5 rebar in a concrete footing exposed to earth and weather according to ACI 318?
Correct Answer
C) 3 inches
ACI 318 requires a minimum of 3 inches of concrete cover for reinforcing steel in footings and other structural members cast against and permanently exposed to earth.
Why This Is the Correct Answer
ACI 318 specifically requires 3 inches of concrete cover for reinforcing steel in footings and other structural members that are cast against and permanently exposed to earth. This increased cover requirement protects the rebar from moisture, chemicals, and other corrosive elements present in soil. The 3-inch requirement applies regardless of the rebar size (#5 in this case) when the concrete is in direct contact with earth and exposed to weather conditions.
Why the Other Options Are Wrong
Option A: 1.5 inches
1.5 inches is insufficient cover for concrete exposed to earth and weather. This cover thickness might be appropriate for interior slabs or beams not exposed to harsh environmental conditions, but does not meet ACI 318 requirements for earth-exposed footings.
Option B: 2 inches
2 inches of cover is inadequate for footings exposed to earth and weather according to ACI 318. While 2 inches might be acceptable for some interior structural elements or concrete exposed to weather but not earth, it does not provide sufficient protection against soil moisture and chemicals.
Option D: 4 inches
4 inches exceeds the minimum requirement and would be unnecessarily conservative for this application. While not technically wrong from a structural standpoint, it's not the minimum required by ACI 318 and would result in additional concrete costs without code-mandated benefit.
Memory Technique
Use the mnemonic 'Feet in Earth = 3' - footings in earth need 3 inches of cover. Also remember the progression: interior (1.5"), weather only (2"), earth contact (3").
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 (Reinforcement Details), Table 20.6.1.3.1 - Minimum concrete cover requirements
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