What is the minimum concrete cover required for #4 rebar in a concrete footing that will be in contact with soil?
Correct Answer
C) 3 inches
According to ACI 318, concrete cast against and permanently exposed to earth requires a minimum cover of 3 inches for reinforcing steel. This protects the rebar from corrosion and ensures proper bond.
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 applies regardless of the rebar size (#4, #5, etc.) when the concrete element will be in direct contact with soil. The 3-inch cover provides adequate protection against corrosion from moisture and chemicals in the soil while ensuring proper bond between the concrete and reinforcing steel.
Why the Other Options Are Wrong
Option A: 1.5 inches
1.5 inches is insufficient cover for concrete in contact with soil. This cover requirement might apply to interior concrete elements not exposed to weather or earth, but does not provide adequate corrosion protection for soil-exposed concrete.
Option B: 2 inches
2 inches is the minimum cover requirement for concrete exposed to weather or earth where concrete quality is assured by regular inspection, but this still falls short of the 3-inch requirement for concrete cast against and permanently exposed to earth per ACI 318.
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 code-required minimum and would be wasteful of materials.
Memory Technique
Think 'Dirt = 3' - whenever concrete touches dirt/soil, remember 3 inches minimum cover. You can also remember 'Ground level = 3 level' as a play on words.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 (Reinforcement Details), Table 20.6.1.3.1 - Minimum Concrete Cover
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