What is the minimum concrete cover required for #6 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 bars. This protects the steel from corrosion.
Why This Is the Correct Answer
According to ACI 318 Building Code Requirements for Structural Concrete, concrete cast against and permanently exposed to earth requires a minimum cover of 3 inches for all reinforcing bars regardless of size. This increased cover requirement protects the steel reinforcement from corrosion caused by moisture and chemicals in the soil. The 3-inch minimum applies specifically to footings, foundation walls, and other concrete elements in direct contact with soil.
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 thickness might be appropriate for interior concrete elements not exposed to weather or soil, but does not provide adequate protection against corrosion in earth-contact applications.
Option B: 2 inches
2 inches of cover is inadequate for concrete cast against earth. While 2 inches might be acceptable for concrete exposed to weather but not in contact with soil, the harsh environment of soil contact requires the greater protection that 3 inches provides.
Option D: 4 inches
4 inches exceeds the minimum requirement and would be unnecessarily conservative. While not technically wrong from a structural standpoint, it's not the minimum required by code and would waste concrete and increase costs without additional benefit.
Memory Technique
Use the phrase 'Three inches for Trees' - since soil is where trees grow, and soil contact requires 3 inches of cover. Also remember the progression: 1.5' for interior, 2' for weather exposure, 3' for soil contact.
Reference Hint
ACI 318 Building Code Requirements for Structural Concrete, Chapter 20 (Durability Requirements), Table 20.5.1.3.1 - Minimum Concrete Cover
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