What is the minimum concrete cover required for rebar in a concrete footing that will be in direct contact with soil?
Correct Answer
C) 3 inches
According to ACI 318, concrete cast against and permanently exposed to earth requires a minimum of 3 inches of concrete cover for reinforcing steel. This protects the rebar from corrosion and ensures proper bond strength.
Why This Is the Correct Answer
ACI 318 Building Code Requirements for Structural Concrete specifically mandates 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, chemicals, and other corrosive elements present in soil. The 3-inch cover also provides sufficient concrete thickness to develop proper bond strength between the concrete and reinforcing steel, which is critical for structural integrity.
Why the Other Options Are Wrong
Option A: 1.5 inches
1.5 inches is insufficient cover for concrete in contact with soil. This amount of cover is typically used for interior concrete elements not exposed to weather or earth, such as beams and columns in dry conditions.
Option B: 2 inches
2 inches of cover is used for concrete exposed to weather or earth where #6 bars and larger are used, but not for concrete cast directly against earth. This cover requirement applies to formed concrete surfaces exposed to weather.
Option D: 4 inches
4 inches exceeds the minimum requirement and would be unnecessarily conservative for standard footing applications. While not structurally wrong, it's not the code minimum and would waste concrete and increase costs unnecessarily.
Memory Technique
Think 'Dirt = 3' - whenever concrete touches dirt (earth), you need 3 inches of cover. Also remember the progression: Interior (1.5"), Weather (2"), Earth (3").
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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