What is the minimum concrete cover required for #4 rebar in a concrete footing that will be in direct contact with earth?
Correct Answer
D) 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 concrete protection.
Why This Is the Correct Answer
According to ACI 318 Building Code Requirements for Structural Concrete, reinforcing steel in concrete that is cast against and permanently exposed to earth requires a minimum concrete cover of 3 inches. This substantial cover protects the rebar from moisture, soil chemicals, and other corrosive elements that could cause deterioration. The 3-inch requirement applies specifically to footings and other concrete elements in direct contact with soil, regardless of the rebar size. This protection is critical for maintaining the structural integrity of the foundation over time.
Why the Other Options Are Wrong
Option A: 1.5 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 direct soil contact, it does not meet the ACI 318 requirement for earth-contact applications.
Option C: 4 inches
1.5 inches is insufficient cover for concrete in contact with earth. This amount of cover might be appropriate for interior concrete elements not exposed to weather or soil, but does not provide adequate protection against soil moisture and corrosive elements.
Memory Technique
Use the phrase 'Dirty Dozen' - Dirt (earth contact) needs a Dozen quarters (3 inches = 12 quarters). 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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