What is the minimum concrete cover required for rebar in a concrete foundation wall exposed to earth according to ACI 318?
Correct Answer
B) 3 inches
ACI 318 requires a minimum of 3 inches of concrete cover for reinforcing steel in concrete cast against and permanently exposed to earth. This protects the rebar from corrosion and ensures proper bond strength.
Why This Is the Correct Answer
ACI 318 specifically requires 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. This standard applies to foundation walls, footings, and other structural elements in direct contact with earth.
Why the Other Options Are Wrong
Option A: 1 inch
4 inches of cover is not a standard ACI 318 requirement and would be unnecessarily conservative, adding cost and reducing usable space without structural benefit.
Option C: 4 inches
2 inches of cover is used for concrete exposed to weather or earth where #6 bars and larger are used, but not for the general case of earth-exposed concrete which requires 3 inches.
Option D: 2 inches
1 inch of cover is insufficient for earth-exposed concrete and would only be appropriate for interior applications with controlled environments where corrosion risk is minimal.
Memory Technique
Use the phrase 'Dirty Three' - when concrete gets dirty from earth contact, it needs 3 inches of cover to protect the rebar.
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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