Residential Building Inspector B1Wall Construction and Wall CoveringsHard
An inspector is reviewing plans for a residential building with exterior concrete walls. The plans indicate the concrete wall is 7.5 inches thick. What is the minimum specified compressive strength (f'c) of concrete required for a residential exterior wall in a moderate weathering potential zone?
- A2,000 psi
- B3,500 psi
- C2,500 psi
- D3,000 psi
Show answer & explanationAnswer & explanation
Correct answer: C. 2,500 psi
According to IRC Table R402.2 for concrete walls, in a moderate weathering potential zone, the minimum specified compressive strength (f'c) for concrete is 2,500 psi. The wall thickness is irrelevant to this specific minimum f'c based on weathering.
Why the other options are wrong
- A. 2,000 psi is typically for interior non-structural elements or very mild conditions, not suitable for exterior walls in a moderate weathering zone.
- B. 3,500 psi is for very severe weathering conditions or highly stressed structural concrete, not the minimum for this scenario.
- D. 3,000 psi is required for severe weathering potential or specific structural design, exceeding the minimum for moderate weathering.
Concrete f'c (Exterior Walls)
The minimum specified compressive strength (f'c) for concrete in exterior walls depends on the local weathering potential to ensure durability against freeze-thaw cycles.
- Mild weathering: 2,500 psi (air-entrained).
- Moderate weathering: 2,500 psi (air-entrained).
- Severe weathering: 3,000 psi (air-entrained).
- Air-entrainment is crucial for freeze-thaw resistance.
Memory trick: Exterior concrete needs 'muscle' (strength) and 'fluff' (air) to fight the weather.