Why might concrete require detailing to prevent spalling during fire exposure?

• A. Because concrete has inherent fire resistance but may need detailing to prevent spalling and ensure protection.
• B. Because concrete has no fire resistance at all.
• C. Because concrete always spalls regardless of design.
• D. Because only steel requires detailing.

Answer: (A)

Concrete naturally resists fire well because its heavy mass can slow heat transfer and keep internal temperatures from rising quickly. But during a severe fire, moisture inside the concrete turns to steam and thermal expansion creates internal pressures. If the concrete is restrained or lacks pathways for that steam to escape, surface layers can crack and pop off—this is spalling. Detailing helps prevent that by managing moisture, heat transfer, and internal stresses.

So the best answer recognizes that while concrete has inherent fire resistance, without specific detailing to control how it behaves under high heat, spalling can still occur and protection can be compromised. Practices like adding fibers that melt and form channels for steam, using air-entraining admixtures to create micro air voids, ensuring adequate concrete cover, selecting protective coatings or insulation, and ensuring proper curing and moisture control all contribute to reducing spalling risk. The other statements aren’t accurate: concrete does have fire resistance, spalling isn’t inevitable regardless of design, and detailing isn’t exclusive to steel.