Which material is most likely to fail by spalling under fire conditions?

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Multiple Choice

Which material is most likely to fail by spalling under fire conditions?

Spalling happens when a fire heats a material fast enough that moisture inside turns to steam and internal pressures build up, causing surface layers to break away. Concrete is highly prone to this because it’s porous and contains water in the cement paste and aggregates, and because reinforcement inside (steel) expands with heat and restrains outward movement. That combination creates high tensile stresses at the surface, making chunks pop off or explode outward as the material fails. Gypsum wallboard tends to crumble or burn rather than spall explosively; aluminum will weaken, warp, or melt before spalling becomes a primary failure mode; stone is dense and while it can crack from heat, it doesn’t spall in the same explosive way as reinforced concrete.

Spalling happens when a fire heats a material fast enough that moisture inside turns to steam and internal pressures build up, causing surface layers to break away. Concrete is highly prone to this because it’s porous and contains water in the cement paste and aggregates, and because reinforcement inside (steel) expands with heat and restrains outward movement. That combination creates high tensile stresses at the surface, making chunks pop off or explode outward as the material fails. Gypsum wallboard tends to crumble or burn rather than spall explosively; aluminum will weaken, warp, or melt before spalling becomes a primary failure mode; stone is dense and while it can crack from heat, it doesn’t spall in the same explosive way as reinforced concrete.

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