When concrete heats up in a fire, at some point the steel reinforcement in the concrete also heats up. The heating of the steel reinforcement is slowed down by the concrete coating, as heat transfer through concrete is relatively slow. Moreover, in the temperature range 200-800 ºC, the concrete itself loses its load-bearing capacity due to internal micro-fracturing and chemical transformation (dehydration) of the cement phase. Typically, design standards simplify this gradual loss of strength by assuming a concrete limit temperature of 500 ºC.
If the thickness of the concrete cover is insufficient to keep the temperature of the steel reinforcement low enough to prevent collapse, cracking of the concrete may occur or if the concrete itself has deteriorated, fire protection is needed. Concrete can be protected from fire by fire barrier tiles, fire barrier paints, fire barrier wool or fire barrier plaster.
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