The failure of concrete due to fire is mainly a result of the differential expansion of the hot surface layers and the cooler concrete in the inte­ rior. There is also the opposing actions of the cement, which normally shows a net shrinkage and the aggregate, which expands with increasing temperature. These effects lead to the cracking and spalling of the concrete that may be severe enough to expose reinforcement. Exposed reinforcement conducts heat rapidly and the resulting expansion of the reinforcement relative to the surrounding concrete causes further damage.

14.1.1 The effect of temperature on the cement