IN THE FIRING LINE

This brief promotional article considers the vulnerability of concrete to fire damage, and outlines a case study of additional protection against fire. Reinforced and prestressed concrete are more resistant to fire than unprotected structural steel. However, various factors affect the performance, in a fire, of concrete that is used for structural members subjected to bending, tension, and/or compression. Significant factors include: (1) total concrete thickness; (2) concrete cover to reinforcement or tendons; (3) concrete density; and (4) the aggregate used in the concrete. The probability of spalling as the result of a fire increases with the concrete's compression and moisture content. Different national authorities give different critical temperatures for fires and concrete, which are often difficult and complex to interpret. The type of fire also affects what happens to the concrete. The disastrous fire in the Channel Tunnel in November 1996, which badly damaged some of its concrete tunnel lining, is discussed briefly in relation to these considerations. The article also describes briefly the fire protection upgrading of concrete at Silsoe Tower in London, which was constructed in the early 1970s. This case study indicates one of a range of problems that should be addressed when a concrete structure needs upgrading.