It is important to correct the serious misunderstandings of the behaviour of concrete in fire by RW Brewerton (NCE 16 May) and by Derek Tordoff (NCE 23 May ).
Tordoff refers to concrete as 'a product about whose behaviour is little known in these conditions'. In fact the behaviour of concrete and concrete structures in fire has been extensively investigated for many decades, and my own research in this field spans 25 years.
Behaviour depends very much upon the mix design.
Deflections in fire depend upon the type of aggregate used, while transient creep acts to relieve thermal stresses during heating.
Repeated tests have also shown that concrete containing the right type and amount of polypropylene fibres will not spall even when subjected to tunnel fires that are more severe than the hydrocarbon fire mentioned in Brewerton's letter. The fibres melt at temperatures of 130infinityC-167infinityC thus creating channels for the steam to escape.
Load bearing steel must be protected against fire but properly designed concrete is inherently fire resistant. Our focus should now be to enhance the level of fire protection of steel buildings.
Dr Gabriel Alexander Khoury, chairman - FIB international committee 4.3.1 on Fire Design of Concrete Structures - Materials & Modelling, Imperial College of Science, Technology and Medicine, London SW7 2BU