How fibres can improve concrete fire safety

Recent tests have proved that incorporating polypropylene fibres in high-grade concrete mixes can prevent splintering of the building material in fire.

The use of high-grade concrete in buildings is an important innovation that can reduce the size of structural elements compared with those made from normal-grade mixes, according to tests carried out by the Building Research Establishment (BRE) in England.

This enables more efficient construction but concern had been expressed over the fire performance of the material including the possibility of an increased susceptibility to spalling (splintering). This may expose the steel reinforcement, increasing the risk of it being affected by the heat from the fire, which in turn could bring problems with structural strength and possible stability.

In addition, spalling can be a safety hazard, for example it presents an additional, if relatively small risk, to firefighters.

Suggestions that polypropylene fibres in the mix can reduce the susceptibility to spalling in fire were put to the test by BRE. The study confirmed the beneficial effect regarding spalling, although it also found that the ability of concrete columns to survive the fire test was not affected whether or not polypropylene fibres were included. The residual strengths of the columns after the tests were increased by incorporating polypropylene fibres but not dramatically.

Strength tests on specimens found that the cube compressive strength of concrete containing polypropylene fibres to be significantly reduced because of the resulting lower concrete density. BRE emphasises that this needs to be allowed for in design.

For further information please contact Nigel Clayton