Fibres from old tires can improve fire resistance of concrete

22 February 2019

A new way of protecting concrete
from fire damage using materials recycled from old tyres has been successfully
tested by researchers at the University of Sheffield.

The team used fibres extracted
from the textile reinforcement embedded into tyres to guarantee their
performance. Adding these fibres to the concrete mix was shown to reduce the
concrete’s tendency to spall — where surface layers of concrete break off —
explosively under the intense heat from a fire.

Using human-made polypropylene
(PP) fibres to protect concrete structures from damage or collapse if a fire
breaks out is a relatively well-known technique. Many modern structures,
including engineering projects such as Crossrail, have used concrete that
includes PP fibres for protection against fire spalling.

The Sheffield study is the first
to show that these fibres do not have to be made from raw materials, but can
instead be reclaimed from used tyres.

“We’ve shown that these recycled
fibres do an equivalent job to ‘virgin’ PP fibres which require lots of energy
and resources to produce,” explains lead author Dr Shan-Shan Huang, in the
Department of Civil and Structural Engineering at the University of Sheffield.

“Using waste materials in
this way is less expensive, and better for the planet.”

The fibres melt under the intense
heat from a fire, leaving networks of tiny channels. This means that moisture
trapped within the concrete is able to escape, rather than becoming trapped,
which causes the concrete to break out explosively.

“Because the fibres are so
small, they don’t affect the strength or the stiffness of the concrete,”
says Dr Huang.

“Their only job is to melt
when heat becomes intense. Concrete is a brittle material, so will break out
relatively easily without having these fibres help reducing the pressure within
the concrete.”

Protecting the concrete from fire
spalling means that steel reinforcement is also protected. When steel
reinforcement is exposed to extreme heat it weakens quickly, making a structure
more likely to collapse. The Liverpool Waterfront Car Park suffered this kind
of damage during a fire in 2017, leading to the entire structure having to be

Collaborating with Twincon, a
Sheffield-based company that develops innovative solutions for the construction
industry, the researchers have also developed technologies for reclaiming the
fibres from the used tyres.

The team plan to continue testing the material with different ratios of the fibres to concrete, and also using different types of concrete. They also plan to find out more about how the materials react to heat at the microstructure level.

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