Old tyres being used to improve concrete fire resistance

Researchers from the UK have successfully tested a new way or protecting concrete from fire damage using materials recycled from old tyres.

The team from the University of Sheffield used fibres extracted from the textile reinforcement commonly embedded into tyres.

Adding the fibres to the concrete mix showed a reduction in the concrete’s tendency to spall – where layers of concrete break off – explosively under intense heat from a fire.

Man-made polypropylene fibres (PP) are often used to protect concrete structures if a fire breaks out, with many modern structure using concrete that includes these fibres for protection against fire spalling.

According to the University of Sheffield, the 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,” lead author Dr Shan-Shan Huang, in the Department of Civil and Structural Engineering at the University of Sheffield, explained.

“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,” Dr. Huang said.

“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 reinforcements running through the concrete are also protected. When the steel reinforcements are exposed to extreme heat they weaken very quickly, meaning a structure is much more likely to collapse.

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

This involves separating the fibres from the tyre rubber, untangling the fibres into strands, and then distributing them evenly into the concrete mixture.

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.

The results are published in the journal Fire Technology.

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