Fire Resistance of Concrete Can Be Enhanced by Adding Fibers from Old Tires

Scientists from the University of Sheffield have developed and successfully tested a new way of protecting concrete from fire damage using materials recycled from used tires.

The Sheffield team used fibers extracted from the textile reinforcement generally embedded into tires to ensure their performance. Incorporating these fibers to the concrete mix was proven to decrease the concrete’s propensity to spall, meaning surface layers of concrete break off, explosively due to the extreme heat from a fire.

Applying manmade polypropylene (PP) fibers to safeguard concrete structures from damage or breakage if a fire breaks out is a comparatively established method. A number of contemporary structures, including large scale engineering projects such as Crossrail, have used concrete that includes PP fibers for safeguarding against fire spalling.

The study from Sheffield is the first to demonstrate that these fibers do not have to be created from raw materials, but can rather be reclaimed from old tires. The findings have been published in the journal Fire Technology.

We’ve shown that these recycled fibres do an equivalent job to ‘virgin’ PP fibres which require lots of energy and resources to produce. Using waste materials in this way is less expensive, and better for the planet.

Dr Shan-Shan Huang, Study Lead Author, Department of Civil and Structural Engineering, University of Sheffield.

The fibers melt under the strong heat from a fire, leaving networks of minute channels. This means that moisture stuck within the concrete is able to escape, instead of becoming trapped, which would result in the concrete breaking 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.

Dr Shan-Shan Huang, Study Lead Author, Department of Civil and Structural Engineering, University of Sheffield.

Along with the concrete getting protected from fire spalling, the steel reinforcements found within the concrete are also protected. When the steel reinforcements experience extreme heat they deteriorate very rapidly, meaning a structure is a lot more likely to collapse. During a fire in 2017, the Liverpool Waterfront Car Park suffered this sort of damage, ultimately leading to the whole structure having to be demolished.

Working together with Twincon, a Sheffield-based company that creates innovative solutions for the construction sector, the scientists have also designed technologies for reclaiming the fibers from the old tires.

This required separating the fibers from the tire rubber, straightening out the fibers into strands, and then spreading them uniformly into the concrete mixture.

The Sheffield researchers plan to pursue testing of the material with varied ratios of the fibers to concrete, and also using various types of concrete. They also aim to learn more about how the materials respond to heat at the microstructure level. By scanning the concrete as it is heated, they will be able to clearly see the structural changes occurring inside the material.

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