Earlier this year, demolition work on the Liverpool Waterfront Car Park was completed.

The car park had to be pulled down due to the structural damage that occurred to the concrete and the steel reinforcement when a fire ripped through the building on New Year’s Eve 2017. (Luckily no-one was hurt in the blaze.)

But researchers at Sheffield University have now come up with a way to use materials from old tyres to boost concrete fire resistance. This technique has the potential to help save fire-ravaged buildings – like the Liverpool multi-storey – from needing to be torn down and rebuilt.

The team has used fibres extracted from the textile reinforcement that is commonly embedded into tyres to improve their performance. Mixing these fibres into concrete reduces the concrete spalling. Their results have been published in the journal, Fire Technology.

As you probably know, spalling is where intense heat affects the water in the concrete, causing the surface layers of the concrete to break off explosively. It can also occur when fire fighters apply cold water to the heated concrete surface while they work to contain the fire.

The fibres added to the concrete will melt when heat is applied, leaving networks of tiny channels that allow moisture to escape. This prevents the moisture getting trapped and then leaving the concrete explosively.

Lead author, Dr Shan-Shan Huang explains, “Because the fibres are so small, they don’t affect the strength or the stiffness of the concrete. Their only job is to melt when heat becomes intense.”

Protecting the concrete in this way also protects the steel reinforcement running through the concrete. This is important, as the reinforcement can weaken very quickly when exposed to extreme heat. It is this weakening that led to the Liverpool car park needing to be demolished.

The researchers collaborated with Sheffield firm Twincon to develop a method for reclaiming fibres from used tyres. Their method saw them separating the fibres from the rubber tyre, untangling the fibres into strands and then distributing them through the concrete mixture evenly.

Using man-made polypropylene fibres to protect concrete structures from damage or collapse is a reasonably well-known technique, but this research demonstrates that the strands can be recovered from used tyres, rather than being manufactured for the purpose.

Clearly this method will require less energy and resources. As Dr Huang says, “Using waste materials in this way is less expensive, and better for the planet.”

The team in Sheffield now plans to continue testing different ratios of fibres to concrete, and also test different types of concrete. Researchers will also scan the concrete as it is heated to better understand how the materials react at the microstructure level.

We already have a good track record for recycling tyres in the UK and across Europe, with the European Tyre and Rubber Manufacturers’ association reporting that 96% of end of life tyres are recycled (2013 figure).

But with the number of cars on our roads steadily increasing, it is a positive development that we have another way to repurpose this waste material, and an additional way to increase the longevity of our concrete structures.

If you need any advice or assistance with the structural elements of an upcoming project, please do get in touch.