There may be a new way of protecting our concrete from fire damage using materials recycled from old tires. Successfully tested by researchers at the University of Sheffield, the team used fibers extracted from the textile reinforcement that’s commonly embedded into tires. Adding these fibers to the concrete mix reduced the concrete’s tendency to spall, a concept where surface layers of the concrete break off if exposed to fire and intense heat.
Commonly, people already use fabricated polypropylene (PP) fibers to protect concrete structures from fires. Some modern structures, such as the large-scale engineering project Crossrail, used concrete that integrated PP fibers for protection against fire spalling.
The study shows that these fibers do not have to be made from raw materials, but can instead be created from used tires. The results were published in the journal Fire Technology.
“We’ve shown that these recycled fibers do an equivalent job to ‘virgin’ PP fibers which require lots of energy and resources to produce,” says 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 process works when the fibers melt under intense heat, which leaves a network of tiny channels. This means that moisture trapped within the concrete can escape through these channels, rather than being trapped which is the cause of explosive concrete.
“Because the fibers 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 fibers help reducing the pressure within the concrete.”
Protecting concrete from fire spalling means that steel reinforcements running through the concrete are also protected. Normally, if the steel reinforcements are exposed to extreme heat, the structure weakens and is more likely to collapse.
In 2017, the Waterfront Car Park underwent this kind of damage and led to the entire structure having to be demolished.
The researchers are also collaborating with Twincon, a Sheffield-based company that develops innovative solutions for the construction industry. The two are working on developing technologies for reclaiming the fibers used from the tires. This process involves separating the fibers from the tire rubber by untangling the fibers into strands, and dispersing it evenly into the concrete mixture.
The team plans to continue testing the material with a variety of different ratios of fibers to concrete, and wants to experiment with different types of concrete. They hope to learn more about the materials’ reactions to heat at a microstructure level, by scanning the concrete as it is heated. Using this method, the researchers will be able to visualize the structural changes taking place inside the material.