Recycled tires may help concrete take the heat
Although concrete doesn't burn, it can "spall" when subjected to extreme heat – this means that surface layers of the material explosively break off, potentially causing structures made from it to collapse. According to a new study, however, fibers obtained from discarded tires can help keep that from happening.
Already, some companies have been adding polypropylene fibers to concrete, to prevent spalling. The idea is that when the concrete is heated by fire, those fibers will melt, creating networks of tiny channels throughout the material. Any moisture present within the concrete can then escape through those channels – it would otherwise remain trapped, turn to steam, and force the material to break.
Typically, the fibers used for this purpose are composed of virgin polypropylene, which requires a considerable amount of energy and resources to produce. Scientists at Britain's University of Sheffield, though, have determined that fibers harvested from old tires are just as effective. More precisely, those fibers come from a textile reinforcement material that is commonly used in tires.
The researchers are now working with Sheffield-based construction firm Twincon, refining a cost-effective technique for separating the fibers from tire rubber, untangling them, and then distributing them evenly within a concrete mixture. They are also looking at various fiber-to-concrete ratios, and at using different types of concrete.
"Because the fibers are so small, they don't affect the strength or the stiffness of the concrete," says Dr. Shan-Shan Huang, lead author of a paper on the study. "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."
The paper was recently published in the journal Fire Technology.
Researchers at Canada's University of British Columbia have been conducting similar research, making concrete more crack-resistant by adding polymer fibers taken from discarded tires.