Concrete is an incredible material, without which the modern world couldn't exist. It's not perfect though. It needs reinforcement to remain stable under tension, and it can react negatively to heat.
I'll explain. When a concrete structure -- say, a bridge -- gets heated by fire, the moisture trapped in the concrete can turn to steam and cause the concrete to break apart explosively in a phenomenon known as spalling. Having a bridge undergo spalling weakens the structure and can lead to a collapse.
According to a report on Wednesday by New Atlas, scientists figured out that if you add polypropylene fibers to the concrete mix, the fibers can melt, leaving tiny passages that allow the steam to escape the concrete matrix, thus preventing spalling. Cool, right?
"Because the fibers are so small, they don't affect the strength or the stiffness of the concrete," said Shan-Shan Huang, lead author of a paper on the study published on Tuesday in Fire Technology. "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 to reduce the pressure within the concrete."
But despite being, behind polyethylene, the world's second most common thermoplastic -- meaning that it melts, rather than burns -- polypropylene takes a lot of energy and resources to make. That has caused scientists to go looking for an affordable and more environmentally friendly solution to their problem.
Scientists at Sheffield University in the UK figured out that by dismantling used tires, they could use the fiber cordage that usually is encased inside the tire's rubber for structure to add to concrete as a replacement for the virgin polypropylene. They just needed to find a cheap and efficient way of getting the fibers free of the rubber, something that is easier said than done.
The scientists are working with British firm Twincon to figure out how to separate the fibers and rubber, untangle the strands efficiently and distribute them evenly throughout the concrete mixture. They're also trying to nail down the exact ratio of fiber to concrete to make the best use of the materials available.
Extracting the fibers would then, in theory, leave the rest of a used tire's recyclable materials (rubber, steel belts and so on) available to be reused.