Tyred idea bounces back

American researchers have found that a footpath surface created from recycled tyres could make cheap and joint-friendly leisure trails for exercisers.

“Some 290 million scrap tyres are generated in the United States annually. That’s literally mountains of tyres,” said Dr Robert Amme, professor of physics and materials science and manager of the Environmental Materials Laboratory at the University of Denver.

“Our motivation was to find new ways to recycle them. This paving material appears to present a potentially major means of doing that. The process consumes rubber from about 6,000 to 7,000 tyres per mile of trail.”

The rubberised surface for footpaths has been developed through extensive laboratory study and multiple field tests using varying compositions. The work was done by Amme, his graduate student Haifeng Ni, and William Meggison.

Their mixture of asphalt, ground-up tyre rubber and a chemical modifier is softer and more resilient for pedestrian traffic than traditional concrete or asphalt, but firm enough for bicycle riding. It’s already drawn some commercial interest. The University of Denver has filed for a patent, which is pending.

“We want to call the material SofTrails,” said Amme.

Most footpaths in the US are composed of crushed rock bound with traditional asphalt or concrete, and are tough on the feet, ankles, and knees of exercisers, Amme said the group’s material uses granulated tyre rubber instead of rock. For recreational users, it offers a comfortable, shock-cushioning surface and good traction even when wet. The material is also highly durable and resistant to wear, cracking, water penetration, and ultraviolet radiation.

“Pedestrian trails are becoming more popular all the time, and making them truly comfortable for users is an important concept,” said Dr. Amme.

While various rubberised pavements are already currently in commercial use, they’re costly because they employ polyurethanes or latex as the binders. They are typically applied only to small areas such as tennis courts, running tracks, and short paths.

The material developed by Amme and Meggison, however, uses less expensive ingredients, making it economical even for long trails and large expanses. “The cost is well below that of outdoor polyurethane and latex products, and is comparable to that of a standard mix of asphalt with crushed rock,” said Amme.

The new rubberised pavement is a blend with ground rubber particles as the major component, plus asphalt and a few percent of a bonding agent called Vestenamer Coloring can also be added.

A fine grind of rubber is first mixed with the asphalt to make the binder, which is then blended with a coarser grind of rubber particles and the Vestenamer. The Vestenamer helps bond the asphalt/rubber mixture with the rubber aggregate, and reduces the tackiness.

The end result may be spread as a top coat on asphalt or concrete surfaces. It may also be applied to areas without an existing surface, but the ground first would need to be extensively prepared, much the same as if it were going to be paved with conventional asphalt or concrete.

The cushioning and durability are comparable to that of more expensive rubberised surfaces containing polyurethanes or latex, Amme said. The field tests indicated the material has a lifetime of at least 10 years even in climates with harsh winter weather.