The sun can often wreak havoc on asphalt roads and parking lots in more than one way. Powerful UV rays weaken the pavement causing cracking, surface unevenness, and water seepage. And once the weather switches to cold, the large temperature difference causes the pavement to crack even further, which is why you sometimes see potholes forming at the end of both the warm and cold seasons.
Regular maintenance and replacement of asphalt roads is just a fact of modern life, but that doesn't mean we have to be content with the status quo. Researchers at RMIT University in Australia performed a series of experiments in which they used rubber from used tires in the composition of freshly lied asphalt, finding that this rubber-bitumen mix halves the rate of sun damage, which could help roads last a lot longer.
Besides improving road and pavement durability, this approach also tackles our used tire problem. In the United States alone, over 300 million scrap tires are produced, most of which end up in landfills since they are almost impossible to recycle using conventional methods.
Sunscreen for roads
While most research so far has mainly focused on enhancing road durability to traffic load, little attention has been given to the wear and tear on asphalt owed to the sun. But virtually all regions of the world are affected by it. The stripping of pavement markings on both parking lots and roads is often owed to the asphalt oxidation due to chemical reactions caused by UV rays -- and we've all seen it.
There's a silver lining, though. Researchers in Australia found that incorporating rubber crumbs from old tires could dramatically improve road durability to the sun.
The researchers employed a UV machine specially designed for asphalt studies that can simulate the long-term effect of solar degradation on roads. They fired this machine in the lab at bitumen mixed with three different types of rubber concentrations: a low concentration of 7.5%, a medium one of 15%, and a high concentration of 22.5%. The machine operated continuously for a month and a half, simulating about a year of UV radiation around Melbourne.
When they measured the chemical and mechanical properties of the bitumen, they found that the bitumen with a high concentration of crumb rubber exhibited 50% less UV damage compared to conventional asphalt.
“We found that the ageing trend is actually slowed down when you add crumb rubber, which is recycled from scrap tyres, into the top layer of a road,” Associate Professor Filippo Giustozzi at RMIT University, lead author of the new study, said in a statement.
“This acts so effectively as a sunscreen for roads that it actually makes the surface last twice as long as regular bitumen.
“We knew that UV would be a factor in road degradation, but not by what degree or how to protect against it, as nobody has really been looking at this aspect.”
However, while more rubber improved UV resistance, it also declined mechanical performance. The sweet spot between UV resistance and mechanical performance was found to lie between 18% and 22% rubber in the bitumen mix.
“You don’t want something that is UV resistant but not truck resistant,” Giustozzi said.
Previously, researchers from the RMIT and the University of South Australia incorporated recycled rubber crumbs into concrete, which proved economically viable and even more durable than conventional concrete in a real-world setting. Now, this new research adds another way to give old tires a new life and offset their environmental impact.
The findings appeared in the Journal of Cleaner Production.