Sunscreen for roads?

Researchers at Melbourne’s RMIT University have found a way to reduce the degradation of our roads while tackling the Australia’s growing crisis of used tyres – by mixing crumb recycled rubber with bitumen.

Adding the used tyres to fresh bitumen effectively acts as a form of ‘sunscreen’ for the road, with recent testing revealing that roads with an optimal blend of recycled rubber showed 50 per cent less ultraviolet (UV) radiation damage when compared with regular bitumen.

Sun damage slowly leads to the degradation of road surfaces, which eventually form cracks. The deterioration can eventually render the road unsafe, necessitating costly road repairs and ongoing maintenance.

With road maintenance costing $2.9 billion in 2019 to 2020 (National Transport Commission data), the potential savings by using bitumen with recycled rubber are huge, says RMIT. And at the same time, harnessing the vast stockpiles of used tyres in this country will help alleviate another problem that is only accelerating – Australia has had an export ban on used tyres in place since the end of 2020.

The new research is a result of a collaboration between RMIT and Tyre Stewardship Australia (TSA), which promotes the development of viable markets for end-of-life tyres. Previous work has focused on traffic load, thermal ageing, and weather-related events, but sun damage to roads had previously received little attention

According to Associate Professor Filippo Giustozzi, the new research opens up new worlds of possibilities.

“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,” Giustozzi said.

“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.”

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RMIT used a UV machine traditionally used to assess the impact of UV on paint to conduct its research. Researchers studied the effects of using different concentrations of crumb rubber in the bitumen, to arrive at an optimal blend that maximises UV protection while balancing this with mechanical performance.

“You don’t want something that is UV resistant but not truck resistant,” said Giustozzi.

“We found adding between 18 per cent and 22 per cent of crumb rubber generates an ideal balance in terms of improving rut and fatigue resistance to traffic loads, while resisting UV ageing.”

TSA CEO, Lina Goodman, said the findings gave fresh hope for addressing Australia’s growing used tyre problem.

“We’re excited to collaborate on this project with industry and leading researchers at RMIT University,” she said.

“A multi-organisational approach paves the way for new innovation and the opportunity to turn this resource into a value-added product.”

While crumb rubber is already used widely in many different applications, including road construction, this additional benefit of increased sun protection was not previously understood. Now researchers hope the findings, which were published recently in Journal of Cleaner Production, will encourage local and state authorities to, where possible, adopt the practice on a widespread basis.