Used tyres provide 'sunscreen' for roads

Rubber from used tyres acts like sunscreen for roads and halves the rate of sun damage when mixed with bitumen, new research has found.  

RMIT University engineers collaborated with Tyre Stewardship Australia (TSA) to reveal a bitumen blend that is both UV-resistant and withstands traffic loads, with the potential to save governments millions on road maintenance annually.

Unlike much outdoor infrastructure – such as playground equipment and outdoor furniture – roads are not designed with any sun protection, making them prone to cracking and potentially unsafe to drive on. Australian states and territories spent nearly $2.9 billion on road maintenance in 2019  –2020, according to the National Transport Commission.

The invention also provides a promising sustainable solution to Australia’s used-tyre crisis. Used tyres in Australia have been subject to an export ban since December 2021, which means new methods for recycling and reprocessing them locally is increasingly important.

While research efforts have focused on improving the durability of roads in terms of traffic load, thermal ageing and weather-related events, sun damage has received little attention – until now.

The new study, led by Associate Professor Filippo Giustozzi at RMIT University provides a sustainable solution to UV protection for roads, with results published in the Journal of Cleaner Production.

“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.”

RMIT is one of the few universities in Australia to have a UV machine for asphalt studies, which can simulate weather-related ageing and is usually used for testing outdoor furniture paints.

Giustozzi’s team used this machine to simulate the long-term effect of solar degradation in the lab on bitumen with different concentrations of crumb rubber: from a low concentration of 7.5 per cent to a medium of 15 per cent and a high of 22.5 per cent.

After a month and a half of continuous exposure in the UV machine – equivalent to about a year of Melbourne’s UV radiation – they measured the changes in bitumen’s chemical and mechanical properties.

Giustozzi said bitumen mixed with the high concentration of crumb rubber from recycled tyres showed 50 per cent less UV damage compared to regular bitumen.

While using more rubber was better in terms of UV resistance, Giustozzi said it was also important to balance this with mechanical performance.

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

Used tyres in Australia cannot be exported, making new methods for recycling and reprocessing them locally increasingly important.

Lina Goodman, TSA Chief Executive Officer, said while Australia produced about 450,000 tonnes of end-of-life tyres in 2021, only about 70 per cent of those were recycled or reprocessed, making it a critical problem to solve.

“We are encouraged by the research in showcasing the viability and benefits of using crumb rubber from end-of-life tyres, not only in roads and civil infrastructure, but across multiple sectors,” Goodman said.

“We’re excited to collaborate on this project with industry and leading researchers at RMIT University. A multi-organisational approach paves the way for new innovation and the opportunity to turn this resource into a value-added product.”

Giustozzi said an added advantage of crumb rubber was that it was already widely in use, including in some roads, but that the councils and state authorities using it were not aware of this ‘sunscreen’ effect revealed in the research.

“We hope this research will change that and open new opportunities.”