road tarmac asphalt cracked by the sun

Mixing tyre rubber with bitumen can act as a ‘sun cream’ for roads

Image credit: Dreamstime

Mixing rubber from used tyres with bitumen can act as a 'sun cream' for roads that helps reduce sun damage to their surface, a study has found.

Engineers at RMIT University in Australia have discovered a bitumen blend that is both UV-resistant and withstands traffic loads, with the potential to save governments millions on road maintenance annually.

Roads are typically not designed with any sun protection, which makes them prone to cracking and eventually unsafe to drive on. 

Incorporating recycled rubber not only offers sun protection but offers a sustainable way to recycle the material in many countries.

“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,” said associate professor Filippo Giustozzi.

“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.”

The researchers used a UV machine for asphalt studies, which can simulate weather-related ageing and is usually used for testing outdoor furniture paints. It was able 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.

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

The 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 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.”

While Australia produced around 450,000 tonnes of end-of-life tyres in 2021, only around 70 per cent of those were recycled or reprocessed.

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.

Another team from RMIT University had previously demonstrated that incorporating rubber into the base road layer helped to reduce cracking.

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