Old tyres and building rubble could be used to make sustainable roads, researchers claim 

Old tyres and building rubble could be used to make sustainable roads while recycling waste that would otherwise end up in landfill, researchers have claimed.

Developed by researchers from Australia, the new road-covering material is the first to combine rubble and rubber in a mix optimised to meet road safety standards.

The recycled blend, designed to be used for road base layers, has the advantage of being more flexible than standard materials to help stop roads roads from cracking.

According to the team, the ‘zero-waste solution’ will also support the economy.

Approximately half of the world’s annual waste production comes through construction, renovation and demolition.

Meanwhile, around one billion scrap tyres are generated globally each year.

According to engineer Mohammad Saberian Boroujeni of Melbourne’s RMIT University, use of the rubble-rubber mix has the potential to deliver both environmental and engineering benefits.

‘Traditional road bases are made of unsustainable virgin materials — quarried rock and natural sand,’ he added.

‘Our blended material is a 100 per cent recycled alternative that offers a new way to reuse tyre and building waste, while performing strongly on key criteria like flexibility, strength and permanent deformation.’

‘As we push towards a circular economy that can eliminate waste and support the continual use of resources, our recycled blend is the right choice for better roads and a better environment.’

In Australia, where the research was conducted, only 16 per cent of scrap tyres are domestically recycled. 

Meanwhile, some 3.15 million tons of processed building rubble — known as recycled concrete aggregate (RCA) — is added to stockpiles each year, rather than being reused, experts said.

RCA has the potential to be used to form the base layers of roads — however, the experts have shown that the recycled material can be significantly enhanced by the addition of waste rubber. 

Roads are typically formed of four distinct layers — the subgrade, base, sub-base and the topmost asphalt covering — all of which need to be strong enough to withstand the pressures of supporting heavy vehicle graphic.

At the same time, however, they must also be flexible enough to allow for movement, as so that the road doesn’t crack.

In previous studies, the researchers demonstrated that their rubble-rubber blend performs well in tests for stress, acid and water resistance, as well as its strength deformation and dynamic properties.

The material has good flexibility and low shrinkage, which lowers the risk a road made using the recycled blend will crack. 

In their latest study, the team investigated at how the mix would withstand the pressures of being driven over by millions of vehicles over its entire lifetime.

The researchers used special machinery to assess the blended material’s performance under frictional force, as well as to compare the performance of different types and ratios of the crumbed rubber mixed with the RCA.

The team identified the optimal mixture — of 0.5 per cent fine crumb rubber to 99.5 per cent RCA — that conferred sufficient shear strength while maintaining good cohesion between the two materials.

While the recycling of construction waste and scrap tyres have both been growing, both industries continue to generate significantly more waste than is currently reused, said paper author and civil engineer Jie Li, also of RMIT.

‘Solutions to our waste problems will come not only from reducing how much goes to landfill and increasing how much we recycle — developing new and innovative uses for our recycled materials is absolutely vital,’ he added.

The full findings of the study were published in the journal Construction and Building Materials.