How to mix old tyres and building rubble to make sustainable roads

Researchers have shown how a blend of old tyres and building rubble could be used as a sustainable road-making material, in a zero-waste solution to boost recycling and support the circular economy.

Construction, renovation and demolition account for about half the waste produced annually worldwide, while around 1 billion scrap tyres are generated globally each year.

The new material, developed by researchers at RMIT University, is the first to combine recycled rubble and rubber in a mix that is precisely optimised to meet road engineering safety standards.

Designed to be used for base layers, the recycled blend is more flexible than standard materials, making roads less prone to cracking.

Lead researcher Dr Mohammad Boroujeni said the rubble-rubber mix could deliver both environmental and engineering benefits.

“Traditional road bases are made of unsustainable virgin materials – quarried rock and natural sand,” Boroujeni said.

“Our blended material is a 100% 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, only 16% of scrap tyres are domestically recycled. About 3.15 million tons of processed building rubble – known as recycled concrete aggregate (RCA) – is added to stockpiles each year rather than being reused.

In 2019, federal and state governments agreed to ban the export of certain waste materials, with the aim of building Australia’s capacity to generate high value recycled commodities and associated demand.

As part of the agreement, whole used tyres will be banned from export by December 2021.

Only 16% of scrap tyres are domestically recycled in Australia.

On the road to a circular economy

Roads are made of four layers – a subgrade, base and sub-base, with asphalt on top.

All the layers must be strong enough to withstand the pressures of heavy vehicles, while being flexible enough to allow the right amount of movement so a road doesn’t easily crack.

RCA can potentially be used on its own for road base layers, but adding recycled rubber can significantly enhance the finished product.

In previous research, the RMIT School of Engineering team has shown their rubble-rubber blend performs well when tested for stress, acid and water resistance, as well as strength, deformation and dynamic properties. Its low shrinkage and good flexibility reduce the risk of cracking.

The new study published in Construction and Building Materials looked at how the mix would withstand the pressures of being driven over by countless vehicles over its lifetime.

Researchers used special machinery to assess the blended material’s performance under frictional force, or shear stress, and compared different types of crumb rubber (fine and coarse) mixed into the RCA at different ratios.

The team identified an optimal mixture – 0.5% fine crumb rubber to 99.5% RCA – that delivered on shear strength while maintaining good cohesion between the two materials.

Chief investigator Professor Jie Li said while the recycling of construction waste and scrap tyres was growing, both industries continued to produce significantly more waste than is currently reused.

“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,” Li said.

Image of the rubble-rubber mix, the first material to combine recycled concrete aggregate and scrap tyres in a mix that meets road engineering safety standards.

The new material is the first to combine recycled concrete aggregate and scrap tyres in a mix that meets road engineering safety standards.

‘An experimental study on the shear behaviour of recycled concrete aggregate incorporating recycled tyre waste’ is published in Construction and Building Materials (DOI: 10.1016/j.conbuildmat.2020.120266).

Story: Gosia Kaszubska

Return to RMIT News

Society and Environment

Technology

30 July 2020

Society and Environment

Technology

30 July 2020

Sustainability
Research
Engineering
Advanced Materials
Property & Construction
Environment

Engage

Related News

Coffee offers performance boost for concrete

Engineers in Australia have found a way of making stronger concrete with roasted used-coffee grounds, to give the drink-additive a “double shot” at life and reduce waste going to landfills.

Recycled roads pave the way to a sustainable future

New roads mixed with recycled plastics at 10 sites across Victoria will demonstrate a viable circular-economy solution to the nation, experts say.

RMIT takes giant leap forward in global rankings

RMIT has ranked 140th – a rise of 50 places since last year – in the latest QS World University Rankings, reflecting continued excellent performance on research impact, reputation and sustainability.

Engineers “strike gold” with innovation that recovers heavy metals from biosolids

Engineers in Melbourne have developed a cost-effective and environmentally friendly way to remove heavy metals, including copper and zinc, from biosolids.

Acknowledgement of Country

RMIT University acknowledges the people of the Woi wurrung and Boon wurrung language groups of the eastern Kulin Nation on whose unceded lands we conduct the business of the University. RMIT University respectfully acknowledges their Ancestors and Elders, past and present. RMIT also acknowledges the Traditional Custodians and their Ancestors of the lands and waters across Australia where we conduct our business - Artwork 'Luwaytini' by Mark Cleaver, Palawa.

More information

How to mix old tyres and building rubble to make sustainable roads