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Construction waste and old tyres combined to create sustainable road material

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Researchers have blended used tyres with building rubble to create a sustainable road-making material that they believe could cut the vast quantities of waste generated by the construction sector.

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

The team at RMIT University in Melbourne, Australia, say this is the first time recycled rubble and rubber have been combined in a mix that meets 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.

“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.”

Most roads are typically made up 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.

Processed building rubble, otherwise known as recycled concrete aggregate (RCA), can potentially be used on its own for road base layers, but adding recycled rubber can significantly enhance the finished product.

The team has previously demonstrated that their rubble-rubber blend performs well when tested for stress, acid and water resistance, as well as strength, deformation and dynamic properties.

The new study shows 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 per cent fine crumb rubber to 99.5 per cent RCA - that delivered on shear strength while maintaining good cohesion between the two materials.

Lead researcher 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.

Plastic waste has also been identified as a potential material for building and repairing roads. Last year, a factory opened in Scotland dedicated to recycling plastic to produce a material suitable for roads.

Several other materials and composites are also being trialled worldwide as a way to build better, greener and more manageable roads as alternatives to asphalt and concrete. 

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