Australian research blends concrete, scrap tires into pavement

Researchers at RMIT University in Melbourne, Australia, say they have shown how a blend of processed scrap tires and crushed concrete can be used to create a road paving base layer material, in what they call “a zero-waste solution to boost recycling and support the circular economy.”

The researchers say the new material it the first attempt that they know of to combine recycled concrete and rubber in a mix that is “precisely optimized 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, says RMIT. Lead researcher Dr. Mohammad Boroujeni says 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 says. “Our blended material is a 100 percent recycled alternative that offers a new way to reuse tire and building waste, while performing strongly on key criteria like flexibility, strength and permanent deformation.”

Continues Boroujeni, “As we push toward 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.”

Recycled concrete aggregate (RCA) can potentially be used on its own for road base layers, but adding recycled rubber can enhance the finished product, say the researchers.

Through its research, the RMIT School of Engineering says it has shown its 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, they add.

The new study, published in the Netherlands-based Construction and Building Materials journal, looks at how the mix would withstand the pressures of being driven over by countless vehicles over its lifetime.  Researchers say they 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 percent fine crumb rubber to 99.5 percent RCA – that delivered on shear strength while maintaining good cohesion between the two materials.

Chief investigator Professor Jie Li says that while the recycling of concrete and scrap tires has been growing, in some places both industries continue to produce more discarded material than is currently recycled.

“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,” says Li.

RMIT says construction, renovation and demolition account for about half the discarded materials produced annually worldwide, while around 1 billion scrap tires are generated globally each year.

RMIT previously has conducted research on using discarded steel industry slag as an additive to concrete products.