RMIT University scientists have combined old tires and building rubble to form a new sustainable road-making material.
According to the scientists, construction, renovation and demolition account for about half the waste produced annually worldwide, while around 1 billion scrap tires are generated globally each year.
In Australia alone, only 16% of scrap tires are domestically recycled, and 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.
It is for this reason that the RMIT material is being heralded as a game changer as it offers a zero-waste solution, has been precisely optimized to meet road engineering safety standards, and could prove integral in supporting Australia’s circular economy.
The recycled blend is designed to be used as base layers and is more flexible than standard materials, making roads less prone to cracking.
“Traditional road bases are made of unsustainable virgin materials – quarried rock and natural sand,” points out lead researcher, Dr Mohammad Boroujeni.
“Our blended material is a 100% 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.”
Roads are generally 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 significantly enhances the finished product.
In a previous study, the RMIT team showed their rubble-rubber blend performed well when tested for stress, acid and water resistance – as well as strength, deformation and dynamic properties.
Its low shrinkage and good flexibility also helps reduce the risk of cracking.
In the new study, the scientists demonstrated how the mix can withstand the pressures of being driven over by countless vehicles over its lifetime.
They used special machinery to assess the blended material’s performance under frictional force (shear stress), and compared different types of crumb rubber (fine and coarse) mixed into the RCA at different ratios.
Based on these tests, they were able to identify 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.
Content and image: Gosia Kaszubska-RMIT