A new material has been developed that combines recycled rubble and rubber in a mix that is 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.

Traditional road bases are made of unsustainable virgin materials — quarried rock and natural sand. The new blended material is a 100 percent recycled alternative that offers a new way to reuse tires and building waste, while providing flexibility, strength, and permanent deformation.

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.

Processed building rubble — known as recycled concrete aggregate (RCA) — is added to stockpiles each year rather than being reused. 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 researchers demonstrated that 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.

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 percent fine crumb rubber to 99.5 percent RCA — that delivered on shear strength while maintaining good cohesion between the two materials.

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