A typical roadway comprises of 4 basic layers:
- A subgrade
- A base
- A sub-base and
- An asphalt layer
All those layers must withstand the forces applied by the vehicles and must also not experience significant subsidence, a fact that would lead to road anomalies or cracks.
The new mix is expected to be utilized as a base material and has never been studied before. It was developed by researchers from RMIT University in Melbourne, Australia and an experimental study on its shear behaviour was recently published.
Currently, the construction industry, including demolition and renovation projects, is responsible for about 50% of the total waste produced worldwide. Despite a global attempt to recycle construction and tires waste is currently underway, both industries are far from satisfied the equilibrium. Given that around 1 billion waste tires are generated annually, the need for a manner to recycle and re-use those materials again is crucial and the unique solution to overcome waste accumulation.
In Australia, the government decided to stop the export of specific waste materials in order to increase the country's capability of recycling. In addition, it will be completely prohibited to export used tires as of December 2021.
The research team conducted a series of large-scale direct shear tests (LDST) using special machinery to examine the effect of different amounts and sizes of the recycles tires on the shear strength of the material. Regarding the material's capability of replacing normal roadway base layer, they found that mixes "with two different sizes (i.e., fine and coarse rubber) and three different percentages (i.e., 0.5%, 1% and 2%) of crumb rubber satisfied the shear strength requirements for use in pavement base/subbase applications."
The mixture that acquired the higher shear strength consisted of 0.5% fine crumb rubber and 99,5 recycled concrete aggregate.
Moreover, the material proved to be better in another aspect compared to typical road bases that are made of quarried rock and sand. In particular, it presented high flexibility that would lead to less road cracking. “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,” Dr. Mohammad Boroujeni, lead author of the study and a research assistant at RMIT university, stated.