The City of Mitcham, in South Australia, is leading the way in testing new mixes of crumbed rubber asphalt that can improve road durability and offer a significant recycling use for the millions of used tyres Australia generates each year.
On Friday, December 7 a 335m stretch of the innovative road surface was laid at Stanlake Avenue, St Marys, in the Adelaide satellite municipality. The asphalt trial is being funded by Tyre Stewardship Australia (TSA) as part of the organisation’s focus on supporting research and development that can increase local markets for tyre-derived product.
Australia generates more than 56 million end-of-life tyres each year. Only about 10% of that volume is recycled domestically, in all uses. Crumbed rubber asphalt and rubberised road surface spray seals offer the potential of a dual benefit of higher recycling rates and improved roads.
Crumbed rubber asphalt has been in extensive use overseas, in climatic conditions similar to Australia. Long-term use in California, Arizona and South Africa has delivered excellent road performance results and great sustainability outcomes.
The testing by the City of Mitcham is of a specific warm mix dense-graded crumb rubber modified asphalt already laboratory tested and suitable for use in challenging underlying soil conditions, such as reactive clay. It will be focused on a range of performance factors, such as cracking, rutting, moisture retention and general durability. It is expected that the results of the test will further drive the move to increase the specification of such roads not only state-wide but nation-wide.
If successful, the test will contribute to a doubling of the use of recycled tyre rubber in Australian road building, leading to an increase in the percentage of annual volume of old tyres consumed, from around 5% to 10%, within a very short time.
City of Mitcham Mayor, Heather Holmes-Ross says the city is trialing the crumb rubber asphalt because of the significant environmental benefits as well as the opportunity to improve the quality and life of road pavements, particularly in areas of reactive clay soils.
"Not only is there a sustainability dividend, but the asphalt will also have the potential to directly lower maintenance costs, given it is less prone to cracking and rutting," she says.
The City of Mitcham recycled about 850 used tyres in the trial asphalt resurfacing of Stanlake Avenue, with 1.5 end-of-life tyres being used for every ton of asphalt laid. In addition, the laying of the asphalt, which was mixed at 160 degrees and laid at 140 degrees, occurred without any workability or fuming issues, despite an over 35C ambient temperature.
TSA’s work in the crumbed rubber asphalt space has also recently resulted in the publication, with the Australian Asphalt Pavement Association, of two national specifications for commonly used forms of crumbed rubber asphalt.
Tyre Stewardship Australia Acting CEO Steve Clifford welcomed the foresight of the City of Mitcham in conducting the test.
“The council is to be congratulated for grasping the opportunity to deliver better infrastructure whist addressing a sustainability challenge. The work done in South Australia will play an important role in creating valuable domestic recycling outcomes for end-of-life tyres. Outcomes that can also deliver new green jobs.”
Ongoing testing is scheduled to run for two years, with results monitored on a regular basis to assess the key performance parameters.
Details of the mix used, and the testing parameters can be obtained by contacting TSA.