The management, recovery, and reuse of Off-the-Road (OTR) tyres has become an important topic. As the Australian Flexible Pavement Association writes, more work needs – and is – being done to counter the carbon impacts of this material.
Off-the-Road (OTR) tyres are an essential component in industries like mining, agriculture, and construction, where heavy-duty machinery operates in rugged conditions. These massive tyres, which are designed to withstand extreme pressure and harsh environment, pose a significant environmental challenge once they reach the end of their lifecycle.
Across Australia 130,000 tonnes of OTR reach their end of life each year, with only 10 per cent being recovered and the rest mostly buried, stockpiled or sent to landfill (Tyre Stewardship Australia, 2023). This is below the Federal Government’s 2030 target of 80 per cent recovery rate for all waste streams.
OTR tyres are not easily recycled due to their size and the locations where they are used. While automotive tyres are typically in metropolitan areas and easily recovered, most OTR tyres are used in remote areas of Australia, far from established processing facilities.
Due to limited recycling services and transportation distances, many OTR tyres are buried or stockpiled on-site, resulting in waste and potential negative impacts on the environment and community. From a report published by Tyre Stewardship Australia (TSA) in 2023, Western Australia and Queensland are the largest OTR tyre generators.
One of the solutions to reuse end of life tyres is to use the rubber in roading applications. Crumb rubber technology is well known in Australia and already widely adopted for spray sealing applications. CR-modified binders are manufactured by adding the rubber from processed tyres to a conventional bitumen to enhance the bitumen elastic and durability properties.
The use of the rubber from end-of-life tyres as an elastomeric modifier for bitumen represents a high value recycling opportunity. In the past years, due to the joint effort of TSA, various state road authorities, AfPA and Austroads, several research and field projects are being promoted to ensure broader adoption of crumb rubber in road pavement applications.
A recent project funded by the TSA investigated the opportunity to create a circular economy in Queensland by repurposing waste tyres from the construction industry into valuable resource for reuse. The project, led by the former AfPA Director of Technology, Anna D’Angelo, in collaboration with Sunshine Coast Council and Boral Asphalt, assessed the constructability and performance of Crumb Rubber Gap Graded (GGA) mixes using crumb rubber manufactured from 100 per cent OTR tyres. The OTR tyres for the project were sourced internally by Boral from its West Burleigh Quarry site, and the crumb rubber manufactured by Carroll Engineering.
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The chemical analysis and binder tests, performed by RMIT University, showed that the OTR crumb rubber had slightly more natural rubber and less synthetic rubber compared to standard crumb rubber, and could be effectively used in bitumen blends. In addition, the binder samples were also analysed using a Suntest Atlas weathering chamber to compare the ageing due to solar radiation.
The UVA (Ultraviolet A) and UVB (Ultraviolet B) radiation data collected daily in Sunshine Coast in 2022 by the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) were used to calculate the total UV radiant exposure, considering a clear sky (i.e., worst-case scenario).
Results showed that the unmodified C320 was severely affected by photo-oxidative ageing to a much larger extent than the CR-modified binder. Further testing showed that the ageing of the CR-modified binder, due to UV damage, is significantly less than that of conventional bitumen, showing that the addition of crumb rubber slows down the deterioration of the base binder.
Less UV damage entails greater resistance to environmental cracking and, overall, longer road durability. This aspect is especially relevant for local council roads where most damage is caused by environmental factors rather than traffic loads.
Asphalt mixes using the OTR crumb rubber bitumen manufactured by Puma Bitumen, were laid on different road types and were tailored to the needs of the Sunshine Coast Regional Council with respect to suitable applications for collector roads, residential streets, and rural residential street applications and as an alternative to the conventional dense graded asphalt.
The performance testing conducted on the asphalt mixes showed improved cracking resistance and reduced UV damage compared to unmodified bitumen.
Anna D’Angelo – former AfPA Executive Director Technology – Leadership says the project provided an opportunity to demonstrate that crumb rubber derived from OTR tyres can be interchanged with common crumb rubber in bitumen blends and confirmed the industry’s readiness and capability to manufacture and pave CR asphalt mixes.
“The project, an example of a circular economy approach and industry collaboration, demonstrated a viable solution to recycling end-of-life OTR tyres essential for the transition of society towards a more sustainable future.”
This article was originally published in the November edition of our magazine. To read the magazine, click here.