Increasing the use of crumb rubber asphalt in local government roads

The outcome

The primary outcome of this project was the development of a new Department of Transport (DoT) Specification (Section 422) allowing for the incorporation of crumb rubber into asphalt mixes for lightly trafficked roads. The kind of roads that are suitable for local government use. This initiative is an Australian first and demonstrates strong leadership in the use of recycled materials in Victorian roads.

The inclusion of crumb rubber enhances performance, creating better flexural and elastic recovery of the asphalt layer while supporting the use of sustainable materials.

The asphalt product has since been demonstrated across Victorian local government and has also been transferred across to other states. Tyre Stewardship Australia (TSA) released a Low Traffic Crumb Rubber Fund, supporting 7 projects nationwide. Successful applicants included Fulton Hogan Tasmania (6 local councils from Tasmania), the City of Greater Dandenong, Melton City Council, Frankston City Council, Cardinia Shire Council, Banyule City Council, and Boral Asphalt Bendigo Region.

The need

End-of-life tyres can be stored for reuse or recycling. However, stockpiles are a hazard to communities and the environment due to the risk of fire. To avoid unnecessary stockpiling of tyres there is need to expand existing end markets for recycled rubber. This is supported via the development, testing and validation of road materials and products that utilise recycled rubber.

The opportunity

The research project looked at developing a specification to enable local government investment in crumb rubber in asphalt mix. Crumb rubber is a powder-like product of highly refined tyre rubber and its size is typically less than 1mm. During the tyre recycling process, steel and tire cord (fluff) are removed, leaving tyre rubber with a granular consistency.

Crumb rubber enhances the performance of a variety of playing and sports surfaces, including sports fields, running tracks and equestrian surfaces. Previous research and trials have indicated that tyre crumb rubber in asphalt is a viable option for low traffic roads. With 85% of roads managed by local councils and significantly more low traffic roads found nationally, there is a big opportunity to utilise recycled crumbed rubber in roads and create a better performing and longer lasting road network. The inclusion of crumb rubber in asphalt allows for improved performance of the road such as a better flexural and elastic surface.

It is estimated that upwards of 200,000 tonnes of asphalt is produced for local government roads per annum. Depending on the uptake from local governments a conservative estimate of 10% could account for 20,000 tonnes of crumbed rubber per annum, considering the minimum amount prescribed in the specification is 100 tonnes.

State road agency specifications are key to implementing recycled and reused materials in road infrastructure.

Developing the solution

The project was delivered through 4 stages including stakeholder engagement, development of draft specification, targeted industry consultation, laboratory testing and final specification and publication.

Laboratory testing allowed the research team to experiment with dry and wet mixes, different temperature settings and varying quantities of bitumen or binder required. It was found that:

• Crumb rubber modified bitumen (in this case, S45Rbinder) could be added into asphalt mixes without any major issues. The size and grading of the aggregates, the type of materials, as well as the temperature at which the asphalt was compacted all influenced the performance of the crumb rubber modified asphalt.
• Dry and wet mixing of crumb rubber into asphalt required separate specification limits, including the minimum amount of crumb rubber permissible and compaction temperature.
• The amount of crumb rubber specified will greatly influence the amount of bitumen or binder required in the mix.

A key project learning was that effective collaboration with all stakeholders is critical when implementing new materials and technologies into business-as-usual practices. This was supported by having a well-defined problem statement, practical and straightforward solution, stakeholder buy-in and support from the outset.

The partnership

The Australian Roads Research Board was the project lead and worked closely with DoT (formally VicRoads), consulted Australian Flexible Pavement Association (AFPA, formally Australian Asphalt Pavement Association) and Institute of Public Works Engineering Australasia (IPWEA) to complete the research.

Increasing the use of tyre-derived products in roads assists DoT to achieve their goal to reuse one million tyres in road works annually over the next five years across country Victoria.

Pathway to commercialisation

Following the completion of the project, TSA awarded $500,000 in grant funding to local councils to utilise crumb rubber in low traffic asphalt across Australia. Six Victorian councils were awarded funding for demonstration projects utilising the crumb rubber mix. These include City of Greater Dandenong, Melton City Council, Frankston City Council, Cardinia Shire Council, Banyule Council and City of Greater Bendigo.

The modified specification could greatly increase the demand for crumb rubber processed from waste tyres and in turn reduce tyre stockpiling. Inclusion of crumb rubber in a DoT specification means that local governments will be able to confidently specify crumb rubber asphalt and asphalt manufacturers will be able to readily produce large quantities.

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