Crumbed rubber asphalt trial

With recent acceleration in the uptake of recycled material in roads by local councils in the likes of New South Wales and Victoria, the City of Mitcham is paving the way for crumbed rubber in South Australia, with help from Tyre Stewardship Australia

While recycled glass is being experimented with in asphalt mixes in Fremantle, printer toner cartridges finding new life in Moreton Bay roads and plastic bags incorporated in asphalt resurfacing in Craigieburn, a South Australian council is taking crumb rubber asphalt to the next level.

In response to existing road infrastructure issues it was facing with expansive clay causing premature failure of the road seal, City of Mitcham commenced trial of a specific warm mix dense-graded cru mb rubber modified asphalt on a 335-metre stretch of road at Stanlake Avenue in St Marys, Adelaide.

Tyre Stewardship Australia funded the crumbed rubber asphalt trial, which took place in December last year, with an aim of determining how suitable the road alternative is through cracking, rutting, moisture retention and general durability tests especially as it is a denser mix.

While the process of using crumb rubber asphalt is commonly used in Victoria, the US and South Africa, the asphalt trial in South Australia is attempting to replicate the positive results that open- and-gap grade mixes have, with a more densely graded asphalt mix that incorporates more crumbed tyre rubber.

The two-year trial is implementing three separate mix types on the one stretch of suburban road – polymer, traditional asphalt and the mix using crumbed rubber. It will investigate standard road-wear indicators including the surface’s resistance to cracking, presence of rutting and deformation where the optimal road will maintain its form over time.

While the trial is still in its early stages, starting in December last year, positive results are already rolling in with some lab testing being conducted to examine durability and performance benefits.

The initial laying of asphalt saw 850 used tyres crumbed and mixed with asphalt at 160 degrees Celsius, resulting in no fuming or workability issues. With looming future success over the life of the trial, TSA anticipates this will contribute to the potential annual volume of used tyres recycled into roads doubling from 5 to 10 per cent in a short time.

Tyre Stewardship Australia Market Development Manager Liam O’Keefe says rubberised dense grade mixes are uncommon in Australia with a brief test in the City of Casey, but not to the extent of testing and monitoring of this trial.

“The beauty of this Mitcham project is that it could have been a very technically-oriented project that didn’t broadly engage with the sector but the city held an event, hosting 10 to 20 councils,” Mr. O’Keefe says. “We didn’t think it was going to have the outreach that it eventually had. The Mitcham teams’ enthusiasm and leadership created a bigger and better project — it just shows what a couple of personnel from council can create if they really want to give something a crack.

“It brings together a network of people who want to make a positive difference and gives them the ability to connect with other within their profession to develop the practice within the industry.”

Interest has grown in the product after the Mitcham installation, with councils across Queensland and New South Wales reaching out to TSA with requests.

“We’ll be funding crumb rubber-oriented projects in different states across the year, it has created some really positive interest,” Mr. O’Keefe says.

“I’d like to commend Mitcham and the project team for wanting to do more and to build upon standard practice. They were willing to try something different, to put resources behind it and to give it a crack.

“From a TSA perspective, the only way we can do good work and make a positive difference, is through working with other people, so we’re very grateful for Mitcham and Topcoat.”

Mr. O’Keefe notes that while a crumbed rubber mix may not always be the cheapest option up front, the evidence of its effectiveness that he’s seen from world-leading experts from California and South Africa makes it a cheaper and more viable product over its lifetime, lasting an extra five years or more.

The trial isn’t just about the isolated success of Mitcham, TSA aims to use its meticulously gathered empirical evidence to become a sector-wide advocate for the innovation and facilitate a network that captures these benefits.

With further crumbed rubber trials scheduled for 2019 and testing of the Mitcham surface ongoing, crumbed rubber investigations at TSA will be headlining its year.

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