Where the rubber hits the road

As a material derived from end-of-life tyres, crumb rubber boasts a number of environmental benefits as a recycled product – benefits that are being realised in myriad industrial sectors, including road surfacing and maintenance.

Crumb rubber has been used in spray seal binders in Australia since the 1970s, and is continuously being explored across the country by producers and contractors alike as a cost-effective maintenance treatment.

As a prominent Australian bituminous products supplier, and part of the Colas Group, SAMI Bitumen Technologies has been involved in the production of crumb rubber-modified (CRM) binder for road sealing applications for a number of years.

Cameron Nisbett, SAMI’s Queensland State Manager, says the environmental and sustainability benefits of the material are bolstered by its performance and durability.

He says the modification of bitumen by incorporating crumb rubber improves the bitumen properties so that it’s more durable and less prone to bleeding, cracking and stone loss.

“One of the main considerations is obviously its use of a recycled material. Old tyres contain valuable engineering compounds that can be beneficial to the binder performance, namely natural rubber and carbon black. The latter is an antioxidant, which retards the ageing of the binder. So, the tyres we use on our vehicles that use these roads, are, in turn, being reused to improve the performance of our roads – you don’t need to import expensive polymer from overseas, but you can reuse rubber from old tyres in Australia,” Mr. Nisbett explains. “Because of these sustainability and environmental benefits, it’s really taken a foothold in the market.”

SAMI continues to explore the potential for CRM binder in Australia and is tackling the challenges to its greater use head-on.

Mr. Nisbett says traditionally, the use of preblended CRM binder has been limited to areas close to the point of manufacture, restricting its application for more remote jobs. Given the sheer size of Australia, this poses a major issue for remote projects.

“The difficulty of long distance travel is that the crumb rubber particles can settle out at the bottom of the road tanker,” he says.

With that particular challenge in mind, SAMI developed a technique to produce a CRM binder that meets the Austroads Standard that is more storage stable during prolonged heating and transportation. “We also stepped up our control processes for our drivers so that they have capacity to prevent any additional settling so that when the material arrives on site, it’s ready to use.”

In the summer of 2016-17, SAMI supplied approximately two million litres of this CRM binder to an SRS Roads resealing contract for the Queensland Department of Transport and Main Roads (TMR) across multiple sites in the south western district of Queensland.

“SRS won the initial contract based on its alternative proposal, which put forward the S45R binder. It wasn’t in the initial specification from TMR but the department was happy with the proposed alternative and accepted the new approach,” Mr. Nisbett says.

The material was transported from SAMI’s Pinkenba facility in Brisbane – up to 1100 kilometres away – without the rubber particles dropping out of suspension or the binder properties degrading during transport.

Mr. Nisbett says previously, if CRM binder was to be used it would need to be blended within 300 kilometres of the point of use. The newly formulated CRM binder overcomes this limitation, and is aided by the use of specially modified road tankers and special handling protocols during the material’s transportation.

Last year, SAMI was awarded the 2017 National Australian Asphalt Pavement Association (AAPA) Innovation Award for the preblended CRM binder used on the project. The award recognised that the innovation now allows remote Australian roads to derive the sustainability benefits of crumb rubber, breaks down the operational limitations of the past and delivers a product that reduces cost and extends asset life. It was a win-win for both the environment and the asset owner through addressing a tyre disposal problem and providing a surfacing with increased life.

This year alone, SAMI has been supplying six million litres of the preblended crumb rubber modified S45R binder to Colas Queensland’s contracting business for TMR across the state’s south west. Mr. Nisbett says the long-haulage benefits of SAMI’s CRM binder are being realised in Queensland, particularly given the remoteness of the projects in southwest Queensland. “It gives industry capacity to innovate and supply CRM binder across long distances, which hasn’t been done before in Queensland.”

Following recognition of its technological achievement through practical outcomes for its client –TMR – and the AAPA award, SAMI is exploring new avenues for the use of crumb rubber and its benefit for clients across Australia, especially in Queensland.

“A major project that’s currently underway is the demonstration of an open-graded asphalt on the Gold Coast that uses SAMI’s warm mix CRM binder as one of the binders for the asphalt,” Mr. Nisbett says.

Making the grade

To facilitate the use of CRM binder in spray seals in Queensland, TMR, Tyre Stewardship Australia and the Queensland Department of Environment and Science are funding research exploring its use in asphalt and seals. The Australian Road Research Board (ARRB) has been engaged by TMR under its National Asset Centre of Excellence (NACoE) research program to help explore the potential for the increased use of crumb rubber in roads in Queensland.

Joe Grobler, Principal Professional Leader at ARRB, says the multi-year research project is exploring the use of crumb rubber in three phases: in spray seals, open-graded asphalt and gap-graded asphalt.

TMR recently changed its sealing specification to allow use of crumbed rubber in binders, as an alternative to polymer-modified binders.

Deputy Chief Engineer Peter Evans says TMR delivered a crumb rubber research project with the Department of Environment and Heritage Protection and Tyre Stewardship Australia. “This led to some successful demonstration projects on the Darling Downs and increased use of crumbed rubber seals in southwest Queensland,” Mr. Evans says.

“It is pleasing Queensland industry is now tooling up to crush local tyres to produce the fine grading required for successful crumbed rubber seals, and now has the ability to transport them over vast distances with minimal segregation.

“As well as providing a good technical solution, potentially lowering costs and delivering longer pavement life, incorporation of rubber tyres in bitumen has waste benefits.”

Mr. Grobler says TMR constructed an Australian-first demonstration project for CRM binder in open-graded asphalt at the beginning of 2017 on the Sunshine Coast, which used a pilot specification developed by TMR and ARRB. After that, the City of Gold Coast became aware of this technology and saw the benefits of using recycled tyres in this application,” Mr. Grobler explains.

The second demonstration project on the Gold Coast, funded by the City of Gold Coast, was undertaken at the end of January this year, with Fulton Hogan constructing the road and SAMI supplying the CRM binder. ARRB wasn’t officially engaged for the demonstration project itself, but observed its implementation under NACoE.

Mr. Grobler says the project on the Gold Coast – located at Nielsens Road in Carrara – involved laying open-graded asphalt surface in three sections. “The first section involved placement of a conventional polymer-modified open-graded asphalt as the control section. The second section included CRM binder open-graded asphalt and the third was CRM binder open-graded asphalt with warm mix additives,” he says. Roughly 100 tonnes of each material was laid.

“The purpose was to demonstrate that local contractors can manufacture the binder and the asphalt and place it to specification, but also observe any differences in construction techniques required,” he says. “That was the main purpose, but another aim is to monitor the long term performance of the CRM binder open-graded asphalt.”

Mr. Grobler adds that the purpose behind the warm mix additive was to lower temperatures, which in turn reduces emissions and environmental impacts. The use of warm mix CRB in open-graded asphalt is expected to provide a longer lasting product due to thicker binder films, which are less prone to oxidisation.

While the results from the demonstration project are pending, Mr. Grobler says construction using the CRM binder showed no issues. “We didn’t notice any differences in construction practices of the CRM binder asphalt compared with the conventional polymer-modified binder asphalt on the night,” he says. “This is the second demonstration of this technology in Australia – so it’s a very good step for Queensland.

“There’s ongoing research work with use of the CRM binder for open-graded asphalt and the next phase is looking at CRM binder in gap-graded asphalt,” he adds.

“There is industry excitement, we’ve had two contractors and two material suppliers on board already,” he says. “The development of this pilot specification is a significant step and once it becomes more understood, it will hopefully increase the use of crumb rubber binder across the state.”

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