Charles Darwin University researchers investigate whether old tyres can strengthen roads
Researchers are hoping to discover the key to stronger roadways through their tyre recycling work. (ABC News: Michael Franchi)
In short:
Researchers in Darwin are investigating whether recycled materials can be used to build stronger, longer-lasting roads suited to the NT's extreme climate.
Laboratory testing is now underway, but if successful, the project may save millions of dollars a year and save discarded tyres and plastics from landfill.
What's next?
Road trials are expected to begin this year, with an independent expert saying the idea shows promise but needs to be proven with real-world tests.
Repurposing old tyres may be the key to building stronger, longer-lasting roads to handle the Northern Territory's harsh climate, say researchers.
About 400 tonnes of tyres are discarded by Darwin residents and commercial operators every year.
They are dropped off at Shoal Bay Waste Management Facility, stored, then sent interstate or overseas for recycling.
Crumb rumber from old tyres, along with plastics from shrink wrap and shampoo bottles are among the materials being repurposed. (ABC News: Tilda Colling)
But researchers at Charles Darwin University (CDU) are investigating whether recycled materials, including granulated crumb rubber from ground-up tyres and plastics, can instead be used to improve NT roads.
CDU has been collaborating with the NT Department of Logistics and Infrastructure to test this theory since late 2021.
PhD student with the university, Ramin Shahbazi, said flexible materials — which bend and flex under the weight of traffic — were often used in the road construction process.
Roads in the NT face some of the harshest weather conditions in the country, from blistering heat to drenching rains. (ABC News: Michael Franchi)
But he said a different approach was needed in places such as the NT, where extreme weather conditions proved challenging.
"When we have a flexible pavement made of asphalt, it's constantly changing when it's exposed to hot weather and moisture from the rain," he said.
"We wanted to try and replace regular material that was being used in the pavements with recycled alternatives — but try to keep the performance as it is, or also maybe improve it."
Ramin Shahbazi says flexible pavements made of asphalt can crack under the pressure of extreme weather in the NT. (ABC News: Tilda Colling)
Reclaimed asphalt, crushed glass, recycled concrete and crumb rubber from tyres and plastics are being tested with the aim of improving road durability, a Department of Logistics and Infrastructure spokesperson explained.
Senior CDU engineering lecturer and PhD supervisor, Ali Rajabipour, said both council budgets and the environment would benefit from giving the alternative materials a new life.
Tyres waiting to be recycled at the Shoal Bay Waste Management Facility in Karama. (ABC News: Michael Franchi)
"Some countries [burn tyre waste], that's not the best way to use crumb rubber … it produces fumes, which are not very healthy,"he said.
Dr Rajabipour said the NT could save about $2 million a year by recycling materials dumped in landfill.
Ali Rajabipour says the NT could save millions of dollars by repurposing waste. (ABC News: Tilda Colling)
Circular economy is the goal
The City of Darwin has committed to a "circular economy", where waste materials are reused and recycled.
But the council's head of environment and waste, Nick Fewster, said achieving that goal could be logistically challenging.
Nick Fewster says materials are often sent overseas for processing. (ABC News: Michael Franchi)
Mr Fewster said repurposing disused tyres locally would reduce the environmental impact made by freight activity as transporting waste — including sending materials off-shore for processing — produced carbon emissions.
"We're all about diverting waste from landfill and reusing materials where possible as part of the circular economy,"he said.
But waste management is only part of the equation.
Nik Kleine and Nick Fewster inspecting the recycling facility in Karama. (ABC News: Michael Franchi)
Council's head of infrastructure, Nik Kleine, said Darwin roads faced unique weather challenges across both the NT's wet and dry seasons which could shorten the life span of road surfaces.
"You'll see cracking, you'll see potholes," he said.
Mr Kleine said the CDU trial was an opportunity to give new life to products that would otherwise be sent to landfill.
Tyres that are no longer roadworthy can be repurposed into new products. (ABC News: Michael Franchi)
What happens next?
If the research proves successful, Mr Kleine said City of Darwin would consider trialling the recycled materials in local roads.
"It's done through a tender process … and [this project] would definitely tick the sustainability and environment box,"he said.
Filippo Giustozzi, professor of civil and infrastructure engineering at RMIT University, said the investigation aligned with existing evidence on the benefits of crumb rubber in asphalt — but warned its effectiveness would need to be proven under territory conditions.
"Challenging environments like the Northern Territory — with extreme heat, UV exposure and intense tropical rainfall — require site-specific testing to confirm durability, ageing behaviour and moisture resistance over time," he said.
The rubber from old tyres can be recycled. (ABC News: Michael Franchi)
Professor Giustozzi also said recycled plastics were still relatively new in road construction and often needed to be combined with traditional materials to ensure long-term performance.
The NT Department of Logistics and Infrastructure said laboratory testing was about 75 per cent complete, with more than 8,000 tests conducted so far.
Road trials using recycled materials are expected to begin early this year.