Paving with plastic: the rise of plastics in road construction

Councils are using plastic bags and soft plastic packaging as a sustainable alternative to virgin polymers for bitumen binder to construct longer lasting roads.

Plastic bags are typically used once before ending up in landfill where they can take centuries to break down, according to the Northern Territory Environment Protection Authority (NTEPA).

On top of this, the NTEPA finds local and state governments spend more than $200 million per year picking up plastic litter that entered the environment, where they pose dangers to wildlife that mistake them for food. The sheer volume of plastic bags and packaging can have significant environmental impacts, as millions enter the country’s waterways and oceans each year.

Australians use more than four billion plastic bags every year but only 3 per cent of these are recycled, according to Sustainability Victoria. Kerbside recycling collection often cannot handle soft plastics as they can potentially cause issues with sorting machinery at materials recovery facilities.

One potential use for these plastic bags is as a material in road construction. The soft plastic can be melted down and turned into a bitumen additive to enhance the physical properties of a road.

Compared with VicRoads standard specified asphalt, for instance, soft plastic enhanced asphalt has provided up to 65 per cent improvement in fatigue resistance for roads under stress from heavy traffic.

The innovation to turn plastic bags and packaging into a valuable road material has come from a partnership with Downer and Close the Loop.

Soft plastics, which are plastics that can typically be scrunched up, can be collected by recycling companies through special bins at participating supermarkets. These are then sent Close the Loop and Downer to create the bitumen additive for use in council roads.

The low melting point of soft plastics is what allows them to be used when compared with other types of plastics. When mixed at manufacturing temperatures with other recycled materials such as glass, printer cartridges and reclaimed asphalt pavement to create the asphalt, soft plastics can’t be separated into beads like other plastics, meaning they cannot break down into microplastics.

Stuart Billing, Downer General Manager – Pavements, says the major sustainability benefit of the material is the reduced need for virgin materials to create the polymer-enhanced bitumen.

“Polymers have been used to improve on the strength of pure bitumen for around 25 years, but now soft plastics allow us to create a similar product from a more sustainable source,” he says.

“This provides us with the physical benefits of enhanced polymer bitumen for a lower cost.”

The sustainable asphalt mix works on all roads including those that carry significant amounts of traffic. Testing of the asphalt by Downer finds that the increased fatigue resistance should allow the road to last longer than standard asphalt, and has the potential to improve the value of the council’s road assets, requiring less funding to maintain and repair.

Mr. Billing says using a sustainable asphalt product provides councils with an opportunity to meet sustainability aspirations and reduces the amount of waste that is sent to landfill.

“The community of the local government authority also plays a significant role, as residents will often expect their local governments to step up to the challenge and play their part to reduce reliance on virgin materials,” he says.

“The asphalt is also able to be recycled when the road needs to be repaired, as the asphalt can be collected and used in the paving of another road.”

The process is undergoing further laboratory and field trials to refine the mixture of the soft plastics to further improve the performance of the asphalt.

Mr. Billing says Downer has reached the stage where the company is confident it has created a reliable additive that can be incorporated into the road construction process.

“Application of the asphalt is no different to building any other road. It can be carted onto sites, placed and compacted in the same way we would use any other asphalt and our teams don’t need to change any of our processes to get it on the ground,” Mr. Billing says.

Further research and development is being undertaken by both Downer and Close the Loop to find more opportunities to reuse materials from other common waste streams.

ROAD TESTING

The first use of the additive was trialled in May to construct a road in Craigieburn, a suburb in Melbourne’s north. Downer and Close the Loop partnered with Hume City Council for the trial, which saved the equivalent of around 200,000 plastic bags and packaging equivalents and 63,000 glass bottles from landfill.

Peter Waite, Hume City Council Director, Sustainable Infrastructure and Services, says the council has always been receptive to trialling new ideas that provide better outcomes for the community.

“When Downer, which is a local employer at the company’s Somerton asphalt plant and has a multi-year contract with the council for road resurfacing, approached us about the trial, we were very keen to help,” he says. “The laying of the asphalt in Rayfield Avenue this year occurred without a hitch. To date, the new road surface is performing as expected and looks like any other asphalt road.

“It’s early days but so far so good – we will get a much better idea over the next few years when the surface is exposed to different seasons, including hot summers. Hume City Council will continue to monitor the condition of the road.”

The council has previously also allowed its contractors and land developers to use recycled material in road-making material, which has led to recycled materials such as concrete, asphalt and glass being used in footpaths and roads.

If the trial is considered successful by the council, it will look at using the product on more of its roads where suitable.

Sutherland Shire Council has also been involved in similar trials, using 220 tonnes of the recycled asphalt mix to construct the road along Old Princes Highway. Each tonne of the mix is estimated to incorporate around 800 plastic bag equivalents, 252 glass bottles and 300 kilograms of recycled asphalt.

The testing has raised a significant amount of interest from other local governments, according to Mr. Billing. “More than 15 other local government authorities have contacted us and told us that they are interested in using the product in their roads,” he explains. “It is clear councils are keen to help improve their roads and provide strong end market products for recycled materials.”