The plastic road ahead
With more and more recycled plastic being used to repave highways and roads around the world, we might be driving toward a future with a lot less plastic pollution.
If you thought asphalt paving would always remain what it has always been – an aggregate of sand and gravel held together by black asphalt as a binder – it’s time to think again. As recent examples from around the world show, the use of recycled plastic-modified (RPM) asphalt binders and mixtures are beginning to make inroads in paving technology.
There’s a backdrop to the quest to improve blacktop: as freeze-thaw cycles, UV rays, moisture, and traffic pressure wear down traditional asphalt pavement, it breaks down, forming cracks and potholes. Over time, it needs to be replaced, and every driver has suffered through the result: traffic gridlock as departments of transportation using milling machines laboriously take up the old pavement while pouring fresh asphalt concrete.
Incorporating recycled plastic into the asphalt mixture may help to alleviate these issues by making the pavement more durable, and also has other complementary sustainable benefits: it improves overall resource efficiency and enhances the circular economy by reducing the amount of post-consumer plastic going into landfills; extends the limited supply of the petroleum in asphalt; and can be reused immediately on-site, whereas traditional pavement is ground up and reused at a later time.
It’s important to realize that there are several methods used to repurpose recycled plastic into roadways, and they’re not all created equal. One method, which tends to be used in some developing countries or areas with foot traffic only, is to literally create “plastic roads,” where waste plastic is compacted and used to pave a road with minimal or no asphalt. “These types of mostly ‘plastic roads’ perform to a different standard – perhaps suitable for lower traffic conditions or bike or pedestrian paths – but aren’t capable of meeting the engineering requirements specified by the transportation authorities from Canada and the U.S., so they’re not viable for widespread paving application in North America,” said Carla Toth, senior vice president of sales and marketing with GreenMantra Technologies, a Brantford, Ont.-based company that’s pioneering new ways to incorporate recycled plastic in asphalt. “Another method to create an RPM asphalt mixture is to utilize a lower dosage of recycled plastic to modify the asphalt formulation, and this is the focus of most North American projects that involve using recycled plastics in roads.”
RPM asphalt mixtures are created through several steps: the recycled plastic – usually water bottles, soda bottles, and single-use plastic bags – is sorted by polymer type, such as polyethylene (PE) plastic bags in one group and PET bottles in the other. Each polymer type varies in how durable and pliable it is. Once the plastics are separated and pressed into pellets, they can be mixed with hot asphalt to create the RPM asphalt binder. Some recycled plastics are added to black tarry asphalt before the aggregate to enhance the performance of the asphalt, and some are added with the aggregate and the milled pavement to act as a binding agent for the gravel and sand.
A challenge, however, is to balance the asphalt performance with gains in recycling and sustainability as well as environmental concerns. In some early applications, where waste plastic was simply ground up and tossed into the mix, the plastic agglomerated near the road surface, creating the opportunity for small pieces to break away and generate microplastic pollution. This problem can be overcome by recent technologies like those from GreenMantra. “GreenMantra changes and redesigns the carbon chain of recycled PE plastic feedstock, creating a more functional shorter chain wax that easily melts into and integrates seamlessly with the asphalt and doesn’t create microplastic pieces,” Toth said.
There’s also concern about the potential for certain types of melted plastic to release toxic fumes. An October 2020 report by the U.S.-based National Asphalt Pavement Association (NAPA) acknowledged the risks of running the wrong plastics through an asphalt plant and advised against using recycled PVC in paving applications, as it releases toxins when heated. The report highlighted that PE is the primary plastic that could be incorporated safely into asphalt mixtures because of its low melting point, with polypropylene as a second viable candidate.
MADE IN CANADA
The first known plastic and asphalt road project in Canada dates back to the early 1980s, when the City of Edmonton ground up Fisher-Price toys to use to repave a local street, followed by several road mixes that used non-recycled plastic. Later, in 1990, an experimental section of Highway 401 around Toronto – then and now the busiest highway in Canada – was paved with asphalt reinforced with plastic from recycled milk jugs. These projects and a few others like them remained isolated instances in Canada up to the late 2000s. But as technology continues to improve, RPM asphalt mixtures have more recently been used in a range of Canadian paving projects, including a Vancouver International Airport runway; a portion of the South Fraser Perimeter Road, a new four-lane expressway along the south side of the Fraser River in B.C.; and a parking lot in Burnside, N.S. paved with asphalt that included two tonnes of material made from plastic shopping bags in a demonstration project undertaken by Goodwood Plastic Products Ltd., of Shortts Lake, N.S.
GreenMantra, a pioneer in the field of advanced recycling technologies in Canada, is promoting a new approach to using plastics in roads. “Unmodified recycled plastic is relatively inert and can impair asphalt stability and performance, whereas GreenMantra’s products used in asphalt paving applications are PE waxes derived from recycled plastic items such as films, containers, and bottle caps, and they’re molecularly different than unmodified recycled plastic,” Carla Toth said. “Traditional waxes derived from petroleum have been used for decades to enhance the performance of asphalt. GreenMantra’s advanced recycling technology creates a new sustainable wax that’s derived from recycled plastic. As waxes have a much lower viscosity and softening point, this translates into differentiated performance in the asphalt. When added to the liquid asphalt, our PE wax readily melts and fully incorporates with the asphalt, and once mixed, remains very stable. We’re changing the paradigm towards a performance-enhancing additive that doesn’t sacrifice properties of asphalt.”
GreenMantra’s first paving project was the “Blue Box to Green Roads” program with the City of Vancouver in 2014, and it has been involved in several new projects within the past year. In one, it partnered with Nova Chemicals Corp. in a project that incorporated its PE wax – equivalent to 113,000 single-use plastic bags – to pave two pathways, approximately 1,700 feet long by eight feet wide and two inches thick, at Nova’s construction site for its new PE facility in Sarnia, Ont.; in a second, the company was selected to participate in the “Plastics Research in Action” program alongside Northern Alberta Institute of Technology and petroleum development company Inter Pipeline, with its waxes being evaluated in asphalt paving test strips in Strathcona and Sturgeon counties in Alberta. “We’ve also been invited by the National Center for Asphalt Technology (NCAT) to submit our waxes for evaluation for a test track that will be paved this upcoming summer, and we have several other projects and trials underway in North America, Europe, and the Middle East,” Toth said. “The positive environmental and societal impact of these combined projects is enormous, as each kilometre of road paved with our waxes can divert the equivalent of 2.6 million single-use plastic bags from landfills.”
AROUND THE WORLD
Like Canada, Europe and other parts of the world are edging into the use of more complex post-consumer plastics for paving projects. India is widely considered a pioneering nation for widespread mixing of plastics and asphalt, putting down its first waste plastic road in 2002 with material supplied by KK Plastic Waste Management in Bangalore. India has also published a code for the hot and cold mixing of plastic waste at plants. Since its first road, according to World Highways Magazine, KK Plastic’s product has been used on 3,000 kilometres of Bangalore road with its KK Poly Blend mixed at a rate of eight per cent to asphalt. And Dow Chemical Co. recently worked with government officials in India and waste collectors in Bangalore and Pune to pave 40 kilometres of roads with its Elvaloy polymer-modified asphalt technology, diverting the equivalent of 25 million flexible pouches from landfills. Dow sees demand for this technology growing throughout the Asia-Pacific region – where plastic roads have already been constructed in Thailand, the Philippines, and Vietnam – and the chemical maker is also piloting the technology in cities across the U.S.
An emergent supplier is Lockerbie, Scotland-based asphalt specialist MacRebur, which offers three different types of pellets – which vary in durability and pliability – that it sells into the international asphalt market. Each kilometre of road laid with its pellet mix uses up to the equivalent weight of 740,541 single-use plastic bags, company officials said, and one tonne of MacRebur mix contains the equivalent of 80,000 plastic bottles. The firm has paved roads throughout the U.K. – including a project in June 2020 that involved repaving a major road in Carlisle, in the North West of England – and has also taken part in projects as far afield as New Zealand, Australia, and South Africa. The company’s first project in the U.S., at the University of California at San Diego early last year, involved paving a small test area in front of a graduate housing complex, and the university may introduce the plastic asphalt throughout the campus if it proves viable. MacRebur already has a facility in San Diego, and now is finalizing plans for a new plant in Tampa, Fla.
Also in California, another paving company is responsible for a pilot project in July 2020 that repaved three lanes on a 1,000-foot section of highway in the town of Oroville using recycled asphalt pavement and liquid plastic from single-use plastic bottles – the first time the California Department of Transportation (Caltrans) has paved a road using 100 per cent recycled materials. Developed by Redding, Calif.-based TechniSoil Industrial, the process employs a recycling train of equipment that grinds up the top three inches of pavement and mixes the grindings with a liquid plastic polymer binder, which comes from a high amount of recycled, single-use bottles. The new asphalt material is then placed on the top surface of the roadway, eliminating the need for trucks to bring in outside material for a paving operation. Caltrans is testing the material for later use throughout the state.
Coupled with the advocacy and support of paving associations like NAPA and NCAT, the industry continues to evaluate the expanded use of RPM asphalt mixtures as a means to promote sustainability and demonstrate a second-life application for recycled plastics. The Washington, D.C.-based Plastics Industry Association has committed to work collaboratively with its member companies in partnership with NCAT on the “New End Market Opportunities for Film Asphalt” project. The first of several projects from the association to explore RPM asphalt was initiated in November 2020, when Dutch multinational chemical company LyondellBasell used recycled PE – the equivalent of 71,000 plastic retail bags – to pave 2,885 square yards of the LyondellBasell Cincinnati Technology Center parking lot in Ohio.
At present, there are over 200 field projects using recycled plastic in asphalt pavements throughout the world. Many of these projects are only a few years old, which means the long-term durability of the pavements have yet to be determined, but one thing seems certain: As the asphalt industry advances and makes strides to become more sustainable, recycling post-consumer plastic into asphalt pavement mixtures is, increasingly, the responsible action. “The ability to use recycled plastic in asphalt could address two of our most challenging problems: the plastic waste crisis and our aging infrastructure,” Carla Toth said.
Which means it’s the end of the road for a lot of waste plastics