Pursuing a different approach, PlasticRoad in the Netherlands avoids traditional asphalt altogether. In 2018, the company completed a 100-foot pilot project in Zwolle, billed as the world’s first recycled plastic bike path. A second one followed in Giethoorn. Cheap to produce and easy to install, these paths are built with hollow modules made of single-use discarded plastics. In Ghana, Nelplast mixes shredded plastic waste with sand and molds the mixture into pavement blocks.
In India, where 50 percent of the country’s roads were unpaved only a few years ago, as many as 14,000 miles of new roads have been installed since India’s Minister for Road Transport made it mandatory, in 2016, to add waste plastic into bituminous roads. India’s plastic road technology grew out of experimentation done in 2001 by R. Vasudevan, a chemistry professor at the Thiagarajar College of Engineering in Madurai.
Recognizing the similarities between plastic and bitumen, both derived from petroleum, he mixed shredded plastic with gravel, then bitumen, and saw a good bonding effect. Vasudevan’s method reportedly employs two types of plastic: LDPE, or low-density polyethylene used in plastic bags, and PET, polyethylene terephthalate, used in soda bottles. MacRebur’s McCartney recalls being in India in 2016 and noticing people repairing potholes by plugging them with plastic bags and lighting them on fire. It gave him the idea behind MacRebur.
How environmentally friendly are plastic roads? One concern is that heating plastic for making asphalt can create carbon emissions, thus negating any emissions savings from using less bitumen. Vasudevan says that for his own method, it’s only necessary to heat plastic to 170 degrees Celsius (338 degrees Fahrenheit), which is well within a safe range.
“Plastics, as they’re heated, go from solid to liquid to gas, and it’s only above 270 degrees C — when they’re at their gassiest — that they release gases,” explained Troutman, who is also an environmental scientist. McCartney calculates that for every ton of bitumen left out of asphalt, as much as a ton in CO2 emissions is saved, since less petroleum is heated for bitumen’s extraction. The processing of petroleum-based asphalt is responsible for sizable greenhouse gas emissions each year.
If we keep pumping out more and more plastic, we’ll never be able to manage it in a sustainable way.
Another concern about plastic roads is that they will shed microplastics. No one has yet reported that this has occurred, and those interviewed for this article say they don’t see microplastics as a problem.
“Road material is relatively inert, a solid block of asphalt,” noted Troutman. “In fact, the largest source of microplastics on the planet is abrasion of tires.”
Last summer, a pilot project in California drove home just how much rigorous testing has to occur before a road, if paved with a novel material like plastic, is deemed drivable and safe, especially a major highway driven over by big rigs with heavy loads. Highway 162 in Oroville was in the headlines last August when Caltrans, the California Department of Transportation, working with TechniSoil Industrial, which supplied the liquified plastic, paved a 1,000-foot test strip.
It was Caltrans’ first time using this new approach. “I hate plastic,” said Tom Pyle, who heads Caltrans’ Office of Asphalt Pavement Program. “I won’t even drink out of a plastic bottle — and if there’s a way of using waste plastic to make a road last longer, let’s do it.”
Their machines went out, ground up the top layer of old road, turned it to gravel, mixed in PET from recycled soda bottles — which has the consistency of “Gorilla Glue,” Pyle noted — and lay the mixture back down. No extra gravel or bitumen was used. Later, an engineer checking the job sent word that the new surface “moved” and felt unsafe. Caltrans ended up replacing it with traditional asphalt. “That was our first trial section for plastic,” said Pyle. “We didn’t want any accident for any reason to taint the goal of building a plastic road.”
Far from being deterred, Caltrans likely will install another test section in Oroville next spring. Pyle said that they will use new construction methods and aim for “higher strength.” “We don’t yet know how thick this material needs to be to carry thousands of trucks a day,” he said.
Troutman views plastic roads as “a promising advance,” especially in a country like Ghana with a backlog of road projects. And yet, with the looming prospect that by 2050 the world will produce over three times as much plastic waste as it ever has, she stresses the importance of Ghana’s curtailing all unnecessary use of new plastics. “That’s the first step,” she noted. “If we keep pumping out more and more plastic, we’ll never be able to manage it in a sustainable way.”