Recycled Plastic Roads Essential to Reduce Asphalt Pollution

Polymer-based roads are becoming a reality, just in time to mitigate pollution released by extreme heat days.

A new effort to push plastic-based roads into the mainstream is underway in Staten Island, New York. A Scottish company, MacRebur, has been testing a process of adding recycled bottle plastic to asphalt for three years. Each ton of asphalt, they note, contains about 80,000 plastic bottles worth of plastic. 

The mix uses waste plastic, both commercial and post consumer, not recycled plastics. This is important, because it’s actually reducing the waste in landfills and oceans, not just juggling existing plastics.

Plastic Road Goes Down Like Asphalt

What makes the process appealing to road contractors is that it doesn’t involve a lot of retooling and retraining. The hot mix goes down just like asphalt. Typically, one of the big CO2 factors with asphalt is heating it to about 180 degrees Fahrenheit. The plastic is granulated so that it melts at about 120 degrees, requiring no additional heat.

A New York team is laying plastic-based asphalt test roads in Staten Island, New York.

“In simple terms, asphalt is made of bitumen and stone,” the company’s literature explains, “but with our technology, part of the bitumen can be extended with our mix – reducing the amount of fossil fuel used. We can do this because we are turning the plastic into its original oil-based state and binding it to the stone with the help of our activator.”

Other companies are also exploring plastic in roads, including Technisoil Industrial, in California. Bitumen represents about 10 percent of the typical asphalt mix, but it’s the petroleum-based, intensive component of asphalt. 

Electric Vehicles and Toxic Heating

As EVs become more common, the polluting aspect of asphalt is likely to rise in the public consciousness. At certain temperatures, such as when it is first put down, asphalt gives off toxic pollutants. In fact, some estimates put that pollution in excess of particles emitted by gas vehicles.

But the problem with asphalt offgassing may actually get worse, as extreme heat days become more common. This makes replacement of the bitumen even more urgent.

A study in California raised many troublesome findings. Researchers found that “the greatest amount of semivolatile organic compounds escaped when the (asphalt) pavement was heated to 140°C, (280°F) the temperature of road-paving, the team reports in Science Advances. Emissions fell as the asphalt cooled, but remained constant and significant at 60°C (140°F), a typical temperature for asphalt in Los Angeles during the summer, for the duration of the 3-day experiment. This suggests that asphalt could be a long-lasting source of pollution.”

As this chart shows, at temperatures in the 90s, asphalt can reach 140°F, at which point it becomes a significant air polluter. Source 

The use of waste plastics as a bitumen replacement is promising, to say the least. 

As testing continues, I would like to see data on plastic-infused asphalt to confirm that it has a lower level of offgassing than bitumen. Also, some types of plastic bottles have been shown to leach antimony at temperatures above 50°C. Antimony is metal-based additive that can have “acute and chronic” health effects if it gets into drinking water.  

With the right chemistry, however, perhaps plastic-based roads can become the new normal, and be recycled at the end of their lifespan.

Technical Data Effect of MR on Asphalt Fumes 

Technical Data Leaching of MR modified asphalt