Junk in the Road: How Recycled Waste Is Turning Roadways Greener
Cities and companies are transforming plastic and even cigarette butts into asphalt admixtures and alternatives.
Beginning in the 1960s, rubberized asphalt — a mix of asphalt and crumb rubber made from recycled tires — began to be used as paving material for roadways. That new technology was a sustainability success as it made for better, quieter roads and recycled a problematic waste product. Currently, about 12 million tires are incorporated annually into American roadways.
Now, new paving technologies are getting set to make use of even bigger waste sources, such as single use plastics, with the potential for huge sustainability gains along with more durable roads that are cheaper to build.
A pilot project in Rotterdam will build a bicycle path out of modules made entirely from recycled plastic. The lightweight modules, currently in prototype, will be prefabricated in a factory, trucked to the site and assembled by cranes in a process that looks a lot like Lego blocks snapping together. The modules come with grooves, hollows and sockets that allow for the laying of cables and pipelines and the installation of light poles and traffic sensors. The plastic path is expected to be durable, lasting as long as 50 years according to Dutch construction company VolkerWessels. When the modules do wear out, they can be recycled again.
That project is just getting started, and questions remain about the performance of 100 percent plastic roads. But many new roadways are incorporating plastic waste in the same way rubber tires have been used for decades. For example, the city of Jamshedpur in eastern India collects plastic bottles and wrappers, shreds them and mixes the shreds with asphalt. It claims to have paved 50 kilometers (31 miles) of road with plasticized asphalt.
Cigarette butts are another promising source of cheap, durable aggregate material to be mixed into asphalt. Almost 6 trillion cigarettes are produced annually, yielding 1.2 million tons of toxic butt waste containing chemicals and heavy metals. Researchers at RMIT University in Melbourne, Australia, have demonstrated that the butts can be used in clay-fired bricks in ways that improve brick quality while safely containing the arsenic, cadmium, chromium and other metals found in butts. More recently, the team has incorporated cigarette butts into asphalt that can handle heavy loads while also reducing thermal conductivity.
Developing new sources of durable, cheap admixtures for asphalt is important because asphalt itself is a non-sustainable natural resource. As asphalt sources diminish, prices rise. Since 2003, asphalt prices have risen 200 percent compared with a 37 percent increase for concrete according to the Portland Cement Association. But asphalt roads aren’t going away anytime soon — about 90 percent of new roadways are still made with asphalt. Therefore, finding new, cheap, sustainable ways to increase the quantity of roadway asphalt while also extending roadway lifespans will continue to be a focus of modern roadway technology development.