In an attempt to be the greenest city in the world by 2020, Vancouver is trying out some ways to cut greenhouse gas emissions and boost energy efficiency. One of the projects the city has taken on is paving its roads with recycled plastic-containing asphalt. City engineers have come up with a special process that allows recycled plastic to be used in the mix and it has proven to reduce air pollution in the city.
The process converts 100 percent post-consumer recycled plastic content into a wax that can be combined with partially reclaimed asphalt at lower temperatures than traditional asphalt mixing. The lower temperature saves energy and emissions -- the trials have shown a 20 percent reduction in gas used for heating asphalt mix.
"Warm mix asphalt is not all that new, but what is unique in our application is using a wax that was derived from recycled plastics," Karyn Magnusson from Vancouver's Engineering Services told Gizmag. "We have been trialing warm mix since 2008 with different kinds of additives designed to reduce the viscosity to make placement easier at lower temperatures. We have now paved three sections of Vancouver roads with this latest trial."
"The mix was a 19 mm Superpave, surface coarse warm-mix, with 20 percent reclaimed asphalt pavement and wax derived from blue box plastics," said Markovic. "The temperature was reduced from our typical 320°F [160ºC] to 250°F [121ºC], there's a significant reduction in VOC and CO readings at the plant, and visible reductions in fumes at both the paver and the plant."
Another benefit of this new process is that the recycled plastic wax helps to prevent the aging of the oils in asphalt, which means the recycled plastic containing asphalt could be re-used in greater amounts than conventional asphalt. Also, the lower temperatures of the warm mix allow for higher percentages of recycled asphalt than a high temperature mix.
Vancouver will pave more roads with the recycled mix in the spring and continue testing its performance. If it continues to show the benefits of the initial trials, the city plans to use the special mix exclusively. The city also plans to find a way to make the wax locally from its own plastic waste. Right now a company in Toronto is supplying the wax.