Demystifying Science | Plastic in Asphalt

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There is a lot of promising work on the subject. So much so that there should be plastic in asphalt within a few years.

In an interview, Alan Carter, an asphalt engineer at the École de technologie supérieure (ETS), points out that engineers around the world are currently evaluating the addition of plastic to “coating” (also called bitumen or asphalt) to help stop plastic pollution. “There are still things to check, but it’s promising.”

Plastic asphalt will be operational within a few years, but because changing industry practices and government tenders takes time, Carter expects it will be a decade before the first such resurfacings are seen.

Carter said adding plastic to asphalt could use up all of the plastics in certain categories that are sent to landfills in Canada. This asphalt would contain less than 3% plastic, by weight.

What problems remain to be solved?

Other points that are still being researched: the possibility of microplastics leaching from the asphalt, the possibility of reusing the plastic-asphalt mixture (as is currently done for asphalt) and the impact on asphalt of the hardening of the plastic over the years, which makes it more fragile.

Preliminary results on these points, particularly at the ETS, are encouraging, Mr. Carter reports.

His work stems from a request from the Gaspésie authorities, who are responsible for plastic recycling for a wider region.

The temperature factor

You can’t mix all plastics because they melt at different temperatures. “Some melt at 100 degrees Celsius, while others are still rigid at 200 degrees,” Carter says. If you heat some plastics too much, they can burn. And asphalt shouldn’t be heated above 170 degrees because it can be damaged.

Some plastics, such as soft drink bottles, are easy to recycle. “We are mainly targeting soft plastics, such as single-use bags or plastic textile bags.”

Plastic also tends to separate from the rest of the asphalt, which complicates the situation. To eliminate this problem, researchers at the Northern Alberta Institute of Technology (NAIT) are relying on a wax made from plastic by an Ontario company, Greenlandplast.

“It seems to improve stability a lot in all temperatures,” says Adetoyese Oyedun of NAIT. Greenlandplast already uses its plastic wax to make shingle tiles for roofing.

The Australian model

The world leader in incorporating plastic into asphalt is Australia, Carter says. “They were the first to fund a research program. It’s certainly more interesting because it rarely gets very cold there.”

Filippo Giustozzi of the Royal Melbourne Institute of Technology (RMIT) confirms the Australian lead. “With some plastics, the ageing of asphalt is even slowed down, because they act as a sunscreen,” adds Mr Giustozzi, author of the book Plastic Waste for Sustainable Asphalt Roads, published in 2022.

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