Asphalt with recycled plastic may last longer
Asphalt mixed with recycled plastic resists wear better. Does the plastic it contains get released again as microplastics?
(Image: Georgii Shipin / Shutterstock.com)
Researchers at Pennsylvania State University (Penn State) found that asphalt mixed with recycled plastic lasts longer as a road surface than conventional asphalt. The scientists believe the more durable pavement releases fewer plastic particles as microplastics over its service life.
Penn State researchers added low-density polyethylene (LDPE) to asphalt by mixing the plastic with aggregate, reclaimed asphalt pavement (RAP) and a binder to hold the material together. The basic idea is to reuse plastics on a large scale and keep them out of landfills. The plastic could also improve asphalt’s properties, the scientists write in the study “Microplastics release from recycled plastic modified asphalt: Detection, characterization, and environmental implications”, published in the Journal of Cleaner Production.
Stress tests
In the lab, the researchers ran two tests on the new asphalt to determine how well it holds up under sustained traffic loads. They also tested how weather affects the material and whether the plastic particles are released again as harmful microplastics over its service life. In the “Hamburg Wheel Tracking Test”, steel wheels roll over asphalt samples immersed in hot water. This is designed to simulate traffic loads along with heat and moisture. In the “Moisture-Induced Stress Tester”, the asphalt was exposed to high heat, moisture and repeated hydrostatic water pressure. After the tests, the scientists collected particles released by these forces and analyzed them for plastic content.
The testing method used was labor-intensive. First, the researchers created a reference library from the chemical signatures of the original asphalt components. They measured the size of the wear particles using infrared imaging and compared them with the chemical reference materials. This allowed the team to identify particles resembling the LDPE in the original asphalt. To compare the samples, the scientists calculated the total surface area of the identified LDPE-like particles relative to the weight of the asphalt tested.
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Penn State researchers found that asphalt mixed with recycled plastic held up better and produced less wear overall than the same asphalt without LDPE. Based on this property, the scientists conclude that little microplastic is released under stress in general, too. However, the researchers say a field study with stress tests under real-world conditions is needed to draw precise conclusions. They therefore cannot yet rule out the possibility that more LDPE plastic is released as microplastics.
(olb)
