Paving the road to a circular economy: Analysis of microplastic and plastic additive leachates from asphalt containing recycled plastics in Hawai'i

As support for a plastic circular economy increases, research aimed at recycling waste plastics into infrastructure is gaining momentum. On O'ahu, Hawai'i, a pilot project evaluated further modifying a standard polymer-modified asphalt (PMA) binder, typically prepared with the virgin co-polymer styrene-butadiene-styrene, with recycled post-industrial high-density polyethylene (HDPE) plastic. This study provides the first in-depth analysis of microplastic and plastic additive leaching from asphalt pavement containing recycled plastics. Three different asphalt mixes were tested: standard PMA binder, PMA binder further modified with recycled post-industrial HDPE pellets, and conventional (unmodified) binder modified with recycled post-industrial HDPE pellets. Triplicate high-purity water samples were collected for microplastic and plastic additive analysis following two mechanical performance tests (Moisture Induced Sensitivity Test (MIST) and Hamburg Wheel Tracker Test (HWTT)) and a simulated rainfall on a public experimental roadway. For microplastic analysis, water samples were filtered through 20 μm polycarbonate filters, density separated with a sodium polytungstate solution, and analyzed using micro-Fourier transform infrared spectroscopy (MIST and HWTT) and pyrolysis-gas chromatography/mass spectrometry (HWTT and Road). Results from laboratory testing show minimal HDPE particles leaching from all asphalt mixes, with no difference between the standard and recycled plastic mixes. Water samples from the experimental road are currently undergoing final analysis. To evaluate potential plastic additives (e.g., phthalates, flame retardants) and chemicals of concern (i.e., 6PPDQ and PAHs), water samples were subjected to solid phase extraction and elutions were condensed under a steady stream of nitrogen to await gas chromatography/mass spectrometry analysis. Our study provides novel methods to detect, characterize, and quantify microplastics and plastic additives leaching from asphalt roadways while contributing solutions to mitigate the deleterious effects of plastic waste on Hawaii's environment and beyond. Final microplastic and plastic additive quantification results will be presented. Also see: https://micro2024.sciencesconf.org/559041/document