Microplastics Generated from Recycled Plastic Modified Asphalt Pavement: Method Development and Laboratory Evaluation

The use of recycled plastics in asphalt pavements, known as recycled plastics-modified (RPM) asphalt, has attracted attention for its potential to enhance the sustainability of asphalt pavement and reduce plastics waste. While research has been focused on RPM asphalt performance, little is known about its potential to shed microplastics over time. As awareness of microplastics pollution grows, concerns have arisen about this. However, analytical methods related to microplastics are not standardized and many are not well-suited for application to microplastics generated from RPM asphalts. This study is intended to address these knowledge gaps: an analytical method was developed to identify and quantify microplastics generated from RPM asphalts and used to collect preliminary data on the presence of microplastics in artificially abraded RPM asphalt material. Cantabro testing was performed on material from two RPM mixtures containing polyethylene (P1) and polyethylene terephthalate–based (P2) additives. These samples were analyzed using a thermogravimetric analysis–Fourier transform infrared (TGA-FTIR) spectroscopy technique. Results showed median P1 microplastics concentrations ranging from 1.6 ± 4.5 mg/g to 7.25 ± 6.9 mg/g, depending on particle size. The laboratory-based approach used is replicable but would require further adaptations for application to field-collected samples. The results suggest that future enhancement of the analytical procedure should include additional sample preparation and the replacement of FTIR spectroscopy by mass spectrometry to better differentiate polymer types present in a sample. Ongoing research will investigate application of these enhancements to the analytical method and apply them to samples of stormwater runoff and sediment collected from RPM asphalt sites.