Investigating the potential release of microplastics from recycled plastic modified asphalt pavement

Due to the ever-increasing volume of plastic waste, researchers are exploring alternative end destinations for recycling and repurposing, with civil infrastructure systems seen as promising hosts. One area that has seen exponential growth in research interest is Recycled Plastics Modified Asphalt (RPMA) pavement. Despite significant progress in this field, several issues remain relatively underexplored, including the potential release of microplastics from RPMAs under stress conditions. This study attempts to help bridge this gap. RPMAs and control asphalt pavement samples were prepared in the laboratory and mechanically tested using standard performance tests, including the Hamburg Wheel Tracking Test (HWTT) and Moisture-Induced Sensitivity Test (MiST), to simulate long-term aggravated service conditions. RPMAs used an agricultural Low-density Polyethylene (LDPE) as the modifier. Leachate solutions with debris from these tests, along with background solutions and samples of raw materials, were screened for microplastic presence using Laser Direct Infrared Imaging (LDIR) and Attenuated Total Reflectance (ATR). The analysis revealed a variety of polymeric and non-polymeric particles across all tested samples. However, the quality of identification and the percentage of polymeric particles generally remained low. Pervasive polymeric background contamination, coupled with challenges in spectral similarities between different ingredients, complicates efforts to definitively determine whether RPMAs specifically released microplastics, as various types of polymeric particles were detected and identified in the control samples as well. Future studies are recommended to implement more rigorous contamination controls and to incorporate complementary analytical techniques to improve identification confidence.