The purpose of this study was to assess recycled plastic-modified (RPM) asphalt mixtures field trials constructed in Virginia. This study documented and evaluated the constructability and laboratory performance of two plant-produced RPM mixtures compared with the Virginia Department of Transportation (VDOT) typical D and E surface mixtures as reference mixtures. D and E refer to medium to high and high to extremely high traffic, respectively. No changes from the established routine practices in terms of surface preparation, plant production, or paving operations were reported. Moreover, this study attempted to detect and quantify the presence of microplastics in material generated from pavement wear that could potentially be mobilized via stormwater runoff. As RPM asphalt mixtures are novel materials, this objective includes the identification and development of appropriate laboratory analysis methods for microplastics. Overall, this effort is among the first and few to document findings and lessons learned regarding the incorporation of recycled plastic into asphalt mixtures through field trials.
The four mixtures were evaluated in terms of durability, dynamic modulus, resistance to rutting, and resistance to cracking using multilevel performance tests (basic, intermediate, and advanced). All the observations indicated that RPM mixtures can demonstrate similar durability and better rutting and cracking performance properties compared with D mixtures. However, the observations, when compared with E mixtures, suggest that the resistance to cracking might have decreased for RPM mixtures with long-term aging. Furthermore, representative samples of RPM mixtures were generated and subjected to solvent extraction and gradation, followed by thermogravimetric and infrared testing to assess and quantify (if possible) the presence of microplastics. Overall, the findings were that solvent extraction followed by thermogravimetric and infrared testing could be an effective method for identifying and quantifying discrete plastic particles present in artificially abraded RPM asphalt mixtures modified with recycled polyethylene. However, this extraction method is not suitable for RPM asphalt mixtures modified with Polyethylene Terephthalate-based additives. Furthermore, it is still uncertain whether these particles are released into the environment under typical wear and tear of the pavement.
The study recommends that VDOT consider allowing the use of RPM surface mixtures as another alternative for surface mixtures with D designation based on the laboratory performance of corresponding asphalt mixtures. As explained in the implementation section, a stakeholder group should develop a roadmap to address questions related to this recommendation. Because the sections evaluated in this study were placed in 2021, the 2-year performance data and corresponding observations are still considered preliminary. Continued monitoring of field performance will be needed to quantify more accurate benefits of including recycled plastics in asphalt mixtures compared with regular unmodified and styrene-butadiene-styrene-modified surface mixtures. The study also recommends additional field trials with RPM mixtures for further performance and benefit-cost evaluation, as well as life-cycle assessment. Furthermore, this study also recommends pursuing opportunities for research to apply the microplastic analysis methods developed during this study to field samples to investigate further the use of performance-based testing to design RPM mixtures and to explore necessary steps to repurpose plastic waste generated in Virginia and engineer it for responsible inclusion in asphalt mixtures.
The full report can be found here.
Supplemental files can be found here.