Mechanical Properties of Laboratory Produced Recycled Plastic Modified (RPM) Asphalt Binders and Mixtures

In late 2016, media reports and online networks began generating an interest in the possibility of using recycled plastic waste in asphalt mixtures. The idea was marketed as an opportunity to simultaneously improve the quality of asphalt pavements and help address the issue of waste plastic in cities, towns, and waterways across the United States. While magazine articles and videos have trumpeted positive impacts of using recycled plastic modified (RPM) asphalt, such as increased service life and reduced need for polymers to modify asphalt binders, and while preliminary research suggests some of these benefits maybe realized, a full program of research to confidently back these claims is lacking. The current waste plastic challenge is a critical concern; however, there is equal concern about the current state of the aging transportation infrastructure in the United States. Investment in our system must focus on delivering long-lasting, high performing pavements as cost-effectively as possible. This research will be used to assess the feasibility of using RPM asphalt as a sustainable solution for improving both the performance of asphalt mixtures and reducing the amount of plastic waste in the United States. Several international papers have recently appeared extolling the virtues of using waste plastics in asphalt. Such “recycled” plastics can be included as a substitute for aggregates, as an aggregate coating, as an asphalt binder modifier, or some combination of the three. For example, Dalhat et al. (2019) used “Recycled Plastic Waste (RPW)” consisting of a mixture of low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS) as a partial aggregate substitute in asphalt mixtures. They also modified the asphalt binder with RPW. The experiment included many variables and modifiers and was highly confounded, but the authors did conclude that using recycled plastics in asphalt could enhance asphalt mixture rutting characteristics. Pre-coating aggregates with recycled plastics prior to their incorporation into asphalt mixtures has also been studied by researchers who have reported that recycled plastic materials tend to increase aggregate toughness, while decreasing water absorption. Asphalt mixtures containing plastic-coated aggregates have also tended to show improved asphalt mixture moisture susceptibility properties. Using recycled plastics as asphalt binder modifiers appears to decrease binder penetration and ductility and increase softening point and viscosity. Researchers have used such results to suggest the use of recycled plastics in asphalt binders would be good for areas that struggle with permanent deformation in asphalt pavements. These same authors are mostly silent about what such binder modification could do for pavement cracking, as stiffening binders will tend to increase cracking. Finally, when incorporated in asphalt mixtures, researchers tend to agree that recycled plastics appear to enhance an asphalt mixture’s mechanical properties, although Dalhat et al. (2019) are one of the few groups that have used more modern mixture test methods, such as determining dynamic modulus and flow number and using a wheel tracking test. Other researchers have used Marshall stability and flow to determine the merits of recycled plastics in asphalt, with experimental plans that are often lacking. While there does appear to be a mounting body of literature on the use of recycled plastics in asphalt, much of the work being reported has lacked a clear experimental plan and suffers from the use of dated test methods. Additionally, from a review of the literature, there does not appear to be a cohesive, well thought out plan to answer the many questions raised about recycled plastics in asphalt. The objective of this research is to evaluate the impact that recycled plastics—including but not limited to low density polyethylene (LDPE), high density polyethylene (HDPE), and polypropylene)—have on the mechanical properties of both asphalt binders and mixtures when added to asphalt binders using a wet process or asphalt mixtures using a plant-mixed or dry process. Accomplishment of this objective shall require the following tasks: (1) develop a work plan for completing Tasks 2 through 7; (2) conduct a literature review of current and past research related to the use of recycled plastics in asphalt mixtures that includes both laboratory and field studies which provide a clearer understanding of RPM asphalt mixture performance; (3) submit an interim report including the results of Tasks 1 and 2; (4) determine the impacts of recycled plastics on the rheological stability properties of asphalt binders by evaluating the impacts of binder source, plastic dosage rate, and stabilizer, cohesive and adhesive properties, and aging on rheological and stability properties; (5) determine the impacts of recycled plastics on the mechanical properties of asphalt mixtures using RPM asphalt binders and RPM asphalt mixtures where the plastic is introduced using a dry process by evaluating for low temperature cracking, fatigue cracking, top-down cracking, rutting, and moisture susceptibility performance; (6) develop a best practices manual for handling and using recycled plastics in a laboratory setting and, if warranted, for handling and quality control of the incoming RPM streams; and (7) submit a final report and hold a workshop with state agencies, the Federal Highway Administration, and industry to discuss the results. The final report will include changes to AASHTO asphalt standards if warranted.

Language

  • English

Project

  • Status: Proposed
  • Funding: $500000
  • Contract Numbers:

    Project 09-66

  • Sponsor Organizations:

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Harrigan, Edward

  • Start Date: 20200520
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01739632
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 09-66
  • Files: TRB, RiP
  • Created Date: May 18 2020 3:06PM