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 U.S. 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 set 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 U.S.’s aging transportation infrastructure. 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 objective of this
research is to evaluate the impact 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.
Currently, the use of recycled plastics being
used to improve the performance of asphalt mixtures is being marketed as a
solution to help stem the plastic waste issue worldwide. While marketing is
being conducted, there is little to no scientific research which backs up the
current claims. In the near future, state and federal agencies may be prompted to make decisions on the use of RPM asphalt binders and
mixtures without adequate data to support their decisions. This research
project will provide agencies with the data they can use to decide if RPM
asphalt is a viable option for use on their highway infrastructure.
Standard asphalt mixture design specifications may need to be altered to
include the use of recycled plastics. A new standard which include acceptable
plastic dosage rates may need to be developed. Currently, the National Asphalt
Pavement Association and the Asphalt Institute have a joint task force
evaluating this work. This group should be included in the coordination to ensure that industry
understands the research implications on operations. This research will also
need to be followed with field projects and evaluations on worker health &
safety, long-term field performance, environmental impacts of milling RPM
asphalt mixtures, plant emissions from RPM asphalt mixtures, and recyclability
of RPM asphalt mixtures.
A number of 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 so many variables and modifiers that it 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 indicate 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.
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 international 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, it does not appear to be a cohesive, well thought out plan to
answer the many questions raised about recycled plastics in asphalt.
The objective will be met
by completing the following tasks:
Develop a work plan for completing Tasks 2
Conduct a literature review of current and past
research related to the use of recycled plastics in asphalt mixtures. This
review should include both laboratory and field studies which provide a clearer
understanding of RPM asphalt mixture performance.
Write an interim report including the results of
Tasks 1 and 2.
Determine the impacts of recycled plastics on
the rheological stability properties of asphalt binders. This work should
evaluate the impacts of binder source, plastic dosage rate, and stabilizer,
cohesive and adhesive properties, and aging on rheological and stability
Determine the impacts of recycled plastics on
the mechanical properties of asphalt mixtures using RPM asphalt binders and RPM
asphalt mixtures where the plastic was introduced using a dry process. At a
minimum, these mixtures should be evaluated for low temperature cracking,
fatigue cracking, top-down cracking, rutting, and moisture susceptibility
Develop a best practices manual for handling and
using recycled plastics in a laboratory setting. If Tasks 2 through 5 warrant
it, consideration should be also made on handling and quality control of the
incoming RPM streams.
Produce 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.
Materials and Design
Engineers will be responsible for using the research results. Specifications may need to be modified or
changed for the use of this material. Most
DOT’s have the capability within their own organizations to modify or changes
specifications upon the receipt of new information or research results. AASHTO COMP is ready to review the results of
this and make necessary changes in its standards if necessary.
|Sponsoring Committee:||AFK10, Critical Issues and Emerging Technologies in Asphalt
|Research Period:||Longer than 36 months|
|RNS Developer:||Richard Willis, PhD, Vice President for Engineering, Research, and Technology, National Asphalt Pavement Association|
|Source Info:||Dr. Samuel Cooper III, (LADOTD), Erich Biehl (Ohio DOT), Dr. John E Haddock (Purdue University), Dr. Jean-Pascal Planche (University of Wyoming, WRI), and Harold “Skip” Paul, Retired LTRC Director |
Proposed Problem Monitor - Samuel Cooper III, Materials Research Administrator, Louisiana Transportation Research Center, Louisiana Department of Transportation and Development and members of AASHTO COMP TS 2d.
Submitted October 2019 to AASHTO COMP Samuel Cooper III, Louisiana Department of Transportation and Development, Oak Metcalf, Montana Department of Transportation, Derek Nener-Plante, Maine Department of Transportation, and Eric Biehl, Ohio Department of Transportation
|Index Terms:||Mechanical properties, Recycled materials, Plastics, Bituminous binders, Asphalt mixtures, |