Infrastructure use of plastic waste is promising but challenging

  Image credit: National Academies of Science

The National Academies of Science July 2023 prepublication report, Recycled Plastic in Infrastructure, takes an in-depth look at how plastic waste can be recycled for use in transportation infrastructure. The results show promise, but a number of challenges must be overcome before progress can be made.

The study was mandated by the U.S. Congress. In response, the U.S. Department of Transportation (USDOT) and the U.S. Environmental Protection Agency (USEPA) asked the National Academies to identify:

• Opportunities for repurposing plastic waste in infrastructure,
• The characteristic and qualities of the plastic waste stream needed to enable cost-effective and safe applications that provide acceptable service and environmental performance, and
• How plastics recycling processes and upstream plastics manufacturing can be made more compatible with the recycling of plastics waste for use in infrastructure.                                                                            

The report noted the following possible uses of recycled plastic in infrastructure, “some of which have been considered for decades.”

• Concrete additives and aggregates
• Asphalt pavement mixes
• Railroad ties
• Marine piles
• Drainage pipes

To date, “only one product, drainage pipe (where recycled plastic feedstocks are being substituted for virgin plastic feedstocks), has generated significant demand.”

Each of the possible uses has potential downsides. For example, although plastic has been used extensively in asphalt in India, the specifications and standards are significantly different in the U.S. It raises questions about the “long-term material and structural performance, pavement recyclability, and the potential for release of microplastics from the pavement as it wears.” More research is needed to address these issues and others.

Four types of plastic are suitable

Ironically, despite the need for more recycling, the report noted that there are limited supplies of recycled plastic, which is not surprising given last year’s report by the Ball Corporation that showed many states with recycling rates that bordered on non-existent. Significant and reliable supplies of appropriate recycled plastics will be required if it is to be successfully used in transportation infrastructure projects.

Only four types of plastic have the physical and chemical properties “with minimal contamination” needed. Descriptions are from the State University of New York.

1. Polyethylene terephthalate #1 (carbonated beverage bottles, water bottles, heatable food trays)
2. High-density polyethylene #2 (noncarbonated beverage (e.g., milk) containers, grocery bags, household chemical bottles)
3. Low-density polyethylene #4 (squeeze bottles and flexible films, (e.g., trash bags, bread bags, dry cleaning garment bags))
4. Polypropylene #5 (straws, cups, yogurt containers, ketchup bottles, hangers, automobile battery casings)

Competition is stiff for available supplies

These four types of plastic have suitable melting points and service temperature ranges, chemical resistance, and strength to be used in infrastructure. Demand for these recycled plastics is competitive, however. Many non-infrastructure uses compete for the limited supplies, including bottles, carpet, and clothing. The report says, “it will be important, from a societal standpoint, to understand the full economic and environmental benefits and costs of candidate applications to make the best use of these supplies.”

Report Recommendations

The report made the following recommendations (summarized for brevity)

1. The USEPA should support the research and data collection that will be required to understand and evaluate each use’s potential environmental, human health, economic, and performance implications.
2. The USEPA should expand the means for tracking and modeling the supply of recycled plastic and the demand that is generated by different applications.
3. The USEPA should build out the general concepts and goals of the 2021 National Recycling Strategy for improved plastics waste management and reuse.
4. The USEPA should build on the tools and guidance offered in its Green Chemistry program.
5. The USEPA should take steps to encourage and facilitate more collaboration among plastic manufacturers, suppliers, recyclers, and industrial and infrastructure users.
6. The USEPA should work with members of the community of practice to identify specific policies and regulations that have been shown or hold promise, to support and incentivize plastics recycling in an efficient and equitable manner.
7. The USEPA should lead in strengthening interagency coordination of federal agencies.
8. The USDOT and the Federal Highway Administration (FHA) should build on existing efforts that are underway to support a multiyear field-testing program.
9. The USDOT should work with states in collaboration with the American Association of State Highway and Transportation Officials, local transportation agencies, and other standards-setting organizations.
10. The USDOT should, with the involvement of modal agencies, inventory all current and prospective transportation applications of recycled plastics.

While the National Academies report is an important effort, it also underscores a core challenge: many organizations, rule-setting options, and information-gathering efforts will be involved to assess how recycled plastics can be used for transportation infrastructure. And this is just one segment of the overall approach that must be investigated to come closer to a circular economy.