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Incorporating plastic waste into asphalt pavement and other types of infrastructure projects shows some limited promise, according to a new report published Tuesday by the National Academies of Sciences, Engineering, and Medicine.
But those efforts are hampered by an American recycling system that lacks clear economic and environmental goals and suffers from a dearth of scientific and engineering information, the chairman of the research committee said Monday.
“As we got into this, one question that came up to the committee is, ‘What problem are we trying to solve?,’” said David Dzombak, who chaired a panel of 12 experts tasked by Congress to look into ways to recycle plastic waste into roads, railroad ties, drainage pipes, utility poles and other common types of infrastructure applications. “Are we trying to keep (plastic waste) out of landfills? Or reduce litter or leakage into the environment that ends up in the ocean or along roads and rivers? Are we trying to reduce greenhouse gas emissions?
“Determining exactly which pathways to pursue, however, depends on goals, policy, and economics,” he said. “A coordinated direction for policy and research is key for advancement of plastics recycling in the U.S.”
The committee members included consultants, academic researchers and various state transportation officials. They looked into plastic recycling in infrastructure applications such as asphalt pavement mixes, drainage pipes, railroad ties, bike paths, composite utility poles and highway sound barriers. A range of factors inhibit their adoption, however, such as uncertainties over how to make the infrastructure components with recycled plastic and “unknowns regarding environmental impacts―including the potential release of microplastics―and effects on long-term performance.”
The report comes amid a growing awareness in the United States and throughout the world of a global plastics crisis, and as 175 nations have agreed to find a way by the end of next year to stop future plastic production from choking ocean and land ecosystems and clean up legacy plastic pollution.
The United Nations Environment Program in May reported that the world produces 430 million metric tons of plastics each year, of which over two-thirds are short-lived products that soon become waste. Plastic production is set to triple by 2060 under a “business-as-usual” scenario.
Two years ago, a different committee of the National Academies of Science, Engineering, and Medicine found that in 2016, the United States led the world in the generation of plastic waste at 287 pounds per person and needed a comprehensive strategy to curb the waste’s devastating impact on ocean health, marine wildlife and communities.
EPA has said the U.S. recycling rate of plastic is 8 percent; others have estimated it to be even lower.
The lack of national direction, Dzombak said, stems in part from the fact that the United States has no national recycling law. Recycling, according to the committee’s 407-page report, lacks coordination between public and private sectors, with recycling policies varying from state to state. Research and development into the capture, processing and reuse of plastic products and materials is also not very advanced in the United States, the report concluded.
But the report also found that it is in society’s interests to expand and standardize plastics waste collection, increase recycling and explore new applications for plastics waste in infrastructure, even as it outlined potential risks to public health and the environment by doing so.
“There is isolated activity that is very promising that is reusing recycled plastics, so there is reason for optimism here, if we can share more data and information,” said Dzombak, the Hamerschlag University Professor Emeritus at Carnegie Mellon University’s Civil and Environmental Engineering Department.
One economic segment the committee examined and found to successfully reuse waste plastic was the manufacturing of drainage pipes. But beyond that, the committee found little success, despite decades of attempts, according to the report.
As a result, he said, “it is unclear how much of a solution” integrating plastic waste into infrastructure applications will be to help solve the plastic waste problem.
The report found the most promise with the recycling of plastic waste from manufacturing processes, and said those plastics are in high demand. Unlike the mixed plastic waste people dump in recycling bins, post-manufacturing waste is more uniform in its chemical make-up and clean, making it easier to recycle.
Mixed plastic waste that people toss in their recycling bins consist of many different kinds of plastic, made with many different chemicals, and as a result are harder to recycle. This post-consumer waste can also be contaminated with other kinds of waste products or chemicals.
The report focused mostly on what’s called mechanical methods of recycling of plastic, involving cleaning, sorting and shredding of plastics before they are molded or added into new products. It also noted new industry investment in processes that seek to break down waste plastic into chemical feedstocks, often called “chemical” or “advanced” recycling, including a process called pyrolysis, but said its environmental benefits were “considerably lower than for mechanical recycling and may even be worse than the status quo.”
Turning products like old bottles, bags or yogurt tubs into a material that goes into asphalt has not been tested extensively, for performance or environmental risks, the report found. It may not hold up as well under the wear and tear of cars and trucks, and some research has found it could increase the spread of dangerous microplastics as the road surface breaks down, the report observed.
Judith Enck, founder and president of the environmental group Beyond Plastics and a former EPA regional administrator, said she has her doubts about whether plastics can be effectively recycled into roads or other infrastructure applications.
“While I appreciate work to try to make the best of a bad situation there are a number of serious problems with these attempted solutions to the growing problem of plastic pollution,” Enck said. “Perhaps the most significant is abrasion causing the release of microplastics into the air and water. I don’t see this as a viable solution to the plastics problem.”
The health and environmental implications of microplastics have become a focus of intense research as scientists have found them throughout the world and inside human bodies. In May, research out of the United Kingdom found that even the process of mechanical recycling can produce a lot of microplastics.
The new national academies report recommended the Department of Transportation conduct field-testing to assess the environmental and health impacts, overall service life and effects of plastics additives on the use and recyclability of asphalt pavements. It further recommended that EPA support research and data collection required to understand and evaluate the potential environmental, human health, economic and performance implications of each new use of recycled plastics.
“Given the limited supplies of recycled plastics having the requisite properties and quality for infrastructure applications, it will be important, from a societal standpoint, to understand the full economic and environmental benefits and costs of candidate applications to make best use of these sup- plies,” the report concluded. “Ideally, this understanding will be informed by assessments made on a life-cycle basis that take into account the stream of benefits and costs associated with the complete product life, including manufacturing, installation, maintenance, service life, and end-of-life management.”
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