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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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Suggested Citation:"1 Introduction." National Academies of Sciences, Engineering, and Medicine. 2023. Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities. Washington, DC: The National Academies Press. doi: 10.17226/27172.
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9 Plastics production and use in the United States and globally has increased steadily since the development and introduction of the first synthetic poly- mers more than a century ago (NASEM 2022). Today, plastics are ubiqui- tous in our society. As synthetic materials designed with an end application in mind, plastics offer unique qualities that make them materials of choice for many prod- ucts. Their material properties, such as stiffness, toughness, ductility, low weight, corrosion resistance, and biological inertness provide performance characteristics that make them attractive—in some cases, necessary—for a wide range of applications. Durability and low cost have also contributed to the expansion and use of plastics in industrial and consumer products. These advantages, however, also have contributed to the expanding use of plastics for short-term, single-use applications and the rapid growth of plastic debris in our waterways and oceans and on land. Less than 10 percent of the world’s plastic is recycled annually (OECD 2022). According to the U.S. Environmental Protection Agency (USEPA), plastics accounted for more than 36 million tons of waste in the United States in 2018, ap- proximately 12 percent of the total waste generated (USEPA 2022a). Only 3 million tons (8 percent) of that plastics waste was recycled. These statistics stand out against increasing interest in using recycled plastics in new manu- factured products. A growing number of industries, manufacturers, brands, and retailers are interested in using recycled plastic as feedstock, as long as the recycled materials meet the needed quality requirements. There are technical and practical challenges to increasing plastics re- cycling. An important factor is that there are numerous types of plastic, 1 Introduction

10 RECYCLED PLASTICS IN INFRASTRUCTURE and they have different chemical compositions and physical properties. Recycling requires plastics to be sorted based on certain properties such as melting point, density, thickness, and color. The plastic also needs to be decontaminated and reconfigured into pellets or flakes for future reuse. This processing can be complicated because different types of plastics can be found in the same waste stream and even in the composition of individual plastic products. One potential use for recycled plastics waste in infrastructure is in asphalt pavements; decades of research and pilot testing exist for this ap- plication. A 2021 literature review identified more than 200 field projects using recycled plastics in asphalt pavements, including projects on city streets, county roads, principal arterials, and airport runways, especially in Europe and India (NCAT et al. 2021). Most of these projects were con- structed for field testing, but some—especially in India—included full-scale deployment. In addition to interest in using recycled plastics in pavements, the literature review also revealed myriad other candidate applications in transportation and nontransportation infrastructure, including in drainage pipes, railroad ties, marine piles, plastic lumber, geosynthetics, and highway sound barriers. STUDY CHARGE House Appropriations Committee Report 116-452 (July 16, 2020) directed the U.S. Department of Transportation (USDOT) to enter into an agreement with the National Academies of Sciences, Engineering, and Medicine for a study on the use of recycled plastic materials in transportation infrastruc- ture. The report called for a study to identify domestic and international examples of transportation infrastructure projects that have used recycled plastic materials and projects in which recycled plastic materials have been incorporated into or used with other transportation infrastructure. The report further called for the study to review and assess • the effectiveness and utility of recycled plastic materials; • the extent to which recycled plastic materials are consistent with recognized specifications and standards for transportation infrastructure; • relevant impacts of recycled plastic materials compared to non- waste plastic materials; • the health, safety, and environmental impacts of recycled plastic materials on humans and animals; • the ability of recycled plastic materials to withstand natural disas- ters and extreme weather events; and • the potential economic benefits of recycled plastic materials.

INTRODUCTION 11 In passing the Transportation, Housing and Urban Development, and Related Agencies (THUD) Appropriations Act of 2021 (enacted on Decem- ber 21, 2020), Congress appropriated US$800,000 for the conduct of the study originally called for in the House report; however, the study scope was narrowed to focus on recycled plastics in asphalt (Conference Report Division L). Separately, the Save Our Seas Act 2.0 (SOS 2.0) (enacted on December 8, 2020) directed USDOT and USEPA to enter into an arrangement with the National Academies to conduct a study on the uses of plastics waste in infra- structure more generally. Thus, the study requirements in the THUD FY2021 and SOS 2.0 acts were nearly identical, but the latter legislation called for a broader examination of infrastructure applications that go beyond asphalt and transportation. Although Congress separately requested two studies, their similarities prompted USDOT and USEPA to combine them into a single National Academies study. Thus, in commissioning this study, the USDOT Office of the Assistant Secretary for Research and Technology and the USEPA Office of Resource Conservation and Recovery worked with the National Academies to develop the study task statement, shown in Box 1-1, to fulfill the requirements of both acts. It merits noting that the task statement, in response to USEPA interest, also calls for the study to consider the longer-term challenges associated with ensuring that plastic materials and their recycling methods are more conducive to the reuse of plastics in infrastructure. STUDY APPROACH AND SCOPE DECISIONS To conduct the study, the National Academies appointed an interdisciplin- ary committee consisting of 13 members with expertise in infrastructure performance, asphalt pavements, construction engineering, chemical and materials engineering, resource economics, plastic recycling and waste man- agement, plastics manufacturing, environmental engineering, life-cycle as- sessment, and sustainability. To fulfill its broad charge and inform its recommendations, the commit- tee organized its information gathering and analysis to focus on the following areas: 1. Providing an overview of the state of practice and research on the use of recycled plastic in infrastructure, including ˚ the research and deployment status of specific candidate applica-tions in transportation and nontransportation infrastructure; ˚ consistency of potential applications with recognized specifica-tions and standards;

12 RECYCLED PLASTICS IN INFRASTRUCTURE BOX 1-1 Statement of Task In response to requests from Congress, this study will identify domestic and inter- national examples of transportation and nontransportation infrastructure projects that have used recycled plastic materials. Based on an examination of these projects and a review of other relevant research and sources of information, the study committee will review and assess • the effectiveness and utility of the uses of plastics waste in infrastructure, including when it is incorporated into the asphalt mixes of pavements and other materials used in transportation and nontransportation infrastructure; • the extent to which plastics waste materials are consistent with recog- nized specifications and standards for asphalt and other infrastructure of different types and that are subject to different service levels and performance demands (e.g., strength, maintainability, service life, ride quality); • the health, safety, and environmental impacts of plastics waste on hu- mans and animals when used in transportation and nontransportation infrastructure; • the ability of infrastructure containing plastics waste to withstand wors- ening natural disasters, extreme weather events, and other hazards; • any other relevant impacts of plastics waste materials when used in asphalt and other transportation and nontransportation infrastructure; and • new material applications that could lead to the greater utilization of waste plastics in infrastructure and any potential economic advantage of using plastics waste in infrastructure. On the basis of this assessment, the committee will identify opportunities for repurposing plastics waste in infrastructure and the characteristics and qualities of the waste streams needed to enable cost-effective and safe applications that provide acceptable service and environmental performance when considered on a life-cycle basis. The study will consider options for better connecting the prod- uct design with end-of-use stages of the plastic life cycle, including new polymer options and approaches that reduce the impacts of plastics that enter the envi- ronment and that improve recycling of plastics through mechanical and chemical methods. In doing so, consideration will be given to the life-cycle impacts from repurposing plastics waste, including on greenhouse gas emissions and to the potential for infrastructure containing plastics in material to perform effectively under changing climate and environmental conditions. The committee may make recommendations, as appropriate, on additional research and demonstrations needed for the repurposing of plastics waste in infrastructure and on policy op- tions for furthering understanding and use of these materials in infrastructure. Informed by this assessment, the committee will take a longer-term view by considering how plastics recycling processes and upstream plastics manufactur- ing and product uses can be made more compatible with the recycling and re- purposing of plastics waste for infrastructure. The committee may choose to make research and policy recommendations with respect to these issues as appropriate.

INTRODUCTION 13 ˚ understanding of potential health, safety, and environmental im-pacts from these applications; and ˚ understanding of the ability of these applications to make infra-structure more resilient. 2. Employing a life-cycle approach for identifying the most promising opportunities for repurposing plastics waste in infrastructure and understanding characteristics and quality of the plastic streams needed to enable cost-effective and safe reuse in infrastructure with acceptable service and environmental performance. 3. Examining how plastics recycling processes and upstream plastics manufacturing and product uses can be made more compatible with the recycling and repurposing of plastics waste for infrastructure. As it pursued its work, the committee had to make a number of deci- sions about how it would define and use several common terms, including some contained in its charge, and how it would bound the study scope. These decisions and their rationale are explained next. Terms Used and Defined “Repurposing” means to adapt the use of a product, without transforming the product itself, to a new purpose that differs from its original applica- tion. Recycling, however, is the process of collecting and processing materi- als that would otherwise be thrown away as waste and turning them into new products (definition adapted from USEPA 2022b). To avoid confusion, the committee simply refers to the use of recycled plastics in infrastructure, as opposed to repurposing. The term “infrastructure” has taken on broad connotations and is now used for a growing number of systems. To clarify the applications described in this report, the committee adopted a definition of infrastruc- ture as the basic, large-scale physical facilities and networks (e.g., roads, ports, airports, drinking water and wastewater systems, buildings, electric transmission systems) needed to enable, sustain, and enhance society. The use of recycled plastics in infrastructure and related construction materials is an emerging market. Therefore, while the committee examined a wide range of research and trade literature and spoke with diverse researchers, manufacturers, and industry analysts, the exploration conducted is not ex- haustive of all the possible products and applications of recycled plastics. Beyond a focus on transportation infrastructure, the committee decided to examine an array of materials (e.g., construction blocks, lumber) used primarily in major infrastructure projects, while also in smaller-scale con- struction. For example, plastic lumber can be used for small-building and park infrastructure applications. However, the report does not include case

14 RECYCLED PLASTICS IN INFRASTRUCTURE studies or examples that do not apply to major infrastructure (e.g., applica- tions that are mainly for residential construction). The term “circular economy” has been used in a wide variety of set- tings, not always with a consistent meaning. As described in Chapter 4, circular economy is a combination of efforts to reduce, reuse, and recycle products (Kirchherr et al. 2017). However, in common practice, the term “circularity” refers mostly to end-of-life material capture and reprocess- ing/recycling for a new use (i.e., efforts to reduce are not considered). The committee decided to generally use the term circular economy based on the popular practice (i.e., materials use in a closed loop, with repeated use of recycled plastic). With that mindset, the committee concurred that increasing circularity of plastics by their reuse in infrastructure might be a worthwhile goal only if the circularity of other materials that are already recycled in large amounts (e.g., asphalt) is not impaired. Box 1-2 provides other definitions chosen by the committee for consis- tency of terminology and meaning of important terms in the report, while Appendix I provides a more comprehensive glossary of terms used in the report. Considering Recycled Plastics as a Resource For recycled plastics waste to be considered a resource for infrastructure, the committee presumes that the material must • exhibit the desired properties consistently, • be available in sufficient supply, • be cost-competitive with the related conventional or virgin plastic material, • be environmentally safe, and • be socially acceptable and permitted under the law. Starting from the plastics waste itself, the study examined only the potential use of thermoplastics1 waste in infrastructure. Consideration was not given to thermoset plastic wastes. Because of their material properties (i.e., thermosets harden upon heating and cannot easily be molded after their initial formation) and difficulty with their recycling, these plastics are not economical options for reuse in infrastructure applications.2 The 1 Thermoplastics are plastics that can be repeatedly heated and cooled without loss of structure. 2 Chapter 6 includes information on the lessons learned of the use of recycled tires in asphalt pavements. This is a limited use of recycled thermosets in infrastructure. In the United States, the use of recycled tires in asphalt pavements has been adopted only in Arizona, California, Nevada, and Texas.

INTRODUCTION 15 definitions and properties of thermoplastics and thermoset plastics are discussed in Chapter 2. While some thermoplastics such as expanded polystyrene are recyclable but not commonly recycled because of expense in doing so, reengineering of such plastic products could be done to make some of them more easily and economically recyclable. Chapter 8 discusses this issue. The committee considered both post-industrial and post-consumer re- cycled plastic streams as potential supplies of plastics waste. Each of these BOX 1-2 Definitions Infrastructure—The basic, large-scale physical facilities and networks (e.g., roads, ports, airports, electric transmission lines supplies, drinking water and wastewater systems, buildings, electric transmission systems) needed to enable, sustain, and enhance society.a Polymer—Chemical compound that is made of small molecules that are ar- ranged in a simple repeating structure to form a larger molecule. Polymers can be natural (e.g., silk) or synthetic (e.g., nylon). Plastics—Synthetic organic polymers made from petroleum products and other natural sources.b Microplastics—Plastics waste less than 5 mm in diameter.c Post-industrial recycled plastic—Plastic materials diverted from the waste stream during a manufacturing process that have never reached the end user.d Post-consumer recycled plastic—Plastic material diverted from waste prod- ucts that have served a previous consumer purpose (e.g., laundry detergent containers).d Recycling—Process of collecting and processing materials that would otherwise be thrown away as trash and turning them into new products.e Repurposing—Giving a new purpose or use to a given product.f a Derived from ASCE (2018). b For example, cellulose acetate and rayon start from cotton or wood. c Adapted from NOAA (2021). d Adapted from AASHTO M 294-21 2021. e Adapted from USEPA (2022b). f Adapted from Merriam-Webster. https://www.merriam-webster.com/dictionary/ repurpose.

16 RECYCLED PLASTICS IN INFRASTRUCTURE streams offers opportunities but also poses challenges for the end user of the recycled plastics, especially for post-consumer plastics. These issues are discussed in more detail in Chapter 3. Policy Issues and Their Relevance to Potential Actions The amount of recycled plastics waste in the United States is low when compared to the potential demand for it (Ravi et al. [see Appendix E]). Therefore, it is important to consider that the use of recycled plastics in infrastructure could divert resources from other important uses. The ques- tion of diverting recycled plastics from other high-value applications also prompted a series of recurring questions for the committee: • Does it make sense to use recycled plastics in asphalt roads and other infrastructure assets? • What value do recycled plastics bring to infrastructure? • How does use of recycled plastics in infrastructure affect performance? • How will public policies on plastics waste influence its recycling and reuse? Although not part of the scope of this study, assessing the most so- cietally valuable uses of recycled plastics is paramount for the effective use of this resource. From the perspective of using recycled plastics in infrastructure, the committee favored a perspective of life-cycle analysis3 and life-cycle cost analysis as the two key frameworks to support decision making. It is important to note that whether the use of recycled plastic in infrastructure is the optimum societal choice or not is dependent on many factors, including what problem is trying to be solved, such as reduction of plastics waste disposal in landfills, reduction of plastic debris in rivers and the ocean, or reduction of greenhouse gas emissions. Answers to these important policy questions can entail different and sometimes conflicting implications that life-cycle analysis can help evaluate. The questions need to be answered at a policy level. Without establishing the problem to solve, policy making will be challenging. This perspective was further reinforced through a series of discussions with experts held during the information- gathering phase of the study. In addition, two white papers were commis- sioned to examine frameworks for life-cycle analysis of use of recycled 3 Life-cycle analysis and life-cycle assessment are synonyms. While in the United States the term “life-cycle analysis” is commonly used, the ISO 14040 nomenclature is “life-cycle assessment.”

INTRODUCTION 17 plastics in infrastructure. These are presented in Appendixes G and H and include some detailed case studies. Global and U.S. Perspectives The committee looked at global issues, but the analysis—in particular, in- frastructure applications of reusing plastics waste—and recommendations are focused on the United States. Given market dynamics, upstream issues related to plastics generation, waste, and recycling—including sources of supply of raw materials for manufacturing, locations of demand for products, and so on—are more global in nature. Therefore, upstream issues are covered more globally both from the regional perspective as well as in product consideration and development. For example, when discussing issues of supply of and demand for recycled plastics for infrastructure, the committee had no choice but to consider the fact that the demand for recycled plastics in other markets could impact infrastructure applications. REPORT ORGANIZATION The remainder of this report is organized into eight chapters as follows: • Chapter 2 provides background information on plastics produc- tion, including types of plastics, and market drivers. • Chapter 3 starts with an introduction to plastics waste manage- ment in the United States and then reviews plastic recycling meth- ods and plastics waste availability and costs. • Chapter 4 provides a life-cycle assessment perspective on the use of recycled plastics in infrastructure and explores the impacts (i.e., benefits and costs) that need to be considered in deciding whether use of recycled plastics is the best option for this resource. • Chapter 5 provides an overview of policies relevant to plastics recycling and examines the impact of policy on plastics waste man- agement in the United States and supply for infrastructure uses as well as other competing applications. • Chapter 6 presents the state of research and implementation of several applications of use of recycled plastics in pavements, with a focus on asphalt, and identifies gaps in knowledge. • Chapter 7 describes the state of research and adoption of several applications of recycled plastics in infrastructure and identifies research and development needs. The chapter focuses on a limited number of nonpavement applications of recycled plastics use in

18 RECYCLED PLASTICS IN INFRASTRUCTURE infrastructure, centered on those high-volume applications that could advance use of meaningful amounts of plastics waste. • Chapter 8 provides an overview of ongoing research and develop- ment on new plastics and processes that will facilitate recycling of plastics waste in infrastructure and other applications. • Chapter 9 presents the recommendations from the study and their rationales. Appendixes E through H present white papers commissioned by the committee to support the study. Appendix D provides results of a survey of plastics use by state transportation departments; it was conducted in- dependently and presented to the committee. Appendixes D through H are cited at various places in the report. Appendix I provides a glossary of terms. Appendixes A and C provide information about the committee and the speakers who briefed the committee. REFERENCES American Society of Civil Engineers (ASCE). 2018. What Is Infrastructure? https://www. youtube.com/watch?v=wpvbVyUCi78 House Appropriations Committee Report 116-452. Departments of Transportation, Hous- ing and Urban Development, and Related Agencies Appropriations Bill, 2021. 116th Congress (2019-2020). https://www.congress.gov/congressional-report/116th-congress/ house-report/452 Kirchherr, J., Reike, D., and Hekkert, M. 2017. Conceptualizing the circular economy: An analysis of 114 definitions. Resources, Conservation and Recycling 127(Septem- ber):221-232. https://doi.org/10.1016/j.resconrec.2017.09.005 National Academies of Sciences, Engineering, and Medicine (NASEM). 2022. Reckoning with the U.S. Role in Global Ocean Plastic Waste. Washington, DC: The National Academies Press. https://doi.org/10.17226/26132 National Center for Asphalt Technology (NCAT), WRI, GHK, and Dow. 2021. Performance Properties of Laboratory Produced Recycled Plastic Modified (RPM) Asphalt Binders and Mixtures. Interim Report, NCHRP Project 9-66. https://onlinepubs.trb.org/Online- pubs/nchrp/docs/NCHRP9-66InterimReportwithAppendixFINAL.pdf National Oceanic and Atmospheric Administration (NOAA). 2021. What Are Microplastics? https://oceanservice.noaa.gov/facts/microplastics.html Organisation for Economic Co-operation and Development (OECD). 2022. Plastic Pollution Is Growing Relentlessly as Waste Management and Recycling Fall Short, Says OECD. https://www.oecd.org/environment/plastic-pollution-is-growing-relentlessly-as-waste- management-and-recycling-fall-short.htm Save Our Seas Act 2.0. 116th Congress (2019-2020). https://www.congress.gov/ bill/116th-congress/senate-bill/1982/text U.S. Environmental Protection Agency (USEPA). 2022a. National Overview: Facts and Figures on Materials, Wastes and Recycling | USEPA. https://www.epa.gov/facts-and-figures-about- materials-waste-and-recycling/national-overview-facts-and-figures-materials#Recycling/ Composting –––. 2022b. The U.S. Recycling System. https://www.epa.gov/recyclingstrategy/us-recycling- system

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In the U.S., most plastics waste is disposed in landfills, but a significant amount also ends up as litter on land, rivers, and oceans. Today, less than 10 percent of plastics waste is recycled in the U.S. annually. The use of recycled plastics in infrastructure applications has potential to help expand the market and demand for plastics recycling.

These are among the findings in TRB Special Report 347: Recycled Plastics in Infrastructure: Current Practices, Understanding, and Opportunities from the Transportation Research Board of the National Academy of Sciences, Engineering, and Medicine.

The report emphasizes that pursuing the recycling of plastics in infrastructure depends on goals, policy, and economics. To that end, life cycle economic and environmental assessments should be conducted to inform policies on plastics waste reuse.

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