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Suggested Citation:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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:"4 Life-Cycle Considerations." 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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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

65 Replacing the use of common construction materials and virgin plastics in infrastructure with recycled plastics requires consideration of the life- cycle implications of these material substitutions. Using plastics waste as feedstock to manufacture infrastructure components involves different supply chains, processing methods, and material properties compared to manufacturing with primary feedstocks. These differences have qualitative and quantitative implications for material flows, transportation, product performance and durability, product end-of-life management, product en- vironmental footprint, costs, and other aspects of the plastic product life cycle (see Figure 4-1). In this chapter, we outline the range of issues involved with performing life-cycle assessments of using recycled plastics in infrastructure and pro- vide a framework for conducting such assessments. Assessing the potential impacts of using recycled plastics in infrastructure components requires a systems approach that considers both direct and indirect consequences. This chapter examines the need to consider the relationship of the system to relevant inputs (e.g., raw materials and energy) and outputs (e.g., manu- factured products, co-products, and emissions). A holistic life-cycle assess- ment is needed to avoid overlooking important burdens or benefits within either the plastics system or the infrastructure system. Key questions that must be answered to frame such an assessment for use of plastics waste in infrastructure are presented and discussed. To supplement the outline presented in this chapter, Appendix G (Li and Lepech) provides a couple of case studies and Appendix H (Siriwardana 4 Life-Cycle Considerations

66 RECYCLED PLASTICS IN INFRASTRUCTURE et al.) describes life-cycle environmental benefits and trade-offs with a focus on pavement materials. LIFE-CYCLE ASSESSMENT OF RECYCLED PLASTICS USE IN INFRASTRUCTURE: BENEFITS AND COSTS The durability of plastics, which allows these materials to be integral to in- dustry, has led to growing concerns about how to deal with rapidly expand- ing amounts of plastics waste. Assessing the potential impacts of recycling this waste into infrastructure can best be done by utilizing a holistic systems approach that considers both direct and indirect consequences of any recy- cling program. This includes taking into consideration all the component processes of recycling and the associated impacts to planning, designing, constructing, and maintaining the infrastructure that uses recycled plastics. Recycling is often conceived in popular imagination as a simple process where materials are recovered and easily reused. In practice, the process is complex (see Box 4-1) and mediated by availability, challenges with col- lection and especially contamination and difficulty of separation, limits on functionality of reused materials, and the need for energy input in any manu- facturing (or remanufacturing) process. Furthermore, when considering re- cycling plastic into infrastructure (rarely an all or mostly plastic product) the potential impacts multiply given the complexity of the infrastructure system. FIGURE 4-1 Generic life cycle of infrastructure assets. SOURCE: Adapted from Merchan et al. 2017. RAW MATERIALS PRODUCTION PRODUCTS OPERATIONMAINTENANCE & MATERIAL RENEWAL CONSTRUCTIONENDOFLIFE

LIFE-CYCLE CONSIDERATIONS 67 From primary resource extraction to material manufacturing to use and disposal, both plastics and infrastructure have direct and indirect impacts on the economy and the environment. A change in one part of the life cycle (e.g., “disposing” of plastics in infrastructure) will have cascading impacts. A holistic, “cradle-to-grave” approach not only allows a more robust analysis than focusing on a single input or output, but it also provides an ability to identify key or critical points within the life cycle, as well as con- sequential impacts or feedback loops. External factors, actions, or policies may have consequential impacts on the viability of using recycled plastics. For example, the viability of future projects could be impacted by changes in policy directed toward the fossil fuel industry, or considerations of en- vironmental justice (EJ) (see Box 4-2). Another consideration is the impact of redirection of virgin plastics currently used in infrastructure if displaced by recycled plastics. Virgin plastics could be those coming in directly from petrochemical sources, or, as pointed out in Chapter 8, from redesign of plastics (existing and new plastics from nonpetrochemical sources) for use in infrastructure. There is not a single methodology that provides a systems approach for LCA. Rather, there are multiple components in a system, and each component may have an associated method that provides input into the system. For example, an assessment of the economics of plastics recycling in infrastructure may be impacted by a range of factors, including the focus (e.g., if it is technologically feasible, is it economically viable?), the breadth of assessment (e.g., is the assessment focusing only on a private outcome, like profitability, or a social outcome, like net social benefits?), or market BOX 4-1 Complicated Versus Complex Developing a consequentiala environmental life-cycle analysis (eLCA) or eco- nomic assessment of utilizing recycled plastics in infrastructure is a complex problem, in contrast to a complicated problem. While complicated problems can have multiple facets and complicated interactions, the outcomes of such prob- lems can be estimated with some degree of certainty. In contrast, with complex problems, the number of unknowns and the relationships between disparate sectors result in outcomes that cannot, as yet, be ascertained with a degree of certainty (Chester and Allenby 2019). Thus, the economic and environmental impacts cannot be fully estimated. a In contrast to attributional life-cycle analysis (LCA), which describes the environmentally relevant flows to and from a life cycle, consequential LCA describes how environmentally relevant flows will transform in response to possible decisions (Finnveden et al. 2009).

68 RECYCLED PLASTICS IN INFRASTRUCTURE characteristics (e.g., supply chain issues, or market power). Expanding the assessment to consider nonmarket environmental impacts of recycling in- creases the complexity of an assessment. Within environmental assessments, there is a range of approaches. For example, attributional environmental LCAs allocate a share of global environmental consequences to the prod- uct, while consequential assessments consider future market and economic impacts. Environmental life-cycle assessment (eLCA) is a process of evaluating the environmental impacts of manufacturing and using a product by taking into account both upstream (e.g., materials extraction) and downstream (e.g., disposal) impacts. One of the goals of eLCA is to avoid burden shift- ing1 between life stages or products (see Box 4-3). An environmental life- cycle assessment will further be impacted by the scope and boundaries of the assessment (e.g., is the disposal at the end of life of the infrastructure considered? How many years of use are assessed?). While uncertainty is considerable when LCA is used to try to pro- vide absolute quantities of environmental impacts, LCA is most useful in providing relative quantitative decision support for comparing options in cases for which the scopes and functions of the product systems are consis- tent. Consideration of the systems-scale impacts of recycling plastics into infrastructure requires looking at both the systems relationship to inputs (e.g., raw material supply) and outputs (e.g., net impact on greenhouse gas [GHG] emissions). For such an analysis, however, it must be recognized that there is currently little knowledge of the ultimate answers. What does exist is enough research and experience-motivated concern to know that 1 Burden shifting is defined as an action or policy that mitigates one environmental impact but creates another. BOX 4-2 Justice40 Initiative There is an increasing focus on environmental justice and community impacts from past and future projects. The Justice40 initiative of the Biden Administration (Executive Order 14008) requires 40 percent of benefits from covered programs to go to disadvantaged communities. Disadvantaged communities are defined based on several metrics, including health, economic, sustainability, equity, resilience, and transportation. To the extent that future programs will utilize re- cycled plastics in infrastructure, the Justice40 initiative could impact the location of activities related to some programs, based on either the benefits or the costs that could accrue to a community.

LIFE-CYCLE CONSIDERATIONS 69 BOX 4-3 An Introduction to eLCA Environmental life-cycle assessment is a process for evaluating the environmen- tal impacts of manufacturing of a product, taking into account both upstream (e.g., materials extraction) and downstream (e.g., disposal) impacts of the cre- ation and use of that product. eLCAs evaluate the environmental costs and ben- efits of a product against a range of categories (including climate change, ozone depletion, human toxicity, acidification, eutrophication, urban land occupation, and resource depletion) and their associated consequences (e.g., on human health, ecosystems, and resource availability). eLCA has been formalized by the International Organization for Standardization (ISO) and most commonly includes “production of materials, manufacturing of the studied product, use, recycling and waste treatment” (ISO 2006; SAIC 2006). In addition, the consequential impacts of the manufacturing of a product can be a very important part of a full environmental accounting, especially for larger products like infrastructure (Saxe et al. 2020). These consequential impacts are mediated through the market (e.g., requiring minimum plastic in infrastructure could change the economics of other parts of the plastics supply chain; the construction of new roadways incentivizes more driving and more pollution). eLCA historically focused on evaluating the environmental costs and benefits of consumer products (e.g., Coca Cola bottles). Over time it has been used to evaluate the impacts of a growing range of prod- ucts, from small goods to large systems (e.g., energy systems, transportation systems) (Guinee et al. 2011). The relative impact of plastic versus glass bottles for Coca Cola is widely identified as one of the first eLCAs in North America. Completed in 1969, Coca Cola found that plastic had advantages due to its lower weight (and the high pollution impacts of shipping in the 1960s) and the recyclability of plastic over glass at the time (Matthews et al. 2014). In the built environment/construction sector, early eLCA analyses focused on buildings, including whole building analysis and building components. Since 2000, eLCA of infrastructure projects has become more common. Life-cycle analysis to consider environmental, economic, and social impacts has also been introduced into pavement programs (FHWA 2019). A fundamental early step of eLCA is to define the goal and scope of the as- sessment. What is the question being asked? What are the spatial and temporal boundaries of the assessment being included? Formally, the goal of an eLCA includes establishing “the intended application, the reasons for carrying out the study, the intended audience, and whether the results are intended to be used in comparative assertions” (ISO 2006). The scope includes “the product system to be studied, the functions of the product system, the functional unit, and the system boundary.” For example, an eLCA with a 1-year horizon can come to different conclusions than one with a 50-year horizon, as they will capture differ- ences in maintenance, replacement needs, disposal impacts, and consequential changes. This is especially the case for infrastructure products that are long- lived. Detailed eLCA requires data gathering on each life stage of a product in scope from manufacturing to use to end of life. Carrying out an eLCA on an early-stage technology (e.g., most applications of recycled plastics in infrastruc- continued

70 RECYCLED PLASTICS IN INFRASTRUCTURE the questions matter. To achieve real-world benefits from the recycling of plastics into infrastructure a holistic assessment is needed to avoid over- looking important burdens or benefits within either the plastics system or the infrastructure system. This will require more research and experiments in the future to confidently establish answers to questions raised below. It is possible for well-intentioned changes in one part of a product system to have significant negative indirect impacts that completely wipe out or reverse the imagined benefit (e.g., land-use change [Searchinger et al. 2008] and water quality impacts [NRC 2008] related to biofuels). While there is a growing body of knowledge in the redesign of plastics, which could facilitate plastics recycling and increase the amount of recycled plastics available, the field is nascent (see Chapter 8). The eLCA methods in use at present (see Box 4-3) do not account for these uncertainties. FRAMING A LIFE-CYCLE ASSESSMENT FOR USE OF RECYCLED PLASTICS IN INFRASTRUCTURE: SELECTED IMPORTANT HOLISTIC QUESTIONS What Is the Problem? The foundational question for any LCA is “What is the problem we are trying to solve?” Plastic products and waste have attracted attention in part due to a range of unintended/undesirable impacts that accompany their use. At the start of life of a plastic material, the extraction and later conver- sion of fossil fuels into plastic results in pollution (e.g., GHG emissions). Zheng and Suh (2019) projected that plastics will account for 15 percent BOX 4-3 Continued ture) requires special considerations due to lack of scale, lack of data, and other uncertainties (Bergerson et al. 2020). In addition to the initial phase of defining the goal and scope of the assess- ment, ISO identifies three more phases of an eLCA: • Life-cycle inventory analysis involving data collection and estimation to quantify material inputs and outputs as well as the energy use associ- ated with a product system under study; • Life-cycle impact assessment involving the classification, characteriza- tion, normalization, and weighting of potential environmental impacts; and • Life-cycle interpretation, including the development of conclusions and recommendations based on the analysis.

LIFE-CYCLE CONSIDERATIONS 71 of global GHG emissions by 2050. At the end of life, landfilling of plastics occupies space for a long time; the plastic degrades slowly, meaning long- term storage is required, and pollutants can leach into soil, water, and air during degradation (Morath 2022). As discussed in Chapter 3, landfilling of plastics can also be viewed as carbon storage. A significant challenge with plastic is uncontrolled disposal (leakage), where plastic products and microplastics are not properly collected or controlled at the end of life and end up creating widespread pollution. Twelve million metric tons leak into the marine environment annually (de Oliveira et al. 2021; NASEM 2022). In contrast with controlled disposal of plastics, the manufacturing of primary plastics dominates life-cycle environmental impacts (Geyer et al. 2016). The consequences of leakage (e.g., plastic in the oceans) receive a lot of attention. Even within environmental impacts (e.g., GHG emissions versus land use and contaminations), preferable disposal options can vary (incineration versus landfilling) (Basuhi et al. 2021). The appropriateness of any solution, like recycling plastics into infrastructure, depends on if it addresses the relevant problem. A holistic assessment needs to be tailored to the question at hand. Definition of the end point of focus for plastics waste is critical to a holistic LCA. The plastic leakage end point is a problem of collection and waste management. A different end point for plastics waste (e.g., reuse in infrastructure) does not directly change waste collection but would indi- rectly rely on increasing the value on recycled products to incentivize more waste collection. If the concern is land use for landfilling, a different end point for plastics waste, such as use in infrastructure, may temporarily reduce the need to landfill plastics waste but likely only until the end of life of the infrastructure product, at which point it may result in increases in overall disposal needs, as mixed material products are harder to recycle (Tam and Tam 2006). Recycling plastics into infrastructure will reduce the impacts of pri- mary production of plastic only if it reduces the demand for virgin plastics. If used to replace other infrastructure materials (e.g., binder in asphalt), downward pressure on plastic production would not be expected, and the question becomes, “What is the relative impact of using recycled plastic compared to the other material it would displace?” Using current pro- cesses, sorting plastics waste emits 0.026-0.043 kgCO2e/kg, energy recov- ery emits 0.826-0.852 kgCO2e/kg, pyrolysis saves 0.01-0.05 kgCO2e/kg, and mechanical recycling results in GHG savings of 0.928-0.965 kgCO2e/ kg (based on assuming displacement of primary plastic production) (Basuhi et al. 2021). Environmental impacts will vary dramatically based on how recycling plastics into infrastructure changes the plastics manufacturing and disposal market. Furthermore, recycling plastic into infrastructure is an end-of-life solution to deal with plastics waste once it has already been

72 RECYCLED PLASTICS IN INFRASTRUCTURE created; it will not reduce the problem of too much plastics waste occurring in the first place. To reduce the environmental burden of end-of-life plastics waste, Basuhi et al. (2021) highlight utilizing waste heat from direct energy recovery, landfilling low-quality/contaminated plastics waste instead of in- cinerating it, and catalytic pyrolysis and better product design for recycling as key areas for intervention. To proceed in any holistic LCA the main problem requires definition, as it influences the scope of what should be included, as well as the temporal and spatial boundaries of assessment. For example, if the temporal scale is focused on plastics waste generation and management, any assessment might end once the plastics waste is recycled into the infrastructure. This focus, however, would overlook the potentially significant impacts on the infrastructure itself, suggesting that for assessment of recycled plastics in infrastructure, temporal assessments should be framed to be long and scaled to infrastructure timelines. What Is Being Replaced/Displaced? Recycling plastics waste into infrastructure can take many forms. Recycled plastics can be used in infrastructure products, like stormwater pipes, which are already often manufactured from plastics. Recycled plastic replacements for wood infrastructure products (e.g., rail ties, marine pilings) are another possibility, as is the use of recycled plastics as a binder in asphalt or ag- gregate replacement in concrete. The environmental impact of each of these replacements requires dif- ferent considerations. If displacing primary plastic with recycled plastics, the assessment can be narrower and more focused on the technical process of recycling and the quality of the plastic product after recycling. If the ap- plication displaces a nonplastic material, questions of relative impact, func- tion, and cost compared to the original material need further exploration. Limited research has explored the material displacement question for infra- structure components, but for packaging replacing a virgin material with a recycled version of the same material (e.g., a plastic bottle made of recycled plastic) the environmental benefits are correlated with recycled content and recycling generally has positive environmental impacts (Vendries et al. 2020). However, when recycled materials are used to displace a material of a different type (e.g., rock aggregate with plastic), the ultimate outcome often involves larger overall environmental impacts (Vendries et al. 2020). In agreement with this concept, recent research has shown environmental benefits when using an attributional life-cycle approach to assess the use of recycled plastics in asphalt to replace virgin plastic additives (Siriwardana et al. 2022, Appendix H). There is limited research on using plastics to replace

LIFE-CYCLE CONSIDERATIONS 73 nonplastic construction material, and few applications have been deployed past the laboratory scale or limited in-field piloting (see Chapter 7). How Does Using Recycled Plastics Affect Durability? For both economic and environmental assessment, the ultimate durability of infrastructure containing recycled plastics is a critical issue for consid- eration. Lifetime extension of infrastructure is necessary, for example, to reduce total material needs and associated environmental emissions (Hert- wich et al. 2019). There is limited experience with recycling plastics into infrastructure in practice (see Chapters 6 and 7; Siriwardana et al. 2022, Appendix H), and thus little experience with long-term performance of recycling plastic infrastructure products. In some cases, recycled plastic elements may be more durable than the nonplastic product they replace, in others much less. In instances where the use of recycled plastics reduces the viable service life of the infrastructure, the need for earlier replacement will dramatically increase cost and environmental impacts over time. In pave- ment and concrete applications, for example, the recycled plastic share of the material is small. If this small share of material causes early failure of the infrastructure product (e.g., early road resurfacing or reconstruction), the ultimate environmental and economic costs will be many times more than the hoped-for benefit of incorporating the recycled plastics in the first place. Some recent tests of plastics waste use in asphalt formulations for high- way pavement sections illustrate the importance of the durability question for LCAs. A test of highway sections containing recycled plastic pellets in asphalt in Argentina found generally good performance over 2 years but also total failure in one of the test sections. The authors hypothesized that the failures were due to unfamiliarity with the necessary construction prac- tices to work with the new material rather than an insurmountable material challenge (Angelone et al. 2022). Similarly, a test section of asphalt pave- ment formulated with inclusion of recycled plastics in California experi- enced significant function issues and was quickly rebuilt with conventional materials (Parson 2021). These experiences point to either major material challenges or major skill challenges in switching to road construction with incorporation of recycled plastics. At lower temperatures (e.g., 5°C), as- phalt with recycled plastics has been found to crack more and release more microplastics (Enfrin et al. 2022). Chapter 6 provides more information on the current state of research and practice for incorporating recycled plastics in asphalt pavements. Tests of other infrastructure components that incorporate recycled plas- tics also highlight the importance of the recycled plastics for durability. A review of 84 studies examining recycled plastic aggregate and/or fibers in

74 RECYCLED PLASTICS IN INFRASTRUCTURE concrete found potential durability impacts ranging from changes in water absorption of the concrete to greater shrinkage (Gu and Ozbakkaloglu 2016). A building cladding panel replacing 75 percent of virgin plastic with recycled plastic (by weight) could tolerate a 13-year reduction in service life (from 60 to 47 years) while maintaining a net GHG advantage (Li and Lepech [see Appendix G]). Experiments have shown both increased and de- creased properties of construction materials incorporating recycled plastic in the laboratory (Tang et al. 2020) and variable tolerances for reduced life service when balanced against upfront environment savings. Overall, the long-term performance and durability of recycled plastics in concrete, asphalt, and other infrastructure applications in development are unknown and in need of further research. See Chapter 7 for other uses of plastics in infrastructure and the challenges associated with performance, durability, and related information that could be considered when develop- ing an eLCA for nonpavement applications of plastics waste. What Happens to Infrastructure Containing Recycled Plastics at the End of Life? Infrastructure is, at best, a long but temporary stopping point along the life cycle of plastics. Modern infrastructure service lives are measured in decades, and eventually the materials containing recycled plastics will need to be disposed of or recycled again. The long-term impact on disposal of the overall infrastructure is a necessary consideration, particularly when the plastic is mixed with other materials. Asphalt pavement is one of the infrastructure products that has re- ceived significant attention for the potential inclusion of recycled plastics. Currently, reclaimed asphalt pavement (RAP) is one of the most recycled products in the United States, with 89.2 million tons (90.6 million metric tons) recycled in 2019 (Williams et al. 2020). This replaced an estimated 24 million barrels of virgin asphalt binder and 84 million tons of aggregate together worth US$3.2 billion and saving 60 million cubic yards of landfill space (Williams et al. 2020). It is not yet clear what effects the inclusion of recycled plastics will have on the recyclability or other disposal options of asphalt. However, the potential negative impact of disrupting asphalt recycling could be both economically and environmentally large. What Is the Impact of the Market on the Availability of Plastics? Life-cycle costs of any product depend not only on the environmental impacts (eLCA), but on the market conditions. This includes the supply of and de- mand for the good, but also characteristics of the market, including market structure, bottlenecks, or market power. The market for recycled plastics

LIFE-CYCLE CONSIDERATIONS 75 is no different. As the volume of plastics that must be either disposed of or recycled continues to grow in the United States and around the world, the impacts have also grown. Post-consumer plastics in municipal solid waste, litter, and, more recently, microplastics in the environment (Smith et al. 2022) are some of the factors with which society must now contend. Suggested solu- tions, including the use of recycled plastics in infrastructure, provide potential paths forward to reduce the burden, but the complexity of the market and potential barriers for successful economic solutions are substantial. Supply In economics, a market is often described as a mechanism to bring parties together to strike a price and quantity of a good for a transaction. The par- ties involved are those who produce the good (supply) and those who con- sume the good (demand). In the case of plastics, the supply is heterogeneous, including not only the different types of plastic but also the origin of the polymer (e.g., virgin, post-consumer, or post-industrial). The supply of plas- tics from each of these streams depends on the availability of the resource, recycling feasibility production costs, as well as the alternative opportunities. The availability of the resource (plastics waste) is not a barrier. While estimates vary, the U.S. Environmental Protection Agency (USEPA 2020a) estimates that more than 35.6 million tons of plastics waste were generated in 2018. At an aggregate level, about 8.7 percent (~3 million tons) of this plastic material was recycled, while approximately 75 percent was disposed of in landfills. The amount recycled varies greatly by type of plastic, as shown in Table 4-1. The percentage of plastics recycled, by type, in the United States de- pends on a number of drivers, including post-consumer and post-industrial recycling habits and incentives. Policies, the technical feasibility of recy- cling—including the collection and/or separation of plastics—as well as alternatives to recycling for waste management all play a role. Post-consumer, or residential, recycling focuses on the actions of house- holds. Do they recycle or not? Utilizing a national survey of the United TABLE 4-1 Percentage (by Weight) of Plastics Recycled by Type in 2018 Plastic Type PET HDPE PVC LDPE/LLDPE PLA PP PS Other Total % Recycled 18.5 8.9 NA 4.3 NA 0.6 0.9 26.7 8.7 NOTE: HDPE = high density polyethylene; LDPE = low density polyethylene; LLDPE = linear low density polyethylene; NA = not available; PET = polyethylene terephthalate; PLA = poly- lactic acid; PP = polypropylene; PS = polystyrene; PVC = polyvinyl chloride. SOURCE: USEPA 2020a.

76 RECYCLED PLASTICS IN INFRASTRUCTURE States, Saphores and Nixon (2014) found that 42 percent of the partici- pants did not recycle plastics, while 34 percent indicated that they recycled plastics more than 90 percent of the time. They found that socioeconomic factors were, for the most part, not statistically significant. The exceptions were that young adults (ages 18-29 years) tended to recycle less, as did African Americans. Rural residents were more likely to recycle all four materials included in the survey (glass, plastic, aluminum, and other met- als). The authors hypothesized that this may be due to lack of curbside recycling in many rural areas and so those households that do recycle, recycle everything. They also found that internal attitudes are important (e.g., perceived ease of recycling), suggesting that education may be of value. Finally, they found that policies that make recycling more conve- nient, like curbside recycling, may be more effective than policies focusing on the marginal cost of recycling, such as bottle deposits. These findings are relatively consistent with other work and suggest that there may be nu- anced factors in post-consumer recycling choices, which would need to be considered if large-scale increases in recycling are a desired outcome. For example, a recent Pew Research Center poll (Pew Charitable Trust 2019) found that 72 percent of respondents were reducing their use of single-use plastics because of their potential impact on the environment. When it comes to industrial plastics recycling, the drivers may be more profit based and may depend on the relative costs of disposal and recy- cling, the availability of a recycling market, or the policies in place. The technology required for a specific type of plastic can impact the cost and, consequently, the availability of that type of plastic. Whether or not recycling is available in a specific area, the feasibility of recycling may be impacted by the type of plastic, the collection method (which may impact the separation needed and the type of separation pro- cess), the recycling technology necessary (see Chapter 3), or the policies in place that impact recycling (see Chapter 5). The result is a cost for recy- cling, which, coupled with the market price for the recycled plastics, must be cost effective, relative to alternative disposal choices. Alternative disposal could include landfill or incineration. The average tipping fee2 varies across the United States by region. The Environmental Research & Education Foundation (2021) estimated that the ton-weighted average tipping fee ranged from a low of slightly more than US$38 in the South Central region of the United States (Arkansas, Louisiana, New Mexico, Oklahoma, and Texas) to more than US$72 in the Northeast (Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, 2 The tipping fee, or gate fee, is the fee charged by landfill owners or operators for the ac- ceptance of solid waste for disposal.

LIFE-CYCLE CONSIDERATIONS 77 Virginia, and West Virginia). The national average was about US$52. Not surprisingly, there is a correlation between recycling levels and tipping fees. In a study commissioned by the Ball Corporation, Eunomia (2021) found that 7 of the 10 top recycling states also had high disposal costs, suggesting that the trade-off between recycling and disposing of plastics in landfills is an economic decision. These factors all impact the availability of recycled plastics potentially available for use in infrastructure. From a societal perspective, there are potential benefits from reducing waste disposed of in landfills, but, as dis- cussed earlier in this chapter, those benefits must be weighed against any po- tential long-term environmental and social impacts of use in infrastructure. Demand The demand for plastics is the other side of the market equation. Demand for recycled plastics depends on the source and availability, the price, as well as alternative materials. As discussed in Chapter 6, a main focus of recycling plastics in infrastructure is in asphalt. At present, there is no de- finitive answer to the potential value of using recycled plastics in asphalt, specific to increased durability and/or the extension of functional life of the material. Another infrastructure application of recycled plastics is compos- ite railroad ties, which have been piloted as replacement ties in existing rail systems. Although more expensive than wooden ties, the total cost of wood harvest may somewhat offset the higher expense. However, as discussed in Chapter 7, the overall engineering performance, economic, societal, and en- vironmental impacts of using composite ties is not yet known. Furthermore, as discussed in an earlier section of this chapter, the total eLCA results and perspective remain unknown. The overall demand for recycled plastics was negatively impacted by China’s 2018 decision to greatly reduce its imports of recycled plastics. The new policy especially affected recyclers with relatively high levels of con- tamination, requiring them to do more sorting and raising costs (Brooks et al. 2018; Wen et al. 2021). This impacted the demand side of the market, reducing the value of recycled plastics. This, in turn, changed the dynamics for many locations, as their supply was no longer being demanded. The result was curtailment of many recycling programs. The current demand for recycled plastics in the United States remains uncertain. Changes in supply have resulted in shortages for some indus- tries that use those plastics and discouraging others from moving toward recycled materials. These factors all suggest that the use of recycled plastics in infrastruc- ture faces significant uncertainty in terms of the market and nonmarket (environmental) costs. If the infrastructure components that incorporate

78 RECYCLED PLASTICS IN INFRASTRUCTURE recycled plastics are found to be competitive with, or superior to, those made with traditional materials, from an economic perspective the cost to obtain the material will still be a consideration. Market Dynamics The above discussion on the supply and demand for recycled plastics is framed mainly from static analysis. However, as most technologies for using recycled plastics in infrastructure are still in the early stages, the dynamics of the system and the need for a holistic assessment cannot be overstated. Going back to the early market for plastics and their popularity, driven largely by durability and cost, there was little discussion of what would be done with the waste, and the general assumption was that plastics could be disposed of in landfills or incinerated. What was not adequately considered was the growth in the market and the environmental burden posed by the proliferation of plastics waste. Considering the current characteristics of the plastics market, includ- ing the relatively small amount of recycled plastic that is used within a “circular economy” (see Box 4-4), the challenge going forward may be to simultaneously model the cradle-to-grave benefits and costs of the entire system by (1) conducting economic modeling of the waste plastics market, which can be examined in a dynamic way using well-established comput- able equilibrium models, for example, and (2) carrying out eLCA model- ing that compares environmental impacts of different end-of-life options for plastics. The global market has a significant level of uncertainty of the potentially available supply, as well as competing demand. Policy choices made at local, state, or federal levels (see Chapter 5) may greatly impact future supply. Aggregate demand for recycled plastics will depend on the availability of recycled plastics, relative to virgin feedstock (which in turn may be impacted by the push toward green energy). And, finally, for re- cycled plastics in infrastructure, demand by other applications will impact price. Market characteristics adjust as circumstances change, suggesting an improved dynamic model of the market could provide improved informa- tion with which to make decisions. The overall outcome, however, cannot be considered without the incorporation of the nonmarket impacts from an eLCA. In an ideal world, a dynamic benefit-cost analysis (BCA) of plastics recycling into infrastructure would be completed. A BCA incorporates all relevant factors in the system developing the impacts in comparable units (dollars). Benefits or costs would be either direct (market) or indirect (nonmarket). And relevant costs would include the value of the next best alternative (an opportunity cost), as well as the cost associated with risk. Early benefit-cost studies often focused on the product design for ease of

LIFE-CYCLE CONSIDERATIONS 79 BOX 4-4 Circular Economy The concept of a circular economy is increasingly receiving attention as an actionable goal toward sustainability, which is often seen as too vague a goal or concept. Circularity is discussed in contrast to a linear economy, where virgin resources are turned into products, used once (or for one lifetime), and then disposed of. The circular economy is a combination of efforts to reduce, reuse, and recycle products (Kirchherr et al. 2017; USEPA 2022b). There is a hierarchy within circular economy efforts, with interventions earlier in the life cycle (e.g., reducing upfront manufacturing) having more of an impact than those later in the life cycle (e.g., post-consumer recycling). The figure below illustrates nine types of circularity interventions with rising levels of circularity. Colloquially, circularity is often used to refer mostly or only to end-of-life reprocessing/recycling; within this document the more holistic approach (e.g., as represented in the figure) is what is used. Care must be taken in discussing long-life products (like plastics and infrastructure) to differentiate the usable service life of the product from the temporal aspects of its persistence if released in whole or degraded form to the environment. Some argue that the plastics economy has characteristics that make it fundamentally not capable of being circular (e.g., Greenpeace 2022). The persistence of single-use plastics in the environment is a challenge to a circular economy; the long service life of well-designed/well-maintained infrastructure is not. SOURCE: The 9R Framework for the circular economy from Kirchherr et al. (2017) after Pot- ting et al. (2017). CC BY 4.0.

80 RECYCLED PLASTICS IN INFRASTRUCTURE recycling (e.g., Chen et al. 1994). More recent studies utilize variations of BCA, including environmental impacts. The majority of these studies are international. For example, Denne and Bond-Smith (2012) focused on the impacts of reduced waste in New Zealand, while Torkashvand et al. (2021) focused on the life-cycle costs of plastics waste in Iran. Denne and Bond- Smith (2012) conclude that market costs for landfill disposal do not lead to optimal levels of waste minimization and disposal if landfill charges do not reflect all the related costs borne by society and these are not charged at the time of disposal. Torkashvand et al. (2021) conducted a BCA com- parison of scenarios and presented financial aspects for plastic solid waste management in Iran but left the evaluation of health and environmental impacts to future studies. The difficulties of developing a BCA for recycling plastics in infrastruc- ture are that it requires information and understanding that is not currently available, as detailed in the previous sections of this chapter. The nascent technologies that are being investigated may not be viable. The competition for recycled plastics may impact the economics feasibility, or the environ- mental impacts may not be well understood. If/When There Is More Supply, Should It Be Put in Infrastructure? This question is not a simple one to answer. In some cases, the use of recy- cled plastics in infrastructure has been perfected and is economically viable, for example, the use of recycled plastics in pipes. Other uses of recycled plastics in infrastructure are in the exploratory or nascent stage (e.g., use in asphalt); thus, the question remains not only of economic viability, but also of technological viability. In addition, even if the use of recycled plastic is technologically viable, from an economic perspective, the question remains as to alternative resources that could be used, as well as the competing uses of recycled plastics. More information is needed to answer these questions. First, from an economic perspective, for those markets where the use of recycled plastics has been established as viable, what are the bottlenecks or inefficiencies in the market and can those inefficiencies be ameliorated? Specific to the use of recycled plastics in infrastructure, which is mostly at an exploratory stage, the fundamental question begins with technologi- cal viability, followed by economic (market) feasibility and environmental (nonmarket) impact, which can provide an improved assessment of this complex problem. Economic feasibility requires recycled plastics use in infrastructure to be at least as viable as the conventional material already in use. The environmental impact should be less than that of the alterna- tive material (e.g., conventional material, alternative novel material). As discussed in previous sections, the availability of plastics waste stock, the

LIFE-CYCLE CONSIDERATIONS 81 cost of processing the plastics waste, and the competition for the processed plastics waste all impact the economic viability. 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 supplies. Future work that assists in providing the information to the above will aid in answering the question of whether recycling plastics into infra- structure is the most efficient use or whether it is productive and societally beneficial. 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 product manufacturing, installation, maintenance, service life, and end-of-life recyclability. FINDINGS • The potential to use recycled plastics in infrastructure is a complex problem involving a set of interrelated systems, a large number of unknowns, and interactions between systems that are poorly understood. As a result, the overall system cannot, as yet, be de- scribed with a degree of certainty. Thus, the economic and envi- ronmental impacts of utilizing recycled plastics in infrastructure cannot be fully estimated at this point. • Assessing the potential impacts of using plastics waste in infra- structure can best be done utilizing a holistic systems approach that considers both the direct and indirect consequences of any program to capture, process, and reuse plastics waste. Focusing on just one part of the overall system will result in an incomplete analysis. • Defining the end focus (e.g., reducing leakage to the environment, reducing the amount landfilled, increasing displacement of virgin plastics) is critical to framing a holistic life-cycle assessment. • For both economic and environmental life-cycle assessments, the ultimate durability of infrastructure containing recycled plastics is a critical factor that will impact the outcome of the assessment. • Plastics are designed and used to perform specific product func- tions. If virgin plastics do not add performance (i.e., necessary durability, safety, strength for a product’s function) and economic value to a product, recycled plastics would not either. This philoso- phy is applicable to any product, whether a consumer product or an infrastructure component. • The market for plastics waste is incomplete (i.e., a market with constraints on the exchange of goods) in that it is characterized by supply and demand components without an efficient system to strike price and quantity, due to competing objectives within the

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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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