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215 Appendix D Utilization of Plastics Waste in Transportation Infrastructure in State Departments of Transportation Stephanie C. Bolyard North Carolina Department of Environmental Quality (Formerly with North Carolina Department of Transportation) The increased interest in sustainability efforts in the academic community has resulted in a growing body of knowledge on the use of plastics waste in transportation infrastructure. As these projects get closer to implementa- tion, there is a gap in understanding if state departments of transportation (DOTs) are receptive to the use of these novel materials in infrastructure as well as what information is needed to evaluate the suitability of plastics waste to meet performance specifications. The goal of this effort was to survey state DOTs to understand if any recycled plastics are permitted for use in transportation infrastructure, what research or implementation projects might be under way, and what might be the hesitation to use these materials. Outcomes of this survey will help inform future research and implementation efforts. METHODOLOGY A brief survey was developed and sent out to state DOTs through theÂ Amer- ican Association of State Highway and Transportation Officials Research Advisory Committee during August through September 2022. This com- mittee is primarily comprised of Research Managers of DOT research and development units. The target respondents were individuals familiar with current research being conducted within each DOT and/or individuals
216 RECYCLED PLASTICS IN INFRASTRUCTURE responsible for the testing certification in the approval of materials used for transportation projects. RESULTS A total of 25 responses were received which represents 50 percent of DOTs across the United States (see Figure D-1). One response was received from the British Columbia Ministry. Respondents included subject-matter ex- perts across the materials and tests, research, engineering standards, geo- technical, and technical services units/divisions. SUMMARY OF KNOWN APPROVED USES Of these responses, only three state DOTs (12 percent) specified that in some capacity recycled plastics are allowed to be utilized in transportation infrastructure. These uses, types, and sources of plastics are summarized in Table D-1. CURRENT RESEARCH EFFORTS In addition to understanding if plastics waste is currently approved for use in transportation infrastructure, the survey also collected information FIGURE D-1 Summary of state DOT responses. NOTE: States in blue responded to the survey.
APPENDIX D 217 on which DOTs were conducting research to work toward approving the beneficial use of plastics waste. A total of six DOTs (24 percent) stated that they are currently conducting research in this area. These projects primarily focused on the use of plastics waste in asphalt mixtures at both the laboratory and field scales. There is an active pooled fund study at the National Center for Asphalt Technology (NCAT) Test Track that is evaluating recycled plasticâmodified asphalt mixtures, which includes two dedicated test sections. DEMONSTRATION AND IMPLEMENTATION PROJECTS The implementation of research is important to be able to bring in- novation into state DOTs. There were five DOTs that stated they ei- ther completed or have ongoing demonstration projects. These projects primarily focused on using plastic in asphalt pavement mixtures. For example, in Virginia there are six demonstration projects that were con- structed between 2021 and 2022. These projects included the use of five recycled plasticâbased proprietary products. Delaware DOT tested the use of paving a country road with recycled plastic bottles. This specific country road experiences damage from horseshoes and rutting in Amish communities. The plastic used was processed in Arizona and shipped to Delaware. There is no formal report, but it was stated that rutting was experienced again on this road. Colorado DOT is working with a local recycled plastic pellet supplier to discuss piloting a hot-mix asphalt proj- ect utilizing waste plastics. TABLE D-1 Summary of Allowed Uses of Recycled Plastics in Transportation Infrastructure Main Use Types Source of Plastics Nevada Possibly use polymers derived from plastics waste in polymer-modified asphalts â â Virginia Asphalt concrete dense-graded mixtures for surface layers in pavement structures (research demonstration field trials) #2 HDPEa Mainly post-consumer North Carolina Recycled plastic resins are allowed in HDPE Pipeb #2 HDPE Post-consumer/ industrial plastics a Trials featured mainly the use of Types 1, 2, and 4 (and possibly Types 5 and 6). b The use of recycled plastics for polypropylene, polyvinyl chloride, or chlorinated polyvinyl chloride pipes varies. NOTE: HDPE stands for high-density polyethylene.
218 RECYCLED PLASTICS IN INFRASTRUCTURE CONCERNS WITH APPROVING THE USE OF RECYCLED PLASTICS IN TRANSPORTATION INFRASTRUCTURE Although there is a growing body of research around the use of recycled plastics in transportation infrastructure and transitions to field demonstra- tion projects, there are still numerous concerns by DOTs around approving the use of these materials. A total of 22 DOTs responded to this question, and within these responses there were 37 different concerns that were identified. The summary of these responses is outlined in Table D-2. The primary concerns that were repeatedly brought up between DOTs included being able to demonstrate the long-term performance of transportation infrastructure and quantifying the cost and benefits of replacing virgin ma- terials with plastics. One respondent highlighted that they were unsure that the recycled material was actually improving performance and also if there were any cost savings. The environmental impacts were another concern that reflects the attention microplastics have received by the broader public and researchers. This concern is commonly brought up anytime plastics are mentioned in association with a transportation project that can undergo any type of weathering or abrasion. Beyond these primary concerns the re- maining comments revolved around the overall feasibility of implementing infrastructure consisting of recycling plastics and needing additional infor- mation. This information includes waiting on results from current NCAT and National Cooperative Highway Research Program (NCHRP) projects, determining the types of plastics that are compatible with paving materials, mix design effects, and impacts on future recyclability. TABLE D-2 Summary of Concerns by State DOTs Around Approving the Use of Recycled Plastics in Transportation Infrastructure Specified Concerns Count of Responses Demonstrate long-term performance/longevity/durability 15 Cost-benefit analysis 7 Environmental impacts (e.g., microplastics) 3 Waiting on results from current research (NCAT, NCHRP) 3 Feasibility (types of waste plastics that are compatible with paving material) 5 Future recyclability potential 2 Safety (e.g., plastics fumes) 2