Review and Perspectives of End-of-Life Tires Applications for Fuel and Products

Applications of end-of-life tires (ELT) for energy recovery and new products can contribute to a circular economy. This paper reviews the environmental, health, and economic aspects of various applications of ELT, focusing specifically on the use of ELT in fuel, energy, and construction. Impediments to a more widespread application of repurposed ELT include a lack of streamlined handling and recycling processes; a poor understanding of the long-term ecological, human health, and safety consequences; and very few application-specific techno-economic assessments and life-cycle analyses. The prospects for rubberized asphalt as an economical and environmentally benign application of ELT are reviewed in four areas: (1) rubber pretreatment─the most effective techniques are chemical or microwave radiation, and the most sustainable technique is microbial devulcanization; (2) aging behavior─rubber particles delay aging in asphalt through several mechanisms; (3) techno-economic benefits─rubberized asphalt improves the cost-efficiency and energy-efficiency of asphalt; and (4) environmental emissions and leakage concerns─the risk of heavy metals and hazardous pollutants such as polycyclic aromatic hydrocarbons and volatile organic compounds contaminating the ecosystem or causing occupational diseases in workers. There are four priority directions for future research on rubberized asphalt: (1) determine the critical aging point; (2) describe the self-rejuvenating behavior; (3) quantify the long-term leachate under extensive weathering; and (4) compare the ecological aspects of pretreatment techniques in terms of potential greenhouse gas emissions and human health.