Remanufactured waste tire by-product valorization: Quantitative–qualitative sustainability-based assessment

Automotive tires are a major waste stream and there are currently numerous options for reusing, recycling, and remanufacturing the waste tire rubber (WTR) and other components. Some competing technologies (retreading, product repurposing, energy recovery, pyrolysis oil, waste-tire crumbing, and devulcanized rubber) are discussed here to demonstrate the broad scope of possible applications and identify the advantages/disadvantages of the processes. Based on the industrial maturity of the processes, this study performed a qualitative–quantitative fuzzy analysis of twelve alternative by-products of WTR, including 1) devulcanized or desulfurized rubber; 2) tiles, mats, and rod barriers; 3) composite materials; 4) bitumen; 5) asphalt; 6) heat energy; 7) crude oil; 8) diesel; 9) char and carbon black; 10) gasification gas; 11) activated adsorption carbon; and 12) lightweight concrete. Quantitative sustainability considerations were applied to weight the technical, economic, environmental, and social sustainability factors according to their importance, while qualitative factors were applied to weight the sustainability criteria of productivity, reliability, efficiency, waste tire size range, remanufacturing time, remanufacturing cost, ergonomics, human development, and employment potential based on insights from the published literature. Comparative literature-based statistical analysis of potential tire resources and conventional waste-tire recycling was performed. The results identified remanufacturing of WTR into devulcanized rubber sheets as the best sustainable business option with the highest sustainability index of 0.628, while lightweight concrete was the worst by-product option with a low sustainability index of 0.012. Other very-high-potential options include producing value-added rubber products and composite materials from the devulcanized rubber. These findings provide valuable insights for stakeholders in the field of waste-tire management and small-to-medium businesses looking to add further value to their WTR products. Furthermore, these findings could guide international research to help focus on the most sustainable use of WTR.