Does material circularity rhyme with environmental efficiency? Case studies on used tires

The need for circularity assessment tools to prevent undesirable effects (e.g. recycling processes requiring more energy) is gaining recognition. Preserving resources and relieving pollution reservoirs are both necessary conditions to achieve a sustainable circular economy (CE), and the corresponding assessment tools should be selected accordingly. We chose life cycle assessment (LCA) and the Material Circularity Indicator (MCI). In this paper, we tested the tools through two case studies from the tire industry. The Brazilian case proposes three scenarios to process used tires: baseline, retreading and regrooving. The European case suggests collecting secondary material from end-of-life (EoL) tires to produce recycled content (RC) at 4% and 10% rates. These rates were chosen to illustrate the change in tire performance in the use phase. We propose an approach to discuss MCI and LCA results that identifies four pathways toward or away from the CE goal: coupling, decoupling, trade-off on resources or trade-off on reservoirs. The case studies reveal that extending lifetime through retreading and introducing recycled material improves the MCI of a tire but do not necessarily improve impacts on human health and ecosystems. Also, discrepancies in the results between the MCI and the LCA's resource indicator highlight relevant issues for new CE experts seeking to design assessment tools. Even though LCA provides a broader scope than the MCI, it still reflects a relative contribution to environmental sustainability while the MCI focuses on micro-scale improvements in resource use efficiency.