An advanced method for assessing circular economy performance of built environment

Circular economy (CE) plays a key role in improving resource efficiency and reducing environmental burdens of buildings and infrastructure, i.e., built environment. However, an integrated CE assessment that simultaneously evaluates circularity and sustainability has not yet been fully developed. In particular, CE performances of built environment need to be modelled by considering the time-variant and uncertain nature of influencing factors, e. g., structural degradation rate, recycling rate and efficiency, and embodied impact coefficient. This paper develops a CE index that comprehensively evaluates material circularity indicator, embodied carbon and embodied energy considering the above influencing factors. Time-dependent reliability theory is employed to quantify the probability of unsatisfactory CE performance throughout the life cycle of built environment. The developed CE index is then demonstrated through a case study of concrete structures with various CE strategies, e.g., design for disassembly (DfD), closed-loop and open-loop recycling. It is found that a combined DfD and open-loop recycling strategy produces a higher CE index, i.e., a lower probability of unsatisfactory CE performance compared to other CE strategies. This highlights the importance of improving the durability of reusable structural components as well as reducing their embodied impacts in CE practices. In addition, using more recycled aggregate does not necessarily improve the long-term CE performances of concrete structures. Material circularity and environmental sustainability must be evaluated simultaneously, particularly when combining different CE strategies, e. g., reuse and recycling. These outcomes will help manage and monitor the circularity, sustainability and overall CE performance of the built environment in its whole life.