Developing a building-scale circularity indicator through fuzzy analytical hierarchy process and Gini index-based circularity calculation methods

Circular economy (CE) aims to achieve sustainable development by optimizing resource efficiency through innovative system designs. The built environment plays a crucial role in this transition, yet the absence of standardized indicators hinders effective circularity assessment. This study introduces a structured building-scale circularity indicator (BuCI) to support industry and academia in evaluating buildings' circularity levels and facilitating the shift towards a circular built environment. Based on a thorough review of CE, the methodology involves the generation of a model, its implementation on a selected case study and evaluation. The proposed model integrates the shearing layer and building lifecycle concepts to establish a measurement framework with defined criteria and key performance indicators. Fuzzy analytical hierarchy process and Gini index are used to formulate circularity calculation. Then, the BuCI is implemented on three different case studies, two steel and one reinforced concrete buildings. CS1 and CS2 reached 60% circularity level, thanks to the material advantages and certain design principles such as modularity, disassembly and flexibility, whereas CS3 calculated as 31.05% circular due to material and design decisions. The study contributes to the field by introducing a novel indicator for the industry, academia and authorities to accelerate the circular transition. For future studies, it is suggested to integrate cost and cultural heritage related criteria.