Methodologies for assessing building embodied carbon in a circular economy perspective

Abstract

The global warming effect represents an increasingly severe environmental issue in the contemporary world, with the construction industry contributing up to 40% of greenhouse gas emissions. Therefore, as advancements in technology have enabled the realization of net-zero energy buildings, there has recently been a growing focus on research primarily aimed at reducing the embodied carbon (EC) of building materials. Assessment and calculation of EC emissions in buildings typically utilize life cycle assessment (LCA) methodologies, evaluating both direct and indirect carbon emissions throughout all stages, from raw material extraction to end-of-life demolition. However, the substantial potential of carbon reduction within the material beyond life cycle stage in the building, which is the decisive process of closing the loop of circular economy, is often overlooked. This paper examines a large number of research cases on EC in buildings over the past 20 years, selectively identifying those including the benefits beyond life cycle of buildings. By conducting a case-by-case analysis of methods and tools employed for the assessment of circular practices, their respective strengths, weaknesses, and variances are evaluated. Following the normalization of EC in phase A-D, a significant research finding revealing that buildings can offset an average of -113.9 kg CO2e/m2 of carbon emissions through recycling and reuse in phase D, accounting for 16.85% of the total EC assessed in LCA. Steel recycling offsets the highest amount of carbon emissions, with an average number of -183.86 kg CO2e/m2. The objective of this paper is to identify the key factors that influence carbon emissions in the circular economy and to identify methods and tools for integrating building materials at the early design stage to minimize EC emissions throughout the entire lifecycle of buildings.