Life cycle assessment in circular economy for built environment

Built environment, also referred to as the product of construction industry, encompasses all buildings and infrastructure and exerts tremendous impact on the natural environment. The concept of the circular economy is increasingly being applied to improve resource efficiency and reduce environmental burdens of the built environment. During the implementation of a circular economy, adopting life cycle assessment is necessary to evaluate the trade-offs between circularity and sustainability. This thesis systematically investigates the application of life cycle assessment in the circular economy for the built environment. The research identifies inherent limitations of life cycle assessment methods that hinder their applications and compares various standards of life cycle assessment, quantifying the inconsistency between the assessment results based on these standards. New methods for circular economy assessment are developed to evaluate material circularity and environmental sustainability of the built environment simultaneously. By incorporating reliability methods, circular economy indexes are developed to quantify the probabilities of unsatisfactory circularity, sustainability, and overall circular economy performances. Various uncertain variables, such as structural degradation rate, recycling rate, and embodied impact coefficients, are considered in different life cycle stages of the built environment, such as product, construction, use, and end-of-life stages. In addition, the developed method and indexes are further demonstrated through multiple case studies. A wide range of circular economy applications are considered, such as mass timber structures, design for disassembly, and closed- and open-loop recycling. This research highlights that incorporating life cycle thinking and adopting circular economy assessment can facilitate the management and monitoring of circular economy applications in the built environment. This research contributes to the knowledge of circular economy assessment as well as its implementation throughout the life cycle of the built environment.