Systematic Assessment and Dynamic Optimization of End-of-Life Carbon in Modular Integrated Construction

Modular integrated construction (MiC) has emerged as an effective construction technique for mitigating carbon emissions from buildings. Despite the great efforts dedicated to quantifying the carbon generated by MiC buildings, the carbon values and savings potential during the end-of-life (EoL) phase have never been made explicit. This study aims to systematically evaluate and dynamically optimize the EoL carbon in relation to MiC buildings. An innovative carbon assessment model was developed by integrating system dynamics (SD) into the life cycle assessment (LCA) framework and then empirically validated through a case study of a steel residential MiC building in Hong Kong. The results reveal that the direct carbon emissions during the EoL stage are estimated to be 12.39 kg CO2e/m2, most of which are attributed to waste processing, followed by transportation, demolition, and waste disposal. Due to the reuse of modular materials and the recycling of waste materials, EoL carbon savings amount to 990.78 kg CO2e/m2, leading to net emissions of -978.39 kg CO2e/m2. Despite this substantial reduction potential, it is significantly affected by building maintenance, recycling subsidies, and landfill charges. In contrast, energy-related strategies demonstrate a limited impact on overall net emissions. This study makes an original contribution to understanding the extent of carbon emissions and savings during the EoL phase of MiC buildings. These findings provide valuable insights for contractors in making demolition decisions on how to minimize carbon emissions, thereby pushing the transition toward carbon neutrality within the construction sector.