Carbon emission analysis and multi-objective optimization of modular integrated construction using petri net simulation

China, as one of the world's largest carbon emitters, has developed goals to transition to low-carbon energy sources and improve energy efficiency. However, achieving these targets remains challenging, particularly within the building sector, which holds considerable potential for supporting low-carbon development. Modular Integrated Construction (MiC) has gained global attention for its efficiency and sustainability, but only a limited number of lifecycle studies have assessed its environmental performance. This study aims to use Petri net simulation to assess the carbon emissions of MiC throughout its entire lifecycle. Furthermore, a multi-objective optimization model is developed to reduce carbon emissions, control costs, and shorten project duration. This study examines a modular construction demonstration project in China, with a prefabrication rate of about 70%. The finding reveals that the project's total carbon emissions are calculated to be 19,996,619.99 kgCO_2e and the total unit carbon emissions amount to 577.16 kgCO_2e/m². The material supply and transportation stage accounts for the largest share (556.89 kgCO_2e/m²). Performance optimization is tested across 30 scenarios, yielding key findings: (1) supply–demand balance in the module supply chain significantly impacts project schedules; (2) faster module production enhances supply chain flexibility; (3) slower production reduces costs but increases carbon emissions; (4) early warehouse use improves scheduling; (5) larger warehouse capacity mitigates delays caused by production-installation speed differences; and (6) information sharing between factories and project sites reduces production interruptions. These findings could provide practical insights into enhancing efficiency and sustainability of MiC.