Properly designed
modular construction offers the potential for easy disassembly, relocation, and reuse across multiple use cycles. However, the environmental benefits and burdens resulting from the reuse of modular components over these cycles are not well understood. The study aimed to assess the environmental credits and loads associated with reusing modular components over multiple use cycles. This aim was achieved through two approaches. Firstly, three dedicated
life cycle assessment (LCA) allocation rules were adopted, namely, cut-off with Module D, the Product
Environmental Footprint (PEF), and the Circular Footprint Formula (CFF), to evaluate the environmental impacts of production, reuse, repair, replacement, recycling, and disposal of a modular unit (including the steel frame,
concrete slab, and steel connector) across different life cycle stages (Module A, Module C, and Module D) and use cycles (first, intermediate, and last). The PEF approach was determined to be the most suitable for interpreting the environmental credits and burdens associated with reuse. The study found that the reuse and recycling of the modular unit resulted in approximately 9007 ± 362 kg, 2925 ± 602 kg, and 8433 ± 544 kg of equivalent
carbon dioxide emissions in the first, intermediate, and last use cycles, respectively. Secondly, a global sensitivity analysis was performed to assess how uncertain input parameters related to future use cycles (e.g., reuse rate, direct
reusability rate,
recyclability rate, and transport distance) influenced the LCA outcomes. The results revealed that it is beneficial to achieve a higher level of
reusability (i.e., direct reusability) and
recyclability for the steel frame to maximize the environmental advantages. The impact associated with a relatively lower level of reusability (i.e., repairable) and
recyclability for subcomponents is considered environmentally acceptable. However, the lowest level of reusability of subcomponents (i.e., replaceable) should be avoided to minimize the impact associated with replacements. With a view to ensuring net environmental benefits from reuse, it is crucial to attain the desirable reusability level through developing proper design and deconstruction strategies for individual modular components.
