Carbon Emission Assessment During the Recycling Phase of Building Meltable Materials from Construction and Demolition Waste: A Case Study in China

The improper disposal of construction and demolition waste (CDW) exacerbates the consumption of raw materials and emissions of greenhouse gasses. In this study, due to the high recycling rate, focusing on the meltable materials of CDW, the recycling phase of CDW is divided into four stages, namely the on-site disposal stage, the transportation stage, the reprocessing stage, and the reproduction stage. Second, based on these four stages, a carbon emission accounting model (CEAM) is established to evaluate the carbon emission benefits of meltable materials during these stages. Third, the CEAM is applied to a typical old residential area to evaluate the carbon emission reduction benefits of the CDW recycling. The results indicate that (1) the full-process carbon emissions of recycled steel, recycled flat glass, and recycled aluminum per unit mass are 677.77 kg/t, 1041.54 kg/t, and 845.39 kg/t, respectively, which are far lower than their corresponding ordinary meltable building materials (OMBMs); (2) the carbon emissions during the reproduction stage represent the primary component of carbon emissions in the MW recycling phase, accounting for 88.52% to 97.45% of the total carbon emissions; and (3) the carbon emissions generated by the recycling of cullet per unit mass are very high, reaching 1768 kg/t, which is 4.3 times that of scrap steel (409.05 kg/t) and 3.6 times that of scrap aluminum (483.76 kg/t). The research findings could provide theoretical methods and experimental data for decision-makers to formulate treatment plans for meltable materials in CDW, thereby empowering urban carbon emission reduction and promoting sustainable development. Construction parties engaged in demolition tasks should enhance on-site sorting and collaborate with recycling companies to ensure its efficient recycling. Recycling companies need to focus on high-carbon-emission stages, such as the reproduction stage, and strengthen technological research to improve carbon reduction benefits.