Developing a CO2-e accounting method for quantification and analysis of embodied carbon in high-rise buildings

Considerable amounts of greenhouse gas (GHG) emissions in buildings are embodied carbon from the manufacturing processes and transportation of various construction materials. Reduction of embodied carbon in buildings becomes important in the context of limiting GHG emissions into atmosphere. However, previous studies focused on analysis of low-rise buildings while high-rise buildings were seldom evaluated. Therefore, this study aims to develop a method used for the quantification and analysis of embodied carbon in high-rise buildings. The proposed method is used to evaluate the impacts of different procurement strategies (e.g., the choice of material manufacturing processes, the amounts of recycled steel scrap and cement substitutes, and the source locations), based on a case study of embodied carbon for a 60-story composite core-outrigger reference building (i.e., the most commonly-used structure in high-rise building design). The results show that structural steel and rebar from traditional blast furnace account for 80% of the embodied carbon in the core-outrigger building, while ready-mixed concrete contributes only 20%. If steel is produced from electric arc furnace with 100% recycled steel scrap as the feedstock, the embodied carbon of the building can be reduced by over 60%. As for ready-mixed concrete, 10-20% embodied carbon reduction in buildings can be achieved by utilizing cement substitutes (35% fly ash or 75% slag). However, using concrete with large amounts of cement substitutes has longer setting periods and affects the construction time. In projects with strict construction schedules, contractors may use less cement substitutes, leading to increased embodied carbon emissions in buildings. When large amounts of recycled steel and cement substitutes are used in construction, the carbon emissions from transportation can increase up to 20% of the embodied carbon in a building. In such cases, a trade-off analysis considering both the embodied carbon and the material availability is needed in order to determine the optimal source locations.