Carbon emissions of prefabricated steel structure components: A case study in China

Abstract

China has been vigorously promoting the use of prefabricated steel structure buildings (PSSBs)1 in recent years. However, owing to the deficit in carbon emission (CE) research and the lack of basic CE parameters for PSSB components (PSCs), it is not feasible to conduct reliable CE calculations or develop scientific strategies for CE reduction. Based on the actual situation in China, this study investigated the CE of upstream raw steel sheet production (CEA1-A3), measured the CEs of PSC prefabrication (CEA3+), and obtained a carbon emission factor (CEF) for PSCs in the “cradle-to-gate” stage. The CEF of PSCs was found to be 2175.7 kgCO2e/t; CEA1-A3 contributed 1959 kgCO2e/t (90.0%), while CEA3+ contributed 216.7 kgCO2e/t (10.0%). Previous studies focused almost exclusively on CEA1-A3, whereas this study systematically investigated the direct, indirect, and embodied CEs for the A3+ stage of PSCs. The sources of CEA3+ were quantified; this showed that the CEs for energy and material consumption accounted for 59.6% and 40.4%, respectively. Compared with CEA1-A3, the CE types of CEA3+ were more diverse, with indirect CE (52.4%) > embodied CE (38.4%) > direct CE (9.2%). For this reason, CE calculation methods suitable for these characteristics were discussed, mainly based on consumption–production (CP) and process analysis (PA). In the CO2 gas-shielded welding test, it was found that the CO2 shielding gas decomposed in large quantities during the welding process, and the degree of decomposition was positively correlated with the welding power; the CP method regarded the CO2 supply as the direct CE and overestimated the CEA3+. In this study, the CE parameters of the main prefabrication processes were measured and the corresponding empirical formulas were fitted, which made the PA-based CE calculations feasible. Finally, the temporal and spatial ranges of the results were clarified, and the CEF trends for PSCs were predicted according to the expected CEs for crude steel and power grids in China. The results show that the scrap proportion in the production of raw steel sheets has a major impact on the CEFs of PSCs, whereas low-carbon electricity offers considerable CE reduction potential for PSC prefabrication.