Construction and Empirical Study of a Panoramic Carbon Flow Model for High-Speed Railway Bridge Construction
The refined quantification of carbon footprint in engineering construction projects is critical for formulating targeted carbon reduction strategies during the materialization phase. This study integrates material flow analysis (MFA) with the emission factor method to establish a panoramic carbon flow model for engineering projects. Construction activities are categorized into processing and construction, and office and daily operations, clarifying material and carbon flow relationships within the system boundary and with external systems. Empirical analysis was conducted on the Hejiawan Bridge of Section 11 of the Xiyu High-Speed Railway. Results show that the total carbon flow amounts to 27,482,432.11 kg CO2eq, with direct carbon flow (fuel oil, gasoline) accounting for 7.6% and indirect carbon flow (products, transportation, electricity) accounting for 92.4%. From the material flow perspective, the total carbon flow comprises product carbon flow (72.88%), resource and energy carbon flow (25.73%), transportation carbon flow (1.04%), waste carbon flow (0.35%), and service carbon flow (0.01%). In terms of activity scope, construction-related carbon flow accounts for 99.17%, while office and daily operations account for 0.46%. Two indicators, material consumption carbon flow rate and energy consumption carbon flow rate, are proposed for the first time. Comparative analysis of five girder bridges reveals that the Hejiawan Bridge has a material consumption carbon flow rate of 3.91 kg CO2eq/kg, ranking highest among similar bridges, while its energy consumption carbon flow rate is 13.40 kg CO2eq/kg ec, at a medium level. The assessment indicates relatively high material consumption, suggesting potential for carbon reduction through structural and geological optimization.