Analysis of Influencing Factors and a Refined Calculation Method of Carbon Emission in the Materialization Stage of a Steel–Concrete Composite Beam Bridge

To clarify the carbon emission characteristics of steel–concrete bridges and address the gap in carbon emission accounting standards within the bridge sector, this study focuses on carbon emissions during the materialization phase of bridge engineering. Employing inventory analysis and emission factor methods, combined with the specific carbon emission patterns of this phase, a carbon emission accounting model was developed, a carbon emission factor database was established, and carbon emissions were calculated for a prestressed steel–concrete bridge on a highway in Shandong Province. The calculation results indicate that the carbon emissions during the materialization phase of prestressed reinforced concrete bridges amount to 3,092,237.79 kg CO2e. Of this total, 77.74% of carbon emissions are concentrated in the building materials production stage, with emissions from building materials in the superstructure and lower structure accounting for 81.25% of the emissions across materials production stages. Material transportation and on-site construction account for 9.87% and 12.39%, respectively. Among these, high-carbon equipment constitutes less than 10% of the total quantity but contributes over 70% of emissions. Due to the coal-dependent energy structure in North China, the total carbon emissions are 31.90% higher than the national average. The multi-factor sensitivity analysis shows that the aggregate transportation distance becomes the most sensitive parameter, which changes the traditional cognitive paradigm of “material quantity dominance”. Some emission reduction measures are provided for the sources of key carbon emissions in the materialization stage of bridges.