Key Takeaways & Executive Findings
- •• • The Hejiawan Bridge total carbon flow is 27,482,432.11 kg CO2eq, with indirect carbon flow dominating at 92.4% (25,388,873.07 kg CO2eq), underscoring the need to target supply chain and material efficiency for decarbonization. • • Product carbon flow constitutes 72.88% of total carbon flow, and combined with resource and energy carbon flow (25.73%), accounts for 98.61%, indicating that material selection and energy optimization are the primary levers for emission reduction. • • The material consumption carbon flow rate of 3.91 kg CO2eq/kg is the highest among five girder bridges, signaling significant potential for material efficiency improvements through structural design and construction methods. • • The energy consumption carbon flow rate of 13.40 kg CO2eq/kg ec is at a medium level, while a comparable bridge using cast-in-place technology exhibits a higher rate of 16.08 kg CO2eq/kg ec, demonstrating that prefabrication and structural optimization can reduce energy-related carbon intensity.
Abstract
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.
1. Introduction
Engineering construction projects contribute substantially to global carbon emissions, yet their carbon footprint quantification remains coarse, hindering the formulation of effective mitigation strategies. Existing approaches often rely on aggregated emission factors without capturing the intricate material and energy flows across the project lifecycle. This lack of granularity impedes the identification of specific high-impact activities and materials, particularly in infrastructure sectors like high-speed railway construction, where diverse materials, transportation, and on-site processes interact.
To address this bottleneck, the present study develops a panoramic carbon flow model that integrates material flow analysis with emission factor methodology, enabling a comprehensive mapping of carbon flows across all construction activities. By categorizing activities into processing/construction and office/daily operations, and distinguishing direct and indirect emissions, the model provides a systematic framework for pinpointing carbon hotspots. Empirical application to the Hejiawan Bridge demonstrates the model's utility in benchmarking material and energy consumption rates against similar structures, thereby revealing targeted reduction opportunities that conventional carbon accounting fails to expose.
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LI Min, WANG Yinsheng, SUN Jiazhen, LIU Jie, WANG Minglu, ZHAO Peng, ZHU Li (2026). Construction and Empirical Study of a Panoramic Carbon Flow Model for High-Speed Railway Bridge Construction. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202605024
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Frequently Asked Questions
What are the primary sources of indirect carbon flow in the Hejiawan Bridge, and how can they be reduced?
Indirect carbon flow accounts for 92.4% of total emissions, primarily from product (72.88%) and resource/energy (25.73%) flows. Reduction strategies include optimizing material selection (e.g., using low-carbon cement or recycled steel), improving transportation logistics to reduce fuel consumption, and enhancing energy efficiency in construction equipment. The material consumption carbon flow rate of 3.91 kg CO2eq/kg indicates significant potential for material efficiency improvements.
How does the material consumption carbon flow rate of the Hejiawan Bridge compare to other girder bridges, and what implications does this have for design?
The Hejiawan Bridge exhibits a material consumption carbon flow rate of 3.91 kg CO2eq/kg, the highest among five girder bridges analyzed. This suggests that its material usage is less efficient, possibly due to structural design or geological conditions. Designers should explore structural optimization, such as reducing material overdesign or adopting high-performance materials, to lower this rate and achieve carbon savings.
What is the significance of the energy consumption carbon flow rate, and how does it inform construction technology choices?
The energy consumption carbon flow rate of the Hejiawan Bridge is 13.40 kg CO2eq/kg ec, which is at a medium level compared to similar bridges. Notably, a bridge using cast-in-place technology has a higher rate of 16.08 kg CO2eq/kg ec, indicating that prefabrication and modular construction can reduce energy-related emissions. This metric helps in selecting construction methods that minimize energy intensity.
How does the panoramic carbon flow model improve upon traditional carbon footprint methods for construction projects?
Traditional methods often use aggregated emission factors, missing the granularity needed to identify specific carbon hotspots. The panoramic model integrates material flow analysis with emission factors, categorizing activities and distinguishing direct vs. indirect emissions. This allows for a detailed breakdown of carbon flows by material type, activity, and scope, enabling targeted reduction strategies. For instance, it reveals that product carbon flow alone accounts for 72.88% of total emissions, guiding prioritization.
What are the limitations of comparing carbon flow rates across different bridge types, and how should such comparisons be interpreted?
Carbon flow intensity is influenced by bridge type, structure, and site conditions, making cross-type comparisons misleading. However, for bridges of the same type, comparing material and energy consumption carbon flow rates can effectively assess resource efficiency. The Hejiawan Bridge's high material consumption rate relative to similar bridges indicates potential for improvement, but such comparisons must account for design and geological factors to avoid unfair benchmarking.
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