Intelligent assessment method of life-cycle carbon emission during the highway construction phase

The Chinese government has announced its “carbon peak and carbon neutrality goals” for 2030 and 2060, respectively. All industry sectors are working toward developing carbon policies to support the national dual carbon goals. The transportation industry, which is one of the three major sources of CO₂ emission in China, has indirectly contributed to the greenhouse effect and global warming and serves as a threat to human living spaces. Therefore, highway construction projects are the key targets for emission reduction in China. This paper presents a detailed analysis of the carbon emission inventories and carbon emission factor catalogs in the domestic and foreign transportation industries. The carbon emission factor data of China’s transportation industry are compiled and summarized based on the existing estimation indices for highway projects and the unit price calculation sheet of construction machinery and equipment in China’s traditional transportation industry. A “bottom-up” approach to measuring carbon emissions of highway projects, based on the attribution life-cycle assessment (ALCA) method, is adopted. In this method, the project activities are divided into subprojects, divisional projects, and unit projects during the construction period of the highway project, thereby establishing a carbon emission database and a carbon emission assessment model. Accordingly, intelligent assessment software for the carbon emission of highway projects was developed using MATLAB, and the carbon emissions of pavement projects for a certain mileage of two domestic highway feeders were estimated and analyzed. In general, our method enables the rapid assessment and statistical analysis of carbon emissions using information about the highway mileage, highway grade, and engineering volume. Moreover, it can intelligently track the carbon emission elements at each stage and identify the major carbon emitters during the construction of highway projects. Based on the assessment of two case studies of pavement projects, the software shows that the major carbon emitters that accounted for 75% of overall emissions were C32.5 cement, gravel, and modified asphalt in the different concrete layers. This implies that the construction phase is the dominant contributor to the overall carbon emissions. Among the machinery and equipment, the asphalt mixture mixing equipment is the major carbon emitter, with emissions of 380 t·h⁻¹, accounting for roughly 30% of the overall carbon emissions from the machinery and equipment. In asphalt pavement engineering, the main source of carbon emissions is the stable soil base and the asphalt pavement layer, accounting for more than 99.6% of the total carbon emissions, while the emissions from the pavement cushion and sporadic engineering are almost negligible. Therefore, our intelligent assessment method can provide robust data and a theoretical basis for energy conservation and the reduction of emissions in the transportation industry.