A BIM-based carbon footprinting of earthworks in road construction process

Carbon dioxide emissions are a major component of greenhouse gases and their evaluation during the life cycle of civil infrastructures is increasingly becoming a pivotal criterion for project tendering. During construction activities, the use of heavy-duty vehicles generally accounts for most of the energy consumption. However, the CO₂ emissions deriving from earthwork machines have not been thoroughly calculated yet due to the inner complexity of such task. In this regard, this research streamlines a quantitative assessment process of carbon dioxide leveraging digital tools and considering a bicycle lane project stretching approximately 3 km in Trondheim, Norway. Building Information Modelling (BIM) is adopted to define the necessary earthwork operations and provide accurate data to appraise quantity take-off volumes. Three earthwork tasks, namely excavation, transport and compaction, are investigated. The corresponding CO₂ emissions are subsequently quantified considering three operating modes for excavator (idling, moving and working), three types of transport vehicles (wheel dozer, tractor scraper and articulated dump truck) and two models of compaction machines (sheepsfoot and vibratory rollers). The results indicate that 75.5 t CO₂ emissions are generated from the on-site heavy machines. In particular, the transport activities contribute to the largest proportion of CO₂ emissions (56 %), half of which is produced while moving excess soil to the dump pit. Besides, the amount of carbon dioxide (2.9 t) generated during the idling and moving statuses of excavator is not negligible. Therefore, an optimized construction workflow and proper planning process are required to reduce machine fuel consumptions as well as increase the working efficiency. Bearing in mind the strategic importance represented by early planning for sustainable construction activities, this study provides innovative insights regarding the assessment of carbon footprints generated by earthwork machines.