Embodied greenhouse gas assessment of a bridge: A comparison of preconstruction Building Information Model and construction records

Abstract

This paper presents an embodied GHG assessment of a completed highway bridge renewal project in Canada and offers new insights on the strengths and limitations of BIM-based GHG assessments. Bridges play a critical role in transportation infrastructure. As reducing environmental impacts has taken on increasing urgency across the construction sector, bridges have received relatively little study. A quantitative understanding of the embodied greenhouse gas emissions (GHG) in bridges is needed to inform future infrastructure planning, design, and construction. Recent efforts to streamline environmental assessment in construction have led to the creation and adoption of Building Information Model (BIM)-based embodied GHG assessments, taking advantage of the quantity take-off functionality of BIM. However, as BIMs are rarely developed with environmental assessment as the primary goal, their effectiveness for GHG accounting can be limited. GHG assessments of the case study bridge using a BIM prepared before construction and using material and energy quantities records collected on-site during construction, are compared. Using only the quantities from preconstruction BIM, the embodied GHG for the case study bridge is 1.3 × 106 kgCO2e. After the adjustments for on-site data collection and factors commonly excluded from BIM, such as on-site fuel use from machinery, it rises to 4.06 × 106 kgCO2e, an increase of 212%. Results illustrate the need to change the scope and detail of BIMs if they are to be effective for embodied GHG assessment, and the potential limitations of using BIM in embodied GHG assessment.