Concrete structures represent a huge investment in terms of materials and energy and they lead to significant environmental impacts. Thus, there is a need to choose the most sustainable and eco-friendly alternative.
From this perspective, this report aims to evaluate the environmental impacts associated with the construction of two fictitious structures: a bridge and a tunnel. To fully assess and fairly compare the environmental burdens of those two structures, the life cycle assessment (LCA) has been chosen. Prior to the case studies, the LCA process is described and a literature review related to LCAs of road structures is performed thus revealing the key facts and key figures of such studies.
Based on this literature review, a simplified LCA is performed; it relies on public databases and only takes into account the construction phase. Because of data constraints, the indicators that are considered are NOx, SO2 and CO2 emissions, and the categories that are taken into account are energy consumption, global warming potential and photochemical oxidant formation. Characterization factors come from the REciPE method. Three different stages are considered and compared during this LCA study; the production of materials, the construction processes and the transportation phase.
Results show that the environmental impacts of the bridge are higher than the ones of the tunnel and that the amount of concrete has a strong influence on the final results and consequently on the interpretation phase.
This study also emphasizes the importance of assumptions and describes their potential influence on the final results by considering two different alternatives related to the concrete’s manufacturing. Making the concrete directly on site instead of bringing it by truck significantly decreases the environmental impacts of both structures; indeed, for the bridge structure, it leads to a diminution in CO2 emissions, global warming potential and energy consumption by more than 60%.
The main constraint of this study has been the data collection for the life cycle inventory; indeed, many data were missing or coming from different public databases which result in a lack of thoroughness and precision (e.g. different geographical representativeness).
Results of this study strongly depend on the various assumptions and on the data that have been collected, and technical choices, methodologies of construction or structural design mainly depend on the project’s location; consequently, results and conclusions cannot be generalized and should be handled carefully.
Author: Boulenger, Maxime