Effects of aggregate reuse for overpass reconstruction-extension projects on energy conservation and greenhouse gas reduction: A case study from Shanghai City

Currently urban overpasses (new-construction, reconstruction and extension) are being constructed on a large scale in China. While the construction projects are beneficial to the economic and social development, they have also caused serious ecological and environmental problems. On one hand, the final disposal of construction wastes requires a large amount of land, and the extraction of virgin aggregate destroys the local ecological environment. On the other hand, the energy consumption and the greenhouse gas (GHG) emissions during the entire life cycle are massive. To reduce the ecological and environmental impacts and to improve the resource use efficiency during the overpass construction, it is necessary to change the traditional linear resource use mode (aggregate-buildings-garbage) into a circular mode (aggregate-buildings-reused/regenerated aggregate-buildings). Using the life cycle inventory (LCI) method, the energy consumption and the GHG emissions are investigated for two different kinds of reconstruction and extension projects for overpasses in Shanghai City, using virgin and regenerated aggregates, respectively. Through that, the actual energy conservation and the GHG reduction benefits from using the regenerated aggregate are determined. Important first-hand data on the extraction of aggregate, the regeneration of aggregate, and the demolition of the discarded overpass, in a real situation, are gathered. The results show that, for the life cycle of aggregate, the energy consumption and the GHG emissions from reused aggregate can be reduced to 45.27% and 43.91%, respectively, compared to the virgin aggregate. For the life cycle of road concrete, the figures mentioned above would be 3.48% and 1.33%, respectively. In order to reduce the total energy consumption and GHG emissions from the reconstruction and extension projects of the overpasses, it is essential to find a way to reduce the amount of cement used, as well as the energy consumed and the GHG emitted during the cement production.