Comparative sustainability and seismic performance analysis of reinforced conventional concrete and UHPC bridge piers

Ultra-high performance concrete (UHPC) boasts excellent mechanical properties, but it comes at a high cost and has a significant environmental impact. This study conducts a comprehensive life-cycle analysis (LCA) on reinforced concrete bridge piers to investigate the environmental implications of integrating conventional concrete (CC) and UHPC in seismic design. The analysis covers both materials and members. At the material level, the global warming potential (GWP) from UHPC manufacturing is calculated using a comprehensive database that includes UHPC mixture details, fiber quantity, geometry, mixing and curing processes, loading age, and compressive strength. At the member level, seismic performance is assessed through capacity-to-demand ratios of strength and ductility. A total of 1280 CC and 2240 UHPC bridge piers are virtually tested with comparable functional unit values, and their GWPs are calculated. The study reveals a proportional relationship between GWP per m3 of UHPC manufacturing and its compressive strength. The GWP of CC and UHPC piers designed using the strength-based approach increases with the capacity-to-demand ratio. When the capacity-to-demand ratio is relatively large, the GWP exhibits rapid nonlinear growth. Adding more reinforcement to achieve a higher capacity-to-demand ratio is inefficient. Moreover, both CC and UHPC piers designed using the ductility-based approach show no strong correlation between GWP and the capacity-to-demand ratio. Surprisingly, using a higher grade of UHPC does not improve seismic resistance; instead, it leads to increased GWP. Effective strategies, such as reducing cross-sectional area and increasing the reinforcement ratio, prove beneficial in enhancing material efficiency and reducing GWP. Additionally, the utilization of a specific pipe section enhances material efficiency, improves seismic resistance, and results in lower GWP.