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Cost and Ecological Feasibility of Using Ultra-High Performance Concrete in Highway Bridge Piers
AuthorJoe, Christopher David
AdvisorMoustafa, Mohamed A.
Civil and Environmental Engineering
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There is a growing interest in expanding the use of ultra-high performance concrete (UHPC) from bridge deck joints for accelerated bridge construction to complex architectural and advanced structural applications. The high costs currently associated with UHPC might limit its widespread use. However, the more compact cross-sections, higher strength, and durability of UHPC should result in safer structures and a much longer service life with minimal maintenance. This study aims at exploring the extended use of UHPC to entirely replace conventional concrete in a multi-column bent of a typical California highway bridge. This is to provide a pilot design and investigate the structural and seismic performance of UHPC piers for potential future use in highway bridges. The objective of the investigation is to see whether using UHPC in bridge columns and bent caps is economically and environmentally feasible if UHPC cross-sections are optimized to have a comparable structural and seismic response to conventional concrete bridges.Four different UHPC mix designs of varying mechanical properties were considered to design a two-column bridge bent using current analytical tools (OpenSees) while following standard AASHTO and Caltrans design guidelines. Sectional analysis was used for initial, cross-sectional design optimization. Nonlinear lateral pushover and time history analyses were used to perform seismic capacity checks and compare the seismic performance of UHPC piers to a conventional concrete design. The results show that the comparable-strength designed UHPC piers can achieve lower peak (maximum) displacements, ductility demands, maximum drift ratios, and residual displacements along with higher maximum base shear capacities when compared to a conventional concrete pier. For economic and environmental analysis, a bill of quantities was created to calculate the amount of materials consumed and saved. While UHPC mix designs consume much higher values of cement, if the cross-section is optimized well enough to its perspective reinforcement ratio, there can be a medium where the UHPC section will consume the same amount of cement as the conventional concrete case. For fewer UHPC design cases where there was a savings in cement consumption, a direct, positive impact is made possible on carbon dioxide emissions caused by the harsh clinker production processes in the cement industry. The study also found significant water savings, due to UHPC’s low water-to-cement ratio, with savings averaging approximately 50% of the conventional concrete design case. This attribute to UHPC can help combat water shortages for many drought stricken states or for construction sites where water is hard to transport. With the lowered embodied carbon dioxide and savings in water consumption, UHPC has potential to be an environmentally-friendly material. Lastly, using the optimized UHPC sections, a cost analysis was performed and found that UHPC designs are not necessarily cheaper, but will only add a slight percent increase in overall costs; a sacrifice worth considering for a safer structure, longer service life, and minimal maintenance.