UC Berkeley

Given the state of aging infrastructure in the United States, reinforcement corrosion is proving to be costly in direct maintenance and replacement costs, as well as indirect costs, such as traffic delays and loss of productivity. Seismicity complicates this issue due to the looming threat of extreme loading on the heavily-used bridge structures that connect our communities. It is important to understand mechanisms of corrosion damage and their impacts on structural behavior in order to ensure that future repairs and new designs are sustainable, long-term solutions. The research presented in this dissertation investigates the combined action of corrosion and seismic loading on bridge columns. Fiber reinforcement is proposed as a means of extending the service life of reinforced concrete components and providing resistance to damage from environmental and mechanical action. Hybrid Fiber Reinforced Concrete (HyFRC) and its self-consolidating variant, SC-HyFRC, were utilized in these experiments to investigate their durability against the expansion of corrosion products and their ductility during mechanical loading. Of specific interest in this research is the intersection between corrosion damage in reinforced concrete and HyFRC column elements and mechanical behavior under seismic loading.

Steel reinforced self-consolidating concrete (SCC) and SC-HyFRC columns are exposed to corrosion damage through long term exposure in a chloride-contaminated environment, in which 2% chloride by weight of binder materials was admixed when column elements were cast to investigate the corrosion propagation phase in isolation. Corrosion rate and surface cracking behavior was monitored during a 125-week corrosion exposure period. Mechanical behavior was then investigated through compressive testing of corrosion-damaged column elements and tensile testing of corroded reinforcing steel. While the SC-HyFRC clearly exhibited less corrosion damage compared to the SCC control specimen, the large difference in compressive strength between the SC-HyFRC and SCC implies that a difference in their matrix/rebar interfaces made a comparison in their crack propagation behavior less conclusive.

Hybrid Simulation (HS) is utilized to investigate the system-level seismic performance of reinforced concrete structures with corrosion damaged components. This technique combines physical testing with computer simulation to impose realistic, dynamic loading conditions on a physically manageable test-specimen. An HS test procedure was developed to investigate the seismic behavior of a single-column highway bridge, where the lower portion of the column serves as the experimental element. The setup was validated and calibrated using a steel hollow structural section (HSS) column element. The HS procedure was also utilized with reinforced concrete and HyFRC column elements that were exposed to an applied current to accelerate corrosion damage prior to testing. HyFRC columns were more effective at preventing spalling as well as retaining their stiffness following severe seismic damage, even with pre-existing corrosion damage.

Many reinforced concrete bridges are simultaneously exposed to the combined hazard of seismicity and corrosion damage. It is of great importance to improve the understanding of existing infrastructure so that we can develop efficient and long-lasting repair or replacement strategies to keep communities safe while more effectively utilizing innovative materials to extend the service lives of structures. HS improves accuracy by incorporating the true behavior of a physical specimen into a numerical model to capture the full response of the structure, even if some components are difficult to explicitly model. This also increases efficiency of experimental testing as a large portion of the structure can remain as a computational model, eliminating the need perform expensive system-level tests.