ABSTRACT
Ultra-high performance concrete (UHPC) is a novel construction material associated with enhanced mechanical and durability characteristics compared to traditional concrete, such as very high compressive and tensile strengths, high ductility, and low permeability to aggressive materials. In reinforced concrete structures, the development of cracks accelerates the corrosion of steel as water and aggressive ions are able to infiltrate the concrete more easily. Accelerated steel corrosion leads to increased corrosion products which subsequently induces more cracks. Consequently, the corrosion of steel in cracked concrete is a time-dependent coupled process. Additionally, reinforced concrete structures are often under sustained loading, which can affect the initial and time-dependent damage state of the structure. In this paper, the steel corrosion process and flexural behavior of both reinforced concrete and reinforced UHPC beams subjected to sustained loading and chloride attack are investigated through multi-physics simulation techniques. Numerical simulations are conducted on members considering the time-dependent deterioration process. First, a service load acting on the beams was selected to induce an initial damage state. Second, the mass transport of chloride in normal reinforced concrete and reinforced UHPC was modeled considering the initial cracking due to the service load. Next, the active area of the rebar was chosen based on the critical chloride value to initiate corrosion. The corrosion of the reinforcement was then simulated and the resulting rust expansion thickness was calculated. Finally, the combined effects of corrosion product expansion and mechanical loading was simulated. In the next time step, the process was repeated until severe damage was observed. The simulation results show that the reinforced UHPC beams exhibit distributed cracking patterns and smaller crack widths while the reinforced concrete beams had localized cracking behavior and major cracks under initial mechanical loading. Unlike the pitting corrosion mode in concrete without initial damage reported from many experimental results, both reinforced concrete and reinforced UHPC beams have more uniform corroding areas of the reinforcing bar when initial cracks from mechanical loading are simulated. Reinforced UHPC beams experienced significantly slower chloride ingress than reinforced concrete beams due to smaller crack widths and higher material density. Furthermore, the reinforced UHPC beam showed smaller corrosion current densities along the reinforcing bar resulting in less rust expansion. With lower rust expansion and higher damage tolerance, the reinforced UHPC beam shows better damage control after corrosion. The simulation results show that the reinforced concrete beam experiences much faster deterioration. In contrast, the reinforced UHPC beam provides excellent resistance to chloride attack and negligible increase of damage area under sustained loading even after a much longer time in a harmful environment.
