Effect of endogenous chloride ion on the corrosion behavior of reinforcement embedded in sea-sand UHPC matrix in different immersion environments

Abstract

Ultra-high performance concrete (UHPC) is an innovative cement-based composite material characterized by extremely high durability and mechanical properties, which provides a potential possibility of using non-desalted sea-sand as aggregate. However, the long-term steel corrosion behavior in UHPC prepared by simulated sea-sand under different immersion environments remains unclear, which is of great significance for the application of sea-sand UHPC in practical engineering. In this study, the pore structure of sea-sand UHPC matrix was measured using nitrogen adsorption/desorption method. The corrosion behavior of rebar in sea-sand UHPC with different endogenous chloride ion contents soaking in pure water and NaCl solution was characterized by linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP). The experimental results show that the initial UHPC pore structure is refined by incorporation of sea-sand, and is similar to that of ordinary UHPC at the later hydration. Regardless of the endogenous chloride ion content and immersion environment, the corrosion rate evaluated by corrosion current density (icorr) and polarization resistance (Rp) of reinforcement in UHPC is extremely low. The measurement of EIS shows that UHPC group has higher matrix resistance (Rc) and charge transfer resistance (Rct), while lower electric double layer capacitance (CPEdl) of reinforcement, which indicates that the steel in UHPC made of sea-sand is still in a state of passivation. However, the steel bar in comparison specimen OPC soaking in NaCl solution is in the corrosion stage. Furthermore, sea-sand UHPC possesses of excellent ability of anti-pitting corrosion of reinforcement after 180 days of immersion in NaCl solution.