Effects of lightweight sand and steel fiber contents on the corrosion performance of steel rebar embedded in UHPC

Abstract Ultra-high-performance concrete (UHPC) is able to provide better protection for embedded steel rebar from corrosion due to its superior impermeability characteristics. Lightweight sand (LWS) and steel fibers are utilized in mixing UHPC to promote internal curing and improve flexural strength, respectively. But the effects of different contents of LWS and steel fibers on the corrosion performance of steel rebar and resistance of UHPC matrix are rarely investigated. In this study, steel bar reinforced UHPC specimens with different LWS and steel fiber contents were prepared for electrochemical tests, involving open circuit potential (OCP), Tafel polarization, linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS). The experiment results indicated OCPs values based on ASTM C876 could not be applied to decide the corrosion state of steel rebar since lower content of oxygen in UHPC reduced the cathodic reaction, which led to lower OCP values. Chloride ions did not penetrate into UHPC matrix and steel rebar were in passive state in the whole test period of 147 days (d). Corrosion resistance of steel rebar, and resistance of UHPC matrix and passive film displayed an increasing trend with time. Generally, the resistance decreased when the LWS and steel fiber contents were increased. This is because LWS increased the permeability of UHPC and steel fibers led to shortcut of current. For better electrical resistance and compressive strength of UHPC, it is recommended to limit the LWS replacement ratio to 25%. It is also concluded that, steel fiber with the volume content up to 3% will not lead to corrosion of steel rebar and can be safely used in UHPC.