Fracture of the Passive Film on Reinforcing Steel in Concrete Under Mechanical Loading

ABSTRACT This study investigates the fracture of the passive film on reinforcing steel when steel elongation exceeds a threshold value, in the absence of aggressive species such as chlorides or carbon dioxide. Reinforced concrete specimens are subjected to three‐point bending to generate a load‐induced crack. Steel coupons embedded in the concrete are electrically connected to the reinforcing steel to measure the macro cell corrosion current when an anodic site forms. Once the critical load for concrete cracking is exceeded, a macro cell corrosion current is recorded as soon as the load increases, indicating rupture of the passive film and, consequently, anodic activity at the crack location, associated with the formation of a new passive film that heals the passive film fracture. The elongation threshold is close to 950 microstrain (or 190 MPa). As soon as the load stops increasing, the corrosion current sharply decreases, suggesting rapid repair of the passive film. After this repair, small variations in the tensile stress of the reinforcement lead to measurable corrosion currents, indicating that the repaired zone may constitute a weak point in the passive film.