Influence of defects at the steel-mortar interface on the corrosion behavior of steel

The different corrosion behaviors of top part and bottom part of horizontal steel (with respect to casting direction) in mortars after exposure to 3.5% NaCl solution were investigated. The results of electrochemical impedance spectroscopy (EIS), X-ray computed tomography (X-CT) confirm non-destructively that the formation of loose and porous defects at the bottom steel-mortar interface results in low corrosion resistance of adjacent steel, whereas few distinct defects can be found at the top steel-mortar interface. It is confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) analysis that the defects at the steel-mortar interface play a dual negative role on the corrosion resistance of steel: the passive films gradually lose their stability due to the depletion of the protective Ca(OH)2 layer in the defects, and chlorides are prone to accumulate in the defects which further attack the passive films of steel.