Electrochemical Characteristics and Equivalent Circuit Representation of Mortar-Coating-Steel Systems by EIS

摘要

This paper summarizes an experimental study on the electrochemical characteristics of various mortar-coating-steel systems and on the equivalent electrical circuit modeling for their representative behaviors. Mortar cylinders with uncoated, enamel-coated, and fusion bonded epoxy (FBE)-coated steel bars were investigated in 3.5 wt.% NaCl solution up to 244 days using electrochemical impedance spectroscopy (EIS). The microstructure of a mortar-coating-steel system was examined using scanning electron microscopy (SEM), and the effects of water cement ratio and exposure condition were considered. SEM images showed a thin porous mill scale on the surface of uncoated steel bars, a 150 urn thick coating with air bubbles of enamel-coated bars, and a 300 urn thick coating with air bubbles distributed near the FBE-coated steel bars. EIS results indicated that the frequency ranges of mortar/coating matrix, passive film, and solution-steel interface can be completely separated for specimens with uncoated steel bars, and but not for specimens with enamel and FBE-coated steel bars. Moreover, the mortar-coating-steel systems can be modeled by an electrical circuit that consists of a series of components representing different material layers. The effect of water cement ratio on the evolution of impedance spectra was less significant than the effect of exposure conditions.