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Three arcs, corresponding to the bulk, interfacial, and electrode responses, are apparent in the impedance spectrum of cement paste / reinforcing steel systems. The 3-point impedance technique, without potentiostat, is capable of simultaneously and continuously monitoring these three responses over several orders of frequency (MHz-mHz). The high frequency (MHz) bulk arc provides such parameters as diffusivity and permeability of the paste, which in turn have implications for the ingress of corrosive species, such as chloride ions, known to greatly affect the corrosion rate of reinforcing steels. The double layer arc (Hz) provides insight into the nature of the near interfacial zone of the paste/ steel system, where the higher degree of porosity may affect corrosive behavior. The low frequency (mHz) electrode arc is related to the passive nature of the steel. Oxide film thickness can be inferred, as well as corrosion rates in active, passive, and pitting regimes.
impedance spectroscopy, cement, steel, diffusion, permeability, passivation, corrosion
Research Assistant, Northwestern University, Evanston, IL
Professor, Northwestern University, Evanston, IL