Investigation on the polarization resistance of steel embedded in highly resistive cementitious systems - An attempt and challenges

Concretes with fly ash, slag, limestone calcined clay, etc. exhibiting high resistivity are being used to enhance the chloride resistance of structures - to achieve durability. Prior to use, the engineers need to determine the chloride threshold (Cl-th) of such highly resistive steel cementitious (S-C) systems (a key parameter to estimate service life). Most Cl-th tests involve repeated measurements of polarization resistance (R-p) and detection of corrosion initiation of steel embedded in hardened cementitious system (a sol-gel structure with partially filled pores). The high resistivity of such systems should be considered while interpreting the electrochemical response to determine R-p. This paper experimentally evaluates the suitability of LPR and EIS techniques for assessing R-p of steel embedded in highly resistive systems. Experiments were conducted with lollipop type specimens (steel reinforcement embedded in mortar cylinders). The following three types of mortar having various resistivities were prepared: (i) ordinary portland cement (OPC), (ii) OPC + fly ash, and (iii) limestone calcined clay cement. Experimental observations on how the following three factors affect the electrochemical response in highly resistive S-C systems are provided: (i) resistivity of concrete covering the embedded steel, (ii) electrode configuration, and (iii) electrochemical test parameters. It was found that electrochemical impedance spectroscopy (EIS) can detect corrosion initiation in highly resistive systems at earlier stages than the linear polarization resistance (LPR) technique. Also, the guidelines on how to use EIS technique to determine the R-p of steel embedded in highly resistive S-C systems are provided. (C) 2019 Elsevier Ltd. All rights reserved.