PLS multivariate analysis applied to corrosion studies on reinforced concrete

There are few techniques available to calculate the corrosion rate (i(corr)) of reinforcing steel in concrete structures. This is due not only to a lack of instrumentation but also because it is necessary to take into account that polarization can irreversibly modify the metal surface and can affect the results or the future state of the metal. This is the reason some researchers prefer to test reinforcing steel with reversible techniques. The main objective of this study is to predict the corrosion rate of reinforced concrete using electrochemical methods combined with statistical tools such as multivariate analysis. Using reinforcements embedded in mortar samples, the corrosion rates were determined at different ages using the Tafel method, and values obtained were compared with other techniques: linear polarization resistance (LPR), potentiostatic pulse testing (PPT), and AC electrochemical impedance spectroscopy (EIS). In addition, these values were compared to those obtained using a mixed technique based on partial least squares (PLS). With this technique, we were able to automatically analyze the current data obtained from LPR, PPT, and EIS and to predict the i(corr) value. The study allows us to conclude that it is possible to obtain reliable i(corr) values, very close to those obtained with the Tafel method by using PLS combined with PPT or LPR. Furthermore, it presents several advantages, such as being able to directly treat data without requiring an established Stern-Geary constant (B) for LPR and not having to use an equivalent circuit (EC) in EIS to calculate i(corr) because only the impedance spectra are necessary.