PSI - Issue 67

Gabriele Milone et al. / Procedia Structural Integrity 67 (2025) 90–106 G. Milone et al./ Structural Integrity Procedia 00 (2024) 000 – 000

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2.3. Experimental program

2.3.1. Accelerated corrosion test The corrosion test required a unique setup to induce accelerated corrosion within the mortar specimens, focusing on electrochemical attack kinetics. The sensing property capability of smart coatings was related to the mechanical effect induced by the corrosive electrochemical attack in the steel/cement interface. Prior to initiating the accelerated corrosion, the depasivation state of the rebar, as a consequence of the addition of NaCl to the mortar, was assessed through the measurement of electrochemical methods, offering insights into the initial corrosion status of the steel rebars. This was based on the linear polarization test (R p ) which relies on the linearity of polarization curves around the corrosion potential (i.e., E corr ± 20 mV) (Stern, 1958). By applying a small amplitude through an alternating signal to the working electrode (i.e., steel rebar), the corrosion current (I corr ) was determined using the Stern-Geary equation (Stern and L.G., 1957): I corr =B/R p (1) The constant B can be determined from Tafel slopes of the cathodic and anodic polarization curves (Song, 2000; Kouřil, Novák, and Bojko, 2006), and it was assumed equal to 26 mV in this investigation (Andrade and Alonso, 1996). The resultant value was adjusted to account for the ohmic drop between the working and reference electrodes. The obtained output (I corr ) was compared with the standards – UNE 112072:2011 – to obtain an understanding of the system’s corrosion level. Following the initial 7 -day curing of the mortar prisms (before sensor application), such a value was expected not to be excessively high; nonetheless, due to the presence of NaCl in the matrix, the corrosion current was not negligible and, therefore, its measurement was required for the subsequent corrosion acceleration. The application of a constant corrosion current, facilitated by a TG 97 Galvanostat (Bank Elektronik, Germany), standardized the rate of oxide formation across specimens, ensuring a controlled environment for studying the corrosion's mechanical impact and the subsequent response of the smart coatings. Figure 4 displays the setup used in this study where a stainless-steel sheet worked as the counter electrode (cathode) connected to the rebar which became the working electrode (anode). The galvanostatic forced polarization ensured that the cathode behaved as the negative electron donor and the positive anode was the corroded rebar (Shi, Jia, and Atrens, 2012). Both the crack elongation and the oxide propagation within the matrix were visually assessed with a manual optical microscope ( RS PRO USB digital microscope 5M , RS components, Spain).