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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Figure 10. Graphical representation of crack width and FCR development as functions of attack penetration: (a) A.P. < 70 μm and (b) A.P. < 120 μm. The electrical patterns here plotted belong to sensor Y for each sample (i.e., #1, #2 and #3).

In the case of samples #1 and #2, after 10 days of accelerated corrosion (47 μm), the superficial fracture reached openings of 23 and 31 μm, respectively. This caused an inversion of the electrical trend for the sensors, characterized by a slower FCR increment. This performance was attributed to oxide production above and below the rebar (Figure 11a-h), resulting in a complex stress development within the cementitious matrix. It is plausible to assume that the initial crack opening on the top surface facilitated oxide movement, reducing the stress on that surface while increasing it on the other sides (Amalia et al. , 2018). When A.P. > 60 μm, the primary oxide propagation towards the top surface caused further crack widening at the substrate level, leading to a significant jump in the coatings’ electrical response. The sensors were able to measure crack development until excessive widening (i.e., 80 ± 9 μm for sensors Y and 116 ± 45 μm for X, Y and Z ), which caused the breakage of the coating, hindering the electrical continuity and