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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techniques mentioned above, this corrosion sensing method has the potential to monitor broader areas while preserving the substrate structure. The research methodology involves the sensing capabilities of smart coatings in chloride-induced corrosion scenarios. To emulate such corroding conditions in a brief amount of time, an accelerated corrosion test was pursued on all reinforced mortar specimens (Miró et al. , 2021). This test spanned 24 days and permitted the development of corrosion approximately 53 times faster than natural settings. By employing CB-based smart coatings, a link between electrochemical attacks and the mechanical effects induced by corrosion was established. Sensors were utilized as high-precision gauges to quantify the increase in internal stress and strain due to oxide formation and propagation within the matrix (Andrade, Alonso, and Molina, 1993). Visual analysis proceeded in parallel to qualitatively assess the oxides’ propagation and their influence on the mortar’s inner state of stress. This sensing capability was measured in both free and partially confined rebar scenarios, showing the versatility of the coatings under different structural conditions. This work serves as a starting point for cementitious coatings in corrosive environments, setting the stage for further exploration of multifunctional sensors. 2. Materials and methods 2.1. Materials The smart coatings used in this study were formulated by combining Portland cement (CEM I – 52.5N, supplied by Hanson Cement, UK), conforming to BS EN 197-1, with conductive carbon black powder, as outlined in Table 1 (sourced from Alfa Aesar, US). To ensure uniformity and optimal workability across different carbon black concentrations, MasterGlenium C315 (BASF, UK) was utilized as a superplasticizer by weight of carbon black.

Table 1. Carbon black properties as per the manufacturer. Appearance (colour) Black Form Powder Ash (%) ≤ 0.50 Electrical resistivity (Ω∙cm) ≤ 0.25 pH 7.6 Moisture (%) 0.12 Average particle size (nm) 42 Surface area (m 2 /g) 75 Bulk density (g/L) 170-230

These sensors had dimensions equal to 7.5 mm × 3 mm × 30 mm and embedded two copper wires (20 mm in length, 1 mm in thickness), procured from RS Components, UK. Their application was aided by the use of small pincers that controlled the position of the electrodes and prevented movement during casting and curing. To ensure that the thickness of the sensors was in line with their nominal value, five thickness measurements were obtained for all coatings along their longitudinal direction by means of a caliper. The resistivity was calculated on this basis to prevent geometrical variability in the samples. Table 2 displays the mix design used for casting the sensor coatings for electromechanical testing.

Table 2. Mix design of the coating composition tested in this study (kg/m 3 ).

Name

Cement

Water

Carbon black

Dispersant

CB dosage [wt%]

CB dosage [vol%]

CB3

2906.8

1327.5

85.9

8.6

3.0

15.7

For the substrate preparation, the reinforced mortar was designed in view of the corrosion test. The mortar mix comprised cement CEM I – 42.5R (supplied by Ciments molins, Spain), standardized sand (produced at IETcc) as per UNE EN 196-1, and water, with a water-cement ratio maintained at 0.5 for all samples. To simulate chloride-induced