PSI - Issue 78

Israel Sousa et al. / Procedia Structural Integrity 78 (2026) 1815–1822

1819

estimated at each cycle which exhibits degradation due to cracking of the specimen. Fractional change in resistance (FCR) was also obtained across Eq. 6 to establish a relation with the mechanical response of the material: = ∆ 0 , (6) where R 0 corresponds to the initial resistance at the beginning of the test. 3. Results Figure 5 shows the evolution of electrical resistivity in lime-based mortars at 20, 53, and 74 days. The reference specimens exhibited a notable increase over time, reaching approximately 2725.39 kΩ·m at 74 days. The CNT modified mortar showed an even high er resistivity of 4041.01 kΩ·m, while the CF 0.5% mix maintained a consistently low resistivity of around 0.48 kΩ·m, indicating significantly enhanced electrical conductivity. This low resistivity is attributed to the establishment of a well-connected conductive network, characteristic of an overpercolated system achieved with 0.5 wt.% of CCMF. In contrast, the 1.0 wt.% CNT content was insufficient to reach the percolation threshold. However, the elevated resistivity observed in the CNT sample, may be attributed to poor nanotube dispersion, implying a non-uniform distribution of conductive fillers within the mortar matrix, as well as the high porosity of these samples, which, combined with the presence of nanoparticles, is unable to form effective conductive paths. Figure 5 presents resistivity evolution over time of the investigated samples.

0,01 0,1 1 10 100 1000 10000 Resistivity (k Ω *m)

CF 0.5% CNT 1.0% REF

0

20

40

60

80

Time (days)

Fig. 5. Resistivity over time of the specimens (CF: carbon fibers, CNT: carbon nanotubes, and REF. reference specimens).

Figure 6 presents the relationship between FCR and strain over time for the studied samples. In the reference sample (Fig. 6a), FCR increased nearly linearly throughout the test, with minimal variation near crack formation, indicating limited sensitivity to localized damage. In Fig. 6b, the region where the crack appears in the reference sample can be identified by a sudden peak in FCR, likely due to microcrack formation. Although the signal stabilizes afterward, a subtle increase in FCR during the initial loading cycles suggests the development and opening of the crack. The CNT doped sample (Fig. 6c) also shows an initial linear FCR rise, followed by a decline, indicating a distinct response compared to the reference. In contrast, Fig. 6d displays a modest FCR increase (approximately 1%), pointing to crack initiation. The CCMF-doped sample (Fig. 6e) exhibits a sharp FCR rise after crack formation, demonstrating greater sensitivity to damage.