PSI - Issue 78

Paolino Cassese et al. / Procedia Structural Integrity 78 (2026) 607–614

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Testing machine

F

Load cell

Rubber

Specimen

Electrodes

Strain gauge

LCR meter / Source Unit

Rubber

F

Esternal load cell

Acquisition system

Fig. 3. Sketch of specimen and test setup.

3. Results and discussion Results obtained from the compressive cyclic loading procedure on the SSCC are presented in Figs. 4 and 5 for specimens C075W050 and C075W042, respectively. Notice that, for the sake of convenience, the first part of the loading history is not considered in the figures, which are associated only with the cyclic load. Specifically, in Figs. 4 and 5, the force F , the strain  , and the FCR are shown as functions of time t . A general good correspondence between the applied compressive load, the measured deformation, and the FCR is observed. The magnitude of FCR increases with the increase in the absolute value of the compressive load F and decreases when the force F decreases. This reflects that, as the compressive load increases, the resistance of SSCCs tends to decrease, because the MWCNTs embedded within the cementitious matrix become closer due to the compression, enhancing the conductive mechanisms, in particular by reducing the tunneling distance and increasing contact points, so creating an efficient conductive path. By comparing the FCR curves (green) of Figs. 4 and 5, respectively, some significant differences can be noted. The curve of Fig. 4, associated with the specimen C075W050, appears slightly irregular, due to a higher noise level with respect to the corresponding curve of Fig. 5. Furthermore, for specimen C075W042, the FCR curve is characterized by sharper peaks corresponding to the load extremes, denoting a higher sensitivity to the applied load. The specimen C075W050 was characterized by lower FCR absolute values compared to the specimen C075W042, with a maximum absolute value at the first cycle equal to 1.97% and a minimum absolute value of 1.84% at the last cycle, resulting in a 6.8% change in the peak amplitude at -5 kN during the loading cycles, proving a mild positive signal drift over time. Conversely, the  signal was characterized by a negative drift (i.e., the absolute value of strain increased with the progressive compressive cycles) equal to -1.0%, consistent with an eventual little microstructural damage accumulation. The experimental results also showed discrete reversibility and stability upon the application of cyclical loading. Indeed, the peak-to-peak amplitude, i.e., the absolute value of the difference between the maximum and minimum peaks in one cycle, was almost constant among the cycles and equal to 0.48%. The recorded absolute FCR values for the specimen C075W042 for a compressive load of -5 kN were 2.77% and 2.92%, respectively at the first and last loading cycle, resulting in a -5.4% change in the peak amplitude during the loading cycles, proving a mild negative signal drift over time consistent with the trend of the  signal, characterized by a drift equal to -1.3%. The self-sensing response was stable and reversible, with a peak-to-peak amplitude of 0.87%.