# Applications of Cement-Based Smart Composites to Civil Structural Health Monitoring: A Review
## 3 Applications to SHM of Structural Prototypes
### Reduced-Scale Members
From the results of three-point bending tests, the Authors concluded that: (i) CBCS with 2% CB exhibited the best sensing performance; (ii) the embedded sensor close to the loading point presented the largest electrical resistivity changes because of the higher stress magnitude; (iii) sensors in the compression zones exhibited gradual decrease in electrical resistivity but they suddenly returned to their initial resistivity values when approaching the flexural failure, whereas the counterparts in the tension zones experienced an increase in electrical resistivity followed by an abrupt jump near the flexural failure. Figure 2: Scheme of testing on embedded CSC sensors (adapted from [71]). [PERSON] and his co-authors [73] carried out experimental tests on reduced-scale beam and column; CSCs doped with different nanocomposite were embedded into those elements. Sensors were realized by using three different conducting filler types (MWCNTs, CFs, and G) combined with each other. Cement mortar matrix was used to ensure proper strength, and w/c ratio equal to 0.45 was assumed. Sensors had dimensions 50 \(\times\) 50 \(\times\) 20 mm\({}^{3}\) and were equipped with two electrodes in the central part. Concerning  
Figure 3: Layouts of CBCSC sensors: Configuration I (**a**), II (**b**), and III (**c**) (adapted from [72]). mix-preparation, CFs were directly mixed with cement and sand in the dry state, whereas both G and MWCNTs were priorly sonicated with water. Electro-mechanical three-point flexural tests were performed first on sensor specimens, respectively with 0.25% and 0.50% of nanomaterials by weight of cement. Results showed that higher nanomaterial percentage (i.e., 0.50%) enhanced flexural strength and electric properties without signal fluctuation. Therefore, such sensor was embedded into the beam and the column, both of sizes 100 \(\times\) 100 \(\times\) 500 mm\({}^{3}\). A three-point flexural test was conducted on the beam, and a uniaxial compression test was performed on the column. The recorded measurements in terms of load and electric resistance were characterized by trends very similar to the ones corresponding to the initial sensor testing, in spite of some observed anomalies requiring further development of sensors. The combination of CNTs and CB as conductive fillers in CSC sensors embedded into reduced-scale columns under both monotonic and cyclic axial load tests was experimentally investigated in [74]. The reason of such combination lies in the easier dispersion without sonication with respect to CNTs alone. Fly ash was also added to the mixing. Sensors had dimensions 20 \(\times\) 20 \(\times\) 50 mm\({}^{3}\) and stainless-steel gauzes were used as electrodes. Overall, twelve columns were casted, divided into two groups associated with different concrete strength (C30 and C50, respectively). Three columns for each group were equipped with a sensor placed at the center of the solid during pouring, whereas the remaining three columns were used as benchmark in order to evaluate the influence of the embedded sensor on the mechanical response of the concrete member. Cyclic loading within the elastic limit was applied first to both sensors and concrete columns; then monotonic tests were carried out up to failure. Experimental results showed that: (i) sensors exhibited stable and repeatable measurements under cyclic and monotonic compression either they were embedded into concrete columns or not; (ii) the presence of sensors did not affect the mechanical response of the column; (iii) a difference was recorded between signals collected from embedded and not-embedded sensors, due to the different mechanical properties of concrete and sensors.