# Applications of Cement-Based Smart Composites to Civil Structural Health Monitoring: A Review
## 3 Applications to SHM of Structural Prototypes
### Medium and Full-Scale Members
The experimental results demonstrated the effectiveness of sensors under static loads, while fairly accurate strain measurements were obtained at the very low strain levels associated with the applied dynamic loads; nevertheless, Power Spectral Densities (PSDs) computed by processing the dynamic signals from traditional strain gauges and CSC sensors confirmed that the latter were promising also for modal testing. The same research group performed further experimental studies on the RC beam of Figure 8 with the aims of investigating the performance of CSCs in resolving the dynamic response of the beam [80] and of validating a multichannel strain measurement technique able to retrieve strain distribution along the member under static load [62]. In the first study [80] the electromechanical response of sensors was first assessed by means of cyclic load tests, aimed at calibrating relevant sensor parameters before embedment; vibration tests were conducted on the RC beam afterwards. This study remarks the importance of a specific calibration of the sensor before embedment into structural members. The results also showed that sensors were able to reveal impulsive loads and to provide dynamic strain measurements useful for modal identification of the beam. In order to evaluate the reliability of results, traditional transducers (piezoelectric accelerometers) were installed on the beam; results from embedded CSC sensors and piezoelectric accelerometers were in good agreement with each other, confirming the promising applicative perspectives of CSC sensors for SHM of full-scale concrete structures. Figure 8: Distributed embedded sensors in a RC beam (adapted from [53]). Figure 7: Cast-in-situ CSC sensors installed at top and bottom surfaces of the midspan section of a RC beam (adapted from [79]). In [62] the RC beam was subjected to four point bending loading (with CSCs under compression) and, starting from each sensor output, the strain distribution along the structural member was derived. The comparison of the retrieved strain distribution with the results of a simplified analytical model revealed satisfactory sensing performance. [PERSON] and [PERSON] [54] proposed an experimental study on CSCs aimed at assessing their potential for vibration-based SHM of large structures. MWCNTs were introduced into cement paste. Three different types of MWCNTs were considered: one non-functionalized pristine-MWCNT (P-MWCNT) and two chemically functionalized MWCNT, one by hydroxyl(-OH) group and the other by carboxyl acid (-COOH) group. SDBS was also used as dispersant. The adopted w/c ratio was equal to 0.4 for all the mixtures. A combination of chemical and physical methods in series were adopted for filler dispersion (i.e., dispersion in solvent followed by sonication). For each group of MWCNTs, four different dosages were considered: 0.10, 0.25, 0.50, 0.75 (%) by weight of cement. Three samples of size 50 \(\times\) 50 \(\times\) 50 mm\({}^{3}\) for each MWCNT type were fabricated. Electrical conductivity as a function of MWCNT dosage was measured by means of preliminary electrical tests. Then, experimental tests under cyclic compression were performed on cubic sensors with maximum applied load equal to 25% of the capacity, showing that: (i) for CNT concentrations lower than 0.50% the change in electrical resistance was not reversible and stable; (ii) the sensitivity of COOH-MWCNT was higher than others due to the enhanced chemical bond between fillers and surrounding cement matrix, increasing the load transfer capacity; (iii) the relationship between FCR and strain was linear. The evaluation of the vibration sensing capacity of CSCs was conducted afterwards by exciting through an impulse hammer a RC full-scale beam, 4500 mm long and representative of an existing bridge girder, on which CSCs were installed on top surface at the mid-span by means of a mechanical anchor device (Figure 9). The sensor was electrically isolated by means of two plastic sheets and the benchmark was given by three accelerometers placed at the bottom of the beam.