# Applications of Cement-Based Smart Composites to Civil Structural Health Monitoring: A Review
## 3 Applications to SHM of Structural Prototypes
### Reduced-Scale Members  
The monitoring capacity of CSCs doped with carbon black (CBCSCs) when embedded in reduced-scale unreinforced concrete (UC) columns was investigated in [71]. CB in the amount of 15% by weight of cement was used as filler, with a w/c equal to 0.4. 30 \(\times\) 40 \(\times\) 50 mm\({}^{3}\) CBCSC samples were equipped with four copper nets across the whole cross-section. Sensors were cured in moist room for 28 days and, subsequently, dried at 60 \({}^{\circ}\)C for 48 h and, finally, encapsulated with an epoxy layer providing waterproof protection. CBCSC sensors were tested under cyclic axial loading, showing a stable and reversible response for low loading levels, whereas, for high stress levels with respect to the compressive strength (i.e., 70%), measurements were unstable. Two groups of six reduced-scale UC columns of size 100 \(\times\) 100 \(\times\) 300 mm\({}^{3}\) were built: they were characterized by different concrete strength class (equal to C40 and C80, respectively). Sand and coarse aggregate were added to the same cement matrix of sensors. For each group, three columns were equipped with sensors and the remaining were considered as reference case, aiming at investigating also the possible influence of the embedded sensors on the mechanical response. Cyclic axial loading was applied (up to 30% of theoretical column axial capacity), first; monotonic tests were performed afterwards up to failure (Figure 2). Measurements from traditional transducers and strain gauges were used as benchmark. The stability of CBCSC sensor measurements in the case of cyclic loading in elastic regime was confirmed. Conversely, under monotonic loading, the embedded sensors showed good strain sensing capacity in elastic regime, whereas measurements were not reliable beyond the elastic limit, probably due to increasing transverse deformation. Failures of sensors and columns were not simultaneous: this result points out that matching of strength between sensor and concrete matrix is crucial to guarantee efficiency of strain sensing measures. Such matching should consider the triaxial loading strength of CBCSCs. Sensing performance of CBCSCs embedded in reduced-scale beams subjected to monotonic as well as cyclic axial compression and three-point bending loading was investigated in [72]. The choice of the CB filler was due to its reduced cost with respect to CNTs. Three CBCSC types different for CB concentrations were realized and, due to decreased flowability, higher w/c ratios were applied, ranging between 0.35 and 0.45. The first admixing method was adopted and the resulting composite was poured into 10 \(\times\) 10 \(\times\) 60 mm\({}^{3}\) metal molds. Four copper meshes were inserted into each sensor. After a standard curing process, each piece was cut in the middle to obtain two 10 \(\times\) 10 \(\times\) 30 mm\({}^{3}\) CBCSCs. 40 \(\times\) 40 \(\times\) 160 mm\({}^{3}\) beams were realized with the same material. CSC specimens were directly inserted into the beams during the vibration process both in compression and tension zones, according to the configurations depicted in Figure 3. Before the execution of three-point bending tests, under monotonic and cyclic low-level regimes, three beams equipped with as many sensors as the different CB-concentrations considered in the study were subjected to pure cyclic compression with the aim of assessing their self-sensing capacity. Sensor with 2% CB exhibited the best fractional changes of resistivity (FCR) and monitoring sensitivity compared to those with 0.5% and 1% CB, even if repeatability of measures increased as CB content decreased and, at low stress values, the difference in FCR readings among the sensors were more limited.