# 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
Figure 5: Resistivity measurement layout for RC shear-critical columns (adapted from [76]). Experimental results showed that both CNFs and CFs were able to measure superficial strain, even if better sensing capacity was achieved by 2% CNF sensors. Furthermore, the thinner the sensor the better the performance, probably due to the large adhesion surface (wide as the RC beam) and to the reduced strain gradient along sensor depth. Finally, negligible effect of the installation method on the sensing capacity was observed. The influence of loading rate on the sensing capacity of CSCs doped with CNFs was investigated by [PERSON] and his co-authors [78]. 25.4 mm wide cubic sensors, equipped with four copper mesh electrodes, were installed in critical regions of four full-scale RC columns designed to fail in shear. Specifically, sensors were electrically isolated with epoxy resin and fixed to stirrups involved in the shear-resisting mechanism by using plastic zip ties before concrete casting. Cyclic loading with increasing amplitude was applied at different rates for each column. Based on the experimental results, the Authors concluded that sensors performed reasonably well under a qualitative point of view, even if further studies would have been needed to establish a quantitative relationship between damage levels and measured electrical resistance variation. In [79] the effect of micro-CFs on the strain sensing ability and structural capacity of RC beams in the absence of stirrups was experimentally investigated. Three beams with 125 \(\times\) 350 \(\times\) 1500 mm\({}^{3}\) dimensions and characterized by different longitudinal reinforcement ratios were monotonically tested up to failure under four-point bending scheme. CFs were introduced in the concrete mix and this was poured at top and bottom surfaces of mid span sections for a length of 350 mm and a depth of 78 mm (Figure 7). Electrically conductive paint was applied on top and bottom surface of RC beam close to the point of application of the load. Copper wires were connected to the conductive paths via adhesive tape. Before loading, different initial electrical resistance values and gauge factors between compression and tension side were recorded, due to the presence of longitudinal reinforcement. However, this did not significantly affect the experimental results, yielding well correlated strain and electrical resistance variation both in tension and compression; specific equations obtained through regression analysis of measurements were proposed to evaluate the strain known the fractional change in electrical resistance, in order to continuously monitor the beam response. Figure 6: Distribution of CSC sensors and patches on RC beam under four-point bending test (adapted from [77]). The first experimental study focusing on the structural monitoring performance of CSCs doped with MWCNTs and embedded into RC beams subjected to static and dynamic excitations is reported in [53]. Cubic CSCs (with 5 cm edge) were prepared. Cement paste was doped with 1% MWCNTs by weight of cement and w/c ratio was 0.45. Filler dispersion was achieved by using dispersant and sonication. Resistivity measurements were performed by employing both two-probe and four-probe configurations in DC current and under controlled temperature. The electromechanical tests carried out on cubic sensors under both cyclical and dynamic compressive loads confirmed the strain sensitive properties of sensors. Furthermore, the response was almost constant with respect to frequency, although for some sensors a linear trend was observed. After CSC characterization, seven sensors were embedded at the top of a full-scale simply-supported RC beam subjected to both static bending loading (CSC under compression stress) and dynamic impulse loads (Figure 8).