# 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  
RC beams strengthened by means of RC layers doped with CFs (CFRC) were tested under four-point bending by [PERSON] and his co-authors [75] in order to investigate their viability as strengthening solution as well as monitoring system (see Figure 4). A total of eighteen 3000 mm long beams characterized by different location and thickness of strengthening layers were tested. These layers consisted of a mix of CFs (5% by weight of cement), cement, fine aggregate, coarse aggregate, and water. Steel reinforcement was wrapped by epoxy resin to prevent metallic conductivity, whereas four stirrups spaced at 200 mm in the central part of the beam were used as electrodes. CFRC layers were put on plain concrete during casting operations. The electrical resistance measurements were made by means of the principle of Wheatstone bridge according to which the initial electrical resistance of the whole beam (included  
Figure 4: RC beam strengthened by CF-doped RC layers (adapted from [75]). top and bottom layers connected in parallel) was first measured; known the resistance of the remaining bridge arms, the resistance of the beam depending on the applied load was derived. Hence, the presence of CFRC layers directly affected the electrical properties of the beams, decreasing the initial electrical resistance and yielding a larger increase of the electrical resistance at increasing layer thickness. Nevertheless, the adopted measuring method prevented a separate monitoring of top and bottom layers. Somehow consistent relationships between electrical resistance, loading, deflection/strain and cracks were observed only from a qualitative point of view. Furthermore, the construction technology seems quite complex and expensive to be applied at large scale. A comparative analysis of the experimental results obtained from cyclic tests on three RC shear-critical columns was presented in [76]; two columns were doped with SFs and carbon nano-fibers (CNFs), respectively, whereas the remaining one was made of plain RC and used as benchmark case. Assessing if functional fillers enhanced structural performance and created self-sensing capacity were the objectives of the research. All the columns had low aspect-ratio. CNFs and SFs were introduced in the mixing at a dosage of 1% by volume, based on the results of an extensive number of trials. Wire meshes with soldered gauge copper wire were placed at four cross-sections (four-probe method), as shown in Figure 5. The experimental outcomes proved that the addition of SFs and CNFs to concrete improved the structural capacity of the column, but only SFs showed a potential as a solution for SHM, at least in the elastic field. CSCs doped with CNFs and CFs have been applied to RC beams as strain and damage sensors in [77]. Cement paste was used as matrix for the sensors, with a fixed 0.5 w/c ratio. Five different dosages of conductive admixtures were prepared: one with 2% CNFs, two with 1% of different types of CFs, and the others with CFs subjected to an oxidation treatment. Mechanical stirring and sonication were applied for mixing and dispersion. Two different sizes of prismatic sensors were made, namely 20 \(\times\) 20 \(\times\) 80 mm\({}^{3}\) (Type A) and 200 \(\times\) 7 \(\times\) 80 mm\({}^{3}\) (Type B). The four electrical contacts consisted of strips of silver paint applied on the perimeter, to which four copper wires were wrapped. A total number of 28 sensors were installed on a RC beam of dimensions 200 \(\times\) 300 \(\times\) 3900 mm\({}^{3}\); they were placed in the central part of the beam at different locations (Figure 6). Under the four-point bending scheme, all sensors were subjected to the same value of bending moment. Two different installation methods were applied: bonding by means of epoxy resin and direct casting. Both strain-sensing and damage-sensing cyclic tests were performed; they were respectively characterized by reduced maximum load and increasing loading up to failure.