Issue 40

Z.S. Metaxa et al, Frattura ed Integrità Strutturale, 40 (2017) 61-73; DOI: 10.3221/IGF-ESIS.40.06 64 According to Nahata et al. [23] mortars cured using the aforementioned procedure demonstrate a slightly lower compressive strength compared to specimens cured in water immersion (specimens cured in water tank at room temperature) demonstrating that the curing procedure adopted in this study does not compromise the mechanical performance of the material. At the age of 28 days the specimens with the embedded sensors were uncovered and were ready for mechanical testing (Fig. 2a and b), while for several specimens the sensor was externally attached (Fig. 2c) before testing. Mechanical testing For the execution of the mechanical tests, a number of experimental devices were used (Fig. 3) that will be explained in the following. An MTS Insight loading frame was used to record the changes in crosshead displacement and mechanical load, a multimeter for the electrical resistance of the embedded PVA-CNT fiber, an interrogator for the respective measurements of the FOBG sensor and finally a data logger for the measurements of the strain gauges. (a) (b) (c) Figure 2 : (a) Prismatic specimen with embedded PVA – CNT fiber (Type I), (b) specimen with embedded PVA – CNT fiber and FOBG fiber and (c) specimen with externally attached PVA – CNT fiber (Type II). Figure 3 : Flow diagram of the experimental procedure. Two types of prismatic specimens were evaluated. The first one (Type I) has embedded sensors and the second one (Type II) has surface attached sensors. The geometrical dimensions of all specimens can be seen in Fig. 4a (Type I specimen is shown), while the loading supports (four point bending) can be seen in Fig. 4b. The three-point bending tests had been performed on specimens with embedded PVA-CNT fiber on the tensile region (fiber close on bottom surface of the specimen). The correctly adjusted / placed specimen at the jigs of the testing machine can be seen in Fig. 5a, where surface-attached strain gauges were also used to monitor the strain changes at the bottom surface of the prismatic specimens (Fig. 5b). As the incremental loading steps have been made to specific levels of fracture stress of the material,