## 3 Results and Discussion
### FRAAM Composite: Mechanical Behavior  
Direct tensile and direct shear tests were carried out to investigate the load-bearing capacity, bond strength on substrate and failure modes of FRAAM composites. In Figure 12, the tensile tests, reported in terms of stress vs. strain response curves are shown. Stress was calculated according to Equation (2). Strain was calculated by dividing the recorded displacements by measurement base of the devices. Based on the obtained response curves, it can be concluded that the behavior of the material is similar to the generally accepted relationship, which is shown in Figure 13. Region I corresponds to the un-cracked stage in which the mortar contributes to both the stiffness and the load-bearing capacity of the composite; region II, which begins with the occurrence of the first crack in the matrix, corresponds to the crack development stage; finally, region III, which corresponds to the post-cracking stage, is followed by failure of the reinforcement [6; 14]. When the composites show, under direct tensile test, a tri-linear stress-strain response curve the behavior can be assessed by computing the stress and strain at the first mortar cracking, that represents the transition between region I and II and tensile modulus of elasticity in region I; the stress and strain at the transition between region II and III and tensile modulus of elasticity in region II; the ultimate stress, strain and tensile modulus of elasticity in region III, that were evaluated according to [PERSON] et al. [45]. Furthermore, exploitation ratio can be obtained as follows:  
\[\text{Exploitation ratio [vs. textile]}=\sigma_{\text{u}}/\sigma_{\text{f}}\]  
where  
\(\sigma_{\text{u}}=\text{composite ultimate tensile strength}\)  
\(\sigma_{\text{f}}=\text{textile tensile strength}\)  
Figure 12: Tensile test: stress vs. strain response curves. All the calculated values, for each specimen tested, as well as their average and exploitation ratios, are reported in Table 4.  
The high \(\varepsilon_{\text{I}}\) scattering is associated with the presence, in some specimens' response curve, of a linear branch followed by a non-linear response up to the onset of the first crack. The presence of a nonlinear response in region I was also observed by [PERSON] et al. [45] and was attributed to a gradual microcracking or pre-existing microcracks of the matrix not visible to the naked eye [46], resulting in the first macro-crack. In this case, \(\text{E}_{\text{I}}\) was evaluated as the slope of the linear branch [45]. For the examined composite, pre-existing microcracks could have formed during curing as a consequence of mortar shrinkage. In region II the slope of the crack development stage was calculated by fitting the stress-strain curve between points (\(\sigma_{\text{I}}\), \(\varepsilon_{\text{I}}\)) and (\(\sigma_{\text{II}}\), \(\varepsilon_{\text{II}}\)) [45]. Stress \(\sigma_{\text{II}}\) and the corresponding strain \(\varepsilon_{\text{II}}\) define the point of transition between region II and region III, which corresponds to the onset of the linear branch of the stress-strain curve where the applied load is carried out only by the fibers. The fitting process provides a slope that is different from that corresponding to the line connecting points (\(\sigma_{\text{I}}\), \(\varepsilon_{\text{I}}\)) and (\(\sigma_{\text{II}}\), \(\varepsilon_{\text{II}}\)). In region II, multiple cracking occurs that causes the stress-strain curves to show several drops, which indicate abrupt, brief partial unloading of the specimen due to formation of new cracks and therefore redistribution of deformations over the specimen length [6]. The higher dispersion of the