## 3 Results and Discussions  
In Table 1, the tensile properties of _Arundo donax_ fibers are reported in terms of the average value for the 10 specimens, with the corresponding 95% confidence interval according to ISO 22157:2019 ([PERSON], 2019), where as Figure 7 shows the relationship between the applied load and the resulting fiber elongation. From the analyses carried out, it was found that these natural fibers have a remarkably high tensile strength before their yield point, especially if we consider that for an ordinary steel used for construction, the reference value is about 400-700 N mm\({}^{-2}\). Moreover, as highlighted by other authors ([PERSON] et al., 2019), this resistance value is also higher than that of other different natural fibers, such as Spanish broom, which showed lower tensile strength and deformation properties, specifically 41.53 N mm\({}^{-2}\) (natural sprig) and 36.62 N mm\({}^{-2}\) (rope). Indeed, this difference would depend on several factors, such as the origin of the fiber, the manufacturing process, the environment of origin, and the part of the fiber considered. Moreover, the value obtained here for _Arundo donax_ is in line with the value obtained by [PERSON] et al. (2019), who carried out tensile tests on parts of the internode of length equal to 150 cm. They calculated the average elastic modulus of the epidermis for internodes extracted in the central part and at the base of the culm of about 10 GPa, i.e., a value of the same magnitude as that detected during our experimental tests (2.53 GPa--considering a length of 15 cm--see Table 1). In Table 2, the results of the Brazilian tests on the different types of cylindrical concrete sample are reported for each AR, and for the cylindrical concrete sample without any additive fiber. These results are presented in terms of maximum applied load, consequent deformation, and tensile strength. Each of these characteristics is reported as its average value and corresponding 95% confidence interval. In order to give a possible comparison, the tensile strength values by Italian law are also reported in Table 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Maximum Tensile** & **Elongation at Yield** & **Yield Point** & **Young Modules** \\
**Strength [MPa]** & **Point [mm]** & **[MPa]** & **[GPa]** \\ \hline
133.9 \(\pm\) 0.33 & 7.9 \(\pm\) 0.045 & 131.8 \(\pm\) 0.45 & 2.5 \(\pm\) 0.0072 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tensile strength of the _Arundo donax_ fibers experimentally tested. Figure 6: Breakage of the sample, after maximum applied load, along the transversal (**left**) and longitudinal (**right**) directions. Table 2 and Figure 8 show that there is a direct proportionality between the AR of the _Arundo donax_ fibers and the corresponding tensile strength of the reinforced concrete blocks: it increases from a value of 2.2 MPa to 3.4 MPa, corresponding to an increase in the AR from 30 to 70. This increase appears very significant when compared to the small dimensions of our blocks, and especially when compared to the values of the sample without natural fiber (1.6 MPa). It indicates that a proportional increase in the maximum load was tolerated before breaking, and hence a consequent improvement in the deformability characteristics of the composite material. The tensile strength values are in line with the values provided by the Italian Technical Standards for Construction (also reported in the table), in which the strength of the generic sample is calculated as follows:  
\[\text{Tensile Strength}=\frac{(2\times F)}{(\pi\times L\times d)}\]  
where \"F\" is the break load, \"L\" is the sample length, \"\(d\)\" is the diameter of the cylindrical sample.