## 3 Results and Discussion  
The results of helium piconmetry analysis on untreated and boiled fibers (Figure 5) showed that the thermal treatment is supposed to modify the chemical composition of the diss fibers probably due to the removal of sugar and extractives as also reported by other authors in the literature [8,13]. SEM image analysis of the two types of plants (Figure 6) evidenced the different surface morphology between diss and crimson fountaingrass fibers. In fact, the former are characterized by the presence of spines, which may improve the adhesion between fibers and cementitious matrix due to the better mechanical interlocking, while the latter present a smooth surface. It is also important noting that the thermal treatment does not affect the morphology of the fibers as can be demonstrated by observing the Figure 7 that shows the permanence of the spines on the diss fibers' surface after the boiling treatment. Quantitative EDX analysis (Figure 8) on the ashes of untreated diss and crimson fountaingrass evidenced the higher content of silicon in the former (approximately 22% by weight) compared to the latter (approximately 9%). This result may indicate that diss fibers are characterized by either better mechanical properties or higher reactivity with the cementitious matrix. The latter can be due to the SiO\({}_{2}\) content in the fibers may react with the portlandite present in the matrix to produce further calcium silicate hydrates which are responsible for the mechanical properties of the cement. The STA results confirmed those obtained by  
Figure 5: Density results of untreated and treated diss and crimson fountaingrass fibers. EDX since the amount of uncombusted was higher for the diss rather than the crimson fountaingrass fibers (Figure 9). Figure 8: Comparison of quantitative elemental composition between diss (**left**) and crimson fountaingrass ashes (**right**). Figure 6: Comparison between untreated diss (**left**) and crimson fountaingrass fibers (**right**). Figure 7: Comparison between untreated (**left**) and boiled (**right**) diss fibers. The results of the heat flow meter test of the fibers shown in Table 1 evidenced good insulating properties of both the types of plants with values of thermal conductivity equal to 0.059 W/mK and 0.054 W/mK, respectively for diss and crimson fountaingrass aggregates. These results are in accordance to the higher apparent density of the pile of the _Ampelodesmos mauritanicus_ fibers compared to the _Pennisetum staceum_ ones (Table 1). The results of the mechanical tests (Figures 10 and 11) on the mortars showed that diss aggregate leads to better performances both in terms of flexural and compression strength compared to crimson fountaingrass one. This can be due to either the better morphology or the chemical composition of the diss compared to the crimson fountaingrass fibers as verified by the results of the fibers' characterization. The thermal treat \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Type of Aggregate**} & \multicolumn{2}{c}{**Thermal Conductivity \(\lambda\)**} & \multirow{2}{*}{**Amount of Aggregate (g)**} & \multirow{2}{*}{**Volume (cm3)**} & **Apparent Density of the Pile (g/cm3)** \\  & **(W/mK)** & & & **Pile (g/cm3)** \\ \hline _Ampelodesmos_ & \multirow{2}{*}{0.059} & \multirow{2}{*}{280.4} & \multirow{2}{*}{900} & \multirow{2}{*}{0.312} \\ _muritanicus_ & & & & \\ \hline _Pennisetum_ & \multirow{2}{*}{0.054} & \multirow{2}{*}{240.5} & \multirow{2}{*}{900} & \multirow{2}{*}{0.267} \\ _setaceum_ & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Thermal conductivity and Apparent density of the aggregates. Figure 9: STA of diss (**above**) and crimson fountaingrass (**below**) fibers. ment significantly improves the mechanical properties of the mortars additivated with _Ampelodesmos mauritanicus_ aggregates.