## 3 Results and Discussion
### Sustainability Evaluation of the Proposed Technology  
EE and CF parameters of the synthesis of the proposed new filler were considered to evaluate environmental sustainability. Data about EE and CF of the recycled stabilized material were obtained by using the CES Selector software [48] taking into account the stabilization procedure, which involves the bottom ash grinding and considering the mixing of different ashes typologies, as described in the experimental section and discussed in literature [21]. For the stabilized material, an embodied energy ranging from 0.061 to 0.062 MJ/kg and a CO\({}_{2}\) footprint of about 0.03 kg/kg resulted. Table 4 reports the SUB-RAW indices evaluated by comparing the new proposed material with respect to calcite, which is a natural resource that is often used as a filler, to produce some composites. As a reference, this index was also calculated in comparison with sandstone, talc and resin used to synthesize the composites for this work. From calculated SUB-RAW indices, it is evident that the new proposed inert is more sustainable if compared to some natural resources, as for example calcite, talc and sandstone. Obviously it is also more sustainable with respect to a resin [49]. Then, it is possible to conclude that it may be used to produce composited materials. In principle, its market applicability is potentially very promising. To evaluate this, also the price of the materials reported in this work have been considered. Figure 9 shows the EE for several materials (ceramic, glass and composites) as a function of their commercial price. Data were obtained from CES Selector 2019 [48]. Data on the carbon footprint of \begin{table}
\begin{tabular}{c c} \hline \hline
**Materials** & **SUB-RAW Index-New Filler** \\ \hline Sandstone & 1.24 \\ Calcite & 0.83 \\ Talc & 2.24 \\ Resin & 3.31 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: SUB-RAW Indices were calculated comparing the obtained composite using stabilized FA sample with other materials. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & \multicolumn{8}{c}{**Elemental Concentration (\%)**} \\ \cline{2-10}  & **C** & **O** & **Si** & **Cl** & **Ca** & **Al** & **Mg** & **K** & **S** \\ \hline
100\% ER & 66.34 & 29.75 & 2.18 & 1.16 & 0.57 & – & – & – & – \\
10\% CaCO\({}_{3}\) & 66.46 & 29.22 & 1.92 & 0.65 & 1.74 & – & – & – & – \\
30\% CaCO\({}_{3}\) & 57.91 & 30.3 & 8.44 & – & 3.63 & – & – & – & – \\
50\% CaCO\({}_{3}\) & 58.37 & 34.21 & 1.35 & 0.52 & 5.55 & – & – & – & – \\
70\% CaCO\({}_{3}\) & 32.02 & 38.42 & 2.82 & 0.26 & 26.48 & – & – & – & – \\
9\% SSC & 66.81 & 25.96 & 5.04 & 1.07 & 1.12 & – & – & – & – \\
10\% SSC & 68.53 & 29.04 & 0.60 & 1.04 & 0.80 & – & – & – & – \\
30\% SSC & 63.93 & 31.88 & 1.16 & 1.37 & 1.67 & – & – & – \\
50\% SSC & 57.77 & 26.84 & 2.86 & 4.32 & 7.53 & 0.68 & – & – & – \\
70\% SSC & 47.68 & 30.47 & 2.08 & 5.68 & 10.43 & 1.02 & 0.38 & 0.51 & 1.77 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical characterization by SEM analysis of epoxy resin (ER), CaCO\({}_{3}\)-composite (CaCO\({}_{3}\)) and stabilized sample-composite (SSC). the same materials, reported as a function of their commercial price, have the same behavior already shown by [PERSON] et al. [34], therefore they are not reported in this paper. In correspondence of the EE of the new proposed material, an orange dotted horizontal line is reported. From the analysis of Figure 9, it can be seen that the new obtained stabilized material can be compared to wollastonite in terms of the EE environmental parameter used to quantify the sustainability of a material. Figure 9 shows that the energy needed to synthesize the new proposed material is lower than that of the almost majority of ceramic and glass materials. It results evident that it is more sustainable that the previous proposed COSMOS filler, obtained by adding an external silica source [16; 39] to stabilize MSWI FA. Indeed, EE of COSMOS resulted higher than that of calcite.