## 4 Conclusions  
The experimental investigation described in this paper analyzed the feasibility of including sawing sludge in mixtures employed for the formation of Fluidized Thermal Backfills (FTBs). Sawing sludge of two different types was considered and subjected to a thorough preliminary characterization. FTB mixtures containing the two types of sludge and prepared according to a previously developed mix design procedure were characterized in terms of their thermal, mechanical, and environmental properties. The outcomes of the investigation were extremely positive with respect to thermal and mechanical properties. In particular, it was found that the use of sawing sludge was compatible with the achievement of adequate temperature conductivity and stiffness characteristics, which were found to be superior to those of materials commonly employed for backfilling operations around buried electrical high-voltage cables. Furthermore, it was possible to discriminate between the effects produced by \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**FTB Mixture**} & **Ba** & **Cu** & **Zn** & **Co** & **Ni** & **V** & **Cd** & **Cr\({}_{\text{tot}}\)** & **CrVI** & **Pb** & **Fe** \\ \cline{2-11}  & **[mg/L]** & **[mg/L]** & **[mg/L]** & **[g/L]** & **[g/L]** & **[g/L]** & **[g/L]** & **[g/L]** & **[g/L]** & **[g/L]** & **[mg/L]** \\ \hline A-C50-0.85 & \textless{}0.01 & \textless{}0.001 & \textless{}0.001 & \textless{}1 & \textless{}1 & 7.5 & \textless{}1 & 49.6 & 0.04 & \textless{}1 & 51.9 \\ A-C100-0.75 & \textless{}0.01 & \textless{}0.001 & \textless{}0.001 & 4 & \textless{}1 & \textless{}1 & \textless{}1 & 62.1 & 0.05 & \textless{}1 & 30.6 \\ B-C50-0.75 & \textless{}0.01 & \textless{}0.001 & \textless{}0.001 & \textless{}1 & \textless{}1 & \textless{}22 & \textless{}1 & 94.9 & 0.08 & \textless{}1 & 49.5 \\ B-C100-0.75 & \textless{}0.03 & \textless{}0.001 & \textless{}0.001 & \textless{}1 & \textless{}1 & \textless{}1 & \textless{}1 & 84.9 & 0.06 & \textless{}1 & 13.3 \\ Threshold limits for reuse & 1 & 0.05 & 3 & 250 & 10 & 250 & 5 & 50 & - & 50 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Results of leaching tests performed on FTB mixtures (threshold limits defined in [43]). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**FTB Mixture** & **Ba** & **Cu** & **Zn** & **Co** & **Ni** & **V** & **Cd** & **Cr\({}_{\text{tot}}\)** & **CrVI** & **Pb** & **Fe** \\ \hline A-C50-0.85 & 24 & 11 & 11 & 9 & 4 & 9 & \textless{}1 & 63 & \textless{}5 & 2 & 5.120 \\ A-C100-0.75 & 27 & 13 & 12 & 10 & 6 & 10 & \textless{}1 & 13 & \textless{}5 & 2 & 6.993 \\ B-C50-0.75 & 29 & 9 & 10 & 2 & 7 & \textless{}1 & 11 & \textless{}5 & 1 & 4.045 \\ B-C100-0.75 & 26 & 15 & 17 & 3 & 11 & 13 & \textless{}1 & 17 & \textless{}5 & 2 & 3.990 \\ Threshold limits for reuse & - & 600 & 1500 & 250 & 500 & - & 15 & 800 & 15 & 1000 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Chemical composition of FTB mixtures (threshold limits defined in [41], values in mg/kg). the two types of sludge, hypothesizing the mechanisms that lead to different resilient modulus and thermal conductivity values. With respect to environmental properties, obtained results were partially negative in the specific case of leaching tests, since current Italian legal limits that define reuse conditions were violated. Such an outcome, which is not consistent with the results of leaching tests carried out on sawing sludge, may be due either to the presence of an excessive quantity of wear and tear residues coming from cutting tools or to the chromium content of cement. Nevertheless, further investigations need to be carried out in order to support this explanation. Furthermore, a Life-Cycle Assessment (LCA) analysis of the proposed FTB mixtures is deemed necessary to highlight their impact on the environment in terms of energy and water consumption, and the release of CO\({}_{2}\) emissions in order to emphasize the environmental-related benefits of reusing the sawing sludges.