## 4 Results and Discussion  
### Recycled Aggregates  
As stated by [PERSON] et al. [22], the properties of the aggregates obtained from the recovery of returned concrete are strongly related to those of the original aggregates used in the initial concrete mixture. The fine and coarse aggregates obtained by the proposed technology can be aesthetically compared to the original natural aggregates. This is mainly due to the fact that \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Component**} & **C10/15** & **C25/30** & **C30/37** \\ \cline{2-4}  & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** & **(kg/m\({}^{3}\))** \\ \hline Ordinary Portland cement 1 ** & 220 & 310 & 360 \\ Water & 140 & 177 & 178 \\ Superplasticizer & 1.3 & 2.0 & 2.3 \\ Fine aggregate (0/7 mm) & 1078 & 998 & 959 \\ Medium aggregate (7/15 mm) & 333 & 320 & 320 \\ Coarse aggregate (15/31.5 mm) & 549 & 565 & 551 \\ w/c ratio & 0.64 & 0.57 & 0.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concrete mix design. the returned fresh concrete is subjected to an efficient washing process that completely eliminates all the cement paste adhered to the original natural aggregate. The experimental results obtained (Table 3) showed that, in terms of geometrical, physical, and chemical properties, the fine and coarse recycled aggregates comply with all the requirements imposed by the UNI EN 12620 and are, therefore, suitable for new concrete production. In particular, density values in the saturated-surface-dry condition (SSD) equal to 2720 kg/m\({}^{3}\) for both fine and coarse aggregates were recorded (values that fully comply with the minimum regulatory limit of 2300 kg/m\({}^{3}\)). Compared to the density of natural aggregates (typically higher than 2600 kg/m\({}^{3}\)) the density of the new aggregates is well aligned, while compared to recycled aggregates obtained from other returned concrete recovery processes, they show higher density. In particular, the aggregates produced by the method proposed by [PERSON] et al. [22], which involves the use of a superabsorbent polymer capable of transforming the returned concrete into a new granular material, exhibit density values in the range of 2350 kg/m\({}^{3}\) and 2450 kg/m\({}^{3}\). In terms of water absorption (WA), the coarse aggregate highlights a WA value of 0.9% that complies with the maximum regulatory limit of 1% required for concretes operating in exposure class XF (freeze/thaw attack resistance). The presence of light organic impurities, radioactivity and alkali-silica reactivity is also not detected. Finally, the content of water-soluble chloride, acid-soluble sulphates and total sulfur is found to be lower than the respective regulatory limit. Figure 5 shows the particle size comparison between the natural aggregates (NA) used to produce concrete and the recycled aggregates (RA) obtained by the proposed method. Figure 5: Particle size distribution of natural aggregates (NA) and recycled aggregates (RA). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Experimental Test** & **U.M.** & **Fine Recycled** & **Coarse Recycled** & **Limit of UNI** \\  & & **Aggregate** & **Aggregate** & **EN 12620** \\ \hline Sand equivalent & - & 89 & - & \(\geq\)80 \\ Methylene blue & (g/kg) & 0.2 & - & 1.5 \\ Particle density, SSD & (kg/m\({}^{3}\)) & 2720 & 2720 & \(\geq\)2300 \\ Water absorption & (\%) & 1.1 & 0.8 & 1 \\ Alkali-silica reactivity & - & not reactive & not reactive & - \\ Water-soluble chloride content & (\%) & \(<\)0.0012 & - & 0.03 \\ Acid-soluble sulphates & (\%) & \(<\)0.001 & - & 0.2 \\ Total sulfur content & (\%) & \(<\)0.001 & - & 1 \\ Petrographic description & - & continental deposits mainly consisting of carbonate rocks & - \\ Light organic impurities & (\%) & 0 & - & 0.5 \\ Radioactivity & (CPM 2) & absent & absent & absence of radioactivity \\ \hline \hline \end{tabular}  
* \({}^{1}\) Regulatory limit imposed for the coarse fraction only. 2 Counts per minute (CPM).  
\end{table}