## 2 Materials and Methods
### Experimental Leaching Tests  
In order to evaluate the influence of particle size and crushing conditions on the leaching behaviour of RAs, three RA samples were collected from the two selected CDW treatment plants (here called plant A and plant B) and subjected to experimental leaching tests. Specifically, based on the type of RA generally produced by the plants, a Mixed Recycled Aggregate (MRA) and a Concrete Recycled Aggregate (RCA) were gathered from plant A and a MRA was sampled from plant B, as shown in Table 1.  
All the samples were collected according to the methodology provided by the standard UNI EN 10802. In particular, based on the RA heap volume (less than 1000 m\({}^{3}\)), 10 increments of mass 2 kg were sampled at different heap levels and carefully mixed to obtain a primary sample of about 20 kg. After that, the primary sample was reduced by quartering operations (EN 932-1) in order to obtain a laboratory sample of 10 kg (Figure 2). In laboratory, this sample was then further volumetrically reduced to 2 kg, and based on its moisture and dry matter content, the test portions for leaching were subsequently identified. \begin{table}
\begin{tabular}{c c c} \hline \hline
**RA Sampling Point** & **Recycled Aggregate Type** & **Original Grain Size** \\ \hline \hline Plant A & MRA & 0–90 mm \\ Plant B & MRA & 0–20 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Origin, type, and dimension of the recycled aggregates sampled. Figure 1: Scheme of the box-plot diagram. On the three selected RAs two types of leaching test were performed (Table 2):  
* batch leaching test according to UNI EN 12457-2 with particle size of at least 95% less than 4 mm;
* batch leaching test according to UNI EN 12457-4 with particle size of at least 95% less than 10 mm. In particular, the UNI EN 12457-2 is the leaching test method adopted in Italy, while the UNI EN 12457-4 is the method applied by some EU countries which have already adopted End of Waste criteria (EoW) for CDWs (i.e., Austria, France). To date, in Italy there are no End of Waste criteria for CDWs. Thus, the purpose of performing new leaching tests taking as reference countries with more developed knowledge and policies could represent a basis for new knowledge to support standardization bodies that will adopt national EoW criteria. As aforementioned, to evaluate the possible influence of size reduction and crushing conditions on the leaching behaviour, both tests were carried out, respectively, under conditions of (Table 3):  
* simple sieving until the maximum diameter required by regulations (4 mm or 10 mm), and
* RA crushing until the maximum diameter required by regulations (4 mm or 10 mm). Twelve parallel batch tests were stirred for 24 h at L/S ratio of 10 L/kg. The eluates sampled from all the tests were collected, filtered with a 0.45 mm membrane, and conserved for chemical analysis. To allow discussion of the results, the concentration values below the Limit Of Detection (LOD) were assumed to be equal to the LOD. To identify potentially critical substances, all the leaching concentrations were compared with the legal limit established by the M.D. 186/2006 for recovery of granular materials. Finally, Figure 3 exemplifies the different stages implemented on-site and at the laboratory to obtain representative samples for each RAs analysed, while Figure 4 shows all the tested RA samples. \begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **UNI EN 12457-2:2004** & **UNI EN 12457-4:2004** \\ \hline D\({}_{\text{max}}\) & 4 mm & 10 mm \\ Leaching agent & demineralized water & demineralized water \\ Liquid-to-solid ratio (L/S) & 10 L/kg & 10 L/kg \\ Duration & 24 h & 24 h \\ Extraction n\({}^{\circ}\) & 1 & 1 \\ \hline \end{tabular}
\end{table} 
Table 2: Comparison between the applied test methods (UNI EN 12457-2 and UNI EN 12457-4).