## 4 Results and Discussion
### Washing Water  
The microfiltered water obtained by the treatment process is characterized as mixing water for new concrete production, according to UNI EN 1008. As stated above, the microfiltered water was subjected to: (1) preliminary evaluation tests, (2) analysis of the chemical properties, (3) evaluation of the cement paste setting times and, finally (4) evaluation of the compressive strength of the normalized mortar samples. In this context, Table 5 shows the results related to the preliminary assessment tests and to the chemical properties of microfiltered water. In particular, the results demonstrate that the microfiltered water fully complies with all the limits imposed by the UNI EN 1008 standard. Specifically, the pH is strongly alkaline (12.8). As stated by [PERSON] et al. [32], [PERSON] et al. [33], and [PERSON] et al. [27], this is probably due to the presence of residual cement particles in the water. \begin{table}
\begin{tabular}{c c c c c} \hline
**Parameter** & **U.M.** & **Fine Recycled Aggregate** & **Coarse Recycled Aggregate** & **Limit of M.D. 186/2006** \\ \hline pH & - & 12 & 10 & 5.5–12 \\ Specific electrical conductivity & (\(\upmu\)S/cm) & 2440 & 77 & - \\ Asbestos & mg/L & (**) & (**) & 30 \\ Nitrates & mg/L & \(<\)1 & \(<\)1 & 50 \\ Fluorides & mg/L & 0.2 & 0.1 & 1.5 \\ Subplates & mg/L & 9 & 3 & 250 \\ Chlorides & mg/L & \(<\)1 & \(<\)1 & 100 \\ Cyanides & \(\upmu\)g/L & \(<\)5 & \(<\)5 & 50 \\ Barium & mg/L & 0.34 & 0.24 & 1 \\ Copper & mg/L & \(<\)0.01 & \(<\)0.01 & 0.05 \\ Zinc & mg/L & 0.06 & \(<\)0.05 & 3 \\ Beryllium & \(\upmu\)g/L & \(<\)0.5 & \(<\)0.5 & 10 \\ Cobalt & \(\upmu\)g/L & \(<\)5 & \(<\)5 & 250 \\ Nickel & \(\upmu\)g/L & \(<\)2 & \(<\)2 & 10 \\ Vanadium & \(\upmu\)g/L & \(<\)5 & \(<\)5 & 250 \\ Arsenic & \(\upmu\)g/L & \(<\)1 & \(<\)1 & 50 \\ Cadmium & \(\upmu\)g/L & \(<\)0.5 & \(<\)0.5 & 5 \\ Total chromium & \(\upmu\)g/L & 13 & \(<\)5 & 50 \\ Lead & \(\upmu\)g/L & 2 & \(<\)1 & 50 \\ Selenium & \(\upmu\)m/L & \(<\)1 & \(<\)1 & 10 \\ Mercury & \(\upmu\)g/L & \(<\)0.1 & \(<\)0.1 & 1 \\ COD & mg/L & 8 & \(<\)5 & 30 \\ \hline \end{tabular} (**) parameter not detectable as the filtration at 0.45 \(\upmu\)m as required by the UNI EN 12457-2 for the preparation of the climate does not allow the passage of identifiable and measurable fibers with the current techniques in use (electron microscopy scanning with energy-dispersive X-ray spectrometry (EDS)).  
\end{table} 
Table 4: Leachate concentrations from fine and coarse recycled aggregates. The amount of chlorides and sulphates is within the required limits and these results confirm what other authors said [29]. The initial setting time obtained on specimens made with the water shall be not less than 1 h and not differ by more than 25% from the initial setting time obtained on specimens made with demineralized water. At the same time, the final setting time shall not exceed 12 h and not differ by more than 25% from the final setting time obtained on specimens made with demineralized water. Table 6 shows the results obtained on the manufactured cement paste samples; both requirements are satisfied. In particular, the control mix achieved an initial setting time of 125 min and a final setting time of 280 min, while samples containing microfiltered water had a slower setting time, giving initial and final setting times that are 20 and 15 min longer than those of the control mix, respectively. This may be due to the fact that microfiltered water still contains some small residual particles of cement which can increase the initial and final setting time. This can also be linked to the presence of particular cements (e.g., blast furnace cements containing blast furnace slag), which are known to increase the setting time of concretes for the same w/c ratio [29]. In fact, the returned concretes treated by the system can have different mix-design and, therefore, it is possible to hypothesize that sometimes different types of cement are used.