## 5 Results and Discussion
### Chemical Characterization (CC) of RA, FA, A1, A2 and A3 Eluate Samples  
The results for the non-metallic and metallic parameters from the CC of the eluate samples obtained from of the raw materials (RA and FA) and concrete mixes (A1, A2, and A3) under study are presented in Table 7. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Parameters**} & **RA** & **FA** & **A1** & **A2** & **A3** \\ \hline \multirow{8}{*}{Non-metallic parameters} & pH at 22 \({}^{\circ}\)C & 12.5 & 11.8 & 12.5 & 12.4 & 12.1 \\  & ELC (\(\mu\)S/cm) & 6950 & 1672 & 6950 & 4300 & 3560 \\  & DOC (mg/kg) & 88 & 23 & 88 & 11 & 100 \\  & TDS (mg/kg) & 17,000 & 6450 & 17,000 & 12,000 & 9200 \\  & Chloride (mg/kg) & 15 & \textless{}30 & 15 & 19 & 34 \\  & Fluoride (mg/kg) & \textless{}10 & \textless{}10 & \textless{}10 & \textless{}10 & \textless{}10 \\  & Sulphate (mg/kg) & \textless{}30 & 4400 & \textless{}30 & \textless{}30 & 37 \\ \hline \multirow{8}{*}{Metallic parameters} & As & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 \\  & Ba & 4.0 & 4.6 & 4.0 & 9.0 & 8.0 \\  & Cd & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 & \textless{}0.1 \\  & Cr & \textless{}0.5 & 2.5 & \textless{}0.5 & 0.5 & 0.7 \\  & Cu & \textless{}1.0 & \textless{}0.5 & \textless{}1.0 & \textless{}1.0 & \textless{}1.0 \\ \multirow{2}{*}{Metallic parameters} & Hg & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 \\  & Mo & \textless{}0.3 & 10.0 & \textless{}0.3 & 0.6 & 1.00 \\  & Ni & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 \\  & Pb & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 \\  & Sb & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 & \textless{}0.4 \\  & Se & \textless{}0.2 & 4.0 & \textless{}0.2 & \textless{}0.2 & \textless{}0.2 \\  & Zn & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 & \textless{}0.5 \\ \hline \hline \end{tabular} Legend: ELC = Electrical conductivity; DOC = Dissolved organic carbon; TDS = Total dissolved solids; RA = Recycled aggregates; FA = Fly ash; A1 = Aggregates recycled from NAC; A2 = Aggregates recycled from C40 FA60 NA100; A3= Aggregates recycled from C40 FA60 NA100.  
\end{table} 
Table 7: Data of the chemical characterization of the eluate samples. Regarding the non-metallic parameters, it was found that all the eluate samples were highly alkaline, with pH values varying in the following order: FA (pH = 11.8) \(<\) A3 (pH = 12.1) \(<\) A2 (pH = 12.4) \(<\) A1 = RA (pH = 12.5) (Table 7). The lower pH value of FA was compared with the results of [PERSON] et al. [45] and [PERSON] et al. [10]. The value from our study was closer to the mean value of [PERSON] et al. [10], possibly because the leachates were produced based on the same standard procedure [31]. The pH values of RA, A1, A2 and A3 eluates are common in this type of construction materials; they are close to concrete's pH (approximately 12.5) and are slightly higher than that of FA (Table 7). These high pH values may be due to the presence of carbonates, oxides and hydroxides formed during combustion processes [26]. On what concerns the concrete mixes, it is worthy to note that the eluate pH slightly decreased (about 0.4 pH units) with the incorporation of 60% of FA and 100% of RA (comparing A3 to A1; Table 7). However, as the pH value of FA depends on the sulphur content of the source coal, it can vary between 4.5 and 12.0 [46; 47]. Therefore, this study suggests that the incorporation of FA in concrete may lead to a decrease of the pH of the respective eluates, possibly contributing to a lower possible negative impact of alkaline eluate runoff (for instance, due to heavy raining) into aquatic environments, in landfills and/or during building service.