## 4 Results and Discussion
### Diffusion Leaching Tests in FRC Specimens Made with RPF
#### 4.3.2 Long Term Behaviour: Dynamic Tank Leaching Test by UNE-EN 15863: 2015  
For a complete characterisation of the leaching behaviour of specimens in the long term, the dynamic tank leaching test was performed according to UNE-EN 15863:2015, to obtain different eluates over time (\"\(i\)\" fractions). To continue with the study of long-term leaching behaviour, the anions were not included due to their despicable release levels observed in previous sections. In the present section, the regulatory limits indicated by the Soil Quality Decree (SQD) [43] are used as a reference because this regulation specifies criteria for the (re)use of mineral materials in construction applications: \"shaped materials\", and the limits are most accurate to apply to FRC specimens (it prescribes the rules for the use of \"shaped\" construction materials). Table 4 shows the \(pD_{e}\)-values (negative logarithm of effective diffusion coefficient) for the elements which showed the highest mobility levels on concrete samples: Cr, Zn, Sb and Ba, along with cumulative emission (\(\epsilon_{\delta d}\)) and the pH at the start and the end of the test. The pH of the eluates collected did not vary significantly over the course of the test, presenting values corresponding to a medium alkaline, as expected. Only the elements Cr, Zn, Sb and Ba are represented because they present the higher mobilities. The cumulative emission for the elements in Table 4 did not present any substantial differences between the samples. The results obtained were consistent with the data obtained by previous researchers, in terms of cumulative emission at 64 days [28; 44] and diffusion coefficient [45] in concrete. The higher \(pD_{e}\) value implies the lower speed of leaching of the component concerned with constant availability \(U_{availability}\). The \(pD_{e}\) value determines the concentration gradient, which is the driving force for diffusion of the pollutant elements studied: \(pD_{e}>12.5\): component with low mobility; \(11.0<pD_{e}<12.5\): component with average mobility; \(pD_{e}<11.0\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Parameters** & **C-REF** & **FRC2-REF** & **FRC2** & **FRC4** & **FRC6** \\ \hline \multirow{5}{*}{Cr} & Initial pH & 10.2 & 10.4 & 10.3 & 10.2 & 10.4 \\  & Final pH & 10.1 & 10.2 & 10.2 & 10.1 & 10.2 \\  & Cumulative emission. \(\varepsilon_{\delta d}\) (mg/m\({}^{2}\)) & 0.125 & 0.189 & 0.135 & 0.185 & 0.168 \\  & Diffusion coefficient. \(D_{e}\) (m\({}^{2}\)/s) & \(1.500\times 10^{-14}\) & \(8.270\times 10^{-14}\) & \(1.580\times 10^{-14}\) & \(2.800\times 10^{-14}\) & \(1.240\times 10^{-14}\) \\  & \(pD_{e}\) & 13.820 & 13.080 & 13.800 & 13.550 & 13.910 \\ Zn & Cumulative emission. \(\varepsilon_{\delta d}\) (mg/m\({}^{2}\)) & 2.271 & 2.778 & 2.504 & 2.020 & 2.207 \\  & Diffusion coefficient. \(D_{e}\) (m\({}^{2}\)/s) & \(3.770\times 10^{-14}\) & \(1.380\times 10^{-14}\) & \(3.410\times 10^{-14}\) & \(1.660\times 10^{-14}\) & \(2.480\times 10^{-15}\) \\  & \(pD_{e}\) & 13.420 & 13.860 & 13.470 & 13.780 & 14.610 \\ Sb & Cumulative emission. \(\varepsilon_{\delta d}\) (mg/m\({}^{2}\)) & 0.717 & 0.643 & 0.861 & 0.342 & 0.729 \\  & Diffusion coefficient. \(D_{e}\) (m\({}^{2}\)/s) & \(4.580\times 10^{-14}\) & \(6.940\times 10^{-14}\) & \(7.010\times 10^{-14}\) & \(1.600\times 10^{-14}\) & \(3.970\times 10^{-14}\) \\  & \(pD_{e}\) & 13.340 & 13.150 & 13.150 & 13.800 & 13.400 \\ Ba & Cumulative emission. \(\varepsilon_{\delta d}\) (mg/m\({}^{2}\)) & 4.261 & 3.965 & 3.992 & 3.277 & 3.403 \\  & diffusion coefficient, \(D_{e}\) (m\({}^{2}\)/s) & \(8.130\times 10^{-14}\) & \(5.480\times 10^{-15}\) & \(5.100\times 10^{-15}\) & \(4.530\times 10^{-15}\) & \(1.710\times 10^{-15}\) \\  & \(pD_{e}\) & 14.090 & 14.260 & 14.290 & 14.340 & 14.770 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Cumulative emission (\(\epsilon_{\delta d}\)), diffusion coefficient (\(D_{e}\)) and \(pD_{e}\). component with high mobility, according to the NEN 7343.