## 3 Results and Discussion
### Air Permeability Torrent Test  
The evolutions of the mean values of the air permeability coefficient \(kT\) and the surface electrical resistivity \(\rho_{s}\) are shown in Figures 5 and 6, respectively. The figures incorporate  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Concrete C** & **Concrete C\({}^{\star}\)** \\ \hline \(D_{\text{\tiny{Hss}}}\) mean value (10\({}^{-12}\) m\({}^{2}\)/s) & 23.3 & 22.2 \\ \(D_{\text{\tiny{Hss}}}\) standard deviation (10\({}^{-12}\) m\({}^{2}\)/s) & 6.4 & 1.6 \\ \(C_{\text{S}}\) mean value (\%) & 0.547 & 0.516 \\ \(C_{\text{S}}\) standard deviation (\%) & 0.034 & 0.031 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Fitted parameters to the [PERSON]’s second law of diffusion.  
Figure 4: Chloride profiles.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Time of Testing (Days) 1** & **Parameter** & **Concrete C** & **Concrete C\({}^{\star}\)** \\ \hline
14 & \(WAC_{150}\)\(\left(10^{-3}\frac{\text{kg}}{\text{m}^{2}\cdot\text{min}}\right)\) & 7.0 & 7.3 \\
14 & Standard deviation of \(WAC_{150}\)\(\left(10^{-3}\frac{\text{kg}}{\text{m}^{2}\cdot\text{min}}\right)\) & 3.1 & 3.4 \\
105 & \(WAC_{150}\)\(\left(10^{-3}\frac{\text{kg}}{\text{m}^{2}\cdot\text{min}}\right)\) & 7.9 & 6.1 \\
105 & Standard deviation of \(WAC_{150}\)\(\left(10^{-3}\frac{\text{kg}}{\text{m}^{2}\cdot\text{min}}\right)\) & 2.6 & 3.3 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Water absorption rate at 150 min determined by the Karsten test.  
the corresponding dispersion bars. According to Figure 5, the concrete C* achieved a considerable reduction in the values of \(kT\) in comparison to the reference concrete C. These reductions were in the range 36-55%, thus indicating a better performance of C* regarding gas permeability.  
At first glance, it would be possible to consider the results of Figure 6 to be in contradiction with those of Figure 2: in Figure 6 the concrete C specimens show higher electrical resistivity than those of concrete C*, while the opposite is observed in Figure 2. However, it should be considered that the bulk resistivity measurements of Figure 2 were performed under conditions of full water saturation of the pore network of concrete, while the surface resistivity measurements of Figure 6 were performed in a drying environment (exposure to the lab atmosphere), see Sections 2.4 and 2.7. The permanent exposure to liquid water allows the concrete C* specimens to develop a more closed pore network, as compared to the concrete C, due to the hydrophilic character of the admixture, thus leading to higher values of \(\rho\) in Figure 2. On the other hand, the results of Figure 6 seem to indicate that the drying process of the concrete C specimens is quicker than that of the concrete C* specimens, most probably due also to a more open pore network of C in comparison to C*.  
The quality of a concrete with respect to its permeability to gases can be established according to Table 7 if the resistivity is high enough, or according to nomogram of Figure 7 in any case [23]. The values of \(kT\) and \(\rho_{s}\) have been plotted in the nomogram of Figure 7, showing that these criteria allow classifying the concrete C* with admixture as a good quality one while the reference concrete C would be classified as a normal quality one.  
Figure 5: Evolutions of the mean values of the air permeability coefficient \(kT\) for both concretes. Times are taken after the end of the curing period.  
Figure 6: Evolutions of the mean values of the surface electrical resistivity \(\rho_{s}\) for both concretes. Times are taken after the end of the curing period.