## 3 Results and Discussion
### Influence of the Type of Binder on the Chloride Penetration Resistance
[9] reported the reduction of porosity and pore refinement in concrete with 27% FA water cured for 90 days, suggesting a greater chloride binding capacity of concrete with FA compared to concrete with CEM I [20]. In fact, the high alumina content of FA may contribute to the chemical binding of chloride ions [2; 3; 4; 5; 9; 56]. Moreover, the extra C-S-H content helps to reduce the concrete permeability and increase the chloride binding by physical adsorption [26]. However, a low chloride binding capacity is expected in the short-term RCMT [23]. According to Chlortest [5], the binding properties in the RCMT should be low, due to its short duration and high voltage. Nevertheless, [PERSON] et al. [26] showed that, in the RCMT, the ionic transport rate and test duration are not fast enough to avoid the chloride binding, confirming its presence. From MIP and SEM analysis, [PERSON] et al. [9] also reported evidence of the formation of Friedel's salt, demonstrating the occurrence of chloride binding during the RCMT. The authors also found that the amount of Friedel's salt increased with the FA content. However, according to [PERSON] et al. [26], the binding is not complete, because it is not an instantaneous process. In this case, less chloride ions are bound, and thus more free chloride ions penetrate further and, consequently, a larger \(D_{cl,RCMT}\) tends to be conservatively obtained. The movement of other ions, such as OH\({}^{*}\) (different content in FA concrete) also alters the pH of pore solution, which is known to affect the chloride binding properties [1; 20; 23; 26], besides the ionic interactions. The substitution of CEM I with LF diluted the amount of hydration products, contributing to a respective reduction on both compressive strength and chloride penetration resistance (Figure 4). For the same amount of binder, the reduction was higher in concrete with LF than with FA. Due to its high specific surface (Table 3), LF would be expected to contribute to the microstructure refinement by filler and nucleation effects [66; 53]. However,these phenomena did not compensate the reduction of CEM I content. The incorporation of LF led to a reduction of the classification level of chloride penetration resistance (Table 5). The chloride diffusion coefficients of the \(\Pi\), \(D_{cl,IT}\), and the WDT, \(D_{cl,WDT}\), after 3 months are presented in Figure 5 In general, the \(D_{cl,IT}\) and the \(D_{cl,WDT}\) were up to about 4 times lower than that of \(D_{cl,RCMT}\). On one hand, as reported in various studies, the \(D_{cl}\) tends to reduce over time [10; 56]. Therefore, the obtained \(D_{cl,IT}\) and \(D_{cl,WDT}\) are apparent values that correspond to the average time-dependent variation of this parameter over time, which is lower in the \(\Pi\) and the WDT, up to 120 days age, than in the almost instantaneous RCMT performed at 28 days. On the other hand, as mentioned, the RCMT leads to more conservative values of \(D_{cl}\), due to the simplifications discussed in Section 1 and because chloride binding is less effective during this test. In general, for a given w/b, comparable \(D_{cl}\) were obtained in the \(\Pi\) and the WDT for concrete with w/b of 0.35 and 0.45. In these cases, a clear variation of the \(D_{cl}\) with the type of test was not observed. As presented in Figure 6, the chloride profiles displayed the same shape in the \(\Pi\) and the WDT, with the predominant development of the diffusion mechanism and absence of a clear convection region. In fact, the saturation level of low w/b concretes in the WDT should be high, given the imposed short drying periods during this test (Section 2.3.4). However, for high w/b concrete, some cases revealed a tendency for higher \(D_{cl}\) in the WDT than in the \(\Pi\) (Table 5). This should be related to the easier drying in these high w/b concretes, where convection was more relevant. Figure 5: Chloride diffusion coefficient \(D_{cl,IT}\) (**a–c**) or \(D_{cl,WDT}\) (**d–f**) as a function of percentage incorporation of SF (**a,d**), FA (**b,e**) and LF (**c,f**).