## 3 Results and Discussion
### Chloride Profile of the CNTs Nano-Modified Mortars
#### 3.2.2 RCT Method  
As aforementioned, following 100 day exposure to salt spray, profile grinding at an increment of 1 mm, a total of 60 interrogations were performed. Figure 7 plots the typical chloride concentration profiles, expressed in % mass of mortar as a function of interrogation depth.  
Figure 5: Current passing through nano-modified mortars with different amount of carbon nanotubes (CNTs).  
It is observed that the profiles had an almost identical shape throughout mortars of variable CNT concentration, with chloride content being at a maximum near the surface and decreasing with interrogation depth. For all specimens, the first one or two measurements, corresponding to the first two grinding steps, show less chloride ions than expected as a result of the aforementioned washout, which was performed following the exposure procedure [58]. These initial data points were not considered in the least-squares regression analysis for the obtainment of the best-fit values of the parameters of Equation (2). Moreover, it is observed that after the first 50 mm below the exposed  
Figure 6: Total charge passed through specimens with different CNT loadings.  
Figure 7: Chloride profile of the nano-modified mortars at different depths.  
surface, ion content drops to less than 0.05% where nanotube presence does not make a difference to the total recorded behavior. Most importantly, at all depths, chloride content was consistently higher for samples with higher CNT concentrations, a finding which signifies that chloride ion concentration is directly affected by nanotube presence. According to Figure 7, the influence is moderate for CNT loadings of 0.2% and 0.4% wt. of cement and more intense in mortars loaded with 0.6% and 0.8% nanotubes. Chloride concentration in mortars with 0.8% wt. cement CNTs is almost 50% higher than that of plain mortars. It is believed that after drying the mortars that were exposed to salt spray, chloride ions are still present in the cement matrix, although the network of pore water which initially carried them and acted as an electrical pathway, is now removed. Resultant chloride-containing crystals are electrically conductive and are now precipitated between networks of conducting carbon nanotubes. This facilitates electrical current flow through the material and absorption of a considerable amount of chloride ions. Inarguably, bigger amounts of chloride ions manage to travel effectively and are trapped to the inner part of the structure as CNT concentration increases. The chloride diffusion coefficient values calculated for nano-modified mortars exposed to 5% NaCl solution following the analysis presented in Section 2.3.2 are shown in Figure 8. It is therein observed that the coefficient increases for the first two nanotube loadings and is at a maximum at a CNT concentration of 0.4% wt. of cement above which it drops again by approximately 30% of the maximum value, to the level of the plain specimens or slightly lower. Joining information from Figures 7 and 8, it can be argued that higher chloride diffusion coefficient values do not necessarily signify larger amounts of chlorides penetration in the specimen. This is because the coefficient expresses how fast the chlorides are transported in the material and depends on external factors such as the degree of hydration and saturation, as well as porosity.