## 3 Results and Discussion
### Assessment of the Sequential Wetting/Drying Cycles  
To assess the mortars' performance subjected to cycles of water absorption/desabsorption, as they will be subjected in real environment conditions, test specimens were submitted, in laboratory conditions (20 \(\pm\) 2 \({}^{\circ}\)C and 65 \(\pm\) 5% RH), to cycles of capillary water absorption followed by drying at different curing ages: 28 (1 st cycle), 90 (2 nd cycle), and 180 (3 rd cycle) days. In the analysis, the following aspects were considered:  
1. Determination of the parameters of water absorption coefficient (CC), asymptotic values (Abs. ), and drying rates (D\({}_{1}\) and D\({}_{2}\)), and compared with specimens that were not subjected to the cycles. 2. Qualitative evaluation, based on visual appearance, during the capillary water absorption/desabsorption test. Regarding the results shown in Figure 11, which shows the capillary water absorption (Figure 11a) and desorption (Figure 11b) values of the mortars after the cycles, with the exception of the mortars with NS, in general, the capillary water absorption coefficient (CC) slightly decreases with the cycles of absorption. This behaviour can be related not only to the progression of carbonation, but also to the reactions of dissolution and reprecipitation of the carbonated binder [5] (Figure 12). For the drying cycles, this trend is not so clear; however, except for the A+Q30% and A+NS mortars, after the 2 nd cycle, all mortars tend to have an increase in their first drying rate (D\({}_{1}\)). This behaviour could be ascribed to the transformation of portlandite into calcium carbonate fulfilling the largest pores which, in general, increase the volume in the capillary porosity range, with a reduction in the main pore diameters [53]. The different behaviour of the mortars with NS is consistent with the previous mechanical and physical results. In fact, this performance can be attributed to the microcracking on the aggregate/binder interface, associated to shrinkage strains (Figure 7a), which leads to a coarsening of pore diameters [55; 56]. Moreover, in the presence of water, the specimens with nanosilica became so fragile that they were broken during the measurements. Considering the use of limestone aggregate (Figure 13), as reported before, in general, the rate of water absorption of the two types of mortar decreases and the drying occurs slower. Furthermore, except for the sand substitution of 30% (M\({}_{1}\)), the number of cycles improves the mortar performances with a reduction in the rate of absorption and of the total water absorption. However, there is a decrease in the water flow, and consequently a decrease in D\({}_{1}\), and thus the values of D\({}_{2}\) increase from the first to the second cycle, which represents the reduction in liquid water transport and progressive increase in water vapour diffusion, probably due to the volume decrease in large capillary pores owing to the carbonation process (Figure 14). Figure 11: Hydric properties of the mortars with siliceous sand, after cycles of the water absorption: (a) water absorption; (b) water desorption. Figure 12: SEM image at high magnification (MAG: 10,000x), with a working distance (WD) of 15.4 mm, at A mortar surface where it is possible to observe the presence of different calcium carbonate crystals, some with an acicular shape attributed to phenomena of dissolution and reprecipitation of the carbonated binder. Figure 13: _Cont._  
The visual assessment of mortars reveals that during the second cycle of water absorption, a pink colouration appears on the C:A:M\({}_{2}\) and C:A:M\({}_{3}\) mortar specimens (Figure 15a), probably due to the presence of microbiological contamination, able to produce coloured compounds such as _Rhodotorula S.P._ or those closely related, which could lead to a biodeteroation of the mortars [57, 58].