## 3 Results and Discussion
### Mechanical Properties  
The compression strength of the hybrid mortars after curing and drying is shown in Figure 7. Drying always improves the mechanical properties of the mortars, as the presence of water inside the pores stiffens and embrittles the materials. In general, a clear inverse correlation can be observed between compressive strength (Figure 7) and porosity (Figures 3 and 4). The HC-6% has the highest compression strength of the mortars under study (Figure 7) due to its reduced porosity (Figures 3 and 4) achieved thanks to its strong activation. The  
Figure 6: (**a**) DTA for the five mortars under study; (**b**) detail of temperature range where the peaks corresponding to the decomposition of phases formed due to nitrate addition can be observed. Figure 7: Compression strength of the samples under study. Striped bars plot the strength values of the mortars just after curing, while full color bars plot the strength of the mortars after the drying step. compression strengths of this mortar could be even higher if small microcracks as those shown in Figure 5c were not generated in its microstructure. Moreover, the influence of microcracks in HC-3% (Figure 5b) can explain that this compression strength is lower than expected because of the porosity of this mortar (Figures 3 and 4a). On the other hand, as for HN mortars, the fragile nature of the reaction products, whose precipitation is favored by the nitrates, negatively affects optimal achievement of mechanical properties (Figure 7). This effect is especially evident when nitrates are added in high amounts (HN-8%). The presence of NO\({}_{3}\)-AFm has been previously reported as negative for the mechanical properties [58,59]. The lower strength of HN mortars can rely on the hydrdcalite phases shown by DTA (Figure 6), as well as on the quick consumption of Portland cement to form NO\({}_{3}\)-AFm. As Portland cement is present in a limited amount (Table 3), the formation of hydration products with good mechanical properties such as C-H-S [38] or other gels is hindered in HN mortars with increasing amounts of nitrates. The mechanical properties of AAM mortars activated with highly alkaline water-glass can be much higher than those of PC and studied hybrid mortars [9], due to the more refined porosity of the AAM [60]. Additionally, the wear performance of the different mortars was evaluated, as it can be a key-factor for certain applications [32,42]. This aspect was evaluated through the Bohme test described in Section 2.2. In Figure 8, it can be seen that none of the new hybrid mortars can improve the wear resistance of the OPC mortar either as-cured or dried. After the 28 days of curing (Figure 8a), the surfaces of the hybrid mortars are clearly less wear-resistant than that of the OPC. The drying step seems to slightly improve the wear performance of the mortars (Figure 8b). The characteristics of Bohme wear tests make the differences found for the same mortar after the two exposure conditions much less relevant than those found in the compression tests (Figure 7). Part of the water of the as-cured samples should be progressively erased from the pores as the abrasion progresses into the mortars. Hence, the detachment of mortar particles that cause the wear takes place in mortar regions that are already water-poor. The relative wear resistances of the mortars have been previously related to their porosity [42]. The sand hardness and its adherence to the binder are key factors for determining the wear resistance of the mortars, and the adhesion is clearly related to binder porosity. However, for the mortars under study, the relationship is clearly more complex, and the sand-binder bonding is also influenced by other factors. Figure 8: Height losses suffered by the mortars under study during the abrasive cycles of the Böhme test: (**a**) as-cured mortars; (**b**) mortars cured and dried at 40% RH.