## 3 Results and Discussion
### Alkali-Aggregate Mitigation by Pozzolanic Additions in Cement Mortars
In some cases, this content should be above 50% [25] or 60% [57]. The lowest effectivity of blast-furnace slag could be attributed to its less content of aluminum. Aluminosilicate pozzolanic materials such as P, V and S have the capacity of suppressing the deleterious effects of ASR. The amount which must be added for a given reactive aggregate can only be determined by testing, whose long-term trustworthily is frequently questioned. It is well-known that pozzolanic materials lower the pH of the cement-based material pore solution. This fact promotes the change in composition of calcium silicate hydrate, C-S-H gel, which is the main binding phase in mentioned cement-based materials. Nevertheless, it has been suggested that pozzolanic materials containing alumina such as coal fly ash are more effective in reducing ASR than those containing only silica [26]. It has been observed that the incorporation of alumina in C-S-H gel does not lower the pH of the pore solution significantly. In addition, reactive aggregates kept in alkaline solutions with alumina deteriorate less than those kept in similar solutions with no alumina [58]. ASR gel formation depends on the rate of rupture of siloxane bonds, i.e., dissolution of amorphous silica [59]. Hydroxyl ions break up the Si-O-Si bonds and negative charges are formed, which later are neutralized by alkalis. This physicochemical process opens the silica microstructure and water penetrates the gel. The dissolution kinetics involved in this process depend on the composition of the pore solution, temperature, and interfacial free energy [60]. The effect of aluminum containing constituent on the amorphous silica dissolution has been widely discussed in the literature [22; 61]. It seems that aluminum is incorporated, as AlO\({}_{4}\) tetrahedra, into SiO\({}_{4}\) tetrahedral sites on the silica framework, not just surface adsorbed. However, a thin layer is enough to significantly reduce amorphous silica dissolution [61]. Furthermore, it has been demonstrated the effect of aluminum on reducing quartz dissolution in the high alkalinities found in cement paste. Nevertheless, the reduction in the dissolution rate of amorphous silica due to the presence of aluminum decreases as the pH increased [62] and the positive effect on the ASR is almost the same irrespective of the aluminum concentration in the pore solution [53] because the aluminum incorporation level is independent of such concentration. Regarding the reference mortar made with the moderate reactive aggregate, it presented an intermediate expansion result between the reference mortar made with the non-reactive aggregate and the high-reactive one (Figure 7). Then, the mitigating effect of the pozzolanic materials was much lower than that found in high-reactive aggregate mortar. This can be explained by the synergetic effect proposed here between the formed ASR gel and the pozzolanic reaction involved in this physicochemical process. Coal fly ash and silica fume are again the most efficient additions in suppressing ASR. However, only high contents of natural pozzolan (40% and 50%) or blast-furnace slag (40%) could be considered quite effective in mitigating ASR in mortars with moderate reactivity aggregates. ASR mitigation degree of natural pozzolan, P, siliceous coal fly ash, V, silica fume, D, and blast-furnace slag, S, additions (from 3% to 50% of content in the blended cement according to Table 2) was assessed with three kinds of aggregates with different reactivity: ASJ_12 (high-reactive) \(>\) VB \(>\) ASJ_2 (non-reactive). The aim is to get the most adequate type of addition and percentage for each aggregate to suppress the ASR. Figure 9 shows a comparison of the effectiveness for the mortars made with three aggregates (non-reactive siliceous sand, ASJ_2; siliceous gravel with moderate reactivity, VB; and a reactive siliceous pebble, ASJ_12).