## 3 Results and Discussion
### Microanalysis of Pozzolanic Cement Mortars  
Following the 90-days accelerated mortar bar test expansion measurement, mortar prisms were kept in a plastic container with a 1 N NaOH solution for 30 months. Afterwards, they were for examination of mortar specimens, made with two reactive aggregates and a non-reactive one, by scanning electron microscopy (SEM) using backscattered electron imaging contrast (Figure 10). Figure 10: _Cont._  
Corresponding to its high expansion, widespread cracking was observed using an SEM in the microstructure of the mortar control sample. The blended cement mortars exhibited lower or non-cracking when examined after 90-days of expansion testing and subsequent preservation in a 1N NaOH solution for 30 months. Several typical micrographs from mortars made without additions and with natural pozzolan, P, siliceous coal fly ash, V, silica fume, D, and blast-furnace slag, S, are shown in Figure 10.  
The reference mortar shows some cracks and pores filled with ASR gel. In addition, the mortar made with cement containing 10% of coal fly ash, V, also presents some cracks. Generally, cracks are filled with ASR gel. Cracks up to 10 um wide were observed at the interface or within reacted aggregates in mortars. On the other hand, mortar elaborated with cement containing 10% of blast-furnace slag, S, or 10% of silica fume or 10% of natural pozzolan showed a cohesive aspect without any visible alteration. Figures 11 and 12 show the composition of C-S-H gel in cement paste contained in the mortars at 30 months obtained by energy dispersive X-ray (EDX). The diagrams represent ([10-(Na\({}_{2}\)O\({}_{\text{eq}}\)) + 4.45-CaO]/SiO\({}_{2}\)) against the expansion and the Si/Ca ratio against the Al/Ca ratio, respectively. The expansion is a linear function of ([10-(Na\({}_{2}\)O\({}_{\text{eq}}\)) + 4.45-CaO]/SiO\({}_{2}\)) in the case of natural pozzolans. However, the expansion is independent such relation. With regard to the mortars made with coal fly ash and silica fume, no clear relationship has been found between the expansion and ([10-(Na\({}_{2}\)O\({}_{\text{eq}}\)) + 4.45-CaO]/SiO\({}_{2}\)). Figure 11: _Cont._  
Figure 10: Backscattered SEM image of mortars made with the high-reactive siliceous pebble, ASJ_12 after 90 days of testing and subsequent preservation in a 1N NaOH solution for 30 months: (**a**) reference mortar; (**b**) reference mortar; (**c**) mortar with 10% of natural pozzolan; (**d**) mortar with 10% of siliceous coal fly ash; (**e**) mortar with 10% of silica fume; (**f**) mortar with 10% of blast-furnace slag. It is noted that the composition of C-S-H gel has a Si/Ca ratio ranging from 0.5 to 0.95. In particular, the values of Si/Ca ratio for the natural pozzolan pastes range from 0.5 to 0.8, for the fly ash pastes from 0.6 to 0.7 and for blast-furnace slag pastes from 0.55 to 0.65. Conversely, pastes with silica fume have much higher ratios, up 0.95. This is due to the high Ca(OH)\({}_{2}\) consumption during the pozzolan  
Figure 11: Relation between ([10-(Na\({}_{2}\)O\({}_{\rm{co}}\)) + 4.45-CaO]/SiO\({}_{2}\)) and expansion of mortars made with the high-reactive siliceous pebble, ASJ\({}_{12}\), and four additions mixed in different percentages after 90 days of testing: (**a**) natural pozzolan, P; (**b**) siliceous coal fly ash, \(V\); (**c**) silica fume, D; (**d**) blast-furnace slag, S.  
Figure 12: Relation between the Si/Ca ratio and the Al/Ca ratio of mortars made with the high-reactive siliceous pebble, ASJ\({}_{12}\), and four additions mixed in different percentages after 90 days of testing: (**a**) natural pozzolan, P; (**b**) siliceous coal fly ash, V; (**c**) silica fume, D; (**d**) blast-furnace slag, S.  
reaction between the reactive silica present in the silica fume and the calcium hydroxide, which was formed during the hydration reaction of the Portland cement. With respect to the Al/Ca ratio, the values range from 0.05 to 0.3.