## 3 Results
### ESEM/EDS Studies
#### 3.3.2 Microscopic Analysis of Alkali-Activated Brick  
After alkaline treatment of raw brick with sodium hydroxide at 90 \({}^{\circ}\)C for 6 days, ESEM analysis revealed that aluminosilicates in the treated brick were aggregates with either spherical or cubic shapes (Figure 3A,B). Their sizes ranged from 8 \(\upmu\)m to 20 \(\upmu\)m for spherical particles and from 15 \(\upmu\)m to 29 \(\upmu\)m for cubic particles. The spatial distribution of framework elements Si, Al, O, and Na revealed a positive correlation between Al, Si, and Na in spherical and cubic specimens, giving evidence for the formation of sodic alumino-silicates as Na-zeolites (Figure 3C). This finding agreed well with XRD studies, revealing characteristic reflections of Na-A and Na-P zeolites (Figure 1). It is worth noting that the spherically shaped specimens observed here by ESEM/EDS were morphologically similar to those reported in the literature for zeolite Na-P [69; 70; 71; 72], while those with cubic forms were comparable with those previously observed for A-type zeolite [73; 74]. A detailed ESEM/EDS analysis was carried out on several cubic and spherical specimens that were targeted on alkali-activated brick samples  
Figure 3: ESEM micrograph of alkali-activated brick aggregates (**A**); ESEM/EDS mapping image reconstituted from spatial distributions of Na, Al, Si, K, and Ti (**B**); Spatial distribution of (extra)-framework elements (**C**). (Light-brown specimens correspond to zeolitic specimens on which Na, Al, and Si atoms predominate). with the aim of assessing the percentages of Al, Si, and Na present in the zeolitic (Na-A and Na-P) structures. Knowing that metakaolinite-derived zeolites should belong to the GIS family, the general chemical formula (based on the crystalline unit cell) of brick-zeolites could be expressed as (M)\({}_{\rm x/m}\)(Al)\({}_{\rm x}\)(Si)\({}_{\rm 16-x}\)(O)\({}_{\rm 32}\cdot\)n\({}_{\rm H2}\)O, where m is the valence of alkali ions and n represents the number of water molecules per unit cell. Next, we attempted to establish the chemical compositions of cubic and spherical specimens and compared them to those of dehydrated zeolites LTA (Na\({}_{\rm 95}\)Al\({}_{\rm 96}\)Si\({}_{\rm 96}\)O\({}_{\rm 384}\)) and Na-P (Na\({}_{\rm 6}\)Al\({}_{\rm 6}\)Si\({}_{\rm 10}\)O\({}_{\rm 32}\)), which were previously reported by [PERSON] and [PERSON] [60]. After averaging ESEM/EDS-analysis data and calculating standard deviations, we found:  
\[\rm(Na)_{93.9\pm 7.1}(?)_{\rm 2}(Al)_{\rm 96.8\pm 10.6}(S!)_{\rm 96}(O)_{\rm 3 0.9\pm 20.5}\qquad\rm(for cubic particles);\]  
\[\rm(Na)_{\rm 6.70\pm 0.92}(?)_{\rm 2}(Al)_{\rm 8.64\pm 0.57}(S!)_{\rm 10}(O)_{ \rm 37.0\pm 1.05}\qquad\rm(for spherical particles).\]  
In these formulas, the stoichiometric coefficients for Na, Al, and O were referenced to that for Si (as those reported for LTA (\"Si\({}_{\rm 96}\)\") and Na-P (\"Si\({}_{\rm 10}\)\") by [PERSON] and [PERSON] [60]), and the atomic deficit for sodium was represented by \"(? )\({}_{\rm z}\)\". Indeed, normally the atomic deficit ought to be compensated for by one or more cations, like K\({}^{+}\), Ca\({}^{2+}\), and/or Mg\({}^{2+}\), which were detected using ESEM/EDS at trace levels in the zeolitic frameworks. In the above formulas, one may note that the Si/Al atomic ratio was close to 1 for cubic specimens (0.99 \(\pm\) 0.10, as expected for zeolite LTA), while that for the spherical specimens (1.16 \(\pm\) 0.08) was somewhat lower than that expected for zeolite Na-P (i.e., 1.66). Also, in these formulas, an excess of oxygen (390.9 for cubic specimens and 37.05 for spherical ones) was observed when compared to those expected in the frameworks of LTA (i.e., \"384\") and Na-P (i.e., \"32\") because of traces of water molecules inside the analyzed zeolitic specimens.