## 3 Results
### Characterization of Brick Composite
#### 3.1.2 ESEM/EDS Analysis  
ESEM micrographs of the treated brick pellets are shown in Figure 2a-c. As can be seen in these ESEM micrographs, the morphological aspects of this material were evidenced at two magnifications. The ESEM micrograph of raw brick is displayed in Figure 2d. Elemental (ESEM/EDS) analysis of alkali-activated brick permitted us to detect the following elements: (i) silicon (Si), aluminum (Al), and oxygen (O) as major elements; and (ii) iron (Fe), titanium (Ti), magnesium (Mg), potassium (K), and calcium (Ca) as  
Figure 1: XRD patterns of brick materials. Raw brick (**a**); alkali-activated brick (**b**). _Illite, I; Quartz, Q; Ruttle, R; Na-P zeolite, \(\frac{\pi}{4}\)_; LTA zeolite, **O**. minor elements. In order to determine their atomic surface contents, several spherical and ellipsoidal surface zones were targeted and analyzed using ESM/ED, as shown in Figure 2e. The averaged atomic percentages of elements constituting the alkali-activated brick surface were estimated: 19.00 \(\pm\) 1.24 at.% for silicon; 10.44 \(\pm\) 0.76 at.% for aluminium; 60.57 \(\pm\) 1.22 at.% for oxygen; 0.92 \(\pm\) 0.33 at.% for iron; 0.42 \(\pm\) 0.36 at.% for titanium; 0.60 \(\pm\) 0.03 at.% for magnesium; 0.97 \(\pm\) 0.49 at.% for potassium; and 0.09 \(\pm\) 0.02 at.% for calcium. Some of these elements were found to be better localized across the brick surfaces, evidencing the presence of SiO\({}_{2}\) (as quartz); alumino-silicates; and, to a lesser extent, iron oxides/hydroxides and titanium oxide [11; 12]. Aluminosilicates present in alkali-activated brick were detected as aggregates with either spherical or cubic shapes. Their sizes varied from 8 \(\upmu\)m to 20 \(\upmu\)m for spherical particles and from 15 \(\upmu\)m to 29 \(\upmu\)m for cubic particles, as shown in Figure 2f. Detailed ESEM/EDS analysis was performed on several cubic and spherical specimens targeted hazardously on alkali-activated brick samples, and the atomic percentages of Al, Si, and Na were determined and averaged. As metakaolinite-derived zeolites ought to belong to the GIS family, the chemical formula (based on the crystalline unit cell) should correspond to the crystalline phases: (M)\({}_{\rm x/m}\)(Al)\({}_{\rm x}\)(Si)\({}_{\rm 32-x}\)(O)\({}_{\rm 32}\cdot\)nH\({}_{\rm 2}\)O, where m is the valence of alkali ions and n represents the number of water molecules per unit cell. Hence, it was possible to establish structural and chemical formulas and calculate standard deviations after averaging ESEM/EDS analysis data. We found:  
(Na)\({}_{\rm 13.86\pm 1.25}\)(? )\({}_{\rm Z}\)(Al)\({}_{\rm 16.43\pm 0.99}\)(Si)\({}_{\rm 15.89\pm 0.98}\)(O)\({}_{\rm 32}\cdot\)nH\({}_{\rm 2}\)O (for cubic particles)  
(Na)\({}_{\rm 12.57\pm 1.05}\)(? )\({}_{\rm Z}\)(Al)\({}_{\rm 14.92\pm 1.14}\)(Si)\({}_{\rm 15.58\pm 1.45}\)(O)\({}_{\rm 32}\cdot\)nH\({}_{\rm 2}\)O (for spherical particles)  
In these formulas, the Si/Al atomic ratios are close enough to 1 (0.97 for cubic specimens and 1.04 for spherical specimens). Note that the atomic deficit for sodium in the formulas is represented by (? )\({}_{\rm Z}\). This deficit was assumed to be compensated for by other cations, like K\({}^{+}\), Ca\({}^{2+}\), and/or Mg\({}^{2+}\), which were detected at trace levels on zeolite frameworks. The spherically shaped specimens were morphologically similar to those reported in the literature for zeolite Na-P [72; 73; 74; 75], while the cubic-shaped specimens were comparable with those observed previously for the A-type zeolite [76; 77]. Note the presence of zeolitic (Na-P) aggregates with \"sponge\" shapes (see Figure 2c). The occurrence of Na-A and Na-P \"zeolitic\" crystals in the brick composite was confirmed using XRD, as described in Section 3.1.1 (see Figure 1). Overall, ESEM/EDS characterizations performed on alkali-activated brick revealed the presence of numerous spherical and cubic (sponge) zeolitic crystalline specimens.