## 3 Results  
### XRD Analysis  
Minerals were identified on the basis of '20' reflection angles and \"hkl\" Miller indices (\"hkl\" indices are given in the parenthesis). Quartz was as a major crystalline phase in the raw brick. This mineral was also detected in the XRD diffractogram of alkali-activated brick (Figure 1). The characteristic peaks of quartz were identified: 20.9\({}^{\circ}\) (100), 26.6\({}^{\circ}\) (011), 36.5\({}^{\circ}\) (110), 39.5\({}^{\circ}\) (102), 40.3\({}^{\circ}\) (111), 42.4\({}^{\circ}\) (200), 45.8\({}^{\circ}\) (201), and 50.1\({}^{\circ}\) (112) (ICSD Collection Code: 89276). Compared to raw brick, the intensity of the quartz peaks did not seem to be affected by alkaline treatment because of the relatively strong chemical stability of quartz under our alkaline operational conditions. Illite, and to a lesser extent, rutile were present in the raw brick. Their characteristic XRD peaks were observed in the CuK\({}_{\alpha 1}\) X-ray powder patterns of alkali-brick: illite, 8.8\({}^{\circ}\) (001), 17.9\({}^{\circ}\) (004), 19.8\({}^{\circ}\) (021), and 34.3\({}^{\circ}\) (034) (ICDD (International Centre for Diffraction data): 00-009-0343); and rutile, 27.4\({}^{\circ}\) (110) and 36.1\({}^{\circ}\) (101) (ICSD Collection Code: 168140). Like quartz, illite and rutile were also found to be chemically stable under our alkaline operational conditions, thus allowing the observation of their reflections in the XRD diffractogram of the alkali-activated brick (Figure 1). Alkaline treatment of raw brick led to additional XRD peaks which were attributed to zeolitic crystals. Indeed, the positions of these peaks corresponded to those previously observed for zeolites Na-A and Na-P [60]; see Figure 1. The characteristic peaks of Na-A and Na-P zeolites were observed: Na-A crystals, 7.2\({}^{\circ}\), 10.2\({}^{\circ}\), 12.5\({}^{\circ}\), 16.1, 21.7\({}^{\circ}\), 24.0\({}^{\circ}\), and 30.0\({}^{\circ}\), which correspond to lattice plans of (200), (220), (222), (420), (600, 442), (622), and (644, 820), respectively [60]; and Na-P crystals, 12.5\({}^{\circ}\), 17.7\({}^{\circ}\), 21.7\({}^{\circ}\), and 33.4\({}^{\circ}\), which correspond to the lattice plans of (101, 110), (200, 002), (211, 112, 121), and (132, 123, 231, 213, 312), respectively [60]. In the CuK\({}_{\alpha 1}\) X-ray powder patterns of the alkali-activated brick obtained after heating at 400 \({}^{\circ}\)C, and subsequently at 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C (each thermal step performed for 1 day), reflections characteristic of brick zeolites disappeared progressively (Figure 1). This signal disappearance might have been due to the dehydration of zeolitic micro-crystals, resulting in surface modifications. Indeed, changes in zeolitic surfaces would prevent X-rays from diffracting normally in the lattice planes. After heating at 1000 \({}^{\circ}\)C for 24 h, characteristic reflections of brick illite disappeared completely in the CuK\({}_{\alpha 1}\) X-ray powder patterns of cured brick (see Figure 1), highlighting the thermal instability of illite at this temperature. Moreover, additional reflections were observed in the XRD diffractogram (Figure 1), giving evidence for the formation of cristobalite (SiO\({}_{2}\)) and mulitle ((Al\({}_{2}\)(Al\({}_{2+2}\)Si\({}_{2-2}\))O\({}_{10-x}\)), where x ranges between 0.17 and 0.57 [61]), and  
Figure 1: XRD patterns of alkali-brick materials after different thermal treatments. Illite, **i**; Quartz, **Q**; Zeolite Na-A, **A**; Zeolite Na-P, **P**; Rutile, **R**; Cristobalite, **C**; Analicine-Leucite, **A-L**; Mulitle, **M**. weakly crystalline forms of \(\rm{MASi_{2}0_{6}}\)-type phases with M = Na\({}^{+}\), K\({}^{+}\) (analicine, \(\rm{NaAlSi_{2}O_{6}}\), and leucine, \(\rm{KAlSi_{2}O_{6}}\)).