## 3 Results and Discussion  
### Characterization of the Used WB. From the XRF, chemical analysis of the raw WBs and those modified with NaOH are presented in Table 1. It was found that Med-WB and Jed-WB contained considerable amounts of SiO\({}_{2}\), varying between 50% and 59%, with a general tendency that more SiO\({}_{2}\), Al\({}_{2}\)O\({}_{3}\), and Fe\({}_{2}\)O\({}_{3}\) oxides were present in Jed-BW, compared to Med-WB. However, Med-BW contained more K\({}_{2}\)O, CaO, and Na\({}_{2}\)O percentages. This variation could be related to different starting clays used to prepare the bricks. The silica content was close to that reported for other brick materials from different origins. [33; 34; 41]. Generally, the basic treatment of non-calcined clays results in the dissolution of the amorphous silica phase [43; 44]. After treatment with the NaOH solution, the amount of SiO\({}_{2}\) was slightly decreased in both WB, indicating that SiO\({}_{2}\) content in the WB was mainly present in crystalline phase or the silica phase was strongly attached to the brick grains [33]. The slight decrease of SiO\({}_{2}\) percentage affected the other metal oxide percentages in similar manner. The XRD patterns of Med-WB and Jed-WB are presented in Figure 1. It exhibited crystalline peaks consisting mainly of quartz (silica) peaks around 4.25 A, 3.34A, and 2.45 A [33]. The Med-WB showed a similar XRD pattern, with a lower intensity of the reflections, indicating lower crystallinity degree of later material, compared to Jed-WB (Figure 1). The presence of quartz is due to the use of some sand particles as an additive material in brick manufacturing [43; 45] or as impurities in the starting mixtures. The treatment of waste bricks with base solution did not alter the general feature of the XRD patterns and the reflections related to quartz are still mainly present. The PXRD patterns of the starting mixtures before the preparation of the bricks are presented in Figure 2. The mixture of the Medina brick was mainly composed of silica phase in addition to other phases, while the mixture of the Jed brick contained smectite and kaolinite phases, in addition to silica. This difference could be the origin of the chemical analysis data. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Samples** & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **MgO** & **Fe\({}_{2}\)O\({}_{3}\)** & **CaO** & **K\({}_{2}\)O** & **Na\({}_{2}\)O** \\ \hline Jed-WB & 58.28 & 23.72 & 1.53 & 12.32 & 2.43 & 0.89 & 0.72 \\ Med-WB & 54.60 & 17.57 & 4.48 & 9.42 & 7.40 & 2.53 & 2.19 \\ B-Med \({}^{*}\) & 54.88 & 17.24 & 4.70 & 9.70 & 7.31 & 2.43 & 2.10 \\ B-Jed \({}^{*}\) & 57.54 & 23.41 & 1.32 & 12.34 & 2.38 & 0.56 & 0.53 \\ \hline \hline \end{tabular} \({}^{*}\) stands for sample treated with NaOH solution.  
\end{table} 
Table 1: Metal oxides (weight %) contents of different waste bricks before and after treatment with NaOH solution. Figure 1: Powder x-ray diffraction (PXRD) patterns of (**b**) Med-WB and (**d**) Jed-WB materials. (**a**) and (**c**) correspond to Med and Jed cake mixture before firing. (Q: quartz; M: Montmorillonite; K: kaolinite; A: albite phases). Figure 2: FTIR spectra of (**b**) Med-WB and (**d**) Jed-WB materials. (**a**) and (**c**) correspond to Med and Jed cake mixture before firing. The FTIR spectra of both waste bricks are presented in Figure 2. The results indicated that silica phase (SiO\({}_{2}\)) was the prominent compound in the Med-WB and Jed-WB materials. The FTIR spectrum of Jed-WB exhibited an intense band, 1084 cm\({}^{-1}\). This band was assigned to Si-O asymmetric stretching vibrations. The bands observed at 800 cm\({}^{-1}\) and 700 cm\({}^{-1}\) could be due to Si-O vibrations of the SiO\({}_{2}\) phase. The band at 473 cm\({}^{-1}\) could be assigned to the Si-O-Si bending vibration [46; 47]. The FTIR spectrum of Med-WB revealed bands at 1044 cm\({}^{-1}\) and 779 cm\({}^{-1}\), which were allocated to the asymmetric and symmetric stretching vibration of the Si-O bonds, respectively [46; 47].