## 3 Results and Discussion
### The Characterization of Geopolymer Composites
#### 3.3.2 FTIR Analysis  
The FTIR spectra of the geopolymer material with variable grain size and a comparison with the clay material and glass waste are provided in Figure 6 for the AGW1-G series and in Figure 7 for the AGW2-G series.  
The FTIR spectra of both types of glass waste (AGW1 and AGW2) are identical and contain a broad, intense band in the spectral region of 1240-840 cm\({}^{-1}\), corresponding to the Si-O in asymmetric stretching vibrations (v3) in the SiO\({}_{4}\) tetrahedra. Another band, at 450-470 cm\({}^{-1}\), is ascribed to the O-Si-O bending vibrations (v4) in the SiO\({}_{4}\) tetrahedra [57]. The weak band in the region of 720-840 cm\({}^{-1}\) is attributed to the Si-O-Si symmetric stretching vibrations of the bridging oxygens between the SiO\({}_{4}\) tetrahedra [58].  
The metakaolin-based clay material contains bands attributed to the asymmetric stretching and bending vibrations of Si-O and the asymmetric stretching of Si-O-Al groups, visible at 1087 cm\({}^{-1}\) and -780 cm\({}^{-1}\). The band with more distinctive features at 799 and 777 cm\({}^{-1}\) and another at 467 cm\({}^{-1}\) may be attributed to quartz [57], which is  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**Oxides** & **Na\({}_{2}\)O** & **MgO** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **K\({}_{2}\)O** & **CaO** & **Fe\({}_{2}\)O\({}_{3}\)** & **Bi** & **LOI** & **Residues** \\ \hline AGW1-G & 2.04 & 0.53 & 19.88 & 51.53 & 11.73 & 3.71 & 0.96 & 0.02 & 8.37 & 1.23 \\ AGW2-G & 1.84 & 0.65 & 20.68 & 50.83 & 12.28 & 3.47 & 0.76 & 0.04 & 8.17 & 1.28 \\ \hline \end{tabular}
\end{table}
Table 6: The chemical analysis of AGW-G samples (the main oxides in wt.%).  
Figure 5: AGW2 particles after exposure to the alkaline solution (10,000\(\times\) magnification).  
present in L05 as a minor impurity. The spectral shoulder at \(\sim\)560 cm\({}^{-1}\) is attributable to silicates and/or aluminosilicates with a long-range structural order [59].  
The reaction of L05 with an alkaline activator leads to an increase in the substitution of the tetrahedral Al in the silicate network in the geopolymer matrix. This process is manifested by a spectral shift of the principal band, located at 1087 cm\({}^{-1}\) in the L05 spectrum, to lower wave numbers (\(\sim\)1000 cm\({}^{-1}\)) in the spectra of the geopolymer materials [60]--see Figures 6 and 7. Slight changes in wavenumber positions in the individual spectra of geopolymer materials (999-1001 cm\({}^{-1}\)) are within the resolution limit of the method (up to 4 cm\({}^{-1}\)). New weak bands positioned at around 866-867 cm\({}^{-1}\) and 695-696 cm\({}^{-1}\) can be ascribed to the bending vibration mode of Si-OH [61] and to the stretching and bending vibrations of Si-O-Al, respectively, providing another fingerprint for the formation of the geopolymer structure [62].  
Figure 6: The ATR-FTIR spectra of the geopolymer materials (AGW1-G series with variable grain size) and a comparison with L05 and AGW1.  
Figure 7: The ATR-FTIR spectra of the geopolymer materials (AGW2-G series with variable grain size) and a comparison with the L05 and AGW2.  
The spectra of L05 and geopolymer materials also contain a large peak at 3440 and 3420 cm\({}^{-1}\) and a peak centered at 1640 cm\({}^{-1}\), which are associated with the stretching and bending modes of OH groups in water molecules due to the residual water and moisture content in the materials [62].  
Spectroscopically, all final geopolymer materials (of both the AGW1-G and AGW2-G series) are identical. FTIR analysis has proven that the grain size of waste glass does not affect its final structural properties or phase changes.