# Low-Grade Clay as an Alkali-Activated Material
## 4 Results and Discussion
### FT-IR Analysis  
The FTIR spectra of natural clay, clay pre-treated at 120 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, and alkali-activated mortars for AM 1.0 at dosages of 10% and 15% are presented in Figure 5.  
Figure 5: FTIR spectra: (**a**) clay, (**b**) 10% mortar, and (**c**) 15% mortar. The peaks in the region of 3800-3600 cm\({}^{-1}\) present in the untreated clay and clay treated at 120 \({}^{\circ}\)C are attributed to O-H stretching and bending vibrations of the hydroxyl groups of kaolinite and illite [53; 64; 65]. These disappear in the spectra of the clay pre-treated at 750 \({}^{\circ}\)C, which is consistent with the conversion of kaolinite and illite as observed in the XRD data. The peaks observed between 1650 and 1600 cm\({}^{-1}\) in the clays are associated with the H-O-H vibrations of absorbed water. These decrease in intensity in both the pre-treated clays compared to the untreated clay, as the water is lost during calcination, while the peaks at 1820 and 1480 cm\({}^{-1}\) are identified to be asymmetric C-O stretching due to carbonation [54]. The peak at 1008 cm\({}^{-1}\) is attributed to Si-O-T (asymmetrical vibration; T = Al, Fe, or Si), and 1080-1100 cm\({}^{-1}\) is attributed to Si-O (symmetrical vibrations in SiO\({}_{\text{d}}\)) from the kaolinite and illite, as it is not evident in the 750 \({}^{\circ}\)C spectra [13]. The natural clay and clay pre-treated at 120 \({}^{\circ}\)C show a peak at around 850 cm\({}^{-1}\), which, in the clay pre-treated at 750 \({}^{\circ}\)C, shifted to 880 cm\({}^{-1}\), while the band at 908 cm\({}^{-1}\) for natural clay and 926 cm\({}^{-1}\) for clay pre-treated at 120 \({}^{\circ}\)C attributed to Al (IV)-OH [64; 66] disappeared during clay pre-treatment at 750 \({}^{\circ}\)C. According to [PERSON] (2008), this is due to the transformation of VI-fold coordination of Al into IV-fold coordination [67]. Furthermore, the VI-fold coordinated Al (VI)-OH (stretching vibration) of kaolinite is replaced by the IV-fold coordinated Al (IV)-O (stretching vibration) due to calcination at 750 \({}^{\circ}\)C. This is supported by the XRD, which shows the decomposition of the kaolinite and NMR data that show conversion of Al from VI to the IV-fold coordination. The doublet in the region of 795-770 cm\({}^{-1}\) and the singlet at 695 cm\({}^{-1}\) are attributed to Si-O symmetric stretching vibrations from the quartz. The peak at 470 cm\({}^{-1}\) could be due to the Si-O in-place bending vibration or Fe-O-T stretching. The band at 540 cm\({}^{-1}\) is due to the Si-O-Al (VI) bending vibrations from the kaolinite and illite [54; 57; 64]. According to [PERSON] et al. and [PERSON] et al., the wave range of 1300-800 cm\({}^{-1}\) represents Al\({}_{2}\)SiO\({}_{3}\), where the region between 1300 and 1000 cm\({}^{-1}\) represents glassy Al\({}_{2}\)SiO\({}_{3}\), 1000-900 cm\({}^{-1}\) represents glassy (medium) Al\({}_{2}\)SiO\({}_{3}\), and 900-800 cm\({}^{-1}\) represents (high) Al\({}_{2}\)SiO\({}_{3}\)[68; 69] [PERSON] et al. added that the bonds in the 900-1000 cm\({}^{-1}\) region represents the dominant active bond of Al\({}_{2}\)SiO\({}_{3}\). This is reflected in the broad peak observed in the region between 1100 and 900 cm\({}^{-1}\) in the raw clay, indicative of amorphous material [69]. This peak is observed to flatten out further following calcination at 750 \({}^{\circ}\)C, correlating with the increase in the amorphous content in the clay after calcination. The FT-IR spectra of all the mortar specimens showed significant peaks between 3800 and 3600 cm\({}^{-1}\), clearly showing the presence of water in the mortars. However, there was no evidence of carbonation peaks in the mortar specimens. The 1080-1100 cm\({}^{-1}\) peak broadened and shifted to just below 1000 cm\({}^{-1}\) for all of the 10%- and 15%-dosage mortars, while the peaks in the 500-400 cm\({}^{-1}\) region also broadened and increased in intensity.