## 3 Results and Discussion
### Microstructural Characteristics
#### 3.3.3. Fourier Transform Infrared Spectroscopy (FTIR) Analysis  
In FTIR spectroscopy, a sample is exposed to a beam of infrared radiation that interacts with the chemical bonds within the material. FTIR analysis provided information on the formation of geopolymeric gels and the presence of specific functional groups such as Si-O and Al-O, as well as changes in the molecular structure of the material during curing and over time. The resulting spectrum shows the absorption or transmission of radiation at different frequencies, which corresponds to specific functional groups and chemical bonds within the material. The transmittance (%) in FTIR spectroscopy is influenced by the analyzed material's presence and the strength of different functional groups and chemical bonds within it. Different chemical bonds and functional groups absorb radiation at different frequencies, which can be identified by their characteristic absorption peaks in the FTIR spectrum. Overall, the relationship between the % of transmittance and the material composition in FTIR spectroscopy is based on the absorption or transmission of infrared radiation by specific chemical bonds and functional groups within the material, which is directly related to the molecular structure and chemical composition of the material. The % of transmittance is an important parameter in FTIR spectroscopy because it provides information about the sample's absorption properties. A sample that absorbs a large amount of radiation will have a low % of transmittance, while a sample that absorbs very little radiation will have a high % of transmittance. Figure 21 shows the FTIR spectrum (% transmittance vs. wavelength) of the AAEC samples at the age of 180 days, which shows major bands at 3380 cm\({}^{-1}\), 2072 cm\({}^{-1}\), 1423 cm\({}^{-1}\), 957 cm\({}^{-1}\), 875 cm\({}^{-1}\), and 670 cm\({}^{-1}\). The broadband of the AAEC specimen at 3297 cm\({}^{-1}\) and 2072 cm\({}^{-1}\) characterizes the O-H stretching and H-O-H bending vibrations, respectively. Overall, AAECs with MWCNTs showed the lowest % of transmittance (highest radiation absorbing capacity) followed by those with rGO and MgO. B2C6 had a lower % of transmittance at 3380 cm\({}^{-1}\), which indicated a weaker bond headed by less compressive strength. These vibration modes are due to the weakly bound water molecules that were adsorbed on the surface or trapped in large cavities [88]. Water plays an important role in the process of polymerization as it is associated with the destruction of solid particles and the hydrolysis of dissolved Al\({}^{3+}\) and Si\({}^{4+}\) ions [97]. The absorption band at 1429 cm\({}^{-1}\) is attributed to the presence of sodium carbonate (Na\({}_{2}\)CO\({}_{3}\)), which corresponds to the stretching vibration of the O-C-O bond [98] ([PERSON] and [PERSON], 2002). [PERSON] et al. [99] suggested that the presence of Na\({}_{2}\)CO\({}_{3}\) is due to the atmospheric carbonation of alkaline media. The strongest band of the AAEC specimens at 958 cm\({}^{-1}\), representing Si-O-Si and Si-O-Al, corresponds to the asymmetric stretching vibrations of Si-O-T (T = Si or Al). Moreover, the stretching modes are sensitive to the Si-Al composition of the framework and a lower frequency is obtained with an increasing number of tetrahedral aluminum atoms [100]. [PERSON] et al. [97] suggested that the amorphous aluminosilicate gel formed at this phase is due to the depolymerization and structural reorganization of the amorphous phases in geopolymer materials. Mix B2C6 exhibited a lower % of transmission at 905 wavelengths. The bands in the region between 800 cm\({}^{-1}\) and 550 cm\({}^{-1}\) correlate with the tetrahedral vibrations of the secondary building unit (SBU) and fragments of the aluminosilicate [9]. The bands at 957 cm\({}^{-1}\) observed in Figure 21 are assigned to quartz as the crystalline phase in the original FA [9], whereas the band located at 566 cm\({}^{-1}\) indicates the presence of mulitte. Referring to the finding by [PERSON] et al.