## 4 Conclusions  
Fourier-transform infrared (FTIR) spectroscopy is a very useful tool for the characterization of bonds that exist within the products of cementitious binders, such as calcium silicate hydrate (C-S-H) in ordinary Portland cement (OPC), calcium aluminosilicate (C-A-S-H) in alkaline-activated binders (AABs) or slag (AAS), and sodium/potassium aluminosilicate (Na/K-A-S-H) bonds in geopolymers (GPs). The prominent bands include Si-O, Si-O-T, Si-OH, -OH, HOH, C-O (CO\({}_{3}\)\({}^{2-}\)), and S-O, which can be found in 600-800 cm\({}^{-1}\), 950-1055 cm\({}^{-1}\), 800-890 cm\({}^{-1}\), 3400-3465 cm\({}^{-1}\), 1390-1450 cm\({}^{-1}\), and 602-670 cm\({}^{-1}\), respectively. The bending vibration of Si-O-T may also be found within the wavenumber range of 400-600 cm\({}^{-1}\). Other conclusions include the following:  
1. FTIR is a simple technique for bond characterization and its sampling methods include transmission, attenuated total reflectance (ATR), diffusive reflectance infrared transmittance spectroscopy technique (DRIFTS), and specular aperture grazing angle (SAGA). 2. FTIR can be used to study the aluminosilicate and calcium silicate hydrate bond characteristics in the cementitious binders which include traditional cement (OPC), geopolymers (GPs), and alkaline-activated slag or binders (AASs). The attachment of cations and their atomic weight have effects on the skeletal framework and the frequency of vibration of Si-O-T bonds. 3. FTIR could give an indication of the crystalline nature of the binder, thereby giving hints on the silicate organization by observing Si-O-T within 900-1100 cm\({}^{-1}\). The more the frequency of vibration of the Si-O-Si bond, the more the silicate re-organizes or polymerizes the binder. 4. FTIR spectra bands could also be used to study the durability of a binder qualitatively by observing the Si-O-T and -OH bands upon being exposed to aggressive environments, such as sulfates and acids. \begin{table}
\begin{tabular}{c c c} \hline
**Bonds** & **Wavenumber** & **Assignment** & **References** \\ \hline -N-O (NO\({}_{3}\)) & 1385 cm\({}^{-1}\) & Very strong diffuse asymmetric stretching & [3; 10] \\ -N-O (NO\({}_{3}\)) & 815–840 cm\({}^{-1}\) & Symmetric stretching of nitrate & [10; 95] \\ \hline -P-O (PO\({}_{4}\)) & 1000–1100 cm\({}^{-1}\) & Asymmetric stretching & [10; 95] \\ \hline Si-O-Si & 795 cm\({}^{-1}\) & Symmetric stretching & [3; 116] \\ \hline Si-O-Si, O-Si-O & 470 cm\({}^{-1}\) & bending & [22; 23; 33; 63; 65; 67; 113; 117] \\ \hline Si-O & 1010–1104 cm\({}^{-1}\) & Kaolinite in-plane vibration & [117] \\ \hline T-O & 452 cm\({}^{-1}\) & Associated with the T-O bending & [32] \\ \hline kaolinite & 435 cm\({}^{-1}\) & Strong kaolinite bending & [33; 117] \\ \hline Al-O & 600–800 cm\({}^{-1}\) & Alumina in IV-fold coordination & [87; 118] \\ \hline -OH/HOH & 3500–3600 cm\({}^{-1}\) & -asymmetric stretching & [33; 117; 119] \\ \hline -OH & 875 cm\({}^{-1}\) & bending & [33; 117; 119] \\ \hline Al-O & 700 cm\({}^{-1}\) & Tetrahedra alumina & [120] \\ \hline Al-O & 620 cm\({}^{-1}\) & Octahedral alumina & [120] \\ \hline Si-OH & 875 cm\({}^{-1}\) & Stretching bank & [117] \\ \hline H-O-H & 2350–2800 cm\({}^{-1}\) & -asymmetric stretching & [14; 33; 117; 121] \\ \hline H-O-H & 2810–2924.5 cm\({}^{-1}\) & Hydrogen bonding & [10; 121] \\ \hline H-O-H & 1500–1700 cm\({}^{-1}\) & Unbound water molecules & [122] \\ \hline H-O-H & 1622–1652 cm\({}^{-1}\) & Bending vibration & [75; 76; 113] \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._  
**Funding:** The author extends his appreciation to the Deanship for Research and Innovation Ministry of Education in Saudi Arabia for funding this research through project No. IFP-A-2022-1-10. **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable. **Data Availability Statement:** Not applicable. **Acknowledgments:** The author would like to appreciate the remarks of the anonymous reviewer which have greatly improved the manuscript.