## 1 Introduction
### FTIR Spectra of Si-O-, T-O, Si-O-T and the Degree of Crystallization and Polymerization  
According to [PERSON] et al. [22] and [PERSON] et al. [45], the asymmetric stretching (v\({}_{\text{a}}\)) and bending (\(\delta\)) of Si-O-T are between [830 and 1200 cm\({}^{-1}\)] and [435 and 540 cm\({}^{-1}\)], respectively. These absorption bands are crucial to the skeletal framework of OPC, geopolymers (GPs), alkaline-activated slag (AAS), and alkaline-activated binders (AABs) as cementitious binders [38]. All compounds contain -T-O (T=Si or Al) bonds, either in tetrahedral frames in geopolymers, or linear chains in the hydration product of hydraulic cement [46; 63]. These peaks may provide information regarding the polymerization, crystallization, or amorphosity of the binder, and in some cases, they may even indicate the binder's strength qualitatively. For instance, [PERSON] et al. [27] asserted that the shallowness, narrowness, and sharpness of the Si-O-T band could indicate the crystallinity of the binder. This contrasts with the dome-like or smooth, curved nature of vitreous or amorphous aluminosilicate geopolymer substances. [PERSON] et al. [3], [PERSON] [6], and other researchers reported identical findings [63; 67] because as the Ca/Si ratio increases, the product becomes more crystalline, while polymerization decreases due to its shorter chain length. [PERSON] et al. [73] reported that jeninite (Ca/Si = 1.5) has a higher degree of crystallinity than 1.4 nm-tobermorite (Ca/Si = 0.83). This observation is consistent with that of [PERSON] [74], who identified two systems, G1A (Ca/Si = 1.2) and G2B (Ca/Si = 1.9), as depicted in Figure 4, in which lower Ca/Si ratios indicate more degrees of polymerization due to a higher frequency of vibration, as indicated by a greater wavenumber. However, the presence of alumina within the binder could increase polymerization due to the bonding of Al with Si-O to form additional Si-O-Al bonds within the framework. Si/Al = 2 promotes more polymerization of the aluminosilicate bond than Si/Al = 1, as evidenced by the broader mid-IR bands at 1004 to 1024 cm\({}^{-1}\) (Ca/Si = 1.2) and 1001 to 1028 cm\({}^{-1}\) (Ca/Si = 1.9) [45]. According to [PERSON] et al. [67], the degree of polymerization increases with the attachment of tetrahedral Al ions to silica in IV-fold coordination to form aluminosilicate bonds [45; 63]. The Si/Al ratio decreases due to an increase in Al incorporation (Si-O-Al), whereas the Ca/Si ratio rises due to Ca attachment to the silica chain. The increase in absorption band frequency is a result of the high silicate organization that accompanied the low presence of  
Figure 4: Aluminosilicate (Si-O-T) band due to an increment in C/S ratios (**a**) Si/Al = 1 and (**b**) Si/Al = 2 (From Wiley Ref. [74] with copyright permission). Al within silicate (Si-O-Si) chains. The Si-O bond in the linear silicate chain of OPC is less polymerized, as shown in Figure 5.  
Consequently, the asymmetric stretching of this band was measured to be 972 cm\({}^{-1}\). Due to the overlap of Si-O with Ca(Si-O-Al) and Ca(Si-O-H) bands, the peak is less broad compared to AAS and GP synthesis, whose peaks are not only broad but also prolonged with higher value wavenumbers at 988 and 1028 cm\({}^{-1}\), respectively. This suggests that the material is less amorphous. [PERSON] [75; 76] made the same observation when comparing the effects of C12A7 on a fly ash GP binder, where it is reported that tetrahedra alumina enhances binder polymerization by attaching to the Si-O chain. In other words, the degree of polymerization due to silicate concatenation increases with the silica modulus. [PERSON] et al. [3] and [PERSON] et al. [63] observed that Al incorporation in Si-O-Si influences the order of polymerization and chain formation of the silicate framework.