## 3 Discussion of Results
### Effect of Glass on the Morphology of the Binder  
The decrease in the observable strength can be understood from the morphology of the glass blended paste from the scanning electron microscope/energy dispersive electron spectroscopy (SEM/EDS) results, as shown in Figures 12a,b and 13. There is a discontinuity (spectrum 28, Figure 12a) in the region of embedment of glass within the cement matrix. Figure 10: Compressive strength of glass blended concrete. Figure 11: Correlation between experimental and predicted compressive strength values of glass blended concrete. Figure 12: (**a**) Morphology of glass powder blended paste, (**b**) Morphology of ordinary Portland cement paste (Calcium silicate hydrate (CSH), Calcium silicate (CC)). This discontinuity created an interfacial transition zone (ITZ), which is the weakest point owing to its higher water/cement ratio than other areas within the matrix [37]. Therefore, there could be an initiation of microcracks from the ITZ during the application of loading during the compressive strength test. [PERSON] [21] reported that there is a pozzolanic reaction in ITZ due to the deposition of more Ca\({}^{2+}\) at glass boundaries. Thus, EDS shows that Ca/Si of OPC hydrated (C\({}_{100}\)G\({}_{0}\)) (Figure 12b) and glass blended pastes (C\({}_{90}\)G\({}_{10}\)) (Figure 12a). were 3.94 and 0.23, respectively. The presence of glass particles also caused dilution, which has a significant effect on the early strength development (Figures 8 and 10) and also reduced the formation of Afm when compared to its absence in glass blended paste (Figure 13). Similarly, there is non-uniformity and microstructural disintegration (cracks) of cement paste due to glass incorporation and more especially at the region of Aft formation in the SEM/EDS (Figure 12) [38]. Aft is formed by the interaction of C\({}_{3}\)A with gypsum (G) during the setting process. Therefore, the non-spherical shape of glass powder could be responsible for the microstructural discontinuity in the ITZ, thereby reducing the resultant strength. Both Aft and the proliferation of ITZ are clearly shown in Figure 13.  
Effect of Glass on Hydroxyl Ion, C=O, Water Molecule Vibrations and Silica Reorganization of the Binder  
FTIR spectra (Figure 14) show the asymmetric stretching of hydroxyl ions with strong absorption at wavenumber 3642 cm\({}^{-1}\) in cement paste, whereas the band was weaker with the wavenumber 3640 cm\({}^{-1}\) in the glass blended sample [39]. This also indicates that the  
Figure 13: Microstructure of OPC and glass blended pastes (calcium-silicate-hydrate ((CSH) and Ettringite (Aft)). early hydration reaction is hindered by the presence of glass particles due to the lower production of hydroxyl-based compound (portlandite). In addition, the polymerization of the silica structure is greater in cement mortar with a wavenumber of 962 cm\({}^{-1}\) with a strong peak in comparison with the broad peak and lower vibration frequency (955 cm\({}^{-1}\)) that was observed in glass blended paste (Figure 14). These peaks have been described to be due to Si-O stretching vibrations within the silicate structure. The C=O vibration (CO\({}_{3}\)) is noticed to be less prominent in the glass-cement binder compared to OPC binder with a stronger peak at 2330 cm\({}^{-1}\)[39]. The strong peaks of the asymmetric stretching C-O vibration (CO\({}_{2}\)) at 1436 cm\({}^{-1}\) in C\({}_{100}\)G\({}_{0}\) become broad in C\({}_{80}\)G\({}_{20}\). Therefore, a decrease in the vibration of CO\({}_{2}\) coupled with the reduced formation of portlandite and a lower Ca/Si ratio could be responsible for less carbonation in glass blended concrete. This stretching band of S-O (-SO\({}_{4}\)\({}^{2-}\)) related compound (ettringite-Aft/Afm) at 1119 cm\({}^{-1}\) is noted to be stronger in hydrated cement (C\({}_{100}\)G\({}_{0}\)) [40] compared to the lower frequency at wavenumber 1115 cm\({}^{-1}\) in the glass blended binder (C\({}_{80}\)G\({}_{20}\)) [39].