## 3 Results and Discussion
### Microstructural Studies  
A FESEM study was employed to examine the morphology of geopolymer specimens, with or without PVA fibers. Figure 14 presents the FESEM images of all the geopolymer specimens. In the GP0 specimen there were no fibers and a larger amount of unreacted silica particles in the matrix, which in turn reduced the strength of this geopolymer. In addition, the cracks were formed in GP0, which resulted in a defected and porous matrix [51]. On the other hand, in PVA fibers reinforced geopolymer specimens, fibers were arranged in different manners, producing the fiber-matrix bond interaction, which is the key to increase the strength in those specimens. Inadequacy and agglomeration of fibers were noticed in GP3 and GP7, respectively,  
Figure 14: Field emission scanning electron microscopy (FESEM) images of different geopolymers at ambient temperature. Figure 13: Crack pattern: (**A**) GP0 specimen (**B**) GP5 specimen. whereas, in GP5, the matrix was compacted, mainly due to the regular textures and uniform distribution of the PVA fibers and surrounding composites. FESEM images of geopolymer specimens with PVA fibers (GP5) and without PVA fibers (GP0) after exposure to heat at different temperatures are depicted in Figure 15.  
At elevated temperature, the transformation of GP0 occurred, which made it more porous and, finally, the specimen attained cracks at 800 \({}^{\circ}\)C. At 400 \({}^{\circ}\)C, the PVA fibers melted and lost their integrity in the matrix for the GP5 specimen. The morphology of the matrix at 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C showed intact fly ash particles and significant configuration of hydration products. Furthermore, at 800 \({}^{\circ}\)C, the PVA fibers completely vanished, hence the degradation of strength occurred (Figure 7A). Figure 15: FESEM images of geopolymers at different temperatures: (**A**) Without PVA fibers (left); (**B**) with PVA fibers (right). The elemental analysis by EDS of all the geopolymer specimens are given in Figure 16. In the geopolymeric reaction products, oxygen was the main element, along with silicon and aluminum. An EDS by mapping technique also revealed that the different colors were associated with the distribution of different elements present in the geopolymeric products. The presence of Na, Si, and Al in the EDS map confirmed the formation of N-A-S-H gel. The N-A-S-H gel acted as a binding agent in the matrix [52]. The higher concentration of each color represented the higher concentration of each element in the map. It was observed that the Si/Al ratios for the geopolymeric products were in the range of 3.43 and 5.2. Among all the geopolymer reaction products, the GP5 specimen showed the smaller value of Si/Al ratio, which confirmed the higher strength value of this geopolymer [53]. An FTIR study of GP5 and GP0 geopolymer specimens is shown in Figure 17A. The band around 460 cm\({}^{-1}\) is due to Si-O-Si vibrations. The band between 770 cm\({}^{-1}\) and 820 cm\({}^{-1}\) is associated with Al-O vibrations [54]. The bands at 1650 cm\({}^{-1}\) and 3410 cm\({}^{-1}\) are for OH stretching, presenting the chemically bound water. The band at about 1050 cm\({}^{-1}\) is related to the asymmetric stretching vibration of Si-O-T bonds (T=Al, Si). It is noteworthy that bands at 1374 cm\({}^{-1}\), 1712 cm\({}^{-1}\), and 2915 cm\({}^{-1}\) were only recognized in the GP5 specimen for CH\({}_{2}\) wagging, stretching C=O, and symmetric stretching CH\({}_{2}\), respectively, which confirmed the existence of PVA fibers in the matrix [25; 55]. XRD spectra of different geopolymer specimens cured at 56 days are presented in Figure 17B. In the spectra, different phases were highlighted and marked, clearly indicating the difference between PVA fibers embedded geopolymer specimens with the geopolymers without fibers. It can be seen that the peak, at 20 = 19.6\({}^{\circ}\), evidently represented the crystalline PVA in the GP5 matrix, while it was absent in the GP0 matrix [56].