## 3 Results and Discussion
### Glass Fiber Reinforcement of Geopolymers  
Figure 11 shows the average compressive strength values for fly ash and sand-based geopolymers and geopolymer-cement hybrids (composition given in Table 4) reinforced with E-type glass fiber addition. The highest compressive strength values were obtained for the cemented geopolymer material reinforced with a 2% addition of 12 mm chopped glass fiber (42.3 MPa) and the geopolymer reinforced with a 1% addition of the same type (41.9 MPa). Geopolymer samples reinforced with 2% long fiber (40.9 MPa), 1% chopped fiber, 4.5 mm in length (41.4), and 2% chopped fiber, 4.5 mm in length (41.6 MPa) also reached high and similar values. The lowest average compressive strength values were obtained for the reference geopolymer sample with cement addition and without applied reinforcement (10.2 MPa). In other cases, depending on the applied reinforcement, the compressive strength was higher. A similar trend was observed for geopolymers without cement (29.0 MPa), which was one of the reference samples. The addition of reinforcement increased the compressive strength values for all other fly ash and sand-based samples tested. Figure 12 shows the average flexural strength values for fly ash and sand-based geopolymers and geopolymer-cement hybrids (composition given in Table 4), which were reinforced with the addition of E-type glass fiber. The highest flexural strength values were obtained for the reference geopolymer material without any reinforcement applied (9.7 MPa). Among all the materials reinforced with E-type glass fiber, high flexural strength values were obtained for the geopolymer material with a 2% addition of long fiber (8.8 MPa), a geopolymer-cement hybrid reinforced with a 2% addition of chopped fiber, and a length of 12 mm (8.2 MPa) and a geopolymer reinforced with a 1% addition of long fiber (7.9 MPa). The lowest values were obtained for the geopolymer-cement hybrid with a 1% addition of long fiber. Figure 11: Compressive strength of non E-glass fiber-reinforced cementitious geopolymers and geopolymers with added cement. As a result of the tests, it was observed that the best compressive strength results for specimens with the addition of E-type glass fibers were obtained for geopolymer-cement hybrids with the addition of 12 mm fiber. In comparison to the sample without reinforcement (reference sample), this value increased from 10.2 to 42.3 MPa. Similar values were obtained for geopolymer samples reinforced with 1% of 12 mm glass fiber. In this case, in comparison to the reference sample (29.0 MPa), the compressive strength value was 42.0 MPa. The addition of 1% and 2% of 4 mm glass fibers to the geopolymer matrix increased the compressive strength to approximately 41 MPa. In the flexural strength tests, the addition of glass fiber as a reinforcement to the geopolymer contributed to a decrease in mechanical properties compared to the reference sample. An increase in flexural strength was observed only in the case of geopolymer-cement hybrids for samples reinforced with 1% glass fiber reinforcement 12 mm (6.5 MPa) and for samples reinforced with 2% glass fiber reinforcement 12 mm (8.2 MPa). [PERSON] et al. have paid attention to the production of geopolymer composites from fly ash and glass fiber addition. E-type chopped glass fiber was used in the study. It was added in the range of 0.1 to 0.5% by weight of concrete (measurement step 0.1%). Some of the prepared specimens were left to fully cure in air, and some were placed in an oven. The samples were also tested for curing time. Based on the tests, it was found that the addition of glass fibers caused a change in the mechanical properties of the concrete. The addition of 0.3% provided the highest mechanical properties. Compared to traditional geopolymer concrete, the addition of 0.3% fiber resulted in a 16% increase in compressive strength. The influence of the molar concentration of the alkali solution on the mechanical properties of the tested samples was also confirmed.