## 3 Results and Discussion  
This study aimed to determine the optimal mixture content for geopolymer concrete exposed to high-temperature tests on fibrous specimens. Non-fibrous geopolymer specimens were prepared in varying proportions and subjected to water absorption, compressive strength, freeze-thaw, UPV, and high-temperature tests. The results were analyzed to determine the most suitable mixture content for the geopolymer concrete. Upon examining the water absorption graph in Figure 8, it appears that the GSF50 specimen absorbed less water than the other specimens. It is worth noting that the specimens with low workability, namely G100 and S100, absorbed the most water. The remaining eight specimens, which contained different mineral additives, exhibited similar water absorption values due to their higher workability compared to G100 and S100. It was observed that as the workability of concrete increases, there is a corresponding decrease in the water absorption rate, which can be attributed to the reduction in voids. In order to ensure the compressive strength of geopolymer concrete specimens, 30 sets were prepared without the addition of ceramic fibers. The compressive strength was measured on the 7 th, 28 th, and 90 th day. These results are presented in Figure 9.  
Previous studies in the literature have shown that reducing the amount of slag in geopolymer concrete and replacing it with fly ash results in a decrease in compressive strength [33]. In this study, the compressive strength at 7, 28, and 90 days is reduced by reducing the slag and replacing it with fly ash, similar to other studies in the literature [26; 33; 34; 35]. Figure 7: The flow diameters of pre-test specimens. By reducing the slag content by 10% and adding silica fume instead, the compressive strength increased by 10-20% compared to the 100% slag specimen, and the compressive strength of the 20% silica-added specimen was similar to that of the G100 specimen. Adding a certain amount of silica fume to concrete positively affected the compressive strength [21; 36]. On the other hand, adding more than 10% silica fume to concrete negatively affected the compressive strength [5]. The GS90 specimen had the highest compressive strength values among the other specimens on the 7 th, 28 th, and 90 th day. The specimen that reached 65 MPa compressive strength on the 90 th day was also the most suitable for workability. The compressive strength of the slag-only specimen was about 30% lower than the GS90 specimen. The 10% silica additive in the GS90 specimen improved the physical and mechanical properties of the slag-based mortar, which agrees with other studies in the literature [21; 36]. The test results indicate that increasing the slag rate increases the compressive strength. However, using only slag reduces the compressive strength as the void structure in the material increases due to the decrease in workability. Therefore, it is recommended to add 10% silica fume to improve workability and reduce void structure, increasing compressive strength. When silica fume is added in quantities greater than 10%, the CaO ratio decreases, which in turn leads to a decrease in compressive strength as the slag ratio decreases. It is worth noting that the GS90 specimen exhibits the highest compressive strength value. The UPV test was performed on the 28 th day to predict the void structure within the cast pre-test specimens. The results of the UPV test are shown in Figure 10.  
Figure 8: Water absorption percentages of geopolymer concrete specimens. Figure 9: Compressive strength graph of geopolymer specimens on the 7 th, 28 th, and 90 th days. When the UPV test was performed on the specimens that had been waited for 28 days, it was determined that the substitution of silica fume and fly ash reduced the voids in the specimens. However, it was observed that the compressive strength value decreases when the substitution of silica fume in geopolymer concrete is more than 10% [5].