## 3 Results and Discussion
### Flexural Behavior and Toughness
After exposure to 400 \({}^{\circ}\)C, water re-curing resulted in significant improvement in the load carrying and toughness of concrete. The P\({}_{\text{MOR}}\) and T\({}_{\text{MOR}}\) of plain concrete were measured as 9.05 kN and 2.43 kN mm, which were 12.84% and 5.65% higher than before recurring. However, re-curing with water exhibited more positive effects on fibrous concretes. It provided a 20.41%, 24.09%, 24.77%, and 27.02% improvement in the P\({}_{\text{MOR}}\), P\({}_{\text{L/150}}\), P\({}_{\text{L/100}}\), and P\({}_{\text{L/75}}\) deflection points of the M2 mix series, respectively. The T\({}_{\text{L/100}}\) and T\({}_{\text{L/75}}\) values of the M2 mixture were increased by 28.82% and 28.43%, respectively, compared to before recurring. However, a slight decrease was observed in the T\({}_{\text{MOR}}\) value. This can be attributed to the increase in the concrete stiffness after water re-curing. As seen in Figure 9a, the improvement rates in \(p\) values in the M3 series with water re-curing after 400 \({}^{\circ}\)C were between 10.64% and 23.64%. The recovery rates of the M3 series after water re-curing at the T\({}_{\text{L/100}}\) and T\({}_{\text{L/75}}\) values were determined as 22.37% and 22.18%, respectively. As the basalt fiber content increased to 0.40%, the improvement provided by water re-curing decreased. The toughness values at the L/100 and L/75 deflection points of the M4 series increased from 22.43 to 26.52 kN mm and 29.17 to 33.24 kN mm, respectively. As a result of these  
Figure 9: Effect of fiber mixture series on flexural properties of concrete after 400 \({}^{\circ}\)C and re-curing: (**a**) load carrying capacity; (**b**) toughness. values, the improvement rates were determined as 18.23% and 13.95%. However, especially in the load carrying capacity, decreases were detected at L/150, L/100, and L/75 compared to the pre-re-curing values. This situation can be associated with the increase in strength together with the improvement in the concrete matrix and the weak response and sudden rupture of basalt fibers under this increase in stress. The highest improvements at 400 \({}^{\circ}\)C were obtained from the M5 mixture. The T\({}_{\text{L/100}}\) and T\({}_{\text{L/75}}\) values of the M5 series were 38.36% and 37.38% higher, respectively. The toughness values of mixture M1 determined at the MOR after heating at 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C were 1.18 and 0.80 kN mm, respectively. These values increased to 1.84 and 1.52 kN mm as a result of re-curing. With the increase in temperature to 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C, the highest load carrying capacity and toughness values were obtained from M2 series. The P\({}_{\text{L/75}}\) and T\({}_{\text{L/75}}\) values of the M2 series were 4.85 kN and 26.37 kN mm at 600 \({}^{\circ}\)C and 2.01 kN and 12.38 kN mm at 800 \({}^{\circ}\)C. The T\({}_{\text{L/75}}\) values of mixtures M3, M4, and M5 at 600 \({}^{\circ}\)C were calculated as 22.10, 16.20, and 17.84 kN mm. As the temperature increased to 800 \({}^{\circ}\)C, these values were calculated as 11.78, 8.57, and 6.29 kN mm. Figure 10: Effect of fiber mixture series on flexural properties of concrete after 600 \({}^{\circ}\)C and re-curing: (**a**) load carrying capacity; (**b**) toughness. As seen in Figures 10 and 11, re-curing has a significant effect on load carrying and toughness properties. Unlike 400 \({}^{\circ}\)C, significant increases in P\({}_{\text{MOR}}\) values were observed at 600 and 800 \({}^{\circ}\)C. This increase was determined as approximately 74%, 66%, 52%, and 65% at 600 \({}^{\circ}\)C and 118%, 122%, 116%, and 171% at 800 \({}^{\circ}\)C for the M2, M3, M4, and M5 series, respectively. However, significant decreases were observed in these rates with the increase in deflection points. For example, the improvements in the P\({}_{\text{L/75}}\) values of the M2 series at 600 \({}^{\circ}\)C and 800 \({}^{\circ}\)C were approximately 34% and 24%.