## 3 Results
### Complex Modulus  
The complex modulus determination was conducted on a prismatic beam specimen by the 4 PB-PR test method according to EN 12697-26 [37]. The test was performed at four temperatures (0 \({}^{\circ}\)C, 10 \({}^{\circ}\)C, 20 \({}^{\circ}\)C, and 30 \({}^{\circ}\)C) and 11 selected test frequencies (50, 30, 20, 15, 10, 8, 5, 3, 2, 1, and 0.1 Hz) for each temperature. This test is conducted by applying a haversine load to achieve a target strain amplitude of 50 macrostrains. The testing temperatures should be decreased from the highest to lowest level. However, based on previous experience with this test, at the temperature of 30 \({}^{\circ}\)C, the specimens show damage from time to time. Therefore, the measurement at 30 \({}^{\circ}\)C was carried out at the end of the test process, i.e., as the last measurement after the other temperatures. As for the frequencies of loading, the test starts with the highest frequency and proceeds to the lowest one. The master curves of all mixtures were constructed for a reference temperature of 20 \({}^{\circ}\)C using the principle of time-temperature superposition. The norm of the complex modulus \(|\) E\({}^{*}|\) represents the material's stiffness, which is a tool for achieving a better understanding of the load's distribution on the pavement's structure. The area of low temperatures (high frequencies) is defined on the horizontal axis as higher than 1000 Hz, the area of medium temperatures is in the range of 1-1000 Hz, and the area of high temperatures (low frequencies) starts below 1 Hz. Observing Figure 14, a clear increase in the stiffness of the 0.2% J300 mixture in the high- and medium-temperature region can be noted compared to the reference mixture. At low temperatures (high frequencies), the stiffness levelled off. These findings correspond to the stiffness testing by the IT-CY method, and this is desirable behavior for the mixture. However, the other mixtures without recycling agent did not confirm the correlation, and when testing the complex modulus, there was an equalization or decrease in stiffness. The mixture of 0.1% J300 can be rated as the worst; in this mixture, a decrease in stiffness occurred from a balanced area of low temperatures with a decreasing load frequency (increasing temperature). The mixture with 0.3% fibers, on the other hand, showed a desirable decrease at high frequencies and an effort to match the reference mixture in the range of high temperatures. The stiffness curve of the mixture with alkali-treated fibers followed the curve of the reference mixture. Figure 13: Parameters of the crack propagation test; Gf = fracture energy. Mixes with recycling agents and reference mix. In the mixtures with the recycling agent \"SR\" (Figure 15), a general decrease in stiffness was noted. The exception was the 6%SR mixture without fibers, where a decrease was recorded only in the high temperature area and, conversely, an increase in the low temperature area. This undesirable behavior is also supported by the high value of temperature sensitivity achieved in stiffness testing by the IT-CY method. The mixture J300 6%SR achieved the lowest stiffness in the entire range of frequencies (temperatures). The mixture with NaOH-treated fibers had a similar stiffness to the reference mixture. The master curves of the two latter mixtures demonstrated the same curve as that of the reference mixture. Figure 14: Dynamic (complex) modulus of mixtures without a recycling agent; reference temperature, T = 20 \({}^{\circ}\)C.  
Figure 15: Dynamic (complex) modulus of mixtures with the recycling agent “SR”; reference temperature, T = 20 \({}^{\circ}\)C.  
Figure 16 shows the mixtures with the \"RF\" recycling agent, which had the greatest decrease in stiffness. The desirable behavior of lower stiffness around high frequencies and an increase in stiffness at low frequencies was noted in the 6%RF_RA mixture. The opposite trend was then noted for the mixture with NaOH-treated fibers.