## 3 Results
### Resistance to Crack Propagation  
Testing the crack propagation resistance of the mixtures resulted in the following, in some cases very surprising, findings. Among the most surprising findings was that the crack fracture energy at 0 \({}^{\circ}\)C in mixes with fibers was generally lower than that of the reference mixture. Crack fracture energy is calculated as the difference between total fracture energy and energy of the maximum force reached in the test. This was improved in mixtures with 0.3% lute fibers, alkali-treated fibers, and 10 mm fibers. However, a relatively significant standard deviation in the latter was also observed. Nevertheless, the fibers did not help increase this value as observed with previous types of mixtures with lute fibers [40]. The trend was notable in fiber-reinforced mixtures regardless of the application of recycling agents, which could potentially cause degradation chemical reactions at higher temperatures. So, the root of the problem lies elsewhere. A partial explanation can be provided by the higher stiffness of mixtures with fibers and the absorbency of vegetable fibers, which absorbed part of the free binder. This theory is slightly supported by the results of the best performing mixtures with recycling agents, where there was a decrease in the fracture energy difference if compared to the reference mix.  
The mixtures with fibers and without recycling agents performed well at 25 \({}^{\circ}\)C, as can be seen in Figure 12. It should be noted that the 0.3% J300 mixture was inadvertently tested at 15\({}^{\circ}\). The fracture toughness of this mixture at 25 \({}^{\circ}\)C is provided for interest  
Figure 11: Stiffness results of the mixtures with recycling agents and reference mixture.  
only. Unfortunately, the data for the mix with 10 mm fibers were not recorded because of technical issues. An increase in the fracture toughness at 25 \({}^{\circ}\)C was observed for mixtures with fibers.  
For the mixtures with recycling agents displayed in Figure 13, there was also a decrease in the crack fracture energy at 0 \({}^{\circ}\)C. The most significant decrease was for the 6%SR mix. In the case of the other mixtures, the decrease was mitigated, and, in two cases, there was a significant increase in the total fracture energy (J300 6%SR and NaOH 9%SR). The latter reached the highest values of fracture energy up to the maximum force and total fracture energy, together with the minimum difference in crack energy. The other tested mixes generally reached higher critical fracture toughness values. Unfortunately, the fracture energy parameters at 25 \({}^{\circ}\)C were not recorded in the case of mixtures without fibers. At this temperature, there was generally a slight increase in the fracture energies and, except for the NaOH 9%SR mixture, an increase in the critical values of the fracture toughness. The mixtures of J300 6%SR and J300 6%RF_RA can be considered as the best at 25 \({}^{\circ}\)C. Thus, a slight improvement of the fracture parameters was achieved by applying a recycling agent to the reclaimed asphalt.  
Figure 12: Parameters of the crack propagation test; Gf = fracture energy. Mixes without recycling agents.