## 3 Results and Discussion
### Results of Advanced Performance-Related Characterization Tests  
#### 3.3.1 SAOS Tests  
Preliminary discussion of the results obtained from SAOS tests can be made by referring to isochronal plots, in which the norm of the complex modulus and phase angle recorded at 10 rad/s are represented as a function of test temperature. This is shown in Figures 4 and 5 for SBR-modified binders and PBR-modified binders, respectively. Results obtained on binders in different ageing conditions are grouped separately. Data plotted in Figures 4 and 5 clearly indicate that use of both types of polymers led to an enhancement of the elastic response under loading, which is proven by the remarkable reductions recorded for the phase angle at all temperatures. Such changes were directly dependent upon polymer dosage and were also slightly affected by polymer quality. In particular, when referring to the results of tests carried out on unaged samples, it was observed that by employing waste polymers, higher and lower phase angle values were obtained in the case of binders modified with SBR and PBR, respectively. In the case of RTFO-aged binders, these differences were confirmed for PMBs containing PBR, whereas, for the SBR-modified binders, no clear effects could be identified when comparing blends prepared with polymers of different quality. Figure 3: Results of viscosity tests: (**a**) at 135 \({}^{\circ}\)C; (**b**) at 165 \({}^{\circ}\)C.  
As expected, all polymers had a stiffening effect on neat bitumen at high temperatures, with an increase in the complex modulus that was dependent upon polymer dosage. No specific effects were found when comparing results obtained on PMBs containing polymers of variable quality. Furthermore, the two types of polymer seemed to exhibit a very similar stiffening potential in both considered ageing states. When focusing on low temperatures, it was observed that polymer modification led to an overall stiffness reduction. However, individual effects caused by changes in polymer type, quality, and dosage could not be easily recognized. Figures 6 and 7 display Black diagrams that were drawn from the results of SAOS tests carried out on all binders in their unaged state by plotting measured complex modulus as a function of the corresponding phase angle. Results obtained on binders in different ageing conditions are grouped separately. The continuity of the plots shown in Figures 6 and 7 proves that, for all binders, the time temperature equivalency principle is applicable [39]. Furthermore, the effects of polymer modification are clearly visible, with the downward shifting of all plots corresponding to the PMBs. In the case of the SBR-modified binders, such a change occurred with the creation of multiple curvatures that correspond to the presence of a more elastic phase responding to external loads in combination with the bituminous viscoelastic matrix. More monotonous plots were found for the PMBs containing PBR, which were found to be associated to a higher level of polymer dissolution in the bituminous matrix  
Figure 4: Complex modulus and phase angle isochrones (at 10 rad/s) of SBR-modified binders: (**a**) unaged binders; (**b**) Rolling Thin Film Oven (RTFO)-aged binders. Figure 5: Complex modulus and phase angle isochrones (at 10 rad/s) of PBR-modified binders: (**a**) unaged binders; (**b**) RTFO-aged binders. (see Section 3.1). The effects of variations of polymer dosage and quality were also identified as in the case of isochronal plots. Given the applicability of the time-temperature equivalency principle, master curves were constructed for all binders at the reference temperature of 20 \({}^{\circ}\)C by means of the CA and WLF models described in Section 2.4. Corresponding results are synthesized in Table 5, which contains the values of CA model parameters (\(G_{g}\), \(\omega_{c}\) and \(R\)) and WLF coefficients (\(C_{1}\), \(C_{2}\)) calculated from regression analyses.