## 2 Materials and Methods
### Advanced Performance-Related Characterization of PMBs  
The advanced performance-related characterization of PMBs was based on rheological tests, which were carried out by means of a Dynamic Shear Rheometer (DSR) from Anton Paar Inc. (model MCR301). Performed tests included small amplitude oscillatory shear (SAOS) tests for the assessment of linear viscoelastic properties, Multiple Stress Creep Recovery (MSCR) tests for the evaluation of resistance to permanent deformation, and Linear Amplitude Sweep (LAS) tests for the analysis of fatigue resistance. The objective of these tests was to highlight the effect of polymer modification and to identify possible differences between polymers of variable type and quality. SAOS tests consisted in frequency sweeps covering two log decades of frequency, from 1 rad/s to 100 rad/s. Test temperature was changed from 4 \({}^{\circ}\)C to 82 \({}^{\circ}\)C with 6 \({}^{\circ}\)C increments between each measurement step. In the range comprised between 4 \({}^{\circ}\)C and 34 \({}^{\circ}\)C, tests were carried out with the 8-mm parallel plates system with a 2-mm gap, while at higher temperatures, between 34 \({}^{\circ}\)C and 82 \({}^{\circ}\)C, use was made of 25-mm parallel plates with a 1-mm gap. Measurements were performed with a single repetition in accordance with AASHTO T 315-12 both on unaged and RTFO-aged binders, verifying that imposed strain levels were kept within the linear viscoelastic domain at all temperatures and frequencies. Repeatability of the results was checked on randomly selected PMBs, verifying that the differences in results coming from different repetitions were smaller than 10%. Obtained results were represented in the form of isochronal plots and Black diagrams. Furthermore, they were employed for the construction of master curves, which were fitted to the Christensen and Anderson (CA) model for frequency dependency [27] and to the Williams, Landel and Ferry (WLF) model for temperature dependency [28]. These models are indicated in the following:  
\[\left|G^{*}(\omega)\right|=G_{g}\left[1+\left(\frac{\omega_{c}}{\omega}\right) \right]^{\frac{\log 2}{\log 2}}, \tag{1}\]  
where \(\left|G^{*}(\omega)\right|\) is the norm of the complex modulus at angular frequency \(\omega\), \(G_{g}\) is the glassy modulus, \(\omega_{c}\) is the crossover frequency, and \(R\) is the rheological index  
\[\log\alpha_{T}=\frac{-C_{1}(T-T_{R})}{C_{2}+T-T_{R}}, \tag{2}\]  
where \(\alpha_{T}\) is the shift factor, \(C_{1}\) and \(C_{2}\) are empirically determined constants, and \(T\) and \(T_{R}\) are test and reference temperatures, respectively. MSCR tests were performed with a single repetition on RTFO-aged binders in accordance with AASHTO TP70-13 in the temperature range comprised between 52 \({}^{\circ}\)C and 82 \({}^{\circ}\)C (with 6 \({}^{\circ}\)C increments between each measurement step). Tests entailed the application of 10 loading cycles composed of a creep phase of 1 s followed by a 9-s recovery. As indicated in the AASHTO standard, tests were carried out at each temperature by imposing two stress levels, equal to 0.1 kPa and 3.2 kPa. At each stress level, results were expressed in the form of percentage recovery (R\({}_{0.1}\) and R\({}_{3.2}\)) and non-recoverable creep compliance (J\({}_{\text{nr0.1}}\) and J\({}_{\text{nr3.2}}\)). The percent difference in non-recoverable creep compliance (J\({}_{\text{nndiff}}\)) wasalso considered. Obtained results were employed for the calculation of the high critical temperatures (T\({}_{\text{c}}\)) of investigated binders as per AASHTO M332-14 (see Section 3.3.2). It should be mentioned that MSCR tests were proposed in order to replace the original SUPERPAVE rutting criterion based on the \(G^{\bullet}\)/sin\(\delta\) parameter derived from SAOS tests. In particular, it was shown that such a parameter was not capable of adequately discriminating between neat and polymer-modified binders and did not show a satisfactory correlation with field performance [29; 30; 31].