## 2 Materials and Methods  
### Preparation of PMBs  
Materials used in the experimental investigation for the preparation of PMBs included a 50-70 penetration grade bitumen and four elastomeric polymers. Neat bitumen (NB) was sampled at a production plant in Italy where it was employed on a regular basis for the preparation of PMBs. The four polymers were supplied by a petrochemical factory in Iran: two of them were premium quality SBR and PBR polymers, while the other two were off-grade waste products (indicated in the following as w-SBR and w-PBR). All polymers were provided in bulk form and were shredded into particles smaller than 3 mm before being used as bitumen modifiers. Technical characteristics of the premium quality polymers declared by the producer are reported in Table 1.  
PMBs were prepared in the laboratory by making use of a high shear mixer (Silverson, model LSM-A), which was believed to be necessary in order to guarantee an adequate dispersion of the polymer in the bituminous medium [6; 10].  
The adopted mixing procedure follows the protocol suggested by [PERSON] et al. [16], developed as part of a study that focused on the assessment of homogeneity and storage stability of PMBs containing the same waste polymers employed in the investigation described in this paper. After preheating bitumen at 140 \({}^{\circ}\)C, mixing was started with a speed of 1500 rpm. As the required quantity of polymer was added to bitumen, mixing speed was gradually increased up to 4000 rpm. As a result of the high-speed rotation, temperature of the bitumen-polymer blends slowly increased during mixing.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Polymer Characteristic** & **SBR** & **PBR** \\ \hline Mooney viscosity (MU) & 46–58 & 41–49 \\ Volatile material (\%) & \textless{}0.75 & \textless{}0.75 \\ Ash content (\%) & \textless{}1.0 & \textless{}0.3 \\ Bounded styrene (\%) & 22–5–24.5 & - \\ Cis content (\%) & - & \textgreater{}96.0 \\ Tensile strength (35 min curing) (kg/cm\({}^{2}\)) & \textgreater{}250 & \textgreater{}150 \\ Ultimate elongation (35 min curing) (\%) & \textgreater{}350 & \textgreater{}440 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Technical characteristics of employed premium quality polymers.  
However, care was taken in limiting the maximum blending temperature to 160 \({}^{\circ}\)C. Mixing operations were completed within 40 min for each batch.  
Polymer percentages adopted for the premium quality products (SBR and PBR) were equal to 3.0% and 4.0% (by weight of neat bitumen). When using the waste polymer products (w-SBR and w-PBR), an extra dosage was considered, equal to 5.0%. Selection of these dosage ranges was based on a specific literature review that considered studies focusing on the use of the same types of polymers [9; 10]. PMB samples were associated to alphanumeric codes given by the combination of polymer type (\"S\" for SBR, \"P\" for PBR), quality (\"Q\" for premium quality, \"W\" for waste), and percentage. For example, SW4 was the code given to the binder obtained by making use of 4% of the w-SBR polymer. A complete list of the bituminous binders considered in the investigation is given in Table 2. Laboratory-prepared PMBs were characterized both in their unaged state and in the condition reached after the standard ageing procedure based on the use of the Rolling Thin Film Oven (RTFO) (ASTM D2872).