## 2 Materials and Methods
### Evaluation of Asphalt Binder Characteristics after Interaction with the Plastic Waste  
The use of PEX waste in an asphalt mixture, incorporated by the dry process as an aggregate substitute, will also cause the modification of the base bitumen used in the mixture because PEX is not  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Asphalt Mixture**} & \multicolumn{4}{c}{**Aggregate Fractions Used in the Mixtures (\% in Volume)**} \\ \cline{2-6}  & **6/14 Gravel** & **4/6 Gravel** & **0/4 Dust** & **Filler** & **PEX Waste** \\ \hline Conventional mixture (only with mineral aggregates) & 46.0 & 13.0 & 39.3 & 1.7 & - \\ \hline Mixture incorporating PEX (with mineral aggregates and PEX) & 45.0 & 10.9 & 37.4 & 1.7 & 5.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Percentage of each fraction of aggregates used in this work for asphalt mixture production.  
Figure 1: Aggregate grading curves of: (**a**) Mineral aggregates, filler and cross-linked polyethylene (PEX) waste and; (**b**) Asphalt mixtures (with and without PEX) fitted within the limits of an asphalt concrete mixture AC 14 surf.  
totally cross-linked. Thus, the direct influence of the melting part of PEX waste in the properties of the base bitumen 50/70 was evaluated in this work because the polymer may be able to modify the binder during the short period of asphalt mixture production [13] when PEX and bitumen can interact at very high temperatures.  
In order to simulate the interaction between the bitumen and the PEX waste during the asphalt mixture production, a PEX modified binder was produced by mixing the PEX with bitumen for 2 min at 180 \({}^{\circ}\)C (reproducing the time and temperature used for asphalt mixture production), in an IKA blender at 250 rpm (Figure 2a). The amounts of PEX waste and 50/70 bitumen used to produce the PEX modified binder were proportional to those used for asphalt mixture production. The amount of PEX used in the asphalt mixture is 5% by volume of aggregates, which corresponds to approximately 1.8% by weight due to the low density of PEX in comparison with that of the mineral aggregates. For an asphalt mixture with a bitumen content of 5% (typical value for AC 14 surf mixtures), the amount of PEX waste will be 1.71% by weight of the entire mixture, corresponding to 34.2% by weight of 50/70 bitumen. Thus, in order to produce 1000 g of PEX modified binder, 745 g of bitumen and 255 g of PEX were used. At the end of the mixing process, the binder was filtered with a metal mesh (sieve size of 0.5 mm) in order to separate the cross-linked part of PEX waste (Figure 2b) from the binder that was modified with the melted part of PEX, which will be further characterized to evaluate the actual modification process.  
At the end of this process, the filtered binder was characterized according to the EN 12591 standard. The basic characterization included penetration at 25 \({}^{\circ}\)C (EN 1426) and softening point or ring and ball (R&B) temperature (EN 1427) tests. Dynamic viscosity tests were also carried out in a Brookfield viscometer (EN 13302 standard) in order to evaluate the behaviour at mixing and compaction temperatures. The base bitumen (50/70) and a commercially available PMB (PMB 45/80-60) were also characterized using the same test protocol for comparison purposes and also because they will be used for the production of asphalt mixtures.