# Using Plastic Waste in a Circular Economy Approach to Improve the Properties of Bituminous Binders
## 4 Conclusions  
The use of waxes resulting from the processing of plastic waste is a sustainable route, which contributes to minimizing specific environmental impacts and offers added value to the paving technology and the waste management sector. Several characterization tests of these waxes, and their mixtures with different bitumens, were carried out. The analysis of the obtained results allowed the following conclusions:  
* HDPE waves can be produced in a simple reaction system, with relatively low operating costs, which also makes alternative fuels and does not release hazardous compounds into the atmosphere;
* The melting point of these waxes is about 114 \({}^{\circ}\)C, and the thermal degradation initiation temperature (T\({}_{\text{onset}}\)) is approximately 450 \({}^{\circ}\)C. Both values are similar to those presented by other waxes, which have also been used to modify bituminous binders;
* In the FTIR spectrograms, the PMB with wax showed the characteristic peaks of the oxidative products (carbonyl and sulfoxide), possibly also resulting from ageing during wax mixing, although they were not significant (were minimized due to the inclusion of an anti-oxidant agent);
* When the used wax was blended with a PMB and other functional additives, a reduction in penetration (P @ 25 \({}^{\circ}\)C) of 13 \(\times\) 0.1 mm and an increase in softening point (t\({}_{\text{RAB}}\)) of 18 \({}^{\circ}\)C took place;
* Usually, the addition of waxes can affect the thermal susceptibility of the bituminous binders in an undesired direction but, in this case, thanks to some of the functional additives included, the performance on this parameter was improved (I\({}_{\text{p}}\) = 4.7, it was the highest of the studied five different binders);
* The addition of the type of wax used in this study to various types of neat bitumen can lead to reductions in the dynamic viscosity (\(\eta\)) of the blends (e.g., around 250 mPa-s--measured in a 35/50 traditional bitumen at a temperature of \(\approx\)145 \({}^{\circ}\)C);
* The PMB + wax presented higher complex shear modulus (G*) values (ranging between 3.6 kPa and 169.4 kPa) and lower phase angles (\(\delta\)) (in the range of 51-68\({}^{\circ}\)); therefore, it can induce a better rutting resistance. Naturally, these results were also positively influenced by the ageing that occurred while mixing the wax in the PMB;
* After all, in this specific case and after analysing all tests, the binder that incorporated HDPE wax, and other functional additives, could be included in Class 1 of _\"multigrade paving grade bitumens\"_ (specified in the European standard EN 13924-2 [73]). This research was part of a broader work, the results of which allowed us to conclude that a \"dry pellet supported binder/mastic\" is ready to be developed and used together with a conventional bitumen to produce enhanced bituminous mixtures for almost all manufacturing conditions; for example, conditions involving a lack of storage conditions for using modified/special binders. At the same time, it is also possible to contribute to the mitigation of the consequences of climate change through reusing available industrial waste (plastic and others) and reducing energy consumption and gas emissions, while producing the bituminous mixtures and increasing the durability of flexible pavement materials. It was also confirmed that the bituminous mixtures produced with the developed binder behave more efficiently, and, in general, their direct costs present savings that are not negligible. Furthermore, it can be stressed that plastic waste is inescapable. If non-recyclable plastic waste is used (such as multi-material packaging), its inclusion in bitumen mitigates its incineration or landfilling and contributes to the carbon sequestration in plastics.