# Using Plastic Waste in a Circular Economy Approach to Improve the Properties of Bituminous Binders
## 1 Introduction
However, it is recommended to take into account an extra cost related to the proper pre-sorting and elimination of waste that can give rise to unwanted compounds, as is the case for poly(vinyl chloride) (PVC), PET, or PU (their by-products include hydrochloric acid, benzoic acid, or hydrogen cyanide, respectively) [12; 22; 23]. Usually, the waxes are added (without other additives) to different binders in percentages ranging between 1% and 8% by wt. of bitumen. The primary purpose of its addition is to reduce the manufacturing and/or application temperatures on warm mix asphalt (WMA) [24; 25; 26; 27] and to improve the coating of the aggregates and the workability of the mixture [27]. Many works have proven these benefits, namely, the one carried out in 2012 in Vancouver (Canada) [28] (where a mixing temperature reduction, from 160 \({}^{\circ}\)C to 121 \({}^{\circ}\)C, was achieved). The literature has widely reported the benefits of blending this wax with binders for bituminous mixtures and pavements. Its advantages have been proven at the level of water sensitivity, stiffness modulus, fatigue cracking resistance, and rutting resistance [16; 17], particularly when low traffic speed and adverse climatic conditions have significant impacts on pavements [15] or long-chain waxes (LCW) are used [18]. Other authors [29] concluded that if the wax content in a binder is high, its tendency to develop \"bee-like\" structures increases, which is especially beneficial for self-healing processes. However, these advantages are minimized by the impacts (environmental and economic) resulting from the production and transport of the incorporated additives [30]. Concerning mixing procedures, [PERSON] and [PERSON] [18] warned of the consequences that the protocol followed can introduce on the performance of the binders, namely the ageing caused by the oxidation reactions and volatilization of light compounds during blending. They issued this warning after testing the effect on bitumen performance of two waxes (one from a waste PE and the other was a FTW), in a content of 1.5 wt.% of neat binder, at 180 \({}^{\circ}\)C, stirred at 500/1000 rpm and for up to 300 min. Similar considerations were mentioned in other works that dealt with the mixing in bituminous binders (under different conditions) of several additives, namely nanoclays [31]. In summary, this paper describes the main materials used in this first part of the research (three unmodified bitumen, one PMB, the wax and some of their combinations), the respective samples' preparation, and the equipment and procedures followed in the tests performed. Finally, some results and the principal inferences, findings, and conclusions are aligned. These works are part of more comprehensive research, concluded in 2020 [32], the outcomes of which are not yet fully available due to the protection of reserved information. The main aims of this work were the contribution to the reuse of waste resulting from a sustainable industry--chemical recycling (alternative feedstock or fuel production in the viewpoint of a Circular Economy of plastics [33]) and the improvements that the addition of this by-product can provide to specific bituminous binders (from a hard to a PMB). The most important conclusions reached in this study were: the confirmation of the possibility of taking advantage of the \"waste\" from the processing of an end-of-life plastic (in a circular economy perspective) with benefits for the binders in which it is mixed; and that it is compatible with other modifiers (namely, SBS) and functional additives, substantially improving some of the rheological properties of the blends that include them.