## 1 Introduction  
During recent decades, the world witnessed a change in the manner of using and dealing with materials. From an excessive use of raw materials and a high amount of dumped waste, we have shifted to more sustainable and circular practices, namely, sustainable waste management practices whose main aims are a reduction in the environmental impact of waste, promotion of recycling and resource recovery, and minimizing the use of landfills. Thus, to reduce, reuse, and recycle waste materials became the pillars for a better environment. The road industry is no exception. Asphalt is one of the most widely used materials for roads construction globally due to its ability to withstand heavy traffic loads and diverse weather conditions and its cost-effectiveness. It is estimated that, as of 2021, 94% of U.S. roads [1] and 90% of European roads [2] are surfaced with asphalt, making it one of the most abundant waste materials. Therefore, repurposing asphalt materials from old road surfaces (reclaimed asphalt) and using it in new construction or maintenance projects is essential to operate in a more environmentally friendly and efficient manner. According to the latest data from the European Asphalt Paverment Association (EAPA) (Figure 1), in 2021, a total of 41.3 Mt of reclaimed asphalt were available in the asphalt industry within the Europe. Amounts of reclaimed asphalt, however, vary from one country to another: France, Germany, Great Britain, and Italy are the leading countries and have the most reclaimed asphalt (RA). These are followed by the Czech Republic, with 2.4 Mt. Of this amount, 50% (Figure 2) was reused in hot mix asphalt (HMA), warm mix asphalt (WMA), half-WMA, and cold mix asphalt (CMA) mixtures, and 15% is either landfilled or used in other applications [2]. In the previous year, the data from the EAPA showed that 28% of the available RA was dumped in landfills. Thus, the use of these materials is growing gradually year by year [3]. Reclaimed asphalt is a material generated from removed old road surfaces. It is mainly composed of nonrenewable resources, i.e., aggregates and aged bitumen binder (approximately 95% wt. and 5% wt., respectively). Hence, their use and reuse in new asphalt mixtures tends to reduce the demand for virgin materials, the carbon footprint associated with the production of asphalt, and the dumping of asphalt in landfills, leading to better preservation of the environment and cost-effectiveness. The use of RA has also shown some mechanical advantages and properties such as workability [4, 5], toughness [5, 6], and freeze and thaw resistance [7]. Despite the above-mentioned benefits, the aged binder within RA has arisen as a concern of many researchers since the reclaimed mixtures tend to be stiffer and susceptible to fatigue and thermal cracking if the average content of RA is more than 30% wt. in HMA [8, 9]. As a result, it is essential to improve the performance of asphalt mixtures containing RA. Several methods and strategies have been adopted, such as the use of various additives, including polymers and recycling agents in combination with RA [10]. In fact, the incorporation of polymers such as polyethylene terephthalate (PET) in asphalt mixtures have demonstrated their ability to improve long-term performance and mitigate moisture damage [11]. Thus, the usage of PET with RA has become an effective practice to overcome RA deficiencies. As for the incorporation of recycling agents, this has been proven to decrease reclaimed mixtures' stiffness and restore the aged bituminous binder properties [8, 12]. There are several types of recycling agents available on the market, including modified vegetable oils and biobased oils. Although the aim of these additives is the same, i.e., to improve binder properties in the reclaimed asphalt, they have different capabilities  
Figure 1: Total amount of reclaimed asphalt available in European countries in 2021 [2]. Figure 2: Application of reclaimed asphalt in Czech Republic (2021) [2]. in terms of addressing these deficiencies.