**1. Introduction**

Bitumen combined with stone aggregate creates an asphalt mixture, which is the most common surface layer of the roads. Bitumen in asphalt mixtures ages already during the production, transport and installation of asphalt mixture and the process of ageing continues during the use of asphalt. Ageing processes are influenced by several factors, the most important of them are: temperature, UV radiation and oxygen exposure. Subsequently, bitumen becomes harder and more brittle, its viscosity increases, adhesion and cohesion deteriorate, which leads to the ravelling and the formation of cracks in asphalt mixture [1–3]. With the use of special additives, the so-called rejuvenator, bitumen restores its basic properties [4, 5]. Furthermore, rejuvenators allow mixing and installation at lower temperatures, which reduces production costs and energy consumption, therefore the production of asphalt is more environmentally friendly. The rejuvenator enables to re-install the aged bitumen from reclaimed asphalt (RA) into the fresh asphalt [6]. The first rejuvenator was used as early as 1960 [7]. Over the years, several different products

have been used as rejuvenators: emulsions, oil components with a high content of maltene, soft bitumen with high penetration, tertiary amines, waste vegetable oils, waste motor oils and various combinations of these materials [8, 9]. A rejuvenator made from waste tires by a pyrolysis process, a pyrolytic rejuvenator, was developed in our study [10].

Pyrolysis in technical terms is a process in which the chemical decomposition of a substance takes place at elevated temperatures and without the presence of oxygen. Because of the increasing number of vehicles, demand for car tires is also increasing, and as a consequence their production is increasing (324 million tires were sold in 2019 in Europe [11]), resulting in an increasing number of waste tires at the end of their service life. European Directive on the landfill of waste 1999/31/ EC [12] has prohibited the disposal of waste tires at landfill sites since 2006, as their improper storage may endanger human health and pose a threat to the environment, e.g. fire, the spread of rodents and insects and dangerous emissions that can be released into the air or the earth. In addition to this directive, waste management is also significantly influenced by the waste directive 2008/98/ES [13] which sets out a 5-step waste hierarchy, namely: prevention, preparing for re-use, recycling, other recovery (e.g. energy recovery) and disposal. Pyrolysis is a suitable process for the treatment of waste tires, as it has a small impact on the environment, and at the same time obtained products that can be used further. In the past, pyrolytic products from waste tires have been mainly used as additives to reduce the temperature sensitivity of bitumen [14–17]. The pyrolytic product from waste tires pyrolysis may contain high concentrations of polycyclic aromatic hydrocarbons (PAH). Therefore, the slow pyrolysis process of waste tires was performed at a relatively low temperature where the highest treatment temperature (HTT) did not exceed 500°C. Consequently, a product with low PAH content, i.e. lower than those reported in existing studies [18, 19] was obtained.

In the first phase of the presented study, several different pyrolytic products were developed [20]. Among them, the most appropriate for the purpose of rejuvenator was selected. In the second part, the influence of the pyrolytic rejuvenator on the properties of the non-aged and aged bitumen was examined. Results of the tests proved that the pyrolytic rejuvenator revived aged bitumen [21]. In the last phase, the pyrolytic rejuvenator was used in asphalt mixtures, to which the percentage of reclaimed asphalt was gradually increased [22].
