## 3 Asphalt Pavement Recycling Rate in Various Countries  
Worn asphalt pavement layers are recycled in a cold or hot state. The first phase of the recycling process consists of milling or breaking the asphalt pavement layer. During the cold recycling process, the removed asphalt pavement is crushed to a certain size of grains, suitable for reuse in the production of new (recycled) asphalt mixtures and material mixtures for the construction of road base layers without binders. The cold milling of asphalt pavement layers should be processed so that the different mixes from the different layers are separated if possible. Selectively milled asphalt pavement can be used at the highest level of the value creation according to its origin (e.g., also for asphalt pavement upper courses construction) [41]. Greater economic benefits can be obtained by increasing the proportion of domestically prepared RAP used in the production of recycled hot-mix and warm-mix asphalt mixtures. The model (Figure 1a) shows that the entire amount of RAP prepared in the country in one year is divided into two parts of its use: for RHMA and RWMA mixtures production (\(Q_{R\alpha}\)) and for cold road base materials (\(Q_{MM}\)) production. The amount of RAP prepared in the country \(Q_{RAP}\) depends on the length of the road network, the degree of wear and tear of the asphalt pavement surface, and investments for the development and maintenance of roads in the country. The required amount of the virgin materials that improve the gradation of RAP and the properties of the old bituminous binder (\(m_{VJM}\)) is added to the determined optimal amount of RAP (\(m_{RAP}\)) in the design and production process of the recycled asphalt mixture (Figure 1b). The maximum amount of RAP grains \(m_{RAP}^{\max}\) that can be added to the asphalt mixture depends on the homogeneity of the RAP and the method of the heat energy transfer to the RAP granules in AMP, i.e., RHMA mixture production technologies. The domestic percentage of available RAP reuse in hot and warm mix asphalt production in separate (each) year percentage RR is calculated from formula:  
\[K_{R\alpha}=\frac{Q_{R\alpha}}{Q_{RAP}}.100, \tag{1}\]  
where \(K_{R\alpha}\)--domestic asphalt pavement recycling rate, %; \(Q_{R\alpha}\)--amount of prepared RAP used in recycled hot and warm asphalt mixtures in the country during the research year, t; and \(Q_{RAP}\)--amount of prepared all RAP in research year, t.  
According to formula above, \(K_{R\alpha}\) is calculated considering the data of \(Q_{R\alpha}\) and \(Q_{RAP}\), using statistical data officially published, for example asphalt pavement association. Presented model in (Figure 2) displays RAP used in production of HMA and WMA mixture relative amount to the overall RAP amount. Figure 1: Reuse models of old asphalt pavement: (**a**) Relative recycling rate \(K_{R\alpha}\) in the country and (**b**) RAP percentage mass in the asphalt mixture when heat energy is transferred to it by conduction (1) or convection (2). The recycling rate \(K_{Rec}\) changes from country to country and varies from 0% to 100%. Conditionally, this variation range can be divided into four equal intervals: \(K_{Rec}=0\div 25\%\) (small RAP amount is used to produce HMA and WMA); \(K_{Rec}\)= 25 \(\div\) 50% (satisfactory use); \(K_{Rec}=50\div 75\%\) (good or sufficient utilization); and \(K_{Rec}=75\div 100\%\) (very good utilization). This ratio \(K_{Rec}\) shows the actual potential of the restoration of the country's road infrastructure and the degree of its utilization, to achieve a sustainable economic effect aligned with environmental protection, saving virgin material resources, and reducing the cost of construction. In some case certain amounts of RAP are imported from another country, so its \(K_{Rec}\) can be higher than 100% (Figure 2).