# Long-Term Monitoring of the Behavior of Modified Bitunens of RC Type
## 3. Choice of Binder Type in the Design of Asphalt Mixtures with RAP  
In Europe, in contrast to the USA, the majority of mixing plants are batch mixing plants, whereas in the USA, due to the much longer pavement structures, about 80% of the mixing plants are continuous mixing plants. In European batch mixing plants, the technique of cold addition of RAP only is still widely used. Cold addition limits the amount of RAP added to a maximum of 25%. The best situation is in the Netherlands and Germany, where most of the batch mixing plants preheat the RAP in a parallel drum. There, up to 100% of the RAP can theoretically be preheated. Furthermore, it is still common practice in many European countries to mill all asphalt layers at once and very often there are still very high variations in the quality of RAP depending on the source (road class). For this reason, it is necessary to use a bituminous binder in mixtures with RAP that takes these circumstances into account [23; 24].  
When adding RAP to asphalt mixtures with non-modified binder, the choice of the new binder used is guided by Equation 1, which is given in CSN EN 13108-1 of 2008 [25].  
When rejuvenating additives are used, the calculation of their dosage is carried out according to the manufacturer's recommendations. Further information on the design of the quantity and dosage of rejuvenating additives is given in [26; 27].  
In general, any of the following points can be used for the design and selection of the binder when PmB is used in mixtures containing RAP:  
* Use of a modified binder of a higher (softer) grade (equivalent to the procedure for non-modified binders).
* Use of a binder of the same class but with a higher degree of modification.
* Use of a higher grade with a higher degree of modification.  
If the softening of the aged binder is required, it will be logical that PmBs that are produced from softer base binders, as outlined, for example, in [9] or [28], will be preferred in the design. However, it is safe to say that the higher the RAP content of the asphalt mixture, the higher the modifying additive content of the newly added binder should be [29]. As the content of the modifying agent in the newly dosed PmB increases, the risk of its content in the final asphalt mixture being insufficient decreases [30].  
For this reason, a polymer-modified bitumen has recently been developed that is suitable for use in asphalt mixtures containing RAP. This binder is referred to by the abbreviation 'RC'. This binder is usually formed from a softer input binder, which is intended to compensate for the aged and hardened binder contained in the RAP. At the same time, this RC binder has a higher polymer additive content. This compensates for the properties of the binder contained in the RAP, which does not need to be modified. Alternatively, the polymeric additive contained in the binder of the RAP has already lost its original properties through ageing [31; 32; 33; 34]. Therefore, softer PmBs with an increased dosage of the polymer additive are used. Such a binder is characterized by a high value of elastic recovery (often higher than 95%). Due to this high elasticity, this binder has sufficient reserves to compensate for the 'poor' properties of the RAP binder. The use of this binder also improves low temperature properties, which is associated with a low Fraass breaking point value [35]. From previous experience, the maximum possible amount of RAP for the use of RC binder is about 40-45% [36].