## 2 Literature Review
Blending or diffusion could occur between the RAP and virgin binders in their interaction [19]. The design of individual equipment and the recycling technology plays significant role influencing the process parameters and sequence of hot RAP recycling in an AMP which should be suitable for the application of the most important principles of recycling, which have been systematized and analyzed [20]. Review [21] says that the fundamental thermodynamics and kinematics involved in the plant production of RAP mixtures. This review states that the mixing time, mixture discharge temperature, and silo storage time are fundamental on the mechanical performances of RAP mixtures produced in laboratory or AMP as it was found during experimental studies. In study [22], thermodynamics and heat transfer principles were used to estimate virgin aggregate temperature. Gradation, moisture content, and the mix proportion of virgin aggregates and RAP were the main factors for virgin aggregate temperature estimation in the drum plant. A numerical model was developed to investigate the RAP grain inside melting potential in asphalt mixing drum based on the thermal properties of asphalt materials [23]. The presented model provides the practice-ready calculation of the minimum time needed for any spherical particle to heat to a required temperature considering the initial temperature, ambient temperature, thermal diffusivity, and particle radius. The resulting equation displays that there may occur conditions where the RAP grain core could not be sufficiently heated in asphalt mixing drum. The usual method requires a significant amount of energy for production of bituminous binder, drying aggregates, and subsequent production of HMA at AMP. For example,approximately 6 L of fuel are used for drying and heating one ton of aggregates. A significant amount of greenhouse gases and harmful pollutants are released during the production of tremendous quantities of HMA [24]. Asphalt pavement maintenance and rehabilitation are more frequently performed on porous asphalt (PA), because of its low longevity. This leads to the accumulation of a significant amount of RAP which is not used totally as the use of RAP is not usually allowed in PA [25]. The paper [18] forces us to find a solution on the problem of constituent proportioning with the help of a generalized formulation that does require any prefixing of the quantity (or property) of any of the constituents. A linear programming (LP) method has been proposed. An asphalt mixture designer can minimize the total material cost or maximize of the total RAP quantity to be used in the recycled mixture. The work [26] presents a method for determining the consumption of the recycled hot-mix asphalt (RHMA) mixture, which allows the calculation of the maximum allowable percentage of RAP depending on its homogeneity. Obtaining the established maximum RAP amount as a constant size, the required content of new mineral materials is estimated thus considering bitumen capacities. In recent years, the extent of blending of virgin and old binders and the identification of key influencing factors have increased. Viscosity as a function of temperature, exposure time, and film thickness have been mentioned as the main factors controlling the blending between two binders that are in contact [27]. Researchers say [28] that RAP should not be considered a \"black rock\" because significant blending occurs between the RAP and virgin asphalt binders. In the study it is recommended that blending charts based on virgin and recovered RAP binder properties be used to account for the RAP contribution to the total binder properties and / or to select a lower grade virgin binder when RAP is used in lower quantities. The result [29] indicates with short mixing time, RAP tends to work as inert black rock and the complete blending process proceeds towards if the mixing time significantly increased. However, longer RAP and virgin aggregate mixing times could result in recycled HMA higher stiffness modulus and greater homogeneity.