## 1 Introduction
Frequency sweep tests and multiple stress creep recovery test results indicate that the addition of fine CR improves the complex modulus of the mastic if compared to the one produced with only limestone filler. At the same time, the rubber lowers the mastic thermo-sensitivity, limiting its tendency to glassy modulus at low temperatures and increasing the mastic resistance to thermal cracking. From an environmental point-of-view, recent applications on trial fields have demonstrated that the dry-hybrid technology makes the workers less susceptible to potentially harmful substances produced during the mixing, laying and compaction processes. Still, in terms of performance, the obtained pavement surface texture ensures adequate skid resistance and has acoustic properties allowing the reduction of traffic noise emissions [8]. However, the addition of CR as a partial filler replacement requires further analysis on the behavior of the mastic inside the mixture, with particular reference to the fine aggregates fraction. It is also evident that the SMA mixtures being particularly rich in bituminous mastics, its interaction with aggregates has a significant influence on the properties of the final material. Therefore, a multi-scale approach is needed in order to fully understand the rheo-mechanical behavior of this novel bituminous mixture and characterize the dry-hybrid technology in a range of materials. In this context, the expansion of the investigation field, from mastic to fine aggregate matrix (FAM) with standardized composition, has the primary purpose of evaluating the role of fine CR at different scales in order to optimize the AC design. [PERSON] and [PERSON] [19] considered crucial the FAM behavior, because it is a single length scale smaller than the AC and it is therefore closer in the characteristic size of the damage that occurs within a bituminous mixture. The FAM, in fact, consists of bitumen, filler-sized particles, fine aggregate particles and air. This agglomerate forms the interstitial spaces between the coarse aggregates in a common bituminous mixture. Tests and studies on FAMs have been used to deeply analyze the fatigue damage, moisture sensitivity and healing in ACs. Indeed,all the aforementioned phenomena occur largely between the coarsest aggregate particles. Thus, FAM should provide direct indications of how it affects the ACs [20]. However, a specific analysis of FAM is not enough to have a complete picture of the behavior of ACs. As previously stated, in order to understand completely the macro-mechanical response of a heterogeneous composite, its mechanical response at different length scales must be analyzed. In the light of the above, the main objective of this article is a complete analysis of a SMA mixture containing fine CR according to a dry-hybrid technology, carried out with a multiscale approach, in order to find rheo-mechanical parameters able to optimize its mix design. For a better explanation of the multiscale approach, the following scales of analysis were investigated:  
* Matrix: coarse, fine aggregates and filler with bitumen. * Mortar: fine aggregates and filler with bitumen. * Mastic: filler with bitumen.