## 1 Introduction
Depending on the radius of the tube, the Young's modulus of a CNT can be as high as 1000 GPa [21] and the tensile strength can reach 150 GPa [22]. Because of their small size and large surface area, CNT addition results in improved substrate characteristics as compared to other modifiers. There are two different types of CNTs, i.e., single (called single-walled CNTs) and coaxial tubes (called multiple-walled CNTs) [6]. Multi-walled CNTs (MWCNTs) are less expensive and easier to produce but exhibit lower strength and stiffness than single-wall CNTs [23]. The most common techniques used to produce CNTs are arc discharge, chemical vapor deposition and laser ablation. Different researchers use different dosages of CNTs as a modifier to enhance the properties of asphalt binder. [PERSON] et al. (2017) investigated the effect of CNTs on performance, chemical and structural properties of asphalt binder [24]. [PERSON] et al. (2016) used MWCNTs as an additive in bitumen and concluded that the modification improved both high and low temperature performance of bitumen [9]. [PERSON] et al. (2015) added MWCNTs in asphalt binder and examined the effects on conventional and rheological properties and concluded that CNTs improved the rheological as well as conventional properties of bitumen [25]. Previous studies have also observed that CNTsenhance the resistance of asphalt against ageing, which results in the increase in the pavement life [9; 26]. The biggest challenge in developing CNTs reinforced material is the dispersion of CNTs in base binder. To homogeneously disperse the CNTs in bitumen, long chains of CNTs produced by synthesis and agglomerates of CNTs produced by intermolecular van der Walls forces must be broken [27]. Inappropriate dispersion of CNTs may affect the mechanical properties of modified binder. CNTs are dispersed in bitumen using either dry or wet mixing technique. Most previous work has been carried out using dry mixing, while limited work has been done using the wet mixing technique. [PERSON] et al. (2015) used both wet and dry mixing techniques and concluded that wet mixing technique has better ability to homogeneously disperse CNTs as compared to the dry method. They used kerosene as a solvent [28]. The drawback found by [PERSON] et al. was that kerosene did not fully evaporate from the bitumen after mixing, which may influence the resulting binder properties. [PERSON] et al. (2012) compared different mixers and concluded that, with high shear mixer and ultrasonic mixer, homogeneous dispersion of CNTs can be achieved [29]. In the literature, although wet mixing is a better dispersion technique, the selection of appropriate solvent and its complete evaporation after achieving a homogeneous dispersion matters greatly. Therefore, a thorough study from this perspective was carried out in this study. This study consisted of two parts. The first part of this manuscript focuses on the dispersion of CNTs in asphalt binder, while the second part studies the effect of CNTs on the performance properties of resulting asphalt binder. Dispersion of CNTs in bitumen is a complex phenomenon [24; 28; 29]. Although different researchers use CNTs in asphalt binder to enhance the properties of asphalt binder, to authors' best knowledge, no comprehensive study is available on the dispersion of CNTs in bitumen. In this research, a detailed methodology was developed for the homogeneous dispersion of CNTs in bitumen. In addition, previous work mostly studies the effect of CNTs on the rheological properties of bitumen, but the effect of CNT addition on bitumen-aggregate adhesion and moisture sensitivity needs to be explored.