## 1 Introduction  
An efficient transport network plays a key role in the economic development of a country and, therefore, the kilometrage of paved roads existing in a country is often used as an index to assess the extent of its development [1]. Asphalt mixtures have been widely used for construction of road for a long time now and bitumen is its main constituent [2]. Due to a rapid increase in the traffic loading and volume, pavements in Pakistan fail prematurely and the revival of their serviceability normally requires a lot of resources and finance. Pavements constructed utilizing conventional materials (especially virgin bitumen with softening points far less than the temperatures to which the pavements are exposed) fail many times within the design life, putting a lot of burden on the annual maintenance budget and ultimately increasing the life cycle cost of the pavement. If the bitumen were made to last/survive longer, pavement failures could be delayed, which would minimize the life cycle cost of the pavements. Regular wear and tear are expected but total failure before the end of the design life, as often happens in Pakistan, is not desirable. It not only increases the maintenance costs but also adds nuisances for the road users in terms of delays, accidents, and vehicle operating costs. This study aimed to address this issue [3]. Local traditional pavement materials in Pakistan are falling short in meeting the practical demands for present and future highway pavement construction. Thus, higher quality, more sustainable, more reliable and more environment friendly pavement materials are urgently demanded [4]. Civil engineering materials modification through addition of polymers and other additives such as fly ash and lime has often been utilized [5]. The use of Polymer Modified Asphalts (PMAs) allows the construction of safer roads and important reduction in maintenance costs [6; 7; 8]. Different modifiers such as crumb rubber and polymers are also used to improve the mechanical properties of conventional asphalts. Although modifiers improve the performance of asphalt, increases in traffic loads and volumes, harsh weather conditions, and the ever-increasing asphalt cost call for more research in this area [9]. Pavement engineers continuously look for innovative additives/modifiers to enhance the performance properties of road materials. Nanotechnology has recently gained popularity in the scientific world. Due to remarkable achievements of nanotechnology in other fields of engineering, researchers have started looking into its utilization in the field of civil engineering. Nanotechnology is often used for the modification and enhancement in properties of cement concrete [10; 11]. The effect of nanomaterials on the properties of asphalt concrete is an emerging field that must be explored. Nanotechnology and its influence on improving the characteristics and performance of asphalt pavements has lately received much attention from researchers [12]. Two specific types of nanomaterials, namely nano-metal oxides and nano-inorganic materials, have been widely investigated. Nano-metal oxides such as nano-TiO\({}_{2}\), nano-SiO\({}_{2}\), and nano-ZnO can improve the rutting resistance of bitumen, but have little effect on its low temperature cracking resistance [13; 14; 15]. Nano-inorganic materials including nano-clay and Carbon Nanotubes (CNTs) hold the potential to redefine the field of traditional materials in terms of both performance and potential applications [16; 17; 18]. CNTs are among the most widely used nanomaterials because of their strength properties, light weight, small size, and large surface area. CNTs are basically long hollow cylinders of graphene sheet, which have a diameter starting from approximately 1 nm. They were first discovered by [PERSON] in 1991 [19]. CNTs are characterized by superior mechanical properties when compared with other construction materials [20].