## 1 Introduction  
The increasing vehicular flow, as well as dramatic climate change, are some of the main causes of road asphalt distress; therefore, it is necessary to improve its performance. The growing need of improving the properties of the currently available commercial asphalts has attracted the interest of many research groups in order to study different asphalt modifiers that are able to enhance its properties while minimizing the damage caused by rutting, fractures, raveling, cracking, etc. Moreover, the high production costs, which are directly related to the international prices of crude oil, as well as the high level of pollution involved in the processing of asphalt, are also restrictions demanding new materials that meet not only quality but also environmentally friendly criteria, as well as low cost. These motivations are encouraging researchers to employ waste materials as modifiers of asphalt blends with the purpose of using sustainable resources in asphalt modification technology. Asphalt binder is an asphalt cement that can be classified according to the Standard Specification for Performance Graded Asphalt Binder (ASSHTO). This classification is valid for either modified or unmodified asphalts. In recent years, bio-asphalts have become a popular trend among asphalt modification techniques because their preparation implies using renewable sources of energy, as well as natural materials like bio-oils or biomass [1]; however, their performance at high temperatures is deficient [2; 3], mainly because the addition of oil reduces the viscosity of the asphalt and affects its stiffness. Some studies have reported that the addition of waste wood into bio-asphalts contributes to enhancing their low temperature performance [1], while in some other cases no significant effects on the rutting performance and dynamic modulus are reported [4]. Consequently, a combination of different oils and the incorporation of polymer modifiers, as SBS [5], may be required to improve the asphalt behavior. Nevertheless, the long-term performance of bio-asphalts still needs to be verified [1]. One of the most conventional and easy ways to produce modified asphalts is preparation by hot mixing, since it allows the addition of differently shaped and sized particles, which are responsible for the viscoelastic behavior of the final blend due to the physical interactions between the modifier particles and the asphalt components [6; 7]. Previous works have reported the successful addition of oyster shells as filler substitutes [8]. Various waste materials, such as egg shell powder, have also been evaluated as sustainable modifiers, which has resulted in discovering promising modifiers for asphalt mixtures [9]. Other works have reported that vegetal and mineral fibers [1]; lignin [10]; agroindustrial wastes such sugarcane bagasse, corncobs and rice husk ash [11; 12; 13]; and epoxidized soybean oil [14], can be used to improve the rheological, physical and mechanical properties of asphalt binders when they are used at concentrations ranging from 1% to 20% w.  
Some of the most remarkable agents for asphalt modification include polymer/nanoclay composites [15; 16; 17], recycled polymers like ground rubber, waste polyethylene, and recovered asphalt pavement [18; 19]. Composites can be defined as materials formed by a matrix that can be either ceramic, metallic or polymeric, and a filler, which is added to the matrix with the purpose of enhancing some of its properties. Styrene-butadiene-styrene copolymers (SBS) are thermoplastic polymers that find many fields of application because of the combination of their elastic and viscous natures. This feature is important in asphalt modification because it makes SBS able to transfer elastic properties to the asphalt, despite the fact that using this kind of modifier has both economic and technical limitations.