## 1 Introduction  
Asphalt mixtures can be modified using various additives, including polymers and rubber. Due to increase in traffic and loading magnitudes, the application of polymer and crumb rubber-modified bitumen has significantly increased. Due to increase in cost of crumb rubber and especially the SBS modified asphalt mixtures, alternatives are being tested as a cheaper solution to asphalt binder modification. The major concern behind modification of asphalt binders is to increase the mixture's performance in terms of rutting and fatigue damage. Currently, SBS and crumb rubber-modified bitumen mixtures consist of different proportions of SBS and crumb rubber based on the requirements and project budget. However, the performance of such mixtures can be compromised if a smaller percentage of either SBS or crumb rubber is selected. Basalt fiber, lignin fiber and polyester fiber are alternatives that can be used to enhance the properties of polymer- or crumb rubber-modified asphalt mixtures with low percentage of SBS and CR. This process leads to the development of cost-effective mixtures providing the same performance as asphalt mixtures with high dosage, usually greater than 7% of SBS or CR in asphalt mixtures. Other than basalt fiber, different types of fibers were used for asphalt mixtures including nylon fiber, polyester fiber, carbon fiber and glass fiber [1; 2; 3; 4; 5]. Basalt fiber can be used in different proportions based on the properties of host bitumen and application conditions of asphalt mixtures. However, the ideal dosage recommended for basalt fiber mixtures is 0.3% [6]. Basalt fiber is inorganic and synthetic in nature and is produced during melting of volcanic rocks. Basalt fiber has high storage and chemical stability with low usage costs [7]. Basalt fiber provides high temperature resistance, low water absorption and increased interlocking among the bitumen globules [8]. Basalt fiber has also been used for increasing flexural strength of concrete mixtures [9]. Basalt fiber also offers alkali and acidity resistance, high and low temperature resistance and is considered environmentally friendly. Basalt fiber usually offers high stiffness modulus values when compared to other fiber types, including polyester and lignin fibers [10]. Lignin fiber is a plant fiber and offers good chemical stability along with alkali and acidity resistance, while polyester fiber on the other hand, offers good heat resistance to asphalt mixtures [1]. Lignin fiber is a type of complex organic polymer and is known to improve the anti-aging properties of asphalt mixtures [11]. With the increase in percentage of lignin fiber in the mixture, fatigue damage and cracking occurrence can be delayed [12]. Polyester fiber is a long chain synthetic fiber consisting of long chain polymers and offers good abrasion resistance and low moisture absorption [3]. Polyester fibers are also known to increase rutting resistance, high-temperature performance and fatigue resistance of asphalt mixtures [13]. Polyester fibers also offer higher tensile strength when compared to their natural fiber counterparts, and the optimum dosage for polyester fiber is at 0.3% in terms of increased tensile strength of asphalt mixtures [14]. Basalt fiber can be used in different proportions to the asphalt binder. Previously, basalt fiber was tested with different percentages ranging from 0.2% to 0.6% of the mass of asphalt [15]. Furthermore, different fiber size has also been previously tested in forms of 16 um and 25 um [16]. It is recommended to use the proportion of basalt fiber in asphalt mixture at 0.3% and a smaller fiber size of 16 um that leads to better overall gain in high-temperature performance and low temperature cracking resistance of asphalt mixtures.