###### Abstract
Lignin fiber has flocculent structures, a rough surface, high resistance to heat, and a large specific surface area. Its flocculent structures increase the absorption of bitumen [22]. Thus, the thermal properties and dispersion of bitumen improved when increasing the content of lignin, resulting in increased bitumen content, cohesion, fatigue life, viscosity, and tensile strength, in addition to delayed fracture of pavement asphalt and also an improved anti-aging capability of the asphalt layer [23]. The short lignin fibers prevent the development of small cracks around them. Furthermore, the bonding force between aggregate and asphalt binder is increased as a result of the toughness of lignin fiber. Glass fiber is synthetic with high tensile strength, and its Young's modulus is nearly 70 GPa. Using glass fiber for modifying asphalt mixtures results in improved stability, durability, and ductility due to its high mechanical properties [24]. Moreover, it increases the flow value and resistance to crack propagation in the mixture [25]. At low temperatures, glass fiber can resist the cracks of the pavement as it has a potential resistance towards crack initiation [25]. A considerable amount of literature has been published on the effects of adding lignin fiber [19; 20; 26; 27; 28; 29; 30; 31] and glass fiber [32; 33; 34; 35; 36; 37; 38; 39; 40; 41] to asphalt mixtures. With respect to the composite-reinforcing material (polymers, lignin fiber, and other chemical additives with bitumen) used in a study by [PERSON] et al. [19], tensile strength, tensile strain, ratio of immersion residual stability, and tensile strength ratio (\(TSR\)) were improved significantly as compared to the control mixture. In a study prepared by [PERSON] [26], a laboratory performance evaluation was conducted to analyze the impact of adding lignin fiber with rubber in asphalt mixtures. It was found that increasing the content of lignin fiber to 0.25% improved the low-temperature resistance and \(TSR\), but when the content of the fiber reached 0.30%, the \(TSR\) was reduced. According to the conclusion drawn by [PERSON] et al. [20] with respect to bituminous mixtures modified with composite modifiers (anti-rutting agent with lignin fibers), lignin fiber solely was responsible for the improvement of water stability and the thermal cracking of the asphalt mixture. In another effort by [PERSON] et al. [28], it was discovered that lignin fiber could improve the resistance to low-temperature cracking, but the TSR of asphalt mixture modified with lignin fiber was the lowest. In related research, [PERSON] et al. assessed the water stability of stone matrix asphalt (SMA) [30]. The results showed that residual stability was enhanced by adding lignin fiber (at a percentage of 0.30%) because of its good adhesion. In addition, [PERSON] et al. [29] indicated that lignin fibers increased the ultimate flexural strength and strain of fiber-reinforced asphalt concrete (FRAC). In contrast, the _TSR_ of the base mixture after freezing-thawing was higher before the freezing-thawing of FRAC. In other research, [PERSON] et al. [36] found that adding glass fiber to asphalt mixture delayed the appearance of cracks and improved the TSR by 5%. The results of indirect tensile and freeze-thaw tests of hot mix asphalt mixtures using electrical glass fiber and scraps as reported by [PERSON] and [PERSON] [33] revealed that indirect tensile strength and TSR were twice that of the control mix. In another study carried out by [PERSON] et al. [39] on a compound of diatomic and glass fiber selected to modify the bituminous mix, the results demonstrated that the tensile strength was not affected by adding diatomic and glass fiber, but there was a good impact on the tensile strain, hence mitigating the propagation of the micro-cracks. Recent research by [PERSON] and [PERSON] [32], showed that adding more than 0.4% glass macro-fibers resulted in enhanced maximum stress.