# Influence of Different Fibers on Performance of Bitumen Binders and Thin-Overlay Bitumen Mixtures
## 1 Introduction
Nanoparticles can be effortlessly integrated with bitumen, due to their expansive specific surface area and exceptionally high surface energy [23]. [PERSON] et al. [24] investigated how ferric oxide (Fe\({}_{2}\)O\({}_{3}\)) nanoparticles influence the crack resistance of bitumen mixtures. Their findings indicate that the addition of just 1% of these nanoparticles considerably enhances the mixture's fracture toughness. [PERSON] et al. [25] investigated how various sizes of nano-zinc oxide (ZnO) influence the low-temperature crack resistance of SBS bitumen mixtures. Their findings revealed that the effectiveness of nano-ZnO in enhancing crack resistance diminishes as the particle size increases. In essence, smaller particles yield higher surface energy, resulting in better performance in crack resistance at low temperatures. This characteristic significantly enhances the bonding quality at the interface between the aggregate and bitumen, while also boosting the mixture's resistance to cracking. [PERSON] et al. [26] investigated how bamboo fiber influences the mechanical characteristics of SBS bitumen binder and its mixtures. Their findings indicate that the inclusion of bamboo fiber enhances the flexibility of bitumen at low temperatures and bolsters the mixture's resistance to cracking. [PERSON] et al. [27] discovered that incorporating glass fiber into the epoxy bitumen mixture led to a notable 33.7% increase in both flexural and tensile strength. [PERSON] et al. [28] revealed that using treated basalt fiber significantly boosts the bonding at the interface of the fiber and bitumen, thus enhancing the crack resistance of the fiber-bitumen blend. Therefore, fiber exhibits remarkable oil absorption capabilities and can be fully combined with bitumen, which greatly improves the mixture's structural stability [29]. Additionally, fiber is cost effective and boasts exceptional flexibility. When incorporated into the mix, it not only provides a reinforcing effect but also enhances the mixture's crack resistance and reduces the likelihood of crack propagation. Furthermore, fibers strategically placed at potential crack sites help diminish the formation of micro-cracks, thereby increasing the toughness of the mixture and extending the lifespan of the pavement [30,31]. The typical forms of fiber can be categorized as either bundled or flocculent, with bundled fibers being more commonly utilized due to their superior strength [32]. Incorporating fiber is a key strategy for enhancing the crack resistance of bitumen mixtures. Various fiber types exhibit distinct impacts on bitumen and mixture, driven by their unique material characteristics. However, existing researchers focus on the influence of fiber on bitumen mixtures, and there are few studies on fiber itself and its interaction with bitumen. Moreover, G\({}_{\text{f}}\) or tensile strength is a single index to evaluate the toughness of the mixture. Based on this, we studied three types of bundled fibers: polypropylene, glass, and basalt, while also taking into account the thickness of a thin overlay using the SMA-10-type grading. The study examined both the properties of the fiber and its impact on the crack resistance and toughness of SBS-modified bitumen and bitumen mixtures. The oil absorption rate serves as a metric to assess how effectively fibers bind with oily materials. The G\({}^{\star}\)/sin\(\delta\) and the area of toughness provide insights into how fibers impact bitumen under high- and low-temperature conditions. The influence of fiber type and content on the toughness of the mixture was observed from the change in the toughness index and fracture toughness of the mixture. The effect of fiber on the mechanical properties of the mixture can be observed from the perspective of fracture energy and crack initiation energy. A wealth of evaluation indicators was selected in order to evaluate the effect of fiber toughening from multiple angles. This provides a theoretical basis for improving the performance of thin-layer bitumen mixtures.