Research on the Influence of Fibers on the Mechanical Properties of Asphalt Mixtures

Fiber reinforcement is a promising solution to several problems, however, the impact of fiber characteristics on the mechanical behavior and reinforcement mechanisms of asphalt mixtures remains unclear. Therefore, two distinct forms of basalt fiber—chopped basalt fiber (CBF) and flocculent basalt fiber (FBF)—were employed. A comprehensive experimental program was conducted, encompassing macroscopic and microscopic analyses through semi-circular bending tests integrated with digital image correlation, four-point bending fatigue tests, and dynamic modulus tests. Results indicate that both fiber types significantly improve crack resistance, with FBF demonstrating superior performance. Compared with the ordinary mixture, the flexibility index and fracture energy of the FBF-reinforced asphalt mixture increased by 59.7% and 30.6%, respectively. Fibers exert a crack-bridging effect, delaying the transition of the crack propagation stage by 1.25–2.21 s and reducing the crack propagation rate by 39.6–55.4%. Although fatigue life decreased with increasing strain levels, basalt fibers substantially enhanced fatigue resistance, with FBF-reinforced asphalt mixture achieving 20–40% higher Nf,50 values than CBF. Dynamic modulus tests revealed that fibers reduce modulus at low temperatures while increasing it at high temperatures, with more pronounced reinforcement effects observed in high-frequency regions. These findings underscore the importance of fiber morphology in optimizing asphalt mixture design and provide a theoretical basis for optimizing fiber-reinforced pavement materials to achieve long-term durability under complex environmental and traffic load conditions.