The Influence of Synthetic Reinforcing Fibers on Selected Properties of Asphalt Mixtures for Surface and Binder Layers

Increasing traffic volumes, heavier axle loads, and the growing frequency of premature pavement distress pose major challenges for modern road infrastructure. In many regions, asphalt pavements experience early rutting, cracking, and moisture-induced damage, underscoring the need for improved material performance and longer service life. Reinforcing fibres are increasingly used to enhance asphalt mixture properties, with aramid fibres recognised for their superior mechanical and thermal stability. This study evaluates the effect of FlexForce (FF) fibres on the mechanical and fracture behaviour of two dense-graded asphalt concretes, AC 16 surf and AC 16 bin, produced with different binders and fibre dosages (0.02% and 0.04% by mixture weight). Laboratory tests, including indirect tensile strength ratio (ITSR), indirect tensile stiffness modulus (IT-CY), crack propagation resistance, and dynamic modulus measurements, were performed to assess moisture susceptibility, stiffness, and viscoelastic behaviour. The results showed that fibre addition had little effect on compactability and stiffness under standard conditions but improved temperature stability and stiffness at elevated temperatures, particularly when used with polymer-modified binders. Moisture resistance decreased slightly, while fracture performance improved moderately at intermediate temperatures. Overall, low fibre dosages (~0.02%) provided the most balanced performance, indicating that the mechanical benefits of aramid reinforcement depend strongly on binder rheology, temperature, and interfacial compatibility. These findings contribute to optimising fibre dosage and binder selection for aramid-reinforced asphalt layers in practice.