Influence of Fiber Parameters on Pavement Performance of Asphalt Mixture in Saline Wet Environment

The coastal regions of eastern China are constantly subjected to salt-fog and high-humidity environments, leading to severe performance degradation of asphalt pavements and threatening their durability and service safety. However, existing research has predominantly focused on single-fiber modification, with a lack of systematic investigation into the synergistic enhancement mechanism of hybrid fibers under saline-wet conditions. To address this, this study employs basalt fiber and lignin fiber to modify SMA-13 asphalt mixtures. It aims to clarify the influence of fiber parameters (length, content, and ratio) on the high-temperature stability and water stability of the mixture through multi-factor experiments, and to reveal its performance evolution mechanism under salt-wet cycling. The results showed that the composite fiber group had a dynamic stability of 3627 times/mm after 15 salt wet cycles using the optimal ratio (6 mm basalt fiber, 0.4% total content, 2:1 ratio of basalt fiber to lignin fiber), which was about 18.0% higher than the single basalt fiber group. This indicates that the optimal ratio can significantly improve the high-temperature rutting resistance of the mixture. Salt erosion accelerates the performance deterioration of the mixture, with water stability (residual Marshall stability) being the most sensitive—the unmodified mixture fell below the specification threshold (80%) after only 5 cycles, compared to 11 cycles for high-temperature stability failure. Fiber modification alleviated salt damage to some extent: the hybrid fiber mixture still met the specification requirements for dynamic stability after 15 salt-wet cycles, outperforming the basalt-fiber-only mixture. In terms of water stability, although the hybrid fibers extended the failure cycle to 15 (compared to 12 for the basalt-fiber-only mixture), the final residual stability values differed by less than 0.5%, indicating limited improvement. This research provides a theoretical basis for the design and performance regulation of fiber-reinforced asphalt pavements in saline-wet environments.