Synergistic Adsorption-Enhancement of Bamboo-Aramid Fibers in SMA-13 Asphalt Mixtures

The synergistic use of natural bamboo fiber and synthetic aramid fiber in asphalt mixtures has received limited research attention, particularly regarding the optimal blending ratio under a constant total fiber content and the underlying reinforcement mechanisms. This study systematically investigated the co-blending of bamboo and aramid fibers in SMA-13 asphalt mixtures with a fixed total fiber content of 0.3%. Five mixture groups were prepared, LF (0.3% lignin fiber, control), BF (0.3% bamboo fiber), as well as three hybrid groups: ABF-1 (0.27% bamboo + 0.03% aramid, 9:1), ABF-2 (0.24% bamboo + 0.06% aramid, 4:1), and ABF-3 (0.21% bamboo + 0.09% aramid, 7:3). The mixtures were evaluated using rutting tests, low-temperature flexural beam tests, moisture stability tests, and AMPT dynamic modulus testing. The results demonstrate that hybrid-fiber mixtures outperform single-fiber mixtures, with ABF-2 exhibiting the best overall performance. Compared with LF and BF, ABF-2 achieved a dynamic stability of 6921 passes/mm (increases of 97.7% and 52.7%, respectively); flexural tensile strength increased by 43.1% and 32.1%; maximum flexural tensile strain increased by 42.6% and 35.0%; and retained stability improved by 10.8% and 12.5%. AMPT results indicated a higher dynamic modulus and lower phase angle for the hybrid system, suggesting an enhanced elastic response. The superior performance of ABF-2 is attributed to the complementary adsorption-stabilization effect of bamboo fiber and bridging-reinforcement effect of aramid fiber. This study provides quantitative evidence for the beneficial combination of natural and synthetic fibers in asphalt mixtures and identifies key limitations that warrant future investigation.