Effect of Surface Treatment on the Interfacial Behavior and Rheological Performance of Bamboo-Fiber-Reinforced Asphalt Mastic

To enhance the comprehensive service performance of road asphalt mastic, untreated bamboo fiber (UBF), acid-treated bamboo fiber (ABF), and alkali-treated bamboo fiber (NBF) were prepared for asphalt modification. Basic physical test, contact angle surface energy test, dynamic shear rheometer (DSR), linear amplitude sweep (LAS) fatigue test, and bending beam rheometer (BBR) low-temperature test were conducted to characterize macro-performance, interfacial bonding, high-temperature deformation resistance, fatigue durability, and low-temperature cracking performance. Compared with neat base asphalt, the adhesion energy of NBF-modified asphalt mastic increased by 88.1%, and the 64 °C rutting factor (G*/sin δ) was elevated by 41.3%. At 2.5% strain amplitude, the fatigue life of NBF mastic was 3.2 times that of UBF mastic and 8.3 times that of ABF mastic. Meanwhile, NBF yielded lower BBR creep stiffness modulus S and higher m-value, indicating improved low-temperature crack-resistance performance. Alkali treatment stripped hemicellulose and wax on the fiber surface to expose abundant hydroxyl groups, forming hydrogen bonding interactions with asphalt polar components. Its adhesion energy was 36.2% higher than that of UBF mastic. Acid etching increased fiber surface roughness but failed to form effective polar bonding, leading to only 22.6% improvement in rutting factor and limited fatigue promotion. Comprehensive weighted scoring demonstrated that the comprehensive performance of NBF modified asphalt was 23.9% higher than UBF and 36.2% higher than ABF. Alkali-modified bamboo fiber is a sustainable plant fiber modifier with an excellent effect on multiple performance indices for pavement asphalt.