Rheological Properties and Microscopic Mechanism of MMT-FA Composite Modified Asphalt

To enhance the high-temperature rutting resistance, fatigue performance and low-temperature cracking resistance of base asphalt, and promote the resource utilization of industrial solid waste, this study took 70# asphalt as the base asphalt and selected nano-montmorillonite (MMT) and fly ash (FA) as composite modified fillers. A series of composite modified asphalt samples was prepared with MMT:FA mass ratios of 1:2, 1:3 and 1:4 and total filler contents of 3%, 5% and 7%, respectively. Conventional physical tests, dynamic shear rheometry (DSR), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and bending beam rheometry (BBR) were adopted to systematically evaluate the pavement rheological properties. The microscopic modification mechanism was revealed by thin-layer chromatography with flame ionization detection (TLC-FID) and gel permeation chromatography (GPC). The results show that MMT-FA composite filler can significantly reduce the penetration, increase the softening point, and greatly enhance the high-temperature rutting factor, creep-recovery rate and fatigue life of asphalt, while its influence on low-temperature performance is controllable. For the optimal group, S5, the rutting factor rises by 42.6% at 64 °C, and the fatigue life increases by 58.3% under 5.0% strain compared with the base asphalt. With the increase in filler content, the high-temperature and fatigue performance of asphalt increases first and then slows down, while the low-temperature stiffness rises gradually. Microscopic analysis indicates that the intercalation and strong adsorption of MMT restrict the light components of asphalt and increase the proportion of macromolecules, and FA plays the roles of particle filling and skeleton support. The two fillers synergistically optimize the colloid structure and molecular distribution of asphalt. Based on rheological properties and microscopic mechanism, the optimal ratio is 1:3 for MMT:FA with a total content of 5%, under which the composite modified asphalt achieves the best comprehensive pavement performance and can meet the requirements of heavy-load traffic and areas with large temperature differences. The research results can provide experimental and theoretical support for the material design, performance optimization and engineering application of MMT-FA composite modified asphalt.