Macro–Micro Testing and Molecular Simulation on the Aging Mechanism and Behavior of SBS-Modified High Viscosity Asphalt

In this paper, the thermal oxygen aging test was conducted on the styrene-butadiene-styrene block copolymer (SBS) type high viscosity modifier (HVM), and the appearance, solubility, functional groups, and molecular weight changes were analyzed. The penetration, ductility, softening point, viscosity, high and low temperature performances, fatigue resistance, functional groups, molecular weight, and microscopic morphology changes of base asphalt and high viscosity asphalt (HVA) after thermal oxygen aging were tested. For the original and aged HVA, the diffusion of water or oxygen into HVA and the interface interaction between aggregate and HVA were studied by molecular dynamics simulation. Results show that the influence of temperature on the HVM aging is much greater than that of time. As the HVA aging degree deepens, the penetration and ductility decrease, the softening point and complex modulus increase, and the low-temperature performance and fatigue resistance deteriorates. The degradation of SBS component and the aging of asphalt component in HVA dominate in short-term and long-term aging, respectively. Therefore, the 60°C dynamic viscosity and 170°C Brookfield viscosity of HVA decrease first and then increase, while the phase angle increases first and then decreases. The SBS component and asphalt component in HVA mutually delays the aging. The van der Waals force plays a dominant role in the original or aged HVA-aggregate interface adhesion compared with the Coulomb force. With the HVA aging deepening or water addition, the absolute value of the interface interaction energy decreases, which reflects the adhesion weakening. Aging increases the free volume in HVA, exacerbating the diffusion of oxygen and water molecules into HVA. In the HVA–water–aggregate system, the asphalt-aggregate hydrogen bonds only account for less than 2% in different hydrogen bonds. As the HVA aging deepens, the water–asphalt hydrogen bond proportion increases, which weakens the water stripping resistance of the interface.