Mix design optimization of high-viscosity asphalt mixtures for ultra-thin pavement considering geometric properties and interface slip behavior for aggregate system

Ultra-thin wearing course has been widely applied for the maintenance of old pavements due to its quick construction and good performance. However, it is prone to damage due to its thin thickness and direct exposure to traffic and environmental factors. This work aims at proposing a mix design method from mechanical behavior to improve deformation resistance ability. The high-viscosity asphalt (containing SBS and tackifying resin) and basalt (with particle size less than 8 mm) were applied in the ultra-thin pavement. The shear-slip test for aggregate system and compactability test were introduced to evaluate the skeleton strength and workability of gradations, and their results were then analyzed the correlation with Skeleton Interlock Index and Particle Slip Index calculated by geometric indicators. The shear strength of asphalt mixtures with various asphalt contents was examined by shear-slip test for asphalt mixture to obtain their relationship. Finally, an improved Marshall design method for asphalt mixture in ultra-thin wearing courses was proposed, and the performance of specimens with the traditional and advanced methods was then compared. The results showed a strong correlation between the shear strength of the aggregate system and Particle Slip Index, as well as between the compaction parameter and Particle Slip Index. The product of Skeleton Interlock Index and Particle Slip Index can be used to select gradations with higher strength, while the shear strength of asphalt mixtures can serve as a mechanical indicator for determining the optimal asphalt content. The asphalt mixture using the improved method exhibits good high-temperature, low-temperature, and moisture stability performance, although it has slightly higher asphalt binder leakage loss.