Microcosmic mechanism of reinforced interfacial transition zone in SFP materials

Abstract

Semi-flexible pavement (SFP) is extensively used in airport and tunnel pavements due to its high strength and toughness. As a multiphase composite material, SFP contains widely distributed aggregate-asphalt interface transition zones (ITZ) and asphalt-grout ITZ. These ITZs are the weakest areas in SFP and are susceptible to cracking during operation. To enhance the crack resistance of SFP, this paper proposes an interface immersion method to immerse the porous asphalt mixtures in a silane coupling agent before grouting. However, the cracking mechanism and interface enhancement process of the ITZ in SFP are not clear. This paper employs atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and nanoindentation (NI) to analyze the micro- and nanoscale properties of the aggregate-asphalt ITZ and asphalt-grout ITZ before and after interface reinforcement. Experiment results show that the aggregate-asphalt ITZ exhibits minimal interaction before and after enhancement, with the primary interaction occurring in the asphalt-grout ITZ, which has superior adhesion. Grout diffusion is more pronounced in the asphalt-grout ITZ, where cracks are significantly reduced after reinforcement. The element distribution in the aggregate-asphalt ITZ is uniform with a gradual transition, while the asphalt-grout ITZ shows a denser, more continuous distribution after surface immersion, enhancing mechanical properties. The width of the aggregate-asphalt ITZ remains constant (60–90 μm), while the asphalt-grout ITZ width increases notably after modification (from 60 to 90 μm to 90–120 μm). The research results can provide theoretical support for SFP design and maintenance.