Multi-scale Asphalt Healing Behavior Based On Dynamic Shear Rheometer And Molecular Dynamics Theory

Asphalt material is easy to crack due to fatigue damage under the repeated action of long-time natural environment(temperature,moisture,etc.)and vehicle load,which reduces its road performance and service life.At the same time,under certain conditions,asphalt materials can repair micro cracks by itself so continuously restore its strength.However,the healing ability of asphalt materials has been neglected in the design process of road engineering in our country,so the degradation of the mechanical properties of asphalt materials has been overestimated,and road maintenance costs have been increased.Therefore,it is urgent to understand the healing behavior and mechanism of asphalt,predict the healing rate and potential of different asphalt materials,and develop asphalt regenerants.The combination of dynamic shear rheological test and molecular dynamics simulation can accurately analyze the asphalt healing mechanism from multiple perspectives.The purpose of this paper is to comprehensively understand the healing process and mechanism of asphalt from two aspects: macro experiment and micro simulation.On the macro scale,polymer-modified asphalt X-70 and PAV aged asphalt are used as test materials to conduct dynamic shear rheological tests under different temperatures,different strain levels,different healing start times and different healing durations.The healing index based on pseudo shear stiffness and Ramberg Osgood healing rate model are used to evaluate the healing rate and potential of asphalt under different conditions.Meanwhile,at the micro scale,the four component model of asphalt and aged asphalt was constructed to simulate the molecular dynamics at different temperatures,different damage levels and different interface environments.The density change and diffusion coefficient in the simulation process are used to analyze the microcosmic process of asphalt healing and evaluate the healing rate and healing ability of asphalt under different conditions.The results show that the healing index based on pseudo-shear stiffness and the Ramberg-Osgood healing rate model can accurately evaluate the healing rate and healing potential of different asphalts under different conditions on the macro scale.At the micro scale,the asphalt healing process can be characterized by the density change and diffusion coefficient in the process of molecular dynamics simulation.The increase of temperature can improve the healing performance of asphalt to a certain extent,and the healing performance of asphalt always decreases with the deepening of the damage level.Under the same conditions,although the short-term healing rate of aged asphalt is higher than that of virgin asphalt,its long-term healing rate and healing potential are lower than that of virgin asphalt.As the degree of aging deepens,the healing rate and healing potential of asphalt decrease.Water can hinder the healing process of aged asphalt,while vegetable oil can improve the healing properties of aged asphalt.