Micro-adhesion Characteristics Of Asphalt-aggregate Interface Under Chlorine Salt Erosion Based On MD And AFM

In 2019,the"Outline for Building a Powerful Transportation Country"issued by the Central Committee of the Communist Party of China and the State Council proposed that,by 2035,China should be built into a country that satisfies the people,has strong guarantees and is one of the world’s leading transportation powers.At the same time,China has about 18,000 kilometers of mainland coastline and has built numerous coastal asphalt pavements,and coastal asphalt pavements are highly susceptible to seawater erosion,which affects its road performance and durability.Given the current situation that the adhesion mechanism of the asphalt-aggregate interface under sea salt erosion environment is not clear,this paper analyzes the interface adhesion between asphalt and aggregate under chloride salt erosion environment from the micro-level based on molecular dynamics（MD）and atomic force microscope（AFM）.First,the performance of 70#matrix asphalt was characterized,and the AFM asphalt samples under the chloride salt erosion environment were prepared by heat-cast and soaking methods,and the surface morphology after the chloride salt erosion was analyzed.Subsequently,choose a suitable asphalt molecular model to represent 70#matrix asphalt and verify the model.On this basis,the MD method is used to analyze the influence of chloride salt erosion on the adhesion properties of the asphalt-aggregate interface,and the adhesion contribution of each component of the asphalt is analyzed.Finally,through AFM and Si O₂microsphere modified probes and combined with the surface free energy theory,the effect of chloride salt concentration and chloride salt erosion time on the adhesion properties between asphalt and silica aggregates was analyzed separately and then revealed the asphalt-aggregate interface adhesion mechanism under chloride salt erosion environment.Besides,the physical and chemical properties of nano-silica modified asphalt were researched based on the MD method,which lays the foundation for the in-depth study of the interface adhesion properties between silica/polymer composite modified asphalt and aggregates under sea salt erosion environment.The main results are summarized as follows:（1）The interface adhesion between asphalt and aggregate is mainly physical adsorption rather than chemical adsorption,and this physical adsorption is mainly provided by van der Waals interaction.The interface failure between asphalt and silica under a chloride salt environment is adhesion failure.The adhesion loss may only be related to the immersion of water molecules and the polarization induction of sodium ions and chloride ions and has nothing to do with the surface anisotropy of the aggregate.（2）Due to the hydrophobicity of the asphalt and the hydrophilicity of the aggregate,the water molecules in the chloride salt solution can easily enter the interface between the asphalt and the aggregate through adsorption and diffusion.Na⁺ions and Cl^-ions have a polar effect with the active sites on the aggregate surface to promote more water molecules to enter the interface,thereby accelerating the diffusion and re-arrangement of the asphalt components on the aggregate surface so that some components of the asphalt gradually move away from the aggregate surface.Finally,it causes the asphalt to peel off the aggregate surface.The greater the chloride salt concentration and erosion time,the more obvious this effect will be.（3）The resin,due to its high activity,is easily adsorbed on the surface of the silica aggregate during the diffusion process,thereby providing strong interfacial adhesion.The corrosive effect of the chloride salt will cause the saturate components to accumulate away from the surface of the aggregate,and it is not easy to adsorb on the aggregate surface.As the concentration of chloride salts increases,the distribution of asphaltenes,resin,and aromatic on the silica aggregate surface becomes more uniform,and the adsorption between asphalt components and aggregate may be weakened.（4）The adhesion force between asphalt and silica microsphere modified probe decreases with the increase of chloride salt concentration and chloride salt erosion time.This is mainly since under the chloride salt environment,the light oxygenates in the asphalt will dissolve and ionize to a certain extent,and will react with the Na⁺ions in the sodium chloride solution to form a water-soluble organic sodium salt,the dissolution of polar chemical groups in the asphalt,causes the asphalt film on the surface to crack first,and part of the aggregate is exposed,forming a weaker interface zone.（5）Nano-Si O₂can improve the oxidation aging resistance and high-temperature performance of asphalt,and can significantly increase the viscosity of asphalt.The self-healing properties of asphalt mainly depend on the diffusion of light components such as saturate,while nano-Si O₂only plays an inducing role.As the oxidative aging level of asphalt increases,the instantaneous self-healing ability of asphalt decreases.