Multi-Scale Characterization Of Asphalt-Filler Interaction Behavior And Molecular Dynamic Simulation Of Interfacial Adhesion Mechanism

Asphalt mixture is a kind of dispersion system with a multi-level network structure,which includes a coarse dispersion system(asphalt mixture),a subdivided dispersion system(asphalt mortar),and a differential dispersion system(asphalt mastic).Among them,asphalt mastic plays a crucial role in aggregates bonding,voids filling,load transferring and the pavement performance of asphalt mixtures.Based on the multi-scale characterization methods,the paper investigated the cohesion and adhesion properties of asphalt mastic from the micro and macro characterization of asphalt-filler interaction behavior and the molecular dynamic simulation of asphalt mastic-aggregate interface adhesion behavior,respectively,which is important for revealing the evolutionary mechanism of asphalt material properties and improving the pavement performance.Firstly,the microstructural molecular composition and surface morphology of asphalt mastic were characterized with Fourier transform infrared spectrometer(FTIR),Scanning electron microscopy(SEM)and Atomic force microscopy(AFM),and the physical-chemical interaction mechanism between asphalt and filler was further explored.Secondly,the asphalt-filler interaction ability was evaluated based on the macro rheological indicators and phase separation behavior,then the sensitivity factors affecting the micro-macro performance of asphalt mastic were investigated with grey relational analysis(GRA)method to provide a basis for optimizing the selection of mineral filler for enhancing asphalt mastic performance.Finally,the asphalt mastic-aggregate interface model system was established under wet-heat homoeopathic coupling conditions by molecular dynamic simulation,and the adhesion and debonding failure mechanism of interfacial weak zone of asphalt mixture was revealed based on the molecular orientation theory.The following major conclusions were achieved from this study.(1)The asphalt–filler interaction was mainly caused by physical action.The micro surface texture of the limestone filler particle was more rough and uneven due to the existence of rich folds and protrusions compared with the granite filler and diabase filler,which could increase the asphalt-filler interfacial adhesion ability.The micro-morphological characteristics of asphalt mastics mainly depended on the adsorption effect and dispersion effect of the mineral filler on polar fractions and the wax crystals,respectively,which relies on the filler content.At the relative low filler-asphalt ratio(F/A),the mineral filler would adsorb the polar fractions and weaken the coating ability of polar fractions on the wax crystals.While at the relative high F/A,the dispersive filler particles with the ability to adsorb polar fractions caused the dispersion of wax crystals along with the dispersed fractions,which lead to the small and dense state of“bee structure”.(2)Due to the inhomogeneous multi-phase characteristics of asphalt mastic,the macroscopic phase separation behavior is more likely to occur under high temperature condition compared to neat asphalt.The phase separation behavior of asphalt mastic could reflect the stability of asphalt-filler interface phase and the interaction ability.Besides,the K-B-and K-B-~*results indicated that the interaction ability between asphalt and alkaline mineral filler is obviously stronger than that of neutral and acidic mineral filler,which is consistent with the micro-morphological characteristics of asphalt-filler interface.In addition,the asphalt-filler interaction ability is positively correlated to the filler content before the critical volume fraction of particle structuralization.The GRA method could effectively establish the quantitative relationship between filler properties and micro-macro properties of asphalt mastic,which could furtherly provide theoretical support for cross-scale correlation analysis of asphalt performance.(3)The asphalt mastic-aggregate interface model established under the actual F/A condition is reasonable and reliable to characterize the adhesion and debonding mechanism of the interface weak zone in asphalt mixture.The aggregation and arrangement characteristics of polar components in asphalt mastic on the mineral aggregate surface indicated that the addition of silica particles significantly changed the distribution behaviors of polar components and reduced the van deer Waals energy.However,the silica particles with amounts of residual charges would promote the Coulomb electrostatic energy of the interface.Moreover,the molecular orientation theory demonstrated that the directional adsorption of polar components with high dipole moment to the aggregate surface is the basic reason for asphalt mastic-aggregate interfacial adhesion behavior.The existence of moisture would significantly reduce the work of adhesion of asphalt mastic-aggregate interface and lead to the debonding failure,which is consistent with the prone early moisture distress occurring in asphalt pavement.The study established a coupling analysis system for evaluating the asphalt mastic properties based on cross-scale micro macro characterization and molecular dynamic simulation technology,and gave a deeper insight into the asphalt-filler interaction behavior and asphalt mastic-aggregate adhesion mechanism,which would be expected to support for the refinement design of asphalt pavement materials and extend the service life of pavement.