Study On Adhesion Of Foamed Asphalt-Aggregate Interface Based On Molecular Dynamics Simulation

Foamed asphalt mixture is an economical and environmentally friendly pavement material with foamed asphalt,aggregates and fillers as the main components.Because the foamed asphalt contains residual moisture that has not evaporated,the physical properties of the foamed asphalt and the interface between the asphalt and aggregates in the mixture are caused.Adhesion is affected,thereby affecting the overall performance of the foamed asphalt mixture.At present,the research on the physical properties of foamed asphalt and the adhesion between foamed asphalt and aggregate mainly relies on indoor macroscopic experiments,which cannot fundamentally reveal the physical properties of foamed asphalt and the adhesion mechanism between foamed asphalt and aggregate interface.In view of this,by means of molecular dynamics(MD)simulation method,the physical properties of foamed asphalt,the influencing factors of foamed asphalt-aggregate interface adhesion,and the effect of shearing on the foamed asphalt-aggregate adhesion were analyzed.The content is as follows:(1)Establishment and verification of molecular model of foamed asphaltA 4-component 12-molecule asphalt molecular model was used to simulate foamed asphalt,and water molecules were added to it.The rationality of the model was verified by the density and radial distribution function of foamed asphalt as evaluation indicators.The results show that the foamed asphalt model based on the 4-component 12-molecule asphalt model can represent the real foamed asphalt.(2)Study on physical properties of foamed asphaltThe physical properties of foamed asphalt were studied by calculating the mechanical modulus,free volume fraction,cohesive energy density and van der Waals energy of the foamed asphalt model.The results show that the free volume fraction of the foamed asphalt is larger than that of the base asphalt.The addition of water molecules increases the movement space of the asphalt molecular chain and the distance between the asphalt macromolecules,which weakens the intermolecular force of the asphalt,reduces the viscosity of the foamed asphalt,and improves the foaming asphalt glass transition temperature.(3)Analysis of influence factors on adhesion of foamed asphalt-aggregate interfaceThe foamed asphalt-aggregate interaction model was constructed,and the effects of four factors,namely,moisture content of foamed asphalt,aggregate type,aggregate surface moisture and temperature,on the adhesion of foamed asphalt-aggregate interface were analyzed,the effects of water content,temperature and time on the diffusion of water molecules in foamed asphalt were analyzed by statistical methods.The results show that the interfacial adhesion of foamed asphalt-aggregate increases first and then decreases with the increase of the moisture content of foamed asphalt;no matter under the dry and wet conditions of the aggregate surface,the interfacial adhesion of alkaline aggregate and foamed asphalt is always better than the interface adhesion between acidic aggregate and foamed asphalt;the higher the temperature,the better the adhesion between foamed asphalt and aggregate;temperature and time have a significant effect on the diffusion of water molecules.(4)Study on failure mode and interface adhesion deterioration mechanism of foamed asphalt-aggregate system under shearing actionBy constructing an aggregate-foamed asphalt-aggregate "sandwich" structural model,and applying different shear rates and durations,the failure modes of the aggregate-foamed asphalt-aggregate structural system under shear were studied;by changing the system The influence of environmental and material factors on the shear failure of aggregate-foamed asphalt-aggregate structural system was studied by temperature,aggregate section direction and foamed asphalt moisture content.The results show that when the shear distance is constant,the faster the shear rate is,the easier it is to cause interfacial adhesion failure;the higher the temperature,the higher the moisture content of the foamed asphalt,the easier it is to cause the cohesive failure inside the foamed asphalt;For aggregate anisotropy,the Miller index(h l k)is used to represent the aggregate cut surfaces in different directions.From the peeling of aggregate and asphalt,it can be seen that the order of adhesion between each section of calcium carbonate and foamed asphalt is(018)>(214)>(104);the order of adhesion between each section of silicon oxide and foamed asphalt is(001)>(100)>(101);the force between asphalt and aggregate is mainly van der Waals force.