Study On The Micro-performance Of Recycled Asphalt And Its Interface Interaction With Mineral Aggregate

As China’s existing roads enter a large-scale maintenance period,a large number of Reclaimed Asphalt Pavements（RAP）are generated.These RAP materials are randomly stacked,occupying valuable land resources,and polluting the environment.The recycling technology of asphalt pavement can effectively dispose of RAP,which has gradually become a research hotspot in the field of roads.However,the current research on the microscopic characteristics of recycled asphalt mixture is not perfect,so it is crucial to clarify the microscopic characteristics of recycled asphalt mixture to ensure its regeneration effect and road performance.Starting from the micro level,this paper mainly studies the performance of the recycled asphalt layer on the surface of the mineral aggregate in the recycled asphalt mixture and the interaction behavior between the recycled asphalt and the mineral aggregate interface,providing a theoretical reference for the selection of recycling agents.The main research contents are as follows:A twelve molecule model of asphalt was selected,and a molecular oxide model of asphalt was constructed based on the research results of asphalt aging theory.Using Panjin 90#asphalt as a sample,the component ratios before and after aging were determined.Based on this,a matrix asphalt and aging asphalt model were constructed,and their rationality was verified by density,glass transition temperature,and radial distribution function.Secondly,the molecular models and Si O₂ crystal models of R1regenerant（petroleum based）and R2 regenerant（bio oil）were constructed,and six types of regenerated asphalt models were constructed based on the content of old asphalt and the type of regenerant.On this basis,the asphalt component mineral aggregate interface model,regenerant mineral aggregate interface model,and asphalt mineral aggregate interface model were established.After geometric optimization and annealing treatment,molecular dynamics simulation was performed on the constructed model.The microscopic properties of recycled asphalt were analyzed through evaluation indicators such as solubility parameters,free volume fraction,radial distribution function,viscosity,and bulk modulus.The results show that aging increases the cohesive energy density of asphalt.When the content of old asphalt is low,the compatibility of petroleum based regenerants with asphalt is better,and when the content of old asphalt is high,the compatibility of bio-oil based regenerants with asphalt is better;After aging,the free volume fraction of asphalt decreases by 2.8%-4.9%,and its fluidity decreases.The peak RDF of asphaltene decreased by 31.9%-33.3%,and the self aggregation effect of asphaltene weakened.The peak value of asphalt RDF decreased by 38.7%-55.8%,and the colloidal structure of asphalt changed from sol gel state to gel state.When adding bio-oil regenerants,the RDF peak value of regenerated asphaltene and asphalt with 50%old asphalt content can reach 88.7%-90.1%and86.5%-88%of the base asphalt,respectively.Using diffusion coefficient,concentration distribution,and interfacial energy as evaluation indicators,the interfacial interaction behavior of matrix asphalt,aged asphalt,and recycled asphalt with mineral aggregate was analyzed.The results show that asphaltene is the main factor affecting the diffusion rate and concentration distribution of asphalt on the surface of mineral aggregate,while saturation and aromatic content are the main factors affecting the interfacial energy between asphalt and mineral aggregate.After aging,the diffusion rate of asphalt on the surface of mineral aggregate decreases by 43.1%-64.4%,and the uniformity of concentration distribution decreases by 19.1%-24.4%.When bio-oil regenerants are added,the diffusion rate and concentration distribution uniformity of regenerated asphalt with 50%old asphalt content reach 73.7%-85.1%and 84.4%-96.7%of that of base asphalt.The recovery effect of R2 regenerant is better than that of R1 regenerant,and the regeneration effect of regenerant with smaller molecular weight is better.The regeneration effect of recycling agents on old asphalt decreases as the content of old asphalt increases.This article focuses on the performance of recycled asphalt mixtures with high RAP content.The results show that when the content of old asphalt is 50%,the regeneration effect is better,and when the content of old asphalt reaches 75%,the regeneration effect significantly decreases.The recovery effect on the diffusion rate of asphalt on the surface of mineral aggregate is poor,reaching only 49.4%-69.3%of the base asphalt.