Strength Generation And Failure Mechanism Of Foamed Asphalt Cold Recycled Mixture Based On Molecular Simulation

At present,recycling and reuse of asphalt pavement has become an inevitable requirement for environmental protection.In order to reduce the impact on the environment to a better extent,cold-recycling pavement technology is increasingly favored by scholars and engineers in various countries.Under this background,the cold recycling technology of foamed asphalt has received more extensive attention and application.The cold recycled asphalt foams have the advantages of saving energy,reducing asphalt content and transportation cost,and having both flexible and rigid pavement.However,due to the low content of asphalt and mixing water in the mixing process,the water stability of foamed asphalt mixture is instable,and it is easy to destroy in the water environment.At the same time,the composition of foamed asphalt mixture is complex.It contains pavement milling materials,moisture,asphalt and cement.The reaction order of each component determines the forming mechanism and failure mechanism of foamed asphalt mixture.Based on the above research background,starting from the influence of moisture on foamed asphalt mixture,this paper explores the mechanism of strength generation and failure of mixtures.First,the basic performance test of foamed asphalt mixture is carried out,and then the molecular dynamics simulation is used to analyze the strength generation and failure mechanism of the mixture.Finally,the addition of additives is used to improve the water removal performance and pavement performance of the mixture,and it is verified from two aspects of molecular simulation and macroscopic test.Finally,the practical application of foamed asphalt mixture is instruct.First of all,the basic performance test of foamed asphalt mixture is carried out.From the start of RAP performance test,stone and aging asphalt are extracted and separated from RAP,and its performance test is carried out to evaluate the aging characteristics of the original pavement.The experimental design of foamed asphalt mixture is carried out.Starting from the test of asphalt foaming performance,the appropriate gradation is selected,and the water consumption of asphalt foaming and mixing whipping water are determined through experiments.The road performance test of the foamed asphalt mixture is carried out,mainly including fatigue test,low temperature performance test and dynamic modulus test.Secondly,the molecular model of foamed asphalt mixture is established,which is divided into three parts:RAP molecular model,new asphalt model and cement model.After that,the three models are aggregated together to form the whole model of foamed asphalt mixture.Finally,appropriate conditions such as ensemble,boundary conditions and time step are selected,and the code is written to simulate the molecule with open source software LAMMPS.The data of energy change and atomic trajectory are analyzed.In order to analyze the failure mechanism of foamed asphalt mixture more clearly,an interface shear failure model was established to analyze it.Finally,macroscopic performance test and molecular simulation show that moisture has a negative effect on foamed asphalt mixture,and it has a greater negative impact on durability and so on in the winter freeze-thaw cycle in northern China.Therefore,by adding additives to improve the pavement performance of foamed asphalt mixture under water conditions,three modifications are proposed: oxidation.Zinc replaces some mineral powder,uses coupling agent solution to treat RAP surface,and adds anti-stripping agent to mixing asphalt.The above three modification methods are also verified by two methods: molecular simulation and indoor test.First,microscopic simulation is carried out.On the basis of the foam asphalt mixture model,a small number of Zinc Oxide molecules are added to the RAP model,a small amount of coupling agent is added to the RAP model,and a small number of anti stripping agents are added to the new asphalt model,and the above three new models are introduced.The results of molecular dynamics simulation and interface failure simulation are compared with the results of ordinary foam asphalt mixture simulation.After that,fatigue test,low temperature performance test,dynamic modulus test and other macro tests were carried out to verify the comparison.The result showed that using coupling agent modified RAP and adding anti stripping agent to new asphalt increased the pavement performance of foam asphalt mixture greatly.