Effect Of Asphalt Film Thickness On Mechanical Properties Of Asphalt-aggregate Interface

In recent years,in the development and research of roads,asphalt roads have become the main structural form of modern traffic roads by virtue of their own characteristics.The rapid increase of road traffic flow and the increasing number of heavy-duty vehicles,under the repeated action of wheel dynamic load,the asphalt pavement is shear-deformed,eventually forming ruts,bagging,and other diseases,affecting the normal use of the road,will give Driving safety poses serious hidden dangers.The interfacial phase structure of asphalt mixture is very complicated,and these road diseases are often developed from the interface phase.The asphalt in the asphalt-aggregate interface exists in the form of a bituminous membrane,and the thickness of the asphaltic membrane has a great influence on the mechanical properties of the interfacial phase.Therefore,analyzing the influence of asphalt film thickness on the mechanical properties of asphalt-aggregate interface,understanding the failure mechanism of asphalt aggregate,reducing the damage of asphalt pavement and improving the road performance of asphalt pavement are of great significance to the development of road research,and also the focus of this paper.Firstly,the aggregate-asphalt-aggregate test piece and related preparation tools were designed by ourselves,and the test pieces with different asphalt film thickness were prepared by controlling the forming load of the test piece.The thickness of the test piece asphalt film was measured by electron microscopy,and the relationship between the forming load and the thickness of the bituminous film was obtained,which laid the foundation for later research.Secondly,this paper adopts the shear test method to carry out shear test on specimens with different asphalt film thickness.The test obtained two different types of stress-displacement curves,namely a single peak curve and a double peak curve.In this paper,the stress displacement is subdivided into four types based on the peak position: SPC-1,SPC-2,SPC-3,and DPC.Based on the Gaussian function,four models of stress-displacement curves are constructed.SPC-1 reflects that the asphalt-aggregate interface failure process is dominated by adhesion failure;the SPC-2 curve reflects that the asphalt-aggregate interface failure process is dominated by cohesive failure;SPC-3 and DPC curves reflect The asphalt-aggregate interface failure process is a mixed failure of adhesion and cohesion,and the difference in stress peak position between adhesion stress and cohesive stress determines the type of stress-displacement curve(SPC-3 curve or DPC curve).The probability of obtaining various types of stress curves in the shear test of the specimens with different asphalt film thickness and the influence of the asphalt film thickness of the test specimen on various curve parameters were obtained.From the structural asphalt and free asphalt as the starting point,the failure mechanism of the asphalt-aggregate interface phase is analyzed.The reason for the DPC type curve is analyzed according to the slip theory.Both the slip phenomenon and the slip distance have a certain randomness and the influence factors of the occurrence probability of the slip phenomenon are the thickness of the asphalt film,the viscosity of the structural asphalt and the free asphalt.The effect of asphalt film thickness on the shear resistance of asphalt-aggregate interface was analyzed from the perspective of fracture energy.The results show that as the thickness of the asphalt film increases,the peak position of the single peak shifts back,and the stress peak of the single peak decreases.The probability of occurrence of double peaks varies with the thickness of the asphalt film.The asphalt film thickness is less than 23 ?m or greater than 219 ?m,and the probability of occurrence of a double peak curve is zero.When the asphalt film thickness is in the range of 34 ?m to 129 ?m,the double peak curve phenomenon has a probability.When the thickness of the asphalt film is 83 ?m,the probability of occurrence of double peaks is the largest.The thickness of the asphalt film determines the proportion of free asphalt and structural asphalt in the asphalt film.The proportion of free asphalt determines the failure mechanism of the asphalt-aggregate interface phase,and the appearance of the four types of stress-displacement curves is caused by the difference in interface failure mechanisms of different asphalt film thicknesses.In evaluating the shear resistance of the asphalt-aggregate interface phase of different asphalt film thicknesses,the following aspects need to be referred to.In the process of interface failure,the shear stress is less than the standard value of the fracture energy,the interface shear stress peak,the interface deformation is greater than the standard value of the fracture energy,and the asphalt film thickness interface shear stress-displacement curve has a double peak curve probability.