Analysis On Interlaminar Constraint State Of Asphalt Pavement And Its Influence On Mechanical Properties

The design of highway asphalt pavement supposes a complete continuous interface between layers,while the actual pavement structural interlayers are in a not completely continuous state.Especially the surface-base interface of the semi-rigid base asphalt pavement is the relatively weak part of the whole structure.Such state has a huge influence on the mechanical properties of the pavement structure.Therefore,it is necessary to research on the interlaminar constraint state of the asphalt pavement.Firstly,this paper analyzes the composition mechanism and influencing factors of interlayer strength of semi-rigid base asphalt pavement,and settles the forming scheme of composite surface-base specimen of "SUP-25 surface layer + interlayer treatment technique +cement stabilized macadam base".Using designed direct shear test fixture and oblique shear test fixture with Universal Testing Machine based on Goodman model,direct shear tests and oblique shear tests are carried out in order to explore the interlaminar shear strength and interlaminar bond coefficient influencing law under different influencing factors.Results indicate that the increase of temperature will lead to a sharp decrease of interlaminar strength.The interlaminar parameter at 50℃ is only 7.8%～15.1% of that at 0℃;The interlaminar shear strength and bond coefficient increase with the increase of loading rate,and the effect will not be significant when the loading rate increases to a certain extent;After the first freeze-thaw cycle,the interlaminar strength decreased by 17.0% ～ 17.9%,and the effect of the next two freeze-thaws is less;As interlaminar parameters,shear strength and interlaminar bond coefficient can characterize the effect of vertical force well.Then,the pavement structure model with interlaminar constraint is established,in which the surface-base interlayer state is characterized by the Cohesive Zone Model based on surface constraints.The interlaminar parameters obtained from the above shear tests are taken as the Cohesive Zone Model parameters.With the temperature field conditions and load conditions being considered respectively in ABAQUS analysis,the results indicate that the interlaminar constraint state has a significant effect on the thermal stress at the bottom of the asphalt layer,and the thermal stress of the interlaminar-constraint model is higher than that of the continuous model;Under the load condition,poor interlaminar constraint state can lead to a sharp increase in the stress level at the bottom of the surface and base course,and cause stress mutation between surface-base interface.The tensile strain and shear stress of the interlaminar-constraint model are 5.1 times and 2.9 times higher than those of the continuous model;The interlaminar constraint state also has a great influence on the deformation capacity.The compressive strain of the subgrade top considering interlaminar constraint increases by 23% ～ 45%,and the deflections of pavement surface and subgrade also have the similar trend;Under different interlaminar states,the response of tensile strain at the bottom of the asphalt layer is the most sensitive.The structural checking calculation is carried out for the semi-rigid base asphalt pavement structure under interlaminar constraint state to compare with the results under current pavement design method.It is suggested to consider the influence of interlaminar constraint state when calculating the allowable compressive stress of the subgrade top and the pavement fatigue life.This paper uses indoor test and finite element simulation to research on the surface-base interface state of the semi-rigid base asphalt pavement,and establishes the relationship between the above two research methods.The research analyzes the mechanical properties of pavement structure under interlaminar constraint state,which can give some reference for the study of the interlaminar state of asphalt pavement.