Study On The Application Of Coarse-Grained Stress Absorbing Structure Layer On White And Black Pavement In Heavy Traffic Condition

In view of the shortcomings of the current stress absorption layer,an optimized mixture of coarse grain stress absorption structural layer and its design method are proposed.Three kinds of asphalt mixtures with coarse-grained stress absorption structure layer were designed by CAVF gradation design method,and the road performance of three kinds of coarse-grained stress absorption structure layer mixtures was verified by laboratory tests.Semicircle bending test was built based on ABAQUS finite element software of laboratory scale test and threedimensional finite element model,simulated coarse grain stress absorbing layer structure,material parameters of the mixture,and analyzed under different load position and crack tip stress state under different state of overload,exploring the structure of three kinds of coarse grain type stress absorbing layer mixture under the most unfavorable load level,the internal stress state of combined with laboratory scale test results analysis and forecast the number of material fatigue life under different state of overload.The main results of this study are as follows:(1)The optimal asphalt-stone ratios of the mixtures of SBS,SH-V and ultra-high viscosity coarse-grain stress absorption structure layers are 5.2%,5.5% and 6.0%,respectively.In this case,the shear strength and crack resistance of the mixtures are good.(2)Among the three kinds of coarse grain stress absorption structure layer mixtures,SHV type mixtures have higher shear strength,can bear larger vertical load and better rutting resistance,but their crack resistance is relatively poor due to the limited deformation range of the material itself.The super-high viscosity mixture bears less load when it is destroyed,and its rutting resistance is relatively weak,but its deformation ability is better.(3)The indoor scale test shows that under the same wheel load(0.7MPa),the crack development status and fatigue life times of mixtures with different coarse-grained stress absorption structure layers have great differences.The crack length of the mixture is related to the development direction of the main crack.SH-V type mixture has the longest crack length,and the final penetration crack is oblique crack,while SBS type mixture has the shortest crack length,and the final penetration crack is basically vertical and vertical.SH-V type coarse grain stress absorption structure layer mixture has a large number of fatigue life,good shear strength and crack resistance.(4)From the results of three-dimensional finite element simulation of indoor scale test,it can be seen that when the load is acting directly under the center line of the model,the maximum tensile stress of the whole model appears at the crack tip,which is the position of the most unfavorable load.The surface deflection value of the mixture with coarse grain stress absorption structure layer decreases with the increase of the modulus,while the overall tensile stress increases with the increase of the material modulus.The overall tensile stress and surface deflection of SH-V type coarse grain stress absorption structure layer increase with the increase of load at the most unfavorable position,but the increase of material modulus and load has little effect on the overall shear stress of the mixture.When the load is 2.2MPa,that is,the equivalent overload state is more than 3 times,the bending of the material surface reaches 0.35 mm,and the stress at the crack tip increases to 0.28 MPa.(5)Combined with relevant research results and laboratory test results,the fatigue life times of the mixture under different overload states were evaluated.The results show that when the overloading ratio is more than 50%,the fatigue life times of the mixture decrease sharply,and the fatigue life coefficient reaches 9.4,and the road surface is seriously damaged.The results of this study can provide a technical reference for the selection of reasonable stress absorption structural layer mixture types in practical engineering applications.When the road surface is prone to rutting and the selected materials need to resist large vertical shear stress under heavy traffic conditions,SH-V type coarse-grain stress absorption structural layer mixture can be selected.When there are many cracks in the old cement concrete pavement treated with asphalt overlaid layer,reflective cracks are more likely to appear in the later stage of the treated pavement,so the selected material should have better crack resistance.At this time,the ultra-high viscosity stress absorption structural layer mixture can be selected.Other general environmental conditions,can choose SBS type coarse-grained stress absorption structure layer mixture.