Destruction Mode And Evaluation Method Of Asphalt Treated Base Layer On Old Cement Concrete Pavement Based On Discrete Element

In recent years,most of cement concrete pavements built in the early years in China has been close to or even more than the design years,and those who have not reached the design age because of the traffic volume and the rapid increase of axle load appear broken plate,plate edge plate angle fragmentation,faulting,void and other diseases.At present,the old cement concrete repair technology commonly used in engineering is to add asphalt layer,which improves the stiffness of asphalt pavement structure,improves the smoothness of cement concrete pavement,and prolongs the service life of pavement.However,there are some diseases such as reflective crackings and rutting in the asphalt layer of cement concrete pavement.Based on this,this paper studies the relationship between the mechanical response index of the reflection crack and the rutting of the asphalt overlay and the thickness of the asphalt overlay and the bonding strength between the layers by means of discrete element numerical simulation and laboratory test verification.Firstly,based on EDEM discrete element software,the Hertz-Mindlin model is used to describe the bonding between asphalt stabilized gravel layer material particles,and the Linear Cohesion model is used to depict the bonding effect between cement concrete slabs and asphalt-stabilized gravel layers.Finally,a discrete element model of the solid concrete slab plus asphalt to stabilize the gravel layer was constructed,and the model parameters of EDEM discrete element simulation of the paving surface structure were determined by the indoor straight shear test of the paved surface structure to set up the bonding material between the different layers,and the interlayer adhesion energy density value of the layer bonding element when the discrete element simulation was carried out under the bonding material between the different layers.Secondly,the reflection cracks and rut damage of the asphalt layer of cement concrete pavement are simulated,and the relationship between it and the thickness of asphalt paving layer and the bonding strength between layers is analyzed.The mechanical response index of the two diseases under the action of curved pull load,shear load and temperature load were analyzed respectively,and the open displacement and crack expansion rate of the cracks of the asphalt extension layer were used to evaluate the reflective crack damage of the asphalt paving layer.The vertical displacement of the left and right three points on the surface of the asphalt paving layer was used to evaluate the rut deformation of the asphalt paving layer.According to the simulation results,it is suggested that the thickness of asphalt paving layer is 80 to 100 mm,and the bonding strength between layers is 0.97 MPa or more.Finally,the indoor experiment is carried out on the reflection cracking of the asphalt layer of cement concrete,and the corresponding evaluation method is put forward.In order to evaluate the reflection cracking law of the asphalt layer of cement concrete paving in the experiment,a small-size test piece of cement concrete asphalt stabilization gravel was prepared,and a set of equipment was developed to measure the width of the cracking of concrete.The displacement and expansion rate of cracks in the cutting layer of asphalt overlay are obtained by using UTM equipment to bend and pull the specimens,cut and load,and simulate the temperature loading respectively,and obtain the bonding strength between different layers and the height of different bitumen overlay.According to the results of laboratory experiments,it is found that under the action of bending or shear load,the thicker the asphalt overlay,the longer the service life of the asphalt overlay,and the greater the bonding strength between the layers,which mainly plays the role of reducing the crack propagation rate of the cutting edge of the asphalt overlay,and can not delay the cracking of the asphalt overlay.Under the action of early temperature load,the greater the bonding strength between layers,the smaller the opening displacement of the cutting edge of asphalt overlay,and the open displacement of the cutting edge of asphalt overlay is basically the same when the load time is longer,so the fatigue action times of asphalt overlay under different interlayer bonding strength are not significant.In order to reduce the open displacement of asphalt overlay in the early stage,it is suggested that the bonding strength between layers is greater than 0.97 MPa.