Study On The Bond Failure Behavior Of Porous Asphalt Concrete Based On Discrete Element Method

Porous asphalt concrete pavement is widely used in highway engineering construction,which could be attributed to its excellent drainage,noise reduction,anti-skid and anti-glare.However,there is a problem that bond failure has detrimental effects on its durability.Long-term coupled conditions of climate and wheel loads may accelerate bond failure at aggregate-mortar interface or mortar-mortar interface,leading to pavement looseness.In order to reveal the bond failure behavior mechanism in a mesoscopic perspective and provide a theoretical basis for improving the durability of porous asphalt concrete,discrete element software was utilized to analyze the internal bond failure behavior of porous asphalt concrete.First of all,based on CT scanning technology and digital image processing technology,the two-dimensional structure information of porous asphalt concrete was obtained and a geometric model was constructed.The parallel bonding model,Burgers model,contact stiffness model and sliding model were used to describe the mechanical characteristics of different materials within porous asphalt concrete.Uniaxial compression tests and uniaxial creep tests were performed to calibrate the contact parameters at different conditions.Secondly,the gradation information of CT scan images were used to construct a virtual bond failure test model.The bond failure under static load was studied based on contact parameters under different temperatures and adverse conditions.The research shows that heating,water and freez-thaw cycle could aggravate the growth of deformation and particle peeling of porous asphalt concrete,which could promote bond failure.At 60?,the bond failure may cause some air void compression and small voids will also generate.Meanwhile,air void content decreases,and air void number and long and short axis ratio both keep growth.The porosity,the number of voids,and the average ratio of long axis to short axis all have a clear linear relationship with the quantity of bond failures.Heating and adverse conditions will weaken the effect of the number of bond failure on air void structure deterioration.Increasing depth causes the reduction of the porous asphalt concrete of vertical stress and the order of horizontal stress of porous asphalt concrete is upper layer,lower layer and middle layer.The modulus of porous asphalt concrete decreases at 60?,which causes the horizontal overlap to increase sharply and the horizontal stress to increase significantly.The bond failure has gone through two stages: rapid growth and deceleration growth.The distribution of bond failure locations presents trapezoid,and mainly focus on the diagonal shear zone.Most of the bond failure were cohesive failure,and a few were adhesion failure.Cohesive failure has the fastest rate of development and its number is also largest.Thirdly,half sine wave load was utilized to analyze bond failure.It has been found that heating and adverse conditions could aggregate irrecoverable deformation and increase average contact force.The main force chain will be more likely to form in the area,where the interface has smaller distance and thinner mortar between aggregates and smaller air void number.The bond failure has gone through four stages: low speed growth,fast growth,deceleration growth,and no growth.The energy change has a close relationship with the bond failure.The bond failure keeps growth under the joint action of the bond energy and the strain energy.The bond failure is the main reason of the rise of friction work under load.At 60?,the increase of the target void rate will aggravate bond failure.When the target void rate increases from 18% to 20%,the growth of bond failure is the largest.The increase of Weibull's double parameters in the void gradation at 60 ? without circulation will aggravate the bond failure,in which the adhesion damage has a greater significance effect.Finally,a study of fatigue failure under reciprocating load was conducted.The research found that heating and adverse conditions(water bath,freeze-thaw)will aggravate the fatigue damage of porous asphalt concrete pavement.Fatigue damage may casue the change of force chain structure.In the force chain network parameters,the average shortest path decreases with the increase of fatigue damage,and the average network constraint parameter increases with the increase of fatigue damage.The average clustering coefficient increases at first and then decreases.