Analysis On Craking Mechanism And Extension Process Of Top-Down Cracks On Asphalt Pavement With Complexed Base

Top-Down Cracks is one of the common failure modes of asphalt pavement with flexible or complexed base in the temperature and vehicle loads.Cracks will not only reduce the carrying capacity of the pavement structure,and easily lead to water infiltration,accelerated destruction of the road.Therefore,study on Top-Down Cracks on asphalt pavement with complexed base has important significance,in particularly,material design structural design of the pavement,and guarantee the life of the load.In this article,directed at asphalt pavement with complexed base,bituminous mixture(AC-13,AC-20,AC-25?ATB-25),SCB test specimens with pre-cut seam are made to carry out fracture experiments under different temperature(15?,5?,-5?,-15?)and different loading modes(pure tension Me=1?pure shear Me=0?mixed model Me=0.8?Me=0.5?Me=0,2),get the critical stress intensity factor Kef of different mixures under different conditions.Kef increases with fall of temperture,and increases after decreasing with the increase of shear stress(decrease of load model parameters Me).For bituminous mixture(AC-13,AC-20,AC-25),Kef gets its minimum when Me=0.8,for bituminous stabilized macadam(ATB-25),Kef gets its minimum when Me=0.5,explanate that under tensile and shear interaction Asphalt is easy to produce damage.By selecting a non-uniform load and field model of cooling temperature,building three-dimensional finite element analysis model of asphalt pavement structure with complexed base,analyzed on Top-Down crack cracking mechanism of asphalt pavement with complexed base,under the vehicle load,temperature,vehicle load and temperature combined effect.The results show that under the vehicle load,road surface tensile stress is much less than the tensile strength of the asphalt mixture,and the maximum shear stress values close to the tensile strength of the asphalt mixture,especially overloading,overloading lug tires effects appear more likely to lead to shear vertical cracks in surface.Application of extended finite element method(XFEM)to simulate the SCB specimen with pre-cut crack,verified the feasibility of XFEM method in crack propagation;From the initial temperature,cooling rate,the surface layer modulus,base modulus,load size,etc.,analyzed on the propagation law of Top-Down cracks of asphalt pavement with complexed base under sudden cooling conditions,drawn in the same cooling rate under the condition,the higher the initial temperature is not easy to crack,but at a lower temperature crack propagation is more;More substantial cooling in a short time,create the large temperature stress,the cracks extend deeper depth;higher modulus of the surface layer cracks more susceptible to cracking;cracks under load,basically in the form of a straight line deviate from the direction of expansion of the load,as the load increases,the end of the crack from the pre-cut level the greater the distance from the crack.In the combined effect of temperature and vehicle load,the load position,load size,tensile strength,shear strength,different cooling rate both have a greater impaction on the expansion of cracks.From the control vehicle load,improving asphalt tensile strength,shear strength,reduced modulus of the surface layer to prevent cracking of the surface crack extension.