Investigation On The Fatigue Life Of Asphalt Pavement Bottom-up Cracking Using Overlay Tester

At the present,asphalt pavement is the main form of high grade pavement surface in China,and is widely used in highway and urban road.Because of the influence of temperature and traffic load,asphalt pavement is easy to crack,and the form and reason are varies.Fatigue cracking is one of them.Fatigue cracking,refers to the repeated under vehicle load and temperature effect,Cracks form from the bottom,and the cracks are along the direction perpendicular to the vehicle,which show the transverse crack.The fatigue cracking of asphalt pavement is an important index of asphalt pavement structure design and material design.Therefore,how to obtain the fatigue life of asphalt pavement accurately and to guide the structure design and material design of asphalt pavement.It has great significance for improving the service life of asphalt pavement.In current asphalt pavement structure design,when structure cracks,the asphalt pavement damages,and according to it designs the asphalt surface thickness.In fact,even if the asphalt layer fatigue failures and it does not mean the asphalt pavement structure instability,and cannot be used.as long as the crack does not develop to the top,the rain still not seep into the pavement structure,and will not be accelerated pavement damage;On the other hand,existing studies have shown that a reasonable combination of pavement structures,which may allow the development of fatigue cracks slowly and even not develop to the top of the asphalt.Therefore,it is wrong to simply use the fatigue crack of asphalt pavement layer as the standard of asphalt pavement structure design,and it is necessary to consider the expansion of cracks.Based on the existing fatigue cracking model of asphalt pavement,this paper studies the development of fatigue cracking and tries to obtain more accurate fatigue life of asphalt pavement.In this paper,the life composition of fatigue crack is studied and analyzed.Firstly,fatigue cracking and fatigue propagation should be included.Secondly,based on the existing fatigue cracking model,in order to keep up with asphalt pavement structure design in our country,choose the specificationrecommended equation of fatigue cracking.The pavement structurethree-dimensional finite element model was established based on ANSYS finite element numerical analysis software,and to calculate the tensile stress at the bottom of the asphalt layer,and to calculate the life of fatigue cracking;Then utilize the OT test to simulate the development of cracks and obtain the relationship between the maximum load curves to cycles.And the relationship is obtained between the stress intensity factor curves to the crack length by finite element OT test three-dimensional finite element,through an algorithm to calculate the fracture parameters of asphalt mixture A and n.Finally,the Paris formula proposed by fracture mechanics is used to describe the expansion of fatigue fracture,and the fatigue propagation life is calculated by the fracture parameters.The results show that the increase of asphalt thickness can improve the fatigue life of pavement structure;For the fatigue life of pavement structure,the propagation life of crack is increased rapidly with the increase of temperature;When the fatigue life analysis of pavement structure is calculated,the fatigue life of the crack at different temperatures should be considered,and it is necessary to obtain the fatigue propagation life of asphalt pavement.Therefore,to accurately obtain the fatigue life of asphalt pavement,consider the fatigue crack life and fatigue propagation life.