The Fatigue Fracture Analysis Of Asphalt Pavement Structure Under The Temperature Effect

Low temperature cracking of the asphalt pavement is the main form of damagesto the road construction. Too quickly cooling rate will lead to producing temperaturestress and surface cracking, even in climate appropriate area. At present, currenthighway asphalt pavement design specifications lack adequate index and controllingparameters in our country. Thus, the fatigue cracking research of the temperature ofasphalt pavement structure has a certain practical significance in engineering.Based on the theory of fracture mechanics，a coupled thermal stress analysismethod was used by simulating three-dimensional finite element model in this paper.The stress intensity factors of semi-rigid base asphalt pavement with basic cracks andflexible base asphalt pavement with surface cracks were studied under the largetemperature differences. The stress intensity factors of semi rigid and flexible baseasphalt pavement were also studied under the traffic loads and temperature load.Cracking mechanism of asphalt pavement was studied and fatigue life of the pavementstructure was evaluated by using Pairs formulas. Measures and methods werediscussed for slowing surface cracking. This paper researches on the main content ofthe following:(1)3D finite element model of pavement structure system was established,considering the vertical load. Analysis of the stress intensity factors of different asphaltpavement structure with crack. The stress intensity factors of the crack tip arecalculated respectively, considering the symmetric load and partial symmetry loads ofdifferent asphalt pavement structure. The rules of the stress intensity factor withdifferent crack length were given under symmetric loads and partial symmetry loads.Various influence factors for the stress intensity around the crack tip were got.(2) The relationships between crack depth and stress intensity factor of thedifferent asphalt pavement were considered under different temperature loads. At the same time, the relationships between crack depth and stress intensity factor of thedifferent asphalt pavement were considered under the temperature load and trafficload.(3)According to the calculation of the stress intensity factor and the prediction ofthe fatigue propagation of the pavement crack by the Paris formula, the fatigue life ofasphalt pavement was analyzed under the temperature load and traffic load, and somesuggestions were given for improving the fatigue propagation life of the surface crack,based on the failure mechanism.(4) According to the analysis results, some conclusions were got. Based on theresearch of this paper, the author gives reasonable suggestions and points out thefurther research work.The main research results are as follows:Initial crack depth is longer, the stress intensity factor is bigger in the coolingprocess. In other words, it is more tend to cracking. With the increase of cooling range,stress intensity factor are increasing rapidly, and two kinds of crack development arefaster.The responses of the flexible base asphalt pavement structure and semi-rigid baseasphalt pavement structure are significantly different under the same load. Open typeof the stress intensity factor of the flexible base asphalt pavement with flexible base isbigger. The shear stress intensity factor of the semi-rigid asphalt pavement is morethan the former. So failure mode of two kinds of structure has a big difference. Thephenomenon of dry shrinkage and temperature shrinkage is the characteristic of thesemi rigid material. Flexible base asphalt pavement is the top-down cracking, while thelatter is the reflective crack.The method of prediction fatigue life considering the temperature effect of theasphalt pavement is more close to the actual and is consistent with current codes, andmeanwhile has a certain reference value.