Analysis Of Asphalt Pavement Surface Crack Using Finite Element Method

At present, our country's highway constructions are at a rapid development stage. There are many serious problems of early destruction among highways being operating and the fatigue cracking is one of the main forms. Due to traffic load and low temperature stress acting on asphalt pavement repeatedly, the micro cracks propagate and connect reciprocally and form the macro cracks at last which bring about the reduction of the service life of pavement structure. The traditional asphalt pavement structure design using elastic layered system model can't reflect the present situation that the asphalt pavement structure has been working with cracks in its most of the time of the whole life cycle. The emergence and development of fracture mechanics is one of the important achievements in the field of mechanics in the twentieth century, and its research results are widely used in many engineering fields. It's a effective way that combines the fracture mechanics theory with the finite element method when we analyze the problems on the asphalt pavement surface crack. It will be closer to the real pavement materials damage if we make use of the fracture mechanics theory and consider the stress singularity on the crack tip when we research the crack extension under the action repeated of driving load. From these, in this paper, we discuss the relationship between surface crack tip stress intensity factors and calculated parameters of pavement structure and create finite element models based on the fracture mechanics theory. We also discuss the relationship between the rule of crack propagation and the fatigue life using Paris formula. From the study in this paper, we can draw the following conclusions:(1) In pavement structure parameters under the condition of constant, stress intensity factors of surface course increase slowly while crack depth increase. In the condition of the same crack depth, stress intensity factors decrease gradually while the thickness of the surface course increases. The fatigue life and crack-resistance enhance while the thickness of the surface course increases. However, when the thickness of the surface course adds to a certain extent, it has little influence on stress intensity factors and fatigue life.(2) Surface course modulus has a great influence on stress intensity factors and the fatigue life, and determining the surface course modulus and the ratio of surface course modulus to base course modulus is very important. In the condition of lower modulus (< 1400MPa), the relationship of stress intensity factors and crack depth is a wave shape curve. In the condition of higher modulus (> 1400MPa), stress intensity factors increase while crack depth increase and there is a rapid increase near the bottom of surface course. In the condition of the same crack depth, stress intensity factors increase while surface course modulus increases.(3) Base course modulus should not be less than surface course modulus too much and its change must be in a certain range. As base course modulus increases, stress intensity factors of surface course decrease, and stress intensity factors of surface course decrease while base course modulus increases. In the condition of higher modulus (> 1500MPa), the relationship of stress intensity factors and crack depth is a wave shape curve. In the condition of lower modulus (< 1500MPa), stress intensity factors increase while crack depth increase and there is a rapid increase near the bottom of surface course. When base course modulus larger than 1500MPa, it has little influence on fatigue life of surface course.(4) The influences of the thickness of subbase course bring to the stress intensity factors and fatigue life of surface course are not very big. With the increase of the thickness of subbase course, stress intensity factors of surface course decrease gradually and the fatigue life will increase, but the effect is not obvious. Therefore, in road design, it is not comprehensive that subbase course is regard as the design layer and a pavement structure design takes the deflection value as the design index even the only one. In order to perfect the pavement structure design, we should put forward some new control indexes aiming at the control of some local stress in the asphalt pavement structure and the satisfaction of durability.