The Research On Top-Down Crack Of Asphalt Pavement Based On Dynamic Modulus

Top-Down Cracks,as a kind of failure modes of the asphalt pavement,have great impact on pavement’s functional performance,thus Top-Down Cracks is more harmful than traditional cracks.In actual use,the asphalt pavements are not only affected by the impact in the vertical direction,but also influenced by the displacement in the horizontal direction.All the changes of the mechanical properties of the asphalt mixtures will influence the stress distribution in the pavement structure,and then affect the development of cracks.So it is particularly important to analysis asphalt pavement though dynamic elastic layer theory But because the dynamic elastic layer theory is so complicated that its application cannot be realized entirely in reality.Dynamic modulus,as the most important parameter in all dynamic parameters,can describe the mechanical properties and the ability of bearing loads of the asphalt mixture.So this paper study Top-Down cracks based on dynamic modulus in this paper.1、In order to achieve the purpose of the study,three kinds of gradation are tested and analyzed to select a design gradation which meets all the requirement.based on Superpave,the study designed two different bituminous mixture with different air voids(4%,6%)to be the research subjects.2、According to the long-term aging and the short-term aging proposed by SHRP,this paper develop the aging program.Then the specimens are shaped by SGC,and tested under different temperature to get the dynamic modulus.3、Based on the relationship between the center of stiffness,stress,strain and modulus of the asphalt mixture,the expression of the modulus of the top,bottom and geometric centers of the asphalt specimen was calculated.Taking the asphalt pavement of Chongqing Changshou to Liangping Expressway as an example,the vertical linear load is applied to the specimen.The strain value on each side of the specimen is measured by using strain gauges under different temperature(10℃、 20℃、30℃).Then,the dynamic modulus gradient curve is obtained.4、The asphalt mixture specimens with cracks are tested through semi-circular bending test(SCB),and according to the collected data,the load-displacement curve is drawn.The fracture energy is then obtained by calculating the area of the curve under the peak load,which is the energy absorbed by the specimen until damaged.5、The finite element model of the asphalt pavement structure with Top-Down cracks is established based on the dynamic modulus.Then the mechanism of Top-Down cracks is analyzed though stress intensity factor and J integral outputting by the finite element model.The main conclusions that have been obtained include:1、The longer the aging of asphalt mixture is,the greater the dynamic modulus value is;The effect of the length of aging time on the dynamic modulus shift factor is not significant.;the higher temperature is,the lower the dynamic modulus value and the shift factor is;the effect of temperature on the dynamic modulus of the asphalt mixture is greater than that of the aging time;the greater the loading frequency is,the greater the dynamic modulus of the asphalt mixture is.2、It is verified that the dynamic modulus gradient curve of asphalt mixture can be obtained by using the derived formula,and the dynamic modulus gradient curve of asphalt mixture can be obtained by using direct compression test.The results show that the dynamic modulus of the top layer of asphalt mixture is the largest,and the bottom layer is the smallest,and the dynamic modulus of asphalt mixture decreases with the increase of depth.3、The fracture energy of asphalt mixture decreases with the increase of porosity;Asphalt aging has a significant effect on the crack resistance of asphalt mixture.4、The shear stress intensity factor plays a major role in the expansion of Top-Down cracks;the stress at the crack tip of the Top-Down fracture is the maximum,that is,the stress is concentrated.