Research On Crack Propagation Of Asphalt Pavement With Semi-rigid Base Based On Cohesion Model

Semi-rigid base asphalt pavement is the main form of pavement structure of high-grade highways in my country.Cracks are one of the common diseases of semi-rigid base asphalt pavement.It is difficult to accurately predict the cracking and damage of asphalt pavement by laboratory tests alone.In view of this,this paper aims to provide an auxiliary method for the future research on the crack resistance of semi-rigid base asphalt pavement,using numerical simulation method to analyze the main cracking form of semi-rigid base asphalt pavement and the factors affecting crack propagation from a meso angle.Firstly,a random aggregate delivery program is written based on Matlab to generate a random aggregate delivery model of dense graded asphalt concrete(AC)and asphalt mastic lipid(SMA),which is obtained from the CT scan from the aspects of aggregate shape,size,distribution,etc.The test results were compared to verify the feasibility of the random aggregate delivery model.Secondly,through the compilation of Python program to realize the batch embedding of cohesive units,combined with the generated random aggregate drop model,a two-dimensional meso-fracture model of asphalt mixture was established.The ABAQUS software is used to numerically simulate the low temperature cracking of asphalt mixture from a meso angle,and the obtained results are compared with the test results.The two have good consistency,indicating that the mesoscopic fracture simulation model of asphalt mixture is applicable.On this basis,the effects of different aggregate distribution,average aggregate area and pre-notch orientation on the low-temperature cracking performance of the asphalt mixture were studied.Next,the numerical simulation of the temperature shrinkage cracks and temperature fatigue cracks caused by the rapid temperature reduction of the asphalt mixture is carried out.The research results show that the expansion rate of the temperature shrinkage cracks is not only related to the temperature reduction in a short time,but also related to the temperature before and after temperature.The change of daily temperature difference directly affects the initial propagation time and growth rate of temperature fatigue cracks,and this effect exhibits nonlinear characteristics with the change of daily temperature difference.Finally,the meso-fracture model of the semi-rigid base asphalt pavement was established to study the propagation of reflective cracks and the fatigue life of the asphalt surface under the action of temperature stress and load stress alone and the coupling of the two.And the effects of asphalt surface layer thickness and base layer modulus on the fatigue crack propagation of reflection crack under temperature stress alone,and the effects of heavy load and asphalt surface voidage on the fatigue crack growth of reflective crack under load stress alone are analyzed.When the temperature stress acts alone,as the thickness of the asphaltsurface layer increases,its fatigue life does not show a linearly increasing law.The fatigue life of the reflective cracks of the entire surface layer is mainly provided by the middle and lower layers.When the reflective cracks extend to the upper layer area It has basically entered the stage of fatigue failure of surface structure.As the modulus of the base layer decreases,the location of fatigue failure of the surface layer shows a shallower trend in the thickness direction.When the load stress acts alone,the heavy load makes the reflective crack area be subjected to the axial load earlier than the standard axial load,thereby accelerating the propagation rate of the reflective crack in this area.The increase in the porosity of the asphalt surface layer leads to a decrease in the overall density of the surface layer structure,which is prone to micro damage and micro cracks when subjected to repeated loads,weakening the overall strength of the surface layer and greatly reducing the fatigue life of the asphalt surface layer.Comparing the fatigue life obtained under the three load states respectively,the effects of temperature stress and load stress on the fatigue propagation process of reflective cracks on semi-rigid asphalt pavement are analyzed.The results show that: temperature stress dominates the propagation rate of reflective cracks,The load stress mainly changes the propagation form of reflective cracks.