| Semi-flexible composite road surface is a kind of road surface formed by filling cement as the main component into the open-graded large-porosity asphalt mixture base road surface.Since its appearance,the pavement has been widely used in heavy load areas such as airports,parking lots and seaports due to its outstanding pavement performance and fatigue performance.But due to the complex of climate factor,temperature changes in some places the road all the year round in a smaller and smaller environmental impact on the pavement conditions,and in some places in winter in a cold environment,summer is a hot environment,hot and cold cycle for a long time and vehicle load under the action of will easily lead to the destruction of the pavement structure.Therefore,it is of great significance to study the cracking evolution law of semi-flexible composite pavement under the action of cooling and heating cycle.The gradation of large void parent asphalt mixture was determined by volume method,and the optimal mixture ratio of cement slurry was designed by orthogonal test method.Finally,three kinds of mixture ratios with the target void ratio of 21%,23% and25% were determined and the optimal mixture ratio of cement slurry was determined.The strength and fluidity of cement slurry is the main element influenced by the percentage of water and glue.The larger percentage of water and glue is,the strength of cement slurry decreases,and the shorter the fluidity time.The effects of sand dosage and extruding were not significant.Based on the theory and the test data of related papers,the composition of semi-flexible composite pavement materials and the temperature response characteristics of each material are discussed,and the three stages of cracking mechanism of semi-flexible composite pavement are analyzed emphatically.The composite material is composed of parent asphalt mixture and cement mortar.The asphalt mixture contains more coarse aggregate and less fine aggregate,filler and asphalt.The asphalt,a viscoelastic material,has a strong temperature sensitivity,which becomes soft at high temperature and brittle at low temperature.Stone almost does not deform with temperature;Cement slurry shrinks at low temperature and expands and deforms at high temperature.The three cracking stages are as follows: at the beginning of cracking,due to the filling of cement slurry,the modulus and strength of each layer are different,and a weak transition layer is formed between the surface layer and the base layer;In the middle period,due to the different linear expansion coefficient of various materials,the deformation is not consistent,which leads to the stress concentration and causes the failure of the transition layer and the formation of the separation interface.In the later stage,under the combined action of long-term temperature and load,the cracks generated gradually expand to the road surface,providing a way for the road water to enter the base,leading to the settlement of the subgrade and eventually the destruction of the structural integrity.In this paper,ABAQUS was used to establish a two-dimensional pavement model and analyze the mechanical response of semi-flexible composite pavement under the action of the temperature cooling and heating cycle range of-5℃ ～ 35℃.It was found that the bottom shear stress of surface layers and the bending value of road surface increased during the heating process,and the increasing trend was more severe with the increasing temperature.It was found that in the process of heating up,the bottom shear stress of surface layers and the bending value of road surface increased,and the increasing trend was more severe with the increasing temperature.When the temperature drops,the compressive stress,shear stress and surface deflection also decrease,and the decreasing trend of bottom compressive stress and shear stress gradually slows down.It can be obtained that the internal stress of pavement structure is large under the cold and hot cycle,and it is easy to crack.The tensile stress and strain values at the bottom of the base are almost not affected by temperature,but only affected by the upper vehicle load.The fatigue cracking test of semi-flexible composite pavement under the action of cold and hot cycle was carried out by the indoor four-point bending fatigue test method.The results show that with the increase of temperature,the ultimate strength of the composite decreases,the stiffness modulus decreases more obviously,and the fatigue life times are less.The sensitivity of the composite to strain level increases with the decrease of temperature.The fatigue life of semi-flexible composite pavement is relatively long in the region where the periodic temperature difference is small.Based on the above research results,the specific values of the voidage of the parent asphalt mixture for the suitable semi-flexible composite pavement in hot,cold and mild areas are optimized,which provides a more reliable basis for the application of semi-flexible composite pavement in future projects. |
