Research On Mesoscopic Cracking Behavior Of Asphalt Mixture In Gobi Desert Area

With the advancement of our "Belt and Road" strategy and the development of our transportation industry,the focus of our highway construction has gradually shifted to the western region of our country.However,there are a lot of Gobi desert areas in the west of our country,and the harsh natural environment also has a great impact on the use of asphalt pavement.In the Gobi Desert area of our country,the severe climatic characteristics such as frequent extreme temperature,long sunshine time and high solar radiation amount lead to the early and severe asphalt pavement disease in this area.It is difficult to establish the relationship between different meso-factors and anti-cracking performance of asphalt mixture because the traditional macro-test can not study the cracking mechanism of asphalt mixture in essence.This research uses X-ray CT technology and Digital Image Processing technology combined with PFC2D discrete element numerical simulation,in this paper,the force chain and displacement of particle element for low temperature cracking and fatigue cracking of asphalt mixture in Gobi Desert area are studied from the microscopic point of view,the relationship between different loading rate,loading frequency,void rage,stress level,aggregate friction coefficient,bond strength between mortars,bond strength between aggregates and mortars and anti-cracking performance of asphalt mixture in Gobi Desert area was studied by control variable method.The main research contents and results of this paper are as follows.Taking the Gobi Desert area of Gansu province as an example,firstly,through the data investigation of high-grade highway and secondary highway in the Gobi Desert area of Gansu province,the structure layer design and disease types are analyzed.Based on the pavement performance of two typical 15-segment roads,the paper analyzes the characteristics of asphalt pavement disease in Gobi Desert area.It is found that the PCI value of pavement in Gobi Desert area is lower than that in non-Gobi desert area,the rate of pavement damage is higher than that of other diseases,especially the crack disease.The low temperature cracking and fatigue cracking of asphalt pavement in Gobi Desert area are the key points of follow-up research.Secondly,according to the climate characteristics of the Gobi Desert,the aging pretreatment is used to simulate the extreme high temperature and long sunshine time in the Gobi Desert.For the pre-processed asphalt mixture trabecular specimens,through X-ray CT technology scanning,the asphalt mixture meso-interface gray image.OpenCV and other image processing software combined with image processing technology and algorithm to asphalt mixture gray image enhancement,sharpening,edge detection,binarization,vectorization and other processing,the vectorized image containing asphalt mixture interface information is imported into PFC discrete element to reconstruct asphalt mixture model.It is found that the reconstructed asphalt mixture model accurately restores the meso-interface characteristics of the Gobi Desert asphalt mixture,it provides a good foundation for the construction of discrete element model of asphalt mixture.Then,a suitable mechanical model is chosen to describe the mechanical behavior of aggregate units,asphalt mortar units,asphalt mortar and aggregate units.The linear stiffness model and Burgers model and the parallel bond model were selected to characterize the viscoelastic behavior of asphalt mortar.The Burgers model was calibrated by uniaxial creep test of asphalt mortar,and the accuracy of the model was verified by indoor and virtual beam tests,the discrete element model of asphalt mixture can well reflect the mechanical behavior of asphalt mixture.Finally,the virtual test of low temperature cracking and fatigue cracking of asphalt mixture in Gobi Desert area is carried out to analyze the tension-pressure chain and displacement state between particle units in the mixture.The effect of different factors on crack resistance of asphalt mixture was studied by control variable method.The results show that the effect of the bond strength between mortar and aggregate,the bond strength between mortar and aggregate,and the void ratio on the low temperature crack resistance and fatigue crack resistance of asphalt mixture is consistent The aggregate friction coefficient and loading rate can affect the lowtemperature anti-cracking performance of asphalt mixture in a certain range,and the stress level and loading rate have a negative correlation with the fatigue anti-cracking performance of asphalt mixture.