Investigation Of Anti-cracking Asphalt Mixture Based On Mesomechanical Property

After nearly forty years of efforts,China has basically solved the problem of road bearing capacity while taking an asphalt pavement with semi-rigid base as a typical structure.However,the crack problem remains one of the main causes of early damage,maintenance and rehabilitation of asphalt pavement.Taking Guangdong Province as an example,mass road condition survey data show that the main cause of decline in PCI is crack,accounting for 85% to 95%.These cracks mainly include transverse cracks(semi-rigid base reflective cracks)with a fixed spacing and a small number of Top-down cracks.The highway engineering industry has tried to reduce the cracking rate by using modified asphalt binder or adding fiber,rubber,etc.But in order to balance the rutting and skid resistances,the pavement cracking is not obviously improved with increased construction cost.Under such background,the basic relationship between the material composition and performance of asphalt mixture as well as the pavement structure is studied.According to the structural requirements,a “functional” asphalt mixture with excellent crack-resistance was developed through a integrated design of materials and structures.It is of great significance to extend the road maintenance cycle and reduce the cost of pavement maintenance and rehabilitation.In this study,discrete element analysis and digital image processing were used to analyze the mesoscopic characteristics of each component in asphalt mixture.The fracture characteristics of asphalt mixture were analyzed from the mesoscopic point of view.The influences of gradation,shape and distribution of aggregates,mortar strength as well as voids on the performance of crack-resistance of asphalt mixture structure were revealed.The development of crack during the stress fracture process of asphalt mixture was also studied.The findings can provide theoretical basis for the design of anti-cracking functional asphalt mixture.Given that balanced design can't solve the contradiction between anti-rutting and anti-cracking performances of asphalt mixture,this study proposes a new design idea of asphalt mixture used in friction course.Aiming at asphalt mixture designed for anti-rutting,a new type of spray-type material was developed,which has high permeability at normal temperature and high bond strength after consolidation.The innovative results of this paper are as follows:(1)According to the concept of material design and the actual condition of asphalt pavement deterioration,this study puts forward the concept and design method of anti-cracking functional asphalt mixture.(2)Code of cohesive constitutive model was developed based on discrete element software,which can be applied to simulate the fracture test of 2D and 3D discrete element models,laying a good foundation of analysis and digital design of anti-cracking functional asphalt mixture.(3)Based on the virtual experiment,the influence of the relationship between the maximum nominal size of aggregate and the layer thickness on the crack resistance of asphalt mixture was studied.It was found that there is a range of nominal maximum particle size with the best crack-resistance performance for a specific layer thickness.Therefore,the optimum layer thickness ratio of the anti-cracking asphalt mixture is 4.0 to 5.5.(4)Through the virtual test and laboratory test,it is found that the content of coarse aggregate and the surface area of the aggregate particles are the main factors affecting the crack-resistance performance of the asphalt mixture,which follow a parabolic law,respectively.According to this,the optimum coarse aggregate content of AC-20 crack-resistance asphalt mixture is given,which is 51%~54%,and the surface area ranges from 5.7~6.2m2/kg.(5)The design method of anti-cracking functional asphalt mixture is proposed:(1)determine the maximum nominal particle size of the gradation according to the layer thickness;(2)determine the coarse aggregate content and specific surface area with the best crack-resistance performance;(3)define the gradation curve by the fractal dimension;(4)apply 2D or 3D discrete element software and cohesion model to analyze and optimize the grading range of anti-cracking functional asphalt mixture;(5)verify road performance of anti-crack functional asphalt mixture by laboratory test.The design method provides a new solution to improve the crack-resistance performance of the asphalt mixture of base course and resist reflection cracks.(6)Considering that the existing balanced design method can not maximize the single performance of rutting or cracking resistance of asphalt mixture,this study developed a new type of spraying material — Permeating and Solidifying Seal Coat,for reinforcing the shearing and crack resistance performance of pavement.It provides a method to prevent or restrain the top-down crack while taking compression strength,rutting-resistance performance and cracking-resistance performance into consideration at the same time.The permeable seal layer not only improves the shear and crack resistance of the pavement,but also improves other pavement performance(such as corrosion resistance,water resistance,skid resistance,flaking resistance,etc.)and can be used for preventive maintenance of asphalt pavement.