A Research On Viscoelastic Damage Evolution And Cracking Controll Of AC Pavement

Currently, the length of the national superhighway is totally 50,000 kilometers, resides the second in the world. The bituminous concrete road has 75% of the highway. But the pavement cracks have been key problem that perplexed the construction and protect of highway. Therefore, the damage evolution of asphalt congcrete (AC) pavement becomes a hot problem in the fields of communication and mechanics. The damage evolution of AC pavement keeps company with propagation of the cracks in the pavement. And AC is viscoelastic. Thus, it is necessary to consider the viscoelastic behavior of the AC in the research on the AC pavement. In this paper, the process and mechanism of the damage and evolution of the AC pavement are researched. Through adding the geosynthetics overlay and applying the fiber-reinforced measures to arrive the aim of retarding the development of cracks in the pavement. The main contents researched in the paper are shown as following.1. Establishment of viscoelastic and damage model of AC. From viscoelasticity theory and time-temperature equivalent principle, the generalized Maxwell model is established by paralleling 6 Maxwell model to simulating the viscoelastic damage behavior. Applying the coupling analysis of Sidoroff’s damage model and fracture mechanics, the boundary equations of damage and fracture zones obtain was obtained for one inclined crack under axial tension and the radial sizes of the initial damage and fracture zones for the inclined crack are determined. The concept of the radius strain energy within crack-tip fracture zone was put forward. On the base of this concept, the Criterion of Minimum Radial Strain Energy (CMRSE) within crack-tip fracture zone was proposed. The cracking angle in the crack-tip fracture zone and the coordinates of cracking points were determined, which will theoretically provide the support for refinement of finite elements in the vicinity of crack-tip to simulate the crack propagation.2. Establishment of mechanical model of AC pavement with cracks. The models of surface-crack and reflective-crack in the AC pavement were set up. The elements are locally refined according to the coordinates of cracking points determined. The size of the models and element category used in finite element analysis were determined. The meshes were divided into three different zones to simulate the initial damage zone and fracture zone. The refinest, refiner and sparse zones are corresponding to crack-tip, damage and viscoelastic zones, respectively.3. Numerical simulation of AC pavement with cracks based on viscoelastic damage evolution. Relax properties for AC with surface cracks under temperature load and with reflective-cracks under vehicle load are simulated, respectively. Analysis of damage and evolution of AC pavement with cracks is conducted such as the effects of initial crack length, temperature and time to stress level and average damage factor and the radius of damage zone and the radius of fracture zone。The results of the couple analysis of stress relax and damage show that damage evolution takes place continuously. This means that the AC pavement degraded constantly, and the lower the temperature, the seiouser the degradation. The damage evolution is trend to stable with increasing of relax time.4. Research on properties of geosynthetics overlay retarding the propagation of crack. The effectiveness of the geosynthetics overlay retarding the propagation of reflective cracks in AC is studied numerically under vehicle load. The effects of temperature, time and elastic modulus of the geosynthetics overlay to tensile stress at the bottom layer and normal stresses on the line of extensional crack-tip is analyzed. The results show that the elastic modulus of the optimum geosynthetics overlay is 1000MPa.5. Viscoelastic damage analysis of fiber-reinforced AC pavement. On the basis of composite theory and experimental researching, it was found that the optimum content of the fiber is 0.2% by mass. From finite element analysis, it was shown that the fatigue life of the fiber-reinforced pavement increases by 34.13%.The coupling analysis of relaxation-damage of fiber-reinforced AC pavement is performed, and the effects of fiber content is analyzed to average damage factor, the radius of damage zone and fracture zone. The results obtained from the coupling analysis show that the relaxation factor of fiber-reinforced AC pavement is reduced by 8.38% in comparison with the AC pavement, and the radius of damage zone for fiber-reinforced AC pavement are reduced by 66.34% and 64.16%, respectively.