Research On Material Of Stress-absorbing Layer Asphalt Mixture And Anti-cracking Performance

The stress-absorbing layer between the asphalt surface course and old pavement or base course, can significantly reduce the load stress and thermal stress at the bottom of asphalt surface course, decrease the phenomenon of stress concentration in the cracks or joints and the amplitude of crack-tip stress intensity factor, effectively dissipate or absorb the stress and deformation caused by the traffic load and environmental temperature factor, delay the formation and propagation of reflective cracking in the asphalt surface course, and at last increase the service life of asphalt surface course. At present, domestic research about the material composition of the stress absorbing layer is still a gap, and so developing a type of special asphalt binder for stress-absorbing layer, researching the mixture ratio design of stress-absorbing layer asphalt mixture and anti-crack performance, and recommending a reasonable thickness for the stress-absorbing layer are of great significance to popularize stress-absorbing layer technology.Asphalt pavement based on stress-absorbing layer is analyzed with the 3-D finite element numerical simulation method to study the impact of traffic load on load stress of stress-absorbing layer and the impact of its module on load stress and thermal stress at the bottom of asphalt surface course joints, The results indicate stress-absorbing layer is in composite shear and extension condition and the performance of stress-absorbing layer mixture is evaluated by anti-shearing and extension, stress-absorbing layer with low module may significantly decrease load stress and thermal stress at the bottom of asphalt surface course. Considering its requirement in construction and material performance, it is reasonable that its module is about 400-600MPa under the normal temperature. Furthermore, from its function of proof-water, the design void rate of its mixture should belongs to 1.0-2.0%.Through a large number of lab experiments, the Sampave special modified asphalt binder was finally developed. The reasonable mixing and compaction temperatures was determined by viscosity-temperature characteristics, which was very useful for the temperature control during the construction. Based on the in-depth research about Sampave special modified asphalt binder mastic, analysed the influence of filler bitumen ratio to high and low temperature properties and viscosity-temperature characteristics, a reasonable range of filler bitumen ratio was recommended.Penetration test and direct tensile test were used, and it's found that the penetration dissipation energy of mineral aggregate and penetration shear deformation energy, tensile deformation energy of the mixture are important indications of mineral materials and mixture. Balancing the shear and tensile performance of the mixture, and the aggregate grading tendency of stress-absorbing layer was recommended, which was useful for the choice of aggregate grading during the mixture ratio design.Based on SGC test, the influence of gyration compaction numbers and asphalt content on the mixture compaction were analyzed, the reasonable design gyration compaction numbers was determined. The impact of aggregate grading and asphalt content on modulus was analyzed, and then the mixture ratio design index system of stress-absorbing layer was perfected, which use penetration test and direct tensile test to choose grading and determine the optimum asphalt content. Finally, the mixture ratio design method based on shear and tensile performance was proposed.In order to conduct DTT tensile fracture, creep, damage and healing test, author developed a device and established parameters of experiment. The DTT experiment verify feasibility of Sampave special modified program and the reliability of the preferred mix design gradation and optimum asphalt aggregate ratio, which strongly support for the mix design results.A simulation device of reflection cracks extension in asphalt pavement was developed, The anti-cracking performance of asphalt pavement structure with sampave was verified. Finally, there is a reasonable scope for Sampave thickness and suggest it belongs to 2.0～3.0cm, which provided test basis for asphalt pavement structure design with stress-absorbing layer.