Study On The Evaluation Method Of Pavement Materials Damage Under Hydrodynamic Pressure

Asphalt pavements with semi-rigid bases have been widely used since 1980s, with the construction and development of high-grade highway. Because of the effect of load and natural factors, the premature failures are increasingly evidently, many of which are water-related. In pavement engineering area, lots of researches and practices about moisture damages have been done. The large-area moisture damages happened in 1990s has been controlled currently, but the ones on local road sections occur sometimes. The fine rough-surface unifies the contradiction between skid-resistance and moisture damage, while failing to satisfy the requirement of noise reduction. The understanding of semi-rigid base is still not widely accepted. The erosion and pumping have already affected the application of cement concrete pavement on expressways. The problem of moisture damages is still not solved perfectly because of its complexity. The evaluation indexes and methods need to be further investigated, as well as the damage mechanism, as well as damage mechanism, anti-slide measure, noise reduction and internal drainage. Therefore, by means of damage theory, this paper studies the damage of HMA after multiple freeze-taw cycles and proposes the hydrodynamic pressure method focusing on the damage of semi-rigid materials under the coupling application of water and load.1.The hydrodynamic pressure generator developed in this research is used to simulate the repeated application of hydrodynamic pressure in pavement structure to materials in the process of infliction and remove of vehicle load (pump-absorb action). Its maximum pressure is IMPa and highest frequency is 25Hz. The pressure and frequency are both adjustable. The device, in conjunction with tri-axial test equipment can be used to study the damage process of pavement materials under repeated application of different coupling types of water and load in three-dimensional stress state.2.The relaxation test of semi-rigid materials using hydrodynamic pressure generator:â‘ It can determine the condition-depended deterioration process and mechanism of relaxation modulus under the repeated application of hydrodynamic pressure.â‘¡The relaxation modulus is proposed as the macroscopic mechanical index of hydrodynamic pressure damage. The relative value of stress relaxation at 600s is suggested to evaluate the material capability of resisting moisture damage.â‘¢The damage and its mechanism of semi-rigid base under the application of hydrodynamic pressure are demonstrated, based on the reanalysis of the premature failures on the pavement of Shanghai Outer Ring (first stage).It is also indicated that the developed hydrodynamic pressure damage test can be used to evaluate the erosion resistance capability of the base course of cement concrete pavement relatively well.3.Study on the deterioration process of compressive and tensile strength of HMA is carried out by means of freeze-thaw cyclic tests, due to the lack of temperature controlling equipment in hydrodynamic pressure test. The deterioration process of mechanical properties of HMA is evaluated by non-destructive test using ultrasonic. The contradiction between complexity and generalization ability of mathematical model from small sample data is solved by the prediction model of compressive strength of HMA Marshall test specimens based on support vector machine, avoiding the over-learning problem of BP network. The gradation selection of HMA is analyzed and demonstrated though the study on freezing-thawing damage of HMA, as well as the influence and effectiveness of hollow fiber to asphalt mixture. An evaluation method that using the strength deterioration of asphalt mixture after multiple freeze-thaw cycles to appraise its moisture damage properties is proposed.