Evaluation On The Influence Of Dynamic Pore Water Pressure On The Damage Of Asphalt Pavement Considering Multi-Factor Coupling Effects

When a vehicle drives on asphalt pavement with surface runoff,a dynamic environment of pore water pressure will be formed as water flow is continually driven by tires.The dynamic water environment not only aggravates the adverse stress state of dynamic structural response but also erodes asphalt materials,which finally causes the distress of moisture damage and decreases both the service quality and life of entire asphalt pavement.It is gradually realized that dynamic water environment tends to induce severe damage on asphalt pavement,but the existing research is still not sufficient.This dissertation systematically evaluated the damage of dynamic pore water pressure on asphalt pavement using various methods,such as numerical simulation,full-scale accelerated loading test and multi-scale lab tests.Dynamic response of pavement structure in dry and saturated conditions were compared,and so did the impact of factors such as pore water pressure magnitude,water temperature and conditioning duration on asphalt materials' service performance.Further,relevant mechanism of damage induced by dynamic water environment on asphalt materials was analyzed at multiple scales.The main conclusions are drawn as follows:(1)A two-dimensional finite element model of asphalt pavement structure was constructed using the ABAQUS software to investigate its dynamic response in both dry and saturated conditions.Water makes the structural response more complicated.The increase of vehicle load would significantly improve the magnitudes of indicators such as stress,strain and pore water pressure.Meanwhile,both the positive and negative pore water pressure would obviously grow with the increase of vehicle speed,but stress would gradually decrease and show a more sensitive downtrend especially in dry condition.(2)The tire tracks can be precisely controlled in the full-scale accelerated loading test system.Dynamic response of asphalt pavement in saturated condition showed stronger indicators than that in dry condition.Stress and strain increased slowly with vehicle load but decreased relatively quick with vehicle speed,while pore water pressure was more sensitive to vehicle speed than vehicle load.The magnitude of pore water pressure generated by the front tire was larger than that produced by the heavier rear tire,as the surface runoff was squeezed away from the wheel track by the front tire.(3)Both the variations of dynamic response indicators and the spatial distribution characteristics of pore water pressure concluded from numerical simulation and field test showed a consistency tendency,which verified the effectiveness of the proposed numerical model to simulate dynamic response of asphalt pavement in different conditions.Further,a prediction model of dynamic pore water pressure was proposed based on the full-scale accelerated loading tests.(4)Dynamic pore water pressure environment degrades the performance of asphalt materials,while the erosion ability of which is often between the static water immersion and freeze-thaw,and sometimes even more strict than the former.The ranking of factors impacting asphalt mixture mechanical performance was water temperature,followed by pore water pressure and conditioning duration.A representative parameter combination of 60?,0.345 MPa,and 4000 cycles was thus recommended to simulate dynamic water environment,and the uniaxial penetration strength test with its indicator of fracture work density were proposed to inspect retained performance for asphalt mixture.(5)The low temperature performance of asphalt materials was evaluated using the bending beam rheometer method.The master curve of creep compliance for asphalt mixture gradually moved up as the increase of the severity of dynamic water environment,while master curve of relaxation modulus showed a downward trend.The moisture sensitivity of the mastic component inside asphalt mixture,which is often called fine aggregate mixture(FAM),greatly affected the resistance to moisture damage induced by dynamic water environment for the entire asphalt mixture.The erosion effect of short-term conditioning in a harsh dynamic water environment was comparable to that of long-term conditioning in a mild environment.Specially,after the FAM component on the surface of an asphalt mixture sample being scoured away,the retained coarse aggregate skeleton made the entire sample still remain a certain mechanical strength and anti-erosion ability.(6)The water stability indicator calculated based on parameters of surface free energy for asphalt materials was greatly affected by dynamic water environment.The combinations between asphalt binder and different aggregates with acidic and alkaline properties showed different moisture sensitivity.The variation of the absorption peak intensity in different wave number ranges in Fourier transform infrared spectroscopy for asphalt binder,verified the fact that dynamic water environment brought more damage to asphalt binder compared with static water immersion and freeze-thaw,and its impact degree will increase as the conditioning duration.The dissertation adopted a variety of techniques to systematically analyze the influence of both the loading factors and dynamic water environment factors on dynamic structural response and asphalt materials' performance at multiple scales,respectively.The erosion damage mechanism induced by dynamic water environment was deeply discussed for both asphalt mixture and its components,which laid a theoretical and experimental foundation for the scientific issues related to the damage of asphalt pavement caused by dynamic pore water pressure environment.