Permeable Asphalt Mixture Pavement Service Performance Under Dynamic Loading And Water Coupling:a Temporal Regular Pattern Study

OGFC（Open Graded Friction Course）is an environment-friendly pavement layer characterized by good drainage,noise reduction and skid resistance.However,OGFC pavement in service has the problems of low durability and road performance degradation,which attributes mainly to the combined action of dynamic load and water.Therefore,a systematic study of the time history response of OGFC pavement under dynamic load and water coupling in order to explore the failure mechanism and improve the road performance of OGFC,is of great significance before OGFC pavement can play its due role in sponge cities.Thanks to the research project of“Research on fatigue failure of OGFC pavement under the coupling action of dynamic load and water（KJQN201804001）”granted by Chongqing Municipal Education Commission,this dissertation aims to explore the time history road performance of OGFC pavement under dynamic load and water coupling by means of experimental research,numerical simulation and theoretical analysis.The research work and conclusions are summarized as follows:（1）The optimal asphalt-aggregate ratio of OGFC asphalt mixture is determined by the inflection point method and the permeability coefficient is measured by a self-made permeameter.Through a leaking test at 185℃for one hour,the leaking rate of OGFC asphalt mixture is obtained.The fitting curve of the leaking rate and asphalt-aggregate ratio is obtained by power function.The optimal asphalt-aggregate ratio of OGFC asphalt mixture is determined by the“inflection point”of the curve.The relative density of OGFC asphalt mixture is measured by the vacuum sealing method.The road performance of OGFC with the optimal asphalt-aggregate ratio and mineral aggregate gradation is evaluated.The OGFC asphalt mixture samples meeting the technical specifications are thus obtained.A constant head permeameter is designed and made to measure the permeability coefficient of OGFC asphalt mixture samples,and the optimum constant head is 40～50 cm in height.（2）The creep damage of aggregate-asphalt-aggregate is studied and a corresponding damage model is established.A layer of asphalt film with thickness similar to the asphalt film on the coarse aggregate surface is obtained by keeping the surplus asphalt at 155℃for about 20 min.Two asphalt-coated rock core samples with 21mm and 38mm in diameter are bonded together.The tensile strength and shear strength between the two rock core samples are tested at the rate of 50 mm/s.The rock core-asphalt-rock core tensile creep strength test is carried out by an electro-hydraulic servo universal testing machine（UTM-100）.The results show that the rock core-asphalt-rock core static creep deformation is a power function of time,and the tensile creep deformation is related to time and load.Through the tensile creep test at different stress ratios,an aggregate-asphalt-aggregate creep damage model is thus established,which provides the basis for a parallel discrete element OGFC fatigue damage model.（3）The time-history OGFC road performance based on accelerated loading tests is studied.An indoor OGFC is paved with 2.93 m in length,1.10 m in width and 0.04 m in thickness.The gross bulk density,rutting and elastic modulus of the OGFC pavement is measured through a one-third full scale accelerated loading test system（MMLS3）,a non-nuclear densitometer,a rut tester and a portable surface wave instrument.Then,the time history road performance of the OGFC pavement is obtained.The results show that,the gross bulk density of the OGFC pavement is significantly affected by the times of accelerated loading.The rutting change is large in the range of 0～80,000 times of fatigue loading,while afterwards the rutting change is small.Generally,rutting changes linearly.At the point 200,the elastic modulus turns from increase to decrease.After5000 times of fatigue loading,the elastic modulus reaches the maximum value.At the center line 0,the relative density of the OGFC asphalt mixture increases as a whole,while around the point 200,the relative density decreases generally.（4）The permeability characteristics of OGFC asphalt 0the stress field is established.The relationship between the void fraction,permeability and the number of repeated uniaxial compression on OGFC asphalt mixture samples is obtained.The total void content and effective void content of the OGFC asphalt mixture samples are tested by the vacuum sealing method.A non-Darcy flow permeameter is designed and made to test the permeability of the OGFC asphalt mixture samples.The results show that,with the same damage factor,the number of uniaxial repeated compression under the coupling action of the seepage field and stress field is 0.6 million times,which is less than the number of 2 million times for uniaxial repeated compression under the mere action of the stress field.When the total void ratio is 21%,the number of uniaxial repeated compression in the non-permeability field is twice than that under the coupling action,while it changes to 3.9 times when the effective void fraction is 17.5%.Under the same permeability coefficient and water conductivity coefficient,the permeability field has a positive impact on the times of uniaxial repeated compression.When the permeability coefficient is 500 m/s,the number of uniaxial repeated compression in the non-permeability field is 1-2 times than that under the coupling action of the permeability field and stress field.（5）The relationship between the water conductivity coefficient and load,the crack permeability coefficient and crack spacing is studied.The quasi-Newton methods（BFGS）plus general global optimization are used to fit the water conductivity coefficient,load and the times of uniaxial repeated compression.The relationship between the water conductivity coefficient and the times of uniaxial repeated compression under the coupling action of the permeability field and the stress field is thus obtained.A constant head permeameter is designed and made to measure the permeability coefficient of cracks.The relationship between the crack permeability coefficient and the crack spacing is established through the aggregate-asphalt-aggregate crack permeability test.（6）The time history OGFC road performance is studied by the discrete element method PFC^2D.A two-dimensional discrete element fatigue damage model under the coupling action of the permeability field and the stress field is established by using the discrete element method PFC^2Dand fish language.The excess pore water pressure generated by the void deformation of the OGFC asphalt mixture as well as the coupling effect of excess pore water pressure and vehicle load on the fatigue damage of the OGFC asphalt mixture are measured.The dynamic mechanical properties of the OGFC pavement are thus obtained.The results show that with the increase of time,the excess pore water pressure causes the increase of the compressive stress and strain at the bottom of the OGFC pavement.With the increase of the maximum value and decrease of the minimum value of the excess pore water pressure,the average value decreases.When the roller is operating on the road,the excess pore water pressure keeps changing from positive to negative.