Study On The Micromechanical Characteristic And Void Reduction Behavior For Porous Asphalt Pavement

The dissertation is supported by the National Natural Science Foundation(Project Number:50608006) and Transportation Applied Basic Research Project of Ministry of Communications(Project Number:2006 319 812 120).The main characteristic of porous asphalt pavement is high voids which is about 20%. Good properties for road use are produced by high voids such as low-noise,slideproof property,water permeability and security.However,the poor result caused by high voids is that the void of porous asphalt pavement will bring about reduction in spatial morphology and result in two kinds of results to the structure voids of asphalt mixture:First,the total amount and distribution of the structure voids will both take place reduction;Second,the total amount of structure voids will not change,but the structure voids distribution changes. The former occurs mainly during construction stage,the latter occurs mainly during operational stage.The latter is more important especially for porous asphalt pavement,which is directly related to its drainage capacity and functions' continuity.Consequently,revealing the void spatial morphology and void distribution,studying the mechanical properties of micro-void,analyzing the void reduction behavior after loading for porous asphalt pavement will be of great significance.This dissertation surrounded the void reduction of porous asphalt pavement,then the conceptual model of void was given from microscopic view.The mechanical morphology of simplified void model was analyzed drawing on porous solid mechanics.And,the void bulk modulus applied to porous asphalt pavement was derived according to Betti reciprocal theorem,then the void reduction law was studied using continuum mechanics method combined with Gompertz "growth" model.In addition,asphalt binder,aggregates and asphalt mixture were reconstructed by discrete element method,and the reduction characteristic of finite void was simulated with numerical method.Finally,the displacement vectors and the contact force vectors of aggregate particles composing void structure were analyzed and the void deformation mechanism was clarified from microscopic view.Through theoretical derivation and numerical simulation of the discrete element method, the specific results obtained in this dissertation are as follows: (1) The conceptual model of porous asphalt mixture was given and the bulk modulus' concept was proposed for porous asphalt mixture including the bulk modulus of mixture and void bulk modulus.Next,the equation used to interpret bulk modulus of porous asphalt mixture was derived completely under dry and saturated states,and the relation between void bulk modulus and temperature was studied as well;(2) The void model of porous asphalt mixture was simplified and the mechanical analysis was taken to the simplified void model.The deformation of simplified void model was 0.05mm according to the specific example;(3) The differences between theoretical values and predicted values were compared to study the reduction law of void bulk modulus according to Gompertz predicted model.The maximum error rate was only 9.25%.Therefore,it was feasible to apply Gompertz predicted model to prodict void bulk modulus.(4) Digital reconstruction was applied to asphalt binder,aggregates and asphalt mixture by discrete element method.Different micro-contact models were selected and the skeleton contact force vectors were given under different voids;(5) The deformation characteristics for three kinds of void models under loading were simulated by discrete element method.The deformation of equilateral triangle void model with parallel bond was the smallest,the most stable.And the displacement vectors and contact force vectors of particles which composed void structure were given;(6) Indirect tensile test was simulated for three kinds of asphalt mixture,i.e.(Fine Resolution Parallel-Bonded Material A(Afp),Coarse Resolution Parallel-Bonded Material A(Acp),Gross Resolution Parallel-Bonded Material A(Agp)).The splitting tensile strength of Afp was the largest and the internal micro-cracks were the most.And the change laws of particles' contact force vectors and displacement vectors which compose asphalt mixture specimen were analyzed;(7) Indirect tensile tests were simulated for Acp under different loading rates,and the conclusion was that the splitting tensile strength increased as the loading rates increased;(8) The mechanical responses for porous asphalt pavement were simulated under loading. The vertical displacements of pavement structure in horizontal direction and along depth direction were obtained and the deformation properties in different pavement structure layers under different loadings were analyzed.