Mechanical Behavior Within Multi Scales And United Models Of Asphalt Pavement Materials

As referring to material components of asphalt mixture,their complicated morphology at surfaces and random distribution among a spatial space result in undeniable characteristics related to multi scales phenomenon.Moreover,macro mechanical behavior and damage evaluation rule of asphalt mixture are directly related to its micro and meso characteristics.To solve application problems in engineering fields,statistical average properties of asphalt mixture at macroscale are guidelines to select optimized pavement materials.Asphalt pavement structure design method based on layered elastic theory adopts the homogeneous material assumption known as a basic premise used in the continuum mechanics.Mechanical property evaluation on small size specimens at a single scale and numerical analysis on the basis of continuum mechanical frame cannot explain the mechanical behavior and damage mechanism of asphalt pavement materials even structures from the perspective of multi scales.Thus,research about mechanical behavior at multi scales and interactive relation between various scales of asphalt pavement materials might provide an insight into understanding,analyzing,and predicting mechanical properties of asphalt mixture.Furthermore,this dissertation could provide theatrical and data support on property optimization of asphalt pavement materials under multi scales,which might be utilized to unfold damage mechanisms for asphalt pavement materials.To explore the influence of micro interaction at aggregate-asphalt interface,differences of micro morphology between aggregate surface and AggregateInterface Zone(AIZ)were analyzed by using the Scanning Electron Microscope(SEM)and Atomic Force Microscopy(AFM).Aggregate mineral components were detected firstly,wetting angle of asphalt at high temperatures dropping onto limestone and basalt was obtained and differentiated,distribution feature of mechanical indexes for AIZ at intermediate temperatures was analyzed via force curve from AFM.Based on the self-developed aggregate parallel plates,the Dynamic Shear Rheometer(DSR)test and Direct Test(DT)were conducted by bonding with aggregate plates.Results show that micro morphology differences at aggregate surfaces are known as a decisive factor to affect binder coating condition at micro-scale.Shearing and tensile characteristics of aggregateasphalt-aggregate film was obviously sensitive to aggregate type,its rheological performances and resistance to tensile fracture show selectivity on limestone and basalt.Micro interaction of AIZ is dependent on temperatures-frequency,film thickness,and load pattern,a thickness range makes this interaction effective.By including micro interaction of AIZ,aggregate parallel plates are suitable to optimize the aggregate type.Research results related to AIZ were employed into the rheological parameter calculation of AIZ within United Models at Multi-scale(UMM).To conduct quantitative evaluation on viscoelastic and low-temperature characteristics of asphalt Fine Aggregate Matrix(FAM),a fabrication equipment suitable for small size FAM specimens was developed and the corresponding DSR test method was provided.Frequency sweep test,stress relaxation test,stress fatigue test and static creep test were carried out,the reproducibility of testing results was proved to be applicable.Bending Beam Rheometer(BBR)test for FAM at low temperatures was accomplished.Freeze-thaw cycle and natural aging were included and the influence on low-temperature bending properties of FAM was summarized.Results show that volumetric indexes of FAM have a close relation to material compositions of FAM.Furthermore,when the effective asphalt content was smaller than a critical value,the air void content gets a rapid increment.Shearing characteristics of FAM present a direct relation to its gradation,asphalt content and air void content.The optimal asphalt content and the proper compaction energy would guarantee the resistance to low-temperature bending for FAM.Structural features of air void could contribute to mechanism difference of freeze-thaw damage between FAM and asphalt mixture.On the other hand,FAM with a high asphalt content suffers not only freeze-thaw damage but also physical hardening.A proper compaction gyration reduces the cracking risk rate at low temperatures for FAM due to natural aging action,and early aging occurs within FAM.The DSR test and BBR test for FAM meet the testing precision and performance evaluation requirements.Research results related to FAM were used to calculate the rheological parameters of FAM within UMM.To comprehensively depict distribution rule of meso-structural parameters for asphalt mixture,fractal dimension,shape index,angularity index,and Fourier series were used to represent the variation degree of coarse aggregate outline at surfaces.Critical air void volume was determined to divide the critical air void structure between FAM and asphalt mixture.Fractal dimension calculation and meso-structural characterization of air void outline were completed.Voids in Coarse Aggregate(VCA),Centroid Spatial Distribution(CSD),and Skeleton Spatial Distribution(SSD)were chosen as indexes to evaluate characteristics of skeleton distribution.Characteristic Parameters at Meso-scale(CPM)related to the low-and high-temperature performances were determined finally.Results show that the variation degree along the most outside outline of a 3D coarse aggregate shows an extreme value,which proves that morphology at coarse aggregate surfaces shows complex fluctuations.Air void with a volume lager than the critical size value was regarded as initial defects within asphalt mixtures,and air void distribution were investigated to be some of transverse isotropy.VCA,CSD,and SSD show positive correlation with each other,the skeleton structure of Stone Matrix Asphalt(SMA)ranks as the densest distribution among six mixture types.CPM related to high-and low-temperature performance and tension strain filed distribution was concluded to be the skeleton structure,the air void structure,and the air void distribution,respectively.Research results related to meso structure were utilized to illustrate the meso-structural parameters within UMM.To realize a developed material design method based on virtual experiments for asphalt mixture,material parameters equivalence of meso equivalent element for asphalt mixtures were processed by including the impact of AIZ,initial air void defects,and material damage.Analysis on mechanical behavior of Meso Element Equivalent Method(MEEM)model was concluded considering the impact of micro gradient strain and laboratory testing material parameters.Analysis on mechanical behavior of UMM including the anisotropy was conducted based on the Perzyna’s viscoelastic-plasticity theory.Results show that micro gradient strain reduces the time-cost without losing the accuracy of numerical approach method.Micro gradient strain and laboratory testing material parameters seem to be key factors,because those factors make MEEM model more appropriate when comparing with laboratory results.Relation of mechanical results between UMM and MEEM model was following positive correlation.The most comprehensive mechanical behavior was found in the SMA type,which is directly related to its material compositions and meso-structural distribution.According to the transitive relation among micro gradient strain,MEEM model,and UMM,the scale transit mechanism for asphalt road materials is preliminarily established.