Mesostructure And Stress Strain Transfer Mechanism Of Skeleton Filling System Of Asphalt Mixture

Asphalt mixture include aggregate,asphalt,filler and other additives,and the complex composition lead to the different types of failures.It is difficult for tranditional empirical methods to obtain the internal material distribution and the stress strain transfer mechanism under the loading.Therefore tranditional methods can not be utilized for revealing the failure mechanism.The mesoscale research test methods including packing theory,digital image process and computed tomography provide new thinking for mesostructure and stress strain transfer mechanism.In the mesoscale,asphalt mixture consist of skeleton aggregate and asphalt mortar for filling the voids between the skeleton and that is the skeleton filling system.This thesis focus on the skeleton filling system of asphalt mixture.Based on the meso scale methods,the evaluation method of skeleton filling system is proposed.The mesostructure extraction method is developed to analyse the effect of skeleton filling system on mesostructured.Further studies are strain field distribution and stress transfer mechanism.The contents and results are shown as follow:Based on the skeleton and filling function of aggregate on asphalt mixture,the aggregate can be devided into skeleton particle,disruption particle and filling particle.According to the packing density of multi-level particles obtained by CPM model,the packing volume and void rate can be calculated by gradation curve,and then disruption and filling factors of different asphalt mixtures can be obtained.The 2D cross section images of asphalt mixture can be obtained by industrial computed tomography,then the noise reduction and enhancement method based on fuzzy theory is utilized.Comparing with the traditional noise reduction and enhancement method,fuzzy method can effectively reduce the gray level fluctuation and retain the gradient of interface.H maximum transformation,multiple threshold Otsu method,morphological processing and watershed algorithm are ulitilized for image segmentation,holes filling and overlapping segmentation,then the partilcle size distribution of cross section image is obtained.According to stereology method,the 2D gradation is transferred into 3D gradation.Comparing with the real gradation,the mesostructured recognition althorithm in this research is effective and accurate.Based on the mesostructured recognition althorithm,the methods of particle contact number and effective mortar film thickness are proposed.According to analyse the contact property of particles,higher disruption factor will result in more disruption particle contact and less main skeleton particle contact in asphalt mixture.According to analyse the distribution of effective mortar film,the effective mortar film between main skeleton particle is thinnest,and the effective mortar film is thinner in the mixture with higher filling factor.By fractal theory,the relation between disruption and filling factor,void volume distribution continuity and spatial position distribution homogeneity is obtained.By virtual translation and shear test,calculation accuracy and optimal testing parameters of digital image correlation(DIC)are obtained.Combining digital image processing method,the strain field extraction method of asphalt mortar is proposed.According to analyze the strain field of asphalt mortar,the mean value is lower and area is higher in the high strain region of asphalt mixture with lower filling factor.By analyzing the particle distribution in the high strain area,it show that the proportion of distruption particle in high strain area increase continunally and skeleton particle proportion decrease.It illustrate high strain area frist occurs around skeleton particle,and then propagate disruption particle.Modelling the asphalt mixture by discrete element method(DEM)and digital image process method.Marco viscoelastic parameters can obtained by dynamic shear rheometer for deducing the micro viscoelastic parameters of Burgers model in DEM.The simulation results are compared with the test results of DIC to verify the validity of DEM model.From the analysis of the effect of skeleton on the aggregate and mortar contact force,it illustrate the skeleton particles is the main force transmission medium and the lower the disruption level,the higher the relative contact force of main skeleton particle.The variable coefficient of contact force is higher in the asphalt mixture with lower filling factor,and it means there is a stronger contact force concentration.From the analysis of the effect of mortar property on the aggregate contact force,the results show the variable coefficient of mortar contact force decrease with the increase of mortar modulus.It illustrate lower mortar modulus will cause the higher contact force concentration which mean local failure.