Micromechanics Analysis On Moisture Damage Of Asphalt Mixture Under The Action Of Dry-wet Cycles

Moisture damage of asphalt mixture is the major cause of pavement moisture damage.At present,the evaluation about moisture damage is mainly based on indoor freeze-thaw and water immersion tests,while the pavement was affected by the temperature history and rainfall in the service stage,and the asphalt mixture will be damaged and cracked under the long-term coupling actions of moisture and temperature.Therefore,analyzing moisture damage of asphalt concrete semicircular specimens under above coupling action is significant to clarify the damage mechanism of asphalt pavement under the coupling action of moisture,mechanics and thermodynamics.In this paper,the two-dimensional model of real asphalt mixture semicircular specimens is established using digital image process technology to provide an in-depth analysis of asphalt concrete moisture damage.The research content and results of this thesis are as follows:(1)CCD(Charge Coupled Device)camera is used to collect the surface information of semicircle specimen;MATLAB image processing software is used for digital image processing;R2V software is used to vectorize the processed image,so as to realize the separation and extraction of asphalt mortar and aggregate;Finally,the two-dimensional reconstruction of the real specimen is completed by using ABAQUS;Insertion of zero-thickness cohesive elements inside the mortar and at the interface of aggregate-mortar inserted by a self-programmed MATLAB program,and the cohesive zone model is used to describe constitutive relationship of cohesive elements.(2)The moisture diffusion coefficients of aggregate and asphalt mortar at different temperatures are measured.The moisture diffusion of asphalt concrete is analyzed to determine the internal dry-wet state inside of asphalt concrete after the action of different temperature and rainfall histories.The moisture dependent mechanical parameters were coupled with moisture concentration through USDFLD subroutine.The bending performance and crack evolution of asphalt mixture after moisture conditioning were simulated.(3)The cohesive zone model parameters were obtained through semi-circular bend tests of asphalt concrete,and the control group and the immersed specimens were tested to verify the correctness of moisture damage simulation results of asphalt mixture.The increase in temperature leads to an increase in moisture concentration inside the mixture,which reduces the flexural strength of the asphalt mixture and gradually weakens the damage energy consumption,and the density of microcracks also gradually increases.Compared with adhesive damage,cohesive damage has more influence on the strength of mixture.(4)The more the dry-wet cycles or the shorter the rainfall interval,the more the moisture enters asphalt concrete,the greater the moisture concentration,the lower flexural strength and energy consumed for fracture.The flexural strength for 20 cycles was reduced by 57% compared to the non-immersed condition.The moisture will continue to diffuse to the interior in the drying stage.The shorter the drying period,the greater the flexural strength damage of the mixture.When the drying period is not less than 3 days,the influence of drying period on flexural strength is weakened.The drying period is shortened or the wet-dry cycles is increased,the initiation time of microcrack will be shortened and the main crack growth rate will be accelerated.