| Cracking creats major distress in asphalt pavements,it includes crack propagation,crack branching and crack coalescence process.Obtaing the crack branching and crack coalescence procedures are very cricual for accurately quantifying the crack paths in the asphalt mixtures.However,the crack branching and crack coalescence procedures can not be predicted by the fracture mechanics,damage mechanics and dissipated energy theory.The relevant researches about the asphalt mixture crack branching and crack coalesce are in the primary stage,and the crack branching and crack coalesce have not been quantitated.This study attempts to address these deficiencies by establishing the asphalt mixture crack branching and crack coalescence theory,conducting cracking branching and crack coalescence numerical simulations and quantifying the crack branching and crack coalescence paths.The major conclusions are summarized as follows:(1)The force density tensors in the ordinary state-based peridynamics are converted into the force density tensors in the viscoelastic state by extended elasticviscoelastic correspondence principle.The Semi-circular bending test and virtual crack thchnique were conducted to obtain the fracture enery of fine aggregate mixture and coarse aggregate,respectively.The box-counting method is used to obtain the lb x-lb N curve,the absolute value of the slopes for lb x-lb N curve are the fracral dimension of crack branching and crack coalescence paths,which can quantify the crack branching and crack coalescence paths in the asphalt mixtures.(2)The coarse aggregate,fine aggregate mixure and air void distributions were obtained by the asphalt mixture X-ray computed tomography scanning images.These distributions can be converted into 0-1 matrixs by the MATLAB Computing Platform.The 0-1 matrixs are utilized to determine the material properties in the asphalt mixture peridynamic numerical model,which was complied by the Fortran programming language.(3)The asphalt mixture peridynamic numerical model was validated by threepoint bending tests with preset notch at midspan and 40 mm off-center,and Semicircular tests with preset notch of 0° and 45° inclination angle.The numerical model can simulate the crack paths in three-point bending beams and Semi-circular bending specimens.The numerically simulated crack paths position and fractal dimension were compared with the crack paths position and fractal dimension obtained by three-piont bending and Semi-circular experimental specimens,the relative position error and fracral dimension errors were smaller than 5%,which indicated that the OSB-PD simulated crack path matches well with the experimental crack path.It validated the proposed OSB-PD method had the capability to accurately simulate the crack paths in asphalt mixtures.(4)There are two stages in the crack branching procedures.During the first stage,the crack branching generates diagonal cracks,wing cracks,splitting cracks and horsetail cracks after the crack emanated in the asphalt mixture,which is corresponded to the crack branching fractal dimension cruve rapidly growing stages.During the second stage,the diagonal cracks,wing cracks,splitting cracks and horsetail cracks emanated crack branching,which is corresponded to the crack branching fractal dimension cruve slowly growing stages.The crack branching paths constitute four crack branching types in the AC-13,AC-25 and PAC-13 asphalt mixtures,it constitutes five crack branching types in the AC-20 asphalt mixture.The crack branching process include dynamic crack propagation,crack propagation deflection,propagation of branched crack,the fractal dimension of crack branching paths can reach 1.6±0.4.(5)The crack coalescence is generated among diagonal cracks,wing cracks,splitting cracks and horsetail cracks,as well as the branched cracks of these cracks.The crack coalescence paths constitute four crack coalescence types in the AC-13,AC-20,AC-25 and PAC-13 asphalt mixtures.The crack coalescence process include dynamic crack propagation,crack tip contaction and crack tip coalesce with each other,the fractal dimension of crack coalescence paths can reach 1.8±0.1.According to the asphalt mixture crack branching and crack coalescence peridynamic numerical simulation research,this study constitutes the asphalt mixture cracking branching and crack coalescence theory,and establishes the asphalt mixture peridynamic numerical simulation model.The crack branching and crack coalescence paths are obtained,which can be quantified by the fractal dimension. |
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