The Research On Microscopic Mechanism Of Top-down Cracking In Asphalt Pavement

Top-down cracking(TDC)has been one of the main type of damage in high-grade asphalt pavement.Recent studies of the cause and the propagation law of top-down cracking have not been completely understood.Existed macroscopical means was not able to collect the internal stress distribution and stress-strain responses of mixture accurately,to explore the failure mechanism and the internal stress-strain responses of top-down crack from the perspective of meso-level,the method of combining numerical analysis with mesco-experimental was used in this paper.Firstly,the top-down crack investigation in the Xiangtan to Shaoyang expressway of Hunan province was carried out in this paper,the distribution characteristics of top-down cracking and the reasons why the asphalt pavement occurred top-down cracking was also analyzed.It was believed that the top-down crack of asphalt mixture pavement was mainly manifested in the form of longitudinal fracture.And the cracking was caused by the force of the driving load on the road.The propagation path of top-down crack is single and has no bifurcate crack.Then,the indirect tensile tests simulation was carried out in the two-dimensional discrete element model which was established based on CT images of actual asphalt mixtures.According to the comparison and analysis of simulation test and laboratory test results,it was found that the distribution characteristics of crack in the discrete element model and the trend of load-displacement curve in the simulation test was consistent with the indoor test.The feasibility and applicability of the discrete element model was verifiedFinally,the splitting fatigue simulation test was carried out in the discrete element model and in the laboratory.The stress-strain curve and characteristics of crack distribution of simulation test and different stages of indoor splitting fatigue test was compared and analyzed,it was found that the results of two kinds of experiment was basically identical。The propagation of crack and the internal stress strain response of asphalt mixture in top-down cracking can be expressed well by the splitting fatigue simulation test.the failure mechanism of top-down cracking of asphalt mixture pavement was elaborated.That is there was a kind of transverse drawing stress in the interior of pavement structure when the compressive stress passed down,the repeation of transverse drawing stress lead to the fatigue failure of the bond between aggregate and asphalt mortar,the particles where the bond was damaged moved to different direction,that resulted in the pavement cracking.After the pavement cracking,there was inhomogeneous compressive stress and concentrated tensile near the crack,that made the particles move to different direction or move different distance to same direction,the mixture take place shear failure and flexural failure.Then,the crack extended downward along contact interface between aggregate and mortar.The mechanism of the crack was verified by the investigation of top-down cracking on asphalt mixture pavement.