| In recent years,shear flow rutting and top-down cracking under wheel tracks have become the main forms of asphalt pavement damage,which seriously affects its durability.Based on core sampling and finite element calculations,this passage analyzes the causes of the defects in the pavement wheel tracks,and proposes the penetration shear fatigue test method to evaluate the shear fatigue resistance of typical asphalt mixtures.Firstly,the results of core samples show that most of the wheel tracks of asphalt pavement damage are shearing flow rutting and top-down cracking.The finite element calculation of the typical asphalt pavement structure in Beijing proved that the shear stress is the main reason for the damage at the wheel track,and it is not caused by the excessive single shear stress,but the shear fatigue of repeated loads.Secondly,in order to evaluate the damage of asphalt pavement wheel tracks,it is necessary to find a test method for the shear fatigue performance of the asphalt mixture.Comparing various shear tests and finite element calculations,it is found that the shear force distribution inside the repeated penetration shear specimen is similar to that of the edge of the wheel tracks,its damage form is the same as the actual shear flow rutting and Top-Down cracking,the effectiveness of the method is proved,so the penetration shear fatigue test at 60℃ and 15℃ is proposed to evaluate the shear flow rutting and Top-Down cracks at the wheel track.Then,since the main factors affecting the shear performance of asphalt mixture are the type of mixture and the asphalt material,the upper layer adopts AC-13 typical gradation.The asphalt performance was evaluated through DSR,BBR and adhesion tests.Three representative cements were selected as matrix asphalt,SBS modified and rubberized SBS composite modified asphalt,and the shear test of the mixture was carried out.Thirdly,the shear strength of different asphalt mixtures was measured by uniaxial penetration tests at 60℃ and 15℃,and the shear strength attenuation law after UV aging and freeze-thaw cycles was studied.The penetration shear fatigue test evaluates the anti-shear fatigue performance of the asphalt mixture.The penetration shear fatigue test is carried out at60℃,and four stress levels of 0.7,0.9,1.1,and 1.3 MPa,measure the shear fatigue life of three asphalt mixtures to evaluate their anti-shear flow rutting performance;The penetration shear fatigue test is carried out at 15℃,and four stress ratios of 0.2,0.3,0.4,and 0.5 are selected for cyclic loading.The change point of the residual ratio of stiffness modulus is proposed as the failure criterion of shear fatigue cracking,and its resistance to Top-Down shear fatigue cracking is evaluated.Experimental research shows that the rubberized SBS composite modified asphalt mixture has the best anti-shear fatigue and aging properties,followed by SBS modified asphalt,and the matrix asphalt is the worst;The shear stress under the cyclic rolling of the vehicle is the main external force causing the damage in the asphalt pavement wheel tracks,and the aging of the external environment exacerbates the occurrence of the damage.Finally,based on the MMLS3 accelerated loading equipment,the shear durability of asphalt mixture was studied.The experimental results show that the rubberized SBS composite modified asphalt has the best shear durability after being rolled by the accelerated loading equipment.The unstable flow rutting and top-down cracking at the wheel track of asphalt pavement are not independent of each other,rutting will aggravate the expansion of cracking,and cracking will also accelerate the generation of rutting.Therefore,in the design stage of asphalt pavement,the unstable flow rutting and top-down cracking caused by insufficient shear fatigue life should be comprehensively considered,and the material with better shear resistance should be selected,which is of great significance to reduce the damage of asphalt pavement wheel tracks and improve its durability. |
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