Experimental Analysis On Shear Mechanical Properties Of Asphalt-aggregate Specimens

Asphalt mixture is widely used in the construction of urban roads and highways.Under the influence of vehicles and the environment,asphalt pavement will produce various diseases,affecting the speed of traffic and also producing safety hazards.When the vehicle passes through the intersection and bend,due to the change of speed,it will produce shear stress on asphalt pavement.When it exceeds the shear strength of asphalt pavement,it will produce permanent deformation.The asphalt-aggregate interface is relatively weak.Due to the irregular shape and different properties of aggregates,the local area of the interface is prone to stress concentration,so the internal damage and cracks are generally initiated at the interface.In this paper,the specimens needed for the test are made,and two tests are carried out.One is the observation test of asphalt film thickness,and the other is the shear test.The influence of asphalt film thickness,temperature and shear rate on the shear mechanical properties of asphalt-aggregate interface is analyzed from multiple angles.The main research contents are as follows.(1)Making specimens for asphalt film thickness observation test and asphalt-aggregate interface shear test;(2)The asphalt film of the molded specimen was observed by scanning electron microscope,and the actual thickness of the asphalt film under two molding loads was obtained.(3)Shear tests were carried out on the formed sandwich columns,and the shear stress-displacement curves under different asphalt film thicknesses,temperatures and shear rates were obtained.The curves were classified as single-peak curves(SPCs)and double-peak curves(DPCs),and the characteristics of the two curves were summarized.(4)The effects of asphalt film thickness,temperature and shear rate on the mean value of peak stress and peak displacement of the interface are discussed.The morphology of the interface section after shearing is analyzed.The different failure modes of the interface caused by asphalt film thickness,temperature and shear rate are analyzed.The synergistic effect of asphalt film thickness,temperature and shear rate is analyzed.(5)The effects of asphalt film thickness,temperature and shear rate on the adhesion performance of asphalt-aggregate interface were analyzed from the perspectives of shear fracture energy and ultimate displacement;The shear slip theory is used to explain the generation of double-peak phenomenon,and the failure mechanism of asphalt-aggregate interface is explained and evaluated in combination with the related theory of viscoelastic mechanics.The results show that the forming load is feasible to control the thickness of asphalt film.The stress-displacement curves obtained from the test are divided into SPCs and DPCs.When the thickness of asphalt film is 112μm,the stress-displacement curve has SPCs and DPCs;When the thickness of asphalt film is 222 μm,the stress-displacement curves are all SPCs.Under the same test condition,the two stress peaks of DPCs are lower than those of SPCs,and DPCs are almost enveloped by SPCs.The failure modes of shear test include adhesion failure mode,cohesion failure mode and adhesion-cohesion composite failure mode.With the increase of temperature,the failure of asphalt-aggregate interface changes from adhesion failure mode to cohesion failure mode.DPCs are due to the shear slip of the interface,which is the adhesion-cohesion composite failure mode.The first stress wave peak is mainly adhesion failure mode,and the second stress wave peak is mainly cohesion failure mode.With the increase of temperature,the shear strength(peak stress)of asphalt-aggregate interface decreases,and the influence of shear rate on peak stress mean is getting smaller and smaller.When the temperature and asphalt film thickness are the same,the greater the shear rate,the greater the mean peak stress,and the shorter the shear time.The failure mode of SPCs may be adhesion failure or cohesion failure,and the failure mode is affected by temperature and asphalt film thickness.Shear slip leads to the generation of DPCs,which reduces the energy required for shear failure of asphalt-aggregate interface and weakens the adhesion performance of interface.The peak displacement of SPCs and one peak displacement of DPCs are concentrated,while the two peak displacement of DPCs is discrete,which is also caused by shear slip.