Study On The Adhesion Attenuation Behavior Of Asphalt-Aggregate Under Water Vapor

Moisture damage is one of the main disease of asphalt pavement.The cause of the disease is that water molecules enter the asphalt or asphalt-aggregate interface,which reduces the adhesion of asphalt and aggregate under the further action of vehicle load and temperature.A lot of researches have been carried out on how liquid water affects the adhesion of asphalt-aggregate,but there is still a lack of research on the effect of gaseous water on the adhesion performance of asphalt-aggregate.Therefore,in this paper,the adhesion test between asphalt and aggregate was carried out to quantitatively evaluate the influence of water vapor on asphalt-aggregate adhesion,and try to explore the mechanism of water vapor-induced attenuation of asphalt-aggregate adhesion performance.The main research contents and results of this paper are as follows:(1)The manufacturing process of the improved pull-out test specimen,as well as the control method for the thickness of the asphalt film and the roughness of the aggregate are clarified.Numerical simulation was used to determine the curing time of the drawn specimens to be 4 months.A normal stress perpendicular to the asphalt layer was applied to the asphalt-aggregate through the pull-out test,and the adhesion between asphalt and aggregate under different water vapor concentrations was quantitatively described by the pull-out strength and asphalt peeling rate.The test results show that with the increase of water vapor concentration,the adhesion between asphalt and aggregate gradually decreases,especially in high humidity state,and the failure mode of asphalt-aggregate interface changes from cohesive failure to adhesion failure.(2)Based on the surface energy theory,the static drop method was used to test the surface energy of asphalt after curing with different water vapor concentrations,and the vapor adsorption method was used to test the surface energy of aggregates under dry conditions,and the aggregate surface energy under different water vapor concentrations was calculated by combining with relevant theories.the surface energy of the material.Combined with the theoretical model of Gv OC surface energy,asphalt cohesive energy and asphalt-aggregate adhesion energy under different water vapor concentrations were obtained.The test results show that asphalt is a hydrophobic material,and its surface energy parameters basically do not change with relative humidity;aggregate is a humidity-sensitive material,and the surface energy of aggregate decreases rapidly with the increase of water vapor concentration.Under dry conditions,the asphalt-aggregate adhesion energy is greater than the asphalt cohesive energy;with the increase of water vapor concentration,the adhesion energy gradually decreases,and finally is smaller than the asphalt cohesive energy.This conclusion explains the mechanism of the transformation of asphalt-aggregate failure types.Combined with the parameters of the pull-out test,a method for evaluating asphaltaggregate adhesion was developed by combining the pull-out test and the microscopic surface energy test.The interface energy was used to evaluate the adhesion between asphalt and aggregate under different water vapor concentrations.(3)Atomic force microscopy was used to obtain the microstructure of asphalt surface under different water vapor concentrations.Image processing software was used to count the number of "bee-like structures" on the asphalt surface,and Nano Scope Analysis software was used to extract the characteristic values and microscopic surface roughness of asphalt "bee-like structures".The test results show that the number and roughness of the "bee-like structure" of the SBS modified asphalt are higher than those of the 70# base asphalt.Adhesion of asphalt and aggregate decreased.The correlation analysis between the micro-roughness and the adhesion of the asphalt surface was carried out,and the attenuation mechanism of the asphaltaggregate adhesion under the action of water vapor was revealed from the perspective of the micro-morphology of the asphalt surface.In this study,the experiment on asphalt and aggregate is carried out,the variation trend of asphalt-aggregate adhesion under different moisture was analyzed and the asphalt-aggregate adhesion properties was quantitatively characterized by combining asphalt-aggregate pull-out test and surface energy test.At the same time,atomic force microscopy was used to explore the change of the microscopic morphology of the asphalt surface under the action of water vapor,and then to reveal the mechanism of the adhesion attenuation between asphalt and aggregate caused by water vapor.