The Surface Character Analysis Of Bitumen And Aggregates And The Evaluation Of The Adhesion Between Them

Asphalt mixture is a kind of composite material which is composed of aggregate and asphalt binder.In the process of adhesion,first need a good infiltration of asphalt to the aggregate surface,and under a series of physical and chemical action,the adhesion formed.This process is directly influenced by factors such as bitumen composition,aggregate lithology and surface properties of the aggregate,and further determines the various road properties and durability of the asphalt mixture,such as water damage,loose peeling,and cracking resistance.At present,the research on the infiltration characteristics of asphalt and aggregate is still insufficient,and there are many defects on the evaluation method of adhesion between asphalt and aggregate in China's current specification.In this paper,the mercury injection test,SEM scanning electron microscope test,laser confocal scanning test and AFM test were conducted,and the pore and texture parameters of the aggregate surface were measured,and the porosity,average pore size,pore volume were used to characterize the pore surface.The parameters,such as arithmetic mean deviation and root mean square deviation of the profile were used to characterize the surface roughness of asphalt and aggregate.Through the laser confocal scanning test and mercury injection test,and combined with theoretical analysis,the infiltration model of asphalt and aggregate were established.Surface energy test and stirred water adsorption test were conducted,and the adhesion work,wetting work and peeling rate were used to characterize and evaluate the adhesion.The diffusion test of asphalt on the surface of the aggregate was designed,and the diffusion and wetting characteristics of asphalt on the surface of aggregate were evaluated by diffusion rate.The Positest AT-A adhesion tester was used to measure the adhesive force between different asphalt and aggregates.So that,the damage location of asphalt-aggregate adhesion system,factors affecting adhesion,and self-healing property of adhesion were researched,on this basis,the adhesion foce after immersion and the adhesion foce ratio were proposed as the evaluating indicator of the adhesion.Besides,the adhesion force between aggregate and asphalt mortar was measured,and the effects of powder binder ratio,the content of stone powder,clay powder and slaked lime were analyzed.The CFD-ACE+ software was used to simulate the effect of hydrodynamic pressure on pores of mixture,and the effects of load pressure,pore diameter and pore connectivity on dynamic water erosion were analyzed.Lastly,combined with the water stability test,the correlation between the adhesion and water stability was analyzedThe main conclusions of this study include: the surface pore size of the aggregate can be divided into large pores(>100?m),medium pores(100?m~0.1?m),small pores(0.1?m~0.01?m),and micro pores(<0.01?m)according to its distribution.About 50% of the total pore volume is dominated by large pores,20% is dominated by medium pores,and about 20% is dominated by small pores,and the pore volume dominated by micro pores was less than 10%.The effect of these factors on the amount of adsorbed asphalt decreases in the following order: pore volume>porosity > fractal dimension> pore surface area > average pore diameter.Thus,the amount of adsorbed asphalt is largely related to pore volume,and its correlation with pore size is relatively low.The fractal dimension of the pore and texture of the aggregate surface represents the development and distribution characteristics of the pore and texture of the aggregate surface,and directly affects the adsorption amount of asphalt and the adhesion between asphalt and aggregate.The infiltration model of asphalt and aggregate considering the aggregate surface porosity and texture was established.Parameters of wetting and surface energy can be used to evaluate the adhesion.The diffusion rate of asphalt on the surface of stone is affected by the surface roughness and the types and aging time of asphalt.When the bonding temperature is 50?,and the thickness of asphalt film is about 0.1mm,the damage of asphalt aggregate adhesion system is the adhesion failure.The standard recommended value of the adhesion foce after immersion and the adhesion foce ratio were proposed.The adhesion between asphalt and stone mainly comes from colloid.The decay rate of adhesion force is the fastest in the initial stage of asphalt aging,and after 10 hours of asphalt aging,the decay rate decreased,and then stabilized after aging for about 18 hours.The damage caused by water erosion is mainly concentrated in the inlet channel and outlet channel,and the influence of water flow on pore erosion is significantly affected by the load pressure,pore size and connectivity.Although water stability is affected by many factors such as grading,volume index and aggregate particle shape,it is still closely related to the adhesion index.