| Porous asphalt pavement has the advantages of noise reduction,drainage,skid resistance and so on.More and more roads have been paved with porous asphalt pavement.However,in the process of use,due to the rapid aging of asphalt,high dynamic moisture pressure,vacuum negative pressure suction and other factors,the adhesion property between asphalt and aggregate is significantly reduced,resulting in the stripping of asphalt film,and the moisture stability and crack resistance of porous asphalt pavement are significantly decreased.Some diseases such as threshing,loose,pit and so on.shorten the service life of porous asphalt pavement.In view of this,in order to improve the moisture stability performance of porous asphalt pavement,this paper first studies the diffusion behavior of moisture in asphalt film,and then improves the adhesion performance between asphalt and aggregate interface from two aspects of asphalt composite modification and aggregate surface hydrophobic modification,so as to improve the moisture stability performance of porous asphalt mixture.Finally,by etching the hydrophobic coating on the surface of the porous asphalt mixture to improve its hydrophobicity,reduce the direct and indirect damage caused by moisture in the process of using the porous asphalt pavement,further improve the moisture stability of the porous asphalt pavement,which is of great significance for extending the service life of the porous asphalt pavement and improving the driving safety in rain and snow days.Firstly,the asphalt membrane was bathed in moisture under different test conditions,and the change value of hydroxyl peak area after moisture entered the asphalt membrane was quantitatively calculated by infrared spectrum tester（FTIR）.The moisture diffusion process was divided into two stages,and the function fitting was carried out respectively,and the diffusion coefficients in different diffusion processes were calculated.The results showed that at the beginning of the moisture bath process,the diffusion coefficient of asphalt film was large and the diffusion rate was fast.With the increase of moisture diffusion,the content of free moisture in asphalt film tended to be saturated,and the free moisture began to become a part of the bound moisture,resulting in the decrease of the diffusion coefficient and moisture absorption rate.At the same time,through the comparison of the control group,it was found that with the increase of temperature,the larger the diffusion coefficient was,the saturated amount of moisture absorbed by the asphalt membrane increased,and the order of magnitude of the diffusion coefficient reached 10-13.The diffusion coefficient of moisture in the 70#road petroleum asphalt membrane was higher than that in the SBS modified asphalt membrane,further indicating that the 70#road petroleum asphalt was more prone to moisture damage.Secondly,70#road petroleum asphalt was modified with non-amine anti-stripping agent and Nano-Zn O.The adhesion strength,adhesion work,stripping work,compatibility between modifier and asphalt,and moisture stability performance of asphalt mixture before and after modification were studied by visible light ultraviolet spectrophotometer,optical contact Angle tester,FTIR and moisture stability performance test.The results showed that the adhesion strength between the modified asphalt and aggregate was improved,the adhesion work and energy parameters increased,and the stripping work decreased,which effectively improved the moisture stability of the asphalt mixture.It was found that the anti-stripping agent and Zn O have good compatibility with asphalt and can fully modify asphalt,and the effect of the asphalt modified by Zn O and anti-stripping agent was better than that of the asphalt modified by only using anti-stripping agent.Then,the surface hydrophobic modification of the basalt aggregate was performed with silane coupling agent（SCA）.Boiling method,optical contact Angle tester,FTIR,environmental scanning electron microscope（ESEM）and moisture stability tests were used to study the adhesion strength,adhesion work,stripping work,the modification mechanism of aggregate by SCA and the improvement of moisture stability performance of asphalt mixture.The results showed that the modified aggregate surface changed from hydrophilic to oilphilic,the interface adhesion strength with asphalt was significantly improved,the adhesion work and energy parameters were increased,the stripping work was reduced,and the moisture stability of asphalt mixture was improved.The modification mechanism of SCA on aggregate was that the oilphilic base group was introduced on aggregate surface,and irregular villous network"bumps"were formed to increase the contact area with asphalt,and the modification effect of different SCA was not completely the same.SCA improves the surface hydrophobicity of aggregates,which helped to improve the moisture stability of asphalt mixtures.Finally,the hydrophobic coating was etched on the surface of the porous asphalt pavement and the surface of the internal pores.The moisture stability and moisture seepage performance of the rut specimen without etched hydrophobic coating and the rut specimen with etched hydrophobic coating were tested through the moisture stability performance test,the immersed rut test and the moisture seepage performance test.The results showed that the moisture seepage performance and moisture stability of the rut specimen were improved after the hydrophobic coating was etched,mainly because the moisture could not enter the asphalt film after being separated by the coating,which reduced the peeling of the asphalt film.At the same time,the moisture on the coating was spherical,easy to roll,and the contact time with the porous asphalt mixture was short,and the drainage speed was fast,which was not easy to produce hydrodynamic pressure and frost swelling damage.In conclusion,this paper first analyzes the diffusion behavior of moisture in asphalt film,and then improves the moisture stability performance of porous asphalt mixture through three different modification methods.The three different modification methods are simple and convenient,which is of great significance to effectively improve the moisture stability performance of porous asphalt pavement,prolong the service life of porous asphalt pavement,and improve driving safety. |
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