Multi Scale Study On Interface Of Semi Flexible Pavement Materials

Semi flexible pavement material is a kind of composite pavement formed by pouring special cement mortar into microporous asphalt mixture.Its traditional research mostly focuses on the overall macro mechanical properties and pouring materials,while the interface between asphalt mortar and asphalt stone is often ignored because it is difficult to study and changes greatly.However,the interface between asphalt mortar and asphalt stone is often ignored because it is difficult to study and change greatly.But in the actual pavement structure,the pavement cracks often result from the defects of interface between different materials and stress concentration,and reduce the service life of the pavement.Based on the above reasons,the interaction mechanism of asphalt mortar interface is studied from three aspects: nano view,micro and macro,using macro interface testing technology,atomic force microscope test technology and molecular dynamics simulation technology.The main contents of the study are as follows:It is found that moisture in humid air can accelerate the hydration rate of mortar before14 d age,enhance the strength of cement mortar and interfacial tensile strength when curing in high humidity environment.After 14 d age,moisture invades into asphalt and asphalt granite interface,resulting in asphalt emulsification and interfacial bonding failure,thus reducing the interfacial tension Surface tensile strength.The required ages for better interaction and adhesion between the three kinds of asphalt and mortar are: 70# petroleum asphalt and mortar for 3days;PG76-22 modified asphalt and mortar for 7 days;S-HV modified asphalt and mortar for21 days.When using three kinds of asphalt as interface binder to construct semi flexible pavement,the water damage resistance ability from weak to strong is: 70#petroleum asphalt as binder,PG76-22 modified asphalt as binder,S-HV modified asphalt as binder;considering the interaction between interfaces,it is suggested that the age of 70# petroleum asphalt semi flexible pavement should be 3 days Above,PG76-22 modified asphalt semi flexible pavement needs more than 7 days,S-HV modified asphalt semi flexible pavement needs more than 14days;among them,PG76-22 modified asphalt needs to focus on the adhesion between asphalt and stone.The PF-QNM mode of atomic force microscope is used to evaluate the asphalt interface and asphalt mortar interface.It is found that the surface modulus of S-HV modified asphalt changes greatly in PF-QNM mode,but the statistical data show that the data show normal distribution,and most of them are concentrated in the middle of 50-100 MPa.According to the statistics,the young’s modulus of the asphalt is 74.74 MPa,and the standard deviation is 16.52 MPa.The mean value of adhesion energy is 1.45 nN and the standard deviation is 0.17 nN.The data of dissipated energy accord with lognormal distribution,the mean value is 0.55 KeV,and the standard deviation is 0.177 KeV.The adhesion of asphalt mortar interface is good,and the modulus transition curve does not break.And the modulus of transition zone increases exponentially,and finally the modulus is stable between 175-200 MPa.And the change of adhesion energy and dissipation energy also corresponds to it.The final result is that the asphalt mortar interface transition zone is 21 um.Molecular dynamics simulation of mortar asphalt interface was carried out from nano scale.It was found that adhesion between different kinds of asphalt and C-S-H gel was mainly supplied by Coulomb static electricity,and accounted for more than 99%.The adhesion between different kinds of bitumen and C-S-H gels is ranked from small to large: 70# asphalt,PG76-22 modified asphalt and S-HV modified asphalt.With the increase of temperature,the electrostatic interaction between asphalt and C-S-H gel increased,and the adhesion of Coulomb static electricity increased to a certain extent.The adsorption rates of the four components of 70#asphalt on C-S-H gel surface ranged from small to large: asphaltene,gum,aromatic phenol and saturated phenol.The polar functional groups of 70# asphalt components will have a great influence on the diffusion speed of C-S-H asphalt surface.The molecular weight of each component of asphalt is one of the important factors affecting the molecular diffusion rate.An appropriate amount of SBS modifier will reduce the diffusion rate of asphaltene,and an excessive amount of SBS modifier will weaken this effect.The parameters of SBS modifier will affect the diffusion rate of each component of asphalt,and the most influential one is saturated phenol.With the increase of modifier dosage,the diffusion rate will decrease in varying degrees.There are two main peaks in the solubility curve of 70# asphalt saturated phenol,the first is between 0 and 6 ?,and the second is between 15 and 30 ?.The adsorption capacity of saturated phenol and aromatic phenol on the surface of C-S-H gel increased with increasing temperature,making it close to the surface of C-S-H gel.70# asphalt colloid is clustered away from the surface of C-S-H gel.Now,with the increase of temperature,the asphaltene of 70# asphalt appears in the distribution phenomenon,and its distribution is more uniform.At 20 C,the solubility curves of saturated phenol from various asphalts showed that the highest peak distance from C-S-H gel surface was from 70# to PG76-22,and S-HV to modified asphalt.This is proportional to the parameters of SBS modifier.Proper amount of SBS modifier can adjust the adsorption of aromatic phenol and C-S-H gel in asphalt.The addition of SBS modifier improved the adsorption ability between the gel and C-S-H gel,which made the distribution of asphalt sub fractions more uniform and enhanced its durability.