Study On Modification Mechanism And Micro-properties Of Poly-phosphoric Acid Modified Asphalt Considering Aging Performance Base Don AFM

With the development of highway construction in our country,the research of asphalt pavement material performance is deepening.The performance of asphalt is the key factor related to the service performance and service life of asphalt pavement,therefore,it is necessary to study asphalt materials in depth.Polyphosphoric acid is an economical modifier and the polyphosphoric acid modified asphalt has good technical performance and storage stability.So there is a good prospect for development.However,the research on the modification mechanism is still to be further studied.In recent years,scholars at home and abroad have focused on the performance of asphalt at the macro level,such as rheological properties,viscoelastic properties,bonding characteristics,and so on,but the research on the micro-properties of asphalt is relatively few.In this paper,it is found that the modification mechanism of PPA modified asphalt is chemical through the four components experiments?SARA?,infra-red spectrum?IR?andatomic force microscope experiments?AFM?.By analyzing the morphology and phase diagram of pure asphalt and PPA modified asphalt obtained by AFM,it is found that the area of para-phase decreases obviously,the area of peri-phase increases on the contrary,and the valley of bee-like structure?catana-phasease?becomes wider,which illustrate that after adding PPA,the content of asphaltene in asphalt will increase and the low temperature cracking resistance will be weaken.the content of asphaltene in asphalt will increase and the low temperature cracking resistance will be weakened.The AFM morphologies of asphalt samples show that the number of bee-like structure of SBS modified asphalt,PPA modified asphalt and PPA-SBS mixed modified asphalt are obviously more than that of pure asphalt.Moreover,PPA modified asphalt exhibits the characteristics of increasing bee-like structures volume,while SBS modified asphalt exhibits the characteristics of increasing the number of small bee-like structures,and PPA mixed modified asphalt shows two different characteristics mentioned above at the same time.After TFOT aging,the pure asphalt and SBS-modified asphalt surface change significantly.The peak zone size increased significantly and was more intense,but the PPA-modified asphalt and PPA mixed modified asphalt changed only slightly.Thus,the PPA-modified asphalt is better than SBS-modified asphalt and pure asphalt in terms of resisting aging.After PAV aging,all four asphalt surfaces change dramatically.The peak zone size decreased and was more smooth,while the number of bee-like structure of PPA mixed modified asphalt is still the most.The results show that after PAV-aging,the asphalt changes from multiphase structure to simple phase structure,and the phase difference decreases gradually.By calculating the roughness parameters of each asphalt before and after aging:root mean square roughness roughness?R_q?and density of summits(S_ds),it was found that the R_q of SBS modified asphalt is slightly larger than that of PPA modified asphalt,larger than that of PPA modified asphalt and pure asphalt,which illustrated that the surface of SBS modified asphalt and PPA composite modified asphalt is rougher and the self-healing performance is better.After TFOT aging,the R_q of the four kinds of asphalt increased,among which the increase of base asphalt and SBS modified asphalt was larger,while the increase of PPA modified asphalt and PPA mixed modified asphalt was smaller,which show that the aging resistance of PPA and PPA mixed asphalt is better than that of SBS modified asphalt and pure asphalt.After aging with PAV,R_q of the four kinds of asphalt decreased significantly,among which,the decrease of pure asphalt and SBS modified asphalt was larger,while that of PPA modified asphalt and PPA compound modified asphalt was smaller than that of PPA modified asphalt and PPA modified asphalt.By comparing the Sds of all bitumen,it is found that the Sds of pure asphalt is the largest and that of SBS modified asphalt is the second.PPA mixed modified asphalt is the smallest,indicating that the surface of PPA mixed modified asphalt is more homogeneous and has better resistance to deformation.After TFOT and PAV aging,the Sds of the four asphalts decreased,the damping of PPA modified asphalt and PPA mixed modified asphalt is small,while that of pure asphalt and SBS modified asphalt is larger.The results show that PPA modified asphalt and PPA mixed modified asphalt have better resistance performance to deformation and aging.By comparing the AFM force curves of each asphalt sample,it is found that after the TFOT and PAV aging,the values of each point on the adhesion curve of the four kinds of bitumen are obviously reduced.Combined with the aging data,it is found that the maximum separation force of PPA-modified mixed asphalt is always the maximum.The maximum separation force of PPA-modified asphalt is always higher than that of SBS modified asphalt and pure asphalt.The results show that the adhesion property of PPA modified asphalt is better than that of PPA modified asphalt and pure asphalt before and after aging.In addition,the adhesion force,Young's modulus,contact stiffness and surface energy were calculated according to the image and related models.The results show that the anti-deformation ability of the PPA mixed modified asphalt is slightly weaker than that of the PPA modified asphalt,but better than that of SBS modified asphalt and pure asphalt.But the adhesion property of the PPA mixed modified asphalt is better than that of the other three kinds of asphalt.SBS modified asphalt is superior to pure asphalt in deformation resistance and adhesion property.To sum up,the AFM mixed modified asphalt has better self-healing and anti-deformation properties and the adhesion properties and related anti aging properties of PPA mixed asphalt are superior to those of the other three kinds of bitumen.And it can improve the low temperature performance of single PPA modified asphalt and the defect of single SBS modified asphalt's insufficient deformability,so it has certain complex modification significance.