Performance And Mechanism Of Asphalt Modified With Polyphosphoric Acid And Polyphosphoric Acid/Polymer

Polyphosphoric Acid(PPA)as a kind of asphalt modifier is attracting the attention of many domestic researchers because of its advantages such as low cost and simple modification process.For now,there are still some controversies needed further research,such as the modification mechanism of PPA and how PPA affects the low-temperature performance and the water stability of PPA modified asphalt.In this paper some experiments and microanalysis are carried out to research the modification mechanism and performances of the asphalt separately modified by different contents of PPA and PPA-polymer composite modifier.The asphalt composition analysis,Fourier Transform Infrared Spectroscopy(FTIR),Gel Permeation Chromatography(GPC),Thermogravimetry-FTIR(TG-FTIR)are chosen to investigate the mechanism of PPA on asphalt.The composition analysis shows that PPA can prompt the colloid component converted to asphaltene.The FTIR images show that the asphalt has a slight absorption peak at the strong absorption peak of PPA and the characteristic absorption peak also marked changed by PPA.These phenomenas indicate that part of PPA can react the crosslinking reaction with asphalt and the rest part of PPA modifies the asphalt by physical modification,thus improving the high temperature stability of asphalt.The result of GPC manifests that PPA can improve the weight-average molecular weight,the index of molecular weight distribution and the content of large molecular weight of asphalt.The TG-FTIR test indicates PPA can increase the residual amount of reaction,the starting and stop temperature of the thermal decomposition process of asphalt,and the peak temperature corresponding to the maximum reaction.It means that PPA could react with small molecules in asphalt to change the composition and chemical properties of asphalt,consequently tackifies asphalt and improves its thermostability.The fluorescence microscope and Atomic Force Microscope(AFM)are used to observe the multi-scale morphology features of the different asphalt separately modified by different contents of PPA,PPA/SBS and PPA/SBR.The fluorescence microscope images show that PPA can obviously enhance the compatibility between asphalt and polymer modifier which means the improvement of the high-temperature and the storage stability of the ploymer modified asphalt.The AFM images show an irregular relationship between the size and uniformity of bee structure and different PPA dosage.The observation results of AFM can be explained by the complex adsorption and destructive effect of asphalt and wax microcrystals.Some tests are conducted to evaluate the performances of the different asphalt separately modified by PPA,PPA/SBS and PPA/SBR wiht different contents of PPA,such as the penetration test,softing point test,ductility test,Multi Stress Creep Recovery(MSCR)test,Linear Amplitude Sweep(LAS)test,force ductility test and surface energy test.The results show that PPA can significantly enhance the high-temperature and fatigue performance of the asphalt.however,PPA weakens the low temperature performance of asphalt in varying degree.Moreover,PPA can evidently improve the adhesion of asphalt and SBS modified asphalt,but no obvious influence on SBR modified asphalt.By comprehensive analyzing all the test results,the optimum PPA dosage to the three kinds of asphalt should be between 0.5% and 1% by mass of the asphalt.