Research On Modification Mechanisms Of Polyphosphoric Acid On Asphalt And The Performance Of Polyphosphoric Acid Modified Asphalt Mixture

The polymer modifiers,popularly used in China,are mostly the physical modification,lack of hot storage stability and segregation easily because of the poor compatibility with asphalt.Moreover,the high price and complex processing technique will rise the expense on the road construction.Polyphosphoric acid(PPA)can significantly improve the performance of asphalt by chemical modification,with the advantages of low price and simple processing technique.However,the modification mechanism,road performance and mechanical parameters of PPA modified asphalt are not researched sufficiently,which limits its popularization and application in China.This paper is to research the modification mechanism of PPA on asphalt and evaluate the road and mechanical performance of PPA modified asphalt mixture.Firstly,fractionation tests,infrared spectrum tests,fluorescence microscopy tests and differential scanning calorimetry tests were conducted on asphalt binders modified with PPA.The results show that the asphaltene content increase with increasing dosage of PPA and sol structure of binder gradually changes to sol-gel structure.The cross-linking,grafting actions among SBS and space mesh structure of modified asphalt are strengthened with the addition of PPA,which boosts the compatibility between SBS with asphalt.The SBS is reduced to smaller particles and the swelling is improved,so that the modification effectiveness of SBS is further exploited.The glass transition temperature is not significantly influenced by the addition of PPA.Secondly,triaxial repeated load tests,low temperature shrinkage coefficient tests,indirect tensile creep tests and indirect tensile strength tests were conducted on two kinds of modified asphalt mixtures(1.5% PPA+4% SBS and 5% SBS modified asphalt),which determines the “Flow Number” and critical cracking temperatures,to evaluate the road performance of mixtures.The results show that the “Flow Number” increases and the permanent deformation decreases with the addition of PPA,which will improve the high temperature anti-deforming capability of mixtures.The critical cracking temperatures of mixtures are almost same,which indicate that the low temperature performance of mixtures is not significantly influenced by the addition of PPA.Lastly,the viscoelastic response were analyzed for typical highway asphalt pavement structure using self-developed viscoelastic layer system software APRA(Asphalt Pavement Response Analysis)based on the mechanical parameters of asphalt mixture,which determined by the dynamic modulus test.The results show that the addition of PPA can improve the value of dynamic modulus,and decrease the vertical strain of asphalt layer,which indicates that PPA can resist the deformation of asphalt mixture in high temperature.