Research On The Microstructure And Technical Performance Of Polyphosphoric Acid Modified Asphalt

The traditional polymer modified asphalt is usually physical modification, has some widespread problems such as poor compatibility between modifier and asphalt, insufficient thermal storage stability, complex processing technique etc. The modified asphalt efficiency is restricted in a certain extent because of these problems. Based on the chemical modified on the asphalt, the polyphosphoric acid significantly improves its road performance, has the advantages of low cost and simple processing technique, so the good promising application can be expected.However, the polyphosphoric acid modified asphalt is rarely used on engineering in China, because it is lack of systematic and in-depth studies on the material design, the technical standard, mechanism analysis and microscopic structure, thus, to a certain degree, which limits its popularization and application.The paper in-depth studies the technical performance, modified mechanism and microstructure of the polyphosphoric acid modified asphalt and its mixture based on theory analysis and laboratory experiment.This paper takes a research on the technical performance of the polyphosphoric acid modified asphalt from the aspects of the basis asphalt type, the polyphosphoric acid level and dose, the compound polymer type and compound polymer dose. The test result shows that polyphosphoric acid can effectively improve several performances of the basis asphalt such as the high-temperature performance and resistance to aging, its reasonable adding amount should be in 0.5%--1%. By adding SBS and SBR polymer, it can effectively improve the low temperature crack resistance of the polyphosphoric acid modified asphalt after aging.This paper uses the Fourier Transform Infrared Spectroscopy(FTIR) method to research the chemical modification mechanism of the polyphosphoric acid modified asphalt. The test results show that, with the content of the adding polyphosphoric acid increased, the band near 800—1300cm-1 has a substantial migration in the infrared spectrum, and a new mixed absorption peak generates.By analyzing the characteristics of the newborn functional group according to the peak data results of the curve fitting through Gauss and Lorentz composite function, it is founded that the hydroxyl –OH in bisphenol A of the asphalt will react to the poly phosphoric acid and phosphate ester is produced.This paper quantitatively determines the Pyrolysis parameter of the polyphosphoric acid modified asphalt of different doses through thermogravimetry; and researches the influence of the polyphosphoric acid when temperature changes on the aspects such the asexothermic peak, endothermic peak of the asphalt and thermal decomposition temperature using the method of Differential thermal analysis. The results show that the polyphosphoric acid can obviously improve the thermal stability of the asphalt.This paper also determines the size and distribution of the asphalt molecular weight through gel permeation chromatography analysis method. When adding polyphosphate acid, the weight-average molecular weight, the number-average molecular weight and dispersion coefficient of the asphalt all improve to different degrees, which indicates that the polyphosphoric acid can efficiently improve the high temperature stability of the asphalt.The structural changes of the moleculer of the polyphosphoric acid modified asphalt is quantitatively observed by atomic force microscopy before and after modified. And through the self-developed image processing software, this article studies the changes of the characteristic parameters of the modified asphalt and establishes the relationship between the microstructure and the usage performance of the modified asphalt.The results show that, these microstructure parameters such as area of asphaltenes, area of resins, area of saturates and aromatics, length of asphaltenes, number of asphaltenes and the maximum resins radius, have both good correlation with the dose of polyphosphoric acid and the technical performance of the polyphosphoric acid modified asphalt.This article selects polyphosphoric acid modified asphalt mixture of different gradation types, such as AC-13 and AC-20, and different polymer types, such as SBS and SBR, to take mix design and pavement performance research, uses statistical methods for the analysis of the effects of the polyphosphoric acid, polymer and the gradation on the pavement performance. The test results show that, by adding the polyphosphoric acid, it has a significant effect on improving the high temperature stability of the asphalt mixture, but it doesn’t have a significant effect on the moisture susceptibility, and it enables the low temperature crack resistance have a slightly decline. However, the mixture, by adding 0.75% polyphosphoric acid to the 3% SBS modified asphalt or by adding 0.75% polyphosphoric acid to the 2.5% SBR modified asphalt, has these advantages such as high temperature stability, low temperature cracking resistance and moisture susceptibility.