Study On Linear Viscoelastic Behavior Of Polyphosphoric Acid And SBS Composite Modified Asphalt And Its Mixture

In the course of highway development at home and abroad, early damage and durability of asphalt pavement has been plagued by road workers. In order to solve these two problems, scholars of domestic and foreign have been working on the application of modified asphalt materials. Polymer modified asphalt is one of the most widely used modified asphalt in the world, and its application in pavement engineering has achieved remarkable results. But the traditional polymer modifier still has some problems, such as poor compatibility with asphalt, polymer modified expensive and complicated processing technology. The use of poly phosphoric acid (short for PPA) can be a good solution to the shortcomings of polymer modification. The chemical modification of poly-phosphoric acid can significantly improve the performance of the asphalt mixture, and it has been widely used in foreign countries for its low cost and simple process. But, the performance index of the modified asphalt is difficult to meet the requirement of domestic standard for, which has resulted in the problem of the large scale application of poly-phosphoric acid modified asphalt in China. In order to solve the practical problems of the application of the modified poly phosphoric acid modified asphalt, the composite modified asphalt with poly-phosphoric acid and SBS was put forward. At present, the research on poly phosphoric acid modified asphalt is still in its infancy in our country.In this paper, the study on the composite modified asphalt with poly-phosphoric acid and SBS was carried out. This paper mainly carried out two aspects of research. Firstly, by adjusting the content of poly-phosphoric acid and additives with lowing SBS content, the performance of poly-phosphoric acid and SBS composite modified asphalt and mixture can meet the requirements of domestic specifications. Secondly, based on the study of the viscoelastic properties, the performance of the composite modified asphalt and asphalt mixture was analyzed and the influence of the additives on the properties of the composite modified asphalt was analyzed studied. The specific research contents include the following aspects.First of all, according to the requirements of the domestic standard, the proportioning scheme of compound modified asphalt were carried out by adjusting the dosage of modifier. Through the penetration and softening point test, ductility test, the appropriate proportioning scheme was choose, and by the storage stability of asphalt test, aging test and rutting test of asphalt mixture, beam test and freeze-thaw splitting test of composite asphalt, the basic performance is evaluated. From the above test data analysis, the adjustment of the compound solution can be obtained in accordance with the requirements of the domestic specifications with lowing SBS content of the composite modified asphalt.Secondly, the frequency sweep test of the compound modified asphalt was carried out by the test method of the viscoelastic principle. According to the analysis of the modulus and phase angle of the asphalt from the frequency sweep test, the poly-phosphoric acid can reduce the temperature sensitivity of asphalt and do not affect the low temperature performance of the modified asphalt. The master curves were calculated by temperature equivalent principle at 45?, such as modulus, phase angle, rutting factor and the fatigue factor. The WLF model was used to construct the modulus master curve of the composite modified asphalt and Sigmoidal function was used to fit the model. The results show that the Sigmoidal function can fit the modulus data of the modified asphalt well in this paper. Comprehensive analysis of viscoelastic properties, it indicate that the evaluation method based on the "three indexes" of poly phosphoric acid and SBS modified asphalt has some limitations. Three indexes can not characterize the composite modified asphalt performance fully within the range of wide domain of frequency or temperature.Finally, the dynamic modulus and creep test of asphalt mixture were studied with method of the viscoelastic principle. The modulus of the composite modified asphalt mixture was obtained by the dynamic modulus test at 20?. The data showed that the poly-phosphoric acid could increase the modulus of the mixture and achieve the ability to resist rutting. Based on the time temperature equivalence principle, the modulus master curve of asphalt mixture is established, and compared with the main curve of Hirsch model, the analysis results show that the Hirsch model can not predict the modulus of composite modified asphalt. Creep performance test results show that poly phosphoric acid can improve the high temperature anti deformation capacity of low content SBS modified asphalt, and the creep characteristics of the modified asphalt with high SBS content can be achieved by the performance of the modified asphalt.In this paper, the viscoelastic behavior of poly-phosphoric acid and SBS compound modified asphalt is studied deeply, which provides the technical support for the future engineering application.