Modification mechanism of asphalt modified with Sasobit and Polyphosphoric acid (PPA)

The laboratory performance and modification mechanism of asphalt modified with Sasobit and Polyphosphoric acid (PPA) were studied through a comprehensive laboratory program. The base asphalt was mixed with 3% Sasobit to produce Warm Mix Asphalt (WMA) and then modified with four different percentages of PPA (0.5%, 1.0%, 1.5% and 2.0%) by mass of base asphalt, respectively. The rolling thin film oven (RTFO) and the pressure aging vessel (PAV) procedures were conducted to simulate the aging of asphalt. Experiments were conducted for asphalts under different aging conditions. The rheological property of asphalt was measured by conventional tests, the Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR). The morphological characteristic of asphalt was evaluated by Fourier Transform Infrared Spectroscopy (FT-IR), Fluorescence microscopy, Thermogravimetric (TG) and Differential Scanning Calorimetry (DSC). It is concluded that the rheological properties of asphalts were enhanced after Sasobit and PPA were added. The penetration of asphalts decreased and softening point increased, proving that deformation resistance was enhanced and high-temperature stability improved. The ductility decreased to an acceptable level when the PPA content was less than 1.0%. High-temperature deformation resistance and aging resistance were enhanced for asphalts under different aging conditions. In order to guarantee the low-temperature property of asphalt, PPA content in WMA should be no more than 1.5%. The modification effect of Sasobit and PPA on asphalt included chemical and physical processes. The compatibility between PPA, Sasobit and base asphalt is good and the microstructure of the modified asphalt is beneficial in improving the performance of asphalt. The addition of Sasobit restricted the decomposition process of the asphalt component, and the addition of PPA further alleviated the decomposition process and enhanced the stability of asphalt.