Laboratory investigation on performance and mechanism of polyphosphoric acid modified bio-asphalt

As a green and clean road material, the bio-asphalt is a research hotspot in road engineering. It is known, the poor high-temperature performance of bio-asphalt limits its application in practical engineering. In order to solve this problem, the polyphosphoric acid (PPA) was used to modify the bio-asphalt. According to the principle of polymer compatibility, the liquid polymer can be well compatible with the asphalt. The matrix asphalt was first heated to a fluid state, and different contents of PPA and bio-oil were then added and stirred. The high-speed shear equipment was finally used to prepared the polyphosphoric acid modified bio-asphalt (PPAMB). The viscosity, dynamic shear rheology, and low-temperature bending creep tests of PPAMB were carried out, and its mechanism was revealed by the Fourier transform infrared spectroscopy (FTIR), fluorescence microscope (FM), scanning electron microscope (SEM), and atomic force microscope (AFM). The results showed that the PPAMB had excellent rheological performance at high and low temperatures. The optimum content of PPA and bio-oil in PPAMB for the composite modification of asphalt were 2% and 7.5% respectively. The PPA reacted with the asphalt to form new functional groups, but the bio-oil had no chemical reaction. Through the FM and SEM analysis, it could be seen that the PPAMB had outstanding uniformity, and smooth surface without aggregation phenomenon; compared with that of bio-asphalt, the size of bee-like structure of PPAMB increased, but its number decreased; compared with that of PPA modified asphalt, the number of bee-like structure of PPAMB increased instead.