Rheological performance and modification mechanism of corn stover oil/polyphosphoric acid composite-modified asphalt

To improve the high-temperature performance of corn stover oil (CSO) bio-asphalt and facilitate biomass utilization, polyphosphoric acid (PPA) was introduced to prepare CSO/PPA composite binders with different modifier combinations. The binder properties were evaluated through conventional tests, temperature sweep (TS), multiple stress creep recovery (MSCR), bending beam rheometer (BBR), and Fourier-transform infrared spectroscopy (FTIR). Two-factor ANOVA identified significant CSO × PPA interactions in penetration, viscosity at 135 °C, and MSCR responses, with the strongest effect observed for J nr ,3.2 (partial η 2 = 0.795), while no significant interaction was found for G*/sin δ or BBR parameters. PPA improved stiffness-related properties and high-temperature deformation resistance by increasing the softening point, viscosity, rutting parameter, and MSCR recovery, while decreasing non-recoverable creep compliance; however, excessive PPA increased low-temperature stiffness and reduced the m-value. CSO showed a pronounced softening and plasticizing effect, improving low-temperature ductility and stress-relaxation capacity at the expense of high-temperature stability. Considering the conventional, TS, MSCR, and BBR results together, a PPA dosage of 3%–4.5% is recommended when the CSO content is 8%, whereas 4.5% PPA is recommended when the CSO content is 10%. FTIR spectra showed phosphorus-related absorption features near 1150 and 1002 cm -1 after PPA addition and a new feature near 1709 cm -1 after CSO incorporation, indicating composition-related changes in characteristic functional groups.