Performance and modification mechanism of low SBS content composite modified asphalt under the synergistic effects of PPA and DOTP

Styrene–butadiene–styrene (SBS) modified asphalt offers excellent pavement performance, but high cost limits broader application. To balance cost and performance, SBS was partially replaced by polyphosphoric acid (PPA), and dioctyl terephthalate (DOTP) was incorporated to prepare high performance, low cost SBS/PPA/DOTP composite asphalt. Orthogonal design determined optimal preparation parameters. Conventional physical, bending beam rheometer (BBR), and dynamic shear rheometer (DSR) tests evaluated high and low temperature properties; confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analysed microstructure and modification mechanisms; inductively coupled plasma optical emission spectrometry (ICP-OES) assessed leaching toxicity. Owing to PPA-DOTP synergy, the composite outperformed 5% SBS asphalt in high and low temperature performance and aging resistance at lower SBScontents. The formulation with 2.5% SBS, 1.25% PPA, and 4% DOTP performed best. Leaching and economic analyses showedcost effectiveness and no significant leaching toxicity risk, supporting its development and application.