Rheological properties and anti-aging mechanism of asphalt synergistically modified by polyphosphoric acid and SEBS

SBS-modified asphalt suffers from bottlenecks such as inadequate thermal storage stability, poor resistance to UV and thermal oxidation, and high cost. This study aims to develop an alternative modified asphalt that offers superior storage stability, excellent rheological properties across a broad temperature range, and enhanced long-term durability. To this end, polyphosphoric acid (PPA) and styrene-ethylene/butylene-styrene block copolymer (SEBS) were utilized to synergistically modify asphalt. Dynamic shear rheometer (DSR) tests showed that the rutting factor (G*/sin δ) of the composite asphalt containing 1.2% PPA and 5% SEBS at 82℃ was 3.9 and 4.7 times greater than that of the asphalts containing 1.6% PPA or 6% SEBS, respectively. Quantitative fluorescence microscopy (FM) analysis revealed that PPA reduced the critical SEBS dosage required to form a cross-linked network and facilitated the formation of an Interpenetrating Polymer Network (IPN) structure in the composite modified asphalt. The composite asphalt with 0.8% PPA retained low-temperature flexibility (comparable BBR creep Stiffness and Creep Rate to the SEBS-modified asphalt) while exhibiting significantly superior aging resistance. Molecular dynamics simulations and FTIR analysis elucidated the potential mechanism involved in the modification process. It was found that PPA, via passivation and steric protection on the chains of SEBS, effectively inhibited the formation of characteristic oxidation products, such as C O and S O groups, during aging. This led to a marked enhancement in the material's resistance to thermo-oxidative degradation. In conclusion, the PPA/SEBS composite simultaneously enhances asphalt performance and reduces cost, providing a strong rationale for developing high-performance, durable, and economical pavement materials.