Multiscale Analysis and Modification Mechanism of Plasticizer/Polyphosphoric Acid Modified Asphalt

Abstract

In seasonally frozen regions, asphalt pavements are prone to cracking and freeze–thaw damage, while high-temperature deformation is relatively minor. Developing an asphalt system suitable for such regions can maximize material performance and reduce costs. In this study, a composite modified asphalt was prepared using the plasticizer diisononyl adipate (DINA) and polyphosphoric acid (PPA) to enhance overall thermal performance. The study employed macroscopic tests, microstructural analysis, and molecular dynamics simulations to evaluate its performance and mechanisms. The results indicated that PPA effectively compensated for the high-temperature performance loss caused by the plasticizer. The formulation containing 3.5% DINA and 1% PPA (D3.5P1) exhibited high-temperature deformation resistance comparable to the base asphalt, and its fatigue life was 1,110 times greater, demonstrating strong applicability for heavy-load traffic. DINA significantly improved low-temperature flexibility, with the maximum bending strain of D3.5P1 increasing by 39%. The composite system also enhanced moisture resistance, with a TSR 4.5% higher than that of the base asphalt. Fourier transform infrared spectroscopy and fluorescence imaging confirmed that DINA modified asphalt through physical interaction, whereas PPA induced chemical reactions, locally altering the spatial distribution of DINA. Simulations revealed that plasticizer molecules acted as lubricants within the polar fractions, with PPA interacting with asphaltenes and redistributing plasticizer molecules toward nonpolar regions. This composite system provides enhanced low-temperature properties with adequate high-temperature stability, demonstrating strong potential for cold-region pavement applications.