Feasibility of Polyphosphoric Acid in Emulsified Asphalt Modification: Emulsification Characteristics, Rheological Properties, and Modification Mechanism

Polyphosphoric acid (PPA), a chemical modifier widely used in petroleum asphalt, results in significant performance improvements. However, its effectiveness for modified emulsified asphalt has not yet been thoroughly verified. This study aims to investigate the emulsification properties, rheological characteristics, compatibility, and modification mechanisms of PPA-modified emulsified asphalt and validate the feasibility of applying PPA for modification. Initially, PPA-modified emulsified asphalt was prepared at different dosages (0%, 0.5%, 1.0%, 1.5%, and 2.0%), and its emulsification characteristics, including evaporation residue properties and storage stability, were evaluated. Subsequently, the rheological performance and compatibility of PPA-modified emulsified asphalt at various temperatures were evaluated using a dynamic shear rheometer. Finally, Fourier transform infrared spectroscopy (FTIR) and fluorescence microscopy (FM) were utilized to investigate the effects of PPA modification on the chemical composition and microscopic characteristics of emulsified asphalt. The results indicated that, with increasing PPA dosage, the softening point of modified emulsified asphalt initially decreased and then increased, while penetration and ductility first increased and then decreased, accompanied by reduced storage stability. Furthermore, PPA modification can enhance the high-temperature stability, fatigue properties, and low-temperature performance of emulsified asphalt, but the effectiveness depended on the dosage of PPA. Specifically, optimal compatibility of modified emulsified asphalt was achieved at a PPA dosage of 1.0%. Notably, PPA underwent hydrolysis within the emulsified asphalt system, leading to modification mechanisms distinct from those observed in base asphalt modification. At a PPA dosage of 1.0%, asphalt particles within the emulsified asphalt exhibited the most uniform distribution. Conversely, excessive PPA dosage (e.g., 2.0%) caused significant particle aggregation, consequently weakening the modification effect.