Polyphosphoric acid and plasticizer modified asphalt: Rheological properties and modification mechanism

Plasticizers have been proven to be effective in improving the low temperature flexibility of asphalt; however, plasticizer modified asphalts exhibit compromised high temperature stability. In this regard, polyphosphoric acid (PPA) may offer some advantages. This study aims to investigate the conventional properties, rheological behavior, thermal storage stability, and microstructure of plasticizer and PPA (plasticizer/PPA) modified asphalts. The experimental design comprises two plasticizers (dioctyl phthalate (DOP) and trioctyl trimelliate (TOTM)) and four PPA contents (0.5, 1, 1.5, and 2 wt%). The prepared plasticizer/PPA modified asphalts are examined by rotational viscometer, dynamic shear rheometer, bending beam rheometer, thermal storage, and Fourier transform infrared (FTIR) spectroscopy tests. The results show that the high temperature deformation resistance and elastic recovery ability of the plasticizer modified asphalts are effectively improved by the addition of PPA, and the improvement degree is positively correlated to the PPA content. PPA also has a beneficial effect on the low temperature performance of the plasticizer modified asphalts; however, the effect weakens with the PPA content increase. Moreover, the results of Analysis of Variance - Tukey's HSD analysis show that DOP/PPA and TOTM/PPA modified asphalts have significant difference in high and low temperature performance. The results of the thermal storage tests demonstrate that the plasticizer/PPA modified asphalts have excellent storage ability. The FTIR results show that the plasticizers are physically mixed with base asphalt, whereas there is a chemical reaction between PPA and the plasticizer modified asphalts. In general, the preparation process of plasticizer/PPA modified asphalts is simple and they have good comprehensive performance, which illustrate that combined plasticizer and PPA modification is a promising technology.