Effect of concentration of polyphosphoric acid on the high and low temperature performance of asphalt

The purpose of this study is to gain a deeper understanding of PPA modified asphalt and to investigate the effect of PPA concentration on the high and low temperature performance of the asphalt. Four different concentration levels of PPA modified asphalt were prepared. The zero-shear viscosity (ZSV) at 60 ℃ was measured using a dynamic shear rheometer (DSR) to evaluate its high temperature performance. The creep parameters were measured using a bending beam rheometer (BBR), and the creep compliance derivative (J′(t)) was calculated based on the Burgers model to evaluate its low temperature performance. The statistical analysis method was used to discuss the significant difference in the effect of PPA concentration on the high and low temperature performances of asphalt. The modification mechanism of asphalt by PPA concentration was revealed using gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The results show that there is a significant difference in the effect of PPA concentration on viscosity. As the concentration increases, the viscosity also increases, leading to a more obvious improvement in high temperature performance. PPA can slightly improve the low temperature performance of asphalt, but the effect of PPA concentration on low temperature performance is not significant. PPA narrows the distribution range of asphalt molecular weight, and a large proportion of small molecular size is converted to medium molecular size, which increases the average molecular weight. There is a good linear relationship between the weight-average molecular weight (Mw) of PPA modified asphalt at different concentrations and the corresponding viscosity value. The glass transition temperature (Tg) of the PPA modified asphalt is slightly lower than that of the original asphalt. However, there is no notable difference in Tg among the PPA modified asphalts at different concentrations. These findings provide valuable guidance for the selection of raw materials for PPA modified asphalt.