Gray correlation entropy analysis of zero shear viscosity and high-temperature rheological parameters of phosphogypsum-modified asphalt

The high-temperature rheological properties of solid waste-modified asphalt are useful indicators for ensuring the effective operation of asphalt pavements, and inhibiting their rutting. However, there are numerous high-temperature rheological indicators, and only a few key indicators of high-temperature properties of solid waste modified asphalt are reported. This leads to a lack of uniformity in the evaluation of high-temperature performance indicators. In this study, the variables that affect the high-temperature parameters of phosphogypsum-modified asphalt were analyzed. Various contents of phosphogypsum (0 %, 4 %, 8 %, 12 %, 16 %, and 20 %) were mixed with 70# asphalt binder to form phosphogypsum-modified asphalt. Penetration, ring and ball tests were applied to describe the conventional high-temperature properties of the phosphogypsum-modified asphalt. Moreover, the rheological properties were determined using temperature sweep, frequency sweep, and multiple stress creep and recovery experiments to determine the complex modulus (G*), phase angle (δ), SHRP rutting (G*/sinδ) and Shenoy rutting (G*/(1−(1/sinδtanδ))) parameters, zero shear viscosity (ZSV), the percent recovery (R), and the nonrecoverable creep compliance (Jnr) of the phosphogypsum-modified asphalt. Further, a gray correlation entropy analysis of ZSV and high-temperature rheological parameters was performed. The penetration of asphalt gradually decreased with adding phosphogypsum while softening point increased. At a constant temperature, the G* of asphalt binders increased with the increase in phosphogypsum content. Additionally, the δ decreased slightly, and the G*/sinδ and G*/(1−(1/sinδtanδ)) increased significantly. The G* increased with the increase in frequency from 0.1 to 100 rad/s. Phosphogypsum improved the R and reduced the Jnr of the asphalt binder. The ZSV fitted by the Carreau and Cross models exhibited a similar trend, indicating that phosphogypsum could improve the ZSV of the base binder. The gray entropy correlation degree between the ZSV and R values at 0.1 and 3.2 kPa, G*/(1−(1/sinδtanδ)), G*/sinδ, and G* were larger than 0.99. In contrast, Jnr exhibited a low correlation was about 0.96. Thus, R and ZSV can be adapted to assess the high-temperature properties of phosphogypsum-modified asphalt.