Measurement and thermodynamic modeling of wax precipitation in asphalt binder

Considering asphalt as a mixed system composed of multiple solid and liquid phases based on the prin-ciple of phase equilibrium and regular solution theory, in this paper, the activity coefficient was used to describe the non-ideality of solid and liquid phases. According to the phase equilibrium equation, mass equilibrium equation, and normalization equation, the solid-liquid fraction under the equilibrium condi-tion was calculated, and then the precipitation temperature of paraffin wax in asphalt and the precipita-tion amount at each temperature were determined. The gas chromatography-mass spectrometry experiment was conducted to measure the paraffinic, naphthenic and aromatic distribution of the asphalt as the input parameter of the prediction model. After the calculation results of the wax precipitation tem-perature (WPT) and wax precipitation curve (WPC) were compared with measured values acquired from experimental methods (viscosity method, Fourier-transform infrared spectroscopy (FTIR) method), it was found that the trend of WPC is approximately similar, but the WPT of the theoretical model was signif-icantly higher than that of FTIR. The authors believe that this was caused by the overestimation of the thermodynamic properties of the aromatic components. After reducing the melting point and enthalpy of the aromatic components to a certain extent, satisfactory results were obtained. (c) 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study considers asphalt as a mixed system with multiple solid and liquid phases and describes the non-ideality of these phases using activity coefficients. By applying phase equilibrium and regular solution theory, the researchers calculated the solid-liquid fraction under equilibrium conditions and determined the precipitation temperature and amount of paraffin wax in asphalt. Gas chromatography-mass spectrometry was used to measure the distribution of paraffinic, naphthenic, and aromatic components in the asphalt. The results were compared to experimental measurements, and adjustments were made to improve the accuracy of the theoretical model.