Thermal effects of asphalt SARA fractions, kinetic parameter calculation using isoconversional method and distribution models

Abstract

To discuss the thermal decomposition mechanism of asphalt materials, the kinetic parameters were calculated and their distribution models were established based on differential scanning calorimetry (DSC) test results of saturates, aromatics, resins and asphaltenes (SARA) fractions in asphalt. Results indicate that the thermal decomposition processes of SARA fractions are accompanied by complicated endothermic and exothermic reactions, and the exothermic reactions are predominant. The DSC curve is shifted to higher temperature when the heating rate is elevated, and the thermal effects, reaction progress and decomposition rate are increased simultaneously. Also, the Friedman–Reich–Levi (FRL) isoconversional method is suitable to calculate the kinetic parameters during the thermal decomposition of SARA fractions. The conversion ratio (α) of each SARA fraction shows obvious effects on the calculated activation energy (E). As the α of each SARA fraction is increased, the calculated E of saturates is more accurate at a lower α at the decomposition stages 1 and 3, but is always accurate at stage 2. Additionally, the calculated E is more accurate at the lower and higher α than that at the middle α at the two decomposition stages of aromatics. The calculated E of resins is fluctuated between 99 and 112 kJ mol−1, and its accuracy is satisfactory. The calculated E of asphaltenes is changed between 8 and 80 kJ mol−1, and is more accurate at the lower and higher α than that at the middle α. Finally, the distributed activation energy models of each SARA fraction are established to provide an insight into thermal decomposition mechanism of asphalt materials.