Thermal-oxidative aging mechanism of asphalt binder based on isothermal thermal analysis at the SARA level

To better understand the thermal-oxidative aging mechanism of asphalt binder at the component level, a new isothermal aging method was developed to discuss thermal behaviors of saturates, aromatics, resins and asphaltenes (SARA) fractions. Volatile constituents released from SARA fractions were identified and the changes in chemical compositions, morphology and elements of SARA fractions were characterized before and after the thermal-oxidative aging. Results indicate that the mass losses of saturates and resins are 2.1% and 0.7%, respectively. However, the aromatics and asphaltenes masses are increased by 2.0% and 5.2%, respectively. Also, endothermic reactions occur in saturates and aromatics, and endothermic and exothermic reactions are basically equivalent in resins, and exothermic reactions occur in asphaltenes. Further, CO, CO2, CH4 and light oxygen-containing compounds are released during the aging of SARA fractions, and short-chain alkanes are generated in saturates. Low molecular hydrocarbons, CO2, and SO2 are emitted, and more aromatic ring products are generated in aromatics. Carboxylic acids, small molecular unsaturated hydrocarbons and SO2 are volatilized, and fused aromatic rings, alcohols and ethers are produced in resins. Unsaturated hydrocarbons are released, and the molecular polymerization becomes obvious in asphaltenes. Additionally, after the isothermal aging, pores or bulges are left in saturates, and obvious folds and pores appear on aromatics. Cluster whiskers, lumps and disordered lamellar layers are observed on resins, and resins and asphaltenes become loose, dry and rough. C element content is increased, but O element content is decreased. Finally, various volatiles are released from SARA fractions at different aging stages. The thermal-oxidative aging of asphalt binder consists of the volatilization of light components and the oxidation of side chains in benzene methyls and aliphatic hydrocarbons, leading to the content changes of SARA fractions in asphalt binder. (C) 2020 Elsevier Ltd. All rights reserved.