Investigation of aging behaviors of asphalt under the coupling conditions of salt and water

The thermal-oxidative aging of asphalt is extensively researched in recent years. However, the aging behavior of asphalt in salt and water environment receives less attention. A virgin asphalt binder was treated by various coupling conditions of salt and water in this work aiming at understanding the aging behaviors, and then the physical indexes, rheological parameters, chemical structures, four fractions and contact angles of asphalt before and after aging were measured to evaluated the effects of different aging environments on the physicochemical properties of asphalt. Results indicate that the aged asphalt has higher softening point and complex modulus while lower penetration and phase angle in comparison with unaged asphalt, implying the asphalt becomes harder and more brittle after aging. Although asphalt aged in salt and water conditions exhibits similar changes in macro-properties to thermal-oxidative aged asphalt, the analysis of chemical composition indicates that the aging of asphalt under salt and water environment is caused by unique inducements, which can be divided into two parts, that is, separating out of aromatics and saturates from asphalt by combined action of salt out and emulsification, and increasing of asphaltenes and resins caused by oxidation. These two factors work together leading to the change of colloidal structure and finally cause the deteriorate of macro-properties. Besides, the results of contact angle test indicate the increasing polar functional groups resulting from aging enhance hydrophily of asphalt and increase the possibility of water to enter the interior of asphalt, exacerbating the performance degradation of asphalt.