Simulation and investigation of the mild-moderate aging properties of SBS modified bitumen: Physical, microscopic and rheological properties.

Styrene-butadiene-styrene block copolymer (SBS) modified bitumen (SMB) is unable to meet usage requirements after being exposed to sun-light, heat and oxygen. The researches show that it is difficult to restore bitumen effectively when the penetration of the aged bitumen is below 20 dmm. Therefore, the penetration of 20 dmm is taken as the dividing line in this paper. Higher than 20 dmm is considered as mild-moderate aging, while lower than 20 dmm is considered as severe aging. The traditional rotating thin-film ovens (RTFO) and pressure aging vessels (PAV) methods are similar to simulate the aging behavior of the upper layer of bitumen pavement, but they are difficult to simulate the aging in the depth direction of bitumen pavement. In this paper, the aging of the modified bitumen is simulated by extending the aging time and deepening the depth of the aging mold, and then it is graded according to the penetration. We aimed to investigate the differences in physical, microscopic and rheological properties of SMB with including 0 wt%, 1.5 wt%, 2.5 wt%, 3.5 wt%, 4.5 wt% and 5.5 wt% SBS content before and after aging. Through the physical performance, such as penetration, softening point, ductility and elastic recovery, it was observed that a high SBS content leads to strong anti-aging ability. Fourier Transform Infrared (FTIR), fluorescence microscopy (FM), scanning electron microscopy (SEM) and atomic-force microscope (AFM) revealed that a good network structure can be formed through absorbing light components when the SBS exceeds 3.5 wt%. After that, it was found that there is a positive correlation between aromatic index and penetration, as well as a positive correlation between butadiene index and softening point. Additionally, rheological frequency scanning and temperature scanning indicated that the modulus was increased and the phase angle was decreased with increasing SBS content or aging. After aging, the rutting resistance of SMB was enhanced but the cracking resistance was weakened. This research can establish a theoretical support and foundation for the regeneration of the mild-moderate aged SMB. [Display omitted] • The simple method for judging SMB aging degree is further improved. • The physical properties, microscopic properties and rheological properties of mild-moderate SMB are systematically studied. • The aging mechanism of SMB with mild-moderate aging is obtained, which provided a theoretical basis for regeneration. [ABSTRACT FROM AUTHOR]