Properties Of Repetitive Aged And Regenerated SBS Modified Bitumen

The SBS modified bitumen aging caused by oxygen, temperature, ultraviolet light and other factors always lead to that many distresses happen on SBS modified bitumen pavement. So the bitumen pavement needs to be maintained, which produces a large amount of reclaimed SBS modified bitumen pavement materials. Regenerating the aged SBS modified bitumen can make the reclaimed SBS modified bitumen pavement materials to be reused. However, the aging will also happen on the regenerated SBS modified bitumen. It will produce a lot of reclaimed SBS modified bitumen pavement materials again when the pavement building with the regenerated SBS modified bitumen reaches its service life. The repetitive regeneration of the aged SBS modified bitumen is very important for solving the problems caused by the RAP materials better, because the materials for road construction such as bitumen and stone are non-renewable resources.In this paper, the aged SBS modified bitumen was prepared under PAV, UV and long thermo-oxidative aging conditions, respectively; and each sample was regenerated with the introduction of CR, RRA and RRB, respectively; next,the regenerated SBS modified bitumen was aged again under the corresponding aging conditions, then the samples were regenerated with the corresponding rejuvenator again, until three times; finally, CR-A-SMB, RRA-A-SMB, RRB-A-SMB, CR-R-SMB, RRA-R-SMB and RRB-R-SMB were obtained through repetitive aging and regeneration. Effect of repetitive aging and regeneration on the physical properties, rheological properties, chemical structure and microstructure of SBS modified bitumen was studied. The main conclusions are as follows:(1)Penetration, ductility and softening point of the SBS modified bitumen decrease while viscosity of that increases after PAV aging, UV aging and long thermo-oxidative aging, respectively. Especially, the ductility of SBS modified bitumen decreases more obviously among the physical properties. The ductility of SBS modified bitumen decreases from 28.5 cm to 1.2 cm, 3.4 cm and 3.3 cm after PAV aging, UV aging and long thermo-oxidative aging, respectively.(2)The physical properties of CR-A-SMB and CR-R-SMB quickly become poor after repetitive aging and regeneration under PAV, UV and long thermo-oxidative aging conditions, especially ductility. Under PAV aging condition, the ductility of the SBS modified bitumen containing CR aged twice and three times is 0.3 cm and 0 cm, respectively. The ductility of the SBS modified bitumen regenerated once, twice and three times with CR is 9.1 cm, 0.9 cm and 0.1 cm, respectively. It also reveals that CR almost has no effect on improving the ductility of the SBS modified bitumen aged twice.(3)Compared with CR-A-SMB and CR-R-SMB, the physical properties of RRB-A-SMB and RRB-R-SMB can be kept well by RRB during the repetitive aging and regeneration process under PAV, UV and long thermo-oxidative aging conditions. Under UV aging condition, the ductility of the SBS modified bitumen containing RRB aged twice and three times is 10.9 cm and 6 cm, respectively. The ductility of the SBS modified bitumen regenerated once, twice and three times with RRB is 34.8 cm,28.2 cm and 16 cm, respectively. Even though the SBS modified bitumen is aged twice, its ductility can be restored to the ductility grade of virgin SBS modified bitumen.(4)Compared with CR, the rheological properties of the aged SBS modified bitumen can be improved more effectively with RRB under both PAV and UV aging condition. And the rheological properties of CR-A-SMB and CR-R-SMB quickly become poor with increasing repetitive aging and regeneration times which tend to be fatigue cracking at low temperature, while RRB-A-SMB and RRB-R-SMB have better rheological properties to avoid fatigue cracking at low temperature.( 5)Fourier transform infrared spectroscopy results reveal that: Fourier transform infrared spectroscopy results reveal that: C=C in the SBS is broken and oxidized to form C=O compounds during the SBS modified bitumen aging. Using RRB to regenerate the aged SBS modified bitumen, ester compounds is generated through the reaction between the compounds with epoxy functional groups in RRB and the oxidative compounds with oxygen-containing group(such as carboxylic) formed because of the degradation of SBS. RRB-A-SMB and RRB-R-SMB has lower C=O and S=O content and higher C=C content in comparison with CR-A-SMB and CR-R-SMB. It suggests that the SBS network structure restored to some extent by the reaction between RRB and the oxidative compounds of SBS lighten the SBS degradation degree during the process of repetitive aging.(6)Fluorescence microscope results further confirm that the reaction between RRB and the oxidative compounds of SBS happens so that some thin and intensive SBS network structure appears in the SBS modified bitumen regenerated with RRB. That can be ascribed to the coupling reaction among the broken SBS chain segments caused by the reaction between the compounds with the epoxy functional groups in RRB and the oxygen-containing groups(e.g. carboxyl) of the degraded SBS chain segments. The compatibility between bitumen phase and SBS phase improves with repetitive aging, and the SBS network structure in the RRB-R-SMB reduces gradually during the process of repetitive regeneration. Even though the aged SBS modified bitumen is regenerated three times with RRB, it still has some SBS network structure.