Workability and Rheological Property Evolution of Active Rejuvenated Styrene–Butadiene–Styrene-Modified Bitumen in the Early Stage

Abstract

To improve the performance of rejuvenated styrene− butadiene−styrene (SBS)-modified bitumen mixture and realize its highvalue recycling, active rejuvenators and biorejuvenators were combined to regenerate the aged SBS-modified bitumen. The effect of active rejuvenators on the workability of active rejuvenated SBS-modified bitumen (ARSMB) was studied; meanwhile, the evolution of rheological properties and chemical structure of ARSMB in the early stage was also investigated comprehensively. The results show that active rejuvenators can lower the viscosity of the rejuvenated binder and improve its workability, which is attributed to the large amount of carbon dioxide produced during the mixing process of reaction regeneration. The complex modulus and rutting factor of ARSMB increase gradually with the extension of curing time, and a higher curing temperature can significantly accelerate this process. In addition, the phase angles of ARSMB at 0 °C decrease by only 1.5 and 2.3°for the curing temperatures of 25 and 50 °C after 15 days, implying that the negative effect on its low-temperature performance is very limited. The analysis of repeated creep recovery performance indicates that the high-temperature deformation resistance and deformation recovery ability of ARSMB would be improved significantly after paving for several days in practice. The infrared spectrum shows that the residual isocyanate rejuvenators would continue to react gradually, and the reaction index decreases sharply in the first few days, then its decrease rate slows down with the extension of curing time, which also confirms the evolution law of rheological properties of ARSMB.

Development on the Rheological Properties and Micromorphology of Active Reagent-Rejuvenated SBS-Modified Asphalt

“…Due to the long-term exposure to high temperature, light, and oxygen, the SBS molecular structure in SBSMA is susceptible to a CC bond breakage, resulting in the formation of polar carboxyl and carbonyl functional groups and polymer radicals . Binary reactive chemical reagents (HMDI and HDE) will be utilized in this study to effectively link the polymer radicals and thus reorganize the SBS molecular structure.…”

“…Due to the long-term exposure to high temperature, light, and oxygen, the SBS molecular structure in SBSMA is susceptible to a C�C bond breakage, resulting in the formation of polar carboxyl and carbonyl functional groups and polymer radicals. 23 Binary reactive chemical reagents (HMDI and HDE) will be utilized in this study to effectively link the polymer radicals and thus reorganize the SBS molecular structure. Figure 2 shows the chemical reactions of HMDI and HDE with the fragmented SBS molecular structure, where (1)−(4) represent the chemical reactions of HMDI with broken chains of SBS, (1) and ( 2) are the hydroxyl and carboxyl group linkage reactions with isocyanate, respectively, (4) represents the reaction of isocyanate with the small amount of water present in aged asphalt, and ( 5) and ( 6) are reactions between the hydroxyl and carboxyl groups attached to epoxy functional groups.…”

Minireview on the Rejuvenation of Aged Styrene–Butadiene–Styrene (SBS) Modified Bitumen: State-of-the-Art and Outlook

“…Relatively, the benzene ring structures in HMDI adversely affected the low-temperature performance. Besides, Cao et al found that the isocyanate reaction was affected by curing time and temperature. Specifically, higher curing temperature and longer curing time could significantly build up the performance of aged SBS modified bitumen.…”

“…Given that different reactive chemicals had different reaction mechanisms and rejuvenation effectiveness, some scholars attempted to add different reactive chemicals to restore the performance of aged SBS modified bitumen. , Due to the findings that MDI and HDI were beneficial to enhance the high-temperature and low-temperature performance respectively, Cao et al applied HDI, MDI, and cashew shell oil to rejuvenate aged SBS modified bitumen. Apart from the addition of similar chemicals, Xu et al applied the compound reactive rejuvenators containing BUDGE and MDI in the rejuvenation of aged SBS modified bitumen because BUDGE and MDI can improve low-temperature cracking resistance and high-temperature rutting resistance, respectively.…”

“…Compared with TDI and HDI, RCERs could more efficiently recover the cross-linking network structure of degraded SBS modifiers and thus better recover the physical properties including the resistance to lowtemperature cracking and high-temperature rutting because of the long flexible chains in RCERs. Furthermore, Han et al 67 synthesized isocyanate terminated long chain active rejuvenators (ITLCARs) including TDI/HDI and HTPB and then combined ITLCARs and aromatic hydrocarbon oil to prepare novel composite rejuvenators (NCRs) to recover the performance of aged SBS modified bitumen, as presented in Figure 10b. The results demonstrated that the molecular weight and physical performance of aged SBS modified bitumen were recovered to the level of virgin SBS modified bitumen by this rejuvenator, and T-HTPB had the better rejuvenation effectiveness in comparison with H-HTPB.…”