Effect of reactive rejuvenators on structure and properties of UV-aged SBS modified bitumen

This paper mainly investigates the effect of the reactive rejuvenator diphenyl methane diisocyanate (MDI) and 1,4-butanediol diglycidyl ether (BUDGE) on chemical structures of aged SBS and rejuvenated structures, rejuvenation mechanisms, physical and rheological properties of UV-aged SBS modified bitumen (SMB). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) show the hydroxyl and carbonyl groups have formed on aged SBS, which indicates that the broken-chain structures of SBS have formed after UV radiation. Meanwhile, the disappeared hydroxyl groups and formed amide bond in FTIR spectrum of MDI rejuvenated SBS, and the associated hydroxyl groups and another appeared carbonyl groups in FTIR spectrum of BUDGE rejuvenated SBS indicate MDI and BUDGE can act as a “bridge” to connect the broken-chain SBS together at 150 °C. Moreover, the performance results show rejuvenation temperature and time have little impact on the physical properties of rejuvenated SMB whatever the rejuvenator is selected. With the increasing content of MDI, the softening point of rejuvenated SMB can be improved and the ductility at low temperature remains almost unchanged. However, the softening point of rejuvenated SMB decreases and the ductility increases as the rising content of BUDGE. Phase angle results indicate MDI can further increase the elasticity of aged SMB, and BUDGE can to some extent restore the viscosity characteristic. From the results of fatigue and rutting performance, 1% BUDGE weakens the fatigue limit temperature of aged SMB from 20.1 °C to 14.9 °C and 1% MDI increases the rutting limit temperature from 79.6 °C to at least 80 °C, which indicates BUDGE and MDI can respectively help improve the fatigue resistance and rutting resistance. Based on the analysis of FTIR spectra and the relative functional group indexes, the results show the increasing concentration of INHCO in MDI rejuvenated SMB and ICOC in BUDGE rejuvenated SMB, indicating the chemical reaction between reactive rejuvenators and aged SMB can be occurred. The rejuvenation of aged SMB with MDI or BUDGE abides by the addition reaction mechanism or condensation reaction mechanism.