Property evolution and mechanism of rejuvenated bitumen during rejuvenation and secondary aging based on form and unsaturation of fatty acids

This study aims to evaluate the effects of fatty acids form (FAF) and fatty acids unsaturation (FAU) on the rejuvenation efficiency of rejuvenated bitumen (RB), and to investigate the properties evolution and mechanisms for the RB during rejuvenation and secondary aging mediated by free fatty acids (FFA)-containing rejuvenators. The FAF and FAU of three bio-oils were characterized using chemical structure and composition testing, respectively. The rejuvenation effects of rejuvenator category, dosage, FAF, and FAU on the basic physical properties and rheological behaviors of RB were evaluated through corresponding experimental tests, while chemical composition and structural changes were examined through two chemical characterization methods. Furthermore, the evolution of properties and underlying mechanisms of RB at different FFA-containing rejuvenator dosages during the secondary aging was also explored. Results demonstrated that FFA exerted pronounced rejuvenation effects on the aged bitumen (AB), with high FAU corresponding to greater rejuvenation efficiency. TRBs generally outperformed unaged bitumen in aging resistance, and carboxyl groups outperformed C C bonds in AB rejuvenation. Revealing that the carbonyl groups increased during rejuvenation but fell during secondary aging due to FFA involvement. The variation patterns of the colloidal stability and sulfonyl groups were consistent with most previous studies, and both of them were significantly correlated with the properties of bitumen. The drawn findings of this study confirmed that FFA exhibited prominent rejuvenation efficiency, offering a novel strategy for high-value utilization of waste tall oil from papermaking.