Endowing Bitumen with Photothermal Coupling Aging Resistance: Lignin/Expanded Vermiculite/Chitosan Composites

Bituminous pavement in service is subjected to multiple environmental factors such as heat, oxygen, and ultraviolet (UV) light, resulting in its continuous photothermal coupling aging behavior (namely, thermal-oxidative and UV aging behavior). Lignin and expanded vermiculite have been proven to heighten the resistance of bitumen to UV radiation or thermal oxidation, but their protection against bitumen aging is not comprehensive. The composite preparation of lignin with expanded vermiculite is expected to yield composites with excellent dispersion in bitumen and a more comprehensive improvement in bitumen aging resistance, but this has not been reported. For reinforcing the photothermal coupling aging resistance of bitumen, this study synthesized a lignin/expanded vermiculite/chitosan composite (LEC) as a modifier and employed an X-ray diffractometer (XRD), a field-emission scanning microscope (FESEM), a Fourier transform infrared spectrometer (FTIR), a UV–visible spectrometer (UV–vis), and static contact angle test to investigate the microphysical structure, morphology, chemical structure, UV absorption capacity, and hydrophilicity of the composite, respectively. Afterward, LEC was applied for bitumen modification, and its enhancing effect on bitumen antiaging properties was assessed using evaluation methodologies including physical property aging index, chemical functional group index, and the percentage of large molecular size (PLMS). The results show that LEC is a composite material formed by mainly coating lignin and chitosan on the surface of expanded vermiculite, which provides a two-dimensional layered structure that blocks heat and oxygen, excellent UV protection, and favorable affinity for bitumen. LEC comprehensively improves the photothermal coupling aging resistance of bitumen. Specifically, after undergoing different aging processes, LEC-modified bitumen (LECB) exhibits the lowest increment in the physical property index, chemical functional group index, and PLMS. This study provides an experimental reference for resisting bitumen aging toward thermal oxidation and UV radiation.