Abstract
By synthesizing zinc oxide/expanded vermiculite (ZnO/EVMT) with a modified hydrolytic precipitation method, the composite could remarkably strengthen the resistance of bitumen to thermo-oxidative and ultraviolet (UV) aging. Nonetheless, the microstructure of the composite synthesized using different methods and their effects on microstructure and aging resistance of bitumen have been insufficiently researched. Thus, a modified sol–gel (SG) method and the hydrolytic precipitation (HP) method were used to produce ZnO/EVMT composite (remarked as SG-ZnO/EVMT and HP-ZnO/EVMT respectively) in this study. Then, the effects of two synthesis methods on the microstructure of ZnO/EVMT composite and its corresponding modified bitumen were characterized with a series of experiments, including X-ray diffractometer (XRD), field emission scanning microscopy (FESEM), Fourier transform infrared spectrometer (FTIR) and ultraviolet–visible spectrometer (UV–Vis) tests. Finally, the resistance of the two ZnO/EVMT composite modified bitumen to short-term aging, long-term UV aging and long-term thermo-oxidative aging was evaluated with softening point increment and viscosity aging index. Results indicated that the two methods are feasible to synthesize ZnO/EVMT composite, and ZnO particles in HP-ZnO/EVMT have higher crystallinity and purity with the HP method. Furthermore, HP-ZnO/EVMT has a more homogeneous distribution of ZnO particles, higher UV absorption capacity and better bituminous compatibility than SG-ZnO/EVMT. With the addition of the SG-ZnO/EVMT or HP-ZnO/EVMT into bitumen, intercalated phase structures are formed in the corresponding modified bitumen. Additionally, the ZnO particle composition completely separated with EVMT composition in the SG-ZnO/EVMT modified bitumen, but HP-ZnO/EVMT composite in its corresponding modified bitumen still maintained the original characteristics. Based on the above, bitumen modified by HP-ZnO/EVMT has stronger aging resistance than that of SG-ZnO/EVMT regardless of the aging conditions. Therefore, the HP method is recommended to synthesize ZnO/EVMT composite for bitumen modification.
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