Influence of zinc oxide/expanded vermiculite composite on the rheological and anti-aging properties of bitumen

Abstract

The bitumen modifier, zinc oxide (ZnO)/expanded vermiculite (EVMT) composite (ZnO/EVMT), was introduced into the bitumen with a dosage of 4%, 5%, and 6%. The surface morphology of EVMT and ZnO/EVMT was characterized by a field emission scanning microscope (FESEM). Further, the Superpave continuous grade of bitumen containing different amounts of ZnO/EVMT was determined by the dynamic shear rheometer (DSR) test and bending beam rheometer (BBR) test. The bitumen samples were aged by thin film oven test (TFOT), pressure aging vessel (PAV) aging test and ultraviolet (UV) aging test, and the influence of different amounts of ZnO/EVMT on both physical and rheological properties of the bitumen before and after aging were investigated. Moreover, the influence of ZnO/EVMT on the molecular distribution during aging was investigated by analyzing the change in the proportion of large molecular size (LMS) obtained from gel permeation chromatography (GPC). The FESEM result shows the ZnO particles are uniformly supported on the EVMT surface. Moreover, ZnO/EVMT slightly influences the high-temperature performance and improves the low-temperature cracking resistance of bitumen. In addition, no matter what aging method is adopted, ZnO/EVMT effectively increases the retained penetration and phase angle aging index, and decreases the viscosity aging index and complex modulus aging index of the bitumen, demonstrating the effectiveness of ZnO/EVMT in both resisting the thermo- and photo-oxidative aging of bitumen. Meanwhile, 6% and 4% ZnO/EVMT exhibit the best inhibitory effect on thermo- and photo-oxidative aging of bitumen, respectively. According to the GPC results, the composite inhibits the transformation of small molecules to large molecules during aging, resulting in a lower LMS increment and better anti-aging properties of the modified bitumen.