Previous studies showed that Mg-Al layered double hydroxides (Mg-Al LDHs) had well anti-ultraviolet (anti-UV) aging properties when used in the asphalt materials, but it cannot contribute to improve the self-healing properties to repair cracks caused by UV aging under the microwave radiation. Fe3O4 has well microwave absorption and based on the layered structure and large surface area of Mg-Al LDHs, the primary objective of this work was to synthesize Fe3O4-decorated Mg-Al layered double hydroxides magnetic nanosheets, to envisage that the added bitumen modifier has both enhanced anti-UV aging properties and microwave absorption properties. Three modifiers were obtained by the adhesion of Fe3O4 magnetic particles on the surface of Mg-Al LDHs nanosheets, and named as L1F1 (the mass ratio of LDHs: Fe3O4 = 1:1), L2F1 (the mass ratio of LDHs: Fe3O4 = 2:1) and L1F2 (the mass ratio of LDHs: Fe3O4 = 1:2). Morphology, phase composition, chemical structure, anti-UV aging properties, static magnetic properties and microwave absorption properties of them were detected by different analytical methods. Results demonstrate that all magnetic nanosheets present the ferromagnetic behavior, L2F1 shows the lowest MS value among three types of magnetic nanosheets, and the value increases from 28.67 emug۱ to 56.78 emug۱ with augmented Fe3O4-LDHs ratio. Additions of Fe3O4 significantly enhance the anti-UV aging properties and microwave absorption properties of Mg-Al LDHs. The maximum RL value of L1F2 is recorded as more than two times of that of LDHs, and L1F2 shows the best anti-UV aging properties and microwave absorption properties among all magnetic nanosheets.

Introduction

Layered double hydroxides (LDHs) is a type of multifunctional inorganic supramolecular materials, which is formed by the orderly assembly of positively charged metal cation twodimensional laminate and interlayer anions [1–۳]. The nanometer two-dimensional laminates of LDHs are arranged in a longitudinal order to form a three-dimensional crystal structure, which mainly composed of Mg2+ and other metal cations [4,5]. The chemical formula of LDHs can be represented by [M2+ 1xM3+ x (OH)2] x+(An)x/n- mH2 O, where M2+ and M3+ represent divalent and trivalent metal cations, respectively [6–۹]. Studies have shown that the layered structure of LDHs has well shielding effect on ultraviolet rays, and can effectively improve the anti-ultraviolet (anti-UV) aging properties of the asphalt materials [5,10]. Zeng added 3% of Mg-Al layered double hydroxides (Mg-Al LDHs) into AH-90, AH-90 and SBS modified bitumen as anti-UV aging agent. The comparisons of equivalent brittle point and fatigue parameters showed that LDHs could effectively reduce the photo-oxidative aging rate of bitumen [11]. This is because when ultraviolet light passes through LDHs, the main layer of metal hydroxide can reflect and absorb ultraviolet light for multiple times. To a certain extent, it can also absorb ultraviolet rays, and the physical shielding effect of the layers on ultraviolet rays is dominant.