Microwave Sensitivity Enhanced Asphalt Mastic with Magnetite Powder and Its Performance after Microwave Heating  
Weixiao Yu  
National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083, China; [EMAIL_ADDRESS] (W.Y. ); [EMAIL_ADDRESS] (L.Z. ); [EMAIL_ADDRESS] (Z.G. ); [EMAIL_ADDRESS] (S.W.) Letao Zhang  
Yinghao Miao  
used for asphalt pavement maintenance and study the effects of microwave heating on asphalt aging. Microwaves are an electromagnetic wave with a frequency of 300 MHz to 300 GHz and a wavelength of 1 mm to 1 m. Microwave heating mechanisms include polarized relaxation loss and conductive loss of materials, and thermal energy is generated by the energy conversion within the electromagnetic field [6]. The microwave sensitivity of materials is closely related to their electromagnetic characteristics and determines the microwave heating efficiency [7]. Furthermore, the matching attenuation features of materials are also important conditions for achieving efficient microwave absorption [8]. Traditional asphalt mixtures have poor electromagnetic wave absorption abilities [9], which limits the application of microwave heating technology in asphalt pavement. Researchers have developed and added various microwave-sensitive additives into asphalt mixtures to improve their microwave heating efficiency, such as silicon carbide [10], activated carbon powder [11], manganese dioxide powder [12], steel wool fibers [13], steel slag [14; 15], magnetite powders [16], and so on. Magnetic powders, with their high dielectric properties, low costs, and high abundance of material, are promising, microwave-absorbing materials and have been widely used in practice [17; 18; 19]. Researchers have achieved abundant results in studying asphalt pavement self-healing (APSH) and de-icing using microwave heating, including the effect of microwave-sensitive additives on APSH [10; 20], the evaluation indicators of APSH [21], the effect of microwave heating modes and time on APSH [22; 23; 24], microwave de-icing mechanisms [25], and microwave de-icing characteristics [26]. Asphalt aging due to microwave heating has also attracted researchers' attention. [PERSON] et al. [27] and [PERSON] et al. [28] found that the physical and rheological properties of asphalt binders cause regression after microwave heating treatment. Microwave radiation also leads to the changing of sulfoxide groups. [PERSON] et al. [29] found that microwave radiation causes a distinct aging impact on binders during the first 10 cycles, after which the values become constant. [PERSON] et al. [30] compared asphalt aging induced by microwave heating to infrared radiant heating through tests of penetration, softening points, and rheological properties. Their results showed that microwave heating has less of an influence on asphalt aging than infrared radiant heating. However, the studies on asphalt aging caused by microwave heating are still insufficient. Little attention has been paid to the high-temperature rheological and fatigue properties of asphalt mastics with magnetite powder after microwave heating, for example. The dynamic shear rheometer (DSR) is usually used to analyze the high temperature rheological and fatigue properties of asphalt binders and asphalt mastics using temperature sweep tests and frequency sweep tests. [PERSON] et al. [31] used temperature sweep tests to analyze the effects of steel slag filler on the rheological properties of asphalt mortar. [PERSON] et al. [32] employed temperature sweep tests to study the influence of four different fibers on the rheological properties of asphalt mastics. [PERSON] et al. [33] adopted frequency sweep tests to study high-temperature rheological properties of crumb rubber modified asphalt binders. [PERSON] et al. [34] investigated the high-temperature rheological properties of amorphous poly alpha olefin (APAO) and ethylene-vinyl acetate copolymer (EVA) compound-modified asphalt via temperature sweep tests and frequency sweep tests.