## 1 Introduction  
In seasonal frozen areas, asphalt pavement will suffer severe freeze-thaw (F-T) damage in the presence of water as well as temperature, which is the accumulation process of microdamage inside the bitumen materials determined by internal and external factors [1; 2; 3; 4]. Under long-term F-T cycles, the asphalt and aggregate surface of asphalt pavement will peel off, and the damage will continue to accumulate, resulting in pavement looseness, peeling, potholes and other degradation [5; 6; 7; 8], and the mechanical behaviours of bitumen are subject to varying degrees of decline. At present, researchers have worked on F-T damage to asphalt mixture mainly by comparing and analyzing various properties of bitumen mix during the action of F-T conditions to explore F-T damage characteristics [9; 10; 11]. [PERSON] et al. [12] studied the effect of the F-T cycle on bitumen mix with dense gradation and gap gradation and discussed the damage principle in the space of the bitumen mix in the whole treatment process. They concluded that bitumen mix with gap gradation has preferable F-T resistance. [PERSON] et al. [13] used diatomite and basalt fiber to improve the performance of asphalt mixture in seasonal freezing areas, analyzed the influence of the F-T cycle on its strength and strain energy through the indirect tensile test, and proposed the stress ratio of the linear zone as well as the nonlinear zone as an evaluation index. [PERSON] et al. [14] used nanomaterials in asphalt mixture for improved freezing and thawing and carried out predictive analysis. [PERSON] et al. [15] adopted interface bonding intensity for the evaluation of the bitumen mix in F-T conditions by considering the bonding of aggregate and bitumen. [PERSON] et al. [16] studied the water stability as well as the permeability of bitumen mix in frozen conditions, and evaluated the degree of correlation using the grey correlation entropy analysis theory, which is important for early water damage and frost damage. [PERSON] et al. [17] proposed a multi-scale mechanical model to link F-T damage with mechanical property damage. Based on the energy damage and cohesion model, the influence of the F-T condition was simulated to evaluate its degree. The above studies mainly characterize the F-T damage for bitumen from the perspective of macromechanical properties; it is difficult to reveal bitumen's F-T damage mechanism. Some researchers began to discuss the frost failure mechanization for bitumen from a meso perspective, as well as via acoustic technology. [PERSON] et al. [18] performed the model reconstruction of bitumen based on CT and DIP, used an indirect tensile experiment for determining its tensile strength, and proposed a research method for an asphalt mixture performance mechanism based on the evolution of pore fractal dimension. [PERSON] et al. [19] analyzed the internal structure through CT images during the whole treatment process, and the results showed that its porosity as well as water content had a good relevance with mechanical strength for bitumen. [PERSON] et al. [20] adopted CT scanning technology to discuss the relationship between micro characteristics and performances for a porous bitumen mix and then quantitatively analyzed their corresponding relationships. [PERSON] et al. [21] discussed the self-similarity of microcrack distribution through the amplitude of acoustic emission signals so as to analyze the damage evolution of the structure. [PERSON] et al. [22; 23] studied the correlation between the acoustic emission (AE) characteristics of asphalt mixture and its damage behavior. [PERSON] et al. [24] used clustering theory for classifying the failure mode of permeable bitumen based on the indirect parameters of acoustic emission signals, namely, RA and AF values. There are some research projects about F-T damage and its attenuation law with asphalt mixtures. However, damage evolution research is not comprehensive and systematic.