# Anti-Aging Performance and Action Mechanism of Asphalt Modified by Composite Modification
## 1 Introduction  
As a critical component in road engineering, asphalt pavement directly influences the service life and safety of roads [1; 2]. However, over time, asphalt undergoes aging due to exposure to environmental factors such as ultraviolet (UV) light, oxygen, and temperature variations [3; 4; 5]. This aging process can lead to problems such as the cracking, peeling, and hardening of the pavement, ultimately reducing the road's service life and driving comfort. UV aging, in particular, significantly impacts the physical and rheological properties of asphalt, making it a key focus in asphalt pavement aging research [6; 7]. To improve the aging resistance of asphalt, researchers have employed various modifiers, including chemical and polymer additives. However, the effectiveness of single-modifier treatments is often limited and accompanied by several application issues. These issues are detailed as follows:  
Limited aging resistance: Single anti-aging modifiers generally address only one type of aging mechanism [8; 9; 10]. For example, antioxidants primarily delay oxidative aging, while UV absorbers focus on photodegradation [11; 12]. Consequently, when asphalt is exposed to multiple aging environments (such as UV light, oxygen, high temperatures, and moisture), a single modifier often cannot provide comprehensiveprotection and struggles to address complex aging conditions [13]. This limitation leads to inconsistent performance and difficulty in extending the overall service life of the asphalt in practical applications. Insufficient longevity of anti-aging effects: The effectiveness of single anti-aging modifiers tends to diminish over time. While antioxidants are effective under high-temperature oxidative conditions, they may lose their activity due to volatilization or chemical degradation after prolonged exposure. Similarly, UV absorbers can degrade under extended UV exposure, resulting in a gradual decline in their UV aging resistance. Therefore, the stability of the anti-aging performance of single modifiers is relatively poor over long-term use. Compatibility issues with asphalt: Compatibility between single modifiers and the asphalt matrix is also a critical concern [14]. The dispersion and stability of anti-aging modifiers in asphalt affect their effectiveness. Poor compatibility may lead to phase separation within the asphalt, affecting its uniformity and potentially degrading pavement quality [15]. Commonly used UV resistance modifiers mainly consist of inorganic and organic types of modifiers. For inorganic modifiers, carbon black, nano oxides, layered silicates, and layered dihydroxy composite metal hydroxides (LDHs) are widely used in the UV aging control of asphalt. Inorganic modifiers often have a significant UV resistance effect on asphalt material, especially for LDHs, and the UV resistance performance of asphalt could be improved by about 40% [16]. However, the poor compatibility between inorganic modifiers and asphalt would degrade the UV resistance effect on asphalt substantially [17]. For organic modifiers, light stabilizers and UV absorbers are commonly used modifiers for polymers. Light stabilizers and UV absorbers could eliminate the compatibility issue in asphalt because of their perfect dispersion and stability [18]. But the UV resistance effect of light stabilizers and UV absorbers on asphalt is not stable and the service period could not be guaranteed. Given these issues, composite modification technology has emerged as a research hotspot [19]. By combining two or more modifiers, this approach aims to enhance the mechanical properties, thermal stability, and aging resistance of asphalt more effectively. Through the combination of inorganic and organic modifiers, the disadvantages might be mitigated and the advantages could be improved. Therefore, this study focuses on composite modification technology by selecting hydrotalcite and UV absorbers as anti-aging modifiers. The goal is to clarify their impact on the UV aging resistance of asphalt and understand the underlying mechanisms.