# Effect of Aging and Moisture Damage on Fatigue Cracking Properties in Asphalt Mixtures
## 1 Introduction  
The moisture damage phenomenon that occurs in asphalt pavements is defined as the loss of rigidity and durability due to adhesion and viscosity between the asphalt film. The aggregate of the asphalt mixture is weakened because of the penetration of moisture by precipitation [1]. The moisture damage of asphalt pavement is associated with various common properties, such as bleeding, cracking, plastic deformation, labeling, and potholes. Additionally, it is affected by various factors, such as hydrophilicity of the aggregate, traffic volume and traffic load, pavement design, and construction [2]. The mechanism of moisture damage in asphalt pavement is very complex, and research to identify the factors causing moisture damage is still in progress by various researchers. Various indoor test methods have been developed to simulate the properties of asphalt mixtures for moisture damage. In addition, the effect of aging and also cracking study of asphalt mixtures and bituminous materials has also been investigated in recent years [3; 4; 5; 6; 7]. According to [PERSON] et al. (2000), the tensile strength ratio (TSR) of the asphalt mixture before and after moisture damage prescribed in AASHTO T 283 is the most effective method for understanding the sensitivity of asphalt mixture to moisture damage, which is a representative and simple test method generally applied natively and in other countries [8]. TSR specified in AASHTO T 283 is an evaluation method that compares only the tensile strength of the asphalt mixture before and after moisture damage [9]. Therefore, it cannot be used to determine the mechanical properties of the asphalt mixture and thedirect cause of moisture damage based on the test results, thus limiting the prediction of the service life of pavement owing to moisture damage [10]. In general, the aging of asphalt pavement occurs because of various factors, and the stiffness of the asphalt pavement gradually increases with aging. However, the increased stiffness is inevitably vulnerable to moisture. [PERSON] and [PERSON] (2016) reported that the stiffness of asphalt mixtures with short-term aging (STA) and long-term aging (LTA) increased in the range of 7-54%, and its fatigue life reduced in the range of 70-87% owing to moisture damage [11]. The brittleness of asphalt binder increased with aging, viscous properties of asphalt deteriorated with increased stiffness, and fatigue life decreased owing to the loss of adhesion and viscosity between the aggregate and asphalt binder. [PERSON] et al. (2015) developed a fracture energy simulation model using various aging and moisture damage methods to study the effects of aging of asphalt mixture and moisture on the service life of asphalt pavement. It was observed that the moisture damage was accelerated by the loss of adhesion and viscosity of the asphalt binder due to aging [12]. [PERSON] et al. (2017) predicted the pavement lifespan at the design stage by measuring the dynamic modulus of the asphalt mixture, which is a material property used for mechanical-empirical pavement design before and after moisture damage and reported that moisture damage reduced the fatigue life of the pavement resulting in plastic deformation [10]. Recently, the damage of asphalt pavements in South Korea has increased because of direct and indirect factors caused by abnormal climatic changes, such as torrential rains, prolonged heatwaves in summer, and heavy snowfall in winter, along with the effects of medium and heavy vehicles. Recent pothole damage on national roads increased by more than 1.5 times from 25,231 cases in 2009 to 38,382 cases in 2012. In particular, the number of potholes in Seoul, which is the capital of South Korea, increased by 2.6 times in one year from approximately 30,000 in 2009 to 78,000 in 2010 [13]. Figure 1 shows, for Seoul, the amount of precipitation and the number of days that saw precipitation, compared to the number of potholes over the past 10 years (2010-2020) [14].