# Effect of Aging and Moisture Damage on Fatigue Cracking Properties in Asphalt Mixtures
## 5 Conclusions  
This study analyzed the effect of aging on resistance to fatigue cracking of asphalt mixtures due to moisture damage and aging. Additionally, the changes in material properties according to the indoor aging process and moisture damage were evaluated for HMA and WMA mixtures prepared with the same grade of asphalt binder at different initial production and construction temperatures. The dynamic modulus and change in the elastic modulus for each mixture were calculated accordingly. To evaluate the effect of aging and moisture damage on fatigue cracking, the experimental coefficient values of the predictive model were calculated for each condition. * The elastic modulus of HMA and WMA mixtures increased with aging. For the HMA mixture, elastic modulus increased by approximately 35% as the aging time progressed from the initial stage, whereas that of the WMA mixture increased by approximately 50%, suggesting that the WMA mixture has a higher sensitivity to aging according to time and temperature;
* The change in elastic modulus induced by moisture damage after aging was analyzed for both the mixtures. It was observed that the value of elastic modulus significantly reduced compared to that before moisture damage. In particular, in the WMA mixture, the initial modulus of elasticity was reduced by approximately 50%, owing to moisture damage. This was because of the initial aging time and temperature considering the nature of the WMA mixture, which required a certain period of time (approximately 48 h) to develop a certain stiffness (elastic modulus). The experimental coefficient values (\(k_{1}\), \(k_{2}\), and \(k_{3}\)) of the fatigue model to predict the fatigue cracking cycles caused by aging and moisture damage after aging of HMA and WMA mixtures were  
Figure 16: Analysis of fatigue effects after moisture damage for each stage of aging according to service period (HMA). calculated and presented for each condition. Additionally, the prediction of fatigue cracking cycles due to aging and moisture damage after aging of HMA and WMA mixtures was conducted through indoor experiments;
* Based on fatigue life prediction results using the coefficient values and tensile strain for each condition through the fatigue test, the fatigue life of the HMA mixture decreased with aging, whereas the fatigue life of the WMA mixture increased with aging;
* The fatigue lives of both the mixtures decreased rapidly after the moisture damage. The fatigue life of the HMA mixture was reduced by 60-70%, and that of the WMA mixture was reduced by 80% or more after moisture damage compared to that before moisture damage. Moisture damage had a greater effect on the change in fatigue life than the aging properties;
* In the HMA mixture, the fatigue life before and after moisture damage decreased as aging progressed, indicating that the effect of aging gradually increased with an increase in the service period. As the service period progressed, it was more vulnerable to fatigue damage caused by moisture such as potholes;
* In this study, short-term and long-term aging were carried out step-by-step, after which it was subjected to water treatment. By this, the moisture damage of the asphalt mixture while it aged was simulated through water treatment. Unlike the water treatment level suggested by AASHTO T 283, the specimen was subjected to water damage in advance while short-term and long-term aging were performed to evaluate the aging and moisture damage according to the common years of packaging. The results of this evaluation revealed that moisture damage in the aged packaging can rapidly shorten its life and cause significant damage. In this study, the material properties of the HMA mixture varied with aging and moisture damage, and the service life of the pavement was reduced by approximately 40-80% on average. In particular, the initial service life was reduced by approximately 70% owing to moisture, while the effect of aging on fatigue life increased with an increase in the service life.