# Effect of Aging and Moisture Damage on Fatigue Cracking Properties in Asphalt Mixtures
## 4 Test Results  
### Dynamic Modulus Test Results  
The dynamic modulus master curve was plotted for a reference temperature of 5 \({}^{\circ}\)C in semi-log and log-log scale graphs. The semi-log scale clearly indicates the change in elastic modulus in the low-temperature region, and the log-log scale clearly indicates the change in elastic modulus in the high-temperature region. As the temperature increases, the phase angle master curve first increases and then decreases after a certain temperature. At low temperatures (high loading cycle, high frequency), elastic properties of the asphalt binder are dominant rather than the interlocking of the aggregates. As the temperature increases (low loading cycle, low frequency), elastic properties of the asphalt binder gradually decrease while the elastic properties increase owing to the interlocking between the aggregates resulting in a decrease in the phase angle. In this study, a dynamic modulus  
Figure 7: Curves depicting the changes in dynamic modulus and phase angles according to loading [23]. master curve was prepared using the FlexMAT program presented by the Federal Highway Administration (FHWA). Figures 8 and 9 show the dynamic modulus test results for the HMA and WMA mixtures for each stage of aging. The dynamic modulus increases with aging in both HMA and WMA mixtures. The increase is higher in the WMA mixture than in the HMA mixture because the STA method applied to both the mixtures was different. Thus, the dynamic modulus after STA was higher in the HMA mixture than in the WMA mixture. Even with aging, the elastic modulus of the HMA mixture was consistently higher. The effect of early aging (STA) seemed to have a lasting effect on the WMA mixture compared to the HMA mixture. The dynamic modulus of the HMA mixture increased by approximately 10-35% based on STA at 10 Hz. As aging progressed, the modulus of elasticity increased by approximately 50% with an increase in the temperature or decrease in the loading cycle. However, the modulus of elasticity increased by approximately 20-60% in the WMA mixture at 10 Hz as a result of STA. With an increase in the temperature or a decrease in the loading cycle, the modulus of elasticity increased by approximately 100% or more, indicating that the WMA mixture was more sensitive to aging than the HMA mixture. Thus, the aging effect was accelerated as the initial aging was lower than that of the HMA mixture. This was consistent with the results of the study by [PERSON] et al. (2014), who reported a trend in the difference between HMA and WMA due to early aging, which gradually decreased as aging progressed [PERSON] et al. (2014). Figure 8: Dynamic modulus test results of HMA for each stage of aging: (**a**) dynamic modulus master curve (semi-log scale), (**b**) dynamic modulus master curve (log-log scale), (**c**) phase angle master curve, and (**d**) shift factor. Figures 10 and 11 show the results of the dynamic modulus test conducted on HMA and WMA mixtures after moisture damage for each stage of aging. After moisture damage, the dynamic modulus of the HMA mixture increased by approximately 15-42% at 20 \({}^{\circ}\)C and 10 Hz; however, the size of the overall dynamic modulus was smaller than that before moisture damage. In addition, the increase in the rate of the dynamic modulus after moisture damage on the WMA mixture was approximately 50-100%, indicating that the change in physical properties was larger than that before moisture damage. The WMA mixture also exhibited a lower overall dynamic modulus after the moisture damage than that before moisture damage. In both HMA and WMA mixtures, the change in material properties after moisture damage was greater than that before moisture damage. After moisture damage, the dynamic modulus increased with aging; however, the dynamic modulus after moisture damage was lower than that before moisture damage, suggesting that moisture damage reduced the performance of the material.