# Effect of Aging and Moisture Damage on Fatigue Cracking Properties in Asphalt Mixtures
## 4 Test Results
### Analysis of Fatigue Effects Due to Aging and Moisture Damage  
The concept of fatigue damage was used to determine the effect of aging and moisture damage on the fatigue damage of HMA and WMA mixtures due to aging. The lifespan was predicted based on the change in elastic modulus and tensile strain of the asphalt mixtures as well as the fatigue cracking model equation, and the degree of fatigue cracking damage was determined based on the predicted lifespan. The fatigue life (\(N_{f}\)) of the asphalt pavement was evaluated by assessing the fatigue cracking performance based on the elastic modulus and coefficient determined through the fatigue cracking resistance test. The damage (D) occurring in the asphalt pavement can be defined by Equation (5) based on Miner's rule.  
\[\text{D }=\frac{N_{fi}}{N_{f}}, \tag{5}\]  
where D is the fatigue cracking damage, \(N_{f}\) is the baseline fatigue cracking cycles of asphalt pavement, and \(N_{fi}\) is the fatigue cracking cycles of asphalt pavement with aging and moisture damage.  
In this study, the fatigue cracking cycles for each condition were determined using the coefficient values selected from the previously selected prediction model for the allowable fatigue cracking cycles. Figure 16 shows the fatigue effect of the HMA mixture before and after moisture damage as a function of aging time. As mentioned above, the analysis of the WMA mixture before and after moisture damage was excluded from this study because of its behavior that is different from that of the HMA mixture according to aging time. As a result of analyzing the effect of fatigue damage on HMA mixture under STA conditions, the fatigue life gradually decreased with aging that reduced by approximately 40% after 10-15 years of service life. However, the fatigue life was rapidly reduced after moisture damage during the first stage of LTA, which was 4-5 years of service life, showing a  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Coefficients**} \\ \cline{2-4}
**Mix** & \(k_{1}\) & \(k_{2}\) & \(k_{3}\) \\ \hline HMA\_STA\_FT & \(7.04\times 10^{1}\) & 1.80 & 1.28 \\ HMA\_LTA1\_FT & \(6.03\times 10^{1}\) & 1.80 & 1.28 \\ HMA\_LTA2\_FT & \(3.39\times 10^{1}\) & 1.85 & 1.28 \\ HMA\_LTA3\_FT & \(1.89\times 10^{1}\) & 1.90 & 1.28 \\ WMA\_STA\_FT & \(8.94\times 10^{-1}\) & 2.05 & 1.28 \\ WMA\_LTA1\_FT & \(3.61\) & 1.99 & 1.28 \\ WMA\_LTA2\_FT & \(9.78\) & 1.92 & 1.28 \\ WMA\_LTA3\_FT & \(1.42\times 10^{1}\) & 1.92 & 1.28 \\ \hline \hline \end{tabular}
\end{table}
Table 8: Fatigue cracking prediction model coefficients of HMA and WMA mixtures after moisture damage for each stage of aging.  
reduction of 70% compared to the 100% fatigue life in the initial stage. As the service period progressed, the fatigue life due to aging gradually increased while the change in fatigue life due to moisture damage gradually decreased. Although moisture damage had a dominant influence on fatigue life in general, the effect of aging gradually increased as the service period progressed. In the first stage of LTA (4-5 years), the factors affecting the fatigue life were associated with aging by approximately 20% and moisture damage by approximately 55%; in the second stage of LTA (7-8 years), aging accounted for approximately 25%, and moisture damage accounted for approximately 50%; in the third stage of LTA (10 years or longer), aging and moisture damage accounted for approximately 40%. Thus, it was observed that the effect of aging was more significant than the effect of moisture damage as the service period progressed.