# Evaluation of Short-Term Aging Protocol for Asphalt Mixtures
## 3 Results and Discussion  
### Asphal Mixture Test Results  
The coefficient of variation (CoV = standard deviation/mean) of the complex modulus value was used to evaluate the variability of test data and the repeatability of the testing method. The variability of the dynamic modulus value obtained in this study is shown in Figure 6. In general, 81% of the dynamic modulus values showed CoVs below 10%. Only 4% and 4% of data showed CoVs of 15-20% and greater than 20%, respectively, with the highest CoV value being 23%. According to AASHTO T342-11 (2015) [28], the estimated accuracy of dynamic modulus for two replicates and three LVDTs per specimen was 13.1%. Thus, the test data appeared to be sufficiently consistent and reproducible in this study. Figure 5: (a) Extraction unit and (b) rotavapor setup for recovery of asphalt binder from asphalt mixture. Figure 6: Variability in raw dynamic modulus data. Table 3 shows the summary of average dynamic modulus test results on the base mixture with an unmodified binder (mixture 1) collected from the field and prepared in the laboratory for different aging conditions. As one would expect, the dynamic modulus values increased when the samples were subjected to higher aging temperatures and durations. For example, when the aging duration increased from 2 to 4 h at 135 \({}^{\circ}\)C, the dynamic modulus at 1 Hz frequency increased from 17,416 to 20,677 MPa, 5606 to 7823 MPa, and 622 to 914 MPa for tests at 4, 20, and 40 \({}^{\circ}\)C, respectively. The phase angle had a decreasing trend with the increase in aging duration. However, at high temperatures and very low frequencies (e.g., 0.01 and 0.1 HZ at 40 \({}^{\circ}\)C), there was no clear trend. This could be due to the aggregate interlock effects at high temperatures [33]. A master curve was constructed for each set of specimens at a reference temperature of 20 \({}^{\circ}\)C. The goodness of fit statistics, _Se/Sy_ (standard error of estimate/standard deviation), and coefficient of correlation (\(R^{2}\)) of the master curves were in the range of 0.03-0.09 and 0.98-0.99, respectively. This indicates that the correlation between the laboratory-measured modulus and master curve fit equation was very good and rated as excellent according to the criteria (i.e., \(S_{o}\)/\(S_{y}\) \(<\) 0.35 and \(R^{2}\)\(>\) 0.9) used by [PERSON] and [PERSON] [34]. Field base mixtures and laboratory-prepared mixtures were compared to develop the short-term aging protocol based on dynamic modulus values. Figure 7 shows the comparison between the master curves for field and laboratory mixtures for different aging conditions. For the high-temperature/low-frequency region (right-hand side of the graph), the field mixture master curve lay between the master curves of the laboratory specimens conditioned at 135 \({}^{\circ}\)C for 3 and 4 h (see Table 3 and Figure 7). Therefore, it may seem that the short-term aging protocol for the field loose mixture lay between 3 and 4 h of conditioning at 135 \({}^{\circ}\)C in a forced draft oven. However, it was found that the short-term aging protocol lay between 2 and 3 h for the low-temperature/high-frequency region (see inset photo in linear scale \(|E^{\star}|\) value). For the loose mixtures from the plant (mix 2), a similar increase in the dynamic modulus with an increase in the conditioning time was observed, as shown in Table 4. For the plant wearing mixture, the short-term aging protocol at 135 \({}^{\circ}\)C lay close to 4 h for the high-temperature/low-frequency region (see Table 4 and Figure 8) and between 3 and 4 h of conditioning at 135 \({}^{\circ}\)C for the low-temperature/high-frequency region (see inset photo). \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Mix 1 from**} & & & & & & & \\ \multicolumn{4}{c}{**Site**} & & & & & & & & \\ \hline
**Temp. ** & **Feq. ** & **Feq.