# Evaluation of Short-Term Aging Protocol for Asphalt Mixtures
## 3 Results and Discussion
### Binder Test Results  
Recovered binders were tested to evaluate their rheological properties. Binder testing included rotational viscosity (ASTM D 4402-13, 2013) [35], a performance grading (PG) test (AASHTO T 315, 2012) [36], and multiple stress creep and recovery (MSCR) tests (AASHTO T350, 2014) [37] by a dynamic shear rheometer (DSR). The same tests were also conducted on original binders (OB) and rolling thin film oven (RTFO)-conditioned samples. The binder test results for the unmodified and modified mixtures are summarized in Tables 6 and 7, respectively. The original binder was subjected to RTFO at 163 \({}^{\circ}\)C for 85 min. The RTFO-conditioned samples were tested and compared with those recovered from field and plant mixtures. As can be seen in Tables 6 and 7, the RTFO-conditioned binder closely simulated the binder recovered from mixtures 1-3. It is also noted from Table 6 and Figures 10 and 11 that heating the mixtures for 1.5 h prior to compaction did not affect the properties of the binder much. Therefore, the loose mixtures collected from the field/plant were not subjected to any unwanted additional aging (i.e., minimal heating for warming purpose only) in the laboratory due to handling and processing. Unmodified binders recovered from the field base mixture (mixture 1) had higher viscosity values at 135 and 165 \({}^{\circ}\)C compared with those recovered from the plant wearing mixture (mixture 2). This could be due to the fact that mixture 1 was collected from the construction site, whereas mixture 2 was from the asphalt plant. Hence, the additional time required during transportation and laying of the mixture at elevated temperatures contributed to further aging the binder. In the PG system, a binder is aged in the RTFO and tested in DSR to check its rutting potential. The purpose of the test is to determine the changes that would take place to an asphalt binder after it is subjected to heat and oxygen at the HMA plant and in the paving process. The test is conducted at high temperatures, usually the pavement's maximum temperature. It passes the test against rutting if the value of \(G\)_*sin\(\delta\)_ is greater than 2.2 kPa. The test is conducted at a certain temperature and if it passes at that temperature, then another temperature (generally low to high) is selected and continued until the binder fails the criteria for rutting resistance. The maximum temperature for which the criterion is met is the true-grade high temperature. On the other hand, the RTFO-aged binder is further aged in PAV and tested in DSR at intermediate temperatures to check its fatigue resistance. If the value of \(G\)_*sin\(\delta\)_ is less than 5000 kPa, the binder is believed to perform satisfactorily against fatigue cracking. This test is conducted from high to low until the PG criteria for fatigue (i.e., \(G\)_*sin\(\delta>\)_5000 kPa) is reached. The lowest temperature for which the criterion is met is the true-grade intermediate temperature. Due to aging, the binder becomes stiffer and, hence, the resistance to rutting (i.e., \(G\)_*sin\(\delta\)_) is increased. Here, the true-grade intermediate temperature of the mixture 1 binder increased in comparison with mixture 2, which indicates lesser resistance against fatigue. The MSCR test results also showed a high value of nonrecoverable compliance (J\({}_{\rm nr}\)) for the mixture 2 binder in comparison with mixture 1, which indicates a higher level of aging of the mixture 1 binder. Figure 10: Comparison of viscosity results of unmodified binders recovered from mixture 1.