## 2 Materials and Methods
### Mixes Performance Tests  
Based on the OBC, other sets of ACW14 mixes were prepared for each RAP content. Mechanical performance tests were performed, namely, resilient modulus (\(\text{M}_{\text{R}}\)), moisture susceptibility, indirect tensile fatigue, and mass loss test. The following sections describe these performance tests in more detail. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Mix Type**} & \multirow{2}{*}{**RAP (\%)**} & \multirow{2}{*}{**NA (\%)**} & \multicolumn{5}{c}{**Modified Binder Content (g/kg)**} \\ \cline{4-9}  & & & **4.5\%** & & **5.0\%** & **5.5\%** & **6.0\%** & **6.5\%** \\ \hline R0 (control & & & & & & & \\ mix) & 0 & 100 & 45.0 & 50.0 & 55.0 & 60.0 & 65.0 \\ R30 & 30 & 70 & 32.3 & 37.2 & 42.3 & 47.3 & 52.3 \\ R50 & 50 & 50 & 23.8 & 28.8 & 33.8 & 38.8 & 43.8 \\ R70 & 70 & 30 & 15.3 & 20.3 & 25.3 & 30.3 & 35.3 \\ R100 & 100 & 0 & 2.6 & 7.6 & 12.5 & 17.6 & 22.6 \\ \hline \hline \end{tabular} Note: RAP consists of a 4.1% aged binder.  
\end{table} 
Table 3: The composition of each mix. The M\({}_{\rm R}\) value demonstrates the reaction of the pavement system to traffic loading [73,74]. Samples were tested for M\({}_{\rm R}\) using the Universal Testing Apparatus (UMATTA), according to AASHTO T 342 method [75] for the five mixes. The samples were kept at 25 \({}^{\circ}\)C for four hours before the test. The M\({}_{\rm R}\) test conditions included the application of haversine loading shape, 1000 N peak loading, 0.1 s loading time, and 3.0 s pulse repetition period. Furthermore, a pavement comes into contact with moisture in many ways, especially in the tropics. Hence, it is crucial to consider the effect of moisture on the design of the pavement. A wet-versus-dry moisture conditioning test is widely used in the laboratory to evaluate moisture susceptibility [76,77]. The TSR is the indicator of the resistance capacity of the sample to moisture damage and was measured according to the AASHTO T 283 standard [78], commonly known as the modified Lottman test. It is defined as the ratio of the indirect tensile strength (ITS) of the samples under wet and dry conditions (TSR = \(\frac{\Pi\text{TS}_{\text{dry}}}{\Pi\text{TS}_{\text{dry}}}\)). In general, a higher TSR value indicates a higher resistance to moisture damage. TSR had an 0.80 minimum requirement [63,79]. Two sets of samples with a height of 63 \(\pm\) 1 mm and a diameter of 101.6 \(\pm\) 0.1 mm were prepared with 7 \(\pm\) 0.5% air voids. The first set of samples (3 out of 6 samples) was classified as a controlled (dry) subset, while the others were classified as a conditioned (wet) subset. The dry subset was immersed in water at 25 \(\pm\) 0.5 \({}^{\circ}\)C for 2 h \(\pm\) 10 min. Conversely, the wet subset was immersed in a hot water bath at 60 \(\pm\) 1 \({}^{\circ}\)C for 24 \(\pm\) 1 h and then kept in another bath for 2 h \(\pm\) 10 min to maintain the temperature at 25 \(\pm\) 0.5 \({}^{\circ}\)C. All samples were tested using the Marshall apparatus to determine the ITS value at a given distortion rate of 50 mm/min at 25 \({}^{\circ}\)C. The TSR was calculated as the wet subset's ITS value ratio to the dry (control) subset's ITS value. It was also imperative to determine the fatigue characteristics of pavement materials due to the fact that fatigue failure is one of the major asphalt distresses as a result of exhausted traffic loading and environmental impact [80]. Indirect tensile fatigue testing is an effective method that can be performed either under a controlled stress (more acceptable for thick pavement layers) or control strain (more acceptable for thin pavement layers). In this study, the controlled stress (while the strain values were changeable) was used according to the BS EN 12697-24:2018 standard [81]. The major test conditions included the temperature, loading force, loading shape, loading time, and rest time at 25 \({}^{\circ}\)C, 2600 N, haversine, 0.1 s, and 0.4 s, respectively.