# Experimental Study on Physical and Rheological Properties of Trinidad Lake Asphalt Modified Binder
## 3 Results and Discussion
### TLA Content Effect on Rheological Properties of Modified Binders  
#### 3.2.1 Complex Modulus and Phase Angle  
The plots of the complex modulus (G*) and phase angle (\(\delta\)) versus frequency at test temperature from 40 \({}^{\circ}\)C to 60 \({}^{\circ}\)C and various TLA content levels are shown in Figure 6. The TLA content has a huge impact on stiffness (G*) and viscous response (\(\delta\)) of the modified binders. As expected, the addition of TLA in 35/50 bitumen resulted in increased stiffness of the modified binders. The isothermal curves in Figure 6 clearly show that the TLA content resulted in a vertical shift of the (G*) curve to higher values but without the change of the curve shape. Consistent with trends observed in the viscoelastic response, the (G*) value of the binders increased as the temperature of the test was reduced. The (G*) value at the test temperature in the range of 40 \({}^{\circ}\)C to 60 \({}^{\circ}\)C increased with increasing load frequency. Figure 6 also shows that for all binders the phase angle (\(\delta\)) decreased with increasing frequency, suggesting a more elastic response with loading time decreasing at each test temperature. Moreover, the TLA content in the base bitumen increased the elastic response, as shown by the reduction of the (\(\delta\)) value due to an especially high elastic response in TLA. These characteristics are comparable with those observed in the base bitumen. The complex modulus (G*) and phase angle (\(\delta\)) of the TLA-modified binders versus test temperature are shown in Figure 7. At a specific test temperature, the complex moduli of the modified binders were higher than that of base bitumen. The G* value increased with the increase of TLA content, which reveals that the modified binders had a better deformation resistance. The phase angle decreased gradually with TLA content increasing, showing that at a specific temperature the modified binders with higher TLA content were more elastic than those with lower content. Figure 8 presents the black curves of the TLA-modified binders, i.e., the plots of complex modulus (G*) versus phase angle (\(\delta\)) with no reference to frequency or temperature, used mostly for evaluation of differences in bitumen products. The effects caused by modification are highlighted by this form of presentation. Figure 8 shows that the modified binders have black curves very well comparable to that of the base bitumen; however, none shifted towards a stiffer and more elastic response. Typically, a modified binder has a lower phase  
The measured and calculated (based on the Cross model) data of complex viscosities (\(\eta^{\bullet}\)) versus the angular frequency (\(\omega\)) in the temperature range of 40 \({}^{\circ}\)C to 60 \({}^{\circ}\)C are shown in Figure 9 on a log-log plot. At any frequency, the TLA addition increased the complex viscosity (\(\eta^{\bullet}\)) and the viscosity stiffening effect of TLA depends on the TLA content at a specific temperature. The higher the TLA concentration, the stiffer the modified binder, which is compatible with the physical test results. The plots show that at the specific temperature the base bitumen was similarly frequency-dependent as the TLA-modified binders. For all binders, the complex viscosity (\(\eta^{\bullet}\)) generally decreased with the load frequency (\(\omega\)) increase, pointing out that at the tested temperature the TLA-modified binders tend towards base bitumen behavior. As shown in Figure 9, for the modified binders the slopes of the curves at 50 \({}^{\circ}\)C are flatter comparing to the slopes at 40 \({}^{\circ}\)C and 60 \({}^{\circ}\)C.