# Experimental Study on Physical and Rheological Properties of Trinidad Lake Asphalt Modified Binder
## 4 Conclusions  
A comprehensive investigation of TLA-modified binders was presented in this study. The most popular base bitumen with 35/50 grade penetration was modified with five different TLA content in the range of 10% to 50% by weight. The physical and rheological tests were performed in the laboratory to evaluate the relevant properties of TLA-modified binders. The following observations were made as a result of the study:  
* The addition of TLA to the 35/50 base bitumen caused the penetration reduction and the softening point increase, as expected based on previous research. These physical values were proportional to the TLA content of less than 50%. * The penetration and softening point values were not exactly anticipated by the conventional mixture formulas. The calculated penetration values were lower than the measured ones, while the predicted values of the softening point were overestimated. * TLA content of less than 50% caused an increase of the complex modulus (G*) and a reduction of the phase angle (\(\varphi\)) of the base bitumen, indicating that the addition of TLA into 35/50 bitumen results in increased stiffness and elastic response of the modified binder. This also reveals that the TLA-modified binder has a better deformation resistance. * The DSR test revealed an increase of viscosity value at each temperature after the addition of TLA. The higher the TLA content, the stiffer the modified binder, which is compatible with the physical test results. For all binders the complex viscosity (\(\eta^{*}\)) generally decreased with load frequency (\(\omega\)) increase, highlighting that, at the tested temperature, the TLA-modified binders tend towards base bitumen behavior. * The ZSV decrease was observed with a decrease in TLA content and an increase in the temperature. The highest ZSV increase was observed at 40 \({}^{\circ}\)C; more than a two-fold  
Figure 15: ZSV from creep test versus ZSV from the Cross model. ZSV increase was obtained for 10% TLA content and about the three-fold increase for 20% TLA compared to the base bitumen. * Within the diversity of the binders and the test temperature range, the very comparable ZSV values were obtained using both testing methods, i.e., the Cross method and the creep method. This study revealed that ZSV may be reliably determined from either frequency sweeps or single cycle creep tests. * The TLA content added as a modifier in the 35/50 base bitumen should be in the range of 10% to 20% by weight. Higher contents of TLA may make the binder very stiff, which could induce low-temperature cracks in mastic asphalt. * The TLA-modified binders can enhance the deformation resistance of base bitumen by increasing the stiffness and extending the durability of the respective mastic asphalt bridge pavement. The main findings of the current study let us anticipate how the TLA content in base bitumen can improve the properties of an MA mixture to make it more resistant to plastic deformations under heavy traffic. The research results revealed the appropriate TLA content for the 35/50 base bitumen as one of the possible solutions for MA against those reported in the literature, i.e., application of harder asphalt 20/30 or softer asphalt 50/70 with more TLA content (30%). Thus, the supplier and/or contractor can choose the binder (base bitumen and appropriate modification) and, taking into account both technological and economical aspects, use the best composition to achieve a durable MA pavement, resistant to plastic deformations. Further research should include testing the TLA-modified binder properties after short-term aging and long-term aging and finally composing and testing the resultant mastic asphalt mixture to confirm its adequate resistance to plastic deformations. Furthermore, based on the literature, it can be concluded that ZSV is a good parameter of resistance to permanent deformation of conventional asphalt mixtures. However, it has not been studied more extensively in the context of mastic asphalt.