###### Abstract  
This study investigates the combined impact of Trinidad Lake Asphalt (TLA) and styrene-isoprene-styrene (SIS) on the performance of PG 64-22 asphalt binder. The study specifically examines how the addition of TLA and SIS affects the stiffness, viscoelastic properties, and ability to resist deformation of the asphalt binder, using the Superpave test method. The findings demonstrate that the addition of SIS improves the ability to withstand deformation, with the best results seen in the mixture containing 20% TLA and 5% SIS. This blend achieves a harmonious combination of stiffness, pliability, and ease of use. Increasing the SIS content to 10% and combining it with a 20% TLA greatly enhances resistance to rutting, but it also decreases workability. In addition, a mixture consisting of 10% TLA and 10% SIS provides excellent resistance to fatigue and possesses viscoelastic properties that are well suited for reducing oxidative aging and cracking. Although SIS typically enhances the performance of binders, an excessive quantity can result in unwanted rigidity, requiring meticulous optimization. The results highlight the importance of customizing TLA-SIS combinations according to specific environmental conditions in order to optimize advantages. Subsequent studies should investigate the prolonged impacts and alternative combinations of additives to further improve the performance of binders. T +
Footnote †: journal: Applied sciences  
feasible. As a result, TLA is commonly mixed with petroleum-based asphalt in specific ratios [3]. Integrating TLA improves the asphalt's capacity to withstand deformation under high temperatures, but it also increases the likelihood of fatigue cracking under lower temperatures, thereby restricting its practicality [4]. In order to resolve this problem, polymers are incorporated into the asphalt mixture. Studies suggest that polymers such as plastomers and thermoplastic elastomers enhance the characteristics of asphalt by decreasing its sensitivity to temperature changes and enhancing its ability to withstand permanent deformation. Although concerns regarding the long-term storage of polymer-modified asphalt were acknowledged in 1978, subsequent field tests, including those carried out in Texas in 1976, demonstrated favorable outcomes [5]. Several polymers, such as styrene-butadiene-styrene (SBS), ethylene-vinyl-acetate (EVA), styrene-ethylene-butylene-styrene (SEBS), polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), have undergone testing in hot asphalt mixtures. These polymers increase the material's ability to withstand changes in temperature and stress caused by traffic, thereby improving important characteristics such as stability, resistance to moisture, and strength against fatigue [6; 7; 8; 9], and out of all polymers, SBS is commonly utilized in asphalt paving because of its dependable performance over a wide range of temperatures [10]. That is why the study investigates the potential use of styrene-isoprene-styrene (SIS) as a substitute for SBS, due to its comparable characteristics as a thermoplastic elastomer derived from petroleum. The primary distinction between SIS and SBS lies in their molecular structure. SIS replaces the butadiene component in the SBS molecular chain with an isoprene component, leading to a chain composed of alternating isoprene and styrene groups. SIS can be categorized as either linear or star-shaped, based on its molecular configuration. SIS possesses enhanced toughness and compatibility with other additives due to the inclusion of a branched methyl group in the isoprene [11]. Therefore, this study involved the combination of a petroleum-based binder, specifically PG 64-22, with Trinidad Lake Asphal (TLA) in ratios of 10% and 20%, as well as the addition of SIS in ratios of 5% and 10%. Prior research [12] has established a maximum threshold of 20% for TLA content and a replacement limit of 10% for SIS, which aligns with similar findings [13].