# Phase Separation Study on the Storage of Technically Specification Natural Rubber Modified Bitumen
## 1 Introduction  
Asphalt modification with polymer addition has long been an important material for road construction [1; 2; 3]. This process significantly enhances the binding properties of asphalt, reduces rutting on the road at high temperatures, increases flexibility on the road at low temperatures to reduce cracking, improves durability, and increases the binding capacity of asphalt to aggregate [2; 3; 4]. Polymer-modified asphalt is a widely used material for road construction and maintenance around the world. This method has proven effective and efficient in improving the performance and durability of asphalt pavements. In the United States and Sweden, waste rubber, such as scrap tires or recycled rubber, is the preferred polymer raw material for producing high-quality polymer-modified asphalt [5; 6]. In Europe, elastomer polymers such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and ethyl vinyl acetate (EVA) are used [7]. Asian countries, such asChina, Thailand, Malaysia, Vietnam, and Indonesia, primarily use elastomeric polymers, specifically natural rubber. Natural rubber is derived from the sap of the rubber tree (Hevea Brasiliensis). This plant is widely grown in Southeast Asian countries including Thailand, Indonesia, Vietnam, and Malaysia. Rubber trees produce rubber latex, also known as latex. Late is a raw material used to make a variety of rubber products, including lump, technical specification, and crepe rubber. A variety of natural rubbers can be used as raw materials for asphalt modification [4; 8; 9; 10]. The utilization of natural rubber as an additive to enhance the quality of asphalt or asphalt modified with natural rubber demonstrates remarkable performance and suitability. Increased asphalt hardness, decreased temperature sensitivity to prevent putting, increased flexibility to prevent cracking, and increased asphalt binding to aggregate to prevent raveling are the most significant enhancements [4; 11; 12; 13; 14; 15]. Natural rubber was chosen as an additive to improve asphalt quality based on several considerations, including its abundant availability in Indonesia, the stickiness and plastic properties of natural rubber are also good, and the price is economical enough to reduce the production cost of natural-rubber-modified asphalt. Polymer-modified bitumen, a crucial component in road construction, must possess favorable storage stability in order to maintain its quality as a binder material [16]. Therefore, the storage stability of polymer-modified asphalt has long been studied, but not all cases can be resolved [16; 17]. This might make it harder to use polymer-modified asphalt in the long term. Polymer-modified asphalt does not store well because the polymer and asphalt do not mix well and have very different densities. Because polymer-modified bitumen is unstable when stored, it will separate into a polymer-rich phase and an asphalt-rich phase on one side [16; 17; 18; 19]. Phase separation in polymer-modified asphalt is a complex process that is influenced by many factors, including gravity, diffusion, density, viscosity, and temperature [6; 20; 21; 22]. Phase instability issues with natural rubber as an asphalt modifier have been identified in multiple studies as being nearly as prevalent as those with other polymer-modified asphalt. Phase instability of asphalt mixtures modified with polymers during storage at high temperatures is the source of the issue. The specifications were satisfied by the asphalt modified with 5% cup lump, which indicates that the mixtures of cup lump and asphalt were uniform, stable, and well dispersed following treatment at elevated temperatures. With a higher cup lump content, however, the difference in softening point after storage was quite substantial for the modified bitumen (10 and 15%). According to this finding, phase instability in the mixture is induced when the cup lump content is increased as an asphalt modifier [23; 24; 25].