# Phase Separation Study on the Storage of Technically Specification Natural Rubber Modified Bitumen
## 3 Results and Discussion
### Storage Stability of TSNR-Modified Asphalt  
Storage stability of modified bitumen is a major concern for researchers and contractors involved in the production and quality control of asphalt concrete. The issue of storage stability is an important one to address today. Before being used to make asphalt concrete, asphalt is stored at temperatures ranging from 150 to 180 \({}^{\circ}\)C for an extended period. Asphalt concrete requires the stability of asphalt as a binder to produce optimal pavement [51]. The storage stability test of modified asphalt at 160 \({}^{\circ}\)C for 48 h was performed to assess the storage stability of TSNR-modified asphalt according to ASTM D7173. The evaluation was performed as a softening point test at the top and bottom, and the results are shown in Figures 4-6. There is no visible difference between the top and bottom of the TSNR-modified asphalt after the storage stability test. The difference is noticeable when the top and bottom surfaces are pressurized or loaded. The top surface softened with storage time, while the bottom became harder. This indicates that phase separation occurs at high temperatures  
Figure 3: Softening point of TSNR-modified asphalt before storage stability test. and with the length of storage time [21; 48]. The change in hardness of the top surface indicates the accumulation of the TSNR phase with lower density [4; 29; 48]. According to Figures 4-6, the 8%, 10%, and 12% TSNR-modified bitumen had stability issues as the storage time at 160 \({}^{\circ}\)C increased. Storage stability issues were observed in less than 24 h and lasted up to 48 h. The storage instability of TSNR-modified asphalt is caused by phase separation, which forms the polymer-rich phase on one side and the asphalt-rich phase on the other [6; 17; 29]. The worst storage stability of TSNR-modified asphalt occurs at 8% TSNR with a difference in the top and bottom softening point of 20.6 \({}^{\circ}\)C. At 10% TSNR, the difference in softening point decreased to 11.6 \({}^{\circ}\)C and increased again to 18.7 \({}^{\circ}\)C at 12% TSNR. The storage stability of TSNR-modified asphalt is very poor, which is influenced by the compatibility  
Figure 4: Storage stability test of 8% TSNR-modified asphalt. Figure 5: Storage stability test of 10% TSNR-modified asphalt. Figure 6: Storage stability test of 12% TSNR-modified asphalt. between its constituent components. Compatibility between asphalt and natural TSNR is difficult to achieve due to several influencing factors, including the swelling phenomenon of TSNR, the thermal stability of the mixture, density, and viscosity of TSNR [40; 43; 44; 52]. The TSNR swells and absorbs the majority of the maltene fractions (saturate and aromatic). The high concentration of maltene fraction absorbed results in a TSNR phase rich in saturates and aromatics. Finally, the swelling of TSNR causes phase instability, resulting in phase separation [41]. The phase separation of TSNR in asphalt is preceded by coalescence and flocculation phenomena, and the swollen particles will bind to each other to form gel clumps [41; 42]. The illustration of coalescence and flocculation in polymer-modified asphalt can be seen in Figure 7.  
Because of the coalescence and flocculation phenomena, the TSNR phase, which is high in saturates and aromatics, clumps and accumulates larger TSNR gels, increasing molecular weight and decreasing thermal stability. At 160 \({}^{\circ}\)C, the accumulation of large-sized TSNR gel and decreased thermal stability resulted in a faster buoyancy effect for the TSNR phase. Therefore, the TSNR phase with high saturated and aromatic content will be at the top, and the opposite side will form an asphalt-rich phase [6; 39; 41; 43]. The density and viscosity of the components are also important factors in determining how quickly or slowly phase separation occurs. Coalescence and flocculation have an impact on the density and viscosity of TSNR.