# Phase Separation Study on the Storage of Technically Specification Natural Rubber Modified Bitumen
## 3 Results and Discussion  
Penetration of Technically Specified Natural Rubber (TSNR)-Modified Asphalt before Storage Stability Tests  
Penetration testing is conducted to assess component stability in technically specified natural rubber (TSNR)-modified asphalt prior to storage stability testing. Examining the asphalt's penetration or hardness at the top and bottom of the TSNR-modified sample completes the evaluation. As the TSNR content rises, Figure 1 illustrates how the penetration of TSNR-modified asphalt first declines before trending upward. With an average penetration value of 61 mm, the 8% TSNR-modified asphalt penetration dropped by 12.67%. Additionally, the penetration was increased to 5-8% by adding 10% and 12% TSNR. The change in asphalt hardness after TSNR addition is influenced by the shift in the equilibrium ratio of asphaltene and maltene fractions. Adding a certain amount of TSNR absorbs maltene fraction components such as saturates and aromatics and increases the composition of asphaltene and resin fractions [17; 39; 40]. Resin in the asphalt phase is important in increasing asphalt hardness by forming a stable colloidal structure and improving the compatibility of TSNR and asphalt components [39; 41]. This also increases the elasticity properties of modified asphalt; the binding network becomes stiffer, and the softening point increases [41; 42]. The increased amount of rubber component in modified asphalt was originally believed to absorb more maltene fraction (saturate and aromatic). It correlated with the decrease in penetration of modified asphalt [41; 43]. However, because the addition of TSNR is larger, the asphalt penetration increases more than before. Figure 1 shows that the penetration of modified asphalt increased by 5-8% after adding 10 and 12% TSNR. The increased modified asphalt penetration as TSNR content increases is due to the volume expansion process, also known as the swelling phenomenon, in TSNR. Swelling promotes the formation of TSNR-rich phases, which saturate and aromatize to form a gel, as illustrated in Figure 2. Finally, the large amount of TSNR gel phase will limit the interaction between asphalt components such as asphaltene and resin, affecting the hardness of modified asphalt, making it softer [44]. Figure 1: Penetration of TSNR-modified asphalt before storage stability test. The mechanism of volume expansion or swelling of TSNR into gel shown in Figure 2 occurs in four stages, namely, Stage 1: immersion; at this stage, TSNR is only submerged in asphalt. Stage 2: TSNR volume expansion; at this stage, the TSNR starts to expand by absorbing the maltene fraction (saturate and aromatic) in the asphalt and forming a gel layer. Stage 3: Post volume expansion and beginning of degradation, TSNR swelling continues until TSNR reaches equilibrium. Meanwhile, chemical degradation occurs by breaking the cross-linking network and polymer chains. In addition, molar mass and degree of branching affect the degradation of chemical structure. The swollen TSNR further splits into smaller pieces due to the breakdown of the network structure. Stage 4: TSNR degradation; at this stage, TSNR is degraded into smaller sizes with low molecular weight [45]. In the process of asphalt modification with TSNR, TSNR degradation is very difficult to control; heating at temperatures higher than the melting point of TSNR (130-160 \({}^{\circ}\)C) can accelerate TSNR degradation. As a result, the size of TSNR will be much smaller with lower weight in large quantities, which affects the hardness of modified asphalt to be softer with the penetration of asphalt increasing, indicating an increase in dense proportion [46; 47; 48]. The increase in the amount of TSNR with low molecular weight and the change of TSNR from solid to gel in asphalt forms new properties in the modified asphalt mixture, which should be hard and stiff to be more flexible [41; 43]. This contributed to increased penetration value and decreased viscoelasticity of modified asphalt as the TSNR content increased.