# Performance and Mechanism of Asphalt Modified by Butadiene-Rubber
## 4 Results and Discussion  
### High-Temperature Performance  
Figure 2 shows the viscosity of BRA and BRA-SBR modified asphalt. As the temperature increases, the viscosity of all modified asphalt samples decreased, but the amplitude reduced. Increasing temperature from 135 to 145 \({}^{\circ}\)C or from 165 to 175 \({}^{\circ}\)C, the viscosity of asphalt modified with BRA and 2% SBR lowered 36.4% and 21.7%. As presented in Figure 2, at different experimental temperatures and SBR contents, the viscosity of asphalt modified with 15% BRA and SBR A was higher than that of BRA and BRA-SBR B modified asphalt. Viscosity is a measure of resistance to flow deformation at high temperatures. The highest viscosity value of BRA-SBR A asphalts meant the best flow deformation resistance among the three modified asphalts. It is well known that the introduction of rock asphalt could notably enhance the high-temperature performance of asphalt systems [6; 27]. Additionally, when BRA was mixed with the SBR A, the high-temperature performance of asphalt would be further enhanced. This could be influenced by the enhanced stiffening properties of the asphalt binder due to the use of SBR A in BRA modified asphalt [19]. The viscosity increased more obviously as the SBR A content increased. Although higher viscosity may cause the increase of the mixing and compaction temperatures during construction, the viscosity measured at 135 \({}^{\circ}\)C could still be in line with the Superpave specification that the viscosity of asphalt binder should be no more than \"3 Pa-s\". However, for the BRA modified asphalt, the use of SBR B caused a slight decrease in the viscosity. The viscosity of BRA modified asphalt was slightly affected by the amount of SBR B. The high-temperature fluidity of BRA modified asphalt was influenced slightly by SBR B. The high-temperature performance of asphalt binders modified with two materials was further compared by the rheological parameters of the DSR test. The phase angle of un-aged specimens is presented in Figure 3, which is usually used for reflecting the viscoelastic characteristics of materials. The smaller the phase angle, the more elastic components and the less viscous components exist in the asphalt. The increase in the elastic portion is more conducive to the enhancement of the deformation resistance capacity [28]. As Figure 3 shows, the mixed addition of 15% BRA and SBR A lowered the phase angel of BRA modified asphalt. The smaller phase angle of compound modified asphalt manifested that the addition of SBR A made it possible for asphalt binder to achieve more elastic recovery when resisting shearing. The increase in the elastic network and reduction in the viscous network increased the high-temperature performance of the asphalt binder. On the contrary, the phase angle curves of SBR B-BRA modified asphalt were located higher than that of BRA modified asphalt. SBR B decreased the elastic property of BRA modified asphalt. Figure 2: _Cont._Figure 3: Phase angle of specimens. (**a**) BRA and BRA-SBR A modified asphalt; (**b**) BRA and BRA-SBR B modified asphalt. Figure 2: Viscosity of specimens. (**a**) BRA and 2%BRA-SBR modified asphalt; (**b**) BRA and 4%BRA-SBR modified asphalt; (**b**) BRA and 6%BRA-SBR modified asphalt; (**d**) BRA and 8%BRA-SBR modified asphalt. Figure 4 shows the variation of the complex shear modulus of asphalt. Both SBR A-BRA and SBR B-BRA compound modified asphalt displayed a rapid decline in complex modulus as the experimental temperature increased, implying the deterioration of high-temperature deformation resistance in asphalt. This may attribute to the reason that asphalt has a transformation from a high-elastic state in low temperature to a high-viscous state in relatively higher temperatures [29]. The raise in temperature caused the volume of asphalt to expand. The spacing of molecules increased, and the random movement of molecules intensified.