# Performance and Mechanism of Asphalt Modified by Butadiene-Rubber
## 1 Introduction  
Asphalt has been widely used as a binder. However, due to the increasing traffic loads and changeable environment, the pavement constructed with virgin asphalt always failed to achieve an expected service life [1; 2]. Therefore, physical modification, chemical modification, or modification combining physical and chemical methods has been the favorable method to improve the road performance and durability of asphalt pavement [3; 4; 5; 6]. A series of physicochemical modification studies have been successively carried out to verify the effect of the modifier on base asphalt and their mechanism. [PERSON] et al. [7] found that Styrene-Butadiene-Styrene (SBS) could improve the high-temperature resistance to rutting, low-temperature crack resistance, fatigue resistance, and water stability of asphalt mixtures. [PERSON] et al. [8] compared the performance of Styrene-Butadiene-Rubber (SBR) modified asphalt with matrix asphalt and SBS modified asphalt. They found that SBR modified asphalt had the highest ductility. [PERSON] et al. [9] discovered that the bitumen binder and mixtures with the addition of Xinjiang rock asphalt were more competent in resisting permanent deformation, fatigue performance, and moisturesusceptibility. [PERSON] et al. [10] found that the aging rate of the rock asphalt modified mixtures was slightly lower by comparing the normalized ratio J'(t) (defined as the changing rate of creep compliance with time) of the mixtures before and after long-term aging. All the results showed that a single modifier improved the performance of asphalt to a certain degree. However, some other properties of asphalt could not be improved only by a single modifier, and the compound modified asphalt should be taken into consideration. As mentioned above, the SBS modified asphalt has lower anti-aging properties due to the presence of unsaturated carbon-carbon double bonds [7]. The anti-aging performance of SBR modified asphalt is lower due to structural instability [8]. The anti-cracking capacity at low temperatures was immolated because of the increased stiffness of rock asphalt modified asphalt [9]. The asphalt used as a binder must be qualified for a wide temperature range, moisture environment, and loading capacity because the service environment of asphalt pavement bears the effects of vehicle loading and environment factors, such as moisture, high and low temperature, simultaneously. Most of the single modified asphalt cannot balance the comprehensive road performance. Thus, it is highly important to finding a better combination of several materials to improve the performance of base asphalt. In this regard, the compound modification method is often utilized to ameliorate the road performance of asphalt from multiple aspects. By adding Nano-clay and SBR, [PERSON] et al. [11] found that the rheological properties of base asphalt increased, and the temperature sensitivity decreased. In order to improve the compatibility, low-temperature, and high-temperature performance of SBR modified asphalt, [PERSON] et al. [12] simultaneously added SBR and PPA to the matrix asphalt. Their results showed that PPA replenished the insufficiency of high-temperature performance and compatibility of SBR powder, and the good low-temperature performance provided by SBR powder was not affected by the addition of PPA. [PERSON] et al. [13] combined the rock asphalt, Nano-silica, and SBS as modifiers, and they found that the compound modified asphalt had outstanding performances. [PERSON] et al. [14] proposed the Nano-silica and rock asphalt modified asphalt. They found that the compound modified asphalt had better rheological performance and effective cost, and the good rheological property was partly attributed to presence of rock asphalt. It can be seen that the compound modification method is an effective way to obtain asphalt binder with good comprehensive performance.