## 1 Introduction  
With rapid economic development the transportation industry is gradually evolving and road engineering in China has made significant progress. In road engineering, pavement can be divided into bitumen concrete and cement concrete pavements. Bitumen pavements are widely used on all levels of road surfaces in China because of their advantages, such as comfortable driving and pronounced noise reduction. However, with increasing traffic volume and traffic load bitumen pavements are subjected to a highly complex environment during the service phase and often some unavoidable problems occur, such as cracks, rutting, pits, and loosening, which can reduce their actual service life [1]. Therefore, in recent years, various scholars have applied modified bitumen to the paving of roads to improve the road performance, thus increasing their service life [2]. However, the traditional hot-mix bitumen mixture requires significant energy during construction owing to the high mixing and rolling temperatures and it generates substantial pollution of waste gases and dust, which impacts environmental management. In this context, a warm-mix bitumen technology has been developed and is widely used in all pavement construction projects. The mixing temperature of warm-mix bitumen mixture is lower than that of hot-mix bitumen mixture by approximately 20-40 \({}^{\circ}\)C, which can significantly reduce energy consumption while meeting the road performance requirements of bitumen mixture. It can also reduce polluting gases and dust emissions, significantly improving the construction environment. Thus, it is a typical energy-saving and emission-reducing construction technology [3; 4]. Currently, the commonly used warm-mix bitumen mixture technologies are divided into three categories: foaming technology, chemical additives, and organic additives [4; 5; 6; 7; 8]. The warm-mix modifiers selected for this paper include XT-W3, Evotherm, and Sasobit. Recently, various scholars have studied the addition of warm-mix modifiers to virgin bitumen, which can reduce the construction temperature and energy consumption, protect the environment, and improve bitumen performance. [PERSON] et al. found that Sasobit can reduce bitumen penetration, increase the softening point and rutting factor, and improve the deformation resistance of bitumen [9]. [PERSON] et al. found that Sasobit reduced the mixing temperature of rubber bitumen and improved the water stability, fatigue resistance, and rutting resistance of rubber bitumen [10]. [PERSON] and [PERSON] showed that Sasobit reduced the bitumen viscosity and improved its fatigue resistance [11]. Using Brookfield rotational viscosity, dynamic shear rheology, and bending beam rheology tests, [PERSON] et al. found that Sasobit modifiers can improve the high-temperature stability of bitumen mixtures; however, they harm low-temperature crack resistance [12]. [PERSON] and [PERSON] studied the rheological properties of Sasobit-modified bitumen and found that increasing the Sasobit admixture can improve the elastic properties and permanent deformation resistance of bitumen [13]. [PERSON] studied the effects of different doses of Sasobit, EC120, and Evotherm on porous and highly viscous bitumen pavements, and using dynamic shear rheology and low-temperature small beam-bending tests, they determined that the warm-mix additive improved the high-temperature stability of the bitumen mixture and negatively affected the low-temperature cracking resistance [14]. [PERSON] studied the effect of Sasobit on the rheology and conventional properties of high-viscosity bitumen using dynamic mechanical analysis (DMA), which showed that Sasobit modifiers have an excellent viscosity reduction effect and can increase the softening point and rutting factor and reduce the penetration and ductility indicating that Sasobit can significantly improve high-temperature rutting performance; however, the low-temperature cracking resistance is reduced [15].