# Performance of Warm-Mixed Flame Retardant Modified Asphalt Binder
## 1 Introduction  
In recent years, with the rapid development of China's economy, the country's pavement engineering has also developed very quickly, especially in Western China. A large number of roads and tunnels must be built due to complex terrain and geology conditions. At present, asphalt pavement is widely applied in tunnel engineering due to its superior pavement performance. However, because asphalt binder is flammable, it can easily burn in relatively closed tunnels in the event of a fire hazard. In this case, heat can't be expelled fast enough, and the diffuse smoke, in addition to high temperatures and toxic gas, can bring about huge challenges for safe excavation and rescue, thus seriously threatening the safety of human life and property. Furthermore, because of the narrow and closed tunnel space and poor atmospheric conditions, a great deal of heat and harmful smoke is generated in the process of paving construction, which leads to a terrible construction environment in the tunnel and severe damage to the health of on-site construction personnel. It is therefore imperative to carry out research on warm-mixed flame-retardant asphalt technology [1; 2]. Research on warm mix and flame-retardant asphalt technology started earlier in foreign countries. In 1995, warm mix technology was first developed in Europe. [PERSON] and [PERSON] first reported the technology in the German Asphalt Forum in 1997, the First International Asphalt Pavement Conference in 2000, and the Second European Asphalt Conference in Barcelona in 2000 [3]. Subsequently, Europe, Japan, Australia, and the United States began to use warm mix technology on a large scale [4]. In general, warm mix technology includes three major systems: Organic additives,chemical additives, and foaming technologies. Sasobit is a typical viscosity-reducing organic additive, and the related research indicates that Sasobit has good pavement performance. For example, [PERSON] and [PERSON] studied the rheological properties of Sasobit modified asphalt binder at different concentrations [5; 6]. Results show that Sasobit can effectively improve the high temperature performance of the asphalt binder and improve the rutting resistance of asphalt mixtures. [PERSON], [PERSON], and [PERSON] evaluated the CO\({}_{2}\) discharge and heat needed to heat the aggregate and asphalt binder from 25 \({}^{\circ}\)C to the mixing temperature at different Sasobit concentrations. The results show that 1% Sasobit can reduce CO\({}_{2}\) discharge by 3% and energy consumption by 2.8% [7]. [PERSON], [PERSON], and [PERSON] focused on the rheological properties of Sasobit modified asphalt binder and proved that Sasobit could effectively improve the pavement performance of asphalt mixture. In addition, the life cycle of Sasobit modified asphalt binder was evaluated [8]. In some foreign countries, researchers have also focused on flame retardant agents. In 1986, the Asahi Rekisei company in Japan published a patent on the preparation of flame retardant and smoke suppression modified asphalt binder [9]. In 1991, Grube publicized the patent of flame retardant and smoke suppression modified asphalt binder, in which borate was applied as the flame retardant [10]. In 2011, [PERSON] pointed out that the action process of inorganic flame retardants was more complex than that of halogen flame retardants, and the actions were different in different polymers [11]. In 2013, Bonina researched the flame retardant and smoke suppression effects of aluminum hydroxide, and combined it with nano composite adhesives to improve the flammability of asphalt mixtures [12]. Some Chinese scholars have also carried out a series of studies on the warm mixed and flame-retardant asphalt technology. [PERSON] studied the rutting resistance of asphalt mixtures at different conditions, including two kinds of moisture content (0% and 5%) of aggregate, two kinds of mineral powder content (1% and 2%), three kinds of warm mix asphalt (WMA) additives (Sasobit, Evotherm and Aspha-Min), and three kinds of aggregate sources.