## 1 Introduction  
Basalt fiber (BF) is a typical silicate fiber with outstanding high temperature resistance, good compatibility with cement and concrete, superior mechanical properties and high chemical stability [1; 2; 3]. The manufacturing process of BF consumes less energy and no additives, which makes it cheaper than glass or carbon fiber [4]. Basalt fibers have been used as concrete reinforcement due to their superior performance and a lot of research has been conducted on it. As a kind of concrete reinforced composite material, BFRC has higher strength, toughness and better impact resistance than ordinary concrete, because the randomly distributed fibers form networks to hinder the formation and expansion of micro and macro cracks [2; 5; 6; 7; 8]. Therefore, in recent years, the application of BFRC has been expanding continuously, such as underground engineering, protection engineering, etc. With the development of social economy and the expansion of application range, people put forward higher and higher requirements for concrete structures, such as impact, explosion, elevated temperature and other extreme loads on the structure. Heat damage is a common risk to the safety of concrete structure. The mechanical properties and durability of concrete materials after exposure to elevated temperatures will deteriorate [9]. In industrial building fires and nuclear power plant accidents, the structures not only are damaged by high temperatures, but also usually suffer the impact load caused by explosion, collapse of the superstructure, etc. [10]. So the research of the dynamic mechanical properties and constitutive model of BFRC under complex stress after exposure to high temperature is of great significance for the evaluation and repair of the damaged structure.  
Compared with the study on static mechanical properties of BFRC [2; 5; 6; 11; 12; 13], less studies on the dynamic mechanical properties and constitutive model have been conducted, mainly include: [PERSON] [14], [PERSON] [15; 16], [PERSON] [17], [PERSON] et al. [18] studied the dynamic mechanical properties of BFRC, analyzed the influence factors of dynamic strength; [PERSON] et al. [19; 20] studied the fractal characteristics and dynamic characteristics of BFRC exposed to high temperature and analyzed the influencing factors such as strain rate, fiber content, temperature, porosity, etc. [PERSON] [21] and [PERSON] et al. [22]. conducted split Hopkinson pressure bar (SHPB) tests on concrete and analyzed the fractal dimension and energy dissipation of fragments. Whereas the research about dynamic mechanical properties of BFRC under the coupling action of elevated temperature and confining pressure have not been reported. [PERSON] [23], [PERSON] et al. [18] established the BFRC dynamic constitutive model based on SHPB test and ZWT model, but the model needs many parameters to fit the test curve well.  
Therefore, in this paper, a 50 mm split Hopkinson pressure bar (SHPB, produced by Luoyang Liwei Technology Co., Ltd., Luoyang, China) apparatus was used to investigate the dynamic mechanical properties of BFRC with different fiber contents (0.0%, 0.1%, 0.2%, 0.3%, 0.4%), and exposed to different temperatures (20 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, 800 \({}^{\circ}\)C), the factors include strain rate, fiber content, confining pressure and temperature were analyzed based on the test results. A new constitutive model of BFRC which needs few parameters was established based on component combination model.