# Experimental Study of the Thermal and Dynamic Behaviors of Polypropylene Fiber-Reinforced Concrete
## 1 Introduction
The fibers added to the concrete can significantly influence the performance of the fiber-reinforced concrete when exposed to loadings and high temperatures [12; 13; 14; 15]. Steel fiber, glass fiber, polymer fiber, and basalt fiber are the most commonly used materials for the reinforcement of concrete [29; 30; 31; 32; 33]. Different properties can be introduced by different types of reinforcing fibers [34]. For example, the addition of steel fiber or basalt fiber could improve the concrete's performance, such as its tensile strength, strain capacity, toughness, energy absorption capacity, and so on [35; 36]. Carbon fiber can improve the electrical conductivity, pressure sensitivity, and magnetic sensitivity of concrete [37; 38]. Compared with normal concrete, fiber-reinforced concrete exhibits a high compressive and tensile strength [39; 40], high fracture toughness [41; 42], and high impact resistance [43; 44; 45]. Additionally, due to the superior material properties of fiber-reinforced concrete, it has been widely used in many engineering projects. At present, steel fiber is the most commonly used fiber to add to concrete due to its excellent structural properties [46]. However, the durability properties, particularly the corrosion of steel-fiber-reinforced concrete, are a significant drawback that increases the importance of other types of fibers [47]. However, polypropylene-fiber-reinforced concrete can overcome the drawbacks of steel-fiber-reinforced concrete. Therefore, research about adding polypropylene fibers to concrete has developed rapidly in recent years [48; 49]. As polypropylene is a low-cost material, its addition not only makes concrete more durable, but polypropylene fiber-reinforced concrete is also more economical than other fiber-reinforced concrete [48]. Moreover, polypropylene fiber has a low melting point, so when polypropylene-fiber-reinforced concrete is heated to a high temperature, this fiber would melt and provide pathways for water vaporization. Because of the decrease in inner vapor pressure, the microstructure of the concrete is protected [34]. Meanwhile, after heating, the spalling resistance of the concrete could be improved by polypropylene fiber [50; 51]. Concrete is a kind of non-uniform composite material that is widely used in construction, water conservancy, hydropower, national defense, and other important projects. Due to the different ratios of raw materials and additives, the mechanical and thermal properties of concrete differ under the effect of high temperatures as a series of physical and chemical changes occur inside the concrete. In recent years, many scholars have studied the influence of high temperatures on the dynamic and static properties of concrete and conducted a large number of basic tests, achieving many significant research results. However, these experimental studies mainly focus on ordinary concrete and high-strength performance concrete. However, in practical engineering applications, concrete with a strength grade of C20 to C50 are more widely used. There are few studies on high-performance concrete with medium- and low-strength grades--i.e., a strength grade of C20 to C50, especially under the condition of dynamic loading after being heated to a high temperature. Thus, this research focuses on low-strength HPC. In this study, polypropylene fiber-reinforced high-performance concrete (HPC) was developed and three different strength grades of concrete were made for studying the thermal and dynamic behavior of the polypropylene fiber-reinforced high-performance concrete.