# Study on Dynamic Splitting Properties of S-PP Hybrid Fiber Concrete after High Temperatures
###### Abstract
[PERSON] [14] studied the influence of the mixed-use of steel and polypropylene fibers of different specifications on the pore pressure of concrete and believed that adding fine polypropylene fibers could effectively reduce the pore pressure of concrete, improve the spalling phenomenon, and improve the high-temperature burst resistance. Researchers at home and abroad have conducted many experimental studies on the tensile properties of SP-HFRC. Still, the research conditions are mainly in the range of low strain rate. The current uniaxial tensile strength design specifications for concrete structures are based on common strain rate conditions, which cannot meet the requirements of resisting high strain rate loads caused by explosion and impact. It is not safe to take it as the strength reference value of building components. Meanwhile, it is found that there are few reports on the tensile properties of SP-HFRC under the coupling effect of impact load and temperature caused by fire and explosion. It is necessary to further study the dynamic splitting tensile properties of SP-HFRC under impact load after high temperature. For the static tensile test of concrete, because the direct tensile test is difficult to operate, the indirect test method is usually used to measure the tensile properties. The most commonly used is the Brazilian disc test, also known as the splitting tensile test [15]. The dynamic splitting test is based on the static Brazilian disc theory. It uses an SHPB device to obtain the dynamic tensile strength of brittle materials such as concrete under high strain rate. During the loading process, stress concentration is easy to occur at both ends of the specimen, resulting in crushing failure, which will make the measurement results inaccurate. To make the test simple and avoid the unreasonable mode of failure of the force application point first in the loading process, researchers have improved the dynamic splitting test by using the methods of flattened Brazilian disc [16] and cushion [17] which have been better applied. This paper plans to carry out dynamic splitting tests at different temperature levels (25 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 200 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, 600 \({}^{\circ}\)C, and 800 \({}^{\circ}\)C) for SP-HFRC with six different fiber dosage combinations. Taking splitting strength as a measurement standard, this paper studies the change rule of the fiber hybrid effect after high temperatures obtain the optimal fiber dosage combination and sets PC as the control group test. The influence of temperature on dynamic splitting damage of concrete is analyzed from the perspective of dissipative energy. At the same time, the damage variable of dynamic splitting damage of SP-HFRC after high temperatures is defined based on dissipative energy. Combined with physical experiments and numerical analysis methods, the influence of high temperature on the failure forms of SP-HFRC and PC is further analyzed to provide a theoretical basis for the safety evaluation, repair, and reconstruction of tensile failure of SP-HFRC materials after high temperature.