Experimental study on the effect of polypropylene fiber on compressive strength and fracture properties of high-strength concrete after elevated temperatures

Polypropylene fibers improve the toughness of concrete and reduce the susceptibility of highstrength concrete (HSC) to high temperature spalling. And the mechanical properties of polypropylene fiber reinforced concrete (PFRC) become important after exposure to high temperatures, especially in situations related to engineering uses or repairing concrete structures damaged by fire. This paper presents an experimental study on the compressive strength and fracture properties of PFRC experiencing different temperatures with different fiber contents and lengths. It was shown that the fracture path of concrete becomes longer after experiencing high temperatures. The rate of debonding of mortar and coarse aggregate increases with the temperature rising. The compressive strength of concrete and the peak load and fracture energy of threepoint bending beams were both increased by the addition of polypropylene fibers at room temperature, and the compressive strength increased with the increase of fiber content. The addition of polypropylene fibers is able to increase the compressive strength of concrete compared to the control group at experiencing temperatures less than 300 oC. The peak forces of the three-point bending of the concrete beams all show a decreasing trend with the increase in the experienced temperature. The initial slopes of the rising part of the force -loading point displacement and force -crack mouth opening displacement (CMOD) curves all decrease with increasing of temperature, and curves gradually become slower. Addition of polypropylene fibers decreases the peak force of concrete after high temperature. There is no significant pattern in the effect of polypropylene fiber content and length on the peak force and fracture energy of concrete threepoint bending beams.