Review: Residual Compressive Strength Analysis of Fiber-Mixed Concrete Exposed to High Temperatures

This study analyzed the high-temperature properties of concrete mixed with polypropylene (PP) and steel (ST) fibers, based on previous research cases. To examine the effects of different fiber types on concrete under high temperatures, fiber-mixed concrete was categorized into PP, ST, and PP+ST fibers, and the target concrete strengths were set at three levels: 40-60 MPa, 60-80 MPa, and 80-100 MPa. The temperature range for analysis was set at 20-900 °C, and the heating rate range was set at 0.5-20 °C/min. The residual strength of concrete exposed to high temperatures was analyzed based on target strengths and fiber types, and the results were compared with the CEB code. Based on the results of thermogravimetric analysis and differential scanning calorimetry, PP fibers were observed to melt at approximately 170 °C and vaporize at 341 °C, forming pores in the concrete matrix, whereas ST fibers underwent decarburization and carbonation at approximately 700 °C. Fiber-mixed concrete categorized by target strength showed that concrete with a target strength of 80-100 MPa had approximately 8% higher residual compressive strength at 600 °C compared with other target strength levels. The residual compressive strength analysis revealed that most concrete samples exhibited residual strength approximately 10%-31% higher compared with the CEB code above 600 °C.