Residual strength and toughness properties of 3D, 4D and 5D steel fiber-reinforced concrete exposed to high temperatures

Abstract

Conventional single-hooked (3D) steel fibers are one of the most widely used fibers to improve the strength, ductility and toughness properties of plain concrete. Recently, multi-hook 4D and 5D steel fibers with modified end geometries have been widely used in concrete applications as an alternative to 3D conventional steel fibers. The primary aim of this study was to compare mass loss, compressive and flexural strength, and toughness capacities of 3D, 4D and 5D steel fiber-reinforced concrete (SFRC) at room conditions and after high-temperature effects. Fibers were added to cement mortars at 0.5% and 1.5% by volume. All specimens were exposed to temperature effects of 300, 500 and 800 °C. According to the results obtained, the residual strength and toughness capacities of control and 3D, 4D and 5D SFRC specimens decreases significantly at 500 and 800 °C. However, when compared to control concrete, 3D, 4D and 5D SFRC specimens have higher residual compressive and flexural strength and residual toughness capacity after high-temperature effects. Furthermore, 5D steel fibers are more effective than 3D and 4D steel fibers to enhance the residual compressive and flexural strength and residual toughness capacity of concrete due to superior end geometry and higher tensile strength. In addition, this increase was more pronounced when the fiber volume ratio increased from 0.5% to 1.5%.