Flexural behavior of high-strength reinforced concrete beam with hybrid fiber under normal and high temperature

The low cost of basalt and steel fibers makes their use in enhancing concrete properties very attractive, this paper presents experimental research on the use of Basalt Fibers (BF) and Steel Fibers (SF) and their effect on compressive, tensile, and flexural behavior of reinforced concrete beams under normal and elevated temperatures. Nineteen beams, 114 cubes, and 114 cylinders were tested to find the optimum percentage of fibers. The percentages of BF used were 1%, 2%, and 3.5% by cement weight, while the percentages of SF were 0%, 0.5%, 1%, and 1.5%. Heated samples were subjected to 600 ℃ for 3 hours and left to cool off naturally before testing. The test results show that using BF and SF significantly increased the tensile strength of unheated cylinders, with the optimum fiber content of 1% BF - 1.5% SF achieving an increase of 163% over the control. For heated cylinders, the optimum fiber content was (2% BF - 1.5% SF) achieving an increase of 175%. For compressive strength, enhancement was more modest for most of the fiber content ratios used, and the optimum mix of (1% BF - 1% SF) achieved an enhancement for unheated and heated conditions of 27% and 44%, respectively. Flexural results show that beams employing a mix of 2% BF and 1% SF yielded the most favorable result at normal temperature, enhancing the capacity by 27% compared to the control. While at high temperatures, using an optimum mix of 1% BF and 1.5% SF achieved a 27.2% increase compared to control. The use of BF and SF in concrete has also been proven to increase the ductility of the beams and has moved the failure mode from shear to flexural failure.