Amirkabir University of Technology Amirkabir Journal of Civil Engineering 2588-297X 56 9 2024 11 21 The effect of hybrid fibers with various dimensions on the impact strength of concrete containing mineral additives The effect of hybrid fibers with various dimensions on the impact strength of concrete containing mineral additives 1079 1102 5505 10.22060/ceej.2024.23050.8097 FA Ahmad Ramazani Department of civil engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran Maysam Samadi Department of civil engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran 0000-0003-4485-4174 Mohammad Fayyaz University of Imam Hussein (AS), Tehran, Iran Journal Article 2024 03 12 <span style="letter-spacing: .05pt;">Improving the mechanical characteristics of concrete as the most basic material in the construction of various structures, especially its tensile, bending, and impact resistance, has long been the focus of various researchers. In this research, the effect of adding different steel fibers along with polypropylene fibers in different dimensional ratios together with commonly used mineral additives to improve the impact resistance of concrete has been investigated. The considered parameters included the percentage of polypropylene and steel fibers, the ratio of length to diameter of steel fibers (L/D), the percentage of fly ash, microsilica, and epoxy additives, and the age of the specimen. Experiments aimed at determining the impact, tensile, bending, and compressive strength of the studied concrete specimens were carried out. To determine the impact resistance, a new laboratory method was introduced and used. The results obtained from the strength of concrete samples at different ages of 7, 28, and 90 days show the significant effect of using composite fibers with optimal aspect ratio on increasing the tensile and impact resistance and to a lesser extent on the compressive and bending strength of concrete. These values have increased by 23% for tensile strength and 11% and 18% for compressive and bending strength, respectively, compared to the control sample in 28-day samples. Also, it was observed that the use of mineral additives is more effective in increasing the flexural strength of concrete than the use of fibers. A comparison of samples with L/D ratio of different steel fibers showed that fibers with a lower L/D ratio lead to greater improvement in the mechanical properties of concrete. Finally, using combined fibers with optimal L/D and mineral additives has increased the impact resistance and energy absorption by 4.97 times of the optimal concrete samples compared to the witness concrete sample.</span> <span style="letter-spacing: .05pt;">Improving the mechanical characteristics of concrete as the most basic material in the construction of various structures, especially its tensile, bending, and impact resistance, has long been the focus of various researchers. In this research, the effect of adding different steel fibers along with polypropylene fibers in different dimensional ratios together with commonly used mineral additives to improve the impact resistance of concrete has been investigated. The considered parameters included the percentage of polypropylene and steel fibers, the ratio of length to diameter of steel fibers (L/D), the percentage of fly ash, microsilica, and epoxy additives, and the age of the specimen. Experiments aimed at determining the impact, tensile, bending, and compressive strength of the studied concrete specimens were carried out. To determine the impact resistance, a new laboratory method was introduced and used. The results obtained from the strength of concrete samples at different ages of 7, 28, and 90 days show the significant effect of using composite fibers with optimal aspect ratio on increasing the tensile and impact resistance and to a lesser extent on the compressive and bending strength of concrete. These values have increased by 23% for tensile strength and 11% and 18% for compressive and bending strength, respectively, compared to the control sample in 28-day samples. Also, it was observed that the use of mineral additives is more effective in increasing the flexural strength of concrete than the use of fibers. A comparison of samples with L/D ratio of different steel fibers showed that fibers with a lower L/D ratio lead to greater improvement in the mechanical properties of concrete. Finally, using combined fibers with optimal L/D and mineral additives has increased the impact resistance and energy absorption by 4.97 times of the optimal concrete samples compared to the witness concrete sample.</span> https://ceej.aut.ac.ir/article_5505_07ff46bb6597a4f81eed4f59360ff835.pdf