The present study evaluates the effect of ground granulated blast furnace slag (GGBFS) with steel and carbon fibers on concrete’s mechanical properties and durability. To this end, the effect of GGBFS at weight percentages of 30, 40, and 50%, steel fibers at 0.5, 1, and 1.5%, and carbon fibers at 0.2, 0.4, and 0.6% were assessed. Additionally, fresh and hardened concrete densities and fresh concrete slump values were determined. Compressive, splitting tensile, and flexural strengths, as well as an abrasion test (100, 200, and 300 cycles), were used to investigate the mechanical properties of concrete at 28 and 90 days of age. Furthermore, the water absorption percentage of the specimens was evaluated at 90 days. The results indicated that the maximum slump reduction was observed in the specimen with 50% GGBFS, along with 1.5% steel fiber and 0.6% carbon fiber. Specimens containing 50% GGBFS alternative, 1.5% steel fiber, and 0.4% carbon fiber had the highest compressive strength, splitting tensile strength, abrasion resistance, and lowest water absorption percentage. The optimum level of GGBFS, steel, and carbon fibers content in terms of compressive strength, splitting tensile strength, flexural strength, abrasion resistance, and water absorption were found to be 50, 1.5, and 0.4%, respectively. Also, the flexural strengths of the optimal mixing design were 5.62 and 6.12 MPa at the ages of 28 and 90 days, respectively. Moreover, scanning electron microscopy (SEM) was used to characterize the microstructure of concrete containing GGBFS. SEM images of the concrete containing GGBFS revealed dense microstructures

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