In this study, the mechanical properties and durability of Forta-Ferro fiber-reinforced concrete containing compressed nylon waste were investigated. To this end, a total of 126 specimens were prepared with different percentages of Forta-Ferro fibers and compressed nylon waste, and then, the concrete properties, including compressive strength, elastic modulus, tensile strength, water absorption, porosity, as well as fracture mode were evaluated. Moreover, prediction models were proposed to predict the mechanical parameters of concrete in terms of compressed nylon content and fiber volume fraction. The results demonstrated that the mechanical properties of concrete are improved by adding Forta-Ferro fibers to the mixes while the replacement of nylon waste aggregates with natural sand reduces the concrete mechanical properties. The compressive strength of fiber-reinforced concrete decreased by 14–18% and 21–29%, respectively, when 5 and 10% nylon were substituted as compared to that of the corresponding mixes without nylon. In addition, adding a fiber volume fraction of up to 1% to mixtures with 0, 5, and 10% nylon waste increased the tensile strength by 27, 37, and 49%, respectively. The highest amounts of water absorption and porosity occurred in a specimen containing the highest compressed nylon content and fiber volume fraction, with an increase of 108 and 103%, respectively, compared to those of the reference concrete. Finally, using the response surface method (RSM), an optimal solution was proposed for the design parameters by maximizing the compressive and tensile strengths of concrete containing compressed nylon waste and Forta-Ferro fibers, in which the optimal percent volume of Forta-Ferro fibers and nylon waste was determined to be 0.37 and 5.7%, respectively.
