Designing high-performance concrete with adequate workability, high mechanical strength, and durability remains a key challenge in precast concrete barrier production. This study investigates the effect of high-carbon steel fibers on the fresh, mechanical, and durability properties of concrete and determines the optimum fiber dosage. Five mixes were prepared, including a reference mix and four fiber-reinforced mixes containing 10, 20, 30, and 40 kg/m³ of fibers at a constant water-to-cement ratio of 0.40. The experimental program included slump, compressive strength, splitting tensile strength, flexural behavior, energy absorption, water absorption, and freeze–thaw scaling resistance in the presence of de-icing salts. Increasing fiber content reduced slump from 65 to 15 mm while maintaining uniformity and constructability. Compared with the reference mix, compressive, tensile, and flexural strengths increased by approximately 34%, 45%, and 80%, respectively. Fiber addition also enhanced first-crack and ultimate loads and post-cracking load-carrying capacity, resulting in a transition from brittle to more ductile behavior. Although fibers had a limited effect on water absorption, they improved resistance to freeze–thaw scaling by controlling crack propagation through the fiber-bridging mechanism. Despite the superior overall performance of the 40 kg/m³ mix, 30 kg/m³ was identified as the optimum dosage considering its comparable performance and economic advantages.