This study investigates the effect of 1% sodium hydroxide (NaOH)-treated and untreated Ronier fibers (Borassus aethiopum) on concrete’s mechanical and durability properties. Ronier fibers were incorporated into concrete at proportions of 0.5%, 1%, and 1.5% by volume. The fibers treated with 1% NaOH underwent chemical modification to enhance their bonding with the cement matrix and improve their durability in aggressive environments. The performance of the concrete was assessed through tests for compressive strength, tensile strength, flexural strength, durability properties such as water absorption, and resistance to sulfuric acid attacks. The results indicated that treatment with 1% NaOH significantly improved the performance of the fibers. Among the variations studied, concrete reinforced with 1% treated fibers demonstrated the best combination of mechanical and durability properties. The treated fibers increased the concrete’s tensile and flexural strength while maintaining adequate compressive strength. Durability assessments showed that 1% treated fibers effectively reduced water absorption and enhanced resistance to sulfuric acid, improving the concrete’s performance in aggressive environments. Although higher dosages of fibers (1.5%) provided better crack control, they slightly reduced workability and compressive strength.