Hybrid effect of basalt fibers and carbon fibers on concrete mechanical and environmental properties

• Investigates synergistic effects of basalt and carbon nanofibers in concrete. • Response surface technique models the impact on mechanical properties. • Optimal fiber mix enhances compressive strength by 34.58 %. • Eco-efficient mix reduces embodied carbon while improving durability. • Contributes to sustainable concrete solutions for modern engineering demands. In recent years, the construction industry has actively pursued novel materials to improve the efficiency and long-term viability of concrete. In this research synergistic effects of basalt fiber (BF) and carbon fibers (CF) have been investigated on the mechanical and environmental properties of hybrid fiber reinforced concrete (HFRC). The incorporation of hybrid fibers is crucial as it combines the beneficial properties of different fiber types, leading to improved mechanical performance, durability, and reduced environmental impact. Response surface technique (RSM) was used to construct models for each response containing two independent variables BF (0 ≥ 1.5 %) and CF (0 ≥ 0.5 %). There were seven different dependent variable including compressive strength (CS), split tensile strength (STS), flexural strength (FS), modulus of elasticity (MOE), ultra-sonic pulse velocity (UPV), embodied carbon (EC) and eco-strength efficiency (ESE). For each response predictive models were developed. Significant improvements were observed in concrete by the synergistic effect of BF and CF. Optimal percentage of fibers in concrete was found as 1.5 % of BF and 0.5 % of CF resulted in improving the CS, STS, FS, MOE, and UPV by 34.58 %, 30.57 %, 19.025 %, 19.11 % and 20.95 % respectively. It was evaluated that increasing the CF content in concrete results in amounting the EC. Concrete mix containing 1.5 % of BF and 0.3 % CF was found as most eco-efficient mix among all other proportions. This research contributes to a growing body of knowledge aimed at developing high-performance concrete materials that meet modern engineering demands while addressing environmental concerns.