Study on Mechanical Properties and Synergistic Mechanism of Concrete Reinforced with Hybrid Basalt Fibers of Different Lengths

Basalt fiber (BF) is an effective reinforcement for improving concrete’s mechanical properties and crack resistance due to its high tensile strength and bridging ability. To investigate the influence of fiber length combinations on the mechanical performance of concrete, basalt fiber-reinforced concrete (BFRC) specimens were prepared using single and hybrid blending methods. Compressive and splitting tensile tests, scanning electron microscopy, and numerical simulations were conducted to evaluate the effects of fiber content and length hybridization, and analyze the possible reinforcement mechanisms. Results showed that for single-blended BFRC with 18 mm BF, both compressive and tensile strengths peaked at a 0.2% dosage, then declined. Conversely, the strengths of hybrid BFRC continuously increased with fiber content, reaching 33.00 MPa and 2.38 MPa at a 0.3% dosage, significantly outperforming the single-length fiber systems. Microstructural observations and numerical analyses suggested that fibers with different lengths contributed to complementary reinforcement effects during the loading process. The improved performance was attributed to the combined effects of crack bridging and stress redistribution provided by fibers with different lengths.