Experimental and numerical investigations on fracture energy of double-helix macro BFRP fiber-reinforced concrete

A novel type of fiber, the double-helix macro BFRP (Basalt Fiber Reinforced Polymer) fiber, has been proposed to effectively increase the cracking, tensile strength, and ductility of concrete. BFRP material offers high tensile strength, good corrosion resistance, and low costs, while the double-helix geometry provides excellent bond-slip performance for the fiber and concrete matrix. This study conducted a series of three-point bending tests to measure the fracture energy of concrete reinforced with double-helix BFRP fibers and analyzed the influences of fiber orientation (aligned fibers and random fibers) on cracking loads, peak loads, flexural strengths, and fracture energy. The test results revealed a significant improvement in the fracture energy of concrete reinforced with double-helix macro BFRP fibers, with aligned fibers showing a 26.4% higher fracture energy compared to random fibers. Additionally, the flexural strength of concrete reinforced with aligned fibers increased by 29.7% compared to random fibers. Finite element models of the three-point bending tests were established using LS-DYNA software, and the concrete model developed by Karagozian & Case, Inc.(K&C) was calibrated based on the fracture energy results to obtain the material model of the fiber-reinforced concrete considering fiber orientation. The errors between the simulated and tested maximum load values for three-point bending tests of plain concrete, FRC, and FRCSS were 8.3%, 4.0%, and 11.4%, respectively, which indicates that the simulation results were found to be in good agreement with the test results. This study provides theoretical foundations and technical support for the practical engineering applications of double-helix BFRP fibers.