Abstract：The fracture performance of three-point notched beams of two-grade aggregate concrete reinforced by hybrid steel fiber were tested. The effects of steel fiber volume contents (0.5%, 0.8%, 1% and 1.2%) , the lengths of steel fiber (30 mm, 60 mm) and the water-cement ratio on the fracture properties were studied, including P-CMOD curves, fracture toughness, instability of toughness and fracture energy. The stress-strain relationship for fracture damage of hybrid steel fiber reinforced concrete was proposed based on the damage mechanics theory. The results show that concrete mixed with steel fiber has better ductility than the ordinary concrete. The mixed use of steel fibers with different lengths has effects on the fracture toughness and fracture energy of two-grade aggregate concrete. The optimal combination of concrete with better fracture toughness is suggested as steel fiber mixing amount of 1.2%, long fiber proportion of 50% and watercement ratio of 0.58. The fracture energy can be greatly improved by a desired combination proportion of 1.2% steel fiber mixing amount, 65% long fiber proportion and 0.33 water-cement ratio. The stress-strain model established in this paper is in good agreement with the experimental results.
