Abstract: Through cube compression test, splitting tensile test, and three point bending test, the effects of high replacement ratio of recycled coarse and fine aggregate, and steel fiber content on the mechanical and fracture properties of recycled concrete were investigated. The cube compressive strength, splitting tensile strength, and double K fracture toughness of the sample for 28 d were tested, and the correlation between the basic mechanical properties and fracture properties of recycled aggregate concrete was analyzed. The computational relationships between the initiation fracture toughness, unstable fracture toughness, and splitting tensile strength of steel fiber reinforced concrete with large amounts of recycled aggregate were proposed. The results show that, the compressive strength and splitting tensile strength of recycled coarse and fine aggregate with a mass substitution ratio of 50% replace natural crushed stone and river sand and 1.0% volume fraction of steel fiber reach the highest, reaching 77.12% and 93.97% of those of natural concrete, respectively. After adding 1.0% volume fraction of steel fiber, the unstable fracture toughness of the test block significantly increases, and unstable fracture toughness exceedes that of natural concrete when the recycled fine aggregate content is 50%.

Key words: recycled aggregate concrete, three-point bending beam test, splitting tensile strength, cube compressive strength, initiation fracture toughness, unstable fracture toughness