Testing Research On The Fracture Properties Of Fiber Reinforced High-Strength Concrete

With the extensive use of fiber reinforced concrete and the development of structural analysis method, experimental technique, design means, the research on the fracture properties of fiber reinforced concrete has been extensively regarded. As the project supported by the Natural Science Foundation of HENAN Province (0311052800), the following research works have been accomplished in this paper:1 .By the wedge-splitting tensile test on seventy-two specimens of steel fiber reinforced high-strength concrete (HSC) with the size of 200mmxl70mmx 100mm, the impacts of steel fiber volume ratio, notch depth ratio and different types of steel fiber upon the fracture properties, such as critical stress intensity factor (K\c), fracture energy (Gf), critical crack mouth opening displacement (CMODc) as well as critical crack tip opening displacement (CTODc) of HSC have been studied. The correlativity between steel fiber aspect ratio and fracture properties of HSC reinforced with steel fiber has been established. The notch sensitivity of HSC and steel fiber reinforced HSC and the strain field of HSC reinforced with steel fibers ahead of the crack tip have been analyzed. The test results indicated that the addition of steel fiber can significantly improve the fracture properties of HSC. As the increase of steel fiber volume ratio, the fracture parameters of steel fiber reinforced HSC increase differently. In comparison with the milled steel fiber and waved steel fiber, the addition of bowed steel fiber to HSC improves its fractural properties more. The HSC and steel fiber reinforced HSC are all have notch sensitivity. The addition of steel fiber to the HSC has extensively improved the strain filed ahead of the crack tip.2. By the wedge-splitting tensile test on the twenty-four specimens of polypropylene fiber reinforced HSC with the size of 200mmx170mmx 100mm, the impacts of polypropylene dosage upon the fracture properties, such as stress intensity factor, fracture energy, as well as critical crack mouth opening displacement of polypropylene reinforced HSC have been investigated, and the strain field ahead of the crack tip of polypropylene fiber reinforced HSC has been researched. The test results indicate that the addition of polypropylene has no impacts upon the KIC, but increases the GF and CMODc. With the increase dosage of polypropylene, GV and the increment ratio of GF increase respectively, but CMODc decreased, and the varying of increment ratio of CMODc has no disciplinarian, and the influence of strain field ahead of crack tip is small. Polypropylene improves the properties of HSC at the post-cracking zone.3. By the wedge-splitting tensile test on the forty-two specimens of hybrid (steel and polypropylene) fiber reinforced HSC with the size of 200mmx 170mmx 100mm, the fracture properties of hybrid fiber reinforced HSC and the synergy effect on HSC have been investigated.The test results indicate that the addition of fiber has extensively improved the fracture properties of HSC. A positive synergy effect between steel fiber and polypropylene has been observed at low fiber dosage and the synergy effect disappears with the increase of fiber dosage. Steel fiber plays a key role on the improvement of fracture properties of hybrid fiber reinforced HSC. The improvement effect of polypropylene on the fracture properties of hybrid reinforced HSC is small. Bowed steel fiber is more effective on the improvement of fracture properties of hybrid fiber reinforced HSC than other two types of steel fiber.