STUDY ON EQUIVALENT FRACTURE TOUGHNESS OF RECYCLED STEEL FIBER-REINFORCED CONCRETE BASED ON DIGITAL IMAGE CORRELATION TECHNOLOGY

Recycled steel fiber-reinforced concrete is a new hybrid high performance environmental protection composite material, which can be widely used in the construction industry and provide a new research direction for national green and sustainable development. In this study, three-point bending beams with a prefabricated incision were used to evaluate the fracture performance of plain concrete, steel fiber-reinforced concrete and recycled steel fiber-reinforced concrete with different fiber volume contents, fiber length- diameter ratios and relative incision depths based on digital image correlation technology. The results show that recycled steel fibers can improve the crack resistance of concrete beams better than ordinary steel fibers; The crack resistance of specimens increases with the increases of volume ratio of recycled steel fibers, and when the fiber content is from 0.0% to 1.0%, the increased amplitude of the crack resistance of specimens increases gradually, when the fiber content is from 0.5% to 1.0%, the increased amplitude of the crack resistance of specimens reaches the maximum, and when the fiber content is from 1.0% to 1.5%, the increased amplitude of the crack resistance of specimens decreases; The crack resistance of specimens increases with the increases of length-diameter ratio of recycled steel fibers, and when the fiber length- diameter ratio is from 30 to 50, the crack resistance of specimens increases relatively large, when the fiber length-diameter ratio is from 50 to 70, the crack resistance of specimens increases relatively small; The crack resistance of specimens decreases with the increases of relative incision depth of specimens, and when the relative incision depth is from 0.2 to 0.3, the crack resistance of specimens decreases relatively large, when the relative incision depth is from 0.3 to 0.4, the crack resistance of specimens decreases relatively small; The equivalent fracture toughness of concrete beams does not change with the changes in the relative incision depth. The simulated results correlated well with the experimental results, except some macroscopic phenomena during the cracking process. This study can provide references for the research of fracture behavior of steel fiber-reinforced concrete materials and the recycling of steel wire from waste tires.