Research On The Fracture Performance Of Self-compacting Concrete Reinforced By High Volume Steel Fiber

Steel fibers are mainly used to reinforce the strength and toughness of self-compacting concrete. Previous studies always focused on self-compacting concrete reinforced by ordinary steel fiber, and the steel fibers adopted are mainly in the length of 15~35mm, slenderness ratio of 40 to 65 and volume content of less than 1.5%. Ordinary steel fibers have a certain degree of improvement to the strength and toughness of self-compacting concrete. But the increase range is limited, which can be formulated by adjusting the mixing ratio of the ordinary self-compacting concrete with the same strength grade. In addition, when the fiber volume content exceeds 1.5%, the fiber dispersion is deteriorated, the mixing becomes difficult, clumping emerges, and the mobility reduces, leading to the hard achievement of self-compacting, and the continued improvement to the basic performance of the material is difficult to be achieved.Based on fracture mechanics crack resistance enhancement mechanism, and on the premise of meeting the self-compacting concrete work, the paper proposed a research methods of rigid fiber-modified cement-based composite materials, achieving high steel fiber content which can hardly be achieved in traditional steel fiber reinforced self-compacting concrete and thus obtaining a high-content fine flat steel fiber reinforced self-compacting concrete(SFRSCC), which owns a high strength and high toughness properties. The fracture performance tests were conducted focusing on the susceptibility defects caused by high-strength characteristics. That is to say, the presence of a high-strength material with early cracks may lead to the doubling of its imperfection sensitivity due to its high strength advantage. The paper, on the basis of a lot of workability and basic mechanical properties test, uses three-point bending notched beams to study the static fracture properties. The conclusions are as follows:①Based on the mechanisms in fracture mechanics, the SFRSCC mixture owns a good workability. When the steel fiber volume content is 6%, the slump extension of the SP of the fine straight steel fiber reinforced self-compacting concrete mix exceeds 600 mm, and the steel fibers were uniformly distributed in the mixture without aggregate accumulation phenomenon. And the mixture is of excellent segregation performance with the screen residue of 1.3%. Saying the gap for steel is about 3 × 40 mm, when the volume content is 0 to 3.0%, the parameters H2 / H1 can reach more than 90%. When the volume content of 4.5% to 6.0%, there will be a slight accumulation phenomenon.②Compared with those of the referencing C40 and C50 concrete, the mechanical properties of SFRSCC were improved with the increase of the fiber volume content. When the fiber volume content reaches 6%, C40 group(A group) SFRSCC cube compressive strength increased by 111.4%, the flexural strength increased by 214.2%, the splitting tensile strength increased by 133.2%, the compressive elasticity modulus increase by 13.1%, the bending elasticity modulus increase by 9.3%, the first crack strength increased by 217.1%, the equivalent flexural strength increased by 1083.3%, and the bending toughness ratio increase by 300%; C50 group(B group) SFRSCC cube compressive strength increased by 73.0%, the flexural strength increased by 143.2%, the splitting tensile strength increased by 173.6%, the compressive elasticity modulus increase by 16.5%, the bending elasticity modulus increase by 9.8%, the first crack strength increased by125.0%, the equivalent flexural strength increased by 1080.3%, and the bending toughness ratio increase by 264.7%.③The three-point bending notched beams fracture tests showed that, in the same presplit case, compared with C40 and C50 concrete, the average effective fracture height of C40 group(A group) SFRSCC increased by 51.8%, the fracture toughness average increased by 193.7%, initial fracture toughness average increased by 139.6 %, unstable fracture toughness average increased by 195.7%, the maximum load point displacement average increased by 1002.4%, the fracture energy gain ratio the average increased by 23.0. The average effective fracture height of the C50 group(B group) SFRSCC increased by 102.6%, the fracture toughness average increased by 236.5%, the initial fracture toughness average increased by 98.1%, unstable fracture toughness average increased by 285.6%, the maximum load point displacement average increased by 1071.1%, the fracture energy gain ratio the average increased by 23.37. When the fiber layer ≥60mm, the effective crack length(ac) with increasing fiber layer thickness slow growth and stabilized, reaches 1/3 of the beam height(including pre-crack length). Fracture toughness values have stabilized. The SFRSCC specimen of P-CMOD curves and load-displacement curves showed significant plastic behavior. Plain self-compacting concrete drops rapidly after the peak load curve, lose carrying capacity. The SFRSCC not only have non-linear elastic stage, after the peak load has a long plastic stage. Curve declines, the crack stable extension have a long time, the crack tip opening displacement increase significantly, with high toughness properties.④By using ANSYS finite element analysis software, it is concluded that the fracture toughness value and fracture toughness value increase with the fiber layer thickness, which is consistent with the change, verifying the accuracy of the gap trabecular of fracture toughness.In conclusion, compared with the ordinary self-compacting concrete, the working performance and mechanical performance of the high volume ratio of steel fiber reinforced self-compacting concrete designed in the experiment are excellent, which owns a broad application prospect.