Concrete based on high-strength and high-toughness steel fibers and preparation method thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to concrete based on high-strength and high-toughness steel fiber and a preparation method thereof.The concrete comprises cement, a composite active admixture, fine aggregate, coarse aggregate, modified steel fiber, a composite admixture and water, and the concrete is prepared through the specific proportion and the optimized forming technology; the composite active admixture is prepared by mixing silica fume, metakaolin and limestone micro powder and modifying the mixture with a nano silicon source, and has excellent activity and nucleation effect; the surface of the modified steel fiber is coated with a nano SiO2 / graphene composite layer, so that the interface bonding strength with a matrix is remarkably improved; and the composite admixture synergistically improves the fluidity, the early strength and the fiber anchoring capability. Through the synergistic effect of the components, the toughness and fracture energy of the concrete are greatly improved while the high strength of the concrete is ensured, and the concrete is suitable for the high-requirement structural fields such as high-performance bridges, tunnels and anti-seismic components.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a concrete based on high-strength and high-toughness steel fibers and a preparation method thereof. BACKGROUND

[0002] Ordinary concrete is prone to cracking due to its brittleness, insufficient tensile strength and toughness, which limits the durability and safety of the structure. Therefore, the existing research generally adopts fiber reinforcement to improve its performance. Among various types of reinforcing fibers, steel fibers have been widely used due to their high strength and high elastic modulus, which have outstanding performance in improving the crack resistance, impact resistance and ductility of concrete.

[0003] However, the existing steel fiber reinforced concrete still has many shortcomings: firstly, conventional steel fibers have limitations in strength and toughness. When subjected to high load or bending, the fibers are prone to breakage or pullout, resulting in unstable reinforcement effect; secondly, the bonding performance of the steel fiber and the cement matrix interface is insufficient, especially when the fiber surface morphology is single or the processing technology is poor, the interface is prone to slip, and the bridging effect of the steel fiber cannot be fully utilized; thirdly, when a high dosage is used, the steel fibers are prone to agglomeration and uneven distribution, affecting the workability of the concrete, and even leading to local strength degradation.

[0004] In addition, steel fiber reinforced concrete often needs to balance between high strength and high toughness in practical applications. Although traditional steel fiber reinforced concrete can improve the toughness to a certain extent, its improvement effect is limited for high-strength concrete systems, especially in ultra-high performance concrete (UHPC), high-strength bridge structures or seismic components, it is still difficult to meet the energy dissipation and ductility requirements of the structure under extreme loads. On the other hand, some high-performance steel fibers have deficiencies in preparation cost and process complexity, which restricts their large-scale application in engineering.

[0005] In summary, although the steel fiber reinforced concrete in the prior art has made some progress in improving toughness and strength, it still faces the following problems: insufficient fiber strength and toughness, leading to unsatisfactory reinforcement effect under complex stress environment; poor interface bonding performance, and the bridging effect of the fiber is not fully utilized; poor fiber dispersibility, easy to agglomerate and reduce workability; at the same time, in high-strength concrete systems, the fiber reinforcement effect is limited, and it is difficult to meet the requirements of high strength and high toughness.

[0006] Therefore, there is an urgent need for a concrete system based on high-strength and high-toughness steel fibers and a preparation method thereof to significantly improve the toughness and crack resistance while ensuring the high strength of the concrete, so as to meet the needs of future large-scale infrastructure, seismic structures and durable engineering. SUMMARY

[0007] The application aims to provide a high-strength and high-toughness steel fiber based concrete and a preparation method thereof, and to solve the problems of the existing steel fiber concrete in strength, toughness, interface adhesion and construction performance by improving the fiber performance and dispersion mode, so as to realize the excellent toughness and crack resistance of the concrete under high-strength conditions and meet the application requirements in complex engineering environments.

[0008] In order to achieve the above-mentioned purpose, the application provides the following technical solutions.

[0009] The first aspect of the application provides a high-strength and high-toughness steel fiber based concrete, which comprises the following raw materials in parts by mass: cement 360-420 parts, composite active admixture 90-120 parts, fine aggregate 650-720 parts, coarse aggregate 950-1050 parts, modified steel fiber 40-70 parts, composite admixture 5-12 parts, and water 135-165 parts.

[0010] Further, the composite active admixture is prepared by mixing and modifying silica fume, metakaolin and limestone powder in a mass ratio of (3-4):(1-1.5):1.

[0011] Further, the composite active admixture is prepared by the following method:

[0012] (1) mixing and stirring silica fume, metakaolin and limestone powder to obtain a premixed powder; mixing nano-silica sol and a Ca(OH)2 saturated solution to obtain a modified liquid containing SiO2 / Ca(OH)2; 2+ (2) spraying the modified liquid onto the premixed powder, stirring, then drying to constant weight, sieving, and obtaining the composite active admixture.

[0013] (2) spraying the modified liquid onto the premixed powder, stirring, then drying to constant weight, sieving, and obtaining the composite active admixture.

[0014] Further, the mass fraction of SiO2 in the nano-silica sol is 12%-16%.

[0015] Further, the molar ratio of Si:Ca in the nano-silica sol and the Ca(OH)2 saturated solution is 1.2-1.5:1.

[0016] Further, the mass ratio of the modified liquid to the premixed powder is controlled at 0.15-0.20:1.

[0017] The composite active admixture is prepared by mixing silica fume, metakaolin and limestone powder and then modifying. The silica fume is a high-activity superfine powder with high silica content and large specific surface area, which can generate C-S-H gel by secondary reaction with Ca(OH)2 generated in hydration, thereby significantly improving the compactness and impermeability of the matrix. The metakaolin contains a large amount of active Al2O3 and SiO2, which can quickly participate in the pozzolanic reaction in an alkaline environment, consume Ca(OH)2 to improve the stability of the hydration product, and generate additional hydrated aluminosilicate phase to improve the early strength. The limestone powder itself has good filling effect and nucleation effect, which can improve the fluidity of the slurry and the compactness of the aggregate interface transition zone, and to a certain extent, react with aluminate to generate stable hydration products.

[0018] The present application uses nano-silica sol and Ca(OH)2 saturated solution to modify the mixture of the three, so that a small amount of C-S-H seeds are deposited in situ on the surface of the powder. These nanoscale nuclei can act as nucleation centers during concrete mixing and early curing, accelerating the hydration reaction rate and promoting the generation of more C-S-H gel, thereby effectively improving the early strength and long-term compactness of the concrete.

[0019] Further, the modified steel fiber is prepared by the following method:

[0020] (1) Select a steel wire with a tensile strength ≥ 2500 MPa and an elongation after fracture ≥ 4%, cut it into a length of 10-15 mm and a diameter of 0.15-0.25 mm, and then immerse the chopped wire in a 5%-10% dilute hydrochloric acid or dilute sulfuric acid solution to remove the surface oxide layer and form a rough surface, then rinse it with deionized water until it is neutral, and dry it to obtain a steel fiber;

[0021] (2) Put the steel fiber into a coating liquid mixed by nano-silica sol and graphene dispersion liquid at a volume ratio of (3-5):1, and stir to form a SiO2 / graphene composite layer on the surface of the steel fiber;

[0022] (3) Heat the coated steel fiber to 500-600℃, keep it at this temperature for 30-60 min, and then cool it to obtain the modified steel fiber.

[0023] Further, the SiO2 mass concentration in the nano-silica sol in step (2) is 20%-30%, and the graphene mass concentration in the graphene dispersion liquid is 0.1%-0.5%.

[0024] Steel fiber in concrete mainly plays a role in bridging micro-cracks, inhibiting crack propagation and improving toughness, but ordinary steel fiber often has problems such as insufficient adhesion with the matrix, easy pull-out and uneven distribution in use, resulting in unstable reinforcing effect. The modification process of pickling and roughening the surface of the steel fiber, coating a nano-SiO2 / graphene composite layer and heat treatment makes it exhibit better interfacial bonding and reinforcing effect in concrete. The SiO2 / graphene composite layer forms a dense and uniform nano-scale coating on the surface of the steel fiber, in which the silicon dioxide can react with the Ca 2+ The chemical action occurs to generate calcium silicate hydrate, enhancing the chemical bonding; graphene has high strength and high specific surface area, which can further improve the mechanical properties and durability of the coating. After heat treatment, the coating is more firmly combined with the steel matrix, ensuring that the fiber does not easily peel off during service, and the adhesion between the coating and the cement matrix is further strengthened.

[0025] Through the modification measures of the present application, the bridging capacity of steel fiber in concrete is significantly enhanced, the pull-out resistance and energy dissipation capacity are greatly improved, and the development of cracks is effectively delayed; at the same time, the interface between the modified steel fiber and the matrix is dense, reducing the probability of fiber pull-out, so that the fiber can fully play the role of crack resistance and toughness improvement.

[0026] Further, the composite admixture is compounded by polycarboxylate superplasticizer, aminopropyl triethoxysilane and lithium sulfate, and the mass ratio is 1:(0.04-0.10):(0.20-0.45).

[0027] The composite admixture of the present application is compounded by polycarboxylate superplasticizer, aminopropyl triethoxysilane and lithium sulfate. The polycarboxylate superplasticizer has a main chain of acrylic acid polymer and a side chain of polyether, which can disperse cement particles through electrostatic repulsion and steric hindrance, reduce particle agglomeration, and make the system have good fluidity and workability at a lower water-binder ratio. Aminopropyl triethoxysilane is easily hydrolyzed to form silanol groups in cement paste, which further condense to form Si-O-Si or Si-O-Ca bonds, which can form stable chemical bonding with the surface of cement hydration products, and the amino group can react with the surface of steel fiber, thereby improving the interfacial adhesion strength and enhancing the anchoring effect of the fiber in the matrix. Lithium sulfate can be quickly dissolved to release Li + ions to promote the hydration of C3S, accelerate the generation speed of C-S-H gel and shorten the early hardening time. The compounding of the three can ensure the fluidity of concrete while improving the interfacial bonding between steel fiber and matrix, and significantly improve the early strength and structural density of concrete.

[0028] The second aspect of the present application provides a preparation method of the above-mentioned concrete based on high-strength and high-toughness steel fiber, comprising the following steps:

[0029] (1) mixing cement, composite active admixture, fine aggregate and coarse aggregate to obtain premix;

[0030] (2) dissolving composite admixture in water to obtain admixture solution;

[0031] (3) mixing the premix with the admixture solution and stirring uniformly to form slurry;

[0032] (4) adding modified steel fiber to the slurry and continuing to stir to obtain fresh concrete;

[0033] (5) forming and curing the fresh concrete to obtain the high-strength and high-toughness steel fiber-based concrete.

[0034] Compared with the prior art, the advantages and beneficial effects of the present application are:

[0035] Compared with the prior art, the concrete system of the present application significantly improves the mechanical properties of the material while maintaining good construction performance. First, the composite active admixture uses a synergistic system of silica fume, metakaolin and limestone powder, and through chemical deposition treatment of nano-silica sol and Ca(OH)2, C-S-H crystal nuclei are generated in situ on the surface of the powder, significantly accelerating the hydration reaction and improving the matrix density and early strength. Second, the steel fiber is modified by three-step modification process of acid pickling, nano-SiO2 / graphene composite coating and heat treatment, which improves the surface activity of the fiber and the interfacial bonding force with the matrix. Third, the composite admixture introduces three components of polycarboxylic acid water reducer, silane coupling agent and lithium sulfate, which has the functions of dispersion, adhesion enhancement and early strength improvement, so that the fluidity and structural stability of the concrete are optimized simultaneously. In summary, the present application realizes comprehensive improvement in compressive strength, crack resistance and fracture toughness, and is particularly suitable for engineering application scenarios with high strength bearing and high toughness requirements. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] The raw materials used in the embodiments are ordinary commercially available products unless otherwise specified, and the following sources are exemplary.

[0038] Cement was purchased from Shanshui Cement Group P.O 42.5R; fine aggregate was purchased from Huaxin Cement (Chibi) Co., Ltd., fineness modulus 2.3-3.0; coarse aggregate was purchased from Huaxin Cement (Chibi) Co., Ltd., particle size 5-25 mm; silica fume was purchased from Jiangxi Kete Fine Powder Co., Ltd., 325 mesh; metakaolin was purchased from Jiangxi Kete Fine Powder Co., Ltd., 1250 mesh; limestone powder was purchased from Jiangxi Kete Fine Powder Co., Ltd., 325 mesh; nano-silica sol was purchased from Jicang Nanotechnology Co., Ltd., average particle size 20 nm, SiO2mass concentration 25%; graphene was purchased from Jicang Nanotechnology Co., Ltd.; polycarboxylate superplasticizer was purchased from Shanghai Lücheng New Material Co., Ltd., P550 polycarboxylate superplasticizer.

[0039] Example 1

[0040] The present embodiment provides a kind of concrete based on high-strength high-toughness steel fiber, including the following raw materials by mass fraction: cement 360 parts, composite active admixture 120 parts, fine aggregate 660 parts, coarse aggregate 1000 parts, modified steel fiber 45 parts, composite admixture 6 parts, water 150 parts.

[0041] Wherein, composite active admixture is prepared according to the following method:

[0042] (1) silica fume, metakaolin, limestone powder are respectively dried in electric heating air drying oven at 105 DEG C for 4h, and cooled to room temperature for standby use;Silica fume, metakaolin, limestone powder are mixed in a mixing machine at a speed of 60 rpm for 5 min, to obtain uniform premix powder.

[0043] Preparation of modified liquid: take nano-silica sol, and the amount of SiO2 is 1.5% of the mass of premix powder, the silica sol is added into Ca (OH) 2 saturated solution, and the molar ratio of Si: Ca is adjusted to 1.3:1, to obtain the modified liquid containing SiO2 / Ca 2+ .

[0044] (2) the premix powder is put into a high-speed mixer, and the stirring speed is set to 300 rpm. Under the stirring state, the modified liquid is uniformly sprayed into the powder through a spraying device. After spraying, continue to stir for 5 min, and the liquid-solid ratio is controlled at 0.18:1. The material is in the form of slightly wet sand. Then the material is evenly laid on a stainless steel tray and placed in a hot air circulating drying oven at 60 DEG C for 8h. The dried material is crushed by a crusher and sieved through a 300 mesh sieve to obtain the composite active admixture.

[0045] Modified steel fiber is prepared according to the following method:

[0046] (1) Select the cold-drawn low-carbon steel wire with tensile strength of about 2600 MPa and elongation of about 4.5%, cut it into 12 mm long chopped wire on a wire cutting machine, and control the diameter to be 0.20 mm. The obtained chopped wire is placed in a polypropylene acid-resistant tank, 7% hydrochloric acid solution is added, and soaked for 8 min to remove the surface oxide layer and form a rough microstructure on the surface. After taking out, rinse with a large amount of deionized water until the solution pH is about 7, and place it in an electric heating air drying oven at 105°C for 2h to obtain a surface roughened steel fiber.

[0047] (2) Take the nanometer silicon dioxide sol (SiO2 mass concentration 25%, average particle size 20 nm) and graphene water dispersion (graphene mass concentration 0.2%), mix them in a volume ratio of 3:1, and magnetically stir for 15 min to obtain a coating solution. The steel fiber obtained in step (1) is put into the coating solution, and the mass ratio of steel fiber to coating solution is 1:2. Ultrasonic dispersion is carried out in an ultrasonic cleaning machine for 30 min to make the fiber surface uniformly adsorb and coat to form a nanometer SiO2 / graphene composite layer.

[0048] (3) Take out the coated steel fiber and place it in a muffle furnace. Heat it to 550°C at a rate of 10°C / min in an air atmosphere, keep it at this temperature for 45 min, and then naturally cool it to room temperature to obtain a modified steel fiber.

[0049] The composite admixture is compounded by polycarboxylic acid water reducing agent, aminopropyl triethoxysilane and lithium sulfate, and the mass ratio is 1:0.05:0.4.

[0050] The above-mentioned concrete based on high-strength and high-toughness steel fiber is prepared as follows:

[0051] (1) Put cement, composite active admixture, fine aggregate and coarse aggregate into a concrete mixer, dry mix for 2 min to obtain a premix.

[0052] (2) Add the composite admixture to water, and stir with a high-speed stirrer for 3 min to obtain an admixture solution.

[0053] (3) Pour the admixture solution into the premix, first stir at low speed for 1 min, then stir at high speed for 2 min to form a uniform slurry.

[0054] (4) Under the condition of continuous stirring of the slurry, add the modified steel fiber gradually, add it in three times, stir for 1 min after each addition, until the fiber has no obvious agglomeration, to obtain fresh concrete.

[0055] (5) The fresh concrete is filled into a cubic mold, vibrated on a vibrating table for 30 s, and the surface is smoothed. After standing for 24 h, the test piece is demolded. The demolded test piece is placed in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for curing until 28 d, to obtain the high-strength and high-toughness steel fiber-based concrete.

[0056] Example 2

[0057] The example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the following raw materials are included by mass fraction: cement 420 parts, composite active admixture 90 parts, fine aggregate 660 parts, coarse aggregate 950 parts, modified steel fiber 66 parts, composite admixture 10 parts, and water 150 parts.

[0058] Example 3

[0059] The example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the mass ratio of silica fume, metakaolin, and limestone powder in the composite active admixture is 3:1:1.

[0060] Example 4

[0061] The example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the volume ratio of nano-silica sol (SiO2 mass concentration 25%, average particle size 20 nm) and graphene water dispersion (graphene mass concentration 0.2%) in step (2) is 5:1.

[0062] Example 5

[0063] The example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the mass ratio of polycarboxylic acid water reducer, aminopropyl triethoxysilane, and lithium sulfate is 1:0.1:0.25.

[0064] Comparative Example 1

[0065] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the following raw materials are included by mass fraction: cement 390 parts, composite active admixture 60 parts, fine aggregate 660 parts, coarse aggregate 1000 parts, modified steel fiber 75 parts, composite admixture 6 parts, and water 150 parts.

[0066] Comparative Example 2

[0067] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the composite active admixture is mixed by silica fume, metakaolin, and limestone powder in a mass ratio of 4:1.5:1, and is directly used without modification.

[0068] Comparative Example 3

[0069] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the composite active admixture is modified by mixing silica fume and metakaolin at a mass ratio of 4:2.5, and the modification method is the same as that of example 1.

[0070] Comparative example 4

[0071] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the composite active admixture is modified by mixing fly ash, metakaolin and limestone powder at a mass ratio of 4:1.5:1, and the modification method is the same as that of example 1.

[0072] Comparative example 5

[0073] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the steel fiber is directly used without modification.

[0074] Comparative example 6

[0075] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the composite admixture is compounded by polycarboxylic acid water reducer and lithium sulfate, and the mass ratio is 1:0.4.

[0076] Comparative example 7

[0077] The comparative example provides a high-strength and high-toughness steel fiber-based concrete, which is different from example 1 in that the composite admixture is compounded by polycarboxylic acid water reducer and aminopropyl triethoxysilane, and the mass ratio is 1:0.05.

[0078] Performance test

[0079] To verify the mechanical properties of the concrete prepared in examples 1-5 and comparative examples 1-7, the compressive strength, splitting tensile strength, flexural strength and fracture energy of the samples were tested. All test pieces were 150mmx150mmx150mm cubes, which were tested after standard curing for 28 days under the conditions of 20±2℃ and relative humidity of about 95%. The test results are shown in Table 1.

[0080] Table 1 Performance test results

[0081]

[0082]

[0083] The above results show that the concrete of Examples 1-5 as a whole exhibits higher compressive strength and excellent toughness index, significantly improving the interface structure and energy dissipation capacity of the concrete. In Comparative Example 1, the insufficient amount of composite active admixture leads to a low amount of hydration products, and both the strength and the fracture energy are significantly reduced. In Comparative Example 2, the composite active admixture is not modified, and lacks the promoting effect of surface C-S-H seeds, resulting in insufficient interface density and lower strength and toughness than the examples. In Comparative Example 3, the ratio of the composite active admixture is unreasonable, and the amount of metakaolin is too high, leading to insufficient release of activity, and lower strength and fracture energy than the examples. In Comparative Example 4, silica fume is replaced by fly ash, which has poor activity and micro-filling effect, resulting in a decline in overall performance. In Comparative Example 5, the steel fiber is not modified, and the interface bonding force between the fiber and the matrix is insufficient, making the fiber easy to pull out, resulting in a significant decrease in toughness. In Comparative Example 6, the composite admixture lacks silane coupling agent, and the interface chemical bonding effect is insufficient, resulting in a decrease in fiber anchoring force, and lower strength and fracture energy than the examples. In Comparative Example 7, the composite admixture lacks lithium sulfate, and the early hydration promoting effect is insufficient, resulting in lower overall strength and toughness than the examples.

[0084] The above is a preferred embodiment of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application. These improvements and refinements should also be considered within the scope of the present application.

Claims

1. A high-strength and high-ductility steel fiber based concrete, comprising the following raw materials in parts by mass: cement 360-420 parts, composite active admixture 90-120 parts, fine aggregate 650-720 parts, coarse aggregate 950-1050 parts, modified steel fiber 40-70 parts, composite admixture 5-12 parts, and water 135-165 parts.

2. The high-strength and high-ductility steel fiber-based concrete according to claim 1, characterized by, The composite active admixture is prepared by mixing silica fume, metakaolin, and limestone powder in a mass ratio of (3-4) :(1-1.5) :

1.

3. The high-strength and high-ductility steel fiber-based concrete according to claim 2, characterized by, The composite active admixture is prepared by the following method: (1) mixing, stirring silica fume, metakaolin and limestone powder to obtain premixed powder; mixing nano-silica sol and Ca(OH)2 saturated solution to obtain modified liquid containing SiO2 / Ca 2+ ​ (2) spraying the modified liquid onto the premixed powder, stirring, then drying to constant weight, sieving, and obtaining the composite active admixture.

4. The high-strength and high-ductility steel fiber-based concrete according to claim 3, characterized by, The mass fraction of SiO2 in the nanosilica sol is 12-16%.

5. The high-strength and high-ductility steel fiber-based concrete according to claim 3, characterized by, The molar ratio of Si:Ca in the nanosilica sol and the Ca(OH)2 saturated solution is 1.2-1.5:

1.

6. The high-strength and high-ductility steel fiber-based concrete according to claim 3, characterized by, The mass ratio of the modified liquid to the premixed powder is controlled at 0.15-0.20:

1.

7. The high-strength and high-ductility steel fiber-based concrete according to claim 1, wherein The modified steel fiber is prepared by the following method: (1) selecting steel wire with a tensile strength of ≥2500 MPa and an elongation after fracture of ≥4%, cutting into short-cut wire with a length of 10-15 mm and a diameter of 0.15-0.25 mm; immersing the short-cut wire in 5-10% dilute hydrochloric acid or dilute sulfuric acid solution to remove the surface oxide layer and form a rough surface, then washing with deionized water until neutral, drying, and obtaining the steel fiber; (2) immersing the steel fiber into a coating liquid prepared by mixing nanosilica sol and graphene dispersion liquid in a volume ratio of (3-5) :1, stirring, and coating the surface of the steel fiber to form a SiO2 / graphene composite layer; (3) heating the coated steel fiber to 500-600℃, maintaining for 30-60 min, and cooling to obtain the modified steel fiber.

8. The high-strength high-ductility steel fiber-based concrete according to claim 7, characterized by, In step (2), the mass concentration of SiO2 in the nanosilica sol is 20-30%, and the mass concentration of graphene in the graphene dispersion liquid is 0.1-0.5%.

9. The high-strength and high-ductility steel fiber-based concrete according to claim 1, wherein The composite admixture is prepared by compounding polycarboxylic acid water reducer, aminopropyl triethoxysilane, and lithium sulfate in a mass ratio of 1:(0.04-0.10):(0.20-0.45). 10.A method for preparing the high-strength and high-ductility steel fiber based concrete according to any one of claims 1-9, comprising the following steps: (1) mixing cement, composite active admixture, fine aggregate, and coarse aggregate to obtain a premix; (2) dissolving the composite admixture in water to obtain an admixture solution; (3) mixing the premix and the admixture solution, stirring uniformly, and forming a slurry; (4) adding the modified steel fiber to the slurry, continuing to stir, and obtaining fresh concrete; (5) shaping and curing the fresh concrete to obtain the high-strength and high-ductility steel fiber based concrete.

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