Cement-based composite material mixed with surface-modified steel fiber and preparation method thereof

Abstract

The present invention provides a cement-based composite material and preparation method of a surface-modified steel fiber. The raw material composition includes 300-750 parts of cement, 60-100 parts of fly ash, 80-200 parts of silica fume, 40-100 parts of mineral powder, 300-600 parts of coarse aggregate, 400-800 parts of fine aggregate, 10-60 parts of zinc oxide whiskers, 50-200 parts of modified steel fiber, 150-200 parts of tap water, and 8-25 parts of water reducer. The modified steel fiber used is treated with surface mineralization to introduce CaCO3 particles, which on the one hand provides a large number of fixing sites and on the other hand gives the fiber surface roughness, hydrophilicity and affinity with cement mortar, aiming to improve the interfacial compatibility and bonding between the steel fiber and the cement matrix to overcome the gravity effect of the steel fiber. At the same time, low-density zinc oxide whiskers replace part of the steel fiber, also reducing the gravity effect. In addition, the dense filling effect of zinc oxide whiskers further improves the internal microstructure of concrete, reduces the generation of voids, and improves the density of concrete. The present invention obtains a cement-based composite material with uniformly dispersed fibers and enhanced toughness.

Description

Technical Field

[0001] The invention belongs to the field of building materials, and particularly relates to a cement-based composite material mixed with surface-modified steel fibers and a preparation method thereof. Background Art

[0002] Ultra-high-performance concrete (UHPC), a cement-based composite material with excellent mechanical properties and good durability, is one of the most widely used and widely used building materials in construction projects. The uniform distribution of steel fibers in the cement matrix is ​​a prerequisite for the strengthening and toughening of UHPC. If the fibers are unevenly dispersed, the reinforcing effect of the fiber mesh skeleton when the UHPC is subjected to specific loads is greatly reduced. Stress cannot be effectively transferred from the matrix to the fibers, leading to stress concentration, the development of microcracks, and the generation of macrocracks within the concrete, thus affecting its service life. Current UHPC systems cannot fully utilize the reinforcing effect of steel fibers, resulting in insufficient improvement in matrix toughness and poor brittle characteristics when destroyed.

[0003] Existing technologies for evaluating and controlling the uniformity of steel fiber dispersion primarily focus on aspects such as raw material composition and ratio, steel fiber volume fraction, or mixing and vibrating during processing. However, due to the smooth and inert surface of steel fibers, and the presence of a certain degree of hydrophobicity after anti-rust treatment, the bonding between steel fibers and the UHPC matrix is ​​relatively poor, with the interface initially debonding under stress. Furthermore, the gravity effect of the fibers results in a denser distribution of fibers at the bottom and sparser at the top of the concrete. Therefore, challenging the surface properties of steel fiber materials and improving their interfacial compatibility and bonding with the UHPC matrix to overcome the gravity effect of steel fibers is one of the new research directions for improving the dispersion of steel fibers in UHPC.

[0004] The main methods for improving the bonding performance between steel fibers and UHPC matrices include: 1) regulating the type and density of surface charge, such as chemical methods like adding electrolytes and surfactants, or physical methods like changing pH and heat treatment; and 2) regulating the fiber surface energy, such as surface coating, nanomaterial loading, or sandpaper polishing. For example, Chinese invention patent application number 202311169850.X, entitled "A Method for Surface Modification of Steel Fibers," uses self-polymerizing and oxidizing dopamine to form a polydopamine coating on the surface of steel fibers, enhancing their bonding strength with the interface. However, dopamine is expensive and easily oxidizes in air, making it difficult to store and transport. Further research and improvement based on the surface properties of steel fibers is necessary. Summary of the Invention

[0005] In response to the defects or shortcomings of the existing technology, the present invention aims to provide a cement-based composite material mixed with surface-modified steel fibers, based on the functional modification of the surface of the steel fiber material and the introduction of nanoparticles through layer-by-layer mineralization, thereby improving the surface properties of the material and improving the uniformity of steel fiber dispersion.

[0006] The purpose of the present invention is achieved through the following technical solutions.

[0007] A cement-based composite material mixed with surface-modified steel fiber, comprising, by weight, 300-500 parts of cement, 60-100 parts of fly ash, 80-200 parts of silica fume, 40-100 parts of mineral powder, 300-600 parts of coarse aggregate, 400-800 parts of fine aggregate, 10-60 parts of zinc oxide whiskers, 50-200 parts of modified steel fiber, 150-200 parts of tap water, and 8-25 parts of a water reducer.

[0008] The steel fiber has been subjected to a surface mineralization modification treatment, the steps of which are as follows:

[0009] S1: Pretreatment of steel fiber: Clean the steel fiber with a neutral detergent, ethanol, and water in sequence, and dry it to obtain clean steel fiber;

[0010] S2: Surface mineralization modification of steel fiber: The clean steel fiber is immersed in an aqueous solution of biophenolic hydroxy acid, and the steel fiber is taken out and washed with deionized water; then the steel fiber is immersed in CaCl2 solution and Na2CO3 solution at room temperature in turn, and the immersion process is placed on a shaker for shaking. After the immersion, the steel fiber is taken out and washed with deionized water; after repeating the operation of alternating immersion in CaCl2 solution and Na2CO3 solution and washing with deionized water 1 to 4 times, the steel fiber is dried to constant weight and cooled to obtain modified steel fiber.

[0011] Preferably, the biological phenolic hydroxy acid is at least one of phytol acid and phytol acid; the phytol acid includes at least one of phytic acid, alginic acid and tartaric acid; the phytol acid includes at least one of tannins and flavanols; the flavanols include at least one of gallic acid, epicatechin, epigallocatechin, epicatechin gallate and epigallocatechin gallate.

[0012] Preferably, the biological phenolic hydroxy acid is at least one of tannic acid, phytic acid, gallic acid, and alginic acid; more preferably, phytic acid and tannic acid.

[0013] Preferably, the concentration of the biophenolic hydroxy acid solution is 0.1-2.0 wt %; the concentration of the CaCl 2 and Na 2 CO 3 aqueous solutions is 0.1-1.0 mol / L, more preferably 0.2-0.5 mol / L.

[0014] Preferably, the immersion conditions of the biophenolic hydroxy acid are 40-80°C for 10-40 min; the immersion time of the CaCl2 and Na2CO3 solutions is 5-30 min, the shaking frequency of the shaker is 20-50 rpm; and the drying temperature of the steel fiber is 50-80°C.

[0015] Preferably, the steel fiber is selected from one or more of straight, hook-end or wavy steel fibers with a diameter of 0.15-0.35 mm, an aspect ratio of 40-75, and a tensile strength of ≥2000 MPa;

[0016] Preferably, the steel fiber is selected from at least one of ordinary steel fiber, copper-plated steel fiber and galvanized steel fiber.

[0017] Preferably, the mass ratio of the zinc oxide whisker to the modified steel fiber is (0.5-3):5; more preferably (1-2):5.

[0018] Preferably, the zinc oxide whiskers are four-needle structures with a diameter of 0.5 to 5 m m, length 10~50 m m.

[0019] Whiskers are whisker-like crystals that resemble short fibers but are much smaller. Their addition replaces some of the weight of the steel fibers, reducing the gravitational effect of the steel fibers to a certain extent. The tetrapod-shaped zinc oxide whiskers used are single crystals with virtually no structural defects, resulting in extremely high mechanical strength and elastic modulus. Their unique three-dimensional tetrapod structure provides isotropic reinforcement, facilitating uniform distribution within the cement matrix and imparting enhanced toughness to cement-based composites.

[0020] The present invention also provides a method for preparing a cement-based composite material mixed with surface-modified steel fibers, which is characterized by comprising the following steps:

[0021] First, cement, fly ash, silica fume, mineral powder, and zinc oxide whisker are added to a mixer and stirred for 3 to 4 minutes; then water and a water reducer are added and stirred for another 3 to 4 minutes to obtain a uniform wet mixture; modified steel fibers are added one by one, stirred for 1 to 2 minutes, and then molded, vibrated, formed, and cured to obtain the cement-based composite material.

[0022] Biophenolic hydroxy acid is one of the most widely distributed substances in the plant kingdom. It contains a large number of hydroxyl groups and can act as a chelating agent to chelate with metal ions to form stable metal complexes. The present invention uses the metal on the surface of steel fiber (iron or copper or zinc contained in plated metal steel fiber) as the source of metal ions and utilizes the coordination effect of hydroxyl groups and metal ions to first complete the functional modification of biophenolic hydroxy acid on the surface of steel fiber. The added Ca 2+Further cross-linking with biological phenolic hydroxy acids to form a stable double-layer complex network; 2+ With CO3 2- The alternating deposition of CaCO3 nanoparticles realizes the interlaced growth of CaCO3 nanoparticles in the complex network; 2+ The strong composite network entanglement structure formed by the iron / copper / zinc and biological phenolic hydroxy acid on the fiber surface can anchor the deposited particles tightly on the fiber.

[0023] The introduction of nanoparticles provides numerous anchoring sites, promoting adhesion to the cement mortar. The excellent compatibility of CaCO3 particles with the cement mortar enhances the bond strength between the steel fibers and the cement mortar matrix. Furthermore, the deposited particles impart surface roughness and hydrophilicity to the fibers, increasing friction between the steel fibers and the cement mortar during mixing. This allows the steel fibers to be more easily dragged along by the flow of the cement mortar throughout the concrete mixture, resulting in a more even dispersion.

[0024] Beneficial effects of the present invention:

[0025] The technical solution described in the present invention starts from adjusting the material properties of steel fibers, functionalizing the steel fibers with biophenolic hydroxy acids and introducing nanoparticles through layer-by-layer mineralization treatment to enhance the interfacial bonding stress between the steel fibers and the cement matrix, thereby overcoming the gravity effect of some steel fibers and improving the uniformity of the dispersion of the steel fibers in the cement matrix. Furthermore, the chemical bonds of the complex network strengthen the stability of the combination of the two.

[0026] The present invention employs an in-situ CaCO3 addition method, effectively avoiding the problems of particle flaking or agglomeration that occur with conventional external particle addition. The accumulated CaCO3 particles increase the fiber's surface area and active sites, enhancing contact and friction between the steel fiber and the cement mortar. They also impart physical roughness and hydrophilicity to the fiber surface, promoting more uniform dispersion. Simultaneously, the pre-deposition of biophenolic hydroxyl acids on the steel fiber also imparts hydrophilic polar groups, such as hydroxyl groups, to the steel fiber surface, further enhancing wettability and facilitating adhesion of the cementitious material to the steel fiber surface during hydration.

[0027] When biophenolic hydroxy acid is complexed on the metal surface, it forms a dense monomolecular protective film on the metal surface, which can also effectively prevent oxygen and other substances from contacting the metal surface and resist the corrosion of steel fibers.

[0028] The addition of zinc oxide whiskers, on the one hand, can leverage their dense filling effect to improve the internal microstructure of steel fiber concrete, refine the pore structure, achieve concrete densification, and reduce porosity. It also reduces the surface tension and additional pressure of water within the pores, reducing drying shrinkage of the concrete. The micron-sized zinc oxide whiskers can also wrap particles and penetrate into the cement matrix, preventing crack propagation and enhancing physical adhesion to the cement matrix. Furthermore, the zinc oxide whiskers replace some of the weight of the steel fibers, reducing the gravitational effect of the steel fibers to a certain extent. Furthermore, zinc oxide's inherent radiation shielding and radio wave absorption properties enhance UHPC's radiation protection and antistatic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 3 and 4 are steel fiber pull-out load-slip curves of Comparative Example 1 and Examples 1, 3 and 4. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below through specific implementations, but the embodiments of the present invention are not limited thereto. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0031] Sheared copper-coated steel fibers and ordinary steel fibers, with the same technical parameters as those of ordinary steel fibers: diameter 0.2 mm, length 13 mm, tensile strength 2850 MPa, were purchased from Shanghai Qingbei New Materials Technology Co., Ltd.

[0032] Tannic acid, gallic acid, alginic acid, AR, were purchased from Aladdin Reagent Company; phytic acid (50%), anhydrous calcium chloride, anhydrous sodium carbonate, AR, were purchased from MacLean Reagent Company;

[0033] Zinc oxide whiskers, diameter 0.5-5 m m, length 10-50 m m, purchased from Hangzhou Jikang New Materials Co., Ltd.;

[0034] Conch brand P·Ⅱ52.5 silicate cement has a measured strength of 62.5MPa and a specific surface area of ​​360m 2 / kg;

[0035] Class F, Grade I power plant fly ash, with a specific surface area of ​​440m 2 / kg, Guangzhou Hengyun Thermal Power Co., Ltd.;

[0036] Silica fume, SiO2 content ≥95%, water content ≤2%, Gansu Yuyang New Materials Co., Ltd.;

[0037] S95 mineral powder, specific surface area is 450m2 / kg, density is 2.6g / cm 3 , Lingshou County Shengbang Mineral Products Processing Plant;

[0038] Polycarboxylate superplasticizer, solid content 40%, water reduction rate 25-45%, Sika (China) Co., Ltd.

[0039] The coarse aggregate is washed, dried and continuously graded Class I construction crushed stone with a particle size of 5-8 mm and a mud content of ≤0.5%;

[0040] The fine aggregate is continuously graded medium sand with a fineness modulus of 2.5 and a mud content of ≤0.5%.

[0041] Example 1

[0042] A cement-based composite material mixed with surface-modified steel fibers is first prepared by the following process:

[0043] S1: Pretreatment of steel fiber: Use neutral detergent to remove stains from steel fiber, use alcohol to degrease steel fiber, use warm water to remove residual alcohol and detergent, and dry to obtain clean steel fiber;

[0044] S2: Surface mineralization modification of steel fiber:

[0045] 50 parts of clean steel fibers were immersed in 200 parts of 2.0 wt% tannic acid solution at 60°C for 30 min and then washed thoroughly with deionized water to remove residual tannic acid molecules.

[0046] The steel fiber was immersed in 0.5 mol / L CaCl2 solution and 0.5 mol / L Na2CO3 solution for 15 min and 10 min respectively. The immersion conditions were room temperature and shaking on a shaker with a shaking frequency of 30 rpm. After each immersion, the steel fiber was taken out and washed with deionized water to remove excess substances. After repeating the operation of alternating immersion in CaCl2 solution and Na2CO3 solution and washing with deionized water twice, the steel fiber was dried at 60°C to obtain modified steel fiber.

[0047] Next, a cement-based composite material mixed with surface-modified steel fibers was prepared. The raw materials included cement, fly ash, silica fume, sand, stone, the modified steel fibers described above, water, and a water reducer. The raw materials were weighed according to the mix ratio shown in Table 1. Each mortar was mechanically mixed at 50 rpm using a forced mixer (maximum mixing capacity of 60 L). First, the cement, fly ash, silica fume, mineral powder, and zinc oxide whiskers were added to the mixer and stirred for 3–4 minutes. Water and the water reducer were then added and stirred for another 3–4 minutes until the wet mix was uniform. Finally, the modified steel fibers were added incrementally and stirred for 1–2 minutes to obtain a fresh UHPC mix.

[0048] Table 1 UHPC raw material ratio in Example 1 (parts by weight)

[0049]

[0050] Example 2-Example 4

[0051] The operation is the same as that of Example 1, except that the steel fiber is alternately immersed in the CaCl2 solution and the Na2CO3 solution for 1, 3, and 4 times respectively.

[0052] Example 5-Example 6

[0053] The operation is the same as that of Example 1, except that in step S2, the steel fiber is immersed in the CaCl2 solution and the Na2CO3 solution with concentrations of 0.2 mol / L and 1.0 mol / L, respectively.

[0054] Example 7-Example 9

[0055] The operation is the same as that of Example 1, except that the tannic acid in step S2 is replaced by phytic acid, gallic acid, and alginic acid, respectively.

[0056] Example 10-Example 12

[0057] The operation was the same as in Example 1, except that the mass ratios of zinc oxide whisker to modified steel fiber were 1:5, 2:5 and 3:5, respectively, that is, the steel fiber content was fixed, while the zinc oxide whisker content was 20 parts, 40 parts and 60 parts, respectively.

[0058] Example 13

[0059] The operation is the same as in Example 1, except that the steel fiber is replaced with copper-plated steel fiber.

[0060] Comparative Example 1

[0061] The operation is the same as that of Example 1, except that step S2 is omitted, that is, the steel fiber is not subjected to surface modification treatment, and a steel fiber reinforced cement-based composite material is prepared.

[0062] Comparative Example 2

[0063] The operation is the same as that of Example 1, except that the mineralization deposition treatment of the steel fiber is omitted, that is, the steel fiber is only impregnated with the tannic acid solution.

[0064] Comparative Example 3

[0065] The operation is the same as that of Example 1, except that the impregnation treatment with the tannic acid solution is omitted, that is, the surface mineralization modification of the steel fiber is directly performed.

[0066] Comparative Example 4

[0067] The operation is the same as that of Example 1, except that zinc oxide whiskers are removed from the concrete components during the preparation of the cement-based composite material.

[0068] For the UHPC mixtures obtained in all the above examples and comparative examples, their pressure bleeding rates were first measured.

[0069] Compressive strength: The specimen size is 100 mm × 100 mm × 100 mm, and the test is carried out in accordance with the relevant provisions of GB / T 50081-2019;

[0070] Flexural strength: The specimen size is 100 mm × 100 mm × 400 mm, and the test is carried out in accordance with the relevant provisions of GB / T 50081-2019;

[0071] Since some embodiments use copper-plated steel fibers with very poor magnetic properties, it is impossible to measure their fiber orientation using the electromagnetic induction method; therefore, the fiber dispersion coefficient is used uniformly. β Quantitative evaluation of fiber distribution, the specific process includes:

[0072] (1) X-ray micro-computed tomography was used to detect the distribution of steel fibers in concrete. The number of all fibers in the specimen sample area was counted and the average value was obtained. µ。

[0073] (2) Divide the sample area in the obtained 3D image and perform statistics n In the grid i The number of fibers in a grid cell x i , calculate the coefficient of variation of fiber distribution :

[0074]

[0075] µ ——the average number of fibers contained in the test specimen; x i ——Test pieces are divided into n After the unit, i The number of fibers contained in a unit; n ——The total number of areas into which the specimen is divided.

[0076] (3) Calculate the fiber dispersion coefficient using the obtained coefficient of variation β , β It is a quantitative indicator that describes the uniformity of fiber dispersion in concrete:

[0077]

[0078] Theoretically, when the mesh is completely filled with fibers, x i =1; in fact, when x i ∈[0.6, 1], indicating that the area has been mostly filled with dispersed fibers and can be considered as a whole with adjacent units with similar fiber numbers to form a fiber bundle. x i =0 means that there is only cement in the area and no fiber. It may also mean that the fibers in the adjacent area may be clustered or lumped. When the number of fibers in each unit in the pattern is equal, that is, the steel fibers are evenly distributed, F =0, β =1; if one unit concentrates all the steel fibers, and the number of steel fibers in other units is 0, then F →∞, β =0.

[0079] The test results of the concrete test blocks of various embodiments and comparative examples are shown in Table 2.

[0080] Table 2 Test results of concrete of various embodiments and comparative examples

[0081]

[0082] Compared with Comparative Example 1, the steel fibers in Examples 1 to 4 were subjected to surface mineralization modification with different deposition times, and the pressure water bleeding rate of the obtained fresh mixture was significantly reduced and the dispersion coefficient of the cement-based composite material was improved. This is because the surface distribution density and area of ​​the accumulated calcium carbonate on the surface of the steel fiber increased, providing contact sites with the cementitious material, making the slurry and steel fiber more evenly mixed; the improvement of the roughness and hydrophilicity of the steel fiber reduced the volume of free water in the calcium carbonate and cement matrix, reduced the water bleeding rate, and made the mechanical performance more outstanding. However, if the deposition times are too many, as shown in Example 4, the mechanical properties will decrease slightly. This shows that the deposition layer of calcium carbonate particles is too thick, resulting in insufficient contact with water during mixing, resulting in an increase in internal defects and voids in the concrete, thereby increasing free water, making the mixture slurry more prone to water bleeding, and deteriorating the dispersibility of the steel fiber. The number of calcium carbonate deposition times is more preferably 2 to 3 times.

[0083] Furthermore, the single fiber pull-out test was conducted on the embodiment with different deposition times and the comparative example 1. Figure 1The typical pull-out load-slip curve of the steel fiber is shown. In the initial good bonding area stage, the slopes of the load-slip curves of different samples are similar. The pull-out load rises sharply, while the slip increases only slightly. The load and slip have a linear elastic relationship. In the subsequent partial peeling area, the load-slip curve shows a nonlinear relationship, and as the degree of calcium carbonate deposition increases, the corresponding peak load also gradually increases, and the required pull-out energy also increases; among them, the strengthening trend of Examples 3 and 4 with deposition times of 3 and 4 is obvious. This is the result of the increased bonding force between the steel fiber and the cement matrix. The pull-out energy of Example 4 is slightly smaller than that of Example 3, which shows that the excessive thickness of calcium carbonate deposition reduces the bonding strength, resulting in the appearance of cracks and a decrease in mechanical properties, which is consistent with the results shown in Table 2.

[0084] Example 5, which involved two depositions of calcium carbonate particles onto the steel fiber surface at a lower deposition concentration (0.2 mol / L), achieved mechanical properties similar to those of Example 2 (i.e., a single deposition at a concentration of 0.5 mol / L). Example 6 and Example 4 had the same theoretical deposition amount—two depositions at a concentration of 1 mol / L and four depositions at a concentration of 0.5 mol / L, respectively—but the mechanical properties of Example 6 were worse. This demonstrates that multiple depositions at low concentrations are more efficient than single depositions at high concentrations. Therefore, the calcium carbonate deposition concentration can be further optimized to 0.2-0.5 mol / L.

[0085] In combination with Example 1, Example 7-Example 9, there are differences in the strength of the complexing forces between the four biological phenolic hydroxy acids and metals. Furthermore, phytic acid> tannic acid> gallic acid> alginic acid, so there are obvious differences in the efficiency and density of their functional modification of steel fibers, which in turn affects the number and area of ​​subsequent in-situ growth points of calcium carbonate, resulting in different dispersion effects and mechanical properties. Phytic acid is a polyanionic chelating agent with 12 polarizable acid protons and 6 negatively charged phosphate groups, and has a strong complexing ability; tannic acid has multiple ortho-phenolic hydroxyl structures, which can be used as a polyhydroxy ligand to react with metal ions, and two adjacent phenolic hydroxyl groups can form a stable five-membered ring chelate with metal ions in the form of oxygen anions.

[0086] In general, the preferred biological phenolic hydroxy acids are phytic acid and tannic acid.

[0087] Combined with Example 1, Example 10-Example 12 and Comparative Example 4, the dosage of zinc oxide whisker will also affect its composite effect with modified steel fiber, and thus affect the mechanical strength of concrete. The cement-based composite material of Comparative Example 4 without zinc oxide whisker has good mechanical strength but limited improvement in its dispersibility; when a small amount of zinc oxide whisker is added, that is, when the ratio of zinc oxide whisker to modified steel fiber is low, the fluidity and dispersibility of the cement paste are not significantly weakened, and it has a significant strengthening and toughening effect; as the dosage of zinc oxide whisker increases, although the flexural strength continues to increase, the compressive strength of the concrete is significantly deteriorated.

[0088] The dosage range of steel fiber / modified steel fiber is further preferably (1.5~2):5.

[0089] The results of Examples 1 and 13 demonstrate the universal applicability of the steel fiber surface hydroxyl functionalization and mineralization modification methods provided by the present invention. Furthermore, Example 13 is slightly inferior to Example 1 in terms of mechanical performance and dispersibility. This is because the complexation speed and strength of tannic acid with high-valent metallic iron are superior to those with divalent metallic copper.

[0090] The results of Comparative Examples 2 and 3 demonstrate the additive effects of the hydroxyl acid functionalization and mineralization treatments on the steel fiber surface provided by the present invention on both steel fiber and concrete optimization. Comparative Example 2, which performed functionalization with biophenolic hydroxyl acids alone, only formed a protective film, limiting its ability to improve the steel fiber's dispersibility in concrete. Comparative Example 3, which performed only mineralization, lacked attachment growth points on the inert steel fiber surface, resulting in a sharp decrease in growth efficiency and concrete durability.

[0091] The above embodiments are merely examples for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A cement-based composite material mixed with surface-modified steel fibers, characterized in that: The raw materials include, by weight, 300-750 parts of cement, 60-100 parts of fly ash, 80-200 parts of silica fume, 40-100 parts of mineral powder, 300-600 parts of coarse aggregate, 400-800 parts of fine aggregate, 10-60 parts of zinc oxide whiskers, 50-200 parts of modified steel fiber, 150-200 parts of tap water, and 8-25 parts of water reducer; the zinc oxide whiskers have a diameter of 0.5-5 μm and a length of 10-50 μm; The mass ratio of the zinc oxide whisker to the modified steel fiber is (0.5-3):5; The modified steel fiber is subjected to surface mineralization modification treatment, and the steps are as follows: S1: Pretreatment of steel fiber: Clean the steel fiber with a neutral detergent, ethanol, and water in sequence, and dry it to obtain clean steel fiber; S2: Surface mineralization modification of steel fiber: clean steel fiber is immersed in a biological phenolic hydroxy acid aqueous solution, after which the steel fiber is taken out and washed with deionized water; the steel fiber is then immersed in a CaCl2 solution and a Na2CO3 solution at room temperature in sequence, and the immersion process is shaken on a shaker, after which the steel fiber is taken out and washed with deionized water; after repeating the operation of alternating immersion in CaCl2 solution and Na2CO3 solution and washing with deionized water for 2 to 4 times, the steel fiber is dried to a constant weight and cooled to obtain a modified steel fiber; The concentration of the biophenolic hydroxy acid solution in step S2 is 0.1-2.0 wt%; the concentration of the CaCl2 and Na2CO3 aqueous solutions is 0.1-1.0 mol / L; the immersion conditions of the biophenolic hydroxy acid in step S2 are 40-80°C for 10-40 min; the layer-by-layer immersion time of the CaCl2 and Na2CO3 solutions is 5-30 min; the shaking frequency of the shaker is 20-50 rpm; and the steel fiber drying temperature is 50-80°C.

2. The cement-based composite material according to claim 1, characterized in that: The biological phenolic hydroxy acid is at least one of plant alcoholic acid and plant phenolic acid; the plant alcoholic acid includes at least one of phytic acid, alginic acid, and tartaric acid; the plant phenolic acid includes at least one of tannic acid and flavanols; the flavanols include at least one of gallic acid, epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate.

3. The cement-based composite material according to claim 2, characterized in that: The biological phenolic hydroxy acid is at least one of phytic acid and tannic acid.

4. The cement-based composite material according to claim 1, characterized in that: The steel fibers are selected from one or more of straight, hook-end or wavy steel fibers with a diameter of 0.15-0.35 mm, an aspect ratio of 40-75, and a tensile strength of ≥2000 MPa.

5. The cement-based composite material according to claim 1, characterized in that: The steel fiber is selected from at least one of ordinary steel fiber, copper-plated steel fiber and galvanized steel fiber.

6. The method for preparing the cement-based composite material according to any one of claims 1 to 5, characterized in that: The following steps are involved: First, cement, fly ash, silica fume, mineral powder, and zinc oxide whisker are added to a mixer and stirred for 3 to 4 minutes; then water and a water reducer are added and stirred for 3 to 4 minutes to obtain a uniform wet mixture; modified steel fibers are added one by one, stirred for 1 to 2 minutes, and then molded, vibrated, formed, and cured to obtain the cement-based composite material.

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