Green low-carbon modified steel fiber and application

Abstract

The application discloses a kind of green low-carbon modified steel fiber, waste concrete powder suspension or cement mortar waste liquid is mixed with steel fiber stirring, after reaction 10-300min steel fiber is washed, dry in flue gas atmosphere and obtain modified steel fiber;The pH in the waste concrete powder suspension or cement mortar waste liquid is 9-13, Ca 2+ Concentration is greater than or equal to 1 ppm;The waste concrete powder is derived from cement-based building material crushing recovery stage, and the particle size is 5-40 μm;The steel fiber is copper-plated steel fiber;The water-cement ratio of waste concrete powder suspension or cement mortar waste liquid is (5-20):1;The mass ratio of steel fiber and waste concrete powder or cement mortar is (0.3-1.2):1;The application can greatly improve the interfacial bonding strength of steel fiber and cement matrix, and the preparation process not only realizes the utilization of solid waste resources, but also realizes the capture and effective utilization of carbon dioxide in flue gas, reduces greenhouse gas emissions.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a modified steel fiber. BACKGROUND

[0002] With the increasing demand for material performance in the construction industry, ultra-high performance concrete (UHPC) has become an important engineering material due to its excellent mechanical properties and durability. The compressive strength of UHPC exceeds 150 MPa, and the tensile strength exceeds 20 MPa. These characteristics make it widely used in bridge construction, high-rise buildings, marine engineering, and protective facilities. In the composition of UHPC, the addition of steel fibers plays a key role in improving the crack resistance and toughness of the material, and is an important factor in achieving high performance of UHPC.

[0003] However, one of the main problems limiting the performance of UHPC is the insufficient interfacial bonding between steel fibers and the cement matrix. The insufficient interfacial bonding will cause the steel fibers to be unable to effectively transfer stress to the matrix when subjected to load, thereby affecting the overall mechanical properties of the material. In addition, the weak bonding of the interface may also cause the pull-out and fracture of the steel fibers in the concrete, thereby reducing the durability and service life of the material. Therefore, how to improve the interfacial bonding between steel fibers and the cement matrix has become a key technical problem to be solved in the research and application of UHPC.

[0004] In traditional solutions, researchers have tried various methods to improve the surface properties of steel fibers, including chemical modification, physical treatment, and surface coating. These methods have achieved certain results in improving interfacial bonding, but also have problems such as high cost, complex process, and possible adverse effects on the environment. Chemical modification methods such as silane coupling agent treatment and phosphate treatment can effectively increase the roughness and chemical activity of the fiber surface, but the production process may produce harmful by-products and pollute the environment. Physical treatment methods such as mechanical grinding and plasma treatment can change the surface morphology of steel fibers, but they have high energy consumption and high requirements for equipment. Surface coating methods can form an adhesive layer on the surface of steel fibers, but the coating materials used may contain harmful substances, and the durability of the coating is also a major challenge.

[0005] Under the background of global climate change and environmental protection, the building materials industry is facing pressure for green transformation. Low-carbon and environmentally friendly production processes have become a new trend in the industry. Therefore, developing a modification method that can both improve the interfacial bonding between steel fibers and the cement matrix and meet the low-carbon green concept is of great significance for promoting the sustainable development of UHPC. Such a modification method should be able to effectively improve material performance while reducing energy consumption and environmental pollution during production, achieving the sustainability of building materials production. SUMMARY

[0006] The application aims to provide a green and low-carbon modified steel fiber, which can greatly improve the interfacial bonding force between the steel fiber and the cement matrix, and the preparation process can not only realize the utilization of solid waste resources, but also realize the capture and effective utilization of carbon dioxide in flue gas, and reduce greenhouse gas emissions.

[0007] To achieve the above-mentioned purpose, the technical scheme is as follows:

[0008] A green and low-carbon modified steel fiber is prepared in the following manner:

[0009] The waste concrete powder suspension or cement mortar waste liquid is mixed and stirred with the steel fiber, the steel fiber is rinsed after reacting for 10-300 min, and then dried in a flue gas atmosphere to obtain the modified steel fiber.

[0010] According to the above scheme, the pH of the waste concrete powder suspension or cement mortar waste liquid is 9-13, Ca 2+ The concentration is greater than or equal to 1 ppm.

[0011] According to the above scheme, the waste concrete powder is derived from the crushing and recycling stage of cement-based building materials, and the particle size is 5-40 μm.

[0012] According to the above scheme, the steel fiber is a steel fiber plated with brass on the surface.

[0013] According to the above scheme, the water-cement ratio of the waste concrete powder suspension or cement mortar waste liquid is (5-20):1; the mass ratio of the steel fiber to the waste concrete powder or cement mortar is (0.3-1.2):1.

[0014] According to the above scheme, the mixing and stirring rate is 500-830 rpm.

[0015] According to the above scheme, the carbon dioxide concentration in the flue gas atmosphere is 5-38%, the drying temperature is 20-90°C, and the drying time is 25-400 min.

[0016] A preparation method of a green and low-carbon modified steel fiber, comprising the following steps:

[0017] The waste concrete powder suspension or cement mortar waste liquid is mixed and stirred with the steel fiber, the steel fiber is rinsed after reacting for 10-300 min, and then dried in a flue gas atmosphere to obtain the modified steel fiber.

[0018] The application of the above-mentioned modified steel fiber in ultra-high performance concrete material, the content of the modified steel fiber is 1-3 vt%.

[0019] According to the above scheme, the cement raw materials (cement, silica fume, fly ash, mineral powder, quartz sand, and high-efficiency polycarboxylate superplasticizer) are uniformly mixed to obtain a slurry, and the modified steel fibers are uniformly mixed into the slurry to obtain an ultra-high performance concrete slurry.

[0020] The construction waste such as cement mortar waste liquid or waste concrete suspension is used to prepare a suspension, a hydration reaction in the construction waste suspension is utilized to form a layer of hydration product on the surface of the steel fiber, and then drying is performed in a flue gas atmosphere, carbon dioxide in the flue gas reacts with the hydration product to form calcium carbonate, thereby forming a stable calcium carbonate layer on the surface of the steel fiber, and the bonding force with the cement matrix is enhanced. The method recycles the construction waste for suspension leaching and cooperates with the carbonation reaction in the flue gas drying process, not only improves the interfacial bonding force of the steel fiber, but also realizes the capture and effective utilization of carbon dioxide, reduces the emission of greenhouse gases, and meets the development trend of green building materials.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] 1. Environmental friendliness: The present application utilizes carbon dioxide in the flue gas for carbonation reaction, which converts carbon dioxide in industrial waste gas into stable calcium carbonate product, which not only reduces the emission of greenhouse gases, but also helps to slow down the trend of global climate change. This environmentally friendly modification method meets the current requirements of the building materials industry for sustainable development and green production.

[0023] 2. Economic benefits: Compared with traditional chemical modification methods, the present application uses waste concrete suspension and flue gas drying treatment at a lower cost. Waste concrete powder, as a widely available industrial waste, has a relatively stable and low price, and flue gas drying as a waste utilization process hardly increases additional cost. Therefore, the modification method of the present application improves the material performance while reducing the production cost and improving the economic benefits.

[0024] 3. Process simplicity: The modification process of the present application is simple and easy to operate, and does not require complex equipment or special operating conditions. The preparation of waste concrete powder suspension and flue gas drying treatment can be carried out in conventional industrial equipment, which is convenient for modification and application on existing production lines, and is conducive to rapid promotion and implementation.

[0025] 4. Improved material performance: Through the modification method of the present application, the calcium carbonate layer on the surface of the steel fiber not only provides better mechanical anchoring and chemical bonding, but also acts as a protective layer to prevent steel fiber corrosion, thereby significantly improving the compressive strength, tensile strength and durability of UHPC. The modified steel fiber can more effectively bear and disperse the load, reduce the generation and propagation of cracks, and prolong the service life of the structure.

[0026] 5. Expanding application range: due to the high efficiency and environmental protection of the modification method of the present application, the modified steel fiber can be widely used in various high-performance concrete structures, such as bridges, high-rise buildings, offshore platforms, etc., to improve the safety and reliability of these structures. In addition, this method can also be applied to other types of composite materials, such as cement-based composites, ceramic-based composites, etc., further expanding the application field. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 : Unmodified steel fiber surface scanning electron micrograph.

[0028] Figure 2 : Unmodified steel fiber surface scanning electron micrograph.

[0029] Figure 3 : Modified steel fiber surface scanning electron micrograph.

[0030] Figure 4 : Modified steel fiber surface scanning electron micrograph. DETAILED DESCRIPTION

[0031] The following examples further illustrate the technical solutions of the present application, but are not intended to limit the scope of protection of the present application.

[0032] The specific embodiment provides a green and low-carbon modified steel fiber, and the preparation process comprises the following steps:

[0033] The steel fiber is placed in the waste concrete powder suspension or cement mortar waste liquid and rapidly stirred for 10-300 min, the steel fiber is rinsed and dried in a flue gas atmosphere to obtain the modified steel fiber.

[0034] Specifically, the pH of the waste concrete powder suspension or cement mortar waste liquid is 9-13, Ca 2+ Concentration ≥ 1 ppm

[0035] Specifically, the waste concrete powder is derived from the crushing and recycling stage of cement-based building materials, and the particle size is 5-40 μm.

[0036] Specifically, the water-cement ratio of the waste concrete powder suspension or cement mortar waste liquid is (5-20):1; the mass ratio of steel fiber to waste concrete powder or cement mortar is (0.3-1.2):1.

[0037] Specifically, the steel fiber is a steel fiber plated with brass.

[0038] Specifically, the rapid stirring rate is 500-830 rpm.

[0039] Specifically, the carbon dioxide concentration in the smoke atmosphere is 5-38%, the drying temperature is 20-90℃, and the drying time is 25-400min.

[0040] The specific embodiments also provide an application of the modified steel fiber in the super high performance concrete material, which comprises mixing cement, silica fume, fly ash, mineral powder, quartz sand, and high-efficiency polycarboxylic acid water reducer uniformly, adding water to stir until a slurry state appears, then adding 1-3 vol.% of the modified steel fiber, and continuously stirring for 3-7min to obtain the super high performance concrete with uniform mixing.

[0041] Six different modified steel fiber systems are designed in the specific embodiments, and the parameters of each group are given in Table 1. The particle size of the waste concrete powder is 9.86μm, and the CaO content is 64.8%. The fast stirring rate is 650rpm. The steel fiber used is an end hook type, with a diameter of 0.3mm, a length of 25mm, and a tensile strength of 2800MPa. The smoke gas used is a cement kiln tail gas, and the carbon dioxide content is 28%.

[0042] Table 1 Different cement modified steel fiber systems

[0043]

[0044] An equal amount of cement, silica fume, fly ash, mineral powder, quartz sand, and high-efficiency polycarboxylic acid water reducer are mixed uniformly, an equal amount of water is added to stir until a slurry state appears, then the modified steel fiber obtained in the above examples is added respectively, and the stirring is continued for 5min to obtain the super high performance concrete with uniform mixing. The mass ratio of cement, silica fume, fly ash, mineral powder, quartz sand, high-efficiency polycarboxylic acid water reducer, and water is 300:65:20:43:435:0.47:8.5, and the steel fiber content is 2vol.%. In addition, a comparative example is set, in which unmodified steel fiber is added.

[0045] After 90℃ steam curing for 2d, the performance detection is carried out, the specimen size is 40mm×40mm×160mm, and the compressive strength and flexural strength are detected according to GB / T 17671-2021. The detection results are shown in Table 2.

[0046] Table 2

[0047]

[0048]

[0049] The results above show that, except for Example 1, the steel fibers dried in the flue gas atmosphere improved the mechanical properties of the UHPC system to varying degrees, with compressive strength and flexural strength increasing by 22% and 43%, respectively. The significant decrease in mechanical properties caused by Example 1 was due to the excessively long flue gas drying time; the high temperature and acidic atmosphere damaged the protective layer of hydration products on the steel fiber surface, causing corrosion and thus reducing the mechanical properties of the UHPC system. Therefore, rationally adjusting the flue gas drying parameters (optimized drying time is 30-200 min) and controlling the growth of calcium carbonate particles on the steel fiber surface not only reduces greenhouse gas emissions but also enhances the mechanical anchoring and bridging effect of the steel fibers, thereby improving UHPC performance.

[0050] The scanning electron microscope image and magnified partial image of the unmodified steel fiber surface are attached. Figure 1 and 2 As shown. The scanning electron microscope image and partial magnified image of the modified steel fiber surface obtained in Example 3 are attached. Figure 3 and 4 As shown, attached Figure 4 It is evident that calcite products adhere to the modified steel fibers.

[0051] The above embodiments are merely illustrative examples and are not intended to limit the implementation in any way. For those skilled in the art, any equivalent modifications and substitutions to this invention are also within the scope of protection of the claims of this invention.

Claims

1. A green low-carbon modified steel fiber, characterized in that Prepared in the following way: The waste concrete powder suspension or cement mortar waste liquid is mixed and stirred with steel fibers, the steel fibers are rinsed after reacting for 10-300 min, and the modified steel fibers are obtained by drying in a flue gas atmosphere; The water-cement ratio of the waste concrete powder suspension or cement mortar waste liquid is (5-20):1, the pH is 9-13, the Ca 2+ The concentration is ≥1 ppm; the mass ratio of the steel fiber to the waste concrete powder or cement mortar is (0.3-1.2):1; The carbon dioxide concentration in the flue gas atmosphere is 5-38%, the drying temperature is 20-90℃, and the drying time is 30-200 min.

2. The green low-carbon modified steel fiber according to claim 1, characterized in that The waste concrete powder is derived from the crushing and recycling stage of cement-based building materials, and the particle size is 5-40μm.

3. The green low-carbon modified steel fiber according to claim 1, wherein The steel fibers are copper-plated steel fibers.

4. The green low carbon modified steel fiber according to claim 1, wherein The mixing and stirring rate is 500-830 rpm.

5. The method of claim 1, wherein the green low carbon modified steel fiber is prepared by the steps of: The method comprises the following steps: ​ The waste concrete powder suspension or cement mortar waste liquid is mixed and stirred with steel fibers, the steel fibers are rinsed after reacting for 10-300 min, and the modified steel fibers are obtained by drying in a flue gas atmosphere.

6. Use of the modified steel fiber according to claim 1 in ultra high performance concrete materials, characterized in that The content of the modified steel fibers is 1-3vol.%.

7. Use of the modified steel fiber according to claim 6 in ultra-high performance concrete materials, characterized in that The method comprises the following steps: uniformly mixing cement raw materials to obtain a slurry, adding the modified steel fibers and uniformly mixing to obtain an ultra-high performance concrete slurry.

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