High-strength and high-ductility concrete, and preparation method and application thereof

Abstract

This invention discloses a high-strength, high-ductility concrete, its preparation method, and its application. The concrete comprises: 40-52 parts silicate cement, 3.5-6 parts silica fume, 18-25 parts fine aggregate, 0.9-1.5 parts modified steel fiber, 0.75-1 part organic fiber, 0.08-0.13 parts water-reducing agent, and 16-30 parts water. The preparation of the modified steel fiber includes: (1) heating the steel fiber in a protective atmosphere to the two-phase region and holding it at that temperature, then quenching it to the bainitic region and holding it at that temperature, and finally water-cooling the obtained steel fiber to room temperature. (2) spraying a mixture of liquid film-forming agent and gypsum powder onto the steel fiber obtained in step (1) to coat it, and then drying it to obtain the modified steel fiber. This invention uses modified steel fiber and organic fiber to overcome the problems of insufficient bonding force between organic fiber and concrete matrix in high-ductility concrete and the limited improvement of crack resistance of concrete by organic fiber.

Description

Technical Field

[0001] This invention relates to the field of high-ductility concrete technology, and in particular to a high-strength, high-ductility concrete, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] A large number of existing masonry structures, some three or four decades old and still in use, suffer from poor structural integrity and low load-bearing capacity due to their age and the limitations of their original design. With increasing use, the safety and reliability of these structures have significantly decreased. Therefore, many early masonry structures require reinforcement and renovation. Furthermore, changes in building function during use have led to insufficient load-bearing capacity, resulting in a continuous expansion of the repair and reinforcement scale for older brick masonry structures. Newly constructed masonry structures also require repair and reinforcement due to damage caused by improper design, construction errors, or other reasons.

[0004] High-ductility concrete (ECC) is a special type of concrete with high crack resistance and ductility, composed of cementitious materials, fine aggregates, admixtures, and fibers. Because its deformation capacity far exceeds that of ordinary concrete, it is also known as "flexible concrete." As a reinforcing material, it can effectively improve the load-bearing capacity, ductility, and seismic resistance of masonry structures. Currently, high-ductility concrete mainly improves toughness by adding fibers. However, the aforementioned fibers are primarily organic fibers, which have limited tensile strength, thus offering limited improvement in the crack resistance of concrete. Furthermore, as the concrete matrix gradually hardens and shrinks, cracks easily form between the fibers and the concrete matrix, resulting in a weakened bond between them, thereby reducing the fiber's contribution to improving the crack resistance of concrete. Summary of the Invention

[0005] In view of this, the present invention provides a high-strength, high-ductility concrete (HECC), its preparation method, and its application. It utilizes modified steel fibers and organic fibers to overcome the problems of insufficient bonding strength between organic fibers and the concrete matrix, and the limited improvement in crack resistance of concrete by organic fibers in traditional high-ductility concrete (ECC). To achieve the above objectives, the present invention discloses the following technical solution.

[0006] First, this invention discloses a high-strength, high-ductility concrete, the raw material composition of which includes: 40-52 parts by weight of silicate cement, 3.5-6 parts by weight of silica fume, 18-25 parts by weight of fine aggregate, 0.9-1.5 parts by weight of modified steel fiber, 0.75-1 part by weight of organic fiber, 0.08-0.13 parts by weight of water-reducing agent, and 16-30 parts by weight of mixing water. The preparation of the modified steel fiber includes the following steps:

[0007] (1) Heat the steel fiber to the two-phase region in a protective atmosphere and keep it at that temperature. After that, quench the steel fiber to the bainite region and keep it at that temperature. Finally, cool the steel fiber to room temperature with water to obtain the final product.

[0008] (2) Mix the liquid film-forming agent with the gypsum powder evenly, then coat the surface of the steel fiber obtained in step (1) with the resulting mixture, and dry it to obtain the modified steel fiber.

[0009] Furthermore, in step (1), the holding time of the two-phase region is 3 to 7 minutes. By heating the two-phase region of the steel fiber, ferrite and austenite phases are formed in the steel fiber. The temperature range of the two-phase region of the steel fiber is related to the composition of the steel fiber and can be determined by means of a thermal expansion phase transformation instrument.

[0010] Furthermore, in step (1), the protective atmosphere includes any one of nitrogen, argon, etc., and its main function is to reduce the oxidation of the steel fiber surface.

[0011] Further, in step (1), the steel fiber is added to a salt bath where the temperature is maintained in the bainitic region of the steel fiber for heat preservation. Optionally, the heat preservation time in the bainitic region is 5-10 minutes. The temperature range in which the bainitic region of the steel fiber is located is related to the composition of the steel fiber and can be determined by means of a thermal expansion phase transformation instrument, etc. The salt bath is a commonly used salt bath quenching medium. By heat preservation in this temperature range, some of the austenitic phase in the steel fiber is transformed into bainite, and the remaining austenitic phase becomes retained austenite in the steel fiber, which exerts a TRIP effect when the concrete is subjected to load, thereby improving the crack resistance of the concrete.

[0012] Further, in step (2), the ratio of gypsum powder to liquid film-forming agent is 1g:10-15ml. Optionally, the liquid film-forming agent includes any one of ethylene-vinyl acetate emulsion, acrylate emulsion, styrene-acrylic emulsion, waterborne polyurethane emulsion, etc. The particle size of the gypsum powder is 400-500 mesh. The solid content of the liquid film-forming agent is 20-30%.

[0013] Further, in step (2), the ratio of the mixture to the steel fiber is 3-5 ml: 1 g.

[0014] Further, in step (2), the drying method is to dry at room temperature for 20 to 24 hours to solidify the film-forming agent coating the surface of the steel fiber into a film, while using the film layer to load the gypsum powder onto the surface of the steel fiber.

[0015] Furthermore, the organic fiber is a modified organic fiber, and its preparation method includes the following steps: mixing a liquid film-forming agent with gypsum powder evenly, then coating the surface of the organic fiber with the resulting mixture, and drying it after completion to obtain the modified organic fiber.

[0016] Furthermore, the ratio of the mixture to the organic fiber is 2–3.5 ml: 1 g. The composition and proportions of the mixture are as described above.

[0017] Furthermore, the drying method involves drying at room temperature for 18 to 20 hours to allow the film-forming agent coating the surface of the organic fibers to solidify into a film, while simultaneously using the film layer to load the gypsum micropowder onto the surface of the organic fibers.

[0018] Furthermore, the organic fiber includes, but is not limited to, at least one of polypropylene fiber and polyvinyl alcohol fiber. Optionally, the organic fiber has a length of 10–30 mm and a diameter of 0.2–0.5 mm.

[0019] Preferably, the steel fibers are wavy, thereby increasing the difficulty of pulling them out of the concrete matrix. Optionally, the steel fibers have a length of 10–20 mm and a diameter of 0.2–0.5 mm.

[0020] Furthermore, the water-reducing agent includes any one of polycarboxylate water-reducing agents, naphthalene-based water-reducing agents, aliphatic water-reducing agents, etc.

[0021] Secondly, the present invention discloses a method for preparing high-strength and high-ductility concrete, comprising the following steps: mixing silicate cement, silica fume, fine aggregate, modified steel fiber and organic fiber evenly, then adding the water-reducing agent and mixing water to the obtained dry mix, and stirring evenly to obtain the final product.

[0022] Finally, this invention discloses the application of the high-strength, high-ductility concrete in the repair and reinforcement of masonry structures in buildings.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] This invention incorporates modified steel fibers into concrete, which, compared to organic fibers, can better improve the crack resistance of concrete. It also helps reduce cracks between the fibers and the concrete matrix caused by the gradual hardening and shrinkage of the matrix, thus mitigating the fiber's contribution to improving the concrete's crack resistance. This is because: First, the steel fibers are treated as described in step (1) above, transforming them into TRIP steel fibers primarily composed of ferrite, bainite, and retained austenite. Further, the TRIP steel fibers are coated with a mixture of liquid film-forming agent and gypsum powder. After curing, this mixture forms a protective film on the steel fiber surface, and the gypsum powder is loaded onto the steel fiber surface using this protective film. When this modified steel fiber enters the concrete matrix, the protective film on the steel fiber surface significantly reduces the contact between moisture and the steel fiber itself, thus preventing the steel fiber from failing due to corrosion or its ability to strengthen the concrete during the service life of the high-strength, high-ductility concrete of this invention. Simultaneously, after the modified steel fibers enter the concrete matrix, the gypsum powder fixed in the protective film reacts with the tricalcium aluminate in the silicate cement to form ettringite, which has micro-expansion properties and coats the surface of the steel fibers. This not only fills the gaps between the steel fibers and the concrete matrix caused by shrinkage during hydration and hardening, but also, as a medium, strengthens the bond between the steel fibers and the concrete matrix, effectively improving the bonding strength. This increases the energy required for separation between the steel fibers and the concrete matrix during cracking under load, thus enhancing the concrete's crack resistance. Furthermore, during cracking under load, the retained austenite in the steel fibers undergoes a transformation-induced plasticity (TRIP) effect under stress, transforming into martensite. This process absorbs the load on the concrete, delaying cracking and increasing its toughness. Furthermore, during the aforementioned TRIP effect, a raised surface effect can also be formed on the steel fiber surface. This means that the residual austenite in the steel fiber transforms into martensite, causing a raised surface on the steel fiber. This further increases the difficulty of extracting the steel fiber from the concrete, thereby improving the crack resistance of the concrete. It can be seen that the modified steel fiber of this invention not only initiates the enhancement of concrete crack resistance during the hydration and hardening stage, but also transforms traditional steel fibers into TRIP steel fibers, forcing the steel fibers to further delay concrete cracking through phase transformation, thus fully utilizing the load on the concrete to improve its crack resistance.In addition, the present invention also modifies the organic fibers to form a coating film with gypsum powder on the surface of the organic fibers. When the organic fibers enter the high-strength and high-ductility concrete of the present invention, they can also play a role in improving the bonding force between the concrete matrix and the fibers, increasing the difficulty of extracting the organic fibers from the concrete, thereby improving the strengthening ability of the organic fibers to enhance the crack resistance of the concrete. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0026] Figure 1 Metallographic image of the steel fiber prepared in Example 1 of this invention.

[0027] Figure 2 This is a test diagram of the tensile strength of the specimen tested in Embodiment 1 of the present invention.

[0028] Figure 3 Metallographic image of the steel fiber prepared in Example 2 of this invention.

[0029] Figure 4 Metallographic image of the steel fiber prepared in Example 3 of this invention.

[0030] Figure 5 Metallographic image of the steel fiber prepared in Example 4 of this invention. Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. The present invention will now be further described with reference to specific embodiments.

[0032] It should be noted that the following embodiments and materials are for illustrative purposes only and are not intended to limit the technical solutions of the present invention. For example, the main chemical components of the steel fibers listed below are merely examples and do not explicitly or implicitly suggest that the preparation of the high-strength and high-ductility concrete material of the present invention is limited to steel fibers with the following components.

[0033] The steel fibers described in the following examples are made of low-carbon medium-manganese steel, whose main components include: 0.27% C, 5.7% Mn, 1.1% Si, 0.09% P, 0.013S, 0.1% Ti, with the balance being Fe and unavoidable impurities.

[0034] Example 1

[0035] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0036] 1. Preparation of modified steel fibers:

[0037] (1) Steel fibers (mainly 10-15 mm in length and 0.2-0.3 mm in diameter) were heated to 800°C in a nitrogen atmosphere at a heating rate of 10°C / min and held for 5 min. After heating, the resulting steel fibers were placed in a salt bath at 420°C and held for 8 min. Finally, the steel fibers were cooled to room temperature in water and then removed and dried to remove residual moisture. The microscopic image under a metallographic microscope is shown below. Figure 1 As shown, it can be seen that it contains a large amount of white residual austenite phase.

[0038] (2) An acrylic emulsion with a solid content of 30% and 500-mesh gypsum powder are mixed at a ratio of 12ml:1g and stirred evenly to form a mixture. The steel fibers obtained in step (1) are placed in a coating machine, and the mixture is sprayed onto the continuously rolling steel fibers in the coating machine at a ratio of 4ml:1g for coating. After completion, the fibers are dried at room temperature for 24 hours to allow the acrylic emulsion coating the surface of the steel fibers to solidify into a film, thus obtaining the modified steel fibers.

[0039] 2. Prepare the following raw materials: 47 parts by weight of 42.5 ordinary Portland cement, 5 parts by weight of silica fume, 22 parts by weight of fine aggregate, 1.3 parts by weight of the modified steel fiber prepared in this embodiment, 0.9 parts by weight of polypropylene fiber, 0.1 parts by weight of polycarboxylate superplasticizer, and 25 parts by weight of mixing water. The length of the polypropylene fiber is mainly distributed between 10 and 20 mm, and the diameter is mainly distributed between 0.2 and 0.3 mm; the water reduction rate of the superplasticizer is 25%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0040] 3. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and polypropylene fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0041] According to JC / T 2461-2018 "Test Methods for Mechanical Properties of High-Ductility Fiber-Reinforced Cementitious Composites", the mechanical properties of specimens prepared from the concrete slurry described in this embodiment were tested at 28 days of age using a universal testing machine (see reference). Figure 2 The results were: compressive strength = 67.31 MPa, flexural strength = 21.03 MPa, and tensile strength = 14.02 MPa.

[0042] Example 2

[0043] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0044] 1. Preparation of modified steel fibers:

[0045] (1) Steel fibers (mainly 10-15 mm in length and 0.2-0.3 mm in diameter) were heated to 780°C in a nitrogen atmosphere at a heating rate of 10°C / min and held for 7 min. After heating, the steel fibers were placed in a salt bath at 400°C and held for 10 min. Finally, the steel fibers were cooled to room temperature in water and then removed and dried to remove residual moisture from the surface. The microscopic image of the fibers under a metallographic microscope is shown below. Figure 3 As shown, it can be seen that it contains a large amount of white residual austenite phase.

[0046] (2) A waterborne polyurethane emulsion with a solid content of 20% and 450-mesh gypsum powder are mixed at a ratio of 10 ml: 1 g and stirred evenly to form a mixture. The steel fibers obtained in step (1) are placed in a coating machine, and the mixture is sprayed onto the continuously rolling steel fibers in the coating machine at a ratio of 3 ml: 1 g for coating. After completion, the mixture is dried at room temperature for 20 hours to allow the waterborne polyurethane emulsion coated on the surface of the steel fibers to solidify into a film, thus obtaining the modified steel fibers.

[0047] 2. Prepare the following raw materials: 52 parts by weight of 42.5 ordinary silicate cement, 6 parts by weight of silica fume, 25 parts by weight of fine aggregate, 1.5 parts by weight of the modified steel fiber prepared in this embodiment, 0.75 parts by weight of polyvinyl alcohol fiber, 0.13 parts by weight of polycarboxylate superplasticizer, and 30 parts by weight of mixing water. The length of the polyvinyl alcohol fiber is mainly distributed between 10 and 20 mm, and the diameter is mainly distributed between 0.2 and 0.3 mm; the water reduction rate of the superplasticizer is 20%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0048] 3. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and polyvinyl alcohol fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0049] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composites", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 64.23 MPa, flexural strength = 20.32 MPa, and tensile strength = 14.97 MPa.

[0050] Example 3

[0051] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0052] 1. Preparation of modified steel fibers:

[0053] (1) Steel fibers (mainly 14-20 mm in length and 0.3-0.5 mm in diameter) were heated to 810°C in a nitrogen atmosphere at a heating rate of 10°C / min and held for 3 min. After heating, the resulting steel fibers were placed in a salt bath at 440°C and held for 5 min. Finally, the steel fibers were cooled to room temperature in water. The fibers were then removed and dried to remove residual moisture. The microscopic image under a metallographic microscope is shown below. Figure 4 As shown, it can be seen that it contains a large amount of white residual austenite phase.

[0054] (2) Mix ethylene-vinyl acetate emulsion with a solid content of 20% with 400-mesh gypsum powder at a ratio of 15ml:1g and stir until homogeneous to form a mixture. Place the steel fibers obtained in step (1) into a coating machine, and then spray the mixture onto the continuously rolling steel fibers in the coating machine at a ratio of 5ml:1g to coat them. After completion, air dry at room temperature for 24 hours to allow the ethylene-vinyl acetate emulsion coated on the surface of the steel fibers to solidify into a film, thus obtaining modified steel fibers.

[0055] 2. Preparation of modified organic fibers: Ethylene-vinyl acetate emulsion with a solid content of 20% was mixed with 400-mesh gypsum powder at a ratio of 15 ml: 1 g and stirred until homogeneous to form a mixture. Polypropylene fibers (mainly 15–30 mm in length and 0.3–0.5 mm in diameter) were placed in a coating machine, and the mixture was sprayed onto the continuously rotating steel fibers in the coating machine at a ratio of 3.5 ml: 1 g for coating. After completion, the fibers were air-dried at room temperature for 20 hours to allow the ethylene-vinyl acetate emulsion coating the surface of the steel fibers to solidify into a film, thus obtaining the modified polypropylene fibers.

[0056] 3. Prepare the following raw materials: 45 parts by weight of 42.5 ordinary silicate cement, 4 parts by weight of silica fume, 20 parts by weight of fine aggregate, 1.1 parts by weight of the modified steel fiber prepared in this embodiment, 0.8 parts by weight of the modified polypropylene fiber prepared in this embodiment, 0.1 parts by weight of polycarboxylate superplasticizer, and 21 parts by weight of mixing water; the water reduction rate of the superplasticizer is 25%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0057] 4. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and modified polypropylene fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0058] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composite Materials", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 69.57 MPa, flexural strength = 21.68 MPa, and tensile strength = 15.88 MPa.

[0059] Example 4

[0060] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0061] 1. Preparation of modified steel fibers:

[0062] (1) Steel fibers (mainly 14-20 mm in length and 0.3-0.5 mm in diameter) were heated to 800°C in a nitrogen atmosphere at a heating rate of 10°C / min and held for 5 min. After heating, the resulting steel fibers were placed in a salt bath at 410°C and held for 7 min. Finally, the steel fibers were cooled to room temperature in water. The fibers were then removed and dried to remove residual moisture. The microscopic image under a metallographic microscope is shown below. Figure 5 As shown, it can be seen that it contains a large amount of white residual austenite phase.

[0063] (2) A styrene-acrylic emulsion with a solid content of 25% and 450-mesh gypsum powder are mixed at a ratio of 13 ml: 1 g and stirred evenly to form a mixture. The steel fibers obtained in step (1) are placed in a coating machine, and the mixture is sprayed onto the steel fibers that are continuously rolling in the coating machine at a ratio of 4.5 ml: 1 g for coating. After completion, the mixture is dried at room temperature for 24 hours to allow the styrene-acrylic emulsion coating the surface of the steel fibers to solidify into a film, thus obtaining the modified steel fibers.

[0064] 2. Preparation of modified organic fibers: A 25% solids content styrene-acrylic emulsion and 450-mesh gypsum powder were mixed at a ratio of 13 ml: 1 g and stirred until homogeneous to form a mixture. Polyvinyl alcohol fibers (with a length mainly between 15 and 30 mm and a diameter mainly between 0.3 and 0.5 mm) were placed in a coating machine, and the mixture was sprayed onto the continuously rolling steel fibers in the coating machine at a ratio of 2 ml: 1 g for coating. After completion, the fibers were air-dried at room temperature for 18 hours to allow the styrene-acrylic emulsion coating the surface of the steel fibers to solidify into a film, thus obtaining the modified polyvinyl alcohol fibers.

[0065] 3. Prepare the following raw materials: 40 parts by weight of 42.5 ordinary silicate cement, 3.5 parts by weight of silica fume, 18 parts by weight of fine aggregate, 0.9 parts by weight of the modified steel fiber prepared in this embodiment, 1 part by weight of the modified polyvinyl alcohol fiber prepared in this embodiment, 0.13 parts by weight of naphthalene-based water-reducing agent, and 16 parts by weight of mixing water; the water-reducing agent has a water reduction rate of 30%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0066] 4. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and modified polyvinyl alcohol fiber in a mixer and mix for 10 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0067] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composites", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 70.26 MPa, flexural strength = 21.55 MPa, and tensile strength = 16.31 MPa.

[0068] Example 5

[0069] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0070] 1. Prepare the following raw materials: 47 parts by weight of 42.5 ordinary Portland cement, 5 parts by weight of silica fume, 22 parts by weight of fine aggregate, 1.3 parts by weight of steel fiber, 0.9 parts by weight of polypropylene fiber, 0.1 parts by weight of polycarboxylate superplasticizer, and 25 parts by weight of mixing water. The steel fiber is the unmodified raw steel fiber from Example 1 above. The polypropylene fiber has a length mainly between 10 and 20 mm and a diameter mainly between 0.2 and 0.3 mm; the water-reducing agent has a water reduction rate of 25%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0071] 2. First, place the silicate cement, silica fume, fine aggregate, steel fiber and polypropylene fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0072] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composite Materials", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 55.46 MPa, flexural strength = 13.79 MPa, and tensile strength = 10.96 MPa.

[0073] Example 6

[0074] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0075] 1. Preparation of modified steel fibers: Steel fibers (with a length mainly between 10 and 15 mm and a diameter mainly between 0.2 and 0.3 mm) are heated to 800°C in a nitrogen atmosphere at a heating rate of 10°C / min and held at that temperature for 5 min. After that, the steel fibers are placed in a salt bath at 420°C and held for 8 min. Finally, the steel fibers are placed in room temperature water and cooled to room temperature. Then, the steel fibers are taken out and dried to remove residual moisture from the surface, thus obtaining modified steel fibers.

[0076] 2. Prepare the following raw materials: 47 parts by weight of 42.5 ordinary Portland cement, 5 parts by weight of silica fume, 22 parts by weight of fine aggregate, 1.3 parts by weight of the modified steel fiber prepared in this embodiment, 0.9 parts by weight of polypropylene fiber, 0.1 parts by weight of polycarboxylate superplasticizer, and 25 parts by weight of mixing water. The length of the polypropylene fiber is mainly distributed between 10 and 20 mm, and the diameter is mainly distributed between 0.2 and 0.3 mm; the water reduction rate of the superplasticizer is 25%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0077] 3. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and polypropylene fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0078] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composite Materials", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 59.71 MPa, flexural strength = 16.85 MPa, and tensile strength = 12.04 MPa.

[0079] Example 7

[0080] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0081] 1. Preparation of modified steel fibers:

[0082] (1) The steel fibers (with a length mainly between 10 and 15 mm and a diameter mainly between 0.2 and 0.3 mm) are heated to 780°C in a nitrogen atmosphere at a heating rate of 10°C / min and held for 7 min. After that, the steel fibers are placed in a salt bath at 400°C and held for 10 min. Finally, the steel fibers are placed in room temperature water to cool to room temperature. Then, the steel fibers are taken out and dried to remove the residual moisture on the surface for later use.

[0083] (2) Place the steel fiber obtained in step (1) into a coating machine, and then spray the water-based polyurethane emulsion with a solid content of 20% onto the steel fiber that is constantly rolling in the coating machine at a ratio of 3ml:1g for coating. After completion, air dry at room temperature for 20 hours to allow the water-based polyurethane emulsion coated on the surface of the steel fiber to solidify into a film, thus obtaining the modified steel fiber.

[0084] 2. Prepare the following raw materials: 52 parts by weight of 42.5 ordinary silicate cement, 6 parts by weight of silica fume, 25 parts by weight of fine aggregate, 1.5 parts by weight of the modified steel fiber prepared in this embodiment, 0.75 parts by weight of polyvinyl alcohol fiber, 0.13 parts by weight of polycarboxylate superplasticizer, and 30 parts by weight of mixing water. The length of the polyvinyl alcohol fiber is mainly distributed between 10 and 20 mm, and the diameter is mainly distributed between 0.2 and 0.3 mm; the water reduction rate of the superplasticizer is 20%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0085] 3. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and polyvinyl alcohol fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0086] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composites", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 60.81 MPa, flexural strength = 17.49 MPa, and tensile strength = 12.83 MPa.

[0087] Example 8

[0088] A method for preparing high-strength, high-ductility concrete includes the following steps:

[0089] 1. Preparation of modified steel fibers: Aqueous polyurethane emulsion with a solid content of 20% and 450-mesh gypsum powder are mixed at a ratio of 10ml:1g and stirred evenly to form a mixture. Steel fibers (mainly 10-15mm in length and 0.2-0.3mm in diameter) are placed in a coating machine, and the mixture is sprayed onto the continuously rotating steel fibers in the coating machine at a ratio of 3ml:1g for coating. After completion, the fibers are air-dried at room temperature for 20 hours to allow the aqueous polyurethane emulsion coating the surface of the steel fibers to solidify into a film, thus obtaining the modified steel fibers.

[0090] 2. Prepare the following raw materials: 52 parts by weight of 42.5 ordinary silicate cement, 6 parts by weight of silica fume, 25 parts by weight of fine aggregate, 1.5 parts by weight of the modified steel fiber prepared in this embodiment, 0.75 parts by weight of polyvinyl alcohol fiber, 0.13 parts by weight of polycarboxylate superplasticizer, and 30 parts by weight of mixing water. The length of the polyvinyl alcohol fiber is mainly distributed between 10 and 20 mm, and the diameter is mainly distributed between 0.2 and 0.3 mm; the water reduction rate of the superplasticizer is 20%; the fine aggregate is continuously graded quartz sand with a particle size between 0.3 and 0.6 mm.

[0091] 3. First, place the silicate cement, silica fume, fine aggregate, modified steel fiber and polyvinyl alcohol fiber in a mixer and mix for 15 minutes. Then, add the water-reducing agent and mixing water to the obtained dry mix and stir for 5 minutes to obtain concrete slurry.

[0092] According to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composites", the mechanical properties of the specimens prepared from the concrete slurry in this embodiment were tested at 28 days of age using a universal testing machine. The results were: compressive strength = 57.19 MPa, flexural strength = 16.43 MPa, and tensile strength = 11.64 MPa.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, high-ductility concrete, characterized in that, The raw material composition of this concrete includes: 40-52 parts by weight of silicate cement, 3.5-6 parts by weight of silica fume, 18-25 parts by weight of fine aggregate, 0.9-1.5 parts by weight of modified steel fiber, 0.75-1 parts by weight of organic fiber, 0.08-0.13 parts by weight of water-reducing agent, and 16-30 parts by weight of mixing water; wherein, the preparation of the modified steel fiber includes the following steps: (1) Heat the steel fiber to the two-phase region in a protective atmosphere and hold it at that temperature. After that, quench the steel fiber to the bainitic region and hold it at that temperature. Finally, cool the steel fiber to room temperature with water to obtain the desired product. (2) Mix the liquid film-forming agent with the gypsum powder evenly, then coat the surface of the steel fiber obtained in step (1) with the resulting mixture, and dry it to obtain the modified steel fiber.

2. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (1), the heat preservation time of the two-phase region is 3 to 7 minutes.

3. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (1), the protective atmosphere includes either nitrogen or argon.

4. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (1), the steel fiber is added to a salt bath where the temperature is maintained in the bainitic region of the steel fiber for heat preservation.

5. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (1), the heat preservation time of the bainitic region is 5~10 min.

6. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the ratio of gypsum powder to liquid film-forming agent is 1g:10~15ml.

7. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the liquid film-forming agent includes any one of ethylene-vinyl acetate emulsion, acrylate emulsion, styrene-acrylic emulsion, and waterborne polyurethane emulsion.

8. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the solid content of the liquid film-forming agent is 20-30%.

9. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the particle size of the gypsum powder is 400~500 mesh.

10. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the ratio of the mixture to the steel fiber is 3~5ml:1g.

11. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the drying method is to let it stand at room temperature for 20 to 24 hours.

12. The high-strength, high-ductility concrete according to any one of claims 1-5, characterized in that, The organic fiber includes at least one of polypropylene fiber and polyvinyl alcohol fiber.

13. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the steel fiber is wavy.

14. The high-strength, high-ductility concrete according to claim 1, characterized in that, The organic fibers have a length of 10-30 mm and a diameter of 0.2-0.5 mm.

15. The high-strength, high-ductility concrete according to claim 1, characterized in that, In step (2), the steel fiber has a length of 10~20mm and a diameter of 0.2~0.5mm.

16. The high-strength, high-ductility concrete according to claim 1, characterized in that, The water-reducing agent includes any one of polycarboxylate water-reducing agents, naphthalene-based water-reducing agents, and aliphatic water-reducing agents.

17. The high-strength, high-ductility concrete according to any one of claims 1-16, characterized in that, The organic fiber is a modified organic fiber, and its preparation method includes the following steps: mixing a liquid film-forming agent with gypsum powder evenly, then coating the surface of the organic fiber with the resulting mixture, and drying it after completion to obtain the modified organic fiber.

18. The high-strength, high-ductility concrete according to claim 17, characterized in that, The ratio of gypsum powder to liquid film-forming agent is 1g:10~15ml; the ratio of mixture to organic fiber is 2~3.5ml:1g.

19. The high-strength, high-ductility concrete according to claim 17, characterized in that, The method for drying the mixture after spraying it onto the organic fibers is to let it stand at room temperature for 18-20 hours.

20. The method for preparing high-strength, high-ductility concrete according to any one of claims 1-19, characterized in that, The process includes the following steps: mixing the silicate cement, silica fume, fine aggregate, modified steel fiber and organic fiber evenly, then adding the water-reducing agent and mixing water to the resulting dry mix, and stirring evenly to obtain the final product.

21. The application of the high-strength, high-ductility concrete according to any one of claims 1-19 or the high-strength, high-ductility concrete obtained by the preparation method according to claim 20 in the repair and reinforcement of masonry structures of buildings.

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