Preparation method of electromagnetic shielding concrete with porous cross-linked structure

Abstract

The invention discloses a preparation method of electromagnetic shielding concrete with a porous cross-linked structure, which comprises the following steps: (1) dispersing steel fibers into water, then adding alkali liquor, and then carrying out stirring reaction under a heating condition; and adding iron ions and / or ferrous ions, uniformly mixing, separating out the steel fibers, and carrying out heat treatment on the steel fibers to obtain the pretreated steel fibers. And (2) dispersing the pretreated steel fiber into a polyvinyl alcohol solution, then adding nano powder with an electromagnetic shielding function, stirring, and then separating out the fiber, thereby obtaining the modified steel fiber. And (3) uniformly mixing a cementing material, the modified steel fiber, a water reducing agent and mixing water to obtain slurry, pouring the slurry into a concrete structure, and performing freeze-drying treatment after final setting to obtain the pretreated concrete. The steel fibers are subjected to surface modification to be converted into the electromagnetic shielding fibers, so that the strength of the concrete can be remarkably improved, and the electromagnetic shielding performance of the concrete can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic shielding concrete, and in particular to a method for preparing electromagnetic shielding concrete with a porous cross-linked structure. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Since the beginning of the new century, the rapid development of information technology has made communication and electronic equipment an indispensable tool in people's daily work and life. Mobile phones, computers, microwave ovens, televisions, X-ray generators and other equipment will generate a large number of electromagnetic waves of different bands and frequencies, which have a huge impact on human life and the environment. The electromagnetic radiation pollution problem brought about by this has attracted more and more attention. Especially in the military industry, electromagnetic radiation brings certain interference to military facilities and there is a certain risk of leakage. How to reduce the radiation and interference of electromagnetic waves has become one of the hot issues studied by scientists.

[0004] Electromagnetic shielding concrete is a kind of concrete that can protect or block electromagnetic waves by introducing electromagnetic shielding functional components into concrete. It can prevent electromagnetic waves from leaking inside the building, and can also prevent external electromagnetic pollution from harming indoor equipment and human body. At present, the preparation of electromagnetic shielding concrete generally adopts the method of adding electromagnetic shielding functional components into concrete, and uses the absorption or reflection effect of functional components on electromagnetic waves to achieve the purpose of electromagnetic shielding. However, on the one hand, the electromagnetic shielding functional components have poor adaptability and distribution uniformity with concrete, which easily causes the deterioration of the performance of concrete itself. On the other hand, the functional components have limited effect in absorbing or reflecting electromagnetic waves, resulting in poor electromagnetic shielding performance. In addition, the high cost problem caused by a large amount of electromagnetic shielding functional components is also an important factor restricting the development of electromagnetic shielding concrete. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing electromagnetic shielding concrete with a porous cross-linked structure, which converts steel fibers into electromagnetic shielding fibers by surface modification of steel fibers, thereby significantly improving the strength of concrete and improving the electromagnetic shielding performance of concrete. Specifically, the technical solution of the present invention is as follows.

[0006] A method for preparing electromagnetic shielding concrete with a porous cross-linked structure, comprising the steps of: (1) After dispersing the steel fibers in water, an alkali solution is added, and then the mixture is stirred under heating conditions. After the reaction is completed, iron ions and / or ferrous ions are added and mixed evenly, and then the steel fibers are separated and heat-treated to convert the iron hydroxide and / or ferrous hydroxide on the steel fibers into iron oxide, thereby obtaining pretreated steel fibers.

[0007] (2) The pretreated steel fiber is dispersed in a polyvinyl alcohol solution, and then the nano powder with electromagnetic shielding function is added and stirred. After completion, the fiber is separated to obtain the modified steel fiber with electromagnetic shielding function.

[0008] (3) Cement, silica fume, filler and nano powder with electromagnetic shielding function are dispersed in a non-aqueous solvent, and then subjected to ultrasonic dispersion treatment. After completion, the solid matter is separated and dried to obtain a dense cementitious material system.

[0009] (4) The dense cementitious material system, the modified steel fiber, the water reducing agent and the mixing water are uniformly mixed to obtain a slurry, which is poured into a concrete structure, and then freeze-dried after the slurry is finally set, thereby obtaining a pretreated concrete structure.

[0010] (5) The pretreated concrete structure is placed in a saturated liquid containing at least one of ferric ions and ferrous ions for curing. After curing, sodium borohydride is added and mixed evenly. After the reaction is completed, the concrete structure is taken out and dried to obtain electromagnetic shielding concrete.

[0011] Furthermore, in step (1), the length of the steel fiber is 12-14 mm, and the diameter is 0.2-0.25 mm.

[0012] Furthermore, in step (1), the mass fraction of the alkali solution in the water is 5-15%. Optionally, the alkali solution includes at least one of a sodium hydroxide solution, a potassium hydroxide solution, and the like.

[0013] Furthermore, in step (1), the heating temperature is 40-60° C. and the reaction time is 8-12 h.

[0014] Furthermore, in step (1), the molar ratio of the alkaline component to the iron ion and / or ferrous ion in the alkali solution is 2 to 3: 1. Optionally, the iron ion is provided by at least one of ferric chloride, ferric sulfate, ferric nitrate, etc. The ferrous ion is provided by at least one of ferrous chloride, ferrous sulfate, ferrous nitrate, etc.

[0015] Furthermore, in step (1), the heat treatment temperature is 400-500° C. and the time is 20-40 min.

[0016] Furthermore, in step (2), the ratio of the pretreated steel fiber to the polyvinyl alcohol solution is 1 g: 10-30 ml. Optionally, the mass fraction of the polyvinyl alcohol solution is 10-20%.

[0017] Furthermore, in step (2), the mass ratio of the pretreated steel fiber to the nano powder is 1:3-5. Preferably, the nano powder is composited by an inorganic electromagnetic shielding material and an organic electromagnetic shielding material in any proportion. Optionally, the inorganic electromagnetic shielding material includes at least one of ferrite, metal powder, etc. The organic electromagnetic shielding material includes at least one of graphite powder, carbon black, etc.

[0018] Furthermore, in step (2), the stirring time is 1 to 2 hours.

[0019] Furthermore, in step (3), the non-aqueous solvent includes at least one of anhydrous methanol, anhydrous ethanol, isopropanol, etc., and the nanopowder having electromagnetic shielding function is as described above.

[0020] Furthermore, in step (3), the filler includes at least one of quartz powder, calcium carbonate powder, mica powder, etc. Optionally, the particle size of the filler is not less than 500 mesh.

[0021] Furthermore, in step (3), the stirring treatment time is 10 to 20 minutes.

[0022] Furthermore, in step (4), the proportions of the raw materials are as follows: the dense cementitious material system includes 600-800 parts by weight of cement, 50-200 parts by weight of silica fume, 50-100 parts by weight of filler, 20-35 parts by weight of nano powder with electromagnetic shielding function, 100-250 parts by weight of steel fiber, and 200-300 parts by weight of mixing water.

[0023] Furthermore, in step (4), the amount of the water reducer is 1.5-3% of the content of the dense cementitious material system. Optionally, the water reducer includes at least one of a naphthalene-based water reducer, an aliphatic water reducer, a polycarboxylic acid water reducer, and the like.

[0024] Furthermore, in step (4), the cement includes any one of ordinary Portland cement, sulphoaluminate cement, etc.

[0025] Furthermore, in step (4), the freeze-drying treatment temperature is -20 to 40°C, and then vacuum drying is performed at room temperature for 2 to 5 hours.

[0026] Furthermore, in step (5), the ratio of the pretreated concrete structure to the saturated liquid is 1 g: 20-40 ml. Optionally, the ferric ions / ferrous ions are provided by at least one of ferric chloride, ferric sulfate, ferric nitrate, ferrous chloride, ferrous sulfate, ferrous nitrate, and the like.

[0027] Furthermore, in step (5), the curing time is not less than one week, and water is added in a timely manner during the curing process to ensure that the concrete structure is completely immersed.

[0028] Furthermore, in step (5), sodium borohydride is added in a ratio such that the concentration of sodium borohydride in the saturated solution is 1 to 5 mol / L.

[0029] Furthermore, in step (5), the reaction time is 1 to 2 hours, and the drying time is 3 to 5 days.

[0030] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects: First, the present invention utilizes alkali solution to etch steel fiber, increases its surface roughness, and then generates nano iron oxide particles in situ reaction on the surface, and loads nano powder with electromagnetic shielding function on the surface of steel fiber through polyvinyl alcohol solution. The above-mentioned graded loading solves the agglomeration problem of nano powder, and also greatly increases the roughness of the surface of steel fiber, effectively enhances its performance of emitting and absorbing electromagnetic waves and the bonding force between steel fiber and concrete matrix, and improves the mechanical strength of concrete structure. Secondly, the present invention freezes the concrete structure after final setting and hardening and then performs vacuum heating. In this process, the ice crystals formed by the water in the concrete structure are sublimated and removed to form a porous cross-linked structure system interlaced with the steel fiber. Further, the present invention places the pre-treated concrete structure obtained by the above process in a saturated liquid containing iron ions / ferrous ions for curing and then uses sodium borohydride for reduction. In this process, on the one hand, the pre-treated concrete structure can continue to undergo hydration reaction to ensure its mechanical strength. On the other hand, after the ferric ions / ferrous ions enter the pre-treated concrete structure, they can react with the hydration product calcium hydroxide therein to form ferric hydroxide / ferrous iron, which reduces the product calcium hydroxide of the hydration reaction, and calmly promotes the balance of the hydration reaction to move in the direction of the hydration reaction, forming more hydrated gelling components, and improving the strength of the concrete. At the same time, the ferric hydroxide / ferrous iron helps to compact the micropores in the concrete structure, improve the strength and waterproof performance of the concrete structure. On the other hand, the nano iron particles formed after the remaining ferric ions / ferrous ions are reduced by sodium borohydride are solidified on the wall of the hole by the hydrated gelling components, thereby forming an electromagnetic shielding layer on the wall of the hole that can reflect and absorb electromagnetic waves.

[0031] When electromagnetic waves pass through this porous cross-linked concrete structure, on the one hand, the nano-powder with electromagnetic shielding function can absorb and reflect electromagnetic waves, weakening the propagation of electromagnetic signals. On the other hand, when electromagnetic waves pass through steel fibers, the nano-iron oxide on the fiber surface and the nano-powder with electromagnetic shielding function first absorb and reflect part of the electromagnetic waves, and secondly, the steel fibers can also reflect part of the signal. On the other hand, the cross-linking system composed of the steel fibers and the porous cross-linked structure causes electromagnetic waves to be continuously absorbed, refracted and emitted, and the electromagnetic wave signal intensity is greatly weakened, effectively improving the electromagnetic shielding effectiveness of concrete. The above method of the present invention effectively overcomes the problems of traditional electromagnetic shielding concrete with many leakage points, low shielding effectiveness, and narrow shielding range. The electromagnetic shielding concrete prepared by the present invention greatly increases the ability of concrete to absorb, reflect and refract electromagnetic wave signals, improves the degree of signal loss, greatly reduces the negative impact of electromagnetic shielding components on concrete strength, and comprehensively improves the electromagnetic shielding performance of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] It should be noted that the drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention and do not constitute an improper limitation of the present invention.

[0033] Figure 1 The scanning electron microscope image of the electromagnetic shielding concrete with porous cross-linked structure prepared in the following Example 1; Figure 2 This is a compressive strength test diagram of the porous cross-linked structure prepared in the following Examples 1 and 4. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Unless otherwise defined, all professional and scientific terms used in the present invention have the same meaning as those familiar to those skilled in the art. The preferred implementation methods and materials described in the present invention are only for demonstration purposes. The reagents or raw materials used in the invention can be purchased through conventional channels. If there are no special instructions, the reagents or raw materials used in the present invention are used in a conventional manner in the art or are used according to the product specification. Now the technical scheme of the present invention is further described in conjunction with specific embodiments.

[0035] Example 1 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: (1) Add steel fiber (length 12 mm, diameter 0.2 mm) to water and then add it to a 10% by mass sodium hydroxide solution, then heat it to 50°C and stir it for 10 hours. After completion, add iron sulfate in a ratio of 2:1 between sodium hydroxide and iron ions in the sodium hydroxide solution, mix well, and let it stand for 20 minutes, then separate the steel fiber and heat it to 460°C for 30 minutes to obtain pretreated steel fiber for standby use.

[0036] (2) The pretreated steel fiber and a 20% by mass polyvinyl alcohol solution are mixed in a ratio of 1 g:15 ml and stirred evenly, and then a nano powder with electromagnetic shielding function (nano iron powder: nano carbon black mass ratio = 1:1) is added and stirred for 2 hours, and the mass ratio of the pretreated steel fiber to the nano powder is 1:4. After completion, the fiber is separated to obtain a modified steel fiber with electromagnetic shielding function, which is set aside.

[0037] (3) Disperse 700 parts by weight of 42.5 ordinary Portland cement, 100 parts by weight of silica fume, 70 parts by weight of 500-mesh quartz powder, and 30 parts by weight of the nanopowder with electromagnetic shielding function in this embodiment in 1000 parts by weight of anhydrous ethanol according to the following proportions, and then perform ultrasonic dispersion treatment for 10 minutes. After completion, separate the solid matter, dry it, and obtain a dense cementitious material system for standby use.

[0038] (4) The dense cementitious material system, 180 parts by weight of the modified steel fiber of this embodiment, a polycarboxylic acid water-reducing agent (the amount of which is 2% of the content of the dense cementitious material system), and 240 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure. After the slurry is finally set, it is placed in a freeze dryer for freeze-drying treatment (first frozen to -30°C, and then vacuum dried at room temperature for 4 hours), thereby obtaining a pretreated concrete structure.

[0039] (5) The pretreated concrete structure is placed in a saturated solution of iron sulfate for curing for 7 days, with the ratio of the two being 1g:25ml. Then, sodium borohydride is added in a ratio of 2 mol / L in the saturated solution and stirred evenly. After reacting for 1 hour, the concrete structure is taken out and dried naturally for 4 days to obtain an electromagnetic shielding concrete structure, whose internal microstructure is as follows: Figure 1 shown.

[0040] Performance test: 1. According to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GBT 50081-2019), the compressive strength of the electromagnetic shielding concrete structure prepared in this embodiment was tested (such as Figure 22. According to ASTM 4935 (flange coaxial method), the shielding effectiveness SE (SE=R+A+M, where: R is reflection loss, A is absorption loss, M is multiple reflection loss, the larger the decibel value of SE, the stronger the shielding effectiveness) of the electromagnetic shielding concrete structure prepared in this embodiment is tested against electromagnetic waves. The test results are shown in the following table.

[0041] Example 2 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: (1) Add steel fiber (length 14 mm, diameter 0.25 mm) to water and then add it to a 5% by mass sodium hydroxide solution, then heat it to 40°C and stir it for 12 hours. After completion, add ferrous sulfate in a ratio of 3:1 between sodium hydroxide and ferrous ions in the sodium hydroxide solution, mix well, and let it stand for 20 minutes, then separate the steel fiber and heat it to 500°C for 20 minutes to obtain pretreated steel fiber for later use.

[0042] (2) The pretreated steel fiber and a 15% by mass polyvinyl alcohol solution are mixed in a ratio of 1 g:10 ml and stirred evenly, and then a nano powder with electromagnetic shielding function (nano ferroferric oxide powder: nano graphite powder mass ratio = 2:1) is added and stirred for 1 hour, and the mass ratio of the pretreated steel fiber to the nano powder is 1:3. After completion, the fiber is separated to obtain a modified steel fiber with electromagnetic shielding function, which is set aside.

[0043] (3) 800 parts by weight of 42.5 ordinary Portland cement, 200 parts by weight of silica fume, 100 parts by weight of 550-mesh calcium carbonate powder, and 35 parts by weight of the nanopowder with electromagnetic shielding function of this embodiment are dispersed in 1100 parts by weight of isopropanol according to the following proportions, and then ultrasonically dispersed for 20 minutes. After completion, the solid matter is separated and dried to obtain a dense cementitious material system for standby use.

[0044] (4) The dense cementitious material system, 250 parts by weight of the modified steel fiber of this embodiment, a polycarboxylic acid water-reducing agent (the amount of which is 3% of the content of the dense cementitious material system), and 300 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure. After the slurry is finally set, it is placed in a freeze dryer for freeze-drying treatment (first frozen to -20°C, and then vacuum dried at room temperature for 5 hours), thereby obtaining a pretreated concrete structure.

[0045] (5) The pretreated concrete structure is placed in a saturated ferrous sulfate solution for curing for 10 days, with the ratio of the two being 1 g:40 ml. Then, sodium borohydride is added in a ratio of 1 mol / L in the saturated solution and stirred evenly. After reacting for 2 hours, the concrete structure is taken out and naturally dried for 5 days to obtain an electromagnetic shielding concrete structure.

[0046] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0047] Example 3 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: (1) Add steel fiber (length 12 mm, diameter 0.2 mm) to water and then add it to a 15% by mass potassium hydroxide solution, then heat it to 60°C and stir it for 8 hours. After completion, add ferrous nitrate in a ratio of 2.5:1 between sodium hydroxide and ferrous ions in the sodium hydroxide solution, mix well, and let it stand for 20 minutes, then separate the steel fiber and heat it to 400°C for 40 minutes to obtain pretreated steel fiber for later use.

[0048] (2) The pretreated steel fiber and a 10% by mass polyvinyl alcohol solution are mixed at a ratio of 1 g:30 ml and stirred evenly, and then a nano powder with electromagnetic shielding function (nano ferroferric oxide powder: nano graphite powder mass ratio = 2:1) is added and stirred for 2 hours, and the mass ratio of the pretreated steel fiber to the nano powder is 1:5. After completion, the fiber is separated to obtain a modified steel fiber with electromagnetic shielding function, which is set aside.

[0049] (3) Disperse 600 parts by weight of 42.5 ordinary Portland cement, 50 parts by weight of silica fume, 50 parts by weight of 600-mesh mica powder, and 20 parts by weight of the nanopowder with electromagnetic shielding function in this embodiment in 1000 parts by weight of anhydrous methanol according to the following proportions, and then perform ultrasonic dispersion treatment for 10 minutes. After completion, separate the solid matter, dry it, and obtain a dense cementitious material system for standby use.

[0050] (4) The dense cementitious material system, 100 parts by weight of the modified steel fiber of this embodiment, a naphthalene-based water reducer (the amount of which is 1.5% of the content of the dense cementitious material system), and 200 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure. After the slurry is finally set, it is placed in a freeze dryer for freeze drying (first frozen to -40°C, and then vacuum dried at room temperature for 2 hours) to obtain a pretreated concrete structure.

[0051] (5) The pretreated concrete structure is placed in a saturated solution of ferrous nitrate for curing for 10 days, with the ratio of the two being 1 g:20 ml. Then, sodium borohydride is added in a ratio of 5 mol / L in the saturated solution and stirred evenly. After reacting for 1.5 hours, the concrete structure is taken out and naturally dried for 3 days to obtain an electromagnetic shielding concrete structure.

[0052] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0053] Example 4 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: (1) The dense cementitious material system of Example 1, 180 parts by weight of steel fibers (length 12 mm, diameter 0.2 mm), a polycarboxylic acid water-reducing agent (the amount of which is 2% of the content of the dense cementitious material system), and 240 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure, and after final setting, it is placed in a freeze dryer for freeze drying (first frozen to -30°C, and then vacuum dried at room temperature for 4 hours), thereby obtaining a pretreated concrete structure.

[0054] (2) The pretreated concrete structure is placed in a saturated iron sulfate solution for curing for 7 days, with the ratio of the two being 1 g:25 ml. Then, sodium borohydride is added in a ratio of 2 mol / L in the saturated solution and stirred evenly. After reacting for 1 hour, the concrete structure is taken out and naturally dried for 4 days to obtain an electromagnetic shielding concrete structure.

[0055] Performance test: The compressive strength of the electromagnetic shielding concrete structure prepared in this embodiment was tested using the same method as in the above embodiment 1 (e.g. Figure 2 The test results are shown in the following table) and the shielding effectiveness SE against electromagnetic waves.

[0056] Example 5 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure, which differs from the above-mentioned embodiment 2 in that the pretreated steel fiber prepared in embodiment 2 is used instead of the modified steel fiber with electromagnetic shielding function, that is: (1) The dense cementitious material system of Example 2, 250 parts by weight of the pretreated steel fiber of Example 2, a polycarboxylic acid water-reducing agent (the amount of which is 3% of the content of the dense cementitious material system), and 300 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure, and after final setting, it is placed in a freeze dryer for freeze drying (first frozen to -20°C, and then vacuum dried at room temperature for 5 hours), so as to obtain a pretreated concrete structure.

[0057] (2) The pretreated concrete structure is placed in a saturated ferrous sulfate solution for curing for 10 days, with the ratio of the two being 1 g:40 ml. Then, sodium borohydride is added in a ratio of 1 mol / L in the saturated solution and stirred evenly. After reacting for 2 hours, the concrete structure is taken out and naturally dried for 5 days to obtain an electromagnetic shielding concrete structure.

[0058] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0059] Example 6 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: (1) The dense cementitious material system of Example 1, 180 parts by weight of the modified steel fiber of Example 1, a polycarboxylic acid water-reducing agent (the amount of which is 2% of the content of the dense cementitious material system), and 240 parts by weight of mixing water are mixed and stirred evenly, and then the obtained slurry is cast into a concrete structure, and after the final setting, it is naturally cured for 3 days to obtain a pretreated concrete structure.

[0060] (2) The pretreated concrete structure is placed in a saturated iron sulfate solution for curing for 7 days, with the ratio of the two being 1 g:25 ml. Then, sodium borohydride is added in a ratio of 2 mol / L in the saturated solution and stirred evenly. After reacting for 1 hour, the concrete structure is taken out and naturally dried for 4 days to obtain an electromagnetic shielding concrete structure.

[0061] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0062] Example 7 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: The pretreated concrete structure prepared in Example 3 was placed in clean water for curing for 10 days, with the ratio of the two being 1 g: 20 ml. The concrete structure was then taken out and naturally dried for 3 days to obtain an electromagnetic shielding concrete structure.

[0063] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0064] Example 8 A method for preparing electromagnetic shielding concrete with a porous cross-linked structure comprises the following steps: The pretreated concrete structure prepared in Example 2 was placed in a saturated ferrous sulfate solution for curing for 10 days, with the ratio of the two being 1 g:40 ml. The concrete structure was then taken out and naturally dried for 5 days to obtain an electromagnetic shielding concrete structure.

[0065] Performance test: The compressive strength and shielding effectiveness SE of the electromagnetic shielding concrete structure prepared in this embodiment are tested by the same method as in the above-mentioned embodiment 1. The test results are shown in the following table.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made shall be included in the protection scope of the present invention.

Claims

1. A method for preparing electromagnetic shielding concrete with a porous cross-linked structure, characterized in that: The steps include: (1) dispersing the steel fibers in water, adding alkali solution, and then stirring under heating conditions; after the reaction is completed, adding ferrous sulfate and mixing evenly, then separating the steel fibers and performing heat treatment on them to convert the iron hydroxide and / or ferrous hydroxide on the steel fibers into iron oxide, thereby obtaining pretreated steel fibers; (2) dispersing the pretreated steel fiber into a polyvinyl alcohol solution, then adding a nano powder having an electromagnetic shielding function and stirring, and separating the fiber after completion, thereby obtaining a modified steel fiber having an electromagnetic shielding function; (3) dispersing cement, silica fume, filler and nano powder with electromagnetic shielding function in a non-aqueous solvent, and then performing ultrasonic dispersion treatment; After completion, the solid matter is separated and dried to obtain a dense gel material system; (4) mixing the dense cementitious material system, the modified steel fiber, the water reducing agent and the mixing water to obtain a slurry, casting the slurry into a concrete structure, and performing freeze-drying treatment after the slurry is finally set, thereby obtaining a pretreated concrete structure; (5) placing the pretreated concrete structure in a saturated liquid containing at least one of ferric ions and ferrous ions for curing; adding sodium borohydride and mixing evenly after the reaction is completed, taking out the concrete structure after the reaction is completed, and obtaining electromagnetic shielding concrete after drying.

2. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (1), the mass fraction of the alkali solution in the water is 5-15%; Optionally, in step (1), the alkali solution includes at least one of a sodium hydroxide solution and a potassium hydroxide solution; Optionally, in step (1), the heating temperature is 40-60° C. and the reaction time is 8-12 h; Optionally, in step (1), the steel fiber has a length of 12-14 mm and a diameter of 0.2-0.25 mm.

3. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (1), the molar ratio of the alkaline component to the ferric ion and / or ferrous ion in the alkali solution is 2 to 3:1; Optionally, in step (1), the iron ions are provided by at least one of ferric chloride, ferric sulfate and ferric nitrate; Optionally, in step (1), the ferrous ions are provided by at least one of ferrous chloride, ferrous sulfate, and ferrous nitrate; Optionally, in step (1), the heat treatment temperature is 400-500°C and the time is 20-40 minutes; Optionally, in step (2), the ratio of the pretreated steel fiber to the polyvinyl alcohol solution is 1 g: 10-30 ml; Optionally, in step (2), the mass fraction of the polyvinyl alcohol solution is 10-20%.

4. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (2), the mass ratio of the pretreated steel fiber to the nano powder is 1:3-5; Preferably, the nano powder is composited by inorganic electromagnetic shielding material and organic electromagnetic shielding material in any proportion; Optionally, the inorganic electromagnetic shielding material includes at least one of ferrite and metal powder; Optionally, the organic electromagnetic shielding material includes at least one of graphite powder and carbon black; Optionally, in step (2), the stirring time is 1 to 2 hours.

5. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (3), the non-aqueous solvent includes at least one of anhydrous methanol, anhydrous ethanol, and isopropanol; Optionally, in step (3), the nanopowder having electromagnetic shielding function includes at least one of ferrite, metal powder, graphite powder and carbon black; Optionally, in step (3), the filler includes at least one of quartz powder, calcium carbonate powder, and mica powder; Optionally, the particle size of the filler is not less than 500 mesh; Optionally, in step (3), the stirring treatment time is 10 to 20 minutes.

6. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (4), the proportions of the raw materials are as follows: the dense cementitious material system includes 600-800 parts by weight of cement, 50-200 parts by weight of silica fume, 50-100 parts by weight of filler, 20-35 parts by weight of nano powder with electromagnetic shielding function, 100-250 parts by weight of steel fiber, and 200-300 parts by weight of mixing water.

7. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (4), the freeze-drying treatment temperature is minus 20 to 40°C, and then vacuum drying is performed at room temperature for 2 to 5 hours.

8. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (5), the ratio of the pretreated concrete structure to the saturated liquid is 1 g: 20-40 ml; Optionally, in step (5), the ferric ions / ferrous ions are provided by at least one of ferric chloride, ferric sulfate, ferric nitrate, ferrous chloride, ferrous sulfate, and ferrous nitrate; Optionally, in step (5), the curing time is not less than one week, and water is added in a timely manner during the curing process to ensure that the concrete structure is completely immersed.

9. The method for preparing electromagnetic shielding concrete with porous cross-linked structure according to claim 1, characterized in that: In step (5), sodium borohydride is added in a ratio such that the concentration of sodium borohydride in the saturated solution is 1 to 5 mol / L; Optionally, in step (5), the reaction time is 1 to 2 hours, and the drying time is 3 to 5 days.

10. The method for preparing electromagnetic shielding concrete with a porous cross-linked structure according to any one of claims 1 to 9, characterized in that: In step (4), the amount of the water reducing agent is 1.5-3% of the content of the dense cementitious material system; Optionally, in step (4), the water reducer includes at least one of a naphthalene-based water reducer, an aliphatic water reducer, and a polycarboxylic acid water reducer; Optionally, in step (4), the cement includes any one of ordinary Portland cement and sulphoaluminate cement.

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