High-performance electromagnetic shielding cement mortar based on charcoal coating functional aggregate

Abstract

The invention provides high-performance electromagnetic shielding cement mortar based on charcoal coating functional aggregate, and belongs to the technical field of cement-based composites.The high-performance electromagnetic shielding cement mortar is prepared from a cementing material, the charcoal coating functional aggregate, conductive fibers and water, the charcoal coating functional aggregate is a fine aggregate coated with a charcoal coating on the surface, and the fine aggregate is obtained by electrostatic self-assembly of modified charcoal rich in negative charges on the surface and a surface amino-functionalized fine aggregate. According to the high-performance electromagnetic shielding cement mortar provided by the invention, based on the design and synergistic effect of steel slag powder cement matrix-charcoal coating functional aggregate-carbon fiber multistage electromagnetic absorption / reflection channels, the electromagnetic shielding performance is greatly enhanced, and meanwhile, the mechanical property is also improved; a new thought is provided for improving the electromagnetic shielding performance of the cement-based composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cement-based composite materials, in particular to a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate and a preparation method and application thereof. BACKGROUND

[0002] Electromagnetic interference not only hinders the normal operation of precision electronic instruments, but also may cause potential harm to human health. Although traditional electromagnetic shielding materials (such as metals and their composites) have excellent shielding performance, they still have disadvantages such as heavy weight, high cost, and easy corrosion, which limit their large-scale popularization and application.

[0003] Cement-based composites are considered as potential electromagnetic shielding material carriers due to their low cost, wide raw material sources, strong plasticity, and convenient construction. In recent years, mainly by directly adding conductive or magnetic functional additives to the cement matrix, the electromagnetic shielding performance is improved. Among them, high-quality functional additives such as carbon nanotubes and graphene can significantly enhance the shielding effect, but the high cost seriously restricts the actual engineering application. In contrast, biochar not only has good electrical conductivity, but also has a rich pore structure, which can not only enhance electromagnetic wave reflection through impedance mismatch, but also promote electromagnetic energy dissipation through its multi-scale interface, and is a functional material with application prospect.

[0004] At present, the common method of adding biochar is to directly mix 5-20 wt% of biochar based on the mass of cement as a functional filler into cement, and then mix it with aggregate, water and other components to prepare a composite material. However, this method easily leads to serious agglomeration of biochar in the cement matrix, which not only significantly affects the workability of the mixture, but also adversely affects the mechanical properties and electromagnetic shielding efficiency of the cement-based material, thereby limiting the practical application of such cement-based materials in engineering. SUMMARY

[0005] In view of the technical problems in the background art, the present application provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate and a preparation method thereof, aiming to solve the technical problems of biochar agglomeration and poor electromagnetic shielding performance of cement-based materials.

[0006] The technical solution of the present application is as follows: In a first aspect, the present application provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate, the raw materials of which include cementitious materials, biochar-coated functional aggregate, conductive fibers and water, wherein the cementitious materials are composed of cement and steel slag powder, and the biochar-coated functional aggregate is a fine aggregate coated with a biochar coating obtained by electrostatic self-assembly of modified biochar with a surface rich in negative charges and surface amino-functionalized fine aggregate.

[0007] In the high-performance electromagnetic shielding cement mortar, the water-binder ratio is preferably 0.35-0.55, and the binder-sand ratio is preferably 0.30-0.32. It can be understood that the water-binder ratio is the mass ratio of water to binder, and the binder-sand ratio is the mass ratio of binder to biochar coating functional aggregate.

[0008] In the technical scheme of the present application, biochar coating functional aggregate is used to replace natural aggregate (such as river sand) by 100%; and the present application grafts biochar to the surface of aggregate by “electrostatic adsorption”, effectively avoiding the agglomeration problem caused by directly mixing biochar with cement, fully playing the unique multi-scale interface effect of biochar, and greatly increasing the electromagnetic energy dissipation.

[0009] In the technical scheme of the present application, steel slag powder is used to partially replace cement, and experimental data show that the introduction of an appropriate amount of steel slag powder can reduce the amount of cement and improve the electromagnetic shielding performance of the slurry. The replacement rate of steel slag powder relative to cement is preferably 5-15% (based on the mass of cement), and the particle size of the steel slag powder is 1-30 μm, the 28-day activity index is greater than 80%, and the content of magnetic components (iron oxides) is 5-15%.

[0010] In the technical scheme of the present application, electrically conductive carbon fibers are added to the cement mortar, the length of the electrically conductive carbon fibers is preferably 3-10 mm, the diameter is preferably 7-9 μm, and the mass of the electrically conductive carbon fibers is preferably 0.05-1% of the mass of the binder (cement and steel slag powder). The length of the electrically conductive carbon fibers has a significant effect on the electrical properties of the cement mortar. Under the same amount of addition, carbon fibers of 3-10 mm can connect the biochar coating functional aggregate (the theoretical spacing of the aggregate is about 100 μm), and the shorter the carbon fibers, the more the number under the same amount of addition. The electrical properties of the mortar with 3 mm carbon fibers perform better.

[0011] In the technical scheme of the present application, the cement can be Portland cement, such as ordinary Portland cement (P·O 42.5) used in some embodiments of the present application.

[0012] In the technical scheme of the present application, the biochar coating functional aggregate can be prepared by the following steps: S1, pyrolyzing municipal sludge at 500-700°C to obtain biochar, and using ozone to oxidize the cleaned biochar to obtain modified biochar rich in negative charges; S2, using ethanol-diluted silane coupling agent to modify the surface of fine aggregate to graft amino groups on the surface, thereby obtaining amino-functionalized fine aggregate; S3, preparing a biochar dispersion liquid with a mass fraction of 5-20%, adding the amino-functionalized fine aggregate and stirring, and drying the obtained product to constant weight.

[0013] By using the preparation method, the uniform and stable biochar coating layer can be formed on the surface of the fine aggregate.

[0014] In the preparation process of the biochar coating functional aggregate, the obtained biochar is a sheet-shaped porous carbon material (i.e., a sludge-based biochar) prepared by pyrolyzing municipal sludge at 500-700°C, has a carbon content of 35-45%, a size of 100-200 μm, a specific surface area of 100-350 m 2 / g, and an electrical conductivity of 0.1-100 S / m.

[0015] In step S1, the biochar is preferably cleaned multiple times (e.g., 3-5 times) using deionized water for thorough cleaning, and the cleaned biochar can be dried at 100-110°C to a constant weight.

[0016] Preferably, the conditions for the oxidation treatment in step S1 are that the biochar is placed in an ozone reactor and treated at a gas flow of 0.5-2.0 L / min and an ozone concentration of 20-80 mg / L for 30-60 min.

[0017] In the preparation process of the biochar coating functional aggregate, the fine aggregate used is natural river sand with a particle size of 0.075-4.75 mm, and has an apparent density of 2600-2700 kg / m 3 , and a specific surface area of 20-50 m 2 / kg.

[0018] In some embodiments of the present application, the ethanol used in step S2 is 70% ethanol, and the silane coupling agent used is 3-aminopropyl triethoxysilane; preferably, the volume ratio of ethanol to 3-aminopropyl triethoxysilane is 8:1-10:1.

[0019] Preferably, the surface modification in step S2 is carried out under heating and stirring, and after the modification is completed, the product is washed and dried to obtain the amino-functionalized fine aggregate; more preferably, the heating temperature is 60-65°C, the stirring speed is 50-80 r / min, the stirring time is 30-60 min, the drying temperature is 100-110°C, and the drying time is 24-72h.

[0020] In some embodiments of the present application, step S3 uses a cell crusher to disperse the biochar with a negative surface charge in deionized water through mechanical stirring, wherein the power of the cell crusher is 200-600W, and the treatment time is 10-20 min.

[0021] Preferably, in step S3, the stirring speed is 50-80 r / min, and the stirring time is 10-20 min; the temperature of the drying process is 100-110°C, and the time is 24-72h.

[0022] In a second aspect, the present application provides a method for preparing the high-performance electromagnetic shielding cement mortar, which comprises the following steps: dry mixing cement, steel slag powder and conductive carbon fibers in a certain proportion, stirring at a low speed after adding water, then adding biochar coating functional aggregate, stirring at a low speed and then stirring at a high speed, thereby obtaining the cement mortar; wherein the stirring speed at the low speed is 60-65 r / min, and the stirring time is 3-5 min; the stirring speed at the high speed is 115-135 r / min, and the stirring time is 1-3 min.

[0023] In a third aspect, the present application provides an application of the high-performance electromagnetic shielding cement mortar in preparing electromagnetic shielding products, such as underground civil air defense works, medical buildings, 5G base station infrastructure and transportation infrastructure, etc.

[0024] Compared with the prior art, the present application has at least the following beneficial effects: 1) The present application provides a new type of biochar coating functional aggregate, and the biochar with a negative charge on the surface is grafted to the surface of the aggregate through "electrostatic adsorption" with the amino-functionalized fine aggregate on the surface, thereby avoiding the agglomeration problem caused by directly mixing biochar with cement, fully exerting the unique multi-scale interface effect of biochar, and greatly increasing the electromagnetic energy dissipation.

[0025] 2) By using the new type of biochar coating functional aggregate, the present application further forms a "conductive framework structure" inside the cement-based composite material, and always overlaps with the randomly distributed conductive carbon fibers, thereby connecting the biochar coating functional aggregate through the conductive carbon fibers, constructing a "three-dimensional conductive network structure", and greatly enhancing the reflection loss of the composite material to electromagnetic waves by improving the electrical conductivity of the material.

[0026] 3) In the high-performance electromagnetic shielding cement mortar provided by the present application, the magnetic components of the steel slag powder enhance the electromagnetic wave absorption capacity of the cement matrix through the magnetic loss mechanism, and in combination with the "biochar coating functional aggregate connected by conductive carbon fibers", a multi-stage electromagnetic absorption / reflection channel is constructed inside the mortar, thereby greatly improving the electromagnetic shielding performance of the mortar. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced as follows. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0028] Figure 1 It is a schematic diagram for the preparation process of the biochar coating functional aggregate in the embodiments of the present application. Figure 2 This is an appearance diagram of the natural fine aggregate used in the embodiments of the present invention; Figure 3 This is an appearance diagram of the biochar-coated functional aggregate prepared using natural fine aggregate in an embodiment of the present invention; Figure 4 This is a schematic diagram of the internal multi-level electromagnetic absorption / reflection channel distribution of the high-performance electromagnetic shielding cement mortar prepared according to an embodiment of the present invention. Detailed Implementation

[0029] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the invention.

[0031] Cement-based composite materials are considered to be promising carriers for electromagnetic shielding materials. Biochar, due to its good conductivity, porous structure, and low cost, has become a preferred additive for improving the electromagnetic shielding performance of cement-based composite materials. However, when biochar is directly added to cement as a functional filler, it is prone to agglomeration, which not only significantly affects the workability of the mixture but also has an adverse effect on its mechanical properties and electromagnetic shielding effectiveness.

[0032] To address the technical problems caused by direct incorporation of biochar, this invention provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregates. By grafting a biochar layer onto the aggregate surface and combining it with the introduction of conductive carbon fibers and steel slag powder, multi-level electromagnetic absorption / reflection channels are constructed inside the mortar, significantly improving the electromagnetic shielding performance of the cement mortar while preventing biochar agglomeration.

[0033] Reference Figure 1 The method for preparing biochar-coated functional aggregate provided in this embodiment of the invention includes the following steps: (1) The biochar is thoroughly washed with water and dried to obtain biochar with impurities removed; the washed biochar is then subjected to surface oxidation treatment in an ozone environment to form modified biochar with a surface rich in negative charges. (2) Fine aggregate is added to a silane coupling agent solution diluted with ethanol, and after heating and stirring, the surface of the fine aggregate is modified to graft amino functional groups onto its surface, and then dried to obtain surface amino functionalized fine aggregate. (3) Add the surface amino-functionalized fine aggregate to the modified biochar dispersion with negative surface charge, stir at low speed and dry, and form a uniform and stable biochar coating on the surface of the aggregate through electrostatic self-assembly, thereby obtaining biochar-coated functional aggregate.

[0034] Furthermore, in some embodiments, the biochar is a sheet-like porous carbon material produced by pyrolyzing municipal sludge at 500-700℃, with a carbon content of 35-45%, a size of 100-200 μm, and a specific surface area of ​​100-350 m². 2 / g, with an electrical conductivity of 0.1-100S / m; the oxidation treatment is carried out in an ozone generator with a gas flow rate of 0.5-2.0 L / min, an ozone concentration of 20-80 mg / L, and a treatment time of 30-60 min.

[0035] Furthermore, in some embodiments, the silane coupling agent is 3-aminopropyltriethoxysilane, and the heating temperature in step (2) is 60-65°C, the stirring speed is 50-80 r / min, the stirring time is 30-60 min, and the drying temperature is 100-110°C.

[0036] Furthermore, in some embodiments, the modified biochar is prepared into a dispersion of 5-20% (mass fraction) using a cell disruptor, and the stirring speed in step (3) is 50-80 r / min, the stirring time is 10-20 min, and the drying temperature is 100-110℃.

[0037] See Figure 2 and Figure 3 This technical solution allows biochar with an ultra-large specific surface area to be fully exposed on the aggregate surface, effectively leveraging its multi-scale interface effect and significantly enhancing the dissipation efficiency of electromagnetic energy, while avoiding the agglomeration problem that is easily caused when biochar is directly incorporated into cement.

[0038] Based on biochar-coated functional aggregates, this invention provides a high-performance electromagnetic shielding cement mortar, which is prepared by: dry mixing cement, steel slag powder and conductive carbon fiber in a certain proportion, adding water and stirring at low speed, then adding biochar-coated functional aggregates, stirring at low speed first and then at high speed to obtain cement mortar; wherein, the substitution rate of steel slag powder relative to cement is 5-15%, the mass of carbon fiber is 0.05-0.1% of the mass of cementitious materials, the water-cement ratio is 0.35-0.55, and the cement-mortar ratio is 0.30-0.32.

[0039] Furthermore, in some embodiments, the low-speed stirring speed is 60-65 r / min, and the stirring time is 3-5 min; the high-speed stirring speed is 115-135 r / min, and the stirring time is 1-3 min.

[0040] This invention also provides a cement composite material product with electromagnetic shielding properties. High-performance electromagnetic shielding cement mortar is poured into a mold, subjected to 30 seconds of high-frequency vibration (60-80 Hz) to achieve compaction, and then cured in a standard curing room for 28 days. Experimental data shows that after 28 days, the conductivity increased by one order of magnitude, and the electromagnetic shielding capability was improved by 252%.

[0041] See Figure 4 The introduction of biochar-coated functional aggregates forms a "conductive skeleton structure" within the cement mortar, which overlaps with randomly distributed carbon fibers. Through the series connection of conductive carbon fibers and biochar-coated functional aggregates, a "three-dimensional conductive network structure" is constructed. This significantly enhances the conductivity of the mortar, thereby greatly increasing the reflection loss of electromagnetic waves. Simultaneously, the partial replacement of cement with steel slag powder not only reduces cement usage, energy consumption, and carbon emissions, but also utilizes the magnetic components in the steel slag to further enhance the matrix's absorption capacity for electromagnetic waves through a magnetic loss mechanism. Therefore, based on the multi-level electromagnetic absorption / reflection channel design and synergistic effect of "steel slag powder cement matrix - biochar-coated functional aggregates - carbon fibers," this invention significantly improves the electromagnetic shielding performance of cement mortar while also enhancing its mechanical properties.

[0042] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0043] Example 1 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate, and its preparation method is as follows: (1) Preparation of modified biochar with a surface rich in negative charge.

[0044] Sheet-like porous carbon material produced by pyrolysis of municipal sewage sludge at 600℃ (carbon content 40%, average size 160 μm, specific surface area 320 m²) 2 / g, with an electrical conductivity of 68 S / m) was used as biochar; and the biochar was washed 5 times with deionized water to thoroughly clean it. The cleaned biochar was placed in a drying oven and dried at 105℃ to constant weight to obtain biochar with impurities removed.

[0045] The biochar obtained in the above steps is oxidized in an ozone environment to form modified biochar with a negatively charged surface. Specifically, the biochar is spread evenly on a sample tray inside the ozone reactor, ensuring that the material layer is not too thick to guarantee that the ozone gas can fully contact all particles; gas is first introduced (flow rate of 1.0 L / min), then the ozone generator is started and adjusted to the required ozone concentration (60 mg / L); ozone is continuously passed through the biochar sample for a certain period of time (40 min) to obtain modified biochar with a negatively charged surface.

[0046] (2) Preparation of fine aggregates with amino functionalized surface.

[0047] The fine aggregate used in this example is natural river sand with a particle size of 0.075-4.75 mm and an apparent density of 2650 kg / m³. 3 Specific surface area is 45 m² 2 / kg.

[0048] The surface of the above-mentioned fine aggregate was modified using a silane coupling agent solution diluted with ethanol, thereby grafting amino functional groups onto its surface to obtain surface-amino-functionalized fine aggregate. The specific process involves mixing 70% ethanol with 3-aminopropyltriethoxysilane (purity 98%, density 0.82 g / cm³). 3 The silane coupling agent solution was obtained by mixing the aggregates at a volume ratio of 9:1 with ethanol. The fine aggregates were then added to the ethanol-diluted silane coupling agent solution, heated and stirred, and then dried to constant weight. The treated sand particles were washed five times with deionized water and dried to constant weight to obtain surface amino-functionalized fine aggregates. The heating temperature was 60℃, the stirring speed was 60 r / min, the stirring time was 30 min, the drying temperature was 105℃, and the drying time was 24 h.

[0049] (3) Preparation of biochar-coated functional aggregates.

[0050] The surface-amino-functionalized fine aggregate prepared in step (2) is added to the dispersion of modified biochar prepared in step (1). During the stirring process, a uniform and stable biochar coating is formed on the surface of the aggregate through electrostatic self-assembly. Finally, the biochar-coated functional aggregate is obtained after drying. The specific process is as follows: the negatively charged biochar is uniformly dispersed in deionized water using a cell pulverizer with a power of 400W and a processing time of 15 min. The mass fraction of biochar in the resulting modified biochar dispersion is 10%. The surface-amino-functionalized fine aggregate is added to the above dispersion. The mixture is stirred at a stirring speed of 60 r / min for 10 min using a UJZ-15 vertical mortar mixer. Subsequently, the mixture is dried (dried at 105℃ for 24 h) to obtain the biochar-coated functional aggregate.

[0051] (4) Prepare high-performance electromagnetic shielding cement mortar.

[0052] The cement used in this example is ordinary Portland cement (P·O 42.5); the steel slag powder used has a particle size of 1-30 μm, a 28-day activity index greater than 80%, and a magnetic component (iron oxide) content of 10%; the conductive carbon fiber used is short-cut carbon fiber with a length of 3 mm, a diameter of 7 μm, a Young's modulus of 240 GPa, and a resistivity of 1.5 × 10⁻⁶. -3 Ω·cm.

[0053] Steel slag powder partially replaces cement and is mixed with conductive carbon fiber at low speed. Water is added and mixed at low speed to obtain a slurry. Then it is mixed with the biochar coating functional aggregate obtained in step (3). After low-speed combination and high-speed mixing, a high-performance electromagnetic shielding cement mortar based on biochar coating functional aggregate is finally obtained. The specific process is as follows: steel slag powder is used to partially replace cement to obtain cementitious material, and the replacement rate of steel slag powder relative to cement is 10% (by mass ratio of cement); the cementitious material and conductive carbon fiber are stirred at 60 r / min for 3 min, and then water is added and stirred at low speed to obtain a slurry, wherein the amount of conductive carbon fiber is 0.05% of the mass of cementitious material; then, the above-mentioned biochar-coated functional aggregate (i.e., the replacement rate of biochar-coated functional aggregate relative to natural aggregate (river sand) is 100%) is added, and the mixture is first stirred at low speed (60 r / min) for 3 min, and then stirred at high speed (120 r / min) for 1 min. The resulting mixture is poured into an oiled mold and subjected to high-frequency vibration (65 Hz) for 30 s to compact it. Then, it is placed in a standard curing room for curing, and the curing age of the specimen is 28 days; in the high-performance electromagnetic shielding cement mortar prepared in this example, the water-cement ratio of the mortar system is 0.5, and the cement-sand ratio is 0.30.

[0054] Example 2 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. The difference between this mortar and Example 1 is that the biochar used in this example is a sheet-like porous carbon material produced by pyrolyzing municipal sludge at 500℃.

[0055] Example 3 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. The difference between this mortar and Example 1 is that the biochar used in this example is a sheet-like porous carbon material produced by pyrolyzing municipal sludge at 700℃.

[0056] Example 4 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that the oxidation treatment process in step (1) is as follows: The biochar was spread evenly on the sample tray inside the ozone reactor, ensuring that the material layer was not too thick to guarantee that the ozone gas could fully contact all particles. Gas was first introduced (flow rate of 0.5 L / min), and then the ozone generator was started and adjusted to the required ozone concentration (20 mg / L). The ozone was continuously passed through the biochar sample for 30 min to obtain modified biochar.

[0057] Example 5 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that the oxidation treatment process in step (1) is as follows: The biochar was spread evenly on the sample tray inside the ozone reactor, ensuring that the material layer was not too thick to guarantee that the ozone gas could fully contact all particles. Gas was first introduced (flow rate of 2.0 L / min), and then the ozone generator was started and adjusted to the required ozone concentration (80 mg / L). The ozone was continuously passed through the biochar sample for 60 min to obtain modified biochar.

[0058] Example 6 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that the fine aggregate used in this example is natural river sand with a particle size of 0.075-2.36 mm.

[0059] Example 7 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that, in step (3), the mass fraction of biochar in the dispersion of modified biochar is 5%.

[0060] Example 8 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that, in step (3), the mass fraction of biochar in the dispersion of modified biochar is 20%.

[0061] Example 9 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that the steel slag powder has a 5% replacement rate with cement in the cementitious material used in step (4).

[0062] Example 10 This example provides a high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate. Its preparation differs from that of Example 1 in that the steel slag powder has a 15% replacement rate with cement in the cementitious material used in step (4).

[0063] Comparative Example 1 This example provides an electromagnetic shielding cement mortar, the preparation of which differs from that of Example 1 in that conductive carbon fiber and steel slag powder are not added in step (4), and the preparation process of step (4) is as follows: Cement and water were mixed at low speed to obtain a slurry. Then the biochar coating functional aggregate prepared in step (3) was added. The mixture was first mixed at low speed (60 r / min) for 3 min, and then at high speed (120 r / min) for 1 min. The resulting mixture was poured into an oiled mold and subjected to high-frequency vibration (65 Hz) for 30 s to compact it. Then it was placed in a standard curing room for curing. The curing age of the specimen was 28 days. In the electromagnetic shielding cement mortar prepared in this example, the water-cement ratio of the mortar system was 0.5 and the cement-sand ratio was 0.30.

[0064] Comparative Example 2 This example provides an electromagnetic shielding cement mortar, the preparation of which differs from that of Example 1 in that conductive carbon fibers are not added in step (4), and the preparation process of step (4) is as follows: The cementitious material is obtained by partially replacing cement with steel slag powder, and the replacement rate of steel slag powder with cement is 10%. The cementitious material is mixed with water at low speed to obtain a slurry. Then the biochar coating functional aggregate prepared in step (3) is added. The mixture is first stirred at low speed (60 r / min) for 3 min, and then stirred at high speed (120 r / min) for 1 min. The mixture is poured into an oiled mold and subjected to high-frequency vibration (65 Hz) for 30 s to compact it. Then it is placed in a standard curing room for curing. The curing age of the specimen is 28 days. In the electromagnetic shielding cement mortar prepared in this example, the water-cement ratio of the mortar system is 0.5 and the cement-sand ratio is 0.30.

[0065] Comparative Example 3 This example provides an electromagnetic shielding cement mortar, the preparation of which differs from that of Example 1 in that steel slag powder is not added in step (4), and the preparation process of step (4) is as follows: Cement and conductive carbon fiber were stirred at 60 r / min for 3 min, and then water was added and stirred at low speed to obtain a slurry. The amount of conductive carbon fiber was 0.05% of the mass of cementitious material. Then the biochar coating functional aggregate prepared in step (3) was added. The mixture was first stirred at low speed (60 r / min) for 3 min, and then stirred at high speed (120 r / min) for 1 min. The mixture was poured into an oiled mold and subjected to high-frequency vibration (65 Hz) for 30 s to compact it. Then it was placed in a standard curing room for curing. The curing age of the specimen was 28 days. In the electromagnetic shielding cement mortar prepared in this example, the water-cement ratio of the mortar system was 0.5 and the cement-sand ratio was 0.30.

[0066] Comparative Example 4 This example provides an electromagnetic shielding cement mortar, the preparation process of which is as follows: (1) Preparation of modified biochar with a surface rich in negative charge.

[0067] The preparation process is the same as step (1) in Example 1.

[0068] (2) Prepare electromagnetic shielding cement mortar.

[0069] The sheet-like porous carbon material (i.e., sludge-based biochar, which does not require oxidation treatment) produced by pyrolyzing municipal sludge at 600℃ was uniformly dispersed in deionized water using a cell disruptor. The cell disruptor had a power of 400 W and a processing time of 15 min. The biochar mass fraction in the resulting modified biochar dispersion was 10%.

[0070] Cement, steel slag powder, conductive carbon fiber, biochar dispersion, and residual water were stirred at low speed to obtain a biochar-modified cement paste. Then, natural river sand (fine aggregate) was added, and the mixture was stirred at low speed (60 r / min) for 3 min, followed by high speed (120 r / min) for 1 min. The resulting mixture was poured into an oiled mold and subjected to 30 s of high-frequency vibration (65 Hz) to compact it. The mold was then placed in a standard curing room for 28 days. Specifically, the parameters and amounts of cement, steel slag powder, conductive carbon fiber, and natural river sand used in this example are the same as in Example 1.

[0071] Comparative Example 5 This example provides a pure cement mortar, the preparation process of which is as follows: Cement and water were mixed at low speed to obtain a slurry. Then, natural river sand (fine aggregate) was added, and the mixture was first mixed at low speed (60 r / min) for 3 minutes, followed by high speed (120 r / min) for 1 minute. The resulting mixture was poured into an oiled mold and subjected to high-frequency vibration (60-80 Hz) for 30 seconds to compact it. The mold was then placed in a standard curing room for 28 days to obtain pure cement mortar. The parameters and amounts of cement and natural river sand used in this example are the same as in Example 1.

[0072] The following performance tests were performed on the specimens prepared in the above embodiments and comparative examples: The compressive and flexural strengths of cement mortar specimens were tested according to the requirements of GB / T 17671-1999. The specimen dimensions for flexural strength testing were 40 mm × 40 mm × 160 mm, and the cross-sectional area for compressive strength testing was 40 mm × 40 mm. The specimen dimensions for mortar resistivity testing were 40 mm × 40 mm × 160 mm, and the four-electrode method was used. The electromagnetic interference shielding performance of the mortar was tested using a vector network analyzer in conjunction with a waveguide, with a test frequency range of 8.2–12.4 GHz (X-band). Each performance indicator was tested in triplicate, and the results were averaged. The test results are shown in the table below.

[0073] Comparing Examples 1, 2, and 3, it can be seen that the biochar, a sheet-like porous carbon material produced from pyrolysis of municipal sludge, exhibits better pore structure, larger specific surface area, superior conductivity, and better retention of functional groups, resulting in higher electromagnetic shielding efficiency, as the preparation temperature (within the range of 500-700℃) is higher. Comparing Examples 1, 4, and 5, it can be seen that the ozone concentration and treatment time of the ozone generator determine the degree of oxidation of the biochar (the number of negative charges on the biochar surface), ultimately determining the quality of the biochar-coated aggregate. The test results show that when the ozone gas flow rate is 2.0 L / min, the ozone concentration is 80 mg / L, and the treatment time is 60 min, the prepared modified biochar with a surface rich in negative charges has the best quality (lowest resistivity). SE T The total shielding loss is highest per millimeter of thickness; however, the overall difference is not significant. Comparing Examples 1 and 6, it is evident that the smaller the particle size of the fine aggregate, the larger the specific surface area, and the more biochar can be coated on the aggregate surface, thus improving the conductivity and electromagnetic shielding performance of the mortar. Comparing Examples 1, 7, and 8, it is evident that the higher the amount of biochar used (within the range of 5-20%), the higher the quality of the prepared biochar-coated functional aggregate. Given that the specific surface area of ​​fine aggregate is fixed, the amount of biochar that can be coated on the aggregate surface is limited; therefore, the amount of biochar used has no significant impact on the conductivity and electromagnetic shielding performance of the mortar. Comparing Examples 1, 9, and 10, it is evident that the greater the amount of steel slag powder replacing cement, the more significant the energy-saving and carbon-reduction effect, and the magnetic components in the steel slag further enhance the matrix's absorption capacity for electromagnetic waves through a magnetic loss mechanism. Comparing Example 1 with Comparative Examples 1, 2, and 3, it can be seen that this technical solution, based on the multi-level electromagnetic absorption / reflection channel design and synergistic effect of "steel slag powder cement matrix - biochar coating functional aggregate - carbon fiber," significantly improves the electromagnetic shielding performance of cement mortar. In Example 1... SE TThe total shielding loss per millimeter thickness was increased by 21.7%, 15.1%, and 6.3% compared to Comparative Examples 1, 2, and 3, respectively. Comparing Example 1 and Comparative Example 4, it can be seen that the 28-day conductivity of the mortar prepared using this technical solution increased by one order of magnitude compared to cement mortar prepared by directly adding biochar to cement. SE T The total shielding loss per millimeter of thickness was increased by approximately 252%, and the adverse effects of directly adding biochar on the strength of cement mortar were avoided.

[0074] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A high-performance electromagnetic shielding cement mortar based on biochar-coated functional aggregate, characterized in that, The raw materials include cementitious materials, biochar-coated functional aggregates, conductive fibers, and water. The cementitious materials are composed of cement and steel slag powder. The biochar-coated functional aggregates are fine aggregates with a biochar coating on their surface, obtained by electrostatic self-assembly of modified biochar with a negatively charged surface and surface amino-functionalized fine aggregates.

2. The high-performance electromagnetic shielding cement mortar according to claim 1, characterized in that, In the high-performance electromagnetic shielding cement mortar, the water-cement ratio is 0.35-0.55, and the mortar-cement ratio is 0.30-0.

32.

3. The high-performance electromagnetic shielding cement mortar according to claim 1, characterized in that, The steel slag powder has a particle size of 1-30 μm and a relative cement substitution rate of 5-15%; and / or, The conductive carbon fiber has a length of 3-10 mm, a diameter of 7-9 μm, and a mass of 0.05-1% of the mass of the cementitious material.

4. The high-performance electromagnetic shielding cement mortar according to claim 1, characterized in that, The preparation of the biochar-coated functional aggregate includes the following steps: S1. Biochar is obtained by pyrolyzing municipal sludge at 500-700℃. Ozone is used to oxidize the cleaned biochar to obtain modified biochar rich in negative charge. S2. Use ethanol-diluted silane coupling agent to modify the surface of fine aggregate, so as to graft amino groups onto the surface and obtain amino-functionalized fine aggregate. S3. Prepare a biochar dispersion with a mass fraction of 5-20%, add amino-functionalized fine aggregate and stir, and dry the resulting product to constant weight.

5. The high-performance electromagnetic shielding cement mortar according to claim 4, characterized in that, The biochar has a carbon content of 35-45%, a size of 100-200 μm, and a specific surface area of ​​100-350 m². 2 / g, with an electrical conductivity of 0.1-100 S / m.

6. The high-performance electromagnetic shielding cement mortar according to claim 4, characterized in that, The fine aggregate has a particle size of 0.075-4.75 mm and an apparent density of 2600-2700 kg / m³. 3 Specific surface area is 20-50 m² 2 / kg.

7. The high-performance electromagnetic shielding cement mortar according to claim 4, characterized in that, The oxidation treatment conditions are as follows: biochar is placed in an ozone reactor and treated for 30-60 min at a gas flow rate of 0.5-2.0 L / min and an ozone concentration of 20-80 mg / L.

8. A method for preparing the high-performance electromagnetic shielding cement mortar of claim 1, characterized in that, Cement, steel slag powder, and conductive carbon fiber are dry-mixed in a certain proportion. Water is added and the mixture is stirred at low speed. Then, biochar-coated functional aggregate is added, and the mixture is stirred at low speed first and then at high speed to obtain cement mortar. The low-speed stirring speed is 60-65 r / min and the stirring time is 3-5 min. The high-speed stirring speed is 115-135 r / min and the stirring time is 1-3 min.

9. The application of the high-performance electromagnetic shielding cement mortar as described in any one of claims 1-7 in the preparation of electromagnetic shielding products.

10. A multifunctional cement-based material, characterized in that, The cement-based material is prepared using the high-performance electromagnetic shielding cement mortar described in any one of claims 1-7.

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