Method for producing recycled fiber reinforced cement with electromagnetic shielding properties

Abstract

This invention discloses a method for preparing recycled fiber reinforced cement with electromagnetic shielding properties. It includes: obtaining recycled carbon fibers; cutting the recycled carbon fibers; pre-dispersing the recycled carbon fibers; preparing cement mortar; mixing the mixture, using nanocellulose as a dispersant to achieve uniform dispersion of recycled carbon fibers of different lengths in the cement matrix, thereby constructing a homogeneous conductive network; using 5-6 cm long recycled carbon fibers to form the skeleton of the homogeneous conductive network, enhancing the mechanical strength of the cement matrix; and dispersing 0.1-0.2 cm long recycled carbon fibers in the gaps of the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix; molding and curing to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties. This invention effectively controls the over-dispersion and bonding force of recycled carbon fibers in the cement-based composite material system, resulting in high electromagnetic shielding cement with excellent mechanical properties; and simultaneously promotes the high-value green reuse of CFRP.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology, specifically to a method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties. Background Technology

[0002] With the development of information technology, the harm of electromagnetic radiation to the human body and devices, as well as information leakage in critical situations, has gradually intensified. Electromagnetic protection technology has thus become a crucial engineering and technological field. Electromagnetic shielding materials are one of the important means of electromagnetic protection. As a type of material capable of blocking the penetration of electromagnetic waves, electromagnetic shielding materials can not only reduce the harm of electromagnetic radiation to the human body and devices, but also prevent information leakage in important situations.

[0003] The preparation of building materials with electromagnetic shielding functions is receiving increasing attention. Cement is one of the most widely used building materials. Applying cement with electromagnetic shielding functions to buildings with electromagnetic shielding requirements can meet the requirements of reducing environmental electromagnetic radiation or reducing information leakage, and has broad application prospects.

[0004] Generally, electromagnetic shielding materials need to have good conductivity. High conductivity not only allows for the reflection of electromagnetic waves through high impedance mismatch with the medium (such as air), but also enables the material to respond to electromagnetic waves and dissipate them through macroscopic current generated by carrier migration. The combined effect of reflection and absorption achieves the purpose of shielding electromagnetic waves. However, cement, whose main component is silicate, has a slightly higher conductivity than insulators in its dry state, resulting in very low conductivity. Therefore, ordinary cement needs to be modified to enhance its electromagnetic shielding performance.

[0005] Current common modification methods mainly involve introducing highly conductive functional materials into the cement matrix to construct a conductive network. These functional materials mainly fall into three categories:

[0006] The first type is conductive or magnetic metal materials, such as iron particles, which can enhance electromagnetic shielding performance. However, metallic functional materials have high density, poor corrosion resistance, are prone to failure, and have a short lifespan.

[0007] The second type is ceramics, polymers, etc. Because the preparation process of ceramic and polymer materials is complex and the cost is high, it is not conducive to the cost control of cement.

[0008] The third type is carbon materials, including carbon fibers, carbon nanotubes, and graphene, which have advantages such as being lightweight and corrosion-resistant. Among them, carbon fiber is an inorganic non-metallic carbon-based material with high mechanical strength, excellent reinforcement effect, good conductivity, and strong corrosion resistance, improving electromagnetic shielding performance while enhancing mechanical properties. However, traditional commercial carbon fibers are expensive, and the production process uses polymer slurry, which limits the conductivity of carbon fibers and the interfacial properties between carbon fibers and the matrix to a certain extent, making it difficult to use them as a single blend, thus increasing the complexity of the preparation process of carbon fiber reinforced cement. In addition, the dispersion of carbon fibers is difficult, which can easily lead to uneven distribution of carbon materials, which is not conducive to the construction of electromagnetic shielding conductive networks.

[0009] In existing technologies, carbon fiber reinforced resin matrix composites (CFRP), with resin as the matrix and carbon fiber as the reinforcing / functional phase, possess the characteristics of corrosion resistance, high mechanical strength, and low density, and are widely used in aerospace, energy, automotive, and construction fields. Using CFRP as a reinforcing agent in cement-based composites can strengthen and toughen concrete, and introduce electromagnetic shielding properties through high conductivity. However, the use of CFRP presents the following problems: due to the corrosion resistance, refractory / infusible nature of the resin matrix, and its poor solubility in most solvents, the recycling and reuse of waste CFRP has become a challenge. Currently, my country has accumulated over 2 million tons of CFRP waste, and this amount is increasing by more than 100,000 tons annually. Summary of the Invention

[0010] To address the shortcomings of existing technologies, this invention proposes a method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties. The method involves pyrolyzing waste CFRP to obtain discontinuous recycled carbon fibers with no slurry on the surface. Controlled shearing technology is used to cut the recycled carbon fibers into different length grades. Nanocellulose is then added as a dispersant to effectively regulate the hyperdispersion and binding force of the recycled carbon fibers in the cement-based composite system, constructing a homogeneous conductive network. The long-grade recycled carbon fibers form the skeleton of the homogeneous conductive network, enhancing the mechanical strength of the cement matrix. The short-grade recycled carbon fibers disperse the gaps in the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix. This preparation method not only recycles waste CFRP but also produces electromagnetically shielding cement with excellent mechanical properties.

[0011] To achieve the above objectives, the present invention provides a method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties, characterized by the following steps:

[0012] S1) To obtain recycled carbon fiber, CFRP is placed in a nitrogen atmosphere at 400–650°C with an oxygen volume fraction of 3%–20%, causing the resin to decompose and vaporize upon heating, resulting in recycled carbon fiber with a bent shape and severe agglomeration. The surface of the recycled carbon fiber is not coated with sizing agent, thus exhibiting clean surface and high electrical conductivity. Simultaneously, the thermal decomposition atmosphere causes minimal damage to the graphitization of the recycled carbon fiber, and the nitrogen in the decomposition gas can repair micro-defects on the surface of the recycled carbon fiber, ensuring that the recycled carbon fiber retains a high rate of mechanical property retention.

[0013] S2) Cutting recycled carbon fiber: Using controlled shearing technology, the recycled carbon fiber is cut into lengths of 5-6 cm and 0.1-0.2 cm respectively;

[0014] S3) Pre-dispersed recycled carbon fiber: Recycled carbon fiber with a length of 5-6 cm, recycled carbon fiber with a length of 0.1-0.2 cm, and nanocellulose are mixed in deionized water and stirred for 12-24 hours to obtain a pre-dispersed recycled carbon fiber solution; the nanocellulose is used as a dispersant to break the electrostatic adsorption and mechanical entanglement between recycled carbon fibers of different lengths.

[0015] S4) Prepare cement mortar;

[0016] S5) Mixing the mixture: While slowly stirring the cement mortar in step S4), gradually add it to the recycled carbon fiber pre-dispersion liquid in step S3). After slowly stirring for 1 to 2 minutes, stir rapidly for 3 to 5 minutes to form a mixture.

[0017] The nanocellulose in the mixture acts as a dispersant to achieve uniform dispersion of recycled carbon fibers of different lengths in the cement matrix, thereby constructing a homogeneous conductive network.

[0018] The 5-6 cm long recycled carbon fibers in the mixture form the skeleton of a homogeneous conductive network, enhancing the mechanical strength of the cement matrix.

[0019] The 0.1-0.2 cm long recycled carbon fibers in the mixture are dispersed in the gaps of the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix.

[0020] Meanwhile, the surfaces of recycled carbon fibers of different lengths are not coated with sizing agent, and the surfaces are smooth and easy to wet, resulting in better adhesion to cement and nanocellulose.

[0021] S6) Molding and curing to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

[0022] Furthermore, in S1), CFRP is a waste carbon fiber reinforced resin matrix composite material.

[0023] Furthermore, in S3), the specific proportions of recycled carbon fiber, nanocellulose, and deionized water are as follows: 1-5 parts of recycled carbon fiber with a length of 5-6 cm, 1-5 parts of recycled carbon fiber with a length of 0.1-0.2 cm, 1-10 parts of nanocellulose, and 50 parts of deionized water.

[0024] Furthermore, in S4), the cement mortar formula is: 450-600 parts cement, 150-200 parts silica fume, 150-200 parts water, 0-1 part defoamer, and 5-10 parts water-reducing agent.

[0025] Furthermore, in S5), the raw material ratio in the mixture is as follows: the ratio of nanocellulose to recycled carbon fiber is 1:1 to 1:2, the amount of recycled carbon fiber is 0.1 to 1 wt% of cement, the amount of silica powder is 30 to 40 wt% of cement, the amount of defoamer is 0 to 0.2 wt% of cement, the amount of water-reducing agent is 2 to 8 wt% of cement, and the ratio of cement to water is 2:1 to 3:1.

[0026] Furthermore, in S6), the specific molding process is as follows: the mixed material is poured into the mold, vibrated to defoam and the surface is smoothed, and the mold is demolded after 1 day of pouring to obtain the cement module.

[0027] Furthermore, in S6), the specific curing process is as follows: after demolding, the cement module is moved into a standard curing box and cured for 28 days at 20±2℃ and 95% relative humidity to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

[0028] The advantages of this invention are:

[0029] 1. This invention recycles waste CFRP through pyrolysis to obtain recycled carbon fibers that are bent, severely agglomerated, and have no slurry on the surface. The recycled carbon fibers are used as the reinforcing and functional phases of electromagnetic shielding cement. The mechanical properties and conductivity of the recycled carbon fibers are maintained through a relatively mature pyrolysis recycling process. Cement, silica powder, and recycled carbon fibers are mixed in a certain proportion. After component dispersion and mixing, casting and molding, and curing, recycled carbon fiber reinforced cement with electromagnetic shielding properties is obtained.

[0030] 2. This invention addresses the problems of bent shape, uneven surface, negative charge, and severe agglomeration of recycled carbon fibers. First, controlled shearing technology is used to cut the recycled carbon fibers into different length grades. The longer grade recycled carbon fibers form the skeleton of a homogeneous conductive network, enhancing the mechanical strength of the cement matrix. The shorter grade recycled carbon fibers disperse in the gaps of the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix. Then, nanocellulose is used as a dispersant and binder to achieve uniform dispersion of the recycled carbon fibers in the cement matrix, constructing a homogeneous continuous conductive network. Energy absorption through fiber stress transmission provides reinforcement and toughness, while the carbon fiber conductive network reflects and dissipates electromagnetic wave pollution, improving electromagnetic shielding effectiveness.

[0031] 3. This invention utilizes the characteristics of recycled carbon fiber, which has no slurry and a smooth, easily wettable surface, to achieve better bonding with cement and nanocellulose, realizing the recycling of waste CFRP. It has outstanding economic and ecological benefits and promotes the high-value green reuse of CFRP.

[0032] This invention relates to a method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties. The method involves cutting recycled carbon fibers obtained from the thermal decomposition of waste CFRP into recycled carbon fibers of different lengths, and then adding nanocellulose as a dispersant. This effectively controls the super-dispersion and bonding force of the recycled carbon fibers in the cement-based composite material system, constructing a homogeneous conductive network to obtain high electromagnetic shielding cement with excellent mechanical properties. Simultaneously, it promotes the high-value green reuse of CFRP, resulting in significant economic and ecological benefits. Attached Figure Description

[0033] Figure 1 This is a SEM image of the recycled carbon fiber obtained by the pyrolysis recovery technology used in this invention.

[0034] Figure 2 This is a flowchart of the preparation method of the regenerated fiber reinforced cement with electromagnetic shielding properties according to the present invention. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0037] like Figure 2 As shown, the preparation method of recycled fiber-reinforced cement with electromagnetic shielding properties according to the present invention includes the following steps:

[0038] S1) To obtain recycled carbon fiber, CFRP is placed in a nitrogen atmosphere at 400-650°C with an oxygen volume fraction of 3%-20%, causing the resin to decompose and vaporize upon heating, resulting in recycled carbon fiber with a bent shape and severe agglomeration. The surface of the recycled carbon fiber is not coated with sizing agent, thus exhibiting surface cleanliness and high electrical conductivity. Simultaneously, the thermal decomposition atmosphere causes minimal damage to the graphitization of the recycled carbon fiber, and the nitrogen in the decomposition gas can repair micro-defects on the surface of the recycled carbon fiber, ensuring that the recycled carbon fiber retains a high rate of mechanical property retention.

[0039] Compared to virgin carbon fibers coated with sizing agents, recycled carbon fibers have a cleaner surface, improved electrical conductivity, and better interfacial bonding when preparing composite materials, such as... Figure 1 As shown.

[0040] Specifically, CFRP is a waste carbon fiber reinforced resin matrix composite material.

[0041] S2) Cut the recycled carbon fiber. Use controlled shearing technology to cut the recycled carbon fiber into lengths of 5-6 cm and 0.1-0.2 cm respectively.

[0042] Limited by pyrolysis recycling technology, the recycled carbon fibers are bent and severely agglomerated, making it difficult to disperse them evenly in cement composites. Therefore, controlled shearing technology is used to cut the recycled carbon fibers into shorter pieces to avoid mechanical entanglement between them.

[0043] S3) Pre-dispersed recycled carbon fiber: Recycled carbon fiber with a length of 5-6 cm, recycled carbon fiber with a length of 0.1-0.2 cm, and nanocellulose are mixed in deionized water and stirred for 12-24 hours to obtain a pre-dispersed recycled carbon fiber solution; the nanocellulose is used as a dispersant to break the electrostatic adsorption and mechanical entanglement between recycled carbon fibers of different lengths.

[0044] The recycled carbon fibers obtained from recycling exhibit high dispersibility in their microstructure, geometry, and mechanical properties, making it difficult to fully realize their performance advantages. Therefore, based on the morphology, surface, and wettability characteristics of recycled carbon fibers, nanocellulose dispersants are added. This allows for effective energy absorption through stress transfer between fibers, thereby improving the mechanical and electromagnetic shielding properties of recycled carbon fiber cementitious composites.

[0045] In S3), the specific proportions of recycled carbon fiber, nanocellulose, and deionized water are as follows: 1-5 parts of recycled carbon fiber with a length of 5-6 cm, 1-5 parts of recycled carbon fiber with a length of 0.1-0.2 cm, 1-10 parts of nanocellulose, and 50 parts of deionized water.

[0046] S4) Prepare cement mortar.

[0047] Specifically, the formula for cement mortar is as follows: 450-600 parts cement, 150-200 parts silica fume, 150-200 parts water, 0-1 part defoamer, and 5-10 parts water-reducing agent.

[0048] S5) Mixing the mixture: While slowly stirring the cement mortar in step S4), gradually add it to the recycled carbon fiber pre-dispersion liquid in step S3). After slowly stirring for 1 to 2 minutes, stir rapidly for 3 to 5 minutes to form a mixture.

[0049] The nanocellulose in the mixture acts as a dispersant, enabling the uniform dispersion of recycled carbon fibers of different lengths in the cement matrix, thereby constructing a homogeneous conductive network.

[0050] The 5-6 cm length of recycled carbon fiber in the mixture forms the skeleton of a homogeneous conductive network, enhancing the mechanical strength of the cement matrix. In this embodiment, 5 cm lengths of recycled carbon fiber are cut to form the skeleton of the homogeneous conductive network.

[0051] The recycled carbon fibers with a length of 0.1 to 0.2 cm in the mixture are dispersed in the gaps of the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix. In this embodiment, recycled carbon fibers with a length of 0.1 cm are sheared and dispersed in the gaps of the homogeneous conductive network.

[0052] Meanwhile, the surfaces of recycled carbon fibers of different lengths are not coated with sizing agent, resulting in a smooth and easily wetted surface that provides better adhesion to cement and nanocellulose.

[0053] Preferably, the raw material ratio in the mixture is as follows: the ratio of nanocellulose to recycled carbon fiber is 1:1 to 1:2, the amount of recycled carbon fiber is 0.1 to 1 wt% of cement, the amount of silica powder is 30 to 40 wt% of cement, the amount of defoamer is 0 to 0.2 wt% of cement, the amount of water-reducing agent is 2 to 8 wt% of cement, and the ratio of cement to water is 2:1 to 3:1.

[0054] S6) Molding and curing to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

[0055] Specifically, the molding process involves pouring the mixed material into a mold, vibrating it to remove bubbles and smoothing the surface, and demolding it after 1 day to obtain a cement module.

[0056] Specifically, the curing process involves transferring the demolded cement modules into a standard curing box and curing them for 28 days at 20±2℃ and 95% relative humidity to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

[0057] The recycled carbon fibers obtained in this invention exhibit high dispersibility in their microstructure, geometry, and mechanical properties, making it difficult to fully realize their performance advantages. Therefore, based on the morphology, surface, and wettability characteristics of the recycled carbon fibers, a nano-cellulose dispersant is added. This allows for effective energy absorption through stress transfer between fibers, thereby improving the mechanical and electromagnetic shielding properties of the recycled carbon fiber cementitious composite material.

[0058] The following are more detailed embodiments, which further illustrate the technical solution of the present invention and the technical effects that can be obtained.

[0059] Example 1

[0060] Five parts of recycled carbon fiber with a length of 5 cm and five parts of recycled carbon fiber with a length of 0.1 cm were weighed and mixed with 10 parts of nanocellulose in 50 parts of deionized water and stirred for 24 hours. Five parts of cement, 150 parts of silica powder, 200 parts of water, 1 part of defoamer, and 5 parts of water-reducing agent were weighed and stirred for 2 minutes to obtain cement mortar. While slowly stirring the cement mortar, recycled carbon fiber pre-dispersion liquid was gradually added. After slowly stirring for 1 minute, it was quickly stirred for 5 minutes to obtain a mixture. The mixture was poured into a mold, vibrated to defoam and the surface was smoothed. After pouring for 1 day, it was demolded and then transferred to a standard curing box. After curing for 28 days at 20℃ (±2℃) and 95% relative humidity, recycled carbon fiber reinforced cement A with electromagnetic shielding properties was obtained.

[0061] Example 2

[0062] Weigh 10 parts of recycled carbon fiber with a length of 5cm, mix it with 10 parts of nanocellulose in 50 parts of deionized water, and stir for 24 hours; weigh 550 parts of cement, 150 parts of silica powder, 200 parts of water, 1 part of defoamer, and 5 parts of water-reducing agent, and stir for 2 minutes to obtain cement mortar; while slowly stirring the cement mortar, gradually add the pre-dispersed liquid of recycled carbon fiber, stir slowly for 1 minute, and then stir rapidly for 5 minutes to obtain a mixture; pour the mixed mixture into a mold, vibrate to defoam and smooth the surface, demold after 1 day of pouring, and then transfer it to a standard curing box, and cure it for 28 days at 20℃ (±2℃) and 95% relative humidity to obtain recycled carbon fiber reinforced cement B with electromagnetic shielding properties.

[0063] Example 3

[0064] Ten parts of recycled carbon fiber with a length of 0.1 cm were weighed and mixed with 10 parts of nanocellulose in 50 parts of deionized water and stirred for 24 hours. 550 parts of cement, 150 parts of silica powder, 200 parts of water, 1 part of defoamer, and 5 parts of water-reducing agent were weighed and stirred for 2 minutes to obtain cement mortar. While slowly stirring the cement mortar, the pre-dispersed liquid of recycled carbon fiber was gradually added. After slowly stirring for 1 minute, it was quickly stirred for 5 minutes to obtain a mixture. The mixture was poured into a mold, vibrated to defoam and the surface was smoothed. After pouring for 1 day, it was demolded and then transferred to a standard curing box. After curing at 20℃ (±2℃) and 95% relative humidity for 28 days, recycled carbon fiber reinforced cement C with electromagnetic shielding properties was obtained.

[0065] Comparative Example 1

[0066] Weigh out 550 parts cement, 150 parts silica fume, 200 parts water, 1 part defoamer, and 5 parts water-reducing agent, and stir for 2 minutes to obtain cement mortar. Pour the cement mortar into a mold, vibrate to defoam and smooth the surface. Demold after 1 day of pouring, and then transfer it to a standard curing box. After curing at 20℃ (±2℃) and 95% relative humidity for 28 days, recycled carbon fiber reinforced cement D with electromagnetic shielding properties is obtained.

[0067] Comparative Example 2

[0068] Weigh 10 parts of recycled carbon fiber with a length of 5cm, mix with 50 parts of deionized water, and stir for 24 hours; weigh 550 parts of cement, 150 parts of silica powder, 200 parts of water, 1 part of defoamer, and 5 parts of water-reducing agent, and stir for 2 minutes to obtain cement mortar; while slowly stirring the cement mortar, gradually add the pre-dispersed liquid of recycled carbon fiber, stir slowly for 1 minute, and then stir rapidly for 5 minutes to obtain a mixture; pour the mixed mixture into a mold, vibrate to defoam and smooth the surface, demold after 1 day of pouring, and then transfer it to a standard curing box. After curing at 20℃ (±2℃) and 95% relative humidity for 28 days, recycled carbon fiber reinforced cement E with electromagnetic shielding properties is obtained.

[0069] Comparative Example 3

[0070] Weigh 10 parts of recycled carbon fiber with a length of 0.1 cm, mix with 50 parts of deionized water, and stir for 24 hours; weigh 550 parts of cement, 150 parts of silica powder, 200 parts of water, 1 part of defoamer, and 5 parts of water-reducing agent, and stir for 2 minutes to obtain cement mortar; while slowly stirring the cement mortar, gradually add the pre-dispersed liquid of recycled carbon fiber, stir slowly for 1 minute, and then stir rapidly for 5 minutes to obtain a mixture; pour the mixed mixture into a mold, vibrate to defoam and smooth the surface, demold after 1 day of pouring, and then transfer it to a standard curing box. After curing at 20℃ (±2℃) and 95% relative humidity for 28 days, recycled carbon fiber reinforced cement F with electromagnetic shielding properties is obtained.

[0071] The compressive strength and electromagnetic shielding effectiveness of the recycled carbon fiber reinforced cement A to F with electromagnetic shielding properties obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were tested respectively. The specific test results are shown in Table 1 below.

[0072] Table 1 Performance Test Results

[0073]

[0074] Note:

[0075] 1. The compressive strength of recycled carbon fiber reinforced cement with electromagnetic shielding properties was tested in accordance with GB / T 36535-2018.

[0076] 2. The average electromagnetic shielding effectiveness of recycled carbon fiber reinforced cement with electromagnetic shielding properties in the X-band was measured and calculated using the waveguide method.

[0077] Comparing Example 1 with Comparative Example 1, it can be seen that the long and short recycled carbon fibers added to the cement can serve as a skeleton, enhancing the compressive strength of the cement in terms of mechanical properties, and introducing electromagnetic shielding performance through the excellent conductivity of the recycled carbon fibers.

[0078] Comparing Example 2 with Comparative Example 2, it can be seen that the 5cm recycled carbon fiber is prone to entanglement and uneven mixing with cement. Introducing nanocellulose can effectively improve its uniformity.

[0079] Comparing Example 3 with Comparative Example 3, it can be seen that 0.1cm recycled carbon fiber is easy to disperse in the system because of its short length. However, it is more difficult to form a continuous conductive network skeleton, so the improvement in mechanical properties is not as good as that of 5cm recycled carbon fiber.

[0080] A horizontal comparison of Examples 1, 2, and 3 shows that, under the dispersion and bonding of nanocellulose, long-gauge recycled carbon fibers can effectively form a mechanically enhanced skeleton and a conductive network, while short-gauge recycled carbon fibers can further fill the gaps between the fiber and cement, thereby further improving the electromagnetic shielding performance and structural stability.

[0081] As can be seen from Table 1, the cement composite material prepared by this invention has high compressive strength and electromagnetic shielding effectiveness. It can not only be used as a multifunctional building material to reduce electromagnetic interference pollution in specific environments, but also realize the high-value reuse of recycled carbon fiber, bringing certain environmental benefits.

[0082] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties, characterized in that, Includes the following steps: S1) Obtaining recycled carbon fiber: CFRP is placed in a nitrogen atmosphere at 400~650℃ with an oxygen volume fraction of 3%~20%, causing the resin to decompose and vaporize upon heating, resulting in recycled carbon fiber with a bent shape and severe agglomeration. The surface of the recycled carbon fiber is not coated with sizing agent, thus exhibiting surface cleanliness and high electrical conductivity. Simultaneously, the thermal decomposition atmosphere causes minimal damage to the graphitization of the recycled carbon fiber, and the nitrogen in the decomposition gas can repair micro-defects on the surface of the recycled carbon fiber, ensuring that the recycled carbon fiber retains a high rate of mechanical property retention. S2) Cutting recycled carbon fiber: Using controlled shearing technology, the recycled carbon fiber is cut into lengths of 5-6 cm and 0.1-0.2 cm respectively; S3) Pre-dispersed recycled carbon fiber: Recycled carbon fiber with a length of 5-6 cm, recycled carbon fiber with a length of 0.1-0.2 cm, and nanocellulose are mixed in deionized water and stirred for 12-24 hours to obtain a pre-dispersed recycled carbon fiber solution; the nanocellulose is used as a dispersant to break the electrostatic adsorption and mechanical entanglement between recycled carbon fibers of different lengths. The specific ratio of recycled carbon fiber, nanocellulose, and deionized water is as follows: 1-5 parts of recycled carbon fiber with a length of 5-6cm, 1-5 parts of recycled carbon fiber with a length of 0.1-0.2cm, 1-10 parts of nanocellulose, and 50 parts of deionized water. S4) Prepare cement mortar; S5) Mixing the mixture: While slowly stirring the cement mortar in step S4), gradually add it to the recycled carbon fiber pre-dispersion liquid in step S3). After slowly stirring for 1-2 minutes, stir rapidly for 3-5 minutes to form a mixture. The raw material ratio in the mixture is as follows: the ratio of nanocellulose to recycled carbon fiber is 1:1 to 1:2, and the amount of recycled carbon fiber is 0.1 to 1 wt% of the cement. The nanocellulose in the mixture acts as a dispersant to achieve uniform dispersion of recycled carbon fibers of different lengths in the cement matrix, thereby constructing a homogeneous conductive network. The 5-6 cm long recycled carbon fibers in the mixture form the skeleton of a homogeneous conductive network, enhancing the mechanical strength of the cement matrix. The 0.1-0.2 cm long recycled carbon fibers in the mixture are dispersed in the gaps of the homogeneous conductive network, enhancing the conductivity and stress absorption of the cement matrix. Meanwhile, the surfaces of recycled carbon fibers of different lengths are not coated with sizing agent, and the surfaces are smooth and easy to wet, resulting in better adhesion to cement and nanocellulose. S6) Molding and curing to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

2. The method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties according to claim 1, characterized in that: In S1), CFRP is a waste carbon fiber reinforced resin matrix composite material.

3. The method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties according to claim 1, characterized in that: In S4), the cement mortar formula is: 450-600 parts cement, 150-200 parts silica fume, 150-200 parts water, 0-1 part defoamer, and 5-10 parts water-reducing agent.

4. The method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties according to claim 2, characterized in that: In S6), the specific molding process is as follows: the mixed material is poured into the mold, vibrated to defoam and the surface is smoothed, and the mold is demolded after 1 day of pouring to obtain the cement module.

5. The method for preparing recycled fiber-reinforced cement with electromagnetic shielding properties according to claim 4, characterized in that: In S6), the specific curing process is as follows: after demolding, the cement module is moved into a standard curing box and cured for 28 days at 20±2℃ and 95% relative humidity to obtain recycled carbon fiber reinforced cement with electromagnetic shielding properties.

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