3D printing of electromagnetic wave absorbing concrete based on spherical water-absorbing resin

Abstract

The application is based on spherical water-absorbing resin reinforced 3D printing electromagnetic wave absorbing concrete, the concrete includes cement-based material and spherical water-absorbing resin, in the mixing process of the spherical water-absorbing resin and the cement-based material, it is necessary to ensure uniform mixing and that the spherical water-absorbing resin does not expand obviously, obtain printing slurry, and send the printing slurry to the printing nozzle of the 3D printer for 3D printing; the sample after 3D printing is protected by a protective film, and is maintained and watered regularly, the concrete is completely solidified after one day, forming a permanent spherical water-absorbing resin expansion support state, and then obtaining the spherical water-absorbing resin reinforced 3D printing electromagnetic wave absorbing concrete with regular air holes after 28d water maintenance and drying. The spherical water-absorbing resin is used to prepare 3D printing electromagnetic wave absorbing concrete for the first time, which significantly improves the electromagnetic wave absorbing performance of the 3D printing electromagnetic wave absorbing concrete.

Description

Technical Field

[0001] This invention relates to the field of 3D printed electromagnetic wave absorbing concrete technology, specifically to a 3D printed electromagnetic wave absorbing concrete based on spherical water-absorbing resin and its preparation method. Background Technology

[0002] With the development of technologies such as smart homes and the Internet of Things, electromagnetic interference has become an unavoidable problem in communication, radar, and signal transmission activities. To address this issue, electromagnetic absorbing concrete, as a novel electromagnetic absorbing material, can effectively absorb and dissipate electromagnetic waves, thereby reducing interference. Electromagnetic absorbing concrete has broad market prospects in the construction field, improving the reliability and performance of communication and radar equipment. It can also play an important role in high-rise buildings, military facilities, and other areas, enhancing national security capabilities.

[0003] Electromagnetic absorbing concrete is a material with excellent properties and broad application prospects in electromagnetic wave interference suppression and protection, building thermal insulation and sound insulation, fire resistance and corrosion resistance. Electromagnetic absorbing concrete can absorb and dissipate electromagnetic waves, converting them into micro-heat, thus reducing interference while protecting the safety of electronic equipment.

[0004] 3D-printed concrete is a novel method for preparing concrete materials. This technology boasts advantages such as high production efficiency, significant design freedom, and low process complexity. However, when using 3D-printed concrete, it is crucial to fully consider factors such as material strength, toughness, and durability to ensure the practicality and safety of the resulting concrete structures. Furthermore, it is necessary to strengthen research and develop corresponding standards and specifications to promote the standardization and industrialization of this technology. This technology has broad application prospects in architecture, culture and art, and engineering. However, the wave-absorbing performance of 3D-printed electromagnetic wave-absorbing concrete currently requires further improvement. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing 3D-printed electromagnetic absorbing concrete reinforced with spherical water-absorbing resin. This invention innovatively utilizes spherical water-absorbing resin in the preparation of 3D-printed electromagnetic absorbing concrete. The preparation method of this invention fully considers the properties of each raw material, setting reasonable curing methods, extrusion speeds, and printing speeds, significantly improving the electromagnetic absorption performance of the 3D-printed electromagnetic absorbing concrete and facilitating its application in practical engineering.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A type of 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin is characterized by comprising cement-based materials and spherical water-absorbing resin. During the mixing process of the spherical water-absorbing resin and cement-based materials, it is necessary to ensure both uniform mixing and that the spherical water-absorbing resin does not undergo significant expansion to obtain a printing slurry. The printing slurry is then fed into the print head of a 3D printer for 3D printing. The 3D-printed sample is protected with a protective film and cured with water regularly. For the first 2 hours, water is applied every 10-15 minutes to allow the spherical water-absorbing resin to continuously absorb water until it fully expands. Afterward, water is applied every 3-4 hours to maintain the expanded state of the spherical water-absorbing resin. After one day, the concrete completely solidifies, forming a permanent expanded support state of the spherical water-absorbing resin. After 28 days of water curing and drying, a 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin and exhibiting regular air cavities is obtained.

[0008] The cement-based material contains a metallic microwave absorber, and the spherical water-absorbing resin has a liquid absorption rate as high as 245 g / cm³. 3 It can absorb a large amount of water in a short time and form a gel state, creating a three-dimensional space mainly composed of water inside the concrete. After the concrete hardens, the water-absorbing resin shrinks and dries, eventually forming regular air cavities. This improves the matching performance between the impedance of the concrete and the impedance of the electromagnetic waves in the space. When electromagnetic waves are incident on the interior of the concrete and propagate, they will be reflected and scattered multiple times on the surface of each air cavity, resulting in energy loss of the electromagnetic waves. In addition, when electromagnetic waves are incident from one closed air cavity to an adjacent air cavity, the phase changes in the direction of the cavity wall and interference occurs, further causing electromagnetic energy attenuation, enhancing the gradient of air-concrete-metal absorber, and thus improving the absorption effect of electromagnetic waves.

[0009] The metal microwave absorber is at least one of iron tailings, nano iron oxide, nano iron tetroxide, nano copper, and nano copper oxide.

[0010] The 3D printing process settings are as follows: the nozzle exit cross-sectional area is set to 120mm. 2 The horizontal printing speed is 170–180 cm / min, the vertical printing speed is 0.7–0.8 m / h, and the extrusion speed is 0.02–0.04 m / h. 3 Then print using the / h command.

[0011] The concrete comprises the following components by weight: 42.5# ordinary Portland cement: 5-6 parts, silica fume: 0.4-0.6 parts, spherical water-absorbing resin: 0.0095-0.019 parts, quartz sand: 4.8-5.2 parts, copper slag: 1.4-1.6 parts, thickener: 0.002-0.006 parts, water-reducing agent: 0.009-0.011 parts, and water: 1.7-1.8 parts.

[0012] The thickener is carboxymethyl cellulose with a viscosity of 200,000; the quartz sand is 90-110 mesh; the water-reducing agent is melamine water-reducing agent, model F10; the spherical superabsorbent polymer is polyvinyl alcohol, and the density of the non-absorbent spherical superabsorbent polymer is 1.141 g / cm³. 3 The average diameter of the spherical water-absorbing resin particles when they are not absorbing water is 0.5-1 mm, and the average diameter of the particles after they are saturated with water is 2-3 mm; the average particle size of the copper slag is 100-150 μm.

[0013] The method for preparing 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin includes the following steps:

[0014] S1. Mix 5-6 parts by weight of ordinary Portland cement, 0.4-0.6 parts of silica fume, 4.8-5.2 parts of quartz sand and 1.4-1.6 parts of copper slag evenly.

[0015] S2. Add 0.002 to 0.006 parts of thickener to step S1 above and mix thoroughly.

[0016] S3. Add 0.0095 to 0.019 parts of spherical water-absorbing resin by dry weight to step S2 above. Pour the resin into the mixer all at once, then add 0.009 to 0.011 parts of water-reducing agent and 1.7 to 1.8 parts of water and mix well. Stop mixing when the mixture is uniform and the spherical water-absorbing resin has not expanded significantly. Control the mixing time to 350-410 seconds to obtain the printing paste.

[0017] S4. The printing paste obtained in step S3 is fed into the print head of the 3D printer, and the print head outlet cross-sectional area is set to 120mm². 2 The horizontal printing speed is 170–180 cm / min, the vertical printing speed is 0.7–0.8 m / h, and the extrusion speed is 0.02–0.04 m / h. 3 Then print;

[0018] The 3D-printed sample was protected with a protective film and watered regularly. For the first 2 hours, water was applied every 10-15 minutes to allow the spherical water-absorbing resin to continuously absorb water and grow completely. After that, water was applied every 4 hours to keep the spherical water-absorbing resin in an expanded state. After one day, the concrete was completely solidified, forming a permanent expanded support state of the spherical water-absorbing resin. After 28 days of water curing and drying, 3D-printed electromagnetic wave absorbing concrete with regular air cavities based on spherical water-absorbing resin was obtained.

[0019] Under the same conditions, introducing spherical water-absorbing resin into 3D printed concrete can significantly improve the wave absorption performance, reduce the peak reflectivity of concrete absorption, and broaden the electromagnetic wave absorption bandwidth.

[0020] The volumetric dosage of the spherical water-absorbing resin after it becomes saturated with water is 20-40% of that in concrete.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. This invention creatively utilizes spherical water-absorbing resin in 3D-printed electromagnetic wave-absorbing concrete. Spherical water-absorbing resin is a novel polymer functional material, characterized by a liquid absorption rate as high as 245 g / cm³. 3 This material can absorb a large amount of water in a short time and form a gel state, creating a three-dimensional space mainly composed of water inside the concrete. Spherical water-absorbing resin is filled into the electromagnetic wave-absorbing composite material. After regular curing and watering, the resin shrinks and dries after the concrete hardens, ultimately forming regular air cavities, which can be considered equivalent to a closed-cell honeycomb structure. After thorough mixing, it forms a multiphase composite structure of air, concrete, and conductive materials. This effectively improves the impedance matching performance between the concrete composite material and the spatial electromagnetic wave impedance, reducing the direct reflection effect of electromagnetic waves caused by the strongly magnetic and conductive materials. When electromagnetic waves propagate inside the composite material, they undergo multiple reflections and scatterings on the inner surfaces of each honeycomb structure particle, resulting in energy loss. Furthermore, when electromagnetic waves enter from one closed pore to an adjacent pore, the phase changes in the pore wall direction, causing interference and further attenuation of electromagnetic energy. Based on these principles, the gradient of the air-concrete-metal absorbing agent is further enhanced, thereby increasing the absorption bandwidth of electromagnetic waves. Under the same conditions, introducing spherical water-absorbing resin into 3D-printed concrete significantly improves its wave absorption performance.

[0023] 2. Because the 3D printing process creates periodically arranged wavy surface textures on the surface layer, the impedance of the electromagnetic wave absorbing concrete material changes from a step-like abrupt change to a continuous variation. This alters the direction of penetration into the concrete and changes the direction of electromagnetic wave reflection, reducing the received electromagnetic waves. This increases the number of electromagnetic wave incidents and the transmission distance, increasing the probability of loss. Furthermore, there is a certain probability of interference loss between multiple reflected and refracted waves, which is beneficial for the full incidence and loss of electromagnetic waves, especially obliquely incident electromagnetic waves. The higher extrusion speed in this invention enhances the impact of the surface texture on the electromagnetic wave absorption performance, further improving the electromagnetic wave absorption performance.

[0024] 3. Printing Performance: Through the rational proportioning of various materials and the matching settings of extrusion and printing speeds, this invention enables the concrete to possess excellent fluidity and extrudability, meeting the construction requirements of 3D printed concrete structures. The prepared 3D printed concrete exhibits characteristics such as good rheological properties, strong stability, fast setting time, high early strength, non-shrinkage of later strength, and good durability.

[0025] 4. Electromagnetic Absorption Performance: 3D-printed electromagnetic absorbing concrete prepared from 0.019 parts dry weight of spherical water-absorbing resin can absorb more than 90% of electromagnetic waves in the 13.97GHz frequency band. In the 7.53GHz frequency band, the peak reflectivity of this concrete reaches -19.117dB, absorbing 98.77% of electromagnetic waves. This significantly exceeds the electromagnetic absorption bandwidth (1.5-2GHz) and reflectivity of traditional cast concrete, and can be widely used in the field of electromagnetic protection. It has excellent electromagnetic absorption performance. This invention uses copper slag and dry spherical water-absorbing resin as raw materials. Copper slag itself absorbs and loses electromagnetic waves, exhibiting a gradually changing impedance "broadband" absorber and a thin-layer absorber that attenuates surface current. After curing, the spherical absorbent resin dries and loses water, transforming into small, dehydrated spheres. This creates spherical spaces formed during curing due to the expansion of the resin and its compression of the surrounding concrete. These spaces, after dehydration, become spherical air cavities. These spherical air cavities are surrounded by electromagnetically absorbing concrete containing a metallic microwave absorber. Relative to the direction of the electromagnetic wave, the direction of incident electromagnetic wave is the surface layer, and the direction of exit from the air cavity is the bottom layer. The two reflected waves from the surface and bottom layers, with equal amplitude and opposite phase, interfere and cancel each other out. The air cavities formed by the copper slag and the spherical absorbent resin absorb the vast majority of the electromagnetic waves, while the copper slag also partially supports the structure.

[0026] 5. High environmental benefits and close alignment with carbon emission standards: This invention utilizes a large amount of copper slag, an industrial waste, which significantly reduces the environmental and ecological damage caused by using natural sand and gravel, lowers the price of 3D printed concrete materials, and achieves a green and environmentally friendly effect, thus promoting the practical engineering application of 3D printed concrete. Simultaneously, the spherical absorbent resin is an environmentally friendly material, free of harmful substances, and will not pollute the environment.

[0027] 6. Wide Range of Applications: Specifically, the improvement and enhancement of electromagnetic protection provided by this invention can significantly improve the electromagnetic radiation protection capabilities of structures such as television transmitting stations, base stations, microwave laboratories, hospitals, and substations, reducing the impact of electromagnetic interference and promoting human physical and mental health in electromagnetic environments. This invention can also be extended to improve the stealth capabilities of military structures against radar detection. It is of great significance for the electromagnetic stealth capabilities of military radar stations, transmitting platforms, ammunition depots, etc. Attached Figure Description

[0028] Figure 1 These are comparison images of concrete samples from the three embodiments.

[0029] Figure 2 These are comparison charts of concrete electromagnetic wave absorption reflectivity tests in three embodiments.

[0030] Figure 3This is a schematic diagram of the internal structure of 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin.

[0031] Figure 4 This is a schematic diagram of the wave absorption principle of the present invention.

[0032] Figure 5 This is a CT scan of Example 3 of electromagnetic wave absorbing concrete based on spherical water-absorbing resin-reinforced 3D printing. Detailed implementation method:

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention involves 3D printing the provided concrete and conducting relevant performance tests on the printed structure, including constructability evaluation and electromagnetic wave absorption performance evaluation. The tests show that printing with the concrete of this invention can ensure the smooth progress of the printing process while meeting the proposed printing requirements, and the resulting structure is stable and solid.

[0035] The electromagnetic wave reflectivity test employs the bow-shaped frame reflection method, using a vector network analyzer (Agilent N5232A) to emit electromagnetic waves. The reflectivity of the material's electromagnetic wave absorption is measured through transmission between the transmitter and receiver. The electromagnetic wave absorption performance test of this invention strictly adheres to the national military standard "Test Method for Reflectivity of Radar Absorbing Materials" (GJB2038-1994). The concrete used for the electromagnetic wave reflectivity test must undergo at least 28 days of standard curing (relative humidity 95±5%, curing temperature 20±1℃). After curing, the concrete specimens are dried at a low temperature of 60℃ to reduce the influence of moisture content on the electromagnetic wave reflectivity. Subsequently, a smooth 180mm*180mm aluminum plate is placed under the specimen, and the test is conducted in the 1-18GHz frequency band.

[0036] Set the printhead exit cross-sectional area to 120mm. 2 The horizontal printing speed is 170–180 cm / min, the vertical printing speed is 0.7–0.8 m / h, and the extrusion speed is 0.02–0.04 m / h. 3 Then, the mixture is printed to obtain 3D printed spherical water-absorbing resin electromagnetic wave-absorbing concrete.

[0037] This invention relates to 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin. The concrete comprises the following components by weight: 42.5# ordinary Portland cement: 5-6 parts, silica fume: 0.4-0.6 parts, spherical water-absorbing resin: 0.0095-0.019 parts, quartz sand: 4.8-5.2 parts, copper slag: 1.4-1.6 parts, thickener: 0.002-0.006 parts, water-reducing agent: 0.009-0.011 parts, and water: 1.7-1.8 parts.

[0038] The cement is 42.5 grade ordinary Portland cement; the thickener is carboxymethyl cellulose with a viscosity of 200,000; the quartz sand is 90-110 mesh; the water-reducing agent is melamine water-reducing agent, model F10; the spherical water-absorbing resin is polyvinyl alcohol, with an average particle diameter of 0.5-1 mm when the spherical water-absorbing resin is not absorbing water, and an average particle diameter of 2-3 mm after water absorption saturation; the average particle size range of the copper slag is 100-150 μm.

[0039] The method for preparing 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin includes the following steps:

[0040] S1. Mix 5-6 parts by weight of ordinary Portland cement, 0.4-0.6 parts of silica fume, 4.8-5.2 parts of quartz sand and 1.4-1.6 parts of copper slag evenly.

[0041] S2. Add 0.002 to 0.006 parts of thickener to step S1 above and mix thoroughly.

[0042] S3. Add 0.0095 to 0.019 parts (dry weight) of spherical water-absorbing resin to step S2 above. Pour the resin into the mixer all at once. Then add 0.009 to 0.011 parts of water-reducing agent and 1.7 to 1.8 parts of water and mix thoroughly. Stop mixing when the mixture is uniform and the spherical water-absorbing resin has not expanded significantly. Control the mixing time to about 400 seconds to obtain the printing paste. Ensure that the paste is thoroughly mixed. At the same time, prevent the mixing time from being too long, which may cause the water-absorbing resin to absorb water and expand too much. Under the action of external force, the structure may be damaged, resulting in irregular air cavities. This will weaken the ability of interference cancellation and reduce the electromagnetic wave absorption performance.

[0043] S4. The printing paste obtained in step S3 is fed into the print head of the 3D printer, and the print head outlet cross-sectional area is set to 120mm². 2 The horizontal printing speed is 170–180 cm / min, the vertical printing speed is 0.7–0.8 m / h, and the extrusion speed is 0.03–0.04 m / h. 3 Then print / h.

[0044] The 3D-printed samples were protected with a protective film and cured with water regularly. For the first two hours, water was applied every 15 minutes to allow the spherical water-absorbing resin to absorb water and fully expand. Afterward, water was applied every four hours to keep the spherical water-absorbing resin in an expanded state. After one day, the concrete completely solidified, forming a permanent expanded support structure of the spherical water-absorbing resin. Following 28 days of water curing and drying, a 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin and featuring regular air cavities was obtained. The size of the air cavities was 2-3 mm.

[0045] Example 1

[0046] This embodiment describes a 3D-printed electromagnetic wave-absorbing concrete, which comprises the following components by weight: 5 parts of 42.5# ordinary Portland cement, 0.5 parts of silica fume, 5 parts of quartz sand, 1.5 parts of copper slag, 0.002 parts of thickener, 0.01 parts of water-reducing agent, and 1.75 parts of water.

[0047] The specific surface area of ​​the 42.5 grade ordinary Portland cement is 348 m². 2 / kg, density is 3.0g / cm³ 3 The standard consistency water requirement is 25.9%, the initial setting time is 170 min, the final setting time is 210 min, the loss on ignition is 3.5%, the magnesium oxide content is 2.18%, the 3-day flexural strength is 5.7 MPa, and the 3-day compressive strength is 30 MPa.

[0048] The density of the silica fume is 2.3 g / cm³. 3 Specific surface area is 25-29 m² 2 / g; the quartz sand is 90-110 mesh; the copper slag has a density of 2.6 g / cm³. 3 The average particle size is 106 μm, and the iron oxide solid content is 53%. The thickener is carboxymethyl cellulose with a viscosity of 200,000. The quartz sand is 90-110 mesh, and the water-reducing agent is melamine water-reducing agent with model F10.

[0049] Its preparation method includes the following steps:

[0050] S1. Mix 5 parts by weight of ordinary Portland cement, 0.5 parts of silica fume, 5 parts of quartz sand and 1.5 parts of copper slag evenly.

[0051] S2. Add 0.002 parts of thickener to step S1 above and mix thoroughly.

[0052] S3. Add 0.01 parts of water-reducing agent and 1.75 parts of water to step S2 above, mix and stir evenly for 400 seconds;

[0053] S4. The printing paste obtained in step S3 is fed into the print head of the 3D printer, and the print head outlet cross-sectional area is set to 120mm². 2 The horizontal printing speed is 180 cm / min, the vertical printing speed is 0.8 m / h, and the extrusion speed is 0.04 m / h. 3 Then print using the / h command.

[0054] In this embodiment, a higher extrusion speed is used to form a deeper 3D printing texture without overprinting. The reasonable extrusion speed setting improves the electromagnetic wave absorption performance and avoids the problem of vertical material accumulation at the printing nozzle.

[0055] Electromagnetic absorption performance evaluation:

[0056] This embodiment was tested according to the requirements of "Test Method for Reflectivity of Radar Absorbing Materials" (GJB2038-1994). Example 1 serves as a control group; the test results are attached. Figure 2 As shown, the 3D-printed electromagnetic absorbing concrete prepared without the addition of spherical water-absorbing resin exhibits an absorption rate exceeding 90% in the 13.08 GHz frequency band, far surpassing the electromagnetic absorption bandwidth (1.5-2 GHz) of traditional cast concrete. Furthermore, in the 7.42 GHz frequency band, this concrete also demonstrates a peak reflectivity of -15.24 dB, absorbing 97.01% of electromagnetic waves. This means that most electromagnetic waves are absorbed, and the reflection and scattering of electromagnetic waves are effectively suppressed. This not only improves the absorption efficiency of electromagnetic waves but also protects surrounding equipment and the environment from electromagnetic radiation.

[0057] Example 2

[0058] The composition of each part in this embodiment is the same as that in Embodiment 1, except that 0.0095 parts of spherical water-absorbing resin are added in this embodiment.

[0059] The density of the non-absorbent spherical superabsorbent polymer is 1.141 g / cm³. 3 The average diameter of the spherical particles is 0.5–1 mm;

[0060] This embodiment is based on 3D-printed electromagnetic wave absorbing concrete reinforced with spherical water-absorbing resin, and its preparation method includes the following steps:

[0061] S1. Mix 5 parts by weight of ordinary Portland cement, 0.5 parts of silica fume, 5 parts of quartz sand and 1.5 parts of copper slag evenly.

[0062] S2. Add 0.002 parts of thickener to step S1 above and mix thoroughly.

[0063] S3. Add 0.0095 parts of spherical water-absorbing resin by dry weight to step S2 above. Pour the resin into the mixer all at once, then add 0.01 parts of water-reducing agent and 1.75 parts of water and mix well. Stop mixing when the mixture is uniform and the spherical water-absorbing resin has not swelled significantly. The mixing time should be controlled at about 400 seconds to prevent the water-absorbing resin from absorbing too much water and swelling, which would damage the structure.

[0064] S4. Feed the concrete obtained in step S3 into the print head of the 3D printer, and set the print head outlet cross-sectional area to 120mm². 2 The horizontal printing speed is 175 cm / min, the vertical printing speed is 0.75 m / h, and the extrusion speed is 0.04 m / h. 3 Then print / h.

[0065] The 3D-printed samples were protected with a protective film and cured with water regularly. For the first two hours, water was applied every 10-15 minutes to allow the spherical water-absorbing resin to absorb water and fully expand. Afterward, water was applied every four hours to keep the spherical water-absorbing resin in an expanded state. After one day, the concrete completely solidified, forming a permanent expanded support structure of the spherical water-absorbing resin. Following 28 days of water curing and drying, a 3D-printed electromagnetic wave absorbing concrete with regular air cavities, reinforced with spherical water-absorbing resin, was obtained. The particle size of the expanded water-absorbing resin was controlled to approximately 2-3 mm.

[0066] Electromagnetic absorption performance evaluation:

[0067] This embodiment was tested according to the requirements of "Test Method for Reflectivity of Radar Absorbing Materials" (GJB2038-1994). The test results of this embodiment 2 are attached. Figure 2As shown, 3D-printed electromagnetic absorbing concrete prepared with 20% volumetric admixture (equivalent volume after water absorption) of spherical water-absorbing resin exhibits an absorption rate exceeding 90% in the 13.66 GHz frequency band, far surpassing the electromagnetic absorption bandwidth (1.5-2 GHz) of traditional cast concrete. Furthermore, in the 7.27 GHz frequency band, the concrete achieves a peak reflectivity of -17.377 dB, absorbing 98.17% of electromagnetic waves. Compared to Example 1, this embodiment has a bandwidth of 0.58 GHz and an absorption peak value of 1.16%. This is because the air cavities provided by the spherical water-absorbing resin, combined with the 3D printing process, form periodically arranged wave-like surface textures on the surface layer. This changes the impedance of the electromagnetic wave-absorbing concrete material from the original step-like abrupt change to a continuous change, resulting in a change in the direction of penetration into the concrete and altering the direction of electromagnetic wave reflection from the surface. This reduces the received electromagnetic waves, increases the number of electromagnetic wave incidents and the transmission distance, and improves the probability of loss. There is also a certain probability of interference loss between the multiple reflected and refracted waves between different air cavities, which is beneficial for the full incident and loss of electromagnetic waves, especially obliquely incident electromagnetic waves, thereby improving the absorption bandwidth of electromagnetic waves.

[0068] Example 3

[0069] The composition and preparation method of each part in this embodiment are the same as those in Example 2. The difference is that 0.019 parts of spherical water-absorbing resin are added in this embodiment (equivalent to 40% volume of water absorption).

[0070] The 3D printing process is set as follows: the printing paste is fed into the print head of the 3D printer, and the print head exit cross-sectional area is set to 120mm². 2 The horizontal printing speed is 170 cm / min, the vertical printing speed is 0.7 m / h, and the extrusion speed is 0.025 m / h. 3 Then print / h.

[0071] The 3D-printed sample was protected with a protective film and watered regularly. For the first 2 hours, water was applied every 10-15 minutes to allow the spherical water-absorbing resin to continuously absorb water and grow completely. After that, water was applied every 4 hours to keep the spherical water-absorbing resin in an expanded state. After one day, the concrete was completely solidified, forming a permanent expanded support state of the spherical water-absorbing resin. After 28 days of water curing and drying, 3D-printed electromagnetic wave absorbing concrete with regular air cavities based on spherical water-absorbing resin was obtained.

[0072] In this embodiment, compared to Embodiment 2, with an increased content of spherical absorbent resin, reducing the printing and extrusion speeds allows for the formation of regular air cavities. Figure 5The CT pore distribution map shows that the spherical water-absorbing resin is basically intact, and it can have a good electromagnetic wave absorption effect for electromagnetic waves of similar wavelengths with similar diameters.

[0073] Electromagnetic absorption performance evaluation:

[0074] This embodiment was tested according to the requirements of "Test Method for Reflectivity of Radar Absorbing Materials" (GJB2038-1994). The test results of this embodiment 3 are attached. Figure 2 As shown, the absorption rate in the 13.97 GHz band is over 90%, far exceeding the electromagnetic absorption bandwidth (1.5-2 GHz) of traditional cast concrete. Furthermore, in the 7.53 GHz band, the concrete's peak reflectivity reaches -19.117 dB, absorbing 98.77% of the electromagnetic waves. Compared to Example 2, this embodiment has a bandwidth of 0.31 GHz and an absorption peak increase of 0.6%. The 40% volumetric water-absorbing resin can increase the number of electromagnetic wave incidents and the transmission distance, improving the probability of loss. It also increases the probability of interference loss between multiple reflected and refracted waves, which is beneficial for sufficient incident and attenuation of electromagnetic waves, especially obliquely incident electromagnetic waves, thereby improving the electromagnetic wave absorption bandwidth.

[0075] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A type of 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin, characterized in that, The concrete comprises cement-based materials and spherical water-absorbing resin. During the mixing process of the spherical water-absorbing resin and cement-based materials, it is necessary to ensure uniform mixing while preventing significant expansion of the spherical water-absorbing resin to obtain a printing slurry. The printing slurry is then fed into the print head of a 3D printer for 3D printing. The 3D-printed sample is protected with a protective film and cured by watering regularly. For the first 2 hours, water is applied every 10-15 minutes to allow the spherical water-absorbing resin to continuously absorb water until it fully expands. Thereafter, water is applied every 3-4 hours to maintain the expansion of the spherical water-absorbing resin. After one day, the concrete is completely solidified, forming permanent spherical water-absorbing resin. The resin expands and supports the structure, and after 28 days of water curing and drying, 3D-printed electromagnetic absorbing concrete with regular air cavities is obtained based on spherical water-absorbing resin. After curing, the spherical water-absorbing resin dries and loses water, becoming shriveled spheres. This results in spherical spaces formed during curing due to the expansion of the spherical water-absorbing resin and the compression of the surrounding concrete. After losing water, these spherical air cavities are formed by electromagnetic absorbing concrete containing metal absorbing agents. Relative to the direction of the electromagnetic wave, the direction of electromagnetic wave incident is the surface layer, and the direction of electromagnetic wave exiting the air cavity is the bottom layer. The two reflected waves from the surface layer and the bottom layer have equal amplitudes and opposite phases, which interfere and cancel each other out. The concrete comprises the following components by weight: 42.5# ordinary Portland cement: 5-6 parts, silica fume: 0.4-0.6 parts, spherical water-absorbing resin: 0.0095-0.019 parts, quartz sand: 4.8-5.2 parts, copper slag: 1.4-1.6 parts, thickener: 0.002-0.006 parts, water-reducing agent: 0.009-0.011 parts, and water: 1.7-1.8 parts. The average diameter of the spherical superabsorbent polymer particles when they are not absorbing water is 0.5~1mm, and the average diameter of the particles after they are saturated with water is 2~3mm. The cement-based material contains a metallic microwave absorber, and the spherical water-absorbing resin has a liquid absorption rate as high as 245 g / cm³. 3 It can absorb a large amount of water in a short time and form a gel state, creating a three-dimensional space mainly composed of water inside the concrete. After the concrete hardens, the water-absorbing resin shrinks and dries, eventually forming regular air cavities. This improves the matching performance between the impedance of the concrete and the impedance of the electromagnetic waves in the space. When electromagnetic waves are incident on the interior of the concrete and propagate, they will be reflected and scattered multiple times on the surface of each air cavity, resulting in energy loss of the electromagnetic waves. In addition, when electromagnetic waves are incident from one closed air cavity to an adjacent air cavity, the phase changes in the direction of the cavity wall and interference occurs, which further causes electromagnetic energy attenuation, enhances the gradient of air-concrete-metal absorber, and thus improves the absorption effect of electromagnetic waves. The method for preparing 3D-printed electromagnetic wave-absorbing concrete reinforced with spherical water-absorbing resin includes the following steps: S1. Mix 5-6 parts by weight of ordinary Portland cement, 0.4-0.6 parts of silica fume, 4.8-5.2 parts of quartz sand and 1.4-1.6 parts of copper slag evenly. S2. Add 0.002~0.006 parts of thickener to step S1 above and mix thoroughly; S3. Add 0.0095~0.019 parts of spherical water-absorbing resin by dry weight to step S2 above. Pour the resin into the mixer all at once, then add 0.009~0.011 parts of water-reducing agent and 1.7~1.8 parts of water and mix well. Stop mixing when the mixture is uniform and the spherical water-absorbing resin does not expand significantly. Control the mixing time to 350-410 seconds to obtain the printing paste. S4. The printing paste obtained in step S3 is fed into the print head of the 3D printer, and the print head outlet cross-sectional area is set to 120mm². 2 The horizontal printing speed is 170~180cm / min, the vertical printing speed is 0.7~0.8m / h, and the extrusion speed is 0.02~0.04m / h. 3 Then print; The 3D-printed sample was protected with a protective film and watered regularly. For the first 2 hours, water was applied every 10-15 minutes to allow the spherical water-absorbing resin to continuously absorb water and grow completely. After that, water was applied every 4 hours to keep the spherical water-absorbing resin in an expanded state. After one day, the concrete was completely solidified, forming a permanent expanded support state of the spherical water-absorbing resin. After 28 days of water curing and drying, 3D-printed electromagnetic wave absorbing concrete with regular air cavities based on spherical water-absorbing resin was obtained.

2. The 3D-printed electromagnetic wave-absorbing concrete based on spherical water-absorbing resin reinforced according to claim 1, characterized in that, The metal microwave absorber is at least one of iron tailings, nano iron oxide, nano iron tetroxide, nano copper, and nano copper oxide.

3. The 3D-printed electromagnetic wave-absorbing concrete based on spherical water-absorbing resin reinforced according to claim 1, characterized in that, The thickener is carboxymethyl cellulose with a viscosity of 200,000; the quartz sand is 90-110 mesh; the water-reducing agent is melamine water-reducing agent, model F10; the spherical superabsorbent polymer is polyvinyl alcohol, and the density of the non-absorbent spherical superabsorbent polymer is 1.141 g / cm³. 3 The average particle size range of the copper slag is 100-150 μm.

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