Red mud-based ceramic granule, preparation method thereof and application thereof in wave-absorbing functional concrete

Abstract

The application discloses a red mud-based ceramsite with high strength and wave-absorbing function, a preparation method thereof and application of the red mud-based ceramsite in wave-absorbing function concrete, and belongs to the technical field of building materials. Bayer red mud is mixed with additives (vanadium-titanium magnetite and the like) and granulated, the obtained granules are dried and oxidized and calcined, and the red mud-based ceramsite is obtained; the obtained red mud-based ceramsite has excellent wave-absorbing performance and high mechanical strength, and has a porous surface, and can be used for preparing wave-absorbing function concrete with excellent electromagnetic wave absorption capacity and high mechanical strength by partially replacing siliceous aggregates such as quartz sand.

Description

Technical Field

[0001] This invention relates to a type of expanded clay aggregate, particularly to a red mud-based expanded clay aggregate with high strength and wave-absorbing properties, and also to a method for preparing the red mud-based expanded clay aggregate with high strength and wave-absorbing properties and its application in wave-absorbing concrete, belonging to the field of building materials technology. Background Technology

[0002] Red mud is a highly alkaline industrial solid waste generated during the alkaline leaching of bauxite. For every ton of alumina produced, 1-2 tons of red mud are generated. Red mud is strongly alkaline, with a pH value as high as 10.5-13.5, and also exhibits typical characteristics such as ultra-fine particle size, high fluidity, and easy migration of sodium. Large-scale stockpiling of red mud not only severely damages the soil structure and ecological environment of the surrounding area, but the alkali metal ions it contains also cause continuous pollution to the groundwater system through leaching and seepage by rainwater. Currently, the global comprehensive utilization rate of red mud is less than 10%. If it is not effectively disposed of and utilized as a resource in the long term, its strong alkalinity and heavy metal migration characteristics will pose a continuous and serious threat to the ecological environment and human health. Therefore, achieving large-scale, high-value utilization of red mud has become a major environmental and resource challenge that urgently needs to be addressed.

[0003] Currently, the construction industry is facing the severe challenge of increasingly depleted natural sand and gravel resources. Utilizing metallurgical industrial solid waste to replace natural sand and gravel in the preparation of building materials can effectively alleviate the shortage and supply-demand tension of sand and gravel resources, and also achieve large-scale, high-value resource utilization of industrial solid waste. This is an important direction for the green and low-carbon development of the current building materials field. Meanwhile, electromagnetic radiation has been recognized as the fourth largest source of environmental pollution after air, water, and noise pollution. Developing new building materials that combine structural load-bearing and electromagnetic wave absorption functions has significant engineering value and practical significance for improving the electromagnetic protection level of buildings. Although ordinary cement-based materials are excellent dielectric loss absorbing matrices, their inherent absorption performance is relatively weak, and functional absorbing admixtures are usually introduced to modify and enhance them. Red mud is rich in metallic elements such as Fe and Ti, and has potential for electromagnetic loss and wave absorption applications. However, directly adding powdered red mud to concrete can easily induce alkali-aggregate reaction, resulting in a significant decrease in the mechanical properties and durability of concrete. Moreover, the current red mud admixture content is generally less than 10%, making it difficult to achieve large-scale, high-dosage resource utilization.

[0004] Existing technologies have reported attempts to use red mud to prepare red mud-based ceramsite with microwave absorption capabilities. For example, Chinese patent (authorization publication number: CN115594518A) discloses a method of uniformly mixing a mixed powder containing high-iron red mud, hematite concentrate, purified cobalt-manganese slag, manganese source, and nickel source with an organic binder and water, followed by pelletizing. The resulting green pellets are then dried, preheated, calcined, and cooled to obtain functional ceramsite. The average strength of the ceramsite is 700 N / particle, and the porosity is 28%. Furthermore, the ceramsite material exhibits a reflectivity of -18 dB for electromagnetic waves in the 2-18 GHz frequency range, demonstrating excellent microwave absorption performance and making it suitable as lightweight aggregate for microwave-absorbing concrete. However, existing red mud-based ceramsite generally suffers from technical problems such as low mechanical strength, poor microwave absorption effect, and low alkali metal curing efficiency. Direct application in concrete makes it difficult to simultaneously achieve both structural mechanical properties and electromagnetic protection functions, significantly limiting the application of red mud-based ceramsite with microwave absorption capabilities in functional concrete. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a red mud-based ceramsite with high strength and wave-absorbing properties. This red mud-based ceramsite combines excellent wave-absorbing performance with high mechanical strength and has a porous surface, and can partially replace siliceous aggregates such as quartz sand in wave-absorbing concrete.

[0006] The second objective of this invention is to provide a method for preparing red mud-based ceramsite with high strength and wave-absorbing function. This method uses Bayer process red mud as the main raw material, realizes the resource utilization of metallurgical solid waste, and the resulting red mud-based ceramsite has excellent wave-absorbing performance and high mechanical strength, and has a porous surface, which meets the application requirements of wave-absorbing concrete, and truly realizes the resource utilization of metallurgical solid waste.

[0007] The third objective of this invention is to provide an application of red mud-based ceramsite with high strength and wave-absorbing function in wave-absorbing concrete. Replacing part of the quartz sand as aggregate with it can obtain high-strength concrete with excellent wave-absorbing performance. This solves key technical problems in the prior art, such as the low utilization rate of red mud solid waste resources, the increasing shortage of natural sand and gravel resources, the lack of electromagnetic wave-absorbing function in ordinary concrete, and the decline in the overall performance of concrete caused by directly adding red mud powder.

[0008] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing red mud-based ceramsite with high strength and wave absorption function. The method involves mixing Bayer process red mud with additives and granulating it. The resulting granules are then dried and oxidized and calcined to obtain red mud-based ceramsite. The additives include at least one of vanadium-titanium magnetite, ilmenite concentrate, high-titanium slag, manganese source, strontium source, and barium source.

[0009] This invention utilizes Bayer process red mud and additives such as vanadium-titanium magnetite to achieve phase reconstruction of the red mud through high-temperature oxidative roasting. During the high-temperature oxidative roasting process, iron oxides in the red mud undergo a solid-phase reaction with additives such as vanadium-titanium magnetite to generate multi-metal composite ferrites, giving the ceramsite good microwave absorption properties. Meanwhile, components such as Si, Al, and Ca in the red mud react to generate a high-strength ceramic phase, giving the ceramsite high mechanical strength. Simultaneously, during the oxidative roasting process, the evaporation of water and the decomposition of organic matter in the red mud generate gas, causing the ceramsite to expand and form a porous structure. The ceramsite prepared by this invention not only has a porous structure but also generates a multi-metal composite ferrite phase at reduction sites. The composite ferrite can provide magnetic loss, while the porous structure can generate interface scattering and cavity attenuation. The two work synergistically to significantly improve the electromagnetic wave absorption performance of the ceramsite. In addition, the oxidative roasting process can stabilize and solidify the alkali metals in the red mud within the ceramsite structure, effectively reducing the risk of alkali metal leaching and significantly improving the environmental safety of the material.

[0010] As a preferred embodiment, the mass of the additive is 25-50% of the mass of Bayer process red mud. When the additive content is less than 25%, it is not conducive to the formation of multi-metal composite ferrite, and it is difficult to obtain red mud-based ceramsite with excellent wave absorption function. When the additive content is more than 50%, it will significantly reduce the mechanical strength of red mud-based ceramsite, and at the same time, the red mud solid waste disposal rate is low.

[0011] As a preferred embodiment, the iron content of the Bayer red mud is 30 wt.% to 50 wt.%.

[0012] As a preferred embodiment, the purity of the additive is not less than 85%.

[0013] As a preferred embodiment, the mass of at least one of the manganese source, strontium source, and barium source in the additive is not less than 80% of the total mass of the additive. Additives with at least one of the manganese source, strontium source, and barium source as the main component can produce composite ferrites with superior microwave absorption properties. The manganese source, strontium source, and barium source can be common minerals such as manganese dioxide, strontium carbonate, and barium carbonate.

[0014] As a preferred embodiment, the oxidative roasting conditions are: roasting at 1100℃~1300℃ for 20min~180min in an air atmosphere. Under these preferred oxidative roasting conditions, Bayer red mud and additives can achieve phase reconstruction, generating multi-metal composite ferrite, and simultaneously forming a porous ceramsite structure with high mechanical strength. The electromagnetic loss characteristics of the multi-metal composite ferrite significantly enhance the electromagnetic absorption capability of the ceramsite.

[0015] This invention also provides a red mud-based ceramsite with high strength and microwave absorption properties, obtained by the aforementioned preparation method. The red mud-based ceramsite of this invention features high mechanical strength, excellent microwave absorption performance, and a porous surface.

[0016] This invention also provides an application of red mud-based ceramsite with high strength and wave-absorbing properties for the preparation of wave-absorbing concrete. This invention uses red mud-based ceramsite as aggregate and utilizes cementitious materials for hydration reactions. The hydration reaction products (such as hydrated calcium silicate gel) penetrate deep into the pores of the red mud-based ceramsite, forming a ceramsite-cement matrix interlocking interface. The interface transition zone has a dense structure and a high Ca / Si ratio, which can significantly improve the overall mechanical strength of the concrete.

[0017] As a preferred option, red mud-based ceramsite and quartz sand are used as aggregates, mixed with cementitious materials, admixtures and water, molded and cured to obtain wave-absorbing functional concrete.

[0018] As a preferred embodiment, the aggregate is composed of red mud-based ceramsite and quartz sand in a mass ratio of 10-50%:50-90%. The proportion of red mud-based ceramsite needs to consider both the adsorption properties and workability of the concrete. Under the preferred proportion of red mud-based ceramsite, the utilization of red mud can be maximized while ensuring the workability of the concrete, and the wave-absorbing properties of the concrete can be improved.

[0019] As a preferred embodiment, the cementitious material is composed of silicate cement and fly ash in a mass percentage ratio of 45-46%:54-55%. The silicate cement is ordinary silicate cement. The fly ash is Grade I fly ash. Using an appropriate amount of fly ash as an admixture can optimize the pore structure of concrete and improve the density of the interface transition zone.

[0020] As a preferred embodiment, the mass ratio of the aggregate to the cementitious material is 30-50:100. At the preferred aggregate dosage, the functional advantages of red mud-based ceramsite can be maximized while ensuring the mechanical and durability properties of concrete, achieving a synergistic balance between performance, function, and solid waste utilization. If the aggregate dosage is too low, the wave-absorbing function of the red mud-based ceramsite cannot be effectively utilized, resulting in low solid waste disposal and a weak effect on modifying the wave-absorbing performance of concrete. Furthermore, if the aggregate dosage is too low, too many interconnected pores are introduced, leading to a decrease in the durability and volume stability of the concrete.

[0021] As a preferred embodiment, the additives include water-reducing agents and PVA fibers.

[0022] This invention replaces part of the silica aggregates such as quartz sand with red mud-based ceramsite, and mixes it with cementitious materials, admixtures and water in a mixer according to the specified ratio. Then, an aqueous solution containing water-reducing agent and PVA fiber is slowly added and stirred until the system is homogeneous. The mixture is then poured into a mold, sealed with a polyethylene film to keep it moist, and cured at room temperature for 26 to 30 days. Finally, it is dried in an oven to obtain wave-absorbing functional concrete.

[0023] The red mud-based ceramsite of the present invention is obtained by particle size classification to obtain ceramsite with a particle size range of 2~8mm.

[0024] In the hydration and curing processes, the microwave-absorbing concrete of this invention utilizes gel products and water-reducing agents to transform harmful macropores in the concrete into harmless or even beneficial mesopores and gel pores. The optimized pore structure increases the proportion of mesopores and gel pores while decreasing the proportion of macropores, simultaneously improving the concrete's compressive strength, interfacial polarization, porous resonance attenuation, and electromagnetic wave scattering loss capacity.

[0025] The wave-absorbing functional concrete of this invention can be used as a structural layer or protective layer in electromagnetic protection buildings, green energy-saving buildings, and municipal engineering buildings. It is particularly suitable for building scenarios with high requirements for electromagnetic shielding and wave absorption, such as communication base stations, electronic equipment factories, and electromagnetic laboratories.

[0026] The wave-absorbing functional concrete of this invention simultaneously improves mechanical strength, enhances electromagnetic wave absorption performance, and solidifies alkali metal sodium ions, resulting in significantly better overall performance than ordinary concrete and powdered red mud mixed concrete.

[0027] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0028] 1) This invention realizes the large-scale harmless utilization of red mud. After the red mud is prepared into red mud-based ceramsite, it replaces 10-50% of silica aggregates such as quartz sand in the preparation of concrete. This solves the problem of alkali-aggregate reaction caused by directly adding red mud powder. The alkali metals in the red mud are efficiently solidified inside the red mud-based ceramsite after oxidation and calcination. The alkali metal leaching of concrete samples with red mud-based ceramsite replacing 50% of silica aggregates such as quartz sand is reduced by nearly two times, avoiding environmental pollution and concrete performance degradation caused by alkali metal migration.

[0029] 2) The microwave-absorbing concrete of this invention possesses both excellent mechanical properties and electromagnetic wave absorption performance. A meshing interface transition zone is formed between the red mud-based ceramsite and the cement matrix. The hydrated cement gel penetrates into the interior of the ceramsite, significantly improving the interfacial bonding strength. At the same time, the proportion of large pores inside the concrete is reduced, and the structure is more compact. The compressive strength of 7mm reconstructed red mud ceramsite concrete can reach 47.06MPa, which is 4.2MPa higher than that of ordinary reference concrete. The ferrite phase in the ceramsite provides magnetic loss, and the porous structure provides structural loss. The synergistic effect of the two makes the minimum reflection loss of the concrete at a thickness of 20mm reach -40 to -30dB. The effective microwave absorption area is increased by up to 2.82dB·GHz compared with ordinary concrete, and the microwave absorption performance is significantly better than that of ordinary cement-based materials.

[0030] 3) The preparation method of red mud-based ceramsite of the present invention is simple and convenient to operate. The raw materials used are all conventional raw materials in the construction industry. The preparation process of red mud-based ceramsite does not require complicated equipment. The concrete preparation process is consistent with that of conventional concrete, which is easy to industrialize and promote its application. At the same time, the use of red mud to replace silica aggregates such as quartz sand alleviates the problem of natural sand and gravel resource shortage, reduces the raw material cost of concrete, and has both environmental and economic benefits.

[0031] 4) The wave-absorbing functional concrete of the present invention has multiple functions. It not only has the structural load-bearing capacity of conventional concrete, but also has excellent electromagnetic wave absorption performance. It can be directly applied to building scenarios that require electromagnetic protection without the need for additional wave-absorbing layers, which simplifies the building construction process, improves the electromagnetic protection effect of buildings, and expands the application fields of concrete materials.

[0032] 5) The red mud-based ceramic particles of the present invention have both excellent wave absorption performance and high mechanical strength, as well as a porous surface. Detailed Implementation

[0033] The present invention will be further explained and illustrated below with reference to specific embodiments. These embodiments are only for better understanding of the present invention and are not intended to limit the scope of protection of the claims of the present invention.

[0034] Microwave absorption performance test method description: Powder samples are tested using the coaxial method, and block samples are tested using the arc method.

[0035] Example 1

[0036] The raw materials used in this embodiment include: Bayer process red mud (iron content 35.56%) with Fe2O3 content 35.56%, Al2O3 content 21.71%, SiO2 content 7.74%, Na2O content 5.10%, TiO2 content 3.53%, and CaO content 1.46%; vanadium-titanium magnetite and manganese ore (manganese dioxide) with a purity greater than 85%; ordinary silicate cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2, 50~100 mesh, 100%); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Co., Ltd., Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0037] The specific preparation process of the 4mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0038] 1) Preparation of red mud-based ceramsite: Bayer process red mud and vanadium-titanium magnetite + manganese ore additives (80% manganese ore) at a mass ratio of 4:1 were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, the pellets were sieved to obtain red mud-based ceramsite with a particle size of 4 mm. The average strength of the 4 mm red mud-based ceramsite was 705 N / particle, and the porosity was 32%. The ceramsite material exhibited a reflectivity of -25.12 dB for electromagnetic waves in the frequency range of 2–18 GHz, demonstrating excellent wave absorption performance and making it suitable as a quartz sand aggregate for preparing wave-absorbing concrete.

[0039] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 18.25 parts of quartz sand, and 18.25 parts of red mud-based ceramsite (4 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of high-efficiency water-reducing agent and 2.1 parts of PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 4 mm red mud-based ceramsite concrete.

[0040] The concrete has a compressive strength of 44.32 MPa, a minimum reflection loss of -31.47 dB at a thickness of 20 mm, an effective absorption area of ​​10.48 dB·GHz, and an effective bandwidth of 1.57 GHz at -10 dB.

[0041] Example 2

[0042] The raw materials used in this embodiment include: red mud (iron content 35.56%) with Fe2O3 content 35.56%, Al2O3 content 21.71%, SiO2 content 7.74%, Na2O content 5.10%, TiO2 content 3.53%, and CaO content 1.46%; MnO2 with a purity greater than 85%; ordinary Portland cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2, 50~100 mesh, 100%); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Co., Ltd., Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0043] The specific preparation process of the 5mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0044] 1) Preparation of red mud-based ceramsite: Bayer process red mud and MnO2 at a mass ratio of 3:1 were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, the pellets were sieved to obtain red mud-based ceramsite with a particle size of 5 mm. The average strength of the 5 mm red mud-based ceramsite was 756 N / particle, and the porosity was 30%. The 5 mm red mud-based ceramsite exhibited a reflectivity of -28.36 dB for electromagnetic waves in the frequency range of 2–18 GHz, demonstrating excellent wave absorption performance and making it suitable as a quartz sand aggregate for preparing wave-absorbing concrete.

[0045] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 18.25 parts of quartz sand, and 18.25 parts of red mud-based ceramsite (5 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of water-reducing agent and 2.1 parts of high-efficiency PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 5 mm red mud-based ceramsite concrete.

[0046] The concrete has a compressive strength of 46.16 MPa, a minimum reflection loss of -25.93 dB at a thickness of 20 mm, an effective absorption area of ​​7.90 dB·GHz, and an effective bandwidth of 1.26 GHz at -10 dB.

[0047] Example 3

[0048] The raw materials used in this embodiment include: Bayer process red mud (iron content 35.56%, from an alumina plant in Henan Province) with Fe2O3 content of 35.56%, Al2O3 content of 21.71%, SiO2 content of 7.74%, Na2O content of 5.10%, TiO2 content of 3.53%, and CaO content of 1.46%; BaCO3 with a purity greater than 85%; ordinary silicate cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Corporation, Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0049] The specific preparation process of the 6mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0050] 1) Preparation of red mud-based ceramsite: Bayer process red mud and BaCO3 at a mass ratio of 2:1 were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, red mud-based ceramsite with a particle size of 6 mm was obtained by sieving. The 6 mm red mud-based ceramsite has an average strength of 703 N / particle and a porosity of 28%. The ceramsite material exhibits an electromagnetic wave reflectivity of -21 dB in the 2–18 GHz frequency range, demonstrating excellent wave absorption performance and can be used as quartz sand aggregate to prepare wave-absorbing concrete.

[0051] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 18.25 parts of quartz sand, and 18.25 parts of red mud-based ceramsite (6 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of high-efficiency water-reducing agent and 2.1 parts of PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 6 mm red mud-based ceramsite concrete.

[0052] The concrete has a compressive strength of 45.62 MPa, a minimum reflection loss of -29.57 dB at a thickness of 20 mm, an effective absorption area of ​​9.88 dB·GHz, and an effective bandwidth of 1.12 GHz at -10 dB.

[0053] Example 4

[0054] The raw materials used in this embodiment include: red mud (iron content 35.56%) with Fe2O3 content 35.56%, Al2O3 content 21.71%, SiO2 content 7.74%, Na2O content 5.10%, TiO2 content 3.53%, and CaO content 1.46%; MnO2 with a purity greater than 85%; ordinary Portland cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Corporation, Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0055] The specific preparation process of the 7mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0056] 1) Preparation of red mud-based ceramsite: Red mud at a mass ratio of 3:1 and MnO2 with a purity of 85% were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, the pellets were sieved to obtain red mud-based ceramsite with a particle size of 7 mm. The average strength of the 7 mm red mud-based ceramsite was 803 N / particle, and the porosity was 29%. The 7 mm red mud-based ceramsite exhibited a reflectivity of -32 dB for electromagnetic waves in the frequency range of 2–18 GHz, demonstrating excellent wave absorption performance and making it suitable as a quartz sand aggregate for preparing wave-absorbing concrete.

[0057] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 18.25 parts of quartz sand, and 18.25 parts of red mud-based ceramsite (7 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of water-reducing agent and 2.1 parts of PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 5 mm red mud-based ceramsite concrete.

[0058] The concrete has a compressive strength of 47.06 MPa, a minimum reflection loss of -35.81 dB at a thickness of 20 mm, an effective absorption area of ​​8.69 dB·GHz, and an effective bandwidth of 1.18 GHz at -10 dB.

[0059] Example 5

[0060] The raw materials used in this embodiment include: Bayer process red mud (iron content 35.56%) with Fe2O3 content 35.56%, Al2O3 content 21.71%, SiO2 content 7.74%, Na2O content 5.10%, TiO2 content 3.53%, and CaO content 1.46%; vanadium-titanium magnetite with a purity greater than 85%; ordinary silicate cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2, 50~100 mesh, 100%); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Co., Ltd., Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0061] The specific preparation process of the 4mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0062] 1) Preparation of red mud-based ceramsite: Bayer process red mud and vanadium-titanium magnetite at a mass ratio of 4:1 were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, the pellets were sieved to obtain red mud-based ceramsite with a particle size of 4 mm. The average strength of the 4 mm red mud-based ceramsite was 701 N / particle, and the porosity was 34%. The ceramsite material exhibited a reflectivity of -16.24 dB for electromagnetic waves in the frequency range of 2–18 GHz, demonstrating excellent wave absorption performance and making it suitable as a quartz sand aggregate for preparing wave-absorbing concrete.

[0063] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 18.25 parts of quartz sand, and 18.25 parts of red mud-based ceramsite (4 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of high-efficiency water-reducing agent and 2.1 parts of PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 4 mm red mud-based ceramsite concrete.

[0064] The concrete has a compressive strength of 40.54 MPa, a minimum reflection loss of -24.65 dB at a thickness of 20 mm, an effective absorption area of ​​6.67 dB·GHz, and an effective bandwidth of 1.14 GHz at -10 dB.

[0065] Comparative Example 1

[0066] The raw materials used in this comparative example include: ordinary Portland cement (PO 42.5R grade), quartz sand aggregate (main component: SiO2), grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.), PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Corporation, Japan), and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixtures Co., Ltd., China).

[0067] The specific preparation process of the ordinary reference concrete described in this comparative example is as follows:

[0068] By weight (1 kg = 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, and 36.5 parts of quartz sand, add them to a mixer and mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of water-reducing agent and 2.1 parts of PVA fiber), stir for 15 minutes until the mixture is uniform, pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80°C for 10 hours to obtain ordinary reference concrete.

[0069] The concrete has a compressive strength of 42.86 MPa, a minimum reflection loss of -21.85 dB at a thickness of 20 mm, an effective absorption area of ​​5.87 dB·GHz, and an effective bandwidth of 0.75 GHz at -10 dB.

[0070] Comparative Example 2

[0071] The raw materials used in this embodiment include: red mud (iron content 35.56%) with Fe2O3 content 35.56%, Al2O3 content 21.71%, SiO2 content 7.74%, Na2O content 5.10%, TiO2 content 3.53%, and CaO content 1.46%; MnO2 with a purity greater than 85%; ordinary Portland cement (PO 42.5R grade); quartz sand aggregate (main component: SiO2); grade I fly ash (main components: SiO2, Al2O3, Fe2O3, CaO, etc.); PVA fiber (main component: polyvinyl alcohol, purchased from Kuraray Corporation, Japan); and high-efficiency water-reducing agent (main component: polycarboxylate components, purchased from Shandong Hongxiang Building Admixture Co., Ltd., China).

[0072] The specific preparation process of the 7mm red mud-based ceramsite concrete described in this embodiment is as follows:

[0073] 1) Preparation of red mud-based ceramsite: Red mud at a mass ratio of 3:1 and MnO2 with a purity of 85% were added to a vibratory mill and mixed evenly. The mixture was then pelletized into green pellets using a disc pelletizer. The green pellets were dried at 60℃ for 12 hours, followed by oxidative calcination at 1200℃ for 3 hours in air. After calcination, the pellets were sieved to obtain red mud-based ceramsite with a particle size of 7 mm. The average strength of the 7 mm red mud-based ceramsite was 803 N / particle, and the porosity was 29%. The 7 mm red mud-based ceramsite exhibited a reflectivity of -32 dB for electromagnetic waves in the frequency range of 2–18 GHz, demonstrating excellent wave absorption performance and making it suitable as a quartz sand aggregate for preparing wave-absorbing concrete.

[0074] 2) Concrete preparation: By weight (1 kg as 1 part), take 45.5 parts of ordinary Portland cement, 54.5 parts of grade I fly ash, 31.25 parts of quartz sand, and 5.25 parts of red mud-based ceramsite (7 mm) and add them to the mixer to mix evenly. Slowly add 35 parts of aqueous solution (containing 0.6 parts of water-reducing agent and 2.1 parts of PVA fiber) and stir for 15 minutes until the mixture is uniform. Pour the mixture into a mold, seal it with polyethylene film, and cure it at room temperature for 4 weeks. Then dry it in an oven at 80℃ for 10 hours to obtain 5 mm red mud-based ceramsite concrete.

[0075] The concrete has a compressive strength of 38.15 MPa, a minimum reflection loss of -21.34 dB at a thickness of 20 mm, an effective absorption area of ​​5.12 dB·GHz, and an effective bandwidth of 1.01 GHz at -10 dB.

[0076] As can be seen from the above embodiments and comparative examples, the compressive strength of the red mud-based ceramsite concrete of the present invention is higher than that of ordinary reference concrete, and it has better electromagnetic wave absorption performance, with a significantly improved effective wave absorption area, thus achieving a synergistic improvement in mechanical and functional performance.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the specific implementation of the present invention and not to limit it. Those skilled in the art should understand that any equivalent substitutions or obvious modifications made to the implementation of the present invention without changing its performance or use, without departing from the spirit of the present invention, should be covered within the scope of protection claimed by the present invention.

Claims

1. A method for preparing red mud-based ceramsite with high strength and wave-absorbing properties, characterized in that: Bayer process red mud is mixed with additives and granulated. The resulting granules are dried and oxidized and roasted to obtain red mud-based ceramsite. The additives include at least one of vanadium-titanium magnetite, ilmenite concentrate, high-titanium slag, manganese source, strontium source, and barium source.

2. The method for preparing red mud-based ceramsite with high strength and wave-absorbing function according to claim 1, characterized in that: The additive is 25-50% of the mass of Bayer red mud. The mass of at least one of the manganese source, strontium source and barium source in the additive shall not be less than 80% of the total mass of the additive.

3. The method for preparing red mud-based ceramsite with high strength and wave-absorbing function according to claim 1, characterized in that: The iron content of the Bayer process red mud is 30 wt.%~50 wt.%; The purity of the additive is not less than 85%.

4. A method for preparing red mud-based ceramsite with high strength and wave-absorbing function according to any one of claims 1 to 3, characterized in that: The conditions for the oxidation calcination are: calcination at 1100℃~1300℃ for 20min~180min in an air atmosphere.

5. A type of red mud-based ceramsite with high strength and wave-absorbing properties, characterized in that: It is obtained by the preparation method described in any one of claims 1 to 4.

6. The application of the red mud-based ceramsite with high strength and wave-absorbing function as described in claim 5, characterized in that: Used to prepare microwave-absorbing concrete.

7. The application of red mud-based ceramsite with high strength and wave-absorbing function according to claim 6, characterized in that: Red mud-based ceramsite and quartz sand are used as aggregates, mixed with cementitious materials, admixtures and water, molded and cured to obtain wave-absorbing concrete.

8. The application of red mud-based ceramsite with high strength and wave-absorbing function according to claim 7, characterized in that: The aggregate is composed of red mud-based ceramsite and quartz sand in a mass ratio of 10~50%:50~90%.

9. The application of red mud-based ceramsite with high strength and wave-absorbing function according to claim 7, characterized in that: The cementitious material is composed of silicate cement and fly ash in a mass percentage ratio of 45-46%:54-55%.

10. The application of red mud-based ceramsite with high strength and wave-absorbing function according to any one of claims 7 to 9, characterized in that: The mass ratio of the aggregate to the cementitious material is 30~50:100.