Cement-based wave-absorbing material and preparation method thereof

Abstract

The invention relates to the technical field of composite functional building materials, in particular to a cement-based wave-absorbing material and a preparation method thereof.The cement-based wave-absorbing material is prepared from cement, wave-absorbing functional SAP, tap water and a water reducing agent, and the wave-absorbing functional SAP is prepared through modification of nano Fe3O4. According to the invention, polyacrylamide type SAP is modified by a wave-absorbing agent nano Fe3O4, the wave-absorbing agent is loaded in an SAP network structure, and the wave-absorbing functional SAP is doped into the cement-based material, so that the wave-absorbing performance of the cement-based material is improved, and meanwhile, the mechanical property of the cement-based material is not obviously damaged; therefore, the cement-based material has good wave-absorbing property and high-strength property.

Description

Technical Field

[0001] The present invention relates to the technical field of composite functional building materials, and in particular to a cement-based wave-absorbing material and a preparation method thereof. Background Art

[0002] With the advancement of human science and technology, modern electronic information technology continues to achieve breakthroughs, and its application in the military field is becoming increasingly widespread. During operation, electronic information equipment uses electromagnetic waves as a carrier of information, transmitting information through electromagnetic radiation. However, this also leads to significant risks of information leakage in military infrastructure and strategic target buildings, which directly endangers national political, economic, and military security. Therefore, the development of electromagnetic protection materials is one of the most effective means to enhance military survivability and strategic target effectiveness.

[0003] Cement-based materials are one of the most widely used building materials in the military engineering industry and are the most commonly used material for constructing fixed military facilities. They possess excellent structural load-bearing capacity. Existing research indicates that using cement-based materials in construction can provide buildings with a certain degree of electromagnetic wave absorption and attenuation. However, due to the poor electromagnetic loss performance of cement-based materials themselves, and the dense internal structure formed by hardening cement, low porosity, and poor impedance matching, electromagnetic waves transmitted to the cement surface are difficult to penetrate into the cement matrix. Consequently, electromagnetic waves are prone to significant reflection from the cement surface. Generally, the electromagnetic wave RL of cement-based materials is only around -3dB, resulting in poor electromagnetic protection. Therefore, cement-based absorbing materials, formed by modifying cement-based materials for electromagnetic absorption, have gradually become a research focus in the field of structural absorbing materials.

[0004] However, current methods for improving the electromagnetic absorption properties of cement-based materials present numerous challenges. Common approaches include introducing high-performance electromagnetic absorbing components or introducing transparent aggregates (such as expanded perlite, vitrified microspheres, expanded polystyrene particles, and porous ceramsite) into cement-based materials. For example, patent CN107311555A discloses a cement-based absorbing material incorporating graphene oxide and a preparation method thereof. This method utilizes nano-ferrous oxide and graphene oxide as absorbing components. However, after hardening, cement-based materials develop a dense internal structure with low porosity and poor impedance matching, making it difficult for electromagnetic waves transmitted to the cement surface to enter the cement matrix. Therefore, simply introducing high-performance electromagnetic absorbing components alone does not significantly improve absorption. Furthermore, the high cost of graphene oxide has limited the widespread application of this approach. Patent CN107032703A discloses a cement-based absorbing material and its preparation method using a composite of ferroferric oxide and hollow fly ash microspheres. Transparent aggregates such as expanded perlite and hollow microspheres are introduced into the cement-based material. The complex internal structure of the transparent aggregate increases the number of electromagnetic wave reflections and extends the transmission distance within the cement-based material, significantly enhancing the cement-based material's absorbing performance. However, this results in a significant decrease in the cement-based material's mechanical properties, making it difficult to meet the mechanical and durability requirements of military infrastructure. Therefore, ensuring that the cement-based material possesses both good absorbing properties and good mechanical properties remains a current technical challenge. Summary of the Invention

[0005] In light of this, the present invention proposes a cement-based absorbing material and its preparation method to address the current technical problem of cement-based materials struggling to balance absorbing and mechanical properties. Based on the synthesis of polyacrylamide-based SAP, the present invention modifies the polyacrylamide-based SAP with the absorbent nano-Fe₃O₄. The absorbent is then incorporated into the SAP network structure, and the absorbing SAP is incorporated into the cement-based material. This improves the cement-based material's absorbing properties without significantly compromising its mechanical properties, resulting in a cement-based material that combines excellent absorbing performance with high strength.

[0006] The technical solution of the present invention is achieved as follows: On the one hand, the present invention provides a cement-based absorbing material, the raw materials of which include cement, absorbing functional SAP, tap water and a water reducer; the absorbing functional SAP is prepared by modification with nano-Fe3O4.

[0007] On the basis of the above scheme, preferably, the preparation method of the wave-absorbing functional SAP comprises the following steps: S1, add acrylamide and deionized water into a beaker, stir until the acrylamide is completely dissolved, and then add nano-Fe3O4 for ultrasonic treatment; S2, heating the mixed solution in step S1 under a nitrogen atmosphere, adding N,N'-methylenebisacrylamide and ammonium persulfate, stirring until the system becomes viscous, stopping stirring and keeping warm for 2-4 hours; S3, cutting the hydrogel obtained in step S2 into pieces, and soaking them in deionized water and then in anhydrous ethanol until the hydrogel becomes hard white block particles; S4, drying the block particles obtained in step S3 to a constant weight, crushing, grinding, and sieving to obtain wave-absorbing functional SAP particles.

[0008] On the basis of the above scheme, preferably, in terms of weight, the acrylamide is 12 to 24 parts, and the nano-Fe3O4 is 75 to 105 parts.

[0009] On the basis of the above scheme, it is further preferred that the mass ratio of the nano-Fe3O4 to acrylamide is (4-7):1.

[0010] Based on the above scheme, preferably, based on parts by mass, the N,N'-methylenebisacrylamide is 1.44-1.80 parts, the ammonium persulfate is 0.12-0.24 parts, and the anhydrous ethanol is 1440-1560 parts.

[0011] On the basis of the above scheme, preferably, in step S1, the stirring speed is 200~500rpm / min, and the ultrasonic power is 600~800W; further preferably, the stirring speed is 300~400rpm / min, and the ultrasonic power is 650~750W.

[0012] On the basis of the above scheme, further preferably, 18 parts of acrylamide and 162 parts of deionized water are added to a beaker, stirred at room temperature of 25°C for 15 minutes, and the stirring speed is 300 rpm / min; 90 parts of nano-Fe3O4 are added to the acrylamide solution for ultrasonic treatment, the ultrasonic power is 750W, and the ultrasonic time is 15 minutes; the mixed solution is transferred to a three-necked flask, the water bath temperature is raised to 70°C in an N2 atmosphere, and 1.62 parts of N,N'-methylenebisacrylamide are added. The enamide was slowly stirred with 0.18 parts of ammonium persulfate until the system became viscous, then the stirring was stopped and the mixture was kept warm for 3 hours; the hydrogel was cut into pieces and soaked in 1200 parts of deionized water for 2 hours to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1500 parts of anhydrous ethanol for 48 hours until the hydrogel became hard white block particles; the block particles were placed in a 70°C forced air drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a standard 100-mesh sieve to obtain wave-absorbing functional SAP particles.

[0013] On the basis of the above scheme, preferably, in terms of weight, the cement is 900-1100 parts, the wave-absorbing functional SAP is 48-72 parts, the tap water is 400-460 parts, and the water reducer is 2.8-3.2 parts.

[0014] Based on the above solution, preferably, the mass ratio of the cement to the wave-absorbing functional SAP is (13-20):1.

[0015] On the basis of the above scheme, it is further preferred that, calculated by weight, the cement is 1100 parts, the wave-absorbing functional SAP is 72 parts, the tap water is 430 parts, and the water reducer is 3 parts.

[0016] In a second aspect, a method for preparing the cement-based absorbing material as described above is provided. Preferably, cement and absorbing functional SAP are mixed evenly, and then tap water and a water reducer are added and mixed evenly to obtain the cement-based absorbing material.

[0017] Based on the above solution, preferably, the particle size of the wave-absorbing SAP is distributed between 100 mesh and 200 mesh, the water reducer is a polycarboxylic acid type water reducer, the SAP is a polyacrylamide type, and the cement is ordinary Portland cement.

[0018] The cement-based absorbing material and its preparation method of the present invention have the following advantages over the prior art: (1) The present invention is based on the need to take into account both the mechanical and wave-absorbing properties of cement-based materials. During the preparation of cement-based materials, wave-absorbing functional SAP is added. After the SAP releases water, the wave-transmitting ability of the cement-based material is enhanced. At the same time, the wave-absorbing agent nano-Fe3O4 is loaded inside the SAP network structure, so that the wave-absorbing agent exists inside the pores after the SAP releases water. The electromagnetic waves are reflected multiple times in the pores, which increases the number of times they come into contact with the wave-absorbing agent and prolongs the transmission distance inside the cement-based material, thereby greatly improving the wave-absorbing ability of the cement-based material. The cement-based material added with the wave-absorbing functional SAP has good wave-absorbing ability while its mechanical properties do not show a significant decrease. Its mechanical properties are better than those of cement-based wave-absorbing materials currently on the market. Thus, a cement-based material with both wave-absorbing and mechanical properties is prepared. (2) The method for synthesizing the wave-absorbing functional SAP provided by the present invention is low-cost and produces stable product performance. It does not require a large number of organic reagents, nor does it require synthesis conditions such as high temperature and high pressure, thereby avoiding environmental problems caused by chemical reagents and energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a flow chart of the preparation process of the cement-based absorbing material of the present invention. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] Acrylamide and ammonium persulfate in the present invention were purchased from Sinopharm Chemical Reagent Co., Ltd., N,N'-methylenebisacrylamide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., nano-Fe3O4 was purchased from Shanghai MacLean Biochemical Technology Co., Ltd., cement was purchased from Huaxin Cement Co., Ltd., and polycarboxylic acid water reducer was purchased from Jiangsu Subote New Materials Co., Ltd.

[0023] Example 1 This embodiment prepares a high-strength cement-based material with good wave-absorbing performance, and the preparation method includes the following steps: 18 g acrylamide and 162 g deionized water were added to a beaker and stirred at room temperature of 25°C for 15 min at a stirring speed of 300 rpm / min; 90 g nano-Fe3O4 was added to the acrylamide solution for ultrasonic treatment at an ultrasonic power of 750 W and an ultrasonic time of 15 min; the mixed solution was transferred to a three-necked flask, the water bath temperature was raised to 70°C in a N2 atmosphere, 1.62 g N, N'-methylenebisacrylamide and 0.18 g ammonium persulfate were added and slowly stirred until the system became viscous, then stirring was stopped and kept warm for 3 h; the hydrogel was cut into pieces and soaked in 1200 g deionized water for 2 h to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1500 g anhydrous ethanol for 48 h until the hydrogel became hard white block particles; the block particles were placed in a 70°C blast drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a 100 mesh standard sieve to obtain wave-absorbing functional SAP particles; 1100g of cement and 72g of wave-absorbing functional SAP were mixed evenly, and then 430g of tap water and 3g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material with high strength and good wave-absorbing performance.

[0024] Example 2 This embodiment prepares a high-strength cement-based material with good wave-absorbing performance, and the preparation method includes the following steps: 12g acrylamide and 150g deionized water were added to a beaker and stirred at room temperature of 25°C for 10min at a stirring speed of 200rpm / min; 75g nano-Fe3O4 was added to the acrylamide solution for ultrasonic treatment at an ultrasonic power of 600W and an ultrasonic time of 10min; the mixed solution was transferred to a three-necked flask, the water bath temperature was raised to 70°C in an N2 atmosphere, 1.44g N,N'-methylenebisacrylamide and 0.12g ammonium persulfate were added and slowly stirred until the system became viscous, then stirring was stopped and kept warm for 3h; the hydrogel was cut into pieces and soaked in 1080g deionized water for 2h to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1440g anhydrous ethanol for 48h until the hydrogel became hard white block particles; the block particles were placed in a 70°C blast drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a 100-mesh standard sieve to obtain wave-absorbing functional SAP particles; 900 g of cement and 48 g of wave-absorbing functional SAP were mixed evenly, and then 400 g of tap water and 2.8 g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material with high strength and good wave-absorbing performance.

[0025] Example 3 This embodiment prepares a high-strength cement-based material with good wave-absorbing performance, and the preparation method includes the following steps: 24 g acrylamide and 174 g deionized water were added to a beaker and stirred at room temperature of 25°C for 20 min at a stirring speed of 500 rpm / min; 105 g nano-Fe3O4 was added to the acrylamide solution for ultrasonic treatment at an ultrasonic power of 800 W and an ultrasonic time of 20 min; the mixed solution was transferred to a three-necked flask, the water bath temperature was raised to 70°C in an N2 atmosphere, 1.80 g N, N'-methylenebisacrylamide and 0.24 g ammonium persulfate were added and slowly stirred until the system became viscous, then stirring was stopped and kept warm for 4 h; the hydrogel was cut into pieces and soaked in 1320 g deionized water for 2 h to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1560 g anhydrous ethanol for 48 h until the hydrogel became hard white block particles; the block particles were placed in a 70°C blast drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a 100 mesh standard sieve to obtain wave-absorbing functional SAP particles; 1000g of cement and 60g of wave-absorbing functional SAP were evenly mixed, and then 460g of tap water and 3.2g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material with high strength and good wave-absorbing performance.

[0026] Example 4 This embodiment prepares a high-strength cement-based material with good wave-absorbing performance, and the preparation method includes the following steps: 12g acrylamide and 174g deionized water were added to a beaker and stirred at room temperature of 25°C for 15min at a stirring speed of 400rpm / min; 105g nano-Fe3O4 was added to the acrylamide solution for ultrasonic treatment at an ultrasonic power of 750W and an ultrasonic time of 15min; the mixed solution was transferred to a three-necked flask, the water bath temperature was raised to 70°C in an N2 atmosphere, 1.80g N,N'-methylenebisacrylamide and 0.24g ammonium persulfate were added and slowly stirred until the system became viscous, then stirring was stopped and kept warm for 3h; the hydrogel was cut into pieces and soaked in 1320g deionized water for 2h to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1560g anhydrous ethanol for 48h until the hydrogel became hard white block particles; the block particles were placed in a 70°C blast drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a 100-mesh standard sieve to obtain wave-absorbing functional SAP particles; 1100g of cement and 60g of wave-absorbing functional SAP were mixed evenly, and then 460g of tap water and 3.2g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material with high strength and good wave-absorbing performance.

[0027] Example 5 This embodiment prepares a high-strength cement-based material with good wave-absorbing performance, and the preparation method includes the following steps: 24g acrylamide and 150g deionized water were added to a beaker and stirred at room temperature of 25°C for 20min at a stirring speed of 350rpm / min; 75g nano-Fe3O4 was added to the acrylamide solution for ultrasonic treatment at an ultrasonic power of 650W and an ultrasonic time of 20min; the mixed solution was transferred to a three-necked flask, the water bath temperature was raised to 70°C in an N2 atmosphere, 1.44g N,N'-methylenebisacrylamide and 0.12g ammonium persulfate were added and slowly stirred until the system became viscous, then stirring was stopped and kept warm for 4h; the hydrogel was cut into pieces and soaked in 1080g deionized water for 2h to remove unreacted monomers; the water inside the hydrogel was replaced by soaking in 1440g anhydrous ethanol for 48h until the hydrogel became hard white block particles; the block particles were placed in a 70°C blast drying oven and dried to constant weight. After crushing and grinding, the particles were passed through a standard 100-mesh sieve to obtain wave-absorbing functional SAP particles; 1000g of cement and 48g of wave-absorbing functional SAP were mixed evenly, and then 400g of tap water and 2.8g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material with high strength and good wave-absorbing performance.

[0028] Example 6 In this embodiment, a high-strength cement-based material with good wave-absorbing performance is prepared. The preparation method is the same as that in Example 1, except that 12 g of acrylamide and 105 g of nano-Fe 3 O 4 are added.

[0029] Example 7 In this embodiment, a high-strength cement-based material with good wave-absorbing performance is prepared. The preparation method is the same as that in Example 1, except that 24 g of acrylamide and 75 g of nano-Fe 3 O 4 are added.

[0030] Example 8 In this embodiment, a cement-based material with high strength and good wave-absorbing performance is prepared. The preparation method is the same as that in Example 1, except that 48 g of wave-absorbing functional SAP is added.

[0031] Example 9 In this embodiment, a cement-based material with high strength and good wave-absorbing performance is prepared. The preparation method is the same as that in Example 1, except that 60 g of wave-absorbing functional SAP is added.

[0032] Comparative Example 1 1100 g of cement and 12 g of ordinary polyacrylamide-type SAP were uniformly mixed, and then 430 g of tap water and 3 g of polycarboxylic acid-type water reducer were added and stirred to prepare a cement-based material.

[0033] Comparative Example 2 1100 g of cement and 60 g of nano-Fe3O4 were mixed evenly, and then 430 g of tap water and 3 g of polycarboxylic acid type water reducer were added and stirred to prepare a cement-based material.

[0034] Comparative Example 3 The cement-based material prepared in this comparative example was prepared in the same manner as in Example 1, except that 9 g of acrylamide and 111 g of nano-Fe 3 O 4 were added.

[0035] Comparative Example 4 The cement-based material prepared in this comparative example was prepared in the same manner as in Example 1, except that 27 g of acrylamide and 72 g of nano-Fe 3 O 4 were added.

[0036] Comparative Example 5 The cement-based material prepared in this comparative example was prepared in the same manner as in Example 1, except that 84 g of the wave-absorbing functional SAP was added.

[0037] Comparative Example 6 The cement-based material prepared in this comparative example was prepared in the same manner as in Example 1, except that 36 g of the wave-absorbing functional SAP was added.

[0038] The wave absorption and mechanical property tests were performed on the cement-based materials prepared in Examples 1 to 9 and Comparative Examples 1 to 6, respectively. The results are shown in Table 1.

[0039] Table 1 Wave absorption and mechanical properties test data of cement-based materials of Examples 1 to 9 and Comparative Examples 1 to 6

[0040] Table 1 shows that the high-strength cement-based material with excellent wave-absorbing performance prepared in the optimal embodiment of the present invention has a maximum reflection loss of -12.5 dB in the 8-18 GHz range, an effective wave-absorbing bandwidth of 10.0 GHz with RL <-7 dB, and can fully cover the 8-18 GHz frequency range. Furthermore, with optimal wave-absorbing performance, the 28-day compressive strength can reach 36.4 MPa. This demonstrates that the cement-based wave-absorbing material prepared in the present invention can effectively solve the technical problem of existing cement-based wave-absorbing materials that cannot balance wave-absorbing and mechanical properties.

[0041] When ordinary polyacrylamide-type SAP without nano-Fe3O4 modification is added or only nano-Fe3O4 is added, the wave absorption performance of the prepared cement-based material is greatly reduced; when the ratio of acrylamide and nano-Fe3O4 added in the synthesis process of the wave-absorbing functional SAP is too low or too high, the wave absorption performance of the cement-based material is poor; when the content of the added wave-absorbing functional SAP is too low, the wave transmission ability of the cement-based material is poor, resulting in its poor wave absorption performance; when the content of the added wave-absorbing functional SAP is too high, although the cement-based material has good wave absorption performance, its mechanical properties are greatly reduced.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cement-based absorbing material, characterized by: The raw materials of the cement-based wave-absorbing material include cement, wave-absorbing functional SAP, tap water and a water-reducing agent; the wave-absorbing functional SAP is prepared by modification with nano-Fe3O4.

2. The cement-based absorbing material according to claim 1, wherein: The preparation method of the wave-absorbing functional SAP comprises the following steps: S1, add acrylamide and deionized water into a beaker, stir until the acrylamide is completely dissolved, and then add nano-Fe3O4 for ultrasonic treatment; S2, heating the mixed solution in step S1 under a nitrogen atmosphere, adding N,N'-methylenebisacrylamide and ammonium persulfate, stirring until the system becomes viscous, stopping stirring and keeping warm for 2-4 hours; S3, cutting the hydrogel obtained in step S2 into pieces, and soaking them in deionized water and then in anhydrous ethanol until the hydrogel becomes hard white block particles; S4, drying the block particles obtained in step S3 to a constant weight, crushing, grinding, and sieving to obtain wave-absorbing functional SAP particles.

3. The cement-based absorbing material according to claim 2, wherein: In step S1, the amount of acrylamide is 12 to 24 parts by mass, and the amount of nano-Fe3O4 is 75 to 105 parts by mass.

4. The cement-based absorbing material according to claim 3, wherein: The mass ratio of the nano-Fe3O4 to acrylamide is (4-7):

1.

5. The cement-based absorbing material according to claim 2, wherein: In steps S2 and S3, based on parts by mass, the amount of N,N'-methylenebisacrylamide is 1.44-1.80 parts, the amount of ammonium persulfate is 0.12-0.24 parts, and the amount of anhydrous ethanol is 1440-1560 parts.

6. The cement-based absorbing material according to claim 2, wherein: In step S1, the stirring speed is 200-500 rpm / min, the time is 10-20 min, the ultrasonic power is 600-800 W, and the time is 10-20 min.

7. The cement-based absorbing material according to claim 1, wherein: Calculated by weight, the cement is 900-1100 parts, the wave-absorbing SAP is 48-72 parts, the tap water is 400-460 parts, and the water reducer is 2.8-3.2 parts.

8. The cement-based absorbing material according to claim 7, wherein: The mass ratio of the cement to the wave-absorbing functional SAP is (13-20):

1.

9. The method for preparing a cement-based wave absorbing material according to any one of claims 1 to 8, wherein: The cement and the wave-absorbing functional SAP are mixed evenly, and then tap water and a water-reducing agent are added and mixed evenly to obtain a cement-based wave-absorbing material.

10. The method for preparing a cement-based wave absorbing material according to claim 9, wherein: The particle size of the wave-absorbing functional SAP is distributed between 100 meshes and 200 meshes, and the water reducer is a polycarboxylic acid type water reducer.

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