Cement-based wave-absorbing material and preparation method thereof

Abstract

The invention discloses a cement-based wave-absorbing material which comprises a cement matrix and a wave-absorbing reinforcement body, the cement matrix comprises concrete, the concrete comprises cement, sand and water, the wave-absorbing reinforcement body comprises biochar and nano ferroferric oxide, and the cement matrix and the wave-absorbing reinforcement body comprise, by mass, 150-250 parts of cement, 1-2 parts of sand and 1-2 parts of water. The invention relates to an environment-friendly brick which comprises the following components in parts by weight: 400-600 parts of sand, 75-125 parts of water, 1-5 parts of charcoal and 10-30 parts of nano ferroferric oxide. Therefore, the combination of the biochar and the nano ferroferric oxide is used as a wave-absorbing enhancing component, so that more electromagnetic waves can be absorbed, and meanwhile, the loss capacity of the cement-based wave-absorbing material is improved by utilizing the dielectric loss capacity of the biochar and the magnetic loss capacity of the nano ferroferric oxide; therefore, the wave-absorbing performance of the cement-based wave-absorbing material is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of concrete, in particular to a cement-based wave-absorbing material. Background Art

[0002] With the rapid development and popularization of electronic products and the electronics industry, electromagnetic waves, as the fastest and most common information transmission carrier, have been widely used in military and civilian fields. However, in addition to transmitting information, electromagnetic waves also radiate energy to the surrounding environment. The electromagnetic interference and leakage caused by electromagnetic radiation not only threaten the security of national political, military and economic information, but also cause serious damage to humans and other organisms. In order to solve the hazards caused by electromagnetic radiation, electromagnetic wave absorbing materials have gradually been derived. Through these electromagnetic wave absorbing materials, electromagnetic wave energy can be converted into other forms of energy, thereby playing the role of absorbing and eliminating waves.

[0003] Cement-based materials are the most widely used materials in civil engineering and are the most important building materials of this century. However, due to the low magnetic permeability of traditional cement materials, impedance matching performance is poor and loss capacity is weak, so it cannot fully meet the requirements for absorbing performance. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a cement-based absorbing material, which uses biochar and nano-ferroferric oxide as absorbing enhancement components, thereby increasing the impedance matching characteristics and loss capacity of the cement-based absorbing material, so that the cement-based material has better absorbing characteristics.

[0005] A cement-based absorbing material according to a first aspect of an embodiment of the present invention comprises: a cement matrix and an absorbing reinforcement, wherein the cement matrix comprises concrete, the concrete comprises cement, sand and water, and the absorbing reinforcement is biochar and nano-ferroferric oxide, wherein the mass ratio between the cement matrix and the absorbing reinforcement is: 150-250 parts of cement, 400-600 parts of sand, 75-125 parts of water, 1-5 parts of biochar, and 10-30 parts of nano-ferroferric oxide.

[0006] A method for preparing a cement-based wave absorbing material according to a second aspect of an embodiment of the present invention comprises the following steps:

[0007] Add biochar and nano-ferroferric oxide to concrete and mix them to obtain cement-based absorbing materials.

[0008] According to some embodiments of the present invention, the method for preparing biochar comprises: placing the crushed biomass in a pyrolysis furnace for pyrolysis to obtain biochar, wherein the temperature range of the biomass pyrolysis is 600°C-700°C.

[0009] According to some embodiments of the present invention, the biomass is placed in the pyrolysis furnace and heated to a target pyrolysis temperature at a heating rate of 2° C. to 8° C. per minute.

[0010] According to some embodiments of the present invention, the biomass is placed in the pyrolysis furnace for 3.5 hours.

[0011] According to some embodiments of the present invention, the biomass is any one of corn straw, wheat straw, sorghum straw, peanut shell, coconut shell, and fir, or a combination of at least two of them.

[0012] According to some embodiments of the present invention, the particle size of the nano-ferroferric oxide is in the range of 50-200 nanometers.

[0013] According to some embodiments of the present invention, the biomass content ranges from 1.0 wt.% to 1.5 wt.%.

[0014] According to some embodiments of the present invention, the dosage of the nano-ferrosoferric oxide is 10 wt.%.

[0015] Specifically, the conventional cement material has low magnetic permeability, which results in poor impedance matching performance and poor loss capability. Therefore, it is difficult for electromagnetic waves to enter the material, resulting in a large amount of reflection at the incident surface.

[0016] Since nano-iron tetroxide has high magnetic properties, it can enhance the magnetic permeability of cement-based materials, and thus overcome the problem of poor impedance matching performance of cement-based materials to a certain extent, making it easier for electromagnetic waves to be better "absorbed" into cement materials and reducing the reflection of electromagnetic waves.

[0017] Furthermore, biomass can be used to prepare biochar, and the high dielectric constant and high dielectric loss of biochar can be used to convert incident electromagnetic waves into heat and other forms of energy in a timely manner to solve the defect of weak loss capacity of cement-based materials.

[0018] Among them, a large number of oxygen-containing functional groups on biochar can be regarded as polarization centers, which can produce dipole polarization losses under the action of electromagnetic waves. At the same time, the porous structure of biochar will produce a large number of uneven interfaces, hindering the movement of free electrons, thereby producing a large amount of interface polarization. Then, through the unique porous structure of biochar, a large number of electromagnetic waves will be reflected and scattered, which is conducive to promoting the dielectric loss caused by dipole polarization and interface polarization.

[0019] In addition, biochar and nano-ferroferric oxide will also produce a coupling effect in cement materials, so that the cement-based materials and the wave absorption enhancer can form an organic whole. Specifically, on the one hand, the addition of biochar and nano-ferroferric oxide can promote the hydration of cement-based materials. Among them, biochar has many active groups, which can serve as nucleation sites for cement to promote hydration, and the nucleation effect of nano-ferroferric oxide promotes hydration, which is conducive to the production of more hydrated calcium silicate, calcium hydroxide, calcium aluminate and other hydration products, and these hydration products can promote the scattering of electromagnetic waves in the cement matrix, which is conducive to the occurrence of electromagnetic wave loss and improves the wave absorption performance.

[0020] On the other hand, the addition of biochar and nano-ferroferric oxide improves the pore structure of cement-based materials, produces more nano-scale pores, significantly increases the pore area, and promotes the interfacial polarization loss and scattering of electromagnetic waves. Specifically, the addition of biochar can introduce many nucleation sites to promote hydration and refine the pore structure. At the same time, biochar has strong water absorption and can change the local water-cement ratio in the cement paste, thereby reducing the porosity. In addition, the small-size filling effect of biochar and nano-ferroferric oxide also further optimizes the pore structure. Therefore, the addition of biochar and nano-ferroferric oxide can promote cement hydration and improve the pore structure, thereby improving the wave absorption performance while increasing the strength of cement.

[0021] Beneficial effects:

[0022] The present invention utilizes a combination of biochar and nano-ferroferric oxide as a wave absorption enhancement component, which helps to "absorb" more electromagnetic waves. At the same time, the dielectric loss capacity of biochar and the magnetic loss capacity of nano-ferroferric oxide are used to improve the loss capacity of cement-based wave absorbing materials, thereby effectively improving the "wave absorption" performance of cement-based wave absorbing materials.

[0023] In addition, compared with traditional carbon materials (carbon black, carbon fiber), the biochar used in the present invention has abundant pores and a large specific surface area. These porous structures can not only provide a new path for the transmission of electromagnetic waves, but also cause a large amount of reflection and scattering of electromagnetic waves, thereby greatly increasing the dielectric loss and providing a new way for the absorption of electromagnetic waves, thereby improving the "wave absorbing" performance of cement-based absorbing materials.

[0024] The biochar and nano-ferroferric oxide in the present invention can also promote cement hydration and improve the pore structure of cement, thereby increasing the strength of cement while improving the wave absorbing performance.

[0025] The preparation method of the cement-based absorbing material in the present invention has the advantages of low cost and green environmental protection, is easy to construct, and has a low cost, and is suitable for industrial production. In addition, the raw materials of biomass materials are solid wastes, which are abundant in resources and low in cost. After the biomass is prepared into biochar and used as the electromagnetic wave absorption and enhancement component of the cement-based material, the absorption performance can be improved, thereby realizing the recycling of resources, which has great prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0027] Figure 1 This is the SEM image of the fir biochar of Example 1 of the present invention;

[0028] Figure 2 This is a SEM image of corn straw biochar of Example 4 of the present invention;

[0029] Figure 3 This is a schematic diagram of the dielectric constant of Chinese fir biochar according to Example 1 of the present invention;

[0030] Figure 4 Schematic diagram of reflectivity curves of cement-based materials of Example 1 and Comparative Examples 1-3 of the present invention;

[0031] Figure 5 Schematic diagram of the mechanical properties of cement-based materials of Example 1 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0032] The following is a clear and complete description of the technical solutions in the embodiments of the present disclosure in conjunction with the drawings in the embodiments disclosed in this application. The description of the embodiments is actually only illustrative and exemplary, and does not serve as any limitation to the present disclosure and its application or use; based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without carrying out creative work should fall within the scope of protection of the present disclosure. In addition, the techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods or equipment should be regarded as part of the specification.

[0033] Example 1

[0034] In this embodiment, the cement-based absorbing material is prepared according to the following steps:

[0035] Step 1: Dry the fir wood at 60° C. for 12 hours, and grind it with a grinder to obtain fir wood chips.

[0036] Step 2: Place the fir wood chips in a rotary kiln, heat them to 700°C at a rate of 5°C per minute, and maintain the temperature for 3.5 hours. Take out the biochar after the temperature drops naturally. Nitrogen should be introduced into the biomass all the time during the pyrolysis process in the rotary kiln.

[0037] Step 3: Dry mix 100 parts of cement, 200 parts of sand, 1.5 parts of biochar, and 10 parts of nano-ferroferric oxide in a mixer for 5 minutes, then add 60 parts of water and stir for 3 minutes to obtain a cement-based absorbing material slurry.

[0038] Specifically, in order to facilitate the unified testing of the performance of cement-based materials, the cement-based absorbing material slurry obtained above can be poured into a mold of 180mm×180mm×15mm, and the mold can be removed after curing at 20±2℃ and relative humidity>95% for 24h; the test block is placed in a standard curing box for curing for 28 days to obtain a test block of cement-based absorbing material.

[0039] Among them, the SEM image of the biochar prepared in this example is as follows Figure 1 The dielectric constant is shown as Figure 3 shown.

[0040] The cement-based absorbing material prepared in this embodiment was tested for its absorbing performance in the range of 2-18 GHz by the bow method. Before the test, the cement-based absorbing material was dried at 60° C. for 24 hours. The absorbing performance of the cement-based absorbing material after the test is shown in Tables 1 and Figure 4 .

[0041] The mechanical properties of the cement-based samples prepared in this example are as follows: Figure 5 shown.

[0042] Example 2

[0043] In this embodiment, the cement-based absorbing material is prepared according to the following steps:

[0044] Step 1: Dry the fir wood at 60° C. for 12 hours, and grind it with a grinder to obtain fir wood chips.

[0045] Step 2: Place the fir wood chips in a rotary kiln, heat them up to 600°C at a rate of 5°C per minute, and maintain the temperature for 3.5 hours, and take out the biochar after the temperature drops naturally. It is worth noting that nitrogen should be introduced into the biomass during the pyrolysis process in the rotary kiln.

[0046] Step 3: Dry mix 100 parts of cement, 200 parts of sand, 1.5 parts of biochar, and 10 parts of nano-ferroferric oxide in a mixer for 5 minutes, then add 60 parts of water and stir for 3 minutes to obtain a cement-based absorbing material slurry.

[0047] Specifically, in order to facilitate the unified testing of the performance of cement-based materials, the cement-based absorbing material slurry obtained above can be poured into a mold of 180mm×180mm×15mm, and the mold can be removed after curing at 20±2℃ and relative humidity>95% for 24h; the test block is placed in a standard curing box for curing for 28 days to obtain a test block of cement-based absorbing material.

[0048] The cement-based absorbing material prepared in this embodiment was tested for its absorbing performance in the range of 2-18 GHz using the bow method. Before the test, the cement-based absorbing material was dried at 60° C. for 24 hours. The absorbing performance is shown in Table 1.

[0049] Example 3

[0050] In this embodiment, the cement-based absorbing material is prepared according to the following steps:

[0051] Step 1: Dry the fir wood at 60° C. for 12 hours, and grind it with a grinder to obtain fir wood chips.

[0052] Step 2: Place the fir wood chips in a rotary kiln, heat them up to 700°C at a rate of 5°C per minute, and maintain the temperature for 3.5 hours, and take out the biochar after the temperature drops naturally. It is worth noting that nitrogen should be introduced into the biomass during the pyrolysis process in the rotary kiln.

[0053] Step 3: Dry mix 100 parts of cement, 200 parts of sand, 1 part of biochar, and 10 parts of nano-ferroferric oxide in a mixer for 5 minutes, then add 60 parts of water and stir for 3 minutes to obtain a cement-based absorbing material slurry.

[0054] Specifically, in order to facilitate the unified testing of the performance of cement-based materials, the cement-based absorbing material slurry obtained above can be poured into a mold of 180mm×180mm×15mm, and the mold can be removed after curing at 20±2℃ and relative humidity>95% for 24h; the test block is placed in a standard curing box for curing for 28 days to obtain a test block of cement-based absorbing material.

[0055] The cement-based absorbing material prepared in this embodiment was tested for its absorbing performance in the range of 2-18 GHz using the bow method. Before the test, the cement-based absorbing material was dried at 60° C. for 24 hours. The absorbing performance is shown in Table 1.

[0056] Example 4

[0057] In this embodiment, the cement-based absorbing material is prepared according to the following steps:

[0058] Step 1: Dry the corn stalks at 60° C. for 12 hours, and crush them with a crusher to obtain fir wood chips.

[0059] Step 2: Place the fir wood chips in a rotary kiln, heat them up to 700°C at a rate of 5°C per minute, and maintain the temperature for 3.5 hours, and take out the biochar after the temperature drops naturally. It is worth noting that nitrogen should be introduced into the biomass during the pyrolysis process in the rotary kiln.

[0060] Step 3: SEM image of biochar Figure 2 As shown, 100 parts of cement, 200 parts of sand, 1.5 parts of biochar, and 10 parts of nano-ferroferric oxide were dry-mixed in a mixer for 5 minutes, and then 60 parts of water were added and stirred for 3 minutes to obtain a cement-based absorbing material slurry.

[0061] Specifically, in order to facilitate the unified testing of the performance of cement-based materials, the cement-based absorbing material slurry obtained above can be poured into a mold of 180mm×180mm×15mm, and the mold can be removed after curing at 20±2℃ and relative humidity>95% for 24h; the test block is placed in a standard curing box for curing for 28 days to obtain a test block of cement-based absorbing material.

[0062] The SEM image of the biochar prepared in this example is shown in Figure 2 The prepared cement-based absorbing material was tested for its absorbing performance in the range of 2-18 GHz by the bow method. Before the test, the cement-based absorbing material was dried at 60°C for 24 hours. The absorbing performance is shown in Table 1.

[0063] Comparative Example 1

[0064] 100 parts of cement and 200 parts of sand by mass were dry-mixed in a mixer for 5 minutes, and then 60 parts of water were added and stirred for 3 minutes to obtain a cement-based material slurry.

[0065] The fresh slurry of the absorbing material was poured into a mold of 180 mm × 180 mm × 15 mm, and after curing for 24 hours at 20 ± 2 ° C and relative humidity > 95%, the mold was removed, and the test block was placed in a standard curing box for curing for 28 days to obtain a cement-based material.

[0066] The cement-based material prepared in this comparative example was tested for its wave absorbing performance in the range of 2-18 GHz by the bow method. Before the test, the cement-based wave absorbing material was dried at 60° C. for 24 hours. The wave absorbing performance is shown in Tables 1 and Figure 4 .

[0067] In addition, the mechanical properties of the cement-based samples prepared in this comparative example are as follows Figure 5 shown.

[0068] Comparative Example 2

[0069] 100 parts of cement, 200 parts of sand and 10 parts of nano-ferroferric oxide were dry-mixed in a mixer for 5 minutes, and then 60 parts of water were added and stirred for 3 minutes to obtain a cement-based material slurry.

[0070] The freshly mixed slurry of the absorbing material is poured into a mold of 180mm×180mm×15mm; after curing for 24 hours at 20±2°C and relative humidity>95%, the mold is removed; the test block is placed in a standard curing box and cured for 28 days to obtain a cement-based material.

[0071] The cement-based material prepared in this comparative example was tested for its wave absorbing performance in the range of 2-18 GHz by the bow method. Before the test, the cement-based wave absorbing material was dried at 60° C. for 24 hours. The wave absorbing performance is shown in Tables 1 and Figure 4 .

[0072] In addition, the mechanical properties of the cement-based samples prepared in this comparative example are as follows Figure 5 shown.

[0073] Comparative Example 3

[0074] Step 1: Dry the fir wood at 60° C. for 12 hours, and grind it with a grinder to obtain fir wood chips.

[0075] Step 2: Place the fir wood chips in a rotary kiln, heat them up to 700°C at a rate of 5°C per minute, and maintain the temperature for 3.5 hours, and take out the biochar after the temperature drops naturally. It is worth noting that nitrogen should be introduced into the biomass during the pyrolysis process in the rotary kiln.

[0076] Step 3: Dry mix 100 parts of cement, 200 parts of sand, and 1.5 parts of biochar in a mixer for 5 minutes, then add 60 parts of water and stir for 3 minutes to obtain a cement-based absorbing material slurry.

[0077] The freshly mixed slurry of the absorbing material is poured into a mold of 180mm×180mm×15mm; after curing for 24 hours at 20±2°C and relative humidity>95%, the mold is removed; the test block is placed in a standard curing box for curing for 28 days to obtain a cement-based absorbing material.

[0078] The cement-based absorbing material prepared in this comparative example 3 was tested for its absorbing performance in the range of 2-18 GHz by the bow method. Before the test, the cement-based absorbing material was dried at 60° C. for 24 hours. The absorbing performance is shown in Tables 1 and Figure 4 .

[0079] In addition, the mechanical properties of the cement-based samples prepared in this comparative example are as follows Figure 5 shown.

[0080] The test results of the wave absorption performance of the cement-based materials of the above embodiments and comparative examples are summarized as shown in the following Table 1.

[0081] Table 1. Test results of wave absorption performance of cement-based materials of Examples and Comparative Examples

[0082]

[0083] From the comparison between the embodiment and the comparative example, it can be seen that the addition of biochar and nano-trioxide greatly improves the wave absorption performance of cement-based wave absorbing materials. Among them, comparative example 1 uses traditional cement materials, the minimum reflectivity of which is -11dB, the effective bandwidth is only 4.1GHz (<-7dB) and 0.8GHz (<-10dB), and it is obvious that the traditional cement materials have weak electromagnetic wave absorption capacity.

[0084] After adding nano-ferroferric tetroxide in Comparative Example 2, the absorption performance of the cement-based material is further improved. This is mainly because the magnetic properties of nano-ferroferric tetroxide are relatively high, the magnetic permeability of the cement-based material is enhanced, and the impedance matching performance of the cement-based material is improved.

[0085] Furthermore, the effective bandwidth of Comparative Example 3 is only 5.9 GHz (<-7dB) and 3.3 GHz (<-10dB), which indicates that the dielectric loss capacity of biochar itself can improve the electromagnetic wave loss capacity of cement-based samples.

[0086] Of course, compared with the comparative example, the cement-based absorbing material of Example 1 has the widest absorption bandwidth and the best absorbing effect. This is mainly because the combination of biochar and nano-ferroferric oxide can couple with each other, so that the impedance matching performance and loss capacity are improved.

[0087] In addition, by Figure 3 It can be seen that the real and imaginary parts of the dielectric constant of biochar are above 12 and 5 respectively, and it has a high dielectric loss capacity.

[0088] Depend on Figure 4 It can be seen that the wave absorbing effect of the cement-based absorbing material in Example 1 is the best, while the wave absorbing effect of the cement-based absorbing material in Comparative Document 3 is second only to the wave absorbing effect of Example 1. Therefore, after comparing the parameters with Comparative Document 2, it can be seen that the combination of biochar and cement material is slightly better than the combination of nano-ferroferric oxide and cement material, but the wave absorbing effect is still inferior to the combination of biochar, nano-ferroferric oxide and cement material.

[0089] Depend on Figure 5 It can be seen that the compressive strength and flexural strength of Example 1 are 27.5 MPa and 6.2 MPa, respectively, which are significantly better than the compressive strength and flexural strength parameters of the traditional cement material of Comparative Example 1.

[0090] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0091] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0092] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A cement-based absorbing material, It is characterized in that include: The cement matrix and the wave-absorbing reinforcement are provided. The cement matrix comprises concrete, and the concrete comprises cement, sand and water. The wave-absorbing reinforcement is biochar and nano-ferroferric oxide.

2. The method for preparing a cement-based absorbing material according to claim 1, It is characterized in that The mass ratio between the cement matrix and the wave-absorbing reinforcement is: 150-250 parts of cement, 400-600 parts of sand, 75-125 parts of water, 1-5 parts of biochar, and 10-30 parts of nano-ferroferric oxide.

3. A method for preparing a cement-based wave absorbing material, It is characterized in that The following steps are involved: Biochar and nano-ferroferric oxide are added into concrete and stirred to obtain cement-based absorbing material.

4. The method for preparing a cement-based absorbing material according to claim 3, It is characterized in that The method for preparing biochar comprises: placing crushed biomass in a pyrolysis furnace for pyrolysis to obtain biochar, wherein the temperature range of the biomass pyrolysis is 600° C.-700° C.

5. The method for preparing a cement-based absorbing material according to claim 4, It is characterized in that The biomass is placed in the pyrolysis furnace and heated to a target pyrolysis temperature at a heating rate of 2° C. to 8° C. per minute.

6. The method for preparing a cement-based wave absorbing material according to claim 5, It is characterized in that The biomass is placed in the pyrolysis furnace for 3.5 hours of pyrolysis.

7. The method for preparing a cement-based absorbing material according to claim 4, It is characterized in that The biomass is any one of corn straw, wheat straw, sorghum straw, peanut shell, coconut shell and fir wood, or a combination of at least two of them.

8. The method for preparing a cement-based absorbing material according to claim 3, It is characterized in that The particle size of the nano-ferroferric oxide is in the range of 50-200 nanometers.

9. The method for preparing a cement-based wave absorbing material according to claim 3, It is characterized in that The biomass content ranges from 1.0 wt.% to 1.5 wt.%.

10. The method for preparing a cement-based wave absorbing material according to claim 3, It is characterized in that The dosage of the nano-ferrosoferric oxide is 10wt.%.

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