Foam concrete capable of being used for rail transit sound absorption low wall and preparation method of foam concrete

Abstract

The invention belongs to the field of concrete, and particularly discloses foam concrete capable of being used for a rail transit sound absorption low wall and a preparation method of the foam concrete. The foam concrete is prepared from the following raw materials: a cementing material, water, a foaming agent, a water repellent and an early strength agent, the mass ratio of the cementing material to the water is 1: (0.4-0.8); the mass ratio of the cementing material to the foaming agent is 1: (0.0005-0.0009); the mass ratio of the cementing material to the water repellent is 1: (0.01-0.03); the mass ratio of the cementing material to the early strength agent is 1: (0.001-0.003). According to the foam concrete disclosed by the invention, macropores which occupy 60-85% of the cross-sectional area and have the diameter of more than 1500 microns are formed in the hardened foam concrete by regulating and controlling the proportion of each component, so that multiple refraction and energy consumption in a sound wave transmission process are increased, and the sound absorption coefficient within 400-1200Hz is further improved.

Description

Technical Field

[0001] The present invention belongs to the field of concrete, and particularly relates to a foamed concrete that can be used for sound-absorbing low walls of rail transit and a preparation method thereof. Background Art

[0002] During the high-speed operation of urban rail transit, noise will be generated. Rail noise mainly consists of wheel-rail noise, traction noise, and aerodynamic noise. Among them, wheel-rail noise dominates, and its energy is concentrated in the frequency range of 400 - 1200 Hz, belonging to medium and low-frequency noise that is difficult to control. In particular, the noise in the frequency range of 400 - 800 Hz is even more difficult to control. The methods for noise control are divided into two categories: active noise reduction and passive noise reduction. Passive noise reduction mainly uses physical means, and various sound-absorbing, sound-insulating, and vibration-isolating materials and structures are used to block, absorb, or reflect noise, thereby reducing the propagation and impact of noise.

[0003] Currently, the passive noise reduction solutions used beside rail transit mainly include vertical sound barriers and near-rail sound-absorbing low walls. The former has a certain blocking effect on medium and high-frequency noise, but the absorption effect on the low-frequency noise generated by wheel-rail collision is poor. At the same time, vertical sound barriers are mostly composed of large-area rigid plates spliced together. Their tall and regular shapes often cause a visual sense of abruptness, and they are prone to tilting and collapsing in bad weather, endangering the safety of surrounding personnel and facilities. In case of an emergency, it is not easy to evacuate passengers. The near-rail sound-absorbing low wall, which has the characteristics of saving space, low cost, convenient construction and maintenance, and good landscape coordination, is used to absorb low-frequency wheel-rail noise. However, the commonly used metal / aluminum fiber perforated plate near-rail low wall has a narrow sound absorption frequency band and high cost; the commonly used rubber-like filling materials for near-rail low walls are flammable, prone to aging, have high safety hazards, and short service life; the construction of the mineral fiber-like filling materials for near-rail low walls is difficult, and the environmental friendliness is poor, which severely restricts the development of near-rail sound-absorbing low walls. Summary of the Invention

[0004] In order to overcome at least one of the above-mentioned technical problems existing in the prior art, one of the purposes of the present invention is to provide a foamed concrete, which has low cost, no adverse impact on the environment, easy construction, and a large number of macropores with stable structures and diameters greater than 1500 μm inside the foamed concrete, realizing good sound absorption effects in both the low-frequency stage and the high-frequency stage, especially better low-frequency sound absorption effect.

[0005] Another purpose of the present invention is to provide a preparation method of the foamed concrete.

[0006] Another purpose of the present invention is to provide a sound-absorbing structure.

[0007] Another purpose of the present invention is to provide the application of the above-mentioned foamed concrete and / or sound-absorbing structure in the field of rail transit sound absorption or building sound absorption.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a foamed concrete, which is prepared from raw materials including: a cementitious material, water, a foaming agent, a water repellent and an early strength agent; the mass ratio of the cementitious material to water is 1:(0.4 - 0.8); the mass ratio of the cementitious material to the foaming agent is 1:(0.0005 - 0.0009); the mass ratio of the cementitious material to the water repellent is 1:(0.01 - 0.03); the mass ratio of the cementitious material to the early strength agent is 1:(0.001 - 0.003). In some embodiments of the present invention, the cementitious material includes cement and a supplementary cementitious material; the supplementary cementitious material is selected from at least one of fly ash, slag, and volcanic ash.

[0009] In some embodiments of the present invention, the foamed concrete has a porous structure.

[0010] In some embodiments of the present invention, the average diameter of the pores in the foamed concrete is 400 - 1800 μm.

[0011] In some embodiments of the present invention, the mass ratio of the cement to the supplementary cementitious material is 1:(0.1 - 5).

[0012] In some embodiments of the present invention, the cement is Portland cement.

[0013] In some embodiments of the present invention, the water repellent includes at least one of potassium methyl silicate solution and potassium methylene silicate solution.

[0014] In some embodiments of the present invention, the solid content of the water repellent is 30 - 40%.

[0015] In some embodiments of the present invention, the early strength agent includes sodium nitrate.

[0016] In some embodiments of the present invention, the sedimentation distance of the foaming agent in 1 hour is 6 - 8 mm.

[0017] In some embodiments of the present invention, the bleeding water volume of the foaming agent in 1 hour is 63 - 75 mL.

[0018] In some embodiments of the present invention, the foaming agent is prepared by diluting a foaming agent with water by 20 - 30 times and then foaming it 70 - 80 times with a foaming machine.

[0019] In some embodiments of the present invention, the foaming agent is a sodium lauryl polyoxyethylene ether sulfate solution with a solid content of 16 - 20%.

[0020] The second aspect of the present invention provides a method for preparing the foamed concrete according to the first aspect of the present invention, comprising the following steps: The foamed concrete is prepared by mixing a cementitious material, water, a water repellent agent and an early strength agent, and then mixing with a foaming agent.

[0021] The third aspect of the present invention provides a sound absorbing structure, comprising a PC board frame and a perforated plate arranged on the PC board frame; concrete material is arranged inside the PC board frame; the concrete material is formed by curing the foam concrete.

[0022] In some embodiments of the present invention, the sound absorbing structure further comprises a cavity.

[0023] In some embodiments of the present invention, the perforated plate has a thickness of 2-3 mm, a pore size of 7-10 mm, and a perforation rate of 10%-15%.

[0024] In some embodiments of the present invention, the thickness of the concrete material is 3 to 7 cm.

[0025] In some embodiments of the present invention, the sound absorbing structure is a sound absorbing low wall.

[0026] The fourth aspect of the present invention provides the use of the foamed concrete described in the first aspect of the present invention and / or the sound absorbing structure described in the third aspect of the present invention in the field of rail transit sound absorption or the field of building sound absorption.

[0027] The beneficial effect of the present invention is that the foamed concrete in the present invention adjusts the ratio of the cementitious material, the water repellent agent and the foaming agent to control the pore structure of the foamed concrete, thereby obtaining foamed concrete with low cost and excellent low-frequency sound absorption performance. After hardening, large pores with a diameter greater than 1500 μm that occupy 60% to 85% of the cross-sectional area are formed inside the foamed concrete, so as to increase multiple refractions and energy consumption during the transmission of sound waves, thereby improving its low-frequency sound absorption coefficient.

[0028] In addition, the sound-absorbing low wall of the present invention contains a perforated plate and a concrete material made of foam concrete, and has a good sound-absorbing effect in a wider frequency band, especially in a low-frequency band, and has a better sound-absorbing effect than the existing foam concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a three-dimensional schematic diagram of the sound-absorbing low wall in Example 4.

[0030] Figure 2 for Figure 1 Schematic diagram of the cross section after cutting along direction II.

[0031] Figure 3Side view of the sound-absorbing low wall in Example 4.

[0032] Figure 4 Top view of the sound-absorbing low wall in Example 4.

[0033] Figure 5 Sound absorption coefficient test chart of the foamed concrete in Examples 1 - 3 and Comparative Example 1.

[0034] Reference numerals: Perforated plate 1; Concrete material 2; PC board frame 3; Rubber pad 4. Detailed implementation manners

[0035] The following further describes the specific implementation of the present invention in detail in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. Reagents or instruments without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0036] In some embodiments of the present invention, a foamed concrete is provided, which is prepared from the following raw materials: cementitious materials, water, foaming agent, water repellent, and early strength agent; the mass ratio of the cementitious materials to water is 1:(0.4 - 0.8); the mass ratio of the cementitious materials to the foaming agent is 1:(0.0005 - 0.0009); the mass ratio of the cementitious materials to the water repellent is 1:(0.01 - 0.03); the mass ratio of the cementitious materials to the early strength agent is 1:(0.001 - 0.003). By adjusting the ratios of the cementitious materials, water, foaming agent, water repellent, and early strength agent in the foamed concrete of the present invention, the curing time of the cementitious materials can be regulated, so that large pores with a diameter greater than 1500 μm and occupying 60% - 85% of the cross-sectional area are formed inside the cured foamed concrete, and foamed concrete with low cost and excellent low-frequency sound absorption performance can be obtained, which is an excellent filling material for developing near-rail sound-absorbing low walls.

[0037] The pore diameters in the existing foamed concrete are much smaller than 1500 μm, and the sound absorption frequency band is mainly concentrated in the high frequency, and it cannot efficiently absorb sound in the low-frequency band of 400 - 800 Hz. In addition, a technical difficulty encountered in developing the foamed concrete of the present invention is how to form a stable large-pore structure, especially during the process of small pores merging into large pores, preventing their rupture so that the large-pore structure in the concrete can be cured and preserved. The present invention solves the above technical problems by adjusting the types and ratios of the cementitious materials, foaming agent, water repellent, and early strength agent, so that a large number of stable large-pore structures with a diameter greater than 1500 μm are retained in the cured concrete.

[0038] In some embodiments of the present invention, the foamed concrete has a porous structure.

[0039] In some embodiments of the present invention, the average diameter of the pores in the foamed concrete is 400 - 1800 μm; in some embodiments of the present invention, the average diameter of the pores in the foamed concrete is 1100 - 1800 μm. In some embodiments of the present invention, the average diameter of the pores in the foamed concrete is any value among 400μm, 438μm, 500μm, 600μm, 700μm, 800μm, 900μm, 1000μm, 1100μm, 1164μm, 1200μm, 1300μm, 1400μm, 1500μm, 1600μm, 1700μm, 1745μm, 1800μm or the range value formed by any two of them.

[0040] In some embodiments of the present invention, the cross-sectional area of the foamed concrete is S 截面 ; the total area of the pores in the foamed concrete is denoted as S 孔 ; S 孔 / S 截面 is 60 - 85%, for example, S 孔 / S 截面 is any value among 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 68.43%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 75.21%, 76%, 77%, 78%, 79%, 80%, 81%, 81.99%, 82%, 83%, 84%, 85% or the range value formed by any two of them.

[0041] In some embodiments of the present invention, the mass ratio of the cementitious material to water can be any value among 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 or the range value formed by any two of them.

[0042] In some embodiments of the present invention, the mass ratio of the gelling material to the foaming agent is any value among 1:0.00050, 1:0.00051, 1:0.00052, 1:0.00053, 1:0.00054, 1:0.00055, 1:0.00056, 1:0.00057, 1:0.00058, 1:0.00059, 1:0.00060, 1:0.00062, 1:0.00064, 1:0.00066, 1:0.00068, 1:0.00070, 1:0.00072, 1:0.00074, 1:0.00076, 1:0.00078, 1:0.00080, 1:0.00081, 1:0.00082, 1:0.00083, 1:0.00084, 1:0.00085, 1:0.00086, 1:0.00087, 1:0.00088, 1:0.00089, 1:0.00090 or the range value of any two of them.

[0043] In some embodiments of the present invention, the mass ratio of the gelling material to the water-repellent agent is any value among 1:0.01, 1:0.02, 1:0.03 or the range value of any two of them. In some embodiments of the present invention, the mass ratio of the gelling material to the early strength agent is any value among 1:0.001, 1:0.002, 1:0.003 or the range value of any two of them.

[0044] In some embodiments of the present invention, the gelling material includes cement and supplementary gelling material; the supplementary gelling material is selected from at least one of fly ash, slag, and volcanic ash.

[0045] In some embodiments of the present invention, the fly ash is Class I ash, Class II ash or F-class ash.

[0046] In some embodiments of the present invention, the activity index of the slag is S95 or S105; S95 means that the 28-day activity index of the slag is not less than 95%, and S105 means that the 28-day activity index of the slag is not less than 105%.

[0047] In some embodiments of the present invention, the mass ratio of cement to supplementary cementitious materials is 1:(0.1 - 5); in some embodiments of the present invention, the mass ratio of cement to supplementary cementitious materials is any value among 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or the range value formed by any two of them. The present invention uses supplementary cementitious materials and early strength agents to regulate the setting time of the cementitious material system, and uses a water repellent to regulate the stability of foam coalescence, and then modulates a macroporous foam structure with a diameter greater than 1500 μm occupying 60% - 85% of the cross-sectional area based on the adaptability of the two, and obtains lightweight foam concrete with low cost and excellent low-frequency sound absorption performance.

[0048] In some embodiments of the present invention, the cement is Portland cement. In some embodiments of the present invention, the strength grade of the cement is 42.5; in some embodiments of the present invention, the cement is P·O42.5R cement.

[0049] In some embodiments of the present invention, the water repellent includes at least one of potassium methyl silicate solution and potassium methylene silicate solution. In some embodiments of the present invention, the water repellent is potassium methyl silicate and / or potassium methylene silicate solution, and the solid content in the water repellent is 30% - 40%.

[0050] In some embodiments of the present invention, the early strength agent includes sodium nitrate.

[0051] In some embodiments of the present invention, the settlement distance of the foaming agent in 1 hour is 6 - 8 mm; in some embodiments of the present invention, the settlement distance of the foaming agent in 1 hour is any value among 6 mm, 7 mm, 8 mm or the range value formed by any two of them.

[0052] In some embodiments of the present invention, the bleeding water volume of the foaming agent in 1 hour is 63 - 75 mL; in some embodiments of the present invention, the bleeding water volume of the foaming agent in 1 hour is any value among 63 mL, 64 mL, 65 mL, 66 mL, 67 mL, 68 mL, 69 mL, 70 mL, 71 mL, 72 mL, 73 mL, 74 mL, 75 mL or the range value formed by any two of them.

[0053] In some embodiments of the present invention, the foaming agent is prepared by diluting the foaming agent with water by 20 to 30 times and then foaming it by 70 to 80 times using a foaming machine. In some embodiments of the present invention, the dilution multiple can be any value among 20 times, 21 times, 22 times, 23 times, 24 times, 25 times, 26 times, 27 times, 28 times, 29 times, 30 times or the range value formed by any two of them. In some embodiments of the present invention, the foaming multiple can be any value among 70 times, 71 times, 72 times, 73 times, 74 times, 75 times, 76 times, 77 times, 78 times, 79 times, 80 times or the range value of any two of them.

[0054] In some embodiments of the present invention, the foaming agent is a sodium lauryl polyoxyethylene ether sulfate solution with a solid content of 16% to 20%. In some embodiments of the present invention, the solid content can be any value among 16%, 17%, 18%, 19%, 20% or the range value formed by any two of them.

[0055] In some embodiments of the present invention, the foaming agent needs to be used within 20 to 40 s after being prepared.

[0056] In some embodiments of the present invention, the present invention provides a method for preparing the above-mentioned foamed concrete, including the following steps: Mix the gelling material, water, water repellent and early strength agent, and then mix with the foaming agent to obtain foamed concrete.

[0057] In some embodiments of the present invention, the mixing is carried out by stirring.

[0058] In some embodiments of the present invention, the stirring rate is 140 to 160 revolutions per minute.

[0059] In some embodiments of the present invention, the mixing time is 3 to 10 minutes.

[0060] In some embodiments of the present invention, the present invention also provides a sound absorption structure, including a PC board frame 3 and a perforated board 1 arranged on the PC board frame 3, and a concrete material 2 is arranged inside the PC board frame 3; the concrete material 2 is formed after the above-mentioned foamed concrete is cured. The PC board frame 3 is rectangular parallelepiped-shaped, and has a rectangular parallelepiped cavity inside, and the above-mentioned foamed concrete is filled in the rectangular parallelepiped cavity. A perforated board 1 is arranged on the PC board frame 3, and the perforated board 1 is located on the sound receiving surface.

[0061] The present invention forms the PC board frame 3 by using PC boards, sets the perforated board 1 on the sound receiving surface, and fills the inside of the PC board frame 3 with the concrete material 2. For example: the sound receiving surface of the PC board frame 3 is set as the perforated board 1, and the above-mentioned foamed concrete material is filled inside it. The obtained sound absorption structure has good sound absorption effects in both high frequencies and low frequencies and has a wide sound absorption range.

[0062] In some embodiments of the present invention, a rubber pad 4 is provided on the inner wall of the PC board frame 3.

[0063] In some embodiments of the present invention, curing refers to curing after injecting the foam concrete.

[0064] In some embodiments of the present invention, the sound-absorbing structure further contains a cavity.

[0065] In some embodiments of the present invention, the perforated plate 1 has a thickness of 2 - 3 mm, a pore diameter of 7 - 10 mm, and a perforation rate of 10% - 15%.

[0066] In some embodiments of the present invention, the thickness of the concrete material 2 is 3 - 7 cm.

[0067] In some embodiments of the present invention, the shape of the sound-absorbing structure can be at least one of I-shaped, L-shaped, Y-shaped, T-shaped, cuboid-shaped, and cube-shaped.

[0068] In some embodiments of the present invention, the sound-absorbing structure is a sound-absorbing low wall.

[0069] The sound-absorbing structure in the present invention can obtain a near-rail foam concrete sound-absorbing structure with a high sound absorption coefficient and broadband sound absorption performance at low frequencies by laminating and using a perforated plate, foam concrete, and an optionally designed cavity, and optimizing the thickness, pore diameter, perforation rate of the perforated plate, the forming shape of the foam concrete, the position of the cavity, and the external shape of the assembled structure. It has the advantages of low carbon, environmental friendliness, low cost, simple production and construction processes, excellent low-frequency sound absorption performance, and adjustable sound absorption bandwidth, and can be used as a near-rail sound-absorbing low wall. The sound-absorbing structure in the present invention combines the impedance matching and Helmholtz resonance sound absorption principles by combining the perforated plate, foam concrete, and cavity, can reduce the resonance frequency, broaden the sound absorption bandwidth, and improve the multiple reflection and refraction losses of sound waves by optimizing the internal / external shape of the sound-absorbing structure, further improving the low-frequency sound absorption performance.

[0070] The sound absorption principle of the sound absorption structure in the present invention is as follows: 1) The selection of the thickness, pore diameter, and perforation rate of the perforated plate is mainly based on the matching of its acoustic impedance and the acoustic impedance of air. Through resonance and air resistance, part of the sound wave energy is consumed; 2) As a porous material, when sound waves impinge on the irregular surface of the foam concrete, scattering occurs. The holes and pore walls will also cause multiple reflections and refractions of the sound waves, thereby enabling the sound waves to propagate and dissipate multiple times inside the material. Compared with the cavity-perforated plate combination, the use of foam concrete increases the acoustic resistance of the composite sound absorption structure. Compared with the traditional small-aperture foam concrete-perforated plate combination, the sound absorption mechanism of the sound absorption structure in the present invention is no longer just resonance, but also includes multiple reflections and refractions of sound waves caused by large-aperture foam concrete and frictional losses, thereby improving the sound absorption coefficient of the sound absorption structure at low frequencies; 3) The forming shape inside or outside the sound absorption structure can be designed. The foam concrete is poured in the forms of flat plates, concave-convex, wedges, and square frames, etc. The external shape of the assembled structure including T, L, or Y shapes can be designed. Through multiple reflections and refractions of sound waves, the sound absorption performance of the composite sound absorption structure can be further improved.

[0071] Example 1 This example provides a kind of foam concrete, which is prepared from the following raw materials in parts by weight: 1 part of cement, 0.25 part of slag, 0.75 part of water, 0.025 part of potassium methyl silicate solution, 0.00075 part of foaming agent, and 0.0021 part of early strength agent. Among them, P·O42.5R cement is used as the cement, which is an early strength type ordinary portland cement, and the strength of the cement in 28 days is greater than 42.5 MPa. The cement and slag are used together as the cementitious materials.

[0072] The solid content of the potassium methyl silicate solution (i.e., the mass percentage of potassium methyl silicate) is 38%, and the solvent is water. It is used as a water repellent to adjust the pore structure of the foam concrete.

[0073] The foaming agent is sodium lauryl polyoxyethylene ether sulfate solution, and the active ingredient is sodium lauryl polyoxyethylene ether sulfate. Its solid content is 16%, and it is obtained by diluting 25 times with water and then foaming with a foaming machine. The bleeding water volume of the foam in 1 h is 74 mL, the sedimentation distance is 6 mm, and the foaming multiple is 73.42.

[0074] The early strength agent is sodium nitrate.

[0075] The foam concrete in this example is prepared by a preparation method including the following steps: First, stir and mix cement and slag for 1 minute, then add water, early strength agent and potassium methyl silicate solution and stir at a speed of 140 revolutions per minute for 5 minutes. Pause, dilute the sodium lauryl polyoxyethylene ether sulfate solution 25 times with water, add it to the foaming machine to produce foam, then add a foaming agent with a preparation time not exceeding 30 s, and continue to stir at a speed of 140 revolutions per minute for 5 minutes to obtain the foam concrete in this example.

[0076] Inject the foam concrete prepared in this example into a mold, then cure it in a standard curing box (temperature 20 ± 1°C, humidity ≥ 95%) for 72 hours and demold it. Then place it in the air (temperature 20 ± 2°C) for natural curing until the specified age and wait for testing.

[0077] Example 2 The difference between the foam concrete in this example and that in Example 1 is only that: this example uses equal mass of fly ash to replace the slag in Example 1.

[0078] Example 3 The difference between the foam concrete in this example and that in Example 1 is only that: all the cementitious materials are cement, that is, slag is not used in this example.

[0079] Comparative Example 1 The difference between the foam concrete in this example and that in Example 1 is only that: all the cementitious materials are cement, and potassium methyl silicate and sodium nitrate are not added.

[0080] Example 4 This example provides a sound-absorbing low wall made of foam concrete. The sound-absorbing low wall in this example is rectangular in shape, with an external length of 120 cm, a width of 25 cm, and a height of 7.2 cm. The structural combination is PC board frame 3 + perforated board 1 + concrete material 2. A perforated board 1 is arranged on the top of the PC board frame 3, and the perforation rate of the perforated board 1 is 11% - 12%. The inside of the PC board frame 3 is filled with the foam concrete in Example 3, and after curing, it forms the concrete material 2; the thickness of the concrete material 2 is 6.5 cm, the thickness of the perforated board 1 is 2 mm, the pore diameter is 7 mm, a 2-mm-thick rubber pad 4 is arranged at the bottom of the PC board frame 3, and a 5-mm-thick rubber pad 4 is coated on one side of the outside of the PC board frame 3 to reduce vibration damage; the PC board frame 3 is surrounded by PC boards with a thickness of 3 mm; the PC board frame 3 extends 10 cm in the length direction and has a 5-mm-thick rubber pad 4 to facilitate the connection and assembly of the low walls. The three-dimensional view of the sound-absorbing low wall in this example is as Figure 1 shown, along the three-dimensional Figure 1 the sectional schematic view of I-I in Figure 2 shown, the side view is as Figure 3 shown, and the top view is as Figure 4 shown.

[0081] The sound-absorbing low wall of foamed concrete in this example is prepared by a preparation method including the following steps: Inject the foamed concrete prepared in Example 3 into the sound-absorbing low wall mold (i.e., the mold formed by enclosing the PC board frame 3 and the perforated board 1), then cure it in a standard curing box (temperature 20±1°C, humidity ≥95%) for 72 hours and then demold it, and then place it in the air (temperature 20±2°C) for natural curing until the specified age for testing.

[0082] Comparative Example 2 The difference between the sound-absorbing low wall in this example and that in Example 4 is only that: asbestos fibers are filled in the PC board frame 3 in this example.

[0083] Performance test Respectively test the fluidity of the foamed concrete in Examples 1 to 3 and Comparative Example 1, as well as the dry density, peak sound absorption coefficient value, sound absorption frequency bandwidth, and compressive strength data of the concrete specimens made of the foamed concrete in Examples 1 to 3 and Comparative Example 1. The compressive strength test of the foamed concrete refers to ASTM C869-2020 "Test Method for Compressive Strength of Precast Foamed Concrete". The specimens are prepared into standard cubes of 100 mm×100 mm×100 mm, and a universal testing machine (UTM) with a capacity of 50 kN is used to carry out the test under the condition of axial compressive load at a constant load rate of 0.1 kN / s (corresponding stress rate of 0.01 MPa / s, based on the cross-sectional area of the specimen of 10000 mm 2 conversion), and the loading is continued until the specimen fails. The final compressive strength of each group of foamed concrete takes the average value of three parallel specimens. The specific test results are shown in Table 1 below.

[0084] The specific test methods for the sound absorption coefficient and dry density are as follows: Inject the foamed concrete in Examples 1 to 3 and Comparative Example 1 into a cylinder model with a diameter of 10 cm and a height of 5 cm respectively, cure it in a standard curing box (temperature 20±1°C, humidity ≥95%) for 72 hours and then demold it, and then place it in the air (20±2°C) for natural curing until 7 days for testing. Then polish the surface of the specimen, polish the thickness to 6 cm, remove the surface residue by a blower and water flow, and then dry the specimen, record the dry density, and use the B&K impedance tube test system (vertical incidence sound absorption coefficient test device) to test the sound absorption coefficient of the foamed concrete based on JGJ-T341-2014. The specific test results are shown in Table 1 below, where the sound absorption frequency bandwidth is based on the sound absorption coefficient higher than 0.65, and the sound absorption coefficient curve is as Figure 5 shown.

[0085] Table 1 Performance data of the foamed concrete in Examples 1 to 3 and Comparative Example 1

[0086] As can be seen from Table 1, when the fluidity, dry density of the foamed concrete in Examples 1 to 3 are comparable to those in Comparative Example 1, its gel time is significantly longer than that in Comparative Example 1. This is beneficial for the merging of small pores into large pores of the foam. The sound absorption frequency corresponding to the peak sound absorption coefficient decreases from 1594 Hz to 600 - 696 Hz, and the bandwidth corresponding to the sound absorption coefficient > 0.65 increases significantly. Its compressive strength can also be maintained at the same level as that in Comparative Example 1. Based on this, the combined use of potassium methyl silicate water repellent, fatty alcohol polyoxyethylene ether sodium sulfate foaming agent, sodium silicate early strength agent and gel material can obtain foamed concrete with high fluidity, simple construction process, light weight, low carbon and high sound absorption, and has good low-frequency sound absorption effect and wide absorption spectrum.

[0087] The porosity and average pore diameter of the foamed concrete in Examples 1 to 3 and Comparative Example 1 were tested. The specific test method was as follows: Samples were taken from specimens cured in a curing room at 20 °C and 95% humidity for 7 days. The sampling position was 2 - 3 cm from the specimen surface. The undamaged part of the sample was photographed using an optical microscope with a magnification of 35 times. Image processing software was used to distinguish pores, and then the percentage of the pore area in the cross-sectional area was calculated. Among them, the porosity was the ratio of the pore area to the total area, and the average pore diameter was calculated as the Feret’s diameter of all pores (the maximum distance between two points on the boundary of the selected area). The porosity and average pore diameter data of the foamed concrete obtained according to the above test method and calculation method are shown in Table 2 below.

[0088] Table 2 Porosity and average pore diameter of foamed concrete

[0089] As can be seen from Table 2, the average pore diameter of the foamed concrete in Examples 1 to 3 of the present invention is 400 - 1800 μm, and the porosity is greater than 75%, which is much higher than the average pore diameter and porosity in Comparative Example 1. Among them, there are a large number of large pores with a diameter greater than 1500 μm and a large number of micropores in Example 3. Therefore, the average pore diameter of Example 3 is 438 μm. After the foamed concrete in Examples 1 to 3 hardens, large pores with a diameter greater than 1500 μm that occupy 68% - 82% of the cross-sectional area are formed inside it to increase the multiple refractions and energy consumption during the sound wave transmission process, thereby improving the low-frequency sound absorption coefficient.

[0090] Sound absorption experiments were respectively conducted on the sound absorption low walls in Example 4 and Comparative Example 2. The specific test method was as follows: The sound absorption low walls in Example 4 and Comparative Example 2 were respectively placed in an anechoic chamber, and a sound level meter was used to record their equivalent and maximum sound pressure levels under a whistling sound source (frequency from 400 Hz to 2500 Hz). At the same time, the equivalent and maximum sound pressure levels without setting the sound absorption low wall (i.e., without a sound absorption wall) were tested. The sound absorption experiment test results measured according to this test method are shown in Table 3 below.

[0091] Table 3 Test Results of Sound Absorption Laboratory

[0092] As can be seen from Table 3, compared with the sound-absorbing low wall filled with asbestos fibers in Comparative Example 2, the equivalent sound pressure level LAeq of the foam concrete-filled sound-absorbing low wall in Example 4 is reduced by 1.2 dB; the maximum sound pressure level LAmax is reduced by 1.9 dB, and there are different noise reduction effects of 1-2 dB in the frequency band of 400 Hz to 2500 Hz. This means that if the foam concrete in Examples 1-3 is used, the sound absorption effect of the sound-absorbing low wall will be continuously improved significantly.

[0093] In summary, the foam concrete in the present invention can regulate the pore structure of the foam concrete by adjusting the mix ratio of the cementitious material, water repellent, early strength agent and foaming agent, and obtain foam concrete with low cost and excellent low-frequency sound absorption performance. Large pores with a diameter greater than 1500 μm and occupying 60% - 85% of the cross-sectional area are formed inside the hardened foam concrete to increase the multiple refraction and energy consumption during the transmission of sound waves, thereby improving its low-frequency sound absorption coefficient. The mechanism for forming this special pore structure is as follows: (1) The use of supplementary cementitious materials such as fly ash, slag, and volcanic ash can extend the setting time of cement, providing time for small bubbles to merge into large bubbles; 2) Methyl / methylene potassium silicate water repellent uses hydrophobic groups to reduce the surface tension of the cement paste, improve the hydrophobicity of the liquid film, and can reduce the viscosity of the paste, making it easier for bubbles to form and stably exist during the merging process; in addition, methyl / methylene potassium silicate water repellent can also delay the hydration reaction and reduce the destructive effect of Ca 2+ and OH⁻ on the foam during the initial hydration stage; 3) The early strength agent can act together with supplementary cementitious materials such as fly ash, slag, and volcanic ash and the water repellent to adjust the setting time of cement to adapt to the merging and stable time of the foam, thereby obtaining a stable large pore structure suitable for low-frequency sound absorption; when sound propagates into the large pore voids, more sound energy is consumed by friction, thereby absorbing sound. In addition, the sound-absorbing low wall filled with the foam concrete in the present invention has different noise reduction effects of 1-2 dB in the frequency band of 400 Hz to 2500 Hz, further indicating that the foam concrete in the present invention has excellent sound absorption effects.

[0094] The above has made a detailed description of the embodiments of the present invention. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention within the knowledge scope of those of ordinary skill in the art. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A foam concrete, characterized in that: It is prepared from raw materials including: a gelling material, water, a foaming agent, a water repellent, and an early strength agent; the mass ratio of the gelling material to water is 1:(0.4 - 0.8); the mass ratio of the gelling material to the foaming agent is 1:(0.0005 - 0.0009); the mass ratio of the gelling material to the water repellent is 1:(0.01 - 0.03); the mass ratio of the gelling material to the early strength agent is 1:(0.001 - 0.003).

2. The foamed concrete according to claim 1, characterized in that: The gelling material includes cement and a supplementary gelling material; the supplementary gelling material is selected from at least one of fly ash, slag, and volcanic ash.

3. The foamed concrete according to claim 2, characterized in that: The cement is Portland cement. And / or, the water repellent includes at least one of potassium methyl silicate solution and potassium methylene silicate solution. And / or, the early strength agent includes sodium nitrate.

4. The foamed concrete according to claim 1, wherein: The foamed concrete has a porous structure, and the average diameter of the pores is 400 - 1800 μm.

5. The foamed concrete according to claim 1, wherein: The foaming agent has at least one of the following characteristics: (a) The sedimentation distance of the foaming agent in 1 hour is 6 - 8 mm; (b) The bleeding water volume of the foaming agent in 1 hour is 63 - 75 mL; (c) The foaming agent is prepared by diluting a foaming agent with water by 20 - 30 times and then foaming it 70 - 80 times with a foaming machine.

6. The foamed concrete according to claim 5, characterized in that: The foaming agent is a sodium lauryl polyoxyethylene ether sulfate solution with a solid content of 16 - 20%.

7. The preparation method of the foamed concrete according to any one of claims 1 to 6, characterized in that: It includes the following steps: Mix the gelling material, water, water repellent, and early strength agent, and then mix with the foaming agent to obtain the foamed concrete.

8. An acoustic absorption structure, characterized in that: It includes a PC board frame and a perforated board arranged on the PC board frame; a concrete material is arranged inside the PC board frame; the concrete material is formed after the foamed concrete according to any one of claims 1 - 6 is cured.

9. The sound-absorbing structure according to claim 8, wherein: The sound absorption structure also contains a cavity; And / or, the thickness of the perforated board is 2 - 3 mm, the hole diameter is 7 - 10 mm, and the perforation rate is 10% - 15%; And / or, the thickness of the concrete material is 3 - 7 cm.

10. The application of the foamed concrete according to any one of claims 1 - 6 and / or the sound absorption structure according to any one of claims 8 - 9 in the field of rail transit sound absorption or building sound absorption.

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