Foamed concrete for rail transit sound absorption low wall and preparation method thereof

Abstract

This invention belongs to the field of concrete, specifically disclosing a foamed concrete suitable for use in sound-absorbing low walls in rail transit and its preparation method. The foamed concrete is made from the following raw materials: cementitious materials, water, foaming agent, water-repellent agent, and early-strength agent; the mass ratio of cementitious materials to water is 1:(0.4~0.8); the mass ratio of cementitious materials to foaming agent is 1:(0.0005~0.0009); the mass ratio of cementitious materials to water-repellent agent is 1:(0.01~0.03); and the mass ratio of cementitious materials to early-strength agent is 1:(0.001~0.003). The foamed concrete of this invention, by controlling the proportions of each component, forms large pores with a diameter greater than 1500μm occupying 60%~85% of the cross-sectional area inside the hardened foamed concrete, thereby increasing the multiple refractions and energy dissipation during sound wave transmission and thus improving the sound absorption coefficient within the 400~1200Hz range.

Description

Technical Field

[0001] This invention belongs to the field of concrete, specifically relating to a foamed concrete that can be used for sound-absorbing low walls in rail transit and its preparation method. Background Technology

[0002] Urban rail transit generates noise during high-speed operation. Track noise mainly consists of wheel-rail noise, traction noise, and aerodynamic noise, with wheel-rail noise being the dominant factor. Its energy is concentrated in the 400–1200 Hz frequency range, which is considered a difficult-to-manage low-to-mid-frequency noise, especially the noise in the 400–800 Hz frequency range. Noise control methods are divided into two categories: active noise reduction and passive noise reduction. Passive noise reduction mainly uses physical means, utilizing various sound-absorbing, sound-insulating, and vibration-damping materials and structures to block, absorb, or reflect noise, thereby reducing its propagation and impact.

[0003] Currently, passive noise reduction solutions used near rail transit mainly include two types: vertical sound barriers and near-rail sound-absorbing low walls. The former offers some blocking effect for mid-to-high frequency noise, but its absorption effect on low-frequency noise generated by wheel-rail collisions is poor. Furthermore, vertical sound barriers are mostly constructed from large areas of rigid panels, and their tall, uniform shape often creates a visually jarring effect. They are prone to tilting and collapsing in severe weather, endangering the safety of surrounding personnel and facilities, and making it difficult to evacuate passengers in emergencies. Near-rail sound-absorbing low walls, with their advantages of space saving, low cost, convenient construction and maintenance, and good landscape coordination, are used to absorb low-frequency wheel-rail noise. However, commonly used metal / aluminum fiber perforated panel near-rail walls have a narrow sound absorption frequency band and high cost. Commonly used rubber-based filling materials for near-rail walls are flammable, prone to aging, pose high safety hazards, and have a short service life. Mineral wool fiber filling materials for near-rail walls are difficult to construct and have poor environmental friendliness, severely limiting the development of near-rail sound-absorbing low walls. Summary of the Invention

[0004] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a foamed concrete that is low in cost, has no adverse environmental impact, is easy to construct, and has a large number of structurally stable large pores with a diameter greater than 1500 μm inside, thereby achieving good sound absorption effect in both low-frequency and high-frequency stages, especially with superior low-frequency sound absorption effect.

[0005] The second objective of this invention is to provide a method for preparing foamed concrete.

[0006] The third objective of this invention is to provide a sound-absorbing structure.

[0007] The fourth objective of this invention is to provide the application of the above-mentioned foamed concrete and / or sound-absorbing structures in the fields of rail transit sound absorption or building sound absorption.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides a foamed concrete, which is made from raw materials comprising: a cementitious material, water, a foaming agent, a water-repellent agent, and an early-strength agent; wherein 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 agent is 1:(0.01~0.03); and the mass ratio of the cementitious material to the early-strength agent is 1:(0.001~0.003).

[0010] In some embodiments of the present invention, the cementitious material includes cement and supplementary cementitious material; the supplementary cementitious material is selected from at least one of fly ash, slag, and volcanic ash.

[0011] In some embodiments of the present invention, the foamed concrete has a porous structure.

[0012] In some embodiments of the present invention, the average diameter of the pores in the foamed concrete is 400~1800 μm.

[0013] In some embodiments of the present invention, the mass ratio of the cement to the supplementary cementitious material is 1:(0.1~5).

[0014] In some embodiments of the present invention, the cement is silicate cement.

[0015] In some embodiments of the present invention, the hydrophobic agent includes at least one of potassium methylsilicate solution and potassium methylenesilicate solution.

[0016] In some embodiments of the present invention, the solid content of the hydrophobic agent is 30-40%.

[0017] In some embodiments of the present invention, the early strength agent includes sodium nitrate.

[0018] In some embodiments of the present invention, the settling distance of the foaming agent is 6-8 mm per hour.

[0019] In some embodiments of the present invention, the amount of water exuded by the foaming agent in 1 hour is 63-75 mL.

[0020] In some embodiments of the present invention, the foaming agent is prepared by diluting a foaming agent with water by 20 to 30 times and then foaming it by 70 to 80 times using a foaming machine.

[0021] In some embodiments of the present invention, the foaming agent is a sodium fatty alcohol polyoxyethylene ether sulfate solution with a solid content of 16-20%.

[0022] A second aspect of the present invention provides a method for preparing the foamed concrete described in the first aspect of the present invention, comprising the following steps:

[0023] The foamed concrete is prepared by mixing cementitious materials, water, water-repellent agent and early-strength agent, and then mixing with foaming agent.

[0024] A third aspect of the present invention provides a sound-absorbing structure, including a PC board frame and a perforated plate disposed on the PC board frame; the PC board frame is provided with concrete material; the concrete material is formed by curing the foamed concrete.

[0025] In some embodiments of the present invention, the sound-absorbing structure further includes a cavity.

[0026] In some embodiments of the present invention, the thickness of the perforated plate is 2-3 mm, the aperture is 7-10 mm, and the perforation rate is 10%-15%.

[0027] In some embodiments of the present invention, the thickness of the concrete material is 3 to 7 cm.

[0028] In some embodiments of the present invention, the sound-absorbing structure is a low sound-absorbing wall.

[0029] The fourth aspect of the present invention provides the application 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 sound absorption in rail transit or in the field of sound absorption in buildings.

[0030] The beneficial effects of this invention are: by adjusting the ratio of cementitious materials, water-repellent agents, and foaming agents, the pore structure of the foamed concrete in this invention can be controlled, resulting in low-cost foamed concrete with excellent low-frequency sound absorption performance. After hardening, large pores with a diameter greater than 1500 μm occupying 60% to 85% of the cross-sectional area are formed inside the foamed concrete, which increases the multiple refractions and energy dissipation during the sound wave transmission process, thereby improving its low-frequency sound absorption coefficient.

[0031] Furthermore, the sound-absorbing low wall in this invention contains perforated panels and concrete material made of foamed concrete, which has a good sound absorption effect over a wide frequency range, especially in the low frequency range, where it has a better sound absorption effect than existing foamed concrete. Attached Figure Description

[0032] Figure 1 This is a three-dimensional schematic diagram of the sound-absorbing low wall in Example 4.

[0033] Figure 2 for Figure 1 A schematic diagram of the cross-section after being cut along direction II.

[0034] Figure 3 This is a side view of the sound-absorbing low wall in Example 4.

[0035] Figure 4 This is a top view of the sound-absorbing low wall in Example 4.

[0036] Figure 5 The graphs show the sound absorption coefficient test results of the foamed concrete in Examples 1-3 and Comparative Example 1.

[0037] Figure label:

[0038] 1. Perforated board; 2. Concrete material; 3. PC board frame; 4. Rubber pad. Detailed Implementation

[0039] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0040] In some embodiments of the present invention, a foamed concrete is provided, which is made from the following raw materials: cementitious material, water, foaming agent, water-repellent agent and early-strength agent; the mass ratio of cementitious material to water is 1:(0.4~0.8); the mass ratio of cementitious material to foaming agent is 1:(0.0005~0.0009); the mass ratio of cementitious material to water-repellent agent is 1:(0.01~0.03); the mass ratio of cementitious material to early-strength agent is 1:(0.001~0.003).

[0041] The foamed concrete of this invention can control the curing time of the cementitious material by adjusting the ratio of cementitious material, water, foaming agent, water-repellent agent and early strength agent. This allows the solidified foamed concrete to form large pores with a diameter greater than 1500 μm, occupying 60% to 85% of the cross-sectional area. This results in low-cost foamed concrete with excellent low-frequency sound absorption performance, making it an excellent filling material for developing near-rail sound-absorbing low walls.

[0042] Existing foamed concrete has pore sizes much smaller than 1500 μm, and its sound absorption frequency range is mainly concentrated in the high frequency range, making it unable to achieve efficient sound absorption in the low frequency range of 400~800 Hz. Furthermore, a technical challenge encountered in developing the foamed concrete of this invention is how to form a stable macroporous structure, especially preventing the rupture of small pores during the merging of macropores, thus allowing the macroporous structure in the concrete to solidify and be preserved. This invention solves the above technical problems by controlling the types and proportions of cementitious materials, foaming agents, water-repellent agents, and early-strength agents, enabling the cured concrete to retain a large number of structurally stable macroporous structures with diameters greater than 1500 μm.

[0043] In some embodiments of the present invention, the foamed concrete has a porous structure.

[0044] 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 or a range formed by any two of the following: 400 μm, 438 μm, 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, 1000 μm, 1100 μm, 1164 μm, 1200 μm, 1300 μm, 1400 μm, 1500 μm, 1600 μm, 1700 μm, 1745 μm, and 1800 μm.

[0045] In some embodiments of the present invention, the cross-sectional area of ​​the foamed concrete is S. 截面 The total area of ​​the holes in foamed concrete is denoted as S. 孔 S 孔 / S 截面 It is 60-85%, for example, S 孔 / S 截面 The range of values ​​is any one of the following: 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 any combination thereof.

[0046] In some embodiments of the present invention, the mass ratio of the cementitious material to water can be any value of 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8 or a range of both.

[0047] In some embodiments of the present invention, the mass ratio of the cementitious material to the foaming agent is 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, or 1:0.00068. The range of any one of the following values, or any two of them: 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.

[0048] In some embodiments of the present invention, the mass ratio of the cementitious material to the water-repellent agent is any one of 1:0.01, 1:0.02, 1:0.03, or a range of both. In some embodiments of the present invention, the mass ratio of the cementitious material to the early-strength agent is any one of 1:0.001, 1:0.002, 1:0.003, or a range of both.

[0049] In some embodiments of the present invention, the cementing material includes cement and supplementary cementing material; the supplementary cementing material is selected from at least one of fly ash, slag, and volcanic ash.

[0050] In some embodiments of the present invention, the fly ash is Grade I ash, Grade II ash, or Grade F ash.

[0051] 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%.

[0052] In some embodiments of the present invention, the mass ratio of cement to supplementary cementitious material is 1:(0.1~5); in some embodiments of the present invention, the mass ratio of cement to supplementary cementitious material is any value or a range of any two of the following: 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. The present invention uses supplementary cementitious material and an early-strength agent to regulate the setting time of the cementitious material system, and uses a water-repellent agent to regulate the stability of foam aggregation. Based on the adaptability of these two agents, a large-pore foam structure with a diameter greater than 1500 μm occupying 60%~85% of the cross-sectional area is modulated, resulting in low-cost foamed concrete with excellent low-frequency sound absorption performance.

[0053] In some embodiments of the present invention, the cement is silicate 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.

[0054] In some embodiments of the present invention, the hydrophobic agent includes at least one of potassium methylsilicate solution and potassium methylenesilicate solution. In some embodiments of the present invention, the hydrophobic agent is potassium methylsilicate and / or potassium methylenesilicate solution, and the solid content of the hydrophobic agent is 30-40%.

[0055] In some embodiments of the present invention, the early strength agent includes sodium nitrate.

[0056] In some embodiments of the present invention, the settling distance of the foaming agent over 1 hour is 6-8 mm; in some embodiments of the present invention, the settling distance of the foaming agent over 1 hour is any value of 6 mm, 7 mm, 8 mm or a range formed by any two of them.

[0057] In some embodiments of the present invention, the amount of water exuded by the foaming agent in 1 hour is 63-75 mL; in some embodiments of the present invention, the amount of water exuded by the foaming agent in 1 hour is any value or a range formed by any two of the following: 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.

[0058] In some embodiments of the present invention, the foaming agent is prepared by diluting a 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 ratio can be any value or a range formed by any combination of 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 times. In some embodiments of the present invention, the foaming ratio can be any value or a range formed by any combination of 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, and 80 times.

[0059] In some embodiments of the present invention, the foaming agent is a sodium fatty alcohol polyoxyethylene ether sulfate solution with a solid content of 16-20%. In some embodiments of the present invention, the solid content can be any value of 16%, 17%, 18%, 19%, 20%, or a range formed by any combination of both.

[0060] In some embodiments of the present invention, the foaming agent needs to be used within 20 to 40 seconds after it is prepared.

[0061] In some embodiments of the present invention, the present invention provides a method for preparing the above-mentioned foamed concrete, comprising the following steps:

[0062] Foamed concrete is prepared by mixing cementitious materials, water, water-repellent agent and early-strength agent, and then mixing with foaming agent.

[0063] In some embodiments of the present invention, mixing is performed by stirring.

[0064] In some embodiments of the present invention, the stirring rate is 140-160 rpm.

[0065] In some embodiments of the present invention, the mixing time is 3 to 10 minutes.

[0066] In some embodiments of the present invention, a sound-absorbing structure is also provided, including a PC board frame 3 and a perforated plate 1 disposed on the PC board frame 3. The PC board frame 3 contains concrete material 2, which is formed by curing the aforementioned foamed concrete. The PC board frame 3 is cuboid in shape and has a cuboid cavity filled with the aforementioned foamed concrete. The perforated plate 1 is disposed on the PC board frame 3 and is located on the sound-receiving surface.

[0067] This invention utilizes a PC board frame 3 composed of PC boards, with a perforated plate 1 on the sound-receiving surface, and the interior of the PC board frame 3 filled with concrete material 2. For example, if the sound-receiving surface of the PC board frame 3 is a perforated plate 1 filled with the aforementioned foamed concrete material, the resulting sound-absorbing structure exhibits good sound absorption performance at both high and low frequencies, with a wide sound absorption range.

[0068] In some embodiments of the present invention, a rubber pad 4 is provided on the inner wall of the PC board frame 3.

[0069] In some embodiments of the present invention, curing refers to curing the foamed concrete after it has been injected.

[0070] In some embodiments of the present invention, the sound-absorbing structure further includes a cavity.

[0071] In some embodiments of the present invention, the thickness of the perforated plate 1 is 2-3 mm, the hole diameter is 7-10 mm, and the perforation rate is 10%-15%.

[0072] In some embodiments of the present invention, the thickness of the concrete material 2 is 3 to 7 cm.

[0073] In some embodiments of the present invention, the shape of the sound-absorbing structure can be at least one of I-shape, L-shape, Y-shape, T-shape, cuboid shape, and cube shape.

[0074] In some embodiments of the present invention, the sound-absorbing structure is a low sound-absorbing wall.

[0075] The sound-absorbing structure of this invention, through the combined use of perforated plates, foamed concrete, and optionally designed cavities, and by optimizing the thickness, pore size, perforation rate of the perforated plates, the molding shape of the foamed concrete, the cavity position, and the overall shape of the assembled structure, achieves a near-rail foamed concrete sound-absorbing structure with high sound absorption coefficient and wide-bandwidth sound absorption performance at low frequencies. It boasts advantages such as low carbon footprint, environmental friendliness, low cost, simple production and construction processes, excellent low-frequency sound absorption performance, and a narrow but adjustable sound absorption bandwidth, making it suitable for use as a near-rail sound-absorbing low wall. By combining perforated plates, foamed concrete, and cavities, the sound-absorbing structure of this invention incorporates impedance matching and Helmholtz resonance sound absorption principles, reducing the resonant frequency and broadening the sound absorption bandwidth. Furthermore, by optimizing the internal / external shape of the sound-absorbing structure, it improves the multiple reflections and refraction losses of sound waves, further enhancing low-frequency sound absorption performance.

[0076] The sound absorption principle of the sound-absorbing structure in this invention is as follows: 1) The selection of the thickness, pore size, and perforation rate of the perforated plate is mainly based on the matching of its acoustic impedance with the air acoustic impedance. Through resonance and air resistance, some sound wave energy is consumed; 2) As a porous material, foamed concrete causes sound waves to strike its irregular surface, resulting in scattering. The pores and pore walls also cause multiple reflections and refractions of sound waves, which in turn causes sound waves to propagate and dissipate multiple times within the material. Compared with the cavity-perforated plate combination, the use of foamed concrete increases the acoustic impedance of the composite sound-absorbing structure. Compared with the traditional small-pore foamed concrete-perforated plate combination, the sound absorption mechanism of the sound-absorbing structure in this invention is no longer just resonance, but also includes multiple reflections and refractions of sound waves caused by large-pore foamed concrete and frictional loss, thereby improving the sound absorption coefficient of the sound-absorbing structure at low frequencies; 3) By designing the internal or external molding shape of the sound-absorbing structure, foamed concrete can be poured in the form of flat plates, concave and convex shapes, wedges, and U-shapes, and the assembly structure shape 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-absorbing structure can be further improved.

[0077] Example 1

[0078] This example provides a foamed concrete, which is made from the following raw materials in parts by weight: 1 part cement, 0.25 parts slag, 0.75 parts water, 0.025 parts potassium methylsilicate solution, 0.00075 parts foaming agent, and 0.0021 parts early strength agent.

[0079] The cement used is P·O42.5R cement, which is an early-strength ordinary Portland cement with a 28-day strength greater than 42.5 MPa. The cement and slag are used together as a binder.

[0080] The solid content (i.e., the mass percentage of potassium methylsilicate) of the potassium methylsilicate solution is 38%, and the solvent is water. It is used as a water-repellent agent to adjust the pore structure of foamed concrete.

[0081] The foaming agent is a sodium fatty alcohol polyoxyethylene ether sulfate solution, with sodium fatty alcohol polyoxyethylene ether sulfate as the active ingredient. Its solid content is 16%, and it is obtained by diluting it 25 times with water and then foaming it using a foaming machine. The foam has a water exudation volume of 74 mL after 1 hour, a settling distance of 6 mm, and a foaming ratio of 73.42.

[0082] The early strength agent is sodium nitrate.

[0083] The foamed concrete in this example was prepared using a method that includes the following steps:

[0084] First, mix cement and slag for 1 minute. Then, add water, early strength agent and potassium methylsilicate solution and stir at 140 rpm for 5 minutes. Pause, dilute sodium fatty alcohol polyoxyethylene ether sulfate solution with water 25 times and add it to the foaming machine to obtain foam. Then, add foaming agent with a preparation time of no more than 30 seconds and continue stirring at 140 rpm for 5 minutes to obtain foamed concrete in this example.

[0085] The foamed concrete prepared in this example was poured into a mold, then cured in a standard curing chamber (temperature 20±1℃, humidity ≥95%) for 72 hours before demolding. After that, it was placed in the air (temperature 20±2℃) for natural curing until the specified age before testing.

[0086] Example 2

[0087] The only difference between the foamed concrete in this example and that in Example 1 is that the same mass of fly ash is used instead of the slag in Example 1.

[0088] Example 3

[0089] The only difference between the foamed concrete in this example and Example 1 is that all the cementitious materials used are cement, meaning that slag is not used in this example.

[0090] Comparative Example 1

[0091] The only difference between the foamed concrete in this example and Example 1 is that all the cementitious materials used are cement, and no potassium methylsilicate or sodium nitrate is added.

[0092] Example 4

[0093] This example provides a foamed concrete sound-absorbing low wall. The sound-absorbing low wall in this example is rectangular, with an external length of 120 cm, a width of 25 cm, and a height of 7.2 cm. The structure consists of a PC board frame 3, a perforated plate 1, and concrete material 2. The perforated plate 1, with a perforation rate of 11%~12%, is placed on top of the PC board frame 3. The interior of the PC board frame 3 is filled with the foamed concrete described in Example 3, which, after curing, forms concrete material 2. The thickness of concrete material 2 is 6.5 cm. The perforated plate 1 is 2 mm thick with a 7 mm aperture. A 2 mm thick rubber pad 4 is placed at the bottom of the PC board frame 3, and a 5 mm thick rubber pad 4 is wrapped around one side of the PC board frame 3 to reduce vibration damage. The PC board frame 3 is composed of 3 mm thick PC boards. A 10 cm long, 5 mm thick rubber pad 4 extends from the PC board frame 3 to facilitate the assembly of the low walls. A three-dimensional view of the sound-absorbing low wall in this example is shown below. Figure 1 As shown, along the three-dimensional Figure 1 The cross-sectional diagram of II in the figure is as follows Figure 2 As shown, the side view is as follows Figure 3 As shown, the top view is as follows Figure 4 As shown.

[0094] The foamed concrete sound-absorbing low wall in this example is prepared using a method that includes the following steps:

[0095] The foamed concrete prepared in Example 3 was injected into the sound-absorbing low wall mold (i.e., the mold formed by the PC board frame 3 and the perforated plate 1). After curing in a standard curing chamber (temperature 20±1℃, humidity ≥95%) for 72 hours, it was demolded and then placed in the air (temperature 20±2℃) for natural curing until the specified age before testing.

[0096] Comparative Example 2

[0097] The only difference between the sound-absorbing low wall in this example and that in Example 4 is that asbestos fibers are filled in the PC board frame 3 in this example.

[0098] Performance testing

[0099] The flowability of the foamed concrete in Examples 1-3 and Comparative Example 1 was tested, as were the dry density, peak sound absorption coefficient, sound absorption bandwidth, and compressive strength of the concrete specimens made from the foamed concrete in Examples 1-3 and Comparative Example 1. The compressive strength of the foamed concrete was tested according to ASTM C869-2020, "Test of Compressive Strength of Precast Foamed Concrete". Specimens were prepared as 100 mm × 100 mm × 100 mm standard cubes and tested using a 50 kN universal testing machine (UTM) under axial compressive loading conditions at a constant load rate of 0.1 kN / s (corresponding to a stress rate of 0.01 MPa / s, based on a specimen cross-sectional area of ​​10000 mm²). 2 (Conversion), loading continued until the specimen failed. The final compressive strength of each group of foamed concrete was taken as the average of three parallel specimens. The specific test results are shown in Table 1 below.

[0100] The specific testing methods for sound absorption coefficient and dry density are as follows: The foamed concrete from Examples 1-3 and Comparative Example 1 was poured into cylindrical models with a diameter of 10 cm and a height of 5 cm. After curing in a standard curing chamber (temperature 20±1℃, humidity ≥95%) for 72 hours, the models were demolded and then naturally cured in air (20±2℃) for 7 days before testing. The surface of the specimens was then polished to a thickness of 6 cm. Surface residue was removed using a fan and water flow, and the specimens were dried. The dry density was recorded. The sound absorption coefficient of the foamed concrete was tested using a B&K impedance tube testing system (vertical incident sound absorption coefficient testing device) based on JGJ-T341-2014. The specific test results are shown in Table 1 below, where the sound absorption bandwidth is defined as a sound absorption coefficient higher than 0.65. The sound absorption coefficient curve is shown in Table 1 below. Figure 5 As shown.

[0101] Table 1 Performance data of foamed concrete in Examples 1-3 and Comparative Example 1

[0102]

[0103] As shown in Table 1, the foamed concrete in Examples 1-3, with comparable fluidity and dry density to Comparative Example 1, exhibited a significantly longer gel time. This facilitates the merging of small pores into large pores, reducing the absorption frequency corresponding to the peak sound absorption coefficient from 1594 Hz to 600-696 Hz. Furthermore, the bandwidth corresponding to a sound absorption coefficient > 0.65 significantly increased, while maintaining compressive strength comparable to Comparative Example 1. Based on this, the combined use of potassium methylsilicate hydrophobic agent, sodium fatty alcohol polyoxyethylene ether sulfate foaming agent, sodium silicate early-strength agent, and gelling material can yield foamed concrete with high fluidity, simple construction process, lightweight, low carbon content, and high sound absorption, exhibiting good low-frequency sound absorption and a wide absorption spectrum.

[0104] The porosity and average pore diameter of the foamed concrete in Examples 1-3 and Comparative Example 1 were tested. The specific testing method was as follows: Samples were taken from specimens cured in a 20 ℃, 95% humidity curing chamber for 7 days, at a distance of 2-3 cm from the specimen surface. Undamaged areas of the samples were photographed using an optical microscope at a magnification of 35x. Pores were identified using image processing software, and the percentage of pore area to cross-sectional area was calculated. The porosity is the ratio of pore area to total area. The average pore diameter was calculated as the Feret's diameter of all pores, i.e., 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 testing and calculation methods are shown in Table 2 below.

[0105] Table 2 Porosity and average pore size of foamed concrete

[0106]

[0107] As shown in Table 2, the average pore size of the foamed concrete in Examples 1-3 of this invention is 400-1800 μm, and the porosity is greater than 75%, which is much higher than the average pore size and porosity in Comparative Example 1. In Example 3, there are a large number of macropores with diameters greater than 1500 μm and a large number of micropores; therefore, the average pore size of Example 3 is 438 μm. After hardening, the foamed concrete in Examples 1-3 forms macropores with diameters greater than 1500 μm occupying 68%-82% of its cross-sectional area, increasing the multiple refractions and energy dissipation during sound wave transmission, thereby improving the low-frequency sound absorption coefficient.

[0108] Sound absorption experiments were conducted on the sound-absorbing walls in Example 4 and Comparative Example 2, respectively. The specific testing method was as follows: the sound-absorbing walls in Example 4 and Comparative Example 2 were placed in an anechoic chamber, and their equivalent and maximum sound pressure levels under a howling sound source (frequency from 400 Hz to 2500 Hz) were recorded using a sound level meter. Simultaneously, the equivalent and maximum sound pressure levels were also measured without the sound-absorbing walls (i.e., no sound-absorbing walls). The sound absorption experimental results obtained according to this testing method are shown in Table 3 below.

[0109] Table 3. Sound Absorption Laboratory Test Results

[0110]

[0111] As shown in Table 3, compared with the sound-absorbing wall filled with asbestos fiber in Comparative Example 2, the equivalent sound pressure level LAeq of the foam concrete-filled sound-absorbing wall in Example 4 is reduced by 1.2 dB; the maximum sound pressure level LAmax is reduced by 1.9 dB, and there is a noise reduction effect of 1-2 dB in the frequency band from 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 wall will continue to be greatly improved.

[0112] In summary, the foamed concrete of this invention can control the pore structure of the foamed concrete by adjusting the proportions of cementitious materials, water-repellent agents, early-strength agents and foaming agents, thereby obtaining low-cost foamed concrete with excellent low-frequency sound absorption performance. The hardened foamed concrete forms large pores with a diameter greater than 1500 μm, occupying 60% to 85% of the cross-sectional area, to increase the multiple refractions and energy dissipation during the sound wave transmission process, thereby improving its low-frequency sound absorption coefficient. The mechanism for forming this special pore structure is: (1) The use of supplementary cementitious materials such as fly ash, slag, and volcanic ash can prolong the setting time of cement, providing time for small foams to merge into large foams; (2) Methyl / methylene potassium silicate water-repellent agents reduce the surface tension of cement paste by using hydrophobic groups, improve the hydrophobicity of the liquid film, and reduce the viscosity of the paste, thereby making it easier for bubbles to form and exist stably during the merging process; In addition, methyl / methylene potassium silicate water-repellent agents can also delay the hydration reaction and reduce the Ca produced in the early stage of hydration. 2+ 3) The early-strength agent can work together with supplementary cementitious materials such as fly ash, slag, and volcanic ash, as well as water-repellent agents, to adjust the setting time of cement to match the merging and stabilization time of foam, thereby obtaining a stable macroporous structure suitable for low-frequency sound absorption; when sound propagates into the macroporous pores, friction consumes more sound energy, thus absorbing sound. In addition, the sound-absorbing low wall filled with foamed concrete in this invention has a noise reduction effect of 1-2 dB in the frequency band from 400 Hz to 2500 Hz, further demonstrating that the foamed concrete in this invention has excellent sound absorption effect.

[0113] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A type of foamed concrete, characterized in that: It is prepared from the following raw materials: cementitious material, water, foaming agent, water-repellent agent, and early-strength agent; the mass ratio of cementitious material to water is 1:(0.4~0.8); the mass ratio of cementitious material to foaming agent is 1:(0.0005~0.0009); the mass ratio of cementitious material to water-repellent agent is 1:(0.01~0.03); the mass ratio of cementitious material to early-strength agent is 1:(0.001~0.003). The cementitious material includes cement and supplementary cementitious material; the supplementary cementitious material is selected from at least one of fly ash, slag, and pozzolanic material. The water-repellent agent includes at least one of potassium methylsilicate solution and potassium methylenesilicate solution; The early strength agent is sodium nitrate; The foaming agent is prepared by diluting a foaming agent with water by 20 to 30 times and then foaming it by 70 to 80 times using a foaming machine. The foaming agent is a sodium fatty alcohol polyoxyethylene ether sulfate solution with a solid content of 16-20%. The foamed concrete has a porous structure with an average pore diameter of 438~1800 μm; In the foamed concrete, the area of ​​pores with a diameter greater than 1500μm accounts for 60~85% of the cross-sectional area of ​​the foamed concrete.

2. The foamed concrete according to claim 1, characterized in that: The cement is silicate cement.

3. The foamed concrete according to claim 1, characterized in that: The foaming agent has at least one of the following characteristics: (a) The settling distance of the foaming agent after 1 hour is 6~8 mm; (b) The amount of water exuded by the foaming agent in 1 hour is 63~75 mL.

4. The method for preparing foamed concrete according to any one of claims 1 to 3, characterized in that: Includes the following steps: The foamed concrete is prepared by mixing cementitious materials, water, water-repellent agent and early-strength agent, and then mixing with foaming agent.

5. A sound-absorbing structure, characterized in that: It includes a PC board frame and a perforated plate disposed on the PC board frame; the PC board frame is filled with concrete material; the concrete material is formed by curing the foamed concrete as described in any one of claims 1 to 3.

6. The sound-absorbing structure according to claim 5, characterized in that: The sound-absorbing structure also contains a cavity; And / or, the thickness of the perforated plate is 2~3 mm, the aperture is 7~10 mm, and the perforation rate is 10%~15%; And / or, the thickness of the concrete material is 3 to 7 cm.

7. The application of the foamed concrete according to any one of claims 1 to 3 or the sound-absorbing structure according to any one of claims 5 to 6 in the field of sound absorption in rail transit or building.

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