Composite red mud foamed concrete, preparation method and application thereof

Abstract

The application discloses a composite red mud foamed concrete and a preparation method and application thereof, and relates to the technical field of environmental protection. The composite red mud foamed concrete comprises red mud and fly ash as main aggregates, cement as a main cementing material, 30% hydrogen peroxide as a foaming agent, calcium stearate as a foam stabilizer, 80% phosphoric acid as an activator, polyacrylamide as a water reducing agent, a coagulation accelerator and fiber filaments as auxiliary materials. Compared with traditional foamed concrete, the foamed concrete prepared by using red mud and fly ash as main aggregates has the characteristics of low cost, good fire resistance, good heat preservation and sound insulation, etc. In addition to reducing the economic cost, the foamed concrete also changes the solid waste (red mud) which cannot be utilized in large quantities into valuable resources, reduces the waste of non-renewable resources, relieves the pressure of resource shortage, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a composite red mud foamed concrete, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Foamed concrete, due to its porous structure, is lightweight and high-strength, which can reduce the structural self-weight, decrease the foundation load, save on steel reinforcement and concrete usage, and lower the overall cost. However, it also has some inherent drawbacks, including: the strength decreases significantly as the density decreases; and the stability of the foam, the compatibility of the foaming agent and cement during the preparation process have a significant impact on the quality of the finished product.

[0004] Red mud is a polluting waste residue discharged during the extraction of alumina in the aluminum industry. It is named for its red color due to the high iron oxide content. The amount of red mud generated varies depending on the ore, production process, and technical parameters, but in most cases, 1 to 1.8 tons of red mud are produced for every 1 ton of alumina produced. As an industrial solid waste generated during the alumina refining process from bauxite, red mud has become a global environmental problem due to its strong alkalinity, high salinity, and complex composition. Currently, damming and stockpiling is the main method of red mud disposal. This not only requires a large amount of land resources, but its strong alkalinity and the soluble sodium salts it contains also lead to serious ecological problems such as soil alkalization and groundwater pollution in the stockpiling area and surrounding areas.

[0005] Red mud is a porous material with a large internal surface area and a density of 2840–2870 kg / m³. 3 Red mud has a water content of 86.01%–89.97%, a saturation of 94.4%–99.1%, a water holding capacity of 79.03%–93.23%, a plasticity index of 17.0–30.0, a particle diameter of 0.088–0.25 mm, a bulk density of 0.8–1.0, and a melting point of 1200–1250℃. Due to its large specific surface area, numerous pore structures, and high plasticity, red mud can be used to produce porous lightweight ceramsite. However, existing red mud-based foamed concrete uses red mud instead of cement as a binder, which easily leads to lower concrete strength and consistency. Furthermore, the lack of aggregate within the concrete makes it prone to cracking and damage under excessive pressure.

[0006] Existing technologies disclose the dealkalization of red mud using calcium chloride waste liquid, reducing the alkali content to meet the requirements of concrete use. Adding fly ash, gypsum gel, and cement clinker replenishes the red mud, increasing the concrete's strength and facilitating the bonding of various materials. Adding a gypsum activator activates the gypsum gel material, enhancing its performance. This addresses the problems of existing red mud-based foamed concrete, where red mud is used instead of cement as a gelling agent, leading to lower strength and consistency, and the lack of fine sand (1-4mm diameter) within the concrete, making it prone to cracking under excessive pressure. However, this method requires adding large amounts of calcium chloride and gypsum for red mud dealkalization. Cement has a high tricalcium aluminate content, and excessive gypsum reacts to form large amounts of ettringite (AFt). While a suitable amount of ettringite contributes to early strength, the continuous formation of ettringite later causes volume expansion, leading to microcracks within the foamed concrete, and even specimen disintegration or decreased long-term durability. Furthermore, gypsum itself has low strength and poor water resistance. On the one hand, excessive addition will reduce the overall skeletal strength of the hardened paste; on the other hand, in a humid environment, unreacted dihydrate gypsum may dissolve or transform into other forms, leading to increased porosity and a significant decrease in compressive strength (i.e., the "strength reversal" phenomenon). When gypsum and calcium chloride are present simultaneously, one acts as a retarder and the other as an accelerator, and even small fluctuations in their ratio can cause significant differences in setting time, resulting in substantial differences in the compressive strength of foamed concrete. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a composite red mud foamed concrete, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a composite red mud foamed concrete, which uses red mud and fly ash as the main aggregates, cement as the main binding material, 30% hydrogen peroxide as the foaming agent, calcium stearate as the foam stabilizer, phosphoric acid with a concentration of more than 80% as the activator, polyacrylamide as the water reducing agent, accelerator and fiber as auxiliary materials, and sodium aluminate as the accelerator.

[0009] In this invention, the accelerator is sodium aluminate, the main purpose of which is to improve the overall performance of concrete; the fiber is polypropylene fiber, the main purpose of which is to prevent concrete from cracking.

[0010] In some embodiments of the present invention, the mixture includes 150-200 parts of red mud, 200-230 parts of fly ash, 400-460 parts of cement, 2-5 parts of foam stabilizer, 1.5-2.5 parts of fiber, 5-9 parts of foaming agent, 1.75-2.25 parts of activator, 2.1-2.9 parts of coagulant, and 0.95-1.15 parts of water-reducing agent.

[0011] Preferably, the masterbatch ratio of cement, red mud, and fly ash is 2:0.4:1 to 2:0.8:1, with 2:0.8:1 being more preferred. The water-cement ratio is 0.4 to 0.6.

[0012] Preferably, the foaming agent is 5-6 parts and the foam stabilizer is 3-5 parts.

[0013] In some embodiments of the present invention, the mixture includes 172 parts of red mud, 215 parts of 100-mesh fly ash, 430 parts of cement, a water-cement ratio of 0.55, 2-5 parts of foam stabilizer, 1.5-2.5 parts of fiber, 5-9 parts of foaming agent, 2 parts of activator, 2.58 parts of coagulant, and 1.05 parts of water-reducing agent.

[0014] Secondly, the present invention provides a method for preparing composite red mud foamed concrete, comprising the following steps: S1: Grind the cement, red mud, and fly ash separately and then sieve them for later use; S2: Take the sieved red mud, fly ash, cement, foam stabilizer, fiber and other dry materials and mix them evenly. Then add water and stir. Add activator, accelerator and water reducer and continue stirring. Finally add foaming agent. Stir immediately after adding foaming agent and then pour in place or pour into mold. S3: Curing begins after the cast-in-place construction or injection into the mold.

[0015] In step S1, the red mud particle size is 18~200 mesh, more preferably 18 mesh.

[0016] In step S1, the fly ash particle size is 60~200 mesh, preferably 100 mesh.

[0017] In step S1, the ground cement is passed through a 60-mesh sieve for later use, the red mud is passed through an 18-mesh sieve for later use, and the fly ash is passed through a 100-mesh sieve for later use.

[0018] In step S2, the water-aggregate mass ratio is 0.4~0.6, preferably 0.55, which is the ratio of water to the mass of aggregate containing cement, red mud, and fly ash. The selection of the water-cement ratio needs to take into account both fluidity and strength: if the water-cement ratio is too low (<0.4), the slurry consistency will be too high, making foaming difficult; if the water-cement ratio is too high (>0.6), the slurry will be too thin, the air bubbles will easily float and merge, and the strength will decrease.

[0019] In step S2, after adding the activator and coagulant, the activator reacts preferentially with the fly ash, thereby avoiding the premature decomposition of hydrogen peroxide caused by the reaction between the activator and hydrogen peroxide.

[0020] Adding phosphoric acid at a concentration of 80% or higher can enhance the activity of fly ash, thereby increasing the compressive strength of foamed concrete. When the phosphoric acid concentration is below 80%, the excessive moisture content not only reduces the activation effect but also dilutes the system, hindering strength development.

[0021] In step S2, the dry materials are stirred for 5 minutes to mix evenly; after adding water, a mixer is used to stir at a speed of 1000 r / min for 3 minutes; after adding the activator and foaming agent, the mixture is stirred for 8 seconds immediately before on-site pouring or injection into a mold. In some embodiments of the present invention, it has been found that the control of stirring time is crucial: if the stirring time is too short (<5 seconds), the foaming agent is unevenly distributed; if the stirring time is too long (>12 seconds), the generated bubbles are mechanically sheared and destroyed, resulting in increased pore size and uneven distribution.

[0022] In step S3, the foamed concrete is cured for 28 days using the standard industrial production curing method in the construction industry. The curing method and time for the foamed concrete in S3 are natural curing, placing it in a cool, dry place and regularly spraying it with water.

[0023] The solution provided by this invention does not contain gypsum or calcium chloride, resulting in more uniform foaming and lower cost. It consumes as much red mud as possible while ensuring the performance of concrete.

[0024] To achieve uniform pores, this invention uses a foam stabilizer and controls the stirring speed and time. After adding the foaming agent, the speed is adjusted to 1000 r / min, and the mixture is immediately poured into the mold after stirring for 8 seconds.

[0025] The initial purpose of adding activators is to activate fly ash and thus improve the compressive strength of foamed concrete. In the experiment, the activators can improve the foaming height of foamed concrete to a certain extent, but the effect on compressive strength is not obvious.

[0026] In this invention, the accelerator is sodium aluminate, the main purpose of which is to improve the overall performance of concrete; the fiber is polypropylene fiber, the main purpose of which is to prevent concrete from cracking.

[0027] Compressive strength and pore size are the two main aspects of this invention. Uniform pore size is one of the advantages. The foam pore size is related to the compressive strength; dense and small pores result in higher compressive strength, while large and sparse pores result in lower compressive strength. The advantage of the foam pore size is that it can be controlled between 0.5mm and 1mm. This pore size range has a certain compensating effect on compressive strength and dry density.

[0028] Thirdly, the present invention provides the application of the composite red mud foamed concrete described in the first aspect in wall panels and roof panels.

[0029] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: This invention, from the perspective of saving production costs and reducing production processes, explores the feasibility of preparing industrially produced composite foamed concrete by comparing experiments with different amounts of fly ash, activators, and accelerators.

[0030] Existing technologies increase the strength of red mud by adding gypsum. However, research has shown that this method requires strict control of the amount of gypsum added; even slight deviations can lead to strength fluctuations. Furthermore, the poor compatibility between gypsum and red mud easily causes micro-cracks at the interface. Additionally, gypsum softens or even dissolves easily in humid environments, resulting in a significant decrease in long-term durability. The red mud foamed concrete provided by this invention abandons the gypsum system. Instead, it is based on the alkaline environment of red mud and the pozzolanic reaction of fly ash, forming a dense hydrated aluminosilicate network under the accelerating effect of sodium aluminate. This improves both early strength and enhances impermeability and corrosion resistance. Product testing showed that after 28 days of curing, the compressive strength of the sample reached 5.8 MPa, with a mass loss rate of less than 0.3%, fully meeting the application standards for non-load-bearing wall panels.

[0031] Meanwhile, the gypsum-free foamed concrete provided by this invention eliminates the need for waterproofing agents, avoiding the waterproofing requirements associated with gypsum and significantly reducing overall costs. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0033] Figure 1 The pore size of the completed sample was examined using an optical micrograph (magnified 20x), which showed that the pore size was distributed between 0.5 and 1.0 mm, and the bubbles were spherical and evenly distributed. Detailed Implementation

[0034] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] The present invention will be further described below with reference to the embodiments.

[0036] In some embodiments of the present invention, a composite red mud foamed concrete is provided, which uses red mud and fly ash as the main aggregates, cement as the main binder, 30% hydrogen peroxide as the foaming agent, calcium stearate as the foam stabilizer, phosphoric acid with a concentration of more than 80% as the activator, polyacrylamide as the water-reducing agent, accelerator and fiber as auxiliary materials, and sodium aluminate as the accelerator.

[0037] It should be noted that the red mud used in this invention is industrial waste generated during the Bayer process or sintering process for alumina production, and must be dried, crushed, and screened before use. The fly ash is Grade I or Grade II fly ash, and its glass content should not be less than 50% to ensure the full utilization of pozzolanic activity.

[0038] In this invention, the accelerator is sodium aluminate (NaAlO2), whose main purpose is to improve the overall performance of concrete and accelerate the hydration reaction process; the fiber is polypropylene fiber with a length of 6-12 mm and a diameter of 18-48 μm, whose main purpose is to prevent concrete from drying shrinkage cracking and improve crack resistance.

[0039] One of the innovations of this invention lies in the use of phosphoric acid with a concentration of over 80% as an activator. The introduction of phosphoric acid accelerates the depolymerization process of fly ash glass, increasing the dissolution rate of aluminosilicate species by 2 to 3 times. Simultaneously, phosphate ions (PO2)... 3- Phosphoric acid can react with calcium ions to form calcium phosphate minerals, which fill the pores and act as fine aggregates. However, the amount of phosphoric acid added needs to be strictly controlled: if the amount is too low (<1.75 parts), the activation effect is not obvious; if the amount is too high (>2.25 parts), the excess phosphoric acid will react excessively with calcium ions, consuming the calcium source required for cement hydration and thus reducing strength. The preferred range of 1.75 to 2.25 parts in this invention is the optimal range determined through a large number of orthogonal experiments.

[0040] In this invention, the addition of sodium aluminate has a dual effect: on the one hand, sodium aluminate can shorten the setting time, allowing bubbles to stabilize rapidly before the slurry initially sets; on the other hand, in the alkaline environment of red mud, the glassy structure of fly ash is oxidized by OH groups. - Ion erosion damages and releases active silicate and aluminate ions. These ions react with calcium ions in the red mud and calcium hydroxide produced during cement hydration to form hydrated calcium silicate (CSH gel) and hydrated calcium aluminate (CAH gel), which in turn react with AlO2 provided by sodium aluminate. - Further reaction generates hydrated calcium aluminosilicate (CASH gel), regulating the pore structure and making the pore size distribution more concentrated in the ideal range of 0.5–1.0 mm. When the amount of sodium aluminate added is 2.1–2.9 parts, the initial setting time of the slurry can be controlled within 15–25 minutes, which ensures the feasibility of the foaming operation and avoids bubble merging or collapse.

[0041] The JC / T 2475-2018 standard for foamed concrete wall panels and roof panels specifies the following physical and mechanical performance requirements for wall panel products: Dry density of interior wall panels ≤ 730 kg / m³. 3 Compressive strength ≥ 3.5 MPa, dry density of exterior wall panels ≤ 1030 kg / m³ 3 Compressive strength ≥ 5.0 MPa.

[0042] In this embodiment of the invention, during the compressive strength test, the sample is cut into 10mm×10mm×10mm cubes, and its compressive strength is tested.

[0043] Example 1 A composite red mud foamed concrete, the preparation method of which includes the following steps; S1: Grind cement, red mud, and fly ash into powder separately. After grinding, pass the cement through a 60-mesh sieve for later use, pass the red mud through an 18-mesh sieve for later use, and pass the fly ash through a 100-mesh sieve for later use. S2: Take 172 g of 18-mesh sieved red mud, 215 g of 100-mesh sieved fly ash, 430 g of cement, with a water-cement ratio of 0.55, 3 g of foam stabilizer, 2 g of fiber filaments (polypropylene fiber filaments, length 6-12 mm, diameter 18-48 μm), 6 g of foaming agent, and 2 g of activator. First, place the dry materials of cement, red mud, fly ash, foam stabilizer, and fiber filaments in a container and stir manually for about 5 minutes to mix them evenly. Then, add 450 g of tap water to the container and stir with a mixer at a speed of 1000 r / min for about 3 minutes. While stirring, add 80% phosphoric acid as an activator, 2.58 g of sodium aluminate as a coagulant, and 1.05 g of polyacrylamide as a water-reducing agent. After 1 minute, add 30% hydrogen peroxide as a foaming agent. Immediately after adding the foaming agent, increase the speed to 2000 r / min and stir for about 8 seconds. Pour into a 10×10×10 cm mold. S3: After injection into the mold, curing begins. The industrial production curing method of foamed concrete (JG / T 266-2011) construction industry standard is adopted. After the molded and demolded samples are labeled, they are placed in plastic bags and placed in a cool and ventilated place for curing. During the curing process, the samples are sprayed with water regularly. The compressive strength is tested after 7 days and 28 days of curing. S4: Cut the sample into 10mm×10mm×10mm cubes, place them on an electronic universal testing machine, and test their compressive strength.

[0044] Test results: At 28 days, the compressive strength was 6.30 MPa and the density was 0.63 g / cm³. 3 The aperture is 0.5 to 1.0 mm.

[0045] Example 2 Based on Example 1, the material addition amounts were adjusted. In step S2, 86 g of 18-mesh sieved red mud, 215 g of 100-mesh sieved fly ash, 430 g of cement, a water-cement ratio of 0.55, 3 g of foam stabilizer, 2 g of fiber filaments, 6 g of foaming agent, and 2 g of activator were taken. First, the dry materials of cement, red mud, fly ash, foam stabilizer, and fiber filaments were placed in a container and manually stirred for about 5 minutes to ensure uniform mixing. Then, 400 g of tap water was added to the container, and the mixture was stirred using a mixer at a speed of 1000 r / min for about 3 minutes. The other steps were the same as in Example 1.

[0046] At 28 days, the product's compressive strength was 9.73 MPa and its density was 0.87 g / cm³. 3 .

[0047] It is evident that when the mass ratio of cement, red mud, and fly ash is 2:0.4:1, the compressive strength can be significantly improved, but the density increases.

[0048] Example 3 In this embodiment of the invention, based on Example 1, the amount of materials added is adjusted. In step S2, 108 g of red mud, 215 g of 100-mesh fly ash, 430 g of cement, a water-cement ratio of 0.55, 2 g of foam stabilizer, 1.5 g of fiber, 8 g of foaming agent, and 2 g of activator are taken. First, the dry materials of cement, red mud, fly ash, foam stabilizer, and fiber are placed in a container and manually stirred for about 5 minutes to mix them evenly. Then, 415 g of tap water is added to the container, and a mixer is used to stir at a speed of 1000 r / min for about 3 minutes. Other steps are the same as in Example 1. At the same time, the performance test results of the product obtained by comparing different particle sizes of red mud particles are as follows: Table 3 Results of products with different red mud particle sizes

[0049] In this embodiment, compared with Examples 1 and 2, product No. 2 shows an increased amount of foaming agent, which effectively reduces the product density. While the compressive strength decreases somewhat, it still meets the standard compressive strength requirements for exterior wall panels. Based on this amount of foaming agent, other conditions are further adjusted, and the effects of different parameters are compared.

[0050] The results show that 18-mesh red mud has better performance, and its compressive strength and other parameters meet the standard requirements for external wall foamed concrete. At the same time, considering the cost, lower mesh count has lower energy consumption and lower cost.

[0051] Example 4 Based on Example 3, No. 2, different masterbatch ratios were adjusted, while other parameters and preparation processes remained unchanged. The performance test results of the obtained products are as follows: Table 4 Results of products with different masterbatch ratios

[0052] The results showed that as the proportion of red mud increased from 0.4 to 0.8, the density increased from 0.74 g / cm³. 3 Reduced to 0.56 g / cm³ 3 The 28-day compressive strength decreased from 9.33 MPa to 7.22 MPa. Despite the decrease in strength, the 28-day strength of all mix proportions was still higher than the 5.0 MPa required by the standard for exterior wall panels. The 2:0.8:1 mix ratio achieved the lowest density while meeting the strength requirements, making it more suitable for applications with high lightweighting requirements.

[0053] Example 5 Based on Example 3, No. 2, different water-cement ratios were adjusted while other parameters remained unchanged. The performance test results of the product are as follows: Table 5 Results of products with different water-cement ratios

[0054] The results showed that the highest foaming height (3.77 cm) and the 28-day compressive strength reached 5.46 MPa, indicating the best overall performance, were achieved at a water-cement ratio of 0.55. At a water-cement ratio of 0.4, the slurry was too thick, resulting in a foaming height of only 2.63 cm; at a water-cement ratio of 0.6, the slurry was too thin, leading to decreased bubble stability, an increase in pore size to 1 mm, and a slight decrease in strength.

[0055] Example 6 Based on Example 3, No. 2, different fly ash particle sizes were adjusted, while other parameters remained unchanged. The preparation process was the same as in Example 1, and the performance test results of the product are as follows: Table 6 Results of fly ash products with different particle sizes

[0056] Example 7 Based on Example 3, No. 2, the amount of activator added was adjusted, while other parameters remained unchanged. The preparation process was the same as in Example 1, and the performance test results of the product are as follows: Table 7 Results of products with different amounts of activator

[0057] Example 8 Based on Example 3, No. 2, the amount of fiber added was adjusted, while other parameters remained unchanged. The preparation process was the same as in Example 1, and the performance test results of the product are as follows: Table 8 Results of products with different fiber addition amounts

[0058] Example 9 Based on Example 3, No. 2, different amounts of foaming agent were added, while other parameters remained unchanged. The preparation process was the same as in Example 1, and the performance test results of the product are as follows: Table 9 Results of products with different foaming agent dosages

[0059] Example 10 Based on Example 3, No. 2, the amount of foam stabilizer added was adjusted, while other parameters remained unchanged. The preparation process was the same as in Example 1, and the performance test results of the product are as follows: Table 10 Results of products with different amounts of foam stabilizer added

[0060] Example 11 Based on Example 3, No. 2, and based on Example 1, different water temperatures were adjusted, and the product performance test results are as follows: Table 11 Results of products at different water temperatures

[0061] The results showed that the foaming effect was best and the compressive strength was highest when the water temperature was 30℃; when the water temperature exceeded 40℃, the hydrogen peroxide decomposed too quickly, causing the bubbles to merge or even the mold to collapse.

[0062] Example 12 Based on Example 1, the performance test results of the product after adding a foaming agent and stirring for different times are as follows: Table 13 Product Results for Different Stirring Times

[0063] Comparative Example The same preparation process as in Example 1 was used, except that sodium aluminate and 80% phosphoric acid activator were not added, and 40g of gypsum gel and 5g of gypsum activator were added.

[0064] Test case Durability test: In accordance with the provisions of GB / T 11969-2020 "Test Method for Performance of Autoclaved Aerated Concrete", the two groups of specimens (plaster-added group vs. non-plaster-added group) were subjected to wet-dry cycle test (65℃ drying + 20℃ immersion in water, 15 cycles) to test the wet-dry strength coefficient.

[0065] The experiment was conducted according to the dry-wet cycle test in GB / T 11969-2020 "Test Methods for Performance of Autoclaved Aerated Concrete" to simulate the natural environment of alternating rain erosion and intense sunlight exposure, and to verify the weather resistance of the material.

[0066] The experimental procedure was as follows: Samples were prepared from the products of Example 1 and Comparative Example 1, with three parallel samples for each product. A 100mm × 100mm × 100mm cubic sample and the parallel samples were placed together in an electric heating drying oven and dried at (60±5)℃ until constant weight. The axial dimensions of length, width, and height were measured with vernier calipers or digital calipers, accurate to 0.1mm. The parallel samples were sealed and placed indoors. The samples were cooled indoors at (20±5)℃ for 20 minutes, then placed in a wire mesh box (constant temperature water bath or tank) and immersed in water at (20±5)℃. The water level was 30mm above the upper surface of the sample. After maintaining this level for 5 minutes, the sample was removed and air-dried indoors for 30 minutes. It was then placed in an electric heating drying oven and dried at (60±5)℃ for 7 hours, followed by 20 minutes of cooling indoors, constituting one wet-dry cycle. This wet-dry cycle was repeated 15 times. When the test was interrupted, the samples should be dried and placed indoors to await the continuation of the test. After 15 wet-dry cycles, the specimens were dried to constant weight at (60±5)℃, removed, sealed, and cooled to room temperature. Tensile strength tests were then performed on the specimens and parallel specimens after the wet-dry cycles, and the average tensile strength of each group was calculated. The compressive strength loss rate was calculated, and the mass loss rate was recorded.

[0067] As a result, after 15 dry-wet cycles using the above method, the changes in each product are as follows:

[0068] Example 1: The specimen surface was basically intact with no visible cracks. After 15 cycles, the compressive strength loss rate was only 4%, and the mass loss rate was less than 1%, demonstrating good weather resistance.

[0069] Comparative Example 1: The specimens showed obvious peeling at the edges and corners, and fine network cracks were visible on the surface. After 30 cycles, the compressive strength loss rate was as high as 25%, and the mass loss rate was over 5%. Some specimens exhibited "mudification" and disintegration in the later stages of the cycles.

[0070] Conclusion: The above comparison shows that the introduction of gypsum exacerbates the performance degradation of red mud foamed concrete in alternating wet and dry environments. This is mainly because the ettringite formed by gypsum undergoes dissolution and recrystallization during repeated wet and dry processes, generating expansion stress, which leads to irreversible damage to the internal structure of the material, resulting in significantly poorer durability compared to red mud foamed concrete without gypsum.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite red mud foamed concrete, characterized in that, Red mud and fly ash are used as the main aggregates, cement as the main binder, 30% hydrogen peroxide as the foaming agent, calcium stearate as the foam stabilizer, phosphoric acid with a concentration of over 80% as the activator, polyacrylamide as the water-reducing agent, and accelerators and fiber filaments as auxiliary materials, with sodium aluminate as the accelerator.

2. The composite red mud foamed concrete according to claim 1, characterized in that, It includes 150-200 parts red mud, 200-230 parts fly ash, 400-460 parts cement, 2-5 parts foam stabilizer, 1.5-2.5 parts fiber, 5-9 parts foaming agent, 1.75-2.25 parts activator, 2.1-2.9 parts coagulant, and 0.95-1.15 parts water-reducing agent.

3. The composite red mud foamed concrete according to claim 1, characterized in that, The foaming agent is 5-6 parts; the foam stabilizer is 3-5 parts.

4. A method for preparing composite red mud foamed concrete, characterized in that, Includes the following steps: S1: Grind the cement, red mud, and fly ash separately and then sieve them for later use; S2: Take the sieved red mud, fly ash, cement, foam stabilizer, fiber and other dry materials and mix them evenly. Then add water and stir. Add activator and accelerator and continue stirring. Finally add foaming agent. Stir immediately after adding foaming agent and then pour in place or inject into mold. S3: Curing begins after the cast-in-place construction or injection into the mold.

5. The method for preparing composite red mud foamed concrete according to claim 4, characterized in that, In step S2, the red mud particle size is 18~200 mesh, more preferably 18 mesh.

6. The method for preparing composite red mud foamed concrete according to claim 4, characterized in that, In step S2, the fly ash particle size is 60~200 mesh, preferably 100 mesh.

7. The method for preparing composite red mud foamed concrete according to claim 4, characterized in that, In step S2, the water-aggregate mass ratio is 0.4~0.6, preferably 0.55; In step S2, the masterbatch ratio is 2:0.4:1 to 2:0.8:

1.

8. The method for preparing composite red mud foamed concrete according to claim 4, characterized in that, In step S2, the dry materials are mixed evenly for 5 minutes; after adding water, the mixture is stirred with a mixer at a speed of 1000 r / min for 3 minutes; after adding the activator and foaming agent, the mixture is stirred for 8 seconds before being poured on-site or injected into a mold.

9. The method for preparing composite red mud foamed concrete according to claim 4, characterized in that, The resulting product has an aperture range of 0.1~1mm.

10. The application of the composite red mud foamed concrete according to any one of claims 1 to 3 in wall panels and roof panels.

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