Mechanically activated kaolin-modified fly ash phosphate-based polymer and method of making same

Abstract

The application discloses a kind of mechanically activated kaolin modified fly ash phosphoric acid geopolymer and preparation method thereof, the geopolymer is made of the following weight parts of raw materials: fly ash 30~75 parts, mechanically activated kaolin 15~60 parts, red mud 8~40 parts, surface modifier 0.5~2 parts, acid activator 10~35 parts, solvent 10~35 parts.The application not only optimizes the performance of geopolymer, improves its early and final compressive strength, but also reduces the preparation cost, reduces energy consumption and environmental impact through the synergistic effect of red mud and mechanically activated kaolin, while providing a new way for resource utilization of fly ash and other industrial by-products.The geopolymer of the application is suitable for road construction, foundation reinforcement, environmental remediation and other civil engineering projects due to its excellent mechanical properties, excellent durability and environmental adaptability, and meets the needs of sustainable development.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and particularly relates to a mechanically activated kaolin-modified fly ash phosphoric acid base polymer and its preparation method. Background Technology

[0002] Geopolymers are cementing materials synthesized through chemical activation of precursor materials, and are widely used in civil engineering, such as road construction, foundation reinforcement, and environmental remediation. These materials are highly favored due to their excellent mechanical properties, superior durability, and environmental adaptability. Traditionally, geopolymer precursors are primarily metakaolinite, but with the demands of sustainable development, many experts and scholars have begun exploring the use of solid waste materials such as slag, granite powder, and coal gangue as alternatives. Although acid-activated geopolymers exhibit faster hardening speeds and better weather resistance than alkali-activated materials, fly ash-based acid-activated geopolymers still have shortcomings in early strength and preparation processes, limiting their widespread use in structural applications.

[0003] In current technology, although fly ash is rich in useful components such as silicates, aluminates, and iron oxides, and is theoretically suitable for producing geopolymers, acid-activated geopolymers based on fly ash often fail to meet engineering requirements due to insufficient mechanical strength. This is mainly because the acid activation process fails to effectively promote the full reaction of active components in fly ash and may cause inhomogeneity in the microstructure of the material. Summary of the Invention

[0004] The purpose of this invention is to propose a mechanically activated kaolin-modified fly ash phosphate-based polymer and its preparation method. While ensuring the large-scale consumption of bulk solid wastes such as fly ash and red mud, it increases the early strength, long-term strength, durability and economic efficiency of the polymer, and reduces the energy consumption and carbon emissions caused by calcining kaolin, making it more suitable for various civil engineering projects such as road construction, foundation reinforcement, and environmental remediation.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] In a first aspect, the present invention provides a mechanically activated kaolin-modified fly ash phosphoric acid base polymer, wherein the base polymer is made from the following raw materials in parts by weight: 30-75 parts fly ash, 15-60 parts mechanically activated kaolin, 8-40 parts red mud, 0.5-2 parts surface modifier, 10-35 parts acid activator, and 10-35 parts solvent.

[0007] In the above technical solutions, the surface modifier includes at least one of polyethylene glycol, hexadecyltrimethylammonium bromide, ethylenediaminetetraacetic acid, and ethoxysilane.

[0008] In the above technical solution, the preparation method of the mechanically activated kaolin is as follows:

[0009] Kaolin and zirconia balls are placed in a ball mill with a mass ratio of zirconia balls to kaolin of (5-20):1. The rotation speed is 300-1500 r / min and the grinding time is 30-300 min to obtain the mechanically activated kaolin.

[0010] In the above technical solution, the red mud is Bayer process red mud, the mass fraction of Fe2O3 in the red mud is not less than 15%, and the particle size D50 is 40-60 μm.

[0011] In the above technical solution, the fly ash is grade F fly ash with a particle size D50 of 20-30 μm.

[0012] In the above technical solution, the particle size D50 of the mechanically activated kaolin is 4.00~7.00um.

[0013] In the above technical solution, the acid activator is a mixture of phosphoric acid and acetic acid, with an acetic acid concentration of 1-5 mol / L, a phosphoric acid concentration of 5-9 mol / L, and a mass ratio of phosphoric acid to acetic acid of (7-13):1.

[0014] Secondly, the present invention provides a method for preparing the above-mentioned geopolymer, comprising the following steps:

[0015] S1: Mix the fly ash, mechanically activated kaolin, surface modifier, and red mud evenly to obtain mixture 1;

[0016] S2: Mix the mixture 1 with the acid activator and solvent evenly, and then cure and mold to obtain the geopolymer.

[0017] In the above technical solutions, the curing temperature is 20-30℃ and the curing time is 16-38h.

[0018] This invention utilizes the synergistic effect of fly ash, red mud, and mechanically activated kaolin, along with the application of surface modifiers, to significantly optimize the interactions of these industrial byproducts in geopolymers, thereby significantly improving the performance of the final product. This method not only enhances the structure and durability of geopolymers but also achieves a significant reduction in production costs and efficient resource recovery from bulk solid waste by using various solid waste materials as precursors.

[0019] Furthermore, this invention overcomes the limitations of using traditional fly ash as a concrete admixture, expands its application scope in building materials, environmental remediation, and other fields, reduces dependence on natural resources and the complexity of the production process, and provides a new path for sustainable road construction, foundation reinforcement, and environmental remediation.

[0020] The mechanically activated kaolin-modified fly ash-phosphate base polymer of this invention exhibits an early compressive strength exceeding 20 MPa at 3 days, and further increases to over 35 MPa at 14 days. Compared to traditional single fly ash-phosphate activated base polymers, its paste compressive strength is increased by 4.5-6 times. The principle behind this significant improvement includes:

[0021] (1) Mechanical activation of Al in kaolin and fly ash 3+ With PO4 in phosphoric acid 3- The reaction forms an AlPO4 gel. The rapid formation of this gel is a key mechanism for achieving early strength in geopolymers.

[0022] (2) The alkaline environment provided by red mud promotes the dissolution of more silicon (Si) and aluminum (Al) from fly ash and mechanically activated kaolin, increasing the availability and reaction potential of these active components, thereby enhancing the structure and properties of the material.

[0023] (3) The iron oxides in the red mud participate in the reaction and form the Fe-OP chain structure, which not only enhances the structural integrity of the material, but also improves its overall stability and connectivity, thereby enhancing the durability and compressive strength of the geopolymer.

[0024] (4) Surface modifiers enhance the interparticle bonding force by improving the surface properties of fly ash and other solid components. This enhanced bonding force effectively reduces the corrosive effect of water on the geopolymer structure, further improving the stability and durability of the material.

[0025] These combined effects ensure that the geopolymer exhibits high compressive strength in its early stages, and its properties continue to improve as curing time increases.

[0026] The mechanically activated kaolin-modified fly ash-phosphate base polymer of this invention exhibits no strength reduction in its later stages, reaching 50–65 MPa after 90 days. This is 4.8 to 6.5 times that of a single fly ash-phosphate-activated geopolymer, and significantly exceeds the compressive strength of metakaolin-modified fly ash-phosphate base polymers by 2.0 to 3.5 times. This significant strength increase is attributed to the abundant silicon (Si) and aluminum (Al) sources provided by the mechanically activated kaolin, which promotes the formation of complex aluminum phosphate silicates (Si-O-Al-OP, Al-OP) in a phosphoric acid environment. The formation of these structures not only stabilizes the microstructure of the geopolymer but also inhibits the formation of low-strength Si-OP products, ensuring the material's high performance and long-term stability. The spherical particles of fly ash reduce the agglomeration of the mechanically activated kaolin layers, promote the dissolution of Si and Al, and further increase the density and uniformity of the geopolymer, which is particularly important for improving the material's compressive strength.

[0027] This invention overcomes the limitations of fly ash, which has low early-stage strength in phosphate-based polymers and can only be used as an additive in traditional applications. This invention not only significantly improves the utilization rate of bulk solid wastes such as fly ash and red mud, but also significantly reduces the potential risk of heavy metals (such as Pb and Zn) they contain posing a source of environmental pollution, while simultaneously lowering the costs of environmental remediation and waste treatment.

[0028] In this invention, mechanical activation of kaolin promotes the reaction of more silicates and aluminates in fly ash, forming complex aluminosilicate phosphate (Si-O-Al-OP, Al-OP) structures. These structures provide higher compressive strength and durability. Furthermore, compared to traditional calcined kaolin treatment, the mechanical activation process significantly reduces energy consumption and carbon emissions, providing an environmentally friendly material processing method.

[0029] Furthermore, the mechanically activated kaolin-modified fly ash phosphoric acid-based polymer of this invention has strong resistance to freeze-thaw cycles, wet and dry conditions, brine erosion, and carbonization, making it an ideal building material suitable for a variety of extreme environmental conditions.

[0030] The beneficial effects of this invention are as follows:

[0031] This invention enhances the activity of fly ash by employing acid activation technology, thereby improving its utilization rate in geopolymerization reactions. This transforms fly ash into a structural material with high early strength, whereas previously it had low early strength and low reactivity. Compared to existing technologies, where fly ash is typically used for landfill or simple concrete filling, resulting in significant underutilization of this resource, this invention effectively expands the application scope of fly ash and increases its economic value.

[0032] This invention utilizes mechanically activated kaolin, which not only saves energy consumption caused by high-temperature calcination but also significantly reduces CO2 emissions. Compared to existing technologies that enhance the activity of metakaolin through calcination, resulting in higher energy consumption and carbon emissions, mechanically activated kaolin provides higher compressive strength than traditional metakaolin. This is because mechanical activation more effectively increases the material's specific surface area and reactivity, thereby improving the performance of the polymer products.

[0033] This invention uses an acid activation solution (a mixture of phosphoric acid and acetic acid), eliminating the need for other complex dissolution steps, significantly simplifying the preparation process and reducing production costs. In contrast, existing alkaline activation techniques often involve dissolving solid powders in a liquid, a complex and costly process. Furthermore, the acid activation method avoids the potential environmental and safety issues associated with alkaline activation, improving the environmental friendliness and economic efficiency of the entire production process.

[0034] This invention achieves an optimized P / (Al+Si) ratio by precisely controlling the mixing ratio of acetic acid and phosphoric acid, maintaining the chemical equilibrium of the reaction and thus promoting the effective dissolution of silicon and aluminum. Compared to existing technologies where the acid activator is typically singular, potentially leading to uneven reaction rates or improper control, this control strategy not only accelerates the release rate of useful components but also ensures uniform polymerization by regulating the reaction rate, thereby improving the overall quality and performance of the product.

[0035] In this invention, the addition of red mud not only promotes the dissolution of Si in fly ash and mechanically activated kaolin under acidic conditions, but also the alkaline components of red mud are more conducive to the release of silicon in this environment. Furthermore, by providing additional iron elements, it enhances the density of the geopolymer products, resulting in a more stable and uniform structure.

[0036] This invention eliminates the need for high-temperature curing, reducing energy consumption and environmental impact, compared to existing technologies where acid-activated geopolymers require high-temperature curing to achieve suitable material properties. Furthermore, the compressive strength at 28 days reaches 43.7 MPa, meeting the standards of GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete," even exceeding the standard for 425 grade cement. This provides broader practical application possibilities, particularly suitable for the construction and infrastructure sectors. Attached Figure Description

[0037] Figure 1 This is a flowchart of the method for preparing mechanically activated kaolin-modified fly ash phosphoric acid base polymer according to the present invention;

[0038] Figure 2 This is a flowchart of the preparation method of mechanically activated kaolin-modified fly ash phosphoric acid base polymer in Example 1 of the present invention. Detailed Implementation

[0039] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below in conjunction with specific embodiments. This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. This invention will be defined only by the claims.

[0040] This invention discloses a mechanically activated kaolin-modified fly ash phosphoric acid base polymer, which is made from the following raw materials in parts by weight: 30-75 parts fly ash, 15-60 parts mechanically activated kaolin, 8-40 parts red mud, 0.5-2 parts surface modifier, 10-35 parts acid activator, and 10-35 parts solvent. These raw materials and their proportions ensure that the base polymer has higher compressive strength.

[0041] Preferably, the raw materials for preparing the polymer, by weight, include: 35-70 parts fly ash, 25-55 parts mechanically activated kaolin, 10-30 parts red mud, 0.5-1.5 parts surface modifier, 20-35 parts acid activation solution, and 20-35 parts solvent.

[0042] In this invention, the preparation method of mechanically activated kaolin is as follows: kaolin and zirconia balls are placed in a ball mill, the mass ratio of zirconia balls to kaolin is (5-20):1, the rotation speed is 300-1500 r / min, and the grinding time is 30-300 min, thus obtaining mechanically activated kaolin.

[0043] Preferably, the ball mill speed is 500-1300 r / min, the grinding time is 60-240 min, and the mass ratio of zirconia balls to kaolin is 8-18:1.

[0044] Preferably, the ball mill speed is 1000 r / min, the grinding time is 80 min, and the mass ratio of zirconia balls to kaolin is 15:1.

[0045] In mechanically activated kaolin, the coordination environment of aluminum changes; aluminum, which originally existed primarily in a six-coordinate form, partially transforms into a four- or five-coordinate form. This coordination change can be achieved through… 27 Al solid-state NMR technology confirmed that the particle size D50 of mechanically activated kaolinite was 4.00–7.00 μm. Mechanical activation not only improved the chemical activity of kaolinite but also significantly reduced energy consumption and carbon dioxide release compared to calcination.

[0046] In this invention, the surface modifier includes at least one of polyethylene glycol, hexadecyltrimethylammonium bromide, ethylenediaminetetraacetic acid, and ethoxysilane.

[0047] The red mud is Bayer process red mud, with a Fe2O3 mass fraction of not less than 15% and a particle size D50 of 40-60 μm.

[0048] The fly ash is grade F fly ash with a particle size D50 of 20-30 μm.

[0049] The acid activator is a mixture of phosphoric acid and acetic acid. By introducing acetic acid, the concentration of -COOH in the system increases, the acid environment becomes milder, the dissolution rate of Si and Al becomes more uniform and the dissolution amount increases. Since -COOH forms flexible complexes with Si and Al, they are more evenly distributed in the reaction solution, the amount of polymerization products also increases, and the compressive strength also increases accordingly.

[0050] The acetic acid concentration is 1–5 mol / L, and the phosphoric acid concentration is 5–9 mol / L. Preferably, the acetic acid concentration is 3.5 mol / L, and the phosphoric acid concentration is 7 mol / L.

[0051] The mass ratio of phosphoric acid to acetic acid is (7-13):1. Within this ratio range, mechanically activated kaolin-modified fly ash phosphoric acid-based polymers exhibit higher compressive strength. A ratio of 11:1 is preferred.

[0052] The solvent can be water or deionized water.

[0053] This invention also discloses a method for preparing a mechanically activated kaolin-modified fly ash phosphoric acid-based polymer, comprising the following steps:

[0054] S1: Mix fly ash, mechanically activated kaolin, surface modifier and red mud evenly to obtain mixture 1;

[0055] S2: Mix mixture 1 with acid activator and solvent evenly, and then cure and mold to obtain geopolymer.

[0056] In this invention, the molding method is vibration molding.

[0057] In this invention, the curing temperature is 20–30°C and the curing time is 16–38 hours.

[0058] The preparation method of this invention introduces red mud and mechanically activated kaolin as optimized precursors. The mechanically activated kaolin transforms its structure from layered crystals to a more reactive amorphous structure, significantly increasing its specific surface area and chemical activity. When combined with fly ash, the complementary effect of the two significantly enhances the overall reactivity and cementing ability of the geopolymer, thereby strengthening the early and long-term stability of the material. Furthermore, the alkaline properties of red mud help promote the dissolution of silicon and aluminum from fly ash, while its iron oxide content enhances the material's density and durability.

[0059] This invention not only optimizes the performance of geopolymers and improves their early and final compressive strength, but also reduces preparation costs, energy consumption and environmental impact through the synergistic effect of red mud and mechanically activated kaolin. At the same time, it provides a new way for the resource utilization of fly ash and other industrial by-products.

[0060] The mechanically activated kaolin-modified fly ash phosphoric acid-based polymer of this invention is suitable for various civil engineering projects such as road construction, foundation reinforcement, and environmental remediation due to its excellent mechanical properties, superior durability, and environmental adaptability, thus meeting the needs of sustainable development.

[0061] The following will explain the specific implementation plan and product testing results.

[0062] Example 1

[0063] The mechanically activated kaolin-modified fly ash phosphoric acid base polymer of this invention is obtained by the following preparation method, including the following steps:

[0064] S1: First, put kaolin, fly ash and red mud into an oven and dry them until their quality no longer changes. After cooling to room temperature, you will get dried kaolin, fly ash and red mud.

[0065] S2: Place the dried kaolin into a ball mill and ball mill it at a speed of 1000 r / min for 80 min to obtain mechanically activated kaolin powder 1.

[0066] S3: Place 40 parts of mechanically activated kaolin powder, 50 parts of fly ash, 10 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide into a mixer and stir for 25 minutes to obtain mixture 1 for later use;

[0067] S4: Place 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) and 30 parts of water into a magnetic stirrer and stir for 24 hours to obtain mixed activator solution 1 for later use.

[0068] S5: Add mixed activator solution 1 to mixture 1 and stir with a stirrer for 8 minutes to obtain mechanically activated kaolin-modified fly ash phosphoric acid base polymer slurry;

[0069] S6: Pour the above slurry into a 20mm×20mm×20mm six-piece mold and vibrate to form it. Place it in a 25℃ oven for curing for 12 hours to obtain the cured geopolymer.

[0070] The geopolymer obtained by this method has a 28-day compressive strength of 43.7 MPa and a 90-day compressive strength of 65 MPa.

[0071] Example 2

[0072] The mechanically activated kaolin-modified fly ash phosphoric acid base polymer of this invention is obtained by the following preparation method, including the following steps:

[0073] S1: First, put kaolin, fly ash and red mud into an oven and dry them until their quality no longer changes. After cooling to room temperature, you will get dried kaolin, fly ash and red mud.

[0074] S2: Place the dried kaolin into a ball mill and ball mill it at a speed of 800 r / min for 100 min to obtain mechanically activated kaolin powder 1.

[0075] S3: Place 45 parts of mechanically activated kaolin powder, 35 parts of fly ash, 20 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide into a mixer and stir for 25 minutes to obtain mixture 1 for later use;

[0076] S4: Place 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) and 30 parts of water into a magnetic stirrer and stir for 24 hours to obtain mixed activator solution 1 for later use.

[0077] S5: Add mixed activator solution 1 to mixture 1 and stir with a stirrer for 8 minutes to obtain mechanically activated kaolin-modified fly ash phosphoric acid base polymer slurry;

[0078] S6: Pour the above slurry into a 20mm×20mm×20mm six-piece mold and vibrate to form it. Place it in a 25℃ oven for curing for 12 hours to obtain the cured geopolymer.

[0079] The geopolymer obtained by this method has a 28-day compressive strength of 39 MPa and a 90-day compressive strength of 43 MPa.

[0080] Example 3

[0081] The mechanically activated kaolin-modified fly ash phosphoric acid base polymer of this invention is obtained by the following preparation method, including the following steps:

[0082] S1: First, put kaolin, fly ash and red mud into an oven and dry them until their quality no longer changes. After cooling to room temperature, you will get dried kaolin, fly ash and red mud.

[0083] S2: Place the dried kaolin into a ball mill and ball mill it at a speed of 600 r / min for 120 min to obtain mechanically activated kaolin powder 1.

[0084] S3: Place 30 parts of mechanically activated kaolin powder, 60 parts of fly ash, 10 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide into a mixer and stir for 25 minutes to obtain mixture 1 for later use;

[0085] S4: Place 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) and 30 parts of water into a magnetic stirrer and stir for 24 hours to obtain mixed activator solution 1 for later use.

[0086] S5: Add mixed activator solution 1 to mixture 1 and stir with a stirrer for 8 minutes to obtain mechanically activated kaolin-modified fly ash phosphoric acid base polymer slurry;

[0087] S6: Pour the above slurry into a 20mm×20mm×20mm six-piece mold and vibrate to form it. Place it in a 25℃ oven for curing for 12 hours to obtain the cured geopolymer.

[0088] The geopolymer obtained by this method has a 28-day compressive strength of 35 MPa and a 90-day compressive strength of 38 MPa.

[0089] Example 4

[0090] The mechanically activated kaolin-modified fly ash phosphoric acid base polymer of this invention is obtained by the following preparation method, including the following steps:

[0091] S1: First, put kaolin, fly ash and red mud into an oven and dry them until their quality no longer changes. After cooling to room temperature, you will get dried kaolin, fly ash and red mud.

[0092] S2: Place the dried kaolin into a ball mill and ball mill it at a speed of 1200 r / min for 180 min to obtain mechanically activated kaolin powder 1.

[0093] S3: Place 30 parts of mechanically activated kaolin powder, 50 parts of fly ash, 20 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide into a mixer and stir for 25 minutes to obtain mixture 1 for later use;

[0094] S4: Place 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) and 30 parts of water into a magnetic stirrer and stir for 24 hours to obtain mixed activator solution 1 for later use.

[0095] S5: Add mixed activator solution 1 to mixture 1 and stir with a stirrer for 8 minutes to obtain mechanically activated kaolin-modified fly ash phosphoric acid base polymer slurry;

[0096] S6: Pour the above slurry into a 20mm×20mm×20mm six-piece mold and vibrate to form it. Place it in a 25℃ oven for curing for 12 hours to obtain the cured geopolymer.

[0097] The geopolymer obtained by this method has a 28-day compressive strength of 29 MPa and a 90-day compressive strength of 34 MPa.

[0098] Example 5

[0099] The mechanically activated kaolin-modified fly ash phosphoric acid base polymer of this invention is obtained by the following preparation method, including the following steps:

[0100] S1: First, put kaolin, fly ash and red mud into an oven and dry them until their quality no longer changes. After cooling to room temperature, you will get dried kaolin, fly ash and red mud.

[0101] S2: Place the dried kaolin into a ball mill and ball mill it at a speed of 900 r / min for 80 min to obtain mechanically activated kaolin powder 1.

[0102] S3: Put 20 parts of mechanically activated kaolin powder, 50 parts of fly ash, 30 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide into a mixer and stir for 25 minutes to obtain mixture 1 for later use;

[0103] S4: Place 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) and 30 parts of water into a magnetic stirrer and stir for 24 hours to obtain mixed activator solution 1 for later use.

[0104] S5: Add mixed activator solution 1 to mixture 1 and stir with a stirrer for 8 minutes to obtain mechanically activated kaolin-modified fly ash phosphoric acid base polymer slurry;

[0105] S6: Pour the above slurry into a 20mm×20mm×20mm six-piece mold and vibrate to form it. Place it in a 25℃ oven for curing for 12 hours to obtain the cured geopolymer.

[0106] The geopolymer obtained by this method has a 28-day compressive strength of 23 MPa and a 90-day compressive strength of 30 MPa.

[0107] Comparative Example 1

[0108] In Example 1, 40 parts of mechanically activated kaolin powder, 50 parts of fly ash, 10 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide were replaced with 50 parts of mechanically activated kaolin powder, 50 parts of fly ash, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide, while the remaining steps were the same as in Example 1.

[0109] The geopolymer obtained in Comparative Example 1 had a 28-day compressive strength of 22 MPa and a 90-day compressive strength of 35 MPa. Compared with Example 1, the 28-day strength decreased by approximately 20 MPa and the 90-day strength decreased by approximately 30 MPa. This is because the solubility of Si in fly ash and mechanically activated kaolin is greater under alkaline conditions than under acidic conditions. The absence of red mud leads to a decrease in the Si / Al ratio of the geopolymer, resulting in poor structural stability of the generated geopolymer. Furthermore, low-concentration Si(OH)4 (in the dissolved form of SiO2) is relatively stable and difficult to participate in the geopolymerization reaction, ultimately leading to a decrease in the compressive strength of the geopolymer.

[0110] Comparative Example 2

[0111] In Example 1, 40 parts of mechanically activated kaolin powder, 50 parts of fly ash, 10 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide were replaced with 50 parts of fly ash, 50 parts of red mud, 0.9 parts of polyethylene glycol, and 0.6 parts of hexadecyltrimethylammonium bromide, while the remaining steps were the same as in Example 1.

[0112] The geopolymer obtained in Comparative Example 2 had a 28-day compressive strength of 15 MPa and a 90-day compressive strength of 18 MPa. Compared to Example 1, the 28-day strength decreased by approximately 28 MPa, and the 90-day strength decreased by approximately 47 MPa. This is because the low activity of fly ash leads to a reduced effective utilization rate of silicon and aluminum elements, and some of the acid activators participating in the geopolymerization reaction are consumed by the red mud, resulting in incomplete geopolymerization and a large number of unreacted or partially reacted areas, ultimately leading to a decrease in the compressive strength of the geopolymer product.

[0113] Comparative Example 3

[0114] In Example 1, replace 40 parts mechanically activated kaolin powder, 50 parts fly ash, 10 parts red mud, 0.9 parts polyethylene glycol, and 0.6 parts hexadecyltrimethylammonium bromide with 50 parts mechanically activated kaolin, 50 parts red mud, 0.9 parts polyethylene glycol, and 0.6 parts hexadecyltrimethylammonium bromide, and the remaining steps are the same as in Example 1.

[0115] The geopolymer obtained in Comparative Example 3 had a 28-day compressive strength of 19 MPa and a 90-day compressive strength of 26 MPa. Compared to Example 1, the 28-day strength decreased by approximately 25 MPa, and the 90-day strength decreased by approximately 39 MPa. This is because the active Al in the mechanically activated kaolinite cannot fully participate in the geopolymerization reaction and exists as unreacted particles; the lamellar structure of the metakaolinite increases agglomeration; the lack of the spherical structure of fly ash reduces the amount of acid activator participating in the geopolymerization reaction; and the consumption of red mud leads to incomplete geopolymerization, ultimately resulting in a decrease in the compressive strength of the geopolymer product.

[0116] Comparative Example 4

[0117] Replace the 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) in Example 1 with 30 parts of 7 mol / L phosphoric acid, and follow the same steps as in Example 1.

[0118] The geopolymer obtained in Comparative Example 4 had a 28-day compressive strength of 25 MPa and a 90-day compressive strength of 42 MPa. Compared to Example 1, the 28-day strength decreased by approximately 19 MPa, and the 90-day strength decreased by approximately 23 MPa. This is because the amount of dissolved Si and Al in the mechanically activated kaolin, fly ash, and red mud decreased, leading to a reduction in the products participating in the geopolymerization reaction. Furthermore, the rate of Si and Al dissolution in the system was too rapid, resulting in an uneven distribution of the geopolymerization products, increasing the porosity and inhomogeneity of the structure, ultimately reducing the compressive strength.

[0119] Comparative Example 5

[0120] Replace the 30 parts of acid activation solution in Example 1 (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) with 30 parts of acid activation solution (a mixture of 12 parts of 5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid), and the remaining steps are the same as in Example 1.

[0121] The geopolymer obtained in Comparative Example 5 had a 28-day compressive strength of 30 MPa and a 90-day compressive strength of 45 MPa. Compared to Example 1, the 28-day strength decreased by approximately 14 MPa, and the 90-day strength decreased by approximately 20 MPa. This is because the amount and rate of Al dissolution decreased, resulting in a reduced amount of aluminosilicate phosphosilicate products, which increased the brittleness of the geopolymer products. Furthermore, the reduced geopolymerization rate was due to the increased pH of the system, leading to a decrease in the amount of products generated by the geopolymerization reaction and an increase in the porosity of the system, ultimately resulting in a decrease in the compressive strength of the geopolymer products.

[0122] Comparative Example 6

[0123] Replace the 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 7 mol / L phosphoric acid) in Example 1 with 30 parts of acid activation solution (a mixture of 2 parts of 3.5 mol / L acetic acid and 28 parts of 9 mol / L phosphoric acid), and the remaining steps are the same as in Example 1.

[0124] The compressive strength of the cementitious material obtained in Comparative Example 6 was 32 MPa at 28 days and 49 MPa at 90 days. Compared with Example 1, the strength decreased by approximately 12 MPa at 28 days and approximately 16 MPa at 90 days. This is because, with the increase of phosphoric acid concentration, excess H₂PO₄ in the system... - PO4 3- With Al 3+ The reaction becomes more vigorous, forming aluminum phosphate precipitate. Due to the consumption of aluminum-oxygen tetrahedra, the amount of silicon-aluminum phosphate generated by the geopolymerization reaction decreases, resulting in a decline in the structural integrity and properties of the geopolymer product, ultimately leading to a decrease in the compressive strength of the geopolymer product.

[0125] Comparative Example 7

[0126] The ball mill speed of Example 1 (1000 r / min, grinding time 80 min) was changed to 1200 r / min, grinding time 80 min, and the remaining steps were the same as in Example 1.

[0127] The geopolymer obtained in Comparative Example 7 had a 28-day compressive strength of 39 MPa and a 90-day compressive strength of 56 MPa. Compared to Example 1, the 28-day strength decreased by approximately 5 MPa, and the 90-day strength decreased by approximately 9 MPa. This is because the increased rotational speed led to the agglomeration of the mechanically activated kaolin. The agglomerated mechanically activated kaolin provided fewer reaction sites, resulting in a decrease in dissolved Al and silicon elements, and consequently, a reduction in the geopolymer reaction products, ultimately leading to a decrease in the compressive strength of the geopolymer product.

[0128] Comparative Example 8

[0129] The ball mill speed of Example 1 (1000 r / min, grinding time 80 min) was changed to 1000 r / min, grinding time 120 min, and the remaining steps were the same as in Example 1.

[0130] The geopolymer obtained in Comparative Example 8 had a 28-day compressive strength of 29 MPa and a 90-day compressive strength of 38 MPa. Compared to Example 1, the 28-day strength decreased by approximately 15 MPa, and the 90-day strength decreased by approximately 27 MPa. This is because the extended grinding time led to excessively small particle size and agglomeration of the mechanically activated kaolin, reducing the effective reaction area and dispersibility, resulting in a decrease in the amount of geopolymer products formed, ultimately leading to a decrease in the compressive strength of the geopolymer products.

[0131] Comparative Example 9

[0132] In Example 1, replace 40 parts mechanically activated kaolin powder, 50 parts fly ash, 10 parts red mud, 0.9 parts polyethylene glycol, and 0.6 parts hexadecyltrimethylammonium bromide with 40 parts mechanically activated kaolin powder, 50 parts fly ash, and 10 parts red mud, and the remaining steps are the same as in Example 1.

[0133] The geopolymer obtained in Comparative Example 9 had a 28-day compressive strength of 36 MPa and a 90-day compressive strength of 51 MPa. Compared to Example 1, the 28-day strength decreased by approximately 8 MPa, and the 90-day strength decreased by approximately 14 MPa. This is because the dissolution rates of Si and aluminum were uneven, resulting in reduced dispersion of the dissolved silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra and octahedrons. This led to an excessively rapid and uneven geopolymerization reaction rate, reducing the quantity and uniformity of the geopolymer products, ultimately resulting in a decrease in the compressive strength of the geopolymer product.

[0134] Table 1 Compressive strength of various materials at different ages, in MPa

[0135] Group 28-day compressive strength 90d compressive strength Example 1 43.7 65.0 Example 2 39 43 Example 3 35 38 Example 4 29 34 Example 5 23 30 Comparative Example 1 22 35 Comparative Example 2 15 18 Comparative Example 3 19 26 Comparative Example 4 25 42 Comparative Example 5 30 45 Comparative Example 6 32 49 Comparative Example 7 39 56 Comparative Example 8 29 38 Comparative Example 9 36 51

[0136] As shown in the table above, the geopolymers prepared in Examples 1-5 of this invention have better 28-day and 90-day compressive strengths than those in Comparative Examples 1-9. Due to their excellent mechanical properties, superior durability and environmental adaptability, the geopolymers of this invention are suitable for various civil engineering projects such as road construction, foundation reinforcement and environmental remediation, and meet the needs of sustainable development.

[0137] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A mechanically activated kaolin-modified fly ash phosphoric acid-based polymer, characterized in that: The geopolymer is made from the following raw materials in parts by weight: 30-75 parts fly ash, 15-60 parts mechanically activated kaolin, 8-40 parts red mud, 0.5-2 parts surface modifier, 10-35 parts acid activator, and 10-35 parts solvent; the surface modifier includes at least one of polyethylene glycol, hexadecyltrimethylammonium bromide, ethylenediaminetetraacetic acid, and ethoxysilane; the red mud contains not less than 15% Fe2O3 by mass; and the acid activator is a mixture of phosphoric acid and acetic acid.

2. The geopolymer according to claim 1, characterized in that: The method for preparing the mechanically activated kaolin is as follows: Kaolin and zirconia balls are placed in a ball mill with a mass ratio of zirconia balls to kaolin of (5~20):

1. The rotation speed is 300~1500 r / min and the grinding time is 30~300 min to obtain the mechanically activated kaolin.

3. The geopolymer according to claim 1, characterized in that: The red mud is Bayer process red mud with a particle size D50 of 40~60 μm.

4. The geopolymer according to claim 1, characterized in that: The fly ash is grade F fly ash with a particle size D50 of 20~30 μm.

5. The geopolymer according to claim 2, characterized in that: The particle size D50 of the mechanically activated kaolin is 4.00~7.00um.

6. The geopolymer according to claim 1, characterized in that: The acid activator contains acetic acid at a concentration of 1-5 mol / L and phosphoric acid at a concentration of 5-9 mol / L, with a mass ratio of phosphoric acid to acetic acid of (7-13):

1.

7. A method for preparing the geopolymer according to any one of claims 1-6, characterized in that: Includes the following steps: S1: Mix the fly ash, mechanically activated kaolin, surface modifier, and red mud evenly to obtain mixture 1; S2: Mix the mixture 1 with the acid activator and solvent evenly, and then cure and mold to obtain the geopolymer.

8. The preparation method according to claim 7, characterized in that: The curing temperature is 20~30 ℃, and the curing time is 16~38 hours.

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