Coal gangue-based reinforced cement composite material and preparation method thereof

Abstract

The application discloses a coal gangue-based reinforced cement composite material and a preparation method thereof, and relates to the technical field of building materials; the coal gangue-based reinforced cement composite material is composed of coal gangue-based reinforced admixture, calcium ion doped modified multi-walled carbon nanotubes, polypropylene fibers, P.O42.5 Portland cement, metakaolin, silica fume, polycarboxylate superplasticizer and water; the calcium ion doped modified multi-walled carbon nanotubes and the coal gangue-based reinforced admixture are added into the cement matrix, seamless filling from nanometers to microns is realized, a strong and tough interface transition zone is formed, the dense matrix and the strong interface jointly bear the pressure, the compressive strength and the flexural strength of the material are significantly enhanced, and meanwhile, the migration of water and ions is effectively blocked, and the impermeability of the material is improved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically referring to a coal gangue-based reinforced cement composite material and its preparation method. Background Technology

[0002] Cement production is a typical high-carbon emission process. Using auxiliary cementitious materials to reduce the amount of clinker in cement products is considered an effective way to reduce the carbon emissions of commercial cement. However, with the adjustment of production capacity in industries such as thermal power generation and steel, and the continuous growth in market demand for relatively high-quality auxiliary cementitious materials such as slag, fly ash, and silica fume, these traditional materials are facing a situation of supply falling short of demand. Therefore, it is urgent to develop more new and high-quality auxiliary cementitious materials.

[0003] Against this backdrop, the resource utilization of coal gangue, a solid waste generated during coal washing, has attracted much attention. Currently, most coal gangue is still stockpiled or landfilled, lacking effective means for its treatment or utilization. However, coal gangue powder, after being calcined and activated at an appropriate temperature, exhibits certain pozzolanic activity and has the potential to be used as an auxiliary cementing material. Introducing coal gangue into cement material systems not only provides a new way for the comprehensive utilization of bulk industrial solid waste and effectively alleviates its environmental accumulation pressure, but also broadens the feasibility of developing low-carbon and new building materials, achieving a win-win situation for both environmental and resource benefits.

[0004] The existing technology currently suffers from the following main problems:

[0005] The inherent porosity and high water absorption of coal gangue reduce the mechanical and impermeability properties of cement materials, thus limiting their usability. Summary of the Invention

[0006] In view of the above situation and to overcome the defects of the prior art, the present invention proposes a coal gangue-based reinforced cement composite material, comprising the following components in parts by weight: 20-30 parts of coal gangue-based reinforcing admixture, 0.08-0.12 parts of calcium ion-doped modified multi-walled carbon nanotubes, 0.5-1.5 parts of polypropylene fiber, 90-100 parts of P.O42.5 silicate cement, 10-15 parts of metakaolin, 5-10 parts of silica fume, 1.5-2.0 parts of polycarboxylate superplasticizer, and 25-35 parts of water.

[0007] The preparation method of the coal gangue-based reinforced admixture specifically includes the following steps:

[0008] a. Crush 9.0-10.0g of coal gangue and pass it through a 200-mesh sieve. Collect the crushed coal gangue and dry it in a 105℃ oven. Then add it to 200mL of a 6.8-7.2% hydrochloric acid solution and place it in a 60-80℃ water bath. Stir for 2-3 hours. Pour off the hydrochloric acid solution. Wash the solid repeatedly with deionized water until the pH reaches 7.0. Dry it at 105-110℃ for 12-18 hours. Finally, place it in a tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. After reacting at a warm temperature for 1-2 hours and naturally cooling, the material is removed, ground, and then subjected to a combination of acid washing and calcination. This process optimizes the pore structure of the coal gangue, reduces the proportion of open pores and the overall water absorption rate. Simultaneously, the clay minerals such as kaolinite in the coal gangue dehydrate and decompose, generating highly active amorphous Al2O3 and SiO2. These amorphous Al2O3 and SiO2 can partially melt and fill the micropores, and can also undergo a pozzolanic reaction to generate hydration gel when used as cement admixtures, further improving the overall mechanical properties and impermeability of cement materials, thus obtaining activated coal gangue powder.

[0009] b. Add 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol, then add 3-5 mL of deionized water. Adjust the pH to 4.0-5.0 using acetic acid. Let it stand for hydrolysis for 30-40 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use. Add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate and react at 50-60℃ for 5-6 h. Filter the mixture, dry the precipitate at 60-80℃, and grind it. The activated coal gangue powder with a porous structure has a layer of 3-aminopropyltriethoxysilane molecules firmly grafted onto its surface through Si-O-Si covalent bonds, introducing ammonia... The functional groups enhance the chemical compatibility and adhesion between coal gangue and cement hydration products, improve the fragile interface transition zone, and enhance the load-bearing capacity. The strengthened interface can also effectively transfer and disperse stress, reduce the initiation of microcracks, and thus improve the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, the introduced hydrophobic alkyl chains form a hydrophobic film on the inner wall of cement capillary channels, which can block water intrusion. The uniformly dispersed hydrophobic particles not only further cut off the connectivity of capillary pores and enhance the impermeability of the material, but also fully fill the micropores, making the structure more compact, thus obtaining 3-aminopropyltriethoxysilane-grafted activated coal gangue powder.

[0010] c. Disperse carboxylated graphene oxide in 1000 mL of deionized water using ultrasonication to form a carboxylated graphene oxide dispersion. Then, weigh 8.0-10.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b and add it to the carboxylated graphene oxide dispersion. First, ultrasonicate the dispersion for 20-30 min, then continuously stir at 600-800 rpm at room temperature, adjusting the pH to 9.0-10.0 during the stirring process. React in a 60-80℃ water bath for 4-6 h. After the reaction is complete, filter the product and wash it alternately with anhydrous ethanol and deionized water 3-5 times. Finally, dry the product at 60℃ to remove the carboxylated graphene oxide. Graphene is coated on the surface of 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Through the covalent bonding of amide and amino groups, it can effectively prevent the propagation of microcracks and act as a nanotemplate to guide the orderly growth of hydration products, thereby significantly improving compressive and flexural strength. Furthermore, the carboxyl functional groups on the surface can improve the compatibility with cement paste. Through its steric hindrance effect, it can improve the uniform dispersion of coal gangue composite powder in the paste, reduce structural defects, and enhance mechanical properties. At the same time, the uniformly dispersed composite powder further forms a more homogeneous barrier network in the paste, improving the overall uniformity of impermeability, thus obtaining modified grafted activated coal gangue composite powder.

[0011] d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of ammonia solution with a mass fraction of 25-28% evenly. Then add 0.4-0.8 g of hexadecyltrimethylammonium bromide and stir at room temperature for 4-6 hours to form a sol for later use. Ultrasonically disperse the modified grafted activated coal gangue composite powder described in step c in 50-100 mL of anhydrous ethanol to form an active dispersion for later use. Slowly add the active dispersion to the sol at 500-600 rpm and stir at 50-60°C for 6-10 hours. Then let it stand for 12-24 hours, centrifuge, collect the solid product, and wash it alternately with anhydrous ethanol and deionized water 3-5 times. Dry it at 60-80°C. Finally,... After drying, the powder is placed in a tube furnace and heated to 450-550℃ at a rate of 5℃ / min under a nitrogen atmosphere. The temperature is held for 1-3 hours. After calcination, an ordered mesoporous silica shell is coated on the surface of the modified grafted activated coal gangue composite powder. The mesoporous shell can adsorb and slowly release moisture, continuously promoting the later hydration of the internal coal gangue and cement, reducing self-shrinkage. The active silica in the shell participates in the hydration reaction to generate more CSH gel, which not only optimizes the interface transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix, significantly reducing porosity. The coating effect of the dense mesoporous silica shell further prevents the intrusion of moisture and corrosive ions, thereby improving the impermeability and obtaining a coal gangue-based reinforced admixture.

[0012] Preferably, in step b, the amount of 3-aminopropyltriethoxysilane added is 5-7 mL. The long organic chain of 3-aminopropyltriethoxysilane imparts hydrophobicity to the surface of coal gangue, effectively preventing the adsorption of water and the penetration of capillary channels.

[0013] Preferably, in step c, the amount of carboxylated graphene oxide added is 1.0-2.0g, the sheet diameter is 0.5-5μm, and the thickness is 0.8-1.2nm. The carboxylated graphene oxide sheets provide huge attachment and nucleation sites for hydration products, guiding the CSH gel to grow more densely and orderly, forming a high-strength matrix. This ordered and dense hydration product structure naturally has lower porosity and more tortuous channels, directly hindering the penetration of water and ions.

[0014] This invention also provides a method for preparing a coal gangue-based reinforced cement composite material, specifically including the following steps:

[0015] S1. Place multi-walled carbon nanotubes into an extraction flask, then add 150 mL of acetone solution. Heat under reflux at 70°C for 2-4 hours. Pour off the acetone solution and wash the multi-walled carbon nanotubes 6-10 times with anhydrous ethanol and deionized water, respectively. After washing, vacuum dry the multi-walled carbon nanotubes at 60-80°C for 8-12 hours to obtain pretreated multi-walled carbon nanotubes. Place them in a round-bottom flask connected to a reflux condenser and operate in a dedicated fume hood. Add 150 mL of a mixed acid solution of concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:4). Heat at 50-60°C for 4-6 hours and centrifuge at high speed (10000-1200 rpm). Centrifuge at 000 rpm for 6-10 min. Wash the precipitate 6-10 times with anhydrous ethanol and deionized water, then filter it through a 0.1-0.5 μm microporous membrane, and finally dry it. Through strong acid oxidation treatment, a large number of carboxyl and hydroxyl functional groups are introduced on the surface of multi-walled carbon nanotubes, which serve as sites for heterogeneous nucleation of hydration products, accelerate and optimize the cement hydration process, make the microstructure more compact, and improve strength and toughness. In addition, the bridging effect of multi-walled carbon nanotubes can effectively inhibit the generation and propagation of microcracks, reduce the channels for water and corrosive ions to enter, and thus further improve the impermeability, resulting in oxidized multi-walled carbon nanotubes.

[0016] S2. Add N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol, then add 3.6-4.5 mL of deionized water. Adjust the pH to 4.5-5.5 using acetic acid, stir for 30-40 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane solution for later use. Immerse the oxidized multi-walled carbon nanotubes obtained in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane solution, reflux at 60-70 °C for 2-3 h, centrifuge, wash the solid material 3-5 times with anhydrous ethanol and deionized water, and dry. The N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane in the oxidized multi-walled carbon nanotubes... Organic molecular chains grafted onto the surface of multi-walled carbon nanotubes enable amination modification, forming a more uniform and stable three-dimensional network within the cement matrix. This physically blocks the migration channels of moisture and corrosive ions. The amino groups at the ends of the molecular chains form strong hydrogen or ionic bonds with oxygen atoms or hydroxyl groups in cement hydration products, greatly enhancing interfacial adhesion. The dense interfacial bond and the enhanced multi-walled carbon nanotube matrix provide complete support for higher flexural and compressive strength. The strong interfacial bond also eliminates the weak transition zone between traditional admixtures and the cement matrix, significantly reducing interfacial microcracks and pores. The amino groups in the middle of the molecular chains have strong complexing ability, which is beneficial for subsequent induced mineralization, resulting in modified multi-walled carbon nanotubes.

[0017] S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1000-1500 mL of deionized water, then add 1.0-1.5 g of sodium dodecyl sulfate, and sonicate for 30-40 min. Next, add 150 mL of calcium chloride solution with a mass fraction of 10-12%, adjust the pH to 9.0-10.0, and continue sonicating for 20-30 min. While stirring at 600-800 rpm, add 150 mL of carbonate solution with a mass fraction of 9-10% at a rate of 1 drop / second using a constant pressure dropping funnel. Sodium solution is added dropwise, heated to 50-60℃, reacted for 1-2 hours, centrifuged, and the precipitate is washed 3-5 times alternately with anhydrous ethanol and deionized water, and finally dried at 80℃. In this process, modified multi-walled carbon nanotubes are used as the core, covered with an in-situ generated nano-calcium carbonate shell. The calcium carbonate shell tightly wraps around the surface of the modified multi-walled carbon nanotubes, which can fill the pores and increase the surface roughness and nucleation activity. Together with the modified multi-walled carbon nanotubes, the two significantly improve the mechanical properties and impermeability of cement materials, resulting in calcium ion-doped modified multi-walled carbon nanotubes.

[0018] S4. Disperse the calcium ion-doped modified multi-walled carbon nanotubes described in step S3 in 1 / 3 of the water, place them in an ice-water bath, and ultrasonically disperse them at 800-1000W for 20-30 minutes to form a suspension. Then add 1 / 2 of the polycarboxylate superplasticizer to the suspension, followed by polypropylene fiber, and stir at 200-300 rpm for 10-15 minutes to obtain a mixed slurry for later use. Mix P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume in a mixer for 1-2 minutes, then add the remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water. Stir for 3-5 minutes, then add the mixed slurry and continue stirring for 3-5 minutes. Discharge the material. Calcium ion-doped modified multi-walled carbon nanotubes fill the nanopores, and coal gangue-based reinforcing admixtures fill the micron pores, achieving seamless filling from nano and micron, making the cement matrix extremely dense. At the same time, the coal gangue-based reinforcing admixtures can optimize the interface transition zone, while the calcium ion-doped modified multi-walled carbon nanotubes act as rivets at the interface. The joint interface of the two transforms the fragile transition zone into a strong and tough composite material interface, thereby improving the mechanical properties and impermeability of the cement material, resulting in a coal gangue-based reinforced cement composite material.

[0019] Preferably, in step S1, the amount of multi-walled carbon nanotubes added is 1.0-2.0g, with a diameter of 8-15nm and a length of 50μm. The multi-walled carbon nanotubes are embedded in the cement hydration products and act as nano-reinforcing steel, which can effectively improve the compressive strength of the matrix. When microcracks propagate, the multi-walled carbon nanotubes can bridge the two sides of the crack, transfer stress, consume fracture energy, and greatly improve the compressive strength of the material. The nucleation effect of multi-walled carbon nanotubes and their own filling of pores can refine the capillary channels inside the cement stone, block the connected permeation path, improve the anti-permeability, and thus reduce the penetration depth of chloride ions.

[0020] Preferably, in step S2, the amount of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane added is 8.0-8.6 mL. The introduction of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability, and also improves the steric hindrance of multi-walled carbon nanotubes, making them more uniformly and stably dispersed in cement materials.

[0021] The beneficial effects achieved by this invention are as follows:

[0022] This invention achieves seamless filling from nanometer to micrometer scale by synergistically incorporating calcium ion-doped modified multi-walled carbon nanotubes and coal gangue-based reinforcing admixtures into a cement matrix. This creates a strong and tough interfacial transition zone, where the dense matrix and strong interface work together to withstand pressure, significantly enhancing the material's compressive and flexural strength. Simultaneously, it effectively blocks the migration of moisture and ions, improving the material's impermeability. In the coal gangue-based reinforcing admixture, 3-aminopropyltriethoxysilane molecules are first firmly grafted onto the surface of the oxidized multi-walled carbon nanotubes. Then, through covalent bonding of amide and amino groups, carboxylated graphene oxide is encapsulated on the surface of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Finally, calcination treatment is performed to modify the grafted activated... The coal gangue composite powder is coated with an ordered mesoporous silica shell, which not only overcomes the inherent defects of coal gangue, such as its porous structure and high water absorption, but also forms a multi-level composite structure. This further optimizes the mechanical properties and impermeability of the cement matrix. The carboxylated graphene oxide sheets effectively prevent microcrack propagation and act as nanotemplates to guide the orderly growth of hydration products, significantly improving compressive and flexural strength. Simultaneously, the carboxyl functional groups improve compatibility with the cement paste, enhancing the uniform dispersion of the coal gangue composite powder in the paste through their steric hindrance effect, reducing structural defects, and contributing to improved mechanical properties and overall impermeability uniformity. The mesoporous silica shell can adsorb and slowly release moisture, continuously... This process promotes the later-stage hydration of internal coal gangue and cement, generating more CSH gel. This not only optimizes the interfacial transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix. The encapsulation effect of the mesoporous silica shell prevents the intrusion of moisture and corrosive ions, thus improving impermeability. In the calcium ion-doped modified multi-walled carbon nanotubes, the grafting of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane onto the surface of the oxidized multi-walled carbon nanotubes constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability. This surface can form a more uniform and stable three-dimensional network within the cement matrix, effectively blocking the migration channels of moisture and corrosive ions. Simultaneously, the amino groups at the molecular chain ends interact with the cement hydration products... Oxygen atoms or hydroxyl groups form strong hydrogen bonds or ionic bonds, which strengthen interfacial adhesion. The dense interfacial bonding and the complete support of the multi-walled carbon nanotube core provide higher flexural and compressive strength. The strong interfacial bonding also eliminates interfacial microcracks and pores, improving impermeability. Meanwhile, the amino groups in the middle of the molecular chain have strong complexing ability, which can guide the formation of nano-calcium carbonate shells through in-situ mineralization. The calcium carbonate shells tightly wrap the surface of the modified multi-walled carbon nanotubes, which can both fill pores and increase surface roughness and nucleation activity. Together with the modified multi-walled carbon nanotubes, they significantly improve the mechanical properties and impermeability of cement materials. This invention uses coal gangue-based reinforcing admixtures, calcium ion-doped modified multi-walled carbon nanotubes, polypropylene fibers, and P.O42.A coal gangue-based reinforced cement composite material was prepared by combining silicate cement, metakaolin, silica fume, polycarboxylate superplasticizer, and water. This composite material not only effectively improved the compressive and flexural strengths of the material but also significantly enhanced its impermeability. Attached Figure Description

[0023] Figure 1 The figures show the mechanical properties of Examples 1-4 and Comparative Examples 1-3 of the present invention.

[0024] Figure 2 The graph shows the chloride ion diffusion coefficient results for Examples 1-4 and Comparative Examples 1-3 of this invention.

[0025] Figure 3 The image shows Fourier transform infrared (FT-IR) spectra of the coal gangue-based reinforcing admixture and calcium ion-doped modified multi-walled carbon nanotubes of this invention. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0028] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; unless otherwise specified, the experimental materials used in the following embodiments are all purchased from commercial channels.

[0029] Example 1

[0030] This embodiment proposes a coal gangue-based reinforced cement composite material, comprising the following components in parts by weight: 30 parts of coal gangue-based reinforcing admixture, 0.12 parts of calcium ion-doped modified multi-walled carbon nanotubes, 1.5 parts of polypropylene fiber, 100 parts of P.O42.5 silicate cement, 15 parts of metakaolin, 10 parts of silica fume, 2.0 parts of polycarboxylate superplasticizer, and 35 parts of water.

[0031] The preparation method of coal gangue-based reinforced admixtures specifically includes the following steps:

[0032] a. Crush 10.0g of coal gangue and pass it through a 200-mesh sieve. Collect the crushed coal gangue and dry it in an oven at 105℃. Then add it to 200mL of 7.2% hydrochloric acid solution and place it in an 80℃ water bath. Stir for 3 hours. Pour off the hydrochloric acid solution. Wash the solid repeatedly with deionized water until the pH reaches 7.0. Dry it at 110℃ for 18 hours. Finally, place it in a tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. Hold the temperature for 2 hours and allow it to cool naturally. However, after extraction and grinding, the pore structure of the coal gangue was optimized through a combination of acid washing and calcination, reducing the proportion of open pores and the overall water absorption rate. At the same time, the clay minerals such as kaolinite in the coal gangue were dehydrated and decomposed to generate highly active amorphous Al2O3 and SiO2, which can not only partially melt and fill the micropores, but also undergo pozzolanic reaction to generate hydration gel when used as cement admixture, further improving the overall mechanical properties and impermeability of cement materials, thus obtaining activated coal gangue powder.

[0033] b. Add 7 mL of 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol. The long organic chain of 3-aminopropyltriethoxysilane imparts hydrophobicity to the surface of the coal gangue, effectively hindering the adsorption of water and the permeation of capillary channels. Then add 5 mL of deionized water and adjust the pH to 5.0 using acetic acid. Let it stand for hydrolysis for 40 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use. Add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate and react at 60 °C for 6 h. Filter, dry the precipitate at 80 °C, and grind it. The activated coal gangue powder with a porous structure has a surface structure formed by Si-O-Si covalent bonds. A layer of 3-aminopropyltriethoxysilane molecules was firmly grafted onto the coal gangue. The introduced amino functional groups enhanced the chemical compatibility and adhesion between the coal gangue and the cement hydration products, improved the fragile interface transition zone, and enhanced the load-bearing capacity. The strengthened interface can also effectively transfer and disperse stress, reduce the initiation of microcracks, and thus improve the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, the introduced hydrophobic alkyl chains formed a hydrophobic film on the inner wall of the cement capillary channels, which can block water intrusion. The uniformly dispersed hydrophobic particles not only further cut off the connectivity of the capillaries and enhanced the impermeability of the material, but also fully filled the micropores, making the structure more compact, thus obtaining 3-aminopropyltriethoxysilane-grafted activated coal gangue powder.

[0034] c. Carboxylated graphene oxide (CSH) was ultrasonically dispersed in 1000 mL of deionized water. The amount of CSH added was 2.0 g, with a sheet diameter of 5 μm and a thickness of 1.2 nm. The CSH sheets provided large attachment and nucleation sites for the hydration products, guiding the CSH gel to grow more densely and orderly, forming a high-strength matrix. This ordered and dense hydration product structure naturally has lower porosity and more tortuous channels, directly hindering water and ion penetration, forming a CSH dispersion for later use. Then, 10.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b was weighed and added to the CSH dispersion. The mixture was ultrasonically treated for 30 min, and then continuously stirred at 800 rpm at room temperature. During the continuous stirring process, the pH was adjusted to 10.0. The reaction was then carried out in an 80℃ water bath for 6 hours. After the reaction was completed, the mixture was filtered, and the product was washed five times alternately with anhydrous ethanol and deionized water. Finally, it was dried at 60℃. Carboxylated graphene oxide was coated on the surface of 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Through the covalent bonding of amide and amino groups, it can effectively prevent the propagation of microcracks and act as a nanotemplate to guide the orderly growth of hydration products, thereby significantly improving compressive strength and flexural strength. In addition, the carboxyl functional groups on the surface can improve the compatibility with cement paste. Through its steric hindrance effect, it can improve the uniform dispersion of coal gangue composite powder in the paste, reduce structural defects, and enhance mechanical properties. At the same time, the uniformly dispersed composite powder further forms a more homogeneous barrier network in the paste, improving the overall uniformity of impermeability, thus obtaining modified grafted activated coal gangue composite powder.

[0035] d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of 28% ammonia solution until homogeneous. Then add 0.8 g of hexadecyltrimethylammonium bromide and stir at room temperature for 6 hours to form a sol. The modified grafted activated coal gangue composite powder from step c is ultrasonically dispersed in 100 mL of anhydrous ethanol to form an active dispersion. The active dispersion is slowly added to the sol at 600 rpm and stirred at 60°C for 10 hours. After standing for 24 hours, the mixture is centrifuged, and the solid product is collected. The solid product is washed five times alternately with anhydrous ethanol and deionized water, dried at 80°C, and finally placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 550℃ at a rate of 5℃ / min and held for 3 hours. After calcination, an ordered mesoporous silica shell was coated on the surface of the modified grafted activated coal gangue composite powder. The mesoporous shell can adsorb and slowly release moisture, continuously promoting the later hydration of the internal coal gangue and cement, reducing autogenous shrinkage. The active silica in the shell participates in the hydration reaction, generating more CSH gel, which not only optimizes the interface transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix, significantly reducing porosity. The encapsulation effect of the dense mesoporous silica shell further prevents the intrusion of moisture and corrosive ions, thereby improving the impermeability and obtaining a coal gangue-based reinforced admixture.

[0036] This embodiment provides a method for preparing a coal gangue-based reinforced cement composite material, specifically including the following steps:

[0037] S1. 2.0 g of multi-walled carbon nanotubes (MWCNTs) with a diameter of 15 nm and a length of 50 μm were placed in an extraction bottle. The MCCNTs embedded in the cement hydration products act as nano-reinforcing steel, effectively improving the compressive strength of the matrix. When microcracks propagate, the MCCNTs bridge the cracks, transferring stress and consuming fracture energy, significantly increasing the material's compressive strength. The nucleation effect of the MCCNTs and their own pore-filling properties refine the capillary channels within the cement stone, blocking interconnected permeation paths, improving anti-permeation ability, and thus reducing the penetration depth of chloride ions. Next, 150 mL of acetone solution was added, and the mixture was heated under reflux at 70 °C for 4 hours. The acetone solution was then poured off, and the MCCNTs were washed 10 times sequentially with anhydrous ethanol and deionized water. The washed MCCNTs were then vacuum-dried at 80 °C for 12 hours to obtain pretreated MCCNTs. The mixture was placed in a round-bottom flask connected to a reflux condenser and operated in a dedicated fume hood. 150 mL of a mixed acid of concentrated nitric acid and concentrated sulfuric acid was added, with a volume ratio of 1:4. The mixture was heated at 60 °C for 6 h, centrifuged at 12000 rpm for 10 min, and the precipitate was washed 10 times with anhydrous ethanol and deionized water. Then, it was filtered through a 0.5 μm microporous membrane and dried. Through strong acid oxidation treatment, a large number of carboxyl and hydroxyl functional groups were introduced on the surface of the multi-walled carbon nanotubes, which served as sites for heterogeneous nucleation of hydration products, accelerating and optimizing the cement hydration process, making the microstructure more compact, which is beneficial to improving strength and toughness. Furthermore, the bridging effect of the multi-walled carbon nanotubes can effectively inhibit the generation and propagation of microcracks, reduce the channels for water and corrosive ions to enter, and thus further improve the impermeability, resulting in oxidized multi-walled carbon nanotubes.

[0038] S2. Add 8.6 mL of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol. The introduction of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability. It also improves the steric hindrance of multi-walled carbon nanotubes, making them more uniformly and stably dispersed in cement materials. Then add 4.5 mL of deionized water, adjust the pH to 5.5 with acetic acid, and stir for 40 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution for later use. Immerse the oxidized multi-walled carbon nanotubes obtained in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution, reflux at 70 °C for 3 h, and centrifuge. The solid material was rinsed five times with anhydrous ethanol and deionized water and dried. The organic molecular chains grafted onto the surface of the multi-walled carbon nanotubes by N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane achieved the amination modification of the multi-walled carbon nanotubes, which can form a more uniform and stable three-dimensional network in the cement matrix, physically blocking the migration channels of water and corrosive ions. Among them, the amino groups at the end of the molecular chain form strong hydrogen bonds or ionic bonds with oxygen atoms or hydroxyl groups in cement hydration products, which greatly strengthens the interfacial adhesion. The dense interfacial bonding and the enhanced multi-walled carbon nanotube matrix completely support the higher flexural and compressive strength. The strong interfacial bonding also eliminates the weak transition zone between traditional admixtures and cement matrix, greatly reducing interfacial microcracks and pores. The amino groups in the middle of the molecular chain have strong complexing ability, which is conducive to subsequent induced mineralization, thus obtaining modified multi-walled carbon nanotubes.

[0039] S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1500 mL of deionized water, then add 1.5 g of sodium dodecyl sulfate, ultrasonically disperse for 40 min, then add 150 mL of 12% calcium chloride solution, adjust the pH to 10.0, continue ultrasonic dispersion for 30 min, and add 150 mL of 10% sodium carbonate solution at a rate of 1 drop / second using a constant pressure dropping funnel while stirring at 800 rpm. After the addition is complete, heat to 60°C and react for 2 h. Centrifuge, wash the precipitate 5 times alternately with anhydrous ethanol and deionized water, and finally dry at 80°C. In this process, the modified multi-walled carbon nanotubes serve as the core, covering an in-situ generated nano-calcium carbonate shell. The calcium carbonate shell tightly wraps around the surface of the modified multi-walled carbon nanotubes, which can both fill the pores and increase the surface roughness and nucleation activity, synergistically modifying the multi-walled carbon nanotubes. Both significantly improve the mechanical properties and impermeability of cement materials, resulting in calcium ion-doped modified multi-walled carbon nanotubes.

[0040] S4. Disperse the calcium ion-doped modified multi-walled carbon nanotubes described in step S3 in 1 / 3 of the water, place it in an ice-water bath and ultrasonically disperse it at 1000W for 30 minutes to form a suspension. Then add 1 / 2 of the polycarboxylate superplasticizer to the suspension, followed by polypropylene fiber, and stir at 300rpm for 15 minutes to obtain a mixed slurry for later use. Mix P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume in a mixer for 2 minutes, add the remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water, and stir for 5 minutes. Then add the mixed slurry, continue stirring for 5 minutes, and discharge the material. Calcium ion-doped modified multi-walled carbon nanotubes fill the nanopores, and coal gangue-based reinforcing admixtures fill the micron pores, achieving seamless filling from nano and micron, making the cement matrix extremely dense. At the same time, the coal gangue-based reinforcing admixtures can optimize the interface transition zone, while the calcium ion-doped modified multi-walled carbon nanotubes act as rivets at the interface. The joint interface of the two transforms the fragile transition zone into a strong and tough composite material interface, thereby improving the mechanical properties and impermeability of the cement material, resulting in a coal gangue-based reinforced cement composite material.

[0041] Example 2

[0042] This embodiment proposes a coal gangue-based reinforced cement composite material, comprising the following components in parts by weight: 20 parts of coal gangue-based reinforcing admixture, 0.08 parts of calcium ion-doped modified multi-walled carbon nanotubes, 0.5 parts of polypropylene fiber, 90 parts of P.O42.5 silicate cement, 10 parts of metakaolin, 5 parts of silica fume, 1.5 parts of polycarboxylate superplasticizer, and 25 parts of water.

[0043] The preparation method of coal gangue-based reinforced admixtures specifically includes the following steps:

[0044] a) Crush 9.0g of coal gangue and pass it through a 200-mesh sieve. Collect the crushed coal gangue and dry it in a 105℃ oven. Then add it to 200mL of 6.8% hydrochloric acid solution and place it in a 60℃ water bath. Stir for 2 hours. Pour off the hydrochloric acid solution. Wash the solid repeatedly with deionized water until the pH reaches 7.0. Dry it at 105℃ for 12 hours. Finally, place it in a tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. Hold the temperature for 1 hour and allow it to cool naturally. The coal gangue was extracted, ground, and then subjected to a combination of acid washing and calcination to optimize its pore structure, reduce the proportion of open pores and the overall water absorption rate. At the same time, the clay minerals such as kaolinite in the coal gangue were dehydrated and decomposed to generate highly active amorphous Al2O3 and SiO2, which can not only partially melt and fill the micropores, but also undergo a pozzolanic reaction to generate hydration gel when used as a cement admixture, further improving the overall mechanical properties and impermeability of the cement material, thus obtaining activated coal gangue powder.

[0045] b. Add 5 mL of 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol. The long organic chain of 3-aminopropyltriethoxysilane imparts hydrophobicity to the surface of the coal gangue, effectively hindering the adsorption of water and the permeation of capillary channels. Then add 3 mL of deionized water and adjust the pH to 4.0 using acetic acid. Let it stand for hydrolysis for 30 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use. Add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate and react at 50 °C for 5 h. Filter, dry the precipitate at 60 °C, and grind it. The activated coal gangue powder with a porous structure has a surface structure formed by Si-O-Si covalent bonds. A layer of 3-aminopropyltriethoxysilane molecules was firmly grafted onto the coal gangue. The introduced amino functional groups enhanced the chemical compatibility and adhesion between the coal gangue and the cement hydration products, improved the fragile interface transition zone, and enhanced the load-bearing capacity. The strengthened interface can also effectively transfer and disperse stress, reduce the initiation of microcracks, and thus improve the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, the introduced hydrophobic alkyl chains formed a hydrophobic film on the inner wall of the cement capillary channels, which can block water intrusion. The uniformly dispersed hydrophobic particles not only further cut off the connectivity of the capillaries and enhanced the impermeability of the material, but also fully filled the micropores, making the structure more compact, thus obtaining 3-aminopropyltriethoxysilane-grafted activated coal gangue powder.

[0046] c. Carboxylated graphene oxide (CSH) was ultrasonically dispersed in 1000 mL of deionized water. The amount of CSH added was 1.0 g, with a sheet diameter of 0.5 μm and a thickness of 0.8 nm. The CSH sheets provided large attachment and nucleation sites for the hydration products, guiding the CSH gel to grow more densely and orderly, forming a high-strength matrix. This ordered and dense hydration product structure naturally has lower porosity and more tortuous channels, directly hindering water and ion penetration, forming a CSH dispersion for later use. Then, 8.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b was weighed and added to the CSH dispersion. The mixture was ultrasonically treated for 20 min, and then continuously stirred at 600 rpm at room temperature. During the continuous stirring process, the pH was adjusted to 9.0. The reaction was then carried out in a 60℃ water bath for 4 hours. After the reaction was completed, the mixture was filtered, and the product was washed three times alternately with anhydrous ethanol and deionized water. Finally, it was dried at 60℃. Carboxylated graphene oxide was coated on the surface of 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Through the covalent bonding of amide and amino groups, it can effectively prevent the propagation of microcracks and act as a nanotemplate to guide the orderly growth of hydration products, thereby significantly improving the compressive strength and flexural strength. In addition, the carboxyl functional groups on the surface can improve the compatibility with cement paste. Through its steric hindrance effect, it can improve the uniform dispersion of coal gangue composite powder in the paste, reduce structural defects, and enhance mechanical properties. At the same time, the uniformly dispersed composite powder further forms a more homogeneous barrier network in the paste, improving the overall uniformity of impermeability, thus obtaining modified grafted activated coal gangue composite powder.

[0047] d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of 25% ammonia solution until homogeneous. Then add 0.4 g of hexadecyltrimethylammonium bromide and stir at room temperature for 4 hours to form a sol. The modified grafted activated coal gangue composite powder from step c is ultrasonically dispersed in 50 mL of anhydrous ethanol to form an active dispersion. The active dispersion is slowly added to the sol at 500 rpm and stirred at 50°C for 6 hours. After standing for 12 hours, the mixture is centrifuged, and the solid product is collected. The product is washed three times alternately with anhydrous ethanol and deionized water, and dried at 60°C. Finally, the dried powder is placed in a tube furnace and... Under a nitrogen atmosphere, the temperature was increased to 450℃ at a rate of 5℃ / min and held for 1 hour. After calcination, an ordered mesoporous silica shell was coated on the surface of the modified grafted activated coal gangue composite powder. The mesoporous shell can adsorb and slowly release moisture, continuously promoting the later hydration of the internal coal gangue and cement, reducing autogenous shrinkage. The active silica in the shell participates in the hydration reaction, generating more CSH gel, which not only optimizes the interface transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix, significantly reducing porosity. The coating effect of the dense mesoporous silica shell further prevents the intrusion of moisture and corrosive ions, thereby improving the impermeability and obtaining a coal gangue-based reinforced admixture.

[0048] This embodiment provides a method for preparing a coal gangue-based reinforced cement composite material, specifically including the following steps:

[0049] S1. Place 1.0 g of multi-walled carbon nanotubes (MWCNTs) into an extraction bottle. The MCCNTs have a diameter of 8 nm and a length of 50 μm. Embedded in cement hydration products, the MCCNTs act as nano-reinforcing steel, effectively improving the compressive strength of the matrix. When microcracks propagate, the MCCNTs bridge the cracks, transferring stress and consuming fracture energy, significantly enhancing the material's compressive strength. The nucleation effect of the MCCNTs and their own pore-filling properties refine the capillary channels within the cement paste, blocking interconnected permeation paths and improving anti-permeation capabilities, thereby reducing the penetration depth of chloride ions. Then, add 150 mL of acetone solution and heat under reflux at 70 °C for 2 h. Pour off the acetone solution and wash the MCCNTs six times sequentially with anhydrous ethanol and deionized water. After washing, vacuum dry the MCCNTs at 60 °C for 8 h to obtain pretreated MCCNTs. The mixture was placed in a round-bottom flask connected to a reflux condenser and operated in a dedicated fume hood. 150 mL of a mixed acid of concentrated nitric acid and concentrated sulfuric acid was added, with a volume ratio of 1:4. The mixture was heated at 50 °C for 4 h, centrifuged at 10,000 rpm for 6 min, and the precipitate was washed 6 times with anhydrous ethanol and deionized water. Then, it was filtered through a 0.1 μm microporous membrane and dried. Through strong acid oxidation treatment, a large number of carboxyl and hydroxyl functional groups were introduced on the surface of the multi-walled carbon nanotubes, which served as sites for heterogeneous nucleation of hydration products, accelerating and optimizing the cement hydration process, making the microstructure more compact, which is beneficial to improving strength and toughness. Furthermore, the bridging effect of the multi-walled carbon nanotubes can effectively inhibit the generation and propagation of microcracks, reduce the channels for water and corrosive ions to enter, and thus further improve the impermeability, resulting in oxidized multi-walled carbon nanotubes.

[0050] S2. Add 8.0 mL of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol. The introduction of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability. It also improves the steric hindrance of multi-walled carbon nanotubes, making them more uniformly and stably dispersed in cement materials. Then add 3.6 mL of deionized water, adjust the pH to 4.5 with acetic acid, and stir for 30 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution for later use. Immerse the oxidized multi-walled carbon nanotubes described in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution and reflux at 60-70 °C for 2 h. The solid material was rinsed three times with anhydrous ethanol and deionized water and dried. The organic molecular chains grafted onto the surface of the multi-walled carbon nanotubes by N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane achieved the amination modification of the multi-walled carbon nanotubes, which can form a more uniform and stable three-dimensional network in the cement matrix, physically blocking the migration channels of water and corrosive ions. Among them, the amino groups at the end of the molecular chain form strong hydrogen bonds or ionic bonds with oxygen atoms or hydroxyl groups in cement hydration products, which greatly strengthens the interfacial adhesion. The dense interfacial bonding and the enhanced multi-walled carbon nanotube matrix completely support the higher flexural and compressive strength. The strong interfacial bonding also eliminates the weak transition zone between traditional admixtures and cement matrix, greatly reducing interfacial microcracks and pores. The amino groups in the middle of the molecular chain have strong complexing ability, which is conducive to subsequent induced mineralization, thus obtaining modified multi-walled carbon nanotubes.

[0051] S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1000 mL of deionized water, then add 1.0 g of sodium dodecyl sulfate, ultrasonically disperse for 30 min, then add 150 mL of 10% calcium chloride solution, adjust the pH to 9.0, continue ultrasonic dispersion for 20 min, and add 150 mL of 9% sodium carbonate solution at a rate of 1 drop / second using a constant pressure dropping funnel while stirring at 600 rpm. After the addition is complete, heat to 50°C, react for 1 h, centrifuge, wash the precipitate three times alternately with anhydrous ethanol and deionized water, and finally dry at 80°C. In this process, the modified multi-walled carbon nanotubes serve as the core, covered by an in-situ generated nano-calcium carbonate shell. The calcium carbonate shell tightly wraps around the surface of the modified multi-walled carbon nanotubes, which can both fill the pores and increase the surface roughness and nucleation activity, synergistically modifying the multi-walled carbon nanotubes. Both significantly improve the mechanical properties and impermeability of cement materials, resulting in calcium ion-doped modified multi-walled carbon nanotubes.

[0052] S4. Disperse the calcium ion-doped modified multi-walled carbon nanotubes described in step S3 in 1 / 3 of the water, place it in an ice-water bath and ultrasonically disperse it at 800W for 20 minutes to form a suspension. Then add 1 / 2 of the polycarboxylate superplasticizer to the suspension, followed by polypropylene fiber, and stir at 200rpm for 10 minutes to obtain a mixed slurry for later use. Mix P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume in a mixer for 1 minute, add the remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water, and stir for 3 minutes. Then add the mixed slurry, continue stirring for 3 minutes, and discharge. Calcium ion-doped modified multi-walled carbon nanotubes fill the nanopores, and coal gangue-based reinforcing admixtures fill the micron pores, achieving seamless filling from nano and micron, making the cement matrix extremely dense. At the same time, the coal gangue-based reinforcing admixtures can optimize the interface transition zone, while the calcium ion-doped modified multi-walled carbon nanotubes act as rivets at the interface. The joint interface of the two transforms the fragile transition zone into a strong and tough composite material interface, thereby improving the mechanical properties and impermeability of the cement material, resulting in a coal gangue-based reinforced cement composite material.

[0053] Example 3

[0054] This embodiment proposes a coal gangue-based reinforced cement composite material, comprising the following components in parts by weight: 25 parts of coal gangue-based reinforcing admixture, 0.10 parts of calcium ion-doped modified multi-walled carbon nanotubes, 1.0 part of polypropylene fiber, 95 parts of P.O42.5 silicate cement, 12.5 parts of metakaolin, 7.5 parts of silica fume, 1.75 parts of polycarboxylate superplasticizer, and 30 parts of water.

[0055] The preparation method of coal gangue-based reinforced admixtures specifically includes the following steps:

[0056] a) Crush 9.5g of coal gangue and pass it through a 200-mesh sieve. Collect the crushed coal gangue and dry it in a 105℃ oven. Then add it to 200mL of 7.0% hydrochloric acid solution and place it in a 70℃ water bath. Stir for 2.5h, pour off the hydrochloric acid solution, and wash the solid repeatedly with deionized water until the pH reaches 7.0. Dry it at 107℃ for 15h, and finally place it in a tube furnace. Under a nitrogen atmosphere, heat the mixture to 800℃ at a rate of 5℃ / min and hold it at that temperature for 1.5h. Cooling, removal, grinding, and a combination of acid washing and calcination optimize the pore structure of coal gangue, reducing the proportion of open pores and the overall water absorption rate. At the same time, clay minerals such as kaolinite in the coal gangue dehydrate and decompose, generating highly active amorphous Al2O3 and SiO2, which can not only partially melt and fill the micropores, but also undergo pozzolanic reaction to generate hydration gel when used as cement admixtures, further improving the overall mechanical properties and impermeability of cement materials, thus obtaining activated coal gangue powder.

[0057] b. Add 6 mL of 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol. The long organic chain of 3-aminopropyltriethoxysilane imparts hydrophobicity to the surface of the coal gangue, effectively hindering the adsorption of water and the permeation of capillary channels. Then add 4 mL of deionized water, adjust the pH to 4.5 with acetic acid, and let it stand for hydrolysis for 35 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use. Add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate and react at 55 °C for 5.5 h. Filter, dry the precipitate at 70 °C, grind, and the activated coal gangue powder with a porous structure, through Si-O-Si covalent bonds, has a surface... A layer of 3-aminopropyltriethoxysilane molecules was firmly grafted onto the surface. The introduced amino functional groups enhanced the chemical compatibility and adhesion between coal gangue and cement hydration products, improved the fragile interface transition zone, and enhanced the load-bearing capacity. The strengthened interface can also effectively transfer and disperse stress, reduce the initiation of microcracks, and thus improve the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, the introduced hydrophobic alkyl chains formed a hydrophobic film on the inner wall of the cement capillary channels, which can block water intrusion. The uniformly dispersed hydrophobic particles not only further cut off the connectivity of the capillaries and enhanced the impermeability of the material, but also fully filled the micropores, making the structure more compact, thus obtaining 3-aminopropyltriethoxysilane-grafted activated coal gangue powder.

[0058] c. Carboxylated graphene oxide (CSH) was ultrasonically dispersed in 1000 mL of deionized water. The amount of CSH added was 1.5 g, with a sheet diameter of 3 μm and a thickness of 1.0 nm. The CSH sheets provided large attachment and nucleation sites for the hydration products, guiding the CSH gel to grow more densely and orderly, forming a high-strength matrix. This ordered and dense hydration product structure naturally has lower porosity and more tortuous channels, directly hindering water and ion penetration, forming a CSH dispersion for later use. Then, 9.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b was weighed and added to the CSH dispersion. The mixture was ultrasonically treated for 25 min, and then continuously stirred at 700 rpm at room temperature. During the continuous stirring process, the pH was adjusted to 9.5. The mixture was then reacted in a 70℃ water bath for 5 hours. After the reaction was completed, it was filtered, and the product was washed four times alternately with anhydrous ethanol and deionized water. Finally, it was dried at 60℃. Carboxylated graphene oxide was coated on the surface of 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Through the covalent bonding of amide and amino groups, it can effectively prevent the propagation of microcracks and act as a nanotemplate to guide the orderly growth of hydration products, thereby significantly improving compressive strength and flexural strength. In addition, the carboxyl functional groups on the surface can improve the compatibility with cement paste. Through its steric hindrance effect, it can improve the uniform dispersion of coal gangue composite powder in the paste, reduce structural defects, and enhance mechanical properties. At the same time, the uniformly dispersed composite powder further forms a more homogeneous barrier network in the paste, improving the overall uniformity of impermeability, thus obtaining modified grafted activated coal gangue composite powder.

[0059] d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of ammonia solution with a mass fraction of 26.5% evenly. Then add 0.6 g of hexadecyltrimethylammonium bromide and stir at room temperature for 5 h to form a sol for later use. Ultrasonically disperse the modified grafted activated coal gangue composite powder described in step c in 75 mL of anhydrous ethanol to form an active dispersion for later use. Slowly add the active dispersion to the sol at 550 rpm and stir at 55 °C for 8 h. Then let it stand for 18 h, centrifuge, collect the solid product, and wash it four times alternately with anhydrous ethanol and deionized water. Dry it at 70 °C. Finally, place the dried powder in a tube furnace. Under a nitrogen atmosphere, the temperature is increased to 500℃ at a rate of 5℃ / min and held for 2 hours. After calcination, an ordered mesoporous silica shell is coated on the surface of the modified grafted activated coal gangue composite powder. The mesoporous shell can adsorb and slowly release moisture, continuously promoting the later hydration of the internal coal gangue and cement, reducing autogenous shrinkage. The active silica in the shell participates in the hydration reaction, generating more CSH gel, which not only optimizes the interface transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix, significantly reducing porosity. The coating effect of the dense mesoporous silica shell further prevents the intrusion of moisture and corrosive ions, thereby improving the impermeability and obtaining a coal gangue-based reinforced admixture.

[0060] This embodiment provides a method for preparing a coal gangue-based reinforced cement composite material, specifically including the following steps:

[0061] S1. 1.5 g of multi-walled carbon nanotubes (MWCNTs) with a diameter of 12 nm and a length of 50 μm were placed in an extraction bottle. The MCCNTs embedded in the cement hydration products act as nano-reinforcing steel, effectively improving the compressive strength of the matrix. When microcracks propagate, the MCCNTs bridge the cracks, transferring stress and consuming fracture energy, significantly increasing the material's compressive strength. The nucleation effect of the MCCNTs and their own pore-filling properties refine the capillary channels inside the cement stone, blocking interconnected permeation paths and improving anti-permeation ability, thereby reducing the penetration depth of chloride ions. Then, 150 mL of acetone solution was added, and the mixture was heated under reflux at 70 °C for 3 hours. The acetone solution was then discarded, and the MCCNTs were washed eight times sequentially with anhydrous ethanol and deionized water. After washing, the MCCNTs were vacuum-dried at 70 °C for 10 hours to obtain pretreated MCCNTs. The sample was placed in a round-bottom flask connected to a reflux condenser and operated in a dedicated fume hood. 150 mL of a mixed acid of concentrated nitric acid and concentrated sulfuric acid was added, with a volume ratio of 1:4. The mixture was heated at 55 °C for 5 h, centrifuged at 11,000 rpm for 8 min, and the precipitate was washed 8 times with anhydrous ethanol and deionized water. Then, it was filtered through a 0.3 μm microporous membrane and dried. Through strong acid oxidation treatment, a large number of carboxyl and hydroxyl functional groups were introduced on the surface of the multi-walled carbon nanotubes, which served as sites for heterogeneous nucleation of hydration products, accelerating and optimizing the cement hydration process, making the microstructure more compact, which is beneficial to improving strength and toughness. Furthermore, the bridging effect of the multi-walled carbon nanotubes can effectively inhibit the generation and propagation of microcracks, reduce the channels for water and corrosive ions to enter, and thus further improve the impermeability, resulting in oxidized multi-walled carbon nanotubes.

[0062] S2. Add 8.3 mL of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol. The introduction of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability. It also improves the steric hindrance of multi-walled carbon nanotubes, making them more uniformly and stably dispersed in cement materials. Then add 4.0 mL of deionized water, adjust the pH to 5.0 with acetic acid, and stir for 35 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution for later use. Immerse the oxidized multi-walled carbon nanotubes obtained in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution and reflux at 65 °C for 2.5 h. The solid material was rinsed four times with anhydrous ethanol and deionized water and dried. The organic molecular chains grafted onto the surface of the multi-walled carbon nanotubes by N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane achieved the amination modification of the multi-walled carbon nanotubes. This can form a more uniform and stable three-dimensional network in the cement matrix, physically blocking the migration channels of water and corrosive ions. Among them, the amino groups at the end of the molecular chain form strong hydrogen bonds or ionic bonds with oxygen atoms or hydroxyl groups in cement hydration products, which greatly strengthens the interfacial adhesion. The dense interfacial bonding and the enhanced multi-walled carbon nanotube matrix completely support higher flexural and compressive strength. The strong interfacial bonding also eliminates the weak transition zone between traditional admixtures and cement matrix, greatly reducing interfacial microcracks and pores. The amino groups in the middle of the molecular chain have strong complexing ability, which is conducive to subsequent induced mineralization, thus obtaining modified multi-walled carbon nanotubes.

[0063] S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1250 mL of deionized water, then add 1.25 g of sodium dodecyl sulfate, ultrasonically disperse for 35 min, then add 150 mL of 11% calcium chloride solution, adjust the pH to 9.5, continue ultrasonic dispersion for 25 min, and add 150 mL of 9.5% sodium carbonate solution at a rate of 1 drop / second using a constant pressure dropping funnel while stirring at 700 rpm. After the addition is complete, heat to 55°C and react for 1.5 h. Centrifuge, wash the precipitate four times alternately with anhydrous ethanol and deionized water, and finally dry at 80°C. In this process, the modified multi-walled carbon nanotubes serve as the core, covering an in-situ generated nano-calcium carbonate shell. The calcium carbonate shell tightly wraps around the surface of the modified multi-walled carbon nanotubes, which can both fill the pores and increase the surface roughness and nucleation activity, synergistically improving the mechanical properties and impermeability of cement materials, thus obtaining calcium ion-doped modified multi-walled carbon nanotubes.

[0064] S4. Disperse the calcium ion-doped modified multi-walled carbon nanotubes described in step S3 in 1 / 3 of the water, place it in an ice-water bath and ultrasonically disperse it at 900W for 25 minutes to form a suspension. Then add 1 / 2 of the polycarboxylate superplasticizer to the suspension, followed by polypropylene fiber, and stir at 250rpm for 12.5 minutes to obtain a mixed slurry for later use. Mix P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume in a mixer for 1.5 minutes, add the remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water, and stir for 4 minutes. After stirring for 4 minutes, the mixed slurry is added and stirred for another 4 minutes. The mixture is then discharged. Calcium ion-doped modified multi-walled carbon nanotubes fill the nanopores, while coal gangue-based reinforcing admixtures fill the micron pores, achieving seamless filling from the nano and micron levels. This results in an extremely dense cement matrix. Simultaneously, the coal gangue-based reinforcing admixtures optimize the interface transition zone, while the calcium ion-doped modified multi-walled carbon nanotubes act as rivets at the interface. Together, they transform the fragile transition zone into a strong and tough composite material interface, thereby improving the mechanical properties and impermeability of the cement material, resulting in a coal gangue-based reinforced cement composite material.

[0065] Example 4

[0066] This embodiment proposes a coal gangue-based reinforced cement composite material, comprising the following components in parts by weight: 30 parts of coal gangue-based reinforcing admixture, 0.08 parts of calcium ion-doped modified multi-walled carbon nanotubes, 1.5 parts of polypropylene fiber, 100 parts of P.O42.5 silicate cement, 15 parts of metakaolin, 10 parts of silica fume, 2.0 parts of polycarboxylate superplasticizer, and 35 parts of water.

[0067] The preparation method of coal gangue-based reinforced admixtures specifically includes the following steps:

[0068] a. Crush 10.0g of coal gangue and pass it through a 200-mesh sieve. Collect the crushed coal gangue and dry it in an oven at 105℃. Then add it to 200mL of 7.2% hydrochloric acid solution and place it in an 80℃ water bath. Stir for 3 hours. Pour off the hydrochloric acid solution. Wash the solid repeatedly with deionized water until the pH reaches 7.0. Dry it at 110℃ for 18 hours. Finally, place it in a tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. Hold the temperature for 2 hours and allow it to cool naturally. However, after extraction and grinding, the pore structure of the coal gangue was optimized through a combination of acid washing and calcination, reducing the proportion of open pores and the overall water absorption rate. At the same time, the clay minerals such as kaolinite in the coal gangue were dehydrated and decomposed to generate highly active amorphous Al2O3 and SiO2, which can not only partially melt and fill the micropores, but also undergo pozzolanic reaction to generate hydration gel when used as cement admixture, further improving the overall mechanical properties and impermeability of cement materials, thus obtaining activated coal gangue powder.

[0069] b. Add 5 mL of 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol. The long organic chain of 3-aminopropyltriethoxysilane imparts hydrophobicity to the surface of the coal gangue, effectively hindering the adsorption of water and the permeation of capillary channels. Then add 5 mL of deionized water, adjust the pH to 5.0 with acetic acid, and let it stand for hydrolysis for 40 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use. Add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate and react at 60 °C for 6 h. Filter, dry the precipitate at 80 °C, and grind it. The activated coal gangue powder with a porous structure has a surface structure formed by Si-O-Si covalent bonds. A layer of 3-aminopropyltriethoxysilane molecules was firmly grafted onto the coal gangue. The introduced amino functional groups enhanced the chemical compatibility and adhesion between the coal gangue and the cement hydration products, improved the fragile interface transition zone, and enhanced the load-bearing capacity. The strengthened interface can also effectively transfer and disperse stress, reduce the initiation of microcracks, and thus improve the mechanical properties of the material, such as compressive strength and flexural strength. At the same time, the introduced hydrophobic alkyl chains formed a hydrophobic film on the inner wall of the cement capillary channels, which can block water intrusion. The uniformly dispersed hydrophobic particles not only further cut off the connectivity of the capillaries and enhanced the impermeability of the material, but also fully filled the micropores, making the structure more compact, thus obtaining 3-aminopropyltriethoxysilane-grafted activated coal gangue powder.

[0070] c. Carboxylated graphene oxide (CSH) was ultrasonically dispersed in 1000 mL of deionized water. The amount of CSH added was 1.0 g, with a sheet diameter of 5 μm and a thickness of 1.2 nm. The CSH sheets provided large attachment and nucleation sites for the hydration products, guiding the CSH gel to grow more densely and orderly, forming a high-strength matrix. This ordered and dense hydration product structure naturally has lower porosity and more tortuous channels, directly hindering water and ion penetration, forming a CSH dispersion for later use. Then, 10.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b was weighed and added to the CSH dispersion. The mixture was ultrasonically treated for 30 min, and then continuously stirred at 800 rpm at room temperature. During the continuous stirring process, the pH was adjusted to 10.0. The reaction was then carried out in an 80℃ water bath for 6 hours. After the reaction was completed, the mixture was filtered, and the product was washed five times alternately with anhydrous ethanol and deionized water. Finally, it was dried at 60℃. Carboxylated graphene oxide was coated on the surface of 3-aminopropyltriethoxysilane-grafted activated coal gangue powder. Through the covalent bonding of amide and amino groups, it can effectively prevent the propagation of microcracks and act as a nanotemplate to guide the orderly growth of hydration products, thereby significantly improving compressive strength and flexural strength. In addition, the carboxyl functional groups on the surface can improve the compatibility with cement paste. Through its steric hindrance effect, it can improve the uniform dispersion of coal gangue composite powder in the paste, reduce structural defects, and enhance mechanical properties. At the same time, the uniformly dispersed composite powder further forms a more homogeneous barrier network in the paste, improving the overall uniformity of impermeability, thus obtaining modified grafted activated coal gangue composite powder.

[0071] d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of 28% ammonia solution until homogeneous. Then add 0.8 g of hexadecyltrimethylammonium bromide and stir at room temperature for 6 hours to form a sol. The modified grafted activated coal gangue composite powder from step c is ultrasonically dispersed in 100 mL of anhydrous ethanol to form an active dispersion. The active dispersion is slowly added to the sol at 600 rpm and stirred at 60°C for 10 hours. After standing for 24 hours, the mixture is centrifuged, and the solid product is collected. The solid product is washed five times alternately with anhydrous ethanol and deionized water, dried at 80°C, and finally placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 550℃ at a rate of 5℃ / min and held for 3 hours. After calcination, an ordered mesoporous silica shell was coated on the surface of the modified grafted activated coal gangue composite powder. The mesoporous shell can adsorb and slowly release moisture, continuously promoting the later hydration of the internal coal gangue and cement, reducing autogenous shrinkage. The active silica in the shell participates in the hydration reaction, generating more CSH gel, which not only optimizes the interface transition zone and improves mechanical properties, but also efficiently fills the pores in the cement matrix, significantly reducing porosity. The encapsulation effect of the dense mesoporous silica shell further prevents the intrusion of moisture and corrosive ions, thereby improving the impermeability and obtaining a coal gangue-based reinforced admixture.

[0072] This embodiment provides a method for preparing a coal gangue-based reinforced cement composite material, specifically including the following steps:

[0073] S1. 2.0 g of multi-walled carbon nanotubes (MWCNTs) with a diameter of 15 nm and a length of 50 μm were placed in an extraction bottle. The MCCNTs embedded in the cement hydration products act as nano-reinforcing steel, effectively improving the compressive strength of the matrix. When microcracks propagate, the MCCNTs bridge the cracks, transferring stress and consuming fracture energy, significantly increasing the material's compressive strength. The nucleation effect of the MCCNTs and their own pore-filling properties refine the capillary channels within the cement stone, blocking interconnected permeation paths, improving anti-permeation ability, and thus reducing the penetration depth of chloride ions. Next, 150 mL of acetone solution was added, and the mixture was heated under reflux at 70 °C for 4 hours. The acetone solution was then poured off, and the MCCNTs were washed 10 times sequentially with anhydrous ethanol and deionized water. The washed MCCNTs were then vacuum-dried at 80 °C for 12 hours to obtain pretreated MCCNTs. The mixture was placed in a round-bottom flask connected to a reflux condenser and operated in a dedicated fume hood. 150 mL of a mixed acid of concentrated nitric acid and concentrated sulfuric acid was added, with a volume ratio of 1:4. The mixture was heated at 60 °C for 6 h, centrifuged at 12000 rpm for 10 min, and the precipitate was washed 10 times with anhydrous ethanol and deionized water. Then, it was filtered through a 0.5 μm microporous membrane and dried. Through strong acid oxidation treatment, a large number of carboxyl and hydroxyl functional groups were introduced on the surface of the multi-walled carbon nanotubes, which served as sites for heterogeneous nucleation of hydration products, accelerating and optimizing the cement hydration process, making the microstructure more compact, which is beneficial to improving strength and toughness. Furthermore, the bridging effect of the multi-walled carbon nanotubes can effectively inhibit the generation and propagation of microcracks, reduce the channels for water and corrosive ions to enter, and thus further improve the impermeability, resulting in oxidized multi-walled carbon nanotubes.

[0074] S2. Add 8.0 mL of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol. The introduction of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane constructs a dual-amino functional surface with high reactivity and strong interfacial bonding ability. It also improves the steric hindrance of multi-walled carbon nanotubes, making them more uniformly and stably dispersed in cement materials. Then add 4.5 mL of deionized water, adjust the pH to 5.5 with acetic acid, and stir for 40 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution for later use. Immerse the oxidized multi-walled carbon nanotubes obtained in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution, reflux at 70 °C for 3 h, and centrifuge. The solid material was rinsed five times with anhydrous ethanol and deionized water and dried. The organic molecular chains grafted onto the surface of the multi-walled carbon nanotubes by N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane achieved the amination modification of the multi-walled carbon nanotubes, which can form a more uniform and stable three-dimensional network in the cement matrix, physically blocking the migration channels of water and corrosive ions. Among them, the amino groups at the end of the molecular chain form strong hydrogen bonds or ionic bonds with oxygen atoms or hydroxyl groups in cement hydration products, which greatly strengthens the interfacial adhesion. The dense interfacial bonding and the enhanced multi-walled carbon nanotube matrix completely support the higher flexural and compressive strength. The strong interfacial bonding also eliminates the weak transition zone between traditional admixtures and cement matrix, greatly reducing interfacial microcracks and pores. The amino groups in the middle of the molecular chain have strong complexing ability, which is conducive to subsequent induced mineralization, thus obtaining modified multi-walled carbon nanotubes.

[0075] S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1500 mL of deionized water, then add 1.5 g of sodium dodecyl sulfate, ultrasonically disperse for 40 min, then add 150 mL of 10% calcium chloride solution, adjust the pH to 10.0, continue ultrasonic dispersion for 30 min, and while stirring at 800 rpm, add 150 mL of 9% sodium carbonate solution at a rate of 1 drop / second using a constant pressure dropping funnel. After the addition is complete, heat to 60°C, react for 2 h, centrifuge, wash the precipitate 5 times alternately with anhydrous ethanol and deionized water, and finally dry at 80°C. In this process, the modified multi-walled carbon nanotubes serve as the core, covering an in-situ generated nano-calcium carbonate shell. The calcium carbonate shell tightly wraps around the surface of the modified multi-walled carbon nanotubes, which can both fill the pores and increase the surface roughness and nucleation activity, synergistically modifying the multi-walled carbon nanotubes. Both significantly improve the mechanical properties and impermeability of cement materials, resulting in calcium ion-doped modified multi-walled carbon nanotubes.

[0076] S4. Disperse the calcium ion-doped modified multi-walled carbon nanotubes described in step S3 in 1 / 3 of the water, place it in an ice-water bath and ultrasonically disperse it at 1000W for 30 minutes to form a suspension. Then add 1 / 2 of the polycarboxylate superplasticizer to the suspension, followed by polypropylene fiber, and stir at 300rpm for 15 minutes to obtain a mixed slurry for later use. Mix P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume in a mixer for 2 minutes, add the remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water, and stir for 5 minutes. Then add the mixed slurry, continue stirring for 5 minutes, and discharge the material. Calcium ion-doped modified multi-walled carbon nanotubes fill the nanopores, and coal gangue-based reinforcing admixtures fill the micron pores, achieving seamless filling from nano and micron, making the cement matrix extremely dense. At the same time, the coal gangue-based reinforcing admixtures can optimize the interface transition zone, while the calcium ion-doped modified multi-walled carbon nanotubes act as rivets at the interface. The joint interface of the two transforms the fragile transition zone into a strong and tough composite material interface, thereby improving the mechanical properties and impermeability of the cement material, resulting in a coal gangue-based reinforced cement composite material.

[0077] Comparative Example 1

[0078] This comparative example provides a coal gangue-based reinforced cement composite material, which differs from Example 1 in that the coal gangue-based reinforcing admixture does not contain carboxylated graphene oxide; the preparation method of the coal gangue-based reinforcing admixture does not include step (3); the preparation method of the coal gangue-based reinforced cement composite material is the same as that of Example 1.

[0079] Comparative Example 2

[0080] This comparative example provides a coal gangue-based reinforced cement composite material, which differs from Example 1 in that the coal gangue-based reinforcing admixture does not contain silicon dioxide; the preparation method of the coal gangue-based reinforcing admixture does not include step (4); and the preparation method of the coal gangue-based reinforced cement composite material is the same as that of Example 1.

[0081] Comparative Example 3

[0082] This comparative example provides a coal gangue-based reinforced cement composite material, which differs from Example 1 in that the calcium ion-doped modified multi-walled carbon nanotubes do not contain N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; the preparation method of the coal gangue-based reinforcing admixture is the same as that of Example 1; the preparation method of the coal gangue-based reinforced cement composite material does not include step S2.

[0083] In the above preparation process, Fourier transform infrared spectroscopy (FTIR) was used to characterize the coal gangue-based reinforcing admixture and the calcium ion-doped modified multi-walled carbon nanotubes. Figure 3As shown, in the FTIR results of the coal gangue-based reinforced admixture, the characteristic peaks of NH and CH confirm the successful grafting of 3-aminopropyltriethoxysilane; the appearance of amide bonds (-CO-NH-) indicates that carboxylated graphene oxide is wrapped on the surface of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder, and is covalently bonded to amino groups through amide groups; the Si-O-Si peak and Si-OH shoulder peak confirm the successful coating of the mesoporous silica shell; in the FTIR results of calcium ion-doped modified multi-walled carbon nanotubes, the characteristic peaks of NH and CH confirm the successful grafting of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; the simultaneous appearance of the characteristic peak of calcium carbonate confirms the successful in-situ formation of the calcium carbonate shell on the surface of the modified carbon nanotubes.

[0084] Experimental Example 1

[0085] Mechanical property test

[0086] Test samples: Coal gangue-based reinforced cement composites prepared in Examples 1-4 and Comparative Examples 1-3.

[0087] Test method: The test sample was molded in a mold with dimensions of 40mm×40mm×160mm. After demolding, it was placed in a standard curing chamber (temperature 20±1℃, humidity ≥95%) and cured for 28 days. The compressive strength and flexural strength were tested according to the "Test Method for Strength of Cement Mortar (ISO Method): GBT17671—2021". The flexural and compressive strength of the mortar were measured by a computer-controlled compressive strength testing machine. The flexural test was conducted by uniformly applying a load at a rate of 50 N / s vertically to the opposite sides of the prism with a loading cylinder until the specimen broke. The compressive test was conducted on the side of the half prism, with a uniform load applied at a rate of 2.4 kN / s until the specimen failed.

[0088] Figure 1The figures show the mechanical property results of Examples 1-4 and Comparative Examples 1-3. As shown, the compressive strength and flexural strength of Example 1 are 92 MPa and 20 MPa, respectively; the compressive strength and flexural strength of Example 2 are 88 MPa and 18 MPa, respectively; the compressive strength and flexural strength of Example 3 are 90 MPa and 19 MPa, respectively; and the compressive strength and flexural strength of Example 4 are 85 MPa and 17 MPa, respectively, indicating strong mechanical properties. The compressive strength and flexural strength of Comparative Example 1 are 52 MPa and 6 MPa, respectively; the compressive strength and flexural strength of Comparative Example 2 are 73 MPa and 13 MPa, respectively; and the compressive strength and flexural strength of Comparative Example 3 are 65 MPa and 10 MPa, respectively, indicating relatively weak mechanical properties. Generally speaking, the coal gangue-based reinforcing admixture in Comparative Example 1 does not contain carboxylated graphene oxide, so it cannot prevent microcrack propagation through carboxylated graphene oxide sheets, nor can it act as a nanotemplate to guide the orderly growth of hydration products, resulting in generally poor mechanical properties. The coal gangue-based reinforcing admixture in Comparative Example 2 does not contain silica, so it cannot adsorb and release moisture through the mesoporous silica shell, which is not conducive to continuously promoting the later hydration of internal coal gangue and cement, and is not conducive to generating more CSH gel, resulting in generally poor mechanical properties. The calcium ion-doped modified multi-walled carbon nanotubes in Comparative Example 3 do not contain N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, so it cannot introduce a dual-amino functional surface with high reactivity and strong interfacial bonding ability, resulting in generally poor mechanical properties.

[0089] Experiment Example 2

[0090] Permeability test

[0091] Test samples: Coal gangue-based reinforced cement composites prepared in Examples 1-4 and Comparative Examples 1-3.

[0092] Test method: The test sample was made into a cylinder with a diameter of 100mm and a diameter of 50mm, and then placed in a standard curing chamber (temperature 20±1℃, humidity ≥95%). After curing for 28 days, the sample was subjected to chloride ion diffusion test. The specific operation was performed according to the RCM method in the "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T50082-2024). The chloride ion diffusion coefficient (×10) was finally obtained. -12 m 2 / s).

[0093] Figure 2 The graph shows the chloride ion diffusion coefficients for Examples 1-4 and Comparative Examples 1-3. As shown in the figure, the chloride ion diffusion coefficients for Examples 1-4 are 1.5 × 10⁻⁶. -12 m 2 / s, 2.8×10 -12 m 2 / s, 2.3×10 -12 m2 / s, 3.1×10 -12 m 2 / s indicates good impermeability; the chloride ion diffusion coefficients of comparative examples 1-3 are 6.9×10 -12 m 2 / s, 10.7×10 -12 m 2 / s, 5.3×10 -12 m 2 / s indicates that the impermeability is average. The coal gangue-based reinforcing admixture in Comparative Example 1 does not contain carboxylated graphene oxide, thus lacking the barrier effect of carboxylated graphene oxide sheets, resulting in average impermeability. The coal gangue-based reinforcing admixture in Comparative Example 2 does not contain silica, which is not conducive to optimizing the interface transition zone, cannot efficiently fill the pores in the cement matrix, and cannot exert the encapsulating effect of the mesoporous silica shell, thus not conducive to preventing the intrusion of moisture and corrosive ions, resulting in average impermeability. The calcium ion-doped modified multi-walled carbon nanotubes in Comparative Example 3 do not contain N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, which is not conducive to forming a uniform and stable three-dimensional network in the cement matrix through the dual-amino functional surface, thus not conducive to blocking the migration channels of moisture and corrosive ions, resulting in average impermeability.

[0094] The above experimental results show that the mechanical properties and impermeability of Examples 1-4 of the present invention are significantly better than those of Comparative Examples 1-3. Among them, Example 1, which uses coal gangue-based reinforcing admixture and calcium ion-doped modified multi-walled carbon nanotubes, has stronger mechanical properties and better impermeability. The synergistic addition of calcium ion-doped modified multi-walled carbon nanotubes and coal gangue-based reinforcing admixture to the cement matrix not only achieves seamless filling from nanometer to micrometer, but also forms a strong and tough interface transition zone. The dense matrix and strong interface jointly bear the pressure, significantly enhancing the compressive strength and flexural strength of the material. At the same time, it effectively blocks the migration of moisture and ions, improving the impermeability of the material.

[0095] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

[0096] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A coal gangue-based reinforced cement composite material, characterized in that: The coal gangue-based reinforced cement composite material comprises the following components in parts by weight: 20-30 parts of coal gangue-based reinforcing admixture, 0.08-0.12 parts of calcium ion-doped modified multi-walled carbon nanotubes, 0.5-1.5 parts of polypropylene fiber, 90-100 parts of P.O42.5 silicate cement, 10-15 parts of metakaolin, 5-10 parts of silica fume, 1.5-2.0 parts of polycarboxylate superplasticizer, and 25-35 parts of water. The method for preparing the calcium ion-doped modified multi-walled carbon nanotubes includes the following steps: S1. Place multi-walled carbon nanotubes into an extraction bottle, then add 150 mL of acetone solution, heat and reflux at 70°C for 2-4 hours, pour out the acetone solution, wash the multi-walled carbon nanotubes with anhydrous ethanol and deionized water 6-10 times in sequence, and vacuum dry the washed multi-walled carbon nanotubes at 60-80°C for 8-12 hours to obtain pretreated multi-walled carbon nanotubes. Place them in a round-bottom flask connected to a reflux condenser and operate in a special fume hood. Add 150 mL of a mixed acid of concentrated nitric acid and concentrated sulfuric acid, wherein the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:4, heat at 50-60°C for 4-6 hours, centrifuge at high speed at 10000-12000 rpm for 6-10 minutes, wash the precipitate with anhydrous ethanol and deionized water 6-10 times, filter it with a 0.1-0.5 μm microporous membrane, and finally dry it to obtain oxidized multi-walled carbon nanotubes. S2. Add N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane to 360 mL of anhydrous ethanol, then add 3.6-4.5 mL of deionized water, adjust the pH to 4.5-5.5 with acetic acid, stir for 30-40 min to form an N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution for later use. Immerse the oxidized multi-walled carbon nanotubes obtained in step S1 into the N-(β-aminoethyl)-γ-aminopropyltrimethoxysilanol solution, reflux at 60-70 °C for 2-3 h, centrifuge, wash the solid material with anhydrous ethanol and deionized water 3-5 times, and dry to obtain modified multi-walled carbon nanotubes. S3. Disperse the modified multi-walled carbon nanotubes described in step S2 in 1000-1500 mL of deionized water, then add 1.0-1.5 g of sodium dodecyl sulfate, sonicate for 30-40 min, then add 150 mL of calcium chloride solution with a mass fraction of 10-12%, adjust the pH to 9.0-10.0, continue sonication for 20-30 min, and add 150 mL of sodium carbonate solution with a mass fraction of 9-10% at a rate of 1 drop / second using a constant pressure dropping funnel while stirring at 600-800 rpm. After the addition is complete, heat to 50-60℃ and react for 1-2 h. Centrifuge, wash the precipitate alternately with anhydrous ethanol and deionized water 3-5 times, and finally dry at 80℃ to obtain calcium ion-doped modified multi-walled carbon nanotubes. The preparation method of the coal gangue-based reinforced admixture specifically includes the following steps: a. Crush 9.0-10.0g of coal gangue and pass it through a 200-mesh sieve. Collect the coal gangue powder and dry it in an oven at 105℃. Then add it to 200mL of hydrochloric acid solution with a mass fraction of 6.8-7.2% and place it in a water bath at 60-80℃. Stir for 2-3 hours. Pour off the hydrochloric acid solution. Wash the solid repeatedly with deionized water until the pH is 7.

0. Dry it at 105-110℃ for 12-18 hours. Finally, place it in a tube furnace and heat it to 800℃ at a rate of 5℃ / min under a nitrogen atmosphere. Hold the temperature for 1-2 hours. Cool it naturally, take it out, grind it, and obtain activated coal gangue powder. b. Add 3-aminopropyltriethoxysilane to 193 mL of anhydrous ethanol, then add 3-5 mL of deionized water, adjust the pH to 4.0-5.0 with acetic acid, let stand for hydrolysis for 30-40 min to form a 3-aminopropyltriethoxysilane hydrolysate for later use, add the activated coal gangue powder from step a to the 3-aminopropyltriethoxysilane hydrolysate, react at 50-60℃ for 5-6 h, filter, dry the precipitate at 60-80℃, grind to obtain 3-aminopropyltriethoxysilane-grafted activated coal gangue powder; c. Disperse carboxylated graphene oxide in 1000 mL of deionized water using ultrasonication to form a carboxylated graphene oxide dispersion for later use. Then, weigh 8.0-10.0 g of the 3-aminopropyltriethoxysilane-grafted activated coal gangue powder described in step b and add it to the carboxylated graphene oxide dispersion. First, ultrasonically treat for 20-30 min, then continuously stir at 600-800 rpm at room temperature. During the continuous stirring process, adjust the pH to 9.0-10.

0. Then, react in a water bath at 60-80℃ for 4-6 h. After the reaction is complete, filter the product and wash it alternately with anhydrous ethanol and deionized water 3-5 times. Finally, dry it at 60℃ to obtain the modified grafted activated coal gangue composite powder. d. Mix 5.2 mL of tetraethyl orthosilicate, 9.5 mL of anhydrous ethanol, 1.9 mL of deionized water, and 0.65 mL of ammonia solution with a mass fraction of 25-28% until homogeneous. Then add 0.4-0.8 g of hexadecyltrimethylammonium bromide and stir at room temperature for 4-6 hours to form a sol for later use. Ultrasonically disperse the modified grafted activated coal gangue composite powder described in step c in 50-100 mL of anhydrous ethanol to form an active dispersion for later use. The dispersion was slowly added to the sol at 500-600 rpm and stirred at 50-60℃ for 6-10 h. After standing for 12-24 h, the solid product was collected by centrifugation and washed 3-5 times alternately with anhydrous ethanol and deionized water. The product was dried at 60-80℃ and then placed in a tube furnace. Under a nitrogen atmosphere, the temperature was increased to 450-550℃ at a rate of 5℃ / min and held for 1-3 h to obtain the coal gangue-based reinforced admixture.

2. A method for preparing a coal gangue-based reinforced cement composite material according to claim 1, characterized in that: Specifically, the following steps are included: The prepared calcium ion-doped modified multi-walled carbon nanotubes were dispersed in 1 / 3 of the water and placed in an ice-water bath for ultrasonic dispersion at 800-1000W for 20-30 minutes to form a suspension. Then, 1 / 2 of the polycarboxylate superplasticizer was added to the suspension, followed by polypropylene fibers. The mixture was stirred at 200-300 rpm for 10-15 minutes to obtain a mixed slurry for later use. P.O42.5 silicate cement, coal gangue-based reinforcing admixture, metakaolin, and silica fume were stirred in a mixer for 1-2 minutes. The remaining 1 / 2 of the polycarboxylate superplasticizer and the remaining 2 / 3 of the water were added and stirred for 3-5 minutes. Then, the mixed slurry was added and stirred for another 3-5 minutes. The mixture was then discharged to obtain a coal gangue-based reinforced cement composite material.

3. The method for preparing the coal gangue-based reinforced cement composite material according to claim 2, characterized in that: In step S1, the amount of multi-walled carbon nanotubes added is 1.0-2.0g, with a diameter of 8-15nm and a length of 50μm.

4. The method for preparing the coal gangue-based reinforced cement composite material according to claim 3, characterized in that: In step S2, the amount of N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane added is 8.0-8.6 mL.

5. The method for preparing the coal gangue-based reinforced cement composite material according to claim 4, characterized in that: In step b, the amount of 3-aminopropyltriethoxysilane added is 5-7 mL.

6. The method for preparing the coal gangue-based reinforced cement composite material according to claim 5, characterized in that: In step c, the amount of carboxylated graphene oxide added is 1.0-2.0 g, the sheet diameter is 0.5-5 μm, and the thickness is 0.8-1.2 nm.

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