Carbonized fly ash-based super-hydrophobic mortar, preparation method and application thereof

Abstract

The application provides a carbonized fly ash based super-hydrophobic mortar and a preparation method and application thereof, and belongs to the technical field of building materials. The preparation method of the super-hydrophobic mortar comprises the following steps: adding carbide slag and fly ash into a magnesium chloride aqueous solution, stirring, introducing CO2, and performing carbonization reaction; after the reaction is completed, filtering and drying are performed to obtain carbonized fly ash; cement, the carbonized fly ash and fine sand are mixed and uniformly mixed, then water containing fluorosilane is added, stirring is uniformly performed, cement mortar is obtained, the obtained cement mortar is introduced into a mold, and curing is performed to obtain the super-hydrophobic mortar. Through the synergistic carbonization of fly ash and carbide slag and the crystal type regulation of magnesium chloride, the application prepares mineralized fly ash, combines fluorosilane, realizes the super-hydrophobic performance of the mortar, and further prolongs the durability of concrete as repair mortar.

Description

Technical Field

[0001] This invention relates to a superhydrophobic mortar based on carbonized fly ash, its preparation method and application, belonging to the field of building materials technology. Background Technology

[0002] Concrete is a porous material with interconnected pores and capillary channels. Water can permeate and migrate through these pores. When the water contains harmful ions (such as chloride ions and sulfate ions), it triggers a series of chemical reactions that accelerate concrete deterioration, easily leading to cracks, spalling, and other problems, severely reducing the mechanical properties and durability of concrete. Therefore, preventing water penetration is crucial for improving concrete durability.

[0003] The "lotus effect" can be used to prepare superhydrophobic coatings, which can effectively improve the resistance of concrete to freezing, impermeability, and chemical erosion. The construction of superhydrophobic coatings requires low surface energy materials and micro / nano structures. Common preparation methods suffer from problems such as high cost, complex processes, low yield, or stringent equipment requirements, which limit their large-scale application.

[0004] Fly ash is a byproduct of coal-fired power plants. Unused fly ash is stored in landfills, and improper disposal can pollute water sources and soil. The calcium carbide process for acetylene production produces calcium carbide slag; the storage of calcium carbide slag occupies large amounts of land, causing water pollution and impacting the surrounding ecological environment. Therefore, developing a simple method for preparing superhydrophobic concrete mortar using fly ash and calcium carbide slag, employing a solid waste co-mineralization approach, is of significant importance. This invention is proposed to this end. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the poor durability of concrete due to water permeability, this invention provides a superhydrophobic mortar based on carbonized fly ash, its preparation method, and its application. This invention employs a solid waste synergistic mineralization approach, using carbide slag as the calcium source and fly ash as the matrix. The two work together to promote heterogeneous nucleation of calcium carbonate, thereby forming micro-nano structures on the surface of fly ash particles, resulting in carbonized fly ash. Carbonized fly ash is used to replace a portion of the cement in the preparation and application of superhydrophobic mortar. Through synergistic carbonation and crystal form regulation, the mortar achieves superhydrophobicity, extending the lifespan of concrete. This invention prepares carbonized fly ash through synergistic carbonation of fly ash and carbide slag, with magnesium chloride regulating the crystal form. Combined with fluorosilanes, this achieves superhydrophobic properties in the mortar, serving as a repair mortar to further extend the durability of concrete.

[0006] To solve the above technical problems, the technical solution of the present invention is as follows:

[0007] A method for preparing superhydrophobic mortar based on carbonized fly ash includes the following steps:

[0008] (1) Add carbide slag and fly ash to magnesium chloride aqueous solution, stir, and then introduce CO2 to carry out carbonization reaction; after the reaction is completed, filter and dry to obtain carbonized fly ash;

[0009] (2) Mix cement, carbonized fly ash and fine sand evenly, then add water containing fluorosilane and stir evenly to obtain cement mortar. Pour the obtained cement mortar into a mold and cure it to obtain superhydrophobic mortar based on carbonized fly ash.

[0010] According to a preferred embodiment of the present invention, the carbide slag in step (1) comprises the following components in parts by mass: 85-88 parts CaO, 3-4 parts SiO2, 3-5 parts SO3, 1-2 parts Al2O3, and 0.1-0.5 parts MgO; the particle size of the carbide slag is 2-10 μm, more preferably 4 μm.

[0011] According to a preferred embodiment of the present invention, the fly ash in step (1) comprises the following components in parts by mass: 50-55 parts SiO2, 30-36 parts Al2O3, 4.5-5.5 parts Fe2O3, 2-3 parts CaO, and 0.5-1 parts MgO; the particle size of the fly ash is 1-8 μm, more preferably 6 μm, and the specific surface area of ​​the fly ash is 450-500 m². 2 / g.

[0012] According to a preferred embodiment of the present invention, the mass of the carbide slag in step (1) is 5-15% of the total mass of carbide slag and fly ash. As the amount of carbide slag increases, the amount of calcium carbonate generated on the surface of fly ash increases, the surface roughness of fly ash particles increases, and the contact angle increases. When the amount of carbide slag is too high, too much calcium carbonate coats the surface of fly ash, the roughness decreases, and the hydrophobic effect deteriorates. Therefore, it is necessary to control this proportion within the range of the present invention.

[0013] According to a preferred embodiment of the present invention, the concentration of the magnesium chloride aqueous solution in step (1) is 0.15-0.3 mol / L, more preferably 0.25 mol / L; the volume ratio of the magnesium chloride aqueous solution to the total mass of carbide slag and fly ash is 5-10 mL:1 g, more preferably 8 mL:1 g.

[0014] According to a preferred embodiment of the present invention, the stirring speed in step (1) is 500-1000 rpm, and CO2 is introduced after stirring until the pH of the system remains unchanged.

[0015] According to a preferred embodiment of the present invention, the flow rate of CO2 in step (1) is 1-2 L / min; controlling the flow rate of CO2 can effectively control the crystal nucleus size and distribution.

[0016] According to a preferred embodiment of the present invention, the temperature of the carbonization reaction in step (1) is 20-60°C, more preferably 40°C; when CO2 is introduced and the reaction is stopped when the pH of the system reaches 7-8; the specific reaction temperature of the present invention can suppress the excessive formation of calcite.

[0017] According to a preferred embodiment of the present invention, in step (1), the stirring rate during the carbonation reaction is 500-1000 rpm. If the stirring rate is too low, the calcium carbonate will be unevenly distributed; if the stirring rate is too high, the calcium carbonate will easily fall off, reducing the coverage.

[0018] According to a preferred embodiment of the present invention, the drying in step (1) is performed at 103-107°C for 24-48 hours.

[0019] According to a preferred embodiment of the present invention, the mass of the carbonized fly ash in step (2) is 20-40% of the total mass of the carbonized fly ash and cement; the ratio of the total mass of the cement and carbonized fly ash to the mass of the fine sand is 1:1.

[0020] According to a preferred embodiment of the present invention, the fluorosilane in step (2) is perfluorodecyltriethoxysilane (CAS No.: 101947-16-4); the mass of the fluorosilane is 0.3-1.0% of the total mass of cement, carbonized fly ash and fine sand, more preferably 0.5%.

[0021] According to a preferred embodiment of the present invention, in step (2), the water-cement ratio is 0.3-0.4, where the water-cement ratio is the mass ratio of water to cement.

[0022] According to a preferred embodiment of the present invention, the stirring speed in step (2) is 5000-7000 rpm and the stirring time is 20-40 min.

[0023] According to a preferred embodiment of the present invention, the curing step in step (2) is to cure at room temperature for 20-30 hours; room temperature has a well-known meaning in the art, referring to 25±5℃.

[0024] The present invention also provides a superhydrophobic mortar based on carbonized fly ash, which is prepared by the above preparation method.

[0025] According to the present invention, the above-mentioned superhydrophobic mortar based on carbonized fly ash is used as a repair mortar to extend the durability of concrete.

[0026] The technical features and beneficial effects of this invention are as follows:

[0027] 1. This invention utilizes a wet carbonation process, mixing pretreated fly ash, carbide slag, and magnesium chloride solution, followed by the introduction of carbon dioxide to initiate a reaction. The carbide slag and fly ash undergo synergistic mineralization, allowing calcium carbonate to disperse and adhere ectopically to the fly ash surface. This structure differs from that of carbonation products from single carbide slag, contributing to improved carbon fixation rate and product performance, as well as better product stability. Magnesium chloride, acting as a crystal form regulator, dissolves and releases ionized magnesium ions. Due to its high charge density and small ionic radius, magnesium ions exchange with calcium ions and adsorb onto the surface of calcium carbonate crystal nuclei, influencing nucleus growth and promoting the formation of aragonite-type calcium carbonate. The unique growth pattern of aragonite-type calcium carbonate significantly increases the surface roughness of fly ash, while the effect of calcite-type calcium carbonate is weaker. When aragonite reaches a certain proportion, its needle-like or columnar crystals intertwine with calcite, constructing a suitable microstructure and increasing surface roughness. This invention can achieve a balance between superhydrophobic properties and mechanical properties by adjusting the ratio of calcite to aragonite in the calcium carbonate on the surface of fly ash, thereby changing the Ra roughness of the surface of the carbonized fly ash.

[0028] 2. This invention uses fly ash, an industrial waste, as the main raw material, realizing the resource utilization of waste and reducing environmental pollution. Compared with traditional superhydrophobic coating preparation methods, the raw material cost is significantly reduced, resulting in good economic and environmental benefits.

[0029] 3. In this invention, the surface of the carbonized fly ash is covered with calcium carbonate particles, forming numerous protrusions that significantly increase surface roughness. According to Cassie theory, this rough structure reduces the actual contact area between the liquid and the solid, forming an air layer between the droplet and the solid surface, promoting droplet rolling and laying the foundation for superhydrophobic properties. Fluorosilanes have extremely low surface energy and hydrolyze to form silanols upon contact with carbonized fly ash. Silanols undergo dehydration condensation with the hydroxyl groups on the surface of fly ash and calcium carbonate particles, grafting fluoroalkyl groups onto their surfaces, significantly reducing surface energy, increasing the droplet contact angle, and further enhancing superhydrophobic properties. When cement is mixed with water, a hydration reaction occurs, and the resulting hydration products not only tightly bind the carbonized fly ash particles to form an integral mortar structure but also fill the voids between particles, improving the density and strength of the mortar, giving the superhydrophobic mortar better durability and stability in practical use.

[0030] 4. This invention abandons the complex equipment and stringent processes in traditional superhydrophobic coating preparation, employing a simple and easy-to-implement preparation process to complete the preparation of superhydrophobic mortar from fly ash carbonization. Precise control of reaction parameters is key to this invention. Temperature significantly affects the crystal form of calcium carbonate. While increasing the temperature accelerates the reaction rate, it causes the metastable crystal form to transform into calcite, which is detrimental to the formation of aragonite required for roughness. Increasing the carbon dioxide flow rate reduces particle size; therefore, controlling the carbon dioxide flow rate controls the crystal nucleus size and distribution. Lower termination pH leads to a more complete reaction, but excessively low pH will cause calcium carbonate to form calcium bicarbonate, which is unfavorable for achieving roughness. Therefore, this invention controls the pH at 7-8. This invention avoids the decrease in mechanical properties caused by excessively high roughness by regulating the termination pH and temperature; simultaneously, temperature control inhibits excessive calcite formation. Precise control of these parameters ensures efficient and stable reaction, reduces production costs and technical barriers, and creates conditions for large-scale industrial production. Overall, this invention, through two key steps—carbonization and surface modification—successfully constructs a superhydrophobic mortar structure using simple processes and conventional equipment, greatly improving the feasibility of industrial production.

[0031] 5. This invention controls the calcium carbonate crystal ratio in carbonized fly ash by adjusting the magnesium chloride concentration, resulting in a superhydrophobic mortar with excellent performance. By controlling the carbonation process to achieve a calcium carbonate-to-slate ratio of 50% on the surface of the carbonized fly ash, the Ra roughness can reach up to 216 nm, the compressive strength ≥35 MPa, and the contact angle greater than 150°. This effectively blocks the penetration of moisture and harmful ions, significantly improving the concrete's resistance to freezing, impermeability, and chemical erosion. Furthermore, the coating exhibits good durability, maintaining stable superhydrophobic properties even after long-term use, providing long-term protection for concrete structures and significantly extending their service life. It has great potential for application in the field of building protection. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the carbonization reaction apparatus of the present invention.

[0033] Figure 2 The images shown are SEM images of the carbonized fly ash obtained in Example 1, where (a) is a high-magnification SEM image and (b) is a low-magnification SEM image.

[0034] Figure 3 The image shows the AFM pattern of the carbonized fly ash surface obtained in Example 1.

[0035] Figure 4 The image shows the surface contact angle test diagram of the superhydrophobic mortar obtained in Example 1.

[0036] Figure 5 The image shows the AFM pattern of the carbonized fly ash surface obtained in Example 2. Detailed Implementation

[0037] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments, but this is not the only description. Anything not described in detail in the present invention is based on conventional technology in the field.

[0038] The fly ash used in the examples comprises the following components in parts by weight: 52.23 parts SiO2, 34.36 parts Al2O3, 4.94 parts Fe2O3, 2.76 parts CaO, and 0.87 parts MgO;

[0039] The carbide slag comprises the following components in parts by mass: CaO 86.26 parts, SiO2 3.13 parts, SO3 4.01 parts, Al2O3 1.39 parts, MgO 0.21 parts, with a particle size of 4 μm.

[0040] Cement: PO 42.5 ordinary Portland cement with a density of 3150 kg / m³ is used. 3 .

[0041] Sand: Standard sand.

[0042] Perfluorodecyltriethoxysilane: Industrial grade, purity ≥98%.

[0043] Experimental instruments

[0044] Electronic balance: accuracy is 0.01g.

[0045] Mortar mixer: planetary type, with adjustable mixing speed.

[0046] Atomic force microscope (AFM): Equipped with a tapping mode, scanning range of 0.1μm-100μm, used to measure the surface roughness of carbonized fly ash, by fixing carbonized fly ash onto a dot adhesive for testing.

[0047] Contact angle meter: used to measure the water contact angle of mortar surfaces and evaluate superhydrophobic properties;

[0048] The contact angle test method is as follows: First, place a clean superhydrophobic mortar sample on a stable platform, turn on the instrument and calibrate all parameters, then use a microsyringe to draw 5 μL of deionized water to slowly generate a droplet on the sample surface. After the droplet stabilizes, the instrument's image acquisition system captures the image, and the built-in software analyzes the contact point between the droplet profile and the sample surface to calculate the hydrophobic angle.

[0049] QXRD Determination of Aragonite to Calcite Ratio: The ratio of aragonite to calcite in calcium carbonate on the surface of carbonized fly ash was determined by quantitative X-ray diffraction (QXRD). The main steps are as follows: The carbonized fly ash was ground to a particle size <10μm, and the sample was prepared using the back pressure method or side-loading method to reduce preferred orientation. Instrument parameters: Cu target (λ=1.5406Å), scanning range 20°-80°, step size 0.02°-0.05°, voltage 40kV, current 40mA. Data analysis: RIR method: The non-overlapping characteristic peaks of the two phases (aragonite 26.2°, calcite 29.4°) were selected, and the mass fraction was calculated by combining the reference intensity ratio (RIR). Rietveld full spectrum refinement: The crystal structure file was imported, the peak shape and background parameters were optimized, and the phase fraction was refined to residual convergence (Rwp<10%) for higher accuracy. The preferred orientation (aragonite needle-like crystals) was corrected, and instrument errors were calibrated (using standard samples). Verification was performed using cross-validation with TGA or SEM-EDS. Sample homogeneity was ensured, parameters were optimized, and data analysis was performed to correct for errors, guaranteeing a result error of <5%, which is a method currently used in this field.

[0050] Calcium carbonate coverage testing method: Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS): SEM can reveal the microscopic morphology of fly ash particles, while EDS can analyze elements in specific areas. The fly ash sample is first pretreated, dried, and sputter-coated with gold. Images are then acquired under SEM at an appropriate magnification. EDS is used to confirm the distribution of calcium carbonate, and finally, image analysis software is used to calculate the coverage.

[0051] Example 1

[0052] A method for preparing superhydrophobic mortar based on carbonized fly ash includes the following steps:

[0053] (1) Add 4g of carbide slag, 36g of fly ash (particle size of 6μm, specific surface area of ​​463.6m / g) and 320mL of 0.25mol / L magnesium chloride aqueous solution to a three-necked flask. Place the flask in a water bath and then turn on the magnetic stirrer. Stir at 600rpm until the pH value is stable. Then, introduce CO2 at a flow rate of 2L / min and carry out the carbonization reaction at 600rpm and 40℃ until the pH of the suspension is stable at 7. Stop introducing CO2. After the reaction is completed, filter and dry the solid at 105℃ for 24h to obtain carbonized fly ash.

[0054] (2) Place cement, carbonized fly ash and fine sand screened through a 60-mesh sieve into a beaker, place the beaker under a high-speed mixer, and stir at 3000 rpm for 30 seconds to make it uniformly mixed. Then add water containing perfluorodecyltriethoxysilane and stir at 6000 rpm for 30 minutes to obtain cement mortar. The mass of carbonized fly ash is 30% of the total mass of carbonized fly ash and cement, the ratio of the total mass of cement and carbonized fly ash to the mass of fine sand is 1:1, the mass of perfluorodecyltriethoxysilane is 0.5% of the total mass of cement, carbonized fly ash and fine sand, and the water-cement ratio is 0.3. Pour the obtained cement mortar into a mold and place it indoors for curing. After 24 hours of hardening, a superhydrophobic mortar based on carbonized fly ash is obtained.

[0055] In this embodiment, the ratio of calcium carbonate aragonite to calcite covering the surface of the carbonized fly ash is approximately 5:5. The SEM image of the obtained carbonized fly ash is shown below. Figure 2 As shown, by Figure 2 It can be seen that the generated aragonite-type calcium carbonate and calcite-type calcium carbonate adhere to the fly ash, forming a micro-nano structure, with calcium carbonate particles distributed in an ectopic manner. Figure 3 The AFM diagram of carbonized fly ash is shown by... Figure 3 It can be seen that its Ra roughness is 216 nm; the calcium carbonate coverage of the obtained carbonized fly ash surface is about 55%.

[0056] The superhydrophobic mortar obtained in this embodiment has a surface contact angle of 156.8°, and its contact angle test diagram is shown below. Figure 4 As shown.

[0057] Example 2

[0058] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the fly ash is replaced with a material with a specific surface area of ​​487.52 m². 2 / g of fly ash.

[0059] In this embodiment, the ratio of calcium carbonate sulphite to calcite covering the surface of the carbonized fly ash is approximately 5:5. Figure 5 For the AFM diagram of the obtained carbonized fly ash, we have Figure 5 It can be seen that its Ra roughness is 203 nm; the calcium carbonate coverage of the obtained carbonized fly ash surface is about 55%.

[0060] The superhydrophobic mortar obtained in this embodiment has a surface contact angle of 155.8°.

[0061] Example 3

[0062] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that CO2 is stopped when the pH of the suspension stabilizes at 8 in step (1).

[0063] The superhydrophobic mortar obtained in this embodiment has a surface contact angle of 152.1°.

[0064] Comparative Example 1

[0065] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the carbonization temperature in step (1) is 10°C.

[0066] In this comparative example, the ratio of calcium carbonate slab to calcite on the surface of the carbonized fly ash is approximately 4:6, and its Ra roughness is 162 nm.

[0067] The superhydrophobic mortar obtained in this comparative example has a surface contact angle of 145.8°.

[0068] Comparative Example 2

[0069] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the carbonization temperature in step (1) is controlled at 80°C.

[0070] In this comparative example, the ratio of calcium carbonate slab to calcite on the surface of the carbonized fly ash is approximately 9:1, and its Ra roughness is 152 nm.

[0071] The surface contact angle of the superhydrophobic mortar obtained in this comparative example is 142.7°.

[0072] Comparative Example 3

[0073] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that an equal volume of water is used instead of magnesium chloride aqueous solution in step (1).

[0074] In this comparative example, the ratio of calcium carbonate slab to calcite covering the surface of the carbonized fly ash is 1:20, and its Ra roughness is 125 nm.

[0075] The surface contact angle of the superhydrophobic mortar obtained in this comparative example is 144.6°.

[0076] Comparative Example 4

[0077] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the concentration of magnesium chloride aqueous solution used in step (1) is 0.1 mol / L.

[0078] The surface contact angle of the superhydrophobic mortar obtained in this comparative example is 145.6°.

[0079] Comparative Example 5

[0080] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the concentration of magnesium chloride aqueous solution used in step (1) is 0.5 mol / L.

[0081] In this comparative example, the ratio of calcium carbonate slab to calcite on the surface of the carbonized fly ash is approximately 2:8, and its Ra roughness is 168 nm.

[0082] The surface contact angle of the superhydrophobic mortar obtained in this comparative example is 146.8°.

[0083] Comparative Example 6

[0084] A method for preparing superhydrophobic mortar based on carbonized fly ash is described in Example 1, except that the carbonization reaction is terminated at pH 6 in step (1).

[0085] In this comparative example, the ratio of calcium carbonate slab to calcite on the surface of the carbonized fly ash is approximately 5:5, and its Ra roughness is 188 nm.

[0086] The superhydrophobic mortar obtained in this comparative example has a surface contact angle of 148.7°.

[0087] In summary, the superhydrophobic mortar of the present invention can be used as a concrete repair material, which can alleviate the problem of concrete damage caused by water penetration, and the material is more environmentally friendly.

Claims

1. A method for preparing superhydrophobic mortar based on carbonized fly ash, characterized in that, The steps include the following: (1) Add carbide slag and fly ash to a magnesium chloride aqueous solution, stir, and then introduce CO2 to carry out a carbonization reaction; after the reaction is completed, filter and dry to obtain carbonized fly ash; the mass of the carbide slag is 5-15% of the total mass of carbide slag and fly ash; the concentration of the magnesium chloride aqueous solution is 0.15-0.3 mol / L; the volume ratio of the magnesium chloride aqueous solution to the total mass of carbide slag and fly ash is 5-10 mL:1 g; the temperature of the carbonization reaction is 20-60℃; When CO2 is introduced, the reaction is stopped when the pH of the system reaches 7-8. (2) Cement, carbonized fly ash and fine sand are mixed evenly, and then water containing fluorosilane is added and stirred evenly to obtain cement mortar. The obtained cement mortar is poured into a mold and cured to obtain superhydrophobic mortar based on carbonized fly ash. The mass of the carbonized fly ash is 20-40% of the total mass of carbonized fly ash and cement. The ratio of the total mass of cement and carbonized fly ash to the mass of fine sand is 1:

1. The fluorosilane is perfluorodecyltriethoxysilane. The mass of the fluorosilane is 0.3-1.0% of the total mass of cement, carbonized fly ash and fine sand.

2. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The carbide slag mentioned in step (1) comprises the following components in parts by mass: CaO 85-88 parts, SiO2 3-4 parts, SO3 3-5 parts, Al2O3 1-2 parts, MgO 0.1-0.5 parts; the particle size of the carbide slag is 2-10 μm; The fly ash comprises the following components in parts by weight: SiO2 50-55 parts, Al2O3 30-36 parts, Fe2O3 4.5-5.5 parts, CaO 2-3 parts, and MgO 0.5-1 parts; the particle size of the fly ash is 1-8 μm, and the specific surface area of ​​the fly ash is 450-500 m². 2 / g.

3. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The concentration of the magnesium chloride aqueous solution in step (1) is 0.25 mol / L; the volume ratio of the magnesium chloride aqueous solution to the total mass of carbide slag and fly ash is 8 mL: 1 g.

4. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The stirring speed in step (1) is 500-1000 rpm. After stirring until the pH of the system remains unchanged, CO2 is introduced. The flow rate of the CO2 is 1-2 L / min.

5. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The carbonization reaction in step (1) is carried out at a temperature of 40°C.

6. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The stirring rate during the carbonization reaction in step (1) is 500-1000 rpm; the drying is carried out at 103-107℃ for 24-48 h.

7. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, The mass of the fluorosilane mentioned in step (2) is 0.5% of the total mass of cement, carbonized fly ash and fine sand.

8. The method for preparing superhydrophobic mortar based on carbonized fly ash according to claim 1, characterized in that, In step (2), the water-cement ratio is 0.3-0.4; the stirring speed is 5000-7000 rpm and the stirring time is 20-40 min; the curing step is to cure at room temperature for 20-30 h.

9. A superhydrophobic mortar based on carbonized fly ash, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. The application of the superhydrophobic mortar based on carbonized fly ash as described in claim 9, characterized in that, As a repair mortar, it is used to extend the durability of concrete.

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