Preparation method of modified nano calcium hydroxide and application thereof in prefabricated components

Abstract

The application discloses a preparation method of modified nano calcium hydroxide and application of the modified nano calcium hydroxide in prefabricated components and belongs to the technical field of concrete admixture materials. The modified nano calcium hydroxide prepared by the method has an average particle size of 50-90 nm, and after being mixed into cement, the modified nano calcium hydroxide can not only play a role in adjusting alkalinity, but also more importantly, can provide a crystal nucleus effect for cement hydration. Moreover, the nano calcium hydroxide prepared by the method has good stability, can quickly promote early strength of ordinary Portland cement, and has no influence on later strength.

Description

Technical Field

[0001] This invention belongs to the technical field of concrete admixture materials, specifically relating to a method for preparing modified nano-calcium hydroxide and its application in precast components. Background Technology

[0002] Precast components are building components made from concrete as the basic material and prefabricated in a factory. In recent years, with the rapid development of my country's construction industry, green development has been gradually integrated into the industry, resulting in an increasing demand for prefabricated buildings in the construction market. In the production process of precast concrete components, to accelerate the turnover of precast component molds and improve production efficiency, methods such as steam curing and the addition of early-strength agents are commonly used to improve the early strength of the components.

[0003] Steam curing requires high curing temperatures and consumes large amounts of fuel oil or coal, increasing production costs and polluting the environment. Furthermore, the long curing time, coupled with rudimentary equipment and outdated processes, reduces concrete durability. Therefore, this method has gradually been phased out by the market. Chemical accelerators often sacrifice later-stage strength to enhance early-stage strength, and they also present various other problems. For example, triethanolamine-based accelerators have compatibility issues; excessive use can lead to retarded setting and reduced early strength. Chlorine-containing accelerators can easily cause steel corrosion. Sulfate-based accelerators can reduce the impermeability and corrosion resistance of concrete, resulting in poorer concrete durability.

[0004] Nanocrystalline nucleus-type early-strength materials are a new type of harmless cement early-strength agent developed in recent years. Nanomaterials are characterized by their small size and large specific surface area, allowing them to fill voids in the cement paste and provide nucleation sites for the hydration products of cement. Currently, nano-cementing materials synthesized from hydration products are widely used as early-strength agents.

[0005] Chinese patent CN 104402009B discloses a hydrated calcium silicate gel solution early strength agent and its preparation method, which discloses a method for preparing hydrated calcium silicate gel using sodium silicate as the silicon source and calcium nitrate as the calcium source. CN106277901B discloses a fibrous nano-silicate concrete admixture and its preparation method, which discloses a method for preparing a fibrous nano-silicate concrete admixture using sodium silicate as the silicon source, calcium nitrate as the calcium source, and magnesium nitrate as the magnesium source. CN107032651B discloses a nucleation-type concrete early strength agent and its preparation method, which discloses a nucleation-type concrete early strength agent using polymers, sodium metasilicate, and calcium nitrate as raw materials. However, the early strength agents provided by the above patents have complex compositions and cumbersome preparation processes; moreover, the silicon source in the preparation methods of the early strength agents provided by the above patents all use sodium silicate or sodium metasilicate containing alkali (potassium and sodium ions), and the increase in alkali content will adversely affect the later strength and durability of concrete. In summary, the effect of early strength agents on improving concrete performance is currently very limited, and they cannot meet the requirements for the use of precast components. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a modified nano-calcium hydroxide, which can be used as an early strength agent for concrete while meeting the performance requirements of precast components.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0009] (1) Dissolve calcium nitrate tetrahydrate in water to obtain solution A, and simultaneously dissolve acrylic acid and sodium hydroxide in water to obtain solution B. Pour solution A and solution B into a colloid mill for emulsification and shearing to obtain a mixture.

[0010] (2) The mixture was placed in a nitrogen atmosphere to protect the reaction. After the reaction was completed, it was washed with deionized water and dried to obtain surface-modified nano-calcium hydroxide.

[0011] (3) Under nitrogen protection, the surface-modified nano-calcium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid, and azobisisobutyronitrile were placed in a container, deionized water was added, and the mixture was dispersed and mixed by ultrasonic vibration. The mixture was heated and stirred continuously at a constant temperature for 4-6 hours.

[0012] After natural cooling, the modified nano-calcium hydroxide is obtained by centrifugation and washing with ethanol 3-5 times and vacuum drying.

[0013] Preferably, in step (1), the mass concentration of calcium nitrate tetrahydrate in solution A is (0.14-0.2) g / mL, the mass concentration of acrylic acid in solution B is (0.12-0.16) g / mL, and the mass concentration of sodium hydroxide in solution B is 0.12 g / mL.

[0014] Preferably, the emulsification and shearing time in the colloid mill in step (1) is 2 min, and the shearing speed of the colloid mill is 5000 r / min.

[0015] Preferably, in step (2), the mixture is placed under nitrogen for 1-1.5 hours for protection and the reaction temperature is 0-10℃; the mixture is washed with deionized water 4-6 times and dried by vacuum drying.

[0016] Preferably, the mass ratio of the nano-calcium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid, azobisisobutyronitrile and deionized water in step (3) is (2-4):(1-3):(0.1-0.4):(40-60).

[0017] Preferably, in step (3), the temperature is raised to 60-80℃ and stirred continuously at a constant temperature of 60-80℃ at a stirring speed of 600r / min.

[0018] Preferably, the modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm.

[0019] Preferably, the dosage of modified nano-calcium hydroxide is 0.5-2% of the cement mass.

[0020] Modified nano-calcium hydroxide is incorporated into cement as an early-strength agent, and the resulting cement is used to prepare precast components.

[0021] Beneficial effects

[0022] (1) The present invention proposes a method for preparing and using modified nano-calcium hydroxide. First, acrylic acid (AA) is used to modify the surface of nano-calcium hydroxide during the synthesis process using a colloid mill, achieving rapid organication of the nano-calcium hydroxide surface compared to the co-precipitation method. Subsequently, the active chain of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is used to copolymerize with the active groups on the surface of nano-calcium hydroxide to anchor the polymer on the surface of nano-calcium hydroxide. The modified nano-calcium hydroxide has good dispersibility, is not prone to agglomeration, has good stability, and the nano-calcium hydroxide particles are significantly smaller than those before modification.

[0023] (2) This invention prepares a modified nano-calcium hydroxide with an average particle size of 50-90 nm. When incorporated into cement, it not only regulates alkalinity but, more importantly, provides nuclei for cement hydration, thus lowering the barrier to CSH gel formation and promoting its growth. Particles that are too large or too small will not function as nuclei and will only regulate alkalinity. Furthermore, the nano-calcium hydroxide prepared by this invention exhibits good stability, rapidly promoting the early strength of ordinary silicate cement without affecting its later strength, making it suitable for application in precast concrete. Attached Figure Description

[0024] Figure 1 The particle size distribution diagrams are for the nano-calcium hydroxide prepared in Embodiment 2 and Comparative Example 1 of this invention. Detailed Implementation

[0025] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0026] Example 1

[0027] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0028] (1) 7g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 6g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both diluted solutions A and B were simultaneously and quickly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 5°C for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0029] (2) 4 g of nano-calcium hydroxide, 1 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.1 g of azobisisobutyronitrile (AIBN), and 40 mL of deionized water were mixed in a 100 mL flask and dispersed by ultrasonic vibration for 3 min. The mixture was then heated to 70 °C and stirred with a magnetic stirrer for 5 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed five times by centrifugation with ethanol and then vacuum dried to obtain modified nano-calcium hydroxide.

[0030] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0031] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0032] Example 2

[0033] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0034] (1) 7g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 8g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both solutions A and B were simultaneously and rapidly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 5°C for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0035] (2) 4 g of nano-calcium hydroxide, 3 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.1 g of azobisisobutyronitrile (AIBN), and 50 mL of deionized water were mixed in a 100 mL flask and dispersed by ultrasonic vibration for 3 min. The mixture was then heated to 70 °C and stirred with a magnetic stirrer for 5 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed five times by centrifugation with ethanol and dried under vacuum to obtain modified nano-calcium hydroxide.

[0036] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0037] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0038] Example 3

[0039] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0040] (1) 7g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 6g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both diluted solutions A and B were simultaneously and quickly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 5°C for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0041] (2) 4 g of nano-calcium hydroxide, 2 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.1 g of azobisisobutyronitrile (AIBN), and 60 mL of deionized water were mixed in a 100 mL flask and dispersed by ultrasonic vibration for 3 min. The mixture was then heated to 70 °C and stirred with a magnetic stirrer for 5 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed five times by centrifugation with ethanol and dried under vacuum to obtain modified nano-calcium hydroxide.

[0042] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0043] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0044] Example 4

[0045] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0046] (1) 7g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 8g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both solutions A and B were simultaneously and rapidly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 5°C for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0047] (2) 2 g of nano-calcium hydroxide, 2 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.1 g of azobisisobutyronitrile (AIBN), and 50 mL of deionized water were mixed in a 100 mL flask and dispersed by ultrasonic vibration for 3 min. The mixture was then heated to 70 °C and stirred with a magnetic stirrer for 5 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed five times by centrifugation with ethanol and then vacuum dried to obtain modified nano-calcium hydroxide.

[0048] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0049] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0050] Example 5

[0051] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0052] (1) 7g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 8g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both solutions A and B were simultaneously and rapidly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 5°C for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0053] (2) 3g of nano-calcium hydroxide, 2g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.1g of azobisisobutyronitrile (AIBN), and 45mL of deionized water were mixed in a 100mL flask and dispersed by ultrasonic vibration for 3min. The mixture was then heated to 70℃ and stirred with a magnetic stirrer for 5 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed 5 times by centrifugation with ethanol and dried under vacuum to obtain modified nano-calcium hydroxide.

[0054] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0055] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0056] Example 6

[0057] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0058] (1) 10g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 7g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both diluted solutions A and B were simultaneously and rapidly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 0℃ for 1.5 hours. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0059] (2) 4 g of nano-calcium hydroxide, 3 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.4 g of azobisisobutyronitrile (AIBN), and 60 mL of deionized water were mixed in a 100 mL flask and dispersed by ultrasonic vibration for 5 min. The mixture was then heated to 80 °C and stirred with a magnetic stirrer for 6 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed five times by centrifugation with ethanol and dried under vacuum to obtain modified nano-calcium hydroxide.

[0060] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0061] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0062] Example 7

[0063] A method for preparing modified nano-calcium hydroxide includes the following preparation steps:

[0064] (1) 8.5g of calcium nitrate tetrahydrate was placed in a 50ml volumetric flask and diluted with water to obtain solution A. 7g of acrylic acid (AA) and 6g of sodium hydroxide were placed in a 50ml volumetric flask and diluted with water to obtain solution B. Both diluted solutions A and B were simultaneously and quickly poured into a colloid mill for rapid emulsification and shearing for 2 minutes. The mixture was then removed and reacted under nitrogen protection at 10℃ for 1 hour. After washing five times with deionized water by centrifugation, the mixture was vacuum dried to obtain nano-calcium hydroxide with acrylic acid surface modification.

[0065] (2) 3g of nano-calcium hydroxide, 2g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS), 0.2g of azobisisobutyronitrile (AIBN), and 50mL of deionized water were mixed in a 100mL flask and dispersed by ultrasonic vibration for 3min. The mixture was then heated to 60℃ and stirred with a magnetic stirrer for 4 hours at this temperature. The entire process was carried out under nitrogen protection. After cooling to room temperature, the mixture was washed 5 times by centrifugation with ethanol and dried under vacuum to obtain modified nano-calcium hydroxide.

[0066] The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm as measured by a nanoparticle size analyzer.

[0067] When used, the cementitious material used in the concrete is ordinary Portland cement, with an admixture dosage of 1% of the mass of ordinary Portland cement. The compressive strength data are shown in Table 1.

[0068] Example 8

[0069] The preparation method of a modified calcium hydroxide is the same as in Example 2.

[0070] When used, the cementitious material used in the concrete is ordinary Portland cement, and the admixture is 0.5% of the mass of ordinary Portland cement.

[0071] Example 9

[0072] The preparation method of a modified calcium hydroxide is the same as in Example 2.

[0073] When used, the cementitious material used in the concrete is ordinary Portland cement, and the admixture is 2% of the mass of ordinary Portland cement.

[0074] Comparative Example 1

[0075] This comparative example uses existing technology to prepare nano-calcium hydroxide. Compared with Example 2 of this invention, it only does not involve modifying nano-calcium hydroxide with organic polymers. The preparation method is as follows:

[0076] Dissolve 7g of calcium nitrate tetrahydrate in 50ml of distilled water and place the solution in a 250ml three-necked flask. At 5°C, add a 50ml solution containing 6g of sodium hydroxide dropwise using a peristaltic pump. The entire synthesis process is carried out under nitrogen protection. After all the solution has been added, wash five times with deionized water by centrifugation and dry under vacuum to obtain nano-calcium hydroxide.

[0077] The obtained nano-calcium hydroxide, measured by a nanoparticle size analyzer, had an average particle size of 300-600 nm.

[0078] When used, the cementitious material used in the concrete is ordinary Portland cement, and the admixture is 1% of the mass of ordinary Portland cement.

[0079] Figure 1 The figures show the particle size distribution of the final products, nano-calcium hydroxide, obtained in Comparative Example 1 and Example 2 of this invention. As can be seen from the figures, the average particle size of Example 2, after effective treatment, is smaller and the distribution is narrower. In contrast, Comparative Example 1 has larger particle sizes and a wider distribution, which may be due to partial agglomeration.

[0080] Comparative Example 2

[0081] The commercially available nano-calcium hydroxide with an average particle size of 10-40nm was purchased from Guilin Haowang New Materials Co., Ltd.

[0082] Comparative Example 3

[0083] The commercially available nano-calcium hydroxide with an average particle size of 100-200nm was purchased from Guilin Haowang New Materials Co., Ltd.

[0084] Performance testing

[0085] The performance of the nano-calcium hydroxide obtained in the embodiments and comparative examples of this invention was determined according to GB 8076-2008 "Concrete Admixtures". To verify the stability of the modified nano-calcium hydroxide, the stability of Examples 1-9 and Comparative Example 1 at 20℃ for 24 hours was tested. Specifically, 10 ml of the undried calcium hydroxide mother liquor synthesized in Examples 1-9 and Comparative Example 1 was placed in a 10 ml volumetric flask, and the flask was placed in a constant temperature room. The amount of solid deposited at the bottom of the nano-calcium hydroxide was recorded after 24 hours. Specific data are shown in Table 1.

[0086] Table 1 Comparison of properties of different modified nano-calcium hydroxide

[0087]

[0088] As shown in Table 1, compared with the comparative examples, the modified nano-calcium hydroxide in this application exhibits a significantly improved early compressive strength at the same dosage. This is because the modified nano-calcium hydroxide, with its suitable particle size, not only regulates alkalinity when incorporated into cement, but more importantly, provides nucleation sites for cement hydration, effectively lowering the barrier to CSH gel formation and promoting its formation. Comparative examples 1-3, with particle sizes that are either too large or too small, fail to function as nucleation sites, merely regulating alkalinity. Furthermore, excessively small particle sizes tend to agglomerate after addition to cement, negatively impacting cement strength.

[0089] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing modified nano-calcium hydroxide, characterized in that, The preparation steps include the following: (1) Dissolve calcium nitrate tetrahydrate in water to obtain solution A, and simultaneously dissolve acrylic acid and sodium hydroxide in water to obtain solution B. Pour solution A and solution B into a colloid mill for emulsification and shearing to obtain a mixture. (2) The mixture was placed in a nitrogen atmosphere to protect the reaction. After the reaction was completed, it was washed with deionized water and dried to obtain surface-modified nano-calcium hydroxide. (3) Under nitrogen protection, the surface-modified nano calcium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid and azobisisobutyronitrile were placed in a container, deionized water was added, and the mixture was dispersed and mixed by ultrasonic vibration. The mixture was heated and stirred continuously at a constant temperature for 4-6 hours. After natural cooling, the mixture was washed 3-5 times by centrifugation with ethanol and then vacuum dried to obtain modified nano calcium hydroxide.

2. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, In step (1), the mass concentration of calcium nitrate tetrahydrate in solution A is (0.14-0.2) g / mL, the mass concentration of acrylic acid in solution B is (0.12-0.16) g / mL, and the mass concentration of sodium hydroxide in solution B is 0.12 g / mL.

3. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, Step (1) The emulsification and shearing time in the colloid mill is 2 min, and the shearing speed of the colloid mill is 5000 r / min.

4. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, Step (2) The mixture is placed in a nitrogen environment for 1-1.5 hours for protection and the reaction temperature is 0-10℃; the mixture is washed with deionized water 4-6 times and dried by vacuum drying.

5. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, In step (3), the mass ratio of the surface-modified nano-calcium hydroxide, 2-acrylamido-2-methylpropanesulfonic acid, azobisisobutyronitrile and deionized water is (2-4): (1-3): (0.1-0.4): (40-60).

6. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, Step (3) Heat to 60-80℃ and keep stirring at a constant temperature of 60-80℃ for a stirring speed of 600r / min.

7. The method for preparing modified nano-calcium hydroxide according to claim 1, characterized in that, The modified nano-calcium hydroxide obtained in step (3) has an average particle size of 50-90 nm.

8. The application of a method for preparing modified nano-calcium hydroxide according to any one of claims 1-7, characterized in that, The prepared modified nano-calcium hydroxide is incorporated into cement as an early strength agent, and the resulting cement is used to prepare precast components.

9. The application of the preparation method of modified nano-calcium hydroxide according to claim 8, characterized in that, The dosage of modified nano-calcium hydroxide is 0.5-2% of the cement mass.

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