Slow-release material for improving the flexural performance of cement-based materials and application thereof
By using alkali-activated slow-release capsules to control the polymerization time, in-situ polymerization in cement-based materials was achieved, improving flexural strength while maintaining compressive strength. This solves the problem of strength reduction caused by polymer toughening in existing technologies and provides a simple and controllable preparation method.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGSU SOBUTE NEW MATERIALS CO LTD
- Filing Date
- 2023-08-07
- Publication Date
- 2026-07-14
AI Technical Summary
Existing technologies for enhancing concrete toughness often result in reduced compressive strength due to polymer toughening methods. Furthermore, the polymerization and hydration processes are difficult to match, making it impossible to prepare polymer/cement-based composite materials with adjustable and controllable properties.
Alkali-activated slow-release capsules are used as carriers, containing a nano-silica coating layer and active initiating components. The polymerization time is controlled so that the monomers do not polymerize before cement hydration, avoiding excessively large polymer particles that may affect the mechanical properties of cement-based materials. In-situ polymerization improves flexural strength.
It effectively improves the flexural strength of cement-based materials while maintaining compressive strength. The preparation process is simple and environmentally friendly. The reaction between nano-silica and cement-based materials optimizes the structure of hydration products and enhances material performance.
Smart Images
Figure CN119430734B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of building material admixtures technology, specifically, it relates to a slow-release material and its application for improving the flexural strength of cement-based materials. Background Technology
[0002] Currently, concrete toughening methods include fiber toughening, polymer toughening, and nanomaterial toughening, which adjust the microstructure of concrete at various scales to improve its tensile strength and fracture energy. However, these toughening methods all have shortcomings: among fiber toughening methods, steel fiber toughening is the most widely used and has an existing industrial application base, but steel fibers are prone to agglomeration and do not improve the matrix toughness of concrete; directly adding polymers for toughening can affect cement hydration and easily form defects in concrete; and nanomaterial toughening methods can lead to nanomaterial agglomeration and are difficult to industrialize.
[0003] Common and easy-to-operate cement-polymer paste mixing methods include directly mixing cement with polymers as binders or additives, or immersing hardened cement paste in polymer solutions. This single physical addition blending method has many drawbacks, preventing effective optimization and adjustment of the modified concrete's performance. Most experimental results show a significant improvement in flexural strength, but compressive strength decreases after polymer modification. Therefore, adding polymer solutions at high dosages leads to retardation, lower hydration levels, and insignificant flexural strength enhancement. Adding polymer emulsions, with organic polymer phase sizes ranging from 10 to 500 μm, creates "macroscopic defects" in the cement matrix, and the larger the polymer phase size, the more pronounced the mechanical strength reduction effect. Therefore, current polymer addition methods for toughening concrete sacrifice compressive strength. These drawbacks severely limit its widespread application in modern concrete. Achieving improved concrete toughness is currently a research hotspot and challenge both domestically and internationally.
[0004] To address this challenge, in-situ polymerization is currently considered a highly feasible approach by researchers. Small monomers are added to concrete before polymerization, initiating polymer polymerization simultaneously with cement hydration, thus achieving in-situ polymerization in cement-based materials. However, current in-situ polymerization processes cannot control the polymerization process, making it difficult to match the polymerization and hydration processes, and thus preventing the preparation of polymer / cement-based composite materials with adjustable and controllable properties. Controlling the polymer polymerization time to prevent monomer polymerization before cement hydration, thus avoiding interference with cement hydration, while simultaneously preventing excessively large polymer particles that could lead to phase separation within the cement matrix and affect the mechanical properties of cement-based materials, remains a key challenge that needs to be overcome in current research. Summary of the Invention
[0005] To address the technical problem of enhancing concrete toughness without affecting its compressive strength in existing technologies, this invention provides a slow-release material for improving the flexural strength of cement-based materials. This slow-release material contains slow-release capsules using alkali-activated capsule slow-release materials as carriers. Active initiating components are introduced into the slow-release material, enabling it to break down during the hydration process of the cement-based material. This allows for in-situ polymerization within the cement-based material, controlling the polymerization time and preventing monomers from polymerizing before cement hydration, thus avoiding interference with cement hydration. Simultaneously, it avoids excessively large polymer particles that could lead to phase separation within the cement matrix, affecting the mechanical properties of the cement-based material, and effectively increasing the toughness of the cement-based material.
[0006] On the other hand, the present invention also provides an application of a slow-release material for improving the flexural strength of cement-based materials.
[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0008] A slow-release material for improving the flexural strength of cement-based materials includes solution A and solution B; solution A is a mixture of alkali-activated slow-release capsules and monomer solution; the monomer solution is an acrylamide solution or a sodium acrylate solution, and solution B is an oxidizing initiator solution;
[0009] The alkali-activated sustained-release capsule comprises a core, an intermediate coating layer, and an outer coating layer; the core is nano-silica, the intermediate coating layer is nano-silica modified with tertiary amine groups, and the outer coating layer is nano-silica.
[0010] The mass ratio of the active ingredient in the monomer solution to the alkali-activated sustained-release capsule is 30:1-30;
[0011] The mass ratio of the active ingredient in the monomer solution to the active ingredient in solution B is 30:0.03-0.3.
[0012] Furthermore, the core diameter is 70-120nm, the thickness of the intermediate coating layer is 6-14nm, and the thickness of the outer coating layer is 8-20nm.
[0013] The nano-silica modified with tertiary amine groups is produced by the hydrolysis of diethylaminomethyltriethoxysilane (ND-22) into siloxane.
[0014] Furthermore, the oxidizing initiator may be selected from sodium persulfate or ammonium persulfate.
[0015] In another aspect, the present invention also provides a method for preparing the alkali-activated sustained-release capsule, specifically including the following steps:
[0016] (1) Add an alkaline solution to an organic solvent to adjust the pH of the solution system to 11-13; then add tetraethyl orthosilicate to obtain a precursor solution; mechanically stir the precursor solution to obtain a suspension;
[0017] (2) Add an alcoholic solution of tetraethyl orthosilicate to the suspension to induce a siloxane hydrolysis reaction; once the reaction is complete, the core nano-silica is obtained.
[0018] (3) Continue to raise the temperature of the reaction system to 50-60℃, and add diethylaminomethyltriethoxysilane to cause siloxane hydrolysis reaction. After the reaction is completed, the intermediate coating layer is coated onto the surface of the core nano silica.
[0019] (4) Cool the reaction system to room temperature and continue to add an alcoholic solution of tetraethyl orthosilicate to the reaction system to cause siloxane hydrolysis. After the reaction is completed, the reaction product is post-processed to obtain a solid sample, which is the alkali-activated sustained-release capsule.
[0020] Furthermore, in step (1), the alkaline solution is one or a combination of sodium hydroxide solution and ammonia water; in step (1), the organic solvent is ethanol or isopropanol.
[0021] Furthermore, the mechanical stirring speed in step (1) is 300-500 rpm, and the stirring time is 2-3 hours.
[0022] The mass proportions of each raw material in the preparation method of the alkali-activated sustained-release capsule are as follows: 2-5 parts of tetraethyl orthosilicate in step (1), 1-3 parts of tetraethyl orthosilicate in step (2), 1-3 parts of diethylaminomethyltriethoxysilane in step (3), and 2-5 parts of tetraethyl orthosilicate in step (4).
[0023] The present invention also provides an application of a slow-release material for improving the flexural strength of cement-based materials, wherein solution A and solution B in the slow-release material for improving the flexural strength of cement-based materials are respectively added to the cement-based materials, wherein the mass of the effective component of the monomer solution is 1%-3% of the total mass of the cementitious material in the cement-based materials.
[0024] Compared with the prior art, the present invention has the following advantages:
[0025] 1. The method for increasing flexural strength provided by the present invention comprises nano-silica as the effective component. Since nano-silica itself is an excellent reinforcing material, its unique pozzolanic activity can react with cement-based materials, optimizing the structure and composition of hydration products and strengthening the cement-based materials.
[0026] 2. The method for reinforcing cement-based materials provided by the present invention uses the small molecule monomer diethylaminomethyltriethoxysilane, rather than a polymer. It has little impact on cement-based materials and can improve flexural strength without affecting the hydration of cement-based materials.
[0027] 3. The active ingredient, nano-silica, has a slow-release effect. It does not expose the active amino functional groups during the early hydration stage. After a period of hydration, that is, after the silica shell has dissolved for a period of time, the active amino components are exposed, which initiates polymerization, thus minimizing the impact of the polymer on cement hydration.
[0028] 4. The preparation method provided by this invention has a wide range of raw material sources, is safe and environmentally friendly, and has a simple and easy-to-control preparation process. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the structure of the alkali-activated sustained-release capsule prepared in Example 8 of the present invention;
[0030] Figure 2 This is a SEM image of the alkali-activated sustained-release capsules prepared in Example 8 of this invention;
[0031] Figure 3 This refers to the dimensional changes during the preparation of alkali-activated sustained-release capsules in Example 8 of the present invention.
[0032] Figure 4 The release curve of the alkali-activated sustained-release capsule prepared according to Example 8 of the present invention is shown in solution. Detailed Implementation
[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0034] Example 1
[0035] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0036] Add 60g of ethanol to the container, adjust the pH of the system to 11.5 with sodium hydroxide, and then add 2mL of tetraethyl orthosilicate to the solution.
[0037] The solution obtained above was mechanically stirred at 300 rpm for 2 hours.
[0038] Add 1 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 70 nm.
[0039] Heat to 60℃, add 1mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6nm.
[0040] Cool to room temperature, and continue to add 5 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 20 nm.
[0041] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S1.
[0042] Example 2
[0043] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0044] Add 60g of ethanol to the container, adjust the pH of the system to 12 with ammonia, and then add 5mL of tetraethyl orthosilicate to the solution.
[0045] The solution obtained above was mechanically stirred at 300 rpm for 2 hours.
[0046] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0047] Heat to 60℃, add 3mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 14nm.
[0048] Cool to room temperature, and continue to add 2 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 8 nm.
[0049] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S2.
[0050] Example 3
[0051] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0052] Add 60g of ethanol to the container, adjust the pH of the system to 11 with ammonia, and then add 5mL of tetraethyl orthosilicate to the solution.
[0053] The solution obtained above was mechanically stirred at 300 rpm for 2 hours.
[0054] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0055] Heat to 60℃, add 1mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6nm.
[0056] Cool to room temperature, and continue to add 3 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 15 nm.
[0057] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S3.
[0058] Example 4
[0059] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0060] Add 60g of isopropanol to the container, adjust the pH of the system to 12.5 with ammonia, and then add 5mL of tetraethyl orthosilicate to the solution.
[0061] The solution obtained above was mechanically stirred at 300 rpm for 2 hours.
[0062] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0063] Heat to 55℃, add 1mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6nm.
[0064] Cool to room temperature, and continue to add 5 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 20 nm.
[0065] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S4.
[0066] Example 5
[0067] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0068] Add 60g of ethanol to the container, adjust the pH of the system to 11.5 with sodium hydroxide, and then add 5mL of tetraethyl orthosilicate to the solution.
[0069] The solution obtained above was mechanically stirred at 300 rpm for 3 hours.
[0070] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0071] Heat to 60℃, add 2mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 10nm.
[0072] Cool to room temperature, and continue to add 5 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 20 nm.
[0073] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S5.
[0074] Example 6
[0075] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0076] Add 60g of ethanol to the container, adjust the pH of the system to 11.5 with sodium hydroxide, and then add 5mL of tetraethyl orthosilicate to the solution.
[0077] The solution obtained above was mechanically stirred at 300 rpm for 3 hours.
[0078] Add 1 mL of tetraethyl silicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 100 nm.
[0079] Heat to 60℃, add 1mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6nm.
[0080] Cool to room temperature, and continue to add 5 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 20 nm.
[0081] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S6.
[0082] Example 7
[0083] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0084] Add 60g of ethanol to the container, adjust the pH of the system to 11.5 with sodium hydroxide, and then add 5mL of tetraethyl orthosilicate to the solution.
[0085] The solution obtained above was mechanically stirred at 300 rpm for 3 hours.
[0086] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0087] Heat to 50°C, add 1 mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6 nm.
[0088] Cool to room temperature, and continue to add 5 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 20 nm.
[0089] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S7.
[0090] Example 8
[0091] The alkali-activated sustained-release capsules provided in this embodiment are prepared using the following method:
[0092] Add 60g of ethanol to the container, adjust the pH of the system to 11 with sodium hydroxide, and then add 5mL of tetraethyl orthosilicate to the solution.
[0093] The solution obtained above was mechanically stirred at 300 rpm for 3 hours.
[0094] Add 3 mL of tetraethyl silicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0095] Heat to 50°C, add 1 mL of ND-22 to the solution, stir for 2 hours, and the thickness of the intermediate coating layer is about 6 nm.
[0096] Cool to room temperature, and continue to add 2 mL of tetraethyl orthosilicate alcohol solution dispersed in 20 g of ethanol to the suspension. React for 2 h, and the outer coating layer thickness is about 8 nm.
[0097] The solution obtained above was centrifuged at 8000 rpm, and the solid sample was washed twice with ethanol solution and dried under vacuum to obtain sample S8.
[0098] Comparative Example 1
[0099] This comparative example is based on Example 3, except that it does not have an outer coating layer of nano-silica.
[0100] The alkali-activated sustained-release capsules provided in this comparative example were prepared using the following method:
[0101] Add 60g of ethanol to the container, adjust the pH of the system to 11 with ammonia, and then add 5mL of tetraethyl orthosilicate to the solution.
[0102] The solution obtained above was mechanically stirred at 300 rpm for 2 hours.
[0103] Add 3 mL of tetraethyl orthosilicate solution dispersed in 20 g of ethanol to the solution obtained above at a dropping rate of 1 mL / min to obtain nano-silica with a core diameter of about 120 nm.
[0104] Heat to 60℃, add 1mL of ND-22 to the solution, stir for 2 hours, the coating thickness is about 6nm, cool to room temperature, centrifuge the above solution at 8000rpm, the solid sample is washed twice with ethanol solution, and vacuum dried to obtain sample SD1.
[0105] Application Examples
[0106] Figure 1 This is a schematic diagram of the structure of the alkali-activated sustained-release capsule prepared in Example 8; Figure 2 The image shows a scanning electron microscope image of the alkali-activated sustained-release capsules prepared in Example 8.
[0107] The particle size change during the synthesis process of the alkali-activated sustained-release capsules prepared in Example 8 was tested by dynamic light scattering (DLS), and the test results are as follows: Figure 3 As shown, the initial core radius was 58.98 nm and the diameter was 117.96 nm. After adding ND-22, the radius became 65.27 nm, and after adding tetraethyl orthosilicate, the radius became 73.38 nm. Particle size change testing shows that the nano-silica gradually increases in size, meaning that each layer of coating is effective.
[0108] The release rate of nano-silica from the alkali-activated sustained-release capsules prepared in Example 8 was tested in water and alkaline solutions. The mass of the alkali-activated sustained-release capsules was 1% of the solution mass, and the alkaline solution was a saturated calcium hydroxide solution. The alkali-activated sustained-release capsules were added to the solution with stirring, and samples were taken at different time points. The TOC (Total Carbon Content) was used to analyze the carbon content in the solution to calculate the mass of released tertiary amine groups. The test results are as follows: Figure 4 As shown. By Figure 4 It is known that alkali-activated sustained-release capsules release almost nothing in aqueous solution, but begin to release slowly in alkaline solution, accelerating to complete release within 300-500 minutes. This is because the silica shell dissolves slowly in alkaline solution initially, but dissolution accelerates once most of the outer silica layer has dissolved.
[0109] Cement mortar flowability test:
[0110] The effects of alkali-activated slow-release capsules obtained in each embodiment and comparative example on the flowability of cement mortar were tested. Cement mortar flowability was determined according to the national standard GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures," using a naphthalene-based high-efficiency water-reducing agent (Subote). -A), the dosage of which is the mass percentage relative to cement, and the comparison results are shown in Table 1. In the fluidity test, no acrylamide monomer was added to the sample, and the dosage was the mass percentage of the alkali-activated slow-release capsules relative to cement.
[0111] Table 1 Comparison of Mortar Flowability Tests
[0112]
[0113] As can be seen from the data in Table 1, when the silica slow-release capsules of the present invention are added, the fluidity of the corresponding cement-based material does not change significantly, proving that the inorganic admixture has no effect on the workability of cement.
[0114] To verify the performance of the slow-release material for improving the flexural strength of cement-based materials as described in this invention when applied to cement-based materials, the alkali-activated slow-release capsules obtained in the above embodiments and comparative examples were mixed with monomer solutions to form solution A. Solution A and solution B were added to cement-based materials simultaneously, and the relevant properties of the corresponding cement-based materials were measured.
[0115] Mortar was prepared using the mortar material proportions shown in Table 2, along with the alkali-activated slow-release capsule material provided in the above embodiments to enhance the flexural strength of cement-based materials. Specific dosages are shown in Table 3, where the dosage of the alkali-activated slow-release capsule is relative to the cement dosage, the monomer solution dosage is relative to the effective component dosage of the cement dosage, and the B solution dosage is relative to the effective component dosage of the monomer solution. During mortar mixing and molding, solutions A and B were mixed to replace the water required for molding, and the mortar was cured at room temperature. A control group was also set up, in which the obtained slow-release capsules were not added; only acrylamide monomer and ammonium persulfate initiator solution were added.
[0116] Table 2 Mortar Mix Proportion
[0117]
[0118] Table 3. Proportioning of slow-release materials to improve the flexural strength of cement-based materials
[0119]
[0120]
[0121] The mechanical properties of mortars incorporating different slow-release materials (distinguished by different amounts of alkali-activated slow-release capsules) configured according to Table 3 to enhance the flexural strength of cement-based materials were tested at various ages. The test methods are referenced (Construction and Building Materials, 2013, 49:121). The test results are as follows:
[0122] Table 4. Mechanical properties of mortar (dosage based on cement mass)
[0123]
[0124]
[0125] As shown in Table 4, the cement specimens with the slow-release capsules provided by this invention exhibited significantly improved flexural and compressive strength at 7 days and 28 days compared to the reference and blank samples, with minimal differences in the impact of different dosages on mechanical properties. Due to the retarding effect of the monomers, the compressive strength decreased slightly at 7 days. Specifically, the flexural and compressive strength increased by up to 24.7% at 7 days and by up to 48.7% at 28 days. Furthermore, SD-1, lacking a slow-release coating, directly triggered polymerization upon addition, leading to severe retarding and a decrease in both compressive and flexural strength. However, it still exhibited a certain retarding effect after 28 days of curing.
[0126] These examples demonstrate that the sustained-release capsule material provided by this invention can be used to enhance the mechanical properties of cement-based materials.
Claims
1. A slow-release material for improving the flexural strength of cement-based materials, characterized in that, It includes solution A and solution B; solution A is a mixture of alkali-activated sustained-release capsules and monomer solution; The monomer solution is an acrylamide solution or a sodium acrylate solution, and solution B is an oxidizing initiator solution; The alkali-activated sustained-release capsule comprises a core, an intermediate coating layer, and an outer coating layer; the core is nano-silica, the intermediate coating layer is nano-silica modified with tertiary amine groups, and the outer coating layer is nano-silica. The mass ratio of the active ingredient in the monomer solution to the alkali-activated sustained-release capsule is 30:1-30; The mass ratio of the active ingredient in the monomer solution to the active ingredient in solution B is 30:0.03-0.3; The nano-silica modified with tertiary amine groups is produced by the hydrolysis of diethylaminomethyltriethoxysilane via siloxane hydrolysis.
2. The slow-release material for improving the flexural strength of cement-based materials according to claim 1, characterized in that, The core diameter is 70-120 nm, the thickness of the middle coating layer is 6-14 nm, and the thickness of the outer coating layer is 8-20 nm.
3. The slow-release material for improving the flexural strength of cement-based materials according to claim 1, characterized in that, The oxidizing initiator is selected from sodium persulfate and ammonium persulfate.
4. The slow-release material for improving the flexural strength of cement-based materials according to claim 1, characterized in that, The preparation method of the alkali-activated sustained-release capsule specifically includes the following steps: (1) Add the alkaline solution to the organic solvent to adjust the pH of the solution system to 11-13; then add tetraethyl orthosilicate to obtain the precursor solution; The precursor solution was mechanically stirred to obtain a suspension; (2) Add an alcoholic solution of tetraethyl orthosilicate to the suspension to induce a siloxane hydrolysis reaction; once the reaction is complete, the core nano-silica is obtained. (3) Continue to raise the temperature of the reaction system to 50-60℃, and add diethylaminomethyltriethoxysilane to cause siloxane hydrolysis reaction. After the reaction is completed, coat the core nano silica surface with the intermediate coating layer. (4) Cool the reaction system to room temperature and continue to add an alcoholic solution of tetraethyl orthosilicate to the reaction system to cause a siloxane hydrolysis reaction. After the reaction is completed, the reaction product is post-processed to obtain a solid sample, which is the alkali-activated sustained-release capsule.
5. The slow-release material for improving the flexural strength of cement-based materials according to claim 4, characterized in that, In step (1), the alkaline solution is one or a combination of sodium hydroxide solution and ammonia solution.
6. The slow-release material for improving the flexural strength of cement-based materials according to claim 4, characterized in that, The organic solvent in step (1) is ethanol or isopropanol.
7. The slow-release material for improving the flexural strength of cement-based materials according to claim 4, characterized in that, The mass proportions of each raw material in the preparation method of the alkali-activated sustained-release capsule are as follows: 2-5 parts of tetraethyl orthosilicate in step (1), 1-3 parts of tetraethyl orthosilicate in step (2), 1-3 parts of diethylaminomethyltriethoxysilane in step (3), and 2-5 parts of tetraethyl orthosilicate in step (4).
8. The application of the slow-release material for improving the flexural strength of cement-based materials according to any one of claims 1-7, characterized in that, Solution A and solution B of the slow-release material that improves the flexural strength of cement-based materials are added to the cement-based materials respectively, wherein the mass of the effective component of the monomer solution is 1%-3% of the total mass of the cementitious material in the cement-based materials.