Special waterproofing admixture for concrete, preparation method and application

Abstract

The application discloses a special waterproofing admixture for concrete, a preparation method and application, and belongs to the technical field of concrete admixtures. In order to solve the problem of performance attenuation of the existing waterproofing admixture in extreme environments, the admixture comprises a perfluorosilane modified graphene-hexagonal boron nitride composite phase, a hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, a hydroxyl-terminated polyether ether ketone water reducing agent, a benzene type polyimide-bisphenol A epoxy resin crosslinking agent and an additive; wherein the weight ratio of graphene to hexagonal boron nitride is (3-5):(6-8), and the composite phase is grafted with 8%-12% of the total mass of the composite phase of perfluorooctyltriethoxysilane; the hydrothermal phase has a particle size of 25-45 nm and contains 5%-8% of nano-titanium dioxide. The admixture can be used for deep-sea engineering, cold region tunnel, high-salinity soil building and nuclear power station waterproofing engineering.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture technology, specifically to a special waterproof concrete admixture for extreme environment engineering, its preparation method, and its application. Background Technology

[0002] The waterproof and impermeable properties of concrete are important indicators for measuring its durability. As infrastructure construction extends to extreme environments such as deep-sea engineering, cold-region tunnels, high-salinity soil buildings, and nuclear power plants, higher performance requirements are placed on concrete waterproofing admixtures: they not only need to have excellent impermeability (such as an impermeability grade of P14 or higher and a 24-hour water absorption rate of less than 2%), but also need to withstand long-term salt erosion, freeze-thaw cycles, and ultraviolet aging, and have good compatibility with high-performance concrete with a strength grade of C30 and above.

[0003] Currently, the main technical approaches for concrete waterproofing admixtures include: adding organosilicon or perfluoroalkyl hydrophobic components to reduce water absorption; incorporating inorganic fillers such as nano-silica and nano-calcium carbonate to fill capillary pores; using polycarboxylate superplasticizers to improve workability; or introducing film-forming substances such as epoxy resin to form a surface protective layer. However, the following technical problems still exist in practical applications: the hydrophobic components are simple physical mixtures, making it difficult to form a stable and continuous superhydrophobic interface inside the concrete, and the protective effect is easily reduced under ultraviolet radiation, salt solution erosion, or freeze-thaw cycles; nanofillers are mostly single components or simple mixtures with a wide particle size range, lacking precise design for concrete nanoscale capillary pores (typical size 10-100 nm), resulting in limited improvement in impermeability; conventional water-reducing agents and crosslinking systems cannot meet the long-term stability requirements of high-dosage nanomaterial systems under extreme environments such as wide temperature range and strong radiation.

[0004] The closest prior art to this application includes: Chinese invention patent application CN108793818A (publication date November 13, 2018, an admixture for improving concrete durability and its preparation method), Chinese invention patent CN118125742B (authorization announcement date September 5, 2025, a preparation method and application method of an anti-impact concrete admixture under freeze-thaw corrosion environment), and Chinese invention patent CN117466579B (authorization announcement date February 24, 2026, a polymer repair mortar for marine concrete and its preparation method).

[0005] The aforementioned existing technologies primarily focus on improving the impermeability, freeze-thaw resistance, corrosion resistance, or repair bonding of concrete, emphasizing simple compounding of hydrophobic components and nanomaterials. However, none of these existing technologies address the material system design requirements for long-term waterproofing under extreme environments, nor do they disclose the following technical features: 1) Covalent grafting modification of graphene and hexagonal boron nitride composite phases using perfluorosilanes to construct a stable superhydrophobic nanosheet interface; 2) Preparation of a multi-level filled phase of nano-hydroxyapatite-titanium dioxide with a specific particle size of 25–45 nm using a hydrothermal in-situ composite method to achieve precise clogging of nanoscale capillary pores in concrete; 3) Replacement of conventional polycarboxylate superplasticizers with hydroxyl-terminated polyetheretherketone superplasticizers to improve the dispersibility and water reduction rate of high-dosage nanomaterial systems; 4) Forming a three-dimensional covalent cross-linked network with a thermal decomposition temperature ≥300℃ using homopolymer polyimide-modified epoxy resin to enhance the aging resistance of admixtures under extreme environments such as strong ultraviolet radiation, high salt content, and freeze-thaw cycles.

[0006] Therefore, existing technologies have failed to solve the technical problems of concrete waterproofing admixtures in terms of long-term stability of superhydrophobic interfaces, full-scale filling of nanopores, construction of high heat-resistant cross-linked networks, and comprehensive durability in extreme environments. There is an urgent need to provide a special concrete waterproofing admixture and its preparation method that can simultaneously achieve the synergistic effect of "superhydrophobic interface construction - nano-level pore filling - three-dimensional covalent cross-linking water locking". Summary of the Invention

[0007] To address the shortcomings of existing concrete waterproofing admixtures, such as reduced waterproofing performance in extreme environments (deep sea, cold regions, high salinity soil, nuclear power plants, etc.), poor compatibility with high-strength concrete (C30~C90), insufficient adaptability to wide temperature range construction, and poor resistance to ultraviolet aging, this paper provides a special concrete waterproofing admixture, its preparation method, and its application. This admixture achieves long-lasting waterproofing and seepage prevention through the synergistic effect of superhydrophobic interface construction, nano-level multi-pore filling, and three-dimensional covalent cross-linking water locking, and also has good resistance to salt corrosion, freeze-thaw resistance, and aging resistance.

[0008] This invention provides a special waterproofing admixture for concrete, the admixture comprising the following components:

[0009] Perfluorosilane-modified graphene-hexagonal boron nitride composite phase, hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, hydroxyl-terminated polyether ether ketone water-reducing agent, pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, maltitol-boric acid compound retarder, polyether branched modified polymethylsiloxane defoamer, and primary deionized water.

[0010] In the perfluorosilane-modified graphene-hexagonal boron nitride composite phase, the weight ratio of graphene nanosheets to hexagonal boron nitride is (3~5):(6~8), and the surface of the composite phase is grafted with perfluorooctyltriethoxysilane, with the grafting amount being 8~12% of the total mass of the composite phase;

[0011] The hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase is composed of nano-hydroxyapatite and in-situ composite nano-titanium dioxide with a particle size of 25~45nm, wherein the mass of titanium dioxide accounts for 5~8% of the total mass of the phase.

[0012] Further, by weight, the additive comprises:

[0013] 12-19 parts of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, 7-13 parts of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, 5-10 parts of hydroxyl-terminated polyether ether ketone water-reducing agent, 4-8 parts of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, 2-5 parts of maltitol-boric acid compound retarder, 1-2.2 parts of polyether branched modified polymethylsiloxane defoamer, and 38-52 parts of primary deionized water.

[0014] Furthermore, the water reduction rate of the hydroxyl-terminated polyetheretherketone water-reducing agent is ≥40%;

[0015] The thermal decomposition temperature of the homobenzene polyimide-bisphenol A epoxy resin crosslinking agent is ≥300℃.

[0016] In the maltitol-boric acid compound retarder, the weight ratio of maltitol to boric acid is (4~6):(1~2).

[0017] The solid content of the polyether-branched modified polymethylsiloxane defoamer is ≥40%.

[0018] This invention also provides a method for preparing the special waterproofing admixture for concrete, comprising the following steps:

[0019] S01: Heat primary deionized water to 55~60℃, add hydroxyl-terminated polyether ether ketone water-reducing agent and stir to dissolve to obtain water-reducing agent aqueous solution;

[0020] S02: Add perfluorosilane-modified graphene-hexagonal boron nitride composite phase and hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase to the aqueous solution of the water-reducing agent, stir at 700~800 r / min for 50~60 min, and ultrasonically disperse for 8 min every 15 min during the process to obtain a mixed dispersion.

[0021] S03: Add a homopolymer polyimide-bisphenol A epoxy resin crosslinking agent to the mixed dispersion, heat to 75~80℃, and stir at a constant temperature of 500~550r / min for 35~40min to form a crosslinking system;

[0022] S04: Cool to 45~50℃, add maltitol-boric acid compound retarder and polyether branched modified polymethylsiloxane defoamer, stir at 350~400r / min for 20~25min to obtain the additive stock solution;

[0023] S05: The additive stock solution is sequentially filtered through a 2μm primary filter and a 1μm secondary filter, and then degassed under reduced pressure for 20 minutes at a vacuum of -0.085 to -0.095 MPa and a temperature of 65 to 70°C. The finished product is then metered and packaged.

[0024] Furthermore, the power of the ultrasonic dispersion in step S02 is 450~500W.

[0025] Furthermore, the perfluorosilane-modified graphene-hexagonal boron nitride composite phase is prepared through the following steps:

[0026] S11: Graphene nanosheets with a thickness of 0.5~2nm and a sheet diameter of 60~120nm are mixed with hexagonal boron nitride with a particle size of 40~80nm at a weight ratio of (3~5):(6~8), and 15~20 times the weight of N-methylpyrrolidone is added. The mixture is ultrasonically dispersed at 35~40℃ and 450~500W for 90~120min to obtain a nano-mixed dispersion.

[0027] S12: Add 8-12% of the total mass of perfluorooctyltriethoxysilane to the nano-mixed dispersion, adjust the pH to 9.0-9.5, and stir at a constant temperature of 85-90℃ and 350-380r / min for 5h to obtain the fluorine-modified precursor solution.

[0028] S13: The fluorine-modified precursor solution is vacuum distilled to remove N-methylpyrrolidone under vacuum conditions of -0.095 to -0.10 MPa and temperature of 95 to 100°C to obtain a solid product;

[0029] S14: The solid product is vacuum dried at 110~115℃ for 10h, and then ball-milled until the particle size is ≤5μm to obtain the product.

[0030] Furthermore, the hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase is prepared through the following steps:

[0031] S21: Mix calcium nitrate and diammonium hydrogen phosphate at a molar ratio of 10:6, add 20 to 25 times the weight of deionized water and stir to dissolve, add 5 to 8% of the total mass of calcium nitrate and diammonium hydrogen phosphate and nano-titanium dioxide with a particle size of 15 to 30 nm, and ultrasonically disperse at 380 to 420 W for 40 to 50 min to obtain the mixed precursor solution.

[0032] S22: Adjust the pH of the mixed precursor solution to 10.5~11.0, stir for 4 hours at 70~75℃ and 280~300r / min, transfer to a high-pressure reactor, and hydrothermally react at 190~210℃ for 8~10 hours, then cool naturally to room temperature;

[0033] S23: Filter and wash the reaction product until neutral, dry at 90~95℃ for 8 hours, and ball mill to a particle size of 25~45nm to obtain the final product.

[0034] The present invention also provides the application of the special waterproof admixture for concrete in the preparation of waterproof concrete, wherein the admixture is added at a dosage of 2.5 to 4.0% of the total mass of concrete cementitious materials.

[0035] Furthermore, the waterproof concrete is used for waterproofing projects in deep-sea engineering, cold-region tunnels, high-salinity soil buildings, or nuclear power plants.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Synergistic effect of superhydrophobic interface and nanofiller significantly improves waterproof and seepage-proof performance: Perfluorosilane modified graphene-hexagonal boron nitride composite phase forms a low surface energy nanosheet superhydrophobic barrier inside concrete. Hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase fills the capillary pores and microcracks of concrete. The synergistic effect of the two makes the concrete seepage resistance grade reach P14 or above (maximum P16), with a 24h water absorption rate ≤1.8%. Compared with commercially available waterproof admixtures (seepage resistance grade P10, 24h water absorption rate 4.2%), the seepage resistance grade is improved by 4 to 6 grades and the water absorption rate is reduced by about 60%.

[0038] 2. Three-dimensional covalent cross-linking network enhances durability and aging resistance: The thermal decomposition temperature of the polyimide-bisphenol A epoxy resin cross-linking agent is ≥300℃. During the concrete hydration process, it forms a stable three-dimensional cross-linking structure, enabling the admixture to maintain a waterproof rating of P13 or higher after UV aging (commercially available products only have P8), freeze-thaw cycle strength retention rate ≥92% (commercially available products have approximately 73%), and salt erosion strength retention rate ≥96% (commercially available products have approximately 76%). It can meet the long-term waterproofing requirements of extreme environments such as deep sea, cold regions, and high-salt soil.

[0039] 3. High water reduction and good workability: The water reduction rate of the hydroxyl-terminated polyether ether ketone water-reducing agent is ≥40%, which is better than that of conventional polycarboxylate water-reducing agents. It effectively improves the workability of concrete mixing and makes the admixture have good compatibility with C30~C90 full strength grade concrete. It also has excellent adaptability to construction in a wide temperature range.

[0040] 4. Synergistic effect of each component, not simple superposition: This invention adopts an integrated design of "superhydrophobic interface construction - nano-level pore filling - three-dimensional covalent cross-linking water locking". The four types of functional components support and interact with each other in terms of function, producing a comprehensive waterproof effect that cannot be achieved by using each component alone or in any combination.

[0041] 5. Stable process and easy to industrialize: The preparation process provided by this invention uses conventional equipment, operates under mild conditions (temperature ≤80℃, normal pressure or low vacuum), the steps are clear and controllable, the product performance is stable, and it is suitable for large-scale industrial production. Attached Figure Description

[0042] Figure 1 This is a schematic diagram illustrating the preparation process of the special waterproofing admixture for concrete provided in an embodiment of the present invention. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the embodiments and comparative examples. The scope of protection of the present invention is not limited to these embodiments. Any modifications, equivalent substitutions, improvements, etc. within the concept of the present invention should be included within the scope of protection of the present invention.

[0044] All the main raw materials used in this embodiment are commercially available, and their specific specifications are as follows:

[0045] Graphene nanosheets: thickness 0.8~1.5nm, sheet diameter 80~100nm, specific surface area ≥580m² / g, industrial grade;

[0046] Hexagonal boron nitride: particle size 50~70nm, purity ≥99.8%, specific surface area ≥110m² / g, industrial grade;

[0047] Perfluorooctyltriethoxysilane: purity ≥98.8%, industrial grade;

[0048] Nano titanium dioxide: particle size 20~25nm, purity ≥99.7%, industrial grade;

[0049] Calcium nitrate: purity ≥ 99.0%, analytical grade;

[0050] Diammonium hydrogen phosphate: purity ≥ 98.5%, analytical grade;

[0051] Hydroxyl-terminated polyether ether ketone water-reducing agent: molecular weight 3000~4000, solid content 52%, water reduction rate 42%, industrial grade;

[0052] Pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent: Pyromellitic dianhydride-diaminodiphenyl ether polyimide and bisphenol A epoxy resin are compounded at a weight ratio of 2.5:1.5, with a number average molecular weight of 2200, thermal decomposition temperature ≥300℃, industrial grade;

[0053] Maltitol: Purity ≥ 99.5%, food grade;

[0054] Boric acid: purity ≥ 99.5%, analytical grade;

[0055] Polyether-branched modified polymethylsiloxane defoamer: Polyether-branched modified polymethylsiloxane and fumed silica are compounded at a weight ratio of 10:1.5, with a solid content of 42% and industrial grade.

[0056] Grade I deionized water: meets the requirements of Grade I water in GB / T 6682-2008.

[0057] The perfluorosilane-modified graphene-hexagonal boron nitride composite phase was prepared according to the following steps:

[0058] S11: Graphene nanosheets with a thickness of 0.8~1.5nm and a sheet diameter of 80~100nm are mixed with hexagonal boron nitride with a particle size of 50~70nm at a weight ratio of 4:7. Take 100g of the total weight of the mixture and add 1800g of N-methylpyrrolidone (18 times the weight). Disperse the mixture ultrasonically at 38℃ and 480W for 105min to obtain a nano-mixed dispersion.

[0059] S12: Add 10% of the total mass of perfluorooctyltriethoxysilane (i.e., about 20g) to the nano-mixed dispersion, adjust the pH to 9.2 with a 10% potassium hydroxide aqueous solution, and stir at 88℃ and 360r / min for 5h to obtain the fluorine-modified precursor solution.

[0060] S13: The fluorine-modified precursor solution was vacuum distilled at a vacuum degree of -0.098 MPa and a temperature of 98 °C to remove N-methylpyrrolidone, yielding a solid product;

[0061] S14: The solid product is vacuum dried at 112℃ for 10h, and then intermittently ball-milled with silicon nitride balls at 2100r / min for 60min (ball-to-material ratio 8:1) until the particle size is ≤5μm, thus obtaining the perfluorosilane modified graphene-hexagonal boron nitride composite phase.

[0062] The hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase was prepared according to the following steps:

[0063] S21: Weigh 236g (1.0 mol) of calcium nitrate (Ca(NO3)2·4H2O) and 79g (0.6 mol) of diammonium hydrogen phosphate ((NH4)2HPO4), add about 4500g of deionized water (about 22 times the total weight of the mixture) and stir to dissolve. Then add 6.5% of the total mass of calcium nitrate and diammonium hydrogen phosphate nano-titanium dioxide (particle size 20~25nm), and ultrasonically disperse at 400W for 45min to obtain the mixed precursor solution.

[0064] S22: The pH of the mixed precursor solution was adjusted to 10.8 using 10% ammonia water, stirred at 72℃ and 290r / min for 4 hours, transferred to a high-pressure reactor, and hydrothermally reacted at 200℃ for 9 hours, then naturally cooled to room temperature.

[0065] S23: The reaction product was filtered, washed with deionized water until neutral, dried at 92℃ for 8 hours, and then ball-milled with zirconia balls at 1900 r / min for 35 min (ball-to-material ratio 7:1) to obtain a product with a particle size of 30~40 nm, which is the hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase. Analysis showed that titanium dioxide accounted for 6.2% of the total mass of this phase.

[0066] Example 1

[0067] This embodiment provides a special waterproofing admixture for concrete, which is composed of the following components by weight:

[0068] 12 parts of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, 7 parts of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, 5 parts of hydroxyl-terminated polyether ether ketone water-reducing agent, 4 parts of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, 2 parts of maltitol-boric acid compound retarder (maltitol:boric acid = 5:1.5 by weight), 1 part of polyether branched modified polymethylsiloxane defoamer, and 38 parts of primary deionized water.

[0069] The preparation steps are as follows:

[0070] S01: Heat primary deionized water to 55°C, add hydroxyl-terminated polyether ether ketone water-reducing agent under stirring at 400 r / min, stir for 25 min until completely dissolved, and obtain an aqueous solution of water-reducing agent;

[0071] S02: Add perfluorosilane-modified graphene-hexagonal boron nitride composite phase and hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase to the aqueous solution of the water-reducing agent, stir at 700 r / min for 50 min, and ultrasonically disperse for 8 min every 15 min (ultrasonic power 450 W) to obtain a mixed dispersion.

[0072] S03: Heat to 75℃, add pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, and stir at a constant temperature of 500r / min for 35min to form a crosslinking system;

[0073] S04: Cool to 45℃, add maltitol-boric acid compound retarder and polyether branched modified polymethylsiloxane defoamer, stir at 350r / min for 20min to obtain the additive stock solution;

[0074] S05: The additive stock solution is sequentially filtered through a 2μm primary filter and a 1μm secondary filter, and then degassed under reduced pressure for 20 minutes at a vacuum of -0.085MPa and a temperature of 65℃. The solution is then metered and packaged to obtain the finished product.

[0075] Example 2

[0076] The difference between this embodiment and Embodiment 1 lies in the different weight parts of the components, as detailed below:

[0077] 19 parts of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, 13 parts of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, 10 parts of hydroxyl-terminated polyether ether ketone water-reducing agent, 8 parts of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, 5 parts of maltitol-boric acid compound retarder, 2.2 parts of polyether branched modified polymethylsiloxane defoamer, and 52 parts of primary deionized water.

[0078] In the preparation steps:

[0079] S01 heating temperature 60℃, stirring for 30 min;

[0080] SO2 rotation speed 800 r / min, stirring for 60 min, ultrasonic dispersion power 500 W;

[0081] The SO3 temperature is raised to 80℃ and stirred at 550r / min for 40min.

[0082] Cool the SO4 to 50℃ and stir at 400r / min for 25min.

[0083] S05 vacuum degree -0.095MPa, temperature 70℃.

[0084] The rest is the same as in Example 1.

[0085] Example 3

[0086] The difference between this embodiment and Embodiment 1 lies in the different weight parts of the components, as detailed below:

[0087] 15 parts of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, 10 parts of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, 7.5 parts of hydroxyl-terminated polyether ether ketone water-reducing agent, 6 parts of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, 3.5 parts of maltitol-boric acid compound retarder, 1.6 parts of polyether branched modified polymethylsiloxane defoamer, and 45 parts of primary deionized water.

[0088] In the preparation steps:

[0089] S01 heating temperature 58℃, stirring for 28min;

[0090] SO2 rotation speed 750r / min, stirring for 55min, ultrasonic dispersion power 480W;

[0091] The SO3 temperature was increased to 78℃ and stirred at 520r / min for 38min.

[0092] Cool the SO4 to 48℃ and stir at 380r / min for 22min.

[0093] S05 vacuum degree -0.09MPa, temperature 68℃. The rest is the same as in Example 1.

[0094] Comparative Example 1

[0095] Compared with Example 3, no perfluorosilane-modified graphene-hexagonal boron nitride composite phase was added, the amount of this component was adjusted to an equal amount of primary deionized water, and the remaining components and preparation steps were the same as in Example 3.

[0096] Comparative Example 2

[0097] Compared with Example 3, no hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase was added, and the amount of this component was adjusted to an equal amount of primary deionized water. The remaining components and preparation steps were the same as in Example 3.

[0098] Comparative Example 3

[0099] Compared with Example 3, the perfluorosilane-modified graphene-hexagonal boron nitride composite phase was replaced with an unmodified graphene-hexagonal boron nitride mixture (that is, graphene nanosheets and hexagonal boron nitride were simply mixed at the same weight ratio of 4:7 without perfluorosilane grafting modification or ultrasonic dispersion composite). The remaining components and preparation steps were the same as in Example 3.

[0100] Comparative Example 4

[0101] Compared with Example 3, the hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase was replaced with single nano-hydroxyapatite (commercially available, particle size 30nm), and the remaining components and preparation steps were the same as in Example 3.

[0102] Comparative Example 5

[0103] Compared with Example 3, no pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent was added, the amount of this component was adjusted to an equal amount of primary deionized water, and the remaining components and preparation steps were the same as in Example 3.

[0104] Comparative Example 6

[0105] Use commercially available concrete waterproofing admixtures (mainly composed of organosilicon hydrophobic agents, polycarboxylate superplasticizers, and nano-silica) and apply them according to the recommended dosage in the product instructions.

[0106] Performance testing

[0107] Concrete mix proportions and specimen preparation: C60 concrete was used as the test substrate, and its mix proportions were: cement 450 kg / m³, fly ash 60 kg / m³, sand 680 kg / m³, crushed stone 1100 kg / m³, and water 160 kg / m³.

[0108] The admixtures of Examples 1-3 and Comparative Examples 1-6 were added at 3.5% of the total mass of concrete cementitious materials (cement + fly ash), and a blank control group (without any admixtures) was set up.

[0109] Prepare 100mm×100mm×100mm cubic specimens, cure them under standard conditions for 28 days, and then conduct performance tests. The average value of 3 specimens is taken for each test group.

[0110] Test method:

[0111] Water permeability grade: determined according to the water permeability test method (stepwise pressure method) in GB / T 50082-2024 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete";

[0112] 24-hour water absorption rate: determined according to the water absorption rate test method in GB / T 50082-2024;

[0113] 28-day compressive strength: determined according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete";

[0114] Salt erosion strength retention rate: After the specimens cured for 28 days were immersed in 5% NaCl solution for 30 days, the compressive strength was tested, and the ratio of the compressive strength to that of the standard cured specimens was calculated.

[0115] Freeze-thaw cycle strength retention rate: After 200 freeze-thaw cycles according to the rapid freezing method in GB / T 50082-2024, the compressive strength retention rate is tested.

[0116] Permeability grade and 24-hour water absorption rate after aging: After the admixture stock solution was continuously irradiated in an ultraviolet aging chamber (irradiance 0.89W / m², wavelength 340nm, temperature 60℃, relative humidity 60%) for 500 hours, concrete specimens were prepared with the same admixture dosage. After curing for 28 days, the permeability grade and 24-hour water absorption rate were tested.

[0117] Performance testing

[0118] Table 1. Performance test results of Examples 1-3, Comparative Examples 1-6 and the blank control group

[0119] impermeability grade P6 P14 P16 P15 P8 P9 P11 P10 P12 P10 24-hour water absorption rate (%) 8.5 1.7 1.5 1.6 5.8 4.9 3.2 3.5 2.8 4.2 28-day compressive strength (MPa) 58.2 68.5 72.3 70.4 62.1 63.5 65.8 64.7 66.2 61.8 Salt erosion intensity retention rate (%) 65.3 96.2 97.5 96.8 78.3 81.5 88.6 86.4 90.2 76.5 Freeze-thaw cycle strength retention rate (%) 58.7 92.3 94.1 93.2 75.6 78.8 85.4 83.7 87.9 73.2 Water resistance grade after aging P4 P13 P15 P14 P6 P7 P9 P8 P10 P8 Water absorption rate (%) after 24 hours of aging 10.2 2.0 1.8 1.9 6.5 5.6 3.8 4.1 3.3 4.9

[0120] Test Result Analysis:

[0121] Test results show that the admixtures prepared in Examples 1-3 of this invention have a permeability grade of P14 or higher (maximum P16) after being added to concrete, a 24-hour water absorption rate of ≤1.7%, a 28-day compressive strength of ≥68.5MPa, a salt erosion strength retention rate of ≥96.2%, a freeze-thaw cycle strength retention rate of ≥92.3%, a permeability grade of ≥P13 after aging, and a 24-hour water absorption rate of ≤2.0% after aging. All performance characteristics are superior to the blank group and comparative examples 1-6.

[0122] Comparative Example 1, without the addition of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, and Comparative Example 3, using an unmodified graphene-hexagonal boron nitride mixture, showed that the impermeability grades of the concrete decreased to P8 and P11, respectively, and the 24-hour water absorption rates increased to 5.8% and 3.2%, respectively. This indicates that the superhydrophobic interface construction of the perfluorosilane-modified graphene-hexagonal boron nitride composite phase is the key to improving waterproof performance. Furthermore, the performance of Comparative Example 3 was better than that of Comparative Example 1 but still lower than that of the example, indicating that fluorosilane grafting modification brought about performance improvement.

[0123] Comparative Example 2 without the addition of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase and Comparative Example 4 using single nano-hydroxyapatite, the impermeability grade of concrete decreased to P9 and P10 respectively, and the 24h water absorption rate increased to 4.9% and 3.5% respectively, indicating that the multi-level pore filling effect of the hydrothermal in-situ composite phase is better than that of simple mixing or single nanomaterials.

[0124] In Comparative Example 5, without the addition of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, the impermeability grade of the concrete dropped to P12, and after aging, the impermeability grade dropped to P10, indicating a significant decrease in aging resistance. This demonstrates that the three-dimensional crosslinked water-locking network is crucial for improving durability.

[0125] The overall performance of Comparative Example 6, which uses commercially available waterproofing additives, and the blank group was lower than that of the embodiments of the present invention, proving that the technical solution of the present invention has outstanding substantive features and significant progress.

[0126] Comparative data from Examples 1-3 and Comparative Examples 1-5 show that there is a synergistic effect among the four core functional components of this invention (perfluorosilane-modified graphene-hexagonal boron nitride composite phase, hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, hydroxyl-terminated polyether ether ketone water-reducing agent, and pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent). The comprehensive waterproofing effect of this invention cannot be achieved if any component is missing or replaced with conventional materials. Each component supports each other in function, and the overall technical effect is better than the sum of the effects of each component.

[0127] The special waterproofing admixture for concrete provided by this invention has mild preparation process conditions (temperature ≤80℃, normal pressure or low vacuum), and the equipment used are all conventional equipment in the chemical and building materials fields (stirring kettle, ultrasonic dispersion device, high pressure reactor, filter, vacuum degassing tank, etc.). The raw materials are all commercially available, the operation steps are clear and controllable, the product performance is stable, and it is suitable for large-scale industrial production.

[0128] This admixture can be widely used in fields with stringent requirements for waterproofing performance, such as deep-sea engineering, tunnels in cold regions, buildings in highly saline soil, and waterproofing projects for nuclear power plants.

Claims

1. A special waterproofing admixture for concrete, characterized in that, The additive comprises the following components: perfluorosilane-modified graphene-hexagonal boron nitride composite phase, hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, hydroxyl-terminated polyether ether ketone water-reducing agent, pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, maltitol-boric acid compound retarder, polyether branched modified polymethylsiloxane defoamer, and primary deionized water; wherein, in the perfluorosilane-modified graphene-hexagonal boron nitride composite phase, the weight ratio of graphene nanosheets to hexagonal boron nitride is (3~5):(6~8), and the surface of the composite phase is grafted with perfluorooctyltriethoxysilane, the grafting amount being 8~12% of the total mass of the composite phase; the hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase is composed of nano-hydroxyapatite and in-situ composite nano-titanium dioxide, with a particle size of 25~45nm, wherein the mass of titanium dioxide accounts for 5~8% of the total mass of the phase.

2. The special waterproofing admixture for concrete according to claim 1, characterized in that, By weight, the additives comprise: 12-19 parts of perfluorosilane-modified graphene-hexagonal boron nitride composite phase, 7-13 parts of hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase, 5-10 parts of hydroxyl-terminated polyether ether ketone water-reducing agent, 4-8 parts of pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent, 2-5 parts of maltitol-boric acid compound retarder, 1-2.2 parts of polyether branched modified polymethylsiloxane defoamer, and 38-52 parts of primary deionized water.

3. The special waterproofing admixture for concrete according to claim 1, characterized in that, The water reduction rate of the hydroxyl-terminated polyether ether ketone water-reducing agent is ≥40%; the thermal decomposition temperature of the pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent is ≥300℃; in the maltitol-boric acid compound retarder, the weight ratio of maltitol to boric acid is (4~6):(1~2); and the solid content of the polyether branched modified polymethylsiloxane defoamer is ≥40%.

4. A method for preparing the special waterproofing admixture for concrete according to any one of claims 1 to 3, characterized in that, Includes the following steps: S S01: Heat primary deionized water to 55-60℃, add hydroxyl-terminated polyether ether ketone water-reducing agent and stir to dissolve, obtaining an aqueous solution of water-reducing agent; S02: Add perfluorosilane-modified graphene-hexagonal boron nitride composite phase and hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase to the aqueous solution of water-reducing agent, stir at 700-800 r / min for 50-60 min, and ultrasonically disperse for 8 min every 15 min during the process, to obtain a mixed dispersion; S03: Add pyromellitic polyimide-bisphenol A epoxy resin crosslinking agent to the mixed dispersion, and heat to 75-80℃. Stirring at a constant temperature of 500~550 r / min for 35~40 min to form a cross-linked system; S04: Cooling to 45~50℃, adding maltitol-boric acid compound retarder and polyether branched modified polymethylsiloxane defoamer, stirring at 350~400 r / min for 20~25 min to obtain the admixture stock solution; S05: Passing the admixture stock solution through a 2μm primary filter and a 1μm secondary filter in sequence, degassing under reduced pressure for 20 min at a vacuum degree of -0.085~-0.095 MPa and a temperature of 65~70℃, and metering and packaging to obtain the finished product.

5. The preparation method according to claim 4, characterized in that, The power of ultrasonic dispersion in step S02 is 450~500W.

6. The preparation method according to claim 4, characterized in that, The perfluorosilane-modified graphene-hexagonal boron nitride composite phase is prepared by the following steps: S11: Graphene nanosheets with a thickness of 0.5~2nm and a sheet diameter of 60~120nm are mixed with hexagonal boron nitride with a particle size of 40~80nm at a weight ratio of (3~5):(6~8), and 15~20 times the weight of N-methylpyrrolidone is added. The mixture is ultrasonically dispersed at 35~40℃ and 450~500W for 90~120min to obtain a nano-mixed dispersion; S12: The total mass of the nano-mixed dispersion is added to the nano-mixed dispersion. 8-12% perfluorooctyltriethoxysilane was added, and the pH was adjusted to 9.0-9.

5. The mixture was stirred at a constant temperature of 85-90℃ and 350-380 r / min for 5 h to obtain a fluorine-modified precursor solution. S13: The fluorine-modified precursor solution was vacuum distilled at a vacuum degree of -0.095 to -0.10 MPa and a temperature of 95-100℃ to remove N-methylpyrrolidone, and a solid product was obtained. S14: The solid product was vacuum dried at 110-115℃ for 10 h and ball-milled to a particle size ≤5 μm to obtain the final product.

7. The preparation method according to claim 4, characterized in that, The hydrothermal in-situ composite nano-hydroxyapatite-titanium dioxide phase is prepared by the following steps: S21: Calcium nitrate and diammonium hydrogen phosphate are mixed at a molar ratio of 10:6, and 20-25 times their weight of deionized water is added and stirred to dissolve. 5-8% of the total mass of calcium nitrate and diammonium hydrogen phosphate, with a particle size of 15-30 nm, is added and ultrasonically dispersed at 380-420 W for 40-50 min to obtain a mixed precursor solution; S22: The pH of the mixed precursor solution is adjusted to 10.5-11.0, and stirred at 70-75℃ and 280-300 r / min for 4 h. The mixture is then transferred to a high-pressure reactor and hydrothermally reacted at 190-210℃ for 8-10 h, and naturally cooled to room temperature; S23: The reaction product is filtered, washed until neutral, dried at 90-95℃ for 8 h, and ball-milled to a particle size of 25-45 nm to obtain the final product.

8. The application of the special waterproofing admixture for concrete according to any one of claims 1 to 3 in the preparation of waterproof concrete, characterized in that, The admixture is added at a rate of 2.5 to 4.0% of the total mass of the concrete cementitious materials.

9. The application according to claim 8, characterized in that, The waterproof concrete is used for waterproofing projects in deep-sea engineering, cold-region tunnels, high-salinity soil buildings, or nuclear power plants.

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