A method for preparing an inorganic water-based transparent coating for concrete durability protection and its application.

Abstract

This invention discloses a method for preparing an inorganic water-based transparent coating for concrete durability protection and its application, relating to the field of building materials technology. The preparation method includes: mixing and diluting lithium silicate and potassium silicate, then adding nano-silica sol to react and obtain a composite mother liquor; adding soluble zinc salt and boric acid to the composite mother liquor and mixing evenly to obtain a transparent coating; applying the transparent coating to the concrete surface, where silicate ions in the coating react with calcium ions in the concrete, and under the crystal induction effect of zinc ions, nanofiber-like hydrated calcium silicate whiskers are generated in situ. The whiskers overlap to form a three-dimensional network structure, and after drying, an inorganic water-based transparent coating is obtained. This invention solves the problem of high brittleness and easy cracking of pure inorganic coatings by in-situ generation of nano-whiskers to enhance the network through zinc salt induction, while maintaining high transparency of the coating. It also has the advantages of chemical bonding with concrete, excellent durability, and simple construction.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a method for preparing an inorganic water-based transparent coating for durable protection of concrete and its application. Background Technology

[0002] As the most widely used building material, the durability of concrete has always been a focus of attention in the engineering field. During service, concrete structures are affected by factors such as carbonation, chloride ion erosion, freeze-thaw cycles, and steel corrosion, and their service life is often far shorter than the design life. Applying a protective coating to the concrete surface is one of the important means to improve its durability.

[0003] Currently, concrete protective coatings are mainly divided into two categories: organic coatings and non-nano-organic coatings.

[0004] Organic coatings use water-based acrylic, silicone acrylic, fluorocarbon and other polymer emulsions as the main film-forming substances. For example, Chinese patent CN103333559B discloses a multifunctional concrete structure durability protectant and its preparation and application method, which uses organic polymer emulsion as the film-forming substance and has good waterproof and carbonation-proof performance and one-way breathability. However, the chemical bonding between organic coatings and concrete substrates is weak, and they are prone to peeling due to interfacial stress or ultraviolet aging during long-term service. Their durability is limited by the aging life of the organic polymer itself.

[0005] Inorganic coatings use silicates, silica sols, and other materials as their main active components. For example, US Patent 12091369B2 discloses a concrete protective coating that uses alkali metal silicates and fillers to form an inorganic coating that is chemically bonded to concrete and has good durability. However, such inorganic coatings are prone to microcracks due to capillary stress during the drying process, exhibiting greater brittleness. In addition, the micron-sized fillers introduced to enhance the mechanical properties of the coating will significantly reduce the transparency of the coating, making it difficult to meet the requirements of applications such as fair-faced concrete where there are high requirements for the appearance of buildings.

[0006] To improve the brittleness of inorganic coatings, existing technologies attempt to introduce organic components for toughening modification, forming an organic-inorganic composite system. Although such systems can balance the film-forming properties of organic materials with the durability of inorganic materials to a certain extent, the introduction of organic components still cannot fundamentally eliminate the aging problem, and the structure of the composite system is relatively complex.

[0007] In summary, existing concrete protective coating technologies still fall short in achieving a synergistic effect of high transparency and good toughness while maintaining the excellent durability and chemical bonding ability of inorganic systems. Therefore, developing an inorganic waterborne coating that combines high transparency, high toughness, and high durability, and further constructing a matching surface protection system, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] This invention provides a method for preparing an inorganic water-based transparent coating for durable protection of concrete and its application.

[0009] To achieve the above objectives, the technical solution of the present invention is as follows:

[0010] In a first aspect, a method for preparing an inorganic water-based transparent coating for concrete durability protection is provided, comprising the following steps:

[0011] S1, Prepare composite mother liquor by mixing lithium water glass and potassium water glass, diluting with deionized water, adding nano silica sol under shear conditions, and obtaining composite mother liquor containing nano crystal seeds after reaction.

[0012] S2, introduce crystal form regulator and crosslinking promoter, add soluble zinc salt and boric acid to the composite mother liquor obtained in step S1, mix evenly to obtain transparent coating;

[0013] S3, Coating and In-situ Reinforcement: The transparent coating obtained in step S2 is coated on the concrete surface. The silicate ions in the transparent coating penetrate into the concrete surface and react with the calcium ions in the concrete. Under the crystal induction of soluble zinc salt, nanofiber-like hydrated calcium silicate whiskers are generated in-situ. The whiskers overlap to form a three-dimensional network structure. After drying, an inorganic water-based transparent coating is obtained.

[0014] S4, on the surface of the inorganic water-based transparent coating obtained in step S3, a layer of concrete surface sealant is further coated. The surface sealant, by mass percentage, has the following composition: nano-... The composition is 4-5%, isobutyltriethoxysilane is 70-80%, pure water is 15-25%; the balance is surfactant.

[0015] Preferably, in step S1, the modulus of the lithium silicate is 4.0-6.0, the modulus of the potassium silicate is 3.5-5.0, and the mass ratio of lithium silicate to potassium silicate is 1:2 to 2:1.

[0016] Preferably, the particle size of the nano silica sol in step S1 is 10-20 nm, and its addition amount is 5%-15% of the total mass of lithium silicate and potassium silicate.

[0017] Preferably, the reaction temperature in step S1 is 50-60°C and the reaction time is 2-4 hours.

[0018] Preferably, the soluble zinc salt in step S2 is zinc nitrate or zinc acetate, and its addition amount is 0.5%-2% of the mass of the composite mother liquor;

[0019] The amount of boric acid added is 0.1%-0.5% of the mass of the composite mother liquor.

[0020] Preferably, the mixing time in step S2 is 30 minutes.

[0021] Preferably, the inorganic water-based transparent coating obtained in step S3 has a visible light transmittance greater than 90%, an ultimate tensile strain greater than 0.3%, and a porosity less than 5%.

[0022] Preferably, the rotational speed of the shearing condition in step S1 is 2000-3000 rpm.

[0023] Secondly, the application of the inorganic water-based transparent coating prepared by the above method in the durable protection of concrete surfaces is provided.

[0024] Beneficial effects

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention achieves a synergistic unity of high transparency and high toughness by transforming conventional amorphous hydrated calcium silicate gel into nanofiber whiskers through the crystal-inducing effect of zinc salts. The whisker diameter is 20-50nm, which is much smaller than the wavelength of visible light and does not scatter light, thus achieving high transparency of the pure inorganic coating. At the same time, the whiskers overlap to form a three-dimensional network structure, which absorbs cracking energy through the bridging and pull-out effect of the whiskers, significantly improving the toughness of the coating and solving the technical problems of high brittleness and easy cracking of existing pure inorganic coatings.

[0027] With strong chemical bonding to the concrete substrate, the main component of the coating of this invention is in-situ generated hydrated calcium silicate whiskers, which are homologous to the hydration products of the concrete substrate. The coating and the substrate form an integrated structure through chemical bonding, resulting in strong adhesion and avoiding coating peeling problems.

[0028] Excellent long-term durability: The coating of this invention is a pure inorganic system, without organic polymer components, which fundamentally eliminates the performance degradation problem caused by ultraviolet aging and thermo-oxidative aging of organic coatings. The coating durability is matched with the concrete substrate, which can achieve long-term durable protection of concrete structures.

[0029] With multiple protective functions, the coating of this invention has high density, hydrophobicity and anti-carbonation ability. The three-dimensional whisker network effectively fills the pores of the coating, blocking the penetration of moisture, carbon dioxide and chloride ions. At the same time, the coating surface has a hydrophobic effect, which can give concrete structures comprehensive and durable protection.

[0030] Environmentally friendly and easy to apply, the coating of this invention uses water as a solvent and does not contain volatile organic compounds, making the application process environmentally friendly; the coating is a single-component system, requiring no on-site mixing, making application simple and suitable for surface protection of various concrete structures;

[0031] The present invention further coats the surface of the inorganic water-based transparent coating with nano-containing... The topcoat layer, combined with isobutyltriethoxysilane, forms a composite protective system of primer and topcoat. The topcoat and primer are chemically compatible and have a tight interfacial bond, imparting excellent hydrophobicity, stain resistance, self-cleaning ability, and UV shielding to the concrete surface. Simultaneously, it further reduces the carbonation depth. The nano-sized components in the topcoat... It has photocatalytic activity and can decompose organic matter attached to the surface to achieve self-cleaning; isobutyltriethoxysilane forms a low surface energy hydrophobic layer, which effectively blocks the penetration of water and ions. This composite system significantly improves the coating system's resistance to ultraviolet aging and long-term weather resistance without sacrificing the high adhesion and high density of the primer. Attached Figure Description

[0032] Figure 1 A process flow diagram for preparing an inorganic water-based transparent coating for concrete durability protection provided by the present invention;

[0033] Figure 2 This is a bar chart comparing the visible light transmittance of Examples 1-6 and Comparative Examples 1-3 of the present invention.

[0034] Figure 3 This is a bar chart comparing the ultimate tensile strain of Examples 1-6 and Comparative Examples 1-3 of the present invention;

[0035] Figure 4 This is a bar chart comparing the carbonization depth of Examples 1-6 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0036] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, exemplary embodiments will be described in detail below. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of methods and systems consistent with some aspects of this application as detailed in the appended claims.

[0037] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a” and “the” as used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0038] Those skilled in the art will understand that, in order to achieve the self-aligned patterned mask and selective metallization of the present invention, thermally induced phase change materials, coating methods, heating methods, metal deposition methods, etc., can all be reasonably selected within the following ranges to achieve similar technical effects.

[0039] The following are preferred embodiments, which provide a detailed description of the specific implementation methods, features, and effects of the present invention.

[0040] Example 1

[0041] Please refer to Figure 1 This embodiment provides a method for preparing an inorganic water-based transparent coating for concrete durability protection;

[0042] The raw materials used in this embodiment are as follows:

[0043] Lithium-ion water glass, industrial grade, module 5.5, solid content 30%, commercially available;

[0044] Potassium silicate, industrial grade, modulus 4.5, solid content 35%, commercially available;

[0045] Nano silica sol, industrial grade, particle size 12nm, solid content 30%, commercially available;

[0046] Zinc nitrate Analytical grade, purity ≥99.0%, commercially available;

[0047] boric acid Analytical grade, purity ≥99.5%, commercially available;

[0048] Deionized water, prepared in the laboratory, conductivity ≤10μS / cm;

[0049] The concrete substrate uses C40 concrete test blocks with dimensions of 100mm×100mm×100mm. After standard curing for 28 days, the surface is ground to remove laitance before use, cleaned with deionized water and dried to constant weight.

[0050] In a reactor equipped with a stirrer and a heating device, lithium silicate and potassium silicate are added at a mass ratio of 1.5:1. The mixture is stirred and mixed thoroughly. Deionized water is then added to dilute the mixture to a solid content of 25%.

[0051] Turn on the high-speed shearing machine and control the shearing speed at 2800 rpm. Under continuous shearing conditions, slowly add nano silica sol dropwise at a rate of 5-10 mL / min. The amount added is 8% of the total mass of lithium silicate and potassium silicate. After the addition is complete, heat the reaction system to 58°C and keep it at that temperature for 3.5 hours. After the reaction is complete, let it cool naturally to room temperature to obtain a composite mother liquor containing nanocrystalline seeds, which is denoted as mother liquor A.

[0052] Take the above mother liquor A and place it in a mixing tank. Under stirring conditions, with a speed of 500 rpm, add zinc nitrate and boric acid in sequence.

[0053] The amount of zinc nitrate added is 1.0% of the mass of mother liquor A, and the amount of boric acid added is 0.2% of the mass of mother liquor A. After the addition is completed, the mixture is stirred at room temperature for 30 minutes to ensure that the components are fully mixed and homogeneous, and a transparent coating is obtained, which is denoted as coating B.

[0054] Paint B was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature of 25±2℃ and relative humidity of 50%±5% to air dry for 24 hours.

[0055] During the drying process, silicate ions in coating B penetrate into the pores of the concrete surface and react chemically with calcium ions in the concrete pore liquid. Under the induction of zinc ions provided by zinc nitrate, the reaction product changes from conventional amorphous hydrated calcium silicate gel to nanofiber-like hydrated calcium silicate whiskers. The whiskers have a diameter of 30-50 nm and an aspect ratio of about 15. They overlap to form a three-dimensional network structure.

[0056] After drying, a uniform, transparent, and dense protective coating is formed on the concrete surface, denoted as coating C.

[0057] Example 2

[0058] The raw material preparation in this embodiment is the same as in Embodiment 1, except that the following process parameters are used:

[0059] Lithium silicate with a modulus of 4.0 and potassium silicate with a modulus of 3.5 are mixed at a mass ratio of 1:2, and then diluted with deionized water to a solid content of 20%.

[0060] Under a shear speed of 2000 rpm, nano-silica sol with a particle size of 10 nm was slowly added dropwise at a rate of 5% of the total mass of lithium silicate and potassium silicate. After the addition was complete, the reaction system was heated to 50°C and kept at that temperature for 2 hours. After the reaction was completed, it was naturally cooled to room temperature to obtain the composite mother liquor.

[0061] Add zinc nitrate to the above-mentioned composite mother liquor at a rate of 0.5% of the mother liquor's mass.

[0062] Add boric acid at a rate of 0.1% of the mass of the composite mother liquor.

[0063] Stir at room temperature for 30 minutes to ensure thorough mixing of all components and obtain a transparent coating.

[0064] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to air dry for 24 hours to form a protective coating on the concrete surface.

[0065] Example 3

[0066] The raw material preparation in this embodiment is the same as in Embodiment 1, except that the following process parameters are used:

[0067] Lithium silicate (6.0 modulus) and potassium silicate (5.0 modulus) are mixed at a mass ratio of 2:1 and diluted with deionized water to a solid content of 30%.

[0068] Under a shearing speed of 3000 rpm, nano-silica sol with a particle size of 20 nm was slowly added dropwise at an amount of 15% of the total mass of lithium silicate and potassium silicate.

[0069] After the addition is complete, the reaction system is heated to 60°C and kept at that temperature for 4 hours. After the reaction is complete, it is naturally cooled to room temperature to obtain the composite mother liquor.

[0070] Zinc acetate was added to the above-mentioned composite mother liquor at a rate of 2.0% of the mother liquor's mass.

[0071] Add boric acid at a rate of 0.5% of the mass of the composite mother liquor.

[0072] Stir at room temperature for 30 minutes to ensure thorough mixing of all components and obtain a transparent coating.

[0073] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to air dry for 24 hours to form a protective coating on the concrete surface.

[0074] Example 4

[0075] The raw material preparation in this embodiment is the same as in Embodiment 1, except that the following process parameters are used:

[0076] Lithium silicate with a modulus of 5.0 and potassium silicate with a modulus of 4.2 are mixed at a mass ratio of 1:1 and diluted with deionized water to a solid content of 25%.

[0077] Under a shear speed of 2500 rpm, nano-silica sol with a particle size of 15 nm was slowly added dropwise. The amount added was 10% of the total mass of lithium water glass and potassium water glass. After the addition was completed, the reaction system was heated to 55°C and kept at that temperature for 3 hours. After the reaction was completed, it was naturally cooled to room temperature to obtain the composite mother liquor.

[0078] Zinc nitrate was added to the above-mentioned composite mother liquor at a concentration of 1.2% of the mother liquor's mass.

[0079] Add boric acid at a rate of 0.3% of the mass of the composite mother liquor.

[0080] Stir at room temperature for 30 minutes to ensure thorough mixing of all components and obtain a transparent coating.

[0081] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to air dry for 24 hours to form a protective coating on the concrete surface.

[0082] Example 5

[0083] The raw material preparation in this embodiment is the same as in Embodiment 1, except that the following process parameters are used:

[0084] Lithium silicate with a modulus of 5.5 and potassium silicate with a modulus of 4.5 are mixed at a mass ratio of 1.5:1 and diluted with deionized water to a solid content of 25%.

[0085] Under a shear speed of 2800 rpm, nano-silica sol with a particle size of 12 nm was slowly added dropwise at an amount of 8% of the total mass of lithium silicate and potassium silicate. After the addition was complete, the reaction system was heated to 58°C and kept at that temperature for 3.5 hours. After the reaction was completed, it was naturally cooled to room temperature to obtain the composite mother liquor.

[0086] Zinc nitrate was added to the above-mentioned composite mother liquor at a rate of 1.0% of the mother liquor's mass.

[0087] Add boric acid at a rate of 0.2% of the mass of the composite mother liquor.

[0088] Stir at room temperature for 30 minutes to ensure thorough mixing of all components and obtain a transparent coating.

[0089] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to air dry for 24 hours to form a protective coating on the concrete surface.

[0090] Example 6

[0091] This embodiment provides a method for preparing a composite coating including a topcoat, while the primer portion is the same as in Embodiment 1.

[0092] First, following steps S1 to S3 of Example 1, an inorganic water-based transparent coating, i.e. a primer, is prepared on the concrete surface. After the primer dries naturally for 24 hours in an environment with room temperature of 25±2℃ and relative humidity of 50%±5%, the topcoat is applied.

[0093] The topcoat is prepared by weighing each component according to the following mass percentages:

[0094] nanometer Anatase type, with a particle size range of 5-15 nm and a mass percentage of 4.5%;

[0095] Isobutyltriethoxysilane, purity 98% or higher, density 0.88 g / ml, mass percentage 75.0%;

[0096] Pure water, 20.0% by mass;

[0097] The remainder is surfactant;

[0098] The above components were stirred in a high-speed disperser at 2000 rpm for 30 minutes to obtain a uniform concrete surface sealant.

[0099] For topcoat application, the above-mentioned surface sealant is evenly applied to the dried primer surface using a sprayer or roller. The coating amount is controlled at 150g / m², and one coat is applied. After coating, the surface is placed in an environment with room temperature of 25±2℃ and relative humidity of 50%±5% to air dry for 24 hours to obtain a composite coating.

[0100] Comparative Example 1

[0101] The preparation method of this comparative example is basically the same as that of Example 4, except that soluble zinc salt is not added in step S2;

[0102] The specific preparation process is as follows:

[0103] Lithium silicate with a modulus of 5.0 and potassium silicate with a modulus of 4.2 are mixed at a mass ratio of 1:1 and diluted with deionized water to a solid content of 25%.

[0104] Under a shear speed of 2500 rpm, nano-silica sol with a particle size of 15 nm was slowly added dropwise. The amount added was 10% of the total mass of lithium water glass and potassium water glass. After the addition was completed, the reaction system was heated to 55°C and kept at that temperature for 3 hours. After the reaction was completed, it was naturally cooled to room temperature to obtain the composite mother liquor.

[0105] Add boric acid to the above composite mother liquor at a rate of 0.3% of the mass of the composite mother liquor, without adding soluble zinc salt, and stir at room temperature for 30 minutes to ensure that all components are fully mixed and homogeneous, thereby obtaining a transparent coating.

[0106] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to dry naturally for 24 hours, forming a protective coating on the concrete surface, which was recorded as the control coating D1.

[0107] Comparative Example 2

[0108] The preparation method of this comparative example is basically the same as that of Example 4, except that boric acid is not added in step S2;

[0109] The specific preparation process is as follows:

[0110] Lithium silicate with a modulus of 5.0 and potassium silicate with a modulus of 4.2 were mixed at a mass ratio of 1:1 and diluted with deionized water to a solid content of 25%. Nano-silica sol with a particle size of 15 nm was slowly added dropwise at a shear speed of 2500 rpm. The amount added was 10% of the total mass of lithium silicate and potassium silicate. After the addition was complete, the reaction system was heated to 55°C and kept at that temperature for 3 hours. After the reaction was completed, it was naturally cooled to room temperature to obtain the composite mother liquor.

[0111] Add zinc nitrate to the above composite mother liquor at a rate of 1.2% of the mass of the composite mother liquor, without adding boric acid, and stir at room temperature for 30 minutes to ensure that all components are fully mixed and homogeneous, thereby obtaining a transparent coating.

[0112] The transparent coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 250g / m². After coating, the test block was placed in an environment with room temperature and relative humidity of 50%±5% to air dry for 24 hours, forming a protective coating on the concrete surface, which was recorded as the control coating D2.

[0113] Comparative Example 3

[0114] This comparative example strictly follows the method and proportions of Example 13 in prior art document US12091369B2 to prepare the inorganic protective coating;

[0115] The raw materials used in this comparative example are as follows:

[0116] Liquid components:

[0117] Potassium silicate solution, brand name KASIL 6, contains approximately 39% potassium silicate and 61% water, modulus approximately 3.9, commercially available;

[0118] Potassium hydroxide flakes, analytical grade, purity ≥95%, commercially available;

[0119] Deionized water, conductivity ≤10μS / cm, prepared in the laboratory;

[0120] Powder components:

[0121] Volcanic ash microspheres, average particle size 50μm, commercially available;

[0122] Zirconia powder, average particle size 5μm, purity ≥99%, commercially available;

[0123] Zinc oxide powder, average particle size 1μm, purity ≥99%, commercially available;

[0124] Titanium dioxide powder, anatase type, average particle size 0.5μm, commercially available;

[0125] Alumina powder, average particle size 3μm, purity ≥99%, commercially available;

[0126] Wollastonite fiber, average length 100μm, aspect ratio approximately 20:1, commercially available;

[0127] Discrete carbon fiber, average length 200μm, diameter 7μm, commercially available;

[0128] Metakaolin, average particle size 10μm, commercially available;

[0129] Densifying agent components:

[0130] Silicic acid, powder, average particle size 10μm, purity ≥98%, commercially available;

[0131] The concrete substrate is the same as in Example 1, using C40 concrete test blocks with dimensions of 100mm×100mm×100mm. After standard curing for 28 days, the surface is ground to remove laitance before use, cleaned with deionized water and dried to constant weight.

[0132] According to Example 13 of US12091369B2, the weight ratio of the liquid portion is 70 parts of KASIL 6 silicate solution, 10 parts of potassium hydroxide flakes, and 20 parts of water.

[0133] Weigh 70 parts by weight of KASIL 6 potassium silicate solution, add 10 parts by weight of potassium hydroxide flakes, and then add 20 parts by weight of deionized water. Under stirring conditions, the mixture is stirred at 500 rpm to fully dissolve and mix evenly to obtain liquid component L.

[0134] According to Example 13 of US12091369B2, the mass percentage of each component in the powder portion relative to the total powder volume is as follows:

[0135]

[0136] Weigh each powder raw material according to the above proportions, place them in a high-speed mixer, and mix at 2000 rpm for 30 minutes to ensure that each component is fully dispersed and uniform, thus obtaining powder component P;

[0137] According to Example 13 of US12091369B2, the final coating consists of 32 parts by weight of liquid, 67 parts by weight of powder and 1 part by weight of densifier.

[0138] Liquid component L, powder component P and silica densifier are mixed and stirred at 1000 rpm for 10 minutes to obtain a uniform inorganic coating.

[0139] The coating was evenly applied to the surface of the pretreated concrete test block by spraying, with the coating amount controlled at 300g / m². After coating, the test block was placed in an environment with room temperature of 25±2℃ and relative humidity of 50%±5% to air dry for 48 hours, forming a protective coating on the concrete surface, which was recorded as the control coating D3.

[0140] The coatings prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance tests. The specific test methods and results are as follows:

[0141] Visible light transmittance was tested using a UV-Vis spectrophotometer. The coating was applied to a transparent glass substrate measuring 50mm × 50mm × 2mm, with a thickness controlled at 50±5μm. After the coating was completely dry, the sample was placed in the sample cell of the spectrophotometer, with an uncoated blank glass substrate as a reference. The sample was scanned in the visible light wavelength range of 380nm to 780nm, and the transmittance at each wavelength was recorded. The arithmetic mean of the transmittance in the wavelength range of 380-780nm was taken as the visible light transmittance of the sample.

[0142] The ultimate tensile strain test was conducted in accordance with the provisions of Section 8.2 Tensile Properties in the national standard GB / T 16777-2008 "Test Methods for Waterproof Coatings for Buildings". The coating was applied to a polytetrafluoroethylene mold to form dumbbell-shaped specimens with a thickness of 1.0 mm ± 0.1 mm. The specimen dimensions were 25 mm gauge length and 6 mm width. The specimens were cured for 7 days under standard conditions: temperature 23℃ ± 2℃, relative humidity 50% ± 5%. Tensile tests were then performed using an electronic universal testing machine with a tensile rate of 5 mm / min. The elongation at fracture was recorded. Five specimens were tested for each sample, and the arithmetic mean was taken as the ultimate tensile strain of the sample.

[0143] Porosity testing was performed using mercury porosimetry to determine the porosity of the coating. The coating was carefully peeled off from the concrete substrate, cut into 3mm×3mm×3mm pieces, and dried in a 60℃ vacuum drying oven for 24 hours until constant weight. The mercury porosimetry was then used for testing, with a pressure range of 0 to 200 MPa and a pore size measurement range of 3 nm to 360 μm. The pore size distribution of mercury entering the pores at each pressure was calculated using the Washburn equation. The ratio of total pore volume to total sample volume was taken as the porosity of the coating. Three specimens were tested for each sample, and the arithmetic mean was taken.

[0144] For the contact angle test, the static water contact angle of the coating surface was measured using a contact angle measuring instrument. The coating was applied to the surface of the concrete block and dried. Five test points were selected at different locations on the coating surface. 5 μL of deionized water was added to each test point using a micro-syringe. After the droplet stabilized for 30 seconds, the droplet image was captured by the built-in camera system of the instrument. The contact angle was calculated using the circle fitting method, and the arithmetic mean of the five test points was taken as the contact angle of the sample.

[0145] Carbonation depth testing was conducted according to the provisions of Chapter 11, Carbonation Test, in the national standard GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". A concrete specimen with a protective coating, measuring 100mm × 100mm × 100mm, was placed in a carbonation chamber. The carbon dioxide concentration in the chamber was controlled at 20% ± 3%, the temperature at 20℃ ± 2℃, and the relative humidity at 70% ± 5%. After 28 days of carbonation, the specimen was removed and split along its centerline. A 1% phenolphthalein alcohol solution was sprayed onto the split surface (1g of phenolphthalein dissolved in 100mL of anhydrous ethanol). After standing for 30 minutes, the depth of the undiscolored portion was measured using a carbonation depth measuring instrument with an accuracy of 0.1mm. The arithmetic mean of the measurements from five different locations on the specimen was taken as the carbonation depth of the sample.

[0146] Adhesion testing was conducted in accordance with the national standard GB / T 5210-2006 "Paints and Varnishes - Pull-off Adhesion Test". A pull-off adhesion tester was used. The surface of the concrete test block coated with the protective coating was sanded smooth and cleaned with acetone. A 20mm diameter aluminum alloy test column was then adhered to the coating surface with epoxy resin adhesive and cured for 24 hours under standard conditions. The tester was connected to the test column, and a tensile force was applied at a rate of 1mm / min. The maximum tensile force when the coating peeled off the substrate was recorded. The adhesion was calculated by dividing this tensile force by the cross-sectional area of ​​the test column. Five test columns were tested for each sample, and the arithmetic mean was taken. The failure mode was also recorded.

[0147] Microstructure analysis was performed on the coatings prepared in Examples 1-5 and Comparative Examples 1-3. The coatings were peeled off from the concrete substrate to prepare samples of appropriate size. The microstructure of the coatings was observed using scanning electron microscopy and transmission electron microscopy, and a comprehensive inference was made in combination with the mechanical property test results.

[0148] The microstructure analysis results of Example 1 show that there are a large number of fibrous structures inside the coating. These fibrous structures overlap to form a dense three-dimensional network. Combined with the ultimate tensile strain test result of 0.42% and the porosity test result of 3.8% in Example 1, it can be inferred that the fibrous structure is a nanoscale hydrated calcium silicate whisker. Its size characteristics are consistent with the characteristics of conventional hydrated calcium silicate crystals in the field, with a diameter of about 30-50 nm, a length of about 500-700 nm, and an aspect ratio of about 15. The formation of this whisker network structure is the key to the coating obtaining excellent mechanical properties and density.

[0149] The microstructure analysis results of Example 2 show that there is a fibrous structure inside the coating. The fibrous structures overlap to form a network, but the network density is slightly lower than that of Example 1. Combined with its ultimate tensile strain of 0.32% and porosity of 4.5%, it can be inferred that the fibrous structure is also a hydrated calcium silicate whisker with a diameter of about 30-50 nm, a length of about 300-500 nm, and an aspect ratio of about 12.

[0150] The microstructure analysis results of Example 3 show that there is a fibrous structure inside the coating. The fibrous structures overlap to form a relatively dense network. Based on its ultimate tensile strain of 0.35% and porosity of 4.2%, it can be inferred that the fibrous structure is hydrated calcium silicate whiskers with a diameter of about 35-50 nm, a length of about 400-600 nm, and an aspect ratio of about 14.

[0151] The microstructure analysis results of Example 4 show that there is a fibrous structure inside the coating. The fibrous structures overlap to form a uniform and continuous network. Based on its ultimate tensile strain of 0.38% and porosity of 4.0%, it can be inferred that the fibrous structure is calcium silicate hydrate whiskers with a diameter of about 30-50 nm, a length of about 400-650 nm, and an aspect ratio of about 15.

[0152] The microstructure analysis results of Example 5 show that there is a fibrous structure inside the coating. The fibrous structures overlap to form a well-developed network. Based on its ultimate tensile strain of 0.40% and porosity of 4.1%, it can be inferred that the fibrous structure is calcium silicate hydrate whiskers with a diameter of about 30-50 nm, a length of about 450-650 nm, and an aspect ratio of about 14.

[0153] The microstructure analysis results of Example 6 show that the coating exhibits a distinct double-layer structure. The bottom layer is an inorganic water-based transparent coating prepared by the method of Example 1, which contains dense nanofiber-like hydrated calcium silicate whiskers. The whiskers overlap to form a well-developed three-dimensional network structure with a diameter of approximately 30-50 nm, a length of approximately 450-650 nm, and an aspect ratio of approximately 14. The top layer is a concrete surface sealant coating with uniform thickness, continuous density, and tight bonding with the bottom layer interface. No delamination or cracks were observed. The top layer contains uniformly distributed nanofibers. The particles, with a diameter of about 10 nm, are embedded in a hydrophobic film formed by isobutyltriethoxysilane. This bilayer structure works synergistically, with the bottom layer providing mechanical support and chemical bonding, and the top layer imparting hydrophobic, antifouling and UV shielding functions. Its overall performance is superior to that of a single coating.

[0154] The microstructure analysis results of Comparative Example 1 show that the coating has an amorphous gel structure and no fibrous structure. Combined with its ultimate tensile strain of 0.08% and porosity of 8.5%, it can be inferred that since no soluble zinc salt was added, the reaction product is an amorphous hydrated calcium silicate gel, which failed to form a whisker-reinforcing network, resulting in a significant decrease in the mechanical properties and density of the coating.

[0155] The microstructure analysis results of Comparative Example 2 show that there is a small amount of amorphous gel inside the coating and no obvious fibrous structure. Combined with its ultimate tensile strain of 0.12% and porosity of 7.2%, it can be inferred that due to the lack of boric acid, the cross-linking effect is insufficient, the coating network structure is loose, and the mechanical properties and density are poor.

[0156] Microstructure analysis of Comparative Example 3 showed that the coating contained a large number of micron-sized particles and fibrous fillers, such as volcanic ash microspheres, wollastonite fibers, and carbon fibers. The fillers were dispersed in the silicate matrix, and no in-situ fibrous network structure was observed. Combined with its ultimate tensile strain of 0.25% and porosity of 12.0%, it can be inferred that the toughening mechanism of the coating depends on the added fiber fillers rather than the in-situ generated whisker network. Furthermore, the poor bonding between the fillers and the matrix resulted in low coating density.

[0157] Table 1 Test Results

[0158]

[0159] Please refer to Figure 2 The visible light transmittance of Examples 1-6 is greater than 90%, with the highest reaching 93.5%. In contrast, Comparative Examples 1-2 have slightly lower transmittance than 90% due to the lack of zinc salt or boric acid, resulting in decreased coating density. Comparative Example 3 has a transmittance of only 72.6% due to the presence of a large amount of micron-sized filler, which causes severe light scattering. This indicates that the present invention achieves high transparency by generating nanocrystals in situ.

[0160] Please refer to Figure 3 The ultimate tensile strain of Example 1 was the highest, and that of Examples 2-6 was greater than 0.32%, while the strain of Comparative Example 1 was only 0.08% and that of Comparative Example 2 was only 0.12%. This indicates that the synergistic effect of the whisker toughening induced by zinc salt and the cross-linking reinforcement of boric acid was significant. Comparative Example 3 had a strain of 0.25% due to the presence of fiber filler, but it was still lower than that of the present invention. Moreover, its toughening depended on the added fiber rather than in-situ self-reinforcement.

[0161] Example 1 had the lowest porosity, Examples 2-6 all had porosity below 4.5%, while Comparative Examples 1-2 had porosity above 7%, and Comparative Example 3 had porosity of 12.0%, indicating that the whisker network effectively filled the internal pores of the coating and improved its compactness.

[0162] Examples 1-6 all have contact angles greater than 95°, exhibiting good hydrophobic effects, while the comparative examples all have contact angles less than 90°;

[0163] Please refer to Figure 4 Carbonization depth tests showed that Example 6 had the lowest carbonization depth, while Examples 1-5 were all below 0.8 mm, which was far superior to Comparative Examples 1-2 and Comparative Example 3, demonstrating its excellent resistance to carbonization.

[0164] Examples 1-6 all showed adhesion greater than 2.5 MPa, and the failure mode was concrete body failure, indicating that the coating-substrate bond strength exceeded the concrete cohesion, while the comparative examples showed lower adhesion, especially Comparative Example 1, which only showed 1.5 MPa.

[0165] Based on the analysis of comprehensive mechanical property data and reaction mechanism, it can be inferred that nanofiber-like hydrated calcium silicate whiskers were generated in Examples 1-6, with the whisker network of Example 1 being the most developed. Comparative Examples 1-2 failed to form whisker structures due to the lack of key components. Comparative Example 3 is an external filler stacking structure, and the generation of this whisker network is the key to achieving the excellent performance of the present invention.

[0166] Finally, it should be noted that the device models used in this embodiment are only for verification and do not limit the scope of this application. The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A method for preparing an inorganic water-based transparent coating for durable protection of concrete, characterized in that, Includes the following steps: S1, Prepare composite mother liquor by mixing lithium water glass and potassium water glass, diluting with deionized water, adding nano silica sol under shear conditions, and obtaining composite mother liquor containing nano crystal seeds after reaction. S2, introduce crystal form regulator and crosslinking promoter, add soluble zinc salt and boric acid to the composite mother liquor obtained in step S1, mix evenly to obtain transparent coating; S3, Coating and In-situ Reinforcement: The transparent coating obtained in step S2 is coated onto the concrete surface. The silicate ions in the transparent coating penetrate into the concrete surface and react with the calcium ions in the concrete. Under the crystal induction effect of the soluble zinc salt, nanofiber-like hydrated calcium silicate whiskers are generated in-situ. The whiskers overlap each other to form a three-dimensional network structure. After drying, an inorganic water-based transparent coating is obtained. S4, on the surface of the inorganic water-based transparent coating obtained in step S3, a layer of concrete surface sealant is further coated. The surface sealant, by mass percentage, has the following composition: nano-... The composition is 4-5%, isobutyltriethoxysilane is 70-80%, pure water is 15-25%; the balance is surfactant.

2. The preparation method according to claim 1, characterized in that, In step S1, the lithium-ion glass has a modulus of 4.0-6.0, the potassium-ion glass has a modulus of 3.5-5.0, and the mass ratio of lithium-ion glass to potassium-ion glass is 1:2 to 2:

1.

3. The preparation method according to claim 1, characterized in that, The nano-silica sol in step S1 has a particle size of 10-20 nm and is added in an amount of 5%-15% of the total mass of the lithium silicate and potassium silicate.

4. The preparation method according to claim 1, characterized in that, The reaction in step S1 is carried out at a temperature of 50-60°C for 2-4 hours.

5. The preparation method according to claim 1, characterized in that, The soluble zinc salt mentioned in step S2 is zinc nitrate or zinc acetate, and its addition amount is 0.5%-2% of the mass of the composite mother liquor; The amount of boric acid added is 0.1%-0.5% of the mass of the composite mother liquor.

6. The preparation method according to claim 1, characterized in that, The mixing time for step S2 is 30 minutes.

7. The preparation method according to claim 1, characterized in that, The inorganic water-based transparent coating obtained in step S3 has a visible light transmittance greater than 90%, an ultimate tensile strain greater than 0.3%, and a porosity less than 5%.

8. The preparation method according to claim 1, characterized in that, The rotational speed of the shearing condition described in step S1 is 2000-3000 rpm.

9. The application of the inorganic water-based transparent coating prepared by the preparation method according to any one of claims 1 to 8 in the durable protection of concrete surfaces.

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