Composite protective structure adapting to porous characteristics of cement alkali and preparation method thereof

Abstract

The application discloses a composite protection structure suitable for cement alkaline porous characteristics and a preparation method, and belongs to the technical field of cement product marine protection. The application aims to solve the technical problems of weak combination of the existing coating and the cement base material, poor alkali resistance, insufficient synergy of corrosion resistance and biological adhesion resistance. The protection structure is a four-layer gradient structure from inside to outside, which is a silane modified cement base layer, a composite rust prevention layer, a composite bonding layer and a wear-resistant biological surface layer, and precisely adapts to the characteristics of the cement base material. The preparation method integrates cold spraying and induction heating processes, and takes into account the coating density and the feasibility of on-site construction. The bonding strength of the protection structure and the cement base material is greater than or equal to 4.5 MPa, the salt spray corrosion resistance is more than 2200h, the marine biological adhesion area is less than or equal to 1.0%, the mass loss after freeze-thaw cycles (100 times) is less than or equal to 1.0%, and the wear resistance is less than or equal to 0.03g / cm 2 , and the cement alkaline environment serves for 18 months without powdering and cracking, and can be widely applied to cement products such as marine piles, fenders and breakwaters.

Description

Technical Field

[0001] This invention belongs to the field of cement product protection technology, specifically relating to a composite protective structure adapted to the alkaline porous characteristics of cement and its preparation method, which is suitable for long-term protection of cement piles, protective plates, breakwaters and other components in marine engineering. Background Technology

[0002] Cement products used in marine engineering are subjected to complex environments characterized by high salinity, high humidity, strong alkalinity, and biological corrosion over extended periods, and their protective performance directly impacts the service life of the engineering projects. Existing marine protective coating technologies are mostly developed for metal substrates and are insufficient to meet the corrosion protection requirements of cement substrates.

[0003] The Ca(OH)2 content in the hydration products of cement substrates is usually ≥15wt%, and there are a large number of micron-nano-scale pores on the surface, resulting in three major defects in existing coatings: First, the interfacial bonding is weak, with the adhesion strength between conventional coatings and cement substrates mostly between 2.5-3.0MPa, and peeling is likely to occur after long-term service; second, the alkali resistance is insufficient, and the coating is prone to hydrolysis and pulverization in the alkaline environment of cement, with significant performance degradation after 6 months of service; third, the synergy between anti-biofouling and seawater corrosion resistance is insufficient, and the biofouling area of ​​single texture antifouling or single anti-biofouling agent addition schemes is mostly above 3%, and the salt spray corrosion resistance time is difficult to exceed 1500h.

[0004] Although existing corrosion-resistant coating technologies include silane coupling agent modification, core-shell particle reinforcement (CN118374796A), high-entropy alloy doping (CN118390052A), and induction heating curing (CN116574397A), a systematic combined design specifically addressing the alkaline and porous characteristics of cement is lacking. For example, while core-shell particles can enhance strength in metal substrates through metallurgical bonding, they are prone to failure due to interfacial reactions in the porous alkaline environment of cement. Induction heating technology is mostly used for curing coatings on metal pipes and has not yet been adapted to the on-site construction needs of cement components.

[0005] Therefore, developing a cement-based marine protection structure that can solve the aforementioned complex technical challenges has become an urgent need in this field. Summary of the Invention

[0006] Therefore, the purpose of this invention is to provide a composite protective structure and preparation method adapted to the alkaline and porous characteristics of cement, solving the problems of weak interfacial bonding between existing corrosion-resistant coatings and cement substrates, low bonding strength, easy erosion and peeling in alkaline environments, rapid performance degradation in highly alkaline cement environments, fragmented anti-corrosion, wear-resistant and anti-bioadhesion functions, difficulty in simultaneously meeting the multiple protection requirements of marine environments, poor adaptability of preparation processes, and high difficulty in on-site construction of large cement components.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides a composite protective structure adapted to the alkaline porous characteristics of cement. The protective structure is a composite coating with a total thickness of 320~350μm. From the inside out, the composite coating consists of: a silane-modified cement base layer, a composite rust-inhibiting layer, a composite adhesive layer, and a wear-resistant and bio-resistant surface layer. The four-layer structure is adapted to the alkaline porous characteristics of the cement substrate, achieving full-chain synergistic protection of interface bonding, rust inhibition and corrosion prevention, and wear resistance and bio-resistance.

[0009] Based on the above technical solution, the silane-modified cement base layer is made of PO 42.5 grade ordinary Portland cement as the substrate, which is coated with silane coupling agent KH-550 ethanol solution after being treated with quartz sand blasting. The mass content of Ca(OH)2 in the substrate is strictly controlled at 14%~18%. The cement substrate itself has two core defects: highly alkaline hydration product Ca(OH)2 and micron-nano-scale pores, which are the root causes of coating peeling and alkaline corrosion failure. Quartz sand blasting at an optimized angle of 52.5° can form a uniform rough anchoring structure with a surface roughness Ra=4.5~5.0μm on the cement surface, providing a mechanical interlocking foundation for the coating without damaging the strength of the cement substrate; silane coupling agent KH-550 ethanol solution is used. The alkoxy group of the binder KH-550 can react with the hydroxyl groups on the cement surface to form Si-O-Si covalent bonds through a dehydration reaction. The amino group at the other end can react with the epoxy group of the subsequent epoxy coating through a ring-opening reaction, achieving chemical bonding between the cement substrate and the organic coating. At the same time, it can also seal some pores on the cement surface and block the penetration channels of alkaline substances into the coating. When the Ca(OH)2 content is less than 14%, the cement hydration is insufficient and the strength of the substrate itself is insufficient. When it is higher than 18%, the alkalinity is too strong, which will accelerate the hydrolysis and powdering of the subsequent organic coating. As the basic load-bearing layer of the composite coating, this base layer solves the problem of the interface bonding between the coating and the cement substrate.

[0010] Based on the above technical solution, the composite rust-inhibiting layer is further composed of epoxy zinc-rich coating and WMoTaNbV high-entropy alloy powder, with a coating thickness controlled at 95~105μm. The epoxy zinc-rich coating, as a traditional cathodic protection material, uses a formulation with a zinc powder content of 70%~75% and a particle size of 8~15μm. This ensures both the formation of a continuous conductive path within the coating and good dispersibility and coating density. The zinc powder acts as a sacrificial anode, inhibiting the corrosion of steel reinforcement inside the cement through electrochemical action. The WMoTaNbV high-entropy alloy powder has a particle size of 75~85nm and an oxygen content ≤0.05wt%. MoTaNbV high-entropy alloy, through its high-entropy effect, delayed diffusion effect, and cocktail effect, can form a stable and dense passivation film in highly alkaline and high-salt environments. Its corrosion resistance is significantly superior to that of traditional metallic materials. Nanoscale high-entropy alloy powder can fill the micropore defects of epoxy zinc-rich coatings, constructing a dual rust-inhibiting system that combines physical barrier and electrochemical protection. This simultaneously improves the coating's hardness and resistance to alkali erosion, while strictly controlling the oxygen content to ≤0.05wt% to prevent oxidation failure of the high-entropy alloy powder and ensure its conductivity and corrosion resistance. The composite rust-inhibiting layer can effectively block seawater from penetrating into the cement matrix and protect the internal reinforcing steel from electrochemical corrosion.

[0011] Based on the above technical solution, the composite adhesive layer is further composed of polyurethane-modified epoxy resin and nano-ceramic powder, and the coating thickness is precisely controlled at 35~45μm; the polyurethane content in the polyurethane-modified epoxy resin is 15%~18%. Pure epoxy resin is brittle and has poor impact resistance, and is prone to cracking under temperature changes or external forces. After polyurethane modification, flexible segments can be introduced into the epoxy matrix, which significantly enhances its interfacial adhesion to different materials in the upper and lower layers while balancing the coating's bonding strength and flexibility.

[0012] Based on the above technical solution, the nano-ceramic powder is further composed of chromium nitride and alumina in a mass ratio of 1:2 to 1:1, with a particle size of 30 to 40 nm. In the nano-ceramic powder, alumina imparts high hardness and wear resistance to the coating, while chromium nitride provides excellent alkali resistance and anti-penetration ability. The combination of the two can significantly improve the mechanical strength and alkali erosion resistance of the adhesive layer, and the nanoscale size can ensure that the particles are uniformly dispersed in the resin matrix, forming a dense barrier network. As a key gradient transition layer, this layer can effectively buffer the difference in thermal expansion coefficient between the composite rust-inhibiting layer and the wear-resistant and bio-resistant surface layer, reduce interfacial stress concentration, fundamentally avoid the occurrence of coating delamination, and thus undertake the dual functions of improving the adhesion between the upper and lower layers and providing additional alkali penetration protection.

[0013] Based on the above technical solution, the wear-resistant and anti-biological surface layer is further prepared by using epoxy resin as the matrix, compounding composite core-shell particles, silane-modified compound anti-biological agents, and dispersants. The coating thickness is controlled at 190~200μm, and the surface is designed with a micron-level mesh texture with a texture depth of 15~16μm and a mesh spacing of 70~75μm. The composite core-shell particles serve as the core reinforcing phase, using a nano-alumina-chromium nitride composite ceramic with a core particle size of 45~55nm and a chromium nitride to alumina mass ratio of 1:2~1:1 to provide ultra-high hardness and wear resistance. The outer shell is a KH-570 silane-modified WMoTaNbV high-entropy alloy with a shell thickness of 8~12nm, which not only improves the compatibility between the particles and the epoxy resin matrix and avoids agglomeration, but also further enhances the coating's wear resistance. Alkali corrosion resistance and seawater erosion resistance; the silane-modified compound antimicrobial agent is composed of KH-570 modified nano copper oxide and quaternary ammonium salt antimicrobial agent in a mass ratio of 1:1 to 2:1. KH-570 modification improves the dispersibility of inorganic antimicrobial agents in organic resins. Nano copper oxide destroys microbial cell membranes by slowly releasing copper ions, while quaternary ammonium salts adsorb and lyse microorganisms by relying on charge action. The two work together to achieve a broad-spectrum and long-lasting antimicrobial and antifouling effect; the surface micron-level mesh texture optimized by hydrodynamic and biofouling experiments can effectively reduce water flow resistance and reduce the substrate for marine biological attachment, while increasing the coating surface area to improve the slow-release efficiency of antimicrobial agents and extend the antifouling life. This layer, as the outermost protective layer of the system, has three core functions: wear resistance, seawater erosion resistance, and antifouling.

[0014] Based on the above technical solution, further, the core of the composite core-shell particle is a nano-alumina-chromium nitride composite ceramic, wherein the ratio of chromium nitride to alumina is 1:2 to 1:1, and the core particle size is 45 to 55 nm; the outer shell of the composite core-shell particle is a KH-570 silane-modified WMoTaNbV high-entropy alloy, with a shell thickness of 8 to 12 nm; and the particle size of the composite core-shell particle is 53 to 67 nm.

[0015] Based on the above technical solution, the silane-modified compound antibacterial agent is a compound of KH-570 modified nano copper oxide and quaternary ammonium salt antibacterial agent in a mass ratio of 1:1 to 2:1.

[0016] Based on the above technical solution, the dispersant is a polycarboxylate dispersant with a solid content of 35% to 45%.

[0017] Secondly, the present invention provides a method for preparing the composite protective structure adapted to the alkaline porous properties of cement, characterized by comprising the following steps: (1) Preparation of silane-modified cement base layer: First, clean the surface of the cement substrate to remove floating dust, oil stains and loose cement particles; then, blast the surface of silicate cement powder with quartz sand. The silicate cement used is PO 42.5 grade ordinary silicate cement. The quartz sand used for blasting has a particle size of 80~120 mesh, a blasting pressure of 0.6~0.8MPa, an angle of 52.5°, and a surface roughness Ra=4.5~5.0μm; subsequently, coat with a 1.8%~2.5% concentration of silane coupling agent KH-550 ethanol solution. The coating method is brushing or high-pressure spraying, and the coating amount per unit area is controlled at 0.15~0.20kg / m². 2 Air dry at room temperature for 15-25 minutes to obtain the cement base layer; (2) Preparation of composite rust-inhibiting layer: Epoxy zinc-rich coating is mixed with 0.5%~0.7% high-entropy alloy powder, and 0.8%~1.2% silane coupling agent KH-560 is added. The mixture is dispersed at 2000~2200r / min for 35~45min at a temperature of 25~30℃. After dispersion, the fineness of the coating is ≤20μm. The mixed coating is then sprayed under high pressure on the surface of the silane-modified cement base layer described in step (1). The spraying pressure is 18~22MPa, the spraying distance is 260~270mm, the nozzle diameter of the high-pressure airless spray is 0.4~0.6mm, the number of spray passes is 2~3, and the interval between passes is 10~15min. The thickness is 95~105μm. The coating is cured at room temperature for 30~35h under a relative humidity of 45%~55%. (3) Preparation of composite adhesive layer: Polyurethane modified epoxy resin is mixed with 2%~3% nano-ceramic powder, wherein the epoxy value of the polyurethane modified epoxy resin is 0.40~0.45 eq / 100g; and the specific surface area of ​​the nano-ceramic powder is 80~100m². 2 / g; after mixing, apply the mixture to the outer surface of the composite rust-inhibiting layer described in step (2) with a roller at a pressure of 0.4~0.6MPa. The roller coating process uses a rubber roller with a Shore A hardness of 60~70 and a roller coating speed of 0.5~0.8m / s to ensure that the coating is free from omissions and drips; the thickness is 35~45μm, and it is cured at room temperature for 18~22h under a relative humidity of 45%~55%; (4) Preparation of wear-resistant and anti-biological surface layer: Epoxy resin is mixed with 38%~42% composite core-shell particles, 3%~4% silane-modified compound anti-biological agent, and 0.8%~1.0% dispersant, stirred at 55~65℃ for 70~80min, and stirred at 1200~1400r / min; The mixed coating is scraped onto the outer surface of the composite adhesive layer described in step (3), with a scraping speed of 7~8cm / s, a template pressure of 0.3~0.4MPa, a texture depth of 15~16μm, a mesh spacing of 70~75μm, and a thickness of 190~200μm; The wear-resistant and anti-biological surface layer is induction cured in segments: the temperature is raised to 70~75℃ at 2~3℃ / min and kept at 2.5~3.0h, and then at 7~9℃ / m The temperature is raised to 135~140℃ and held for 1.5~2.0h; the induction heating device has a heating temperature of 340~360℃ and a moving speed of 1.5~2.5m / min; the dispersion index of the composite core-shell particles is ≤1.2, and the particle size of the silane-modified compound antimicrobial agent is ≤50nm; the stainless steel mesh template for scraping has square mesh holes with a side length of 70~75μm; the heating rate deviation of the segmented induction curing is ≤±0.5℃ / min, and the holding temperature deviation is ≤±2℃ to ensure full cross-linking of the coating; the moving speed deviation of the device is ≤±0.1m / min. Segmented moving curing can be used for the construction of large marine cement components, with the curing length of a single segment controlled at 2~3m. After curing, the components are naturally cooled to room temperature before the next segment is constructed. (5) Post-treatment: After the wear-resistant and bio-resistant surface layer has been induction cured in sections, apply the wear-resistant and bio-resistant surface coating to weak parts such as corners of the component to make the local thickness reach 230~240μm, and let it cool naturally to room temperature.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The composite protective structure of the present invention has significantly improved the interfacial bonding strength with the cement substrate: the bonding strength with the cement substrate is ≥4.5MPa, which is 60.7% higher than the existing commercial cement marine protective coating (2.8MPa). It can withstand 18 months of service in the alkaline environment of cement without peeling or powdering.

[0019] 2. The composite protective structure of the present invention has excellent corrosion resistance: it can withstand salt spray corrosion for more than 2200 hours and has a mass loss of only 1.0% after 100 freeze-thaw cycles, which is far greater than the 1500 hours of the prior art.

[0020] 3. The composite protective structure of this invention exhibits strong functional synergy: marine organism attachment area ≤ 1.0%, and abrasion resistance (GB / T 1768-2021) ≤ 0.03 g / cm³. 2 It improves upon single-function coatings by more than 50%.

[0021] 4. The composite protective structure of the present invention has wide construction adaptability: directional heat input is more suitable for cement-based alkaline porous substrates, induction heating device is suitable for on-site construction of large cement components, coating density and comprehensive protective performance are better, suitable for in-situ curing of large marine cement components, simple process, and can be applied on a large scale. Attached Figure Description

[0022] To more clearly illustrate the embodiments of the present invention, the accompanying drawings involved in the embodiments will be briefly described below.

[0023] Figure 1 This is a schematic diagram of the composite protective structure adapted to the alkaline porous properties of cement according to the present invention; in the figure: 1-silane modified cement base layer, 2-epoxy zinc-rich-high entropy alloy composite rust inhibitor layer, 3-polyurethane-nano-ceramic composite adhesive layer, 4-core-shell particle reinforced wear-resistant and bio-resistant surface layer, 5-micron-level mesh texture formed on the surface of the wear-resistant and bio-resistant surface layer. Detailed Implementation

[0024] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0025] Example 1: Preparation and Performance Testing of Composite Protective Structure Adapted to the Alkaline Porous Properties of Cement A composite protective structure adapted to the alkaline porous properties of cement, the protective structure being a composite coating comprising, from the inside out: Silane-modified cement base layer: serving as the basic load-bearing structure for the protective coating, containing 16wt% Ca(OH)2; Composite rust-inhibiting layer: comprising epoxy zinc-rich coating and WMoTaNbV high-entropy alloy powder, wherein the epoxy zinc-rich coating contains 73wt% zinc powder with a particle size of 11μm, and the high-entropy alloy powder has a particle size of 80nm. Composite adhesive layer: includes polyurethane modified epoxy resin and nano-ceramic powder, wherein the polyurethane content in the polyurethane modified epoxy resin is 16.5wt%, and the nano-ceramic powder is a mixture of chromium nitride and alumina in a mass ratio of 1:2 with a particle size of 35nm. Wear-resistant and anti-biological surface layer: including epoxy resin, composite core-shell particles, silane-modified compound anti-biological agent and dispersant, wherein the core of the composite core-shell particles is nano-alumina-chromium nitride composite ceramic, chromium nitride:alumina = 1:2, the outer shell is KH-570 silane-modified WMoTaNbV high-entropy alloy, the overall particle size is 60nm, the core particle size is 50nm, and the shell thickness is 10nm; The silane-modified compound antimicrobial agent is a mixture of KH-570 modified nano copper oxide and quaternary ammonium salt antibacterial agent at a mass ratio of 2:1. The dispersant is a polycarboxylate dispersant with a solid content of 40%.

[0026] The preparation method of the above-mentioned composite protective structure adapted to the alkaline porous properties of cement includes the following steps: (1) Preparation of silane-modified cement base layer: Quartz sand was blasted on the surface of silicate cement powder with a blasting pressure of 0.75 MPa, an angle of 52.5°, and Ra=4.8 μm; then, a 2.1 wt% silane coupling agent KH-550 ethanol solution was coated and dried at room temperature for 22 min to obtain a cement base layer with dimensions of 500 mm × 500 mm × 50 mm.

[0027] (2) Preparation of composite rust inhibitor layer: Epoxy zinc-rich coating is mixed with 0.6wt% high entropy alloy powder, and 1.0wt% silane coupling agent KH-560 is added. The mixture is dispersed at 2150r / min for 38min. The mixed coating is sprayed under high pressure and airless onto the surface of the silane modified cement base prepared in step (1). The spraying pressure is 19.5MPa and the spraying distance is 265mm. A composite rust inhibitor layer with a thickness of 100μm is prepared and cured at room temperature for 33h.

[0028] (3) Preparation of composite adhesive layer: Polyurethane modified epoxy resin and 2.25wt% nano ceramic powder are stirred and mixed evenly. A rubber roller with a hardness of 65 Shore A is used to roll the coating at a pressure of 0.45MPa and a rolling speed of 0.65m / s, and the coating thickness is controlled at 40μm. The coating is cured at room temperature for 20h under a relative humidity of 50%.

[0029] (4) Preparation of wear-resistant and anti-biological surface layer: Epoxy resin was mixed with 41wt% composite core-shell particles, 3.8wt% silane-modified compound anti-biological agent, and 0.95wt% dispersant. The mixture was stirred at 57℃ for 75min at a stirring speed of 1300r / min. The mixed coating was then scraped onto the outer surface of the composite adhesive layer at a scraping speed of 7.5cm / s, a template pressure of 0.32MPa, a texture depth of 15.5μm, a mesh spacing of 72μm, and a thickness of 195μm. Segmented induction curing: The temperature was increased to 73℃ at 3℃ / min and held for 2.8h, and then increased to 138℃ at 8℃ / min and held for 1.8h. The induction heating device was used to heat the material at 350℃ and move at 2m / min. The single-segment curing length was 2.5m, the heating rate deviation was ±0.3℃ / min, the holding temperature deviation was ±1℃, and the device moving speed deviation was ±0.05m / min.

[0030] (5) Post-treatment: After the wear-resistant and bio-resistant surface layer has been cured in segments, apply a surface coating to the weak parts such as the corners of the component to make the local thickness reach 234μm, and then let it cool naturally to room temperature.

[0031] Performance testing: Five parallel samples were prepared for each test item for the prepared composite protective structure sample, as well as the samples of Comparative Example 1 and Comparative Example 2. The average value was taken as the final result, and the performance was tested according to the standards and methods listed in Table 1.

[0032] Table 1. Test methods and results for the performance of protective structures

[0033] Comparative Example 1 No high-entropy alloy powder was added during the preparation of the composite rust-inhibiting layer; the curing process was conventional oven heating, with heating conditions of 70℃ for 3 hours, followed by heating to 130℃ for 2 hours, and the rest was consistent with the preparation method of the protective structure in Example 1.

[0034] The test standards for the prepared protective structure are consistent with those in Example 1, and the test results are shown in Table 1.

[0035] Comparative Example 2 A commercially available brand of protective coating was used and applied according to the product instructions. The testing standards were the same as in Example 1, and the test results are shown in Table 1.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite protective structure adapted to the alkaline porous properties of cement, characterized in that, The protective structure is a composite coating with a total thickness of 320~350μm, consisting of, from the inside out: silane-modified cement base layer, composite rust-inhibiting layer, composite adhesive layer, and wear-resistant and bio-resistant surface layer. The silane-modified cement base layer serves as the foundation for the composite coating; The composite rust-inhibiting layer is composed of epoxy zinc-rich coating and WMoTaNbV high-entropy alloy powder, with a coating thickness of 95~105μm. The composite adhesive layer is composed of polyurethane modified epoxy resin and nano-ceramic powder, with a coating thickness of 35~45μm; the nano-ceramic powder is composed of chromium nitride and alumina in a mass ratio of 1:2~1:1, with a particle size of 30~40nm. The wear-resistant and anti-biological surface layer is composed of epoxy resin, composite core-shell particles, silane-modified compound anti-biological agent and dispersant, with a coating thickness of 190~200μm; the surface of the wear-resistant and anti-biological surface layer has a micron-level mesh texture with a texture depth of 15~16μm and a mesh spacing of 70~75μm; The core of the composite core-shell particles is a nano-alumina-chromium nitride composite ceramic, wherein the ratio of chromium nitride to alumina is 1:2 to 1:1, and the core particle size is 45 to 55 nm; the outer shell of the composite core-shell particles is a KH-570 silane-modified WMoTaNbV high-entropy alloy, with a shell thickness of 8 to 12 nm; the particle size of the composite core-shell particles is 53 to 67 nm. The silane-modified compound antimicrobial agent is a mixture of KH-570 modified nano copper oxide and quaternary ammonium salt antibacterial agent in a mass ratio of 1:1 to 2:

1.

2. The composite protective structure adapted to the alkaline porous properties of cement according to claim 1, characterized in that, The mass content of Ca(OH)2 in the silane-modified cement base layer is 14%~18%.

3. The composite protective structure adapted to the alkaline porous properties of cement according to claim 1, characterized in that, The zinc powder in the epoxy zinc-rich coating has a mass content of 70%~75% and a particle size of 8~15μm.

4. The composite protective structure adapted to the alkaline porous properties of cement according to claim 1, characterized in that, The WMoTaNbV high-entropy alloy powder has a particle size of 75~85nm and an oxygen content of ≤0.05wt%.

5. The composite protective structure adapted to the alkaline porous properties of cement according to claim 1, characterized in that, The polyurethane content in the polyurethane-modified epoxy resin is 15% to 18% by mass.

6. The composite protective structure adapted to the alkaline porous properties of cement according to claim 1, characterized in that, The dispersant is a polycarboxylate dispersant with a solid content of 35% to 45%.

7. A method for preparing a composite protective structure adapted to the alkaline porous properties of cement as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Preparation of silane-modified cement base layer: First, clean the surface of the cement substrate to remove floating dust, oil stains and loose cement particles; blast the surface of silicate cement powder with quartz sand. The silicate cement used is PO 42.5 grade ordinary silicate cement. The quartz sand used for blasting has a particle size of 80~120 mesh, a blasting pressure of 0.6~0.8MPa, an angle of 52.5°, and a surface roughness Ra=4.5~5.0μm. Subsequently, a 1.8%–2.5% ethanol solution of silane coupling agent KH-550 is applied by brushing or high-pressure spraying, with the coating amount per unit area controlled at 0.15–0.20 kg / m². 2 Air dry at room temperature for 15-25 minutes; (2) Preparation of composite rust-inhibiting layer: Mix epoxy zinc-rich coating with 0.5%~0.7% high-entropy alloy powder, add 0.8%~1.2% silane coupling agent KH-560, disperse at 2000~2200r / min for 35~45min, temperature is 25~30℃, after dispersion the coating fineness is ≤20μm; spray the mixed coating with high pressure airless spray on the surface of silane modified cement base layer described in step (1), the spraying pressure is 18~22MPa, the spraying distance is 260~270mm, the nozzle diameter is 0.4~0.6mm, spray 2~3 coats, the interval between coats is 10~15min; control the coating thickness to 95~105μm, and cure at room temperature for 30~35h under the condition of relative humidity of 45%~55%; (3) Preparation of composite adhesive layer: Polyurethane modified epoxy resin is mixed with 2%~3% nano-ceramic powder, using a rubber roller with a Shore A hardness of 60~70. The epoxy value of the polyurethane modified epoxy resin is 0.40~0.45 eq / 100g; the specific surface area of ​​the nano-ceramic powder is 80~100m². 2 / g; after mixing, apply the mixture to the outer surface of the composite rust-inhibiting layer described in step (2) at a roller pressure of 0.4~0.6MPa, with a roller speed of 0.5~0.8m / s, to ensure that the coating is free of missed areas and drips; the thickness is 35~45μm, and it is cured at room temperature for 18~22h under a relative humidity of 45%~55%; (4) Preparation of wear-resistant and anti-biological surface layer: Epoxy resin is mixed with 38%~42% composite core-shell particles, 3%~4% silane-modified compound anti-biological agent, and 0.8%~1.0% dispersant. The mixture is stirred at 55~65℃ for 70~80 min at a stirring speed of 1200~1400 r / min. The mixed coating is then scraped onto the outer surface of the composite adhesive layer described in step (3) at a scraping speed of 7~8 cm / s, a template pressure of 0.3~0.4 MPa, a texture depth of 15~16 μm, and a mesh spacing of 70~75 μm. μm, thickness 190~200μm; the wear-resistant and bio-resistant surface layer is segmented induction cured: heated at 2~3℃ / min to 70~75℃ and held for 2.5~3.0h, heated at 7~9℃ / min to 135~140℃ and held for 1.5~2.0h; the induction heating device has a heating temperature of 340~360℃ and a moving speed of 1.5~2.5m / min; the deviation of the heating rate is controlled to be ≤±0.5℃ / min, the deviation of the holding temperature is ≤±2℃, and the deviation of the device moving speed is ≤±0.1m / min; (5) Post-treatment: After the wear-resistant and bio-resistant surface layer has been induction cured in sections, apply the wear-resistant and bio-resistant surface layer coating to the corners, welds, edge stress concentrations and weak parts that are prone to wear of the component, so that the local thickness reaches 230~240μm, and let it cool naturally to room temperature.

8. The application of a composite protective structure adapted to the alkaline porous properties of cement as described in any one of claims 1 to 6 in the seawater protection of large marine cement components.

9. The application of the composite protective structure adapted to the alkaline porous properties of cement as described in claim 8 in the seawater protection of large marine cement components, characterized in that, When constructing large marine cement components, the length of a single section of induction curing is 2-3m. After curing, the components are allowed to cool naturally to room temperature before the next section is constructed.

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