A temperature-difference freeze-thaw resistant multilayer hydrophobic-aerogel composite protective coating suitable for highland environment and a preparation method thereof

Abstract

The application discloses a temperature-difference freeze-thaw resistant multilayer hydrophobic-aerogel composite protective coating suitable for a plateau environment and a preparation method thereof, which comprises the following steps: a bottom layer of a pore wall hydrophobic modification layer is arranged on the side close to a concrete base, and is used for penetrating into the near-surface layer pores of the concrete and hydrophobically modifying the pore wall; an intermediate thermal insulation and temperature stabilization layer is arranged on the pore wall hydrophobic modification layer, and is used for reducing heat conduction and weakening the temperature difference gradient between the surface and the interior of the concrete; and a surface sealing protective layer is arranged on the outer side of the thermal insulation and temperature stabilization layer, and is used for inhibiting water from entering the intermediate thermal insulation and temperature stabilization layer. The application organically combines the hydrophobic modification, thermal insulation regulation and control and freeze-thaw resistance by constructing a multilayer composite protective structure, improves the water resistance and weather resistance of the concrete, effectively relieves the temperature difference stress and delays the occurrence of freeze-thaw damage, and improves the service stability and durability of the concrete structure under complex environmental conditions as a whole.

Description

Technical Field

[0001] This invention belongs to the field of concrete structure surface protection technology, and in particular relates to a multi-layer hydrophobic-aerogel composite protective coating suitable for high-altitude environments and its preparation method. Background Technology

[0002] High-altitude regions such as the Qinghai-Tibet Plateau are characterized by extreme environments including strong solar radiation, large diurnal temperature variations, frequent freeze-thaw cycles, and wind and sand erosion. Under the combined effects of these multiple factors, concrete structures are prone to thermal fatigue cracks, gradual deterioration of pore structure, and continuous accumulation of interface damage, resulting in a significant decrease in durability and seriously affecting the safety and service life of engineering structures.

[0003] Existing concrete protection technologies mainly include two categories: hydrophobic impregnation coatings and aerogel thermal insulation coatings. Hydrophobic coatings reduce the surface energy of concrete and inhibit moisture intrusion, thereby improving freeze-thaw resistance to some extent. However, they cannot effectively reduce thermal stress caused by diurnal temperature differences. Aerogel thermal insulation coatings, due to their low thermal conductivity, can slow down temperature transfer and reduce temperature gradients. However, their porous structure easily absorbs water, making them prone to structural damage and performance degradation in freeze-thaw environments.

[0004] Although existing technologies have proposed various concrete protective coatings or aerogel insulation materials, there are still significant shortcomings in the multi-layered synergistic protection system for concrete structures to resist temperature differences and freeze-thaw cycles in high-altitude environments.

[0005] Chinese patent application CN121895817A discloses a method for preparing a composite aerogel thermal insulation coating. This application mainly focuses on improving the preparation process of the aerogel thermal insulation coating. The technical solution includes: controlling the solubility parameters between the film-forming resin and the solvent system to form swollen gel clusters in a partially dissolved state of the resin molecular chains; graded mixing of hydrophobic silica aerogel powder and high-strength hollow glass microspheres; shear kneading under low temperature and high viscosity conditions, utilizing the hollow glass microspheres to share the shear stress; and subsequently inducing controlled unwinding of the resin molecular chains by gradually adding a good solvent, thereby reducing the degree of resin intrusion into the aerogel pore structure. The advantage of this method is that it can reduce the loss of thermal insulation performance caused by resin entering the aerogel nanopores to a certain extent and reduce the damage to the aerogel framework structure caused by the high-shear process. However, the technical focus of this application lies in optimizing the formulation and preparation process of the single aerogel thermal insulation coating itself. It primarily addresses the issues of maintaining the aerogel pore structure and thermal insulation performance during coating preparation, without addressing the hydrophobic modification of the near-surface pores of the concrete substrate or constructing a multi-layered synergistic protection system. Therefore, it is difficult to provide systematic protection against the coupled problems faced by concrete structures in high-altitude environments, such as capillary water absorption, diurnal temperature variation, freeze-thaw cycles, UV aging, and wind and sand erosion.

[0006] Chinese patent application CN119264773A discloses a wear-resistant superhydrophobic thermal insulation coating and its preparation method. The technical solution of this application mainly includes a resin layer disposed on the surface of a substrate and an HNTs / SiO2 composite aerogel layer covering the surface of the resin layer. The HNTs / SiO2 composite aerogel is modified with hydrophobic fluorosilane, enabling it to possess superhydrophobic, thermal insulation, and wear-resistant properties to a certain extent. The advantage of this solution lies in using halloysite nanotubes as a reinforcing phase to improve the mechanical strength and wear resistance of traditional SiO2 aerogel materials, and enhancing the adhesion between the coating and the substrate through the resin layer. However, this application mainly focuses on constructing a resin layer and a composite aerogel functional layer on the surface of a general substrate. The underlying resin primarily serves a bonding function and does not perform hydrophobic modification on the concrete pore walls, making it difficult to inhibit water from entering the near-surface pores of the concrete from the capillary water absorption source. In addition, the functional layer in this scheme is mainly a hydrophobically modified composite aerogel layer. Although it has both hydrophobic and heat insulation functions, it does not form a multi-layer synergistic structure, nor does it systematically design the impact of strong ultraviolet rays, large temperature difference, alternating wet and dry conditions such as rain and snow, and wind and sand erosion on the long-term stability of the heat insulation layer in the high-altitude environment.

[0007] Chinese patent application CN121825328A discloses a high-efficiency photothermal superhydrophobic anti-icing / de-icing coating with a "sandwich" structure and its preparation method. The design comprises, from bottom to top, an aerogel insulation layer, an intermediate adhesive layer, and a photothermal superhydrophobic functional layer. The aerogel insulation layer reduces heat transfer to the substrate, the intermediate adhesive layer enhances interlayer bonding, and the photothermal superhydrophobic functional layer absorbs light energy and converts it into heat energy through photothermal materials, while simultaneously reducing ice and water adhesion through its superhydrophobic surface, thus achieving anti-icing or de-icing effects. The advantage of this application lies in improving the heat utilization efficiency during photothermal de-icing through the combination of the insulation layer and the photothermal superhydrophobic layer, and improving the anti-icing / de-icing performance of the coating under specific lighting conditions. However, the technical approach of this application mainly relies on the active light absorption and heating effect of the photothermal materials; its core objective is anti-icing and de-icing, rather than long-term protection against heat-wet coupling freeze-thaw damage within concrete structures. This solution does not address the capillary water absorption problem in concrete pore walls by incorporating a permeable hydrophobic bottom layer, nor does it resolve the issues of low water content retention and crack resistance stability of the aerogel insulation layer under long-term moisture intrusion, freeze-thaw cycles, and wind and sand erosion. Therefore, it differs significantly from technical approaches that achieve freeze-thaw resistance through a synergistic combination of pore wall hydrophobicity, thermal insulation and temperature stabilization, and surface sealing.

[0008] Chinese patent application CN118930318A discloses a gradient composite protective coating for hydraulic concrete and its preparation method. The technical solution of this application includes an isolation layer and a protective layer disposed on the surface of the hydraulic concrete. The isolation layer can be made of YEP toughened epoxy putty, and the protective layer can be made of a high-performance elastic coating or a high-toughness coating. An interface layer can be set between the two layers as needed. This solution mainly addresses the problems of delamination, cracking, blistering, and interface damage that easily occur in protective coatings of hydraulic concrete under long-term immersion environments. It improves the service stability of the coating system under water pressure, temperature variations, and long-term immersion conditions by achieving a gradient transition of mechanical properties between the rigid concrete substrate, the tough isolation layer, and the elastic or high-toughness protective layer. The advantage of this solution lies in its emphasis on the mechanical matching and interface stability between the coating system and the concrete substrate, which can improve the cracking and debonding problems of traditional rigid coatings in hydraulic environments. However, this application primarily targets scenarios involving long-term immersion and water pressure in hydraulic concrete. Its core focus is on the gradient transition of mechanical properties and the adhesion stability of the protective layer. It does not introduce an aerogel thermal insulation and temperature stabilization layer, nor does it address the freeze-thaw problem caused by temperature differences in high-altitude environments by reducing the internal temperature gradient of the concrete and inhibiting capillary water absorption through the pore walls. Furthermore, its material system mainly consists of epoxy, polyurea, or other elastic / high-toughness organic coatings, and it does not specifically address the maintenance of low moisture content and structural integrity of the insulation layer under conditions of strong ultraviolet radiation, wind and sand erosion, large diurnal temperature differences, and the coupled effects of freeze-thaw cycles in high-altitude environments.

[0009] Chinese patent application CN118421144A discloses a water-based thermal insulation coating for the surface protection of railway bridge concrete and its preparation method. This application primarily focuses on the surface protection of railway bridge concrete, proposing a water-based thermal insulation coating system composed of water-based resin emulsion, hollow glass microspheres, titanium dioxide, and modified aerogel. Through the synergistic effect of reflective thermal insulation fillers and low thermal conductivity fillers, the coating's thermal insulation performance, weather resistance, and surface protection effect on bridge concrete are improved. The advantage of this approach lies in its water-based system, which offers certain construction adaptability, and the improvement of the thermal protection performance of the concrete surface through the compounding of various thermal insulation fillers. However, this application essentially still belongs to the optimization of the water-based thermal insulation coating formulation system. Its technical focus is on improving the thermal insulation, weather resistance, and surface protection performance of a single coating layer, without forming a layered synergistic structure that involves permeation and hydrophobic modification of the concrete pore walls, thermal insulation and temperature stabilization in the intermediate layer, and hydrophobic sealing protection on the outer surface. Regarding the heat-moisture coupling damage caused by capillary water absorption, diurnal temperature difference, and freeze-thaw cycles in high-altitude environments, this application does not explicitly propose a technical solution to maintain the low water content of the aerogel layer through internal and external double water barrier, nor does it systematically design the crack resistance and toughening of the aerogel insulation layer under low-temperature temperature difference cycles.

[0010] In summary, although existing technologies have proposed different solutions in terms of hydrophobic protection, aerogel insulation, photothermal de-icing, elastic protection, and water-based heat-insulating coatings, they are still insufficient to meet the comprehensive protection requirements of concrete structures against temperature differences and freeze-thaw cycles in high-altitude environments. Its shortcomings are mainly reflected in the following aspects: First, existing hydrophobic coatings mainly focus on reducing surface wettability or improving impermeability, but they are difficult to weaken the temperature gradient and thermal stress caused by strong solar radiation and diurnal temperature differences; Second, although existing aerogel thermal insulation coatings can reduce heat conduction, their porous structure is prone to increased thermal conductivity after water intrusion, and cracking, pore structure damage or performance degradation under freeze-thaw action; Third, existing multilayer or composite coatings mainly focus on bond enhancement, mechanical gradient transition, active photothermal de-icing or single-layer material formulation optimization, but have not yet carried out synergistic regulation of the two key causes of freeze-thaw damage: capillary water absorption and temperature gradient in concrete; Fourth, existing technologies lack an integrated structural design for coupled environments such as strong ultraviolet radiation at high altitudes, large temperature differences, low-temperature freeze-thaw, wind and sand erosion, and alternating wet and dry conditions, especially lacking a composite protection system with synergistic effects of "hydrophobic pore walls - thermal insulation and temperature stabilization - surface sealing".

[0011] To address the aforementioned issues, it is necessary to provide a multi-layered hydrophobic-aerogel synergistic composite protective system suitable for high-altitude environments. This system should be able to form a hydrophobic modified pore wall structure within the near-surface pores of concrete, reducing capillary water absorption at the source; it should be able to weaken the temperature gradient between the concrete surface and interior through the aerogel thermal insulation and stabilizing layer, reducing thermal stress caused by temperature cycling; and it should also be able to prevent external moisture from entering the insulation layer through a surface sealing protective layer, improving the system's resistance to UV aging, wind and sand erosion, and rain and snow cycles. Through the synergistic effect of these functional layers, the thermal insulation and stabilizing layer can maintain a low moisture content for a long period, reducing the risk of cracking and performance degradation under low temperature and temperature cycling conditions, thereby comprehensively improving the concrete structure's resistance to temperature fatigue and freeze-thaw durability in the complex environment of high-altitude areas. Summary of the Invention

[0012] To address the issues of water absorption, thermal fatigue cracking, freeze-thaw erosion, and coating failure in concrete structures exposed to strong ultraviolet radiation, large diurnal temperature variations, frequent freeze-thaw cycles, wind and sand erosion, and alternating wet and dry conditions caused by rain and snow in high-altitude environments, this invention provides a multi-layered hydrophobic-aerogel composite protective coating suitable for high-altitude environments and its preparation method. This coating is applicable to the protection of concrete structures exposed to complex environmental conditions for extended periods, and is particularly suitable for environments with simultaneous large temperature differences, low-temperature freeze-thaw cycles, and moisture erosion.

[0013] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A multi-layer hydrophobic-aerogel composite protective coating suitable for high-altitude environments and resistant to temperature difference freeze-thaw cycles is provided. The composite protective coating is used to protect concrete substrates and includes: a bottom layer of hydrophobic modified pore walls, an intermediate heat-insulating and temperature-stabilizing layer, and a surface sealing and protective layer. The bottom pore wall hydrophobic modification layer is located on the side close to the concrete substrate and is used to penetrate into the near-surface pores of the concrete and modify the pore walls hydrophobically. The hydrophobic material used is a bissilane synergistic modified nano-inorganic particle composite hydrophobic material; the bissilane includes dodecyltrimethoxysilane and 3-(isobutenoyloxy)propyltrimethoxysilane; the nano-inorganic particles are selected from one or a combination of nano-CaCO3, nano-ZnO, and nano-SiO2. The intermediate heat-insulating and temperature-stabilizing layer is disposed on the hydrophobic modified layer of the pore wall to reduce heat conduction and weaken the temperature gradient between the concrete surface and the interior. It includes aerogel material and film-forming base material. The surface sealing protective layer is disposed on the outside of the heat insulation and temperature stabilization layer to inhibit moisture from entering the intermediate heat insulation and temperature stabilization layer.

[0014] Furthermore, the hydrophobic material used in the bottom pore wall hydrophobic modification layer comprises, by mass fraction: 4%–5% dodecyltrimethoxysilane, 2%–3% 3-(isobutenoyloxy)propyltrimethoxysilane, 5%–6% nano-CaCO3, 1%–2% nano-ZnO, 0.5%–1.0% formic acid, 10%–11% water, and the balance being isopropanol.

[0015] Furthermore, the aerogel material is SiO2 aerogel, and the film-forming matrix is ​​selected from one or a combination of aqueous acrylic emulsion, aqueous polyurethane emulsion, and silicone acrylic emulsion.

[0016] Furthermore, the intermediate thermal insulation and temperature stabilizing layer also includes a toughening component.

[0017] Furthermore, the toughening component includes waterborne polyurethane and / or modified polyvinyl alcohol, wherein the modified polyvinyl alcohol is used to surface-modify PVA fibers using KH550.

[0018] Furthermore, the waterborne polyurethane has a mass fraction of 5% to 15%, and the modified polyvinyl alcohol has a mass fraction of 0.3% to 1.0%.

[0019] Furthermore, the thickness of the heat insulation and temperature stabilizing layer is 1 to 10 mm.

[0020] Furthermore, the surface sealing protective layer is made of the dual-silane synergistic modified nano-inorganic particle composite hydrophobic material.

[0021] This invention also provides a method for preparing the aforementioned multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments, comprising: Dodecyltrimethoxysilane and 3-(isobutenoyloxy)propyltrimethoxysilane were hydrolyzed in an acidic solution. Then, nano-inorganic particles were added and dispersed evenly. The mixture was then heated and stirred to obtain a hydrophobic composite material of nano-inorganic particles with synergistic modification of bissilane. This material was then applied to the surface of concrete to allow it to penetrate into the pores and form a hydrophobic modified layer on the pore walls. SiO2 aerogel material and film-forming matrix are mixed and dispersed to form a uniform aerogel composite coating, which is then coated on the surface of the hydrophobic modified layer of the pore wall to form a heat insulation and temperature stabilizing layer. A surface-sealed protective layer is formed on the outside of the thermal insulation and temperature-stabilizing layer.

[0022] Furthermore, the acidic solution includes isopropanol, water, and formic acid; the nano-inorganic particles include nano-CaCO3 and nano-ZnO; and the aerogel composite coating further includes toughening components.

[0023] The core idea of ​​this invention is to move away from relying solely on a single hydrophobic or thermally insulating coating for protection. Instead, it constructs a multi-layered composite structure with functional zones on the surface of a concrete substrate. Different functional layers then perform functions such as hydrophobicity of the pore walls, thermal insulation and temperature stabilization, surface sealing, and weather protection. Through interlayer synergy, it achieves simultaneous regulation of moisture migration and temperature gradients. This composite protection system enables the thermal insulation and temperature stabilization layer to maintain a low water content over a long period, thus preventing the aerogel insulation layer from absorbing water and increasing its thermal conductivity, and also preventing it from cracking and forming water seepage channels under temperature cycling and freeze-thaw cycles.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By constructing a multi-layer structure consisting of a bottom hydrophobic impregnation layer, an intermediate aerogel insulation layer, and a surface hydrophobic sealing layer, the synergistic effect of different functions is achieved. The bottom layer can hydrophobically modify the interior of concrete pores and reduce capillary water absorption; the intermediate layer reduces heat transfer through the low thermal conductivity of the aerogel material; and the surface layer forms a continuous hydrophobic protective film, further preventing moisture intrusion and improving surface weather resistance. Through the above structural design, the problem of the single function of existing single coatings is effectively overcome.

[0025] (2) Significantly improved the hydrophobic properties of concrete surface. Through synergistic modification with bissilane, a stable low surface energy structure is formed on the concrete surface, which can effectively prevent water wetting and reduce water retention on the surface, thereby reducing the possibility of water penetrating into the interior.

[0026] (3) Improve the crack resistance of the material and enhance the structural stability. By introducing toughening components into the insulation layer, the aerogel composite material still has good deformation capacity under low temperature conditions. Experimental results show that the maximum strain and fracture strain of the toughened material are significantly increased, thereby inhibiting the formation of cracks in the insulation layer under temperature difference cycling conditions.

[0027] (4) Maintain the insulation layer in a low water content state to prevent performance degradation. The present invention uses the synergistic effect of the hydrophobic modification layer on the pore wall and the surface sealing protective layer to block water from entering the insulation layer from both the inside and outside, so that it is kept in a low water content state for a long time, avoiding the problem of increased thermal conductivity and structural damage caused by water absorption.

[0028] (5) Achieving multi-functional synergy to comprehensively improve freeze-thaw resistance. This invention does not simply superimpose hydrophobic, heat-insulating, and surface-sealing functions, but achieves synchronous regulation of moisture transport and heat conduction through the synergistic effect between multiple layers. Among them, the hydrophobic layer reduces the source of moisture, the heat-insulating layer reduces the temperature difference driving force, the toughening measures ensure the structural integrity, and the surface sealing further blocks the intrusion of external moisture, thereby effectively inhibiting freeze-thaw damage under the coupling effect of temperature difference and moisture.

[0029] (6) Overall performance is superior to single protective measures. Comparative experiments show that single hydrophobic treatment or single thermal insulation treatment is difficult to simultaneously achieve both water absorption control and temperature difference regulation. However, the composite system of the present invention can simultaneously achieve low water absorption rate, low temperature difference and good crack resistance, demonstrating a comprehensive protective effect that is significantly better than existing single technical solutions.

[0030] In summary, this invention, by constructing a multi-layered, functionally synergistic composite protective structure, organically combines hydrophobic modification, thermal insulation regulation, and freeze-thaw resistance. This improves the water resistance and weather resistance of concrete while effectively mitigating thermal stress and delaying freeze-thaw damage, thereby enhancing the overall service stability and durability of concrete structures under complex environmental conditions. This technical solution is highly targeted and widely adaptable, meeting the long-term protection needs of concrete structures in high-altitude and other extreme environments, and possesses promising engineering application prospects and widespread value. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This involves testing the hydrophobic properties of DTMS with different dosages. Figure 2This involves testing the hydrophobic properties of KH-570 with different dosages; Figure 3 This is a graph showing the relationship between the number of freeze-thaw cycles and the mass loss rate; Figure 4 The sensitivity of different aerosol paint thicknesses to indoor temperature; Figure 5 It is the sensitivity of aerogel paint to indoor and outdoor temperatures; Figure 6 This is a graph showing the results of the tensile property test; Figure 7 This is a diagram showing the test results of the coating's water permeability. Figure 8 This is a SEM image showing the effect of UV aging on the surface of a hydrophobic-inorganic coating. Figure 9 This is a graph showing the relationship between the number of freeze-thaw cycles and the mass loss rate under different operating conditions. Detailed Implementation

[0033] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0034] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0035] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0036] In some specific embodiments, the multi-layer hydrophobic-aerogel composite protective coating of the present invention, suitable for high-altitude environments and resistant to temperature differences and freeze-thaw cycles, includes a multi-functional partitioned structure acting sequentially on the surface of a concrete substrate. The multi-functional partitioned structure includes at least: a bottom layer with hydrophobic wall modification, an intermediate thermal insulation and temperature-stabilizing layer, and a surface sealing protective layer. This forms a multi-layered synergistic protective system combining bottom-layer water blocking, intermediate thermal insulation, and surface sealing. The pore wall hydrophobic modification layer is used to penetrate into the near-surface pores of concrete and modify the pore walls hydrophobically to reduce capillary water absorption capacity. The heat insulation and temperature stabilizing layer is disposed on the pore wall hydrophobic modification layer to reduce heat conduction and weaken the temperature gradient between the concrete surface and interior. The surface sealing and protective layer is disposed on the outside of the heat insulation and temperature stabilizing layer to inhibit moisture ingress and improve weather resistance. The pore wall hydrophobic modification layer and the surface sealing and protective layer work together to keep the heat insulation and temperature stabilizing layer in a low moisture content state, thereby maintaining its heat insulation performance and inhibiting freeze-thaw damage caused by the coupling effect of temperature difference and moisture.

[0037] Specifically, the hydrophobic modification layer for pore walls is located on the side closest to the concrete substrate and is formed of a hydrophobic material with permeability. This layer can penetrate into the near-surface pores of the concrete and construct a low surface energy structure on the pore wall surface, transforming the originally easily wetted pore walls into hydrophobic pore walls, thereby reducing the capillary water absorption capacity of the concrete. Unlike traditional coatings that only form a thin film on the surface, this hydrophobic modification layer for pore walls does not remain only on the outer surface of the concrete but can penetrate into the near-surface pores to hydrophobize the pore walls. Therefore, even if the surface is locally affected by wind and sand erosion or ultraviolet aging, the near-surface pore walls can still maintain a certain water-blocking capacity.

[0038] The hydrophobic material used in the pore wall hydrophobic modification layer can be a silane, a siloxane, or a composite system thereof. Preferably, the hydrophobic material comprises a long-chain hydrophobic component and a coupling component with reactive functional groups. The long-chain hydrophobic component is an alkylsilane, and the coupling component is a silane coupling agent containing reactive functional groups. The long-chain hydrophobic component is used to reduce the surface energy of the pore wall, and the coupling component with reactive functional groups is used to enhance the interfacial bonding between the hydrophobic component and inorganic particles, the concrete pore wall, and subsequent functional layers, thereby simultaneously achieving surface energy reduction and interfacial structure enhancement.

[0039] More preferably, the hydrophobic material is a diasilane synergistic modified nano-inorganic particle composite system. The diasilanes include dodecyltrimethoxysilane (DTMS) and 3-(isobutenoyloxy)propyltrimethoxysilane (KH-570). DTMS contains a long-chain alkyl structure, which can significantly reduce the surface energy of the material and impart good hydrophobicity to the pore walls; KH-570 contains reactive functional groups and silane groups, which can participate in hydrolysis-condensation reactions to form a siloxane network, and improve the bonding stability between the organosilicon component, nanoparticles, and concrete pore walls. Through the synergistic effect of DTMS and KH-570, a hydrophobic modified structure with both low surface energy and stable interfacial bonding ability can be formed on the near-surface pore walls of concrete.

[0040] Furthermore, the hydrophobic material also includes nano-inorganic particles to construct a micro / nano rough structure and enhance coating stability. The nano-inorganic particles can be nano-CaCO3, nano-ZnO, nano-SiO2, or combinations thereof, preferably including nano-CaCO3 and nano-ZnO. Nano-CaCO3 can participate in constructing the micro / nano rough structure and, to a certain extent, fill the small pores on the concrete surface, improving the surface density; nano-ZnO can improve the coating's resistance to UV aging and help enhance the system's weather resistance. Condensation or interfacial bonding can occur between the nanoparticles and the silanols generated by the hydrolysis of bissilanes, fixing the nanoparticles within the siloxane network, thereby improving the stability and durability of the hydrophobic layer.

[0041] In a preferred embodiment, the hydrophobic material comprises, by mass fraction: 4%–5% DTMS, 2%–3% KH-570, 5%–6% nano-CaCO3, 1%–2% nano-ZnO, 0.5%–1.0% formic acid, 10%–11% deionized water, and the balance being isopropanol. More preferably, the composition is 4% DTMS, 2% KH-570, 5% nano-CaCO3, 1% nano-ZnO, 0.5% formic acid, 10% deionized water, and the balance being isopropanol. Formic acid provides an acidic catalytic environment to promote silane hydrolysis; deionized water provides the moisture required for silane hydrolysis; and isopropanol serves as a dispersion medium, facilitating the uniform dispersion of the silane components and nanoparticles.

[0042] The hydrophobic material uses isopropanol as the main dispersion medium, resulting in a low system viscosity that improves wetting and spreading of the concrete capillary walls. DTMS and KH-570 are pre-hydrolyzed under formic acid catalysis and in the presence of water to form active silanol components. Before curing, these components can enter the near-surface pores of the concrete along with the solvent and undergo condensation reactions at the hydroxyl groups on the pore walls to form a stable siloxane network. Nano-calcium carbonate and nano-zinc oxide are ultrasonically dispersed in an ice-water bath to maintain a fine and uniform dispersion, preventing particle agglomeration and clogging of the pores. At the same time, they construct micro-nano rough structures on the pore walls and surface. After pre-drying, the free water in the pores of the concrete substrate is reduced, and capillary adsorption is enhanced, thereby further promoting the penetration of the hydrophobic material into the near-surface layer of the concrete.

[0043] Specifically, the heat-insulating and temperature-stabilizing layer is disposed on top of the hydrophobic modified layer, used to reduce heat conduction and weaken the temperature gradient between the concrete surface and interior. This layer includes an aerogel material and a film-forming matrix, wherein the aerogel material provides low thermal conductivity, preferably SiO2 aerogel. SiO2 aerogel has a porous structure and low thermal conductivity, which can effectively extend the heat conduction path and reduce the rate of heat transfer in the coating system. By setting a heat-insulating and temperature-stabilizing layer on the concrete surface, the rapid transfer of external heat to the interior of the concrete can be reduced under strong solar radiation during the day, and the rapid loss of heat from the interior of the concrete can be slowed under low-temperature conditions at night, thereby reducing the daily temperature difference inside the concrete and the temperature difference between the surface and interior.

[0044] The film-forming base material is used to fix aerogel particles and form a continuous coating. The film-forming base material can be selected from water-based acrylic emulsions, water-based polyurethane emulsions, silicone-acrylic emulsions, or other water-based resin systems suitable for building concrete surfaces. Water-based systems are preferred to improve application adaptability and reduce volatile organic compound (VOC) release. The thermal insulation and temperature-stabilizing layer may also contain additives such as hollow glass microspheres, defoamers, thickeners, film-forming aids, and coupling agents to improve the coating's thermal insulation performance, application rheological properties, film-forming properties, and interfacial bonding performance.

[0045] To address the issue of aerogel insulation layers becoming brittle and prone to cracking under low-temperature and temperature cycling conditions, this invention further introduces toughening components into the thermal insulation and temperature stabilization layer to improve its crack resistance under temperature cycling and low-temperature environments, thereby preventing moisture penetration and insulation performance failure due to cracking. The toughening components include waterborne polyurethane (WPU) and / or modified polyvinyl alcohol (PVA). Waterborne polyurethane improves the coating's flexibility and low-temperature deformation capacity, while modified polyvinyl alcohol enhances the system's cohesive strength and improves structural stability during film formation. Their synergistic effect reduces the risk of brittle cracking in the aerogel insulation layer under diurnal temperature cycling and freeze-thaw conditions.

[0046] The modified polyvinyl alcohol used in this process involves surface modification of PVA fibers using KH550. The method involves immersing the PVA fibers in an ethanol solution of KH-550 for 40 minutes, followed by cleaning and drying in a drying oven.

[0047] Preferably, the waterborne polyurethane has a mass fraction of 5% to 15%, more preferably 10%; the modified polyvinyl alcohol has a mass fraction of 0.3% to 1.0%, more preferably 0.6%. When the toughening component is within the above range, the thermal insulation and temperature-stabilizing layer can improve its ductility and crack resistance at low temperatures while maintaining low thermal conductivity. If the content of the toughening component is too low, it will be difficult to effectively improve the brittleness of the aerogel layer; if the content of the toughening component is too high, it may affect the dispersion state of the aerogel particles and the thermal insulation performance. Therefore, the above-mentioned toughening component content range can achieve a better balance between thermal insulation performance and crack resistance performance.

[0048] In a preferred embodiment, the thermal insulation and temperature stabilizing layer is a composite toughened aerogel thermal insulation layer, comprising, by mass fraction: 5%–15% waterborne polyurethane emulsion, 0.3%–1.0% modified polyvinyl alcohol fiber, and the balance being aerogel waterborne thermal insulation material. The aerogel waterborne thermal insulation material includes aerogel material and a film-forming base material.

[0049] The aerogel water-based thermal insulation material is commercially available, such as the ETU aerogel water-based thermal insulation coating from Hunan Liuyi New Material Technology Co., Ltd., which comprises: water-based acrylic emulsion (film-forming base material), KH550-modified hydrophobic SiO2 aerogel microspheres, thickener, hollow glass microspheres, and defoamer. Its preparation method is as follows: hydrophobic SiO2 aerogel microspheres, water, and KH550 are mixed and dispersed for 10-15 hours; then, a thickener is added and stirred until uniformly dispersed to obtain an aerogel coating slurry; next, water-based acrylic emulsion, hollow glass microspheres, and defoamer are added to the aerogel coating slurry, and the mixture is stirred at 65-75°C for 2.5-3.5 hours.

[0050] The thickness of the thermal insulation and temperature stabilizing layer is 1–10 mm, preferably 3–6 mm, and more preferably 5 mm. When the thickness is too small, the thermal insulation and temperature stabilizing effect is limited, making it difficult to sufficiently reduce the temperature gradient caused by the diurnal temperature difference at high altitudes. When the thickness is too large, although the thermal insulation performance may be further improved, the amount of coating material used increases, and it may lead to problems such as shrinkage cracking, construction difficulties, or decreased adhesion stability. Therefore, controlling the thickness of the thermal insulation and temperature stabilizing layer within the above-mentioned range is beneficial for balancing thermal insulation performance, construction performance, and long-term service stability.

[0051] Specifically, the surface-sealing protective layer is disposed on the outside of the thermal insulation and temperature-stabilizing layer to inhibit moisture ingress and improve weather resistance. This layer is preferably a hydrophobic sealing layer, which reduces the direct wetting of the thermal insulation and temperature-stabilizing layer by external rainwater, snowmelt, or water vapor, preventing moisture from entering the porous structure of the aerogel and causing an increase in thermal conductivity. Simultaneously, the surface-sealing protective layer also reduces the direct damage to the intermediate thermal insulation and temperature-stabilizing layer caused by ultraviolet radiation, wind and sand erosion, rain and snow erosion, and wet-dry cycles, improving the service stability of the entire composite protection system.

[0052] The surface sealing protective layer can be made of the same or similar hydrophobic material as the pore wall hydrophobic modification layer, or it can be other weather-resistant coating materials with hydrophobic sealing properties. This prevents external moisture from entering the thermal insulation and temperature stabilizing layer and reduces the degradation of thermal conductivity caused by water absorption. Preferably, the surface sealing protective layer is formed using the aforementioned dual-silane synergistic modified inorganic nanoparticle composite hydrophobic material, so that the surface layer simultaneously possesses low surface energy, a micro-nano rough structure, and good UV stability. The surface sealing protective layer and the pore wall hydrophobic modification layer work together to restrict moisture from entering the thermal insulation and temperature stabilizing layer from both the inside and outside, keeping the thermal insulation and temperature stabilizing layer in a low-moisture state for a long time.

[0053] In the composite protection system of this invention, the pore wall hydrophobic modification layer, the thermal insulation and temperature stabilization layer, and the surface sealing protective layer are not simply superimposed, but form a continuous and synergistic protective chain. The pore wall hydrophobic modification layer reduces capillary water absorption capacity from the pores near the surface of the concrete, thus reducing the source of moisture; the thermal insulation and temperature stabilization layer weakens the temperature gradient caused by diurnal temperature differences by reducing heat conduction, thereby reducing the accumulation of thermal stress; the surface sealing protective layer blocks moisture from entering the thermal insulation and temperature stabilization layer from the outside and protects it from direct damage from the external environment; the toughening component further improves the low-temperature crack resistance of the thermal insulation and temperature stabilization layer, preventing cracks from becoming channels for moisture migration and freeze-thaw damage propagation. Thus, this invention achieves synergistic protection of water blocking, thermal insulation, sealing, and crack resistance.

[0054] The present invention also provides a method for preparing the above-mentioned multilayer hydrophobic-aerogel composite protective coating resistant to temperature difference freeze-thaw cycles, comprising: Hydrophobic materials are applied to the concrete surface, allowing them to penetrate the pores and form a hydrophobic modified layer on the pore walls; A heat-insulating and temperature-stabilizing layer is formed on the surface of the hydrophobic modified layer of the pore wall; A surface-sealed protective layer is formed on the outside of the thermal insulation and temperature-stabilizing layer; The layers are constructed sequentially in the order described above to ensure that the insulation layer is in a low moisture content state.

[0055] Specifically, it includes the following steps: The first step is to pretreat the concrete substrate. Remove dust, loose particles, oil, and laitance from the surface of the concrete substrate, ensuring it is dry and clean. For newly prepared concrete specimens, surface treatment can be performed after standard curing has reached the specified age; for existing concrete structures, weak layers and contaminants can be removed by grinding, blowing, or washing. Substrate pretreatment improves the penetration of hydrophobic materials and the bonding ability of subsequent coatings.

[0056] The second step is the preparation of the hydrophobic material. Isopropanol, deionized water, and formic acid are mixed, then DTMS and KH-570 are added and stirred to ensure uniform dispersion. A hydrolysis reaction is then carried out under acidic conditions (preferably 20-40 min) to generate silanol from the silane component. Subsequently, nano-CaCO3 and nano-ZnO are added, and the nanoparticles are uniformly distributed in the system under ice-water bath conditions using ultrasonic dispersion or mechanical stirring (20-40 min). This allows the hydrolyzed silanol to condense or interfacially bond with the hydroxyl groups on the nanoparticle surface or the active groups on the concrete pore walls. The temperature is raised to 65-75℃, and stirring continues for 2-4 h to obtain the bissilane synergistic modified inorganic nanoparticle composite hydrophobic material.

[0057] The third step is to form a hydrophobic modified layer for the pore walls. The aforementioned hydrophobic material is applied to the surface of the concrete substrate, using methods such as spraying, brushing, rolling, or dipping. The hydrophobic material penetrates the near-surface pores of the concrete through capillary action, forming a low surface energy structure on the pore wall surface. After application, natural curing or low-temperature drying treatment (preferably room temperature curing for 20-30 hours) is performed to further condense and solidify the silane components, thereby forming a stable hydrophobic modified layer for the pore walls. This layer primarily reduces the near-surface water absorption capacity of the concrete, providing a low-moisture substrate for the subsequent thermal insulation and temperature stabilization layer.

[0058] The fourth step is to prepare the thermal insulation and temperature-stabilizing coating. The SiO2 aerogel material, film-forming base material, toughening components, and other additives are mixed and dispersed (preferably with a stirring time of 10-30 minutes) to form a uniform aerogel composite coating. The toughening components include waterborne polyurethane and / or modified polyvinyl alcohol, used to improve the crack resistance of the thermal insulation and temperature-stabilizing layer. During the preparation process, excessive shearing should be avoided to prevent damage to the aerogel structure, while ensuring that the aerogel particles are uniformly dispersed in the film-forming base material.

[0059] The fifth step is to form a thermal insulation and temperature-stabilizing layer. The aerogel composite coating is then applied to the concrete surface where the hydrophobic modified pore wall layer has been formed. This can be done by scraping, spraying, or rolling, and the final thickness of the thermal insulation and temperature-stabilizing layer is achieved by controlling the number of coats or the thickness of each coat, resulting in a thickness of 1–10 mm, preferably 5 mm. After coating, curing is performed (preferably, each coat is cured for 3 days under natural ventilation conditions at 15–30°C and 40%–70% relative humidity) to allow the coating to fully form a continuous thermal insulation structure. This layer reduces heat conduction and weakens the temperature gradient between the concrete surface and its interior.

[0060] Step 6: Forming a surface-sealing protective layer. After the thermal insulation and temperature stabilizing layer has cured, a hydrophobic sealing material is applied to its outer side to form a surface-sealing protective layer. This layer can be formed by spraying, brushing, or roller coating, and is applied to the outer surface of the thermal insulation and temperature stabilizing layer after drying and curing (preferably at room temperature for 20-30 hours). The surface-sealing protective layer reduces the wetting and intrusion of external moisture into the thermal insulation and temperature stabilizing layer, while improving the system's resistance to UV aging, wind and sand abrasion, and rain and snow cycles.

[0061] In the above construction method, each layer should be constructed sequentially in the order of "hydrophobic modification layer of pore wall - thermal insulation and temperature stabilization layer - surface sealing and protective layer". If the thermal insulation and temperature stabilization layer or the surface sealing and protective layer is formed first, it may hinder the penetration of hydrophobic materials into the concrete pores, affecting the hydrophobic modification effect of the pore wall. If the surface sealing and protective layer is missing, the intermediate aerogel thermal insulation and temperature stabilization layer may be directly exposed to moisture, ultraviolet rays and wind and sand, leading to increased moisture content, deterioration of thermal conductivity or structural cracking. Therefore, the above construction sequence is conducive to ensuring that each functional layer can play its full role and keeping the thermal insulation and temperature stabilization layer in a low moisture content state.

[0062] Through the above technical solution, this invention can form a multi-layered synergistic protective system on the concrete surface, with each layer acting sequentially from the inside out. This system not only reduces moisture penetration but also weakens temperature gradients and improves the long-term stability of the insulation layer through toughening and surface sealing measures. Compared to single hydrophobic protection or single aerogel insulation protection, this invention can more effectively adapt to the coupled effects of multiple factors such as moisture, temperature difference, freeze-thaw cycles, ultraviolet radiation, and wind and sand in high-altitude environments, thereby improving the concrete structure's resistance to temperature differences and freeze-thaw cycles and its long-term durability.

[0063] Example 1: Preparation of a multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments and resistant to temperature differences and freeze-thaw cycles. 1. Substrate pretreatment and construction conditions In this embodiment, C40 concrete was used as the concrete substrate. After standard curing for 28 days, the specimens were placed in an oven at (60±5)℃ for 48 hours to dry. They were then taken out and cooled to room temperature. Oil-free compressed air was used to remove surface dust, loose particles and laitance to keep the surface to be coated dry and clean, so as to ensure the quality of the interface bonding between the coating and the substrate.

[0064] 2. Preparation and spraying of hydrophobic modification layer for pore walls First, a hydrophobic modification layer for the pore walls was prepared. In this embodiment, the mass fraction of dodecyltrimethoxysilane (DTMS) was 4%, the mass fraction of 3-(isobutenoyloxy)propyltrimethoxysilane (KH-570) was 2%, nano-CaCO3 was 5%, nano-ZnO was 1%, formic acid was 0.5%, deionized water was 10%, and the balance was isopropanol. Isopropanol, deionized water, and formic acid were first added to a container, followed by DTMS and KH-570. After stirring until homogeneous, the mixture was allowed to stand at room temperature for approximately 30 minutes. Then, nano-CaCO3 and nano-ZnO were added to the solution, and the mixture was ultrasonically dispersed for 30 minutes under ice-water bath conditions. The mixture was then heated to 70°C and stirred continuously for 3 hours to form a homogeneous solution. During this process, the silane component under acidic conditions underwent hydrolysis to generate silanol, which further condensed to form a siloxane network structure.

[0065] The aforementioned hydrophobic modification solution was uniformly applied to the surface of concrete specimens using a spraying method, allowing it to penetrate into the pore structure of the concrete surface under capillary action. Subsequently, the specimens were dried under natural conditions for 24 hours, enabling the silane components to form a stable hydrophobic network structure on the pore wall surface, thereby constructing a hydrophobic modification layer for the pore walls.

[0066] 3. Preparation and coating of thermal insulation and temperature stabilizing layer After completing the base treatment, the thermal insulation and temperature stabilization layer is constructed. This layer uses aerogel water-based thermal insulation coating as the base material, and incorporates water-based polyurethane emulsion (WPU) and polyvinyl alcohol fiber (PVA) modified with silane coupling agent KH550 for composite toughening. Specifically, by weight, the water-based polyurethane emulsion comprises approximately 10% of the total thermal insulation and temperature stabilization layer, the modified polyvinyl alcohol fiber comprises approximately 0.6%, and the remainder is aerogel water-based thermal insulation coating. The aerogel water-based thermal insulation coating used is ETU aerogel water-based thermal insulation coating from Hunan Liuyi New Material Technology Co., Ltd.

[0067] Aerogel waterborne thermal insulation coating was mixed with waterborne polyurethane (WPU) and modified polyvinyl alcohol (PVA), wherein the mass fraction of waterborne polyurethane was approximately 10% and the mass fraction of modified polyvinyl alcohol was approximately 0.6%. A uniformly dispersed aerogel composite slurry was formed by mechanical stirring for approximately 10 minutes to ensure that the aerogel particles were evenly distributed in the matrix. This slurry was then uniformly coated onto the concrete surface where a hydrophobic modified layer had been formed. Each coat of aerogel thermal insulation coating was cured for 3 days under standard conditions, and the coating thickness was controlled to approximately 5 mm to form a continuous and dense thermal insulation and temperature-stabilizing layer.

[0068] The preparation method of modified polyvinyl alcohol fiber is as follows: First, KH-550 is slowly added to anhydrous ethanol (10wt% KH-550, the remainder is anhydrous ethanol) and mixed evenly; then, the PVA fiber is immersed in SCA solution for 40 minutes; finally, the PVA fiber is washed with water and then placed in a hot air drying oven to dry for 3 hours.

[0069] 4. Spraying of surface sealing protective layer After the intermediate aerogel insulation layer has completely cured, a second layer of hydrophobic composite material of bissilane synergistic modification prepared in step 2 is sprayed onto its outer surface as a surface hydrophobic sealing layer. The spraying amount is controlled at 0.15 g / cm³. 2 Curing at room temperature for 24 hours. The surface hydrophobic sealing layer reduces water droplet wetting and retention on the outer surface, and also seals and protects the pore surface of the intermediate aerogel insulation layer, reducing the risk of increased thermal conductivity and freeze-thaw damage caused by moisture entering the insulation layer. The resulting specimen's bottom, middle, and surface layers respectively fulfill the functions of water resistance, thermal insulation, and sealing protection, working synergistically to improve the concrete's resistance to temperature difference fatigue and freeze-thaw durability in high-altitude environments.

[0070] It should be noted that the above layers must be constructed in the following order: "Hydrophobic Modification Layer for Pore Walls—Temperature Insulation and Stabilization Layer—Surface Sealing and Protective Layer." The bottom hydrophobic treatment provides a low-moisture environment for the insulation layer, the middle layer controls temperature difference, and the surface sealing layer further prevents moisture intrusion. Changing this order, for example, forming the sealing layer first, will hinder the penetration of the hydrophobic material and affect the overall performance.

[0071] The composite system constructed through the above steps can form a functional gradient from the inside to the outside in its structure, thereby achieving synergistic regulation of moisture transport and heat conduction.

[0072] Example 2: Construction of a hydrophobic modified layer for pore walls and optimization of its water control performance This embodiment is used to verify the construction method of the hydrophobic modified layer on the pore wall and its inhibitory effect on water migration, and to determine the optimal ratio of hydrophobic components. Comparative tests are conducted on concrete specimens under different ratio conditions.

[0073] 1. Preparation of hydrophobic agents The hydrophobic agent is mainly composed of dodecyltrimethoxysilane (DTMS), 3-(isobutenoyloxy)propyltrimethoxysilane (KH-570), nano-CaCO3, nano-ZnO, isopropanol, formic acid and deionized water.

[0074] In the preparation process, isopropanol, deionized water, and formic acid were first added to a container. Isopropanol served as the dispersion medium, deionized water provided the water required for silane hydrolysis, and formic acid acted as an acidic catalyst to promote the hydrolysis of methoxysilanes. DTMS and KH-570 were then added, and the mixture was stirred until homogeneous. The mixture was then allowed to stand at room temperature for approximately 30 minutes to allow the two silanes to fully hydrolyze and form a mixed silanol solution containing long-chain alkyl groups and active functional groups. Nano-CaCO3 and nano-ZnO were then added to this solution, and the mixture was ultrasonically dispersed for 30 minutes under ice-water bath conditions. This allowed the hydrolyzed silanol molecules to undergo a condensation grafting reaction with the hydroxyl groups on the surface of the nanoparticles. The mixture was then heated to 70°C and stirred continuously for 3 hours to further promote the condensation of the silanols to form a siloxane network. Simultaneously, the modified nanoparticles were locked within the network structure. After cooling and filtration, a hydrophobic composite liquid with synergistic modification of inorganic nanoparticles by two silanes was obtained.

[0075] 2. Experimental design and variable control In this embodiment, different mass fractions of dodecyltrimethoxysilane (DTMS) and 3-(isobutenoyloxy)propyltrimethoxysilane (KH-570) were selected and combined, while keeping the proportions of other components constant. By changing the content of DTMS and KH-570, multiple hydrophobic modification solutions were prepared and applied to the surface of concrete specimens respectively.

[0076] 3. Effect of DTMS Dosage on Hydrophobicity To determine the optimal dosage of DTMS, contact angle and roll-off angle tests were conducted with different DTMS mass fractions, and the formulations are shown in Table 1.

[0077] Table 1. DTMS Single-Ingredient Experimental Proportions (%)

[0078] Depend on Figure 1 It can be seen that when DTMS increases from 0% to 2%, the contact angle increases from 110.6° to 148.6°, significantly enhancing hydrophobic properties. When DTMS increases to 4%, the contact angle stabilizes above 152.3°, while the roll-off angle decreases to 8.63°, indicating that a relatively good balance is achieved between surface low-energy properties and droplet roll-off performance. When DTMS continues to increase to 6%–10%, the increase in contact angle is limited, and the roll-off angle rebounds, indicating that excessive DTMS easily leads to molecular accumulation and uneven surface energy distribution, introducing new droplet pinning points. Therefore, a DTMS mass fraction of 4% is preferred.

[0079] 4. Effect of KH-570 Dosage on Interfacial Properties Based on a DTMS mass fraction of 4%, the KH-570 doping amount was further optimized, and the formulation is shown in Table 2.

[0080] Table 2. KH-570 Single Blend Test Proportions (%)

[0081] Depend on Figure 2 It can be seen that when the KH-570 content increases from 0% to 2%, the contact angle increases from 141.3° to 162.3°, reaching a superhydrophobic state, while the roll-off angle remains at a low level of approximately 9°. However, when the KH-570 content continues to increase to 4%, 6%, and 8%, the contact angle decreases, while the roll-off angle gradually increases. At 8%, the contact angle drops to 148.3°, and the roll-off angle increases to 13.9°. This is because an appropriate amount of KH-570 can enhance the bonding between nanoparticles and the siloxane network through coupling, improving coating continuity and interfacial adhesion. Excessive KH-570, on the other hand, can cause localized agglomeration or multilayer stacking, weakening the micro / nano rough structure formed by the nanoparticles. Therefore, a KH-570 mass fraction of 2% is preferred.

[0082] 5. Determination of the optimal ratio of hydrophobic agents and improvement of anti-permeability and freeze-thaw resistance The above results show that as the DTMS content increases, the surface contact angle gradually increases, but the increasing trend slows down after exceeding a certain range. Meanwhile, the introduction of KH-570 helps improve the stability and adhesion of the coating on the substrate surface. Based on the above optimization results, the preferred composition of the hydrophobic agent in this embodiment is: DTMS 4%, KH-570 2%, nano-calcium carbonate 5%, and nano-zinc oxide 1%.

[0083] Further water absorption tests were conducted. The test results are shown in Table 3. The average water absorption rate of the untreated concrete was 5.44%, and after spraying the hydrophobic agent, the average water absorption rate decreased to 2.33%, a reduction of approximately 57.2%.

[0084] Table 3 Water Absorption Rate of Hydrophobic Coating

[0085] The freeze-thaw resistance was tested according to the "Standard for Test Scheme of Long-Term Performance and Durability of Concrete" (GB / T 50082-2024). Three 100mm×100mm×100mm concrete specimens were used for each working condition test. The freeze-thaw cycle procedure was carried out according to section 4.2 of (GB / T 50082-2024). After each 25 cycles, the specimens were removed, surface debris was cleaned, and the surface was dried. External damage was checked, and the mass loss rate W of the specimens was measured. niIf the quality loss rate exceeds 5%, the test should be stopped immediately.

[0086] like Figure 3 As shown, after 200 freeze-thaw cycles, the mass loss rate of untreated concrete (control) was 10.68%, while the mass loss rate of concrete after spraying with the hydrophobic agent was 3.58%. This indicates that the bissilane synergistic modified hydrophobic agent can effectively reduce the water absorption rate of concrete and significantly reduce the mass loss caused by freeze-thaw cycles.

[0087] The above results indicate that the constructed hydrophobic modified layer can effectively reduce the adsorption and transport capacity of concrete pores for water, thereby reducing the amount of water entering the thermal insulation and temperature stabilization layer and providing a low-moisture working environment for the subsequent thermal insulation layer.

[0088] Example 3: Construction of thermal insulation and temperature stabilization layer and optimization of its temperature difference regulation performance This embodiment is used to verify the construction method of the aerogel thermal insulation and temperature stabilization layer and its ability to control the temperature difference gradient, and to determine reasonable layer thickness parameters and conduct comparative tests on aerogel coatings under different thickness conditions.

[0089] 1. Variable Design The thickness of the aerogel insulation layer directly affects the thermal resistance, construction difficulty, risk of drying shrinkage and cracking, and engineering economy of the composite coating. To determine the optimal thickness suitable for high-altitude environments, aerogel insulation layer specimens with thicknesses of 1 mm, 3 mm, 5 mm, and 10 mm were prepared according to the method in Example 1, and indoor low-temperature sensitivity tests and continuous outdoor temperature monitoring for 24 hours were conducted.

[0090] 100mm×100mm×100mm concrete specimens were used, and the concrete was poured in batches. After pouring half of the concrete in the first batch, a K-type thermocouple probe was embedded in the center of the concrete. After the concrete had initially set, the second batch of concrete was poured. The test was divided into indoor and outdoor tests. In the indoor test, after curing for 28 days, aerogel paint was applied to all six sides. After the paint was applied, the specimens were placed in the room for curing at room temperature for 3 days. After the aerogel paint had developed strength, all the prepared specimens were left to stand for 48 hours to allow the internal temperature field of the specimens to become completely uniform and to reach equilibrium with the environment. All thermocouples were connected to the data acquisition instrument, the program was started, and the initial stable temperature of all measuring points was recorded. Then, the specimens were quickly transferred to a high and low temperature test chamber that had been pre-cooled to (-20±0.5)°C. The chamber door was closed, and the data acquisition instrument automatically began to continuously record the temperature change of each measuring point over time for 300 minutes. After the indoor test is completed, the outdoor test block is placed in a natural environment that can receive direct sunlight for 1 hour before the test is conducted outdoors. This allows the internal temperature field of the specimen to become completely uniform and to reach equilibrium with the environment. All thermocouples are then connected to the data acquisition instrument, the program is started, and the initial stable temperature of all measuring points is recorded. During this period, the thermocouples are connected to the data acquisition instrument to measure the internal temperature of the concrete, and the temperature gun measures the surface temperature and the ambient temperature for 24 hours.

[0091] 2. Analysis of Indoor Low Temperature Transfer Characteristics Indoor test results as follows Figure 4 As shown, under low-temperature conditions, increasing the thickness of the aerogel insulation layer significantly slows down the cooling rate inside the concrete. After 60 minutes, the internal temperature of the specimen without the aerogel insulation layer had already dropped to [a value missing]. The temperature reached 7.2℃, while the 5mm thick aerogel insulation layer specimen remained at 2.5℃, and the 10mm thick specimen at 5.2℃; after 120 minutes, the internal temperature of the specimen without an aerogel insulation layer dropped to 7.2℃. 19.1℃, 5mm thick specimen 9.7℃, 10mm thick specimen 4.9℃. This result indicates that the aerogel insulation layer can significantly delay the transmission of low temperatures into the concrete interior and reduce the internal temperature gradient caused by sudden temperature changes.

[0092] 3. Outdoor daily temperature difference response analysis Outdoor continuous 24-hour temperature monitoring results are as follows Figure 5As shown, the lowest temperature of the unprotected concrete surface during the day was 8.5℃, and the highest temperature was 32.6℃, with a daily temperature difference of 24.1℃, indicating that exposed concrete is sensitive to both solar radiation and nighttime heat dissipation. After installing the aerogel insulation layer, specimens of different thicknesses all exhibited a peak-shaving and valley-filling effect, that is, the daytime peak temperature decreased and the nighttime valley temperature increased. The internal daily temperature differences corresponding to 1mm, 3mm, 5mm, and 10mm thick aerogel insulation layers were 18.3℃, 15.2℃, 11.1℃, and 10.2℃, respectively. Compared with the unprotected specimen, the 5mm thick aerogel insulation layer can reduce the internal daily temperature difference to 11.1℃, and the total daily temperature difference is reduced by about 13.0℃, showing a significant temperature stabilization effect.

[0093] 4. Determining the optimal thickness of the thermal insulation and temperature stabilization layer Further comparison of 5mm and 10mm thicknesses reveals that while the 10mm thickness offers slightly better insulation, it only reduces the internal diurnal temperature range by approximately 0.9℃ compared to the 5mm thickness, resulting in a significantly reduced gain. Furthermore, increasing the thickness leads to longer construction periods, increased material usage, and a higher risk of drying shrinkage cracking and interface instability. Therefore, considering insulation performance, construction feasibility, durability risks, and economic efficiency, this embodiment preferentially selects a 5mm thickness for the intermediate aerogel insulation layer. This thickness effectively mitigates the concrete temperature gradient caused by diurnal temperature differences at high altitudes, reduces thermal stress generated during temperature cycling, and avoids cracking and adverse construction effects associated with excessively thick coatings.

[0094] Example 4: Toughening modification of thermal insulation and temperature stabilizing layer and optimization of its crack resistance This embodiment is used to verify the role of toughening components in the thermal insulation and temperature stabilization layer, determine their preferred ratio, and conduct low-temperature mechanical property tests on aerogel composite materials under different toughening conditions.

[0095] Because aerogel is a porous, lightweight insulation material, it is prone to brittle cracking under temperature cycling, freeze-thaw cycles, and alternating wet and dry conditions. Once a through crack forms in the intermediate layer, moisture will enter the coating and interface area along the crack, freezing and expanding under low-temperature conditions, further widening the crack and weakening the bond between the insulation layer and the concrete matrix. Therefore, it is necessary to enhance the toughness of the intermediate insulation and temperature-stabilizing layer.

[0096] In this embodiment, waterborne polyurethane (WPU) and modified polyvinyl alcohol fiber (PVA) are used to composite toughen the aerogel insulation layer. WPU, as a flexible film-forming component, can form a continuous flexible phase between aerogel particles, waterborne resin, and hollow glass microspheres, improving the coating's cohesive strength and deformation compatibility. PVA fibers play a bridging role during crack initiation and propagation, transforming a few wide cracks into multiple fine cracks, thus improving the energy dissipation capacity of crack propagation. To enhance the interfacial bonding between PVA fibers and the aerogel matrix, KH550 is used to modify the surface of the PVA fibers, forming a siloxane-containing interfacial layer on its surface, thereby improving fiber dispersibility and bridging efficiency.

[0097] To determine the optimal dosing of WPU and modified PVA, aerogel coating samples with different dosings were prepared according to the method in Example 1, and dumbbell-shaped specimens were prepared for tensile testing according to GB 9641-1988. The results are as follows: Figure 6 As shown.

[0098] With increasing WPU content, the maximum stress corresponding to the strain ε of the aerogel coating... max and fracture strain ε b All showed a significant increase. When WPU increased from 0% to 10%, ε max Increased from 0.92% to 2.24%, ε b The most significant improvement was observed when the content was increased from 1.57% to 3.23%. Further increases to 15% and 20% resulted in continued improvement in ductility, but the gains slowed down, and excessively high polymer content could affect the pore structure and construction stability of the insulation layer. Therefore, a WPU content of 10% is preferred.

[0099] Modified PVA fibers were further added to the WPU toughening base. When the modified PVA content was too low, the bridging effect was insufficient, making it difficult to effectively inhibit crack propagation; when the content was too high, the fibers were prone to agglomeration and disrupting the coating uniformity. Considering elongation, dispersibility, and film stability, the optimal modified PVA content was 0.6%. Temperature-coupled tensile testing results showed that the WPU and modified PVA composite toughening system... It can still maintain high ductility at a low temperature of 20℃, ε max Up to 2.22%, ε b The yield can reach 2.96%, indicating that the composite toughening system can adapt to the thermal expansion and contraction deformation requirements under high-altitude, low-temperature and large-temperature-difference environments.

[0100] Example 5: Synergistic Effect and Overall Performance Comparison of Composite Protection Systems To verify the comprehensive protective advantages of the multilayer hydrophobic-aerogel synergistic composite protective system described in this invention compared to single protective methods and two-layer composite structures, this embodiment comprehensively analyzes the effects of different protective structures in terms of waterproof performance, thermal insulation and temperature stability, anti-aging performance, and freeze-thaw resistance. It should be noted that this embodiment is based on a summary of the results of various specific performance tests, used to illustrate the synergistic effect of the multilayer composite structure in water blocking, thermal insulation and temperature stability, and durability maintenance.

[0101] 1. Comparison of protection system settings This embodiment sets up unprotected concrete, a single hydrophobic layer, a single aerogel insulation layer, a two-layer composite structure, and a three-layer composite structure as comparative systems, all prepared according to the method of Example 1. The single hydrophobic layer is used to evaluate the effect of hydrophobic treatment on water-blocking and freeze-thaw resistance; the single aerogel insulation layer is used to evaluate its thermal insulation and temperature stabilization effect and its stability under service disturbances; the two-layer composite structure is used to evaluate the performance changes after combining the hydrophobic layer and the aerogel layer; the three-layer composite structure is a composite protective system composed of a bottom hydrophobic layer, a middle aerogel insulation layer, and a top hydrophobic layer, used to evaluate the multi-layer synergistic protective effect described in this invention.

[0102] The permeability test method is performed according to Appendix A of JG / T 210-2018 "Primers for Interior and Exterior Walls of Buildings": the permeability test device is placed in a standard environment for 24 hours. After standing, the change in scale liquid level or the permeation is recorded. The smaller the amount of water seepage and the slower the liquid level drops, the stronger the water-blocking ability of the coating and the more complete the film layer and interface are.

[0103] In the water permeability test, the test conditions are set as follows: W-0 is only spraying a hydrophobic layer, W-1 is only coating an aerogel insulation layer, W-2 is a bottom hydrophobic layer plus a top aerogel layer, W-3 is a bottom aerogel layer plus a top hydrophobic layer, and W-4 is a triple protection system of bottom hydrophobic layer, middle aerogel layer and top hydrophobic layer.

[0104] The freeze-thaw resistance was tested according to the "Standard for Test Scheme of Long-Term Performance and Durability of Concrete" (GB / T 50082-2024). Three 100mm×100mm×100mm concrete specimens were used for each working condition test. The freeze-thaw cycle procedure was carried out according to section 4.2 of (GB / T 50082-2024). After each 25 cycles, the specimens were removed, surface debris was cleaned, and the surface was dried. External damage was checked, and the mass loss rate W of the specimens was measured. ni If the quality loss rate exceeds 5%, the test should be stopped immediately.

[0105] In the freeze-thaw cycle test, the test conditions were set as follows: D-0 was unprotected concrete, D-1 was only sprayed with a hydrophobic layer, D-2 was only coated with an aerogel insulation layer, D-3 was a bottom hydrophobic layer plus a top aerogel layer, D-4 was a bottom aerogel layer plus a top hydrophobic layer, and D-5 was a three-layer composite structure.

[0106] 2. Waterproof performance verification Regarding waterproofing performance, a permeability test was used to evaluate the water-blocking effect of different protective structures. The test results are as follows: Figure 7 As shown, the seepage volumes over 24 hours were: 3.2 mL for W-1, 2.7 mL for W-0, 1.6 mL for W-2, 1.5 mL for W-3, and 0.7 mL for W-4.

[0107] The results show that due to its porous structure, the single aerogel insulation layer still allows moisture to enter the system through pores or interfacial channels, resulting in a high 24-hour water permeation rate. While the single hydrophobic layer can reduce surface wettability, seepage channels may still exist under local defects or continuous water pressure. In contrast, the water permeation rate of the two-layer composite structure is significantly lower than that of the single structure, indicating that the combination of the hydrophobic layer and the aerogel layer can produce a certain composite water-blocking effect.

[0108] Among them, the three-layer composite structure W-4 had the lowest 24-hour water infiltration rate, at only 0.7 mL, which was about 74.1% lower than that of the single hydrophobic layer W-0 and about 78.1% lower than that of the single aerogel insulation layer W-1. This result indicates that the hydrophobic modification of the bottom layer, the path blocking of the middle aerogel layer, and the hydrophobic sealing of the surface layer can form a continuous water-blocking path, making it difficult for external moisture to directly enter the pores of the concrete and the interior of the insulation layer, thus demonstrating the synergistic anti-seepage effect of the multi-layer structure.

[0109] 3. Comparison of thermal insulation and temperature stability performance Regarding thermal insulation and temperature stability performance, the daily temperature difference changes inside unprotected concrete and systems with aerogel insulation layers were compared through continuous outdoor monitoring. The results showed that the daily temperature difference inside unprotected concrete reached 24.1℃, while when the thickness of the aerogel insulation layer was 5mm, the daily temperature difference inside the system could be reduced to 11.1℃.

[0110] These results demonstrate that aerogel insulation layers can reduce heat flux transfer through their porous structure. During the day, under solar radiation, the aerogel insulation layer can weaken the rapid transfer of external heat into the concrete interior; at night, it can inhibit the rapid loss of heat from the concrete interior, thereby reducing the temperature fluctuation range inside the concrete.

[0111] For high-altitude environments, large diurnal temperature variations are a significant factor contributing to thermal fatigue cracks in concrete. By installing an aerogel insulation and temperature-stabilizing layer, the temperature gradient between the concrete surface and interior can be significantly reduced, minimizing the accumulation of thermal stress caused by repeated thermal expansion and contraction, thereby helping to lower the risk of thermal fatigue damage.

[0112] In summary, the aerogel thermal insulation and temperature stabilizing layer can significantly reduce the daily temperature difference inside concrete, effectively weakening the temperature fluctuation amplitude of concrete under the alternating effects of day and night temperatures. This temperature stabilizing effect not only helps reduce the temperature gradient and thermal stress concentration, but also mitigates temperature fatigue damage induced by repeated heating and cooling in high-altitude environments. Therefore, the thermal insulation and temperature stabilizing layer mainly plays a role in temperature difference regulation in the composite protection system of this invention, and is an important component for achieving synergistic protection against temperature differences and freeze-thaw cycles.

[0113] 4. Anti-aging performance verification Anti-aging performance is typically evaluated according to the test methods in the standard GB / T 1865-2009, "Artificial Climate Aging and Artificial Radiation Exposure to Filtered Xenon Arc Radiation for Paints and Varnishes". In this test, the standard plain radiation intensity is typically 0.68 W / m². 2 As altitude increases, radiation intensity also increases. To simulate a high-altitude environment, this study increased the radiation intensity of the benchtop anti-aging test chamber to 1.3 W / m². 2 The aging program was set as follows: 8 hours of irradiation (50℃, 1.3W / m²) + 10 minutes of rain + 4 hours of dew (10℃). After 5 days of continuous operation, the performance changes of the samples under each condition were measured. The evaluation method varied depending on the design protection period of the coating, which required different test irradiation times. Generally, a design protection period of 10 years requires 1000 hours of irradiation, and 20 years requires 2000 hours of irradiation. The quality of the coating's weather resistance was judged based on whether blistering, peeling, or chalking appeared on the coating surface after irradiation.

[0114] In terms of anti-aging performance, accelerated aging comparisons were conducted on a single aerogel insulation layer, a single hydrophobic layer, and a three-layer composite structure. The morphological changes after aging are as follows: Figure 8 As shown. Figure 8 The operating conditions are as follows: T-0 is coated only with aerogel paint; T-1 is sprayed only with a dual-silane synergistic modified Nano-CaCO3 coating; T-2 is a triple protection system consisting of a bottom hydrophobic layer, an intermediate aerogel paint layer, and a top hydrophobic layer. After aging, the single aerogel insulation layer exhibited obvious cracks and interconnected pores, indicating that porous inorganic insulation layers are prone to shrinkage and cracking under temperature and humidity cycles and ultraviolet radiation, thus forming channels for moisture ingress and crack propagation. After aging, the single hydrophobic layer showed localized porosity and structural inhomogeneity, indicating that its micro-nano rough structure and low surface energy layer would be damaged to some extent under ultraviolet irradiation, water spraying cycles, and temperature changes.

[0115] In contrast, the three-layer composite structure showed an increase in the number of micropores after aging, but did not form obvious large-scale through cracks. This result indicates that the surface hydrophobic sealing layer can reduce the direct damage to the intermediate aerogel insulation layer caused by UV radiation, water spray, and temperature and humidity cycling; the intermediate aerogel insulation layer can buffer temperature fluctuations; and the bottom hydrophobic impregnated layer continues to maintain the water-blocking function of the concrete near the surface pore walls. Therefore, the three-layer composite structure exhibits better structural integrity retention under accelerated aging conditions.

[0116] 5. Freeze-thaw resistance verification In terms of freeze-thaw resistance, the following structures were compared: D-0 unprotected concrete, D-1 only sprayed with a hydrophobic layer, D-2 only coated with an aerogel layer, D-3 bottom hydrophobic layer plus top aerogel layer, D-4 bottom aerogel layer plus top hydrophobic layer, and D-5 three-layer composite structure.

[0117] The results are as follows Figure 9 As shown, after 200 freeze-thaw cycles, the mass loss rate was 10.93% for D-0, 3.58% for D-1, 2.57% for D-2, 0.14% for D-3, 0.05% for D-4, and [missing data] for D-5. 0.67%. This shows that unprotected concrete suffers significant mass loss under freeze-thaw cycles, indicating that moisture entering the pores generates frost heave pressure during repeated freezing and thawing, leading to surface spalling and internal damage. Both a single hydrophobic layer and a single aerogel insulation layer can reduce freeze-thaw damage to some extent. The single hydrophobic layer mainly protects by reducing water absorption, while the single aerogel insulation layer mainly protects by reducing temperature fluctuations. The two-layer composite structures D-3 and D-4 showed mass loss rates of 0.14% and 0.05% respectively after 200 freeze-thaw cycles, indicating that the combination of the hydrophobic and aerogel layers can simultaneously provide some water resistance and temperature stability. The three-layer composite structure D-5 exhibited near-zero mass change, demonstrating optimal freeze-thaw stability.

[0118] The results show that the three-layer composite structure can significantly suppress mass loss caused by freeze-thaw cycles by simultaneously reducing water ingress, weakening temperature gradient and maintaining structural integrity through the synergistic effect of hydrophobic modification of the bottom pore wall, thermal insulation and temperature stabilization of the middle aerogel and hydrophobic sealing of the surface layer.

[0119] In summary, the three-layer composite coating offers superior overall protection compared to a single hydrophobic layer, a single aerogel insulation layer, and a two-layer composite structure. This is because the bottom hydrophobic impregnation layer preferentially hydrophobizes the concrete pore walls, reducing capillary water absorption at the source; the middle aerogel insulation layer reduces heat conduction, mitigating the temperature gradient caused by diurnal temperature variations; and the surface hydrophobic sealing layer inhibits external moisture wetting and protects the middle insulation layer from direct damage from UV radiation, wind, sand, and rain / snow cycles. The three-layer structure is not simply a superposition of materials, but rather enhances the long-term durability of concrete in high-altitude environments with strong UV radiation, large temperature differences, frequent freeze-thaw cycles, and wind and sand erosion through the synergistic effects of water blocking, heat insulation, sealing, and crack resistance.

[0120] It should be noted that although existing technologies disclose hydrophobic treatment technology and aerogel insulation technology, these technologies typically optimize a single property, such as reducing water absorption through hydrophobic modification or reducing thermal conductivity through aerogel materials. However, in actual high-altitude environments, freeze-thaw damage to concrete structures mainly stems from the coupling effect of moisture migration and temperature changes, and it is difficult to solve both problems simultaneously using a single technology.

[0121] Furthermore, while aerogel materials possess excellent thermal insulation properties, they inherently exhibit drawbacks such as easy water absorption and high brittleness. Without structural optimization, their performance can rapidly degrade due to water absorption or cracking. Therefore, simply combining hydrophobic materials with aerogel materials does not necessarily guarantee stable overall performance.

[0122] This invention constructs a multi-layered structure comprising a hydrophobic modified pore wall layer, a thermal insulation and temperature stabilizing layer, and a surface sealing and protective layer, and introduces toughening components into the thermal insulation layer to create a synergistic functional relationship between the layers. Specifically, the hydrophobic modified pore wall layer reduces moisture sources, the surface sealing and protective layer blocks external moisture intrusion, keeping the thermal insulation layer at a low moisture content; the thermal insulation and temperature stabilizing layer reduces the temperature gradient; and the toughening components ensure structural integrity, thereby preventing moisture penetration due to cracks. The combined effect of these factors achieves simultaneous regulation of moisture migration and temperature gradient effects.

[0123] In summary, addressing the shortcomings of existing technologies where single hydrophobic or thermally insulating coatings cannot simultaneously achieve water intrusion resistance and temperature difference control, aerogel materials are prone to water absorption and lack durability, and there is a lack of multi-layer synergistic protection systems, this invention provides a multi-layer hydrophobic-aerogel composite protective coating for resistance to freeze-thaw cycles and its preparation method. This coating consists of a bottom hydrophobic impregnation layer, an intermediate aerogel thermal insulation layer, and a surface hydrophobic sealing layer. The bottom layer achieves hydrophobicity of the concrete pore walls through synergistic modification with dual silanes to inhibit capillary water absorption. The intermediate layer utilizes the low thermal conductivity of SiO2 aerogel to weaken the temperature gradient between the concrete interior and surface. The surface layer forms a hydrophobic sealing structure to enhance resistance to UV aging and wind erosion, thereby constructing a synergistic protection system of water blocking, thermal insulation, and weather resistance. Through this structural design, the water absorption rate and temperature fluctuation range of concrete can be significantly reduced, the freeze-thaw cycle resistance and temperature difference fatigue resistance can be improved, crack development can be delayed, and overall durability can be enhanced. This invention achieves systematic control of key factors of freeze-thaw damage based on the heat-humidity coupling mechanism, and has good engineering applicability and promotional value. The protective system of this invention is particularly suitable for complex environmental conditions such as strong solar radiation, large temperature difference between day and night, frequent freeze-thaw cycles, and wind and sand erosion in plateau areas.

[0124] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments and resistant to temperature differences and freeze-thaw cycles, characterized in that, The composite protective coating is used to protect concrete substrates and includes: a bottom hydrophobic modification layer for pore walls, an intermediate heat-insulating and temperature-stabilizing layer, and a surface sealing and protective layer. The bottom pore wall hydrophobic modification layer is located on the side close to the concrete substrate and is used to penetrate into the near-surface pores of the concrete and modify the pore walls hydrophobically. The hydrophobic material used is a bissilane synergistic modified nano-inorganic particle composite hydrophobic material; the bissilane includes dodecyltrimethoxysilane and 3-(isobutenoyloxy)propyltrimethoxysilane; the nano-inorganic particles are selected from one or a combination of nano-CaCO3, nano-ZnO, and nano-SiO2. The intermediate heat-insulating and temperature-stabilizing layer is disposed on the hydrophobic modified layer of the pore wall to reduce heat conduction and weaken the temperature gradient between the concrete surface and the interior. It includes aerogel material and film-forming base material. The surface sealing protective layer is disposed on the outside of the heat insulation and temperature stabilization layer to inhibit moisture from entering the intermediate heat insulation and temperature stabilization layer.

2. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 1, characterized in that, The hydrophobic material used in the bottom pore wall hydrophobic modification layer comprises, by mass fraction: 4%–5% dodecyltrimethoxysilane, 2%–3% 3-(isobutenoyloxy)propyltrimethoxysilane, 5%–6% nano-CaCO3, 1%–2% nano-ZnO, 0.5%–1.0% formic acid, 10%–11% water, and the balance being isopropanol.

3. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 1, characterized in that, The aerogel material is SiO2 aerogel, and the film-forming base material is selected from one or a combination of aqueous acrylic emulsion, aqueous polyurethane emulsion, and silicone acrylic emulsion.

4. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 1, characterized in that, The intermediate thermal insulation and temperature stabilizing layer also includes toughening components.

5. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 4, characterized in that, The toughening component includes waterborne polyurethane and / or modified polyvinyl alcohol, wherein the modified polyvinyl alcohol is used to surface-modify PVA fibers using KH550.

6. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 5, characterized in that, The waterborne polyurethane has a mass fraction of 5% to 15%, and the modified polyvinyl alcohol has a mass fraction of 0.3% to 1.0%.

7. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 1, characterized in that, The thickness of the heat insulation and temperature stabilizing layer is 1 to 10 mm.

8. The multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments according to claim 1, characterized in that, The surface sealing protective layer is made of the dual-silane synergistic modified nano-inorganic particle composite hydrophobic material.

9. A method for preparing a multilayer hydrophobic-aerogel composite protective coating suitable for high-altitude environments, as described in any one of claims 1 to 8, characterized in that, include: Dodecyltrimethoxysilane and 3-(isobutenoyloxy)propyltrimethoxysilane were hydrolyzed in an acidic solution. Then, nano-inorganic particles were added and dispersed evenly. The mixture was then heated and stirred to obtain a hydrophobic composite material of nano-inorganic particles with synergistic modification of bissilane. This material was then applied to the surface of concrete to allow it to penetrate into the pores and form a hydrophobic modified layer on the pore walls. SiO2 aerogel material and film-forming matrix are mixed and dispersed to form a uniform aerogel composite coating, which is then coated on the surface of the hydrophobic modified layer of the pore wall to form a heat insulation and temperature stabilizing layer. A surface-sealed protective layer is formed on the outside of the thermal insulation and temperature-stabilizing layer.

10. The preparation method according to claim 9, characterized in that, The acidic solution includes isopropanol, water, and formic acid; the nano-inorganic particles include nano-CaCO3 and nano-ZnO; and the aerogel composite coating also includes toughening components.

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