A multi-scale porous structure geopolymer-based fireproof coating and a preparation method thereof

Abstract

The application discloses a kind of multi-scale pore structure geopolymer base fireproof coating and preparation method thereof, belong to building fireproof material technical field.Solve the problem that existing geopolymer base fireproof coating is easily peeled off by fire, limited heat insulation performance and insufficient bonding strength with base material.The fireproof coating includes: geopolymer film-forming base 36~60 parts by mass, composite alkali activator 15~25 parts, reinforcing material 3~10 parts, pore-forming material 28~46 parts.The geopolymer film-forming base is a ternary system composed of fly ash, metakaolin and waste pit mud, and can form a quaternary system by adding calcined purple mud;The composite alkali activator is composed of sodium water glass, sodium carbonate, sodium hydroxide, trace amounts of aminotri (methylene) phosphonic acid and lithium metaaluminate tetrahydrate;The reinforcing material is a three-level cross-scale material of millimeter-micron-nanometer;Through the synergistic effect of multi-scale pore regulation and full-scale crack resistance enhancement, a fireproof coating with light weight, high strength, high adhesion and excellent heat insulation performance is prepared.

Description

Technical Field

[0001] This invention belongs to the field of building fireproof coating technology, specifically relating to a multi-scale porous structure geopolymer-based fireproof coating and its preparation method. Background Technology

[0002] With the frequent occurrence of urban building fires in my country, and the rapid urbanization process leading to denser and taller buildings, fire risks and rescue difficulties are further amplified. Therefore, enhancing the fire resistance of buildings is crucial, and applying fire-retardant coatings is an effective and convenient method. Fire-retardant coatings are mainly divided into two categories: intumescent and non-intumescent. Intumescent coatings rely on organic film-forming materials, which have problems such as the easy generation of toxic fumes and low expansion efficiency. Non-intumescent coatings are mainly based on inorganic materials, offering advantages such as low cost and environmental friendliness. Geopolymer fire-retardant coatings fall into the category of non-intumescent fire-retardant coatings. As an amorphous three-dimensional aluminosilicate cementitious material formed by the reaction of active aluminosilicates and alkali activators, geopolymer fire-retardant coatings possess near-ceramic thermal stability and excellent fire resistance and heat insulation properties at high temperatures, becoming a new research direction in the field of inorganic fire-retardant coatings in recent years. Furthermore, they can utilize industrial solid wastes such as metakaolin, slag, and fly ash as raw materials, aligning with the green development needs of the construction industry. However, geopolymer-based fire-retardant coatings generally suffer from poor film-forming ability, insufficient adhesion to building structures, and susceptibility to cracking and peeling at high temperatures.

[0003] The key to improving the fire resistance of polymer-based fire-retardant coatings lies in their thermal insulation performance and high-temperature stability. Thermal insulation performance is primarily influenced by the internal pore structure of the coating; a good thermal insulation performance hinders heat transfer and slows down the degradation of the coated substrate at high temperatures. Meanwhile, high-temperature stability can be mainly determined by the volume change caused by the crystal phase transformation at high temperatures, and the volume shrinkage of the polymer due to dehydration at high temperatures. When a polymer-based fire-retardant coating exhibits good high-temperature stability, it is less prone to cracking and peeling at high temperatures.

[0004] Patent No. CN 120004561 A uses industrial waste such as fly ash, coal gangue, and granulated blast furnace slag as silica-alumina raw materials, sodium silicate as an alkali activator, and expanded perlite as a thermal insulation filler. Although it achieves solid waste resource utilization, this material system does not add toughening materials, and the coating is prone to cracking and peeling at high temperatures. In contrast, this invention uses a three-level cross-scale reinforcement material compound system at the millimeter, micrometer, and nanometer scales, which effectively inhibits the propagation of cracks at different scales and significantly improves the high-temperature volume stability of the coating.

[0005] Patent No. CN 117264445 B describes the preparation of a geopolymer fire-retardant interior wall coating using metakaolin composite silica fume, which enhances the bonding strength (up to 1.16 MPa) through a composite phosphate binder. This invention, however, achieves superior bonding performance by synergistically balancing a multi-scale porous structure and a composite reinforcement system, combined with a composite alkali activator containing trace amounts of aminotrimethylene phosphonic acid and lithium aluminate tetrahydrate, resulting in a bonding strength of 0.8~2.0 MPa between the coating and concrete / steel structure substrates.

[0006] Patent No. CN 114479524 B employs a binary silicon-aluminum system of metakaolin and mineral powder, forming potassium-based polymers through potassium silicate activation. Simultaneously, fillers such as mullite fibers, silicon carbide particles, and hollow alumina spheres are added to enhance the coating's fire resistance. In its embodiments, the highest fire resistance limit time at 250℃ is 105 minutes. This invention, however, utilizes a three-stage pore-forming process—pre-foamed with plant-based foaming agents, hollow glass microspheres, hollow alumina microspheres, and nano-bubble water—to synergistically construct a continuous multi-scale porous thermal insulation structure. This allows the coating's unexposed surface to achieve a fire resistance limit time of up to 137 minutes at 250℃, exhibiting superior fireproof and thermal insulation performance at a lower raw material cost.

[0007] Patent No. CN 106277980 B uses fly ash and metakaolin to prepare geopolymer fire-retardant coatings. The highest bonding strength in its examples is only 0.14 MPa, indicating poor bonding performance. In contrast, this invention, through optimizing the ratio of ternary active silica-alumina film-forming base materials, controlling the composite alkali activator, and constructing a multi-scale reinforcement system, produces a multi-scale porous geopolymer-based fire-retardant coating with a bonding strength up to 2.0 MPa, demonstrating significantly improved interfacial bonding performance.

[0008] In summary, existing geopolymer-based fire-retardant coatings still suffer from limited fire-resistant and heat-insulating properties, insufficient adhesion strength to the substrate, and high preparation costs. To address these issues, this invention constructs a four-core functional system using geopolymers as a continuous film-forming matrix. A ternary active silica-alumina film-forming matrix is ​​composed of fly ash, metakaolin, and waste pit mud. Fly ash improves the fluidity of the slurry coating, metakaolin enhances the mechanical strength and adhesion of the film-forming matrix, and waste pit mud regulates the surface drying and setting time of the coating. This multi-component compounding process ensures the comprehensive performance of the coating while utilizing industrial solid waste and reducing raw material costs. A composite alkali activator is formed by compounding trace amounts of aminotrimethylenephosphonic acid and lithium aluminate tetrahydrate with sodium silicate, sodium carbonate, and sodium hydroxide as the base, precisely controlling the polymerization rate and gel phase structure of the geopolymer. Finally, a multi-scale reinforcement is formed by compounding millimeter-scale, micrometer-scale, and nanometer-scale reinforcing materials. The coating comprises millimeter-scale reinforcing materials selected from one or two of basalt fibers and brucite fibers; micrometer-scale reinforcing materials selected from one or two of calcium sulfate whiskers and calcium carbonate whiskers; and nanometer-scale reinforcing materials selected from one or two of multi-walled carbon nanotubes and nano-active silica. Surface modification of the millimeter-scale and micrometer-scale reinforcing materials is achieved through a silane coupling agent, followed by a stepwise dispersion process from large to small scales. This effectively improves the volume stability and crack and spalling resistance of the coating under high-temperature fire conditions. The core component utilizes the synergistic effect of plant-based foaming agents, hollow glass microspheres, hollow alumina microspheres, and nano-bubble water to construct a multi-scale porous thermal insulation structure with continuous distribution at macroscopic, mesoscopic, and microscopic levels, significantly enhancing the fireproof and thermal insulation performance of the coating. This invention effectively overcomes the shortcomings of existing technologies, providing a multi-scale porous polymer-based fireproof coating technology that combines excellent fireproof and thermal insulation performance, high-strength adhesion, and low preparation cost, with a dry density of 550~650 kg / m³. 3 The 28-day compressive strength is 5.0~6.5MPa, the bond strength with concrete substrate is 0.8~2.0MPa, the maximum fire resistance limit time for the unexposed surface of the coating to reach 250℃ is 137min, the surface drying time is 40~60min, and the flowability is 140~170mm. Summary of the Invention

[0009] This invention aims to provide a multi-scale porous structure geopolymer-based fire-retardant coating and its preparation method. The coating uses geopolymer as a continuous film-forming matrix, comprising a ternary active silica-alumina film-forming matrix composed of fly ash, metakaolin, and waste pit mud, and a quaternary composite system formed by optional calcined purplish-red mud. A composite alkali activator is formed by combining sodium silicate, sodium carbonate, sodium hydroxide, trace amounts of aminotrimethylenephosphonic acid, and lithium aluminate tetrahydrate. The core of the coating utilizes the synergistic effect of plant-based foaming agents, hollow glass microspheres, hollow alumina microspheres, and nano-bubble water to construct and precisely control a multi-scale porous thermal insulation structure with continuous macroscopic, mesoscopic, and microscopic connections within the geopolymer matrix, significantly improving the coating's fire-retardant and thermal insulation performance. Simultaneously, the coating forms a full-scale crack-resistant network by incorporating millimeter-, micrometer-, and nano-scale cross-scale reinforcing materials, greatly improving the coating's high-temperature volume stability and crack and spalling resistance under fire conditions. This invention effectively solves the technical problems of existing geopolymer-based fire retardant coatings, such as easy cracking and peeling when exposed to fire, limited heat insulation performance, and insufficient adhesion strength to the substrate, while efficiently disposing of industrial solid waste and reducing preparation costs.

[0010] This invention provides a multi-scale porous structure geopolymer-based fire-retardant coating and its preparation method. The fire-retardant coating comprises the following components and their mass fractions: 36-60 parts of geopolymer film-forming base material, 15-25 parts of compounded alkali activator, 3-10 parts of reinforcing material, and 28-46 parts of pore-forming material.

[0011] The geopolymer film-forming matrix system consists of three core active silica-alumina components: fly ash, metakaolin, and waste pit mud; or four active silica-alumina components: fly ash, metakaolin, waste pit mud, and calcined purplish-red mud, forming the continuous film-forming phase of the coating. The mass ratio of each core component is (10~16):(5~8):(4~7):(0~5). The fly ash is Grade I fly ash with an absolute density of 2150~2200 kg / m³. 3 The particle size exhibits a bimodal distribution, with a median particle size D. 50 ≤1.5μm, coarse particle size D 90 ≤12.0μm; the metakaolin is obtained by calcining kaolin at 750~800℃ for 2h, with an absolute density of 2700~2750kg / m³. 3 Median particle size D 50 ≤1.3μm, coarse particle size D 90 ≤9.0μm; the waste cellar mud is obtained by adding mineral degumming agent and pH adjuster to waste cellar mud from liquor brewing in a certain proportion, then dehydrating it by pressure filtration, lightly calcining it at 150℃, and grinding it until it passes through a 200-mesh standard sieve, with an absolute density of 2550~2600 kg / m³. 3 Median particle size D 50 ≤1.5μm, coarse particle size D 90≤60.0μm; the calcined purplish-red clay is obtained by calcination at 600℃~700℃, and its microstructure is an amorphous, irregular sheet-like structure with an absolute density of 2600~2650kg / m³. 3 Median particle size D 50 ≤1.6μm, coarse particle size D 90 ≤65.0μm.

[0012] The composite alkali activator is composed of sodium silicate, sodium carbonate, sodium hydroxide, aminotrimethylenephosphonic acid and lithium aluminate tetrahydrate in a mass ratio of (12.5~21.0):(0.3~0.5):(2.1~3.5):(0.01~0.05):(0.01~0.03), and the sodium silicate has a modulus of 1.2.

[0013] The reinforcing material system is composed of a three-level cross-scale composite of millimeter-scale, micrometer-scale, and nanometer-scale materials in a mass ratio of (1~3):(2~6):(0.1~0.5), dispersed in the geopolymer film-forming matrix to form a full-scale crack-resistant network. The millimeter-scale reinforcing material is selected from one or two of basalt fiber and brucite fiber, the micrometer-scale reinforcing material is selected from one or two of calcium sulfate whiskers and calcium carbonate whiskers, and the nanometer-scale reinforcing material is selected from one or two of multi-walled carbon nanotubes and nano-active silica; wherein both the millimeter-scale and micrometer-scale reinforcing materials are pretreated with a silane coupling agent for surface modification.

[0014] The pore-forming material system is composed of a mixture of mesoscopic, microscopic, and macroscopic pore-forming components in a mass ratio of (3~6):(15~25):(10~15), which construct thermal insulation pores of different scales during the geopolymer film formation process. The mesoscopic pore-forming components are hollow glass microspheres and hollow alumina microspheres, wherein the hollow glass microspheres have a particle size of 5~40μm and a bulk density of 0.25~0.30g / cm³. 3 The actual density is 0.41~0.50 g / cm³. 3 Hollow alumina microspheres have a temperature resistance of ≥1600℃, preventing the collapse of mesopores at high temperatures. The micropore-forming component is nano-bubble water, and the macropore-forming component is pre-foamed using plant-based foaming agents.

[0015] The above-mentioned multi-scale porous structure geopolymer-based fire-retardant coating and its preparation method include the following steps: (1) Pretreatment of geopolymer film-forming base material: Dry fly ash, metakaolin, waste pit mud and optional calcined purple red mud at 105℃~110℃ for 5~6h, mix evenly according to the formula, and set aside. (2) Preparation of composite alkali activator: Sodium silicate, sodium carbonate, sodium hydroxide, aminotrimethylene phosphonic acid and lithium aluminate tetrahydrate are weighed in the mass ratio of (12.5~21.0):(0.3~0.5):(2.1~3.5):(0.01~0.05):(0.01~0.03). After mixing by stepwise low-speed and high-speed stirring, the mixture is sealed and aged in the dark for 24 hours for later use. (3) Pretreatment of reinforcing materials: Millimeter-sized, micrometer-sized, and nanometer-sized reinforcing materials are compounded in a mass ratio of (1~3): (2~6): (0.1~0.5). The millimeter-sized and micrometer-sized materials are ultrasonically treated with 1%~2% KH-550 silane coupling agent ethanol solution and then dried for modification. The nanometer-sized materials are used directly. They are dispersed by stepwise low-speed stirring according to the particle size from large to small and are ready for use. (4) Pre-preparation of pore-forming materials: Hollow glass microspheres, hollow alumina microspheres, nano-bubble water and plant foaming agent are pre-treated by a three-stage pore-forming process to prepare foam for later use; (5) Hollow glass microspheres, hollow alumina microspheres, geopolymer film-forming base material, and reinforcing material are premixed into powder; nano bubble water and activator are mixed to prepare an activating liquid containing stable nano bubbles; after the two are stirred at high speed to form a slurry, pre-made plant foam is added and stirred at low speed to synergistically form a multi-scale porous geopolymer slurry with a total porosity of 50%~60%; (6) Remove dust, oil, rust and loose attachments from the surface of the substrate to be coated, and sand until clean and dry; (7) Apply the obtained slurry to the substrate surface by brushing, spraying or scraping, control the coating thickness to be 0.5~3cm, and cure for 28 days at room temperature and relative humidity of 60%~70%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention constructs a gelling system synergistically combining a geopolymer film-forming matrix and a composite alkali activator. The geopolymer film-forming matrix adopts a ternary core system composed of fly ash, metakaolin, and waste pit mud, or a quaternary composite system formed by adding calcined purple-red mud. It is combined with a composite alkali activator system consisting of sodium silicate, sodium carbonate, sodium hydroxide, trace amounts of aminotrimethylenephosphonic acid, and lithium aluminate tetrahydrate. In the silica-alumina system, the spherical glass microspheres in the fly ash reduce interparticle friction, significantly improving the coating performance; metakaolin enhances the mechanical strength and substrate adhesion of the film-forming matrix by increasing the degree of polymerization; waste pit mud can precisely adjust the surface drying and setting time of the coating, while supplementing the active silica-alumina components; calcined purple-red mud further enriches the source of active silica-alumina, realizing the efficient and high-value utilization of various industrial solid wastes such as fly ash and waste pit mud. In the composite alkali activator, sodium silicate is used to improve the rheological properties of the coating slurry; sodium hydroxide provides a strongly alkaline activation environment and controls the system modulus to the target value; sodium carbonate reacts with calcium ions in the system to generate calcium carbonate, which delays the setting time and regulates the slurry fluidity; trace amounts of aminotrimethylenephosphonic acid precisely control the polymerization rate of the geopolymer through chelation, preventing the slurry from setting rapidly; lithium aluminate tetrahydrate supplements the active aluminum source, optimizes the three-dimensional network structure of the gel phase, and further enhances the coating adhesion strength. This raw material system, through the multiple complementarities of its components at the physical scale and in chemical reactions, significantly reduces the preparation cost while ensuring the mechanical and fire-retardant properties of the coating, and simultaneously improves the controllability of the system reaction and the interfacial adhesion performance. 2. This invention achieves precise control over the continuous interconnected pore structure of geopolymer fire-retardant coatings at the macroscopic, mesoscopic, and microscopic levels through the synergistic effect of a multi-scale pore construction system, significantly reducing the dry density of the coating and significantly improving its fire-resistant and heat-insulating performance. The mesoscopic pore-forming component consists of hollow glass microspheres and hollow alumina microspheres with a temperature resistance of ≥1600℃. The hollow glass microspheres achieve basic lightweighting and mesoscopic heat insulation, while the hollow alumina microspheres effectively prevent the collapse of mesoscopic pores at high temperatures, ensuring that the coating still has a stable heat-insulating structure under ultra-high temperature conditions. Nano-bubble water is not only used to construct the microscopic pore structure, but the surface energy released when it breaks within the system helps to promote the reaction process of the geopolymer, thereby reducing the decrease in mechanical properties caused by the introduction of the porous structure while ensuring the high porosity and heat insulation performance of the coating. Plant-based foaming agents pre-form foam to construct uniform macroscopic pores, further reducing the fire resistance limit time of the coating. This invention constructs a full-scale crack-resistant reinforcement system by multiplying millimeter-scale, micrometer-scale, and nanometer-scale reinforcing materials. The millimeter-scale reinforcing materials are selected from one or both of basalt fiber and brucite fiber. After surface modification with a silane coupling agent, the interfacial bonding strength with the geopolymer matrix is ​​significantly improved. Basalt fiber, utilizing its high melting point and thermal stability, plays a skeletal support and fiber bridging role in the early to mid-stages of fire exposure, preventing the propagation of macroscopic cracks. Brucite fiber decomposes upon heating, releasing water of crystallization and generating high-temperature resistant magnesium oxide, providing both physical bridging and chemical heat absorption and flame retardancy. The micrometer-scale reinforcing materials are selected from one or both of calcium sulfate whiskers and calcium carbonate whiskers. After surface modification with a silane coupling agent, they are uniformly dispersed in the matrix. The lamellar crystalline phases generated in the alkaline environment refine the micropores inside the coating through spatially staggered stacking, and undergo dehydration and decomposition to absorb heat in the early to mid-stages of fire exposure. The nanoscale reinforcing materials are selected from one or two of multi-walled carbon nanotubes and nano-active silica. They can bridge nanoscale microcracks and fill internal defects in the matrix, further improving the coating's density and mechanical properties. The tertiary reinforcing materials complement each other in terms of physical scale, applicable temperature range, and mechanism of action, synergistically improving the volume stability and crack and spalling resistance of porous geopolymer-based fire-retardant coatings across the entire temperature range from room temperature to ultra-high temperature. Attached Figure Description

[0017] Figure 1 The following are images of the fire resistance test of a multi-scale porous fiber-reinforced geopolymer-based fire-retardant coating provided by this invention: (a) physical diagram of the device, (b) schematic diagram of thermocouple arrangement and flame distribution range, (c) schematic diagram of test system connection, and (d) comparison diagram of the average temperature of the fire-exposed surface and the standard temperature rise curve, and (e1) physical diagram of the sample under fire test, (e2) infrared thermal image of the sample under fire test below, (e3) infrared thermal image of the sample under fire test above, and (e4) physical diagram of the sample after burning. Figure 2 The heating curves of the fire-retardant coating substrates prepared in different embodiments and comparative examples and the sample images after testing are shown, where (a) is Example 2, (b) is Example 3, (c) is Comparative Example 1, and (d) is Comparative Example 2. Figure 3 SEM images of fire-retardant coating substrates prepared in different embodiments and comparative examples, wherein (a) is Example 2, (b) is Example 3, (c) is Comparative Example 1, and (d) is Comparative Example 2. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described in detail below through specific embodiments.

[0019] Example 1: Example 1 of the present invention is a multi-scale porous structure geopolymer-based fire-retardant coating, its preparation method and performance determination.

[0020] I. Preparation method: (1) Pre-treated silicon-aluminate raw materials: Grade I fly ash, metakaolin obtained by calcination at 750℃ for 2 hours, and waste pit mud after pretreatment are dried at 105℃ for 5 hours and mixed evenly in proportion to obtain ternary silicon-aluminate mixed raw materials. (2) Preparation of composite alkali activator: First, dissolve sodium hydroxide in deionized water and stir at a low speed of 120 r / min until completely clear. Then add sodium carbonate and continue stirring for 8 min until there is no solid residue. Then add aminotrimethylene phosphonic acid and lithium aluminate tetrahydrate and stir for 4 min until uniformly dispersed. Finally, add sodium silicate with a modulus of 1.2 and stir at a high speed of 220 r / min for 18 min. After cooling to room temperature, seal and age in the dark for 24 h for later use. (3) Pretreatment of reinforcing materials: Basalt fibers and calcium sulfate whiskers were immersed in a 1.5% KH-550 silane coupling agent ethanol solution, ultrasonically treated for 15 min, and then dried at 105℃ for 3.5 h. Multi-walled carbon nanotubes do not need to be modified and can be used directly. (4) Pre-preparation of pore-forming materials: Hollow glass microspheres and hollow alumina microspheres are dried at 105℃ for 5h for later use; Nano bubble water is treated with water in a nano bubble generator at a pressure of 0.4MPa and a frequency of 180Hz, and then left to stand for 2h to break the unstable foam before use; Plant foaming agent pre-prepared foam is prepared by mixing plant foaming agent and water at a mass ratio of 1:50, and then foamed at 95Hz using a physical foaming machine until it is stable before use. The stable foam prepared under these process conditions has a bubble diameter range of 0.1~0.4mm. (5) Dry mixing stage: Add the ternary silicon-aluminum mixed raw materials from step (1), hollow glass microspheres and hollow alumina microspheres from step (4) into a high-speed mixer. First, add the pretreated basalt fiber and stir at 150 r / min for 1 min. Then, add the pretreated calcium sulfate whiskers and stir for 1.5 min. Finally, add the multi-walled carbon nanotubes and stir at 220 r / min for 1.5 min until the materials are mixed evenly. (6) Wet mixing stage: The composite alkali activator of step (2) and the nano bubble water of step (4) are slowly added to the dry mixed material of step (5), and the initial polymerization is initiated by stirring at a low speed of 220r / min for 1.5min. Then, the plant foaming agent of step (4) is added to pre-foam, and the mixture is stirred at 350r / min for 2min until the coating system is uniform and free of lumps. The multi-scale porous structure geopolymer-based fireproof coating is obtained. (7) Coating and curing: The prepared fireproof coating is applied to the substrate surface by brushing, spraying or scraping. The coating thickness is controlled to be 15mm. The coating is cured for 28 days at room temperature (25℃) and relative humidity of 70% to complete the coating preparation.

[0021] II. Performance Testing Fire resistance performance testing: Following the large-panel burning method in GB 12441-2018 "Decorative Fire Retardant Coatings", wood was used as the fire retardant coating substrate, with a coating thickness of 15mm. An alcohol torch was used as the ignition source. During the test, the alcohol torch nozzle was 6cm away from the fire retardant coating to ensure the center of the coating was continuously exposed to the high-temperature flame. Thermocouples were pre-placed between the coating and the back-coated substrate, and their temperatures were recorded every 60 seconds during the fire resistance performance test. When the temperature of any thermocouple at the center of the back of the sample reached 250℃ (the ignition point of wood), the sample structure was considered destroyed, and the test was stopped. The experimental setup, thermocouple arrangement and flame distribution diagram, test system connection diagram, comparison of the average temperature of the exposed surface with the standard temperature rise curve, and the actual sample under fire and infrared thermal imaging images are shown below. Figure 1 As shown.

[0022] Mechanical property testing: The samples were prepared and tested according to the test methods for bonding strength and compressive strength in GB 14907-2018 "Fireproof Coatings for Steel Structures".

[0023] Flowability testing: The truncated cone mold method is used for determination. A well-stirred paint slurry is poured into a standard truncated cone mold (upper diameter 36mm, lower diameter 60mm, height 60mm) placed on a horizontal glass plate in one go, compacted, and the surface is leveled. The truncated cone mold is then lifted vertically upwards at a uniform speed. After the slurry stops flowing, the maximum diameter of the slurry droplet in two mutually perpendicular directions is measured using vernier calipers, and the average value is taken as the flowability of the paint.

[0024] Surface drying time test: The test was conducted according to the relevant provisions of GB 12441-2018 "Decorative Fire-retardant Coatings" and GB / T 1728-2020 "Determination of Drying Time of Paint Films and Putty Films". The finger-touch method was used. Under normal temperature (20℃~25℃) and relative humidity of 60%~70%, the coating surface was lightly touched with a finger at regular intervals. When the coating surface felt slightly sticky to the finger, but no paint adhered to the finger, it was considered to be surface dry, and the time elapsed was recorded.

[0025] Dry density testing: Sample preparation and testing were conducted according to the provisions of GB 14907-2018 "Fire-retardant Coatings for Steel Structures". The prepared coating was poured into standard molds and cured at room temperature and relative humidity of 60%~70% until the specified age. The test blocks were then demolded and transferred to an oven, where they were dried to constant weight at the specified temperature. The dimensions of the test blocks were precisely measured using vernier calipers to calculate the volume, and the mass of the dried blocks was weighed using an electronic balance. Finally, the dry density of the coating was calculated by the ratio of mass to volume.

[0026] Example 2: The multi-scale porous polymer-based fire-retardant coating of this example is composed of the following components in parts by weight: 38 parts fly ash, 5 parts metakaolin, 2 parts waste kiln mud, 15.10 parts sodium silicate, 0.38 parts sodium carbonate, 2.52 parts sodium hydroxide, 0.02 parts aminotrimethylenephosphonic acid, 0.01 parts lithium aluminate tetrahydrate, 11 parts plant-based foaming agent, 20 parts nano-bubble water, 4 parts hollow glass microspheres, 1 part hollow alumina microspheres, 3 parts basalt fiber, 3 parts calcium sulfate whiskers, and 0.2 parts multi-walled carbon nanotubes. The surface temperature rise curve of the fire-retardant coating substrate prepared from the above components and the sample image after testing are shown below. Figure 2 As shown in (a), the SEM image is as follows: Figure 3 As shown in (a).

[0027] The preparation steps and performance testing methods of the above-mentioned multi-scale porous structure geopolymer-based fire-retardant coating are the same as those in Example 1.

[0028] Example 3: The multi-scale porous polymer-based fire-retardant coating of this example is composed of the following components in parts by weight: 38 parts fly ash, 5 parts metakaolin, 2 parts waste kiln mud, 15.10 parts sodium silicate, 0.38 parts sodium carbonate, 2.52 parts sodium hydroxide, 0.02 parts aminotrimethylenephosphonic acid, 0.01 parts lithium aluminate tetrahydrate, 11 parts plant-based foaming agent, 20 parts nano-bubble water, 4 parts hollow glass microspheres, 1 part hollow alumina microspheres, 1.5 parts basalt fiber, 1.5 parts calcium sulfate whiskers, and 0.1 parts multi-walled carbon nanotubes. The surface temperature rise curve of the fire-retardant coating substrate prepared from the above components and the sample image after testing are shown below. Figure 2 As shown in (b), the SEM image is as follows: Figure 3 As shown in (b).

[0029] The preparation steps and performance testing methods of the multi-scale porous structure geopolymer-based fire-retardant coating described above are the same as those in Example 1.

[0030] Comparative Example 1: The composition of the geopolymer-based fire-retardant coating in this comparative example is basically the same as that in Example 1, except that no reinforcing materials were added. Specifically, the amounts of millimeter-sized basalt fibers and brucite fibers, micron-sized calcium sulfate whiskers and calcium carbonate whiskers, and nano-sized multi-walled carbon nanotubes and nano-activated silica were all 0 parts. The surface temperature rise curves of the fire-retardant coating substrate prepared from the above components and the sample images after testing are shown below. Figure 2 As shown in (c), the SEM image is as follows: Figure 3 As shown in (c).

[0031] The preparation steps and performance testing methods are the same as in Example 1.

[0032] Comparative Example 2: The geopolymer-based fire-retardant coating in this comparative example is a blank sample of pure film-forming base material. Its components include only: 38 parts fly ash, 5 parts metakaolin, 2 parts waste kiln mud, 15.10 parts sodium silicate, 0.38 parts sodium carbonate, 2.52 parts sodium hydroxide, 0.02 parts aminotrimethylenephosphonic acid, 0.01 parts lithium aluminate tetrahydrate, and 20 parts ordinary deionized water for adjusting flowability. No pore-forming materials (plant-based foaming agents, hollow glass microspheres, hollow alumina microspheres, and nano-bubble water) or any reinforcing materials (millimeter-sized basalt fibers, brucite fibers, micron-sized calcium sulfate whiskers, calcium carbonate whiskers, nano-sized multi-walled carbon nanotubes, and nano-activated silica) were added. The surface temperature rise curve of the fire-retardant coating substrate prepared from the above components and the sample image after testing are shown below. Figure 2 As shown in (d), the SEM image is as follows: Figure 3 As shown in (d).

[0033] The preparation steps and performance testing methods of the above-mentioned geopolymer-based fireproof coating are basically the same as those in Example 1. However, since no reinforcing materials or pore-forming materials are added, the preparation stages of surface modification pretreatment of reinforcing materials, pore-forming material pretreatment, and pre-foaming with plant-based foaming agents are not included. In the dry mixing stage, only the geopolymer film-forming base material is mixed, and in the wet mixing stage, only the composite alkali activator and ordinary deionized water are added and stirred evenly.

[0034] The coatings prepared in Examples 2 and 3, as well as Comparative Examples 1 and 2 (denoted as samples S1, S2, D1, and D2, respectively) were subjected to comprehensive performance tests. According to the aforementioned test methods and relevant standards, the thermal insulation performance (fire resistance limit time), mechanical properties (28-day compressive strength and bond strength), dry density, surface drying time, and flowability of each sample were determined. The specific test results are shown in Table 1. Table 1: As shown in Table 1, comparing S1 and D2, the introduction of a three-level continuous interconnected pore system (macro-meso-micro) significantly reduced the coating dry density by 51.6% (from 1326.4 kg / m³).3 Reduced to 642.5 kg / m 3 Meanwhile, the fire resistance limit was significantly improved (from 36 minutes to 137 minutes), fully demonstrating that the multi-scale porous structure is the core factor in improving the thermal insulation performance of the coating. Comparing S1 and D1, it can be seen that the three-level cross-scale reinforcement system, which incorporates millimeter-sized basalt fibers, micron-sized calcium sulfate whiskers, and nano-sized multi-walled carbon nanotubes, although slightly increasing the dry density of the coating, improved the 28-day compressive strength by 62.9% (from 4.37 MPa to 7.12 MPa), the bond strength by 77.8% (from 1.08 MPa to 1.92 MPa), and extended the fire resistance limit by 48 minutes. This verifies the effective bridging and suppression of cracks by the full-scale reinforcement system, as well as the significant improvement in the high-temperature structural integrity of the coating. Comparing S1 and S2, it can be seen that when the total amount of reinforcing material is halved, the compressive strength of the coating decreases by 15.0%, the bond strength decreases by 18.8%, and the fire resistance limit is shortened by 24 minutes, further clarifying the positive correlation between the amount of reinforcing system and the overall performance of the coating. The comparative experimental data above fully demonstrate that the present invention, through the synergistic combination of multi-scale pore regulation and full-scale crack resistance enhancement, has prepared a geopolymer-based fireproof coating that combines lightweight, high strength, high adhesion and excellent thermal insulation performance.

[0035] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A multi-scale porous structure polymer-based fire-retardant coating, characterized in that, By weight, the geopolymer film-forming base material comprises 36-60 parts of a premixed mixture of fly ash, metakaolin, waste pit mud, and optionally calcined purplish-red clay; 15-25 parts of activator; 3-10 parts of reinforcing material; and 28-46 parts of pore-forming material. The pore-forming material consists of 3-6 parts of hollow glass microspheres and hollow alumina microspheres, 15-25 parts of nano-bubble water, and 10-15 parts of pre-made foam using plant-based foaming agent. The activator is a compound of sodium silicate, sodium carbonate, sodium hydroxide, aminotrimethylene phosphonic acid, and lithium aluminate tetrahydrate, in a mass ratio of (12.5-21.0):(0). 0.3~0.5): (2.1~3.5): (0.01~0.05): (0.01~0.03); The reinforcing material is composed of millimeter-level reinforcing material, micrometer-level reinforcing material and nanometer-level reinforcing material in a mass ratio of (1~3): (2~6): (0.1~0.5); The millimeter-level reinforcing material is selected from one or two of basalt fiber and brucite fiber, the micrometer-level reinforcing material is selected from one or two of calcium sulfate whiskers and calcium carbonate whiskers, and the nanometer-level reinforcing material is selected from one or two of multi-walled carbon nanotubes and nano-active silica.

2. The multi-scale porous structure geopolymer-based fire-retardant coating according to claim 1, characterized in that, The geopolymer film-forming matrix is ​​composed of three active silica-alumina components: fly ash, metakaolin, and waste pit mud, with a mass ratio of (40~64):(20~32):(16~28). The fly ash is Grade I fly ash, the metakaolin is a calcined kaolin product, and the waste pit mud is waste pit mud from liquor brewing, which is obtained by adding mineral degumming agent and pH adjuster in a certain proportion, then filtration and dehydration, lightly calcining at 150℃, and grinding until it passes through a 200-mesh standard sieve.

3. The multi-scale porous structure geopolymer-based fire-retardant coating according to claim 2, characterized in that, The geopolymer film-forming base material is prepared by a continuous calcination process using fly ash, metakaolin, and waste pit mud. The specific process is as follows: the three raw materials are mixed evenly and ground for 30 minutes; then, the mixed powder, after passing through a 200-mesh standard sieve, is placed in a muffle furnace and heated to 150°C at a uniform rate of 3-10°C / min, held for 0.5-1 hour, then further heated at a uniform rate of 10-20°C / min to 500-800°C, held for 1.5-3 hours, and then naturally cooled to room temperature with the furnace; the calcined mixture is then crushed to a median particle size D. 50 ≤1.6μm, ultimately forming geopolymer film-forming base powder.

4. The multi-scale porous structure geopolymer-based fire-retardant coating according to claim 1, characterized in that, The activator is prepared by the following steps: first, sodium hydroxide is dissolved in deionized water and stirred at a low speed of 100-150 r / min until completely clear; then sodium carbonate is added and stirring is continued for 5-10 min until no solid residue remains; then aminotrimethylenephosphonic acid and lithium aluminate tetrahydrate are added and stirred for 3-5 min until uniformly dispersed; finally, sodium silicate is added and stirred at a high speed of 500-650 r / min for 5-10 min; after cooling to room temperature, it is sealed and aged for 24 h to finally form the activator.

5. The multi-scale porous structure geopolymer-based fire-retardant coating according to claim 1, characterized in that, Both the millimeter-scale and micrometer-scale reinforcing materials undergo surface modification treatment with a silane coupling agent. The modification process involves immersing each reinforcing material in a 1%–2% (w / w) KH-550 silane coupling agent ethanol solution, ultrasonically treating it for 10–20 minutes, and then drying it at 105°C–110°C for 3–4 hours. The nanometer-scale reinforcing material requires no modification and can be used directly. During dispersion, the modified millimeter-scale reinforcing material and the geopolymer film-forming matrix are first stirred at a low speed of 150~200 r / min for 1 min, then the modified micron-scale reinforcing material is added and stirred for 1~2 min, and finally the nano-scale reinforcing material is added and stirred at 200~250 r / min for 1~2 min. Ultimately, this forms a reinforcing material.

6. The multi-scale porous structure geopolymer-based fire-retardant coating according to claim 1, characterized in that, A multi-scale porous structure for fire-retardant coatings is achieved through a three-stage pore-forming process. The specific preparation method is as follows: First, hollow glass microspheres with a pore size range of 10-80 μm and hollow alumina microspheres with a pore size range of 30-60 μm are weighed out according to a specific ratio and simultaneously added to the geopolymer film-forming base and reinforcing material, then mixed thoroughly to form a mixed powder for later use. Second, deionized water is passed through a nanobubble generator to prepare nanobubble water under a pressure of 0.4-0.6 MPa and a frequency of 160-180 Hz, and the mixture is allowed to stand for 2 hours to break the bubbles. After removing unstable foam, the mixture is thoroughly mixed with an activator to obtain an activator mixture containing stable nanobubbles, which is used to subsequently construct nanoscale pores with a pore size ≤1μm inside the coating. In the third step, the above-mentioned nanobubble-containing water activator mixture is mixed with the powder mixture formed in the first step and stirred at a high speed of 550~600r / min for 5min to form a geopolymer coating slurry. In the fourth step, a plant-based foaming agent is prepared by mixing plant-based foaming agent and water at a mass ratio of 1:50, and then physically foamed at 90~100Hz until the foam density reaches 0.05~0.08g / cm³. 3 Stir at a low speed of 200~500r / min for 1~3min, control the macroscopic pore diameter to be 0.1~0.4mm, and add it to the above slurry. After stirring evenly, a geopolymer slurry is formed. Thus, through the coordinated control of the above three-stage process, the total porosity of the coating is stabilized at 50%~60%, and the three-stage pores are interconnected and uniformly distributed.

7. The multi-scale porous structure geopolymer-based fire-retardant coating according to any one of claims 1 to 6, characterized in that, The core performance parameters of the fire-retardant coating are: coating thickness of 0.5~3cm and dry density of 550~650kg / m³. 3 28-day compressive strength 5.0~6.5MPa, bonding strength with concrete / steel structure substrate 0.8~2.0MPa, fire resistance time of the coating surface at 250℃ ≥110min, surface drying time 40~60min, flowability 140~170mm.

8. A method for preparing a multi-scale porous structure geopolymer-based fire-retardant coating as described in any one of claims 1 to 7, characterized in that, The main operating steps include the following: (1) Weigh out the geopolymer film-forming base material, activator, reinforcing material, hollow glass microspheres, hollow alumina microspheres, nano bubble water and plant foaming agent that constitute the pore-forming material according to the mass parts, and prepare the foam by surface modification pretreatment of the above-mentioned reinforcing materials separately for later use. (2) The components of the above-mentioned pore-forming material are uniformly compounded with the geopolymer film-forming base material, the pretreated reinforcing material and the activator through a composite foaming and graded mixing process to prepare a multi-scale porous geopolymer fireproof coating slurry. (3) Remove dust, oil, rust and loose attachments from the surface of the substrate to be coated, and sand until clean and dry; (4) Apply the slurry obtained in step (2) to the substrate surface by brushing or spraying, control the coating thickness to be 0.5~3cm, and cure for 28 days at room temperature and relative humidity of 60%~70%.

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