Magnesia cement-based fireproof coating for steel structure and preparation method thereof

Abstract

The application relates to a magnesium cement-based steel structure fireproof coating and a preparation method thereof, and belongs to the technical field of fireproof coatings. In view of the problems of thick coating, large weight, poor adhesion to the base body, long drying time and insufficient durability of the existing steel structure fireproof coating, a magnesium cement-based steel structure fireproof coating with light weight and long fire resistance limit is prepared by using a magnesium cement base body, functional fillers, a flame retardant, an inorganic foaming agent and an additive material without adding a polymer latex binder and generating harmful gas, that is, the dry density of the magnesium cement-based steel structure fireproof coating is not higher than 600 Kg / m3, and the fire resistance limit can reach 3.6h, which fully meets the requirements of the steel structure fireproof coating standard, and solves the balance between the fireproof performance and environmental protection requirements, the balance between the durability and the convenience of construction, the adaptability of different base materials and the aging problem of the fireproof coating.

Description

Technical Field

[0001] This invention belongs to the field of fire-retardant coating technology, specifically a magnesium cement-based fire-retardant coating for steel structures and its preparation method. Background Technology

[0002] Compared to other traditional building structures, steel structure buildings offer higher strength while being lighter, making installation and transportation easier. The steel base material also boasts better plasticity and stability than concrete, preventing sudden cracking. Steel structures are also characterized by uniform material distribution and good dispersion. However, steel structures have certain drawbacks. When exposed to fire, the strength of the steel base material begins to decrease after reaching 300℃, and at 500℃, the softening of the steel base material poses a risk of collapse. Therefore, existing steel structure buildings require fire protection measures to reduce the damage and impact of fires. The most economical and effective fire protection measure is the use of fire-retardant coatings.

[0003] Fire-retardant coatings for steel structures can be classified into intumescent and non-intumescent types based on their fire-retardant mechanism. Intumescent fire-retardant coatings, the majority of their components—film-forming agents, acid sources, carbon sources, and gas sources—are organic materials, which may release harmful gases and smoke upon contact with fire. Whether used outdoors or indoors, intumescent fire-retardant coatings are subject to various complex environmental factors such as ultraviolet radiation, humidity, and temperature, leading to degradation and aging of the coating components. Because the main components are organic materials, their aging resistance and durability are not well-defined. Non-intumescent fire-retardant coatings, unlike intumescent coatings, do not expand upon contact with a fire source. Instead, they form a dense fire-resistant and heat-insulating layer through a chemical reaction, thus achieving fire protection. This fire-retardant property effectively protects steel structures during a fire, prolonging their combustion time and providing valuable time for evacuation and firefighting. Non-intumescent fire-retardant coatings are generally made of inorganic materials, containing no volatile organic compounds, and have a smaller impact on the environment and human health. Furthermore, the production process of this type of coating consumes less energy, aligning with the principles of green building.

[0004] Although current non-intumescent fire-retardant coatings for steel structures can form a fire-resistant and heat-insulating layer when exposed to fire, the fire resistance of existing fire-retardant coatings at high temperatures still needs improvement. At high temperatures, the coating may melt, flow, and peel off, leading to a decrease in fire resistance and failing to meet the fire safety requirements of buildings. Poor adhesion can also occur during application. Patent CN109133841A prepared a magnesium oxysulfate cement-based fire-retardant coating with a fire resistance limit of 120 minutes, a thermal conductivity of 0.08-0.20 W / (m·K), and a maximum drying time of 360 minutes. Patent CN106497157B prepared a potassium magnesium phosphate cement-based fire-retardant coating for steel structures, along with its preparation and application methods, wherein the coating thickness is 20 mm, the fire resistance limit is 2.6 hours, and the bond strength is 0.08 MPa. Therefore, fire-retardant coatings for steel structures still have certain shortcomings in terms of short fire resistance time, adhesion, weather resistance, environmental friendliness, and application difficulty, requiring further improvement. This invention, through the research and development of green fire-retardant coatings, improves the performance of coatings and can provide lighter, safer, more environmentally friendly, and easier-to-apply fire-retardant materials. Summary of the Invention

[0005] To address the aforementioned shortcomings, this invention provides a magnesium cement-based fireproof coating for steel structures and its preparation method. This method utilizes a magnesium cement matrix, flame retardant, functional filler, inorganic foaming agent, and additives to prepare a lightweight magnesium cement-based fireproof coating for steel structures with a long fire resistance limit, without adding polymer latex binders or generating harmful gases. This fully meets the requirements of the "Fireproof Coatings for Steel Structures" standard and solves the problems of balancing fire resistance performance and environmental protection requirements, durability and ease of construction, adaptability to different substrates, and aging of fireproof coatings.

[0006] The technical solution of this invention is:

[0007] A magnesium cement-based fireproof coating for steel structures, characterized in that the composition of the magnesium cement-based fireproof coating for steel structures is:

[0008] Matrix: The binder consists of brucite powder, potassium dihydrogen phosphate, and a retarder. The molar ratio of MgO to potassium dihydrogen phosphate in the brucite is 4 / 1 to 5 / 1; the retarder consists of borax and citric acid, both of which are added at 5% of the mass of MgO in the brucite.

[0009] Functional fillers: one or more of mica powder, talc powder, bentonite, aluminum tripolyphosphate, fly ash, metakaolin, and slag powder, with an admixture amount of 20-30% of the total mass of brucite powder and potassium dihydrogen phosphate; one or more of polymer fibers and mineral fibers, with an admixture amount of 1-2% of the total mass of brucite powder and potassium dihydrogen phosphate.

[0010] Flame retardant: at least one of expanded perlite, expanded vermiculite, polystyrene foam particles, vitrified microspheres, aluminum hydroxide powder, and calcium silicate powder, with an admixture amount of 5-10% of the matrix mass.

[0011] Inorganic foaming agent: one or more of potassium bicarbonate, sodium bicarbonate, calcium carbonate, calcium magnesium carbonate, potassium aluminum sulfate, and ammonium nitrite, with a dosage of 1-3% of the matrix mass.

[0012] Additives: These include hydroxypropyl methylcellulose and nano-silica. The amount of hydroxypropyl methylcellulose is 1-2% of the matrix mass; the amount of nano-silica is 0.5-1.5% of the matrix mass.

[0013] The brucite powder has a particle size of 30-150 μm, an MgO content of >50%, and an MgCO3 content of >5%; potassium dihydrogen phosphate, borax, and citric acid are all of industrial purity.

[0014] In the functional filler, the mica powder and talc powder have a particle size of 50-150 μm; the bentonite contains ≥85% montmorillonite; and the fly ash is spherical ultrafine fly ash with a particle size of 1-10 μm and a specific surface area of ​​700-1000 m². 2 / kg; the particle size of metakaolin is 1-10μm, and the activity index is greater than 100;

[0015] The polymer fibers include polypropylene fibers, polyvinyl alcohol fibers, polyacrylonitrile fibers, and polyamide fibers, with an average diameter of 5-10 μm and a length of 1-3 mm; the mineral fibers include aluminum silicate fibers, high-silica fibers, glass fibers, and ceramic fibers.

[0016] The flame retardant comprises expanded perlite with a particle size of 1-3 mm and a thermal conductivity of 0.035-0.055 W / (m·K); expanded vermiculite with a particle size of 1-3 mm and a thermal conductivity of 0.05-0.1 W / (m·K); polystyrene foam particles with a particle size of 1.5-3 mm, a wall thickness of 0.5 mm, and a thermal conductivity of 0.033-0.043 W / (m·K); vitrified microspheres with a thermal conductivity ≤0.070 W / (m·K), a water absorption rate <50%, and a melting temperature of 1200℃; and aluminum hydroxide powder and calcium silicate powder with a particle size of 50-180 μm.

[0017] The foaming agent has a foaming capacity of 270-350 ml / g.

[0018] The above-mentioned method for preparing magnesium cement-based fireproof coatings for steel structures is characterized by the following steps:

[0019] (1) First, remove rust, dust, impurities and oil stains from the surface of the steel structure to keep the surface clean.

[0020] (2) First, mix potassium dihydrogen phosphate, retarder, flame retardant, functional filler and water evenly, then add magnesia powder and additives, and finally add inorganic foaming agent to obtain magnesium cement-based steel structure fireproof coating.

[0021] (3) Apply the magnesium cement-based fireproof coating for steel structure prepared in step (2) to the surface of the steel structure substrate within 30 minutes. The thickness of the bottom layer coating is 1-3 mm. After the bottom layer expands and dries, the thickness of each main layer coating is controlled within 5 mm until the coating thickness required by the design is achieved.

[0022] (4) Place the coated specimen from step (3) horizontally on the test bench with the coating side facing up and dry for 7 days. Then conduct physical and chemical tests and fire resistance limit tests on the fireproof coating for steel structures.

[0023] The coating method of the magnesium cement-based fireproof coating for steel structures is characterized in that the coating method includes, but is not limited to, spraying, brushing, rolling, and troweling.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1) Lightweight and highly fire-resistant

[0026] This invention utilizes a combination of magnesium cement, inorganic foaming agent, and flame retardant to improve the thermal insulation performance of fire-retardant coatings for steel structures. Magnesia hydrate contains MgCO3, which generates a stable gas in a phosphate environment, resulting in a lighter structure, reduced coating density, and thus reduced heat transfer, slowing the temperature rise of the steel structure in a fire. Simultaneously, the addition of functional fillers improves the compressive strength and impact resistance of the coating, enhancing its durability. This invention selects mineral admixtures and fibers as functional fillers for magnesium phosphate cement fire-retardant coatings. Polymer fibers effectively prevent coating peeling during fire, while composite fiber enhances residual mechanical properties after high temperatures.

[0027] 2) Strong adhesion to the matrix

[0028] Silicate cement is typically used as the binder for non-intumescent fire-retardant coatings. However, silicate cement exhibits poor alkali resistance and durability over long-term use. Furthermore, some fire-retardant coatings use melamine as a foaming agent to improve fire resistance; however, melamine releases ammonia gas during the reaction, causing environmental pollution and contradicting current environmental protection requirements. The magnesium cement calcination process used in this invention requires less clay resources than silicate cement, making it a sustainable binder. One of its raw materials, natural brucite powder, is a high-temperature resistant material, and magnesium cement demonstrates superior durability and bonding properties compared to traditional silicate cement.

[0029] 3) Reduced carbon emissions

[0030] Compared to traditional fire-resistant materials, magnesia cement has lower carbon emissions and can make extensive use of mining solid waste, which is of great significance for promoting the synergistic effect of reducing pollution and carbon emissions and for the sustainable development of the ecological environment. When preparing magnesia cement, natural brucite powder is used instead of magnesium oxide obtained through high-temperature calcination, greatly reducing energy consumption, and the preparation process is simple. Furthermore, relevant literature shows that magnesia cement absorbs carbon dioxide during the molding process (approximately 0.4 tons of carbon dioxide per ton of magnesia cement), with total energy consumption 1 / 2 lower than silicate cement and 2 / 3 lower than gypsum, and carbon dioxide emissions approximately 1 / 2 that of silicate cement and 2 / 3 that of gypsum.

[0031] 4) The construction process is simple and saves time and costs.

[0032] Existing non-intumescent fire-retardant coatings for steel structures require the addition of large amounts of polymer latex (adhesive) during application. Adding adhesive thickens the coating, increasing application difficulty, leading to uneven coating, and prolonged drying time, thus extending the entire application process. This not only impacts the application process but may also reduce the coating's fire-retardant performance, preventing it from achieving the desired fire-retardant effect. This invention utilizes the high adhesiveness of magnesium phosphate cement in the production of the fire-retardant coating for steel structures. This is because soluble phosphates react with iron to form iron phosphate compounds, resulting in not only physical adhesion but also a strong binding force due to the dense hydration structure. This not only reduces the complexity of the application process but also effectively prevents the coating from peeling off the steel surface, thus reducing the fire protection effect. The inorganic foamed fire-retardant coating can be applied by brushing, rolling, or spraying, offering flexible application methods and adaptability to various substrate surfaces. Simultaneously, the inorganic foaming agent improves the coating's application performance, making it easier to apply to steel structure surfaces and enhancing the uniformity and integrity of the coating. Detailed Implementation

[0033] To further demonstrate the effectiveness of this invention, the following detailed description is provided in conjunction with specific application examples.

[0034] Example 1

[0035] A magnesium-based cement-based fireproof coating for steel structures, with the following formulation and preparation steps:

[0036] 1. The composition of magnesium cement-based fireproof coating for steel structures is:

[0037] Matrix: The binder consists of brucite powder, potassium dihydrogen phosphate, and a retarder. The molar ratio of MgO to potassium dihydrogen phosphate in the brucite is 4 / 1; the retarder consists of borax and citric acid, both added at 5% of the mass of MgO in the brucite.

[0038] The functional fillers are mica powder and polypropylene fiber. The amount of mica powder is 20% of the total mass of brucite powder and potassium dihydrogen phosphate, and the amount of polypropylene fiber is 2% of the total mass of brucite powder and potassium dihydrogen phosphate.

[0039] Expanded perlite is used as the flame retardant, and its dosage is 10% of the matrix mass.

[0040] Potassium bicarbonate is selected as the inorganic foaming agent, and its dosage is 1.5% of the matrix mass.

[0041] Additives: including hydroxypropyl methylcellulose and nano-silica. The amount of hydroxypropyl methylcellulose is 2% of the matrix mass, and the amount of nano-silica is 1% of the matrix mass.

[0042] 2. The brucite powder has a particle size of 80 μm, an MgO content of 52%, an MgCO3 content of 6%, and potassium dihydrogen phosphate, borax, and citric acid are all of industrial purity.

[0043] 3. The mica powder has a particle size of 100μm, the polypropylene fiber has a diameter of 6μm and a length of 2mm; the expanded perlite has a particle size of 2mm and a thermal conductivity of 0.038W / (m·K); and the foaming agent potassium bicarbonate has a foaming amount of 270ml / g.

[0044] 4. A method for preparing fire-retardant coatings for magnesium cement steel structures, the steps of which are:

[0045] (1) First, remove rust, dust, impurities and oil stains from the surface of the steel structure to keep the surface clean.

[0046] (2) First, mix potassium dihydrogen phosphate, retarder, flame retardant, functional filler and water evenly, then add magnesia powder and additives, and finally add inorganic foaming agent to obtain magnesium cement-based steel structure fireproof coating.

[0047] (3) Apply the magnesium cement-based fireproof coating for steel structure prepared in step (2) to the surface of the steel structure substrate within 30 minutes. The thickness of the bottom layer is 2 mm. After the bottom layer expands and dries, apply the main layer 4 mm each time until the coating thickness reaches 16 mm.

[0048] (4) Place the coated specimen from step (3) horizontally on the test bench with the coating side facing up and dry for 7 days. Then conduct physical and chemical tests and fire resistance limit tests on the fireproof coating for steel structures.

[0049] Example 2

[0050] A magnesium-based cement-based fireproof coating for steel structures, with the following formulation and preparation steps:

[0051] 1. The composition of magnesium cement-based fireproof coating for steel structures is:

[0052] Matrix: The binder consists of brucite powder, potassium dihydrogen phosphate, and a retarder. The MgO / potassium dihydrogen phosphate molar ratio in the brucite is 4.5 / 1; the retarder consists of borax and citric acid, both added at 5% of the MgO mass in the brucite.

[0053] The functional fillers are talc powder and polyvinyl alcohol fiber. The amount of talc powder is 25% of the total amount of brucite powder and potassium dihydrogen phosphate, and the amount of polyvinyl alcohol fiber is 1.5% of the total mass of brucite powder and potassium dihydrogen phosphate.

[0054] The flame retardant is composed of expanded perlite and vitrified microspheres (mass ratio 3:1), with a total dosage of 7.5% of the matrix mass. The inorganic foaming agent is sodium bicarbonate, with a dosage of 2% of the matrix mass.

[0055] Additives: including hydroxypropyl methylcellulose and nano-silica. The amount of hydroxypropyl methylcellulose is 2% of the matrix mass, and the amount of nano-silica is 1% of the matrix mass.

[0056] 2. The brucite powder has a particle size of 100 μm, an MgO content of 58%, an MgCO3 content of 8%, and potassium dihydrogen phosphate, borax, and citric acid are all of industrial purity.

[0057] 3. The talc powder has a particle size of 100 μm; the polyvinyl alcohol fiber has a diameter of 6 μm and a length of 1.5 mm; the expanded perlite has a particle size of 3 mm and a thermal conductivity of 0.04 W / (m·K); the vitrified microspheres have a thermal conductivity of 0.070 W / (m·K), a water absorption rate of 30%, and a melting temperature of 1200℃; the foaming agent sodium bicarbonate has a foaming amount of 280 ml / g.

[0058] 4. A method for preparing fire-retardant coatings for magnesium cement steel structures, the steps of which are:

[0059] (1) First, remove rust, dust, impurities and oil stains from the surface of the steel structure to keep the surface clean.

[0060] (2) First, mix potassium dihydrogen phosphate, retarder, flame retardant, functional filler and water evenly, then add magnesia powder and additives, and finally add inorganic foaming agent to obtain magnesium cement-based steel structure fireproof coating.

[0061] (3) Apply the magnesium cement-based fireproof coating for steel structure prepared in step (2) to the surface of the steel structure substrate within 30 minutes. The thickness of the bottom layer is 2 mm. After the bottom layer expands and dries, apply the main layer 4 mm each time until the coating thickness reaches 16 mm.

[0062] (4) Place the coated specimen from step (3) horizontally on the test bench with the coating side facing up and dry for 7 days. Then conduct physical and chemical tests and fire resistance limit tests on the fireproof coating for steel structures.

[0063] Example 3

[0064] A magnesium-based cement-based fireproof coating for steel structures, with the following formulation and preparation steps:

[0065] 1. The composition of magnesium cement-based fireproof coating for steel structures is:

[0066] Matrix: The binder consists of brucite powder, potassium dihydrogen phosphate, and a retarder. The molar ratio of MgO to potassium dihydrogen phosphate in the brucite is 4 / 1; the retarder consists of borax and citric acid, both added at 5% of the mass of MgO in the brucite.

[0067] The functional fillers are fly ash and polyacrylonitrile fiber. The fly ash content is 20% of the total mass of brucite powder and potassium dihydrogen phosphate, and the polyacrylonitrile fiber content is 2% of the total mass of brucite powder and potassium dihydrogen phosphate. The flame retardant is expanded vermiculite, with a total content of 10% of the matrix mass.

[0068] The inorganic foaming agent is calcium carbonate, and the dosage is 1.5% of the matrix mass.

[0069] Additives: including hydroxypropyl methylcellulose and nano-silica. The amount of hydroxypropyl methylcellulose is 2% of the matrix mass, and the amount of nano-silica is 1% of the matrix mass.

[0070] 2. The brucite powder has a particle size of 120 μm, an MgO content of 55%, an MgCO3 content of 7%, and potassium dihydrogen phosphate, borax, and citric acid are all of industrial purity.

[0071] 3. The fly ash is spherical ultrafine fly ash with a particle size of 5μm and a specific surface area of ​​800m². 2 / kg; the diameter of the polyacrylonitrile fiber is 7μm and the length is 1.5mm; the particle size of the expanded vermiculite is 2mm and the thermal conductivity is 0.06W / (m·K); the foaming agent calcium carbonate has a foaming amount of 274ml / g.

[0072] 4. A method for preparing fire-retardant coatings for magnesium cement steel structures, the steps of which are:

[0073] (1) First, remove rust, dust, impurities and oil stains from the surface of the steel structure to keep the surface clean.

[0074] (2) First, mix potassium dihydrogen phosphate, retarder, flame retardant, functional filler and water evenly, then add magnesia powder and additives, and finally add inorganic foaming agent to obtain magnesium cement-based steel structure fireproof coating.

[0075] (3) Apply the magnesium cement-based fireproof coating for steel structure prepared in step (2) to the surface of the steel structure substrate within 30 minutes. The thickness of the bottom layer is 2 mm. After the bottom layer expands and dries, apply the main layer 4 mm each time until the coating thickness reaches 16 mm.

[0076] (4) Place the coated specimen from step (3) horizontally on the test bench with the coating side facing up and dry for 7 days. Then conduct physical and chemical tests and fire resistance limit tests on the fireproof coating for steel structures.

[0077] Example 4

[0078] A magnesium-based cement-based fireproof coating for steel structures, with the following formulation and preparation steps:

[0079] 1. The composition of magnesium cement-based fireproof coating for steel structures is:

[0080] Matrix: The binder consists of brucite powder, potassium dihydrogen phosphate, and a retarder. The MgO / potassium dihydrogen phosphate molar ratio in the brucite is 4.5 / 1; the retarder consists of borax and citric acid, both added at 5% of the MgO mass in the brucite.

[0081] The functional fillers are metakaolin and polyamide fiber, with the metakaolin content being 25% of the total mass of brucite powder and potassium dihydrogen phosphate, and the polyamide fiber content being 1.5% of the total mass of brucite powder and potassium dihydrogen phosphate; the flame retardant is expanded vermiculite and vitrified microspheres (mass ratio 2:1), with a total content of 7.5% of the matrix mass.

[0082] The inorganic foaming agent is calcium magnesium carbonate, and the dosage is 2% of the matrix mass.

[0083] Additives: including hydroxypropyl methylcellulose and nano-silica. The amount of hydroxypropyl methylcellulose is 2% of the matrix mass, and the amount of nano-silica is 1% of the matrix mass.

[0084] 2. The brucite powder has a particle size of 140 μm, an MgO content of 60%, an MgCO3 content of 6%, and potassium dihydrogen phosphate, borax, and citric acid are all of industrial purity.

[0085] 3. The metakaolin has a particle size of 5 μm and an activity index of 105; the polyamide fiber has a diameter of 5 μm and a length of 1.5 mm; the expanded vermiculite has a particle size of 1.5 mm and a thermal conductivity of 0.05 W / (m·K); the vitrified microspheres have a thermal conductivity of 0.060 W / (m·K), a water absorption rate of 40%, and a melting temperature of 1200℃; the foaming agent, calcium magnesium carbonate, has a foaming amount of 274 ml / g.

[0086] 4. A method for preparing fire-retardant coatings for magnesium cement steel structures, the steps of which are:

[0087] (1) First, remove rust, dust, impurities and oil stains from the surface of the steel structure to keep the surface clean.

[0088] (2) First, mix potassium dihydrogen phosphate, retarder, flame retardant, functional filler and water evenly, then add magnesia powder and additives, and finally add inorganic foaming agent to obtain magnesium cement-based steel structure fireproof coating.

[0089] (3) Apply the magnesium cement-based fireproof coating for steel structure prepared in step (2) to the surface of the steel structure substrate within 30 minutes. The thickness of the bottom layer is 2 mm. After the bottom layer expands and dries, apply the main layer 4 mm each time until the coating thickness reaches 16 mm.

[0090] (4) Place the coated specimen from step (3) horizontally on the test bench with the coating side facing up and dry for 7 days. Then conduct physical and chemical tests and fire resistance limit tests on the fireproof coating for steel structures.

[0091] Comparative Example 1

[0092] This comparative example uses a non-expanding ordinary silicate cement-based fireproof coating for steel structures, which is mainly composed of ordinary silicate cement, fillers (expanded vermiculite, vitrified microspheres), polymer latex (powder), and additives (defoamer, anti-settling agent).

[0093] Comparative Example 2

[0094] This comparative example uses a non-expanding gypsum-based fireproof coating for steel structures, which is mainly composed of gypsum, expanded perlite, aluminum silicate fiber cotton, and adhesive (polymer latex).

[0095] As can be seen from the comparative examples and embodiments (Tables 1-2), the performance of the magnesium cement-based fireproof coating for steel structures of the present invention is significantly better than that of ordinary silicate cement-based and gypsum-based fireproof coatings for steel structures. The lowest dry density in the embodiments can reach 530 kg / m³. 3 Its compressive strength can reach up to 1.3 MPa, and its bonding strength can reach up to 0.33 MPa. Compared with ordinary silicate cement-based fireproof coatings for steel structures, its dry density is reduced by 13.1% and its compressive strength is increased by 160%; compared with gypsum-based fireproof coatings for steel structures, its dry density is reduced by 14.5% and its compressive strength is increased by 117%.

[0096] As shown in Table 2, within the range of the formula in this patent, the reduction in insulation efficiency is as follows: heat resistance to exposure to heat reaches 15-17%; damp heat resistance reaches 17-19%; freeze-thaw cycle resistance reaches 15-17%; thermal cycle resistance reaches 14-16%; water resistance reaches 14-16%; acid resistance reaches 16-18%; alkali resistance reaches 15-16%; salt spray corrosion resistance reaches 15-17%; ultraviolet radiation resistance reaches 16-18%; and the fire resistance limit can reach 3-4 hours.

[0097] Table 1. Composition of different embodiments and comparative examples

[0098]

[0099] Table 2. Experimental tests of fire-retardant coatings in different embodiments and comparative examples.

[0100]

[0101] Note: The tests include heat resistance test, damp heat resistance test, freeze-thaw cycle resistance test, thermal cycling resistance test, water resistance test, and acid resistance test.

[0102] The characterization method for alkali resistance test, salt spray corrosion resistance test and ultraviolet radiation resistance test is the amount of heat insulation efficiency reduction.

[0103] The experimental results clearly show that, within the scope of the patent claims, this invention, without adding polymer latex binders or generating harmful gases, can fully utilize the beneficial effects of the aforementioned raw materials by adjusting the ratio of magnesium cement, functional fillers, and inorganic foaming agents, thereby improving the physical and chemical properties of the fire-retardant coating. Simultaneously, the durability and fire resistance limit of the magnesium cement-based fire-retardant coating for steel structures are significantly improved. Therefore, this invention provides a method for preparing a lightweight magnesium cement-based fire-retardant coating for steel structures with a long fire resistance limit, fully meeting the requirements of the "Fire-retardant Coatings for Steel Structures" standard. It can be widely used and has great application prospects in the field of fire-retardant coatings.

[0104] Finally, the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.

Claims

1. A magnesia cement based fireproofing coating for steel structures, characterized in that, The composition of the magnesium cement-based steel structure fireproof coating is: The base: the binder is brucite powder, potassium dihydrogen phosphate, and retarder; the molar ratio of MgO in brucite to potassium dihydrogen phosphate is 4 / 1-5 / 1; the retarder is borax and citric acid, and the mixing amount of both is 5% of the mass of MgO in brucite; the particle size of the brucite powder is 30-150 μm, the content of MgO is >50%, and the content of MgCO3 is >5%; potassium dihydrogen phosphate, borax, and citric acid are all industrial pure; Functional fillers: one or more of mica powder, talc powder, bentonite, aluminum tripolyphosphate, fly ash, metakaolin, and slag powder, the mixing amount is 20-30% of the total mass of brucite powder and potassium dihydrogen phosphate; one or more of polymer fibers and mineral fibers, the mixing amount is 1-2% of the total mass of brucite powder and potassium dihydrogen phosphate; Flame retardants: one or more of expanded perlite, expanded vermiculite, vitrified microbeads, aluminum hydroxide powder, and calcium silicate powder, the mixing amount is 5-10% of the mass of the base; Inorganic foaming agent: one or more of potassium bicarbonate, sodium bicarbonate, calcium carbonate, and calcium-magnesium carbonate, the mixing amount is 1-3% of the mass of the base; Auxiliary agents are hydroxypropyl methyl cellulose and nano silicon oxide; the mixing amount of hydroxypropyl methyl cellulose is 1-2% of the mass of the base; the mixing amount of nano silicon oxide is 0.5-1.5% of the mass of the base; Water; The preparation method of the coating comprises the following steps: (1) first remove rust, dust, impurities, and oil stains on the surface of the steel structure to keep the surface clean; (2) mix potassium dihydrogen phosphate, retarder, flame retardant, and functional fillers with water and stir until uniform, then add brucite powder and auxiliary agents, and finally add inorganic foaming agent to obtain the magnesium cement-based steel structure fireproof coating; (3) apply the magnesium cement-based steel structure fireproof coating prepared in step (2) to the surface of the steel structure base within 30 min, the thickness of the bottom layer is 1-3 mm, and the thickness of each main layer is controlled to be less than 5 mm after the bottom layer is dried until the designed coating thickness is reached; (4) place the coated test piece horizontally on the test bench with the coating facing up and dry for 7 d.

2. The magnesium oxychloride based fireproof coating for steel structure according to claim 1, characterized in that, In the functional filler, the particle size of mica powder and talc powder is 50-150 μm; the content of montmorillonite in bentonite is ≥ 85%; the fly ash is spherical super-fine fly ash, the particle size is 1-10 μm, and the specific surface area is 700-1000 m 2 / kg; the particle size of metakaolin is 1-10 μm, and the activity index is greater than 100.

3. The magnesium oxychloride based fireproof coating for steel structure according to claim 1, characterized in that, The polymer fibers include polypropylene fibers, polyvinyl alcohol fibers, polyacrylonitrile fibers, and polyamide fibers, the average diameter is 5-10 μm, and the length is 1-3 mm; the mineral fibers include aluminum silicate fibers, high-silica fibers, glass fibers, and ceramic fibers.

4. The magnesium oxychloride based fireproof coating for steel structure according to claim 1, characterized in that, In the flame retardant, the particle size of expanded perlite is 1-3 mm, and the thermal conductivity is 0.035-0.055 W / (m·K); the particle size of expanded vermiculite is 1-3 mm, and the thermal conductivity is 0.05-0.1 W / (m·K); the thermal conductivity of vitrified microbeads is ≤0.070 W / (m·K), the water absorption rate is <50%, and the melting temperature is 1200 ℃; the particle size of aluminum hydroxide powder and calcium silicate powder is 50-180 μm.

5. The magnesium oxychloride based fireproof coating for steel structure according to claim 1, characterized in that, The foaming amount of the foaming agent is 270-350 ml / g.

6. The magnesium oxychloride based fireproof coating for steel structure according to claim 1, characterized in that, The coating method is spraying, brushing, rolling, or smearing.

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