Gypsum-based steel structure fireproof coating

Abstract

A gypsum-based steel structure fireproof coating is characterized by comprising the following components in parts by weight: 450-550 parts of gypsum, 80-120 parts of modified fibers, 160-240 parts of modified closed-cell expanded perlite, 80-120 parts of light calcium carbonate, 40-60 parts of mica, 4-6 parts of glass fibers, 10-15 parts of latex powder, 1-3 parts of cellulose and 2-4 parts of a retarder, the fire endurance of the coating is 2.5-2.9 h according to the coating thickness of 25 mm, and the fire endurance of the coating is 0.5-1.5 h according to the coating thickness of 25 mm. And the compressive strength is 1.3 to 1.6 Mpa.

Description

Technical Field

[0001] The present invention relates to a gypsum-based steel structure fireproof coating, which adopts a closed-cell expanded perlite that can be prepared by gas furnace expansion and has excellent strength and water resistance, and has excellent water resistance, strength and low cost. Background Art

[0002] With the development of steel structure application technology and the increasing maturity of steel structure fire protection technology, steel structures, as a form of high-rise building structures, have been widely used in the construction industry due to their high strength, good plasticity and toughness, light self-weight, good extensibility, seismic resistance and short construction period. Although steel belongs to non-combustible materials, its fire resistance is very poor. So far, four main measures have been taken to protect steel structures: namely, direct cladding protection method, shielding protection method, water spray and flushing and cooling protection method. Among the four measures, the direct cladding method is the most commonly used in engineering due to its simplicity, good protection performance and economic cost. The direct cladding method refers to directly applying fireproof materials such as building clay bricks, pouring concrete, plastering, spraying fireproof coatings and enclosing fireproof boards on the surface or periphery of steel structure components to enclose or cover the exposed steel components, so as to achieve the purpose of improving the fire resistance of steel structures. Among them, fireproof coatings can be divided into intumescent fireproof coatings and non-intumescent fireproof coatings.

[0003] Non-intumescent fireproof coatings mainly rely on their own non-combustibility, low thermal conductivity and heat absorption to protect buildings. One type forms a protective layer during the fireproof process, which can also play a role in isolating oxygen, so that oxygen cannot contact the flammable substances to be protected, thus avoiding or reducing the combustion reaction; the other type is the crystal water bound in the material, which is released when encountering fire, so that the critical temperature of the materials to be protected including steel bars is about 100 °C until all the water is released. The thermal conductivity of this type of product itself is relatively low, and it is a good heat insulator.

[0004] The application scenarios of non - intumescent fire - retardant coatings mainly include various places such as indoor concealed places, steel structures, concrete tunnel linings, petrochemical industries, outdoor use, and chip workshops. Thick - type steel - structure fire - retardant coatings are generally used for indoor steel structures where the fire - resistance limit requirement exceeds 2 hours, such as columns in high - rise civil buildings and columns supporting multiple floors in general industrial and civil buildings. Among them, the main components of inorganic non - intumescent fire - retardant coatings include binders (ordinary Portland cement, high - alumina cement, and gypsum), flame retardants (gypsum powder or other substances containing crystal water such as bauxite, kaolin), light fillers (expanded vermiculite, polystyrene particles, expanded perlite, sepiolite, fly ash cenospheres, etc.), fibers (aluminum silicate fiber, glass fiber, sepiolite fiber), polymers (including emulsions and redispersible polymer powder), fillers, and other additives such as retarders, accelerators, cellulose ethers, air - entraining agents, etc. Generally speaking, the mainstream products on the market are lightweight cement (gypsum) mortars containing expanded vermiculite, where expanded vermiculite serves as a lightweight heat - insulating filler. All steel - structure fire - retardant coatings must meet the performance requirements of the national standard for steel - structure fire - retardant coatings (GB14907 - 2018).

[0005] At present, there have been many studies on non-expansive fireproof coatings with gypsum as the binder in the industry. CN107176815A discloses a gypsum-based steel structure fireproof protection material containing reinforcing fibers. The fireproof protection material is prepared by mixing the following components by mass percentage: 82%-95% of desulfurized gypsum, 3%-15.5% of lightweight heat-insulating material, 0.5%-2% of reinforcing fibers, 0.1%-0.5% of water retention agent, 0.1%-1% of redispersible latex powder, 0.1%-0.5% of retarder, and 0.01%-0.1% of air-entraining agent; the lightweight heat-insulating material is one or two of vitrified microspheres, closed-cell expanded perlite, expanded vermiculite, or flaky mica; the reinforcing fibers are one or two of glass fibers, sepiolite fibers, aluminum silicate fibers, or polypropylene fibers. Among them, the closed-cell expanded perlite is prepared by means of electric furnace heating. Through gradient heating of perlite ore sand and precise control of the residence time, the surface of the product is melted, the pores are closed, the internal honeycomb structure remains unchanged, and the shape is irregular particles. The closed-cell expanded perlite not only has the advantages of light weight, fireproof, and green environmental protection of traditional expanded perlite, but also overcomes the disadvantages of large water absorption rate, low strength, and poor fluidity of traditional expanded perlite. The bulk density of the used closed-cell expanded perlite is 120-150 kg / m3, the volume water absorption rate is below 50%, and the thermal conductivity is less than 0.05 W / (m·K). CN112679184A discloses a gypsum-based non-expansive steel structure fireproof coating. Fireproof coating is a simple and effective means for steel structure fire protection, and the fireproof and flame-retardant effect is achieved by adding lightweight and high flash point filling materials to the cementitious material. The present invention finds that in current gypsum-based fireproof materials, a large amount of polystyrene particles are added as filling materials. However, the above materials are flammable under high temperature conditions and release a large amount of harmful gases. In view of the above research status, it provides an optimized gypsum-based fireproof coating, which is composed of 390-450 parts of gypsum, 85-135 parts of lightweight filling material, 20-35 parts of reinforcing fibers, and 3-5 parts of retarder. The fireproof material has a simple composition. After mixing, the coating has good construction performance and fireproof performance, and is applied to the fire protection of steel structures in the construction industry. It is light in weight, environmentally friendly, and safer to use.CN112321253A discloses a multifunctional thermal insulation material, which is composed of the following components in parts by mass: gypsum: 65-85 parts; lightweight aggregate: 10-30 parts; cellulose: 0.15-0.35 parts; latex powder: 0.5-1 part; thixotropic agent: 0.05-0.1 part; retarder: 0.1-0.2 part; hydrated lime: 4-7 parts. The lightweight aggregate is one or more of vitrified microspheres, expanded perlite, polystyrene particles, ceramic microspheres, sepiolite or closed-cell perlite. The cellulose is one or more of hydroxypropyl methylcellulose, ethyl cellulose or carboxymethyl cellulose. The latex powder is one or more of redispersible latex powder, VAE latex powder or resin latex powder. The thixotropic agent is one or two of fumed silica, organic bentonite, asbestos, magnesium aluminum silicate or kaolin. The advantages are as follows: The method for preparing the multifunctional thermal insulation material of the present invention is simple and feasible. The thermal insulation material has the characteristics of low density, high strength and low thermal conductivity, which makes the subsequent construction operation simple and can save a large amount of labor.

[0006] Both expanded perlite and expanded vermiculite can be used as lightweight fireproof fillers, but their characteristics and application focuses are different. Expanded perlite has a better thermal conductivity than expanded vermiculite, and its price is usually lower than that of expanded vermiculite (about 30%-400% lower), but its water absorption rate is significantly higher than that of expanded vermiculite, which not only affects the fireproof performance of the fireproof board, but also has a greater negative impact on the forming of the fireproof board. Therefore, during actual use, hydrophobic pretreatment is required. Although this improves the waterproof property, it cannot be compared with expanded vermiculite, and the cost increases significantly. At the same time, expanded perlite is extremely easy to break, and the strength of the prepared fireproof board is poor. In recent years, compared with traditional expanded perlite (open pores), closed-cell expanded perlite and vitrified microspheres have been developed, and their water absorption rate and compressive strength have been significantly improved, but they also have obvious problems. First of all, both closed-cell expanded perlite and vitrified microspheres are produced by precisely controlling the gradient heating and residence time of the raw material ore sand to make the surface of the product melt and the pores close. This requires very strict temperature control of the production process, and low-cost gas furnaces cannot meet the requirements. Since electric furnaces have higher temperature control advantages than gas furnaces, in actual production at present, both closed-cell expanded perlite and vitrified microspheres must be produced by electric furnaces, and their cost is much higher than that of the gas furnaces used for open-cell expanded perlite. Secondly, the low closed-cell rate of closed-cell expanded perlite has always been a difficult problem in the industry. The closed-cell rate obtained by general processes is only close to 60%. Although some literatures claim that it exceeds 70% or even more than 80%, in technical discussions in the industry and actual sold products, industry experts have a consensus that it is difficult for the closed-cell rate of mass-produced closed-cell expanded perlite to exceed 70%, and the performance of different batches is unstable. Relatively speaking, vitrified microspheres have a higher closed-cell rate and better performance, but the production of vitrified microspheres has high requirements for raw materials and can only use dacrylitic rock in perlite, with low output, complex process and high cost.

[0007] As can be seen from the above patents and technology market analysis, the lightweight thermal insulation materials currently used in steel structure fireproof coatings still mainly rely on expanded vermiculite with excellent performance. Even when expanded perlite is used, as described in CN107176815A, the closed-cell expanded perlite used therein is produced by the method of electric furnace heating. Through gradient heating of perlite ore sand and precise control of the residence time, the surface of the product is melted, the pores are closed, the internal honeycomb structure remains unchanged, and the shape is irregular granular. Although it overcomes the disadvantages of traditional expanded perlite such as high water absorption, low strength, and poor fluidity, the process is complex and the cost is extremely high. Although its volume water absorption can reach below 25%, there is still a certain gap compared with expanded vermiculite. This results in a loose and rough surface after the coating is formed, and there are also gaps in waterproofness and strength compared with the fireproof coating using expanded vermiculite as the lightweight heat insulation filler. Therefore, it has become an urgent need in the industry to develop a fireproof board with waterproofness and strength that can meet the industrial performance requirements and cost control requirements, using expanded perlite as the main lightweight fireproof filler. Summary of the Invention

[0008] The present invention relates to a gypsum-based steel structure fireproof coating, which, by weight, comprises the following components: 450-550 parts of gypsum, 80-120 parts of modified fiber, 160-240 parts of modified closed-cell expanded perlite, 80-120 parts of light calcium carbonate, 40-60 parts of mica, 4-6 parts of glass fiber, 10-15 parts of re-dispersible latex powder, 1-3 parts of cellulose, and 2-4 parts of retarder. The fire resistance limit (coating thickness 25 mm) of this fireproof coating is 2.5-2.9 h, and the compressive strength (MPa) is 1.3-1.6.

[0009] Furthermore, 500 parts of gypsum, 100 parts of modified fiber, 200 parts of modified closed-cell expanded perlite, 100 parts of light calcium carbonate, 50 parts of mica, 5 parts of glass fiber, 12 parts of re-dispersible latex powder, 2 parts of cellulose, and 3 parts of retarder.

[0010] The gypsum is β building gypsum.

[0011] The retarder is one or two of sodium citrate, sodium tripolyphosphate, or sodium hexametaphosphate.

[0012] The cellulose is one or more of hydroxypropyl methylcellulose, ethyl cellulose, or carboxymethyl cellulose.

[0013] The re-dispersible latex powder includes one or two of ethylene / vinyl acetate copolymer, vinyl acetate / vinyl versatate copolymer, and acrylic copolymer.

[0014] Further, the redispersible latex powder includes one or two of ethylene / vinyl acetate copolymer, vinyl acetate / vinyl versatate copolymer, and acrylic copolymer; specifically, it can be FX3300.

[0015] Further, the modified fiber is sepiolite fiber and / or basalt fiber.

[0016] Further, the gypsum-based steel structure fireproof coating also contains 5-7 parts of aluminum hydroxide and 1.5-2.5 parts of zinc borate.

[0017] The preparation method of the fireproof coating includes the following steps: (1) Weigh gypsum, modified fiber, glass fiber, latex powder, cellulose, and retarder according to the proportion, and add them to a mixer (such as a double-screw conical mixer), and mix at a low speed for 10-15 minutes until uniform.

[0018] (2) Then add modified closed-cell expanded perlite, light calcium carbonate, and mica, and mix at a low speed for 10-15 minutes until uniform to obtain a powder material.

[0019] (3) Add water to the powder material and stir to obtain a uniform slurry. The weight ratio of the powder material to water is 1:(0.9-1.1).

[0020] The speed in step (1) or step (2) is 200-400 rpm.

[0021] Among them, the preparation method of the modified closed-cell expanded perlite includes the following steps: 1. Preheat and dry Preheat and dry the perlite raw material at a temperature of 300-450°C for a heat preservation time of 5-30 minutes to obtain a perlite raw material with a combined water moisture content of 1.5-3%.

[0022] 2. Preliminary expansion Pre-expand at a temperature of 800-900°C for 5-10 seconds, using a rotary furnace.

[0023] 3. Spray the coating material Cool the preliminarily expanded expanded perlite to room temperature. First, spray a certain amount of sodium silicate solution on its surface, then spray aluminum sulfate solution, and continuously stir for a period of time; the continuous stirring time is 5-10 minutes; 4. Secondary expansion At 1100-1150 degrees Celsius for 2-10 seconds to obtain closed-cell expanded perlite; use a gas jet type expansion furnace or a vertical expansion furnace for secondary expansion.

[0024] For the said closed-cell expanded perlite, the bulk density (Kg / m 3)(40 - 150), the thermal conductivity (at 25 °C) (w / (m*K)) is 0.035 - 0.048, the water absorption rate (for 24 h, %) is 15 - 35, the cylinder compressive strength / kPa is 150 - 220, and the volume floating rate ≥ 85%; the closed pore rate ≥ 85%.

[0025] In the preheating and drying process of Step 1, further, the preheating temperature is 400 - 450 °C, and the heat preservation time is 8 - 10 minutes; further, the preheating and drying is carried out in a rotary kiln or a vertical preheater; Further, before preheating and drying, natural perlite ore is selected and subjected to crushing and screening, divided into coarse crushing and fine crushing, and the water content is 2 - 6%; The particle size of the fine - crushed perlite is 20 - 325 mesh (45 μm - 850 μm), preferably 40 - 200 mesh (75 μm - 425 μm); The inventor also found that when applied to fire - proof materials such as coatings and perlite boards, if the raw materials are used to prepare graded expanded perlite, the heat - insulation effect is better. Through a large number of experimental studies, the preferred ratio is: the mass ratio of perlite ore with (40 - 60 mesh):(80 - 120 mesh):(140 - 200 mesh) is (1 - 3):(4 - 6):(2 - 4).

[0026] In the preliminary expansion process of Step 2, it is preferably pre - expanded at a temperature of 850 °C, and the further time is 8 - 10 seconds In the process of spraying coating in Step 3, further, the water glass solution contains 10 - 20 wt% of water glass; further, in the aluminum sulfate solution, it contains 10 - 20 wt% of aluminum sulfate; further, based on the mass of the raw materials for the reaction, the mass ratio of water glass, aluminum sulfate, and pre - expanded perlite is: (4 - 5):(3.2 - 3.6):(72 - 152). In the theoretical reaction, the molar ratio of water glass to aluminum sulfate should be 3:1, and its mass ratio is about 107:100. In actual technology development, it is found that water glass needs to be added slightly more. This may be because in the prior spraying of the water glass solution, part of the water glass is adsorbed into the pores of the pre - expanded perlite and does not participate in the subsequent reaction with aluminum sulfate.

[0027] In the secondary expansion process of Step 4, the expansion temperature is 1100 °C, and the time is 3 - 5 seconds to obtain closed - pore expanded perlite; Technical effects The present invention uses modified closed-cell expanded perlite to replace traditional expanded vermiculite as the main lightweight fireproof filler to prepare a gypsum-based steel structure fireproof coating, overcoming the negative impacts of traditional steel structure fireproof coatings on water resistance and strength. Its water resistance, strength, and fireproof performance are close to those of a steel structure fireproof protection board using expanded vermiculite as the main lightweight fireproof filler, and the cost is significantly reduced, providing a new idea of using expanded perlite instead of expanded vermiculite.

[0028] The present invention successfully uses expanded perlite as the main lightweight fireproof filler in the steel structure fireproof coating, replacing expanded vermiculite. Moreover, the water resistance, strength, and fireproof performance of the prepared fireproof coating are all close to those of the fireproof coating using expanded vermiculite as the main filler. Additionally, this expanded perlite has a simpler process compared to vitrified microspheres and a significantly reduced cost.

[0029] Regarding modified closed-cell expanded perlite, for the problem that the existing closed-cell expanded perlite has a low closed-cell rate in a gas furnace and requires an electric heating expansion furnace with precise temperature control, which has a complex process and a high cost, the present invention uses aluminum sulfate and sodium silicate to coat the pre-expanded perlite and then performs secondary expansion. Through the special pre-coating process, expanded perlite with a high closed-cell rate is prepared using a gas furnace. At the same time, the special pretreatment process also reduces the expansion temperature, greatly shortens the high-temperature expansion time, and significantly reduces the production cost and improves the production efficiency.

[0030] After secondary expansion, the surface of the expanded perlite is covered with a gray coating layer. The inventor speculates that its main components are albite, nepheline, etc. This should be due to the double decomposition reaction of aluminum sulfate and sodium silicate on the surface of the pre-expanded perlite, producing aluminum silicate and sodium sulfate. Among them, aluminum silicate may also exist in the form of a composite colloid precipitate of aluminum hydroxide and silicic acid and / or a precipitate of aluminum silicate in a small part. Under the condition of 1100 - 1150 degrees Celsius, it is obtained by the reaction of aluminum silicate, sodium sulfate with SiO2, Al2O3, etc. in the perlite. Among them, sodium sulfate may undergo a decomposition reaction. Relatively speaking, vitrified microspheres and traditional closed-cell perlite require a long time and temperature to sufficiently soften and melt the surface perlite to form a vitreous layer on the perlite surface. Currently, the expansion temperature of the traditional process is 1250 - 1300 °C, and the time is at least 5 - 20 seconds, or at most 2 - 5 minutes.

[0031] In the expansion stage of the process of the present invention, due to the use of the pre-coating technology, precise temperature control and long-time expansion are not required. Therefore, gas furnaces can be used for all equipment, instead of electric furnaces with high construction costs and operating costs. Since the closed-cell expanded perlite of the invention is compatible with the equipment of open-cell expanded perlite, the production line of open-cell expanded perlite can be directly used to produce closed-cell expanded perlite, which not only reduces the cost but also avoids the trouble of technological transformation of the production line.

[0032] Due to the adoption of the pre-coating technology, the closed-cell rate of the closed-cell expanded perlite of the present invention exceeds that of the mainstream closed-cell expanded perlite products with a closed-cell rate of 50-70% in the current market, reaching more than 90%, approaching that of vitrified microspheres, but the cost is greatly reduced compared with vitrified microspheres, and the raw material requirements are much lower than those of vitrified microspheres.

[0033] The surface-coated albite, nepheline, etc. not only have high strength but also excellent waterproofness due to their dense crystal structure and low surface energy, thus significantly improving the cylinder compressive strength and waterproofness of expanded perlite.

[0034] In addition, compared with the current finished products of spraying inorganic waterproof materials such as silica sol or water glass or organic waterproof materials such as VAE emulsion and polyurethane for closed-cell or open-cell expanded perlite, the coating material of the present invention is added during the preparation process of expanded perlite and reacts in situ to generate a dense coating layer of albite and nepheline. It not only has a high closed-cell rate but also high strength and excellent waterproofness. At the same time, the coating before the finished product reduces the phenomenon of the coating material being adsorbed into the pores, not only reducing the usage amount of the coating material but also avoiding the filling of the pores of expanded perlite by the coating material, reducing its heat insulation and fireproof performance.

[0035] In addition, the inventor also found that when using perlite ore raw materials with different mesh number combinations in the process of spraying sodium silicate and aluminum sulfate solutions after pre-expansion, the coating effect of the above composite solution is significantly higher than that of perlite ore with a single mesh number. This may be because fewer voids in perlite are beneficial to the coating of the composite solution on the surface of perlite. Secondly, the closed-cell expanded perlite products with different mesh number combinations also achieved better heat insulation and fireproof effects. This may be because the closed-cell expanded perlite with different particle sizes reduces the packing voids, prevents the formation of microscopic thermal bridges, and significantly improves the heat insulation and fireproof effects of closed-cell expanded perlite.

[0036] The present invention also further attempts to add aluminum hydroxide and zinc borate. Aluminum hydroxide absorbs heat and reduces the temperature in the medium and low temperature stages, delaying the heating of the substrate; zinc borate generates a boron silicate to enhance the stability of the heat insulation layer through carbonization and vitrification reactions at high temperatures. The two can jointly increase the smoke suppression effect. Aluminum hydroxide dehydrates to produce microcracks, and the melting and filling effect of zinc borate can reduce the cracks of aluminum hydroxide, reducing the escape of smoke. Examples

[0037] Example 1 Preparation of Closed-Cell Expanded Perlite A Select perlite ores with mesh numbers (40 - 60 mesh) : (80 - 120 mesh) : (140 - 200 mesh) respectively, with a mass ratio of 2:5:3, and stir and mix them. Preheat and dry the perlite at a temperature of 400 °C for a holding time of 10 minutes to obtain perlite ore with a combined water moisture content of less than 2%; perform preliminary expansion at a temperature of 850 °C for 8 seconds; cool the preliminarily expanded expanded perlite to room temperature, then first spray sodium silicate with a concentration of 15 wt% on its surface, and then spray aluminum sulfate with a concentration of 10 wt%. Based on the mass of the raw materials for the reaction, the mass ratio of sodium silicate, aluminum sulfate, and pre-expanded perlite is: 4.5:3.5:92, and continuously stir for 7 minutes; perform secondary expansion on the pre-expanded perlite with the coating treatment at 1100 °C for 4 seconds to obtain closed-cell expanded perlite A.

[0038] Example 2 Preparation of Closed-cell Expanded Perlite B Select perlite ore with a mesh number of 80 - 120, preheat and dry the perlite at a temperature of 400 °C for a holding time of 10 minutes to obtain perlite ore with a combined water moisture content of less than 2%; perform preliminary expansion at a temperature of 850 °C for 8 seconds; cool the preliminarily expanded expanded perlite to room temperature, then first spray sodium silicate with a concentration of 15 wt% on its surface, and then spray aluminum sulfate with a concentration of 10 wt%. Based on the mass of the raw materials for the reaction, the mass ratio of sodium silicate, aluminum sulfate, and pre-expanded perlite is: 4.5:3.5:92, and continuously stir for 7 minutes; perform secondary expansion on the pre-expanded perlite with the coating treatment at 1100 °C for 4 seconds to obtain closed-cell expanded perlite B.

[0039] Comparative Example 3 Preparation of Closed-cell Expanded Perlite C In the process of spraying the coating, only spray sodium silicate with a concentration of 15 wt%, and the mass ratio of sodium silicate to pre-expanded perlite is: 8:92. Other processes are the same as those in Example 1 to obtain closed-cell expanded perlite C.

[0040] Comparative Example 4 Preparation of Closed-cell Expanded Perlite D In the process of spraying the coating, only spray aluminum sulfate solution with a concentration of 10 wt%, and the mass ratio of aluminum sulfate to pre-expanded perlite is: 8:92. Other processes are the same as those in Example 1 to obtain closed-cell expanded perlite D.

[0041] Comparative Example 5 Preparation of Closed-cell Expanded Perlite E Omit the process of spraying the coating, cool the pre-expanded perlite to room temperature and then perform secondary high-temperature expansion. Other processes are the same as those in Step 1 to obtain closed-cell expanded perlite E.

[0042] Example 6 Preparation of Gypsum-based Steel Structure Fireproof Coatings A - E Gypsum-based fire protection material for steel structures, which is composed of the following components by weight ratio: 500 parts of gypsum, 100 parts of modified fiber, 200 parts of closed-cell expanded perlite, 100 parts of light calcium carbonate, 50 parts of mica, 5 parts of glass fiber, 12 parts of latex powder, 2 parts of cellulose, and 3 parts of retarder.

[0043] The preparation method of the fire protection coating includes the following steps: (1) Weigh gypsum, modified fiber, glass fiber, latex powder, cellulose, and retarder according to the ratio, and add them to a mixer (such as a double-screw conical mixer), and mix at a low speed of 400 rpm for 12 minutes until uniform.

[0044] (2) Then add modified closed-cell expanded perlite, light calcium carbonate, and mica, and mix at a low speed of 200 rpm for 10 minutes until uniform to obtain a powder material.

[0045] (3) Add water to the powder material and stir to obtain a uniform slurry, and the weight ratio of the powder material to water is 1:1.

[0046] Step (1) or step (2) is at 200 - 400 rpm.

[0047] Among them, the closed-cell expanded perlite uses the closed-cell expanded perlite A - E prepared in Examples 1 - 5, so as to obtain the corresponding gypsum-based fire protection coatings A - E for steel structures.

[0048] Example 7 Preparation of gypsum-based fire protection coating F for steel structures Use expanded vermiculite to replace the closed-cell expanded perlite A in Example 6, and the other raw materials and method steps are the same as those in Example 6 to prepare the gypsum-based fire protection coating F Performance test: Conduct the test according to the regulations of 《GB14907 - 2018》 Table 1 Performance of gypsum-based fire protection coatings for steel structures Gypsum-based steel structure fireproof coating Main lightweight fireproof filler Water resistance (number of days of foaming, delamination, and peeling) Fire resistance limit (coating thickness 25mm) Compressive strength (MPa) Initial drying crack resistance Fireproof coating A Closed-cell expanded perlite A Qualified 2.8h 1.48 No cracks Fireproof coating B Closed-cell expanded perlite B Qualified 2.6h 1.33 No cracks Fireproof coating C Closed-cell expanded perlite C Unqualified 1.8h 0.73 Unqualified Fireproof coating D Closed-cell expanded perlite D Unqualified 1.4h 0.55 Unqualified Fireproof coating E Closed-cell expanded perlite E Unqualified 1.5h 0.62 Unqualified Fireproof coating F Expanded vermiculite Qualified 3.0h 1.60 No cracks As can be seen from the above table, for the fire protection coating prepared by using the modified closed-cell expanded perlite prepared by the present invention as the main light fire protection filler, its water resistance, compressive strength, initial drying crack resistance, and fire resistance are close to those of the fire protection coating prepared by using expanded vermiculite as the main light fire protection filler, but its cost has decreased significantly.

Claims

1. A gypsum-based fireproof coating for steel structures, characterized in that, By weight parts, it comprises the following components: 450 - 550 parts of gypsum, 80 - 120 parts of modified fiber, 160 - 240 parts of modified closed-cell expanded perlite, 80 - 120 parts of light calcium carbonate, 40 - 60 parts of mica, 4 - 6 parts of glass fiber, 10 - 15 parts of redispersible latex powder, 1 - 3 parts of cellulose, 2 - 4 parts of retarder. Calculated by a coating thickness of 25 mm, the fire resistance limit of this coating is 2.5 - 2.9 h and the compressive strength is 1.3 - 1.6 MPa; The said modified closed-cell expanded perlite is prepared by the following steps: (1) Preheating and drying: Preheat and dry the perlite raw material at a temperature of 300 - 450 °C for a heat preservation time of 5 - 30 minutes to obtain a perlite raw material with a combined water moisture content of 1.5 - 3%; (2) Primary expansion: Pre-expand at a temperature of 800 - 900 °C for 5 - 10 seconds; (3) Cool the preliminarily expanded expanded perlite to room temperature. First, spray a certain amount of sodium silicate solution on its surface, then spray aluminum sulfate solution, and continuously stir for a period of time; The continuous stirring time is 5 - 10 minutes; (4) Secondary expansion: At 1100 - 1150 °C for 2 - 10 seconds to obtain the modified closed-cell expanded perlite.

2. The steel structure fire protection board according to claim 1, characterized in that, The modified closed-cell expanded perlite has a bulk density of 40-150 Kg / m 3 , a thermal conductivity (at 25°C) (w / (m*K)) of 0.035-0.048, a water absorption rate (for 24 hours) of 15-35%, a cylinder compressive strength of 150-220 kPa, a volume floating rate of ≥85%; and a closed-cell rate of ≥85%.

3. The gypsum-based steel structure fireproof coating according to claim 1, wherein, The said gypsum is β building gypsum.

4. The gypsum-based steel structure fireproof coating according to claim 1, wherein The said retarder is one or two of sodium citrate, sodium tripolyphosphate or sodium hexametaphosphate.

5. The gypsum-based steel structure fireproof coating according to claim 4, characterized in that, The said cellulose is one or more of hydroxypropyl methylcellulose, ethyl cellulose or carboxymethyl cellulose.

6. The gypsum-based steel structure fireproof coating according to claim 1, wherein The said redispersible latex powder includes one or two of ethylene / vinyl acetate copolymer, vinyl acetate / vinyl versatate copolymer, acrylic copolymer.

7. The gypsum-based steel structure fireproof coating according to claim 1, characterized in that, The said modified fiber is sepiolite fiber and / or basalt fiber.

8. The gypsum-based steel structure fireproof coating according to claim 1, wherein In the process of spraying the coating material in step (3), the mass ratio of sodium silicate, aluminum sulfate and pre-expanded perlite is: (4 - 5) : (3.2 - 3.6) : (72 - 152).

9. The gypsum-based steel structure fireproof coating according to claim 1, characterized in that, In the secondary expansion process of step (4), the expansion temperature is 1100 °C and the time is 3 - 5 seconds to obtain the modified closed-cell expanded perlite.

10. The gypsum-based steel structure fireproof coating according to claim 1, characterized in that, It contains 5 - 7 parts of aluminum hydroxide and 1.5 - 2.5 parts of zinc borate.