Preparation method of flame-retardant aerated concrete block

Abstract

The invention discloses a preparation method of a flame-retardant aerated concrete block, relates to the field of concrete blocks, and successfully prepares an aerated concrete block with good flame retardant property and mechanical property through a series of rigorous process steps such as proportioning, stirring, pouring and aerating, cutting, autoclaved curing and the like. According to the method, cement and lime are used as cementing materials to provide strength, sand is used as an aggregate supporting structure, aluminum powder is aerated to form pores, and magnesium hydroxide or aluminum hydroxide is used as a flame retardant to endow the flame-retardant property; the preparation accuracy, the stirring uniformity, the control of pouring gas generation, the cutting precision, the temperature, the pressure, the time and other parameters of autoclaved curing are set in stages, the temperature rise, the pressure rise, the temperature reduction and the pressure reduction speed are correspondingly and reasonably controlled, the building blocks are prevented from being damaged due to the too large internal and external temperature difference and the too large pressure difference, the rejection rate of the building blocks is reduced, and the production cost is reduced. The strength and the flame-retardant effect of the building block are furthest ensured.

Description

Technical Field

[0001] The invention relates to the technical field of concrete blocks, in particular to a method for preparing a flame retardant aerated concrete block. Background Art

[0002] With the rapid development of the modern construction industry, the performance requirements for building materials are increasing day by day. Aerated concrete blocks are widely used due to their excellent properties such as light weight, thermal insulation, sound absorption and sound insulation. However, in some places with high requirements for fire safety, such as high-rise buildings, shopping malls, hospitals, etc., the flame retardant properties of ordinary aerated concrete blocks can no longer meet the needs.

[0003] For example, Chinese patent CN103332921B discloses a fire-retardant aerated concrete block and a preparation method thereof, which is made of the following raw materials in parts by weight: 15-20 of cement, 10-15 of quicklime, 8-12 of gypsum, 20-25 of loess, 0.2-0.3 of aluminum powder, 1-2 of cellulose ether, 20-25 of corn stalk powder, 10-15 of pepper vine powder, 8-10 of oil feet, 3-5 of aluminum hydroxide, 3-5 of ammonium alum, 2-3 of ammonium persulfate, and 10-15 of sodium metasilicate.

[0004] However, in the prior art, the heating, pressure increase, cooling and pressure reduction speeds during the autoclave curing process are not precisely controlled. Rapid temperature and pressure changes can easily cause cracks or deformation in the green body, affecting the strength and flame retardant effect of the blocks. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a flame retardant aerated concrete block to solve the problems raised by the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing a flame retardant aerated concrete block, comprising the following steps:

[0007] S1. Weigh cement, lime, sand, aluminum powder and flame retardant according to the designed proportion, and dry mix the cement, lime and sand;

[0008] S2, add appropriate amount of water and mix wet, then add aluminum powder and flame retardant and mix again;

[0009] S3, pouring the stirred slurry into a mold and transferring it to a curing room for gasification;

[0010] S4. Cut the gasified green body into suitable shapes and sizes according to the actual required block size;

[0011] S5. Put the cut green body into the autoclave for autoclave curing. Specific steps:

[0012] S51. First, the air in the autoclave must be evacuated, and then the temperature and pressure are slowly increased. The temperature increase rate is generally controlled at 1-2°C / minute, and the pressure increase rate is controlled at 0.05-0.1MPa / minute;

[0013] S52, after reaching the set temperature and pressure, maintaining constant temperature and pressure for a period of time;

[0014] S53. After the curing is completed, the pressure and temperature should be slowly reduced. The pressure reduction rate is generally controlled at 0.05-0.1MPa / minute, and the temperature reduction rate is controlled at 1-2℃ / minute;

[0015] S6. After the autoclave curing is completed, the blocks are taken out from the autoclave for inspection.

[0016] Preferably, in step S1, the raw materials include 10-30 parts by weight of cement, 10-25 parts by weight of lime, 40-0 parts by weight of sand, 0.04-0.08 parts by weight of aluminum powder and 5-15 parts by weight of flame retardant.

[0017] Preferably, the fineness modulus of the sand is between 2.3 and 3.0, and the flame retardant is magnesium hydroxide or aluminum hydroxide and the particle size is generally required to be between 1 and 100 μm.

[0018] Preferably, in step S1, cement, lime and sand are put into a mixer for dry mixing for 3-5 minutes, and the rotation speed is controlled at 20-30 rpm.

[0019] Preferably, in the step S2, it specifically includes:

[0020] S21. After dry mixing and stirring, water is added for wet mixing, the water-cement ratio is between 0.5-0.7, and the stirring time is 5-8 minutes;

[0021] S22. Add aluminum powder and flame retardant, and stir for another 1-2 minutes, with the speed controlled at 30-40 rpm.

[0022] Preferably, in the step S3, it specifically includes:

[0023] S31. Before pouring, apply a release agent inside the mold;

[0024] S32, when pouring, slowly and evenly pour the slurry into the mold;

[0025] S33, the mold is transferred to a curing room for gasification, the temperature is controlled at 40-60°C and the relative humidity is controlled at 70%-90%, and the gasification time is 1-2 hours.

[0026] Preferably, in step S4, cutting is performed within 30-60 minutes after the gas generation is completed, using a wire cutting saw, with the wire tension controlled between 100-200N and the cutting speed being 1-2 m / min.

[0027] Preferably, in the step S5, it specifically includes:

[0028] S51. Place the blocks after leaving the autoclave in a well-ventilated and dry place for natural cooling to remove floating dust and impurities on the surface;

[0029] S52. Inspect the finished products. Inspection items include compressive strength, dry density and flame retardant properties. Qualified products can be packaged.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. In this method, cement and lime are used as cementitious materials to provide strength, sand is used as aggregate support structure, aluminum powder is used to generate gas to form pores, magnesium hydroxide or aluminum hydroxide is used as flame retardant to impart flame retardant properties, and parameters such as accuracy of ingredients, uniformity of mixing, control of gas generation during pouring, precision of cutting, and temperature, pressure and time of autoclave curing are set in stages, and the speeds of heating, pressure increase, cooling and pressure reduction are all reasonably controlled accordingly to avoid damage to blocks due to excessive internal and external temperature and pressure differences, reduce the scrap rate of blocks, and maximize the strength and flame retardant effect of blocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flowchart of a method for preparing a flame retardant aerated concrete block. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the implementation regulations described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example: Refer to Figure 1 As shown: A method for preparing a flame retardant aerated concrete block, comprising the following steps:

[0035] Step 1: Weigh cement, lime, sand, aluminum powder and flame retardant according to the designed proportion and dry mix them.

[0036] Ordinary Portland cement is used as cement, which has good gelling properties and stability. The strength grade is usually 42.5, which can provide moderate early and late strength to meet the strength development requirements of aerated concrete blocks at different curing stages;

[0037] Cement undergoes a hydration reaction after adding water. The generated hydration products, such as calcium silicate gel, bind other raw material particles together to form a solid matrix structure, giving the block strength. Its dosage generally accounts for 10%-30% of the total dry material. For example, when preparing 1 cubic meter of aerated concrete blocks, the total amount of several materials is about 700kg, and the amount of cement can be adjusted between 70-210kg. Too little cement will lead to insufficient strength of the block, while too much cement may affect other properties of the block, such as increased shrinkage.

[0038] Lime is quicklime, and the effective calcium content is required to be above 70%. High effective calcium content can quickly generate calcium hydroxide after reacting with water, providing a sufficient alkaline environment for the subsequent gasification reaction of aluminum powder and promoting the smooth progress of the gasification process;

[0039] Lime and cement act together as cementitious materials, and they work together in the hydration process to further enhance the strength of the block. Its dosage accounts for about 10%-25% of the total dry material. An appropriate amount of lime helps to improve the pore structure and durability of the block, but excessive use may cause the carbonization shrinkage of the block to increase, affecting its long-term stability.

[0040] Sand can be river sand or machine-made sand. River sand particles are relatively round and soft; machine-made sand has sharp edges and a rough surface. The fineness modulus of sand is generally between 2.3-3.0. This fineness of sand can ensure that the blocks have sufficient skeleton strength while giving the slurry good fluidity and plasticity, which is conducive to casting and uniform distribution of pores.

[0041] Sand is the main aggregate of aerated concrete blocks, and its usage accounts for 40%-70% of the total dry material. A higher sand content can increase the volume stability and compressive strength of the blocks, but if the amount of sand is too large, the viscosity of the slurry will increase, affecting the gas generation effect, resulting in uneven pore structure, thereby reducing the thermal insulation performance of the blocks.

[0042] Aluminum powder is used as a gas-generating agent, and its active aluminum content should be above 90%. Highly active aluminum powder can quickly react with calcium hydroxide in an alkaline environment to produce hydrogen, causing the concrete paste to expand and form a pore structure;

[0043] The dosage of aluminum powder is generally 0.04%-0.08% of the total dry material. For example, the dosage of aluminum powder per cubic meter of dry material may be between 0.28-0.56kg. In an alkaline environment, the chemical equation for the reaction of aluminum powder with calcium hydroxide is: 2Al+3Ca(OH) 2 +6H 2 O→3CaO·Al 2 O 3 6H 2 O+3H 2 ↑. The hydrogen produced by the reaction forms tiny bubbles inside the slurry. As the bubbles continue to be generated and aggregated, the slurry gradually expands, and finally forms an aerated concrete body with a uniform pore structure. Too little aluminum powder will lead to insufficient gas generation and increased block density; too much aluminum powder will make the pores too large and uneven, reducing the strength and stability of the blocks.

[0044] Commonly used flame retardants include magnesium hydroxide, aluminum hydroxide, etc. Magnesium hydroxide will decompose when the temperature rises: Mg(OH) 2 →MgO+H 2 O, the reaction absorbs a lot of heat, lowering the ambient temperature, and the generated magnesium oxide is a refractory material that can prevent the spread of flames to a certain extent. The flame retardant principle of aluminum hydroxide is similar, and its decomposition reaction is: 2Al(OH) 3 →Al 2 O 3 +3H 2 O, absorbs heat and produces aluminum oxide during decomposition. Aluminum oxide has a high melting point and stability, and can play a role in heat insulation and flame retardancy;

[0045] The particle size of flame retardant is generally required to be between 1-100μm. The appropriate particle size can ensure that the flame retardant is evenly distributed in the concrete paste and give full play to its flame retardant effect. The amount of flame retardant generally accounts for 5%-15% of the total dry material. Too little flame retardant is difficult to achieve the ideal flame retardant effect, while too much may have an adverse effect on the mechanical properties and other physical properties of the block, such as reducing strength and increasing water absorption.

[0046] First, put cement, lime and sand into the mixer for dry mixing. The dry mixing time is generally 3-5 minutes, the purpose is to make these dry materials fully mixed and uniform, to prevent local composition differences. During the dry mixing process, the mixer speed should be moderate, generally controlled at 20-30 rpm, to ensure that the materials can be fully tumbled and mixed, but will not cause dust or material separation due to excessive speed.

[0047] Step 2: Add appropriate amount of water and stir wet, then add aluminum powder and flame retardant and stir again.

[0048] After dry mixing and stirring evenly, add an appropriate amount of water, and the water-cement ratio is generally between 0.5-0.7. The amount of water added should be adjusted appropriately according to the characteristics of the raw materials, ambient temperature and humidity and other factors. For example, in a high-temperature dry environment, the amount of water can be appropriately increased to ensure the fluidity of the slurry; in a low-temperature and humid environment, the amount of water should be reduced to prevent the slurry from being too thin. Continue stirring after adding water, and the wet mixing time is about 5-8 minutes to allow the material to form a uniform slurry. During the wet mixing process, pay attention to observe the fluidity of the slurry. A suitable slurry should have good fluidity, be able to fill the mold smoothly during pouring, and not have water seepage. If the slurry is not fluid enough, the mixing time can be appropriately extended or a small amount of water reducer can be added for adjustment; if water seepage occurs, the amount of water should be reduced or the amount of cementitious materials such as cement should be increased;

[0049] Finally, add aluminum powder and flame retardant and stir for another 1-2 minutes. Since the amount of aluminum powder and flame retardant is relatively small, it is necessary to ensure that they are evenly dispersed in the slurry. When stirring, the speed of the mixer can be appropriately increased, generally controlled at 30-40 rpm, so that the aluminum powder and flame retardant can be quickly and evenly dispersed in the slurry. At the same time, avoid stirring for too long to prevent the aluminum powder from gassing prematurely or the flame retardant from agglomerating.

[0050] Step 3: Pour the stirred slurry into the mold and transfer it to the curing room for gasification.

[0051] Pour the stirred slurry into the mold. The mold is generally made of steel or aluminum alloy, which has sufficient strength and rigidity to withstand the weight of the slurry and the pressure of gas expansion. The size of the mold can be designed according to the actual required size of the aerated concrete blocks, such as the common sizes of 600mm×200mm×200mm. Before pouring, a release agent, such as waste engine oil or a special release agent, should be applied to the inside of the mold to facilitate demolding of the blank and prevent damage to the surface of the block during demolding. When pouring, pour the slurry into the mold slowly and evenly to avoid generating bubbles or impacting the mold wall, which will affect the quality and appearance of the blank;

[0052] After pouring, the slurry begins to gas and expand due to the reaction of aluminum powder with calcium hydroxide in the slurry to produce hydrogen. The gassing process needs to be carried out under certain temperature (generally 40-60°C) and humidity (relative humidity 70%-90%) conditions, and this environment can be controlled by the curing room. In the early stage of gassing, the gassing of the slurry should be closely observed to ensure uniform gassing. If it is found that the local gassing is too fast or too slow, it may be caused by uneven mixing of raw materials or fluctuations in environmental conditions. Measures should be taken in time to adjust it, such as adjusting the temperature and humidity of the curing room or gently stirring the unevenly gassed parts. The gassing time is about 1-2 hours. After the gassing is completed, the green body should have a uniform pore structure and a smooth surface.

[0053] Step 4: Cut the aerated green body into suitable shapes and sizes according to the actual required block size.

[0054] When the slurry has finished gassing, its strength is still relatively low. At this time, it can be cut using cutting equipment. Cutting equipment generally includes wire cutting saws, etc. Wire cutting saws have the advantages of high cutting accuracy and little damage to the blank. The timing of cutting is critical. Cutting too early will cause the blank to collapse and deform, while cutting too late will make the blank too strong, increase the difficulty of cutting, and even damage the cutting equipment. Generally, it is more appropriate to cut within 30-60 minutes after the gassing ends. At this time, the blank has a certain strength and can maintain a stable shape, but it is not too hard.

[0055] According to the actual required block size, the gasified green body is cut into suitable shapes and sizes. The cutting process should be gentle to avoid damaging the pore structure of the green body. When cutting, the tension of the steel wire should be moderate, generally controlled between 100-200N, and the cutting speed should not be too fast, generally 1-2 meters / minute. At the same time, to ensure the cutting accuracy, the cutting size deviation should be controlled within ±2mm to ensure that the size of the block meets the construction requirements.

[0056] Step 5: Place the cut green body into an autoclave for autoclave curing.

[0057] Autoclaving is a key step in the preparation of aerated concrete blocks. The principle is that under high temperature and high pressure conditions, the hydration reaction of cementitious materials such as cement and lime is accelerated to generate more hydration products, thereby significantly improving the strength of the blocks. At the same time, the high temperature and high pressure environment also helps to improve the pore structure of the blocks, making them more dense and uniform, and improving the durability and stability of the blocks;

[0058] The curing temperature is generally 180-200℃, the pressure is 1.0-1.3MPa, and the curing time is 6-12 hours. During the autoclave curing process, the air in the autoclave must first be emptied, and then the temperature and pressure must be slowly increased. The heating rate is generally controlled at 1-2℃ / minute, and the pressure increase rate is controlled at 0.05-0.1MPa / minute to prevent the green body from cracking or deforming due to rapid changes in temperature and pressure. After reaching the set temperature and pressure, maintain constant temperature and pressure for a period of time to allow the cementitious material to fully hydrate. After the curing is completed, the pressure and temperature must be slowly reduced. The pressure reduction rate is generally controlled at 0.05-0.1MPa / minute, and the cooling rate is controlled at 1-2℃ / minute to prevent the blocks from being damaged due to excessive internal and external temperature and pressure differences.

[0059] Step 6. After the autoclave curing is completed, the blocks are taken out from the autoclave for inspection. The main inspection items include compressive strength, dry density and flame retardant properties.

[0060] After the autoclave curing is completed, the blocks are taken out of the autoclave. At this time, the blocks have high strength and good flame retardant properties. During the process of taking the blocks out of the autoclave, be careful to avoid collision and falling to prevent damage to the blocks. The blocks should be placed in a well-ventilated and dry place for natural cooling and sorting, remove the dust and impurities on the surface, and make the surface of the blocks clean;

[0061] The finished products are inspected, and the main inspection items include compressive strength, dry density, flame retardant properties, etc. The compressive strength is generally required to reach 3.5-7.5MPa, which can be tested using a pressure testing machine according to the standard (GB / T11969-2020). The dry density is generally 500-700kg / m 3 The flame retardant performance must meet the relevant building fire protection standards, such as the combustion performance level reaching A1 or A2, etc., and can be tested with oxygen index tester, cone calorimeter and other equipment. Qualified products can be packaged and sold for use in building walls and other fields. Unqualified products should be analyzed and processed to find out the reasons and correct them in time.

[0062] In this method, cement and lime are used as cementitious materials to provide strength, sand is used as aggregate support structure, aluminum powder is used to generate gas to form pores, and magnesium hydroxide or aluminum hydroxide is used as a flame retardant to impart flame retardant properties. During the preparation process, parameters such as accuracy of ingredients, uniformity of mixing, control of gas generation during pouring, precision of cutting, and temperature, pressure and time of autoclave curing are set in stages, and the speeds of heating, increasing pressure, cooling and reducing pressure are all reasonably controlled accordingly to avoid damage to the blocks due to excessive temperature and pressure differences between inside and outside. Each link is carefully operated and reasonably controlled to produce high-quality flame-retardant aerated concrete blocks that meet the needs of the construction industry, which helps to improve the fire safety and energy-saving and thermal insulation performance of buildings, and promote the construction industry to develop in a greener and safer direction.

[0063] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a flame retardant aerated concrete block, characterized in that: The following steps are involved: S1. Weigh cement, lime, sand, aluminum powder and flame retardant according to the designed proportion, and dry mix the cement, lime and sand; S2, add appropriate amount of water and mix wet, then add aluminum powder and flame retardant and mix again; S3, pouring the stirred slurry into a mold and transferring it to a curing room for gasification; S4. Cut the gasified green body into suitable shapes and sizes according to the actual required block size; S5. Put the cut green body into the autoclave for autoclave curing. Specific steps: S51. First, the air in the autoclave must be evacuated, and then the temperature and pressure are slowly increased. The temperature increase rate is generally controlled at 1-2°C / minute, and the pressure increase rate is controlled at 0.05-0.1MPa / minute; S52, after reaching the set temperature and pressure, maintaining constant temperature and pressure for a period of time; S53. After the curing is completed, the pressure and temperature should be slowly reduced. The pressure reduction rate is generally controlled at 0.05-0.1MPa / minute, and the temperature reduction rate is controlled at 1-2℃ / minute; S6. After the autoclave curing is completed, the blocks are taken out from the autoclave for inspection.

2. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In step S1, the raw materials include 10-30 parts by weight of cement, 10-25 parts by weight of lime, 40-0 parts by weight of sand, 0.04-0.08 parts by weight of aluminum powder and 5-15 parts by weight of flame retardant.

3. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: The fineness modulus of the sand is between 2.3 and 3.0, and the flame retardant is magnesium hydroxide or aluminum hydroxide and the particle size is generally required to be between 1 and 100 μm.

4. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In the step S1, cement, lime and sand are put into a mixer for dry mixing for 3-5 minutes, and the rotation speed is controlled at 20-30 rpm.

5. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In the step S2, it specifically includes: S21. After dry mixing and stirring, water is added for wet mixing, the water-cement ratio is between 0.5-0.7, and the stirring time is 5-8 minutes; S22, add aluminum powder and flame retardant, and stir for another 1-2 minutes, with the speed controlled at 30-40 rpm.

6. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In the step S3, it specifically includes: S31. Before pouring, apply a release agent inside the mold; S32, when pouring, slowly and evenly pour the slurry into the mold; S33, the mold is transferred to a curing room for gasification, the temperature is controlled at 40-60°C and the relative humidity is controlled at 70%-90%, and the gasification time is 1-2 hours.

7. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In the step S4, cutting is specifically performed within 30-60 minutes after the gas generation is completed, using a wire cutting saw, with the wire tension controlled between 100-200N and the cutting speed being 1-2 m / min.

8. The method for preparing a flame retardant aerated concrete block according to claim 1, characterized in that: In the step S5, it specifically includes: S51. Place the blocks after leaving the autoclave in a well-ventilated and dry place for natural cooling to remove floating dust and impurities on the surface; S52. Inspect the finished products. Inspection items include compressive strength, dry density and flame retardant properties. Qualified products can be packaged.

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