A method for preparing autoclaved aerated blocks by using circulating fluidized bed ash and magnesium slag

Abstract

This invention discloses a method for preparing autoclaved aerated concrete (AAC) blocks using circulating fluidized bed ash and magnesium slag. The AAC blocks prepared using circulating fluidized bed ash and magnesium slag have the following raw material composition by weight percentage: 70%~75% circulating fluidized bed ash, 10%~15% magnesium slag, 6%~9% lime, 1%~3% cement, 1%~3% gypsum, and 0.10%~0.12% aluminum powder, with a water-to-solid ratio controlled at 0.65~0.72. The preparation process of the AAC blocks using circulating fluidized bed ash and magnesium slag includes: raw material pretreatment, raw material mixing, casting and static curing, autoclaving, and cutting. The compressive strength of the AAC blocks prepared using circulating fluidized bed ash and magnesium slag can reach 3.5~3.8 MPa, and the dry density is 573~621 kg / m³. 3 The autoclaved aerated concrete (AAC) blocks use circulating fluidized bed ash as the siliceous raw material and magnesium slag partially replaces cement and lime as the calcareous raw material. Autoclaving effectively activates the activity of the circulating fluidized bed ash and magnesium slag, and eliminates their potential expansion hazards. This invention achieves large-scale resource utilization of circulating fluidized bed ash and magnesium slag, with a short preparation cycle, and significant economic, environmental, and social benefits.

Description

Technical Field

[0001] This invention belongs to the field of autoclaved aerated concrete (AAC) block preparation technology. It relates to a method for preparing AAC blocks using circulating fluidized bed ash and magnesium slag. Background Technology

[0002] Circulating fluidized bed (CFB) ash is a solid waste generated from coal combustion in CFB boilers. Currently, the main disposal method for CFB ash is open-air stockpiling, which not only occupies a large amount of land resources but also easily induces air, soil, and groundwater pollution, causing significant ecological and environmental risks. Therefore, promoting the resource-efficient utilization of CFB ash is of great practical significance and application value for reducing and disposing of solid waste and improving the regional ecological environment.

[0003] Magnesium slag is an industrial waste residue emitted during the production of metallic magnesium, with C2S as its main mineral component. The large-scale discharge of magnesium slag not only occupies land resources but also causes soil alkalization and pollution. Most of the C2S in magnesium slag is γ-C2S, which has very low activity at room temperature but can be activated under high temperature and high pressure conditions. Magnesium slag also contains a large amount of f-CaO and MgO, which can cause volume expansion when used in cement-based materials, adversely affecting their volume stability and strength.

[0004] Autoclaved aerated concrete (AAC) blocks are porous, lightweight building materials suitable for use in walls, floors, roofs, and other applications. Currently, AAC blocks are primarily produced using siliceous raw materials such as fly ash and quartz sand, along with cement and lime as calcareous materials. However, the high cost of cement and lime contributes to the high cost of AAC blocks. Utilizing industrial waste to replace some of the cement and lime in AAC block production is an effective way to achieve solid waste resource utilization and reduce production costs.

[0005] Circulating fluidized bed ash contains a certain amount of active SiO2 and Al2O3, exhibiting pozzolanic activity and potential cementitious properties. It can replace fly ash and quartz sand as siliceous raw materials for the preparation of autoclaved aerated concrete (AAC) blocks. However, the f-CaO contained in the circulating fluidized bed ash easily leads to poor volume stability of the product. C2S in magnesia slag reacts rapidly under high temperature and pressure, potentially partially replacing cement and lime as calcareous raw materials for AAC block preparation. However, the γ-C2S in magnesia slag has extremely low hydration reactivity at room temperature, and its contained f-CaO and MgO easily produce an expansion effect. This invention proposes a novel AAC block preparation scheme that uses circulating fluidized bed ash to replace traditional siliceous raw materials and utilizes magnesia slag to partially replace cement and lime in the preparation of AAC blocks. This not only eliminates the inherent defects of circulating fluidized bed ash and magnesia slag but also significantly reduces the amount of cement and lime used, thereby lowering production costs and realizing the resource utilization of circulating fluidized bed ash and magnesia slag. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing autoclaved aerated concrete (AAC) blocks using circulating fluidized bed ash and magnesium slag. By replacing traditional siliceous raw materials with circulating fluidized bed ash and partially replacing cement and lime with magnesium slag, the production cost of AAC blocks is reduced. Through autoclaving, the activity of the circulating fluidized bed ash and magnesium slag is effectively activated, solving the technical problems of poor volume stability and low activity of the circulating fluidized bed ash and magnesium slag. This invention achieves the technology of preparing high-performance AAC blocks within a short production cycle using circulating fluidized bed ash as the main siliceous raw material and magnesium slag partially replacing cement and lime as the calcareous material.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing autoclaved aerated concrete (AAC) blocks using circulating fluidized bed ash and magnesium slag, characterized in that the AAC blocks prepared using circulating fluidized bed ash and magnesium slag have the following raw material mass percentage composition: 70%~75% circulating fluidized bed ash, 10%~15% magnesium slag, 6%~9% lime, 1%~3% cement, 1%~3% gypsum, and 0.10%~0.12% aluminum powder, with a water-to-solid ratio controlled at 0.65~0.72.

[0008] According to the above scheme, the circulating fluidized bed ash is composed of 40%~60% circulating fluidized bed ash and 40%~60% circulating fluidized bed slag.

[0009] According to the above scheme, the circulating fluidized bed ash is dried at 95~110℃ for 2~4h and ball-milled for 10~30min, and its particle size is ≤200µm.

[0010] According to the above scheme, the circulating fluidized bed slag is dried at 95~110℃ for 2~4h and ball-milled for 30~50min, and its particle size is ≤200µm.

[0011] According to the above scheme, the chemical composition of the circulating fluidized bed ash is as follows: SiO2 45.0~51.0%, Al2O3 17.0~21.0%, Fe2O3 4.0~5.0%, CaO 13.0~17.0%, MgO 1.5~2.5%, K2O 1.0~2.5%, Na2O 0.5~1.2%, SO3 1.0~2.5%.

[0012] According to the above scheme, the chemical composition of the circulating fluidized bed slag is as follows: SiO2 49.0~56.0%, Al2O3 19.0~23.5%, Fe2O3 4.5~5.8%, CaO 9.0~13.0%, MgO 1.8~3.0%, K2O 0.7~1.8%, Na2O 0.3~0.9%, SO3 0.4~1.2%.

[0013] According to the above scheme, after the magnesium slag is dried at 95~110℃ for 2~4h and ball-milled for 40~60min, its particle size is ≤200µm.

[0014] According to the above scheme, the chemical composition of the magnesium slag is as follows: SiO2 26.0~32.0%, Al2O3 0.5~1.8%, Fe2O3 3.0~5.0%, CaO 55.0~63.0%, MgO 5.0~8.5%, K2O 0.01~0.10%, Na2O 0.05~0.20wt.%, SO3 0.01~0.10%.

[0015] According to the above scheme, the desulfurized gypsum is used as an auxiliary agent to control the setting time, and the CaSO4 content is ≥85%.

[0016] According to the above scheme, the cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength ≥42.5MPa.

[0017] According to the above scheme, the CaO content in the lime is >95.0%.

[0018] According to the above scheme, the aluminum powder is used as a gas-generating agent, and the active aluminum content is ≥91%.

[0019] The present invention discloses a method for preparing autoclaved aerated concrete blocks using circulating fluidized bed ash and magnesium slag, characterized by comprising the following steps:

[0020] A. Pretreatment of raw materials

[0021] The circulating fluidized bed ash, magnesium slag, lime, and gypsum were placed in a drying oven at 90-105℃ and dried until the moisture content was <1%, then ground for later use. The particle size of the circulating fluidized bed ash, magnesium slag, lime, and gypsum after ball milling was ≤200µm.

[0022] B. Raw material mixing

[0023] First, dry-mix the ground circulating fluidized bed ash, magnesium slag, lime, cement, and gypsum according to the specified proportions. Then, add water at 40-60℃ and mix thoroughly with a stirrer for 2-3 minutes. Next, add aluminum powder and stir again for 40-80 seconds.

[0024] C. Pouring and Static Curing

[0025] The mixed slurry is poured into a 15 cm × 15 cm × 15 cm steel mold, and the mold is placed together in an oven and cured at 40~60℃ for 3~6 hours. After curing, the mold is removed and a sample is taken.

[0026] D. Steam curing

[0027] After demolding, the sample is placed in an autoclave for 7-10 hours, with the curing pressure controlled at 1.0-1.4 MPa and the temperature maintained at 175-200℃.

[0028] E. Cutting

[0029] After autoclaving, the samples are cut to the specified size using a cutting machine and stacked neatly.

[0030] The principle of this invention is as follows:

[0031] Circulating fluidized bed ash contains a certain amount of active SiO2 and Al2O3, exhibiting pozzolanic activity and potential cementing properties, making it a suitable siliceous raw material for preparing autoclaved aerated concrete (AAC) blocks. However, the f-CaO contained in the circulating fluidized bed ash easily leads to poor volume stability of the product. Magnesia slag has a chemical and mineral composition similar to cement, possessing the potential to replace conventional cement and lime as a calcareous raw material for preparing AAC blocks. However, the C2S in magnesium slag mainly exists in the form of low-activity γ-C2S, with extremely low hydration reaction at room temperature. Furthermore, the f-CaO and MgO contained in magnesium slag easily produce an expansion effect, damaging the block structure and posing significant application drawbacks. This invention employs an autoclaving process to synergistically stimulate the cementing activity of both circulating fluidized bed ash and magnesium slag, effectively eliminating the expansion hazards they themselves cause. Under the high-temperature and high-pressure autoclaving environment, the f-CaO in the circulating fluidized bed ash can fully participate in the hydrothermal reaction and be consumed in advance, fundamentally solving the problem of volume stability failure in the later stages of product preparation. Meanwhile, the hydration rate of inert γ-C2S in magnesium slag is significantly enhanced under high temperature and high pressure conditions, sustainably providing Ca(OH)2 for the hydrothermal synthesis reaction of the system. This effectively promotes the formation of a large number of tobermorite crystals, optimizes the microscopic pore structure and crystal stacking state inside the blocks, and significantly improves the overall mechanical strength of circulating fluidized bed ash and magnesium slag-based autoclaved aerated concrete blocks. This invention can effectively solve the volume stability problems easily caused by circulating fluidized bed ash and the inherent material defects of magnesium slag, such as low room temperature activity and expansion effect. It enables the use of magnesium slag to replace part of the cement in the production of autoclaved aerated concrete blocks to reduce production costs and achieves efficient and stable resource utilization of two types of industrial solid waste.

[0032] Compared with existing aerated concrete blocks and their preparation processes, the autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag proposed in this invention has the following advantages:

[0033] (1) The present invention can realize the high utilization of circulating fluidized bed ash and slag, with a content of 70%~75% and magnesium slag content of 10%~15%, which can replace half of the cement and lime content of conventional autoclaved aerated blocks. The cement content can be reduced to 1% and the lime content can be reduced to 6%, effectively reducing the production cost of autoclaved aerated blocks.

[0034] (2) The autoclaved aerated concrete blocks prepared by the present invention using circulating fluidized bed ash and magnesium slag have a compressive strength of 3.5~3.8MPa and a dry density of 573~621kg / m³. 3 This product combines excellent mechanical strength with lightweight properties. All performance parameters meet the requirements of the national standard GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks". Detailed Implementation

[0035] To better understand the technical solution of the present invention, the technical solution provided by the present invention will be described in detail below with reference to embodiments.

[0036] In the following embodiments, the chemical composition of the circulating fluidized bed ash is as follows: SiO2 52.49%, Al2O3 22.09%, CaO 9.65%, Fe2O3 5.85%, SO3 2.71%, MgO 1.79%, and loss on ignition 3.03%.

[0037] The chemical composition of the circulating fluidized bed slag is as follows: SiO2 52.50%, Al2O3 21.25%, Fe2O3 5.15%, CaO 11.00%, MgO 2.40%, K2O 1.25%, Na2O 0.60%, SO3 0.80%.

[0038] The circulating fluidized bed ash, after being dried at 100℃ for 3 hours and ball-milled for 20 minutes, has a particle size ≤200µm.

[0039] The circulating fluidized bed slag, after being dried at 100℃ for 3 hours and ball-milled for 45 minutes, has a particle size ≤200µm.

[0040] The magnesium slag, after being dried at 100℃ for 3 hours and ball-milled for 50 minutes, has a particle size ≤200µm.

[0041] The chemical composition of the magnesium slag is as follows: SiO2 29.0%, Al2O3 1.15%, Fe2O3 4.0%, CaO 59.0%, MgO 6.75%, K2O 0.05%, Na2O 0.12%, SO3 0.05%.

[0042] The desulfurized gypsum is used as an aid to control the setting time, and its CaSO4 content is 85%.

[0043] The cement is P·O 42.5 ordinary Portland cement with a 28-day compressive strength of 45.2 MPa.

[0044] The lime contains 96.0% CaO.

[0045] The aluminum powder is used as a gas-generating agent, and its active aluminum content is 91%.

[0046] Example 1

[0047] The raw material composition of an autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag is shown in Table 1:

[0048] Table 1 Raw material ratios for Example 1

[0049]

[0050] The preparation process includes the following steps:

[0051] A. Pretreatment of raw materials

[0052] The circulating fluidized bed ash, magnesium slag, lime, and gypsum were placed in a 100℃ drying oven and dried until the moisture content was <1%, then ground for later use. The particle size of the circulating fluidized bed ash, magnesium slag, lime, and gypsum after ball milling was ≤200µm.

[0053] B. Raw material mixing

[0054] First, dry-mix the ground circulating fluidized bed ash, magnesium slag, lime, cement, and gypsum according to the specified proportions. Then, add water at 50°C and mix thoroughly with a stirrer for 2 minutes. Next, add aluminum powder and stir again for 60 seconds.

[0055] C. Pouring and Static Curing

[0056] The mixed slurry was poured into a 15 cm × 15 cm × 15 cm steel mold, and the mold was placed together in an oven and cured at 45°C for 6 hours. After curing, the mold was removed and samples were taken.

[0057] D. Steam curing

[0058] After demolding, the sample was placed in an autoclave for 7 hours, with the curing pressure controlled at 1.2 MPa and the temperature maintained at 190℃.

[0059] E. Cutting

[0060] After autoclaving, the sample was cut into 10 cm × 10 cm × 10 cm cubes using a cutting machine.

[0061] According to the national standard GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks", the various properties of an autoclaved aerated concrete block prepared in Example 1 using circulating fluidized bed ash and magnesium slag were tested, and the results are shown in Table 2.

[0062] Table 2 Performance indicators of autoclaved aerated concrete blocks prepared in Example 1

[0063]

[0064] Example 2

[0065] The raw material composition of an autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag is shown in Table 3:

[0066] Table 3 Raw material ratios for Example 2

[0067]

[0068] The preparation process includes the following steps:

[0069] A. Pretreatment of raw materials

[0070] The circulating fluidized bed ash, magnesium slag, lime, and gypsum were placed in a 100℃ drying oven and dried until the moisture content was <1%, then ground for later use. The particle size of the circulating fluidized bed ash, magnesium slag, lime, and gypsum after ball milling was ≤200µm.

[0071] B. Raw material mixing

[0072] First, dry-mix the ground circulating fluidized bed ash, magnesium slag, lime, cement, and gypsum according to the specified proportions. Then, add water at 50°C and mix thoroughly with a stirrer for 2 minutes. Next, add aluminum powder and stir again for 60 seconds.

[0073] C. Pouring and Static Curing

[0074] The mixed slurry was poured into a 15 cm × 15 cm × 15 cm steel mold, and the mold was placed together in an oven and cured at 45°C for 6 hours. After curing, the mold was removed and samples were taken.

[0075] D. Steam curing

[0076] After demolding, the sample was placed in an autoclave for 7 hours, with the curing pressure controlled at 1.2 MPa and the temperature maintained at 190℃.

[0077] E. Cutting

[0078] After autoclaving, the sample was cut into 10 cm × 10 cm × 10 cm cubes using a cutting machine.

[0079] According to the national standard GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks", the various properties of an autoclaved aerated concrete block prepared in Example 2 using circulating fluidized bed ash and magnesium slag were tested, and the results are shown in Table 4.

[0080] Table 4 Performance indicators of autoclaved aerated concrete blocks prepared in Example 2

[0081]

[0082] Example 3

[0083] The raw material composition of an autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag is shown in Table 5:

[0084] Table 5 Raw material ratios for Example 3

[0085]

[0086] The preparation process includes the following steps:

[0087] A. Pretreatment of raw materials

[0088] The circulating fluidized bed ash, magnesium slag, lime, and gypsum were placed in a 100℃ drying oven and dried until the moisture content was <1%, then ground for later use. The particle size of the circulating fluidized bed ash, magnesium slag, lime, and gypsum after ball milling was ≤200µm.

[0089] B. Raw material mixing

[0090] First, dry-mix the ground circulating fluidized bed ash, magnesium slag, lime, cement, and gypsum according to the specified proportions. Then, add water at 50°C and mix thoroughly with a stirrer for 2 minutes. Next, add aluminum powder and stir again for 60 seconds.

[0091] C. Pouring and Static Curing

[0092] The mixed slurry was poured into a 15 cm × 15 cm × 15 cm steel mold, and the mold was placed together in an oven and cured at 45°C for 6 hours. After curing, the mold was removed and samples were taken.

[0093] D. Steam curing

[0094] After demolding, the sample was placed in an autoclave for 7 hours, with the curing pressure controlled at 1.2 MPa and the temperature maintained at 190℃.

[0095] E. Cutting

[0096] After autoclaving, the sample was cut into 10cm×10cm×10cm cubes using a cutting machine.

[0097] According to the national standard GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks", the various properties of an autoclaved aerated concrete block prepared in Example 3 using circulating fluidized bed ash and magnesium slag were tested, and the results are shown in Table 6.

[0098] Table 6 Performance indicators of autoclaved aerated concrete blocks prepared in Example 3

[0099]

[0100] The above embodiments demonstrate that the present invention uses circulating fluidized bed ash as the main siliceous raw material, partially replaces cement and lime with magnesium slag, and combines it with autoclaving to prepare autoclaved aerated concrete blocks. The overall process is scientifically feasible. The prepared autoclaved aerated concrete blocks meet all the requirements of GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks".

[0101] The proportions and process parameters (time, temperature, etc.) involved in this invention are not limited to the above embodiments, and can be implemented within the range of values.

Claims

1. An autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag, characterized in that, The raw materials are composed of the following percentages by weight: 70%~75% circulating fluidized bed ash, 10%~15% magnesium slag, 6%~9% lime, 1%~3% cement, 1%~3% gypsum, and 0.10%~0.12% aluminum powder, with the water-to-solid ratio controlled at 0.65~0.

72.

2. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The circulating fluidized bed ash is composed of 40% to 60% circulating fluidized bed ash and 40% to 60% circulating fluidized bed slag.

3. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The circulating fluidized bed ash is dried at 95~110℃ for 2~4h and ball-milled for 10~30min, and its particle size is ≤200µm.

4. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The circulating fluidized bed slag is dried at 95~110℃ for 2~4h and ball-milled for 30~50min, and its particle size is ≤200µm.

5. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The chemical composition of the circulating fluidized bed ash is as follows: SiO2 45.0~51.0%, Al2O3 17.0~21.0%, Fe2O3 4.0~5.0%, CaO 13.0~17.0%, MgO 1.5~2.5%, K2O 1.0~2.5%, Na2O 0.5~1.2%, SO3 1.0~2.5%.

6. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The chemical composition of the circulating fluidized bed slag is as follows: SiO2 49.0~56.0%, Al2O3 19.0~23.5%, Fe2O3 4.5~5.8%, CaO 9.0~13.0%, MgO 1.8~3.0%, K2O 0.7~1.8%, Na2O 0.3~0.9%, SO3 0.4~1.2%.

7. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The magnesium slag is dried at 95-110℃ for 2-4 hours and ball-milled for 40-60 minutes, and its particle size is ≤200µm.

8. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The chemical composition of the magnesium slag is as follows: SiO2 26.0~32.0%, Al2O3 0.5~1.8%, Fe2O3 3.0~5.0%, CaO 55.0~63.0%, MgO 5.0~8.5%, K2O 0.01~0.10%, Na2O 0.05~0.20wt.%, SO3 0.01~0.10%.

9. The autoclaved aerated concrete block prepared using circulating fluidized bed ash and magnesium slag according to claim 1, characterized in that, The lime contains >95.0% CaO.

10. A method for preparing autoclaved aerated concrete blocks using circulating fluidized bed ash and magnesium slag according to any one of claims 1 to 9, characterized in that, Includes the following steps: A. Pretreatment of raw materials The circulating fluidized bed ash, magnesium slag, lime, and gypsum were placed in a drying oven at 90-105℃ and dried until the moisture content was <1%, then ground for later use. The particle size of the circulating fluidized bed ash, magnesium slag, lime, and gypsum after ball milling was ≤200µm. B. Raw material mixing First, dry-mix the ground circulating fluidized bed ash, magnesium slag, lime, cement, and gypsum according to the specified proportions. Then, add water at 40-60℃ and mix thoroughly with a stirrer for 2-3 minutes. Next, add aluminum powder and stir again for 40-80 seconds. C. Pouring and Static Curing The mixed slurry is poured into a 15 cm × 15 cm × 15 cm steel mold, and the mold is placed together in an oven and cured at 40~60℃ for 3~6 hours. After curing, the mold is removed and a sample is taken. D. Steam curing After demolding, the sample is placed in an autoclave for 7-10 hours, with the curing pressure controlled at 1.0-1.4 MPa and the temperature maintained at 175-200℃. E. Cutting After autoclaving, the samples are cut to the specified size using a cutting machine and stacked neatly.

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