Calcaceous material special for autoclaved aerated concrete and preparation method thereof

Abstract

The application discloses a kind of calcium materials special for autoclaved aerated concrete and a preparation method thereof, the calcium materials include: 90~96wt% limestone, 2~6wt% iron raw materials, 0~2wt% gypsum, 0~2wt% silicate material, its mineral includes by mass ratio: f-CaO content is 42~55wt%, C4A3S content is 0~3wt%, the sum of C2S, C3S content is 22~45wt%, the sum of C3A, C4AF content is 5~20wt%, periclase content is 0~1.5wt%, gypsum content is 0~2wt%, other impurity mineral content is 0~6wt%.The application optimizes mineral component, especially controls the content and activity of f-CaO, guarantees the content of silicate mineral, so that mineral component ratio is beneficial to the process production and quality control of aerated concrete;Through low-temperature calcination of new dry method kiln, improve the utilization rate of calcium raw material, reduce energy consumption.

Description

Technical Field

[0001] This invention relates to the field of cementitious materials technology, specifically to a calcium-based material for autoclaved aerated concrete and its preparation method. Background Technology

[0002] Autoclaved aerated concrete (AAC) is a lightweight, porous silicate product made from calcareous materials (quicklime, cement) and siliceous materials (quartz sand, river sand, fly ash, and silica-containing tailings, etc.) as basic components, with appropriate amounts of gypsum as modifiers. The process involves grinding the calcium and silica materials into a slurry, batching, adding aluminum powder paste and other foaming agents, mixing, pouring, pre-curing, cutting, and autoclaving. AAC possesses numerous advantages, including lightweight, heat insulation, fire resistance, sound insulation, and environmental friendliness. According to incomplete statistics, fly ash accounts for approximately 80% of the total AAC production in China, while sandstone and river sand account for about 20%. Quicklime and ordinary 42.5R cement are used as calcareous raw materials, with the amount and proportion of these materials varying depending on the company's production situation. Some manufacturers use quicklime in proportions exceeding 80% of the total quicklime and cement content.

[0003] The free calcium oxide content and activity of quicklime mainly depend on its purity and degree of calcination. Currently, most quicklime supplied for autoclaved aerated concrete (AAC) production is produced in numerous traditional kilns of varying quality. These kilns suffer from unstable raw material properties, inefficient management, low calcium carbonate decomposition rates, low CaO content, and high production costs. The large fluctuations in digestion rate, digestion temperature, slurry production volume, and hydration heat release make AAC production prone to problems such as unstable slurry pouring and gas expansion, and difficulty in controlling the hardening of the green body, causing significant trouble for enterprises. At a given temperature, the calcination rate of limestone depends on its particle size: the larger the particle size, the slower the calcination rate. The decomposition of calcium carbonate in limestone proceeds layer by layer from the surface inwards. Quicklime has a lower thermal conductivity than limestone; the thicker the lime layer, the worse the thermal conductivity and the longer the heat transfer time. Furthermore, the further in the limestone, the more difficult it is for the released CO2 to escape, resulting in the CaO crystals gradually increasing in size due to prolonged exposure to high temperatures, thus slowing down the decomposition rate. Even with advanced quicklime production processes, problems such as low output, high energy consumption, and unstable quality persist. The calcination rate of limestone also depends on the particle size of the limestone and the temperature of the limestone surface, unlike cement clinker production where powdered limestone rapidly completes the decomposition reaction within the decomposition furnace and pipelines using new dry-process kilns.

[0004] With technological advancements in the aerated concrete industry, production often requires increased efficiency and reduced costs. This necessitates the use of high-grade cement or cements with faster setting and hardening rates, such as 42.5R and 52.5 silicate cement, which increases raw material costs. The most beneficial minerals for the process performance of aerated concrete systems are the active calcium in quicklime, silicate minerals in cement, and gypsum. Other admixtures, such as inert materials like limestone and inert slag, offer no benefit to the static curing process of aerated concrete and do not react during steam curing to generate structural minerals like tobermorite that contribute to performance. Therefore, a novel calcareous material system is needed to improve the utilization rate of calcareous raw materials, which would benefit the process production and quality control of aerated concrete. Summary of the Invention

[0005] The purpose of this invention is to provide a calcium-based material for autoclaved aerated concrete and its preparation method, so as to at least solve some of the above-mentioned technical problems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A calcium-based material for autoclaved aerated concrete (AAC) comprises the following raw materials in the following mass ratio:

[0008]

[0009] The calcareous material comprises, by mass ratio, 42-55 wt% f-CaO. The content is 0-3 wt%, the sum of C2S and C3S is 22-45 wt%, the sum of C3A and C4AF is 5-20 wt%, the content of periclase is 0-1.5 wt%, the content of gypsum is 0-2 wt%, and the content of other impurity minerals is 0-6 wt%; among which, It represents sulfur; S represents silicon.

[0010] The other impurity minerals include perovskite, quartz, calcareous feldspar, and potassium alum.

[0011] Furthermore, the iron raw material is at least one of non-ferrous metal ash slag, copper slag, iron tailings, iron ore, blast furnace slag, and sulfuric acid slag.

[0012] Furthermore, the gypsum is at least one of dihydrate gypsum, anhydrite, desulfurized gypsum, phosphogypsum, and desulfurized ash.

[0013] Furthermore, the silicon-aluminate material is at least one of low-grade bauxite, aluminum smelting waste, aluminum tailings, and fly ash.

[0014] A method for preparing a calcium-based material specifically for autoclaved aerated concrete includes the following steps:

[0015] S1. Crush limestone, iron raw materials, gypsum and aluminosilicate materials separately and set aside for later use;

[0016] S2. The crushed limestone, iron raw materials, gypsum and aluminosilicate materials are weighed into the raw meal mill according to the given ratio by an electronic belt scale and then dried and ground to obtain powdered materials (raw meal);

[0017] S3. Powdered materials (raw materials) are fed into a new type of dry process kiln for calcination, and then cooled by a cooler to obtain clinker;

[0018] S4. Grind the clinker into powder to obtain the calcium material.

[0019] Furthermore, in S2, the fineness of the powdered material (raw material) is such that the residue on a 0.08mm square-hole sieve is ≤22%.

[0020] Furthermore, in S3, the time from entering the kiln to exiting the kiln is 30-45 minutes, the firing temperature of the calcining zone is 1320-1380℃, and the firing time of the calcining zone is 10-15 minutes.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. This invention optimizes the mineral composition, specifically controlling the content and activity of f-CaO. At 800-900℃, CaO undergoes a solid-state reaction with SiO2, Al2O3, and Fe2O3 to generate CA and C. 12 A7, CF, C2F, and C2S react with the firing temperature to produce C3A, C4AF, C2AS, and a small amount of other compounds as the firing temperature increases further to 900-1100℃. When the temperature rises to 1100-1200℃, large amounts of C3A, C4AF, and C2S are generated. Because the KH content of this clinker is very high, free calcium oxide is encapsulated by flux minerals such as C3A, C4AF, and CaSO4, further increasing the calcination temperature. Some C2S reacts to form C3S in the presence of a certain liquid phase and a high CaO content. The final clinker's mineral composition conforms to the scope specified in the claims, and the mineral composition ratio is more beneficial to the production process and quality control of autoclaved aerated concrete. It also makes the pore structure of autoclaved aerated concrete more uniform, reduces green body sinking, and improves overall quality stability. The calcium-based material of this invention has high hydration activity and fast green body hardening speed, improving production efficiency and ensuring higher structural strength of the finished product while maintaining the required dry density.

[0023] 2. This invention solves the problem of unstable lime quality in calcined raw materials by using a novel dry kiln for low-temperature calcination, thereby improving the utilization rate of calcined raw materials and reducing energy consumption. At the same time, by using lower grade limestone, it improves resource utilization efficiency and reduces carbon emissions to a certain extent. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0025] The chemical composition of the raw materials used in the embodiments and comparative examples of this invention is shown in Table 1.

[0026] Table 1

[0027] raw materials <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> <![CDATA[SO3]]> LOI <![CDATA[1 # limestone 2.30 0.01 1.37 52.77 0.64 0.24 0.16 0.01 42.23 <![CDATA[2 # limestone 4.26 0.53 1.27 50.64 1.08 0.50 0.10 0.02 40.98 sulfuric acid residue 7.53 8.70 68.52 9.48 3.22 0.51 0.01 4.38 -3.52 Hard plaster 1.90 0.26 0.42 25.67 3.32 0.21 0.05 47.62 7.44 Low-grade bauxite 32.90 33.03 10.98 4.16 1.21 0.51 0.07 0.12 14.05

[0028] Example 1

[0029] As a preferred embodiment of the present invention, the raw material composition of a special calcium-based material for autoclaved aerated concrete disclosed in this embodiment is shown in Table 2.

[0030] Table 2

[0031] raw materials mass ratio / wt% limestone 93 sulfuric acid residue 4 Hard plaster 1 Low-grade bauxite 2

[0032] This embodiment discloses a method for preparing a special calcareous material for autoclaved aerated concrete as follows:

[0033] S1. Crush limestone, sulfuric acid residue, anhydrite and low-grade bauxite separately and set aside for later use;

[0034] S2. The crushed limestone, sulfuric acid slag, anhydrite and low-grade bauxite are weighed into the raw meal mill by an electronic belt scale according to the mass ratio corresponding to Table 2, and then dried and ground to obtain powdered materials (raw meal).

[0035] S3. Powdered materials (raw materials) are fed into a new type of dry process kiln for calcination, and then cooled by a cooler to obtain clinker;

[0036] S4. Grind the calcined clinker to a surface area of ​​360m². 2 / kg yields the calcium material of this embodiment.

[0037] In step S2, the fineness of the powdered material (raw material) is such that the residue on a 0.08mm square-hole sieve is ≤22%.

[0038] In S3, the time from entering the kiln to exiting the kiln is 40 minutes, the firing temperature of the calcining zone is 1330℃, and the firing time of the calcining zone is 12 minutes.

[0039] In this embodiment, the lime used is 1 # limestone.

[0040] Example 2

[0041] As a preferred embodiment of the present invention, the raw material composition of a special calcium-based material for autoclaved aerated concrete disclosed in this embodiment is shown in Table 3.

[0042] Table 3

[0043] raw materials mass ratio / wt% limestone 94 sulfuric acid residue 3 Hard plaster 1 Low-grade bauxite 2

[0044] This embodiment discloses a method for preparing a special calcareous material for autoclaved aerated concrete as follows:

[0045] S1. Crush limestone, sulfuric acid residue, gypsum and low-grade bauxite separately and set aside for later use;

[0046] S2. The crushed limestone, sulfuric acid slag, gypsum and low-grade bauxite are weighed into the raw meal mill by electronic belt scale according to the mass ratio corresponding to Table 3, and then dried and ground to obtain powdered materials (raw meal).

[0047] S3. Powdered materials (raw materials) are fed into a new type of dry process kiln for calcination, and then cooled by a cooler to obtain clinker;

[0048] S4. Grind the calcined clinker to a surface area of ​​355 m². 2 / kg yields the calcium material of this embodiment.

[0049] In step S2, the fineness of the powdered material (raw material) is such that the residue on a 0.08mm square-hole sieve is ≤22%.

[0050] In S3, the time from entering the kiln to exiting the kiln is 38 minutes, the firing temperature of the calcining zone is 1360℃, and the firing time of the calcining zone is 10 minutes.

[0051] In this embodiment, the lime used is 1 # limestone.

[0052] Comparative Example 1

[0053] In this comparative example, the lime content was 2. # Limestone, and everything else is the same as in Example 1.

[0054] Comparative Example 2

[0055] Except for the mass ratio of limestone, sulfuric acid slag, anhydrite, and low-grade bauxite being 95.0 wt%: 1.5 wt%: 1.5 wt%: 2 wt%, the comparative example is the same as Example 1.

[0056] Because the amount of iron raw materials added in this comparative example is small, the amount of liquid phase is small during calcination in the new dry process kiln, which cannot granulate normally. As a result, the clinker entering the grate cooler after exiting the kiln cannot work properly, and the dust concentration in the kiln is too high, which prevents normal production.

[0057] Test Example 1

[0058] Aerated concrete blocks were produced using calcareous materials from Examples 1, 2, and Comparative Example 1 as cementing materials, with the following mass proportions:

[0059] Cementitious materials: 14.5 wt%;

[0060] Sand slurry: 59.4 wt%;

[0061] Waste slurry: 26.1% wt;

[0062] The amount of aluminum powder added is 0.065 wt% of the above raw material mass.

[0063] Test Example 2

[0064] Aerated concrete blocks are produced using calcareous materials made from quicklime and ordinary Portland cement 42.5R as cementing materials, with the following mix proportions:

[0065] Quicklime: 9.7 wt%;

[0066] Ordinary Portland cement 42.5R: 4.8 wt%;

[0067] Sand slurry: 59.4 wt%;

[0068] Waste slurry: 26.1 wt%;

[0069] The amount of aluminum powder added is 0.065% of the mass of the above raw materials.

[0070] Record the static settling time of the aerated concrete blocks prepared in Test Example 1 and Test Example 2. The appearance and performance of the products were tested in accordance with GB / T11968-2020 "Autoclaved Aerated Concrete Blocks" and GB / T 11969-2020 "Test Methods for Performance of Autoclaved Aerated Concrete", as shown in Table 4 below.

[0071] Table 4

[0072]

[0073] As shown in Table 4, the calcium-based material prepared in the example significantly shortens the static curing time and improves production efficiency. After steam curing, the mechanical properties and dry density of the product meet the quality requirements of A3.5 B06 grade aerated concrete blocks, and the mechanical properties are significantly better than those of the comparative example. This indicates that the calcium-based material provided by the present invention can significantly improve the production efficiency of aerated concrete and improve the performance of aerated concrete.

[0074] Finally, it should be noted that the above embodiments are merely preferred embodiments of the present invention used to illustrate the technical solutions of the present invention, and are not intended to limit them, let alone limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention. That is to say, any changes or refinements made to the main design idea and spirit of the present invention that have no substantial meaning, but solve the same technical problem as the present invention, should be included within the protection scope of the present invention. In addition, the direct or indirect application of the technical solutions of the present invention to other related technical fields are similarly included within the patent protection scope of the present invention.

Claims

1. A calcium-based material specifically for autoclaved aerated concrete, characterized in that, The following raw materials are included in the following mass ratio: The calcareous material comprises, by mass ratio, 42-55 wt% f-CaO. The content is 0-3 wt%, the sum of C2S and C3S is 22-45 wt%, the sum of C3A and C4AF is 5-20 wt%, the content of periclase is 0-1.5 wt%, the content of gypsum is 0-2 wt%, and the content of other impurity minerals is 0-6 wt%.

2. The calcium-based material for autoclaved aerated concrete according to claim 1, characterized in that, The iron-based raw material is at least one of non-ferrous metal ash, copper slag, iron tailings, iron ore, blast furnace slag, and sulfuric acid slag.

3. The calcium-based material for autoclaved aerated concrete according to claim 1, characterized in that, The gypsum is at least one of dihydrate gypsum, anhydrite, desulfurized gypsum, phosphogypsum, and desulfurized ash.

4. The calcium-based material for autoclaved aerated concrete according to claim 1, characterized in that, The silicon-aluminate material is at least one of low-grade bauxite, aluminum smelting waste, aluminum tailings, and fly ash.

5. A method for preparing a special calcareous material for autoclaved aerated concrete according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1. Crush limestone, iron raw materials, gypsum and aluminosilicate materials separately and set aside for later use; S2. The crushed limestone, iron raw materials, gypsum and silica-alumina materials are weighed according to the corresponding mass ratio and then ground and mixed to obtain powdered materials. S3. The powdered material is calcined in a new dry kiln and cooled to obtain calcined clinker. S4. Grind the calcined clinker into powder to obtain the calcium material.

6. The method for preparing a special calcareous material for autoclaved aerated concrete according to claim 5, characterized in that, In step S2, the powdered material is a powder with a sieve residue fineness of ≤22% obtained by uniformly passing through a 0.08mm square hole sieve.

7. The method for preparing a special calcareous material for autoclaved aerated concrete according to claim 5, characterized in that, In S3, the time from entering the kiln to exiting the kiln is 30-45 minutes, the firing temperature of the calcining zone is 1320-1380℃, and the firing time of the calcining zone is 10-15 minutes.

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