Fly ash aerated concrete and curing method thereof

Abstract

The fly ash aerated concrete is prepared from the following raw materials: 10 to 20 parts of ordinary Portland cement, 10 to 15 parts of lime, 60 to 70 parts of fly ash, 3 to 5 parts of gypsum, 45 to 50 parts of water, 0.05 to 0.1 part of a water reducing agent and 0.08 to 0.12 part of an air entraining agent, a mixed atmosphere containing carbon dioxide gas and high-temperature saturated steam is adopted as a curing condition. Carbon-containing gas and high-temperature saturated steam conditions are introduced in the autoclaved curing process of the aerated concrete, the reaction process of a traditional autoclaved curing process is changed and optimized, good mechanical performance, shrinkage performance and the like are considered, meanwhile, the constant-temperature curing period can be shortened, and a new thought can be provided for preparation of the high-performance aerated concrete; carbon dioxide and heat in industrial waste gas can be effectively utilized, the maintenance cost is reduced, and the production efficiency and the product quality are improved; the method has remarkable economic and environmental benefits and is convenient to popularize and apply.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to fly ash aerated concrete and a curing method thereof. Background Art

[0002] At present, the most commonly used curing methods for fly ash aerated concrete are steam curing and autoclave curing. When using 50-100℃ steam curing, the energy consumption is low, but the curing time is long. Since the hydration products are loose, basically no tobermorite is generated, and the products have problems such as low strength and high shrinkage. When using autoclave curing, the curing time is short. Since the hydration products are tightly packed, a large amount of tobermorite is generated. The prepared aerated concrete has the advantages of high strength and low shrinkage value, but it needs to consume a large amount of high-temperature and high-pressure steam, and the energy consumption is high.

[0003] Under the premise of ensuring the performance and turnover efficiency of aerated concrete, reducing energy consumption and carbon emissions during the curing process, carbonation curing has become an important direction for the current development of the industry. For the carbonation curing of fly ash aerated concrete, the current main research direction is to use carbon dioxide with a certain concentration and pressure for secondary curing after the body is autoclaved, but there are obvious problems: the curing cycle is significantly increased; it is easy to cause uneven carbonation reaction, which leads to performance degradation. Summary of the invention

[0004] The main purpose of the present invention is to provide a fly ash aerated concrete in view of the problems and shortcomings of the prior art. By adjusting the curing atmosphere of the fly ash aerated concrete, good mechanical properties and shrinkage properties are taken into account under the premise of energy saving and emission reduction. The curing method involved is relatively simple, easy to operate, and has a short preparation cycle, which is suitable for promotion and application.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A fly ash aerated concrete, the raw materials of which include: 10-20 parts of ordinary Portland cement, 10-15 parts of lime, 60-70 parts of fly ash, 3-5 parts of gypsum, 45-50 parts of water, 0.05-0.1 parts of water reducing agent, 0.08-0.12 parts of air entraining agent; after mixing and molding, curing is carried out, and the curing condition adopts a mixed atmosphere containing carbon dioxide gas and high-temperature saturated steam.

[0007] In the above scheme, the grade of ordinary Portland cement is P·O42.5 and above.

[0008] In the above scheme, the calcium oxide content of the lime is above 75wt%, the digestion time is 5 to 10min, and the residue on 80μm sieve is 10% to 20%.

[0009] In the above scheme, the silicon content of the fly ash is more than 50wt%, the loss on ignition is not higher than 10%, and the 45μm sieve residue is less than 45%.

[0010] In the above scheme, the content of calcium sulfate dihydrate in the gypsum is above 85wt%, and the pH value is 6-9.

[0011] In the above scheme, the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, and the water reduction rate is 35-45%.

[0012] In the above scheme, the air entraining agent can be aluminum powder or the like.

[0013] Furthermore, the aluminum powder is a water-based aluminum powder, with a solid content of more than 70wt%, active aluminum in the solid content of more than 85wt%, and a 16min gas evolution rate of more than 80%.

[0014] The above-mentioned method for preparing fly ash aerated concrete comprises the following steps:

[0015] 1) Measure ordinary Portland cement, lime, fly ash, gypsum, water and water reducing agent according to the proportion, stir evenly (stir at a speed of 900-1200r / min for 2-4min) to obtain a mixed slurry;

[0016] 2) Mix the slurry and air entraining agent according to the proportion, stir evenly (stir at a speed of 900-1200 r / min for 30-60s), pour the obtained slurry into the mold frame to stop gasification and harden, demold, and cut to obtain the fly ash aerated concrete body.

[0017] 3) placing the obtained green body in a curing kettle, first evacuating the air, and then filling it with carbon-containing gas;

[0018] Continue to charge the kettle with high-temperature saturated steam until the target curing temperature and target curing pressure are reached, perform heat preservation and pressure maintenance, cool down, and take the kettle out to obtain the finished fly ash aerated concrete product.

[0019] In the above scheme, the temperature used in the static gas hardening step is 45-55° C., the relative humidity is not less than 80%, and the static time is 2.5-3.5 hours.

[0020] In the above scheme, the vacuum is drawn to a degree of -0.04 to -0.06 MPa.

[0021] In the above scheme, carbon-containing gas is charged until the pressure in the kettle is 0.15-0.3 MPa.

[0022] In the above scheme, the temperature of the carbon-containing gas is 80-200° C., the concentration of carbon dioxide is 10-100 vol%, and the relative humidity is 50-90%.

[0023] Furthermore, the carbon-containing gas includes but is not limited to cement kiln tail gas, metal smelter tail gas, etc., preferably with a temperature of 120-180° C., a carbon dioxide concentration of 20-50%, and a relative humidity of 60-70%.

[0024] In the above scheme, the high-temperature saturated steam has a temperature of 190-200°C and a pressure of 1.3-1.6 MPa.

[0025] In the above scheme, the target curing temperature is 160-180°C, and the target curing pressure is 0.8-1.3MPa.

[0026] Furthermore, in step 3), the flow rate and velocity of the high-temperature saturated steam are controlled to control the heating rate in the kettle to 2-3°C / min.

[0027] In the above scheme, the heat preservation and pressure maintenance time is 3 to 5 hours, the temperature in the kettle is controlled at 160 to 180° C., and the pressure is controlled at 0.8 to 1.3 MPa.

[0028] In the above scheme, the temperature is lowered to 80-100°C at a rate of 2-3°C / min during the cooling process, and then the kettle is opened to end the curing.

[0029] The performance optimization mechanism of cement brick curing of the present invention includes:

[0030] 1) When carbon dioxide diffuses into the interior of the green body, a large amount of carbonized products are first generated on the surface of the green body, which significantly increases the strength of the green body surface; the problem of low green body strength during the heating stage and cracking caused by large temperature stress at the corners of the green body due to uneven heating is solved; the method of the present invention can increase the heating rate and shorten the time required for the heating stage. In addition, the carbonization reaction process releases a large amount of heat, which also helps to increase the green body temperature and further shorten the heating time.

[0031] 2) When the green body is directly cured by steam autoclaving, the concentration of calcium hydroxide in the liquid phase of the green body is higher than that of silicon dioxide in the initial stage, generating high-alkalinity calcium silicate hydrate with low strength; as the curing process proceeds, the concentration of silicon dioxide in the liquid phase gradually increases, and the high-alkalinity calcium silicate hydrate gradually forms stable low-alkalinity calcium silicate hydrate, namely CSH(Ⅰ) gel; part of the CSH(Ⅰ) gel further crystallizes at high temperature to form tobermorite, and the strength is further increased; since the conversion between the reaction products requires a certain amount of time, its curing cycle is difficult to be effectively shortened further; in addition, due to the presence of a large number of gel pores and capillaries, a higher capillary tension is generated during drying and water loss, resulting in greater shrinkage. In view of the above problems, the present invention proposes for the first time that when a certain concentration of carbon dioxide is introduced under high temperature and pressurized steam curing conditions, the concentration of calcium hydroxide in the liquid phase can be significantly reduced, and the formation of calcite and CSH (I) gel is promoted in the initial stage; the carbonization products and hydration products formed are interspersed and overlapped with each other, which is more conducive to the strength development; in addition, since the CSH (I) gel formation time is advanced, the constant temperature curing time can be effectively shortened while ensuring the performance.

[0032] 3) After being filled with carbon-containing gas, the green body is heated by the carbon-containing gas, and the heat released by the carbonization reaction further increases the temperature of the green body, thereby reducing the temperature difference between the green body and the high-temperature steam, effectively inhibiting the formation of condensed water on the green body surface, and providing the necessary conditions for the diffusion of carbon dioxide into the green body.

[0033] 4) The green body has a porous structure, which is convenient for the diffusion of carbon dioxide, and the high temperature environment can significantly increase the diffusion rate of carbon dioxide, avoiding the performance degradation caused by uneven reaction inside and outside the green body; in addition, the formed calcite has high strength, small shrinkage, and good water resistance. It is partially interspersed in the CSH (Ⅰ) gel, which can significantly reduce the shrinkage value of aerated concrete.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) The present invention proposes for the first time to introduce carbon-containing gas and high-temperature saturated steam conditions during the autoclave curing process of aerated concrete, change and optimize the reaction process of the traditional autoclave curing process, take into account good mechanical properties and shrinkage properties, etc., and at the same time shorten the constant temperature curing cycle, which can provide a new idea for the preparation of high-performance aerated concrete.

[0036] 2) Compared with the existing fly ash aerated concrete production process, the present invention can effectively reduce maintenance costs, improve production efficiency and product quality; and can effectively utilize carbon dioxide and heat in industrial waste gas, with significant economic and environmental benefits, and is easy to promote and apply. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with the embodiments to facilitate a clearer understanding of the present invention, but they do not limit the present invention.

[0038] In the following examples and comparative examples, the grade of ordinary Portland cement used is P·O42.5. The lime calcium oxide content is 82%, the digestion time is 8 minutes, and the 80μm sieve residue is 13%. The fly ash silicon content is 55%, the ignition loss is not higher than 8%, and the 45μm sieve residue is 29%. The gypsum calcium sulfate dihydrate content is 88%, and the pH value is 6.5. The water reduction rate of the polycarboxylate water reducer is 42%. The aluminum powder is a water-based aluminum powder, with a solid content of 75%, active aluminum in the solid content is not less than 92%, and a 16min gasification rate of 89%.

[0039] The carbon-containing gas used is cement kiln tail gas, with a temperature of 150°C, a carbon dioxide concentration of 22 vol%, and a relative humidity of 68%. The high-temperature saturated steam used has a temperature of 200°C and a pressure of 1.5 MPa.

[0040] Example 1

[0041] A method for preparing a fly ash aerated concrete body comprises the following steps:

[0042] (1) Take 18 parts of ordinary Portland cement, 12 parts of lime, 67 parts of fly ash, 3 parts of gypsum, 48 parts of water, and 0.08 parts of water reducing agent, and stir at a speed of 1200 r / min for 4 minutes to obtain a mixed slurry;

[0043] (2) taking the mixed slurry and 0.1 part of aluminum powder, stirring at a speed of 1200 r / min for 45 seconds, pouring the uniformly stirred slurry into a mold frame, and then placing it in a static room for gas hardening, wherein the temperature in the static room is 48° C., the relative humidity is 85%, and the static time is 3 hours. After the slurry is hardened, demolding is performed, and the fly ash aerated concrete body is obtained after cutting;

[0044] (3) The curing method of fly ash aerated concrete body comprises the following steps:

[0045] 1) The green body is placed in a curing kettle, first evacuated to -0.05MPa, and then filled with carbon-containing gas until the pressure in the kettle reaches 0.15MPa;

[0046] 2) Continue to charge the kettle with high-temperature saturated steam until the temperature and pressure in the kettle reach the target curing temperature of 170°C and the target curing pressure of 1.0 MPa, respectively; wherein, in this step, the heating rate in the kettle is controlled to be 2.5°C / min by controlling the flow rate and flow velocity of the high-temperature saturated steam;

[0047] 3) Perform heat preservation and pressure maintenance, wherein the temperature in the kettle is controlled at 170°C, the pressure is controlled at 1.0MPa, and the constant temperature time is 3h;

[0048] 4) The temperature is lowered to 95°C at a rate of 2.5°C / min, and the autoclave is opened to end the curing, and the fly ash aerated concrete product is obtained after the autoclave is taken out.

[0049] Example 2

[0050] A fly ash aerated concrete, whose preparation method and curing method are substantially the same as those of Example 1, except that: in the heat preservation and pressure curing step, the temperature in the kettle is controlled at 180° C., the pressure is controlled at 1.3 MPa, and the constant temperature time is 5 hours.

[0051] Example 3

[0052] A fly ash aerated concrete, whose preparation method and curing method are roughly the same as those of Example 1, except that: the green body is placed in a curing kettle, first evacuated to -0.05MPa, and then filled with carbon-containing gas to a pressure of 0.3MPa.

[0053] Comparative Example 1

[0054] A fly ash aerated concrete, whose preparation method and curing method are roughly the same as those of Example 1, except that: the body is placed in a curing kettle, first evacuated to -0.05MPa, and then directly filled with high-temperature saturated steam. During the constant temperature stage, the temperature in the kettle is controlled at 170°C, the pressure is controlled at 1.0MPa, and the constant temperature time is 3h.

[0055] Comparative Example 2

[0056] A fly ash aerated concrete, the preparation method and curing method of which are substantially the same as those of Example 1, except that: the green body is placed in a curing kettle, first evacuated to -0.05 MPa, and then directly charged with high-temperature saturated steam. During the constant temperature stage, the temperature in the kettle is controlled at 180°C, the pressure is controlled at 1.2 MPa, and the constant temperature time is 6 hours.

[0057] Comparative Example 3

[0058] A fly ash aerated concrete, whose preparation method and curing method are roughly the same as those of Example 1, except that: the green body is placed in a curing kettle, first evacuated to -0.05MPa, and then filled with carbon-containing gas until the pressure in the kettle is 0.1MPa and 0.5MPa respectively.

[0059] Comparative Example 4

[0060] A fly ash aerated concrete, whose preparation method and curing method are roughly the same as those of Example 1, except that: the green body is placed in a curing kettle, first evacuated to -0.05MPa, and then filled with carbon-containing gas until the pressure in the kettle is 0.5MPa, and then filled with high-temperature saturated steam after carbonization for 24 hours. During the constant temperature stage, the temperature in the kettle is controlled at 170°C, the pressure is controlled at 1.0MPa, and the constant temperature time is 3h.

[0061] The fly ash aerated concrete obtained in Examples 1 to 3 and Comparative Examples 1 to 4 was subjected to performance tests according to standard GB / T 11969-2008. The results are shown in Table 1.

[0062] Table 1 Cement brick performance test results

[0063]

[0064] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A fly ash aerated concrete, characterized in that: The raw materials include: 10-20 parts of ordinary Portland cement, 10-15 parts of lime, 60-70 parts of fly ash, 3-5 parts of gypsum, 45-50 parts of water, 0.05-0.1 parts of water reducing agent, and 0.08-0.12 parts of air entraining agent; the curing conditions adopt a mixed atmosphere containing carbon dioxide gas and high-temperature saturated steam.

2. The fly ash aerated concrete according to claim 1, characterized in that: The curing conditions include: first evacuating the air and filling the kettle with carbon-containing gas; continuously filling the kettle with high-temperature saturated steam until the target curing temperature and target curing pressure are reached, performing heat preservation and pressure curing, cooling the kettle, and obtaining a finished product of fly ash aerated concrete.

3. The fly ash aerated concrete according to claim 1, characterized in that: The temperature of the carbon-containing gas is 80-200° C., the concentration of carbon dioxide is 10-100 vol%, and the relative humidity is 50-90%.

4. The fly ash aerated concrete according to claim 1, characterized in that: The high-temperature saturated steam has a temperature of 190-200° C. and a pressure of 1.3-1.6 MPa.

5. The fly ash aerated concrete according to claim 1, characterized in that: The grade of ordinary Portland cement is P·O42.5 and above; the silicon content of fly ash is above 50wt%, the loss on ignition is not higher than 10%, and the 45μm sieve residue is below 45%.

6. The fly ash aerated concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid high efficiency water reducing agent, and the water reducing rate is 35-45%.

7. The fly ash aerated concrete according to claim 1, characterized in that: The air entraining agent is aluminum powder.

8. The method for preparing fly ash aerated concrete according to any one of claims 1 to 7, characterized in that: The steps include: 1) Measure ordinary Portland cement, lime, fly ash, gypsum, water and water reducing agent according to the proportion, stir evenly to obtain a mixed slurry; 2) Mix the slurry and air entraining agent according to the proportion, stir evenly (stir at a speed of 900-1200 r / min for 30-60s), pour the obtained slurry into the mold frame to stop gasification and harden, demold, and cut to obtain the fly ash aerated concrete body; 3) placing the obtained green body in a curing kettle, first evacuating the air, and then filling it with carbon-containing gas; Continue to charge the kettle with high-temperature saturated steam until the target curing temperature and target curing pressure are reached, perform heat preservation and pressure maintenance, cool down, and take the kettle out to obtain the finished fly ash aerated concrete product.

9. The preparation method according to claim 8, characterized in that: Fill the kettle with carbon-containing gas until the pressure inside the kettle is 0.15-0.3MPa.

10. The preparation method according to claim 8, characterized in that: The heat preservation and pressure maintenance time is 3 to 5 hours, the temperature in the kettle is controlled at 160 to 180° C., and the pressure is controlled at 0.8 to 1.3 MPa.

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