Method for manufacturing autoclaved aerated concrete products and products thereof

Abstract

This invention provides a method for manufacturing autoclaved aerated concrete (AAC) products and the finished product itself. The method uses waste powder with a particle size less than 0.075 mm, which is the last sieve screener in a manufactured sand production line, as a siliceous raw material. The waste powder is prepared into a slurry, heated to 40-60 degrees Celsius with high-temperature steam, and then calcareous raw materials, including at least cement and quicklime powder, are added. The slurry is then heated to 40-60 degrees Celsius with high-temperature steam again, and the AAC product is obtained through pouring, static curing, pre-curing before autoclaving, and high-temperature, high-pressure constant-pressure autoclaving. The advantages of this invention are that it promotes the initial degradation of the flocculant polyacrylamide in the waste powder, allowing the waste powder to be used as a siliceous raw material in the manufacture of AAC products without affecting their performance, thus turning waste into a valuable resource. Furthermore, the waste powder does not require further grinding, significantly saving energy and grinding media.

Description

Technical Field

[0001] This invention relates to autoclaved aerated concrete (AAC) technology, and more particularly to AAC products and their manufacturing methods. Background Technology

[0002] In recent years, manufactured sand, used to replace river sand and sea sand, has become widely used and has played a positive role in environmental protection. However, the waste generated from the production of manufactured sand has not been effectively utilized, especially the waste powder with a particle size of less than 0.075mm that is screened out at the last stage of the manufactured sand production line, which is rampant and seriously affects the ecological environment. Summary of the Invention

[0003] The purpose of this invention is to transform the aforementioned waste powder into a valuable resource by providing a method for manufacturing autoclaved aerated concrete (AAC) products. For the same purpose, this invention also provides an AAC product.

[0004] This invention is achieved as follows: a method for manufacturing autoclaved aerated concrete (AAC) products, using waste powder with a particle size less than 0.075mm from the last screen of a manufactured sand production line as the siliceous raw material for manufacturing AAC products, through the following steps:

[0005] (1) The waste powder is mixed with water to form a waste powder slurry, and the waste powder slurry is heated to 40-60 degrees Celsius with high-temperature steam;

[0006] (2) After the waste powder slurry has been heated to 40-60 degrees Celsius, calcium raw materials including at least cement and quicklime powder are added to the waste powder slurry, and the mixture is stirred evenly to form a mixed slurry. The mixed slurry is then heated to 40-60 degrees Celsius with high-temperature steam.

[0007] (3) Add foaming agent to the slurry at 40-60 degrees Celsius, stir for a while, and then immediately pour it into the mold frame;

[0008] (4) Place the mold frame in a curing room at 40-50 degrees Celsius for 2.5-3.5 hours to allow the mixed slurry in the mold frame to harden into a blank that meets the cutting hardness requirements;

[0009] (5) Let the billet stand for 1 to 3 hours to complete the pre-curing before the kettle;

[0010] (6) Place the pre-cured blank into an autoclave for 5 to 10 hours of high temperature and high pressure constant pressure autoclaving. The temperature of the autoclave is 174.5 to 197 degrees Celsius and the constant pressure is 0.8 to 1.4 MPa. Once the autoclaving is completed, the autoclaved aerated concrete product is obtained.

[0011] As the preferred implementation method, the method of heating the waste powder slurry to 40-60 degrees Celsius with high-temperature steam in step (1) is to first heat the water to above 50 degrees Celsius with the residual gas in the autoclave steam curing process, and then add the waste powder to the water and stir to mix, so that the waste powder slurry formed reaches 40-60 degrees Celsius.

[0012] As a preferred embodiment, high-silica tailings are added to the waste powder slurry in step (1) or the mixed slurry in step (2).

[0013] As the preferred embodiment, in step (1), the ratio of waste powder to water is determined according to the requirement that the specific gravity of the waste powder slurry reaches 1.4 to 1.7 at 40 to 60 degrees Celsius.

[0014] As a preferred embodiment, fly ash is added to the waste powder slurry in step (1) and / or the mixed slurry in step (2); high silica tailings are added to the waste powder slurry in step (1) and / or the mixed slurry in step (2); and gypsum powder is added to the waste powder slurry in step (1) and / or the mixed slurry in step (2). The weight ratio of various raw materials according to their dry basis content is as follows: 40-45 parts of waste powder, 35-40 parts of high silica tailings, 5-6 parts of fly ash, 10-12 parts of cement, 8-10 parts of high-calcium quicklime with an effective calcium oxide content of more than 80%, and 1-2 parts of gypsum powder.

[0015] On the other hand, the autoclaved aerated concrete product of the present invention is characterized by being made using the above-described method.

[0016] The advantages of this invention are: by heating the waste powder slurry formed by mixing the waste powder with water, the flocculant polyacrylamide originally added to the waste powder is initially degraded, so that the silica in the waste powder can undergo a preliminary hydration reaction with the calcium oxide in cement and lime in step (4), which is conducive to accelerating the hydrothermal synthesis reaction in step (6) to generate monoalkali hydrated calcium silicate CSH(I) and tobermorite and other strength substances. In this way, the waste powder can be used as a siliceous raw material for manufacturing autoclaved aerated concrete products without affecting the performance of autoclaved aerated concrete products, thus realizing the purpose of turning the waste powder into a treasure. On the other hand, most of the siliceous raw materials used in existing autoclaved aerated concrete products are made by grinding river sand or stone powder. They need to be ground continuously day and night by large ball mills (diameter 1.5 meters to 3.2 meters, length 5.7 meters to 15 meters) to be finely ground. The power of the ball mill motor ranges from 130 kilowatts to 1600 kilowatts, which consumes a lot of energy and also consumes a large number of steel balls, steel forgings and other grinding media. The waste powder used in this invention has a particle size that fully meets the fineness requirements of siliceous raw materials for autoclaved aerated concrete products, eliminating the need for further grinding and greatly saving energy and grinding media. Implementation

[0017] The invention will now be described in more detail. The invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a more thorough and complete understanding of the invention.

[0018] The manufacturing method described in this invention is characterized by using waste powder with a particle size of less than 0.075 mm, which is the material passing through the last screen of the manufactured sand production line, as the siliceous raw material for manufacturing autoclaved aerated concrete products. Manufactured sand refers to rock particles with a particle size of less than 4.75 mm, produced by a sand making machine from various siliceous rocks such as granite, basalt, and pebbles. The material passing through the last screen in the sand making process is waste powder with a particle size of less than 0.075 mm; this waste powder is the waste powder described in this invention.

[0019] The method described in this invention comprises the following steps (1) to (6):

[0020] (1) The waste powder is mixed with water to form a waste powder slurry, and the waste powder slurry is heated to 40-60 degrees Celsius using high-temperature steam. In this step, the waste powder can be heated using the residual gas from the autoclave curing process while water is being added, or it can be heated using the residual gas from the autoclave curing process after the waste powder is mixed with water. However, as the preferred embodiment, the water should first be heated to above 50 degrees Celsius using the residual gas from the autoclave curing process, and then the waste powder should be added to the water and stirred to mix, so that the waste powder slurry finally reaches 40-60 degrees Celsius. The advantage of this heating method is that the flocculant polyacrylamide in the waste powder can be initially degraded more quickly, and the waste powder slurry can be homogenized more quickly.

[0021] This step essentially replaces the existing siliceous raw materials made from river sand or stone powder used in autoclaved aerated concrete (AAC) products with the aforementioned waste powder. Compared to traditional siliceous raw materials made from river sand or stone powder, the waste powder has a lower silica content. To compensate for this deficiency, high-silica tailings can be added to the water in this step. High-silica tailings refer to tailings with a silica content exceeding 85% in solids, a fineness of 10-30% residue on a 0.08mm sieve, and no further grinding required. For example, tailings from the production of glass or quartz slab raw materials can be used as high-silica tailings. The high-silica tailings can be added to the waste powder slurry either by adding the high-silica tailings to the water together with the waste powder, or by adding the high-silica tailings after the waste powder and water have been mixed to form a waste powder slurry.

[0022] This step can also involve adding gypsum powder to the waste powder slurry to inhibit quicklime slaking and slow down the slurry thickening rate. The method for adding gypsum powder to the waste powder slurry can be either to add the gypsum powder to the water together with the waste powder, or to add the gypsum powder after the waste powder and water have been mixed to form a waste powder slurry.

[0023] This step can also involve adding coal ash to the waste powder slurry to fully utilize the coal ash waste and reduce production costs. The method for adding coal ash to the waste powder slurry can be either to add the coal ash and the waste powder together with water, or to add the coal ash after the waste powder and water have been mixed to form a waste powder slurry.

[0024] As the preferred implementation, this step is preferably performed by determining the ratio of waste powder to water according to the requirement that the specific gravity of the waste powder slurry reaches 1.4 to 1.7 at 40 to 60 degrees Celsius. If gypsum powder, fly ash, or high-silica tailings are added in this step, the ratio of waste powder to water is also determined according to this principle. The waste powder slurry prepared in this way allows only a small amount of water to be added or even no water to be added in step (2), thereby enabling the preparation of a mixed slurry in a shorter time (e.g., 2 to 3 minutes). Homogenizing the mixed slurry in a shorter time is more conducive to obtaining brick blanks with uniform density at the top, middle, and bottom.

[0025] Waste powder slurry with a temperature of 40-60 degrees Celsius can be stored in a storage tank for later use. The residual gas from the autoclave curing process is used to heat the waste powder slurry in the storage tank to maintain the temperature at 40-60 degrees Celsius.

[0026] (2) After the waste powder slurry has been heated to 40-60 degrees Celsius, calcium-based raw materials, including at least cement and quicklime powder, are added to the waste powder slurry and stirred evenly to form a mixed slurry. The mixed slurry is then heated to 40-60 degrees Celsius with high-temperature steam. The high-temperature steam used in this step can be the residual gas from the autoclave curing process.

[0027] Similar to step (1) above, to compensate for the low silica content of the waste powder, this step can also add the high-silica tailings described in step (1) to the mixed slurry. The high-silica tailings can be added to the mixed slurry either by adding the high-silica tailings together with cement and quicklime powder to the waste powder slurry, or by adding the high-silica tailings after the mixed slurry is prepared.

[0028] This step can also involve adding gypsum powder to inhibit the slaking of quicklime and slow down the thickening rate of the slurry. The gypsum powder can be added to the mixed slurry either by adding it together with the cement and quicklime powder to the waste powder slurry, or by adding it after the mixed slurry has been prepared.

[0029] This step can also involve adding fly ash to fully utilize the fly ash waste and reduce production costs. Fly ash can be added to the mixed slurry either by adding it together with cement and quicklime powder to the waste powder slurry, or by adding it after the mixed slurry is prepared.

[0030] It should be noted that when adding calcium-based raw materials such as cement and quicklime powder in this step, the waste powder slurry does not need to be kept at 40-60 degrees Celsius. It can be lower than this temperature range due to natural heat dissipation or other reasons. However, after adding the calcium-based raw materials and stirring evenly to form a mixed slurry, the mixed slurry must be heated to 40-60 degrees Celsius with high-temperature steam.

[0031] (3) When the slurry reaches 40-60 degrees Celsius, add a foaming agent to the slurry, stir for a while, and then immediately pour it into the mold frame. The foaming agent can be aluminum powder paste or aluminum powder. The stirring time should be 40-60 seconds. It is best to also add a certain amount of foam stabilizer to the slurry in this step.

[0032] (4) Place the mold frame in a curing room at 40-50 degrees Celsius for 2.5-3.5 hours to allow the mixed slurry in the mold frame to harden into a blank that meets the cutting hardness.

[0033] (5) Let the billet stand for 1 to 3 hours to complete the pre-curing before the kettle.

[0034] It should be noted that after step (4), the blank can be cut into various sizes according to the required dimensions of the finished product before proceeding to this step. Before this step, the cut blanks can be cleaned with an edge-cleaning device and grouped with a grouping device. Here, the wastewater discharged from the edge-cleaning device can be recycled and used as water in step (1). Of course, if the blanks produced in step (4) already meet the requirements of the finished product dimensions, cutting may not be necessary.

[0035] (6) Place the pre-cured blank into an autoclave for 5 to 10 hours of high temperature and high pressure constant pressure autoclaving. The temperature of the autoclave is 174.5 to 197 degrees Celsius and the constant pressure is 0.8 to 1.4 MPa. Once the autoclaving is completed, the autoclaved aerated concrete product of the present invention is obtained.

[0036] The proportions of the various raw materials involved in this invention, except for the waste powder, can be referenced from the proportions used in existing autoclaved aerated concrete products. The following lists the weight percentage ranges of various raw materials based on dry basis content: 10-85 parts waste powder, 0-50 parts high-silica tailings, 5-6 parts fly ash, 10-12 parts cement, 8-10 parts quicklime with an effective calcium oxide content exceeding 60%, and 1-2 parts gypsum powder.

[0037] However, this invention provides an optimized formulation: the various raw materials, by weight percentage (dry basis), are as follows: 40-45 parts waste powder, 35-40 parts high-silica tailings, 5-6 parts fly ash, 10-12 parts cement, 8-10 parts high-calcium quicklime with an effective calcium oxide content exceeding 80%, and 1-2 parts gypsum powder. Autoclaved aerated concrete products made using this optimized formulation have lower dry density and significantly improved strength and frost resistance, making them more suitable for producing B05 grade blocks and wall panels, as well as B03 and B04 grade insulation products.

Claims

1. A method of manufacturing autoclaved aerated concrete products, characterized by: The method comprises the following steps: (1) mixing the waste powder with water to form a waste powder slurry, and heating the waste powder slurry to 40-60 DEG C by using high-temperature steam; (2) after the waste powder slurry is heated to 40-60 DEG C, adding calcium raw materials including cement and quicklime powder into the waste powder slurry, stirring to form a mixed slurry, and heating the mixed slurry to 40-60 DEG C by using high-temperature steam; (3) adding a foaming agent into the mixed slurry heated to 40-60 DEG C, stirring for a while, and then pouring the mixed slurry into a mold frame; (4) placing the mold frame in a static room at 40-50 DEG C for 2.5-3.5 hours to harden the mixed slurry in the mold frame into a green body meeting the cutting hardness; (5) allowing the green body to stand for 1-3 hours to complete pre-curing; (6) placing the green body after pre-curing into an autoclave for high-temperature and high-pressure constant-pressure autoclaving for 5-10 hours, wherein the temperature of the autoclave is 174.5-197 DEG C, and the constant-pressure pressure is 0.8-1.4 MPa, and the autoclaved product is obtained.

2. The method of manufacturing autoclaved aerated concrete products according to claim 1, characterized in that: In the step (1), the waste powder slurry is heated to 40-60 DEG C by using the residual gas in the autoclave during autoclaving to heat the water to above 50 DEG C, and then the waste powder is added into the water to form the waste powder slurry.

3. The method for manufacturing autoclaved aerated concrete products as described in claim 1, characterized in that: in The waste powder slurry in the step (1) or the mixed slurry in the step (2) is added with high-silicon tailings.

4. The method for manufacturing autoclaved aerated concrete products as described in claim 1, characterized in that: in In the step (1), the ratio of the waste powder to water is determined according to the requirement that the specific gravity of the waste powder slurry is 1.4-1.7 at 40-60 DEG C.

5. The method of manufacturing autoclaved aerated concrete products according to claim 1, characterized in that the mixture is subjected to the autoclaving process in a pressure vessel. The waste powder slurry in the step (1) and / or the mixed slurry in the step (2) is added with coal ash, high-silicon tailings, and anhydrite powder, and the weight ratio of the various raw materials according to the dry basis content is as follows: the waste powder 40-45 parts, the high-silicon tailings 35-40 parts, the coal ash 5-6 parts, the cement 10-12 parts, the high-calcium quicklime with an effective calcium oxide content of more than 80% 8-10 parts, and the anhydrite powder 1-2 parts.

6. An autoclaved aerated concrete product characterised in that The autoclaved aerated concrete product is made by using the method according to any one of claims 1-5.