Fly ash unfired haydite and its preparation method

Abstract

The application provides a fly ash unfired haydite and a preparation method thereof. The fly ash unfired haydite is obtained by granulation to obtain a haydite base body, and then a secondary pelletization is performed to construct a shell structure, and finally a composite curing method is adopted; the haydite base body is prepared from fly ash, cement, gypsum, alkali activator and water; and the material for the shell is fly ash and cement. The application solves the problems of insufficient fly ash activity, less reaction product and low strength of the fly ash unfired haydite, solves the technical problem of low haydite granulation efficiency caused by the difficulty in accurate control of the traditional water adding method during granulation, and solves the problems of poor initial structure stability and durability of the conventional unfired haydite, thereby solving the problem of weak mechanical performance of the fly ash unfired haydite when applied in the field of concrete.

Description

Technical Field

[0001] This invention belongs to the field of non-fired ceramsite preparation, specifically relating to a fly ash non-fired ceramsite and its preparation method. Background Technology

[0002] Fly ash is a fine ash captured from coal-fired flue gas and is a solid waste emitted by thermal power plants. It has become my country's largest single source of solid pollution, with its annual emissions increasing year by year. However, the overall utilization rate of fly ash remains low. Currently, the main uses of fly ash include cement, concrete, and building material production. With continuous technological advancements, building materials are developing towards lightweight and high-performance, giving rise to the development of ceramsite. Non-fired fly ash ceramsite refers to ceramsite prepared without calcination, using fly ash as the main raw material, with the addition of admixtures and binders, and granulated through natural curing, steam curing, or autoclaving. Its strength development mechanism is through chemical activation. During the curing process, active oxides such as SiO2 and Al2O3 in the fly ash react with alkaline substances, and with Ca... 2+ The reaction produces hydrated calcium silicate (CSH) and hydrated calcium aluminate (CAH) hydraulic cementitious products, which improve the mechanical properties of the ceramsite. Compared with sintered fly ash ceramsite, it has higher raw material utilization, simpler process, requires no large-scale equipment, and is environmentally friendly, thus having broader development prospects and conforming to the national circular economy development strategy.

[0003] Therefore, the activation degree of fly ash pozzolanic activity is particularly crucial. This invention demonstrates that simple pretreatment with alkaline solutions such as NaOH, and the simple addition of calcium such as Ca(OH)2 or gypsum, cannot enhance the strength of ceramsite. However, the fly ash activation method of adding calcium after alkaline pretreatment can effectively improve fly ash activity. Furthermore, the addition of calcium can induce a silicon-calcium reaction in the system, significantly enhancing the mechanical properties of the fly ash ceramsite. Simultaneously, a secondary pelletizing process for non-fired fly ash ceramsite, constructing a core-shell structure, can significantly improve its structural stability. On the other hand, precise control of water usage is a prerequisite for forming uniformly sized fly ash pellets. The optimal water addition should fill all the gaps between fly ash particles without forming a water film on the pellet surface. Currently, the water addition method in the fly ash ceramsite granulation process often involves spraying mist water onto the dry material as it rotates on the pelletizing disc. This process is complex and difficult to control, easily causing material adhesion to the pelletizing disc and reducing raw material utilization. Furthermore, the reaction in fly ash pellets is a slow and continuous process, which is often affected by external curing conditions such as temperature, humidity and pressure. Therefore, the composite curing method of this invention, which combines multiple curing regimes, can rapidly improve the strength of fly ash ceramsite, reduce the curing age and lower costs compared to single-form curing, and has good application advantages.

[0004] Existing technologies for preparing non-fired ceramsite from fly ash generally involve: mixing dried fly ash with a measured amount of cement, quicklime, or water glass powder, and then mixing the mixture in a mixer or similar device. The resulting material is then fed into a disc granulator or similar granulation equipment. The disc angle and rotation speed are set, and the granulator is started. Once the rotation speed is constant and the internal rolling state of the material stabilizes, water is slowly sprayed onto the material, with a fixed spraying time and interval. After 1-2 minutes, the granulation process is observed. The resulting spherical particles are then removed and cured. After a certain curing period, non-fired ceramsite from fly ash is obtained. (Detailed explanation follows.)

[0005] 1. The above-mentioned fly ash categories are mostly Grade I to II fly ash, the cement is ordinary Portland cement, and the type is mostly P.O52.5 or PO42.5. The main component of quicklime is CaO, and it is mostly ordinary commercial quicklime or CaO chemical reagent. The main component of water glass is Na2SiO3, and it is usually ordinary commercial water glass or Na2SiO3 chemical reagent.

[0006] 2. Most of the above-mentioned disc granulators are ordinary commercial granulation equipment. The diameter of the granulator ranges from 400 to 800 mm, the height of the baffle ranges from 100 to 350 mm, the disc inclination angle is generally 35° to 55°, and the rotation speed is 30 to 35 r / min.

[0007] 3. The above-mentioned watering method generally involves adding water from a spray bottle, often set as a shower head or a spray pattern. Each spray lasts about 1 second, with an interval of 5 to 10 seconds between each spray, lasting 1 to 2 minutes. The amount of water added is generally 10% to 35% (total material mass fraction).

[0008] 4. The granulation time is generally 8 to 20 minutes. After granulation, curing should be carried out directly.

[0009] 5. Most of the above maintenance methods are natural maintenance, with an age of 28 days.

[0010] 6. The specific preparation technology of the above-mentioned fly ash non-fired ceramsite is as follows:

[0011] (1) After drying to constant weight, weigh the raw materials according to the proportion of each ingredient;

[0012] (2) Place the raw materials in a mixer or other mixing device and mix for 60 seconds to obtain a uniform dry mixture.

[0013] (3) Pour the dry mixed material into a granulation equipment such as a disc granulator. Taking a disc granulator as an example, set the disc tilt angle to 35°~55°, the rotation speed to 30~35r / min, and the baffle height to 100~350mm.

[0014] (4) Start the disc granulator. After 30 seconds, when the speed is constant and the rolling state of the internal material tends to be stable, use a sprayer to slowly spray water onto the material. The sprayer is set to a sprinkler or a cluster sprayer. Each spray lasts about 1 second, with an interval of 5 to 10 seconds between each spray, and continues for 1 to 2 minutes. The amount of water added is generally 10% to 35% (total material mass fraction).

[0015] (5) After spraying water for 1-2 minutes, observe the granulation situation, take out the spherical particles, continue to spray water in the above water addition method, and continuously take out the ceramsite raw material balls. The granulation time is about 8-20 minutes until the remaining material cannot be granulated. The obtained ceramsite raw material balls are cured. Natural curing is to place them in an indoor environment for 28 days. Steam curing is to place the ceramsite raw material balls in a steam curing box for 6-24 hours after pretreatment such as room temperature static or drying. The temperature is generally 60-90℃. Finally, fly ash non-fired ceramsite is obtained.

[0016] Disadvantages of existing technology:

[0017] (1) In existing fly ash non-fired ceramsite preparation technologies, the fly ash activity is not sufficiently activated, and the alkaline activator is usually a single water glass or quicklime, resulting in insufficient internal reaction products in the fly ash non-fired ceramsite, which reduces its mechanical properties. Increasing the amount of alkaline activator will increase the preparation cost. In addition, in traditional fly ash non-fired ceramsite preparation technologies, in order to improve the overall performance of ceramsite, a large amount of cement is often used as ceramsite binder, with an admixture of 20% to 50% (total dry material mass fraction), which is costly and not conducive to the disposal of fly ash.

[0018] (2) In the existing process of preparing fly ash non-fired ceramsite, the traditional sprayer water addition process is relatively complicated, and the amount of water added is not easy to control precisely, resulting in a large error. In addition, spraying water can easily cause the material to adhere to the pelletizing disc, reducing the utilization rate of raw materials. Moreover, the moisture content of the raw ceramsite pellets formed in a single batch is often different from the optimum moisture content, resulting in a large dispersion of ceramsite particle size and strength from the set values.

[0019] (3) In the existing fly ash non-fired ceramsite performance enhancement process, the secondary pelletizing process is relatively complicated. It often involves curing the ceramsite matrix for 3 to 7 days before constructing the core-shell structure, and the proportion of cement in the outer shell material is relatively high.

[0020] (4) In the existing curing stages of fly ash non-fired ceramsite, natural curing or steam curing are generally used, which have a long curing period or high cost. During 28-day natural curing, the temperature and humidity that significantly affect the internal reaction of ceramsite cannot be kept constant. Before steam curing, the raw ceramsite pellets need to be pretreated, and the long steam curing period can easily cause the ceramsite to be subjected to continuous thermal shock, which can damage its surface and reduce its mechanical properties. Summary of the Invention

[0021] The purpose of this invention is to provide a fly ash-based non-fired ceramsite and its preparation method, solving the problems of insufficient fly ash activity leading to low reaction products and low strength in fly ash-based non-fired ceramsite, and addressing the technical challenge of low granulation efficiency caused by the difficulty in precisely controlling water addition in traditional granulation methods. Furthermore, it solves the problem of poor initial structural stability and durability of conventional non-fired ceramsite, thus addressing the issue of fly ash-based non-fired ceramsite becoming a weak point in the mechanical properties of concrete.

[0022] To achieve the above objectives, the present invention adopts the following technical solution:

[0023] A method for preparing fly ash-based non-fired ceramsite: The fly ash-based non-fired ceramsite is obtained by granulation to form a ceramsite matrix, followed by secondary pelletizing to construct an outer shell structure, and then cured using a composite curing method; the ceramsite matrix is ​​prepared from fly ash, cement, gypsum, alkali activator, and water, wherein fly ash accounts for 86.2wt%~90.9wt% of the total dry materials, cement accounts for 10% of the fly ash mass, gypsum accounts for 2% of the fly ash mass, alkali activator accounts for 2%~5% of the fly ash mass, and water is added at 25% of the fly ash mass; the outer shell is made of fly ash and cement; the total outer shell material is 10% of the fly ash mass used in the ceramsite matrix.

[0024] Preferably, the equipment used for granulation is a disc granulator with a diameter of 600 mm.

[0025] Preferably, the fly ash is Class II, Type F, the cement is ordinary Portland cement, type PO 42.5, and the gypsum is dihydrate gypsum.

[0026] Preferably, the alkali activator is composed of calcium oxide, sodium silicate and sodium hydroxide, all of which are pure chemical reagents. The amount of calcium oxide is 2% to 3% of the mass of fly ash, the amount of sodium silicate is 0.25% to 1% of the mass of fly ash, the amount of sodium hydroxide is 0.25% to 1% of the mass of fly ash, the fly ash used in the shell accounts for 90 wt% of the shell material, and the cement accounts for 10 wt% of the shell material.

[0027] Preferably, the water is added after the materials are dry-mixed evenly.

[0028] Preferably, the composite curing is a combination of natural curing, constant temperature and humidity curing, and steam curing, performed in sequence, with each of the three curing methods lasting 12 hours.

[0029] A method for preparing fly ash non-fired ceramsite includes the following steps:

[0030] (1) Dry the fly ash to constant weight, and weigh each raw material according to the proportion;

[0031] (2) Pour fly ash, cement and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry mixture.

[0032] (3) Pour sodium hydroxide and sodium silicate into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain a wet mixture. Add calcium oxide and continue stirring for 60 seconds.

[0033] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60r / min, and the baffle height to 30~100mm;

[0034] (5) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is sprinkled on the surface of the ceramic aggregate matrix. The matrix is ​​rotated in the granulator for 30 seconds for secondary pelletizing and then removed. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0035] (6) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0036] Key points of this invention:

[0037] (1) The water addition method adopted in this invention is to add water after the dry material is stirred evenly, which is different from the water addition method of spray bottle in the conventional granulation process. This point is quite special.

[0038] (2) This invention uses a method of pretreatment with sodium silicate and sodium hydroxide alkaline solution followed by the addition of calcium substances (calcium oxide) to activate fly ash, which differs from the traditional method of using a single type of activator for fly ash. Furthermore, the amount of cement used in this invention is 10% of the fly ash mass fraction, significantly lower than the traditional cement dosage.

[0039] (3) The present invention adopts a process of secondary pelletizing immediately after the raw material of fly ash non-fired ceramsite is formed to construct a core-shell structure, which is different from the conventional fly ash non-fired ceramsite matrix being cured before secondary pelletizing.

[0040] (4) The present invention uses a composite curing method to cure fly ash non-fired ceramsite, which is different from the traditional single curing method for fly ash non-fired ceramsite.

[0041] The advantages of this invention are:

[0042] (1) This invention avoids the problems of traditional granulation processes where water is added via a spray bottle, which can easily cause material to adhere to the pelletizing disc and reduce raw material utilization. This invention precisely controls the amount of water used by adding water and stirring, eliminating the need for additional water during subsequent granulation. This increases the proportion of fly ash particles in a capillary state during granulation, avoiding the difficulties in granulation when water is insufficient, and the problems of excessive water causing particle enlargement, collapse, and deformation of the ceramsite spheres, which negatively impacts the early strength of the ceramsite. Furthermore, the water addition method provided by this invention can be used as a pretreatment process for fly ash alkaline solution, activating the fly ash before granulation.

[0043] (2) This invention avoids the problems of insufficient activation of fly ash, which leads to fewer products generated inside the fly ash-fired ceramsite, resulting in low strength and high water absorption. This invention uses an alkaline solution pretreatment followed by the addition of calcium compounds to activate the fly ash in OH... - Under the action of ions, the network structure on the surface of the glass is destroyed, the degree of polymerization of the network polymer is greatly reduced, and the active oxides of SiO2 and Al2O3 are dissolved and released, which significantly stimulates the pozzolanic activity of fly ash. The addition of calcium causes the active oxides to undergo chemical reactions to generate cementing substances such as CSH and C-(A)-SH and products such as ettringite, which improves the mechanical properties of ceramsite.

[0044] (3) The core-shell structure ceramsite constructed by the present invention has the characteristics of simple process, low cement consumption and excellent physical properties. At the same time, it does not require the ceramsite matrix to be cured and then subjected to secondary pelletizing, saving time and cost. In addition, the composite curing process adopted by the present invention significantly shortens the curing period. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the preparation process of fly ash non-fired ceramsite according to the present invention. Detailed Implementation

[0046] To make the above-mentioned features and advantages of the present invention more apparent and understandable, specific embodiments are described below in detail. Unless otherwise specified, the methods of the present invention are conventional methods in the art.

[0047] This embodiment provides a fly ash-based non-fired ceramsite and its preparation method. The fly ash-based non-fired ceramsite is obtained by granulation to obtain a ceramsite matrix, followed by secondary pelletizing to construct an outer shell structure, and then cured using a composite curing method. The ceramsite matrix is ​​prepared from fly ash, cement, gypsum, alkali activator, and water. The fly ash is Class II, Type F, accounting for 86.2 wt% to 90.9 wt% of the total dry matter. The cement type is PO 42.5, and its dosage is 10% of the fly ash mass. The gypsum is dihydrate gypsum, and its dosage is 2% of the fly ash mass. The alkali activator is composed of calcium oxide, sodium silicate, and sodium hydroxide, all of which are pure chemical reagents. The dosage of calcium oxide is 2% to 3% of the fly ash mass, the dosage of sodium silicate is 0.25% to 1% of the fly ash mass, and the dosage of sodium hydroxide is 0.25% to 1% of the fly ash mass. The amount of water added is 25% of the fly ash mass.

[0048] Fly ash accounts for 90 wt% of the shell material, and cement accounts for 10 wt% of the shell material.

[0049] The water is added after the materials are dry-mixed evenly.

[0050] The secondary pelletizing process involves immediately sprinkling fly ash and cement into the granulated material to construct a core-shell structured ceramic aggregate.

[0051] The composite curing method consists of natural curing, constant temperature and humidity curing, and steam curing.

[0052] Comparative Example 1

[0053] (1) Weigh out 3000 parts of Class II F fly ash dried to constant weight, 600 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 90 parts of calcium oxide chemical reagent (analytical grade, CaO content ≥98%), and 700 parts of water according to the mass ratio. Pour the water into a spray bottle and set aside.

[0054] (2) Place the weighed fly ash, cement, gypsum and calcium oxide into a mixer and stir for 60 seconds to obtain a uniform dry mixture.

[0055] (3) Pour the dry mixture into the disc granulator, set the disc tilt angle to 45°, the rotation speed to 30 r / min, and the baffle height to 150 mm;

[0056] (4) After starting the disc granulator for 30 seconds, slowly spray water onto the material using a sprayer. Set the sprayer to a sprinkler shape, spray water for 1 second at a time, with a 5-second interval between each spray, for a total of 90 seconds.

[0057] (5) Observe the granulation situation, take out the spherical particles, continue to spray water according to the above water addition method, and continuously take out the ceramsite raw material balls. The granulation time is 15 minutes until the remaining material cannot be granulated. Place the prepared ceramsite raw material balls in an indoor environment for natural curing for 28 days.

[0058] Comparative Example 2

[0059] (1) Weigh out 3000 parts of Class II F fly ash dried to constant weight, 600 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 90 parts of calcium oxide chemical reagent (analytical grade, CaO content ≥98%), and 700 parts of water according to the mass ratio. Pour the water into a spray bottle and set aside.

[0060] (2) Place the weighed fly ash, cement, gypsum and calcium oxide into a mixer and stir for 60 seconds to obtain a uniform dry mixture.

[0061] (3) Pour the dry mixture into the disc granulator, set the disc tilt angle to 45°, the rotation speed to 30 r / min, and the baffle height to 150 mm;

[0062] (4) After starting the disc granulator for 30 seconds, slowly spray water onto the material using a sprayer. Set the sprayer to a sprinkler shape, spray water for 1 second at a time, with a 5-second interval between each spray, for a total of 90 seconds.

[0063] (5) Observe the granulation situation, take out the spherical particles, continue to spray water according to the above water addition method, and continuously take out the ceramsite raw material balls. The granulation time is 15 minutes until the remaining material cannot be granulated. Place the prepared ceramsite raw material balls in an indoor environment and let them stand for 6 hours, and then place them in a 90℃ steam curing box for 24 hours.

[0064] Comparative Example 3

[0065] (1) Weigh out 3000 parts of Class II F fly ash dried to constant weight, 600 parts of PO 42.5 ordinary silicate cement, 60 parts of gypsum dihydrate, 75 parts of sodium silicate chemical reagent (analytical grade, Na2SiO3≥98%), and 700 parts of water according to the following mass proportions: place sodium silicate in water and stir evenly, pour the sodium silicate solution into a spray bottle, and set aside.

[0066] (2) Place the weighed fly ash, cement and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry mixture.

[0067] (3) Pour the dry mixture into the disc granulator, set the disc tilt angle to 45°, the rotation speed to 30 r / min, and the baffle height to 150 mm;

[0068] (4) After starting the disc granulator for 30 seconds, slowly spray sodium silicate solution onto the material using a sprayer. Set the sprayer to a sprinkler shape, spray water for 1 second at a time, with a 5-second interval between each spray, for a total of 90 seconds.

[0069] (5) Observe the granulation situation, take out the spherical particles, continue to spray water according to the above water addition method, and continuously take out the ceramsite raw material balls. The granulation time is 15 minutes until the remaining material cannot be granulated. Place the prepared ceramsite raw material balls in an indoor environment for natural curing for 28 days.

[0070] Comparative Example 4

[0071] (1) Weigh out 3000 parts of Class II F fly ash dried to constant weight, 600 parts of PO 42.5 ordinary silicate cement, 60 parts of gypsum dihydrate, 75 parts of sodium silicate chemical reagent (analytical grade, Na2SiO3≥98%), and 700 parts of water according to the following mass proportions: place sodium silicate in water and stir evenly, pour the sodium silicate solution into a spray bottle, and set aside.

[0072] (2) Place the weighed fly ash, cement and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry mixture.

[0073] (3) Pour the dry mixture into the disc granulator, set the disc tilt angle to 45°, the rotation speed to 30 r / min, and the baffle height to 150 mm;

[0074] (4) After starting the disc granulator for 30 seconds, slowly spray sodium silicate solution onto the material using a sprayer. Set the sprayer to a sprinkler shape, spray water for 1 second at a time, with a 5-second interval between each spray, for a total of 90 seconds.

[0075] (5) Observe the granulation situation, take out the spherical particles, continue to spray water according to the above water addition method, and continuously take out the ceramsite raw material balls. The granulation time is 15 minutes until the remaining material cannot be granulated. Place the prepared ceramsite raw material balls in an indoor environment and let them stand for 6 hours, and then place them in a 90℃ steam curing box for 24 hours.

[0076] Example 1

[0077] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 60 parts of calcium oxide (analytical grade), 7.5 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0078] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0079] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0080] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0081] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0082] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0083] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0084] Example 2

[0085] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 60 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0086] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0087] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0088] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0089] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0090] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0091] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0092] Example 3

[0093] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 60 parts of calcium oxide (analytical grade), 22.5 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0094] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0095] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0096] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0097] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0098] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0099] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0100] Example 4

[0101] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 60 parts of calcium oxide (analytical grade), 30 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0102] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0103] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0104] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0105] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0106] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0107] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0108] Example 5

[0109] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 75 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0110] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0111] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0112] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0113] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0114] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0115] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0116] Example 6

[0117] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 90 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), and 750 parts of water according to the following mass percentages: Weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement for the outer shell material, and set aside.

[0118] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0119] (3) Pour the weighed sodium silicate powder into water and stir clockwise until it is completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0120] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0121] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0122] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0123] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0124] Example 7

[0125] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 75 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), 7.5 parts of sodium hydroxide granules (analytical grade), and 750 parts of water according to the following mass percentages: For the outer shell material, weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement, and set aside.

[0126] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0127] (3) Pour the weighed sodium silicate powder and sodium hydroxide granules into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0128] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0129] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0130] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0131] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0132] Example 8

[0133] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 75 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), 15 parts of sodium hydroxide granules (analytical grade), and 750 parts of water according to the following mass percentages: For the outer shell material, weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement, and set aside.

[0134] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0135] (3) Pour the weighed sodium silicate powder and sodium hydroxide granules into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0136] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0137] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0138] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0139] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0140] Example 9

[0141] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 75 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), 22.5 parts of sodium hydroxide granules (analytical grade), and 750 parts of water according to the following mass percentages: For the outer shell material, weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement, and set aside.

[0142] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0143] (3) Pour the weighed sodium silicate powder and sodium hydroxide granules into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0144] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0145] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0146] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0147] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0148] Example 10

[0149] (1) Weigh out 3000 parts of F-grade Class II fly ash dried to constant weight, 300 parts of PO 42.5 ordinary Portland cement, 60 parts of gypsum dihydrate, 75 parts of calcium oxide (analytical grade), 15 parts of sodium silicate powder (analytical grade), 30 parts of sodium hydroxide granules (analytical grade), and 750 parts of water according to the following mass percentages: For the outer shell material, weigh out 270 parts of F-grade Class II fly ash and 30 parts of PO 42.5 ordinary Portland cement, and set aside.

[0150] (2) Pour fly ash, cement, and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry-mixed material.

[0151] (3) Pour the weighed sodium silicate powder and sodium hydroxide granules into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add the weighed calcium oxide and continue stirring for 60 seconds.

[0152] (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm.

[0153] (5) Place the weighed shell material in a small mixer and stir for 60 seconds;

[0154] (6) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is coated on the surface of the formed ceramic aggregate matrix. After rotating in the granulator for 30 seconds for secondary pelletizing, it is taken out. By continuously reducing the height of the baffle (from 100mm to 30mm), the granulation-sprinkling of outer shell material-secondary pelletizing steps are repeated. The granulation and secondary pelletizing steps are carried out continuously until the granulation is completed. The entire granulation process lasts for 15 minutes.

[0155] (7) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

[0156] According to the national standard "Lightweight aggregates and their test methods - Part 2: Lightweight aggregates test methods" (GB / T17431.2-2010), the performance parameters of Comparative Examples 1-4 and Examples 1-10 are shown in Table 1.

[0157] Table 1. Performance test results of fly ash non-fired ceramsite in Comparative Examples 1-4 and Examples 1-10

[0158]

[0159] Results analysis:

[0160] The properties of conventional fly ash non-fired ceramsite from Comparative Examples 1-4 show that a single type of activator cannot fully activate the pozzolanic activity of fly ash, and sodium silicate or calcium oxide alone cannot provide sufficient OH groups to the system. - The steam curing process disrupts the glassy structure of fly ash (mainly the Si-O-Si and Si-O-Al network structures), resulting in less dissolution of active SiO2 and Al2O3. This leads to fewer CSH and C-(A)-SH gels and ettringite crystals formed in the system, resulting in lower density of the internal microstructure and generally lower physical properties of the ceramsite. Comparative Examples 2 and 4, using steam curing, benefit from a high-temperature environment that accelerates the dissolution of active substances in the fly ash, increasing the internal reaction rate of the ceramsite raw material. Simultaneously, it facilitates the gradual penetration of moisture from the outside to the inside, increasing the amount of reaction products and improving the density of the internal and external structures of the raw material. Therefore, Comparative Examples 2 and 4 outperform Comparative Examples 1 and 3, respectively. However, due to insufficient active substances within the ceramsite, the steam curing method has a limited effect on improving its performance. In addition, the method of adding water by spraying causes the powder that comes into contact with water to slurry first, but during the rotation process, the water gradually penetrates into the remaining material, reducing the moisture content of the first batch of raw material balls, which is not conducive to the internal reaction. At the same time, it increases the moisture content of subsequent batches of raw material balls, making the balling process extremely difficult to control, and the prepared ceramsite particles are of inconsistent size and have low strength.

[0161] As can be seen from the properties of the fly ash-based non-fired ceramsite used in Examples 1-10 of this invention, the addition of calcium after pretreatment with an alkaline solution can significantly improve the pozzolanic activity of the fly ash. Simultaneously, the method of adding water and stirring the material can improve the uniformity of alkaline activation of the fly ash. Precise control of the water volume can maintain the capillary state (water filling all pores) during the fly ash granulation process. The force on the fly ash particles expels the air filling the gaps between the particles, and the voids are filled by water and fly ash particles. There is no water film on the particle surface, and the ceramsite raw material balls are compressed more densely. A secondary pelletizing process is then performed. During the natural curing stage, while the internal structure of the ceramsite raw material balls maintains a certain stability, the outer shell material rapidly hardens to form a hard shell layer. Subsequently, during the constant temperature and humidity curing stage, sufficient moisture is provided, and errors caused by changes in the external environment are reduced, allowing the ceramsite matrix and shell to react further. Finally, high-temperature steam curing is performed, providing a high-temperature and high-humidity chemical reaction environment to accelerate the internal chemical reaction of the ceramsite.

[0162] Step-by-step analysis:

[0163] From the properties of the fly ash-free ceramsite used in Examples 1-4 of this invention, it can be seen that after pretreatment with sodium silicate solution, OH... -Under the action of ions, the network structure on the surface of fly ash glass is destroyed, the degree of polymerization of the network polymers is greatly reduced, active SiO2 and Al2O3 are dissolved and released, and the activity of fly ash latent pozzolanic material is activated. The subsequent addition of calcium oxide further enhances the OH- ion activity of the system. - The quantity, at the same time, enriched Ca 2+ This process causes the active oxides to react chemically, generating a cementitious substance that improves the mechanical properties of the ceramsite. It is noteworthy that the compressive strength of the ceramsite initially increases and then decreases with increasing sodium silicate solution concentration. The ceramsite exhibits the best performance when its content is 0.5% of fly ash by mass, subsequently decreasing gradually. This is because the SiO2 in sodium silicate is more reactive than the SiO2 in fly ash, reacting with Ca(OH)2 before the fly ash, consuming some of the Ca(OH)2 and reducing the strength of the ceramsite.

[0164] As can be seen from the properties of the fly ash-free ceramsite used in Examples 3, 5, and 6 of this invention, the performance of the ceramsite increases with the increase of calcium oxide content. The reaction of calcium oxide with water is exothermic, which can further enhance the activity of the fly ash during the stirring stage. In addition, it can provide sufficient Ca to the system. 2+ With OH - Reactants, in OH - Under the influence of the action, the network structure on the surface of fly ash particles breaks down, the degree of polymerization of the network aggregate decreases, and Ca 2+ It can promote the formation of CSH gel in the gelation system.

[0165] As can be seen from the properties of the fly ash-free ceramsite used in Examples 7-10 of this invention, the addition of sodium hydroxide further enhances the activity of fly ash, promotes the degree of reaction inside the ceramsite, and significantly improves the overall performance of the fly ash-free ceramsite. In the alkaline environment of the system, most of the vitreous phase of fly ash is eroded, exhibiting strong depolymerization ability. A large amount of active SiO2 and Al2O3 dissolve and undergo hydration reactions to generate cementitious substances, increasing strength. Furthermore, the main component of gypsum in the system is CaSO4, and fly ash reacts with SO42-. 2- With Ca 2+ Under the dual action of [the process], it reacts with active Al2O3 to generate hydrated calcium sulfoaluminate (calcium aluminate), thereby increasing the strength of the ceramsite.

[0166] The main chemical reactions involved are:

[0167]

[0168] Conclusion: Compared with conventional fly ash-based non-fired ceramsite, the preparation method provided by this invention can not only precisely control the water content, maintain the capillary state of fly ash during granulation, and improve the density of the ceramsite raw material balls, but also fully activate the pozzolanic activity of fly ash. Even with low cement content, it can still dissolve and precipitate more active substances such as SiO2 and Al2O3, generating a large amount of CSH and C-(A)-SH gels and ettringite crystals, significantly improving the performance of ceramsite. Examples 1-10 of the fly ash-based non-fired ceramsite prepared by this invention all exhibit excellent performance, with a compressive strength of 6.53-8.98 MPa, a water absorption rate of 12.53%-17.24%, and a bulk density of 810.84-857.24 kg·m³. -3 The apparent density is 1412.24~1667.46 kg·m³. -3 The softening coefficient is 0.82~0.92, which meets the relevant requirements of Grade 900 high-strength lightweight coarse aggregate in the national standard "Lightweight aggregates and their test methods Part 1: Lightweight aggregates" (GB / T17431.2-2010), making the present invention applicable to the field of lightweight structural concrete.

[0169] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing fly ash non-fired ceramsite, characterized in that: The fly ash-based non-fired ceramsite is obtained by granulation to form a ceramsite matrix, followed by secondary pelletizing to construct an outer shell structure, and then cured using a composite curing method. The ceramsite matrix is ​​prepared from fly ash, cement, gypsum, alkali activator, and water. Fly ash accounts for 86.2 wt% to 90.9 wt% of the total dry materials, cement accounts for 10% of the fly ash mass, gypsum accounts for 2% of the fly ash mass, alkali activator accounts for 2% to 5% of the fly ash mass, and water is added at 25% of the fly ash mass. The outer shell is made of fly ash and cement, with the total outer shell material accounting for 10% of the fly ash mass used in the ceramsite matrix. The method for preparing fly ash non-fired ceramsite includes the following steps: (1) Dry the fly ash to constant weight, and weigh each raw material according to the proportion; (2) Pour fly ash, cement and gypsum into a mixer and mix for 60 seconds to obtain a uniform dry mixture. (3) Pour sodium hydroxide and sodium silicate into water and stir clockwise until completely dissolved in water. Then pour the solution into the dry mixture and stir for 90 seconds to obtain the wet mixture. Add calcium oxide and continue stirring for 60 seconds. (4) Pour all materials into the disc granulator, set the disc tilt angle to 50°, the rotation speed to 60 r / min, and the baffle height to 30~100 mm; (5) After granulation for 60 seconds, a ceramic aggregate matrix is ​​obtained. The outer shell material is sprinkled on the surface of the ceramic aggregate matrix. The pelletizer is rotated for 30 seconds to perform secondary pelletization and then removed. By continuously reducing the height of the baffle from 100 mm to 30 mm, the granulation-sprinkling outer shell material-secondary pelletization steps are repeated. The granulation and secondary pelletization steps are carried out continuously until the granulation is completed. (6) All the secondary pelletized ceramsite was placed in an indoor environment for 12 hours for natural curing, and then moved into a constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95%. After curing for 12 hours, it was placed in a steam curing box with a temperature of 90℃ for 12 hours. After standing to room temperature, fly ash non-fired ceramsite was obtained.

2. The method for preparing fly ash non-fired ceramsite according to claim 1, characterized in that, The equipment used for granulation is a disc granulator with a diameter of 600 mm.

3. The method for preparing fly ash non-fired ceramsite according to claim 1, characterized in that, The fly ash is Class II, Type F; the cement is ordinary Portland cement, type PO 42.5; and the gypsum is dihydrate gypsum.

4. The method for preparing fly ash non-fired ceramsite according to claim 1, characterized in that, The alkaline activator is composed of calcium oxide, sodium silicate and sodium hydroxide, all of which are pure chemical reagents. The amount of calcium oxide is 2% to 3% of the mass of fly ash, the amount of sodium silicate is 0.25% to 1% of the mass of fly ash, and the amount of sodium hydroxide is 0.25% to 1% of the mass of fly ash. The fly ash used in the shell accounts for 90 wt% of the shell material, and the cement accounts for 10 wt% of the shell material.

5. The method for preparing fly ash non-fired ceramsite according to claim 1, characterized in that, The water is added after the materials are dry-mixed evenly.

6. The method for preparing fly ash non-fired ceramsite according to claim 1, characterized in that, The composite curing process combines natural curing with constant temperature and humidity curing and steam curing, performed in sequence, with each of the three curing methods lasting 12 hours.

7. Fly ash non-fired ceramsite prepared by the preparation method according to any one of claims 1-6.

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