Low-alkali accelerator, its preparation method and application

Abstract

The application relates to the technical field of coal-based solid waste resource utilization and coal mine shotcrete supporting materials, and discloses a low-alkali accelerator as well as a preparation method and application thereof. The method comprises the following steps: mixing alumina clinker, aluminum sulfate and polyacrylamide, wherein, relative to 100 parts by weight of the alumina clinker, the amount of the aluminum sulfate is 5-16 parts by weight, and the amount of the polyacrylamide is 0.1-5 parts by weight; performing aging treatment on the mixture obtained in the foregoing step by using water, then drying the product after aging, and obtaining a solid semi-finished product with a water content of 3% or less; and performing ball milling on the solid semi-finished product. The low-alkali accelerator disclosed by the application has a lower alkali content, can reduce problems such as an increase in porosity, corrosion of steel members and alkali-aggregate reaction in a high-alkali environment, and simultaneously promotes the generation of early ettringite and C-S-H gel through active aluminum ions, so that the material has both rapid setting ability and is not prone to the phenomenon of late strength reduction.

Description

Technical Field

[0001] This invention relates to the field of coal-based solid waste resource utilization and coal mine shotcrete support materials, specifically to a low-alkali quick-setting agent, its preparation method, and its application. Background Technology

[0002] Surface reinforcement materials for coal mine roadways need to meet requirements such as rapid setting, early load-bearing capacity, and stable strength in the later stages. Traditional shotcrete materials mainly consist of silicate cement and washed sand, supplemented with accelerators to achieve rapid support. However, existing technologies have the following shortcomings: First, traditional powdered quick-setting agents have high dosage, low quick-setting efficiency, and poor later strength retention, making it difficult to meet both the requirements of rapid setting and long-term service.

[0003] Secondly, high alkalinity accelerators have a high alkali content, which can easily lead to problems such as increased porosity, corrosion of steel components, and alkali-aggregate reaction in the later stage, causing a reduction in strength in the later stage and affecting the durability of the support system.

[0004] Third, although existing coal-based solid waste spraying material technologies attempt to replace some traditional raw materials with coal gasification slag and fly ash, these are mostly simple replacements and lack synergistic design with quick-setting agents. This results in insufficient early activity of coal-based solid waste materials, increased water demand, and slow strength development, making it difficult to achieve stable and high-proportion resource utilization.

[0005] At the same time, coal-based solid wastes such as coal gasification slag and fly ash are generated in large quantities and are under high storage pressure, while natural resources such as washed sand are becoming increasingly scarce and their prices continue to rise. There is an urgent need to develop a surface reinforcement material that can take into account early rapid setting, stable strength in the later stage, low alkali and environmental protection, and achieve efficient and synergistic utilization of coal-based solid wastes.

[0006] Therefore, developing a coal-based solid waste surface reinforcement material based on a low-alkali powdered quick-setting agent, through the synergistic design of fly ash, coal gasification slag and low-alkali quick-setting agent, can solve the problems of low quick-setting efficiency, subsequent strength reduction and insufficient utilization of solid waste in the existing technology, which is of great engineering significance. Summary of the Invention

[0007] The purpose of this invention is to address the problems of low rapid setting efficiency, later-stage strength reduction, and insufficient utilization of solid waste in existing technologies for concrete. It provides a low-alkali rapid setting agent, its preparation method, and its application. Compared with traditional high-alkali rapid setting agent systems, the low-alkali rapid setting agent of this invention has a lower alkali content, which can reduce problems such as increased porosity, steel component corrosion, and alkali-aggregate reaction in high-alkali environments. Simultaneously, it promotes the early formation of ettringite and CSH gel through active aluminum ions, enabling the material to possess both rapid setting ability and less tendency for later-stage strength reduction.

[0008] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a low-alkali quick-setting agent, the method comprising the following steps: (1) Aluminum oxide clinker, aluminum sulfate and polyacrylamide are mixed, wherein, relative to 100 parts by weight of the aluminum oxide clinker, the amount of aluminum sulfate is 5 to 16 parts by weight and the amount of polyacrylamide is 0.1 to 5 parts by weight. (2) The mixture obtained in step (1) is treated with water to mature it, and then the matured product is dried to obtain a solid semi-finished product with a water content of less than 3% by weight. (3) The solid semi-finished product is ball-milled.

[0009] Preferably, the alumina clinker contains 30-40% by weight sodium oxide, 30-40% by weight aluminum oxide, 10-15% by weight calcium oxide, 1-5% by weight magnesium oxide, 1-10% by weight silicon dioxide, 1-5% by weight potassium oxide and 1-5% by weight sulfur trioxide.

[0010] Preferably, before implementing step (1), the method further includes: screening the aluminum oxide clinker through an 80-100 mesh sieve, so that the undersize material obtained is mixed with the aluminum sulfate and the polyacrylamide.

[0011] Preferably, before implementing step (1), the method further includes drying aluminum sulfate to obtain aluminum sulfate with a free water content of not more than 1% by weight.

[0012] Preferably, in step (1), the mixing process specifically includes: mixing aluminum sulfate and aluminum oxide clinker once under stirring conditions, and then mixing the resulting primary mixture with polyacrylamide a second time.

[0013] Preferably, the conditions for the first mixing include: a stirring speed of 10~100 r / min and a stirring time of 10~20 min.

[0014] Preferably, the stirring speed of the secondary mixing is 10~100 r / min, and the stirring time of the secondary mixing is 5~10 min.

[0015] Preferably, in step (2), the aging process is carried out under stirring conditions.

[0016] Preferably, the solid-liquid ratio of the mixture obtained in step (1) to the water is 1:1 to 10, more preferably 1:3 to 5.

[0017] Preferably, the conditions for the maturation treatment include: a temperature of 50~60℃, a time of 20~60min, and a stirring speed of 10~100r / min.

[0018] Preferably, in steps (1) and (2), the stirring process includes: single-phase stirring by a stirring paddle, and applying ultrasonic vibration stirring to the material along the radial direction of the stirring paddle rotation.

[0019] Preferably, the ultrasonic vibration stirring has at least two vibration sources, and the included angle between two adjacent vibration sources is 30° to 120°.

[0020] Preferably, in step (2), the drying process employs microwave heating drying and high-temperature airflow drying.

[0021] Preferably, in step (2), the drying temperature is 80~90℃.

[0022] Preferably, in step (2), there are at least three microwave heating heat sources. The microwave heating heat sources are embedded in the inner side of the side wall of the stirring mechanism and are distributed in a linear or spiral shape around the stirring shaft. At the same time, the axes of two adjacent microwave heating heat sources form an angle of 30° to 60°.

[0023] Preferably, in step (2), the high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is not lower than 60°C, the air pressure is not lower than 300 kPa, and the diameter of a single airflow is 5~20 cm.

[0024] Preferably, in step (3), the conditions for ball milling include: temperature of 20~200℃, time of 0.5~2h, and rotation speed of 50~100r / min.

[0025] A second aspect of the present invention provides a low-alkali quick-setting agent prepared by the method described above.

[0026] A third aspect of the present invention provides a concrete, wherein, based on the total weight of the concrete, the concrete contains 17-18% by weight of cement, 2-3% by weight of fly ash, 15-25% by weight of sand and gravel, 15-25% by weight of coal gasification slag, 35-45% by weight of gravel and 6-8% by weight of the low-alkali quick-setting agent described above.

[0027] Compared with traditional powdered accelerator technology, the low-alkali powdered accelerator described in this invention can achieve rapid setting at a lower dosage and significantly improve the later strength retention performance. Compared with traditional high-alkali accelerator systems, the low-alkali powdered accelerator used in this invention has a lower alkali content, which can reduce problems such as increased porosity, steel component corrosion, and alkali-aggregate reaction in high-alkali environments. At the same time, it promotes the early formation of ettringite and CSH gel through active aluminum ions, so that the material has both rapid setting ability and is not prone to later strength reduction. Compared with existing coal-based solid waste spraying materials that partially replace traditional raw materials with coal gasification slag and fly ash, this invention does not simply replace solid waste, but synergistically designs fly ash, coal gasification slag, and low-alkali powdered accelerator, solving the problems of insufficient early activity, increased water demand, and slow strength development of coal-based solid waste materials. Attached Figure Description

[0028] Figure 1 This is a schematic diagram comparing the 8-hour compressive strength, 1-day compressive strength, and 28-day compressive strength of concretes S1 and S2 prepared in Application Example 1 and Application Example 2.

[0029] Figure 2 This is a schematic diagram comparing the 1-day and 28-day compressive strength of concrete S3~S10 prepared using Examples 3-10.

[0030] Figure 3 This is a schematic diagram comparing the 1-day and 28-day compressive strength of concrete S11~S13 prepared using Examples 11-13. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In this invention, the term "low-alkali quick-setting agent" refers to a quick-setting agent with an alkali content of less than 5% by weight, wherein the alkali contained in the low-alkali quick-setting agent is calcium hydroxide and aluminum hydroxide.

[0034] The preparation method of the low-alkali quick-setting agent of the present invention includes the following steps: (1) Aluminum oxide clinker, aluminum sulfate and polyacrylamide are mixed, wherein, relative to 100 parts by weight of the aluminum oxide clinker, the amount of aluminum sulfate is 5 to 16 parts by weight, preferably 7 to 14 parts by weight, more preferably 10 to 12 parts by weight; and the amount of polyacrylamide is 0.1 to 5 parts by weight, preferably 0.5 to 3 parts by weight, more preferably 1 to 2 parts by weight. (2) The mixture obtained in step (1) is treated with water to mature it, and then the matured product is dried to obtain a solid semi-finished product with a water content of less than 3% by weight. (3) The solid semi-finished product is ball-milled.

[0035] In this invention, the alumina clinker is a clinker formed by sintering bauxite, carbon mother liquor (sodium carbonate), and limestone, with a phase composition mainly consisting of Na₂O·Al₂O₃ and 2CaO·SiO₂. In this invention, the alumina clinker contains 30-40% by weight of sodium oxide, 30-40% by weight of aluminum oxide, 10-15% by weight of calcium oxide, 1-5% by weight of magnesium oxide, 1-10% by weight of silicon dioxide, 1-5% by weight of potassium oxide, and 1-5% by weight of sulfur trioxide. As a specific example, the alumina clinker can be the alumina clinker provided by Ningxia Saima Cement Co., Ltd., whose composition includes 34.56% Na₂O, 3.95% MgO, 37.94% Al₂O₃, 5.21% SiO₂, 1.69% K₂O, 11.15% CaO, and 3.86% SO₃.

[0036] In this invention, the chemical formula of the polyacrylamide is -[CH2CH(CONH2)] n - is a polymer formed by the polymerization of acrylamide monomers, with a weight-average molecular weight of 8 million to 18 million. As a specific example, the polyacrylamide can be the grade 9003-05-8 polyacrylamide provided by Henan Zesheng Water Purification Materials Co., Ltd., which has a weight-average molecular weight of 8 million to 18 million.

[0037] In some embodiments, before implementing step (1), the method may further include: screening the alumina clinker through an 80-100 mesh sieve, so that the undersize material obtained is mixed with the aluminum sulfate and the polyacrylamide.

[0038] In some embodiments, before performing step (1), the method may further include drying aluminum sulfate to obtain aluminum sulfate with a free water content of not more than 1% by weight.

[0039] In some embodiments, the mixing process in step (1) may specifically include: mixing aluminum sulfate and aluminum oxide clinker once under stirring conditions, and then mixing the resulting primary mixture with polyacrylamide a second time.

[0040] In a preferred embodiment, the conditions for the first mixing include: a stirring speed of 10-100 r / min and a stirring time of 10-20 min.

[0041] In a preferred embodiment, the stirring speed of the secondary mixing is 10~100 r / min, and the stirring time of the secondary mixing is 5~10 min.

[0042] In some embodiments, the aging process in step (2) can be carried out under stirring conditions.

[0043] In the method described in this invention, the solid-liquid ratio of the mixture obtained in step (1) to the water can be 1:1 to 10, for example 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10, preferably 1:3 to 5. In this invention, the alumina clinker in the mixture contains sodium aluminate. Sodium aluminate combines with gypsum to prevent the formation of ettringite on the surface of cement particles, allowing C3A to react immediately, thereby enabling the concrete material to set quickly.

[0044] In the method described in this invention, the conditions for the aging process may include: a temperature of 50-60°C, a time of 20-60 min, and a stirring speed of 10-100 r / min.

[0045] In some embodiments, the stirring process in steps (1) and (2) may include: single-phase stirring by a stirring paddle and applying ultrasonic vibration stirring to the material along the radial direction of the stirring paddle rotation.

[0046] In a preferred embodiment, there are at least two ultrasonic vibration sources for stirring, and the included angle between two adjacent vibration sources is 30° to 120°.

[0047] In some embodiments, the drying process in step (2) may employ microwave heating drying and high-temperature airflow drying.

[0048] In a preferred embodiment, the drying temperature in step (2) is 80~90°C.

[0049] In a preferred embodiment, in step (2), there are at least three microwave heating heat sources. The microwave heating heat sources are embedded in the inner side of the side wall of the stirring mechanism and are distributed in a linear or spiral shape around the stirring shaft. At the same time, the axes of two adjacent microwave heating heat sources are at an angle of 30° to 60°.

[0050] In a preferred embodiment, in step (2), the high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is not lower than 60°C, the air pressure is not lower than 300 kPa, and the diameter of a single airflow is 5~20 cm.

[0051] In the method described in this invention, the conditions for ball milling in step (3) may include: a temperature of 20~200℃, a time of 0.5~2h, and a rotation speed of 50~100r / min.

[0052] This invention also provides a low-alkali accelerator prepared by the method described above. Compared with traditional powdered accelerator technology, this invention uses a novel low-alkali powdered accelerator, which can achieve rapid setting at a lower dosage and significantly improve the later-stage strength retention performance. Experimental results show that the optimal dosage of this low-alkali powdered accelerator is 6%-8%. At a dosage of 6%-8%, the mortar compressive strength reaches 13.7 MPa after 1 day and 45.08 MPa after 28 days. In contrast, the optimal dosage of the traditional 782 type powdered accelerator needs to reach 9%-11%, and at a dosage of 5%, the mortar compressive strength is only 9.8 MPa after 1 day and 39.46 MPa after 28 days. This demonstrates that the low-alkali powdered accelerator used in this invention is superior to traditional powdered accelerators in terms of setting efficiency, dosage economy, and later-stage strength retention.

[0053] This invention also provides a concrete, based on the total weight of the concrete, comprising 17-18% by weight cement, 2-3% by weight fly ash, 15-25% by weight gravel, 15-25% by weight coal gasification slag, 35-45% by weight gravel, and 6-8% by weight of the aforementioned low-alkali accelerator. In this invention, the active aluminum ions and aluminum hydroxide components in the low-alkali powdered accelerator can react rapidly with minerals such as tricalcium aluminate in the cement and co-crystallize with the ettringite products produced by the cement, significantly increasing the initial hydration rate and exothermic rate of silicate cement, thereby achieving rapid setting and early hardening. Simultaneously, this accelerator does not essentially encapsulate cement particles during the reaction process, thus avoiding the later-stage strength reduction problem caused by traditional high-alkali accelerators; the active silica-alumina components in the fly ash and coal gasification slag undergo a secondary reaction with Ca(OH)₂ in the later stages, generating more CSH gel, improving the internal structural density and later-stage strength stability of the material. The test results show that the coal-based solid waste surface reinforcement material prepared by using fly ash, coal gasification slag and low-alkali powdered quick-setting agent can achieve a compressive strength of about 4 MPa after 8 hours, a compressive strength of 7.3 to 9.0 MPa after 1 day, and a compressive strength of 33.7 to 36 MPa after 28 days. It can meet the requirements of rapid support and long-term service of coal mine roadway surface reinforcement materials.

[0054] In a preferred embodiment, based on the total weight of the concrete, the concrete contains 17.5-18% by weight of cement, 2-2.5% by weight of fly ash, 20-25% by weight of sand and gravel, 15-16% by weight of coal gasification slag, 40-42% by weight of gravel and 6-7% by weight of the low-alkali quick-setting agent described above.

[0055] In the most preferred embodiment, based on the total weight of the concrete, the concrete contains 17.8% by weight of cement, 2.2% by weight of fly ash, 23.1% by weight of sand and gravel, 15.4% by weight of coal gasification slag, 41.5% by weight of gravel and 6% by weight of the low-alkali quick-setting agent described above.

[0056] According to the preferred embodiments described above, this invention does not simply replace solid waste, but rather synergistically designs fly ash, coal gasification slag, and a low-alkali powdered quick-setting agent to solve problems such as insufficient early-stage activity, increased water demand, and slow strength development in coal-based solid waste materials. The coal-based solid waste surface reinforcement material prepared using fly ash, coal gasification slag, and a low-alkali powdered quick-setting agent achieves a compressive strength of 4 MPa after 8 hours of curing, 7.3–9.0 MPa after 1 day of curing, and 33.7–36 MPa after 28 days of curing, meeting the requirements for early support and later load-bearing capacity in coal mine roadway surface reinforcement.

[0057] In this invention, the concrete can be mixed with water when used, and the solid-liquid ratio of the concrete to the water is 1 to 5:1, preferably 2:1.

[0058] In this invention, the composition of the fly ash may include SiO2, Al2O3, CaO, Fe2O3, and other oxides. As a specific example, the fly ash may be provided by Ningxia Ningdong Taihua Thermal Power Co., Ltd., and its composition includes 41.22% SiO2, 16.31% Al2O3, 14.64% CaO, 1.25% MgO, 12.62% Fe2O3, 2.48% K2O, 4.86% SO3, 1.07% TiO2, 0.205% MnO, and 9.25% other oxides.

[0059] In this invention, the gravel is washed sand, which is construction sand produced by washing and classifying natural silica sand or manufactured sand using a sand washing machine. After washing and classification, different specifications such as coarse sand, medium sand, and fine sand can be obtained, with the mud content strictly controlled within the standard of ≤1% by weight. As a specific example, the gravel can be washed sand provided by Ningxia Zhihui Sand and Gravel Co., Ltd.

[0060] In this invention, the coal gasification slag is an industrial solid waste produced during the high-temperature gasification of coal in modern coal chemical processes (such as coal-to-methanol and coal-to-natural gas). It consists of unburned residual carbon and inorganic minerals (silicon, aluminum, etc.). As a specific example, the coal gasification slag can be the coal gasification slag provided by the Coal-to-Oil Branch of Ningxia Coal Industry Co., Ltd. of China Energy Investment Corporation, whose composition includes 55.56% SiO2, 20.08% Al2O3, 8.19% Fe2O3, 7.831% CaO, 2.28% MgO, 1.89% K2O, 1.84% Na2O, 0.831% TiO2, 0.009% CuO, 0.69% SO3, 0.2359% SrO, 0.226% BaO, 0.14% P2O5, 0.136% MnO, 0.0221% ZrO2, and 0.02% Cl.

[0061] The following examples further illustrate the low-alkali quick-setting agent, its preparation method, and its application according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0062] Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods in the art.

[0063] Unless otherwise specified, all experimental materials used in the following examples are commercially available.

[0064] In the following application examples and comparative examples, the test method for compressive strength is implemented in accordance with GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete".

[0065] In the following examples, comparative examples, application examples, and application comparative examples, the alumina clinker can be the alumina clinker provided by Ningxia Saima Co., Ltd. The composition and content of this alumina clinker are shown in the table below:

[0066] The polyacrylamide can be the grade 9003-05-8 provided by Henan Zesheng Water Purification Materials Co., Ltd., with a weight-average molecular weight of 8 million to 18 million.

[0067] The fly ash can be fly ash provided by Ningxia Ningdong Taihua Thermal Power Co., Ltd., and its composition includes 41.22% SiO2, 16.31% Al2O3, 14.64% CaO, 1.25% MgO, 12.62% Fe2O3, 2.48% K2O, 4.86% SO3, 1.07% TiO2, 0.205% MnO, and 9.25% other oxides. The gravel can be washed sand provided by Ningxia Zhihui Sand and Gravel Co., Ltd.

[0068] The coal gasification slag can be the coal gasification slag provided by the Coal-to-Oil Branch of Ningxia Coal Industry Co., Ltd., a subsidiary of China Energy Investment Corporation. Its composition includes 55.56% SiO2, 20.08% Al2O3, 8.19% Fe2O3, 7.831% CaO, 2.28% MgO, 1.89% K2O, 1.84% Na2O, 0.831% TiO2, 0.009% CuO, 0.69% SO3, 0.2359% SrO, 0.226% BaO, 0.14% P2O5, 0.136% MnO, 0.0221% ZrO2, and 0.02% Cl. Example 1 (1) 100g of cement clinker containing the following components is screened through a 90-mesh sieve. The screened clinker is added to a mixing device and stirred at a speed of 50r / min. The stirring is carried out by single-phase stirring with a stirring paddle, and ultrasonic vibration stirring is applied to the material along the rotational radial direction of the stirring paddle. There are two vibration sources for the ultrasonic vibration stirring, and the included angle between the two vibration sources is 90°. Then, aluminum sulfate is dried, and 10g of aluminum sulfate with a free water content of no more than 1% is added to the clinker in the stirring state and stirred together for 13min. Then, 3g of polyacrylamide is added to the mixing device for synchronous stirring and mixing.

[0069] (2) While maintaining the stirring state, add deionized water to the mixture at a solid-liquid ratio of 1:4, then heat the mixture at a constant rate to 55°C while stirring, and stir at a constant temperature for at least 40 minutes. Finally, heat the mixture to 85°C for microwave heating and high-temperature airflow drying. There are three microwave heating heat sources, which are embedded in the inner side of the stirring mechanism and distributed in a spiral shape around the stirring shaft. At the same time, the axes of two adjacent microwave heating heat sources form a 90° angle. The high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is 60°C, the air pressure is 300 kPa, and the diameter of a single airflow is 10 cm. Finally, a solid semi-finished product with a water content of 1% is obtained.

[0070] (3) Crushing and collecting: Add the solid semi-finished material to the ball mill at 150°C and ball mill at a rate of 60r / min for 30min to obtain 90-mesh powdered finished material. Then, after the powdered finished material is naturally cooled to room temperature, it is packaged to obtain the finished low-alkali quick-setting agent, which is denoted as A1.

[0071] Example 2 (1) 100g of cement clinker containing the following components is screened through an 80-mesh sieve. The screened clinker is added to a mixing device and stirred at a speed of 10r / min. The stirring is carried out by single-phase stirring with a stirring paddle, and ultrasonic vibration stirring is applied to the material along the rotational radial direction of the stirring paddle. There are two vibration sources for the ultrasonic vibration stirring, and the included angle between the two vibration sources is 30°. Then, aluminum sulfate is dried, and 5g of aluminum sulfate with a free water content of no more than 1% is added to the clinker in the stirring state and stirred together for 10min. Then, 0.1g of polyacrylamide is added to the mixing device for synchronous stirring and mixing.

[0072] (2) While maintaining the stirring state, add deionized water to the mixture at a solid-liquid ratio of 1:3, then heat the mixture at a constant rate to 50°C while stirring, and stir at a constant temperature for at least 60 minutes. Finally, heat the mixture to 80°C for microwave heating and high-temperature airflow drying. There are three microwave heating heat sources, which are embedded in the inner side of the stirring mechanism and are spirally distributed around the stirring shaft. At the same time, the axes of two adjacent microwave heating heat sources are at a 30° angle. The high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is 60°C, the air pressure is 300 kPa, and the diameter of a single airflow is 10 cm. Finally, a solid semi-finished product with a water content of 1% is obtained.

[0073] (3) Crushing and collecting: Add the solid semi-finished material to the ball mill at 150°C and ball mill at a rate of 60r / min for 35min to obtain 80-mesh powdered finished material. Then, after the powdered finished material is naturally cooled to room temperature, it is packaged to obtain the finished low-alkali quick-setting agent, which is denoted as A2.

[0074] Example 3 (1) 100g of cement clinker containing the following components is screened through a 100-mesh sieve. The screened clinker is added to a mixing device and stirred at a speed of 100r / min. The stirring is carried out by single-phase stirring with a stirring paddle, and ultrasonic vibration stirring is applied to the material along the rotational radial direction of the stirring paddle. There are two vibration sources for the ultrasonic vibration stirring, and the included angle between the two vibration sources is 120°. Then, aluminum sulfate is dried, and 16g of aluminum sulfate with a free water content of no more than 1% is added to the clinker in the stirring state and stirred together for 15min. Then, 5g of polyacrylamide is added to the mixing device for synchronous stirring and mixing.

[0075] (2) While maintaining the stirring state, add deionized water to the mixture at a solid-liquid ratio of 1:5, then heat the mixture at a constant rate to 60°C while stirring, and stir at a constant temperature for at least 20 minutes. Finally, heat the mixture to 90°C for microwave heating and high-temperature airflow drying. There are three microwave heating heat sources, which are embedded in the inner side of the stirring mechanism and distributed in a spiral shape around the stirring shaft. At the same time, the axes of two adjacent microwave heating heat sources form a 120° angle. The high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is 60°C, the air pressure is 300 kPa, and the diameter of a single airflow is 10 cm. Finally, a solid semi-finished product with a water content of 1% is obtained.

[0076] (3) Crushing and collecting: Add the solid semi-finished material to the ball mill at 150°C and ball mill at a rate of 60r / min for 40min to obtain 100-mesh powdered finished material. Then, after the powdered finished material is naturally cooled to room temperature, it is packaged to obtain the finished low-alkali quick-setting agent, which is denoted as A3.

[0077] Example 4 This embodiment is implemented according to the method described in Embodiment 1, except that in step (1), the cement clinker is replaced with an equal amount of silicate cement clinker, which contains 55.24% by weight of tricalcium silicate, 20.12% by weight of dicalcium silicate, 7.12% by weight of tricalcium aluminate, and 8.17% by weight of tetracalcium aluminoferrite. The resulting low-alkali quick-setting agent is denoted as A4.

[0078] Example 5 This embodiment is implemented according to the method described in Embodiment 1, except that the aluminum sulfate is not dried in step (1). The resulting low-alkali quick-setting agent is denoted as A5.

[0079] Example 6 This embodiment is implemented according to the method described in Embodiment 1, except that in steps (1) and (2), no ultrasonic source is provided in the stirring device, and ultrasonic vibration stirring is not performed. The resulting low-alkali quick-setting agent is denoted as A6.

[0080] Example 7 This embodiment is implemented according to the method described in Embodiment 1, except that in step (2), the solid-liquid ratio of water added is 1:1. The resulting low-alkali quick-setting agent is denoted as A7.

[0081] Example 8 This embodiment is implemented according to the method described in Embodiment 1, except that in step (2), the solid-liquid ratio of water added is 1:10. The resulting low-alkali quick-setting agent is denoted as A8.

[0082] Example 9 This embodiment is implemented according to the method described in Embodiment 1, except that in step (2), the maturation temperature is 30°C and the time is 2 hours. The resulting low-alkali quick-setting agent is denoted as A9.

[0083] Example 10 This embodiment is implemented according to the method described in Embodiment 1, except that in step (2), the matured product is dried in an oven. The resulting low-alkali quick-setting agent is denoted as A10.

[0084] Comparative Example 1 This comparative example was carried out according to the method described in Example 1, except that in step (1), the amount of aluminum sulfate with a free water content of no more than 1% was 20g, and the amount of polyacrylamide was 10g. The resulting low-alkali quick-setting agent was denoted as D-A1.

[0085] Comparative Example 2 This comparative example was carried out according to the method described in Example 1, except that in step (1), the amount of aluminum sulfate with a free water content of no more than 1% was 1g, and the amount of polyacrylamide was 0.05g. The resulting low-alkali quick-setting agent was denoted as D-A2.

[0086] Comparative Example 3 This comparative example was carried out according to the method described in Example 1, except that microwave heating drying and high-temperature airflow drying were not performed in step (2). The resulting low-alkali quick-setting agent was denoted as D-A3.

[0087] Application Example 1 20g of cement, 44g of washed sand, 36g of gravel, 50g of water, and 9.6g of the low-alkali quick-setting agent A1 prepared in Example 1 were mixed and cured. Then, grouting was performed using a feeding device, followed by curing. The resulting concrete was denoted as S1. The test results are as follows: Figure 1 As shown in (F0C0), the compressive strength of S1 after 8 hours of curing is 4.3 MPa, the compressive strength after 1 day of curing is 12.6 MPa, and the compressive strength after 28 days is 32.3 MPa.

[0088] Application Example 2 17.8g of cement, 2.2g of fly ash, 44g of washed sand, 36g of gravel, 50g of water, and 9.6g of the quick-setting agent prepared in Example 1 were mixed and cured. Then, grouting was performed using a feeding device, followed by curing. The resulting concrete was denoted as S2. The test results are as follows: Figure 1As shown in (F10C0), the compressive strength of this embodiment after 8 hours of curing is 4.0 MPa, and the compressive strength after 1 day of curing is 11.4 MPa, which is slightly lower than that of Example 1. However, when cured for 28 days, its strength is close to that of Application Example 1, indicating that fly ash mainly plays a physical filling role in the early stage, and generates secondary CSH gel through pozzolanic reaction in the later stage, which has a compensating effect on the later strength of the material.

[0089] Application Examples 3-10 Based on the fixed replacement of 10% by weight of cement with fly ash, an application example of gradient replacement of washed sand with coal gasification slag was set up: Concrete was prepared according to the method described in Application Example 2, except that 13.2g, 17.6g, 22g, 26.4g, 30.8g, 35.2g, 39.6g, and 44g of coal gasification slag were used to replace an equal mass of washed sand, that is, coal gasification slag was used to replace 30% by weight of washed sand (F10C30), 40% by weight of washed sand (F10C40), 50% by weight of washed sand (F10C50), 60% by weight of washed sand (F10C60), 70% by weight of washed sand (F10C70), 80% by weight of washed sand (F10C80), 90% by weight of washed sand (F10C90), and 100% by weight of washed sand (F10C100). The resulting concrete was denoted as S3~S10. The experimental results are as follows. Figure 2 As shown, with the increase in the replacement ratio of gasification slag, the overall 1-day compressive strength of the material slightly decreased, but remained close to 8.0 MPa, which meets the early support requirements of shotcrete materials. The 28-day compressive strength remained stable at around 33 MPa, exceeding the engineering requirement of 25 MPa. Based on the comprehensive analysis of early strength and later stability, the optimal replacement ratio of gasification slag with washed sand is around 40% by weight. This is because gasification slag has the dual function of being both a fine aggregate and an active admixture, filling slurry pores and improving the aggregate-slurry interface structure. However, an excessively high replacement ratio can have a negative impact on early strength.

[0090] Application Examples 11-13 Based on the substitution of 10% by weight of cement with fly ash and 40% by weight of washed sand with coal gasification slag, application examples were set up with the following dosages of low-alkali accelerator A1: 6% by weight (F10C40-1-6%), 7% by weight (F10C40-1-7%), and 8% by weight (F10C40-1-8%). Specifically, when the dosage of low-alkali accelerator A1 was 6% by weight, the mix proportions were: 17.8g cement, 2.2g fly ash, and 23g... 0.1g of washed sand, 15.4g of coal gasification slag, 41.50g of gravel, 50g of water, and 9.6g of low-alkali quick-setting agent A1 were used to prepare concrete according to the method described in Application Example 4, denoted as S11. When the admixture dosage was 7% by weight and 8% by weight, except that the dosage of low-alkali quick-setting agent A1 was adjusted to 11.3g and 13g respectively, the other components remained the same, and concrete was prepared according to the method described in Application Example 4, denoted as S12 and S13. The test results are as follows... Figure 3 As shown, when the dosage of low-alkali accelerator A1 is 6% by weight, the 1-day compressive strength of the material is approximately 8.0 MPa, and the 28-day compressive strength is approximately 35 MPa. When the dosage is increased to 7% by weight, the 1-day compressive strength decreases to approximately 7.5 MPa, and the 28-day compressive strength decreases to approximately 30 MPa. When the dosage is further increased to 8% by weight, the 1-day compressive strength is approximately 7.0 MPa, and the 28-day compressive strength is approximately 26 MPa. This indicates that with the increase of the dosage of low-alkali powdered accelerator, the early and late strengths of the coal-based solid waste surface reinforcement material show a decreasing trend. This is because excessively high dosage of accelerator will cause the material to solidify too quickly during the stirring stage, leading to internal agglomeration and increased porosity, which is not conducive to improving the density of the sample. Therefore, the dosage of low-alkali powdered accelerator is preferably controlled at around 6% by weight.

[0091] Application Example 14 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A2 prepared in example 2, and the concrete prepared is denoted as S14.

[0092] Application Example 15 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A3 prepared in example 3, and the concrete prepared is denoted as S15.

[0093] Application Example 16 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A4 prepared in example 4, and the concrete prepared is denoted as S16.

[0094] Application Example 17 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A5 prepared in example 5, and the concrete prepared is denoted as S17.

[0095] Application Example 18 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A6 prepared in example 6, and the concrete prepared is denoted as S18.

[0096] Application Example 19 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A7 prepared in example 7, and the concrete prepared is denoted as S19.

[0097] Application Example 20 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A8 prepared in example 8, and the concrete prepared is denoted as S20.

[0098] Application Example 21 This application embodiment is implemented according to the method described in application embodiment 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A9 prepared in embodiment 9, and the concrete prepared is denoted as S21.

[0099] Application Example 22 This application example is implemented according to the method described in application example 11, except that the low-alkali quick-setting agent A1 is replaced with an equal mass of the low-alkali quick-setting agent A10 prepared in example 10, and the concrete prepared is denoted as S22.

[0100] Application Comparative Example 1 This comparative application was carried out according to the method described in Application Example 11, except that the low-alkali quick-setting agent A1 was replaced with an equal mass of the low-alkali quick-setting agent D-A1 prepared in Comparative Example 1, and the resulting concrete was denoted as D-S1.

[0101] Application Comparative Example 2 This comparative application was carried out according to the method described in Application Example 11, except that the low-alkali quick-setting agent A1 was replaced with an equal mass of the low-alkali quick-setting agent D-A2 prepared in Comparative Example 2, and the resulting concrete was denoted as D-S2.

[0102] Application Comparative Example 3 This comparative application was carried out according to the method described in Application Example 11, except that the low-alkali quick-setting agent A1 was replaced with an equal mass of the low-alkali quick-setting agent D-A3 prepared in Comparative Example 3, and the resulting concrete was denoted as D-S3.

[0103] Test Example 1 The 1-day and 28-day compressive strengths of concretes S1~S23 and D-S1~D-S3 prepared using Examples 1-23 and Comparative Examples 1-3 were tested, and the results are shown in Table 1.

[0104] Table 1

[0105] As shown in Table 1, the working principle of this invention is as follows: the active aluminum ions and aluminum hydroxide components in the low-alkali powdered quick-setting agent can react rapidly with minerals such as tricalcium aluminate in cement and co-crystallize with the ettringite products produced by cement, significantly increasing the initial hydration rate and heat release rate of silicate cement, thereby achieving rapid setting and early hardening. Simultaneously, this quick-setting agent does not essentially encapsulate cement particles during the reaction process, thus avoiding the later-stage strength reduction problem caused by traditional high-alkali quick-setting agents; the active silica-alumina components in fly ash and coal gasification slag undergo a secondary reaction with Ca(OH)2 in the later stages, generating more CSH gel, improving the internal structural density and later-stage strength stability of the material.

[0106] The test results show that the coal-based solid waste surface reinforcement material prepared by using fly ash, coal gasification slag and low-alkali powdered quick-setting agent can achieve a compressive strength of about 4 MPa after 8 hours, a compressive strength of 7.3 to 9.0 MPa after 1 day, and a compressive strength of 33.7 to 36 MPa after 28 days. It can meet the requirements of rapid support and long-term service of coal mine roadway surface reinforcement materials.

[0107] Compared with the traditional water-washed sand-cement spraying material system, this invention uses fly ash to replace part of the cement and coal gasification slag to replace part of the water-washed sand, significantly reducing the amount of natural raw materials and material costs while ensuring the mechanical properties of the spraying material. Calculated according to the optimized ratio, the total cost of each cubic meter of coal-based solid waste surface reinforcement material is approximately RMB 297.9 to 344.4, which is about RMB 50 lower than that of traditional roadway surface reinforcement materials. At the same time, each cubic meter consumes 41.6 kg of fly ash and 356.8 kg of coal gasification slag, achieving both cost reduction and solid waste resource utilization.

[0108] Compared with traditional powdered accelerator technology, this invention uses a novel low-alkali powdered accelerator, which can achieve rapid setting at a lower dosage and significantly improve the later-stage strength retention performance. Experimental results show that the optimal dosage of this low-alkali powdered accelerator is 6%-8%. At a dosage of 6%-8%, the mortar compressive strength reaches 13.7 MPa after 1 day and 45.08 MPa after 28 days. In contrast, the optimal dosage of the traditional 782 type powdered accelerator requires 9%-11%, and at a dosage of 5%, the mortar compressive strength is only 9.8 MPa after 1 day and 39.46 MPa after 28 days. This demonstrates that the low-alkali powdered accelerator used in this invention is superior to traditional powdered accelerators in terms of setting efficiency, dosage economy, and later-stage strength retention.

[0109] Compared with traditional high-alkali accelerator systems, the low-alkali powdered accelerator used in this invention has a lower alkali content, which can reduce problems such as increased porosity, steel component corrosion, and alkali-aggregate reaction in high-alkali environments. Simultaneously, it promotes early formation of ettringite and CSH gel through active aluminum ions, enabling the material to have both rapid setting ability and less tendency for later strength reduction. Furthermore, this accelerator can achieve an initial setting time of less than 5 minutes and a final setting time of less than 12 minutes for the cement paste, while ensuring stable later-stage strength of the coal-based solid waste surface reinforcement material.

[0110] Compared with existing coal-based solid waste spraying materials that partially replace traditional raw materials with coal gasification slag and fly ash, this invention does not simply replace solid waste. Instead, it synergistically designs fly ash, coal gasification slag, and a low-alkali powdered quick-setting agent, solving problems such as insufficient early-stage activity, increased water demand, and slow strength development in coal-based solid waste materials. The document summarizes that the coal-based solid waste surface reinforcement material prepared using fly ash, coal gasification slag, and a low-alkali powdered quick-setting agent can achieve a compressive strength of 4 MPa after 8 hours of curing, 7.3–9.0 MPa after 1 day of curing, and 33.7–36 MPa after 28 days of curing, meeting the requirements for early support and later load-bearing capacity in coal mine roadway surface reinforcement.

[0111] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a low-alkali quick-setting agent, characterized in that, The method includes the following steps: (1) Aluminum oxide clinker, aluminum sulfate and polyacrylamide are mixed, wherein, relative to 100 parts by weight of the aluminum oxide clinker, the amount of aluminum sulfate is 5 to 16 parts by weight and the amount of polyacrylamide is 0.1 to 5 parts by weight. (2) The mixture obtained in step (1) is treated with water to mature it, and then the matured product is dried to obtain a solid semi-finished product with a water content of less than 3% by weight. (3) The solid semi-finished product is ball-milled.

2. The method according to claim 1, characterized in that, The alumina clinker contains 30-40% by weight sodium oxide, 30-40% by weight aluminum oxide, 10-15% by weight calcium oxide, 1-5% by weight magnesium oxide, 1-10% by weight silicon dioxide, 1-5% by weight potassium oxide and 1-5% by weight sulfur trioxide.

3. The method according to claim 1 or 2, characterized in that, Before implementing step (1), the method further includes: screening the aluminum oxide clinker through an 80-100 mesh sieve, so that the undersize material obtained is mixed with the aluminum sulfate and the polyacrylamide.

4. The method according to claim 1 or 2, characterized in that, Before implementing step (1), the method further includes drying aluminum sulfate to obtain aluminum sulfate with a free water content of not more than 1% by weight.

5. The method according to claim 1 or 2, characterized in that, In step (1), the mixing process specifically includes: mixing aluminum sulfate and aluminum oxide clinker once under stirring conditions, and then mixing the resulting primary mixture with polyacrylamide a second time. Preferably, the conditions for the first mixing include: a stirring speed of 10~100 r / min and a stirring time of 10~20 min; Preferably, the stirring speed of the secondary mixing is 10~100 r / min, and the stirring time of the secondary mixing is 5~10 min.

6. The method according to claim 1 or 2, characterized in that, In step (2), the ripening process is carried out under stirring conditions; Preferably, the solid-liquid ratio of the mixture obtained in step (1) to the water is 1:1 to 10, more preferably 1:3 to 5; Preferably, the conditions for the maturation treatment include: a temperature of 50~60℃, a time of 20~60min, and a stirring speed of 10~100r / min.

7. The method according to claim 5 or 6, characterized in that, In steps (1) and (2), the stirring process includes: single-phase stirring by a stirring paddle, and applying ultrasonic vibration stirring along the radial direction of the stirring paddle rotation to the material; Preferably, the ultrasonic vibration stirring has at least two vibration sources, and the included angle between two adjacent vibration sources is 30° to 120°.

8. The method according to claim 1 or 2, characterized in that, In step (2), the drying process employs microwave heating drying and high-temperature airflow drying; Preferably, in step (2), the drying temperature is 80~90℃.

9. The method according to claim 8, characterized in that, In step (2), there are at least three microwave heating sources. These microwave heating sources are embedded in the inner sidewall of the stirring mechanism and are distributed linearly or spirally around the stirring shaft. The axes of adjacent microwave heating sources form an angle of 30° to 60°. And / or, In step (2), the high-temperature airflow flows from bottom to top along the axis of the stirring mechanism, and the high-temperature airflow forms a closed-loop airflow through the air supply system. The temperature of the high-temperature airflow is not lower than 60°C, the air pressure is not lower than 300 kPa, and the diameter of a single airflow is 5~20 cm.

10. The method according to claim 1 or 2, characterized in that, In step (3), the conditions for ball milling include: temperature of 20~200℃, time of 0.5~2h, and rotation speed of 50~100r / min.

11. A low-alkali quick-setting agent prepared by the method according to any one of claims 1-10.

12. A type of concrete, characterized in that, Based on the total weight of the concrete, the concrete contains 17-18% by weight of cement, 2-3% by weight of fly ash, 15-25% by weight of sand and gravel, 15-25% by weight of coal gasification slag, 35-45% by weight of gravel and 6-8% by weight of the low-alkali quick-setting agent as described in claim 9.

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