Low-carbon cementing material for coal mine paste filling

Abstract

The invention discloses a low-carbon cementing material for coal mine paste filling, and belongs to the technical field of coal mine filling. The invention discloses a low-carbon cementing material for coal mine paste filling. The low-carbon cementing material comprises the following raw materials in parts by mass: 200-240 parts of furnace slag, 50-80 parts of carbide slag, 40-65 parts of desulfurized gypsum, 330-360 parts of fly ash, 10-20 parts of an active activator and 5-10 parts of a coagulant, wherein the active exciting agent is a mixed compound of sodium aluminate and sodium orthosilicate; the coagulant is a mixed compound of sodium thiocyanate and anhydrous calcium chloride. The cementing material adopts all solid waste raw materials, can be used for preparing a coal mine paste filling material, can reduce the filling cost of coal mining, improves the working efficiency of coal mining, and is beneficial to promoting the healthy and sustainable development of coal mine enterprises.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine filling, and particularly relates to a low-carbon cementitious material for paste filling in coal mines. Background Art

[0002] With the continuous growth of global energy demand and the in-depth adjustment of the energy structure, while pursuing the maximization of mining efficiency, coal mine enterprises are also facing increasingly severe environmental protection pressures. While traditional mining methods improve production capacity, they are often accompanied by a series of environmental problems such as surface subsidence, groundwater pollution, and accumulation of solid waste, seriously restricting the sustainable development of mining areas. Against this background, filling mining technology, as a green mining method, provides an innovative solution for achieving "waste-free mining".

[0003] Filling mining technology is a systematic project, and its core lies in timely filling the mined-out area by means of material backfilling. This technology mainly includes two major functions: one is to support the surrounding rock through the filling body, effectively control the ground pressure, prevent surface deformation and collapse, and ensure the safe production of the mine; the other is to realize the resource utilization of solid waste, and use waste materials such as tailings and coal gangue generated during the mining process as filling materials after treatment, achieving the dual purposes of environmental protection and resource utilization. From the perspective of technical characteristics, filling mining has significant advantages: it has strong flexibility and can adapt to different geological conditions and mining methods; it has high resource utilization rate and can realize the recycling of solid waste; it is environmentally friendly and can minimize the impact of mining activities on the ecological environment.

[0004] However, despite the significant environmental benefits and safe production advantages of filling mining technology, its full promotion and application in coal mine mining still face many challenges. The primary problem is economic constraints. Filling mining requires the construction of a dedicated filling system, including infrastructure such as the preparation of filling materials and the laying of conveying pipelines, resulting in high initial investment and operating costs. Secondly, at the technical level, the currently widely used cement-based filling materials have problems such as low early strength and are difficult to meet the process requirements of rapid mining. In addition, key technologies such as the optimization of the filling material ratio and the precise control of the filling process still need to be further broken through.

[0005] In response to the above problems, the current research focuses mainly on the following aspects: one is to develop new low-cost filling materials, such as using industrial waste residues to prepare cementitious materials to reduce the filling cost; the other is to optimize the filling process parameters to improve the early strength of the filling body. These technological breakthroughs will help promote the large-scale application of filling mining technology in coal mine mining and promote the mining industry to develop towards the direction of green, efficient, and sustainable. Summary of the Invention

[0006] In view of the above technical problems, the present invention proposes a low-carbon cementitious material for paste filling in coal mines.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the objects of the present invention is to provide a low-carbon cementitious material for coal mine paste filling, comprising the following raw materials in parts by mass: 200-240 parts of slag, 50-80 parts of carbide slag, 40-65 parts of desulfurized gypsum, 330-360 parts of fly ash, 10-20 parts of activity activator, and 5-10 parts of coagulant;

[0009] Among them, the activity activator is a mixed compound of sodium aluminate and sodium orthosilicate; the coagulant is a mixed compound of sodium thiocyanate and anhydrous calcium chloride.

[0010] The present invention uses industrial solid waste as raw materials. By adding an activity activator and a coagulant, the aluminum-silicon components in the cementitious material are effectively activated, so that the coal mine paste filling material obtained by compounding has high early strength, can reach more than 6.0 MPa in 7 days, and greatly improves the filling efficiency of coal mine goaf. At the same time, all the materials used are solid waste, which is beneficial to reducing the filling cost of coal mine goaf.

[0011] Further, the CaO content in the dry basis of the slag is ≥40 wt%, and the MgO content is ≥5 wt%.

[0012] Further, the Ca(OH)2 content in the dry basis of the carbide slag is ≥90%.

[0013] Further, the SO3 content in the desulfurized gypsum is ≥35 wt%.

[0014] Further, the mass ratio of sodium aluminate to sodium orthosilicate is (5-9):(11-15).

[0015] The molar ratio of alumina to sodium oxide in sodium aluminate is 1.2:1, and the modulus n of sodium orthosilicate is 0.8. Sodium aluminate can promote the generation of C-S-H gel and the formation of ettringite, consume carbide slag, thereby promoting the further dissolution of carbide slag, which is beneficial to improving the early strength. Sodium orthosilicate has strong alkalinity, and a large amount of hydroxide ions will be generated after dissolving in water, and it also has a very large pH buffer value, ensuring that the slag powder exists in an environment conducive to the hydration reaction to the greatest extent.

[0016] Further, the mass ratio of sodium thiocyanate to anhydrous calcium chloride is (3-5):(5-7).

[0017] The incorporation of calcium chloride can increase the solubility of minerals and accelerate the hydration rate of ground granulated blast-furnace slag. CaCl2 can react with the alumina tetrahedra in slag and fly ash to form calcium chloroaluminate hydrate that is almost insoluble in water and CaCl2 solution. CaCl2 can also react with Ca(OH)2 in carbide slag to form calcium oxychloride with extremely low solubility (CaCl2·3Ca(OH)2·12H2O and CaCl2·Ca(OH)2·H2O), reducing the concentration of Ca(OH)2 in the slurry, which is beneficial to the hydration reaction of C3S. The early precipitation of calcium chloroaluminate hydrate and calcium oxychloride solids accelerates the formation of the gelling structure and is conducive to the development of early strength.

[0018] Sodium thiocyanate is a strong electrolyte that can rapidly dissociate into sodium ions (Na + ) and thiocyanate ions (SCN - ) in water. Thiocyanate ions have high activity and can react with calcium ions (Ca 2+ ) in cement or gelling materials to form insoluble calcium thiocyanate (Ca(SCN)2), thereby accelerating the hydration reaction of cement. By accelerating the hydration reaction, sodium thiocyanate can promote the formation of more hydration products (such as C-S-H gel, ettringite, etc.) at an early stage. These hydration products can quickly fill the pores of the gelling materials, forming a dense structure, thus significantly improving the early strength. The use of sodium thiocyanate requires strict control of the dosage because it may have a certain impact on the environment at high concentrations. In the gelling material formula, the dosage of sodium thiocyanate is usually controlled at a low level to ensure its accelerating effect while avoiding potential hazards to the environment.

[0019] When sodium thiocyanate and anhydrous calcium chloride are used together as accelerators, they can play a synergistic role. Calcium chloride itself has an accelerating effect, while sodium thiocyanate can further accelerate the progress of the hydration reaction. The combination of the two can more effectively improve the early strength.

[0020] Furthermore, the raw materials further include nano-silica or nano-calcium carbonate; the content of nano-silica or nano-calcium carbonate is 5-15% of the total mass of the activity activator.

[0021] The mechanism of action of nano-silica or nano-calcium carbonate is reflected in the following aspects:

[0022] 1. Filling effect: Nano-materials (such as nano-silica, nano-calcium carbonate, etc.) have extremely high specific surface areas and small particle sizes. They can fill into the pores and micro-cracks of gelling materials, reducing the porosity and increasing the density of the materials. This filling effect can significantly improve the microstructure of gelling materials, thereby enhancing the early strength.

[0023] 2. Nucleation: Nanomaterials can act as nucleating agents to promote the hydration reaction in cementitious materials. For example, nano-silica can provide a large number of active sites, accelerating the hydration reaction of portland cement, promoting the formation of hydration products. These hydration products (such as C-S-H gel) can quickly fill the pores, forming a dense structure, thus improving the early strength.

[0024] 3. Chemical activity: Nanomaterials usually have high chemical activity. Taking nano-silica as an example, its surface is rich in a large number of hydroxyl groups (-OH) and silicon-oxygen bonds (Si-O), which can react with calcium ions (Ca 2+ ) in the cement hydration products to generate more hydration products (such as calcium silicate hydrate). These products can not only fill the pores but also interact with cement particles to form a more stable network structure, thus improving the early strength.

[0025] 4. Alkaline buffering effect: Nanomaterials (such as nano-calcium carbonate) have a certain alkaline buffering ability, which can adjust the pH value of cementitious materials, keeping it in an alkaline environment suitable for the hydration reaction. This alkaline environment is beneficial to the hydration reaction of cement, thus accelerating the development of early strength.

[0026] 5. Interface strengthening effect: Nanomaterials can improve the interfacial bonding strength between particles in cementitious materials. Due to the small particle size and high surface energy of nanomaterials, they can form good interfacial bonding with cement particles, fly ash and other components. This interface strengthening effect can reduce interface defects and improve the overall strength of the material.

[0027] 6. Accelerating hydration reaction: Nanomaterials can accelerate the hydration reaction rate of cementitious materials. For example, nano-silica can react with tricalcium silicate (C3S) and dicalcium silicate (C2S) in cement to generate more hydration products. These products can quickly fill the pores, forming a dense structure, thus improving the early strength.

[0028] 7. Improving microstructure: Nanomaterials can improve the microstructure of cementitious materials, making it more uniform and dense. By filling pores and microcracks, nanomaterials can reduce the internal defects of the material and improve the mechanical properties of the material.

[0029] The particle size of the nano-silica is 10 - 50 nm, preferably 20 - 30 nm; Nano-silica with a particle size of 20 - 30 nm has an extremely high specific surface area (usually exceeding 200 m 2 / g) can provide more active sites, thus significantly enhancing the interaction with cement hydration products and promoting early strength development. Moreover, nano-silica within this particle size range is more easily dispersed in the cementitious material system, avoiding agglomeration, and thus can uniformly fill the pores, improving the density of the material. Meanwhile, nano-silica within this particle size range can act as a nucleating agent to accelerate the progress of cement hydration reaction, promote the formation of C-S-H gel, thereby enhancing the early strength, and will also form a good interfacial bond with cement particles, reducing interfacial defects and further improving the overall strength of the material.

[0030] The particle size of the nano-calcium carbonate is 30 - 80 nm, preferably 40 - 60 nm. Nano-calcium carbonate with a particle size of 40 - 60 nm has a certain alkaline buffering capacity, can adjust the pH value of the cementitious material, maintain a suitable alkaline environment, and thus promote the hydration reaction of cement. Nano-calcium carbonate within this particle size range can effectively fill the pores in the cementitious material, reduce the porosity, improve the density and strength of the material. Nano-calcium carbonate can react with calcium ions in cement during the hydration process to form stable hydration products, further enhancing the early strength of the material. Nano-calcium carbonate with a particle size of 40 - 60 nm has good dispersibility in the cementitious material system and can be evenly distributed in the matrix, avoiding agglomeration.

[0031] The second object of the present invention is to provide a preparation method of a low-carbon cementitious material for coal mine paste filling, comprising the following steps:

[0032] Weigh slag, carbide slag, desulfurized gypsum and fly ash by mass, dry and stir them to mix, obtaining a mixture;

[0033] Perform grinding treatment on the mixture to obtain mixed powder;

[0034] Add an activity activator and a coagulant to the mixed powder and continue stirring to obtain a low-carbon cementitious material.

[0035] Further, the drying is: drying until the moisture content of the raw materials is less than 1%; and / or

[0036] The stirring time is 10 - 15 minutes; and / or

[0037] The grinding treatment is: grinding until the specific surface area of the material is 450 - 550 m 2 / kg; and / or

[0038] The time of the continued stirring is 30 - 60 minutes.

[0039] The third object of the present invention is to provide a coal mine paste filling material, comprising the low-carbon cementitious material for coal mine paste filling described above.

[0040] A fourth object of the present invention is to provide a preparation method of a coal mine paste filling material, comprising the following steps: mixing the low-carbon cementitious material for coal mine paste filling with gangue and water to obtain the coal mine paste filling material.

[0041] Further, the mass ratio of the low-carbon cementitious material for coal mine paste filling to gangue is 1:6.

[0042] A fifth object of the present invention is to provide an application of a low-carbon cementitious material for coal mine paste filling in the field of coal mine filling.

[0043] Compared with the prior art, the present invention has the following advantages and technical effects:

[0044] The novel coal mine paste filling material provided by the present invention uses all-solid waste raw materials, which can reduce the filling cost of coal mine mining, improve the working efficiency of coal mine mining, and contribute to the healthy and sustainable development of coal mine enterprises. Detailed Embodiments

[0045] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the range.

[0047] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0048] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and embodiments of the present invention are only exemplary.

[0049] As used herein, terms such as "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0050] An embodiment of the present invention provides a low-carbon cementitious material for coal mine paste filling, comprising the following raw materials in parts by mass: 200-240 parts of slag, 50-80 parts of carbide slag, 40-65 parts of desulfurized gypsum, 330-360 parts of fly ash, 10-20 parts of activity activator, and 5-10 parts of coagulant accelerator;

[0051] Among them, the activity activator is a mixed compound of sodium aluminate and sodium orthosilicate; the coagulant accelerator is a mixed compound of sodium thiocyanate and anhydrous calcium chloride.

[0052] Exemplarily, in the following preferred embodiments of the present invention:

[0053] The low-carbon cementitious material for coal mine paste filling contains 200 parts, 240 parts of slag, or any range or sub-range between the aforementioned ratios;

[0054] The low-carbon cementitious material for coal mine paste filling contains 50 parts, 65 parts, 80 parts of carbide slag, or any range or sub-range between the aforementioned ratios;

[0055] The low-carbon cementitious material for coal mine paste filling contains 40 parts, 65 parts of desulfurized gypsum, or any range or sub-range between the aforementioned ratios;

[0056] The low-carbon cementitious material for coal mine paste filling contains 330 parts, 360 parts of fly ash, or any range or sub-range between the aforementioned ratios;

[0057] The low-carbon cementitious material for coal mine paste filling contains 10 parts, 15 parts, 20 parts of activity activator, or any range or sub-range between the aforementioned ratios;

[0058] The low-carbon cementitious material for coal mine paste filling contains 5 parts, 10 parts of coagulant accelerator, or any range or sub-range between the aforementioned ratios.

[0059] In the following embodiments, the CaO content in the dry basis of the slag is ≥40wt%, and the MgO content is ≥5wt%.

[0060] In the following embodiments, the Ca(OH)2 content in the dry basis of the carbide slag is ≥90%.

[0061] In the following embodiments, the SO3 content in the desulfurized gypsum is ≥35wt%.

[0062] In some feasible embodiments, the mass ratio of sodium aluminate to sodium metasilicate is (5-9):(11-15). Among them, the molar ratio of alumina to sodium oxide in sodium aluminate is 1.2:1, and the modulus n of sodium metasilicate is 0.8. Exemplarily, in the following preferred embodiments of the present invention, the mass ratio of sodium aluminate to sodium metasilicate can be selected as 5:15, 7:13 or 9:11.

[0063] In some feasible embodiments, the mass ratio of sodium thiocyanate to anhydrous calcium chloride is (3-5):(5-7). Exemplarily, in the following preferred embodiments of the present invention, the mass ratio of sodium thiocyanate to anhydrous calcium chloride can be selected as 3:7, 4:6 or 1:1.

[0064] The preparation method of the low-carbon cementitious material for coal mine paste filling includes the following steps:

[0065] (1) Weigh slag, carbide slag, desulfurized gypsum and fly ash by mass, dry and stir them to mix, and obtain a mixture;

[0066] (2) Grind the mixture to obtain mixed powder;

[0067] (3) Add an activity activator and a coagulant to the mixed powder, and continue to stir to obtain a low-carbon cementitious material.

[0068] In some feasible embodiments, the drying is: drying until the moisture content of the raw materials is less than 1%; the stirring time is 10-15 minutes; the grinding treatment is: grinding until the specific surface area of the material is between 450-550m 2 / kg; the continuous stirring time is 30-60 minutes, and the purpose of stirring is to mix the raw materials evenly.

[0069] In some additional embodiments, the raw materials further include nano-silica or nano-calcium carbonate; the content of nano-silica or nano-calcium carbonate is 5-15% of the total mass of the activity activator. Exemplarily, in the following preferred embodiments of the present invention, the content of nano-silica or nano-calcium carbonate can be set to 10% of the total mass of the activity activator. The particle size of the nano-silica is 10-50nm, preferably 20-30nm; the particle size of the nano-calcium carbonate is 30-80nm, preferably 40-60nm. The specific preparation method is:

[0070] (1) Weigh slag, carbide slag, desulfurized gypsum and fly ash by mass, dry and stir them to mix, and obtain a mixture;

[0071] (2) Grind the mixture to obtain mixed powder;

[0072] (3) Add an activity activator and a coagulation promoter to the mixed powder material, continue stirring, then add nano-silica or nano-calcium carbonate, and stir to obtain a low-carbon cementitious material.

[0073] In some feasible embodiments, the drying is: drying until the moisture content of the raw materials is less than 1%; the stirring time is 10 - 15 minutes; the grinding treatment is: grinding until the specific surface area of the material is between 450 - 550 m 2 / kg; the continuous stirring time is 30 - 60 minutes.

[0074] To further improve the performance of concrete, other raw materials can be selectively added to the above formula. The specific technical solution is:

[0075] An improved low-carbon cementitious material for paste filling in coal mines, comprising the following raw materials in parts by mass: 200 - 240 parts of slag, 50 - 80 parts of carbide slag, 40 - 65 parts of desulfurized gypsum, 330 - 360 parts of fly ash, 10 - 20 parts of activity activator, 5 - 10 parts of coagulation promoter, 10 - 20 parts of modified metakaolin, and nano-silica / nano-calcium carbonate (the " / " here means "or", that is, nano-silica can be added alone, or nano-calcium carbonate can be added alone);

[0076] Among them, the activity activator is a mixed complex of sodium aluminate and sodium orthosilicate; the coagulation promoter is a mixed complex of sodium thiocyanate and anhydrous calcium chloride; the addition amount of the nano-silica / nano-calcium carbonate is 5 - 15% of the total mass of the activity activator.

[0077] In the following embodiments, the specific preparation steps of the modified metakaolin include: heating and stirring metakaolin in an oil bath at 60 - 80 °C, with a stirring rate of 1774 r / min. After stirring for 5 min, add the coupling agent drop by drop, and continue stirring for 20 min to complete the pretreatment; place the pretreated metakaolin in a high-speed mixer, keep the rotation speed of the mixer constant at 34000 r / min, and crush for 2 min to obtain the modified metakaolin.

[0078] The coupling agent is KH-550 or KH570. Exemplarily, in the following embodiments of the present invention, KH570 is taken as an example for effect verification.

[0079] The addition amount of the coupling agent is 1 - 5% of the mass of metakaolin. Exemplarily, in the following embodiments of the present invention, 3% is taken as an example for effect verification.

[0080] The molecular structure of silane coupling agents contains hydrolyzable alkoxy groups (such as methoxy and ethoxy) and organic functional groups (such as amino groups and epoxy groups). The silanol groups (Si-OH) generated after the hydrolysis of alkoxy groups can undergo a condensation reaction with the hydroxyl groups on the surface of inorganic materials (such as the hydroxyl groups on the surface of kaolin), forming strong Si-O-Si bonds. This chemical bonding not only enhances the surface activity of inorganic materials but also improves their compatibility with the matrix, thereby enhancing the compressive strength. Through chemical bonding, the interfacial bonding force between the modified metakaolin and the cementitious material matrix is significantly enhanced. This interfacial enhancement enables stress to be transmitted more effectively, avoiding stress concentration, and thus improving the overall mechanical properties of the material. In addition, chemical bonding also reduces interfacial defects, further enhancing the compressive strength of the material.

[0081] The preparation method of the improved low-carbon cementitious material for coal mine paste filling includes the following steps:

[0082] (1) Weigh slag, carbide slag, desulfurized gypsum, and fly ash by mass, dry and stir them to mix, obtaining a mixture.

[0083] (2) Grind the mixture to obtain mixed powder.

[0084] (3) Add an activity activator, a coagulant, and modified metakaolin to the mixed powder, continue stirring, and then add nano-silica or nano-calcium carbonate and stir to obtain a low-carbon cementitious material.

[0085] In some feasible embodiments, the drying is: drying until the moisture content of the raw materials is less than 1%; the stirring time is 10 - 15 minutes; the grinding treatment is: grinding until the specific surface area of the material is between 450 - 550 m 2 / kg; the continuous stirring time is 30 - 60 minutes.

[0086] The embodiment of the present invention also provides a coal mine paste filling material, including the low-carbon cementitious material for coal mine paste filling or the improved low-carbon cementitious material for coal mine paste filling described above.

[0087] The embodiment of the present invention also provides a preparation method of a coal mine paste filling material, including the following steps: Mix the low-carbon cementitious material for coal mine paste filling with coal gangue and water to obtain a coal mine paste filling material.

[0088] In the following embodiments, the mass ratio of the low-carbon cementitious material for coal mine paste filling to coal gangue is 1∶6, and the addition amount of water is based on the dry matter amount of the obtained coal mine paste filling material being 82%.

[0089] The low-carbon cementitious material for coal mine paste filling can be applied in the field of coal mine filling.

[0090] Unless otherwise specified, the "parts" mentioned in the present invention refer to parts by mass.

[0091] All raw materials used in the present invention are obtained by purchasing on the market.

[0092] In the following examples of the present invention, the compositions of the slag used are shown in Table 1, the compositions of the carbide slag are shown in Table 2, and the compositions of the desulfurized gypsum are shown in Table 3.

[0093] Table 1 Dry-base composition of slag

[0094]

[0095] Table 2 Dry-base composition of carbide slag

[0096]

[0097] Table 3 Dry-base composition of desulfurized gypsum

[0098]

[0099] The technical solutions of the present invention will be further described below through examples.

[0100] Examples 1-6, Comparative Examples 1-4

[0101] A preparation method of a low-carbon cementitious material for paste filling in coal mines includes the following steps:

[0102] (1) Weigh the slag, carbide slag, desulfurized gypsum and fly ash according to the raw material ratios in Table 4 and Table 5, dry them until the moisture content of the raw materials is less than 1%, mix and stir for 10 minutes to obtain a mixed material;

[0103] (2) Grind the mixed material until the specific surface area of the material is between 450-550 m 2 / kg to obtain a mixed powder;

[0104] (3) Add an activity activator and a coagulation accelerator to the mixed powder, and continue to stir for 50 minutes to obtain a low-carbon cementitious material.

[0105] Table 4 Raw material ratio of low-carbon cementitious material (parts by mass)

[0106]

[0107]

[0108] Table 5 Ratio of activity activator and coagulation accelerator (mass ratio)

[0109]

[0110] Application Examples 1-6, Comparative Application Examples 1-4

[0111] A preparation method of a paste filling material for coal mines: The low-carbon cementitious materials prepared in Examples 1-6 and Comparative Examples 1-4 are respectively mixed with coal gangue (particle size ≤ 25 mm, continuous gradation) at a mass ratio of 1:6, and then water is added to obtain paste filling materials for coal mines with a dry matter content of 82% respectively.

[0112] Use a test mold of 70.7 mm × 70.7 mm × 70.7 mm for slurry pouring and molding, place it in a curing box at a temperature of 20 ± 1 °C and a humidity of 95 ± 3% for curing. Demold after one day of pouring, and continue to cure until each test age (3d, 7d, and 28d). Test the compressive strength of the specimens according to GB / T 35156-2017 "Technical Requirements for Paste Filling Materials for Filling Mining". The results are shown in Table 6.

[0113] Table 6 Compressive Strength Test Results (MPa)

[0114]

[0115]

[0116] It can be seen from Table 6 that the cementitious materials prepared in Application Examples 1-6 of the present invention have high early strength and can reach more than 3.0 MPa in 7 days. Comparing Application Example 1 with Application Example 5, the carbide slag is replaced with slag in equal mass, and it is found that the compressive strength decreases slightly, indicating that the selection and proportion of raw materials are the key technical means affecting the material performance. Even if they are all solid wastes, different dosage ratios will result in materials with different performances; comparing Application Example 2 with Application Example 5, the dosages of the activity activator and the coagulant change. It is found that when the dosages of the activity activator and the coagulant in Comparative Application Example 2 exceed the dosage range, the performance will decline; comparing Application Example 3 and Comparative Application Example 4 with Application Example 5, the compositions of the activity activator and the coagulant change. It is found that when there is only a single-component activity activator and coagulant, the performance will decrease significantly.

[0117] Example 7

[0118] A preparation method of a low-carbon cementitious material for paste filling in coal mines, which is different from Example 5 in that the raw materials further include nano-silica (particle size 20-30 nm), and the specific steps are as follows:

[0119] (1) Weigh 240 parts of slag, 80 parts of carbide slag, 40 parts of desulfurized gypsum, and 330 parts of fly ash, dry until the moisture content of the raw materials is less than 1%, mix and stir for 10 minutes to obtain a mixture;

[0120] (2) Grind the mixture to a specific surface area of the material between 450-550 m 2between / kg to obtain the mixed powder material;

[0121] (3) Add 20 parts of an activity activator (including sodium aluminate and sodium metasilicate, with a mass ratio of 9:11) and 5 parts of a coagulant accelerator (including sodium thiocyanate and anhydrous calcium chloride, with a mass ratio of 1:1) to the mixed powder material, continue stirring for 50 minutes, then add nano-silica with a mass of 10% of the total mass of the activity activator, and stir for 10 minutes to obtain the low-carbon cementitious material.

[0122] Example 8

[0123] A preparation method of a low-carbon cementitious material for coal mine paste filling, which is different from Example 5 in that the raw materials further include nano-calcium carbonate (with a particle size of 40 - 60 nm), and the specific steps are as follows:

[0124] (1) Weigh 240 parts of slag, 80 parts of carbide slag, 40 parts of desulfurized gypsum, and 330 parts of fly ash, dry until the moisture content of the raw materials is less than 1%, mix and stir for 10 minutes to obtain the mixed material;

[0125] (2) Grind the mixed material until the specific surface area of the material is between 450 - 550 m 2 / kg to obtain the mixed powder material;

[0126] (3) Add 20 parts of an activity activator (including sodium aluminate and sodium metasilicate, with a mass ratio of 9:11) and 5 parts of a coagulant accelerator (including sodium thiocyanate and anhydrous calcium chloride, with a mass ratio of 1:1) to the mixed powder material, continue stirring for 50 minutes, then add nano-calcium carbonate with a mass of 10% of the total mass of the activity activator, and stir for 10 minutes to obtain the low-carbon cementitious material.

[0127] Comparative Example 5

[0128] Same as Example 1, the difference is that the addition amount of nano-calcium carbonate is 20% of the total mass of the activity activator.

[0129] Application Examples 7 - 8, Comparative Application Example 5

[0130] A preparation method of a coal mine paste filling material: respectively mix the low-carbon cementitious materials prepared in Examples 7 - 8 and Comparative Example 5 with coal gangue (with a particle size ≤ 25 mm, in continuous gradation) according to a mass ratio of 1:6, and then add water to obtain coal mine paste filling materials with a mass concentration of 82% respectively.

[0131] Use a test mold of 70.7mm×70.7mm×70.7mm for slurry pouring and molding. Place it in a curing box at a temperature of 20±1°C and a humidity of 95±3% for curing. Demold after one day of pouring and continue curing until each test age (3d, 7d, and 28d). Test the compressive strength of the specimens according to GB / T 35156-2017 "Technical Requirements for Paste Filling Materials for Filling Mining". The results are shown in Table 7.

[0132] Table 7 Test Results of Compressive Strength (MPa)

[0133]

[0134] As can be seen from Table 7, after adding nano-calcium carbonate and nano-silica in Application Example 7 and Application Example 8, the performance of the obtained cementitious materials has been significantly improved. After increasing the dosage of nano-calcium carbonate in Comparative Example 5, the performance has decreased instead. The reason is that nano-calcium carbonate has a small particle size, a large specific surface area, and a high surface energy, and it is easy to agglomerate. When the addition amount is too much, the agglomeration phenomenon will be more serious, resulting in the inability of nano-calcium carbonate to be uniformly dispersed in the cementitious material system.

[0135] Example 9

[0136] A preparation method of a low-carbon cementitious material for paste filling in coal mines, which is different from Example 8 in that the raw materials also include modified metakaolin. The specific steps are as follows:

[0137] (1) Weigh 240 parts of slag, 80 parts of carbide slag, 40 parts of desulfurized gypsum, and 330 parts of fly ash, dry until the moisture content of the raw materials is less than 1%, mix and stir for 10 minutes to obtain a mixture;

[0138] (2) Grind the mixture to a specific surface area of the material between 450 - 550m 2 / kg to obtain a mixed powder;

[0139] (3) Add 20 parts of an activation agent (including sodium aluminate and sodium metasilicate, with a mass ratio of 9:11), 5 parts of a coagulant (including sodium thiocyanate and anhydrous calcium chloride, with a mass ratio of 1:1), and 15 parts of modified metakaolin to the mixed powder, continue to stir for 50 minutes, and then add nano-calcium carbonate with a mass of 10% of the total mass of the activation agent, and stir for 10 minutes to obtain a low-carbon cementitious material.

[0140] Among them, the specific preparation steps of the modified metakaolin include: heating and stirring metakaolin in an oil bath at 70 °C with a stirring rate of 1774 r / min. After stirring for 5 min, KH570 is added dropwise (the addition amount of KH570 is 3% of the mass of metakaolin), and stirring continues for 20 min to complete the pretreatment; the pretreated metakaolin is placed in a high-speed mixer, and the rotation speed of the mixer is kept at 34000 r / min. After pulverizing for 2 min, the modified metakaolin is obtained.

[0141] Comparative Example 6

[0142] Same as Example 9, except that the modified metakaolin is replaced with kaolin.

[0143] Comparative Example 7

[0144] Same as Example 9, except that 10 parts of montmorillonite are added.

[0145] Application Example 9, Comparative Application Examples 6 - 7

[0146] A preparation method of a coal mine paste filling material: The low-carbon cementitious materials prepared in Example 9 and Comparative Examples 6 - 7 are respectively mixed with coal gangue (particle size ≤ 25 mm, continuous gradation) in a mass ratio of 1:6, and then water is added to obtain coal mine paste filling materials with a mass concentration of 82% respectively.

[0147] A 70.7 mm × 70.7 mm × 70.7 mm mold is used for slurry pouring and molding, and it is placed in a curing box at a temperature of 20 ± 1 °C and a humidity of 95 ± 3% for curing. After demolding one day after pouring, continue to cure until each test age (3 d, 7 d, and 28 d), and test the compressive strength of the specimens according to GB / T 35156 - 2017 "Technical Requirements for Paste Filling Materials for Filling Mining". The results are shown in Table 8.

[0148] Table 8 Compressive Strength Test Results (MPa)

[0149]

[0150] As can be seen from Table 8, in Application Example 9 with the addition of modified metakaolin, the material properties are greatly improved. On the contrary, in Comparative Application Example 6, due to the use of kaolin, its properties have no obvious change compared with Application Example 8; in Comparative Application Example 7, on the basis of Application Example 9, the montmorillonite component is added, and the obtained material properties do not increase but decrease, indicating that the materials in the present invention need to be combined in a specific ratio. It is not the simple superposition of the effects of single materials, but there is an interaction relationship. Therefore, the performance of Comparative Example 7 decreases instead after adding montmorillonite.

[0151] The above are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A low-carbon cementitious material for paste filling in coal mines, characterized in that, It includes raw materials in the following parts by mass: 200 - 240 parts of slag, 50 - 80 parts of carbide slag, 40 - 65 parts of desulfurized gypsum, 330 - 360 parts of fly ash, 10 - 20 parts of activity activator, and 5 - 10 parts of coagulant promoter; Among them, the activity activator is a mixed compound of sodium aluminate and sodium metasilicate; the coagulant promoter is a mixed compound of sodium thiocyanate and anhydrous calcium chloride.

2. The low-carbon cementitious material for coal mine paste filling according to claim 1, wherein the content of CaO in the dry basis of the slag is ≥40wt%, and the content of MgO is ≥5wt%; and / or the content of Ca(OH)2 in the dry basis of the carbide slag is ≥90%; and / or the content of SO3 in the desulfurized gypsum is ≥35wt%.

3. The low-carbon cementitious material for coal mine paste filling according to claim 1, wherein the mass ratio of sodium aluminate to sodium metasilicate is (5 - 9)∶(11 - 15); and / or the mass ratio of sodium thiocyanate to anhydrous calcium chloride is (3 - 5)∶(5 - 7).

4. The low-carbon cementitious material for paste filling in coal mines according to claim 1, characterized in that, The raw materials further include nano-silica or nano-calcium carbonate; the content of nano-silica or nano-calcium carbonate is 5 - 15% of the total mass of the activity activator.

5. A preparation method of a low-carbon cementitious material for paste filling in coal mines according to any one of claims 1-4, characterized in that, It includes the following steps: Weigh the slag, carbide slag, desulfurized gypsum and fly ash by mass, dry and stir them to mix, and obtain a mixed material; Perform grinding treatment on the mixed material to obtain a mixed powder; Add the activity activator and the coagulant promoter to the mixed powder, and continue to stir to obtain a low-carbon cementitious material.

6. The preparation method of the low-carbon cementitious material for coal mine paste filling according to claim 5, wherein the drying is: drying until the moisture content of the raw materials is less than 1%; and / or the stirring time is 10 - 15 minutes; and / or The grinding treatment is: grinding to a specific surface area of the material of 450 - 550 m 2 / kg; and / or the time of continuing to stir is 30 - 60 minutes.

7. A paste filling material for coal mines, characterized in that, It includes the low-carbon cementitious material for coal mine paste filling according to any one of claims 1 - 4.

8. A preparation method of the paste filling material for coal mines as described in claim 7, characterized in that, It includes the following steps: Mix the low-carbon cementitious material for coal mine paste filling with coal gangue and water to obtain a coal mine paste filling material.

9. The preparation method of the paste filling material for coal mines according to claim 8, characterized in that, The mass ratio of the low-carbon cementitious material for coal mine paste filling to coal gangue is 1∶6.

10. The application of the low-carbon cementitious material for coal mine paste filling according to any one of claims 1 - 4 in the field of coal mine filling.

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