Mine underground safety support material and preparation method thereof

Abstract

The invention provides a mine underground safety supporting material and a preparation method thereof, and belongs to the technical field of reinforcing materials. The invention provides a mine underground safety support material, which is prepared from the following raw materials in parts by mass: 30 to 50 parts of Portland cement, 10 to 15 parts of sulphoaluminate cement, 3 to 5 parts of fiber, 25 to 58 parts of coal gangue, 30 to 50 parts of fly ash, 0.1 to 3 parts of gypsum, 0.1 to 0.5 part of retarder, 5 to 12 parts of paraffin, 0.8 to 3.5 parts of water reducing agent and water. The water cement ratio of the mine underground safety supporting material is 0.3-1.2. Results of the embodiment show that the mine underground safety supporting material provided by the invention is excellent in mechanical property, good in supporting effect, low in hydration heat, good in durability, capable of achieving the supporting effect for a long time, free of failure due to rusting, excellent in crack resistance and applicable to different mine environments.

Description

Technical Field

[0001] This invention relates to the field of reinforcement materials technology, and in particular to a safety support material for underground mines and its preparation method. Background Technology

[0002] During underground coal mining, the original mechanical balance within the rock mass is disrupted. After the coal seam is extracted, a goaf is formed. Under the influence of gravity, the overlying rock strata bend, fracture, and collapse, affecting the surface and forming subsidence basins, sinkholes, and step-like collapses. Numerous ground fissures appear on the surface, damaging the land and structures. Simultaneously, the stability of the rock and soil mass above the goaf decreases, becoming unstable under the influence of gravity and rainfall. The release of tectonic stress triggers mine seismic activity, leading to landslides and collapses. To address these problems, it is necessary to use underground mine support materials for reinforcement.

[0003] However, existing underground mine support materials such as anchor bolts and cables can only provide localized support. When encountering loose coal and rock masses, anchor bolts and cables lose their grip, resulting in poor anchoring performance. Moreover, under conditions of underground water spray, anchor bolts and cables will rust and fail over time, leading to a significant reduction in their service life. Ordinary fiberglass / polymer materials have insufficient toughness. Grouting / shotcrete materials are brittle, have poor deformation adaptability, and cannot cope with the dynamic loads, high humidity, and gas environment of deep roadways, resulting in insufficient safety redundancy.

[0004] Therefore, providing a mine underground safety support material with good support effect, good durability and excellent crack resistance has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a safety support material for underground mines and its preparation method. The safety support material for underground mines provided by this invention has excellent mechanical properties, good support effect, low heat of hydration, good durability, can provide support for a long time, will not fail due to rust, has excellent crack resistance, and can be applied to different underground mining environments.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a safety support material for underground mines, which, by weight, is prepared from the following raw materials: 30-50 parts silicate cement, 10-15 parts sulfoaluminate cement, 3-5 parts fiber, 25-58 parts coal gangue, 30-50 parts fly ash, 0.1-3 parts gypsum, 0.1-0.5 parts retarder, 5-12 parts paraffin wax, 0.8-3.5 parts water-reducing agent, and water; the water-cement ratio of the safety support material for underground mines is 0.3-1.2.

[0007] Preferably, the silicate cement is silicate cement with a strength grade of 42.5 or 52.5.

[0008] Preferably, the sulfoaluminate cement is a sulfoaluminate cement with a strength grade of 42.5 or 52.5.

[0009] Preferably, the fiber is glass fiber, steel fiber or basalt fiber, the fiber length is 5~60mm and the fiber diameter is 10~30μm.

[0010] Preferably, the particle size of the coal gangue is ≤2mm.

[0011] Preferably, the residue of the fly ash passing through a 45μm square hole sieve is ≤20%.

[0012] Preferably, the gypsum is natural anhydrous gypsum and / or natural hemihydrate gypsum.

[0013] Preferably, the retarder is citric acid and / or sucrose.

[0014] Preferably, the water-reducing agent is a polycarboxylate water-reducing agent.

[0015] This invention provides a method for preparing the underground mine safety support material described in the above-mentioned technical solution, comprising the following steps: (1) Silicate cement, sulfoaluminate cement, fiber, coal gangue, fly ash, gypsum and paraffin are mixed to obtain dry material; (2) Mix the retarder, water-reducing agent and water to obtain a wet material, and then mix the wet material with the dry material obtained in step (1) to obtain a slurry; (3) The slurry obtained in step (2) is injected to obtain underground safety support material for the mine.

[0016] This invention provides a safety support material for underground mines, which, by weight, is prepared from the following raw materials: 30-50 parts silicate cement, 10-15 parts sulfoaluminate cement, 3-5 parts fiber, 25-58 parts coal gangue, 30-50 parts fly ash, 0.1-3 parts gypsum, 0.1-0.5 parts retarder, 5-12 parts paraffin wax, 0.8-3.5 parts water-reducing agent, and water; the water-cement ratio of the safety support material for underground mines is 0.3-1.2. This invention uses silicate cement as the main gelling material, which can undergo a hydration reaction with water to generate a viscous cement paste that firmly binds aggregates such as sand and stone together to form a solid whole, significantly improving the later-stage compressive and flexural strength of concrete. Sulfoaluminate cement has an extremely rapid hydration rate, giving underground mine safety support materials high early-stage strength. Simultaneously, the structure of sulfoaluminate cement after hydration and hardening is more dense, with low total porosity and small average pore size, enabling underground mine safety support materials to have higher impermeability and corrosion resistance, thus ensuring they can withstand underground water infiltration. It has long durability; furthermore, the combined use of sulfoaluminate cement and gypsum can improve the volume stability of underground mine safety support materials, preventing cracking and other problems; by adding a certain amount of fiber, it can withstand tensile stress caused by drying shrinkage and temperature changes, preventing and inhibiting the generation and development of primary cracks, thereby significantly improving the crack resistance of underground mine safety support materials; at the same time, fibers can improve the tensile strength, flexural strength and impact strength of underground mine safety support materials. When the matrix cracks, the fibers can cross the cracks to bear tensile stress, thereby delaying crack propagation; fibers can fundamentally... The fiber structure alters the failure mode of underground mine safety support materials, transforming it from brittle fracture to ductile failure. Even if the concrete cracks, the fiber can still provide load-bearing capacity, giving it a certain degree of ductility and energy absorption capacity. Coal gangue can be used as aggregate to improve density, thereby enhancing the mechanical properties of underground mine safety support materials. Furthermore, as a solid waste material, coal gangue occupies a large amount of land and causes land and air pollution when dumped; using it as a raw material allows for the reuse of coal gangue, resulting in excellent environmental benefits. The addition of fly ash can fill the voids between aggregates and lubricate them. Particles improve the cohesiveness and plasticity of underground mine safety support materials; at the same time, fly ash can reduce water consumption, increase cementitious material content, and ensure higher strength in the later stage through long-term pozzolanic reaction; the addition of fly ash can reduce the heat of hydration, reduce large-volume temperature cracks, and maintain the integrity and stability of the structure; it can also improve the impermeability, carbonation resistance and frost resistance of concrete, thereby improving the durability of concrete and effectively preventing alkali-aggregate reaction; by adding the phase change material paraffin, it can absorb the heat generated by the hydration reaction during the hydration process, thereby reducing the temperature of the heat of hydration.The results of the embodiments show that the 28-day compressive strength of the underground mine safety support material provided by the present invention is >80MPa, the flexural strength is >20MPa, and the heat of reaction is less than 40℃, which is far below the requirement of the national standard AQ1089-2020 for the maximum heat of reaction of 100℃ for polymer reactive reinforcement materials in coal mines. Detailed Implementation

[0017] This invention provides a safety support material for underground mines, which, by weight, is prepared from the following raw materials: 30-50 parts silicate cement, 10-15 parts sulfoaluminate cement, 3-5 parts fiber, 25-58 parts coal gangue, 30-50 parts fly ash, 0.1-3 parts gypsum, 0.1-0.5 parts retarder, 5-12 parts paraffin wax, 0.8-3.5 parts water-reducing agent, and water; the water-cement ratio of the safety support material for underground mines is 0.3-1.2.

[0018] Unless otherwise specified, all raw materials used in this invention are commercially available products well known to those skilled in the art.

[0019] The raw materials for preparing the underground mine safety support material provided by this invention, by weight, include 30-50 parts of silicate cement; the silicate cement is preferably silicate cement with a strength grade of 42.5 or 52.5. As one embodiment of this invention, the weight of the silicate cement can be 30, 32, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, or 50 parts. This invention uses silicate cement as the main gelling material, which can undergo a hydration reaction with water to generate viscous cement stone, firmly binding aggregates such as sand and stone together to form a solid whole; the hydrated calcium silicate and other crystals produced by the hydration reaction can significantly improve the compressive and flexural strength of concrete in the later stages; at the same time, the cement slurry formed after mixing silicate cement and water can act as a lubricant, allowing for better spraying and pouring; by controlling the strength grade of the silicate cement, the mechanical properties of the underground mine safety support material can be further improved.

[0020] The raw materials for preparing the underground mine safety support material provided by this invention include 10-15 parts of sulfoaluminate cement, based on a mass fraction of 30-50 parts of silicate cement; the sulfoaluminate cement is preferably sulfoaluminate cement with a strength grade of 42.5 or 52.5. In one embodiment of this invention, the mass fraction of the sulfoaluminate cement can be 10, 11, 12, 13, 14, or 15 parts. In this invention, the hydration rate of sulfoaluminate cement is extremely fast, which can impart high early strength to the underground mine safety support material and greatly shorten the construction period; at the same time, the structure of the hydrated and hardened sulfoaluminate cement is more compact, with low total porosity and small average pore size, which can give the underground mine safety support material higher impermeability and corrosion resistance, thus enabling it to have a long durability even when exposed to underground water; in addition, the combined use of sulfoaluminate cement and gypsum can also improve the volume stability of the underground mine safety support material and avoid cracking and other problems.

[0021] This invention, by combining silicate cement and sulfoaluminate cement, can improve the early mechanical properties of underground mine safety support materials, and also ensure that they retain excellent mechanical properties in the later stages. At the same time, it can also significantly improve the compactness, durability and corrosion resistance of underground mine safety support materials.

[0022] The raw materials for preparing the underground mine safety support material provided by the present invention include 3-5 parts of fiber, based on 30-50 parts by weight of silicate cement; the fiber is preferably glass fiber, steel fiber, or basalt fiber; the length of the fiber is preferably 5-60 mm, more preferably 10-30 mm; the diameter of the fiber is preferably 10-30 μm. In one embodiment of the present invention, the mass fraction of the fiber can be 3 parts, 3.5 parts, 4 parts, 4.5 parts, or 5 parts. This invention, by incorporating a certain amount of fiber, enables the material to withstand tensile stress caused by drying shrinkage and temperature changes, preventing and inhibiting the generation and development of primary cracks, thereby significantly improving the crack resistance of underground mine safety support materials. Simultaneously, the fiber enhances the tensile strength, flexural strength, and impact strength of the underground mine safety support materials. When the matrix cracks, the fiber can cross the cracks to bear tensile stress, thus delaying crack propagation. Furthermore, the fiber fundamentally alters the failure mode of underground mine safety support materials, transforming it from brittle fracture to ductile failure. Even if the concrete cracks, the fiber can still provide load-bearing capacity, giving it a certain degree of ductility and energy absorption capacity.

[0023] The raw materials for preparing the underground mine safety support material provided by this invention include 25-58 parts of coal gangue, based on 30-50 parts by weight of silicate cement; the particle size of the coal gangue is preferably ≤2mm, more preferably ≤1.3mm. As one embodiment of this invention, the mass fraction of the coal gangue can be 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, 52, 55, or 58 parts. By adding coal gangue, this invention can, on the one hand, improve the density as aggregate, thereby enhancing the mechanical properties of the underground mine safety support material; on the other hand, as a solid waste material, coal gangue occupies a large amount of land and causes land and air pollution when dumped. Using it as a raw material allows for the reuse of coal gangue, resulting in excellent environmental protection.

[0024] The raw materials for preparing the underground mine safety support material provided by this invention include 30-50 parts of fly ash, based on 30-50 parts by weight of silicate cement; the residue of the fly ash passing through a 45μm square-hole sieve is preferably ≤20%. In this invention, the addition of fly ash can fill the voids between aggregates, lubricate aggregate particles, and improve the cohesiveness and plasticity of the underground mine safety support material; at the same time, fly ash can reduce water consumption, increase the content of cementitious materials, and prevent long-term pozzolanic reaction, ensuring higher strength in the later stage; the incorporation of fly ash can reduce the heat of hydration, reduce large-area cracks caused by temperature changes, and maintain the integrity and stability of the structure; it can also improve the impermeability, carbonation resistance, and frost resistance of concrete, thereby improving the durability of concrete and effectively preventing alkali-aggregate reaction; finally, fly ash is inexpensive, which can significantly reduce raw material costs, and the use of industrial waste is in line with the development direction of green building and circular economy, reducing the pollution of power plant waste to the environment.

[0025] The raw materials for preparing the underground mine safety support material provided by this invention include 0.1 to 3 parts gypsum, based on a mass fraction of 30-50 parts of silicate cement; the gypsum is preferably natural anhydrous gypsum and / or natural hemihydrate gypsum. In one embodiment of this invention, the mass fraction of the gypsum can be 0.1, 0.2, 0.5, 0.8, 1, 1.5, 2, 2.5, or 3 parts. In this invention, the gypsum reacts with tricalcium aluminate in the cement to form ettringite, which covers the surface of the cement particles, preventing rapid water intrusion and slowing down the hydration rate of the cement, thus avoiding rapid setting and providing the necessary workable time for pouring the underground mine safety support material; simultaneously, it reduces the heat generated by hydration, preventing the slurry from quickly losing its fluidity and becoming unusable for normal construction.

[0026] The raw materials for preparing the underground mine safety support material provided by this invention include 0.1 to 0.5 parts of a retarder, based on 30 to 50 parts by weight of silicate cement; the retarder is preferably citric acid and / or sucrose. In one embodiment of this invention, the retarder may be 0.1, 0.2, 0.3, 0.4, or 0.5 parts by weight. By adding a retarder, this invention achieves two effects: firstly, the retarder adsorbs onto the surface of cement particles, forming a protective gel coating that hinders the contact between water and cement; secondly, its molecules can complex with calcium ions in the cement paste, inhibiting the nucleation and growth of hydration products, thereby slowing down the hydration process and reducing the temperature rise caused by hydration heat.

[0027] The raw materials for preparing the underground mine safety support material provided by this invention include 5-12 parts paraffin wax, based on 30-50 parts by weight of silicate cement. In one embodiment of this invention, the mass fraction of the paraffin wax can be 5, 6, 7, 8, 9, 10, 11, or 12 parts. By adding the phase change material paraffin wax, this invention can absorb the heat generated by the hydration reaction during the hydration process, thereby reducing the temperature of the heat of hydration.

[0028] The raw materials for preparing the underground mine safety support material provided by this invention include 0.8 to 3.5 parts of a water-reducing agent, based on 30 to 50 parts by weight of silicate cement; the water-reducing agent is preferably a polycarboxylate water-reducing agent. As one embodiment of this invention, the water-reducing agent can be 0.8, 1, 1.5, 2, 2.5, 3, or 3.5 parts by weight. In this invention, the water-reducing agent can maintain the fluidity of the support material while reducing cement usage, improving its strength and durability, improving the workability of the support material, reducing the water-cement ratio of the support material, reducing shrinkage and cracking of the support material, and improving durability and service life.

[0029] The raw materials for preparing the underground mine safety support material provided by this invention include water, calculated based on 30-50 parts by weight of silicate cement. This invention does not impose specific limitations on the exact amount of water used, as long as the water-cement ratio meets the requirements.

[0030] In this invention, the water-cement ratio (mass ratio of water to cement) of the underground mine safety support material is 0.3~1.2, preferably 0.5~1.0, and more preferably 0.6~0.8. As one embodiment of this invention, the water-cement ratio of the underground mine safety support material can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, or 1.2. By controlling the water-cement ratio, this invention enables the mixed raw materials to have good fluidity, thus allowing them to be better injected into the voids after coal seam mining, while also achieving higher strength and better filling effect.

[0031] This invention also provides a method for preparing the underground mine safety support material described in the above technical solution, comprising the following steps: (1) Silicate cement, sulfoaluminate cement, fiber, coal gangue, fly ash, gypsum and paraffin are mixed to obtain dry material; (2) Mix the retarder, water-reducing agent and water to obtain a wet material, and then mix the wet material with the dry material obtained in step (1) to obtain a slurry; (3) The slurry obtained in step (2) is injected to obtain underground safety support material for the mine.

[0032] This invention mixes silicate cement, sulfoaluminate cement, fiber, coal gangue, fly ash, gypsum and paraffin to obtain a mixed dry material.

[0033] The present invention does not impose any special limitation on the mixing method, as long as the components are mixed evenly.

[0034] After obtaining the dry material, the present invention mixes the retarder, water-reducing agent and water to obtain the wet material, and then mixes the wet material and the dry material to obtain the slurry.

[0035] The present invention does not impose any special limitation on the mixing method, as long as the components are mixed evenly.

[0036] This invention, by mixing the retarder, water-reducing agent, and water separately, can avoid the rapid solidification of raw materials caused by the hydration reaction triggered by mixing gel materials such as silicate cement and sulfoaluminate cement with water in advance.

[0037] After obtaining the slurry, the present invention injects the slurry to obtain underground mine safety support material.

[0038] The present invention does not impose any special limitations on the specific operation of the grouting, and any grouting method known to those skilled in the art can be used.

[0039] The preparation method provided by this invention is simple, and the resulting slurry has excellent fluidity and will not solidify in a very short time. This ensures smooth grouting to form a mine underground safety support material with excellent mechanical properties and crack resistance. At the same time, it can be used in conjunction with anchor bolts and anchor cables to provide strong support.

[0040] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Example 1 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 45 parts silicate cement, 15 parts sulfoaluminate cement, 3 parts fiber, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. The silicate cement is silicate cement with a strength grade of 42.5; the sulfoaluminate cement is sulfoaluminate cement with a strength grade of 42.5; the fiber is basalt fiber with a length of 5-20 mm and a diameter of 10-30 μm; the coal gangue has a particle size ≤2 mm; the fly ash has a sieve residue of ≤20% after passing through a 45 μm square-hole sieve; the gypsum is natural anhydrous gypsum; the retarder is citric acid; and the water-reducing agent is polycarboxylate superplasticizer. The preparation method of the underground mine safety support material comprises the following steps: (1) Mix silicate cement, sulfoaluminate cement, fiber, coal gangue, fly ash, gypsum and paraffin wax evenly to obtain dry material; (2) Mix the retarder, water-reducing agent and water evenly to obtain a wet material, and then mix the wet material and the dry material obtained in step (1) evenly to obtain a slurry; (3) The slurry obtained in step (2) is injected to obtain underground safety support material for the mine.

[0042] Example 2 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 45 parts silicate cement, 15 parts sulfoaluminate cement, 4 parts fiber, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0043] Example 3 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 45 parts silicate cement, 15 parts sulfoaluminate cement, 5 parts fiber, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0044] Example 4 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 50 parts silicate cement, 12 parts sulfoaluminate cement, 5 parts fiber, 35 parts coal gangue, 40 parts fly ash, 0.2 parts gypsum, 0.2 parts retarder, 5 parts paraffin wax, 3 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0045] Example 5 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 50 parts silicate cement, 12 parts sulfoaluminate cement, 5 parts fiber, 35 parts coal gangue, 40 parts fly ash, 0.2 parts gypsum, 0.2 parts retarder, 8 parts paraffin wax, 3 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0046] Example 6 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 50 parts silicate cement, 12 parts sulfoaluminate cement, 5 parts fiber, 35 parts coal gangue, 40 parts fly ash, 0.2 parts gypsum, 0.2 parts retarder, 10 parts paraffin wax, 3 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0047] Example 7 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 50 parts silicate cement, 12 parts sulfoaluminate cement, 5 parts fiber, 35 parts coal gangue, 40 parts fly ash, 0.2 parts gypsum, 0.2 parts retarder, 12 parts paraffin wax, 3 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0048] Comparative Example 1 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 45 parts silicate cement, 15 parts sulfoaluminate cement, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0049] Comparative Example 2 A type of underground mine safety support material, prepared by weight, is composed of the following raw materials: 50 parts silicate cement, 12 parts sulfoaluminate cement, 5 parts fiber, 35 parts coal gangue, 40 parts fly ash, 0.2 parts gypsum, 0.2 parts retarder, 3 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0050] Comparative Example 3 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 60 parts silicate cement, 3 parts fiber, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0051] Comparative Example 4 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 60 parts sulfoaluminate cement, 3 parts fiber, 30 parts coal gangue, 32 parts fly ash, 0.5 parts gypsum, 0.3 parts retarder, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0052] Comparative Example 5 A type of underground mine safety support material, by weight, is prepared from the following raw materials: 45 parts silicate cement, 15 parts sulfoaluminate cement, 3 parts fiber, 30 parts coal gangue, 32 parts fly ash, 10 parts paraffin wax, 2.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.6. Other conditions are the same as in Example 1.

[0053] The compressive strength and flexural strength of the underground mine safety support materials provided in Examples 1-7 and Comparative Examples 1-5 were tested, and the results are shown in Table 1: Table 1 shows the compressive and flexural strengths of the underground mine safety support materials provided in Examples 1-7 and Comparative Examples 1-5.

[0054] As shown in Table 1, the compressive strength of the underground mine safety support materials provided in Examples 1-3 and Comparative Example 1 is basically the same. However, the flexural strength of Examples 1-3 is significantly better than that of Comparative Example 1, indicating that the addition of fibers in this invention can improve the flexural strength of the material. The compressive strength and flexural strength of the underground mine safety support materials provided in Examples 4-7 are slightly higher than those in Comparative Example 2, indicating that the addition of paraffin wax in this invention can improve the mechanical properties of the material. The comparison between Examples 1 and Comparative Examples 3-5 shows that this invention, by using a composite of silicate cement and sulfoaluminate cement and introducing gypsum and a retarder, can give the material high early strength and later strength. However, Comparative Example 3 has low early strength because it does not contain sulfoaluminate cement. Comparative Example 4 does not contain silicate cement, although it has high early strength, but it seriously affects the grouting operation during use. Comparative Example 5 also has the problem of affecting the grouting operation after omitting gypsum and a retarder.

[0055] According to the reaction heat of the underground safety support materials provided in Examples 1-7 and Comparative Examples 1-5 of the national standard AQ1089-2020 for polymer reactive reinforcement materials in coal mines, the results are shown in Table 2: Table 2 shows the heat of reaction of the underground safety support materials provided in Examples 1-7 and Comparative Examples 1-5.

[0056] As can be seen from Table 2, by optimizing the composition of the underground safety support material, the present invention can significantly reduce its heat of reaction. The addition of the phase change material paraffin can absorb heat and change its form as the temperature rises, and can also improve the mechanical properties of the underground safety support material.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A safety support material for underground mining, characterized in that, The material is prepared by weight from the following raw materials: 30-50 parts silicate cement, 10-15 parts sulfoaluminate cement, 3-5 parts fiber, 25-58 parts coal gangue, 30-50 parts fly ash, 0.1-3 parts gypsum, 0.1-0.5 parts retarder, 5-12 parts paraffin wax, 0.8-3.5 parts water-reducing agent, and water; the water-cement ratio of the underground mine safety support material is 0.3-1.

2.

2. The underground mine safety support material according to claim 1, characterized in that, The silicate cement is silicate cement with a strength grade of 42.5 or 52.

5.

3. The underground mine safety support material according to claim 1, characterized in that, The sulfoaluminate cement is a sulfoaluminate cement with a strength grade of 42.5 or 52.

5.

4. The underground mine safety support material according to claim 1, characterized in that, The fiber is glass fiber, steel fiber or basalt fiber, with a length of 5~60mm and a diameter of 10~30μm.

5. The underground mine safety support material according to claim 1, characterized in that, The particle size of the coal gangue is ≤2mm.

6. The underground mine safety support material according to claim 1, characterized in that, The residue of the fly ash passing through a 45μm square hole sieve is ≤20%.

7. The underground mine safety support material according to claim 1, characterized in that, The gypsum is natural anhydrous gypsum and / or natural hemihydrate gypsum.

8. The underground mine safety support material according to claim 1, characterized in that, The retarder is citric acid and / or sucrose.

9. The underground mine safety support material according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate water-reducing agent.

10. A method for preparing the underground mine safety support material according to any one of claims 1 to 9, comprising the following steps: (1) Silicate cement, sulfoaluminate cement, fiber, coal gangue, fly ash, gypsum and paraffin are mixed to obtain dry material; (2) Mix the retarder, water-reducing agent and water to obtain a wet material, and then mix the wet material with the dry material obtained in step (1) to obtain a slurry; (3) The slurry obtained in step (2) is injected to obtain underground safety support material for the mine.

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