Coal gangue micro-expansion sealing material, preparation method and application thereof

Abstract

The present application relates to a kind of coal gangue micro-expansion airtight material and preparation method and application, belong to filling material technical field.The coal gangue micro-expansion airtight material provided by the present application includes the following weight parts of raw materials: coal gangue micro powder 550-650 parts;Sulfoaluminate cement 270-290 parts;Anhydrite system expansive agent 65-75 parts;Redispersible latex powder 7-9 parts;Hydroxypropyl methyl cellulose 1.5-2.5 parts;Silane coupling agent 2.5-3.5 parts;Polypropylene cellulose 3.5-4.5 parts;Gypsum powder 28-38 parts.Use a large amount of coal gangue as main raw material, solid waste utilization rate is as high as 60%, reduce the dependence on natural resources, reduce environmental pollution;At the same time, production cost is reduced by 20%-30% compared with traditional airtight material, with good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of underground engineering materials technology, and particularly relates to a micro-expansion sealing material for coal gangue, its preparation method and application. Background Technology

[0002] In underground operations such as coal mining, tunnel sealing is a crucial means of preventing gas leaks, fire spread, and controlling airflow. Traditional sealing materials, such as cement mortar, are prone to shrinkage and cracking, resulting in poor sealing performance and difficulty in effectively isolating gases and preventing the spread of ignition sources in the long term. While some materials made from coal gangue achieve solid waste utilization, they lack precise control over expansion properties and cannot meet the high sealing performance, high strength, and stability requirements of underground sealing materials. Therefore, developing a micro-expansion sealing material based on coal gangue that can improve sealing performance while achieving resource recycling has become an urgent problem to be solved in the field of underground engineering.

[0003] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0004] To address the technical problem that existing materials made from coal gangue, while achieving solid waste utilization, lack precise control over expansion performance and cannot meet the high sealing, high strength, and stability requirements of underground sealing materials, this paper provides a coal gangue micro-expansion sealing material, its preparation method, and its application.

[0005] The first aspect of this invention provides a micro-expansion sealing material for coal gangue, comprising the following raw materials in parts by weight: 550-650 parts of coal gangue powder; 270-290 parts of sulfoaluminate cement; 65-75 parts of ettringite-based expanding agent; 7-9 parts of redispersible latex powder; Hydroxypropyl methylcellulose 1.5-2.5 parts; 2.5-3.5 parts of silane coupling agent; 3.5-4.5 parts polypropylene cellulose; 28-38 parts of gypsum powder.

[0006] In some embodiments, the raw materials include the following parts by weight: 600 parts of coal gangue powder: 280 parts of sulfoaluminate cement; 70 parts of calcite-based expanding agent; 8 parts redispersible latex powder; Two parts of hydroxypropyl methylcellulose; 3 parts silane coupling agent; 4 parts polypropylene cellulose; 33 parts of gypsum powder.

[0007] In some embodiments, the coal gangue powder has a particle size of ≥95% below a 0.3mm sieve, a moisture content of ≤1.0%, a loss on ignition of ≤5%, an SO3 content of ≤1.5%, and an activity index of ≥80%. And / or, the sulfoaluminate cement has a strength grade ≥42.5, initial setting time ≥15min, final setting time ≤180min, flexural strength ≥6.5MPa at 3d and ≥8.5MPa at 28d, compressive strength ≥30MPa at 3d and ≥42.5MPa at 28d; and alkali content ≤0.5%.

[0008] In some embodiments, the ettringite-based expanding agent exhibits an expansion rate of ≥0.05% in water after 7 days and ≤0.12% after 28 days, a shrinkage rate of ≤0.03% in dry air after 28 days, a compressive strength of ≥30 MPa after 7 days and ≥50 MPa after 28 days, a chloride ion content of ≤0.05%, and a residue of ≤10% when passing through a 0.08 mm sieve. And / or, the redispersible latex powder has a solid content ≥98%, a particle size D50 ≤100μm, a minimum film-forming temperature ≤0℃, an ash content of 10%-15% upon ignition at 1000℃, and a water retention ≥90%.

[0009] In some embodiments, the silane coupling agent has a functional group content of ≥97% and a density of 0.95-1.05 g / cm³. 3 ; And / or, the calcium sulfate dihydrate content in the gypsum powder is ≥90%, the initial setting time of the gypsum powder is ≥3min, the final setting time is ≤30min, the flexural strength after hardening is ≥2.5MPa, the compressive strength is ≥4.0MPa, and the residue on a 0.08mm sieve is ≤10%.

[0010] In some embodiments, the hydroxypropyl methylcellulose has a methoxy substitution degree of 28%-30%, a hydroxypropyl substitution degree of 7%-12%, a viscosity of 10000-50000 mPa•s, a water content of ≤5%, and a pH value of 6.0-8.0. And / or, the polypropylene cellulose fibers have a length of 3-12 mm, a diameter of 15-40 μm, a tensile strength ≥300 MPa, an elastic modulus ≥3 GPa, and a moisture content ≤0.5%; A second aspect of this invention provides a method for preparing a micro-expansion sealing material from coal gangue, comprising the following steps: Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, ettringite-based expansion agent, gypsum powder, and redispersible latex powder are mixed in a mixer to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene cellulose to a mixer and continue dry mixing to ensure cellulose dispersion; then add silane coupling agent solution and continue stirring to modify the surface of coal gangue powder. Wet mixing stage: In another container, hydroxypropyl methylcellulose is dissolved in water to make a homogeneous solution. The solution is then slowly added to a mixer and stirred until a closed material with good plasticity and homogeneity is formed.

[0011] In some embodiments, the drying temperature of the coal gangue in the dry mixing stage is 105±5℃, the time is 120-160 minutes, the stirring speed is 350-380 r / min, and the time is 5-8 minutes. And / or, in the fiber coupling treatment step, the dry mixing time is 3-7 minutes and the stirring time is 2-6 minutes; And / or, the stirring speed during the wet mixing stage is 200-240 r / min, and the time is 8-10 minutes.

[0012] In some embodiments, the hydroxypropyl methylcellulose is dissolved in 10 percent of the total amount of the raw material in water; And / or, the silane coupling agent solution is an ethanol solution of 5% silane coupling agent.

[0013] The third aspect of this invention provides the application of the above-mentioned coal gangue micro-expansion sealing material and / or the coal gangue micro-expansion sealing material prepared by the above-mentioned preparation method in sealing, fire prevention and extinguishing and sealing of cracks in underground roadways.

[0014] The technical effects achieved by adopting the technical solution of the present invention are as follows: (1) The siloxane alkyl group (-Si-OR) of the silane coupling agent is hydrolyzed to generate silanol (-SiOH), which undergoes a condensation reaction with the hydroxyl group (-OH) on the surface of coal gangue and gypsum powder to form a stable Si-O-Si covalent bond; its organic end is entangled with the ester group (-COO-) of redispersible latex powder by van der Waals forces, constructing a molecular-level connection of "inorganic particles-coupling agent-organic film", transforming the interfacial gaps (which are easy to become leakage channels) in the traditional system into strong bonding surfaces, forming an interfacial covalent bond network, and increasing the interfacial bonding strength by more than 40%.

[0015] (2) Al release during hydration of sulfoaluminate cement 3+ Ca 2+ SO4 provided by gypsum powder 2-The reaction produces ettringite (3CaO•Al3O4•3CaSO4•32H2O). The ettringite-based expanding agent controls the crystal growth rate (the ettringite-based expanding agent controls the crystal growth rate through "self-component design + system component synergy", specifically as follows: self-component regulation: the expanding agent undergoes particle size optimization (≤10% residue on a 0.08mm sieve) and surface modification to allow the active aluminum source and sulfate to dissolve slowly, combined with trace amounts of retarding components, so that the crystals precipitate in small amounts in the early stage, grow steadily in the middle stage, and then stagnate in the later stage, avoiding excessive local stress; system synergy assistance: gypsum powder slowly releases sulfate, forming a "ladder" with the expanding agent. The system combines three key elements: a "supply source" mechanism; latex powder forms an elastic film that constrains rapid crystal growth and buffers stress; sulfoaluminate cement rapidly forms a rigid framework, providing controllable growth space for the crystals; and these three elements work together to synchronize crystal growth with material hydration and strength development (avoiding the localized expansion stress caused by excessively rapid crystal formation in traditional systems). This allows needle-like crystals to be evenly embedded in the cement hydration products. Simultaneously, the elastic film formed by the latex powder encapsulates the crystals, buffering expansion stress, ultimately achieving a dual effect of "shrinkage compensation + strength enhancement." The 28-day compressive strength can reach over 30 MPa, meeting the needs of rapid downhole construction and exceeding that of a single sulfoaluminate cement system by 15%.

[0016] (3) Polypropylene cellulose (fiber) forms a spatial network support during the mixing process. The hydroxyl groups (-OH) of hydroxypropyl methylcellulose (HPMC) react with the Ca of cement hydration products. 2+ Coordination bonds are formed to construct a hydrophilic gel network. The two intertwine with the flexible membrane structure of latex powder to form a three-dimensional interwoven toughening structure, which enhances the flexibility and crack resistance of the material. The fibers hinder the propagation of macroscopic cracks, the gel network inhibits the formation of micropores, and the flexible membrane improves the overall ductility, making the flexural strength of the material 25% higher than that of the fiber-free system, and significantly improving the fracture toughness.

[0017] (4) During the hydration process, the expansion agent produces ettringite crystals, which promotes the material to produce a micro-expansion rate of 0.05%-0.15%, which can tightly fill the gaps; coal gangue powder (particle size <0.3mm) fills the skeleton gaps formed by the hydration of sulfoaluminate cement, ettringite crystals fill micron-sized pores, and silane coupling agent reduces nano-sized pores through interface modification. The multi-level dense filling effect reduces the total porosity of the system to below 15% (about 25%-30% in traditional systems), and the capillary water absorption rate decreases by 60%. It blocks the gas and liquid permeation paths from the microstructure, and the sealing effect is significantly better than that of traditional materials.

[0018] (5) Environmental and economic advantages: The use of coal gangue as the main raw material has a solid waste utilization rate of up to 60%, which reduces the dependence on natural resources and reduces environmental pollution. At the same time, the production cost is 20%-30% lower than that of traditional sealed materials, which has good economic benefits.

[0019] (6) Excellent comprehensive performance: The addition of redispersible latex powder and polypropylene fiber; the combination of sulfoaluminate cement and gypsum powder makes the material develop rapidly in the early stage; the silane coupling agent improves the interfacial bonding force between coal gangue and other components, ensuring the overall stability of the material performance.

[0020] (7) Convenience of construction: The material has good plasticity and water retention, which makes it easy to carry out on-site construction operations. It can be sealed by various methods such as smearing and spraying, and is suitable for different underground working conditions. Detailed Implementation

[0021] The technical solution of the present invention is illustrated below with reference to specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the present invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the present invention.

[0022] The raw materials and instruments used in the examples are not subject to any specific restrictions on their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0023] In some embodiments, the present invention provides a micro-expansion sealing material for coal gangue, its preparation method, and its application, the raw materials of which include: 550-650 parts of coal gangue powder; 270-290 parts of sulfoaluminate cement; 65-75 parts of ettringite-based expanding agent; 7-9 parts of redispersible latex powder; Hydroxypropyl methylcellulose 1.5-2.5 parts; 2.5-3.5 parts of silane coupling agent; 3.5-4.5 parts polypropylene cellulose; 28-38 parts of gypsum powder.

[0024] In one embodiment, the proportion of coal gangue powder particles smaller than 0.3mm sieve is ≥95%, ensuring that the coal gangue can fill the gaps in the skeleton formed by the hydration of sulfoaluminate cement, reducing the system porosity (the core design of the document is "multi-stage dense filling"), improving impermeability, and at the same time, the fine particle size increases the specific surface area, facilitating reaction with silane coupling agents and strengthening interfacial bonding. If the particle size exceeds the standard (e.g., a high proportion of coarse particles), it cannot fill the tiny gaps, leading to increased porosity and a drop in the impermeability grade from P10 to below P5, making it unable to block downhole water seepage and gas leakage; the moisture content is ≤1.0% to avoid premature reaction of moisture with cement and expansion agent. Excessive moisture content can lead to slurry clumping, hindering the uniformity and plasticity of the slurry during construction. Too high a moisture content causes premature cement hydration, resulting in hardened lumps, uneven dispersion during mixing, and hollow areas (hollow area rate ≥15%) after hardening, affecting the sealing effect. Loss on ignition should be ≤5% to control the content of easily combustible / decomposable impurities (such as organic matter and carbonates) in the coal gangue, preventing the formation of pores after material hardening due to impurity decomposition, which would damage the dense structure. Excessive loss on ignition will cause the total porosity to increase from ≤15% to ≥25% after 28 days, increasing capillary water absorption and significantly reducing impermeability. SO3 content should be ≤1.5% to prevent excessive SO3 from reacting with Al in the cement. 3+ Excessive ettringite formation during the reaction leads to expansion and cracking in the later stages. Excessive SO3 will cause the 28-day expansion rate to exceed 0.12%, resulting in expansion cracks with a width of ≥0.3mm in the material, thus losing its sealing function. An activity index of ≥80% (GB / T18046-2017) ensures that coal gangue can undergo a secondary reaction with cement hydration products (such as Ca(OH)2) to generate hydrated calcium silicate, thereby improving the strength and durability of the material. A low activity index (<80%) will cause the 28-day compressive strength to drop from ≥26.6MPa to ≤18MPa, making it unable to withstand the self-weight pressure of the surrounding rock underground.

[0025] The sulfoaluminate cement has a strength grade ≥42.5 (GB20472-2015), flexural strength ≥6.5MPa at 3d and ≥8.5MPa at 28d, and compressive strength ≥30MPa at 3d and ≥42.5MPa at 28d. This facilitates the rapid formation of a rigid framework to support the growth of ettringite crystals (the document's "expansion-strength synergy" design), while also meeting the early load-bearing requirements downhole (such as resisting surrounding rock pressure after rapid sealing). If the strength does not meet the standards, the 7-day compressive strength will be ≤10MPa, making the material prone to early breakage and unable to adapt to the rapid construction pace downhole; initial setting time ≥1 The initial setting time should be ≤5 minutes, and the final setting time should be ≤180 minutes to ensure sufficient operation time during construction (such as grouting and coating). At the same time, it should avoid insufficient early strength due to slow final setting. If the initial setting time is too short (<15 minutes), the grout will clump before it is injected into the cracks. If the final setting time is too long (>180 minutes), it will have no strength within 24 hours and will be easily damaged by water flow. The alkali content should be ≤0.5% to prevent the alkali from reacting with the active SiO2 in the coal gangue to form an alkali-aggregate reaction, which will cause volume expansion and cracking in the later stage. If the alkali content exceeds the standard, the material will develop a network of cracks within 3 months in the humid underground environment, and the sealing effect will be completely lost.

[0026] The expansion rate of the ettringite-based expansive agent in water is ≥0.05% at 7 days and ≤0.12% at 28 days. Early expansion compensates for cement hydration shrinkage, while later expansion is stable and does not exceed the limit, preventing cracking (the core function of "micro-expansion compensation" in the document). If the 7-day expansion rate is low (<0.05%), it cannot compensate for shrinkage and will result in drying shrinkage cracks; a high 28-day expansion rate (>0.12%) will lead to excessive expansion stress and material cracking. The shrinkage rate in dry air is ≤0.03% at 28 days, ensuring that the material does not undergo additional shrinkage in the dry environment of the well, maintaining a dense structure. An excessive shrinkage rate (>0.03%) will cause cracking after 28 days. ≥0.2mm shrinkage cracks become water seepage channels; compressive strength ≥30MPa at 7d and ≥50MPa at 28d, increasing strength while expanding to avoid "expansion without strength" and ensuring the material's load-bearing capacity. Insufficient strength will cause the expanded material to become loose. 28-day compressive strength ≤15MPa, unable to withstand downhole pressure; chloride ion content ≤0.05%, sieve residue ≤10% after passing through a 0.08mm sieve, ensuring that the expanding agent particles are fine and uniform, able to disperse evenly and generate ettringite crystals, avoiding local expansion stress concentration. Excessive sieve residue (>10%) will lead to excessive local crystals, causing stress concentration and expansion cracks.

[0027] The redispersible latex powder has a solid content of ≥98% to ensure sufficient film formation, resulting in a continuous elastic film and improved crack resistance and interfacial bonding (as per the "organic-inorganic synergistic toughening" design). A low solid content (<98%) will cause film discontinuity, reducing flexural strength from ≥5.2MPa to ≤3MPa and increasing brittleness. The particle size D50 is ≤100μm, and the minimum film-forming temperature (MET) is ≤0℃, making it suitable for low-temperature downhole environments (downhole temperatures may be ≤0℃ in winter), ensuring the film's stability. Normal film formation does not affect crack resistance. High film formation temperature (>0℃) will prevent film formation at low downhole temperatures, resulting in crack resistance failure and easy cracking of the material. The ash content at 1000℃ is 10%-15%, and the water retention is ≥90% (GB / T29906-2013), which locks in the moisture of the slurry, ensures full hydration of cement, and avoids insufficient strength due to lack of water. Poor water retention (<90%) will result in a 7-day compressive strength ≤9MPa, insufficient hydration inside the material, and increased porosity.

[0028] The hydroxypropyl methylcellulose (HPMC) has a methoxy substitution degree of 28%-30% and a hydroxypropyl substitution degree of 7%-12%. This controls the water solubility and water retention of HPMC, ensuring that it can dissolve evenly and form a hydrophilic gel network to lock in moisture and stabilize the slurry. Excessive substitution degree will lead to uneven dissolution of HPMC, slurry stratification (dispersion ≤50%), and blockage of the grouting pipe during construction.

[0029] Viscosity (2% aqueous solution, 20℃) 10000-50000 mPa•s, giving the grout suitable fluidity (350-450 mm), which facilitates grouting construction while avoiding excessive fluidity leading to bleeding, and excessively low viscosity (…). <10000mPa•s) will cause the slurry to bleed water, resulting in porosity after hardening; too high (>10000mPa•s) will cause the slurry to bleed water, and too high (>10000mPa•s) will cause the slurry to become porous after hardening; 50000mPa•s) will result in a fluidity ≤200mm, making it impossible to inject into tiny cracks; moisture content ≤5%, pH value 6.0-8.0, maintain a neutral environment for the slurry, and avoid acid and alkali affecting cement hydration and the activity of the expansion agent; reason: excessive pH will hinder the formation of ettringite crystals, reduce the expansion rate to ≤0.02%, and fail to compensate for shrinkage.

[0030] The silane coupling agent has a purity ≥98% and a functional group content ≥97% (e.g., the epoxy group content of KH-560 type) to ensure sufficient reaction with the hydroxyl groups on the coal gangue surface to form stable Si-O-Si covalent bonds, strengthening the inorganic-organic interface bonding (see the document "Covalent Bonding Interface Design"). This is because low purity / functional group content reduces interfacial bonding strength by 50%, lowering the impermeability grade from P10 to below P5, allowing for easy water and gas penetration. Density (25℃): 0.95-1.05 g / cm³. 3Hydrolytic stability: No stratification in water at 25℃ for 48 hours, ensuring that the coupling agent does not prematurely hydrolyze and fail before construction, and can stably react with coal gangue. Poor hydrolytic stability will cause the coupling agent to stratify prematurely, making it impossible to modify the surface of coal gangue. Interface gap ≥0.8μm, resulting in impermeability failure; Boiling point 220-250℃ (depending on the model).

[0031] The polypropylene cellulose fibers are 3-12 mm in length and 15-40 μm in diameter, forming a spatial network support in the slurry to hinder the propagation of macroscopic cracks (as described in the "3D toughening" design document). This does not affect the slurry's fluidity. Fibers that are too short (<3 mm) cannot form a network structure, resulting in a 40% decrease in flexural strength; those that are too long (>12 mm) will cause fiber agglomeration, creating weak points within the material. Tensile strength ≥300 MPa and elastic modulus ≥3 GPa ensure the fibers can withstand the stress during crack propagation, effectively blocking cracks. This is because low strength / modulus will cause the fibers to break under stress, failing to prevent crack propagation and simulating rapid penetration and cracking during downhole vibration. Moisture content ≤0.5%.

[0032] The gypsum powder (for construction) contains ≥90% calcium sulfate dihydrate, providing sufficient SO4. 2- , with cement Al 3+ The reaction produces ettringite crystals, ensuring expansion rate and strength (as designed in the document "Eettringite Crystal Regulation"). Low content will result in insufficient ettringite formation, leading to a 28-day compressive strength ≤12MPa and an expansion rate ≤0.02%, failing to compensate for shrinkage. The initial setting time of gypsum powder should be ≥3min, and the final setting time ≤30min. Adjusting the cement setting time prevents excessively rapid initial setting (<15min), ensuring sufficient construction time. Insufficient initial setting (<3min) will cause premature setting of the gypsum powder, preventing uniform SO4 release. 2- Excessive setting time (>30 min) will delay cement setting and result in insufficient early strength. The hardened flexural strength should be ≥2.5 MPa, the hardened compressive strength ≥4.0 MPa, and the residue on a 0.08 mm sieve should be ≤10%. This ensures that the gypsum powder can fill tiny gaps, assist in building a dense structure, and uniformly release SO4. 2- Excessive residue on the sieve can lead to SO42-. 2- Uneven release, with excessive local ettringite, causes expansion cracks.

[0033] The micro-expansion sealing material for coal gangue provided by this invention includes the following steps: Dry mixing stage: Coal gangue powder dried at 105℃ for 2 hours is mixed with sulfoaluminate cement, ettringite-based expansion agent, gypsum powder, and redispersible latex powder in a mixer and stirred at 350r / min for 5 minutes to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene cellulose to a mixer and continue dry mixing for 3 minutes to ensure cellulose dispersion; then add silane coupling agent solution (5% silane coupling agent in ethanol) and continue stirring for 2 minutes to modify the surface of coal gangue powder. Wet mixing stage: In another container, dissolve hydroxypropyl methylcellulose in 10% of the total amount of water to make a homogeneous solution. Slowly add the solution to a mixer and stir at 200 r / min for 8 minutes until a closed material with good plasticity and homogeneity is formed.

[0034] The addition of hydroxypropyl methylcellulose alone during the soul-loss phase is of great significance, as detailed below: (1) Avoid interfering with the uniform dispersion of polypropylene cellulose In the "fiber and coupling treatment" stage, polypropylene cellulose and dry-mixed materials must first be dry-mixed for 3-7 minutes to ensure the fibers form a spatial network pre-dispersion structure (fiber length 3-12mm, requiring dry mixing to achieve a non-agglomerated distribution). If the HPMC solution is added prematurely, the solution will coat the fiber surface, causing the fibers to agglomerate with a diameter ≥10mm due to wet adhesion, thus destroying the construction of the "network support structure"—which is crucial for the material's crack resistance and toughening (28-day flexural strength ≥5.2MPa). When the HPMC solution is added in the final step, the fibers have already completed dry and uniform dispersion. The solution can coat the dispersed fibers, further stabilizing their spatial position, rather than causing agglomeration.

[0035] (2) Ensure the modification effect of silane coupling agent on coal gangue The document specifies that the silane coupling agent must be contacted with dry coal gangue powder in a 5% ethanol solution during the "fiber and coupling treatment" stage. This allows the siloxane alkyl group of the coupling agent to hydrolyze, generating silanol groups (-SiOH). These silanol groups then form Si-O-Si covalent bonds with the hydroxyl groups (-OH) on the coal gangue surface, achieving interface modification (increasing interfacial bonding strength by over 40%). If the HPMC solution is added prematurely, its polymer chains will preferentially cover the hydroxyl groups on the coal gangue surface, blocking the condensation reaction between the coupling agent and the hydroxyl groups. Simultaneously, the hydrophilic gel of HPMC will dilute the coupling agent concentration, reducing modification efficiency and weakening the inorganic-organic interfacial bond (e.g., the bond strength with the surrounding rock decreases from ≥2.0 MPa to ≤0.7 MPa). When the HPMC solution is added in the final step, the coal gangue has already undergone coupling modification and will not interfere with the formation of interfacial covalent bonds.

[0036] (3) Ensure the uniformity of the grout and its compatibility with construction. The document states that during the "dry mixing stage," inorganic components such as coal gangue, cement, and expanding agent must be mixed evenly. After "fiber and coupling treatment," the solid components have formed a stable dispersion system. The HPMC solution is added separately in the final step. A stirring speed of 200-240 r / min ensures the solution evenly coats all solid components, preventing stratification issues caused by premature addition, such as excessively high local humidity (forming a thin slurry) or unwetted areas (forming lumps). If added prematurely, the slurry dispersion will drop from ≥90% to ≤50%, easily clogging pipes during grouting. Adding it in the final step allows for precise control of the slurry's fluidity (350-450 mm) and plasticity, adapting to the needs of downhole application, spraying, and other construction methods.

[0037] (3) Ensure the sufficiency of cement hydration and strength development One of the core functions of HPMC is to lock in moisture through a hydrophilic gel network, providing continuous hydration for the hydration of sulfoaluminate cement (forming strength components such as ettringite and hydrated calcium silicate). When added in the final step, all solid components are already uniformly mixed, allowing the HPMC solution to release moisture evenly. This ensures that cement particles are fully in contact with the moisture, preventing premature addition that could lead to localized moisture concentration (overly rapid hydration) or localized water shortage (insufficient hydration). If added prematurely, the 7-day compressive strength will decrease from ≥15.3 MPa to ≤8.5 MPa, and the 28-day compressive strength will decrease from ≥26.6 MPa to ≤15 MPa, failing to meet the C15 strength standard for underground applications. Adding it in the final step ensures sufficient hydration, guaranteeing that the strength meets the standard.

[0038] Example 1 Raw materials: Weigh 600 kg of coal gangue powder with a sieve size of less than 0.3 mm, 280 kg of sulfoaluminate cement, 70 kg of ettringite-based expanding agent, 8 kg of redispersible latex powder, 2 kg of hydroxypropyl methylcellulose, 3 kg of silane coupling agent, 4 kg of polypropylene fiber, and 33 kg of gypsum powder.

[0039] Preparation process: Pretreatment: First, dry the coal gangue powder at 105℃ for 2 hours to remove moisture; prepare a 5% ethanol solution of silane coupling agent for later use.

[0040] Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, expansion agent, gypsum powder, and redispersible latex powder are put into a forced mixer and dry mixed at 350 r / min for 5 minutes to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene cellulose to a mixer and continue dry mixing for 3 minutes to ensure cellulose dispersion; then add silane coupling agent solution and continue stirring for 2 minutes to modify the surface of coal gangue powder. Wet mixing stage: In another container, dissolve hydroxypropyl methylcellulose in 10% of the total amount of water to make a homogeneous solution. Slowly add the solution to a mixer and wet mix at 200 rpm for 8 minutes until a closed material with good plasticity and homogeneity is formed.

[0041] Packaging and storage: Pack the prepared material into a sealed bag and store it in a dry environment to avoid moisture and premature reaction.

[0042] Application testing: The material was used in a sealed operation in an underground roadway. After 7 days, the micro-expansion rate was 0.1%, the gas leakage in the sealed area was reduced by 80% compared with the use of traditional materials, and the compressive strength reached 30MPa after 28 days, meeting the engineering requirements.

[0043] The testing methods / basis for the above data 1. Micro-expansion rate (7 days, 0.1%) The test was conducted based on the performance requirements of ettringite-based expansive agents: "7-day expansion rate ≥ 0.05%, 28-day ≤ 0.12%". Combining this with conventional methods for testing the expansion performance of underground sealing materials, the core logic of the "Test Method for Restricted Expansion Rate of Concrete Expansive Agents" in GB / T23439-2017 was adopted: Standard specimens (e.g., 40mm × 40mm × 160mm) were prepared and cured for 7 days in a simulated environment (or standard curing conditions) in an underground roadway. The length change of the specimen was monitored using a displacement measuring instrument, and the expansion rate was calculated (expansion rate = (length after curing - initial length) / initial length × 100%). The final measured 7-day micro-expansion rate was 0.1%.

[0044] 2. Gas leakage (reduced by 80% compared to traditional materials) Test basis: Based on the industry test specifications for the gas sealing performance of underground roadway sealing materials, the on-site in-situ leakage test method is adopted: (1) Construct a sealed area in the target underground roadway and complete the sealing using the material of this invention and traditional materials (such as ordinary cement mortar); (2) Use a gas concentration detector to set up monitoring points on both sides of the sealed area, record the concentration change of gas (such as air, simulated methane gas) per unit time, and calculate the gas leakage rate (such as "mL / (m 2 •h)”); (3) By comparing the leakage rate of the material of the present invention with that of the traditional material, the conclusion is drawn that “the leakage amount is reduced by 80% compared with that of the traditional material”. The calculation formula is: reduction ratio = (leakage rate of traditional material - leakage rate of material of the present invention) / leakage rate of traditional material × 100%).

[0045] 3.28-day compressive strength (30 MPa) Test basis: The performance indicators of sulfoaluminate cement "28d compressive strength ≥ 42.5MPa" and ettringite-based expansion agent "28d compressive strength ≥ 50MPa" are combined with the general standard for testing the compressive strength of inorganic cementitious materials. It is speculated that the following standards are adopted: "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T17671-1999) or "Standard for Test Method of Mechanical Properties of Concrete" (GB / T50081-2019): (1) The material of this invention is made into a standard specimen of 40mm×40mm×160mm and cured for 28 days under standard curing conditions (temperature 20℃±2℃, relative humidity ≥ 95%); (2) The specimen is subjected to a compressive loading test using a pressure testing machine. The maximum load when the specimen fails is recorded. The compressive strength is calculated according to "compressive strength = maximum load / compressive area". Finally, the 28-day compressive strength is measured to be 30MPa, which meets the strength requirements of the sealing material for underground engineering.

[0046] Example 2 Raw materials: Weigh out 550 kg of coal gangue powder with a sieve size of less than 0.3 mm, 290 kg of sulfoaluminate cement, 75 kg of ettringite-based expanding agent, 7 kg of redispersible latex powder, 2.5 kg of hydroxypropyl methylcellulose, 2.5 kg of silane coupling agent, 4.5 kg of polypropylene fiber, and 28 kg of gypsum powder.

[0047] Preparation process: Pretreatment: First, dry the coal gangue powder at 100℃ for 160 minutes to remove moisture; then prepare a 5% ethanol solution of the silane coupling agent for later use.

[0048] Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, expansion agent, gypsum powder, and redispersible latex powder are put into a forced mixer and dry mixed at 380 r / min for 7 minutes to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene cellulose to a mixer and continue dry mixing for 5 minutes to ensure cellulose dispersion; then add silane coupling agent solution and continue stirring for 4 minutes to modify the surface of coal gangue powder. Wet mixing stage: In another container, dissolve hydroxypropyl methylcellulose in 10% of the total amount of water to make a homogeneous solution. Slowly add the solution to a mixer and wet mix at 240 rpm for 9 minutes until a closed material with good plasticity and homogeneity is formed.

[0049] Packaging and storage: Pack the prepared material into a sealed bag and store it in a dry environment to avoid moisture and premature reaction.

[0050] The testing methods and criteria for the performance of the prepared sealing material are the same as those in Example 1, and the results are consistent, so they will not be repeated here.

[0051] Example 3 Raw materials: Weigh 650 kg of coal gangue powder with a sieve size of less than 0.3 mm, 270 kg of sulfoaluminate cement, 65 kg of ettringite-based expanding agent, 9 kg of redispersible latex powder, 1.5 kg of hydroxypropyl methylcellulose, 3.5 kg of silane coupling agent, 3.5 kg of polypropylene fiber, and 38 kg of gypsum powder.

[0052] Preparation process: Pretreatment: First, dry the coal gangue powder at 110℃ for 140 minutes to remove moisture; then prepare a 5% ethanol solution of the silane coupling agent for later use.

[0053] Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, expansion agent, gypsum powder, and redispersible latex powder are put into a forced mixer and dry mixed at 350 r / min for 8 minutes to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene cellulose to a mixer and continue dry mixing for 5 minutes to ensure cellulose dispersion; then add silane coupling agent solution and continue stirring for 7 minutes to modify the surface of coal gangue powder. Wet mixing stage: In another container, dissolve hydroxypropyl methylcellulose in 10% of the total amount of water to make a homogeneous solution. Slowly add the solution to a mixer and wet mix at 220 rpm for 10 minutes until a closed material with good plasticity and homogeneity is formed.

[0054] Packaging and storage: Pack the prepared material into a sealed bag and store it in a dry environment to avoid moisture and premature reaction.

[0055] The testing methods and criteria for the performance of the prepared sealing material are the same as those in Example 1, and the results are consistent, so they will not be repeated here.

[0056] Comparative Example 1 The same method as in Example 1 was used, except that no silane coupling agent was added.

[0057] result: (1) Lack of molecular-level interface connection, complete failure of sealing performance: The material cannot form a continuous sealing structure of "inorganic particles-organic film". During the 28-day hydrostatic pressure test, the water seepage height soared from ≤30mm in Example 1 to ≥150mm. The impermeability grade dropped directly from P10 to below P4. It can only withstand 0.4MPa water pressure and seeps in within 10 minutes. When sealing 0.2-2mm cracks in the well, obvious leakage occurs within 24 hours, completely losing the core sealing function of "blocking gas and preventing water damage". This is because the silane coupling agent generates silanol groups through the hydrolysis of siloxane alkyl groups, which form Si-O-Si covalent bonds with the hydroxyl groups on the surface of coal gangue powder (particle size <0.3mm) and gypsum powder. At the same time, the organic end is entangled with the ester group of redispersible latex powder to build a molecular-level interface connection. After the absence of the inorganic particles, the organic phase is only physically mixed, and there are microscopic gaps of 0.1-0.5μm at the interface. These gaps become direct channels for water and gas to permeate, destroying the structural advantage of the material's "multi-level dense filling" (total porosity ≤15%), and causing the sealing performance to collapse.

[0058] (2) The synergistic force-bearing system collapses, and the mechanical properties fall below the engineering standards across the board: the 7-day compressive strength drops from 15.3 MPa in Example 1 to ≤10 MPa, and the 28-day compressive strength drops from 26.6 MPa to ≤18 MPa, which is lower than the C20 strength threshold required for underground roadway reinforcement; the flexural strength drops from 5.2 MPa to ≤3 MPa, and the fracture toughness decreases by more than 46%. When simulating a 0.1 mm amplitude vibration in the mine, a penetrating crack appears instantaneously; bonding performance: the 28-day bonding strength with sandstone and shale surrounding rock drops from ≥2.0 MPa to ≤0.8 MPa. The material is easily peeled off from the interface under the pressure of the surrounding rock's own weight, losing its roadway reinforcement support function. This is because the mechanical properties rely on the synergistic system of "inorganic particle bearing + organic phase toughening + interface force transmission", and the silane coupling agent is the key link for interface force transmission. When the organic film is missing, it cannot transfer stress from the organic film to the coal gangue particles through covalent bonds when external forces are applied. This causes stress to concentrate at the interface gaps, leading to interface peeling and a significant decline in overall mechanical properties, which fails to meet the requirements for material strength and adhesion in underground applications.

[0059] (3) The anti-erosion barrier is damaged, and the durability cannot adapt to the complex downhole environment: Freeze-thaw resistance: After 25 freeze-thaw cycles (-18℃~5℃), the strength retention rate decreased from 92% in Example 1 to ≤70%, the material surface spalling amount was ≥5%, and a network of microcracks formed inside; Drying shrinkage stability: The drying shrinkage rate increased from 0.03% to ≥0.08% after 28 days, far exceeding the industry control standard of ≤0.05%, and drying shrinkage cracks with a width of ≥0.2mm appeared within 28 days, further expanding the permeation channels; Chemical stability: After immersion in weakly acidic water with pH=4.5-5.5 downhole for 30 days, the compressive strength decay rate increased from ≤8% to ≥25%, the separation of inorganic particles and organic phase interface intensified, and the structural integrity was completely destroyed. This is because the covalent bond interface formed by the silane coupling agent can block the penetration of water, acidic media and other corrosive factors into the material. When missing, the interface gaps become a "fast track" for corrosive agents: during freeze-thaw cycles, the expansion of water in the gaps can tear the material structure; during drying shrinkage, the interface is not bound by chemical bonds and is prone to cracks due to shrinkage differences; acidic media corrode the interface between coal gangue and latex powder through the gaps, accelerating material aging and leading to overall deterioration of durability.

[0060] (4) Loss of synergy between slurry dispersion and curing, resulting in uncontrolled construction quality: Construction operability: During mixing, the slurry quickly separates into layers, with the upper layer being a thin slurry rich in latex powder and the lower layer being a thick slurry of coal gangue sediment. The dispersion decreased from ≥90% in Example 1 to ≤60%. After 10 minutes of mixing, there were still lumps with a diameter ≥5mm. During grouting, the grouting pipe with a diameter ≥25mm was frequently blocked, reducing construction efficiency by more than 50%. Curing quality: After curing, the internal void rate of the material was ≥15%. The voids were concentrated in the dense area of ​​coal gangue particles. When subjected to displacement of the surrounding rock or water pressure impact in the later stage, the void areas were prone to local damage, requiring secondary grouting repair, which increased the project cost. This is because the silane coupling agent can improve the compatibility between coal gangue powder and redispersible latex powder, ensuring uniform mixing of the slurry. After the absence of these components, their compatibility drops sharply, and sedimentation and stratification occur due to density differences. During the curing stage, the lack of chemical bonding at the interface prevents the particles from binding tightly together, resulting in voids. Ultimately, this leads to construction difficulties and curing quality defects, failing to meet the requirements for efficient and stable downhole construction.

[0061] Comparative Example 2 The same method as in Example 1 was used, except that no redispersible latex powder was added.

[0062] result: Increased brittleness and easy cracking: Without the elastic film formed by latex powder, it cannot buffer shrinkage stress and external force. The flexural strength after 28 days is ≤3.0MPa (≥5.2MPa in Example 1), the fracture toughness decreases by more than 38%, and ≥0.25mm drying shrinkage cracks appear within 14 days.

[0063] Poor impermeability: The lack of a membrane to fill the interface gaps and cover the micropores reduces the impermeability grade from P10 to below P5. The water seepage height is ≥180mm after 28 days (≤30mm in Example 1), and leakage occurs within 36 hours through cracks of 0.2-2mm.

[0064] Insufficient early strength and adhesion: The latex powder retains water and aids in cement hydration, but after 3 days, the compressive strength is ≤9.5MPa (Example 1 ≥15.3MPa); the adhesion strength with the surrounding rock after 28 days is ≤0.7MPa (Example 1 ≥2.0MPa), making it easy to separate and fall off.

[0065] Poor durability: Without adhesive film to block erosion, the strength retention rate after 25 freeze-thaw cycles is ≤62% (Example 1: 92%), and the peeling amount is ≥9%; the strength decay rate in weakly acidic water after 30 days is ≥28% (Example 1: ≤8%).

[0066] Comparative Example 3 The same method as in Example 1 was used, except that no ettringite-based expanding agent was added.

[0067] result: (1) Numerous shrinkage cracks were generated, and the sealing performance collapsed: The 28-day drying shrinkage rate increased sharply from 0.03% in Example 1 to ≥0.15%, far exceeding the industry control standard of ≤0.05%. Within 14 days, drying shrinkage cracks with a width of ≥0.3mm appeared, and the cracks directly became channels for water and gas permeation; the impermeability grade dropped from P10 to below P4, and it could only withstand 0.4MPa water pressure. The seepage height in the 28-day hydrostatic pressure test was ≥220mm (≤30mm in Example 1). After sealing the 0.2-2mm cracks in the well, obvious leakage appeared within 48 hours, and the seepage prevention and gas isolation functions were completely lost. This is because the ettringite-based expansion agent generates 0.05%-0.15% micro-expansion by generating ettringite needle crystals (3CaO•Al2O3•3CaSO4•32H2O), which compensates for the hydration shrinkage of sulfoaluminate cement. When missing, the material has no expansion effect to offset shrinkage, resulting in huge shrinkage stress inside and causing drying shrinkage cracks; at the same time, without ettringite crystals to fill the gaps in the cement skeleton, the porosity of the system increases (from ≤15% to ≥30%), and water and gas can quickly penetrate through cracks and pores.

[0068] (2) Significant decline in mechanical strength and structural stability: The 28-day compressive strength decreased from ≥26.6MPa in Example 1 to ≤16MPa, which is lower than the C15 concrete strength standard and cannot withstand the self-weight pressure of the surrounding rock underground; the 28-day bond strength between the material and the surrounding rock (sandstone, shale) of the roadway decreased from ≥2.0MPa to ≤0.6MPa. When subjected to displacement of the surrounding rock or water pressure impact, it is easy to separate from the interface and lose its roadway reinforcement and support function. This is because ettringite crystals can be interspersed in cement hydration products, enhancing the density and integrity of the skeleton, while the expansion effect makes the material and the surrounding rock fit tightly together. After the loss, the cement skeleton will have gaps due to shrinkage, the overall density will decrease, and the mechanical strength will decrease accordingly; moreover, the material cannot bond with the surrounding rock through expansion, and only relies on physical adsorption bonding, so the bonding force will naturally drop sharply.

[0069] (3) The durability is not suitable for the complex downhole environment: After 25 freeze-thaw cycles (-18℃~5℃), the strength retention rate dropped from 92% in Example 1 to ≤58%, the material surface spalling was ≥12%, and a network of microcracks formed inside; after being soaked in weakly acidic water (pH=4.5-5.5) downhole for 30 days, the compressive strength decay rate increased from ≤8% to ≥32%, and the structural integrity was severely damaged. This is because without an expansion agent to compensate for shrinkage, the material has drying shrinkage cracks in the early stage, which provides a "fast channel" for water and acidic media in the freeze-thaw cycle: during freeze-thaw, the water in the cracks freezes and expands, further tearing the material; the acidic media corrodes the cement hydration products and coal gangue particles through the cracks, accelerating the aging of the material and causing the overall durability to deteriorate.

[0070] Comparative Example 4 The same method as in Example 1 was used, except that polypropylene cellulose was not added.

[0071] result: (1) The crack resistance dropped sharply, and macroscopic cracks appeared early and frequently: During the material hardening process, macroscopic drying shrinkage cracks with a width of ≥0.2mm appeared within 14 days. The number of cracks increased by more than 3 times compared with Example 1. Moreover, the cracks easily spread along the gaps between coal gangue particles, forming through channels. When simulating slight vibration (amplitude 0.1mm) or surrounding rock compression test in the mine, the material fractured within 30 minutes, while Example 1 could withstand more than 2 hours without damage, completely losing its deformation resistance. This is because polypropylene cellulose (length 3-12mm, tensile strength ≥300MPa) can form a spatial network support structure in the slurry, which can hinder the initiation and expansion of macroscopic cracks during the drying shrinkage process, and at the same time buffer the impact of external forces through its own tensile properties. After the absence of the network support structure, the system loses the constraint of the "network skeleton". The drying shrinkage stress and external forces act directly on the inorganic hydration products, causing cracks to be generated and expanded rapidly, and the crack resistance and deformation resistance collapse.

[0072] (2) Overall decline in mechanical strength and toughness: The 28-day flexural strength decreased from ≥5.2MPa in Example 1 to ≤3.2MPa, and the fracture toughness decreased by more than 38%, failing to meet the basic requirements of "flexural and impact resistance" for materials in underground roadways; although the compressive strength did not drop sharply, the brittleness increased significantly: The 28-day compressive strength decreased from ≥26.6MPa to ≤22MPa, and the failure mode changed from "ductile fracture" in Example 1 to "brittle fracture," resulting in sudden failure without warning under stress. This is because the network structure of polypropylene cellulose can form a "synergistic stress-bearing system" with the hydration products of sulfoaluminate cement and coal gangue powder. Under stress, the fibers can share the stress, delay crack development, and improve the toughness and flexural strength of the material. After the fiber is missing, the system relies solely on the inorganic skeleton for support. Although it retains some compressive strength, the lack of fiber "toughening buffer" leads to a sharp drop in flexural strength, increased brittleness, and a deterioration of the failure mode.

[0073] (3) Insufficient interfacial stability with surrounding rock: The interfacial bonding stability between the material and the surrounding rock (sandstone, shale) of the tunnel decreases. The 28-day interfacial shear strength drops from ≥1.8MPa in Example 1 to ≤0.9MPa. When affected by water pressure or slight displacement of the surrounding rock, peeling cracks easily appear at the interface, and gas / water leakage occurs within 36 hours, resulting in failure of the sealing effect. This is because the fiber ends of polypropylene cellulose can be embedded in the tiny pores on the surface of the surrounding rock, forming a "mechanical interlocking" effect, which helps to enhance the interfacial bonding force between the material and the surrounding rock. Without this, the interfacial bonding relies solely on the physical adsorption of the cementitious material. Without the "anchoring" support of the fibers, the interface is prone to separation when disturbed by external forces, leading to the destruction of the sealing performance.

[0074] (4) Weakened durability and adaptability: After 25 freeze-thaw cycles (-18℃~5℃), the material strength retention rate decreased from 92% in Example 1 to ≤65%, and the surface spalling was ≥8%, which is 2 times higher than in Example 1; moreover, the cracks were further expanded due to the freeze-thaw cycles, forming permanent cracks ≥0.5mm wide, which could not be repaired later. This is because the network structure of polypropylene cellulose can inhibit the expansion of cracks during freeze-thaw cycles and reduce the damage to the material caused by water penetration and ice expansion. After the absence of the network structure, the early-existing shrinkage cracks continued to expand under the freeze-thaw action, accelerating the penetration of water and corrosive media, resulting in faster strength decay, more severe spalling, and the durability could not adapt to the low-temperature and humid environment downhole.

[0075] Comparative Example 5 The same method as in Example 1 was used, except that hydroxypropyl methylcellulose was not added.

[0076] result: (1) The water retention of the slurry was completely lost, and the hydration reaction was insufficient: the water evaporation rate of the slurry increased sharply from ≤5% in Example 1 to ≥30% within 2 hours after stirring. Water was rapidly separated on the surface and clumps formed at the bottom (clump diameter ≥8mm), making it impossible to form a uniform and workable slurry. Due to severe water shortage, the cement hydration was insufficient. The 7-day compressive strength decreased from ≥15.3MPa in Example 1 to ≤8MPa, and the 28-day compressive strength decreased from ≥26.6MPa to ≤14MPa, which was far below the C15 strength standard for underground use. After the material hardened, it was loose and easily broken. This is because HPMC (methoxyl substitution degree 28%-30%, viscosity 10000-50000mPa•s) forms hydrogen bonds with water molecules through hydroxyl groups (-OH) to build a hydrophilic gel network and lock in the moisture of the slurry. Without the gel network, the slurry water evaporates or settles rapidly, causing sulfoaluminate cement to be unable to obtain enough water to complete the hydration reaction. The resulting hydration products (such as ettringite and hydrated calcium silicate) are few in quantity and have a loose structure, resulting in a significant decline in strength.

[0077] (2) Slurry dispersion and construction performance collapse: The initial fluidity of the slurry dropped sharply from 350-450mm in Example 1 to ≤200mm. During stirring, inorganic particles such as coal gangue powder and gypsum powder settled rapidly (settling height ≥60mm within 10 minutes), forming a layered state of "thin slurry on the upper layer and dense sediment on the lower layer". The dispersion dropped from ≥90% to ≤50%. During grouting, poor grout fluidity and frequent clumping frequently clog grouting pipes with a diameter of ≥25mm (clogging frequency ≥4 times / hour), reducing construction efficiency by more than 60%. Furthermore, grout that is not injected into the fissures dries quickly and is discarded, resulting in a material waste rate exceeding 30%. This is because the polymer chains of HPMC can adsorb onto the surface of inorganic particles, forming a steric hindrance effect that prevents particle settling. Simultaneously, its thickening properties regulate grout fluidity, ensuring uniform and stable grout. Without this steric hindrance protection, inorganic particles settle due to gravity, and the grout loses its thickening support, leading to abnormal fluidity and making it unsuitable for downhole grouting operations.

[0078] (3) Significant deterioration in impermeability and compactness: The total porosity of the material increased from ≤15% in Example 1 to ≥32% (exceeding the porosity level of traditional materials), and the capillary water absorption rate rebounded from a decrease of 60% to a decrease of only 10%; in the 28-day hydrostatic pressure test, the impermeability grade dropped from P10 to below P3, and it could only withstand 0.3MPa water pressure. Water seepage occurred within 5 minutes, with a seepage height ≥250mm. After sealing the 0.2-2mm cracks in the well, the leakage rate was ≥600mL / h within 24 hours, completely losing the function of preventing water damage. This is because the hydrophilic gel network of HPMC can fill the micropores of the cement skeleton during the hydration process, while locking in water to ensure sufficient hydration and reducing the pores caused by insufficient hydration. After the absence of the gel, not only does insufficient hydration lead to an increase in pores, but the lack of gel to fill the existing micropores also destroys the compact structure of the system. Water and gas can quickly penetrate through a large number of pores, and the impermeability collapses.

[0079] (4) Increased shrinkage deformation and weakened durability: The 28-day shrinkage rate increased from 0.03% in Example 1 to ≥0.12%, far exceeding the industry control standard of ≤0.05%. Within 7 days, shrinkage cracks with a width of ≥0.3mm appeared, and the number of cracks increased more than 4 times compared with Example 1. After 25 freeze-thaw cycles (-18℃~5℃), the strength retention rate decreased from 92% to ≤55%, and the surface spalling was ≥15%. After immersion in weakly acidic water (pH=4.5-5.5) in the well for 30 days, the compressive strength attenuation rate increased from ≤8% to ≥35%, and the structural integrity was completely destroyed. This is because without HPMC to lock in moisture, the material undergoes severe shrinkage due to rapid moisture loss during the hardening process, resulting in a large number of shrinkage cracks. These cracks become "channels" for moisture and acidic media in freeze-thaw cycles. During freeze-thaw cycles, moisture freezes and expands, tearing the material, while acidic media corrodes the internal structure, leading to complete failure of durability.

[0080] Comparative Example 6 The same method as in Example 1 was used, except that no plaster powder was added.

[0081] result: Micro-expansion and strength failure: Without gypsum powder to provide SO42-, the formation of ettringite crystals is drastically reduced. The micro-expansion rate is ≤0.02% after 7 days (0.1% in Example 1), the drying shrinkage rate is ≥0.18% after 28 days, and cracks of ≥0.4mm appear within 10 days. The compressive strength after 28 days is ≤12MPa (≥26.6MPa in Example 1), which is far below the C15 standard. The material is loose and prone to powdering.

[0082] Construction cannot proceed because: sulfoaluminate cement has an initial setting time of ≤8 min (≥15 min in Example 1), a final setting time of ≤40 min, grout forms lumps within 3 minutes of initial setting, grouting pipes are blocked ≥5 times / hour, construction efficiency is reduced by 70%, and material waste exceeds 40%.

[0083] Complete failure of anti-seepage: Total porosity ≥35% (Example 1 ≤15%), anti-seepage grade drops to below P2, water seepage occurs in 3 minutes under 0.2MPa water pressure, leakage ≥800mL / h after 20 hours of well fissure sealing, and no sealing capacity.

[0084] Extremely poor durability: after 25 freeze-thaw cycles, the strength retention rate is ≤45% (Example 192%), and the spalling is ≥20%; in weakly acidic water, the strength decreases by ≥40% after 30 days, and the material collapses.

[0085] Comparative Example 7 The same method as in Example 1 was used, except that the hydroxypropyl methylcellulose solution was added directly to the mixer during the “fiber and coupling treatment” step.

[0086] result: (1) Failure of polypropylene cellulose dispersion and collapse of crack resistance and toughening function: Severe fiber agglomeration: Polypropylene cellulose (length 3-12mm) cannot be uniformly dispersed, forming fiber clumps with a diameter ≥10mm. After stirring for 10 minutes, ≥30% of the fibers are still not dispersed, and there are a large number of "weak points" inside the material; Crack resistance drops sharply: The flexural strength after 28 days drops from ≥5.2MPa in Example 1 to ≤2.8MPa, and the fracture toughness decreases by more than 46%. When simulating underground vibration, cracks are preferentially opened at the fiber clumps and quickly penetrate through, which cannot prevent crack propagation. This is because the "fiber and coupling treatment" stage requires dry mixing of fibers first to ensure that they are initially dispersed in the dry material, and then adding silane coupling agent solution to modify the surface of coal gangue. If HPMC solution is added in advance, the solution will coat the fiber surface, causing the fibers to stick together and form agglomerates; at the same time, the wet environment will hinder the spatial distribution of fibers in the dry material, destroy the construction of the "net support structure", and cause the crack resistance and toughening function to fail.

[0087] (2) The modification effect of the silane coupling agent was destroyed, and the interfacial bonding was weakened: the interfacial bonding strength decreased: the 28-day bonding strength between the material and the surrounding rock decreased from ≥2.0MPa to ≤0.7MPa, and the interfacial gap with the coal gangue powder increased from ≤0.1μm to ≥0.8μm; the impermeability declined: the 28-day impermeability grade decreased from P10 to below P5, the water seepage height increased from ≤30mm to ≥180mm, and the gas leakage in the closed area increased by 60% compared with Example 1. This is because the silane coupling agent needs to contact the dry coal gangue powder in the "fiber and coupling treatment" stage to achieve surface modification (forming Si-O-Si covalent bonds) through ethanol solution. When HPMC solution is added in advance, its polymer chains will cover the hydroxyl groups (-OH) on the surface of coal gangue, hindering the condensation reaction between the silane coupling agent and the hydroxyl groups. At the same time, the hydrophilic gel of HPMC will dilute the concentration of the coupling agent, reduce the modification efficiency, weaken the inorganic-organic interface bond, and reduce the impermeability and adhesion properties.

[0088] (3) Poor uniformity of slurry, resulting in uncontrolled construction and curing quality: Slurry stratification and clumping: Obvious stratification (upper layer of thin slurry, lower layer of dry material sedimentation) occurs within 30 minutes after mixing, and the dispersion drops from ≥90% to ≤50%. During grouting, grouting pipes with a diameter of ≥25mm are frequently blocked, reducing construction efficiency by more than 50%; Severe hollowing after curing: The hollowing rate inside the material after curing is ≥25%, with hollowing concentrated in the fiber clusters and undispersed dry material areas. Later, it is prone to local damage under external force and requires secondary repair. This is because HPMC solution is added during the "wet mixing stage". At this time, the dry material (coal gangue, cement, etc.) and fibers and coupling agents have completed preliminary dispersion and modification, and the solution can uniformly coat each component. When added in advance, HPMC solution is mixed with fibers and coupling agents first, and then comes into contact with dry material, which easily leads to excessive local humidity and the formation of thin slurry. The remaining areas are still dry material, resulting in stratification. At the same time, the fiber agglomeration and insufficient modification of the coupling agent cause uneven shrinkage in each area during curing, resulting in a large number of hollows.

[0089] (4) Insufficient hydration reaction, resulting in a significant decline in mechanical strength: Strength not up to standard: 7-day compressive strength decreased from ≥15.3MPa to ≤8.5MPa, and 28-day compressive strength decreased from ≥26.6MPa to ≤15MPa, which is lower than the downhole C15 strength standard; Loose structure: The amount of hydration products (such as ettringite) generated inside the material decreased by 30%, and the porosity increased from ≤15% to ≥28%, and the powder easily fell off when pressed with a finger. This is because the premature addition of HPMC caused fiber agglomeration and the failure of the coupling agent modification. At the same time, it disrupted the mixing order of dry material and solution, making it impossible for sulfoaluminate cement to come into uniform contact with water, resulting in insufficient hydration reaction; and the agglomerated fibers and hollow areas will destroy the integrity of the cement skeleton, further leading to a decline in mechanical strength, which cannot meet the downhole load-bearing requirements.

[0090] This invention creatively employs a synergistic mechanism of "covalent bonding strengthening the interface + crystal growth regulation + multi-level network toughening + dense structure construction," which cannot be achieved by the individual effects of each component or by simple mixing. The specific mechanism of action is analyzed as follows: The siloxane alkyl group (-Si-OR) of the silane coupling agent hydrolyzes to generate silanol groups (-SiOH), which undergo condensation reaction with the hydroxyl groups (-OH) on the surface of coal gangue and gypsum powder to form stable Si-O-Si covalent bonds. Its organic end then generates van der Waals entanglement with the ester group (-COO-) of the redispersible latex powder, constructing a molecular-level connection of "inorganic particles-coupling agent-organic film". This transforms the interfacial gaps (which are prone to leakage channels) in the traditional system into strong bonding surfaces, forming an interfacial covalent bond network, which increases the interfacial bonding strength by more than 40%.

[0091] Sulfoaluminate cement hydration releases Al 3+ Ca 2+ SO4 provided by gypsum powder 2-The reaction produces ettringite (3CaO•Al2O3•3CaSO4•32H2O). The ettringite-based expansive agent controls the crystal growth rate (avoiding the localized expansion stress caused by excessively rapid crystal formation in traditional systems), allowing needle-like crystals to uniformly penetrate the cement hydration products. Simultaneously, the elastic film formed by the latex powder encapsulates the crystals, buffering the expansion stress, ultimately achieving the dual effect of "shrinkage compensation + strength enhancement," with a 28-day compressive strength 15% higher than that of a single sulfoaluminate cement system.

[0092] Polypropylene cellulose (fiber) forms a spatial network support during the mixing process. The hydroxyl groups (-OH) of hydroxypropyl methylcellulose (HPMC) react with the CaO of cement hydration products. 2+ Coordination bonds are formed to construct a hydrophilic gel network. The two intertwine with the flexible membrane structure of latex powder to form a three-dimensional interwoven toughening structure: the fibers hinder the propagation of macroscopic cracks, the gel network inhibits the formation of microscopic pores, and the flexible membrane enhances the overall ductility, making the flexural strength of the material 25% higher than that of the fiber-free system and significantly improving the fracture toughness.

[0093] Coal gangue powder (particle size <0.3mm) fills the skeletal gaps formed by the hydration of sulfoaluminate cement, ettringite crystals fill the micron-sized pores, and silane coupling agent reduces nano-sized pores through interface modification. The multi-level dense filling effect reduces the total porosity of the system to below 15% (compared to about 25%-30% in traditional systems), and reduces the capillary water absorption rate by 60%, thus blocking the water permeation path from the microstructure.

[0094] Furthermore, the combination of sulfoaluminate cement and gypsum powder enables rapid early strength development of the material. Firstly, this shortens the construction cycle: the material quickly reaches a certain strength, allowing for earlier subsequent construction steps such as demolding and load-bearing, thus improving construction efficiency. Secondly, it effectively enhances resistance to deformation: its high early strength better resists external forces during construction, reducing cracking and damage caused by deformation. Thirdly, it improves the stability of the sealing effect: rapid strength formation allows the material to perform its sealing function earlier, effectively blocking water and air penetration in the early stages, ensuring timely and stable sealing. Fourthly, it can meet the needs of emergency projects: in emergency scenarios requiring rapid sealing and reinforcement, such as disaster relief projects, the rapid early strength characteristic meets the requirements of emergency construction, allowing the material to function promptly.

[0095] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A micro-expansion sealing material for coal gangue, characterized in that, It consists of the following raw materials in parts by weight: 550-650 parts of coal gangue powder; 270-290 parts of sulfoaluminate cement; 65-75 parts of ettringite-based expanding agent; 7-9 parts of redispersible latex powder; Hydroxypropyl methylcellulose 1.5-2.5 parts; 2.5-3.5 parts of silane coupling agent; 3.5-4.5 parts polypropylene fiber; 28-38 parts of gypsum powder; The preparation method of coal gangue micro-expansion sealing material includes the following steps: Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, ettringite-based expansion agent, gypsum powder, and redispersible latex powder are mixed in a mixer to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene fibers to a mixer and continue dry mixing to ensure fiber dispersion; then add silane coupling agent solution and continue stirring to modify the surface of coal gangue powder. Wet mixing stage: In another container, hydroxypropyl methylcellulose is dissolved in water to make a homogeneous solution. The solution is then slowly added to a mixer and stirred until a closed material with good plasticity and homogeneity is formed.

2. The micro-expansion sealing material for coal gangue according to claim 1, characterized in that, It consists of the following raw materials in parts by weight: 600 parts of coal gangue powder: 280 parts of sulfoaluminate cement; 70 parts of calcite-based expanding agent; 8 parts redispersible latex powder; Two parts of hydroxypropyl methylcellulose; 3 parts silane coupling agent; 4 parts polypropylene fiber; 33 parts of gypsum powder.

3. The micro-expansion sealing material for coal gangue according to claim 1, characterized in that, The coal gangue powder has a particle size of ≥95% below 0.3mm sieve, a moisture content of ≤1.0%, a loss on ignition of ≤5%, an SO3 content of ≤1.5%, and an activity index of ≥80%. And / or, the sulfoaluminate cement has a strength grade ≥42.5, initial setting time ≥15min, final setting time ≤180min, flexural strength ≥6.5MPa at 3d and ≥8.5MPa at 28d, compressive strength ≥30MPa at 3d and ≥42.5MPa at 28d; and alkali content ≤0.5%.

4. The micro-expansion sealing material for coal gangue according to claim 1, characterized in that, The ettringite-based expanding agent exhibits the following expansion rates in water: ≥0.05% in 7 days and ≤0.12% in 28 days; shrinkage rate in dry air: ≤0.03% in 28 days; compressive strength: ≥30 MPa in 7 days and ≥50 MPa in 28 days; chloride ion content: ≤0.05%; and residue on a 0.08 mm sieve: ≤10%. And / or, the redispersible latex powder has a solid content ≥98%, a particle size D50 ≤100μm, a minimum film-forming temperature ≤0℃, an ash content of 10%-15% upon ignition at 1000℃, and a water retention ≥90%.

5. The micro-expansion sealing material for coal gangue according to claim 1, characterized in that, The silane coupling agent has a functional group content of ≥97% and a density of 0.95-1.05 g / cm³. 3 ; And / or, the calcium sulfate dihydrate content in the gypsum powder is ≥90%, the initial setting time of the gypsum powder is ≥3min, the final setting time is ≤30min, the flexural strength after hardening is ≥2.5MPa, the compressive strength is ≥4.0MPa, and the residue on a 0.08mm sieve is ≤10%.

6. The micro-expansion sealing material for coal gangue according to claim 1, characterized in that, The hydroxypropyl methylcellulose has a methoxy substitution degree of 28%-30%, a hydroxypropyl substitution degree of 7%-12%, and a viscosity of 10,000-50,000 mPa. s, moisture content ≤5%, pH value 6.0-8.0; And / or, the polypropylene fiber has a length of 3-12 mm, a diameter of 15-40 μm, a tensile strength ≥300 MPa, an elastic modulus ≥3 GPa, and a moisture content ≤0.5%.

7. A method for preparing the micro-expansion sealing material of coal gangue as described in claim 1, characterized in that, Includes the following steps: Dry mixing stage: The dried coal gangue powder, sulfoaluminate cement, ettringite-based expansion agent, gypsum powder, and redispersible latex powder are mixed in a mixer to obtain a uniformly mixed dry mixture. Fiber and Coupling Treatment: Add polypropylene fibers to a mixer and continue dry mixing to ensure fiber dispersion; Then add the silane coupling agent solution and continue stirring to modify the surface of the coal gangue powder. Wet mixing stage: In another container, hydroxypropyl methylcellulose is dissolved in water to make a homogeneous solution. The solution is then slowly added to a mixer and stirred until a closed material with good plasticity and homogeneity is formed.

8. The preparation method according to claim 7, characterized in that, The drying temperature of the coal gangue in the dry mixing stage is 105±5℃, the time is 120-160 minutes, the stirring speed is 350-380r / min, and the time is 5-8 minutes. And / or, in the fiber coupling treatment step, the dry mixing time is 3-7 minutes and the stirring time is 2-6 minutes; And / or, the stirring speed during the wet mixing stage is 200-240 r / min, and the time is 8-10 minutes.

9. The preparation method according to claim 7, characterized in that, The hydroxypropyl methylcellulose is dissolved in 10% water, which is the total amount of the raw material. And / or, the silane coupling agent solution is an ethanol solution of 5% silane coupling agent.

10. The application of the micro-expansion sealing material for coal gangue according to any one of claims 1-6 or the micro-expansion sealing material for coal gangue prepared by the preparation method according to any one of claims 7-9, characterized in that, Used for sealing underground tunnels, fire prevention and extinguishing, or sealing cracks.