Low-temperature preparation method and system of grouting hole sealing material suitable for coal seam extraction

Abstract

The application discloses a low-temperature preparation method and system of a grouting hole sealing material suitable for coal seam extraction, and particularly relates to the technical field of cement-based building materials, and the grouting hole sealing material is composed of sulphate aluminate cement clinker, ordinary Portland cement, activated coal gangue micro powder, slag micro powder, silica fume, a composite early-strength activator, gradient expansion components, a retarding and plasticizing component, a water reducing agent and a defoaming agent. The preparation method comprises the following steps: crushing, calcining and activating coal gangue to obtain activated coal gangue micro powder; mixing the activated coal gangue micro powder with the remaining components to obtain dry mixture; and finally, mixing the dry mixture at low temperature to obtain grouting slurry. The application also provides a corresponding low-temperature preparation system. Through the synergistic hydration of the three-phase composite cementing system, the slow-release early strength of the core-shell structure and the gradient expansion compensation, the application realizes the synergy of low-temperature rapid early strength and controllable operation time, and guarantees the volume stability and sealing performance of the material.

Description

Technical Field

[0001] This invention relates to the field of cement-based building materials technology, and more specifically, to a low-temperature preparation method and system for grouting and sealing materials suitable for coal seam extraction. Background Technology

[0002] Coal seam gas drainage is a key technical means to prevent coal mine gas disasters and promote the utilization of gas resources. During the gas drainage process, injecting grouting material into the borehole to seal the annular gap between the borehole and the coal and rock mass to form a highly efficient sealed section is the core link to ensure the concentration and efficiency of gas drainage. The quality of the sealing directly affects the gas drainage effect and the safety of underground operations.

[0003] Currently, the sealing technologies for coal mine gas drainage boreholes mainly include cement mortar sealing, polymer material sealing, and mine sealing devices. Sealing materials are mainly divided into three categories: cement-based materials, high-water-content materials, and polyurethane polymer materials.

[0004] However, existing sealing materials still have the following shortcomings in practical applications: Ordinary Portland cement and other cement-based materials exhibit a significantly reduced hydration rate at low temperatures, resulting in slow early strength development. While existing technologies have attempted to improve low-temperature early strength performance by adding sulfoaluminate cement, it remains difficult to simultaneously meet the requirements for both early strength and workability. Cement-based sealing materials shrink during the solidification process, which can easily form annular microcracks between the grout and the borehole wall, becoming a channel for gas leakage and resulting in insufficient sealing durability of the sealing section. Polyurethane grouting materials release a large amount of heat during the curing process, posing a safety hazard of spontaneous combustion of coal seams. The preparation of existing sealing materials mostly focuses on optimizing material formulations, lacking systematic preparation processes and supporting equipment for low-temperature construction environments, resulting in unstable sealing quality under low-temperature conditions.

[0005] In view of the above situation, the present invention provides a low-temperature preparation method and system for grouting and sealing materials suitable for coal seam extraction. Summary of the Invention

[0006] To achieve the above objectives, the present invention provides the following technical solution: On one hand, the present invention provides a low-temperature preparation method for grouting and sealing materials suitable for coal seam extraction, wherein the grouting and sealing materials are composed of the following components in parts by weight: The composition includes: 25-40 parts of sulfoaluminate cement clinker, 15-25 parts of ordinary Portland cement, 10-20 parts of activated coal gangue powder, 5-12 parts of slag powder, 3-8 parts of silica fume, 2-6 parts of composite early strength activator, 0.5-3.0 parts of gradient expansion component, 0.1-0.8 parts of retarding and plasticizing component, 0.2-1.0 parts of water-reducing agent, and 0.05-0.2 parts of defoamer. The composite early strength activator includes a nano-SiO2-coated early strength component, which is a core-shell structured particle with an early strength salt as the core and nano-SiO2 as the shell. The gradient expansion component consists of a gypsum-based expansion source, aluminum powder paste, and ettringite-type expansion agent; The low-temperature preparation method includes the following steps: S1. The coal gangue raw material is crushed and ground to below 200 mesh, calcined and activated at 700-850℃ for 1-2 hours, cooled and ground to a specific surface area ≥500m² / kg to obtain activated coal gangue micro powder. S2. Weigh each component according to the proportion, put them into a three-dimensional motion mixer, and mix them at a speed of 20-40 r / min for 15-30 min until they are uniformly dispersed to obtain the dry mixture of grouting and sealing material. S3. Mix the dry mixture with the mixing water, with a water-cement ratio of 0.30 to 0.45, a mixing water temperature of 10 to 25°C, a mixing speed of 60 to 120 r / min, and a mixing time of 3 to 8 min to obtain the grouting slurry. The slurry outlet temperature is controlled at 5 to 15°C.

[0007] Preferably, in step S1, the coal gangue raw material is first crushed to ≤5mm by a jaw crusher, then fed into a ball mill and ground to ≤10% residue on a 200-mesh sieve, and then placed in a rotary kiln for calcination and activation. After calcination, it is ground into an ultrafine ball mill to a specific surface area ≥500m² / kg.

[0008] Preferably, the content of anhydrous calcium sulfoaluminate in the sulfoaluminate cement clinker is not less than 55%, and the specific surface area is 350-450 m² / kg; The ordinary Portland cement is P·O 42.5 grade or P·O 52.5 grade ordinary Portland cement; The slag powder is granulated blast furnace slag powder of grade S95 or above, with a specific surface area ≥400m² / kg; The silica fume has a SiO2 content of ≥85%, a specific surface area of ​​≥15000m² / kg, and an average particle size of 0.1~0.3μm.

[0009] Preferably, the composite early strength activator is composed of the following components by mass percentage: calcium formate 30-50%, aluminum sulfate 15-30%, sodium sulfate 10-20%, triethanolamine 2-8%, and nano-SiO2-coated early strength component 10-25%.

[0010] Preferably, the preparation method of the nano-SiO2 coated early strength component is as follows: a saturated solution of calcium formate or aluminum sulfate is spray-granulated using nano-SiO2 sol with a solid content of 20-30% and a particle size of 20-50 nm as the coating material, and the granulation is carried out in a fluidized bed granulator at 80-120°C to form core-shell structured particles with a particle size of 50-150 μm.

[0011] Preferably, the gradient expansion component comprises the following components by mass percentage: 40-60% gypsum-based expansion source, 5-15% aluminum powder paste, and 25-45% ettringite-type expansion agent; The gypsum-based expansion source is selected from at least one of anhydrite or hemihydrate gypsum; The ettringite-type expanding agent is selected from at least one of UEA expanding agent or CSA expanding agent.

[0012] Preferably, the retarding and plasticizing component is selected from one or more of sodium gluconate, citric acid, or boric acid; The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a solid content ≥40% and a water reduction rate ≥25%. The defoamer is a silicone-based defoamer or a polyether-based defoamer.

[0013] Preferably, in step S3, the mixing is carried out using a low-temperature mixing unit, and the grouting slurry is injected into the sealing section of the coal seam borehole at an ambient temperature of 0 to 10°C and a grouting pressure of 0.5 to 2.0 MPa, with a pressure stabilization time of 5 to 15 minutes.

[0014] On the other hand, the present invention also provides a low-temperature preparation system for grouting and sealing materials suitable for coal seam extraction, for implementing the above-mentioned low-temperature preparation method, comprising: The raw material storage and batching unit is used to store each raw material component and to meter and batch it according to the ratio. It includes a powder storage silo with an insulation jacket and an internal electric heating device, as well as an electronic metering and batching system with a metering accuracy of ±0.5%. The activation pretreatment unit is used to crush, grind and calcinate coal gangue raw materials, including a jaw crusher, a ball mill, a rotary kiln with a calcination temperature of 700-850℃ and an ultrafine ball mill. The dry mixing unit is used to mix the various powder components evenly to obtain the dry mixture of grouting and sealing material. The dry mixing unit is a three-dimensional motion mixer. A low-temperature mixing unit is used to mix dry materials with mixing water under low-temperature conditions to obtain grouting slurry. The low-temperature mixing unit includes a low-temperature mixing tank with a jacketed cooling / heating system, an agitator installed in the low-temperature mixing tank, a water temperature control system connected to the low-temperature mixing tank, and a slurry outlet temperature monitoring device installed on the low-temperature mixing tank. The water temperature control system automatically adjusts the mixing water temperature according to the ambient temperature to control the slurry outlet temperature to be maintained at 5-15℃. The rotation speed of the agitator is adjustable from 60 to 120 r / min. The intelligent control system is used to integrate and control the operating parameters of the raw material storage and batching unit, the activation pretreatment unit, the dry mixing unit, and the low-temperature mixing unit. The intelligent control system is a PLC programmable logic controller, including a touch screen human-machine interface and a data recording and traceability module, which is used to set and monitor temperature, speed, time, and proportioning process parameters, and automatically record the production data for each batch. The outlet of the raw material storage and batching unit is connected to the inlet of the dry mixing unit, the outlet of the dry mixing unit is connected to the inlet of the low-temperature mixing unit, and the outlet of the activation pretreatment unit is connected to the inlet of the raw material storage and batching unit.

[0015] The technical effects and advantages of this invention are as follows: 1. This invention achieves a balance between rapid early strength and sustained strength development in the later stages under low-temperature conditions through the synergistic hydration mechanism of a three-phase composite cementitious system consisting of sulfoaluminate cement, ordinary silicate cement, and alkali-activated geopolymer. Sulfoaluminate cement provides early strength through rapid hydration in a low-temperature environment, while ordinary silicate cement ensures sustained strength growth in the middle and later stages. The geopolymer gel formed by activated coal gangue under alkaline activation fills the micropores between the cement hydration products. The hydration products of these three components form a complementary and reinforced composite network structure at the microscale, effectively solving the technical problem of insufficient early strength in existing cement-based sealing materials under low-temperature conditions. 2. This invention employs a nano-SiO2-coated core-shell structure early-strength component. The physical barrier effect of the shell layer slows down the release rate of the internal early-strength component in the initial mixing stage, preventing premature slurry setting. As hydration progresses, the shell layer gradually dissolves in the alkaline environment, allowing for the controlled release of the internal early-strength component and continuously promoting cement hydration. This mechanism achieves a synergistic optimization of rapid setting and hardening under low-temperature conditions with sufficient workability, overcoming the inherent defect of existing early-strength grouting materials that sacrifice workability to achieve low-temperature early-strength performance. This meets the actual requirements of underground coal mine construction for slurry workability. 3. This invention employs a gradient expansion component composed of gypsum-based expansion sources, aluminum powder paste, and ettringite-type expansion agents. These three expansion sources are activated sequentially and in succession during the plastic stage, early hardening stage, and late hardening stage of the hydration process, forming a continuous full-lifecycle volume compensation curve. This achieves full-process volume stability from plastic expansion to early expansion and then to long-term stability. This mechanism effectively avoids the annular micro-crack gas leakage problem caused by solidification shrinkage of the sealing material, significantly improving sealing quality and gas extraction efficiency. Simultaneously, the hydration temperature rise of the all-inorganic cementitious system is much lower than that of polyurethane-based organic sealing materials, avoiding the safety hazard of spontaneous combustion of coal seams caused by exothermic reactions. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method of the present invention.

[0017] Figure 2 This is a system diagram of the present invention.

[0018] The attached diagram is labeled as follows: 1. Raw material storage and batching unit; 2. Activation pretreatment unit; 3. Dry mixing unit; 4. Low-temperature mixing unit; 5. Intelligent control system. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0020] Example 1 This embodiment provides a low-temperature preparation method for grouting and sealing materials suitable for coal seam extraction.

[0021] The grouting and sealing material is formulated with the following components in parts by weight: 32 parts of sulfoaluminate cement clinker, 20 parts of ordinary silicate cement P·O 42.5 grade, 15 parts of activated coal gangue powder, 8 parts of slag powder S95 grade, 5 parts of silica fume, 4 parts of composite early strength activator, 1.5 parts of gradient expansion component, 0.3 parts of sodium gluconate, 0.5 parts of polycarboxylate superplasticizer, and 0.1 parts of organosilicon defoamer.

[0022] The composite early strength activator is composed of the following components by mass percentage: calcium formate 40%, aluminum sulfate 20%, sodium sulfate 15%, triethanolamine 5%, and nano-SiO2-coated early strength component 20%.

[0023] The gradient expansion component consists of the following components by mass percentage: 50% anhydrite, 10% aluminum powder paste, and 40% UEA expansion agent.

[0024] The preparation of the nano-SiO2-coated early strength component is as follows: Calcium formate was prepared into a saturated solution with a concentration of 45 wt%. Nano-SiO2 sol with a solid content of 25% and a particle size of 20-50 nm was used as the coating material. The solution was then subjected to fluidized bed spray coating granulation at 100 °C in a fluidized bed granulator to form core-shell structured particles with a particle size of 50-150 μm, which were then set aside for later use.

[0025] The preparation of activated coal gangue powder is as follows: The raw coal gangue is first crushed to less than or equal to 5mm by a jaw crusher, then fed into a ball mill and ground until the residue on a 200-mesh sieve is less than or equal to 10%. Then it is placed in a rotary kiln and calcined and activated at 800℃ for 1.5h. After calcination, it is naturally cooled and ground into activated coal gangue micro powder by an ultrafine ball mill until the specific surface area is 520m² / kg.

[0026] The low-temperature preparation method in this embodiment includes the following steps: S1. Activated coal gangue powder was prepared according to the above method; S2. Weigh out 32 parts of sulfoaluminate cement clinker, 20 parts of ordinary silicate cement, 15 parts of activated coal gangue powder, 8 parts of slag powder, 5 parts of silica fume, 4 parts of composite early strength activator, 1.5 parts of gradient expansion component, 0.3 parts of sodium gluconate, 0.5 parts of polycarboxylate superplasticizer, and 0.1 parts of organosilicon defoamer according to the proportion, and put them into a three-dimensional motion mixer. Mix them at a speed of 30 r / min for 20 min until they are uniformly dispersed to obtain the dry mix of grouting and sealing material. S3. Mix the dry mix with mixing water at a water-cement ratio of 0.38, control the mixing water temperature at 20℃, the mixing speed at 90 r / min, and the mixing time at 5 min to obtain the grouting slurry. The slurry outlet temperature is 12℃. This slurry has no bleeding and does not segregate.

[0027] Example 2 The components, by weight, are as follows: 38 parts of sulfoaluminate cement clinker, 16 parts of ordinary silicate cement P·O 42.5 grade, 12 parts of activated coal gangue powder, 6 parts of slag powder S95 grade, 4 parts of silica fume, 5 parts of composite early strength activator, 2.0 parts of gradient expansion component, 0.5 parts of citric acid, 0.6 parts of polycarboxylate superplasticizer, and 0.08 parts of polyether defoamer.

[0028] The composite early strength activator is composed of the following components by mass percentage: calcium formate 35%, aluminum sulfate 25%, sodium sulfate 12%, triethanolamine 6%, and nano-SiO2-coated early strength component 22%. The nano-SiO2-coated early strength component uses aluminum sulfate as the core, with a saturated aluminum sulfate solution concentration of 40 wt%. The coating material is nano-SiO2 sol with a solid content of 20% and a particle size of 20–50 nm. The fluidized bed granulation temperature is 90℃, forming core-shell structured particles with a particle size of 50–150 μm.

[0029] The gradient expansion component consists of the following components by mass percentage: 45% hemihydrate gypsum, 12% aluminum powder paste, and 43% CSA expansion agent.

[0030] The preparation conditions for activated coal gangue powder are as follows: calcination temperature is 750℃, calcination time is 2h, and after natural cooling, it is ground to a specific surface area of ​​510m² / kg.

[0031] In the low-temperature preparation method, step S2 uses a three-dimensional motion mixer with a rotation speed of 25 r / min and a mixing time of 25 min. In step S3, the water-cement ratio is 0.35, the mixing water temperature is 15℃, the mixing speed is 100 r / min, the mixing time is 4 min, and the slurry outlet temperature is 10℃. The slurry exhibits no bleeding and no segregation.

[0032] Example 3 The components, by weight, are as follows: 26 parts of sulfoaluminate cement clinker, 24 parts of ordinary silicate cement P·O 52.5 grade, 18 parts of activated coal gangue powder, 10 parts of slag powder S95 grade, 6 parts of silica fume, 3 parts of composite early strength activator, 1.0 part of gradient expansion component, 0.6 parts of boric acid, 0.4 parts of polycarboxylate superplasticizer, and 0.15 parts of organosilicon defoamer.

[0033] The composite early strength activator is composed of the following components by mass percentage: 45% calcium formate, 18% aluminum sulfate, 18% sodium sulfate, 4% triethanolamine, and 15% nano-SiO2-coated early strength component. The nano-SiO2-coated early strength component uses calcium formate as the core, with a saturated calcium formate solution concentration of 45 wt%. The coating material is a nano-SiO2 sol with a solid content of 30% and a particle size of 20–50 nm. The fluidized bed granulation temperature is 80℃, forming core-shell structured particles with a particle size of 50–150 μm.

[0034] The gradient expansion component consists of the following components by mass percentage: 55% anhydrite, 8% aluminum powder paste, and 37% UEA expansion agent.

[0035] The preparation conditions for activated coal gangue powder are as follows: calcination temperature is 700℃, calcination time is 2h, and after natural cooling, it is ground to a specific surface area of ​​500m² / kg.

[0036] In the low-temperature preparation method, step S2 uses a three-dimensional motion mixer with a rotation speed of 20 r / min and a mixing time of 30 min. In step S3, the water-cement ratio is 0.42, the mixing water temperature is 25℃, the mixing speed is 60 r / min, the mixing time is 8 min, and the slurry outlet temperature is 15℃. This slurry exhibits no bleeding and no segregation.

[0037] Example 4 This embodiment provides a low-temperature preparation system for grouting and sealing materials suitable for coal seam extraction, used to implement embodiments 1-3 above. The system includes: a raw material storage and batching unit 1, an activation pretreatment unit 2, a dry mixing unit 3, a low-temperature mixing unit 4, and an intelligent control system 5, wherein: Raw material storage and batching unit 1 is used to store various raw material components and to meter and batch them according to the specified proportions. This unit includes a powder storage silo equipped with an insulated jacket and an electric heating device, maintaining the internal temperature of the powder storage silo at 10–30°C. This unit also includes an electronic metering and batching system with a metering accuracy of ±0.5%.

[0038] Activation pretreatment unit 2 is used for crushing, grinding, and calcining activation treatment of coal gangue raw materials. This unit includes a jaw crusher, a ball mill, a rotary kiln, and an ultrafine ball mill. The jaw crusher has a feed particle size of ≤100mm and a discharge particle size of ≤5mm. The ball mill is used for coarse grinding to a residue of ≤10% on a 200-mesh sieve. The rotary kiln has a calcination temperature of 700–850℃ and is equipped with a temperature control system. The ultrafine ball mill is used for grinding to a specific surface area of ​​not less than 500m² / kg.

[0039] Dry mixing unit 3 is used to mix the various powder components evenly to obtain the dry mixture of grouting and sealing material. This dry mixing unit 3 is a three-dimensional motion mixer with a volume of 1000L and an adjustable speed of 20-40r / min.

[0040] The low-temperature mixing unit 4 is used to mix the dry mixture with mixing water under low-temperature conditions to obtain the grouting slurry. This low-temperature mixing unit 4 includes a low-temperature mixing tank with a jacketed cooling / heating system, an agitator installed inside the low-temperature mixing tank, a water temperature control system connected to the low-temperature mixing tank, and a slurry outlet temperature monitoring device installed on the low-temperature mixing tank. The agitator speed is adjustable from 60 to 120 r / min. The water temperature control system controls the mixing water temperature between 10 and 25°C. The slurry outlet temperature monitoring device is used to display and record the slurry outlet temperature in real time. The water temperature control system automatically adjusts the mixing water temperature according to the ambient temperature to maintain the slurry outlet temperature between 5 and 15°C.

[0041] The intelligent control system 5 is used to integrate and control the operating parameters of the raw material storage and batching unit 1, the activation pretreatment unit 2, the dry mixing unit 3, and the low-temperature mixing unit 4. This intelligent control system 5 is a PLC programmable logic controller, including a touchscreen human-machine interface and a data recording and traceability module. It is used to set and monitor temperature, speed, time, and proportioning process parameters, and automatically record production data for each batch.

[0042] In the above system, the outlet of the activation pretreatment unit 2 is connected to the inlet of the raw material storage and batching unit 1, the outlet of the raw material storage and batching unit 1 is connected to the inlet of the dry mixing unit 3, and the outlet of the dry mixing unit 3 is connected to the inlet of the low-temperature mixing unit 4. The units are connected by sealed pipelines to form a complete low-temperature preparation production line.

[0043] Using the system of this embodiment, and preparing at low temperature according to the proportions and process parameters of Example 1, grouting slurry that meets the performance requirements can be stably obtained, with good batch-to-batch quality consistency and slurry outlet temperature fluctuation range of less than or equal to ±1.5℃.

[0044] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: no activated coal gangue powder, slag powder and silica fume are added, and the above three components are replaced with an equal amount of ordinary silicate cement, that is, 52 parts of ordinary silicate cement are replaced with 20 parts of ordinary silicate cement, 15 parts of activated coal gangue powder, 8 parts of slag powder and 5 parts of silica fume in Example 1.

[0045] The remaining components and preparation methods are the same as in Example 1.

[0046] Comparative Example 1 was used to verify the contribution of the three-phase composite cementitious system composed of activated coal gangue powder, slag powder and silica fume to low-temperature strength.

[0047] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the nano-SiO2-coated early-strength component is not added, but replaced with an equal amount of calcium formate. That is, the composite early-strength activator consists of the following components by mass percentage: 60% calcium formate, 25% aluminum sulfate, 10% sodium sulfate, and 5% triethanolamine. The amount of calcium formate is increased from 1.6 parts in the original formulation to 2.4 parts to make up the 20% proportion of the nano-SiO2-coated early-strength component.

[0048] The remaining components and preparation methods are the same as in Example 1.

[0049] Comparative Example 2 was used to verify the effect of the slow-release early strength component of the core-shell structure on the synergistic effect of low-temperature rapid hardening and workability time.

[0050] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the gradient expansion component uses only aluminum powder paste as an expansion source, that is, 1.5 parts of aluminum powder paste, without gypsum and UEA expansion agent.

[0051] The remaining components and preparation methods are the same as in Example 1.

[0052] Comparative Example 3 was used to verify the impact of the gradient expansion mechanism on volume stability and sealing performance.

[0053] The performance of Examples 1-3 and Comparative Examples 1-3 will be tested below. The specific test methods are as follows: 1. Setting time determination: The determination was carried out in accordance with GB / T 1346 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement". The mixed grout was poured into a circular mold and cured at a temperature of 5℃ and a relative humidity of not less than 90%. The initial setting time and final setting time were determined using a Vicat apparatus.

[0054] 2. Workability Time Determination: The determination shall be conducted according to GB / T 2419 "Method for Determination of Flowability of Cement Mortar". The mixed grout shall be poured into a truncated conical mold, and the grout expansion diameter shall be measured after 25 vibrations on a vibrating table. The workability time shall be defined as the time within which the grout expansion diameter is not less than 180 mm.

[0055] 3. Slurry outlet temperature measurement: The slurry outlet temperature monitoring device on the low-temperature mixing unit 4 is used to read and record the slurry outlet temperature within 30 seconds after the mixing is completed, with an accuracy of 0.1℃.

[0056] 4. Grout bleeding rate determination: The determination shall be carried out in accordance with GB / T 50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The mixed grout shall be poured into a measuring cylinder, allowed to stand for 2 hours at an ambient temperature of 5℃, and the surface bleeding height shall be measured to calculate the bleeding rate.

[0057] 5. Mechanical Property Testing: Compressive strength was determined according to GB / T 17671 "Test Method for Strength of Cement Mortar - ISO Method". The mixed grout was injected into a 40mm×40mm×160mm triple mold. After curing in the mold for 24 hours at 5℃ and relative humidity not less than 90%, the mold was removed, and curing continued in water at 5℃ until the specified age was reached. The specified age included 8h, 24h, 72h, and 28 days. The compressive strength was tested using a pressure testing machine at a loading rate of 2.4kN / s.

[0058] 6. Determination of Free Expansion Rate: The determination of restricted expansion rate was performed according to GB / T 23439 "Concrete Expansion Agent". The mixed grout was poured into a 30mm×30mm×280mm mold, with copper probes installed at both ends. After curing in the mold for 24 hours at 5℃ and relative humidity not less than 90%, the mold was removed, and the initial length was immediately measured. The molded specimens were then cured in water at 5℃ until the specified curing age was reached. The specified curing ages included 3 days, 7 days, and 28 days. The length of the specimens at each curing age was measured using a length comparator, and the free expansion rate was calculated.

[0059] The formula for calculating the free expansion rate is: , in, The free expansion rate is % The specimen length in mm at age t; The initial length is in mm; The length of the copper head is in mm.

[0060] 7. Volume shrinkage rate determination: The volume change determination method in GB / T 749 "Test Method for Sulfate Attack Resistance of Cement" shall be followed. The mixed grout shall be injected into a 25mm×25mm×250mm mold and cured at 5℃ and relative humidity ≥90% for 28 days as specified. The change in length of the specimen shall be measured using a length comparator, and the shrinkage rate shall be expressed as a negative value.

[0061] 8. Hydration temperature rise test: The test was conducted using an automatic hydration heat analyzer. The mixed grout was placed in an insulated curing container, and the internal temperature of the grout was continuously monitored using thermocouples at an ambient temperature of 5℃. The highest temperature rise was recorded, and the monitoring was conducted continuously for 72 hours.

[0062] 9. Gas Drainage Concentration Test: The on-site sealing effect test was conducted according to AQ 1027 "Coal Mine Gas Drainage Specification". A gas drainage borehole was selected underground in the coal mine, and a two-plug-one-injection sealing process was adopted. Grouting slurry was injected into the sealing section at a grouting pressure of 1.2 MPa and stabilized for 10 minutes. After sealing, the gas drainage pipeline was connected, and the gas drainage concentration was continuously monitored using a gas drainage comprehensive parameter measuring instrument. The average gas drainage concentration within 30 days after sealing was used as the evaluation index for the sealing effect.

[0063] The performance test results of each embodiment and comparative example are shown in Tables 1-6 below: Table 1: Condensation time and operable time for each embodiment and comparative example

[0064] As shown in Table 1, the initial setting time of Examples 1-3 was 28–38 min, and the final setting time was 68–88 min, achieving rapid setting under low temperature conditions. The workable time of Examples 1-3 was 25–45 min, achieving synergistic optimization of rapid hardening at low temperature and sufficient workable time.

[0065] Comparative Example 2, lacking a core-shell structure coating, experienced premature release of the early-strength component, resulting in a significantly shortened initial setting time of 18 minutes and a workable time of only 8 minutes, failing to meet on-site construction requirements. This indicates that the nano-SiO2-coated core-shell structure effectively slows down the release rate of the early-strength component through the shell's controlled-release barrier, achieving a controllable release curve that is initially slow and then accelerates.

[0066] The slurry bleeding rate of all embodiments did not exceed 0.2%, with the bleeding rate of Embodiments 1 and 2 being 0%, indicating that the slurry of the present invention has excellent water retention and stability under low temperature conditions, with no bleeding and no segregation.

[0067] Table 2: Compressive strength of each embodiment and comparative example at different ages

[0068] As shown in Table 2, Example 1 achieved a compressive strength of 6.2 MPa after 8 hours, 13.5 MPa after 24 hours, 26.8 MPa after 72 hours, and 42.5 MPa after 28 days under curing conditions at 5℃. Comparative Example 1, which did not contain activated coal gangue, slag powder, or silica fume, had a 24-hour strength of only 4.8 MPa. This indicates that the synergistic hydration mechanism of the three-phase composite cementitious system—comprising sulfoaluminate cement, ordinary Portland cement, activated coal gangue, slag powder, and silica fume—significantly improved the early-stage strength at low temperatures.

[0069] Example 2 still exhibits excellent early strength performance at a lower temperature of 3°C, with a strength of 7.8 MPa after 8 hours, demonstrating the advantage of a high proportion of early strength components.

[0070] The low-temperature early strength performance of Example 1 is significantly better than the compressive strength of about 3.6 MPa at 4℃ for 24 hours in the prior art, with an improvement of about 275%, indicating that the three-phase composite cementitious system of the present invention has an unexpected synergistic enhancement effect in a low-temperature hydration environment.

[0071] Table 3: Free expansion rate of each embodiment and comparative example

[0072] As shown in Table 3, the free expansion rates of Example 1 at 3d, 7d, and 28d were 0.12%, 0.18%, and 0.22%, respectively, showing a convergence trend. That is, 28d is greater than 7d, which is greater than 3d, but the increase rate is decreasing. This indicates that the gradient expansion component has achieved continuous volume compensation of plastic expansion, early expansion, and long-term stability.

[0073] Comparative Example 3, using only aluminum powder paste as a single expansion source, showed an expansion rate as high as 0.25% at 3 days, indicating excessive expansion. This rate decreased to 0.08% at 7 days, representing rapid expansion decay, and a shrinkage of -0.05% at 28 days, indicating volume shrinkage. This demonstrates that a single expansion source cannot achieve volume stability throughout the entire process. In contrast, the three expansion sources of this invention are activated sequentially and compensate for each other over time, fundamentally solving the problem of air leakage through microcracks caused by the solidification shrinkage of the sealing material.

[0074] Comparative Example 1 showed a low overall expansion rate, only 0.10% after 28 days. This was attributed to the lack of rigid framework constraints provided by the hydration products of the three-phase composite cementing system, such as ettringite and geopolymer gel, for the expansion reaction. This indicates a synergistic effect between the three-phase composite cementing system and the gradient expansion components. The former provides the structural framework, while the latter provides volume compensation; both are indispensable.

[0075] Table 4: Maximum hydration temperature rise of each embodiment and comparative example

[0076] As shown in Table 4, the highest hydration temperature rise in Examples 1-3 was 20-24℃, far lower than the exothermic temperature rise of traditional polyurethane sealing materials. The exothermic temperature rise of polyurethane sealing materials is typically greater than 100℃. The low heat of hydration characteristic of the all-inorganic system effectively avoids the safety hazard of spontaneous combustion of coal seams. The hydration temperature rise in Comparative Example 1 was 28℃, higher than in the other examples, indicating that the substitution of cement clinker by slag powder and activated coal gangue effectively reduced the system's heat of hydration.

[0077] Table 5: Gas extraction concentrations in each embodiment and comparative example

[0078] As shown in Table 5, the average gas extraction concentration of Example 1 reached 52% 30 days after sealing, which was significantly better than 35% of Comparative Example 1 and 38% of Comparative Example 3.

[0079] Comparative Example 1, lacking a three-phase composite cementing system, suffered from insufficient low-temperature strength, leading to microcracks between the sealing body and the borehole wall, resulting in a gas extraction concentration of only 35%. Comparative Example 3, due to the inability of a single expansion source to achieve full-process volume stability, experienced later-stage shrinkage leading to gas leakage, resulting in a gas extraction concentration of only 38%.

[0080] The gas extraction concentration in Example 1 was 52%, which is significantly higher than the conventional level achieved by traditional cement-based materials for sealing in existing technologies. The gas extraction concentration achieved by traditional cement-based materials for sealing in the industry is typically below 30%. This demonstrates that the present invention significantly improves sealing quality and gas extraction efficiency through the synergistic effect of a three-phase composite cementitious system, core-shell structure with slow-release early strength, and gradient expansion.

[0081] Table 6: Statistics on Solid Waste Utilization Rate of Each Embodiment As shown in Table 6, the total amount of solid waste, namely activated coal gangue and slag powder, in Examples 1-3 was 18-28 parts, accounting for 30.0-41.2% of the total cementitious material, realizing the large-scale resource utilization of industrial solid waste. Comparative Example 1 had 0% solid waste content, and its performance indicators were significantly inferior to those of the examples, further verifying that the activation and utilization of solid waste not only has environmental benefits but is also an indispensable technical means in the present invention. The geopolymer gel formed by activated coal gangue under alkaline activation forms a complementary reinforcing network with cement hydration products, which is one of the key factors in achieving low-temperature high early strength.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature preparation method for grouting and sealing materials suitable for coal seam extraction, characterized in that: The grouting and hole sealing material is composed of the following components by weight: 25-40 parts of sulphoaluminate cement clinker, 15-25 parts of ordinary Portland cement, 10-20 parts of activated coal gangue micro powder, 5-12 parts of slag micro powder, 3-8 parts of silica fume, 2-6 parts of composite early strength activator, 0.5-3.0 parts of gradient expansion component, 0.1-0.8 parts of setting retarding and plastic retaining component, 0.2-1.0 parts of water reducing agent, and 0.05-0.2 parts of defoaming agent; The composite early strength activator comprises a nano-SiO2 coated early strength component, which is a core-shell structure particle with early strength salt as the core and nano-SiO2 as the shell. The gradient expansion component is composed of a gypsum type expansion source, aluminum paste and ettringite type expansion agent. The low-temperature preparation method comprises the following steps: S1, crushing and grinding the coal gangue raw material to 200 mesh or less, calcining and activating at 700-850 DEG C for 1-2 hours, and then grinding to a specific surface area of 500 m2 / kg or more after cooling to obtain activated coal gangue micro powder; S2, weighing the components according to the ratio, feeding into a three-dimensional motion mixer, mixing at a speed of 20-40 r / min for 15-30 min to obtain a dry mixture of the grouting and hole sealing material; S3, mixing the dry mixture with mixing water, the water-cement ratio is 0.30-0.45, the temperature of the mixing water is controlled at 10-25 DEG C, the mixing speed is 60-120 r / min, the mixing time is 3-8 min, and the grouting slurry is prepared, the temperature of the slurry out of the machine is controlled at 5-15 DEG C.

2. The low temperature preparation process of claim 1, wherein: In step S1, the coal gangue raw material is first crushed to ≤5 mm by a jaw crusher, then fed into a ball mill to be ground to 200 mesh with a sieve residue of ≤10%, and then placed in a rotary kiln for calcination and activation. After calcination, the material is ground by a superfine ball mill to a specific surface area of 500 m2 / kg or more.

3. The low temperature preparation process of claim 1, wherein: The content of anhydrous calcium sulphoaluminate in the sulphoaluminate cement clinker is not less than 55%, and the specific surface area is 350-450 m2 / kg; The ordinary Portland cement is P·O 42.5 grade or P·O 52.5 grade ordinary Portland cement; The slag micro powder is S95 grade or above granulated blast furnace slag micro powder, and the specific surface area is 400 m2 / kg or more; The SiO2 content of the silica fume is 85% or more, the specific surface area is 15000 m2 / kg or more, and the average particle size is 0.1-0.3 μm.

4. The cryogenic manufacturing method of claim 1, wherein: The composite early strength activator is composed of the following components by mass percentage: calcium formate 30-50%, aluminum sulfate 15-30%, sodium sulfate 10-20%, triethanolamine 2-8%, and nano-SiO2 coated early strength component 10-25%.

5. The cryogenic manufacturing process of claim 1, wherein: The preparation method of the nano-SiO2 coated early strength component is as follows: a saturated solution of calcium formate or aluminum sulfate is coated on nano-SiO2 sol with a solid content of 20-30% and a particle size of 20-50 nm by spray granulation technology in a fluidized bed granulator at 80-120 DEG C to form core-shell structure particles with a particle size of 50-150 μm.

6. The cryogenic manufacturing process of claim 1, wherein: The gradient expansion component is composed of the following components by mass percentage: gypsum type expansion source 40-60%, aluminum paste 5-15%, and ettringite type expansion agent 25-45%. The gypsum-based expansion source is selected from at least one of anhydrite or hemihydrate gypsum; The ettringite-type expansion agent is selected from at least one of UEA expansion agent or CSA expansion agent.

7. The cryogenic manufacturing process of claim 1, wherein: The retarding and plasticizing component is selected from one or more of sodium gluconate, citric acid or boric acid; The water reducing agent is a polycarboxylic acid-based superplasticizer with a solid content of ≥40% and a water reducing rate of ≥25%; The defoaming agent is a silicone-based defoaming agent or a polyether-based defoaming agent.

8. The cryogenic manufacturing process of claim 1, wherein: In step S3, the mixing is performed by a low-temperature mixing unit (4), and the grouting slurry is used to inject the coal seam borehole sealing section at an environmental temperature of 0-10°C and a grouting pressure of 0.5-2.0 MPa, with a pressure stabilizing time of 5-15 min.

9. A low temperature preparation system of grouting and sealing materials for coal seam extraction, for implementing the low temperature preparation method according to any one of claims 1-8, characterized in that it comprises: It comprises: A raw material storage and batching unit (1) for storing each raw material component and batching according to the proportion, including a powder storage bin with a heat preservation interlayer and an internal electric heating device, and an electronic batching system with a batching accuracy of ±0.5%; An activation pretreatment unit (2) for crushing, grinding and calcination activation treatment of coal gangue raw materials, including a jaw crusher, a ball mill, a rotary kiln with a calcination temperature of 700-850°C and a superfine ball mill; A dry mixing unit (3) for uniformly mixing each powder component to prepare a dry mixed material of grouting sealing material, wherein the dry mixing unit (3) is a three-dimensional motion mixer; A low-temperature mixing unit (4) for mixing the dry mixed material with mixing water under low-temperature conditions to prepare a grouting slurry, wherein the low-temperature mixing unit (4) comprises a low-temperature mixing tank with a jacket cooling / heating system, a stirrer arranged in the low-temperature mixing tank, a water temperature control system communicated with the low-temperature mixing tank, and an outflow slurry temperature monitoring device arranged on the low-temperature mixing tank, the water temperature control system automatically adjusts the mixing water temperature to control the outflow slurry temperature to maintain at 5-15°C according to the environmental temperature, and the rotational speed of the stirrer is adjustable at 60-120 r / min; An intelligent control system (5) for integrated control of the operating parameters of the raw material storage and batching unit (1), the activation pretreatment unit (2), the dry mixing unit (3) and the low-temperature mixing unit (4), wherein the intelligent control system (5) is a PLC programmable logic controller, including a touch screen human-machine interface and a data recording and tracing module, for setting and monitoring temperature, rotational speed, time and batching process parameters, and automatically recording each batch of production data; The discharge port of the raw material storage and batching unit (1) is connected to the feeding port of the dry mixing unit (3), the discharge port of the dry mixing unit (3) is connected to the feeding port of the low-temperature mixing unit (4), and the discharge port of the activation pretreatment unit (2) is connected to the feeding port of the raw material storage and batching unit (1).

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