A grouting material for coal and rock fractures suitable for long-distance transportation and its preparation method

Abstract

This invention belongs to the field of mining engineering and geotechnical reinforcement technology, and discloses a coal and rock mass fracture grouting material suitable for long-distance transportation and its preparation method. The cement:fly ash:water ratio provided by this invention is 2:8:10. Experimental verification shows that it meets the performance requirements of grouting materials, with a grouting strength >1MPa meeting engineering requirements, and an initial setting time of 27h10min meeting the requirements for long-distance transportation. Furthermore, in terms of engineering cost, it utilizes waste fly ash from power plants to replace 80% of the cement, significantly reducing the cost of grouting materials and solving the environmental pollution problem caused by fly ash stockpiling. This invention can be considered the preferred mix ratio for grouting and roof reinforcement projects in coal mines directly overlying caving zones.

Description

Technical Field

[0001] This invention relates to the fields of mining engineering and soil and rock reinforcement technology, and in particular to a coal and rock mass fissure grouting material suitable for long-distance transportation and its preparation method. Background Technology

[0002] Fly ash, the fine ash collected from the flue gas after coal combustion, is a major solid waste discharged from coal-fired power plants. The main oxide components of fly ash from my country's thermal power plants are SiO2, Al2O3, FeO, Fe2O3, CaO, and TiO2. With the development of the power industry, the amount of fly ash emitted by coal-fired power plants has increased year by year, becoming one of the largest industrial wastes in my country. Large amounts of untreated fly ash will generate dust and pollute the atmosphere; if discharged into water systems, it will cause river siltation, and the toxic substances in it will also harm human health and other organisms. Fly ash particles have a porous honeycomb structure with a large specific surface area and high adsorption activity. Furthermore, the bead walls have a porous structure with a porosity of 50-80%, exhibiting strong water absorption. Adding fly ash to cement slurry as an additive for concrete and cement grouting not only realizes the resource utilization of fly ash but also reduces environmental pollution.

[0003] For coal and rock mass fracture grouting projects, grouting materials are one of the most crucial aspects of the grouting technology. The performance of different materials directly affects the quality of the grouting project, while their price determines the overall cost. Therefore, researching grouting materials with good performance and reasonable prices is of great significance for improving project quality and reducing project expenses.

[0004] In the existing technology, the application scope of high-volume fly ash-cement mixed grouting materials is not wide, and there are no relevant regulations or standards to follow. Therefore, for shallow coal and rock mass fracture grouting projects, how to make the ratio of cement, fly ash and water to achieve the best grouting consolidation effect while keeping the project cost low, and finding the optimal balance between the two is a difficult problem in current research. Summary of the Invention

[0005] The purpose of this invention is to provide a coal and rock mass fracture grouting material suitable for long-distance transportation and its preparation method. By optimizing the ratio of cement, fly ash and water, a grouting material with low viscosity, long setting time, low cost and sufficient consolidation strength is prepared, solving the problems of easy pipe blockage and high cost in long-distance transportation.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a coal and rock mass fracture grouting material suitable for long-distance transportation, the grouting material being composed of cement, fly ash and water; The mass ratio of cement to fly ash is 2:8, and the water-cement ratio is 1:1.

[0007] Furthermore, in the coal and rock mass fracture grouting material suitable for long-distance transportation, the particle size of the fly ash is ≤5mm; The fly ash comprises SiO2, Al2O3, CaO and Fe2O3; by mass fraction, SiO2 10~70%, Al2O3 10~38%, CaO 0.5~30%, and Fe2O3 3~15%.

[0008] Furthermore, in the aforementioned coal and rock mass fracture grouting material suitable for long-distance transportation, the cement is PO 42.5 ordinary Portland cement.

[0009] Furthermore, in the aforementioned coal and rock mass fracture grouting material suitable for long-distance transportation, the water supply capacity is ≥40m. 3 / h.

[0010] Furthermore, in the coal and rock mass fracture grouting material suitable for long-distance transportation, the initial setting time of the grouting material is 27-28 hours, and the final setting time of the grouting material is 38-39 hours.

[0011] Furthermore, in the coal and rock mass fracture grouting material suitable for long-distance transportation, the 28-day unconfined compressive strength of the grouting material is >1 MPa.

[0012] This invention also provides a method for preparing a coal and rock mass fracture grouting material suitable for long-distance transportation, comprising the following steps: Weigh cement, fly ash, and water according to the mass ratio; mix cement and fly ash dry, then add water to mix, to obtain the grouting material.

[0013] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) Under the ratio (2:8:10) of the present invention, the Marsh funnel viscosity of the slurry is about 16.00s, which is low and has good fluidity. The spherical glass microspheres in the fly ash act as ball bearings in the slurry, which significantly reduces the slurry transport resistance and is suitable for long-distance pipeline transport from the ground to the mine.

[0014] (2) The high content of fly ash delays the hydration reaction. The initial setting time under this ratio is more than 27 hours, which provides sufficient time for long-distance transportation and full penetration into micro-cracks, avoiding the risk of pipe blockage.

[0015] (3) Although the fly ash content is as high as 80%, by using a reasonable ratio of fly ash to water (1:1), the hydration products of cement (Ca(OH)2) are used to activate the pozzolanic activity of fly ash. The generated calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) gels can still maintain the strength of the stone body at about 1.03 MPa after 28 days, which meets the basic requirements for seepage prevention and reinforcement.

[0016] (4) Using waste fly ash from power plants to replace 80% of cement significantly reduces the cost of grouting materials and solves the environmental pollution problem caused by fly ash stockpiling. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Figure 1 The curve showing the relationship between the grouting material mix ratio and density; Figure 2 The curve showing the relationship between the grouting material ratio and viscosity; Figure 3 Water separation rate curves for grouting materials with different proportions; Figure 4 Curves showing the stone settling rate of grouting materials with different proportions; Figure 5 The 7-day compressive strength of grouting materials with different proportions; Figure 6 The 28-day compressive strength of grouting materials with different proportions. Detailed Implementation

[0019] This invention provides a coal and rock mass fracture grouting material suitable for long-distance transportation, the grouting material being composed of cement, fly ash and water; The mass ratio of cement to fly ash is 2:8, and the water-cement ratio is 1:1.

[0020] In this invention, the particle size of the fly ash is preferably ≤5mm, more preferably ≤500μm, and even more preferably ≤300μm.

[0021] In this invention, the fly ash preferably comprises SiO2, Al2O3, CaO, and Fe2O3; by mass fraction, SiO2 10~70%, Al2O3 10~38%, CaO 0.5~30%, and Fe2O3 3~15%. The fly ash also includes MgO, TiO2, Na2O, and K2O.

[0022] In this invention, the fly ash is preferably solid waste discharged from coal-fired power plants.

[0023] In this invention, the cement is preferably PO 42.5 ordinary Portland cement.

[0024] In this invention, the water supply capacity is preferably ≥40m³. 3 / h, further optimized for ≥42m 3 / h, more preferably ≥45m 3 / h.

[0025] In this invention, the water-cement ratio refers to the ratio of the mass of water to the sum of the masses of cement and fly ash.

[0026] In this invention, the water only needs to meet the quality standards for concrete mixing water.

[0027] In this invention, the initial setting time of the grouting material is preferably 27-28h, more preferably 27h0min-27h10min, and even more preferably 27h10min; the final setting time of the grouting material is preferably 38-39h, more preferably 38h10min-38h20min, and even more preferably 38h20min.

[0028] In this invention, the 28-day unconfined compressive strength of the grouting material is preferably >1 MPa, more preferably >1.03 MPa, and even more preferably >1.05 MPa.

[0029] This invention also provides a method for preparing a coal and rock mass fracture grouting material suitable for long-distance transportation, comprising the following steps: Weigh cement, fly ash, and water according to the mass ratio; mix cement and fly ash dry, then add water to mix, to obtain the grouting material.

[0030] In this invention, the conditions for dry mixing are not limited; it is sufficient to mix the cement and fly ash evenly.

[0031] In this invention, the conditions for adding water and mixing are not limited, as long as the slurry is uniform and free of lumps.

[0032] In this invention, the reason why the cement, fly ash, and water ratio of 2:8:10 can balance long-distance transportation and strength is that: (1) Physical properties: The glass microspheres in fly ash act as ball bearings in the slurry, reducing the friction between particles and allowing the slurry to maintain high fluidity even at a low water-cement ratio (relative to pure cement slurry). (2) Chemical characteristics: Fly ash has potential pozzolanic activity, which comes from the soluble active components such as SiO2 and Al2O3 in the glassy particles (porous glass and glass beads) formed after melting and rapid cooling; ordinary cement paste contains a large amount of Ca(OH)2 in its hydration products. When water is present, the active SiO2 and Al2O3 in fly ash react with Ca(OH)2 to generate calcium silicate hydrate (CSH) and calcium aluminate hydrate (ASH). (3) Synergistic effect: At a ratio of 2:8, the amount of hydration products produced by cement is just enough to bind a large number of fly ash particles. There is no shortage of cementing material due to excessive fly ash, nor is there excessive cost due to excessive cement.

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] To determine the optimal mix ratio for long-distance transport, multiple control experiments were designed. The key indicators investigated were viscosity (affecting transport capacity), setting time (affecting transport distance and permeability), and compressive strength (affecting reinforcement effect).

[0035] Example 1

[0036] Mixing ratio: cement: fly ash: water = 2:8:10 (by mass); The fly ash is produced by Huaibei Mining Linhuan Zhongli Power Plant. Its composition is shown in Table 1, and the particle size distribution of the fly ash is shown in Table 2. Table 1. Chemical composition of fly ash

[0037] Table 2. Particle composition of fly ash

[0038] The cement is PO 42.5 ordinary Portland cement, manufactured by Huaibei Xiangshan Cement Plant. Other specifications are shown in Table 3. Table 3. Parameters of PO 42.5 ordinary Portland cement used in the experiment

[0039] The fineness is the residue after passing through a 0.08mm square-hole sieve; Water supply capacity ≥40m 3 / h; Weigh the raw materials according to the mass ratio of cement:fly ash:water. First, dry mix the cement and fly ash evenly, then add water and stir in a mixer for at least 3 minutes until the slurry is uniform and free of lumps. The resulting grouting material is denoted as PB-2.

[0040] Comparative Examples 1-5 were prepared using the same method as Example 1, except that: Comparative Example 1 Mixing ratio: cement: fly ash: water = 3:7:10, the resulting grouting material is denoted as PB-1.

[0041] Comparative Example 2

[0042] Mixing ratio: cement: fly ash: water = 1.5: 8.5: 10, the resulting grouting material is denoted as PB-3.

[0043] Comparative Example 3

[0044] Mixing ratio: cement: fly ash: water = 1:9:10, the resulting grouting material is designated as PB-4.

[0045] Comparative Example 4

[0046] Mixing ratio: cement: fly ash: water = 2:8:8, water-cement ratio 0.8, the resulting grouting material is designated as PB-5.

[0047] Comparative Example 5

[0048] Mixing ratio: cement: fly ash: water = 1:9:8, water-cement ratio 0.8, the resulting grouting material is designated as PB-6.

[0049] The grouting materials obtained in Example 1 and Comparative Examples 1-5 were subjected to the following tests, and the test results are shown in Table 4. Figures 1 to 6 As shown.

[0050] 1. Slurry density determination

[0051] 1) The mass of the test container was determined using a balance. m 1; 2) Fill the container with water and measure the total mass of the container when it is full. m 2; 3) Pour out the water from the container, wipe the water droplets off the inside of the container with a dry paper towel, and let it stand for a while until the water film on the inside of the container has completely evaporated; 4) Fill the container with the liquid to be tested and weigh the total mass. m 3.

[0052] The formula for processing test results is shown in Formula 1: Formula 1; In formula 1: d -Slurry density; dw - The density of water; ρ g -Specific gravity of the slurry.

[0053] 2. Determination of slurry viscosity (Madrid funnel viscometer)

[0054] 2.1 Instrument Calibration

[0055] (1) Wet the viscometer with water and place it on the instrument stand. After installing the sieve, place the 1000mL open measuring cup horizontally under the viscometer. (2) Block the bottom outlet of the funnel with your finger and pour clean water into the funnel until the scale line inside the funnel is reached; (3) Release your finger and start the stopwatch. When the water flows out to the 946mL mark, stop timing. The stopwatch value is the viscosity of the water. The standard time is 26±0.5s. Otherwise, the funnel viscometer should be replaced.

[0056] 2.2 Viscosity Measurement

[0057] Take slurry samples according to the above procedure and conduct the test. Each group is tested three times, and the average of the three measurements is taken as the test result, accurate to 0.01s.

[0058] 3. Test of slurry water separation rate

[0059] (1) Take 3 graduated cylinders with a maximum graduation of 100mL, a minimum graduation of 1mL, and an inner diameter of 27mm; (2) Pour the prepared slurry into a graduated cylinder, with the liquid level at 100 mL, and let it stand; (3) Read the reading every 10 minutes.

[0060] This experiment used a static method to test the free water separation process of a mixture of cement, fly ash, and water under gravity. The fly ash particles were selected with a diameter ≤0.1mm, and the cement was ensured to be free of lumps. A 100mm glass graduated cylinder was used to test the free water separation of the slurry under static conditions. Each test group had to be repeated 3 times, and the average value was taken as the data to ensure the accuracy of the data.

[0061] 4. Determination of slurry stone formation rate

[0062] (1) Mix the slurry evenly according to the designed mix ratio; (2) Pour the stirred slurry into a clean 100mL graduated cylinder, up to the 100mL mark, and record the volume at this point as V0. Seal with plastic wrap. (3) Place the sealed measuring cylinder steadily into the concrete standard curing box, and use the curing box to keep the slurry at a constant temperature of 20±2℃ and a humidity of more than 95%. Let it stand for 24 hours according to the specifications or design requirements. (4) After the specified time has elapsed, gently remove the graduated cylinder from the curing box and observe the contents of the cylinder. The slurry usually consists of two layers: the upper layer is the precipitated water (bleeding water), and the lower layer is the deposited solid (stone body). Read the volume of the lower layer of stone body (solidified material) and record it as V. S Each experiment was repeated three times, and the average value was used as the data to ensure accuracy.

[0063] 5. Slurry setting time

[0064] Setting time refers to the time required for the cement hydration reaction, and is divided into initial setting time and final setting time. The preparation sequence for cement-fly ash slurry is as follows: first, add fly ash and water according to the mix ratio; after the cement and fly ash are fully mixed, add water. The initial setting time is the time required from the addition of cement until the slurry begins to lose its relative fluidity; the final setting time is the time required for the slurry to completely lose its relative fluidity. Initial and final setting times are measured using a Vicat apparatus. When measuring the initial setting time, the slurry is considered to have initially set when the initial setting needle is 4 mm ± 1 mm from the bottom of the mold; when measuring the final setting time, the slurry is considered to have finally set when the final setting needle no longer leaves a ring-shaped mark on the specimen. Each test is repeated three times, and the average value is used to ensure data accuracy.

[0065] 6. Determination of compressive strength

[0066] The unconfined compressive strength test specimens were formed using a manual injection method. The mixed cement-soil mixture was poured into the mold using a 100mm×100mm×100mm mold. Before molding, a release agent (such as machine oil) was applied to the inner wall of the steel mold. The mixed, fluid-like slurry was poured into the mold in two stages, with each layer being approximately the same thickness to obtain a uniform specimen. After each stage was filled, the specimen was pressed down evenly from the inside out using both thumbs, and then placed on a vibrating table until no air bubbles were released. After molding, excess slurry was scraped off, and the surface was smoothed with a trowel to prevent unevenness. Finally, a plastic film was placed over the specimen to prevent further moisture evaporation. Demolding was performed after 24 hours. After consolidation, the samples were demolded and transferred to a constant temperature and humidity chamber for curing. The curing time was recorded, and the test curing times were 7 days and 28 days. The compressive strength was measured using an unconfined compressive strength tester. Each test was repeated 3 times, and the average value was taken as the data to ensure the accuracy of the data.

[0067] Table 4. Physical and mechanical properties of grouting materials with different mix proportions

[0068] Figure 1 The curve showing the relationship between the grouting material mix ratio and density is shown. Figure 2 This is a curve showing the relationship between the grouting material ratio and viscosity. Figure 3The water separation rate curves are for grouting materials with different proportions. Figure 4 The stone settling rate curves are for grouting materials with different mix proportions. Figure 5 The 7-day compressive strength of grouting materials with different proportions, Figure 6 The 28-day compressive strength of grouting materials with different proportions.

[0069] From Table 4 and Figures 1 to 6 The results show that: The density of PB-2 is 1.422 g / cm³. 3 The viscosity is 16.00 s (Madrick funnel viscosity), which is extremely low, indicating excellent fluidity. The water separation rate is 19.32% (after standing for 120 min), and the high water separation rate means that the grout is not prone to thickening during dynamic transportation. The stone-forming rate is 74%, and the volume shrinkage after solidification is within an acceptable range. The setting time is 27 h 10 min for initial setting and 38 h 20 min for final setting. The compressive strength is 0.38 MPa at 7 days and 1.03 MPa at 28 days. This shows that the PB-2 mix design minimizes costs while ensuring strength (>1 MPa) and provides an extremely long workable time, making it very suitable for long-distance grouting.

[0070] PB-1 has a 28-day strength of up to 3.22 MPa, but its initial setting time is relatively short, about 23.5 hours, and it requires a large amount of cement, resulting in high costs, which does not meet the principle of low-cost, large-volume grouting.

[0071] PB-3 has a consistency of 16.07s, good fluidity, and an initial setting time of 33h20min. However, its 28d compressive strength is only 0.86MPa, which is lower than the engineering requirement of 1MPa, and it cannot play an effective supporting and reinforcing role.

[0072] PB-4 has a consistency of 16.27s, indicating good fluidity, and an initial setting time of 40h. However, its 28d compressive strength is only 0.36MPa, far below the engineering requirement of 1MPa, and it cannot play an effective supporting and reinforcing role.

[0073] The reduced water-cement ratio of PB-5 resulted in poorer fluidity, with a consistency of 16.44s, and the strength did not improve significantly, with a 28-day strength of only 0.33 MPa, actually lower than PB-2. Furthermore, the low water-cement ratio is not conducive to long-distance pumping.

[0074] The reduced water-cement ratio of PB-6 resulted in poorer fluidity, with a consistency of 16.57s and an initial setting time of 95h40min. Furthermore, the strength did not improve significantly, with a 28-day strength of only 0.12MPa, which is far lower than that of PB-2.

[0075] The cost of the coal gangue-based geopolymer grouting material provided in this embodiment is as follows: The fly ash used in this experiment has a market price of 80.5 yuan / ton; the cement used in the experiment is PO 42.5 ordinary Portland cement, with a market price of 475.2 yuan / ton.

[0076] The total cost is as follows: 80.5×0.8+475.2×0.2=159.44 yuan / ton.

[0077] The proportioning method provided in this application (cement:fly ash:water = 2:8:10) has a cost of 159.44 yuan / ton, which is significantly lower than the cost of 475.2 yuan / ton for ordinary Portland cement PO 42.5.

[0078] The mixing ratio method provided by this invention (cement:fly ash:water = 2:8:10) has been experimentally verified to achieve the best balance in terms of engineering cost, grouting strength (>1MPa) and setting time (to meet long-distance transportation requirements). It is recommended as the preferred mixing ratio scheme for grouting and roof reinforcement projects in coal mining areas directly overlying caving zones.

[0079] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A grouting material for coal and rock mass fractures suitable for long-distance transportation, characterized in that, The grouting material is composed of cement, fly ash and water; The mass ratio of cement to fly ash is 2:8, and the water-cement ratio is 1:

1.

2. The coal and rock mass fracture grouting material suitable for long-distance transportation according to claim 1, characterized in that, The particle size of the fly ash is ≤5mm; The fly ash comprises SiO2, Al2O3, CaO and Fe2O3; by mass fraction, SiO2 10~70%, Al2O3 10~38%, CaO 0.5~30%, and Fe2O3 3~15%.

3. The coal and rock mass fracture grouting material suitable for long-distance transportation according to claim 1, characterized in that, The cement is PO 42.5 ordinary Portland cement.

4. The coal and rock mass fracture grouting material suitable for long-distance transportation according to claim 1, characterized in that, The water supply capacity is ≥40m. 3 / h.

5. A coal and rock mass fracture grouting material suitable for long-distance transportation according to any one of claims 1 to 4, characterized in that, The initial setting time of the grouting material is 27-28 hours, and the final setting time of the grouting material is 38-39 hours.

6. A coal and rock mass fracture grouting material suitable for long-distance transportation according to claim 5, characterized in that, The grouting material has an unconfined compressive strength of >1 MPa over 28 days.

7. A method for preparing a coal and rock mass fracture grouting material suitable for long-distance transportation as described in any one of claims 1 to 6, characterized in that, Includes the following steps: Weigh cement, fly ash, and water according to the mass ratio; mix cement and fly ash dry, then add water to mix, to obtain the grouting material.

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