Early-strength low-resistance long-distance conveying filling paste and preparation method thereof

Abstract

The invention discloses early-strength low-resistance long-distance conveying filling paste and a preparation method thereof, and belongs to the technical field of cementing materials. The filling paste is prepared from the following components in percentage by weight: 1%-2% of nano silicon dioxide, 0.1%-0.5% of a microbial agent, 25%-35% of low-quality fly ash, 40%-60% of fine aggregate, 0.5%-3% of a suspending agent, 1%-5% of a water reducing agent, 0.1%-2% of a surfactant, 0.1%-3% of a surface modifier, 0.5%-2% of urea and 10%-30% of water, wherein the sum of the weight fractions of the components is 100%. The microstructure of the filling material is enhanced through the high specific surface area and surface activity of the nano silicon dioxide, and the cementing performance is enhanced through calcium carbonate deposition induced by microorganisms. According to the surface modifier modification technology, the particle surface characteristics are improved, the inter-particle acting force increased due to the cementation effect of a nano material and microorganisms is reduced, the fluidity and construction performance of the material are improved, and the conveying resistance is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of cementitious materials, and particularly relates to an early-strength low-resistance long-distance conveying filling paste and a preparation method thereof. Background Art

[0002] Mining, as an important part of China's economic structure, plays a crucial role. The filling mining method has gradually been favored by mining enterprises due to its advantages in controlling the environmental impact of mine exploitation. As the core element of the filling mining method, the performance of the filling material is directly related to the efficiency, cost, and safety of the filling project. Currently, the industry is actively exploring and developing new filling materials to meet the urgent market demands for environmental protection, high efficiency, and low cost.

[0003] However, traditional filling materials still have problems such as high cost, insufficient early strength, and high bleeding rate during application, which limit the widespread adoption of the filling mining method. Especially in the pipeline transportation link of the filling material, due to the intense friction between the slurry and the pipe wall and the collision and extrusion between solid-phase particles, serious problems such as pipeline wear and pipe burst occur, posing a significant impact on the safety and stability of the filling project.

[0004] To address these challenges, the industry has taken measures such as reducing the particle size of coarse aggregates, adjusting the slurry concentration, and increasing the cement dosage, attempting to reduce the pipeline transportation resistance of the filling paste. However, these methods often come at the cost of increasing the filling cost and reducing the transportation efficiency, and may cause the phenomenon of bleeding and stratification of the filling paste, making it difficult to meet the dual requirements of current environmental protection and efficiency. Summary of the Invention

[0005] One technical problem solved by the present invention is to provide an early-strength low-resistance long-distance conveying filling paste. By introducing nano-silica as a modifier, more C-S-H gels are formed, enhancing the microstructure of the filling material; using specific microorganism-induced calcium carbonate deposition to enhance the cementing performance of the filling material; and using a surface modifier to change the surface characteristics of the particles, improving the fluidity and stability of the filling paste. Another technical problem to be solved by the present invention is to provide a preparation method for an early-strength low-resistance long-distance conveying filling paste, which uses a large amount of industrial solid waste, greatly reducing the material cost and being suitable for large-scale production applications.

[0006] Technical Solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] An early-strength, low-resistance, long-distance transport filling paste is composed of the following components by weight fraction: 1% - 2% of nano-silica, 0.1% - 0.5% of microbial inoculant, 25% - 35% of low-quality fly ash, 40% - 60% of fine aggregate, 0.5% - 3% of suspending agent, 1% - 5% of water-reducing agent, 0.1% - 2% of surfactant, 0.1% - 3% of surface modifier, 0.5% - 2% of urea, 10% - 30% of water, and the sum of the weight fractions of the above components is 100%; preferably, it is composed of the following components by weight fraction: 1% - 2% of nano-silica, 0.3% - 0.5% of microbial inoculant, 25% - 26% of low-quality fly ash, 47% - 53% of fine aggregate, 0.5% - 3% of suspending agent, 3% - 4.5% of water-reducing agent, 1% - 2% of surfactant, 2% - 3% of surface modifier, 1% - 1.5% of urea, 10.6% - 13% of water, and the sum of the weight fractions of the above components is 100%; further preferably, it is composed of the following components by weight fraction: 2% of nano-silica, 0.4% of microbial inoculant, 25% of low-quality fly ash, 53% of fine aggregate, 0.5% of suspending agent, 4% of water-reducing agent, 1% of surfactant, 2.5% of surface modifier, 1% of urea, 10.6% of water.

[0008] For the early-strength, low-resistance, long-distance transport filling paste, the average particle size of nano-silica is 15 - 20 nm, and the specific surface area is 200 - 400 m 2 / g. As a modifier, using its high specific surface area and surface activity, it enhances the microstructure of the filling material, improves the early strength and stability; preferably, the average particle size of nano-silica is 15 nm, and the specific surface area is 300 m 2 / g.

[0009] For the early-strength, low-resistance, long-distance transport filling paste, the microbial inoculant is one or both of spherical bacillus inoculant or thermophilic bacillus inoculant. This microbial inoculant has alkali resistance and high urease activity, and is a freeze-dried powder, with the viable count ≥ 1×10 9 CFU / g. It can continuously catalyze the hydrolysis of urea in the alkaline environment of the filling paste, release CO3 2- ions, combine with Ca 2+ to form nano-calcium carbonate crystals (particle size 50 - 100 nm), fill the material pores and enhance the cementation network, thereby rapidly improving the cementation strength; preferably, the microbial inoculant is a mixture of spherical bacillus inoculant and thermophilic bacillus inoculant with a mass ratio of 1:1.

[0010] The early-strength, low-resistance, long-distance transported and filled paste uses low-quality fly ash as grade II or grade III fly ash discharged from coal-fired power plants, with a loss on ignition ≤ 8% and fineness (residue on 45μm sieve) ≤ 25%, which serves as the main cementitious material to reduce costs. Preferably, the low-quality fly ash is grade II fly ash, with a loss on ignition of 6.5% and a fineness of 20% for the residue on 45μm sieve.

[0011] For the early-strength, low-resistance, long-distance transported and filled paste, the fine aggregate is any one of crushed coal gangue, metal mine tailings, and desert sand; during use, the fine aggregate needs to be crushed and screened to a particle size ≤ 2.36mm and a specific surface area ≥ 300m 2 / kg to meet the requirements of fluidity and cementitious properties.

[0012] For the early-strength, low-resistance, long-distance transported and filled paste, the suspending agent is one or two of sodium carboxymethylcellulose, sodium polyacrylate, xanthan gum, hydroxypropylated starch, or acetylated starch, which improves the suspension stability and anti-stratification performance of the slurry, reduces the friction and wear of particles during pipeline transportation, and thus reduces the transportation resistance.

[0013] For the early-strength, low-resistance, long-distance transported and filled paste, the water-reducing agent is one or two of naphthalene-based water-reducing agents, aliphatic water-reducing agents, polycarboxylate water-reducing agents, or melamine formaldehyde resin water-reducing agents, which reduces the water consumption, improves the fluidity of the slurry, and facilitates long-distance transportation and construction.

[0014] For the early-strength, low-resistance, long-distance transported and filled paste, the surfactant is one or two of fatty acid methyl ester ethoxylates, polyoxyethylene castor oil, alkylphenol polyoxyethylene ethers, or polyvinylpyrrolidone, which reduces the surface tension of the slurry, enhances the dispersibility, and reduces the pipeline transportation resistance of the slurry.

[0015] For the early-strength, low-resistance, long-distance transported and filled paste, the surface modifier is one or two of silane coupling agents, polysaccharide derivatives, polyacrylic acid and its salts, polyvinyl alcohol, or polyacrylic acid resin to improve the surface characteristics of particles.

[0016] For the early-strength, low-resistance, long-distance transported and filled paste, the mass ratio of urea to the microbial inoculant is 2:1 to 6:1 to ensure the synergistic balance between microbial metabolic efficiency and fly ash activation; urea serves as the substrate for microbial mineralization reactions, and at the same time activates the active components of fly ash by increasing the pH value of the system, promotes the hydration reaction to generate C-S-H gel, and synergistically optimizes the fluidity and dispersibility of the slurry with surfactants and water-reducing agents; as the substrate for the metabolism of the microbial inoculant, it is catalytically hydrolyzed by urease to generate CO3 2- and NH3, and NH3 dissolves in water to form an alkaline environment (pH 10 - 12), activating the active SiO2 and Al2O3 in fly ash and promoting their reaction with Ca 2+The reaction generates C-S-H gel; it can also enhance the dispersibility of fly ash particles through hydrogen bonding with surfactants, reduce agglomeration, delay the adsorption and consumption of water reducers, extend the retention time of the fluidity of the paste, and meet the requirements of long-distance transportation; preferably, the mass ratio of urea to the microbial inoculant is 2.5:1 to 5:1.

[0017] The preparation method of the early-strength low-resistance long-distance transportation filling paste described above includes the following steps:

[0018] S1 Bacterial agent activation: Before use, the microbial inoculant is pre-cultured and activated at a temperature of 20-40 °C to ensure its optimal activity in the filling paste.

[0019] S2 Mixing and stirring: Add low-quality fly ash, fine aggregate, nano-silica, suspending agent, water reducer, surfactant, surface modifier, urea and water in sequence, and stir for 10 minutes; finally add the activated bacterial agent and continue to stir until a uniform and stable mixture is formed; in the mixing stage of the filling paste, the activated microbial inoculant is added last to ensure full mixing with other components such as nano-silica and fly ash and uniform dispersion in the filling material, and stir until a uniform and stable mixture is formed.

[0020] The combination of nano-material modification technology and microbial mineralization technology, on the one hand, strengthens the microstructure of the filling material through the high specific surface area and surface activity of nano-silica, and on the other hand, enhances the cementing performance through microbially induced calcium carbonate precipitation. The two work together to improve the early strength and stability of the filling material.

[0021] The microbial metabolites form hydrogen bonds with the surface hydroxyl groups of nano-silica, promoting the uniform dispersion of nano-particles and avoiding agglomeration; at the same time, the surface modifier regulates the inter-particle force by hydrophobically modifying the surface of calcium carbonate crystals, reducing its electrostatic adsorption with fly ash particles and further optimizing the fluidity.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0023] (1) The present invention adopts nano-material modification technology, introduces nano-silica as a modifier, and utilizes its high specific surface area and surface activity to significantly improve the early strength and stability of the filling paste. The 24-hour compressive strength is increased by 65%-80%, and the 72-hour strength is increased by 40%-50%. The introduction of nano-silica enhances the microstructure of the filling material by forming more C-S-H gel.

[0024] (2) The present invention combines microbial mineralization technology and uses calcium carbonate deposition induced by specific microorganisms to enhance the cementing performance of the filling material, so that the calcium carbonate content in the cementing phase reaches 12% - 15%, and the strength at 28 days shows no attenuation, significantly improving the long-term stability. This eco-friendly cementing mechanism reduces the dependence on traditional cement, lowers the cost, and at the same time improves the environmental compatibility and long-term stability of the filling material.

[0025] (3) The present invention uses a surface modifier to change the surface characteristics of the particles, effectively reducing the interaction forces between the particles, including van der Waals forces, electrostatic forces, and chemical bond forces, thereby improving the fluidity and stability of the filling paste, increasing the slump of the filling paste by 30% - 35%, and achieving the purpose of reducing the pipeline transportation resistance.

[0026] (4) The present invention uses a large amount of industrial solid wastes, replaces cement with low-quality fly ash (Grade II / III), and uses coal gangue, metal tailing sand, etc. as fine aggregates, greatly reducing the material cost. Specific Embodiments

[0027] The following further clarifies the present invention in conjunction with specific embodiments. The embodiments are implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0028] Example 1

[0029] An early-strength low-resistance long-distance transportation filling paste S1 is composed of the following components by weight fraction: nano-silica (15 nm, specific surface area of 300 m 2 / g) 1%, spherical bacillus agent (freeze-dried powder, viable bacteria count ≥ 1×109 CFU / g) 0.5%, low-quality fly ash (Grade II, loss on ignition 6.5%, 45μm sieve residue fineness 20%) 25%, crushed coal gangue 47%, sodium carboxymethyl cellulose 3%, melamine formaldehyde resin water reducer 4.5%, alkylphenol polyoxyethylene ether 2%, polyvinyl alcohol 3%, urea 1%, water 13%.

[0030] The preparation method of the above filling paste includes the following steps:

[0031] 1. Agent activation: Activate the spherical bacillus agent at 35°C for 2 hours;

[0032] 2. Mixing and stirring: Add fly ash, crushed coal gangue, nano-silica, suspending agent, water reducer, surfactant, surface modifier, urea and water in sequence, and stir for 10 minutes; finally add the activated agent and continue to stir until a uniform and stable mixture is formed.

[0033] Example 2

[0034] An early-strength, low-resistance, long-distance transport filling paste S2, which is composed of the following components by weight fraction: nano-silica (15 nm, specific surface area of 300 m 2 / g) 1.5%, spherical bacillus agent (freeze-dried powder, viable bacteria count ≥ 1×10 9 CFU / g) 0.3%, low-quality fly ash (Grade II, loss on ignition 6.5%, 45μm sieve residue fineness 20%) 26%, desert sand 50%, sodium polyacrylate 2%, polycarboxylate water reducer 3%, polyvinylpyrrolidone 1.5%, silane coupling agent 2%, urea 1.5%, water 12.2%.

[0035] The preparation method is the same as that of Example 1.

[0036] Example 3

[0037] An early-strength, low-resistance, long-distance transport filling paste S3, which is composed of the following components by weight fraction: nano-silica (15 nm, specific surface area of 300 m 2 / g) 2%, microbial agent (spherical bacillus agent and thermophilic bacillus agent are mixed in a mass ratio of 1:1, freeze-dried powder, viable bacteria count ≥ 1×109 CFU / g) 0.4%, low-quality fly ash (Grade II, loss on ignition 6.5%, 45μm sieve residue fineness 20%) 25%, metal mine tailings 53%, xanthan gum 0.5%, aliphatic water reducer 4%, polyoxyethylene castor oil 1%, polysaccharide derivative 2.5%, urea 1%, water 10.6%.

[0038] The preparation method is the same as that of Example 1.

[0039] Comparative Example 1

[0040] A filling paste F1, which is composed of the following components by weight fraction: ordinary silica fume (specific surface area 45 m 2 / g) 1%, spherical bacillus agent (freeze-dried powder, viable bacteria count ≥ 1×109 CFU / g) 0.5%, low-quality fly ash (Grade II, loss on ignition 6.5%, 45μm sieve residue 20%) 25%, crushed coal gangue 47%, carboxymethyl cellulose sodium 3%, melamine formaldehyde resin water reducer 4.5%, alkylphenol polyoxyethylene ether 2%, polyvinyl alcohol 3%, urea 1%, water 13%.

[0041] The preparation method is the same as that of Example 1.

[0042] Comparative Example 2

[0043] A filling paste F2, which is composed of the following components by weight fraction: ordinary silica fume (specific surface area 45 m 2 / g) 1%, Bacillus sphaericus bactericide (freeze-dried powder, viable bacteria count ≥ 1×109 CFU / g) 0.5%, low-quality fly ash (Grade II, loss on ignition 6.5%, residue on 45μm sieve 20%) 27%, crushed coal gangue 47%, sodium carboxymethyl cellulose 3%, melamine formaldehyde resin water reducer 4.5%, alkylphenol polyoxyethylene ether 2%, urea 1%, water 14%.

[0044] The preparation method is the same as that of Example 1.

[0045] Comparative Example 3

[0046] A filling paste F3, composed of the following components by weight fraction: ordinary silica fume (specific surface area 45m 2 / g) 1%, Bacillus sphaericus bactericide (freeze-dried powder, viable bacteria count ≥ 1×109 CFU / g) 0.5%, low-quality fly ash (Grade II, loss on ignition 6.5%, residue on 45μm sieve 20%) 27%, crushed coal gangue 47%, sodium carboxymethyl cellulose 3%, melamine formaldehyde resin water reducer 4.5%, alkylphenol polyoxyethylene ether 2%, water 15%.

[0047] The preparation method is the same as that of Example 1.

[0048] The compressive strength of the above 5 pastes was tested according to GB / T 17671-2021 "Test Method for Cement Mortar Strength (ISO Method)", the slump of the paste was tested according to GB / T 50080-2016 "Standard Test Method for Properties of Ordinary Concrete Mixtures", the bleeding rate was tested according to JC / T1083-2008 "Test Method for Compatibility of Cement and Water Reducer", and the pipeline transportation resistance of the filling paste was tested according to NB / T 10726-2021 "Technical Requirements for Pipeline Transportation of Coal Mine Paste Filling". The results are shown in Table 1.

[0049] Table 1 Test performance results of 6 pastes prepared in Examples 1-3 and Comparative Examples 1-3

[0050]

[0051]

[0052] The data in the table show that the 24-hour compressive strength of the filling paste (S1-S3) of the present invention reaches 4.8-5.5 MPa, which is 60%-83% higher than that of the traditional paste (≤3 MPa); the 72-hour strength reaches 12.5-15.8 MPa, meeting the early strength requirements of mine filling. The 28-day strength has no attenuation, and the long-term stability is excellent, significantly better than the traditional cement-based paste. The slump reaches 255-270 mm, and the pipeline transportation resistance is reduced to 0.07-0.09 MPa / m, which can reduce pipeline wear and energy consumption and meet the requirements of long-distance pumping.

[0053] Nano-silica enhances the microstructure by forming C-S-H gel. When replaced with ordinary silica fume (F1), the compressive strength decreases significantly. The surface modifier hydrophobically modifies the particle surface, reducing the van der Waals force. When not added (F2), the slump decreases, the pipeline transportation resistance increases, and the long-distance pumping is difficult.

[0054] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An early-strength low-resistance long-distance conveying filling paste, characterized in that, It is composed of the following components by weight fraction: 1% - 2% of nano-silica, 0.1% - 0.5% of microbial inoculant, 25% - 35% of low-quality fly ash, 40% - 60% of fine aggregate, 0.5% - 3% of suspending agent, 1% - 5% of water reducing agent, 0.1% - 2% of surfactant, 0.1% - 3% of surface modifier, 0.5% - 2% of urea, 10% - 30% of water, and the sum of the weight fractions of the above components is 100%.

2. The early-strength low-resistance long-distance transported filling paste according to claim 1, characterized in that The average particle size of the nano-silica is 15 to 20 nanometers, and the specific surface area is 200 to 400 m 2 / g.

3. The early-strength low-resistance long-distance conveying filling paste according to claim 1, wherein The microbial inoculant is one or both of spherical bacillus inoculant or thermophilic bacillus inoculant, and is a freeze-dried powder with viable bacteria count ≥ 1×109 CFU / g.

4. The early-strength low-resistance long-distance conveying filling paste according to claim 1, wherein The low-quality fly ash is class II or class III fly ash discharged from coal-fired power plants, with loss on ignition ≤ 8% and residue on 45μm sieve ≤ 25%.

5. The early-strength low-resistance long-distance conveying filling paste according to claim 1, characterized in that The fine aggregate is any one of crushed coal gangue, metal mine tailings or desert sand; when in use, the fine aggregate is crushed and screened to a particle size of ≤2.36 mm and a specific surface area of ≥300 m 2 / kg.

6. The early-strength low-resistance long-distance transported filling paste according to claim 1, wherein The suspending agent is one or both of sodium carboxymethyl cellulose, sodium polyacrylate, xanthan gum, hydroxypropylated starch or acetylated starch.

7. The early-strength low-resistance long-distance transported filling paste according to claim 1, characterized in that, The water reducing agent is one or both of naphthalene series water reducing agent, aliphatic water reducing agent, polycarboxylate water reducing agent or melamine formaldehyde resin water reducing agent.

8. The early-strength low-resistance long-distance transported filling paste according to claim 1, wherein The surfactant is one or both of fatty acid methyl ester ethoxylate, polyoxyethylene castor oil, alkylphenol polyoxyethylene ether or polyvinylpyrrolidone; the surface modifier is one or both of silane coupling agent, polysaccharide derivatives, polyacrylic acid and its salts, polyvinyl alcohol or polyacrylic acid resin.

9. The early-strength low-resistance long-distance transported filling paste according to claim 1, characterized in that The mass ratio of the urea to the microbial inoculant is 2:1 - 6:

1.

10. The preparation method of the early-strength low-resistance long-distance conveying filling paste according to claim 1, characterized in that, It includes the following steps: S1 Inoculant activation: Pre-culture and activate the microbial inoculant at a temperature of 20 - 40°C. S2 Mixing and stirring: Add low-quality fly ash, fine aggregate, nano-silica, suspending agent, water reducing agent, surfactant, surface modifier, urea and water in sequence, stir and mix evenly; finally add the activated inoculant in step S1, and continue to stir until a uniform and stable mixture is formed.

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