A terminal accelerator and its preparation method and application

Abstract

The present application relates to a kind of end accelerator and its preparation method and application, belong to mining filling mining technical field.End accelerator includes the following mass percentages of components: aluminum sulfate 20%~28%, sodium metaaluminate 5%~10%, calcium formate 6%~10%, nano-silica sol 8%~15%, graphene oxide dispersion 1%~3%, triethanolamine 1.5%~3.0%, polycarboxylic acid dispersant 1.5%~3.0%, thickening stabilizer 0.1%~0.3%, and the balance is water.Among them, aluminum sulfate and sodium metaaluminate constitute double aluminum phase accelerator system, quickly generate ettringite in paste alkaline environment, realize rapid coagulation;Nano-silica sol provides nanoscale crystal nucleus effect, accelerates hydration reaction;Graphene oxide dispersion forms interface reinforcing network in cement hydration product, improve the interface combination of filling body and surrounding rock.

Description

Technical Field

[0001] This invention belongs to the field of mining backfilling technology, specifically relating to an end-setting accelerator, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Paste backfilling technology is one of the core technologies for controlling surface subsidence in coal and metal mines and achieving green mining. It uses solid waste such as coal gangue and fly ash as aggregates, and has advantages such as low cost, wide availability, and significant environmental benefits. In actual operation, pastes containing fly ash, coal gangue, and other components are prepared at the mixing plant. These pastes are then transported to the filling sites via pipelines, typically 1 to 3 kilometers long. The pastes are required to solidify quickly after exiting the pipeline to achieve filling or sealing. Because the addition of fly ash prolongs the initial setting time of the paste, it is difficult to achieve the rapid operation requirement of "same-day filling and same-day sealing." Therefore, it is necessary to add quick-setting components to the paste. However, if quick-setting agents or early-strength agents are added in advance at the mixing plant, the paste is prone to premature solidification during the 1 to 3-kilometer pipeline transport process, leading to pipe blockage accidents. Therefore, a quick-setting agent addition point is usually added at the end of the paste delivery pipeline at a set distance from the filling point. The quick-setting agent is then incorporated into the paste to achieve rapid solidification of the paste at the filling point.

[0004] Existing sodium carbonate-sodium sulfate-silica system end-setting accelerators have poor compatibility with high fly ash content pastes and slow hydration product formation rates, which restricts the efficiency of underground mining operations. Existing aluminum-based inorganic cementitious accelerators are designed for shotcrete and are difficult to apply directly to end-filling scenarios in mine pastes. They also exhibit reduced effectiveness at high fly ash content, and are prone to problems such as false setting and stagnant strength in later stages. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an end-setting agent, its preparation method, and its application. It employs a fully soluble liquid additive, constructs a dual-aluminum phase quick-setting system through soluble aluminum salts, and combines the nucleation effect of nano-silica and the interfacial reinforcement effect of graphene oxide to achieve rapid solidification and early high-strength development of the paste after addition at the end of the pipeline.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, an end-setting accelerator comprises the following components by mass percentage: Aluminum sulfate 20%~28%, sodium aluminate 5%~10%, calcium formate 6%~10%, nano silica sol 8%~15%, graphene oxide dispersion 1%~3%, triethanolamine 1.5%~3.0%, polycarboxylic acid dispersant 1.5%~3.0%, thickening stabilizer 0.1%~0.3%, balance water.

[0007] Secondly, the preparation method of the aforementioned terminal quick-setting agent includes: mixing and dispersing nano-silica sol, graphene oxide dispersion, polycarboxylic acid dispersant and water accounting for 20-40 wt% of the total water volume to obtain a pre-dispersion; adding aluminum sulfate, sodium aluminate, calcium formate and triethanolamine to the remaining water, stirring to obtain a solution, and then sequentially adding the pre-dispersion and thickening stabilizer to the solution, and continuing to stir to obtain the terminal quick-setting agent.

[0008] Thirdly, the application of the aforementioned terminal accelerator includes: mixing the terminal accelerator with the paste filling system in a ratio of (1.5~3.0):(97~98.5) to obtain an accelerator filling mixture, which is then injected into the goaf.

[0009] The beneficial effects of this invention are as follows: This invention replaces traditional alumina clinker and sulfoaluminate cement with aluminum sulfate and sodium aluminate, fundamentally solving the technical problem of pipe blockage during long-distance transportation of powdered accelerators. Aluminum sulfate and sodium aluminate form a dual-alumina phase accelerator system, rapidly generating ettringite in the alkaline environment of the paste, achieving rapid setting. Nano-silica sol provides a nanoscale nucleation effect, accelerating the hydration reaction. Graphene oxide dispersion forms an interface-reinforcing network in the cement hydration products, improving the interfacial bonding between the filling material and the surrounding rock. The synergistic effect of these three components achieves a balance between rapid setting and early strength. Through the synergistic activation of soluble aluminum and calcium salts, even with a fly ash content of 30-50 wt%, the initial setting time can still be controlled within 60 minutes, the compressive strength reaches 1.8-2.5 MPa at 8 hours, and 3.5-4.5 MPa at 24 hours, effectively overcoming the retarding effect of fly ash. Detailed Implementation

[0010] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0011] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0012] The existing sodium carbonate-sodium sulfate-silica system has poor compatibility with high fly ash paste. When the fly ash content is 30~50wt%, the initial setting time of the paste is still as long as 4~6h, which is far from meeting the requirement of ≤1h for initial setting in engineering. Moreover, it cannot destroy the inert glassy surface layer of fly ash, the hydration product generation rate is slow, and the filling body has basically no effective compressive strength after 8h, which seriously restricts the efficiency of underground mining. Aluminum-based inorganic cementitious accelerators are designed specifically for shotcrete and are difficult to apply to end-fill scenarios: Spray-type accelerators set instantly in seconds, and after end-fill injection, the viscosity of the slurry increases sharply and the pipe pressure surges, resulting in uneven material mixing and easy premature solidification and blockage in downstream short pipelines, preventing the slurry from flowing and spreading in the goaf; moreover, their formula cannot target and activate the active components of fly ash, and is only suitable for pure cement systems. Under high fly ash conditions, the accelerator effect is greatly reduced, and false setting and stagnation of strength in the later stage are likely to occur; the bonding force between the filling body and the roadway roof and floor and the surrounding rock interface is weak, and it is easy to delaminate and generate separation cracks under pressure, creating hidden dangers for roof support safety.

[0013] One or more embodiments of the present invention provide an end-setting accelerator comprising the following components by mass percentage: Aluminum sulfate 20%~28%, sodium aluminate 5%~10%, calcium formate 6%~10%, nano silica sol 8%~15%, graphene oxide dispersion 1%~3%, triethanolamine 1.5%~3.0%, polycarboxylic acid dispersant 1.5%~3.0%, thickening stabilizer 0.1%~0.3%, balance water.

[0014] Of the above components, aluminum sulfate contains aluminum ions (Al³⁺). + ) and the aluminate ions (AlO2) of sodium aluminate - In the alkaline environment of the paste, it not only reacts rapidly with Ca(OH)2 produced by cement hydration to form ettringite (AFt), but more importantly, Al³⁺… + With AlO2 -When coexisting, the common ion effect accelerates the breaking of AlSi bonds on the surface of fly ash glass, and the superposition of charge neutralization and dissolution overcomes the retarding effect of fly ash, achieving an effect that cannot be achieved by a single aluminum phase. Nano-silica sol provides nucleation sites with ultra-high specific surface area, inducing rapid precipitation of CSH gel; graphene oxide (GO) chemically bonds with CSH through its oxygen-containing functional groups on its surface, constructing a 'nano-micro' cross-scale reinforcing network, which improves the interfacial bonding strength between the infill and the surrounding rock by more than 30% while accelerating the setting process. Through the synergy of polycarboxylic acid dispersant and thickening stabilizer, the high concentration of aluminum salt and nanoparticles are kept uniformly dispersed in the liquid, solving the risk of sedimentation and pipe blockage in pipelines of traditional powder accelerators, and enabling the fully soluble product to have a storage stability period of more than 6 months.

[0015] The functions of triethanolamine include the following: Accelerating the dissolution and complexation of aluminate minerals. Triethanolamine molecules contain amino and hydroxyl groups, which can react with Al in solution. 3+ This process forms a stable, soluble complex. This complexation prevents premature hydrolysis and precipitation of aluminum ions during storage, extending the product's shelf life. Furthermore, when the quick-setting agent is incorporated into the alkaline environment of the paste, the complex rapidly dissociates, uniformly releasing active Al. 3+ This ensures that the formation reaction of ettringite (AFt) occurs synchronously and efficiently throughout the entire system, avoiding uneven localized rapid setting. Triethanolamine promotes the hydration of C3A and C4AF in cement, acting as a cement hydration accelerator, particularly exhibiting a significant catalytic effect on the early hydration of tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF). In a paste-like environment, triethanolamine accelerates the precipitation of hydration products from these mineral phases, providing sufficient Ca(OH)2 and an active aluminum matrix for ettringite formation, forming a positive feedback synergistic effect with the dual-aluminum phase system, further shortening the initial setting time. It can also improve the early microstructure of the filler. While promoting hydration, triethanolamine can regulate the crystal morphology and size of the hydration products, resulting in finer, more uniform, and denser ettringite crystals. This optimized microstructure is beneficial for improving the early strength of the filler, complementing the nucleation effect of nano-silica and the interfacial reinforcement effect of graphene oxide, jointly achieving a balance between rapid setting and early strength.

[0016] Optionally, aluminum ions (Al³⁺) in aluminum sulfate + ) and the aluminate ions (AlO2) of sodium aluminate -The molar ratio of Al to Si is 1:(0.037~1.04); preferably, the molar ratio is 1:(0.5~1.0), more preferably, the molar ratio is 1:0.7~1.0; this molar ratio can overcome the retarding effect of fly ash and achieve the effect that a single aluminum phase cannot achieve: the retarding effect of fly ash mainly stems from the dense Si-O-Al network structure on its glassy surface, which dissolves slowly in an alkaline environment, resulting in extremely low dissolution rates of active Al and Si, which cannot quickly participate in the hydration reaction. A single aluminum phase (containing only Al) 3+ Or containing only AlO2 - Excitation can only be performed from a single charge direction, resulting in low efficiency; however, this invention precisely controls Al³⁺. + With AlO2 - Based on the aforementioned molar ratio, a "two-aluminum phase synergistic excitation system" was constructed, the mechanism of which is as follows: Bidirectional charge neutralization and ion pair attack, Al... 3+ Carrying a positive charge, while AlO2 - Carrying a negative charge; in the alkaline environment of the paste, both coexist in the same liquid phase system, respectively affecting the negatively charged Si-O on the glassy surface of fly ash. - Site and positively charged Al + The sites are attacked synchronously; this "positive-negative" bidirectional neutralization greatly weakens the stability of the vitreous network structure, and its destructive efficiency far exceeds that of a single-charge aluminum ion. Maintaining a locally high concentration of aluminum chemical potential drives dissolution equilibrium, when Al... 3+ With AlO2 - When the molar ratio of aluminum to hydroxyl groups is in the range of 1:(0.5~1.0), a partial pre-reaction occurs, forming a highly reactive hydroxyl aluminum polymer precursor. These precursors create a "chemical potential field" on the surface of fly ash particles that maintains a high aluminum concentration gradient. Through the common ion effect, this accelerates the breaking of Al-Si bonds in the fly ash glass and the continuous dissolution of active aluminum silicon. Due to the "lock-in" effect of uniform precipitation, ettringite produced by a single aluminum phase often appears as needle-like or long columnar shapes with disordered growth direction. It tends to grow rapidly in localized areas, forming a loose skeleton that cannot effectively encapsulate fly ash particles. Under the aforementioned molar ratio, the dual aluminum phase can make the generated ettringite crystals more closely resemble fine, short columnar or granular shapes. These crystals, along with the silicon and aluminum species dissolved from the surface of fly ash particles, precipitate together to form a dense reaction ring, "locking" the fly ash particles within the overall hydration network. This completely overcomes the technical bottlenecks of "rapid setting without early strength" and "incompatibility with high fly ash content" that occur when simply increasing the dosage of a single aluminum salt. It achieves controllable rapid setting and synergistic early strength under high fly ash content conditions.

[0017] Optionally, the solid content of the nano-silica sol is 25-35 wt%, wherein the nano-silica particles with a D50 of 10-30 nm are added in the form of nano-silica sol; then the nano-silica content in the end-setting accelerator is 2.0-5.3 wt%, used to provide nucleation sites and induce rapid precipitation of CSH gel. Compared with other silicas that can provide nucleation sites (such as silica fume, fumed silica, etc.), nano-silica has the following advantages: It has a large number of nucleation sites, with a particle size of only 10-30 nm, much smaller than silica fume (150-300 nm). At the same dosage, it provides hundreds of times more nucleation sites, inducing rapid and dense precipitation of CSH gel. It has higher reactivity, with a surface rich in highly active silanol groups, and can react rapidly with cement hydration products Ca(OH)2 at room temperature to generate CSH gel in situ, eliminating the weak interface between traditional nucleating agents and the matrix. It exhibits superior dispersibility and stability, being added in a pre-dispersed sol form. The nanoparticles are already in a monodisperse state, eliminating the need for shear deagglomeration like powder materials, allowing for instantaneous and uniform dispersion in the paste and preventing localized clumping. It also possesses a physical filling effect; the extremely fine particle size can fill the nanoscale pores between CSH gel layers, achieving a synergistic effect of "chemical nucleation + physical filling," resulting in a denser matrix and higher early strength.

[0018] Optionally, if the solid content of the graphene oxide dispersion is 0.5~1.0 wt% and the graphene oxide sheet diameter is 0.5~5 μm, then the graphene oxide content in the end-forming agent is 0.005~0.03 wt%. The oxygen content of the graphene oxide is 30~50%, which refers to the mass percentage of oxygen in the graphene oxide, determined by X-ray photoelectron spectroscopy (XPS). Too low an oxygen content (<30%) will result in poor hydrophilicity of the graphene oxide, easy aggregation in water, insufficient surface active sites, and a significant weakening of the interface enhancement effect; too high an oxygen content (>50%) will result in increased lattice defects, decreased mechanical properties, and interaction with Ca. 2+ Excessive cross-linking leads to localized flocculation and significantly increases costs; an oxygen content of 30-50% is the optimal range that balances water dispersibility, interfacial enhancement, structural integrity, and economy.

[0019] Optionally, the thickening stabilizer is xanthan gum or zeolite; used to improve the product's storage stability.

[0020] Optionally, it also includes 2-5% ethylene glycol. Ethylene glycol, as an antifreeze, is suitable for low-temperature environments below 5°C and can be stored and used in low-temperature environments.

[0021] Optionally, the pH of the terminal accelerator is 6.0–7.5, adjusted by citric acid or sodium hydroxide as a pH adjuster. This pH ensures the stability of the two-aluminum phase system (Al). 3+ With AlO2 -It can coexist stably within a neutral range, avoiding hydrolysis and precipitation during storage; it can also achieve a targeted response of "inert during storage and rapid solidification upon contact with alkali", ensuring rapid formation of ettringite after mixing with alkaline pastes; at the same time, it takes into account operational safety and compatibility with organic components, avoiding problems of acid corrosion or alkaline precipitation; it also works synergistically with triethanolamine and nano silica to precisely control the rapid solidification reaction window.

[0022] One or more embodiments of the present invention provide a method for preparing the above-mentioned terminal accelerator, comprising: mixing and dispersing nano-silica sol, graphene oxide dispersion, polycarboxylic acid dispersant and water accounting for 20-40 wt% of the total water volume to obtain a pre-dispersion; adding aluminum sulfate, sodium aluminate, calcium formate and triethanolamine to the remaining water, stirring to obtain a solution, and then sequentially adding the pre-dispersion and thickening stabilizer to the solution, and continuing to stir to obtain the terminal accelerator.

[0023] In the above process, a pre-dispersion solution is first prepared, then added to the solution, and finally a thickener and stabilizer are added. In the pre-dispersion stage: the nanomaterials are pre-stabilized to prevent salting-out and agglomeration; adverse reactions occur due to direct contact between aluminum salts and nanomaterials; the system viscosity is reduced, and dispersion efficiency is improved. In the stage of adding the pre-dispersion solution, the nano-components are gently introduced, avoiding excessively high local concentrations; the dual-aluminum phase system is preferentially established; and temperature rise and pH fluctuations during mixing are controlled. Finally, the thickener is added: to prevent the thickener from interfering with the initial dispersion effect; to prevent complexation precipitation between the thickener and aluminum salts; and to achieve final viscosity control and suspension stability of the product. The core logic of this "three-step progressive" sequence is: first, to stabilize the most difficult-to-disperse nanomaterials under optimal conditions; then, to gently introduce them into the already balanced aluminum salt system; and finally, to control viscosity based on the completed dispersion. These three steps work together to ensure the effectiveness of the product's microscopic uniformity, storage stability, and rapid solidification function.

[0024] Optionally, the mass percentage of ethylene glycol added is 2-5%. Ethylene glycol is added during the solution preparation stage of the preparation method, i.e., it is dissolved in the remaining water along with aluminum sulfate, sodium aluminate, calcium formate, and triethanolamine. This is because ethylene glycol is completely miscible with water, and adding it together with inorganic salts is simple; it also avoids introducing interference with the dispersion stability of nanomaterials during the pre-dispersion stage; it prevents uneven mixing or damage to the thickening network caused by adding it in the final stage; and it ensures that the antifreeze is uniformly distributed at the molecular level in the system.

[0025] Optionally, the mixing and dispersion method includes stirring at 800~1200 rpm for 15~20 min.

[0026] Optionally, the temperature during the stirring and dissolving process should not exceed 40℃. Excessive temperature can lead to: aluminum sulfate hydrolysis to form aluminum hydroxide precipitate, resulting in the loss of active aluminum; sodium aluminate hydrolysis, disrupting the dual aluminum phase equilibrium; gelation of nano-silica sol, resulting in the loss of the crystal nucleation effect; thermal desorption of oxygen-containing functional groups in graphene oxide, weakening the reinforcing effect; oxidative decomposition of triethanolamine, reducing the hydration-promoting effect; and affecting the batch stability of the product.

[0027] Optionally, the method of obtaining the solution by stirring includes stirring at 400-600 rpm for 10-15 minutes.

[0028] Optionally, the solution is kept stirred during the addition of the pre-dispersion liquid and thickening stabilizer, and the pre-dispersion liquid and thickening stabilizer are added slowly.

[0029] Optionally, after adding the thickener and stabilizer, continue stirring for 20-30 minutes to promote uniform dispersion of all components.

[0030] Optionally, the following steps may also be included: adding citric acid or sodium hydroxide to adjust the pH of the system to 6.0~7.5; the main reason being to ensure Al 3+ With AlO2 - It can coexist stably under near-neutral conditions, avoiding hydrolysis and precipitation during storage; at the same time, it achieves a targeted response of "inert during storage and rapid coagulation upon contact with alkali", ensuring rapid formation of ettringite after mixing with alkaline paste; and it takes into account both equipment safety and compatibility with organic components.

[0031] Optionally, the process may also include: filtration through a 150-250 mesh filter followed by packaging; this is primarily to remove undispersed nano-agglomerates and trace amounts of insoluble matter, prevent stratification and sedimentation during storage, ensure smooth operation of the product in metering pumps and pipelines, avoid clogging, and improve the product's appearance quality.

[0032] One or more embodiments of the present invention provide the application of the above-mentioned terminal quick-setting agent, including: mixing the terminal quick-setting agent with the paste filling system in a ratio of (1.5~3.0):(97~98.5) to obtain a quick-setting filling mixture, and injecting it into the goaf.

[0033] Optionally, the quick-setting filler mixture contains 2.0 wt% of an end-setting quick-setting agent.

[0034] Optionally, the paste filling system comprises the following components in parts by weight: 30-50 parts fly ash, 8-15 parts cement, 35-55 parts coal gangue, and 18-25 parts water, all of which are parts by weight; wherein the fly ash content is as high as 30-50 parts, accounting for 67%-86% of the total cementitious material, which belongs to a high fly ash paste system; the terminal accelerator of the present invention, through the synergistic activation of the dual aluminum phase, can effectively destroy the inert glassy surface layer of fly ash, and can still achieve rapid setting and early strength development under high fly ash content conditions.

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] Example 1 An end-setting accelerator comprises the following components by weight percentage: The composition is as follows: 24% aluminum sulfate, 8% sodium aluminate, 8% calcium formate, 11% nano silica sol, 2% graphene oxide dispersion, 2.2% triethanolamine, 2.2% polycarboxylic acid dispersant, 0.2% thickening and stabilizing agent, and the balance is water.

[0037] The above components include: aluminum sulfate (industrial grade, purity ≥99%); sodium aluminate (industrial grade, purity ≥98%); calcium formate (industrial grade, purity ≥98%); nano-silica sol (purchased, solid content 30%, particle size D50 = 10~30nm); graphene oxide dispersion (purchased, solid content 0.5%~1.0%, flake size 0.5~5μm, oxygen content ≥30%); triethanolamine (industrial grade, purity ≥99%); polycarboxylic acid dispersant (industrial grade, solid content 40%); and a thickening and stabilizing agent, Wenlun colloid (food grade, purity ≥99%). All raw materials are commercially available and do not require in-house preparation.

[0038] Preparation methods include: Nano-silica sol, graphene oxide dispersion, polycarboxylic acid dispersant, and water accounting for 30 wt% of the total water volume were mixed and dispersed, and stirred at 1000 rpm for 18 min to obtain a pre-dispersion.

[0039] Add aluminum sulfate, sodium aluminate, calcium formate, and triethanolamine to the remaining water, and stir at 500 rpm for 13 minutes until completely dissolved to obtain a solution. During the process, control the temperature to not exceed 40°C.

[0040] While keeping the solution stirred, slowly add the pre-dispersed liquid while stirring at 500 rpm for 13 minutes to obtain the solution.

[0041] Continue stirring, slowly sprinkle the thickening and stabilizing agent into the solution, and continue stirring for 25 minutes.

[0042] Add citric acid or sodium hydroxide to adjust the pH of the system to 7.0±0.5, filter through a 200-mesh filter, and package.

[0043] Example 2 An end-setting accelerator comprises the following components by weight percentage: The composition is as follows: 20% aluminum sulfate, 5% sodium aluminate, 6% calcium formate, 8% nano silica sol, 1% graphene oxide dispersion, 1.5% triethanolamine, 1.5% polycarboxylic acid dispersant, 0.1% thickening and stabilizing agent, and the balance is water.

[0044] The requirements for each raw material and the preparation method are the same as in Example 1.

[0045] Example 3 An end-setting accelerator comprises the following components by weight percentage: The composition is as follows: 28% aluminum sulfate, 10% sodium aluminate, 10% calcium formate, 15% nano silica sol, 3% graphene oxide dispersion, 3.0% triethanolamine, 3.0% polycarboxylic acid dispersant, 0.3% thickening and stabilizing agent, and the balance is water.

[0046] The requirements for each raw material and the preparation method are the same as in Example 1.

[0047] Example 4 An end-setting accelerator comprises the following components by weight percentage: Aluminum sulfate 28%, sodium aluminate 10%, calcium formate 10%, nano silica sol 15%, graphene oxide dispersion 3%, triethanolamine 3.0%, polycarboxylic acid dispersant 3.0%, thickening stabilizer 0.3%, ethylene glycol 3.5%, balance water.

[0048] The difference from Example 1 is that ethylene glycol is added to the components; in the preparation method, ethylene glycol is added together with aluminum sulfate, sodium aluminate, calcium formate and triethanolamine in the step of adding aluminum sulfate, sodium aluminate, calcium formate and triethanolamine to the remaining water.

[0049] The requirements and preparation methods for other raw materials are the same as in Example 1.

[0050] Comparative Example 1 An end-setting accelerator differs from Example 1 in that it does not contain nano-silica sol, while the other raw materials and preparation methods are the same as in Example 1.

[0051] Comparative Example 2 An end-setting accelerator, which differs from Example 1 in that sodium aluminate is not added, while other raw materials and preparation methods are the same as in Example 1.

[0052] Comparative Example 3 An end-setting accelerator, which differs from Example 1 in that it does not contain triethanolamine.

[0053] Example 5 The terminal quick-setting agents prepared in Examples 1-4 and Comparative Examples 1-3 were mixed with the paste filling system at a mass ratio of 2.0:98.0 to obtain quick-setting filling mixtures, which were then injected into the goaf.

[0054] The paste filling system includes the following components by weight: 40 parts fly ash, 10 parts cement, 45 parts coal gangue, and 20 parts water; among which, the fly ash content accounts for 80% of the total amount of cementitious materials (fly ash + cement), which belongs to a high-content fly ash paste system.

[0055] The preparation method of the paste filling system includes: pre-stirring each component evenly to simulate the state after transportation in a 1-3 km pipeline; then adding the end-setting agent under high-speed stirring conditions and continuing stirring for 30 seconds to simulate the mixing process at the end-setting agent addition point of the pipeline.

[0056] The performance tests include: flowability, initial setting time, compressive strength, 2-hour slump loss, interfacial bond strength, and storage stability. The test methods for each property are as follows.

[0057] Flowability: The slump cylinder method is used for testing. The mixed slurry is filled with a standard slump cylinder, lifted vertically, and the slump height of the slurry is measured (unit: cm). The larger the value, the better the flowability and the better the pumpability. The qualified standard is: slump ≥ 18cm.

[0058] Initial setting time: Refer to GB / T1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", and use a Vicat apparatus for testing. Pour the mixed slurry into a mold and cure under standard curing conditions (20±1℃, relative humidity ≥95%). Periodically test with a test needle until the needle sinks 4±1mm into the slurry from the bottom plate; record the time. This is the initial setting time. Acceptable standard: ≤60min.

[0059] Compressive strength: The mixed slurry was injected into a triple mold of 70.7mm×70.7mm×70.7mm. The molds were cured for 8h and 24h under standard curing conditions (20±1℃, relative humidity ≥95%). The compressive strength (unit: MPa) was tested using a pressure testing machine at a loading rate of 0.5~0.8MPa / s. The average value of 3 specimens in each group was taken.

[0060] 2-hour slump loss: The mixed slurry is left to stand at room temperature for 2 hours (simulating the transportation time of 1-3 kilometers of pipeline), and the slump is tested again. The difference between the initial slump and the slump after 2 hours is calculated (unit: cm). The smaller the difference, the stronger the fluidity of the slurry in the pipeline and the lower the risk of pipe blockage.

[0061] Interfacial bond strength: The mixed grout is poured onto the surface of the pre-prepared simulated surrounding rock (sandstone). After standard curing for 28 days, the interfacial bond strength between the filling body and the surrounding rock is tested using the splitting method (unit: MPa). Five specimens are tested in each group and the average value is taken. This index reflects the integrity of the filling body with the roadway roof and floor and the surrounding rock. The larger the value, the lower the risk of delamination and separation.

[0062] Storage stability period: Take 500 mL of each of the terminal accelerators prepared in each example and comparative example, put them into sealed polyethylene plastic bottles, and store them at room temperature (25±2℃). Observe the appearance of the products periodically and test the pH value and the effective ingredient (Al). 3+ The rate of change of concentration; the storage stability period (unit: month) is defined as the time during which the product does not separate into layers, precipitate, or gel, the pH fluctuation is ≤ ±0.5, and the retention rate of active ingredients is ≥ 95%.

[0063] The results are shown in Table 1.

[0064] Table 1

[0065] As can be seen from Table 1: In terms of flowability, the slump of Examples 1-4 was 21-23 cm, all greater than 18 cm, which meets the requirements for pipeline pumping; Comparative Example 2 was 20 cm, slightly lower than the other samples, but still pumpable.

[0066] Regarding the initial setting time, the initial setting time of Examples 1 to 4 was 43 to 53 minutes, all ≤60 minutes, which met the engineering requirement of "filling and sealing on the same day"; Comparative Example 2 was as long as 85 minutes, which could not meet the requirements for rapid filling.

[0067] Regarding compressive strength, the 8-hour compressive strength of Examples 1-4 was 1.9-2.4 MPa, and the 24-hour compressive strength was 3.7-4.5 MPa, both significantly better than the comparative examples (8-hour strength 0.7-1.4 MPa, 24-hour strength 1.6-2.5 MPa). Among them, Example 3 showed the best results.

[0068] Regarding the slump loss over 2 hours, the slump loss in Examples 1-4 was only 2 cm, and the slurry maintained good fluidity after being transported through the simulated pipeline, with no risk of pipe blockage. Comparative Examples 1 and 3 showed a loss of 4 cm, and Comparative Example 2 showed a loss of 5 cm, indicating a potential risk of pipe blockage.

[0069] Regarding the interfacial bond strength, the 28-day interfacial bond strength of Examples 1-4 was 1.0-1.3 MPa, which is 33%-58% higher than that of the comparative example (0.5-0.8 MPa). This indicates that the interfacial reinforcement network of graphene oxide effectively improves the integrity of the infill and the surrounding rock and reduces the risk of delamination and separation.

[0070] Regarding the storage stability period, the storage stability period of Examples 1 to 4 is ≥6 months, and the products do not separate or precipitate during long-term storage; the stability period of Comparative Examples 1 to 3 is only 2 to 3 months, and precipitation, separation or gelation occurs.

[0071] The above analysis shows that this invention, through a dual-aluminum phase synergistic and nano-modified liquid end-setting accelerator, precisely controls the accelerator reaction window, efficiently activates fly ash activity, and simultaneously achieves rapid setting, early strength, interfacial enhancement, and pipeline transportation safety. The end-setting accelerators (Examples 1-4) in high-fly ash (80%) paste systems achieve comprehensive superior performance in terms of rapid setting, early strength, high fluidity retention, strong interfacial adhesion, and long-term storage stability, fully meeting the rapid operation requirements of "same-day filling and same-day sealing" for mine paste filling.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A terminal accelerator, characterized in that, Components including the following mass percentages: Aluminum sulfate 20%~28%, sodium aluminate 5%~10%, calcium formate 6%~10%, nano silica sol 8%~15%, graphene oxide dispersion 1%~3%, triethanolamine 1.5%~3.0%, polycarboxylic acid dispersant 1.5%~3.0%, thickening stabilizer 0.1%~0.3%, balance water.

2. The terminal accelerator as described in claim 1, characterized in that, The solid content of the nano silica sol is 25~35wt%, and the particle size D50 of the nano silica contained therein is 10~30nm; Alternatively, the molar ratio of aluminum ions in the aluminum sulfate to aluminate ions in the sodium aluminate is 1:0.37~1.04; preferably, the molar ratio is 1:0.5~1.0; more preferably, the molar ratio is 1:0.7~1.

0.

3. The terminal accelerator as described in claim 1, characterized in that, The solid content of the graphene oxide dispersion is 0.5~1.0wt%, and the graphene oxide sheet diameter is 0.5~5μm; or, the oxygen content of the graphene oxide is 30~50%.

4. The terminal accelerator as described in claim 1, characterized in that, The thickening stabilizer is xanthan gum or hummus; Alternatively, it may also include 2-5% ethylene glycol; Alternatively, the pH of the terminal accelerator may be 6.0 to 7.

5.

5. A method for preparing an end-setting accelerator as described in any one of claims 1-4, characterized in that, Nano-silica sol, graphene oxide dispersion, polycarboxylic acid dispersant, and water accounting for 20-40 wt% of the total water volume are mixed and dispersed to obtain a pre-dispersion. Aluminum sulfate, sodium aluminate, calcium formate, and triethanolamine are added to the remaining water, and the mixture is stirred to obtain a solution. The pre-dispersion and thickening stabilizer are added to the solution in sequence, and stirring is continued to obtain the terminal quick-setting agent.

6. The method for preparing the terminal accelerator as described in claim 5, characterized in that, When the formula contains ethylene glycol, the ethylene glycol, along with aluminum sulfate, sodium aluminate, calcium formate, and triethanolamine, is added to the remaining water and dissolved.

7. The method for preparing the terminal accelerator as described in claim 5, characterized in that, Mixing and dispersing methods include: stirring at 800~1200 rpm for 15~20 min; Alternatively, the method of obtaining the solution by stirring includes: stirring at 400~600 rpm for 10~15 min; Alternatively, the temperature during the stirring and dissolving process should not exceed 40°C; Alternatively, the solution can be stirred while adding the pre-dispersant and thickening stabilizer.

8. The method for preparing the terminal accelerator as described in claim 5, characterized in that, It also includes the step of adding citric acid or sodium hydroxide to adjust the pH of the system to 6.0~7.

5.

9. An application of the terminal accelerator as described in any one of claims 1-4, characterized in that, The terminal quick-setting agent and the paste filling system are mixed in a ratio of (1.5~3.0):(97~98.5) to obtain a quick-setting filling mixture, which is then injected into the goaf.

10. The application as described in claim 9, characterized in that, The quick-setting filler mixture contains 2.0 wt% of terminal quick-setting agent; Alternatively, the paste filling system may comprise the following components in parts by weight: 30-50 parts fly ash, 8-15 parts cement, 35-55 parts coal gangue, and 18-25 parts water.

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