A set accelerator for shotcrete and a method for preparing the same

Abstract

The application belongs to the technical field of building materials, and particularly relates to a rapid hardener for shotcrete and a preparation method thereof. The rapid hardener for shotcrete comprises the following raw materials in parts by weight: aluminum sulfate 50-70 parts, magnesium sulfate 10-25 parts, modified aluminum hydroxide 10-17 parts, triethanolamine 8-12 parts, stabilizer 5-10 parts, and water 60-70 parts. The rapid hardener is designed and improved in formula, and can not only realize rapid hardening, but also provide sustained and stable early strength growth, avoid premature consumption of the rapid hardener, provide moisture for the continuous hydration of cement in the later period, and help maintain the later strength of the concrete. In addition, the rapid hardener can also reduce the rebound loss in the spraying process, effectively wrap and adsorb fine particles, reduce construction dust, improve construction efficiency, and ensure the long-term stability of components, and is a high-performance rapid hardener for shotcrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a quick-setting agent for shotcrete and its preparation method. Background Technology

[0002] Shotcrete is a type of concrete that uses compressed air or other power sources to spray a concrete mixture prepared in a specific ratio at high speed onto a target surface, where it rapidly sets and hardens to form a dense concrete layer. It is widely used in tunnel engineering, slope protection, building reinforcement, underground engineering, and many other fields. Its core advantages lie in its high construction efficiency and its ability to bond tightly to rock surfaces of various shapes, forming a robust support system. Accelerators enable rapid setting of concrete and are commonly used admixtures in shotcrete; their performance directly determines the quality of shotcrete projects. Early accelerators were high-alkali accelerators represented by sodium aluminate and sodium silicate. While they achieved rapid setting, the large amount of alkali metal ions they introduced led to significant strength loss in the later stages of concrete development, affecting the long-term durability of the structure, and were also highly corrosive to construction workers. To overcome these shortcomings, accelerators with aluminum sulfate and magnesium sulfate as main components have emerged and become a current research hotspot. However, existing accelerator systems still face the following pressing problems in practical applications:

[0003] First, the core accelerator components of low-alkali quick-setting agents, such as aluminum sulfate, often aggregate and adsorb with highly surface-active aluminum hydroxide in the system. Aluminum hydroxide is rich in hydroxyl groups, which readily attract aluminum and magnesium ions in the solution through hydrogen bonds and Coulomb forces, forming aggregates. This aggregation not only reduces the storage stability of the quick-setting agent but also consumes effective accelerator ions in the system, resulting in fluctuating quick-setting effects and prolonged setting time, failing to meet the stringent requirements of rapid support in high-intensity construction. Second, to achieve rapid setting, existing quick-setting agents often rapidly and violently consume the active components in the system during the initial hydration stage. This may lead to a loose structure of early hydration products, making it difficult to guarantee later strength and even causing microcracks. Furthermore, the high rebound rate during shotcrete construction not only causes significant material waste but also reduces construction efficiency. Third, current quick-setting agents focus too much on improving the material's accelerator effect, neglecting its impact on the quick-setting agent's stability. Existing methods, such as adding thickeners, cannot effectively achieve long-term stable storage of quick-setting agents.

[0004] Therefore, by innovating component design and improving processes, it is possible to provide quick-setting agents for shotcrete that not only achieve rapid setting but also provide excellent early and late strength, reduce rebound loss during spraying, and ensure long-term stability of components and construction efficiency. These agents have broad application prospects. Summary of the Invention

[0005] The primary objective of this invention is to provide a quick-setting agent for shotcrete, which, through the design and improvement of its formulation, achieves excellent quick-setting effect, early strength, late strength, good workability, and storage stability, making it a high-performance quick-setting agent for shotcrete.

[0006] The second objective of this invention is to provide a method for preparing a quick-setting agent for shotcrete. The preparation method of this invention is simple, does not require harsh reaction conditions, and is beneficial to saving energy consumption and costs in the production process.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A quick-setting agent for shotcrete, comprising the following raw materials by weight: 50-70 parts aluminum sulfate, 10-25 parts magnesium sulfate, 10-17 parts modified aluminum hydroxide, 8-12 parts triethanolamine, 5-10 parts stabilizer, and 60-70 parts water.

[0009] The preparation process of the modified aluminum hydroxide is as follows: aluminum hydroxide is added to an aqueous ethanol solution, then chitosan and glyceric acid are added, and the mixture is heated to react and obtain modified aluminum hydroxide.

[0010] Furthermore, the mass ratio of aluminum hydroxide, chitosan, and glyceric acid is 1:(5-7):(6-9), and the volume ratio of aluminum hydroxide to ethanol aqueous solution is 1g:80-100mL.

[0011] Furthermore, the ethanol aqueous solution is prepared by mixing anhydrous ethanol and water in a volume ratio of (3-4):1.

[0012] Furthermore, the heating reaction is carried out at a temperature of 80-90°C for 2-5 hours.

[0013] Furthermore, the particle size of the aluminum hydroxide is 2-12 μm.

[0014] Furthermore, the weight-average molecular weight of the chitosan is 50,000-60,000 Da.

[0015] Furthermore, the stabilizer is composed of phosphotungstic acid and mannose erythritol ester.

[0016] Furthermore, the mass ratio of phosphotungstic acid to mannose erythritol ester is 1:(0.1-0.35).

[0017] A method for preparing a quick-setting agent for shotcrete, the method comprising the following steps: mixing and stirring aluminum sulfate, magnesium sulfate, modified aluminum hydroxide, triethanolamine, stabilizer and water according to the specified ratio to obtain the agent.

[0018] The beneficial technical effects of this invention are as follows:

[0019] 1. This invention discloses a quick-setting agent for shotcrete, which contains modified aluminum hydroxide. The aluminum hydroxide is modified by chitosan and glyceric acid. Glyceric acid can promote the adsorption of chitosan on the surface of aluminum hydroxide. The carboxyl group of glyceric acid can undergo amidation reaction with the amino group of chitosan or esterification reaction with the hydroxyl group. The hydroxyl group on glyceric acid can form hydrogen bonds with the hydroxyl group of chitosan, ultimately forming a three-dimensional network structure to encapsulate aluminum hydroxide particles.

[0020] The surface of aluminum hydroxide has a high concentration of hydroxyl groups, which easily aggregate and adsorb with aluminum sulfate and magnesium sulfate in accelerators, reducing the content of effective components in the accelerator and affecting the accelerating effect. This invention improves this aggregation and adsorption by modifying aluminum hydroxide with chitosan and glyceric acid, shortening the initial and final setting times. At the same time, the polymer layer encapsulating the surface of aluminum hydroxide has significant steric hindrance, which can improve its dispersibility in cement.

[0021] During cement hydration, the coating layer on the surface of aluminum hydroxide is destroyed. This surface coating can fill the pores of cement hydration products, improving the density of the concrete structure. Aluminum ions are released, increasing the aluminum ion content in the concrete and generating products such as ettringite that accelerate setting. This provides continuous and stable early strength growth and prevents the premature depletion of accelerators. The inertness of aluminum hydroxide itself can inhibit abnormal hydration reactions inside the cement. Glyceric acid has good water retention properties, providing moisture for the continued hydration of cement in the later stages, which helps maintain the later strength of the concrete. Chitosan can increase the viscosity of the concrete paste, reduce rebound loss during spraying, and effectively encapsulate and adsorb fine particles, reducing construction dust and improving construction efficiency.

[0022] 2. This invention uses phosphotungstic acid and mannoerythritol ester as stabilizers to improve the stability of the quick-setting agent during storage. The quick-setting agent for shotcrete of this invention can be stabilized for up to 1 year.

[0023] 3. This invention provides a method for preparing a quick-setting agent for shotcrete. The preparation process adopted in this invention is simple and does not require stringent reaction conditions. This method not only significantly reduces the investment in production equipment and the difficulty of operation, but also directly reduces energy consumption and costs in the production process, laying a solid foundation for achieving efficient and economical large-scale industrial production. Attached Figure Description

[0024] Figure 1 This is an electron microscope image of the modified aluminum hydroxide obtained in Example 1 of the present invention. Detailed Implementation

[0025] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0026] Example 1

[0027] A quick-setting agent for shotcrete, comprising the following raw materials by weight: 60 parts aluminum sulfate, 20 parts magnesium sulfate, 15 parts modified aluminum hydroxide, 10 parts triethanolamine, 8 parts stabilizer, and 65 parts water.

[0028] The preparation process of the modified aluminum hydroxide is as follows: Anhydrous ethanol and water are mixed at a volume ratio of 3:1 to prepare an ethanol-water solution. Aluminum hydroxide with a particle size of 2-12 μm is selected and added to the ethanol-water solution, controlling the ratio of aluminum hydroxide to ethanol-water solution to be 1 g:90 mL. Chitosan (weight average molecular weight of 50,000-60,000 Da) and glyceric acid are then added, with a mass ratio of aluminum hydroxide, chitosan, and glyceric acid of 1:6:7. The mixture is heated at 85 °C for 4 h. The resulting solution is filtered, washed three times with deionized water, and dried to obtain the modified aluminum hydroxide. The electron micrograph of the modified aluminum hydroxide is shown below. Figure 1 As shown.

[0029] The stabilizer mentioned above is composed of phosphotungstic acid and mannose erythritol ester (MEL-A) in a weight ratio of 1:0.2.

[0030] This embodiment also provides a method for preparing a quick-setting agent for shotcrete, the preparation method comprising the following steps: mixing and stirring aluminum sulfate, magnesium sulfate, modified aluminum hydroxide, triethanolamine, stabilizer and water according to the specified ratio to obtain the agent.

[0031] Example 2

[0032] A quick-setting agent for shotcrete, comprising the following raw materials by weight: 50 parts aluminum sulfate, 10 parts magnesium sulfate, 10 parts modified aluminum hydroxide, 8 parts triethanolamine, 5 parts stabilizer, and 60 parts water.

[0033] The preparation process of the modified aluminum hydroxide is as follows: Anhydrous ethanol and water are mixed at a volume ratio of 4:1 to prepare an ethanol-water solution. Aluminum hydroxide with a particle size of 5-12 μm is selected and added to the ethanol-water solution. The volume ratio of aluminum hydroxide to ethanol-water solution is controlled at 1 g: 80 mL. Chitosan (weight average molecular weight of 50,000-60,000 Da) and glyceric acid are then added. The mass ratio of aluminum hydroxide, chitosan and glyceric acid is 1:5:6. The mixture is heated at 80 °C for 5 h. The solution after reaction is filtered, washed three times with deionized water, and dried to obtain modified aluminum hydroxide.

[0034] The stabilizer mentioned above is composed of phosphotungstic acid and mannose erythritol ester in a weight ratio of 1:0.1.

[0035] This embodiment also provides a method for preparing a quick-setting agent for shotcrete, the preparation method comprising the following steps: mixing and stirring aluminum sulfate, magnesium sulfate, modified aluminum hydroxide, triethanolamine, stabilizer and water according to the specified ratio to obtain the agent.

[0036] Example 3

[0037] A quick-setting agent for shotcrete, comprising the following raw materials by weight: 70 parts aluminum sulfate, 25 parts magnesium sulfate, 17 parts modified aluminum hydroxide, 12 parts triethanolamine, 10 parts stabilizer, and 70 parts water.

[0038] The preparation process of the modified aluminum hydroxide is as follows: Anhydrous ethanol and water are mixed at a volume ratio of 4:1 to prepare an ethanol aqueous solution. Aluminum hydroxide with a particle size of 5-12 μm is selected and added to the ethanol aqueous solution. The volume ratio of aluminum hydroxide to ethanol aqueous solution is controlled at 1 g: 100 mL. Chitosan (weight average molecular weight of 50000-60000 Da) and glyceric acid are then added. The mass ratio of aluminum hydroxide, chitosan and glyceric acid is 1:7:9. The mixture is heated at 90 °C for 2 h. The solution after reaction is filtered, washed three times with deionized water, and dried to obtain modified aluminum hydroxide.

[0039] The stabilizer mentioned above is composed of phosphotungstic acid and mannose erythritol ester in a weight ratio of 1:0.35.

[0040] This embodiment also provides a method for preparing a quick-setting agent for shotcrete, the preparation method comprising the following steps: mixing and stirring aluminum sulfate, magnesium sulfate, modified aluminum hydroxide, triethanolamine, stabilizer and water according to the specified ratio to obtain the agent.

[0041] Comparative Example 1

[0042] Comparative Example 1 is basically the same as Example 1, except that modified aluminum hydroxide is replaced with aluminum hydroxide.

[0043] Comparative Example 2

[0044] Comparative Example 2 is basically the same as Example 1, except that aluminum hydroxide and chitosan are added directly to the quick-setting agent.

[0045] Comparative Example 3

[0046] Comparative Example 3 is basically the same as Example 1, except that the stabilizer is replaced with phosphotungstic acid.

[0047] Test case

[0048] The performance of the quick-setting agents for shotcrete obtained in Examples 1-3 and Comparative Examples 1-3 of this invention was tested:

[0049] 1. The quick-setting agents for shotcrete obtained in Examples 1-3 and Comparative Examples 1-3 were mixed with ordinary Portland cement P.O42.5. The quick-setting agent dosage was 6% of the cement mass. Referring to the testing standard of GB / T35159-2017 "Quick-setting Agents for Shotcrete", the initial setting time and final setting time of cement paste (cement to water mass ratio of 400:140) were tested, as were the compressive strength of cement mortar (cement, standard sand, and water mass ratio of 900:1350:450) at day 1 and day 28, and the 28-day compressive strength ratio. The test results are shown in Table 1.

[0050] 2. Add the quick-setting agent at 6% of the cement mass to the concrete (the mass ratio of cement, river sand, crushed stone, and water is 500:859:845:166), and test the rebound rate according to the test method in JGJ / T372-2016 "Technical Specification for Application of Shotcrete". The test results are shown in Table 2.

[0051] 3. Stability tests were conducted, recording the time it took for each group of accelerators to settle at room temperature until precipitation occurred. The dust generation during construction was also analyzed, and the test results are shown in Table 2.

[0052] Table 1

[0053]

[0054] As shown in Table 1, the accelerator for shotcrete provided by this invention has an initial setting time of less than 3 minutes and a final setting time of less than 5 minutes. The initial and final setting times of Example 1 are higher than those of Comparative Examples 1-3. Examples 1-3 are also higher than Comparative Examples 1-3 in terms of 1-day compressive strength, 28-day compressive strength, and 28-day compressive strength ratio. These results indicate that the accelerator of this invention can not only shorten the initial and final setting times of cement paste, but also effectively improve the early and late strength of shotcrete.

[0055] In Comparative Example 1, the modified aluminum hydroxide was replaced with aluminum hydroxide. Compared to Example 1, the initial setting time and final setting time were significantly reduced, and the compressive strength also decreased significantly. This is because the surface of aluminum hydroxide has a high concentration of hydroxyl groups, which easily aggregate and adsorb with aluminum sulfate and magnesium sulfate in the accelerator, reducing the content of effective components in the accelerator and affecting the accelerator's setting effect. Furthermore, the unmodified aluminum hydroxide lacks a coating layer on its surface, which may lead to an overly vigorous hydration reaction and premature consumption. Although it may result in instantaneous solidification, it cannot form a stable and orderly hydration product structure, leading to insufficient early strength growth and severe later strength loss.

[0056] Comparative Example 2 involved directly adding aluminum hydroxide and chitosan to the accelerator. The performance was also lower than in Example 1. This is because aluminum ions were fixed within the aggregates, significantly reducing the concentration of free, effective aluminum ions in the accelerator, leading to prolonged initial and final setting times. Furthermore, directly adding aluminum hydroxide and chitosan failed to achieve a slow release of aluminum ions, and compared to Example 1, it lacked the ability to provide moisture to the cement in the later stages, thus resulting in a decline in its performance.

[0057] Table 2

[0058]

[0059] As shown in Table 2, the rebound rate of the quick-setting agent for shotcrete in Examples 1-3 of this invention is lower than that in Comparative Examples 1-3, indicating good storage stability. Furthermore, it can reduce dust concentration during construction and improve construction efficiency.

[0060] Compared to Example 1, Comparative Example 1 showed an increased rebound rate and more severe dust generation. This was because the lack of a modification process for aluminum hydroxide affected the full hydration of the cement, causing the concrete slurry to drip or slip more easily. During spraying, aggregates and cement particles rebounded more readily, and fine dust was more easily dispersed, leading to material waste and a deteriorated construction environment.

[0061] In Comparative Example 2, aluminum hydroxide and chitosan were directly added to the quick-setting agent. Compared with Example 1, the rebound loss during the spraying process increased, the dust concentration increased, and the stability decreased.

[0062] In Comparative Example 3, the stabilizer was replaced with phosphotungstic acid, and the storage stability was significantly lower than that of Example 1. This indicates that phosphotungstic acid alone cannot provide effective stabilization, thus proving that the combined use of phosphotungstic acid and mannoerythritol ester can synergistically improve the stability of the accelerator.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A quick-setting agent for shotcrete, characterized in that, By weight, it includes the following raw materials: 50-70 parts aluminum sulfate, 10-25 parts magnesium sulfate, 10-17 parts modified aluminum hydroxide, 8-12 parts triethanolamine, 5-10 parts stabilizer, and 60-70 parts water. The preparation process of the modified aluminum hydroxide is as follows: aluminum hydroxide is added to an aqueous ethanol solution, then chitosan and glyceric acid are added, and the mixture is heated to react and obtain modified aluminum hydroxide.

2. The quick-setting agent for shotcrete according to claim 1, characterized in that, The mass ratio of aluminum hydroxide, chitosan, and glyceric acid is 1:(5-7):(6-9), and the volume ratio of aluminum hydroxide to ethanol aqueous solution is 1g:80-100mL.

3. The quick-setting agent for shotcrete according to claim 1, characterized in that, The ethanol-water solution is prepared by mixing anhydrous ethanol and water in a volume ratio of (3-4):

1.

4. The quick-setting agent for shotcrete according to claim 1, characterized in that, The heating reaction is carried out at a temperature of 80-90℃ for 2-5 hours.

5. The quick-setting agent for shotcrete according to claim 1, characterized in that, The aluminum hydroxide has a particle size of 2-12 μm.

6. The quick-setting agent for shotcrete according to claim 1, characterized in that, The weight-average molecular weight of the chitosan is 50,000-60,000 Da.

7. The quick-setting agent for shotcrete according to claim 1, characterized in that, The stabilizer consists of phosphotungstic acid and mannose erythritol ester.

8. The quick-setting agent for shotcrete according to claim 7, characterized in that, The mass ratio of phosphotungstic acid to mannose erythritol ester is 1: (0.1-0.35).

9. A method for preparing a quick-setting agent for shotcrete according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: aluminum sulfate, magnesium sulfate, modified aluminum hydroxide, triethanolamine, stabilizer, and water are mixed and stirred according to the specified ratio to obtain the final product.

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