A shotcrete reducing agent and a method for preparing the same

Abstract

The application discloses a shotcrete rebound-reducing agent and a preparation method thereof. The shotcrete rebound-reducing agent is prepared from the following raw materials in mass percentage: 15-30% of a quick-setting component, 2-5% of a viscosity-increasing component, 10-15% of a reinforcing component, 2-5% of an anti-freezing component, 1-4% of a stabilizer, and the rest of water; and the viscosity-increasing component is a combination of polyvinylpyrrolidone and modified carboxymethyl cellulose. The prepared shotcrete rebound-reducing agent has the advantages of good sprayability, high hourly strength, good anti-freezing and stability, and the like, can improve the working performance of shotcrete, reduce the content of a quick-setting agent and significantly reduce the rebound rate of shotcrete, and has good economic benefits.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a shotcrete elasticity reducer and its preparation method. Background Technology

[0002] Shotcrete, as one of the main forms of support for tunnels and underground engineering projects, has seen a dramatic increase in usage with the further development of infrastructure construction. However, in my country's current shotcrete construction, due to fluctuations in raw material quality, unreasonable mix proportions, and poor spraying techniques, a high rebound rate is prevalent. Reducing rebound is a problem the industry is currently working to solve. Excessive rebound not only directly affects the cost of shotcrete support but also impacts construction speed and increases material costs. Furthermore, the dosage of alkali-free accelerators used in on-site construction remains high. During tunnel shotcreting, the flow rate of accelerators in wet spraying robotic arms often fails to meet the design dosage requirements, possibly due to insufficient accelerator pump power, low factory current settings, or excessively high accelerator viscosity, severely impacting the spraying effect and quality. Currently, there are no mature, widely applicable shotcrete reduction agents on the market. Therefore, developing a shotcrete reduction agent that can reduce the rebound rate, improve the workability of shotcrete, and reduce the dosage of alkali-free accelerators is essential.

[0003] In existing technologies, methods to reduce the rebound rate of shotcrete include adding composite fibers, thickeners, early-strength agents, air-entraining agents, and nano-admixtures. Patent CN114920491A discloses a shotcrete rebound-reducing admixture and its preparation method, comprising: 30-50 parts of organic acid-activated silicate admixture, 0.15-0.5 parts of cellulose thickener, 30-50 parts of rapid-hardening cement, and 5-20 parts of early-strength agent; this improves the cohesiveness of concrete and promotes cement hydration, thereby reducing the rebound rate. Patent CN117105566A discloses a nano-rebound inhibitor for shotcrete, comprising 30%-40% nanospheres, 20%-25% epoxy resin emulsion, 10%-15% polycarboxylate superplasticizer, 2%-6% redispersible latex powder, and 1%-3% thickener, which can effectively control the rebound rate. However, existing technologies improve the cohesiveness of shotcrete and reduce rebound rate by adding quick-hardening cement, nanospheres, thickeners, etc. The addition of quick-hardening cement is difficult to meet the workability retention requirements of wet shotcrete, and the single thickening component has poor effect on improving the cohesiveness and workability of concrete. In addition, some raw materials are not easy to obtain and the cost is high, which makes it unsuitable for large-scale promotion and use. Summary of the Invention

[0004] 1. The technical problem to be solved:

[0005] To address the aforementioned technical problems, this invention provides a shotcrete elasticity reducer and its preparation method, which has excellent workability, can improve the cohesiveness of shotcrete and shorten the setting time, improve the sprayability of shotcrete, can maintain slump for more than three hours, can significantly reduce the rebound rate of shotcrete, and the overall rebound rate can be controlled within 8%, without adversely affecting the strength.

[0006] 2. Technical Solution:

[0007] A shotcrete elasticity reducer, characterized in that it is composed of the following raw materials in the following mass percentages: 15%-30% quick-setting component, 2%-5% thickening component, 10%-15% reinforcing component, 2%-5% antifreeze component, 1%-4% stabilizer, and the remainder being water; wherein the thickening component is a composition of polyvinylpyrrolidone and modified carboxymethyl cellulose.

[0008] The preparation method of modified carboxymethyl cellulose is as follows: epichlorohydrin, a crosslinking agent, is added to carboxymethyl cellulose. Epichlorohydrin reacts with the carboxyl groups on the molecular chain of carboxymethyl cellulose to form a network structure between molecules, thereby generating modified carboxymethyl cellulose.

[0009] Furthermore, the quick-setting component is one or a combination of two of aluminum sulfate and magnesium sulfate.

[0010] Furthermore, the reinforcing component is a combination of CSH nucleation early strength agent and sodium sulfate.

[0011] Furthermore, the antifreeze component is one of ethylene glycol and sodium nitrite.

[0012] Furthermore, the stabilizer is a modified alcohol amine.

[0013] Furthermore, the modified alcohol amine is triethanolamine borate ester, which is prepared by adding boric acid to triethanolamine in a four-necked flask equipped with a stirring and condensing device, with a molar ratio of 3:1. The temperature is raised to 65°C, concentrated sulfuric acid is added as a catalyst, and the temperature is raised to 95°C for 1-2 hours.

[0014] A method for preparing a shotcrete elasticity reducer includes the following steps:

[0015] Step 1: Add water to the reaction vessel and heat to 40℃-50℃;

[0016] Step 2: Turn on the stirrer and add the quick-setting component, thickening component and strengthening component in sequence until completely dissolved;

[0017] Step 3: Add the antifreeze component to the solution generated in Step 2, continue stirring for 20 minutes, and then slowly add the stabilizer dropwise using a constant flow pump. The addition should be completed within 1 hour. The resulting homogeneous and stable solution is the elasticity reducer.

[0018] 3. Beneficial effects:

[0019] (1) The preparation method of the shotcrete elasticity reducer of the present invention combines the advantages of multiple technical routes. Among them, the modified carboxymethyl cellulose, a thickening component, forms a network structure between molecules compared with commonly used cellulose, resulting in better thickening, water retention and stabilization effects. Polyvinylpyrrolidone, as a water-soluble polymer compound, has the functions of thickening, dispersing, air entraining and solubilizing. While increasing the viscosity of the system, it can also assist in the dissolution of other components and improve stability.

[0020] (2) The shotcrete reducing agent prepared by this method can improve the viscosity of shotcrete while maintaining good fluidity. Its air-entraining effect makes the slurry fuller, thus significantly improving the overall workability. The pumping pressure is low, the shotcrete has good sprayability, and the blockage caused by poor gradation of manufactured sand or other raw materials during the shotcrete construction process is avoided.

[0021] (3) The shotcrete elasticity reducer prepared by this method improves the cohesiveness of the shotcrete system, making it easier for the material to adhere to the rock surface after spraying, quickly forming a buffer layer. This prevents the coarse aggregate from directly colliding with the rock surface, thus avoiding rebound. At the same time, due to the high viscosity of the cement, a thick cement layer adheres to the surface of the aggregate, which buffers the impact of the coarse aggregate. The increased viscosity resistance of the coarse aggregate when passing through the mortar makes it easier for the concrete to adhere to the sprayed surface, improving the bonding ability between the concrete and the contact surface, thereby reducing rebound.

[0022] (4) The shotcrete rebound reducer prepared by this method contains aluminum sulfate and magnesium sulfate, which are commonly used components of shotcrete quick-setting agents. Both can promote the rapid hydration of tricalcium aluminate to form a tightly connected ettringite structure, and also have a certain reinforcing effect. When the quick-setting component in the rebound reducer is used in conjunction with an alkali-free quick-setting agent, the setting time of the sprayed material can be further shortened, allowing it to set and harden quickly. This prevents the sprayed material from falling off due to gravity, thereby reducing the rebound rate of shotcrete. It also solves the industry problem of excessively high dosage of alkali-free quick-setting agents.

[0023] (5) The shotcrete elasticity reducer prepared by this method has a CSH nucleation accelerator as its reinforcing component, which can increase the cement hydration reaction rate, significantly reduce the activation energy of the cement hydration reaction, and promote early strength development within 24 hours. Simultaneously, the polycarboxylate dispersant used in its synthesis process can improve the flow retention performance of shotcrete and reduce slump caused by the introduction of quick-setting components. The incorporation of sodium sulfate not only improves the early strength of shotcrete but also enhances the compatibility of the elasticity reducer with various cementitious materials.

[0024] (6) The shotcrete elasticity reducer prepared by this method has antifreeze components, ethylene glycol and sodium nitrite, which can lower the freezing point of the solution, ensuring the normal use of the elasticity reducer product under low temperature conditions. The incorporation of the stabilizer modified alkanolamine, namely triethanolamine borate, can complex the quick-setting components to improve the stability of the solution and has a certain reinforcing effect, and can significantly improve the anti-corrosion performance of shotcrete with wire mesh. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments and comparative examples.

[0026] Example 1:

[0027] By weight percentage, the components include: aluminum sulfate (20%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (3%), CSH nucleating agent (8%), sodium sulfate (4%), ethylene glycol (3%), triethanolamine borate (2%), and the remainder is water. A method for preparing a shotcrete elasticity reducer includes the following steps:

[0028] (1) Add water to the reaction vessel and heat to 40℃-50℃;

[0029] (2) Start stirring and add aluminum sulfate, polyvinylpyrrolidone, modified carboxymethyl cellulose, CSH nucleation agent and sodium sulfate in sequence until completely dissolved;

[0030] (3) Add ethylene glycol to the above solution, continue stirring for 20 minutes, and then slowly add triethanolamine borate using a constant flow pump. The addition should be completed within 1 hour. The resulting homogeneous and stable solution is the elasticity reducer.

[0031] Example 2:

[0032] The components, by mass percentage, include: aluminum sulfate (22%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (1%), CSH nucleating agent (9%), sodium sulfate (2%), ethylene glycol (3.5%), triethanolamine borate (2.5%), and the remainder is water. The preparation method is as described in Example 1.

[0033] Example 3:

[0034] The components, by mass percentage, include: aluminum sulfate (10%), magnesium sulfate (10%), polyvinylpyrrolidone (1%), modified carboxymethyl cellulose (1%), CSH nucleating agent (5%), sodium sulfate (5%), ethylene glycol (5%), triethanolamine borate (2%), and the remainder is water. The preparation method is as described in Example 1.

[0035] Example 4:

[0036] By mass percentage, the components include: aluminum sulfate (15%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (1%), CSH nucleating agent (12%), sodium sulfate (3%), ethylene glycol (2%), triethanolamine borate (1%), and the remainder is water. The preparation method is as described in Example 1.

[0037] Example 5:

[0038] By mass percentage, the components include: magnesium sulfate (30%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (2%), CSH nucleating agent (5%), sodium sulfate (7%), sodium nitrite (2%), triethanolamine borate (4%), and the remainder is water. The preparation method is as described in Example 1.

[0039] Example 6:

[0040] By mass percentage, the components include: aluminum sulfate (25%), magnesium sulfate (5%), polyvinylpyrrolidone (1%), modified carboxymethyl cellulose (2%), CSH nucleating agent (2%), sodium sulfate (8%), ethylene glycol (5%), triethanolamine borate (1%), and the remainder is water. The preparation method is as described in Example 1.

[0041] Comparative Example 1:

[0042] The components, by mass percentage, include: aluminum sulfate (10%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (1%), CSH nucleating agent (9%), sodium sulfate (2%), ethylene glycol (3.5%), triethanolamine borate (2.5%), and the remainder is water. The preparation method is as described in Example 1.

[0043] Comparative Example 2:

[0044] The components, by mass percentage, include: aluminum sulfate (22%), polyvinylpyrrolidone (0.5%), modified carboxymethyl cellulose (0.5%), CSH nucleating agent (9%), sodium sulfate (2%), ethylene glycol (3.5%), triethanolamine borate (2.5%), and the remainder is water. The preparation method is as described in Example 1.

[0045] Comparative Example 3:

[0046] The components, by mass percentage, include: aluminum sulfate (22%), polyvinylpyrrolidone (4%), modified carboxymethyl cellulose (4%), CSH nucleating agent (9%), sodium sulfate (2%), ethylene glycol (3.5%), triethanolamine borate (2.5%), and the remainder is water. The preparation method is as described in Example 1.

[0047] Comparative Example 4:

[0048] By mass percentage, the components include: aluminum sulfate (22%), polyvinylpyrrolidone (2%), modified carboxymethyl cellulose (1%), CSH nucleating agent (4%), sodium sulfate (3%), ethylene glycol (3.5%), triethanolamine borate (2.5%), and the remainder is water. The preparation method is as described in Example 1.

[0049] Blank group:

[0050] No elasticity reducer added

[0051] Application example:

[0052] The rebound rate test of shotcrete was conducted according to JGJ 372-2016 "Technical Specification for Application of Shotcrete". The dosage of the elasticity reducer was uniformly set at 5% of the binder. The actual dosage of the accelerator was recorded, and the workability retention time was tested. Simultaneously, the concrete specimens were formed and tested using the shotcrete method. The mix proportions and test results are shown in Tables 1 and 2, respectively.

[0053] Table 1 Mix Proportions for Shotcrete

[0054] C30 injection 470 850 850 174 4.7 23.5 37.6

[0055] Table 2 Comparison of Test Results

[0056]

[0057] The results above show that the blank group mix proportion, without the addition of elasticity reducer, is the conventional shotcrete mix proportion on site. During construction, the rebound rate of the sidewalls reached 16.6%, the rebound rate of the arch was as high as 32.5%, the actual dosage of the quick-setting agent was 8.2%, the slump retention time was 2 hours, the 6-hour strength was low at only 1.4 MPa, and the 1-day strength was 10.3 MPa.

[0058] After using the elasticity-reducing agent provided by this invention in Examples 1-6, a comparison revealed a significant reduction in the rebound rate of the sidewalls and arches, with the sidewall rebound rate decreasing by more than 10% and the arch rebound rate decreasing by more than 20%. Simultaneously, the actual dosage of the accelerator was reduced to below 6%, the slump retention time increased to over 3 hours, and the 6-hour and 1-day strengths of the concrete were significantly improved, with the 6-hour strength increase exceeding 360% and the 1-day strength increase exceeding 57%. The product can be stably stored for over 30 days at -5℃. The incorporation of the antifreeze component lowers the freezing point of the solution, ensuring the normal use of the elasticity-reducing agent under low-temperature conditions. The incorporation of the stabilizer-modified alkanolamine, namely triethanolamine borate, can complex the accelerator component, improving solution stability and providing a certain reinforcing effect. The incorporation of the above-mentioned elasticity-reducing agent effectively improves the cohesiveness, fluidity, and sprayability of shotcrete, significantly reduces the rebound rate, and significantly increases the hourly strength. It solves common technical problems of wet-mixed shotcrete while bringing significant economic benefits, demonstrating good comprehensive performance and proving the effectiveness of this invention.

[0059] Comparing Comparative Examples 1-4, it can be observed that in Comparative Example 1, the proportion of the quick-setting component is significantly lower than in Examples 1-6, ultimately leading to a significant increase in the rebound rate of the sidewalls and arch. Furthermore, the actual dosage of the quick-setting agent is higher. This is because the setting time of the shotcrete is longer, and concrete that does not set in time is prone to detaching under gravity, resulting in spalling and rebound. In Comparative Example 2, the proportion of the thickening component is lower, and the rebound rate is also significantly increased. This is because the improvement in cohesiveness and workability is insufficient, resulting in insufficient adhesion between the sprayed material and the rock surface and interface, leading to a higher rebound rate. In Comparative Example 3, the proportion of the thickening component is too high. Although the rebound rate is lower than in Comparative Example 2, it is still higher than in Examples 1-6. Moreover, the excessive addition of the thickening component leads to a rapid loss of workability, with a slump retention time of only 1 hour. Therefore, a moderate proportion of the thickening component helps to ensure rheological properties while increasing the viscosity of the shotcrete, thereby improving the sprayability and adhesion of the shotcrete. In Comparative Example 4, the low proportion of reinforcing components resulted in a smaller increase in early strength and a higher rebound rate. The combination of CSH nucleating accelerator and sodium sulfate in the reinforcing components can promote cement hydration and improve the early and final compressive strength of concrete.

[0060] The above results show that the shotcrete elasticity reducer of the present invention achieves the expected effects of improved workability, reduced rebound and increased hourly strength based on the synergistic effect of the different components. If any component is missing, the above benefits cannot be achieved. Each component is essential and the proportions must be appropriate.

[0061] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A shotcrete elasticity reducer, characterized in that: It is composed of the following raw materials in the following mass percentages: 15%-30% quick-setting component, 2%-5% thickening component, 10%-15% reinforcing component, 2%-5% antifreeze component, 1%-4% stabilizer, and the remainder is water; the thickening component is a combination of polyvinylpyrrolidone and modified carboxymethyl cellulose. The preparation method of modified carboxymethyl cellulose is as follows: epichlorohydrin, a crosslinking agent, is added to carboxymethyl cellulose. Epichlorohydrin reacts with the carboxyl groups on the molecular chain of carboxymethyl cellulose to form a network structure between molecules, thereby generating modified carboxymethyl cellulose.

2. The shotcrete reducing agent according to claim 1, characterized in that: The quick-setting component is one or a combination of two of aluminum sulfate and magnesium sulfate.

3. The shotcrete reducing agent according to claim 1, characterized in that: The reinforcing component is a combination of CSH nucleation early strength agent and sodium sulfate.

4. The shotcrete reducing agent according to claim 1, characterized in that: The antifreeze component is one of ethylene glycol and sodium nitrite.

5. The shotcrete reducing agent according to claim 1, characterized in that: The stabilizer is a modified alcohol amine.

6. The shotcrete reducing agent according to claim 5, characterized in that: The modified alcohol amine is triethanolamine borate ester, and its preparation method is as follows: In a four-necked flask equipped with a stirring and condensing device, boric acid is added to triethanolamine in a molar ratio of 3:

1. The temperature is raised to 65°C, concentrated sulfuric acid is added as a catalyst, and the temperature is raised to 95°C for 1-2 hours.

7. A method for preparing a shotcrete elasticity reducer, used to prepare the elasticity reducer as described in any one of claims 1-6, characterized in that: Includes the following steps: Step 1: Add water to the reaction vessel and heat to 40℃-50℃; Step 2: Turn on the stirrer and add the quick-setting component, thickening component and strengthening component in sequence until completely dissolved; Step 3: Add the antifreeze component to the solution generated in Step 2, continue stirring for 20 minutes, and then slowly add the stabilizer dropwise using a constant flow pump. The addition should be completed within 1 hour. The resulting homogeneous and stable solution is the elasticity reducer.

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