Coagulating early strength agent for sprayed concrete as well as preparation method and application of coagulating early strength agent

Abstract

The invention relates to the technical field of cement-based admixtures, in particular to a coagulation-accelerating early strength agent for sprayed concrete and a preparation method and application of the coagulation-accelerating early strength agent for sprayed concrete. High-activity early strength powder is used as a main component, and self-made microsphere components with slow release precise control and spraying process tolerance are added; the accelerating early strength agent provided by the invention overcomes the defect that a traditional accelerating agent dissipates or loses efficacy too early in a spraying environment, and realizes the accurate triggering of the accelerating early strength effect and the effective regulation and control of the release opportunity; and a brand new technical support is provided for improving instantaneity and reliability of shotcrete support.

Description

Technical Field

[0001] This invention relates to the field of cement-based admixtures, and in particular to an accelerator for shotcrete with early setting and strength, its preparation method, and its application. Background Technology

[0002] Shotcrete technology, due to its convenient and efficient construction and good adaptability to complex structural surfaces, has become an indispensable key support technology in fields such as tunnels, water conservancy and hydropower, slope protection, mining, and underground engineering. Its core principle is to spray the mixed concrete materials at high speed onto the construction surface using a shotcrete machine with the help of high-pressure gas, allowing it to quickly solidify and harden.

[0003] However, this process places special and stringent requirements on the setting and early strength properties of concrete materials: rapid initial setting is necessary to reduce rebound, and sufficient initial strength for support must be established quickly. Existing technology CN107840593A discloses an early-strength liquid alkali-free quick-setting agent for shotcrete, composed of 60-75 wt% modified polyaluminum sulfate solution, 5-15 wt% modified alkanolamine solution, 0-3 wt% performance modifier, 0-4 wt% stabilizer, and water. CN110104987A discloses a high early-strength alkali-free liquid quick-setting agent composed of the following raw materials by weight percentage: 40-50% polyaluminum sulfate, 5-10% metakaolin, 5-15%... The composition of the agent is as follows: nano-silica sol, 3-6% alkanolamine, 1-4% organic acid, 0.01-0.05% thickener, 0.01-0.05% dispersant, and the balance is water. CN118955003A discloses a low-resilience, high-permeability liquid alkali-free quick-setting agent, comprising the following raw materials by mass percentage: 60%-67% quick-setting agent, 5%-8% solubilizer, 2%-4% waterproofing agent, 2%-3% early-strength agent, 1%-2% pH adjuster, 0.5%-1.5% suspending agent, and the balance being water.

[0004] In the existing technology, conventional accelerators for setting and early strength mainly consist of inorganic salts with aluminum salts as the main component, such as aluminum sulfate. Under the physical impact and airflow disturbance in the high-speed jet environment, they often disperse and fail prematurely or have uneven effects, making it difficult to accurately control the setting and hardening behavior. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides an accelerator for shotcrete. Specifically, this invention uses highly active early-strength powder as the main component, adds self-made microsphere components with precise slow-release control and tolerance to the spraying process, and adds a retarder to prevent the risk of pipe blockage caused by rapid setting of shotcrete. This accelerator overcomes the defects of traditional accelerators that dissipate or fail prematurely in the spraying environment, and achieves precise triggering and effective control of the accelerator effect, providing new technical support for improving the immediacy and reliability of shotcrete support.

[0006] Specifically, the accelerator for shotcrete of the present invention is composed of the following raw materials in parts by weight: 65-75 parts of early-strength powder, 12-20 parts of microspheres, and 1-5 parts of retarder.

[0007] The early-strength powder of this invention is a key component, which provides basic hydration products and micro-aggregate effect. The microsphere component is the core component of this invention, contributing precise slow release and impact resistance. The retarder regulates the hydration induction period, avoids construction risks (such as pipe blockage) caused by excessively rapid setting, and ensures workability.

[0008] Preferably, the early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum salt in a mass ratio of 45-55:25-35:8-12:5-15.

[0009] Preferably, the aluminum salt is at least one of aluminum sulfate and aluminum fluoride.

[0010] Preferably, the microsphere component consists of a core material and a coating layer. The core material consists of CSH nanocrystal nuclei, calcium formate, calcium thiocyanate, and triethanolamine in a mass ratio of 45-55:30-40:8-12:3-7. The coating layer consists of ethyl cellulose, hydrophobic fumed silica, and a plasticizer in a mass ratio of 70-75:12-18:5-15.

[0011] The composition of the core microsphere components of this invention exhibits a synergistic effect. Among them, calcium formate is a highly effective calcium dissolving source with a rapid dissolution rate, providing a high concentration of Ca. 2+The four substances work together to rapidly promote the dissolution and hydration of tricalcium silicate. CSH nanocrystals act as "seeds," shortening the hydration induction period and promoting the directional growth of the hydration product CSH gel around the crystal nucleus, thus improving density. Calcium thiocyanate is a highly conductive calcium source, and its strong conductivity can further accelerate ion diffusion. Triethanolamine mainly promotes the early dissolution of tricalcium aluminate and the formation of hydration products. The four substances work together to accelerate the early hydration process. The coating layer of this invention is dense, balanced, has low surface adhesion, and possesses hydrophobic properties. Ethyl cellulose is the main film-forming matrix, which can dissolve in solvents (such as ethanol) to form a continuous film and serves as the barrier. Hydrophobic fumed silica is uniformly dispersed in the ethyl cellulose matrix, which can significantly enhance the coating layer strength, improve hydrophobicity, and reduce the film friction coefficient, effectively preventing physical damage (such as scratches and abrasion) and water vapor penetration erosion of microspheres during the mixing and transportation process. Plasticizers are used to improve the flexibility and film-forming properties of the EC membrane. During concrete mixing, pumping, and passage through the spray hose, the coating layer can effectively protect the core layer from damage. Only at the moment of impact with the high-pressure jet on the substrate, the powerful mechanical impact force (impact force and airflow pressure) causes the microsphere coating layer to rupture (or the solubility to change drastically), allowing the active ingredients of the core layer to be released instantaneously, directly acting on the cement particles and instantly initiating a high-intensity accelerated hydration mode.

[0012] Preferably, the plasticizer is at least one of diethyl phthalate and triethyl citrate.

[0013] Preferably, the retarder is at least one of sodium gluconate, citric acid, sodium citrate, and boric acid.

[0014] Preferably, the microsphere component preparation steps are as follows: 1) Core material preparation: CSH nanocrystal nuclei, calcium formate, and calcium thiocyanate were mixed and ground to a density of D90 ≤ 5 μm. After wet mixing with triethanolamine solution, the mixture was spray-granulated to obtain 80-150 μm core particles, which were then dried to obtain the core material. 2) Preparation of coating solution: Dissolve ethyl cellulose in an appropriate amount of ethanol, add plasticizer, stir evenly, add hydrophobic fumed silica, and disperse evenly. 3) Coating and curing: The core material is placed in a fluidized bed and sprayed into a coating liquid to coat the microspheres. The coated microspheres are then cured and collected by sieving to obtain 150-300μm particles.

[0015] Preferably, in step 1), the triethanolamine solution is a triethanolamine ethanol solution with a mass fraction of 8-12% composed of triethanolamine and ethanol, the inlet air temperature of the spray granulation is 42-48℃, the pressure is 0.28-0.32MPa, and the drying temperature is 40-45℃.

[0016] Preferably, in step 2), ethyl cellulose is dissolved in ethanol to form a solution with a mass fraction of 7-9%.

[0017] Preferably, in step 3), the fluidized bed inlet air temperature is 36-40℃, and the fluidizing air velocity is 0.7-0.9 m / s. 3 / h, atomization pressure is 0.23-0.27MPa.

[0018] The present invention also relates to a method for preparing the above-mentioned accelerator for shotcrete, specifically including the following steps: mixing the accelerator powder, microsphere component and retarder evenly to obtain the product.

[0019] This invention also relates to the application of the aforementioned accelerator for shotcrete in the preparation and construction of shotcrete.

[0020] Preferably, the amount of the accelerator for setting and early strength in this invention is 5-15% of the mass of cement in the shotcrete.

[0021] Preferably, the method of using the accelerator of the present invention is as follows: after weighing the materials, the accelerator is first mixed evenly with cement, then water and aggregate are added and mixed evenly to complete the preparation of the shotcrete mixture, and then the mixture is sprayed through the spraying equipment.

[0022] The retarder in the mixture plays an early hydration regulation role, ensuring the construction time of the mixture. The coating layer of the microsphere component can resist the mechanical and dissolving impacts during wet mixing. The active substances of the core material are effectively protected and not released at this time. After entering the spraying equipment, the mixture is pressurized by the spraying machine and driven at high speed through the spraying hose and nozzle under the drive of high-pressure air or liquid flow (wet spraying method). In the spraying pipeline, the coating layer of the microsphere component can still withstand continuous flow friction and pressure. When the concrete slurry with huge kinetic energy and impact force hits the construction surface (wall, rock mass, foundation, etc.) through the nozzle, the powerful impact force acts on the microspheres. The coating layer of the microsphere component is ruptured under high pressure impact, and the active components of the core layer are released instantaneously and in a concentrated manner. Due to its ultra-fine dispersion state (ground in the preparation process), it quickly disperses and penetrates into the area adjacent to the cement particles. The core components work together: high concentration of Ca 2+ +Effective nucleation induction site (CSH) +Promoter (TEA) +Highly conductive ions (SCN) - Multiple mechanisms rapidly induce the rapid dissolution, precipitation, and network crystallization of C3S and C3A, significantly shortening the induction period. Nucleation sites densely form CSH gel, rapidly establishing an early network structure, thereby significantly improving the initial setting speed and early strength of concrete. After impacting the base surface, the sprayed mixture quickly solidifies (within seconds to minutes) and begins to rapidly develop strength, while the rebound rate is also reduced.

[0023] Preferably, the shotcrete using the accelerator of the present invention can be used in the construction of tunnel lining base surfaces, slope reinforcement base surfaces, mine roadway support surfaces, and foundation waterproofing structure base surfaces.

[0024] This invention has the following technical advantages: 1. Excellent resistance to mechanical shock: The unique EC-hydrophobic SiO2 reinforced composite coating layer endows the self-made microsphere components with excellent resistance to physical wear, friction and shear damage during stirring, pumping and pipeline transportation, effectively protecting the core active components until they reach their destination. 2. Precisely Triggered Release: The microsphere component coating layer ruptures only at the moment of high-pressure impact when the concrete is sprayed onto the substrate, releasing the core material. This achieves precise and concentrated supply of early-strength active substances at key locations, overcoming the shortcomings of existing additives that either disperse and fail prematurely or have uncontrollable timing of action. 3. Significantly accelerates early strength development: The core material components are scientifically designed with obvious synergistic effects: Highly soluble calcium source and highly conductive calcium source provide sufficient ionic environment and charge induction, CSH nanocrystal nuclei greatly reduce nucleation barriers and induce in-situ directional crystallization to shorten the induction period, TEA synergistically stimulates aluminate reaction, and provides high-concentration instantaneous supply at the base surface contact point, realizing a leapfrog acceleration of the setting and hardening process of sprayed concrete, significantly reducing the rebound rate, and rapidly improving the early and final strength of spraying. Detailed Implementation

[0025] To characterize the technical effect of this invention, an accelerator for setting and early strength was prepared and its performance was tested. During the test, 300 kg / m³ of P·O42.5 cement was used. 3 100kg / m³ of fly ash 3 Mineral powder 50kg / m 3 5-10mm crushed stone 952kg / m 3 900 kg / m³ of graded medium sand 3 The mixture was prepared with 1.5% polycarboxylate superplasticizer, 8% cement accelerator, and a water-cement ratio of 0.4. After initial slump and spread tests and 1-hour slump and spread tests, it was sprayed into shape using a small spraying machine.

[0026] Example 1 The accelerator for early setting and strength is characterized by comprising the following raw materials in parts by weight: 72 parts of early-strength powder, 18 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum sulfate in a mass ratio of 50:25:10:15. The microspheres consist of a core material and a coating layer. The core material consists of CSH nanocrystals, calcium formate, calcium thiocyanate, and triethanolamine in a mass ratio of 52:33:9:6. The coating layer consists of ethyl cellulose, hydrophobic fumed silica, and diethyl phthalate in a mass ratio of 75:15:10.

[0027] The test results showed that the initial slump of the mixture was 245 mm, the initial spread was 570 mm, the slump at 1 hour was 230 mm, the spread at 1 hour was 550 mm, the compressive strength at 3 hours was 1.5 MPa, the compressive strength at 6 hours was 6.6 MPa, the compressive strength at 24 hours was 19.8 MPa, the compressive strength at 28 days was 46.2 MPa, and the crown rebound rate was 5.9%.

[0028] Example 2 The early-strength and early-setting agent is characterized by being composed of the following raw materials in parts by weight: 70 parts of early-strength powder, 20 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum sulfate in a mass ratio of 55:30:8:7. The microspheres consist of a core material and a coating layer. The core material is composed of CSH nanocrystals, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7. The coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 72:16:12.

[0029] The test results showed that the initial slump of the mixture was 255 mm, the initial spread was 580 mm, the slump at 1 hour was 240 mm, the spread at 1 hour was 565 mm, the compressive strength at 3 hours was 1.7 MPa, the compressive strength at 6 hours was 6.9 MPa, the compressive strength at 24 hours was 22.3 MPa, the compressive strength at 28 days was 48.5 MPa, and the crown rebound rate was 5.2%.

[0030] Comparative Example 1 The formulation of Example 1 of patent CN110510906A was adopted.

[0031] The test results showed that the initial slump of the mixture was 240 mm, the initial spread was 550 mm, the compressive strength at 3 hours was 1.0 MPa, the compressive strength at 6 hours was 3.4 MPa, the compressive strength at 24 hours was 13.1 MPa, the compressive strength at 28 days was 41.2 MPa, and the crown rebound rate was 9.3%.

[0032] Comparative Example 2 The early-strength and early-setting agent is characterized by being composed of the following raw materials in parts by weight: 70 parts of early-strength powder, 20 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of fly ash, sulfoaluminate cement clinker, and aluminum sulfate in a mass ratio of 63:30:7. The microspheres consist of a core material and a coating layer. The core material is composed of CSH nanocrystals, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7. The coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 72:16:12.

[0033] The test results showed that the initial slump of the mixture was 240 mm, the initial spread was 565 mm, the slump at 1 hour was 210 mm, the spread at 1 hour was 520 mm, the compressive strength at 3 hours was 1.2 MPa, the compressive strength at 6 hours was 5.3 MPa, the compressive strength at 24 hours was 17.1 MPa, the compressive strength at 28 days was 40.7 MPa, and the crown rebound rate was 8.6%.

[0034] Comparative Example 3 The early-strength and early-setting agent is characterized by being composed of the following raw materials in parts by weight: 70 parts of early-strength powder, 20 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum sulfate in a mass ratio of 55:30:8:7. The microspheres consist of a core material and a coating layer. The core material is composed of polyaluminum sulfate, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7. The coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 72:16:12.

[0035] The test results showed that the initial slump of the mixture was 250 mm, the initial spread was 570 mm, the slump at 1 hour was 245 mm, the spread at 1 hour was 560 mm, the compressive strength at 6 hours was 1.8 MPa, the compressive strength at 24 hours was 8.6 MPa, the compressive strength at 28 days was 41.4 MPa, and the crown rebound rate was 12.5%.

[0036] Comparative Example 4 The early-strength and early-setting agent is characterized by being composed of the following raw materials in parts by weight: 70 parts of early-strength powder, 20 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum sulfate in a mass ratio of 55:30:8:7. The microspheres consist of a core material and a coating layer. The core material consists of fly ash microspheres, calcium formate, and triethanolamine in a mass ratio of 50:43:7. The coating layer consists of ethyl cellulose, hydrophobic fumed silica, and diethyl phthalate in a mass ratio of 72:16:12.

[0037] The test results showed that the initial slump of the mixture was 240 mm, the initial spread was 575 mm, the slump at 1 hour was 230 mm, the spread at 1 hour was 550 mm, the compressive strength at 24 hours was 7.7 MPa, the compressive strength at 28 days was 40.6 MPa, and the crown rebound rate was 14.7%.

[0038] Comparative Example 5 The early-strength and early-setting agent is characterized by being composed of the following raw materials in parts by weight: 70 parts of early-strength powder, 20 parts of microspheres, and 3 parts of sodium gluconate. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum sulfate in a mass ratio of 55:30:8:7. The microspheres consist of a core material and a coating layer. The core material is composed of CSH nanocrystals, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7. The coating layer is composed of ethyl cellulose and diethyl phthalate in a mass ratio of 88:12.

[0039] The test results showed that the initial slump of the mixture was 250 mm, the initial spread was 560 mm, the 6-hour compressive strength was 4.9 MPa, the 24-hour compressive strength was 15.5 MPa, the 28-day compressive strength was 42.5 MPa, and the crown rebound rate was 9.6%.

[0040] 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. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A quick-setting and early-strength agent for shotcrete, characterized in that, Composed of the following raw materials in parts by weight: 65-75 parts early-strength powder, 12-20 parts microspheres, and 1-5 parts retarder. The early-strength powder is composed of silica fume, sulfoaluminate cement clinker, lithium slag powder, and aluminum salts in a mass ratio of 45-55:25-35:8-12:5-15. The microspheres consist of a core material and a coating layer. The core material consists of CSH nanocrystals, calcium formate, calcium thiocyanate, and triethanolamine in a mass ratio of 45-55:30-40:8-12:3-7. The coating layer consists of ethyl cellulose, hydrophobic fumed silica, and a plasticizer in a mass ratio of 70-75:12-18:5-15.

2. The accelerator for shotcrete according to claim 1, characterized in that, The aluminum salt is at least one of aluminum sulfate and aluminum fluoride.

3. The accelerator for shotcrete according to claim 1, characterized in that, The plasticizer is at least one of diethyl phthalate and triethyl citrate.

4. The accelerator for shotcrete according to claim 1, characterized in that, The retarder is at least one of sodium gluconate, citric acid, sodium citrate, and boric acid.

5. The accelerator for shotcrete according to claim 1, characterized in that, The microsphere component preparation steps are as follows: 1) Core material preparation: CSH nanocrystal nuclei, calcium formate, and calcium thiocyanate were mixed and ground to a density of D90 ≤ 5 μm. After wet mixing with triethanolamine solution, the mixture was spray-granulated to obtain 80-150 μm core particles, which were then dried to obtain the core material. 2) Preparation of coating solution: Dissolve ethyl cellulose in an appropriate amount of ethanol, add plasticizer, stir evenly, add hydrophobic fumed silica, and disperse evenly. 3) Coating and curing: The core material is placed in a fluidized bed and sprayed into a coating liquid to coat the microspheres. The coated microspheres are then cured and collected by sieving to obtain 150-300μm particles.

6. The accelerator for shotcrete according to claim 5, characterized in that, Step 1) The triethanolamine solution is a triethanolamine ethanol solution with a mass fraction of 8-12% composed of triethanolamine and ethanol. The inlet air temperature for spray granulation is 42-48℃, the pressure is 0.28-0.32MPa, and the drying temperature is 40-45℃.

7. The accelerator for shotcrete according to claim 5, characterized in that, Step 2) Ethyl cellulose is dissolved in ethanol to form a solution with a mass fraction of 7-9%.

8. The accelerator for shotcrete according to claim 5, characterized in that, Step 3) The inlet air temperature of the fluidized bed is 36-40℃, and the fluidizing air velocity is 0.7-0.9m. 3 / h, atomization pressure is 0.23-0.27MPa.

9. The method for preparing the accelerator for shotcrete according to any one of claims 1-8, characterized in that, The process includes the following steps: mixing the early-strength powder, microsphere components, and retarder evenly to obtain the final product.

10. The application of the accelerator for shotcrete according to any one of claims 1-8 in the preparation and construction of shotcrete.