Accelerating early strength agent for shotcrete and preparation method and application thereof

Abstract

The present application relates to the technical field of cement-based admixtures, and particularly relates to a set-accelerating early-strength agent for shotcrete, a preparation method and application thereof, the set-accelerating early-strength agent is prepared by taking high-activity early-strength powder as a main component, adding self-made microspheres with slow-release precise control and resistance to the spraying process, and adding a retarder to prevent the risk of pipe blockage caused by the rapid setting of shotcrete, the set-accelerating early-strength agent overcomes the defects of traditional accelerators in the spraying environment, such as premature dissipation or failure, realizes the precise triggering and effective regulation of the release time of the set-accelerating early-strength effect, and provides new technical support for improving the instantaneity and reliability of shotcrete support.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cement-based admixtures, in particular to a set-accelerating early-strength agent for shotcrete and a preparation method and application thereof. BACKGROUND

[0002] Shotcrete technology has become an indispensable key support technology in the fields of tunnels, water conservancy and hydropower, slope protection, mining and underground engineering, etc. due to its convenient construction, high efficiency and good adaptability to complex structural surfaces. The core of shotcrete technology is to mix the concrete materials, which are then rapidly solidified by high-pressure gas through a shotcrete machine.

[0003] However, this process has special and stringent requirements for the setting and early strength performance of concrete materials: rapid initial setting to reduce rebound and rapid establishment of initial strength to support sufficient strength. The prior art CN107840593A discloses a liquid alkali-free accelerator for shotcrete, which is composed of 60-75 wt% of modified polyaluminum sulfate solution, 5-15 wt% of modified alcohol amine solution, 0-3 wt% of performance modifier, 0-4 wt% of stabilizer and water. CN110104987A discloses a high-early-strength alkali-free liquid accelerator, which is composed of the following raw materials in weight percentage: 40-50% of polyaluminum sulfate, 5-10% of metakaolin, 5-15% of nano-silica sol, 3-6% of alcohol amine, 1-4% of organic acid, 0.01-0.05% of thickening agent, 0.01-0.05% of dispersing agent, and the balance of water. CN118955003A discloses a low-rebound high-anti-permeability liquid alkali-free accelerator, which comprises the following raw materials in mass percentage: 60%-67% of accelerator, 5%-8% of solubilizer, 2%-4% of anti-permeability waterproof agent, 2%-3% of early-strength agent, 1%-2% of pH regulator, 0.5%-1.5% of suspending agent, and the balance of water.

[0004] The conventional set-accelerating early-strength agent in the prior art mainly uses inorganic salts with aluminum salts as the main component, such as aluminum sulfate, which often disperses prematurely and fails to act uniformly under the physical impact and air flow disturbance in the high-speed spraying environment, making it difficult to accurately control the setting and hardening behavior. SUMMARY

[0005] To solve the problems in the prior art, the present application provides a kind of shotcrete with early strength accelerator, specifically, the present application uses high-activity early strength powder as the main component, adds self-made microsphere component with slow-release precision control and resistance to spraying process, and adds a retarder to prevent the risk of pipe blockage caused by fast setting of shotcrete.The early strength accelerator of the present application overcomes the defects of traditional accelerators in early dissipation or failure in spraying environment, realizes the precise triggering and release timing of early strength effect, and provides new technical support for improving the immediacy and reliability of shotcrete support.

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

[0007] The early strength powder of the present application is a key component, which provides basic hydration products and micro-aggregate effect.The microsphere component is the core component of the present application, which provides precise slow-release and impact resistance function.The retarder adjusts the hydration induction period to avoid the construction risk (such as pipe blockage) caused by too fast setting, and ensures the workability.

[0008] Preferably, the early strength powder is composed of silica fume, sulphoaluminate 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 is composed of core material and coating layer, the core material is composed of C-S-H nanocrystalline core, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 45-55:30-40:8-12:3-7, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica and plasticizer in a mass ratio of 70-75:12-18:5-15.

[0011] The components of the core material of the microsphere component of the present application have a synergistic effect, wherein calcium formate is a strong calcium source with fast dissolution rate, which can provide high concentration Ca 2+The C-S-H nanocrystalline nucleus can accelerate the dissolution and hydration of tricalcium silicate, shorten the hydration induction period, promote the directional growth of the hydration product C-S-H gel around the crystal nucleus, and improve the compactness; the calcium thiocyanate is a strong conductive calcium source, and the strong conductivity can further accelerate ion diffusion; the triethanolamine mainly promotes the early dissolution of tricalcium aluminate and the formation of the hydration product, and the four substances can cooperate to accelerate the early hydration process. The coating layer has the advantages of compactness, compatibility, low surface adhesion, and hydrophobicity. Ethyl cellulose is the main film-forming matrix, which can be dissolved in a solvent (such as ethanol) to form a continuous film, and is the barrier subject. The hydrophobic fumed silica is uniformly dispersed in the ethyl cellulose matrix, which can significantly enhance the strength of the coating layer, improve the hydrophobicity, and reduce the friction coefficient of the film, effectively prevent the physical damage (such as scratches and abrasion) and water vapor permeation erosion of the microspheres in the stirring and conveying process, and the plasticizer is used to improve the flexibility and film-forming property of the EC film. In the concrete mixing, pumping and through the spray hose stage, the coating layer can effectively protect the core layer from being damaged. Only in the moment of high-pressure jet impact on the base surface, the strong mechanical impact force (impact force and airflow pressure) makes the microsphere coating layer break (or the solubility changes sharply), and the active ingredients in the core layer are released instantaneously, directly acting on the cement particles, and starting the high-strength 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 step is:

[0015] 1) Core material preparation: the C-S-H nanocrystalline nucleus, calcium formate and calcium thiocyanate are mixed and ground to D90≤5 μm, then sprayed into a triethanolamine solution for wet mixing, followed by spray granulation to obtain 80-150 μm core particles, and drying to obtain the core material,

[0016] 2) Coating liquid preparation: the ethyl cellulose is dissolved in an appropriate amount of ethanol, then a plasticizer is added and stirred uniformly, and then hydrophobic fumed silica is added and dispersed uniformly,

[0017] 3) Coating and curing: the core material is placed in a fluidized bed, and the coating liquid is atomized and sprayed to coat the core material to obtain coated microspheres, and the coated microspheres are cured and sieved to collect 150-300 μm particles.

[0018] Preferably, the triethanolamine solution in step 1) is a triethanolamine ethanol solution with a mass fraction of 8-12% of triethanolamine mixed with ethanol, the inlet air temperature for spray granulation is 42-48 ℃, the pressure is 0.28-0.32 MPa, and the drying temperature is 40-45 ℃.

[0019] Preferably, in step 2), ethyl cellulose is dissolved in ethanol to form a solution with a mass fraction of 7-9%.

[0020] Preferably, in step 3), the fluidized bed inlet air temperature is 36-40℃, the fluidized air speed is 0.7-0.9m / s, and the atomization pressure is 0.23-0.27MPa. 3

[0021] The present application also relates to a preparation method of the early strength accelerator for shotcrete, which specifically comprises the following steps: uniformly mixing the early strength powder, the microsphere component and the retarder, and obtaining the product.

[0022] The present application also relates to the application of the early strength accelerator for shotcrete in the preparation and construction of shotcrete.

[0023] Preferably, the addition amount of the early strength accelerator is 5-15% of the cement mass in the shotcrete.

[0024] Preferably, the use method of the early strength accelerator is as follows: after weighing, the early strength accelerator is first uniformly mixed with the cement, then water and aggregates are added and uniformly mixed to complete the preparation of the shotcrete mixture, and then the mixture is sprayed through the spraying equipment.

[0025] The retarder in the mixture plays a role in early hydration control to ensure the construction time of the mixture, the coating layer of the microsphere component can resist mechanical and solubility impact during wet mixing, and the active substances in 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 by high-pressure air or liquid flow (wet spraying method) at high speed through the spraying hose and nozzle. In the spraying pipeline, the coating layer of the microsphere component can still withstand the continuous flow friction and pressure. At the moment when the concrete slurry with great kinetic energy and impact force hits the construction surface (wall, rock mass, foundation, etc.) through the nozzle, the strong impact force acts on the microspheres, the coating layer of the microsphere component is broken under the action of high-pressure impact, and the active components in the core layer are released instantaneously and concentrated. Since they are in a superfine dispersed state (prepared by grinding), they quickly disperse and penetrate into the adjacent area of the cement particles. The core components work together: high-concentration Ca 2+ + effective nucleation induction points (C-S-H) + accelerant (TEA) + high-conductivity ions (SCN - ), multiple mechanisms rapidly induce rapid dissolution, precipitation and network crystallization of C3S and C3A, significantly shorten the induction period, and form dense C-S-H gel nucleation points to quickly establish an early network structure, thereby significantly improving the initial setting speed and early strength of the concrete. The shotcrete mixture quickly (within a few seconds to a few minutes) solidifies and begins to develop strength after hitting the base surface, and the rebound rate is also reduced.

[0026] ​Preferably, the shotcrete using the setting accelerating early strength agent of the present application can be used in tunnel lining base, slope reinforcement base, mine roadway support surface, foundation waterproof structure base and other engineering construction.

[0027] The present application has the following technical advantages:

[0028] 1. Excellent mechanical impact resistance: unique EC-hydrophobic SiO2 reinforced composite coating, giving the self-made microsphere component excellent resistance to physical wear, friction and shear damage during mixing, pumping and pipeline transportation, effectively protecting the core active components until the destination,

[0029] 2. Precise trigger release: the microsphere component coating only breaks and releases the core material at the moment of high pressure impact of the concrete jet impacting the base, achieving precise and concentrated supply of early strength active substances at key positions, overcoming the defects of premature dispersion and uncontrollable action time of existing additives,

[0030] 3. Significant acceleration of early strength development: the core material components are designed scientifically, with obvious synergistic effect: high solubility calcium source and strong conductivity calcium source provide sufficient ion environment and charge induction, C-S-H nanocrystal core greatly reduces the nucleation barrier, induces in-situ directional crystallization to shorten the induction period, and TEA cooperates to stimulate aluminate reaction, providing high concentration instant supply at the contact point of the base, achieving a leap in the setting and hardening process of the shotcrete, significantly reducing the rebound rate and rapidly improving the early and final strength of the shotcrete. DETAILED DESCRIPTION

[0031] To characterize the technical effect of the present application, a setting accelerating early strength agent was prepared and its performance was detected. During the test, a mixture was prepared according to the following proportions: P·O42.5 cement 300 kg / m 3 , fly ash 100 kg / m 3 , slag 50 kg / m 3 , 5-10 mm crushed stone 952 kg / m 3 , graded sand 900 kg / m 3 , total amount of polycarboxylic acid water reducer 1.5%, total amount of setting accelerating early strength agent 8%, and water-binder ratio 0.4. The initial slump and spread were detected, and then the 1h slump and spread were detected, and then a small shotcrete machine was used for shotcrete molding.

[0032] Example 1

[0033] The setting accelerating early strength agent is characterized by consisting of the following raw materials by weight: early strength powder 72 parts, microsphere component 18 parts, sodium gluconate 3 parts,

[0034] The early strength powder is composed of silica fume, sulphoaluminate cement clinker, lithium slag powder and aluminum sulfate in a mass ratio of 50:25:10:15,

[0035] The microsphere component is composed of a core material and a coating layer, the core material is composed of C-S-H nanocrystalline nucleus, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 52:33:9:6, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 75:15:10.

[0036] It is detected that the initial slump of the mixture is 245 mm, the initial spread is 570 mm, the 1h slump is 230 mm, the 1h spread is 550 mm, the 3h compressive strength is 1.5 MPa, the 6h compressive strength is 6.6 MPa, the 24h compressive strength is 19.8 MPa, the 28d compressive strength is 46.2 MPa, and the vault rebound rate is 5.9%.

[0037] Example 2

[0038] The accelerating early strength agent is characterized by being composed of the following raw materials in parts by weight: early strength powder 70 parts, microsphere component 20 parts, sodium gluconate 3 parts,

[0039] The early strength powder is composed of silica fume, sulphoaluminate cement clinker, lithium slag powder and aluminum sulfate in a mass ratio of 55:30:8:7,

[0040] The microsphere component is composed of a core material and a coating layer, the core material is composed of C-S-H nanocrystalline nucleus, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 72:16:12.

[0041] It is detected that the initial slump of the mixture is 255 mm, the initial spread is 580 mm, the 1h slump is 240 mm, the 1h spread is 565 mm, the 3h compressive strength is 1.7 MPa, the 6h compressive strength is 6.9 MPa, the 24h compressive strength is 22.3 MPa, the 28d compressive strength is 48.5 MPa, and the vault rebound rate is 5.2%.

[0042] Comparative Example 1

[0043] The CN110510906A patent embodiment 1 formula is adopted.

[0044] It is detected that the initial slump of the mixture is 240 mm, the initial spread is 550 mm, the 3h compressive strength is 1.0 MPa, the 6h compressive strength is 3.4 MPa, the 24h compressive strength is 13.1 MPa, the 28d compressive strength is 41.2 MPa, and the vault rebound rate is 9.3%.

[0045] Comparative Example 2

[0046] The setting accelerator is characterized in that it is composed of the following raw materials in parts by weight: early strength powder 70 parts, microsphere component 20 parts, and sodium gluconate 3 parts,

[0047] The early strength powder is composed of fly ash, sulphoaluminate cement clinker, and aluminium sulfate in a mass ratio of 63:30:7,

[0048] The microsphere component is composed of core material and coating layer, the core material is composed of C-S-H nanocrystalline core, calcium formate, calcium thiocyanate, and triethanolamine in a mass ratio of 50:35:8:7, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica, and diethyl phthalate in a mass ratio of 72:16:12.

[0049] It is detected that the initial slump of the mixture is 240 mm, the initial spread is 565 mm, the 1h slump is 210 mm, the 1h spread is 520 mm, the 3h compressive strength is 1.2 MPa, the 6h compressive strength is 5.3 MPa, the 24h compressive strength is 17.1 MPa, the 28d compressive strength is 40.7 MPa, and the vault rebound rate is 8.6%.

[0050] Comparative Example 3

[0051] The setting accelerator is characterized in that it is composed of the following raw materials in parts by weight: early strength powder 70 parts, microsphere component 20 parts, and sodium gluconate 3 parts,

[0052] The early strength powder is composed of silica fume, sulphoaluminate cement clinker, lithium slag powder, and aluminium sulfate in a mass ratio of 55:30:8:7,

[0053] The microsphere component is composed of core material and 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, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica, and diethyl phthalate in a mass ratio of 72:16:12.

[0054] It is detected that the initial slump of the mixture is 250 mm, the initial spread is 570 mm, the 1h slump is 245 mm, the 1h spread is 560 mm, the 6h compressive strength is 1.8 MPa, the 24h compressive strength is 8.6 MPa, the 28d compressive strength is 41.4 MPa, and the vault rebound rate is 12.5%.

[0055] Comparative Example 4

[0056] The setting accelerator is characterized in that it is composed of the following raw materials in parts by weight: early strength powder 70 parts, microsphere component 20 parts, and sodium gluconate 3 parts,

[0057] The early strength powder is composed of silica fume, sulphoaluminate cement clinker, lithium slag powder, and aluminium sulfate in a mass ratio of 55:30:8:7,

[0058] The microsphere component is composed of a core material and a coating layer, the core material is composed of fly ash microbeads, calcium formate and triethanolamine in a mass ratio of 50:43:7, and the coating layer is composed of ethyl cellulose, hydrophobic fumed silica and diethyl phthalate in a mass ratio of 72:16:12.

[0059] It is detected that the initial slump of the mixture is 240mm, the initial spread is 575mm, the 1h slump is 230mm, the 1h spread is 550mm, the 24h compressive strength is 7.7MPa, the 28d compressive strength is 40.6MPa, and the vault rebound rate is 14.7%.

[0060] Comparative Example 5

[0061] The accelerating early strength agent is characterized by being composed of the following raw materials in parts by weight: early strength powder 70 parts, microsphere component 20 parts, sodium gluconate 3 parts,

[0062] The early strength powder is composed of silica fume, sulphoaluminate cement clinker, lithium slag powder and aluminum sulfate in a mass ratio of 55:30:8:7,

[0063] The microsphere component is composed of a core material and a coating layer, the core material is composed of C-S-H nanocrystal core, calcium formate, calcium thiocyanate and triethanolamine in a mass ratio of 50:35:8:7, and the coating layer is composed of ethyl cellulose and diethyl phthalate in a mass ratio of 88:12.

[0064] It is detected that the initial slump of the mixture is 250mm, the initial spread is 560mm, the 6h compressive strength is 4.9MPa, the 24h compressive strength is 15.5MPa, the 28d compressive strength is 42.5MPa, and the vault rebound rate is 9.6%.

[0065] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for part or all of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

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.