A high-performance shotcrete and its preparation method

Abstract

The present invention discloses a high-performance shotcrete and a preparation method thereof, belonging to the technical field of shotcrete. The concrete comprises the following components by weight: 430-450 parts of cement, 800-850 parts of coarse aggregate, 850-900 parts of fine aggregate, 170-180 parts of water, 4-5 parts of a water reducer, 34-41 parts of an early-strength accelerator, 4-8 parts of a solidifying and durable component, and 1.0-1.4 parts of polypropylene fiber. A corresponding preparation method is also provided. The present invention achieves high performance shotcrete by selecting an early-strength accelerator and a solidifying and durable component and optimizing the preparation method. This can effectively reduce rebound, promote rapid development of early strength, and fully guarantee the long-term durability of shotcrete. Its application in tunnel engineering can significantly improve the performance of shotcrete, thereby improving the quality of the engineering structure and fully guaranteeing the service safety of tunnel engineering, thus having broad prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of shotcrete, in particular to high-performance shotcrete and a preparation method thereof. Background Art

[0002] Shotcrete is a type of concrete that is formed by spraying a pre-mixed material at high speed onto a surface using a spraying machine, where it solidifies and hardens. Its unique process allows for rapid formation, freedom from support, and strong adaptability, leading to its widespread application in tunnel initial support, slope protection, and structural reinforcement. With the development of shotcrete technology, its application in civil engineering is increasing. However, current issues with shotcrete include high rebound during construction, low early strength, and insufficient long-term durability, hindering its further development.

[0003] The pumpability of shotcrete requires a water-to-binder ratio that cannot be too low. Otherwise, frequent pipe blockages will occur, affecting construction efficiency. This conflicts with the goal of achieving both early strength and long-term durability. Furthermore, the jet-forming method used in shotcrete also determines that its internal pore structure differs significantly from that of conventional cast-in-place concrete. These characteristics have made it difficult to achieve breakthroughs in shotcrete's high-performance technology, characterized by low rebound, early high strength, and high durability.

[0004] In the prior art, patent publication number CN118757183A discloses a low-rebound, high-performance shotcrete. This technology primarily reduces rebound by adding rebound-suppressing materials and admixtures, using a mechanized spraying system equipped with real-time monitoring, calculation, and control of spraying parameters. While achieving good technical results, this technology does not significantly improve early strength. Patent publication number CN119143440A proposes a green, low-carbon, high-performance shotcrete using activated regenerated micropowder, along with its preparation method and construction process, to achieve high performance. However, this technology also fails to achieve high early strength and has limited improvements in durability.

[0005] Based on the above problems, a high-performance shotcrete and a preparation method thereof are proposed. Summary of the Invention

[0006] The object of the present invention is to provide a high-performance shotcrete and a preparation method thereof, so as to solve the problems in the background technology.

[0007] To achieve the above object, the present invention provides a high-performance shotcrete comprising the following components in parts by mass:

[0008] 430-450 parts of cement, 800-850 parts of coarse aggregate, 850-900 parts of fine aggregate, 170-180 parts of water, 4-5 parts of water reducer, 34-41 parts of early strength quick-setting admixture, 4-8 parts of solidifying and durable component, and 1.0-1.4 parts of polypropylene fiber.

[0009] Preferably, the early strength quick-setting agent comprises, by mass, 30-50 parts of aluminum sulfate, 10-20 parts of calcium nitrate, 2-5 parts of triethanolamine, 5-10 parts of polycarboxylic acid water reducer, 5-15 parts of silica sol, and 20-40 parts of water.

[0010] Preferably, the reinforced durable component is an alumina aerogel material with fly ash as reinforcement, and is added in the form of replacing cement in equal amounts.

[0011] Preferably, the tensile strength of the polypropylene fiber is ≥500 MPa and the length is 10-12 mm.

[0012] The present invention also provides a method for preparing high-performance shotcrete, comprising the following steps:

[0013] Cement, cementitious materials, strengthening and durable components, coarse aggregate and fine aggregate are put into a mixer in proportion by mass and mixed evenly; then polypropylene fiber is evenly dispersed in water, water and water reducer are added and mixed thoroughly, and then put into a wet spraying trolley and combined with early strength accelerating agent, and sprayed onto the sprayed surface to form.

[0014] Preferably, the preparation steps of the reinforced durable component are as follows:

[0015] S1. Dissolve aluminum isopropoxide in ethanol and stir until completely dissolved. Slowly add deionized water and continue stirring. Adjust the pH and stir until a uniform sol is formed.

[0016] S2, dispersing fly ash in ethanol and ultrasonically treating;

[0017] S3, adding the dispersed fly ash to the alumina sol, stirring until uniformly mixed, and allowing the mixed solution to stand until a wet gel is formed;

[0018] S4, aging the wet gel in ethanol, and then replacing the water in the wet gel with ethanol or acetone;

[0019] S5. Place the wet gel into a supercritical drying device and dry it using supercritical CO2 to obtain a reinforced and durable component.

[0020] Preferably, in S1, the mass ratio of aluminum isopropoxide to ethanol is 1:10~1:15, the stirring rate is 200~400rpm, the stirring time is 30~60min, the molar ratio of aluminum isopropoxide to deionized water is 3:1~4:1, the dropping rate of deionized water is 1~2mL / min, and stirring is continued for 30min after the deionized water is added dropwise. The pH adjustment process is to add nitric acid to adjust the pH to 3.5~4.5.

[0021] Preferably, in S2, the mass ratio of fly ash to ethanol is 1:20-1:30, and the ultrasonic time is 30-60 min;

[0022] In S3, the mass ratio of fly ash to sol is 2:3-2:5, the stirring rate is 200-300 rpm, the stirring time is 30-60 min, the standing temperature is 25° C. or 40-50° C., and the standing time is 12-24 h;

[0023] In S4, the aging time is 24 to 48 hours, the ethanol is replaced every 12 hours during the aging process, and the replacement process is 3 to 5 times, each soaking for 6 to 12 hours;

[0024] In the step S5, the drying conditions are: drying at 40-50° C. and 7.5-10 MPa for 6-12 hours.

[0025] Preferably, the preparation method of the early strength accelerating setting agent is as follows: dissolving calcium nitrate in water, stirring until completely dissolved, slowly adding aluminum sulfate, controlling the temperature to ≤40°C, continuously stirring until a transparent solution is obtained, adding an alkaline regulator, adjusting the pH to 6-7, then adding silica sol, stirring for 25-35 minutes to mix evenly, adding triethanolamine, continuing stirring for 8-12 minutes, and finally adding a polycarboxylic acid water reducer, stirring for 18-25 minutes, and filtering to obtain the finished product.

[0026] Preferably, the spraying wind pressure of the wet spraying trolley is 0.3~0.5MPa, the nozzle is perpendicular to the sprayed surface, the deflection angle is less than 6°, the spraying distance is 0.8~1.2m, and the slump of the concrete is 160~180mm.

[0027] Therefore, the present invention provides a high-performance shotcrete and a preparation method thereof. In the prepared shotcrete, an early-strength accelerating setting agent can fully stimulate hydration, promote the formation of cement hydration products, and quickly form strength; the solidifying and durable component can fully fill the internal pores of the concrete; the hydrophobicity and low density of the aerogel help reduce water penetration, enhance the freeze-thaw resistance and chemical corrosion resistance of the concrete, extend the service life, and also reduce the shrinkage and cracking of the concrete, thereby improving the structural integrity and durability; the presence of polypropylene fiber can reduce the segregation and bleeding of the concrete, improve workability and uniformity, and at the same time, the appropriate dosage is conducive to reducing microcracks inside the concrete, reducing permeability, and enhancing the anti-seepage ability.

[0028] The present invention addresses the problems of high rebound rate, low early strength and insufficient long-term durability in existing shotcrete technology. By selecting early-strength quick-setting agents and solidifying and durable components and optimizing the preparation method, the high performance of shotcrete is achieved. This can effectively reduce rebound, promote rapid development of early strength, and fully guarantee the long-term durability of shotcrete. Its application in the initial support of tunnels can significantly improve the performance of shotcrete, thereby improving the quality of engineering structures, fully guaranteeing the service safety of tunnel projects, and has broad prospects.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a preparation flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0033] Example

[0034] Prepare shotcrete according to the following weight ratios: cement: coarse aggregate: fine aggregate: water: water reducing agent: early strength accelerating agent: solidifying and durable component: polypropylene fiber = 444: 830: 870: 175: 4.5: 36: 6: 1.2. Figure 1 The specific steps are as follows:

[0035] S1. Prepare early strength accelerating setting agent: dissolve 15 parts of calcium nitrate in water, stir until completely dissolved, slowly add 40 parts of aluminum sulfate, control the temperature ≤40℃, continue stirring until a transparent solution is obtained, then add NaOH solution, adjust the pH to 6-7, then add 10 parts of silica sol, stir for 30 minutes to mix evenly, add 3 parts of triethanolamine, continue stirring for 10 minutes, finally add 8 parts of polycarboxylic acid water reducer, stir for 20 minutes, and filter to obtain the finished product.

[0036] S2. Prepare the durable component. The steps are as follows:

[0037] 1) Dissolve aluminum isopropoxide in ethanol at a mass ratio of 1:10. Stir at 200 rpm for 45 minutes until completely dissolved. Slowly add deionized water (molar ratio of aluminum isopropoxide to water: 3:1) at a rate of 2 mL / min. Continue stirring for 30 minutes. Add nitric acid to adjust the pH to 4.5. Stir until a uniform sol is formed.

[0038] 2) Disperse fly ash in ethanol at a mass ratio of 1:20 and ultrasonicate for 45 minutes to ensure uniform dispersion;

[0039] 3) Add the dispersed fly ash to the alumina sol in a fly ash to alumina sol mass ratio of 2:3, stir at 250 rpm for 60 minutes until uniformly mixed, and place the mixed solution at room temperature (25°C) for 12 hours until a wet gel is formed;

[0040] 4) Aging the wet gel in ethanol for 36 hours, replacing the ethanol every 12 hours to replace the water in the wet gel with ethanol, and replacing it five times, soaking for 6 hours each time;

[0041] 5) The wet gel was placed in a supercritical drying device and dried using supercritical CO2 at 40°C and 10 MPa for 8 h to obtain alumina aerogel with fly ash as reinforcement.

[0042] S3. Forming large-plate specimens: Cement, cementitious materials, strengthening and durable components, coarse aggregate, and fine aggregate are placed in a mixer according to the mass ratio and mixed evenly; then, polypropylene fibers are evenly dispersed in water, and water and a water reducer are added and mixed thoroughly. Subsequently, the mixture is placed in a wet spraying trolley and combined with an early-strength accelerator, and sprayed onto the sprayed surface to form large-plate specimens, and then subjected to rebound rate, mechanical property, and durability tests.

[0043] Comparative Example 1

[0044] Shotcrete was prepared according to the following weight ratio: cement: coarse aggregate: fine aggregate: water: water reducer: ordinary accelerator: solidifying and durable component: polypropylene fiber = 444:830:870:175:4.5:36:6:1.2. Large plate specimens were formed using the molding method of S3 in Example 1, and the rebound rate, mechanical properties, and durability tests were carried out.

[0045] Comparative Example 2

[0046] Shotcrete was prepared according to the following weight proportions: cement: coarse aggregate: fine aggregate: water: water reducer: early strength accelerating agent: solidifying and durable component: polypropylene fiber = 448:830:870:175:4.5:36:2:1.2. Large plate specimens were formed using the molding method of S3 in Example 1, and the rebound rate, mechanical properties, and durability tests were carried out.

[0047] Comparative Example 3

[0048] Shotcrete was prepared according to the following weight proportions: cement: coarse aggregate: fine aggregate: water: water reducer: early strength accelerating agent: solidifying and durable component: polypropylene fiber = 440: 830: 870: 175: 4.5: 36: 10: 1.2. Large plate specimens were formed using the molding method of S3 in Example 1, and the rebound rate, mechanical properties, and durability tests were carried out.

[0049] Comparative Example 4

[0050] Shotcrete was prepared according to the following weight proportions: cement: coarse aggregate: fine aggregate: water: water reducer: early strength accelerating agent: solidifying and durable component: polypropylene fiber = 444:830:870:175:4.5:36:6:0.8. Large plate specimens were formed using the molding method of S3 in Example 1, and the rebound rate, mechanical properties, and durability tests were carried out.

[0051] Comparative Example 5

[0052] Shotcrete was prepared according to the following weight ratio: cement: coarse aggregate: fine aggregate: water: water reducer: early strength accelerating agent: solidifying and durable component: polypropylene fiber = 444:830:870:175:4.5:36:6:1.6. Large plate specimens were formed using the molding method of S3 in Example 1, and the rebound rate, mechanical properties, and durability tests were carried out.

[0053] The above test results are shown in Table 1.

[0054] Table 1 Test results of different groups

[0055] ;

[0056] By comparing the examples with comparative example 1, when the ordinary accelerator is replaced by an early-strength accelerator, the early strength is significantly reduced and the rebound rate is increased due to the lack of early-strength components in the accelerator.

[0057] By comparing the embodiment and comparative example 2, when the solidifying and durable component is lower than the limited dosage, the filling effect of the solidifying and durable component is difficult to fully exert, so the rebound rate increases and the durability deteriorates significantly.

[0058] By comparing the embodiment and comparative example 3, when the amount of the solidifying and durable component is higher than the limited dosage, the amount of cement replaced increases, which will lead to a decrease in strength and an increase in rebound rate.

[0059] By comparing the embodiment with comparative example 4, when the polypropylene fiber dosage is lower than the specified value, the improvement effect of the fiber on the cohesiveness of the concrete is reduced, the defects of the concrete increase, resulting in an increase in the rebound rate and a deterioration in the density.

[0060] By comparing the embodiment and comparative example 5, when the polypropylene fiber content is higher than the specified value, the concrete is too viscous and not conducive to construction, resulting in an increase in the rebound rate.

[0061] Therefore, the present invention provides a high-performance shotcrete and a preparation method thereof, which realizes high performance of shotcrete by selecting an early-strength accelerator and a durable strengthening component and optimizing the preparation method. It can effectively reduce rebound, promote rapid development of early strength, and fully guarantee the long-term durability of shotcrete. Its application in tunnel engineering can significantly improve the performance of shotcrete, thereby improving the quality of engineering structures, fully guaranteeing the service safety of tunnel engineering, and has broad prospects.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high performance shotcrete, characterized in that: The following components are included in parts by mass: 430-450 parts of cement, 800-850 parts of coarse aggregate, 850-900 parts of fine aggregate, 170-180 parts of water, 4-5 parts of water reducer, 34-41 parts of early strength accelerating admixture, 4-8 parts of solidifying and durable component, 1.0-1.4 parts of polypropylene fiber; The early strength quick-setting admixture comprises, by mass, 30 to 50 parts of aluminum sulfate, 10 to 20 parts of calcium nitrate, 2 to 5 parts of triethanolamine, 5 to 10 parts of polycarboxylic acid water reducer, 5 to 15 parts of silica sol, and 20 to 40 parts of water; The reinforced durable component is an alumina aerogel material with fly ash as reinforcement; The tensile strength of the polypropylene fiber is ≥500 MPa, and the length is 10-12 mm.

2. A method for preparing high-performance shotcrete according to claim 1, characterized in that: The following steps are involved: (1) Preparation of a reinforced durable component, as follows: S1. Dissolve aluminum isopropoxide in ethanol and stir until completely dissolved. Slowly add deionized water and continue stirring. Adjust the pH and stir until a uniform sol is formed. S2, dispersing fly ash in ethanol and ultrasonically treating; S3, adding the dispersed fly ash to the alumina sol, stirring until uniformly mixed, and allowing the mixed solution to stand until a wet gel is formed; S4, aging the wet gel in ethanol, and then replacing the water in the wet gel with ethanol or acetone; S5, placing the wet gel into a supercritical drying device and drying it using supercritical CO2 to obtain a reinforced durable component; (2) Preparation of early strength accelerating setting agent, specifically: Dissolve calcium nitrate in water and stir until completely dissolved. Slowly add aluminum sulfate, control the temperature ≤40°C, continue stirring until a transparent solution is obtained, add an alkaline regulator, adjust the pH to 6-7, then add silica sol, stir for 25-35 minutes to mix evenly, add triethanolamine, continue stirring for 8-12 minutes, finally add a polycarboxylic acid water reducer, stir for 18-25 minutes, and filter to obtain the finished product. (3) Put cement, strengthening and durable components, coarse aggregate and fine aggregate into a mixer according to the mass ratio and mix them evenly; Then disperse the polypropylene fiber evenly in the water, add water and water reducer to mix thoroughly, then put it into the wet spraying trolley and combine it with the early strength quick-setting agent, and spray it onto the sprayed surface to form it.

3. The method for preparing high-performance shotcrete according to claim 2, wherein: In S1, the mass ratio of aluminum isopropoxide to ethanol is 1:10-1:15, the stirring rate is 200-400 rpm, the stirring time is 30-60 min, the molar ratio of aluminum isopropoxide to deionized water is 3:1-4:1, the dropping rate of deionized water is 1-2 mL / min, and stirring is continued for 30 min after the deionized water is added. The pH adjustment process is to add nitric acid to adjust the pH to 3.5-4.

5.

4. The method for preparing high-performance shotcrete according to claim 2, wherein: In S2, the mass ratio of fly ash to ethanol is 1:20-1:30, and the ultrasonic time is 30-60 min; In S3, the mass ratio of fly ash to sol is 2:3-2:5, the stirring rate is 200-300 rpm, the stirring time is 30-60 min, the standing temperature is 25° C. or 40-50° C., and the standing time is 12-24 h; In S4, the aging time is 24 to 48 hours, the ethanol is replaced every 12 hours during the aging process, and the replacement process is 3 to 5 times, each time soaking for 6 to 12 hours; In the step S5, the drying conditions are: drying at 40-50° C. and 7.5-10 MPa for 6-12 hours.

5. The method for preparing high-performance shotcrete according to claim 2, wherein: The spraying air pressure of the wet spraying trolley is 0.3~0.5MPa, the nozzle is perpendicular to the sprayed surface, the deflection angle is less than 6°, and the spraying distance is 0.8~1.2m.

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