Low-shrinkage high-toughness sprayed concrete material as well as preparation method and application thereof

Abstract

The invention discloses a low-shrinkage high-toughness sprayed concrete material as well as a preparation method and application thereof, and the low-shrinkage high-toughness sprayed concrete material is prepared from the following materials in parts by mass: 400 to 440 parts of cement, 50 to 70 parts of coal ash, 20 to 40 parts of silica fume, 170 to 190 parts of water, 850 to 880 parts of fine aggregate, 770 to 810 parts of coarse aggregate, 30 to 50 parts of accelerator and 3.2 to 6.0 parts of water reducing agent. Hybrid fibers: 30 to 50 parts of steel fibers and 0.9 to 2.7 parts of organic fibers. The low-shrinkage high-toughness sprayed concrete material provided by the invention can ensure high compressive strength and toughness, also has good durability and stability, effectively improves the construction quality of tunnel engineering, and has very excellent market prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete preparation, and particularly relates to a low-shrinkage and high-toughness shotcrete material, a preparation method thereof, and an application thereof. Background Art

[0002] As an efficient support material, shotcrete is widely used in tunnel engineering, slope reinforcement, underground structure repair and other fields. It is quickly formed by a high-pressure spraying process, can effectively fit complex rock surfaces, provide support strength in a timely manner, and inhibit the deformation of surrounding rocks. Tunnels have become an effective way to solve traffic barriers such as across seas, with advantages such as little environmental impact and round-the-clock travel.

[0003] Currently, traditional shotcrete has problems such as insufficient toughness, significant brittleness, and large shrinkage causing cracking. Compared with ordinary concrete, due to the incorporation of accelerators, shotcrete will accelerate the early hydration reaction, and thus its early shrinkage performance will be greater than that of ordinary concrete. Due to the special working characteristics of shotcrete, it participates in the initial support force immediately after forming. Therefore, the shrinkage deformation of shotcrete and the resulting cracking problem are extremely important for the safety of the tunnel support structure and the stability of surrounding rocks. Excessive shrinkage of shotcrete will cause a gap between the shotcrete and the steel arch, thus providing a channel for water conveyance. In addition, the shrinkage deformation of shotcrete generates a large shrinkage stress under the restraint of the steel mesh and surrounding rocks, resulting in restrained shrinkage cracking. This exacerbates the leakage of the initial support structure. The shrinkage process of shotcrete is the key factor leading to the cracking of tunnel structures. Especially in tunnels with frequent dynamic loads and complex geological conditions, the early cracking and long-term durability deficiency of concrete seriously threaten the project safety. To solve the above problems, the research direction of shotcrete materials mainly focuses on raw material improvement and construction process optimization.

[0004] 103626444A discloses a construction process of steel fiber shotcrete, CN106810155A discloses a tunnel reinforcement lining, a method for bonding new and old steel fiber shotcrete, and an adhesive, CN110981345A discloses a shotcrete and a construction method thereof, CN108046712A discloses a high-strength and low-rebound shotcrete and a construction process thereof. However, in the above-mentioned shotcrete, excessive steel fibers are difficult to disperse and easily cause shotcrete blockage problems, and the control effect of steel fibers on early plastic cracks and microcracks is not obvious. In addition, steel fibers are prone to corrosion in a chloride ion or humid environment, resulting in volume expansion damage, so that the durability of concrete is insufficient to meet the requirements of tunnel structure design. Summary of the Invention

[0005] In view of the deficiencies of the existing technology, the present invention proposes a new type of green shotcrete material with low shrinkage and high toughness. The shotcrete material provided by the present invention can ensure its high compressive strength and toughness while also having good durability and stability, has excellent market prospects, and effectively improves the construction quality of tunnel engineering.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] As a first aspect of the present invention, it provides a low shrinkage and high toughness shotcrete material, which contains the following materials in parts by mass:

[0008] Cement: 400 - 440 parts,

[0009] Fly ash: 50 - 70 parts,

[0010] Silica fume: 20 - 40 parts,

[0011] Water: 170 - 190 parts,

[0012] Fine aggregate: 850 - 880 parts,

[0013] Coarse aggregate: 770 - 810 parts,

[0014] Accelerator: 30 - 50 parts,

[0015] Water reducing agent: 3.2 - 6.0 parts,

[0016] Hybrid fiber: Steel fiber: 30 - 50 parts, Organic fiber: 0.9 - 2.7 parts.

[0017] Preferably, the organic fiber is selected from at least one of polypropylene fiber, polyethylene fiber or polyacrylonitrile fiber.

[0018] Preferably, in the low shrinkage and high toughness shotcrete material, the dosage range of steel fiber per cubic meter of concrete is 30 kg / m 3 -50 kg / m 3 , and the dosage range of polypropylene fiber per cubic meter of concrete is 0.9 kg / m 3 -2.7 kg / m 3 ; preferably, the fiber dosage per cubic meter of concrete is 35 kg / m of steel fiber 3 and 2.25 kg / m of polypropylene fiber 3 .

[0019] Preferably, in the low shrinkage and high toughness shotcrete material, the dosage of fly ash per cubic meter of concrete is 60 kg / m 3 , and the dosage of silica fume is 30 kg / m 3 .

[0020] In an embodiment of the present invention, the low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass: cement: 420 parts, fly ash: 60 parts, silica fume: 30 parts, water: 180 parts, sand: 860 parts, gravel: 790 parts, accelerating agent: 40 parts, water-reducing agent: 5.1 parts, steel fiber: 35 parts, organic fiber: 2.25 parts.

[0021] As a second aspect of the present invention, there is provided a method for preparing a low-shrinkage and high-toughness shotcrete material, comprising the following steps:

[0022] S1: Premix and premix river sand, gravel, and fibers for 1 - 2 min to evenly disperse the fibers and obtain a premixed material;

[0023] S2: Dry mix cement, fly ash, silica fume, and the premixed material for 1 - 2 min to obtain a dry-mixed material;

[0024] S3: Mix and stir the dry-mixed material with the water-reducing agent and water for 2 - 4 min to obtain a wet-mixed material; during use, mix the wet-mixed material (mixing material) with the accelerating agent through a concrete wet shotcreting machine and spray it out to obtain the low-shrinkage and high-toughness shotcrete material.

[0025] As a third aspect of the present invention, there is provided an application of the low-shrinkage and high-toughness shotcrete material as a support material.

[0026] In the present invention, fly ash and high-content silica fume are used to replace part of the cement to participate in the hydration reaction. Utilizing the synergistic effect of silica fume and fly ash, silica fume compensates for the disadvantage of low early activity of fly ash in the early stage and improves the early strength. The continuous pozzolanic effect of fly ash aims to improve the later-stage density and durability. And silica fume can reduce plastic shrinkage, fly ash reduces the temperature rise, and they synergistically inhibit shrinkage cracks. In addition, the present invention uses a composite incorporation of steel fibers and polypropylene fibers. Through the complementary and synergistic effects of the fiber material properties, crack control is achieved from the micro to the macro scale at all stages, thereby improving the overall performance of the shotcrete. And by combining mineral admixtures and alkali-free accelerating agents to optimize the hydration process, fiber-matrix synergistic strengthening is realized. In the preparation process, a premixing fiber dispersion technology is adopted to ensure the mutual overlap between fibers, reduce the occurrence of fiber agglomeration, ensure the uniform distribution of fibers and rapid setting. This research aims to solve the problems of fiber toughening and large shrinkage of shotcrete causing cracking, and provide theoretical support and technical breakthroughs for the durability and safety of shotcrete under complex geological conditions.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. This application provides a low-shrinkage and high-toughness shotcrete material. By replacing part of the cement with fly ash and silica fume, it can not only reduce carbon emissions and achieve greenization, but also significantly improve the compactness, crack resistance, and durability of concrete through the pozzolanic effect and micro-filling effect. At the same time, in the present invention, the high content of fly ash is beneficial to the "ball bearing effect" of smooth and spherical fly ash particles, which can reduce internal friction and thus improve the fluidity and pumpability of concrete.

[0029] 2. This application provides a low-shrinkage and high-toughness shotcrete material. By mixing steel fibers and polypropylene fibers, it can not only improve the mechanical strength of shotcrete, but also improve the cohesion and fluidity of concrete. Through experimental exploration and comparison, the contents of polypropylene fibers and steel fibers with better effects are proposed. Using polypropylene fibers to replace part of the steel fibers can reduce the resistance to fluidity caused by excessive steel fibers in the concrete system, thereby improving its fluidity and reducing the problem of pipe blockage.

[0030] 3. This application provides a low-shrinkage and high-toughness shotcrete material. By mixing steel fibers and polypropylene fibers, it gives play to the advantages of both and the advantages of their mutual synergy to limit the generation of early cracks and the development of late cracks. Steel fibers bear the main load, and polypropylene fibers delay the generation and propagation of microcracks. The combination of the two significantly improves the energy absorption efficiency. Using polypropylene fibers to replace part of the steel fibers can not only form a good fiber network to fill capillary pores, but also reduce the material cost while ensuring performance.

[0031] 4. This application provides a low-shrinkage and high-toughness shotcrete material, and its preparation and construction methods are simple, without involving the use of more construction equipment, thus avoiding an increase in construction costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0033] Figure 1 It is the SEM diagram of the fibers in the shotcrete in Example 1, where a is polypropylene fiber and b is steel fiber;

[0034] Figure 2 It is the change diagram of the cumulative void volume of the shotcrete in Examples 1-5 and Comparative Examples 1-5 at 28 days;

[0035] Figure 3 It is the change diagram of the compressive strength of the shotcrete in Examples 1-5 and Comparative Examples 1-5;

[0036] Figure 4Graphs showing the changes in splitting tensile strength and flexural strength of shotcrete for Examples 1-5 and Comparative Examples 1-5;

[0037] Figure 5 Graph showing the drying shrinkage rate changes of shotcrete for Examples 1-5 and Comparative Examples 1-5;

[0038] Figure 6 Graph showing the slump changes of shotcrete for Examples 1-5 and Comparative Examples 1-5. Detailed implementation manners

[0039] The following will further illustrate and demonstrate the technical solutions in the above-mentioned inventive content of the present application in the form of specific implementation manners. And the following embodiments are only actual embodiments for explaining and interpreting the content of the technical solutions in the specification, and should not limit the scope of the claims to be protected by the present application. All technical products based on the technical solutions described in the inventive content of the present application should be covered within the scope to be protected by the present application.

[0040] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0041] I. A low-shrinkage and high-toughness shotcrete material provided by the present invention, in parts by weight, the shotcrete material includes a mixture of the following components:

[0042] Cement: 400 - 440 parts (such as 400 parts, 410 parts, 420 parts, 430 parts, 440 parts),

[0043] Fly ash: 50 - 70 parts (such as 50 parts, 55 parts, 60 parts, 65 parts, 70 parts),

[0044] Silica fume: 20 - 40 parts (such as 20 parts, 25 parts, 30 parts, 35 parts, 40 parts),

[0045] Water: 170 - 190 parts (such as 170 parts, 175 parts, 180 parts, 185 parts, 190 parts),

[0046] River sand: 850 - 880 parts (such as 850 parts, 860 parts, 865 parts, 870 parts, 880 parts),

[0047] Gravel: 770 - 810 parts (such as 770 parts, 780 parts, 790 parts, 800 parts, 810 parts),

[0048] Accelerator: 30 - 50 parts (such as 30 parts, 35 parts, 40 parts, 45 parts, 50 parts),

[0049] Water reducing agent: 3.2 - 6.0 parts (such as 3.2 parts, 4.0 parts, 4.8 parts, 5.2 parts, 6.0 parts),

[0050] Hybrid fiber: Steel fiber: 30 - 50 parts (such as 30 parts, 35 parts, 40 parts, 45 parts, 50 parts or any number between 30 and 50 parts), organic fiber: 0.9 - 2.7 parts (such as 0.9 parts, 1.35 parts, 1.8 parts, 2.25 parts, 2.7 parts or any number between 0.9 and 2.7 parts); The organic fiber is selected from at least one of polypropylene fiber, polyethylene fiber or polyacrylonitrile fiber.

[0051] Among them, the steel fiber is a copper-plated end-hooked steel fiber with a length of 20 - 30 mm and a diameter of 0.5 - 0.75 mm, and the organic fiber is a polypropylene fiber with a length of 10 - 20 mm and a diameter of about 0.02 - 0.05 mm.

[0052] A low-shrinkage and high-toughness shotcrete material provided by the present invention, the preparation method includes the following steps:

[0053] Premix and premix river sand, stones and fibers for 1 - 2 minutes to make the fibers evenly dispersed to obtain a premixed material; then dry mix cement, fly ash, silica fume and the premixed material for 1 - 2 minutes to obtain a dry-mixed material; then mix and stir the dry-mixed material with the water reducing agent and water for 2 - 4 minutes to obtain a wet-mixed material; during use, mix the wet-mixed material with a quick-setting agent through a concrete wet shotcreting machine and spray it out to obtain the low-shrinkage and high-toughness shotcrete material.

[0054] Second, the raw materials used in the present invention are as follows:

[0055] 1. The cement is ordinary Portland cement PO42.5, purchased from Qingdao Shanshui Group Co., Ltd.;

[0056] 2. The fly ash is Class F Grade I fly ash, and the silica fume is microsilica, both purchased from Jiangsu Sobute New Materials Co., Ltd.;

[0057] Silica fume composition (%)

[0058]

[0059] Fly ash composition (%)

[0060]

[0061]

[0062] 2. The river sand is medium sand in Zone II with an average particle size of 0.05 mm - 0.25 mm, purchased from Yizheng Hongmao Filter Material Co., Ltd., and the stone material is continuously graded stone with a size of 5 - 10 mm, purchased from Zhenjiang Kaiyu Building Materials Co., Ltd.;

[0063] 3. The water reducing agent is a polycarboxylate superplasticizer with a water reducing rate of 30 - 40%, purchased from Jiangsu Sobute New Materials Co., Ltd.;

[0064] 4. The accelerating agent is an early - strength liquid fluoride - free and alkali - free accelerating agent, purchased from Jiangsu Sobute New Materials Co., Ltd.

[0065] 5. The steel fiber is end - hooked steel fiber with a diameter of 0.5 mm, a length of 30 mm, and a tensile strength ≥ 1000 MPa; the organic fiber is at least one of polypropylene fibers with a diameter of 0.02 mm, a length of 12 mm, and a tensile strength ≥ 500 MPa.

[0066] Example 1, a low - shrinkage and high - toughness shotcrete material

[0067] It includes the following materials in parts by mass:

[0068] Cement: 420 parts

[0069] Fly ash: 60 parts

[0070] Silica fume: 30 parts

[0071] Water: 180 parts

[0072] Sand: 860 parts

[0073] Gravel: 790 parts

[0074] Accelerating agent: 40 parts

[0075] Water reducing agent: 5.1 parts

[0076] Hybrid fiber: Steel fiber: 35 parts, Organic fiber: 2.25 parts.

[0077] Its preparation method is:

[0078] Premix and pre - mix river sand, gravel, and fibers for 1 - 2 min to evenly disperse the fibers and obtain a premix; then dry - mix cement, fly ash, silica fume with the premix for 1 - 2 min to obtain a dry - mix; then mix the dry - mix with the water reducing agent and water and stir for 2 - 4 min to obtain a wet - mix; during use, mix the wet - mix with the accelerating agent through a concrete wet - spraying machine and spray out to obtain the low - shrinkage and high - toughness shotcrete material.

[0079] Example 2, a low - shrinkage and high - toughness shotcrete material

[0080] It includes the following materials in parts by mass:

[0081] Cement: 420 parts

[0082] Fly ash: 50 parts

[0083] Silica fume: 40 parts

[0084] Water: 180 parts

[0085] Sand: 860 parts

[0086] Gravel: 790 parts

[0087] Quick-setting agent: 40 parts

[0088] Water-reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 35 parts Organic fiber: 2.25 parts. Prepared by the preparation method of Example 1.

[0089] Example 3, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0090] Cement: 420 parts

[0091] Fly ash: 60 parts

[0092] Silica fume: 30 parts

[0093] Water: 180 parts

[0094] Sand: 860 parts

[0095] Gravel: 790 parts

[0096] Quick-setting agent: 40 parts

[0097] Water-reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 40 parts Organic fiber: 1.8 parts. Prepared by the preparation method of Example 1.

[0098] Example 4, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0099] Cement: 420 parts

[0100] Fly ash: 60 parts

[0101] Silica fume: 30 parts

[0102] Water: 180 parts

[0103] Sand: 860 parts

[0104] Gravel: 790 parts

[0105] Quick-setting agent: 40 parts

[0106] Water-reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 45 parts Organic fiber: 1.35 parts. Prepared by the preparation method of Example 1.

[0107] Example 5, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0108] Cement: 420 parts

[0109] Fly ash: 60 parts

[0110] Silica fume: 30 parts

[0111] Water: 180 parts

[0112] Sand: 860 parts

[0113] Gravel: 790 parts

[0114] Accelerator: 40 parts

[0115] Water reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 35 parts Organic fiber: 2.7 parts. Prepared by the preparation method of Example 1.

[0116] Comparative Example 1, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0117] Cement: 440 parts

[0118] Fly ash: 70 parts

[0119] Water: 180 parts

[0120] Sand: 860 parts

[0121] Gravel: 790 parts

[0122] Accelerator: 40 parts

[0123] Water reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 35 parts Organic fiber: 2.25 parts. Prepared by the preparation method of Example 1.

[0124] Comparative Example 2, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0125] Cement: 470 parts

[0126] Silica fume: 40 parts

[0127] Water: 180 parts

[0128] Sand: 860 parts

[0129] Gravel: 790 parts

[0130] Accelerator: 40 parts

[0131] Water reducing agent: 5.1 parts Hybrid fiber: Steel fiber: 35 parts Organic fiber: 2.25 parts. Prepared by the preparation method of Example 1.

[0132] Comparative Example 3, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0133] Cement: 420 parts

[0134] Fly ash: 60 parts

[0135] Silica fume: 30 parts

[0136] Water: 180 parts

[0137] Sand: 860 parts

[0138] Gravel: 790 parts

[0139] Quick-setting agent: 40 parts

[0140] Water-reducing agent: 5.1 parts

[0141] Hybrid fiber: Steel fiber: 50 parts.

[0142] Prepared by using the preparation method of Example 1.

[0143] Comparative Example 4, a low-shrinkage and high-toughness shotcrete material comprises the following materials in parts by mass:

[0144] Cement: 420 parts

[0145] Fly ash: 60 parts

[0146] Silica fume: 30 parts

[0147] Water: 180 parts

[0148] Sand: 860 parts

[0149] Gravel: 790 parts

[0150] Quick-setting agent: 40 parts

[0151] Water-reducing agent: 5.1 parts

[0152] Organic fiber: 2.7 parts.

[0153] Prepared by using the preparation method of Example 1.

[0154] Comparative Example 5

[0155] Cement: 420 parts

[0156] Fly ash: 60 parts

[0157] Silica fume: 30 parts

[0158] Water: 180 parts

[0159] Sand: 860 parts

[0160] Gravel: 790 parts

[0161] Quick-setting agent: 40 parts

[0162] Water reducing agent: 5.1 parts

[0163] Hybrid fiber: Steel fiber: 35 parts, Organic fiber: 2.25 parts.

[0164] Dry mix river sand, gravel, fiber, cement, fly ash, and silica fume for 1 - 2 min to obtain a dry mix; then mix the dry mix with the water reducing agent and water and stir for 2 - 4 min to obtain a wet mix; during use, mix the batching (wet mix) with a quick-setting agent through a concrete wet shotcreting machine and spray it out to obtain the shotcrete material.

[0165] Test examples

[0166] 1. For the relevant experiments on the compressive strength, flexural strength, and splitting tensile strength of concrete, follow the standard of "Test Scheme for Mechanical Properties of Ordinary Concrete" (GB / T 50081 - 2019). For the splitting tensile test, apply the load continuously and uniformly at a rate of 0.07 MPa / s until failure. For the flexural test, the test specimens are molded into 100 mm × 100 mm × 400 mm specimens and tested after curing for 28 d under standard curing conditions. Among them, the higher the splitting tensile strength and flexural strength, the better the crack resistance of the shotcrete.

[0167] 2. Conduct the shrinkage test on the concrete according to the specification (GB / T 50082 - 2024). After the specimens are molded, they should be cured with the mold for 1 d, and the specimens should not be damaged when the mold is removed. After the specimens are demolded, they should be immediately sent to a standard curing room with a temperature of (20 ± 2) °C and a relative humidity of more than 95% for curing.

[0168] The shrinkage strain of the specimens can be characterized by the following formula:

[0169]

[0170] Among them, ε st is the shrinkage rate of the concrete at test day t; L b is the measured gauge length of the specimen (mm); L0 is the length of the specimen measured at the initial time (mm); L t is the length of the specimen measured at the curing age of t days (mm). The calculation is accurate to 1.0×10 -6 .

[0171] 3. Use a field emission scanning electron microscope (SEM) to observe the bonding situation between the fiber and the matrix.

[0172] The SEM image of the fiber in the shotcrete in Example 1 is as shown in Figure 1As shown by a and b, it can be seen that the steel fibers are closely combined with the matrix to form physical anchoring, creating a "skeleton support" at the macroscopic cracks. The polypropylene fibers have a smooth and fine surface, and their flexibility allows for local deformation, enabling them to act better in the microcrack area. The rigidity of the steel fibers and the flexibility of the polypropylene fibers complement each other, forming a gradient interface structure, thereby better enhancing the overall interfacial toughness and forming a multi-layer crack resistance barrier.

[0173] 4. Use the PQ001 low-field nuclear magnetic resonance analyzer produced by Suzhou Niumai Company to detect the pore structure of the specimens. The specimens need to be first placed in a standard curing room (the temperature of this curing room is maintained at 20 ± 2 °C, and the relative humidity should not be less than 95% RH) for 28 days of curing. After reaching the curing period, take them out, carefully break them with a small hammer, select the fragments without cracks from them, conduct saturated water treatment on these fragments. After the treatment is completed, put the prepared specimens to be tested into the cylindrical tube of the LF-NMR instrument, and then make corresponding adjustments to the relevant parameters of the instrument, and then carry out the testing work.

[0174] 5. Conduct the slump test on the wet concrete mixture (mixing material) prepared in step S3 according to the "Standard Test Method for Performance of Ordinary Concrete Mixtures" (GB / T 50080 - 2016).

[0175] The results are as Figure 2 shown. It can be seen that the total porosity of Example 1 is the lowest, which is consistent with the change law of its compressive strength test. This indicates that at this ratio, the synergistic effect of fly ash, silica fume, and the two types of fibers is the best, which can effectively reduce the porosity of the shotcrete and form a denser shotcrete structure.

[0176] The diagrams of the pore structure changes, compressive strength changes, splitting tensile strength, flexural strength changes, and drying shrinkage rate changes of the shotcrete for Examples 1, 2, 3, 4, 5 and Comparative Examples 1, 2, 3, 4, 5 are respectively as Figures 3 - 5 well as shown in Table 1 and Table 2:

[0177] Table 1

[0178]

[0179]

[0180] Table 2

[0181] Example 1d shrinkage rate 3d shrinkage rate 7d shrinkage rate 28d shrinkage rate Example 1 10.4 28.18 97 253 Example 2 25.31 46.36 98.18 312 Example 3 13.37 35 110.91 301 Example 4 15 76 207 355 Example 5 13.1 44.7 146.2 331 Comparative Example 1 113 250 355 469 Comparative Example 2 86 214 339 540 Comparative Example 3 37 131 225 381 Comparative Example 4 21 68 158 367 Comparative Example 5 15.7 68.16 221.1 377

[0182] The slump results are as shown in Table 3 and Figure 6 shown:

[0183] Table 3

[0184]

[0185]

[0186] Comparing Comparative Examples 1, 3, 4, and 5, while keeping the dosages of fly ash and silica fume unchanged, the fiber dosage per cubic meter of concrete is 35 kg / m of steel fiber 3 and 2.25 kg / m of polypropylene fiber 3 (Example 1), the compressive strength at 1 day, the compressive strength at 28 days, the splitting tensile strength, and the flexural strength of the shotcrete are relatively high, and the shrinkage rate is relatively low. This indicates that at this ratio, the synergistic effect of the two fibers is the best, which can effectively reduce the porosity of the shotcrete and form a denser concrete structure, thereby improving the mechanical properties and shrinkage durability of the shotcrete.

[0187] Comparing Examples 1 and 2, when the fiber dosage remains unchanged, the fly ash dosage per cubic meter of concrete is 60 kg / m 3 and the silica fume dosage is 30 kg / m 3 (Example 1), all properties are optimal. This shows that at this ratio, fly ash and silica fume play a good synergistic hydration effect. Silica fume makes up for the disadvantage of low early activity of fly ash and improves the early strength. The continuous pozzolanic effect of fly ash improves the later-stage density. However, when there is too much silica fume, it causes too many fine particles to easily form local agglomeration and destroys the uniformity. Therefore, the early strength of Example 2 is still slightly lower than that of Example 1.

[0188] In Comparative Example 1, only fly ash is used to replace part of the cement, and in Comparative Example 2, only silica fume is used to replace part of the cement. The mechanical properties of both are lower than those of Example 1. This shows that single doping of a certain fly ash or silica fume cannot effectively improve the performance of the shotcrete like the compound doping of fly ash and silica fume, reflecting the advantage of compound doping of fly ash and silica fume. In Comparative Example 3, only steel fibers are incorporated, and in Comparative Example 4, only polypropylene fibers are incorporated. The mechanical properties and shrinkage properties of both are lower than those of Example 1. This shows that the two enhance each other synergistically. Steel fibers bear the main load, and polypropylene fibers delay the generation and propagation of microcracks. The combination of the two makes the shrinkage rate of the shotcrete decrease relatively. It can be seen that Example 1 is the optimal ratio.

[0189] In Comparative Example 5, fiber agglomeration phenomenon appears in the pre-mixing, and from the test results, it further affects the performance of the shotcrete. It can be seen that pre-mixed fibers have a better effect on the performance of the shotcrete. Analyzing the reason: Pre-mixed fiber materials can disperse the fibers well and form a denser structural system.

[0190] Such as Figure 6For the change in the slump of shotcrete, it can be seen from the figure that the slump of Example 1 is only slightly lower than that of Comparative Example 1 and Comparative Example 4 and higher than other groups. This is because the fly ash content in Comparative Example 1 is high, and the fly ash particles are smooth and spherical, with a significant "ball bearing effect", which can reduce internal friction and thus improve the fluidity of the concrete. However, the 1-day and 28-day compressive strengths of Comparative Example 1 are not as good as those of Example 1, and the shrinkage rate during the entire cycle is much greater than that of Example 1. Although the slump of Comparative Example 4 is slightly higher than that of Example 1 due to the absence of steel fibers, the flexural strength of Comparative Example 4 is much lower than that of Example 1, making it difficult to meet the structural safety requirements. From the perspective of engineering practicability, Example 1 not only has excellent fluidity and pumpability, but also has excellent mechanical properties and shrinkage properties. Therefore, Example 1 is the optimal mix ratio.

[0191] Through the performance detection test, it can be seen that the concrete material provided by the present invention, as a support material, can have good effects in tunnel engineering, slope reinforcement, and underground structure repair.

[0192] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A low-shrinkage and high-toughness shotcrete material, characterized in that, The materials include the following parts by mass: Cement: 400 - 440 parts, Fly ash: 50 - 70 parts, Silica fume: 20 - 40 parts, Water: 170 - 190 parts, Fine aggregate: 850 - 880 parts, Coarse aggregate: 770 - 810 parts, Quick-setting agent: 30 - 50 parts, Water-reducing agent: 3.2 - 6.0 parts, Hybrid fiber: Steel fiber: 30 - 50 parts, Organic fiber: 0.9 - 2.7 parts.

2. The low-shrinkage and high-toughness shotcrete material according to claim 1, wherein The organic fiber is selected from at least one of polypropylene fiber, polyethylene fiber or polyacrylonitrile fiber.

3. The low-shrinkage and high-toughness shotcrete material according to claim 1, characterized in that, The cement is ordinary portland cement PO42.5; the fly ash is Class F Grade I fly ash; the silica fume is microsilica.

4. The low-shrinkage and high-toughness shotcrete material according to claim 1, characterized in that, The water-reducing agent is polycarboxylate water-reducing agent with a water-reducing rate of 30 - 40%; the quick-setting agent is a fluoride-free and alkali-free quick-setting agent.

5. The low-shrinkage and high-toughness shotcrete material according to claim 1, wherein The fine aggregate is river sand with an average particle size of 0.05 mm - 0.25 mm; the coarse aggregate is stone with an average particle size of 5 mm - 10 mm.

6. The low-shrinkage and high-toughness shotcrete material according to claim 1, wherein The steel fiber is copper-plated end-hook steel fiber with a length of 20 - 30 mm and a diameter of 0.5 - 0.75 mm, and the organic fiber is polypropylene fiber with a length of 10 - 20 mm and a diameter of 0.02 - 0.05 mm.

7. The low-shrinkage and high-toughness shotcrete material according to claim 1, wherein In the hybrid fibers, the dosage range of steel fibers in each cubic meter of concrete is 30 kg / m 3 - 50 kg / m 3 , and the dosage range of polypropylene fibers in each cubic meter of concrete is 0.9 kg / m 3 - 2.7 kg / m 3 .

8. The low-shrinkage and high-ductility shotcrete material according to claim 1, characterized in that, The materials include the following parts by mass: Cement: 420 parts, Fly ash: 60 parts, Silica fume: 30 parts, Water: 180 parts, River sand: 860 parts, Stone: 790 parts, Quick-setting agent: 40 parts, Water-reducing agent: 5.1 parts, Steel fiber: 35 parts, Organic fiber: 2.25 parts.

9. A preparation method of a low-shrinkage and high-toughness shotcrete material, characterized in that, It includes the following steps: S1: Premix and pre-mix the river sand, stone and fiber for 1 - 2 min to make the fibers disperse evenly, obtaining a premixed material; S2: Dry-mix the cement, fly ash, silica fume and the premixed material for 1 - 2 min to obtain a dry-mixed material; S3: Mix and stir the dry-mixed material with the water-reducing agent and water for 2 - 4 min to obtain a wet-mixed material; during use, mix the wet-mixed material with the quick-setting agent through a concrete wet spraying machine and spray it out to obtain a low-shrinkage and high-toughness sprayed concrete material.

10. Application of the low-shrinkage and high-toughness sprayed concrete material according to any one of claims 1 - 8 as a support material.

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