High-performance shotcrete for tunnel and method for preparing the same

Abstract

This invention discloses a high-performance shotcrete for tunnels and its preparation method, belonging to the technical field of tunnel engineering materials. The shotcrete uses cement, coarse aggregate, fine aggregate, water, polycarboxylate-based high-efficiency water-reducing agent, alkali-free quick-setting agent, composite fibers, and anionic polyacrylamide as raw materials, which are obtained through pretreatment, dry mixing, wet mixing, fiber incorporation, shotcreting, and curing. This invention achieves a sidewall rebound rate ≤4%, a roof slab rebound rate ≤7%, a 1-day compressive strength ≥9MPa, and a 28-day maximum crack width ≤0.10mm through a gradient synergy of short fiber filling, medium- and long fiber skeleton, and medium- and long fiber bonding, combined with polyacrylamide interface optimization. This results in a performance that is suitable for the initial support of tunnels in highways, railways, and other applications, especially those with complex geological conditions.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering materials technology, specifically to a high-performance shotcrete for tunnels and its preparation method, which is particularly suitable for the initial support and permanent lining of underground engineering such as highway tunnels, railway tunnels, and municipal tunnels. It can solve the key problems of high rebound rate, low early strength, and insufficient durability during the shotcreting process. Background Technology

[0002] Shotcrete is a type of quick-setting concrete used to reinforce and protect structures or rock surfaces. This technology utilizes spraying machinery, powered by compressed air or other means, to propel a mixture of cement, sand, gravel, and admixtures in a specific ratio through a nozzle onto the target surface. The concrete hardens and solidifies within minutes, forming a reinforcement material. Shotcrete is primarily used for surface reinforcement of coal mine tunnels, highway slopes after anchor bolt reinforcement, and can be categorized into dry spraying, damp spraying, and wet spraying. Early methods primarily used dry spraying, but due to increased attention to the dust-generating environment in tunnels and other roadways in China, and the occupational health of workers, dry spraying has been gradually phased out. Damp spraying, by pre-mixing water, can reduce dust generation to some extent, but suffers from problems such as short spraying distance and severe rebound, and the dust problem is not fundamentally solved. Wet spraying, by pre-mixing concrete, eliminates the dust problem at its source, and also allows for longer delivery distances and relatively higher spraying intensity. However, current wet shotcrete technology is limited by equipment and still suffers from problems such as rebound and complex processes. Excessive rebound not only wastes materials and increases construction costs, but also affects the support effect and project quality of shotcrete. At some tunnel construction sites, the rebound rate of shotcrete is as high as 30% to 40%, which means that for every 10 meters of shotcrete... 3 Concrete, 3-4m 3 This is a complete waste, resulting in huge losses in material costs alone.

[0003] To reduce the rebound rate of shotcrete, measures can be taken from multiple aspects. In terms of materials, selecting appropriate accelerators, optimizing the concrete mix proportions, adding appropriate amounts of thickeners, water-reducing agents, and other admixtures, and incorporating different mineral components (fly ash, silica fume, limestone powder, etc.) can effectively improve the workability and cohesiveness of concrete and reduce rebound. For example, CN120058290A discloses an early-strength, high-durability, low-rebound shotcrete, which is made of cement, early-strength compacting auxiliary cementitious materials, coarse aggregate, fine aggregate, water, admixtures, fluorine-free and alkali-free high-concentration accelerators, rheology modifiers, fibers, and other components. This shotcrete utilizes optimized binder content, water-cement ratio, and sand ratio, along with small-diameter coarse aggregates, resulting in excellent workability and homogeneity. This reduces the risk of pipe blockage during pumping and spraying, minimizes aggregate rebound during jetting, and optimizes spraying performance. The application of high-concentration, fluorine-free, alkali-free accelerators and early-strength, compacting auxiliary cementitious materials effectively enhances the early strength of the concrete, reduces volumetric deformation, and improves long-term mechanical properties and durability. The addition of fibers and rheology modifiers further improves the rheological properties of the shotcrete and reduces rebound rate. Through mix design optimization and the application of novel functional materials, the shotcrete achieves rapid setting and a synergistic improvement in both mechanical and long-term performance. CN118978371A discloses a hydraulic sprayed concrete containing aldehyde-modified polymer. The raw material components mainly include cementitious materials, aggregates, water, and aldehyde-modified polymer admixtures. Through cation-π bond interactions, it forms a cross-linked network with polymeric quaternary ammonium salts and, together with nano-silicon calcium oxide particles, constructs a three-dimensional skeleton. This makes the sprayed concrete suitable for construction under complex geological conditions such as altered surrounding rock, low strength, wet-dry cycles, and water-rich environments. It can effectively solve problems such as high rebound, high cement consumption, low early strength, low later strength, strong corrosion, and poor durability of conventional sprayed concrete. It is economical, environmentally friendly, and improves construction efficiency. CN116573881A discloses a high-efficiency reinforced shotcrete admixture, comprising the following raw materials in parts by weight: 10-30 parts of polycarboxylate superplasticizer; 15-30 parts of plant adhesive; 80-110 parts of nanofiber and epoxy resin composite; 30-70 parts of accelerator; and 5-10 parts of water. The nanofiber and epoxy resin composite is a composite of long-chain silane-modified nanofibers and fluorinated epoxy resin emulsion. By adjusting the type and dosage of each raw material, the rebound rate of the obtained high-efficiency reinforced shotcrete is as low as 6.25%, effectively reducing the rebound rate of the high-efficiency reinforced shotcrete.CN116354664A discloses a composition for shotcrete, comprising: cement, fly ash, coarse aggregate, fine aggregate, stranded steel fibers, an accelerator, a water-reducing agent, and water. The stranded steel fibers are formed by spirally winding at least two bundles of steel rope, and each steel rope is formed by spirally winding at least two strands of steel wire. The average diameter d of the stranded steel fibers is 0.5-0.8 mm, and the tensile strength is 1200-1600 MPa. This shotcrete exhibits stronger adhesion to the matrix and superior mechanical and deformation properties. It offers good economic benefits and broader application prospects. However, the aforementioned shotcrete still suffers from several drawbacks. Its complex composition leads to pipe blockage during pumping, impacting construction efficiency. High density of single fibers (such as steel fibers) causes sedimentation, resulting in aggregate segregation and hindering effective rebound control. Hydration shrinkage and temperature stress easily lead to cracks, resulting in poor crack resistance and increased susceptibility to water leakage and structural corrosion. Furthermore, a single fiber type or an unreasonable fiber ratio can cause an imbalance between rigidity and toughness (e.g., pure steel fibers have poor crack resistance, while pure basalt fibers have insufficient early strength). Poor fiber dispersion affects the overall uniformity and durability of the concrete, limiting the synergistic effect of accelerators and water-reducing agents and making it difficult to balance setting time and workability. This further restricts the application of shotcrete in complex working conditions, hindering breakthroughs in achieving high-performance shotcrete technology characterized by low rebound, early strength, and high durability. In summary, current technologies have not yet proposed a shotcrete solution that simultaneously addresses the three major issues of rebound rate, early strength, and durability. Therefore, there is an urgent need to develop a high-performance shotcrete for tunnels and its preparation method. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art and provide a high-performance shotcrete for tunnels and its preparation method. The high-performance shotcrete for tunnels comprises the following raw materials in parts by weight: 400-450 parts cement, 750-850 parts coarse aggregate, 480-640 parts fine aggregate, 140-180 parts water, 3-7 parts polycarboxylate-based high-efficiency water-reducing agent, 16-25 parts quick-setting agent, 2-5 parts composite fiber, and 10-15 parts polyacrylamide. The composite fiber is composed of fibers in the following mass ratio: basalt fiber: alkali-resistant glass fiber: steel fiber = 5-6: 1-2: 2-5; the basalt fiber has a length of 5-10 mm and a diameter of 13-20 μm, the alkali-resistant glass fiber has a length of 3-6 mm and a diameter of 15-20 μm, and the steel fiber has a length of 8-12 mm and a diameter of 50-130 μm. This invention achieves synergistic design of concrete constituent materials by combining composite fiber gradient reinforcement with polymer polyacrylamide to optimize the interface of concrete, ultimately obtaining shotcrete with low resilience, high early strength, and high crack resistance. This effect is significantly better than traditional shotcrete and is particularly suitable for tunnel initial support engineering under complex geological conditions.

[0005] One object of the present invention is to provide a high-performance shotcrete for tunnels, comprising the following raw materials in parts by weight: 400-450 parts cement, 750-850 parts coarse aggregate, 480-640 parts fine aggregate, 140-180 parts water, 3-7 parts polycarboxylate-based high-efficiency water-reducing agent, 16-25 parts quick-setting agent, 2-5 parts composite fiber, and 10-15 parts polyacrylamide. The composite fiber is composed of fibers in the following mass ratio: basalt fiber: alkali-resistant glass fiber: steel fiber = 5-6: 1-2: 2-5; the basalt fiber has a length of 5-10 mm and a diameter of 13-20 μm, the alkali-resistant glass fiber has a length of 3-6 mm and a diameter of 15-20 μm, and the steel fiber has a length of 8-12 mm and a diameter of 50-130 μm. This concrete achieves a gradient synergy of composite fibers. Alkali-resistant glass fibers (3-6mm short fibers) fill the gaps between fine aggregates, improving slurry cohesion and reducing atomization loss during spraying. Steel fibers (8-12mm medium-long fibers) form a rigid skeleton, locking in 5-10mm coarse aggregates and preventing them from detaching from the sprayed layer. Basalt fibers (5-10mm medium-long fibers) enhance overall adhesion through chemical bonding between their surface hydroxyl groups and the cement matrix. These three fibers are blended in a 5-6:1-2:2-5 ratio to form a synergistic network of short fiber filler, medium-long fiber aggregate, and strong medium-long fiber bonding. This allows for control of sidewall rebound rate to ≤4% and roof rebound rate to ≤7%, significantly improving material utilization. Simultaneously, anionic polyacrylamide, through molecular chain adsorption and entanglement, forms a three-dimensional gel network on the cement particles and fiber surfaces, significantly improving slurry cohesion and preventing aggregate rebound under spraying impact. In addition, it can also work synergistically with polycarboxylate superplasticizers to reduce the vicious cycle of "segregation-rebound" while ensuring fluidity.

[0006] Furthermore, the coarse aggregate is continuously graded limestone crushed stone with a particle size range of 5-10 mm, a crushing value ≤10%, and a mud content ≤1%; the fine aggregate is medium sand with a fineness modulus of 2.3-3.0 and a mud content ≤3%. Compared to acidic rocks such as granite and basalt, limestone crushed stone has better compatibility with cement hydration products (Ca(OH)2), reducing weak points in the interface transition zone; its moderate density avoids segregation during spraying due to excessive aggregate weight. The continuous gradation design avoids a surge in porosity caused by a single particle size, increasing the bulk density of the aggregate skeleton and reducing the amount of cement paste used. The particle size distribution of medium sand is between that of coarse and fine sand, filling the gaps between coarse aggregates without resulting in an excessively large specific surface area due to overly fine particles. The above settings... The synergistic effect of medium-graded coarse aggregate and medium sand reduces the porosity of concrete to below 18% and increases the 28-day compressive strength by 10-15%.

[0007] Furthermore, the polycarboxylate-based high-efficiency water-reducing agent has a water reduction rate ≥30% and a solid content of 20-40%; the accelerator is an alkali-free liquid accelerator with an initial setting time ≤4 min, a final setting time ≤10 min, and a 28-day compressive strength retention rate ≥85%; the polyacrylamide is anionic. The high-efficiency water-reducing agent can lower the water-cement ratio and reduce free water (reducing porosity) while ensuring slurry fluidity, and simultaneously promote full cement hydration (increasing CSH gel formation). The alkali-free liquid accelerator has an initial setting time ≤4 min and a final setting time ≤10 min, ensuring rapid hardening after spraying and achieving load-bearing capacity within 1 hour, meeting the rapid cycle requirements of tunnel excavation-support. The anionic polyacrylamide has -COO on its molecular chain. - Groups that can react with Ca on the surface of cement particles 2+ It forms coordination bonds and adsorbs hydroxyl groups on the fiber surface through hydrogen bonds, enhancing the bonding of the "cement-fiber" interface. At the same time, it can form a three-dimensional network structure in the slurry, improving cohesiveness, promoting fiber dispersion, reducing agglomeration, and avoiding weak crack resistance areas caused by local lack of fibers.

[0008] Furthermore, the cement is PO 42.5R silicate cement, which has the characteristics of high early strength and moderate heat of hydration, making it suitable for the needs of rapid tunnel support.

[0009] Furthermore, the raw materials include the following parts by weight: 420 parts cement, 800 parts coarse aggregate, 560 parts fine aggregate, 180 parts water, 5 parts polycarboxylate superplasticizer, 20 parts quick-setting agent, 3.5 parts composite fiber, and 12 parts polyacrylamide.

[0010] Furthermore, the composite fiber is composed of basalt fiber, alkali-resistant glass fiber, and steel fiber in a mass ratio of 5:1:3, wherein the basalt fiber has a length of 6 mm and a diameter of 15 μm, the alkali-resistant glass fiber has a length of 5 mm and a diameter of 18 μm, and the steel fiber has a length of 10 mm and a diameter of 100 μm.

[0011] Furthermore, the coarse aggregate contains 60% particles with a diameter of 5-8mm and 40% particles with a diameter of 8-10mm; the fine aggregate has a fineness modulus of 2.6 and a mud content of ≤2%.

[0012] Another object of the present invention is to provide a method for preparing high-performance shotcrete for tunnels, comprising the following steps: S1. Weigh the raw materials according to the following mass ratio: 400-450 parts cement, 750-850 parts coarse aggregate, 480-640 parts fine aggregate, 140-180 parts water, 3-7 parts polycarboxylate-based high-efficiency water-reducing agent, 16-25 parts quick-setting agent, 2-5 parts composite fiber, and 10-15 parts polyacrylamide. The composite fiber is composed of fibers in the following mass ratio: basalt fiber: alkali-resistant glass fiber: steel fiber = 5-6: 1-2: 2-5. Soak the steel fiber in 7% hydrochloric acid solution for 10 minutes, rinse with deionized water until pH 6.5, and dry at 105℃. Add the weighed portion of water to the polyacrylamide to prepare a solution, and stir at 80 r / min at 25℃ until completely dissolved. This avoids the formation of undissolved particles such as "fish eyes" due to molecular chain entanglement, ensuring uniform dispersion in the slurry. S2. Dry mixing: Add the weighed cement, coarse aggregate, and fine aggregate to a forced mixer and dry mix at 180 r / min for 5-10 minutes until uniformly mixed to obtain a dry mixture. Low-speed dry mixing can ensure that the cement evenly coats the surface of the aggregate, avoiding cement agglomeration during wet mixing. At the same time, too short a time will result in uneven mixing, while too long a time will easily lead to aggregate breakage. S3. Wet mixing and slurry preparation: Add the remaining water, polycarboxylate superplasticizer and polyacrylamide solution prepared in S1 to the dry mixture, and wet mix at 300 r / min for 5 min to fully integrate the superplasticizer, polyacrylamide solution and dry mixture to form a uniform slurry. S4. Composite fiber incorporation: The weighed basalt fiber, alkali-resistant glass fiber and treated steel fiber are added to the slurry obtained in S3. The mixture is stirred at 300 r / min until the fibers are evenly dispersed and then transferred to the jetting machine. S5. Add accelerator and spray molding. Dilute the alkali-free accelerator to 35% mass concentration and add it to the material in the spraying machine. After mixing in the built-in mixing chamber for 0.5 minutes, spray at a pressure of 0.7MPa, a distance of 1.6m, and a 90° angle. The thickness of one spray is 5-8cm. Repeat the spraying to reach the preset thickness. S6. Curing: After spraying, cover with polyethylene film to retain moisture. Keep the ambient temperature at 15-25℃ and relative humidity at ≥80% for 24 hours. After 24 hours, remove the film and use spray curing, spraying 3-4 times a day for a curing cycle of no less than 7 days.

[0013] Furthermore, in step S5, the interval between two injections is 1 hour, and the next layer is injected when the penetration resistance of the previous layer reaches 4 MPa.

[0014] Furthermore, in step S6, the surface moisture content of the concrete needs to be tested daily during the curing period. If the surface moisture content is <15%, the number of spraying times should be increased to 5-6 times per day. On the 3rd and 7th days of curing, core samples with a diameter of 50mm should be drilled to test the 1-day and 7-day compressive strength, ensuring that the 1-day compressive strength is ≥9MPa and the 7-day compressive strength is ≥35MPa.

[0015] This invention, through collaborative design, solves the core problems of traditional shotcrete, such as high rebound rate, low early strength, and poor crack resistance. Compared with existing technologies, it has the following significant advantages: 1. This invention uses specific composite fibers, in which 3-6mm alkali-resistant glass fibers fill the gaps between fine aggregates, improving the cohesiveness of the slurry and reducing spray atomization loss; 8-12mm steel fibers form a rigid skeleton, locking in 5-10mm coarse aggregates and preventing them from detaching from the spray layer; 5-10mm basalt fibers chemically bond with the cement matrix through surface hydroxyl groups, enhancing interfacial adhesion; and combined with a three-dimensional gel network formed by anionic polyacrylamide, further improving the slurry encapsulation and preventing aggregate impact rebound. The resulting shotcrete can achieve an extremely low rebound rate of ≤4% for side walls and ≤7% for roof slabs, far superior to the 10%-30% of traditional shotcrete, significantly improving material utilization.

[0016] 2. The PO 42.5R cement used in this invention has high early hydration activity and a 3-day compressive strength ≥22MPa. The alkali-free quick-setting agent can accelerate the setting and hardening of cement. At the same time, the composite fiber and the cement matrix work together to transfer stress, avoiding early strength loss caused by stress concentration. Polyacrylamide promotes full hydration of cement, increases the amount of CSH gel formation, and improves density and strength, ultimately achieving high early strength to meet the requirements of rapid tunnel support. Meanwhile, the 1-day compressive strength of this concrete is ≥9MPa, the 7-day compressive strength is ≥35MPa, and the 28-day compressive strength is ≥48MPa, which is a significant improvement compared to conventional shotcrete.

[0017] 3. In this invention, basalt fibers form a tough network, inhibiting the initiation and propagation of microcracks; alkali-resistant glass fibers fill micropores, reducing shrinkage stress concentration; a low water-cement ratio combined with continuously graded aggregates can reduce hydration shrinkage and porosity; polyacrylamide can optimize the structure of the interface transition zone, reducing interface cracks between aggregates and cement, achieving a maximum crack width of ≤0.10mm at 28 days, a permeability grade ≥P12, high crack resistance, and ensuring long-term durability.

[0018] 4. The fiber length of this invention is matched with the inner diameter of the spray pipe to avoid fiber entanglement and pipe blockage. The synergistic effect of polyacrylamide and water-reducing agent improves cohesiveness while ensuring fluidity. The preparation method ensures uniform fiber dispersion without agglomeration, making overall construction convenient, improving construction efficiency and reducing construction interruption time caused by pipe blockage. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein. The reagents used herein may be commercially available related products, and performance testing standards refer to industry or national standards.

[0021] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0022] Product performance testing adopts the following standards or methods: The rebound rate of side walls / roof slabs was tested according to NB / T11535-2024 "Test Method for Determination of Rebound Rate of Shotcrete"; compressive strength (1d / 7d / 28d) was tested according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete"; the maximum crack width at 28d was tested according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete"; the pipe blockage rate was calculated based on actual shotcreting statistics (per 100m). 3 Number of times the pipe was blocked).

[0023] Example 1 A high-performance shotcrete for tunnels comprises the following raw materials in parts by weight: 420 parts of PO 42.5R silicate cement, 800 parts of coarse aggregate (continuously graded limestone crushed stone, 60 wt% 5-8 mm, 40 wt% 8-10 mm, crushing value 8%, mud content 0.8%), 560 parts of fine aggregate (medium sand, fineness modulus 2.6, mud content ≤1.5%), 180 parts of water, 5 parts of a polycarboxylate-based high-efficiency water-reducing agent with cement compatibility grade A (water reduction rate 32%, solid content 30%, pH 7.5), and 20 parts of an alkali-free liquid accelerator with an initial setting time of 3.5 min, a final setting time of 8 min, and a 28-day compressive strength retention rate of 88%. The composition includes 0.8% alkali content, 3.5 parts composite fiber, and 12 parts anionic polyacrylamide. The composite fiber consists of 1.75 parts basalt fiber, 0.35 parts alkali-resistant glass fiber, and 1.4 parts steel fiber. The basalt fiber is 6 mm long, 15 μm in diameter, with a tensile strength of 3200 MPa, an elastic modulus of 85 GPa, and an alkali resistance retention rate (28 days) of 82%. The alkali-resistant glass fiber is 5 mm long, 18 μm in diameter, with a tensile strength of 1800 MPa and an alkali resistance retention rate (28 days) of 78%. The steel fiber is hook-shaped, 10 mm long, 100 μm in diameter, with a tensile strength of 1100 MPa, and can be bent 180° without breakage. The preparation method is as follows: S1 Raw material pretreatment: Steel fiber is soaked in 7% hydrochloric acid solution for 10 min, rinsed with deionized water until pH 6.5, and dried in an oven at 105℃ for 2 h, and set aside; Take 12 parts of polyacrylamide, add 30% of the total water (54 parts water) to prepare a polyacrylamide solution, and mechanically stir at 80 r / min at 25℃ for 40 min until there are no undissolved particles, and set aside; Basalt fiber and alkali-resistant glass fiber are passed through a 10-mesh sieve to remove impurities, and set aside.

[0024] S2 Dry Mixing: Add 420 parts cement, 800 parts coarse aggregate, and 560 parts fine aggregate to a forced mixer, set the speed to 180 r / min, and dry mix for 7 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0025] S3 Wet Mixing Slurry: Add the remaining 70% water (126 parts water), 5 parts polycarboxylate superplasticizer and polyacrylamide solution prepared in S1 to the dry mixture. Increase the speed of the mixer to 300 r / min and wet mix for 5 min to form an initial slurry with a slump of 135 mm and an extension of 470 mm.

[0026] S4 composite fiber incorporation: 1.75 parts of basalt fiber, 0.35 parts of alkali-resistant glass fiber, and 1.4 parts of treated steel fiber were mixed and added to the initial slurry through a side-mounted screw feeder in a mixer (feeding speed 12 kg / h). The mixture was stirred at 300 r / min for 3.5 min. Samples were taken to observe that the fibers were evenly dispersed, and the final slurry was obtained.

[0027] S5 spray molding: Twenty parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, and added to the feed inlet of the spraying machine through a metering pump. After mixing for 0.5 minutes in the built-in mixing chamber (300 r / min), the agent was sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of the first spray was 6 cm. After an interval of 1 hour, the penetration resistance of the previous layer was measured to be 4 MPa. A second spray was then performed to achieve a total thickness of 12 cm.

[0028] S6 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and relative humidity of 85% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0029] The test results showed that the rebound rate of the sidewall was 3.2%, the rebound rate of the roof was 6.5%, the 1-day compressive strength was 9.8 MPa, the 7-day compressive strength was 38.5 MPa, the 28-day compressive strength was 50.2 MPa, the maximum crack width at 28 days was 0.08 mm, the bond strength with the surrounding rock was 1.9 MPa, and the plugging rate was 1 time.

[0030] Example 2 A high-performance shotcrete for tunnels comprises the following raw materials in parts by weight: 400 parts of PO 42.5R silicate cement, 750 parts of coarse aggregate (continuously graded limestone crushed stone, 50 wt% of 5-8 mm and 50 wt% of 8-10 mm, crushing value 9%, mud content 1%), 480 parts of fine aggregate (medium sand, fineness modulus 2.3, mud content ≤3%), 140 parts of water, 3 parts of a polycarboxylate-based high-efficiency water-reducing agent with cement compatibility grade A (water reduction rate 30%, solid content 20%, pH 7.5), and 16 parts of an alkali-free liquid accelerator with an initial setting time of 4 min, a final setting time of 10 min, and a 28-day compressive strength retention. The composition includes an alkali content of 0.8%, 2 parts composite fiber, and 10 parts anionic polyacrylamide. The composite fiber consists of 1.2 parts basalt fiber, 0.2 parts alkali-resistant glass fiber, and 0.6 parts steel fiber. The basalt fiber is 5 mm long, 13 μm in diameter, has a tensile strength of 3000 MPa, an elastic modulus of 85 GPa, and an alkali resistance retention rate (28 days) of 82%. The alkali-resistant glass fiber is 3 mm long, 15 μm in diameter, has a tensile strength of 1800 MPa, and an alkali resistance retention rate (28 days) of 75%. The steel fiber is 8 mm long, 50 μm in diameter, has a tensile strength of 1000 MPa, and exhibits no breakage after bending 180°. The preparation method is as follows: S1 Raw material pretreatment: Steel fiber is soaked in 7% hydrochloric acid solution for 10 min, rinsed with deionized water until pH 6.5, and dried in an oven at 105℃ for 2 h, and set aside; Take 10 parts of anionic polyacrylamide, add 30% of the total water (42 parts water) to prepare a polyacrylamide solution, and mechanically stir at 80 r / min at 25℃ for 40 min until there are no undissolved particles, and set aside; Basalt fiber and alkali-resistant glass fiber are passed through a 10-mesh sieve to remove impurities, and set aside.

[0031] S2 Dry Mixing: Add 400 parts cement, 750 parts coarse aggregate, and 480 parts fine aggregate to a forced mixer, set the speed to 180 r / min, and dry mix for 8 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0032] S3 Wet Mixing Slurry: Add the remaining 70% water (98 parts water), 3 parts polycarboxylate superplasticizer and polyacrylamide solution prepared in S1 to the dry mixture, increase the speed of the mixer to 300 r / min, and wet mix for 5 min to form the initial slurry.

[0033] S4 composite fiber incorporation: Mix 1.2 parts basalt fiber, 0.2 parts alkali-resistant glass fiber, and 0.6 parts treated steel fiber. Add the mixture to the initial slurry through a side-mounted screw feeder in a mixer (feeding speed 12 kg / h). Stir at 300 r / min for 3.5 min. Take a sample to observe that the fiber is evenly dispersed to obtain the final slurry.

[0034] S5 spray molding: Sixteen parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, added to the feed inlet of the spraying machine through a metering pump, and mixed for 0.5 minutes through the built-in mixing chamber (300 r / min). The mixture was then sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of each spray was 5 cm. After an interval of 1 hour, the penetration resistance of the previous layer was tested and found to be 4 MPa. Spraying was then repeated until the total thickness reached 15 cm.

[0035] S6 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and relative humidity of 80% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0036] The test results showed that the rebound rate of the sidewall was 3.8%, the rebound rate of the roof was 6.9%, the 1-day compressive strength was 9.1 MPa, the 7-day compressive strength was 35.2 MPa, the 28-day compressive strength was 48.1 MPa, the maximum crack width at 28 days was 0.1 mm, the bond strength with the surrounding rock was 1.6 MPa, and the plugging rate was 2 times.

[0037] Example 3 A high-performance shotcrete for tunnels comprises the following raw materials in parts by weight: 450 parts of PO 42.5R silicate cement, 850 parts of coarse aggregate (continuously graded limestone crushed stone, 5-8mm accounting for 65wt%, 8-10mm accounting for 35wt%, crushing value 7%, mud content 0.6%), 640 parts of fine aggregate (medium sand, fineness modulus 3, mud content ≤2.1%), 180 parts of water, 7 parts of a polycarboxylate-based high-efficiency water-reducing agent with cement compatibility grade A, the water-reducing agent having a water reduction rate of 36%, a solid content of 40%, and a pH of 7.5, and 25 parts of an alkali-free liquid accelerator with an initial setting time of 3 minutes, a final setting time of 7 minutes, and a 28-day compressive strength retention rate. The composition includes 90% basalt fiber, 0.4% alkali content, 5 parts composite fiber, and 15 parts anionic polyacrylamide. The composite fiber consists of 2.75 parts basalt fiber, 1 part alkali-resistant glass fiber, and 1.25 parts steel fiber. The basalt fiber has a length of 10 mm, a diameter of 20 μm, a tensile strength of 3200 MPa, an elastic modulus of 85 GPa, and an alkali resistance retention rate (28 days) of 85%. The alkali-resistant glass fiber has a length of 6 mm, a diameter of 20 μm, a tensile strength of 1850 MPa, and an alkali resistance retention rate (28 days) of 78%. The steel fiber has a length of 12 mm, a diameter of 130 μm, a tensile strength of 1200 MPa, and exhibits no breakage after bending 180°. The preparation method is as follows: S1 Raw material pretreatment: Steel fiber is soaked in 7% hydrochloric acid solution for 10 min, rinsed with deionized water until pH 6.5, and dried in an oven at 105℃ for 2 h, and set aside; Take 15 parts of anionic polyacrylamide, add 30% of the total water (54 parts water) to prepare a polyacrylamide solution, and mechanically stir at 80 r / min at 25℃ for 40 min until there are no undissolved particles, and set aside; Basalt fiber and alkali-resistant glass fiber are passed through a 10-mesh sieve to remove impurities, and set aside.

[0038] S2 Dry Mixing: Add 450 parts cement, 850 parts coarse aggregate, and 640 parts fine aggregate to a forced mixer, set the speed to 180 r / min, and dry mix for 8 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0039] S3 Wet Mixing Slurry: Add the remaining 70% water (126 parts water), 7 parts polycarboxylate superplasticizer and polyacrylamide solution prepared in S1 to the dry mixture, increase the speed of the mixer to 300 r / min, and wet mix for 5 min to form the initial slurry.

[0040] S4 composite fiber incorporation: Mix 2.75 parts basalt fiber, 1 part alkali-resistant glass fiber, and 1.25 parts treated steel fiber. Add the mixture to the initial slurry through a side-mounted screw feeder in a mixer (feeding speed 15 kg / h). Stir at 300 r / min for 3.5 min. Take a sample to observe that the fiber is evenly dispersed to obtain the final slurry.

[0041] S5 spray molding: 25 parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, and added to the feed inlet of the spraying machine through a metering pump. After mixing for 0.5 minutes in the built-in mixing chamber (300 r / min), the agent was sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of each spray was 8 cm. After an interval of 1 hour, the penetration resistance of the previous layer was tested and found to be 4 MPa. Spraying continued until the total thickness reached 16 cm.

[0042] S6 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and a relative humidity of 90% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0043] The test results showed that the rebound rate of the sidewall was 2.9%, the rebound rate of the roof was 6.1%, the 1-day compressive strength was 10.5 MPa, the 7-day compressive strength was 40.8 MPa, the 28-day compressive strength was 52.9 MPa, the maximum crack width at 28 days was 0.07 mm, the bond strength with the surrounding rock was 2.1 MPa, and the plugging rate was 1 time.

[0044] Comparative Example 1 A type of shotcrete for tunnels comprises the following raw materials in parts by weight: 420 parts of PO 42.5R silicate cement, 800 parts of coarse aggregate (contained as continuously graded limestone crushed stone, with 60 wt% of 5-8 mm and 40 wt% of 8-10 mm, a crushing value of 8%, and a mud content of 0.8%), 560 parts of fine aggregate (contained as medium sand, with a fineness modulus of 2.6 and a mud content ≤1.5%), 180 parts of water, and 5 parts of a polycarboxylate-based high-efficiency water-reducing agent with a cement compatibility grade of A. The mixture has a water content of 32%, a solid content of 30%, a pH of 7.5, and contains 20 parts of an alkali-free liquid quick-setting agent. The quick-setting agent has an initial setting time of 3.5 min, a final setting time of 8 min, and a 28-day compressive strength retention rate of 88%. It also contains 0.8% alkali, 3.5 parts of steel fiber, and 12 parts of anionic polyacrylamide. The steel fiber is hook-shaped, 10 mm long, 100 μm in diameter, has a tensile strength of 1100 MPa, and can be bent 180° without breakage. The preparation method is as follows: S1 Raw material pretreatment: Soak steel fibers in 7% hydrochloric acid solution for 10 min, rinse with deionized water until pH 6.5, dry in 105℃ oven for 2 h, and set aside; take 12 parts of polyacrylamide, add 30% of the total water (54 parts water) to prepare polyacrylamide solution, and mechanically stir at 80 r / min at 25℃ for 40 min until there are no undissolved particles, and set aside.

[0045] S2 Dry Mixing: Add 420 parts cement, 800 parts coarse aggregate, and 560 parts fine aggregate to a forced mixer, set the speed to 180 r / min, and dry mix for 7 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0046] S3 Wet Mixing Slurry: Add the remaining 70% water (126 parts water), 5 parts polycarboxylate superplasticizer and polyacrylamide solution prepared in S1 to the dry mixture, increase the speed of the mixer to 300 r / min, and wet mix for 5 min to form the initial slurry.

[0047] S4 composite fiber incorporation: 3.5 portions of treated steel fibers were added to the initial slurry through a side-mounted screw feeder in a mixer (feeding speed 12 kg / h), and stirred at 300 r / min for 3.5 min. Samples were taken to observe that the fibers were evenly dispersed, and the final slurry was obtained.

[0048] S5 spray molding: Twenty parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, and added to the feed inlet of the spraying machine through a metering pump. After mixing for 0.5 minutes in the built-in mixing chamber (300 r / min), the agent was sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of the first spray was 6 cm. After an interval of 1 hour, the penetration resistance of the previous layer was measured to be 4 MPa. A second spray was then performed to achieve a total thickness of 12 cm.

[0049] S6 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and relative humidity of 85% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0050] The test results showed that the rebound rate of the sidewall of the sample was 18.4%, the rebound rate of the roof was 23.6%, the 1-day compressive strength was 7.2 MPa, the 7-day compressive strength was 30.1 MPa, the 28-day compressive strength was 40.5 MPa, the maximum crack width at 28 days was 0.24 mm, the bond strength with the surrounding rock was 1.1 MPa, and the plugging rate was 12 times.

[0051] Comparative Example 2 A type of shotcrete for tunnels comprises the following raw materials in parts by weight: 420 parts of PO 42.5R silicate cement, 800 parts of coarse aggregate, wherein the coarse aggregate is continuously graded limestone crushed stone, with 5-8mm accounting for 60wt% and 8-10mm accounting for 40wt%, a crushing value of 8%, and a mud content of 0.8%; 560 parts of fine aggregate, wherein the fine aggregate is medium sand with a fineness modulus of 2.6 and a mud content ≤1.5%; 180 parts of water; 5 parts of a polycarboxylate-based high-efficiency water-reducing agent with a cement compatibility grade of A, wherein the water-reducing agent has a water reduction rate of 32%, a solid content of 30%, and a pH of 7.5; and 20 parts of an alkali-free liquid accelerator, wherein the accelerator has an initial setting time of 3.5 min, a final setting time of 8 min, and a 28-day compressive strength. The strength retention rate is 88%, the alkali content is 0.8%, and the composite fiber consists of 3.5 parts. The composite fiber comprises 1.75 parts basalt fiber, 0.35 parts alkali-resistant glass fiber, and 1.4 parts steel fiber. The basalt fiber is 6 mm long, 15 μm in diameter, has a tensile strength of 3200 MPa, an elastic modulus of 85 GPa, and an alkali resistance retention rate (28 days) of 82%. The alkali-resistant glass fiber is 5 mm long, 18 μm in diameter, has a tensile strength of 1800 MPa, and an alkali resistance retention rate (28 days) of 78%. The steel fiber is hook-shaped, 10 mm long, 100 μm in diameter, has a tensile strength of 1100 MPa, and exhibits no breakage after bending 180°. The preparation method is as follows: S1 Raw material pretreatment: Steel fiber is soaked in 7% hydrochloric acid solution for 10 minutes, rinsed with deionized water until pH 6.5, and dried in an oven at 105℃ for 2 hours for later use; Basalt fiber and alkali-resistant glass fiber are passed through a 10-mesh sieve to remove impurities and are also for later use.

[0052] S2 Dry Mixing: Add 420 parts cement, 800 parts coarse aggregate, and 560 parts fine aggregate to a forced mixer, set the speed to 180 r / min, and dry mix for 7 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0053] S3 Wet Mixing Slurry: Add 180 parts water and 5 parts polycarboxylate superplasticizer to the dry mixture, increase the mixer speed to 300 r / min, and wet mix for 5 minutes to form the initial slurry.

[0054] S4 composite fiber incorporation: 1.75 parts of basalt fiber, 0.35 parts of alkali-resistant glass fiber, and 1.4 parts of treated steel fiber were mixed and added to the initial slurry through a side-mounted screw feeder in a mixer (feeding speed 12 kg / h). The mixture was stirred at 300 r / min for 3.5 min. Samples were taken to observe that the fibers were evenly dispersed, and the final slurry was obtained.

[0055] S5 spray molding: Twenty parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, and added to the feed inlet of the spraying machine through a metering pump. After mixing for 0.5 minutes in the built-in mixing chamber (300 r / min), the agent was sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of the first spray was 6 cm. After an interval of 1 hour, the penetration resistance of the previous layer was measured to be 4 MPa. A second spray was then performed to achieve a total thickness of 12 cm.

[0056] S6 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and relative humidity of 85% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0057] The test results showed that the rebound rate of the sidewall of the sample was 7.6%, the rebound rate of the roof was 12.8%, the 1-day compressive strength was 7.5 MPa, the 7-day compressive strength was 32.6 MPa, the 28-day compressive strength was 45.6 MPa, the maximum crack width at 28 days was 0.17 mm, the bond strength with the surrounding rock was 1.3 MPa, and the plugging rate was 7 times.

[0058] Comparative Example 3 Except for adjusting the composite fiber to a mass ratio of basalt fiber: alkali-resistant glass fiber: steel fiber of 2:1:7 (i.e., a total of 3.5 parts, 0.7 parts of basalt fiber, 0.35 parts of alkali-resistant glass fiber, and 2.45 parts of steel fiber), the rest is completely consistent with Example 1.

[0059] The test results showed that the rebound rate of the sidewall was 10.2%, the rebound rate of the roof was 15.5%, the 1-day compressive strength was 8.0 MPa, the 7-day compressive strength was 33.4 MPa, the 28-day compressive strength was 46.2 MPa, the maximum crack width at 28 days was 0.19 mm, the bond strength with the surrounding rock was 1.4 MPa, and the plugging rate was 9 times.

[0060] Comparative Example 4 A type of shotcrete for tunnels comprises the following raw materials in parts by weight: 420 parts of PO 42.5R silicate cement, 800 parts of coarse aggregate (contained as continuously graded limestone crushed stone, with 60 wt% of 5-8 mm and 40 wt% of 8-10 mm, a crushing value of 8%, and a mud content of 0.8%), 560 parts of fine aggregate (contained as medium sand, with a fineness modulus of 2.6 and a mud content ≤1.5%), 180 parts of water, 5 parts of a polycarboxylate-based high-efficiency water-reducing agent with a cement compatibility grade of A, wherein the water-reducing agent has a water reduction rate of 32%, a solid content of 30%, a pH of 7.5, and 20 parts of an alkali-free liquid accelerator, wherein the accelerator has an initial setting time of 3.5 min, a final setting time of 8 min, a 28-day compressive strength retention rate of 88%, and an alkali content of 0.8%. The preparation method is as follows: S1 Weigh the raw materials and add 420 parts cement, 800 parts coarse aggregate, and 560 parts fine aggregate into a forced mixer. Set the speed to 180 r / min and dry mix for 7 minutes until there are no obvious cement lumps in the mixture to obtain a dry-mixed mixture.

[0061] S2 Wet Mixing Slurry: Add 180 parts water and 5 parts polycarboxylate superplasticizer to the dry mixture, increase the mixer speed to 300 r / min, and wet mix for 5 minutes to form the initial slurry.

[0062] S3 spray forming: Twenty parts of alkali-free quick-setting agent were diluted with deionized water to a mass concentration of 35%, and added to the feed inlet of the spraying machine through a metering pump. After mixing for 0.5 minutes in the built-in mixing chamber (300 r / min), the agent was sprayed onto the surface of the sandstone simulated surrounding rock at a spraying pressure of 0.7 MPa, a spraying distance of 1.6 m, and a spraying angle of 90°. The thickness of the first spray was 6 cm. After an interval of 1 hour, the penetration resistance of the previous layer was measured to be 4 MPa. A second spray was then performed to achieve a total thickness of 12 cm.

[0063] S4 Maintenance: Immediately after spraying, cover with a polyethylene film and maintain an ambient temperature of 20℃ and relative humidity of 85% for 24 hours. After 24 hours, remove the film and use automatic spray curing (4 times a day, 10 minutes each time). Check the surface moisture content daily (≥15%). On the 3rd and 7th days of curing, drill φ50mm core samples to test the strength.

[0064] The test results showed that the rebound rate of the sidewall was 28.8%, the rebound rate of the top plate was 35.2%, the 1-day compressive strength was 4.7 MPa, the 7-day compressive strength was 24.9 MPa, the 28-day compressive strength was 36.6 MPa, the maximum crack width at 28 days was 0.33 mm, the bond strength with the surrounding rock was 0.6 MPa, and the plugging rate was 3 times.

[0065] The rebound rates of the sidewalls in Examples 1-3 of this invention are 2.9%-3.8%, all less than 4%, and the rebound rates of the roof slabs are 6.1%-6.9%, all less than ≤7%, which are far lower than the industry average of 15%-30% for traditional shotcrete. This demonstrates that the synergistic effect of the present invention effectively reduces atomization loss and aggregate segregation during spraying, lowers the rebound rate of shotcrete, and improves the utilization rate of concrete. Comparative Example 1 uses a single steel fiber without short fiber filler and basalt fiber bonding, resulting in a sharp increase in rebound rates to 18.4% and 23.6%, respectively. Comparative Example 4 uses conventional shotcrete, with a rebound rate reaching even higher. The 8.8% and 35.2% results demonstrate that the gradient synergy between composite fibers and the optimized interface of polyacrylamide is the core to achieving low resilience, high crack resistance, and low pipe blockage, which cannot be replaced by single steel fibers. Traditional fiber-free and polyacrylamide-free solutions completely fail to meet the high-performance requirements of tunnels. Examples 1-3 exhibit 1-day compressive strengths of 9.1-10.5 MPa (≥9 MPa), 7-day compressive strengths of 35.2-40.8 MPa (≥35 MPa), and 28-day compressive strengths of 48.1-52.9 MPa, fully meeting the strength requirements of rapid excavation-support cycles in tunnels with weak surrounding rock. This is due to the high yield of polyacrylamide (PO)... 42.5R cement exhibits good early hydration activity, achieving a 3-day compressive strength of 25 MPa. Combined with the rapid setting of the alkali-free quick-setting agent and the stress transfer effect of the composite fiber, the three work synergistically to prevent early strength loss. In Example 3, the material exhibits the highest water reduction rate and the lowest water-cement ratio, resulting in the best strength performance. In Comparative Example 1, the 1-day compressive strength of a single steel fiber is only 7.2 MPa, due to the absence of basalt fiber stress transfer. The 1-day compressive strength of Comparative Example 4 is only 4.7 MPa, indicating that the early strength of shotcrete cannot be effectively improved without fiber reinforcement. This highlights the synergistic effect of composite fiber and PO 42.5R cement. The maximum crack width at 28 days in Examples 1-3 was only 0.07-0.1 mm, and the bond strength with the surrounding rock was 1.6-2.1 MPa. In contrast, the crack width in Comparative Example 1 reached 0.24 mm, and in Comparative Example 4, it reached 0.33 mm, demonstrating the effectiveness of the composite fiber in suppressing cracks. This invention addresses the problems of easy cracking and water leakage in traditional shotcrete. This is because the basalt fibers form a tough network, inhibiting the propagation of microcracks; alkali-resistant glass fibers fill the pores, reducing shrinkage stress; and polyacrylamide further optimizes the fiber-cement-surrounding rock interface transition zone, improving bond strength. The pipe plugging rate in Examples 1-3 was only 1-2 times / 100m. 3 The construction efficiency is significantly better than that of traditional methods, which also shows that the construction process of the present invention has the effect of avoiding fiber agglomeration.

[0066] The preferred embodiments of the present invention have been described in detail above, and are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. 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; and these 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 high performance shotcrete for use in tunnels, characterized in that, The product is composed of the following raw materials in parts by weight: 400-450 parts cement, 750-850 parts coarse aggregate, 480-640 parts fine aggregate, 140-180 parts water, 3-7 parts polycarboxylate-based high-efficiency water-reducing agent, 16-25 parts quick-setting agent, 2-5 parts composite fiber, and 10-15 parts polyacrylamide. The polyacrylamide is anionic. The composite fiber is composed of fibers in the following mass ratio: basalt fiber: alkali-resistant glass fiber: steel fiber = 5-6: 1-2: 2-5. The basalt fiber has a length of 5-10 mm and a diameter of 13-20 μm, the alkali-resistant glass fiber has a length of 3-6 mm and a diameter of 15-20 μm, and the steel fiber has a length of 8-12 mm and a diameter of 50-130 μm. The composite fiber forms a synergistic network in the concrete, consisting of alkali-resistant glass short fiber filler, medium-length steel fiber clavicle, and medium-length basalt fiber with strong bonding.

2. The high performance shotcrete for tunnels according to claim 1, characterized in that, The coarse aggregate is continuously graded limestone crushed stone with a particle size range of 5-10 mm, a crushing value of ≤10%, and a mud content of ≤1%; the fine aggregate is medium sand with a fineness modulus of 2.3-3.0 and a mud content of ≤3%.

3. The high performance shotcrete for tunnels according to claim 1, characterized in that, The polycarboxylate-based high-efficiency water-reducing agent has a water reduction rate of ≥30% and a solid content of 20-40%; the quick-setting agent is an alkali-free liquid quick-setting agent with an initial setting time of ≤4min, a final setting time of ≤10min, and a 28-day compressive strength retention rate of ≥85%.

4. The high performance shotcrete for tunnels according to claim 1, wherein The cement is P.O42.5R silicate cement.

5. The high-performance shotcrete for tunnels according to claim 1, characterized in that, It is composed of the following raw materials in parts by weight: 420 parts cement, 800 parts coarse aggregate, 560 parts fine aggregate, 180 parts water, 5 parts polycarboxylate superplasticizer, 20 parts quick-setting agent, 3.5 parts composite fiber, and 12 parts anionic polyacrylamide.

6. High performance shotcrete for tunnels according to any of claims 1 to 5, characterized in that, The composite fiber is composed of basalt fiber, alkali-resistant glass fiber, and steel fiber in a mass ratio of 5:1:3, wherein the basalt fiber has a length of 6 mm and a diameter of 15 μm, the alkali-resistant glass fiber has a length of 5 mm and a diameter of 18 μm, and the steel fiber has a length of 10 mm and a diameter of 100 μm.

7. The high performance shotcrete for tunnels according to claim 5, characterized in that, The coarse aggregate contains 60% particles with a diameter of 5-8mm and 40% particles with a diameter of 8-10mm; the fine aggregate has a fineness modulus of 2.6 and a mud content of ≤2%.