Impermeable and crack-resistant shotcrete and its construction method

Abstract

This invention relates to the field of civil engineering materials technology, providing a permeability-resistant and crack-resistant shotcrete made of gravel and its construction method. The concrete is composed of cementitious materials, aggregates, fibers, and admixtures in a specific ratio. The cementitious materials include cement, nano-silica fume, fly ash, and a water-reducing agent. The aggregates are gravel and river sand with a specific continuous gradation. The fibers are selected from at least one of metal fibers, polymer fibers, or inorganic fibers. A multi-scale synergistic reinforcement mechanism is formed through finely graded gravel to construct a dense skeleton, micro-scale filling optimization of the slurry with nano-silica fume, synergistic reinforcement by multiple types of fibers, and adaptation to a layered wet spraying process. The resulting concrete achieves a permeability grade of P12 or higher, a tensile strength of not less than 5 MPa, a 28-day compressive strength of not less than 50 MPa, and a shotcrete rebound rate controlled within 10%. It combines high permeability resistance, high crack resistance, and excellent construction performance, making it suitable for tunnel lining, dam repair, and bridge reinforcement projects.

Description

Technical Field

[0001] This invention relates to the field of civil engineering materials technology, and in particular to a seepage-resistant and crack-resistant shotcrete and its construction method. Background Technology

[0002] Shotcrete is widely used in tunnel support, slope reinforcement, and other fields due to its rapid forming characteristics, but its performance defects severely restrict the durability of engineering projects. Traditional shotcrete suffers from the following technical bottlenecks: I. The structural contradiction between aggregate gradation and impermeability Traditional shotcrete uses coarse aggregate (5-15mm in diameter) with a loose gradation, resulting in a porosity as high as 15%-20%, and its impermeability grade is generally lower than P8. Traditional methods optimize paste density by adding silica fume, but due to the lack of synergistic optimization of aggregate gradation, weak seepage channels form at the coarse aggregate interface, making it impossible to break through the P10 impermeability grade. Some methods employ a strategy of reducing aggregate particle size, which can lower the rebound rate, but the increased aggregate specific surface area leads to insufficient paste coating, making it difficult to achieve a 28-day compressive strength of C50. More importantly, traditional methods lack fine gradation design for ≤8mm aggregate, failing to establish a continuous dense skeleton, resulting in a trade-off between high impermeability and high strength.

[0003] II. Interfacial Bonding and Durability Defects in Fiber Reinforced Systems Traditional fiber reinforcement technology has three main problems: (1) Corrosion of metal fibers: Although ordinary steel fibers (diameter > 0.5 mm, slenderness ratio < 100) can improve tensile strength to 3-4 MPa, they are prone to corrosion, which leads to volume expansion, causing the concrete protective layer to peel off and the durability to deteriorate. Moreover, without surface treatment, the fiber-matrix bond strength is < 2.0 MPa, and the crack control ability is limited. (2) Insufficient polymer fiber bonding: Polypropylene fiber has poor alkali resistance (<90%) and weak bonding force with cement matrix, making it difficult to effectively suppress early plastic shrinkage cracks; Polyvinyl alcohol fiber (PVA) has alkali resistance ≥95%, but its elastic modulus is insufficient when used alone, and its contribution to the tensile strength of hardened concrete is less than 1MPa. (3) Difficulty in dispersing inorganic fibers: Although carbon fiber and basalt fiber have high tensile strength (>1500MPa), fibers with a diameter of 5-15μm are prone to agglomeration. When the surface is not oxidized or treated with coupling agent, the bonding strength is <3.0MPa. Furthermore, they have poor compatibility with coarse aggregates, and pipe blockage occurs frequently during the spraying process.

[0004] Traditional composite fiber technology often involves simply stacking steel fibers and synthetic fibers, resulting in a mismatch between the fiber network and the aggregate gradation, making it difficult to break through 5MPa in tensile strength and insufficient crack resistance.

[0005] III. Lack of material-process synergy leads to deterioration in rebound rate and appearance quality. Traditional methods for improving shotcrete strength typically involve increasing cement content. However, exceeding this limit significantly increases hydration heat, exacerbating temperature shrinkage and autogenous shrinkage, leading to a higher risk of cracking. Simultaneously, to maintain workability, the proportion of coarse aggregate is often excessively high, resulting in persistently high rebound rates and difficulty in controlling surface smoothness. Furthermore, existing layered shotcrete processes lack systematic optimization for fine aggregate characteristics. The selection of pressure parameters and spraying angles lacks synergistic design with material composition. The premixing of aggregates and fibers, the order of feeding, and the method of water addition in the preparation process are also not standardized, leading to uneven fiber dispersion and poor paste encapsulation, failing to achieve a synergistic improvement in rebound control and surface quality. In the curing stage, traditional methods lack temperature and humidity control measures compatible with the material system, making the concrete susceptible to plastic shrinkage cracks or freeze-thaw damage in low or high temperature environments, further degrading durability.

[0006] IV. Gap in the Synergistic Optimization of Multi-Scale Enhancement and Microstructure Density Traditional approaches fail to establish a collaborative mechanism for cross-scale material design. At the microscale, the optimization of nanomaterial filling and cementing systems operates independently, failing to form an effective dense microporous structure. At the mesoscale, the selection of fiber reinforcement systems and surface treatments lack specificity, and the matching degree between fiber type, geometric parameters, and matrix bonding performance is insufficient, making it difficult to form an effective crack bridging network. At the macroscale, the collaborative optimization of aggregate gradation design and slurry volume is lacking, making it difficult to form a continuous dense skeleton. The lack of systematic integration among these three aspects leads to the superposition of microstructural defects and macroscopic performance degradation.

[0007] In terms of process adaptation, traditional solutions fail to establish a correspondence between layered spraying parameters and material composition tailored to the characteristics of fine aggregates. Spraying thickness, pressure control, and aggregate particle size distribution are disconnected. Furthermore, curing regimes are not synergistic with the material system, and temperature and humidity control measures lack environmentally adaptable design. This dual disconnect between materials and processes makes it impossible to simultaneously achieve the comprehensive performance goals of high impermeability, high tensile strength, high strength, and low resilience. In particular, there is a lack of a multi-fiber compounding mechanism dominated by metal fibers, and adaptation of curing technologies under extreme temperature conditions.

[0008] In summary, traditional shotcrete technology suffers from multiple fragments in terms of material composition, gradation design, fiber surface treatment, preparation process, and construction parameters. There is an urgent need for a high-permeability, crack-resistant, and high-strength shotcrete solution based on fine gradation of aggregate, nano-silica fume microfilling, and a multi-scale reinforcement system dominated by metal fibers, which can be synergistically adapted to layered spraying and precise curing processes. Summary of the Invention

[0009] The purpose of this invention is to solve at least one technical problem in the background art and to provide impermeable and crack-resistant shotcrete and its construction method.

[0010] To achieve the above objectives, the present invention provides a permeable and crack-resistant shotcrete, comprising the following components per cubic meter of concrete: Cementitious material: composed of cement, nano-silica fume, fly ash and water-reducing agent. The amount of cement in each cubic meter of concrete is 400-480 kg; the amount of nano-silica fume is 5-8% of the total mass of cementitious material; the amount of fly ash is 10-15% of the total mass of cementitious material; the amount of water-reducing agent is 0.8-1.2% of the total mass of cementitious material; the water-cement ratio of the cementitious material is 0.35-0.40. Aggregate: Composed of gravel and river sand, wherein the gravel is continuously graded crushed stone with a particle size ≤8mm, and its gradation is: 30-40% of 5-8mm particle size, 30-40% of 2-5mm particle size, and 20-30% of ≤2mm particle size; the amount of gravel used is 650-800 kg / m³. 3 The amount of river sand used is 280-320 kg / m³. 3 ; Fiber: Selected from at least one of metal fibers, polymer fibers, and inorganic fibers, with a dosage of 1.5-4.0 kg / m³. 3 ; The concrete has an impermeability grade ≥ P12, tensile strength ≥ 5 MPa, 28-day compressive strength ≥ 50 MPa, and a shotcrete rebound rate ≤ 10%.

[0011] According to one aspect of the present invention, the metal fiber is an amorphous alloy fiber with a diameter of 20-50 μm, a length of 10-15 mm, a slenderness ratio ≥250, and a surface treated with a silane coupling agent, and a bonding strength ≥3.0 MPa. The polymer fiber is polyvinyl alcohol fiber, polypropylene fiber, or aramid fiber, with a tensile strength ≥1000MPa and an alkali resistance ≥95%. The inorganic fiber is carbon fiber, basalt fiber or alkali-resistant glass fiber, with a tensile strength ≥1500MPa, a diameter of 5-15μm, a length of 10-20mm, and a surface treated with oxidation or coupling agent.

[0012] According to one aspect of the invention, when the fiber comprises metal fibers, polymer fibers and / or inorganic fibers, the metal fibers account for more than 30% of the total mass of the fiber.

[0013] According to one aspect of the invention, the polyvinyl alcohol fiber has an elastic modulus ≥25 GPa and a bonding strength ≥2.0 MPa.

[0014] According to one aspect of the invention, the carbon fiber surface is oxidized, has a bond strength ≥4.0 MPa, and its dosage in concrete is ≤1.0 kg / m³. 3 .

[0015] According to one aspect of the invention, the cement is 52.5R grade ordinary Portland cement, and the fly ash is Grade I fly ash or Grade II fly ash.

[0016] According to one aspect of the invention, the water-reducing agent has a water reduction rate of ≥25%.

[0017] To achieve the above objectives, the present invention also provides a method for constructing the above-mentioned concrete, comprising: (1) Premixed aggregate and fiber: dry mix gravel, river sand and fiber to obtain premixed material; (2) Staged feeding: First, dry mix cement, fly ash and nano silica fume, then add premixed materials and continue dry mixing; (3) Add water and water-reducing agent: Add water and water-reducing agent in two batches. First, add 50-70% water and 50-70% water-reducing agent for initial mixing, and then add the remaining 30-50% water and 30-50% water-reducing agent for supplementary mixing. (4) Layered spraying: Use a wet spraying machine with a nozzle diameter of 30-40mm, an initial spraying pressure of 0.4-1MPa, a spraying angle of 75-85°, and a thickness of 40-50mm; and a re-spraying pressure of 0.6-1.2MPa, a spraying angle of 80-90°, and a thickness of 30-40mm. (5) Surface treatment: Smooth the surface before final setting, with a flatness deviation of ≤3mm / 2m; (6) Curing: After final setting, cover with non-woven fabric and spray curing for ≥7 days with humidity ≥90%.

[0018] According to one aspect of the present invention, when the ambient temperature is below 5°C, heat preservation measures are adopted to keep the concrete surface temperature ≥10°C; when the ambient temperature is above 30°C, spraying and covering are combined for moisture retention and curing.

[0019] To achieve the above objectives, the present invention also provides an application of the above-mentioned concrete or construction method in tunnel lining, dam repair or bridge reinforcement projects.

[0020] According to one aspect of the present invention, the impermeable and crack-resistant shotcrete with gravel, per cubic meter of concrete, comprises the following components: Cementitious material: composed of cement, nano-silica fume, fly ash, and a water-reducing agent; the cement content per cubic meter of concrete is 420-480 kg; the nano-silica fume content is 5-8% of the total mass of the cementitious material; the fly ash content is 10-15% of the total mass of the cementitious material; the water-reducing agent content is 0.8-1.2% of the total mass of the cementitious material; the water-cement ratio of the cementitious material is 0.35-0.40; Aggregate: composed of gravel and river sand; the gravel is continuously graded crushed stone with a particle size ≤8 mm, and its gradation is: 30-40% for 5-8 mm particle size, 30-40% for 2-5 mm particle size, and 20-30% for ≤2 mm particle size; the amount of gravel is 680-720 kg / m³. 3 The amount of river sand used is 280-320 kg / m³. 3 Fiber: Selected from at least one of metal fibers, polymer fibers, and inorganic fibers, with a dosage of 1.5-4.0 kg / m³. 3 The concrete exhibits a permeability grade ≥ P12, tensile strength ≥ 5 MPa, 28-day compressive strength ≥ 50 MPa, and shotcrete rebound rate ≤ 10%. This invention, through a precisely sized aggregate, forms a continuous and dense skeletal structure, effectively reducing porosity and solving the problem of permeability grades below P8 caused by traditional loose coarse aggregate gradations, achieving a permeability grade above P12. Simultaneously, this gradation design synergistically works with the micro-filling effect of nano-silica fume, which fills the micropores of cement paste, further optimizing the microstructure density and blocking water seepage channels in the interface transition zone. The introduction of a fiber system, matched with the fine gradation, ensures high bond strength with the matrix through the high aspect ratio and surface silane treatment of amorphous alloy fibers, effectively bridging cracks and achieving a tensile strength above 5 MPa. The combination of water-cement ratio and water-reducing agent reduces water consumption while ensuring workability, improving slurry density and achieving a 28-day compressive strength above 50 MPa. Furthermore, the particle size characteristics of the aggregate are well-suited to the wet spraying process, significantly reducing aggregate rebound and keeping the rebound rate below 10%, while also improving surface smoothness. The incorporation of fly ash into the cementitious material optimizes particle size distribution, reduces heat of hydration, minimizes temperature shrinkage cracks, and improves long-term durability.

[0021] According to one aspect of the present invention, the metal fiber is an amorphous alloy fiber with a diameter of 20-50 μm, a length of 10-15 mm, a slenderness ratio ≥250, and a surface treated with a silane coupling agent, exhibiting a bond strength ≥3.0 MPa; the polymer fiber is polyvinyl alcohol fiber, polypropylene fiber, or aramid fiber, with a tensile strength ≥1000 MPa and an alkali resistance ≥95%; the inorganic fiber is carbon fiber, basalt fiber, or alkali-resistant glass fiber, with a tensile strength ≥1500 MPa, a diameter of 5-15 μm, a length of 10-20 mm, and a surface treated with oxidation or a coupling agent. The amorphous alloy metal fiber, compared to ordinary steel fiber, exhibits superior corrosion resistance, avoiding the volume expansion and protective layer peeling problems caused by steel fiber corrosion, significantly improving the durability of concrete. Its high slenderness ratio enhances the mechanical interlocking between the fiber and the matrix, and the surface silane treatment improves the bond strength, enabling the fiber to effectively transfer stress during crack propagation and inhibiting the development of microcracks. Polymer fibers exhibit good compatibility between their elastic modulus and the cement matrix, effectively suppressing early plastic shrinkage cracks. The high strength and stiffness of inorganic fibers provide additional load-bearing capacity, while surface oxidation or coupling agent treatment improves interfacial adhesion and prevents fiber pull-out. The parameter constraints of these three fiber types ensure fiber dispersibility and compatibility with aggregate gradation, avoiding pipe blockage and fiber agglomeration problems.

[0022] According to one aspect of the present invention, when the fiber comprises metal fibers, polymer fibers, and / or inorganic fibers, the metal fibers account for more than 30% of the total fiber mass. This proportion of metal fibers ensures their dominant role in the fiber-reinforced system, fully utilizing the high bonding strength and crack bridging ability of amorphous alloy fibers, while simultaneously supplementing the synergistic effect of polymer fibers or inorganic fibers to form a multi-scale fiber network. This formulation design avoids the performance limitations of single fiber types, such as insufficient elastic modulus of pure polymer fibers or difficulty in dispersing pure inorganic fibers, achieving a balance between toughness and strength, and improving the crack resistance and impact resistance of concrete.

[0023] According to one aspect of the present invention, the elastic modulus of the polyvinyl alcohol (PVA) fiber is ≥25 GPa, and the bond strength is ≥2.0 MPa. This configuration ensures effective bonding and stress transfer between the PVA fiber and the cement matrix, allowing it to continue to provide reinforcement after the concrete has hardened, inhibiting the propagation of drying shrinkage cracks, and improving long-term crack resistance.

[0024] According to one aspect of the present invention, the carbon fiber surface is oxidized, the bond strength is ≥4.0 MPa, and its dosage in concrete is ≤1.0 kg / m³. 3This configuration significantly improves the interfacial bonding performance between carbon fiber and the cement matrix, fully leveraging its ultra-high tensile strength for reinforcement. Controlled dosage avoids dispersion difficulties and increased costs caused by excessive fiber, ensuring both reinforcement effectiveness and workability.

[0025] According to one aspect of the present invention, the cement is 52.5R grade ordinary Portland cement, and the fly ash is Grade I fly ash. The 52.5R grade cement ensures the basic strength of the cementitious material; the Grade I fly ash guarantees low water demand and high activity, optimizing workability and subsequent strength development.

[0026] According to one aspect of the present invention, the water-reducing agent has a water reduction rate of ≥25%. With a water reduction rate of ≥25%, the water-reducing agent maintains good dispersion even under low water-cement ratio conditions, improves slurry fluidity, ensures uniform dispersion of fibers and aggregates, reduces segregation and bleeding, and improves the homogeneity and durability of concrete.

[0027] According to one aspect of the present invention, by premixing aggregates and fibers, uniform dispersion of fibers in the aggregates is ensured, avoiding fiber agglomeration. Staged feeding allows fly ash and nano-silica fume to be uniformly mixed with cement first, leveraging the micro-aggregate effect and pozzolanic effect, before being combined with aggregate fibers, improving the density of the interfacial transition zone. Two-stage water addition and the use of water-reducing agents optimize the hydration process, avoiding bleeding and segregation caused by instantaneous large-volume water addition. The total wet mixing time of 6-8 minutes ensures the uniformity and workability of the slurry. In the layered spraying process, the initial spray ensures effective adhesion and dense filling between the bottom layer and the substrate; the secondary spray improves the surface density and surface smoothness.

[0028] According to the present invention, this invention systematically solves the technical problems of traditional shotcrete's difficulty in achieving both impermeability and strength, the mutual constraint between fiber reinforcement and durability, and the compromise between material properties and construction performance through a four-level multi-scale synergistic reinforcement mechanism: fine gradation of gravel to construct a dense skeleton, micro-scale filling of nano-silica fume to optimize the slurry, synergistic reinforcement of multiple types of fibers (meso-scale bridging of amorphous alloy fibers to control cracking), and layered spraying process adapted to molding. It achieves the simultaneous attainment of four core indicators: impermeability P12-P15, tensile strength 5-8MPa, compressive strength 50-60 MPa, and rebound rate ≤10%. This provides an advanced solution with both high durability and high construction efficiency for major projects such as tunnel lining, water conservancy repair, and bridge reinforcement. Attached Figure Description

[0029] Figure 1 A flowchart illustrating a concrete construction method according to one embodiment of the present invention is shown. Detailed Implementation

[0030] The invention will now be discussed with reference to exemplary embodiments. It should be understood that the described embodiments are merely intended to enable those skilled in the art to better understand and thus implement the invention, and are not intended to imply any limitation on the scope of the invention.

[0031] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment".

[0032] To achieve the above objectives, the present invention provides a permeable and crack-resistant shotcrete, comprising the following components per cubic meter of concrete: Cementitious material: composed of cement, nano-silica fume, fly ash, and water-reducing agent (e.g., polycarboxylate superplasticizer). The cement content in each cubic meter of concrete is 400-480 kg; the nano-silica fume content is 5-8% of the total mass of cementitious material; the fly ash content is 10-15% of the total mass of cementitious material; the water-reducing agent content is 0.8-1.2% of the total mass of cementitious material; the water-cement ratio of the cementitious material is 0.35-0.40. Aggregate: Composed of gravel and river sand, wherein the gravel is continuously graded crushed stone with a particle size ≤8mm, and its gradation is: 30-40% of 5-8mm particle size, 30-40% of 2-5mm particle size, and 20-30% of ≤2mm particle size; the amount of gravel used is 650-800 kg / m³. 3 The amount of river sand used is 280-320 kg / m³. 3 The river sand is medium sand with a fineness modulus of 2.4-2.8, a mud content of ≤1.5%, and a clay lump content of ≤0.5%, and its dosage is 280-320 kg / m³. 3 ; Fiber: Selected from at least one of metal fibers, polymer fibers, and inorganic fibers, with a dosage of 1.5-4.0 kg / m³. 3 ; The concrete has an impermeability grade ≥ P12, tensile strength ≥ 5 MPa, 28-day compressive strength ≥ 50 MPa, and shotcrete rebound rate ≤ 10%.

[0033] In this embodiment, by defining a fine gradation of the aggregate, a continuous and dense skeleton structure is formed, effectively reducing porosity and solving the problem of impermeability grades below P8 caused by the loose gradation of traditional coarse aggregate, thus achieving an impermeability grade of P12 or higher. Simultaneously, this gradation design works synergistically with the micro-filling effect of nano-silica fume; the nano-silica fume fills the micropores of the cement paste, further optimizing the microstructure density and blocking water seepage channels in the interface transition zone. The introduction of the fiber system, matched with the fine gradation, ensures high bonding strength with the matrix through the high aspect ratio and surface silane treatment of the amorphous alloy fibers, effectively bridging cracks and achieving a tensile strength of over 5 MPa. The combination of water-cement ratio and water-reducing agent reduces water consumption while ensuring workability, improving slurry density, and achieving a 28-day compressive strength of over 50 MPa. Furthermore, the aggregate particle size characteristics are compatible with the wet spraying process, significantly reducing aggregate rebound, controlling the spray rebound rate to within 10%, and improving surface smoothness. The incorporation of fly ash into cementitious materials optimizes particle size distribution, reduces heat of hydration, decreases temperature shrinkage cracks, and improves long-term durability.

[0034] Furthermore, according to one embodiment of the present invention, the metal fiber is an amorphous alloy fiber with a diameter of 20-50 μm, a length of 10-15 mm, a slenderness ratio ≥250, and its surface is treated with a silane coupling agent, with a bonding strength ≥3.0 MPa. The polymer fiber is made of polyvinyl alcohol, polypropylene, or aramid fiber, with a tensile strength ≥1000MPa and an alkali resistance ≥95%. The inorganic fibers are carbon fiber, basalt fiber or alkali-resistant glass fiber, with a tensile strength ≥1500MPa, a diameter of 5-15μm, a length of 10-20mm, and a surface treated with oxidation or coupling agent.

[0035] In this embodiment, the metal fibers are amorphous alloy fibers. Compared to ordinary steel fibers, amorphous alloy fibers have excellent corrosion resistance, avoiding the volume expansion and protective layer peeling problems caused by steel fiber corrosion, and significantly improving the durability of concrete. Their high slenderness ratio enhances the mechanical interlocking between the fiber and the matrix, and the surface silane treatment improves the bond strength, enabling the fiber to effectively transfer stress during crack propagation and inhibiting the development of microcracks. The polymer fibers have a good match between their elastic modulus and the cement matrix, effectively inhibiting early plastic shrinkage cracks. The high strength and stiffness of the inorganic fibers provide additional load-bearing capacity, and surface oxidation or coupling agent treatment improves interfacial bonding, preventing fiber pull-out. The parameter constraints of the three types of fibers ensure fiber dispersion and compatibility with aggregate gradation, avoiding pipe blockage and fiber agglomeration problems.

[0036] Furthermore, according to one embodiment of the present invention, when the fiber comprises metal fibers, polymer fibers, and / or inorganic fibers, the metal fibers account for more than 30% of the total fiber mass. In this embodiment, the metal fibers account for more than 30% of the total fiber mass, ensuring the dominant position of the metal fibers in the fiber-reinforced system, fully utilizing the high bonding strength and crack bridging ability of the amorphous alloy fibers, while being supplemented by the synergistic effect of polymer fibers or inorganic fibers to form a multi-scale fiber network. This proportioning design avoids the performance limitations of a single fiber type, such as the insufficient elastic modulus of pure polymer fibers and the difficulty in dispersing pure inorganic fibers, achieving a balance between toughness and strength, and improving the crack resistance and impact resistance of concrete.

[0037] Furthermore, according to one embodiment of the present invention, the elastic modulus of the polyvinyl alcohol fiber is ≥25 GPa, and the bond strength is ≥2.0 MPa. This configuration ensures effective bonding and stress transfer between the PVA fiber and the cement matrix, allowing it to continue to provide reinforcement after the concrete has hardened, inhibiting the propagation of drying shrinkage cracks and improving long-term crack resistance.

[0038] Furthermore, according to one embodiment of the present invention, the carbon fiber surface is oxidized, the bond strength is ≥4.0 MPa, and its dosage in concrete is ≤1.0 kg / m³. 3 This configuration significantly improves the interfacial bonding performance between carbon fiber and the cement matrix, fully leveraging its ultra-high tensile strength for reinforcement. Controlled dosage avoids dispersion difficulties and increased costs caused by excessive fiber, ensuring both reinforcement effectiveness and workability.

[0039] Furthermore, according to one embodiment of the present invention, the cement is 52.5R grade ordinary Portland cement, and the fly ash is Grade I fly ash or Grade II fly ash. The 52.5R grade cement ensures the basic strength of the cementitious material; the Grade I fly ash guarantees low water demand and high activity, optimizing workability and subsequent strength development.

[0040] Furthermore, according to one embodiment of the present invention, the water-reducing agent has a water reduction rate of ≥25%. A water reduction rate of ≥25% allows the water-reducing agent to maintain good dispersion even under low water-cement ratio conditions, improving slurry fluidity, ensuring uniform dispersion of fibers and aggregates, reducing segregation and bleeding, and improving the homogeneity and durability of concrete.

[0041] Furthermore, to achieve the above objectives, the present invention also provides a method for constructing the above-mentioned concrete, such as... Figure 1 As shown, it includes: (1) Premixed aggregate and fiber: Dry mix gravel, river sand and fiber for 3-5 minutes to obtain premixed material; (2) Staged feeding: First, dry mix cement, fly ash and nano silica fume for 2 minutes, then add premixed material and continue to dry mix for 3 minutes; (3) Add water and water-reducing agent: Add water and water-reducing agent in two batches. First, add 50-70% water and 50-70% water-reducing agent for initial mixing, and then add the remaining 30-50% water and 30-50% water-reducing agent for supplementary mixing. The total wet mixing time is 6-8 minutes. (4) Layered spraying: Use a wet spraying machine with a nozzle diameter of 30-40mm, an initial spraying pressure of 0.4-1MPa, a spraying angle of 75-85°, and a thickness of 40-50mm; and a re-spraying pressure of 0.6-1.2MPa, a spraying angle of 80-90°, and a thickness of 30-40mm. (5) Surface treatment: Smooth the surface before final setting, with a flatness deviation of ≤3mm / 2m; (6) Curing: After final setting, cover with non-woven fabric and spray curing for ≥7 days with humidity ≥90%.

[0042] In this embodiment, premixing aggregates and fibers ensures uniform fiber dispersion within the aggregates, preventing fiber agglomeration. Staged feeding allows fly ash and nano-silica fume to be uniformly mixed with cement first, leveraging the micro-aggregate and pozzolanic effects, before being combined with aggregate fibers, improving the density of the interfacial transition zone. Two-stage water addition and the use of a water-reducing agent optimize the hydration process, avoiding bleeding and segregation caused by sudden large-volume water addition. The total wet mixing time of 6-8 minutes ensures the uniformity and workability of the slurry. In the layered spraying process, the initial spray ensures effective adhesion and dense filling between the bottom layer and the substrate; the secondary spray improves surface density and surface smoothness.

[0043] Furthermore, according to one embodiment of the present invention, when the ambient temperature is below 5°C, heat preservation measures are adopted to keep the concrete surface temperature ≥10°C; when the ambient temperature is above 30°C, spraying and covering are combined for moisture retention and curing.

[0044] Furthermore, to achieve the above objectives, the present invention also provides an application of the above-described concrete or construction method in tunnel lining, dam repair, or bridge reinforcement projects.

[0045] According to the above-mentioned scheme of the present invention, the present invention systematically solves the technical problems of traditional shotcrete's difficulty in achieving both impermeability and strength, the mutual constraint between fiber reinforcement and durability, and the compromise between material properties and construction performance through a four-level multi-scale synergistic reinforcement mechanism of finely graded aggregate, nano-silica fume micro-scale filling optimization slurry, multi-type fiber synergistic reinforcement (amorphous alloy fiber meso-scale bridging crack control), and layered spraying process adaptation. It achieves the simultaneous attainment of four core indicators: impermeability P12-P15, tensile strength 5-8MPa, compressive strength 50-60 MPa, and rebound rate ≤10%. It provides an advanced solution with both high durability and high construction efficiency for major projects such as tunnel lining, water conservancy repair, and bridge reinforcement.

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely one preferred embodiment of the invention and are only used to explain the invention. They do not limit the scope of protection of the invention. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0047] (a) Experimental Design The experiment consisted of 5 sets of example cases and 4 sets of comparative cases, mainly investigating the effects of fiber type, admixture, aggregate gradation, and spraying process on the impermeability, tensile strength, compressive strength, rebound rate, and crack control ability of concrete. The test methods were based on the standards GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" and GB / T 50082 "Standard for Test Methods of Long-Term Performance and Durability of Concrete".

[0048] (II) Results and Analysis of the Examples Example 1

[0049] Mix proportion: Cement 450 kg / m³ 3 Nano-silica fume 30 kg / m 3 (5.5% of the total mass of cementitious materials), fly ash 66 kg / m³ 3 (12.1% of the total mass of cementitious materials), water-reducing agent 5.5 kg / m 3 (1.0% of the total mass of cementitious materials), water 204 kg / m³ 3 Water-cement ratio 0.37; aggregate gradation (5-8mm: 35%, 2-5mm: 35%, ≤2mm: 30%) 680 kg / m³ 3 River sand (zone II medium sand, fineness modulus 2.6, mud content 0.8%) 320 kg / m³ 3 Amorphous alloy fiber 2.0 kg / m 3 (Surface silane treatment).

[0050] Spraying parameters: initial spray 0.5 MPa / 40 mm, secondary spray 0.7 MPa / 40 mm, total thickness 120 mm; Test results: impermeability grade P13, tensile strength 5.8 MPa, 28-day compressive strength 53.6 MPa, resilience rate 8.2%, crack width <0.02 mm.

[0051] Analysis: Due to its high aspect ratio and surface treatment, amorphous alloy fibers significantly improve the fiber-matrix bonding strength and effectively inhibit the development of microcracks. At the same time, nano-silica ash fills the micropores, together achieving high impermeability and high tensile strength.

[0052] Example 2

[0053] Mix proportion: Cement 460 kg / m³ 3 Nano-silica fume 35 kg / m 3 (6.2% of the total mass of cementitious materials), fly ash 68 kg / m³ 3 (12.0% of the total mass of cementitious materials), water-reducing agent 5.7 kg / m 3 (1.0% of the total mass of cementitious materials), water 211 kg / m³ 3 Water-cement ratio 0.37; 700 kg / m³ of gravel (5-8mm: 35%, 2-5mm: 35%, ≤2mm: 30%) 3 River sand (zone II medium sand, fineness modulus 2.6, mud content 0.8%) 300 kg / m³ 3 PVA fiber 1.5 kg / m 3 (Alkali resistance 98%, elastic modulus 28 GPa), amorphous alloy fiber 1.0 kg / m 3 .

[0054] Spraying parameters: Single-layer spraying 0.6 MPa / 80 mm, thickness 80 mm; Test results: impermeability grade P15, tensile strength 6.3 MPa, compressive strength 55.1 MPa, resilience 9.1%, crack width ≤0.03 mm.

[0055] Analysis: PVA fibers have high elastic modulus and alkali resistance. Together with amorphous alloy fibers, they form a multi-scale fiber network, which significantly improves toughness and crack resistance, and further enhances impermeability.

[0056] Example 3

[0057] Mix proportion: Cement 480 kg / m³ 3 Nano-silica fume 40 kg / m 3 (6.7% of the total mass of cementitious materials), fly ash 72 kg / m³3 (12.1% of the total mass of cementitious materials), water-reducing agent 6.0 kg / m³ 3 (1.0% of the total mass of cementitious materials), water 221 kg / m³ 3 Water-cement ratio 0.37; aggregate gradation (5-8mm: 40%, 2-5mm: 30%, ≤2mm: 30%) 720 kg / m³ 3 River sand (zone II medium sand, fineness modulus 2.6, mud content 0.8%) 280 kg / m³ 3 ; Carbon fiber 0.8 kg / m 3 (Surface oxidation treatment, bonding strength ≥4.0MPa).

[0058] Spraying parameters: initial spray 0.6 MPa / 40 mm, secondary spray 0.8 MPa / 40 mm, total thickness 150 mm.

[0059] Test results: tensile strength 7.8 MPa, compressive strength 58.4 MPa, impermeability grade P14, resilience 7.5%, crack width <0.01 mm.

[0060] Analysis: Carbon fiber has ultra-high tensile strength and stiffness. After surface oxidation treatment, the interfacial bonding strength is significantly improved, effectively bearing tensile stress and enhancing overall mechanical properties and durability.

[0061] Example 4

[0062] Mix proportion: Cement 430 kg / m³ 3 Nano-silica fume 30 kg / m 3 (5.7% of the total mass of cementitious materials), fly ash 63 kg / m³ 3 (12.0% of the total mass of cementitious materials), water-reducing agent 5.2 kg / m 3 (1.0% of the total mass of cementitious materials), water 194 kg / m³ 3 Water-cement ratio 0.37; gravel (5-8mm: 35%, 2-5mm: 35%, ≤2mm: 30%) 690 kg / m³, river sand (zone II medium sand, fineness modulus 2.6, mud content 0.8%) 310 kg / m³ 3 Amorphous alloy fiber 1.5 kg / m 3 .

[0063] Spraying parameters: initial spray 0.45 MPa / 45 mm, secondary spray 0.65 MPa / 35 mm, total thickness 100 mm.

[0064] Test results: impermeability grade P12, tensile strength 5.1 MPa, compressive strength 50.3 MPa, resilience 8.9%.

[0065] Analysis: Under the premise of ensuring performance standards are met, the material cost can be controlled by optimizing the fiber content and gradation, making it suitable for projects with general impermeability requirements.

[0066] Example 5

[0067] The mixing ratio is the same as in Example 2. The construction environment temperature is 35℃, and the curing method is a combination of spraying and covering to maintain moisture.

[0068] Test results: impermeability grade P14, tensile strength 6.0 MPa, compressive strength 54.2 MPa, no plastic shrinkage cracks on the surface.

[0069] Analysis: This demonstrates that the present invention still possesses good construction adaptability and performance stability under high-temperature environments.

[0070] (III) Comparative Results and Analysis Comparative Example 1 Mixing ratio: Except for the absence of fiber, the rest is the same as in Example 1 (cement 450 kg / m³). 3 Nano-silica fume 30 kg / m 3 fly ash 66 kg / m³ 3 Water-reducing agent 5.5 kg / m 3 Water 204 kg / m 3 680 kg / m³ 3 River sand 320 kg / m 3 ).

[0071] Test results: impermeability grade P6, tensile strength 2.9 MPa, compressive strength 46.8 MPa, resilience 18.5%, and multiple cracks with a width >0.2 mm appeared on the surface.

[0072] Analysis: Without fiber reinforcement, the tensile and crack resistance of concrete decreases significantly, the rebound rate is high, and the impermeability is poor.

[0073] Comparative Example 2 Mixture ratio: 2.0 kg / m² ordinary steel fiber 3 (Untreated, 0.6 mm in diameter, 80 in aspect ratio), otherwise the same as in Example 1.

[0074] Test results: impermeability grade P8, tensile strength 4.2 MPa, compressive strength 49.5 MPa, resilience 14.2%, and obvious corrosion after 28 days.

[0075] Analysis: Steel fibers are prone to corrosion, which affects durability. Furthermore, without surface treatment, the interfacial adhesion is weak, resulting in limited improvement in impermeability and crack resistance.

[0076] Comparative Example 3 The proportions are changed to 5-8mm:50%, 2-5mm:30%, ≤2mm:20%, and the rest are the same as in Example 1.

[0077] Test results: Impermeability grade P9, tensile strength 4.8 MPa, compressive strength 48.7 MPa, resilience 16.8%.

[0078] Analysis: An excessively high proportion of coarse aggregate leads to increased porosity, a weak interfacial transition zone, decreased impermeability and tensile strength, and increased resilience.

[0079] Comparative Example 4 Composition ratio: 3.0 kg / m² amorphous alloy fiber 3 PVA fiber 2.0 kg / m 3 Total dosage: 5.0 kg / m³ 3 The rest is the same as in Example 1.

[0080] Test results: The mixture has poor workability, frequent pipe blockage during spraying, and visible fiber agglomeration inside after molding. The compressive strength is 51.2 MPa, but the tensile strength is only 4.9 MPa.

[0081] Analysis: Excessive fiber content leads to difficulties in fiber dispersion and an increase in interface defects, which in turn reduces the reinforcing effect and deteriorates the workability.

[0082] Comparative analysis of the above embodiments and comparative examples shows that the present invention achieves a balanced improvement in impermeability, crack resistance, strength, and workability through fine gradation of aggregate, microporous filling with nano-silica fume, and synergistic reinforcement with multiple types of fibers, combined with a layered spraying process. Experimental data indicates that, within the optimized parameter range, the concrete impermeability grade can reach P12-P15, tensile strength 5-8 MPa, compressive strength 50-60 MPa, rebound rate controlled within 10%, and excellent surface quality, making it suitable for various harsh engineering environments.

[0083] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this application.

[0084] It should be understood that the sequence number of each step in the invention and its embodiments does not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. Impermeable and crack-resistant shotcrete, characterized in that, Per cubic meter of concrete, it contains the following components: Cementitious material: composed of cement, nano-silica fume, fly ash and water-reducing agent. The amount of cement in each cubic meter of concrete is 400-480 kg; the amount of nano-silica fume is 5-8% of the total mass of cementitious material; the amount of fly ash is 10-15% of the total mass of cementitious material; the amount of water-reducing agent is 0.8-1.2% of the total mass of cementitious material; the water-cement ratio of the cementitious material is 0.35-0.

40. Aggregate: Composed of gravel and river sand, wherein the gravel is continuously graded crushed stone with a particle size ≤8mm, and its gradation is: 30-40% for 5-8mm particle size, 30-40% for 2-5mm particle size, and 20-30% for ≤2mm particle size; the amount of gravel used is 650-800 kg / m³. 3 The amount of river sand used is 280-320 kg / m³. 3 ; Fiber: Selected from at least one of metal fibers, polymer fibers, and inorganic fibers, with a dosage of 1.5-4.0 kg / m³. 3 ; The concrete has an impermeability grade ≥ P12, tensile strength ≥ 5 MPa, 28-day compressive strength ≥ 50 MPa, and a shotcrete rebound rate ≤ 10%.

2. The impermeable and crack-resistant shotcrete according to claim 1, characterized in that, The metal fiber is an amorphous alloy fiber with a diameter of 20-50 μm, a length of 10-15 mm, a slenderness ratio of ≥250, and a surface treated with a silane coupling agent, exhibiting a bonding strength of ≥3.0 MPa. The polymer fiber is polyvinyl alcohol fiber, polypropylene fiber, or aramid fiber, with a tensile strength ≥1000MPa and an alkali resistance ≥95%. The inorganic fiber is carbon fiber, basalt fiber or alkali-resistant glass fiber, with a tensile strength ≥1500MPa, a diameter of 5-15μm, a length of 10-20mm, and a surface treated with oxidation or coupling agent.

3. The impermeable and crack-resistant shotcrete according to claim 2, characterized in that, When the fiber contains metal fibers, polymer fibers and / or inorganic fibers, the metal fibers account for more than 30% of the total fiber mass.

4. The impermeable and crack-resistant shotcrete according to claim 2, characterized in that, The polyvinyl alcohol fiber has an elastic modulus ≥25 GPa and a bonding strength ≥2.0 MPa.

5. The impermeable and crack-resistant shotcrete according to claim 2, characterized in that, The carbon fiber surface is oxidized, and its bond strength is ≥4.0 MPa. Its dosage in concrete is ≤1.0 kg / m³. 3 .

6. The impermeable and crack-resistant shotcrete according to claim 1, characterized in that, The cement is 52.5R grade ordinary Portland cement, and the fly ash is Grade I fly ash or Grade II fly ash.

7. The impermeable and crack-resistant shotcrete according to claim 1, characterized in that, The water-reducing agent has a water reduction rate of ≥25%.

8. The method for constructing concrete according to any one of claims 1-7, characterized in that, include: (1) Premixed aggregate and fiber: dry mix gravel, river sand and fiber to obtain premixed material; (2) Staged feeding: First, dry mix cement, fly ash and nano silica fume, then add premixed materials and continue dry mixing; (3) Add water and water-reducing agent: Add water and water-reducing agent in two batches. First, add 50-70% water and 50-70% water-reducing agent for initial mixing, and then add the remaining 30-50% water and 30-50% water-reducing agent for supplementary mixing. (4) Layered spraying: Use a wet spraying machine with a nozzle diameter of 30-40mm, an initial spraying pressure of 0.4-1MPa, a spraying angle of 75-85°, and a thickness of 40-50mm; and a re-spraying pressure of 0.6-1.2MPa, a spraying angle of 80-90°, and a thickness of 30-40mm. (5) Surface treatment: Smooth the surface before final setting, with a flatness deviation of ≤3mm / 2m; (6) Curing: After final setting, cover with non-woven fabric and spray curing for ≥7 days with humidity ≥90%.

9. The construction method according to claim 8, characterized in that, When the ambient temperature is below 5℃, insulation measures should be taken to keep the concrete surface temperature ≥10℃; when the ambient temperature is above 30℃, a combination of spraying and covering should be used for moisturizing and curing.

10. The application of concrete according to any one of claims 1-7 or the construction method according to claim 8 or 9 in tunnel lining, dam repair or bridge reinforcement projects.

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