Wet spraying protective coating for tunnel and underground engineering, preparation method and construction method

Abstract

The invention discloses a wet-spraying protective coating for tunnels and underground engineering, a preparation method and a construction method. The coating is prepared from 40%-55% of ordinary Portland cement, 0.3%-2% of sulphoaluminate cement, 10%-15% of silica fume (SiO is larger than or equal to 92%), 12%-16% of acrylic latex powder, 2%-5% of hydrophobic modified nano-silica, 12%-20% of graded quartz sand, 0.1%-0.5% of antistatic fiber, 1%-2.5% of polycarboxylate superplasticizer, 0.8%-1.5% of calcium nitrite, 0.2%-0.5% of HPMC and 0.05%-0.3% of bentonite. The total percentage of the components is 100%. The preparation method comprises the steps of raw material pretreatment, staged mixing and vacuum packaging, and a three-stage mixing process is adopted to ensure uniform dispersion of fibers. During construction, water is added for stirring on site, and the material has high toughness, excellent impermeability and good bonding strength and is an environment-friendly system; the method is suitable for durability protection of concrete structures such as tunnels and underground engineering.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a single-component, wet-spray, cement-based protective coating suitable for concrete structures such as tunnels and underground engineering projects. It is a single-component dry powder premix. Specifically, it relates to the wet-spray protective coating for tunnels and underground engineering projects, its preparation method, and its application method. Background Technology

[0002] Currently, epoxy resin-based coatings or polyurethane waterproof membranes are commonly used for concrete protection in tunnels and underground structures. While epoxy resin coatings offer excellent impermeability, they are brittle, their adhesion to concrete is easily affected by interface humidity, and they release volatile organic compounds (VOCs) during curing, resulting in harsh construction environments. Polyurethane materials, although possessing a certain degree of elasticity, rely on isocyanate-based curing agents, posing a fire and explosion risk, and have poor resistance to UV aging, easily powdering and failing with long-term exposure. Furthermore, the significant difference in thermal expansion coefficients between these organic coatings and concrete makes them prone to peeling cracks under alternating temperature conditions, failing to meet the long-term protection requirements under complex working conditions. While ordinary cement-based mortar is more environmentally friendly, its brittleness and insufficient impermeability make it unsuitable for the deformation adaptability requirements of dynamically loaded tunnels. Single-component dry powder mortars often rely on latex powder compounding. By adding VAE latex powder and cellulose ether to ordinary cement-based materials to make up for the mortar's deficiencies, this results in a high elastic modulus (>15GPa) and a low ultimate strain (<5%), which cannot adapt to the micro-deformation of the concrete matrix. In addition, the Cl⁻ diffusion coefficient is generally higher than 1×10⁻¹² m² / s, resulting in insufficient resistance to ion penetration. Summary of the Invention

[0003] To address the problems of existing technologies, this invention proposes a wet spray protective coating for tunnels and underground engineering, along with its preparation and application methods.

[0004] The technical solution of the present invention is as follows:

[0005] A wet-spray protective coating for tunnels and underground structures, comprising the following components by weight percentage:

[0006] Ordinary silicate cement 40-55%, sulfoaluminate cement 0.3-2%, silica fume (SiO2≥92%) 10-15%, acrylic latex powder 12-16%, hydrophobically modified nano-silica 2-5%, graded quartz sand 12-20%, antistatic fiber 0.1-0.5%, polycarboxylate superplasticizer 1-2.5%, calcium nitrite 0.8-1.5%, hydroxypropyl methylcellulose (HPMC) 0.2-0.5%, bentonite 0.05-0.3%; total components 100%.

[0007] The hydrophobically modified nano-silica is nanoparticles surface-treated with silane coupling agent KH-550 or KH-570. The amount of silane coupling agent added is 1-2% of the mass of nano-silica, and the contact angle after modification is ≥120°. The hydrophobically modified nano-silica can be replaced with hydrophobically modified nano-alumina or nano-calcium carbonate. After replacement, the specific surface area of ​​the nanoparticles is ≥150 m² / g, and the surface contact angle is ≥110°.

[0008] The antistatic fiber is selected from at least one of polypropylene fiber, polyvinyl alcohol fiber, or basalt fiber, with a fiber diameter of 6-20 μm and a length of 2-5 mm. The surface is treated with 0.3-0.8% quaternary ammonium salt antistatic agent, resulting in a surface resistivity ≤1×10⁻⁶. 8 Ω.

[0009] The particle size distribution of the graded quartz sand meets the following ratios: 60-70% for 0.15-0.3mm, 25-35% for 0.1-0.15mm, and ≤5% for fine powder <0.1mm; the fineness modulus is 1.8-2.6, and the maximum particle size does not exceed 0.3mm; the graded quartz sand can be replaced with manufactured sand, recycled sand, or lightweight aggregate, and the replaced aggregate must meet the following conditions:

[0010] Particle size distribution: The proportion of particles with a diameter of 0.1-0.3 mm should not be less than 90%, and the maximum particle size should not exceed 0.35 mm; Mud content: ≤0.5%; Water absorption rate: For manufactured sand and recycled sand, the water absorption rate should be ≤5%.

[0011] For lightweight aggregates, the apparent density should be in the range of 300-900 kg / m³, the water absorption rate should be ≤30%, and the compressive strength should be not less than 0.5 MPa.

[0012] The polycarboxylate superplasticizer is replaced with a naphthalene-based superplasticizer or an aminosulfonate superplasticizer, and the water reduction rate after replacement must be ≥20%.

[0013] The ordinary Portland cement is grade 42.5-52.5, preferably 52.5R early-strength type; C3A content is 6-8%, and specific surface area is 350±10 m² / kg. Ordinary Portland cement can be wholly or partially replaced with slag Portland cement, fly ash Portland cement, or composite Portland cement. After replacement, the total amount of cementitious materials should remain at 40-55%, and the specific surface area of ​​the replaced cement should be ≥340 m² / kg, with a C3A content ≤8%.

[0014] The sulfoaluminate cement contains ≥28% Al2O3 and ≥10% SO3.

[0015] The acrylic latex powder has a glass transition temperature (Tg) ≤ 0℃ and a minimum film-forming temperature ≤ -5℃. After film formation, it forms a continuous phase in the coating and forms an interpenetrating network structure with cement hydration products. The acrylic latex powder can be replaced with styrene-acrylic latex powder or styrene-butadiene latex powder. After replacement, the glass transition temperature (Tg) of the latex powder is ≤ 5℃ and the minimum film-forming temperature is ≤ 0℃.

[0016] After all the above materials are replaced, the core properties of the cured coating must meet the following requirements: elastic modulus 5-10 GPa; Cl⁻ diffusion coefficient < 5 × 10⁻¹³ m² / s; tensile strength > 12 MPa; bond strength with concrete matrix > 5 MPa.

[0017] The preparation method of the wet-spray type protective coating for tunnels and underground engineering structures according to the present invention includes the following steps:

[0018] (1) Quartz sand pretreatment: Dry at 105±5℃ until the moisture content is ≤0.2%, and control the particle size distribution by vibrating screen classification; the vibrating screen classification adopts a three-layer screen, with the upper screen hole being 0.3mm (rejection rate ≥99%), the middle screen hole being 0.15mm, and the lower screen hole being 0.1mm. After classification, the content of particles >0.3mm in the quartz sand is ≤0.1%;

[0019] (2) Modification of nano-silica: Nano-SiO2 and silane coupling agent are mixed at a mass ratio of 98:2-97:3 and treated in a high-speed disperser at 1800-2200r / min for 8-12min;

[0020] (3) Fiber treatment: Apply 0.3-0.8% quaternary ammonium salt antistatic agent solution by spraying, with atomization pressure of 0.1-0.3MPa, coverage rate ≥95%, and drying temperature of 50-70℃;

[0021] (4) Phased mixing:

[0022] Base material premixing: Add ordinary cement, silica fume, sulfoaluminate cement, modified nano-SiO2, HPMC and bentonite in sequence, and mix at 40±5 r / min for 5-8 min;

[0023] Fiber dispersion: Turn on a pulsed airflow of 0.2-0.5MPa at a frequency of 6-10 times / min, and mix for 3-5 minutes after sprinkling in the fiber;

[0024] Final mixing: Add quartz sand, latex powder, water-reducing agent, and calcium nitrite, and mix at 60±5 r / min for 12-18 min;

[0025] Vacuum packaging: Uses aluminum foil composite bags with a thickness of ≥80μm, a vacuum degree of ≥90kPa, and contains silica gel desiccant.

[0026] The application method of the wet-spray protective coating for tunnels and underground structures of the present invention includes the following steps:

[0027] (1) Base surface treatment: The moisture content of the concrete surface is controlled at 6-10% and there is no standing water. The crack grouting uses epoxy resin-cement composite grout with a viscosity ≤30s.

[0028] (2) Slurry preparation: water-cement ratio 0.20-0.28, the mixing procedure is as follows: dry powder premix and 80% water are mixed at a mixing speed of 300±50r / min for 1-2min → the remaining water is added and mixed at 1200±100r / min for 2-3min → stand for 3-5min to mature;

[0029] (3) Wet spraying construction: Use a rotor piston wet spraying machine with a working pressure of 0.6-0.8MPa, a nozzle diameter of 8-12mm, a spraying distance of 20-40cm, and spray in layers to a total thickness of 2.0±0.3mm;

[0030] (4) Maintenance and management: After initial setting, cover with a 0.1mm thick PE water-retaining film, spray with moisture every 2 hours within 24 hours, maintain the temperature at ≥5℃ and the humidity at ≥90%.

[0031] When applying the wet spray method described above, the thickness of a single coat should be ≤1mm, the interval between coats should be 10-15min, the ambient temperature should be 5-35℃, and the wind speed should be ≤3m / s.

[0032] After spraying and curing, a flame-retardant and impermeable layer with a thickness of 1.8~2.2mm is formed.

[0033] The powder mixing equipment is a twin-shaft forced mixer, and the mixing temperature is controlled at 15~35℃.

[0034] The water-cement ratio of the slurry is 0.20~0.28, preferably 0.22~0.25. When the ambient temperature is >30℃, the water-cement ratio is increased to 0.25~0.28, and a retarder (sodium gluconate) of 0.1%~0.3% is added.

[0035] During the staged mixing process, the mixing temperature is controlled at ≤35℃ in the premixing stage and ≤40℃ in the final mixing stage, and the uniformity of mixing is qualified by the coefficient of variation of Ca²⁺ content ≤3%.

[0036] The nozzle of the wet sprayer is made of hard alloy with an inner wall roughness Ra≤0.8μm and a nozzle length-to-diameter ratio (L / D) of 6:1-8:1.

[0037] 0.1-0.5% pigment or 0.05-0.2% rust inhibitor slow-release microcapsules can be added to the coating, and the fluctuation range of the core performance indicators after addition is ≤5%.

[0038] Used for surface protection of tunnels, underground utility tunnels, bridge piers or marine concrete structures, the coating forms a flame-retardant and impermeable layer with a thickness of 1.8~2.2mm after spraying and curing.

[0039] The formulation of this invention comprises a cementitious material system, a polymer and nano-reinforcing system, an aggregate and fiber system, and a functional additive system; wherein: hydrophobically modified nano-SiO is surface-modified with a silane coupling agent (KH-570), polypropylene fibers are treated with quaternary ammonium salts for antistatic properties (surface resistivity ≤1×10⁻⁶). 8 Ω), sulfoaluminate cement regulates setting time and compensates for shrinkage, silica fume fills pores and participates in pozzolanic reaction, acrylic latex powder forms a flexible polymer network, calcium nitrite is a rust inhibitor, hydroxypropyl methylcellulose is a water-retaining and thickening agent, and bentonite is a thixotropic modifier.

[0040] The preparation method of the wet-spray protective coating for tunnels and underground engineering structures of the present invention is as follows: Figure 1 As shown, it includes the following steps:

[0041] (1) Quartz sand pretreatment: dry at 105±5℃ until the moisture content is ≤0.2%, and control the particle size distribution by vibrating screen grading;

[0042] The vibrating screen uses a three-layer screen for grading: the upper layer has a screen aperture of 0.3 mm (rejection rate ≥99%), the middle layer has a screen aperture of 0.15 mm, and the lower layer has a screen aperture of 0.1 mm. After grading, the content of particles >0.3 mm in the quartz sand is ≤0.1%.

[0043] (2) Modification of nano-silica: Nano-SiO2 and silane coupling agent are mixed at a mass ratio of 98:2-97:3 and treated in a high-speed disperser at 1800-2200r / min for 8-12min;

[0044] (3) Fiber treatment: Apply 0.3-0.8% quaternary ammonium salt antistatic agent solution by spraying, with atomization pressure of 0.1-0.3MPa, coverage rate ≥95%, and drying temperature of 50-70℃;

[0045] (4) Phased mixing:

[0046] 1. Premixing stage: Add cement, silica fume, sulfoaluminate cement, nano silica, HPMC and bentonite into a twin-shaft mixer and mix at a low speed of 40±5 r / min for 5~8 min;

[0047] 2. Fiber dispersion: Add the fiber and turn on the pulse airflow device (pressure 0.2~0.5MPa, frequency 6-10 times / min). After sprinkling the fiber, mix for 3~5 minutes until the fiber monofilaments are dispersed.

[0048] 3. Final mixing stage: Add quartz sand, latex powder, water-reducing agent and calcium nitrite in sequence, increase the speed to 60±5 r / min and mix for 12-18 min until homogeneous;

[0049] 4. Packaging and storage: Sealed in a moisture-proof aluminum foil bag, using an aluminum foil composite bag with a thickness of ≥80μm, a vacuum degree of ≥90kPa, and a humidity of ≤60%. It contains silica gel desiccant and has a shelf life of 6~12 months.

[0050] The coating described in this invention is a single-component dry powder premix, which is shipped as a solid powder (water-free). The amount of water added needs to be dynamically adjusted according to on-site construction conditions (such as substrate humidity and ambient temperature).

[0051] In the preparation method of the wet spray protective coating for tunnel structures, during the staged mixing process, the premixing temperature of the base material is ≤35℃, the mixing temperature of the final mixing stage is ≤40℃, and the uniformity of mixing is qualified by the coefficient of variation of Ca²⁺ content CV ≤3% (tested according to GB / T 176-2017).

[0052] Compared to the traditional "extensive one-step mixing" production model of coatings, this invention establishes a systematic preparation method based on "precision pretreatment, multi-stage energy-sequential construction, and end-to-end activity assurance." First, a dedicated raw material pretreatment process (precision gradation of quartz sand, in-situ hydrophobic modification of nano-silica, and antistatic treatment of fibers) lays the material foundation for the high-performance system. Then, a staged mixing process—sequentially premixing of the base material, pulsed airflow-assisted fiber dispersion, and final mixing—with precisely controlled rotation speed and airflow, solves the problems of fiber agglomeration and component separation. Finally, high-vacuum aluminum foil packaging ensures the chemical stability of the highly active components during storage and transportation. This entire process is deeply coupled with the high-performance formulation, becoming an indispensable core technological guarantee for achieving the product's superior performance.

[0053] The construction method of the wet-spray type protective coating for tunnel structures of the present invention is as follows: Figure 2 ,include:

[0054] (1) Base surface treatment: The moisture content of the concrete surface is controlled at 6-10% and there is no standing water. The crack grouting uses epoxy resin-cement composite grout (viscosity ≤30s).

[0055] (2) Slurry preparation: water-cement ratio 0.20-0.28, the mixing procedure is as follows: dry powder premix is ​​mixed with 80% water at low speed (300±50r / min) for 1-2min → the remaining water is added and mixed at high speed (1200±100r / min) for 2-3min → stand for maturation for 3-5min;

[0056] (3) Wet spraying construction: Use a rotor piston wet spraying machine with a working pressure of 0.6-0.8MPa, a nozzle diameter of 8-12mm, a spraying distance of 20-40cm, and spray in layers to a total thickness of 2.0±0.3mm. See the support diagram. Figure 3 .

[0057] The nozzle of the wet sprayer is made of hard alloy with an inner wall roughness Ra≤0.8μm and a nozzle length-to-diameter ratio (L / D) of 6:1-8:1.

[0058] (4) Maintenance and management: After initial setting, cover with a 0.1mm thick PE water-retaining film, spray with moisture every 2 hours within 24 hours, maintain the temperature at ≥5℃ and the humidity at ≥90%.

[0059] In the substrate treatment stage, setting the optimal interface moisture content and employing epoxy-cement composite grouting technology laid a stable foundation for high bonding strength. In the grout preparation stage, a programmed step-by-step mixing and maturation process ensured the uniformity and workability of the ultra-high density grout. In the core spraying stage, a dense and uniform ultra-thin coating was achieved through customized hard alloy nozzles (with specific aspect ratios and extremely low roughness) and precise process parameter control. In the curing stage, an active water-retaining curing system combining "covering and timed spraying" thoroughly guaranteed the final performance and future development of the material.

[0060] When applying the wet spray method described above, the thickness of a single coat should be ≤1mm, the interval between coats should be 10-15min, the ambient temperature should be 5-35℃, and the wind speed should be ≤3m / s.

[0061] The coating differs from traditional coatings in that it can contain 0.1-0.5% pigment or 0.05-0.2% rust inhibitor slow-release microcapsules, depending on actual needs, and the fluctuation range of the core performance indicators after addition is ≤5%.

[0062] The moisture content of the substrate is controlled as follows: the moisture content of the substrate before spraying is 6%~10%, and there is no standing water.

[0063] Used for surface protection of tunnels, underground utility tunnels, bridge piers or marine concrete structures, the coating forms a flame-retardant and impermeable layer with a thickness of 1.8~2.2mm after spraying and curing.

[0064] The coating exhibits an initial impermeability pressure of ≥0.8MPa (7 days) and a long-term impermeability pressure of ≥1.5MPa (28 days) after spraying. Its long-term impermeability performance (≥1.5MPa) is 50% to 275% higher than that of conventional cement-based protective materials, and it achieves a leap in early impermeability (≥0.8MPa in 7 days), demonstrating a strong ability to continuously improve performance. It overcomes the inherent defects of organic coatings, such as high brittleness, easy aging, and poor compatibility with concrete.

[0065] The powder mixing equipment is a twin-shaft forced mixer, and the mixing temperature is controlled at 15~35℃.

[0066] The water-cement ratio of the slurry is 0.20~0.28, preferably 0.22~0.25. When the ambient temperature is >30℃, the water-cement ratio is increased to 0.25~0.28, and a retarder (sodium gluconate) of 0.1%~0.3% is added.

[0067] This invention proposes an enhancement system: an interpenetrating network formed by hydrophobically modified nano-SiO2 (2.5-4.0%) and acrylic latex powder (12-16%), wherein the surface of nano-SiO2 is modified by a silane coupling agent, the contact angle is ≥120°, and the glass transition temperature Tg of the latex powder is ≤0℃ to ensure low-temperature film formation.

[0068] In a method for preparing a single-component dry powder premix of the present invention, a three-stage mixing process is proposed: base material premixing → pulsed airflow dispersion of fibers → final mixing, so that the fiber monofilament rate is ≥95%.

[0069] The application of the single-component dry powder premix of the present invention in construction requires the addition of water and mixing on site, with a water-cement ratio of 0.20-0.28. A rotor piston wet spraying machine is used to achieve an ultra-thin spraying of 2.0±0.3mm. Compared with traditional processes, the coating has strong adhesion, can be formed in one spraying, and the mechanization saves time and manpower, improving the overall construction efficiency by 50%.

[0070] The micro-expansion of sulfoaluminate cement compensates for shrinkage, and silica fume fills the micropores to make the porosity ≤5%.

[0071] The performance indicators of the coating of the present invention after curing meet the following requirements:

[0072] Elastic modulus 5-10 GPa (GB / T 50081-2019), tensile strength >12 MPa (GB / T 2567-2008), ultimate strain ≥10% (GB / T 50082-2009), Cl⁻ diffusion coefficient <5×10⁻¹³ m² / s (ASTM C1556), bond strength >5 MPa (JGJ / T 70-2009), oxygen index ≥28% (GB / T 2406.2-2009). Linear shrinkage rate: ≤0.02%; initial impermeability pressure (7 days): ≥0.8 MPa; long-term impermeability pressure (28 days): ≥1.5 MPa.

[0073] Existing technologies are typically based on simple physical modification of a single cementitious system (ordinary cement or ordinary cement + a small amount of admixtures) and low-dosage ordinary latex powder. This invention, through a composite cementitious system of "ordinary cement + sulfoaluminate cement", utilizes the complementary hydration characteristics of the two cements to achieve a balance between "rapid hardening and early strength" and "long-term stability", and improves volume stability. It uses ultra-high dosage (12-16%) of acrylic latex powder to form a continuous organic network, realizing the transformation from rigidity to significant flexibility, giving the material excellent crack bridging and deformation adaptability. It also innovatively introduces hydrophobically modified nano-silica, which, while achieving nanoscale physical filling, gives the coating active hydrophobicity. Combined with calcium nitrite rust inhibitor, it jointly constructs an active multi-protection system from physical barrier to chemical and electrochemical protection.

[0074] This invention's coating uses ordinary silicate cement as a base material. Through the compounding of acrylic latex powder, nano-modified materials, and functional admixtures, it achieves high toughness characteristics with an elastic modulus of 5-10 GPa, tensile strength >12 MPa, and ultimate strain ≥10%, while also possessing excellent impermeability with a Cl⁻ diffusion coefficient <5×10⁻¹³ m² / s. This material employs a solvent-free wet spraying process. Its formulation design eliminates traditional toxic and harmful components (such as isocyanates and amine curing agents), using an environmentally friendly material system. After curing, it forms a dense waterproof membrane layer approximately 2 mm thick, effectively blocking chloride ion penetration and improving structural durability. It also possesses flame retardancy, chemical corrosion resistance, and a bonding strength to the substrate >5 MPa, adapting to the needs of mechanized spraying construction and suitable for concrete surface protection under complex working conditions. Attached Figure Description

[0075] Figure 1 Dry powder premix production flow chart

[0076] Figure 2 Construction process diagram

[0077] Figure 3 Support diagram Detailed Implementation

[0078] Example 1

[0079] 1. Components and percentage content of wet-spray protective coatings:

[0080] Ordinary Portland cement (52.5R): 53.30%

[0081] Sulfoaluminate cement: 0.60%

[0082] Silica fume (SiO2≥92%): 12.00%

[0083] Acrylic latex powder (Tg=-5℃): 14.00%

[0084] Hydrophobically modified nano-SiO2 (KH-550 treatment): 3.00%

[0085] Graded quartz sand: 14.00%

[0086] Antistatic polypropylene fiber: 0.20%

[0087] Polycarboxylate superplasticizer: 1.60%

[0088] Calcium nitrite: 0.90%

[0089] HPMC (40,000 viscosity): 0.30%

[0090] Bentonite: 0.10%

[0091] Total: 100.00%

[0092] 2. Coating preparation

[0093] (1) Quartz sand pretreatment: dried at 105℃ to a moisture content of 0.15%, and classified by a three-layer vibrating screen to control the content of particles >0.3mm to ≤0.1%;

[0094] (2) Modification of nano-SiO2: Nano-SiO2 and KH-550 were treated in a high-speed disperser at 2000r / min for 10min at a mass ratio of 97.5:2.5. The contact angle after modification was 125°.

[0095] (3) Fiber treatment: Spray treatment with 0.5% quaternary ammonium salt solution, atomization pressure of 0.2 MPa, coverage of 96%, and the surface resistivity of the fiber after drying is 5×10. 7 Ω;

[0096] (4) Staged mixing: premixing of base material (40r / min, 6min, temperature 30℃) → turning on pulse airflow (pressure 0.3MPa, frequency 8 times / min) to sprinkle in fiber, disperse and mix for 4min → final mixing (adding quartz sand, latex powder, water reducing agent and calcium nitrite, 60r / min, 15min, temperature 38℃), mixing uniformity CV=2.5%;

[0097] (5) Vacuum packaging: 85μm aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0098] The prepared dry powder premix has good flowability, no lumps, and uniform fiber dispersion.

[0099] 3. Construction process

[0100] It is applied to the surface protection of concrete lining in a subway tunnel.

[0101] (1) Surface treatment: The concrete surface is rinsed with a high-pressure water gun (pressure 15MPa) to remove floating dust and loose materials, and then air-dried until the surface moisture content is 8% and there is no standing water. For any minor cracks, pressure grouting is used to seal them.

[0102] (2) Slurry preparation: Take the above dry powder premix and add clean tap water at a water-cement ratio of 0.23. First, mix 80% of the water and dry powder in a mixer at a low speed of 300 r / min for 1.5 min. Then add the remaining 20% ​​of the water and increase the mixer speed to 1200 r / min for a high speed of 2.5 min. Then let it stand and mature for 4 min to obtain a uniform, particle-free slurry with an expansion of 185 mm.

[0103] (3) Wet spraying: A rotary piston wet spraying machine is used, equipped with a carbide nozzle (10mm diameter, L / D=7:1, Ra=0.6μm). The working pressure is set to 0.7MPa, and the spraying distance is controlled at 30cm. Layered spraying is adopted, with a single spray thickness of about 0.7mm, an interval of 12min between layers, and a total of 3 sprays, with the total thickness controlled at 2.1mm.

[0104] (4) Maintenance and management: After the coating is surface dry, immediately cover it with a 0.1mm thick PE water-retaining film. Within 24 hours, moisturize and maintain the coating every 2 hours through a spray system. Maintain the ambient temperature at 15-25℃ and the humidity at >90%. Perform performance testing after 7 days of natural curing.

[0105] 4. Performance Testing:

[0106] The coated samples and composite specimens with the substrate were tested after 28 days of curing, and the results are as follows:

[0107] Elastic modulus: 8.2 GPa (GB / T 50081-2019), tensile strength: 13.5 MPa (GB / T 2567-2008), ultimate strain: 12.3% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 3.8×10⁻¹³ m² / s (ASTM C1556), bond strength: 5.8 MPa (JGJ / T 70-2009), initial impermeability pressure (7 days): 0.9 MPa (GB / T 23440-2009), long-term impermeability pressure (28 days): 1.6 MPa (GB / T 23440-2009).

[0108] Results: Using the composition and proportions of this embodiment, and through standard preparation and construction processes, all core performance indicators are excellent, far exceeding those of traditional cement-based materials, and fully meet the invention's preset requirements for high toughness and high impermeability, verifying the feasibility and superiority of the formulation and process system of this invention.

[0109] Example 2

[0110] 1. Components and percentage content of wet-spray protective coatings:

[0111] Ordinary Portland cement: 50.3%

[0112] Sulfoaluminate cement: 0.8%

[0113] Silica fume: 12.0%

[0114] Acrylic latex powder: 15.0%

[0115] Hydrophobically modified nano-SiO2: 3.0%

[0116] Graded quartz sand: 15.2%

[0117] Basalt fiber: 0.3%

[0118] Polycarboxylate superplasticizer: 1.8%

[0119] Calcium nitrite: 1.2%

[0120] HPMC: 0.25%

[0121] Bentonite: 0.15%

[0122] Total: 100.00%

[0123] In this example, the particle size distribution of the graded quartz sand is designed as follows: 70% 0.15-0.3mm, 25% 0.1-0.15mm, and 5% <0.1mm fine powder.

[0124] 2. Coating preparation:

[0125] (1) Quartz sand pretreatment: Screening is carried out according to the above gradation requirements, and the sand is dried at 105℃ to a moisture content of 0.18%.

[0126] (2) Nano SiO2 modification: KH-570 was used for surface modification. The treatment conditions were: the mass ratio of nano SiO2 to KH-570 was 97.8:2.2, and the treatment was carried out in a high-speed disperser at 2100 r / min for 11 min.

[0127] (3) Fiber treatment: Basalt fiber is sprayed with 0.6% quaternary ammonium salt solution at an atomization pressure of 0.25 MPa and a coverage of ≥97%. After drying, it is ready for use.

[0128] (4) Staged mixing: premixing of base material (42r / min, 7min, temperature 32℃) → turning on pulse airflow (pressure 0.35MPa, frequency 7 times / min) to sprinkle in fiber, disperse and mix for 4min → final mixing (add graded quartz sand, latex powder, water reducing agent and calcium nitrite, 62r / min, 16min, temperature 37℃), mixing uniformity CV=2.8%;

[0129] (5) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0130] 3. Construction process:

[0131] Used for concrete protection of the maintenance access road of a highway tunnel.

[0132] (1) Base surface treatment: After cleaning, the moisture content of the base surface is controlled at 9%, with no standing water.

[0133] (2) Slurry preparation: Take dry powder premix and add water at a water-cement ratio of 0.24. First, mix 80% of the water with the dry powder at a low speed of 320 r / min for 1 min, then add the remaining water and mix at a high speed of 1150 r / min for 3 min, and let it stand for 3 min to mature.

[0134] (3) Wet spraying: A robotic arm-assisted rotor piston wet sprayer is used. The working pressure is 0.65 MPa, the nozzle diameter is 9 mm, and the spraying distance is 35 cm. The thickness of a single coat is 0.8 mm, the interval between coats is 12 min, and the total thickness is 2.0 mm. The ambient temperature during construction is 28℃ and the humidity is 85%.

[0135] (4) Maintenance and management: Cover with PE water-retaining film after spraying, and spray moisturizing every 2 hours within 24 hours.

[0136] 4. Performance Testing:

[0137] Elastic modulus: 9.1 GPa (GB / T 50081-2019), tensile strength: 14.2 MPa (GB / T 2567-2008), ultimate strain: 11.8% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.2×10⁻¹³ m² / s (ASTM C1556), bond strength: 6.1 MPa (JGJ / T 70-2009), initial impermeability pressure (7 days): 0.85 MPa (GB / T23440-2009), long-term impermeability pressure (28 days): 1.55 MPa (GB / T 23440-2009), abrasion resistance: 0.05 g / cm² (GB / T 1768-2006).

[0138] Effect description: By adjusting the aggregate gradation, this embodiment improves the elastic modulus, tensile strength and wear resistance of the coating while maintaining excellent impermeability, making it suitable for parts that may experience mechanical wear.

[0139] Example 3

[0140] 1. Components and percentage content of wet-spray protective coatings:

[0141] Ordinary Portland cement: 50.1%

[0142] Sulfoaluminate cement: 1.0%

[0143] Silica fume: 14.0%

[0144] Low-temperature acrylic latex powder (Tg=-10℃): 16.0%

[0145] Hydrophobically modified nano-SiO2: 4.0%

[0146] Graded quartz sand: 12.0%

[0147] Polyvinyl alcohol fiber: 0.15%

[0148] Polycarboxylate superplasticizer: 1.5%

[0149] Calcium nitrite: 0.8%

[0150] HPMC: 0.4%

[0151] Bentonite: 0.05%

[0152] Total: 100.00%

[0153] 2. Coating preparation:

[0154] (1) Quartz sand pretreatment: dry at 105℃ until the moisture content is ≤0.2%, and screen to control the particle size distribution to meet the requirements.

[0155] (2) Nano SiO2 modification: Nano SiO2 and KH-550 are mixed at a mass ratio of 97:3 and treated in a high-speed disperser at 2200r / min for 12min.

[0156] (3) Fiber treatment: PVA fibers are sprayed with 0.4% quaternary ammonium salt solution and then dried.

[0157] (4) Stage mixing: Sodium gluconate at 0.2% of the total dry powder mass is added during the base material premixing stage. Base material premixing (40r / min, 7min, temperature 28℃) → turn on pulse airflow (pressure 0.4MPa, frequency 10 times / min) to sprinkle in the fiber, disperse and mix for 4min → final mixing (add quartz sand, latex powder, water reducing agent and calcium nitrite, 60r / min, 15min, temperature 35℃).

[0158] (5) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0159] 3. Construction process:

[0160] Simulates the tunnel construction environment in northern winter.

[0161] (1) Base surface treatment: The base surface temperature is about 0°C. It is preheated and blown by a hot air blower to control the surface moisture content to about 7% and to remove ice crystals.

[0162] (2) Slurry preparation: Use warm water at about 15℃ and adjust the water-cement ratio to 0.26. Stirring program: low speed (300r / min) stirring for 2min → high speed (1200r / min) stirring for 2min → stand and mature for 5min.

[0163] (3) Wet spraying construction: Use a heat-insulated wet spraying machine with a working pressure of 0.7MPa and a spraying distance of 25cm. Ambient temperature -2℃.

[0164] (4) Curing and management: After spraying, cover with PE water-retaining film and lay electric heating blanket. Use stepped temperature increase curing: 5℃ (4h) → 10℃ (4h) → 15℃ (constant temperature curing until 24h), with a temperature increase rate of about 2℃ / h.

[0165] 4. Performance Testing:

[0166] Elastic modulus: 7.6 GPa (GB / T 50081-2019), Tensile strength: 13.0 MPa (GB / T 2567-2008), Ultimate strain: 12.0% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.1×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.5 MPa (JGJ / T 70-2009), Initial permeability pressure (7 days): 0.82 MPa (GB / T23440-2009), Long-term permeability pressure (28 days): 1.52 MPa (GB / T 23440-2009), Low-temperature film-forming properties: No cracking when sprayed at -5℃ (refer to JGJ / T 104-2011), Freeze-thaw resistance: After 50 freeze-thaw cycles, the mass loss was 0.3% and the strength retention rate was 92% (GB / T 50082-2009).

[0167] Results Description: This embodiment successfully achieved coating application at -2℃ by using low-temperature film-forming latex powder and strict heat preservation and curing. The coating's core performance met the standards and it has excellent freeze-thaw resistance.

[0168] Example 4

[0169] 1. Components and percentage content of wet-spray protective coatings:

[0170] Ordinary Portland cement: 50.0%

[0171] Sulfoaluminate cement: 0.5%

[0172] Silica fume: 11.0%

[0173] Acrylic latex powder: 13.0%

[0174] Hydrophobically modified nano-SiO2: 2.8%

[0175] Recycled aggregate: 18.5%

[0176] Polypropylene fiber: 0.25%

[0177] Polycarboxylate superplasticizer: 2.0%

[0178] Calcium nitrite: 1.5%

[0179] HPMC: 0.35%

[0180] Bentonite: 0.1%

[0181] Total: 100.00%

[0182] 2. Coating preparation:

[0183] (1) Pretreatment of recycled aggregate: The manufactured sand is washed with water and screened twice to control the particle size to 0.1-0.35mm, of which 92% are 0.1-0.3mm particles and the mud content is 0.3%. It is dried at 105℃.

[0184] (2) Modification of nano-SiO2: The composite coupling agent of KH-550 and KH-570 in a mass ratio of 1:1 was used for modification. The treatment conditions were: the mass ratio of nano-SiO2 to composite coupling agent was 98:2, and the treatment was carried out in a high-speed disperser at 2000r / min for 10min.

[0185] (3) Fiber treatment: Polypropylene fibers are sprayed with 0.5% quaternary ammonium salt solution at an atomization pressure of 0.2 MPa and a coverage of 96%, and then dried.

[0186] (4) Staged mixing: The mixing temperature is controlled below 30℃ throughout the process. Base material premixing (40r / min, 6min, temperature 28℃) → Pulsed airflow dispersion of fibers (pressure 0.3MPa, frequency 8 times / min, time 4min) → Final mixing (add recycled aggregate, latex powder, water reducing agent and calcium nitrite, 60r / min, 15min, temperature 32℃).

[0187] (5) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0188] 3. Construction process:

[0189] Used in a city's underground integrated pipe gallery renovation project, the base material is old concrete.

[0190] (1) Base surface treatment: Nano-silicate grouting solution is used to stop water seepage at local seepage points. The overall moisture content of the base surface is controlled at 9%.

[0191] (2) Slurry preparation: water-cement ratio 0.22. First, mix the dry powder premix with 80% water at a low speed of 300r / min for 1.5min, then add the remaining water and mix at a high speed of 1200r / min for 2.5min, and let it stand for 4min to mature.

[0192] (3) Wet spraying construction: Use a conventional wet spraying machine with a working pressure of 0.6MPa, a spraying distance of 25cm, and a total thickness of 2.0mm. Maintain ventilation during construction.

[0193] (4) Maintenance and management: Cover with PE film and spray with moisture regularly.

[0194] 4. Performance Testing:

[0195] Elastic modulus: 7.5 GPa (GB / T 50081-2019), Tensile strength: 12.5 MPa (GB / T 2567-2008), Ultimate strain: 11.5% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.5×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.3 MPa (JGJ / T 70-2009), Initial seepage pressure (7 days): 0.83 MPa (GB / T23440-2009), Long-term seepage pressure (28 days): 1.53 MPa (GB / T 23440-2009), Radioactivity index: IRa=0.8, Iγ=1.1 (GB 6566-2010), Sulfate erosion resistance coefficient: K=0.92 (GB / T 50082-2009).

[0196] Results: This embodiment verifies the feasibility of completely replacing natural quartz sand with qualified recycled aggregates. The coating still possesses excellent overall performance, demonstrating the potential of this invention in promoting the circular economy.

[0197] Example 5

[0198] 1. Components and percentage content of wet-spray protective coatings:

[0199] Slag silicate cement (S95 grade): 53.9%

[0200] Sulfoaluminate cement: 0.4%

[0201] Silica fume: 12.0%

[0202] Acrylic latex powder: 13.0%

[0203] Hydrophobically modified nano-SiO2: 3.2%

[0204] Graded quartz sand: 14.0%

[0205] Steel fiber: 0.25%

[0206] Polycarboxylate superplasticizer: 1.7%

[0207] Calcium nitrite: 1.1%

[0208] HPMC: 0.35%

[0209] Bentonite: 0.1%

[0210] Total: 100.0%

[0211] 2. Coating preparation:

[0212] (1) Pretreatment of slag cement: heat treatment at 450℃ for 2 hours before use.

[0213] (2) Quartz sand pretreatment: dry at 105℃ until the moisture content is ≤0.2%, and screen to control the particle size distribution.

[0214] (3) Nano SiO2 modification: Nano SiO2 and KH-550 were treated in a high-speed disperser at 2000r / min for 10min at a mass ratio of 97.5:2.5.

[0215] (4) Steel fiber treatment: No antistatic treatment.

[0216] (5) Stage mixing: premix the base material (40r / min, 6min, temperature 30℃) → turn on the pulse airflow (pressure 0.3MPa, frequency 8 times / min) sprinkle in steel fiber, disperse and mix for 6min → final mixing (add quartz sand, latex powder, water reducing agent and calcium nitrite, 60r / min, 18min, temperature 40℃).

[0217] (6) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0218] 3. Construction process:

[0219] It is applied to a section of a cable tunnel with high fire protection requirements.

[0220] (1) Base surface treatment: The moisture content of the base surface is 7%.

[0221] (2) Slurry preparation: water-cement ratio 0.23. First, mix the dry powder premix with 80% water at a low speed of 300r / min for 1.5min, then add the remaining water and mix at a high speed of 1200r / min for 2.5min, and let it stand for 4min to mature.

[0222] (3) Wet spraying construction: a high-pressure wet spraying machine is used with a working pressure of 0.8MPa, and the coating is applied in layers to a total thickness of 2.1mm.

[0223] (4) Maintenance and management: Cover with PE water-retaining film and use a fine water mist system to maintain humidity >95%.

[0224] 4. Performance Testing:

[0225] Elastic modulus: 9.8 GPa (GB / T 50081-2019), Tensile strength: 14.8 MPa (GB / T 2567-2008), Ultimate strain: 10.5% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.0×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.5 MPa (JGJ / T 70-2009), Initial impermeability pressure (7 days): 0.88 MPa (GB / T23440-2009), Long-term impermeability pressure (28 days): 1.58 MPa (GB / T 23440-2009), Impact resistance: 12.5 kJ / m² (GB / T 1843-2008), Refractoriness: No cracking or peeling after being burned at 1000℃ for 1 hour (refer to GB / T 9978.1-2008).

[0226] Effect description: This embodiment uses a slag cement and steel fiber system. The coating exhibits higher elastic modulus, excellent impact resistance and fire resistance, and is suitable for scenarios with fire protection requirements.

[0227] Example 6

[0228] 1. Components and percentage content of wet-spray protective coatings:

[0229] Ordinary Portland cement: 40.0%

[0230] Sulfoaluminate cement: 0.3%

[0231] Silica fume: 10.0%

[0232] Acrylic latex powder: 12.0%

[0233] Hydrophobically modified nano-SiO2: 2.5%

[0234] Manufactured sand (0.1-0.3mm, mud content ≤0.5%): 18.0%

[0235] Carbon fiber (3mm long, 8μm in diameter): 0.1%

[0236] Polycarboxylate superplasticizer: 1.2%

[0237] Calcium nitrite: 0.8%

[0238] HPMC: 0.2%

[0239] Bentonite: 0.05%

[0240] 2. Paint preparation:

[0241] (1) Pretreatment of manufactured sand: Wash and remove dust with water to ensure that the mud content is ≤0.5% and the particle size distribution meets the requirements, and then dry at 105℃.

[0242] (2) Nano SiO2 modification: Nano SiO2 and KH-550 were treated in a high-speed disperser at 2000r / min for 10min at a mass ratio of 97.5:2.5.

[0243] (3) Carbon fiber treatment: Antistatic treatment with 0.8% quaternary ammonium salt solution and spray drying.

[0244] (4) Staged mixing: premixing of base material (40 r / min, 5 min, temperature 30℃) → turning on pulsed airflow (pressure 0.2 MPa, frequency 6 times / min) to sprinkle carbon fiber, disperse and mix for 3 min → final mixing (adding manufactured sand, latex powder, water-reducing agent and calcium nitrite, 60 r / min, 12 min, temperature 35℃). Mixing uniformity CV=2.8%.

[0245] (5) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0246] 3. Construction process:

[0247] Used in areas of a certain integrated utility tunnel that require anti-static properties.

[0248] (1) Base surface treatment: The moisture content of the base surface is 6%.

[0249] (2) Slurry preparation: water-cement ratio 0.25. First, mix the dry powder premix with 80% water at a low speed of 300r / min for 1.5min, then add the remaining water and mix at a high speed of 1200r / min for 2.5min, and let it stand for 4min to mature.

[0250] (3) Wet spraying construction: A rotor piston wet spraying machine (nozzle diameter 10mm, L / D=7:1, Ra=0.6μm) is used, with a working pressure of 0.7MPa. The thickness of a single spraying is 1.0mm, the interlayer interval is 15min, and the total thickness is 2.1mm.

[0251] (4) Maintenance and management: After the coating is dry, cover it with a 0.1mm thick PE water-retaining film, spray it with moisture every 2 hours within 24 hours, maintain the temperature ≥5℃ and the humidity ≥90%.

[0252] 4. Performance Testing:

[0253] Elastic modulus: 5.3 GPa (GB / T 50081-2019), Tensile strength: 12.1 MPa (GB / T 2567-2008), Ultimate strain: 10.5% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.9×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.1 MPa (JGJ / T 70-2009), Initial permeability pressure (7 days): 0.80 MPa (GB / T23440-2009), Long-term permeability pressure (28 days): 1.50 MPa (GB / T 23440-2009), Abrasion resistance: 0.08 g / cm² (GB / T 1768-2006), Coating volume resistivity: 5×10⁻¹³ m² / s (ASTM C1556), 8 Ω·cm.

[0254] Results: This embodiment uses the lower limit of the content of each component for verification. The test results show that even under this extreme condition, the core performance indicators of the coating still fully meet the stringent requirements set by the invention, proving the rationality and feasibility of the scope of the claims.

[0255] Example 7

[0256] 1. Components and percentage content of the coating:

[0257] Ordinary Portland cement: 49.3%

[0258] Sulfoaluminate cement: 0.7%

[0259] Silica fume: 14.0%

[0260] Acrylic latex powder: 15.0%

[0261] Hydrophobically modified nano-SiO2: 3.8%

[0262] Graded quartz sand: 13.23%

[0263] Composite fiber (PP+PVA): 0.25%

[0264] Polycarboxylate superplasticizer: 1.9%

[0265] Calcium nitrite: 1.3%

[0266] HPMC: 0.4%

[0267] Bentonite: 0.12%

[0268] Total: 100.0%

[0269] 2. Paint preparation:

[0270] (1) Quartz sand pretreatment: dry at 105℃ until the moisture content is ≤0.2%, and screen to control the particle size distribution.

[0271] (2) Nano SiO2 and a portion of acrylic latex powder (about 1 / 3) are premixed for 2 minutes.

[0272] (3) Fiber treatment: PP fiber and PVA fiber are sprayed with 0.5% quaternary ammonium salt solution and then dried.

[0273] (4) Stage mixing: Base material premixing (40r / min, 6min, temperature 30℃) → In the fiber dispersion stage, the two fibers are mixed and then added. The variable frequency pulse airflow mode (pressure varies between 0.3-0.5MPa, frequency 6-10 times / min) is used to assist dispersion. Mix for 5min → Final mixing (add quartz sand, remaining latex powder, water reducing agent and calcium nitrite, 60r / min, 16min, temperature 38℃).

[0274] (5) Vacuum packaging: 85μm thick aluminum foil composite bag with a vacuum degree of 92kPa and built-in silica gel desiccant.

[0275] 3. Construction process:

[0276] Used for concrete protection in the tidal zone of a cross-sea bridge pier.

[0277] (1) Base treatment: Remove marine organisms and loose layer, rinse with high pressure fresh water, and control the moisture content at 8%.

[0278] (2) Slurry preparation: water-cement ratio 0.22, using fresh water for mixing. First, mix the dry powder premix with 80% water at a low speed of 300r / min for 1.5min, then add the remaining water and mix at a high speed of 1200r / min for 2.5min, and let it stand for 4min to mature.

[0279] (3) Wet spraying construction: A special anti-corrosion wet spraying machine is used. The working pressure is 0.75MPa and the ambient temperature is 25℃.

[0280] (4) Maintenance and management: Immediately after spraying, cover with a double-layer PE water-retaining film to prevent seawater from splashing. Spray moisturizing under the film every 2 hours within 24 hours (using fresh water).

[0281] 4. Performance Testing:

[0282] Elastic modulus: 6.5 GPa (GB / T 50081-2019), Tensile strength: 14.0 MPa (GB / T 2567-2008), Ultimate strain: 13.8% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 3.5×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.7 MPa (JGJ / T 70-2009), Initial permeability pressure (7 days): 0.90 MPa (GB / T23440-2009), Long-term permeability pressure (28 days): 1.60 MPa (GB / T 23440-2009), Crack control capability: Average width of drying shrinkage cracks ≤0.05mm (GB / T 50082-2009), Fatigue resistance: 10 6 The bond strength retention rate after each cycle of loading is 85% (refer to JTG D60-2015).

[0283] Effect description: This embodiment uses PP and PVA fiber composite to form a multi-scale reinforcement network, which has extremely high ultimate strain, excellent crack control ability and fatigue resistance, making it very suitable for marine structures that bear dynamic loads.

[0284] Example 8

[0285] 1. Components and percentage content of the coating:

[0286] Ordinary Portland cement: 47.1%

[0287] Sulfoaluminate cement: 1.0%

[0288] Silica fume: 15.0%

[0289] Acrylic latex powder: 16.0%

[0290] Hydrophobically modified nano-SiO2: 4.0%

[0291] Lightweight aggregate (expanded perlite): 12.45%

[0292] Basalt fiber: 0.3%

[0293] Polycarboxylate superplasticizer: 2.0%

[0294] Calcium nitrite: 1.5%

[0295] HPMC: 0.5%

[0296] Bentonite: 0.15%

[0297] Total: 100.0%

[0298] 2. Paint preparation:

[0299] (1) Lightweight aggregate pretreatment: The surface is sprayed with hydrophobic solution of silane coupling agent KH-550 and then dried.

[0300] (2) Nano SiO2 modification: KH-570 was used for surface modification. The treatment conditions were: the mass ratio of nano SiO2 to KH-570 was 97.8:2.2, and the treatment was carried out in a high-speed disperser at 2100 r / min for 11 min.

[0301] (3) Fiber treatment: Basalt fibers are sprayed with 0.6% quaternary ammonium salt solution and then dried.

[0302] (4) Staged mixing: The temperature is controlled to be ≤35℃ throughout the process. Base material premixing (40r / min, 6min, temperature 30℃) → Pulsed airflow to disperse fibers (pressure 0.35MPa, frequency 7 times / min, time 4min) → In the final mixing stage, add lightweight aggregate first, mix at 55r / min for 2min, then add quartz sand, latex powder, water reducing agent and calcium nitrite, and restore to 60r / min to mix for the specified time.

[0303] (5) Vacuum packaging: Use an 85μm thick aluminum foil composite bag, vacuumed to 85kPa, with silica gel desiccant inside.

[0304] 3. Construction process:

[0305] It is used for the protection of the roof (back side) of an underground garage, and also has the requirement of heat preservation.

[0306] (1) Surface preparation: The surface is dry with a moisture content of 6%.

[0307] (2) Slurry preparation: water-cement ratio 0.25. First, mix the dry powder premix with 80% water at a low speed of 300r / min for 1.5min, then add the remaining water and mix at a high speed of 1200r / min for 2.5min, and let it stand for 4min to mature.

[0308] (3) Wet spraying construction: A rotor piston wet spraying machine is used with a working pressure of 0.7MPa, and the coating is applied in layers to a total thickness of 2.1mm.

[0309] (4) Maintenance and management: After the coating is dry to the touch, cover it with a 0.1mm thick PE water-retaining film and spray it with moisture every 2 hours within 24 hours.

[0310] 4. Performance Testing:

[0311] Elastic modulus: 5.8 GPa (GB / T 50081-2019), Tensile strength: 13.2 MPa (GB / T 2567-2008), Ultimate strain: 13.0% (GB / T 50082-2009), Cl⁻ diffusion coefficient: 4.3×10⁻¹³ m² / s (ASTM C1556), Bond strength: 5.6 MPa (JGJ / T 70-2009), Initial permeability pressure (7 days): 0.84 MPa (GB / T23440-2009), Long-term permeability pressure (28 days): 1.54 MPa (GB / T 23440-2009), Acid resistance (5% H₂SO₄, 30 days): Tensile strength retention rate 88% (GB / T 176-2017), Thermal conductivity: 0.35 W / (m·K),

[0312] Dry density: 1.2 g / cm³.

[0313] Results: This embodiment successfully prepared a lightweight and high-toughness protective coating. While maintaining excellent mechanical properties and impermeability, the dry density was significantly reduced, and it also has significant thermal insulation function. It is suitable for engineering parts with special requirements for weight and thermal insulation.

[0314] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A wet-spray protective coating for tunnels and underground structures, characterized in that, It consists of the following components by mass percentage: The composition comprises: 40-55% ordinary silicate cement, 0.3-2% sulfoaluminate cement, 10-15% silica fume, 12-16% acrylic latex powder, 2-5% hydrophobically modified nano-silica, 12-20% graded quartz sand, 0.1-0.5% antistatic fiber, 1-2.5% polycarboxylate superplasticizer, 0.8-1.5% calcium nitrite, 0.2-0.5% hydroxypropyl methylcellulose, and 0.05-0.3% bentonite; the total composition is 100%; the silica fume contains ≥92% SiO2.

2. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The hydrophobically modified nano-silica is nanoparticles surface-treated with silane coupling agent KH-550 or KH-570, with the amount of silane coupling agent added being 1-2% of the mass of nano-silica, and the contact angle after modification being ≥120°; or the hydrophobically modified nano-silica can be replaced with hydrophobically modified nano-alumina or nano-calcium carbonate, and the specific surface area of ​​the nanoparticles after replacement is ≥150m² / g, and the surface contact angle is ≥110°.

3. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The antistatic fiber is selected from at least one of polypropylene fiber, polyvinyl alcohol fiber, or basalt fiber, with a fiber diameter of 6-20 μm and a length of 2-5 mm. The surface is treated with 0.3-0.8% quaternary ammonium salt antistatic agent, and the surface resistance after treatment is ≤1×10⁻⁶. 8 Ω.

4. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The particle size distribution of the graded quartz sand meets the following requirements: 60-70% of particles are 0.15-0.3mm, 25-35% are 0.1-0.15mm, and ≤5% are fine powder smaller than 0.1mm; the fineness modulus is 1.8-2.6, and the maximum particle size does not exceed 0.3mm; or the graded quartz sand can be replaced with manufactured sand, recycled sand, or lightweight aggregate; the replaced aggregate must meet the following requirements: the proportion of particles with a particle size of 0.1-0.3mm is not less than 90%, the maximum particle size does not exceed 0.35mm, and the mud content is ≤0.5%; when replaced with manufactured sand or recycled sand, the water absorption rate should be ≤5%; when replaced with lightweight aggregate, its apparent density is 300-900 kg / m³, the water absorption rate should be ≤30%, and the compressive strength is not less than 0.5MPa.

5. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The polycarboxylate superplasticizer is replaced with a naphthalene-based superplasticizer or an aminosulfonate superplasticizer, and the water reduction rate after replacement is ≥20%.

6. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The ordinary Portland cement is grade 42.5, 52.5, or 52.5R early-strength type, with a C3A content of 6-8% and a specific surface area of ​​350±10 m² / kg; the sulfoaluminate cement has an Al2O3 content ≥28% and an SO3 content ≥10%; or the ordinary Portland cement is wholly or partially replaced with slag Portland cement, fly ash Portland cement, or composite Portland cement, and the total mass of cementitious materials after replacement remains at 40-55%, and the specific surface area of ​​the replaced cement is ≥340 m² / kg, and the C3A content is ≤8%.

7. The wet-spray protective coating for tunnels and underground structures as described in claim 1, characterized in that, The acrylic latex powder has a glass transition temperature Tg ≤ 0℃ and a minimum film-forming temperature ≤ -5℃; or, the acrylic latex powder can be replaced with styrene-acrylic latex powder or styrene-butadiene latex powder, and the glass transition temperature Tg of the replaced latex powder is ≤ 5℃ and the minimum film-forming temperature is ≤ 0℃.

8. The method for preparing a wet-spray type protective coating for tunnels and underground structures according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Quartz sand pretreatment: Dry at 105±5℃ until the moisture content is ≤0.2%, and then use a vibrating screen to classify and control the particle size distribution. After classification, the content of particles larger than 0.3mm in the quartz sand is ≤0.1%; (2) Modification of nano-silica: Nano-SiO2 and silane coupling agent are mixed at a mass ratio of 98:2 to 97:3 and treated in a high-speed disperser at a speed of 1800-2200 r / min for 8-12 minutes; (3) Fiber treatment: Apply a quaternary ammonium salt antistatic agent solution with a mass concentration of 0.3-0.8% to the fiber surface by spraying, with an atomization pressure of 0.1-0.3 MPa and a coverage rate of ≥95%, and then dry it at 50-70℃; (4) Phased mixing: Base material premixing: Add ordinary Portland cement, silica fume, sulfoaluminate cement, modified nano silica, hydroxypropyl methylcellulose, and bentonite in sequence, and mix for 5-8 minutes at a speed of 40±5 r / min, with a mixing temperature ≤35℃; Fiber dispersion: Turn on a pulsed airflow of 0.2-0.5 MPa at a frequency of 6-10 times / minute, sprinkle in the treated fibers, and mix for 3-5 minutes; Final mixing: Add graded quartz sand, acrylic latex powder, polycarboxylate superplasticizer, and calcium nitrite. Mix at a speed of 60±5 r / min for 12-18 minutes, with a mixing temperature ≤40℃. The uniformity of mixing is considered acceptable if the coefficient of variation (CV) of the Ca²⁺ content in the mixture is ≤3%. (5) Vacuum packaging: Pack the uniformly mixed dry powder into an aluminum foil composite bag with a thickness of ≥80μm, evacuate to a vacuum degree of ≥90 kPa, and place silica gel desiccant inside.

9. A method for applying the wet-spray protective coating for tunnels and underground structures prepared according to claim 8, characterized in that, Includes the following steps: (1) Base surface treatment: The moisture content of the concrete base surface is controlled at 6-10% and there is no standing water. The cracks are grouted with epoxy resin-cement composite grout with a viscosity ≤30s. (2) Slurry preparation: Mix the dry powder premix with water at a water-cement ratio of 0.20-0.28; the mixing procedure is as follows: first mix the dry powder premix with 80% of the water at a speed of 300±50 r / min for 1-2 minutes, then add the remaining 20% ​​of water, increase the speed to 1200±100 r / min and mix for 2-3 minutes, and finally let it stand for 3-5 minutes to mature; (3) Wet spraying construction: A rotor piston wet sprayer is used for spraying. The working pressure of the wet sprayer is 0.6-0.8 MPa, the nozzle diameter is 8-12 mm, and the spraying distance is 20-40 cm. Layered spraying is adopted, with a single spray thickness ≤1 mm, an interlayer interval of 10-15 minutes, and a total spray thickness of 2.0±0.3 mm. The nozzle is made of hard alloy material, with an inner wall roughness Ra≤0.8 μm and a length-to-diameter ratio L / D of 6:1 to 8:

1. The construction environment temperature is 5-35℃ and the wind speed is ≤3 m / s. (4) Maintenance and management: After the coating has initially set, cover it with a 0.1 mm thick polyethylene water-retaining film and spray it with moisture every 2 hours within 24 hours. The ambient temperature during maintenance is ≥5℃ and the humidity is ≥90%.

10. The construction method as described in claim 9, characterized in that, The water-cement ratio of the slurry is preferably 0.22-0.25; when the ambient temperature is higher than 30℃, the water-cement ratio is increased to 0.25-0.28, and sodium gluconate is added as a retarder at a ratio of 0.1%-0.3% of the total mass of the dry powder premix. Alternatively, 0.1-0.5% of pigment or 0.05-0.2% of rust inhibitor slow-release microcapsules may be added to the dry powder premix or the slurry, and the core performance index fluctuation of the cured coating after addition shall be ≤5%.

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