Composite high-performance shotcrete damping agent, preparation method and application thereof

Abstract

The application relates to the field of concrete elastic-reducing agents, and discloses a composite high-performance sprayed concrete elastic-reducing agent and a preparation method and application thereof. The composite high-performance sprayed concrete elastic-reducing agent comprises the following raw materials in parts by weight: finely ground fly ash 40-50 parts; finely ground mineral powder 30-40 parts; modified silica fume 10-20 parts; and modified redispersible latex powder 3-8 parts. The concrete elastic-reducing agent can fully utilize the synergistic effect of the components, can reduce the rebound rate of sprayed concrete, can optimize the internal pore structure of the concrete, can improve the compressive strength of hardened sprayed concrete and the bonding strength with rocks, and can meet the construction requirements of high-performance sprayed concrete.

Description

Technical Field

[0001] This application relates to the technical field of concrete elasticity reducers, and more specifically, to a composite high-performance shotcrete elasticity reducer, its preparation method, and its application. Background Technology

[0002] Shotcrete is a construction method that uses a pressure spray gun to apply and pour fine aggregate concrete. It is commonly used for pouring linings for thin-walled structures such as tunnel linings, walls, and ceilings, as well as for the protective layer of steel structures. Shotcrete is formed by loading pre-mixed cement, sand, gravel, water, and a certain amount of admixtures into a shotcrete machine, using high-pressure air to deliver the mixture to the nozzle and mix it with a quick-setting agent, then spraying it at high speed onto the surface of rock or concrete. However, traditional shotcrete commonly suffers from excessively high rebound rates in actual construction, with unbonded aggregates and slurry bouncing off the sprayed surface. High rebound not only results in significant waste of raw materials such as cement and aggregates, increasing construction costs, but also prolongs the construction cycle due to frequent cleaning of rebound material. Furthermore, the accumulation of rebound material affects the working environment, and excessive dust concentrations pose a threat to the health of construction workers. Therefore, how to effectively reduce the rebound rate of shotcrete has been a long-standing technical challenge in this field.

[0003] To reduce rebound rate, various technical approaches have been developed. One approach involves adjusting spraying process parameters, such as controlling spraying distance, angle, and air pressure. However, this method is highly dependent on operator experience, resulting in inconsistent effectiveness and limited improvement. Another approach involves adding admixtures or additives to the concrete formula. For example, adding mineral admixtures such as silica fume and fly ash can improve the cohesiveness of the slurry, or adding redispersible latex powder can enhance adhesion. For instance, some technical solutions use a mixture of fly ash, mineral powder, silica fume, and adhesive powder in a certain proportion as a rebound reducer, achieving a certain effect in reducing rebound. However, existing admixtures still have significant shortcomings in practical applications: ordinary silica fume tends to agglomerate during transportation and storage, resulting in poor dispersibility in concrete and failing to fully utilize its ultrafine filling and thickening effects; ordinary adhesive powder lacks sufficient chemical affinity with cement paste and rock interfaces, resulting in good flexibility but insufficient rigidity after film formation, limiting its buffering and anchoring capabilities for high-speed shotcrete aggregates. These combined problems lead to insufficient rebound reduction effects from existing rebound reducers. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a composite high-performance shotcrete elasticity reducer, its preparation method, and its application.

[0005] To achieve the above-mentioned objectives, this application adopts the following technical solution: In a first aspect, this application provides a composite high-performance shotcrete elasticity reducer, which, by weight, comprises the following raw materials: 40-50 parts of finely ground fly ash; 30-40 parts of finely ground mineral powder; 10-20 parts of modified silica fume; 3-8 parts of modified redispersible latex powder.

[0006] Furthermore, the preparation method of the modified silica fume is as follows: take dense silica fume with a specific surface area ≥20000m2 / kg, add 3~5% of nano silica by mass of silica fume and 0.5~1% of polycarboxylate superplasticizer by mass of silica fume, mix at room temperature for 10~15min to obtain surface-coated modified silica fume.

[0007] Furthermore, the preparation method of the modified redispersible latex powder is as follows: Step 1: Take 100 parts of ethylene-vinyl acetate redispersible latex powder, add 1-2% of the mass of the latex powder in a mixed solution of γ-aminopropyltriethoxysilane and anhydrous ethanol, wherein the volume ratio of γ-aminopropyltriethoxysilane to anhydrous ethanol is 1:(3-4), stir at 30-40℃ for 15-20 min to allow the silane coupling agent to be uniformly adsorbed on the surface of the latex powder, and obtain silanized latex powder; Step 2: Disperse 3-6% of the latex powder with 20-50 nm nano-silica in anhydrous ethanol and ultrasonically disperse for 15-20 min to form a nano-suspension. Then add the silanized latex powder obtained in Step 1 and reflux and stir for 1-2 h in a water bath at 50-60 °C to chemically graft the nano-silica onto the surface of the latex powder. Filter and vacuum dry at 40 °C to constant weight to obtain nano-silica grafted modified latex powder. Step 3: Mix the nano-silica grafted modified latex powder obtained in Step 2 with potassium methylsilicate or sodium methylsilicate at 0.5-1.5% of the original latex powder mass in a high-speed mixer at room temperature for 5-10 minutes to form an organosilicon hydrophobic film on the surface of the latex powder while retaining the hydrophilic groups inside the powder, thus obtaining a modified redispersible latex powder with a hydrophilic core-hydrophobic surface core-shell structure.

[0008] Furthermore, the composite high-performance shotcrete elasticity reducer, by weight, comprises the following raw materials: 45 parts of finely ground fly ash; 35 parts of finely ground mineral powder; 15 parts modified silica fume; 5 parts of modified redispersible latex powder.

[0009] Furthermore, the specific surface area of ​​the finely ground fly ash is ≥550 m² / kg, and the specific surface area of ​​the finely ground mineral powder is ≥500 m² / kg.

[0010] Secondly, this application provides a method for preparing the aforementioned composite high-performance shotcrete elasticity reducer, comprising the following steps: Step 1: Grind the raw fly ash into a finer powder with a specific surface area ≥550m2 / kg using a mill. After being separated by a classifier, the finely ground fly ash is stored in a semi-finished product tank for later use. Step 2: Grind the mineral powder through a mill until the specific surface area is ≥550m2 / kg to obtain finely ground mineral powder, and store it in a semi-finished product tank for later use; Step 3: Modify the encrypted silica fume to obtain modified silica fume, and store it in a semi-finished product container for later use. Step 4: Modify the redispersible latex powder to obtain modified redispersible latex powder, and store it in a semi-finished product container for later use. Step 5: Weigh 40-50 parts of the finely ground fly ash obtained in Step 1, 30-40 parts of the finely ground mineral powder obtained in Step 2, 10-20 parts of the modified silica fume obtained in Step 3, and 3-8 parts of the modified redispersible latex powder obtained in Step 4 according to the weight ratio, and put them into a double-cycle mixer and mix them evenly to obtain the composite high-performance shotcrete elasticity reducer.

[0011] Furthermore, in steps 1 and 2, the mill is a φ2.2M×7.5M ball mill with a mill output of 30T / h; the classifier is an LCX750 high-efficiency horizontal vortex classifier with a maximum processing capacity of 135T / h and a separation capacity of 27~54T / h. In step 5, the bi-weekly mixer is a UFH800×4000-2 type pneumatic and mechanical composite mixer with a mixing capacity of 200~500m3 / h.

[0012] Thirdly, this application provides the application of the aforementioned composite high-performance shotcrete elasticity reducer in the preparation of modified shotcrete.

[0013] Fourthly, this application provides a modified shotcrete, which, by weight, comprises the following raw materials: 380-420 parts of ordinary Portland cement; 90-120 parts of the composite high-performance shotcrete elasticity reducer according to any one of claims 1 to 5; 800-900 parts fine aggregate; 750-850 parts coarse aggregate; 160-190 parts water; 3-5 parts of polycarboxylate high-performance water-reducing agent; 30-40 parts of alkali-free liquid quick-setting agent.

[0014] In summary, this application has the following beneficial effects: (1) Significantly reduce the rebound rate of shotcrete: This application uses a specific ratio of finely ground fly ash, finely ground mineral powder, modified silica fume and modified redispersible latex powder as a rebound reducer. The components work synergistically: finely ground fly ash optimizes particle size distribution, lubricates the slurry, and retains water and prevents bleeding; finely ground mineral powder enhances hydration activity and slurry cohesion; modified silica fume is modified by coating the surface of nano silica, which greatly improves dispersibility and ultrafine filling effect, significantly increases slurry viscosity, and achieves strong coating of sand and gravel aggregates; modified redispersible latex powder is pretreated with silane coupling agent, chemically grafted with nano silica and hydrophobic with organosilicon three-layer composite modification, forming a nano-level rough structure on the surface of the powder and retaining a hydrophilic core, which not only enhances the chemical bonding and mechanical interlocking between the powder and the cement slurry, but also gives the powder good anti-hygroscopic and anti-caking properties, which can effectively buffer the impact of aggregates and enhance the bonding between the slurry and the rock surface during the spraying process.

[0015] (2) Improve the mechanical and durability properties of shotcrete: The modified silica fume and modified redispersible latex powder in the elasticity reducer of this application synergistically improve the microstructure of concrete. The ultrafine filling effect of the modified silica fume makes the paste denser and significantly reduces the porosity; the modified latex powder forms a flexible film during the cement hydration process, which not only improves the bonding strength of the aggregate-paste interface, but also gives the concrete a certain crack resistance.

[0016] (3) Improved storage stability and ease of application of the elasticity reducer: This application modifies the redispersible latex powder with organosilicon hydrophobicity, forming a nano-scale organosilicon hydrophobic film on the powder surface. This effectively inhibits the moisture absorption and clumping of the powder during storage and transportation, extending the shelf life of the elasticity reducer to more than 24 months and avoiding the problem of traditional powder-based admixtures failing due to moisture absorption. At the same time, the elasticity reducer is in dry powder form and has good compatibility and dispersibility with cement, aggregates and other materials. When used on site, it can be directly added and stirred according to the ratio without additional dissolution or special treatment, making the construction process simple and convenient.

[0017] (4) Green and environmentally friendly, reducing overall construction costs: This application uses a large amount of industrial solid waste such as fly ash and mineral powder as the main raw materials for the rebound agent. On the one hand, it realizes the resource utilization of industrial waste residue and reduces the pressure of waste storage on the environment. On the other hand, by significantly reducing the rebound rate of shotcrete, it reduces the waste of raw materials such as cement and aggregate, reduces material costs and labor costs for cleaning rebound material. At the same time, the dust concentration during construction is greatly reduced, improving the working environment and having significant economic, environmental and social benefits. Detailed Implementation

[0018] The technical solutions and effects of this application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely for explaining the invention and are not intended to limit the invention.

[0019] Raw material specifications or source: Ordinary Portland cement: P.O42.5; Raw fly ash: Grade II ash, ≤25% residue on 45μm sieve; Mineral powder: S95 grade slag powder, specific surface area 400~450m² 2 / kg; High-density silica fume: SiO2 content ≥ 92%, specific surface area ≥ 20000 m² 2 / kg; Redispersible latex powder: Ethylene-vinyl acetate (VAE), model Vinnapas® 5044N, purchased from Wacker Chemie; Nano-silica: Particle size 20~50nm, purity ≥99.5%; γ-aminopropyltriethoxysilane: KH-550, purity ≥98%; Potassium methylsilicate: Solid content 40%; Polycarboxylate high-performance water-reducing agent: powder, water reduction rate ≥25%, purchased from Jiangsu Subote New Material Co., Ltd.; Alkali-free liquid quick-setting agent: AF-LR type, solid content 45%, initial setting ≤3min and final setting ≤8min when the dosage is 7%, purchased from Wuhu Hongma New Materials Co., Ltd. Fine aggregate: manufactured sand, fineness modulus 2.6, zone II medium sand, mud content ≤2.0%; Coarse aggregate: 5~10mm continuously graded crushed stone, with needle-like and flaky content ≤8% and mud content ≤0.5%; Anhydrous ethanol: analytical grade.

[0020] Example 1 This embodiment discloses a composite high-performance shotcrete elasticity reducer, comprising the following raw materials: 40 parts of finely ground fly ash; 30 parts of finely ground mineral powder; 10 parts of modified silica fume; and 3 parts of modified redispersible latex powder.

[0021] The preparation method of modified silica fume is as follows: take samples with a specific surface area ≥20000 m² 2 / kg of high-density silica fume is mixed with 3% nano-silica by weight and 0.5% polycarboxylate superplasticizer by weight, and mixed at room temperature for 10 minutes to obtain surface-coated modified silica fume.

[0022] The method for preparing the modified redispersible latex powder is as follows: Step 1: Take 100 parts of ethylene-vinyl acetate redispersible latex powder and add a mixed solution of γ-aminopropyltriethoxysilane and anhydrous ethanol, accounting for 1% of the mass of the latex powder. The volume ratio of γ-aminopropyltriethoxysilane to anhydrous ethanol is 1:3. Stir at 30°C for 15 minutes to allow the silane coupling agent to be uniformly adsorbed on the surface of the latex powder, thereby obtaining silanized latex powder. Step 2: Disperse 3% of the latex powder with 20-50 nm nano-silica in anhydrous ethanol and ultrasonically disperse for 15 min to form a nano suspension. Then add the silanized latex powder obtained in Step 1 and reflux and stir for 1 h in a 50 °C water bath to chemically graft the nano-silica onto the surface of the latex powder. Filter and vacuum dry at 40 °C to constant weight to obtain nano-silica grafted modified latex powder. Step 3: Mix the nano-silica grafted modified latex powder obtained in Step 2 with potassium methylsilicate or sodium methylsilicate at 0.5% of the original latex powder mass in a high-speed mixer at room temperature for 5 minutes to form an organosilicon hydrophobic film on the surface of the latex powder while retaining the hydrophilic groups inside the powder, thus obtaining a modified redispersible latex powder with a hydrophilic core-hydrophobic surface core-shell structure.

[0023] The specific surface area of ​​finely ground fly ash is ≥550m². 2 / kg, specific surface area of ​​finely ground mineral powder ≥500m² 2 / kg.

[0024] The preparation method of this composite high-performance shotcrete elasticity reducer includes the following steps: Step 1: Grind the raw fly ash into a fine powder using a mill until the specific surface area is ≥550 m². 2 / kg, after being separated by an air classifier, is finely ground fly ash, which is stored in a semi-finished product tank for later use; Step 2: Grind the mineral powder through a mill to a specific surface area ≥ 550 m². 2 / kg, to obtain finely ground mineral powder, which is stored in a semi-finished product tank for later use; Step 3: Modify the encrypted silica fume to obtain modified silica fume, and store it in a semi-finished product container for later use. Step 4: Modify the redispersible latex powder to obtain modified redispersible latex powder, and store it in a semi-finished product container for later use. Step 5: Weigh 40 parts of the finely ground fly ash obtained in Step 1, 30 parts of the finely ground mineral powder obtained in Step 2, 10 parts of the modified silica fume obtained in Step 3, and 3 parts of the modified redispersible latex powder obtained in Step 4 according to the weight ratio, and put them into a double-cycle mixer and mix them evenly to obtain the composite high-performance shotcrete elasticity reducer.

[0025] In steps 1 and 2, the mill is a φ2.2M×7.5M ball mill with a mill output of 30T / h; the classifier is an LCX750 high-efficiency horizontal vortex classifier with a maximum processing capacity of 135T / h and a separation capacity of 27~54T / h. In step 5, the bi-cycle mixer is a UFH800×4000-2 type pneumatic and mechanical composite mixer with a mixing capacity of 200~500m³. 3 / h.

[0026] Example 2 This embodiment discloses a composite high-performance shotcrete elasticity reducer, which differs from Embodiment 1 only in that it includes the following raw materials: 45 parts of finely ground fly ash; 35 parts of finely ground mineral powder; 15 parts of modified silica fume; and 5 parts of modified redispersible latex powder.

[0027] Example 3 This embodiment discloses a composite high-performance shotcrete elasticity reducer, which differs from Embodiment 1 only in that it includes the following raw materials: 50 parts of finely ground fly ash; 40 parts of finely ground mineral powder; 20 parts of modified silica fume; and 8 parts of modified redispersible latex powder.

[0028] Example 4 This embodiment discloses a composite high-performance shotcrete elasticity reducer, which differs from Embodiment 1 only in that the preparation method of the modified silica fume is as follows: taking a specific surface area ≥20000m² 2 / kg of high-density silica fume was mixed with 4% nano-silica by weight and 0.75% polycarboxylate superplasticizer by weight, and mixed at room temperature for 12.5 min to obtain surface-coated modified silica fume.

[0029] Example 5 This embodiment discloses a composite high-performance shotcrete elasticity reducer, which differs from Embodiment 1 only in that the preparation method of the modified silica fume is as follows: taking a specific surface area ≥20000m² 2 / kg of high-density silica fume is mixed with 5% nano-silica and 1% polycarboxylate superplasticizer by mass of silica fume, and then mixed at room temperature for 15 minutes to obtain surface-coated modified silica fume.

[0030] Example 6 This embodiment discloses a composite high-performance shotcrete elasticity reducer, which differs from Embodiment 1 only in that the preparation method of the modified redispersible latex powder is as follows: Step 1: Take 100 parts of ethylene-vinyl acetate redispersible latex powder, add 2% of the mass of latex powder of a mixed solution of γ-aminopropyltriethoxysilane and anhydrous ethanol, wherein the volume ratio of γ-aminopropyltriethoxysilane to anhydrous ethanol is 1:4, stir at 40°C for 20 min to allow the silane coupling agent to be uniformly adsorbed on the surface of the latex powder, and obtain silanized latex powder. Step 2: Disperse 6% of the latex powder with 20-50 nm nano-silica in anhydrous ethanol and ultrasonically disperse for 20 min to form a nano suspension. Then add the silanized latex powder obtained in Step 1 and reflux and stir for 2 h in a 60 °C water bath to chemically graft the nano-silica onto the surface of the latex powder. Filter and vacuum dry at 40 °C to constant weight to obtain nano-silica grafted modified latex powder. Step 3: Mix the nano-silica grafted modified latex powder obtained in Step 2 with potassium methylsilicate or sodium methylsilicate at 1.5% of the original latex powder mass in a high-speed mixer at room temperature for 10 minutes to form an organosilicon hydrophobic film on the surface of the latex powder while retaining the hydrophilic groups inside the powder, thus obtaining a modified redispersible latex powder with a hydrophilic core-hydrophobic surface core-shell structure.

[0031] Comparative Example 1 This comparative example discloses a shotcrete elasticity reducer, which differs from Example 1 only in that it includes the following raw materials: 30 parts of finely ground fly ash; 30 parts of finely ground mineral powder; 5 parts of modified silica fume; and 3 parts of modified redispersible latex powder.

[0032] Comparative Example 2 This comparative example discloses a shotcrete elasticity reducer, which differs from Example 1 only in that it includes the following raw materials: 40 parts of finely ground fly ash; 20 parts of finely ground mineral powder; 5 parts of modified silica fume; and 1 part of modified redispersible latex powder.

[0033] Comparative Example 3 This comparative example discloses a shotcrete elasticity reducer, which differs from Example 1 only in that it includes the following raw materials: 40 parts of finely ground fly ash; 30 parts of finely ground mineral powder; 10 parts of unmodified silica fume; and 3 parts of modified redispersible latex powder.

[0034] Comparative Example 4 This comparative example discloses a shotcrete elasticity reducer, which differs from Example 1 only in that it includes the following raw materials: 40 parts of finely ground fly ash; 30 parts of finely ground mineral powder; 10 parts of modified silica fume; and 3 parts of unmodified redispersible latex powder.

[0035] Comparative Example 5 This comparative example discloses a shotcrete elasticity reducer, which differs from Example 1 only in that it includes the following raw materials: 40 parts of finely ground fly ash; 30 parts of finely ground mineral powder; 10 parts of unmodified silica fume; and 3 parts of unmodified redispersible latex powder.

[0036] Application examples Shotcrete was prepared by using the shotcrete modifiers obtained in Examples 1-6 and Comparative Examples 1-5, and the shotcrete, by weight, included the following raw materials: 400 parts of ordinary Portland cement; 105 parts of shotcrete elasticity reducer prepared in Examples 1-6 or Comparative Examples 1-5; 850 parts fine aggregate; 800 parts coarse aggregate; 180 portions of water; 5 parts of polycarboxylate high-performance water-reducing agent; 35 parts of alkali-free liquid quick-setting agent.

[0037] Performance testing (1) Rebound rate test The test was conducted according to the "Test Method for Determining the Rebound Rate of Shotcrete" (NB / T11535-2024) and the "Technical Specification for Application of Shotcrete" (JGJ / T372-2016). The specific method is as follows: A 3.0m × 3.0m spraying surface was set up at the construction site. An aggregate cloth (canvas or tarpaulin) was laid under the spraying surface to collect the rebound concrete material falling during spraying. Wet spraying was used, with the spraying distance controlled at 1.0~1.5m, the spraying angle perpendicular to the spraying surface, and the spraying air pressure controlled at 0.4~0.6MPa. After spraying, all rebound material on the aggregate cloth was collected, and the mass of the rebound material was weighed. Simultaneously, the total mass of concrete actually sprayed onto the spraying surface was recorded. The rebound rate was calculated using the following formula: Rebound rate (%) = (mass of rebound material / total mass of actual shotcrete) × 100%; Each formulation underwent three independent spraying tests, and the average of the three test results was taken as the final rebound rate.

[0038] (2) Compressive strength test The tests were conducted according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081). Specimens were prepared using the on-site spraying method: concrete was sprayed into a 450mm×350mm×120mm mold, and the surface was smoothed with a trowel after spraying. Specimens were cured under standard curing conditions (temperature 20±2℃, relative humidity ≥95%) for the specified ages (1 day and 28 days). After reaching the curing age, the sprayed layer was cut into 100mm×100mm×100mm cubes using a cutting machine, ensuring the cut surfaces were smooth. Six cubes were prepared for each mix design, and the average compressive strength of the six cubes was taken as the compressive strength value of that mix.

[0039] (3) Test of bond strength with rock The test was conducted according to Appendix D of the "Technical Specification for Application of Shotcrete" (JGJ / T372-2016). A pre-processed rock slab (300mm × 300mm × 50mm, lithology granite or surrounding rock consistent with the actual project) was cleaned and kept dry. Shotcrete was applied to the rock slab surface to a thickness of 100mm. After curing for 7 days under standard conditions, a core sample with a diameter of 50mm was drilled from the shotcrete layer using the core drilling method. The core sample should penetrate the shotcrete layer and extend approximately 10mm into the rock slab. A pull-out test was performed using a pull-out apparatus, with the pull-out speed controlled between 0.5 and 1.0 kN / s. The maximum pull-out force at failure was recorded. The bond strength was calculated using the following formula: Bond strength (MPa) = Maximum pull-out force (N) / Bond area (mm²) 2 ); Five core samples were tested for each batch, and the average value was taken as the final bonding strength.

[0040] (4) Porosity test Porosity was tested using mercury intrusion porosimetry (MIP) according to the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082). Core samples were drilled from the sprayed layer at 28 days of age. Core samples without visible defects were cut into small pieces of approximately 10 mm × 10 mm × 10 mm and dried to constant weight in a vacuum drying oven at 60℃. A mercury intrusion porosimetry instrument (AutoPore IV 9510 model) was used for testing, with a maximum pressure not less than 200 MPa, and a testable pore size range of approximately 5 nm to 300 μm. The ratio of total mercury intrusion volume to sample volume was recorded as the total porosity (%). Three samples were tested for each mix design, and the average value was taken.

[0041] Performance test results The modified shotcrete prepared in each embodiment and comparative example was tested for performance according to the above testing methods. The test results are as follows: ; From the above data, we can see that: A comparison of Comparative Examples 1-2 and Examples 1-3 shows that the dosage of each component of the elasticity reducer has a significant impact on the performance of shotcrete. In Comparative Example 1, the ratio of ground fly ash, ground mineral powder, modified silica fume, and modified redispersible latex powder was 30:30:5:3, with a rebound rate of 15.8% and a 28-day compressive strength of 38.5 MPa. In Comparative Example 2, the ratio of ground fly ash, ground mineral powder, modified silica fume, and modified redispersible latex powder was 40:20:5:1, with a rebound rate as high as 18.3% and a 28-day compressive strength of only 36.2 MPa. In Example 2, using the preferred ratio of 45:35:15:5, the rebound rate decreased to 8.9%, the 28-day compressive strength increased to 48.7 MPa, and the bond strength reached 1.32 MPa. This indicates that the synergistic effect among the components is optimal when the ratio of finely ground fly ash: finely ground mineral powder: modified silica fume: modified redispersible latex powder is 45:35:15:5. Excess or deficiency will weaken the rebound effect.

[0042] Comparing Example 1 (modified silica fume) and Comparative Example 3 (unmodified silica fume), it can be seen that the rebound rate of Comparative Example 3 is 14.5%, and the 28-day compressive strength is 40.3 MPa; while the rebound rate of Example 1 is 11.2%, and the 28-day compressive strength is 45.8 MPa. After the silica fume was modified by surface coating with nano-silica and polycarboxylate superplasticizer, the rebound rate decreased by 3.3 percentage points, and the compressive strength increased by 5.5 MPa. This indicates that the modification treatment effectively solved the problem of silica fume agglomeration, improved its dispersibility in cement paste, and allowed the ultrafine filling effect and thickening effect to be fully utilized.

[0043] Comparing Example 1 (modified adhesive powder) and Comparative Example 4 (unmodified adhesive powder), it can be seen that the rebound rate of Comparative Example 4 is 13.8%, and the 28-day compressive strength is 41.2 MPa; while the rebound rate of Example 1 is 11.2%, and the 28-day compressive strength is 45.8 MPa. After the adhesive powder was pretreated with a silane coupling agent, chemically grafted with nano-silica, and modified with a three-layer composite of hydrophobic organosilicon, the rebound rate decreased by 2.6 percentage points, the compressive strength increased by 4.6 MPa, and the bond strength increased from 1.02 MPa to 1.15 MPa. This indicates that the nanoscale rough structure and chemically grafted layer on the surface of the modified adhesive powder significantly enhance the mechanical interlocking and chemical bonding ability between the adhesive powder and the cement paste.

[0044] Comparative Example 5, using both unmodified silica fume and unmodified adhesive powder, showed a rebound rate of 16.2%, a 28-day compressive strength of 37.8 MPa, and a bond strength of only 0.90 MPa. Example 1, using both modified silica fume and modified adhesive powder, reduced the rebound rate to 11.2%, increased the 28-day compressive strength to 45.8 MPa, and increased the bond strength to 1.15 MPa. Compared to Comparative Example 5, the rebound rate decreased by 5.0 percentage points, the 28-day compressive strength increased by 8.0 MPa, and the bond strength increased by 0.25 MPa. This indicates a significant synergistic effect between modified silica fume and modified adhesive powder: the ultrafine filling effect and thickening effect of modified silica fume, combined with the interfacial reinforcement and buffering effect of modified adhesive powder, mutually promote each other, jointly achieving a comprehensive improvement in the performance of shotcrete.

[0045] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A composite high-performance shotcrete elasticity reducer, characterized in that, By weight, it includes the following ingredients: 40-50 parts of finely ground fly ash; 30-40 parts of finely ground mineral powder; 10-20 parts of modified silica fume; 3-8 parts of modified redispersible latex powder.

2. The composite high-performance shotcrete elasticity reducer according to claim 1, characterized in that, The modified silica fume is prepared by taking a sample with a specific surface area ≥20000 m². 2 / kg of high-density silica fume is mixed with 3-5% nano-silica and 0.5-1% polycarboxylate superplasticizer by weight of silica fume, and mixed at room temperature for 10-15 minutes to obtain surface-coated modified silica fume.

3. The composite high-performance shotcrete elasticity reducer according to claim 1, characterized in that, The method for preparing the modified redispersible latex powder is as follows: Step 1: Take 100 parts of ethylene-vinyl acetate redispersible latex powder, add 1-2% of the mass of the latex powder in a mixed solution of γ-aminopropyltriethoxysilane and anhydrous ethanol, wherein the volume ratio of γ-aminopropyltriethoxysilane to anhydrous ethanol is 1:(3-4), stir at 30-40℃ for 15-20 min to allow the silane coupling agent to be uniformly adsorbed on the surface of the latex powder, and obtain silanized latex powder; Step 2: Disperse 3-6% of the latex powder with 20-50 nm nano-silica in anhydrous ethanol and ultrasonically disperse for 15-20 min to form a nano-suspension. Then add the silanized latex powder obtained in Step 1 and reflux and stir for 1-2 h in a water bath at 50-60 °C to chemically graft the nano-silica onto the surface of the latex powder. Filter and vacuum dry at 40 °C to constant weight to obtain nano-silica grafted modified latex powder. Step 3: Mix the nano-silica grafted modified latex powder obtained in Step 2 with potassium methylsilicate or sodium methylsilicate at 0.5-1.5% of the original latex powder mass in a high-speed mixer at room temperature for 5-10 minutes to form an organosilicon hydrophobic film on the surface of the latex powder while retaining the hydrophilic groups inside the powder, thus obtaining a modified redispersible latex powder with a hydrophilic core-hydrophobic surface core-shell structure.

4. The composite high-performance shotcrete elasticity reducer according to claim 1, characterized in that, By weight, it includes the following ingredients: 45 parts of finely ground fly ash; 35 parts of finely ground mineral powder; 15 parts modified silica fume; 5 parts of modified redispersible latex powder.

5. The composite high-performance shotcrete elasticity reducer according to claim 1, characterized in that, The specific surface area of ​​the finely ground fly ash is ≥550 m². 2 / kg, the specific surface area of ​​the finely ground mineral powder is ≥500m². 2 / kg.

6. The method for preparing the composite high-performance shotcrete elasticity reducer according to any one of claims 1-5, characterized in that, Includes the following steps: Step 1: Grind the raw fly ash into a fine powder using a mill until the specific surface area is ≥550 m². 2 / kg, after being separated by an air classifier, is finely ground fly ash, which is stored in a semi-finished product tank for later use; Step 2: Grind the mineral powder through a mill to a specific surface area ≥ 550 m². 2 / kg, to obtain finely ground mineral powder, which is stored in a semi-finished product tank for later use; Step 3: Modify the encrypted silica fume to obtain modified silica fume, and store it in a semi-finished product container for later use. Step 4: Modify the redispersible latex powder to obtain modified redispersible latex powder, and store it in a semi-finished product container for later use. Step 5: Weigh 40-50 parts of the finely ground fly ash obtained in Step 1, 30-40 parts of the finely ground mineral powder obtained in Step 2, 10-20 parts of the modified silica fume obtained in Step 3, and 3-8 parts of the modified redispersible latex powder obtained in Step 4 according to the weight ratio, and put them into a double-cycle mixer and mix them evenly to obtain the composite high-performance shotcrete elasticity reducer.

7. The preparation method according to claim 6, characterized in that, In steps 1 and 2, the mill is a φ2.2M×7.5M ball mill with a mill output of 30T / h; the classifier is an LCX750 high-efficiency horizontal vortex classifier with a maximum processing capacity of 135T / h and a separation capacity of 27~54T / h. In step 5, the bi-cycle mixer is a UFH800×4000-2 type pneumatic and mechanical composite mixer with a mixing capacity of 200~500m³. 3 / h.

8. The application of the composite high-performance shotcrete modifier according to any one of claims 1-5 in the preparation of modified shotcrete.

9. A modified shotcrete, characterized in that, By weight, it includes the following ingredients: 380-420 parts of ordinary Portland cement; 90-120 parts of the composite high-performance shotcrete elasticity reducer according to any one of claims 1 to 5; 800-900 parts fine aggregate; 750-850 parts coarse aggregate; 160-190 parts water; 3-5 parts of polycarboxylate high-performance water-reducing agent; 30-40 parts of alkali-free liquid quick-setting agent.