Concrete for ultra-deep foundation pit composite wall and preparation method thereof

Abstract

The invention provides concrete for an ultra-deep foundation pit composite wall and a preparation method thereof, and belongs to the technical field of concrete.The concrete is prepared from 260-270 parts of cement, 750-850 parts of coarse aggregate, 500-550 parts of fine aggregate, 30-40 parts of fly ash, 8-12 parts of composite modified basalt fiber, 0.5-1 part of a water reducing agent, 0.5-1.5 parts of an early strength agent and 130-140 parts of water. Wherein the composite modified basalt fiber is prepared by sequentially carrying out etching, surface treatment, silica powder doping and functional solution treatment on basalt fiber. According to the concrete for the ultra-deep foundation pit composite wall, the basalt fiber with a high mixing amount can be well dispersed in the concrete, meanwhile, the concrete has high anti-sliding capacity and bonding strength with slurry, interface pores and micro-cracks can be effectively reduced, and the mechanical strength and anti-seepage performance of the concrete are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and in particular relates to concrete for super-deep foundation pit composite walls and a preparation method thereof. Background Art

[0002] The composite walls of ultra-deep foundation pits are located in a deep underground environment and need to withstand huge pressure from the soil below the ground. They are also affected by long-term infiltration of groundwater. Therefore, the concrete materials used must have sufficiently high mechanical strength and anti-seepage properties to meet the complex working conditions and long-term use requirements of ultra-deep foundation pits.

[0003] Basalt fiber has high mechanical strength and possesses a variety of excellent properties, including corrosion resistance and high-temperature resistance. Furthermore, its production process is environmentally friendly and has minimal environmental pollution, making it a green and environmentally friendly material. my country has listed basalt fiber as one of the four major fiber types for development. In existing technologies, introducing basalt fiber into concrete can act as a micro-reinforcement, reducing internal cracking and significantly improving concrete strength and impermeability. However, high basalt fiber dosages have limited dispersion, making it difficult to achieve a high reinforcement effect. Furthermore, basalt fiber is a hard, smooth material with a weak bond to aggregates and cementitious materials. Pores and microcracks are easily left in the interface transition zone, making it difficult to achieve the desired mechanical strength and impermeability of concrete.

[0004] How to make basalt fiber play a better reinforcing effect in concrete and make concrete achieve higher mechanical strength and anti-permeability performance is a technical difficulty that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In order to solve the problems existing in the background technology, the present invention provides a concrete for ultra-deep foundation pit composite walls and a preparation method thereof. By introducing a high amount of basalt fiber, a higher reinforcement effect can be achieved on the concrete, while effectively avoiding the generation of voids and microcracks, so that the final concrete has higher mechanical strength and anti-permeability performance.

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

[0007] Concrete for super-deep foundation pit composite walls is prepared from the following raw materials: 260-270 parts of cement, 750-850 parts of coarse aggregate, 500-550 parts of fine aggregate, 30-40 parts of fly ash, 8-12 parts of composite modified basalt fiber, 0.5-1 part of water reducing agent, 0.5-1.5 parts of early strength agent and 130-140 parts of water;

[0008] The preparation process of the composite modified basalt fiber includes the following contents:

[0009] A1. Basalt fiber was heated at 200-300°C for 4-6 hours, immersed in an etching solution for 20-40 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 0.5-1 hour. The solution was filtered and dried to produce pretreated basalt fiber.

[0010] A2. Place the pretreated basalt fiber into a silica powder dispersion, add acid to adjust the pH to 2-4, heat to 70-80°C, stir for 1-2h, filter, and dry to obtain a composite basalt fiber;

[0011] A3. The composite basalt fiber is placed in a functional solution at a temperature of 55-65 ° C and stirred for 10-20 minutes to obtain a composite modified basalt fiber. The functional solution is a dispersion of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate in an ethanol aqueous solution.

[0012] Furthermore, the preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 60-80% ethanol aqueous solution, stirred for 10-20 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:2-4:8-12.

[0013] Furthermore, the average particle size of the silicon powder is 1-5 μm.

[0014] Furthermore, the basalt fiber has a diameter of 50-100 μm and a length of 3-15 mm.

[0015] Furthermore, the early strength agent is one of sodium sulfate and aluminum sulfate or a mixture of the two.

[0016] Furthermore, in step A1, the etching solution is a 100-200 g / L sodium hydroxide solution or potassium hydroxide solution, and the mass ratio of the etching solution to the basalt fiber is 8-12:1.

[0017] Furthermore, the silicon micropowder dispersion in step A2 is a dispersion of silicon micropowder dispersed in ethanol, with a concentration of 10-30 g / L.

[0018] The present invention also provides a method for preparing concrete for super-deep foundation pit composite walls, which is used to prepare the above-mentioned concrete for super-deep foundation pit composite walls, and the specific steps are as follows:

[0019] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 10-20 seconds to obtain an aggregate mixture;

[0020] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0021] S3. Add cement slurry to the aggregate mixture and stir evenly for 60-120 seconds. Discharge the mixture after stirring to obtain concrete for super-deep foundation pit composite walls.

[0022] This application has the following beneficial effects:

[0023] 1. The concrete for super-deep foundation pit composite walls provided by the present invention has a special treatment of basalt fiber, which allows high-content basalt fiber to be well dispersed within the concrete. At the same time, the basalt fiber and the slurry have high anti-slip ability and bonding strength, effectively reducing interfacial pores and microcracks, and significantly improving the mechanical strength and anti-seepage performance of the concrete.

[0024] 2. The present invention micro-etches and surface-treats basalt fibers to form active grooves on their surfaces. Silica powder, a micron-sized hard particle with hydroxyl groups on its surface, can adhere to the basalt fiber surface through the active grooves. The addition of silica powder significantly improves the surface roughness and anti-slip ability of the basalt fibers, effectively embedding the basalt fibers in the cementitious material, making them less likely to slip when the concrete is subjected to stress, and significantly enhancing the mechanical strength of the concrete.

[0025] 3. In the functional solution, nano-silica particles are much smaller than the cementitious material particles in concrete. They can fill the micropores between the basalt fiber and the cementitious material, reduce the pores and microcracks in the interface transition zone, make the concrete denser, and improve the anti-seepage performance. The addition of polyvinyl alcohol and sodium hexametaphosphate can improve the surface activity of basalt fiber, improve its dispersion performance and surface coating ability, so that the slurry can be firmly bonded to the surface of the basalt fiber base, improve the mechanical strength and anti-seepage performance of the concrete, and at the same time effectively prevent the agglomeration of cement particles around the silica powder particles, achieve uniform wrapping of the silica powder particles by the slurry, enhance the bonding performance of the silica powder and the cementitious material, and further improve the mechanical strength of the concrete. DETAILED DESCRIPTION

[0026] The present application is further described in detail below with reference to the embodiments.

[0027] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0028] Example 1

[0029] The concrete for the super-deep foundation pit composite wall includes the following raw materials: 265 parts of cement, 800 parts of coarse aggregate, 525 parts of fine aggregate, 35 parts of fly ash, 10 parts of composite modified basalt fiber, 0.8 parts of water reducer, 1 part of early strength agent, and 135 parts of water. The cement used is ordinary Portland cement 42.5, the fine aggregate is medium sand with a fineness modulus of 2.5, the fly ash specification is Class F Grade I, the coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm, the early strength agent is sodium sulfate, and the water reducer is a polycarboxylic acid high-efficiency water reducer with a solid content of 40%.

[0030] The concrete for the super-deep foundation pit composite wall is prepared by the following steps:

[0031] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 15 seconds to obtain an aggregate mixture;

[0032] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0033] S3. Add cement slurry to the aggregate mixture and stir evenly for 90 seconds. After stirring, discharge the mixture to obtain concrete for super-deep foundation pit composite wall.

[0034] The preparation of composite modified basalt fiber includes the following contents:

[0035] A1. Basalt fibers with a diameter of 50-100 μm and a length of 3-15 mm were heated at 250°C for 5 hours, immersed in an etching solution for 30 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 0.5 hours. The solution was filtered and dried to prepare the pretreated basalt fibers. The etching solution consisted of a 150 g / L sodium hydroxide solution, with a mass ratio of etching solution to basalt fiber of 10:1. The concentration of aminopropyltriethoxysilane in the ethanol solution was 5 g / L.

[0036] A2. The pretreated basalt fiber was placed in a silica powder dispersion, acid was added to adjust the pH to 3, heated to 75°C, stirred for 1.5 hours, filtered, and dried to obtain a composite basalt fiber. The silica powder used had an average particle size of 5-15 μm and the silica powder dispersion was a dispersion of silica powder in ethanol at a concentration of 20 g / L.

[0037] A3. The composite basalt fiber was placed in a functional solution at 60°C and stirred for 15 minutes to obtain a composite modified basalt fiber. The functional solution was a dispersion of nano-SiO2, polyvinyl alcohol, and sodium hexametaphosphate in an ethanol-water solution.

[0038] The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 70% ethanol aqueous solution, stirred for 15 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:3:10, the mass fraction of nano-SiO2 in the ethanol aqueous solution is 0.5%, and the mass fraction of stearic acid in the ethanol aqueous solution is 0.2%.

[0039] Example 2

[0040] The concrete for the super-deep foundation pit composite wall includes the following raw materials: 260 parts of cement, 750 parts of coarse aggregate, 500 parts of fine aggregate, 30 parts of fly ash, 8 parts of composite modified basalt fiber, 0.5 parts of water reducer, 0.5 parts of early strength agent, and 130 parts of water. The cement used is ordinary Portland cement 42.5, the fine aggregate is medium sand with a fineness modulus of 2.5, the fly ash specification is Class F Grade I, the coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm, the early strength agent is aluminum sulfate, and the water reducer is a polycarboxylate high-efficiency water reducer with a solid content of 40%.

[0041] The concrete for the super-deep foundation pit composite wall is prepared by the following steps:

[0042] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 10 seconds to obtain an aggregate mixture;

[0043] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0044] S3. Add cement slurry to the aggregate mixture and stir evenly for 60 seconds. After stirring, discharge the mixture to obtain concrete for super-deep foundation pit composite wall.

[0045] The preparation of composite modified basalt fiber includes the following contents:

[0046] A1. Basalt fibers with a diameter of 50-100 μm and a length of 3-15 mm were heated at 200°C for 6 hours, immersed in an etching solution for 20 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 0.5 hours. The solution was filtered and dried to prepare the pretreated basalt fibers. The etching solution consisted of a 100 g / L potassium hydroxide solution, with a mass ratio of etching solution to basalt fiber of 8:1. The concentration of aminopropyltriethoxysilane in the ethanol solution was 4 g / L.

[0047] A2. The pretreated basalt fiber was placed in a silica powder dispersion, acid was added to adjust the pH to 2, the mixture was heated to 70°C, stirred for 2 hours, filtered, and dried to obtain a composite basalt fiber. The silica powder had an average particle size of 5-15 μm and the silica powder dispersion was a dispersion of silica powder in ethanol at a concentration of 10 g / L.

[0048] A3. The composite basalt fiber was placed in a functional solution at a temperature of 55°C and stirred for 20 minutes to obtain a composite modified basalt fiber. The functional solution was a dispersion of nano-SiO2, polyvinyl alcohol, and sodium hexametaphosphate in an ethanol-water solution.

[0049] The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 60% ethanol aqueous solution, stirred for 10 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:2:8, the mass fraction of nano-SiO2 in the ethanol aqueous solution is 0.5%, and the mass fraction of stearic acid in the ethanol aqueous solution is 0.2%.

[0050] Example 3

[0051] The concrete for the super-deep foundation pit composite wall includes the following raw materials: 270 parts cement, 850 parts coarse aggregate, 550 parts fine aggregate, 40 parts fly ash, 12 parts composite modified basalt fiber, 1 part water reducer, 1.5 parts early strength agent, and 140 parts water. The cement used is ordinary Portland cement 42.5, the fine aggregate is medium sand with a fineness modulus of 2.5, the fly ash specification is Class F Grade I, the coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm, the early strength agent is sodium sulfate, and the water reducer is a polycarboxylate high-efficiency water reducer with a solid content of 40%.

[0052] The concrete for the super-deep foundation pit composite wall is prepared by the following steps:

[0053] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 20 seconds to obtain an aggregate mixture;

[0054] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0055] S3. Add cement slurry to the aggregate mixture and stir evenly for 120 seconds. Discharge the mixture after stirring to obtain concrete for super-deep foundation pit composite wall.

[0056] The preparation of composite modified basalt fiber includes the following contents:

[0057] A1. Basalt fibers with a diameter of 50-100 μm and a length of 3-15 mm were heated at 300°C for 4 hours, immersed in an etching solution for 40 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 1 hour. The solution was filtered and dried to prepare the pretreated basalt fibers. The etching solution consisted of a 200 g / L sodium hydroxide solution, with a mass ratio of etching solution to basalt fiber of 12:1. The concentration of aminopropyltriethoxysilane in the ethanol solution was 6 g / L.

[0058] A2. The pretreated basalt fiber was placed in a silica powder dispersion, acid was added to adjust the pH to 4, heated to 80°C, stirred for 1 hour, filtered, and dried to obtain a composite basalt fiber. The silica powder used had an average particle size of 5-15 μm and the silica powder dispersion was a dispersion of silica powder in ethanol at a concentration of 30 g / L.

[0059] A3. The composite basalt fiber was placed in a functional solution at 65°C and stirred for 10 minutes to obtain a composite modified basalt fiber. The functional solution was a dispersion of nano-SiO2, polyvinyl alcohol, and sodium hexametaphosphate in an ethanol-water solution.

[0060] The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to an 80% ethanol aqueous solution, stirred for 20 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:4:12, the mass fraction of nano-SiO2 in the ethanol aqueous solution is 0.5%, and the mass fraction of stearic acid in the ethanol aqueous solution is 0.2%.

[0061] Example 4

[0062] The concrete used for the super-deep foundation pit composite wall includes the following raw materials: 260 parts cement, 850 parts coarse aggregate, 500 parts fine aggregate, 40 parts fly ash, 12 parts composite modified basalt fiber, 0.5 parts water reducer, 1.5 parts early strength agent, and 130 parts water. The cement used is ordinary Portland cement 42.5, the fine aggregate is medium sand with a fineness modulus of 2.5, the fly ash specification is Class F, Grade I, the coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm, the early strength agent is aluminum sulfate, and the water reducer is a polycarboxylate high-efficiency water reducer with a solid content of 40%.

[0063] The concrete for the super-deep foundation pit composite wall is prepared by the following steps:

[0064] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 10-20 seconds to obtain an aggregate mixture;

[0065] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0066] S3. Add cement slurry to the aggregate mixture and stir evenly for 60 seconds. After stirring, discharge the mixture to obtain concrete for super-deep foundation pit composite wall.

[0067] The preparation of composite modified basalt fiber includes the following contents:

[0068] A1. Basalt fibers with a diameter of 50-100 μm and a length of 3-15 mm were heated at 300°C for 4 hours, immersed in an etching solution for 20 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 1 hour. The solution was filtered and dried to prepare the pretreated basalt fibers. The etching solution consisted of a 100 g / L potassium hydroxide solution, with a mass ratio of etching solution to basalt fiber of 12:1. The concentration of aminopropyltriethoxysilane in the ethanol solution was 4 g / L.

[0069] A2. The pretreated basalt fiber was placed in a silica powder dispersion, acid was added to adjust the pH to 2, heated to 75°C, stirred for 1 hour, filtered, and dried to obtain a composite basalt fiber. The silica powder used had an average particle size of 5-15 μm and the silica powder dispersion was a dispersion of silica powder in ethanol at a concentration of 10 g / L.

[0070] A3. The composite basalt fiber was placed in a functional solution at 65°C and stirred for 10 minutes to obtain a composite modified basalt fiber. The functional solution was a dispersion of nano-SiO2, polyvinyl alcohol, and sodium hexametaphosphate in an ethanol-water solution.

[0071] The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 60% ethanol aqueous solution, stirred for 20 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:2:10, the mass fraction of nano-SiO2 in the ethanol aqueous solution is 0.5%, and the mass fraction of stearic acid in the ethanol aqueous solution is 0.2%.

[0072] Example 5

[0073] The concrete for the super-deep foundation pit composite wall includes the following raw materials: 270 parts of cement, 750 parts of coarse aggregate, 550 parts of fine aggregate, 30 parts of fly ash, 10 parts of composite modified basalt fiber, 1 part of water reducer, 0.5 parts of early strength agent, and 140 parts of water. The cement used is ordinary Portland cement 42.5, the fine aggregate is medium sand with a fineness modulus of 2.5, the fly ash specification is Class F Grade I, the coarse aggregate is continuously graded crushed stone with a particle size of 5-20mm, the early strength agent is sodium sulfate, and the water reducer is a polycarboxylate high-efficiency water reducer with a solid content of 40%.

[0074] The concrete for the super-deep foundation pit composite wall is prepared by the following steps:

[0075] S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 10 seconds to obtain an aggregate mixture;

[0076] S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash and stirring to obtain a cement slurry;

[0077] S3. Add cement slurry to the aggregate mixture and stir evenly for 120 seconds. Discharge the mixture after stirring to obtain concrete for super-deep foundation pit composite wall.

[0078] The preparation of composite modified basalt fiber includes the following contents:

[0079] A1. Basalt fibers with a diameter of 50-100 μm and a length of 3-15 mm were heated at 200°C for 5 hours, immersed in an etching solution for 30 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 1 hour. The solution was filtered and dried to prepare the pretreated basalt fibers. The etching solution consisted of a 200 g / L sodium hydroxide solution, with a mass ratio of etching solution to basalt fiber of 8:1. The concentration of aminopropyltriethoxysilane in the ethanol solution was 6 g / L.

[0080] A2. The pretreated basalt fiber was placed in a silica powder dispersion, acid was added to adjust the pH to 4, the mixture was heated to 75°C, stirred for 2 hours, filtered, and dried to obtain a composite basalt fiber. The silica powder used had an average particle size of 5-15 μm and the silica powder dispersion was a dispersion of silica powder in ethanol at a concentration of 20 g / L.

[0081] A3. The composite basalt fiber was placed in a functional solution at 60°C and stirred for 15 minutes to obtain a composite modified basalt fiber. The functional solution was a dispersion of nano-SiO2, polyvinyl alcohol, and sodium hexametaphosphate in an ethanol-water solution.

[0082] The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 70% ethanol aqueous solution, stirred for 15 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:3:8, the mass fraction of nano-SiO2 in the ethanol aqueous solution is 0.5%, and the mass fraction of stearic acid in the ethanol aqueous solution is 0.2%.

[0083] Comparative Example 1

[0084] The only difference between this comparative example and Example 1 is that, in the preparation of the composite modified basalt fiber, the pretreated basalt fiber is not doped with silicon micropowder, that is, in step A2, the silicon micropowder dispersion is replaced with ethanol.

[0085] Comparative Example 2

[0086] The only difference between this comparative example and Example 1 is that, in the preparation of the composite modified basalt fiber, the composite basalt fiber is not treated with the functional solution, that is, in step A3, the functional solution is replaced with an ethanol aqueous solution.

[0087] Comparative Example 3

[0088] The only difference between this comparative example and Example 1 is that, in the preparation of the composite modified basalt fiber, the pretreated basalt fiber is not doped with silicon powder, and the composite basalt fiber is not treated with a functional solution.

[0089] Proven effectiveness

[0090] 1. Mechanical properties: The 28d compressive strength and 28d flexural strength of the concrete prepared in the examples and comparative examples were tested according to GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete";

[0091] 2. Impermeability: The impermeability grade of the concrete was obtained according to the impermeability test (step-by-step pressure method) test examples and comparative examples in SL / T352-2020 "Test Procedures for Hydraulic Concrete".

[0092] Table 1

[0093]

[0094] Result Analysis

[0095] Analysis of Examples 1-5 and Comparative Examples 1-3 and combined with the data in Table 1 shows that the concrete for the super-deep foundation pit composite wall prepared by the present invention has a 28d compressive strength of more than 76.8 MPa, a 28d flexural strength of more than 17.2 MPa, and an anti-seepage grade of P10. It can be seen that the concrete for the super-deep foundation pit composite wall provided by the present invention has high mechanical strength and good anti-seepage performance. The specific analysis is as follows:

[0096] Comparison of Comparative Example 1 with Example 1 shows that, in the preparation of composite modified basalt fiber, the pretreated basalt fiber is doped with silicon powder, and the 28d compressive strength is increased from 67.2 MPa to 78.6 MPa, and the 28d flexural strength is increased from 15.9 MPa to 18.4 MPa, indicating that doping the pretreated basalt fiber with silicon powder can significantly improve the mechanical strength of concrete.

[0097] Comparison between Comparative Example 2 and Example 1 shows that, in the preparation of composite modified basalt fiber, the composite basalt fiber is treated with a functional solution, and the resulting concrete has an impermeability grade increased from P8 to P10, and the impermeability performance is significantly improved. At the same time, the 28d compressive strength and 28d flexural strength are slightly improved, indicating that the doping of pretreated basalt fiber with silica powder can significantly improve the impermeability of concrete and has a certain enhancing effect on improving the mechanical strength of concrete.

[0098] From comparative examples 1-3 and example 1, it can be seen that in the preparation of composite modified basalt fiber, the basalt fiber is treated with a combination of two treatment methods, that is, on the basis of doping with silicon micropowder and then treating with a functional solution, the 28d compressive strength and 28d flexural strength of the prepared concrete are greatly improved, which is significantly greater than the sum of the increases when the two treatment methods are used alone. This shows that the combination of silicon micropowder doping and functional solution treatment of the pretreated basalt fiber can produce a synergistic effect, which can further improve the mechanical strength of the concrete, so that the final concrete has higher mechanical strength and good impermeability.

[0099] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0100] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A concrete for super-deep foundation pit composite wall, characterized in that: Prepared from the following raw materials: 260-270 parts of cement, 750-850 parts of coarse aggregate, 500-550 parts of fine aggregate, 30-40 parts of fly ash, 8-12 parts of composite modified basalt fiber, 0.5-1 part of water reducer, 0.5-1.5 parts of early strength agent and 130-140 parts of water; The preparation process of the composite modified basalt fiber includes the following contents: A1. Basalt fiber was heated at 200-300°C for 4-6 hours, immersed in an etching solution for 20-40 minutes, washed with water, filtered, and then immersed in an ethanol solution containing γ-aminopropyltriethoxysilane for 0.5-1 hour. The solution was filtered and dried to produce pretreated basalt fiber. A2. Place the pretreated basalt fiber into a silica powder dispersion, add acid to adjust the pH to 2-4, heat to 70-80°C, stir for 1-2h, filter, and dry to obtain a composite basalt fiber; A3. The composite basalt fiber is placed in a functional solution at a temperature of 55-65 ° C and stirred for 10-20 minutes to obtain a composite modified basalt fiber. The functional solution is a dispersion of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate in an ethanol aqueous solution.

2. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: The preparation process of the functional solution in step A3 is as follows: polyvinyl alcohol, sodium hexametaphosphate and stearic acid are added to a 60-80% ethanol aqueous solution, stirred for 10-20 minutes, and then nano-SiO2 is added and mixed evenly to obtain a functional solution, wherein the mass ratio of nano-SiO2, polyvinyl alcohol and sodium hexametaphosphate is 1:2-4:8-12.

3. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: The average particle size of the silicon powder in step A2 is 1-5 μm.

4. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: In step A2, the basalt fiber has a diameter of 50-100 μm and a length of 3-15 mm.

5. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: The early strength agent is one of sodium sulfate and aluminum sulfate or a mixture of the two.

6. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: In step A1, the etching solution is a 100-200 g / L sodium hydroxide solution or a potassium hydroxide solution, and the mass ratio of the etching solution to the basalt fiber is 8-12:

1.

7. The concrete for super-deep foundation pit composite wall according to claim 1, characterized in that: The silicon micropowder dispersion in step A2 is a dispersion of silicon micropowder in ethanol with a concentration of 10-30 g / L.

8. A method for preparing concrete for super-deep foundation pit composite walls, for preparing the concrete for super-deep foundation pit composite walls according to any one of claims 1 to 7, comprising the following steps: S1. Mix fine aggregate, coarse aggregate and composite modified basalt fiber uniformly for 10-20 seconds to obtain an aggregate mixture; S2. Mixing a water reducer, an early strength agent, and water to obtain an admixture solution, and then mixing the admixture solution with cement and fly ash, stirring uniformly, to obtain a cement slurry; S3. Add cement slurry to the aggregate mixture and stir evenly for 60-120 seconds. Discharge the mixture after stirring to obtain concrete for super-deep foundation pit composite walls.

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