Concrete for prefabricated lining of shield tunnel and preparation method thereof

Abstract

This invention discloses a precast concrete lining for shield tunnels and its preparation method, relating to the field of civil engineering composite materials technology. The raw materials include: 320-350 parts cement, 650-700 parts coarse aggregate, 60-80 parts organic aggregate, 10-20 parts redispersible latex powder, 500-550 parts sand, 95-130 parts magnetic water-reducing microcapsules, 60-75 parts steel fiber, 150-165 parts water, and 85-90 parts fly ash. The magnetic water-reducing microcapsules contain the following components by weight: 5-7 parts hydroxypropyl cellulose, 3-5 parts γ-Fe₂O₃, 50-70 parts rubber powder, 2-5 parts diallyl phthalate, and 80-110 parts water-reducing agent. This invention regulates the release of the water-reducing agent and rubber powder, improving the fluidity of the concrete while also enhancing compressive strength, impact toughness, and the self-healing effect of microcracks.

Description

Technical Field

[0001] This invention relates to the field of composite materials technology in civil engineering, specifically to a precast assembled concrete for shield tunnel lining and its preparation method. Background Technology

[0002] With the acceleration of urbanization in my country, shield tunnels have been widely used in rail transit engineering, water conservancy and hydropower engineering, highway engineering, and municipal utility tunnels. As the permanent lining structure of tunnels, the quality of traditional reinforced concrete precast segment lining directly determines the service performance and service life of the project. However, this structure has revealed many defects in practical applications: during the construction phase, the segment lining is prone to edge and corner damage and penetrating cracks under hoisting, transportation, and jacking, resulting in a high damage rate; during the operation phase, constrained by the complex surrounding underground hydrogeological environment, its insufficient crack resistance under frequent vibration loads easily leads to steel corrosion and leakage, seriously threatening the long-term safety of the structure and increasing maintenance costs.

[0003] In previous research and engineering applications, steel fiber reinforced concrete has been introduced into the production and manufacturing of tunnel linings as a high-performance composite material. Compared with ordinary reinforced concrete, it significantly improves the tensile, bending, wear resistance, impact resistance and fatigue resistance of the structure, has good post-cracking toughness and crack resistance, can effectively resist various loads throughout the entire life cycle and improve the bearing capacity of various ultimate states.

[0004] However, steel fiber reinforced concrete is prone to rapid slump loss, and the rapid decrease in fluidity makes it difficult for the concrete to level during construction, thus affecting the construction progress. Furthermore, although the mechanism of steel fiber reinforced concrete is to reduce internal microcracks and improve crack resistance by utilizing its random distribution within the concrete, the special application scenarios of segment lining (lifting, transportation, and jacking) necessitate further improvements in the crack resistance of steel fiber reinforced concrete to better meet the application requirements. Therefore, this patent application is filed. Summary of the Invention

[0005] To address the aforementioned technical problems of rapid slump loss and the need for further enhancement of crack resistance in current steel fiber reinforced concrete, this invention provides a precast assembled lining concrete for shield tunnels and its preparation method to solve these problems.

[0006] The present invention adopts the following technical solution:

[0007] The first objective of this invention is to provide a precast concrete lining for shield tunnels, the raw materials of which include the following components: 320-350 parts cement, 650-700 parts coarse aggregate, 60-80 parts organic aggregate, 10-20 parts redispersible latex powder, 500-550 parts sand, 95-130 parts magnetic water-reducing microcapsules, 60-75 parts steel fiber, 150-165 parts water, and 85-90 parts fly ash;

[0008] The raw materials of the magnetic water-reducing microcapsules include the following components in parts by weight: 5-7 parts hydroxypropyl cellulose, 3-5 parts γ-Fe2O3, 50-70 parts rubber powder, 2-5 parts diallyl phthalate, and 80-110 parts water-reducing agent.

[0009] Among the various raw materials in this invention:

[0010] Ordinary silicate cement, such as P・O 42.5, can be used, as it has high early strength and relatively stable heat of hydration.

[0011] The coarse aggregate can be well-graded crushed stone, which helps to improve the uniform distribution of steel fibers and avoid local lack of strength.

[0012] Organic aggregates can be selected from coconut shells, a mixture of rice husks and corn cobs, snail shells, etc.

[0013] Redispersible latex powder can form a polymer film on the mortar surface. The polymer film has pores, and the pore surface can be filled by the mortar to reduce stress concentration and improve the toughness and elasticity of the material.

[0014] The sand can be aggregate with a particle size of less than 4.5mm, such as river sand, manufactured sand, and recycled sand, which can fill the gaps in the coarse aggregate and improve the density of the matrix.

[0015] Magnetic water-reducing microcapsules use magnetic γ-Fe2O3 particles as the capsule wall, with a water-reducing agent and rubber powder encapsulated within the capsule wall as the core material. This allows for controlled and gradient release of the water-reducing agent and rubber powder, reducing the rate of decrease in the flowability of steel fibers. Hydroxypropyl cellulose and γ-Fe2O3 form the capsule wall; hydroxypropyl cellulose allows for slow degradation of the capsule wall to ensure slow release of the water-reducing agent, while the rubber powder enhances the material's impact resistance and fracture toughness. The slow release of the rubber powder into the concrete allows for adaptive crack repair. Diallyl phthalate interacts with hydroxypropyl cellulose, improving its toughness and enhancing the surface adhesion stability between the microcapsules and the substrate. During construction, the magnetic field strength can be controlled by a DC power supply, arranging the water-reducing microcapsules according to a set direction and angle. This allows for adjustment of the microcapsule position based on the distribution characteristics of the steel fibers, precisely controlling the flowability of the concrete and, in conjunction with the "spring" effect of the rubber powder, controlling the improvement of toughness and crack repair.

[0016] As a preferred design, the water-reducing agent is an ester-modified polycarboxylate water-reducing agent.

[0017] As a preferred design, the polycarboxylate superplasticizer is modified using any one of methyl acrylate, hydroxyethyl methacrylate, or polyethylene glycol monomethyl ether acrylate.

[0018] This invention modifies polycarboxylate superplasticizers with ester groups. The purpose is to introduce ester groups into the superplasticizer's structure. Ester groups are easily hydrolyzed. The advantage of this design is that even when the magnetic microcapsules are only slightly damaged, the easy hydrolysis of the ester groups allows the core material to gradually hydrolyze, ensuring that the release of the internal rubber powder and superplasticizer is not affected. This allows for a dual release effect, utilizing the controlled release effect of the microcapsule wall combined with the self-hydrolysis controlled release effect of the internal core material. Simultaneously, introducing ester groups into the superplasticizer's structure also facilitates the dispersion of γ-Fe2O3, resulting in more uniform microcapsule sizes. Furthermore, when some of the ester groups on the superplasticizer hydrolyze and the rest is released, the superplasticizer with ester groups can also help disperse the steel fibers, preventing agglomeration.

[0019] As a preferred design, the steel fiber is copper-plated steel fiber modified with an organosilane coupling agent.

[0020] As a preferred design, the organosilane coupling agent has an amino and / or epoxy group at one end and an alkoxy group at the other end. For example, either 3-aminopropyltriethoxysilane or 3-(methacryloyloxy)propyltrimethoxysilane can be used.

[0021] The purpose of modifying the steel fibers in this invention is to form a uniform lubricating film on the surface of the steel fibers, reducing sliding friction between the fibers, improving the surface fluidity of the steel fibers, and having a better effect on rapid slump loss. Furthermore, the formed lubricating film does not affect the chemical adhesion to the cement matrix. A silane coupling agent with a special structure is selected. The amino or epoxy groups in the silane coupling agent structure are active groups that can react with the hydroxyl groups on the surface-treated copper-plated surface, while the alkoxy groups at the other end are hydrophobic long chains that can form a lubricating interface, reducing the frictional resistance between the steel fibers. The modified steel fibers, due to the presence of active groups, also improve the adhesion to the matrix.

[0022] As a preferred design, the redispersible latex powder is an acrylic powder;

[0023] And / or, the fineness of the rubber powder is 200~240 mesh.

[0024] The second objective of this invention is to provide a method for preparing precast concrete for shield tunnel lining as described in any of the above claims, comprising the following steps:

[0025] Mix and stir the raw materials until uniform to obtain concrete mix;

[0026] The concrete mixture is then placed in a pulsed magnetic field for 1 to 3 hours to obtain the prefabricated assembled lining concrete for the shield tunnel.

[0027] As a preferred design, the preparation process of the magnetic water-reducing microcapsules is as follows:

[0028] (1) Add the rubber powder to ethanol and disperse it by ultrasonication and stir until uniform;

[0029] (2) Hydroxypropyl fibers are mixed with γ-Fe2O3 particles and ultrasonically dispersed to form a magnetic aqueous phase;

[0030] (3) Mix the water-reducing agent, the well-dispersed rubber powder, and diallyl phthalate and stir to form an oil phase;

[0031] (4) The oil phase is slowly dripped into the magnetic aqueous phase and homogenized using a high-speed homogenizer to obtain an emulsion system;

[0032] (5) Heat the emulsion system to 45~60℃, stir at a constant temperature for 3~5 hours, then centrifuge, wash and purify, and dry to obtain the magnetic water-reducing microcapsules.

[0033] As a preferred design, the process of modifying the water-reducing agent with ester groups is as follows:

[0034] (1) Dissolve methyl allyl polyoxyethylene ether in water;

[0035] (2) Mix ammonium persulfate, mercaptopropionic acid and water and stir to dissolve to obtain the first solution;

[0036] Acrylic acid and methyl acrylate were mixed and stirred to dissolve, resulting in a second solution.

[0037] At 60~80℃, the first solution and the second solution are added dropwise at a uniform rate to the aqueous solution of methyl allyl polyoxyethylene ether to induce a copolymerization reaction. After the addition is completed, the solution is kept at the temperature for curing.

[0038] After the reaction was completed, sodium hydroxide was added to the system to adjust the pH to 6-8, and finally filtered to obtain the ester-modified water-reducing agent.

[0039] As a preferred design, the preparation process of the modified copper-plated steel fiber is as follows:

[0040] (1) Add copper-plated steel fibers to acetone solution, sonicate, and then remove;

[0041] The copper-plated steel fibers that have undergone ultrasonic treatment are immersed in hydrochloric acid solution and then rinsed until neutral.

[0042] (2) After hydrolyzing the organosilane coupling agent, add the treated copper-plated steel fiber to it for soaking, and then take out the fiber and drain the excess solution.

[0043] (3) The modified copper-plated steel fiber is cured at 100~120℃, cooled and then sieved to break it apart, thus obtaining the modified copper-plated steel fiber.

[0044] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0045] 1. This invention provides a precast concrete for shield tunnel lining and its preparation method. Magnetic particles γ-Fe2O3 are used as the microcapsule walls, with water-reducing agents and rubber powder encapsulated within the microcapsules as the core material. This allows for controlled and gradient release of the water-reducing agent and rubber powder, reducing the rate of decrease in steel fiber fluidity. Hydroxypropyl cellulose and γ-Fe2O3 serve as the microcapsule walls. Hydroxypropyl cellulose allows for slow degradation of the microcapsule walls to ensure slow release of the water-reducing agent, while the rubber powder enhances the material's impact resistance and fracture toughness. The slow release of rubber powder into the concrete allows for adaptive crack repair. During construction, the magnetic field strength can be controlled by a DC power supply, arranging the water-reducing microcapsules according to a set direction and angle. This adjusts the position of the microcapsules based on the distribution characteristics of the steel fibers, precisely controlling the concrete's fluidity. The "spring" effect of the rubber powder further enhances toughness and crack repair, resulting in significantly improved compressive and flexural strength of the concrete. This method is suitable for special applications in segment lining (lifting, transportation, and jacking).

[0046] 2. In the precast assembled concrete for shield tunnel lining and its preparation method provided by the present invention, the water-reducing agent is modified with ester group, forming a dual regulation result of self-hydrolysis control of the water-reducing agent by the microcapsule wall and the internal core material. This results in a more lasting and better effect on the release control of the water-reducing agent, and also facilitates the uniform dispersion of steel fibers during the preparation process.

[0047] 3. In the precast assembled concrete for shield tunnel lining and its preparation method provided by the present invention, the copper-plated steel fiber is subjected to surface lubrication modification treatment, which significantly improves the fluidity of the steel fiber and enhances the bonding effect with the matrix. It also enhances the compressive strength and flexural strength of the concrete. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. The illustrative embodiments and descriptions of this invention are only used to explain this invention and are not intended to limit this invention.

[0049] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0051] Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially.

[0052] The process is performed sequentially. For example, the method includes steps (a) and (b), indicating that the method may include step (a) performed sequentially.

[0053] (b) may also include steps (b) and (a) performed sequentially. For example, the method may also include step (c).

[0054] This indicates that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c).

[0055] It may also include steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0056] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0057] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0058] Example 1:

[0059] A method for preparing precast assembled concrete for shield tunnel lining is as follows:

[0060] 1. Formula (by weight):

[0061] Cement, P.O 42.5, 350 parts;

[0062] The coarse aggregate consists of 650 parts of 6-18mm granite crushed stone (70% by mass) and 5-10mm steel slag (30% by mass).

[0063] Organic aggregate, made from coconut shells, 60 parts;

[0064] Redispersible latex powder, acrylic powder, 15 parts;

[0065] Sand, selected from river sand with a particle size of less than 4.5 mm, 500 parts;

[0066] 120 portions of magnetic water-reducing microcapsules;

[0067] 60 parts of modified steel fiber;

[0068] 160 portions of water;

[0069] 88 portions of fly ash.

[0070] 2. The formulation of the magnetic water-reducing microcapsules (by weight) is as follows:

[0071] 5 parts hydroxypropyl cellulose;

[0072] γ-Fe2O3 35 parts;

[0073] Rubber powder, 200 mesh, 50 parts;

[0074] 2 parts diallyl phthalate;

[0075] 80 parts of ester-modified polycarboxylate superplasticizer.

[0076] 3. The preparation process of magnetic water-reducing microcapsules is as follows:

[0077] (1) Add rubber powder to 30 parts of ethanol and ultrasonically disperse for 25 minutes, then stir for 30 minutes to obtain a uniformly dispersed rubber powder solution;

[0078] (2) First, dissolve hydroxypropyl cellulose in deionized water and stir until completely dissolved. Then, add γ-Fe2O3 particles and mix. Disperse by ultrasonication for 30 minutes to form a magnetic aqueous phase.

[0079] (3) Mix the water-reducing agent, the well-dispersed rubber powder solution, and diallyl phthalate and stir for 35 minutes until homogeneous to form an oil phase;

[0080] (4) The oil phase was slowly dripped into the magnetic aqueous phase, and then homogenized using a high-speed homogenizer at a speed of 3000 r / min for 25 minutes to obtain the emulsion system.

[0081] (5) Heat the emulsion system to 60°C, stir at a constant temperature for 3 to 5 hours, centrifuge at 3500 r / min for 10 minutes, then wash and purify with deionized water and ethanol 4 times, freeze dry for 24 hours to obtain the magnetic water-reducing microcapsules.

[0082] 4. The preparation process of ester-modified polycarboxylate superplasticizer is as follows:

[0083] (1) Dissolve 300 parts by weight of methyl allyl polyoxyethylene ether in water and stir magnetically at 25°C for 30 minutes to completely dissolve the methyl allyl polyoxyethylene ether.

[0084] (2) Mix 1.3 parts by weight of ammonium persulfate, 1.0 parts by weight of mercaptopropionic acid and water and stir until completely dissolved to obtain the first solution;

[0085] 36 parts by weight of acrylic acid and 30 parts by weight of methyl acrylate are mixed and stirred until completely dissolved and uniformly mixed to obtain a second solution;

[0086] At 80°C, the first solution and the second solution were added dropwise over a period of 2 hours at a uniform rate to the aqueous solution of methyl allyl polyoxyethylene ether. After the addition was completed, the solution was kept at 80°C for 1 hour to cure.

[0087] After the reaction was complete, sodium hydroxide was added to the system to adjust the pH to 6.5. Finally, filtration was performed to remove any remaining impurities, yielding the ester-modified water-reducing agent.

[0088] 5. The preparation process of modified steel fibers is as follows:

[0089] (1) Add copper-plated steel fibers to acetone solution and sonicate for 25 minutes, then remove them. The ratio of the mass of copper-plated steel fibers to the volume of acetone solution is 1:12.

[0090] The copper-plated steel fibers that have undergone ultrasonic treatment are first cleaned with deionized water, then immersed in an 8% hydrochloric acid solution for 6 minutes, then cleaned with deionized water until neutral, and dried for 30 minutes to obtain the treated copper-plated steel fibers.

[0091] (2) Add the organosilane coupling agent 3-aminopropyltriethoxysilane to the mixed solution of water bath ethanol, stir evenly, add glacial acetic acid to the solution, adjust the pH to 5, stir the solution for 45 minutes, and the solution becomes transparent to obtain the hydrolysate;

[0092] The treated copper-plated steel fibers were added to the hydrolysate and soaked for 10 minutes. Then the fibers were removed and excess solution was drained to obtain the modified copper-plated steel fibers.

[0093] (3) The modified copper-plated steel fiber is kept at 100°C for 1 hour for curing. After cooling, it is sieved and dispersed to obtain the modified copper-plated steel fiber.

[0094] 6. The concrete preparation process is as follows:

[0095] (1) According to the formula, mix and stir the raw materials until uniform to obtain concrete mixture;

[0096] (2) The concrete mixture is then placed in a pulsed magnetic field for treatment to obtain the precast assembled lining concrete for the shield tunnel. The intensity of the pulsed magnetic field is constant at 1T, the pulsed magnetic field is an intermittent square wave, the pulse width is 2s, the interval is 6min, the ambient temperature during the treatment is 25℃, the treatment time is 2h, and the concrete mixture is placed in the central area of ​​the magnetic field, with a distance of 15cm between the concrete mixture and the pulsed magnetic field coil.

[0097] Example 2:

[0098] A type of precast concrete for shield tunnel lining differs from Example 1 in that:

[0099] 1. Formula (by weight):

[0100] Cement, P.O 42.5, 320 parts;

[0101] The coarse aggregate consists of 700 parts of 6-18mm granite crushed stone (70% by mass) and 5-10mm steel slag (30% by mass).

[0102] Organic aggregate, made from coconut shells, 70 parts;

[0103] Redispersible latex powder, acrylic adhesive powder, 20 parts;

[0104] Sand, selected from river sand with a particle size of less than 4.5 mm, 520 parts;

[0105] 95 portions of magnetic water-reducing microcapsules;

[0106] 70 parts of modified steel fiber;

[0107] 160 portions of water;

[0108] 85 parts of fly ash.

[0109] 2. The formulation of the magnetic water-reducing microcapsules (by weight) is as follows:

[0110] 7 parts hydroxypropyl cellulose;

[0111] γ-Fe2O3 35 parts;

[0112] Rubber powder, 200 mesh, 70 parts;

[0113] 3 parts diallyl phthalate;

[0114] 100 parts of ester-modified polycarboxylate superplasticizer.

[0115] Everything else is the same as in Example 1.

[0116] Example 3:

[0117] A type of precast concrete for shield tunnel lining differs from Example 1 in that:

[0118] 1. Formula (by weight):

[0119] Cement, P.O 42.5, 330 parts;

[0120] The coarse aggregate consists of 660 parts of 6-18mm granite crushed stone (70% by mass) and 5-10mm steel slag (30% by mass).

[0121] Organic aggregate, made from coconut shells, 80 parts;

[0122] Redispersible latex powder, acrylic adhesive powder, 20 parts;

[0123] Sand, selected from manufactured sand with a particle size of less than 4.5 mm, 520 parts;

[0124] 120 portions of magnetic water-reducing microcapsules;

[0125] 75 parts of modified steel fiber were modified with 3-(methacryloyloxy)propyltrimethoxysilane;

[0126] 160 portions of water;

[0127] 85 parts of fly ash.

[0128] 2. The formulation of the magnetic water-reducing microcapsules (by weight) is as follows:

[0129] 7 parts hydroxypropyl cellulose;

[0130] γ-Fe2O3 35 parts;

[0131] Rubber powder, 200 mesh, 70 parts;

[0132] 3 parts diallyl phthalate;

[0133] 100 parts of ester-modified polycarboxylate superplasticizer were modified with polyethylene glycol monomethyl ether acrylate.

[0134] Everything else is the same as in Example 1.

[0135] Comparative Example 1:

[0136] A precast concrete lining for shield tunnels differs from Example 1 in that it does not contain magnetic water-reducing microcapsules, but instead uses an equal weight of water-reducing agent. All other aspects are the same as in Example 1.

[0137] Comparative Example 2:

[0138] A prefabricated assembled concrete for shield tunnel lining differs from Example 1 in that no rubber powder is added to the magnetic water-reducing microcapsules.

[0139] Comparative Example 3:

[0140] A prefabricated concrete lining for shield tunnels differs from Example 1 in that the microcapsules do not contain γ-Fe2O3 and are non-magnetic.

[0141] Comparative Example 4:

[0142] A prefabricated assembled concrete for shield tunnel lining differs from Example 1 in that the water-reducing agent in the magnetic water-reducing microcapsules is non-ester-modified.

[0143] Comparative Example 5:

[0144] A prefabricated assembled concrete for shield tunnel lining differs from Example 1 in that the copper-plated steel fibers are not modified.

[0145] The concrete obtained from each embodiment and comparative example was tested, including slump, compressive strength, and flexural strength.

[0146] The compressive strength and flexural strength were tested according to standard GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The 7-day compressive strength, 28-day compressive strength and tensile strength (unit: MPa) of each specimen were tested. The results are shown in Table 1.

[0147] Slump testing was conducted according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", testing the slump data of concrete at 0 min and 1 h after mixing. The results are shown in Table 2.

[0148] Table 1

[0149]

[0150] As shown in Table 1, the concrete obtained by this invention exhibits good compressive strength and flexural strength. However, the compressive strength and flexural strength of the comparative examples are inferior to those of the embodiments. In Comparative Example 1, the conventional water-reducing agent was used, lacking rubber powder and without modification, resulting in lower flowability and crack resistance of the steel fibers compared to the embodiments. Comparative Example 2 used magnetic water-reducing microcapsules but did not add rubber powder, leading to a decrease in flexural strength, although still better than Comparative Example 1. The microcapsules in Comparative Example 3 were not magnetic, preventing the use of magnetism to adjust their position and distribution, and hindering the synergistic toughness-increasing effect of the rubber powder and water-reducing agent. Comparative Example 4 lacked water-reducing agent modification, failing to form a dual regulation of microcapsule wall and self-hydrolysis controlled release, resulting in a lower release regulation effect of the water-reducing agent compared to the embodiments, thus affecting the compressive and flexural strength of the concrete. Comparative Example 5 lacked modification of the copper-plated steel fibers, reducing flowability and adhesion to the matrix, leading to varying degrees of decrease in compressive and flexural strength.

[0151] Table 2

[0152]

[0153] As shown in Table 2, the slump of the concrete in each embodiment of the present invention did not decrease significantly after 1 hour, indicating that the concrete of the present invention has good fluidity, good ductility during construction, and minimal slump loss. In Comparative Example 1, a conventional water-reducing agent was used, and without the gradient release of the magnetic water-reducing microcapsules, its initial slump was low, and the slump loss after 1 hour was also significant, increasing construction difficulties. In Comparative Example 2, the absence of rubber powder had no significant impact on its fluidity. In Comparative Example 3, because the magnetic water-reducing microcapsules were non-magnetic, the water-reducing agent could not achieve better distribution under magnetic action, resulting in a low initial slump, but the slump loss within 1 hour was not significant. In Comparative Example 4, the unmodified water-reducing agent could not form a synergistic control effect with the microcapsule wall, resulting in a certain degree of slump loss and adversely affecting the fluidity of the concrete. In Comparative Example 5, the copper-plated steel fibers did not undergo surface modification treatment, did not form a lubricating interface, and thus reduced fluidity.

[0154] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A type of precast assembled concrete for shield tunnel lining, characterized in that, Its raw materials include the following components: 320-350 parts cement, 650-700 parts coarse aggregate, 60-80 parts organic aggregate, 10-20 parts redispersible latex powder, 500-550 parts sand, 95-130 parts magnetic water-reducing microcapsules, 60-75 parts steel fiber, 150-165 parts water, and 85-90 parts fly ash; The raw materials of the magnetic water-reducing microcapsules include the following components in parts by weight: 5-7 parts of hydroxypropyl cellulose, 3-5 parts of γ-Fe2O3, 50-70 parts of rubber powder, 2-5 parts of diallyl phthalate, and 80-110 parts of water-reducing agent. The water-reducing agent is an ester-modified polycarboxylic acid water-reducing agent; The preparation process of the magnetic water-reducing microcapsules is as follows: (1) Add the rubber powder to ethanol and disperse it by ultrasonication and stir until uniform; (2) Hydroxypropyl cellulose and γ-Fe2O3 particles were mixed and ultrasonically dispersed to form a magnetic aqueous phase; (3) Mix the water-reducing agent, the well-dispersed rubber powder, and diallyl phthalate and stir to form an oil phase; (4) The oil phase is slowly dripped into the magnetic aqueous phase and homogenized using a high-speed homogenizer to obtain an emulsion system; (5) Heat the emulsion system to 45~60℃, stir at a constant temperature for 3~5 hours, then centrifuge, wash and purify, and dry to obtain the magnetic water-reducing microcapsules.

2. The concrete for prefabricated assembled lining of a shield tunnel according to claim 1, characterized in that, The polycarboxylate superplasticizer was modified using any one of methyl acrylate, hydroxyethyl methacrylate, or polyethylene glycol monomethyl ether acrylate.

3. The precast concrete for shield tunnel lining according to claim 1, characterized in that, The steel fiber is a copper-plated steel fiber modified with an organosilane coupling agent.

4. The precast concrete for shield tunnel lining according to claim 3, characterized in that, The organosilane coupling agent has an amino and / or epoxy group at one end and an alkoxy group at the other end; And / or, the organosilane coupling agent is any one of 3-aminopropyltriethoxysilane and 3-(methacryloyloxy)propyltrimethoxysilane.

5. The precast concrete for shield tunnel lining according to claim 1, characterized in that, The redispersible latex powder is an acrylic powder. And / or, the fineness of the rubber powder is 200~240 mesh.

6. A method for preparing precast assembled concrete for shield tunnel lining according to any one of claims 1 to 5, characterized in that, Includes the following steps: Mix and stir the raw materials until uniform to obtain concrete mix; The concrete mixture is then placed in a pulsed magnetic field for 1 to 3 hours to obtain the prefabricated assembled lining concrete for the shield tunnel.

7. A method for preparing precast assembled concrete for shield tunnel lining according to claim 6, characterized in that, The preparation process of the magnetic water-reducing microcapsules is as follows: (1) Add the rubber powder to ethanol and disperse it by ultrasonication and stir until uniform; (2) Hydroxypropyl cellulose and γ-Fe2O3 particles were mixed and ultrasonically dispersed to form a magnetic aqueous phase; (3) Mix the water-reducing agent, the well-dispersed rubber powder, and diallyl phthalate and stir to form an oil phase; (4) The oil phase is slowly dripped into the magnetic aqueous phase and homogenized using a high-speed homogenizer to obtain an emulsion system; (5) Heat the emulsion system to 45~60℃, stir at a constant temperature for 3~5 hours, then centrifuge, wash and purify, and dry to obtain the magnetic water-reducing microcapsules.

8. A method for preparing precast assembled concrete for shield tunnel lining according to claim 6, characterized in that, The process of modifying the water-reducing agent with ester groups is as follows: (1) Dissolve methyl allyl polyoxyethylene ether in water; (2) Mix ammonium persulfate, mercaptopropionic acid and water and stir to dissolve to obtain the first solution; Acrylic acid and methyl acrylate were mixed and stirred to dissolve, resulting in a second solution. At 60~80℃, the first solution and the second solution are added dropwise at a uniform rate to the aqueous solution of methyl allyl polyoxyethylene ether to induce a copolymerization reaction. After the addition is completed, the solution is kept at the temperature for curing. After the reaction was completed, sodium hydroxide was added to the system to adjust the pH to 6-8, and finally filtered to obtain the ester-modified water-reducing agent.

9. A method for preparing precast assembled concrete for shield tunnel lining according to claim 6, characterized in that, The preparation process of modified copper-plated steel fibers is as follows: (1) Add copper-plated steel fibers to acetone solution, sonicate, and then remove; The copper-plated steel fibers that have undergone ultrasonic treatment are immersed in hydrochloric acid solution and then rinsed until neutral. (2) After hydrolyzing the organosilane coupling agent, add the treated copper-plated steel fiber to it for soaking, and then take out the fiber and drain the excess solution. (3) The modified copper-plated steel fiber is cured at 100~120℃, cooled and then sieved to break it apart, thus obtaining the modified copper-plated steel fiber.

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