Micro-expansion high-flowability UHPC for wet joint of fabricated structure of underground station and preparation method of micro-expansion high-flowability UHPC

Abstract

The invention provides a micro-expansion high-fluidity UHPC (Ultra High Performance Concrete) for a wet joint of an assembled structure of an underground station and a preparation method of the UHPC. The micro-expansion high-fluidity UHPC for the underground station fabricated structure wet joint is prepared from the following components in parts by weight: 620 to 940 parts of cement, 31 to 47 parts of fly ash, 31 to 47 parts of mineral powder, 52 to 238 parts of silica fume, 62 to 94 parts of quartz powder, 616 to 1354 parts of quartz sand, 2.1 to 3.2 parts of water reducing agent, 0.3 to 0.6 part of defoaming agent, 4.1 to 6.2 parts of expanding agent, 0.5 to 2 parts of steel fiber, 0.05 to 0.2 part of MICP microcapsule and 99 to 188 parts of water. According to the micro-expansion high-flow UHPC for the wet joint, concrete shrinkage can be reduced, the uniformity and strength of a mixture can be improved, the structural durability can be enhanced, and the strength and working performance of the concrete can be improved through the preparation process; the added MICP microcapsules can activate microorganisms to carry out biochemical reaction after being broken, so that deposition of calcium carbonate is triggered, microcracks are repaired, the mechanical property of the concrete is improved, and the reaction can reduce water evaporation and reduce shrinkage.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-high performance concrete, and in particular to a micro-expansion high-fluidity UHPC for wet joints of an underground station prefabricated structure and a preparation method thereof. Background Art

[0002] Ultra-high performance concrete (UHPC), as one of the most innovative cement-based materials, exhibits excellent high strength, excellent toughness and outstanding durability, and therefore has broad application prospects in projects such as the connection of prefabricated assembled structures in underground stations.

[0003] In the traditional UHPC preparation method, a low water-binder ratio is usually used, and the slurry contains a large amount of cement, active mineral admixtures and other ingredients, and the coarse aggregate content is relatively low. These factors lead to differences in the shrinkage of UHPC and prefabricated structures during coagulation and hardening and use, which in turn leads to cracks in the concrete, which easily leads to a decrease in the bonding performance of the interface between the two, has a negative impact on the safety of the structure, and the strength is not high.

[0004] On the other hand, the traditional UHPC preparation process still uses the molding process of ordinary concrete, without making targeted adjustments to the mixing machinery, feeding sequence and mixing time. This method often leads to segregation problems in the prepared UHPC, and the steel fibers are not easily evenly distributed, which in turn has an adverse effect on the strength and durability of UHPC. Summary of the invention

[0005] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a micro-expanding high-flow UHPC for wet joints of prefabricated structures of underground stations, which is used to solve the problems of large shrinkage and easy cracking of UHPC in the prior art. At the same time, the present invention will also provide a preparation method of micro-expanding high-flow UHPC for wet joints of prefabricated structures of underground stations.

[0006] In order to achieve the above-mentioned object and other related objects, the present invention provides the following technical solutions: In a first aspect, the present invention provides a micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations, comprising the following components in parts by weight: 620-940 parts of cement, 31-47 parts of fly ash, 31-47 parts of mineral powder, 52-238 parts of silica fume, 62-94 parts of quartz powder, 616-1354 parts of quartz sand, 2.1-3.2 parts of water reducer, 0.3-0.6 parts of defoamer, 4.1-6.2 parts of expansion agent, 0.5-2 parts of steel fiber, 0.05-0.2 parts of microbial induced calcium deposition (MICP) microcapsules, and 99-188 parts of water; The MICP microcapsules encapsulate microorganisms, urea and a calcium source.

[0007] When cracks appear in concrete, the MICP microcapsules break due to mechanical stress, releasing their contents. After the microorganisms recover, they begin to metabolize urea, and produce calcium carbonate at the cracks through biochemical reactions, thus achieving self-healing of the cracks. Therefore, the addition of MICP microcapsules can achieve self-healing of cracks, thereby achieving self-healing of UHPC. This self-healing process not only improves the durability of UHPC, but also reduces maintenance costs. It is a green and sustainable repair technology.

[0008] Furthermore, the microorganism comprises Spore sac of pasteurii , Bacillus subtilis , Spherical Bacillus These microorganisms can be induced to enter a dormant state (forming spores) during the culture stage, which makes them in an inhibited state during the preparation and storage of microcapsules, avoiding premature precipitation of calcium carbonate. They are activated only when the microcapsules are broken and start biochemical reactions.

[0009] Furthermore, the calcium source includes calcium chloride or calcium nitrate.

[0010] Furthermore, the MICP microcapsules are prepared by the following method: (1) mixing spore-forming microorganisms with urea and a calcium source to obtain a microbial spore mixture; (2) dispersing the microbial spore mixture in the shell material solution using an emulsification technique; (3) Solidify the shell material to form stable MICP microcapsules.

[0011] Wherein, the shell material includes polylactic acid (PLA), polyacrylamide (PAM) or polyvinyl alcohol (PVA).

[0012] In step (3), the shell material is cured by thermal curing or cross-linking agent curing.

[0013] Furthermore, the particle size of the MICP microcapsule is preferably 50-500 μm.

[0014] Furthermore, the quartz sand includes 185-406 parts of 40-70 mesh quartz sand and 431-948 parts of 70-100 mesh quartz sand.

[0015] Furthermore, the water reducer includes at least one of a polycarboxylic acid water reducer, a sulfate water reducer, and a polyether water reducer. The water reducer selected in the present invention has a high water reduction rate, and can reduce the thickness of the water film that wraps the particles in UHPC, reduce the amount of water, improve the density of the slurry, and increase the strength. Among them, the polyether water reducer reduces the surface tension of water in the microstructure, reduces the shrinkage force in the water evaporation process, and thus reduces the shrinkage of concrete, so as to achieve the goal of enhancing the interface performance of the prefabricated structure and the wet joint material.

[0016] In addition, the invention adds a certain amount of defoaming agent to reduce the porosity, improve the density of concrete, and thus reduce shrinkage.

[0017] Furthermore, the expansion agent includes a sulphoaluminate expansion agent or a styrene-butadiene emulsion HP-CSA expansion agent. The expansion agent selected by the present invention can cause the concrete to expand slightly in the early stage, and the expansion energy generated can be converted into compressive stress to offset the shrinkage tensile stress of the concrete during hardening, thereby reducing cracks.

[0018] Furthermore, the steel fiber is made of steel fiber raw material and subjected to polymer surface coating treatment; Wherein, the polymer includes polyethylene, polypropylene or polyvinyl alcohol.

[0019] The present invention can enhance the interfacial bonding between the steel fiber and the concrete by coating a layer of polymer on the surface of the steel fiber to prevent precipitation during the concrete curing process. The polymer coating should have sufficient elasticity and toughness to adapt to the contraction and expansion of the concrete; at the same time, the corrosion resistance of the steel fiber can be improved after coating.

[0020] Furthermore, the steel fiber raw material includes copper-plated steel fibers, which are in an irregular shape, preferably in a corrugated or spiral shape. Compared with long straight steel fibers, corrugated or spiral steel fibers have better load-bearing capacity and deformation performance, and have higher toughness, which can prevent or delay the formation and expansion of cracks at the microscopic level, and resist crack generation by dispersing stress and increasing the ability of concrete; the presence of steel fibers can also change the stress distribution inside the concrete, help reduce the stress concentration phenomenon under concentrated loads, and thus improve the overall durability and mechanical properties of the structure.

[0021] Furthermore, the length of the steel fiber is 10-15 mm, preferably 13 mm.

[0022] The second aspect of the present invention provides a method for preparing a micro-expanded high-flow UHPC for wet joints of an underground station prefabricated structure, comprising the following steps: S1. Weigh water, water reducing agent, defoaming agent and swelling agent in proportion, pour into a blender and stir at low speed for 1-2 minutes; S2. Then, cement is added to the mixer in proportion and stirred rapidly for 1-2 minutes to obtain cement paste. Then, the stirring mode is changed to low-speed stirring, and fly ash, mineral powder, silica fume and quartz powder are added in proportion and stirred rapidly for 2-3 minutes after addition. S3. Slowly add the mixed quartz sand into the mixer, stir at a low speed for 1-2 minutes, and then stir at a high speed for 3-5 minutes; S4. In the fast stirring mode, slowly add the steel fiber. After the steel fiber is completely added, continue to stir rapidly for 2-3 minutes; S5. The stirring mode is changed to slow stirring, and the MICP microcapsules are slowly added and stirred at a low speed for 1-2 minutes to obtain the micro-expanded high-flow UHPC for wet joints of the prefabricated structure of the underground station.

[0023] The entire preparation process takes about 10-15 minutes. After mixing, pouring can be carried out directly. This ratio can achieve a compressive strength of more than 190MPa after 28 days of curing at room temperature. It also has excellent working performance and a fluidity of up to 280-300mm. No vibration is required when pouring at wet joints, and self-leveling can be achieved, ensuring the flexible application of UHPC materials in prefabricated structural engineering of underground stations.

[0024] A third aspect of the present invention provides an application of a micro-expanded high-fluidity UHPC for wet joints of an underground station prefabricated structure, wherein the micro-expanded high-fluidity UHPC for wet joints of an underground station prefabricated structure is used for wet joints of an underground station prefabricated structure.

[0025] As described above, the micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations and the preparation method thereof of the present invention have the following beneficial effects: 1. The present invention improves the comprehensive performance of UHPC by adding homemade MICP microcapsules and polymer-modified steel fibers. The MICP microcapsules activate microorganisms to perform biochemical reactions after rupture, thereby inducing the deposition of calcium carbonate and repairing microcracks, which helps to improve the mechanical properties of concrete. The reaction can also reduce water evaporation and shrinkage. The polymer-modified steel fibers have a stronger bonding force with concrete, are not easy to pull out, and can change the stress distribution inside the concrete to overcome shrinkage stress.

[0026] 2. The micro-expansion high-flow UHPC for wet joints produced by the present invention can reduce concrete shrinkage, improve the uniformity and strength of the mixture, and enhance the durability of the structure. The strength and working performance of concrete can be improved through the preparation process of the present invention. At the same time, the inert cementitious materials such as silica ash and mineral powder used in the present invention replace the cementitious materials in traditional UHPC, and quartz sand and quartz powder with a certain grade are used to replace the original coarse aggregate to reduce the internal porosity, thereby achieving excellent working performance, mechanical properties and durability of the material. The present invention adds an appropriate amount of water reducer, defoamer and expansion agent to increase the flow properties of UHPC materials, reduce shrinkage, and does not affect the development of later strength. DETAILED DESCRIPTION

[0027] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0028] Example 1 Preparation of steel fiber coated with polyvinyl alcohol: 1. Clean the corrugated copper-plated steel fiber and preheat it to 120°C after cleaning; 2. Dissolve polyvinyl alcohol (PVA) in warm water according to the proportion to prepare a 5% (w / v) PVA solution; 3. Add 0.1% glutaraldehyde to the PVA solution, stir evenly, and then immerse the preheated corrugated copper-plated steel fiber in the mixed solution for 10 minutes; 4. Place the coated steel fiber in a dryer and dry at 80°C.

[0029] Example 2 Preparation of MICP microcapsules: (1) dissolving 2% (w / v) urea and 2% (w / v) calcium chloride in water, suspending spore-forming microorganisms in sterile physiological saline, then adding the suspension to the aqueous solution of urea and calcium chloride, and mixing well to obtain a microbial spore mixture; (2) dissolving PLA in dichloromethane to prepare a 5% (w / v) shell material solution, slowly adding the above-mentioned microbial spore mixture to the shell material solution, and simultaneously emulsifying using a high-speed stirrer; (3) Use a syringe pump to slowly squeeze out the emulsion, allowing the solvent to evaporate and solidify to form stable MICP microcapsules.

[0030] Example 3 A micro-expanding high-fluidity UHPC for wet joints of prefabricated structures of underground stations comprises the following components in parts by weight: 882 parts of cement (PO 52.5R), 40 parts of fly ash, 35 parts of mineral powder, 140 parts of silica fume, 81 parts of quartz powder, 335 parts of quartz sand with a mesh size of 40-70, 564 parts of quartz sand with a mesh size of 70-100, 3 parts of a polycarboxylic acid water reducer, 0.4 parts of a defoaming agent, 5 parts of a styrene-butadiene emulsion HP-CSA type expansion agent, 1.5 parts of steel fibers prepared in Example 1, 0.05 parts of MICP microcapsules prepared in Example 2, and 150 parts of water.

[0031] The above-mentioned micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations is obtained by the following preparation method: S1. Weigh water, polycarboxylic acid water reducer, defoamer and styrene-butadiene emulsion HP-CSA type expansion agent according to the above proportions, pour into a blender and stir at low speed for 1 minute to ensure that the water reducer, defoamer and expansion agent are evenly dissolved in the water; S2, then add cement to the mixer in proportion, stir rapidly for 2 minutes to obtain cement paste; then change the stirring mode to low-speed stirring, add fly ash, mineral powder, silica fume and quartz powder in the above proportions, and stir rapidly for 3 minutes after adding; S3, quartz sand of 40-70 mesh and quartz sand of 70-100 mesh are mixed evenly, and the mixed quartz sand is slowly added into the mixer, and stirred at low speed for 1 minute, and then stirred at high speed for 4 minutes; S4. In the rapid stirring mode, slowly add the steel fiber prepared in Example 1. After the steel fiber is completely added, continue to stir rapidly for 3 minutes; S5. The stirring mode is changed to slow stirring, and the MICP microcapsules prepared in Example 2 are slowly added, and stirred at a low speed for 1 minute to obtain the micro-expanded high-flow UHPC for wet joints of the prefabricated structure of the underground station.

[0032] Example 4 A micro-expanding high-fluidity UHPC for wet joints of prefabricated structures of underground stations comprises the following components in parts by weight: 882 parts of cement (PO 52.5R), 40 parts of fly ash, 35 parts of mineral powder, 140 parts of silica fume, 81 parts of quartz powder, 335 parts of 40-70 mesh quartz sand, 564 parts of 70-100 mesh quartz sand, 3 parts of polycarboxylic acid water reducer, 0.4 parts of defoamer, 5 parts of styrene-butadiene emulsion HP-CSA type expansion agent, 1.5 parts of steel fiber prepared in Example 1, 0.1 parts of MICP microcapsules prepared in Example 2, and 150 parts of water.

[0033] The above-mentioned micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations is obtained by the following preparation method: S1. Weigh water, polycarboxylic acid water reducer, defoamer and styrene-butadiene emulsion HP-CSA type expansion agent according to the above proportions, pour into a blender and stir at low speed for 1 minute to ensure that the water reducer, defoamer and expansion agent are evenly dissolved in the water; S2, then add cement to the mixer in proportion, stir rapidly for 2 minutes to obtain cement paste; then change the stirring mode to low-speed stirring, add fly ash, mineral powder, silica fume and quartz powder in the above proportions, and stir rapidly for 3 minutes after adding; S3, quartz sand of 40-70 mesh and quartz sand of 70-100 mesh are mixed evenly, and the mixed quartz sand is slowly added into the mixer, and stirred at low speed for 1 minute, and then stirred at high speed for 4 minutes; S4. In the rapid stirring mode, slowly add the steel fiber prepared in Example 1. After the steel fiber is completely added, continue to stir rapidly for 3 minutes; S5. The stirring mode is changed to slow stirring, and the MICP microcapsules prepared in Example 2 are slowly added, and stirred at a low speed for 1 minute to obtain the micro-expanded high-flow UHPC for wet joints of the prefabricated structure of the underground station.

[0034] Example 5 A micro-expanding high-fluidity UHPC for wet joints of prefabricated structures of underground stations comprises the following components in parts by weight: 882 parts of cement (PO 52.5R), 40 parts of fly ash, 35 parts of mineral powder, 140 parts of silica fume, 81 parts of quartz powder, 335 parts of quartz sand with a mesh size of 40-70, 564 parts of quartz sand with a mesh size of 70-100, 3 parts of a polycarboxylic acid water reducer, 0.4 parts of a defoaming agent, 5 parts of a styrene-butadiene emulsion HP-CSA type expansion agent, 1.5 parts of steel fibers prepared in Example 1, 0.2 parts of MICP microcapsules prepared in Example 2, and 150 parts of water.

[0035] The above-mentioned micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations is obtained by the following preparation method: S1. Weigh water, polycarboxylic acid water reducer, defoamer and styrene-butadiene emulsion HP-CSA type expansion agent according to the above proportions, pour into a blender and stir at low speed for 1 minute to ensure that the water reducer, defoamer and expansion agent are evenly dissolved in the water; S2, then add cement to the mixer in proportion, stir rapidly for 2 minutes to obtain cement paste; then change the stirring mode to low-speed stirring, add fly ash, mineral powder, silica fume and quartz powder in the above proportions, and stir rapidly for 3 minutes after adding; S3, quartz sand of 40-70 mesh and quartz sand of 70-100 mesh are mixed evenly, and the mixed quartz sand is slowly added into the mixer, and stirred at low speed for 1 minute, and then stirred at high speed for 4 minutes; S4. In the rapid stirring mode, slowly add the steel fiber prepared in Example 1. After the steel fiber is completely added, continue to stir rapidly for 3 minutes; S5. The stirring mode is changed to slow stirring, and the MICP microcapsules prepared in Example 2 are slowly added, and stirred at a low speed for 1 minute to obtain the micro-expanded high-flow UHPC for wet joints of the prefabricated structure of the underground station.

[0036] Comparative Example 1 An ultra-high performance concrete comprises the following components in parts by weight: 882 parts of cement (PO 52.5R), 40 parts of fly ash, 35 parts of mineral powder, 140 parts of silica fume, 81 parts of quartz powder, 335 parts of quartz sand with a mesh size of 40-70, 564 parts of quartz sand with a mesh size of 70-100, 3 parts of a polycarboxylic acid water reducer, 0.4 parts of a defoamer, 5 parts of a styrene-butadiene emulsion HP-CSA type expansion agent, 1.5 parts of steel fibers prepared in Example 1, and 150 parts of water.

[0037] The above-mentioned ultra-high performance concrete is obtained by the following preparation method: S1. Weigh water, polycarboxylic acid water reducer, defoamer and styrene-butadiene emulsion HP-CSA type expansion agent according to the above proportions, pour into a blender and stir at low speed for 1 minute to ensure that the water reducer, defoamer and expansion agent are evenly dissolved in the water; S2, then add cement to the mixer in proportion, stir rapidly for 2 minutes to obtain cement paste; then change the stirring mode to low-speed stirring, add fly ash, mineral powder, silica fume and quartz powder in the above proportions, and stir rapidly for 3 minutes after adding; S3, quartz sand of 40-70 mesh and quartz sand of 70-100 mesh are mixed evenly, and the mixed quartz sand is slowly added into the mixer, and stirred at low speed for 1 minute, and then stirred at high speed for 4 minutes; S4. In the rapid stirring mode, slowly add the steel fiber prepared in Example 1. After the steel fiber is completely added, continue rapid stirring for 3 minutes to obtain the ultra-high performance concrete.

[0038] Comparative Example 2 An ultra-high performance concrete comprises the following components in parts by weight: 882 parts of cement (PO 52.5R), 40 parts of fly ash, 35 parts of mineral powder, 140 parts of silica fume, 81 parts of quartz powder, 335 parts of 40-70 mesh quartz sand, 564 parts of 70-100 mesh quartz sand, 3 parts of polycarboxylic acid water reducer, 0.4 parts of defoamer, 5 parts of styrene-butadiene emulsion HP-CSA type expansion agent, 1.5 parts of conventional corrugated copper-plated steel fiber, and 150 parts of water.

[0039] The above-mentioned ultra-high performance concrete is obtained by the following preparation method: S1. Weigh water, polycarboxylic acid water reducer, defoamer and styrene-butadiene emulsion HP-CSA type expansion agent according to the above proportions, pour into a blender and stir at low speed for 1 minute to ensure that the water reducer, defoamer and expansion agent are evenly dissolved in the water; S2, then add cement to the mixer in proportion, stir rapidly for 2 minutes to obtain cement paste; then change the stirring mode to low-speed stirring, add fly ash, mineral powder, silica fume and quartz powder in the above proportions, and stir rapidly for 3 minutes after adding; S3, quartz sand of 40-70 mesh and quartz sand of 70-100 mesh are mixed evenly, and the mixed quartz sand is slowly added into the mixer, and stirred at low speed for 1 minute, and then stirred at high speed for 4 minutes; S4. In the rapid stirring mode, slowly add the steel fiber, and after the steel fiber is completely added, continue to stir rapidly for 3 minutes to obtain the ultra-high performance concrete.

[0040] Performance Testing The ultra-high performance concrete prepared in Examples 3-5 and Comparative Examples 1-2 was tested under the following conditions: Compressive strength, flexural strength: GB / T17671-1999; Ultimate tensile strength: T / CBMF37-2018; Drying shrinkage value: GB / T11972-1997.

[0041] Table 1. Test results of ultra-high performance concrete of Examples 3-5 and Comparative Examples 1-2

[0042] Compared with conventional concrete, the present invention adds self-made MICP microcapsules and polymer-modified steel fibers. After the MICP microcapsules are broken, they will activate microorganisms to carry out biochemical reactions, thereby inducing the deposition of calcium carbonate and repairing microcracks, which is helpful to improve the mechanical properties of concrete. The reaction can also reduce water evaporation and shrinkage. The polymer-modified steel fibers have a stronger bonding force with concrete and are not easy to be pulled out. They can also change the stress distribution inside the concrete and overcome shrinkage stress.

[0043] Through the comprehensive comparison of the test results, it can be seen that the compressive, flexural and tensile strengths of the micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations prepared by the present invention are significantly improved, and the shrinkage after drying is small, it is not easy to produce interface differences, and the durability is better. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0044] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations, characterized in that: The invention comprises the following components in parts by weight: 620-940 parts of cement, 31-47 parts of fly ash, 31-47 parts of mineral powder, 52-238 parts of silica ash, 62-94 parts of quartz powder, 616-1354 parts of quartz sand, 2.1-3.2 parts of water reducing agent, 0.3-0.6 parts of defoaming agent, 4.1-6.2 parts of expansion agent, 0.5-2 parts of steel fiber and 99-188 parts of water.

2. The micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 1 is characterized in that: The micro-expanded high-fluidity UHPC for wet joints of prefabricated structures of underground stations further comprises 0.05-0.2 parts of MICP microcapsules, wherein the MICP microcapsules encapsulate microorganisms, urea and a calcium source.

3. The micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 2 is characterized in that: The microorganisms include Sporosarcina pasteurii , Bacillus subtilis , Bacillus sphaericus At least one of .

4. The micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 3 is characterized in that: The MICP microcapsules are prepared by the following method: (1) mixing spore-forming microorganisms with urea and a calcium source to obtain a microbial spore mixture; (2) dispersing the microbial spore mixture in the shell material solution using an emulsification technique; (3) Solidify the shell material to form stable MICP microcapsules.

5. The micro-expanded high-fluidity UHPC for wet joints of prefabricated structures of underground stations according to claim 4 is characterized in that: The shell material includes polylactic acid, polyacrylamide or polyvinyl alcohol.

6. The micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 1 is characterized in that: The steel fiber is made of steel fiber raw material and subjected to surface coating treatment with a polymer; the polymer includes polyethylene, polypropylene or polyvinyl alcohol.

7. The micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 1 is characterized in that: The quartz sand includes 185-406 parts of 40-70 mesh quartz sand and 431-948 parts of 70-100 mesh quartz sand.

8. The micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 1 is characterized in that: The water reducer includes at least one of a polycarboxylic acid water reducer, a sulfate water reducer, and a polyether water reducer.

9. The micro-expansion high-flow UHPC for wet joints of prefabricated structures of underground stations according to claim 1, characterized in that: The expansion agent includes a sulphoaluminate expansion agent or a styrene-butadiene emulsion HP-CSA expansion agent.

10. A method for preparing the micro-expanded high-flow UHPC for wet joints of prefabricated structures of underground stations as described in any one of claims 1 to 9, characterized in that: The steps include: S1. Weigh water, water reducing agent, defoaming agent and swelling agent in proportion, pour into a blender and stir at low speed for 1-2 minutes; S2. Then, cement is added to the mixer in proportion and stirred rapidly for 1-2 minutes to obtain cement paste. Then, the stirring mode is changed to low-speed stirring, and fly ash, mineral powder, silica fume and quartz powder are added in proportion and stirred rapidly for 2-3 minutes after addition. S3. Slowly add the mixed quartz sand into the mixer, stir at a low speed for 1-2 minutes, and then stir at a high speed for 3-5 minutes; S4. In the fast stirring mode, slowly add the steel fiber. After the steel fiber is completely added, continue to stir rapidly for 2-3 minutes; S5. The stirring mode is changed to slow stirring, and the MICP microcapsules are slowly added and stirred at a low speed for 1-2 minutes to obtain the micro-expanded high-flow UHPC for wet joints of the prefabricated structure of the underground station.

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