A high performance self-compacting concrete composition and a method for preparing the same

Abstract

The present application relates to a kind of high-performance self-compacting concrete composition and its preparation method, belong to the technical field of civil engineering materials.The concrete composition includes cementitious material, steel fiber 28-32 parts, medium sand 851-880 parts, gravel 818-845 parts, mixing water, the water-binder ratio of its dosage with cementitious material is 0.35-0.38;And polycarboxylate composite water reducing agent, the amount of admixture is 1.3-1.5% of the total mass of cementitious material.Gelatinous material includes cement 396-441 parts, composite anti-cracking agent 29-32 parts and microsilica 57-65 parts;Composite anti-cracking agent is composed of nano-SiO2, powdered shrinkage-reducing admixture and temperature-sensitive expansion microcapsule, wherein the shell material of temperature-sensitive expansion microcapsule is polymethyl methacrylate, and the core material is lauric acid.The present application significantly reduces material cost and construction difficulty while ensuring high fluidity, high crack resistance and high bonding strength, and high-quality pouring can be realized without special equipment.

Description

Technical Field

[0001] This invention belongs to the technical field of civil engineering materials, and more specifically, relates to a high-performance self-compacting concrete composition and its preparation method. Background Technology

[0002] In recent years, the number of highway reconstruction and expansion projects in mountainous areas has been increasing. Tunnels that have been in operation for 20 to 30 years are experiencing varying degrees of problems such as lining cracking, spalling, water leakage, lining strength issues, and insufficient lining thickness in some areas, requiring structural reinforcement. The common reinforcement methods for old tunnels at present are mainly as follows: Steel plate and strip reinforcement: Steel plate and strip reinforcement is generally suitable for rapid reinforcement during operation, but its durability and aesthetics are relatively poor.

[0003] Steel arch reinforcement: The construction process of steel arch reinforcement is relatively simple and quick, but the appearance and durability are poor, and the requirements for building clearance space are high.

[0004] Replacing the secondary lining: Replacing the secondary lining has a long construction period, high construction risks, and high costs. At the same time, it is very easy to damage the existing waterproofing system and it is difficult to restore it effectively, resulting in poor waterproofing effect and other problems.

[0005] Arch reinforcement: Using thin, high-strength arches as a permanent reinforcement method offers good reinforcement effect, aesthetics, and durability. However, while ordinary high-strength concrete is cheaper, its workability is generally poor, with limited fluidity and permeability, making it difficult to balance mechanical and workability requirements. In densely reinforced, thin arches, vibration is difficult, easily leading to voids and honeycombing; furthermore, its crack resistance and impermeability are poor. Ultra-high performance concrete (UHPC) offers good strength and workability, but the raw materials are expensive, and the mix design and production process are demanding. Construction requirements are stringent, demanding high levels of technical expertise and experience from construction personnel, pre-mixing equipment, and other skilled workers. Its application in structures is difficult to popularize, its economic efficiency is low, and it is not suitable for large-scale promotion. Summary of the Invention

[0006] This invention addresses the problems of lining structure cracks, insufficient strength or thickness, and water leakage in old tunnels by providing a high-performance self-compacting concrete composition and its preparation method. The composition features no need for vibration, stable performance, and excellent strength and impermeability.

[0007] The objective of this invention can be achieved through the following technical solutions: A high-performance self-compacting concrete composition comprising the following components in parts by weight: The cementitious material comprises 396-441 parts of cement, 29-32 parts of composite crack-resistant agent, and 57-65 parts of silica fume. The composite crack-resistant agent is composed of nano-SiO2, powdered shrinkage reducer and thermosensitive expansion microcapsules in a mass ratio of (10-15):(8-12):(6-10), wherein the shell material of the thermosensitive expansion microcapsules is polymethyl methacrylate and the core material is lauric acid. 28-32 parts steel fiber; 851-880 portions of medium sand; Crushed stone 818-845 parts, particle size 5-20mm continuous gradation; The mixing water, with a water-cement ratio of 0.35-0.38 to the cementitious material, is used in a mixing process. Polycarboxylate-based composite water-reducing agent, the dosage is 1.3-1.5% of the total mass of cementitious materials.

[0008] As a preferred embodiment of the present invention, the temperature-sensitive expansion microcapsules have an average particle size of 10-50 μm and an expansion initiation temperature of 40-50 °C.

[0009] As a preferred embodiment of the present invention, the microsilica powder is SF90 grade microsilica powder.

[0010] As a preferred embodiment of the present invention, the steel fiber is a hook-shaped steel fiber with a length of 12-14 mm, a diameter of 0.21-0.23 mm, and an aspect ratio of 58-62.

[0011] The end-hook type steel fiber has a tensile strength ≥1000MPa, which increases the toughness of concrete.

[0012] As a preferred embodiment of the present invention, the fineness modulus of the medium sand is 2.6-2.9, and the methylene blue value MB ≤ 1.0.

[0013] As a preferred embodiment of the present invention, the cumulative residue of the crushed stone after passing through a 5mm sieve is 0%-10%, after passing through a 10mm sieve is 30%-60%, and after passing through a 16mm sieve is 70%-90%. More preferably, the crushed stone is impact crushed stone.

[0014] As a preferred embodiment of the present invention, in the composite crack-resistant agent, the nano-SiO2 is fumed nano-silica with a specific surface area ≥200m². 2 / g.

[0015] As a preferred embodiment of the present invention, the core-shell mass ratio of the temperature-sensitive expansion microcapsule is (1.5-2.5):1.

[0016] As a preferred embodiment of the present invention, the temperature-sensitive expansion microcapsules are prepared by in-situ polymerization. The preparation method includes the following steps: in a water bath at 45-55°C, preheated and melted lauric acid, methyl methacrylate monomer and initiator are mixed to obtain an oil phase; an emulsifier is dispersed in deionized water to form an aqueous phase; while stirring, the oil phase is continuously dripped into the aqueous phase. After the dripping is completed, the temperature is raised to 65-75°C for polymerization for 3-5 hours, followed by centrifugation, washing and drying to obtain temperature-sensitive expansion microcapsules.

[0017] Further, the initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and potassium persulfate, and the amount used is 1.0%-3.0% of the mass of methyl methacrylate monomer; the emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, Tween 80, Span 80, and betaine, and the amount used is 0.2%-1.0% of the mass of aqueous phase.

[0018] In this process, methyl methacrylate monomers are polymerized to form polymethyl methacrylate. During the reaction, due to interfacial tension, the polymethyl methacrylate spontaneously migrates to the outer layer of the oil droplets. Lauric acid has limited compatibility with polymethyl methacrylate, thus forming a temperature-sensitive expandable microcapsule with lauric acid as the core material and polymethyl methacrylate as the shell material.

[0019] Furthermore, the oil phase accounts for 10-12% of the total mass of the reaction system; the washing and drying refers to washing with deionized water 2-4 times, followed by vacuum drying at 55-65℃ to constant weight.

[0020] Furthermore, the composite crack-resistant agent is composed of nano-SiO2, powdered shrinkage reducer and thermosensitive expansion microcapsules in a mass ratio of (12-14):(9-11):(7-9).

[0021] Furthermore, the composite crack-resistant agent is prepared by mixing nano-SiO2, powdered shrinkage reducer and temperature-sensitive expansion microcapsules according to the mass ratio to obtain the composite crack-resistant agent.

[0022] Furthermore, the mixing speed is 25-35 r / min, and the time is 15-25 minutes.

[0023] Furthermore, both the polycarboxylate composite water-reducing agent and the powdered shrinkage-reducing agent in this technical solution are commercially available. The polycarboxylate composite water-reducing agent has a water reduction rate of ≥30% and contains a slump-retaining component to maintain workability stability for 30 minutes (slump loss rate <10%), and its form is powder. The main component of the powdered shrinkage-reducing agent is an alkyl polyoxyethylene ether polyether compound.

[0024] A method for preparing the high-performance self-compacting concrete composition as described above includes the following steps: S1. Add cement, silica fume and composite crack-resistant agent into the mixer and dry mix for 1-3 minutes; S2. Add medium sand and gravel, and continue to dry mix for 1-3 minutes; S3. Add steel fibers in 2-4 batches, stirring for 0.5-1 minute for each batch to obtain a dry mixture; S4. Mix the polycarboxylate composite water-reducing agent and mixing water to make an aqueous solution, then add it to the dry-mixed material and wet-mix for 3-8 minutes to obtain a high-performance self-compacting concrete composition.

[0025] Furthermore, in step S1, the dry mixing speed is 25-35 r / min; in step S2, the dry mixing speed is 30-40 r / min; and in step S3, the stirring speed is 30-40 r / min.

[0026] Specifically, in step S3, steel fibers are added during the dry mixing stage, and spatial dispersion is achieved by utilizing the shearing-collision effect of aggregate particles on fibers; low-speed mixing of 30-40 r / min can prevent fibers from entangled in the mixing shaft, and at the same time prevent fiber orientation caused by high speed.

[0027] Furthermore, in step S4, the wet mixing speed is 40-50 r / min; after the high-performance self-compacting concrete composition is discharged, it is continuously stirred at a speed of 8-12 r / min, and 5-8 minutes before pouring, the speed is adjusted to 45-55 r / min for stirring.

[0028] Furthermore, in step S4, the discharge temperature of the obtained high-performance self-compacting concrete composition is 15-25℃.

[0029] A thin-layer reinforced arch reinforcement structure for old tunnels, wherein the arch is cast from the above-mentioned high-performance self-compacting concrete composition, the arch thickness is 15-25cm, and the spacing of the steel mesh is 80-100mm.

[0030] Among them, the densely reinforced thin layer of the thin-layer arch reinforcement refers to the layer applied to the inner surface of the original tunnel lining, that is, the side facing the tunnel passage space. The arch reinforcement refers to the reinforcement of the tunnel arch (the top arc section).

[0031] The beneficial effects of this invention are: (1) This invention incorporates a composite crack-resistant agent composed of nano-SiO2, powdered shrinkage-reducing agent, and thermosensitive expansion microcapsules. Nano-SiO2 fills the micropores to improve density, powdered shrinkage-reducing agent reduces shrinkage stress, and thermosensitive microcapsules expand directionally during the hydration exothermic stage to compensate for shrinkage. These three components, together with end-hook steel fibers, construct a triple crack-resistant mechanism of "chemical shrinkage reduction + physical compensation + microstructure reinforcement," significantly improving the crack resistance and toughness of concrete and effectively inhibiting early cracking of thin-layer structures. This invention uses 5-20mm continuously graded crushed stone and finely optimized medium sand, combined with a reasonable sand ratio design, to significantly improve the fluidity and gap passage of concrete, ensuring that the formwork can be completely filled without vibration under densely reinforced thin-layer conditions, avoiding defects such as voids and honeycombs. In addition, the pozzolanic effect and filling effect of microsilica further improve the density and impermeability of concrete, and synergistically enhance the bonding strength between the new and old concrete interfaces with the composite crack-resistant system, effectively preventing peeling between the arch and the original lining, and ensuring the overall working performance of the reinforced structure.

[0032] (2) This invention adds steel fibers in batches during the dry mixing stage and controls the mixing speed to achieve uniform fiber dispersion by utilizing the shear-collision effect of aggregate particles, effectively solving the problem of steel fiber clumping. Combined with a low-speed stabilization strategy after discharge and a high-speed remixing strategy before pouring, it maintains stable workability and adapts to the construction rhythm on-site in tunnels. The concrete of this invention, while ensuring high fluidity, high crack resistance, and high bond strength, significantly reduces material costs and construction difficulty. High-quality pouring can be achieved without special equipment, providing a high-performance, easy-to-construct, vibration-free, and economically feasible green solution for the reinforcement of densely reinforced thin-layer arched tunnels. It possesses both technological advancement and industrialization potential. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to specific embodiments, but the scope of protection of this invention is not limited thereto. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or according to the manufacturer's recommendations. Unless otherwise specified, all reagents and materials used are commercially available.

[0034] Based on the Shantou-Meizhou Expressway reconstruction and expansion project of Guangdong Provincial Road and Bridge Construction Development Co., Ltd., this invention effectively treats structural defects in old tunnels, such as cracks in the lining structure, insufficient strength or thickness, and water leakage, to ensure that the old tunnel structure achieves safety, durability, and aesthetics.

[0035] Raw material description: The polycarboxylate composite water-reducing agent and powdered shrinkage-reducing agent used in this example and comparative example were purchased from Jiangsu Subote New Material Co., Ltd.

[0036] Example 1 A high-performance self-compacting concrete composition comprising the following components in parts by weight: The mixture contains 508 parts of cementitious materials (including 417 parts of P.O42.5 cement, 30 parts of composite crack-resistant agent and 61 parts of microsilica), 30 parts of end-hook steel fiber, 866 parts of medium sand, 833 parts of crushed stone (continuous gradation with a particle size of 5-20mm), 183 parts of mixing water (water-cement ratio of 0.36), and 7.112 parts of polycarboxylate-based composite water-reducing agent (admixture amount is 1.4% of the total mass of cementitious materials).

[0037] The composite crack-resistant agent includes 12 parts of nano-SiO2, 10 parts of powdered shrinkage reducer, and 8 parts of temperature-sensitive expansion microcapsules (the mass ratio of nano-SiO2, powdered shrinkage reducer, and temperature-sensitive expansion microcapsules is 12:10:8).

[0038] The shell material of the temperature-sensitive expansion microcapsule is polymethyl methacrylate, and the core material is lauric acid. The preparation method is as follows: In a 50°C water bath, 60 parts of lauric acid (melting point 44°C, preheated to 50°C to melt), 40 parts of methyl methacrylate monomer, and 0.8 parts of azobisisobutyronitrile (agent, amounting to 2% of the mass of methyl methacrylate monomer) were mixed and magnetically stirred for 10 min until completely dissolved to obtain the oil phase. 2.5 parts of sodium dodecyl sulfate (emulsifier) ​​were dispersed in 800 parts of deionized water and stirred at 300 rpm for 15 min to obtain the aqueous phase. Under high-speed shear emulsification at 8000 rpm, the oil phase was uniformly added dropwise to the aqueous phase over 10 min. After the addition was complete, the temperature was raised to 70°C, and the reaction was carried out for 4 hours under nitrogen protection. Subsequently, the reaction solution was centrifuged at 3000 rpm for 10 min, and the precipitate was washed three times with deionized water (500 mL each time) and then dried in a vacuum drying oven at 55°C to constant weight to obtain temperature-sensitive expandable microcapsules.

[0039] Testing revealed that the thermosensitive expansion microcapsules had an average particle size of 32 μm, a core-to-shell mass ratio of 1.55:1, an expansion initiation temperature of 44℃, and an expansion enthalpy change of 102 J / g (DSC, 10℃ / min).

[0040] The preparation method of the composite crack-resistant agent is as follows: nano-SiO2, powdered shrinkage reducer and temperature-sensitive expansion microcapsules are put into a double cone rotary mixer and mixed at a speed of 30 r / min for 20 ± 2 minutes to obtain the composite crack-resistant agent.

[0041] The preparation method of the above-mentioned high-performance self-compacting concrete composition is as follows: S1. Add cement, silica fume and composite crack-resistant agent into the mixer and dry mix for 1-3 minutes at 30r / min. S2. Add medium sand and crushed stone, and dry mix at 35 r / min for 1-3 minutes; S3. Add steel fibers in 3 batches, stirring for 0.5-1 minute for each batch to obtain a dry mixture; S4. Mix the polycarboxylate composite water-reducing agent and mixing water to make an aqueous solution, then add it to the dry-mixed mixture and wet-mix at 45r / min for 4-5 minutes to obtain a high-performance self-compacting concrete composition.

[0042] Example 2 A high-performance self-compacting concrete composition comprising the following components in parts by weight: The mixture contains 482 parts of cementitious materials (including 396 parts of P.O42.5 cement, 29 parts of composite crack-resistant agent and 57 parts of microsilica), 28 parts of end-hook steel fiber, 851 parts of medium sand, 818 parts of crushed stone (continuous gradation with a particle size of 5-20mm), 169 parts of mixing water (water-cement ratio of 0.35), and 6.266 parts of polycarboxylate-based composite water-reducing agent (admixture amount is 1.3% of the total mass of cementitious materials).

[0043] The preparation method of the above-mentioned high-performance self-compacting concrete composition is the same as that in Example 1.

[0044] Example 3 A high-performance self-compacting concrete composition comprising the following components in parts by weight: The mixture contains 538 parts of cementitious materials (including 441 parts of P.O42.5 cement, 32 parts of composite crack-resistant agent and 65 parts of microsilica), 32 parts of end-hook steel fiber, 880 parts of medium sand, 845 parts of crushed stone (continuous gradation with a particle size of 5-20mm), 204 parts of mixing water (water-cement ratio of 0.38), and 8.07 parts of polycarboxylate-based composite water-reducing agent (admixture amount is 1.5% of the total mass of cementitious materials).

[0045] The preparation method of the above-mentioned high-performance self-compacting concrete composition is the same as that in Example 1.

[0046] Example 4 Compared with Example 1, the difference in this example is that the composite crack-resistant agent in this example includes 13 parts of nano-SiO2, 9 parts of powdered shrinkage-reducing agent, and 8 parts of temperature-sensitive expansion microcapsules (the mass ratio of nano-SiO2, powdered shrinkage-reducing agent, and temperature-sensitive expansion microcapsules is 13:9:8). In the preparation of temperature-sensitive expansion microcapsules, the mass fraction of lauric acid is modified to 80 parts, the mass fraction of deionized water is modified to 884 parts, and sodium dodecyl sulfate is replaced with an equal amount of Tween 80. The remaining components, preparation steps, and parameters are the same.

[0047] The thermosensitive expansion microcapsules prepared had a particle size of 35 μm, a core-to-shell ratio of 2.02:1, an expansion initiation temperature of 45℃, and an enthalpy change of 95 J / g (DSC, 10℃ / min).

[0048] Example 5 Compared with Example 1, this example differs in that the composite crack-resistant agent in this example includes 12 parts of nano-SiO2, 11 parts of powdered shrinkage-reducing agent, and 7 parts of thermosensitive expansion microcapsules (the mass ratio of nano-SiO2, powdered shrinkage-reducing agent, and thermosensitive expansion microcapsules is 12:11:7). In the preparation of the thermosensitive expansion microcapsules, the mass fraction of lauric acid is modified to 100 parts, the mass fraction of deionized water is modified to 1030 parts, and azobisisobutyronitrile is replaced with an equal amount of benzoyl peroxide. The remaining components, preparation steps, and parameters are the same.

[0049] The thermosensitive expansion microcapsules prepared had a particle size of 38 μm, a core-to-shell ratio of 2.48:1, an expansion initiation temperature of 46℃, and an enthalpy change of 85 J / g (DSC, 10℃ / min).

[0050] Comparative Example 1 Compared with Example 1, the difference in this comparative example is that the amount of mixing water used in this comparative example is 205 parts (water-to-gel ratio 0.4), while the other components, preparation steps and parameters are the same.

[0051] Comparative Example 2 Compared with Example 1, the difference in this comparative example is that the composite crack-resistant agent in this comparative example does not contain temperature-sensitive expansion microcapsules. Correspondingly, the amounts of nano-SiO2 and powdered shrinkage-reducing agent in the composite crack-resistant agent are adjusted to 16.4 parts and 13.6 parts, respectively, and the two are mixed to prepare the composite crack-resistant agent. The remaining components, preparation steps and parameters are the same.

[0052] Comparative Example 3 Compared with Example 1, the difference in this comparative example is that the temperature-sensitive expansion microcapsules in the composite anti-cracking agent of this comparative example are replaced with an equal amount of unencapsulated fossil wax (melting point 58°C), while the other components, preparation steps and parameters are the same.

[0053] Comparative Example 4 Compared with Example 1, the difference in this comparative example is that, in the preparation of the temperature-sensitive expandable microcapsules in this comparative example, lauric acid was replaced with an equal amount of paraffin (melting point 58°C, preheated to 60°C to melt), and the water bath temperature was adjusted to 60°C. All other components, preparation steps, and parameters remained the same.

[0054] Comparative Example 5 Compared with Example 1, this comparative example differs in that it does not contain silica fume. Correspondingly, the amount of P.O42.5 cement is adjusted to 478 parts (the missing silica fume is made up with an equal amount of cement). All other components, preparation steps, and parameters are the same.

[0055] Comparative Example 6 Compared with Example 1, the difference in this comparative example is that the amount of hook-shaped steel fiber used in this comparative example is 20 parts. The remaining components, preparation steps and parameters are the same.

[0056] Comparative Example 7 Compared with Example 1, the difference in this comparative example is that the amount of polycarboxylate-based composite water-reducing agent used in this comparative example is 8.636 parts (1.7% of the total mass of the cementitious material). The remaining components, preparation steps and parameters are the same.

[0057] Comparative Example 8 Compared with Example 1, the difference in this comparative example is that the amount of polycarboxylate-based composite water-reducing agent used in this comparative example is 5.588 parts (1.1% of the total mass of the cementitious material). The remaining components, preparation steps and parameters are the same.

[0058] Test method for the properties of the mixture (to be completed within 5 minutes after discharge) (1) Collapse spread (mm) Referring to GB / T50080, wet the slump cone and the base plate, and place the slump cone in the center of the base plate; fill it with the mixture at once, scrape it level, and then lift the slump cone vertically; after the concrete stops flowing, measure the diameter in two mutually perpendicular directions and take the arithmetic mean.

[0059] (2) T500 extended time (s) Referring to GB / T50080, start the stopwatch the moment the slump cone is lifted and record the time required for the concrete to expand to a diameter of 500mm.

[0060] (3) J-ring inner expansion (mm) Referring to JGJ / T283, take ring J (with a steel bar diameter of 16mm and a spacing of 60mm) and place it outside the slump cone; in the same slump spread operation, measure the concrete spread diameter (mm) inside ring J.

[0061] (4) 28-day compressive strength (MPa) Refer to GB / T50081, cast 100mm×100mm×100mm cube specimens (3 sets / formula); demold after 24 hours, and cure under standard conditions for 28 days; record the compressive strength at a press loading rate of (0.5-0.8) MPa / s, and take the average value of 3 specimens (single value deviation >15% is rejected).

[0062] (5) 28-day splitting tensile strength (MPa) According to GB / T50081, cast 100mm×100mm×100mm cubic specimens (3 sets / formula); demold after 24 hours, and cure under standard conditions for 28 days; place spacers on the upper and lower center lines of the specimens, and apply uniform loading until failure; according to formula f ts=2F / (πA) (F is the failure load, A is the splitting surface area), calculate the splitting tensile strength f at 28d. ts .

[0063] (6) Permeability grade Referring to GB / T50082, cast 6 frustum specimens (175mm top diameter, 185mm bottom diameter, and 150mm height); demold after 24 hours, and cure under standard conditions for 28 days; starting from 0.1MPa, increase the pressure by 0.1MPa every 8 hours, and observe the water seepage at the end faces of the specimens. The impermeability grade is P. n : The maximum water pressure (MPa) of 4 out of 6 specimens that did not leak water × 10.

[0064] Note: The preparation, curing, and testing of all concrete specimens in the examples and comparative examples strictly followed the following standards: Test environment: laboratory temperature (20±2)℃, relative humidity ≥50%; standard curing conditions for specimens: (20±2)℃, relative humidity ≥95%.

[0065] The test results are shown in Table 1.

[0066] Table 1

[0067] As shown in Table 1, compared with Comparative Examples 1-8, Examples 1-5 exhibit a J-ring expansion difference (slump expansion - J-ring internal expansion) ≤ 50 mm, meeting the Class II filling requirements of JGJ / T 283-2012. There is no bleeding / segregation, and the T500 is within the 2-5 second range, indicating better workability. Furthermore, after 28 days of standard curing, it demonstrates high compressive strength (≥ 70.5 MPa), impermeability reaching P12, and high toughness (f...). ts (≥5.5MPa), resulting in better overall performance. Among them, in Comparative Example 1, the water-cement ratio exceeded the limit, leading to segregation and a significantly insufficient T500; in Comparative Examples 2-4, the lack of temperature-sensitive expansion microcapsules or component substitution weakened the impermeability; in Comparative Example 5, the lack of microsilica powder caused segregation and a decrease in impermeability; in Comparative Example 6, insufficient steel fiber content led to insufficient toughness; in Comparative Examples 7 and 8, the excessive / inadequate dosage of polycarboxylate composite water-reducing agent resulted in excessively low or high T500, weakening the impermeability.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-performance self-compacting concrete composition, characterized in that, The following components are included by weight: The cementitious material comprises 396-441 parts of cement, 29-32 parts of composite crack-resistant agent, and 57-65 parts of microsilica. The composite crack-resistant agent is composed of nano-SiO2, powdered shrinkage reducer and thermosensitive expansion microcapsules in a mass ratio of (10-15):(8-12):(6-10), wherein the shell material of the thermosensitive expansion microcapsules is polymethyl methacrylate and the core material is lauric acid. 28-32 parts steel fiber; 851-880 portions of medium sand; Crushed stone 818-845 parts, particle size 5-20mm continuous gradation; The mixing water, with a water-cement ratio of 0.35-0.38 to the cementitious material, is used in a mixing process. Polycarboxylate-based composite water-reducing agent, the dosage is 1.3-1.5% of the total mass of cementitious materials.

2. The high-performance self-compacting concrete composition according to claim 1, characterized in that, The average particle size of the temperature-sensitive expandable microcapsules is 10-50 μm, and the expansion initiation temperature is 40-50℃.

3. The high-performance self-compacting concrete composition according to claim 1, characterized in that, The core-shell mass ratio of the thermosensitive expansion microcapsule is (1.5-2.5):

1.

4. The high-performance self-compacting concrete composition according to claim 1, characterized in that, The temperature-sensitive expandable microcapsules are prepared by in-situ polymerization, which includes the following steps: In a water bath at 45-55℃, preheated and melted lauric acid, methyl methacrylate monomer, and initiator are mixed to obtain an oil phase; an emulsifier is dispersed in deionized water to form an aqueous phase; the oil phase is continuously dripped into the aqueous phase while stirring; after the addition is complete, the temperature is raised to 65-75℃ for polymerization for 3-5 hours, followed by centrifugation, washing, and drying to obtain the temperature-sensitive expandable microcapsules.

5. The high-performance self-compacting concrete composition according to claim 4, characterized in that, The initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, and potassium persulfate, and the amount used is 1.0%-3.0% of the mass of methyl methacrylate monomer; The emulsifier is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Tween 80, Span 80, and betaine, and the amount used is 0.2%-1.0% of the mass of the aqueous phase.

6. The high-performance self-compacting concrete composition according to claim 4, characterized in that, The oil phase accounts for 10-12% of the total mass of the reaction system; The washing and drying process refers to washing with deionized water 2-4 times, followed by vacuum drying at 55-65℃ to constant weight.

7. The high-performance self-compacting concrete composition according to claim 1, characterized in that, The nano-SiO2 is fumed nano-silica with a specific surface area ≥200m². 2 / g; The silica powder is SF90 grade silica powder; The steel fiber is a hook-shaped steel fiber with a length of 12-14 mm, a diameter of 0.21-0.23 mm, and an aspect ratio of 58-62; The fineness modulus of the medium sand is 2.6-2.9, and the methylene blue value (MB) is ≤1.

0. The cumulative residue of the crushed stone after passing through a 5mm sieve is 0%-10%, after passing through a 10mm sieve it is 30%-60%, and after passing through a 16mm sieve it is 70%-90%.

8. A method for preparing a high-performance self-compacting concrete composition as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: S1. Add cement, silica fume and composite crack-resistant agent into the mixer and dry mix for 1-3 minutes; S2. Add medium sand and gravel, and continue to dry mix for 1-3 minutes; S3. Add steel fibers in 2-4 batches, stirring for 0.5-1 minute for each batch to obtain a dry mixture; S4. Mix the polycarboxylate composite water-reducing agent and mixing water to make an aqueous solution, then add it to the dry-mixed material and wet-mix for 3-8 minutes to obtain a high-performance self-compacting concrete composition.

9. The preparation method according to claim 8, characterized in that, In step S1, the dry mixing speed is 25-35 r / min; in step S2, the dry mixing speed is 30-40 r / min; in step S3, the stirring speed is 30-40 r / min; in step S4, the wet mixing speed is 40-50 r / min.

10. A densely reinforced thin-layer arch reinforcement structure for old tunnels, characterized in that, The arch is cast from the high-performance self-compacting concrete composition according to any one of claims 1-7, and the thickness of the arch is 15-25cm, and the spacing of the reinforcing mesh is 80-100mm.

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