Multi-scale toughened concrete and preparation method thereof

Abstract

The present invention discloses a multi-scale toughened concrete and its preparation method, belonging to the field of high permeability technology. The concrete comprises ferroaluminate cement, a low-shrinkage auxiliary cementitious material, a water reducer, multi-scale composite fibers, a shrinkage compensator, fine aggregate, coarse aggregate, and water. The present invention breaks through the traditional toughening model. Through magnetron sputtering of metal gradient coatings and laser-induced dendrite structures on coarse fibers, a physical-chemical composite connection interface is established. Under impact loads, a strain hysteresis effect is triggered, converting impact energy into interfacial phase change energy, forming a highly efficient energy dissipation channel. Fine fibers introduce amino functional groups and free radical cross-linking networks, combined with the directional arrangement of carbon nanotubes, to give the fibers microscopic dynamic reinforcement capabilities. This allows the concrete to form a synergistic interaction between macro-crack bridging and micro-crack suppression, significantly improving the crack resistance under complex stresses and effectively inhibiting the propagation of microcracks.

Description

Technical Field

[0001] The present invention relates to the technical field of marine engineering concrete, and in particular to a multi-scale toughened concrete and a preparation method thereof. Background Art

[0002] Concrete products are brittle and face a high risk of cracking during production and application. External corrosive media can easily penetrate the matrix, causing corrosion damage to the concrete itself and inducing corrosion of steel reinforcement, reducing the durability and service life of concrete products. Concrete structures in marine and saline-alkali environments are often subjected to a combination of complex stresses, such as wave loads, water impact, and ship impacts, which further accelerate crack formation and damage. The high toughness of multi-scale toughened concrete can, to a certain extent, resist the crack propagation caused by these complex stresses, improving the integrity and stability of the structure, extending its service life, and reducing maintenance costs.

[0003] For example, Chinese patent CN115650667B utilizes a combination of steel fibers and micron-sized fibers, attempting to achieve synergistic toughening through macrocrack bridging and microcrack suppression. However, steel fibers are primarily bonded to the matrix through physical anchoring, while micron-sized fibers rely on chemical interfacial treatment to enhance bonding. Directly mixing steel fibers and micron-sized fibers with the matrix can weaken the fiber-matrix interface transition zone over long-term use, reducing load transfer efficiency and weakening the multi-scale synergistic effect.

[0004] In addition, although the high dosage of auxiliary cementitious materials (fly ash + silica fume) improves the density, the shrinkage cracks actually increase the porosity. Once the leakage channel is formed, chloride ions, water and other media will quickly penetrate along the channel, causing steel corrosion and freeze-thaw damage. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a multi-scale toughened concrete and a preparation method thereof.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A multi-scale toughened concrete, comprising the following components in parts by weight:

[0008] 75-84 parts of ferroaluminate cement;

[0009] 21-32 parts of low shrinkage auxiliary gelling material;

[0010] 0.8-1.5 parts of water reducer;

[0011] 9-13 parts multi-scale composite fibers;

[0012] 2-3 parts shrinkage compensator;

[0013] 100-120 parts of fine aggregate (quartz sand with a particle size of 0.1-0.5 mm);

[0014] 140-180 parts coarse aggregate (stone);

[0015] 38-45 parts water;

[0016] The low shrinkage auxiliary gelling material is composed of SSF core-shell structure and The dense skeleton of metakaolin is formed by staged hydration through gradient mixing;

[0017] The multi-scale composite fiber comprises modified coarse fiber and modified fine fiber in a mass ratio of 4-6:1-2;

[0018] The shrinkage compensating agent includes activated clay, HCSA and magnesium oxide-loaded glass microspheres in a mass ratio of 1-1.6:2-2.5:1.5-1.8.

[0019] The method for preparing the multi-scale toughened concrete comprises the following steps:

[0020] S1: fiber modification;

[0021] Crude fiber pretreatment: the steel fiber is subjected to composite oxidation pickling to remove the surface oxide layer, and microwave-assisted plasma cleaning is added before drying;

[0022] Crude fiber modification, using magnetron sputtering to deposit a nickel-copper gradient layer, enhances the chemical anchoring force with the substrate;

[0023] The crude fiber is post-treated by laser micro-melting under nitrogen protection to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain a modified crude fiber;

[0024] Fine fiber pretreatment: bombarding silicon carbide fibers with nitrogen-argon mixed plasma to simultaneously achieve surface etching and amino functionalization;

[0025] Fine fiber modification, using glycidyl methacrylate as the core monomer and benzophenone as a photosensitizer, triggers surface free radical polymerization under UV irradiation;

[0026] The fine fibers are post-treated by impregnating them with a KH590 / carbon nanotube composite solution, achieving directional alignment of the nanotubes with the aid of ultrasound, and then curing to obtain modified fine fibers.

[0027] S2: Preparation of low shrinkage auxiliary cementitious materials;

[0028] Nanoparticles were coated on the surface of silica fume by sol-gel method. layer to form an SSF core-shell structure, which was centrifuged and dried;

[0029] The metakaolin was microwave calcined under nitrogen protection. From amorphous to Transform, get metakaolin;

[0030] With the help of ultrasonic, the composite dispersant The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure;

[0031] S3: preparing shrinkage compensating agent;

[0032] Mixing montmorillonite nanoclay with oxalic acid solution and centrifuging to obtain activated clay;

[0033] HCSA high-performance concrete expansion agent particles are impregnated with potassium dihydrogen phosphate-ethanol suspension and dried to form a moisture-proof layer on the surface of HCSA. The activated clay and HCSA are then mixed evenly to obtain a composite precursor.

[0034] The hollow glass microspheres were placed in a magnesium nitrate solution and the gas inside the microspheres was removed by vacuum pumping.

[0035] After loading is completed, the glass beads are dried by gradient temperature increase;

[0036] MgO coating is formed by staged calcination to obtain glass microspheres loaded with magnesium oxide;

[0037] Adding magnesium oxide-loaded glass microspheres into the composite precursor and stirring evenly to obtain a shrinkage compensating agent;

[0038] S4: Fiber dispersion and mixing process

[0039] Preparation of dry mix: ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducing agent, shrinkage compensating agent and fine aggregate are stirred at low speed to obtain dry mix;

[0040] Fine fiber dispersion, which is prepared by mixing modified fine fibers with water and dispersing them with the aid of ultrasound to form a stable suspension;

[0041] Preparation of wet mix: add fine fiber dispersion and remaining water to dry mix, stir at high speed and then at low speed to obtain wet mix;

[0042] Crude fiber incorporation: modified crude fiber is added to the wet mix and stirred at a low speed to obtain the mixture;

[0043] S5: Place the mixture into the mold and remove the mold after hardening;

[0044] S6: Multi-scale toughened concrete obtained by gradient curing.

[0045] Furthermore, S1 specifically includes: removing the surface oxide layer of steel fibers with a diameter of 0.15-0.25 mm by composite oxidative pickling (5% citric acid + 3% oxalic acid mixture, 30-40 minutes), adding microwave-assisted plasma cleaning (argon atmosphere, power 200-300W, 5-8 minutes) and then drying at 40-50°C to remove micron-sized oxides;

[0046] A nickel-copper gradient layer (Ni layer 0.2μm + Cu layer 0.3μm) was deposited by magnetron sputtering to enhance the chemical anchoring force with the substrate;

[0047] Laser micro-melting (power 50-80W, scanning speed 100-120mm / s) is performed under nitrogen protection to form a dendritic interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers and enhance the interface shear strength;

[0048] Nitrogen-argon mixed plasma ( :Ar=3:7) bombarded silicon carbide fibers with a diameter of 8-15 μm at a power of 350-400 W for 5-10 minutes, achieving simultaneous surface etching and amino functionalization;

[0049] Glycidyl methacrylate (5-10% of the mass of the fine fiber) is used as the core monomer, and 0.5-1% benzophenone (here, the mass ratio of silicon carbide fiber and benzophenone is 100:0.5-1) is added as a photosensitizer. Under a wavelength of 254nm ultraviolet light, the irradiation intensity is 30mW / , time 10-15min, surface free radical polymerization is initiated by hydrogen transfer reaction;

[0050] The fibers were immersed in KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion), with a mass ratio of fine fibers to KH590 / carbon nanotube composite solution of 1:7-10. Ultrasonic assistance (40kHz, 30min) was used to achieve directional arrangement of nanotubes. The fibers were pre-cured at 50-60°C for 1-2h and post-cured at 100-120°C for 1.5-2h to form a three-dimensional cross-linked network and a chemically bonded interface to obtain modified fine fibers.

[0051] Furthermore, S2 is specifically: using sol-gel method to coat nanoparticles on the surface of silica fume layer, forming SSF (silica fume-nano The silica fume and nano-silica (particle size 20-50 nm) have a core-shell structure and a mass ratio of 8-9:1-3. After centrifugation, the particles are microwave-dried under nitrogen (power 700-800 W, time 10-15 min) to avoid agglomeration caused by hydroxyl condensation.

[0052] The metakaolin was calcined in a microwave oven under nitrogen protection (power 800W, time 15min). From amorphous to Transform, get Metakaolin, which improves the reactivity with the SSF core-shell structure;

[0053] In combination with a composite dispersant (polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), the The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure;

[0054] The mass ratio of composite dispersant, metakaolin and SSF core-shell structure is 0.4-0.8:6-8:7-9;

[0055] In one mixing step (20-30 min), 7 / 15 of the SSF core-shell structure and 1 / 5 of the metakaolin rapidly hydrate to form a skeleton;

[0056] Second stage mixing (40-60min), 1 / 3 SSF core-shell structure, 1 / 3 metakaolin;

[0057] Three-stage mixing (1-2h), 1 / 5 SSF core-shell structure, 7 / 15 metakaolin.

[0058] Furthermore, S3 is specifically as follows: montmorillonite nanoclay is mixed with 0.8% oxalic acid solution at a solid-liquid ratio of 1:3-5, ultrasonically treated at 60°C (40kHz, 500W) for 30-45min, and centrifuged to obtain activated clay;

[0059] HCSA high-performance concrete expansion agent particles (hereinafter referred to as HCSA) are immersed in a 5% potassium dihydrogen phosphate-ethanol suspension for 40-60 minutes and dried at 100-120°C to form a moisture-proof layer on the surface of the HCSA. The activated clay and HCSA are then mixed evenly to obtain a composite precursor.

[0060] Place hollow glass microspheres (particle size 50-100 μm) in a 20-30% magnesium nitrate solution, evacuate to -0.1 MPa using a vacuum pump, and maintain for 20-30 minutes to remove the gas inside the microspheres and ensure that the magnesium nitrate solution fully penetrates into the inner cavity of the microspheres. Filter to obtain glass microspheres uniformly loaded with magnesium nitrate;

[0061] After loading, the glass beads are dried at a gradient temperature (50°C → 80°C → 120°C) to prevent structural cracking due to rapid water loss and to ensure that magnesium nitrate is evenly deposited on the inner wall.

[0062] Staged calcination to form MgO coating:

[0063] First, heat the sample to 200-300°C at a rate of 3-5°C / min to remove residual moisture and organic matter;

[0064] Then, the temperature is raised to 600-620°C at a rate of 2-4°C / min to decompose the magnesium nitrate into magnesium oxide, thereby obtaining glass microspheres loaded with magnesium oxide;

[0065] The glass microbeads loaded with magnesium oxide are added to the composite precursor, and the mixture is stirred uniformly at 40-50° C. for 20-30 minutes to obtain a shrinkage compensating agent.

[0066] Furthermore, S4 specifically comprises ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducing agent, shrinkage compensating agent, and fine aggregate, which are stirred at a low speed (100-200 r / min, 3-5 min) to obtain a dry mix;

[0067] The modified fine fibers were mixed with water and dispersed with ultrasonic assistance (frequency 40 kHz, power 500 W, 5 min) to form a stable suspension of 8-10 wt%, which is the fine fiber dispersion;

[0068] Add the fine fiber dispersion and the remaining water to the dry mix, stir at high speed (280-350 r / min, 5-8 min) and then stir at low speed (100-200 r / min, 2-4 min) to obtain a wet mix;

[0069] Add modified crude fiber to the wet mix and stir at low speed (100-180r / min, 3-4min) to obtain the mixed material to avoid fiber orientation disorder.

[0070] Furthermore, S6 is specifically as follows: a curing period of 1-2 hours: temperature 30-40°C, sealed curing to inhibit plastic shrinkage;

[0071] Second stage curing: 2-3h: 60℃ steam curing to promote hydration of the expansion agent and compensate for autogenous shrinkage;

[0072] Three-stage curing: 3-5h: Curing at room temperature, nanoclay continuously releases moisture to achieve internal curing.

[0073] Furthermore, the water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder in a mass ratio of 10:1.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] 1. The present invention breaks through the traditional toughening mode. Through the magnetron sputtering metal gradient coating and laser-induced dendrite structure of coarse fibers, a physical-chemical composite connection interface is established, which triggers the strain hysteresis effect under impact load, converts the impact energy into interfacial phase change energy, and forms a high-efficiency energy dissipation channel; fine fibers introduce amino functional groups and free radical cross-linking networks, combined with the directional arrangement of carbon nanotubes, to give the fibers microscopic dynamic reinforcement capabilities, so that the concrete forms a synergistic interaction between macro crack bridging and micro crack suppression, significantly improving the crack resistance under complex stress and effectively inhibiting the propagation of micro cracks.

[0076] 2. The gradient activation technology of the auxiliary gel material of the present invention further optimizes the internal structure of concrete. The core-shell structure design of silica fume is achieved through nano The layer blocks the agglomeration of particles, promotes the full hydration reaction, and participates in the formation of dense hydrated calcium silicate gel to fill the pores, solving the problem of increased porosity of traditional auxiliary cementitious materials due to self-shrinkage; after the crystal transformation of metakaolin, a reactive gradient zone is formed in the ultrasonic-assisted gradient mixing, so that the expansion stress is evenly distributed inside the concrete, avoiding structural damage caused by uneven expansion, while improving the concrete's impermeability and reducing the risk of chloride ion penetration.

[0077] 3. The multi-effect synergistic effect of the shrinkage compensator of this invention is outstanding in improving durability. The activated clay enhances its adsorption and release capabilities through interlayer structural modification. Combined with the moisture-proof coating design of the HCSA expander, it ensures stable and uniform expansion compensation. The magnesium oxide coating of the hollow glass microspheres not only acts as a micro-expansion source to compensate for shrinkage, but also refines the pore structure to hinder chloride ion penetration. Together with the auxiliary cementitious material, it creates a dense pore network, effectively blocking the intrusion of harmful media and significantly reducing the risk of steel corrosion and freeze-thaw damage caused by leakage.

[0078] 4. The present invention overcomes the problems of weak fiber-matrix interface transition zone and attenuated load transfer efficiency in traditional fiber-reinforced systems, and establishes a stable reinforcement network through physical and chemical synergistic modification. At the same time, it solves the durability degradation caused by the self-shrinkage of high-dosage auxiliary cementitious materials, achieves a balance between shrinkage compensation and structural reinforcement, and provides a comprehensive solution with high toughness, expansion controllability and durability for concrete products serving in complex environments, significantly extending the service life of the structure and reducing maintenance costs in complex stress environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0080] Figure 1 This is an electron microscope image of the multi-scale toughened concrete prepared in Comparative Example 3;

[0081] Figure 2 This is an electron microscope image of the multi-scale toughened concrete prepared in Comparative Example 4;

[0082] Figure 3 This is an electron microscope image of the multi-scale toughened concrete prepared in Example 3. DETAILED DESCRIPTION

[0083] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0084] Example 1: This example provides a multi-scale toughened concrete comprising the following components in parts by weight:

[0085] 84 parts of ferroaluminate cement;

[0086] 32 parts of low shrinkage auxiliary cementitious material;

[0087] 1.5 parts of water reducer;

[0088] 13 multi-scale composite fibers;

[0089] 3 parts shrinkage compensator;

[0090] 120 parts of fine aggregate (quartz sand with a particle size of 0.5 mm);

[0091] 180 parts coarse aggregate (stone);

[0092] 45 parts water;

[0093] The low shrinkage auxiliary gelling material is composed of SSF core-shell structure and The dense skeleton of metakaolin is formed by staged hydration through gradient mixing;

[0094] The multi-scale composite fiber comprises modified coarse fiber and modified fine fiber in a mass ratio of 6:2;

[0095] The shrinkage compensating agent includes activated clay, HCSA and magnesium oxide-loaded glass microspheres in a mass ratio of 1.6:2.5:1.8.

[0096] The method for preparing the multi-scale toughened concrete comprises the following steps:

[0097] S1: fiber modification;

[0098] For crude fiber pretreatment, steel fibers with a diameter of 0.25 mm were subjected to composite oxidative pickling (5% citric acid + 3% oxalic acid mixture, 40 min) to remove the surface oxide layer. Microwave-assisted plasma cleaning (argon atmosphere, power 300 W, 8 min) was then added and dried at 50°C to remove micron-sized oxides.

[0099] The crude fiber is modified by magnetron sputtering to deposit a nickel-copper gradient layer (Ni layer 0.2μm + Cu layer 0.3μm) to enhance the chemical anchoring force with the substrate;

[0100] The coarse fibers were post-treated by laser micro-melting (power 80W, scanning speed 120mm / s) under nitrogen protection to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers and enhance the interfacial shear strength.

[0101] Fine fiber pretreatment, nitrogen-argon mixed plasma ( :Ar=3:7) bombarded silicon carbide fibers with a diameter of 15 μm at a power of 400 W for 10 min, achieving simultaneous surface etching and amino functionalization;

[0102] Fine fiber modification, glycidyl methacrylate (glycidyl methacrylate accounts for 10% of the fine fiber mass) as the core monomer, 1% benzophenone (here refers to the mass ratio of silicon carbide fiber and benzophenone is 100:1) as the photosensitizer, under the wavelength of 254nm ultraviolet light, irradiation intensity of 30mW / , time 15min, surface free radical polymerization initiated by hydrogen transfer reaction;

[0103] The fine fibers were post-treated by impregnating them with a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion) at a mass ratio of 1:10. Ultrasonication (40 kHz, 30 min) was used to achieve directional alignment of the nanotubes. The fibers were pre-cured at 60°C for 2 h and post-cured at 120°C for 2 h to form a three-dimensional cross-linked network and a chemically bonded interface, yielding modified fine fibers.

[0104] S2: Preparation of low shrinkage auxiliary cementitious materials;

[0105] Nanoparticles were coated on the surface of silica fume by sol-gel method. layer, forming SSF (silica fume-nano The silica fume and nano-silica (50 nm in diameter) core-shell structure was prepared in a mass ratio of 8-9:1-3. After centrifugation, the particles were microwave-dried under nitrogen (power 800 W, time 15 min) to avoid agglomeration caused by hydroxyl condensation.

[0106] The metakaolin was calcined in a microwave oven under nitrogen protection (power 800W, time 15min). From amorphous to Transform, get Metakaolin, which improves the reactivity with the SSF core-shell structure;

[0107] In the presence of a composite dispersant (polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), the The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure;

[0108] The mass ratio of composite dispersant, metakaolin, and SSF core-shell structure is 0.8:8:9;

[0109] In the first stage of mixing (30 min), 7 / 15 of the SSF core-shell structure and 1 / 5 of the metakaolin rapidly hydrate to form a skeleton;

[0110] Second stage mixing (60 min), 1 / 3 SSF core-shell structure, 1 / 3 metakaolin;

[0111] Three-stage mixing (2 h), 1 / 5 SSF core-shell structure, 7 / 15 metakaolin;

[0112] S3: preparing shrinkage compensating agent;

[0113] Montmorillonite nanoclay was mixed with 0.8% oxalic acid solution at a solid-liquid ratio of 1:5, and ultrasonicated (40 kHz, 500 W) at 60 °C for 45 min. Activated clay was obtained after centrifugation.

[0114] HCSA high-performance concrete expansion agent particles (hereinafter referred to as HCSA) were impregnated with a 5% potassium dihydrogen phosphate-ethanol suspension for 60 minutes and dried at 120°C to form a moisture-proof layer on the HCSA surface. The activated clay and HCSA were then mixed evenly to obtain a composite precursor.

[0115] Hollow glass microspheres (particle size 100 μm) were placed in a 30% magnesium nitrate solution and evacuated to -0.1 MPa using a vacuum pump for 30 minutes to remove the gas inside the microspheres and ensure that the magnesium nitrate solution fully penetrated into the microsphere cavity. Glass microspheres uniformly loaded with magnesium nitrate were obtained by filtration.

[0116] After loading, the glass beads are dried at a gradient temperature (50°C → 80°C → 120°C) to prevent structural cracking due to rapid water loss and to ensure that magnesium nitrate is evenly deposited on the inner wall.

[0117] Staged calcination to form MgO coating:

[0118] First, the temperature was raised to 300°C at a rate of 5°C / min to remove residual moisture and organic matter;

[0119] Then, the temperature was raised to 620°C at a rate of 4°C / min to decompose magnesium nitrate into magnesium oxide, thereby obtaining glass microspheres loaded with magnesium oxide.

[0120] Compensation principle: When the external load or shrinkage stress reaches the critical value of the microbead compressive strength, the microbeads will rupture brittlely, and the MgO on the inner wall of the microbeads will be exposed and released into the crack area. The released MgO will react with the concrete pore water: , effectively compensate for shrinkage, Can be further The reaction produces magnesium carbonate ( ), filling pores and improving density;

[0121] Glass microspheres loaded with magnesium oxide were added to the composite precursor and stirred uniformly at 50°C for 30 minutes to obtain a shrinkage compensator.

[0122] S4: Fiber dispersion and mixing process

[0123] Preparation of dry mix: ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate are stirred at low speed (200 r / min, 5 min) to obtain dry mix;

[0124] The water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder;

[0125] Fine fiber dispersion: the modified fine fibers were mixed with water and dispersed with ultrasonic aid (frequency 40 kHz, power 500 W, 5 min) to form a 10 wt% stable suspension, which is the fine fiber dispersion;

[0126] Preparation of wet mix: Add the fine fiber dispersion and the remaining water to the dry mix, stir at high speed (350 r / min, 8 min) and then stir at low speed (200 r / min, 4 min) to obtain the wet mix;

[0127] Crude fiber incorporation: Modified crude fiber was added to the wet mix and stirred at low speed (180 r / min, 4 min) to obtain the mixed material to avoid fiber orientation disorder;

[0128] S5: Place the mixture into the mold and remove the mold after hardening;

[0129] S6: Multi-scale toughened concrete obtained by gradient curing;

[0130] First stage curing (2h): temperature 40℃, sealed curing to inhibit plastic shrinkage;

[0131] Second stage curing (3h): 60℃ steam curing to promote hydration of the expansion agent and compensate for autogenous shrinkage;

[0132] Three-stage curing (5h): Curing at room temperature, nanoclay continuously releases moisture to achieve internal curing.

[0133] Example 2: This example provides a multi-scale toughened concrete, comprising the following components in parts by weight:

[0134] 75 parts of ferroaluminate cement;

[0135] 21 parts of low shrinkage auxiliary cementitious materials;

[0136] 0.8 parts of water reducer;

[0137] 9 multi-scale composite fibers;

[0138] 2 parts shrinkage compensator;

[0139] 100 parts of fine aggregate (quartz sand with a particle size of 0.1 mm);

[0140] 140 parts coarse aggregate (stone);

[0141] 38 parts water;

[0142] The low shrinkage auxiliary gelling material is composed of SSF core-shell structure and The dense skeleton of metakaolin is formed by staged hydration through gradient mixing;

[0143] The multi-scale composite fiber comprises modified coarse fiber and modified fine fiber in a mass ratio of 4:1;

[0144] The shrinkage compensating agent includes activated clay, HCSA and magnesium oxide-loaded glass microspheres in a mass ratio of 1:2:1.5.

[0145] The method for preparing the multi-scale toughened concrete comprises the following steps:

[0146] S1: fiber modification;

[0147] For crude fiber pretreatment, steel fibers with a diameter of 0.15 mm were subjected to composite oxidative pickling (5% citric acid + 3% oxalic acid mixture, 30 min) to remove the surface oxide layer. Microwave-assisted plasma cleaning (argon atmosphere, power 200 W, 5 min) was then added and dried at 40°C to remove micron-sized oxides.

[0148] The crude fiber is modified by magnetron sputtering to deposit a nickel-copper gradient layer (Ni layer 0.2μm + Cu layer 0.3μm) to enhance the chemical anchoring force with the substrate;

[0149] The coarse fiber was post-treated by laser micro-melting under nitrogen protection (power 50W, scanning speed 100mm / s) to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain modified coarse fiber and enhance the interface shear strength;

[0150] Fine fiber pretreatment, nitrogen-argon mixed plasma ( :Ar=3:7) bombarded silicon carbide fibers with a diameter of 8 μm at a power of 350 W for 5 min, achieving simultaneous surface etching and amino functionalization;

[0151] Fine fiber modification, glycidyl methacrylate (glycidyl methacrylate accounts for 5% of the fine fiber mass) as the core monomer, 0.5% benzophenone (here refers to the mass ratio of silicon carbide fiber and benzophenone is 100:0.5) as the photosensitizer, under the wavelength of 254nm ultraviolet light, irradiation intensity 30mW / , time 10 min, surface free radical polymerization initiated by hydrogen transfer reaction;

[0152] The fine fibers were post-treated by being immersed in a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion) with a mass ratio of 1:7. The nanotubes were aligned by ultrasound (40 kHz, 30 min). The fibers were pre-cured at 50°C for 1 h and post-cured at 100°C for 1.5 h to form a three-dimensional cross-linked network and a chemically bonded interface, thereby obtaining modified fine fibers.

[0153] S2: Preparation of low shrinkage auxiliary cementitious materials;

[0154] Nanoparticles were coated on the surface of silica fume by sol-gel method. layer, forming SSF (silica fume-nano The silica fume and nano-silica (particle size 20 nm) were prepared in a core-shell structure with a mass ratio of 8:1. After centrifugation, the silica fume was microwave-dried under nitrogen (power 700 W, time 10 min) to avoid agglomeration caused by hydroxyl condensation.

[0155] The metakaolin was microwave calcined under nitrogen protection (power 800W, time 15min), so that Al2O3 changed from amorphous to Transform, get Metakaolin, which improves the reactivity with the SSF core-shell structure;

[0156] In the presence of a composite dispersant (polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), the The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure;

[0157] The mass ratio of composite dispersant, metakaolin, and SSF core-shell structure is 0.4:6:7;

[0158] In the first mixing stage (20 min), 7 / 15 of the SSF core-shell structure and 1 / 5 of the metakaolin rapidly hydrate to form a skeleton;

[0159] Second stage mixing (40 min), 1 / 3 SSF core-shell structure, 1 / 3 metakaolin;

[0160] Three-stage mixing (1 h), 1 / 5 SSF core-shell structure, 7 / 15 metakaolin;

[0161] S3: preparing shrinkage compensating agent;

[0162] Montmorillonite nanoclay was mixed with 0.8% oxalic acid solution at a solid-liquid ratio of 1:3, and ultrasonicated (40 kHz, 500 W) at 60°C for 30-45 min. Activated clay was obtained after centrifugation.

[0163] HCSA high-performance concrete expansion agent particles (hereinafter referred to as HCSA) were impregnated with a 5% potassium dihydrogen phosphate-ethanol suspension for 40 minutes and dried at 100°C to form a moisture-proof layer on the HCSA surface. The activated clay and HCSA were then mixed evenly to obtain a composite precursor.

[0164] Hollow glass microspheres (particle size 50 μm) were placed in a 20-30% magnesium nitrate solution and evacuated to -0.1 MPa using a vacuum pump for 20 minutes to remove the gas inside the microspheres and ensure that the magnesium nitrate solution fully penetrated into the inner cavity of the microspheres. The microspheres were then filtered to obtain glass microspheres uniformly loaded with magnesium nitrate.

[0165] After loading, the glass beads are dried at a gradient temperature (50°C → 80°C → 120°C) to prevent structural cracking due to rapid water loss and to ensure that magnesium nitrate is evenly deposited on the inner wall.

[0166] Staged calcination to form MgO coating:

[0167] First, the temperature was raised to 200°C at a rate of 3°C / min to remove residual moisture and organic matter;

[0168] The temperature is then raised to 600°C at a rate of 2°C / min to decompose magnesium nitrate into magnesium oxide, thereby obtaining glass microspheres loaded with magnesium oxide.

[0169] Glass microspheres loaded with magnesium oxide were added to the composite precursor and stirred uniformly at 40°C for 20 min to obtain a shrinkage compensator.

[0170] S4: Fiber dispersion and mixing process

[0171] Preparation of dry mix: ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate are stirred at low speed (100 r / min, 3 min) to obtain dry mix;

[0172] The water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder;

[0173] Fine fiber dispersion: the modified fine fibers were mixed with water and dispersed with ultrasonic assistance (frequency 40 kHz, power 500 W, 5 min) to form a stable suspension of 8 wt%, which is the fine fiber dispersion;

[0174] Preparation of wet mix: Add the fine fiber dispersion and the remaining water to the dry mix, stir at high speed (280 r / min, 5 min) and then stir at low speed (100 r / min, 2 min) to obtain the wet mix;

[0175] Crude fiber incorporation: Modified crude fiber is added to the wet mix and stirred at low speed (100 r / min, 3 min) to obtain the mixed material to avoid fiber orientation disorder;

[0176] S5: Place the mixture into the mold and remove the mold after hardening;

[0177] S6: Multi-scale toughened concrete obtained by gradient curing;

[0178] First stage curing (1h): temperature 30℃, sealed curing to inhibit plastic shrinkage;

[0179] Second stage curing (2h): 60℃ steam curing to promote hydration of the expansion agent and compensate for autogenous shrinkage;

[0180] Three-stage curing (3h): Curing at room temperature, nanoclay continuously releases moisture to achieve internal curing.

[0181] Example 3: This example provides a multi-scale toughened concrete, comprising the following components in parts by weight:

[0182] 81 parts of ferroaluminate cement;

[0183] 25 parts of low shrinkage auxiliary cementitious material;

[0184] 1.1 part water reducer;

[0185] 10 multi-scale composite fibers;

[0186] 2.6 parts shrinkage compensator;

[0187] 113 parts of fine aggregate (quartz sand with a particle size of 0.2 mm);

[0188] 150 parts coarse aggregate (stone);

[0189] 41 parts water;

[0190] The low shrinkage auxiliary gelling material is composed of SSF core-shell structure and The dense skeleton of metakaolin is formed by staged hydration through gradient mixing;

[0191] The multi-scale composite fiber includes modified coarse fiber and modified fine fiber in a mass ratio of 5:1.3;

[0192] The shrinkage compensating agent includes activated clay, HCSA and magnesium oxide-loaded glass microspheres in a mass ratio of 1.2:2.2:1.7.

[0193] The method for preparing the multi-scale toughened concrete comprises the following steps:

[0194] S1: fiber modification;

[0195] For crude fiber pretreatment, steel fibers with a diameter of 0.2 mm were subjected to composite oxidative pickling (5% citric acid + 3% oxalic acid mixture, 38 min) to remove the surface oxide layer. Microwave-assisted plasma cleaning (argon atmosphere, power 250 W, 7 min) was then added and dried at 41°C to remove micron-sized oxides.

[0196] The crude fiber is modified by magnetron sputtering to deposit a nickel-copper gradient layer (Ni layer 0.2μm + Cu layer 0.3μm) to enhance the chemical anchoring force with the substrate;

[0197] The coarse fibers were post-treated by laser micro-melting (power 60W, scanning speed 110mm / s) under nitrogen protection to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers and enhance the interfacial shear strength.

[0198] Fine fiber pretreatment, nitrogen-argon mixed plasma ( :Ar=3:7) bombarded silicon carbide fibers with a diameter of 10 μm at a power of 380 W for 9 minutes, achieving simultaneous surface etching and amino functionalization;

[0199] Fine fiber modification, glycidyl methacrylate (glycidyl methacrylate accounts for 6% of the fine fiber mass) as the core monomer, 0.8% benzophenone (here refers to the mass ratio of silicon carbide fiber and benzophenone is 100:0.7) as a photosensitizer, under a wavelength of 254nm ultraviolet light, irradiation intensity of 30mW / , time 12 min, surface free radical polymerization initiated by hydrogen transfer reaction;

[0200] The fine fibers were post-treated by impregnating them with a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion) at a mass ratio of 1:8. Ultrasonication (40 kHz, 30 min) was used to achieve directional alignment of the nanotubes. The fibers were pre-cured at 52°C for 2 h and post-cured at 105°C for 2 h to form a three-dimensional cross-linked network and a chemically bonded interface, yielding modified fine fibers.

[0201] S2: Preparation of low shrinkage auxiliary cementitious materials;

[0202] Nanoparticles were coated on the surface of silica fume by sol-gel method. layer, forming SSF (silica fume-nano The silica fume and nano-silica (particle size 40 nm) core-shell structure was prepared with a mass ratio of 8:2. After centrifugation, the silica fume was microwave-dried under nitrogen (power 730 W, time 15 min) to avoid agglomeration caused by hydroxyl condensation.

[0203] The metakaolin was calcined in a microwave oven under nitrogen protection (power 800W, time 15min). From amorphous to Transform, get Metakaolin, which improves the reactivity with the SSF core-shell structure;

[0204] In the presence of a composite dispersant (polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), the The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure;

[0205] The mass ratio of composite dispersant, metakaolin, and SSF core-shell structure is 0.5:7:8;

[0206] In the first stage of mixing (25 min), 7 / 15 of the SSF core-shell structure and 1 / 5 of the metakaolin rapidly hydrate to form a skeleton;

[0207] Second stage mixing (50 min), 1 / 3 SSF core-shell structure, 1 / 3 metakaolin;

[0208] Three-stage mixing (1.5 h), 1 / 5 SSF core-shell structure, 7 / 15 metakaolin;

[0209] S3: preparing shrinkage compensating agent;

[0210] Montmorillonite nanoclay was mixed with 0.8% oxalic acid solution at a solid-liquid ratio of 1:4, and ultrasonicated (40 kHz, 500 W) at 60 °C for 44 min. Activated clay was obtained after centrifugation.

[0211] HCSA high-performance concrete expansion agent particles (hereinafter referred to as HCSA) were impregnated with a 5% potassium dihydrogen phosphate-ethanol suspension for 50 minutes and dried at 116°C to form a moisture-proof layer on the HCSA surface. The activated clay and HCSA were then mixed evenly to obtain a composite precursor.

[0212] Hollow glass microspheres (particle size 80 μm) were placed in a 25% magnesium nitrate solution and evacuated to -0.1 MPa using a vacuum pump for 25 minutes to remove the gas inside the microspheres and ensure that the magnesium nitrate solution fully penetrated into the microsphere cavity. Glass microspheres uniformly loaded with magnesium nitrate were obtained by filtration.

[0213] After loading, the glass beads are dried at a gradient temperature (50°C → 80°C → 120°C) to prevent structural cracking due to rapid water loss and to ensure that magnesium nitrate is evenly deposited on the inner wall.

[0214] Staged calcination to form MgO coating:

[0215] First, the temperature was raised to 260°C at a rate of 4°C / min to remove residual moisture and organic matter;

[0216] The temperature was then raised to 610°C at a rate of 3°C / min to decompose magnesium nitrate into magnesium oxide, thereby obtaining glass microspheres loaded with magnesium oxide.

[0217] The magnesium oxide-loaded glass microspheres were added to the composite precursor and stirred uniformly at 45°C for 22 minutes to obtain the shrinkage compensator.

[0218] S4: Fiber dispersion and mixing process

[0219] Preparation of dry mix: ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate are stirred at low speed (130 r / min, 4 min) to obtain dry mix;

[0220] The water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder;

[0221] Fine fiber dispersion: the modified fine fibers were mixed with water and dispersed with ultrasonic aid (frequency 40 kHz, power 500 W, 5 min) to form a 10 wt% stable suspension, which is the fine fiber dispersion;

[0222] Preparation of wet mix: Add the fine fiber dispersion and the remaining water to the dry mix, stir at high speed (300 rpm, 6 min) and then stir at low speed (120 rpm, 3 min) to obtain the wet mix;

[0223] Crude fiber incorporation: Modified crude fiber was added to the wet mix and stirred at low speed (160 r / min, 4 min) to obtain the mixture to avoid fiber orientation disorder;

[0224] S5: Place the mixture into the mold and remove the mold after hardening;

[0225] S6: Multi-scale toughened concrete obtained by gradient curing;

[0226] Stage 1 curing (1h): temperature 38°C, sealed curing to inhibit plastic shrinkage;

[0227] Second stage curing (2h): 60℃ steam curing to promote hydration of the expansion agent and compensate for autogenous shrinkage;

[0228] Three-stage curing (4h): Curing at room temperature, nanoclay continuously releases moisture to achieve internal curing.

[0229] Comparative Example 1: This comparative example differs from Example 3 in that the coarse fibers and fine fibers are not modified separately.

[0230] Comparative Example 2: This comparative example differs from Example 3 in that the components are not modified during the preparation of the auxiliary gelling material, but are directly mixed.

[0231] S2 specifically includes: auxiliary gelling material preparation;

[0232] Silica fume and nano-silica (particle size 40 nm) were mixed in a mass ratio of 8:2, and then microwave-dried under nitrogen protection (power 730 W, time 15 min) to obtain mixture A;

[0233] In the presence of a composite dispersant (polycarboxylate water-reducing agent and hydroxypropyl methylcellulose in a mass ratio of 9:1), metakaolin and mixture A were gradient mixed by 44 kHz ultrasound to obtain an auxiliary gelling material.

[0234] The mass ratio of composite dispersant, metakaolin and mixture A is 0.5:7:8;

[0235] In the first stage of mixing (25 min), 7 / 15 of mixture A and 1 / 5 of metakaolin were quickly hydrated to form a skeleton;

[0236] Second stage mixing (50 min), 1 / 3 mixture A, 1 / 3 metakaolin;

[0237] Three-stage mixing (1.5 h), 1 / 5 mixture A, 7 / 15 metakaolin.

[0238] Comparative Example 3: No shrinkage compensating agent was added.

[0239] Comparative Example 4: No shrinkage compensating agent was added, and the coarse and fine fibers were not modified.

[0240] Comparative Example 5: No shrinkage compensating agent was added, and the components were not modified during the preparation of the auxiliary gelling material, but were directly mixed.

[0241] Experimental Example 1: Electron microscope images of the multi-scale toughened concrete prepared in Example 3 and Comparative Examples 2 and 5 were taken respectively (as shown in FIG. Figure 1-3 As shown in Figure 2), it can be seen from SEM that Figure 3 The surface structure of concrete is highly dense, the transition zones of each component are tightly combined, the interface transition zone has good continuity, and there is no obvious separation phenomenon.

[0242] Figure 1 The surface structure of concrete is relatively loose, the area of ​​the interface transition zone with tight bonding is small, the continuity of the interface transition zone is poor, and obvious separation can be seen in some areas and the pores are relatively obvious.

[0243] Figure 2 The bonding strength of the interface transition zone is between Figure 1 and Figure 3 The interface transition zone is relatively tight, but the continuity is not as good as Figure 3 , slight separation and a small amount of pores can still be seen in some areas.

[0244] Experimental Example 2:

[0245] 2.1 The restricted expansion rate was tested in accordance with GB 50119-2013. Specimens (100 × 100 × 300 mm) were formed using longitudinal restrictors (reinforcement ratio 0.79%). Curing conditions were consistent with gradient curing. The restricted expansion rate was tested after 14 days (the larger the restricted expansion rate, the better the concrete's shrinkage compensation effect).

[0246] 2.2 According to GB / T 50082-2024, the autogenous shrinkage rate is tested using the bellows method at a temperature of 20±2°C for 3 days (the smaller the autogenous shrinkage rate, the better the shrinkage resistance of the concrete).

[0247] 2.3 The compressive and flexural strengths at 28 days were tested according to GB / T 50081-2019. Specimens were 100 × 100 × 100 mm cubes (compressive) and 100 × 100 × 400 mm prisms (flexural). The loading rates were 0.5 MPa / s for compressive strength and 0.05 MPa / s for flexural strength.

[0248] 2.4 According to JGJ / T 221-2010, bending toughness (0-5.5mm deformation energy) was tested and a 100×100×400mm specimen was prepared.

[0249] 2.5 According to GB / T 50082-2024, for the determination of chloride ion migration coefficient, prepare a φ100×50mm drill core specimen, place the specimen in a vacuum container, evacuate to -0.1MPa, and maintain the vacuum for 20-30 minutes to remove the internal gas;

[0250] Inject 3.0% NaCl solution (mass concentration) until the specimen is completely immersed, continue vacuuming for 15 minutes, then return to normal pressure and soak for 18±2 hours;

[0251] Calculate the chloride ion migration coefficient (GB / T 50082-2024) using a chloride ion diffusion coefficient meter (such as the NJ-RCM model).

[0252] The test results are as follows:

[0253]

[0254] The present invention achieves an improvement in the multi-scale toughening effect by modifying coarse fibers and fine fibers separately; among them, the modification of coarse fibers focuses on the improvement of surface activity and the strengthening of interface coupling. After cleaning and impurity removal, the metal gradient coating formed by magnetron sputtering can provide a chemical anchoring effect, and the dendritic structure induced by laser micromelting further enhances the mechanical meshing effect, forming a multi-level physical-chemical composite connection. When subjected to external impact, the interface between the metal coating and the substrate will produce a strain hysteresis effect. This hysteresis response of the microstructure can convert the impact energy into interfacial phase change energy, forming an effective energy dissipation channel. The modification of fine fibers focuses on the introduction of surface active groups and nanoscale enhancement. Plasma bombardment realizes the simultaneous introduction of amino functional groups by micro-nanostructure etching, ultraviolet-induced surface polymerization constructs a free radical cross-linking network, and the directional arrangement and chemical bonding of carbon nanotubes give the fine fibers multi-scale enhancement and signal transmission capabilities. When microcracks in concrete expand, the disentanglement and rearrangement of polymer chain segments can provide additional fracture energy, breaking through the stress transfer limit of traditional fiber reinforcement and expanding the reinforcement mechanism from a simple bridging effect to a dynamic interaction that includes energy dissipation.

[0255] The present invention achieves a controllable expansion effect on concrete by modifying the components of the auxiliary gel material; wherein the surface of the silica fume is coated with nano The core-shell structure formed after the layer can effectively block the agglomeration of silica fume particles. This structure provides more active surfaces for cement hydration, making the hydration reaction more complete. The metakaolin is microwave calcined under nitrogen protection to make it From amorphous to With the help of composite dispersant, The gradient mixing of metakaolin and SSF core-shell structure enables the auxiliary cementitious material to form a reaction activity and expansion controllable performance that gradually changes from the inside to the outside of the concrete, so that the expansion stress inside the concrete is evenly dispersed and effectively constrained, thereby achieving a good expansion controllable effect.

[0256] The present invention reduces autogenous shrinkage and chloride ion penetration depth by adding a shrinkage compensator to concrete. Nanoclay is mixed with an oxalic acid solution and then ultrasonically treated. Oxalic acid molecules insert into the interlayers of montmorillonite, disrupting its original crystal structure, widening the interlayer spacing, weakening interlayer bonding, and increasing the activity and reactivity of the montmorillonite. The activated clay obtained after centrifugation has more flexible interlayer channels, providing favorable conditions for the subsequent adsorption and release of water molecules. HCSA high-performance concrete expansive agent particles are impregnated with a potassium dihydrogen phosphate-ethanol suspension and then dried. The potassium dihydrogen phosphate forms a moisture-proof layer on the HCSA surface. This moisture-proof layer effectively prevents the HCSA from absorbing moisture from the air during storage and transportation, leading to deliquescence and agglomeration, thereby ensuring the activity and reaction uniformity of the expansive agent. The magnesium oxide coating within the hollow glass microspheres acts as a micro-expansion source within the concrete, generating a micro-expansion effect that partially compensates for concrete shrinkage. Furthermore, the magnesium oxide coating has a barrier effect, obstructing the chloride ion penetration path and reducing the chloride ion penetration depth.

[0257] The shrinkage compensator of the present invention compensates for concrete shrinkage through an expansion effect. The coarse fibers bear the main stress when the concrete is subjected to stress, preventing the formation and expansion of macro cracks, while the fine fibers bridge cracks at the micro level and dissipate energy. The three work synergistically to significantly improve the toughness of concrete.

[0258] The shrinkage compensator of the present invention produces micro-expansion inside the concrete through the expansion effect, thereby compensating for the concrete's autogenous shrinkage. The hydration products of silica fume and metakaolin can fill the pores of the concrete, increase the rigidity and strength of the concrete, exert a certain restraining effect on the expansion, make the expansion more uniform and stable, and thus further improve the expansion restriction effect. The core-shell structure of auxiliary cementitious materials such as silica fume and the crystal transformation of metakaolin can optimize the pore structure of the concrete, reduce the porosity, increase the density, and provide a more stable matrix for expansion compensation. At the same time, the low shrinkage characteristics of the auxiliary cementitious materials can reduce the internal stress of the concrete, making the expansion of the shrinkage compensator more efficient and further reducing the autogenous shrinkage rate. Components such as the magnesium oxide coating in the shrinkage compensator can refine the pore structure of the concrete, reduce the number of large pores and interconnected pores, and the addition of the auxiliary cementitious materials further improves the pore distribution of the concrete, making the pores finer and more uniform, reducing the connectivity of the pores, thereby effectively blocking the penetration path of harmful substances such as chloride ions and reducing leakage.

[0259] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A multi-scale toughened concrete, characterized in that: Calculated by weight, it includes the following components: 75-84 parts of ferroaluminate cement; 21-32 parts of low shrinkage auxiliary gelling material; 0.8-1.5 parts of water reducer; 9-13 parts multi-scale composite fibers; 2-3 parts shrinkage compensator; 100-120 parts fine aggregate; 140-180 parts coarse aggregate; 38-45 parts water; The low shrinkage auxiliary gelling material is composed of SSF core-shell structure and The dense skeleton of metakaolin is formed by staged hydration through gradient mixing; The multi-scale composite fiber comprises modified coarse fiber and modified fine fiber in a mass ratio of 4-6:1-2; The shrinkage compensator includes activated clay, HCSA and magnesium oxide-loaded glass microspheres in a mass ratio of 1-1.6:2-2.5:1.5-1.8; A method for preparing multi-scale toughened concrete comprises the following steps: S1: fiber modification; Crude fiber pretreatment: the steel fiber is subjected to composite oxidation pickling to remove the surface oxide layer, and microwave-assisted plasma cleaning is added before drying; Crude fiber modification, using magnetron sputtering to deposit a nickel-copper gradient layer, enhances the chemical anchoring force with the substrate; The crude fiber is post-treated by laser micro-melting under nitrogen protection to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain a modified crude fiber; Fine fiber pretreatment: bombarding silicon carbide fibers with nitrogen-argon mixed plasma to simultaneously achieve surface etching and amino functionalization; Fine fiber modification, using glycidyl methacrylate as the core monomer and benzophenone as a photosensitizer, triggers surface free radical polymerization under UV irradiation; The fine fibers are post-treated by impregnating them with a KH590 / carbon nanotube composite solution, achieving directional alignment of the nanotubes with the aid of ultrasound, and then curing to obtain modified fine fibers. S2: Preparation of low shrinkage auxiliary cementitious materials; Nanoparticles were coated on the surface of silica fume by sol-gel method. layer to form an SSF core-shell structure, which was centrifuged and dried; The metakaolin was microwave calcined under nitrogen protection. From amorphous to Transform, get metakaolin; With the help of ultrasonic, the composite dispersant The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure; S3: preparing shrinkage compensating agent; Mixing montmorillonite nanoclay with oxalic acid solution and centrifuging to obtain activated clay; HCSA high-performance concrete expansion agent particles are impregnated with potassium dihydrogen phosphate-ethanol suspension and dried to form a moisture-proof layer on the surface of HCSA. The activated clay and HCSA are then mixed evenly to obtain a composite precursor. The hollow glass microspheres were placed in a magnesium nitrate solution and the gas inside the microspheres was removed by vacuum pumping. After loading is completed, the glass beads are dried by gradient temperature increase; MgO coating is formed by staged calcination to obtain glass microspheres loaded with magnesium oxide; The glass microbeads loaded with magnesium oxide are added into the composite precursor and stirred evenly to obtain the shrinkage compensating agent.

2. A method for preparing multi-scale toughened concrete according to claim 1, characterized in that: The following steps are also included: S4: Fiber dispersion and mixing process Preparation of dry mix: ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducing agent, shrinkage compensating agent and fine aggregate are stirred at low speed to obtain dry mix; Fine fiber dispersion, which is prepared by mixing modified fine fibers with water and dispersing them with the aid of ultrasound to form a stable suspension; Preparation of wet mix: add fine fiber dispersion and remaining water to dry mix, stir at high speed and then at low speed to obtain wet mix; Crude fiber incorporation: modified crude fiber is added to the wet mix and stirred at a low speed to obtain the mixture; S5: Place the mixture into the mold and remove the mold after hardening; S6: Multi-scale toughened concrete obtained by gradient curing.

3. The method for preparing multi-scale toughened concrete according to claim 1, characterized in that: S1 specifically comprises: subjecting steel fibers with a diameter of 0.15-0.25 mm to composite oxidation pickling for 30-40 minutes to remove the surface oxide layer, then subjecting them to microwave-assisted plasma cleaning at a power of 200-300 W for 5-8 minutes in an argon atmosphere, and drying them at 40-50°C to remove micron-sized oxides; The nickel-copper gradient layer was deposited by magnetron sputtering; Laser micro-melting was performed under nitrogen protection with a power of 50-80W and a scanning speed of 100-120mm / s to form a dendrite interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers; Silicon carbide fibers with a diameter of 8-15 μm were bombarded with nitrogen-argon mixed plasma at a power of 350-400 W for 5-10 minutes; Glycidyl methacrylate is used as the core monomer, accounting for 5-10% of the mass of the fine fiber. 0.5-1% benzophenone is added as a photosensitizer. Under ultraviolet light, it is irradiated for 10-15 minutes to initiate surface free radical polymerization through hydrogen transfer reaction. The fibers were immersed in KH590 / carbon nanotube composite solution, with the mass ratio of fine fibers to KH590 / carbon nanotube composite solution being 1:7-10. Ultrasonic-assisted directional arrangement of nanotubes was achieved. The fibers were pre-cured at 50-60°C for 1-2 hours and post-cured at 100-120°C for 1.5-2 hours to form a three-dimensional cross-linked network and a chemically bonded interface to obtain modified fine fibers.

4. The method for preparing multi-scale toughened concrete according to claim 1, characterized in that: S2 is specifically: using the sol-gel method to coat the surface of silica fume with nanoparticles layer to form an SSF core-shell structure, the mass ratio of silica fume to nano-silica with a particle size of 20-50 nm is 8-9:1-3, after centrifugation, microwave drying is carried out under nitrogen protection with a power of 700-800 W and a time of 10-15 min; The metakaolin was microwave calcined under nitrogen protection. From amorphous to Transform, get metakaolin; With the help of 40-50kHz ultrasonic, the composite dispersant The low shrinkage auxiliary cementitious material is obtained by gradient mixing of metakaolin and SSF core-shell structure; The mass ratio of composite dispersant, metakaolin and SSF core-shell structure is 0.4-0.8:6-8:7-9; Mix for 20-30 minutes to quickly hydrate and form a skeleton; Second stage mixing 40-60min; The three stages were mixed for 1-2 hours.

5. The method for preparing multi-scale toughened concrete according to claim 1, characterized in that: S3 specifically comprises: mixing the nanoclay and oxalic acid solution at a solid-liquid ratio of 1:3-5, ultrasonically treating for 30-45 minutes, and centrifuging to obtain activated clay; HCSA high-performance concrete expansion agent particles are immersed in potassium dihydrogen phosphate-ethanol suspension for 40-60 minutes and dried at 100-120°C to form a moisture-proof layer on the HCSA surface. The activated clay and HCSA are evenly mixed to obtain a composite precursor; Hollow glass microspheres with a particle size of 50-100 μm are placed in a 20-30% magnesium nitrate solution, and the solution is evacuated by a vacuum pump for 20-30 minutes to remove the gas inside the microspheres. The solution is then filtered to obtain glass microspheres uniformly loaded with magnesium nitrate. After loading is completed, the glass beads are dried by gradient temperature increase; Staged calcination to form MgO coating: First, heat the sample to 200-300°C at a rate of 3-5°C / min to remove residual moisture and organic matter; Then, the temperature is raised to 600-620°C at a rate of 2-4°C / min to decompose the magnesium nitrate into magnesium oxide, thereby obtaining glass microspheres loaded with magnesium oxide; The glass microbeads loaded with magnesium oxide are added to the composite precursor, and the mixture is stirred uniformly at 40-50° C. for 20-30 minutes to obtain a shrinkage compensating agent.

6. The method for preparing multi-scale toughened concrete according to claim 2, characterized in that: S4 specifically comprises ferroaluminate cement, low shrinkage auxiliary cementitious material, water reducer, shrinkage compensator and fine aggregate, which are stirred at a low speed of 100-200 r / min for 3-5 minutes to obtain a dry mix; The modified fine fibers are mixed with water and dispersed with the aid of ultrasound to form a stable suspension of 8-10 wt%, which is the fine fiber dispersion; Add the fine fiber dispersion and the remaining water to the dry mix, stir at a high speed of 280-350 r / min for 5-8 minutes, and then stir at a low speed of 100-200 r / min for 2-4 minutes to obtain a wet mix; Add modified crude fiber to the wet mix and stir at a low speed of 100-180 r / min for 3-4 minutes to obtain a mixed material to avoid fiber orientation disorder.

7. The method for preparing multi-scale toughened concrete according to claim 2, characterized in that: S6 specifically includes: one stage of curing for 1-2 hours at a temperature of 30-40°C, sealed curing to inhibit plastic shrinkage; The second stage of curing is 2-3 hours, steam curing, to promote the hydration of the expansion agent and compensate for autogenous shrinkage; Three-stage curing for 3-5 hours, curing at room temperature, nano clay continuously releases moisture to achieve internal curing.

8. The method for preparing multi-scale toughened concrete according to claim 2, characterized in that: The water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder.

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