Multi-scale toughened concrete and preparation method thereof

Abstract

The invention discloses multi-scale toughened concrete and a preparation method thereof, and belongs to the technical field of high leakage, and the multi-scale toughened concrete comprises aluminoferrite cement, a low-shrinkage auxiliary cementing material, a water reducing agent, multi-scale composite fibers, a shrinkage compensation agent, fine aggregate, coarse aggregate and water. A traditional toughening mode is broken through, a physical-chemical composite connection interface is established through a magnetron sputtering metal gradient coating of crude fibers and a laser-induced dendritic crystal structure, a strain hysteresis effect is triggered under an impact load, impact energy is converted into interface phase change energy, and a high-efficiency energy dissipation channel is formed; an amino functional group and free radical cross-linked network is introduced into the fine fibers, and the fibers are endowed with microcosmic dynamic enhancement capability in combination with directional arrangement of the carbon nanotubes, so that the concrete forms cooperative interaction between macroscopic crack bridging and microcosmic crack inhibition, the crack resistance under complex stress is remarkably improved, and microcrack propagation is effectively inhibited.

Description

Technical Field

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

[0002] Concrete products are brittle and have a high risk of cracking during production and application. External corrosive media are easily introduced into the matrix, resulting in corrosion and damage to the concrete itself, and at the same time inducing steel bar corrosion, reducing the durability and service life of concrete products. In marine environments and saline-alkali environments, the structures of concrete products are often subjected to the combined action of multiple complex stresses, such as wave loads, water flow impact forces, ship impact forces, etc. in the ocean, which will further accelerate crack generation and damage. The high toughness of multi-scale toughened concrete can, to a certain extent, resist crack propagation caused by these complex stresses, improve the integrity and stability of the structure, extend the service life of the structure, and reduce maintenance costs.

[0003] For example, in Chinese Patent CN115650667B, steel fibers and micro-scale fibers are combined, attempting to synergistically toughen through macroscopic crack bridging and microscopic crack inhibition. However, the steel fibers and the matrix are mainly combined through physical anchoring, while the micro-scale fibers rely on chemical interface treatment to enhance bonding. When the steel fibers and micro-scale fibers are directly mixed with the matrix, after long-term use, the fiber-matrix interface transition zone may become weak, the load transfer efficiency may decrease, and the multi-scale synergistic effect may be weakened.

[0004] In addition, although the high dosage of supplementary cementitious materials (fly ash + silica fume) improves the compactness, the autogenous shrinkage cracks instead increase the porosity. Once the leakage channels are formed, media such as chloride ions and moisture rapidly penetrate along the channels, leading to steel bar corrosion and freeze-thaw damage. Summary of the Invention

[0005] In view of the above-mentioned drawbacks 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 realized through the following technical solutions:

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

[0008] 75 - 84 parts of ferrite cement;

[0009] 21 - 32 parts of low shrinkage supplementary cementitious materials;

[0010] 0.8 - 1.5 parts of water reducing agent;

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

[0012] 2 - 3 parts of 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 of coarse aggregate (stones);

[0015] 38 - 45 parts of water;

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

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

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

[0019] The preparation method of the multi - scale toughened concrete includes the following steps:

[0020] S1: Fiber modification;

[0021] Pretreatment of coarse fiber: The steel fiber is subjected to composite oxidation pickling to remove the surface oxide layer, followed by microwave - assisted plasma cleaning and then drying;

[0022] Modification of coarse fiber: Magnetron sputtering is used to deposit a nickel - copper gradient layer to enhance the chemical anchoring force with the matrix;

[0023] Post - treatment of coarse fiber: Laser micro - melting is carried out under nitrogen protection to form a dendritic interlocking structure of the nickel - copper gradient layer to obtain modified coarse fiber;

[0024] Pretreatment of fine fiber: Bombardment of silicon carbide fiber with nitrogen - argon mixed plasma to synchronously achieve surface etching and amino functionalization;

[0025] Modification of fine fiber: Glycidyl methacrylate is used as the core monomer, and benzophenone is added as a photosensitizer to initiate surface free - radical polymerization under ultraviolet light irradiation;

[0026] Post - treatment of fine fiber: Impregnation with KH590 / carbon nanotube composite solution, and ultrasonic - assisted orientation arrangement of nanotubes is achieved, followed by curing to obtain modified fine fiber;

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

[0028] The sol - gel method is used to coat a nano layer on the surface of silica fume to form an SSF core - shell structure, followed by centrifugal separation and drying;

[0029] Metakaolin is subjected to microwave calcination under nitrogen protection to make From the amorphous state to transform, and obtain metakaolin;

[0030] With the cooperation of a composite dispersant and assisted by ultrasound, gradually mix metakaolin with the SSF core-shell structure to obtain a low-shrinkage auxiliary cementitious material;

[0031] S3: Prepare a shrinkage compensator;

[0032] Mix montmorillonite-type nano-clay with an oxalic acid solution, and obtain activated clay after centrifugation;

[0033] Impregnate HCSA high-performance concrete expansion agent particles with a potassium dihydrogen phosphate-ethanol suspension, dry them, form a moisture-proof layer on the surface of HCSA, and uniformly mix the activated clay and HCSA to obtain a composite precursor;

[0034] Place hollow glass microspheres in a magnesium nitrate solution, and evacuate the gas inside the microspheres through a vacuum pump;

[0035] After the loading is completed, conduct gradient temperature rise drying on the glass microspheres;

[0036] Conduct staged calcination to form an MgO coating, and obtain glass microspheres loaded with magnesium oxide;

[0037] Add the glass microspheres loaded with magnesium oxide to the composite precursor, and uniformly stir to obtain a shrinkage compensator;

[0038] S4: Fiber dispersion and mixing process

[0039] Prepare a dry mix. Slowly stir calcium aluminate cement, low-shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate to obtain a dry mix;

[0040] Prepare a fine fiber dispersion liquid. Mix the modified fine fibers with water and disperse them with ultrasonic assistance to form a stable suspension, which is the fine fiber dispersion liquid;

[0041] Prepare a wet mix: Add the fine fiber dispersion liquid and the remaining water to the dry mix, stir at high speed and then at low speed to obtain a wet mix;

[0042] Incorporate coarse fibers. Add the modified coarse fibers to the wet mix and stir at low speed to obtain a mixed material;

[0043] S5: Pour the mixed material into a mold, and remove the mold after hardening;

[0044] S6: Gradient curing to obtain multi-scale toughened concrete.

[0045] Further, S1 is specifically as follows: Steel fibers with a diameter of 0.15 - 0.25 mm are subjected to composite oxidative pickling (a mixed solution of 5% citric acid + 3% oxalic acid, for 30 - 40 min) to remove the surface oxide layer, followed by microwave-assisted plasma cleaning (in an argon atmosphere, power 200 - 300 W, for 5 - 8 min), and then dried at 40 - 50 °C to remove micron-scale oxides;

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

[0047] Laser micromelting is carried out under nitrogen protection (power 50 - 80 W, scanning speed 100 - 120 mm / s) to form a dendritic interlocking structure in the nickel-copper gradient layer, obtaining modified coarse fibers and enhancing the interfacial shear strength;

[0048] The silicon carbide fibers with a diameter of 8 - 15 μm are bombarded with a nitrogen-argon mixed plasma ( :Ar = 3:7) at a power of 350 - 400 W for 5 - 10 min to simultaneously achieve surface etching and amino functionalization;

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

[0050] The fine fibers are impregnated with a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion). The mass ratio of the fine fibers to the KH590 / carbon nanotube composite solution is 1:7 - 10. Through ultrasonic assistance (40 kHz, 30 min), the nanotubes are oriented, pre-cured at 50 - 60 °C for 1 - 2 h, and post-cured at 100 - 120 °C for 1.5 - 2 h to form a three-dimensional crosslinked network and a chemical bonding interface, obtaining modified fine fibers.

[0051] Further, S2 is specifically as follows: The sol-gel method is used to coat a nano layer on the surface of silica fume to form an SSF (silica fume - nano layer) core-shell structure. The mass ratio of silica fume to nano-silica (particle size 20 - 50 nm) is 8 - 9:1 - 3. After centrifugal separation, microwave drying is carried out under nitrogen protection (power 700 - 800 W, time 10 - 15 min) to avoid agglomeration caused by hydroxyl condensation;

[0052] The metakaolin is subjected to microwave calcination (power 800 W, time 15 min) under nitrogen protection to make transform from the amorphous state to obtaining metakaolin, improving the reactivity with the SSF core-shell structure;

[0053] Under the coordination of a composite dispersant (a polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), through 40 - 50 kHz ultrasonic assistance, the metakaolin and the SSF core-shell structure are mixed in a gradient manner to obtain a low-shrinkage auxiliary cementitious material;

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

[0055] For the first-stage mixing (20 - 30 min), 7 / 15 of the SSF core-shell structure and 1 / 5 of the metakaolin are used to rapidly hydrate and form a skeleton;

[0056] For the second-stage mixing (40 - 60 min), 1 / 3 of the SSF core-shell structure and 1 / 3 of the metakaolin are used;

[0057] For the third-stage mixing (1 - 2 h), 1 / 5 of the SSF core-shell structure and 7 / 15 of the metakaolin are used.

[0058] Furthermore, S3 specifically is: Mix montmorillonite-type nanoclay with 0.8% oxalic acid solution at a solid-liquid ratio of 1:3 - 5, perform ultrasonic treatment at 60 °C (40 kHz, 500 W) for 30 - 45 min, and obtain activated clay after centrifugation;

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

[0060] The hollow glass microspheres (particle size 50 - 100 μm) are placed in a 20 - 30% magnesium nitrate solution, and the air inside the microspheres is evacuated to -0.1 MPa through a vacuum pump and maintained for 20 - 30 min to remove the internal gas of the microspheres, ensuring that the magnesium nitrate solution fully penetrates into the inner cavity of the microspheres, and then the glass microspheres uniformly loaded with magnesium nitrate are obtained by filtration;

[0061] After the loading is completed, the glass microspheres are dried by gradient heating (50 °C → 80 °C → 120 °C) to avoid the structure of the microspheres from cracking due to rapid water loss and ensure that magnesium nitrate is uniformly deposited on the inner wall;

[0062] Form an MgO coating by staged calcination:

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

[0064] Then, heat it at a rate of 2 - 4 °C / min to 600 - 620 °C to decompose magnesium nitrate into magnesium oxide, and then obtain glass microspheres loaded with magnesium oxide;

[0065] Add the glass microspheres loaded with magnesium oxide to the composite precursor, and stir evenly at 40 - 50 °C for 20 - 30 min to obtain a shrinkage compensator.

[0066] Furthermore, S4 specifically is to obtain a dry - mix material by slowly stirring (100 - 200 r / min, 3 - 5 min) ferric aluminate cement, low - shrinkage auxiliary cementitious material, water - reducing agent, shrinkage compensator, and fine aggregate;

[0067] Mix the modified fine fibers with water, and disperse them 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 material, stir at high speed (280 - 350 r / min, 5 - 8 min) and then at low speed (100 - 200 r / min, 2 - 4 min) to obtain a wet - mix material;

[0069] Add the modified coarse fibers to the wet - mix material, and stir at low speed (100 - 180 r / min, 3 - 4 min) to obtain a mixed material, avoiding disordered fiber orientation.

[0070] Furthermore, S6 specifically is: the first - stage curing for 1 - 2 h: temperature 30 - 40 °C, sealed curing, inhibiting plastic shrinkage;

[0071] the second - stage curing for 2 - 3 h: steam curing at 60 °C, promoting the hydration of the expansive agent, compensating for autogenous shrinkage;

[0072] the third - stage curing for 3 - 5 h: normal - temperature curing, the nano - clay continuously releases water, realizing internal curing.

[0073] Furthermore, the water - reducing agent is a compound of polycarboxylate water - reducing agent and phosphate retarder with a mass ratio of 10:1.

[0074] The beneficial effects of the present invention compared with the prior art are as follows:

[0075] 1. The present invention breaks through the traditional toughening mode. By means of the magnetron sputtered metal gradient coating on the coarse fiber and the laser-induced dendritic structure, a physical-chemical composite connection interface is established. Under impact load, the strain hysteresis effect is triggered, and the impact energy is converted into interface phase change energy to form an efficient energy dissipation channel. The fine fiber introduces amino functional groups and a free radical crosslinking network, combined with the directional arrangement of carbon nanotubes, endowing the fiber with microscopic dynamic strengthening ability, enabling the concrete to form a synergistic interaction between macroscopic crack bridging and microscopic crack inhibition, significantly improving the crack resistance under complex stresses, and effectively inhibiting the propagation of microcracks.

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

[0077] 3. The multi-effect synergistic effect of the shrinkage compensator in the present invention is outstanding in improving durability. The activated clay enhances the adsorption and release ability through the interlayer structure transformation, combined with the moisture-proof coating design of the HCSA expansive agent, ensuring the stability and uniformity of expansion compensation; the magnesium oxide coating of the hollow glass microspheres not only serves as a micro-expansion source to compensate for shrinkage, but also hinders the chloride ion penetration path by refining the pore structure, jointly constructing a dense pore network with the auxiliary cementitious material, effectively blocking the intrusion of harmful media, and significantly reducing the risks of steel bar corrosion and freeze-thaw damage caused by leakage.

[0078] 4. The present invention overcomes the problems such as the weak interface transition zone between the fiber and the matrix and the attenuation of load transfer efficiency in the traditional fiber-reinforced system, and establishes a stable reinforcement network through physical and chemical synergistic modification; at the same time, it solves the durability deterioration caused by the autogenous shrinkage of high-volume auxiliary cementitious materials, realizes the balance between shrinkage compensation and structural strengthening, provides a comprehensive solution with high toughness, controllable expansion and durability for concrete products serving in complex environments, and significantly extends the service life of the structure and reduces the maintenance cost under complex stress environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0080] Figure 1 Electron micrograph of the multi-scale toughened concrete prepared in Comparative Example 3;

[0081] Figure 2 Electron micrograph of the multi-scale toughened concrete prepared in Comparative Example 4;

[0082] Figure 3 Electron micrograph of the multi-scale toughened concrete prepared in Example 3. Detailed implementation mode

[0083] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0084] Example 1: This example provides a multi-scale toughened concrete, which, by weight, comprises the following components:

[0085] 84 parts of ferroaluminate cement;

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

[0087] 1.5 parts of water-reducing agent;

[0088] 13 parts of multi-scale composite fiber;

[0089] 3 parts of shrinkage compensator;

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

[0091] 180 parts of coarse aggregate (stones);

[0092] 45 parts of water;

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

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

[0095] The shrinkage compensator comprises activated clay, HCSA and glass microspheres loaded with magnesium oxide with a mass ratio of 1.6:2.5:1.8.

[0096] The preparation method of the multi-scale toughened concrete comprises the following steps:

[0097] S1: Fiber modification;

[0098] Coarse fiber pretreatment: The steel fiber with a diameter of 0.25 mm is subjected to composite oxidation pickling (a mixed solution of 5% citric acid + 3% oxalic acid, 40 min) to remove the surface oxide layer, followed by microwave-assisted plasma cleaning (argon atmosphere, power 300 W, 8 min) and then drying at 50 °C to remove micron-scale oxides.

[0099] Coarse fiber modification: Magnetron sputtering is used to deposit a nickel-copper gradient layer (0.2 μm Ni layer + 0.3 μm Cu layer) to enhance the chemical anchoring force with the matrix.

[0100] Coarse fiber post-treatment: Laser micromelting is carried out under nitrogen protection (power 80 W, scanning speed 120 mm / s) to form a dendritic interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers and enhance the interfacial shear strength.

[0101] Fine fiber pretreatment: The silicon carbide fiber with a diameter of 15 μm is bombarded with a nitrogen-argon mixed plasma ( :Ar = 3:7) at a power of 400 W for 10 min to simultaneously achieve surface etching and amino-functionalization.

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

[0103] Fine fiber post-treatment: Immerse in a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion). The mass ratio of the fine fiber to the KH590 / carbon nanotube composite solution is 1:10. Through ultrasonic assistance (40 kHz, 30 min), the nanotubes are oriented, pre-cured at 60 °C for 2 h, and post-cured at 120 °C for 2 h to form a three-dimensional crosslinked network and a chemical bonding interface to obtain modified fine fibers.

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

[0105] The sol-gel method is used to coat a nano layer on the surface of silica fume to form a core-shell structure of SSF (silica fume - nano layer). The mass ratio of silica fume to nano-silica (particle size 50 nm) is 8 - 9:1 - 3. After centrifugal separation, microwave drying is carried out under nitrogen protection (power 800 W, time 15 min) to avoid agglomeration caused by hydroxyl condensation.

[0106] Metakaolin is subjected to microwave calcination (power 800 W, time 15 min) under nitrogen protection to transform from the amorphous state to a certain state, obtaining metakaolin, and improving the reactivity with the SSF core-shell structure;

[0107] With the cooperation of a composite dispersant (a polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), under the assistance of 50 kHz ultrasonic waves, metakaolin and the SSF core-shell structure are subjected to gradient mixing to obtain a low-shrinkage auxiliary cementitious material;

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

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

[0110] For the second-stage mixing (60 min), 1 / 3 of the SSF core-shell structure and 1 / 3 of the metakaolin;

[0111] For the third-stage mixing (2 h), 1 / 5 of the SSF core-shell structure and 7 / 15 of the metakaolin;

[0112] S3: Prepare a shrinkage compensator;

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

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

[0115] Hollow glass microspheres (particle size 100 μm) are placed in a 30% magnesium nitrate solution, and the air inside the microspheres is evacuated to -0.1 MPa through a vacuum pump and maintained for 30 min to remove the internal gas of the microspheres, ensuring that the magnesium nitrate solution fully penetrates into the inner cavity of the microspheres, and glass microspheres uniformly loaded with magnesium nitrate are obtained by filtration;

[0116] After the loading is completed, the glass microspheres are dried by gradient heating (50 °C → 80 °C → 120 °C) to avoid the structure of the microspheres from cracking due to rapid water loss, and at the same time ensure that magnesium nitrate is uniformly deposited on the inner wall;

[0117] Segmented calcination is carried out to form an MgO coating:

[0118] First, heat it up to 300 °C at a rate of 5 °C / min to remove residual moisture and organic substances;

[0119] Then, heat it up to 620 °C at a rate of 4 °C / min to decompose magnesium nitrate into magnesium oxide, and thus obtain glass microspheres loaded with magnesium oxide;

[0120] Compensation principle: When the external load or shrinkage stress reaches the critical value of the compressive strength of the microspheres, the microspheres undergo brittle fracture, and the MgO on the inner wall of the microspheres is exposed and released into the crack area. The released MgO reacts with the pore water of the concrete: , effectively compensating for shrinkage, It can further react with to generate magnesium carbonate ( ), filling the pores and improving the density;

[0121] Add the glass microspheres loaded with magnesium oxide to the composite precursor, and uniformly stir at 50 °C for 30 min to obtain a shrinkage compensator;

[0122] S4: Fiber dispersion and mixing process

[0123] Prepare the dry mixture. Stir ferrite cement, low-shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate at a low speed (200 r / min, 5 min) to obtain the dry mixture;

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

[0125] Prepare the fine fiber dispersion liquid. Mix the modified fine fibers with water and disperse them ultrasonically (frequency 40 kHz, power 500 W, 5 min) to form a 10 wt% stable suspension, which is the fine fiber dispersion liquid;

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

[0127] Add the modified coarse fibers to the wet mixture and stir at a low speed (180 r / min, 4 min) to obtain the mixed material, avoiding disordered fiber orientation;

[0128] S5: Pour the mixed material into a mold, and remove the mold after hardening;

[0129] S6: Gradient curing to obtain multi-scale toughened concrete;

[0130] First-stage curing (2 h): Temperature 40 °C, sealed curing to inhibit plastic shrinkage;

[0131] Second-stage curing (3 h): Steam curing at 60 °C to promote the hydration of the expansive agent and compensate for autogenous shrinkage;

[0132] Three-stage curing (5h): Curing at room temperature, with the nano-clay continuously releasing water to achieve internal curing.

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

[0134] 75 parts of ferroaluminate cement;

[0135] 21 parts of low-shrinkage auxiliary cementitious material;

[0136] 0.8 part of water-reducing agent;

[0137] 9 parts of multi-scale composite fiber;

[0138] 2 parts of shrinkage compensator;

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

[0140] 140 parts of coarse aggregate (stones);

[0141] 38 parts of water;

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

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

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

[0145] The preparation method of the multi-scale toughened concrete includes the following steps:

[0146] S1: Fiber modification;

[0147] Pretreatment of the coarse fiber: The steel fiber with a diameter of 0.15mm is subjected to composite oxidation pickling (5% citric acid + 3% oxalic acid mixture, 30min) to remove the surface oxide layer, followed by microwave-assisted plasma cleaning (argon atmosphere, power 200W, 5min) and then drying at 40°C to remove micron-scale oxides;

[0148] Modification of the coarse fiber: Magnetron sputtering is used to deposit a Ni-Cu gradient layer (0.2μm Ni layer + 0.3μm Cu layer) to enhance the chemical anchoring force with the matrix;

[0149] Post-treatment of coarse fibers: Laser micromelting is carried out under nitrogen protection (power 50 W, scanning speed 100 mm / s) to form a dendritic interlocking structure in the nickel-copper gradient layer, obtaining modified coarse fibers and enhancing the interfacial shear strength.

[0150] Pretreatment of fine fibers: The silicon carbide fibers with a diameter of 8 μm are bombarded with a nitrogen-argon mixed plasma ( :Ar = 3:7) at a power of 350 W for 5 min to simultaneously achieve surface etching and amino functionalization.

[0151] Modification of fine fibers: Glycidyl methacrylate (5% of the mass of fine fibers) is used as the core monomer, and 0.5% benzophenone (here referring to the mass ratio of silicon carbide fibers to benzophenone being 100:0.5) is added as a photosensitizer. Under ultraviolet light with a wavelength of 254 nm and an irradiation intensity of 30 mW / , for a time of 10 min, surface radical polymerization is initiated through a hydrogen transfer reaction.

[0152] Post-treatment of fine fibers: Impregnate with a KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion). The mass ratio of fine fibers to the KH590 / carbon nanotube composite solution is 1:7. Through ultrasonic assistance (40 kHz, 30 min), the nanotubes are oriented, pre-cured at 50 °C for 1 h, and post-cured at 100 °C for 1.5 h to form a three-dimensional crosslinked network and a chemical bonding interface, obtaining modified fine fibers.

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

[0154] Using the sol-gel method to coat a nano layer on the surface of silica fume to form an SSF (silica fume - nano layer) core-shell structure. The mass ratio of silica fume to nano-silica (particle size 20 nm) is 8:1. After centrifugal separation, microwave drying is carried out under nitrogen protection (power 700 W, time 10 min) to avoid agglomeration caused by hydroxyl condensation.

[0155] Microwave calcination of metakaolin is carried out under nitrogen protection (power 800 W, time 15 min) to transform Al2O3 from an amorphous state to obtaining metakaolin and improving its reactivity with the SSF core-shell structure.

[0156] With the cooperation of a composite dispersant (a polycarboxylate water reducer and hydroxypropyl methylcellulose with a mass ratio of 9:1), through 40 kHz ultrasonic assistance, metakaolin and the SSF core-shell structure are gradient mixed to obtain low-shrinkage auxiliary cementitious materials.

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

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

[0159] For the second-stage mixing (40 min), 1 / 3 of the SSF core-shell structure and 1 / 3 of the metakaolin;

[0160] For the third-stage mixing (1 h), 1 / 5 of the SSF core-shell structure and 7 / 15 of the metakaolin;

[0161] S3: Prepare the shrinkage compensator;

[0162] Mix montmorillonite-type nano-clay with 0.8% oxalic acid solution at a solid-liquid ratio of 1:3, and ultrasonically treat it at 60 °C (40 kHz, 500 W) for 30 - 45 min. After centrifugation, activated clay is obtained;

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

[0164] Put hollow glass microspheres (particle size 50 μm) into a 20 - 30% magnesium nitrate solution, evacuate to -0.1 MPa through a vacuum pump, and maintain for 20 min to remove the internal gas of the microspheres, ensuring that the magnesium nitrate solution fully penetrates into the inner cavity of the microspheres. Filter to obtain glass microspheres uniformly loaded with magnesium nitrate;

[0165] After loading, the glass microspheres are dried by gradient heating (50 °C → 80 °C → 120 °C) to avoid the structure of the microspheres from cracking due to rapid water loss, and at the same time ensure that magnesium nitrate is evenly deposited on the inner wall;

[0166] Form an MgO coating by staged calcination:

[0167] First, heat up at a rate of 3 °C / min to 200 °C to remove residual moisture and organic matter;

[0168] Then, heat up at a rate of 2 °C / min to 600 °C to decompose magnesium nitrate into magnesium oxide, and then obtain glass microspheres loaded with magnesium oxide;

[0169] Add the glass microspheres loaded with magnesium oxide to the composite precursor and stir evenly at 40 °C for 20 min to obtain the shrinkage compensator;

[0170] S4: Fiber dispersion and mixing process

[0171] Preparation of dry-mixed material: Iron aluminate cement, low-shrinkage supplementary cementitious material, water reducer, shrinkage compensator, and fine aggregate are stirred at a low speed (100 r / min, 3 min) to obtain the dry-mixed material;

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

[0173] Fine fiber dispersion: Modified fine fibers and water are mixed, and ultrasonic-assisted dispersion (frequency 40 kHz, power 500 W, 5 min) is carried out to form a stable suspension of 8 wt%, which is the fine fiber dispersion;

[0174] Preparation of wet-mixed material: The fine fiber dispersion and the remaining water are added to the dry-mixed material, and after high-speed stirring (280 r / min, 5 min), low-speed stirring (100 r / min, 2 min) is carried out to obtain the wet-mixed material;

[0175] Incorporation of coarse fibers: Modified coarse fibers are added to the wet-mixed material, and low-speed stirring (100 r / min, 3 min) is carried out to obtain the mixed material, avoiding disorder of fiber orientation;

[0176] S5: The mixed material is loaded into a mold and demolded after hardening;

[0177] S6: Gradient curing is carried out to obtain multi-scale toughened concrete;

[0178] First-stage curing (1 h): Temperature 30 °C, sealed curing, inhibiting plastic shrinkage;

[0179] Second-stage curing (2 h): Steam curing at 60 °C, promoting the hydration of the expansive agent and compensating for autogenous shrinkage;

[0180] Third-stage curing (3 h): Normal temperature curing, continuous release of water by nano-clay, realizing internal curing.

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

[0182] 81 parts of iron aluminate cement;

[0183] 25 parts of low-shrinkage supplementary cementitious material;

[0184] 1.1 parts of water reducer;

[0185] 10 parts of multi-scale composite fiber;

[0186] 2.6 parts of shrinkage compensator;

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

[0188] 150 parts of coarse aggregate (stones);

[0189] 41 parts of water;

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

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

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

[0193] The preparation method of the multi-scale toughened concrete includes the following steps:

[0194] S1: Fiber modification;

[0195] Coarse fiber pretreatment: Steel fibers with a diameter of 0.2 mm are subjected to composite oxidation pickling (a mixture of 5% citric acid + 3% oxalic acid, 38 min) to remove the surface oxide layer, followed by microwave-assisted plasma cleaning (argon atmosphere, power 250 W, 7 min) and then drying at 41 °C to remove micron-scale oxides;

[0196] Coarse fiber modification: Magnetron sputtering is used to deposit a nickel-copper gradient layer (0.2 μm Ni layer + 0.3 μm Cu layer) to enhance the chemical anchoring force with the matrix;

[0197] Coarse fiber post-treatment: Laser micro-melting is carried out under nitrogen protection (power 60 W, scanning speed 110 mm / s) to form a dendritic interlocking structure in the nickel-copper gradient layer to obtain modified coarse fiber and enhance the interfacial shear strength;

[0198] Fine fiber pretreatment: Nitrogen-argon mixed plasma ( :Ar = 3:7) bombards silicon carbide fibers with a diameter of 10 μm at a power of 380 W for 9 min to simultaneously achieve surface etching and amino functionalization;

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

[0200] Post-treatment of fine fibers: impregnate with KH590 / carbon nanotube composite solution (5% KH590 + 0.5% carboxylated carbon nanotube ethanol dispersion), with the mass ratio of fine fibers to KH590 / carbon nanotube composite solution being 1:8. Achieve the oriented arrangement of nanotubes through ultrasonic assistance (40 kHz, 30 min), pre-cure at 52 °C for 2 h, and post-cure at 105 °C for 2 h to form a three-dimensional cross-linked network and a chemical bonding interface, obtaining modified fine fibers;

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

[0202] Adopt the sol-gel method to coat a nano layer on the surface of silica fume to form a core-shell structure of SSF (silica fume - nano layer). The mass ratio of silica fume to nano-silica (particle size 40 nm) is 8:2. After centrifugal separation, perform microwave drying under nitrogen protection (power 730 W, time 15 min) to avoid agglomeration caused by hydroxyl condensation;

[0203] Calcine metakaolin under nitrogen protection by microwave (power 800 W, time 15 min) to make it transform from amorphous state to obtain metakaolin and improve the reactivity with the SSF core-shell structure;

[0204] Under the coordination of a composite dispersant (a polycarboxylate superplasticizer and hydroxypropyl methylcellulose with a mass ratio of 9:1), through 44 kHz ultrasonic assistance, gradually mix metakaolin with the SSF core-shell structure to obtain low-shrinkage auxiliary cementitious materials;

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

[0206] First-stage mixing (25 min), 7 / 15 of the SSF core-shell structure, 1 / 5 of the metakaolin, for rapid hydration to form a framework;

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

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

[0209] S3: Preparation of shrinkage compensator;

[0210] Mix montmorillonite-type nano-clay with 0.8% oxalic acid solution at a solid-liquid ratio of 1:4, perform ultrasonic treatment at 60 °C (40 kHz, 500 W) for 44 min, and obtain activated clay after centrifugation;

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

[0212] The hollow glass microspheres (particle size 80 μm) are placed in a 25% magnesium nitrate solution, and the air in the microspheres is evacuated to -0.1 MPa by a vacuum pump and maintained for 25 min to remove the internal gas of the microspheres, ensuring that the magnesium nitrate solution fully penetrates into the inner cavity of the microspheres. The glass microspheres uniformly loaded with magnesium nitrate are obtained by filtration;

[0213] After the loading is completed, the glass microspheres are dried by gradient heating (50 °C → 80 °C → 120 °C) to avoid the structure of the microspheres being broken due to rapid water loss, and at the same time ensure that magnesium nitrate is uniformly deposited on the inner wall;

[0214] Segmented calcination is carried out to form an MgO coating:

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

[0216] Then, the temperature is raised to 610 °C at a rate of 3 °C / min, so that magnesium nitrate decomposes into magnesium oxide, and then the glass microspheres loaded with magnesium oxide are obtained;

[0217] The glass microspheres loaded with magnesium oxide are added to the composite precursor and stirred evenly at 45 °C for 22 min to obtain a shrinkage compensator;

[0218] S4: Fiber dispersion and mixing process

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

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

[0221] Fine fiber dispersion liquid: The modified fine fibers and water are mixed, and ultrasonic wave-assisted dispersion (frequency 40 kHz, power 500 W, 5 min) is carried out to form a 10 wt% stable suspension, which is the fine fiber dispersion liquid;

[0222] Preparation of wet mix: The fine fiber dispersion liquid and the remaining water are added to the dry mix, and after high-speed stirring (300 r / min, 6 min), low-speed stirring (120 r / min, 3 min) is carried out to obtain a wet mix;

[0223] Incorporation of coarse fibers: The modified coarse fibers are added to the wet mix, and low-speed stirring (160 r / min, 4 min) is carried out to obtain a mixed material, avoiding disordered fiber orientation;

[0224] S5: Load the mixture into a mold and remove the mold after hardening.

[0225] S6: Gradient curing to obtain multi-scale toughened concrete.

[0226] First-stage curing (1 h): Temperature 38°C, sealed curing to inhibit plastic shrinkage.

[0227] Second-stage curing (2 h): 60°C steam curing to promote the hydration of the expansive agent and compensate for autogenous shrinkage.

[0228] Third-stage curing (4 h): Normal temperature curing, the nano-clay continuously releases water to achieve internal curing.

[0229] Comparative Example 1: The difference between this comparative example and Example 3 is that the coarse fibers and fine fibers were not modified separately.

[0230] Comparative Example 2: The difference between this comparative example and Example 3 is that when preparing the supplementary cementitious material, the components were not modified but directly mixed.

[0231] S2 specifically includes: Preparation of the supplementary cementitious material.

[0232] Mix silica fume and nano-silica (particle size 40 nm) in a mass ratio of 8:2, and perform microwave drying (power 730 W, time 15 min) under nitrogen protection to obtain mixture A.

[0233] Under the coordination of a composite dispersant (a polycarboxylate superplasticizer and hydroxypropyl methylcellulose with a mass ratio of 9:1), and with the assistance of 44 kHz ultrasonic waves, mix metakaolin and mixture A in a gradient manner to obtain the supplementary cementitious material.

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

[0235] First-stage mixing (25 min), 7 / 15 of mixture A and 1 / 5 of metakaolin, quickly hydrate to form a skeleton.

[0236] Second-stage mixing (50 min), 1 / 3 of mixture A and 1 / 3 of metakaolin.

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

[0238] Comparative Example 3: The shrinkage compensator was not added.

[0239] Comparative Example 4: Neither the shrinkage compensator was added nor the coarse fibers and fine fibers were modified.

[0240] Comparative Example 5: No shrinkage compensator was added, and the components were not modified during the preparation of the supplementary cementitious materials, but were directly mixed.

[0241] Experimental Example 1: SEM images of the multi-scale toughened concrete prepared in Example 3, Comparative Example 2 and Comparative Example 5 were taken respectively (as Figures 1-3 shown). It can be seen from the SEM that Figure 3 the surface structure of the concrete shows high density, the transition zones of the components are closely combined, the continuity of the interfacial transition zone is good, and there is no obvious separation phenomenon.

[0242] Figure 1 The surface structure of the concrete is relatively loose, the area of the region where the interfacial transition zone is closely combined is small, the continuity of the interfacial transition zone is poor, obvious separation phenomena can be seen in some regions, and the pores are relatively obvious.

[0243] Figure 2 The bonding strength of the interfacial transition zone is between Figure 1 and Figure 3 , showing that the interfacial transition zone is relatively closely combined, but the continuity is not as good as Figure 3 , and slight separation phenomena and a small number of pores can still be seen in some regions.

[0244] Experimental Example 2:

[0245] 2.1 The restricted expansion rate was detected according to GB 50119-2013. Specimens (100×100×300 mm) were formed using a longitudinal restrictor (reinforcement ratio 0.79%), and the curing conditions were the same as those of the gradient curing. The restricted expansion rate at 14 d was tested (the greater the restricted expansion rate, the better the compensating shrinkage effect of the concrete).

[0246] 2.2 According to GB / T 50082-2024, the autogenous shrinkage rate was detected according to the corrugated pipe method at a temperature of 20±2°C, and the autogenous shrinkage rate at 3 d was tested (the smaller the autogenous shrinkage rate, the better the anti-shrinkage performance of the concrete).

[0247] 2.3 The compressive strength and flexural strength at 28 d were detected according to GB / T 50081-2019. Cubes (100×100×100 mm) (compressive) and prisms (100×100×400 mm) (flexural) were prepared, and the loading rates were 0.5 MPa / s for compression and 0.05 MPa / s for flexure.

[0248] 2.4 The flexural toughness (deformation energy from 0 to 5.5 mm) was detected according to JGJ / T 221-2010, and specimens (100×100×400 mm) were prepared.

[0249] 2.5 According to the determination of chloride ion migration coefficient in GB / T 50082-2024, a core specimen with a diameter of φ100×50mm is prepared. The specimen is placed in a vacuum container, evacuated to -0.1MPa, and maintained for 20 - 30min to remove internal gases;

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

[0251] Through a chloride ion diffusion coefficient measuring instrument (such as NJ-RCM type), calculate the chloride ion migration coefficient (GB / T 50082-2024).

[0252] The test results are as follows:

[0253]

[0254] In the present invention, by modifying the coarse fibers and fine fibers respectively, the improvement of the multi-scale toughening effect is realized; among them, the modification of the 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 micro-melting further enhances the mechanical meshing effect, forming a multi-level physical-chemical composite connection. When subjected to an external impact, the interface between the metal coating and the matrix will produce a strain lag effect, and this hysteretic response of the microstructure can convert the impact energy into interface phase change energy, forming an effective energy dissipation channel. The modification of the fine fibers focuses on the introduction of surface active groups and nano-scale enhancement. Plasma bombardment realizes the synchronous introduction of amino functional groups while etching the micro-nano structure, and ultraviolet-induced surface polymerization constructs a free radical cross-linking network. The oriented arrangement and chemical bonding of carbon nanotubes endow the fine fibers with multi-scale enhancement and signal transmission capabilities. When micro-cracks expand in the concrete, the disentanglement and rearrangement of polymer segments can provide additional fracture energy, breaking through the stress transfer limit of traditional fiber reinforcement and expanding the strengthening mechanism from a simple bridging effect to a dynamic interaction including energy dissipation.

[0255] In the present invention, by modifying the components of the auxiliary gel material, the controllable expansion effect of the concrete is realized; among them, the core-shell structure formed after the surface of silica fume is coated with a nano 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. At the same time, the nano layer participates in the hydration reaction, generating more hydrated calcium silicate gel, filling the pores in the cement stone, reducing the porosity inside the cement stone, and thus improving the density. Metakaolin is calcined by microwave under nitrogen protection to make it transform from amorphous state to Under the cooperation of a composite dispersant, through ultrasonic assistance, The metakaolin is gradient-mixed with the SSF core-shell structure, enabling the auxiliary cementitious material to form a gradually changing reaction activity and controllable expansion performance from the inside to the outside within the concrete, so that the expansion stress inside the concrete is evenly dispersed and effectively constrained, thereby achieving a good controllable expansion effect.

[0256] In the present invention, by adding a shrinkage compensator to the concrete, the autogenous shrinkage rate and the chloride ion penetration depth are reduced; after mixing nano-clay with an oxalic acid solution and subjecting it to ultrasonic treatment, oxalic acid molecules can insert into the interlayer of montmorillonite, destroying its original crystal structure, expanding the interlayer spacing, weakening the interlayer bonding force, and increasing the activity and reactivity of montmorillonite. For the activated clay obtained after centrifugation, its interlayer channels become more flexible, providing favorable conditions for subsequent water molecule adsorption and release; after impregnating the HCSA high-performance concrete expansion agent particles with a potassium dihydrogen phosphate-ethanol suspension and drying, a moisture-proof layer is formed on the surface of the HCSA by potassium dihydrogen phosphate. This moisture-proof layer can effectively prevent the HCSA from absorbing moisture in the air during storage and transportation, thus avoiding deliquescence and agglomeration, and ensuring the activity and reaction uniformity of the expansion agent; the magnesium oxide coating inside the hollow glass microspheres acts as a micro-expansion source inside the concrete, capable of generating a micro-expansion effect to compensate for part of the shrinkage of the concrete. In addition, the magnesium oxide coating also has a certain barrier effect, which can hinder the penetration path of chloride ions and reduce the chloride ion penetration depth.

[0257] The shrinkage compensator of the present invention compensates for the concrete shrinkage through the expansion effect. The coarse fibers bear the main stress when the concrete is stressed, preventing the formation and propagation of macroscopic cracks, while the fine fibers bridge the cracks and dissipate energy at the microscopic level. The three act synergistically to greatly improve the toughness of the concrete;

[0258] The shrinkage compensator of the present invention generates a micro-expansion inside the concrete through the expansion effect, thereby compensating for the autogenous shrinkage of the concrete. The hydration products of silica fume and metakaolin can fill the pores in the concrete, increasing the rigidity and strength of the concrete and exerting a certain constraint on the expansion, making the expansion more uniform and stable, thereby further improving the restricted expansion effect. The core-shell structure of auxiliary cementitious materials such as silica fume and the crystal form transformation of metakaolin can optimize the pore structure of the concrete, reduce the porosity, and increase the density, providing 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, enabling the expansion energy of the shrinkage compensator to play a more efficient role 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 connected pores. At the same time, the addition of the auxiliary cementitious material further improves the pore distribution of the concrete, making the pores smaller and more uniform, reducing the connectivity of the pores, and thus effectively blocking the penetration paths of harmful substances such as chloride ions and reducing the leakage phenomenon.

[0259] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and 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, By weight parts, it includes the following components: 75 - 84 parts of ferroaluminate cement; 21 - 32 parts of low - shrinkage auxiliary cementitious material; 0.8 - 1.5 parts of water - reducing agent; 9 - 13 parts of multi - scale composite fiber; 2 - 3 parts of shrinkage compensator; 100 - 120 parts of fine aggregate; 140 - 180 parts of coarse aggregate; 38 - 45 parts of water; The low-shrinkage auxiliary cementitious material is a dense skeleton formed by the SSF core-shell structure and metakaolin through gradient mixing and staged hydration; The multi - scale composite fiber includes modified coarse fiber and modified fine fiber with a mass ratio of 4 - 6:1 - 2; The shrinkage compensator includes activated clay, HCSA and glass microspheres loaded with magnesium oxide with a mass ratio of 1 - 1.6:2 - 2.5:1.5 - 1.

8.

2. A preparation method of the multi-scale toughened concrete as described in claim 1, characterized in that, It includes the following steps: S1: Fiber modification; Pretreatment of coarse fiber, removing the surface oxide layer of steel fiber by composite oxidation pickling, increasing after microwave - assisted plasma cleaning and drying; Modification of coarse fiber, using magnetron sputtering to deposit a nickel - copper gradient layer to enhance the chemical anchoring force with the matrix; Post - treatment of coarse fiber, under nitrogen protection, laser micro - melting is carried out to make the nickel - copper gradient layer form a dendritic interlocking structure to obtain modified coarse fiber; Pretreatment of fine fiber, bombarding silicon carbide fiber with nitrogen - argon mixed plasma to synchronously achieve surface etching and amino functionalization; Modification of fine fiber, using glycidyl methacrylate as the core monomer, adding benzophenone as a photosensitizer, and initiating surface free - radical polymerization under ultraviolet irradiation; Post - treatment of fine fiber, impregnating with KH590 / carbon nanotube composite solution, realizing the directional arrangement of nanotubes through ultrasonic assistance, and curing to obtain modified fine fiber; S2: Preparation of low - shrinkage auxiliary cementitious material; A nano-layer was coated on the surface of silica fume by the sol-gel method to form an SSF core-shell structure, followed by centrifugal separation and drying; ​ The metakaolin is subjected to microwave calcination under nitrogen protection to make transform from the amorphous state to obtaining metakaolin; With the cooperation of a composite dispersant and assisted by ultrasound, metakaolin and the SSF core-shell structure are gradient-mixed to obtain a low-shrinkage auxiliary cementitious material; S3: Preparation of shrinkage compensator; Mix montmorillonite - type nano - clay with oxalic acid solution, and obtain activated clay after centrifugation; Immerse HCSA high - performance concrete expansion agent particles in potassium dihydrogen phosphate - ethanol suspension, dry, form a moisture - proof layer on the surface of HCSA, and mix the activated clay and HCSA evenly to obtain a composite precursor; Place hollow glass microspheres in magnesium nitrate solution, and evacuate the internal gas of the microspheres through a vacuum pump; After loading, carry out gradient heating drying on the glass microspheres; Segmentally calcine to form an MgO coating to obtain glass microspheres loaded with magnesium oxide; Add the glass microspheres loaded with magnesium oxide into the composite precursor, and stir evenly to obtain a shrinkage compensator; S4: Fiber dispersion and mixing process Preparation of dry - mix material, ferroaluminate cement, low - shrinkage auxiliary cementitious material, water - reducing agent, shrinkage compensator, and fine aggregate are stirred at low speed to obtain dry - mix material; Fine - fiber dispersion liquid, mix the modified fine fiber with water, and disperse it with ultrasonic assistance to form a stable suspension, which is the fine - fiber dispersion liquid; Preparation of wet - mix material: Add the fine - fiber dispersion liquid and the remaining water to the dry - mix material, stir at high speed and then at low speed to obtain wet - mix material; Incorporation of coarse fiber, add the modified coarse fiber into the wet - mix material, and stir at low speed to obtain a mixed material; S5: Load the mixed material into a mold, demold after hardening; S6: Gradient curing to obtain multi - scale toughened concrete.

3. The preparation method of the multi-scale toughened concrete according to claim 2, characterized in that, S1 specifically is: Steel fibers with a diameter of 0.15 - 0.25 mm are subjected to composite oxidation pickling for 30 - 40 min to remove the surface oxide layer. Under an argon atmosphere, microwave-assisted plasma cleaning is carried out with an increased power of 200 - 300 W for 5 - 8 min, and then dried at 40 - 50 °C to remove micron-scale oxides; Magnetron sputtering is used to deposit a nickel-copper gradient layer; Laser micro-melting is carried out under nitrogen protection with a power of 50 - 80 W and a scanning speed of 100 - 120 mm / s to form a dendritic interlocking structure in the nickel-copper gradient layer to obtain modified coarse fibers; The silicon carbide fibers with a diameter of 8 - 15 μm are bombarded with a nitrogen-argon mixed plasma at a power of 350 - 400 W for 5 - 10 min; Glycidyl methacrylate is used as the core monomer, and glycidyl methacrylate accounts for 5 - 10% of the mass of the fine fibers. 0.5 - 1% benzophenone is added as a photosensitizer and irradiated with ultraviolet light for 10 - 15 min to initiate surface radical polymerization through a hydrogen transfer reaction; The fine fibers are impregnated with a KH590 / carbon nanotube composite solution, and the mass ratio of the fine fibers to the KH590 / carbon nanotube composite solution is 1:7 - 10. The nanotubes are oriented by ultrasonic assistance, pre-cured at 50 - 60 °C for 1 - 2 h, and post-cured at 100 - 120 °C for 1.5 - 2 h to form a three-dimensional cross-linked network and a chemical bonding interface to obtain modified fine fibers.

4. The preparation method of the multi-scale toughened concrete according to claim 2, characterized in that Specifically, S2 is as follows: The sol-gel method is used to coat the surface of silica fume with a nano 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 centrifugal separation, microwave drying is carried out under nitrogen protection, with a power of 700 - 800 W and a time of 10 - 15 min; Microwave calcine metakaolin under nitrogen protection to make transform from amorphous state to obtain metakaolin; With the aid of 40 - 50 kHz ultrasonic waves and in the presence of a composite dispersant, metakaolin and the SSF core - shell structure are mixed in a gradient manner to obtain a low - shrinkage auxiliary cementitious material; The mass ratio of the composite dispersant, metakaolin, and the SSF core-shell structure is 0.4 - 0.8:6 - 8:7 - 9; The first-stage mixing is carried out for 20 - 30 min to rapidly hydrate and form a skeleton; The second-stage mixing is carried out for 40 - 60 min; The third-stage mixing is carried out for 1 - 2 h.

5. The preparation method of the multi-scale toughened concrete according to claim 2, characterized in that, S3 specifically is: The nano-clay is mixed with an oxalic acid solution at a solid-liquid ratio of 1:3 - 5, ultrasonically treated for 30 - 45 min, and then centrifuged to obtain activated clay; The HCSA high-performance concrete expansive agent particles are impregnated with a potassium dihydrogen phosphate-ethanol suspension for 40 - 60 min and dried at 100 - 120 °C to form a moisture-proof layer on the surface of the HCSA. The activated clay and the HCSA are mixed evenly 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 internal gas of the microspheres is evacuated by a vacuum pump and maintained for 20 - 30 min to filter and obtain glass microspheres uniformly loaded with magnesium nitrate; After the loading is completed, the glass microspheres are dried by gradient heating; Segmented calcination is carried out to form an MgO coating: First, it is heated at a rate of 3 - 5 °C / min to 200 - 300 °C to remove residual moisture and organic substances; Then, it is heated at a rate of 2 - 4 °C / min to 600 - 620 °C to decompose magnesium nitrate into magnesium oxide, and then glass microspheres loaded with magnesium oxide are obtained; The glass microspheres loaded with magnesium oxide are added to the composite precursor and stirred evenly at 40 - 50 °C for 20 - 30 min to obtain a shrinkage compensator.

6. The preparation method of the multi-scale toughened concrete according to claim 2, characterized in that, S4 specifically is that ferroaluminate cement, low-shrinkage auxiliary cementitious material, water reducer, shrinkage compensator, and fine aggregate are stirred at a low speed of 100 - 200 r / min for 3 - 5 min to obtain a dry-mixed material; Mix the modified fine fibers with water and disperse them with ultrasonic assistance 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 and stir at high speed at 280-350 r / min. After 5-8 min, stir at low speed at 100-200 r / min for 2-4 min to obtain a wet mix; Add the modified coarse fibers to the wet mix and stir at low speed at 100-180 r / min for 3-4 min to obtain a blended mix, avoiding disordered fiber orientation.

7. The preparation method of the multi-scale toughened concrete according to claim 2, wherein, S6 specifically includes: the first-stage curing for 1-2 h at a temperature of 30-40 °C with sealed curing to inhibit plastic shrinkage; the second-stage curing for 2-3 h with steam curing to promote the hydration of the expansive agent and compensate for autogenous shrinkage; the third-stage curing for 3-5 h at normal temperature with the nano-clay continuously releasing water to achieve internal curing.

8. The preparation method of the multi-scale toughened concrete according to claim 2, wherein The water reducer is a compound of a polycarboxylate water reducer and a phosphate retarder.

Images