Microencapsulated healing agent and smart self-healing ultra-high-strength ultra-high-ductility cementitious structural material

Abstract

The application discloses a kind of microencapsulated repair agent and intelligent self-repairing super-high-strength super-high-toughness cement-based structural materials, the microencapsulated repair agent is mainly by humidity response outer layer, pH response middle layer and temperature response inner layer Composed, and the outer layer is modified with silane coupling agent.The intelligent self-repairing super-high-strength super-high-toughness cement-based structural materials are mainly made of above-mentioned microencapsulated repair agent, nano carbon black, nanometer montmorillonite and nanometer cellulose and other raw materials.The application introduces self-repairing microcapsule with specific structure, and nano carbon black, nanometer montmorillonite and nanometer cellulose and other materials, significantly improve the strength, toughness and durability of concrete, and have intelligent self-repairing function.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and specifically relates to a microencapsulated repair agent and an intelligent self-repairing ultra-high-strength and ultra-high-toughness cement-based structural material. BACKGROUND

[0002] With the development of modern construction technology, the performance requirements for building materials are becoming higher and higher. Traditional concrete materials have certain limitations in strength, toughness and durability, and are prone to cracks and damage, affecting the service life and safety of buildings. Especially in extreme environmental conditions, such as earthquakes, freeze-thaw cycles, chemical corrosion, etc., the performance of traditional concrete is more deficient.

[0003] In recent years, researchers have developed a series of high-strength, high-toughness and high-durability concrete materials by introducing high-performance materials and advanced preparation processes. However, these materials still face the problem of cracks and damage during use. The generation of cracks not only reduces the mechanical properties of concrete, but also leads to the penetration of water and other corrosive substances, further accelerating the deterioration of concrete.

[0004] In order to solve the above problems, the research of intelligent self-repairing materials has gradually become a hot spot. Intelligent self-repairing materials introduce self-repairing mechanisms into the material, which can automatically repair cracks and restore their original performance when the material is damaged. Self-repairing mechanisms usually include microcapsules, shape memory alloys, nanomaterials, etc. These materials release repair agents or repair cracks through physical and chemical reactions when subjected to external stimuli (such as crack generation). In the field of concrete, the application of self-repairing technology is still in its infancy, but its potential is enormous. By introducing self-repairing microcapsules into concrete, the durability and service life of concrete can be significantly improved, reducing maintenance costs and resource consumption, and having important economic and social benefits.

[0005] In summary, the research of intelligent self-repairing high-strength and high-toughness ultra-high-performance concrete not only has important theoretical significance, but also has broad prospects in practical applications. By reasonably selecting and optimizing material components and preparation processes, concrete materials with excellent performance can be prepared to meet the needs of modern construction engineering.

[0006] Chinese patent application CN115819034A A kind of ultra-high-performance concrete material with high-temperature self-repairing ability: this patent relates to an ultra-high-performance concrete material capable of self-repairing under high temperature conditions, mainly composed of cement, silica fume, fly ash, quartz sand, steel fiber and high-efficiency water reducing agent, etc. However, the self-repairing effect of this material at room temperature is limited, and the advantages of nanomaterials are not fully utilized. For example, in a room temperature environment, the self-repairing speed and effect of cracks are not ideal, affecting the overall performance of the material.

[0007] Chinese patent application CN103304206A Ultra-high strength self-compacting concrete and its preparation method: This patent discloses an ultra-high strength self-compacting concrete mainly composed of ordinary Portland cement, slag, silica fume, superplasticizer, fine aggregate, coarse aggregate and PVA fiber. Although this material has high strength and self-compacting performance, it lacks self-repairing function and cannot automatically repair after cracks occur. In addition, the toughness and impact resistance of this material under high stress conditions need to be improved.

[0008] Chinese patent application CN202111442118 Self-sensing ultra-high performance concrete: This patent introduces a self-sensing ultra-high performance concrete by adding conductive additives to the concrete, which exhibits electromechanical effects under external load. Although this material has self-sensing function, its self-repairing ability is limited, and the introduction of conductive additives may affect other properties of the concrete. For example, conductive additives may reduce the durability and corrosion resistance of concrete, limiting its application in practical engineering.

[0009] In summary, the existing technology has made some progress in improving the performance of concrete, but there are still many limitations. SUMMARY

[0010] Invention purpose: In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a microencapsulated repair agent and an intelligent self-repairing ultra-high strength and ultra-high toughness cement-based structural material. The present invention introduces self-repairing microcapsules with specific structure, as well as nano-carbon black, nano-montmorillonite and nano-cellulose materials, which significantly improve the strength, toughness and durability of concrete, and have intelligent self-repairing function.

[0011] Technical solution: In order to achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0012] Firstly, the present invention provides a microencapsulated repair agent, which is mainly composed of a humidity-responsive outer layer, a pH-responsive intermediate layer and a temperature-responsive inner layer, and the outer layer is modified with silane coupling agent.

[0013] As a specific embodiment, the inner layer is mainly formed by wrapping the core material repair agent with temperature-responsive shell material; the intermediate layer is mainly formed by a composite made of pH-responsive material; and the outer layer is mainly formed by a polyurea structure crosslinked by humidity-responsive material.

[0014] As a preferred solution, the core material repair agent in the inner layer is selected from epoxy resin, the shell material is selected from poly(N-isopropyl acrylamide) (PNIPAM); the intermediate layer is mainly formed by a complex of chitosan and polyacrylic acid; the outer layer is mainly formed by a polyurea structure made of polyvinyl alcohol and isophorone diisocyanate (IPDI) crosslinking; and the silane coupling agent is selected from one of vinyltriethoxysilane, vinyltrimethoxysilane and vinyltris(β-methoxyethoxy)silane.

[0015] In a second aspect, the present application provides a preparation method of the microencapsulated repair agent, comprising the following steps:

[0016] First, a temperature-responsive inner layer and a pH-responsive intermediate layer are prepared respectively, the inner layer is emulsified, the intermediate layer is added for layer-by-layer self-assembly, then the obtained material is emulsified again, the material for preparing the outer layer is added, a three-layer structure is formed through interfacial polymerization, and finally a silane coupling agent is modified on the surface of the material, thereby obtaining the microencapsulated repair agent.

[0017] As a specific embodiment, the preparation method of the microencapsulated repair agent comprises the following steps:

[0018] (1) Poly(N-isopropyl acrylamide) PNIPAM is dissolved in water to form a PNIPAM solution; epoxy resin is dispersed in an oil phase containing an emulsifier to form an oil phase; the PNIPAM solution is added to the oil phase, and the PNIPAM undergoes a polymerization reaction at the oil-water interface to form an inner layer-microcapsule structure in which the epoxy resin is wrapped by the PNIPAM; the thermal response characteristics of the PNIPAM cause it to undergo a volume phase transition at a specific temperature, thereby forming a spherical or wrapped material that wraps the repair agent, and the solution and the emulsifier (polyvinyl alcohol) form a temperature-responsive inner layer through interfacial polymerization.

[0019] (2) Chitosan and polyacrylic acid are respectively dissolved in an acidic and an alkaline solution, the two solutions are mixed to form a CS-PAA complex; the inner layer is emulsified, and the CS-PAA complex solution is added, and a middle layer+inner layer structure is formed through layer-by-layer self-assembly. CS is positively charged, and PAA is negatively charged, and a multilayer structure is formed in the alternating deposition process. The deposition of each layer is stabilized by electrostatic attraction and hydrogen bonding to form a CS-PAA complex.

[0020] (3) PVA is dissolved in water to form a PVA solution; the middle layer+inner layer structure is emulsified again, and the PVA solution is added, and then isophorone diisocyanate IPDI is added, and a three-layer structure is formed through interfacial polymerization; IPDI reacts with PVA at the interface to form a crosslinked polyurea structure that wraps the multilayer structure.

[0021] (4) Introducing silane coupling agent on the surface of the above-mentioned three-layer structure to carry out surface modification, so as to improve dispersibility and stability. Finally, the prepared microcapsules are dried in a vacuum drying oven to remove the solvent, and the final product is obtained.

[0022] The repair mechanism of the above-mentioned microencapsulated repair agent is as follows:

[0023] Humidity sensing and response: When a crack is formed, the outer humidity-responsive layer senses the change in humidity at the crack and begins to dissolve or swell, exposing the middle layer. This process ensures that the microcapsules can begin to respond at the early stage of crack formation. pH sensing and response: The middle layer pH-responsive layer dissolves or swells when it contacts the alkaline environment in the concrete crack, further exposing the inner layer. This process ensures that the repair agent is effectively released in the high-pH environment at the crack site. The inner layer response layer releases the repair agent, which diffuses in the crack and reacts with the existing curing agent in the original concrete to form a cured product, filling the crack and restoring the strength and impermeability of the concrete.

[0024] In a third aspect, the present application provides the use of the microencapsulated repair agent in the preparation of an intelligent self-repairing ultra-high strength and ultra-high toughness cement-based structural material.

[0025] In a fourth aspect, the present application provides an intelligent self-repairing ultra-high strength and ultra-high toughness cement-based structural material, comprising the following raw materials by weight:

[0026] High-strength cement: 40-50 parts;

[0027] Admixture: 16-23 parts;

[0028] Nano carbon black: 0.5-1 parts;

[0029] Nano montmorillonite: 1-2 parts;

[0030] Nano cellulose: 0.5-1 parts;

[0031] The above-mentioned microencapsulated repair agent: 2-5 parts;

[0032] Water reducing agent: 0.5-1.5 parts;

[0033] Curing agent: 1-2.5 parts;

[0034] Sand: 45-55 parts;

[0035] Water: 7-8 parts.

[0036] As a specific embodiment, the strength grade of the high-strength cement is PII525;

[0037] As a specific embodiment, the admixture is a mixture of fly ash and silica fume, both in a mass ratio of 3: (3-5), wherein the silica fume has a silica content ≥ 90%, a specific surface area of 15-30 m 2 / g, and the fly ash has a specific gravity of 1.77-2.43 g / cm 3 , a fineness of no more than 12%, and a water requirement of 100%-110%;

[0038] As a specific embodiment, the water reducing agent is a polycarboxylic acid water reducing agent, with a water reducing rate ≥ 30%;

[0039] As a specific embodiment, the curing agent is a polyamine curing agent, which is one of ethylenediamine (EDA), diethylenetriamine (DETA), and triethylenetetramine (TETA), or a combination thereof.

[0040] The sand is quartz sand, with a maximum particle size ≤ 1.25 mm and a silica content ≥ 95%.

[0041] As a specific embodiment, the nano-carbon black is mainly composed of carbon elements, usually containing a small amount of impurities such as oxygen and hydrogen, with a density of 1.8-2.1 g / cm 3 , a particle size of 10-50 nm, and a specific surface area of 200-1500 m 2 / g.

[0042] As a specific embodiment, the nano-montmorillonite is mainly composed of magnesium aluminum silicate, and contains a small amount of calcium, sodium and water, with a density of 0.25-0.35 g / cm 3 , an average particle size of 10-50 nm, a wafer thickness of less than 25 nm, and a specific surface area of 750 m 2 / g.

[0043] As a specific embodiment, the nano-cellulose is mainly composed of natural cellulose, which is a polysaccharide composed of glucose units connected by β-1,4-glycosidic bonds, and is mainly a combination of cellulose nanocrystals (CNC) and cellulose nanofibers (CNF). The density is 1.5-1.6 g / cm 3 , the particle size is 10-100 nm, and the specific surface area is 200-400 m 2 / g.

[0044] In a fifth aspect, the present application provides a preparation method of the intelligent self-repairing ultra-high strength and ultra-high toughness cement-based structural material, comprising the following steps:

[0045] (1) Material pretreatment: disperse the nano-carbon black, nano-montmorillonite and nano-cellulose in part of the water respectively, and perform ultrasonic dispersion to form a nano-suspension; mix the curing agent with the remaining water to form a curing agent suspension;

[0046] (2) Dry mixing: Mix high-strength cement, admixture and sand, and stir evenly to form a dry mixture;

[0047] (3) Wet mixing: Gradually add nano-suspension and curing agent suspension to the dry mixture, and stir to form a uniform slurry;

[0048] (4) Add microencapsulated repair agent and continue stirring to evenly distribute the microcapsules;

[0049] (5) Vacuum degassing: degas the mixed slurry under vacuum;

[0050] (6) Pouring and forming: Pour the degassed slurry into the pre-prepared mold, remove the remaining bubbles, shape, demold and maintain.

[0051] Advantages: Compared with the prior art, the present application has the following advantages:

[0052] 1. Enhanced self-repairing ability: mainly realized by microencapsulated repair material: (1) Multiple response mechanism: through the dual sensing mechanism of humidity response layer and pH response layer, it ensures that the microcapsules can effectively respond at different stages of crack formation, improves the repair efficiency and accuracy. (2) Environmental adaptability: this multi-layer structure enables the microcapsules to adapt to different environmental conditions such as humidity change and pH change, enhancing the applicability and durability of the material. (3) High-efficiency repair: the design of the inner response layer ensures the efficient release and curing of the repair agent at the crack site, improving the self-repairing ability and service life of the concrete.

[0053] 2. Synergistic effect of multiple nanomaterials: The high electrical conductivity and thermal conductivity of nano-carbon black enable the concrete to better disperse stress and heat when subjected to stress or temperature change, reducing the occurrence of cracks, while its high specific surface area and spherical particles can effectively fill the small pores in the concrete, improving its density and compressive strength. Nano-montmorillonite has excellent adsorption and ion exchange capacity, which can adsorb and fix organic matter, metal ions and gas molecules, enhancing the durability and corrosion resistance of the concrete, and can form a colloidal suspension in water, which can be uniformly dispersed in the concrete, improving the uniformity and stability of the mixture of different nanomaterials. Nano-cellulose has high strength and high modulus, which can significantly improve the tensile strength and toughness of the concrete. The multi-layer structure of the microencapsulated repair agent can respond to changes in humidity, pH and temperature, and automatically release the repair agent when cracks form to fill the cracks. At the same time, the synergistic effect of nano-carbon black, nano-montmorillonite and nano-cellulose can significantly improve the mechanical properties, durability and corrosion resistance of the concrete. Nano-carbon black fills the micropores, nano-montmorillonite provides adsorption and ion exchange capacity, and nano-cellulose enhances the mechanical properties.

[0054] 3. Excellent mechanical properties: The introduction of various nanomaterials significantly improves the strength, toughness, and impact resistance of concrete through synergistic effects, enabling it to perform more excellently in various complex environments.

[0055] 4. Permeability resistance and corrosion resistance: The addition of nanomontmorillonite enhances the permeability resistance and corrosion resistance of concrete, reducing the penetration of water and other corrosive substances, further extending the service life of concrete.

[0056] 5. Economic and environmental benefits: By improving the durability and self-repairing ability of concrete, maintenance costs and resource consumption are reduced, providing significant economic and social benefits. DETAILED DESCRIPTION

[0057] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0058] The raw materials used in the following examples and comparative examples are as follows:

[0059] "Cement" is PII525 cement.

[0060] "Admixture" is a mixture of fly ash and silica fume in a ratio of 3:4. The specific gravity of fly ash is 2.1 g / cm 3 , fineness is 10%, and water demand ratio is 105%. The silica fume contains 94% silicon dioxide and has a specific surface area of 22 m 2 / g.

[0061] "High-performance water reducer" is a polycarboxylic acid high-performance water reducer with a water-reducing rate of 35%.

[0062] "Nanocarbon black" is mainly composed of carbon, mainly accumulated by graphene layers, with a highly amorphous carbon structure. The morphology is spherical or near-spherical particles, which aggregate into larger aggregates through van der Waals forces, and the surface is porous, with high structural complexity. It is a byproduct obtained by incomplete combustion of petroleum-based heavy oil or creosote in a hot furnace or electric arc furnace. Nanocarbon black is mainly composed of carbon elements, usually containing a small amount of impurities such as oxygen and hydrogen, with a density of 1.9 g / cm 3 , a particle size of 20 nm, and a specific surface area of 1100 m 2 / g;

[0063] "Nanometer montmorillonite" is composed of montmorillonite mineral, the chemical composition is mainly magnesium aluminum silicate, and contains a small amount of calcium, sodium and water, and is subjected to flake dispersion, purification modification and ultrafine classification treatment, the average particle size is between 10-50 nanometers, and the crystal flake thickness is less than 25 nanometers. The montmorillonite is flaked into nanometer scale flake by mechanical and adding dispersant, and the uniform nanometer particles are obtained by ultrafine classification technology. The main component of nanometer montmorillonite is magnesium aluminum silicate, and contains a small amount of calcium, sodium and water, the density is 0.3 g / cm 3 , the average particle size is between 25 nm, the crystal flake thickness is 20 nm, and the specific surface area is 750 m 2 / g.

[0064] "Nanocellulose" is a mixture of cellulose nanocrystals (CNC) and cellulose nanofibers (CNF) in a ratio of 2:5. The former is rod-like or needle-like structure, and the latter is long fiber-like structure. The cellulose is dissociated and dispersed into nanocellulose by high pressure homogenization, ultrasonic treatment and other mechanical methods. The density is 1.55 g / cm 3 , the particle size is 75 nm, and the specific surface area is 300 m 2 / g.

[0065] The "curing agent" is industrial grade ethylenediamine (EDA) with a purity of 99%.

[0066] The "sand" is quartz sand with continuous gradation of 0-1.25 mm, the maximum particle size is ≤1.25 mm, and the silicon dioxide content is 98%.

[0067] The microencapsulated repair agent is prepared by the following method:

[0068] (1) Dissolve poly(N-isopropyl acrylamide) PNIPAM in water, slowly stir at room temperature for 30 min until completely dissolved, to obtain a 5.wt% PNIPAM solution; disperse 10 g of epoxy resin in an oil phase (100 ml) containing an emulsifier (2 g), slowly stir at room temperature for 60 min until completely dissolved, to form a water-in-oil emulsion; mix the above-mentioned PNIPAM solution and water-in-oil emulsion at a volume ratio of 1:1, slowly stir at a temperature of 40 degrees for 120 min, and the PNIPAM undergoes polymerization reaction at the oil-water interface to form an inner layer-microcapsule structure of PNIPAM wrapping epoxy resin. The thermal response characteristics of PNIPAM cause volume phase transition at a specific temperature, thereby wrapping the repair agent to form spherical or wrapped materials, and the solution and emulsifier (polyvinyl alcohol) form a temperature-responsive inner layer through interfacial polymerization.

[0069] (2) Dissolve chitosan and polyacrylic acid into acetic acid and sodium hydroxide solution respectively, stir for 10 minutes at room temperature to form 1.wt% solution, then mix the two solutions with a volume ratio of 1:1, continue to stir for 30 minutes to form CS-PAA complex; emulsify the above inner layer, add CS-PAA complex solution with a volume ratio of 1:1, stir for 30 minutes at room temperature, and form the middle layer+inner layer structure by layer-by-layer self-assembly method. CS is positively charged, PAA is negatively charged, and a multilayer structure is formed in the alternating deposition process. The deposition of each layer is stabilized by electrostatic attraction and hydrogen bonding to form CS-PAA complex.

[0070] (3) Dissolve PVA in water, stir slowly at room temperature for 25 minutes until completely dissolved to form a 5.wt% PVA solution; emulsify the above middle layer+inner layer structure again, add PVA solution with a volume ratio of 1:1, and then add 2g isophorone diisocyanate IPDI, react at 50 degrees for 50 minutes to form a three-layer structure by interfacial polymerization; IPDI reacts with PVA at the interface to form a cross-linked polyurea structure, which encapsulates the multilayer structure.

[0071] (4) Introduce 1.wt% silane coupling agent on the surface of the above three-layer structure to improve dispersibility and stability. Finally, dry the prepared microcapsules in a vacuum drying oven at 40 degrees for 24 hours to remove the solvent and obtain the final product. The preparation method of the low-intelligence self-repairing super-high-strength super-high-toughness cement-based structural material in each example and comparative example specifically includes the following steps:

[0072] (1) Nanomaterial pretreatment: disperse nanocarbon black, nanomontmorillonite and nanocellulose in part of deionized water respectively, use an ultrasonic processor for ultrasonic dispersion, time for 30 minutes, to ensure that the nanomaterials are uniformly dispersed in water to form a nanosuspension; pretreatment of the curing agent: mix the curing agent with the remaining water to ensure uniform dispersion;

[0073] (2) Dry mixing: add high-strength cement, admixture and sand in proportion into a mixer, dry mix for 2-3 minutes to ensure uniform distribution of each component;

[0074] (3) Wet mixing: gradually add the nanosuspension and curing agent suspension obtained in (1) to the dry mixture obtained in (2), continue to stir for 3-5 minutes until a uniform slurry is formed;

[0075] (4) Add microencapsulated repair agent, continue to stir for 2-3 minutes to ensure uniform distribution of microcapsules in concrete;

[0076] (5) Vacuum degassing: place the mixed slurry in (4) in a vacuum degassing device and perform vacuum degassing treatment for 5-10 minutes to remove air bubbles in the concrete and improve its density and mechanical properties;

[0077] (6) Casting: pour the degassed slurry into the prepared mold, use a vibrating table or manual vibration to further remove residual air bubbles and ensure the density of the concrete, shape at 20°C, remove the mold after 24 hours, and place it in a water curing box for 90 days under standard atmospheric pressure.

[0078] Table 1: Content of each component of ultra-high performance concrete in examples and comparative examples

[0079]

[0080] The compressive strength and tensile strength of the ultra-high performance concrete were tested according to GB / T 17671-1999 "Cement mortar strength detection method ISO method". The autogenous shrinkage was detected according to T CECS 10107-2020 Ultra-high performance concrete technical requirements.

[0081] Table 2: Mechanical properties and volume stability of ultra-high performance concrete in examples and comparative examples

[0082]

[0083] From the results in Table 2 above, by introducing self-repairing microcapsules, nano carbon black, nano montmorillonite and nano cellulose, etc. materials, it can be seen that the examples have significant advantages in compressive strength, tensile strength and shrinkage, which reflects the innovation and superiority of the materials and technology. The material is more superior in bearing pressure and is suitable for high strength applications. At the same time, the material performs well in resisting tensile force and is suitable for high tensile strength applications. Most importantly, the material is more stable during use and has less deformation, making it suitable for applications with high dimensional stability requirements.

[0084] Table 3: Effect of application of micro-nano materials on mechanical properties and volume stability of concrete

[0085]

[0086] From the results in Table 3 above, by setting up tests, respectively introducing a variety of nano materials or not adding nano materials, etc. in Comparative Examples 1-4, and comparing with Example 2, it is found that the single and small amount of incorporation of these nano materials has limited improvement on the performance of concrete. Therefore, in order to achieve better strength, toughness and durability, it is necessary to use these materials at the same time.

[0087] In addition, in order to evaluate the self-repairing performance of the material, a crack self-repairing test analysis method is adopted. 1. Preparing a crack: a crack with a width of 0.3 mm is prepared on each concrete sample; 2. Curing condition: the sample is placed in an environment with a temperature of 20°C and a relative humidity of 95% for curing; 3. Observation period: the healing condition of the crack is observed every 7 days, and the observation is continued for 28 days. The change in the crack width is measured and counted using a crack width measuring instrument, and the percentage of crack healing is calculated. The results are shown in the following table.

[0088] Table 4 Mechanical volume stability characterization of the ultra-high performance concrete in the examples and the comparative examples

[0089]

[0090] It can be seen from the results in Table 4 above that the self-repairing effect of the comparative example 5 is obviously not as good as that of the examples. The crack healing rate is low. This indicates that without the introduction of self-repairing microcapsules and nanomaterials, the self-repairing ability and durability of the concrete are significantly reduced.

[0091] The embodiments of the present application are described in detail above in combination with specific examples, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the present application.

Claims

1. A microencapsulated repair agent, characterized in that, The microencapsulated healing agent is composed of a humidity-responsive outer layer, a pH-responsive middle layer and a temperature-responsive inner layer, and the outer layer is modified with a silane coupling agent; The inner layer is formed by a temperature-responsive shell material wrapping a core material healing agent selected from epoxy resin, and the shell material is selected from poly(N-isopropylacrylamide); The middle layer is formed by a complex of chitosan and polyacrylic acid; The outer layer is formed by a polyurea structure made of polyvinyl alcohol and isophorone diisocyanate (IPDI) crosslinking.

2. The microencapsulated repair agent of claim 1, wherein, The silane coupling agent is selected from one of vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltris(β-methoxyethoxy)silane.

3. Process for the preparation of microencapsulated repair agents according to any one of claims 1-2, characterized in that, The method comprises the following steps: First, the temperature-responsive inner layer and the pH-responsive middle layer are prepared respectively, the inner layer is emulsified, the middle layer is added for layer-by-layer self-assembly, then the obtained material is emulsified again, the material for preparing the outer layer is added, a three-layer structure is formed by interfacial polymerization, and finally a silane coupling agent is modified on the surface of the material to obtain the microencapsulated healing agent.

4. The method of claim 3, wherein the microencapsulated repair agent is prepared by a process comprising: The method comprises the following steps: (1) Dissolve poly(N-isopropylacrylamide) PNIPAM in water to form a PNIPAM solution; Disperse the epoxy resin in an oil phase containing an emulsifier to form an oil phase; add the above-mentioned PNIPAM solution to the oil phase, and the PNIPAM undergoes polymerization reaction at the oil-water interface to form an inner layer-microcapsule structure in which the epoxy resin is wrapped by PNIPAM; (2) Dissolve chitosan and polyacrylic acid in acidic and alkaline solutions respectively, mix the two solutions to form a CS-PAA complex; emulsify the above-mentioned inner layer, and add the CS-PAA complex solution to form a middle layer+inner layer structure by layer-by-layer self-assembly; (3) Dissolve PVA in water to form a PVA solution; emulsify the above-mentioned middle layer+inner layer structure again, add the PVA solution, and then add isophorone diisocyanate IPDI to form a three-layer structure by interfacial polymerization; (4) Introduce a silane coupling agent on the surface of the above-mentioned three-layer structure.

5. Use of the microencapsulated healing agent of any one of claims 1-2 in the preparation of an intelligent self-healing ultra-high-strength and ultra-high-toughness cement-based structural material.

6. An intelligent self-healing ultra-high-strength and ultra-high-ductility cementitious structural material, characterized in that, The following raw materials are included by weight: High-strength cement: 40-50 parts; Admixture: 16-23 parts; Nano carbon black: 0.5-1 part; Nano montmorillonite: 1-2 parts; Nanocellulose: 0.5-1 part; The microencapsulated healing agent of any one of claims 1-2: 2-5 parts; Water reducing agent: 0.5-1.5 parts; Curing agent: 1-2.5 parts; Sand: 45-55 parts; Water: 7-8 parts. 7.The intelligent self-healing ultra-high-strength and ultra-high-ductility cementitious structural material of claim 6, wherein, The strength grade of the high-strength cement is PII525; the admixture is a mixture of fly ash and silica fume, and the mass ratio of the two is 3:(3-5), wherein the silica fume contains ≥90% of silicon dioxide, and the specific surface area is 15-30 m 2 / g, the fly ash has a specific gravity of 1.77-2.43 g / cm³, a fineness of not more than 12%, and a water demand ratio of 100-110%; the water reducing agent is a polycarboxylic acid water reducing agent, and the water reducing rate is ≥30%; the curing agent is a polyamine curing agent, which is one of ethylenediamine (EDA), diethylenetriamine (DETA) and triethylenetetramine (TETA), or a combination thereof; and the sand is quartz sand, the maximum particle size of which is ≤1.25 mm, and the silicon dioxide content of which is ≥95%.

8. The intelligent self-healing ultra-high-strength and ultra-high-toughness cement-based structural material according to claim 6, characterized in that it comprises the following steps: The nano-carbon black is composed of carbon element, has a density of 1.8-2.1 g / cm 3 , a particle size of 10-50 nm, and a specific surface area of 200-1500 m 2 / g. The nano-montmorillonite component is magnesium aluminum silicate, with a density of 0.25-0.35 g / cm 3 , an average particle size of 10-50 nm, a wafer thickness of less than 25 nm, and a specific surface area of 750 m 2 / g. The nanocellulose consists of natural cellulose, a polysaccharide in which glucose units are connected by β-1,4-glycosidic bonds, has a density of 1.5-1.6 g / cm 3 , a particle size of 10-100 nm, and a specific surface area of 200-400 m 2 / g.

9. The method for preparing the smart self-healing ultrahigh-strength and ultrahigh-ductility cementitious structural material according to any one of claims 6-8, characterized in that, (1) Material pretreatment: disperse the nano carbon black, nano montmorillonite and nano cellulose in part of the water respectively, and perform ultrasonic dispersion to form nano suspensions; mix the curing agent with the remaining amount of water to form a curing agent suspension; (2) Dry mixing: mix the high-strength cement, admixture and sand, and stir uniformly to form a dry mixture; ​ (3) wet mixing: gradually adding the nano-suspension and curing agent suspension into the dry mixture, stirring to form a uniform slurry; (4) adding the microencapsulated repairing agent, and continuing to stir to make the microcapsules uniformly distributed; (5) vacuum degassing: degassing the mixed slurry under vacuum; (6) pouring and forming: pouring the degassed slurry into a pre-prepared mold, removing residual bubbles, forming, demolding, and curing.

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