A method for preparing a lightweight self-healing concrete

Abstract

The application discloses a preparation method of lightweight self-repairing concrete and relates to the technical field of concrete. The application encapsulates calcium nitrate solution in hollow glass microbeads by using a negative pressure immersion technology; then, a porous zeolite crystal coating is grown on the surface of the microbeads by using a sol-gel method, thereby forming a self-repairing filler with a core-shell-hole gradient structure; when the concrete cracks, the microbeads are broken, Ca²+ in the cavity is quickly released, Ca²+ adsorbed in the zeolite layer is gradually dissociated with water penetration, and new microcracks are continuously repaired. Then, polydopamine is uniformly coated on the surface and in the pores of a carboxymethyl cellulose hydrogel network by in-situ oxidative polymerization, thereby forming a composite hydrogel with photothermal responsiveness; light heating triggers the dissociation of dynamic coordination bonds; meanwhile, heat drives the rapid directional crystallization of repair products by promoting the ion diffusion rate, thereby forming a dense mineralized layer. The prepared concrete has the effects of being lightweight and self-repairing.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a method for preparing lightweight self-healing concrete. Background Technology

[0002] Concrete, as the most widely used man-made building material globally, is extensively applied in construction, bridges, tunnels, and other engineering fields. However, traditional concrete is prone to microcracks during service due to factors such as load, shrinkage, and temperature changes. These cracks become channels for the penetration of corrosive media such as moisture and chloride ions, accelerating the corrosion of internal steel reinforcement and the deterioration of the matrix, leading to a severe decline in structural durability. To extend the lifespan of concrete, existing technologies mainly focus on crack repair: First, self-healing technology based on microbial mineralization, which induces calcium carbonate deposition at cracks by pre-embedding carbonic anhydrase-producing bacteria. However, the activity of these bacteria is easily inhibited by high-alkaline environments, and the repair efficiency is limited by nutrient supply and humidity conditions. Second, repair agents are encapsulated in microcapsules or hollow fibers, relying on crack expansion to trigger release. However, organic repair agents have poor compatibility with the cement matrix, easily forming weak interfaces, and excessive microcapsule dosage can significantly reduce concrete strength. Third, shape memory polymer-assisted repair, which closes cracks through the deformation recovery force of temperature-sensitive polymer materials. However, it requires an external heat source to trigger and is difficult to repair cracks wider than 0.3 mm. The aforementioned technologies generally suffer from drawbacks such as a single repair mechanism, insufficient environmental adaptability, and risk of secondary damage. Furthermore, most solutions do not consider the need for lightweight concrete, which limits their application in scenarios sensitive to material weight, such as high-rise buildings and long-span bridges.

[0003] The development of lightweight self-healing concrete stems from the urgent need for multifunctional material integration in modern engineering. On one hand, traditional concrete's high density leads to excessive structural weight, increasing foundation load and building material consumption. While lightweight concrete can reduce weight by 20%–30% by introducing lightweight aggregates such as expanded clay and hollow microspheres, the porous nature of these aggregates exacerbates the risk of crack initiation. On the other hand, single self-healing technologies are insufficient to cope with complex service environments. For example, marine engineering requires resistance to chloride ion corrosion and wet-dry cycles, while freeze-thaw regions require both crack repair and frost heave resistance. Therefore, synergistically optimizing lightweighting and self-healing functions is key to overcoming existing technological bottlenecks. Lightweight self-healing concrete, through gradient structural design and the integration of intelligent responsive materials, can achieve both rapid crack filling and long-term crack suppression while maintaining low density and high strength mechanical properties. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing lightweight self-healing concrete to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a lightweight self-healing concrete, wherein the concrete is modified with a core-shell-pore structure self-healing filler and a photothermal responsive composite hydrogel, comprising the following preparation steps:

[0006] (1) Calcium nitrate-encapsulated microbeads were immersed in a sol, the volume of which was 3 times the volume of the microbeads. The mixture was stirred at 60°C for 6 hours at a stirring speed of 60 rpm to deposit the sol on the surface of the microbeads. Then the mixture was transferred to a high-pressure reactor and hydrothermally reacted at 120°C for 24 hours to generate porous zeolite crystals. After the reaction was completed, the mixture was centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80°C for 4 hours to obtain a core-shell-pore structure self-healing filler.

[0007] (2) Mix sodium carboxymethyl cellulose solution and ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min at a stirring speed of 200-400 rpm to form Fe³⁺ cross-linked hydrogel; let stand for 12 h to complete cross-linking, cut into gel particles with a particle size of 1-3 mm; immerse the gel particles in a buffer solution containing 2 mg / mL dopamine hydrochloride and tris(hydroxymethyl)aminomethane, introduce oxygen at a flow rate of 0.5 L / (min·L reaction solution), stir at 25℃ in the dark for 24 h at a stirring speed of 120 rpm; after stirring, rinse with deionized water 3 times, freeze dry at -40℃ for 48 h to obtain photothermal responsive composite hydrogel;

[0008] (3) Dry mix cement, fly ash and silica fume for 3 minutes at a speed of 20-30 rpm; add lightweight aggregate, self-healing filler and composite hydrogel, continue to dry mix for 5 minutes at a speed of 40-60 rpm; add water and water-reducing agent, wet mix for 8 minutes until uniform at a speed of 80-100 rpm to obtain lightweight self-healing concrete material; pour into the mold, vibrate to compact, cover with curing film, and cure to obtain lightweight self-healing concrete.

[0009] 2. The method for preparing lightweight self-healing concrete according to claim 1, characterized in that the method for preparing calcium nitrate encapsulated microspheres in step (1) is as follows: immersing hollow glass microspheres in calcium nitrate solution with a solid-liquid ratio of 1:15, placing them in a vacuum reactor and evacuating them to a vacuum degree of -0.095 MPa, with a reaction time of 30-60 min, to remove air from the microsphere cavity; slowly releasing the vacuum to atmospheric pressure, using the pressure difference to allow the calcium nitrate solution to penetrate into the microsphere cavity, repeating the cycle 3 times to increase the loading capacity, then filtering to obtain the microspheres, drying them at 60℃ for 12 h, to obtain calcium nitrate encapsulated microspheres.

[0010] Furthermore, the method for preparing the calcium nitrate solution is as follows: dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1-2 mol / L.

[0011] Furthermore, the hollow glass microspheres have a particle size of 50-200μm, a cavity ratio of 80%, and a shell thickness of 0.5-2μm.

[0012] Furthermore, the vacuum release rate during the slow release of vacuum to atmospheric pressure is 0.02 MPa / min.

[0013] Furthermore, the preparation method of the sol in step (1) is as follows: sodium silicate, sodium aluminate and deionized water are mixed in a silicon-aluminum molar ratio of 2.5:1:10, 0.5 mol / L sodium hydroxide aqueous solution is added to adjust the pH to 11.5, and the mixture is stirred at 120 rpm for 2 hours to form a uniform sol.

[0014] Furthermore, the method for preparing the sodium carboxymethyl cellulose aqueous solution in step (2) is as follows: dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%.

[0015] Furthermore, the method for preparing the ferric chloride solution in step (2) is as follows: ferric chloride is mixed with deionized water to prepare a ferric chloride solution with a concentration of 0.2 mol / L.

[0016] Furthermore, the mass proportion of the raw materials for concrete in step (3) is as follows: P·O 42.5 cement: 100 parts; Grade I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10 mm as lightweight aggregate: 50 parts; self-healing filler: 8-12 parts; composite hydrogel: 3-5 parts; polycarboxylate superplasticizer: 1.2 parts; water: 44 parts.

[0017] Furthermore, the curing conditions in step (3) are: curing for 28 days at a temperature of 25°C and a humidity of 95%.

[0018] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0019] This invention uses a core-shell-pore structure self-healing filler and photothermal responsive composite hydrogel to modify concrete, so as to achieve lightweight and self-healing effects.

[0020] First, calcium nitrate solution is efficiently encapsulated inside hollow glass microspheres using negative pressure impregnation technology. After removing air from the microsphere cavities through vacuuming, the solution is fully immersed into the cavities by pressure difference, increasing the catalyst core loading. Subsequently, a porous zeolite crystal coating is grown in situ on the surface of the microspheres using the sol-gel method, forming a self-healing filler with a core-shell-pore gradient structure. The zeolite layer further adsorbs and stores calcium ions due to its high specific surface area, and the release rate is regulated through nanopores. When concrete cracks, stress concentration causes the microspheres to rupture, and the rapid release of Ca²⁺ in the cavity triggers a rapid reaction between silicate and CO2, generating CSH gel and calcium carbonate to fill the cracks. At the same time, the Ca²⁺ adsorbed in the zeolite layer gradually dissociates with water penetration, and combined with the Na⁺ / Ca²⁺ ion exchange effect of zeolite, it continuously repairs newly formed microcracks, forming a dual mode of rapid repair and long-term sustained release. Furthermore, the hydroxyl groups on the surface of the hydrothermally synthesized zeolite coating chemically bond with the cement matrix, enhancing the interfacial shear strength. This reduces the density of the microsphere-doped concrete to achieve a lightweight effect while maintaining compressive strength. Moreover, in a saltwater environment, the crack healing rate is maximized due to the activation of zeolite ion exchange capacity by Cl⁻.

[0021] Secondly, by uniformly coating the surface and pores of a carboxymethyl cellulose hydrogel network with polydopamine via in-situ oxidative polymerization, a photothermal responsive composite hydrogel is formed. When irradiated with near-infrared light, polydopamine efficiently absorbs light energy and converts it into heat energy, causing a rapid increase in local temperature. This temperature rise triggers the dissociation of the dynamic coordination bonds between Fe³⁺ and the carboxylate groups of carboxymethyl cellulose, accelerating the synergistic release of Fe³⁺ and Ca²⁺ ions. Simultaneously, the heat promotes the rapid directional crystallization of the repair products by accelerating ion diffusion, forming a dense mineralized layer. Furthermore, the dynamic reversibility of the hydrogel allows it to restore its network structure through Fe³⁺-COO⁻ bond recombination after cooling, achieving multiple photothermal cycle repair capabilities and providing long-term repair for concrete. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The testing methods for various indicators of lightweight self-healing concrete prepared in the following embodiments are as follows:

[0024] Durability: According to the provisions of GB / T50082-2009 Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete, the concrete of the example and concrete were made into corresponding sizes and cured for 28 days at a temperature of 25℃ and a relative humidity of 95%. The average carbonation depth of the concrete was measured.

[0025] Self-healing: The press was adjusted to load at a rate of 0.05 mm / min. Loading was stopped when a 0.2 mm crack appeared at the bottom of the tension side of the specimens in the examples and comparative examples, and the load was unloaded after holding for 90 seconds. The specimens were water-cured for 14 days, and the crack extension morphology and repair performance were determined by a 150X crack observation instrument and an electron scanning microscope.

[0026] Example 1

[0027] (1) Dissolve calcium nitrate in deionized water to prepare a 1 mol / L calcium nitrate solution for later use; immerse hollow glass microspheres with a particle size of 50 μm, a cavity ratio of 80%, and a shell thickness of 0.5 μm into the calcium nitrate solution at a solid-liquid ratio of 1:15, place them in a vacuum reactor, evacuate to a vacuum degree of -0.095 MPa, and react for 30 min to remove air from the microsphere cavities; slowly release the vacuum to atmospheric pressure at a vacuum release rate of 0.02 MPa / min, using the pressure difference to allow the calcium nitrate solution to permeate into the microsphere cavities, repeating the cycle 3 times to increase the loading, then filter and collect the microspheres, dry them at 60℃ for 12 h to obtain calcium nitrate encapsulated microspheres; mix sodium silicate, sodium aluminate, and deionized water at a silicon-aluminum molar ratio of 2.5:1:10, add 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH to 11.5, so as to A homogeneous sol was formed by stirring at 120 rpm for 2 hours. Calcium nitrate-encapsulated microbeads were immersed in the sol, with the sol volume being three times the volume of the microbeads. The mixture was stirred at a constant temperature of 60℃ for 6 hours at a stirring speed of 60 rpm to allow the sol to deposit on the surface of the microbeads. Then, it was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120℃ for 24 hours to generate porous zeolite crystals. After the reaction, the mixture was centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80℃ for 4 hours to obtain a core-shell-pore structure self-healing filler.

[0028] (2) Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%; mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2mol / L; mix the sodium carboxymethyl cellulose solution and the ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min at a stirring speed of 200 rpm to form Fe³⁺ cross-linked hydrogel; allow to stand for 12 h to complete cross-linking, and cut into gel particles with a particle size of 1 mm; immerse the gel particles in a buffer solution containing 2 mg / mL dopamine hydrochloride in tris(hydroxymethyl)aminomethane, introduce oxygen at a flow rate of 0.5 L / (min·L reaction solution), stir at 25℃ in the dark for 24 h at a stirring speed of 120 rpm; after stirring, rinse with deionized water 3 times, freeze dry at -40℃ for 48 h to obtain photothermal responsive composite hydrogel;

[0029] (3) The raw material proportions of the concrete by weight are as follows: P·O 42.5 cement: 100 parts; Grade I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10 mm as lightweight aggregate: 50 parts; self-healing filler: 8 parts; composite hydrogel: 3 parts; polycarboxylate superplasticizer: 1.2 parts; water: 44 parts; dry mix cement, fly ash and silica fume for 3 minutes at a stirring speed of 20 rpm; add lightweight aggregate, self-healing filler and composite hydrogel, continue to dry mix for 5 minutes at a stirring speed of 40 rpm; add water and superplasticizer, wet mix for 8 minutes until uniform at a stirring speed of 80 rpm to obtain lightweight self-healing concrete material; pour into the mold, vibrate to compact, cover with curing film, and cure for 28 days at a temperature of 25℃ and a humidity of 95% to obtain lightweight self-healing concrete.

[0030] Example 2

[0031] (1) Dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1.5 mol / L for later use; immerse hollow glass microspheres with a particle size of 125 μm, a cavity ratio of 80%, and a shell thickness of 1.25 μm into the calcium nitrate solution at a solid-liquid ratio of 1:15, place them in a vacuum reactor, evacuate to a vacuum degree of -0.095 MPa, and react for 45 min to remove air from the microsphere cavities; slowly release the vacuum to atmospheric pressure at a vacuum release rate of 0.02 MPa / min, using the pressure difference to allow the calcium nitrate solution to permeate into the microsphere cavities, repeating the cycle 3 times to increase the loading, then filter and collect the microspheres, dry them at 60℃ for 12 h to obtain calcium nitrate encapsulated microspheres; mix sodium silicate, sodium aluminate, and deionized water at a silicon-aluminum molar ratio of 2.5:1:10, add 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH to 11.5, so as to A homogeneous sol was formed by stirring at 120 rpm for 2 hours. Calcium nitrate-encapsulated microbeads were immersed in the sol, with the sol volume being three times the volume of the microbeads. The mixture was stirred at a constant temperature of 60℃ for 6 hours at a stirring speed of 60 rpm to allow the sol to deposit on the surface of the microbeads. Then, it was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120℃ for 24 hours to generate porous zeolite crystals. After the reaction, the mixture was centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80℃ for 4 hours to obtain a core-shell-pore structure self-healing filler.

[0032] (2) Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%; mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2mol / L; mix the sodium carboxymethyl cellulose solution and the ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min at a stirring speed of 300 rpm to form Fe³⁺ cross-linked hydrogel; allow to stand for 12 h to complete cross-linking, and cut into gel particles with a particle size of 2 mm; immerse the gel particles in a tris(hydroxymethyl)aminomethane buffer containing 2 mg / mL dopamine hydrochloride, introduce oxygen at a flow rate of 0.5 L / (min·L reaction solution), stir at 25℃ in the dark for 24 h at a stirring speed of 120 rpm; after stirring, rinse with deionized water 3 times, freeze-dry at -40℃ for 48 h to obtain photothermal responsive composite hydrogel;

[0033] (3) The raw material proportions of the concrete by weight are as follows: P·O 42.5 cement: 100 parts; Grade I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10 mm as lightweight aggregate: 50 parts; self-healing filler: 10 parts; composite hydrogel: 4 parts; polycarboxylate superplasticizer: 1.2 parts; water: 44 parts; dry mix cement, fly ash and silica fume for 3 minutes at a stirring speed of 25 rpm; add lightweight aggregate, self-healing filler and composite hydrogel, continue to dry mix for 5 minutes at a stirring speed of 50 rpm; add water and superplasticizer, wet mix for 8 minutes until uniform at a stirring speed of 90 rpm to obtain lightweight self-healing concrete material; pour into the mold, vibrate to compact, cover with curing film, and cure for 28 days at a temperature of 25℃ and a humidity of 95% to obtain lightweight self-healing concrete.

[0034] Example 3

[0035] (1) Dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 2 mol / L for later use; immerse hollow glass microspheres with a particle size of 200 μm, a cavity ratio of 80%, and a shell thickness of 2 μm into the calcium nitrate solution with a solid-liquid ratio of 1:15, place them in a vacuum reactor, evacuate to a vacuum degree of -0.095 MPa, and react for 60 min to remove air from the microsphere cavity; slowly release the vacuum to atmospheric pressure at a vacuum release rate of 0.02 MPa / min, and use the pressure difference to allow the calcium nitrate solution to permeate into the microsphere cavity. Repeat the cycle 3 times to increase the loading, then filter and take the microspheres, dry them at 60℃ for 12 h to obtain calcium nitrate encapsulated microspheres; add sodium silicate and aluminate Sodium and deionized water were mixed at a silicon-aluminum molar ratio of 2.5:1:10. A 0.5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 11.5, and the mixture was stirred at 120 rpm for 2 hours to form a homogeneous sol. Calcium nitrate-encapsulated microbeads were immersed in the sol, with the sol volume being three times the volume of the microbeads. The mixture was stirred at 60℃ for 6 hours at a stirring speed of 60 rpm to allow the sol to deposit on the surface of the microbeads. The mixture was then transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120℃ for 24 hours to generate porous zeolite crystals. After the reaction, the mixture was centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80℃ for 4 hours to obtain a core-shell-pore structure self-healing filler.

[0036] (2) Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%; mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2mol / L; mix the sodium carboxymethyl cellulose solution and the ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min at a stirring speed of 400 rpm to form Fe³⁺ cross-linked hydrogel; allow to stand for 12 h to complete cross-linking, and cut into gel particles with a particle size of 3 mm; immerse the gel particles in a buffer solution containing 2 mg / mL dopamine hydrochloride in tris(hydroxymethyl)aminomethane, introduce oxygen at a flow rate of 0.5 L / (min·L reaction solution), stir at 25℃ in the dark for 24 h at a stirring speed of 120 rpm; after stirring, rinse with deionized water 3 times, freeze-dry at -40℃ for 48 h to obtain photothermal responsive composite hydrogel;

[0037] (3) The raw material proportions of the concrete by weight are as follows: P·O 42.5 cement: 100 parts; Grade I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10mm as lightweight aggregate: 50 parts; self-healing filler: 12 parts; composite hydrogel: 5 parts; polycarboxylate superplasticizer: 1.2 parts; water: 44 parts; dry mix cement, fly ash and silica fume for 3 minutes at a stirring speed of 30 rpm; add lightweight aggregate, self-healing filler and composite hydrogel, continue to dry mix for 5 minutes at a stirring speed of 60 rpm; add water and superplasticizer, wet mix for 8 minutes until uniform at a stirring speed of 100 rpm to obtain lightweight self-healing concrete material; pour into the mold, vibrate to compact, cover with curing film, and cure for 28 days at a temperature of 25℃ and a humidity of 95% to obtain lightweight self-healing concrete.

[0038] Comparative Example 1

[0039] The difference between Comparative Example 1 and Example 2 lies in step (1). Step (1) is changed to: dissolving calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1.5 mol / L for later use; immersing zeolite with a particle size of 100 μm into the calcium nitrate solution with a solid-liquid ratio of 1:15 and a reaction time of 45 min to obtain a self-healing filler; the remaining steps are the same as in Example 2.

[0040] Comparative Example 2

[0041] The difference between Comparative Example 2 and Example 2 lies in step (1). Step (1) is changed as follows: Sodium silicate, sodium aluminate, and deionized water are mixed at a silicon-aluminum molar ratio of 2.5:1:10. 0.5 mol / L sodium hydroxide aqueous solution is added to adjust the pH to 11.5. The mixture is stirred at 120 rpm for 2 hours to form a uniform sol. Hollow glass microspheres with a particle size of 125 μm, a cavity ratio of 80%, and a shell thickness of 1.25 μm are immersed in the sol. The volume of the sol is 3 times the volume of the microspheres. The mixture is stirred at a constant temperature of 60°C for 6 hours at a stirring speed of 60 rpm to allow the sol to deposit on the surface of the microspheres. Then, the mixture is transferred to a high-pressure reactor and hydrothermally reacted at 120°C for 24 hours to generate porous zeolite crystals. After the reaction, the mixture is centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80°C for 4 hours to obtain the self-healing filler. The remaining steps are the same as in Example 2.

[0042] Comparative Example 3

[0043] The difference between Comparative Example 3 and Example 2 lies in step (1). Step (1) is changed as follows: calcium nitrate is dissolved in deionized water to prepare a calcium nitrate solution with a concentration of 1.5 mol / L for later use; hollow glass microspheres with a particle size of 125 μm, a cavity ratio of 80%, and a shell thickness of 1.25 μm are immersed in the calcium nitrate solution with a solid-liquid ratio of 1:15, placed in a vacuum reactor, and evacuated to a vacuum degree of -0.095 MPa for 45 min to remove air from the microsphere cavity; the vacuum is slowly released to atmospheric pressure at a vacuum release rate of 0.02 MPa / min, and the calcium nitrate solution is allowed to penetrate into the microsphere cavity by using the pressure difference. This cycle is repeated 3 times to increase the loading capacity. Then the microspheres are filtered and dried at 60°C for 12 h to obtain the self-healing filler; the remaining steps are the same as in Example 2.

[0044] Comparative Example 4

[0045] The difference between Comparative Example 4 and Example 2 lies in step (2). Step (2) is changed as follows: Sodium carboxymethyl cellulose is dissolved in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%; the sodium carboxymethyl cellulose solution is stirred at room temperature for 30 min at a stirring speed of 300 rpm to form a hydrogel; after standing for 12 h to complete cross-linking, it is cut into gel particles with a particle size of 2 mm; the gel particles are immersed in a tris(hydroxymethyl)aminomethane buffer containing 2 mg / mL dopamine hydrochloride, oxygen is introduced, and the flow rate is 0.5 L / (min·L reaction solution), and stirred at 25°C in the dark for 24 h at a stirring speed of 120 rpm; after stirring, it is rinsed 3 times with deionized water and freeze-dried at -40°C for 48 h to obtain a composite hydrogel; the remaining steps are the same as in Example 2.

[0046] Comparative Example 5

[0047] The difference between Comparative Example 5 and Example 2 lies in step (2). Step (2) is changed as follows: Sodium carboxymethyl cellulose is dissolved in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4 wt%; ferric chloride is mixed with deionized water to prepare a ferric chloride solution with a concentration of 0.2 mol / L; the sodium carboxymethyl cellulose solution and the ferric chloride solution are mixed at a volume ratio of 10:1, stirred at room temperature for 30 min at a stirring speed of 300 rpm to form Fe³⁺ crosslinked hydrogel; after standing for 12 h to complete the crosslinking, it is cut into composite hydrogels with a particle size of 2 mm; the remaining steps are the same as in Example 2.

[0048] Example of effect

[0049] Table 1 below presents the performance analysis results of a lightweight self-healing concrete using Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention.

[0050] Table 1

[0051]

[0052] A comparison of the experimental data on repair efficiency between the examples and comparative examples reveals that this invention utilizes negative pressure impregnation technology to efficiently encapsulate calcium nitrate solution within hollow glass microspheres. After removing air from the microsphere cavities through vacuum extraction, the solution is fully immersed into the cavities using pressure difference, increasing the catalyst core loading. Subsequently, a porous zeolite crystal coating is grown in situ on the surface of the microspheres using the sol-gel method, forming a self-healing filler with a core-shell-pore gradient structure. The zeolite layer further adsorbs and stores calcium ions due to its high specific surface area, and the release rate is regulated through nanopores. When concrete cracks, stress concentration causes the microspheres to rupture, and the rapid release of Ca²⁺ within the cavity triggers a rapid reaction between silicate and CO₂, generating CSH gel and calcium carbonate to fill the cracks. Simultaneously, the Ca²⁺ adsorbed in the zeolite layer gradually dissociates with water penetration, and combined with the Na⁺ / Ca²⁺ ion exchange effect of zeolite, it continuously repairs newly formed microcracks, forming a dual mode of rapid repair and long-term sustained release. A comparison of experimental data on the average carbonization depth of the examples and comparative examples reveals that the hydroxyl groups on the surface of the zeolite coating synthesized by hydrothermal methods in this invention chemically bond with the cement matrix, enhancing the interfacial shear strength. This reduces the density of the microsphere-doped concrete to achieve a lightweight effect while maintaining compressive strength. Furthermore, in a saline environment, the crack healing rate is maximized due to the activation of zeolite ion exchange capacity by Cl⁻. This invention uniformly coats polydopamine onto the surface and pores of a carboxymethyl cellulose hydrogel network via in-situ oxidative polymerization, forming a photothermally responsive composite hydrogel. When irradiated with near-infrared light, polydopamine efficiently absorbs light energy and converts it into heat energy, causing a rapid increase in local temperature. This temperature rise triggers the dissociation of the dynamic coordination bonds between Fe³⁺ and the carboxylate groups of carboxymethyl cellulose, accelerating the synergistic release of Fe³⁺ and Ca²⁺ ions. Simultaneously, the heat promotes the rapid directional crystallization of the repair products by accelerating ion diffusion, forming a dense mineralized layer. Furthermore, the dynamic reversibility of hydrogels allows them to restore their network structure through Fe³⁺-COO⁻ bond recombination after cooling, achieving multiple photothermal cycle repair capabilities and providing long-term repair for concrete. A comparison of the density experimental data from the examples and comparative examples reveals that this invention utilizes lightweight structures such as hollow glass microspheres, porous zeolite, and hydrogels to improve concrete density.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing lightweight self-healing concrete, characterized in that, The preparation steps include the following: (1) Dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1.5 mol / L for later use; immerse hollow glass microspheres with a particle size of 125 μm, a cavity ratio of 80%, and a shell thickness of 1.25 μm into the calcium nitrate solution with a solid-liquid ratio of 1:15, place them in a vacuum reactor, evacuate to a vacuum degree of -0.095 MPa, and react for 45 min to remove air from the microsphere cavity; slowly release the vacuum to atmospheric pressure at a vacuum release rate of 0.02 MPa / min, and use the pressure difference to allow the calcium nitrate solution to permeate into the microsphere cavity. Repeat the cycle 3 times to increase the loading, then filter and take the microspheres, dry them at 60℃ for 12 h to obtain calcium nitrate encapsulated microspheres; mix sodium silicate, sodium aluminate, and deionized water according to the silicon-aluminum molar ratio A mixture of 2.5:1:10 was prepared, and 0.5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 11.

5. The mixture was stirred at 120 rpm for 2 hours to form a homogeneous sol. Calcium nitrate-encapsulated microbeads were immersed in the sol, with the sol volume being three times the volume of the microbeads. The mixture was stirred at 60℃ for 6 hours at a stirring speed of 60 rpm to allow the sol to deposit on the surface of the microbeads. The mixture was then transferred to a high-pressure reactor and subjected to hydrothermal reaction at 120℃ for 24 hours to generate porous zeolite crystals. After the reaction, the mixture was centrifuged at 8000 rpm for 5 minutes, washed three times with deionized water, and then dried at 80℃ for 4 hours to obtain a core-shell-pore structure self-healing filler. (2) Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4wt%; mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2mol / L; mix the sodium carboxymethyl cellulose solution and the ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min at a stirring speed of 300 rpm to form Fe³⁺ cross-linked hydrogel; allow to stand for 12 h to complete cross-linking, and cut into gel particles with a particle size of 2 mm; immerse the gel particles in a tris(hydroxymethyl)aminomethane buffer containing 2 mg / mL dopamine hydrochloride, introduce oxygen at a flow rate of 0.5 L / (min·L reaction solution), stir at 25℃ in the dark for 24 h at a stirring speed of 120 rpm; after stirring, rinse with deionized water 3 times, freeze-dry at -40℃ for 48 h to obtain photothermal responsive composite hydrogel; (3) The raw material proportions of the concrete by weight are as follows: P·O 42.5 cement: 100 parts; Grade I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10 mm as lightweight aggregate: 50 parts; self-healing filler: 10 parts; composite hydrogel: 4 parts; polycarboxylate superplasticizer: 1.2 parts; water: 44 parts; dry mix cement, fly ash and silica fume for 3 minutes at a stirring speed of 25 rpm; add lightweight aggregate, self-healing filler and composite hydrogel, continue to dry mix for 5 minutes at a stirring speed of 50 rpm; add water and superplasticizer, wet mix for 8 minutes until uniform at a stirring speed of 90 rpm to obtain lightweight self-healing concrete material; pour into the mold, vibrate to compact, cover with curing film, and cure for 28 days at a temperature of 25℃ and a humidity of 95% to obtain lightweight self-healing concrete.

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