Lightweight self-repairing concrete and preparation method thereof

Abstract

The invention discloses light self-repairing concrete and a preparation method thereof, and relates to the technical field of concrete. The method comprises the following steps: firstly, efficiently packaging a calcium nitrate solution in hollow glass beads by utilizing a negative pressure impregnation technology; then growing a porous zeolite crystal coating on the surface of the microbead in situ by adopting a sol-gel method to form a self-repairing filler with a core-shell-hole gradient structure; when the concrete cracks to cause the cracking of the microbeads, the Ca < 2 + > in the cavity is quickly released, and the Ca < 2 + > adsorbed in the zeolite layer is gradually dissociated along with water permeation, so that the new microcracks are continuously repaired. Then, uniformly coating the surface and pores of the carboxymethyl cellulose hydrogel network with polydopamine in an in-situ oxidative polymerization manner to form composite hydrogel with photo-thermal responsiveness; lighting and heating to trigger dynamic coordination bond dissociation; meanwhile, heat drives rapid directional crystallization of a repair product by promoting the ion diffusion rate, and a compact mineralization layer is formed. The concrete prepared by the invention has the effects of light weight and self-repairing.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and specifically relates to a lightweight self-healing concrete and a preparation method thereof. Background Art

[0002] Concrete is widely used in engineering fields such as buildings, bridges, and tunnels. However, during service, traditional concrete is prone to generating microcracks due to factors such as loads, shrinkage, and temperature changes. These cracks become the penetration channels for erosion media such as water and chloride ions, accelerating the corrosion of internal steel bars and the deterioration of the matrix, resulting in a serious decline in the structural durability. To extend the lifespan of concrete, existing technologies mainly focus on crack repair: one is the self-healing technology based on microbial mineralization, which induces calcium carbonate deposition at the cracks by embedding bacteria producing carbonic anhydrase. However, the activity of its strains is easily inhibited by the high-alkali environment, and the repair efficiency is limited by nutrient supply and humidity conditions; the second is to use microcapsules or hollow fibers to encapsulate repair agents, which rely on crack expansion to trigger release. However, the compatibility between organic repair agents and the cement matrix is poor, easily forming a weak interface, and a too high dosage of microcapsules will significantly reduce the strength of concrete; the third is shape memory polymer-assisted repair, which closes cracks through the deformation recovery force of thermosensitive polymer materials, but requires an external heat source to trigger and is difficult to repair wide cracks >0.3 mm. The above technologies generally have defects such as a single repair mechanism, insufficient environmental adaptability, and the risk of secondary damage. Moreover, most solutions do not consider the lightweight requirements of concrete, resulting in limited applications in scenarios sensitive to material self-weight such as high-rise buildings and long-span bridges.

[0003] The research and development demand for lightweight self-healing concrete stems from the urgent requirements of modern engineering for the integration of material functions. On the one hand, traditional concrete has a high density, resulting in an excessive structural self-weight, increasing the foundation load and building material consumption. Lightweight concrete can reduce the self-weight by 20% - 30% by introducing lightweight aggregates such as ceramsite and hollow microspheres. However, the porous characteristics of lightweight aggregates exacerbate the risk of crack initiation. On the other hand, a single self-healing technology is difficult to cope with complex service environments. For example, marine engineering needs to resist chloride ion erosion and dry-wet cycles simultaneously, and freeze-thaw areas need to balance crack repair and frost heaving resistance capabilities. Therefore, synergistically optimizing lightweight and self-healing functions has become the key to breaking through the bottleneck of existing technologies. Lightweight self-healing concrete, through gradient structure design and the combination of intelligent response materials, can not only achieve rapid filling and long-term inhibition of cracks but also maintain mechanical properties of low density and high strength. Summary of the Invention

[0004] The purpose of the present invention is to provide a lightweight self-healing concrete and a preparation method thereof to solve the problems existing in the prior art.

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

[0006] (1) Immerse calcium nitrate encapsulated microspheres into the sol, the volume of the sol is 3 times the volume of the microspheres, stir at a constant temperature of 60 °C for 6 h, and the stirring speed is 60 rpm to deposit the sol on the surface of the microspheres; then transfer to a high-pressure reaction kettle and carry out hydrothermal reaction at 120 °C for 24 h to generate porous zeolite crystals; after the reaction, centrifuge at 8000 rpm for 5 min, then wash 3 times with deionized water, and then dry at 80 °C for 4 h to obtain the core-shell-porous structure self-healing filler;

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

[0008] (3) Dry-mix cement, fly ash, and silica fume for 3 min, and the stirring speed is 20 - 30 rpm; add lightweight aggregate, self-healing filler, and composite hydrogel, and continue dry-mix for 5 min, and the stirring speed is 40 - 60 rpm; add water and water reducer, and wet-mix for 8 min until uniform, and the stirring speed is 80 - 100 rpm to prepare the lightweight self-healing concrete mixture; pour it into the mold, vibrate it densely, cover it with a curing film, and cure it to obtain the lightweight self-healing concrete.

[0009] 2. The preparation method of a lightweight self-healing concrete according to claim 1, wherein the preparation method of the calcium nitrate encapsulated microspheres in the step (1) is: immerse hollow glass microspheres into the calcium nitrate solution, the solid-liquid ratio is 1:15, place them in a vacuum reaction kettle and evacuate to a vacuum degree of -0.095 MPa, and the reaction time is 30 - 60 min to expel the air in the microsphere cavity; slowly release the vacuum to normal pressure, and use the pressure difference to make the calcium nitrate solution penetrate into the microsphere cavity, repeat 3 cycles to increase the loading amount, then filter to obtain the microspheres, and dry at 60 °C for 12 h to obtain the calcium nitrate encapsulated microspheres.

[0010] Furthermore, the preparation method of the calcium nitrate solution is: 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 - 200 μm, a cavity ratio of 80%, and a shell thickness of 0.5 - 2 μm.

[0012] Furthermore, when slowly releasing the vacuum to atmospheric pressure, the vacuum release rate is 0.02 MPa / min.

[0013] Furthermore, the preparation method of the sol in step (1) is as follows: Mix sodium silicate, sodium aluminate, and deionized water according to a silicon - aluminum molar ratio of 2.5:1:10, add a 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH to 11.5, and stir at a speed of 120 rpm for 2 h to form a homogeneous sol.

[0014] Furthermore, the preparation method of the sodium carboxymethylcellulose aqueous solution in step (2) is as follows: Dissolve sodium carboxymethylcellulose in deionized water to prepare a sodium carboxymethylcellulose aqueous solution with a concentration of 4 wt%.

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

[0016] Furthermore, the mass - fraction raw material ratio of the concrete in step (3) is as follows: P·O 42.5 cement: 100 parts; Class 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 d under the conditions of 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] The present invention modifies concrete with a core - shell - pore - structured self - healing filler and a photothermal - responsive composite hydrogel to achieve the effects of light weight and self - healing.

[0020] First, calcium nitrate solution is efficiently encapsulated inside the hollow glass microspheres by using the negative - pressure impregnation technique. After evacuating the air in the microsphere cavity by vacuum pumping, the solution fully immerses into the cavity by means of the pressure difference, improving the catalyst core loading; subsequently, a sol - gel method is adopted to in - situ grow a porous zeolite crystal coating on the surface of the microspheres to form a self - healing filler with a core - shell - pore gradient structure; the zeolite layer further adsorbs and stores calcium ions by virtue of its high specific surface area and regulates the release rate through nanopores; when the concrete cracks, stress concentration causes the microspheres to rupture, and Ca in the cavity 2+The rapid release triggers a rapid reaction between silicate and CO2, generating C-S-H gel and calcium carbonate to fill the cracks; meanwhile, the Ca adsorbed in the zeolite layer 2+ is gradually dissociated as water penetrates, combining with the Na of the zeolite + / Ca 2+ ion exchange effect to continuously repair newly generated microcracks, forming a dual mode of rapid repair and long-term slow release. In addition, the surface hydroxyl groups of the hydrothermally synthesized zeolite coating and the cement matrix are chemically bonded to enhance the interfacial shear strength, reducing the density of the concrete doped with microbeads to achieve a lightweight effect while ensuring the compressive strength. Moreover, in a saline environment, due to the activation of the zeolite ion exchange ability by Cl-, the crack healing rate is maximally optimized.

[0021] Secondly, polydopamine is uniformly coated on the surface and pores of the carboxymethyl cellulose hydrogel network by in-situ oxidative polymerization to form a composite hydrogel with photothermal responsiveness; when irradiated with near-infrared light, polydopamine efficiently absorbs light energy and converts it into heat, rapidly increasing the local temperature; this temperature rise triggers the dissociation of the dynamic coordination bonds between Fe 3+ and the carboxylate groups of carboxymethyl cellulose, accelerating the coordinated release of Fe 3+ and Ca 2+ ions; meanwhile, heat drives the rapid directional crystallization of the repair products by promoting the ion diffusion rate, forming a dense mineralized layer. In addition, due to the dynamic reversibility of the hydrogel, it restores the network structure through the recombination of Fe 3+ -COO- bonds after cooling, achieving the ability of multiple photothermal cycle repairs and providing long-term repair ability for the concrete. Specific embodiments

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. 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 protection scope of the present invention.

[0023] In order to more clearly illustrate the method provided by the present invention, it is described in detail through the following embodiments. The test methods for each index of a lightweight self-repairing concrete prepared in the following embodiments are as follows:

[0024] Durability: According to the provisions of the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082-2009), the embodiments and the concrete are made into corresponding sizes and cured for 28 days under the conditions of a temperature of 25 °C and a relative humidity of 95%, and then the average carbonation depth of the concrete is measured.

[0025] Self-healing property: The press was debugged to load at a rate of 0.05 mm / min. When a 0.2-mm crack appeared at the lowermost end of the tensile side of the specimens of the examples and the comparative examples, the loading was stopped and the load was maintained for 90 s and then unloaded. The specimens were cured by sprinkling water for 14 d, and the crack extension morphology and repair performance were measured by a 150X crack observation instrument and an electron scanning microscope.

[0026] Example 1

[0027] (1) Calcium nitrate was dissolved in deionized water to prepare a calcium nitrate solution with a concentration of 1 mol / L for standby. Hollow glass microspheres with a particle size of 50 μm, a cavity ratio of 80%, and a shell thickness of 0.5 μm were immersed in the calcium nitrate solution with a solid-liquid ratio of 1:15. They were placed in a vacuum reactor and evacuated to a vacuum degree of -0.095 MPa for 30 min to expel the air in the microsphere cavities. The vacuum was slowly released to normal pressure at a rate of 0.02 MPa / min, and the calcium nitrate solution was infiltrated into the microsphere cavities by using the pressure difference. The cycle was repeated 3 times to increase the loading amount. Then, the microspheres were filtered and dried at 60 °C for 12 h to obtain calcium nitrate-encapsulated microspheres. Sodium silicate, sodium aluminate, and deionized water were mixed according to a silicon-aluminum molar ratio of 2.5:1:10, and 0.5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 11.5. Stirring was carried out at a speed of 120 rpm for 2 h to form a uniform sol. The calcium nitrate-encapsulated microspheres were immersed in the sol, and the volume of the sol was 3 times the volume of the microspheres. Stirring was carried out at a constant temperature of 60 °C for 6 h at a stirring speed of 60 rpm to deposit the sol on the surface of the microspheres. Then, they were transferred to a high-pressure reactor and hydrothermally reacted at 120 °C for 24 h to generate porous zeolite crystals. After the reaction, centrifugal separation was carried out at 8000 rpm for 5 min, and then washed 3 times with deionized water and dried at 80 °C for 4 h to obtain a core-shell-porous structure self-healing filler.

[0028] (2) Sodium carboxymethyl cellulose was dissolved in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4 wt%. Ferric chloride and deionized water were mixed to prepare a ferric chloride solution with a concentration of 0.2 mol / L. The sodium carboxymethyl cellulose solution and the ferric chloride solution were mixed at a volume ratio of 10:1 and stirred at room temperature for 30 min at a stirring speed of 200 rpm to form a Fe 3+ cross-linked hydrogel. Standing for 12 h to complete cross-linking, and then cut into gel particles with a particle size of 1 mm. The gel particles were immersed in a tris(hydroxymethyl)aminomethane buffer solution containing 2 mg / mL dopamine hydrochloride, and oxygen was introduced with a flow rate of 0.5 L / (min·L reaction solution). Stirring was carried out at 25 °C in the dark for 24 h at a stirring speed of 120 rpm. After stirring, they were rinsed 3 times with deionized water and freeze-dried at -40 °C for 48 h to obtain a photothermal-responsive composite hydrogel.

[0029] (3) The mass fraction raw material ratio of the concrete is as follows: P·O 42.5 cement: 100 parts; Class 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 water reducer: 1.2 parts; water: 44 parts; Dry mix the cement, fly ash, and silica fume for 3 min at a stirring speed of 20 rpm; add the lightweight aggregate, self-healing filler, and composite hydrogel, and continue dry mixing for 5 min at a stirring speed of 40 rpm; add water and water reducer, and wet mix for 8 min until uniform at a stirring speed of 80 rpm to obtain lightweight self-healing concrete mixture; Pour it into the mold, vibrate and compact it, cover it with a curing film, and cure it for 28 d at a temperature of 25 °C 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 standby; 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 the reaction time is 45 min to expel the air in the microsphere cavity; Slowly release the vacuum to normal pressure, with a vacuum release rate of 0.02 MPa / min, and use the pressure difference to infiltrate the calcium nitrate solution into the microsphere cavity, repeat 3 cycles to increase the loading amount, then filter to obtain the microspheres, and dry them at 60 °C for 12 h to obtain calcium nitrate encapsulated microspheres; Mix sodium silicate, sodium aluminate, and deionized water according to 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, and stir at a speed of 120 rpm for 2 h to form a uniform sol; Immerse the calcium nitrate encapsulated microspheres into the sol, with the sol volume being 3 times the volume of the microspheres, stir at a constant temperature of 60 °C for 6 h, and the stirring speed is 60 rpm to deposit the sol on the surface of the microspheres; Then transfer it to a high-pressure reactor, carry out a hydrothermal reaction at 120 °C for 24 h to generate porous zeolite crystals; After the reaction, centrifuge and separate at 8000 rpm for 5 min, then wash with deionized water 3 times, and then dry at 80 °C for 4 h to obtain the 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 4 wt%; Mix ferric chloride and deionized water to prepare a ferric chloride solution with a concentration of 0.2 mol / L; Mix the sodium carboxymethyl cellulose solution and the ferric chloride solution according to a volume ratio of 10:1, stir at room temperature for 30 min, and the stirring speed is 300 rpm to form Fe 3+Crosslinked hydrogel; crosslinking was completed by standing for 12 h, and the gel was cut into gel particles with a particle size of 2 mm; the gel particles were immersed in a tris(hydroxymethyl)aminomethane buffer solution containing 2 mg / mL dopamine hydrochloride, oxygen was introduced, and the flow rate was 0.5 L / (min·L reaction solution), and stirred at 25 °C in the dark for 24 h, and the stirring speed was 120 rpm; after the stirring was completed, it was rinsed 3 times with deionized water and freeze-dried at -40 °C for 48 h to obtain a photothermal-responsive composite hydrogel;

[0033] (3) The mass fraction raw material ratio of the concrete is as follows: P·O 42.5 cement: 100 parts; Class 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; the cement, fly ash, and silica fume were dry-mixed for 3 min, and the stirring speed was 25 rpm; the lightweight aggregate, self-healing filler, and composite hydrogel were added, and dry-mixed for another 5 min, and the stirring speed was 50 rpm; water and superplasticizer were added, and wet-mixed for 8 min until uniform, and the stirring speed was 90 rpm to prepare a lightweight self-healing concrete mixture; poured into a mold, vibrated and compacted, covered with a curing film, and cured for 28 d at a temperature of 25 °C and a humidity of 95% to obtain lightweight self-healing concrete.

[0034] Example 3

[0035] (1) Calcium nitrate was dissolved in deionized water to prepare a calcium nitrate solution with a concentration of 2 mol / L for standby; hollow glass microspheres with a particle size of 200 μm, a cavity ratio of 80%, and a shell thickness of 2 μm were immersed in the calcium nitrate solution, the solid-liquid ratio was 1:15, placed in a vacuum reactor, evacuated to a vacuum degree of -0.095 MPa, and the reaction time was 60 min to expel the air in the microsphere cavity; the vacuum was slowly released to normal pressure, and the vacuum release rate was 0.02 MPa / min, and the calcium nitrate solution was infiltrated into the microsphere cavity by using the pressure difference, and the cycle was repeated 3 times to increase the loading amount, and then the microspheres were filtered and dried at 60 °C for 12 h to obtain calcium nitrate encapsulated microspheres; sodium silicate, sodium aluminate, and deionized water were mixed according to a silicon-aluminum molar ratio of 2.5:1:10, and 0.5 mol / L sodium hydroxide aqueous solution was added to adjust the pH to 11.5, and stirred at a speed of 120 rpm for 2 h to form a uniform sol; the calcium nitrate encapsulated microspheres were immersed in the sol, and the volume of the sol was 3 times the volume of the microspheres, and stirred at a constant temperature of 60 °C for 6 h, and the stirring speed was 60 rpm to deposit the sol on the surface of the microspheres; then transferred to a high-pressure reactor, and hydrothermally reacted at 120 °C for 24 h to generate porous zeolite crystals; after the reaction was completed, centrifuged at 8000 rpm for 5 min, then washed 3 times with deionized water, and dried at 80 °C for 4 h to obtain a core-shell-porous structure self-healing filler;

[0036] (2) Sodium carboxymethyl cellulose was dissolved in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4 wt%; ferric chloride was 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 were mixed in a volume ratio of 10:1, stirred at room temperature for 30 min at a stirring speed of 400 rpm to form Fe 3+ Cross-linking the hydrogel; standing for 12 hours to complete cross-linking, cutting into gel particles with a particle size of 3 mm; immersing the gel particles in a tris-hydroxymethylaminomethane buffer containing 2 mg / mL dopamine hydrochloride, introducing oxygen at a flow rate of 0.5 L / (min·L reaction solution), stirring at 25°C in the dark for 24 hours at a stirring speed of 120 rpm; after the stirring, rinsing with deionized water three times, and freeze-drying at -40°C for 48 hours to obtain a photothermal responsive composite hydrogel;

[0037] (3) The mass ratio of raw materials for concrete is as follows: P·O 42.5 cement: 100 parts; Class I fly ash: 20 parts; silica fume: 5 parts; ceramsite with a particle size of 5-10 mm as lightweight aggregate: 50 parts; self-repairing filler: 12 parts; composite hydrogel: 5 parts; polycarboxylic acid water reducer: 1.2 parts; water: 44 parts; dry mix the cement, fly ash and silica fume for 3 minutes at a stirring speed of 30 rpm; add the lightweight aggregate, self-repairing filler and composite hydrogel, and continue dry mixing for 5 minutes at a stirring speed of 60 rpm; add water and water reducer, wet mix for 8 minutes until uniform, and stir at a speed of 100 rpm to obtain lightweight self-repairing concrete; pour into the mold, vibrate to compact, cover with curing film, and cure for 28 days at a temperature of 25°C and a humidity of 95% to obtain lightweight self-repairing concrete.

[0038] Comparative Example 1

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

[0040] Comparative Example 2

[0041] The difference between Comparative Example 2 and Example 2 lies in step (1). Modify step (1) as follows: 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, and stir at a speed of 120 rpm for 2 h to form a homogeneous sol; 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 sol. The volume of the sol is 3 times the volume of the microspheres. Stir at a constant temperature of 60 °C for 6 h at a stirring speed of 60 rpm to deposit the sol on the surface of the microspheres; Then transfer to a high-pressure reaction kettle and perform a hydrothermal reaction at 120 °C for 24 h to generate porous zeolite crystals; After the reaction, centrifuge at 8000 rpm for 5 min, then wash 3 times with deionized water, and then dry at 80 °C for 4 h 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). Modify step (1) as follows: Dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1.5 mol / L for standby; 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. The solid-liquid ratio is 1:15. Place it in a vacuum reaction kettle and evacuate to a vacuum degree of -0.095 MPa for 45 min to expel the air in the microsphere cavities; Slowly release the vacuum to normal pressure at a vacuum release rate of 0.02 MPa / min, and use the pressure difference to infiltrate the calcium nitrate solution into the microsphere cavities. Repeat 3 cycles to increase the loading amount, then filter to obtain the microspheres and dry 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). Modify step (2) as follows: Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4 wt%; Stir the sodium carboxymethyl cellulose solution at room temperature for 30 min at a stirring speed of 300 rpm to form a hydrogel; Let it stand for 12 h to complete cross-linking, and cut it into gel particles with a particle size of 2 mm; Immerse the gel particles into a tris(hydroxymethyl)aminomethane buffer solution containing 2 mg / mL dopamine hydrochloride, introduce oxygen, and the flow rate is 0.5 L / (min·L reaction solution). Stir at 25 °C in the dark for 24 h at a stirring speed of 120 rpm; After stirring, rinse 3 times with deionized water and freeze-dry at -40 °C for 48 h to obtain the 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 to: Dissolve sodium carboxymethylcellulose in deionized water to prepare an aqueous sodium carboxymethylcellulose solution with a concentration of 4 wt%; mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2 mol / L; mix the sodium carboxymethylcellulose solution and the ferric chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min, and the stirring speed is 300 rpm to form Fe 3+ crosslinked hydrogel; let it stand for 12 h to complete crosslinking, and cut it into composite hydrogels with a particle size of 2 mm; the remaining steps are the same as those in Example 2.

[0048] Effect Example

[0049] 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 are given in Table 1 below.

[0050] Table 1

[0051]

[0052] From the comparison of the experimental data on the repair efficiency of the examples and comparative examples, it can be found that the present invention uses the negative pressure impregnation technology to efficiently encapsulate the calcium nitrate solution inside the hollow glass microspheres. After evacuating the air in the microsphere cavity by vacuum pumping, the solution is fully immersed in the cavity by means of the pressure difference to increase the catalyst core loading; subsequently, the sol-gel method is used to in-situ grow a porous zeolite crystal coating on the surface of the microspheres to form a self-healing filler with a core-shell-pore gradient structure; the zeolite layer further adsorbs and stores calcium ions by virtue of its high specific surface area, and regulates the release rate through nanochannels; when the concrete cracks, the stress concentration causes the microspheres to rupture, and the Ca 2+ rapidly releases to trigger the rapid reaction of silicate and CO2 to generate C-S-H gel and calcium carbonate to fill the cracks; at the same time, the Ca adsorbed in the zeolite layer 2+ gradually dissociates with the penetration of water, and combines with the Na + / Ca 2+ ion exchange effect of zeolite to continuously repair new microcracks, forming a dual mode of rapid repair and long-term slow release. From the comparison of the experimental data on the average carbonation depth of the examples and comparative examples, it can be found that the surface hydroxyl groups of the zeolite coating synthesized by hydrothermal synthesis of the present invention are chemically bonded to the cement matrix, improving the interfacial shear strength, reducing the density of the concrete doped with microspheres to achieve the lightweight effect while ensuring the compressive strength, and optimizing the crack healing rate due to the activation of the zeolite ion exchange ability by Cl- in the saline environment. The present invention uniformly coats polydopamine on the surface and pores of the carboxymethylcellulose hydrogel network by in-situ oxidative polymerization to form a composite hydrogel with photothermal responsiveness; when irradiated with near-infrared light, polydopamine efficiently absorbs light energy and converts it into heat energy, causing the local temperature to rise rapidly; this temperature rise triggers Fe 3+The dynamic coordination bond dissociation with the carboxylate groups of carboxymethyl cellulose accelerates the release of Fe 3+ and Ca 2 + ions; simultaneously, heat drives the rapid directional crystallization of the repair product by promoting the ion diffusion rate to form a dense mineralized layer. In addition, the dynamic reversibility of the hydrogel enables it to restore the network structure through the recombination of Fe 3+ -COO- bonds after cooling, realizing the ability of multiple photothermal cycle repairs and providing long-term repair ability for concrete. From the comparison of the experimental data of the density of the examples and the comparative examples, it can be found that the present invention uses lightweight structures such as hollow glass microspheres, porous zeolites, and hydrogels to improve the density of concrete.

[0053] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claimed claim.

Claims

1. A lightweight self-healing concrete, characterized in that, The concrete is modified with a core-shell-pore structure self-healing filler and a photothermal-responsive composite hydrogel, and the preparation steps are as follows: (1) Immerse the calcium nitrate encapsulated microspheres in the sol, the volume of the sol is 3 times the volume of the microspheres, stir at a constant temperature of 60 °C for 6 h, and the stirring speed is 60 rpm to deposit the sol on the surface of the microspheres; then transfer to a high-pressure reactor and carry out a hydrothermal reaction at 120 °C for 24 h to generate porous zeolite crystals; after the reaction, centrifuge at 8000 rpm for 5 min, then wash 3 times with deionized water, and then dry at 80 °C for 4 h to obtain the core-shell-pore structure self-healing filler; (2) Mix the sodium carboxymethyl cellulose solution and the iron chloride solution at a volume ratio of 10:1, stir at room temperature for 30 min, and the stirring speed is 200 - 400 rpm to form Fe 3+ crosslinked hydrogel; let it stand for 12 h to complete crosslinking, and cut it into gel particles with a particle size of 1 - 3 mm; immerse the gel particles in a tris(hydroxymethyl)aminomethane buffer solution containing 2 mg / mL dopamine hydrochloride, introduce oxygen, and the flow rate is 0.5 L / (min·L reaction solution), stir at 25 °C in the dark for 24 h, and the stirring speed is 120 rpm; after stirring, rinse with deionized water 3 times, and freeze-dry at -40 °C for 48 h to obtain a photothermal-responsive composite hydrogel; (3) Dry-mix cement, fly ash, and silica fume for 3 min, and the stirring speed is 20-30 rpm; add lightweight aggregate, self-healing filler, and composite hydrogel, and continue dry-mixing for 5 min, and the stirring speed is 40-60 rpm; add water and water reducer, and wet-mix for 8 min until uniform, and the stirring speed is 80-100 rpm to prepare lightweight self-healing concrete; pour into the mold, vibrate and compact, cover with a curing film, and cure to obtain lightweight self-healing concrete.

2. A lightweight self-healing concrete according to claim 1, wherein, The preparation method of the calcium nitrate encapsulated microspheres in the step (1) is: Immerse the hollow glass microspheres in the calcium nitrate solution, the solid-liquid ratio is 1:15, place them in a vacuum reactor and evacuate to a vacuum degree of -0.095 MPa, and the reaction time is 30-60 min to expel the air in the microsphere cavity; slowly release the vacuum to normal pressure, and use the pressure difference to make the calcium nitrate solution penetrate into the microsphere cavity, repeat 3 cycles to increase the loading amount, then filter to obtain the microspheres, and dry at 60 °C for 12 h to obtain the calcium nitrate encapsulated microspheres.

3. The lightweight self-healing concrete according to claim 2, wherein The preparation method of the calcium nitrate solution is: Dissolve calcium nitrate in deionized water to prepare a calcium nitrate solution with a concentration of 1-2 mol / L.

4. A lightweight self-healing concrete according to claim 2, characterized in that, The particle size of the hollow glass microspheres is 50-200 μm, the cavity ratio is 80%, and the shell thickness is 0.5-2 μm.

5. The lightweight self-healing concrete according to claim 2, wherein When slowly releasing the vacuum to normal pressure, the vacuum release rate is 0.02 MPa / min.

6. A lightweight self-healing concrete according to claim 1, characterized in that, The preparation method of the sol in the step (1) is: Mix sodium silicate, sodium aluminate, and deionized water according to the 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, and stir at a speed of 120 rpm for 2 h to form a uniform sol.

7. A lightweight self-healing concrete according to claim 1, characterized in that, The preparation method of the sodium carboxymethyl cellulose aqueous solution in the step (2) is: Dissolve sodium carboxymethyl cellulose in deionized water to prepare a sodium carboxymethyl cellulose aqueous solution with a concentration of 4 wt%.

8. A lightweight self-healing concrete according to claim 1, characterized in that, The preparation method of the ferric chloride solution in the step (2) is: Mix ferric chloride with deionized water to prepare a ferric chloride solution with a concentration of 0.2 mol / L.

9. A lightweight self-healing concrete according to claim 1, characterized in that, The mass ratio of the raw materials of the concrete in the step (3) is: P·O 42.5 cement: 100 parts; Class 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 water reducer: 1.2 parts; water: 44 parts.

10. A lightweight self-healing concrete according to claim 1, characterized in that, The curing conditions in the step (3) are: Cure for 28 d at a temperature of 25 °C and a humidity of 95%.

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