In-situ encapsulated self-healing core-shell structure particles, cementitious and methods of making

Abstract

The present application relates to the technical field of concrete functional materials, and particularly relates to in-situ encapsulated self-healing core-shell structure particles, a cement-based material and a preparation method. In-situ encapsulated self-healing core-shell structure particles are mixed in the cement-based material mixing process, a C-S-H shell layer encapsulates the calcium oxide core in-situ in the cement paste, and is used for blocking the entry of water to prevent the hydration reaction of the calcium oxide core; during the service period, when the cement-based material produces cracks and is accompanied by structure damage, the C-S-H shell layer of the in-situ encapsulated self-healing core-shell structure particles is broken, the calcium oxide core is exposed, and the hydration reaction is caused. The in-situ encapsulated self-healing core-shell structure particle material and the self-healing cement-based material prepared by the present application realize the synergistic self-healing mechanism of "in-situ self-encapsulation-crack triggering-secondary mineralization filling", have the advantages of simple preparation process, low material cost and strong engineering applicability, and have good application prospects in the fields of concrete durability improvement and structure self-repair.

Description

Technical Field

[0001] This invention relates to the field of functional concrete materials technology, specifically to in-situ encapsulated self-healing core-shell structure particles, cement-based materials, and preparation methods. Background Technology

[0002] Concrete is a cement-based material. Concrete is prone to cracking during service. The presence of cracks allows moisture and harmful ions to penetrate, thereby reducing structural durability and shortening service life.

[0003] To address this issue, various self-healing technologies have been proposed in the existing technology field. Among them, inorganic self-healing systems, represented by expansive materials such as calcium oxide, have attracted widespread attention due to their rapid reaction and strong filling capacity.

[0004] However, the applicant found that existing calcium oxide-based self-healing materials still have significant shortcomings in practical applications:

[0005] (1) Calcium oxide is prone to rapid hydration during the mixing stage, which can lead to premature setting or even flash setting of concrete.

[0006] (2) The reaction process is difficult to control, and the self-healing effect lacks specificity and sustainability.

[0007] (3) The slow hydration of embedded overburned calcium oxide in the later stage has a great hazard to the stability of concrete.

[0008] Therefore, designing a self-healing material that can delay the reaction of calcium oxide and achieve "on-demand activation" when cracks occur is of great significance for improving the self-healing efficiency and durability of concrete. Summary of the Invention

[0009] To address the shortcomings of the existing technologies, the technical problem to be solved by this invention is: how to provide an in-situ encapsulated self-healing core-shell structure particle, a cement-based material, and a preparation method thereof. The prepared in-situ encapsulated self-healing core-shell structure particle material and self-healing cement-based material realize a synergistic self-healing mechanism of "in-situ self-encapsulation - crack triggering - secondary mineralization filling". It has the advantages of simple preparation process, low material cost and strong engineering applicability, and has good application prospects in the field of concrete durability improvement and structural self-repair.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] A method for preparing in-situ encapsulated self-healing core-shell structured particles includes:

[0012] S1: Obtain micron-sized calcium oxide powder and ester derivatives of orthosilicic acid;

[0013] S2: Calcium oxide powder, as the calcium oxide core, is mixed with an ester derivative of orthosilicic acid in a certain proportion to obtain a mixture;

[0014] S3: The mixture is uniformly mixed and granulated under stirring conditions to obtain precursor particles;

[0015] S4: Pre-curing the precursor particles with moisture under a preset environment: By utilizing the characteristic that the ester derivatives of orthosilicic acid only undergo hydrolysis and polymerization with moisture on the surface, a diffusion gradient is formed, which extracts and enriches the ester derivatives of orthosilicic acid near the surface of the calcium oxide core, so that the ester derivatives of orthosilicic acid undergo hydrolysis-condensation reaction with moisture in the air to obtain precursor particles with a calcium oxide-silica gel core-shell structure.

[0016] S5: The precursor particles with a calcium oxide-silica core-shell structure are placed in a high-temperature furnace for calcination;

[0017] S6: Cool the calcined precursor particles to obtain in-situ encapsulated self-healing core-shell structured particles with a tricalcium silicate shell on the surface.

[0018] In the mixing process of cement-based materials, in-situ encapsulated self-healing core-shell structured particles are mixed in. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in situ in the cement paste to encapsulate the calcium oxide core, which is used to prevent water from entering and thus prevent the hydration reaction of the calcium oxide core. During service, when the cement-based material develops cracks and is accompanied by structural damage, the CSH shell of the in-situ encapsulated self-healing core-shell structured particles ruptures, exposing the calcium oxide core and causing it to undergo a hydration reaction.

[0019] Preferably, in step S1, the ester derivative of orthosilicic acid is any one of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetraisopropyl silicate, tetrabutyl silicate, and tetraphenyl silicate.

[0020] Preferably, in step S4, the preset environment is an environment with a temperature of room temperature and a humidity greater than 60%RH.

[0021] Preferably, in step S5, the calcination temperature is 1400℃ and the holding time is 2-3 hours.

[0022] Preferably, in step S6, the thickness of the tricalcium silicate shell is 100–1000 μm, and it exhibits a silicon element gradient distribution along the radial direction.

[0023] Preferably, in step S6, when cracks appear in the concrete and structural damage occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structure particles ruptures at the crack, exposing the calcium oxide core. The calcium oxide core undergoes a hydration reaction with water in the crack to generate calcium hydroxide. The calcium ions dissolved in water further react with carbon dioxide in the environment to generate calcium carbonate, which recrystallizes in the crack, achieving secondary filling and repair of the crack. At the same time, the generated structural core is a porous and loose structure, which provides sufficient space for the hydration and expansion reaction of calcium oxide, avoiding the expansion hazards of free calcium oxide in the concrete.

[0024] In-situ encapsulated self-healing core-shell structured particles were prepared based on the in-situ encapsulated self-healing core-shell structured particle preparation method.

[0025] A method for preparing self-healing cement-based materials involves mixing in-situ encapsulated self-healing core-shell structured particles during the mixing process of cement-based materials. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in situ in the cement slurry, encapsulating the calcium oxide core, thereby preparing the self-healing cement-based material.

[0026] The self-healing cement-based material was prepared based on the self-healing cement-based material preparation method.

[0027] When self-healing cement-based materials develop cracks and structural damage occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structure particles ruptures at the crack, exposing the calcium oxide core. The calcium oxide core undergoes a hydration reaction with water in the crack to generate calcium hydroxide. The calcium ions dissolved in the water further react with carbon dioxide in the environment to generate calcium carbonate, which recrystallizes and fills the crack, thereby achieving self-healing of the crack and restoration of mechanical properties.

[0028] Compared with existing technologies, the in-situ encapsulated self-healing core-shell structure particles, cement-based materials, and preparation method of this invention have the following advantages:

[0029] (1) Blocking water from entering: The CSH shell can effectively inhibit the early hydration reaction of the calcium oxide core.

[0030] (2) Improve utilization efficiency: The self-healing component (calcium oxide core) is released when the crack is generated, which improves the utilization rate of in-situ encapsulated self-healing core-shell structure particulate materials.

[0031] (3) Enhanced repair effect: The calcium oxide core reacts with water and carbon dioxide to generate calcium hydroxide and calcium carbonate to fill the cracks and improve the density.

[0032] (4) Improved durability: Significantly reduces water absorption and improves compressive and flexural strength recovery.

[0033] (5) Simple process and easy to promote: The preparation process is simple and suitable for engineering applications.

[0034] Experimental results show that the in-situ encapsulated self-healing core-shell structured particles prepared in this invention can significantly regulate the hydration exothermic process and alkalinity release behavior, verifying their excellent encapsulation effect and activity retention capability. Simultaneously, this in-situ encapsulated self-healing core-shell structured particle material significantly improves the concrete crack healing rate, reduces capillary water absorption, and effectively restores compressive and flexural strength. Especially under wet-dry cycle conditions, concrete cracks can achieve efficient closure, and the recovery of mechanical properties is significantly improved.

[0035] In summary, this invention aims to solve the technical problem of poor concrete volume stability and easy harmful expansion caused by the excessively high early hydration activity of existing calcium oxide-based self-healing agents. This invention uses calcium oxide particles as the core material and utilizes the gradient diffusion and hydrolytic polymerization characteristics of orthosilicate ester derivatives (such as tetraethyl orthosilicate) in a wet environment. Through room temperature curing and high-temperature calcination, a dense tricalcium silicate (C3S) shell is grown in situ on the core material surface, constructing a core-shell structure of "C3S-rich shell - CaO-rich core". In this structure, the CSH shell layer formed during the initial hydration of the outer shell effectively blocks water from entering, preventing the hydration reaction of the calcium oxide core and preventing premature reaction of CaO before the concrete hardens. When the concrete cracks, the outer shell breaks, releasing the internal CaO. The Ca²⁺ generated upon contact with water reacts with external CO₂ to crystallize, achieving self-healing of cracks from the inside out. Experiments show that when the particle dosage is 5wt%, it only causes a 7% decrease in the compressive strength of the matrix, can completely repair a 0.3mm wide crack within 14 days, reduces the capillary water absorption coefficient by 88%, and inhibits approximately 30% of early shrinkage without the risk of later expansion. The in-situ encapsulated self-healing core-shell structure particle material and self-healing cement-based material prepared by this invention achieve a synergistic self-healing mechanism of "in-situ self-encapsulation - crack triggering - secondary mineralization filling," possessing advantages such as simple preparation process, low material cost, and strong engineering applicability. It has promising application prospects in the fields of concrete durability improvement and structural self-repair. Furthermore, this invention eliminates the need for the traditional hot-mix process of Roman concrete, facilitating construction and significantly improving the durability and service life of concrete structures. Attached Figure Description

[0036] To make the objectives, technical solutions, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0037] Figure 1 This is a schematic diagram of the preparation process for an in-situ encapsulated self-healing core-shell structure particle.

[0038] Figure 2 This is a schematic diagram of the formation process of in-situ encapsulated self-healing core-shell structure particles.

[0039] Figure 3 This is a schematic diagram of the physicochemical process of in-situ encapsulated self-healing core-shell structured particles.

[0040] Figure 4 The following are SEM-EDS elemental distribution images of the near-surface region of in-situ encapsulated self-healing core-shell structured particles: (a) is a superimposed image of SEM-EDS elemental distribution; (b) is a superimposed image of silicon (Si) elemental distribution; (c) is a superimposed image of calcium (Ca) elemental distribution; and (d) is the sum spectrum of carbon (C), oxygen (O), silicon (Si), and calcium (Ca).

[0041] Figure 5 The following are SEM-EDS elemental distribution images of the internal region of the in-situ encapsulated self-healing core-shell structured particles: (a) is a superimposed image of SEM-EDS elemental distribution; (b) is a superimposed image of silicon (Si) elemental distribution; (c) is a superimposed image of calcium (Ca) elemental distribution; and (d) is the sum spectrum of carbon (C), oxygen (O), silicon (Si), and calcium (Ca).

[0042] Figure 6 X-ray diffraction pattern of in-situ encapsulated self-healing core-shell structure particles.

[0043] Figure 7 The graph shows the heat release curves of hydration of particles in different states.

[0044] Figure 8 This is a pH change curve of in-situ encapsulated self-healing core-shell structured particles in deionized water.

[0045] Figure 9 This is a schematic diagram of the pre-fabricated cracks and self-healing curing process of the specimen.

[0046] Figure 10 The image shows the crack healing process of a specimen with 5% core-shell structured particles.

[0047] Figure 11 This is a diagram showing the crack evolution process of a specimen without in-situ encapsulated self-healing core-shell structure particles.

[0048] Figure 12 The figure shows the test results of the effect of different dosages of in-situ encapsulated self-healing core-shell structured particles on the compressive and flexural strength of concrete.

[0049] Figure 13 The curves show the variation of the capillary water absorption coefficient of concrete under different admixture conditions.

[0050] Figure 14 The curves show the crack healing rate over time under different dosage conditions. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but only to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0052] The following detailed explanation illustrates the specific implementation methods:

[0053] Example 1:

[0054] This embodiment discloses a method for preparing in-situ encapsulated self-healing core-shell structured particles.

[0055] like Figure 1 As shown, the method for preparing in-situ encapsulated self-healing core-shell structured particles includes:

[0056] S1: Obtain a certain amount of micron-sized calcium oxide (CaO) powder and ester derivatives of orthosilicic acid (Si(OH)4);

[0057] Among them, the ester derivatives of orthosilicic acid (Si(OH)4) include: tetramethyl silicate (orthosilicate), tetraethyl silicate (orthoethyl silicate (TEOS)), tetrapropyl silicate (orthopropyl silicate), tetraisopropyl silicate, tetrabutyl silicate (orthobutyl silicate), tetraphenyl silicate, etc.

[0058] In this embodiment, the micron-sized calcium oxide is high-purity ultrafine calcium oxide powder with a particle size of approximately 50 nm, provided by Hangzhou Metals. The ester derivative of orthosilicic acid (Si(OH)4) is tetraethyl orthosilicate, which is derived from a high-purity analytical grade standard solution provided by Macklin. Specifically, 6-10 g of nano-calcium oxide powder and 4-6 g of tetraethyl orthosilicate are used.

[0059] S2: Calcium oxide powder, as the calcium oxide core, is mixed with tetraethyl orthosilicate in a certain proportion to obtain a mixture;

[0060] S3: Mix the mixture uniformly under stirring conditions and granulate it to obtain precursor particles with a particle size of 3mm-10mm;

[0061] S4: Pre-curing of precursor particles under preset environment (room temperature and humidity greater than 60%RH): By utilizing the characteristic that the ester derivative of orthosilicic acid (i.e., tetraethyl orthosilicate) only undergoes hydrolysis and polymerization with moisture on the surface, a diffusion gradient is formed, which extracts and enriches the (internal) tetraethyl orthosilicate near the surface of the calcium oxide core, so that the tetraethyl orthosilicate undergoes hydrolysis-condensation reaction with the moisture in the air to obtain precursor particles with a calcium oxide-silica gel core-shell structure (tetraethyl orthosilicate is coated on the surface of the calcium oxide core);

[0062] S5: The precursor particles with the calcium oxide-silica gel core-shell structure are placed in a high-temperature furnace for calcination; the calcination temperature is 1400℃ and the holding time is 2-3h.

[0063] S6: Cool the calcined precursor particles to obtain in-situ encapsulated self-healing core-shell structured particles with a tricalcium silicate shell on the surface.

[0064] In the mixing process of cement-based materials (i.e. concrete), in-situ encapsulated self-healing core-shell structured particles are mixed in. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in situ in the cement paste to encapsulate the calcium oxide core, which is used to prevent water from entering and thus prevent the hydration reaction of the calcium oxide core. During service, when the cement-based material develops cracks and is accompanied by structural damage, the CSH shell of the in-situ encapsulated self-healing core-shell structured particles ruptures, exposing the calcium oxide core, which then undergoes a hydration reaction.

[0065] The thickness of the tricalcium silicate shell is 100–1000 μm, and it exhibits a silicon gradient distribution along the radial direction. The tricalcium silicate shell is a dense and continuous structure, which is used to restrict water from entering the calcium oxide core in the early stage, delay the calcium oxide hydration reaction, and realize the timing regulation of the self-healing reaction.

[0066] When concrete cracks and structural failure occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structured particles ruptures at the crack, exposing the calcium oxide core:

[0067] The calcium oxide core undergoes a hydration reaction with water in the crack to generate calcium hydroxide (Ca(OH)2). The calcium ions dissolved in water further react with carbon dioxide in the environment to generate calcium carbonate (CaCO3), which recrystallizes in the crack, achieving secondary filling and repair of the crack. At the same time, the generated structural core is a porous and loose structure, which leaves enough space for the hydration and expansion reaction of calcium oxide and avoids the expansion hazards of free calcium oxide in concrete.

[0068] The in-situ encapsulated self-healing core-shell structured particulate material prepared by the method of this invention has the following beneficial effects:

[0069] (1) Blocking water from entering: The tricalcium silicate shell can effectively inhibit the early hydration of the calcium oxide core.

[0070] (2) Improve utilization efficiency: The self-healing component (calcium oxide core) is released when the crack is generated, which improves the utilization rate of in-situ encapsulated self-healing core-shell structure particulate materials.

[0071] (3) Enhanced repair effect: The calcium oxide core reacts with water and carbon dioxide to generate calcium hydroxide and calcium carbonate to fill the cracks and improve the density.

[0072] (4) Improved durability: Significantly reduces water absorption and improves compressive and flexural strength recovery.

[0073] (5) Simple process and easy to promote: The preparation process is simple and suitable for engineering applications.

[0074] Figure 2 The study demonstrates the structural evolution process of a core-shell structure with free calcium oxide (f-CaO) as the core and tricalcium silicate (C3S) as the shell, reflecting the core-shell structure formation mechanism driven by TEOS diffusion and high-temperature reaction.

[0075] Figure 3 This explains the mechanism by which TEOS preferentially hydrolyzes on the particle surface and diffuses outward from the inside, leading to the enrichment of silicon on the particle surface and the eventual formation of a C3S shell.

[0076] Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that the particles exhibited a distinct core-shell structure, with the shell rich in silicon and the core rich in calcium. Figure 4 and Figure 5 As shown. Among them. Figure 4 The presence of silicon enriched on the particle surface and calcium relatively uniformly distributed verifies the existence of the shell structure. Figure 5 This indicates a significant decrease in silicon content within the particles, further confirming the formation of a silicon-enriched shell and a calcium-enriched core structure. X-ray diffraction analysis shows that the main phase in the shell is C3S, such as... Figure 6 As shown. Among them. Figure 6 The results showed that the main phases in the sample were tricalcium silicate (C3S) and free calcium oxide (f-CaO), verifying the composition of the shell phase.

[0077] Example 2:

[0078] This embodiment discloses an in-situ encapsulated self-healing core-shell structure particle.

[0079] The in-situ encapsulated self-healing core-shell structure particles were prepared based on the in-situ encapsulated self-healing core-shell structure particle preparation method in Example 1.

[0080] Example 3:

[0081] This embodiment discloses a method for preparing a self-healing cement-based material.

[0082] A method for preparing self-healing cement-based materials involves mixing in-situ encapsulated self-healing core-shell structured particles prepared in claim 7 during the mixing process of cement-based materials. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in-situ in the cement slurry, encapsulating the calcium oxide core, thereby preparing a self-healing cement-based material.

[0083] The self-healing cement-based material comprises cement, fine aggregate, water, and a water-reducing agent mixed with in-situ encapsulated self-healing core-shell structure particles. The mixture consists of 140-280 parts cement, 450-650 parts fine aggregate (sand), 10-40 parts in-situ encapsulated self-healing core-shell structure particles, 70-140 parts water, and 1-10 parts water-reducing agent (admixture).

[0084] The cement is ordinary Portland cement with a loss on ignition of less than or equal to 5% and a specific surface area of ​​not less than 300 m2 / kg.

[0085] The fine aggregate (sand) is manufactured sand and / or river sand, with a fineness modulus of 1.5-2.8 and a mud content not exceeding 0.2%.

[0086] The water-reducing agent is a dry powder of polycarboxylate water-reducing agent, with a water reduction rate of not less than 14% and a water bleeding rate of not more than 90%.

[0087] Example 4:

[0088] This embodiment discloses a self-healing cement-based material.

[0089] The self-healing cement-based material was prepared based on the self-healing cement-based material preparation method in Example 3.

[0090] When self-healing cement-based materials develop cracks and structural damage occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structure particles ruptures at the crack, exposing the calcium oxide core. The calcium oxide core undergoes a hydration reaction with water in the crack to generate calcium hydroxide. The calcium ions dissolved in the water further react with carbon dioxide in the environment to generate calcium carbonate, which recrystallizes and fills the crack, thereby achieving self-healing of the crack and restoration of mechanical properties.

[0091] Example 5:

[0092] To better illustrate the advantages of the technical solution of the present invention, the following experiments and tests are disclosed in this embodiment.

[0093] 1. Heat of hydration test

[0094] In this embodiment, the prepared in-situ encapsulated self-healing core-shell structure particles and unmodified calcium oxide were subjected to hydration heat tests, respectively. The results are as follows: Figure 7 As shown (where Figure 7 This includes untreated calcium oxide, intact core-shell particles, and broken particles, reflecting the shell's role in delaying the core's hydration reaction.

[0095] 1) Unmodified calcium oxide exhibits a sharp exothermic peak;

[0096] 2) The exothermic process of adding core-shell structured particles was significantly delayed. In contrast, the hydration rate of the Cal group was significantly reduced, with no significant heat flow in the first 0-6 hours and a peak value in the last 7-8 hours. This indicates that the hydration was delayed by more than 7 hours compared to the CaO group, suggesting that the tricalcium silicate shell has a blocking effect on water entry.

[0097] At the same time, through pH testing, such as Figure 8 (in Figure 8 (This demonstrates the characteristics of particles slowly releasing alkaline substances when intact and rapidly releasing them after breakage.) Therefore:

[0098] 1) In-situ encapsulated self-healing core-shell structure particles exhibit a slower rate of alkalinity increase in water;

[0099] 2) This indicates that it has the characteristic of delayed release activity.

[0100] 2. Self-healing performance verification

[0101] In this embodiment, in-situ encapsulated self-healing core-shell structure particles are incorporated into cement-based materials to prepare specimens, and pre-crack treatment is performed. Figure 9 The experimental procedures for specimen destruction, splicing, and wet-dry cycle curing were demonstrated.

[0102] Concrete mortar specimens with dimensions of 40mm×40mm×160mm were prepared.

[0103] The in-situ encapsulated self-healing core-shell structure particles were added at a rate of 10% of the concrete mass.

[0104] The three-point bending method was used to prefabricate the cracks, and the crack width was controlled to be 0.10-0.50 mm.

[0105] Place the specimen in a wet-dry cycle environment:

[0106] 1) Wet culture: 12 hours in water at 20℃;

[0107] 2) Drying: 12h at 20℃ and RH60%.

[0108] The crack width is approximately 0.1-0.45 mm.

[0109] The specimens were placed in a wet-dry cycle environment for curing, and the crack healing process was observed.

[0110] The results are as follows Figure 10 and Figure 11 As shown (where Figure 10 Including crack morphology at different ages and corresponding binarized images, used for quantitative analysis of healing effect; Figure 11 As a control group, it was shown that the cracks showed virtually no healing.

[0111] 1) The initial cracks are clearly visible;

[0112] 2) Concrete with 10% in-situ encapsulated self-healing core-shell structure particles had already significantly filled the cracks after 3 days, and after 14 days of wet-dry cycles, the cracks were basically completely filled.

[0113] This indicates that the products generated by particle hydration have a good filling effect on cracks.

[0114] 3. Mechanical resistance test

[0115] In this embodiment, compressive and flexural strength tests were conducted on concrete specimens incorporating in-situ encapsulated self-healing core-shell structure particles. The concrete was prepared according to the formulation design. The self-healing agent was added at a specified percentage of the concrete mass during the casting stage. A 50×50×50mm mold was used for the compressive strength test. The results obtained using 50×50×50mm specimens were also converted to the equivalent strength of a standard 150×150×150mm specimen.

[0116] After mixing, the concrete was placed into a mold in three equal layers. Each layer was compacted 25 times with a compaction rod. Excess concrete was knocked off, and the surface was polished smooth. The specimens were demolded after being stored at (20±5)°C for 1 day. The demolded samples were immediately placed in a standard curing chamber (20±2°C, humidity > 95%) until the specified 28-day curing period. Subsequently, the samples were removed, surface moisture was wiped off, and the samples were placed in the center of the pressure plate of the testing machine and continuously loaded at a rate of (3-5) MPa / s until failure; the maximum load was recorded. Self-healing agents (Cal-CaO-0%, Cal-CaO-5%, Cal-CaO-7%, Cal-CaO-10%) were added to the concrete. After 28 days of standard curing, the test results are as follows: Figure 12 As shown:

[0117] The average compressive strength of the Cal-CaO-0% group was 74.15 MPa. Increasing the content decreased the average concentration. Notably, the Cal-CaO-7% and Cal-CaO-10% groups showed reductions of 9.42 MPa and 20.51 MPa, respectively, while the Cal-CaO-5% group showed no significant negative impact. At appropriate dosages, the compressive strength of concrete slightly increased or remained stable.

[0118] 4. Impermeability test

[0119] In this embodiment, the capillary water absorption test is used to evaluate the material's impermeability.

[0120] The results are as follows Figure 13 As shown (where Figure 13 (Reflecting the effect of core-shell structured particles on the impermeability of materials)

[0121] 1) The water absorption coefficient of specimens with activated self-healing core-shell structure particles was significantly reduced. On the third day, the capillary water absorption coefficients of concrete specimens with 5%, 7%, and 10% admixtures decreased to 1.5, 1.2, and 0.85, respectively. After 14 days, the capillary water absorption coefficients of concrete test blocks with 0%, 5%, 7%, and 10% admixtures were 4.1, 0.52, 0.42, and 0.35, respectively. .

[0122] 2) This indicates that the material's density and impermeability are enhanced after the cracks are healed.

[0123] 5. Analysis of the Influence of Dosage

[0124] In this embodiment, a comparative experiment was conducted with different amounts of activated self-healing core-shell structure particles (e.g., 5%, 10%, 15%).

[0125] The results are as follows Figure 14 As shown (where Figure 14 (Reflecting the relationship between self-healing efficiency and doping amount)

[0126] 1) Observation of images showed that the Cal-CaO-10%, Cal-CaO-7%, and Cal-CaO-5% groups clearly exhibited a gradual increase in healing products over time. The Cal-CaO-10% and Cal-CaO-7% groups showed almost complete healing by day 7. The Cal-CaO-5% group showed a gradual increase in healing products, reaching almost complete healing by day 14. The Cal-CaO-0% group showed no significant healing. The crack healing rate increased with increasing dosage.

[0127] 2) The average compressive strength of the Cal-CaO-0% group was 74.15 MPa. Increasing the content decreased the average concentration. Notably, the Cal-CaO-7% and Cal-CaO-10% groups showed reductions of 9.42 MPa and 20.51 MPa, respectively, while the Cal-CaO-5% group showed no significant negative impact. Excessive doping may have some effect on mechanical properties.

[0128] Therefore, the preferred dosing range for activated self-healing core-shell structured particles is 5%-15%.

[0129] Experimental results show that the in-situ encapsulated self-healing core-shell structured particles prepared in this invention can significantly regulate the hydration exothermic process and alkalinity release behavior, verifying their excellent encapsulation effect and activity retention capability. Simultaneously, this in-situ encapsulated self-healing core-shell structured particle material significantly improves the concrete crack healing rate, reduces capillary water absorption, and effectively restores compressive and flexural strength. Especially under wet-dry cycle conditions, concrete cracks can achieve efficient closure, and the recovery of mechanical properties is significantly improved.

[0130] In summary, this invention aims to solve the technical problem of poor concrete volume stability and easy harmful expansion caused by the excessively high early hydration activity of existing calcium oxide-based self-healing agents. This invention uses calcium oxide particles as the core material and utilizes the gradient diffusion and hydrolytic polymerization characteristics of orthosilicate ester derivatives (such as tetraethyl orthosilicate) in a wet environment. Through room temperature curing and high-temperature calcination, a dense tricalcium silicate (C3S) shell is grown in situ on the core material surface, constructing a core-shell structure of "C3S-rich shell - CaO-rich core". In this structure, the CSH shell layer formed during the initial hydration of the outer shell effectively blocks water from entering, preventing the hydration reaction of the calcium oxide core and preventing premature reaction of CaO before the concrete hardens. When the concrete cracks, the outer shell breaks, releasing the internal CaO. The Ca²⁺ generated upon contact with water reacts with external CO₂ to crystallize, achieving self-healing of cracks from the inside out. Experiments show that when the particle dosage is 5wt%, it only causes a 7% decrease in the compressive strength of the matrix, can completely repair a 0.3mm wide crack within 14 days, reduces the capillary water absorption coefficient by 88%, and inhibits approximately 30% of early shrinkage without the risk of later expansion. The in-situ encapsulated self-healing core-shell structure particle material and self-healing cement-based material prepared by this invention achieve a synergistic self-healing mechanism of "in-situ self-encapsulation - crack triggering - secondary mineralization filling," possessing advantages such as simple preparation process, low material cost, and strong engineering applicability. It has promising application prospects in the fields of concrete durability improvement and structural self-repair. Furthermore, this invention eliminates the need for the traditional hot-mix process of Roman concrete, facilitating construction and significantly improving the durability and service life of concrete structures.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing in-situ encapsulated self-healing core-shell structured particles, characterized in that, include: S1: Obtain micron-sized calcium oxide powder and ester derivatives of orthosilicic acid; S2: Calcium oxide powder, as the calcium oxide core, is mixed with an ester derivative of orthosilicic acid in a certain proportion to obtain a mixture; S3: The mixture is uniformly mixed and granulated under stirring conditions to obtain precursor particles; S4: Pre-curing the precursor particles with moisture under a preset environment: By utilizing the characteristic that the ester derivatives of orthosilicic acid only undergo hydrolysis and polymerization with moisture on the surface, a diffusion gradient is formed, which extracts and enriches the ester derivatives of orthosilicic acid near the surface of the calcium oxide core, so that the ester derivatives of orthosilicic acid undergo hydrolysis-condensation reaction with moisture in the air to obtain precursor particles with a calcium oxide-silica gel core-shell structure. S5: The precursor particles with a calcium oxide-silica core-shell structure are placed in a high-temperature furnace for calcination; S6: Cool the calcined precursor particles to obtain in-situ encapsulated self-healing core-shell structured particles with a tricalcium silicate shell on the surface. In the mixing process of cement-based materials, in-situ encapsulated self-healing core-shell structured particles are mixed in. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in situ in the cement paste to encapsulate the calcium oxide core, which is used to prevent water from entering and thus prevent the hydration reaction of the calcium oxide core. During service, when the cement-based material develops cracks and is accompanied by structural damage, the CSH shell of the in-situ encapsulated self-healing core-shell structured particles ruptures, exposing the calcium oxide core and causing it to undergo a hydration reaction.

2. The method for preparing in-situ encapsulated self-healing core-shell structured particles as described in claim 1, characterized in that: In step S1, the ester derivative of orthosilicic acid is any one of tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetraisopropyl silicate, tetrabutyl silicate, and tetraphenyl silicate.

3. The method for preparing in-situ encapsulated self-healing core-shell structured particles as described in claim 1, characterized in that: In step S4, the preset environment is a room temperature environment with a humidity greater than 60%RH.

4. The method for preparing in-situ encapsulated self-healing core-shell structured particles as described in claim 1, characterized in that: In step S5, the calcination temperature is 1400℃ and the holding time is 2-3 hours.

5. The method for preparing in-situ encapsulated self-healing core-shell structured particles as described in claim 1, characterized in that: In step S6, the thickness of the tricalcium silicate shell is 100–1000 μm, and it exhibits a silicon element gradient distribution along the radial direction.

6. The method for preparing in-situ encapsulated self-healing core-shell structured particles as described in claim 1, characterized in that: In step S6, when cracks appear in the concrete and structural damage occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structure particles ruptures at the crack, exposing the calcium oxide core. The calcium oxide core reacts with water in the crack to generate calcium hydroxide. The calcium ions dissolved in water further react with carbon dioxide in the environment to generate calcium carbonate, which recrystallizes in the crack, thus achieving secondary filling and repair of the crack.

7. In-situ encapsulated self-healing core-shell structure particles, characterized in that: The particles were prepared using the in-situ encapsulated self-healing core-shell structure particle preparation method according to any one of claims 1 to 6.

8. A method for preparing self-healing cement-based materials, characterized in that: In the process of mixing cement-based materials, the in-situ encapsulated self-healing core-shell structured particles prepared in claim 7 are mixed in. The tricalcium silicate shell of the in-situ encapsulated self-healing core-shell structured particles generates a CSH shell in situ in the cement slurry to encapsulate the calcium oxide core, thereby preparing a self-healing cement-based material.

9. A self-healing cement-based material, characterized in that: It was prepared based on the method for preparing self-healing cement-based materials according to claim 8.

10. The self-healing cement-based material as described in claim 9, characterized in that: When self-healing cement-based materials develop cracks and structural damage occurs, the CSH shell of the in-situ encapsulated self-healing core-shell structure particles ruptures at the crack, exposing the calcium oxide core. The calcium oxide core undergoes a hydration reaction with water in the crack to generate calcium hydroxide. The calcium ions dissolved in the water further react with carbon dioxide in the environment to generate calcium carbonate, which recrystallizes and fills the crack, thereby achieving self-healing of the crack and restoration of mechanical properties.

Images