An inorganic self-repairing material containing internal dopant, its preparation method and application

Abstract

This invention provides an inorganic self-healing material admixture, its preparation method, and its application, relating to the field of building materials technology. The inorganic self-healing material admixture of this invention comprises the following raw materials in parts by weight: 45-50 parts silicate cement powder, 22-26 parts nano-calcium carbonate, 7-9 parts calcium lactate, 18-22 parts starch-coated sodium silicate, 18-22 parts silane-modified silica nanospheres, and 4-6 parts vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer. This invention improves the efficiency and effect of self-healing of concrete cracks, achieving a 100% repair rate in 28 days, realizing complete healing and restoration of mechanical properties; it improves the density and interfacial bonding of the repair product, ensuring a tight bond between the repair product and the matrix; it also enhances various properties of the inorganic self-healing material admixture, such as flexural and compressive strength, and enables crack repair even under water immersion conditions.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to an inorganic self-repairing material admixture, its preparation method, and its application. Background Technology

[0002] Concrete, due to its excellent compressive strength and wide applicability, is the most widely used building material globally. However, its inherent brittleness and low tensile strength make it prone to microcracks during service. These cracks provide pathways for the intrusion of harmful media such as moisture, chloride ions, and sulfates, and are key factors in inducing steel corrosion, freeze-thaw damage, and chemical corrosion, ultimately leading to structural performance degradation and shortened lifespan. Traditional crack repair methods are mostly passive, reactive external interventions, which suffer from difficulties in construction, high costs, and difficulty in eradicating hidden dangers. Therefore, endowing concrete with self-healing capabilities has become a cutting-edge research direction for improving its durability and sustainability.

[0003] Currently, concrete self-healing technologies mainly include microbial repair, polymer repair, and inorganic material repair. Among them, inorganic repair systems based on unhydrated cement particles, expanding minerals, and crystallization catalysts have attracted much attention due to their good compatibility with the concrete matrix, environmental friendliness, and relatively low cost. However, existing inorganic self-healing systems generally suffer from two major bottlenecks: first, the repair process mainly relies on the single physical triggering of moisture, and the release of the repair agent lacks controllability, posing a risk of premature consumption before cracking; second, the repair reaction rate and product generation are limited, resulting in poor repair effects on wider cracks. To address these issues, this invention proposes an inorganic self-healing material admixture, its preparation method, and its application. Summary of the Invention

[0004] The purpose of this invention is to provide an inorganic self-healing material admixture, its preparation method, and its application, which improves the efficiency and effect of concrete crack self-repair, achieving a 100% repair rate in 28 days, realizing complete healing and restoration of mechanical properties; it improves the density and interfacial bonding of the repair product, ensuring a tight bond between the repair product and the matrix; it also enhances various properties of the inorganic self-healing material admixture, such as flexural and compressive strength, and enables crack repair even under immersion conditions.

[0005] On one hand, the present invention provides an inorganic self-repairing material admixture, comprising the following raw materials in parts by weight: 45-50 parts of silicate cement micro powder, 22-26 parts of nano-calcium carbonate, 7-9 parts of calcium lactate, 18-22 parts of starch-coated sodium silicate, 18-22 parts of silane-modified silica nanospheres, and 4-6 parts of vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer.

[0006] This invention incorporates inorganic self-healing material admixtures to achieve highly efficient self-healing functionality in cement-based composite materials. The addition of nano-calcium carbonate not only enhances the material's density but also acts as an active ingredient in the self-healing process, promoting the formation of calcium carbonate crystals. Calcium lactate acts as a regulator, optimizing the material's flowability and hardening properties, and may also participate in the ion exchange process during the self-healing reaction, promoting the formation of repair products. Starch-coated sodium silicate microcapsules release sodium silicate upon crack formation, reacting with calcium ions in cement hydration products to form calcium silicate gel, filling the cracks. Silane-modified silica nanospheres, through their nanoscale and surface modification, enhance the interfacial bonding with the cement matrix and form a network structure within the cracks, improving the mechanical properties of the repair products. Vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer, as a coating material, not only protects the internal active ingredients but also forms a flexible film during the repair process, enhancing the crack resistance and durability of the repaired area. These components, through their respective chemical reactions and physical actions, work synergistically to achieve a highly efficient and durable self-healing effect when cracks occur.

[0007] Further, the preparation method of the starch-coated sodium silicate includes: mixing starch with deionized water, stirring and gelatinizing at 85-95℃ for 20-40 minutes to obtain a gelatinized liquid with a mass concentration of 8-12%, and cooling it to 50-60℃ for later use; adding sodium silicate nonahydrate powder ground to D90≤45μm, and dispersing and mixing at 50-60℃ and a stirring speed of 200-400rpm for 20-30 minutes to form a uniform suspension slurry; continuing to stir and adding an aqueous solution of sodium sulfate decahydrate with a mass concentration of 5-15%, then lowering the system temperature to 20-25℃, allowing it to stand and age for 2-4 hours, and then centrifuging, washing, and drying to obtain the final product.

[0008] In the preparation of starch-coated sodium silicate, precise control of gelatinization, dispersion, and aging steps ensured effective coating of sodium silicate, forming a microcapsule structure with sustained-release function, guaranteeing stable release of sodium silicate when cracks occur. The preparation of silane-modified silica nanospheres involved activation, ultrasonic treatment, and reflux reaction, successfully grafting octadecyltrimethoxysilane onto the surface of silica nanospheres, significantly improving their compatibility and interfacial bonding with the cement matrix. These innovative preparation processes not only improve the self-healing efficiency of the materials but also enhance the mechanical properties and durability of the repaired products, providing a strong guarantee for the long-term performance stability of cement-based composite materials.

[0009] Furthermore, the weight ratio of sodium silicate nonahydrate, starch, and sodium sulfate decahydrate is 85-92:8-15:12-18.

[0010] Furthermore, the preparation method of the silane-modified silica nanospheres includes: activating the silica nanospheres and adding anhydrous toluene, ultrasonically treating them under nitrogen protection, adding octadecyltrimethoxysilane to the dispersion system under nitrogen protection and mechanical stirring, and refluxing at 105-115℃ for 6-10 hours. After the reaction is completed, the nanospheres are centrifuged, washed, and dried to obtain the final product.

[0011] Furthermore, the feeding ratio of the anhydrous toluene, silica nanospheres and octadecyltrimethoxysilane is (150-250) mL: (8-12) g: (1-3) g.

[0012] Furthermore, the activation step involves drying and activating the silica nanospheres under vacuum conditions at 105-115°C for 2-4 hours.

[0013] On the other hand, the present invention also provides a method for preparing an inorganic self-repairing material dopant, the steps of which include: (1) Weigh the dried and ground silicate cement powder, nano calcium carbonate and calcium lactate and premix them under nitrogen protection. Then add starch-coated sodium silicate microcapsules and continue mixing to obtain the core mixture. (2) Fluidize the above core mixture and control the inlet air temperature to 60±5℃; spray the silane-modified silica nanospheres into the fluidized state and let them collide and adsorb with the core mixture; then continue to maintain fluidized drying at 60±5℃ for 30-40 minutes. (3) Prepare an ethanol solution of vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer as a coating solution; maintain the inlet air temperature of the fluidized bed at 45±5℃ and control the material temperature to be stable at 35±2℃; spray the coating solution at a rate of 4-6mL / min; monitor the material weight gain through an online weighing system, and stop spraying when the total weight gain of 1000g load precursor reaches 50g; continue fluidized drying for 15-20 minutes to obtain the coating solution.

[0014] Furthermore, the mass concentration of the vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer ethanol solution is 4-6%.

[0015] On the other hand, the present invention also provides the application of inorganic self-healing material admixtures in cement-based composite materials.

[0016] Furthermore, the cement-based composite material comprises silicate cement, water, water-reducing agent, and inorganic self-repairing material admixture in a weight ratio of 300-340:150-170:2.5-3.5:10-12.

[0017] The beneficial effects of this invention are as follows: The self-healing mechanism in this technical solution works synergistically with the cement hydration process. In the early stages of cement hydration, the components are uniformly dispersed in the cement matrix, forming a stable structure. When cracks appear, starch-coated sodium silicate microcapsules rupture, releasing sodium silicate, which reacts with calcium ions in the cement hydration products to form calcium silicate gel, filling the cracks. Simultaneously, nano-calcium carbonate and silane-modified silica nanospheres, as active ingredients, participate in the self-healing reaction, promoting the formation of calcium carbonate crystals and network structures, and enhancing the mechanical properties of the repaired product. Furthermore, the vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer coating layer forms a flexible film during the repair process, further improving the crack resistance and durability of the repaired area. This synergistic effect between the self-healing mechanism and the cement hydration process enables the material to rapidly and effectively self-repair after cracks appear, restoring its original mechanical properties and durability. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 This is a schematic diagram of the crack repair process before the inorganic self-repairing material containing the internal additives was prepared according to Example 1 of the present invention. Figure 2 This is an image showing the effect of crack repair after the preparation of the inorganic self-repairing material containing the additives prepared in Example 1 of the present invention; Figure 3 The image shows the repair effect of the inorganic self-repairing material containing dopants prepared in Example 1 of this invention. Figure 4 This is a scan image of a material prepared in Example 1 of the present invention after repair using an inorganic self-repairing material dopant. Figure 5 This is a scan image of a material prepared in Example 1 of the present invention after repair using an inorganic self-repairing material dopant. Figure 6 This is a comparison chart of the water immersion curing results of Examples 1-2 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that the raw materials are all commercially available.

[0021] The silicate cement powder has a P·O 42.5 content and a D50 of 15 μm; the average particle size of the nano-calcium carbonate is 50 nm; the average particle size of the silica nanospheres is 15 nm, and the specific surface area is 200 ± 20 m². 2 / g; Vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer CAS No.: 30581-59-0, boiling point: 187℃ at 760 mmHg; water-reducing agent is polycarboxylate water-reducing agent, model DH-4005. Example 1

[0022] This embodiment provides an inorganic self-repairing material admixture, comprising the following materials in parts by weight: 47.5 parts silicate cement powder, 24 parts nano-calcium carbonate, 8 parts calcium lactate, 20 parts starch-coated sodium silicate, 20 parts silane-modified silica nanospheres, and 5 parts vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer. The preparation method of starch-coated sodium silicate includes: weighing 12g of corn starch and mixing it with 120g of deionized water, placing it in a 90℃ water bath, and gelatinizing it at a constant temperature of 300rpm for 30 minutes to obtain a gelatinized liquid; cooling the gelatinized liquid to 55℃ for later use; weighing 88.0g of sodium silicate nonahydrate powder ground to D90≤45μm, slowly adding it to the above gelatinized liquid, maintaining the system temperature at 55℃, and stirring and dispersing it at 300rpm for 25 minutes to form a uniform mixture. A milky white suspension slurry was prepared. Subsequently, 150 g of a 10% sodium sulfate decahydrate aqueous solution was slowly added dropwise while stirring. After the addition was complete, the system was transferred to 25°C and allowed to stand for 3 hours. The aged slurry was centrifuged at 4000 rpm, and the obtained solid was washed three times alternately with deionized water and anhydrous ethanol. Finally, the solid was dried in a vacuum drying oven at 60°C for 12 hours and ground through a 200-mesh sieve to obtain a white powdery starch-coated sodium silicate. The preparation method of silane-modified silica nanospheres includes: 10g of silica nanospheres were activated in a vacuum drying oven at 110℃ for 3 hours; 200mL of anhydrous toluene was added to a dry 250mL three-necked flask; under nitrogen protection and ultrasonic conditions with a power of 300W, the activated silica nanospheres were slowly added to the toluene and ultrasonically dispersed for 30 minutes to obtain a uniform nanosphere dispersion system; subsequently, the system was placed on a magnetic stirrer, under nitrogen protection, and mechanical stirring was started at 500rpm; 2g of octadecyltrimethoxysilane was slowly added dropwise using a constant pressure dropping funnel; after the addition was completed, the temperature was raised to 110℃ and refluxed for 8 hours; after the reaction was completed, the system was cooled to room temperature, and the product was centrifuged at 8000rpm for 10 minutes to collect the solid; the solid was washed twice each with toluene, acetone, and anhydrous ethanol to remove unreacted silane and byproducts; finally, the product was dried in a vacuum drying oven at 80℃ for 6 hours to obtain hydrophobically modified silica nanospheres. The preparation method of the inorganic self-repairing material dopant in this embodiment includes: P·O 42.5 silicate cement powder ground to a D50 of 20 μm, nano-calcium carbonate, and calcium lactate were premixed for 1 hour under nitrogen protection. Then, starch-coated sodium silicate was added, and mixing continued for 1.5 hours to obtain a core mixture with good flowability. This core mixture was placed in the hopper of a small fluidized bed granulation and coating machine. The equipment was started, and the inlet air temperature was controlled at 60°C to maintain the material in a fluidized state, with a fluidizing air volume of approximately 30 m³ / h. 3 / h; Silane-modified silica nanospheres are uniformly sprayed into the fluidized bed at a constant rate within 15 minutes through a side spraying device; The nanospheres collide and adsorb fully with the core mixture particles in the fluidized state; After the spraying is completed, the inlet air temperature is maintained at 60℃, and fluidized drying is continued for 35 minutes to obtain dry and loose loaded precursor particles. Prepare a 5% (w / w) ethanol solution of vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer as the coating solution; place the loaded precursor particles back into the fluidized bed, set the inlet air temperature to 45℃, control the material temperature at 35±2℃, and spray the coating solution through the bottom spray gun at a rate of 5mL / min. Monitor the material weight gain using an online weighing system. Stop spraying when the total weight gain of 1000g of loaded precursor reaches 50g; continue to introduce 45℃ hot air and fluidize and dry for 18 minutes to obtain the final product.

[0023] The inorganic self-repairing material admixture prepared in Example 1 was used to prepare a cement-based composite material, which included 320 parts of silicate cement, 160 parts of water, 3 parts of water-reducing agent and 11 parts of inorganic self-repairing material admixture. The above materials were placed in a mixer and stirred thoroughly.

[0024] The mortar was poured into specimens measuring 40mm × 40mm × 160mm, and cured under standard conditions for 28 days. A through crack with a width of approximately 0.55mm was pre-cast in the middle of the specimen. In Example 1, the width of the through crack was 0.574mm. Figure 1 As shown, the pre-cracked specimens were immediately placed in a curing chamber at a temperature of 20±2℃ and a relative humidity of over 95% (wet curing); the repair results after 28 days are as follows. Figure 2 As shown. Furthermore, combined with Figure 3 At 3 days, the repair rate of the inorganic self-repairing material prepared in Example 1 reached 43.3%; the repair rate increased at a rate of 14.5% / day; and the repair rate reached 100.0% at 28 days.

[0025] Samples were taken from the cracked areas of the specimens after 28 days of wet curing, and observed under a scanning electron microscope after gold sputtering. The results are as follows: Figure 4 and Figure 5As shown, the cracks are densely filled with a large number of interwoven fibrous / network CSH gels and flaky / spherical calcium carbonate crystals of varying sizes. The repair products are tightly bonded to the original mortar matrix, and the interface transition is good.

[0026] In the inorganic self-healing admixture prepared by this invention, the vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer outer shell is in a shrinkage and compacted state, forming an effective barrier together with the hydrophobic intermediate layer. This isolates the core repair component from the external environment, preventing its ineffective consumption during the early hydration process of concrete and thus maintaining its long-term dormant activity. When microcracks appear in the concrete, neutral moisture from the outside penetrates along the cracks. The local microenvironment pH value at the crack tip drops rapidly, triggering a pH-responsive outer shell. The polymer chains of the outer shell protonate and swell, becoming loose and porous. Moisture then permeates through the outer shell and contacts the intermediate layer. Highly water-soluble calcium lactate dissolves and is released rapidly first, reacting with CO3 from the dissolution of nano-calcium carbonate and CO2 dissolved in the air within the crack space. 2- The combination of these components rapidly generates calcium carbonate crystal deposits. Simultaneously, the swollen outer shell itself also produces a certain degree of physical blockage. This stage primarily focuses on rapid physical crystallization and sealing, aiming to immediately stop water seepage and stabilize the crack. As moisture continues to act, the microcapsule shell completely disintegrates or forms stable channels. When the pre-hydrated cement powder comes into contact with moisture, its surface passivation film is broken, leading to rapid secondary hydration and the generation of a large amount of CSH gel, providing strong chemical bonding. The microencapsulated sodium silicate wall material dissolves, releasing silicate ions that react with calcium ions in the system, further accelerating the formation of CSH gel and promoting the oriented crystallization of calcium carbonate. Nano-calcium carbonate acts not only as a reactant but also as a crystal nucleus. Multiple reaction products, such as CSH gel and calcium carbonate, intertwine and grow within the crack, forming a dense, mechanically superior composite repair, ultimately achieving complete crack healing and restoration of mechanical properties.

[0027] Furthermore, the inorganic self-repairing material dopants prepared in Example 1 were tested according to GB18445-2012, and the results are shown in the table below: Example 2

[0028] Based on the cement-based composite material prepared in Example 1, the amount of inorganic self-repairing material admixture was adjusted to 6 parts, and 5 parts of the inorganic self-repairing material admixture were replaced with cement.

[0029] Comparative Example 1: Based on the cement-based composite material prepared in Example 1, the inorganic self-repairing material admixture was replaced with an equal mass of the loaded precursor particles prepared in Example 1.

[0030] Comparative Example 2: Based on the cement-based composite material prepared in Example 1, the inorganic self-repairing material admixture was replaced with cement, and the amount of inorganic self-repairing material admixture was adjusted to 0 parts.

[0031] The mortar from Examples 1-2 and Comparative Examples 1-2 was poured into 40mm×40mm×160mm specimens, cured under standard conditions for 28 days, and a through crack was pre-cast in the middle of the specimens. Subsequent water immersion curing was then performed. The results are as follows: Figure 6 As shown, the results indicate that the inorganic self-repairing material admixture prepared in the examples can also repair cracks under water immersion conditions.

[0032] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention; those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart 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 self-repairing material additive, characterized in that, The raw materials include the following parts by weight: 45-50 parts silicate cement powder, 22-26 parts nano calcium carbonate, 7-9 parts calcium lactate, 18-22 parts starch-coated sodium silicate, 18-22 parts silane-modified silica nanospheres, and 4-6 parts vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer.

2. The inorganic self-repairing material admixture according to claim 1, characterized in that, The method for preparing the starch-coated sodium silicate includes: mixing starch with deionized water, stirring and gelatinizing at 85-95℃ for 20-40 minutes to obtain a gelatinized liquid with a mass concentration of 8-12%, and cooling it to 50-60℃ for later use; adding sodium silicate nonahydrate powder ground to D90≤45μm, and dispersing and mixing at 50-60℃ and a stirring speed of 200-400rpm for 20-30 minutes to form a uniform suspension slurry; continuing to stir and adding a sodium sulfate decahydrate aqueous solution with a mass concentration of 5-15%, then lowering the system temperature to 20-25℃, allowing it to stand and age for 2-4 hours, and then centrifuging, washing, and drying to obtain the final product.

3. The inorganic self-repairing material admixture according to claim 2, characterized in that, The weight ratio of sodium silicate nonahydrate, starch, and sodium sulfate decahydrate is 85-92:8-15:12-18.

4. The inorganic self-repairing material admixture according to claim 1, characterized in that, The preparation method of the silane-modified silica nanospheres includes: activating the silica nanospheres and adding anhydrous toluene, ultrasonically treating them under nitrogen protection, adding octadecyltrimethoxysilane to the dispersion system under nitrogen protection and mechanical stirring, and refluxing at 105-115℃ for 6-10 hours. After the reaction is completed, the nanospheres are centrifuged, washed, and dried to obtain the final product.

5. The inorganic self-repairing material admixture according to claim 4, characterized in that, The feeding ratio of anhydrous toluene, silica nanospheres and octadecyltrimethoxysilane is (150-250) mL: (8-12) g: (1-3) g.

6. The inorganic self-repairing material admixture according to claim 4, characterized in that, The activation step involves drying and activating the silica nanospheres under vacuum conditions at 105-115°C for 2-4 hours.

7. A method for preparing an inorganic self-repairing material dopant as described in any one of claims 1-6, characterized in that, step... include: (1) Weigh the dried and ground silicate cement powder, nano calcium carbonate and calcium lactate and premix them under nitrogen protection. Then add starch-coated sodium silicate microcapsules and continue mixing to obtain the core mixture. (2) Fluidize the above core mixture and control the inlet air temperature to 60±5℃; spray the silane-modified silica nanospheres into the fluidized state and let them collide and adsorb with the core mixture; then continue to maintain fluidized drying at 60±5℃ for 30-40 minutes. (3) Prepare an ethanol solution of vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer as a coating liquid; maintain the inlet air temperature of the fluidized bed at 45±5℃ and control the material temperature to be stable at 35±2℃; spray the coating liquid at a rate of 4-6mL / min. The material weight gain is monitored by an online weighing system. When the total weight gain of the 1000g load precursor reaches 50g, spraying is stopped; fluidized drying is continued for 15-20 minutes to obtain the final product.

8. The preparation method of the inorganic self-repairing material dopant according to claim 7, characterized in that, The mass concentration of the vinylpyrrolidone-dimethylaminoethyl methacrylate copolymer ethanol solution is 4-6%.

9. The application of the inorganic self-repairing material admixture as described in any one of claims 1-6 in cement-based composite materials.

10. The application according to claim 9, characterized in that, The cement-based composite material comprises silicate cement, water, water-reducing agent, and inorganic self-repairing material admixture as described in any one of claims 1-6, in a weight ratio of 300-340:150-170:2.5-3.5:10-12.

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