A concrete self-repairing admixture and a preparation method thereof

Abstract

The application discloses a kind of concrete self-repairing admixture and preparation method thereof, belong to concrete repair material technical field.The method is prepared first by PEG-PLA soft template method silica-polymer interpenetrating network composite porous material, then active mineral repair powder is prepared by mixing ball milling of metakaolin, anhydrous gypsum, slag powder, finally composite porous material, active mineral repair powder and water-based epoxy resin, ethylene glycol are high-speed stirred and compounded, and self-repairing admixture is prepared.Nanopore of composite porous material can realize the stable loading and uniform dispersion of repair component, and the admixture has dual repair mechanism of resin bonding and mineral filling.The application solves the problem of poor dispersibility of traditional materials, ensures the mechanical properties of concrete, improves the crack repair efficiency and durability, has simple preparation process, controllable cost, is suitable for large-scale production, and has significant engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of concrete repair material preparation technology, specifically relating to a self-healing concrete admixture and its preparation method. Background Technology

[0002] Concrete is one of the most widely used civil engineering materials, but due to its inherent brittleness, it is prone to cracking under load, temperature changes, and wet-dry cycles. Cracks not only reduce the mechanical properties of concrete but also allow corrosive media such as water and chloride ions to penetrate, accelerating steel corrosion and concrete deterioration, severely impacting the durability and service life of concrete structures.

[0003] Against this backdrop, self-healing concrete technology has become a research hotspot in the field of civil engineering. Among them, admixture-based self-healing admixtures have emerged as one of the most promising technologies for engineering applications due to their ease of operation and wide applicability. Admixture-based self-healing admixtures are mainly divided into two categories: one is organic resin-based repair agents, represented by epoxy resin and polyurethane, and the other is inorganic mineral-based repair agents, represented by metakaolin, slag powder, and fly ash. Organic resin-based repair agents can cure upon contact with water at the crack, forming a bonding layer to repair the crack. However, the compatibility between resin molecules and the concrete matrix is ​​poor, and resin particles are prone to agglomeration, leading to defects within the concrete and reducing its strength and density. Inorganic mineral-based repair agents, on the other hand, generate cementitious products through volcanic ash reaction to fill cracks, but their repair speed is slow, and their effectiveness in repairing wide cracks is limited.

[0004] To balance repair efficiency and concrete mechanical properties, existing technologies often employ an organic-inorganic composite approach, blending resins with mineral powders to prepare self-healing admixtures. However, traditional blending methods involve only simple physical mixing, lacking effective interfacial bonding between the resin and mineral powders. The problem of poor dispersibility remains unresolved, and agglomerates easily form in the concrete matrix, failing to fully leverage the synergistic repair advantages of organic-inorganic methods. Therefore, developing a self-healing concrete admixture capable of achieving uniform dispersion of organic resins and inorganic mineral powders while possessing both high repair performance and mechanical compatibility is crucial for promoting the engineering application of self-healing concrete technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects in the prior art where the self-healing materials and resins have poor dispersibility, leading to a decrease in concrete strength, and to provide a self-healing concrete admixture and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a self-healing concrete admixture includes the following steps:

[0008] (1) Dissolve 2-3g of PEG-PLA block copolymer in 20-30mL of dichloromethane; then add 80-100mL of ethanol aqueous solution (ethanol and water volume ratio is 1:1), stir evenly, and evaporate the dichloromethane to obtain PEG-PLA micelle solution.

[0009] The PEG-PLA micelle system is a polymer soft template. Its formation mechanism is as follows: PEG-PLA is a block copolymer of hydrophilic segment (PEG) and hydrophobic segment (PLA). Under the conditions of dichloromethane volatilization and change of dielectric environment of the system, PEG-PLA molecules are driven to self-assemble through hydrophobic interaction to form a core-shell type micelle aggregate with hydrophobic PLA as the core and hydrophilic PEG as the shell.

[0010] (2) Add 2-3 g of N-hydroxymethylacrylamide to the above PEG-PLA micelle solution, heat to 60-70℃ and stir for 30 min; then add 10-15 mL of tetraethyl orthosilicate and 0.2-0.3 mL of concentrated nitric acid (purity of concentrated nitric acid 65.0-68.0%), stir and react for 2-3 h to obtain a premix; transfer the premix to a high-pressure reactor, purge with nitrogen for protection, heat to 80-90℃, add 5-8 mL of an aqueous solution containing 0.2-0.3 parts by mass of ammonium persulfate, keep warm and react for 2-3 h; then add ammonia water to adjust the pH of the system to 8-9, stir to form a gel, dry, and ball mill to obtain the composite porous material;

[0011] The hydroxymethyl group on the N-hydroxymethylacrylamide molecule can undergo a dehydration condensation reaction with the hydroxyl group of the PEG segment in the PEG-PLA micelle shell, achieving the grafting and fixation of N-hydroxymethylacrylamide on the micelle surface. Concentrated nitric acid, as a catalyst, can promote the hydrolysis of tetraethyl orthosilicate to generate silica monomers. The silica monomers further undergo a condensation reaction with the hydroxyl groups on the micelle surface, depositing and forming an initial silica network on the micelle surface. Nitrogen gas protection can prevent the oxidation of free radicals generated by the thermal decomposition of ammonium persulfate. Ammonium persulfate, as an initiator, can initiate the N-hydroxymethylacrylamide reaction. A free radical cross-linking polymerization reaction occurs, causing the silica network and polymer network to interpenetrate and form a composite network structure. Adding ammonia to adjust the pH to 8-9 promotes further condensation of unreacted silica monomers in the system, while neutralizing the acidity of the system, causing the composite network structure to undergo a sol-gel transition to form a gel. After drying and ball milling, the PLA segment of the micelle core will be degraded or removed during the drying process, ultimately forming a composite porous material with a nanoscale pore structure. This porous structure provides sufficient space sites for subsequent loading of active mineral powders and epoxy resin.

[0012] (3) Mix 20-25g of metakaolin, 10-12g of anhydrous gypsum and 5-8g of slag powder evenly, and ball mill at 200-300r / min for 2-3h to obtain active mineral repair powder with a particle size of 100-200 mesh.

[0013] Metakaolin has an amorphous aluminosilicate structure and contains a large number of active silica-alumina groups; anhydrous gypsum can provide sulfate ions; slag powder contains active calcium oxide, silicon dioxide, aluminum oxide and other components; after ball milling, the specific surface area of ​​the three is greatly increased and the active sites are fully exposed; when cracks appear in concrete, external moisture penetrates, and the active mineral powder can react with calcium hydroxide, a product of concrete hydration, to produce volcanic ash reaction, generating cementitious products such as hydrated calcium silicate and hydrated calcium aluminate. At the same time, anhydrous gypsum reacts with hydrated calcium aluminate to generate ettringite crystals, thus achieving mineral filling and repair of cracks.

[0014] (4) Mix 5-8g of the composite porous material obtained in step (2), 10-15g of the active mineral repair powder obtained in step (3), and 5-8g of waterborne epoxy resin with a solid content of 50%-60%, add 60-80mL of ethylene glycol, and stir at 2000-2500r / min for 15-20min to obtain a uniform and viscous concrete self-repairing admixture.

[0015] The nanoscale pores of the composite porous material possess extremely strong adsorption properties, which can adsorb and fix waterborne epoxy resin molecules and active mineral powder particles within the pores, preventing their agglomeration in the concrete matrix. Ethylene glycol, as a polar dispersion medium, can reduce the surface tension of the waterborne epoxy resin and form hydrogen bonds with the hydrophilic groups on the surface of the composite porous material, further enhancing the dispersion stability of each component. High-speed stirring generates strong shear force, ensuring that the components adsorbed within the pores are uniformly dispersed, ultimately forming a stable multiphase dispersion system, guaranteeing that the admixture can be uniformly distributed in the matrix after being incorporated into the concrete.

[0016] The present invention also provides a self-healing concrete admixture prepared by the above preparation method.

[0017] Beneficial effects of the present invention

[0018] (1) The composite porous material prepared by the present invention has a nanoscale pore structure, which can achieve stable loading and uniform dispersion of active mineral powder and waterborne epoxy resin through adsorption, solves the technical problem of poor dispersibility of traditional self-healing materials, avoids the formation of agglomerates in the concrete matrix, and ensures that the mechanical properties of concrete are not affected.

[0019] (2) The self-healing admixture of the present invention has the dual functions of resin bonding repair and mineral filling repair. The two repair mechanisms work together to greatly improve the repair efficiency and repair durability of concrete cracks and effectively extend the service life of concrete structures.

[0020] (3) The preparation method of the present invention is simple, the reaction conditions are mild, the raw materials are widely available and the cost is controllable. It is suitable for large-scale industrial production and has significant economic value and application prospects. Attached Figure Description

[0021] Figure 1 A scanning electron microscope image of the composite porous material prepared in Example 1;

[0022] Figure 2 These are the Fourier transform infrared spectra of Example 1 and Comparative Example 2;

[0023] Figure 3 These are the BET curves of Example 1 and Comparative Example 1;

[0024] Figure 4 (a) and (b) are images of the admixtures prepared in Example 1 and Comparative Example 1, respectively;

[0025] Figure 5 (a)-(c) are scanning electron microscope images of the coatings formed by the additives in Example 1, Comparative Example 1 and Comparative Example 2, respectively.

[0026] Figure 6 (a) and (b) show the scratches on the coatings made with the additives in Example 1 and Comparative Example 2, respectively, at a pencil hardness of 3H.

[0027] Figure 7 This is the XRD spectrum of the additive in Example 1 over time. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] Example 1

[0030] The preparation steps of a self-healing concrete admixture are as follows:

[0031] (1) Preparation of PEG-PLA micelle solution:

[0032] Weigh 2.5g of PEG-PLA block copolymer and dissolve it in 25mL of dichloromethane. Stir until completely dissolved. Then add 90mL of ethanol aqueous solution (ethanol and water volume ratio 1:1), stir continuously for 30min, and let stand to evaporate naturally to remove dichloromethane, thus obtaining a stable PEG-PLA micelle solution.

[0033] (2) Preparation of composite porous materials:

[0034] Add 2.5 g of N-hydroxymethylacrylamide to the above micelle solution, heat to 65 °C and stir for 30 min; then add 12 mL of tetraethyl orthosilicate and 0.25 mL of concentrated nitric acid, stir and react for 2.5 h to obtain a premix; transfer the premix to a high-pressure reactor, purge with nitrogen for protection, heat to 85 °C, add 6 mL of an aqueous solution containing 0.25 g of ammonium persulfate dropwise, and keep the reaction at this temperature for 2.5 h; add ammonia dropwise to adjust the pH of the system to 8.5, stir to form a gel, dry, and ball mill to obtain the composite porous material;

[0035] (3) Preparation of active mineral repair powder:

[0036] Weigh 22g metakaolin, 11g anhydrous gypsum and 6g slag powder, mix them evenly and then place them in a ball mill and ball mill for 3 hours to obtain active mineral repair powder.

[0037] (4) Compounding of self-healing additives:

[0038] Weigh 6g of the composite porous material obtained in step (2) and 12g of the active mineral repair powder obtained in step (3), mix them with 6g of water-based epoxy resin and 70mL of ethylene glycol, stir at 2200r / min for 18min, and let stand at room temperature for 2.5h to obtain a uniform and viscous concrete self-repairing admixture.

[0039] Example 2

[0040] The preparation steps of a self-healing concrete admixture are as follows:

[0041] (1) Preparation of PEG-PLA micelle solution:

[0042] Weigh 2g of PEG-PLA block copolymer, dissolve it in 20mL of dichloromethane, and stir until completely dissolved; add 80mL of ethanol aqueous solution (ethanol and water volume ratio 1:1), stir evenly, and let stand to evaporate the dichloromethane to obtain PEG-PLA micelle solution.

[0043] (2) Preparation of composite porous materials:

[0044] 2g of N-hydroxymethylacrylamide was added to the micelle solution, and the mixture was heated to 60℃ and stirred for 30min. 10mL of tetraethyl orthosilicate and 0.2mL of concentrated nitric acid were added, and the mixture was stirred for 2h to obtain a premix. The premix was transferred to a high-pressure reactor, heated to 80℃ under nitrogen protection, and 5mL of an aqueous solution containing 0.2g of ammonium persulfate was added dropwise. The mixture was kept at this temperature for 2h. The pH was adjusted to 8 with ammonia, and the mixture was stirred to form a gel. The gel was dried and ball-milled to obtain the composite porous material.

[0045] (3) Preparation of active mineral repair powder:

[0046] Weigh 20g metakaolin, 10g anhydrous gypsum, and 5g slag powder, mix and ball mill for 2.5h to obtain active mineral repair powder;

[0047] (4) Compounding of self-healing additives:

[0048] Weigh 5g of composite porous material and 10g of active mineral repair powder, mix them with 5g of water-based epoxy resin and 60mL of ethylene glycol, stir at 2000r / min for 15min, and mature at room temperature for 2h to obtain concrete self-healing admixture.

[0049] Example 3

[0050] The preparation steps of a self-healing concrete admixture are as follows:

[0051] (1) Preparation of PEG-PLA micelle solution:

[0052] Weigh 3g of PEG-PLA block copolymer and dissolve it in 30mL of dichloromethane. Stir until completely dissolved. Add 100mL of ethanol-water solution (ethanol and water volume ratio 1:1), stir evenly, and let stand to evaporate the dichloromethane to obtain PEG-PLA micelle solution.

[0053] (2) Preparation of composite porous materials:

[0054] 3g of N-hydroxymethylacrylamide was added to the micelle solution, and the mixture was heated to 70℃ and stirred for 30 min. 15 mL of tetraethyl orthosilicate and 0.3 mL of concentrated nitric acid were added, and the mixture was stirred for 3 h to obtain a premix. The premix was transferred to a high-pressure reactor, heated to 90℃ under nitrogen protection, and 8 mL of an aqueous solution containing 0.3g of ammonium persulfate was added dropwise. The mixture was kept at this temperature for 3 h. The pH was adjusted to 9 with ammonia, and the mixture was stirred to form a gel. The gel was dried and ball-milled to obtain the composite porous material.

[0055] (3) Preparation of active mineral repair powder:

[0056] Weigh 25g metakaolin, 12g anhydrous gypsum, and 8g slag powder, mix and ball mill for 3.5h to obtain active mineral repair powder;

[0057] (4) Compounding of self-healing additives:

[0058] Weigh 8g of composite porous material and 15g of active mineral repair powder, mix them with 8g of water-based epoxy resin and 80mL of ethylene glycol, stir at 2500r / min for 20min, and mature at room temperature for 3h to obtain a concrete self-healing admixture.

[0059] Comparative Example 1

[0060] Self-healing admixture without PEG-PLA soft template

[0061] (1) Omit step (1), directly measure 90 mL of ethanol-water solution (ethanol and water volume ratio 1:1), add 2.5 g of N-hydroxymethylacrylamide, heat to 65 °C and stir for 30 min; then add 12 mL of tetraethyl orthosilicate and 0.25 mL of concentrated nitric acid, stir and react for 2.5 h to obtain a premixed solution;

[0062] (2) The subsequent processing of the premixed liquid, preparation of active mineral repair powder and compounding of additives are completely consistent with those in Example 1, and a self-healing additive without PEG-PLA soft template is obtained.

[0063] Comparative Example 2

[0064] Self-healing additives without tetraethyl orthosilicate

[0065] (1) Preparation of PEG-PLA micelle solution: The steps are the same as in Example 1;

[0066] (2) Add 2.5g of N-hydroxymethylacrylamide to the micelle solution, heat to 65℃ and stir for 30min. Omit the addition of tetraethyl orthosilicate and concentrated nitric acid, and stir directly for 30min to obtain the premixed solution.

[0067] (3) The subsequent processing of the premixed liquid, preparation of active mineral repair powder and compounding of additives are completely consistent with those in Example 1, and a self-repairing additive without tetraethyl orthosilicate is obtained.

[0068] Figure 1The scanning electron microscope (SEM) image of the composite porous material in Example 1 shows a porous structure with interconnected pores and no obvious agglomeration; the pore walls exhibit a rough, interwoven morphology. This structure is formed by drying and ball milling a silica-polymer interpenetrating network mediated by a PEG-PLA soft template. PEG-PLA self-assembles to form core-shell micelles, and its hydrophobic PLA core is degraded and removed during drying, leaving pores. The silica network formed by the hydrolysis of tetraethyl orthosilicate and the polymer network formed by the polymerization of N-hydroxymethylacrylamide interpenetrate each other, forming a pore wall support structure and ensuring the mechanical stability of the porous material. This demonstrates that the present invention successfully prepares a high-porosity, composite porous carrier using the soft template method, providing sufficient sites for subsequent loading of active mineral powders and waterborne epoxy resin.

[0069] Figure 2 These are the Fourier transform infrared spectra of Example 1 and Comparative Example 2.

[0070] Example 1 in A strong absorption peak appears at this location, corresponding to The stretching and contracting vibration; The peak at this point represents the stretching vibration of C=O, indicating that the silica network and the polymer network have successfully bonded. Comparative Example 2 (without tetraethyl orthosilicate) at... No Si-O-Si characteristic peaks were observed; only the C=O absorption peak of the polymer was present. The silica monomers generated by the hydrolysis of tetraethyl orthosilicate undergo a condensation reaction with the hydroxyl groups on the micelle surface, which is manifested as a Si-O-Si characteristic peak in the infrared spectrum. The presence of this peak indicates that the silica network has been successfully grafted onto the polymer matrix, forming an interpenetrating double network structure.

[0071] Figure 3 These are the BET curves of Example 1 and Comparative Example 1.

[0072] The porosity of Example 1 was significantly higher than that of Comparative Example 1, and the core-shell structure of the PEG-PLA soft template was key to mesoporous formation. In Comparative Example 1, due to the lack of a guiding soft template, silica and polymer only underwent random polymerization, failing to form ordered channels, resulting in a significant reduction in specific surface area and pore volume. High specific surface area and pore volume are the core foundation for achieving efficient loading and uniform dispersion of the repair components.

[0073] Figure 4 (a) and (b) are images of the admixtures prepared in Example 1 and Comparative Example 1, respectively;

[0074] The additive in Example 1 was a uniform, viscous, milky-white liquid. After standing for 6 hours, there was no stratification or precipitation, and the active mineral powder and resin were completely dispersed.

[0075] The additive in Comparative Example 1 was a grayish-white turbid liquid. After standing for 6 hours, a large amount of mineral powder precipitated at the bottom. The composite porous material in Example 1 firmly fixed and uniformly dispersed the mineral powder and resin molecules through the adsorption of nanopores and the dispersion of ethylene glycol. In contrast, the material in Comparative Example 1 lacked a porous carrier, and the mineral powder and resin lacked stable loading sites, resulting in agglomeration and sedimentation in the liquid phase.

[0076] Figure 5 (a)-(c) are scanning electron microscope images of the coatings formed by the additives in Example 1, Comparative Example 1, and Comparative Example 2, respectively. The coating surface of Example 1 is smooth and dense, without obvious pores and agglomerates, and the mineral powder and resin are uniformly distributed in the coating matrix. The coating surface of Comparative Example 1 is rough, with planar defects, a large number of micron-sized pores and agglomerates, and the interface between the coating and the substrate is discontinuous.

[0077] The interpenetrating double network structure of Example 1 imparts good density and uniformity to the coating. This indicates that Comparative Example 1, lacking a PEG-PLA soft template, suffers from poor admixture dispersion, resulting in poor overall coating uniformity. In concrete repair, poor admixture dispersion can also lead to uneven stress after repair, causing secondary cracking. The admixture coating in Comparative Example 2 shows cracking, indicating that the polymer matrix in Comparative Example 2 lacks a silica network, resulting in insufficient polymer matrix strength and susceptibility to cracking during film formation.

[0078] Figure 6 (a) and (b) show the scratches on the coatings of Example 1 and Comparative Example 2 with additives at a pencil hardness of 3H. The coating surface of Example 1 only shows shallow and fine continuous scratches, without coating peeling, flaking or cracking, and the scratch edges are smooth. This is because its composite porous material achieves uniform dispersion of active mineral powder and water-based epoxy resin, and the silica-polymer interpenetrating double network structure gives the coating excellent density, adhesion and mechanical strength, which can withstand the mechanical stress of pencil scratching without being damaged.

[0079] The coating surface of Comparative Example 2 showed deep and wide tear-like scratches. The reason is that Comparative Example 2 omitted the addition of tetraethyl orthosilicate, which could not form a rigid silica network. The coating structure was supported only by the polymer matrix, which led to a significant decrease in the mechanical strength and crack resistance of the coating. Under the external force of pencil scratching, the polymer matrix underwent plastic deformation and fracture, which in turn caused the coating to break.

[0080] Figure 7 XRD patterns of the admixture in Example 1 over time.

[0081] As time goes on, in , , , Characteristic diffraction peaks appeared, corresponding to the characteristic peaks of ettringite and hydrated calcium silicate (CSH) crystals, respectively, and the intensity of the diffraction peaks gradually increased with time (14 days). When the admixture came into contact with moisture, the metakaolinite and slag powder in the active mineral powder reacted with the hydration product calcium hydroxide in a pozzolanic reaction to form CSH gel; anhydrous gypsum provided sulfate ions, which combined with hydrated calcium aluminate to form ettringite crystals. The two products together filled the cracks, achieving self-repair. The increasing intensity of the diffraction peaks over time indicates that the repair products are continuously generated and the crystallinity increases. From a crystallographic perspective, this directly proves the inorganic mineral repair mechanism of the admixture of this invention, forming a synergistic effect with the bonding repair of organic resin.

Claims

1. A method for preparing a self-healing concrete admixture, characterized in that, Includes the following steps: (1) Preparation of PEG-PLA micelle solution; (2) N-hydroxymethylacrylamide, tetraethyl orthosilicate and concentrated nitric acid were added to the PEG-PLA micelle solution and reacted. The reaction was carried out under nitrogen protection, initiated polymerization, pH adjustment to form a gel, dried and ball milled to obtain a composite porous material. (3) Mix and ball-mill metakaolin, anhydrous gypsum and slag powder to obtain active mineral repair powder; (4) The composite porous material, active mineral repair powder, water-based epoxy resin and ethylene glycol are mixed and stirred at high speed to obtain the concrete self-healing admixture.

2. The preparation method according to claim 1, characterized in that, In step (1), the PEG-PLA micelle solution is prepared by dissolving 2-3g of PEG-PLA block copolymer in 20-30mL of dichloromethane; then adding 80-100mL of ethanol aqueous solution, wherein the volume ratio of ethanol to water in the ethanol aqueous solution is 1:1, stirring evenly, and then evaporating the dichloromethane to obtain the PEG-PLA micelle solution.

3. The preparation method according to claim 1, characterized in that, In step (2), the amount of N-hydroxymethylacrylamide added is 2~3g, and after addition, the temperature is raised to 60~70℃ and stirred for 30min; the amount of tetraethyl orthosilicate added is 10-15mL, the purity of concentrated nitric acid is 65.0-68.0%, the amount added is 0.2-0.3mL, and after addition, the mixture is stirred and reacted for 2-3h to obtain a premixed solution.

4. The preparation method according to claim 1, characterized in that, In step (2), the reaction conditions under nitrogen protection are as follows: heat up to 80~90℃, add 5~8mL of aqueous solution containing 0.2~0.3g of ammonium persulfate, and keep the reaction at the temperature for 2~3h; the pH adjustment is to add ammonia water to adjust the pH of the system to 8~9.

5. The preparation method according to claim 1, characterized in that, In step (3), the amount of metakaolin, anhydrous gypsum and slag powder added is 20~25g, 10~12g and 5~8g respectively; the ball mill speed is 200-300r / min and the ball milling time is 2-3h.

6. The preparation method according to claim 1, characterized in that, In step (4), the amount of the composite porous material added is 5-8g, the amount of the active mineral repair powder added is 10-15g, the solid content of the waterborne epoxy resin is 50%-60% and the amount added is 5-8g, and the amount of ethylene glycol added is 60-80mL; the speed of the high-speed stirring is 2000-2500r / min, and the stirring time is 15-20min.

7. A self-healing concrete admixture, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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