A low-temperature resistant repair and crack-resistant additive and its preparation method

Abstract

This invention discloses a low-temperature resistant repair and crack-resistant additive and its preparation method, belonging to the technical field of concrete repair materials. The additive is composed of a matrix component, functional additives, and active repair components in a mass ratio of 80:5-10:5-10. The matrix component includes sulfoaluminate cement clinker and composite mineral filler; the functional additives include modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fibers; the active repair components include microbial capsule-type self-healing materials and internal curing agents, wherein the microbial capsules contain *Bacillus pasteurellii* and *Bacillus urealyticum*. This invention achieves efficient self-repair of microcracks in concrete under low-temperature freeze-thaw conditions through the synergistic effect of microbial capsules and modified nano-silica, while significantly improving the early strength, freeze-thaw resistance, crack resistance, and durability of concrete, making it particularly suitable for the protection and repair of concrete structures in cold regions.

Description

Technical Field

[0001] This invention belongs to the field of concrete repair materials technology, specifically relating to a low-temperature resistant repair and crack-resistant additive and its preparation method. Background Technology

[0002] Concrete, as one of the most widely used building materials in modern construction engineering, boasts advantages such as low cost, high strength, and strong plasticity. However, during long-term use, concrete structures inevitably develop microcracks due to various factors, including environmental influences, loads, and the inherent material properties. This problem is particularly pronounced in cold regions where concrete structures are subjected to freeze-thaw cycles. When microcracks exist within the concrete, moisture seeps in. In low-temperature environments, the expansion of this moisture upon freezing causes significant frost heave stress, leading to the continuous expansion and connection of these microcracks. This weakens the strength and durability of the concrete structure, reduces its service life, increases maintenance costs, and may even pose safety hazards. Therefore, improving the low-temperature crack resistance of concrete in cold regions is crucial for extending its service life.

[0003] Currently, there are numerous methods for repairing microcracks in concrete, such as surface treatment, filling, and grouting. Surface treatment typically involves applying waterproof coatings or repair materials to the concrete surface. This method only provides some sealing for surface microcracks and is difficult to reach deeper internal microcracks. Furthermore, the bond strength between the repair material and the concrete matrix is ​​limited, and the repair effect is not sustainable under harsh environments such as freeze-thaw cycles. Filling generally involves inserting repair material into the microcracks, but this method requires high precision in cleaning and filling the microcracks. Improper handling can easily create new interface defects between the filler material and the concrete, affecting the repair effect. While grouting can repair deeper microcracks, there are many problems with the grout's injectability, compatibility with concrete, and curing performance at low temperatures, significantly limiting its application in cold regions. In addition, most existing repair materials lack sufficient freeze-thaw resistance; under freeze-thaw cycles, the repair material itself is prone to cracking and peeling, failing to effectively prevent the further development of microcracks.

[0004] For example, CN202111583235.4 discloses a crack-resistant cold-mix asphalt for road repair and its preparation method. The cold-mix asphalt is made from raw materials containing the following parts by weight: 3.8-4.6 parts asphalt, 0.485-0.532 parts high-viscosity modifier, 0.09-0.12 parts composite fiber, 72-90 parts coarse aggregate, 10.5-20 parts fine aggregate, and 1-5 parts mineral powder. The composite fiber is composed of polyester fiber and viscose fiber in a weight ratio of 1:0.05-0.1. The preparation method is as follows: coarse aggregate, fine aggregate, and mineral powder are mixed, heated to 180-220℃, and stirred to obtain aggregate. The composite fiber, high-viscosity modifier, and aggregate are mixed and stirred, and then asphalt at a temperature of 145-155℃ is added and stirred evenly to obtain the finished product.

[0005] Therefore, developing a concrete repair material that combines excellent frost resistance, erosion resistance, and self-healing ability has become a key direction for improving the durability of concrete structures in cold regions. Summary of the Invention

[0006] This invention addresses the problems of poor repair performance, low durability, and lack of self-healing function in existing concrete repair materials under low-temperature environments. It provides a multifunctional composite repair material with excellent freeze-thaw resistance, erosion resistance, and self-healing crack repair capabilities. The material consists of a matrix component, functional additives, and an active repair component. The matrix component ensures good adhesion to concrete and low-temperature workability; the functional additives enhance resistance to freeze-thaw cycles and chemical erosion; and the active repair component generates filling precipitates triggered by moisture penetration, achieving dynamic self-healing of microcracks. This invention also provides its preparation method and applications, suitable for long-term protection and damage repair of concrete structures in cold regions, significantly extending the service life of engineering projects.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A low-temperature resistant repair and crack-resistant additive includes a matrix component, a functional additive, and an active repair component, with a mass ratio of 80:5-10:5-10. The matrix component is composed of sulfoaluminate cement clinker and composite mineral filler. The functional additive is composed of modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fibers. The active repair component is composed of microbial capsule-type self-healing material and internal maintenance agent.

[0009] Furthermore, in the matrix components, the mass ratio of sulfoaluminate cement clinker to composite mineral filler is 70-90:10-30, wherein the composite mineral filler is obtained by mixing metakaolin and quartz powder in a mass ratio of (2-3):1.

[0010] The matrix component, with sulfoaluminate cement clinker as its core, endows the material with rapid hardening, early strength, and micro-expansion properties. This not only meets the requirements for rapid construction and strength development in low-temperature environments, but its micro-expansion effect also effectively compensates for shrinkage, reducing the risk of cracking at its source. In the composite mineral filler (metakaolin and quartz powder), metakaolin further optimizes the pore structure through pozzolanic reaction, improving the system's density and later-stage strength stability; quartz powder, as a micro-aggregate, regulates the system's reaction process and reduces shrinkage.

[0011] Furthermore, in the functional additive, the mass ratio of modified nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:1-2:1-3:0.1-0.3.

[0012] Furthermore, the polymer powder is ethylene-vinyl acetate copolymer latex powder (EVA) or acrylate powder; the organic antifreeze is obtained by mixing diethanolamine, sodium acetate, and urea in a mass ratio of 4:3:3; the urea in the organic antifreeze provides antifreeze function to the system, and also provides the necessary nitrogen source and reactants for the microbial-induced mineralization remediation reaction. The crack-resistant fiber is polypropylene fiber or polyvinyl alcohol fiber, with a length of 3-8 mm.

[0013] Furthermore, the method for preparing the modified nano-silica is as follows:

[0014] a. Disperse nano-silica in anhydrous ethanol and sonicate for 10-30 minutes to obtain a nano-silica dispersion.

[0015] b. Mix the silane coupling agent with anhydrous ethanol and deionized water, and hydrolyze for 10-20 minutes to obtain a hydrolyzed silane solution;

[0016] c. Under mechanical stirring, the hydrolyzed silane solution obtained in step b is slowly added dropwise to the nano silica dispersion in step a, and the mixture is reacted in a water bath at 60-70°C for 2-4 hours.

[0017] d. After the reaction is complete, centrifuge to separate the product, wash the product 2-3 times with anhydrous ethanol, and finally vacuum dry at 60-80℃. After grinding, the modified nano-silica powder is obtained.

[0018] Furthermore, the silane coupling agent is γ-aminopropyltriethoxysilane KH-550.

[0019] The functional additives include modified nano-silica, which, after surface modification with the silane coupling agent KH-550, exhibits excellent dispersibility in the cement matrix and can efficiently fill nanoscale pores. Its strong pozzolanic activity accelerates the hydration process, significantly improving the early strength and density of the material. The addition of polymer powder (EVA or acrylates) forms a flexible polymer film within the system, greatly enhancing the material's adhesion, flexibility, and flexural strength, while effectively reducing permeability. The addition of composite organic antifreeze agents (diethanolamine, sodium acetate, urea) lowers the freezing point and promotes low-temperature hydration through multiple mechanisms, ensuring the additives maintain their performance even in sub-zero temperatures. The addition of crack-resistant fibers, randomly distributed in three-dimensional space, effectively transfers and dissipates stress, preventing the initiation and propagation of microcracks, thus providing physical crack resistance.

[0020] Furthermore, in the active repair component, the mass ratio of the microbial capsule-type self-healing material to the internal maintenance agent is 3-5:0.5, and the preparation method of the microbial capsule-type self-healing material is as follows:

[0021] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0022] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0023] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0024] Furthermore, the *Pasteurella pasporioides* (… Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains (s) is 1:1. The strain number of *Pasteurella multocida* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center (CGMCC); the strain number of *Ureaplasma urealyticum* is CGMCC 1.7727, also purchased from the CGMCC. Both strains can be obtained through the collection center and do not require biological preservation.

[0025] Furthermore, the internal protective agent is a complex of molasses and polyacrylamide, wherein the mass ratio of molasses to polyacrylamide is 3:1. Molasses has both moisturizing and carbon source-providing functions for microorganisms; polyacrylamide has strong water retention. The combination of the two can maintain the moisture of the crack interface for a long time, creating a favorable microenvironment for microbial recovery and mineralization reactions.

[0026] A method for preparing a low-temperature repair and crack-resistant additive includes the following steps:

[0027] (1) Preparation of modified nano-silica;

[0028] (2) Preparation of microbial capsule-type self-healing materials;

[0029] (3) Add the modified nano silica, polymer powder, organic antifreeze and anti-crack fiber into a high-speed mixer in sequence according to the mass ratio, control the mixing temperature at 25-30℃ and the speed at 800-1000rpm, mix for 15-20 minutes to obtain the functional additive.

[0030] (4) Mix the sulfoaluminate cement clinker and composite mineral filler in the matrix components evenly, then add the functional additives obtained in step (3), as well as the microbial capsule self-healing material and internal curing agent, and continue to mix in the mixer under the same conditions for 10-15 minutes to ensure that each component is evenly dispersed. Finally, sieve and package to obtain the finished product of the low-temperature repair and crack-resistant additive.

[0031] The method of using the crack-resistant additive of this invention is as follows: When using it, add the crack-resistant additive to the concrete or mortar at 5% of the mass of the cementitious material, and mix it evenly with the aggregate and water before pouring.

[0032] Beneficial effects:

[0033] The core inventiveness of this invention lies in the significant synergistic effect between two specific microorganisms (Bacillus pasteurellii CGMCC 1.3687 and Bacillus urealyticum CGMCC 1.7727) in the active repair component, as well as between the microorganisms and the modified nano-silica.

[0034] Among them, the selected Bacillus pasteurellus strain, as a urease-driven strain, can rapidly hydrolyze urea, quickly increase the environmental pH and generate a high concentration of carbonate ions, providing a driving force for the rapid precipitation of calcium carbonate.

[0035] Ureaplasma urealyticum also possesses urease-producing capabilities and exhibits greater tolerance to highly alkaline environments. More importantly, it can secrete extracellular polymers (EPS). These biopolymers not only serve as templates for calcium carbonate precipitation, guiding its orderly deposition, but also fill cracks themselves, intertwining with calcium carbonate crystals to form a robust organic-inorganic composite repair, avoiding the brittleness of pure mineral repairs and enhancing the durability of the repair effect. The two are combined in a 1:1 ratio, achieving both "rapid initiation" and "long-lasting enhancement" repair capabilities, ensuring efficient repair can be initiated and completed in cracks under various conditions (such as pH and oxygen concentration).

[0036] Furthermore, the uniformly dispersed modified nano-silica, with its large specific surface area and abundant surface functional groups, provides a vast number of evenly distributed nucleation sites for microbially induced calcium carbonate production. This "nano-crystallization" effect significantly reduces the nucleation barrier for calcium carbonate crystallization, guiding calcium carbonate to preferentially grow rapidly and densely on and around the nano-silica surface. This accelerates the microbial mineralization reaction, speeds up the remediation process, and improves the density and adhesion of the precipitate to the matrix. Simultaneously, the denser matrix created by the nano-silica filling also delays the intrusion of harmful media, providing a longer reaction time for microbial remediation.

[0037] In summary, this low-temperature repair and crack-resistant additive exhibits excellent self-healing properties and structural durability under freeze-thaw cycles, making it particularly suitable for rapid repair and long-term protection of concrete projects in cold regions. The synergistic effect of the microbial-nanocomposite system not only significantly improves the material's low-temperature crack resistance and subsequent strength recovery, but also achieves dynamic crack sealing through continuous mineralization, effectively preventing moisture and chloride ion penetration, enhancing erosion resistance, and extending the structural service life. Attached Figure Description

[0038] Figure 1 This is a diagram illustrating the antagonistic effect of co-culturing *Bacillus pasteurellii* CGMCC 1.3687 and *Bacillus urealyticum* CGMCC 1.7727 according to the present invention.

[0039] Figure 2 Microbial culture results extracted from the cracks (3-7℃);

[0040] Figure 3 The results of microbial culture extracted from the cracks (25-30℃);

[0041] Figure 4 Figures showing the changes in crack repair in the blank group and comparative examples 1-3;

[0042] Figure 5 The images show the changes in crack repair in specimens of Example 1 and Comparative Examples 5-6. Detailed Implementation

[0043] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0044] Example 1

[0045] A low-temperature resistant repair and crack-resistant additive includes a matrix component, a functional additive, and an active repair component, with a mass ratio of 80:5:5. The matrix component is composed of sulfoaluminate cement clinker and composite mineral filler. The functional additive is composed of modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fiber. The active repair component is composed of microbial capsule-type self-healing material and internal maintenance agent.

[0046] In the matrix components, the mass ratio of sulfoaluminate cement clinker to composite mineral filler is 70:10, wherein the composite mineral filler is obtained by mixing metakaolin and quartz powder in a mass ratio of 2:1.

[0047] In the functional additive, the mass ratio of modified nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:1:1:0.1.

[0048] The polymer powder is ethylene-vinyl acetate copolymer latex powder (EVA); the organic antifreeze is obtained by mixing diethanolamine, sodium acetate, and urea in a mass ratio of 4:3:3; the crack-resistant fiber is polypropylene fiber or polyvinyl alcohol fiber with a length of 3-8 mm.

[0049] The method for preparing the modified nano-silica is as follows:

[0050] a. Disperse 10g of nano-silica (Shanghai Yunhe Materials Technology Co., Ltd.) with a particle size of 10-20nm in 200mL of anhydrous ethanol, and sonicate for 10 minutes to obtain a nano-silica dispersion.

[0051] b. Mix 1.5g of silane coupling agent with 50mL of anhydrous ethanol and 10mL of deionized water, and hydrolyze for 10 minutes to obtain a hydrolyzed silane solution;

[0052] c. Under mechanical stirring, the hydrolyzed silane solution obtained in step b is slowly added dropwise to the nano silica dispersion in step a, and the mixture is reacted in a water bath at 60-70°C for 2 hours.

[0053] d. After the reaction is complete, centrifuge to separate the product, wash the product 2-3 times with anhydrous ethanol, and finally vacuum dry at 60-80℃. After grinding, the modified nano-silica powder is obtained.

[0054] The silane coupling agent is γ-aminopropyltriethoxysilane KH-550.

[0055] In the active repair component, the mass ratio of the microbial capsule-type self-repairing material to the internal maintenance agent is 3:0.5. The preparation method of the microbial capsule-type self-repairing material is as follows:

[0056] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0057] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0058] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0059] The method for preparing the composite bacterial culture in step a is as follows: *Bacillus pasteurellis* (CGMCC 1.3687) and *Bacillus urealyticum* (CGMCC 1.7727) are cultured separately in LB medium at 30-32℃ and 180 rpm in a shaker for 24-36 hours, until the bacterial culture reaches OD. 600 The value reached 2.0-2.2; the two bacterial solutions were centrifuged at 6000 rpm for 15 minutes respectively, and the two bacterial precipitates were collected; the two bacterial precipitates were mixed at a mass ratio of 1:1 to obtain composite bacterial cells.

[0060] In step a, the mass ratio of the composite bacterial cells to trehalose, polyethylene glycol, and nano-calcium carbonate powder is: composite bacterial cells: trehalose: polyethylene glycol: nano-calcium carbonate = 1:0.3:0.2:0.1.

[0061] In step b, the aqueous solution of hydroxypropyl methylcellulose has a mass concentration of 5% and is sprayed into a fluidized bed at a rate of 5-8 mL / min. The coating is continued until the particle size of the composite freeze-dried powder reaches 100-150 μm. After the spraying is stopped, the drying continues for 1-2 hours to form a hydrogel coating layer.

[0062] In step c, a mixed organic solution of polylactic acid (PLA) and polyethylene glycol (PEG) is prepared according to a mass ratio of PLA:PEG:dichloromethane = 1:0.2:8. The mixed organic solution is sprayed at a rate of 3-5 mL / min. After the solvent (dichloromethane) has completely evaporated, a dense hydrophobic film layer is formed on the outside of the hydrogel layer. After cooling to room temperature, the film is sieved, and particles with a diameter of 120-180 μm are selected, which are the microbial capsule-type self-healing materials.

[0063] The Pasteurella sporeans ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains (s) is 1:1. The strain number of *Pasteurella multocida* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center (CGMCC); the strain number of *Ureaplasma urealyticum* is CGMCC 1.7727, also purchased from the CGMCC. Both strains can be obtained through the collection center and do not require biological preservation.

[0064] This application utilizes a double-layer encapsulation structure to effectively isolate the microorganisms from external environmental damage. The outer layer (hydrophobic film layer) is composed of polylactic acid (PLA) and polyethylene glycol (PEG). PLA is hydrophobic, effectively preventing external moisture and harmful ions (such as chloride ions) from penetrating the capsule under normal conditions, thus avoiding premature activation or death of microorganisms due to moisture contact during storage and the initial service life of concrete. More importantly, during low-temperature freeze-thaw cycles, it physically isolates the microbial cells from mechanical damage caused by external ice crystal formation (ice spikes damage the cell membrane).

[0065] Middle layer (hydrogel layer): Composed of hydroxypropyl methylcellulose (HPMC). When cracks form and extend into the capsule, and water enters, this layer rapidly absorbs water and swells. This swelling process serves two purposes: firstly, it provides initial physical filling of the tiny cracks; secondly, it forms a moisture-rich "gel protective pad," creating a buffered, moist local microenvironment for the revival and activity of internal microorganisms.

[0066] Meanwhile, trehalose and polyethylene glycol were added during the preparation of the bacterial powder. Trehalose can form a glassy protective layer on the cell membrane surface during the dehydration process of microbial cells, stabilizing the cell membrane and protein structure, enabling them to survive for a long time under dry and low-temperature conditions.

[0067] When concrete develops microcracks due to low-temperature shrinkage, frost heave stress, or external forces, these microbial capsules embedded in the concrete penetrate the cracks. External moisture (such as melted snow or rainwater) seeps along the cracks, damaging the capsule shell and reaching the internal hydrogel layer and freeze-dried bacterial powder. In the local microenvironment created by the capsules, the moisture revives the freeze-dried bacterial powder. Simultaneously, the premixed nano-calcium carbonate (as a calcium source) inside the capsules and calcium ions from the concrete matrix dissolve into the water. The microorganisms immediately begin catalyzing the hydrolysis of urea, rapidly increasing the local pH and generating carbonate ions. These carbonate ions combine with calcium ions to form calcium carbonate precipitate. Modified nano-silica acts as a "nano-crystallizer" here; its large specific surface area provides numerous nucleation sites, guiding the rapid and orderly deposition of calcium carbonate, thus efficiently filling the cracks.

[0068] Antagonistic effect test of strains: The antagonistic effect between the two strains was determined by the plate confrontation method. *Bacillus pasteurellii* and *Bacillus urealyticum* were inoculated at opposite ends of LB solid medium and co-cultured at 30°C for 48 hours. No obvious inhibition zone or growth inhibition was observed, indicating that there was no antagonistic effect between the two strains, and they could co-exist. The culture status is shown in the figure below. Figure 1 As shown, both strains exhibited uniform and vigorous growth in the co-culture system, with complete and clear colony morphology and no obvious edge inhibition or clear zone formation.

[0069] The internal curing agent is a complex of molasses and polyacrylamide, wherein the mass ratio of molasses to polyacrylamide is 3:1. Industrial-grade molasses (solid content ≥80%) and polyacrylamide (molecular weight 8-12 million) are weighed out. The polyacrylamide is slowly added to the molasses at 50-60℃ while stirring (150-200 rpm) for 30-40 minutes until the polyacrylamide is completely dissolved and no visible lumps are formed, resulting in a uniform internal curing agent solution. This solution is then spray-dried at 70-80℃ to obtain a solid powder of the internal curing agent.

[0070] A method for preparing a low-temperature repair and crack-resistant additive includes the following steps:

[0071] (1) Preparation of modified nano-silica;

[0072] (2) Preparation of microbial capsule-type self-healing materials;

[0073] (3) Add the modified nano silica, polymer powder, organic antifreeze and anti-crack fiber into a high-speed mixer in sequence according to the mass ratio, control the mixing temperature at 25-30℃ and the speed at 800-1000rpm, mix for 15 minutes to obtain the functional additive.

[0074] (4) Mix the sulfoaluminate cement clinker and composite mineral filler in the matrix components evenly, then add the functional additives obtained in step (3), as well as the microbial capsule self-healing material and internal curing agent, and continue to mix in the mixer under the same conditions for 10 minutes to ensure that each component is evenly dispersed. Finally, sieve and package to obtain the finished product of the low-temperature repair and crack-resistant additive.

[0075] Example 2

[0076] A low-temperature resistant repair and crack-resistant additive includes a matrix component, a functional additive, and an active repair component, with a mass ratio of 80:7:8. The matrix component is composed of sulfoaluminate cement clinker and composite mineral filler. The functional additive is composed of modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fiber. The active repair component is composed of microbial capsule-type self-healing material and internal maintenance agent.

[0077] In the matrix components, the mass ratio of sulfoaluminate cement clinker to composite mineral filler is 80:23, wherein the composite mineral filler is obtained by mixing metakaolin and quartz powder in a mass ratio of 2:1.

[0078] In the functional additive, the mass ratio of modified nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:1:2:0.2.

[0079] The polymer powder is acrylate powder; the organic antifreeze is obtained by mixing diethanolamine, sodium acetate and urea in a mass ratio of 4:3:3; the crack-resistant fiber is polypropylene fiber or polyvinyl alcohol fiber with a length of 3-8 mm.

[0080] The method for preparing the modified nano-silica is as follows:

[0081] a. Disperse 10g of nano-silica (Shanghai Yunhe Materials Technology Co., Ltd.) with a particle size of 10-20nm in 200mL of anhydrous ethanol, and sonicate for 30 minutes to obtain a nano-silica dispersion.

[0082] b. Mix 1.5g of silane coupling agent with 50mL of anhydrous ethanol and 10mL of deionized water, and hydrolyze for 20 minutes to obtain a hydrolyzed silane solution;

[0083] c. Under mechanical stirring, the hydrolyzed silane solution obtained in step b is slowly added dropwise to the nano silica dispersion in step a, and the mixture is reacted in a water bath at 60-70°C for 4 hours.

[0084] d. After the reaction is complete, centrifuge to separate the product, wash the product 2-3 times with anhydrous ethanol, and finally vacuum dry at 60-80℃. After grinding, the modified nano-silica powder is obtained.

[0085] The silane coupling agent is γ-aminopropyltriethoxysilane KH-550.

[0086] In the active repair component, the mass ratio of the microbial capsule-type self-healing material to the internal maintenance agent is 4:0.5. The preparation method of the microbial capsule-type self-healing material is as follows:

[0087] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0088] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0089] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0090] The method for preparing the composite bacterial culture in step a is as follows: *Bacillus pasteurellis* (CGMCC 1.3687) and *Bacillus urealyticum* (CGMCC 1.7727) are cultured separately in LB medium at 30-32℃ and 180 rpm in a shaker for 24-36 hours, until the bacterial culture reaches OD. 600 The value reached 2.0-2.2; the two bacterial solutions were centrifuged at 6000 rpm for 15 minutes respectively, and the two bacterial precipitates were collected; the two bacterial precipitates were mixed at a mass ratio of 1:1 to obtain composite bacterial cells.

[0091] In step a, the mass ratio of the composite bacterial cells to trehalose, polyethylene glycol, and nano-calcium carbonate powder is: composite bacterial cells: trehalose: polyethylene glycol: nano-calcium carbonate = 1:0.3:0.4:0.2.

[0092] In step b, the aqueous solution of hydroxypropyl methylcellulose has a mass concentration of 6% and is sprayed into a fluidized bed at a rate of 5-8 mL / min. The coating is continued until the particle size of the composite freeze-dried powder reaches 100-150 μm. After the spraying is stopped, the drying continues for 1-2 hours to form a hydrogel coating layer.

[0093] In step c, a mixed organic solution of polylactic acid (PLA) and polyethylene glycol (PEG) is prepared according to a mass ratio of PLA:PEG:dichloromethane = 1:0.3:9. The mixed organic solution is sprayed at a rate of 3-5 mL / min. After the solvent (dichloromethane) has completely evaporated, a dense hydrophobic film layer is formed on the outside of the hydrogel layer. After cooling to room temperature, the film is sieved, and particles with a diameter of 120-180 μm are selected as the microbial capsule-type self-healing material.

[0094] The Pasteurella sporeans ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains (s) is 1:1. The strain number of *Pasteurella multocida* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center (CGMCC); the strain number of *Ureaplasma urealyticum* is CGMCC 1.7727, also purchased from the CGMCC. Both strains can be obtained through the collection center and do not require biological preservation.

[0095] The internal curing agent is a complex of molasses and polyacrylamide, wherein the mass ratio of molasses to polyacrylamide is 3:1. Industrial-grade molasses (solid content ≥80%) and polyacrylamide (molecular weight 8-12 million) are weighed out. The polyacrylamide is slowly added to the molasses at 50-60℃ while stirring (150-200 rpm) for 30-40 minutes until the polyacrylamide is completely dissolved and no visible lumps are formed, resulting in a uniform internal curing agent solution. This solution is then spray-dried at 70-80℃ to obtain a solid powder of the internal curing agent.

[0096] A method for preparing a low-temperature repair and crack-resistant additive includes the following steps:

[0097] (1) Preparation of modified nano-silica;

[0098] (2) Preparation of microbial capsule-type self-healing materials;

[0099] (3) Add the modified nano silica, polymer powder, organic antifreeze and anti-crack fiber into a high-speed mixer in sequence according to the mass ratio, control the mixing temperature at 25-30℃ and the speed at 800-1000rpm, mix for 20 minutes to obtain the functional additive.

[0100] (4) Mix the sulfoaluminate cement clinker and composite mineral filler in the matrix components evenly, then add the functional additives obtained in step (3), as well as the microbial capsule self-healing material and internal curing agent, and continue to mix in the mixer under the same conditions for 15 minutes to ensure that each component is evenly dispersed. Finally, sieve and package to obtain the finished product of the low-temperature repair and crack-resistant additive.

[0101] Example 3

[0102] A low-temperature resistant repair and crack-resistant additive includes a matrix component, a functional additive, and an active repair component, with a mass ratio of 80:10:10. The matrix component is composed of sulfoaluminate cement clinker and composite mineral filler. The functional additive is composed of modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fibers. The active repair component is composed of microbial capsule-type self-healing material and internal maintenance agent.

[0103] In the matrix components, the mass ratio of sulfoaluminate cement clinker to composite mineral filler is 90:30, wherein the composite mineral filler is obtained by mixing metakaolin and quartz powder in a mass ratio of 3:1.

[0104] In the functional additive, the mass ratio of modified nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:2:3:0.3.

[0105] The polymer powder is ethylene-vinyl acetate copolymer latex powder (EVA); the organic antifreeze is obtained by mixing diethanolamine, sodium acetate, and urea in a mass ratio of 4:3:3; the crack-resistant fiber is polypropylene fiber or polyvinyl alcohol fiber with a length of 3-8 mm.

[0106] The method for preparing the modified nano-silica is as follows:

[0107] a. Disperse 10g of nano-silica (Shanghai Yunhe Materials Technology Co., Ltd.) with a particle size of 10-20nm in 200mL of anhydrous ethanol, and sonicate for 10-30 minutes to obtain a nano-silica dispersion.

[0108] b. Mix 1.5g of silane coupling agent with 50mL of anhydrous ethanol and 10mL of deionized water, and hydrolyze for 10-20 minutes to obtain a hydrolyzed silane solution;

[0109] c. Under mechanical stirring, the hydrolyzed silane solution obtained in step b is slowly added dropwise to the nano silica dispersion in step a, and the mixture is reacted in a water bath at 60-70°C for 2-4 hours.

[0110] d. After the reaction is complete, centrifuge to separate the product, wash the product 2-3 times with anhydrous ethanol, and finally vacuum dry at 60-80℃. After grinding, the modified nano-silica powder is obtained.

[0111] The silane coupling agent is γ-aminopropyltriethoxysilane KH-550.

[0112] In the active repair component, the mass ratio of the microbial capsule-type self-healing material to the internal maintenance agent is 5:0.5. The preparation method of the microbial capsule-type self-healing material is as follows:

[0113] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0114] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0115] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0116] The method for preparing the composite bacterial culture in step a is as follows: *Bacillus pasteurellis* (CGMCC 1.3687) and *Bacillus urealyticum* (CGMCC 1.7727) are cultured separately in LB medium at 30-32℃ and 180 rpm in a shaker for 24-36 hours, until the bacterial culture reaches OD. 600 The value reached 2.0-2.2; the two bacterial solutions were centrifuged at 6000 rpm for 15 minutes respectively, and the two bacterial precipitates were collected; the two bacterial precipitates were mixed at a mass ratio of 1:1 to obtain composite bacterial cells.

[0117] In step a, the mass ratio of the composite bacterial cells to trehalose, polyethylene glycol, and nano-calcium carbonate powder is: composite bacterial cells: trehalose: polyethylene glycol: nano-calcium carbonate = 1:0.5:0.4:0.2.

[0118] In step b, the aqueous solution of hydroxypropyl methylcellulose has a mass concentration of 8% and is sprayed into a fluidized bed at a rate of 5-8 mL / min. The coating is continued until the particle size of the composite freeze-dried powder reaches 100-150 μm. After the spraying is stopped, the drying continues for 1-2 hours to form a hydrogel coating layer.

[0119] In step c, a mixed organic solution of polylactic acid (PLA) and polyethylene glycol (PEG) is prepared according to a mass ratio of PLA:PEG:dichloromethane = 1:0.3:10. The mixed organic solution is sprayed at a rate of 3-5 mL / min. After the solvent (dichloromethane) has completely evaporated, a dense hydrophobic film layer is formed on the outside of the hydrogel layer. After cooling to room temperature, the film is sieved, and particles with a diameter of 120-180 μm are selected as the microbial capsule-type self-healing material.

[0120] The Pasteurella sporeans ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains (s) is 1:1. The strain number of *Pasteurella multocida* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center (CGMCC); the strain number of *Ureaplasma urealyticum* is CGMCC 1.7727, also purchased from the CGMCC. Both strains can be obtained through the collection center and do not require biological preservation.

[0121] The internal curing agent is a complex of molasses and polyacrylamide, wherein the mass ratio of molasses to polyacrylamide is 3:1. Industrial-grade molasses (solid content ≥80%) and polyacrylamide (molecular weight 8-12 million) are weighed out. The polyacrylamide is slowly added to the molasses at 50-60℃ while stirring (150-200 rpm) for 30-40 minutes until the polyacrylamide is completely dissolved and no visible lumps are formed, resulting in a uniform internal curing agent solution. This solution is then spray-dried at 70-80℃ to obtain a solid powder of the internal curing agent.

[0122] A method for preparing a low-temperature repair and crack-resistant additive includes the following steps:

[0123] (1) Preparation of modified nano-silica;

[0124] (2) Preparation of microbial capsule-type self-healing materials;

[0125] (3) Add the modified nano silica, polymer powder, organic antifreeze and anti-crack fiber into a high-speed mixer in sequence according to the mass ratio, control the mixing temperature at 25-30℃ and the speed at 800-1000rpm, mix for 20 minutes to obtain the functional additive.

[0126] (4) Mix the sulfoaluminate cement clinker and composite mineral filler in the matrix components evenly, then add the functional additives obtained in step (3), as well as the microbial capsule self-healing material and internal curing agent, and continue to mix in the mixer under the same conditions for 15 minutes to ensure that each component is evenly dispersed. Finally, sieve and package to obtain the finished product of the low-temperature repair and crack-resistant additive.

[0127] Comparative Example 1

[0128] In this comparative example, except for the use of ordinary nano-silica, the raw materials and process steps are the same as in Example 1. That is:

[0129] A low-temperature resistant repair and crack-resistant additive includes a matrix component, a functional additive, and an active repair component, with a mass ratio of 80:5:5. The matrix component is composed of sulfoaluminate cement clinker and composite mineral filler. The functional additive is composed of nano-silica, polymer powder, organic antifreeze agent, and crack-resistant fiber. The active repair component is composed of microbial capsule-type self-healing material and internal maintenance agent.

[0130] In the functional additive, the mass ratio of nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:1:1:0.1.

[0131] The nano-silica has a particle size of 10-20 nm and was purchased from Shanghai Yunhe Materials Technology Co., Ltd.

[0132] Comparative Example 2

[0133] This comparative example uses only one active strain of *Bacillus pasteurellii*, while the other raw materials and process steps are the same as in Example 1. That is:

[0134] In the active repair component, the mass ratio of the microbial capsule-type self-repairing material to the internal maintenance agent is 3:0.5. The preparation method of the microbial capsule-type self-repairing material is as follows:

[0135] a. Preparation of bacterial powder: Bacillus pasteurellus was cultured, and the bacterial cells were collected by centrifugation. The bacterial cells were mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain composite freeze-dried powder.

[0136] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0137] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0138] The method for preparing the composite bacterial culture in step a is as follows: Culture *Pasteurella multocida* on LB medium at 30-32℃ and 180 rpm for 24-36 hours, until the bacterial culture reaches OD500. 600 The value reaches 2.0-2.2; the bacterial solution is centrifuged at 6000 rpm for 15 minutes, and the bacterial precipitate is collected to obtain the bacterial cells.

[0139] In step a, the mass ratio of bacterial cells to trehalose, polyethylene glycol, and nano-calcium carbonate powder is: bacterial cells: trehalose: polyethylene glycol: nano-calcium carbonate = 1:0.3:0.2:0.1.

[0140] The strain of *Bacillus pasteurellus* was numbered CGMCC 1.3687 and was purchased from the China General Microbiological Culture Collection Center.

[0141] Comparative Example 3

[0142] This comparative example uses only one active strain of *Bacillus urealyticum*, while the other raw materials and process steps are the same as in Example 1. That is:

[0143] In the active repair component, the mass ratio of the microbial capsule-type self-repairing material to the internal maintenance agent is 3:0.5. The preparation method of the microbial capsule-type self-repairing material is as follows:

[0144] a. Preparation of bacterial powder: Bacillus urealyticum was cultured, and the bacterial cells were collected by centrifugation. The bacterial cells were mixed evenly with trehalose, polyethylene glycol and nano-calcium carbonate powder, and then vacuum freeze-dried to obtain composite freeze-dried powder.

[0145] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0146] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0147] The method for preparing the composite bacterial culture in step a is as follows: Culture *Bacillus urealyticum* in LB medium at 30-32℃ and 180 rpm for 24-36 hours, until the bacterial culture reaches OD500. 600 The value reaches 2.0-2.2; the bacterial solution is centrifuged at 6000 rpm for 15 minutes, and the bacterial precipitate is collected to obtain the bacterial cells.

[0148] In step a, the mass ratio of bacterial cells to trehalose, polyethylene glycol, and nano-calcium carbonate powder is: bacterial cells: trehalose: polyethylene glycol: nano-calcium carbonate = 1:0.3:0.2:0.1.

[0149] The strain of *Bacillus urealyticum* was numbered CGMCC 1.7727 and was purchased from the China General Microbiological Culture Collection Center.

[0150] Comparative Example 4

[0151] In this comparative example, except for changing the mass ratio of *Pasteurella sporogenes* and *Bacillus urealyticum* to 2:1, all other raw materials and process steps were the same as in Example 1. That is, *Pasteurella sporogenes* was dominant.

[0152] In the active repair component, the mass ratio of the microbial capsule-type self-repairing material to the internal maintenance agent is 3:0.5. The preparation method of the microbial capsule-type self-repairing material is as follows:

[0153] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0154] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0155] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0156] The method for preparing the composite bacterial culture in step a is as follows: *Bacillus pasteurellis* (CGMCC 1.3687) and *Bacillus urealyticum* (CGMCC 1.7727) are cultured separately in LB medium at 30-32℃ and 180 rpm in a shaker for 24-36 hours, until the bacterial culture reaches OD. 600 The value reached 2.0-2.2; the two bacterial solutions were centrifuged at 6000 rpm for 15 minutes respectively, and the two bacterial precipitates were collected; the two bacterial precipitates were mixed at a mass ratio of 2:1 to obtain composite bacterial cells.

[0157] The Pasteurella sporeans ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains is 2:1. The strain number of *Bacillus pasteurellus* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center; the strain number of *Bacillus urealyticum* is CGMCC 1.7727, purchased from the China General Microbiological Culture Collection Center.

[0158] Comparative Example 5

[0159] In this comparative example, except for changing the mass ratio of *Pasteurella spp.* to 1:2, the raw materials and process steps were the same as in Example 1. That is, *Bacillus urealyticum* was dominant.

[0160] In the active repair component, the mass ratio of the microbial capsule-type self-repairing material to the internal maintenance agent is 3:0.5. The preparation method of the microbial capsule-type self-repairing material is as follows:

[0161] a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder.

[0162] b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface.

[0163] c. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained.

[0164] The method for preparing the composite bacterial culture in step a is as follows: *Bacillus pasteurellis* (CGMCC 1.3687) and *Bacillus urealyticum* (CGMCC 1.7727) are cultured separately in LB medium at 30-32℃ and 180 rpm in a shaker for 24-36 hours, until the bacterial culture reaches OD. 600 The value reached 2.0-2.2; the two bacterial solutions were centrifuged at 6000 rpm for 15 minutes respectively, and the two bacterial precipitates were collected; the two bacterial precipitates were mixed at a mass ratio of 1:2 to obtain composite bacterial cells.

[0165] The Pasteurella sporeans ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilitica The mass ratio of the two strains is 1:2. The strain number of *Bacillus pasteurellus* is CGMCC 1.3687, purchased from the China General Microbiological Culture Collection Center; the strain number of *Bacillus urealyticum* is CGMCC 1.7727, purchased from the China General Microbiological Culture Collection Center.

[0166] Performance testing

[0167] Raw materials and mix proportions: Fine aggregate: Standard sand, produced by Xiamen Aisiou Standard Sand Co., Ltd.

[0168] Table 1. Mix proportions of mortar specimens (kg / m³) 3 )

[0169]

[0170] Crack-resistant additives were prepared according to the examples and comparative methods. The additives were added at 5% of the cement mass, and a blank control was set up (i.e., no crack-resistant additives were added). According to GB / T 17671-2021, molded mortar specimens were placed indoors at 20±5℃ and relative humidity greater than 50% for 1 day after molding before demolding. After demolding, the specimens were placed in a standard curing room at 20±2℃ and relative humidity above 95% and cured to the appropriate age. Performance tests were then conducted.

[0171] Mechanical property tests were conducted sequentially according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)".

[0172] Durability testing:

[0173] The impact on the durability of the matrix (freezing resistance, carbonation resistance, chloride ion resistance) was tested in accordance with the "Standard for Test Methods of Basic Performance of Building Mortar" (JGJ / T70-2009).

[0174] Freeze resistance:

[0175] After 24 days of standard curing, the specimens were immersed in water at 20±2℃, ensuring the water level was 20-30mm above the top surface of the specimens. After 4 days, the surface moisture was wiped off and the specimens were weighed. The specimens were then placed in a freeze-thaw test chamber, leaving a 20mm gap between the specimens and the chamber wall, with each specimen spaced 30mm apart. The freezing time was started when the temperature inside the freeze-thaw chamber dropped to -15℃. During the freezing phase, the temperature was maintained between -20℃ and -15℃; during the thawing phase, the temperature was controlled between 15℃ and 20℃. Each freeze-thaw cycle consisted of 4 hours for both freezing and thawing. The end of the thawing phase marked the completion of this freeze-thaw cycle. After 300 freeze-thaw cycles, the specimens were weighed, and the average weight of three specimens was taken as the experimental result. The rate of mass change was calculated using the formula.

[0176] In the formula, W is the rate of change of specimen mass after n freeze-thaw cycles (%), m0 is the mass before the freeze-thaw experiment (g); m n — Mass of the specimen after n freeze-thaw cycles, in g.

[0177] Anti-carbonization:

[0178] After 26 days of standard curing, the specimens were removed and dried in a 60℃ oven for 48 hours. Then, heated paraffin wax was used to seal all four sides of the specimens, leaving only two 40×40mm faces exposed for subsequent carbonization. The treated specimens were placed in a carbonization chamber, where the carbon dioxide concentration was maintained at 20±3%, the temperature at 20±2℃, and the relative humidity at 70±5%. At 28 days of carbonization, the specimens were removed and the carbonization depth was measured. For carbonization depth measurement, a 1% phenolphthalein alcohol solution was sprayed onto the test specimens, and the carbonization depth at each point was measured to an accuracy of 0.5mm. Each group was analyzed based on the measurement data of three specimens. The average carbonization depth of the mortar specimens at each test age was calculated using the following formula: In the formula, d l — Specimen carbonization l The average carbonization depth of the measuring point is in mm; di is the carbonization depth of each measuring point in mm; n is the total number of measuring points.

[0179] Resistance to chloride ion penetration:

[0180] Cylindrical specimens with a diameter of 100±1 mm and a height of 200±2 mm were cast according to the mix proportion. After curing for 28 days, three cylindrical sections with a height of 50±2 mm were cut from the middle of the specimen using a cutting machine. The specimens were then placed in a vacuum saturation chamber to retain water for 24 hours. An electric flux meter was connected to the power supply with a 0.3 mol / L NaOH solution at the positive electrode and a 3.0% NaCl solution at the negative electrode. The power supply voltage was 60±0.1 V, and the total electric flux value was recorded over 6 hours.

[0181] Self-healing performance test:

[0182] Mortar specimens with dimensions of 40mm×40mm×160mm were poured to observe crack repair and determine the material's compressive strength recovery rate. Cracks were extracted from the mortar specimens after 7 days of standard curing using a press, with a crack growth rate of 0.5kN / s. Cracks with widths between 100-400μm were selected. After determining the initial crack width, a microbial concentration test was conducted. Approximately 1g of powder sample was extracted from the crack cross-section and inoculated into LB medium. The medium was incubated at 3-7℃ and 25-30℃ for 12 hours. The number of microorganisms was determined using a colony counting method, and the OD was measured. 600 value.

[0183] After determining the initial crack width, the specimens were subjected to a second curing in water. The second curing period was 20 days, and the crack repair was observed using a ZBL-F800 crack comprehensive testing instrument. The crack morphology repair was observed using scanning electron microscopy.

[0184] Crack width repair rate: The crack width repair rate refers to the crack repair status at a given time point, calculated using the image processing software "ImageJ" to determine the width of the repaired crack. The crack width repair rate (L) is calculated according to the following formula: In the formula: L—crack width repair rate (%); l0—initial crack width (mm); lt—crack width after secondary curing and repair (mm). The average value of 3 specimens in each group is taken as the final result.

[0185] Compressive strength recovery rate: After the secondary curing is completed, the mortar specimens repaired by cracks are removed, the surface moisture is wiped off, and the compressive strength is tested again, with the loading rate controlled at 0.5 kN / s. The compressive strength value of the repaired specimens is recorded, and the average value of 3 specimens in each group is taken as the final result. The compressive strength recovery rate (R) is calculated according to the following formula: R = (f t / f0)×100%, where f t f0 represents the compressive strength of the repaired specimen, while f0 represents the compressive strength of the reference specimen that was not cracked but cured under the same conditions to the same age.

[0186] The performance test results are shown in Table 2:

[0187] Table 2 Mortar Performance Test Results

[0188]

[0189] As shown in Table 2, the mortars of Examples 1 to 3 exhibited excellent performance in terms of 28-day compressive strength, flexural strength, freeze-thaw cycle mass loss rate, carbonization depth, electrical flux, crack width repair rate, and compressive strength recovery rate. Compared with Comparative Examples 1 to 5, the crack-resistant additives in these examples significantly improved the overall performance of the mortars, especially in terms of freeze resistance, carbonization resistance, and chloride ion penetration resistance. This indicates that the reasonable ratio of composite microorganisms to protective agents and the preparation process play a crucial role in the performance of microbial capsule-type self-healing materials. In contrast, Comparative Examples 1-5 showed that Comparative Example 1 used ordinary nano-silica without effective modification, resulting in poor dispersibility and weak bonding with the matrix, as well as poor compatibility with microbial microorganisms, leading to a significant reduction in durability and self-healing performance. Comparative Examples 2-5 altered the types or amounts of microbial microorganisms, resulting in a decrease in microbial activity retention and insufficient self-healing product generation, thus affecting crack healing efficiency and structural strength recovery. While the performance of Comparative Examples 4-5 was superior to that of Comparative Examples 2-3 (single-strain), it was still inferior to the 1:1 compounding scheme in Example 1. This demonstrates that a 1:1 mass ratio is the optimal choice for this invention; deviating from this ratio will disrupt the dynamic balance and optimal synergistic efficiency of the two microorganisms during the repair process, leading to a decrease in repair effectiveness and durability.

[0190] from Figure 2-3 The microbial culture results extracted from the cracks also show that Bacillus pasteurellii and Bacillus urealyticum can maintain high activity under low temperature and alkaline conditions, and when the two coexist in equal proportions, they can promote each other and maintain a high activity state.

[0191] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A low-temperature resistant repair and crack-resistant additive, characterized in that, It comprises a matrix component, functional additives, and an active repair component, with a mass ratio of 80:5-10:5-10; the matrix component consists of sulfoaluminate cement clinker and composite mineral filler; the functional additives consist of modified nano-silica, polymer powder, organic antifreeze, and crack-resistant fibers; the active repair component consists of microbial capsule-type self-healing material and internal maintenance agent. The method for preparing the modified nano-silica is as follows: a. Disperse nano-silica in anhydrous ethanol and sonicate for 10-30 minutes to obtain a nano-silica dispersion. b. Mix the silane coupling agent with anhydrous ethanol and deionized water, and hydrolyze for 10-20 minutes to obtain a hydrolyzed silane solution; c. Under mechanical stirring, the hydrolyzed silane solution obtained in step b is slowly added dropwise to the nano silica dispersion in step a, and the mixture is reacted in a water bath at 60-70°C for 2-4 hours. d. After the reaction is complete, centrifuge to separate the product, wash the product 2-3 times with anhydrous ethanol, and finally vacuum dry at 60-80℃. After grinding, the modified nano-silica powder is obtained. In the active repair component, the mass ratio of the microbial capsule-type self-healing material to the internal maintenance agent is 3-5: 0.5, The preparation method of microbial capsule-type self-healing material is as follows: a. Preparation of bacterial powder: Bacillus pasteurellii and Bacillus urealyticum were cultured separately, and the bacterial cells were collected by centrifugation and mixed to obtain a composite bacterial cell. The composite bacterial cell was mixed evenly with trehalose, polyethylene glycol and nano calcium carbonate powder, and then vacuum freeze-dried to obtain a composite freeze-dried powder. b. Intermediate coating: Using a fluidized bed coating device, the composite freeze-dried powder obtained in step a is used as a substrate and sprayed into an aqueous solution of hydroxypropyl methylcellulose. After drying, a hydrogel layer is formed on its surface. Outer coating: Continue in the fluidized bed, spray a mixed organic solution of polylactic acid and polyethylene glycol into the intermediate product obtained in step b. After the solvent evaporates, a dense hydrophobic film layer is formed, and the final microbial capsule-type self-healing material is obtained. The Pasteurella multocida ( Sporosarcina pasteurii ) and Ureaplasma urealyticum ( Gracilibacillus ureilyticu The mass ratio of the two strains is 1:1, and the strain number of *Bacillus pasteurellus* is CGMCC 1.3687; the strain number of *Bacillus urealyticum* is CGMCC 1.7727.

2. The low-temperature repair and crack-resistant additive according to claim 1, characterized in that, In the matrix components, the mass ratio of sulfoaluminate cement clinker to composite mineral filler is 70-90:10-30, wherein the composite mineral filler is obtained by mixing metakaolin and quartz powder in a mass ratio of (2-3):

1.

3. The low-temperature repair and crack-resistant additive according to claim 1, characterized in that, In the functional additive, the mass ratio of modified nano-silica, polymer powder, organic antifreeze agent and crack-resistant fiber is 1:1-2:1-3:0.1-0.

3.

4. The low-temperature repair and crack-resistant additive according to claim 3, characterized in that, The polymer powder is ethylene-vinyl acetate copolymer latex powder or acrylate powder; the organic antifreeze is obtained by mixing diethanolamine, sodium acetate and urea in a mass ratio of 4:3:3; the crack-resistant fiber is polypropylene fiber or polyvinyl alcohol fiber with a length of 3-8 mm.

5. The low-temperature repair and crack-resistant additive according to claim 1, characterized in that, The silane coupling agent is γ-aminopropyltriethoxysilane KH-550.

6. The low-temperature repair and crack-resistant additive according to claim 1, characterized in that, The internal curing agent is a complex of molasses and polyacrylamide, wherein the mass ratio of molasses to polyacrylamide is 3:

1.

7. A method for preparing the low-temperature repair and crack-resistant additive according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of modified nano-silica; (2) Preparation of microbial capsule-type self-healing materials; (3) Add the modified nano silica, polymer powder, organic antifreeze and anti-crack fiber into a high-speed mixer in sequence according to the mass ratio, control the mixing temperature at 25-30℃ and the speed at 800-1000rpm, mix for 15-20 minutes to obtain the functional additive. (4) Mix the sulfoaluminate cement clinker and composite mineral filler in the matrix component evenly, then add the functional additives obtained in step (3) and the microbial capsule self-healing material and internal maintenance agent in the active repair component, and continue to mix in the mixer under the same conditions for 10-15 minutes to ensure that each component is evenly dispersed. Finally, sieve and package to obtain the finished product of the low-temperature repair and crack-resistant additive.

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