Plateau alpine microbial self-repairing concrete and preparation method thereof

Abstract

The application provides a kind of plateau alpine microbial self-repairing concrete and its preparation method, relating to concrete crack self-repairing technology, comprising: ceramic sand preloading nutrient solution; urease type bacillus which is resistant to alkali is low temperature acclimated and low pressure acclimated; the preloading nutrient ceramic sand is placed in vacuum tank, after vacuumizing, the microbial liquid after acclimation is injected; after a certain time of adsorption under vacuum degree, the vacuum is released and the excess microbial liquid is drained to form the bacteria-loaded ceramic sand; in the high-altitude simulation cabin, polycarboxylate superplasticizer and mineralized substrate are dissolved in water and dry mixing material is added and mixed uniformly; the bacteria-loaded ceramic sand is added to the mixture and continues to be stirred to obtain a uniform mixture and is injected into a mold, and a low-frequency vibrating compaction is used to obtain a shaped material. The application solves the problem that the self-repairing concrete is difficult to repair due to microbial inactivation in the plateau alpine environment, can realize self-sealing of cracks, and does not exist harmful substances, effectively guarantees the crack repair effect.

Description

A self-healing microbial concrete for high-altitude and cold regions and its preparation method Technical Field

[0001] This invention relates to the field of self-healing technology for concrete cracks, and more specifically, to a self-healing microbial concrete for high-altitude and cold regions and its preparation method. Background Technology

[0002] Concrete, a common building material in various structures and road access roads, boasts advantages such as readily available resources, simple construction, and high compressive strength. However, its low tensile strength and brittleness make it more susceptible to shrinkage deformation, temperature changes, and external loads in high-altitude and frigid environments, leading to micro-cracks or localized damage. If not addressed promptly, these micro-cracks will gradually expand over time, forming wide cracks. Wide cracks provide entry points for corrosive substances (chlorides, sulfates, etc.), accelerating concrete corrosion and ultimately destroying its structure. Traditional repair techniques for concrete cracks primarily employ passive methods, such as surface treatment, filling and sealing, and pressure grouting, mainly targeting wide cracks. These methods typically use inorganic materials (cement) or organic materials (epoxy resin, polyurethane, etc.), but are ineffective at repairing micro-cracks (0.3~0.5mm) and fine cracks (below 0.3mm). Furthermore, traditional repair methods suffer from poor bonding between the repair materials and concrete, insufficient durability, and difficulty in timely and effective crack repair. In recent years, the concept of active repair has emerged, which involves pre-installing repair agents within concrete to achieve early repair of micro-cracks, preventing crack propagation and thus improving concrete durability. Typical active repair technologies include: crystal-penetrating admixtures, self-healing promoted by mineral admixtures, microcapsule or hollow fiber encapsulated repair agents, self-releasing inorganic salt setting accelerators, and bio-self-repair technology based on microbial-induced calcium carbonate deposition (MICP). Among these, microbial self-repair induces the formation of mineral crystals such as calcium carbonate in cracks or pores, sealing penetration channels, improving density, and restoring mechanical properties to a certain extent, offering potential advantages such as sustainability, repeatability, and good compatibility. However, the applicability of existing active repair technologies, especially microbial self-repair, in complex environments such as high-altitude, cold, and low-pressure conditions still faces multiple challenges. Therefore, how to improve the repair effect of self-healing concrete in high-altitude and cold environments has become an urgent technical problem to be solved. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art or related technologies, and discloses a self-healing concrete made from microorganisms in high-altitude and cold regions and its preparation method. The method involves acclimating microorganisms to high altitude, alkali, and low temperature, thereby solving the problem that the inactivation of microorganisms in high-altitude and cold regions makes it difficult to repair self-healing concrete.

[0004] The first aspect of this invention discloses a method for preparing high-altitude, cold-climate microbial self-healing concrete, comprising:

[0005] Pre-prepared ceramic sand preparation: Remove impurities from the surface of the ceramic sand; place the cleaned ceramic sand in a nutrient solution for microbial culture to adsorb nutrients and obtain pre-loaded nutrient ceramic sand.

[0006] Preparation of microbial culture: Prepare a microbial culture medium, inoculate it with alkali-resistant urease-type Bacillus, and culture at room temperature. After a certain period, remove the strain and re-inoculate it at a lower temperature for further cooling. Repeat this process, reducing the temperature by no more than 5°C each time, until the strain survives at 10°C, obtaining a low-temperature acclimatized strain. Place the low-temperature acclimatized strain in an environment of 1 atm for atmospheric pressure culture. After a certain period, remove it and re-inoculate it in an environment of even lower atmospheric pressure for further depressurization culture. Repeat this process, reducing the pressure by 0.2 atm each time, until the strain survives at 10°C and 0.6 atm, obtaining an alkali-resistant, low-temperature, and low-pressure acclimatized strain with a culture concentration of 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL;

[0007] Preparation of microbially loaded ceramic sand: Pre-loaded nutrient-rich ceramic sand was placed in a vacuum jar, and a vacuum of -0.06 MPa was drawn and maintained for 10 min. Then, the acclimated microbial culture was slowly injected, with the volume of the culture being 1 to 2 times the volume of the ceramic sand. The vacuum was maintained at -0.06 MPa for 20-30 min for adsorption. After the vacuum was released, excess culture was drained, and the mixture was dried in an oven at 80℃ to constant weight to obtain microbially loaded ceramic sand with a microbial survival rate ≥70%.

[0008] Mixing and molding: Cement, fly ash, river sand, and coarse aggregate are dry-mixed in a mixer in a high-altitude simulation chamber to obtain a dry mix; polycarboxylate superplasticizer and mineralized substrate are dissolved in water, stirred evenly, and then added to the dry mix and stirred evenly to obtain a mixture; bacteria-loaded ceramsite is added to the mixture and stirred further to form a homogeneous mixture; the homogeneous mixture is poured into a mold and compacted using low-frequency vibration to obtain a high-altitude, cold-climate microbial self-healing concrete molding material.

[0009] According to the preparation method of high-altitude and cold-resistant microbial self-healing concrete disclosed in this invention, preferably, the pre-prepared ceramic sand preparation steps specifically include: soaking the ceramic sand in a 1% hydrochloric acid solution for 1-3 hours to remove surface impurities, rinsing it with distilled water until neutral, and drying it at 105°C to constant weight; placing the cleaned ceramic sand in a nutrient solution of 0.05-0.15% beef extract and 0.2-0.4% tryptone, adsorbing it at a constant temperature of 20-30°C for 2-6 hours, and drying it at 80°C until the moisture content is ≤10%, to obtain pre-loaded nutrient ceramic sand.

[0010] According to the preparation method of high-altitude and cold-resistant microbial self-healing concrete disclosed in this invention, preferably, the preparation process of the microbial culture medium specifically includes: adding 5g of tryptone, 3g of beef extract and 4.8g of urea to every 1L of deionized water, stirring to dissolve, and then sterilizing at 0.1MPa for 30min at 120℃.

[0011] According to the preparation method of high-altitude and cold-resistant microbial self-healing concrete disclosed in this invention, preferably, the step of culturing microorganisms specifically includes: inoculating 4%-8% by mass of alkali-resistant urease-type Bacillus in a culture medium, culturing it in a shaker at 20℃-40℃ and 120-170rpm for 24h, and then removing it to complete room temperature culture; re-inoculating the strain after room temperature culture into the culture medium, lowering the ambient temperature by 5℃, and culturing for another 24h; gradually lowering the temperature through multiple rounds of culture to 10℃ to complete low-temperature acclimatization; culturing the low-temperature acclimatized strain under normal pressure at 1atm, culturing it in a shaker at 10℃ and 120-170rpm for 24h, and then removing it to complete normal pressure culture; re-inoculating the strain after normal pressure culture into the culture medium, lowering the pressure by 0.2 atmospheres, and culturing for another 24h; gradually lowering the atmospheric pressure through multiple rounds of culture to 0.6atm to obtain the acclimatized strain.

[0012] According to the preparation method of high-altitude and cold-resistant microbial self-healing concrete disclosed in this invention, preferably, the porosity of the ceramic sand is 40%-60%, the pore size is 2μm-50μm, and the particle size of the ceramic sand is ≤4.75mm.

[0013] According to the preparation method of high-altitude and cold-resistant microbial self-healing concrete disclosed in this invention, preferably, the dry mix includes, by mass, 170-200 parts of cement, 140-170 parts of fly ash, 463-473 parts of river sand, and 1050-1075 parts of coarse aggregate; 7-8 parts by mass of polycarboxylate superplasticizer; 4-7 parts by mass of mineralized substrate and 1-3 parts by mass of urea; 160-165 parts by mass of water; and 320-335 parts by mass of bacteria-loaded ceramic sand.

[0014] According to the preparation method of high-altitude and cold-climate microbial self-healing concrete disclosed in this invention, preferably, the coarse aggregate includes natural gravel with a particle size of 10-20 mm.

[0015] The second aspect of the present invention also discloses a high-altitude and cold-climate microbial self-healing concrete, comprising: 170-200 parts by weight of cement, 140-170 parts by weight of fly ash, 600-700 parts by weight of fine aggregate, 1050-1075 parts by weight of coarse aggregate, 150-175 parts by weight of water, 6-9 parts by weight of polycarboxylate superplasticizer, 40-60 parts by weight of microbial self-healing agent, as well as microbial nutrients and mineralized substrate;

[0016] Fine aggregates include river sand and ceramic sand, with a volume ratio of 1:1 between river sand and ceramic sand. The ceramic sand is used to carry microbial nutrients and microbial self-healing agents.

[0017] The microbial self-healing agent includes urease-type Bacillus that has been domesticated to be alkali-resistant, low-temperature-resistant, and low-pressure-resistant, as well as the corresponding culture medium. The inoculation mass fraction of urease-type Bacillus is 4%-8%.

[0018] The microbial nutrients included 0.1-0.2 parts beef extract and 0.3-0.6 parts tryptone;

[0019] The mineralization substrates include 4-7 parts calcium acetate and 1-3 parts urea.

[0020] According to the self-healing microbial concrete for high-altitude and cold regions disclosed in this invention, preferably, the acclimatization process of alkali-resistant, low-temperature-resistant, and low-pressure-resistant Bacillus urease-type bacteria specifically includes: preparing a microbial culture medium; inoculating the culture medium with alkali-resistant Bacillus urease-type bacteria and culturing at room temperature; after a certain period of time, removing the strain and re-inoculating it at a lower temperature for cooling culture; repeating this process, with each temperature reduction controlled within 5°C, until the strain still survives at 10°C, thus obtaining a low-temperature acclimatized strain; placing the low-temperature acclimatized strain in an environment of 1 atm for atmospheric pressure culture, removing it after a certain period of time and re-inoculating it in an environment of even lower atmospheric pressure for depressurization culture; repeating this process, with each reduction of 0.2 atmospheres, until the strain still survives in a culture environment of 10°C and 0.6 atm, thus obtaining an alkali-resistant, low-temperature-resistant, and low-pressure-resistant acclimatized strain with a bacterial concentration of 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL.

[0021] According to the self-healing microbial concrete for high-altitude and cold regions disclosed in this invention, preferably, the ceramic sand undergoes pre-loading nutrient solution treatment and bacterial loading treatment. The specific treatment method includes: removing impurities from the surface of the ceramic sand; placing the cleaned ceramic sand in a nutrient solution for microbial culture to adsorb nutrients, thereby obtaining pre-loaded nutrient-rich ceramic sand; placing the pre-loaded nutrient-rich ceramic sand in a vacuum tank, evacuating it to -0.06 MPa, maintaining this vacuum for 10 minutes, and then slowly injecting acclimatized microbial inoculum, the volume of which is 1 to 2 times the volume of the ceramic sand; maintaining the vacuum at -0.06 MPa for 20 to 30 minutes, releasing the vacuum, draining excess inoculum, and drying in an oven at 80°C to constant weight, thereby obtaining bacterial-loaded ceramic sand with a microbial survival rate ≥70%.

[0022] The beneficial effects of this invention include at least the following: the strain domestication method disclosed in this invention enables microorganisms to maintain a high survival rate and urease activity under high alkalinity, low pressure, and low temperature conditions. Visible closure and dense deposition of mineralized products can be achieved within a 0.3-0.5 mm crack range, with significantly better impermeability and mechanical property recovery than the control group directly added with bacteria. The process uses industrial-grade calcium acetate and urea, conventional polycarboxylate superplasticizer, and readily available drying and vacuum equipment, making it simple and easy to promote and apply in high-altitude areas. The porous structure of the bacteria-loaded ceramic sand promotes the retention of microorganisms and reaction substrates, improves the workability and compactness of the mixture, and reduces air content fluctuations caused by pressure differences. Raw materials are readily available and costs are controllable; the system is compatible with existing concrete production lines and has the potential for large-scale application. By domesticating microorganisms to withstand high altitude, low pressure, alkali, and low temperature conditions at high altitudes, a microbial survival rate of ≥70% is achieved at 0℃-14℃, solving the problem of microbial inactivation in high-altitude and cold environments that makes self-healing concrete difficult to repair. Attached Figure Description

[0023] Figure 1 shows a microscopic morphology of deposits at cracks in a concrete specimen made of the material of Embodiment 1 according to the present invention.

[0024] Figure 2 shows a microscopic morphology of deposits at cracks in a concrete specimen made of the material of Embodiment 2 of the present invention. Detailed Implementation

[0025] To better understand the above-described objects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may be practiced in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0026] According to one embodiment of the present invention, a self-healing microbial concrete for high-altitude and cold regions is disclosed, with a mass ratio of kg / m³. 3 The formula includes the following components: cement 170.0-200.0, fly ash 140.0-170.0, fine aggregate 600.0-700.0, coarse aggregate 1050.0-1075.0, water 150.0-175.0, polycarboxylate superplasticizer 6.0-9.0, microbial self-healing agent, microbial nutrients, and mineralized substrate; the fine aggregate includes natural river sand and precast ceramic sand, with a volume ratio of natural river sand to precast ceramic sand of 1:1, and the ceramic sand particle size ≤4.75mm; the microbial self-healing agent includes microorganism A and the corresponding microbial culture medium, with a total inoculum mass fraction of 4%-8%; microorganism A is a urease-type Bacillus spp. that is resistant to high altitude, low air pressure, alkali, and low temperature acclimatization, with a concentration of 1.6×10 9 -1.9×10 9cells / mL. Microbial nutrients included: beef extract 0.1-0.2, tryptone 0.3-0.6; mineralized substrates included: calcium acetate 4.0-7.0, urea 1.0-3.0.

[0027] In this embodiment, precast ceramic sand is used as a microbial carrier to immobilize microbial culture through vacuum adsorption. The microbial culture medium contains 5 g / L tryptone, 3 g / L beef extract, 4.8 g / L urea and sufficient deionized water. After high-temperature sterilization, microorganism A with a mass fraction of 4%-8% is inoculated. Microorganism A and the microbial culture medium together constitute a microbial solution (microbial self-healing agent).

[0028] According to another embodiment of the present invention, a method for preparing the above-mentioned high-altitude and cold-climate microbial self-healing concrete is also disclosed, comprising:

[0029] Step 1: Preparation of precast ceramic sand:

[0030] Pretreatment of ceramic sand: Soak the ceramic sand in 1% hydrochloric acid solution for 2 hours to remove surface impurities, rinse with distilled water until neutral, and dry at 105℃ to constant weight; Pre-adsorbed nutrient layer: Place the modified ceramic sand in a nutrient solution of 0.1% beef extract and 0.3% tryptone, adsorb at 25℃ for 4 hours, and dry at 60℃ until the moisture content is ≤5% to obtain pre-loaded nutrient ceramic sand;

[0031] Step 2: Preparation of microbial culture:

[0032] Culture medium preparation: Add 5.0g of tryptone, 3.0g of beef extract and 4.8g of urea to each 1L of deionized water, stir to dissolve, autoclave at 120℃ and 0.1MPa for 30min, cool to 30℃, inoculate with microorganism A, and incubate in a shaker at 25℃-35℃ and 120-170rpm for 24h.

[0033] Acclimation and cultivation: After cooling to 30℃, inoculate with microorganism A and incubate in a shaker at 25℃-35℃ and 120-170rpm for 24 hours. Then remove the microorganisms, store them again, re-inoculate, and cultivate at an even lower temperature, decreasing the temperature by approximately 5℃ each time, gradually lowering the cultivation temperature to 10℃ to complete the low-temperature acclimation. The bacterial concentration reaches 1.6×10⁻⁶. 9 -1.9×10 9 cells / mL; Microorganism A, after being acclimated to alkali and low temperatures, was cultured using the same stepwise decreasing acclimation method as before, at 1 atm, 0.8 atm, and 0.6 atm sequentially, ultimately yielding urease-type Bacillus spp. acclimated to alkali and low temperatures under high-altitude, low-pressure conditions, with a concentration reaching 1.6 × 10⁻⁶ cells / mL; 9 -1.9×10 9 cells / mL;

[0034] Step 3: Preparation of bacteria-loaded ceramic sand:

[0035] Vacuum adsorption: Preloaded nutrient-rich ceramic sand is placed in a vacuum tank, and a vacuum of -0.06 MPa is drawn and maintained for 10 minutes. Then, the acclimated microbial solution is slowly injected, with the volume of the solution being 1.2 times the volume of the ceramic sand, ensuring that the solution completely covers the sand. Room temperature curing: The vacuum is maintained at -0.06 MPa for 15-20 minutes. After the vacuum is released, excess solution is drained, and the mixture is dried in an oven at 30℃-40℃ until constant weight, yielding microbial-loaded ceramic sand with a microbial survival rate ≥70%.

[0036] Step 4: Mixing and molding concrete under low pressure:

[0037] Dry mixing: Weigh cement, fly ash, river sand, and coarse aggregate according to the formula in the high-altitude simulation chamber, put them into the mixer and dry mix for 2 minutes until they are evenly mixed;

[0038] Wet mixing: In the high-altitude simulation chamber, dissolve the polycarboxylate superplasticizer, antifreeze agent, and mineral substrate in the mixing water, stir evenly, and then add it to the dry mixing material and stir for 3 minutes;

[0039] Loading material: Add bacteria-laden ceramic sand to the high-altitude simulation chamber and continue stirring for 2 minutes to form a uniform mixture (slump controlled at 180±10mm).

[0040] Molding: The mixture is injected into a mold and placed in a high-altitude simulation chamber. It is then compacted using low-frequency vibration (20-30Hz, 30-60s) to avoid damaging the porous structure of the ceramic sand.

[0041] Example 1

[0042] According to another embodiment of the present invention, a specific formulation used in the above preparation method is also disclosed, comprising:

[0043] Formula composition (kg / m 3 ):

[0044] Cement: 185.0, Fly ash: 155.0, River sand: 468.0, Precast ceramic sand: 182.0, Coarse aggregate: 1062.0, Water: 162.0, Polycarboxylate superplasticizer: 7.5, Microbial A used (1.8×10 9 Inoculation amounts (cells / mL): 5%, beef extract: 0.15, tryptone: 0.45, calcium acetate: 5.5, urea: 1.5.

[0045] Carrier and Microorganisms: Precast Ceramic Sand: The ceramic sand is obtained by washing with 1% hydrochloric acid, pre-adsorbing a nutrient layer, and drying. Microbial Solution (Microbial Self-Healing Agent): Prepared according to the components of the microbial self-healing agent disclosed in the above embodiments, with a mass fraction of 41 parts and a cell concentration controlled at 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL.

[0046] The molding process is the same as in the above embodiments.

[0047] Example 2

[0048] According to another embodiment of the present invention, a simplified method of the preparation method according to the above embodiments is disclosed. As a control experimental group, compared with the above preparation method, this embodiment does not use ceramic sand as a microbial carrier, but directly adds a microbial solution to the concrete to replace part of the water, specifically including:

[0049] Formula composition (kg / m 3 ): Cement: 175; Fly ash: 155; Fine aggregate: 651; Coarse aggregate: 1061; Water: 165; Polycarboxylate superplasticizer: 7.5; Calcium acetate: 4.8; Urea: 1.95; Beef extract: 0.1; Tryptone: 0.3; Microbial solution: 55.5; Microbial A inoculum mass fraction: 5%.

[0050] Microbial solution was added directly to concrete without a clay sand carrier to replace part of the water; the microbial solution was prepared according to the components disclosed in the above embodiments, and the cell concentration was controlled at 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL; concrete specimens prepared according to the above components were used as the control experimental group.

[0051] According to another embodiment of the present invention, a specific process for verifying the self-healing effect of the high-altitude and cold-climate microbial concrete self-healing concrete provided in Embodiments 1 and 2 above is also disclosed, including:

[0052] After molding, the concrete specimens were cured in a high-altitude simulation chamber with a film covering and a chamber temperature of 25°C until the required cracking age was reached.

[0053] Crack pre-fabrication: Using a YAW-2000J pressure testing machine, a 0.3-0.5 mm through crack is pre-fabricated on the surface of the specimen at a loading rate of 0.3-0.5 kN / s;

[0054] Semi-aqueous curing and repair: Place the precast cracked specimen in an environment of 0℃-14℃ and relative humidity of 40%-60%, spray water regularly, once every 2 days, to keep the surface moist. Microorganisms generate calcium carbonate by metabolizing mineralized substrates, which seals the cracks and repairs them for 28 days.

[0055] The characterization indicators of self-healing performance include: area repair rate, compressive strength recovery rate, and water permeability recovery rate.

[0056] The evaluation method for area repair rate includes: acquiring images of specimens with existing cracks that have not yet begun repair; processing the crack surface images using image processing software; adjusting the threshold to distinguish between cracked and non-cracked areas of the concrete specimen; and then calculating the area of ​​the cracked area based on the pixels in the cracked area.

[0057] Crack area repair rate = Where A0 is the initial area of ​​the crack before repair (mm²). 2 A t The crack area (mm²) after repair at time t. 2 ).

[0058] The area repair rates of the specimens from Examples 1 and 2 at 3d, 14d, and 28d after crack repair are shown in Table 1 below:

[0059]

[0060] Evaluation methods for compressive strength recovery rate include: when cement-based materials crack, the cracks are repaired to some extent due to secondary healing caused by cement hydration, but the recovery effect is limited. In contrast, microbial self-healing specimens, due to the calcium-producing ability of microorganisms, have cracks filled with CaCO3 precipitates, and the originally loose mortar matrix is ​​consolidated, thus achieving a higher strength recovery rate.

[0061] Calculate the compressive strength recovery rate:

[0062] Among them, F W W0 represents the compressive strength recovery rate; W0 represents the compressive strength (MPa) of the undamaged specimen after curing; W t The compressive strength (MPa) of the pre-damaged specimen after repair.

[0063] The compressive strength and calculated strength recovery rate of concrete specimens from different embodiment groups before and after crack repair 28 days are shown in Table 2 below:

[0064]

[0065] As shown in Figures 1 and 2, microscopic analysis of the mineralization products at the cracks was performed: 28 days after the specimens were repaired, it was observed that the cracks were filled with sedimentary minerals. The repair products were analyzed using SEM microscopic testing technology. Figure 1 shows the microscopic morphology of the precipitates at the cracks of the specimens made from the material of Example 1, with a scale bar of 10 μm; Figure 2 shows the microscopic morphology of the precipitates at the cracks of the specimens made from the material of Example 2, with a scale bar of 100 μm. It can be found that the microscopic morphology of each group of precipitates exhibits either spheroidal calcium carbonate crystals or calcite-type calcium carbonate crystals.

[0066] In summary, this invention provides a microbial self-healing concrete and its preparation method suitable for high-altitude and cold environments, aiming to overcome the problems of low efficiency, insufficient durability, and difficulty in adapting atmospheric pressure processes to high-altitude environments in existing passive repair methods. This method utilizes ceramic sand as a microbial carrier, combined with vacuum adsorption and immobilization of urease-type microorganisms A with alkali-resistant domestication, industrial-grade mineralized substrates, and low-pressure molding and curing processes. Visible closure and dense calcium carbonate deposition are achieved within the 0.3~0.5mm crack range, resulting in significant recovery of mechanical properties. The method employs industrial-grade calcium acetate and urea, conventional polycarboxylate superplasticizers, and common vacuum and drying equipment, making the process simple, cost-effective, and easy to promote in high-altitude areas. The microbial-loaded ceramic sand promotes the retention and slow release of the repair agent, improves the workability and molding density of the mixture, and reduces air content fluctuations caused by pressure differences, demonstrating potential for engineering and sustainable applications.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing self-healing microbial concrete for high-altitude and cold regions, characterized in that, include: Precast ceramic sand preparation: removing impurities from the surface of the ceramic sand; The cleaned ceramic sand was placed in a nutrient solution for microbial culture to adsorb nutrients, thus obtaining pre-loaded nutrient-rich ceramic sand. Preparation of microbial culture: A microbial culture medium was prepared, and alkali-resistant urease-type Bacillus was inoculated into the medium and cultured at room temperature. After a certain period, the strain was removed and re-inoculated at a lower temperature for further cooling. This process was repeated, with each temperature reduction controlled within 5°C, until the strain survived at 10°C, resulting in a low-temperature acclimatized strain. This low-temperature acclimatized strain was then placed in an environment of 1 atm for atmospheric pressure culture. After a certain period, it was removed and re-inoculated at an even lower atmospheric pressure for further depressurization culture. This process was repeated, with each reduction in pressure by 0.2 atm, until the strain survived at 10°C and 0.6 atm, resulting in an alkali-resistant, low-temperature, and low-pressure acclimatized strain with a culture concentration of 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL; Preparation of microbial-loaded ceramic sand: The pre-loaded nutrient-rich ceramic sand was placed in a vacuum tank, evacuated to -0.06 MPa, and maintained for 10 min. Then, the acclimated microbial liquid was injected, with a volume of 1.0 to 2.0 times that of the ceramic sand. The vacuum was maintained at -0.06 MPa for 20-30 min. After the vacuum was released, the excess liquid was drained, and the mixture was dried in an oven at 80℃ to constant weight to obtain microbial-loaded ceramic sand with a microbial survival rate ≥70%. Mixing and molding: Cement, fly ash, river sand, and coarse aggregate were dry-mixed in a mixer in a high-altitude simulation chamber to obtain a dry mix. Polycarboxylate superplasticizer and mineralized substrate were dissolved in water, stirred evenly, and then added to the dry mix and stirred evenly to obtain a mixture. The microbial-loaded ceramic sand was added to the mixture and stirred to form a uniform mixture. The uniform mixture was injected into a mold and compacted using low-frequency vibration to obtain a high-altitude and cold-weather microbial self-healing concrete molding material.

2. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The steps for preparing the precast ceramic sand specifically include: soaking the ceramic sand in a 1% hydrochloric acid solution for 1-3 hours to remove surface impurities, rinsing it with distilled water until neutral, and drying it at 105°C to constant weight; placing the cleaned ceramic sand in a nutrient solution of 0.05-0.15% beef extract and 0.2-0.4% tryptone, adsorbing it at a constant temperature of 20-30°C for 2-6 hours, and drying it at 80°C until the moisture content is ≤10% to obtain preloaded nutrient ceramic sand.

3. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The preparation process of the microbial culture medium specifically includes: adding 5g of tryptone, 3g of beef extract and 4.8g of urea to every 1L of deionized water, stirring to dissolve, and then autoclaving at 0.1MPa for 30min at 120℃.

4. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The specific steps for culturing microorganisms include: inoculating the culture medium with 4%-8% by mass of alkali-resistant urease-type Bacillus, culturing it in a shaker at 20℃-40℃ and 120-170rpm for 24 hours, and then removing it to complete room temperature culture; re-inoculating the strain after room temperature culture into the culture medium, lowering the ambient temperature by 5℃, and culturing for another 24 hours; gradually lowering the temperature through multiple rounds of culture to 10℃ to complete low-temperature acclimatization; culturing the low-temperature acclimatized strain at 1 atm under normal pressure, culturing it in a shaker at 10℃ and 120-170rpm for 24 hours, and then removing it to complete normal pressure culture; re-inoculating the strain after normal pressure culture into the culture medium, lowering the pressure by 0.2 atm, and culturing for another 24 hours; gradually lowering the atmospheric pressure through multiple rounds of culture to 0.6 atm to obtain the acclimatized strain.

5. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The porosity of the ceramic sand is 40%-60%, the pore size is 2μm-50μm, and the particle size of the ceramic sand is ≤4.75mm.

6. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The dry mix comprises, by weight, 170-200 parts of cement, 140-170 parts of fly ash, 463-473 parts of river sand, and 1060-1075 parts of coarse aggregate; the polycarboxylate superplasticizer comprises 7-8 parts by weight; the mineralized substrate comprises 4-7 parts of calcium acetate and 1-3 parts of urea; the water comprises 160-165 parts by weight; and the bacterial-loaded ceramic sand comprises 320-335 parts by weight.

7. The method for preparing high-altitude, cold-climate microbial self-healing concrete according to claim 1, characterized in that, The coarse aggregate includes natural stones with a particle size of 10-20 mm.

8. A self-healing microbial concrete for high-altitude and cold regions, characterized in that, include: The composition comprises, by weight, 170-200 parts cement, 140-170 parts fly ash, 600-700 parts fine aggregate, 1050-1075 parts coarse aggregate, 150-175 parts water, 6-9 parts polycarboxylate superplasticizer, 40-60 parts microbial self-healing agent, as well as microbial nutrients and mineralized substrates. The fine aggregates include river sand and ceramic sand, with a volume ratio of river sand to ceramic sand of 1:

1. The ceramic sand is used to support the microbial nutrients and the microbial self-healing agent. The microbial self-healing agent comprises urease-type Bacillus urealyticum acclimated to alkali-resistant, low-temperature, and low-pressure conditions, and a corresponding culture medium. The inoculum weight fraction of urease-type Bacillus urealyticum is 4%-8%. The microbial nutrients include 0.1-0.2 parts beef extract and 0.3-0.6 parts tryptone. The mineralized substrates include 4-7 parts calcium acetate and 1-3 parts urea.

9. The high-altitude and cold-climate microbial self-healing concrete according to claim 8, characterized in that, The acclimatization process of the alkali-resistant, low-temperature-resistant, and low-pressure-resistant Bacillus urease-type bacteria specifically includes: preparing a microbial culture medium; inoculating the culture medium with alkali-resistant Bacillus urease-type bacteria and culturing at room temperature; after a certain period of time, removing the strain and re-inoculating it at a lower temperature for cooling culture; repeating this process, with each temperature reduction controlled within 5°C, until the strain still survives at 10°C, thus obtaining a low-temperature-acclimatized strain; placing the low-temperature-acclimatized strain in an environment of 1 atm for atmospheric pressure culture, removing it after a certain period of time and re-inoculating it in an environment of even lower atmospheric pressure for depressurization culture; repeating this process, with each reduction of 0.2 atmospheres, until the strain still survives in a culture environment of 10°C and 0.6 atm, thus obtaining an alkali-resistant, low-temperature-resistant, and low-pressure-resistant acclimatized strain with a bacterial concentration of 1.6 × 10⁻⁶. 9 -1.9×10 9 cells / mL.

10. The high-altitude and cold-climate microbial self-healing concrete according to claim 8, characterized in that, The ceramic sand undergoes pre-loading nutrient solution treatment and bacterial loading treatment. The specific treatment methods include: removing impurities from the surface of the ceramic sand; placing the cleaned ceramic sand in a nutrient solution for microbial culture to adsorb nutrients, obtaining pre-loaded nutrient ceramic sand; placing the pre-loaded nutrient ceramic sand in a vacuum tank, evacuating to -0.06 MPa, maintaining this for 10 minutes, and then slowly injecting acclimatized microbial culture, the volume of which is 1 to 2 times the volume of the ceramic sand; maintaining a vacuum of -0.06 MPa for adsorption for 20 to 30 minutes, releasing the vacuum, draining excess culture, and drying in an 80°C oven to constant weight to obtain bacterial-loaded ceramic sand with a microbial survival rate ≥70%.

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