A method of composite microbial gradient slow-release self-repairing concrete

Abstract

The present application relates to the technical field of self-repairing concrete, and particularly relates to a composite microbial gradient slow-release self-repairing concrete method, which comprises the following steps: S1, preparing a gradient slow-release carrier: S1.1, preparing a core; S1.2, coating a shell; S2, preparing a self-repairing concrete; S3, forming and curing. By adding the gradient slow-release carrier into the concrete, the double-layer structure of the gradient slow-release carrier is utilized, when the concrete is not cracked, the alkaline substance is blocked from invading by the PLA-HA composite film of the shell, and the survival of the core bacterial powder is protected; when the concrete is cracked, the external moisture seeps in through the shell pores, first dissolves the slow-release nutrient substance of the shell, provides continuous energy for the subsequent composite bacterial powder, and at the same time, the moisture triggers the swelling and degradation of the sodium alginate-chitosan gel in the core, releases the composite bacterial powder, and cooperates with the nutrient substance dissolved from the shell, so that the microbial "slow activation and continuous metabolism" is realized.

Description

Technical Field

[0001] This invention relates to the field of self-healing concrete technology, specifically to a method for composite microbial gradient slow-release self-healing concrete. Background Technology

[0002] Existing microbial self-healing concrete technologies primarily involve adding microbial agents (such as Bacillus and Lactobacillus) and nutrients (such as sucrose, lactose, and urea) to the concrete matrix. When cracks appear in the concrete, external moisture and oxygen penetrate, activating microbial metabolism and producing mineral deposits such as calcium carbonate to fill the cracks, thus achieving self-healing. Some technologies use encapsulation to encapsulate microbial agents and nutrients to improve the survival rate of microorganisms in the alkaline environment of concrete; other technologies optimize the microbial growth microenvironment by adjusting the concrete mix proportions.

[0003] In existing technologies, microbial agents are mostly single strains or simple mixed strains, and nutrients are mostly single carbon sources or combinations of nitrogen sources. Encapsulation technology often uses a single material (such as gelatin or sodium alginate), which suffers from low encapsulation efficiency, premature capsule rupture, or difficulty in degrading and releasing the agent at cracks. Furthermore, the microbial repair process is greatly affected by environmental factors such as the alkalinity, humidity, and crack width within the concrete, resulting in unstable repair efficiency and low strength recovery rate in the repaired cracked area, making it difficult to meet actual engineering needs. Specific problems include: (1) Low survival rate of microorganisms: The high alkalinity (pH 8-13) and low permeability of the concrete interior make it easy for unencapsulated microorganisms to become inactive. The capsule material of the existing encapsulation technology has poor alkali resistance and insufficient structural stability, and is prone to breakage during concrete mixing or hardening, or cannot degrade and release the bacterial agent in time when cracks occur, resulting in insufficient number of effective microorganisms. (2) Unstable repair efficiency: Single strains have limited adaptability to the environment. When conditions such as crack width, humidity, and alkalinity change, metabolic activity is easily inhibited. Moreover, single nutrients cannot meet the continuous metabolic needs of microorganisms, resulting in slow crack filling speed and incomplete repair. (3) Poor strength recovery after repair: The calcium carbonate deposit layer generated by the existing technology has a loose structure and is not tightly bonded to the concrete matrix. The compressive strength and tensile strength recovery rate of the area after crack repair is usually less than 70%, and it is prone to cracking again after long-term use. (4) Narrow range of applicable cracks: Existing technologies are mostly applicable to microcracks with a width of less than 0.5 mm. For medium cracks with a width of 0.5-2 mm, the repair effect is significantly reduced because microorganisms and nutrients are difficult to spread evenly to the depth of the crack. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a composite microbial gradient slow-release self-healing concrete method.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for composite microbial gradient slow-release self-healing concrete, comprising the following steps: S1. Preparation of gradient sustained-release carrier: S1.1 Preparation of the core: The composite bacterial powder, glucose, ammonium nitrate and modified sodium alginate-chitosan gel are mixed to obtain the core; S1.2, Coating the outer shell: The core is dispersed in a PLA-HA composite emulsion containing slow-release nutrients, and then spray-dried to form a slow-release carrier with a double-layer core structure; S2. Preparation of self-healing concrete: Dry mix cement, aggregate, and modified nano-calcium carbonate evenly, add water and stir into mortar, and finally add slow-release carrier and stir evenly to obtain self-healing concrete. S3. Molding and curing: The self-healing concrete is poured into shape and cured for 28 days to obtain composite microbial gradient slow-release self-healing concrete.

[0006] Further, in S2, the mass ratio of cement:aggregate:water:slow-release carrier:modified nano-calcium carbonate is 1:2.8:0.45:0.08:0.007.

[0007] Furthermore, the modified nano-calcium carbonate is nano-calcium carbonate with a particle size of 20-50 nm, which has been surface-modified with silane coupling agent KH-550.

[0008] Furthermore, the outer shell is a PLA-HA membrane encapsulating a slow-release nutrient, which is a starch-casein complex with a thickness of 50-100 μm.

[0009] Furthermore, prior to S2, the sustained-release carrier is subjected to plasma treatment to prepare micron-sized pores on the surface of the sustained-release carrier.

[0010] Furthermore, the mass ratio of the composite bacterial powder, glucose, ammonium nitrate, and modified sodium alginate-chitosan gel is 3:1:1:2.

[0011] Further, in S1.1, the compound bacterial powder includes strain A, strain B and strain C in a weight ratio of 1:2:1; The strain A is an alkali-resistant Bacillus, the strain B is a calcium carbonate crystallization-inducing bacterium, and the strain C is an adhesive polysaccharide-producing bacterium.

[0012] Furthermore, the preparation method of the compound bacterial powder is as follows: strains A, B and C are respectively cultured and separated by centrifugation, then mixed in proportion, a freeze-drying protectant is added, and the compound bacterial powder is prepared by freeze-drying.

[0013] Furthermore, the amount of the freeze-drying protectant added is 8% of the total mass of the three strains, including 5% glycerol and 3% skim milk powder.

[0014] Furthermore, the modified sodium alginate-chitosan gel is a sodium alginate-chitosan gel with improved alkali resistance, specifically by adding 2% by mass of nano-silica to the sodium alginate-chitosan gel.

[0015] Furthermore, in step S1.1, after the components are mixed, gel microspheres are prepared using a dropwise addition method, and the core is obtained after cross-linking and curing.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention incorporates a gradient slow-release carrier into concrete. Utilizing the carrier's double-layer structure, when the concrete is not cracked, the PLA-HA composite membrane on the outer shell prevents alkaline substances from penetrating, protecting the survival of the core microbial powder. When cracks appear in the concrete, external moisture seeps in through the pores of the outer shell, first dissolving the slow-release nutrients in the outer shell to provide continuous energy for the subsequent composite microbial powder. Simultaneously, the moisture triggers the swelling and degradation of the sodium alginate-chitosan gel in the core, releasing the composite microbial powder. This, in conjunction with the dissolved nutrients in the outer shell, achieves "slow activation and continuous metabolism" of the microorganisms. 2. This invention adds modified nano-calcium carbonate to the concrete formula, which can fill the microscopic pores of the concrete matrix and at the same time serve as "nucleation sites" for the calcium carbonate crystals produced by microbial metabolism, promoting the lattice matching between the repair products and the matrix. The repaired calcium carbonate deposit layer is dense, effectively blocking the intrusion of harmful substances such as moisture and chloride ions, greatly improving the durability of concrete, increasing the compressive strength and tensile strength of the concrete after crack repair, and forming an integral stress structure with the matrix in the repaired area, making it less prone to cracking again after long-term use. 3. This invention employs a composite microbial powder with synergistic metabolism of three strains. After freeze-drying and alkali-resistant acclimatization, the number of viable bacteria in the composite microbial powder remains high 28 days after concrete hardening, providing sufficient functional microorganisms for repair. Through the rapid production of carbonate by strain A, the regulation of crystal growth by strain B, and the enhancement of interfacial bonding by strain C, combined with a gradient slow-release carrier, a continuous supply of nutrients is achieved. For cracks with a width of 0.1-2mm, it can be repaired quickly and is not easily affected by the alkaline environment of concrete. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a gradient sustained-release carrier according to an embodiment of the present invention.

[0018] In the diagram: 1. Outer shell; 2. Slow-release nutrients; 3. Pores; 4. Core; 5. Nutrient components; 6. Compound bacterial powder. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example: Please see Figure 1 .

[0021] The present invention relates to a method for composite microbial gradient slow-release self-healing concrete, comprising the following steps: S0. Preparation of compound bacterial powder 6: The compound bacterial powder 6 comprises strain A, strain B, and strain C in a weight ratio of 1:2:1; strain A is alkali-resistant Bacillus, strain B is a calcium carbonate crystallization-inducing bacterium, and strain C is an adhesive polysaccharide-producing bacterium; strains A, B, and C are separately cultured and separated by centrifugation, then mixed in proportion, and 5% glycerol and 3% skim milk powder freeze-drying protectant are added. Pre-freezing treatment is performed: complete solidification is achieved by liquid nitrogen quick-freezing (-196℃) or mechanical freezing (-80℃); vacuum drying is carried out: maintaining a vacuum of 0.1-10 Pa for 12-24 hours, and dehydration is achieved through ice crystal sublimation to produce compound bacterial powder 6; S1. Preparation of gradient sustained-release carrier: S1.1 Preparation of Core 4: Mix the composite bacterial powder 6, glucose, ammonium nitrate and modified sodium alginate-chitosan gel (with 2% nano silica added) in a mass ratio of 3:1:1:2. Prepare gel microspheres using the dropwise addition method. Add the composite bacterial powder, glucose and ammonium nitrate dropwise to the modified sodium alginate-chitosan gel through a capillary tube or syringe. Cross-linking and solidification are completed during the droplet falling process to form microspheres. After cross-linking and solidification, core 4 is obtained with a particle size of 500-800μm. S1.2, Outer Shell 1: A PLA-HA composite membrane outer shell 1 is coated on the outside of the core 4. The outer shell 1 is a PLA-HA membrane that encapsulates the slow-release nutrient 2. The slow-release nutrient 2 is a starch-casein complex with a thickness of 50-100μm. It is spray-dried to form a slow-release carrier with a double-layer core structure. The slow-release carrier is subjected to plasma treatment. The plasma treatment technology mainly improves the adhesion, hydrophilicity and composite strength of the material by physicochemical modification of the material surface, cleaning and activating the surface or forming a coating. Micron-sized pores 3 with a pore size of 1-5μm are prepared on the surface of the slow-release carrier. S2. Preparation of self-healing concrete: The mass ratio of cement: aggregate: water: slow-release carrier: modified nano-calcium carbonate is 1:2.8:0.45:0.08:0.007. The cement, aggregate and nano-calcium carbonate modified with silane coupling agent KH-550 are dry-mixed evenly, water is added and stirred into mortar, and finally the slow-release carrier is added and stirred evenly to obtain self-healing concrete. S3. Molding and curing: The self-healing concrete is poured into shape and cured for 28 days to obtain composite microbial gradient slow-release self-healing concrete.

[0022] Crack repair process: When cracks appear in the composite microbial gradient slow-release self-healing concrete after pouring, external moisture seeps in through the pores 3 of the outer shell 1, first dissolving the slow-release nutrients 2 in the outer shell 1, providing continuous energy for subsequent microbial activation. At the same time, the moisture triggers the swelling and degradation of sodium alginate-chitosan gel in the core 4, releasing composite bacterial powder 6. The three strains metabolize synergistically: strain A rapidly produces carbonate, strain B regulates crystal growth, and strain C enhances interfacial bonding. Together with the gradient slow-release carrier, they achieve a continuous supply of nutrients. For cracks with a width of 0.1-2mm, they can quickly repair them and are not easily affected by the alkaline environment of the concrete. Modified nano-calcium carbonate acts as a crystal nucleus to promote the dense growth of calcium carbonate crystals, carry out calcium carbonate deposition, enhance the crystal nucleus interface, and complete the self-healing process of the concrete.

[0023] In compound bacterial powder 6, the three strains have complementary functions: strain A is an alkali-resistant Bacillus that has been acclimatized and can survive in an environment with a pH of 7-14. Its main function is to rapidly decompose nutrient component 5 (glucose and ammonium nitrate) to produce carbonate ions. Strain B is a calcium carbonate crystallizing inducer that can secrete specific proteins to regulate the growth morphology of calcium carbonate crystals and promote dense crystal deposition. Strain C is a polysaccharide-producing bacterium that can generate viscosity, enhancing the interfacial bonding between the calcium carbonate deposit and the concrete matrix. The mixture of the three strains can greatly improve the survival rate in the alkaline environment of concrete.

[0024] The gradient slow-release carrier with a double-layer core structure can effectively isolate the alkaline environment of concrete, and the composite bacterial powder 6, after freeze-drying protection and alkali resistance acclimatization, still maintains a high number of viable bacteria 28 days after the concrete hardens, providing sufficient functional microorganisms for repair. Modified nano-calcium carbonate acts as a nucleus to promote the dense growth of calcium carbonate crystals and enhances the bonding interface, thereby improving the compressive and tensile strength of the concrete after crack repair. The repaired area forms an integral load-bearing structure with the matrix, making it less prone to cracking again after long-term use. The dense calcium carbonate deposit layer after repair effectively blocks the intrusion of harmful substances such as moisture and chloride ions, greatly improving the durability of the concrete. Compared with conventional microbial self-healing concrete, its durability is significantly enhanced. The surface pore design of the gradient slow-release carrier and the gradient release of nutrients allow microorganisms and nutrients to diffuse to the depths of 2mm wide cracks, solving the problem of poor repair effect of existing technologies on medium-width cracks. The applicable crack width range is expanded to 0.1-2mm, covering most actual crack scenarios in engineering. In summary, the synergistic effect of compound bacterial powder 6 solves the problem of poor adaptability of single strains, the gradient slow-release carrier solves the problems of bacterial agent survival and nutrient supply, and the addition of modified nano-calcium carbonate solves the defect of weak bonding between the repair product and the matrix. These three elements form an organic whole, achieving a comprehensive improvement in the performance of self-healing concrete. It will be apparent to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Therefore, it is intended that all changes falling within the meaning and scope of the equivalents of the claims be included within this invention.

Claims

1. A method for composite microbial gradient slow-release self-healing concrete, characterized in that, Includes the following steps: S1. Preparation of gradient sustained-release carrier: S1.1 Preparation of the core (4): Mix the composite bacterial powder (6), glucose, ammonium nitrate and modified sodium alginate-chitosan gel to obtain the core (4); S1.2, Coating shell (1): The outer shell (1) of PLA-HA composite membrane is coated on the outside of the core (4) and spray-dried to form a sustained-release carrier with a double core structure; S2. Preparation of self-healing concrete: Dry mix cement, aggregate, and modified nano-calcium carbonate evenly, add water and stir into mortar, and finally add slow-release carrier and stir evenly to obtain self-healing concrete. S3. Molding and curing: The self-healing concrete is poured into shape and cured for 28 days to obtain composite microbial gradient slow-release self-healing concrete.

2. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, In S2, the mass ratio of cement:aggregate:water:slow-release carrier:modified nano-calcium carbonate is 1:2.8:0.45:0.08:0.

007.

3. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, The modified nano-calcium carbonate is nano-calcium carbonate with a particle size of 20-50 nm, which has been surface modified with silane coupling agent KH-550.

4. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, The outer shell (1) is a PLA-HA membrane that encapsulates the slow-release nutrient (2), which is a starch-casein complex with a thickness of 50-100 μm.

5. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, Before S2, the sustained-release carrier is subjected to plasma treatment to prepare micron-sized pores with a pore size of 1-5 μm on the surface of the sustained-release carrier (3).

6. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, The mass ratio of the compound bacterial powder, glucose, ammonium nitrate, and modified sodium alginate-chitosan gel is 3:1:1:

2.

7. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, In S1.1, the compound bacterial powder (6) comprises strain A, strain B and strain C in a weight ratio of 1:2:1; The strain A is an alkali-resistant Bacillus, the strain B is a calcium carbonate crystallization-inducing bacterium, and the strain C is an adhesive polysaccharide-producing bacterium.

8. The composite microbial gradient slow-release self-healing concrete method according to claim 7, characterized in that, The method for preparing the compound bacterial powder (6) is as follows: strains A, B and C are respectively cultured and separated by centrifugation, then mixed in proportion, a freeze-drying protectant is added, and the compound bacterial powder (6) is prepared by freeze-drying.

9. The composite microbial gradient slow-release self-healing concrete method according to claim 8, characterized in that, The amount of the freeze-drying protectant added is 8% of the total mass of the three strains, including 5% glycerol and 3% skim milk powder.

10. The composite microbial gradient slow-release self-healing concrete method according to claim 1, characterized in that, The modified sodium alginate-chitosan gel is a sodium alginate-chitosan gel with improved alkali resistance, specifically by adding 2% by mass of nano-silica to the sodium alginate-chitosan gel.

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