Method for determining a carrier suitable for use in microbial self-healing concrete

Abstract

The present application relates to the field of concrete crack self-repairing material, and discloses a method for determining a carrier suitable for microbial self-repairing concrete, comprising the following steps: S1: selecting a porous carrier material; S2: testing the water absorption rate of the carrier material under normal pressure and negative pressure conditions; S3: testing the cylinder compressive strength of the carrier material; S4: loading the microorganism with the ability of inducing mineralization into the porous carrier, and drying the loaded carrier in an oven at 30-50 DEG C to constant weight; S5: placing the carrier loaded with the microorganism into a simulated cement solution, standing for 24 hours, taking out and drying; S6: selecting a carrier material suitable for concrete repair. The porous carrier can provide a suitable living space for the microorganism, play a role of physical barrier, avoid direct exposure of the microorganism in a high alkaline environment, and provide more uniform distribution for the microorganism, so that the microorganism can be fully protected in the concrete, thereby prolonging the survival time of the microorganism.

Description

Technical Field

[0001] The present invention relates to the field of concrete crack self-repairing materials, and in particular to a method for determining a carrier suitable for microbial self-repairing concrete. Background Art

[0002] With the rapid development of socio-economic and technological advancements, cement-based materials, as low-cost, durable composite building materials with high compressive strength, have become widely used in various civil engineering fields. However, concrete's inherent brittleness and low toughness can lead to cracking defects at an early stage. Microcracks, caused by both load and non-load factors, can form, allowing harmful media to enter the concrete, severely impairing its performance. Traditional methods for treating concrete cracks include surface treatment, grouting, and structural reinforcement. However, these methods often require significant labor and material resources. Furthermore, these methods are post-processing and fail to quickly and autonomously repair the cracks at their source. Under certain conditions, concrete exhibits a certain degree of self-healing ability, primarily through the continuous hydration of unhydrated cement particles and the carbonization of hydration products in air. However, this self-healing ability is extremely weak. To further enhance concrete's ability to heal itself from damage, researchers introduced microorganisms that induce mineral deposition and corresponding substrates into concrete during the forming stage. Once concrete cracks, the entry of external moisture and oxygen will prompt the germination and growth of microorganisms, and metabolize them to induce the generation of inorganic and organic mixed materials with certain gelling effects, thereby repairing the cracks.

[0003] However, the mixing process of concrete forms high shear stresses, coupled with the continuous hydration of cement, which leads to a denser interior. The hydration products also create a highly alkaline environment, all of which hinder the effective survival of microorganisms within concrete. To mitigate the damage caused by the harsh concrete environment to microorganisms, porous materials are often used to provide a suitable habitat for microorganisms within concrete, ensuring timely and effective repair of concrete cracks. However, there is a lack of a clear method for selecting carrier materials. In concrete crack repair, the use of microbial carriers has two primary functions: first, they stably immobilize microorganisms and nutrients, preventing their loss; second, they provide a favorable microenvironment for microbial growth and metabolism, effectively alleviating the effects of the concrete's alkaline environment and confined space on microbial activity, thereby achieving optimal crack repair results. Therefore, selecting the right carrier and applying it effectively are crucial to ensuring successful concrete crack repair. Currently, while traditional inorganic carriers or gel-like concrete repair materials can effectively protect microorganisms from the highly alkaline environment, direct incorporation into concrete can negatively impact concrete strength and hinder microbial mass transfer, further compromising the repair effectiveness. Therefore, further research is still needed to optimize the vector determination method to address this issue.

[0004] CN109574530A discloses a novel elastic repair agent and its preparation method, designed to achieve self-repair of concrete cracks. The repair agent is composed of rubber particles, microorganisms or microbial spores, and a coating material. The rubber particles act as a carrier for the microorganisms or spores, while the coating material is used to protect these microorganisms or spores, allowing them to be stably stored within the pores of the rubber particles. This technical solution uses aerobic alkaliphilic microorganisms, but their repair ability is limited by oxygen supply, which may make it difficult to effectively repair deep crack areas. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for determining a carrier suitable for microbial self-repair of concrete, which solves the problem that the repair ability of aerobic alkaliphilic microorganisms is limited by oxygen supply, making it difficult to effectively repair deep crack areas.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for determining a carrier suitable for microbial self-repairing concrete comprises the following steps:

[0007] S1: Select a porous carrier material;

[0008] S2: Testing the water absorption rate of the carrier material under normal pressure and negative pressure conditions, including the water absorption rate after immersion for 1 hour and 24 hours at normal temperature and pressure, and the water absorption rate under negative pressure for 5 to 15 minutes;

[0009] S3: Testing the cylinder pressure strength of the carrier material;

[0010] S4: loading the microorganisms having the ability to induce mineralization into the porous carrier, and drying the loaded carrier in an oven at 30 to 50° C. to a constant weight;

[0011] S5: Place the microorganism-loaded carrier in a simulated cement solution and let it stand for 24 hours, then remove it and dry it. Then place the carrier in an aqueous solution and let it stand for 24 hours to evaluate the microorganism release effect.

[0012] S6: Select carrier materials suitable for concrete repair based on water absorption, cylinder pressure strength and microbial release concentration.

[0013] Preferably, in step S1, the porous carrier material is one or more of pottery sand, ceramsite, expanded perlite, recycled brick, volcanic stone and recycled concrete.

[0014] Preferably, in step S4, the microorganisms include one or more combinations of Bacillus pasteurianus, Bacillus sphaericus, yeast, and carbonic anhydrase-producing bacteria.

[0015] Preferably, the cylinder compressive strength of the porous carrier material is not less than 6 MPa.

[0016] Preferably, in step S5, the pH value of the simulated cement solution is 12 to simulate the high alkaline environment inside the concrete.

[0017] Preferably, in the step S5, the microorganism loading step is to introduce the bacterial solution into the communicating channels of the carrier by vacuum negative pressure impregnation or oscillation stirring.

[0018] Preferably, in the step S5, in the step of evaluating the release effect of microorganisms, observation is performed using an ultra-depth-of-field microscope, and the release concentration of the microorganisms is calculated by a plate counting method.

[0019] Preferably, in step S6, the selection of the porous carrier is based on the order of microbial release concentration from high to low.

[0020] The present invention provides a method for determining a carrier suitable for microbial self-repair of concrete. It has the following beneficial effects:

[0021] 1. The present invention can provide a suitable living space for microorganisms through the porous carrier, acting as a physical barrier to prevent microorganisms from being directly exposed to a highly alkaline environment. In addition, the porous carrier can also provide a more uniform distribution of microorganisms, ensuring that they can be fully protected inside the concrete, thereby extending the survival time of the microorganisms.

[0022] 2. The present invention provides a theoretical basis for carrier selection by testing the water absorption rate, cylinder pressure strength and microbial release concentration of different carriers under normal pressure and negative pressure, ensuring that the carrier has good water absorption and strength and can effectively load and release microorganisms.

[0023] 3. The present invention uses negative pressure to load microorganisms, which can release microorganisms in time after concrete cracks, promote self-repair of cracks, reduce subsequent maintenance costs, and improve repair efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of water absorption rate of a carrier under normal pressure in the method for determining a carrier for microbial self-repairing concrete according to the present invention;

[0025] Figure 2 Schematic diagram of water absorption rate of a carrier under negative pressure in a method for determining a carrier for microbial self-repairing concrete according to the present invention;

[0026] Figure 3 Schematic diagram of the carrier cylinder compressive strength of the method for determining the carrier for microbial self-repairing concrete according to the present invention;

[0027] Figure 4 Schematic diagram of the release concentration of microorganisms in a carrier-immobilized unit of the method for determining a carrier for microbial self-repairing concrete according to the present invention;

[0028] Figure 5 Schematic diagram of the release concentration of binary microorganisms immobilized on a carrier applicable to the method for determining a carrier for microbial self-repairing concrete of the present invention;

[0029] Figure 6 It is a schematic diagram of the release concentration of ternary microorganisms immobilized on a carrier according to the method for determining a carrier for microbial self-repairing concrete of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Please see the attached Figure 1-Attached Figure 6 The embodiment of the present invention provides a method for determining a carrier suitable for microbial self-repairing concrete, comprising the following steps:

[0032] S1: Select a porous carrier material;

[0033] S2: Test the water absorption rate of the carrier material under normal pressure and negative pressure conditions, including the water absorption rate after immersion for 1 hour and 24 hours at room temperature and normal pressure, and the water absorption rate under negative pressure for 5 to 15 minutes;

[0034] S3: Test the cylinder pressure strength of the carrier material;

[0035] S4: loading the microorganisms having the ability to induce mineralization into the porous carrier, and drying the loaded carrier in an oven at 30 to 50° C. to a constant weight;

[0036] S5: Place the microorganism-loaded carrier in a simulated cement solution and let it stand for 24 hours, then remove it and dry it. Then place the carrier in an aqueous solution and let it stand for 24 hours to evaluate the microorganism release effect.

[0037] S6: Select carrier materials suitable for concrete repair based on water absorption, cylinder pressure strength and microbial release concentration.

[0038] In step S1, the porous carrier material is one or more of pottery sand, ceramsite, expanded perlite, recycled brick, volcanic stone and recycled concrete.

[0039] In step S4, the microorganisms include one or more combinations of Bacillus pasteurianus, Bacillus sphaericus, yeast, and carbonic anhydrase-producing bacteria.

[0040] The cylinder pressure strength of the porous carrier material is not less than 6MPa.

[0041] In step S5, the pH value of the simulated cement solution is 12 to simulate the high alkaline environment inside the concrete.

[0042] In step S5, the microorganism loading step is to introduce the bacterial solution into the connecting channels of the carrier by vacuum negative pressure impregnation or oscillation stirring.

[0043] In step S5, in the microbial release effect evaluation step, observation is performed using an ultra-depth-of-field microscope, and the released concentration of microorganisms is calculated by the plate counting method.

[0044] In step S6, the selection of the porous carrier is based on the order of microorganism release concentration from high to low, and materials with higher release concentration and higher cylinder pressure strength are preferred.

[0045] The following is an introduction with reference to specific embodiments:

[0046] Example 1: Carrier selection and immobilized microorganism absorption and release operation process

[0047] (1) 5% of Bacillus sphaericus was selected and inoculated into a spore culture medium, and the culture medium was placed in a constant temperature shaking box and cultured for 48 hours at 170 rpm and 35° C. to obtain a spore-containing unit culture medium liquid.

[0048] (2) The cylinder compressive strength of different carriers was tested separately. The cylinder compressive strength of artificial aggregates was tested in accordance with the national standard "Lightweight Aggregates and Their Test Methods Part 2: Test Methods for Lightweight Aggregates" (GB / T1743,2-2010). The cylinder compressive strengths of volcanic rock, expanded perlite, ceramsite, ceramic sand, recycled bricks, and recycled concrete were 6.05 MPa, 0.3 MPa, 0.85 MPa, 7.6 MPa, 7.2 MPa, and 21.5 MPa, respectively.

[0049] (3) Preparation of simulated cement solution: Mix cement and water in a ratio of 1:3 and stir evenly. Stir once every 2 hours in the early stage. After standing for 24 hours, take the supernatant and filter it. Add 0.1 mol / L CAPS solution to the filtered simulated cement solution at a ratio of 10%. Then adjust the pH of the simulated solution to 12 with HCl and NaCl solutions to obtain a simulated cement solution.

[0050] (4) Volcanic rock, expanded perlite, ceramsite, ceramic sand, recycled brick, and recycled concrete were divided into six groups. 1g, 2g, 3g, 4g, and 5g of carriers were taken from each group for microbial loading. The operation steps were as follows: the culture medium inoculated with spherical Bacillus was placed in a constant temperature shaker for 48 hours and then taken out. The bacterial solution and the carrier were placed in a vacuum adsorption pot together, so that the bacterial solution just covered the surface of the carrier. The vacuum pot lid was tightened, the air intake was opened, and the vacuum pump was turned on. The air pressure in the pot gradually decreased. When the air pressure dropped to a negative pressure value of 0.06MPa, the air intake valve was closed and the vacuum pump was immediately stopped. The carrier was subjected to static adsorption treatment. After 15 minutes, the air inlet and air intake of the vacuum pot were opened, and the carrier after the bacterial solution was adsorbed was taken out. The excess bacterial solution was filtered with a sieve and placed in an oven to dry to constant weight.

[0051] (5) Furthermore, the bacteria-loaded volcanic rock, expanded perlite, expanded clay, ceramic sand, recycled bricks, and recycled concrete were divided into six groups. 1g, 2g, 3g, 4g, and 5g of the carriers in each group were taken for microbial release experiments. The carriers immobilized with the bacterial solution were then immersed in a simulated cement solution for a certain period of time. The carriers were then taken out, dried to a constant weight, and immersed in a 50mL aqueous solution for 24h. The release of microorganisms after immobilization on different carriers was calculated by the plate counting method after ultra-depth observation.

[0052] (6) In terms of water absorption rate and microbial release concentration of the carrier, the order of microbial release concentration from high to low is expanded perlite, ceramsite, ceramic sand, recycled brick, volcanic stone, and recycled concrete. Among them, the release concentration of expanded perlite reaches 108 cells / mL, and the release concentrations of ceramsite, ceramic sand, recycled brick, and volcanic stone are also 107 cells / mL. Considering that the carrier needs to have a certain strength, combined with its cylinder pressure strength data, ceramic sand, recycled brick, and volcanic stone can be selected as the microbial loading objects. Expanded perlite has the best release effect, but its strength is poor. It is not suitable for concrete with strength requirements and the dosage should not be too high. Recycled concrete has a dense structure and poor loading effect, so it is not suitable for loading microorganisms.

[0053] Example 2: This example differs from Example 1 in that two microorganisms are mixed and loaded onto the carrier.

[0054] (1) Bacillus pasteurianus and Saccharomyces cerevisiae were selected, inoculated at a ratio of 8:2, and then placed in a constant temperature shaking box for 36 hours to obtain a binary culture medium containing spores.

[0055] (2) Select ceramic sand, ceramsite, expanded perlite, recycled aggregate, volcanic rock, and recycled concrete with a carrier particle size of 1.18 to 4.75 mm and place them in a vacuum cylinder. Vacuum until the vacuum degree reaches -0.06 MPa and stop. Suck in the bacterial solution prepared in step (1) through the pressure relief ball valve. After the suction is completed, close the pressure relief ball valve and open the vacuum cylinder for 15 minutes to obtain a bacterial carrier.

[0056] (3) Place the bacteria-laden carrier in a 40°C forced air drying oven and dry to a constant weight.

[0057] (4) Mix cement and water in a ratio of 1:3 and stir evenly. Stir once every 2 hours in the early stage. After standing for 24 hours, take the supernatant and filter it. Add 0.1 mol / L CAPS solution to the filtered cement simulation solution at a ratio of 10%. Then adjust the pH of the simulation solution to 12 with HCl and NaCl solution to obtain a simulated cement-based pore solution.

[0058] (5) The dried bacteria-carrying carrier was placed in cement solution and allowed to stand for 24 hours, then taken out and dried to constant weight. The carrier was placed in 50 mL of aqueous solution and allowed to stand for 24 hours, and the concentration of microorganisms released was calculated.

[0059] (6) By Figure 5It can be seen that when the carrier is loaded with dual microorganisms, the release concentration is, from highest to lowest, expanded perlite, ceramsite, volcanic rock, ceramic sand, recycled brick, and recycled concrete. Expanded perlite releases 108 cells / mL, while ceramsite, ceramic sand, recycled brick, and volcanic rock release concentrations of 107 cells / mL, all exceeding those of individual microorganisms. Expanded perlite has the best microbial release, followed by ceramsite, and recycled concrete has the worst. Considering their cylinder compressive strength, volcanic rock, ceramic sand, and recycled brick are the preferred carrier repair materials.

[0060] Example 3: This example differs from Example 1 in that three microorganisms are mixed and loaded onto the carrier.

[0061] (1) Bacillus pasteurianus, Saccharomyces cerevisiae, and Carbonic anhydrase mold were selected, inoculated according to a ratio of 7:1:2, and then placed in a constant temperature shaking box for 48 hours to obtain a ternary mixed microbial culture medium containing spores.

[0062] (2) Select ceramic sand, ceramsite, expanded perlite, recycled aggregate, volcanic rock, and recycled concrete with a carrier particle size of 1.18 to 4.75 mm and place them in a vacuum cylinder. Vacuum until the vacuum degree reaches -0.06 MPa and stop. Suck in the bacterial solution prepared in step (1) through the pressure relief ball valve. After the suction is completed, close the pressure relief ball valve and open the vacuum cylinder for 15 minutes to obtain a bacterial carrier.

[0063] (3) Place the bacteria-laden carrier in a 40°C forced air drying oven and dry to a constant weight.

[0064] (4) Mix cement and water in a ratio of 1:3 and stir evenly. Stir once every 2 hours in the early stage. After standing for 24 hours, take the supernatant and filter it. Add 0.1 mol / L CAPS solution to the filtered cement simulation solution at a ratio of 10%. Then adjust the pH of the simulation solution to 12 with HCl and NaCl solution to obtain a simulated cement-based pore solution.

[0065] (5) The dried bacteria-carrying carrier was placed in a cement solution and allowed to stand for 24 hours, then taken out and dried to a constant weight. After being placed in a 50 mL aqueous solution and allowed to stand for 24 hours, its microbial release concentration was calculated. The appropriate carrier material was selected by comparing the release concentration and combining it with the cylinder pressure.

[0066] (6) By Figure 6It can be seen that when the carrier is loaded with ternary microorganisms, the release concentrations are, from high to low, expanded perlite, ceramsite, pottery sand, volcanic stone, recycled bricks, and recycled concrete. The release concentrations of expanded perlite and ceramsite reach 108 cells / mL, and the release concentrations of pottery sand, recycled bricks, and volcanic stone reach 107 cells / mL. Expanded perlite has the best release effect, followed by ceramsite and pottery sand, and all are higher than the release concentrations after loading the unit and binary microorganisms. Considering the strength requirements, pottery sand, volcanic stone, and recycled bricks can be selected as ternary microbial remediation materials.

[0067] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for determining a carrier suitable for microbial self-repairing concrete, characterized in that: The following steps are involved: S1: Select a porous carrier material; S2: Testing the water absorption rate of the carrier material under normal pressure and negative pressure conditions, including the water absorption rate after immersion for 1 hour and 24 hours at normal temperature and pressure, and the water absorption rate under negative pressure for 5 to 15 minutes; S3: Testing the cylinder pressure strength of the carrier material; S4: loading the microorganisms having the ability to induce mineralization into the porous carrier, and drying the loaded carrier in an oven at 30 to 50° C. to a constant weight; S5: Place the microorganism-loaded carrier in a simulated cement solution and let it stand for 24 hours, then remove it and dry it. Then place the carrier in an aqueous solution and let it stand for 24 hours to evaluate the microorganism release effect. S6: Select carrier materials suitable for concrete repair based on water absorption, cylinder pressure strength and microbial release concentration.

2. A method for determining a carrier suitable for microbial self-repairing concrete according to claim 1, characterized in that: In step S1, the porous carrier material is one or more of pottery sand, ceramsite, expanded perlite, recycled brick, volcanic stone and recycled concrete.

3. The method for determining a carrier suitable for microbial self-repairing concrete according to claim 1, characterized in that: In the step S4, the microorganisms include one or more combinations of Bacillus pasteurianus, Bacillus sphaericus, yeast, and carbonic anhydrase-producing bacteria.

4. The method for determining a carrier suitable for microbial self-repairing concrete according to claim 1, characterized in that: The cylinder compressive strength of the porous carrier material is not less than 6 MPa.

5. The method for determining a carrier suitable for microbial self-repairing concrete according to claim 1, characterized in that: In step S5, the pH value of the simulated cement solution is 12 to simulate the high alkaline environment inside the concrete.

6. The method for determining a carrier suitable for microbial self-repairing concrete according to claim 1, characterized in that: In the step S5, the microorganism loading step is to introduce the bacterial solution into the connecting channels of the carrier by vacuum negative pressure impregnation or oscillation stirring.

7. A method for determining a carrier suitable for microbial self-repairing concrete according to claim 6, characterized in that: In the step S5, in the step of evaluating the release effect of microorganisms, observation is performed using an ultra-depth-of-field microscope, and the release concentration of microorganisms is calculated by a plate counting method.

8. The method for determining a carrier suitable for microbial self-repairing concrete according to claim 7, characterized in that: In step S6, the selection of the porous carrier is based on the order of microorganism release concentration from high to low.

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