Determination method suitable for carrier for microbial self-repairing concrete

Abstract

The invention relates to the field of concrete crack self-repairing materials, and discloses a method for determining a carrier suitable for microorganism self-repairing concrete, and the method comprises 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 microorganisms with induced mineralization capability into the porous carrier, and drying the loaded carrier in a drying oven at 30-50 DEG C until the weight is constant; s5, putting the carrier loaded with the microorganisms into a simulated cement solution, standing for 24 hours, taking out and drying; and S6, a carrier material suitable for concrete repairing is selected. The porous carrier can provide an appropriate living space for microorganisms, plays a role of a physical barrier, prevents the microorganisms from being directly exposed in a high-alkalinity environment, can provide more uniform distribution for the microorganisms, and ensures that the microorganisms can be fully protected in the concrete, so that the survival time of the microorganisms is prolonged.

Description

Technical Field

[0001] The 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 social economy and science and technology, cement-based materials, as a composite building material product with low cost, good durability and high compressive strength, are widely used in various civil engineering fields. However, due to its inherent brittleness and low toughness, concrete materials will have crack defects in the early stage and cause cracking problems. Due to the influence of load and non-load factors, microcracks are formed, allowing harmful media to enter the interior of the concrete, resulting in serious damage to the performance of the concrete. There are many traditional methods for treating concrete cracks, such as surface treatment, grouting and structural reinforcement, but these methods often require a lot of manpower and material resources. And it is a post-remediation method, and it is impossible to quickly and autonomously repair cracks from the source. Under certain conditions, concrete itself has a certain ability to heal cracks. It mainly uses the continuous hydration of unhydrated cement particles and the carbonization of hydration products in the air to achieve the purpose of repairing cracks, but this self-healing ability is extremely weak. In order to further enhance the ability of concrete to heal itself, the researchers introduced microorganisms with the effect of inducing mineralization and deposition and the corresponding substrates into concrete during the forming stage. Once cracks occur in concrete, the entry of external moisture and oxygen will prompt the germination and growth of microorganisms, and metabolize them to induce the production of inorganic and organic mixed materials with certain gelling effects, thereby repairing the cracks.

[0003] However, high shear stress will be generated during the mixing process of concrete molding. At the same time, the continuous hydration of cement will cause the interior of the concrete to become increasingly dense, and the hydration products will further form a highly alkaline environment, all of which will hinder the effective survival of microorganisms in the concrete. In order to avoid the damage caused by the harsh environment inside the concrete to microorganisms, porous materials are usually used to provide a suitable living space for microorganisms inside the concrete to ensure that the cracks in the concrete structure can be repaired in a timely and effective manner. However, there is a lack of corresponding determination methods for how to select carrier materials. In concrete crack repair, the use of microbial carriers has two main functions: first, it can stably fix microorganisms and nutrients to prevent their loss; second, the carrier provides a good microenvironment for the growth and metabolism of microorganisms, which can effectively alleviate the effects of the alkaline environment and narrow space of the concrete on the activity of microorganisms, thereby achieving better crack repair effects. Therefore, selecting a suitable carrier and applying it effectively is the key to ensuring the success of concrete crack repair. At present, although traditional inorganic carriers or gel-like concrete repair materials can effectively protect microorganisms from interference from the strong alkaline environment, when directly added to concrete, they may have a negative impact on the strength of concrete and may also hinder the mass transfer process of microorganisms, which will further affect the repair effect. 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 a preparation method thereof, which is intended to achieve self-repair of concrete cracks. The composition of the repair agent includes rubber particles, microorganisms or microbial spores, and a wrapping material. The rubber particles act as carriers of the microorganisms or spores, and the wrapping material is used to protect these microorganisms or spores so that they are stably stored in 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 achieve effective repair of deep crack areas. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for determining a carrier suitable for microbial self-repairing concrete, which solves the problem that the repair ability of aerobic alkaliphilic microorganisms is limited by oxygen supply, making it difficult to achieve effective repair of 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: Selecting 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 compression 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: placing the microorganism-loaded carrier in a simulated cement solution and letting it stand for 24 hours, then taking it out and drying it, and then placing the carrier in an aqueous solution and letting 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 bacteria.

[0015] Preferably, the cylinder pressure 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 allow the bacterial solution to enter the connecting 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-repairing concrete. It has the following beneficial effects:

[0021] 1. The present invention can provide a suitable living space for microorganisms through the porous carrier, which acts as a physical barrier to prevent the microorganisms from being directly exposed to a high alkaline environment. In addition, the porous carrier can also provide a more uniform distribution for the microorganisms, ensuring that they can be fully protected inside the concrete, thereby prolonging 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 It is a schematic diagram of the water absorption rate of the carrier under normal pressure in the method for determining the carrier for microbial self-repairing concrete of the present invention;

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

[0026] Figure 3 It is a 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 It is a 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 It is a schematic diagram of the release concentration of binary microorganisms immobilized on a carrier according 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 technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Please refer to 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: Selecting 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 normal temperature and pressure, and the water absorption rate under negative pressure for 5 to 15 minutes;

[0034] S3: Test the cylinder compression 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: placing the microorganism-loaded carrier in a simulated cement solution and letting it stand for 24 hours, then taking it out and drying it, and then placing the carrier in an aqueous solution and letting 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 ceramic 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 step of evaluating the effect of microbial release, observation is performed using an ultra-depth-of-field microscope, and the release concentration of the 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 in conjunction with specific embodiments:

[0046] Example 1: Selection of carrier and absorption and release process of immobilized microorganisms

[0047] (1) 5% of spherical Bacillus 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 respectively, and the cylinder compressive strength of artificial aggregate was tested in accordance with the national standard "Lightweight Aggregate and Its Test Method Part 2: Lightweight Aggregate Test Method" (GB / T1743,2-2010). The cylinder compressive strengths of volcanic rock, expanded perlite, ceramsite, ceramsite sand, recycled brick, and recycled concrete were 6.05MPa, 0.3MPa, 0.85MPa, 7.6MPa, 7.2MPa, and 21.5MPa, 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 at a ratio of 10% to the filtered simulated cement solution. 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 the carriers in each group were taken 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, and 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, clay 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 loaded with bacterial liquid were then immersed in a simulated cement solution for a certain period of time. The carriers were taken out and dried to constant weight and then immersed in 50mL of aqueous solution for 24h. The release of microorganisms after being immobilized on different carriers was calculated by the plate counting method after ultra-depth observation.

[0052] (6) In terms of water absorption and the microbial release concentration of the carrier, the microbial release concentration is from high to low in the order of expanded perlite, ceramsite, ceramic sand, recycled brick, volcanic stone, and recycled concrete. 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 object. Expanded perlite has the best release effect, but its strength is poor, so it is not suitable for concrete with strength requirements and the dosage should not be too much. Recycled concrete has a dense structure and poor loading effect, so it is not suitable for loading microorganisms.

[0053] Example 2: This example is different from Example 1 in that two kinds of 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 culturing for 36 hours to obtain a binary culture medium containing spores.

[0055] (2) Select ceramic sand, ceramsite, expanded perlite, recycled aggregate, volcanic stone, and recycled concrete with a carrier particle size of 1.18 to 4.75 mm and place them in a vacuum cylinder. Vacuum the mixture until the vacuum degree reaches -0.06 MPa, and then suck 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 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 at a ratio of 10% to the filtered cement simulation solution. Then adjust the pH of the simulation solution to 12 with HCl and NaCl solutions to obtain a simulated cement-based pore solution.

[0058] (5) The dried bacterial carrier was placed in a cement solution and allowed to stand for 24 hours, then taken out and dried to constant weight. The carrier was placed in a 50 mL aqueous solution and allowed to stand for 24 hours, and the microbial release concentration was calculated.

[0059] (6) By Figure 5It can be seen that when the carrier is loaded with binary microorganisms, the release concentration is from high to low in the order of expanded perlite, ceramsite, volcanic stone, pottery sand, recycled brick, and recycled concrete. The release concentration of expanded perlite is 108 cells / mL, and the release concentration of ceramsite, pottery sand, recycled brick, and volcanic stone reaches 107 cells / mL, and the release concentration is higher than that of single microorganisms. Expanded perlite has the best microbial release effect, followed by ceramsite, and recycled concrete is the worst. Combined with their cylinder pressure strength, volcanic stone, pottery sand, and recycled brick can be selected as carrier repair materials.

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

[0061] (1) Bacillus pasteurianus, Saccharomyces cerevisiae, and Carbonic anhydrase mold were selected, inoculated at 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 stone, and recycled concrete with a carrier particle size of 1.18 to 4.75 mm and place them in a vacuum cylinder. Vacuum the mixture until the vacuum degree reaches -0.06 MPa, and then suck 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 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 at a ratio of 10% to the filtered cement simulation solution. Then adjust the pH of the simulation solution to 12 with HCl and NaCl solutions to obtain a simulated cement-based pore solution.

[0065] (5) The dried bacterial carrier was placed in a cement solution and allowed to stand for 24 hours, then taken out and dried to 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, clay sand, volcanic stone, recycled bricks, and recycled concrete. The release concentrations of expanded perlite and ceramsite reached 108 cells / mL, and those of clay sand, recycled bricks, and volcanic stone reached 107 cells / mL. Expanded perlite had the best release effect, followed by ceramsite and clay sand, and all were higher than the release concentrations after loading the unit and binary microorganisms. Considering the strength requirements, clay sand, volcanic stone, and recycled bricks can be selected as ternary microbial remediation materials.

[0067] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present 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: Selecting 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 compression 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: placing the microorganism-loaded carrier in a simulated cement solution and letting it stand for 24 hours, then taking it out and drying it, and then placing the carrier in an aqueous solution and letting 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 the step S1, the porous carrier material is one or more of pottery sand, ceramsite, expanded perlite, recycled brick, volcanic stone and recycled concrete.

3. A 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 bacteria.

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

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. A 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 allow the bacterial solution to enter 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 the microorganisms is calculated by a plate counting method.

8. A method for determining a carrier suitable for microbial self-repairing concrete according to claim 7, characterized in that: In the 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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