A composite microbial cement with short repair period and strong impermeability, a preparation method and application thereof

Abstract

The application belongs to the technical field of microbiology, civil engineering and material science, and discloses a preparation method of composite microbial cement with short repair period and strong anti-permeability, which is composed of composite microbial liquid and nutrient salt; the specific preparation steps are as follows: configure a Pasteuria agglomerate culture medium; prepare high-activity Pasteuria agglomerate fermentation liquor; dissolve low-fat pectin in the fermentation liquor to form the composite microbial liquid; prepare a nutrient salt solution; uniformly mix the composite microbial liquid and the nutrient salt solution and stand for ten minutes, and then the composite microbial cement can be obtained. The composite microbial cement has great potential for large-scale production and sustainable use, practically solves the problem of long repair period of traditional microbial cement in the repair process, conforms to the development trend of ecological environmental protection, and thus has wide application prospect and market value.

Description

Technical Field

[0001] The present invention belongs to the interdisciplinary technical field of microbiology, civil engineering and material science, and in particular relates to a composite microbial cement with a short repair cycle and strong impermeability, a preparation method and an application thereof. Background Art

[0002] Reinforced concrete is one of the most commonly used materials in the global construction industry, but over time, fine cracks may appear inside and on its surface due to factors such as external loads. These cracks weaken the mechanical properties of concrete, promote the penetration of moisture and chemicals, and accelerate structural degradation. Currently, research on concrete repair materials mainly focuses on three categories: inorganic repair materials, organic repair materials, and microbial repair materials. Although inorganic materials such as cement paste and cement mortar are widely used, they have disadvantages such as high brittleness and low bonding strength; while organic materials such as acrylates and epoxy resins are easily affected by contamination and aging. Microbial induced calcium carbonate precipitation (MICP) technology, as a sustainable bioremediation method, can effectively repair cracks in concrete. The resulting calcium carbonate product is called microbial cement, which represents a new generation of repair materials.

[0003] Biocement is environmentally friendly and cost-effective, boasting excellent mechanical properties and high strength. Using low-viscosity, small-particle bacterial solutions and nutrients, it can effectively repair microcracks in concrete and improve the physical and mechanical properties of the repaired material. However, its practical application faces challenges, including long repair cycles, the need for repeated grouting, and poor tolerance to water environments.

[0004] Chinese invention patent application "CN202211268805.5, A concrete surface repair and protection method based on microbial cement" discloses a concrete surface repair and protection method based on microbial cement. This method adds viscose protein to the bacterial solution to increase the toughness of the concrete surface repair layer and improve its crack resistance. However, the activity of the bacteria used is too low, resulting in a repair cycle of up to 15 days, which does not meet the needs of rapid repair in on-site applications.

[0005] The Chinese invention patent application "CN202111436095.8, Sodium alginate-immobilized microorganisms concrete crack repair material and preparation method thereof" discloses a sodium alginate-immobilized microorganisms concrete crack repair material and a preparation method thereof. The method does not mention the content of the method in improving the anti-seepage performance of concrete structure cracks after repair.

[0006] Compared to the aforementioned patent, the present invention simplifies the preparation process, effectively overcoming the limitation of conventional microbial cement, which requires immediate preparation and use, thereby avoiding the problem of excessively long construction cycles. This material not only exhibits superior impermeability but also significantly shortens the repair cycle, demonstrating its potential for on-site application. Summary of the Invention

[0007] The present application aims to overcome the deficiencies in the prior art, and provides a composite microbial cement with short repair cycle and strong impermeability, a preparation method and application.

[0008] The technical solution adopted by the present application to solve its technical problems is:

[0009] A preparation method of a composite microbial cement with short repair cycle and strong impermeability, the composite microbial cement being composed of a composite bacterial solution and nutrient salt; the specific preparation steps are as follows:

[0010] S1 configures a YE-MH Bacillus pasteurii culture medium;

[0011] S2 prepares a high-activity Bacillus pasteurii fermentation broth;

[0012] S3 dissolves low-fat pectin in the fermentation broth to form a composite bacterial solution;

[0013] S4 prepares a nutrient salt solution;

[0014] S5 uniformly mixes the composite bacterial solution and the nutrient salt solution and stands for ten minutes to obtain the composite microbial cement.

[0015] Further, the composition and content of the YE-MH Bacillus pasteurii culture medium in S1 are as follows: yeast extract 30-34 g / L, ammonium sulfate 8-12 g / L, MH broth 6-8 g / L; nickel chloride 200-240 mg / L, and the solvent is water; 6 mol / L NaOH is used to adjust the pH value to 8.4-9.1, and 121℃ high-pressure sterilization is performed for 20 minutes.

[0016] Further, in S2, the YE-MH Bacillus pasteurii culture medium is used for activation culture, and the activation culture conditions are 28-35℃, 180-220 r / min, and shaking bed culture for 15-20 h; according to an inoculation amount of 2-5%, the YE-MH Bacillus pasteurii culture medium is inoculated for expansion culture, and the conditions are 28-35℃, 180-220 r / min, and shaking bed culture for 22-26 h to obtain the high-activity Bacillus pasteurii fermentation broth.

[0017] Further, the OD600 of the high-activity Bacillus pasteurii fermentation broth is 8-15. 600 The urease activity (high activity including high OD600 and high enzyme activity) is 18-24 mM / min or more.

[0018] Further, in S3, low-fat pectin with a mass fraction of 0.5%-1.5% of the fermentation broth is added to the fermentation broth, and stirring is performed at 30-35℃ for 2-4 h to completely dissolve the low-fat pectin to obtain the composite bacterial solution.

[0019] Further, when the width of the concrete structure crack is in the range of 0-0.5mm, 0.5%-1% of the low-fat pectin by weight of the fermentation liquor is added to the fermentation liquor; and when the width of the crack is between 0.5-1mm, 1%-1.5% of the low-fat pectin by weight of the fermentation liquor is added to the fermentation liquor.

[0020] Further, the specific steps for preparing 100ml of the nutrient salt solution in S4 are as follows: 20-25g of calcium acetate solid and 8-10g of urea are dissolved in distilled water, and after complete dissolution, distilled water is added to the solution to a total volume of 100ml, and finally the nutrient salt solution is obtained.

[0021] Further, the specific steps for uniformly mixing the composite microbial solution and the nutrient salt solution and standing for ten minutes in S5 are as follows: the required volume of the nutrient salt solution is mixed with an equal volume of the composite microbial solution to ensure that the composite microbial solution and the nutrient salt are in sufficient contact and form a stable composite system; the mixed solution is placed in an environment of 30-35°C and is allowed to stand for 8-10 minutes to promote the full activity of the microorganisms, and finally the composite microbial cement is formed.

[0022] The composite microbial cement prepared by the preparation method described above has a short repair period and strong impermeability.

[0023] The application of the preparation method described above in the repair of concrete structure cracks.

[0024] The advantages and positive effects obtained by the present application are as follows:

[0025] 1. The method aims to effectively shorten the repair period of microbial cement and significantly improve the impermeability of the repaired material. Specifically, the method first cultures the Paenibacillus polymyxa in a high-nutrient medium to obtain a high-activity bacterial solution. Then, an appropriate amount of low-fat pectin powder is dissolved in the Paenibacillus polymyxa bacterial solution to ensure that the two are uniformly mixed. The introduction of pectin not only increases the local concentration in the reaction system, but also interacts with calcium ions to form a gel, thereby achieving a rapid and effective plugging effect for repairing cracks. As a renewable green material, the composite microbial cement of the present application has great potential for large-scale production and sustainable use, effectively solves the problem of long repair period of ordinary microbial cement in the repair process, and meets the development trend of ecological environmental protection, thus having a wide application prospect and market value.

[0026] 2、The method is a method with fast repair speed, simple process, strong anti-permeability and green environmental protection, and the composite microbial cement prepared by the method is a composite microbial cement for repairing cracks in a concrete structure.

[0027] 3、The preparation method of the present application promotes the growth of Paenibacillus peoriae by optimizing the culture medium, and combines low-fat pectin with the microbial-induced calcium carbonate precipitation (MICP) technology. Compared with ordinary microbial cement, the repair cycle of the present application is shortened from three days to only one day. This not only improves the engineering efficiency, but also reduces the construction cost, providing a more convenient and economical solution for the practical application of microbial cement. Compared with ordinary microbial cement, the anti-permeability recovery rate of the present application is increased from 56.2% to 118.4%. The composite microbial cement prepared by the present application has the characteristic of maintaining a usable state within five days, thereby effectively overcoming the limitation of ordinary microbial cement that needs to be prepared and used immediately, significantly improving the flexibility of its application. Compared with ordinary concrete crack repair methods, the present application not only exhibits strong operational convenience, but also has excellent material compatibility and environmental protection advantages. The introduction of this new type of cement represents a step forward for microbial cement in the field of building materials towards more efficient and sustainable solutions, and helps to promote the development of concrete repair technology. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Figure is a diagram of two parallel tests completed by the composite microbial cement of the present application for repairing 0.3mm concrete structure cracks;

[0029] Figure 2 Figure is a diagram of the anti-permeability performance of the test piece after repair by the composite microbial cement of the present application;

[0030] Figure 3 Figure is a diagram of the biological activity comparison between the bacterial solution fermented by the YE-NH4 original culture medium and the bacterial solution fermented by the YE-MH Paenibacillus peoriae culture medium;

[0031] Figure 4 Figure is a diagram of the repair speed comparison between the microbial cement and the composite microbial cement of the present application; the upper and lower diagrams in the first column are two parallel tests of ordinary microbial cement repair, and the upper and lower diagrams in the second column are two parallel tests of composite microbial cement repair;

[0032] Figure 5 Figure is a diagram of the anti-permeability performance comparison between the test piece repaired by the composite microbial cement and the test piece repaired by high-permeability epoxy resin of the present application;

[0033] Figure 6A permeability resistance comparison chart of the test piece repaired by 1% low-fat pectin composite microbial cement and 1% xanthan gum composite microbial cement in the application;

[0034] Figure 7 A comparison chart of reaction speed of the bacteria liquid fermented by YE-NH4 original culture medium and the bacteria liquid fermented by YE-MH Bacillus pasteurii culture medium in the composite microbial cement in the application; the upper and lower two charts in the first column are two parallel tests of the composite microbial cement with the bacteria liquid fermented by YE-MH Bacillus pasteurii culture medium, and the upper and lower two charts in the second column are two parallel tests of the composite microbial cement with the bacteria liquid fermented by YE-NH4 original culture medium. DETAILED DESCRIPTION

[0035] The application is further described below in combination with examples, which are descriptive rather than limiting, and cannot be used to limit the protection scope of the application.

[0036] The various experimental operations involved in the specific examples are all conventional techniques in the art, and the parts not specially noted in the text can be implemented by referring to various commonly used tool books, scientific and technical literature or related instructions, manuals, etc. before the application date of the application.

[0037] A preparation method of a composite microbial cement with short repair period and strong permeability resistance, the composite microbial cement being composed of a composite bacteria liquid and nutrient salt; the specific preparation steps are as follows:

[0038] S1 configure YE-MH Bacillus pasteurii culture medium;

[0039] S2 prepare high-activity Bacillus pasteurii fermentation liquid;

[0040] S3 dissolve low-fat pectin in the fermentation liquid to form a composite bacteria liquid;

[0041] S4 prepare a nutrient salt solution;

[0042] S5 uniformly mix the composite bacteria liquid and the nutrient salt solution and stand for ten minutes to obtain the composite microbial cement.

[0043] More preferably, the composition and content of the YE-MH Bacillus pasteurii culture medium in S1 are as follows: yeast extract 30-34 g / L, ammonium sulfate 8-12 g / L, MH broth 6-8 g / L; nickel chloride 200 mg-240 mg / L, and the solvent is water; adjust the pH value to 8.4-9.1 with 6 mol / L NaOH, and high-pressure sterilization at 121℃ for 20 minutes.

[0044] Preferably, the activation culture in S2 is carried out using YE-MH Bacillus pasteurii culture medium, the activation culture conditions are 28-35°C, 180-220r / min, and the shaking culture is carried out for 15-20h; the inoculation is carried out in YE-MH Bacillus pasteurii culture medium according to 2-5% inoculation amount, the culture conditions are 28-35°C, 180-220r / min, and the shaking culture is carried out for 22-26h, so as to obtain the high-activity Bacillus pasteurii fermentation liquor.

[0045] Preferably, the OD600 of the high-activity Bacillus pasteurii fermentation liquor is 0.5-1.5. 600 The urease activity (high activity includes high OD600 and high enzyme activity) is 18-24mM / min or above.

[0046] Preferably, in S3, 0.5%-1.5% low-fat pectin of the fermentation liquor is added into the fermentation liquor, and the low-fat pectin is completely dissolved by stirring at 30-35°C for 2-4h, so as to obtain the compound microbial liquor.

[0047] Preferably, when 0.5%-1.5% low-fat pectin of the fermentation liquor is added into the fermentation liquor, 0.5%-1% low-fat pectin of the fermentation liquor is added for the concrete structure cracks with the width in the range of 0-0.5mm, and 1%-1.5% low-fat pectin of the fermentation liquor is added for the cracks with the width in the range of 0.5-1mm.

[0048] Preferably, in S4, the specific steps for preparing 100ml of the nutrient salt solution are as follows: 20-25g of calcium acetate solid and 8-10g of urea are dissolved in distilled water, after the complete dissolution, distilled water is added into the solution until the total volume is 100ml, and finally the nutrient salt solution is obtained.

[0049] Preferably, in S5, the specific steps for uniformly mixing the compound microbial liquor and the nutrient salt solution and standing for ten minutes are as follows: the required volume of the nutrient salt solution is uniformly mixed with the equal volume of the compound microbial liquor, so as to ensure that the compound microbial liquor and the nutrient salt are fully contacted and form a stable compound system; the mixed liquor is placed in the environment with the temperature of 30-35°C and is stood for 8-10 minutes, so as to promote the full play of the activity of the microorganism, and finally the compound microbial cement is formed.

[0050] The compound microbial cement with short repair period and strong impermeability is prepared by the preparation method as described above.

[0051] The application of the preparation method as described above in the repair of the concrete structure cracks.

[0052] Specifically, the related preparation and detection are as follows:

[0053] Example 1

[0054] Preparation of high-activity YE-MH Bacillus pasteurii culture medium

[0055] The components and contents of the culture medium are: yeast extract 32 g / L, ammonium sulfate 10 g / L, MH broth 8 g / L, and nickel chloride 240 mg / L, with water as the solvent. The pH value of the culture medium is adjusted to 9.0 by 6 mol / L sodium hydroxide, and sterilized in a 121℃ high-pressure steam sterilization pot for 20 minutes.

[0056] The culture steps are: ① activation culture using the YE-MH Bacillus pasteurii culture medium, with the activation culture conditions being 30℃, 200 r / min, and shaking bed culture for 18 h; ② after the activation culture is completed, inoculate into the YE-MH Bacillus pasteurii culture medium fermentation culture at an inoculation amount of 3%, and perform expansion culture under the conditions of 30℃, 200 r / min, and shaking bed culture for 24 h, to obtain a high-activity Bacillus pasteurii fermentation broth. The concentration of the bacterial liquid is determined using a UV spectrophotometer, and after being diluted 10 times, the OD 600 value is above 8; the urease activity is determined using the conductivity method, and the determination steps are: take 1 mL of the bacterial liquid, add 9 mL of 1.11 mol / L urea solution, and observe the conductivity change within 5 minutes, to measure the enzyme activity to be above 18 mM / min.

[0057] Example 2

[0058] A preparation method of a composite microbial cement with short repair period and strong impermeability, which is composed of a composite bacterial liquid and nutrient salts; the specific preparation steps are as follows:

[0059] ① Add 1% low-fat pectin of the fermentation liquid prepared in Example 1 to the high-activity Bacillus pasteurii fermentation liquid prepared in Example 1, then set the temperature to 35℃ in a constant-temperature heating magnetic stirrer, and adjust the rotation speed to 200 rpm for high-speed stirring, with a duration of 3 hours, until the low-fat pectin is completely dissolved, to finally obtain a composite bacterial liquid with a concentration of 1%.

[0060] ② Dissolve 23 g of calcium acetate solid and 9 g of urea in distilled water, and after complete dissolution, add distilled water to the solution to a total volume of 100 ml, to finally obtain a nutrient salt solution with both calcium acetate and urea being 1.5 mol / L.

[0061] ③ Uniformly mix the obtained composite bacterial liquid and the nutrient salt solution in a volume ratio of 1:1, and after standing for 10 minutes in an environment of 30℃-35℃, use a syringe to inject the mixed solution into a pre-prepared concrete crack (with a crack size of 80 mm long, 200 mm deep, and 0.3 mm wide), until the crack is completely filled with the repair liquid.

[0062] ④ This repair operation is repeated every 3 hours, and a total of 3 repair operations are performed.

[0063] like Figure 1 As shown in the figure, after three repairs, the composite microbial cement successfully restored the integrity of the cracks, the filling material appeared yellow-white, and the repair effect was significant, which fully demonstrated the application potential of the composite microbial cement prepared by the present invention.

[0064] Example 3

[0065] Preparation and anti-permeability test of a composite microbial cement; the specific steps are:

[0066] ① 1% low-fat pectin by weight of the fermentation broth prepared in Example 1 was added to the highly active Sporosarcina pasteurii fermentation broth prepared in Example 1, and then the temperature was set to 35°C in a constant temperature heating magnetic stirrer, and the speed was adjusted to 200 rpm for high-speed stirring for 3 hours until the low-fat pectin was completely dissolved, finally obtaining a composite bacterial solution with a concentration of 1%.

[0067] ② Dissolve 23g of calcium acetate solid and 9g of urea in distilled water. After they are completely dissolved, add distilled water to the solution to a total volume of 100ml to obtain a nutrient salt solution with 1.5mol / L of calcium acetate and urea.

[0068] ③ Evenly mix the obtained composite bacterial solution and nutrient salt solution in a volume ratio of 1:1. After standing at 30℃~35℃ for 10 minutes, use a syringe to inject the mixed solution into the pre-prepared concrete cracks (crack size is 80mm long, 200mm deep, and 0.3mm wide) until the cracks are completely filled with the repair liquid.

[0069] ④ This repair operation is repeated every 3 hours, and a total of 3 repair operations are performed.

[0070] ⑤ Use the anti-seepage test method. The specific test steps are as follows: After sealing the surrounding areas of the test piece and the unrepaired experimental area with wax, record its mass as M1, then turn the repaired surface upside down and fully immerse it in water. Take it out at different time periods, quickly absorb the surface moisture with a wet towel, and then weigh it immediately, record it as M2. The unrepaired cracked specimen is used as the blank group, and the intact specimen is used as the control group. The water absorption rate E and anti-seepage recovery rate (%) are calculated as follows:

[0071] E = (M2 - M1) / M1 x 100%.

[0072] Anti-seepage recovery rate (%) = E1 / E0×100%

[0073] Where: E0 represents the water absorption rate of the specimen after crack repair, %;

[0074] E1 represents the water absorption rate of the intact test piece, %.

[0075] The test results are shown in Table 1. Figure 2 After the impermeability test, the impermeability recovery rate of the repaired test piece reached 118.39%, the water absorption amount of which was 0.23 ml, while the water absorption amount of the intact test piece was 0.27 ml, and the water absorption amount of the unrepaired test piece was as high as 0.82 ml. These data show that the impermeability of the test piece is significantly improved after the repair treatment according to the present application.

[0076] Comparative Example 1

[0077] This comparative example relates to comparing the activity of the high-activity Paenibacillus pabuli fermentation broth fermented by the YE-MH medium with the activity of the Paenibacillus pabuli fermentation broth fermented by the YE-NH4 original medium, the composition and content of the YE-NH4 original medium being: yeast extract 20 g / L, ammonium sulfate 10 g / L, 0.13 mol / L Tris, solvent being water, and pH value being adjusted to 9 by HCl; the culture conditions of the YE-NH4 original medium fermentation broth being: 30°C, 200 r / min of shaking bed culture for 24 hours. As shown in Table 2, by comparing the activity of the high-activity Paenibacillus pabuli fermentation broth in Example 1 with the activity of the Paenibacillus pabuli fermentation broth fermented by the original medium, it is found that the OD600 value of the former is significantly improved to 12-15, which is doubled compared with the OD600 value of 4-6 of the original medium. In addition, the urease activity is also significantly enhanced, reaching 20-24 mM / min, which is also doubled compared with the urease activity of 12-15 mmol·min-1 of the original medium. Therefore, it can be seen that the optimized medium, the fermentation broth of the optimized medium is better than the fermentation broth of the original medium, and the high-activity medium has higher OD600 and enzyme activity than the medium cultured by the original medium, and the broth with high OD600 and high enzyme activity is more conducive to subsequent rapid repair. Figure 3 600 600 -1

[0078] Comparative Example 2

[0079] This comparative example relates to comparing the repair speed of the composite microbial cement and the microbial cement repair material, and the preparation and repair steps of the microbial cement are as follows:

[0080] ①Preparation of high-activity Paenibacillus pabuli fermentation broth (same as Example 1);

[0081] ②Dissolve 23 g of calcium acetate solid and 9 g of urea in distilled water, and after complete dissolution, add distilled water to the solution to a total volume of 100 ml, finally obtaining a nutrient salt solution with calcium acetate and urea both being 1.5 mol / L;​​​​

[0082] ③Mix the bacterial solution with the nutrient salt at a volume ratio of 1:1 and let it stand for 10 minutes;

[0083] ④Inject the uniformly mixed liquid into the cracks using a syringe;

[0084] ⑤Repeat the repair process three times with an interval of 3 hours. Subsequently, compare the repaired test piece with the repaired test piece in Example 2, as shown in Figure 4 , the results show that the composite microbial cement completes the repair, and there are no cracks on the surface, while the microbial cement fails to achieve repair.

[0085] Comparative Example 3

[0086] This comparative example involves comparing the impermeability of the composite microbial cement with the high-permeability epoxy resin repair material, and the high-permeability epoxy resin repair steps are as follows:

[0087] ①Mix epoxy resin material A and amine-based hardener polyamide resin B uniformly according to a mass ratio of 4:1;

[0088] ②Inject the mixed solution into the cracks using a syringe until the overflow stops;

[0089] ③Repeat the repair process three times with an interval of 3 hours.

[0090] ④After the repair is completed, compare the impermeability of the composite microbial cement (i.e. Example 3) with the high-permeability epoxy resin repair material repaired test piece, and the specific test steps are as follows: After sealing the wax around the test piece and the un-repaired experimental area, record its mass as M1, then invert the repaired surface and immerse it in water, take it out at different time intervals, quickly absorb the surface water with a wet towel, and immediately weigh it, record it as M2, take the un-repaired crack test piece as the blank group, and take the complete test piece as the control group, the water absorption rate E and the impermeability recovery rate (%) are calculated as shown below:

[0091] E = (M2-M1) / M1 x 100%.

[0092] Impermeability recovery rate (%) = E1 / E0 x 100%

[0093] Wherein: E0 represents the water absorption rate of the crack-repaired test piece, %;

[0094] E1 represents the water absorption rate of the complete test piece, %.

[0095] As shown in Figure 5 , the impermeability recovery rate of the test piece repaired with the composite microbial cement reaches 118.4%, which is significantly better than the 40.5% of the high-permeability epoxy resin material.

[0096] Comparative Example 4

[0097] In this comparative example, the low-fat pectin component in the composite microbial cement is replaced with xanthan gum, and the remaining steps are the same as those in Example 3. After the repair is completed, it is compared with Example 3; the specific steps are:

[0098] ① 1% xanthan gum by weight of the fermentation broth prepared in Example 1 was added to the highly active Sporosarcina pasteurii fermentation broth prepared in Example 1, and then the temperature was set to 35°C in a constant temperature heating magnetic stirrer, and the speed was adjusted to 200 rpm for high-speed stirring for 3 hours until the xanthan gum was completely dissolved, finally obtaining a composite bacterial solution with a concentration of 1%.

[0099] ② Dissolve 23g of calcium acetate solid and 9g of urea in distilled water. After they are completely dissolved, add distilled water to the solution to a total volume of 100ml to obtain a nutrient salt solution with 1.5mol / L of calcium acetate and urea.

[0100] ③ Evenly mix the obtained composite bacterial solution and nutrient salt solution in a volume ratio of 1:1. After standing at 30℃~35℃ for 10 minutes, use a syringe to inject the mixed solution into the pre-prepared concrete cracks (crack size is 80mm long, 200mm deep, and 0.3mm wide) until the cracks are completely filled with the repair liquid.

[0101] ④ This repair operation is repeated every 3 hours, and a total of 3 repair operations are performed.

[0102] ⑤ Use the anti-seepage test method. The specific test steps are as follows: After sealing the surrounding areas of the test piece and the unrepaired experimental area with wax, record its mass as M1, then turn the repaired surface upside down and fully immerse it in water. Take it out at different time periods, quickly absorb the surface moisture with a wet towel, and then weigh it immediately, record it as M2. The unrepaired cracked specimen is used as the blank group, and the intact specimen is used as the control group. The water absorption rate E and anti-seepage recovery rate (%) are calculated as follows:

[0103] E = (M2 - M1) / M1 x 100%.

[0104] Anti-seepage recovery rate (%) = E1 / E0×100%

[0105] Where: E0 represents the water absorption rate of the specimen after crack repair, %;

[0106] E1 represents the water absorption rate of the complete specimen, %.

[0107] like Figure 6As shown in the figure, the results show that the permeability recovery rate of the repair test piece with 1% xanthan gum added is 69.2%, and compared with this, the permeability recovery rate of the composite microbial cement repaired by 1% low-fat pectin is significantly improved, reaching 118.39%. This data shows that the effect of low-fat pectin in improving the impermeability of composite microbial cement is obviously better than that of xanthan gum.

[0108] Comparative Example 5

[0109] This comparative example relates to the reaction speed comparison of the high-activity Sporosarcina pasteurii fermentation broth fermented by YE-MH medium and the Sporosarcina pasteurii fermentation broth fermented by YE-NH4 medium. The composition and content of the YE-NH4 original medium are as follows: yeast extract 20 g / L, ammonium sulfate 10 g / L, 0.13 mol / L Tris, solvent is water, and pH value is adjusted to 9 by HCl; the culture conditions of the YE-NH4 original medium fermentation broth are as follows: 30°C, 200 r / min of shaking bed culture for 24 hours.

[0110] ①1% low-fat pectin of the high-activity Sporosarcina pasteurii fermentation broth fermented by the YE-MH medium and the Sporosarcina pasteurii fermentation broth fermented by the YE-MH4 medium prepared in Example 1 are respectively added to the two kinds of fermentation broths, then the temperature of the constant temperature heating magnetic stirrer is set to 35°C, and the rotating speed is adjusted to 200 rpm for high-speed stirring, the duration is 3 hours, until the low-fat pectin is completely dissolved, and finally the concentration of the two kinds of composite microbial liquids is 1%.

[0111] ②23 g of calcium acetate solid and 9 g of urea are dissolved in distilled water, after complete dissolution, distilled water is added to the solution to a total volume of 100 ml, and finally a nutrient salt solution with 1.5 mol / L of calcium acetate and urea is obtained;

[0112] ③The two kinds of fermentation broths and the nutrient salt are fully mixed in a volume ratio of 1:1, and then placed for 10 minutes;

[0113] ④The uniformly mixed liquid is injected into the crack by using a syringe;

[0114] As Figure 7 shown in the figure, the results show that under the same operating conditions, the broth cultured by the YE-MH medium shows higher whiteness within 10 minutes, that is, the calcium carbonate production rate is significantly faster. The composite microbial cement using the broth cultured by the YE-NH4 medium does not show obvious white precipitate within 10 minutes. The 10-minute experimental group has already started the repair process, while the control group has not yet repaired. It can be seen that the composite microbial cement using the broth fermented by the YE-MH medium has more advantages in the repair speed.

[0115] At the same time, by comparing Examples 1-3 and Comparative Examples 4-5, it can be seen that the YE-MH pasteurian sporosarcina culture medium and low-fat pectin in the method of the present invention have a synergistic effect, which can synergistically improve the repair speed, application range and anti-seepage performance of microbial cement.

[0116] Experimental results:

[0117] according to Figure 3 The data showed that the bacterial liquid of Bacillus pasteurianus fermented with the culture medium provided by the present invention exhibited higher biomass and enzyme activity, both of which were more than twice as high as those of the original culture medium. Figure 4 It shows that after three rounds of repair, composite microbial cement successfully repaired 0.3 mm concrete cracks, while ordinary microbial cement still failed to achieve this repair effect. Figure 2 and Figure 5 Results showed that concrete specimens repaired with composite microbial cement achieved an impermeability recovery rate of 118.4%, significantly exceeding the 40.5% achieved with high-permeability epoxy resin. Replacing low-fat pectin with xanthan gum reduced its impermeability by approximately 50%, demonstrating that low-fat pectin is significantly more effective than xanthan gum in improving the impermeability of composite microbial cement.

[0118] This invention proposes a method for preparing a composite microbial cement with a short repair cycle and strong impermeability. This method effectively addresses the shortcomings of conventional microbial cement in terms of repair speed, application range, and impermeability. This innovative technology lays a solid foundation for future developments in the field of concrete repair.

[0119] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing a composite microbial cement with a short repair cycle and strong impermeability, characterized by: The composite microbial cement is composed of composite bacterial liquid and nutrient salts; the specific preparation steps are as follows: S1 is configured with YE-MH pasteurian sporosarcina culture medium; S2 prepares a highly active fermentation broth of Sporosarcina pasteurianus; S3 dissolves low-fat pectin in the fermentation liquid to form a composite bacterial liquid; S4 prepares a nutrient salt solution; S5: uniformly mixing the composite bacterial solution with the nutrient salt solution and allowing the mixture to stand for ten minutes to obtain composite microbial cement; The composition and content of the YE-MH culture medium for Sporosarcina pasteurii in S1 are as follows: 30-34 g / L yeast extract, 8-12 g / L ammonium sulfate, 6-8 g / L MH broth, 200 mg-240 mg / L nickel chloride, and water as the solvent; the pH value is adjusted to 8.4-9.1 with NaOH and sterilized. In S2, activation culture was performed using a YE-MH pasteurian sporosarcina culture medium at 28-35°C, 180-220 r / min, and shaking for 15-20 hours. A 2-5% inoculum was inoculated into a YE-MH pasteurian sporosarcina culture medium for expansion culture at 28-35°C, 180-220 r / min, and shaking for 22-26 hours to obtain a highly active pasteurian sporosarcina fermentation broth. The OD of the highly active Sporosarcina pasteurianus fermentation broth 600 above 8; urease activity is above 18 mM / min; In S3, 0.5% to 1.5% of the mass of the fermentation broth low-fat pectin is added to the fermentation broth, and the mixture is stirred at 30 to 35° C. for 2 to 4 hours to completely dissolve the pectin, thereby obtaining a composite bacterial solution; When adding 0.5% to 1.5% of the fermentation liquid mass of low-fat pectin to the fermentation liquid, for cracks in the concrete structure with a width of 0 to 0.5 mm, 0.5% to 1% of the fermentation liquid mass of low-fat pectin is added; and for cracks with a width of 0.5 to 1 mm, 1% to 1.5% of the fermentation liquid mass of low-fat pectin is added; The specific steps of preparing 100 ml of the nutrient salt solution in S4 are as follows: dissolving 20-25 g of calcium acetate solid and 8-10 g of urea in distilled water, and after they are completely dissolved, adding distilled water to the solution to a total volume of 100 ml, thereby finally obtaining the nutrient salt solution; The specific steps of uniformly mixing the composite bacterial solution and the nutrient salt solution and allowing them to stand for ten minutes in S5 are as follows: fully mixing the required volume of nutrient salt solution with an equal volume of the composite bacterial solution to ensure that the composite bacterial solution and the nutrient salt are in full contact and form a stable composite system; allowing the mixed solution to stand at 30°C to 35°C for 8 to 10 minutes to promote the full activity of the microorganisms and ultimately form the composite microbial cement.

2. The composite microbial cement prepared by the preparation method according to claim 1 has a short repair cycle and strong impermeability.

3. Application of the preparation method as claimed in claim 1 in repairing cracks in concrete structures.

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