Microcapsule aggregate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of building materials, and discloses microcapsule aggregate and a preparation method and application thereof.The preparation method comprises the steps that alkali-resisting bacteria are induced to generate spores, the alkali-resisting bacteria containing the spores are subjected to microencapsulation treatment, and microcapsules are formed; mixing gypsum, slag powder, an alkali activator and water to form mixed slurry; and mixing and molding the microcapsules and the mixed slurry, and then performing crushing, vacuumizing and pressurizing treatment to form the microcapsule aggregate. The microcapsule aggregate obtained by microencapsulation of spore-containing alkali-resistant bacteria, addition of microcapsules into mixed slurry, molding, crushing, vacuumizing and pressurization treatment can better protect the alkali-resistant bacteria and improve the vitality of the spore-containing alkali-resistant bacteria, has the advantages of high bacteria loading capacity, high crack closing rate and reusability, and improves the mechanical properties of concrete. The compatibility with a concrete matrix is enhanced, and the cost is relatively low.

Description

Technical Field

[0001] The invention relates to the field of building materials, and in particular to a microcapsule aggregate and a preparation method and application thereof. Background Art

[0002] Bacteria-based self-healing concrete has previously demonstrated satisfactory healing performance. Many bacteria can survive in alkaline environments, such as Bacillus sphaericus, Bacillus pasteurianus, Bacillus subtilis, and Bacillus alkali, which can all be used as healing agents. In order to protect bacteria from the harsh environment, the cells need to be encapsulated in carriers such as hydrogels, porous materials, or microcapsules; among them, the healing agent with hydrogels and microcapsules as carriers has good healing performance, and cracks with a width of 0.97 mm can be completely closed after 56 days of curing. However, the healing agent with hydrogels or microcapsules as carriers may be affected by mechanical damage or chemical reactions during use, resulting in its performance degradation or failure, and cannot be used a second time. When using expanded clay as a bacterial carrier, bacteria are prone to leak from the porous carrier, thereby reducing the healing performance. Summary of the invention

[0003] In view of this, the present invention provides a microcapsule aggregate and a preparation method and application thereof to solve the problem of poor healing performance of existing self-healing concrete. The microcapsule aggregate prepared by the present invention has good mechanical strength, strong crack healing performance, and secondary repair function.

[0004] In a first aspect, the present invention provides a method for preparing a microcapsule aggregate.

[0005] A method for preparing a microcapsule aggregate comprises the following steps:

[0006] Inducing the alkali-resistant bacteria to produce spores, and microencapsulating the alkali-resistant bacteria containing the spores to form microcapsules;

[0007] mixing gypsum, slag, alkaline activator and water to form a mixed slurry;

[0008] The microcapsules and the mixed slurry are mixed and formed, and then crushed, vacuumed and pressurized to form microcapsule aggregates.

[0009] In some optional embodiments, the alkali-resistant bacteria include one or more of Bacillus pasteurianus, Bacillus subtilis, and alkaliphilic Bacillus;

[0010] And / or, the content of alkali-resistant bacteria containing spores in the microcapsule is (1-9)×10 12 pcs / g;

[0011] And / or, the mass ratio of the gypsum, slag and alkaline activator is 400-800:300-500:300-600;

[0012] and / or, the liquid-to-solid ratio of the mixed slurry is 0.7-0.9;

[0013] And / or, the alkaline activator comprises water glass or a mixture of water glass and sodium hydroxide aqueous solution;

[0014] Optionally, in the mixture of water glass and sodium hydroxide aqueous solution, the modulus of the water glass is 2.8-3.4, the concentration of the water glass is 38-42 degrees Baume; the concentration of the sodium hydroxide aqueous solution is 4-12 mol / L; and the mass ratio of the water glass to the sodium hydroxide aqueous solution is 1.5-2.5:1.

[0015] In some optional embodiments, the mass ratio of the microcapsules to the mixed slurry is 1-10:30-100, and optionally, the mass ratio of the microcapsules to the mixed slurry is 1-10:30-80;

[0016] And / or, the crushed material is evacuated to a pressure of -0.7 to -0.9 bar and maintained for 25-35 minutes, then the temperature is raised to 26-30°C and the pressure is increased to 1.0-1.1 bar and maintained for 20-28 hours;

[0017] The particle size of the crushed material is 2.36mm-4.75mm.

[0018] In some optional embodiments, after the alkali-resistant bacteria produce spores, alkali-resistant bacteria containing spores are formed, and the alkali-resistant bacteria containing spores are placed in a sodium chloride solution, and the alkali-resistant bacteria containing spores are mixed with a buffer solution before microencapsulation treatment to obtain a suspension of alkali-resistant bacteria containing spores for microencapsulation treatment;

[0019] Optionally, the buffer comprises a sodium chloride solution;

[0020] Optionally, before mixing with the buffer, the method further includes a step of washing the alkali-resistant bacteria containing spores with a NaCl-peptone buffer;

[0021] Optionally, the bacterial concentration of the alkali-resistant bacterial suspension containing spores is (1-9)×109 CFU / mL.

[0022] In some optional embodiments, the alkali-resistant bacteria are cultured into vegetative cells, and then the alkali-resistant bacteria are induced to produce spores by heat shock;

[0023] Optionally, the culture conditions include: culturing in a constant temperature shaker at 36-38°C for 6-8 days; the shaking frequency of the shaker is 80-120 rpm;

[0024] Optionally, the culture medium used in the culture process includes: 8-12 g / L urea, 2-4 g / L NaHCO3, 2-4 g / L nutrient solution, 15-25 g / L yeast extract, and the balance is water;

[0025] Optionally, the heat shock includes: culturing the nutrient cells in a bacterial culture medium at 78-82°C for a first time for 8-12 minutes, and then immediately placing them in an ice-water mixture to cool for 4-6 minutes; and then culturing them for a second time at 28-32°C for 40-56 hours to allow the alkali-resistant bacteria to produce spores; the spore production rate is above 90%.

[0026] In some optional embodiments, the microencapsulation comprises: mixing a suspension of alkali-resistant bacteria containing spores with a sodium alginate solution, adding a calcium chloride solution, separating the solid from the liquid, and drying the precipitate to obtain microencapsulated alkali-resistant bacteria containing spores;

[0027] Optionally, the precipitate is washed with water, heated to 75-85° C., and then freeze-dried to obtain microencapsulated alkali-resistant bacteria containing spores.

[0028] In some optional embodiments, the concentration of the sodium alginate solution is 18-22 g / L;

[0029] and / or, the volume ratio of the alkali-resistant bacteria suspension containing spores to the sodium alginate solution is 4-8:18-25;

[0030] and / or, the concentration of the calcium chloride solution is 18-22 g / L, and the amount of the calcium chloride solution added is 2-5% of the total weight of the mixture of the spore-containing alkali-resistant bacteria suspension and the sodium alginate solution;

[0031] And / or, the freeze-drying temperature is minus 18°C ​​to minus 22°C, and the freeze-drying time is 20-28h;

[0032] And / or, pre-freezing with liquid ethanol before freeze-drying.

[0033] In some optional embodiments, gypsum and slag are first mixed, and then water is added to form a mixed liquid; then an alkaline activator is added to the mixed liquid to form a mixed slurry;

[0034] And / or, when the microcapsules are mixed with the mixed slurry, they are first stirred at a low speed for 50-70 seconds, and then stirred at a high speed for 110-130 seconds; wherein the low speed is 45-65 r / min; and the high speed is 130-170 r / min;

[0035] And / or, the gypsum is phosphogypsum;

[0036] And / or, the molding is performed by casting, and after casting, the mixture is cured for 5-7 hours and then crushed.

[0037] In a second aspect, the present invention provides a microcapsule aggregate.

[0038] The microcapsule aggregate is prepared by the preparation method.

[0039] In a third aspect, the present invention provides a self-healing concrete, comprising the microcapsule aggregate.

[0040] In a fourth aspect, the present invention provides a microcapsule aggregate prepared by the preparation method or the use of the microcapsule aggregate in building materials.

[0041] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0042] 1. The present invention provides a method for preparing microcapsule aggregate, comprising inducing alkali-resistant bacteria to produce spores, microencapsulating the alkali-resistant bacteria containing the spores to form microcapsules; mixing gypsum, slag, alkaline activator and water to form a mixed slurry; mixing and molding the microcapsules and the mixed slurry, and then crushing, vacuuming and pressurizing to form microcapsule aggregate. The present application adopts alkali-resistant bacteria containing spores, which can survive in harsh environments, and microencapsulates them to achieve a good encapsulation effect; gypsum and slag are used as carriers to improve the bulk density, compressive strength, volume flotation rate and water absorption rate of microcapsule aggregate; alkaline activators activate gypsum and slag, so that more microcapsules can be accommodated in lightweight aggregate; alkali-resistant bacteria containing spores are microencapsulated, the microcapsules are added to the mixed slurry, crushed after molding, and then vacuumed and pressurized to obtain the microcapsule aggregate, which can better protect the alkali-resistant bacteria and improve the activity of the alkali-resistant bacteria containing spores, has a high bacterial load, a high crack closure rate and can be reused, improves the mechanical properties of concrete, enhances compatibility with the concrete matrix, and has a low cost.

[0043] 2. The results show that the 28-day compressive strength of the PC paste prepared with the microcapsule aggregate of the present invention is 18% higher than that of the control group. This shows that the microcapsule aggregate has good compatibility with other materials in the concrete when the concrete containing the microcapsule aggregate of the present invention is used to pave the road, and the paved road is relatively strong and has good chemical stability.

[0044] 3. The microcapsule aggregate of the present invention has strong crack healing performance. After 5 dry-wet cycles, for cracks several hundred microns wide, the crack closure rate is as high as 93%, and the water permeability reduction rate is as high as 80%. Microstructure observation shows that along the crack surface to the inside, layered rhombic calcite is densely formed along the crack as a whole. These highlight the effectiveness of the proposed functional graded immobilized microbial aggregate microcapsule aggregate for self-healing concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 This is the microscopic examination result of the alkali-resistant bacteria containing spores in Example 1 of the present invention;

[0047] Figure 2 This is a SEM image of the finished microcapsule aggregate of Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0049] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0050] In the present invention, w / v represents the mass-to-volume ratio, the unit of W is gram (g), and the unit of V is milliliter (mL).

[0051] The liquid-to-solid ratio is the mass ratio of liquid to solid.

[0052] The secondary healing effect of the healing agent with hydrogel or microcapsule as carrier is poor. In order to enable the self-healing concrete to self-heal multiple times, the present invention intends to study the self-healing agent with expanded clay (LWA) as carrier.

[0053] When LWA is used as a bacterial carrier, since this lightweight aggregate has open pores of about 10 μm, bacteria may leak out, thereby reducing the healing ability. The present invention studies a suitable encapsulation method using expanded clay as a carrier, and only uses vacuum and pressure treatment to penetrate the bacteria into the pores of EC LWA. Although it can reduce the leakage of high bacteria from the porous carrier, it requires a higher vacuum degree and a larger pressure, and the effect is not significant, and the price of the healing agent is relatively expensive.

[0054] In order to increase the bacterial loading capacity, the present invention proposes to use expanded clay lightweight aggregate (EC LWA) as a carrier, but high-temperature sintering is required during the production process, which consumes a lot of energy, making the price of EC LWA expensive.

[0055] In order to solve the above technical problems, the present invention provides a method for preparing microcapsule aggregate.

[0056] The preparation method of microcapsule aggregate comprises the following steps:

[0057] Inducing the alkali-resistant bacteria to produce spores, and microencapsulating the alkali-resistant bacteria containing the spores to form microcapsules;

[0058] mixing gypsum, slag, alkaline activator and water to form a mixed slurry;

[0059] The microcapsules and the mixed slurry are mixed and formed, and then crushed, vacuumed and pressurized to form microcapsule aggregates.

[0060] The purpose of the present invention is to find a better bacterial carrier for preparing self-healing concrete, so that the cost of the bacterial carrier is low, the bacterial load is high, and it can be reused, paving the way for self-healing research in the construction industry.

[0061] Microorganisms that can grow under alkaline pH conditions, but whose optimum value is not necessarily in the alkaline pH range, are called alkali-resistant bacteria. In order to adapt to the harsh environment of concrete, the present invention selects spore-containing alkali-resistant bacteria to prepare the self-healing agent, because the spore form of bacteria is not very sensitive to the environment and can survive in harsh environments.

[0062] By microencapsulating the alkali-resistant bacteria containing spores, a better encapsulation effect can be achieved without using a high vacuum degree and a high pressure.

[0063] In the present invention, gypsum and slag are used as carriers to immobilize the microbial agent, thereby improving the bulk density, compressive strength, volume flotation rate and water absorption rate of the microcapsule aggregate, thereby affecting the working performance of the concrete.

[0064] The present invention uses an alkaline activator to activate gypsum and slag, so that the lightweight aggregate can accommodate more bacterial spores, so that the microcapsules have a secondary repair function, and avoid the energy consumption caused by high-temperature calcination, reduce the cost and have similar pore characteristics to expanded clay lightweight aggregate (EC LWA).

[0065] During the preparation process, the alkali-resistant bacteria containing spores are microencapsulated, the microcapsules are added to the mixture slurry and mixed, and then crushed after molding to obtain microcapsule aggregates with immobilized microorganisms. This method effectively improves the mechanical strength of lightweight aggregates, enhances the crack healing performance, makes the repair effect more significant, and the cracks are almost completely filled. At the same time, the microcapsules have a secondary repair function, avoiding the problem of traditional lightweight aggregates failing after one repair, improving the secondary repair rate of cracks, improving the compressive strength recovery rate, and effectively increasing the healing rate of cracks. Overall, the present application has achieved significant technical effects in improving concrete.

[0066] In summary, the present application adopts alkali-resistant bacteria containing spores, which can survive in harsh environments, and microencapsulates them to achieve a good encapsulation effect; gypsum and slag are used as carriers to improve the bulk density, compressive strength, volume flotation rate and water absorption rate of the microcapsule aggregate; the alkaline activator activates the gypsum and slag, so that more microcapsules can be accommodated in the lightweight aggregate; the alkali-resistant bacteria containing spores are microencapsulated, the microcapsules are added to the mixed slurry, crushed after molding, and then vacuumed and pressurized to obtain the microcapsule aggregate, which can better protect the alkali-resistant bacteria and improve the activity of the alkali-resistant bacteria containing spores, has a high bacterial load, a high crack closure rate and can be reused, improves the mechanical properties of concrete, enhances compatibility with the concrete matrix, and has a low cost.

[0067] The results showed that the 28-day compressive strength of the hardened PC paste containing immobilized microbial aggregates was 18% higher than that of the control group. This indicates that the immobilized microbial aggregates are strong and highly compatible with the PC matrix. The newly developed functional graded immobilized microbial aggregates have good chemical stability and are compatible with the surrounding PC matrix. Moreover, they have strong crack healing properties. After 5 dry-wet cycles, the crack closure rate is as high as 93% and the water permeability reduction rate is as high as 80% for cracks with a width of several hundred microns. Microstructural observations show that layered rhombic calcite is densely formed along the crack surface to the inside. These highlight the effectiveness of the proposed functional graded immobilized microbial aggregate capsules for self-healing concrete.

[0068] In some embodiments, the alkali-resistant bacteria include one or more of Bacillus pasteurianus, Bacillus subtilis, and alkaliphilic Bacillus;

[0069] And / or, the content of alkali-resistant bacteria containing spores in the microcapsule is (1-9)×10 12 pcs / g;

[0070] And / or, the mass ratio of the gypsum, slag and alkaline activator is 400-800:300-500:300-600; the mixing ratio of gypsum and slag can improve the mechanical strength and crack healing performance of lightweight aggregate, and avoid the problem of failure of traditional microbial carrier repair after one time;

[0071] and / or, the liquid-to-solid ratio of the mixed slurry is 0.7-0.9;

[0072] And / or, the alkaline activator comprises water glass or a mixture of water glass and sodium hydroxide aqueous solution;

[0073] Optionally, in the mixture of water glass and sodium hydroxide aqueous solution, the modulus of the water glass is 2.8-3.4, the concentration of the water glass is 38-42 degrees Baume; the concentration of the sodium hydroxide aqueous solution is 4-12 mol / L; and the mass ratio of the water glass to the sodium hydroxide aqueous solution is 1.5-2.5:1.

[0074] In some embodiments, the particle size of the slag is 30 μm or less;

[0075] The components of the slag mainly include silicon dioxide, aluminum oxide, calcium oxide, iron oxide and magnesium oxide.

[0076] In some embodiments, the mass ratio of the microcapsules to the mixed slurry is 1-10:30-100, and optionally, the mass ratio of the microcapsules to the mixed slurry is 1-10:30-80;

[0077] And / or, the crushed material is evacuated to a pressure of -0.7 to -0.9 bar and maintained for 25-35 minutes, then the temperature is raised to 26-30°C and the pressure is increased to 1.0-1.1 bar and maintained for 20-28 hours; the particle size of the crushed material is 2.36 mm-4.75 mm.

[0078] In some embodiments, after the alkali-resistant bacteria produce spores, alkali-resistant bacteria containing spores are formed, and the alkali-resistant bacteria containing spores are placed in a sodium chloride solution to obtain a suspension of alkali-resistant bacteria containing spores for microencapsulation treatment;

[0079] Among them, the alkali-resistant bacteria containing spores are washed with 0.05-0.15 g / L NaCl-peptone buffer and then placed in a sodium chloride solution;

[0080] And / or, the concentration of the alkali-resistant bacterial suspension containing spores is (1-9)×10 9 CFU / mL.

[0081] In some embodiments, the alkali-resistant bacteria are cultured into vegetative cells and then spore production is induced in the alkali-resistant bacteria by heat shock;

[0082] The culture conditions include: culturing in a constant temperature shaker at 36-38°C for 6-8 days; the shaking frequency of the shaker is 80-120 rpm;

[0083] The culture medium includes: 8-12 g / L urea, 2-4 g / L NaHCO3, 2-4 g / L nutrient solution, 15-25 g / L yeast extract, and the balance is water;

[0084] And / or, the heat shock specifically includes: culturing the nutrient cells in a bacterial culture medium at 78-82°C for a first time for 8-12 minutes, and then immediately placing them in an ice-water mixture for cooling for 4-6 minutes; and then culturing them for a second time at 28-32°C for 40-56 hours to allow the alkali-resistant bacteria to produce spores; the spore production rate is above 90%.

[0085] Alkali-resistant bacteria are added to the above culture medium to be cultured into nutrient cells, and then spores are produced by inducing the alkali-resistant bacteria through heat shock, and alkali-resistant bacteria containing spores are formed after centrifugation; the centrifugation conditions are: centrifugation at 4°C and 8000rpm for 15 minutes.

[0086] Spores need to germinate into vegetative cells before they can actively heal cracks. Yeast extracts, which are usually used as germination agents, can affect the mechanical properties of concrete or mortar. Therefore, it is preferred to first use yeast culture medium to culture alkali-resistant bacteria into vegetative cells and then produce spores as a healing agent, without adding yeast extract to LWA for the germination process.

[0087] In some embodiments, the microencapsulation comprises: mixing a suspension of alkali-resistant bacteria containing spores with a sodium alginate solution, adding a calcium chloride solution, separating the solid from the liquid, washing the precipitate with water, heating it to 75-85° C., and then freeze-drying it to obtain microencapsulated alkali-resistant bacteria containing spores.

[0088] Sodium alginate is used as an encapsulation material in the present invention to encapsulate bacterial spores. The role of calcium chloride is to form gel beads, which form spores encapsulated by sodium alginate through ionic crosslinking. First, the mixed solution is dripped into a hardening solution containing calcium chloride in order to form gel beads through ionic crosslinking, and the spores encapsulated by sodium alginate are fixed in the gel beads. Then, the calcium chloride residue on the surface is removed by water washing to eliminate the influence of calcium chloride on subsequent steps, and to ensure that the final prepared capsule does not contain excess calcium chloride, so as to ensure the quality and stability of the product. This step is conducive to the formation of gel beads and the quality control of the final product.

[0089] In some embodiments, the concentration of the sodium alginate solution is 18-22 g / L;

[0090] and / or, the volume ratio of the alkali-resistant bacteria suspension containing spores to the sodium alginate solution is 4-8:18-25;

[0091] and / or, the concentration of the calcium chloride solution is 18-22 g / L, and the amount of the calcium chloride solution added is 2-5% of the total weight of the mixture of the spore-containing alkali-resistant bacteria suspension and the sodium alginate solution;

[0092] And / or, the freeze-drying temperature is minus 18°C ​​to minus 22°C, and the freeze-drying time is 20-28h;

[0093] And / or, pre-freezing with liquid ethanol before freeze-drying.

[0094] In some embodiments, gypsum and slag are first mixed, and then water is added to form a mixed liquid; then an alkaline activator is added to the mixed liquid to form a mixed slurry;

[0095] And / or, when the microcapsules are mixed with the mixed slurry, they are first stirred at a low speed for 50-70 seconds, and then stirred at a high speed for 110-130 seconds; wherein the low speed is 45-65 r / min; and the high speed is 130-170 r / min;

[0096] And / or, the molding is performed by casting, and after casting, the mixture is cured for 5-7 hours and then crushed.

[0097] The present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0098] The original bacteria of Bacillus pasteurianus used in the examples and comparative examples of the present invention were purchased from Shanghai Collection of Microorganisms Center and are numbered as ATCC11859.

[0099] Bacillus subtilis was obtained from Shanghai Microbiological Collection Center (SHMCC), with strain number: SHMCC (SHBCC) D25055.

[0100] The alkaliphilic Bacillus was obtained from Shanghai Collection of Microorganisms Center (SHMCC), with the strain number SHMCC (SHBCC) D53320.

[0101] The modulus of water glass is 2.8-3.4, and the concentration of water glass is 38-42 degrees Baume.

[0102] The slag is S75 slag powder produced by Yuxi Sanhe New Building Materials Technology Co., Ltd., and its main components include silicon dioxide, aluminum oxide, calcium oxide, iron oxide and magnesium oxide.

[0103] The nutrient solution is composed of 1% tryptone, 0.5% yeast extract, 1% sodium chloride by weight, and the balance is water.

[0104] The specific composition of the bacterial culture medium is 10g / L urea, 2.12g / L NaHCO3, 20g / L yeast extract, and 3g / L nutrient solution. The nutrient solution is composed of 1% tryptone, 0.5% yeast extract, 1% sodium chloride by weight, and the balance is water.

[0105] Example 1

[0106] The present invention provides a microcapsule aggregate, and the preparation method thereof comprises the following steps:

[0107] (1) Preparation of Bacillus pasteurianus suspension containing spores

[0108] S11, incubation: Bacillus pasteurianus was placed in a bacterial culture medium and mixed, and cultured in a water bath shaker at a constant temperature of 37° C. The shaking frequency of the shaker was set to 100 rpm, and the duration was 7 days to obtain a nutrient cell solution, and the OD600 of the nutrient cell solution was detected by a spectrophotometer to be 1.6;

[0109] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0110] S12, inducing spore formation by heat shock, specifically: culturing the nutrient cell solution in a bacterial culture medium at 80°C for 10 minutes, with the volume ratio of the nutrient cell solution to the bacterial culture medium being 1:10, and immediately cooling the solution in ice water to 0°C for 5 minutes; culturing the solution for a second time at 30°C (optimal spore production temperature) for 2 days to obtain a Bacillus pasteurianus solution containing spores, and the spore production rate was detected to be 95%;

[0111] Detection method of sporulation rate: Gram stain the solution of Bacillus pasteurianus containing spores, observe under a microscope to confirm whether spores are formed and the number of bacteria and spores, and compare the number of bacteria and spores before incubation and after the second incubation to calculate the sporulation rate; Figure 1 It is the result of microscopic examination of a solution of Bacillus pasteurianus containing spores;

[0112] S13, centrifuging the pasteurian spore-containing Bacillus solution at 4°C and 8000 rpm for 15 min to obtain the pasteurian spore-containing Bacillus, washing the pasteurian spore-containing Bacillus with 0.1% (w / v) NaCl-peptone buffer, and storing it in 4°C 0.85% (w / v) NaCl solution to obtain a concentration of 5×10 9 CFU / mL suspension of Bacillus pasteurianus containing spores;

[0113] (2) Preparation of microencapsulated spore-containing Bacillus pasteurianus:

[0114] 6 mL of the pasteurian spore-containing Bacillus suspension obtained in step (1) is mixed with 20 mL of a 2% (w / v) sodium alginate solution, and the mixed solution is dripped into a 20 g / L calcium chloride solution, wherein the amount of the calcium chloride solution added is 3% of the total weight of the mixed solution of the pasteurian spore-containing Bacillus suspension and the sodium alginate solution, and the solid-liquid separation is performed to obtain a precipitate as gel beads; the gel beads are washed with distilled water to eliminate the calcium chloride residue on the surface, the washed gel beads are heated to 80° C., placed in liquid ethanol and frozen to form a gel bead ethanol solution (during which part of the ethanol is sublimated), and then freeze-dried at -20° C. for 24 h to obtain microencapsulated pasteurian spore-containing Bacillus (diameter 100 μm-1000 μm), wherein the content of alkali-resistant bacteria containing spores in the microcapsules is 5×10 12 / g; Detection method: grind 10g of freeze-dried microcapsules, add 100g of 0.9% physiological saline, mix evenly, and then examine under a microscope to obtain the number of alkali-resistant bacteria; according to the formula: the content of alkali-resistant bacteria containing spores in microcapsules = the number of alkali-resistant bacteria / the weight of microcapsules, the content of alkali-resistant bacteria containing spores in microcapsules is 1×10 12 / g; stored in a desiccator for future use; adding liquid ethanol can remove water from the surface of the gel beads by partial ethanol sublimation, which is convenient for subsequent freeze-drying treatment and helps to increase the spore content in the lightweight aggregate;

[0115] (3) Preparation of lightweight aggregate, including the following steps:

[0116] S31, mixing 600 g of dried and sieved phosphogypsum and 400 g of slag powder (GGBS) to form a mixed material, and adding water to the mixed material to form a mixed liquid with a liquid-to-solid ratio of 0.78;

[0117] The mixed liquid is mixed with 450g of alkaline activator (water glass and 4 mol / L sodium hydroxide solution in a weight ratio of 1.5:1) ， The mixture was stirred in a cement slurry mixer for 4 minutes to form a mixed slurry, and the microencapsulated spore-containing Bacillus pasteurianus obtained in step (2) was mixed with the mixed slurry at a weight ratio of 5:55, and the mixture was first stirred at a low speed of 55 r / min for 60 seconds, and then stirred at a high speed of 150 r / min for 120 seconds to form a mixture;

[0118] S32, immediately casting the mixture into a mold, and then curing it at 20° C. and a relative humidity (RH) of 40% for 6 hours to form a solid substrate;

[0119] S33, crushing the solid base material in a jaw crusher, sieving, screening out particles with a particle size of 2.36 mm-4.75 mm, and obtaining a semi-finished microcapsule aggregate.

[0120] (4) The lightweight aggregate obtained in step (3) is placed in a sealed bottle, evacuated to a vacuum pressure of -0.8 bar, and the vacuum pressure is maintained for 30 minutes, and then the temperature is raised to 28° C. and the pressure is increased to 1 bar and maintained for 24 hours to form a microcapsule aggregate product. Figure 2 This is the SEM image (scanning electron microscope image) of the finished microcapsule aggregate.

[0121] Example 2

[0122] The present invention provides a microcapsule aggregate, and the preparation method thereof comprises the following steps:

[0123] (1) Preparation of bacterial spore suspension

[0124] S11, incubation: Bacillus subtilis was placed in a bacterial culture medium and mixed, and cultured in a water bath shaker at a constant temperature of 36° C. The shaking frequency of the shaker was set to 120 rpm, and the duration was 6 days to obtain a nutrient cell solution, and the OD600 of the nutrient cell solution was detected by a spectrophotometer to be 1.5;

[0125] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0126] S12, inducing spore formation by heat shock, specifically: culturing the nutrient cell solution in a bacterial culture medium at 75°C for 12 minutes, with the volume ratio of the nutrient cell solution to the bacterial culture medium being 1:10, and immediately placing it in ice water to cool to 0°C for 5 minutes; culturing it for a second time at 28°C (optimal spore production temperature) for 56 hours to obtain a bacterial spore solution, and the spore production rate was detected to be 95%;

[0127] Detection method of sporulation rate: Gram stain the bacterial spore solution, observe under a microscope to confirm whether spores are formed and the number of bacteria and spores, and compare the number of bacteria and spores before incubation and after the second culture to calculate the sporulation rate;

[0128] S13, centrifuging the bacterial spore solution at 4°C and 8000 rpm for 15 min to obtain bacterial spores, washing the bacterial spores with 0.15% (w / v) NaCl-peptone buffer, and storing them in 4°C 0.85% (w / v) NaCl solution to obtain a concentration of 9×10 9 CFU / mL bacterial spore suspension;

[0129] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0130] (2) Preparation of microencapsulated bacterial spores:

[0131] 4 mL of the bacterial spore suspension obtained in step (1) is mixed with 25 mL of a 1.8% (w / v) sodium alginate solution, and the mixed solution is dripped into a 18 g / L calcium chloride solution, wherein the amount of the calcium chloride solution added is 5% of the total weight of the mixed solution of the bacterial spore suspension and the sodium alginate solution, and the solid-liquid separation is performed to obtain a precipitate as gel beads; the gel beads are washed with distilled water to eliminate the calcium chloride residue on the surface, the washed gel beads are heated to 80° C., placed in liquid ethanol and frozen to form a gel bead ethanol solution (during which part of the ethanol is sublimated), and then freeze-dried at -22° C. for 20 h to obtain microencapsulated bacterial spores (with a diameter of 100 μm-1000 μm), wherein the content of alkali-resistant bacteria containing spores in the microcapsules is 9×10 12 / g; stored in a desiccator for later use;

[0132] (3) Preparation of lightweight aggregate, including the following steps:

[0133] S31, mixing 400 g of dried and sieved phosphogypsum and 500 g of slag powder (GGBS) to form a mixed material, and adding water to the mixed material to form a mixed liquid with a liquid-to-solid ratio of 0.7;

[0134] The mixed liquid and 300 g of an alkaline activator (water glass and 12 mol / L sodium hydroxide solution in a weight ratio of 2.5:1) were mixed in a cement slurry mixer for 4 min to form a mixed slurry, and the mixed slurry was mixed with the microencapsulated bacterial spores obtained in step (2) in a weight ratio of 30:1, first stirred at a low speed of 55 r / min for 60 s, and then stirred at a high speed of 150 r / min for 120 s to form a mixture;

[0135] S32, immediately casting the mixture into a mold, and then curing it at 20° C. and a relative humidity (RH) of 40% for 5 hours to form a solid substrate;

[0136] S33, crushing the solid base material in a jaw crusher, sieving, screening out particles with a particle size of 2.36 mm-4.75 mm, and obtaining a semi-finished microcapsule aggregate.

[0137] (4) The lightweight aggregate obtained in step (3) is placed in a sealed bottle, and the vacuum is evacuated to a vacuum pressure of -0.7 bar. After the vacuum pressure is maintained for 35 minutes, the temperature is raised to 28° C. and the pressure is increased to 1.1 bar and maintained for 20 hours to form a finished microcapsule aggregate.

[0138] The lightweight aggregate prepared by the present invention has good mechanical strength and strong crack healing performance, and the microcapsules inside the aggregate have a secondary repair function, thereby avoiding the failure of traditional microbial carriers after one repair.

[0139] Example 3

[0140] The present invention provides a microcapsule aggregate, and the preparation method thereof comprises the following steps:

[0141] (1) Preparation of bacterial spore suspension

[0142] S11, incubation: putting the alkaliphilic Bacillus into the bacterial culture medium and mixing, culturing in a water bath shaker at a constant temperature of 38° C., setting the shaking frequency of the shaker to 80 rpm, and the duration of culturing for 8 days to obtain a nutrient cell solution, and detecting the OD600 of the nutrient cell solution with a spectrophotometer to be 1.7;

[0143] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0144] S12, inducing spore formation by heat shock, specifically: culturing the nutrient cell solution in a bacterial culture medium at 82°C for 8 minutes, with the volume ratio of the nutrient cell solution to the bacterial culture medium being 1:10, and immediately placing it in ice water to cool to 0°C for 5 minutes; and then culturing it for a second time at 32°C (optimal spore production temperature) for 40 hours to obtain a bacterial spore solution, and the spore production rate was detected to be 95%;

[0145] Detection method of sporulation rate: Gram stain the bacterial spore solution, observe under a microscope to confirm whether spores are formed and the number of bacteria and spores, and compare the number of bacteria and spores before incubation and after the second culture to calculate the sporulation rate;

[0146] S13, centrifuging the bacterial spore solution at 4°C and 8000 rpm for 15 min to obtain bacterial spores, washing the bacterial spores with 0.05% (w / v) NaCl-peptone buffer, and storing them in 4°C 0.85% (w / v) NaCl solution to obtain a concentration of 9×10 9 CFU / mL bacterial spore suspension;

[0147] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0148] (2) Preparation of microencapsulated bacterial spores:

[0149] 8 mL of the bacterial spore suspension obtained in step (1) is mixed with 18 mL of a 2.2% (w / v) sodium alginate solution, and the mixed solution is dripped into a 22 g / L calcium chloride solution, wherein the amount of the calcium chloride solution added is 2% of the total weight of the mixed solution of the bacterial spore suspension and the sodium alginate solution, and the solid-liquid separation is performed to obtain a precipitate as gel beads; the gel beads are washed with distilled water to eliminate the calcium chloride residue on the surface, the washed gel beads are heated to 80° C., placed in liquid ethanol and frozen to form a gel bead ethanol solution (during which part of the ethanol is sublimated), and then freeze-dried at -18° C. for 28 h in a freeze dryer to obtain microencapsulated bacterial spores (with a diameter of 100 μm-1000 μm), which are stored in a dryer for standby use; the content of alkali-resistant bacteria containing spores in the microcapsules is 1×10 12 pcs / g;

[0150] (3) Preparation of lightweight aggregate, including the following steps:

[0151] S31, mixing 800 g of dried and sieved phosphogypsum and 300 g of slag powder (GGBS) to form a mixed material, and adding water to the mixed material to form a mixed liquid with a liquid-to-solid ratio of 0.9;

[0152] The mixed liquid and 600 g of alkaline activator are mixed in a cement slurry mixer for 4 min to form a mixed slurry, and the mixed slurry is mixed with the microencapsulated bacterial spores obtained in step (2) at a mass ratio of 55:5, first stirred at a low speed of 45 r / min for 60 s, and then stirred at a high speed of 130 r / min for 120 s to form a mixture;

[0153] S32, immediately casting the mixture into a mold, and then curing it at 20° C. and a relative humidity (RH) of 40% for 7 hours to form a solid substrate;

[0154] S33, crushing the solid base material in a jaw crusher, sieving, screening out particles with a particle size of 2.36 mm-4.75 mm, and obtaining a semi-finished microcapsule aggregate.

[0155] (4) The lightweight aggregate obtained in step (3) is placed in a sealed bottle, and the vacuum is evacuated to a vacuum pressure of -0.9 bar. After the vacuum pressure is maintained for 25 minutes, the temperature is raised to 30° C. and the pressure is increased to 1 bar and maintained for 28 hours to form a finished microcapsule aggregate product.

[0156] The lightweight aggregate prepared by the present invention has good mechanical strength and strong crack healing performance, and the microcapsules inside the aggregate have a secondary repair function, thereby avoiding the failure of traditional microbial carriers after one repair.

[0157] Example 4

[0158] The present invention provides a microcapsule aggregate, and the preparation method thereof comprises the following steps:

[0159] (1) Preparation of bacterial spore suspension

[0160] S11, incubation: Bacillus pasteurianus was placed in a bacterial culture medium and mixed, and cultured in a water bath shaker at a constant temperature of 37° C. The shaking frequency of the shaker was set to 100 rpm, and the duration was 7 days to obtain a nutrient cell solution, and the OD600 of the nutrient cell solution was detected by a spectrophotometer to be 1.6;

[0161] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0162] S12, inducing spore formation by heat shock, specifically: culturing the nutrient cell solution in a bacterial culture medium at 80°C for 10 minutes, with the volume ratio of the nutrient cell solution to the bacterial culture medium being 1:10, and immediately cooling the solution in ice water for 5 minutes to 0°C; culturing the solution in a bacterial culture medium at 30°C (optimal spore production temperature) for 2 days for a second time to obtain Bacillus pasteurianus containing spores, with a spore production rate of 93%;

[0163] Detection method of sporulation rate: Gram staining of spore-containing Bacillus pasteurianus is performed, and microscopic observation is used to confirm whether spores are formed and the number of bacteria and spores. The number of bacteria and spores before incubation and after the second incubation is compared to calculate the sporulation rate;

[0164] S13, centrifuging the pasteurian spore-containing Bacillus at 4°C and 8000 rpm for 15 min to obtain the pasteurian spore-containing Bacillus, washing the pasteurian spore-containing Bacillus with 0.1% (w / v) NaCl-peptone buffer, and storing it in 4°C 0.85% (w / v) NaCl solution to obtain a concentration of 5×10 9 CFU / mL suspension of Bacillus pasteurianus containing spores;

[0165] The specific composition of the bacterial culture medium is 10 g / L urea, 2.12 g / L NaHCO3, 3 g / L nutrient solution, 20 g / L yeast extract, and the balance is water;

[0166] (2) Preparation of microencapsulated bacterial spores:

[0167] 6 mL of the pasteurian spore-containing Bacillus suspension obtained in step (1) is mixed with 20 mL of a 2% (w / v) sodium alginate solution, and the mixed solution is dripped into a 20 g / L calcium chloride solution, wherein the amount of the calcium chloride solution added is 3% of the total weight of the mixed solution of the pasteurian spore-containing Bacillus suspension and the sodium alginate solution, and the solid-liquid separation is performed to obtain a precipitate as gel beads; the gel beads are washed with distilled water to eliminate the calcium chloride residue on the surface, the washed gel beads are heated to 80° C., placed in liquid ethanol and frozen to form a gel bead ethanol solution (during which part of the ethanol is sublimated), and then freeze-dried at -20° C. for 24 h to obtain microencapsulated pasteurian spore-containing Bacillus (diameter 100 μm-1000 μm), wherein the content of alkali-resistant bacteria containing spores in the microcapsules is 5×10 12 / g; stored in a desiccator for later use;

[0168] (3) Preparation of lightweight aggregate, including the following steps:

[0169] S31, mixing 800 g of dried and sieved phosphogypsum and 600 g of blast furnace slag powder (GGBS) to form a mixed material, and adding water to the mixed material to form a mixed liquid with a liquid-to-solid ratio of 0.78;

[0170] The mixed liquid and 450 g of an alkaline activator (water glass and 4 mol / L sodium hydroxide solution in a weight ratio of 1.5:1) were mixed in a cement slurry mixer for 4 min to form a mixed slurry, and the mixed slurry was mixed with the microencapsulated bacterial spores obtained in step (2) in a weight ratio of 100:1, first stirred at a low speed of 55 r / min for 60 s, and then stirred at a high speed of 150 r / min for 120 s to form a mixture;

[0171] S32, immediately casting the mixture into a mold, and then curing it at 20° C. and a relative humidity (RH) of 40% for 6 hours to form a solid substrate;

[0172] S33, crushing the solid base material in a jaw crusher, sieving, screening out particles with a particle size of 2.36 mm-4.75 mm, and obtaining a semi-finished microcapsule aggregate.

[0173] (4) The lightweight aggregate obtained in step (3) is placed in a sealed bottle, and the vacuum is evacuated to a vacuum pressure of -0.8 bar. After the vacuum pressure is maintained for 30 minutes, the temperature is raised to 28° C. and the pressure is increased to 1 bar and maintained for 24 hours to form a finished microcapsule aggregate.

[0174] The lightweight aggregate prepared by the present invention has good mechanical strength and strong crack healing performance, and the microcapsules inside the aggregate have a secondary repair function, thereby avoiding the failure of traditional microbial carriers after one repair.

[0175] Comparative Example 1

[0176] This comparative example provides a method for preparing aggregate, which differs from Example 3 in that step (2) is omitted, and in step (3), the microencapsulated bacterial spores are replaced by the spores obtained in step (1) at a concentration of 10 9 The CFU / mL bacterial spore suspension was mixed with the mixed slurry at a mass ratio of 5:55, and the remaining preparation steps and process conditions were the same as those in Example 3.

[0177] Comparative Example 2

[0178] This comparative example provides a method for preparing a microcapsule aggregate, which differs from Example 3 in that the addition of phosphogypsum is omitted in step (3), and the remaining preparation steps and process conditions are the same as those in Example 3.

[0179] Comparative Example 3

[0180] This comparative example provides a method for preparing a microcapsule aggregate, which differs from Example 3 in that S12 and the step of inducing spore formation by heat shock are omitted in step (1), and the remaining preparation steps and process conditions are the same as those in Example 3.

[0181] Comparative Example 4

[0182] This comparative example provides a method for preparing a microcapsule aggregate, which differs from Example 3 in that the addition of slag powder is omitted in step (3), and the remaining preparation steps and process conditions are the same as those in Example 3.

[0183] Comparative Example 5

[0184] This comparative example provides a method for preparing a microcapsule aggregate, which differs from Example 3 in that the addition of an alkaline activator is omitted in step (3), and the remaining preparation steps and process conditions are the same as those in Example 3.

[0185] Comparative Example 6

[0186] This comparative example provides a lightweight aggregate, which differs from Example 1 in that step (4) is omitted, and the microorganisms are not immobilized by pressurization. The remaining preparation steps and process conditions are the same as those of Example 3.

[0187] The curing conditions in the following tests are all standard curing conditions, that is, the temperature is 20±2℃ and the relative humidity is above 95%.

[0188] Experimental Example 1

[0189] The aggregate products prepared in the above Examples 1-4 and Comparative Examples 1-6 were subjected to compressive strength tests according to the "Test Method for Compressive Strength of Building Materials" issued by the Standardization Administration of the People's Republic of China, and saturated water absorption tests were performed according to the test methods in the "JGJ51-2002 Technical Specification for Lightweight Aggregate Concrete" and "GBT50224-2018 Construction Quality Acceptance Standard for Building Corrosion Protection Projects". The results are shown in the table below.

[0190] The aggregates prepared in the above Examples 1-4 and Comparative Examples 1-6 were respectively used to prepare concrete test blocks according to the following method: 295 kg of cement, 158 kg of water, 1000 kg of gravel, 395 kg of aggregate, 400 kg of sand, 95 kg of fly ash, and 6.63 kg of conventional polycarboxylic acid alkali water agent were weighed according to the following weight proportions; the cement, gravel, sand, fly ash, polycarboxylic acid alkali water agent and aggregate were evenly mixed, and water was added to mix evenly to form concrete slurry, and the concrete slurry was poured into a mold, and a cubic concrete test block (referred to as cube) with a side length of 150 mm was made according to the "Standard for Test Methods for Mechanical Properties of Ordinary Concrete" GB / T50081-2002. Under standard curing conditions (temperature 20±2°C, relative humidity above 95%), after curing for 28 days and 90 days, the compressive strength at 28 days (28d) and 90 days (90d) was tested using a servo pressure testing machine, and the saturated water absorption was tested at the same time. Three replicates were prepared for each test, and the results were averaged. The results are shown in Table 1 below.

[0191] Table 1 Performance test results of various embodiments and comparative examples

[0192]

[0193] As can be seen from the above table, the compressive strength of the concrete test block made of the microcapsule aggregate prepared in Example 1 is the highest. When the content ratio of phosphogypsum to slag powder in Example 4 is too high, the compressive strength of the concrete will be slightly reduced, but the saturated water absorption rate will be increased. This is because when the slag powder content is too high, the phosphogypsum cannot be better bonded, resulting in a higher overall porosity of the concrete and an insufficiently dense structure, thereby reducing the compressive strength of the structure and increasing the water absorption rate of the structure; the compressive strength of the aggregate in Comparative Example 1 is relatively low, because the microorganisms are not microencapsulated, a part of the microorganisms will directly contact the external environment, and will not be fully protected. The microorganisms will die to a certain extent, and calcium carbonate precipitation cannot be induced to fill the pores between the structures, resulting in reduced strength; no phosphogypsum is added to the aggregate in Comparative Example 2, resulting in a decrease in the number of microorganisms in the aggregate, which has a certain impact on the strength of the structure, resulting in a lower compressive strength. The phosphogypsum has the characteristic of high porosity, which can provide more space for the attachment of microorganisms; the compressive strength of the aggregate in Comparative Example 3 is relatively low, because the microorganisms are not induced to produce spores in advance, and the nutrient cells are lost more in the subsequent preparation process, and calcium carbonate precipitation cannot be effectively induced. And spores also need to germinate into vegetative cells first before actively inducing calcium carbonate precipitation, thereby improving the compressive strength of aggregates. However, yeast extracts commonly used as germination agents have a negative impact on the mechanical properties of concrete or mortar. Therefore, the present invention first cultivates alkaline bacteria into vegetative cells and then induces vegetative cells to produce spores. There is no need to add yeast extract, and spores can also be naturally formed into vegetative cells during concrete curing. Comparative Example 4 does not add slag powder, and the strength is reduced. This is because slag powder has potential activity, and its components can react with calcium hydroxide (Ca (OH) 2) generated during cement hydration in an alkaline environment to generate additional CSH gel. This reaction fills the pores and makes the concrete structure more compact, thereby improving the strength and durability of the later period. Comparative Example 5 does not add an alkaline activator, and the strength is reduced. This is because under alkaline conditions, the reaction rate of the active ingredients in cement is accelerated, so that the amount of CSH gel generated in the early stage increases, and the skeleton structure is more compact. And the alkaline activator significantly accelerates the hydration reaction of tricalcium silicate (C3S) and dicalcium silicate (C2S) in cement. Under alkaline conditions, the active silicon and aluminum components in cement are more easily dissolved, thereby accelerating the formation of hydration products such as calcium sulfonate, CSH gel, etc. This process can shorten the setting time of cement mortar and rapidly increase its early strength. Comparative Example 6 does not use pressurized solid microorganisms, and the strength is reduced. This is because although the phosphogypsum-based lightweight aggregate has a large porosity and can provide more space for the attachment of microorganisms, the method of pressurized solid microorganisms is not used, which will cause some microorganisms to fail to fully attach to the pores of the aggregate, and even partially fall off during the mixing process, resulting in a decrease in the microbial content in the aggregate, which has a certain impact on the strength of the structure.

[0194] Experimental Example 2 Repair Function

[0195] The lightweight aggregate products prepared in the above Examples 1-4 and Comparative Examples 1-6 were used to prepare concrete for road paving. The compressive strength test was carried out according to the "Test Method for Compressive Strength of Building Materials" issued by the Standardization Administration of the People's Republic of China. The compressive strength recovery rate test was carried out according to the following method. The results are shown in Table 2 below.

[0196] The cubic concrete specimens of Experimental Example 1 were subjected to a splitting tensile test after 28 days of first curing under standard curing conditions (temperature 20±2°C, relative humidity above 95%) to achieve the purpose of crack induction. Subsequently, the three pre-cracked specimens after splitting tensile were subjected to a second curing of 28 days, and the compressive strength S was tested on the 57th day. 28 The compressive strength test was carried out according to the "Compressive Strength Test Method for Building Materials" and the compressive strength recovery rate was calculated according to the following formula.

[0197]

[0198] RSI%: 28-day compressive strength recovery rate of pre-cracked specimens; S U : Compressive strength of experimental example 1 after the first curing for 28 days; S 28 : Compressive strength after the second curing for 28 days.

[0199] The lightweight aggregates prepared in the above-mentioned Examples 1-5 and Comparative Examples 1-4 were used in accordance with the method of Experimental Example 1 to prepare cubic concrete test blocks with a side length of 150 mm. Cracks were artificially generated after 28 days of use (specifically: steel bars with a diameter of 6 mm and a length of 800 mm were added above the road, and then compression loading was performed using a universal testing machine with a loading rate of 0.5 mm / min until a crack with a width of 500 um was obtained). The cracked test blocks were cured (also called healing) for 28 days after 5 dry-wet cycles (in each dry-wet cycle, the sample was immersed in water for 16 hours and then exposed to an air environment at 25°C and 80% RH for 8 hours). The width of the crack after healing was measured as C wf , and the crack healing rate is calculated at the same time, where the crack width healing rate (r) is used to evaluate the self-healing efficiency of concrete, and the formula is as follows:

[0200]

[0201] Among them, C wi is the initial width of the crack; C wf is the width of the crack after healing;

[0202] Three replicates were set for each test, and the results were averaged. The results are shown in Table 2 below.

[0203] Table 2 Performance test results of various embodiments and comparative examples

[0204]

[0205]

[0206] As can be seen from the above table, the compressive strength recovery rate of the concrete made of the microcapsule aggregate prepared in Example 1 is the highest under the most suitable ratio of all raw materials, and the crack healing rate is the highest. The compressive strength recovery rate and crack healing rate of Comparative Examples 1 and 6 are significantly reduced. This is because the spores are not microencapsulated and the microorganisms are not immobilized by pressurization, which significantly reduces the content of microorganisms in the aggregate. The reduction in the number of microorganisms will directly lead to a reduction in the amount of healing products generated, reducing the efficiency of self-repair of cracks. The compressive strength recovery rate and crack healing rate of Comparative Example 2 are significantly reduced. This is because no phosphogypsum is added during the preparation of the aggregate, then these microbial particles may not be effectively embedded or attached to the aggregate, resulting in a decrease in the effectiveness and activity of the microorganisms, and the reduction or loss of activity of the microorganisms will seriously affect the crack healing process, and due to the reduced efficiency of crack healing, the ability of the concrete to restore compressive strength after damage will also be affected, resulting in a decrease in the overall compressive strength recovery rate. The compressive strength recovery rate and crack healing rate of Comparative Example 3 have decreased significantly. This is because the spores need to germinate into nutrient cells before they can actively induce calcium carbonate precipitation. However, yeast extracts usually used as germination agents have a negative impact on the mechanical properties of concrete or mortar. Therefore, the present invention does not add yeast extract to the mixed slurry after the microcapsules are formed, but induces microorganisms to produce spores in advance. Comparative Example 3 does not perform the operation of inducing spores, which will seriously affect the content and activity of microorganisms in the aggregate, making the aggregate almost incapable of self-healing. The compressive strength recovery rate and crack healing rate of Comparative Examples 4 and 5 have decreased slightly. This is because slag powder and alkaline stimulators can promote the occurrence of hydration reactions to a certain extent, promote the formation of a dense structure of concrete, protect microorganisms to a certain extent, improve the activity of microorganisms, and promote the formation of healing products.

[0207] Experimental Example 3: Secondary repair function

[0208] The aggregates prepared in the above Examples 1-4 and Comparative Examples 1-6 were subjected to compressive strength tests according to the "Test Method for Compressive Strength of Building Materials" issued by the Standardization Administration of the People's Republic of China, and the compressive strength recovery rate test was performed according to the test method of Experimental Example 2. The results are shown in Table 3 below.

[0209] The cubic concrete specimen (referred to as cube) of Experimental Example 1 was artificially cracked after 28 days of the first curing (i.e., a steel bar with a diameter of 6 mm and a length of 800 mm was added above the road, and then a universal testing machine with a loading rate of 0.5 mm / min was used for compression loading until a crack with a width of 500 um was obtained). After 28 days of the second curing (i.e., after the first crack was repaired at an age of 56 days), the second crack was artificially prefabricated (a steel bar with a diameter of 6 mm and a length of 800 mm was added above the specimen, and then a universal testing machine with a loading rate of 0.5 mm / min was used for compression loading until a crack with a width of 500 um was obtained again, and the first crack and the second crack were in the same position). The cracked specimen was subjected to 5 dry-wet cycles (in each dry-wet cycle, the sample was immersed in water for 16 hours, and then exposed to an air environment at 25°C and 80% RH for 8 hours) and a third curing for 28 days was carried out. The compressive strength S of Group B was tested using a servo pressure testing machine. 56 , calculate the compressive strength recovery rate, and test the crack width C wf And calculate the healing rate.

[0210] The compressive strength recovery rate formula is as follows:

[0211]

[0212] RSI%: compressive strength recovery rate after secondary cracks occur in the specimen; S U : Compressive strength of experimental example 1 after the first curing for 28 days; S 56 : Compressive strength after the third curing for 28 days after the secondary cracks occurred.

[0213] The crack width healing rate (r) is used to evaluate the self-healing efficiency of concrete. The formula is as follows:

[0214]

[0215] Among them, C wi is the initial width of the crack; C wf is the width of the crack after healing;

[0216] Three replicates were prepared for each test and the results were averaged. The results are shown in Table 3 below.

[0217] Table 3 Performance test results of secondary repair

[0218]

[0219]

[0220] As can be seen from the above table, the compressive strength of the microcapsule aggregate concrete prepared in Example 1 has the highest recovery rate and the highest crack healing rate under the most suitable ratio of all raw materials. The compressive strength recovery rate and crack healing rate of the examples and comparative examples have a certain decline in the case of secondary repair. This is because the microbial self-repairing concrete relies on minerals such as calcium carbonate secreted by microorganisms to fill the cracks. This process requires nutrients (such as calcium sources or organic matter) and microbial activity. During the first repair, the nutrients and active microorganisms pre-added in the concrete play a self-repairing role at the cracks. However, after one repair, these nutrients may have been mostly exhausted, and the activity of microorganisms may also decrease. Therefore, there may be a lack of sufficient resources to support the repair effect of the same strength during the secondary repair. And after the first crack repair, the exposed surface of the concrete may have changed, and the environmental conditions (such as humidity and temperature) may no longer be ideal, affecting the activity and repair efficiency of the microorganisms. Therefore, even in the case of secondary repair potential, the rate and effect of the repair may still be inferior to the first repair. However, the decrease in the compressive strength recovery rate and crack healing rate of Examples 1-3 is not very obvious. This is because the microcapsule aggregate of the present invention uses microencapsulated alkali-resistant bacteria containing spores, gypsum and slag activated by alkaline stimulants, and a certain number of microorganisms are pressurized and immobilized at the same time. When the microorganisms in Comparative Examples 1-6 are reduced in number or activity due to environmental factors, the microorganisms in the microencapsulated lightweight aggregate of the present invention are less affected by the outside world and can self-repair, thereby achieving a secondary repair effect.

[0221] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing microcapsule aggregate, characterized in that: The following steps are involved: Inducing the alkali-resistant bacteria to produce spores, and microencapsulating the alkali-resistant bacteria containing the spores to form microcapsules; mixing gypsum, slag, alkaline activator and water to form a mixed slurry; The microcapsules and the mixed slurry are mixed and formed, and then crushed, vacuumed and pressurized to form microcapsule aggregates.

2. The method for preparing microcapsule aggregate according to claim 1, characterized in that: The alkali-resistant bacteria include one or more of Bacillus pasteurianus, Bacillus subtilis, and alkaliphilic Bacillus; And / or, the content of alkali-resistant bacteria containing spores in the microcapsule is (1-9)×10 12 pcs / g; And / or, the mass ratio of the gypsum, slag and alkaline activator is 400-800:300-500:300-600; and / or, the liquid-to-solid ratio of the mixed slurry is 0.7-0.9; And / or, the alkaline activator comprises water glass or a mixture of water glass and sodium hydroxide aqueous solution; Optionally, in the mixture of water glass and sodium hydroxide aqueous solution, the modulus of the water glass is 2.8-3.4, the concentration of the water glass is 38-42 degrees Baume; the concentration of the sodium hydroxide aqueous solution is 4-12 mol / L; and the mass ratio of the water glass to the sodium hydroxide aqueous solution is 1.5-2.5:

1.

3. The method for preparing microcapsule aggregate according to claim 1, characterized in that: The mass ratio of the microcapsules to the mixed slurry is 1-10:30-100, and optionally, the mass ratio of the microcapsules to the mixed slurry is 1-10:30-80; And / or, the crushed material is evacuated to a pressure of -0.7 to -0.9 bar and maintained for 25-35 minutes, then the temperature is raised to 26-30°C and the pressure is increased to 1.0-1.1 bar and maintained for 20-28 hours; The particle size of the crushed material is 2.36mm-4.75mm.

4. The method for preparing microcapsule aggregate according to any one of claims 1 to 3, characterized in that: The alkali-resistant bacteria containing spores are first mixed with a buffer solution before microencapsulation to obtain an alkali-resistant bacteria suspension containing spores; Optionally, the buffer comprises a sodium chloride solution; Optionally, before mixing with the buffer, the method further includes a step of washing the alkali-resistant bacteria containing spores with a NaCl-peptone buffer; Optionally, the concentration of the alkali-resistant bacterial suspension containing spores is (1-9)×10 9 CFU / mL.

5. The method for preparing microcapsule aggregate according to any one of claims 1 to 3, characterized in that: The alkali-resistant bacteria were cultured into vegetative cells and then spores were induced by heat shock; Optionally, the culture conditions include: culturing in a constant temperature shaker at 36-38°C for 6-8 days; the shaking frequency of the shaker is 80-120 rpm; Optionally, the culture medium used in the culture process includes: 8-12 g / L urea, 2-4 g / L NaHCO3, 2-4 g / L nutrient solution, 15-25 g / L yeast extract, and the balance is water; Optionally, the heat shock includes: culturing the nutrient cells in a bacterial culture medium at 78-82°C for a first time for 8-12 minutes, and then immediately placing them in an ice-water mixture to cool for 4-6 minutes; and then culturing them for a second time at 28-32°C for 40-56 hours to allow the alkali-resistant bacteria to produce spores; the spore production rate is above 90%.

6. The method for preparing microcapsule aggregate according to claim 4, characterized in that: The microencapsulation comprises: mixing a suspension of alkali-resistant bacteria containing spores with a sodium alginate solution, adding a calcium chloride solution, separating the solid from the liquid, and drying the precipitate to obtain microencapsulated alkali-resistant bacteria containing spores; Optionally, the precipitate is washed with water, heated to 75-85°C, and then freeze-dried to obtain microencapsulated alkali-resistant bacteria containing spores.

7. The method for preparing microcapsule aggregate according to claim 6, characterized in that: The concentration of the sodium alginate solution is 18-22 g / L; and / or, the volume ratio of the alkali-resistant bacteria suspension containing spores to the sodium alginate solution is 4-8:18-25; and / or, the concentration of the calcium chloride solution is 18-22 g / L, and the amount of the calcium chloride solution added is 2-5% of the total weight of the mixture of the spore-containing alkali-resistant bacteria suspension and the sodium alginate solution; And / or, the freeze-drying temperature is minus 18°C ​​to minus 22°C, and the freeze-drying time is 20-28h; And / or, pre-freezing with liquid ethanol before freeze-drying.

8. The method for preparing microcapsule aggregate according to any one of claims 1 to 3, characterized in that: Firstly, gypsum and slag are mixed, and then water is added to form a mixed liquid; then, an alkaline activator is added to the mixed liquid to form a mixed slurry; And / or, when the microcapsules are mixed with the mixed slurry, they are first stirred at a low speed for 50-70 seconds, and then stirred at a high speed for 110-130 seconds; wherein the low speed is 45-65 r / min; and the high speed is 130-170 r / min; And / or, the gypsum is phosphogypsum; And / or, the molding is performed by casting, and after casting, the mixture is cured for 5-7 hours and then crushed.

9. A microcapsule aggregate, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the microcapsule aggregate prepared by the preparation method according to any one of claims 1 to 8, or the microcapsule aggregate according to claim 9 in building materials.

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