3D printing concrete strength improving method based on microorganism induced calcification

Abstract

The invention discloses a 3D printing concrete strength improving method based on microorganism induced calcification. The 3D printing concrete strength improving method comprises the following steps: S1, microorganism domestication; s2, preparing the biological fine aggregate; s3, preparing 3D printing mortar; and S4, printing and curing the concrete structure. According to the method, by domesticating the strains and preparing the active fine aggregate loaded with the microorganisms, the adaptability of the living environment of the microorganisms and the alkaline and anoxic environment in the 3D printing concrete is improved, the microorganisms are loaded into the fine aggregate, and the activity of the microorganisms can be well kept; the enhancement effect of microorganism induced calcification on the strength of the 3D printing concrete is effectively exerted.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printed concrete, and in particular relates to a method for improving the strength of 3D printed concrete based on microbial induced calcification. Background Art

[0002] The typical 3D printing concrete construction method is to squeeze and pump the layers to accumulate and form. The lack of vibration and extrusion and stretching of the printed layers during the forming process makes it easier for pore defects to form inside the 3D printed concrete. And because of the directional movement of the print head during the printing process, the internal pore defects are often arranged in a directional manner. The existence of these defects seriously affects the mechanical strength, shrinkage behavior and long-term durability of the 3D printed concrete structure. The directional arrangement of the pores makes the 3D printed concrete specimen have obvious anisotropy.

[0003] Microbial induced calcium carbonate precipitation is a biomineralization phenomenon that is ubiquitous in nature. It uses the mineralization behavior of microbial metabolic activities to induce calcium carbonate precipitation, and forms mineralized structures such as calcite outside the microbial cells, so that the loose rock and soil particles in the environment can be cemented to form a solid body with a certain hardness. This technology has been widely used in foundation reinforcement, crack repair, and cultural relics restoration. The pore defects inside 3D printed concrete can provide sufficient space for microbial growth and metabolism. The calcium carbonate precipitation generated by metabolism can fill the pores inside the sample, thereby improving the mechanical properties and long-term durability of 3D printed concrete. In recent years, many scholars have studied the changes in the mechanical strength, impermeability, and self-repairing ability of concrete after adding microorganisms to concrete. However, the high alkaline and oxygen-deficient environment of concrete is not conducive to the metabolism and reproduction of microorganisms inside concrete. Direct internal addition of microorganisms will also have a certain impact on the printing performance of 3D printed mortar. These factors limit the application of microbial calcification in the field of 3D printed concrete. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the strength of 3D printed concrete based on microbial induced calcification. By taming the bacterial species and preparing active fine aggregate loaded with microorganisms, the compatibility of the microbial living environment with the alkaline and anoxic environment inside the 3D printed concrete is improved, and the microorganisms are loaded into the fine aggregate, which can better maintain the activity of the microorganisms and effectively exert the enhancing effect of microbial induced calcification on the strength of 3D printed concrete.

[0005] In order to achieve the above purpose, this application adopts the following technical solutions:

[0006] The present invention provides a method for improving the strength of 3D printed concrete based on microbial induced calcification, comprising the following steps:

[0007] S1: Microbial domestication

[0008] S11, inoculating the Bacillus pasteurianus freeze-dried powder into a liquid culture medium, oscillating and culturing in a constant temperature incubator to obtain a cultured Bacillus pasteurianus bacterial solution, adding the cultured bacterial solution into a common 3D concrete printing mortar for printing, and then placing the printed concrete sample in a constant temperature and humidity curing box for curing;

[0009] S12, after the curing is completed, take out a proper amount of the concrete sample, grind and crush it, evenly disperse the crushed concrete sample in sterile water to obtain a microbial concrete mixture, take a proper amount of the microbial concrete mixture and pour it into the liquid culture medium, shake and culture for a certain period of time, measure and record the OD 600 value;

[0010] S13, diluting the microbial concrete mixture obtained by the culture in S12 according to a gradient, and adjusting the concentration gradient to 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , 10 -7 , 10 -8 The microbial concrete mixture is applied to an agar solid medium, the agar solid medium is inverted and placed in a constant temperature incubator for cultivation, and then the microorganisms in the medium are observed under a microscope, and alkali-resistant Bacillus pasteurianus is selected according to morphological characteristics;

[0011] S14, placing the alkali-resistant Bacillus pasteurianus selected in S13 into the liquid culture medium for expansion and then adding it into ordinary 3D concrete printing mortar;

[0012] S15, repeat S11-S14 until the OD measured in S12 600 The value is stable, and the domesticated microorganisms with high adaptability to the concrete environment are obtained;

[0013] S2: Bio-fine aggregate preparation

[0014] S21, inoculating the domesticated microorganisms obtained in S15 into the liquid culture medium for expansion culture to obtain a bacterial liquid, centrifuging the bacterial liquid to obtain bacterial mud, and dispersing the bacterial mud into deionized water to obtain a bacterial suspension;

[0015] S22, taking diatomaceous earth, soy peptone, and casein peptone, placing them in a cement mortar mixer and stirring and mixing them evenly, then adding the bacterial suspension obtained in S21 as a binder, and using a granulator to prepare the biological fine aggregate loaded with microorganisms;

[0016] S3: Preparation of 3D concrete printing mortar containing microorganisms

[0017] Cement, fine aggregate, water reducing agent, thickener, calcium lactate, urea and water are mixed to prepare the 3D concrete printing mortar, wherein the fine aggregate includes the biological fine aggregate and ordinary fine aggregate prepared in S22;

[0018] S4: Printing and curing of concrete structures

[0019] The 3D concrete printing mortar obtained in S3 is poured into the printer, the machine is debugged to ensure normal operation of the machine, and then printing is started. After printing is completed, maintenance is performed to obtain a 3D printed concrete sample.

[0020] S5: Concrete anisotropy and calcium carbonate content test

[0021] After the specimens were cured, the uniaxial compressive strength of the specimens in all directions was tested, and the anisotropy of the specimens was evaluated according to formula (1);

[0022]

[0023] σ x : Uniaxial compressive strength of the sample when loaded parallel to the X direction;

[0024] σ y : Uniaxial compressive strength of the sample when loaded parallel to the Y direction;

[0025] σ z : Uniaxial compressive strength of the sample when loaded parallel to the Z direction;

[0026] Take a 3D printed concrete sample after proper curing, crush it with a planetary grinder, and perform XRD diffraction analysis; match the diffraction spectrum of the sample with the standard spectrum of calcium carbonate. When the diffraction peak of the sample matches the diffraction peak of the standard spectrum of calcium carbonate, it proves that calcium carbonate is generated; after identifying the diffraction peak of calcium carbonate, according to the peak intensity of the diffraction peak, the calcium carbonate content Q in the sample can be roughly analyzed according to formula (2):

[0027]

[0028] I m (θ): diffraction peak intensity function of target mineral;

[0029] I i : Diffraction peak intensity function of a certain mineral in the sample.

[0030] In the above technical solution, in S22, the mass ratio of diatomaceous earth, soy peptone, casein peptone, and the bacterial suspension obtained in S21 is: 200 g: (15-20) g: (3-5) g: (27-44) g.

[0031] In the above technical solution, in S3, the mass ratio of cement: fine aggregate: water reducer: thickener: calcium lactate: urea: water is 1:1: (0.01-0.07): (0.005-0.01): (0.05-0.15): (0.01-0.05): 0.35.

[0032] In the above technical solution, in S3, the mass ratio of the biological fine aggregate to the ordinary fine aggregate prepared in S22 is 1:(3-5).

[0033] In the above technical solution, the biological fine aggregate obtained in S22 is air-dried at room temperature to remove surface moisture before preparing the mortar.

[0034] In the above technical solution, in S3, when preparing the mortar, an equal amount of the water is replaced with the bacterial suspension obtained in S21.

[0035] The beneficial effect of the present invention is that the present invention provides a method for improving the strength of 3D printed concrete based on microbial induced calcification. The method improves the compatibility of the microbial living environment with the alkaline and anoxic environment inside the 3D printed concrete by taming the bacterial species and preparing active fine aggregate loaded with microorganisms. The microorganisms are loaded into the fine aggregate, which can better maintain the activity of the microorganisms and effectively exert the enhancing effect of microbial induced calcification on the strength of 3D printed concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the microbial acclimation process;

[0037] Figure 2 Create a process flow chart for loading microbial fine aggregate;

[0038] Figure 3 is the bacterial acclimation times and OD 600 Relationship diagram;

[0039] Figure 4 It is a schematic diagram of the printing path and loading direction;

[0040] Figure 5 This is the uniaxial compressive strength and anisotropy index diagram of the sample. DETAILED DESCRIPTION

[0041] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. The present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that this disclosure will be thorough and complete, and the concept of the present invention will be fully conveyed to those skilled in the art, and the present invention will only be limited by the claims.

[0042] Example 1

[0043] This embodiment provides a method for improving the strength of 3D printed concrete based on microbial induced calcification, which specifically includes the following steps:

[0044] 1. Culture medium preparation

[0045] (1) Liquid culture medium preparation

[0046] Weigh 20g urea, 15g casein peptone, 5g soy peptone, and 5g sodium chloride, pour into 1L deionized water, stir evenly, and then adjust the pH to about 8.0 with 1mol / L NaOH solution. Put the prepared liquid culture medium into an autoclave at 200℃ for 20min.

[0047] (2) Preparation of agar solid culture medium

[0048] Weigh 20g urea, 15g casein peptone, 5g soy peptone, and 5g sodium chloride, pour into 1L deionized water, stir evenly, and then adjust the pH to about 8.0 with 1mol / L NaOH solution. Put the prepared liquid culture medium into an autoclave at 200℃ for 20min. After sterilization, add 20g agar and stir until the agar is completely dissolved. Then pour the liquid culture medium with agar into a disposable culture dish and inoculate bacteria after it solidifies.

[0049] 2. Microbial culture

[0050] Bacillus pasteurianus freeze-dried powder was purchased from Ningbo Mingzhou Biotechnology Co., Ltd.

[0051] Open the clean bench, turn on the ultraviolet sterilization lamp, sterilize for 30 minutes, and turn off the ultraviolet sterilization lamp. Divide the sterilized liquid culture medium into four equal parts and dispense them into 500mL conical flasks. Use alcohol to disinfect the surface of the conical flask, and then put it into the clean bench. Use an alcohol lamp to sterilize the inoculation loop for 3 minutes. After cooling to room temperature, use the inoculation loop to inoculate the freeze-dried powder of Bacillus pasteurianus into the liquid culture medium. Wrap the sealing film and kraft paper on the mouth of the conical flask, remove the sealing film and place it in a constant temperature incubator at 30°C, 200r / min for 48 hours, and measure the OD of the bacterial solution. 600 Turn off the clean bench.

[0052] 3. Microbial domestication

[0053] (1) Weigh 500g cement, 500g quartz sand, 3.5g water reducer (polycarboxylic acid is used as water reducer in this embodiment), 2.5g thickener (hydroxypropyl methylcellulose is used as thickener in this embodiment), 4.5g calcium lactate, put into a concrete mixer, stir slowly for 30s and then stir quickly for 30s to mix evenly to obtain concrete dry powder. Weigh 100mL tap water, 75mL bacterial liquid, 1.5g urea, mix evenly, then pour the mixed solution containing bacterial liquid and urea into the concrete dry powder, stir slowly for 2min and then stir quickly for 1min to obtain concrete mortar containing microorganisms. Cast a 50mm*50mm*50mm cube, demold after curing at room temperature for 1d, and cure for 7 days at 22℃ and 98% humidity.

[0054] (2) Take 10g of the cured concrete sample, grind it with a planetary grinder for 30s, put it into a conical flask with 100mL of sterile water, and shake it at 180r / min for 30min to evenly disperse the concrete sample in the sterile water to obtain a microbial concrete mixture. Pour an appropriate amount of the microbial concrete mixture into the liquid culture medium, shake and culture it for a certain period of time, and measure and record the OD 600 value.

[0055] (3) Dilute the microbial concrete mixture in a gradient, and select a concentration gradient of 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , 10 -7 , 10 -8 Spread the microbial concrete mixture, absorb 80uL of bacterial suspension and spread it on the agar solid medium, invert the medium and place it in a 28℃ constant temperature incubator for 48h. Then use a microscope to observe the microorganisms in the medium and select alkali-resistant Bacillus pasteurianus according to their sexual morphological characteristics. The acclimation process is as follows Figure 1 shown.

[0056] (4) The alkali-resistant Bacillus pasteurianus obtained in step 3 is placed in a liquid culture medium for expansion and then added into ordinary 3D concrete printing mortar.

[0057] (5) Repeat steps 1-4 until the OD of the bacterial solution measured in step 2 is 600 The value is basically stable, such as Figure 3 As shown, at this time, domesticated microorganisms that are highly adaptable to the concrete environment are obtained.

[0058] 4. Production of microbial-loaded fine aggregate

[0059] The domesticated microorganisms were inoculated into liquid culture medium for expansion and culture to obtain OD 600The values ​​of the bacterial liquid were 0.2, 0.4, 0.6, and 0.8 respectively. Each group of bacterial liquid was centrifuged at 8000r / min for 15min to obtain bacterial mud, and then each group of bacterial mud was dispersed in 100mL of deionized water. Four groups of 200 diatomaceous earth, 1.5g casein peptone, and 0.5g soy peptone were weighed respectively and mixed evenly, and then poured into each group of bacterial suspension as a binder. After slowly stirring in a mortar mixer for 30s, it was poured into a disc granulator with an inclination angle of 45° and a speed of 50r / min until uniform spherical small particles were formed. The prepared spherical particles were sieved through a 70-mesh sieve. The production process is as follows Figure 2 After the surface moisture of the spherical particles is dried at room temperature, they are immediately mixed into concrete for use.

[0060] 5. 3D concrete printing mortar preparation

[0061] Weigh 500g cement, 200g microbial fine aggregate, 300g quartz sand, 3.5g water reducer, 2.5g thickener, 4.5g calcium lactate, put into a concrete mixer, stir slowly for 30s and then stir quickly for 30s to mix evenly. Weigh 175mL tap water and 1.5g urea and mix evenly. Then pour the mixed solution containing urea into the concrete dry powder, stir slowly for 2min and then stir quickly for 1min to obtain 3D concrete printing mortar with different microbial contents.

[0062] 6. Printing samples and maintenance

[0063] The direction perpendicular to the printing plane is defined as the Z direction, the direction of nozzle movement is defined as the X direction, and the direction perpendicular to the nozzle movement is defined as the Y axis. Turn on the concrete 3D printer, use a circular nozzle with a nozzle diameter of 20 mm, set the extruded filament diameter to 20 mm, height to 10 mm, and 45° cross printing (such as Figure 4 As shown). The printing speed and fill rate are set to 1.3mm / s and 100% respectively. Since the printing filament height is set to 10mm, the print head is set to move upward at intervals of 10mm. Import the 80mm*80mm*80mm cube model into the slicing software, adjust the nozzle to 10mm away from the printing base, and start printing. After the sample is printed, mark the X, Y, and Z directions, leave it in place for 3 hours, and after it is finally solidified, put it in a constant temperature and humidity curing box at a temperature of 28℃ and a humidity of 98% for 28 days.

[0064] 7. Strength test

[0065] After curing, the sample was processed into a standard cubic sample of 70.7mm*70.7mm*70.7mm. Since the printing path is a 45° cross printing, the compressive strength is not much different when loading along the X direction and the Y direction, so only the compressive strength when loading along the X direction and the Z direction is tested. The uniaxial compressive strength (σ x ,σ z During the experiment, the failure mode of the sample was recorded by a camera. The failure process was controlled by displacement, and the loading speed was set to 0.002 mm / s. Displacement sensors were set on the top and both sides of the diameter of the specimen. The uniaxial compressive strength of each group of samples in the X and Z directions was measured as follows Figure 5 (a) and calculate the anisotropic indexes of each group of samples according to formula (1).

[0066]

[0067] When loading is only along the X and Z directions, equation (1) is simplified to equation (3), and the result is as follows: Figure 5 (b) as shown:

[0068]

[0069] σ x : Uniaxial compressive strength of the sample when loaded parallel to the X direction;

[0070] σ y : Uniaxial compressive strength of the sample when loaded parallel to the Y direction;

[0071] σ z : Uniaxial compressive strength of the specimen when loaded parallel to the Z direction.

[0072] 8. Calcium carbonate detection

[0073] Take 10g of the 3D printed concrete sample after curing, crush it with a planetary grinder, and perform XRD diffraction analysis. Match the diffraction spectrum of the sample with the standard spectrum of calcium carbonate. After identifying the diffraction peak of calcium carbonate, according to the peak intensity of the diffraction peak, the calcium carbonate content Q in the sample can be roughly analyzed according to formula (2). The measured calcium carbonate content of each group is shown in Table 1.

[0074]

[0075] I m (θ): diffraction peak intensity function of target mineral;

[0076] I i : Diffraction peak intensity function of a certain mineral in the sample.

[0077] Table 1 Calcium carbonate content under different bacterial dosage

[0078]

[0079] 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 improving the strength of 3D printed concrete based on microbial induced calcification, characterized in that: The following steps are involved: S1: Microbial domestication S11, inoculating the Bacillus pasteurianus freeze-dried powder into a liquid culture medium, oscillating and culturing in a constant temperature incubator to obtain a cultured Bacillus pasteurianus bacterial solution, adding the cultured bacterial solution into a common 3D concrete printing mortar for printing, and then placing the printed concrete sample in a constant temperature and humidity curing box for curing; S12, after the curing is completed, take out a proper amount of the concrete sample, grind and crush it, evenly disperse the crushed concrete sample in sterile water to obtain a microbial concrete mixture, take a proper amount of the microbial concrete mixture and pour it into the liquid culture medium, shake and culture for a certain period of time, measure and record the OD 600 value; S13, diluting the microbial concrete mixture obtained by the culture in S12 according to a gradient, and adjusting the concentration gradient to 10 -2 , 10 -3 , 10 -4 , 10 -5 , 10 -6 , 10 -7 , 10 -8 The microbial concrete mixture is applied to an agar solid medium, the agar solid medium is inverted and placed in a constant temperature incubator for cultivation, and then the microorganisms in the medium are observed under a microscope, and alkali-resistant Bacillus pasteurianus is selected according to morphological characteristics; S14, placing the alkali-resistant Bacillus pasteurianus selected in S13 into the liquid culture medium for expansion and then adding it into ordinary 3D concrete printing mortar; S15, repeat S11-S14 until the OD measured in S12 600 The value is stable, and the domesticated microorganisms with high adaptability to the concrete environment are obtained; S2: Bio-fine aggregate preparation S21, inoculating the domesticated microorganisms obtained in S15 into the liquid culture medium for expansion culture to obtain a bacterial liquid, centrifuging the bacterial liquid to obtain bacterial mud, and dispersing the bacterial mud into deionized water to obtain a bacterial suspension; S22, taking diatomaceous earth, soy peptone, and casein peptone, placing them in a cement mortar mixer and stirring and mixing them evenly, then adding the bacterial suspension obtained in S21 as a binder, and using a granulator to prepare the biological fine aggregate loaded with microorganisms; S3: Preparation of 3D concrete printing mortar containing microorganisms Cement, fine aggregate, water reducing agent, thickener, calcium lactate, urea and water are mixed to prepare the 3D concrete printing mortar, wherein the fine aggregate includes the biological fine aggregate and ordinary fine aggregate prepared in S22; S4: Concrete structure printing and maintenance The 3D concrete printing mortar obtained in S3 is poured into the printer, the machine is debugged to ensure normal operation of the machine, and then printing is started. After printing is completed, maintenance is performed to obtain a 3D printed concrete sample.

2. The method according to claim 1, characterized in that: In S22, the mass ratio of diatomaceous earth, soy peptone, casein peptone, and the bacterial suspension obtained in S21 is: 200 g: (15-20) g: (3-5) g: (27-44) g.

3. The method according to claim 1, characterized in that: In S3, the mass ratio of cement: fine aggregate: water reducer: thickener: calcium lactate: urea: water is 1:1: (0.01-0.07): (0.005-0.01): (0.05-0.15): (0.01-0.05): 0.

35.

4. The method according to claim 1, characterized in that: In S3, the mass ratio of the biological fine aggregate and the ordinary fine aggregate prepared in S22 is 1:(3-5).

5. The method according to claim 1, characterized in that: The biological fine aggregate prepared in S22 is air-dried at room temperature to remove surface moisture before preparing the mortar.

6. The method according to claim 1, characterized in that: In S3, when preparing the mortar, the water is replaced with an equal amount of the bacterial suspension obtained in S21.

Images