A method for preparing high-strength microbial mortar by using nano calcium carbonate

Abstract

The application provides a method for preparing high-strength microbial mortar by using nano calcium carbonate, comprising the following steps: mixing quartz sand with different particle sizes to prepare an aggregate matrix, then mixing nano calcium carbonate, water and the quartz sand to prepare nano calcium carbonate-quartz sand mortar, then loading the mortar into a mold to prepare a sample, and finally using a bacterial liquid, a fixing liquid and a cementing liquid for grouting and reinforcement, and obtaining high-strength microbial rock after four times of grouting and reinforcement. The application solidifies sand soil by using the principle of microbial induction of calcium carbonate precipitation, obtains nano calcium carbonate-quartz sand mortar by adding a proper amount of nano calcium carbonate, increases the yield of calcium carbonate by using the nucleation effect of nano calcium carbonate in the process of microbial induction of calcium carbonate precipitation to improve the mechanical properties of the calcium carbonate, and after four times of grouting and reinforcement, the amount of calcium carbonate precipitation is increased by 69.9%, the strength is increased by 277.75%, and the unconfined compressive strength of the solidified sand soil sample can reach 29.2Mpa at most. In addition, the application also has the characteristics of low cost, simple preparation process and small environmental pollution.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microbial mineralization, and particularly relates to a method for preparing high-strength microbial mortar by using nano calcium carbonate. BACKGROUND

[0002] In recent years, the use of microbial induced carbonate precipitation (MICP) technology to reinforce soil has become a research hotspot in the field of geotechnical engineering. MICP technology is a commonly used microbial induced mineralization reaction process that uses some microorganisms to induce the production of calcium carbonate crystals through metabolic action to cement sand particles, such as Pseudomonas aeruginosa, Sporosarcina Pasteurii, etc. Today, MICP technology is widely used in soil improvement, concrete crack repair, cultural relic restoration, and soft rock modification, etc., and has the advantages of low carbon and high efficiency. The ground soil treated by MICP technology has better physical and mechanical properties.

[0003] Sand type ground has the characteristics of low strength, high permeability, and easy liquefaction, and the traditional sand type ground treatment method generally uses physical and chemical methods for reinforcement. The physical method mainly uses mechanical devices to extrude the soil to improve the bearing capacity, such as replacement method, vacuum preloading method, vibration compaction method, and dynamic compaction method, etc. The chemical method mainly uses cement-based chemical materials to cement the soil to form a composite foundation, such as deep mixing pile method, pressure grouting method, and high-pressure jet grouting pile method, etc. These methods have many shortcomings, such as high cost and serious environmental pollution. MICP technology relies on the metabolic action of microorganisms that already exist in nature to solidify the soil, which makes it have good environmental compatibility to use MICP technology to reinforce sand type ground, thus becoming a new technology in the field of geotechnical engineering. However, there are some difficulties in using MICP technology to reinforce sand type soil, one of which is that the strength is generally low, and the other is that the utilization rate of calcium ions in the added calcium source is low, causing resource waste. These two aspects lead to high engineering construction cost, so it is particularly important to find a more effective method to improve this situation. SUMMARY

[0004] To solve the above problems, the present application provides a method for preparing high-strength microbial mortar by using nano calcium carbonate. Using the method of the present application to grout and reinforce sand type ground can achieve 3.8 times the original strength under the same treatment method. After four times of reinforcement, the soil properties change from geotechnical properties to rock properties, and the engineering properties are improved. In addition, the calcium ion utilization rate is greatly improved, with a maximum increase of 69.9%, reducing the waste of raw materials.

[0005] To achieve the above object, the present application is implemented by the following technical solutions:

[0006] A method for preparing high-strength microbial mortar by using nano calcium carbonate, comprising: mixing nano calcium carbonate in quartz sand, and using bacillus pasteurii liquid, fixing liquid and cementing liquid as grouting material to solidify the original loose sandy soil into rock properties.

[0007] As a possible implementation, further, specifically comprising the following steps:

[0008] 1) Different mesh sizes of quartz sand are used as aggregates, and the base material is obtained by mixing according to the proportion;

[0009] 2) Add water and nano calcium carbonate to the base material and mix uniformly to obtain nano calcium carbonate-quartz sand mortar;

[0010] 3) Fill the nano calcium carbonate-quartz sand mortar into the mold in multiple times and vibrate and compact to obtain a mortar sample;

[0011] 4) Inject bacillus pasteurii liquid, fixing liquid and cementing liquid into the sample in multiple times to grout and reinforce the sample;

[0012] 5) Cure the grouted sample at room temperature.

[0013] As a possible implementation, further, the aggregates in step 1) are composed of 18-35 mesh, 35-60 mesh and 60-200 mesh quartz sand particles; wherein the mass ratio of the three different mesh sizes of quartz sand is 25:7:3; the non-uniformity coefficient C u of the base material is 2.69, and the curvature coefficient C c is 1.35.

[0014] As a possible implementation, further, in step 2), the water-sand ratio of the nano calcium carbonate-quartz sand mortar is 4-5%, and the nano calcium carbonate content is 0-2.5%; the purity of the nano calcium carbonate is 99.9%, and the effective particle size is 40-100 nm.

[0015] As a more preferred implementation, preferably, in step 2), the base material, water and nano calcium carbonate are stirred in a stirring pot at 200 rpm / min for 3 min.

[0016] As a possible implementation, further, in step 3), a polypropylene needle cylinder with an inner diameter of 50 mm and a height of 170 mm is used as a mold, and the final height of the mortar sample after vibration and compaction is 11-12 cm, and the dry density range is 1.78-1.86 g / cm 3 .

[0017] As a preferred embodiment, preferably, the material of the sample in step 3) is used in an amount of 300 g of 18-35 mesh quartz sand, 84 g of 35-60 mesh quartz sand, and 36 g of 60-200 mesh quartz sand, a total of 420 g; 20 g of water; and 0-10.5 g of nano calcium carbonate.

[0018] As a possible embodiment, further, the bacillus pasteurii bacterial liquid, the fixing liquid and the cementing liquid in step 4) are injected into the sample four times respectively, the grouting rate is 3 mL / min, and the interval time of each grouting is 12 h; the grouting sequence is bacillus pasteurii bacterial liquid, fixing liquid and cementing liquid.

[0019] As a possible embodiment, further, the total amount of the bacillus pasteurii bacterial liquid in step 4) is 100 mL, the OD value is 3-3.5, and the enzyme activity value is 1.2-1.5 ms / (cm·min);

[0020] The fixing liquid is a 0.04-0.07 mol / L calcium chloride solution, and the total amount is 100 mL;

[0021] The cementing liquid is a 1:1 urea-calcium chloride mixed solution with a concentration of 0.5-1 mol / L, and the total amount is 2 L.

[0022] As a possible embodiment, further, in step 5), after grouting is completed, curing is completed after standing for 2-3 days.

[0023] Compared with the prior art, the beneficial effects of the present application are as follows:

[0024] 1) The nano calcium carbonate added in the present application can improve the adsorption effect of bacteria to a certain extent, and by improving the adsorption performance of the sand sample, more bacillus pasteurii is left in the sample, so that the concentration of calcium carbonate in the sample quickly reaches the supersaturation concentration to produce calcium carbonate precipitation, thereby improving the bacterial adsorption capacity of the sample.

[0025] 2) The additional nano calcium carbonate in the present application can greatly improve the utilization rate of calcium ions in the cementing liquid. The nano calcium carbonate plays a crystal nucleus role inside the sample, has a lower interface energy, and makes calcium carbonate more easily precipitate, so that the utilization rate of calcium ions is maximally improved by 69.9%. This technology can reduce the construction cost to a certain extent, and has economic advantages compared with the prior art.

[0026] 3) The technology used in the present application can achieve the reinforcement effect of chemical grouting materials, the total reinforcement time is 4 days, and the strength of the sample is 15-25 MPa after reinforcement is completed, and the sample with a dosage of 1% at 7d can generally reach 25-30 MPa. In addition, compared with chemical grouting materials, the present application is more environmentally friendly, the raw materials used are non-toxic and non-polluting, and have good environmental compatibility.

[0027] 4) Compared with the existing external addition of nanometer material technology, the present application can obtain higher strength, the highest can make the sample strength increase by 277.75%, and the unconfined compressive strength of the cured sand sample can reach 29.2Mpa, and the operation process is relatively simple.

[0028] 5) The cured sample in the present application has higher calcium carbonate content, which improves the overall performance of the sample, has lower permeability and higher strength. Compared with the prior art, the original soil body can be reinforced into a sample with more rock properties, and the induced mineral is stable calcite, which improves the durability under various natural environmental actions. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The sand grading curve used in the present application;

[0030] Figure 2 The process flow chart of the present application;

[0031] Figure 3 The calcium carbonate generation amount of the sample reinforced by different dosages of nano calcium carbonate;

[0032] Figure 4 The unconfined compressive strength of the sample reinforced by different dosages of nano calcium carbonate;

[0033] Figure 5 The micro-morphology diagram (40000 times) of the nano calcium carbonate used;

[0034] Figure 6 The micrograph (200 times) of the sample reinforced without adding nano calcium carbonate;

[0035] Figure 7 The micrograph (200 times) after adding 1% nano calcium carbonate;

[0036] Figure 8 The mineral diffraction analysis diagram of the sample reinforced without adding nano calcium carbonate (i.e. the dosage of nano calcium carbonate is 0g);

[0037] Figure 9 The mineral diffraction analysis diagram of the sample reinforced by adding 1% nano calcium carbonate. DETAILED DESCRIPTION

[0038] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall into the scope of the present application.

[0039] Referring to the drawings Figure 2 illustrated, the present application provides a method for preparing high-strength microbial mortar by using nano calcium carbonate, comprising the following steps:

[0040] Step 1): using quartz sand as a skeleton, quartz sand with different particle size ratios is cleaned with 1 mol / L HCl solution, the PH value of the aqueous solution after cleaning is between 6.7 and 7.5, and the quartz sand is completely dried in an oven at 105°C for 24 hours, and then cooled to room temperature for use.

[0041] Step 2): 20 g of deionized water and 0-10.5 g of nano calcium carbonate (nano calcium carbonate particle size is 40-100 nm) are added to each 420 g of sand sample, and the mixture is uniformly stirred in a stirring pot at 200 rpm / min for 3 min to obtain a nano calcium carbonate-quartz sand mortar. Among them, the 420 g sand sample is composed of 300 g of 18-35 mesh quartz sand, 84 g of 35-60 mesh quartz sand and 36 g of 60-200 mesh quartz sand, and the particle size grading curve of the quartz sand is as shown in the drawing Figure 1 , the non-uniformity coefficient C u of the quartz sand is 2.69, the curvature coefficient C c is 1.35, d 50 =0.65 mm, and it is a poorly graded soil; the main particle size is between 0.5-1.00 mm, which is medium-coarse sand.

[0042] Step 3): a polypropylene syringe with an inner diameter of 50 mm and a height of 170 mm is used as a mold, the nano calcium carbonate-quartz sand mortar is loaded into the mold in three times, and after each loading, a soil triaxial tamper is used for vibration compaction, so that the height of the loaded sand sample is about 115 mm. Specifically, the bottom of the syringe is padded with a layer of screen mesh, and a layer of gauze with a pore size of about 0.8 mm is laid on the screen mesh to prevent sand particles from leaking out of the mold. Then the mixed sand mortar is loaded into the syringe, and the loading process is divided into three times of vibration, and the height of the vibrated sand sample is controlled at about 115 mm. Then the bottom of the syringe is sealed with a screen mesh to prevent the sample from loosening.

[0043] Step 4): The cultured bacteria solution, fixing solution and cementing solution are measured by a measuring cylinder. The bacteria solution is Bacillus pasteurii, the fixing solution is 0.04-0.07 mol / L calcium chloride solution, and the cementing solution is 0.5-1 mol / L 1:1 urea-calcium chloride solution.

[0044] The preparation methods of the above-mentioned Bacillus pasteurii bacteria solution and cementing solution are as follows:

[0045] a) Preparation of culture medium: the content of each component of the culture medium is 40.0 g yeast extract, 20.0 g ammonium sulfate, 20.0 g 10 μmol / L nickel chloride, and 2 L deionized water.

[0046] b) Adjust the pH of the culture medium to 9-9.5, then sterilize it in a high-pressure steam sterilization pot at 121°C and 0.1 MPa for 40 minutes, and cool it to room temperature.

[0047] c) After inoculation of Bacillus pasteurii, transfer it to a constant-temperature shaking incubator, and continuously shake it at a parameter of 170 rpm / min and 30°C for 20-24 hours. The final prepared microbial solution has an OD value of 3-3.5 and an enzyme activity value of 1.2-1.5 ms / (cm·min).

[0048] Step 5): Connect the grouting pipe to the mold using a peristaltic pump, and inject the bacteria solution, fixing solution and cementing solution at a grouting rate of 3 ml / min, with the volume being 100 ml, 25 ml and 500 ml respectively. After the bacteria solution is injected, stand for 2 h to make the Bacillus pasteurii adsorb as much as possible inside the sand sample, and then inject the fixing solution and cementing solution in turn.

[0049] Step 6): Repeat the grouting and reinforcement process in step 5) four times, and stand for 12 h after each completion before the next grouting and reinforcement, for a total of four batches of reinforcement process.

[0050] Step 7): Place the reinforced sample in a curing room at 25-30°C for 2-3 d.

[0051] Performance test

[0052] The sand soil column samples solidified by adding different amounts of nano calcium carbonate are compared and analyzed.

[0053] 1. Calcium carbonate production test

[0054] The reinforced sample is soaked in deionized water for 48 h to remove the soluble salt components in the sample. Then, it is dried in a constant-temperature oven at 60°C for 48 h, and then weighed to obtain the calcium carbonate content. The calcium carbonate production is calculated according to the following formula:

[0055] M C=M2-M1

[0056] Where: M c —Calcium carbonate production;

[0057] M1—Sample weight before the start of the test;

[0058] M2—The weight of the sample after drying;

[0059] Appendix Figure 3 The figure shows the calcium carbonate production of samples with different doping amounts. It can be seen from the figure that the highest calcium carbonate content was obtained when the nano-calcium carbonate doping amount was 1%.

[0060] 2. Unconfined compressive strength test

[0061] Unconfined compressive strength tests were conducted on the samples after the calcium carbonate formation test. The test method was carried out in accordance with the "Standard for Test Methods of Engineering Rock Mass GBT50266-2013". The test results are attached. Figure 4 As shown in the figure, the highest strength is obtained when the amount of nano-calcium carbonate is 1%.

[0062] 3. SEM electron microscopy analysis

[0063] The electron microscope scanning results are attached. Figures 5 to 7 As shown, Figure 5 The image shows the morphology of nano-calcium carbonate at 40,000x magnification. Figure 6 The microstructure of the sample without nano-calcium carbonate reinforcement is shown at 200x magnification. Figure 7 The microstructure of the sample reinforced with 1% nano-calcium carbonate at 200x magnification is shown. Figure 6 The amount of calcium carbonate crystals in it is small and they are scattered. Figure 7 The presence of numerous calcium carbonate crystals almost completely filled the pores of the sample, exhibiting a compact distribution. This indicates that the strength enhancement achieved by incorporating nano-calcium carbonate in this invention stems from the increased formation of calcium carbonate, providing theoretical support for the high strength of the sample.

[0064] 4. XRD mineral diffraction analysis

[0065] XRD mineral diffraction patterns are attached. Figures 8 to 9 As shown, Figure 8 The diffraction pattern of the sample without the addition of nano-calcium carbonate reinforcement. Figure 9 The image shows the diffraction pattern of the sample reinforced with 1% nano-calcium carbonate. As can be seen from the image, the mineral crystal form induced by Bacillus pasteurellii remained unchanged after the addition of nano-calcium carbonate, indicating that the strength improvement of the sample was achieved by inducing the formation of more calcite.

[0066] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing high-strength microbial mortar using nano calcium carbonate, characterized in that, The method comprises the following steps of: adding nano calcium carbonate into quartz sand, and using the bacillus pasteurii bacteria liquid, fixing liquid and cementing liquid as grouting materials to solidify loose sand into rock; The method for preparing high-strength microbial mortar by using nano calcium carbonate comprises the following steps: 1) quartz sand with different mesh numbers as aggregate, which is mixed according to the proportion to obtain a base material; the aggregate is composed of 18-35 mesh, 35-60 mesh and 60-200 mesh quartz sand particles; wherein the mass ratio of the three different mesh numbers of quartz sand is 25:7:3; the non-uniformity coefficient C u =2.69 and the curvature coefficient C c =1.35 of the base material; 2) adding water and nano calcium carbonate into the base material and mixing them uniformly to obtain nano calcium carbonate-quartz sand mortar; the water-sand ratio of the nano calcium carbonate-quartz sand mortar is 4-5%, and the nano calcium carbonate content is 1%; the purity of the nano calcium carbonate is 99.9%, and the effective particle size is 40-100 nm; 3) using a polypropylene needle cylinder with an inner diameter of 50 mm and a height of 170 mm as a mold, filling the nano calcium carbonate-quartz sand mortar into the mold in multiple times and vibrating and tamping to obtain a mortar sample; the final height of the mortar sample after vibrating and tamping is 11-12 cm, and the dry density range is 1.78-1.86 g / cm 3 ; wherein the material dosage of the mortar sample is: 300 g of 18-35 mesh quartz sand, 84 g of 35-60 mesh quartz sand, and 36 g of 60-200 mesh quartz sand, a total of 420 g; 20 g of water; 4.2 g of nano calcium carbonate; 4) the bacillus pasteurii bacteria liquid, fixing liquid and cementing liquid are injected into the sample in four times respectively to perform grouting reinforcement on the sample; the grouting rate is 3 mL / min, the interval time of each grouting is 12 h, and the grouting sequence is the bacillus pasteurii bacteria liquid, fixing liquid and cementing liquid; The total amount of the bacillus pasteurii bacteria liquid is 100 mL, the OD value is 3-3.5, and the enzyme activity value is 1.2-1.5 ms / (cm·min); the fixing liquid is a 0.04-0.07 mol / L calcium chloride solution, and the total amount is 100 mL; the cementing liquid is a 1:1 urea-calcium chloride mixed solution with a concentration of 0.5-1 mol / L, and the total amount is 2 L; 5) the sample after grouting is maintained at room temperature.

2. The method for preparing high-strength microbial mortar using nano calcium carbonate according to claim 1, characterized in that, In step 2), the base material, water and nano calcium carbonate are stirred in a stirring pot at 200 rpm / min for 3 min.

3. The method for preparing high-strength microbial mortar using nano calcium carbonate according to claim 1, characterized in that, In step 5), the sample is maintained for 2-3 days after grouting.

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