Curing agent with biological self-healing capability and preparation method thereof

Abstract

The invention discloses a preparation method of a curing agent with biological self-healing capability, which comprises the following steps: preparing a bacillus pasteurii bacterial solution, preparing the bacillus pasteurii bacterial solution into an endophytic spore solution, immersing polyvinyl alcohol fibers into a sodium alginate / endophytic spore solution, taking out the polyvinyl alcohol fibers, immediately immersing the polyvinyl alcohol fibers into a calcium acetate solution, drying the polyvinyl alcohol fibers to obtain core fibers with a hydrogel coating, and curing the core fibers with the hydrogel coating to obtain the curing agent with biological self-healing capability. The preparation method comprises the following steps: taking magnesium phosphate cement as a raw material, immediately immersing the magnesium phosphate cement into a chloroform solution of a polystyrene and polylactic acid polymer blend, drying to obtain a coated microbial liquid, premixing urea and glucose, doping the premixed urea and glucose into the magnesium phosphate cement, uniformly stirring, adding the coated microbial liquid, and uniformly stirring to obtain the product. According to the invention, phosphate cement is adopted as the curing agent, has the advantages of high strength, short setting time, strong durability, low alkalinity, good biocompatibility and the like, and compared with the curing agent in the prior art, the curing agent not only has a good curing effect, but also has a crack self-healing function, and is especially suitable for reinforcing foundation soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering, and particularly relates to a curing agent with biological self-healing ability and a preparation method thereof. Background Art

[0002] With the continuous development of China's economy and the acceleration of the urbanization process, the scale of infrastructure construction has been continuously expanding, and the stability problem has become increasingly prominent. There is an urgent need to use a curing agent to ensure the long-term stability of the foundation, prevent the foundation from being gradually damaged when subjected to external loads or natural environmental changes, and thus cause unstable phenomena such as sliding and collapse. The traditional curing agent is ordinary Portland cement, but its production process has high energy consumption and will emit a large amount of carbon dioxide, causing serious environmental impacts. In recent years, with the deepening of the environmental protection concept, the environmental pollution problems caused by traditional soil curing agents during the construction process have received more and more attention.

[0003] In this context, the demand for biological self-healing curing agents, as a new type of environmentally friendly soil curing agent, is particularly urgent. A biological self-healing curing agent refers to a soil curing agent made by using biotechnology or biological materials. Its mechanism of action is to promote the biochemical reaction between soil particles by stimulating the activity of microorganisms in the soil or introducing specific microorganisms, thereby improving the engineering properties of the soil. The biological self-healing curing agent can effectively solidify various soft foundation soils, improve land utilization rate, and is conducive to alleviating the current situation of tense land resources. As the requirements for the rapid construction and long-term stability of foundation treatment technologies in infrastructure construction are getting higher and higher. The biological self-healing curing agent has the advantages of simple construction, high speed, and high early strength, and can meet the needs of rapid construction. At the same time, its self-healing performance ensures the stability of the foundation soil during long-term use and reduces the later maintenance cost.

[0004] On the other hand, compared with other cementitious materials, magnesium phosphate cement has a wide range of advantages: MPC has the ability to set and harden rapidly, which means that it can form structural strength in a very short time after construction, thus accelerating the construction progress; it has high early strength (the compressive strength can reach 28 MPa at 1 h and over 40 MPa at 3 h); MPC can set quickly in a low-temperature environment; MPC has high wear resistance and can resist the effects of abrasion and freeze-thaw cycles, which makes it suitable for structures exposed to harsh environments; MPC has a low drying shrinkage rate, which means that it produces fewer cracks during the hardening process, thus improving the integrity and durability of the structure; MPC has good fire resistance and can maintain its structural integrity even at high temperatures, which is an important property for building structures with high fire protection requirements; MPC has a low coefficient of thermal expansion, which means that its volume changes less when the temperature changes, thus reducing the stress and cracks caused by temperature changes; in addition, magnesium phosphate cement also has low alkalinity and good biocompatibility. However, due to the lack of long-term strength and durability of magnesium phosphate cement, its application in practical engineering is greatly limited, so it is not a commonly used curing agent.

[0005] Based on this, the present invention intends to combine the biological self-healing technology with magnesium phosphate cement to provide a curing agent with biological self-healing ability, and improve the long-term strength and durability of magnesium phosphate cement through the biological self-healing technology to expand its application range. Summary of the Invention

[0006] The object of the present invention is to provide a curing agent with biological self-healing ability and a preparation method thereof in view of the deficiencies of the prior art. The prepared curing agent has good curing effect and also has the function of crack self-healing.

[0007] The present invention uses phosphate cement with low alkalinity and good biocompatibility, and adds endospores of Bacillus pasteurii wrapped by a coating, glucose and urea. When the cured product is cracked, this microbial coating contacts moisture and can automatically release the bacterial endospores. After the bacterial endospores contact moisture and nutrients, they will be automatically activated, and then urea hydrolysis occurs to produce calcium carbonate minerals to repair the cracks. In addition, the present invention also uses biofibers as the carrier of the biological agent, which can introduce the crack growth control ability into the curing agent, not only produce a crack bridging effect, but also improve the mechanical properties after curing. The specific scheme of the present invention is as follows:

[0008] A preparation method of a curing agent with biological self-healing ability includes the following steps:

[0009] (1) Activate Bacillus pasteurii and inoculate it into a liquid medium. Culture at 35°C and 150 rpm for 1 day to obtain a Bacillus pasteurii bacterial solution. Transfer the Bacillus pasteurii bacterial solution to a solid medium containing calcium ions and phosphates. After heat shock treatment, continue to culture at 30 - 37°C. After culturing is completed, scrape the bacterial lawn, suspend it with sterile water, and centrifuge to collect endospores to obtain an endospore solution;

[0010] (2) Add sodium alginate to the endospore solution to obtain a sodium alginate / endospore solution. Immerse polyvinyl alcohol fibers into the sodium alginate / endospore solution, and immediately immerse them into a calcium acetate solution after taking them out. After drying, obtain core fibers with a hydrogel coating. Immediately immerse the core fibers with a hydrogel coating into a chloroform solution of a polystyrene and polylactic acid polymer blend. After drying, obtain a coated microbial bacterial solution;

[0011] (3) Premix urea and glucose and incorporate them into magnesium phosphate cement. After stirring evenly, slowly add the coated microbial bacterial solution and stir evenly to obtain a curing agent with self - healing ability.

[0012] Furthermore, in step (1), the formula of the liquid medium is: 15 - 20 g / L peptone, 5 - 10 g / L soy peptone, 5 - 10 g / L sodium chloride, 15 - 20 g / L urea, pH = 7.3; the formula of the solid medium is: 5 - 10 g / L yeast extract, 5 - 10 g / L tryptone, 5 - 10 g / L sodium chloride, 15 - 20 g / L agar, (0.5 - 0.8) g / L CaCl2·2H2O, (0.1 - 0.2) g / L K2HPO4.

[0013] Furthermore, in step (1), the temperature of the heat shock treatment is 50 - 65°C and the duration is 2 h.

[0014] Furthermore, in step (2), the length of the polyvinyl alcohol fibers is 25 - 35 mm and the diameter is 600 - 650 μm.

[0015] Furthermore, in step (2), in the sodium alginate / endospore solution, the concentration of sodium alginate is (5 - 10) g / L.

[0016] Furthermore, in step (2), the concentration of the calcium acetate solution is 0.22 - 0.25 mol / L.

[0017] Further, in step (2), the mass concentration of the chloroform solution of the polystyrene and polylactic acid polymer blend is 1%; the preparation method of the chloroform solution of the polystyrene and polylactic acid polymer blend: add polystyrene into chloroform, stir and heat to 50 - 80 °C to obtain a polystyrene solution, then add polylactic acid, and the mass ratio of polystyrene to polylactic acid is 1:1.2, stir until completely dissolved to obtain the chloroform solution of the polystyrene and polylactic acid polymer blend.

[0018] Further, in step (3), the mass ratio of urea, glucose, the coated microbial bacterial solution, and magnesium phosphate cement is (1 - 2):(0.5 - 1):(1 - 2):(95 - 97.5), and more preferably 1.6:0.8:1.6:96.

[0019] The curing agent with biological self-healing ability prepared by the above method.

[0020] Advantages of the present invention: The present invention discloses a preparation method of a curing agent with biological self-healing ability. A phosphate cement with low alkalinity and good biocompatibility is mixed with bacterial endospores with a bacterial coating to prepare the curing agent. Compared with the curing agents in the prior art, the present invention has the following advantages:

[0021] 1) The curing agent of the present invention not only has a good curing effect but also has a crack self-healing function.

[0022] 2) The present invention uses cross-linked alginate as the carrier of bacterial endospores, which can release bacterial endospores when encountering water. Alginate is a hydrophilic polymer. When it encounters water, it will absorb water and swell. This hydration can cause the cross-linked alginate network structure to become loose. Therefore, cross-linked alginate has the ability to release bacterial endospores after encountering water.

[0023] 3) The present invention uses polyvinyl alcohol (PVA) fibers as the core fibers to transport endospores. Polyvinyl alcohol fibers have the characteristics of high strength, high modulus, low elongation, wear resistance, acid and alkali resistance, and good weather resistance, and have good affinity and binding properties with substrates such as cement and gypsum. The present invention uses biological fibers to transport the biological self-healing agent containing bacterial endospores into quasi-brittle materials such as concrete. In this way, when cracks appear in the cured product, the bacterial endospores can be activated, and these cracks can be repaired through their growth and metabolic activities, thereby endowing the concrete with the ability of self-healing.

[0024] 4) The present invention uses a mixture of polystyrene and polylactic acid copolymer as the external non-permeable layer. Among them, polystyrene has good transparency and insulation, but is not easily degraded, causing pressure on the environment. Polylactic acid is a biodegradable plastic derived from renewable resources such as corn starch. It can be decomposed by microorganisms under certain conditions, is environmentally friendly, and is commonly used in food packaging, medical implants, 3D printing materials, etc. In the present invention, polystyrene and polylactic acid copolymer are mixed. The addition of polylactic acid can improve the environmental friendliness of the material and partially solve the problem of the difficult degradation of polystyrene. Polystyrene can improve certain physical properties of polylactic acid, such as improving its impact resistance and mechanical strength. The shell layer is designed to withstand the process of soil solidification without any rupture or unnecessary release of biological agents, and it will only rupture when the solidified soil rupture reaches each biological fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Ratio of calcium carbonate in solid residue at different ages after cracks are generated in the curing agent prepared in Example 1;

[0026] Figure 2 Unconfined compressive strength test results of the curing agents in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments.

[0028] To clearly illustrate the present invention, in the following embodiments, the Bacillus pasteurii used was purchased from Shanghai Center for Biotechnology Preservation; the formula of the liquid medium used was: the liquid medium formula: (15 - 20) g / L casein peptone, (5 - 10) g / L soy peptone, 5 - 10 g / L sodium chloride, 15 - 20 g / L urea, pH = 7.3; the formula of the solid medium used: 5 - 10 g / L yeast extract, 5 - 10 g / L tryptone, 5 - 10 g / L sodium chloride, 15 - 20 g / L agar, CaCl2·2H2O (0.5 - 0.8) g / L, K2HPO4 (0.1 - 0.2) g / L. The mass concentration of the chloroform solution of the polystyrene and polylactic acid polymer blend used was 1%. The preparation method of the chloroform solution of the polystyrene and polylactic acid polymer blend: Add polystyrene to chloroform, stir and heat to 50 - 80 °C to obtain a polystyrene solution, then add polylactic acid, and the mass ratio of polystyrene to polylactic acid is 1:1.2, stir until completely dissolved to obtain the chloroform solution of the polystyrene and polylactic acid polymer blend.

[0029] Example 1

[0030] A preparation method of a curing agent with biological self-healing ability, comprising the following steps:

[0031] (1) Activate Bacillus pasteurii and inoculate it into a liquid medium, culture at 35 °C and 150 rpm for 1 day to obtain a Bacillus pasteurii bacterial solution. Measure the bacterial concentration using the absorbance test method, and the number of bacteria per milliliter is 6.57×10 7 . Transfer the Bacillus pasteurii bacterial solution to a solid medium containing calcium ions and phosphates, perform heat shock treatment at 60 °C for 2 h. After completion, continue to culture at 30 - 37 °C. After the culture is completed, scrape the bacterial lawn, suspend it with sterile water, and centrifuge to collect endospores to obtain an endospore solution (the measured spore solution concentration is the number of endospores per milliliter is 5.26×10 7 );

[0032] (2) Add sodium alginate to the endospore solution to obtain a sodium alginate / endospore solution. In the sodium alginate / endospore solution, the concentration of sodium alginate is 8 g / L. Immerse polyvinyl alcohol fibers (length 30 mm, diameter 611 μm) into the sodium alginate / endospore solution, and immediately immerse them into a 0.24 mol / L calcium acetate solution after taking them out. Dry at 23 ± 1 °C and 30 ± 5% relative humidity for 24 h to obtain core fibers with a hydrogel coating. Immediately immerse the core fibers with a hydrogel coating into a chloroform solution of a polystyrene and polylactic acid polymer blend (the mass concentration of the polystyrene and polylactic acid polymer blend is 1%), and dry at 23 ± 1 °C and 30 ± 5% relative humidity for 2 h after taking them out to obtain a coated microbial bacterial solution.

[0033] (3) First, prepare magnesium phosphate cement: 1) Based on the total mass of MgO, granulated blast furnace slag, ammonium dihydrogen phosphate, and fly ash being 100%, add 40% of MgO, 10% of granulated blast furnace slag, and 0.03% of a setting retarder (the setting retarder is composed of sodium bicarbonate and sodium tripolyphosphate with a mass ratio of 1:1) to a mixer and dry mix at low speed for 2 minutes; 2) Add 20% of ammonium dihydrogen phosphate, 30% of fly ash, and 0.03% of a setting retarder (the setting retarder is composed of sodium bicarbonate and sodium tripolyphosphate with a mass ratio of 1:1) to a second mixer and also dry mix at the same low speed for 2 minutes; 3) Slowly add 20% of water to the first mixer and 15% of water to the second mixer, and fully wet mix at high speed for 2 minutes to homogenize the slurry; 4) Quickly mix the two components together, and after high-speed stirring for 30 s, obtain magnesium phosphate cement;

[0034] Premix 10 g of urea and 5 g of glucose and incorporate them into 600 g of magnesium phosphate cement, stir and mix evenly, slowly add 10 g of the coated microbial bacterial solution prepared in step (2), stir evenly to obtain a curing agent with self-healing ability.

[0035] Pour the prepared curing agent with self-healing ability into 20mm and 40mm cubes, cure in the air, then demold, and then further cure the samples in the air (temperature 20°C ± 2°C, humidity 60% ± 5%) for 28 days. After curing is completed, take some samples for unconfined compressive strength testing. The testing method refers to the GB-T50123-2019 Geotechnical Test Methods Standard; additionally, create cracks in some samples (before the cement hardens, pre-cut a crack on the cement surface. The crack width is 2mm, the crack length is 10mm, and the crack depth is 5mm). Gently scrape the sample inside the crack with a knife, use infrared spectroscopy to determine the calcium carbonate content, and then measure the calcium carbonate content at the crack every seven days. After 28 days of healing, measure the unconfined compressive strength (GB-T50123-2019 Geotechnical Test Methods Standard).

[0036] Comparative Example 1

[0037] Use ordinary Portland cement as the comparative example.

[0038] Pour ordinary Portland cement into 20mm and 40mm cubes, cure in the air, and then demold. Then further cure the samples in the air (temperature 20°C ± 2°C, humidity 60% ± 5%) for 28 days. Measure its unconfined compressive strength (GB-T50123-2019 Geotechnical Test Methods Standard).

[0039] Figure 1 For the proportion of calcium carbonate in the solid residue at different ages after cracks are generated in the curing agent prepared in Example 1; from Figure 1 It can be seen that as time goes by, taking the content of calcium carbonate in the solid residue in the sample in the crack, it becomes larger and larger. This shows that microorganisms induce the generation of calcium carbonate minerals, proving the excellent bio-mineralization ability and strong self-healing ability of this bio-self-healing curing agent.

[0040] Figure 2 For the unconfined compressive strength test results of the curing agents in Example 1 and Comparative Example 1, from Figure 2 It can be seen that the unconfined compressive strength of Example 1 is 114MPa, and the unconfined compressive strength of Comparative Example 1 is only 51MPa. This shows that the curing agent prepared in Example 1 of the present invention has excellent strength performance. When artificial cracks are made on the curing agent prepared in Example 1 and then bio-self-healed for 28 days, the result shows that its unconfined compressive strength after 28 days of self-healing is 100MPa. Compared with the unconfined compressive strength without cracks, it has recovered by about 90%, proving the excellent bio-self-healing ability of the curing agent prepared in Example 1 of the present invention.

Claims

1. A method for preparing a curing agent with biological self-healing ability, characterized in that: The steps include: (1) activating Bacillus pasteurianus and inoculating it into a liquid culture medium, culturing it at 35° C. and 150 rpm for 1 day to obtain a Bacillus pasteurianus bacterial liquid, transferring the Bacillus pasteurianus bacterial liquid to a solid culture medium containing calcium ions and phosphates, and subjecting it to heat shock treatment. After the end, the culture is continued at 30-37° C., and after the culture is completed, the bacterial lawn is scraped, suspended with sterile water, and endospores are collected by centrifugation to obtain an endospore solution; (2) adding sodium alginate to the endospore solution to obtain a sodium alginate / endospore solution, immersing the polyvinyl alcohol fiber in the sodium alginate / endospore solution, taking out and immediately immersing it in a calcium acetate solution, and drying to obtain a core fiber with a hydrogel coating, and immediately immersing the core fiber with the hydrogel coating in a chloroform solution of a polystyrene and polylactic acid polymer blend, and drying to obtain a coated microbial bacterial liquid; (3) Premixing urea and glucose and adding them into magnesium phosphate cement, stirring evenly, slowly adding the coated microbial solution, stirring evenly, and obtaining a curing agent with biological self-healing ability.

2. The method for preparing a curing agent having biological self-healing ability according to claim 1, characterized in that: In step (1), the liquid culture medium formula is: 15-20 g / L casein peptone, 5-10 g / L soy peptone, 5-10 g / L sodium chloride, 15-20 g / L urea, pH = 7.3; the solid culture medium formula is: yeast extract 5-10 g / L, tryptic peptone 5-10 g / L, sodium chloride 5-10 g / L, agar 15-20 g / L, CaCl2·2H2O (0.5-0.8) g / L, K2HPO4 (0.1-0.2) g / L.

3. The method for preparing a curing agent having biological self-healing ability as claimed in claim 1, characterized in that In step (1), the temperature of the heat shock treatment is 50-65°C and the duration is 3 hours.

4. The method for preparing a curing agent with biological self-healing ability as claimed in claim 1, characterized in that: In step (2), the length of the polyvinyl alcohol fiber is 25-35 mm and the diameter is 600-650 μm.

5. The method for preparing a curing agent having biological self-healing ability as claimed in claim 1, characterized in that In step (2), the concentration of sodium alginate in the sodium alginate / endospore solution is (5-10) g / L.

6. The method for preparing a curing agent having biological self-healing ability as claimed in claim 1, characterized in that In step (2), the concentration of the calcium acetate solution is 0.22-0.25 mol / L.

7. The method for preparing a curing agent with biological self-healing ability as claimed in claim 1, characterized in that: The mass concentration of the chloroform solution of the polystyrene and polylactic acid polymer blend is 1%; the preparation method of the chloroform solution of the polystyrene and polylactic acid polymer blend is as follows: polystyrene is added to chloroform, stirred and heated to 50-80°C to obtain a polystyrene solution, and then polylactic acid is added, the mass ratio of polystyrene to polylactic acid is 1:1.2, and stirred until completely dissolved to obtain a chloroform solution of the polystyrene and polylactic acid polymer blend.

8. The method for preparing a curing agent having biological self-healing ability according to any one of claims 1 to 7, characterized in that: In step (3), the mass ratio of urea, glucose, coated microbial culture liquid and magnesium phosphate cement is (1-2): (0.5-1): (1-2): (95-97.5).

9. A curing agent with biological self-healing ability prepared by the method according to any one of claims 1 to 8.

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