Preparation method of microbial carbon sequestration reinforced recycled coarse aggregate

Abstract

The present application relates to the technical field of microbial carbon fixation, and particularly relates to a preparation method of microbial carbon fixation reinforced recycled coarse aggregate, which comprises the following steps: firstly, modifying a carrier with large pores on the surface, loading active carbon fixation microorganisms in the micropores of the modified carrier, and then mixing the modified carrier with the recycled coarse aggregate under the action of pneumatic stirring, wherein the carrier with small particle size moves irregularly under the air pressure, and the carrier with small particle size can enter the large gaps on the surface of the recycled coarse aggregate to adhere to the gaps, so that the gaps are pre-filled, the microorganisms are introduced into the gaps through the carrier, the number of the microorganisms and the pre-filled amount of the gaps are increased, the deposition amount of calcium carbonate is improved in the subsequent microbial carbon fixation treatment, the large gaps are filled sufficiently, the reinforcing effect is improved, and the water absorption of the product is reduced.

Description

Technical Field

[0001] This invention relates to the field of microbial carbon fixation technology, and specifically to a method for preparing microbial carbon fixation-enhanced recycled coarse aggregate. Background Technology

[0002] With the acceleration of industrialization and urbanization, the construction area is increasing daily, resulting in a huge amount of waste concrete being demolished each year, and the associated construction waste is rising year by year. Currently, most of the construction waste is directly transported to the suburbs and rural areas for open-air dumping or landfill disposal, consuming a large amount of construction costs such as land acquisition fees, waste transportation fees, and disposal fees.

[0003] According to rough statistics on construction material waste in brick-concrete, cast-in-place, and frame structures, 500-600 tons of construction waste are generated during the construction of every 10,000 square meters of building. Furthermore, the demolition of every 10,000 square meters of old buildings generates 7,000-12,000 tons of construction waste. The inability to scientifically utilize this large amount of construction waste causes significant harm to environmental management. How to scientifically and effectively solve the current construction waste problem and achieve its resource utilization is an urgent issue that needs to be addressed.

[0004] To maintain the sustainable development of the construction industry, alleviate the severe shortage of natural resources, reduce environmental pollution from waste concrete accumulation, and lower carbon emissions from the construction sector, the recycling and resource utilization of construction waste has emerged. During the recycling process, crushing and screening produce coarse particles larger than 4.75 mm. Improving the comprehensive utilization rate of construction waste and achieving resource utilization of these coarse particles is crucial. Currently, recycled aggregates obtained through intensification are applied in practical engineering. However, recycled aggregates produced using simple crushing processes have low strength, high water absorption, large performance dispersion, and poor quality, failing to fundamentally solve the problem of the shortage of natural aggregate resources for structural concrete. Therefore, seeking a method for preparing high-strength, low-water-absorption, and stable high-quality recycled aggregates is urgent. On the other hand, current research on micro-powder is limited, and its utilization rate is extremely low. Large quantities of micro-powder are directly stockpiled, landfilled, or used in roadbed materials. How to efficiently utilize micro-powder has become a bottleneck for the resource utilization of construction waste and achieving zero emissions.

[0005] Microbially induced calcium carbonate precipitation (MICP) refers to the process by which carbon-fixing microorganisms in nature capture CO2 from the air, inducing calcium ions in the environment to precipitate calcium carbonate. Because this process transforms CO2 gas into carbonate minerals, it is also known as microbial carbon fixation. The mineralized product is calcium carbonate, which, as an environmentally friendly natural stone, has excellent compatibility with cement-based materials and has been widely used in recent years for the repair of defects in cement-based materials. In the entire process of bio-carbon fixation, regardless of the type of bacteria, they mainly play two core roles: firstly, providing a carbon source, and secondly, providing nucleation sites for the formation of calcium carbonate crystals.

[0006] Microbial mineralization and deposition of calcium carbonate, due to its excellent adhesion, compatibility, and stability with cement-based materials, is widely used in concrete defect repair, soil cementation and solidification, soil improvement, ancient building restoration, and heavy metal passivation. With the expansion of its application areas, it has also shown initial success in the resource utilization of solid waste, particularly in the strengthening of recycled aggregates. Numerous studies have demonstrated that microbial mineralization deposition technology for strengthening recycled aggregates is indeed feasible. Microorganisms deposit calcium carbonate on the surface and in the defects of recycled aggregates, forming a crystalline protective layer that prevents water and other harmful media from entering, reducing water absorption and increasing strength. Furthermore, microbial calcium carbonate exhibits good compatibility with cementitious materials, improving the interfacial transition zone performance of recycled concrete, thereby enhancing the mechanical properties and durability of recycled concrete.

[0007] The existing method for microbial carbon fixation enhancement involves soaking crushed coarse aggregate particles in a carbon-fixing microbial culture solution, followed by the introduction of carbon dioxide for carbon fixation oxidation. The principle is that microorganisms attached to the particle gaps capture CO2 from the air, inducing calcium ions in the environment to deposit and precipitate calcium carbonate, which fills the gaps in the aggregate, thus enhancing its structure and reducing water absorption. However, its technical drawback is that the gaps formed during the crushing and other pretreatment processes of coarse aggregate vary in size. For smaller gaps, microorganisms can effectively deposit and fill them with calcium carbonate. However, for larger gaps, the number of microorganisms attached to the inner wall of the gap is limited, and the space to be filled is large, making it difficult to produce a large amount of calcium carbonate. This results in poor filling of the gaps and reduces the aggregate enhancement effect. Summary of the Invention

[0008] To address the technical problem that the large gaps between particles in the preparation of microbial carbon fixation enhanced recycled coarse aggregate cannot be effectively filled, thus affecting the strengthening effect, this invention provides a method for preparing microbial carbon fixation enhanced recycled coarse aggregate, which can effectively fill the large gaps between particles in the preparation of coarse aggregate, thereby improving the strengthening effect.

[0009] This invention provides a method for preparing microbial carbon fixation enhanced recycled coarse aggregate, comprising the following steps:

[0010] (1) Take a carrier with large pores on its surface, immerse the carrier in the first microbial culture medium, stir, filter, and air dry to obtain the modified carrier;

[0011] (2) Soak the recycled coarse aggregate in the second microbial culture solution, stir, filter, and air dry to obtain modified recycled coarse aggregate;

[0012] (3) Mix the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2) and stir by spraying. Spray the modified carrier into part of the gaps in the modified recycled coarse aggregate and sieve out the modified carrier that did not enter the gaps.

[0013] (4) Take the sieve material after sieving in step (3), spray the surface of the sieve material with nutrient solution, place it in a microbial carbonization box, and pass carbon dioxide to carry out microbial carbon fixation treatment to obtain microbial carbon fixation enhanced regenerated coarse aggregate.

[0014] Furthermore, in step (1), the carrier is macroporous silica with a particle size of 10~50μm.

[0015] Furthermore, the first microbial culture medium includes microorganisms and culture medium. The microorganisms are one of Bacillus alkalophilus, Bacillus subtilis, or Bacillus mucilaginosus. The inoculum amount of the microorganisms in the culture medium is 8.0%. The culture medium is prepared according to the following concentrations of components: 8 g / L tryptone, 9 g / L soybean peptone, and 2 g / L sodium chloride.

[0016] Furthermore, the second microbial culture medium includes microorganisms and culture medium. The microorganisms are one of Bacillus subtilis, Bacillus alkalophilus, or Bacillus mucilaginosus. The inoculum amount of the microorganisms in the culture medium is 8.0%. The culture medium is prepared according to the following concentrations of components: 8 g / L tryptone, 9 g / L soybean peptone, and 2 g / L sodium chloride.

[0017] Furthermore, the weight ratio of carrier to recycled coarse aggregate is 1~3:15~25.

[0018] Furthermore, in step (2), the recycled coarse aggregate is obtained from construction waste through crushing, screening, washing and drying, and the particle size of the recycled coarse aggregate is >4.75mm.

[0019] Furthermore, in step (2), the recycled coarse aggregate is first pretreated, which includes soaking the recycled coarse aggregate in a mixed solution of urea and ammonia. The purpose is to utilize the enzymatic activity of urease in carbon-fixing microorganisms to decompose urea into carbon dioxide, providing a carbon source. On the other hand, ammonia provides an alkaline environment, which enhances the enzyme's reaction activity.

[0020] Furthermore, in step (4), the nutrient solution is prepared with the following concentrations: 8 g / L tryptone, 9 g / L soybean peptone, and 2 g / L sodium chloride. This serves to provide initial activation for the carbon fixation reaction of microorganisms, thereby improving their growth efficiency.

[0021] Furthermore, in step (4), the process conditions for microbial carbon fixation treatment are: temperature of 36±3℃, humidity of 80%~90%, time of 5~7d, and carbon dioxide pressure of 0.2~0.25MPa.

[0022] The beneficial effects of this invention are as follows:

[0023] (1) The present invention first modifies the carrier with large pores on the surface. The modified carrier is loaded with active carbon-fixing microorganisms in the micropores. Then, the modified carrier is mixed with recycled coarse aggregate under the action of pneumatic stirring. During the mixing, the carrier particles are small and move randomly under air pressure. The smaller carrier particles will enter the larger gaps on the surface of the recycled coarse aggregate and attach to them, thus "pre-filling" the gaps. The carrier introduces microorganisms into the gaps, increasing the number of microorganisms and the amount of pre-filling of the gaps. In the subsequent microbial carbon fixation treatment, the amount of calcium carbonate deposition is increased, which is conducive to fully filling the large gaps, improving the strengthening effect, and reducing the water absorption rate of the product.

[0024] (2) In this invention, the recycled coarse aggregate is soaked in a second microbial culture solution for modification treatment. The purpose is to load all the gaps with active microorganisms, so that the small gaps still contain active microorganisms for calcium carbonate deposition. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the filling structure of the modified carrier in the gaps of modified recycled coarse aggregate according to a specific embodiment of the present invention.

[0027] In the figure, 1-modified recycled coarse aggregate, 11-large-size gap, 12-small-size gap, 2-modified carrier. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0029] The recycled coarse aggregate used in the following examples is obtained by crushing, screening, washing and drying construction waste, and the particle size of the obtained recycled coarse aggregate is 5~10mm.

[0030] Example 1

[0031] A method for preparing microbial carbon fixation enhanced recycled coarse aggregate includes the following steps:

[0032] (1) Take 10g of granular macroporous silica (particle size 10~20μm) carrier, immerse the carrier in the first microbial culture medium, the first microbial culture medium includes microorganisms and culture medium, the microorganism is Bacillus mucilaginosus, the inoculation amount of microorganisms in the culture medium is 8.0%, the culture medium is prepared according to the following concentration of components: 8g / L tryptone, 9g / L soybean peptone, 2g / L sodium chloride, stir after immersion, filter, and air dry naturally to obtain the modified carrier;

[0033] (2) Soak 150g of recycled coarse aggregate in a second microbial culture medium, which includes microorganisms and culture medium. The microorganism is Bacillus mucilaginosus. The inoculation amount of microorganisms in the culture medium is 8.0%. The culture medium is prepared according to the following concentrations: 8g / L tryptone, 9g / L soybean peptone, and 2g / L sodium chloride. Stir, filter, and air dry to obtain modified recycled coarse aggregate.

[0034] (3) Mix the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2), and stir by spraying. Figure 1 During the spraying process, the modified carrier 2 enters the large-size gaps 11 of the modified recycled coarse aggregate 1 and adheres to it. The small-size gaps 12 are too small for the modified carrier 2 particles to enter. The excess modified carrier that does not enter the gaps is screened out.

[0035] (4) Take the sieve residue after sieving in step (3), spray the surface of the sieve residue with nutrient solution and place it in a microbial carbonization box. The nutrient solution is prepared with the following concentrations: 8 g / L tryptone, 9 g / L soybean peptone, and 2 g / L sodium chloride. Carbon dioxide is introduced for microbial carbon fixation treatment. The process conditions for microbial carbon fixation treatment are: temperature 36±3℃, humidity 80%~90%, time 5~7 days, and carbon dioxide pressure 0.2~0.25 MPa. Microbial carbon fixation enhanced recycled coarse aggregate is obtained.

[0036] Example 2

[0037] A method for preparing microbial carbon fixation enhanced recycled coarse aggregate includes the following steps:

[0038] (1) Take 30g of granular macroporous silica (particle size 20~50μm) carrier, immerse the carrier in the first microbial culture medium, the first microbial culture medium includes microorganisms and culture medium, the microorganism is Bacillus subtilis, the inoculation amount of microorganisms in the culture medium is 8.0%, the culture medium is prepared according to the following concentration of components: 8g / L tryptone, 9g / L soybean peptone, 2g / L sodium chloride, stir after immersion, filter, and air dry naturally to obtain the modified carrier;

[0039] (2) Soak 250g of recycled coarse aggregate in a second microbial culture medium, which includes microorganisms and culture medium. The microorganism is Bacillus mucilaginosus. The inoculation amount of microorganisms in the culture medium is 8.0%. The culture medium is prepared according to the following concentrations: 8g / L tryptone, 9g / L soybean peptone, and 2g / L sodium chloride. Stir, filter, and air dry to obtain modified recycled coarse aggregate.

[0040] (3) Mix the modified carrier obtained in step (1) with the modified recycled coarse aggregate obtained in step (2) and stir by spraying. Spray the modified carrier into part of the gaps in the modified recycled coarse aggregate and sieve out the modified carrier that did not enter the gaps.

[0041] (4) Take the sieve residue after sieving in step (3), spray the surface of the sieve residue with nutrient solution and place it in a microbial carbonization box. The nutrient solution is prepared with the following concentrations: 8 g / L tryptone, 9 g / L soybean peptone, and 2 g / L sodium chloride. Carbon dioxide is introduced for microbial carbon fixation treatment. The process conditions for microbial carbon fixation treatment are: temperature 36±3℃, humidity 80%~90%, time 5~7 days, and carbon dioxide pressure 0.2~0.25 MPa. Microbial carbon fixation enhanced recycled coarse aggregate is obtained.

[0042] Example 3

[0043] The difference between Example 3 and Example 2 is that in step (2), the recycled coarse aggregate is first pretreated, which includes soaking the recycled coarse aggregate in a mixed solution of urea and ammonia. The purpose is to utilize the enzymatic activity of urease in carbon-fixing microorganisms to decompose urea into carbon dioxide, providing a carbon source. On the other hand, ammonia provides an alkaline environment, which enhances the enzyme's reaction activity.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include the mixing operations in steps (1) and (3).

[0046] The recycled coarse aggregates prepared in each embodiment and comparative example were tested (the test methods are shown in GB / T 25177-2010), and the specific test data are shown in Table 1.

[0047] Table 1. Performance test data of recycled coarse aggregates obtained in each embodiment and comparative example.

[0048]

[0049] As can be seen from Table 1, the recycled coarse aggregates obtained in the various embodiments of the present invention meet the performance requirements of Class I recycled coarse aggregates in GB / T 25177-2010, have low crushing value and water absorption rate, and the technical effects of the embodiments of the present invention are improved compared with those of the comparative examples.

[0050] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for producing microbial carbonation reinforced recycled coarse aggregate, characterized by, It comprises the following steps: (1) Take the carrier with large holes on the surface, immerse the carrier in the first microbial culture solution, stir, filter, and naturally dry to obtain a modified carrier; (2) Soak the recycled coarse aggregate in the second microbial culture solution, stir, filter, and naturally dry to obtain a modified recycled coarse aggregate; (3) Mix the modified carrier prepared in step (1) with the modified recycled coarse aggregate prepared in step (2), stir by spraying, spray the modified carrier into part of the gap of the modified recycled coarse aggregate, and sieve out the modified carrier that does not enter the gap; (4) Take the sieve residue after sieving in step (3), spray wet nutrient solution on the surface of the sieve residue, and place it in a microbial carbonization box to perform microbial carbon sequestration treatment by introducing carbon dioxide to obtain a microbial carbon sequestration reinforced recycled coarse aggregate.

2. A method of producing microbial carbonation reinforced recycled coarse aggregate according to claim 1, wherein, In step (1), the carrier is large-pore silica, and the particle size of the large-pore silica is 10-50 μm.

3. A method of producing microbial carbonation reinforced recycled coarse aggregate according to claim 1, wherein, The first microbial culture solution comprises microorganisms and a culture solution, the microorganisms are one of alkaliphilic Bacillus, Bacillus subtilis or Bacillus mucilaginosus, the inoculation amount of the microorganisms in the culture solution is 8.0%, and the culture solution is prepared by dispensing the following components at the following concentrations: tryptone 8 g / L, soybean peptone 9 g / L, and sodium chloride 2 g / L.

4. The method for preparing microbial carbon sequestration reinforced recycled coarse aggregate according to claim 1, characterized in that, The second microbial culture solution comprises microorganisms and a culture solution, the microorganisms are one of Bacillus subtilis, alkaliphilic Bacillus or Bacillus mucilaginosus, the inoculation amount of the microorganisms in the culture solution is 8.0%, and the culture solution is prepared by dispensing the following components at the following concentrations: tryptone 8 g / L, soybean peptone 9 g / L, and sodium chloride 2 g / L.

5. The method for preparing microbial carbon sequestration reinforced recycled coarse aggregate according to claim 1, characterized in that, The weight dosage ratio of the carrier to the recycled coarse aggregate is 1-3:15-25.

6. The method for preparing microbial carbon sequestration reinforced recycled coarse aggregate according to claim 1, characterized in that, In step (2), the recycled coarse aggregate is obtained by crushing, screening, washing, and drying of construction waste, and the particle size of the recycled coarse aggregate is >4.75 mm.

7. A method of producing microbial carbonation reinforced recycled coarse aggregate according to claim 1, wherein, In step (2), the recycled coarse aggregate is first pretreated, and the pretreatment comprises soaking the recycled coarse aggregate in a mixed solution of urea and ammonia.

8. A method of producing microbial carbonation reinforced recycled coarse aggregate according to claim 1, wherein, In step (4), the nutrient solution is prepared by dispensing the following components at the following concentrations: tryptone 8 g / L, soybean peptone 9 g / L, and sodium chloride 2 g / L.

9. A method of producing microbial carbonation reinforced recycled coarse aggregate according to claim 1, wherein, In step (4), the process conditions for microbial carbon sequestration treatment are as follows: temperature 36±3℃, humidity 80%-90%, time 5-7 days, and carbon dioxide pressure 0.2-0.25 MPa.

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