Microbial mineralization modified recycled aggregate as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of building materials, and particularly relates to a microorganism mineralization modified recycled aggregate as well as a preparation method and application thereof. The preparation method of the microorganism mineralization modified recycled aggregate provided by the invention comprises the following steps: mixing a bacterium solution of microorganisms with nitrification and denitrification capabilities with a bacterium solution of urealytic bacteria for the first time to obtain a mixed bacterium solution; the isoconcentration bacterial liquid volume ratio of the microorganisms with nitrification and denitrification capabilities to the urealysis bacteria in the mixed bacterial liquid is (2: 1)-(1: 4); mixing the mixed bacterial liquid, the recycled aggregate and a mineralizing liquid for a second time, and then performing biological mineralization to obtain the microorganism mineralized modified recycled aggregate; the mineralization liquid comprises urea and calcium formate. The recycled aggregate is subjected to microbial mineralization under the combined action of microorganisms with nitrification and denitrification capacities and urealysis bacteria in a specific proportion, a calcium carbonate protection layer can be generated, the strength of the recycled aggregate is improved, the generated ammonia gas is less, and large-scale application is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a microbially mineralized modified recycled aggregate, a preparation method thereof, and an application thereof. Background Art

[0002] With the advancement of the urbanization process and the development of civil construction and transportation infrastructure construction projects, the volume of construction solid waste, especially waste concrete, is increasing day by day. At present, the main methods for treating construction solid waste are open-air stacking or landfill, but this method will cause serious environmental pollution.

[0003] Recycling waste concrete as recycled aggregate concrete not only solves the problem of treating construction solid waste but also saves natural resources. The utilization of recycled aggregate has many benefits for the environment. However, compared with natural aggregate, the apparent density of recycled aggregate is lower, and the water absorption rate and crushing value are higher. When using recycled aggregate to replace natural aggregate to make concrete, due to the poor properties of recycled aggregate, the core performance technical indicators such as compressive strength, flexural strength, and frost resistance of recycled aggregate concrete show a significant downward trend compared with natural aggregate concrete. At the same time, due to the above inherent weaknesses of recycled aggregate, when using recycled aggregate to prepare recycled concrete, the replacement rate of recycled aggregate replacing natural aggregate often does not exceed 40% to ensure the mechanical properties and durability of recycled concrete, which greatly limits the utilization efficiency of recycled aggregate.

[0004] In order to improve the properties of recycled aggregate, it is necessary to strengthen the recycled aggregate. Researchers have found that applying bio-mineralization guided by ureolytic bacteria to recycled aggregate can improve the performance of recycled aggregate. However, according to the "Occupational Exposure Limits for Hazardous Agents in the Workplace" GBZ2.1-2019, the short-term exposure limit (STEL) of ammonia is 30 mg / m 3 (about 16.7 ppm), and the time-weighted average allowable concentration (TLV) for an eight-hour workday is 20 mg / m 3 (about 11 ppm). When using ureolytic bacteria to strengthen recycled aggregate, treating 1 kg of recycled aggregate can make a 20 L container reach 75.7 ppm. The amount of ammonia generated in this way is too high and is not suitable for large-scale treatment of strengthened recycled aggregate. Summary of the Invention

[0005] In view of this, the present invention provides a microbially mineralized modified recycled aggregate, a preparation method thereof, and an application thereof. During the process of preparing the microbially mineralized modified recycled aggregate according to the method provided by the present invention, less ammonia is generated, which is easy to be applied industrially.

[0006] In order to solve the above technical problems, the present invention provides a preparation method for a microbially mineralized modified recycled aggregate, comprising the following steps:

[0007] First mix the bacterial solution of microorganisms with both nitrification and denitrification capabilities and the bacterial solution of ureolytic bacteria to obtain a mixed bacterial solution; the volume ratio of the bacterial solutions of microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria with equal concentration in the mixed bacterial solution is 2:1 to 1:4;

[0008] Second mix the mixed bacterial solution, recycled aggregate and mineralization solution and then carry out biomineralization to obtain a microbially mineralized modified recycled aggregate; the mineralization solution includes urea and calcium formate.

[0009] Preferably, the microorganisms with both nitrification and denitrification capabilities include Paracoccus denitrificans and / or Pseudomonas;

[0010] The ureolytic bacteria include Bacillus pasteurii and / or Bacillus megaterium.

[0011] Preferably, the concentration of the bacterial solution of the microorganisms with both nitrification and denitrification capabilities is 10 7 ~10 8 CFU / L;

[0012] The concentration of the bacterial solution of the ureolytic bacteria is 10 7 ~10 8 CFU / L.

[0013] Preferably, the second mixing includes the following steps:

[0014] Third mix the mixed bacterial solution and the recycled aggregate and then let it stand to obtain a recycled aggregate with attached microorganisms;

[0015] Fourth mix the mineralization solution and the recycled aggregate with attached microorganisms.

[0016] Preferably, the mass concentration of urea in the mineralization solution is 6 - 30 g / L, and the mass concentration of calcium formate in the mineralization solution is 40 - 45 g / L; the mass ratio of the recycled aggregate to the volume of the mineralization solution is 1 kg:1.1 - 1.8 L;

[0017] The mass ratio of the mixed bacterial solution to the recycled aggregate is 0.08 - 0.12:1.

[0018] Preferably, the mineralization solution further includes calcium chloride and / or glucose;

[0019] When the mineralization solution includes calcium chloride, the mass concentration of calcium chloride in the mineralization solution is 50 - 60 g / L;

[0020] When the mineralization solution includes glucose, the mass concentration of glucose in the mineralization solution is 0.8 - 1.2 g / L.

[0021] Preferably, after the second mixing, it further includes: mixing the system after the second mixing with a pH regulator to adjust the pH value to 8.5-9.5;

[0022] The pH regulator includes a sodium hydroxide solution.

[0023] Preferably, the biomineralization is to let the system after the second mixing stand still, and the standing time is 7-10 days; the temperature of the standing environment is 20-40 °C.

[0024] The present invention also provides a microbially mineralized modified recycled aggregate prepared by the preparation method described in the above technical solution;

[0025] The water absorption rate of the microbially mineralized modified recycled aggregate is 8.58-8.82%, and the apparent density is 2571-2591 kg / m 3 , and the crushing index is 17.5-18.1%.

[0026] The present invention also provides the application of the microbially mineralized modified recycled aggregate described in the above technical solution in recycled aggregate concrete.

[0027] The present invention provides a preparation method of a microbially mineralized modified recycled aggregate, including the following steps: firstly mixing the bacterial liquid of microorganisms with both nitrification and denitrification capabilities and the bacterial liquid of ureolytic bacteria to obtain a mixed bacterial liquid; the volume ratio of the microorganisms with both nitrification and denitrification capabilities to the equal-concentration bacterial liquid of ureolytic bacteria in the mixed bacterial liquid is 2:1-1:4; secondly mixing the mixed bacterial liquid, recycled aggregate and mineralization liquid and then carrying out biomineralization to obtain a microbially mineralized modified recycled aggregate; the mineralization liquid includes urea and calcium formate. The present invention carries out microbially mineralizes the recycled aggregate under the joint action of microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria in a specific ratio. During the biomineralization process, ureolytic bacteria will decompose urea to produce ammonia and calcium carbonate, and the calcium carbonate adheres to the surface of the recycled aggregate to increase the density and hardness of the recycled aggregate; microorganisms with both nitrification and denitrification capabilities will first convert the ammonia produced by ureolytic bacteria decomposing urea into nitrate ions and then into nitrogen to reduce the production of ammonia, and at the same time generate calcium carbonate attached to the surface of the recycled aggregate to further improve the strength of the recycled aggregate. During the biomineralization process, a dense calcium carbonate protective layer is formed on the surface of the recycled aggregate, which not only improves the strength of the recycled aggregate but also reduces its water absorption rate, thereby improving the performance of recycled aggregate concrete. Description of the Drawings

[0028] Figure 1 It is the SEM image of the surface of the recycled aggregate in Example 1;

[0029] Figure 2 It is the SEM image of the surface of the microbially mineralized modified recycled aggregate prepared in Example 3;

[0030] Figure 3 XRD pattern of the microbially mineralized modified recycled aggregate prepared in Example 3. Detailed implementation mode

[0031] The present invention provides a method for preparing a microbially mineralized modified recycled aggregate, comprising the following steps:

[0032] Firstly, mix the bacterial solutions of microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria to obtain a mixed bacterial solution; the volume ratio of the equal-concentration bacterial solutions of the microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria is 2:1 to 1:4;

[0033] Secondly, secondarily mix the mixed bacterial solution, recycled aggregate and mineralization solution and carry out biomineralization to obtain the microbially mineralized modified recycled aggregate; the mineralization solution includes urea and calcium formate.

[0034] In the present invention, the bacterial solutions of microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria are firstly mixed to obtain a mixed bacterial solution. As a specific implementation mode of the present invention, the microorganisms with both nitrification and denitrification capabilities (SND bacteria) may include Paracoccus azotifigens and / or Pseudomonas sp., and may specifically be a mixed bacterium of Paracoccus azotifigens and Pseudomonas sp., Paracoccus azotifigens or Pseudomonas sp.; the Paracoccus azotifigens may be Paracoccus denitrificans (Pd) (ATCC19367), and the Pseudomonas sp. may be Pseudomonas.Sp (Psp) (ATCC13867). As a specific implementation mode of the present invention, the ureolytic bacteria may include Sporosarcina pasteurii and / or Bacillus megaterium, and may specifically be a mixed bacterium of Sporosarcina pasteurii (Sporosarcina pasteurii) and Bacillus megaterium, Sporosarcina pasteurii or Bacillus megaterium; the Sporosarcina pasteurii may be ATCC 11859 Sporosarcina pasteurii (SP), and the Bacillus megaterium may be Bacillus megaterium de Bary (Bm) (ATCC 25300). As a specific implementation mode of the present invention, the volume ratio of the equal-concentration bacterial solutions of the microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria in the mixed bacterial solution may be 2:1 to 1:4, and may specifically be 1:4, 1:2, 1:1 or 2:1.

[0035] As a specific embodiment of the present invention, the culture medium for cultivating microorganisms with both nitrification and denitrification capabilities may include meat extract powder, sodium chloride, sodium nitrate, and distilled water; the mass concentration of meat extract powder in the culture medium for cultivating microorganisms with both nitrification and denitrification capabilities may be 1-10 g / L, and may also be 5-8 g / L; the mass concentration of sodium chloride may be 5-20 g / L, and may also be 10-15 g / L; the mass concentration of sodium nitrate may be 8.5-42.5 g / L, and may also be 20-30 g / L. The purpose of adding sodium nitrate to the culture medium for cultivating microorganisms with both nitrification and denitrification capabilities in the present invention is to improve the utilization ability of bacteria for nitrate ions.

[0036] As a specific embodiment of the present invention, the culture medium for cultivating ureolytic bacteria may include meat extract powder, sodium chloride, urea, and distilled water; the mass concentration of meat extract powder in the culture medium for cultivating ureolytic bacteria may be 1-10 g / L, and may also be 5-8 g / L; the mass concentration of sodium chloride may be 5-20 g / L, and may also be 10-15 g / L; the mass concentration of urea may be 6-31 g / L, and may also be 10-25 g / L. As a specific embodiment of the present invention, the cultivation temperature for microorganisms with both nitrification and denitrification capabilities and ureolytic bacteria may be 20-40 °C, and may also be 30-35 °C. As a specific embodiment of the present invention, the concentration of the bacterial liquid of the microorganisms with both nitrification and denitrification capabilities may be 10 7 ~10 8 CFU / L, and the concentration of the bacterial liquid of the ureolytic bacteria may be 10 7 ~10 8 CFU / L.

[0037] The present invention has no special requirements for the first mixing method, as long as it can be mixed evenly.

[0038] After obtaining the mixed bacterial liquid, the present invention second-mixes the mixed bacterial liquid, recycled aggregate, and mineralization liquid and then performs biological mineralization to obtain the microorganism-mineralized modified recycled aggregate. As a specific embodiment of the present invention, the second mixing includes the following steps:

[0039] Third-mix the mixed bacterial liquid and the recycled aggregate and then let it stand to obtain the recycled aggregate with attached microorganisms;

[0040] Fourth-mix the mineralization liquid and the recycled aggregate with attached microorganisms.

[0041] As a specific embodiment of the present invention, the recycled aggregate can be obtained by crushing waste concrete, and the waste concrete can be the waste concrete formed by demolishing buildings; the present invention has no special limitation on the particle size, crushing index, water absorption rate and apparent density of the recycled aggregate, and conventional recycled aggregates in the art can be used. As a specific embodiment of the present invention, the mass ratio of the mixed bacterial solution to the recycled aggregate can be 0.08-0.12:1, specifically 0.1:1. As a specific embodiment of the present invention, the third mixing method can be spraying the mixed bacterial solution onto the surface of the recycled aggregate or soaking the recycled aggregate in the mixed bacterial solution for 30-40 min.

[0042] As a specific embodiment of the present invention, the standing time after the third mixing can be 6-12 h, or 8-10 h. Standing in the present invention is beneficial to the full contact between the recycled aggregate and the mixed bacterial solution, so that the bacteria can fully adhere to the surface of the recycled aggregate.

[0043] As a specific embodiment of the present invention, the mineralization solution includes urea and calcium formate; the mass concentration of urea in the mineralization solution can be 6-30 g / L, specifically 10 g / L, 15 g / L, 20 g / L or 25 g / L; the mass concentration of calcium formate in the mineralization solution can be 40-45 g / L, specifically 42 g / L or 44 g / L; the mineralization solution can also include calcium chloride and / or glucose; when the mineralization solution includes calcium chloride, the mass concentration of calcium chloride in the mineralization solution can be 50-60 g / L, specifically 53 g / L, 55.5 g / L or 58 g / L; when the mineralization solution includes glucose, the mass concentration of glucose in the mineralization solution can be 0.8-1.2 g / L, specifically 1 g / L. As a specific embodiment of the present invention, the mass ratio of the recycled aggregate to the volume of the mineralization solution can be 1 kg:1.1-1.8 L, specifically 1 kg:1.1 L, 1 kg:1.2 L, 1 kg:1.3 L, 1 kg:1.4 L, 1 kg:1.5 L, 1 kg:1.6 L, 1 kg:1.7 L or 1 kg:1.8 L. In the present invention, urea is a nutrient for ureolytic bacteria, calcium formate provides calcium ions and a small molecule carbon source to facilitate the formation of carbonate radicals, and glucose can enhance the activity of bacteria.

[0044] As a specific embodiment of the present invention, the fourth mixing method can be spraying the mineralization solution onto the recycled aggregate attached with microorganisms or soaking the recycled aggregate attached with microorganisms in the mineralization solution.

[0045] As a specific embodiment of the present invention, after the second mixing, it may further include: mixing the second mixed system with a pH regulator to adjust the pH value to 8.5 - 9.5; the adjusted pH value may specifically be 9; the pH regulator may include a sodium hydroxide solution; the molar concentration of the sodium hydroxide solution may be 0.08 - 0.12 mol / L, and may specifically be 0.1 mol / L. The present invention has no special requirements for the dosage of the pH regulator, as long as the required pH value is satisfied. Limiting the pH value of the system within the above range is beneficial for the rapid generation of calcium carbonate during the microbial mineralization process.

[0046] As a specific embodiment of the present invention, the microbial mineralization may be to let the second mixed system stand still, and the standing time may be 7 - 10 days, and may specifically be 7 days, 8 days, 9 days or 10 days; the temperature of the standing environment may be 20 - 40 °C, and may specifically be 20 °C, 25 °C, 30 °C, 35 °C or 40 °C.

[0047] As a specific embodiment of the present invention, after the microbial mineralization, it may further include: separating the aggregate after microbial mineralization and then drying it to obtain the microbial mineralization modified recycled aggregate. The present invention has no special requirements for the separation, and conventional methods in the art can be used. As a specific embodiment of the present invention, the drying temperature may be 40 - 60 °C, and may also be 45 - 55 °C. The present invention has no specific limitation on the drying time, as long as the solvent on the solid surface can be removed.

[0048] The present invention selects ureolytic bacteria and screens denitrifying bacteria with nitrification ability to jointly carry out microbial mineralization. While ensuring the mineralization efficiency, it will convert the ammonia generated by the decomposition of urea by ureolytic bacteria into nitrate, and then use the nitrate for the second biomineralization to further strengthen the recycled aggregate, and no ammonia will be generated. In the present invention, the microbial mineralization includes the following processes:

[0049] The first step: the first stage of mineralization (ureolytic bacteria decompose urea to produce calcium carbonate)

[0050] CO(NH2)2 + 2OH - +Ca 2+ → 2NH3 + CaCO3↓;

[0051] The second step: nitrification converts ammonia into nitrate

[0052] NH3 + 2O2 + OH - → NO3 - + 2H2O;

[0053] The third step: the denitrification process produces the second stage of mineralization

[0054] 5HCOO - + 2NO3 - + 5Ca 2+ + 3OH - → 5CaCO3↓ + 4H2O + N2↑。

[0055] The present invention also provides a microbial mineralization modified recycled aggregate prepared by the preparation method described in the above technical solution; the water absorption rate of the microbial mineralization modified recycled aggregate is 8.58 - 8.82%, and the apparent density is 2571 - 2591 kg / m 3 , and the crushing index is 17.5 - 18.1%. The microbial mineralization modified recycled aggregate obtained by the preparation method provided by the present invention has a lower aggregate crushing index, a lower water absorption rate, and a higher strength; the recycled aggregate concrete formed by using the microbial mineralization modified recycled aggregate has higher strength and durability.

[0056] The present invention also provides the application of the microbial mineralization modified recycled aggregate described in the above technical solution in recycled aggregate concrete.

[0057] In order to further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0058] Example 1

[0059] (1), Prepare the bacterial solution. The culture medium consists of meat extract powder (5 g / L), NaCl (10 g / L) and distilled water. After sterilization and cooling to room temperature, the required bacteria are inoculated; when inoculating Sporosarcina pasteurii (SP) (ATCC 11859) into the culture medium, urea is added to make the urea concentration 31 g / L (0.5 mol / L), and it is cultured by shaking at 30 °C until the concentration reaches 10 7 CFU / L; when inoculating Paracoccus denitrificans (Pd) (ATCC 19367) into the culture medium, sodium nitrate is added to make the sodium nitrate concentration 42.5 g / L (0.5 mol / L), and it is cultured by shaking at 30 °C until the concentration reaches 10 7 CFU / L; 20 mL of the bacterial solution of 10 7 CFU / L Paracoccus denitrificans and 80 mL of the bacterial solution of 10 7 CFU / L Sporosarcina pasteurii are mixed to obtain 100 mL of the mixed bacterial solution.

[0060] (2), For 1 kg of recycled aggregate with a crushing index, water absorption rate and apparent density of 21.2%, 11.9% and 2427.7 kg / m 3The recycled aggregate is placed in a 6L transparent container, 100mL of the mixed bacterial solution is sprayed, and it is left standing for 6h to obtain the recycled aggregate with attached microorganisms; the recycled aggregate is obtained by crushing waste concrete, and the crushing index, water absorption rate, and apparent density of the recycled aggregate are tested with reference to GB / T25177-2010 "Recycled Coarse Aggregate for Concrete and Mortar" and GB / T14685-2022 "Pebbles and Crushed Stones for Construction".

[0061] (3), 1.3L of mineralization solution (urea 20g / L, calcium chloride 55.5g / L, calcium formate 42g / L, glucose 1g / L) is added to the mixed system obtained in step (2), and then the pH value is adjusted to 9 with a NaOH solution with a molar concentration of 0.1mol / L. After mixing evenly and leaving it standing (for microbial mineralization) for 168h (7 days), the aggregate is taken out to obtain the microbially mineralized modified recycled aggregate.

[0062] Example 2

[0063] The recycled aggregate is subjected to microbial mineralization treatment according to the method of Example 1, except that the mixed bacterial solution is composed of 33.3mL of a bacterial solution of Paracoccus azotifigens at 10 7 CFU / L and 66.7mL of a bacterial solution of Sporosarcina pasteurii at 10 7 CFU / L mixed together.

[0064] Example 3

[0065] The recycled aggregate is subjected to microbial mineralization treatment according to the method of Example 1, except that the mixed bacterial solution is composed of 50mL of a bacterial solution of Paracoccus azotifigens at 10 7 CFU / L and 50mL of a bacterial solution of Sporosarcina pasteurii at 10 7 CFU / L mixed together.

[0066] Example 4

[0067] The recycled aggregate is subjected to microbial mineralization treatment according to the method of Example 1, except that Sporosarcina pasteurii (SP) ATCC 11859 is replaced by Bacillus megaterium de Bary (Bm) (ATCC 25300); the mixed bacterial solution is composed of 50mL of a bacterial solution of Paracoccus azotifigens at 10 7 CFU / L and 50mL of a bacterial solution of Bacillus megaterium at 10 7 CFU / L mixed together.

[0068] Example 5

[0069] The microbial mineralization treatment of recycled aggregates was carried out according to the method of Example 1, except that Paracoccus denitrificans (Pd) (ATCC19367) was replaced by Pseudomonas.Sp (Psp) (ATCC13867); the mixed bacterial solution was composed of 50 mL of a bacterial solution of Pseudomonas at 10 7 CFU / L and 50 mL of a bacterial solution of Bacillus pasteurii at 10 7 CFU / L mixed together.

[0070] Comparative Example 1 (using a single bacterium for microbial mineralization compared to Example 1)

[0071] (1). Prepare the bacterial solution. The culture medium consists of meat extract powder (5 g / L), NaCl (10 g / L), and distilled water. After sterilization and cooling to room temperature, the required bacteria are inoculated; when inoculating Sporosarcina pasteurii (SP) ATCC11859 into the culture medium, urea is added to make the urea concentration 31 g / L (0.5 mol / L), and it is shaken and cultured at 30 °C until the concentration reaches 10 7 CFU / L; take 100 mL of the bacterial solution of Bacillus pasteurii at 10 7 CFU / L.

[0072] (2). Place 1 kg of recycled aggregates with crushing index, water absorption rate, and apparent density of 21.2%, 11.9%, and 2427.7 kg / m 3 respectively in a 20 L transparent container (since the ammonia concentration is too high in this method and the ammonia concentration in a 6 L container exceeds the range of the detector, a 20 L transparent container is used), spray 100 mL of the bacterial solution of Bacillus pasteurii, and let it stand for 6 h to obtain recycled aggregates with attached microorganisms; the recycled aggregates are obtained by crushing waste concrete.

[0073] (3). Add 1.3 L of mineralization solution (calcium chloride 110 g / L, glucose 1 g / L) to the mixed system obtained in step (2), then use a NaOH solution with a molar concentration of 0.1 mol / L to adjust the pH value to 9, mix evenly and let it stand (for microbial mineralization) for 168 hours (7 days), and then take out the aggregates to obtain microbially mineralized modified recycled aggregates.

[0074] Comparative Example 2

[0075] The microbial mineralization treatment of recycled aggregates was carried out according to the method of Example 1, except that the mixed bacterial solution was composed of 10 mL of a bacterial solution of Paracoccus denitrificans at 10 7 CFU / L and 90 mL of 10 7It is obtained by mixing the bacterial liquid of Bacillus pasteurii. Since the ammonia concentration is too high by this method, the ammonia concentration in the 6L container exceeds the range of the detector, so the volume of the transparent container is increased from 6L to 20L.

[0076] Comparative Example 3

[0077] The recycled aggregates were subjected to microbial mineralization treatment according to the method of Example 1, except that the mixed bacterial liquid was composed of 90 mL of 10 7 CFU / L of Paracoccus azotifigens bacterial liquid and 10 mL of 10 7 CFU / L of Bacillus pasteurii bacterial liquid. Since the ammonia concentration is too high by this method, the ammonia concentration in the 6L container exceeds the range of the detector, so the volume of the transparent container is increased from 6L to 20L.

[0078] The surface of the recycled aggregates in Example 1 was detected by scanning electron microscopy to obtain an SEM image, as Figure 1 shown. The surface of the microbial mineralization modified recycled aggregates prepared in Example 3 was detected by scanning electron microscopy to obtain an SEM image, as Figure 2 shown. From Figure 1 、 2 it can be seen that the combined bacteria filled the loose structure of the recycled aggregates through bio-mineralization, forming a dense calcium carbonate layer.

[0079] The calcium carbonate protective layer on the surface of the microbial mineralization modified recycled aggregates prepared in Example 3 was detected by X-ray diffraction to obtain an XRD pattern, as Figure 3 shown.

[0080] Combined with Figure 2 and Figure 3 it can be seen that by carrying out microbial mineralization according to the method provided by the present invention, the component that fills the voids and cracks on the surface of the recycled aggregates produced by the combined strains is calcium carbonate. Based on the comprehensive XRD and SEM observation results, the existing form of calcium carbonate crystals is calcite.

[0081] During the microbial mineralization of Comparative Examples 1 to 3, the ammonia concentration in the 20L container was detected using the Simma ammonia detector ST9500 at 2h, 4h, 12h, 24h, 36h, 48h, 60h, 72h, 96h, and 168h respectively. The detection results were converted to the ammonia concentration in the 6L container, and the results are listed in Table 1.

[0082] During the microbial mineralization of Examples 1 to 5, the ammonia concentration in the 6L container was detected using the Simma ammonia detector ST9500 at 2h, 4h, 12h, 24h, 36h, 48h, 60h, 72h, 96h, and 168h respectively. The results are listed in Table 1.

[0083] The apparent density, water absorption rate, and crushing index of the microbially mineralized modified recycled aggregates obtained in Test Examples 1 to 5 and Comparative Examples 1 to 3 were tested with reference to GB / T 25177-2010 "Recycled Coarse Aggregates for Concrete and Mortar" and GB / T 14684-2022 "Sand for Construction". The results are listed in Table 2.

[0084] Table 1 Ammonia Concentration in a 6L Container during the Microbial Mineralization Process of Examples 1 to 5 and Comparative Examples 1 to 3

[0085]

[0086] Table 2 Performance Parameters of the Microbially Mineralized Modified Recycled Aggregates of Examples 1 to 5 and Comparative Examples 1 to 3

[0087]

[0088] Combining Table 1 and Table 2, it can be seen that although ureolytic bacteria can effectively improve the performance of recycled aggregates, a large amount of ammonia is generated during the microbial mineralization process; when the number of microorganisms with both nitrification and denitrification abilities is too small, the ability to decompose ammonia is insufficient; when the number of microorganisms with both nitrification and denitrification abilities is too large, the ability to improve recycled aggregates is insufficient. This is because when the number of ureolytic bacteria is too small, the first-step biomineralization is slow, resulting in too few nitrate ions being produced. Without additional supplementation of nitrate ions, the second-step biomineralization also occurs slowly.

[0089] According to the method provided by the present invention, when the volume ratio of the equal-concentration bacterial solutions of microorganisms with both nitrification and denitrification abilities and ureolytic bacteria in the mixed bacterial solution is limited to 2:1 to 1:4, the performance of recycled aggregates is effectively improved while the amount of ammonia generated during the microbial mineralization process is effectively controlled.

[0090] Taking the recycled aggregates in Example 3 as raw materials, after mixing according to the mass ratio of cement: water: fine aggregate: recycled coarse aggregate of 400:170:720:1095, cube test blocks with a side length of 150 mm were cast and cured for 28 days, and then the compressive strength test was carried out in accordance with "Standard for Test Methods of Physical and Mechanical Properties of Concrete" GB / T 50081-2019. The water absorption rate test was carried out in accordance with the regulations of "Recycled Coarse Aggregates for Concrete" GB / T 25177-2010. The results were as follows: the average compressive strength at 28 days was 29.2 Mpa, and the water absorption rate was 8.9%.

[0091] Using the microbial mineralization modified recycled aggregate obtained by the treatment in Example 3 as raw material, after mixing according to the mass ratio of cement: water: fine aggregate: recycled coarse aggregate of 400:170:720:1167, a cube test block with a side length of 150 mm was cast and cured for 28 days, and then the compressive strength test was carried out in accordance with the Standard for Test Methods of Physical and Mechanical Properties of Concrete GB / T 50081-2019. The water absorption test was carried out in accordance with the provisions of Recycled Coarse Aggregate for Concrete GB / T 25177-2010. The results were as follows: the average compressive strength at 28 days was 33.2 Mpa, and the water absorption rate was 7.2%.

[0092] It can be seen from the test results of the test block that after treating the recycled aggregate according to the method provided by the present invention, the microbial mineralization modified recycled aggregate is obtained, and the test block formed by preparing recycled concrete with the microbial mineralization modified recycled aggregate as raw material has high compressive strength and low water absorption rate.

[0093] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments without creative efforts based on this embodiment, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing microbial mineralized modified recycled aggregate, characterized in that: The following steps are involved: The bacterial solution of the microorganisms with both nitrification and denitrification capabilities and the bacterial solution of the urea-lytic bacteria are first mixed to obtain a mixed bacterial solution; the volume ratio of the bacterial solutions of the microorganisms with both nitrification and denitrification capabilities and the urea-lytic bacteria of equal concentration in the mixed bacterial solution is 2:1 to 1:4; The mixed bacterial liquid, the regenerated aggregate and the mineralization liquid are mixed for a second time and then biomineralized to obtain the microbial mineralized modified regenerated aggregate; the mineralization liquid includes urea and calcium formate.

2. The method for preparing microbial mineralized modified recycled aggregate according to claim 1, characterized in that: The microorganisms having both nitrification and denitrification capabilities include Paracoccus azotrophicus and / or Pseudomonas; The urea-lytic bacteria include Bacillus pasteurianus and / or Bacillus megaterium.

3. The method for preparing microbial mineralized modified recycled aggregate according to claim 1 or 2, characterized in that: The concentration of the bacterial solution of the microorganisms having both nitrification and denitrification capabilities is 10 7 ~10 8 CFU / L; The concentration of the urea-lytic bacteria solution is 10 7 ~10 8 CFU / L.

4. The method for preparing microbial mineralized modified recycled aggregate according to claim 1, characterized in that: The second mixing comprises the following steps: The mixed bacterial liquid and the regenerated aggregate are mixed for the third time and then allowed to stand to obtain the regenerated aggregate with attached microorganisms; The mineralized liquid and the recycled aggregate with attached microorganisms are fourthly mixed.

5. The method for preparing microbial mineralized modified recycled aggregate according to claim 1 or 4, characterized in that: The mass concentration of urea in the mineralization solution is 6-30 g / L, the mass concentration of calcium formate in the mineralization solution is 40-45 g / L; the volume ratio of the mass of the recycled aggregate to the mineralization solution is 1 kg: 1.1-1.8 L; The mass ratio of the mixed bacterial liquid to the recycled aggregate is 0.08-0.12:

1.

6. The method for preparing microbial mineralized modified recycled aggregate according to claim 5, characterized in that: The mineralizing solution also includes calcium chloride and / or glucose; When the mineralization solution includes calcium chloride, the mass concentration of calcium chloride in the mineralization solution is 50-60 g / L; When the mineralization solution includes glucose, the mass concentration of glucose in the mineralization solution is 0.8-1.2 g / L.

7. The method for preparing microbial mineralized modified recycled aggregate according to claim 1, characterized in that: The second mixing step further comprises: mixing the second mixed system with a pH adjuster to adjust the pH value to 8.5 to 9.5; The pH adjuster includes sodium hydroxide solution.

8. The method for preparing microbial mineralized modified recycled aggregate according to claim 1, characterized in that: The biomineralization is to let the second mixed system stand for 7 to 10 days; the temperature of the standing environment is 20 to 40°C.

9. The microbial mineralized modified recycled aggregate prepared by the preparation method according to any one of claims 1 to 8; The water absorption rate of the microbial mineralized modified recycled aggregate is 8.58-8.82%, and the apparent density is 2571-2591 kg / m 3 , the crushing index is 17.5~18.1%.

10. Use of the microbial mineralized modified recycled aggregate according to claim 9 in recycled aggregate concrete.

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