Method for modifying recycled coarse aggregate by optimizing microbial denitrification phenomenon and recycled aggregate concrete based on method

Abstract

The invention discloses a method for modifying recycled coarse aggregate by optimizing a microbial denitrification phenomenon and recycled aggregate concrete based on the method. The method for modifying the recycled coarse aggregate comprises the following steps: pouring a high-concentration bacterial liquid on the surface of the dried recycled coarse aggregate, and standing to enable the surface of the recycled coarse aggregate to fully absorb a denitrifying bacteria matrix, so as to obtain the recycled coarse aggregate attached with denitrifying bacteria; soaking the recycled coarse aggregate in a mineralizing solution to obtain the recycled coarse aggregate reinforced by microorganisms; and taking out the microorganism-enhanced recycled coarse aggregate from the mixed solution, cleaning, drying, and finally carrying out vacuum impregnation in a bacterial liquid to obtain the modified recycled coarse aggregate, replacing part of natural coarse aggregate with the modified recycled coarse aggregate, and mixing the modified recycled coarse aggregate with water, cement, sand, the natural coarse aggregate and a deposition medium to obtain the recycled aggregate concrete. According to the invention, the denitrification phenomenon of microorganisms is utilized to modify the performance of the recycled coarse aggregate, and the strength, water absorption and other physical properties of the recycled aggregate concrete are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of microbial modification and recycling of construction waste, and particularly relates to a method for optimizing the use of microbial denitrification phenomenon to modify recycled coarse aggregate and recycled aggregate concrete based on the same. Background Art

[0002] There is an urgent need to find substitutes for natural aggregates to solve the problem of scarce natural aggregate resources. The recycled aggregates obtained by crushing, screening, and classifying construction waste can not only reduce the negative impact of construction waste on the environment and achieve green and sustainable development of the construction industry, but also alleviate the current huge demand for natural sand and gravel.

[0003] Due to the deteriorated physical and mechanical properties of recycled aggregates themselves, the properties of recycled aggregate concrete decline continuously with the increase of the replacement rate of recycled aggregates. In order to strengthen recycled aggregates and ensure the performance of recycled aggregate concrete, existing technologies have used methods such as mechanical grinding, acid solution soaking, and carbonization to treat recycled aggregates and achieved good results. However, the above methods all have different drawbacks, such as high energy consumption, introduction of harmful substances, and long treatment time.

[0004] Using the microbial-induced calcium carbonate precipitation technology to treat recycled aggregates is a new method proposed in recent years, which has the characteristics of environmental friendliness, good compatibility between the precipitate and concrete, and low energy consumption, making it generally considered a promising method for modifying recycled aggregates. At present, ureolytic bacteria are commonly used in the field of modifying recycled aggregates. However, during the mineralization process of such bacteria, toxic gas ammonia is inevitably released, which will also cause adverse effects on the human body and the environment.

[0005] Patent CN112851170A discloses a method for strengthening recycled aggregate concrete by using the microbial denitrification phenomenon and recycled aggregate concrete. During the process of modifying recycled aggregates by using this method, the generation of ammonia is avoided, and the mechanical properties of recycled aggregates and recycled aggregate concrete are effectively improved. However, the mineralization efficiency of denitrifying bacteria is lower than that of ureolytic bacteria, resulting in poor effect of modifying recycled aggregates.

[0006] For the above reasons, there is an urgent need for an optimized method for using denitrifying bacteria to improve the performance of recycled aggregate concrete to improve the effect of using denitrifying bacteria to modify recycled coarse aggregates and recycled aggregate concrete. Summary of the Invention

[0007] Aiming at the problems existing in the above background art, the present invention provides a method for optimizing the use of the microbial denitrification phenomenon to modify recycled coarse aggregates and recycled aggregate concrete based on the same, improving the effect of using the microbial denitrification phenomenon to modify the performance of recycled coarse aggregates, and this technology can greatly improve the physical properties such as the strength and water absorption of recycled aggregate concrete.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for modifying recycled coarse aggregate by optimizing the utilization of microbial denitrification phenomenon, comprising the following steps:

[0010] (1) Pour the high-concentration bacterial solution onto the surface of the dry recycled coarse aggregate, and let it stand still to allow the surface to fully absorb the denitrifying bacteria matrix, obtaining the recycled coarse aggregate attached with denitrifying bacteria;

[0011] (2) Immerse the recycled coarse aggregate attached with denitrifying bacteria obtained in step (1) in the mineralization solution to obtain the recycled coarse aggregate strengthened by microorganisms;

[0012] (3) Take out the recycled coarse aggregate strengthened by microorganisms obtained in step (2) from the mixed solution, wash it, and then place it in a constant-temperature oven to dry to a constant weight;

[0013] (4) Vacuum impregnate the dried recycled coarse aggregate in step (3) with the bacterial solution, so that the strengthened recycled coarse aggregate immobilizes denitrifying bacteria, obtaining the modified recycled coarse aggregate of the present invention;

[0014] The preparation method of the high-concentration bacterial solution in step (1) includes:

[0015] (a) Inoculate bacteria into a sterile liquid medium for cultivation to obtain a denitrifying bacteria solution;

[0016] The bacteria is Pseudomonas denitrificans ATCC13867;

[0017] The sterile liquid medium is obtained by sterilizing the prepared bacterial medium I in a high-pressure sterilizer at 121 °C and 100 kPa for 10 - 25 min. The components of the bacterial medium I include 2 - 5 g / L of beef extract powder, 2 - 5 g / L of sodium chloride, 4 - 10 g / L of peptone, and 4 - 10 g / L of sucrose;

[0018] (b) Mix the pure bacteria body after centrifuging the denitrifying bacteria solution obtained in step (a) with the bacterial medium II to obtain the high-concentration bacterial solution;

[0019] The bacterial medium II is the supernatant after centrifuging the denitrifying bacteria solution, and its dosage is the water absorption corresponding to 1.2 - 1.4 times the water absorption rate of the recycled coarse aggregate. Dilute the pure bacteria body obtained by centrifugation with the bacterial medium II to obtain the high-concentration bacterial solution;

[0020] In step (2), the mineralization solution includes 21 - 23 g / L calcium formate, 7.5 - 8.2 g / L calcium nitrate and the components of bacterial medium III. The components of bacterial medium III include 2 - 5 g / L beef extract powder, 2 - 5 g / L sodium chloride, 4 - 10 g / L peptone, 4 - 10 g / L sucrose, and their dosages are based on each liter of deionized water.

[0021] In step (4), the bacterial solution is obtained by centrifuging the bacterial solution proliferated from bacterial medium I and then rediluting it with a 1 - 3 g / L glucose solution. The OD600 value of the bacterial solution is 0.7 - 1.0, and the bacterium used is Pseudomonas denitrificans ATCC13867.

[0022] Furthermore, in the method for preparing the high - concentration bacterial solution of the present invention, in step (a), the culture temperature is 30 - 35 °C and the culture time is 24 - 48 h.

[0023] Furthermore, in the method for preparing the high - concentration bacterial solution of the present invention, in step (b), the concentration OD of the denitrifying bacterial solution to be centrifuged 600 is 0.7.

[0024] Furthermore, in the method for preparing the high - concentration bacterial solution of the present invention, in step (b), the rotation speed of the centrifugation is 5000 - 7000 rmp / min and the centrifugation time is 5 - 8 min.

[0025] Furthermore, in step (1), the recycled coarse aggregate, by volume fraction, contains 40% recycled concrete aggregate and 60% recycled brick aggregate, and the recycled coarse aggregate is 5 - 20 mm continuous - graded crushed stone.

[0026] Furthermore, the method for preparing the dried recycled coarse aggregate in step (1) of the present invention includes: washing the recycled coarse aggregate with tap water and then drying it in an oven at 60 - 105 °C for 12 - 24 h to obtain the dried recycled coarse aggregate.

[0027] Furthermore, the time for the dried recycled coarse aggregate in step (1) of the present invention to statically absorb the high - concentration denitrifying bacterial solution is 6 - 12 h.

[0028] Furthermore, after the mineralization solution in step (2) of the present invention is prepared, the pH is adjusted to 9 by dropping NaOH solution and HCl solution, and then the recycled coarse aggregate attached with denitrifying bacteria obtained in step (1) is immersed in the solution. The environmental temperature during the immersion is 30 °C and the immersion time is 8 - 12 d; the ratio of the recycled coarse aggregate to the mineralization solution is 1000 g:1000 ml.

[0029] The denitrifying bacteria used in the present invention utilize calcium formate and calcium nitrate as carbon source, nitrogen source, and calcium source, and through a series of chemical reactions, calcium carbonate precipitation is generated. The mineralization principle is shown by the following chemical equation:

[0030] 5Ca(HCOO) 2 +2Ca(NO 3 ) 2 →7CaCO 3 ↓+5H 2 O+2N 2 ↑+3CO 2 ↑

[0031] Further, in step (3) of the present invention, the recycled coarse aggregate after being treated in step (2) is washed with tap water to remove surface impurities and ineffective calcium carbonate precipitation.

[0032] Further, in step (4) of the present invention, the pressure of vacuum impregnation is -0.06 MPa, and the impregnation time is 20 - 30 min.

[0033] A method for preparing recycled aggregate concrete using the above-mentioned modified recycled coarse aggregate includes: taking out the prepared modified recycled coarse aggregate from the impregnation container and drying the surface moisture to make it reach the saturated surface dry state, and then using the modified recycled coarse aggregate carrying bacteria to replace part of the natural coarse aggregate in the fresh concrete, and mixing it with water, cement, sand, natural coarse aggregate, and deposition medium to obtain recycled aggregate concrete;

[0034] The deposition medium is a mixed solution of 7 - 9 kg / m 3 calcium formate and 2.5 - 3.5 kg / m 3 calcium nitrate, and its dosage is based on per cubic meter of concrete;

[0035] The substitution method of the modified recycled coarse aggregate for natural coarse aggregate is equal - volume substitution, and the substitution rate is 20 - 50%.

[0036] Compared with other existing methods for modifying recycled aggregate using microbial - induced calcium carbonate precipitation technology, the present invention has the following beneficial effects:

[0037] (1) It makes full use of recycled concrete aggregate and recycled brick aggregate to make concrete, reduces the exploitation of natural aggregate and is beneficial to environmental protection. Especially, due to its large porosity, recycled brick aggregate can carry more bacteria and effectively protect bacteria from the high - alkali environment of mortar and the negative impact of concrete mixing, and enables it to fully play the role of internal curing during the concrete curing stage and generate calcium carbonate precipitation to fill the pores and micro - cracks in the mortar matrix of concrete.

[0038] (2) The denitrifying bacteria used in the present invention do not require the provision of urea during the mineralization process, thus avoiding the generation of ammonia; the calcium formate and calcium nitrate used can not only form CaCO 3 precipitation with the bacteria during mineralization, but also are a kind of concrete admixture with little negative impact on the performance of concrete. In addition, the brick powder on the surface of the recycled brick aggregate has pozzolanic activity and can react with Ca(OH) 2 to form CaCO 3 precipitation, further filling the ITZ and mortar microcracks and improving the strength of recycled aggregate concrete.

[0039] (3) The recycled coarse aggregate modified by the method of the present invention has greatly improved various physical properties and effectively reduced the amount of calcium carbonate precipitation ineffective for the modified recycled aggregate.

[0040] (4) The recycled aggregate concrete produced by the method of the present invention has physical properties equivalent to those of natural aggregate concrete under the same mix ratio conditions, and its strength is even slightly higher than that of natural aggregate concrete. Detailed Embodiments

[0041] The present invention will be further elaborated and described below in conjunction with specific embodiments. However, the described embodiments are only for helping to understand the invention, and the protection scope of the present invention is not limited thereto.

[0042] The sources of the main materials in the following detailed embodiments are as follows: Denitrifying bacteria (Pseudomonas.Sp homologous ATCC13867, preservation: Guangdong Provincial Microbial Culture Collection Center).

[0043] The recycled coarse aggregate is from a building demolition project in Hebei Province, with a water absorption rate of 11.9%, a crushing value of 21.2%, and an apparent density of 2427.7 kg / m 3 . The natural aggregate is made of basalt, with a water absorption rate of 1.0%, a crushing value of 4.7%, and an apparent density of 2845.1 kg / m 3 . Both are 5 - 20 mm continuously graded crushed stones.

[0044] The cement is P.O42.5R type ordinary Portland cement purchased from Yantai Guotai Building Reinforcement Co., Ltd.; the natural fine aggregate is produced in Jiangxi Province with a fineness modulus of 2.8.

[0045] Example 1

[0046] A method for optimizing the utilization of the microbial denitrification phenomenon to modify recycled coarse aggregate specifically includes the following steps:

[0047] (1) OD 600The bacterial liquid with a value of 0.7 is centrifuged and diluted to obtain a high-concentration bacterial liquid, which is poured into the dry recycled coarse aggregate with a continuous gradation of 5-20 mm and left standing for 6 h;

[0048] The recycled coarse aggregate contains 40% recycled concrete aggregate and 60% recycled brick aggregate by volume fraction;

[0049] The drying method of the recycled coarse aggregate includes: washing the recycled coarse aggregate with tap water and then drying it in an oven at 60-105 °C for 12-24 h to obtain the dry recycled coarse aggregate;

[0050] (2) Weigh 22.5 g / L of calcium formate, 8 g / L of calcium nitrate, and 1000 ml of deionized water to prepare a mixed solution, and adjust the pH to 9 by dropping NaOH solution and HCl solution;

[0051] (3) Weigh 2 g / L of beef extract powder, 2 g / L of sodium chloride, 4 g / L of peptone, and 4 g / L of sucrose and add them to the mixed solution in step (2) to obtain a mineralization solution;

[0052] (4) Pour the mineralization solution prepared in steps (2) and (3) into the recycled coarse aggregate that has absorbed the high-concentration bacterial liquid in step (1) and leave it standing at 30 °C for 10 d, where the ratio of the recycled coarse aggregate to the mineralization solution is 1000 g:1000 ml;

[0053] (5) Take out the recycled coarse aggregate from the mineralization solution, wash it with tap water, then dry it in an oven at 105 °C until it reaches a constant weight and cool it to room temperature;

[0054] (6) Vacuum impregnate the enhanced recycled coarse aggregate obtained in step (5) with the bacterial liquid, the vacuum impregnation pressure is -0.06 MPa, and the impregnation time is 20 min;

[0055] The preparation method of the high-concentration bacterial liquid in step (1) includes:

[0056] (a) Inoculate bacteria into a sterile liquid medium for cultivation to obtain a denitrifying bacterial liquid;

[0057] The bacteria are Pseudomonas denitrificans ATCC13867;

[0058] The sterile liquid medium is obtained by sterilizing the prepared bacterial medium I in an autoclave at 121 °C and 100 kPa for 10-25 min. The components of the bacterial medium I include 5 g / L of beef extract powder, 5 g / L of sodium chloride, 10 g / L of peptone, and 10 g / L of sucrose;

[0059] The cultivation temperature is 30-35 °C, and the cultivation time is 24-48 h;

[0060] (b) Mix the pure bacteria obtained after centrifuging the denitrifying bacteria liquid obtained in step (a) with Bacterial Medium II to obtain the high-concentration bacteria liquid;

[0061] The Bacterial Medium II is the supernatant obtained after centrifuging the denitrifying bacteria liquid, and its dosage is the water absorption corresponding to 1.2 - 1.4 times the water absorption rate of the recycled coarse aggregate. Dilute the pure bacteria obtained by centrifugation with Bacterial Medium II to obtain the high-concentration bacteria liquid;

[0062] The rotation speed of the centrifugation is 5000 - 7000 rmp / min, and the centrifugation time is 5 - 8 min;

[0063] The bacteria liquid described in step (6) is obtained by centrifuging the bacteria solution proliferated by Bacterial Medium I and then re-diluting it with a 1 - 3 g / L glucose solution. The OD600 value of the bacteria liquid is 0.7 - 1.0, and the bacteria used is Pseudomonas denitrificans ATCC13867.

[0064] According to GB / T 25177-2010 "Recycled Coarse Aggregates for Concrete" and GB / T 14685-2022 "Pebbles and Crushed Stones for Construction", test the water absorption rate, crushing value, and apparent density of the recycled coarse aggregates before and after modification to clarify the changes in their physical properties. The results show that the physical properties of the recycled coarse aggregates are significantly improved after modification, and the results are listed in Table 1.

[0065] Table 1 Changes in the properties of recycled coarse aggregates before and after modification

[0066] Name Water absorption rate (%) Crushing value (%) <![CDATA[Apparent density (kg / m 3 )]]> Unmodified recycled coarse aggregate 11.9 21.2 2427.7 Modified recycled coarse aggregate 10.5 17.7 2546.7

[0067] As can be seen from the data in Table 1, after modification, the water absorption rate and crushing value of the recycled coarse aggregates decreased by 11.8% and 16.4% respectively, and the apparent density increased by 4.9%.

[0068] Application implementation method

[0069] Application Example 1

[0070] Use the saturated surface dry modified recycled coarse aggregates and saturated surface dry unmodified recycled coarse aggregates obtained in Example 1 to replace 20% of the natural aggregates in the fresh concrete to produce recycled aggregate concrete, and at the same time produce natural aggregate concrete as the control group. The mix proportions of the three groups of concrete are shown in Table 2.

[0071] Table 2 Mix proportions of concrete with a 20% recycled aggregate replacement rate (kg / m 3 )

[0072] Name Water Cement Sand Natural aggregate Recycled aggregate Natural aggregate concrete 215 536 584 1085 0 Unmodified recycled aggregate concrete 215 536 584 944 202 Modified recycled aggregate concrete 215 536 584 944 209

[0073] The freshly mixed concrete prepared according to the concrete mix proportion in Table 2 was placed in a mold, vibrated, demolded, and then cured in a curing room. When the curing age reached 28 days, the compressive strength, splitting tensile strength, and water absorption of the concrete were tested in accordance with the Standard for Test Methods of Physical and Mechanical Properties of Concrete (GB / T 50081-2019) to investigate the influence of the modified recycled coarse aggregate on the concrete properties. The results are listed in Table 3.

[0074] Table 3 Test Results of Concrete with 20% Recycled Aggregate Replacement Ratio at 28-day Curing Age

[0075] Name Compressive strength (MPa) Splitting tensile strength (MPa) Water absorption rate (%) Natural aggregate concrete 44.1 3.24 3.9 Unmodified recycled aggregate concrete 48.4 3.44 4.8 Modified recycled aggregate concrete 50.7 3.67 4.5

[0076] As can be seen from the results in Table 3, the recycled coarse aggregate modified by the microorganisms in the present invention improves the physical and mechanical properties of the recycled aggregate concrete. The compressive strengths of the unmodified recycled aggregate concrete and the modified recycled aggregate concrete with a 20% recycled aggregate replacement ratio are increased by 9.7% and 14.9% respectively compared with the natural aggregate concrete, and the splitting tensile strengths are increased by 13.3% and 19.1% respectively; the water absorption of the modified recycled aggregate concrete with a 20% recycled aggregate replacement ratio is decreased by 6.3% compared with that of the unmodified recycled aggregate concrete. These improvements are both the result of microbial modification and the improvement of concrete strength by the internal curing effect of the recycled brick aggregate in the saturated surface dry state.

[0077] Application Example 2

[0078] The difference from Application Example 1 is that the recycled aggregate replacement ratio is changed to 50% to prepare recycled aggregate concrete, and the mix proportions of the three groups of concrete are shown in Table 4.

[0079] Table 4 Mix Proportion of Concrete with 50% Recycled Aggregate Replacement Ratio (kg / m 3 )

[0080]

[0081]

[0082] The freshly mixed concrete prepared according to the concrete mix proportion in Table 4 was placed in a mold, vibrated, demolded, and then cured in a curing room. When the curing age reached 28 days, the compressive strength, splitting tensile strength, and water absorption of the concrete were tested in accordance with the Standard for Test Methods of Physical and Mechanical Properties of Concrete (GB / T 50081-2019) to investigate the influence of the modified recycled coarse aggregate on the concrete properties. The results are listed in Table 5.

[0083] Table 5 Test Results of Concrete with 50% Recycled Aggregate Replacement Ratio at 28-day Curing Age

[0084] Name Compressive strength (MPa) Splitting tensile strength (MPa) Water absorption rate (%) Natural aggregate concrete 44.1 3.24 3.9 Unmodified recycled aggregate concrete 44.3 3.16 6.5 Modified recycled aggregate concrete 47.0 3.37 5.7

[0085] As can be seen from Table 5, the strength of recycled aggregate concrete with a recycled aggregate replacement rate of 50% is roughly close to that of natural aggregate concrete. The water absorption rate of the modified recycled aggregate concrete has decreased by 12.3%.

[0086] Application Example 3

[0087] A method for preparing recycled aggregate concrete using the above-mentioned modified recycled coarse aggregate includes: taking out the prepared modified recycled coarse aggregate from the impregnation container, drying the surface moisture to reach the saturated surface dry state, and then using the modified recycled coarse aggregate loaded with bacteria to replace part of the natural coarse aggregate in the freshly mixed concrete, and mixing with water, cement, sand, natural coarse aggregate, and deposition medium to obtain recycled aggregate concrete;

[0088] Replace 20% of the natural coarse aggregate in the concrete with the modified recycled coarse aggregate obtained in Example 1 to prepare concrete. During this process, 7 kg / m 3 calcium formate and 2.5 kg / m 3 calcium nitrate are dissolved in the mixing water; the performance of the concrete made by this method is compared with that of the modified recycled aggregate concrete and natural aggregate concrete in Application Example 1. The mix proportions of the three groups of concrete are shown in Table 6.

[0089] Table 6 Mix Proportions of Concrete with 20% Enhanced Recycled Aggregate Replacement Rate (kg / m 3 )

[0090] Name Water Cement Sand Natural aggregate Recycled aggregate Calcium formate Calcium nitrate Natural aggregate concrete 215 536 584 1085 0 0 0 Application Example 1 215 536 584 944 202 0 0 This application example 215 536 584 944 209 7 2.5

[0091] The freshly mixed concrete made according to the mix proportions in Table 6 is placed in a mold, vibrated, demolded, and then cured in a curing room. When the curing age reaches 28 d, the compressive strength, splitting tensile strength, and water absorption rate of the concrete are tested in accordance with the Standard Test Method for Physical and Mechanical Properties of Concrete GB / T 50081-2019 to investigate the influence of the modified recycled coarse aggregate on the concrete performance. The results are listed in Table 7.

[0092] Table 7 Test Results of Concrete with 20% Enhanced Recycled Aggregate Replacement Rate at 28 d Curing Age

[0093] Name Compressive strength (MPa) Splitting tensile strength (MPa) Water absorption rate (%) Natural aggregate concrete 44.1 3.24 3.9 Modified recycled aggregate concrete 50.7 3.67 4.5 Secondary modified recycled aggregate concrete 52.4 3.79 4.6

[0094] It can be found from the data in Table 7 that, compared with Application Example 1, in this Application Example, by adding a deposition medium during the mixing of concrete, the strength of the recycled aggregate concrete is improved.

[0095] Application Example 4

[0096] The difference from Application Example 3 is that the recycled aggregate replacement rate is changed to 50% to prepare recycled aggregate concrete. The mix proportions of the three groups of concrete are shown in Table 8.

[0097] Table 8 Mix proportion of concrete with 50% recycled aggregate replacement rate (kg / m 3 )

[0098]

[0099] The freshly mixed concrete prepared according to the mix proportion of Table 8 was placed in a mold, vibrated, demolded, and then cured in a curing room. When the curing age reached 28 d, the compressive strength, splitting tensile strength, and water absorption of the concrete were tested in accordance with the Standard for Test Methods of Physical and Mechanical Properties of Concrete (GB / T 50081-2019) to investigate the influence of the modified recycled coarse aggregate on the concrete properties. The results are listed in Table 9.

[0100] Table 9 Test results of concrete with 50% recycled aggregate replacement rate at 28 d age

[0101] Name Compressive strength (MPa) Splitting tensile strength (MPa) Water absorption rate (%) Natural aggregate concrete 44.1 3.24 3.9 Application Example 3 47.0 3.37 5.7 This application example 50.3 3.56 4.9

[0102] It can be found from the data in Table 9 that, compared with Application Example 3, the strength of the recycled aggregate concrete is improved in this application example by adding a deposition medium during the mixing of concrete.

[0103] It can be proved by the above examples that the proposed method of optimizing the use of microbial denitrification phenomenon to improve the properties of recycled aggregate concrete can greatly improve the physical and mechanical properties of recycled aggregate concrete, improve the effect of using denitrifying bacteria to modify recycled aggregate and recycled aggregate concrete, and promote the green and sustainable development of the construction industry to a certain extent.

[0104] The applicant declares that the specific embodiments of the present invention described in the above examples only provide references and do not mean that the present invention can only be implemented relying on the above examples. Those skilled in the relevant art should understand that without departing from the principle of the present invention, improvements and refinements can be made to the replacement of raw materials, addition of auxiliary components, and selection of specific methods of the invention. Therefore, all technical solutions adopting equivalent transformations and improvements fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for optimizing the use of microbial denitrification to modify and regenerate coarse aggregate, characterized in that: The steps include: (1) pouring a high-concentration bacterial solution onto the surface of dry recycled coarse aggregate and allowing the surface to fully absorb the denitrifying bacteria matrix to obtain recycled coarse aggregate with attached denitrifying bacteria; (2) soaking the regenerated coarse aggregate with attached denitrifying bacteria obtained in step (1) in a mineralizing solution to obtain regenerated coarse aggregate strengthened by microorganisms; (3) removing the regenerated coarse aggregate obtained in step (2) from the mixed solution after microbial enhancement, washing it, and drying it in a constant temperature oven to a constant weight; (4) vacuum impregnating the recycled coarse aggregate dried in step (3) into a bacterial solution, so that the enhanced recycled coarse aggregate is immobilized with denitrifying bacteria to obtain the modified recycled coarse aggregate; The method for preparing the high-concentration bacterial solution in step (1) comprises: (a) inoculating bacteria into a sterile liquid culture medium for culturing to obtain a denitrifying bacterial culture; The bacteria is Pseudomonas denitrificans ATCC13867; The sterile liquid culture medium is obtained by placing the prepared bacterial culture medium I in a high pressure sterilizer and sterilizing it at 121°C and 100kpa for 10 to 25 minutes, wherein the bacterial culture medium I comprises 2 to 5 g / L of beef extract powder, 2 to 5 g / L of sodium chloride, 4 to 10 g / L of peptone, and 4 to 10 g / L of sucrose; (b) mixing the pure bacterial cells of the denitrifying bacterial solution obtained by centrifugation in step (a) with bacterial culture medium II to obtain the high-concentration bacterial solution; The bacterial culture medium II is the supernatant after centrifugation of the denitrifying bacterial culture, and its dosage is 1.2 to 1.4 times the water absorption corresponding to the water absorption rate of the recycled coarse aggregate; The mineralization solution in step (2) comprises 21-23 g / L calcium formate, 7.5-8.2 g / L calcium nitrate and bacterial culture medium III component, wherein the bacterial culture medium III component comprises 2-5 g / L beef extract powder, 2-5 g / L sodium chloride, 4-10 g / L peptone and 4-10 g / L sucrose, and the amount thereof is based on per liter of deionized water; The bacterial solution in step (4) is obtained by centrifuging a bacterial solution grown in bacterial culture medium I and then diluting it again with 1-3 g / L glucose solution. The OD600 value of the bacterial solution is 0.7-1.0, and the bacterium is Pseudomonas denitrificans ATCC13867.

2. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: In the method for preparing the high-concentration bacterial solution in step (1), the culture temperature in step (a) is 30 to 35° C. and the culture time is 24 to 48 hours; The concentration of the denitrifying bacteria solution to be centrifuged in step (b) is OD 600 is 0.7; the centrifugal speed is 5000-7000 rpm / min, and the centrifugal time is 5-8 min.

3. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: The recycled coarse aggregate in step (1) comprises 40% recycled concrete aggregate and 60% recycled brick aggregate by volume, and the recycled coarse aggregate is 5-20 mm continuous particle graded crushed stone.

4. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: The method for preparing the dried recycled coarse aggregate in step (1) comprises: washing the recycled coarse aggregate with tap water and then placing it in an oven and drying it at 60 to 105° C. for 12 to 24 hours to obtain the dried recycled coarse aggregate.

5. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: The dried recycled coarse aggregate in step (1) is allowed to stand for 6 to 12 hours to absorb the high concentration of denitrifying bacteria solution.

6. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: After the mineralization solution in step (2) is prepared, the pH is adjusted to 9 by dripping NaOH solution and HCl solution, and then the regenerated coarse aggregate with attached denitrifying bacteria obtained in step (1) is immersed in the solution, the ambient temperature during the immersion is 30° C., and the immersion time is 8 to 12 days; The ratio of recycled coarse aggregate to mineralized solution is 1000g:1000ml.

7. The method for optimizing the utilization of microbial denitrification to modify and regenerate coarse aggregate according to claim 1, characterized in that: The pressure of the vacuum impregnation in step (4) is -0.06 MPa, and the impregnation time is 20 to 30 minutes.

8. A method for preparing recycled aggregate concrete using the modified recycled coarse aggregate obtained by the method according to any one of claims 1 to 7, characterized in that: include: The modified recycled coarse aggregate is taken out from the impregnation container and the surface moisture is wiped off to make it reach a saturated surface dry state, and then the modified recycled coarse aggregate with fixed bacteria is used to replace part of the natural coarse aggregate in the fresh concrete, and mixed with water, cement, sand, natural coarse aggregate, and sedimentation medium to obtain recycled aggregate concrete; The deposition medium is 7-9 kg / m 3 Calcium formate and 2.5~3.5kg / m 3 Mixed solution of calcium nitrate, the amount to be used is based on per cubic meter of concrete; The modified recycled coarse aggregate replaces the natural coarse aggregate by equal volume replacement, and the replacement rate is 20-50%.

Images