Method for mineralizing concrete recycled aggregate by exopolysaccharide compound microorganisms

Abstract

The invention discloses a method for mineralizing concrete recycled aggregate through exopolysaccharide compound microorganisms, and belongs to the technical field of microorganisms and concrete materials. The composite dispersion liquid composed of diammonium hydrogen phosphate, chitin and cellulose is used, the aggregate is soaked from low concentration to high concentration, effective modification of the surface of the aggregate can be achieved, and then the aggregate is treated with a composite microbial agent composed of bacillus subtilis and sporosarcina mectacitae, so that the surface of the aggregate is improved, and the surface of the aggregate is improved. Wherein the mineralization activity is effectively improved after the two selected microbial strains with high high-temperature resistance and alkali resistance are mixed in equal proportion, high-activity urease can be produced in a high-temperature and high-alkali environment, pores and microcracks of the recycled aggregate are effectively filled by formed calcium carbonate, effective regeneration of the waste concrete aggregate is realized, the treatment is convenient, and the efficiency is high. The biological polysaccharide compound microorganism method adopted by the invention has the characteristics of high efficiency, maintenance condition simplification, economy, environmental protection and the like, and formed minerals are stable in property and strong in durability.

Description

Technical Field

[0001] The invention belongs to the technical field of microorganisms and concrete materials, and in particular relates to a method for mineralizing concrete regenerated aggregates using extracellular polysaccharide composite microorganisms. Background Art

[0002] With the rapid expansion of the construction industry, waste concrete has become one of the main types of construction waste. Its large accumulation not only wastes land resources, but also poses a threat to the environment. In order to achieve sustainable development, the reuse of waste concrete has become crucial. Through processes such as cracking, cleaning, and crushing, waste concrete can be converted into recycled aggregates, effectively reducing waste emissions and reducing dependence on natural resources. However, compared with natural aggregates, recycled aggregates have many performance defects, such as large porosity and high water absorption, which limits their application in concrete. Therefore, in order to improve the performance of recycled concrete and promote the high value-added application of recycled concrete in actual engineering, it is necessary to modify the recycled aggregates.

[0003] The modification methods of recycled aggregates mainly include physical modification, chemical modification, carbonization modification, nano-modification and microbial modification, etc. Among them, the microbial modification method (MICP) uses natural microorganisms to induce carbon to fill the pores and micro cracks of recycled aggregates, thereby improving the performance of recycled aggregates.

[0004] For example, Chinese patent application CN201610180571.7 discloses a method for strengthening recycled concrete fine aggregate by depositing calcium carbonate with microorganisms, comprising the following steps: preparing a microbial culture medium, adjusting the pH value to 7-9 by dripping NaOH solution, sterilizing and cooling to room temperature, inoculating pasteurian sporosarcina, adding urea solution at the same time, and shaking culture at 25-37°C; adding recycled concrete fine aggregate to the bacterial culture solution, and continuing to shake culture; adding urea and calcium source mixed solution, mixing evenly, shaking, and taking out the recycled aggregate after the end; drying the recycled aggregate while heating and stirring. Compared with unreinforced recycled aggregate, the recycled fine aggregate obtained by the present invention can reduce the crushing value by nearly 60% and the water absorption rate by nearly 50%.

[0005] Another example is Chinese patent application CN202210331372.7, which discloses a method for preparing a curing agent for the activation and utilization of recycled concrete powder, the steps are: (1) adding composite microbial powder and urban sludge to a stirring pot in a certain proportion, setting a constant temperature, stirring continuously, and stirring for 24-72 hours; (2) adding recycled concrete powder to step (1), stirring continuously, stirring for 12-24 hours, and standing at a constant temperature for 1-12 days; (3) adding cement to step (2), forming a test piece, and placing the test piece in a standard curing room with constant temperature and humidity for curing. The results show that the organic matter in the sludge / sludge is converted into acidic substances by using composite microorganisms to degrade and transform, activate the effective components such as calcium hydroxide in the recycled concrete powder, enhance the activity of the recycled concrete powder, partially replace cement to configure the curing agent, and realize sludge solidification. The present invention uses solid waste recycled concrete powder to realize sludge solidification, treats waste with waste, and has significant ecological benefits.

[0006] However, the existing microorganisms in use have poor environmental adaptability, and their ability to modify and prepare recycled concrete is very limited. The activity of microorganisms will be inhibited by the high alkalinity of concrete. The survival and development ability of spores will gradually decrease as the age of concrete increases and the voids become smaller, and the survival time is short. In addition, although the microbial induced calcium carbonate deposition (MICP) technology can effectively improve the performance of recycled aggregates, such as reducing water absorption and crushing index and increasing apparent density, its self-healing effect still has limitations. For example, in the repair of wide cracks, the effect of microbial self-healing is limited, and the repair process is long, and the repair effect on wide cracks is not good.

[0007] Therefore, how to optimize the current method of microbial modification of recycled aggregates, improve the repair effect, and optimize the performance of recycled aggregates is a technical problem that needs to be solved urgently. Summary of the invention

[0008] In view of the problems of microbial regeneration of aggregate in the prior art, the present invention provides an optimized method for regenerating aggregate in concrete by extracellular polysaccharide composite microbial mineralization. The performance of the regenerated aggregate is significantly improved. Compared with before treatment, the water absorption rate and crushing index are significantly reduced. The effect is remarkable, environmentally friendly, and no secondary pollution is generated.

[0009] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0010] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0011] (1) Pretreatment: Stir the crushed waste concrete at 55-75°C for 30-50 minutes, rinse with water, and dry to obtain pretreated aggregate;

[0012] (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%;

[0013] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0014] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed;

[0015] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0016] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1-0.3 MPa for curing for 4-6 hours. After curing, they are dried to obtain recycled aggregates.

[0017] Furthermore, the preparation method of the extracellular polysaccharide composite dispersion in step (2) is: diammonium hydrogen phosphate, chitin and cellulose are mixed in a mass ratio of 1:1:1 to obtain an extracellular polysaccharide mixture, and then the mixture is dispersed in water to obtain dispersions with a mixture mass concentration of 1-2%, 10-11%, and 20-21%, respectively; 1-3% of the mass of the dispersion is added with Tween 80, and the dispersion is continuously stirred and dispersed for 1-3 hours to obtain extracellular polysaccharide composite dispersions with a mass concentration of 1-2%, 10-11%, and 20-21%, respectively.

[0018] Furthermore, the preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and Sporosarcina macmurdoensis, they are inoculated into a fermentation medium respectively, and cultured for 24-30 hours at a speed of 160-180 r / min and a temperature of 35-45° C. to prepare a bacterial solution containing Bacillus subtilis and Sporosarcina macmurdoensis, and then centrifuged at 6000-8000 rpm for 10-15 minutes at 4° C., and then the nutrients in the upper culture medium are removed to obtain the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis; the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis are mixed in a mass ratio of 1:1, dispersed in an agar solution with a concentration of 20 g / L, and then 0.5-1% of urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0019] Furthermore, the strain number of the McMurdo Sporosarcina is CGMCC No. 1.8646, purchased from the General Microbiological Center of the China Microbiological Culture Collection Administration, and the original preservation time is September 17, 2008; the strain number of the Bacillus subtilis is CCTCC AB 130001, purchased from the China Center for Type Culture Collection, and the original preservation date is January 1, 2014. All the strains involved can be purchased through the collection center without repeated biological preservation.

[0020] Furthermore, the strain activation method is as follows: the frozen target strain is inoculated on an LB solid culture medium plate and cultured at 35-45°C for 36 hours; a single colony is picked and streaked again and transferred to an LB solid culture medium plate, and cultured at 35-45°C for 24 hours to complete the strain activation.

[0021] Furthermore, the composition of the fermentation medium is as follows: per liter of medium contains 3-7g of peptone, 4-6g of beef extract, 6-7g of NaCl, 16-18g of agar, 0.3-0.7g of MgSO4, and the balance is water, and the pH is natural.

[0022] Furthermore, the mass ratio of the pretreated aggregate in step (4) to the extracellular polysaccharide composite solution is 1:(2-6).

[0023] Furthermore, in step (5), the mass ratio of the aggregate to the concentrated bacterial solution is 1:(0.2-0.6).

[0024] Furthermore, in step (6), the carbon dioxide curing concentration is 80%.

[0025] Beneficial effects:

[0026] (1) First, the waste concrete aggregate is crushed and washed with water. By washing with water, the attached cement mortar, dust, steel bars and other impurities can be effectively removed;

[0027] (2) Secondly, prepare an exopolysaccharide composite dispersion composed of diammonium hydrogen phosphate, chitin and cellulose, wherein diammonium hydrogen phosphate can strengthen the hardening cement mortar, and the hydroxyapatite (HAP) precipitation generated on its surface can enhance the durability and adsorption capacity of the recycled aggregate and improve the mechanical properties of the recycled aggregate; and the added chitin, cellulose and other polysaccharide substances, the hydrogen bonding provided by them can significantly increase the subsequent microbial mineralization product formation rate, accelerate the mineralization product deposition effect, and after treating the recycled aggregate, the mineralized calcium carbonate is deposited on the surface of the recycled aggregate to repair and fill the cracks and pores of the recycled aggregate, reducing the water absorption rate; in addition, chitin, cellulose, etc., as a natural polymer material, have good adhesion. Through immersion treatment, the surface properties of the recycled aggregate can be improved. On the one hand, it contains polar groups such as hydroxyl and amino groups, which makes it easier to achieve the fixation and attachment of microorganisms. At the same time, it can fix urease through adsorption and ensure that the urease has a high activity; on the other hand, it is easier to combine with new mortar, thereby improving the overall performance of concrete. At the same time, the composite dispersion composed of the three and the immersion treatment of the aggregate in a gradient concentration from low concentration to high concentration can effectively modify the surface of the aggregate and make the subsequent microbial treatment more effective;

[0028] (3) The aggregate is treated with a composite bacterial agent composed of Bacillus subtilis and McMurdo Sporosarcina, wherein the two selected microbial strains are highly resistant to high temperature and alkali. After the two bacteria are mixed in equal proportions, the mineralization activity is effectively improved. Highly active urease can be produced under high temperature and high alkali conditions. The formed calcium carbonate can effectively fill the pores and microcracks of the recycled aggregate, thereby achieving effective regeneration of waste concrete aggregates, and the treatment is convenient and efficient.

[0029] (4) The biopolysaccharide composite microbial method adopted in the present invention has the characteristics of high efficiency, simplified maintenance conditions, economy and environmental protection, and the formed minerals are stable in nature and durable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A graph of the carbonization depth of concrete measured by stereomicroscope for a concrete specimen prepared from recycled aggregate in Example 1 of the present invention;

[0031] Figure 2 Concrete carbonation depth diagram of concrete specimens prepared with natural aggregates measured by stereomicroscope. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described below in conjunction with specific embodiments, but is not limited thereto.

[0033] Example 1

[0034] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0035] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 30 minutes, washed with water, and dried to obtain pretreated aggregate;

[0036] (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%;

[0037] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0038] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed;

[0039] (5) Microbial treatment: coating the aggregate that has been soaked in step (4) with the concentrated bacterial solution obtained in step (3);

[0040] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 h. After curing, the aggregates are dried to obtain recycled aggregates.

[0041] The preparation method of the extracellular polysaccharide composite dispersion in step (2) is as follows: diammonium hydrogen phosphate, chitin and cellulose are mixed in a mass ratio of 1:1:1 to obtain an extracellular polysaccharide mixture, and then the mixture is dispersed in water to obtain dispersions with a mixture mass concentration of 1-2%, 10-11%, and 20-21%, respectively; 1% of the mass of the dispersion is added with Tween 80, and the dispersion is continuously stirred and dispersed for 1 hour to obtain extracellular polysaccharide composite dispersions with a mass concentration of 1-2%, 10-11%, and 20-21%, respectively.

[0042] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and Sporosarcina macmurdoensis, they are inoculated into a fermentation medium respectively, and cultured for 24 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and Sporosarcina macmurdoensis, and then centrifuged at 6000rpm for 10min at 4°C to remove the nutrients in the upper culture medium to obtain the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis; the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis are mixed in a mass ratio of 1:1, dispersed in an agar solution with a concentration of 20g / L, and then 0.5% urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0043] The strain number of McMurdo Sporosarcina is CGMCC No.1.8646, purchased from the General Microbiological Center of China National Committee for Microbiological Culture Collection, and the original preservation date is September 17, 2008; the strain number of Bacillus subtilis is CCTCC AB 130001, purchased from China Center for Type Culture Collection, and the original preservation date is January 1, 2014. All strains involved can be purchased through the collection center without repeated biological preservation.

[0044] The strain activation method is as follows: the frozen target strain is inoculated on an LB solid culture medium plate and cultured at 35-45°C for 36 hours; a single colony is picked and streaked again on an LB solid culture medium plate and cultured at 35-45°C for 24 hours to complete the strain activation.

[0045] The fermentation medium is composed of: 3-7g of peptone, 4-6g of beef extract, 6-7g of NaCl, 16-18g of agar, 0.3-0.7g of MgSO4, and the balance of water per liter of the medium, with a natural pH.

[0046] In step (4), the mass ratio of the pretreated aggregate to the extracellular polysaccharide composite solution is 1:2.

[0047] In step (5), the mass ratio of aggregate to concentrated bacterial solution is 1:0.2.

[0048] The carbon dioxide curing concentration in step (6) is 80%.

[0049] Example 2

[0050] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0051] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 40 minutes, washed with water, and dried to obtain pretreated aggregate;

[0052] (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%;

[0053] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0054] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed;

[0055] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0056] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 h. After curing, the aggregates are dried to obtain recycled aggregates.

[0057] The preparation method of the extracellular polysaccharide composite dispersion in step (2) is as follows: diammonium hydrogen phosphate, chitin and cellulose are mixed in a mass ratio of 1:1:1 to obtain an extracellular polysaccharide mixture, and then the mixture is dispersed in water to obtain dispersions with a mass concentration of 1-2%, 10-11% and 20-21% respectively, and 2% Tween 80 by mass of the dispersion is added, and the dispersion is continuously stirred and dispersed for 2 hours to obtain extracellular polysaccharide composite dispersions with a mass concentration of 1-2%, 10-11% and 20-21% respectively.

[0058] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and Sporosarcina macmurdoensis, they are inoculated into a fermentation medium respectively, and cultured for 30 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and Sporosarcina macmurdoensis, and then centrifuged at 8000rpm for 15 minutes at 4°C to remove the nutrients in the upper culture medium to obtain the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis; the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis are mixed in a mass ratio of 1:1, dispersed in an agar solution with a concentration of 20g / L, and then 0.5-1% of urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0059] The strain number of McMurdo Sporosarcina is CGMCC No.1.8646, purchased from the General Microbiological Center of China National Committee for Microbiological Culture Collection, and the original preservation date is September 17, 2008; the strain number of Bacillus subtilis is CCTCC AB 130001, purchased from China Center for Type Culture Collection, and the original preservation date is January 1, 2014. All strains involved can be purchased through the collection center without repeated biological preservation.

[0060] The strain activation method is as follows: the frozen target strain is inoculated on an LB solid culture medium plate and cultured at 35-45°C for 36 hours; a single colony is picked and streaked again on an LB solid culture medium plate and cultured at 35-45°C for 24 hours to complete the strain activation.

[0061] The fermentation medium comprises: 3-7g of peptone, 4-6g of beef extract, 6-7g of NaCl, 16-18g of agar, 0.3-0.7g of MgSO4, and the balance of water per liter of the medium, and the pH is natural.

[0062] The mass ratio of the pretreated aggregate to the extracellular polysaccharide composite solution in step (4) is 1:4.

[0063] In step (5), the mass ratio of aggregate to concentrated bacterial solution is 1:0.4.

[0064] The carbon dioxide curing concentration in step (6) is 80%.

[0065] Example 3

[0066] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0067] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 50 minutes, washed with water, and dried to obtain pretreated aggregate;

[0068] (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%;

[0069] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0070] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed;

[0071] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0072] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.3 MPa for curing for 4 h. After curing, the aggregates are dried to obtain recycled aggregates.

[0073] The preparation method of the extracellular polysaccharide composite dispersion in step (2) is as follows: diammonium hydrogen phosphate, chitin and cellulose are mixed in a mass ratio of 1:1:1 to obtain an extracellular polysaccharide mixture, and then the mixture is dispersed in water to obtain dispersions with a mixture mass concentration of 1-2%, 10-11%, and 20-21%, respectively; 3% of the mass of the dispersion is added with Tween 80, and the dispersion is continuously stirred and dispersed for 3 hours to obtain extracellular polysaccharide composite dispersions with a mass concentration of 1-2%, 10-11%, and 20-21%, respectively.

[0074] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and Sporosarcina macmurdoensis, they are inoculated into a fermentation medium respectively, and cultured for 30 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and Sporosarcina macmurdoensis, and then centrifuged at 8000rpm for 15 minutes at 4°C to remove the nutrients in the upper culture medium to obtain the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis; the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis are mixed in a mass ratio of 1:1, dispersed in an agar solution with a concentration of 20g / L, and then urea of ​​1% by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0075] The strain number of McMurdo Sporosarcina is CGMCC No.1.8646, purchased from the General Microbiological Center of China National Committee for Microbiological Culture Collection, and the original preservation date is September 17, 2008; the strain number of Bacillus subtilis is CCTCC AB 130001, purchased from China Center for Type Culture Collection, and the original preservation date is January 1, 2014. All strains involved can be purchased through the collection center without repeated biological preservation.

[0076] The strain activation method is as follows: the frozen target strain is inoculated on an LB solid culture medium plate and cultured at 35-45°C for 36 hours; a single colony is picked and streaked again on an LB solid culture medium plate and cultured at 35-45°C for 24 hours to complete the strain activation.

[0077] The fermentation medium is composed of: 3-7g of peptone, 4-6g of beef extract, 6-7g of NaCl, 16-18g of agar, 0.3-0.7g of MgSO4, and the balance of water per liter of the medium, with a natural pH.

[0078] The mass ratio of the pretreated aggregate to the extracellular polysaccharide composite solution in step (4) is 1:6.

[0079] In step (5), the mass ratio of aggregate to concentrated bacterial solution is 1:0.6.

[0080] The carbon dioxide curing concentration in step (6) is 80%.

[0081] Comparative Example 1

[0082] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0083] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 30 minutes, washed with water, and dried to obtain pretreated aggregate;

[0084] (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%;

[0085] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0086] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed;

[0087] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0088] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 h. After curing, the aggregates are dried to obtain recycled aggregates.

[0089] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis, inoculate them into a fermentation medium respectively, culture them at a speed of 160-180r / min and a temperature of 35-45°C for 24h to prepare a bacterial solution containing Bacillus subtilis, and then centrifuge them at 6000rpm for 10min at 4°C to remove the nutrients in the upper culture medium to obtain Bacillus subtilis cells; disperse the Bacillus subtilis in an agar solution with a concentration of 20g / L, add urea with a mass percentage of 0.5% of the mixed solution, stir evenly, and obtain a bacterial cell concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0090] The strain number of the Bacillus subtilis is CCTCC AB 130001, which was purchased from the China Center for Type Culture Collection, and the original preservation date is January 1, 2014. All strains involved can be purchased through the collection center without repeated biological preservation.

[0091] In this comparative example, except that only Bacillus subtilis was used in the concentrated bacterial solution in step (5), the remaining raw materials and preparation method were the same as those in Example 1.

[0092] Comparative Example 2

[0093] In this comparative example, except that only McMurdo Sporosarcina was used in the concentrated bacterial solution in step (5), the remaining raw materials and preparation method were the same as those in Example 1. That is:

[0094] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating McMurdo spore octahedralis, inoculate them into a fermentation medium respectively, culture them at a speed of 160-180r / min and a temperature of 35-45°C for 24h to prepare a bacterial solution containing McMurdo spore octahedralis, and then centrifuge them at 6000rpm for 10min at 4°C to remove the nutrients in the upper culture medium to obtain the cells of McMurdo spore octahedralis; disperse the McMurdo spore octahedralis in an agar solution with a concentration of 20g / L, add urea with a mass percentage of 0.5% of the mixed solution, stir evenly, and obtain a cell concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0095] Comparative Example 3

[0096] In this comparative example, except that the ratio of Bacillus subtilis to McMurdo Sporosarcina in the concentrated bacterial solution in step (5) is changed to 2:1, the remaining raw materials and preparation method are the same as those in Example 1. That is:

[0097] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and McMurdo Sporosarcina, they are inoculated into a fermentation medium respectively, and cultured for 24 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and McMurdo Sporosarcina, and then centrifuged at 6000rpm for 10min at 4°C, and then the nutrients in the upper culture medium are removed to obtain the bacterial bodies of Bacillus subtilis and McMurdo Sporosarcina; the bacterial bodies of Bacillus subtilis and McMurdo Sporosarcina are mixed in a mass ratio of 2:1, dispersed in an agar solution with a concentration of 20g / L, and then 0.5% urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0098] Comparative Example 4

[0099] In this comparative example, except that the ratio of Bacillus subtilis to McMurdo Sporosarcina in the concentrated bacterial solution in step (5) is changed to 1:2, the remaining raw materials and preparation method are the same as those in Example 1. That is:

[0100] The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and McMurdo Sporosarcina, they are inoculated into a fermentation medium respectively, and cultured for 24 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and McMurdo Sporosarcina, and then centrifuged at 6000rpm for 10min at 4°C, and then the nutrients in the upper culture medium are removed to obtain the bacterial bodies of Bacillus subtilis and McMurdo Sporosarcina; the bacterial bodies of Bacillus subtilis and McMurdo Sporosarcina are mixed in a mass ratio of 1:2, dispersed in an agar solution with a concentration of 20g / L, and then 0.5% urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

[0101] Comparative Example 5

[0102] In this comparative example, except that only a 1-2% mass concentration of extracellular polysaccharide complex solution is used for treatment in step (4), the remaining raw materials and preparation methods are the same as those in Example 1. That is:

[0103] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0104] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 30 minutes, washed with water, and dried to obtain pretreated aggregate;

[0105] (2) preparing a composite dispersion of extracellular polysaccharide with a mass concentration of 1-2%;

[0106] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0107] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in a composite solution of extracellular polysaccharide with a mass concentration of 1-2% for 36 hours, and drying after the treatment;

[0108] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0109] (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 h. After curing, the aggregates are dried to obtain recycled aggregates.

[0110] Comparative Example 6

[0111] In this comparative example, except that only the extracellular polysaccharide complex solution with a mass concentration of 10-11% is used for treatment in step (4), the other raw materials and preparation methods are the same as those in Example 1. That is:

[0112] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0113] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 30 minutes, washed with water, and dried to obtain pretreated aggregate;

[0114] (2) preparing an extracellular polysaccharide composite dispersion having a mass concentration of 10-11%;

[0115] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0116] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in a composite solution of extracellular polysaccharide with a mass concentration of 10-11% for 36 hours, and drying after the treatment;

[0117] (5) Microbial treatment: coating the aggregate that has been soaked in step (4) with the concentrated bacterial solution obtained in step (3);

[0118] Carbon dioxide curing;

[0119] (6) The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 hours, and then dried to obtain recycled aggregates.

[0120] Comparative Example 7

[0121] In this comparative example, except that only the extracellular polysaccharide complex solution with a mass concentration of 20-21% is used for treatment in step (4), the other raw materials and preparation methods are the same as those in Example 1. That is:

[0122] A method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms comprises the following steps:

[0123] (1) Pretreatment: The crushed waste concrete is stirred at 55-75°C for 30 minutes, washed with water, and dried to obtain pretreated aggregate;

[0124] (2) preparing an extracellular polysaccharide composite dispersion having a mass concentration of 20-21%;

[0125] (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution;

[0126] (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in a composite solution of extracellular polysaccharide with a mass concentration of 20-21% for 36 hours, and drying after the treatment;

[0127] (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3);

[0128] Carbon dioxide curing;

[0129] (6) The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1 MPa for curing for 6 hours, and then dried to obtain recycled aggregates.

[0130] Performance Testing

[0131] Test of strain urease production ability: After activating Bacillus subtilis and McMurdo Sporosarcina, pick a single colony and inoculate it into LB liquid culture medium, shake and culture it at 35-45℃ for 24h, then take 2ml of culture solution and centrifuge it at 4℃, 12000r / min for 3min, remove the supernatant to obtain the bacteria to measure the urease activity. The urease activity is determined by the indigo blue colorimetric method, and the activity is defined as one enzyme activity unit for each 1μg NH3-N produced at 37℃. It is expressed as U. During the screening process, the enzyme activity of the strain is shown in Table 1.

[0132] Table 1 Results of enzyme activity test of strains

[0133] strain Urease activity (U) Bacillus subtilis 780.4 McMurdo Sporosarcina 825.1

[0134] The two strains screened by the present invention both have the ability to produce highly active urease. Their activity in a concrete environment is further verified. The heat released during the hydration process of concrete pouring may cause the temperature to rise to above 40°C, and the high temperature stability and alkali stability of the strains are further tested.

[0135] Preparation of bacterial suspension: After activation of Bacillus subtilis and McMurdo Sporosarcina, single colonies were picked and inoculated into LB liquid culture medium, and cultured in a shaking incubator at 35-45°C for 24 hours. Subsequently, 2 ml of the culture medium was taken and incubated at 4°C to obtain two bacterial suspensions.

[0136] The bacterial suspensions of the two strains were treated in a water bath at 40, 45, 50, 55, and 60°C for 60 minutes. After cooling, the stained bacterial suspensions were counted using a hemocytometer to calculate the ratio of live cells to dead cells. The survival rates of Bacillus subtilis and McMurdo Sporosarcina remained above 90% below 60°C, and the thermal stability of the two strains was good.

[0137] Because the hydration process in concrete pouring will make the pH between 12-13, the pH value of the bacterial suspension of the two strains was adjusted to 12.5 with 1 mol / L sodium hydroxide. After standing for 24 hours, the solution was filtered through a 0.22 μm microporous filter membrane, and the solution without pH adjustment was used as a control. The stained bacterial suspension was counted using a hemocytometer. When the pH was 12.5, the survival rate of Bacillus subtilis and McMurdo Sporosarcina remained above 90%, indicating that the strains Bacillus subtilis and McMurdo Sporosarcina have good alkali stability. It is suitable for application in concrete-related fields.

[0138] Recycled aggregate performance test:

[0139] The apparent density, crushing index and water absorption rate of the recycled aggregate obtained in the embodiment and the comparative example were tested according to the "Pebbles and Crushed Stones for Construction" (GB / T14685-2011). Each group of experiments was repeated 10 times and the results were averaged. Untreated aggregate (RCA-0) and natural aggregate (NA) were used for comparison.

[0140] The results are shown in Table 2.

[0141] Table 2 Test results of recycled aggregate performance

[0142]

[0143] From the data in Table 2, we can see that the aggregate regenerated by the embodiment of the present invention has a significantly improved performance in terms of water absorption, apparent density and crushing index relative to the untreated aggregate (RCA-0), and some performances are close to the natural aggregate group. However, the comparative examples 1-4 with changed microbial composition and the comparative examples 5-6 with changed polysaccharide treatment processes all show different degrees of weakening in various performances. This is because the synergistic balance between the two functional strains in the comparative examples 1-4 with changed microbial composition is broken, and its mineralization is weakened, while the comparative examples 5-7 with changed dispersion composition have weakened the surface modification effect on the regenerated aggregate, and the adsorption and fixation effect on the microorganisms is insufficient, thus affecting the regeneration strengthening effect. It can be seen that the selection of the concentrated bacterial solution and the extracellular polysaccharide dispersion of the present invention is the key, and the change of the composition process will affect the realization of the final effect.

[0144] A batch of concrete blocks were prepared using the recycled aggregates of Examples 1-3 and Comparative Examples 1-7, as well as untreated aggregates as coarse aggregates. The formula is shown in Table 3.

[0145] Table 3 Concrete mix ratio

[0146]

[0147] The concrete specimens were cured for 28 days under standard environmental conditions with a relative humidity of more than 95% and a temperature of 20±2℃. The mechanical properties of the concrete were tested according to the Standard Test Methods for Physical and Mechanical Properties of Concrete. The test of concrete resistance to chloride ion penetration was based on GB / T 50082-2009 Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete, and the carbonation depth test was based on GB / T 50082-2009 Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete. The specific experimental results are shown in Table 4. Ten specimens were repeated in each group, and the results were averaged.

[0148] Table 4 Concrete performance test

[0149]

[0150]

[0151] From the data in Tables 1-4, it can be seen that the performance of the concrete specimens of the embodiment of the present invention is close to or even exceeds that of ordinary concrete specimens, and can be used to replace natural aggregates. At the same time, the durability of concrete caused by concrete carbonization, the carbonization resistance of the recycled coarse aggregate concrete of the embodiment of the present invention is also slightly better than that of ordinary concrete.

[0152] It should be noted that the above embodiments are only partial embodiments of the preferred methods of implementing the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for mineralizing concrete recycled aggregate using extracellular polysaccharide composite microorganisms, characterized in that: The following steps are involved: (1) Pretreatment: Stir the crushed waste concrete at 55-75°C for 30-50 minutes, rinse with water, and dry to obtain pretreated aggregate; (2) preparing extracellular polysaccharide composite dispersions with mass concentrations of 1-2%, 10-11%, and 20-21%; (3) Prepare the bacterial cell concentration to be 10 6 -10 7 / mL of concentrated bacterial solution; (4) Soaking treatment: soaking the pretreated aggregate obtained in step (1) in the extracellular polysaccharide composite solution with mass concentrations of 1-2%, 10-11%, and 20-21% in sequence, with the soaking time of each concentration being 12 hours, and the total soaking time being 36 hours. After each concentration treatment is completed, drying is performed and then soaking treatment of the next concentration is performed; (5) Microbial treatment: coating the aggregate after the soaking treatment in step (4) with the concentrated bacterial solution obtained in step (3); (6) Carbon dioxide curing: The aggregates obtained in step (5) are placed in a relative humidity of 70% ± 3% and a CO2 pressure of 0.1-0.3 MPa for curing for 4-6 hours. After curing, they are dried to obtain recycled aggregates.

2. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 1, characterized in that: The preparation method of the extracellular polysaccharide composite dispersion in step (2) is as follows: diammonium hydrogen phosphate, chitin and cellulose are mixed in a mass ratio of 1:1:1 to obtain an extracellular polysaccharide mixture, and the mixture is dispersed in water to obtain dispersions with a mixture mass concentration of 1-2%, 10-11%, and 20-21%, respectively; 1-3% of the mass of the dispersion is added with Tween 80, and the dispersion is continuously stirred and dispersed for 1-3 hours to obtain extracellular polysaccharide composite dispersions with a mass concentration of 1-2%, 10-11%, and 20-21%, respectively.

3. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 1, characterized in that: The preparation method of the concentrated bacterial solution in step (3) is as follows: after activating Bacillus subtilis and Sporosarcina macmurdoensis, they are inoculated into a fermentation medium respectively, and cultured for 24-30 hours at a speed of 160-180r / min and a temperature of 35-45°C to prepare a bacterial solution containing Bacillus subtilis and Sporosarcina macmurdoensis, and then centrifuged at 6000-8000rpm for 10-15min at 4°C, and then the nutrients in the upper culture medium are removed to obtain the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis; the bacterial bodies of Bacillus subtilis and Sporosarcina macmurdoensis are mixed in a mass ratio of 1:1, dispersed in an agar solution with a concentration of 20g / L, and then 0.5-1% of urea by mass of the mixed solution is added, and stirred evenly to obtain a bacterial body concentration of 10 6 -10 7 / mL concentrated bacterial solution.

4. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 3, characterized in that: The strain number of the McMurdo Sporosarcina is CGMCC No.1.8646, which was purchased from the General Microbiological Center of the China National Committee for the Preservation of Microorganisms; the strain number of the Bacillus subtilis is CCTCC AB 130001, which was purchased from the China Center for Type Culture Collection.

5. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 3, characterized in that: The strain activation method is as follows: the frozen target strain is inoculated on an LB solid culture medium plate and cultured at 35-45°C for 36 hours; a single colony is picked and streaked again on an LB solid culture medium plate and cultured at 35-45°C for 24 hours to complete the strain activation.

6. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 3, characterized in that: The fermentation medium comprises 3-7 g of peptone, 4-6 g of beef extract, 6-7 g of NaCl, 16-18 g of agar, 0.3-0.7 g of MgSO4, and the balance of water, with a natural pH value per liter of the medium.

7. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 1, characterized in that: The mass ratio of the pretreated aggregate and the extracellular polysaccharide composite solution in step (4) is 1:(2-6).

8. The method for mineralizing concrete regeneration aggregate by exopolysaccharide composite microorganisms according to claim 1, characterized in that: In step (5), the mass ratio of aggregate to concentrated bacterial solution is 1:(0.2-0.6).

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