Carbonation curing and rapid repairing method of facultative anaerobic microbial concrete

Abstract

The application relates to the technical field of building materials, and discloses a carbonation curing and rapid repairing method for facultative anaerobic microbial concrete, which comprises the following steps: firstly, preparing concrete mixed with a composite facultative anaerobic microbial repairing agent with a mixing amount of 3.0% to 8.0%, and then performing controlled carbonation treatment under the conditions of a carbon dioxide concentration of 15% to 25% and a pressure of 0.10 MPa to 0.15 MPa after pre-curing. The repairing agent is prepared by coating expanded perlite loaded with shewanella, bacillus cohnii and nutrients with an interpenetrating network hydrogel. In the application, the pH value of the pore solution of the concrete is regulated to 10.0 to 11.0 through the carbonation process, the microorganisms are constructed with a suitable living microenvironment while the passivation alkalinity of the steel bars is reserved, when cracks occur, the facultative anaerobic bacteria and mineralizing bacteria utilize endogenous carbon sources to deposit calcium carbonate in situ in deep anoxic areas, the problems of difficult deep crack repairing and low microbial survival rate are solved, and the structural durability is improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete. Background Technology

[0002] Concrete, as the cornerstone of modern human civilization, is consumed in enormous quantities globally each year. However, the inherent brittleness of concrete makes it difficult to avoid the formation of microcracks during its service life. These microcracks not only mark the beginning of structural mechanical performance degradation but also provide convenient pathways for the intrusion of harmful media such as moisture, chloride ions, and carbon dioxide, thus accelerating steel corrosion and concrete deterioration, becoming a core hidden danger threatening structural durability and safety. Traditional crack maintenance relies on manual inspection and external repair, a passive post-treatment mode with drawbacks such as high cost, complex processes, and difficulty in eradicating internal damage. Inspired by the self-healing ability of organisms in nature, self-healing concrete technology utilizing microbial metabolism-induced calcium carbonate precipitation (MICP) has emerged. This technology aims to endow concrete with the ability to intelligently sense and autonomously heal damage, representing a cutting-edge trend in the development of building materials towards green and intelligent directions.

[0003] Despite significant progress in laboratory research, microbial self-healing technology still faces severe technical bottlenecks in its translation into engineering practice. First, the extremely alkaline environment within the concrete matrix (pH values ​​typically exceeding 12.5) poses immense survival pressure on microorganisms. Even alkali-resistant spores experience a substantial decrease in activity under prolonged strong alkaline erosion, rendering the concrete unable to effectively trigger its repair function in the later stages of service, thus failing to meet the long-term needs of infrastructure. Second, most current mainstream microbial repair systems rely on aerobic bacteria (such as Pasteurella multocida), whose mineralization reactions are highly dependent on the supply of external oxygen and carbon dioxide. However, in deep or micro-cracks in concrete, the obstructed gas diffusion creates an anaerobic environment, and external carbon sources are difficult to transport to the depths of the cracks. This results in a repair reaction limited to the surface layer, forming a superficial seal but internal emptiness—a pseudo-repair that fails to truly restore the integrity and impermeability of the deep structure. Furthermore, how to coordinate the compatibility between the introduction of microbial carriers and the physical and mechanical properties of the concrete matrix, avoiding the weakening of early strength and durability due to carrier incorporation, is also a critical issue that urgently needs to be addressed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, which solves the problems of low long-term survival rate of microorganisms in traditional self-healing microbial concrete due to the strongly alkaline environment of the matrix, and the inability to effectively repair deep cracks due to lack of oxygen and obstructed carbon source transport.

[0005] To achieve the above objectives, the present invention provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, employing the following technical solution: A method for carbonation curing and rapid repair of facultative anaerobic microbial concrete includes the following steps: Cement, aggregates, mixing water, admixtures, and composite facultative anaerobic microbial remediation agent are mixed and stirred evenly, then poured into molds and demolded; wherein the dosage of the composite facultative anaerobic microbial remediation agent is 3.0% to 8.0% of the cement mass; After demolding, the concrete specimens were placed in an environment with a relative humidity of 95% to 99% for initial hydration curing, which lasted for 1 to 3 days. The pre-cured concrete specimens were placed in a closed carbonation environment for treatment; the ambient temperature was controlled at 20℃ to 25℃, the relative humidity at 55% to 70%, the carbon dioxide volume concentration at 15% to 25%, the ambient pressure at 0.10MPa to 0.15MPa, and the treatment time at 6h to 24h. After carbonation, the concrete specimens were placed in a natural environment and left to stand for a period of time, followed by standard curing.

[0006] By adopting the above technical solution, this invention utilizes the synergistic effect of a controlled carbonization environment and a specific facultative anaerobic microbial system to solve the technical problems of low repair efficiency of traditional microbial self-healing concrete in deep cracks and low survival rate of microorganisms in strongly alkaline matrices.

[0007] The specific reaction mechanism and innovative effects are described below: First, the initial hydration and curing stage allows the concrete matrix to form a preliminary gel skeleton structure, providing a strength foundation for withstanding subsequent gas pressure.

[0008] Secondly, the controlled carbonation curing process does not aim for complete neutralization of concrete. Instead, it precisely adjusts the pH value of the surface and shallow pore fluid of the concrete by controlling the carbon dioxide concentration (15%-25%) and pressure (0.10-0.15 MPa). This process produces a dual effect: firstly, it reduces the pH value of the matrix pore fluid from strongly alkaline (usually greater than 12.5) to around 10.5. This environment retains the alkalinity required for steel passivation while significantly reducing the chemical erosion of microbial spores and dormant bodies by the high-alkalinity environment, thus improving the survival rate of functional microorganisms; secondly, it induces the formation of a micron-sized calcium carbonate crystal nucleus layer on the pore wall surface. These nuclei act as crystallization sites during subsequent crack repair, lowering the nucleation energy barrier of the repair products and accelerating the mineralization deposition rate.

[0009] Finally, when cracks appear in the concrete, this technical solution establishes a repair mechanism based on endogenous carbonate supply and dual mineralization. The specific reaction process consists of the following three steps: Step 1: Environmental Response and Activation. The formation of cracks allows moisture to seep in and come into contact with the complex facultative anaerobic microbial remediation agent. The coating absorbs water, swells, or ruptures, releasing the internally loaded Bacillus coli (mineralizing bacteria) and Shewanella (facultative carbon-producing bacteria), as well as nutrients.

[0010] Step Two: Facultative Anaerobic Metabolism and Carbon Production. In the anoxic or microaerobic environment deep within the cracks, Shewanella bacteria utilize nitrates as electron acceptors and engage in anaerobic respiration metabolism using organic matter (lactate, etc.). This metabolic process produces carbon dioxide (CO2) and bicarbonate (HCO3) ions in situ within the concrete. - The reaction formula is: (Taking lactate as an example). This step overcomes the mass transfer limitations of traditional single-strain systems, which rely on the slow diffusion rate and low concentration of carbon dioxide from the external air into the depths of cracks.

[0011] Step 3: Synergistic mineralization and sealing. Bacillus coli decomposes urea using urease to produce ammonia and carbon dioxide. By adjusting the pH of the microenvironment to alkaline, and combining the endogenous inorganic carbon source produced by Shewanella with calcium ions in the environment, calcite-type calcium carbonate is rapidly precipitated. The synergistic effect of the two bacteria improved the repair rate and density of cracks, especially deep cracks.

[0012] Preferably, the composite facultative anaerobic microbial remediation agent is prepared by the following steps: Facultative carbon-producing bacteria and mineralizing bacteria were cultured separately to obtain suspensions of facultative carbon-producing bacteria and mineralizing bacteria. The mineralized bacterial suspension and the facultative carbon-producing bacterial suspension were mixed at a volume ratio of 1:2 to 2:1, and nutrients were added to prepare a compound nutrient bacterial solution. The porous carrier was placed under a negative pressure of -0.08 MPa to -0.10 MPa to adsorb the composite nutrient bacterial solution, and then dried to obtain the loaded particles. A sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution was prepared. The loaded particles were immersed in the coating solution, and then cured, cleaned, and dried in a crosslinking solution to obtain the composite facultative anaerobic microbial remediation agent.

[0013] By employing the above technical solution, a microbial carrier system with a core-shell structure was constructed. The porous carrier (expanded perlite) utilizes negative pressure adsorption technology to ensure a high loading of bacterial solution and nutrients within the carrier, providing a physical shelter for the microorganisms. The sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating layer exhibits excellent film-forming properties and toughness, resisting mechanical friction and shear forces from aggregates during concrete mixing and preventing premature loss of internal components. Simultaneously, this coating layer is pH-sensitive and water-sensitive, responding to moisture stimulation and releasing its contents in the cracked environment after concrete hardening, achieving on-demand release of the repair agent. Adjusting the bacterial strain ratio between 1:2 and 2:1 allows for balancing carbon production and mineralization rates according to the engineering application environment (e.g., oxygen-rich or oxygen-deficient levels), ensuring maximum repair efficiency.

[0014] Preferably, the concentration range of the nutrients in the compound nutrient bacterial solution is as follows: calcium lactate 55g / L to 65g / L, urea 25g / L to 35g / L, yeast extract 4g / L to 6g / L, and sodium nitrate 8g / L to 12g / L.

[0015] By employing the above technical solution, high-concentration calcium lactate provides an ample calcium source, urea serves as a substrate for mineralizing bacteria, sodium nitrate acts as an electron acceptor for facultative carbon-producing bacteria under anaerobic conditions, and yeast extract provides basic growth factors. The concentration ratio of each component has been optimized to ensure that the limited space released by the microcapsules can maintain the nutritional supply required for long-term microbial metabolism and support continuous repair capabilities under multiple dry-wet cycles.

[0016] Preferably, the porous carrier is expanded perlite, and the particle size of the expanded perlite ranges from 0.5 mm to 2.0 mm; the adsorption process includes: maintaining the negative pressure for 15 min to 25 min, and then continuing to impregnate for 1.5 h to 2.5 h after restoring normal pressure.

[0017] By adopting the above technical solution and selecting expanded perlite with a particle size of 0.5mm to 2.0mm, sufficient internal pore volume is ensured to support the bacterial solution, while avoiding the adverse effects of excessively large particles on the mechanical properties of concrete. The process combining negative pressure adsorption and normal pressure impregnation utilizes the pressure difference to expel air from the pores, allowing the nutrient solution to penetrate deep into the pores of the carrier and improving the loading efficiency.

[0018] Preferably, the preparation method of the sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution is as follows: Prepare an aqueous solution of sodium alginate with a concentration of 1.5 wt% to 2.5 wt% and an aqueous solution of polyvinyl alcohol with a concentration of 3.0 wt% to 5.0 wt%; mix the aqueous solution of sodium alginate and the aqueous solution of polyvinyl alcohol at a volume ratio of 0.9:1 to 1.1:1, and add sodium bicarbonate to achieve a concentration of 0.10 mol / L to 0.20 mol / L to obtain the sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution.

[0019] By adopting the above technical solution, sodium alginate and polyvinyl alcohol form an interpenetrating network structure through hydrogen bonding, which improves the mechanical strength and water resistance of the coating layer and solves the problem of high brittleness and easy breakage of single calcium alginate gel. The added sodium bicarbonate, as a pore-forming agent precursor and pH adjuster, slightly modulates the microenvironment of the coating layer and helps to form a suitable microporous structure during the curing process, which is beneficial to the subsequent water permeation and mass transfer.

[0020] Preferably, the crosslinking liquid contains 2.0 wt% to 4.0 wt% calcium chloride and 0.8 wt% to 1.2 wt% boric acid; the curing time is 30 min to 60 min.

[0021] By adopting the above technical solution, calcium ions undergo ionic cross-linking with sodium alginate, and borate ions undergo chemical cross-linking with polyvinyl alcohol. The dual cross-linking mechanism endows the coating layer with excellent density and stability, effectively blocking the invasion of highly alkaline ions in the early stage of cement hydration and improving the survival rate of microorganisms.

[0022] Preferably, the preparation process of the mineralized bacterial suspension includes: culturing Bacillus coli at a temperature of 28°C to 32°C, and adding manganese sulfate monohydrate to induce sporulation, thereby obtaining the mineralized bacterial suspension; The preparation process of the facultative carbon-producing bacteria suspension includes: microaerophilic culture of Shewanella in a culture medium with sodium lactate and sodium nitrate added at a temperature of 28°C to 32°C to obtain the facultative carbon-producing bacteria suspension.

[0023] By adopting the above technical solutions, the addition of manganese ions significantly improved the spore formation rate of Bacillus coli. The spore morphology is more resistant to extreme environments (high temperature, high alkali, dryness) than the vegetative cells, making it a key form for achieving long-term repair. Cultivating Shewanella under microaerophilic conditions and inducing it to adapt to the nitrate respiration pathway ensures that it possesses the corresponding metabolic enzyme system before entering the anoxic environment inside concrete, shortening the lag time of the repair reaction.

[0024] Preferably, the raw materials of the concrete mixture, calculated by weight, include: The mixture comprises 400 to 440 parts cement, 630 to 670 parts river sand, 1000 to 1200 parts crushed stone, 160 to 190 parts water, and 3.0 to 4.0 parts water-reducing agent; when the composite facultative anaerobic microbial remediation agent is added, the amount of river sand of the same volume is deducted.

[0025] By adopting the above technical solution and adding the repair agent through the equal volume substitution method, the stability of the concrete aggregate gradation is maintained, and the negative impact of the repair agent on the compressive strength of the matrix is ​​minimized.

[0026] Preferably, the mixing time parameters are: dry mixing time of 60s to 120s and wet mixing time of 120s to 180s.

[0027] By adopting the above technical solutions, a reasonable mixing system ensures the uniform dispersion of the repair agent in the concrete matrix, avoids mechanical weaknesses caused by local agglomeration, and prevents excessive mixing from damaging the coating structure of the repair agent.

[0028] Preferably, the pH value of the pore fluid in the concrete specimen at a depth of 5 mm to 10 mm on the surface of the concrete after controlled carbonation curing is in the range of 10.0 to 11.0.

[0029] By adopting the above technical solution, controlling the pH value within the range of 10.0 to 11.0 is the result of process parameter optimization and the core control indicator of this invention. This pH range is both lower than the initial strong alkalinity of the cement matrix (pH>12.5), thus relieving the inhibition of microbial activity by strong alkali, and higher than the critical pH value for steel corrosion, thus balancing biological activity and structural durability, and providing a suitable microenvironment for the long-term maintenance of microbial mineralization function.

[0030] This invention provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete. It has the following beneficial effects: 1. This invention effectively overcomes the bottleneck of microbial inactivation caused by strong alkaline environment through the synergistic effect of controlled carbonization curing process and interpenetrating network hydrogel coating technology. By controlling carbon dioxide concentration and curing pressure, this slightly alkaline environment not only eliminates the chemical erosion of microbial spores by strong alkali, but also, in conjunction with the physical barrier effect of sodium alginate-polyvinyl alcohol carrier, constructs a suitable microenvironment for the survival of microorganisms, thereby ensuring the long-term effectiveness of the repair system throughout the entire life cycle of concrete.

[0031] 2. This invention constructs a dual-bacterial synergistic system of facultative carbon-producing bacteria (Shewanella) and mineralizing bacteria (Bacillus coli), achieving efficient self-repair of deep cracks. Utilizing the anaerobic metabolic mechanism of Shewanella using nitrate as an electron acceptor in hypoxic or micro-oxygen environments, it can generate endogenous carbonate ions in situ deep within the cracks, solving the mass transfer problem of traditional aerobic mineralization technology, which heavily relies on diffusion from the external air, resulting in poor repair effects of deep cracks. The carbon source generated in situ rapidly combines with the environmental calcium source, achieving rapid and dense filling of cracks from the inside out.

[0032] 3. This invention, while introducing microbial repair function, optimizes the microstructure and mechanical properties of the concrete matrix. Controlled carbonation curing not only pre-places micron-sized calcium carbonate crystal nuclei on the pore wall surface, reducing the nucleation energy barrier of the mineralization reaction, but also improves the density and early strength of the concrete surface layer through pore refinement. In addition, the regulated pH environment not only meets the growth requirements of microorganisms, but also maintains the alkalinity threshold required for the stability of the steel passivation film, avoiding the risk of steel corrosion caused by excessive carbonation and ensuring the long-term safety of the structure. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0035] Polyvinyl alcohol, CAS No. 9002-89-5, has a weight-average molecular weight (Mw) of 75,000 to 80,000 g / mol and a molecular weight distribution index (PDI) of 1.9 to 2.2.

[0036] Sodium alginate, CAS No. 9005-38-3, the sodium alginate used in this example has a weight-average molecular weight (Mw) of 220,000 to 250,000 g / mol.

[0037] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a composite facultative anaerobic microbial remediation agent, the preparation steps of which are as follows: First, the bacterial strains were cultured and enriched separately. *Bacillus coli* was inoculated into a modified liquid culture medium (containing 5 g peptone, 3 g yeast extract, and 20 g urea per liter, pH 9.0) and cultured with shaking at 30°C and 150 rpm for 30 h. Then, a 0.01 mol / L manganese sulfate monohydrate solution was added to induce sporulation. Culture continued until the sporulation rate reached over 90%. The precipitate was collected by centrifugation and resuspended in sterile physiological saline, adjusting the spore concentration to 1.0 × 10⁻⁶. 9 CFU / mL was used to obtain a mineralized bacterial suspension. Shewanella MR-1 was inoculated into LB liquid medium (with an additional 20 mmol sodium lactate and 10 mmol sodium nitrate per liter), and cultured statically at 30°C under microaerophilic conditions for 36 h. The precipitate was collected by centrifugation and resuspended in sterile physiological saline, adjusting the cell concentration to 1.0 × 10⁻⁶. 9 CFU / mL was used to obtain a suspension of facultative carbon-producing bacteria. The above mineralized bacterial suspension and the facultative carbon-producing bacterial suspension were mixed evenly at a volume ratio of 1:1. Calcium lactate pentahydrate (60 g / L), urea (30 g / L), yeast extract (5 g / L), and sodium nitrate (10 g / L) were added to the mixed bacterial solution and stirred until completely dissolved to obtain a compound nutrient bacterial solution.

[0038] Next, a sodium alginate-polyvinyl alcohol (PVA) interpenetrating network hydrogel coating solution was prepared. 2.0 g of sodium alginate powder was dissolved in 100 mL of deionized water to prepare a 2.0 wt% sodium alginate solution; 4.0 g of polyvinyl alcohol (PVA-1788) was dissolved in 100 mL of hot water at 90°C to prepare a 4.0 wt% polyvinyl alcohol solution. After the polyvinyl alcohol solution cooled to room temperature, the two solutions were mixed at a volume ratio of 1:1, stirred thoroughly, and sodium bicarbonate powder was added to achieve a concentration of 0.15 mol / L, thus preparing a pH-sensitive coating solution.

[0039] Finally, vacuum adsorption and encapsulation of the carrier were performed. Expanded perlite particles with a particle size of 1.0 mm to 1.5 mm were placed in a vacuum container, evacuated to -0.09 MPa and maintained for 20 min. The prepared composite nutrient bacterial solution was then aspirated under negative pressure. After restoring to normal pressure, the particles were immersed for another 2 h. The saturated perlite was filtered out and dried at 40 °C to constant weight. The dried carrier particles were immersed in the above coating solution for 30 s, and immediately after removal, they were placed in a composite crosslinking solution containing 3.0 wt% anhydrous calcium chloride and 1.0 wt% boric acid for 45 min for curing. The particles were filtered out and the surface was washed with deionized water. The particles were then dried in a forced-air drying process at 40 °C to obtain the composite facultative anaerobic microbial remediation agent A1.

[0040] Preparation Example 2: This preparation example provides a composite facultative anaerobic microbial remediation agent. The main difference from Preparation Example 1 is that the proportion of bacterial strains and the concentration of coating material are adjusted to support the lower limit range of component content in the claims. The specific preparation steps are as follows: The bacterial culture process was the same as in Preparation Example 1. When preparing the mixed bacterial solution, the mineralized bacterial suspension and the facultative carbon-producing bacterial suspension were mixed at a volume ratio of 1:2 (i.e., the proportion of facultative carbon-producing bacteria was increased), while the amount of nutrients added remained unchanged, thus obtaining a compound nutrient bacterial solution.

[0041] When preparing the coating solution, a 1.5 wt% sodium alginate solution and a 3.0 wt% polyvinyl alcohol solution were prepared and mixed at a volume ratio of 1:1. Sodium bicarbonate was then added to make the concentration 0.10 mol / L.

[0042] In the adsorption and encapsulation process of the carrier, the expanded perlite particle size was selected from 0.5 mm to 1.0 mm, and the vacuum adsorption process was the same as in Preparation Example 1. After drying, it was immersed in the above-mentioned low-concentration coating solution, and then cured for 30 min in a crosslinking solution containing 2.0 wt% anhydrous calcium chloride and 1.0 wt% boric acid. After cleaning and drying, the composite facultative anaerobic microbial remediation agent A2 was obtained.

[0043] Preparation Example 3: This preparation example provides a composite facultative anaerobic microbial remediation agent. The main difference from Preparation Example 1 is that the concentration of the coating material is adjusted to a higher range to support the upper limit range of the component content in the claims. The specific preparation steps are as follows: The bacterial culture process was the same as in Preparation Example 1. When preparing the mixed bacterial solution, the mineralized bacterial suspension and the facultative carbon-producing bacterial suspension were mixed at a volume ratio of 2:1 (i.e., the proportion of mineralized bacteria was increased), while the amount of nutrients added remained unchanged, thus obtaining a compound nutrient bacterial solution.

[0044] When preparing the coating solution, a 2.5 wt% sodium alginate solution and a 5.0 wt% polyvinyl alcohol solution were prepared and mixed at a volume ratio of 1:1. Sodium bicarbonate was added to make the concentration 0.20 mol / L.

[0045] In the adsorption and encapsulation process of the carrier, the expanded perlite particle size was selected from 1.5 mm to 2.0 mm, and the vacuum adsorption process was the same as in Preparation Example 1. After drying, it was immersed in the above-mentioned high-concentration coating solution, and then cured for 60 min in a crosslinking solution containing 4.0 wt% anhydrous calcium chloride and 1.0 wt% boric acid. After cleaning and drying, the composite facultative anaerobic microbial remediation agent A3 was obtained.

[0046] Examples 1-4: Example 1: This embodiment provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, specifically including the following steps: First, the concrete mixture was prepared. According to the mix design for C40 strength grade, 420 kg of ordinary Portland cement, 650 kg of river sand, 1100 kg of crushed stone, 175 kg of tap water (water-cement ratio 0.42), and 3.5 kg of polycarboxylate superplasticizer were weighed. The composite facultative anaerobic microbial remediation agent A1 obtained in Preparation Example 1 was weighed, with a dosage of 5.0% of the cement mass (i.e., 21 kg), and the equivalent volume of river sand was deducted accordingly. The cement, river sand, crushed stone, and microbial remediation agent A1 were added to a forced mixer and dry-mixed for 90 seconds to ensure uniform dispersion of all components. Then, the mixing water containing the superplasticizer was added, and wet-mixing continued for 150 seconds. The mixed concrete was poured into a 100mm × 100mm × 100mm cubic mold, vibrated on a vibrating table for 15 seconds, and the surface was smoothed. After standing at room temperature for 24 hours, the mold was removed.

[0047] Secondly, pre-curing treatment is carried out. The concrete specimens after demolding are placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of more than 95% for initial hydration curing for 2 days, so that the concrete matrix can form a preliminary strength skeleton and prevent the subsequent carbonation process from causing the structure to become loose.

[0048] Finally, controlled carbonation curing was performed. The pre-cured specimens were transferred into a programmed carbonation chamber, with the chamber temperature set at 22℃, relative humidity at 65%, carbon dioxide gas introduced and maintained at a concentration of 20% (volume percentage), and the chamber pressure adjusted to 0.12 MPa (slight positive pressure). Under these conditions, the specimens underwent continuous carbonation treatment for 12 hours, aiming to adjust the pH value of the pore fluid at a depth of 5 to 10 mm on the concrete surface to approximately 10.5 and to form a micron-sized calcium carbonate seed layer. After treatment, the specimens were removed and allowed to stand naturally for 24 hours, followed by standard curing until 28 days of age, yielding the facultative anaerobic microbial concrete product.

[0049] Example 2: This embodiment provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, aiming to verify the implementation effect under lower carbonation curing strength parameters. The method specifically includes the following steps: First, the concrete mixture was prepared. The basic mix proportion was the same as in Example 1. The composite facultative anaerobic microbial remediation agent A2 obtained in Preparation Example 2 was weighed out at a rate of 3.0% of the cement mass (i.e., 12.6 kg), and the amount of river sand was deducted accordingly. The mixing, pouring, vibration, and demolding processes were consistent with those in Example 1.

[0050] Next, pre-curing treatment is carried out. The demolded concrete specimens are placed in a standard curing room for initial hydration curing, which lasts for 1 day.

[0051] Finally, controlled carbonation curing was performed. The specimens were transferred into a carbonation chamber, with the chamber temperature set at 20℃, relative humidity at 55% (lower humidity is conducive to gas diffusion), carbon dioxide concentration maintained at 15% (volume percentage), and chamber pressure at 0.10 MPa. Treatment was carried out under these conditions for 6 hours. After treatment, the specimens were removed and allowed to stand naturally for 24 hours, followed by standard curing until 28 days of age, yielding the facultative anaerobic microbial concrete product.

[0052] Example 3: This embodiment provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, aiming to verify the implementation effect under higher carbonation curing strength parameters. The method specifically includes the following steps: First, the concrete mixture was prepared. The basic mix proportion was the same as in Example 1. The composite facultative anaerobic microbial remediation agent A3 obtained in Preparation Example 3 was weighed out at a rate of 8.0% of the cement mass (i.e., 33.6 kg), and the amount of river sand was deducted accordingly. The mixing, pouring, vibration, and demolding processes were consistent with those in Example 1.

[0053] Secondly, pre-curing treatment is carried out. The concrete specimens after demolding are placed in a standard curing room for initial hydration curing for 3 days to ensure that the concrete has a high resistance to carbonation before high-strength carbonation.

[0054] Finally, controlled carbonation curing was performed. The specimens were transferred into a carbonation chamber, with the internal temperature set at 25℃, relative humidity at 70%, carbon dioxide concentration maintained at 25% (volume percentage), and pressure at 0.15 MPa. The specimens were treated under these conditions for 24 hours. After treatment, the specimens were removed and allowed to stand naturally for 24 hours, followed by standard curing until 28 days of age, yielding the facultative anaerobic microbial concrete product.

[0055] Example 4: This embodiment provides a method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, aiming to verify the implementation effect under different repair agent dosages. The method specifically includes the following steps: First, the concrete mixture was prepared. The basic mix proportion was the same as in Example 1. The composite facultative anaerobic microbial remediation agent A1 obtained in Preparation Example 1 was weighed out at a rate of 6.0% of the cement mass (i.e., 25.2 kg), and the amount of river sand was deducted accordingly. The mixing, pouring, vibration, and demolding processes were consistent with those in Example 1.

[0056] The process parameters for pre-curing and controlled carbonization curing were exactly the same as in Example 1, i.e., pre-curing for 2 days, followed by carbonization curing for 12 hours at a carbon dioxide concentration of 20%, relative humidity of 65%, and pressure of 0.12 MPa. After the treatment, subsequent standard curing was carried out to obtain the facultative anaerobic microbial concrete product.

[0057] Comparative Examples 1-5: Comparative Example 1: Compared to Example 1, the differences are as follows: the composite facultative anaerobic microbial remediation agent A1 was not added to the concrete mix (the original replacement was made up by an equal volume of river sand), and the controlled carbonation curing step was not performed after demolding of the specimens; instead, they were directly placed in a standard curing room for full standard curing until 28 days of age. All other raw materials and preparation processes were the same. This comparative example aims to provide a blank control for ordinary concrete.

[0058] Comparative Example 2: Compared to Example 1, the difference lies in the omission of the controlled carbonization curing step. After demolding, the specimens were directly placed in a standard curing room for full standard curing up to 28 days of age. All other raw materials, repair agent dosages, and preparation processes remained the same. This comparative example aims to verify the necessity of the controlled carbonization curing process for constructing a suitable microenvironment for microbial survival and improving the repair effect.

[0059] Comparative Example 3: Compared to Example 1, the difference lies in the preparation process of the microbial remediation agent (referring to Preparation Example 1). Only a suspension of *Bacillus coli* (mineralizing bacteria) was inoculated, excluding *Shewanella* (facultative carbon-producing bacteria). The missing volume was made up with sterile saline to obtain a single-species remediation agent. The remaining preparation steps of the remediation agent, as well as the concrete preparation and carbonization curing processes, were the same. This comparative example aims to verify the crucial role of facultative carbon-producing bacteria in the composite facultative anaerobic bacterial system in synergistic mineralization and carbon source provision under anoxic conditions.

[0060] Comparative Example 4: Compared to Example 1, the difference lies in that: instead of using a carrier-adsorbed hydrogel-encapsulated repair agent, an equal amount of the composite nutrient bacterial solution prepared in Example 1 was directly added to the concrete mixing water, along with an equal amount of unadsorbed bacterial solution and uncoated dry expanded perlite particles to maintain consistent aggregate gradation. The remaining concrete preparation and carbonation curing processes remained the same. This comparative example aims to verify the importance of carrier encapsulation technology in protecting microorganisms against stirring shear forces and early high-alkalinity environments.

[0061] Comparative Example 5: Compared to Example 1, the difference lies in the process parameters of the controlled carbonation curing step: the carbon dioxide concentration is adjusted to 50% (volume percentage), the relative humidity to 70%, and the treatment time is extended to 72 hours to simulate a high-concentration, long-term deep carbonation process. All other raw materials and preparation processes remain the same. This comparative example aims to verify the importance of controlling the degree of carbonation in balancing the alkaline protection of concrete and the microbial survival environment, thus demonstrating the necessity of moderate control.

[0062] Test Example 1-2: Test Example 1: Construction of Microenvironment Inside Concrete and Verification of Microbial Survival Rate This test case aims to verify the effect of controlled carbonation curing process on the pH value of pore fluid inside concrete, and the impact of the synergistic effect of this microenvironment and carrier encapsulation technology on the long-term survival rate of composite facultative anaerobic microorganisms.

[0063] Experimental procedure: Determination of pH gradient distribution in pore fluid: Concrete specimens from Examples 1-3 and Comparative Examples 2 and 5, with a curing period of 28 days, were selected. A layered drilling method was used to collect concrete powder at three depths: 0-10 mm (surface layer), 10-20 mm (subsurface layer), and over 20 mm (core). The powder from each depth was passed through a 0.08 mm square-hole sieve. 5.00 g of sample was weighed and placed in a beaker, along with 50.00 mL of deionized water. The mixture was magnetically stirred for 30 min, allowed to stand, filtered, and the pH of the filtrate was measured using a precision pH meter (accuracy ±0.01). Three parallel samples were taken from each group of specimens, and the average value was used.

[0064] Monitoring of long-term microbial survival: Concrete specimens from Examples 1 and 4, and Comparative Examples 2 and 4 were selected and destructively sampled at curing ages of 28 days and 180 days, respectively.

[0065] The specimen was crushed, and the concrete fragments containing the carrier particles were collected, ground into powder, and passed through a 0.15mm sieve.

[0066] Weigh 1.00 g of powder sample, add 9.00 mL of sterile physiological saline, and vortex for 10 min to fully elute and release microorganisms.

[0067] The suspension was serially diluted (10) 110 1 to 10 610 6) Take an appropriate amount of the diluted solution and spread it on a modified solid plate culture medium containing urea and calcium source.

[0068] The plates were incubated in a 30℃ constant temperature incubator for 48 hours. The total number of colonies (CFU) was counted and converted into the number of viable bacteria per gram of concrete (CFU / g).

[0069] Experimental data: Table 1: Distribution of pore fluid pH values ​​at different depths in concrete under different curing processes Table 2: Monitoring data on the survival rate of microorganisms inside concrete (unit: CFU / g) Note: Survival retention rate = (Survival amount after 180 days / Survival amount after 28 days) × 100%. The initial theoretical incorporation amount is approximately 1.0 × 10⁻⁶. 9 CFU / g.

[0070] Conclusions and Mechanism Analysis: Based on the test results in Tables 1 and 2, and combined with the innovative mechanism of this invention, the following conclusions are drawn: Controlled carbonization curing has a gradient effect on the regulation of microenvironment pH.

[0071] Table 1 shows that the controlled carbonation process in Example 1 successfully adjusted the pH value of the concrete surface layer (0-10 mm) to approximately 10.42. This value range is lower than the corrosion threshold of strongly alkaline (pH>12.5) on microbial cell walls, but higher than the critical value for inducing steel corrosion (pH<9.0). In contrast, the pH of the entire cross-section of Comparative Example 2 (no carbonation) was close to 13.0, an extremely harsh environment; while the pH of the surface layer of Comparative Example 5 (over-carbonation) dropped to 8.12, which, although conducive to microbial survival, severely impaired the concrete's passivation protection ability for steel reinforcement. The data from Example 1 demonstrate that the carbonation parameters can achieve a moderate neutralization, creating a specific microenvironment that balances biological activity and structural durability.

[0072] The synergistic effect of the microenvironment and carrier ensured the long-term activity of the microorganisms. Table 2 shows that Example 1 maintained a concentration of 1.86 × 10⁻⁶ microorganisms at 180 days of age. 6 The high CFU / g of active bacteria is a stark contrast. In Comparative Example 2, due to the lack of carbonation curing and the high-alkaline environment, the survival rate of microorganisms decreased by three orders of magnitude after 28 days, and they were completely inactive by 180 days. Comparative Example 4, lacking carrier protection, saw almost all microorganisms die under the high shear, high heat, and high-alkaline shocks during mixing and the early stages of hydration. This demonstrates that the present invention effectively solves the bottleneck problem of long-term microbial survival within concrete in existing technologies through a dual protection mechanism of physical shielding by the carrier and chemical regulation of carbonation.

[0073] The facultative anaerobic properties adapt to the anoxic environment inside concrete. In Example 1, in the deep regions of the core (pH>12.63) and subsurface (pH>11.85), despite the high alkalinity, the dense shell structure formed by the carbonized layer prevents external oxygen from entering, creating a stable anaerobic / microaerobic environment. Shewanella (facultative anaerobic bacteria) in the compound microbial agent enters a low-metabolic dormant state or maintains minimal survival using endogenous electron acceptors under this environment, avoiding the death of single aerobic bacteria under anoxic conditions, thus ensuring the on-demand repair potential of microorganisms in long-term concrete.

[0074] Test Example 2: Evaluation of Crack Self-Healing Performance and Continuous Repair Capability This test case aims to quantitatively evaluate the impermeability recovery performance of concrete specimens prepared in the examples and comparative examples after cracking, especially the continuous repair capability under repeated cracking conditions, so as to verify the technical advantages of dual mineralization mechanism and endogenous carbonate supply in terms of repair efficiency and durability.

[0075] Experimental steps: Crack prefabrication: Concrete specimens (100mm×100mm×100mm) cured to 28 days were selected. Splitting tensile loading was applied to the specimens using an electro-hydraulic servo universal testing machine at a rate controlled at 0.2mm / min. The load was immediately unloaded when cracks appeared on the specimen surface, and specimens with surface crack widths between 0.35mm and 0.45mm were selected for subsequent testing using a crack width measuring instrument (accuracy 0.01mm). Specimens failing to meet or exceeding this range were discarded.

[0076] Repair and maintenance system: Pre-fabricated cracked specimens were placed in a simulated wet-dry cycle environment for repair and curing. Each cycle lasted 24 hours, including immersion in 20°C water for 16 hours, followed by drying in room temperature air for 8 hours. This system was designed to simulate the actual service environment and provide the moisture medium required for microbial mineralization.

[0077] Permeability recovery rate determination (single repair): The constant head permeation method was used to determine the changes in seepage during the remediation process.

[0078] At three time points—0 days after crack prefabrication, 7 days after repair and curing, and 28 days after repair—the specimens were fixed in the infiltration device.

[0079] Maintain a water head height of 50 mm and record the amount of water that seeps through the crack (in milliliters) within 10 minutes.

[0080] Crack impermeability recovery rate ( Calculate according to the formula: ,in This represents the initial seepage volume. For repair The amount of water seepage from the Queen.

[0081] Continuous repair capacity test (multiple cycles): The specimens from Example 1, Comparative Example 2, and Comparative Example 3 were selected for cyclic crack repair tests.

[0082] Round 1: Complete the 28-day repair process according to steps 1.1 to 1.3 above, and record the recovery rate.

[0083] Second round: The repaired specimen was reloaded, forcing the original crack to reopen to about 0.40 mm. The dry and wet cycle curing was repeated for 28 days, and the recovery rate was recorded.

[0084] Third round: Repeat the above steps to perform a third round of destruction and repair, and record the recovery rate.

[0085] Experimental data: Table 3: Evolution of impermeability recovery rate during a single crack repair process (%) Table 4: Test on the decay of impermeability recovery rate under cyclic cracking repair conditions (repair age is 28 days, unit: %).

[0086] Conclusions and Mechanism Analysis: Based on the experimental data in Tables 3 and 4, the performance advantages and mechanism of action of the technical solution of the present invention are analyzed as follows: The dual mineralization mechanism significantly improves the early repair rate and final closure.

[0087] Table 3 shows that Example 1 achieved a permeability recovery rate of 68.4% within 7 days, significantly higher than the 38.7% of Comparative Example 3 (single mineralizing bacteria). This confirms that the introduction of Shewanella in the compound microbial agent played a crucial role. In the early stages of crack formation, Shewanella rapidly produced carbon dioxide and bicarbonate through facultative anaerobic metabolism, providing a sufficient carbon source for the alkaline environment produced by Bacillus coli decomposing urea. (Precursor). This in-situ carbon supply mode overcomes the limitation of traditional single-strain systems that rely on the slow diffusion rate of external carbon dioxide, thereby accelerating the precipitation kinetics of calcium carbonate and achieving rapid plugging.

[0088] Controlled carbonization curing is a prerequisite for ensuring the activation of repair functions.

[0089] Comparing the repair rates of Example 1 (97.2%) and Comparative Example 2 (21.4%), it is evident that the specimens lacking carbonization curing almost completely lost their self-healing ability. Combined with the conclusions of Example 1, this is due to the massive death of microorganisms in Comparative Example 2 under a highly alkaline environment. Furthermore, the data from Comparative Example 4 (without a carrier) (19.8%) further confirms that without carrier protection, directly incorporated microorganisms cannot withstand the physicochemical damage during stirring and hardening processes, leading to technical failure.

[0090] Endogenous metabolic cycles enable excellent and continuous repair capabilities.

[0091] In the cyclic tests shown in Table 4, Example 1 maintained a high recovery rate of 81.3% after three cycles of cracking, demonstrating excellent toughness and durability. In contrast, Comparative Example 3 (single bacteria) showed a sharp drop in recovery rate to 24.7% in the second cycle.

[0092] The mechanism is as follows: the facultative carbon-producing bacteria (Shewanella) in Example 1 can utilize the pre-existing nitrates and organic matter inside the concrete for long-term anaerobic metabolism, continuously replenishing carbonate ions; simultaneously, the metastable calcium carbonate layer pre-formed on the pore walls by controlled carbonation curing can act as seed crystals and a source of calcium supplementation when cracks reopen. In contrast, Comparative Example 3 relies solely on limited urea decomposition; once the nutrients within the capsule are depleted and there is a lack of active carbon production capacity, its repair function is exhausted, making it unable to cope with the recurring cracking problems commonly encountered in engineering.

Claims

1. A method for carbonation curing and rapid repair of facultative anaerobic microbial concrete, characterized in that, Includes the following steps: Cement, aggregates, mixing water, admixtures, and composite facultative anaerobic microbial remediation agent are mixed and stirred evenly, then poured into molds and demolded; wherein the dosage of the composite facultative anaerobic microbial remediation agent is 3.0% to 8.0% of the cement mass; After demolding, the concrete specimens were placed in an environment with a relative humidity of 95% to 99% for initial hydration curing, which lasted for 1 to 3 days. The pre-cured concrete specimens were placed in a closed carbonation environment for treatment, with the ambient temperature controlled at 20°C to 25°C, relative humidity at 55% to 70%, carbon dioxide volume concentration at 15% to 25%, ambient pressure at 0.10 MPa to 0.15 MPa, and treatment time at 6 hours to 24 hours. After carbonation, the concrete specimens were placed in a natural environment and left to stand for a period of time, followed by standard curing.

2. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 1, characterized in that, The composite facultative anaerobic microbial remediation agent is prepared by the following steps: Facultative carbon-producing bacteria and mineralizing bacteria were cultured separately to obtain suspensions of facultative carbon-producing bacteria and mineralizing bacteria. The mineralized bacterial suspension and the facultative carbon-producing bacterial suspension were mixed at a volume ratio of 1:2 to 2:1, and nutrients were added to prepare a compound nutrient bacterial solution. The porous carrier was placed under a negative pressure of -0.08 MPa to -0.10 MPa to adsorb the composite nutrient bacterial solution, and then dried to obtain the loaded particles. A sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution was prepared. The loaded particles were immersed in the sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution, and then cured, cleaned and dried in a crosslinking solution to obtain the composite facultative anaerobic microbial remediation agent.

3. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 2, characterized in that, The concentration ranges of the nutrients in the compound nutrient solution are as follows: calcium lactate 55g / L to 65g / L, urea 25g / L to 35g / L, yeast extract 4g / L to 6g / L, and sodium nitrate 8g / L to 12g / L.

4. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 2, characterized in that, The porous carrier is expanded perlite, and the particle size of the expanded perlite ranges from 0.5 mm to 2.0 mm. The adsorption process includes: maintaining the negative pressure for 15 min to 25 min, and then continuing to impregnate for 1.5 h to 2.5 h after restoring normal pressure.

5. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 2, characterized in that, The preparation method of the sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution is as follows: Prepare an aqueous solution of sodium alginate with a concentration of 1.5 wt% to 2.5 wt% and an aqueous solution of polyvinyl alcohol with a concentration of 3.0 wt% to 5.0 wt%; mix the aqueous solution of sodium alginate and the aqueous solution of polyvinyl alcohol at a volume ratio of 0.9:1 to 1.1:1, and add sodium bicarbonate to achieve a concentration of 0.10 mol / L to 0.20 mol / L to obtain the sodium alginate-polyvinyl alcohol interpenetrating network hydrogel coating solution.

6. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 2, characterized in that, The crosslinking solution contains 2.0 wt% to 4.0 wt% calcium chloride and 0.8 wt% to 1.2 wt% boric acid; the curing time is 30 min to 60 min.

7. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 2, characterized in that, The preparation process of the mineralized bacterial suspension includes: Bacillus coli was cultured at a temperature of 28°C to 32°C, and manganese sulfate monohydrate was added to induce sporulation, resulting in the mineralized bacterial suspension. The preparation process of the facultative carbon-producing bacteria suspension includes: microaerophilic culture of Shewanella in a culture medium with sodium lactate and sodium nitrate added at a temperature of 28°C to 32°C to obtain the facultative carbon-producing bacteria suspension.

8. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 1, characterized in that, The raw materials of the concrete mixture, calculated by weight, include: The mixture comprises 400 to 440 parts cement, 630 to 670 parts river sand, 1000 to 1200 parts crushed stone, 160 to 190 parts water, and 3.0 to 4.0 parts water-reducing agent; when the composite facultative anaerobic microbial remediation agent is added, the amount of river sand of the same volume is deducted.

9. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 1, characterized in that, The mixing time parameters are as follows: dry mixing time is 60s to 120s, and wet mixing time is 120s to 180s.

10. The method for carbonation curing and rapid repair of facultative anaerobic microbial concrete according to claim 1, characterized in that, The pH value of the pore fluid in the concrete specimens after controlled carbonation curing at a depth of 5 mm to 10 mm on the surface of the concrete was in the range of 10.0 to 11.0.

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