Microorganism-nano synergistically reinforced cement-based composite material for self-repairing of concrete cracks

Abstract

The invention discloses a microorganism-nano synergistically reinforced cement-based composite material for self-repairing concrete cracks, which realizes the self-repairing and performance improvement of the cracks through the synergistic effect of bacillus pseudofirmus, carbon nanotubes, nano magnesium oxide and red mud. The material has the following characteristics: bacillus pseudofirmus is used as a microbial remediation agent, and dormant spores are activated when meeting water and oxygen and then are subjected to a series of biochemical reactions to induce calcium carbonate precipitation products so as to effectively fill microcracks; the carbon nano tube network structure not only enhances the mechanical property of the concrete, but also can provide a channel for directional deposition of a repairing substance; the nano magnesium oxide compensates shrinkage stress through hydration reaction, and meanwhile, a proper alkaline environment is maintained to guarantee microbial activity; the industrial waste red mud is used for replacing part of cement, so that carbon emission is reduced, and microorganisms are fixed by utilizing the porous characteristic of the red mud.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new multifunctional materials, and mainly relates to a microbial-nano synergistically enhanced cement-based material for concrete crack self-repair. BACKGROUND

[0002] With the acceleration of urbanization and the continuous advancement of infrastructure construction, concrete structures have become one of the most widely used building materials in the world due to their high compressive strength, easy molding, and excellent durability. However, traditional concrete structures face severe challenges in terms of durability due to long-term exposure to various harsh environments, such as freeze-thaw cycles, corrosive media, and dry-wet cycles. This leads to the frequent occurrence of problems such as microcracks, groundwater leakage, salt and alkali erosion, and frost heaving damage, which seriously threaten the structural safety and service life of buildings.

[0003] In recent years, there has been a strong emphasis on the development of cement concrete crack self-repair technology in China, which involves adding functional adhesive components during the preparation of cement concrete. When the structure is damaged by external forces and cracks, the self-repair mechanism can be automatically activated. By filling cracks and improving the microstructure, the compactness and impermeability of concrete are significantly improved, thereby effectively enhancing its durability. Research shows that the development of cement-based materials with self-repairing function provides a new technical approach for improving the durability of concrete. This type of material has a broad market prospect in engineering applications due to its long-lasting waterproof effect and good self-healing performance.

[0004] Abroad, the self-repairing technology of cement-based composite materials has become a research hotspot in the field of civil engineering materials. The core mechanism lies in the pre-addition of specific adhesives to enable the material to activate the self-repairing function after damage. This repair process not only restores the macroscopic properties of the material, but also improves its microstructure characteristics, including reduced porosity and interface strengthening, thereby comprehensively enhancing the durability of the material.

[0005] Traditional concrete crack repair methods, such as surface repair, grouting, and filling, can repair cracks to some extent, but these methods are essentially passive repair, time-consuming and labor-intensive, and have certain limitations. For example, surface repair can only handle surface cracks and cannot reach deep cracks; grouting can fill deep cracks, but requires high technical skills and is costly. Therefore, the development of a self-healing concrete material that can actively and efficiently repair cracks is of great significance for improving the durability of concrete structures, reducing maintenance costs, and ensuring life and property safety.

[0006] The present invention discloses a microbial-nano synergistically reinforced cement-based composite material for self-repair of concrete cracks, which is composed of Bacillus pseudofirmus, red mud, nano-magnesium oxide, carbon nanotubes and other parts. Among them, nano-magnesium oxide can effectively compensate for concrete shrinkage and reduce cracks. It is still active in low-temperature environments when it is hydrated to form Mg(OH)2 to fill cracks. Bacillus pseudofirmus is used as a microbial repair agent. After the dormant spores are activated by water and oxygen, a series of biochemical reactions induce calcium carbonate precipitation products that can effectively fill microcracks. Red mud is a waste material from the aluminum industry. Its high alkalinity and gelling properties can help improve the durability of concrete. Summary of the Invention

[0007] The present invention aims to reduce the problems commonly faced by existing cement-based materials such as crack expansion and leakage. The present invention designs and discloses a microbial-nano synergistically reinforced cement-based composite material for self-repair of concrete cracks.

[0008] According to some embodiments of the present invention, a microbial-nano synergistically reinforced cement-based composite material for self-repair of concrete cracks, Bacillus pseudofirmus needs to undergo specific culture and activation treatment to ensure its survival rate in concrete. The bacteria are inoculated in a liquid culture medium containing 0.5-1.0 wt% calcium lactate, 0.1-0.3 wt% yeast extract and 0.2-0.5 wt% urea, and cultured at 30-37°C and pH 9.3 for 48 hours to reach the logarithmic growth phase, and the bacterial solution concentration is ≥10 8 cfu / ml. The cells were then collected by high-speed centrifuge at 6000 rpm for 10 min, washed twice with phosphate buffer to remove metabolic waste, and finally resuspended in a protective solution containing 5-10 wt% glycerol to form a concentration of ≥10 9 The spore suspension of cfu / ml is stored at 4°C for future use. This method can significantly improve the tolerance of bacteria in high alkaline environments.

[0009] According to some embodiments of the present invention, a microbial-nano synergistically reinforced cement-based composite material for self-repairing concrete cracks comprises red mud dried and heated at 105°C for 24 hours, then ball-milled to a particle size of less than 50 μm. The washed red mud is then soaked in a 0.1-0.5 mol / L hydrochloric acid solution for 2-4 hours to remove excess soluble alkaline substances. The washed red mud is then mixed with a bacterial suspension in a suitable mass ratio and stirred at 50-100 rpm at 25°C for 12 hours. This allows the bacteria to be firmly adsorbed into the pores of the red mud through electrostatic interaction, thereby enhancing the red mud's ability to protect microorganisms.

[0010] According to some embodiments of the present application, a microbial-nano synergistically enhanced cement-based composite material for concrete crack self-repairing, the present application adopts an ultrasonic dispersion process to treat a carbon nanotube and nano-magnesium oxide mixed system, and the specific implementation process is as follows: multi-walled carbon nanotubes and nano-magnesium oxide are mixed according to a mass ratio, wherein the multi-walled carbon nanotubes have a length of 10-50 μm and a diameter of 8-15 nm, and the nano-magnesium oxide has a particle size of 50-100 μm. The mixture is added to an aqueous solution containing 0.3% by mass of polyethylene glycol and 0.2% by mass of sodium dodecyl sulfate, to prepare a suspension with a solid content of 5%-8%. A probe-type ultrasonic processor with a frequency of 2 kHz and a power of 1 kW is used. The material is subjected to intermittent ultrasonic treatment, and the specific parameters are 3 seconds of work and 2 seconds of intermittent, and the total treatment time is 30 to 45 minutes. During the ultrasonic treatment, the temperature is strictly controlled to be no more than 35 degrees Celsius through a circulating water cooling system, and a magnetic stirring auxiliary dispersion with a rotation speed of 300 revolutions per minute is used at the same time.

[0011] According to some embodiments of the present application, a microbial-nano synergistically enhanced cement-based composite material for concrete crack self-repairing, the present application adopts an optimized three-component composite blending process to accurately incorporate functional materials into the concrete system. The specific operation is as follows: the bacteria-loaded Bacillus firmus is replaced and incorporated at 15% to 30% of the cement mass, and the carbon nanotube and nano-magnesium oxide composite suspension is replaced by 10% to 20% of the mixing water. A step-by-step stirring process is adopted: first, the cement, aggregate and bacteria-loaded red mud are dry mixed for 60 seconds to ensure uniform distribution; then, the dispersion liquid containing carbon nanotubes and nano-magnesium oxide is slowly added, and stirring is continued for 120 seconds. The temperature is controlled to be below 30 degrees Celsius during the whole stirring process to maintain the activity of the bacteria.

[0012] According to some embodiments of the present application, a microbial-nano synergistically enhanced cement-based composite material for concrete crack self-repairing, after the uniformly stirred composite cement-based mixture is injected into a 150×150×150 mm standard piece with a compressive strength, it is immediately placed on a laboratory dedicated vibration table, and a 50 Hz fixed frequency is used for 120 seconds of continuous vibration compaction, the vibration acceleration is controlled within the range of 0.5±0.05g, to ensure that the material is fully vented and reaches the maximum density. The surface of the formed test piece is immediately sealed with a 0.1 mm thick polyethylene film, and is transferred to an intelligent control standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for initial curing. The environmental parameters are monitored in real time through a temperature and humidity sensor, and the test piece is demolded after maintaining a constant temperature and humidity for 24 hours. The demolded test piece continues to be cured under the same temperature and humidity conditions, and the standard curing is continued until the 28-day age.

[0013] According to some embodiments of the present application, a microbial-nano synergistically enhanced cement-based composite material for concrete crack self-repairing, compared with the prior art, the present application has the following characteristics: (1) A kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing, due to the network structure of carbon nanotubes enhances the mechanical properties of concrete, thereby higher than ordinary cement-based materials.

[0014] (2) The present study proposes a kind of cement-based composite material based on microbial-nano synergistic enhancement, by coupling the chemical self-healing mechanism of nano magnesium oxide and the biological mineralization of Bacillus pseudomycoides, a double self-repairing system is constructed, which significantly improves the durability and long-term stability of concrete structure. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a schematic diagram of a kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing in the embodiment of the present application.

[0016] In the figure, part number: 1-a kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing concrete schematic sample block, 1-1 red mud, 1-2 Bacillus pseudomycoides, 1-3 nano magnesium oxide, 1-4 carbon nanotubes, 1-5 ordinary Portland cement.

[0017] Figure 2 is a schematic diagram of Bacillus pseudomycoides in the electron microscope of a kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing in the embodiment of the present application.

[0018] Figure 3 is a schematic diagram of nano magnesium oxide in the electron microscope of a kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing in the embodiment of the present application.

[0019] Figure 4 is a schematic diagram of carbon nanotubes in the electron microscope of a kind of microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing in the embodiment of the present application. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be described in detail below, examples of which are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0021] The present application will be further described in detail below in conjunction with the drawings: In combination withFigure 1 The application discloses a microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repairing, which is characterized by the following component ratio of the material after optimization and adjustment: cement 70-85 parts, red mud 15-30 parts, Bacillus firmus with an adding amount of 1 part, carbon nanotubes with a mixing amount of 0.5-2 parts, and nano magnesium oxide with a use amount of 5-10 parts. The water-cement ratio is controlled in the range of 0.35-0.40. The concrete strength is above C40, so as to ensure the self-repairing performance and durability of the material.

[0022] Figure 2 The application discloses a microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repairing, which is characterized by the following component ratio of the material after optimization and adjustment: cement 70-85 parts, red mud 15-30 parts, Bacillus firmus with an adding amount of 1 part, carbon nanotubes with a mixing amount of 0.5-2 parts, and nano magnesium oxide with a use amount of 5-10 parts. The water-cement ratio is controlled in the range of 0.35-0.40. The concrete strength is above C40, so as to ensure the self-repairing performance and durability of the material.

[0023] Figure 3 The application discloses a microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repairing, which is characterized by the following component ratio of the material after optimization and adjustment: cement 70-85 parts, red mud 15-30 parts, Bacillus firmus with an adding amount of 1 part, carbon nanotubes with a mixing amount of 0.5-2 parts, and nano magnesium oxide with a use amount of 5-10 parts. The water-cement ratio is controlled in the range of 0.35-0.40. The concrete strength is above C40, so as to ensure the self-repairing performance and durability of the material.

[0024] Figure 4Figure 1 is a schematic diagram of carbon nanotubes under an electron microscope in a microbial-nano synergistic enhanced cement-based composite material for concrete crack self-repairing according to an embodiment of the present application. The carbon nanotubes are observed under an electron microscope to be uniformly distributed in a three-dimensional network structure in the cement matrix, forming a continuous spatial network framework. These carbon nanotubes are closely combined with cement hydration products and interweave to form a stable reinforcing system. In the crack area, the carbon nanotubes exhibit good bridging effect and can effectively span the two sides of the crack to limit the further expansion of the crack. At the same time, the special structure of the surface of the carbon nanotubes provides ideal attachment sites for the microorganisms, which is conducive to the deposition and crystallization of the repair material. This unique spatial distribution feature enables the carbon nanotubes to not only play a reinforcing role but also cooperate with the microorganisms to complete the crack self-repairing process, and the carbon nanotubes are closely combined with the cement matrix without obvious defects or voids. Embodiment

[0025] The concrete is prepared by using cement 80 kg, red mud 20 kg, Bacillus pseudofirmus 0.5 kg, carbon nanotubes 0.8 kg, and nano-magnesium oxide 5 kg, with a water-binder ratio of 0.35. The 28-day compressive strength reaches 50.2 MPa, which is increased by 25.5% compared with ordinary C40 concrete. The cracks below 0.3 mm in width are completely healed after 14 days, and the cracks below 0.5 mm in width are completely healed after 28 days. In this example, the use strategy of nano-materials focuses on the economic demand of engineering application. Embodiment

[0026] The concrete is prepared by using cement 75 kg, red mud 25 kg, Bacillus pseudofirmus 1.0 kg, carbon nanotubes 1.2 kg, and nano-magnesium oxide 8 kg, with a water-binder ratio of 0.36. The 28-day compressive strength reaches 52.6 MPa, which is increased by 31.5% compared with ordinary C40 concrete. The cracks below 0.3 mm in width are completely healed after 14 days, and the cracks below 0.5 mm in width are completely healed after 28 days. In this example, the carbon nanotubes form a three-dimensional network structure to enhance the crack bridging ability, and the hydration products of nano-magnesium oxide fill the pores to optimize the microstructure and cooperate with the active components of red mud and cement hydration to improve the matrix density, focusing on the high strength of cement-based materials. Embodiment

[0027] The concrete is prepared by using cement 70 kg, red mud 30 kg, Bacillus pseudofirmus 1.5 kg, carbon nanotubes 1.5 kg, and nano-magnesium oxide 10 kg, with a water-binder ratio of 0.38. The 28-day compressive strength reaches 48.8 MPa, which is increased by 22% compared with ordinary C40 concrete. The 0.3 mm wide cracks are completely self-repaired within 14 days, and the cracks below 0.5 mm in width are completely healed after 28 days. In this example, a high content of red mud is used, focusing on the utilization rate of industrial solid waste.

Claims

1. A microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair, characterized by: A concrete sample (1) of a microbial-nano synergistically reinforced cement-based composite material for self-repair of concrete cracks is prepared by mixing Bacillus pseudofirmus (1-1), carbon nanotubes (1-2), nanomagnesium oxide (1-3), and red mud (1-4) in a certain proportion and then casting them together. Among them, the dormant spores of Bacillus pseudofirmus (1-1) are activated by water and oxygen, and then undergo a series of biochemical reactions to induce calcium carbonate precipitation products that can effectively fill microcracks; the carbon nanotubes (1-2) form a network structure to enhance the mechanical properties of concrete and provide channels for the directional deposition of repair materials; the nanomagnesium oxide (1-3) compensates for shrinkage stress through hydration reactions while maintaining a suitable alkaline environment to ensure microbial activity; and the red mud (1-4), as an industrial waste material, replaces part of the cement, which not only reduces carbon emissions but also uses its porous properties to fix microorganisms.

2. The microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair according to claim 1, characterized in that: Bacillus pseudofirmus (1-1) is a natural strain, the urease activity of which is more than 50% higher than that of the wild type, the optimal pH is 9-10, and the survival rate in concrete is ≥80%.

3. The microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair according to claim 1, characterized in that: The carbon nanotubes (1-2) are multi-walled carbon nanotubes with a length of 10-50 μm and a diameter of 8-15 nm. They are added in the form of a pre-dispersed slurry to form a penetrating network structure in the concrete.

4. The microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair according to claim 1, characterized in that: Nano magnesium oxide (1-3) has a particle size of 10-50 μm and has the function of compensating for concrete shrinkage and reducing cracks.

5. The microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair according to claim 1, characterized in that: After optimization and adjustment, the proportions of the various raw materials in the material are calculated by weight as follows: 70-85 parts cement, 15-30 parts red mud, 1 part Bacillus pseudofirmus, 0.5-2 parts carbon nanotubes, and 5-10 parts nanomagnesium oxide. The water-cement ratio is controlled within the range of 0.35-0.

40. The concrete strength is above C40 to ensure the material's self-healing properties and durability.

6. The microbial-nano synergistically reinforced cement-based composite material for concrete crack self-repair according to any one of claims 1 to 5, characterized in that: When cracks with a width of ≤0.3 mm are generated in the material, environmental moisture is used to activate microbial metabolic mineral precipitation. At the healing age of 28 days, a compressive strength recovery rate of ≥90% is achieved, and impermeability is restored to more than 95% before cracking, and the crack width is completely healed.

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