Self-repairing concrete based on modified carbon fibers and preparation method thereof

Abstract

The invention discloses self-repairing concrete based on modified carbon fibers and a preparation method thereof, and belongs to the technical field of building materials. An existing concrete crack repairing technology has two major problems that bonding between carbon fibers and a matrix is poor, and the repairing effect is limited; microbial self-repairing and nutrient adding can reduce the strength of the concrete. According to the solution provided by the invention, firstly, the surface of the carbon fiber is modified by an MICP method to form a stable three-dimensional calcium carbonate coating layer, so that the surface roughness is enhanced, the interface bonding capacity of the carbon fiber and a gelling matrix is greatly improved, and the carbon fiber is stably attached to an interface; then, the modified carbon fibers and concrete raw materials are accurately mixed according to a specific proportion, and the high-strength and good-crack-resistance self-repairing concrete is prepared. When cracks are generated, the carbon fibers limit crack propagation with high strength and high ductility, and surface microorganisms generate calcium carbonate through physiological reaction to fill the cracks; the strength, crack resistance and self-repairing capacity of a concrete structure are improved, the service life is prolonged, and the concrete is suitable for a hydraulic concrete structure in a complex environment and wide in application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a self-repairing concrete based on modified carbon fibers and a preparation method thereof. BACKGROUND

[0002] Concrete, as an important engineering composite material, has been widely used in water conservancy, building and transportation engineering due to its good durability, high compressive strength and abundant raw materials. However, concrete structures are prone to cracks during long-term service due to external environmental factors such as temperature changes, humidity changes, chemical corrosion and load effects. These cracks not only reduce the durability and safety of concrete, but also may lead to water erosion, corrosion and other phenomena, further exacerbating the damage to the structure.

[0003] For the repair of concrete cracks, domestic and foreign scholars have conducted a large number of researches and proposed various repair technologies. Among them, the method of using Microbially Induced Calcite Precipitation (MICP) technology to repair concrete cracks has attracted much attention due to its green environmental protection, good compatibility with concrete materials and long-term repair ability. MICP technology generates calcium carbonate precipitate at the crack site through the mineralization deposition reaction of microorganisms, thereby achieving self-healing of the crack.

[0004] Although MICP technology has shown great potential in repairing concrete cracks, there are still some challenges in its application. First, adding microorganisms and their nutrients directly into concrete often reduces the strength of concrete, because these additional components may interfere with the hydration process of concrete and affect its mechanical properties. Second, the adhesion sites of microorganisms on the fracture surface are few, which leads to poor repair effect of microorganisms at the crack, especially under complex stress conditions and harsh service environments, the repair effect is more limited.

[0005] In order to improve the above problems, the existing technology proposes a method of adding fibers into concrete. Fibers, due to their high strength and high ductility, not only can improve the strength of concrete, but also can enhance its crack resistance. However, the problem of poor adhesion between fibers and cementitious matrix still exists, which is mainly due to the smoothness of the fiber surface, resulting in poor interfacial bonding effect, which can only rely on friction to resist fracture. In addition, the traditional single-phase fiber reinforced system generally has obvious brittle failure and durability decay under complex stress conditions and harsh environments, which seriously restricts its large-scale application in practical engineering.

[0006] Specifically, for example, CN119898996A discloses a green microbial self-repairing concrete and a preparation method thereof, which improves the mechanical properties and self-repairing effect by incorporating modified mesoporous silica and stainless steel fibers. However, this method uses cold spraying mesoporous silica to treat stainless steel fibers, which can increase the surface roughness of the fibers, but will damage the tensile strength of the fibers and accelerate the aging of the stainless steel. Therefore, how to roughen the surface of the fibers without losing their strength and improve their interfacial bonding capacity with the matrix has become a problem to be solved.

[0007] In view of this, the present application aims to provide a modified carbon fiber-based self-repairing concrete and a preparation method thereof, which modifies the surface of carbon fibers by the MICP method to improve their interfacial bonding capacity with the cementitious matrix, thereby significantly improving the compressive strength, crack resistance and self-repairing ability of the concrete without reducing the working performance of the fibers. SUMMARY

[0008] The technical problem to be solved by the present application is to provide a modified carbon fiber-based self-repairing concrete and a preparation method thereof, aiming to solve the problems of poor bonding performance of carbon fibers with the matrix in the existing concrete crack repair technology and reduced concrete strength in the microbial self-repairing technology.

[0009] In order to achieve the above technical target, the technical solution adopted by the present application is as follows: The modified carbon fiber-based self-repairing concrete and the preparation method thereof improve the mechanical properties, crack resistance and long-term self-repairing performance of the concrete through an integrated technical solution of "modified carbon fiber preparation-self-repairing concrete raw material compounding-concrete molding", specifically as follows: (I) Modified carbon fiber-based self-repairing concrete Raw material composition and mixing ratio: The self-repairing concrete is prepared from the following raw materials in parts by weight: water 160-170 parts, cement 280-290 parts, fly ash 65-75 parts, modified carbon fiber 0.5-2.5 parts, coarse aggregate 650-700 parts, fine aggregate 400-500 parts, fine sand 700-800 parts, water reducing agent 2-2.5 parts, and air entraining agent 0.15-0.2 parts.

[0010] Among them, the preferred specifications of each raw material are as follows: Carbon fiber: short carbon fiber bundle with a length of 10 mm is used, each bundle is composed of 1000 single filaments with a diameter of about 7.5 μm, ensuring that the fibers are uniformly dispersed in the concrete and have high strength and high ductility; Aggregate: coarse aggregate is stone with a particle size of 20-40 mm, fine aggregate is stone with a particle size of 5-20 mm, and fine sand is natural yellow sand (particle size 0.1-0.5 mm, fineness modulus 2.2-3), which ensures the compactness of the concrete framework; Gelled material: cement is PO42.5 ordinary portland cement, fly ash is II-class fly ash, and the secondary hydration effect of fly ash is used to optimize the internal structure of concrete; Modified carbon fiber: core functional component, modified by MICP (microbially induced carbonate precipitation) method with bacillus pasteurii and calcium lactate solution, forming a three-dimensional calcium carbonate coating layer on the surface, taking into account roughness and mechanical properties.

[0011] (II) The preparation method of the self-repairing concrete based on the modified carbon fiber is a method for preparing the self-repairing concrete based on the modified carbon fiber, which comprises the preparation of the modified carbon fiber and the mixing of the concrete.

[0012] 1. The method for preparing the modified carbon fiber and the specific process are as follows: Bacterial solution preparation: take the bacterial solution of bacillus pasteurii cultured for 48 h, centrifuge at a speed of 4000 rad / min for 10 min to obtain bacterial slurry; mix the bacterial slurry with pure culture medium to prepare a bacterial solution with an initial bacterial concentration of cells / ml, cells / ml or cells / ml, which is suitable for different repair requirements; Mineralization modification: take 0.5-2.5 parts of the above short carbon fiber bundle and 100 ml of the bacterial solution in a container, add 0.5 mol / L calcium lactate as a calcium source, and incubate at 30°C for 12 h, and use microbial metabolism to induce the deposition of calcium carbonate on the surface of the carbon fiber; Purification treatment: after mineralization, the carbon fiber is repeatedly washed with deionized water to remove the weakly bound calcium carbonate particles on the surface, so as to avoid affecting the homogeneity of the concrete; Drying and shaping: the washed carbon fiber is dried in a laboratory environment with a temperature of 24°C and a relative humidity of 65% for 24 h to obtain modified carbon fiber with a stable three-dimensional calcium carbonate coating layer on the surface.

[0013] 2. In order to ensure the uniform dispersion of the modified carbon fiber and the compactness of the concrete, the mixing of the concrete adopts a step-by-step stirring-vibration forming process, and the specific steps are as follows: Dry material premixing: pour the coarse aggregate, fine aggregate, fine sand and cement into the mixer, and stir at a speed of 15-25 r / min for 3-5 min to ensure uniform mixing of the dry materials and avoid aggregation of the aggregate during subsequent wet mixing; Wet material stirring: add the preset amount of water, air entraining agent and water reducing agent into the mixer, and continue to stir at the same speed for 2-3 min to form a uniform cement paste-aggregate mixture; Fiber incorporation and molding: add modified carbon fibers to the blender in 3-5 times (the amount of each incorporation should not exceed 1 / 3 of the total incorporation amount), continue stirring for 4-6 min until the fibers are not obviously aggregated; pour the uniformly mixed material into a pre-set mold, and oscillate on a vibration table with a frequency of 50-60 Hz for 2-3 min until no obvious bubbles overflow from the material in the mold and the surface is smooth, completing the preparation of the self-repairing concrete.

[0014] The modified carbon fiber-based self-repairing concrete and the preparation method thereof have the following beneficial effects: 1. The application effectively solves the problem of durability and safety reduction of concrete structures caused by cracks in the field of building material technology, and overcomes the limitations of poor carbon fiber and matrix adhesion in existing concrete crack repair technology and the reduction of concrete strength caused by the addition of nutrients in microbial self-repairing technology.

[0015] 2. The application overcomes the two major problems of "poor concrete crack resistance" and "performance degradation after fiber treatment", and the modified carbon fiber retains the original high strength, high ductility and corrosion resistance, which can greatly improve the strength of the concrete matrix.

[0016] 3. The three-dimensional calcium carbonate coating layer on the surface of the modified carbon fiber solves the problem of fiber hydrophobicity, and the interfacial bonding force is increased by more than 30% compared with unmodified carbon fiber, and there is no fiber damage caused by physical / chemical treatment.

[0017] 4. The modified carbon fiber provides a stable attachment site for microorganisms, and when cracks occur, the bacillus pasteurii on the surface of the fiber is exposed along with the cracks, and calcium carbonate is generated by metabolizing calcium lactate to fill the cracks.

[0018] 5. The fiber bridges the cracks to form a network structure, controls the crack width (the average crack opening width can be as low as 1.26 mm, which is reduced by 79.7% compared with the unmodified fiber group), and provides nucleation sites for calcium carbonate deposition, and the repair efficiency is increased by 2-3 times compared with traditional MICP technology.

[0019] 6. The microbial metabolism process can absorb carbon dioxide in the air, reduce industrial carbon emissions, and achieve green environmental protection.

[0020] 7. The calcium lactate is attached to the surface of the fiber by modification in advance, which avoids the reduction of concrete strength caused by directly adding nutrients (the compressive strength is as high as 37.745 MPa, which is increased by 22.8% compared with the comparative example), and there is no need to add additional strength compensation components, which reduces the cost of raw materials.

[0021] 8、The self-repairing concrete prepared by the application has high strength (compressive strength 31.93-37.745 MPa), high crack resistance and corrosion resistance, and is especially suitable for water conservancy concrete structures (such as dams and water pipelines), which can improve the structural durability and prolong the service life by 10-15 years.

[0022] 9、The preparation process of the application does not require special equipment, and the existing concrete mixing station can be directly adapted. The step-by-step incorporation process of the modified carbon fiber is easy to operate, and is convenient for large-scale industrial production, so the application prospect is wide.

[0023] 10、The application significantly improves the strength and crack resistance of the concrete structure, and endows the concrete with self-repairing ability. Experimental data show that the application has significant advantages in compressive strength, splitting tensile strength and concrete ductility.

[0024] 11、The incorporation of the modified carbon fiber enhances the adhesion between the carbon fiber and the concrete matrix, so that the carbon fiber can stably adhere at the interface and effectively limit the continuous expansion of the crack.

[0025] 12、The application solves the problem of poor crack resistance of the concrete in the existing concrete crack repair technology.

[0026] 13、The application solves the problem of poor interfacial bonding effect between the smooth fiber surface and the concrete matrix, and the problem of significant decrease in fiber work performance after physical or chemical treatment, which is not conducive to the long-term work of the concrete structure.

[0027] 14、The application provides more adhesion sites for microorganisms by directly incorporating the modified carbon fiber, so that more microorganisms can be enriched at the exposed part of the crack to generate more calcium carbonate to fill the crack, thereby achieving faster healing effect of the concrete crack.

[0028] 15、The carbon fiber selected by the application is mainly composed of carbon elements, has the characteristics of high temperature resistance, friction resistance, heat conduction and corrosion resistance, and has a sheet shape, softness, high strength and deformation modulus. After being incorporated into the concrete, the strength of the concrete can be greatly improved.

[0029] 16、The application modifies the surface of the carbon fiber by using the MICP method, so that a three-dimensional calcium carbonate coating layer is generated on the surface of the carbon fiber. Due to the hydrophilicity of the calcium carbonate particles, the wettability of the modified carbon fiber surface is improved, and the physical combination of the fiber and the cementitious matrix is easy.

[0030] 17、The incorporation of the fiber has a positive effect on the self-repairing of the secondary hydrated and carbonated concrete. When there are more fiber bridging cracks, a tight space will be formed in the crack, so that the fiber bridging the crack can effectively control the crack width.

[0031] 18、The fiber of the present application can improve the problem of reduced concrete strength caused by the incorporation of microorganisms and other nutrients.

[0032] 19、The present application adopts the form of modifying carbon fiber in advance to make calcium lactate adhere to the fiber and the generated calcium carbonate, avoiding the phenomenon of a substantial decrease in concrete strength caused by directly mixing calcium lactate into concrete.

[0033] 20、The self-healing concrete based on modified carbon fiber of the present application has a crack closure rate of more than 80% after 56 days of self-healing under the condition of a crack width of 0.3mm, significantly improving the self-healing efficiency of the concrete.

[0034] 21、The self-healing concrete prepared by the present application has a 28-day compressive strength of 37.745MPa and a splitting tensile strength of 4.219MPa, the mechanical properties are improved, and the long-term durability and safety of the concrete structure are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application will be further described below in conjunction with the accompanying drawings and implementation examples: Figure 1 The flowchart of the preparation method of the present application is shown in Figure 1. Figure 2 The schematic diagram of the unmodified carbon fiber of Example 10 of the present application is shown in Figure 2. Figure 3 The schematic diagram of the modified carbon fiber of Example 5 of the present application is shown in Figure 3. Figure 4 The schematic diagram of the concrete cracking with unmodified carbon fiber of Example 10 of the present application is shown in Figure 4. Figure 5 The schematic diagram of the concrete cracking with modified carbon fiber of Example 6 of the present application is shown in Figure 5. DETAILED DESCRIPTION

[0036] The technical solutions in the present application will be further described below in conjunction with the accompanying drawings and examples: Example 1 The present example provides a self-healing concrete based on modified carbon fiber, which is prepared by mixing a plurality of raw materials by weight fraction, including water 160-170 parts, cement 280-290 parts, fly ash 65-75 parts, modified carbon fiber 0.5-2.5 parts, coarse aggregate 650-700 parts, fine aggregate 400-500 parts, fine sand 700-800 parts, water reducing agent 2-2.5 parts, and air entraining agent 0.15-0.2 parts.

[0037] Further, the modified carbon fiber is modified by MICP method with Bacillus pasteurii and calcium lactate solution, forming a three-dimensional calcium carbonate coating layer on the surface, the hydrophilicity of the three-dimensional calcium carbonate coating layer improves the wettability of the surface of the modified carbon fiber, and enhances the physical bonding force with the cementitious matrix.

[0038] Further, the carbon fiber is a chopped carbon fiber bundle with a length of 10 mm, and the chopped carbon fiber bundle is composed of 1000 filaments with a diameter of about 7.5 μm.

[0039] Further, the coarse aggregate is a stone with a particle size of 20-40 mm, and the fine aggregate is a stone with a particle size of 5-20 mm.

[0040] Further, the fine sand is natural yellow sand with a particle size range of 0.1-0.5 mm and a fineness modulus of 2.2-3; the cement is P042.5 ordinary portland cement, and the fly ash is grade II fly ash, and the physical properties of the grade II fly ash are shown in Table 1:

[0041] Example 2 In another preferred embodiment, based on the above-mentioned example 1, the present embodiment provides a self-repairing concrete based on modified carbon fiber, and the constituent components and the proportions are as follows: water 165 parts, cement 295 parts, fly ash 80 parts, coarse aggregate 700 parts, fine aggregate 450 parts, fine sand 750 parts, water reducing agent 3 parts, air entraining agent 0.5 parts, and modified carbon fiber 0.84 parts (based on the total volume percentage of the concrete).

[0042] 1. Preparation of modified carbon fiber: Bacterial liquid culture: Bacillus pasteurii was inoculated into a liquid culture medium, and cultured at 30°C and 150 rpm for 24 hours to obtain an initial bacterial liquid.

[0043] Centrifugal treatment: the initial bacterial liquid was centrifuged at 4000 rpm for 10 minutes, and the supernatant was discarded to obtain bacterial slurry.

[0044] Resuspension of bacterial liquid: the bacterial slurry was mixed with pure culture medium to adjust to different initial bacterial concentrations (such as OD600=1.0).

[0045] Carbon fiber modification: the chopped carbon fiber bundle (length 6 mm) was placed in a beaker containing bacterial liquid and calcium lactate solution (concentration 0.2 mol / L), and cultured at 30°C for 72 hours. After mineralization, the carbon fiber surface was washed with deionized water, and dried at 60°C for 24 hours to obtain modified carbon fiber with a three-dimensional calcium carbonate coating on the surface.

[0046] 2. Preparation of concrete: Mixing of raw materials: the cement, fly ash, coarse aggregate, fine aggregate, and fine sand were added into a forced mixer according to the proportions, and dry-mixed for 60 seconds.

[0047] Addition of modified carbon fiber: the modified carbon fiber was uniformly scattered into the mixer, and continued to be stirred for 60 seconds to ensure uniform dispersion of the carbon fiber.

[0048] Adding water and admixtures: Slowly add water and admixture mixture of water-reducing agent and air-entraining agent into the mixer, wet mix for 120 seconds, and obtain uniform self-healing concrete.

[0049] The self-healing concrete prepared in this embodiment has excellent mechanical properties and self-healing ability. Experimental data show that the 28-day compressive strength can reach 37.215 MPa, and the splitting tensile strength can reach 3.821 MPa. Under the condition of crack width of 0.3 mm, after 58 days of self-healing, the crack closure rate is more than 80%, significantly improving the durability and safety of the concrete structure.

[0050] Example 3 In another preferred embodiment, based on the above-mentioned Examples 1 and 2, this embodiment provides a preparation method of self-healing concrete based on modified carbon fibers, including two key steps of modified carbon fiber preparation and concrete mixing.

[0051] Step 1, modified carbon fiber preparation: Step 1.1, strain selection and culture: Bacillus pasteurii with high urease activity is selected as the mineralization strain, inoculated into liquid medium containing urea and yeast extract, and cultured at 30°C under shaking until the logarithmic growth phase.

[0052] Step 1.2, carbon fiber surface treatment: Place the chopped carbon fiber bundle (length 12 mm) in a container containing bacterial solution and calcium chloride solution (concentration 0.5 mol / L), and incubate at 25°C for 48 hours. Through the process of microbial-induced calcium carbonate precipitation (MICP), a uniform three-dimensional calcium carbonate coating is formed on the surface of the carbon fiber.

[0053] Step 1.3, post-treatment: Rinse the carbon fiber surface with deionized water to remove unbound calcium carbonate particles, and dry at 80°C for 12 hours to obtain modified carbon fiber.

[0054] Step 2, concrete mixing: Step 2.1, raw material pretreatment: Mix coarse aggregate (particle size 5-20 mm) and fine aggregate (particle size 0-5 mm) according to the proportion, and sieve to remove impurities.

[0055] Step 2.2, dry material mixing: Add cement, fly ash, pretreated aggregate and fine sand according to the proportion into the mixer, and dry mix for 90 seconds.

[0056] Step 2.3, adding modified carbon fiber: Add modified carbon fiber at 1% of the total volume of concrete into the mixer, continue to stir for 90 seconds to ensure uniform dispersion of carbon fiber.

[0057] Step 2.4, wet material mixing: water and admixture (water reducing agent, air entraining agent) mixture is slowly added into the mixer, wet mixing for 180 seconds, to obtain self-healing concrete with good fluidity.

[0058] The preparation method provided by the embodiment significantly improves the preparation efficiency of the modified carbon fiber and the self-healing performance of the concrete by optimizing the strain culture condition, the carbon fiber surface treatment process and the concrete mixing parameters. Compared with the prior art, the method has the advantages of simple operation, low cost and environmental friendliness, and is suitable for large-scale industrial production.

[0059] Embodiment 4 In another preferred embodiment, based on the above-mentioned embodiments 1 to 3, the embodiment provides a self-healing concrete based on modified carbon fiber, which is prepared by using the following materials: water, cement, fly ash, modified carbon fiber, coarse aggregate, fine aggregate, fine sand, water reducing agent and air entraining agent. The carbon fiber is modified by treating with Bacillus pasteurii and calcium lactate solution, and each raw material is mixed in a mixing ratio of water 166.4 parts, cement 280 parts, fly ash 70 parts, modified carbon fiber 0.84 parts, coarse aggregate 687 parts, fine aggregate 458 parts, fine sand 752 parts, water reducing agent 2.1 parts and air entraining agent 0.16 parts.

[0060] Further, the carbon fiber is a chopped carbon fiber bundle with a length of 10 mm.

[0061] Further, the chopped carbon fiber bundle is composed of 1000 monofilaments with a diameter of about 7.5 μm.

[0062] Further, the coarse aggregate is a stone with a particle size of 20-40 mm, and the fine aggregate is a stone with a particle size of 5-20 mm.

[0063] Further, the fine sand is natural yellow sand with a particle size range of 0.1-0.5 mm and a fineness modulus of 2.2-3.

[0064] Further, the cement is P042.5 ordinary portland cement, and the fly ash is grade II fly ash.

[0065] Further, the sand in the aggregate is medium sand, and the stone is small stone with a size of 520 mm and medium stone with a size of 20-40 mm.

[0066] The preparation method of the self-healing concrete based on the modified carbon fiber includes the preparation of the modified fiber and the mixing of the concrete, as shown in Figure 1 Step 1, preparation of modified carbon fiber Step 1.1: centrifuge the bacterial slurry obtained by centrifuging the bacterial solution cultured for 48 h at 4000 rad / min for 10 min, and mix the bacterial slurry with pure culture medium to obtain 10​6 cells / ml of bacterial solution; Step 1.2: Take 0.5~2.5 parts of 10mm length short-cut carbon fiber bundle and 100ml bacterial solution in a beaker, incorporate 0.5mol / L calcium lactate as calcium source, and incubate at 30 o C for 12h; Step 1.3: After mineralization, rinse the modified carbon fiber with deionized water to remove the weakly bound particles on the surface; Step 1.4: Dry the sample under laboratory conditions (24℃, 65% relative humidity) for 24h.

[0067] Step 2, concrete mixing: Step 2.1: Pour the coarse aggregate, fine aggregate, sand and cement into the mixer and stir evenly; Step 2.2: After the dry materials are stirred evenly, pour the corresponding parts of water, air entraining agent and admixture into the mixer and continue to stir evenly; Step 2.3: After the wet materials are stirred evenly, pour the modified carbon fiber into the mixer in multiple times, and then pour the material into the mold and shake it to make it compact to prepare the self-repairing concrete.

[0068] Example 5 In another preferred embodiment, based on the above-mentioned example 4, the present example provides a self-repairing concrete based on modified carbon fiber, which is mixed by the following raw materials in the mixing ratio of water 166.4 parts, cement 280 parts, fly ash 70 parts, modified carbon fiber 0.84 parts, coarse aggregate 687 parts, fine aggregate 458 parts, fine sand 752 parts, water reducing agent 2.1 parts, air entraining agent 0.16 parts; in addition, the modified carbon fiber is treated with cells / ml of bacterial solution during preparation, and the rest of the ingredients and preparation method are the same as example 4.

[0069] Example 6 In another preferred embodiment, based on example 4, the present example provides a self-repairing concrete based on modified carbon fiber, which is treated with cells / ml of bacterial solution during preparation, and the rest of the ingredients and preparation method are the same as example 4.

[0070] Example 7 In another preferred embodiment, based on the above embodiment 4, this embodiment provides a self-healing concrete based on modified carbon fiber, which is made by mixing the following raw materials in the following proportions: 166.4 parts water, 280 parts cement, 70 parts fly ash, 1.68 parts modified carbon fiber, 687 parts coarse aggregate, 458 parts fine aggregate, 752 parts fine sand, 2.1 parts water-reducing agent, and 0.16 parts air-entraining agent; in addition, the modified carbon fiber preparation process adopts... The bacterial solution with cells / ml was subjected to a three-dimensional coating treatment, and the rest of the preparation method was the same as in Example 4.

[0071] Example 8 In another preferred embodiment, based on Example 7, this embodiment provides a self-healing concrete based on modified carbon fiber, with a modified carbon fiber content of 2.52 parts. Apart from this, the other components and preparation methods are the same as in Example 4.

[0072] Example 9 In another preferred embodiment, based on Example 7, this embodiment provides a self-healing concrete based on modified carbon fiber, wherein the modified carbon fiber is prepared using... The bacterial solution of cells / ml was coated with a three-dimensional coating layer on its surface, and the remaining components and preparation methods were the same as in Example 4.

[0073] Example 10 In another preferred embodiment, based on Example 4, this embodiment provides a self-healing concrete based on modified carbon fiber. The carbon fiber content is 0.84 parts, and the surface is not aligned using the MICP method for three-dimensional coating treatment. Apart from this, the other components and preparation methods are the same as in Example 4.

[0074] The concrete prepared in Examples 4-9 and Example 10 were subjected to compressive strength, splitting tensile strength, and ductility tests. The ductility test procedure was as follows: cracked samples under ultimate stress conditions from the 56-day splitting tensile test were selected, and the crack width was recorded every 10 mm along the concrete height direction (from bottom to top). Three samples were tested for each type of fiber-reinforced concrete. Since the crack width at the top and bottom positions was significantly affected by the spacer strip, data at 0 mm and 100 mm were discarded, and the average crack width at each position was taken. The test results are shown in Table 2. Table 2 Test Results

[0075] Depend on Figures 2 to 5It can be seen that after the surface modification treatment of the carbon fiber by the microorganism, the surface of the carbon fiber has a three-dimensional coating layer of calcium carbonate, so that the surface of the carbon fiber changes from a smooth surface to a surface with a certain roughness, thereby having higher adhesion when combined with the cementitious matrix. As can be seen from the comparison between Example 4 and Example 10, after the carbon fiber with a surface modified by the microorganism is mixed into the concrete, the mechanical properties of the concrete are improved to a certain extent, and the crack resistance is greatly improved. Although calcium carbonate is a coating material for carbon fiber, a part of the calcium carbonate powder will be dispersed into the matrix during the preparation of the concrete. As a mineral material, the calcium carbonate has a strong combination line with the concrete matrix, which helps to strengthen the micro-pores and cracks in the matrix. At the same time, the microorganism in the powder is released in the micro-pores and cracks and starts the mineralization reaction to produce calcium carbonate to fill the pores and micro-cracks, thereby improving the mechanical properties of the concrete. After the fiber is mixed into the concrete, when there are many fibers bridging the cracks, a network fiber network structure is formed in the cracks, and the fibers bridging the cracks not only control the crack width, but also provide nucleation sites for the mineralization reaction of the microorganism, thereby promoting the effective precipitation of the self-healing product. In the cracks without fiber bridging, the calcium carbonate is only deposited from the crack wall, while in the cracks with fiber bridging, calcium carbonate is also deposited in the middle of the cracks away from the crack wall, which has a positive effect on improving the deposition efficiency and plugging effect of calcium carbonate. Figure 3 In some embodiments, Uniform precipitation is uniform precipitation.

[0076] Example 11 In another preferred embodiment, based on the above Examples 1 to 3, this embodiment takes the base parameter type self-healing concrete (bacterial solution concentration cells / ml, fiber content 0.84 parts) as an example to describe the specific parameters, implementation methods and steps of the self-healing concrete based on modified carbon fiber and the preparation method thereof. The specifications of the raw materials not specifically mentioned in the examples meet the basic requirements of the technical solutions of the present application, and the performance tests are performed in accordance with the Standard for Test Methods of Physical and Mechanical Properties of Concrete (GB / T50081-2019).

[0077] 1. Raw material composition and specifications The self-healing concrete of this embodiment is prepared according to the weight fraction, and the specific raw materials and parameters are shown in Table 2: Table 3 Specific raw materials and parameters

[0078] 2. Preparation of modified carbon fiber The preparation of the modified carbon fiber is strictly completed according to the following steps to ensure the formation of a stable three-dimensional calcium carbonate coating layer on the surface: Step 1, bacteria solution preparation: take the bacteria solution of 48h cultured Bacillus pasteurii, centrifuge at 4000 rad / min for 10 min, collect the bottom bacteria mud; mix the bacteria mud with pure culture medium (containing peptone, yeast extract), adjust the initial bacteria concentration to 1.5×108 cells / ml, stir uniformly and stand for 30 min for standby.

[0079] Step 2, mineralization reaction: add 0.84 parts of chopped carbon fiber bundle (actual mass according to weight) and 100 ml of the above bacteria solution into a 250 ml beaker, and then add 0.5 mol / L calcium lactate solution (calcium source). Seal the beaker and place it in a 30°C constant temperature water bath for 12h. Avoid shaking during the process.

[0080] Step 3, purification treatment: after mineralization, rinse the carbon fiber with deionized water for 3 times (50 ml of water each time), to remove the calcium carbonate particles that are not firmly combined on the surface, until the rinse liquid is clear.

[0081] Step 4, drying and shaping: place the rinsed carbon fiber in a constant temperature and humidity box, dry at 24°C and 65% relative humidity for 24h, then take it out and seal it for storage. The modified carbon fiber is obtained.

[0082] 3. Preparation of self-repairing concrete Adopt step-by-step stirring process to ensure uniform dispersion of raw materials and no fiber aggregation: Step 1, dry material premixing: pour coarse aggregate (687 parts), fine aggregate (458 parts), fine sand (752 parts) and cement (280 parts) into a planetary mixer, stir at 20 r / min for 4 min, until the dry materials are evenly colored and there is no obvious particle aggregation.

[0083] Step 2, wet material stirring: add water (166.4 parts), air entraining agent (0.16 parts) and water reducing agent (2.1 parts) to the mixer, continue stirring at 20 r / min for 3 min to form a cement paste-aggregate mixture in a flowing state, ensuring complete dissolution of the water reducing agent.

[0084] Step 3, fiber incorporation and molding: add modified carbon fiber to the mixer in 4 times (0.21 parts each time), stir for 1 min after each addition, total stirring time is 4 min; after stirring, pour the mixture into a 100mm×100mm×100mm cubic mold, place it on a 50Hz vibration table and vibrate for 2.5 min until no bubbles overflow from the mold and the surface is smooth, then cover it with plastic wrap, demold after 24h curing under standard curing conditions (temperature 20±2°C, relative humidity ≥95%), and continue curing until the test age.

[0085] 4. Performance test results ​The mechanical properties and crack resistance are tested after curing for 56 days, and the results are as follows: (1) compressive strength: 31.93 MPa (3.9% higher than the unmodified carbon fiber group (Example 10)); (2) splitting tensile strength: 3.317 MPa (7.1% higher than Example 10); (3) average crack opening width: 3.71 mm (40.4% lower than Example 10 (6.22 mm)); (3) Microscopic characterization: The modified carbon fiber surface three-dimensional calcium carbonate coating layer is complete, and there is no obvious gap between the cement paste interface, and calcium carbonate deposition marks can be seen at the crack.

[0086] Example 12 In another preferred embodiment, based on Example 11 above, this example takes a high bacterial solution concentration type self-healing concrete (bacterial solution concentration cells / ml, fiber content 0.84 parts) as an example to describe the specific parameters, implementation methods and steps of the self-healing concrete based on modified carbon fiber and its preparation method.

[0087] 1. Raw material composition and specification The raw material specifications of this example are completely consistent with those of Example 4, only the bacterial solution concentration in the preparation of modified carbon fiber is adjusted, and the weight fractions of raw materials remain unchanged (water 166.4 parts, cement 280 parts, fly ash 70 parts, modified carbon fiber 0.84 parts, etc.), to ensure that the influence of a single variable (bacterial solution concentration) on performance can be clearly distinguished.

[0088] 2. Preparation of modified carbon fiber The difference from Example 4 is only in the bacterial solution preparation step: after mixing the bacterial sludge with the pure culture medium, the initial bacterial concentration is adjusted to cells / ml, and the remaining steps (mineralization reaction, purification treatment, and drying and shaping) are completely the same, and the modified carbon fiber with a more dense surface calcium carbonate coating layer is finally obtained.

[0089] 3. Preparation of self-healing concrete The preparation steps (dry material premixing, wet material stirring, fiber incorporation and molding) are completely consistent with those of Example 4, to ensure that the process parameters are identical, and only the density of the calcium carbonate coating layer on the surface of the modified carbon fiber affects the final performance.

[0090] 4. Performance test results The test results after curing for 56 days are as follows, showing the performance improvement effect of high bacterial solution concentration: (1) compressive strength: 34.952 MPa (9.5% higher than Example 1, 13.7% higher than Example 10); (2) Splitting tensile strength: 3.806 MPa (14.8% higher than Example 1, 22.9% higher than Example 10); (3) Average crack opening width: 1.78 mm (52.0% lower than Example 1, 71.4% lower than Example 10); (4) Repair efficiency: after artificially creating a 0.3 mm crack, the crack healing rate reached 85% within 56 days (0 for Example 10), and the number of microorganisms attached to the fiber surface was higher due to the high concentration of bacterial solution, and the mineralization calcium production was increased.

[0091] Example 13 In another preferred embodiment, based on Example 12 described above, this embodiment takes a high-fiber content self-healing concrete (bacterial solution concentration cells / ml, fiber content 1.68 parts) as an example to describe the specific parameters, implementation methods and steps of the self-healing concrete based on modified carbon fiber and its preparation method. The specifications and preparation conditions of the raw materials not specifically mentioned in the example meet the basic requirements of the technical solution of the present application, and the performance test is carried out in accordance with the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T50081-2019).

[0092] 1. Raw material composition and specification In this embodiment, the modified carbon fiber content is adjusted to 1.68 parts (2 times that of Example 5), and the weight fractions and specifications of the remaining raw materials are completely consistent with those of Example 12 (water 166.4 parts, cement 280 parts, coarse aggregate 687 parts, etc.). The focus is on verifying the strengthening effect of fiber content on the strength and crack resistance of concrete.

[0093] 2. Preparation of modified carbon fiber The bacterial solution concentration cells / ml, and the mineralization, purification and drying steps are the same, ensuring that the surface state of the modified carbon fiber is uniform, and only by adjusting the content to change the fiber distribution density inside the concrete.

[0094] 3. Preparation of self-healing concrete The difference from Example 5 is only in the fiber incorporation step: due to the increase in fiber content, the modified carbon fiber is added in 6 times (0.28 parts each time), and after each addition, it is stirred for 1 min, and the total stirring time is 6 min to avoid fiber agglomeration; the remaining steps (dry material premixing, wet material stirring, vibration molding) are completely the same, and the vibration table vibration time is extended to 3 min to ensure that the concrete with high-density fibers can still be compacted and formed.

[0095] 4. Performance test results The test results after 56 days of curing are as follows, showing the synergistic strengthening effect of high fiber content: (1) Compressive strength: 35.197 MPa (0.7% higher than Example 2, and 14.5% higher than Example 10); (2) Splitting tensile strength: 3.52 MPa (7.5% lower than Example 2, but still 6.1% higher than Example 1 and 13.7% higher than Example 10); (3) Average crack opening width: 2.12 mm (19.1% larger than in Example 2, but 42.9% smaller than in Example 1 and 65.9% smaller than in Example 10); (4) Crack resistance toughness: The toughness value of concrete at fracture reaches 3.2kJ / m² (2.8kJ / m² in Example 2 and 1.5kJ / m² in Example 10). Due to the enhanced fiber bridging effect, the crack propagation rate is effectively suppressed. Long-term durability: After 50 freeze-thaw cycles (-20℃~20℃), the compressive strength loss rate was only 8.2% (10.5% in Example 2 and 18.3% in Example 10). The corrosion resistance of modified carbon fiber improved the freeze-thaw resistance of concrete.

[0096] Examples 11 to 13 verified the effectiveness of the technical solution of the present invention by controlling a single variable (bacterial solution concentration and fiber content): bacterial solution concentration When the fiber content is 0.84 parts per cell / ml (Example 12), the overall performance of the concrete (strength, crack resistance, and repair efficiency) is optimal. Increasing the fiber content can enhance crack resistance, toughness, and durability, but the mixing process needs to be optimized to avoid agglomeration. Adjusting the bacterial solution concentration can precisely control the density of the calcium carbonate coating layer on the carbon fiber surface, thereby matching the repair efficiency requirements of different projects. None of the examples exhibited the existing technical defects such as "performance degradation after fiber treatment" or "strength reduction due to nutrients," which meets the design objectives of this invention.

[0097] In a preferred embodiment, the modified carbon fiber is obtained by modifying it with Bacillus pasteurellii and calcium lactate solution using the MICP method, forming a three-dimensional calcium carbonate coating layer on its surface. This configuration significantly improves the surface roughness of the modified carbon fiber, enhances its interfacial bonding with the matrix material, effectively improves the mechanical properties and durability of the composite material, and the three-dimensional structure also plays a certain role in toughening and crack resistance.

[0098] In a preferred embodiment, the carbon fiber is a 10mm long chopped carbon fiber bundle, which consists of 1000 single filaments with a diameter of approximately 7.5μm. This configuration allows the carbon fiber to be more uniformly dispersed in the matrix, effectively improving the mechanical properties of the composite material and enhancing its tensile and compressive strength. At the same time, this specification of carbon fiber can also reduce the weight of the material, achieving lightweight design while ensuring performance.

[0099] In the preferred scheme, the coarse aggregate is stone with a particle size of 20-40 mm, and the fine aggregate is stone with a particle size of 5-20 mm; the above settings can ensure that the aggregate gradation of the concrete is reasonable, effectively fill the voids, and improve the density and strength of the concrete; at the same time, this combination can also reduce the cement dosage, reduce the engineering cost, and has good construction performance and is easy to vibrate and compact.

[0100] In the preferred scheme, the fine sand is natural yellow sand with a particle size range of 0.1-0.5 mm and a fineness modulus of 2.2-3; the cement is P042.5 ordinary portland cement, and the fly ash is grade II fly ash; the above settings can ensure that the mixture has appropriate workability and strength. The particle size and fineness modulus of the natural yellow sand are beneficial to the formation of a stable aggregate structure; the P042.5 cement provides sufficient cementitious capacity, and the grade II fly ash can improve the workability, which together guarantees the performance of the engineering material.

[0101] In the preferred scheme, the specific conditions for stirring the dry mixture to uniformity in step 1 are: stirring speed of 15-25 r / min and stirring time of 3-5 min; the above settings can ensure that all types of dry materials are fully contacted and uniformly dispersed, avoid local component aggregation, provide a stable foundation for subsequent reactions, and effectively improve the self-repairing performance and overall quality of the concrete.

[0102] In the preferred scheme, the specific conditions for vibrating and compacting in step 3 are: using a vibration table with a frequency of 50-60 Hz to vibrate for 2-3 min until there are no obvious bubbles overflowing from the mixture in the mold and the surface is smooth; the above settings can effectively ensure that the internal structure of the mixture is uniform and compact, reduce internal pores, improve the physical properties and stability of the material after molding, lay a good foundation for subsequent processes and the quality of the final product, and guarantee that the product meets high quality standards.

[0103] In the preferred scheme, the initial bacterial concentration in step 3.1 is cells / ml, cells / ml, or cells / ml; the above settings can ensure that the number of bacteria in the experiment is within a reasonable range, neither too low to cause the experimental phenomenon to be not obvious, nor too high to cause bacteria aggregation to interfere with the results, laying a foundation for accurate analysis of experimental data in the future.

[0104] In summary, the modified carbon fiber-based self-healing concrete and its preparation method proposed by the present application exhibit significant innovation and practicality. On the one hand, the present application uses the MICP method to modify the surface of the carbon fiber to form a three-dimensional calcium carbonate coating. This way of modifying carbon fiber through biomineralization is unique in the field of concrete crack repair, effectively improving the interfacial bonding ability of carbon fiber and cementitious matrix, and improving the surface roughness and wettability without damaging the mechanical properties of the carbon fiber.

[0105] On the other hand, the modified carbon fiber is applied to the self-healing concrete, which presents a novel combination compared with the existing technology of simply using unmodified carbon fiber or microbial self-healing technology. The three-dimensional calcium carbonate coating formed by the MICP method not only enhances the bonding performance of carbon fiber and cementitious matrix, but also endows carbon fiber with a new function in concrete crack repair, i.e., as a nucleation site for microbial mineralization, promoting the deposition of calcium carbonate at the crack, and significantly improving the self-healing efficiency of concrete. This design successfully solves the problems of poor bonding performance of carbon fiber and matrix and reduced concrete strength in the microbial self-healing technology.

[0106] In addition, this scheme combines the advantages of carbon fiber reinforcement and microbial mineralization self-healing technology, creating a completely new self-healing concrete system. This cross-disciplinary technical integration is innovative in the field of concrete material science, providing a new solution for the long-term durability and safety of concrete structures, and further broadening the application range of existing self-healing concrete. Compared with the existing technology, the present application has significant differences in technical features: the direct addition of carbon fiber greatly improves the problem of easy cracking of concrete, and the excellent physical properties of carbon fiber ensure the long-term effectiveness of the work; the surface roughness of the modified carbon fiber is improved without affecting its own working performance, and the mechanical properties and crack resistance of the concrete mixed with the modified carbon fiber are improved; at the same time, the problem of strength reduction caused by the introduction of microbial nutrients in self-healing concrete is avoided, and it has wide practical application value.

Claims

1. Self-healing concrete based on modified carbon fibers, characterized in that: A number of raw materials are mixed by weight parts to make, including water 160~170 parts, cement 280~290 parts, fly ash 65~75 parts, modified carbon fiber 0.5~2.5 parts, coarse aggregate 650~700 parts, fine aggregate 400~500 parts, fine sand 700~800 parts, water reducing agent 2~2.5 parts, air entraining agent 0.15~0.2 parts.

2. The modified carbon fiber based self-healing concrete according to claim 1, characterized in that: The modified carbon fiber is obtained by MICP method using Bacillus pasteurii and calcium lactate solution, and a three-dimensional calcium carbonate coating layer is formed on the surface.

3. The modified carbon fiber based self-healing concrete according to claim 2, characterized in that: The carbon fiber is a chopped carbon fiber bundle, which is composed of a plurality of filaments.

4. The modified carbon fiber based self-healing concrete according to claim 1, wherein: The coarse aggregate is a stone with a particle size of 20~40mm, and the fine aggregate is a stone with a particle size of 5~20mm.

5. The modified carbon fiber based self-healing concrete according to claim 1, characterized in that: The fine sand is natural yellow sand, the cement is PO42.5 ordinary portland cement, and the fly ash is grade II fly ash.

6. A method for preparing a self-repairing concrete based on modified carbon fibers, which is a method for preparing a self-repairing concrete using the self-repairing concrete based on modified carbon fibers according to any one of claims 1 to 5, characterized in that, The method comprises the following steps: Step 1: preparation of modified carbon fiber; Step 2: mixing of concrete.

7. The method for producing a modified carbon fiber-based self-repairing concrete according to claim 6, characterized by, The preparation of modified carbon fiber in step 1 comprises the following steps: Step 1.1: Take the bacterial solution of Bacillus pasteurii cultured for 48 h, centrifuge at 4000 rad / min for 10 min to obtain bacterial slurry, mix the bacterial slurry with pure culture medium to prepare a bacterial solution with an initial bacterial concentration of 1.5 x 10 cells / ml Step 1.2: 0.5~2.5 parts of chopped carbon fiber bundle and 100ml of bacterial solution prepared in step 1 are placed in a container, 0.5mol / L calcium lactate is added as calcium source, and the container is incubated at 30℃ for 12h; Step 1.3: after the mineralization is completed, the carbon fiber is washed with deionized water to remove the weakly bound particles on the surface; Step 1.4: the washed carbon fiber is dried in an environment with a temperature of 24℃ and a relative humidity of 65% for 24h to obtain the modified carbon fiber.

8. The method for preparing a modified carbon fiber-based self-repairing concrete according to claim 9, characterized in that: The initial bacterial concentration in step 1.1 is cells / ml, cells / ml or cells / ml.

9. The method of claim 6, wherein the modified carbon fiber-based self-repairing concrete is prepared by mixing the modified carbon fiber, the cement, the water, the fine aggregate, the coarse aggregate, and the superplasticizer. The mixing of concrete in step 2 comprises the following steps: Step 2.1: the coarse aggregate, fine aggregate, fine sand and cement are poured into a mixer and stirred until the dry materials are uniformly mixed; Step 2.2: water, air entraining agent and water reducing agent are added to the mixer, and the wet materials are continuously stirred until they are uniformly mixed; Step 2.3: the modified carbon fiber is added to the mixer in multiple times, and the mixture is continuously stirred until all the materials are uniformly mixed, then the mixture is poured into a mold and vibrated to compact, to obtain the self-repairing concrete.

10. The method for producing a modified carbon fiber-based self-repairing concrete according to claim 9, characterized by, In step 2.1, the specific conditions for stirring until the dry materials are uniformly mixed are: the stirring speed of the mixer is 15~25r / min, and the stirring time is 3~5min; in step 2.3, the specific conditions for vibration compaction are: using a vibration table with a frequency of 50~60Hz to vibrate for 2~3min until there are no obvious bubbles overflowing from the mixture in the mold and the surface is smooth.

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