High-frequency foundation pier self-compacting concrete as well as preparation method and application thereof

Abstract

The invention provides high-frequency foundation pier self-compacting concrete as well as a preparation method and application thereof. The concrete comprises a cementing material system, an aggregate system, a functional additive, a fiber reinforced system and a self-repairing component. Wherein the steel fibers are mixed with the sisal fibers subjected to plasma grafting treatment, so that the crack resistance is improved; the diatomite microcapsule loaded with bacillus is used as a self-repairing component to realize the self-healing of the crack. During preparation, the self-compactness and compactness of a concrete mixture are ensured through a step-by-step stirring and high-frequency vibration process. Through fiber modification treatment, a microcapsule self-repairing technology and process optimization, the concrete has low yield stress and high plastic viscosity, the crack resistance and durability in a high-frequency vibration environment are remarkably improved, the crack healing rate can reach 50%, and the concrete is suitable for high-frequency foundation pier construction of bridges, wind power, nuclear power and the like and has good engineering application value.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials and preparation thereof, in particular to a high-frequency self-compacting concrete for a foundation pier, a preparation method thereof and an application thereof. Background Art

[0002] In the field of modern large-scale infrastructure construction, such as cross-sea bridge engineering systems, onshore / offshore wind power generation facility clusters, and nuclear power containment structures and other complex engineering scenarios, high-frequency piers, as key load-bearing components, are continuously subjected to periodic dynamic loads and high-frequency vibration excitation. This type of cyclic dynamic load not only includes traffic loads and conventional vibrations generated by mechanical operation, but also involves complex effects such as seismic response and wind-induced vibrations in extreme environments. This poses unprecedented technical challenges to the self-compacting properties, crack toughness, and long-term durability of the concrete materials used in the piers. As a self-compacting concrete material widely used in the current engineering field, its technical advantage of achieving vibration-free construction based on high fluidity has been fully verified, but there are still significant technical bottlenecks under high-frequency dynamic load conditions:

[0003] (1) Insufficient control of hydration heat and shrinkage: Traditional formulas rely on high cement dosage (≥400kg / m 3 ) and ordinary fly ash, the concentrated heat release of hydration leads to temperature cracks, and the shrinkage compensation mostly uses calcium oxide expansion agents, which easily cause early excessive expansion; (2) The fiber reinforcement effect is limited: the mixed system of steel fiber and plant fiber is prone to fiber agglomeration under high-frequency vibration due to poor interface bonding, resulting in stress concentration; (3) Lack of self-repairing ability: Traditional concrete crack repair relies on external intervention and lacks an active repair mechanism. Especially in concealed projects, the expansion of microcracks can easily lead to chain diseases such as leakage and steel corrosion. Existing self-repairing technologies have problems such as low repair efficiency and poor durability. (4) Insufficient matching between preparation process and performance: Conventional mixing process makes it difficult to achieve uniform dispersion of modified fibers and self-repairing components, low-frequency vibration makes it difficult to achieve directional distribution of fibers, coarse aggregate settlement leads to uneven density, and compressive strength and frost resistance grade cannot meet the long-term load requirements of high-frequency foundation piers. Summary of the Invention

[0004] In view of this, the present invention proposes a high-frequency foundation pier self-compacting concrete and its preparation method and application, aiming to improve the performance of concrete through specific raw material ratios and modification technology to meet the engineering requirements of high-frequency foundation piers.

[0005] The technical solution of the present invention is achieved as follows: a high-frequency self-compacting concrete for foundation piers comprises the following components in amounts per cubic meter:

[0006] Cementitious material system: cement 320-370kg, grade I fly ash 55-70kg, steel slag powder 20-35kg;

[0007] Aggregate system: coarse aggregate 800-840kg, fine aggregate 750-780kg;

[0008] Functional additives: polycarboxylate water reducer 1-3kg, calcium sulfoaluminate expander 8-14kg, cellulose ether thickener 0.001-0.08kg, viscosity 5000-15000mPa·s;

[0009] Fiber reinforcement system: 12-19 kg of a mixed composition of steel fiber and modified sisal fiber, wherein the mass ratio of steel fiber to modified sisal fiber is (9-13):(3-6), and the modified sisal fiber is prepared by plasma grafting sisal fiber;

[0010] Self-repair component: 2-4 kg of diatomaceous earth microcapsules loaded with Bacillus spores, the concentration of the Bacillus spores is ≥10 8 CFU / g, capsule particle size 0.1-0.3mm.

[0011] Furthermore, the cement is silicate cement, and the strength grade of the cement is 42.5R.

[0012] Furthermore, the specific surface area of ​​the steel slag powder is ≥450m 2 / kg, CaO content ≤45%, and magnetic separation to remove iron to Fe2O3 content ≤3%.

[0013] Furthermore, the coarse aggregate is 5-15 mm continuously graded crushed stone, and the content of needle-like flake particles does not exceed 8%; the fine aggregate is medium sand with a fineness modulus of 2.6-3.0, a mud content of not more than 2%, and a mud block content of not more than 0.5%.

[0014] Furthermore, in the fiber reinforcement system, the steel fiber has a length of 12-15 mm and a diameter of 0.2-0.5 mm, and the sisal fiber has a length of 6-8 mm.

[0015] Furthermore, the sisal fiber is subjected to plasma grafting treatment, specifically comprising the following steps:

[0016] a pretreatment: The sisal fiber is placed in a vacuum chamber, evacuated to 5-10Pa, and then argon is introduced until the pressure returns to normal, and repeated three times;

[0017] b. Plasma activation: Apply radio frequency in an argon atmosphere with a power of 250-350W, a gas flow rate of 10-15 sccm, and a treatment time of 50-70s to generate active free radicals on the fiber surface;

[0018] c. Monomer grafting: The activated fibers were immersed in an 8-12% acrylate ethanol solution at a mass ratio of 1:15-20, and the mixture was stirred at a temperature of 40-60°C, a frequency of 28±2kHz, and a power density of 0.5-0.8W / cm 3 Ultrasonic oscillation for 20-40 min to induce free radical grafting reaction;

[0019] d. Post-treatment: After grafting, rinse with deionized water three times and cure in a vacuum drying oven at 50-70°C for 2-4 hours.

[0020] Furthermore, the preparation method of the diatomaceous earth microcapsules loaded with Bacillus comprises the following steps:

[0021] a. Diatomaceous earth pretreatment: diatomaceous earth particles with a particle size of 10-50 μm were immersed in a citric acid solution with a mass fraction of 5-8% at a ratio of 1:8-12 (g / mL), activated at 60-80 ° C for 1-2 h, filtered, and calcined at 550-600 ° C for 30-45 min to obtain a porous carrier;

[0022] b. Bacteria loading: The Bacillus spore suspension was mixed with pretreated diatomaceous earth at a mass ratio of 1:3-5, 0.1-0.3% trehalose was added as a protective agent, and adsorbed at pH 6.5-7.5 and 35-38 ° C for 2-4h;

[0023] c. Microcapsule coating: The diatomaceous earth loaded with bacteria is immersed in a 2-4% sodium alginate-chitosan composite aqueous solution with a mass ratio of sodium alginate to chitosan of 3-5:1. Microcapsules are formed by spray granulation. The inlet temperature is controlled at 120-140°C and the outlet temperature is 50-60°C. The particle size is screened to 0.1-0.3mm.

[0024] d. Curing treatment: Immerse the microcapsules in 0.5-1.5 mol / L calcium chloride solution for cross-linking for 20-40 minutes, and then irradiate with ultraviolet light at a wavelength of 254 nm and an intensity of 30-50 mJ / cm 2 Curing for 10-15 minutes.

[0025] Furthermore, a method for preparing high-frequency self-compacting concrete for foundation piers comprises the following steps:

[0026] S1. Weigh each component according to the volume per cubic meter;

[0027] S2. Put cement, fly ash, steel slag powder, coarse aggregate and fine aggregate into a mixer and dry mix at a speed of 120-180 r / min for 60-90 seconds;

[0028] S3. Mix the polycarboxylate water reducer and water evenly and add them into the mixer. Increase the stirring speed to 200-280r / min and stir for 120-150s.

[0029] S4, add fiber composition, calcium sulfoaluminate expansion agent and viscosity enhancer, continue stirring for 90-120s, finally add self-repairing component, continue stirring for 60-120s,

[0030] S5. Place the stirred concrete mixture on a high-frequency vibration table and vibrate for 3-5 minutes at a vibration frequency of 30-50 Hz and an amplitude of 0.5-1.5 mm to eliminate internal bubbles, thereby obtaining the high-frequency self-compacting concrete for the pier foundation.

[0031] Furthermore, the amount of water added in step S3 is 15-20% of the total mass of the concrete.

[0032] Furthermore, the application of high-frequency foundation pier self-compacting concrete in the construction of high-frequency foundation piers.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Excellent self-compacting properties and stability: The present invention precisely controls the ratio of cementitious materials, functional additives and fiber reinforcement system to control the yield stress of concrete to 0.5-1.0 MPa, maintain the plastic viscosity at 800-1200 mPa·s, achieve an initial expansion of more than 750 mm, a 2-hour expansion retention rate of over 95%, and a water bleeding rate of less than 0.8%.

[0035] (2) Significantly improved crack resistance: The use of a mixture of steel fiber and modified sisal fiber, and the plasma-grafted sisal fiber significantly improves the interfacial adhesion with the cement matrix, working with the steel fiber to bear the primary tensile stress. Under high-frequency vibration conditions, the number of concrete cracks is reduced, and the maximum crack width is controlled to around 0.15mm, significantly reducing the risk of structural cracking and improving load-bearing capacity and safety.

[0036] (3) Highly efficient self-repairing function: Diatomaceous earth microcapsules loaded with Bacillus spores act as self-repairing components. When cracks form, they rupture and release Bacillus spores. Through biomineralization, they induce calcium carbonate deposition, resulting in a crack healing rate of up to 52%. After healing, the crack's impermeability is increased to 1.2 MPa. Compared to traditional self-repairing technologies, this invention achieves autonomous crack repair, effectively preventing the intrusion of external corrosive media, extending the service life of the structure, and reducing maintenance costs. DETAILED DESCRIPTION

[0037] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0038] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0039] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0040] Example 1

[0041] High-frequency self-compacting concrete for foundation piers, the components used per cubic meter volume are:

[0042] (1) Cementitious materials: 320 kg of Portland cement (42.5R); 55 kg of Grade I fly ash; 20 kg of steel slag powder, with a specific surface area of ​​≥450 m 2 / kg, CaO content ≤45%, Fe2O3 content ≤3%;

[0043] (2) Aggregate: 800 kg of 5-15 mm crushed stone, with needle-like particles <8%; 750 kg of medium sand, with a fineness modulus of 2.6 and a mud content of 1.5%;

[0044] (3) Functional additives: 1 kg of polycarboxylate water reducer; 8 kg of calcium sulfoaluminate expansion agent; 0.001 kg of cellulose ether thickener, with a viscosity of 5000 mPa·s;

[0045] (4) Fiber reinforcement system: 9 kg steel fiber, 12 mm in length and 0.2 mm in diameter; 3 kg modified sisal fiber, 6 mm in length;

[0046] (5) Self-repair component: 2 kg of diatomaceous earth microcapsules loaded with Bacillus spores, with a bacterial concentration of ≥10 8 CFU / g, particle size 0.1mm.

[0047] Example 2

[0048] High-frequency self-compacting concrete for foundation piers, the components used per cubic meter volume are:

[0049] (1) Cementitious materials: 370 kg of Portland cement (42.5R); 70 kg of Grade I fly ash; 35 kg of steel slag powder, with a specific surface area of ​​≥ 450 m 2 / kg, CaO content ≤45%, Fe2O3 content ≤3%;

[0050] (2) Aggregate: 840 kg of 5-15 mm crushed stone, with needle-shaped particles <8%; 780 kg of medium sand, with a fineness modulus of 3.0 and a mud content of 1.5%;

[0051] (3) Functional additives: 3 kg of polycarboxylate water reducer; 14 kg of calcium sulfoaluminate expansion agent; 0.08 kg of cellulose ether thickener, with a viscosity of 15000 mPa·s;

[0052] (4) Fiber reinforcement system: 13 kg steel fiber, 15 mm in length, 0.5 mm in diameter; 6 kg modified sisal fiber, 8 mm in length;

[0053] (5) Self-repair component: 4 kg of diatomaceous earth microcapsules loaded with Bacillus spores, with a bacterial concentration of ≥10 8 CFU / g, particle size 0.3mm.

[0054] Example 3

[0055] High-frequency self-compacting concrete for foundation piers, the components used per cubic meter volume are:

[0056] (1) Cementitious materials: 350 kg of Portland cement (42.5R); 60 kg of Grade I fly ash; 30 kg of steel slag powder, with a specific surface area of ​​≥450 m 2 / kg, CaO content ≤45%, Fe2O3 content ≤3%;

[0057] (2) Aggregate: 820 kg of 5-15 mm crushed stone, with needle-shaped particles <8%; 770 kg of medium sand, with a fineness modulus of 2.8 and a mud content of 1.5%;

[0058] (3) Functional additives: 2 kg of polycarboxylate water reducer; 12 kg of calcium sulfoaluminate expansion agent; 0.02 kg of cellulose ether thickener, with a viscosity of 10,000 mPa·s;

[0059] (4) Fiber reinforcement system: 12 kg steel fiber, 13 mm in length, 0.3 mm in diameter; 5 kg modified sisal fiber, 7 mm in length;

[0060] (5) Self-repair component: 3 kg of diatomaceous earth microcapsules loaded with Bacillus spores, with a bacterial concentration of ≥10 8 CFU / g, particle size 0.2 mm;

[0061] The above examples 1-3 adopt the following preparation method:

[0062] (1) Sisal fiber modification:

[0063] a pretreatment: The sisal fiber was placed in a vacuum chamber, evacuated to 8Pa, and then argon was introduced until the pressure returned to normal, and repeated 3 times;

[0064] b. Plasma activation: Apply radio frequency in an argon atmosphere with a power of 300 W, a gas flow rate of 12 sccm, and a treatment time of 60 s to generate active free radicals on the fiber surface;

[0065] c. Monomer grafting: The activated fibers were immersed in a 10% acrylate ethanol solution at a mass ratio of 1:18 at a temperature of 50°C, a frequency of 28 kHz, and a power density of 0.7 W / cm 3Ultrasonic oscillation was performed for 30 min to induce free radical grafting reaction;

[0066] d. Post-treatment: After grafting, rinse with deionized water three times and cure in a vacuum drying oven at 60°C for 3 h.

[0067] (2) Diatomaceous earth microcapsules loaded with Bacillus:

[0068] a. Diatomaceous earth pretreatment: 30 μm diatomaceous earth particles were immersed in a 5-8% mass fraction of citric acid solution at a ratio of 1:10 (g / mL), activated at 70 ° C for 2 h, filtered, and calcined at 580 ° C for 40 min to obtain a porous support;

[0069] b. Bacteria loading: The Bacillus spore suspension was mixed with pretreated diatomaceous earth in a mass ratio of 1:4, 0.2% trehalose by mass of the suspension was added as a protective agent, and adsorption was carried out at pH 7 and 36°C for 3h;

[0070] c. Microcapsule Coating: The diatomaceous earth loaded with bacteria was immersed in a 3% sodium alginate-chitosan composite aqueous solution with a mass ratio of sodium alginate to chitosan of 4:1. Microcapsules were formed by spray granulation with the inlet temperature controlled at 130°C and the outlet temperature at 55°C. The particle size was screened to 0.2 mm.

[0071] d. Curing treatment: The microcapsules were immersed in 1 mol / L calcium chloride solution for cross-linking for 30 min, and then irradiated with ultraviolet light at a wavelength of 254 nm and an intensity of 40 mJ / cm 2 Curing for 12 minutes.

[0072] (3) Concrete preparation:

[0073] S1. Weigh each component according to the volume per cubic meter;

[0074] S2. Put cement, fly ash, steel slag powder, coarse aggregate and fine aggregate into a mixer and dry mix at a speed of 150 r / min for 70 seconds;

[0075] S3. Mix the polycarboxylate water reducer with 18% of the total mass of the concrete and add it to the mixer. Increase the stirring speed to 250 r / min and stir for 130 s.

[0076] S4: Add the fiber composition, calcium sulfoaluminate expansion agent and viscosity enhancer, continue stirring for 100 seconds, and finally add the self-repairing component and continue stirring for 80 seconds.

[0077] S5. The stirred concrete mixture is placed on a high-frequency vibration table and vibrated for 4 minutes at a vibration frequency of 40 Hz and an amplitude of 1 mm to eliminate internal bubbles, thereby obtaining the high-frequency self-compacting concrete for the pier foundation.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 3 is that the sisal fiber is not plasma-treated and is used directly. The raw material ratio and preparation method are the same as those in Example 3.

[0080] Comparative Example 2

[0081] The difference between this comparative example and Example 3 is that the mixed composition of steel fiber and modified sisal fiber is 28 kg.

[0082] Comparative Example 3

[0083] The difference between this comparative example and Example 3 is that no calcium sulfoaluminate expansion agent is added, and the other component proportions and preparation methods are the same as those in Example 3.

[0084] Comparative Example 4

[0085] The difference between this comparative example and Example 3 is that no self-repairing component is added, and the proportions of other components and the preparation method are the same as those in Example 3.

[0086] Comparative Example 5

[0087] The difference between this comparative example and Example 3 is that the diatomaceous earth loaded with Bacillus spores is not microencapsulated, specifically:

[0088] a. Diatomaceous earth pretreatment: 30 μm diatomaceous earth particles were immersed in a 5-8% mass fraction of citric acid solution at a ratio of 1:10 (g / mL), activated at 70 ° C for 2 h, filtered, and calcined at 580 ° C for 40 min to obtain a porous support;

[0089] b. Bacteria loading: The Bacillus spore suspension was mixed with pretreated diatomaceous earth in a mass ratio of 1:4, 0.2% trehalose by mass of the suspension was added as a protective agent, and adsorption was carried out at pH 7 and 36°C for 3h;

[0090] c. Curing treatment: The loaded diatomaceous earth was immersed in 1 mol / L calcium chloride solution for cross-linking for 30 minutes, and then irradiated with ultraviolet light at a wavelength of 254 nm and an intensity of 40 mJ / cm 2 Curing for 12 minutes.

[0091] Comparative Example 6

[0092] The difference between this comparative example and Example 3 is that the vibration frequency in step S5 is 20 Hz and the amplitude is 2 mm.

[0093] The concretes prepared in Examples 1-3 and Comparative Examples 1-6 were tested:

[0094] Test Example 1-Working Performance Test

[0095] 1. Slump expansion: According to GB / T50080-2016, the expansion diameter at the beginning and after 2 hours is measured;

[0096] 2. Bleeding rate: According to GB / T50080 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the mixture is placed in a 5L transparent cylinder, left to stand for 24 hours, and the surface water is collected to calculate the bleeding rate; Bleeding rate (%) = V w / W×100%

[0097] Where:

[0098] V w : Volume of exuded water (mL)

[0099] W: Total water content in concrete mixture (mL)

[0100] 3. Test results

[0101]

[0102] Conclusion: The initial expansion of the embodiment group is ≥750mm, the expansion after 2 hours is maintained at 725-730mm, and the time loss rate is only 3.0%-3.3%, which is significantly better than comparative examples 1-3 and 6. This shows that the present invention effectively suppresses the time-dependent attenuation of the fluidity of the mixture through the synergistic effect of the fiber hybrid system and the functional additives, ensuring that the concrete can still maintain excellent self-compacting properties during high-frequency pier construction.

[0103] The sisal fiber of comparative example 1 was not modified. Due to its low surface activity and poor dispersibility, it was proved that the plasma grafting modification process played a key role in improving the interfacial adhesion between the fiber and the slurry and constructing a stable three-dimensional network structure.

[0104] The total fiber content of Comparative Example 2 exceeded the limit, and the viscosity of the slurry increased abnormally due to fiber agglomeration, and the water bleeding rate significantly exceeded the standard, which shows that the fiber content of the present invention is reasonable;

[0105] Comparative Example 3 lacks the calcium sulfoaluminate expansion agent. The expansion agent of the present invention forms a three-dimensional network structure with the fiber composition, which effectively improves the volume stability of the slurry and reduces the necessity of moisture migration.

[0106] Test Example 2-Mechanical Properties Test

[0107] 1.28-day compressive strength: According to GB / T50081 "Standard for Test Methods for Physical and Mechanical Properties of Concrete", 150mm×150mm×150mm specimens were made and the compressive strength was tested after 28 days of standard curing.

[0108] 2. Flexural strength: As above, make a 150mm×150mm×600mm specimen and test the flexural strength.

[0109] 3. Test results

[0110]

[0111] Conclusion: In Comparative Example 1, because the sisal fibers were not plasma-grafted, the surface hydrophilic groups resulted in a weak layer at the fiber-slurry interface. This made it easy for the fibers to pull out or slip under load, resulting in a decrease in both compressive and flexural strengths. This indicates that the fiber modification process of the present invention effectively improves interfacial bonding strength by introducing active groups.

[0112] In Comparative Example 2, increasing the total fiber content resulted in uneven fiber dispersion, local agglomeration, and increased internal porosity, indicating the preferred ratio of the total fiber content of the present invention.

[0113] Comparative Example 6 uses low-frequency, high-amplitude vibration, which results in inadequate expulsion of bubbles from the concrete, reduced density, and uneven fiber distribution, leading to reduced compressive strength. The high-frequency vibration parameters of Example 3 result in more uniform aggregate distribution and increased slurry density, significantly enhancing mechanical properties.

[0114] Test Example 3-Crack Resistance Test

[0115] 1. High-frequency vibration crack test: Place the specimen on a vibration table (frequency 40 Hz, amplitude 1 mm) and vibrate for 24 hours. Record the number of cracks and the maximum width (a crack width ≤ 0.2 mm is considered to meet the crack resistance standard).

[0116] 2. Plastic shrinkage cracks: Use the flat plate method (1000mm×1000mm×100mm specimen) and maintain it in a constant temperature and humidity chamber (temperature 20±2℃, humidity 60±5%) for 24 hours to observe the number and length of surface cracks.

[0117] 3. Test results

[0118]

[0119] Conclusion: Example 3 has only one crack, the maximum crack width is 0.15 mm, and the total crack length is 135 mm, which is significantly better than Comparative Examples 1, 2, and 6.

[0120] In Comparative Example 1, since the sisal fiber was not plasma grafted, the surface lacked active groups and the interfacial bonding with the cement matrix was weak, resulting in easy slippage of the fiber under load or vibration, forming stress concentration points and a 6-fold increase in the number of cracks.

[0121] In Comparative Example 2, the fibers were too dense, resulting in poor fiber dispersion and reduced crack resistance;

[0122] In Comparative Example 6, due to insufficient vibration energy, bubbles remained inside the concrete and the aggregate was unevenly distributed, forming initial defect sites and the number of cracks increased to 8.

[0123] Test Example 4-Rheological Properties Test

[0124] According to ASTM C1749-17 "Standard Test Method for Rheological Properties of Concrete"

[0125] 1. Sample preparation: Take 600g of fresh concrete, let it stand for 1 minute to defoam, and then test it immediately (ambient temperature 23±2℃).

[0126] 2. Test method: Use a rotational rheometer and test according to the following steps:

[0127] Take fresh concrete paste (pass through a 5mm sieve to remove coarse aggregate) and put it into the test cylinder;

[0128] Set the shear rate to increase linearly from 0 to 100s -1 (3 min), then reduced to 0 (3 min), and the shear stress-shear rate curve was recorded;

[0129] 3. Parameter calculation: By fitting the curve using the Bingham model (τ = τ0 + ηγ), we get:

[0130] Yield stress (τ0): the minimum stress required for concrete to begin to flow (unit: MPa);

[0131] Plastic viscosity (η): The ability to resist shear deformation during flow (unit: mPa·s).

[0132] 4. Test Results

[0133]

[0134] Conclusion: Examples 1-3 are all controlled at 0.68-0.82 MPa, which is in the core range of low yield stress of self-compacting concrete, ensuring that the mixture can flow freely under its own weight (extension 750-755 mm), meeting the filling requirements of complex steel bar gaps in high-frequency piers.

[0135] In Comparative Example 1, the hydrophilic groups on the fiber surface were not activated, resulting in weak adhesion to the slurry interface, requiring higher stress to flow, and the high viscosity resulted in reduced construction performance.

[0136] The poor dispersion of the fibers in Comparative Example 2 leads to local stress concentration, resulting in an increase in yield stress.

[0137] In Comparative Example 3, due to the lack of ettringite crystals to fill the pores, the slurry's ability to wrap the aggregate is reduced and the plastic viscosity is poor.

[0138] Test Example 5-Self-repair effect test

[0139] 1. Crack self-healing rate: Artificially induce a 0.2 mm wide crack and place it in a humid environment (humidity ≥ 90%) for 28 days. The proportion of the crack healed area is observed under a microscope (healing rate = healed area / initial crack area × 100%).

[0140] 2. Test results

[0141]

[0142]

[0143] Conclusion: The Bacillus-loaded diatomaceous earth microcapsules of this invention achieve autonomous crack repair through the active metabolism of microorganisms. The Bacillus, which produces calcium carbonate, is encapsulated in the microcapsules and evenly dispersed within building materials such as concrete. When the material is subjected to external forces and cracks form, the microcapsules rupture and release the Bacillus. These come into contact with moisture, oxygen, and nutrients in the cracks. Under suitable conditions, the microorganisms activate and metabolize to produce calcium carbonate, leading to biomineralization that fills the cracks and restores the material's properties.

[0144] Comparative Example 4 lacked self-repairing properties due to the lack of a self-repairing component. While Comparative Example 5 used diatomaceous earth loaded with Bacillus spores but lacked microencapsulation, its healing rate and impermeability were significantly lower than those of Example 3. This was because the uncoated diatomaceous earth was easily damaged during concrete mixing, prematurely exposing the Bacillus spores to an alkaline environment and causing their inactivation. Furthermore, the lack of protection from the microcapsule wall prevented precise control of nutrient release, significantly reducing repair efficiency.

[0145] The present invention effectively protects the activity of Bacillus through microcapsule structure design and preparation process, and realizes the precise release and efficient utilization of the repair agent, so that the concrete has excellent self-repair performance.

[0146] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-frequency self-compacting concrete for foundation piers, characterized by: The following components are included in the amounts per cubic meter of volume: Cementitious material system: cement 320-370kg, grade I fly ash 55-70kg, steel slag powder 20-35kg; Aggregate system: coarse aggregate 800-840kg, fine aggregate 750-780kg; Functional additives: polycarboxylate water reducer 1-3kg, calcium sulfoaluminate expander 8-14kg, cellulose ether thickener 0.001-0.08kg, viscosity 5000-15000mPa·s; Fiber reinforcement system: 12-19 kg of a mixed composition of steel fiber and modified sisal fiber, wherein the mass ratio of steel fiber to modified sisal fiber is (9-13):(3-6), and the modified sisal fiber is prepared by plasma grafting sisal fiber; Self-repair component: 2-4 kg of diatomaceous earth microcapsules loaded with Bacillus spores, the concentration of the Bacillus spores is ≥10 8 CFU / g, capsule particle size 0.1-0.3mm.

2. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The cement is silicate cement, and the strength grade of the cement is 42.5R.

3. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The specific surface area of ​​the steel slag powder is ≥450m 2 / kg, CaO content ≤45%, and magnetic separation to remove iron to Fe2O3 content ≤3%.

4. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The coarse aggregate is 5-15 mm continuously graded crushed stone, and the content of needle-shaped flake particles does not exceed 8%; the fine aggregate is medium sand with a fineness modulus of 2.6-3.0, a mud content of not more than 2%, and a mud block content of not more than 0.5%.

5. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The steel fiber in the fiber reinforcement system has a length of 12-15 mm and a diameter of 0.2-0.5 mm, and the sisal fiber has a length of 6-8 mm.

6. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The sisal fiber is subjected to plasma grafting treatment, which specifically comprises the following steps: a pretreatment: The sisal fiber is placed in a vacuum chamber, evacuated to 5-10Pa, and then argon is introduced until the pressure returns to normal, and repeated three times; b. Plasma activation: applying radio frequency in an argon atmosphere, the radio frequency power is 250-350W, the gas flow rate is 10-15sccm, and the processing time is 50-70s; c. Monomer grafting: The activated fibers were immersed in an 8-12% acrylate ethanol solution at a mass ratio of 1:15-20, and the mixture was stirred at a temperature of 40-60°C, a frequency of 28±2kHz, and a power density of 0.5-0.8W / cm 3 Ultrasonic oscillation for 20-40 min to induce free radical grafting reaction; d. Post-treatment: After grafting, rinse with deionized water three times and cure in a vacuum drying oven at 50-70°C for 2-4 hours.

7. The high-frequency self-compacting concrete for foundation piers according to claim 1, characterized in that: The preparation method of the diatomaceous earth microcapsules loaded with Bacillus comprises the following steps: a. Diatomaceous earth pretreatment: diatomaceous earth particles with a particle size of 10-50 μm were immersed in a citric acid solution with a mass fraction of 5-8% at a ratio of 1:8-12 (g / mL), activated at 60-80 ° C for 1-2 h, filtered, and calcined at 550-600 ° C for 30-45 min to obtain a porous carrier; b. Bacteria loading: The Bacillus spore suspension was mixed with pretreated diatomaceous earth at a mass ratio of 1:3-5, 0.1-0.3% trehalose was added as a protective agent, and adsorbed at pH 6.5-7.5 and 35-38 ° C for 2-4h; c. Microcapsule coating: The diatomaceous earth loaded with bacteria is immersed in a 2-4% sodium alginate-chitosan composite aqueous solution with a mass ratio of sodium alginate to chitosan of 3-5:

1. Microcapsules are formed by spray granulation. The inlet temperature is controlled at 120-140°C and the outlet temperature is 50-60°C. The particle size is screened to 0.1-0.3mm. d. Curing treatment: Immerse the microcapsules in 0.5-1.5 mol / L calcium chloride solution for cross-linking for 20-40 minutes, and then irradiate with ultraviolet light at a wavelength of 254 nm and an intensity of 30-50 mJ / cm 2 Curing for 10-15 minutes.

8. The method for preparing high-frequency self-compacting concrete for foundation piers according to claim 1, wherein: The following steps are involved: S1. Weigh each component according to the volume per cubic meter; S2. Put cement, fly ash, steel slag powder, coarse aggregate and fine aggregate into a mixer and dry mix at a speed of 120-180 r / min for 60-90 s; S3. Mix the polycarboxylate water reducer with 15-20% of the total mass of the concrete and add it to the mixer. Increase the stirring speed to 200-280r / min and stir for 120-150s. S4, add fiber composition, calcium sulfoaluminate expansion agent and viscosity enhancer, continue stirring for 90-120s, finally add self-repairing component, continue stirring for 60-120s, S5. Place the stirred concrete mixture on a high-frequency vibration table and vibrate for 3-5 minutes at a vibration frequency of 30-50 Hz and an amplitude of 0.5-1.5 mm to eliminate internal bubbles, thereby obtaining the high-frequency self-compacting concrete for the pier foundation.

9. The method for preparing high-frequency self-compacting concrete for a foundation pier according to claim 8, characterized in that: The amount of water added in step S3 is 15-20% of the total mass of the concrete.

10. Use of the high-frequency foundation pier self-compacting concrete according to any one of claims 1 to 7 in the construction of high-frequency foundation piers.

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