High-strength concrete and preparation method thereof

Abstract

The invention relates to the field of concrete, and provides high-strength concrete and a preparation method thereof, and the high-strength concrete comprises modified basalt chopped fiber, a self-repairing agent, cement, fly ash, slag powder, coarse aggregate, natural sand, a water reducing agent and an air entraining agent. The modified basalt chopped fiber is oxidized by hydrogen peroxide, etched by hydrochloric acid and modified by a nano silicon dioxide coating, so that the interface bonding force is enhanced. The self-repairing agent is prepared by adopting expanded perlite to load bacillus through thallus culture, purification, dipping adsorption and low-temperature vacuum drying, CaCO3 deposition can be induced at concrete cracks, and self-repairing is achieved. The invention further provides a preparation method of the concrete. The preparation method comprises the steps of aggregate screening, hydrated liquid preparation, wet mixing, fiber and self-repairing agent adding, vibration forming and curing. The crack resistance of the concrete is improved by enhancing the fiber-matrix interface bonding force, meanwhile, the service life of the concrete is prolonged by utilizing a biological self-repairing technology, and the concrete is suitable for high-durability concrete engineering.

Description

Technical Field

[0001] The present invention relates to the field of concrete, and particularly to a high-strength concrete and a preparation method thereof. Background Art

[0002] In modern infrastructure construction, high-strength concrete is widely used in key fields such as high-rise buildings, bridges, tunnels, and ocean engineering due to its excellent mechanical properties and durability. These engineering structures usually bear complex load conditions, such as heavy load impact, long-term fatigue, extreme temperature changes, and the action of erosive media. Therefore, extremely high requirements are put forward for the mechanical strength, crack resistance, and environmental adaptability of concrete. High-strength concrete not only needs to have high compressive strength to withstand super-large loads, but also needs to have excellent tensile properties to inhibit the generation and expansion of cracks. In addition, since concrete will inevitably be affected by micro-cracks during service, the expansion of cracks may lead to a decline in the overall performance of the structure and even affect safety. Therefore, high-strength concrete with self-healing ability has become the focus of research. The self-healing ability can automatically close the cracks through the self-repair mechanism inside the material, such as chemical reactions to generate fillers or microbial-induced deposition, after the cracks appear, thereby improving the durability and service life of concrete. By improving the strength and self-healing ability of concrete, not only can the maintenance cost be reduced and the engineering life be extended, but also the safety and stability of the structure can be improved, which is of great significance for promoting the development of modern civil engineering and infrastructure construction. Therefore, researching a concrete material with both high strength and self-healing ability is crucial for meeting the development needs of future high-performance concrete.

[0003] At present, high-strength concrete still faces some technical bottlenecks in engineering applications, especially in terms of balancing high strength and self-healing characteristics. For example, Chinese Patent No. CN107151115A discloses a high-strength concrete, which achieves relatively high compressive strength by optimizing the aggregate gradation and cementitious material composition, but lacks an effective self-healing mechanism and cannot self-repair after cracks occur, resulting in insufficient durability. In addition, some studies have tried to introduce self-repairing materials into concrete, such as microcapsule-based self-repairing systems or microbial-induced deposition systems. For example, Chinese Patent No. CN103739223A discloses a preparation method of a slow-release microcapsule-based concrete admixture, which realizes self-repair through microcapsules, but its mechanical properties are not significantly improved compared with ordinary concrete and it is difficult to meet the requirements of high-strength structures. The reasons are as follows: on the one hand, current high-strength concrete mostly relies on high cement consumption and high-density design, which may reduce the permeability of cracks and thus affect the transmission and reaction efficiency of self-repairing materials in cracks; on the other hand, existing self-healing technologies often face problems such as low repair efficiency, long repair time, and poor environmental adaptability, and it is difficult to play a long-term stable role in harsh engineering environments. Therefore, there is an urgent need to develop a concrete material with both high strength and high self-healing ability, which can achieve rapid self-repair of cracks while ensuring mechanical properties to meet the application requirements of future high-performance concrete in complex engineering environments. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of the present invention is to provide a high-strength concrete and its preparation method to solve the problems of insufficient strength and self-healing performance of current concrete.

[0006] (2) Technical solutions

[0007] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0008] A high-strength concrete comprises the following raw materials in parts by weight: 1.5 - 3.5 parts of modified basalt chopped fibers, 2.5 - 3.5 parts of self-repairing agent, 100 - 120 parts of P·II 52.5 cement, 80 - 100 parts of secondary fly ash, 30 - 40 parts of slag fly ash, 180 - 200 parts of water, 622 - 796 parts of basalt coarse aggregate, 750 - 900 parts of natural sand, 9.0 - 14.0 parts of polycarboxylate-based water reducer, and 0.5 - 3.0 parts of rosin-based air-entraining agent.

[0009] The modified basalt chopped fibers are obtained by subjecting basalt chopped fibers to surface oxidation treatment, acid etching treatment, and nano-silica modification treatment;

[0010] The self-repairing agent described above is a composite material obtained by a process of culturing bacteria, centrifugal purification, impregnation adsorption, and low-temperature vacuum drying, with Bacillus bacteria loaded on the surface of expanded perlite particles.

[0011] Furthermore, the preparation method of the self-repairing agent includes the following steps: Dissolve beef extract, peptone, and sodium chloride in deionized water to prepare a nutrient solution, adjust the pH to 9.5 - 10.0 with sodium bicarbonate solution to form an alkaline nutrient solution, inoculate Bacillus bacteria and perform shaking culture to obtain a bacterial solution, and after centrifugal separation, wash and purify the bacteria with a buffer solution to obtain a bacterial suspension; then immerse expanded perlite particles in the bacterial suspension, filter, and finally form a self-repairing agent with a microbial loading layer after vacuum drying treatment.

[0012] Furthermore, the nutrient solution includes 4.0 - 6.0 g / L of beef extract, 10.0 - 12.0 g / L of peptone, 5.0 - 15.0 g / L of glucose, 4.0 - 5.0 g / L of sodium chloride, 1.0 - 3.0 g / L of potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 0.5 - 1.0 g / L of magnesium sulfate heptahydrate.

[0013] Furthermore, the preparation process of the bacterial suspension includes: Inoculate 0.5 - 1.5 parts of Bacillus bacteria into 120 - 150 parts of alkaline nutrient solution, perform constant-temperature shaking culture at 28 - 32 °C and 110 - 130 rpm for 4 - 8 h, then centrifuge at 5500 - 6500 rpm for 4 - 6 min, discard the supernatant, add a sufficient amount of phosphate buffer solution with pH 7.2 - 7.6 to resuspend the bacteria, repeat centrifugation and washing 2 - 3 times to purify the bacteria, and finally dilute the purified bacteria with 30 - 50 parts of sterile water to a cell concentration of 3.2×10 9 ~4.0×10 9 cells / mL to obtain a bacterial suspension, and store it refrigerated at 2 - 6 °C.

[0014] Furthermore, the specific process of impregnation and low-temperature vacuum drying is as follows: Immerse 10 - 15 parts of expanded perlite particles with a particle size of 0.1 - 0.5 mm in the bacterial suspension for 20 - 28 h, filter, and then dry at 38 - 42 °C and 10 - 20 kPa vacuum for 45 - 60 min, control the thickness of the microbial loading layer on the particle surface to be 50 - 80 μm, and the final moisture content of the self-repairing agent ≤ 2.5%, where the viable cell density of Bacillus bacteria in the microbial loading layer is 3.0 - 6.5×108 CFU / g.

[0015] The self - repair agent designed in the present invention is mainly used to enhance the self - repair performance of concrete. The self - repair agent is prepared through processes such as bacterial culture, centrifugal purification, impregnation adsorption, and low - temperature vacuum drying, enabling Bacillus spores to be stably loaded on the surface of expanded perlite particles to ensure their long - term activity inside the concrete and rapidly activating the repair mechanism after cracks form. By optimizing the nutrient solution formula, including beef extract, peptone, glucose, sodium chloride, and a phosphate buffer system, a suitable alkaline environment is provided to promote the proliferation of Bacillus and maintain its metabolic activity, thereby ensuring that the bacteria have good bioremediation capabilities before entering the concrete. During the preparation of the bacterial suspension, the bacteria are purified by centrifugal washing multiple times and resuspended with phosphate buffer to improve the survival rate and stability of the bacteria, while ensuring the activity and concentration of the final bacterial suspension so that it can effectively play a repair function in the concrete. Subsequently, expanded perlite is used as a carrier, and through the impregnation adsorption process, high - concentration bacteria are evenly loaded on the particle surface. Then, the thickness of the microbial load layer is controlled by low - temperature vacuum drying to ensure a sufficient viable bacteria density and reduce the moisture content of the self - repair agent, thereby improving storage stability and durability during service. Inside the concrete, the self - repair agent can activate Bacillus under the stimulation of moisture and nutrients at the crack, causing it to metabolize and produce CaCO3 deposition to fill the crack and achieve the self - repair function. By reasonably designing the particle size range of expanded perlite and the thickness of the bacterial load layer, the self - repair agent has good dispersibility in the concrete matrix and can rapidly release active bacteria after cracks form, improving the repair efficiency. Overall, the self - repair agent designed in the present invention can not only achieve efficient self - repair at concrete cracks but also has a long storage life and stable repair performance, ensuring the long - term durability and structural integrity of concrete in complex service environments.

[0016] Further, the preparation method of the modified basalt short - cut fibers includes the following steps: First, the basalt fibers are subjected to dynamic oxidation treatment with hydrogen peroxide solution, and then etched with hydrochloric acid to obtain a porous surface structure. Subsequently, a nano - silica suspension is prepared, and ultrasonic - assisted impregnation combined with vacuum drying is used to form a nano - silica coating on the surface of the basalt short - cut fibers to obtain the modified basalt short - cut fibers.

[0017] Further, the average length of the modified basalt short - cut fibers is 6.0 - 12.0 mm, and the average diameter is 10.0 - 20 μm.

[0018] Further, the detailed processes of the dynamic oxidation treatment and hydrochloric acid etching are as follows: by weight, first immerse 50-70 parts of chopped basalt fibers in 80-120 parts of 4.5-5.5 wt% hydrogen peroxide solution, perform oscillation treatment at 25-35°C and 200-300 rpm for 1.5-2.5 h to complete surface oxidation, then wash with deionized water until the conductivity ≤ 50 μS / cm and vacuum dry at 55-65°C for 1.5-2.5 h; then immerse the treated fibers in 0.8-1.2 mol / L hydrochloric acid solution, dynamically etch at 40-50°C for 80-100 min, rinse to neutrality and dry with hot air to obtain acid-etched fibers.

[0019] Further, the preparation method of the nano-silica suspension is as follows: by weight, disperse 1.2-1.8 parts of silane coupling agent KH-550 in 180-220 parts of 90-95 wt% ethanol aqueous solution, stir at 500-700 rpm for 25-35 min, then add 5.5-6.5 parts of nano-silica particles and continuously disperse for 40-60 min to obtain the nano-silica suspension.

[0020] Further, the detailed process of the ultrasonic-assisted impregnation combined with vacuum drying is as follows: immerse the acid-etched fibers in the nano-silica suspension, perform ultrasonic impregnation at 40-60 kHz for 25-35 min and vacuum dry at 50-70°C for 120-160 min to form a nano-silica coating with a thickness of 90-120 nm on the surface of the chopped basalt fibers, and obtain modified chopped basalt fibers.

[0021] Further, the preparation method of the nano-silica is as follows: by weight, put 50.0-70.0 parts of sodium silicate and 100.0-150.0 parts of deionized water into a polytetrafluoroethylene reaction kettle, mechanically stir at 200-300 rpm for 10-15 min to form a homogeneous solution, then dropwise add 30.0-50.0 parts of 1.0-2.0 mol / L hydrochloric acid solution, control the dropping rate at 0.5-1.0 mL / min, simultaneously maintain the system pH at 2.0-3.0, after dropping, raise the temperature to 70-80°C and raise the temperature at a rate of 2-3°C / min, age at 80-90°C for 2.0-3.0 h, then add 1.5-2.5 parts of polyethylene glycol-6000 surfactant and perform high-speed shear dispersion at 500-700 rpm for 20-30 min to form a sol, transfer the sol to a vacuum drying oven and dry at a negative pressure of 25-35 kPa and 60-70°C for 4.0-6.0 h, grind the obtained gel with an agate mortar and then place it in a muffle furnace, program the temperature rise at a rate of 5-8°C / min to 550-650°C, and keep the temperature for calcination for 3.0-4.0 h, finally obtain nano-silica with a specific surface area of 200-300 m 2 / g and an average particle size of 50-80 nm.

[0022] The design of the present invention using modified basalt chopped fibers is mainly used to enhance the mechanical properties and interfacial bonding ability of concrete. By precisely controlling the surface structure and chemical composition of the fibers, the compatibility with the cement matrix is improved, thereby optimizing the overall mechanical properties and durability of the concrete. First, the basalt chopped fibers are dynamically oxidized with hydrogen peroxide solution to destroy part of the amorphous phase on the fiber surface, increase the surface roughness, and introduce polar functional groups, thereby improving the hydrophilicity of the fibers and the wettability of the cement paste. Subsequently, the microstructure of the fibers is further regulated by hydrochloric acid etching to remove surface impurities and form a porous structure, enabling the fibers to have a larger specific surface area and increasing the mechanical bite force with the cement matrix. The fibers after oxidation and acid etching not only have increased surface energy but also can enhance the interfacial bonding strength between the fibers and the cement matrix, reduce interfacial defects, and improve the tensile and flexural strengths of the composite material. In order to further enhance the pozzolanic activity of the fibers and the interfacial interaction with the cement hydration products, a nano-silica coating is introduced on the fiber surface. The nano-silica is synthesized by the sol-gel method, and key parameters such as pH, dropping rate, and aging temperature are controlled to ensure its high specific surface area and uniform nano-particle size. Subsequently, a nano-silica suspension is prepared, and through ultrasonic-assisted impregnation combined with vacuum drying process, the nano-silica is uniformly deposited on the surface of the basalt chopped fibers to form a dense and stable coating. This coating can not only improve the pozzolanic activity of the fibers, react with Ca 2 + and OH- in the cement hydration solution in an alkaline environment to generate secondary C-S-H and improve the interfacial bonding strength, but also optimize the charge distribution on the fiber surface and improve the dispersion of the fibers in the cement matrix. At the same time, the presence of the nano-silica coating can promote the deposition of hydration products at the cracks, improve the crack resistance of the concrete, and enhance the crack healing ability. Experiments show that the modified basalt chopped fibers can effectively improve the interfacial bonding performance of the concrete, increase the mechanical strength, and optimize the microstructure of the material, thereby significantly enhancing the durability and crack resistance of the concrete. Through the synergistic effect of oxidation, acid etching, and nano-silica modification technologies, the present invention realizes the enhanced bonding between the fibers and the cement matrix, providing an efficient and feasible reinforcement solution for the preparation of high-performance concrete.

[0023] The present invention also discloses a method for preparing high-strength concrete, comprising the following steps:

[0024] S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 5 - 20 mm, and the particle size of the natural sand is controlled at 0.2 - 2.5 mm. After screening, reserve them. Add P·II 52.5 cement, secondary fly ash and slag fly ash into a mixer according to the ratio, and stir at a low speed of 60 - 100 rpm for 5 - 10 min to make them evenly mixed. Separately take water, add a polycarboxylate superplasticizer and a rosin air-entraining agent in sequence, and stir at 300 - 500 rpm for 4 - 8 min until the solution is clear and there are no obvious bubbles to obtain a hydration solution;

[0025] S2. Add the pretreated basalt coarse aggregate and natural sand into a mixer according to the ratio, stir at a medium speed of 100 - 150 rpm for 1 - 2 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 30 - 60 s, and continue to stir for 3 - 5 min to form a uniform wet-mixed mixture;

[0026] S3. During the wet mixing process, gradually add modified basalt chopped fibers, increase the stirring speed to 150 - 200 rpm, and continuously stir for 20 - 30 min to ensure the uniform dispersion of the fibers. Then slowly add a self-repairing agent and continue to stir for 2 - 4 min to make it evenly distributed. Finally, adjust the stirring speed to 200 - 300 rpm and continuously stir for 4 - 6 min to form a homogeneous concrete mixture, and let it stand for 2 - 5 min to eliminate bubbles;

[0027] S4. Pour the mixed concrete into a mold, vibrate it on a vibrating table at 50 - 100 Hz for 30 - 60 s to complete the molding; the molded specimens are cured in an environment of 20 - 25 °C and relative humidity ≥ 90% for 24 - 36 h. After demolding, continue to cure under standard conditions of 20 - 25 °C and relative humidity ≥ 95% for 10 - 15 days.

[0028] The preparation method of the present invention using high-strength concrete is mainly designed to enhance the mechanical properties and durability of concrete. By reasonably screening basalt coarse aggregate and natural sand, the aggregate gradation is optimized, thereby improving the compactness and compressive performance of concrete. At the same time, the compounding of P·II52.5 cement, secondary fly ash and slag fly ash optimizes the cementitious material system, improves the uniformity of the hydration reaction and the development of later strength. During the preparation process of the hydration liquid, the addition of polycarboxylate superplasticizer effectively reduces the mixing water consumption and improves the fluidity of concrete, while the appropriate introduction of rosin-type air-entraining agent helps to form uniformly distributed tiny air bubbles and improve the freeze-thaw resistance. In the wet mixing stage, by controlling the mixing speed and the liquid addition sequence, the aggregate and the hydration liquid are fully contacted and uniformly wrapped, improving the bonding effect of the paste. On this basis, modified basalt short fibers are gradually introduced, and by increasing the mixing speed, the uniform dispersion of the fibers is ensured, enhancing the crack resistance and toughness of concrete. Subsequently, the self-repair agent is added and uniformly distributed in the concrete matrix, providing guarantee for subsequent crack self-repair. Finally, by precisely controlling the mixing speed and time, the concrete mixture reaches a high degree of homogenization, and the air bubbles are eliminated during the static stage, improving the forming quality. During the vibration forming and standard curing processes, the reasonable vibration compaction frequency ensures the dense internal structure of concrete, optimizes the mechanical properties, and the strictly controlled humidity and temperature conditions further promote the full progress of the hydration reaction, improving the early strength and long-term durability. Generally speaking, through optimizing the aggregate gradation, cementitious material system, admixture ratio, fiber reinforcement and self-repair mechanism, the present invention realizes the high strength, high toughness and self-repair performance of concrete, providing an efficient preparation scheme for durable concrete in complex engineering environments.

[0029] (3) Beneficial technical effects

[0030] 1. By optimizing the preparation process of the self-repair agent, the present invention realizes the stable loading of bacteria on expanded perlite, ensuring their long-term survival inside the concrete and being rapidly activated after the formation of cracks. The bacteria metabolize to produce CaCO3 deposition, filling the cracks and improving the durability of concrete. The phosphate buffer system maintains the activity of the bacteria, and low-temperature vacuum drying controls the thickness of the loading layer, enhancing the storage stability. The synergistic effect of each component optimizes the repair efficiency, which is superior to traditional repair technologies and shows excellent performance in complex engineering environments.

[0031] 2. By oxidizing, acid etching and modifying basalt short fibers with nano-silica, the present invention improves the interfacial bonding force between the fibers and the cement matrix, optimizing the mechanical properties and durability. The nano-silica coating enhances the pozzolanic activity, promotes the formation of hydration products, improves the crack resistance and self-healing ability. The synergistic effect of each component optimizes the microstructure, reduces the interfacial defects, which is superior to traditional strengthening technologies and shows better strength, durability and construction adaptability in the application of high-performance concrete.

[0032] 3. The present invention realizes high strength, high toughness and self - healing ability by optimizing the aggregate gradation, cementitious material system, admixture ratio, fiber reinforcement and self - repair mechanism, which is superior to the traditional concrete preparation method. The modified basalt short - cut fibers enhance the crack - resistance performance, the polycarboxylate - based water - reducing agent improves the fluidity, the rosin - type air - entraining agent enhances the freeze - thaw resistance ability, and the self - repair agent ensures the self - repair of cracks. The synergistic effect of each component optimizes the interfacial bonding, improves the durability, meets the requirements of complex engineering environments, and promotes the development of the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The surface morphology of the basalt short - cut fibers prepared in Example 1 of the present invention.

[0034] Figure 2 The surface morphology of the modified basalt short - cut fibers prepared in Example 1 of the present invention.

[0035] Figure 3 The morphology of the original crack and the crack after 10 days of the high - strength concrete prepared in Example 1 of the present invention.

[0036] Figure 4 The fracture morphology of the modified basalt short - cut fibers prepared in Example 1 of the present invention.

[0037] Figure 5 The fracture morphology of the modified basalt short - cut fibers prepared in Comparative Example 9 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] Example 1

[0040] A kind of high - strength concrete, comprising the following raw materials in parts by weight: 1.5 parts of modified basalt short - cut fibers, 2.5 parts of self - repair agent, 100 parts of P·II 52.5 cement, 80 parts of secondary fly ash, 30 parts of slag fly ash, 180 parts of water, 622 parts of basalt coarse aggregate, 750 parts of natural sand, 9.0 parts of polycarboxylate - based water - reducing agent, and 0.5 part of rosin - type air - entraining agent.

[0041] The modified basalt short - cut fibers are obtained by subjecting basalt short - cut fibers to surface oxidation treatment, acid etching treatment and nano - silica modification treatment; the self - repair agent is a composite material obtained by subjecting bacillus thuringiensis cells loaded on the surface of expanded perlite particles through processes of bacterial body culture, centrifugal purification, impregnation adsorption and low - temperature vacuum drying.

[0042] Preparation method of self-repairing agent, comprising the following steps: Dissolve beef extract, peptone and sodium chloride in deionized water to prepare a nutrient solution, adjust the pH to 9.5 with sodium bicarbonate solution to form an alkaline nutrient solution, inoculate Bacillus spores and perform shaking culture to obtain a bacterial solution, and after centrifugal separation, wash and purify the bacteria with a buffer solution to obtain a bacterial cell suspension; then immerse expanded perlite particles in the bacterial cell suspension, and after filtration, perform vacuum drying treatment to finally form a self-repairing agent with a microbial loading layer. The nutrient solution includes 4.0 g / L of beef extract, 10.0 g / L of peptone, 5.0 g / L of glucose, 4.0 g / L of sodium chloride, 1.0 g / L of potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 0.5 g / L of magnesium sulfate heptahydrate. The preparation process of the bacterial cell suspension includes: inoculate 0.5 parts of Bacillus spores into 120 parts of alkaline nutrient solution, perform constant temperature shaking culture at 28 °C and 110 rpm for 4 h, then centrifuge at 5500 rpm for 4 min, discard the supernatant, add a sufficient amount of phosphate buffer solution with pH 7.2 to resuspend the bacteria, repeat centrifugation and washing 2 times to purify the bacteria, and finally dilute the purified bacteria with 30 parts of sterile water to a cell concentration of 3.2×10 9 cells / mL to obtain a bacterial cell suspension, and store it refrigerated at 2 °C; The specific process of impregnation and low-temperature vacuum drying is: Immerse 10 parts of expanded perlite particles with a particle size of 0.1 mm in the bacterial cell suspension for 20 h, filter, and then dry at 38 °C and 10 kPa vacuum for 45 min, control the thickness of the microbial loading layer on the particle surface to be 50 μm, and the water content of the final self-repairing agent ≤2.5%, wherein the viable cell density of Bacillus in the microbial loading layer is 3.0×108 CFU / g.

[0043] Preparation method of modified basalt chopped fibers, comprising the following steps: First, conduct dynamic oxidation treatment on basalt fibers with hydrogen peroxide solution, then etch with hydrochloric acid and obtain a porous surface structure, then prepare a nano-silica suspension, and adopt ultrasonic-assisted impregnation combined with vacuum drying to form a nano-silica coating on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The average length of the modified basalt chopped fibers is 6.0 mm, and the average diameter is 10.0 μm. The detailed processes of the dynamic oxidation treatment and hydrochloric acid etching are as follows: By weight, first immerse 50 parts of basalt chopped fibers in 80 parts of 4.5 wt% hydrogen peroxide solution, perform surface oxidation by oscillating at 25 °C and 200 rpm for 1.5 h, then wash with deionized water until the conductivity ≤ 50 μS / cm and vacuum dry at 55 °C for 1.5 h; then immerse the treated fibers in 0.8 mol / L hydrochloric acid solution, dynamically etch at 40 °C for 80 min, then rinse to neutral and dry with hot air to obtain acid-etched fibers. The preparation method of the nano-silica suspension is as follows: By weight, disperse 1.2 parts of silane coupling agent KH-550 in 180 parts of 90 wt% ethanol aqueous solution, stir at 500 rpm for 25 min, then add 5.5 parts of nano-silica particles and continuously disperse for 40 min to obtain the nano-silica suspension. The detailed process of ultrasonic-assisted impregnation combined with vacuum drying is as follows: Immerse the acid-etched fibers in the nano-silica suspension, perform ultrasonic impregnation at 40 kHz for 25 min and vacuum dry at 50 °C for 120 min to form a nano-silica coating with a thickness of 90 nm on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The preparation method of nano-silica is as follows: By weight, put 50.0 parts of sodium silicate and 100.0 parts of deionized water into a polytetrafluoroethylene reaction kettle, mechanically stir at 200 rpm for 10 min to form a homogeneous solution, then dropwise add 30.0 parts of 1.0 mol / L hydrochloric acid solution, control the dropping rate at 0.5 mL / min, simultaneously maintain the system pH at 2.0, after dropping, raise the temperature to 70 °C and raise the temperature at a rate of 2 °C / min, age at 80 °C for 2.0 h, then add 1.5 parts of polyethylene glycol-6000 surfactant and shear disperse at 500 rpm for 20 min to form a sol, transfer the sol to a vacuum drying oven and dry at a negative pressure of 25 kPa and 60 °C for 4.0 h, grind the obtained gel with an agate mortar and then place it in a muffle furnace, program the temperature rise at a rate of 5 °C / min to 550 °C, and keep calcining for 3.0 h to finally obtain nano-silica with a specific surface area of 300 m 2 / g and an average particle size of 50 nm.

[0044] A preparation method of high-strength concrete in this embodiment, comprising the following steps:

[0045] S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 5 mm, and the particle size of the natural sand is controlled at 0.2 mm. After screening, reserve them. Add P·II 52.5 cement, secondary fly ash, and slag fly ash into a mixer according to the ratio, and stir at a low speed of 60 rpm for 5 min to make them evenly mixed. Separately take water, add a polycarboxylate-based water reducer and a rosin-based air-entraining agent in sequence, and stir at 300 rpm for 4 min until the solution is clear and there are no obvious bubbles to obtain a hydration solution;

[0046] S2. Add the pretreated basalt coarse aggregate and natural sand into a mixer according to the ratio, stir at a medium speed of 100 rpm for 1 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 30 s, and continue to stir for 3 min to form a uniform wet-mixed mixture;

[0047] S3. During the wet mixing process, gradually add modified basalt chopped fibers, increase the stirring speed to 150 rpm, and continuously stir for 20 min to ensure the uniform dispersion of the fibers. Subsequently, slowly add a self-repairing agent and continue to stir for 2 min to make it evenly distributed. Finally, adjust the stirring speed to 200 rpm and continuously stir for 4 min to form a homogeneous concrete mixture, and let it stand for 2 min to eliminate bubbles;

[0048] S4. Pour the mixed concrete into a mold, compact it with a 50 Hz vibrating table for 30 s to complete the molding; the molded specimens are cured in an environment of 20°C and relative humidity ≥ 90% for 24 h, and after demolding, they are further cured under standard conditions of 20°C and relative humidity ≥ 95% for 10 days.

[0049] It can be seen from Figure 1 that the surface of the unmodified basalt chopped fibers is relatively smooth and lacks an effective rough structure, which is not conducive to the bonding with the cement matrix. Figure 2 shows the surface morphology of the modified basalt chopped fibers, proving that after oxidation treatment, acid etching, and nano-silica modification, a rough and functionally coated structure is formed on the fiber surface, which helps to enhance the interfacial bonding force. Figure 3 shows the original morphology of the high-strength concrete when cracks are formed and the change of the cracks after 10 days, proving that the self-healing system of the present invention can effectively promote the healing of cracks and improve the durability of concrete. Figure 4 Further proves the fracture morphology of the modified basalt chopped fibers, showing that the fiber surface is evenly covered with a nano-silica coating, enhancing the bonding strength between the fiber and the matrix, thereby improving the crack resistance of the concrete.

[0050] Example 2

[0051] A high-strength concrete, comprising raw materials in the following parts by weight: 2.1 parts of modified basalt chopped fibers, 2.8 parts of self-repairing agent, 106 parts of P·II 52.5 cement, 86 parts of secondary fly ash, 33 parts of slag fly ash, 186 parts of water, 674 parts of basalt coarse aggregate, 795 parts of natural sand, 10.5 parts of polycarboxylate superplasticizer, and 1.3 parts of rosin-based air-entraining agent.

[0052] The modified basalt chopped fibers are obtained by subjecting basalt chopped fibers to surface oxidation treatment, acid etching treatment, and nano-silica modification treatment; the self-repairing agent is a composite material prepared by loading Bacillus thuringiensis cells on the surface of expanded perlite particles through processes of bacterial body culture, centrifugal purification, impregnation adsorption, and low-temperature vacuum drying.

[0053] The preparation method of the self-repairing agent comprises the following steps: Dissolve beef extract, peptone, and sodium chloride in deionized water to prepare a nutrient solution, adjust the pH to 9.7 with a sodium bicarbonate solution to form an alkaline nutrient solution, inoculate Bacillus thuringiensis strains and perform shaking culture to obtain a bacterial solution, and after centrifugal separation, wash and purify the bacterial cells with a buffer solution to obtain a bacterial cell suspension; then immerse the expanded perlite particles in the bacterial cell suspension, filter, and finally form the self-repairing agent with a microbial loading layer after vacuum drying treatment. The nutrient solution comprises 4.6 g / L of beef extract, 10.6 g / L of peptone, 8.0 g / L of glucose, 4.3 g / L of sodium chloride, 1.6 g / L of potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 0.7 g / L of magnesium sulfate heptahydrate. The preparation process of the bacterial cell suspension includes: inoculating 0.8 parts of Bacillus thuringiensis strains into 129 parts of the alkaline nutrient solution, performing constant-temperature shaking culture at 29 °C and 116 rpm for 5 h, then centrifuging at 5800 rpm for 5 min, discarding the supernatant, adding a sufficient amount of phosphate buffer solution with a pH of 7.3 to resuspend the bacterial cells, repeating the centrifugation and washing 2 times to purify the bacterial cells, and finally diluting the purified bacterial cells with 36 parts of sterile water to a cell concentration of 3.4×10 9 cells / mL to obtain the bacterial cell suspension, and storing it refrigerated at 3 °C; The specific processes of impregnation and low-temperature vacuum drying are as follows: Immerse 12 parts of expanded perlite particles with a particle size of 0.2 mm in the bacterial cell suspension for 22 h, filter, and then dry at 39 °C and 13 kPa vacuum for 50 min, controlling the thickness of the microbial loading layer on the particle surface to be 59 μm, and the water content of the final self-repairing agent ≤2.5%, wherein the viable cell density of Bacillus thuringiensis in the microbial loading layer is 4.1×108 CFU / g.

[0054] Preparation method of modified basalt chopped fibers, comprising the following steps: First, perform dynamic oxidation treatment on basalt fibers with hydrogen peroxide solution, then etch with hydrochloric acid to obtain a porous surface structure, then prepare a nano-silica suspension, and use ultrasonic-assisted impregnation combined with vacuum drying to form a nano-silica coating on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The average length of the modified basalt chopped fibers is 7.8 mm, and the average diameter is 13.0 μm. The detailed processes of dynamic oxidation treatment and hydrochloric acid etching are as follows: By weight, first immerse 56 parts of basalt chopped fibers in 92 parts of 4.8 wt% hydrogen peroxide solution, perform oscillation treatment at 28 °C and 230 rpm for 1.8 h to complete surface oxidation, then wash with deionized water until the conductivity ≤ 50 μS / cm and vacuum dry at 58 °C for 1.8 h; then immerse the treated fibers in 0.9 mol / L hydrochloric acid solution, dynamically etch at 43 °C for 86 min, then rinse to neutral and dry with hot air to obtain acid-etched fibers. The preparation method of the nano-silica suspension is as follows: By weight, disperse 1.4 parts of silane coupling agent KH-550 in 192 parts of 92 wt% ethanol aqueous solution, stir at 560 rpm for 28 min, then add 5.8 parts of nano-silica particles and continue to disperse for 46 min to obtain the nano-silica suspension. The detailed process of ultrasonic-assisted impregnation combined with vacuum drying is as follows: Immerse the acid-etched fibers in the nano-silica suspension, perform ultrasonic impregnation at 46 kHz for 28 min and vacuum dry at 56 °C for 132 min to form a nano-silica coating with a thickness of 99 nm on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The preparation method of nano-silica is as follows: By weight, put 56.0 parts of sodium silicate and 115.0 parts of deionized water into a polytetrafluoroethylene reaction kettle, mechanically stir at 230 rpm for 12 min to form a homogeneous solution, then dropwise add 36.0 parts of 1.3 mol / L hydrochloric acid solution, control the dropping rate at 0.7 mL / min, simultaneously maintain the system pH at 2.3, after dropping, raise the temperature to 73 °C and raise the temperature at a rate of 2 °C / min, age at 83 °C for 2.3 h, then add 1.8 parts of polyethylene glycol-6000 surfactant and shear disperse at 560 rpm for 23 min to form a sol, transfer the sol to a vacuum drying oven, dry at a negative pressure of 28 kPa and 63 °C for 4.6 h, grind the obtained gel with an agate mortar, and then place it in a muffle furnace, program the temperature to 580 °C at a rate of 6 °C / min, keep the temperature and calcine for 3.3 h, and finally obtain nano-silica with a specific surface area of 280 m 2 / g and an average particle size of 59 nm.

[0055] A preparation method of high-strength concrete in this embodiment, comprising the following steps:

[0056] S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 10 mm, and the particle size of the natural sand is controlled at 0.9 mm. After screening, reserve them. Add P·II 52.5 cement, secondary fly ash, and slag fly ash into a mixer according to the ratio, and stir at a low speed of 72 rpm for 7 min to make them evenly mixed. Separately take water, add a polycarboxylate-based water reducer and a rosin-based air-entraining agent in sequence, and stir at 360 rpm for 5 min until the solution is clear and there are no obvious bubbles to obtain a hydration solution;

[0057] S2. Add the pretreated basalt coarse aggregate and natural sand into a mixer according to the ratio, stir at a medium speed of 115 rpm for 1 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 39 s, and continue stirring for 4 min to form a uniform wet-mixed mixture;

[0058] S3. During the wet mixing process, gradually add modified basalt short fibers, increase the stirring speed to 165 rpm, and continuously stir for 23 min to ensure the uniform dispersion of the fibers. Then slowly add a self-repairing agent, and continue stirring for 3 min to make it evenly distributed. Finally, adjust the stirring speed to 230 rpm and continuously stir for 5 min to form a homogeneous concrete mixture, and let it stand for 3 min to eliminate bubbles;

[0059] S4. Pour the mixed concrete into a mold, vibrate and compact it on a vibrating table at 65 Hz for 39 s to complete the molding; the molded specimens are cured in an environment of 22 °C and a relative humidity of ≥90% for 28 h, and after demolding, they are further cured under standard conditions of 22 °C and a relative humidity of ≥95% for 12 days.

[0060] Example 3

[0061] A high-strength concrete, comprising the following raw materials in parts by weight: 2.7 parts of modified basalt short fibers, 3.1 parts of self-repairing agent, 112 parts of P·II 52.5 cement, 92 parts of secondary fly ash, 36 parts of slag fly ash, 192 parts of water, 726 parts of basalt coarse aggregate, 840 parts of natural sand, 12.0 parts of polycarboxylate-based water reducer, and 2.0 parts of rosin-based air-entraining agent.

[0062] The modified basalt short fibers are obtained by subjecting basalt short fibers to surface oxidation treatment, acid etching treatment, and nano-silica modification treatment; the self-repairing agent is a composite material obtained by subjecting bacillus thuringiensis cells to bacterial culture, centrifugal purification, impregnation adsorption, and low-temperature vacuum drying processes and loading them on the surface of expanded perlite particles.

[0063] Preparation method of self-repairing agent, comprising the following steps: Dissolve beef extract, peptone and sodium chloride in deionized water to prepare a nutrient solution, adjust the pH to 9.8 with sodium bicarbonate solution to form an alkaline nutrient solution, inoculate with Bacillus strains and perform shaking culture to obtain a bacterial liquid, after centrifugal separation, wash and purify the bacterial cells with a buffer solution to prepare a bacterial cell suspension; then immerse expanded perlite particles in the bacterial cell suspension, filter and finally perform vacuum drying treatment to finally form a self-repairing agent with a microbial loading layer. The nutrient solution includes 5.2 g / L of beef extract, 11.2 g / L of peptone, 11.0 g / L of glucose, 4.6 g / L of sodium chloride, 2.2 g / L of potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 0.8 g / L of magnesium sulfate heptahydrate. The preparation process of the bacterial cell suspension includes: inoculate 1.1 parts of Bacillus strains into 138 parts of alkaline nutrient solution, perform constant temperature shaking culture at 30 °C and 122 rpm for 6 h, then centrifuge at 6100 rpm for 5 min, discard the supernatant, add a sufficient amount of phosphate buffer solution with pH 7.4 to resuspend the bacterial cells, repeat centrifugation and washing 3 times to purify the bacterial cells, and finally dilute the purified bacterial cells with 42 parts of sterile water to a cell concentration of 3.7×10 9 cells / mL to obtain a bacterial cell suspension, and store it refrigerated at 4 °C; The specific process of impregnation and low-temperature vacuum drying is: Immerse 13 parts of expanded perlite particles with a particle size of 0.3 mm in the bacterial cell suspension for 25 h, filter, and then dry at 40 °C and 16 kPa vacuum for 54 min, control the thickness of the microbial loading layer on the particle surface to be 68 μm, and the final moisture content of the self-repairing agent ≤2.5%, wherein the viable cell density of Bacillus in the microbial loading layer is 5.1×108 CFU / g.

[0064] Preparation method of modified basalt chopped fibers, comprising the following steps: First, perform dynamic oxidation treatment on basalt fibers with hydrogen peroxide solution, then etch with hydrochloric acid to obtain a porous surface structure, then prepare a nano-silica suspension, and use ultrasonic-assisted impregnation combined with vacuum drying to form a nano-silica coating on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The average length of the modified basalt chopped fibers is 9.6 mm, and the average diameter is 16.0 μm. The detailed processes of the dynamic oxidation treatment and hydrochloric acid etching are as follows: By weight, first immerse 62 parts of basalt chopped fibers in 104 parts of 5.1 wt% hydrogen peroxide solution, perform oscillation treatment at 31 °C and 260 rpm for 2.1 h to complete surface oxidation, then wash with deionized water until the conductivity ≤ 50 μS / cm and vacuum dry at 61 °C for 2.1 h; then immerse the treated fibers in 1.0 mol / L hydrochloric acid solution, dynamically etch at 46 °C for 92 min, then rinse to neutral and dry with hot air to obtain acid-etched fibers. The preparation method of the nano-silica suspension is as follows: By weight, disperse 1.6 parts of silane coupling agent KH-550 in 204 parts of 93 wt% ethanol aqueous solution, stir at 620 rpm for 31 min, then add 6.1 parts of nano-silica particles and continue to disperse for 52 min to obtain the nano-silica suspension. The detailed process of ultrasonic-assisted impregnation combined with vacuum drying is as follows: Immerse the acid-etched fibers in the nano-silica suspension, perform ultrasonic impregnation at 52 kHz for 31 min and vacuum dry at 62 °C for 144 min to form a nano-silica coating with a thickness of 108 nm on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The preparation method of nano-silica is as follows: By weight, put 62.0 parts of sodium silicate and 130.0 parts of deionized water into a polytetrafluoroethylene reaction kettle, mechanically stir at 260 rpm for 13 min to form a homogeneous solution, then dropwise add 42.0 parts of 1.6 mol / L hydrochloric acid solution, control the dropping rate at 0.8 mL / min, simultaneously maintain the system pH at 2.6, after dropping, raise the temperature to 76 °C and raise the temperature at a rate of 3 °C / min, age at 86 °C for 2.6 h, then add 2.1 parts of polyethylene glycol-6000 surfactant and shear disperse at 620 rpm for 26 min to form a sol, transfer the sol to a vacuum drying oven and dry at a negative pressure of 31 kPa and 66 °C for 5.2 h, the obtained gel is ground with an agate mortar and then placed in a muffle furnace, and the temperature is programmed to rise to 610 °C at a rate of 7 °C / min and keep the temperature for calcination for 3.6 h, finally obtaining nano-silica with a specific surface area of 230 m 2 / g and an average particle size of 68 nm.

[0065] A preparation method of high-strength concrete in this embodiment, comprising the following steps:

[0066] S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 14 mm, and the particle size of the natural sand is controlled at 1.6 mm. After screening, reserve them. Add P·II 52.5 cement, secondary fly ash and slag fly ash into a mixer according to the ratio, and stir at a low speed of 84 rpm for 8 min to make them evenly mixed. Separately take water, add a polycarboxylate-based water reducer and a rosin-based air-entraining agent in sequence, and stir at 420 rpm for 6 min until the solution is clear and there are no obvious bubbles to obtain a hydration solution;

[0067] S2. Add the pretreated basalt coarse aggregate and natural sand into a mixer according to the ratio, and stir at a medium speed of 130 rpm for 2 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 48 s, and continue to stir for 4 min to form a uniform wet-mixed mixture;

[0068] S3. During the wet mixing process, gradually add the modified basalt short-cut fibers, increase the stirring speed to 180 rpm, and continuously stir for 26 min to ensure the uniform dispersion of the fibers. Then slowly add the self-repairing agent, and continue to stir for 3 min to make it evenly distributed. Finally, adjust the stirring speed to 260 rpm and continue for 5 min to form a homogeneous concrete mixture, and let it stand for 4 min to eliminate bubbles;

[0069] S4. Pour the mixed concrete into a mold, and compact it with an 80 Hz vibrating table for 48 s to complete the molding; the molded specimens are cured in an environment of 23 °C and relative humidity ≥ 90% for 31 h, and after demolding, they are continuously cured under standard conditions of 23 °C and relative humidity ≥ 95% for 13 days.

[0070] Example 4

[0071] A high-strength concrete, comprising the following raw materials in parts by weight: 3.5 parts of modified basalt short-cut fibers, 3.5 parts of self-repairing agent, 120 parts of P·II 52.5 cement, 100 parts of secondary fly ash, 40 parts of slag fly ash, 200 parts of water, 796 parts of basalt coarse aggregate, 900 parts of natural sand, 14.0 parts of polycarboxylate-based water reducer, and 3.0 parts of rosin-based air-entraining agent.

[0072] The modified basalt short-cut fibers are obtained by subjecting basalt short-cut fibers to surface oxidation treatment, acid etching treatment and nano-silica modification treatment; the self-repairing agent is a composite material in which bacillus thuringiensis cells are loaded on the surface of expanded perlite particles through processes such as bacterial body culture, centrifugal purification, impregnation adsorption and low-temperature vacuum drying.

[0073] Preparation method of self-repairing agent, comprising the following steps: Dissolve beef extract, peptone and sodium chloride in deionized water to prepare a nutrient solution, adjust the pH to 10.0 with sodium bicarbonate solution to form an alkaline nutrient solution, inoculate with Bacillus strains and perform shaking culture to obtain a bacterial solution. After centrifugal separation, wash and purify the bacterial cells with a buffer solution to obtain a bacterial cell suspension; then immerse expanded perlite particles in the bacterial cell suspension, filter and finally perform vacuum drying treatment to finally form a self-repairing agent with a microbial loading layer. The nutrient solution includes 6.0 g / L of beef extract, 12.0 g / L of peptone, 15.0 g / L of glucose, 5.0 g / L of sodium chloride, 3.0 g / L of potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 1.0 g / L of magnesium sulfate heptahydrate. The preparation process of the bacterial cell suspension includes: inoculate 1.5 parts of Bacillus strains into 150 parts of alkaline nutrient solution, perform constant temperature shaking culture at 32 °C and 130 rpm for 8 h, then centrifuge at 6500 rpm for 6 min, discard the supernatant, add a sufficient amount of phosphate buffer solution with a pH of 7.6 to resuspend the bacterial cells, repeat centrifugation and washing 3 times to purify the bacterial cells, and finally dilute the purified bacterial cells with 50 parts of sterile water to a cell concentration of 4.0×10 9 cells / mL to obtain a bacterial cell suspension, and store it refrigerated at 6 °C; The specific process of impregnation and low-temperature vacuum drying is: Immerse 15 parts of expanded perlite particles with a particle size of 0.5 mm in the bacterial cell suspension for 28 h, filter, and then dry at 42 °C and 20 kPa vacuum for 60 min, control the thickness of the microbial loading layer on the particle surface to be 80 μm, and the water content of the final self-repairing agent ≤ 2.5%, wherein the viable cell density of Bacillus in the microbial loading layer is 6.5×10 8 CFU / g.

[0074] Preparation method of modified basalt chopped fibers, comprising the following steps: First, dynamically oxidize basalt fibers with a hydrogen peroxide solution, then etch with hydrochloric acid to obtain a porous surface structure, then prepare a nano-silica suspension, and use ultrasonic-assisted impregnation combined with vacuum drying to form a nano-silica coating on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The average length of the modified basalt chopped fibers is 12.0 mm, and the average diameter is 20 μm. The detailed processes of dynamic oxidation treatment and hydrochloric acid etching are as follows: By weight, first immerse 70 parts of basalt chopped fibers in 120 parts of 5.5 wt% hydrogen peroxide solution, perform surface oxidation by oscillating at 35 °C and 300 rpm for 2.5 h, then wash with deionized water until the conductivity ≤ 50 μS / cm and vacuum dry at 65 °C for 2.5 h; then immerse the treated fibers in 1.2 mol / L hydrochloric acid solution, dynamically etch at 50 °C for 100 min, then rinse to neutral and dry with hot air to obtain acid-etched fibers. The preparation method of the nano-silica suspension is as follows: By weight, disperse 1.8 parts of silane coupling agent KH-550 in 220 parts of 95 wt% ethanol aqueous solution, stir at 700 rpm for 35 min, then add 6.5 parts of nano-silica particles and continue to disperse for 60 min to obtain the nano-silica suspension. The detailed process of ultrasonic-assisted impregnation combined with vacuum drying is as follows: Immerse the acid-etched fibers in the nano-silica suspension, perform ultrasonic impregnation at 60 kHz for 35 min and vacuum dry at 70 °C for 160 min to form a nano-silica coating with a thickness of 120 nm on the surface of basalt chopped fibers to obtain modified basalt chopped fibers. The preparation method of nano-silica is as follows: By weight, mix 70.0 parts of sodium silicate and 150.0 parts of deionized water in a polytetrafluoroethylene reaction kettle, mechanically stir at 300 rpm for 15 min to form a homogeneous solution, then dropwise add 50.0 parts of 2.0 mol / L hydrochloric acid solution, control the dropping rate at 1.0 mL / min, and simultaneously maintain the system pH at 3.0. After dropping, heat up to 80 °C and heat up at a rate of 3 °C / min, age at 90 °C for 3.0 h, then add 2.5 parts of polyethylene glycol-6000 surfactant and shear disperse at 700 rpm for 30 min to form a sol. Transfer the sol to a vacuum drying oven and dry at -35 kPa negative pressure and 70 °C for 6.0 h. The obtained gel is ground with an agate mortar and then placed in a muffle furnace, and the temperature is programmed to rise to 650 °C at a rate of 8 °C / min, and calcined at a constant temperature for 4.0 h to finally obtain nano-silica with a specific surface area of 200 m 2 / g and an average particle size of 80 nm.

[0075] A preparation method of high-strength concrete in this embodiment, comprising the following steps:

[0076] S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 20 mm, and the particle size of the natural sand is controlled at 2.5 mm. After screening, set aside. Add P·II 52.5 cement, secondary fly ash, and slag fly ash into a mixer according to the ratio, and stir at a low speed of 100 rpm for 10 min to make them evenly mixed. Separately take water, add a polycarboxylate-based water reducer and a rosin-based air-entraining agent in sequence, and stir at 500 rpm for 8 min until the solution is clear and there are no obvious bubbles to obtain a hydration solution.

[0077] S2. Add the pretreated basalt coarse aggregate and natural sand into a mixer according to the ratio, stir at a medium speed of 150 rpm for 2 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 60 s, and continue stirring for 5 min to form a uniform wet-mixed mixture.

[0078] S3. During the wet mixing process, gradually add modified basalt chopped fibers, increase the stirring speed to 200 rpm, and continuously stir for 30 min to ensure the uniform dispersion of the fibers. Subsequently, slowly add a self-repairing agent and continue stirring for 4 min to make it evenly distributed. Finally, adjust the stirring speed to 300 rpm and continue for 6 min to form a homogeneous concrete mixture, and let it stand for 5 min to eliminate bubbles.

[0079] S4. Pour the mixed concrete into a mold, compact it with a vibrating table at 100 Hz for 60 s to complete the molding. The molded specimens are cured in an environment of 25 °C and relative humidity ≥ 90% for 36 h, and after demolding, they are continuously cured under standard conditions of 25 °C and relative humidity ≥ 95% for 15 days.

[0080] Comparative Example 1

[0081] It is basically the same as Example 1, except that the modified basalt chopped fibers are not oxidized, resulting in a decrease in the interfacial bonding force between the fibers and the cement matrix, a decline in crack resistance and toughness, and a significant reduction in the flexural strength of the concrete.

[0082] Comparative Example 2

[0083] It is basically the same as Example 1, except that the thallus culture of the self-repairing agent is not washed and purified with a phosphate buffer solution, resulting in lower thallus activity, a significant weakening of the concrete crack self-repairing ability, and a reduction in the repair efficiency.

[0084] Comparative Example 3

[0085] It is basically the same as Example 1, except that the nano-silica coating is not impregnated by ultrasonic assistance, resulting in uneven coating distribution, a reduction in the fiber reinforcement effect, and a decline in the durability and crack resistance of the concrete.

[0086] Comparative Example 4

[0087] Basically the same as Example 1, except that the bacterial suspension impregnated with perlite was not subjected to low-temperature vacuum drying, resulting in a higher water content of the self-repairing agent, a decrease in storage stability, and a weakening of the self-healing ability.

[0088] Comparative Example 5

[0089] Basically the same as Example 1, except that the pH of the nutrient solution was not adjusted to 9.5 - 10.0 but maintained at neutral, resulting in slow growth of Bacillus, a decrease in the final bacterial load density, and a decline in the repair efficiency of the self-repairing agent.

[0090] Comparative Example 6

[0091] Basically the same as Example 1, except that the concentration of the hydrogen peroxide solution was reduced to 3.0 wt%, resulting in insufficient oxidation of basalt fibers, a reduction in surface active functional groups, weak interfacial adhesion, and a decline in the crack resistance of concrete.

[0092] Comparative Example 7

[0093] Basically the same as Example 1, except that the hydrochloric acid etching time was shortened to 40 min, resulting in insufficient surface roughness of the fibers, weakened mechanical biting force with the cement matrix, and a reduction in flexural strength.

[0094] Comparative Example 8

[0095] Basically the same as Example 1, except that the centrifugation speed of the bacterial suspension was reduced to 4000 rpm, resulting in incomplete purification of the bacteria, a decrease in the repair activity of the final self-repairing agent, and poor repair effect of concrete cracks.

[0096] Comparative Example 9

[0097] Basically the same as Example 1, except that silane coupling agent was not used when preparing the nano-silica suspension, resulting in a decrease in the bonding force between the coating and the fibers, a reduction in the modification effect, and a decline in the durability of concrete. Figure 5 The fracture morphology of the modified basalt chopped fibers prepared in Comparative Example 9 shows that the fiber surface is still smooth and lacks an effective interfacial bonding layer, proving that the bonding between the fibers and the cement matrix is weak, which further verifies the necessity and effectiveness of the modification process adopted in the present invention for improving the performance of fiber-reinforced concrete.

[0098] Comparative Example 10

[0099] Basically the same as Example 1, except that the particle size of the expanded perlite increased to 0.8 mm, resulting in a decrease in the dispersibility of the self-repairing agent in concrete, uneven crack repair, and a decline in the repair efficiency.

[0100] Performance test:

[0101] Compressive Strength Test (in accordance with ASTM C39 / C39M-20): Standard cubic or cylindrical specimens (such as 100mm×100mm×100mm cube or Φ100mm×200mm cylinder) are used. After standard curing in accordance with ASTM C192, the compressive strength test is carried out using a universal testing machine at the ages of 7d, 28d, and 90d. The loading rate is controlled at 0.25MPa / s to 0.35MPa / s, the maximum failure load is recorded, and the compressive strength is calculated to evaluate the mechanical properties of the concrete.

[0102] Flexural Strength Test (in accordance with ASTM C78 / C78M-22): A 100mm×100mm×400mm trapezoidal beam specimen is used. After 28d of curing, its flexural strength is tested by the three-point bending method. The loading rate is controlled at 0.05MPa / s to 0.1MPa / s, and the maximum load at the failure of the specimen is recorded to evaluate the toughness and crack resistance of the fiber-reinforced concrete.

[0103] Self-healing Performance Test: Cracks with a width of 0.2mm to 0.5mm are prefabricated on the 28d-cured concrete specimens, and they are cured for 28 days in an environment with a humidity of 95% and a temperature of 25°C. The composition of the crack fillers is analyzed using a scanning electron microscope (SEM) and X-ray diffraction (XRD), and the crack repair rate is measured using a water penetration test to evaluate the repair ability of the self-healing agent.

[0104] Freeze-Thaw Resistance Performance Test (in accordance with ASTM C666-03): Using the rapid freeze-thaw cycle method, the 28d-cured specimens are immersed in water and subjected to freeze-thaw cycles from -20°C to 4°C, with each cycle lasting 4 hours. The mass loss rate and relative dynamic modulus after 300 cycles are tested to evaluate the freeze-thaw resistance ability of the concrete.

[0105] The performances of the concretes in Examples 1-4 and Comparative Examples 1-10 are summarized in Table 1.

[0106] Table 1 Summary of the Performances of the Concretes in Examples 1-4 and Comparative Examples 1-10

[0107]

[0108]

[0109] As can be seen from Table 1, in Example 3, due to the optimization of various parameters, the comprehensive performance is the best, and the compressive strength, flexural strength, self-healing rate, and freeze-thaw resistance all reach the optimal level. In contrast, in Comparative Example 1, since the fibers were not oxidized, the interfacial bonding force decreased, resulting in a decrease in flexural strength, thus affecting the crack resistance performance; in Comparative Example 2, because the phosphate buffer solution was not used for washing during the bacterial culture process, the bacterial activity decreased, and the self-healing rate decreased significantly; in Comparative Example 3, ultrasonic-assisted impregnation was not performed on the nano-silica coating, resulting in uneven coating distribution, affecting the fiber reinforcement effect, and decreasing the flexural strength and durability; in Comparative Example 4, due to the lack of low-temperature vacuum drying treatment, the water content of the self-repair agent was relatively high, affecting the long-term storage stability and resulting in a decrease in the self-healing rate; in Comparative Example 5, since the pH of the nutrient solution was not adjusted to the alkaline range, the bacterial growth was insufficient, affecting the final repair efficiency; in Comparative Example 6, due to the decrease in the hydrogen peroxide oxidation concentration, the surface active functional groups of the fibers decreased, the interfacial bonding force weakened, and the flexural strength decreased; in Comparative Example 7, due to insufficient hydrochloric acid etching time, the surface roughness of the fibers decreased, the mechanical biting force weakened, and the flexural strength decreased; in Comparative Example 8, due to the decrease in the centrifugal rotation speed of the bacterial suspension, the bacterial purification was incomplete, affecting the repair activity of the self-repair agent and resulting in a decrease in the self-healing rate; in Comparative Example 9, since a silane coupling agent was not used when preparing the nano-silica suspension, the bonding force between the coating and the fibers decreased, affecting the flexural strength and durability; in Comparative Example 10, since the particle size of the expanded perlite increased to 0.8 mm, the dispersibility of the self-repair agent in the concrete decreased, and the crack repair was uneven, resulting in a decrease in the self-healing rate. Generally speaking, each parameter has a significant impact on the mechanical properties, durability, and self-healing ability of the concrete. Among them, the optimized combination in Example 3 ensures the best performance.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A high-strength concrete, characterized in that, It comprises raw materials in the following parts by weight: 1.5 - 3.5 parts of modified basalt chopped fibers, 2.5 - 3.5 parts of self-repairing agent, 100 - 120 parts of P·II 52.5 cement, 80 - 100 parts of secondary fly ash, 30 - 40 parts of slag fly ash, 180 - 200 parts of water, 622 - 796 parts of basalt coarse aggregate, 750 - 900 parts of natural sand, 9.0 - 14.0 parts of polycarboxylate superplasticizer, and 0.5 - 3.0 parts of rosin air-entraining agent. The modified basalt chopped fibers are obtained by subjecting basalt chopped fibers to surface oxidation treatment, acid etching treatment and nano-silica modification treatment. The self-repairing agent is a composite material prepared by subjecting Bacillus thuringiensis cells to bacterial body culture, centrifugal purification, impregnation adsorption and low-temperature vacuum drying processes and loading the cells on the surface of expanded perlite particles.

2. The high-strength concrete according to claim 1, wherein The preparation method of the self-repairing agent comprises the following steps: dissolving beef extract, peptone and sodium chloride in deionized water to prepare a nutrient solution, adjusting the pH to 9.5 - 10.0 with a sodium bicarbonate solution to form an alkaline nutrient solution, inoculating a Bacillus thuringiensis strain and performing shaking culture to obtain a bacterial solution, and subjecting the bacterial solution to centrifugal separation and then washing and purifying the bacterial cells with a buffer solution to obtain a bacterial cell suspension; then impregnating expanded perlite particles in the bacterial cell suspension, filtering, and finally performing vacuum drying treatment to form a self-repairing agent with a microbial loading layer.

3. A high-strength concrete according to claim 2, wherein, The nutrient solution comprises 4.0 - 6.0 g / L of beef extract, 10.0 - 12.0 g / L of peptone, 5.0 - 15.0 g / L of glucose, 4.0 - 5.0 g / L of sodium chloride, 1.0 - 3.0 g / L of a potassium dihydrogen phosphate / dipotassium hydrogen phosphate buffer system, and 0.5 - 1.0 g / L of magnesium sulfate heptahydrate.

4. A high-strength concrete according to claim 2, wherein the preparation process of the bacterial suspension comprises: Inoculate 0.5 - 1.5 parts of Bacillus strains into 120 - 150 parts of alkaline nutrient solution, and perform constant temperature shaking culture at 28 - 32 °C and 110 - 130 rpm for 4 - 8 h. Subsequently, centrifuge at 5500 - 6500 rpm for 4 - 6 min. After discarding the supernatant, add a sufficient amount of phosphate buffer with a pH of 7.2 - 7.6 to resuspend the cells, and repeat centrifugation and washing 2 - 3 times to purify the cells. Finally, dilute the purified cells with 30 - 50 parts of sterile water to a cell concentration of 3.2×10 9 ~4.0×10 9 cells / mL to obtain a cell suspension, and store it refrigerated at 2 - 6 °C.

5. The high-strength concrete according to claim 2, characterized in that The specific process of the impregnation and low-temperature vacuum drying is as follows: impregnating 10 - 15 parts of expanded perlite particles with a particle size of 0.1 - 0.5 mm in the bacterial cell suspension for 20 - 28 h, filtering, and then drying under vacuum conditions at 38 - 42 °C and 10 - 20 kPa for 45 - 60 min, controlling the thickness of the microbial loading layer on the particle surface to be 50 - 80 μm, and the water content of the final self-repairing agent ≤ 2.5%, wherein the viable cell density of Bacillus thuringiensis in the microbial loading layer is 3.0 - 6.5 × 108 CFU / g.

6. A high-strength concrete according to claim 1, characterized in that, The preparation method of the modified basalt chopped fibers comprises the following steps: first performing dynamic oxidation treatment of basalt fibers with a hydrogen peroxide solution, then subjecting them to hydrochloric acid etching to obtain a porous surface structure, then preparing a nano-silica suspension, and using ultrasonic-assisted impregnation combined with vacuum drying to form a nano-silica coating on the surface of the basalt chopped fibers to obtain modified basalt chopped fibers.

7. A high-strength concrete according to claim 6, wherein, The average length of the modified basalt chopped fibers is 6.0 - 12.0 mm, and the average diameter is 10.0 - 20 μm.

8. A high-strength concrete according to claim 6, characterized in that, The detailed processes of the dynamic oxidation treatment and hydrochloric acid etching are as follows: by weight, first, 50 - 70 parts of chopped basalt fibers are impregnated in 80 - 120 parts of 4.5 - 5.5 wt% hydrogen peroxide solution, and subjected to oscillation treatment at 25 - 35°C and 200 - 300 rpm for 1.5 - 2.5 h to complete surface oxidation. Subsequently, it is washed with deionized water until the conductivity ≤ 50 μS / cm and vacuum dried at 55 - 65°C for 1.5 - 2.5 h. Then, the treated fibers are immersed in 0.8 - 1.2 mol / L hydrochloric acid solution, dynamically etched at 40 - 50°C for 80 - 100 min, rinsed to neutrality, and dried with hot air to obtain acid-etched fibers. The preparation method of the nano-silica suspension is as follows: by weight, 1.2 - 1.8 parts of silane coupling agent KH-550 are dispersed in 180 - 220 parts of 90 - 95 wt% ethanol aqueous solution, stirred at 500 - 700 rpm for 25 - 35 min, and then 5.5 - 6.5 parts of nano-silica particles are added and continuously dispersed for 40 - 60 min to obtain the nano-silica suspension. The detailed process of ultrasonic-assisted impregnation combined with vacuum drying is as follows: The acid-etched fibers are immersed in the nano-silica suspension, ultrasonically impregnated at 40 - 60 kHz for 25 - 35 min and vacuum dried at 50 - 70°C for 120 - 160 min to form a nano-silica coating with a thickness of 90 - 120 nm on the surface of the chopped basalt fibers, obtaining modified chopped basalt fibers.

9. A high-strength concrete according to claim 6, characterized in that, The preparation method of the nano-silica is as follows: by weight, 50.0 - 70.0 parts of sodium silicate and 100.0 - 150.0 parts of deionized water are mechanically stirred at 200 - 300 rpm for 10 - 15 min in a polytetrafluoroethylene reaction kettle to form a homogeneous solution. Subsequently, 30.0 - 50.0 parts of 1.0 - 2.0 mol / L hydrochloric acid solution are added dropwise, the dropping rate is controlled at 0.5 - 1.0 mL / min, and the pH of the system is maintained at 2.0 - 3.0 simultaneously. After the dropping is completed, the temperature is raised to 70 - 80 °C and the temperature is raised at a rate of 2 - 3 °C / min, and the mixture is aged at a constant temperature of 80 - 90 °C for 2.0 - 3.0 h. Subsequently, 1.5 - 2.5 parts of polyethylene glycol-6000 surfactant are added and sheared and dispersed at a high speed of 500 - 700 rpm for 20 - 30 min to form a sol. The sol is transferred to a vacuum drying oven and dried at a negative pressure of 25 - 35 kPa and a temperature of 60 - 70 °C for 4.0 - 6.0 h. The obtained gel is ground in an agate mortar and then placed in a muffle furnace, and the temperature is programmed to rise to 550 - 650 °C at a rate of 5 - 8 °C / min, and calcined at a constant temperature for 3.0 - 4.0 h, and finally nano-silica with a specific surface area of 200 - 300 m 2 / g and an average particle size of 50 - 80 nm is obtained.

10. The preparation method of a high-strength concrete according to claim 1, characterized in that, It includes the following steps: S1. Screen the basalt coarse aggregate and natural sand. The particle size of the basalt coarse aggregate is controlled at 5 - 20 mm, and the particle size of the natural sand is controlled at 0.2 - 2.5 mm. After screening, reserve them. Add P·II 52.5 cement, secondary fly ash, and slag fly ash into the mixer according to the ratio, and stir at a low speed of 60 - 100 rpm for 5 - 10 min to make them evenly mixed. Separately take water, add polycarboxylate superplasticizer and rosin-based air-entraining agent in sequence, and stir at 300 - 500 rpm for 4 - 8 min until the solution is clear and there are no obvious bubbles to obtain the hydration solution. S2. Add the pretreated basalt coarse aggregate and natural sand into the mixer according to the ratio, stir at a medium speed of 100 - 150 rpm for 1 - 2 min. Under the stirring state, slowly add the hydration solution prepared in step S1, control the liquid addition time at 30 - 60 s, and continue to stir for 3 - 5 min to form a uniform wet-mixed mixture. S3. During the wet mixing process, gradually add the modified chopped basalt fibers, increase the stirring speed to 150 - 200 rpm, and continuously stir for 20 - 30 min to ensure the uniform dispersion of the fibers. Then slowly add the self-repairing agent, continue to stir for 2 - 4 min to make it evenly distributed. Finally, adjust the stirring speed to 200 - 300 rpm and continue for 4 - 6 min to form a homogeneous concrete mixture, and let it stand for 2 - 5 min to eliminate the bubbles. S4. Pour the mixed concrete into the mold, and compact it on a vibrating table with a frequency of 50 - 100 Hz for 30 - 60 s to complete the forming; the formed specimens are left to cure in an environment of 20 - 25 °C and a relative humidity of ≥90% for 24 - 36 h, and after demolding, continue to be cured under standard conditions of 20 - 25 °C and a relative humidity of ≥95% for 10 - 15 days.

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