A high-strength, early-strength special concrete and its preparation method

Abstract

This invention discloses a high-strength, early-strength special concrete and its preparation method, belonging to the field of building materials technology. The core advantage lies in achieving early strength, high strength, high density, and high durability through structural modification of core-shell nanospheres, synergistic hydration of a dual-cementing system, and the compounding of active admixtures. The core-shell nanospheres of this invention have a nanoscale morphology, which can fill the micro-voids of the concrete cementitious system, achieving a micro-aggregate effect and accelerating the hydration reaction of cement and low-alkali sulfoaluminate cement. Simultaneously, the low-alkali sulfoaluminate cement itself has a fast hydration rate, and combined with the hydration-activating effect of MgO, the two work synergistically with the core-shell nanospheres to form a stable hydration product structure in the early stages. This allows for high strength without long-term curing, meeting the special requirements of rapid construction, rapid demolding, and rapid load-bearing in emergency repairs, precast components, and municipal emergency projects.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically a high-strength, early-strength special concrete and its preparation method. Background Technology

[0002] Shotcrete is a specialized concrete construction technique that involves mixing cement, mineral admixtures, aggregates, additives, and water in specific proportions, then spraying the mixture onto the work surface using a wet shotcrete machine and compressed air. In contemporary tunnel lining planning and construction, single-layer permanent lining structures primarily using shotcrete have become a future trend. For strata rich in groundwater, while measures such as water-stopping, dewatering, and drainage can be implemented, low impermeability of the shotcrete can lead to serious seepage problems and excessive ground settlement. In the presence of severe cracks, there is also the potential danger of collapse. Therefore, when constructing in water-rich strata, high requirements are placed on the early strength and impermeability of the shotcrete used in tunnels.

[0003] Cracks are a significant factor affecting the impermeability of concrete structures. They typically occur due to auto-shrinkage, drying shrinkage, and chemical shrinkage. Shotcrete contains a high amount of cementitious materials, thus increasing the risk of cracking. These cracks become major water seepage channels within the concrete, accelerating concrete deterioration and impacting structural stability and safety. Furthermore, conventional shotcrete often suffers from a higher actual water-cement ratio than the design ratio due to water seepage, resulting in poor hardening and slow strength gain, leading to increased rebound and further threatening the safety of construction workers. Therefore, developing shotcrete with high early-age strength and high crack resistance is crucial for the permanent safety of tunnel support. Summary of the Invention

[0004] The purpose of this invention is to provide a high-strength, early-strength special concrete and its preparation method. The core of this invention is to achieve the advantages of early strength, high strength, high density, and high durability through the structural modification of core-shell nanospheres, the synergistic hydration of the dual cementitious system, and the compounding of active admixtures. At the same time, it takes into account the convenience of construction, the environmental friendliness of raw materials, and the low alkalinity and resistance to degradation, thus solving the problems of contradiction between early strength and high strength, later strength decay, and poor durability of ordinary concrete.

[0005] The objective of this invention can be achieved through the following technical solutions: A method for preparing high-strength, early-strength special concrete includes the following steps: After mixing cement, low-alkali sulfoaluminate water, fly ash, MgO, high-strength early-strength core-shell nanospheres, polycarboxylate superplasticizer and water, the mixture is poured into a mold, vibrated to compact, covered with a curing film, and cured for 29-30 days at a temperature of 25-27℃ and a humidity of 90-95% to obtain high-strength early-strength special concrete.

[0006] Furthermore, the dosage ratio of cement, low-alkali sulfoaluminate water, fly ash, MgO, high-strength early-strength core-shell nanospheres, polycarboxylate superplasticizer and water is 100-120g: 140-150g: 20-30g: 6-8g: 9-11g: 2-4g: 40-50g.

[0007] Furthermore, the specific preparation steps for high-strength, early-strength core-shell nanospheres are as follows: Zinc oxide metal-organic framework powder, hollow aminated nanospheres, and N,N-dimethylformamide were added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 400-500 r / min. Then, benzyltriethylammonium chloride was added as a catalyst, and the mixture was heated to 115-120℃ and reacted for another 2-4 h. After naturally cooling to room temperature, the mixture was filtered, and the precipitate was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The precipitate was then vacuum dried at 60-80℃ for 1-2 h to obtain high-strength early-strength core-shell nanospheres.

[0008] Furthermore, the ratio of the amount of epoxy zinc metal-organic framework powder, hollow aminated nanospheres, N,N-dimethylformamide and benzyltriethylammonium chloride is 30-40g:35-40g:1-2L:3-5mL.

[0009] Furthermore, the specific preparation steps of the epoxy zinc metal-organic framework powder are as follows: Hydroxyl-terminated zinc metal-organic framework powder, ethanol, and deionized water were added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 500-600 r / min. The pH was then adjusted to 4 with hydrochloric acid, and (3-glycidylpropoxy)trimethoxysilane was added. The mixture was heated to 80-90℃ and stirred for 12-14 h. After centrifugation at 8000-9000 r / min for 3-5 min, the mixture was filtered. The precipitate was washed 2-4 times with deionized water and anhydrous ethanol, and then vacuum dried at 60-80℃ for 1-2 h to obtain epoxy zinc metal-organic framework powder.

[0010] Furthermore, the ratio of the amount of hydroxyl-terminated zinc metal-organic framework powder, ethanol, deionized water and (3-glycidylpropoxy)trimethoxysilane is 100-110g: 800-900mL: 400-500mL: 80-90mL.

[0011] Furthermore, the specific preparation steps of the hydroxyl-terminated zinc metal-organic framework powder are as follows: Zinc chloride, N,N-dimethylformamide, and a 1 mol / L glacial acetic acid solution were added to a polytetrafluoroethylene reactor. The mixture was stirred for 20-30 minutes at 40-50℃ and 400-500 rpm, and then ultrasonically dispersed for 40-50 minutes. 2-hydroxyterephthalic acid was then added, and the mixture was ultrasonically dispersed for 40-50 minutes. The reaction was carried out at 120-130℃ for 24-26 hours. After naturally cooling to room temperature, the precipitate was centrifuged at 2000-2200 rpm for 3-5 minutes. The precipitate was washed 2-4 times with N,N-dimethylformamide, and then washed 2-4 times with dichloromethane by centrifugation. The precipitate was then vacuum dried at 60-80℃ for 1-2 hours to obtain a hydroxyl-terminated zinc metal-organic framework powder.

[0012] Furthermore, the ratio of zinc chloride, N,N-dimethylformamide, glacial acetic acid solution and 2-hydroxyterephthalic acid is 120-150g: 3000-4000mL: 1-2mL: 200-300g.

[0013] Furthermore, the specific preparation steps of the hollow aminated nanospheres are as follows: Deionized water and 4-aminophenol were added to a reaction vessel and stirred at 10-12℃ and 500-600 r / min for 10-12 min. Then, formaldehyde solution was added and stirring was continued for 10-12 min. Ammonia solution with a concentration of 2.8 mmol / L was added, and the mixture was heated to 28-30℃ and stirred for 30-40 min. The mixture was then filtered under reduced pressure, and the product was washed 2-4 times with deionized water and freeze-dried at -20℃ for 12-14 h to obtain aminophenolic resin. Aminophenolic resin and anhydrous ethanol were added to a reaction vessel and stirred at 28-30℃ and 500-600 r / min for 10-12 min. The mixture was then ultrasonically dispersed for 40-50 min, filtered under reduced pressure, and the product was washed 2-4 times with deionized water and freeze-dried at -20℃ for 12-14 h to obtain hollow aminophenolic nanospheres.

[0014] Furthermore, the ratio of deionized water, 4-aminophenol, formaldehyde solution, and ammonia is 40-45L: 160-180g: 100-120mL: 20-30mL.

[0015] Furthermore, the ratio of amino-modified phenolic resin to anhydrous ethanol is 72-80g:8-9L.

[0016] The beneficial effects of this invention are: 1. The high-strength, early-strength special concrete prepared by this invention achieves the core advantages of early strength, high strength, high density, and high durability through the structural modification of core-shell nanospheres, the synergistic hydration of the dual cementitious system, and the compounding of active admixtures. At the same time, it takes into account the convenience of construction, the environmental friendliness of raw materials, and the low alkalinity and resistance to degradation, thus solving the problems of contradiction between early strength and high strength, later strength decay, and poor durability of ordinary concrete.

[0017] 2. The core-shell nanospheres of this invention have a nanoscale morphology, which can fill the micro-voids of the concrete cementitious system, realize the micro-aggregate effect, and accelerate the hydration reaction of cement and low-alkali sulfoaluminate cement. At the same time, the low-alkali sulfoaluminate cement itself has a fast hydration rate. Combined with the hydration activation effect of MgO, the two work synergistically with the core-shell nanospheres to form a stable hydration product structure in the early stage. It can achieve high strength without long-term curing, meeting the special needs of rapid construction, rapid demolding, and rapid load-bearing in emergency repairs, precast components, and municipal emergency projects.

[0018] 3. The epoxy zinc metal-organic framework powder of the present invention has a regular porous crystal structure, and the amino-modified phenolic resin shell is a hollow nanostructure. The combination of the two not only provides a large number of active sites for hydration reaction, but also adsorbs hydration products and guides their directional growth to form a dense hydration product network. The hollow amino-modified phenolic resin nanospheres are hollow structures, and the epoxy zinc MOF is a porous structure. Both are nanoscale and can fill the nanoscale and microscale micropores of cement paste step by step. Combined with the fine aggregate effect of fly ash, a step-by-step filling system of large pores, small pores and nanopores is formed inside the concrete, which reduces structural defects such as microcracks and micropores from the source and improves the overall density.

[0019] 4. This invention achieves covalent bonding by the ring-opening reaction between the epoxy zinc metal-organic framework powder and the amino groups of the hollow amino-modified phenolic resin shell, resulting in a gapless core-shell interface. At the same time, the active groups such as amino and epoxy groups of the core-shell nanospheres can form chemical bonds with the hydration products of the cementitious system, which greatly enhances the interfacial bonding force between the nanospheres and the cementitious matrix, avoiding the problem of separation between ordinary admixtures and the matrix interface, and ensuring the continuity and stability of the internal structure of concrete. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: A method for preparing high-strength, early-strength special concrete, comprising the following steps: S1: Add 40 L of deionized water and 160 g of 4-aminophenol to a reaction vessel, stir at 10 °C and 500 r / min for 10 min, then add 100 mL of formaldehyde solution, continue stirring for 10 min, then add 20 mL of 2.8 mmol / L ammonia water, heat to 28 °C, continue stirring for 30 min, filter under reduced pressure, wash the product twice with deionized water, and freeze-dry at -20 °C for 12 h to obtain amino-modified phenolic resin; Add 72 g of amino-modified phenolic resin and 8 L of anhydrous ethanol to a reaction vessel, stir at 28 °C and 500 r / min for 10 min, ultrasonically disperse for 40 min, filter under reduced pressure, wash the product twice with deionized water, and freeze-dry at -20 °C for 12 h to obtain hollow amino-modified nanospheres.

[0022] S2: 120g zinc chloride, 3000mL N,N-dimethylformamide and 1mL 1mol / L glacial acetic acid solution were added to a polytetrafluoroethylene reactor. The mixture was stirred for 20min at 40℃ and 400r / min, and then ultrasonically dispersed for 40min. 200g 2-hydroxyterephthalic acid was then added and ultrasonically dispersed for 40min. The mixture was kept at 120℃ for 24h and allowed to cool naturally to room temperature. The mixture was centrifuged at 2000r / min for 3min. The precipitate was washed twice with N,N-dimethylformamide and then twice with dichloromethane by centrifugation. The precipitate was then vacuum dried at 60℃ for 1h to obtain a zinc metal-organic framework powder with terminal hydroxyl groups.

[0023] S3: Add 100g of hydroxyl-terminated zinc metal-organic framework powder, 800mL of ethanol and 400mL of deionized water to a reaction vessel, stir for 20min at 20℃ and 500r / min, then adjust the pH to 4 with hydrochloric acid, add 80mL of (3-glycidylpropoxy)trimethoxysilane, heat to 80℃, continue stirring for 12h, centrifuge at 8000r / min for 3min, filter, wash the precipitate twice with deionized water and anhydrous ethanol respectively, and dry under vacuum at 60℃ for 1h to obtain epoxy zinc metal-organic framework powder.

[0024] S4: 30g of zinc oxide metal-organic framework powder, 35g of hollow aminated nanospheres and 1L of N,N-dimethylformamide were added to a reaction vessel and stirred for 20min at 20℃ and 400r / min. Then, 3mL of benzyltriethylammonium chloride as a catalyst was added, and the mixture was heated to 115℃ and reacted for 2h. After naturally cooling to room temperature, the mixture was filtered, and the precipitate was washed twice with deionized water and anhydrous ethanol, respectively. The precipitate was then dried under vacuum at 60℃ for 1h to obtain high-strength early-strength core-shell nanospheres.

[0025] S5: Mix 100g cement, 140g low-alkali sulfoaluminate water, 20g fly ash, 6g MgO, 9g high-strength early-strength core-shell nanospheres, 2g polycarboxylate superplasticizer and 40g water, pour into a mold, vibrate to compact, cover with a curing film, and cure for 29 days at 25℃ and 90% humidity to obtain high-strength early-strength special concrete.

[0026] Example 2: A method for preparing high-strength, early-strength special concrete, comprising the following steps: S1: 42.5 L of deionized water and 170 g of 4-aminophenol were added to a reaction vessel and stirred at 11 °C and 550 r / min for 11 min. Then, 110 mL of formaldehyde solution was added and stirring was continued for 11 min. Next, 25 mL of 2.8 mmol / L ammonia water was added, and the mixture was heated to 29 °C and stirred for 35 min. The mixture was then filtered under reduced pressure, and the product was washed three times with deionized water and freeze-dried at -20 °C for 13 h to obtain aminophenolic resin. 76 g of aminophenolic resin and 8.5 L of anhydrous ethanol were added to a reaction vessel and stirred at 29 °C and 550 r / min for 11 min. The mixture was then ultrasonically dispersed for 45 min and filtered under reduced pressure. The product was washed three times with deionized water and freeze-dried at -20 °C for 13 h to obtain hollow aminophenolic nanospheres.

[0027] S2: 135g zinc chloride, 3500mL N,N-dimethylformamide, and 1.5mL 1mol / L glacial acetic acid solution were added to a polytetrafluoroethylene reactor. The mixture was stirred at 45℃ and 450r / min for 25min, and then ultrasonically dispersed for 45min. 250g 2-hydroxyterephthalic acid was then added, and the mixture was ultrasonically dispersed for 45min. The mixture was kept at 125℃ for 25h, allowed to cool naturally to room temperature, and centrifuged at 2100r / min for 4min. The precipitate was washed three times with N,N-dimethylformamide, then washed three times with dichloromethane by centrifugation, and finally vacuum dried at 70℃ for 1.5h to obtain a hydroxyl-terminated zinc metal-organic framework powder.

[0028] S3: Add 105g of hydroxyl-terminated zinc metal-organic framework powder, 850mL of ethanol and 450mL of deionized water to a reaction vessel, stir for 25min at 22.5℃ and 550r / min, then adjust the pH to 4 with hydrochloric acid, add 85mL of (3-glycidylpropoxy)trimethoxysilane, heat to 85℃, continue stirring for 13h, centrifuge at 8500r / min for 4min, filter, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 70℃ for 1.5h to obtain epoxy zinc metal-organic framework powder.

[0029] S4: 35g of zinc oxide metal-organic framework powder, 37.5g of hollow aminated nanospheres and 1.5L of N,N-dimethylformamide were added to a reaction vessel and stirred for 25min at 22.5℃ and 450r / min. Then, 4mL of benzyltriethylammonium chloride as a catalyst was added, and the mixture was heated to 117.5℃ and reacted for another 3h. After naturally cooling to room temperature, the mixture was filtered, and the precipitate was washed three times with deionized water and three times with anhydrous ethanol. The precipitate was then dried under vacuum at 70℃ for 1.5h to obtain high-strength early-strength core-shell nanospheres.

[0030] S5: Mix 110g cement, 145g low-alkali sulfoaluminate water, 25g fly ash, 7g MgO, 10g high-strength early-strength core-shell nanospheres, 3g polycarboxylate superplasticizer and 45g water, pour into a mold, vibrate to compact, cover with a curing film, and cure for 29.5 days at a temperature of 26℃ and a humidity of 92.5% to obtain high-strength early-strength special concrete.

[0031] Example 3: A method for preparing high-strength, early-strength special concrete, comprising the following steps: S1: Add 45 L of deionized water and 180 g of 4-aminophenol to a reaction vessel, stir at 12 °C and 600 r / min for 12 min, then add 120 mL of formaldehyde solution, continue stirring for 12 min, then add 30 mL of 2.8 mmol / L ammonia water, heat to 30 °C, continue stirring for 40 min, filter under reduced pressure, wash the product 4 times with deionized water, and freeze-dry at -20 °C for 14 h to obtain aminophenolic resin; Add 80 g of aminophenolic resin and 9 L of anhydrous ethanol to a reaction vessel, stir at 30 °C and 600 r / min for 12 min, ultrasonically disperse for 50 min, filter under reduced pressure, wash the product 4 times with deionized water, and freeze-dry at -20 °C for 14 h to obtain hollow aminophenolic nanospheres.

[0032] S2: Add 150g zinc chloride, 4000mL N,N-dimethylformamide and 2mL 1mol / L glacial acetic acid solution to a polytetrafluoroethylene reactor. Stir for 30min at 50℃ and 500r / min, then sonicate for 50min. Add 300g 2-hydroxyterephthalic acid and sonicate for 50min. Keep the reaction at 130℃ for 26h. Allow to cool naturally to room temperature. Centrifuge at 2200r / min for 5min. Wash the precipitate 4 times with N,N-dimethylformamide, then centrifuge and wash 4 times with dichloromethane. Dry under vacuum at 80℃ for 2h to obtain hydroxyl-terminated zinc metal-organic framework powder.

[0033] S3: 110g of hydroxyl-terminated zinc metal-organic framework powder, 900mL of ethanol and 500mL of deionized water were added to a reaction vessel and stirred at 25℃ and 600r / min for 30min. Then, the pH value was adjusted to 4 with hydrochloric acid, and 90mL of (3-glycidylpropoxy)trimethoxysilane was added. The mixture was heated to 90℃ and stirred for 14h. After centrifugation at 9000r / min for 5min, the mixture was filtered. The precipitate was washed 4 times with deionized water and anhydrous ethanol, respectively, and dried under vacuum at 80℃ for 2h to obtain epoxy zinc metal-organic framework powder.

[0034] S4: 40g of zinc oxide metal-organic framework powder, 40g of hollow aminated nanospheres and 2L of N,N-dimethylformamide were added to a reaction vessel and stirred for 30min at 25℃ and 500r / min. Then, 5mL of benzyltriethylammonium chloride as a catalyst was added, and the mixture was heated to 120℃ and reacted for 4h. After naturally cooling to room temperature, the mixture was filtered, and the precipitate was washed 4 times with deionized water and anhydrous ethanol, respectively. The precipitate was then dried under vacuum at 80℃ for 2h to obtain high-strength early-strength core-shell nanospheres.

[0035] S5: Mix 120g cement, 150g low-alkali sulfoaluminate water, 30g fly ash, 8g MgO, 11g high-strength early-strength core-shell nanospheres, 4g polycarboxylate superplasticizer and 50g water, pour into a mold, vibrate to compact, cover with a curing film, and cure for 30 days at 27℃ and 95% humidity to obtain high-strength early-strength special concrete.

[0036] Comparative Example 1: Based on Example 3, the hollow aminated nanospheres in step S4 were replaced with the aminated phenolic resin in step S1.

[0037] Comparative Example 2: Based on Example 3, the epoxy zinc metal-organic framework powder in step S4 was replaced with the hydroxyl-terminated zinc metal-organic framework powder prepared in step S2.

[0038] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-2. The compressive strength test methods and instruments were strictly performed according to GB / T50081 "Test Methods for Mechanical Properties of Ordinary Concrete"; the flexural strength test methods and instruments were strictly performed according to GB / T50081 "Standard for Test Methods for Mechanical Properties of Ordinary Concrete"; and the slump test methods and instruments were strictly performed according to GB / T50080 "Standard for Test Methods for Performance of Ordinary Concrete Mixtures". The results are shown in Table 1. Table 1 ; As shown in Table 1, Comparative Example 1 loses the core advantage of hollow nanostructure: Aminophenolic resin is an ordinary resin powder without hollow nanomorphology, and cannot achieve "gradual filling of nanoscale and microscale micropores". This leads to an increase in microcracks and voids inside the concrete, a significant reduction in density, and directly results in a decrease in compressive strength to 72.1 MPa, weakening the foundation of durability such as impermeability and crack resistance; The lack of core-shell synergy leads to a significant reduction in early strength performance: It cannot form a "core-shell" structure with epoxy zinc MOF, thus failing to provide sufficient active sites for hydration reactions and failing to adsorb and guide hydration products. Directed growth and lack of nanoscale morphology to accelerate hydration reaction result in a 3-hour flexural strength of only 5.8 MPa, failing to meet the special requirements of rapid construction and high load-bearing capacity. Poor interfacial bonding and insufficient structural stability are also issues: the amino-modified phenolic resin lacks a core-shell covalent bond structure, and its amino groups cannot form stable chemical bonds with zinc epoxy MOF. This leads to loose interfacial bonding with the cementitious matrix, making separation easy and resulting in poor continuity of the concrete's internal structure. Furthermore, the resin powder has poor dispersibility, reducing the slump to 163 mm and decreasing workability, making it prone to defects such as honeycomb and pitting during construction.

[0039] Comparative Example 2 failed to form a stable core-shell structure due to interfacial gaps: the surface of the hydroxyl-terminated zinc MOF is composed of hydroxyl groups and lacks epoxy groups, thus it cannot undergo ring-opening reactions with the amino groups of the hollow aminated nanospheres to form covalent bonds. This results in significant gaps at the core-shell interface, preventing the realization of a synergistic "core-shell" effect. Consequently, the continuity and stability of the concrete's internal structure decrease, and the compressive strength drops to 78.3 MPa. Furthermore, the utilization rate of active sites decreases, and early strength is compromised: without modification by a silane coupling agent, the porous crystal structure of the hydroxyl-terminated zinc MOF fails to adequately expose its active sites, hindering effective... The adsorption and guidance of hydration product growth, coupled with the weakening of chemical bonding with the cementitious matrix, slowed down the hydration reaction rate, resulting in a 3-hour flexural strength of 7.0 MPa and a lack of early strength advantage. Poor dispersibility and slightly reduced workability were also observed: the hydrophilicity of the hydroxyl groups on the surface of the zinc-terminated MOF was less compatible than that of the epoxy-modified product, leading to slightly poorer dispersibility in the cementitious system. Although no significant agglomeration occurred, it still resulted in a slump reduction to 175 mm, a decrease compared to Example 3. This also affected the uniform distribution of hydration products, further weakening the stability of concrete strength.

[0040] In Comparative Example 3, the high-strength performance was completely unattainable: Without the micro-aggregate filling effect of core-shell nanospheres, the large, small, and nanoscale voids inside the concrete could not be filled step-by-step, resulting in extremely poor structural density. Simultaneously, the lack of active sites to guide the hydration reaction led to a loose network of hydration products, resulting in a compressive strength of only 65.8 MPa, far below the performance standards for high-strength concrete. Early-strength performance was also lost: without the accelerating effect of core-shell nanospheres on the hydration reaction, relying solely on the synergy of low-alkali sulfoaluminate cement and MgO, the hydration reaction rate was significantly slowed down, and stable water could not be formed in the early stages. The product structure has a flexural strength of only 4.8 MPa after 3 hours, which cannot meet the special engineering requirements of rapid demolding and rapid load-bearing. It has the worst workability and structural stability. The core-shell nanospheres have a certain dispersing and synergistic effect. After their absence, the dispersibility of the cementitious system decreases, the distribution uniformity of admixtures such as fly ash is insufficient, the slump drops to 152 mm, the workability is the worst, and the construction difficulty increases. At the same time, without the interfacial bonding between the core-shell nanospheres and the cementitious matrix, the internal structure of the concrete is loose, which easily leads to segregation and bleeding. It is also prone to drying shrinkage cracks in the later stage, resulting in extremely poor durability.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing high-strength, early-strength special concrete, characterized in that, Includes the following steps: After mixing cement, low-alkali sulfoaluminate water, fly ash, MgO, high-strength early-strength core-shell nanospheres, polycarboxylate superplasticizer and water, the mixture is poured into a mold, vibrated to compact, covered with a curing film, and cured for 29-30 days at a temperature of 25-27℃ and a humidity of 90-95% to obtain high-strength early-strength special concrete.

2. The method for preparing high-strength, early-strength special concrete according to claim 1, characterized in that, The ratio of cement, low-alkali sulfoaluminate water, fly ash, MgO, high-strength early-strength core-shell nanospheres, polycarboxylate superplasticizer and water is 100-120g: 140-150g: 20-30g: 6-8g: 9-11g: 2-4g: 40-50g.

3. The method for preparing high-strength, early-strength special concrete according to claim 1, characterized in that, The specific preparation steps of the high-strength early-strength core-shell nanospheres are as follows: Zinc oxide metal-organic framework powder, hollow aminated nanospheres, and N,N-dimethylformamide were added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 400-500 r / min. Then, benzyltriethylammonium chloride was added as a catalyst, and the mixture was heated to 115-120℃ and reacted for another 2-4 h. After naturally cooling to room temperature, the mixture was filtered, and the precipitate was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The precipitate was then vacuum dried at 60-80℃ for 1-2 h to obtain high-strength early-strength core-shell nanospheres.

4. The method for preparing high-strength, early-strength special concrete according to claim 3, characterized in that, The ratio of the epoxy zinc metal-organic framework powder, hollow aminated nanospheres, N,N-dimethylformamide and benzyltriethylammonium chloride is 30-40g:35-40g:1-2L:3-5mL.

5. The method for preparing high-strength, early-strength special concrete according to claim 3, characterized in that, The specific preparation steps of the epoxy zinc metal-organic framework powder are as follows: Hydroxyl-terminated zinc metal-organic framework powder, ethanol, and deionized water were added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 500-600 r / min. The pH was then adjusted to 4 with hydrochloric acid, and (3-glycidylpropoxy)trimethoxysilane was added. The mixture was heated to 80-90℃ and stirred for 12-14 h. After centrifugation at 8000-9000 r / min for 3-5 min, the mixture was filtered. The precipitate was washed 2-4 times with deionized water and anhydrous ethanol, and then vacuum dried at 60-80℃ for 1-2 h to obtain epoxy zinc metal-organic framework powder.

6. The method for preparing high-strength, early-strength special concrete according to claim 5, characterized in that, The ratio of the terminal hydroxyl zinc metal-organic framework powder, ethanol, deionized water and (3-glycidylpropoxy)trimethoxysilane is 100-110g: 800-900mL: 400-500mL: 80-90mL.

7. The method for preparing high-strength, early-strength special concrete according to claim 1, characterized in that, The specific preparation steps of the hydroxyl-terminated zinc metal-organic framework powder are as follows: Zinc chloride, N,N-dimethylformamide, and a 1 mol / L glacial acetic acid solution were added to a polytetrafluoroethylene reactor. The mixture was stirred for 20-30 minutes at 40-50℃ and 400-500 rpm, and then ultrasonically dispersed for 40-50 minutes. 2-hydroxyterephthalic acid was then added and ultrasonically dispersed for 40-50 minutes. The mixture was kept at 120-130℃ for 24-26 hours and allowed to cool naturally to room temperature. The mixture was then centrifuged at 2000-2200 rpm for 3-5 minutes. The precipitate was washed 2-4 times with N,N-dimethylformamide and then 2-4 times with dichloromethane. The precipitate was then vacuum dried at 60-80℃ for 1-2 hours to obtain a hydroxyl-terminated zinc metal-organic framework powder. The ratio of zinc chloride, N,N-dimethylformamide, glacial acetic acid solution and 2-hydroxyterephthalic acid is 120-150g: 3000-4000mL: 1-2mL: 200-300g.

8. The method for preparing high-strength, early-strength special concrete according to claim 7, characterized in that, The specific preparation steps of the hollow aminated nanospheres are as follows: Deionized water and 4-aminophenol were added to a reaction vessel and stirred at 10-12℃ and 500-600 r / min for 10-12 min. Then, formaldehyde solution was added and stirring was continued for 10-12 min. Ammonia solution with a concentration of 2.8 mmol / L was added, and the mixture was heated to 28-30℃ and stirred for 30-40 min. The mixture was then filtered under reduced pressure, and the product was washed 2-4 times with deionized water and freeze-dried at -20℃ for 12-14 h to obtain aminophenolic resin. Aminophenolic resin and anhydrous ethanol were added to a reaction vessel and stirred at 28-30℃ and 500-600 r / min for 10-12 min. The mixture was then ultrasonically dispersed for 40-50 min, filtered under reduced pressure, and the product was washed 2-4 times with deionized water and freeze-dried at -20℃ for 12-14 h to obtain hollow aminophenolic nanospheres.

9. The method for preparing high-strength, early-strength special concrete according to claim 8, characterized in that, The ratio of deionized water, 4-aminophenol, formaldehyde solution and ammonia is 40-45L: 160-180g: 100-120mL: 20-30mL; the ratio of aminophenolic resin and anhydrous ethanol is 72-80g: 8-9L.

10. A high-strength, early-strength special concrete, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.