Maintenance-free high-anti-crack clear water concrete and preparation method thereof

Abstract

The application discloses a kind of maintenance-free high crack resistance clear water concrete, each component and the weight fraction including it are as follows: cement 130-180 parts, fly ash 90-150 parts, mineral powder 60-110 parts, sand 750-850 parts, stone 1100-1200 parts, water 120-160 parts, high-performance water reducing agent 3-6 parts, crack-free maintenance additive 4-8 parts;The crack-free maintenance additive is first ultrasonic treated with aliphatic hyperbranched polyester to nano carbon fiber dispersion liquid, and nano carbon fiber reinforced dispersion liquid is obtained;Then add ethylene-tetrafluoroethylene copolymer, and carry out stirring treatment, drying to obtain.The clear water concrete has good apparent quality and mechanical properties, and can effectively optimize the pore structure, reduce the generation of harmful pores, effectively solve the problem of traditional clear water concrete surface bubble, etc.;And the preparation process is relatively simple, the cost is relatively low, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a maintenance-free, high-crack-resistant fair-faced concrete and its preparation method. Background Technology

[0002] Fair-faced concrete utilizes the natural texture of the concrete after molding as its surface finish. Compared to ordinary concrete, fair-faced concrete offers advantages such as better surface color, stronger three-dimensionality, smoother surface, and no environmental pollution. Improving the appearance quality of fair-faced concrete helps enhance its mechanical properties and durability, eliminating problems such as grout leakage, cracks, and porosity that may occur during conventional concrete construction. Current fair-faced concrete typically requires uniform color, dense surface, sharp edges, and a smooth finish, and is widely used in industrial and civil buildings, municipal engineering, and bridge construction.

[0003] Fair-faced concrete often employs curing methods such as water spraying or covering with a membrane, but these methods can lead to issues like color variations and grain lines. Currently, many researchers are exploring various methods to improve the appearance quality of concrete, such as strictly controlling the concrete mix proportions, using defoamers, air-entraining agents, and even high-quality formwork and release agents. However, these methods typically involve complex preparation procedures, and the appearance quality is often difficult to achieve, resulting in limited improvement.

[0004] Therefore, further exploration of curing-free, crack-resistant fair-faced concrete that can simplify the construction process, reduce manufacturing costs, and solve problems such as poor appearance quality is of great research and application significance. Summary of the Invention

[0005] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a maintenance-free, high-crack-resistant fair-faced concrete that exhibits good surface quality even under substandard, unmaintainable, or harsh environmental conditions. This invention effectively solves problems such as surface cracks and numerous air bubbles, simplifies the construction and maintenance process of fair-faced concrete, significantly reduces preparation costs, and is suitable for widespread application.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A type of maintenance-free, high-crack-resistant fair-faced concrete comprises the following components and their respective weight percentages: 130-180 parts cement, 90-150 parts fly ash, 60-110 parts mineral powder, 750-850 parts sand, 1100-1200 parts aggregate, 120-160 parts water, 3-6 parts high-performance water-reducing agent, and 4-8 parts crack-resistant, maintenance-free admixture. The crack-resistant, maintenance-free admixture is obtained by first adding aliphatic hyperbranched polyester to a nano-carbon fiber dispersion and ultrasonically treating it, then adding ethylene-tetrafluoroethylene copolymer, stirring, and drying.

[0008] The specific preparation method of the crack-resistant, maintenance-free admixture in the above scheme includes the following steps:

[0009] 1) Place the carbon nanofibers (VGCF) in warm water and sonicate to obtain a VGCF dispersion; add aliphatic hyperbranched polyester and sonicate under heat preservation to obtain a VGCF reinforced dispersion.

[0010] 2) Add ethylene-tetrafluoroethylene (ETFE) copolymer powder to the obtained VGCF reinforced dispersion, stir and dry to obtain the high crack-resistant, maintenance-free fair-faced concrete admixture.

[0011] In the above scheme, the diameter of the VGCF nanofiber is 30-200 nm, the length is 1-15 μm, and the specific surface area is 15-30 m². 2 / g.

[0012] In the above scheme, the ultrasonic treatment temperature is 50-60℃ and the time is 40-60 min; the heat preservation ultrasonic treatment temperature is 50-60℃ and the time is 30-50 min.

[0013] In the above scheme, the aliphatic hyperbranched polyester has a molecular weight of 1100-3700 g / mol and a hydroxyl value of 560-600 mg KOH / g.

[0014] In the above scheme, the components and their weight percentages in the VGCF reinforced dispersion include: 30-45 parts of nano-carbon fiber VGCF, 20-30 parts of aliphatic hyperbranched polyester, and 30-45 parts of water.

[0015] In the above scheme, the molecular weight of the ethylene-tetrafluoroethylene (ETFE) copolymer powder is 120-140, its melting point is 250-260℃, its tensile strength is 300-410%, and its elongation at break is 28-35MPa.

[0016] In the above scheme, the mass ratio of the ethylene-tetrafluoroethylene (ETFE) copolymer powder to the VGCF-reinforced dispersion is 1:4 to 8.

[0017] In the above scheme, the stirring rate is 200-400 rpm and the time is 1-1.5 h.

[0018] In the above scheme, the drying step adopts a vacuum drying process with a temperature of 40-60℃ and a time of 8-10h.

[0019] In the preparation process of the anti-cracking and maintenance-free admixture of the present invention, firstly, VGCF nanofibers are added to warm water and ultrasonically dispersed to achieve uniformity. Then, aliphatic hyperbranched polyester is added to the mixture, and ultrasonic dispersion is continuously carried out at a temperature of 50-60°C. This allows the VGCF nanofibers to form a network and / or mesh structure in the fluid, which is beneficial to improving the toughness of the VGCF nanofibers. At the same time, it can increase the cohesive force and adhesion of the fluid, inhibit the sedimentation or deposition of VGCF nanofibers in the liquid, and maintain the uniformity of the VGCF-reinforced dispersion. Then, ethylene-tetrafluoroethylene (ETFE) copolymer powder was added to VGCF reinforced dispersion and stirred to further improve the dispersion performance of carbon nanofibers and ensure the workability of the resulting concrete mixture. In addition, it can promote the uniform adsorption of ethylene-tetrafluoroethylene (ETFE) copolymer powder in the network structure of reinforcing fibers, which is beneficial to further improve the crack resistance of the resulting concrete. At the same time, the branches of aliphatic hyperbranched polyester have a certain optimization effect on the internal pore structure of concrete, which can reduce the generation of air bubbles on the surface of fair-faced concrete and further improve the appearance quality of concrete.

[0020] In the above scheme, the high-performance water-reducing agent has a water reduction rate of more than 25%, a solid content of 13-17%, and a pH value of 6-8.

[0021] In the above scheme, the main chemical composition and their mass percentage of the fly ash include: SiO2 25-45%, Al2O3 30-40%, Fe2O3 1-4%, CaO 1-3%, MgO 0-1%, K2O 0-1%, Na2O 0-1%, SO3 0-1%, TiO2 0-1%, and residual carbon 2-8%; the specific surface area is 320-400 m². 2 / kg.

[0022] In the above scheme, the main chemical composition of the mineral powder and its mass percentage include: SiO2 20-40%, Al2O3 15-20%, Fe2O3 1-4%, CaO 32-50%, MgO 0-1%, K2O 0-1%, Na2O 0-1%, SO3 0-1%, TiO2 0-1%, and residual carbon 2-5%; the specific surface area is 500-800 m². 2 / kg.

[0023] In the above scheme, the cement is ordinary Portland cement.

[0024] In the above scheme, the sand is natural sand with a fineness modulus of 2.3 to 2.7, and is medium sand in zone II; the stone is pebble with a particle size of 5 to 20 mm.

[0025] The above-mentioned method for preparing maintenance-free, crack-resistant fair-faced concrete includes the following steps:

[0026] 1) Weigh each raw material according to the proportion. The raw materials and their weight percentages include: 130-180 parts cement, 90-150 parts fly ash, 60-110 parts mineral powder, 750-850 parts sand, 1100-1200 parts stone, 120-160 parts water, 3-6 parts high-performance water-reducing agent, and 4-8 parts crack-resistant and maintenance-free admixture.

[0027] 2) Weigh out the cement, fly ash, mineral powder, sand, stone, water, high-performance water-reducing agent, and crack-resistant, maintenance-free admixture and add them to the mixer for mixing.

[0028] 3) Add the obtained mixture to the template in layers, vibrate, let stand, and remove the template to obtain the maintenance-free, crack-resistant fair-faced concrete specimen.

[0029] Furthermore, during the layered addition of the mixture, a vibrator is used to compact the mixture after each layer is added; finally, the mixture is compacted until the surface of the concrete mixture is covered with slurry and free of air bubbles.

[0030] In the above scheme, the settling time is 24 to 48 hours.

[0031] Furthermore, the obtained concrete specimens were placed in natural environments, especially harsh environments, until the required age was reached. The harsh environments corresponded to temperatures of 35–42°C, humidity of 30–40%, and wind speeds greater than 3.0 m / s.

[0032] The maintenance-free, crack-resistant fair-faced concrete prepared according to the above scheme has a maximum crack width of less than 0.18 mm, a total crack length of less than 310 mm, and a total cracked area per unit area of ​​less than 38.0 mm². 2 / m 2 The maximum bubble diameter is 4.0 mm, the bubble depth is less than 1.6 mm, and the bubble area per square meter is less than 9.7 cm². 2 The 28-day compressive strength is greater than 30MPa; the concrete surface has no color difference, and there are no signs of grout leakage, flow, or erosion.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1) The anti-crack surface curing admixture used in this invention can effectively improve the appearance quality of fair-faced concrete in harsh environments, reduce the risk of cracks appearing on the surface of fair-faced concrete due to untimely or no curing, and effectively optimize the pore structure of concrete, reduce the generation of harmful pores, and solve the problem of many air bubbles on the surface of fair-faced concrete.

[0035] 2) The fair-faced concrete described in this invention can effectively simplify the preparation process and save on the curing cost of fair-faced concrete, making it suitable for widespread application. Attached Figure Description

[0036] Figure 1 The example uses the structural formula of an aliphatic hyperbranched polyester. Detailed Implementation

[0037] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0038] In the following embodiments, the VGCF nanofibers used were provided by Shanghai Foreign Electric International Trade Co., Ltd., with an average length of 6 μm, an average fiber diameter of 150 nm, and a specific surface area of ​​18 m². 2 / g.

[0039] In the following examples, the aliphatic hyperbranched polyester used was provided by (Alpha) Henan Weitixi Chemical Technology Co., Ltd., and its molecular formula is C 155 H 256 O 93 (See structural formula) Figure 1 ), molecular weight 3604 g / mol, hydroxyl value 580 mg KOH / g.

[0040] In the following examples, the ethylene-tetrafluoroethylene (ETFE) copolymer powder used was provided by Dongguan Taotao Plastic Raw Materials Co., Ltd., with a melting point of 250°C, tensile strength of 400%, and elongation at break of 30 MPa.

[0041] In the following examples, the fly ash used was provided by China Construction Western Construction Xinjiang Co., Ltd., and its main chemical composition and its mass percentage include: SiO2 41.93%, Al2O3 35.19%, Fe2O3 2.95%, CaO 3%, MgO 0.74%, K2O 0.46%, Na2O 0.14%, SO3 0.24%, TiO2 0.38%, and residual carbon 8%.

[0042] In the following examples, the mineral powder used was provided by China Construction Western Construction Xinjiang Co., Ltd., and its main chemical composition and its mass percentage include: SiO2 32.5%, Al2O3 19.2%, Fe2O3 1.4%, CaO 37.9%, MgO 0.8%, K2O 0.4%, Na2O 0.6%, SO3 0.6%, TiO2 0.9%, and residual carbon 4.2%.

[0043] The cement used can be P·O 42.5; the sand is natural sand with a fineness modulus of 2.3 to 2.7, belonging to the second zone medium sand; the coarse aggregate used is gravel with a particle size of 5 to 20 mm; the solid content of the high-performance water-reducing agent used is 17%, and the water reduction rate is 28%.

[0044] Example 1

[0045] A type of maintenance-free, crack-resistant fair-faced concrete, the preparation method of which includes the following steps:

[0046] 1) Preparation of crack-resistant, maintenance-free admixtures;

[0047] Weigh 30 parts (by weight, the same below) of carbon nanofiber VGCF and 30 parts of water, and disperse them in an ultrasonic disperser at a frequency of 20 kHz for 40 min while maintaining a temperature of 50 ℃. Weigh 20 parts of aliphatic hyperbranched polyester and add them to the dispersion. Continue ultrasonic dispersion at a temperature of 50 ℃ for 30 min, and then cool to room temperature (25 ℃) to prepare VGCF reinforced dispersion.

[0048] Weigh 1 part of ethylene-tetrafluoroethylene (ETFE) copolymer powder and 4 parts of VGCF reinforced dispersion, stir at 200 rpm for 1 hour, put the mixture into a vacuum drying oven and dry at 40°C for 8 hours, take it out and put it into a desiccator to cool to room temperature (25°C) to obtain a high crack-resistant, maintenance-free fair-faced concrete admixture.

[0049] 2) Weigh 150 parts cement, 130 parts fly ash, 60 parts mineral powder, 785 parts sand, 1150 parts gravel, 145 parts water, 4 parts high-performance water-reducing agent, and 5 parts high-crack-resistant, no-curing fair-faced concrete admixture. After weighing, pour the mixture into a forced mixer and mix for 2 minutes. Pour the mixture into layers and fill them into a 1m×1m×1m steel template with a layer thickness of 50cm. After each layer is filled, use a vibrator to compact the mixture. Stop vibrating when the surface of the concrete mixture is covered with slurry and there are no air bubbles. Let it stand for 24 hours and then remove the template. The resulting concrete specimens are exposed to a harsh natural environment (average temperature 35℃, average humidity 32%, average wind speed 3.5m / s) without any curing. After reaching an age of 28 days, test the surface of the concrete for air bubbles and cracks according to standard JGJ 169.

[0050] Testing revealed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this embodiment was 0.12 mm, the total crack length was 285 mm, and the total cracked area per unit area was 26.8 mm². 2 / m 2 The maximum bubble diameter is 2.6 mm, the bubble depth is 1.2 mm, and the bubble area per square meter is 8.3 cm². 2 The compressive strength after 28 days is 45.6 MPa.

[0051] Example 2

[0052] A type of maintenance-free, crack-resistant fair-faced concrete, the preparation method of which includes the following steps:

[0053] 1) Preparation of crack-resistant, maintenance-free admixtures;

[0054] Weigh 45 parts of VGCF nanofiber and 40 parts of water, and disperse them in an ultrasonic disperser at a frequency of 25 kHz for 60 min while maintaining a temperature of 60 ℃. Weigh 30 parts of aliphatic hyperbranched polyester and add them to the dispersion. Continue ultrasonic dispersion at a temperature of 60 ℃ for 50 min, and then cool to room temperature (25 ℃) to prepare VGCF reinforced dispersion.

[0055] Weigh 1 part of ethylene-tetrafluoroethylene (ETFE) copolymer powder and 6 parts of VGCF reinforced dispersion, stir at 400 rpm for 1.5 h, put the mixture into a vacuum drying oven and dry at 50 ℃ for 9 h, take it out and put it into a desiccator to cool to room temperature (25 ℃) to obtain a high crack-resistant, maintenance-free fair-faced concrete admixture.

[0056] 2) Weigh 180 parts cement, 100 parts fly ash, 110 parts mineral powder, 750 parts sand, 1100 parts gravel, 155 parts water, 5 parts high-performance water-reducing agent, and 8 parts high-crack-resistant, no-curing fair-faced concrete admixture. After weighing, pour the mixture into a forced mixer and mix for 3 minutes. Pour the mixture into layers and fill them into a 1m×1m×1m steel template with a layer thickness of 50cm. After each layer is filled, use a vibrator to compact the mixture. Stop vibrating when the surface of the concrete mixture is covered with slurry and there are no air bubbles. After standing for 48 hours, remove the template. The resulting concrete specimens are exposed to a harsh natural environment (average temperature 36℃, average humidity 30%, average wind speed 3.8m / s) without any curing. After reaching an age of 28 days, test the surface of the concrete for air bubbles and cracks according to standard JGJ 169.

[0057] Testing revealed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this embodiment was 0.10 mm, the total crack length was 230 mm, and the total cracked area per unit area was 22.8 mm². 2 / m 2 The maximum bubble diameter is 1.7 mm, the bubble depth is 1.0 mm, and the bubble area per square meter is 6.5 cm². 2 The compressive strength after 28 days is 47.5 MPa.

[0058] Example 3

[0059] A type of maintenance-free, crack-resistant fair-faced concrete, the preparation method of which includes the following steps:

[0060] 1) Preparation of crack-resistant, maintenance-free admixtures;

[0061] Weigh 40 parts of VGCF nanofiber and 40 parts of water, and disperse them in an ultrasonic disperser at a frequency of 20 kHz for 50 min while maintaining a temperature of 55 ℃. Weigh 25 parts of aliphatic hyperbranched polyester and add them to the dispersion. Continue ultrasonic dispersion at a temperature of 55 ℃ for 40 min, and then cool to room temperature (25 ℃) to prepare VGCF reinforced dispersion.

[0062] 2) Weigh 1 part of ethylene-tetrafluoroethylene (ETFE) copolymer powder and 8 parts of VGCF reinforced dispersion, stir at 300 rpm for 1 hour, put the mixture into a vacuum drying oven and dry at 60°C for 8 hours, take it out and put it into a desiccator to cool to room temperature (25°C) to obtain a high crack-resistant, maintenance-free fair-faced concrete admixture.

[0063] Weigh out 150 parts cement, 110 parts fly ash, 90 parts mineral powder, 800 parts sand, 1200 parts gravel, 150 parts water, 5 parts high-performance water-reducing agent, and 5 parts high-crack-resistant, no-curing fair-faced concrete admixture. After weighing, pour the mixture into a forced mixer and mix for 2 minutes. Pour the mixture into layers and fill them into a 1m×1m×1m steel template with a layer thickness of 50cm. After each layer is filled, use a vibrator to compact the mixture. Stop vibrating when the surface of the concrete mixture is covered with slurry and there are no air bubbles. After standing for 30 hours, remove the template. The resulting concrete specimens are exposed to a harsh natural environment (average temperature 37℃, average humidity 36%, average wind speed 4.1m / s) without any curing. After reaching an age of 28 days, test the surface of the concrete for air bubbles and cracks according to standard JGJ 169.

[0064] Testing revealed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this embodiment was 0.15 mm, the total crack length was 305 mm, and the total cracked area per unit area was 35.8 mm². 2 / m 2 The maximum bubble diameter is 3.5 mm, the bubble depth is 1.6 mm, and the bubble area per square meter is 9.7 cm². 2 The compressive strength after 28 days is 44.7 MPa.

[0065] Comparative Example 1

[0066] A type of fair-faced concrete is prepared using a method largely the same as in Example 3, except that the preparation steps of the admixture are as follows:

[0067] Weigh 60 parts of VGCF nanofibers and 40 parts of water, and disperse them in an ultrasonic disperser at a frequency of 20 kHz for 50 min while maintaining a temperature of 55℃ to obtain a VGCF dispersion.

[0068] Weigh 1 part of ethylene-tetrafluoroethylene (ETFE) copolymer powder and 8 parts of VGCF dispersion, stir at 300 rpm for 1 hour, put the mixture into a vacuum drying oven and dry at 50°C for 8 hours, take it out and put it into a desiccator to cool to room temperature (25°C) to obtain the additive.

[0069] Tests showed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this comparative example was 0.45 mm, the total crack length was 860 mm, and the total cracked area per unit area was 386 mm². 2 / m 2 The maximum bubble diameter is 8.6 mm, the bubble depth is 2.2 mm, and the bubble area per square meter is 18.6 cm². 2 The compressive strength after 28 days is 38.6 MPa.

[0070] Comparative Example 2

[0071] A type of fair-faced concrete is prepared using a method largely the same as in Example 2, except that the preparation steps of the admixture are as follows:

[0072] Weigh 30 parts of aliphatic hyperbranched polyester and 40 parts of water, and disperse them in an ultrasonic disperser at a frequency of 25 kHz for 60 min while maintaining a temperature of 60℃. Then cool to room temperature (25℃) to prepare a dispersion.

[0073] Weigh 1 part of ethylene-tetrafluoroethylene (ETFE) copolymer powder and 6 parts of dispersion, stir at 400 rpm for 1.5 h, put the mixture into a vacuum drying oven and dry at 50 °C for 9 h, take it out and put it into a desiccator to cool to room temperature (25 °C) to obtain the additive.

[0074] Tests showed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this comparative example was 1.2 mm, the total crack length was 1420 mm, and the total cracked area per unit area was 1405 mm². 2 / m 2 The maximum bubble diameter is 9.3 mm, the bubble depth is 2.7 mm, and the bubble area per square meter is 24.3 cm². 2 The compressive strength after 28 days is 35.2 MPa.

[0075] Comparative Example 3

[0076] A type of fair-faced concrete is prepared using a method largely the same as in Example 2, except that the preparation steps of the admixture are as follows:

[0077] 45 parts of VGCF nanofibers and 40 parts of water were weighed and dispersed in an ultrasonic disperser at 25 kHz for 60 min while maintaining a temperature of 60℃. 30 parts of aliphatic hyperbranched polyester were weighed and added to the dispersion, and ultrasonic dispersion was continued for 50 min while maintaining a temperature of 60℃. The mixture was then cooled to room temperature (25℃) to prepare the VGCF-reinforced dispersion. This mixture was placed in a vacuum drying oven and dried at 50℃ for 9 h. After drying, it was placed in a desiccator and cooled to room temperature (25℃) to obtain the additive.

[0078] Testing revealed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this comparative example was 0.42 mm, the total crack length was 940 mm, and the total cracked area per unit area was 385.4 mm². 2 / m 2 The maximum bubble diameter is 8.8 mm, the bubble depth is 2.4 mm, and the bubble area per square meter is 21.6 cm². 2 The compressive strength after 28 days is 39.2 MPa.

[0079] Comparative Example 4

[0080] A type of fair-faced concrete is prepared using a method largely the same as in Example 2, except that the preparation steps of the admixture are as follows:

[0081] Weigh 45 parts of nano-carbon fiber VGCF and 40 parts of water. Under the condition of maintaining the temperature at 60℃, weigh 30 parts of aliphatic hyperbranched polyester and add them to the dispersion. Weigh 20 parts of ethylene-tetrafluoroethylene (ETFE) copolymer powder and stir to mix evenly. Disperse in an ultrasonic disperser at a frequency of 20 kHz for 1 hour. After taking it out, put it in a vacuum drying oven and dry it at 50℃ for 9 hours. After taking it out, put it in a desiccator and cool it to room temperature (25℃) to obtain a high crack-resistant, maintenance-free fair-faced concrete admixture.

[0082] Tests showed that the maximum crack width of the maintenance-free, crack-resistant fair-faced concrete obtained in this comparative example was 0.30 mm, the total crack length was 523 mm, and the total cracked area per unit area was 142.8 mm². 2 / m 2 The maximum bubble diameter is 7.2 mm, the bubble depth is 2.2 mm, and the bubble area per square meter is 15.6 cm². 2 The compressive strength after 28 days is 41.5 MPa.

[0083] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A type of maintenance-free, crack-resistant fair-faced concrete, characterized in that, The components and their respective weight percentages include: 130-180 parts cement, 90-150 parts fly ash, 60-110 parts mineral powder, 750-850 parts sand, 1100-1200 parts stone, 120-160 parts water, 3-6 parts high-performance water-reducing agent, and 4-8 parts crack-resistant and maintenance-free admixture. The crack-resistant and maintenance-free admixture is obtained by first adding aliphatic hyperbranched polyester to a nanofiber dispersion and ultrasonically treating it to obtain a nanofiber reinforced dispersion; then adding ethylene-tetrafluoroethylene copolymer, stirring, and drying.

2. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The VGCF nanofibers have a diameter of 30-200 nm, a length of 1-15 μm, and a specific surface area of ​​15-30 m². 2 / g.

3. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The aliphatic hyperbranched polyester has a molecular weight of 1100~3700 and a hydroxyl value of 560~600 mgKOH / g.

4. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The nanofiber reinforced dispersion contains the following components and their weight percentages: 30-45 parts nanofiber, 20-30 parts aliphatic hyperbranched polyester, and 30-45 parts water.

5. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The mass ratio of the ethylene-tetrafluoroethylene copolymer powder to the nanofiber reinforced dispersion is 1:4~8.

6. The maintenance-free, high-crack-resistant fair-faced concrete according to claim 1, characterized in that, The high-performance water-reducing agent has a water reduction rate of over 25%, a solid content of 13-17%, and a pH value of 6-8.

7. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The main chemical composition and their mass percentages of the fly ash include: SiO2 25-45%, Al2O3 30-40%, Fe2O3 1-4%, CaO 1-3%, MgO 0-1%, K2O 0-1%, Na2O 0-1%, SO3 0-1%, TiO2 0-1%, and residual carbon 2-8%; the specific surface area is 320-400 m². 2 / kg; The main chemical composition of the mineral powder and its mass percentage include: SiO2 20~40%, Al2O3 15~20%, Fe2O3 1~4%, CaO 32~50%, MgO 0~1%, K2O 0~1%, Na2O 0~1%, SO3 0~1%, TiO2 0~1%, residual carbon 2~5%; Specific surface area is 500~800 m² 2 / kg.

8. The maintenance-free, crack-resistant fair-faced concrete according to claim 1, characterized in that, The sand is natural sand with a fineness modulus of 2.3 to 2.7, classified as medium sand in zone II; the stone is pebbles with a particle size of 5 to 20 mm.

9. The method for preparing maintenance-free, crack-resistant fair-faced concrete according to any one of claims 1 to 8, characterized in that, Includes the following steps: 1) Weigh each raw material according to the proportion. The raw materials and their weight percentages include: 130-180 parts cement, 90-150 parts fly ash, 60-110 parts mineral powder, 750-850 parts sand, 1100-1200 parts stone, 120-160 parts water, 3-6 parts high-performance water-reducing agent, and 4-8 parts crack-resistant and maintenance-free admixture. 2) Add the weighed cement, fly ash, mineral powder, sand, stone, water, high-performance water-reducing agent, and crack-resistant, maintenance-free admixture to the mixer for mixing. 3) Add the obtained mixture to the template in layers, vibrate, let it stand, and then remove the template to obtain the maintenance-free, high-crack-resistant fair-faced concrete.

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