An anti-cracking preservative for enhancing concrete and its preparation method

Abstract

The present invention discloses an anti-cracking preservative for enhancing concrete, which comprises the following components in parts by weight: 7-8 parts of tannic acid-modified cerium-doped montmorillonite, 5-6 parts of modified steel fibers, 3-6 parts of modified polypropylene fibers, 8-12 parts of ultra-fine mineral powder, 10-20 parts of calcium hydroxide, and 3-5 parts of air-entraining agent; the modified steel fibers are prepared by coating a carbon nanotube / silica gel coating on the surface of the steel fibers; the modified polypropylene fibers are prepared by coating polydimethylsiloxane / silica on the surface of the polypropylene fibers. The anti-cracking preservative provided by the present invention has good stability, can effectively improve the strength of concrete, and enhance the anti-cracking and anti-corrosion performance of concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and particularly relates to an anti-cracking preservative for enhancing concrete and a preparation method thereof. Background Art

[0002] With the development of the construction industry, the performance requirements for concrete materials are getting higher and higher. For example, the anti-cracking and anti-corrosion performance of concrete. When concrete is not modified, it is often physically damaged and chemically eroded in the natural environment, resulting in surface cracking and affecting the service life of buildings. Therefore, the research on the anti-cracking and anti-corrosion properties of concrete is crucial.

[0003] The patent with the patent number 201310074167.8 provides a special anti-corrosion and anti-cracking enhancer for concrete. The weight percentages of each component are as follows: shrinkage-reducing component 2-5%, early plastic shrinkage resistance component 4-8%, chloride salt erosion resistance component 60-80%, carbonation resistance component 10-30%, air-entraining component 0-0.5%, and setting retarder component 0-2%. The early plastic shrinkage resistance component of concrete is described as polypropylene fiber and polyacrylonitrile fiber, and the chloride salt erosion resistance component is an inorganic non-metallic compound, including a mixture of ultra-fine mineral powder and magnesium oxide. The carbonation resistance component is an active silicon compound. This anti-corrosion and anti-cracking enhancer has the characteristics of wide raw material sources, low cost, simple operation and no pollution. From the above prior art, it can be seen that mineral admixtures are often added at present to prevent concrete from being eroded by improving the compactness of concrete. However, over time, the concrete will eventually be corroded and cracked. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: aiming at the deficiencies existing in the prior art, to provide an anti-cracking preservative for enhancing concrete, which has good stability, can effectively improve the strength of concrete, and improve the anti-cracking and anti-corrosion performance of concrete.

[0005] To solve the above technical problem, the technical solution of the present invention is:

[0006] An anti-cracking preservative for enhancing concrete, in parts by weight, includes the following components:

[0007] 7-8 parts of tannic acid-modified cerium-doped montmorillonite, 5-6 parts of modified steel fiber, 3-6 parts of modified polypropylene fiber, 8-12 parts of ultra-fine mineral powder, 10-20 parts of calcium hydroxide, and 3-5 parts of air-entraining agent; the modified steel fiber is obtained by coating a carbon nanotube / silica gel coating on the surface of the steel fiber; the modified polypropylene fiber is obtained by coating polydimethylsiloxane / silica on the surface of the polypropylene fiber.

[0008] Preferably, the preparation method of the tannic acid-modified cerium-doped montmorillonite is as follows: disperse montmorillonite in deionized water, then add cerium nitrate hexahydrate, heat up and stir, finally centrifuge the reaction solution, wash and dry the precipitate obtained by centrifugation to obtain the cerium-doped montmorillonite material; disperse the cerium-doped montmorillonite material in deionized water and perform ultrasonic treatment, then add ferric nitrate nonahydrate and tannic acid, adjust the pH of the reaction system to 8, stir at room temperature, then filter, wash and dry the obtained precipitate to prepare the tannic acid-modified cerium-doped montmorillonite.

[0009] Preferably, the mass ratio of the montmorillonite to the cerium nitrate hexahydrate is 10:(5 - 6); the mass ratio of the cerium-doped montmorillonite material, ferric nitrate nonahydrate, and tannic acid is 1 - 2:0.01:0.01;

[0010] Preferably, the temperature of the heat-up stirring treatment is 75 - 85°C, the time of the heat-up stirring treatment is 20 - 30 h, and the stirring speed of the heat-up stirring treatment is 600 - 800 revolutions per minute; the power of the ultrasonic treatment is 500 W, and the time of the ultrasonic treatment is 30 - 50 min; the stirring speed of the stirring treatment is 500 - 600 revolutions per minute, and the time of the stirring treatment is 20 - 30 min.

[0011] Preferably, the preparation method of the modified steel fiber is as follows: add carbon nanotubes and a surfactant to ethyl acetate, perform the first stirring, then add a mixture composed of epoxy resin, a curing agent, silica aerogel, and ethyl acetate, perform the second stirring, and spray the obtained mixture on the surface of the steel fiber with a spray gun and dry it to obtain the modified steel fiber.

[0012] Preferably, the surfactant is 1H,1H,2H,2H-perfluorooctyltrimethoxysilane; the curing agent is dicyandiamide; the epoxy resin is E51 type epoxy resin; the mass ratio of the carbon nanotubes, surfactant, ethyl acetate, and the mixture is 1:1:(80 - 100):(140 - 150); the mass ratio of epoxy resin, curing agent, silica aerogel, and ethyl acetate in the mixture is (20 - 30):8:1:100.

[0013] Preferably, the rotation speed of the first stirring is 500 - 600 revolutions per minute, and the time is 1 - 2 h; the rotation speed of the second stirring is 500 - 600 revolutions per minute, and the time is 2 - 3 h. The pressure of the spray gun during spraying is 0.85 MPa, the distance between the liquid outlet of the spray gun and the steel fiber is 20 - 30 cm, and the spraying time is 20 - 30 s.

[0014] As a preference of the above technical solution, the preparation method of the modified polypropylene fiber is as follows: Mix polydimethylsiloxane, ethanol, and tetraethyl orthosilicate and stir, then dropwise add ammonia water and tetrapropylammonium hydroxide for hydrolysis to obtain a polydimethylsiloxane / SiO2 hybrid sol. Stir the hybrid sol at room temperature to remove the solvent, then add polypropylene fibers for dip coating. After that, take out the polypropylene fibers and dry them to obtain the modified polypropylene fiber.

[0015] The mass concentration of the ammonia water is 25 - 30%, and the mass ratio of polydimethylsiloxane, ethanol, tetraethyl orthosilicate, ammonia water, and tetramethylammonium hydroxide is 5:(30 - 40):50:2:50; the rotation speed of the mixing and stirring is 500 revolutions per minute, and the time is 30 min; the temperature of the hydrolysis is room temperature, and the time of the hydrolysis is 2 - 3 h; the time of the dip coating is 20 - 30 min; the temperature of the drying is 100 °C, and the time is 1 - 3 h.

[0016] The air-entraining agent is sodium dodecylbenzenesulfonate; the specific surface area of the ultrafine mineral powder is ≥400 m 2 / kg, and the 7-day activity index is ≥75%.

[0017] In order to better solve the above technical problems, the present invention also discloses a preparation method of the crack-resistant preservative for concrete, including the following steps:

[0018] Mix tannic acid-modified cerium-doped montmorillonite, modified steel fibers, modified polypropylene fibers, ultrafine mineral powder, and calcium hydroxide evenly by stirring, then spray an air-entraining agent solution with a mass concentration of 1 - 2%, and then dry and grind to obtain the product.

[0019] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0020] The crack-resistant preservative provided by the present invention includes tannic acid-modified cerium-doped montmorillonite, modified steel fibers, modified polypropylene fibers, ultrafine mineral powder, calcium hydroxide, and air-entraining agent. When the concrete is in a corrosive environment, the tannic acid-modified cerium-doped montmorillonite will distort the penetration path of corrosive ions, thereby delaying the penetration rate. Moreover, tannic acid and cerium ions have a certain corrosion inhibition effect and can form a passivation layer in the corrosion area. The passivation film is composed of a complex formed by tannic acid and iron ions, insoluble cerium oxides, and hydroxides, effectively improving the long-term anti-corrosion performance of the concrete. The present invention also adds longer steel fibers and shorter polypropylene fibers for synergistic compounding. When cracks form in the concrete, the two fibers can overlap with each other to provide crack bridging and enhance the load-bearing capacity of the cracks, thereby improving the crack-resistant performance of the concrete. To further improve the performance of steel fibers and polypropylene fibers, the present invention also coats a layer of carbon nanotube / silica aerogel coating on the surface of the steel fibers. During preparation, after the mixed solution is sprayed on the surface of the steel fibers, ethyl acetate evaporates rapidly. After the space previously occupied by the solvent escapes from the incompletely cured epoxy resin, a porous structure is formed on the surface of the completely cured coating. The coating surface with a multi-scale structure consists of micron-sized protrusions, pits, and underlying porous structures. The silica aerogel / carbon nanotubes are embedded in the surface protrusions. The micron-sized porous structure can store a large amount of air, thereby forming an air layer on the coating surface, greatly reducing the contact area between the corrosive liquid and the coating, and thus improving the chemical resistance of the steel fibers. The present invention modifies the surface of the polypropylene fibers with a polydimethylsiloxane / silica hybrid material. This hybrid material has good barrier properties and can effectively improve the anti-corrosion performance of the polypropylene fibers.

[0021] The crack-resistant preservative prepared by the present invention has good stability. When added to concrete, it can effectively improve the crack-resistant and anti-corrosion performance of the concrete. Detailed implementation mode

[0022] The present invention will be further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0023] In the following embodiments, the diameter of the steel fibers is 0.3 - 0.4 mm, the length is 30 - 35 mm, the diameter of the polypropylene fibers is 0.1 mm, the length is 12 mm, the diameter of the carbon nanotubes is 8 - 10 nm, and the length is 5 - 8 μm. The specific surface area of the silica aerogel ≥ 600 m 2 / g.

[0024] Example 1

[0025] Disperse 10 g of montmorillonite in 100 ml of deionized water, then add 5.32 g of cerium nitrate hexahydrate, heat up to 80 °C, stir at a speed of 600 revolutions per minute for 24 h, finally centrifuge the reaction solution, wash the obtained precipitate and dry it to obtain a cerium-doped montmorillonite material; Disperse 1 g of the cerium-doped montmorillonite material in 50 ml of deionized water, ultrasonically treat it at a power of 500 W for 30 min, then add 0.01 g of ferric nitrate nonahydrate and 0.01 g of tannic acid, adjust the pH of the reaction system to 8, stir at a speed of 500 revolutions per minute at room temperature for 20 min, then filter, wash the obtained precipitate and dry it to prepare tannic acid-modified cerium-doped montmorillonite;

[0026] Add 0.1 g of carbon nanotubes and 0.1 g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane to 8 g of ethyl acetate, stir for the first time at a speed of 500 revolutions per minute for 1 h, then add a mixture composed of 2.5 g of E51-type epoxy resin, 0.8 g of dicyandiamide, 0.1 g of silica aerogel and 10 g of ethyl acetate, stir for the second time at a speed of 500 revolutions per minute for 2 h, spray the obtained mixture on the surface of steel fibers with a spray gun, the spray gun pressure is 0.85 MPa during spraying, the distance between the spray gun liquid outlet and the steel fibers is 20 cm, the spraying time is 30 s, and dry it to obtain modified steel fibers;

[0027] Mix 5 g of polydimethylsiloxane, 30 g of ethanol and 50 g of tetraethyl orthosilicate, stir at 500 revolutions per minute for 30 min, then dropwise add 2 g of ammonia water with a mass concentration of 28% and 50 g of tetrapropylammonium hydroxide, hydrolyze at room temperature for 2 h to obtain a polydimethylsiloxane / SiO2 hybrid sol, stir the hybrid sol at room temperature to remove the ethanol solvent, then add polypropylene fibers for dip coating for 20 min, and then take out the polypropylene fibers and dry them at 100 °C for 3 h to obtain modified polypropylene fibers;

[0028] By weight, mix 7 parts of tannic acid-modified cerium-doped montmorillonite, 5 parts of modified steel fibers, 4 parts of modified polypropylene fibers, 10 parts of ultrafine mineral powder, and 18 parts of calcium hydroxide and stir evenly to obtain a mixed material. Prepare a solution with a mass concentration of 2% by adding 4 parts of sodium dodecylbenzenesulfonate to water, spray it on the above mixed material and stir evenly, then dry and grind it to obtain an anti-cracking preservative.

[0029] Example 2

[0030] Disperse 10 g of montmorillonite in 100 ml of deionized water, then add 5.32 g of cerium nitrate hexahydrate, heat up to 80 °C, stir at a speed of 800 revolutions per minute for 24 h, finally centrifuge the reaction solution, wash the obtained precipitate and dry it to obtain a cerium-doped montmorillonite material; disperse 2 g of the cerium-doped montmorillonite material in 50 ml of deionized water, ultrasonically treat it at a power of 500 W for 50 min, then add 0.01 g of ferric nitrate nonahydrate and 0.01 g of tannic acid, adjust the pH of the reaction system to 8, stir at a speed of 600 revolutions per minute at room temperature for 30 min, then filter, wash the obtained precipitate and dry it to prepare tannic acid-modified cerium-doped montmorillonite;

[0031] Add 0.1 g of carbon nanotubes and 0.1 g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane to 8 g of ethyl acetate, perform the first stirring at a speed of 600 revolutions per minute for 2 h, then add a mixture composed of 2.5 g of E51-type epoxy resin, 0.8 g of dicyandiamide, 0.1 g of silica aerogel and 10 g of ethyl acetate, perform the second stirring at a speed of 600 revolutions per minute for 3 h, spray the obtained mixture on the surface of steel fibers with a spray gun, when spraying, the spray gun pressure is 0.85 MPa, the distance between the liquid outlet of the spray gun and the steel fibers is 30 cm, the spraying time is 30 s, and dry it to obtain modified steel fibers;

[0032] Mix 5 g of polydimethylsiloxane, 40 g of ethanol and 50 g of tetraethyl orthosilicate, stir at 500 revolutions per minute for 30 min, then dropwise add 2 g of ammonia water with a mass concentration of 28% and 50 g of tetrapropylammonium hydroxide, hydrolyze at room temperature for 3 h to obtain a polydimethylsiloxane / SiO2 hybrid sol, stir the hybrid sol at room temperature to remove the ethanol solvent, then add polypropylene fibers for dip coating for 30 min, and then take out the polypropylene fibers and dry them at 100 °C for 3 h to obtain modified polypropylene fibers;

[0033] By weight, mix 8 parts of tannic acid-modified cerium-doped montmorillonite, 5 parts of modified steel fibers, 4 parts of modified polypropylene fibers, 10 parts of ultrafine mineral powder and 18 parts of calcium hydroxide evenly to obtain a mixed material, prepare a solution with a mass concentration of 2% by adding 4 parts of sodium dodecylbenzenesulfonate to water, spray it on the above mixed material and stir evenly, and then dry and grind it to obtain an anti-cracking preservative.

[0034] Example 3

[0035] Disperse 10 g of montmorillonite in 100 ml of deionized water, then add 5.32 g of cerium nitrate hexahydrate, heat up to 80 °C, stir at a speed of 700 revolutions per minute for 24 h, finally centrifuge the reaction solution, wash the precipitate obtained by centrifugation and dry it to obtain a cerium-doped montmorillonite material; Disperse 1.5 g of the cerium-doped montmorillonite material in 50 ml of deionized water, ultrasonically treat it at a power of 500 W for 40 min, then add 0.01 g of ferric nitrate nonahydrate and 0.01 g of tannic acid, adjust the pH of the reaction system to 8, stir at a speed of 500 revolutions per minute at room temperature for 20 min, then filter, wash the precipitate obtained and dry it to prepare tannic acid-modified cerium-doped montmorillonite;

[0036] Add 0.1 g of carbon nanotubes and 0.1 g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane to 8 g of ethyl acetate, stir for the first time at a speed of 550 revolutions per minute, control the time to 1.5 h, then add a mixture composed of 2.5 g of E51 type epoxy resin, 0.8 g of dicyandiamide, 0.1 g of silica aerogel and 10 g of ethyl acetate, stir for the second time at a speed of 500 revolutions per minute, control the time to 2 h, spray the obtained mixture on the surface of steel fibers by a spray gun, when spraying, the spray gun pressure is 0.85 MPa, the distance between the liquid outlet of the spray gun and the steel fibers is 20 cm, the spraying time is 30 s, and dry it to obtain modified steel fibers;

[0037] Mix 5 g of polydimethylsiloxane, 35 g of ethanol and 50 g of tetraethyl orthosilicate, stir at 500 revolutions per minute for 30 min, then dropwise add 2 g of ammonia water with a mass concentration of 28% and 50 g of tetrapropylammonium hydroxide, hydrolyze at room temperature for 2 h to obtain a polydimethylsiloxane / SiO2 hybrid sol, stir the hybrid sol at room temperature to remove the ethanol solvent, then add polypropylene fibers for dip coating for 30 min, and then take out the polypropylene fibers and dry them at 100 °C for 2 h to obtain modified polypropylene fibers;

[0038] By weight, mix 8 parts of tannic acid-modified cerium-doped montmorillonite, 6 parts of modified steel fibers, 5 parts of modified polypropylene fibers, 9 parts of ultrafine mineral powder and 15 parts of calcium hydroxide and stir evenly to obtain a mixed material, prepare a solution with a mass concentration of 2% by adding 4 parts of sodium dodecylbenzenesulfonate to water, spray it on the above-mentioned mixed material and stir evenly, and then dry and grind it to obtain an anti-cracking preservative.

[0039] Example 4

[0040] Disperse 10 g of montmorillonite in 100 ml of deionized water, then add 5.32 g of cerium nitrate hexahydrate, heat up to 80 °C, stir at a speed of 650 revolutions per minute for 24 h, finally centrifuge the reaction solution, and wash and dry the precipitate obtained by centrifugation to obtain cerium-doped montmorillonite material; Disperse 1 g of cerium-doped montmorillonite material in 50 ml of deionized water, ultrasonically treat it at a power of 500 W for 40 min, then add 0.01 g of ferric nitrate nonahydrate and 0.01 g of tannic acid, adjust the pH of the reaction system to 8, stir at a speed of 500 revolutions per minute at room temperature for 20 min, then filter, wash and dry the obtained precipitate to prepare tannic acid-modified cerium-doped montmorillonite;

[0041] Add 0.1 g of carbon nanotubes and 0.1 g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane to 8 g of ethyl acetate, stir for the first time at a speed of 600 revolutions per minute for 1 h, then add a mixture composed of 2.5 g of E51-type epoxy resin, 0.8 g of dicyandiamide, 0.1 g of silica aerogel and 10 g of ethyl acetate, stir for the second time at a speed of 500 revolutions per minute for 3 h, spray the obtained mixture on the surface of steel fibers with a spray gun, the spray gun pressure is 0.85 MPa during spraying, the distance between the liquid outlet of the spray gun and the steel fibers is 30 cm, the spraying time is 30 s, and dry to obtain modified steel fibers;

[0042] Mix 5 g of polydimethylsiloxane, 40 g of ethanol and 50 g of tetraethyl orthosilicate, stir at 500 revolutions per minute for 30 min, then dropwise add 2 g of 28% ammonia water by mass concentration and 50 g of tetrapropylammonium hydroxide, hydrolyze at room temperature for 2 h to obtain polydimethylsiloxane / SiO2 hybrid sol, stir the hybrid sol at room temperature to remove the ethanol solvent, then add polypropylene fibers for dip coating for 20 min, and then take out the polypropylene fibers and dry them at 100 °C for 1 h to obtain modified polypropylene fibers;

[0043] Take 7.5 parts of tannic acid-modified cerium-doped montmorillonite, 6 parts of modified steel fibers, 5 parts of modified polypropylene fibers, 12 parts of ultrafine mineral powder, and 18 parts of calcium hydroxide by weight, mix and stir evenly to obtain a mixed material, prepare a 2% solution of 4 parts of sodium dodecylbenzenesulfonate in water, spray it on the above mixed material and stir evenly, and then dry and grind to obtain an anti-cracking preservative.

[0044] Take C30 concrete as the experimental object, add the anti-cracking preservative prepared in the above Examples 1-4 to the C30 concrete, the addition amount of the anti-cracking preservative is 5% of the cement content in the concrete, and then perform performance tests on the modified concrete. The test results are shown in Table 1.

[0045] Table 1

[0046] 28d compressive strength, MPa Coefficient of resistance to sulfate attack 56d electric flux, Coulomb Example 1 97.3 0.99 249 Example 2 97.5 1 179 Example 3 97.2 1 179 Example 4 97.4 0.99 250

[0047] As can be seen from the above test results, the crack-resistant preservative prepared by the present invention effectively improves the anti-corrosion performance of concrete when used in C30 concrete. After placing the modified concrete at a water depth of 5 meters for 28 days, it was found that the concrete added with the crack-resistant preservatives prepared in Examples 1-4 had no cracks, while the concrete without the crack-resistant preservative of the present invention had 1-3 cracks with a diameter of 40 mm - 50 mm per square meter.

[0048] In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. An anti-cracking preservative for enhancing concrete, characterized in that, by weight, it comprises the following components: 7-8 parts of tannic acid-modified cerium-doped montmorillonite, 5-6 parts of modified steel fiber, 3-6 parts of modified polypropylene fiber, 8-12 parts of ultra-fine mineral powder, 10-20 parts of calcium hydroxide, and 3-5 parts of air-entraining agent; The modified polypropylene fiber is prepared by coating polydimethylsiloxane / silica on the surface of polypropylene fiber; The preparation of the modified steel fiber is as follows: Carbon nanotubes and a surfactant are added to ethyl acetate and stirred for the first time. Then, a mixture composed of epoxy resin, curing agent, silica aerogel, and ethyl acetate is added and stirred for the second time. The obtained mixture is sprayed onto the surface of steel fiber with a spray gun and dried to obtain the modified steel fiber; The surfactant is 1H,1H,2H,2H-perfluorooctyltrimethoxysilane; The curing agent is dicyandiamide; The epoxy resin is E51 type epoxy resin; The mass ratio of carbon nanotubes, surfactant, ethyl acetate, and the mixture is 1:1:(80-100):(140-150); The mass ratio of epoxy resin, curing agent, silica aerogel, and ethyl acetate in the mixture is (20-30):8:1:

100.

2. An anti-cracking preservative for enhancing concrete according to claim 1, characterized in that, The preparation method of the tannic acid-modified cerium-doped montmorillonite is as follows: Montmorillonite is dispersed in deionized water, then cerium nitrate hexahydrate is added, and the mixture is heated and stirred. Finally, the reaction solution is centrifuged, and the obtained precipitate is washed and dried to obtain the cerium-doped montmorillonite material; The cerium-doped montmorillonite material is dispersed in deionized water and ultrasonically treated. Then, ferric nitrate nonahydrate and tannic acid are added, the pH of the reaction system is adjusted to 8, and the mixture is stirred at room temperature. Then, it is filtered, and the obtained precipitate is washed and dried to prepare the tannic acid-modified cerium-doped montmorillonite.

3. An anti-cracking preservative for enhancing concrete according to claim 2, characterized in that, The mass ratio of montmorillonite to cerium nitrate hexahydrate is 10:(5-6); The mass ratio of the cerium-doped montmorillonite material, ferric nitrate nonahydrate, and tannic acid is 1-2:0.01:0.

01.

4. An anti-cracking preservative for enhancing concrete according to claim 3, characterized in that, The temperature of the heating and stirring treatment is 75-85°C, the time of the heating and stirring treatment is 20-30 h, and the stirring speed of the heating and stirring treatment is 600-800 revolutions per minute; The power of the ultrasonic treatment is 500 W, and the time of the ultrasonic treatment is 30-50 min; The stirring speed of the stirring treatment is 500-600 revolutions per minute, and the time of the stirring treatment is 20-30 min.

5. An anti-cracking preservative for enhancing concrete according to claim 1, characterized in that, The rotation speed of the first stirring is 500 - 600 revolutions per minute, and the time is 1 - 2 hours; the rotation speed of the second stirring is 500 - 600 revolutions per minute, and the time is 2 - 3 hours; during spraying, the spray gun pressure is 0.85 MPa, the distance between the liquid outlet of the spray gun and the steel fiber is 20 - 30 cm, and the spraying time is 20 - 30 seconds.

6. An anti-cracking preservative for enhancing concrete according to claim 1, characterized in that, the preparation method of the modified polypropylene fiber is as follows: mix polydimethylsiloxane, ethanol, and tetraethyl orthosilicate and stir, then dropwise add ammonia water and tetrapropylammonium hydroxide for hydrolysis to obtain a polydimethylsiloxane / SiO2 hybrid sol. Stir the hybrid sol at room temperature to remove the solvent, then add polypropylene fibers for dip coating. After that, take out the polypropylene fibers and dry them to obtain the modified polypropylene fiber.

7. An anti-cracking preservative for enhancing concrete according to claim 6, characterized in that, the mass concentration of the ammonia water is 25 - 30%, and the mass ratio of polydimethylsiloxane, ethanol, tetraethyl orthosilicate, ammonia water, and tetramethylammonium hydroxide is 5:(30 - 40):50:2:50; the rotation speed of the mixing and stirring is 500 revolutions per minute, and the time is 30 minutes; the hydrolysis temperature is room temperature, and the hydrolysis time is 2 - 3 hours; the dip coating time is 20 - 30 minutes; the drying temperature is 100 °C, and the time is 1 - 3 hours.

8. A method for an anti-cracking preservative for enhancing concrete according to any one of claims 1 to 7, characterized in that, it includes the following steps: Mix tannic acid-modified cerium-doped montmorillonite, modified steel fibers, modified polypropylene fibers, ultra-fine mineral powder, and calcium hydroxide evenly by stirring, then spray an air-entraining agent solution with a mass concentration of 1 - 2%, and then dry and grind to obtain it.