A modified permeable recycled concrete, its preparation method and application

Abstract

This invention discloses a modified permeable recycled concrete, its preparation method, and its application, belonging to the field of recycled concrete technology. It involves depositing silica on the surface of fluorinated graphene to improve the interfacial bonding force of the fluorinated graphene, then coating it onto the surface of bentonite via hydrogen bonding. After treatment with a silane coupling agent, a polyvinyl alcohol-vinyl acetate copolymer is polymerized on the surface of bentonite-loaded fluorinated graphene / SiO2 powder. The polyvinyl alcohol-vinyl acetate copolymer can form a tight bond with the soil through hydrogen bonding and cation exchange, adsorbing onto the surface of soil particles to form a network structure with a certain elasticity and toughness, forming a permanent protective layer. Using bentonite-loaded fluorinated graphene-SiO2 as a carrier can improve the copolymer's resistance to ultraviolet radiation and aging. Furthermore, the ion exchange properties of bentonite can promote the interaction between the polyvinyl alcohol-vinyl acetate copolymer and soil particles.

Description

Technical Field

[0001] This invention belongs to the field of recycled concrete technology, specifically a modified permeable recycled concrete, its preparation method, and its application. Background Technology

[0002] With economic and social development and urban construction, the surface of modern cities is gradually covered by reinforced concrete buildings and impermeable pavements. Impermeable pavements hinder rainwater infiltration during rainy weather, preventing rainwater from effectively replenishing groundwater. Coupled with excessive groundwater extraction, urban pavements are prone to subsidence. Furthermore, rainwater flows through drainage ditches, and during heavy rain or storms, rainwater accumulates on the road surface, concentrating in large quantities in motor vehicle and bicycle lanes, causing widespread flooding. In addition, existing concrete pavements are generally dense in structure, resulting in loud tire noise. When vehicles travel at high speeds, the tires compress air between the tire and the road surface as they roll, and the air expands rapidly after the tire passes, producing noise. This noise is particularly noticeable on rainy days, affecting residents' lives and work. In addition, with the progress of municipal construction, a large amount of waste concrete is generated every day. Currently, due to the difficulty in handling waste concrete, its poor adhesion, the road surface paved with it is prone to cracking, it cannot be used in combination with the raw materials in new concrete, and its diverse sources, its disposal is mainly done by open-air stockpiling or landfilling, which causes secondary pollution. If these waste concretes can be recycled and used for road paving without reducing their performance, it will not only save costs and reduce the cost of construction waste transportation and disposal, but also reduce environmental pollution.

[0003] In existing technologies, recycled coarse aggregate is often used to fill concrete. However, the surface of recycled coarse aggregate has high porosity and high water absorption rate due to the residual hardened cement mortar. During the concrete hydration process, the water in the cement that comes into contact with the phase change aggregate is absorbed into the phase change aggregate, resulting in a reduction in the actual bound water of the cement and the inability to achieve complete hydration. This not only affects the mechanical strength of the final concrete, but also leads to poor interfacial bonding between the hardened cement paste and the aggregate, poor performance of the interfacial transition zone, and easy separation under stress, which may even cause the concrete to break and collapse.

[0004] Chinese patent announcement CN107352868B discloses a permeable cement concrete and its construction method. It uses isocyanate-modified phenolic resin as a binder. The addition of short fibers improves the interface condition of coarse aggregates in the cementitious material while ensuring the permeability of the concrete, increases the bonding force between coarse aggregates, and improves the strength of the concrete. However, the isocyanate-modified phenolic resin used as a binder in this scheme is prone to chain segment degradation under ultraviolet light or high temperature, which leads to embrittlement of the network structure. Summary of the Invention

[0005] The purpose of this invention is to provide a modified permeable recycled concrete, its preparation method, and its application. By using bentonite-loaded fluorinated graphene / SiO2 powder as a carrier, polyvinyl alcohol-vinyl acetate copolymer is polymerized on the surface as a modified binder. The high stability of the fluorine groups in the bentonite-loaded fluorinated graphene / SiO2 powder can prevent the polyvinyl alcohol-vinyl acetate copolymer from aging and failing under ultraviolet irradiation.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing modified permeable recycled concrete includes the following steps:

[0008] Step 1: Using the sol-gel method, tetraethyl silicate is hydrolyzed under alkaline catalysis to generate nano-SiO2 particles in situ on the surface of fluorinated graphene. Then, fluorinated graphene / SiO2 is loaded onto bentonite using hydrogen bonding self-assembly to obtain bentonite-loaded fluorinated graphene / SiO2 powder.

[0009] Step 2: Fluorinated graphene / SiO2 is loaded onto bentonite and modified with γ-aminopropyltriethoxysilane, and then polyvinyl alcohol-vinyl acetate copolymer is polymerized on the surface to obtain a modified adhesive.

[0010] Step 3: Mix polycarboxylate superplasticizer and deionized water at a mass ratio of 2.9-3.2:90-110 to obtain a diluted superplasticizer solution; mix silicate cement of type P.O42.5, Class I fly ash of type F, recycled concrete aggregate, modified binder and diluted superplasticizer solution to obtain a modified permeable recycled concrete.

[0011] Furthermore, in step three, the ratio of silicate cement, fly ash, recycled concrete aggregate, modified binder, and water-reducing agent diluent is 260-270kg: 30-40kg: 1100-1200kg: 30-40kg: 150-160kg.

[0012] Furthermore, the specific preparation steps of the bentonite-supported fluorinated graphene / SiO2 powder in step one are as follows:

[0013] Fluorinated graphene and ethanol solution were added to a reaction vessel and stirred for 20-30 min at 20-25℃ and 500-600 r / min. Then, 30-40% ammonia water was added to adjust the pH to 9-10, followed by the addition of tetraethyl silicate. The reaction was continued for 20-24 h, allowing the tetraethyl silicate to hydrolyze in an alkaline environment to form nano-SiO2 particles that were loaded onto the surface of the fluorinated graphene, resulting in a fluorinated graphene suspension. The fluorinated graphene suspension, bentonite, and N,N-dimethylformamide were added to the reaction vessel and stirred for 1-2 h at 20-25℃ and 500-600 r / min. The mixture was filtered, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-80℃ for 1-2 h to obtain bentonite-loaded fluorinated graphene / SiO2 powder.

[0014] Furthermore, the ratio of fluorinated graphene, ethanol solution, ammonia and tetraethyl silicate is 50-60g: 800-900mL: 12-14mL: 70-80mL.

[0015] Furthermore, the ratio of fluorinated graphene suspension, bentonite, and N,N-dimethylformamide is 40-50 mL: 80-90 g: 1-2 L.

[0016] Furthermore, the specific preparation steps of the modified binder in step two are as follows:

[0017] Modified bentonite-supported fluorinated graphene / SiO2 powder and deionized water are added to a reactor and stirred for 40-60 minutes at 20-25℃ and 500-600 r / min. Then, polyvinyl alcohol is added, heated to 90-100℃, and stirred until the material is completely dissolved. The temperature is then lowered to 40-45℃, and octylphenol polyoxyethylene ether is added as an emulsifier. The reaction is continued to be stirred for 30-40 minutes. Then, vinyl acetate and potassium persulfate are added as initiators. The mixture is heated to 65-70℃ and kept at that temperature for 1-2 hours. The temperature is then lowered to 45-50℃, and sodium bicarbonate is added to adjust the pH to 6-7. Finally, dibutyl phthalate is added as a plasticizer, and the mixture is stirred for 40-60 minutes. After natural cooling, the material is discharged to obtain the modified binder.

[0018] Furthermore, the ratio of modified bentonite-supported fluorinated graphene / SiO2 powder, deionized water, polyvinyl alcohol, octylphenol polyoxyethylene ether, vinyl acetate, potassium persulfate, and dibutyl phthalate is 30-40g: 1-2L: 50-60mL: 1-2g: 20-30mL: 1-2g: 1-2g.

[0019] Furthermore, the modified bentonite-supported fluorinated graphene / SiO2 powder was prepared via the following steps:

[0020] γ-aminopropyltriethoxysilane and deionized water were added to a reaction vessel. Sodium hydroxide and acetic acid solution were added to adjust the pH to 6.5-7. The mixture was stirred at 20-25℃ and 500-600 r / min for 40-60 min. After the reaction was completed, the mixture was allowed to stand for 1-2 h. Bentonite-supported fluorinated graphene / SiO2 powder was mixed with 50-60% ethanol solution and added to the reaction vessel. The mixture was stirred at 20-25℃ and 500-600 r / min for 1-2 h. The mixture was filtered, and the filter cake was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The mixture was then vacuum dried at 60-80℃ for 1-2 h to obtain modified bentonite-supported fluorinated graphene / SiO2 powder.

[0021] Furthermore, the ratio of γ-aminopropyltriethoxysilane, deionized water, bentonite-supported fluorinated graphene / SiO2 powder, and ethanol solution is 50-60g: 800-900mL: 30-40g: 100-120mL.

[0022] This invention also provides an application of modified permeable recycled concrete in cement concrete.

[0023] The beneficial effects of this invention are:

[0024] 1. The modified permeable recycled concrete prepared by the present invention has good density and compressive strength, high porosity and good water permeability, and is not prone to cracking due to aging of the binder under long-term ultraviolet radiation.

[0025] 2. This invention improves the interfacial bonding force of fluorinated graphene by depositing silica on the surface of fluorinated graphene, and then coating it onto the surface of bentonite through hydrogen bonding self-assembly, obtaining bentonite-loaded fluorinated graphene / SiO2 powder. After treatment with a silane coupling agent, polyvinyl alcohol-vinyl acetate copolymer is polymerized on the surface of the bentonite-loaded fluorinated graphene / SiO2 powder. The hydrophilic groups on the polymer chain of the polyvinyl alcohol-vinyl acetate copolymer can form a tight connection structure with the soil through hydrogen bonding and cation exchange, while the hydrophobic CC long chains on the main chain adsorb onto the surface of soil particles through penetration, diffusion, and entanglement, forming a network structure with a certain elasticity and toughness, effectively reducing the soil moisture content and density, and forming a permanent protective layer. Using bentonite-loaded fluorinated graphene / SiO2 as a carrier can improve the copolymer's resistance to ultraviolet radiation and aging, and the ion exchange properties of bentonite can promote the interaction between the copolymer and soil particles.

[0026] 3. Fluorinated graphene / SiO2 self-assembles and coats bentonite via hydrogen bonding. SiO2 is deposited on the surface of fluorinated graphene, which can change the surface state of fluorinated graphene and effectively avoid the stacking between fluorinated graphene sheets. This is conducive to the coating of fluorinated graphene on the surface of bentonite. The coating of fluorinated graphene can further improve the overall strength of bentonite. As a carrier of the copolymer, it is beneficial to the interaction between the copolymer and the soil particles. It can also increase the specific surface area and porosity of bentonite and increase the water permeability. Detailed Implementation

[0027] 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.

[0028] Example 1: A method for preparing modified permeable recycled concrete, comprising the following steps:

[0029] S1: Add 50g of fluorinated graphene and 800mL of ethanol solution to a reaction vessel, stir for 20min at 20℃ and 500r / min, then add 12mL of 30% ammonia water to adjust the pH to 9, then add 70mL of tetraethylsilicate, and continue stirring for 20h to allow the tetraethylsilicate to hydrolyze in an alkaline environment to form nano-SiO2 particles and load them on the surface of fluorinated graphene, thus obtaining a fluorinated graphene suspension; add 40mL of the fluorinated graphene suspension, 80g of bentonite and 1L of N,N-dimethylformamide to a reaction vessel, stir for 1h at 20℃ and 500r / min, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain bentonite-loaded fluorinated graphene / SiO2 powder.

[0030] Nano-SiO2 particles are generated in situ on the surface of fluorinated graphene by alkaline catalytic hydrolysis of tetraethyl silicate using a sol-gel method.

[0031] The structure of fluorinated graphene / SiO2 consists of fluorinated graphene sheets loaded with nano-SiO2 particles. By loading nano-SiO2 particles onto the surface of fluorinated graphene, the surface state of fluorinated graphene is changed, which can effectively avoid the stacking between fluorinated graphene sheets, improve the dispersibility and interfacial compatibility of fluorinated graphene in resin, and further enhance the abundance of -F and -OH groups on the fluorinated graphene nanosheets and -OH and -COOH groups on the bentonite, thereby loading fluorinated graphene / SiO2 onto bentonite through hydrogen bond self-assembly.

[0032] S2: Add 50g of γ-aminopropyltriethoxysilane and 800mL of deionized water to a reaction vessel, add sodium hydroxide and acetic acid solution to adjust the pH to 6.5, stir at 20℃ and 500r / min for 40min, let stand for 1h after stirring. Add 30g of bentonite-supported fluorinated graphene / SiO2 powder and 100mL of 50% ethanol solution to the reaction vessel, stir at 20℃ and 500r / min for 1h, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain modified bentonite-supported fluorinated graphene / SiO2 powder.

[0033] Treatment with γ-aminopropyltriethoxysilane hydrolyzes to generate silanol bonds that combine with hydroxyl groups on the surface of bentonite-supported fluorinated graphene / SiO2 powder, thus giving the bentonite-supported fluorinated graphene / SiO2 powder an amino group.

[0034] S3: Add 30g of modified bentonite-supported fluorinated graphene / SiO2 powder and 1L of deionized water to a reactor. Stir for 40min at 20℃ and 500r / min. Then add 50mL of polyvinyl alcohol, heat to 90℃, and stir until the material is completely dissolved. Then cool to 40℃, add 1g of octylphenol polyoxyethylene ether as an emulsifier, and continue stirring for 30min. Then add 20mL of vinyl acetate and 1g of potassium persulfate as an initiator, heat to 65℃, keep warm for 1h, cool to 45℃, add sodium bicarbonate to adjust the pH to 6, and then add 1g of dibutyl phthalate as a plasticizer. Continue stirring for 40min, cool naturally, and discharge to obtain the modified binder.

[0035] After copolymerization modification of vinyl acetate, a polyvinyl alcohol-vinyl acetate copolymer with strong water resistance is obtained. The polymer contains a large number of carboxyl and hydroxyl groups, which can combine with the amino groups on the surface of modified bentonite-supported fluorinated graphene / SiO2 powder, so that the polymer can be fixed on the surface of modified bentonite-supported fluorinated graphene / SiO2.

[0036] S4: Mix 2.9 kg of polycarboxylate superplasticizer and 90 kg of deionized water to obtain a superplasticizer dilution; mix 260 kg of P.O42.5 silicate cement, 30 kg of Class I fly ash, 1100 kg of recycled concrete aggregate, 30 kg of modified binder and 150 kg of superplasticizer dilution to obtain a modified permeable recycled concrete.

[0037] Example 2: A method for preparing modified permeable recycled concrete, comprising the following steps:

[0038] S1: 55g of fluorinated graphene and 850mL of ethanol solution were added to a reaction vessel and stirred for 25min at 22.5℃ and 550r / min. Then, 13mL of 35% ammonia solution was added to adjust the pH to 9.5, followed by 75mL of tetraethylsilicate. The reaction was continued for 22h, allowing the tetraethylsilicate to hydrolyze in an alkaline environment to form nano-SiO2 particles that were loaded onto the surface of the fluorinated graphene, resulting in a fluorinated graphene suspension. 45mL of the fluorinated graphene suspension, 85g of bentonite, and 1.5L of N,N-dimethylformamide were added to a reaction vessel and stirred for 1.5h at 22.5℃ and 550r / min. The mixture was filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 70℃ for 1.5h to obtain bentonite-loaded fluorinated graphene / SiO2 powder.

[0039] S2: Add 55g of γ-aminopropyltriethoxysilane and 850mL of deionized water to a reaction vessel, add sodium hydroxide and acetic acid solution to adjust the pH to 6.75, stir at 22.5℃ and 550r / min for 50min, and let stand for 1.5h after the reaction is completed. Add 35g of bentonite-supported fluorinated graphene / SiO2 powder and 110mL of 55% ethanol solution to the reaction vessel, stir at 22.5℃ and 550r / min for 1.5h, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 1.5h to obtain modified bentonite-supported fluorinated graphene / SiO2 powder.

[0040] S3: Add 35g of modified bentonite-supported fluorinated graphene / SiO2 powder and 1.5L of deionized water to a reactor. Stir for 50min at 22.5℃ and 550r / min. Then add 55mL of polyvinyl alcohol, heat to 95℃, and stir until the material is completely dissolved. Then cool to 42.5℃, add 1.5g of octylphenol polyoxyethylene ether as an emulsifier, and continue stirring for 35min. Then add 25mL of vinyl acetate and 1.5g of potassium persulfate as an initiator, heat to 67.5℃, keep warm for 1.5h, cool to 47.5℃, add sodium bicarbonate to adjust the pH to 6.5, and then add 1.5g of dibutyl phthalate plasticizer. Continue stirring for 50min, cool naturally, and discharge to obtain the modified binder.

[0041] S4: Mix 3.05 kg of polycarboxylate superplasticizer and 100 kg of deionized water to obtain a superplasticizer dilution; mix 265 kg of P.O42.5 silicate cement, 35 kg of Class I fly ash, 1150 kg of recycled concrete aggregate, 35 kg of modified binder and 155 kg of superplasticizer dilution to obtain a modified permeable recycled concrete.

[0042] Example 3: A method for preparing modified permeable recycled concrete, comprising the following steps:

[0043] S1: Add 60g of fluorinated graphene and 900mL of ethanol solution to a reaction vessel and stir for 30min at 25℃ and 600r / min. Then add 14mL of 40% ammonia water to adjust the pH to 10, and then add 80mL of tetraethylsilicate. Continue stirring for 24h to allow the tetraethylsilicate to hydrolyze in an alkaline environment to form nano-SiO2 particles and load them on the surface of fluorinated graphene, thus obtaining a fluorinated graphene suspension. Add 50mL of the fluorinated graphene suspension, 90g of bentonite, and 2L of N,N-dimethylformamide to a reaction vessel and stir for 2h at 25℃ and 600r / min. Filter the mixture and wash the filter cake three times with deionized water and anhydrous ethanol, respectively. Dry the mixture under vacuum at 80℃ for 2h to obtain bentonite-loaded fluorinated graphene / SiO2 powder.

[0044] S2: Add 60g of γ-aminopropyltriethoxysilane and 900mL of deionized water to a reaction vessel, add sodium hydroxide and acetic acid solution to adjust the pH to 7, stir at 25℃ and 600r / min for 60min, let stand for 2h after stirring. Add 40g of bentonite-supported fluorinated graphene / SiO2 powder and 120mL of 60% ethanol solution to the reaction vessel, stir at 25℃ and 600r / min for 2h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 80℃ for 2h to obtain modified bentonite-supported fluorinated graphene / SiO2 powder.

[0045] S3: Add 40g of modified bentonite-supported fluorinated graphene / SiO2 powder and 2L of deionized water to a reactor. Stir for 60min at 25℃ and 600r / min. Then add 60mL of polyvinyl alcohol, heat to 100℃, and stir until the material is completely dissolved. Then cool to 45℃, add 2g of octylphenol polyoxyethylene ether as an emulsifier, and continue stirring for 40min. Then add 30mL of vinyl acetate and 2g of potassium persulfate as an initiator, heat to 70℃, keep warm for 2h, cool to 50℃, add sodium bicarbonate to adjust the pH to 7, and then add 2g of dibutyl phthalate as a plasticizer. Continue stirring for 60min, cool naturally, and discharge to obtain the modified binder.

[0046] S4: Mix 3.2 kg of polycarboxylate superplasticizer and 110 kg of deionized water to obtain a superplasticizer dilution; mix 270 kg of P.O42.5 silicate cement, 40 kg of Class I fly ash, 1200 kg of recycled concrete aggregate, 40 kg of modified binder and 160 kg of superplasticizer dilution to obtain a modified permeable recycled concrete.

[0047] Comparative Example 1: Based on Example 3, the fluorinated graphene in step S1 was replaced with graphene oxide, while the other steps remained unchanged, to prepare modified permeable recycled concrete.

[0048] Comparative Example 2: Based on Example 3, without step S2, the modified bentonite-supported fluorinated graphene / SiO2 powder in step S3 was replaced with the bentonite-supported fluorinated graphene / SiO2 powder in step S1, while the other steps remained unchanged, and modified permeable recycled concrete was prepared.

[0049] Comparative Example 3: Based on Example 3, tetraethyl silicate in step S1 was omitted so that it could not hydrolyze in an alkaline environment to form nano-SiO2 particles and be loaded onto the surface of fluorinated graphene. The remaining steps remained unchanged, and modified permeable recycled concrete was prepared.

[0050] The modified permeable recycled concrete obtained in Examples 1-3 and Comparative Examples 1-3 was poured into molds (100mm×100mm×100mm) and demolded after 24 hours. The concrete samples were then transferred to a curing room for standard curing for 28 days before testing. The ultraviolet aging test was conducted in an ultraviolet aging chamber with an ultraviolet intensity of 210 W / m². 2 The aging temperature was 60℃ and the aging time was 6 days.

[0051] Table 1 Performance Test Table of Modified Permeable Recycled Concrete Before Aging

[0052] ,

[0053] Table 2 Performance Test Table of Aging Modified Permeable Recycled Concrete

[0054] As can be seen from Tables 1 and 2, the modified permeable recycled concrete obtained in Examples 1-3 has significantly better compressive strength, flexural strength, relative density, porosity, and permeability coefficient than the comparative example. Furthermore, after the ultraviolet aging test, the performance degradation of the examples is less than that of the comparative example. This indicates that the modified permeable recycled concrete prepared by the present invention has good density and compressive strength, high porosity and good permeability, and is not prone to cracking due to aging of the binder under long-term ultraviolet irradiation.

[0055] In Comparative Example 1, fluorinated graphene was replaced with graphene oxide. Fluorinated graphene was coated on the surface of bentonite as a filler for recycled concrete. The high stability of the CF bond can improve the anti-aging properties of the polyvinyl alcohol-vinyl acetate copolymer polymerized on the surface. The polyvinyl alcohol-vinyl acetate copolymer can interact with soil particles, which helps to prevent the copolymer from aging.

[0056] In Comparative Example 2, the modified bentonite-supported fluorinated graphene / SiO2 powder was replaced with the bentonite-supported fluorinated graphene / SiO2 powder in step S1. Treatment with γ-aminopropyltriethoxysilane hydrolyzed the powder to generate silanol bonds that bond with the hydroxyl groups on the surface of the bentonite-supported fluorinated graphene / SiO2 powder, thus imbuing the powder with amino groups. These amino groups can bind with polyvinyl alcohol-vinyl acetate copolymers, which contain a large number of carboxyl and hydroxyl groups, enabling them to bond with the amino groups on the surface of the modified bentonite-supported fluorinated graphene / SiO2 powder. This allows the polymer to be fixed on the surface of the modified bentonite-supported fluorinated graphene / SiO2.

[0057] In Comparative Example 3, tetraethyl silicate was omitted, and the structure of fluorinated graphene / SiO2 consisted of nano-SiO2 particles loaded on fluorinated graphene sheets. By loading nano-SiO2 particles onto the surface of fluorinated graphene, the surface state of fluorinated graphene was changed, which could effectively prevent the stacking between fluorinated graphene sheets and improve the dispersibility and interfacial compatibility of fluorinated graphene in resin.

[0058] 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 a modified pervious recycled concrete, characterized by, It comprises the following steps: Step one: by sol-gel method, using alkaline catalytic hydrolysis of tetraethyl silicate, in situ generation of nano SiO2 particles on the surface of fluorinated graphene, and then using hydrogen bond self-assembly to load fluorinated graphene / SiO2 on bentonite to obtain bentonite loaded fluorinated graphene / SiO2 powder; Step two: after the bentonite loaded fluorinated graphene / SiO2 is modified by γ-aminopropyl triethoxysilane, the polyvinyl alcohol-vinyl acetate copolymer is polymerized on the surface to obtain a modified binder; Step three: mix polycarboxylic acid water reducing agent and deionized water according to the mass ratio of 2.9-3.2:90-110 to obtain a water reducing agent diluent; mix Portland cement, fly ash, recycled concrete aggregate, modified binder and water reducing agent diluent to obtain a modified pervious recycled concrete; The specific preparation steps of the modified binder are as follows: The modified bentonite loaded fluorinated graphene / SiO2 powder and deionized water are added into a reaction kettle, stirred at 20-25℃ and 500-600r / min for 40-60min, then polyvinyl alcohol is added, heated to 90-100℃, and stirred until the material is completely dissolved, then cooled to 40-45℃, and octylphenol polyoxyethylene ether is added, and the stirring reaction is continued for 30-40min, then vinyl acetate and potassium persulfate are added, heated to 65-70℃, and kept for 1-2h, cooled to 45-50℃, and sodium bicarbonate is added to adjust the pH value to 6-7, then dibutyl phthalate is added, and the stirring is continued for 40-60min, and then the material is naturally cooled and discharged to obtain the modified binder; The specific preparation steps of the bentonite loaded fluorinated graphene / SiO2 powder in step one are as follows: The fluorinated graphene and ethanol solution are added into a reaction kettle, stirred at 20-25℃ and 500-600r / min for 20-30min, then 30-40wt% ammonia water is added to adjust the pH value to 9-10, then tetraethyl silicate is added, and the stirring reaction is continued for 20-24h to obtain a fluorinated graphene suspension; the fluorinated graphene suspension, bentonite and N,N-dimethylformamide are added into a reaction kettle, stirred at 20-25℃ and 500-600r / min for 1-2h, filtered, washed and vacuum dried to obtain the bentonite loaded fluorinated graphene / SiO2 powder.

2. The method for preparing modified water permeable recycled concrete according to claim 1, characterized in that, The dosage ratio of the Portland cement, fly ash, recycled concrete aggregate, modified binder and water reducing agent diluent in step three is 260-270kg:30-40kg:1100-1200kg:30-40kg:150-160kg.

3. The method for preparing modified water permeable recycled concrete according to claim 1, characterized in that, The dosage ratio of the fluorinated graphene, ethanol solution, ammonia water and tetraethyl silicate is 50-60g:800-900mL:12-14mL:70-80mL.

4. The method for preparing modified water permeable recycled concrete according to claim 1, characterized in that, The dosage ratio of the fluorinated graphene suspension, bentonite and N,N-dimethylformamide is 40-50mL:80-90g:1-2L.

5. The method of claim 1, wherein the modified pervious recycled concrete is prepared by mixing the recycled aggregate, the cement, the water, and the additive. The modified bentonite supported fluorinated graphene / SiO2 powder, deionized water, polyvinyl alcohol, octylphenol polyoxyethylene ether, vinyl acetate, potassium persulfate and dibutyl phthalate are in a ratio of 30-40g: 1-2L: 50-60mL: 1-2g: 20-30mL: 1-2g: 1-2g.

6. The method of claim 1, wherein the modified pervious recycled concrete is prepared by mixing the recycled aggregate, the cement, the water, and the additive. The modified bentonite supported fluorinated graphene / SiO2 powder is prepared by the following steps: The γ-aminopropyl triethoxysilane and deionized water are added into a reaction kettle, sodium hydroxide and acetic acid solution are added to adjust the pH value to 6.5-7, 20-25℃ and 500-600r / min stirring for 40-60min, after the stirring reaction, stand for 1-2h, the bentonite supported fluorinated graphene / SiO2 powder is mixed with 50-60wt% ethanol solution and added into the reaction kettle, 20-25℃ and 500-600r / min stirring for 1-2h, filtration, washing, vacuum drying, to obtain the modified bentonite supported fluorinated graphene / SiO2 powder; The γ-aminopropyl triethoxysilane, deionized water, bentonite supported fluorinated graphene / SiO2 powder and ethanol solution are in a ratio of 50-60g: 800-900mL: 30-40g: 100-120mL.

7. A modified pervious recycled concrete, characterized by, Prepared by the preparation method of any one of claims 1-6.

8. The application of a modified water permeable recycled concrete in cement concrete according to claim 7.

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