Pervious concrete and preparation method thereof

Abstract

The invention relates to the field of building materials, and particularly discloses pervious concrete and a preparation method thereof.The pervious concrete is prepared from cement, coarse aggregate, silica fume, water, a water reducing agent, hydroxypropyl methyl cellulose ether, reinforcing filler and polypropylene fiber; wherein the reinforcing filler is selected from modified ceramsite loaded with biochar, and the modified ceramsite is prepared by soaking porous ceramsite in a citric acid solution, dipping the porous ceramsite in a modification solution containing epoxy resin, biochar, acrylamide and vinyl versatate, and baking the porous ceramsite at a high temperature; the preparation method comprises the following steps: mixing the cement, the coarse aggregate, the silica fume, the reinforcing filler and the polypropylene fiber to prepare a primary mixture; mixing and stirring hydroxypropyl methyl cellulose ether and 1 / 4-1 / 3 of water to prepare a mixed solution; and mixing the water reducing agent with the residual water, adding the mixed solution and the primary mixture, and mixing to obtain the pervious concrete. The preparation method has the characteristic that the prepared concrete is better in strength and durability and has relatively high water permeability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials, more particularly, it relates to a pervious concrete and a preparation method thereof. BACKGROUND

[0002] With the acceleration of urbanization, the large-scale use of impervious paving materials has led to problems such as urban waterlogging and insufficient groundwater recharge, which not only affects the ecological environment of the city, but also has a negative impact on the lives of residents. In order to solve the above problems, pervious concrete as an environmentally friendly building material has gradually attracted attention.

[0003] Pervious concrete has shown great application potential in paving scenarios that require water permeability, such as urban roads, squares, parking lots, and sidewalks, especially in the construction of sponge cities. This material can effectively alleviate urban waterlogging, promote natural infiltration of rainwater and groundwater recharge, and also reduce pollution caused by surface runoff.

[0004] Despite the above-mentioned advantages of pervious concrete, its research and application still face challenges. Current research mainly focuses on balancing the relationship between the strength, durability, and water permeability of pervious concrete. Currently, the realization of high water permeability often accompanies a decrease in concrete strength, and vice versa. Moreover, while relying on interconnected pores to achieve rapid rainwater infiltration, freeze-thaw cycles significantly reduce its durability. This contradiction limits the wider application of pervious concrete, especially in urban areas that bear higher traffic loads.

[0005] Therefore, it is necessary to continue researching a new type of pervious concrete material that can guarantee high water permeability while maintaining sufficient mechanical strength and durability to meet the needs of different application scenarios. SUMMARY

[0006] In order to obtain a concrete with better strength and durability while having high water permeability, the present application provides a pervious concrete and a preparation method thereof.

[0007] In a first aspect, the present application provides a pervious concrete, which adopts the following technical solution: A pervious concrete, comprising the following raw materials by weight: 300-400 parts of cement, 980-1050 parts of coarse aggregate, 60-80 parts of silica fume, 110-120 parts of water, 3-5 parts of water reducing agent, 0.5-1 part of hydroxypropyl methyl cellulose ether, 100-150 parts of reinforcing filler, and 3-8 parts of polypropylene fiber. The modified ceramic is prepared by soaking porous ceramic in a citric acid solution, and then impregnating and treating the soaked porous ceramic in a modified solution containing epoxy resin, biochar, and acrylamide and vinyl versatate, and high-temperature baking.

[0008] By adopting the technical solution, a large amount of coarse aggregate is adopted to form a stable skeleton structure, and the pore blockage caused by the addition of fine aggregate is reduced, the water permeability is provided, a small amount of silica fume is added to fill the micropores, and the density is improved, the water permeable concrete prepared by controlling the ratio of the two has better strength while maintaining better water permeability, in addition, polypropylene fibers are added in the application, the fiber network structure reduces the decrease of water permeability caused by crack expansion. In addition, the modified ceramic loaded with biochar is also added in the application, the porous ceramic is first treated with citric acid to remove impurities on the surface or pores of the porous ceramic, and a porous carrier with better permeability is formed. Then it is soaked and treated in a modified solution containing biochar, the biochar is filled in the pores of the porous ceramic, forming a different graded pore structure, which helps to maintain water permeability, and the filling of biochar helps to improve the strength.

[0009] The addition of epoxy resin helps to improve the adhesion of biochar in the porous ceramic, on the one hand, and on the other hand, the hydroxyl and other functional groups on the surface of biochar and porous ceramic react with epoxy resin to form chemical bonds, anchoring biochar firmly on the surface of ceramic, avoiding subsequent shedding, the addition of acrylamide, the amino group forms a chemical bond with the functional groups such as hydroxyl or carboxyl on the surface of biochar, introduces a double bond, and reacts with the double bond in vinyl versatate, introduces a hydrophobic layer of vinyl versatate, reduces the water permeability of water in the modified ceramic in the subsequent cement slurry, so that the rainwater infiltrates without penetrating into the porous ceramic, causing cracking due to freeze-thaw cycle, reducing the shrinkage cracks caused by the change of water in the modified ceramic, and the surface tension of vinyl versatate polymer is lower than that of water, so that water droplets on the surface of the ceramic form a spherical shape and roll instead of penetrating behavior, thereby reducing the residence time of water in the pores, so that water quickly passes through the pores, indirectly improving the water permeability. The water permeability of the water permeable concrete prepared by the application is improved while maintaining better water permeability.

[0010] Optionally, the modified solution includes the following raw materials by weight: 6-10 parts of epoxy resin, 20-30 parts of biochar, 5-8 parts of acrylamide, 2-5 parts of vinyl versatate, 0.5-1 parts of ammonium persulfate, 1-3 parts of hydroxypropyl methyl cellulose, and 40-50 parts of water.

[0011] By adopting the above technical scheme, hydroxypropyl methyl cellulose as the anti-settling agent helps the uniform distribution of biochar, helps the uniform distribution and loading in the porous ceramicite, and ammonium persulfate as the initiator helps the polymerization of acrylamide and vinyl tertiary carbonate, etc. After the porous ceramicite is immersed in the above modification liquid, the loading of biochar is realized, and the modification of biochar helps to improve the water permeability.

[0012] Optionally, the modified ceramicite is prepared by the following method: 1) The porous ceramicite is first soaked in a mixed solution of 5-10wt% citric acid solution and 2-3wt% phosphoric acid solution for 8-12h, and the pretreated ceramicite is obtained after drying; 2) The prepared pretreated ceramicite is added to the modification liquid, first vacuumed to-(0.08)-(-0.1)MPa and stirred and immersed at 25-30℃ for 30-40min, then immersed at normal pressure and heated to 45-55℃ for 60-90min, and finally heated to 70-80℃ for 20-30min, and the initial modified ceramicite is prepared after filtration; 3) The initial modified ceramicite is first treated at 60-70℃ for 1-2h, then treated at 110-120℃ for 1-2h, and finally heated to 150℃ for 30-60min, and the modified ceramicite is prepared.

[0013] By adopting the above technical scheme, the porous ceramicite is subjected to composite acid etching by the mixed solution of citric acid and phosphoric acid, the surface porosity of the porous ceramicite is increased, and more hydroxyl groups and other functional groups are introduced, then the pretreated ceramicite is treated, first immersed under negative pressure, so that the biochar solution can easily penetrate into the micropores and interlamellar gaps of the ceramicite, and then immersed at normal pressure and high temperature, so that chemical bonds are formed between the porous hollow and the biochar, which helps to improve the bonding strength and the introduction of tertiary carbonate groups, and the physical entanglement between the polypropylene fibers and the biochar can also be formed, and finally the strength of the pervious concrete is further improved.

[0014] Optionally, in step 1) of the preparation process of the modified ceramicite, the mass ratio of the porous ceramicite to the mixed solution is 1:(8-10). In step 2), the mass ratio of the pretreated ceramicite to the modification liquid is 1:(12-15).

[0015] Optionally, 8-15 parts of ethylenediamine are further added to the modification liquid, and the carboxylated polypropylene fibers are prepared by adding carboxylated polypropylene fibers after carboxyl modification.

[0016] By adopting the technical scheme, when the modifying liquid further contains ethylenediamine, amino functional groups are introduced on the surface of the porous ceramicite, which forms chemical cross-linking with the carboxylated polypropylene fibers, and the fiber network formed by the cross-linking limits the relative movement of materials with different specific gravities, inhibits the development of internal capillaries, and forms more connected pores rather than closed pores. Such a structure enables water to more easily pass through the pore network, thereby improving water permeability and increasing strength.

[0017] Optionally, the particle size of the biochar is 0.1-0.5mm, and the particle size of the porous ceramicite is 10-20mm.

[0018] Optionally, the carboxylated polypropylene fiber is prepared by the following method: The polypropylene fiber is first treated in a 4-6wt% nitric acid solution in a water bath at 50-60℃ for 1-2h to obtain pretreated polypropylene fiber; acrylic acid and hydroxyethyl methacrylate are mixed as a monomer mixture, then dissolved in a mixed solution of water and ethanol, and then added to the pretreated polypropylene fiber, followed by the addition of ammonium persulfate, and then reacted in a water bath at 55-65℃ for 2-3h, and then filtered to obtain grafted polypropylene fiber; The grafted polypropylene fiber is completely immersed in silica sol, stirred, then added with amino silane coupling agent, heated to 60-70℃, and then added with ammonia water to adjust the pH value to 8-9, reacted for 2-3h, then filtered, washed with water, and dried to obtain carboxylated polypropylene fiber.

[0019] By adopting the technical scheme, the polypropylene fiber is first oxidized and treated in a nitric acid solution in a water bath to introduce carboxyl or hydroxyl functional groups on the surface of the polypropylene fiber, and then the polypropylene fiber is treated in a mixed monomer containing acrylic acid and hydroxyethyl methacrylate. Under the action of an initiator, hydroxyethyl methacrylate and acrylic acid are grafted onto the surface of the polypropylene fiber to form a polyacrylate graft layer containing hydroxyl groups. In this way, a large number of carboxyl and hydroxyl active functional groups can be introduced on the surface of the polypropylene fiber, which can form hydrogen bonds and other interactions with the cement hydration products and the modified ceramicite. Compared with ordinary polypropylene fibers, which have smooth surfaces, high chemical inertness, and weak bonding with the cement matrix, resulting in slippage or pull-out under stress, the polypropylene fiber treated in the present application significantly improves the bonding with the cement matrix and the action of the porous ceramicite, forming a more stable combined whole, significantly improving the mechanical properties and durability. Moreover, the grafting segment forms a flexible transition layer on the surface of the fiber, which can relieve stress concentration, inhibit crack propagation, and improve durability.

[0020] And the compatibility of the carboxylated fiber surface modification with the cement matrix is improved, the fiber aggregation phenomenon is reduced, the uniformly dispersed fiber can form a better three-dimensional support network, which can not only enhance the integrity of the pervious concrete, but also can avoid blocking the pervious pore, maintain the water permeability and improve the mechanical properties and durability of the pervious concrete. The carboxylated polypropylene fiber is treated in the silica sol, and under the alkaline catalytic condition, the nanoscale silicon dioxide particles are formed. The addition of the amino silane coupling agent makes one end of the amino silane coupling agent react with the carboxyl group on the surface of the fiber and the other end of the amino silane coupling agent combine with the surface of the nanoscale silicon dioxide particles, so that the formed nanoscale silicon dioxide is firmly attached to the surface of the fiber. Moreover, the nanoscale silicon dioxide on the surface of the fiber further improves the anchoring effect between the carboxylated polypropylene fiber, the modified haydite and the cement matrix, further inhibits the slippage and improves the performance of the concrete.

[0021] Optionally, when the carboxylated polypropylene fiber is prepared, the mass ratio of the polypropylene fiber to the nitric acid solution is 1:(6-8); The mass ratio of the acrylic acid to the hydroxyethyl methacrylate is 1:(1.4-1.6), the mass ratio of the water to the ethanol is 1:(0.4-0.6), and the mass ratio of the monomer mixture to the mixed solution is 1:(3-5); The mass ratio of the pretreated polypropylene fiber to the monomer mixture is 1:(1.8-2.5), and the addition amount of the ammonium persulfate is 0.5-1wt% of the monomer mixture; The mass ratio of the grafted polypropylene fiber to the silica sol is 1:(4-6), and the solid content of the silica sol is 25-30% (i.e. the mass ratio of the silicon dioxide is 25-30%, and the rest is water). The addition amount of the amino silane coupling agent is 1-3wt% of the grafted polypropylene fiber.

[0022] By controlling the addition amount of the silica sol and the like, the amount of the nanoscale silicon dioxide generated on the surface of the polypropylene fiber is added, and the comprehensive performance of the water permeability and the mechanical properties of the pervious concrete is more excellent.

[0023] Optionally, the water reducing agent is a polycarboxylic acid water reducing agent, the coarse aggregate includes a mixture of the broken stone with a continuous particle size of 4.75-9.5mm and the broken stone with a continuous particle size of 9.5-16mm, and the mass ratio of the broken stone with a continuous particle size of 4.75-9.5mm is 35-45%, and the mass ratio of the broken stone with a continuous particle size of 9.5-16mm is 55-65%.

[0024] In a second aspect, the application provides a preparation method of the pervious concrete, which adopts the following technical scheme: A preparation method of a pervious concrete, including the following steps: Mixing the cement, the coarse aggregate, the silica fume, the reinforcing filler and the polypropylene fiber to obtain a preliminary mixture; Hydroxypropyl methylcellulose ether was mixed with 1 / 4 to 1 / 3 water and stirred to obtain a mixture. The water-reducing agent is mixed with the remaining water and then added to the mixture and initial mixture to obtain permeable concrete.

[0025] By adopting the above technical solution,

[0026] In summary, this application has the following beneficial effects: 1. This application also includes modified ceramsite loaded with biochar. The porous ceramsite is first treated with citric acid to remove impurities from the surface or pores of the porous ceramsite, forming a porous carrier with better permeability. Then, it is impregnated in a modification solution containing biochar. The biochar fills the pores of the porous ceramsite, forming a pore structure with different gradations, which helps maintain water permeability. At the same time, the filling of biochar helps to improve strength. 2. The introduction of the hydrophobic layer of tert-carbonate in the modified liquid in this application reduces the water penetration of the subsequent cement paste into the modified ceramsite, allowing rainwater to infiltrate downwards instead of penetrating into the porous ceramsite and causing cracking due to freeze-thaw cycles. This also reduces the occurrence of shrinkage cracks caused by changes in moisture content within the modified ceramsite. At the same time, the surface tension of the tert-carbonate ethylene polymer is lower than that of water, making water droplets on the ceramsite surface more likely to form spherical rolling rather than penetrating behavior, thereby reducing the residence time of water in the pores and allowing water to pass through the pores quickly, indirectly increasing the permeability. Ultimately, this application improves the strength while maintaining better permeability through the combination of pore structure between biochar and porous ceramsite. Detailed Implementation

[0027] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0028] In the following examples, the biochar is selected from straw or coffee grounds and other waste materials that have been calcined at high temperature. The biochar has a particle size of 0.1-0.5 mm, a porosity of 50-60%, and a micropore size of 0.1-1 μm. The porous ceramsite has a particle size of 10-20 mm, a pore size of 1-3 mm, and a porosity of 25-30%.

[0029] In the following examples, the epoxy resin used is bisphenol A type epoxy resin with model number E-44; The polycarboxylate superplasticizer selected is from the brand Subote, model number [model number missing]. Polycarboxylate high-performance water-reducing agent; The cement used is P.O42.5 ordinary Portland cement.

[0030] The following preparation example is a preparation example of modified ceramsite Preparation Example 1 A method for preparing modified ceramsite, comprising the following steps: 1) A mixed solution is prepared by mixing a citric acid solution with a mass concentration of 8wt% and a phosphoric acid solution with a mass concentration of 2.5wt% according to a mass ratio of 1:1, then porous ceramsite is added into the mixed solution for soaking for 10h, the addition mass ratio of the porous ceramsite to the mixed solution is 1:9, and the pretreated ceramsite is obtained after drying; 2) A modified liquid is prepared by mixing 8kg of epoxy resin, 25kg of biochar, 6kg of acrylamide, 3kg of vinyl versatate, 0.8kg of ammonium persulfate, 2kg of hydroxypropyl methyl cellulose, and 45kg of water; The prepared pretreated ceramsite is added into the modified liquid, the addition mass ratio of the pretreated ceramsite to the modified liquid is 1:13, first vacuum extraction is performed to a condition of-(0.09)MPa for stirring and impregnation treatment for 35min, then normal pressure and heating to 50℃ are adopted for continuing impregnation treatment for 70min, and the primary modified ceramsite is prepared after filtration; 3) The primary modified ceramsite is first treated at 65℃ for 1.5h, then treated at 115℃ for 1.5h, and finally heated to 150℃ for 40min to prepare the modified ceramsite.

[0031] Preparation Example 2 A method for preparing modified ceramsite, comprising the following steps: 1) A mixed solution is prepared by mixing a citric acid solution with a mass concentration of 5wt% and a phosphoric acid solution with a mass concentration of 2wt% according to a mass ratio of 1:1, then porous ceramsite is added into the mixed solution for soaking for 8h, the addition mass ratio of the porous ceramsite to the mixed solution is 1:8, and the pretreated ceramsite is obtained after drying; 2) A modified liquid is prepared by mixing 6kg of epoxy resin, 20kg of biochar, 5kg of acrylamide, 2kg of vinyl versatate, 0.5kg of ammonium persulfate, 1kg of hydroxypropyl methyl cellulose, and 40kg of water; The prepared pretreated ceramsite is added into the modified liquid, the addition mass ratio of the pretreated ceramsite to the modified liquid is 1:12, first vacuum extraction is performed to a condition of-(0.08)MPa for stirring and impregnation treatment for 40min, then normal pressure and heating to 45℃ are adopted for continuing impregnation treatment for 90min, and the primary modified ceramsite is prepared after filtration; 3) The primary modified ceramsite is first treated at 60℃ for 2h, then treated at 110℃ for 2h, and finally heated to 150℃ for 30min to prepare the modified ceramsite.

[0032] Preparation Example 3 A method for preparing modified ceramsite, comprising the following steps: 1) A solution of citric acid with a mass concentration of 10 wt% and a solution of phosphoric acid with a mass concentration of 3 wt% are mixed in a mass ratio of 1:1 to obtain a mixed solution, then porous ceramic granules are added to the mixed solution for soaking for 12 h, the mass ratio of the porous ceramic granules to the mixed solution is 1:10, and the pretreated ceramic granules are obtained after drying; 2) 10 kg of epoxy resin, 30 kg of biochar, 8 kg of acrylamide, 5 kg of vinyl versatate, 1 kg of ammonium persulfate, 3 kg of hydroxypropyl methylcellulose, and 50 kg of water are mixed to obtain a modification liquid; The prepared pretreated ceramic granules are added to the modification liquid, the mass ratio of the pretreated ceramic granules to the modification liquid is 1:15, vacuum is first applied to a condition of (-0.1) MPa, stirring and impregnation treatment is performed for 30 min, then impregnation treatment is continuously performed for 60 min under normal pressure and at a temperature of 55°C, and the initial modified ceramic granules are obtained after filtration; 3) The initial modified ceramic granules are first treated at 70°C for 1 h, then treated at 120°C for 1 h, and finally treated at 150°C for 60 min, and the modified ceramic granules are obtained.

[0033] Preparation Example 4 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that 12 kg of ethylenediamine is further added to the modification liquid in step 2).

[0034] Preparation Example 5 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that 8 kg of ethylenediamine is further added to the modification liquid in step 2).

[0035] Preparation Example 6 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that 15 kg of ethylenediamine is further added to the modification liquid in step 2).

[0036] Comparative Preparation Example 1 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that vinyl versatate is not added to the modification liquid in step 2).

[0037] Comparative Preparation Example 2 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that acrylamide is not added to the modification liquid in step 2).

[0038] Comparative Preparation Example 3 A method for preparing modified ceramic granules is performed according to the method in Preparation Example 1, except that epoxy resin is not added to the modification liquid in step 2).

[0039] Example 1 A preparation method of pervious concrete, comprising the following steps: Mixing 350 kg of cement, 1000 kg of coarse aggregate, 70 kg of silica fume, and 130 kg of reinforcing filler, and 5 kg of polypropylene fiber to obtain a preliminary mixture; Mixing and stirring 0.8 kg of hydroxypropyl methyl cellulose ether with 40 kg of water to obtain a mixed solution; Mixing 4 kg of water reducing agent with 75 kg of water, and then adding the mixed solution and the preliminary mixture to obtain the pervious concrete.

[0040] The reinforcing filler is the modified ceramsite prepared in the preparation example 1, the coarse aggregate comprises a mixture of gravel with a continuous particle size of 4.75-9.5 mm and gravel with a continuous particle size of 9.5-16 mm, and the mass ratio of the gravel with a continuous particle size of 4.75-9.5 mm is 40%, and the mass ratio of the gravel with a continuous particle size of 9.5-16 mm is 60%.

[0041] Example 2 A preparation method of pervious concrete, comprising the following steps: Mixing 300 kg of cement, 980 kg of coarse aggregate, 60 kg of silica fume, and 100 kg of reinforcing filler, and 3 kg of polypropylene fiber to obtain a preliminary mixture; Mixing and stirring 0.5 kg of hydroxypropyl methyl cellulose ether with 28 kg of water to obtain a mixed solution; Mixing 3 kg of water reducing agent with 82 kg of water, and then adding the mixed solution and the preliminary mixture to obtain the pervious concrete.

[0042] The reinforcing filler is the modified ceramsite prepared in the preparation example 2, the coarse aggregate comprises a mixture of gravel with a continuous particle size of 4.75-9.5 mm and gravel with a continuous particle size of 9.5-16 mm, and the mass ratio of the gravel with a continuous particle size of 4.75-9.5 mm is 35%, and the mass ratio of the gravel with a continuous particle size of 9.5-16 mm is 65%.

[0043] Example 3 A preparation method of pervious concrete, comprising the following steps: Mixing 400 kg of cement, 1050 kg of coarse aggregate, 80 kg of silica fume, and 150 kg of reinforcing filler, and 8 kg of polypropylene fiber to obtain a preliminary mixture; Mixing and stirring 1 kg of hydroxypropyl methyl cellulose ether with 30 kg of water to obtain a mixed solution; Mixing 5 kg of water reducing agent with 90 kg of water, and then adding the mixed solution and the preliminary mixture to obtain the pervious concrete.

[0044] The modified ceramsite prepared in Preparation Example 3 is used as the reinforcing filler, the coarse aggregate includes a mixture of the broken stone with a continuous particle size of 4.75-9.5 mm and the broken stone with a continuous particle size of 9.5-16 mm, and the mass ratio of the broken stone with a continuous particle size of 4.75-9.5 mm is 45%, and the mass ratio of the broken stone with a continuous particle size of 9.5-16 mm is 55%.

[0045] Example 4 A preparation method of the pervious concrete is performed according to the method in Example 1, except that the modified ceramsite prepared in Preparation Example 4 is used as the reinforcing filler, and the polypropylene fiber is prepared after being modified by carboxylation, and the specific operation is as follows: a. The polypropylene fiber is first treated in a 5wt% nitric acid solution in a water bath at 55°C for 1.5h, and the addition mass ratio of the polypropylene fiber to the nitric acid solution is 1:7, to obtain pretreated polypropylene fiber; b. Acrylic acid and hydroxyethyl methacrylate are mixed as a monomer mixture according to a mass ratio of 1:1.5, water and ethanol are mixed to obtain a mixed solution according to an addition mass ratio of 1:0.5, and then the monomer mixture is dissolved in the mixed solution of water and ethanol, and the addition mass ratio of the monomer mixture to the mixed solution is 1:4; Then, the pretreated polypropylene fiber is added into the monomer mixture and the mixed system of ethanol and water, and then ammonium persulfate is added, and the reaction is carried out in a water bath at 60°C for 2.5h, and then the grafted polypropylene fiber is obtained after filtration; The addition mass ratio of the pretreated polypropylene fiber to the monomer mixture is 1:2, and the addition amount of ammonium persulfate is 0.8wt% of the monomer mixture; c. The obtained grafted polypropylene fiber is completely immersed in silica sol with a solid content of 28% (i.e. the mass ratio of silicon dioxide is 28%, and the rest is water), and the addition mass ratio of the grafted polypropylene fiber to the silica sol is 1:5, and then the amino silane coupling agent KH-550 is added after stirring, and the addition amount of the amino silane coupling agent is 2wt% of the grafted polypropylene fiber, and then the temperature is increased to 65°C, and the pH value is adjusted to 8.5 by adding ammonia water, and the reaction is carried out for 2.5h, and then the product is filtered, washed with water, and dried to obtain carboxylated polypropylene fiber.

[0046] Example 5 A preparation method of the pervious concrete is performed according to the method in Example 1, except that the modified ceramsite prepared in Preparation Example 5 is used as the reinforcing filler, and the polypropylene fiber is prepared after being modified by carboxylation, and the specific operation is as follows: a. The polypropylene fiber is first treated in a 4wt% nitric acid solution in a water bath at 50°C for 2h, and the addition mass ratio of the polypropylene fiber to the nitric acid solution is 1:6, to obtain pretreated polypropylene fiber; b. mixing acrylic acid and hydroxyethyl methacrylate in a mass ratio of 1:1.4 as a monomer mixture, mixing water and ethanol in an added mass ratio of 1:0.4 to prepare a mixed solution, then dissolving the monomer mixture in the mixed solution of water and ethanol, and the added mass ratio of the monomer mixture to the mixed solution is 1:3; Then, the pretreated polypropylene fiber is added into the mixed system of the monomer mixture, ethanol and water, and then ammonium persulfate is added, and the reaction is carried out at 55°C in a water bath for 3h, and then the grafted polypropylene fiber is prepared after filtration; The added mass ratio of the pretreated polypropylene fiber to the monomer mixture is 1:1.8, and the added amount of ammonium persulfate is 0.5wt% of the monomer mixture; c. The prepared grafted polypropylene fiber is completely immersed in a silica sol with a solid content of 25% (i.e. the mass ratio of silicon dioxide is 25%, and the rest is water), the added mass ratio of the grafted polypropylene fiber to the silica sol is 1:4, after stirring, the amino silane coupling agent KH-550 is added, the added amount of the amino silane coupling agent is 1wt% of the grafted polypropylene fiber, the temperature is raised to 60°C, ammonia water is added to adjust the pH value to 8, the reaction is carried out for 3h, then the product is filtered, washed with water, and dried to prepare the carboxylated polypropylene fiber.

[0047] Example 6 A method for preparing a pervious concrete, which is carried out according to the method in Example 1, except that the reinforcing filler is the modified ceramsite prepared in Preparation Example 6, and the polypropylene fiber is prepared after being carboxylated, and the specific operation is as follows: a. The polypropylene fiber is first treated in a 6wt% nitric acid solution in a water bath at 60°C for 1h, and the added mass ratio of the polypropylene fiber to the nitric acid solution is 1:8, to prepare the pretreated polypropylene fiber; b. mixing acrylic acid and hydroxyethyl methacrylate in a mass ratio of 1:1.6 as a monomer mixture, mixing water and ethanol in an added mass ratio of 1:0.6 to prepare a mixed solution, then dissolving the monomer mixture in the mixed solution of water and ethanol, and the added mass ratio of the monomer mixture to the mixed solution is 1:5; Then, the pretreated polypropylene fiber is added into the mixed system of the monomer mixture, ethanol and water, and then ammonium persulfate is added, and the reaction is carried out at 65°C in a water bath for 2h, and then the grafted polypropylene fiber is prepared after filtration; The added mass ratio of the pretreated polypropylene fiber to the monomer mixture is 1:2.5, and the added amount of ammonium persulfate is 1wt% of the monomer mixture; c. The prepared grafted polypropylene fibers were completely immersed in a silica sol with a solid content of 30% (i.e., the mass ratio of silica was 30%, and the rest was water), and the mass ratio of the grafted polypropylene fibers to the silica sol was 1:6. After stirring, amino silane coupling agent KH-550 was added, and the amount of the amino silane coupling agent was 3 wt% of the grafted polypropylene fibers. The temperature was raised to 70°C, and ammonia water was added to adjust the pH value to 9. After 2 h of reaction, the product was filtered, washed with water, and dried to obtain carboxylated polypropylene fibers.

[0048] Example 7 A method for preparing a pervious concrete was performed according to the method in Example 1, except that the reinforcing filler was the modified ceramsite prepared in Preparation Example 4.

[0049] Example 8 A method for preparing a pervious concrete was performed according to the method in Example 4, except that when the polypropylene fibers were carboxylated and modified, step c was not performed, and the prepared grafted polypropylene fibers were added as carboxylated polypropylene fibers.

[0050] Comparative Examples 1-3 A method for preparing a pervious concrete was performed according to the method in Example 1, except that the reinforcing filler was the modified ceramsite prepared in Comparative Preparation Examples 1-3, respectively.

[0051] Comparative Example 4 A method for preparing a pervious concrete was performed according to the method in Example 1, except that the modified ceramsite was replaced with an equal amount of unmodified porous ceramsite.

[0052] Comparative Example 5 A method for preparing a pervious concrete was performed according to the method in Example 1, except that no reinforcing filler was added to the raw materials.

[0053] Performance detection The pervious concrete prepared in the above examples and comparative examples was detected for 28 d compressive strength according to the method specified in GB / T 50081-2002 “Standard Test Methods for Mechanical Properties of Ordinary Concrete”, and was detected for water permeability coefficient according to CJJ / T 135-2009 “Technical Specification for Pervious Cement Concrete Pavement”, and was finally detected for mass loss rate after 50 cycles according to GB / T 50082-2009 “Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete”, and the detection results are shown in Table 1 below.

[0054] Table 1: Table 1 (continued): With reference to the detection results in Table 1, the pervious concrete prepared in the embodiments of the present application has excellent water permeability and excellent mechanical properties, especially when the modified ceramsite loaded with biochar and the carboxylated polypropylene fiber are added, the balance between water permeability and mechanical properties and durability is achieved. In combination with the detection results of Example 1 and Examples 4-6, when the modified ceramsite is prepared and the modified liquid also contains ethylenediamine, and the polypropylene fiber is added after carboxylated modification, the carboxylated polypropylene fiber not only has better compatibility and binding with the cement matrix, but also forms a certain action with the modified ceramsite to form a stable combined whole, which significantly improves the mechanical properties and durability while maintaining excellent water permeability. In combination with the detection results of Example 1 and Example 4 and Example 7, when the modified ceramsite is prepared and only ethylenediamine is added without carboxylated treatment of the polypropylene fiber, the addition of ethylenediamine on the surface of the porous ceramsite introduces amino groups to help improve the binding with the cement matrix, but the polypropylene fiber is mainly physically connected, and compared with Example 1, the mechanical properties and durability are improved but weaker than Example 4.

[0055] With reference to the detection results of Example 4 and Example 8, the mechanical properties and durability of the polypropylene fiber in Example 8 are reduced after carboxylated modification without silica sol treatment. With reference to the detection results of Example 1 and Comparative Examples 1-3, when no vinyl carbonate is added in the modified liquid, the water permeability is significantly reduced. In Comparative Example 2, no acrylamide is added, and the water permeability and compressive strength are both reduced. The addition of acrylamide helps to introduce amino groups into the modified ceramsite to improve the water permeability, and the cross-linking structure of the epoxy resin and the like improves the mechanical properties and durability. In combination with the performance of Comparative Example 3 without the addition of epoxy resin, the performance is also reduced. The epoxy resin not only helps to fix the biochar in the porous ceramsite, but also forms a certain cross-linking action between the carboxylated polypropylene fiber and the like, which helps to improve the overall performance of the concrete. In combination with the detection results of Comparative Example 3 and Comparative Example 4, when the reinforcing filler is selected as a common porous microsphere or no reinforcing filler is added, the water permeability and compressive strength and other properties are significantly reduced.

[0056] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contributions after reading the specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A permeable concrete, characterized in that, Including the following parts by weight of raw materials: 300-400 parts cement, 980-1050 parts coarse aggregate, 60-80 parts silica fume, 110-120 parts water, 3-5 parts water-reducing agent, 0.5-1 part hydroxypropyl methylcellulose ether, 100-150 parts reinforcing filler, and 3-8 parts polypropylene fiber; The reinforcing filler is modified ceramsite loaded with biochar. The modified ceramsite is prepared by soaking porous ceramsite in citric acid solution, then impregnating it in a modification solution containing epoxy resin, biochar, acrylamide, and ethylene tert-carbonate, followed by high-temperature baking.

2. The permeable concrete according to claim 1, characterized in that: The modified liquid comprises the following raw materials in parts by weight: 6-10 parts epoxy resin, 20-30 parts biochar, 5-8 parts acrylamide, 2-5 parts ethylene tert-carbonate, 0.5-1 part ammonium persulfate, 1-3 parts hydroxypropyl methylcellulose, and 40-50 parts water.

3. The permeable concrete according to claim 1, characterized in that: The modified ceramsite is prepared by the following method: 1) The porous ceramsite is first soaked in a mixed solution of 5-10 wt% citric acid solution and 2-3 wt% phosphoric acid solution for 8-12 hours, and then dried to obtain pretreated ceramsite. 2) Add the obtained pretreated ceramsite to the modification liquid. First, under vacuum conditions of -0.08-0.1 MPa, stir and impregnate for 30-40 minutes. Then, under normal pressure and temperature of 45-55℃, continue impregnation for 60-90 minutes. After filtration, the initial modified ceramsite is obtained. 3) First, treat the initial modified ceramsite at 60-70℃ for 1-2 hours, then at 110-120℃ for 1-2 hours, and then heat to 150℃ for 30-60 minutes to obtain modified ceramsite.

4. The permeable concrete according to claim 3, characterized in that: In the preparation of modified ceramsite, in step 1), the mass ratio of porous ceramsite to mixed solution is 1:(8-10). In step 2), the mass ratio of pretreated ceramsite to modified liquid is 1:(12-15).

5. The permeable concrete according to claim 2, characterized in that: The modified liquid also contains 8-15 parts of ethylenediamine, and the polypropylene fiber is modified by carboxylation to obtain carboxylated polypropylene fiber.

6. The permeable concrete according to claim 1, characterized in that: The particle size of biochar is 0.1-0.5 mm, and the particle size of porous ceramsite is 10-20 mm.

7. The permeable concrete according to claim 5, characterized in that: The carboxylated polypropylene fiber is prepared by the following method: Pretreated polypropylene fibers are first treated in a 4-6 wt% nitric acid solution at 50-60°C for 1-2 hours to obtain pretreated polypropylene fibers. Acrylic acid and hydroxyethyl methacrylate were mixed as monomers and then dissolved in a mixture of water and ethanol. Pretreated polypropylene fibers were added and then ammonium persulfate was added. The mixture was reacted in a water bath at 55-65℃ for 2-3 hours and then filtered to obtain grafted polypropylene fibers. Grafted polypropylene fibers were completely immersed in silica sol, stirred, and then an aminosilane coupling agent was added. The temperature was raised to 60-70℃, and ammonia was added to adjust the pH value to 8-9. After reacting for 2-3 hours, the mixture was filtered, washed with water, and dried to obtain carboxylated polypropylene fibers.

8. The permeable concrete according to claim 7, characterized in that: When preparing carboxylated polypropylene fibers, the mass ratio of polypropylene fibers to nitric acid solution is 1:(6-8). The mass ratio of acrylic acid and hydroxyethyl methacrylate added is 1:(1.4-1.6), the mass ratio of water and ethanol added is 1:(0.4-0.6), and the mass ratio of monomer mixture to mixed solution added is 1:(3-5). The mass ratio of pretreated polypropylene fiber to monomer mixture is 1:(1.8-2.5), and the amount of ammonium persulfate added is 0.5-1 wt% of the monomer mixture. The mass ratio of grafted polypropylene fiber to silica sol is 1:(4-6), and the solid content of silica sol is 25-30%. The amount of aminosilane coupling agent added is 1-3 wt% of the grafted polypropylene fiber.

9. The permeable concrete according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate superplasticizer, and the coarse aggregate includes a mixture of crushed stone with a continuous particle size of 4.75-9.5mm and crushed stone with a continuous particle size of 9.5-16mm, with the 4.75-9.5mm crushed stone accounting for 35-45% of the mass and the 9.5-16mm crushed stone accounting for 55-65% of the mass.

10. The method for preparing permeable concrete according to any one of claims 1-9, characterized in that: Includes the following steps: Cement, coarse aggregate, silica fume, reinforcing filler, and polypropylene fiber are mixed to obtain a preliminary mixture; Hydroxypropyl methylcellulose ether was mixed with 1 / 4 to 1 / 3 water and stirred to obtain a mixture. The water-reducing agent is mixed with the remaining water and then added to the mixture and initial mixture to obtain permeable concrete.

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