High-water-permeability recycled concrete as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of concrete, and particularly relates to high-water-permeability recycled concrete. The concrete is prepared from 170 to 190 parts of water, 300 to 320 parts of cement, 90 to 120 parts of fly ash, 80 to 120 parts of silica fume, 90 to 110 parts of rice hull ash, 580 to 620 parts of medium sand, 430 to 470 parts of recycled fine aggregate, 1000 to 1100 parts of recycled coarse aggregate, 70 to 100 parts of ceramsite, 6 to 8 parts of a water reducing agent, 2 to 4 parts of an air entraining agent, 1 to 3 parts of a retarder, 110 to 130 parts of fly ash hollow microspheres, 70 to 90 parts of steel slag powder, 30 to 40 parts of silica sol, 20 to 30 parts of cellulosic fibers and 40 to 50 parts of an alkaline activator. 50-60 parts of an organic porous waste material; the composite material has abundant pore structures, strong water permeability, moderate strength, high resource utilization rate, outstanding environmental protection property and the like, improves the utilization rate of rainwater resources, and promotes continuous improvement of ecological environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a highly permeable recycled concrete and its preparation method and application. Background Art

[0002] With the acceleration of the urbanization process, the urban impervious area has increased sharply, resulting in an increase in rainwater runoff and the increasingly serious problem of urban waterlogging. Although traditional dense concrete pavement has high strength and good durability, its impermeability causes rainwater to be unable to penetrate into the ground, not only causing urban waterlogging but also blocking the urban water cycle. To solve this problem, permeable concrete materials have emerged, which can allow rainwater to quickly penetrate into the ground, replenish groundwater, and alleviate the problem of urban waterlogging.

[0003] At present, although the common permeable concrete on the market has certain water permeability, it generally has problems such as low strength, poor durability, and low resource utilization rate. At the same time, with the acceleration of the industrialization and urbanization processes, while consuming a large amount of concrete, a lot of industrial solid wastes such as various waste residues, dust, and other wastes are also generated. These industrial solid waste materials are not only huge in quantity, complex in composition, and diverse in types, but also if not properly treated, will have a serious impact on the environment and human health. Summary of the Invention

[0004] The object of the present invention is to provide a highly permeable recycled concrete and its preparation method and application, which have good water permeability, moderate strength, convenient construction, and maximize the utilization of industrial waste materials to achieve the recycling of resources and are beneficial to the improvement of the urban ecological environment.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] In the first aspect, the present invention provides a highly permeable recycled concrete, which is composed of the following raw materials in parts by weight:

[0007] Cementitious materials: 170 - 190 parts of water, 300 - 320 parts of cement, 90 - 120 parts of fly ash, 80 - 120 parts of silica fume, 90 - 110 parts of rice husk ash;

[0008] Aggregates: 580 - 620 parts of medium sand, 430 - 470 parts of recycled fine aggregate, 1000 - 1100 parts of recycled coarse aggregate, 70 - 100 parts of ceramsite;

[0009] Additives: 6 - 8 parts of water reducer, 2 - 4 parts of air-entraining agent, 1 - 3 parts of retarder;

[0010] Industrial waste composite material: 110 - 130 parts of fly ash hollow microspheres, 70 - 90 parts of steel slag powder, 30 - 40 parts of silica sol, 20 - 30 parts of cellulose fiber, 40 - 50 parts of alkaline activator, 50 - 60 parts of organic porous waste.

[0011] In some other embodiments, by weight parts, it consists of the following raw materials:

[0012] Cementitious material: 180 - 190 parts of water, 310 - 320 parts of cement, 100 - 120 parts of fly ash, 100 - 120 parts of silica fume, 100 - 110 parts of rice husk ash;

[0013] Aggregate: 600 - 620 parts of medium sand, 450 - 470 parts of recycled fine aggregate, 1050 - 1100 parts of recycled coarse aggregate, 80 - 100 parts of ceramsite;

[0014] Additive: 7 - 8 parts of water - reducing agent, 3 - 4 parts of air - entraining agent, 2 - 3 parts of retarder;

[0015] Industrial waste composite material: 120 - 130 parts of fly ash hollow microspheres, 80 - 90 parts of steel slag powder, 35 - 40 parts of silica sol, 25 - 30 parts of cellulose fiber, 45 - 50 parts of alkaline activator, 55 - 60 parts of organic porous waste.

[0016] In some other embodiments, by weight parts, it consists of the following raw materials:

[0017] Cementitious material: 180 parts of water, 310 parts of cement, 100 parts of fly ash, 100 parts of silica fume, 100 parts of rice husk ash;

[0018] Aggregate: 600 parts of medium sand, 450 parts of recycled fine aggregate, 1050 parts of recycled coarse aggregate, 80 parts of ceramsite;

[0019] Additive: 7 parts of water - reducing agent, 3 parts of air - entraining agent, 2 parts of retarder;

[0020] Industrial waste composite material: 120 parts of fly ash hollow microspheres, 80 parts of steel slag powder, 35 parts of silica sol, 25 parts of cellulose fiber, 45 parts of alkaline activator, 55 parts of organic porous waste.

[0021] In some other embodiments, the recycled fine aggregate and the recycled coarse aggregate are construction waste, the particle size of the recycled fine aggregate is 0.15 - 4.75 mm, and the particle size of the recycled coarse aggregate is 4.75 - 19 mm;

[0022] The particle size of the medium sand is 0.315 - 4.75 mm, and the fineness modulus is 2.3 - 3.0;

[0023] The ceramsite is sintered ceramsite with a particle size of 5 - 10 mm and a porosity of 40% - 60%.

[0024] In some other embodiments, the water reducing agent is a polycarboxylate water reducing agent with a water reducing rate greater than 25%;

[0025] Preferably, the polycarboxylate water reducing agent is selected from one of polycarboxylate ether water reducing agents and polycarboxylate water reducing agents;

[0026] The air entraining agent is an organic air entraining agent;

[0027] Preferably, the organic air entraining agent is selected from one or more of aliphatic alcohol amine air entraining agents, rosin resin air entraining agents, and alkyl sulfate air entraining agents;

[0028] The retarder is an organic retarder without chloride ions;

[0029] The organic retarder without chloride ions is selected from one or more of hydroxycarboxylate retarders, sodium gluconate, and citrate;

[0030] In some other embodiments, the fly ash hollow microspheres are lightweight hollow microspheres collected after coal combustion in a thermal power plant, with an average particle size between 20 - 200 μm and a true density of 0.4 - 0.8 g / cm 3 ;

[0031] The specific surface area of the steel slag powder is greater than 400 m 2 / kg;

[0032] The silica sol is an aqueous colloid with a concentration of 30%;

[0033] The cellulose fiber is a natural cellulose fiber with a length of 1 - 5 mm;

[0034] Preferably, the natural cellulose fiber is selected from one or more of hemp fiber, wood cellulose, bamboo cellulose, and straw cellulose;

[0035] More preferably, the natural cellulose fiber is one of wood cellulose and bamboo cellulose with a diameter of 15 - 30 μm and a length of 2 - 4 mm;

[0036] The alkaline activator is a mixture of sodium hydroxide and water glass,

[0037] Preferably, the mixing mass ratio of sodium hydroxide to water glass is 1:(1 - 3);

[0038] The organic porous waste is pretreated waste coffee grounds or sawdust with a particle size between 0.5 - 2 mm;

[0039] The pretreatment method of the organic porous waste is: after drying the waste coffee grounds or sawdust once, soaking in alkali solution, washing, and then drying twice to obtain;

[0040] The temperature of the first drying is 100 - 110 °C, drying for 20 - 24 h, and the water content is less than 2%;

[0041] The alkali solution soaking is carried out in a 2 - 6 wt% sodium hydroxide solution at room temperature for 1 - 3 h;

[0042] The washing is carried out by washing with water 3 - 5 times until the pH is neutral;

[0043] The temperature of the second drying is 75 - 85 °C, and the time is 10 - 12 h.

[0044] The properties and functions of some raw materials in the highly permeable recycled concrete of the present invention are as follows:

[0045] The recycled fine aggregate and recycled coarse aggregate are aggregates obtained by crushing, screening, and processing construction waste, with particle sizes of 0.15 - 4.75 mm and 4.75 - 19 mm respectively. The recycled aggregate is derived from waste concrete components and is formed into qualified recycled aggregate after being processed by professional equipment. Its surface porous structure is conducive to forming interconnected pores inside the concrete, enhancing the overall water permeability.

[0046] The light expanded clay aggregate is sintered expanded clay aggregate with a particle size of 5 - 10 mm, and its porosity is as high as 40% - 60%. It has the characteristics of light weight, porous, and high strength, and can form a stable interconnected pore structure in the concrete.

[0047] The admixture is a polycarboxylate superplasticizer with a water reduction rate greater than 25%. The polycarboxylate superplasticizer can specifically select one or more of polycarboxylate ether superplasticizer and polycarboxylate superplasticizer, such as JM - PCA and TH - PCA. In the present invention, it makes the cementitious material particles disperse evenly, improves the workability, and ensures the workability at a lower water - binder ratio, thereby improving the mechanical properties and durability of the highly permeable recycled concrete material.

[0048] The air - entraining agent is an organic air - entraining agent. The organic air - entraining agent can specifically select one or more of aliphatic alcohol amine air - entraining agents, rosin resin air - entraining agents, and alkyl sulfate air - entraining agents, such as AEA - B, K12, and SJ - 2. It can form uniformly distributed micro - bubbles in the concrete, increase the water permeability of the concrete, and improve its frost resistance at the same time.

[0049] The retarder is an organic retarder without chloride ions. The organic retarder without chloride ions can specifically select one or more of hydroxycarboxylate retarders, sodium gluconate, and citrate, such as RT - A40, RD - 90, and HCA. It can effectively extend the operable time of the concrete and improve the construction convenience.

[0050] The fly ash hollow microspheres described above are lightweight hollow microspheres collected after coal combustion in thermal power plants, with an average particle size between 20 - 200 μm and a true density of 0.4 - 0.8 g / cm 3 , and their spherical hollow structure is conducive to the formation of internal pores in concrete.

[0051] The steel slag powder described above is fine powder obtained by grinding the steel slag produced in steel mills, with a specific surface area of not less than 400 m 2 / kg, having certain potential activity and a rough surface, which is conducive to the formation of a porous structure.

[0052] The silica sol described above is an aqueous colloid with a concentration of 30%, serving as a binder and reinforcing agent for the porous composite material.

[0053] The cellulose fiber described above is a natural cellulose fiber with a length of 1 - 5 mm; the cellulose fiber is a natural cellulose fiber with a length of 1 - 5 mm; specifically, natural cellulose fibers from plant sources such as hemp fiber, lignocellulose, bamboo cellulose, and straw cellulose can be selected; preferably, lignocellulose or bamboo cellulose with a diameter of 15 - 30 μm and a length of 2 - 4 mm can improve the toughness and crack resistance of the porous composite material.

[0054] The alkaline activator described above is a mixture of sodium hydroxide and water glass with a mass ratio of 1:2, used to activate the active components in fly ash and steel slag powder to form a stable gel structure.

[0055] The organic porous waste described above is waste coffee grounds or sawdust, with a particle size between 0.5 - 2 mm, and is used after pretreatment, which can form a durable porous structure.

[0056] In a second aspect, the present invention provides a method for preparing the highly permeable recycled concrete described in the first aspect, which is characterized by including the following steps:

[0057] (1) Mix cement, fly ash, silica fume, and rice husk ash evenly to obtain a first mixture;

[0058] (2) Mix medium sand, recycled fine aggregate, recycled coarse aggregate, and ceramsite evenly to obtain a second mixture;

[0059] (3) Mix the first mixture and the second mixture, add part of the water, and stir evenly to obtain a third mixture;

[0060] (4) Add a water - reducing agent, an air - entraining agent, a retarder, and the remaining part of the water to the third mixture, and stir evenly to obtain a fourth mixture;

[0061] (5) Add the industrial waste composite material to the fourth mixture, and stir evenly to obtain the highly permeable recycled concrete material.

[0062] In some other embodiments, in step (5), the preparation method of the industrial waste composite material includes the following steps:

[0063] Mix fly ash hollow microspheres and steel slag powder evenly to obtain a solid mixture;

[0064] Mix silica sol and an alkaline activator evenly to obtain a liquid mixture;

[0065] Mix the solid mixture with the liquid mixture, add cellulose fiber, and stir evenly;

[0066] Add organic porous waste, stir evenly again to obtain an industrial waste-based porous composite material.

[0067] In some other embodiments, in step (5), the highly permeable recycled concrete material obtained after stirring and mixing evenly should be poured within 25 - 35 minutes, vibrated for 60 - 90 seconds after pouring, leveled on the concrete surface after vibration, and cured by spraying.

[0068] In a third aspect, the present invention provides the application of the highly permeable recycled concrete described in the first aspect in a permeable pavement project, preferably in urban road pavement, parking lots, squares, and park walkways.

[0069] Advantages of the present invention:

[0070] (1) The permeable coefficient of the highly permeable recycled concrete material involved in the technical solution of the present invention can reach 3.0 - 5.0 mm / s, which is much higher than that of ordinary permeable concrete (0.5 - 2.0 mm / s), showing excellent water permeability performance and being able to effectively alleviate the problem of urban waterlogging.

[0071] (2) The highly permeable recycled concrete material involved in the technical solution of the present invention has a compressive strength of 25 - 30 MPa and a flexural strength of 3.5 - 4.5 MPa at 28 days, meeting the requirements of urban roads and landscape projects for concrete strength.

[0072] (3) The highly permeable recycled concrete material involved in the technical solution of the present invention uses an industrial waste-based porous composite material as a reinforcing agent and a water permeability promoter, making full use of industrial wastes such as fly ash, steel slag, and organic waste, realizing the recycling of resources and conforming to the concept of circular economy.

[0073] (4) The preparation process of the highly permeable recycled concrete material involved in the technical solution of the present invention is simple, the operation is convenient, no special equipment is required, it is suitable for implementation under on-site construction conditions, and is conducive to large-scale popularization and application.

[0074] (5) The high-permeability recycled concrete material involved in the technical solution of the present invention achieves a good balance in terms of water permeability, strength performance, resource utilization rate, etc., has excellent comprehensive performance, and has broad application prospects. Detailed implementation manners

[0075] Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. The specific conditions are not specified in the embodiments and are carried out according to conventional conditions or conditions recommended by the manufacturer. Those components not specified by the manufacturer are all conventional products available commercially.

[0076] For the following embodiments, the performance of the raw materials used is described as follows:

[0077] Cement: Ordinary Portland cement grade 42.5, meeting the requirements of GB175-2007;

[0078] Fly ash: Class II fly ash, meeting the requirements of GB / T1596-2017;

[0079] Silica fume: Density 2.2 g / cm 3 , specific surface area > 15000 m 2 / kg;

[0080] Rice husk ash: Prepared by calcining at 600 °C for 2 hours, with silica content > 85%;

[0081] Medium sand: Continuous gradation, particle size 0.315 - 4.75 mm, fineness modulus 2.7, meeting the particle size requirements of medium sand in Zone II in GB / T14684-2011 "Sand for construction";

[0082] Recycled fine aggregate and recycled coarse aggregate are aggregates obtained by crushing, screening and processing construction waste. Among them, recycled fine aggregate: particle size 0.15 - 4.75 mm, water absorption rate < 8%;

[0083] Recycled coarse aggregate: particle size 4.75 - 19 mm, water absorption rate < 5%;

[0084] Lightweight ceramsite: particle size 5 - 10 mm, porosity 40% - 60%, bulk density < 800 kg / m 3 ;

[0085] Water reducing agent: Polycarboxylic ether water reducing agent (powdered polycarboxylic water reducing agent purchased from Jiangsu Sobute New Materials Co., Ltd.), water reduction rate > 25%;

[0086] Air entraining agent: Aliphatic alcohol amine air entraining agent (AEA-08, purchased from Beijing Building Materials Science Research Institute Co., Ltd.), dosage 0.02 - 0.05%;

[0087] Retarding agent: Hydroxycarboxylate-based retarding agent (hydroxycarboxylate composite retarding agent RT-A40, purchased from Shanxi Ruite Technology Co., Ltd.), which can delay the setting time by 2 - 4 hours;

[0088] Fly ash hollow microspheres: Density 0.6 g / cm 3 , particle size 20 - 200 μm;

[0089] Steel slag powder: Fine powder obtained by grinding steel slag produced by steel mills, specific surface area 450 m 2 / kg, activity index > 75%;

[0090] Silica sol: Aqueous silica sol with a concentration of 30%;

[0091] Cellulose fiber: Wood cellulose with a length of 3 mm and a diameter of 20 μm;

[0092] Alkaline activator: A mixture of sodium hydroxide and water glass, mass ratio 1:2, modulus 1.5;

[0093] Organic porous waste: Waste coffee grounds or sawdust, particle size 0.5 - 2 mm, used after the following pre-treatment steps: (1) Dry the waste coffee grounds or sawdust in an oven at 105 ± 5 °C for 24 hours until the moisture content is below 2%; (2) Soak the dried material in 5% sodium hydroxide solution for 2 hours to remove some soluble organic substances; (3) Rinse with clean water 3 - 5 times until neutral; (4) Dry again in an oven at 80 ± 5 °C for 12 hours; (5) Screen to obtain the treated material with a particle size of 0.5 - 2 mm.

[0094] Example 1

[0095] A highly permeable recycled concrete, as shown in Table 1, consists of the following raw materials by weight:

[0096] Cementitious materials: 180 parts of water, 310 parts of cement, 100 parts of fly ash, 100 parts of silica fume, 100 parts of rice husk ash;

[0097] Aggregates: 600 parts of medium sand, 450 parts of recycled fine aggregate, 1050 parts of recycled coarse aggregate, 80 parts of lightweight ceramsite;

[0098] Additives: 7 parts of water reducing agent (JM-PCA), 3 parts of air entraining agent (AEA-B), 2 parts of retarding agent (RT-A40);

[0099] Industrial waste composite materials: 120 parts of fly ash hollow microspheres, 80 parts of steel slag powder, 35 parts of silica sol, 25 parts of cellulose fiber (wood cellulose), 45 parts of alkaline activator, 55 parts of organic porous waste (waste coffee grounds).

[0100] A preparation method of highly permeable recycled concrete, comprising the following steps:

[0101] S1: Weigh each raw material according to the raw material composition of the highly permeable recycled concrete in Example 1;

[0102] S2: Put cement, fly ash, silica fume, and rice husk ash into a mixer and stir for 2 - 3 minutes to obtain the first mixture;

[0103] S3: Put medium sand, recycled fine aggregate, recycled coarse aggregate, and lightweight ceramsite into another mixer and stir for 2 minutes to obtain the second mixture;

[0104] S4: Mix the first mixture and the second mixture, add about 80% of the designed water consumption, and stir for 2 - 3 minutes to obtain the third mixture;

[0105] S5: Mix the water - reducing agent, air - entraining agent, and retarder evenly with the remaining 20% of the water, then add them to the third mixture obtained in S4 and stir for 3 - 4 minutes to obtain the fourth mixture;

[0106] S6: Add the industrial waste - based porous composite material to the fourth mixture obtained in S5 and stir for 3 minutes to obtain the highly permeable recycled concrete material;

[0107] S7: Complete the pouring work of the highly permeable recycled concrete material prepared in S6 within 30 minutes. After pouring, moderately vibrate with a vibrating rod for 80 seconds to avoid pore closure caused by excessive vibration. After vibration, level the surface with a wooden float;

[0108] S8: After pouring, adopt the spray curing method to keep the surface moist but not water - logged. The curing period is 28 days, and the highly permeable recycled concrete is obtained.

[0109] Example 2

[0110] The difference from the raw material formula composition of the highly permeable recycled concrete in Example 1 is that: the water is 170 parts, and the lightweight ceramsite is 90 parts; the other raw material compositions and preparation methods are the same as those in Example 1.

[0111] Example 3

[0112] The difference from the raw material formula composition of the highly permeable recycled concrete in Example 1 is that: the water is 190 parts, the organic porous waste is sawdust, the fly ash is 110 parts, the steel slag powder is 75 parts, and the medium sand is 585 parts; the other raw material compositions and preparation methods are the same as those in Example 1.

[0113] Example 4

[0114] The difference in the raw material formula composition of the highly permeable recycled concrete in Example 1 is that fly ash is 90 parts, lightweight expanded clay is 100 parts, and steel slag powder is 70 parts; the other raw material compositions and preparation methods are consistent with those in Example 1.

[0115] Example 5

[0116] The difference in the raw material formula composition of the highly permeable recycled concrete in Example 1 is that fly ash is 120 parts, lightweight expanded clay is 70 parts, and steel slag powder is 70 parts; the other raw material compositions and preparation methods are consistent with those in Example 1.

[0117] Example 6

[0118] The difference in the raw material formula composition of the highly permeable recycled concrete in Example 1 is that the lightweight expanded clay is 70 parts and the steel slag powder is 90 parts; the other raw material compositions and preparation methods are consistent with those in Example 1.

[0119] Comparative Example 1

[0120] The difference between the raw material formula composition of the highly permeable recycled concrete in Example 1 is that no fly ash is added. Specifically, the raw materials are as follows, calculated by weight:

[0121] Cementitious materials: 190 parts of water, 320 parts of cement, 120 parts of silica fume, 110 parts of rice husk ash;

[0122] Aggregate: 610 parts of medium sand, 450 parts of recycled fine aggregate, 1050 parts of recycled coarse aggregate, 100 parts of lightweight ceramsite;

[0123] Additives: 7 parts of water reducing agent, 3 parts of air entraining agent, 2 parts of retarder;

[0124] Industrial waste composite material: 130 parts of fly ash hollow microspheres, 90 parts of steel slag powder, 35 parts of silica sol, 25 parts of cellulose fiber, 45 parts of alkaline activator, and 55 parts of organic porous waste (waste coffee grounds).

[0125] The preparation method is consistent with that in Example 1.

[0126] Comparative Example 2

[0127] The difference between the raw material formula composition of the highly permeable recycled concrete in Example 1 is that no steel slag powder is added. Specifically, the raw materials are as follows, calculated by weight:

[0128] Cementitious materials: 180 parts of water, 320 parts of cement, 100 parts of fly ash, 100 parts of silica fume, 100 parts of rice husk ash;

[0129] Aggregate: 620 parts of medium sand, 470 parts of recycled fine aggregate, 1050 parts of recycled coarse aggregate, 80 parts of lightweight ceramsite;

[0130] Additives: 7 parts of water-reducing agent, 3 parts of air-entraining agent, 2 parts of retarder;

[0131] Industrial waste composite material: 130 parts of fly ash hollow microspheres, 40 parts of silica sol, 30 parts of cellulose fiber, 50 parts of alkaline activator, 60 parts of organic porous waste (waste coffee grounds).

[0132] The preparation method is the same as that of Example 1.

[0133] Comparative Example 3

[0134] The difference from the raw material formula composition of the highly permeable recycled concrete in Example 1 is that: the water is 190 parts, the fly ash is 80 parts, the medium sand is 560 parts, the lightweight ceramsite is 150 parts, and the steel slag powder is 60 parts; the composition of other raw materials and the preparation method are the same as those of Example 1.

[0135] Comparative Example 4

[0136] The difference from the raw material formula composition of the highly permeable recycled concrete in Example 1 is that: the water is 190 parts, the fly ash is 120 parts, the medium sand is 608 parts, the steel slag powder is 40 parts, and the silica sol is 37 parts; the composition of other raw materials and the preparation method are the same as those of Example 1.

[0137] Comparative Example 5

[0138] The difference from the raw material formula composition of the highly permeable recycled concrete in Example 1 is that the industrial waste-based porous composite material is not added. Specifically, by weight, it is composed of the following raw materials:

[0139] Cementitious materials: 300 parts of water, 350 parts of cement, 120 parts of fly ash, 120 parts of silica fume, 100 parts of rice husk ash;

[0140] Aggregates: 65 parts of medium sand, 500 parts of recycled fine aggregate, 1100 parts of recycled coarse aggregate, 80 parts of lightweight ceramsite;

[0141] Additives: 12 parts of water-reducing agent, 7 parts of air-entraining agent, 3 parts of retarder.

[0142] The composition of other raw materials and the preparation method are the same as those of Example 1.

[0143] The content of each component in the examples is shown in Table 1, and the content of each component in Example 1 and the comparative examples is shown in Table 2, specifically as follows:

[0144] Table 1 Content of Each Component in the Examples

[0145]

[0146]

[0147] Table 2 Contents of Each Component in Example 1 and Comparative Example

[0148]

[0149]

[0150]

[0151] " / " in Table 2 indicates not adding

[0152] Performance Test

[0153] Prepare standard specimens of highly permeable recycled concrete prepared from the examples and comparative examples, and make cube specimens with dimensions of 100mm×100mm×100mm and prism specimens with dimensions of 100mm×100mm×400mm in accordance with GB / T50081-2019 "Standard Test Method for Mechanical Properties of Ordinary Concrete". After standard curing for 28 days, conduct the following performance tests:

[0154] Compressive Strength Test: According to the compressive strength test method in GB / T 50081-2019 "Standard Test Method for Mechanical Properties of Ordinary Concrete", apply axial load to the cube specimens using a digital display pressure testing machine at a loading rate of 0.5 - 0.8 MPa / s until the specimens are damaged, record the failure load, and calculate the compressive strength.

[0155] Flexural Strength Test: According to the flexural strength test method in GB / T 50081-2019 "Standard Test Method for Mechanical Properties of Ordinary Concrete", test the prism specimens using a four-point bending loading method at a loading rate of 0.05 MPa / s, record the failure load, and calculate the flexural strength.

[0156] Permeability Coefficient Test: According to the provisions in Appendix A of CJJ / T 135-2009 "Permeable Bricks and Permeable Plates", use the constant head method to determine the permeability coefficient. Place the specimens in a special test device, maintain a constant head pressure, measure the infiltration water volume per unit time, and calculate the permeability coefficient according to Darcy's law.

[0157] Porosity Test: Refer to ASTM C642-13 "Test Methods for Apparent Specific Gravity, Water Absorption, and Voids in Concrete", use the water immersion - drying method to determine the porosity of the specimens, that is, measure the dry mass, immersed mass, and suspended mass of the specimens, and calculate the porosity.

[0158] Durability Test: According to the rapid freeze - thaw method and chloride ion permeability test method in GB / T 50082-2009 "Standard Test Method for Long - Term Performance and Durability of Ordinary Concrete", evaluate the durability of the concrete, and the results are divided into three grades: "good", "general", and "poor".

[0159] Freeze-thaw resistance test: According to the freeze-thaw cycle method in the Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete (GB / T 50082-2009), record the mass loss and strength loss of the specimens after different numbers of freeze-thaw cycles, and determine the freeze-thaw resistance grade based on the number of freeze-thaw cycles that can be endured, which is represented by the F value (the number after F represents the number of freeze-thaw cycles that can be endured).

[0160] The test results of each example and comparative example are shown in Table 3:

[0161] Table 3 Test data of the properties of highly permeable recycled concrete materials

[0162]

[0163] Note: The durability evaluation results in the table are divided into three grades: "good", "general", and "poor"; the freeze-thaw resistance is represented by the F value, and the number after F represents the number of freeze-thaw cycles that can be endured.

[0164] From Table 3, the compressive strength of all examples of the present invention is above 25 MPa, the flexural strength is above 3.5 MPa, and the water permeability coefficient is above 3.5 mm / s, indicating that their mechanical properties and water permeability properties meet the expected requirements. Through data comparison, in Example 2, the water consumption was reduced compared with Example 1, the lightweight ceramsite was increased, and the compressive strength and flexural strength increased more, but the water permeability performance decreased slightly; in Example 3, the water consumption was increased compared with Example 1, sawdust was used to replace coffee grounds, and at the same time, the proportions of fly ash and steel slag powder were adjusted, resulting in a slight decrease in mechanical properties but an increase in water permeability performance; in Example 4, the dosages of fly ash and steel slag powder were reduced compared with Example 1, and at the same time, the dosage of lightweight ceramsite was increased, and the result was that the water permeability coefficient increased, the porosity increased slightly, and the compressive strength decreased slightly. This shows that increasing the content of lightweight ceramsite can effectively improve the water permeability performance of concrete, but it will have a certain impact on the mechanical properties. The data of the comparative examples further prove the influence of the key components on the performance: in Comparative Example 3, the excessive content of lightweight ceramsite caused the compressive strength to drop to 21.8 MPa, which did not meet the requirements of engineering applications, although the water permeability coefficient reached 5.8 mm / s; in Comparative Example 4, the low content of steel slag powder resulted in poor durability, and only the freeze-thaw resistance of F85 could be achieved; in Comparative Example 5, although no industrial waste composite material was added but the dosage of cementitious material was increased, its compressive strength was high but the water permeability performance decreased significantly and could not meet the requirements of high water permeability. This shows that the key components in the mix proportion have a significant impact on the mechanical properties and water permeability performance of concrete.

[0165] Through a large number of experiments, the highly permeable recycled concrete material of the present invention has the characteristics of rich pore structure, excellent water permeability, moderate strength, high resource utilization rate, and outstanding environmental protection performance. It can effectively solve the water permeability problem in urban roads and landscape projects, improve the utilization rate of rainwater resources, and promote the continuous improvement of the urban ecological environment.

[0166] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly permeable recycled concrete, characterized in that, By weight parts, it consists of the following raw materials: Cementitious material: 170 - 190 parts of water, 300 - 320 parts of cement, 90 - 120 parts of fly ash, 80 - 120 parts of silica fume, 90 - 110 parts of rice husk ash; Aggregate: 580 - 620 parts of medium sand, 430 - 470 parts of recycled fine aggregate, 1000 - 1100 parts of recycled coarse aggregate, 70 - 100 parts of ceramsite; Additive: 6 - 8 parts of water reducing agent, 2 - 4 parts of air entraining agent, 1 - 3 parts of retarder; Industrial waste composite material: 110 - 130 parts of fly ash hollow microspheres, 70 - 90 parts of steel slag powder, 30 - 40 parts of silica sol, 20 - 30 parts of cellulose fiber, 40 - 50 parts of alkaline activator, 50 - 60 parts of organic porous waste.

2. The highly permeable recycled concrete according to claim 1, wherein By weight parts, it consists of the following raw materials: Cementitious material: 180 - 190 parts of water, 310 - 320 parts of cement, 100 - 120 parts of fly ash, 100 - 120 parts of silica fume, 100 - 110 parts of rice husk ash; Aggregate: 600 - 620 parts of medium sand, 450 - 470 parts of recycled fine aggregate, 1050 - 1100 parts of recycled coarse aggregate, 80 - 100 parts of ceramsite; Additive: 7 - 8 parts of water reducing agent, 3 - 4 parts of air entraining agent, 2 - 3 parts of retarder; Industrial waste composite material: 120 - 130 parts of fly ash hollow microspheres, 80 - 90 parts of steel slag powder, 35 - 40 parts of silica sol, 25 - 30 parts of cellulose fiber, 45 - 50 parts of alkaline activator, 55 - 60 parts of organic porous waste.

3. The highly permeable recycled concrete according to claim 1, wherein By weight parts, it consists of the following raw materials: Cementitious material: 180 parts of water, 310 parts of cement, 100 parts of fly ash, 100 parts of silica fume, 100 parts of rice husk ash; Aggregate: 600 parts of medium sand, 450 parts of recycled fine aggregate, 1050 parts of recycled coarse aggregate, 80 parts of ceramsite; Additive: 7 parts of water reducing agent, 3 parts of air entraining agent, 2 parts of retarder; Industrial waste composite material: 120 parts of fly ash hollow microspheres, 80 parts of steel slag powder, 35 parts of silica sol, 25 parts of cellulose fiber, 45 parts of alkaline activator, 55 parts of organic porous waste.

4. The highly permeable recycled concrete according to any one of claims 1 - 3, characterized in that The recycled fine aggregate and the recycled coarse aggregate are construction waste, the particle size of the recycled fine aggregate is 0.15 - 4.75 mm, and the particle size of the recycled coarse aggregate is 4.75 - 19 mm; The particle size of the medium sand is 0.315 - 4.75 mm, and the fineness modulus is 2.3 - 3.0; The ceramsite is sintered ceramsite with a particle size of 5 - 10 mm and a porosity of 40% - 60%.

5. The highly permeable recycled concrete according to any one of claims 1 - 3, characterized in that The water reducing agent is a polycarboxylate - based water reducing agent with a water reducing rate greater than 25%; Preferably, the polycarboxylate - based water reducing agent is selected from one of polycarboxylate ether - type water reducing agents and polycarboxylate - salt - type water reducing agents; The air entraining agent is an organic air entraining agent; Preferably, the organic air entraining agent is selected from one or more of aliphatic alcohol amine - type air entraining agents, rosin resin - type air entraining agents, and alkyl sulfate - type air entraining agents; The retarder is an organic retarder without chloride ions; The chloride-free organic retarder is selected from one or more of hydroxycarboxylate retarders, sodium gluconate, and citrate.

6. The highly permeable recycled concrete according to any one of claims 1-3, characterized in that The fly ash hollow microspheres are lightweight hollow microspheres collected after coal combustion in thermal power plants, with an average particle size between 20 - 200 μm and a true density of 0.4 - 0.8 g / cm 3 ; The specific surface area of the steel slag powder is greater than 400 m 2 / kg; The silica sol is an aqueous colloid with a concentration of 30%; The cellulose fiber is a natural cellulose fiber with a length of 1-5 mm; Preferably, the natural cellulose fiber is selected from one or more of hemp fiber, lignocellulose, bamboo cellulose, and straw cellulose; More preferably, the natural cellulose fiber is one of lignocellulose and bamboo cellulose with a diameter of 15-30 μm and a length of 2-4 mm; The alkaline activator is a mixture of sodium hydroxide and water glass, Preferably, the mixing mass ratio of sodium hydroxide to water glass is 1:(1-3); The organic porous waste is pretreated waste coffee grounds or sawdust with a particle size between 0.5-2 mm; The pretreatment method of the organic porous waste is: after drying the waste coffee grounds or sawdust once, soaking in an alkali solution, washing, and then drying for the second time to obtain; The temperature of the first drying is 100-110 °C, drying for 20-24 h, and the moisture content is less than 2%; The alkali solution soaking is soaking in a 2-6 wt% sodium hydroxide solution at room temperature for 1-3 h; The washing is washing with water 3-5 times until the pH is neutral; The temperature of the second drying is 75-85 °C, and the time is 10-12 h.

7. A method for preparing the highly water-permeable recycled concrete according to any one of claims 1-6, characterized in that, It includes the following steps: (1) Mix cement, fly ash, silica fume, and rice husk ash evenly to obtain a first mixture; (2) Mix medium sand, recycled fine aggregate, recycled coarse aggregate, and ceramsite evenly to obtain a second mixture; (3) Mix the first mixture and the second mixture, add part of the water, and stir evenly to obtain a third mixture; (4) Add a water reducer, an air-entraining agent, and a retarder to the remaining part of the water to the third mixture, and stir evenly to obtain a fourth mixture; (5) Add the industrial waste composite material to the fourth mixture, and stir evenly to obtain a highly permeable recycled concrete material.

8. The preparation method of the highly permeable recycled concrete according to claim 7, characterized in that, In step (5), the preparation method of the industrial waste composite material includes the following steps: Mix fly ash hollow microspheres and steel slag powder evenly to obtain a solid mixture; Mix silica sol and alkaline activator evenly to obtain a liquid mixture; Mix the solid mixture and the liquid mixture, add cellulose fiber, and stir evenly; Add the organic porous waste and stir evenly to obtain an industrial waste-based porous composite material.

9. The preparation method of the highly water-permeable recycled concrete according to claim 7, characterized in that, In step (5), the highly permeable recycled concrete material obtained after stirring and mixing is poured within 25-35 minutes, vibrated for 60-90 seconds after pouring, the concrete surface is leveled after vibration, and spray curing is adopted.

10. The application of the highly permeable recycled concrete according to any one of claims 1-6 in a permeable pavement project, preferably in urban road pavement, parking lots, squares, and park trails.

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