A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure

Abstract

The present invention discloses a method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure, comprising the steps of: (1) soaking the regenerated concrete fine aggregate and lightweight pottery sand in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, then dripping an excess of carbonate concentrate, separating the fine aggregate and the lightweight pottery sand after completion, and drying to obtain a lightweight hydrophobic regenerated fine aggregate. (2) mixing the lightweight hydrophobic regenerated fine aggregate with the red mud powder, cement, organic fiber, water reducer and water to obtain an ECC concrete slurry, curing it after forming and hardening it, and obtaining a pretreated concrete structure. (3) immersing the pretreated concrete structure again in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, then dripping an excess of carbonate concentrate, and obtaining the ECC concrete structure after completion. The process of the present invention not only improves the hydrophobicity of concrete, but also avoids the adverse effects on the mechanical strength of concrete.

Description

Technical Field

[0001] The invention relates to the technical field of ECC concrete preparation, and in particular to a method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] ECC concrete (Engineered Cementitious Composites) is a new type of high-performance concrete material with good tensile-hardening and multi-crack steady-state cracking properties. The design goal of ECC is to overcome the brittleness of traditional concrete and make it crack in multiple cracks, so that it can show better deformation capacity and ductility when bearing loads. Due to the stress-cracking properties of ECC concrete, although it helps to extend the service life of engineering structures, the appearance of cracks also provides a channel for harmful substances to invade the interior of the concrete, weakening the service life and service life of ECC concrete. How to solve the problem of harmful substance intrusion caused by cracking is one of the bottlenecks in the current development of ECC concrete.

[0004] The application of super-hydrophobic surface to ECC concrete can prevent water from invading the interior, thereby significantly improving the durability of concrete. However, the traditional hydrophobic concrete surface is generally achieved by brushing a coating on the outside, but this method faces the problems of peeling and insufficient surface strength. In addition, directly adding a hydrophobic agent to the concrete material can also achieve the hydrophobic function, but this method will cause the hydration reaction of the concrete material to be unable to proceed fully, resulting in damage to the mechanical strength of the concrete. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure, which not only improves the hydrophobic performance of the concrete, but also avoids the adverse effects on the mechanical strength of the concrete. Specifically, the technical solution of the present invention is as follows.

[0006] A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure comprises the following steps:

[0007] (1) The red mud is leached with clean water, and then solid-liquid separation is performed. The solid is ground and dried to obtain red mud powder for later use. Excess carbon dioxide is introduced into the alkaline liquid phase, and then heated and concentrated to form a concentrated liquid for later use.

[0008] (2) The recycled concrete fine aggregate and lightweight pottery sand are soaked in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, and then an excess of the concentrated solution is added dropwise under stirring conditions. After the reaction is completed, the fine aggregate and lightweight pottery sand are separated and dried to obtain lightweight hydrophobic recycled fine aggregate for later use.

[0009] (3) The lightweight hydrophobic recycled fine aggregate is mixed with the red mud powder, cement, organic fiber, water reducing agent and water to obtain an ECC concrete slurry, which is then cured after being molded and hardened to obtain a pretreated concrete structure.

[0010] (4) The pretreated concrete structure is immersed again in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, and then an excess of the concentrated solution is added dropwise under stirring conditions. After the reaction is completed, the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is obtained.

[0011] Furthermore, in step (1), the ratio of red mud to clean water is 1g:20~40ml.

[0012] Furthermore, in step (1), the drying temperature is 100-150°C, and the solid matter is dried to a constant weight at this temperature, and then the solid matter is ground to obtain the red mud powder. Optionally, the fineness of the red mud powder is 300-600 mesh.

[0013] Furthermore, in step (1), the flow rate of the carbon dioxide gas is 3-5 L / min, so that alkaline substances such as sodium hydroxide and potassium hydroxide in the red mud leachate are converted into carbonates.

[0014] Furthermore, in step (1), heating is stopped when solid matter precipitates to obtain the concentrated solution.

[0015] Furthermore, in step (2), the calcium ion source includes at least one of calcium chloride, calcium nitrate, etc.

[0016] Furthermore, in step (2), the magnesium ion source includes at least one of magnesium chloride, magnesium sulfate, magnesium nitrate, etc.

[0017] Furthermore, in step (2), the mass fraction of the silane coupling agent in the mixed system is 0.9-1.5%. Optionally, the silane coupling agent includes at least one of KH550, KH560, KH570, etc.

[0018] Furthermore, in step (2), the ratio of the recycled concrete fine aggregate, lightweight ceramic sand and the mixed system is 1g: 1-2g: 10-20ml. Optionally, the particle size distribution of the fine aggregate is between 0.1-1mm, and the particle size distribution of the lightweight ceramic sand is between 0.5-2mm.

[0019] Furthermore, in step (2), the drying temperature is 40-60° C., and the material is dried at this temperature to a constant weight, thereby obtaining the lightweight hydrophobic recycled fine aggregate.

[0020] Furthermore, in step (3), the ratio of the lightweight hydrophobic recycled fine aggregate, red mud powder, cement, organic fiber, water reducing agent and water is 0.8-1 parts by weight: 1.5-1.8 parts by weight: 1.2-1.5 parts by weight: 0.025-0.035 parts by weight: 0.04-0.06 parts by weight: 0.7-0.9 parts by weight.

[0021] Furthermore, in step (3), the organic fiber includes at least one of polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber, polyacrylonitrile fiber, etc. Optionally, the organic fiber has a diameter of 10-20 μm and a length of 8-16 mm.

[0022] Furthermore, in step (3), the water reducer includes at least one of a polycarboxylate water reducer, a naphthalene-based water reducer, a wood sulfonate water reducer, and the like.

[0023] Furthermore, in step (3), the curing time is not less than 21 days.

[0024] Furthermore, in step (4), the silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources is the same as that in step (2). Optionally, the silane coupling agent-water mixed system can completely immerse the pretreated concrete structure.

[0025] It should be noted that in steps (2) and (4), the excess refers to that the concentrated solution provides an excess of carbonate ions relative to the calcium and magnesium ions in the system, so that the calcium and magnesium ions co-crystallize with the carbonate ions to form Ca X Mg 1-X CO 3 Micro-nano crystals.

[0026] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0027] The present invention soaks recycled concrete fine aggregate and lightweight pottery sand in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, and then drips an excess of the concentrated solution, which not only obtains a super-hydrophobic structure on the surface of the fine aggregate and lightweight pottery sand, so that the concrete structure prepared by the present invention exhibits super-hydrophobic characteristics, but also avoids the adverse effects on the mechanical strength of the concrete structure, and at the same time avoids the problem that the traditional hydrophobic coating is easy to fall off, resulting in the failure of the hydrophobic performance of the concrete structure. This is because Ca 2+ Mg 2+ The concentrate provides CO 32− During the reaction, Ca 2+ Mg 2+ Competition between ions generates Ca X Mg 1-X CO 3 Micro-nano crystals (xCa 2+ +(1-x)Mg 2+ +CO 3 2− → Ca X Mg 1-X CO 3 ), a micro-nano-sized protrusion structure similar to the "lotus leaf surface structure" is constructed on the surface of fine aggregate and pottery sand to achieve surface modification, so that the fine aggregate and pottery sand present super-hydrophobic properties. First of all, when this material is used to prepare concrete, it will not cause a decrease in the mechanical strength of the concrete structure like the method of directly adding a hydrophobic agent to the concrete material. Because the hydrophobic agent will be wrapped on the surface of the cement particles, it will not be able to fully contact with the mixing water, which will in turn cause the hydration reaction to be unable to proceed fully, and the formed hydrated gelling components will be reduced, resulting in a decrease in the strength of the concrete structure. The fine aggregate and pottery sand with a special surface structure prepared by the present invention do not have the above problems and will not affect the hydration reaction of the cement. Therefore, the concrete structure prepared by the present invention has both high strength and super-hydrophobic characteristics. Secondly, the Ca X Mg 1-X CO 3 Crystals can also block the pores in recycled fine aggregate and pottery sand, which can increase the matrix strength of the aggregate on the one hand, and reduce the problem of concrete strength reduction caused by the high water absorption rate of recycled fine aggregate and pottery sand on the other hand. X Mg 1-X CO 3 Crystals can also compact the surface structure of concrete, reduce porosity, and enhance the water resistance of ECC concrete. X Mg 1-X CO 3 During the crystal formation process, the hydrolyzed groups on the silane coupling agent hydrolyze to form silanol groups (SiOH) and the Ca X Mg 1-X CO 3 The hydroxyl (-OH) on the surface of the crystal undergoes a dehydration condensation reaction, thereby utilizing the capture effect of the silane coupling agent to not only help to convert the formed Ca X Mg 1-X CO 3 Crystals are connected to fine aggregate and ceramic sand in time, increasing Ca X Mg 1-X CO 3 The loading capacity of the crystal increases the hydrophobicity; and makes Ca X Mg1-X CO 3 The crystals are more firmly connected to the fine aggregate and clay sand, which helps to reduce shedding during concrete preparation and service.

[0028] In addition, the present invention further uses the above method to process the concrete structure obtained after curing, thereby re-constructing the micro-nano-sized protrusion structure similar to the "lotus leaf surface structure" on the surface of the concrete structure. X Mg 1-X CO 3 The crystals can also effectively block the pores on the surface of the concrete, which not only further enhances the waterproof and anti-permeability capabilities of the concrete structure, but also helps to improve the mechanical strength. The technical solution of the present invention not only realizes the resource utilization of recycled concrete, but also consumes a large amount of carbon dioxide by using red mud leachate, which helps to offset part of the carbon emissions caused by the preparation of ECC concrete, and also uses the coordination between alkaline leachate and carbon dioxide to improve the mechanical properties and waterproof and anti-permeability properties of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] It should be noted that the drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention and do not constitute an improper limitation of the present invention.

[0030] Figure 1 This is a compressive strength test diagram of the ECC concrete structure prepared in Example 1 below.

[0031] Figure 2 This is a surface contact angle test diagram of the ECC concrete structure prepared in the following Example 1. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Unless otherwise defined, all professional and scientific terms used in the present invention have the same meaning as those familiar to those skilled in the art. The preferred implementation methods and materials described in the present invention are only for demonstration purposes. The reagents or raw materials used in the invention can be purchased through conventional channels. If there are no special instructions, the reagents or raw materials used in the present invention are used in a conventional manner in the art or are used according to the product specification. Now the technical scheme of the present invention is further described in conjunction with specific embodiments.

[0033] In the following embodiments, the recycled concrete fine aggregate is the fine aggregate obtained by crushing, grinding and screening the waste concrete generated during the building demolition process, and the particle size distribution is continuously graded between 0.1 and 1 mm.

[0034] In the following examples, the bulk density of the lightweight ceramic sand is 368 kg / m3 The saturated water absorption rate is 6.21%, the porosity is 14.57%, and the particle size distribution is continuously graded between 0.5 and 2 mm.

[0035] Example 1

[0036] A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure comprises the following steps:

[0037] (1) Clean water and Bayer red mud (from Chalco Shandong Co., Ltd.) were mixed in a ratio of 1g:30ml and stirred for 2 hours for leaching treatment. Then, solid-liquid separation was performed by filtration, and the obtained solid was dried at 120°C to constant weight, and then the solid was ground to obtain 500-mesh red mud powder for use. Excess carbon dioxide (flow rate of 4L / min) was continuously introduced into the alkaline liquid phase obtained by filtration, and then the heating was stopped at 70°C until solids precipitated, and the obtained concentrated solution was used for use.

[0038] (2) Dissolve silane coupling agent KH550 in a saturated aqueous solution of calcium chloride and magnesium chloride to form a mixed system, wherein the mass fraction of the silane coupling agent is 1.3%. Soak recycled concrete fine aggregate and lightweight pottery sand in the mixed system at a ratio of 1g:1g:15ml, and then add excess concentrated solution drop by drop under stirring. After completion, filter out the fine aggregate and lightweight pottery sand, place them in an oven at 50°C and dry them to constant weight to obtain lightweight hydrophobic recycled fine aggregate.

[0039] (3) Take the following raw materials in the following proportions: 0.85 parts by weight of the lightweight hydrophobic recycled fine aggregate of this embodiment, 1.6 parts by weight of the red mud powder with a fineness of 400 mesh, 1.3 parts by weight of 42.5 ordinary Portland cement, 0.03 parts by weight of polyvinyl alcohol fiber (diameter between 10 and 20 μm, length 10 mm), 0.05 parts by weight of polycarboxylate water reducer, and 0.75 parts by weight of mixing water. Mix the above raw materials and mix them evenly to obtain ECC concrete slurry, pour it into a mold, demould it after hardening and forming, and naturally cure it until the 28th day to obtain a pretreated concrete structure.

[0040] (4) The pretreated concrete structure is immersed in the mixed system again (same as the above step (1) of this embodiment), and then an excess amount of the concentrated solution is added dropwise under stirring conditions, and a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is obtained after completion.

[0041] The compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested according to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019). Figure 1 As shown), and the surface contact angle of the ECC concrete structure was tested (as Figure 2 The results are as follows: 28d compressive strength = 55.08MPa, contact angle = 138.3°.

[0042] Example 2

[0043] A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure comprises the following steps:

[0044] (1) Clean water and Bayer red mud (from Chalco Shandong Co., Ltd.) were mixed in a ratio of 1g:40ml and stirred for 2 hours for leaching treatment. Then, solid-liquid separation was performed by filtration, and the obtained solid was dried at 150°C to constant weight, and then the solid was ground to obtain 300-mesh red mud powder for use. Excess carbon dioxide (flow rate of 4L / min) was continuously introduced into the alkaline liquid phase obtained by filtration, and then the heating was stopped at 80°C until solids precipitated, and the obtained concentrated solution was used for use.

[0045] (2) Dissolve silane coupling agent KH560 in a saturated aqueous solution of calcium nitrate and magnesium nitrate to form a mixed system, wherein the mass fraction of the silane coupling agent is 0.9%. Soak recycled concrete fine aggregate and lightweight pottery sand in the mixed system at a ratio of 1g:1.5g:10ml, and then add excess concentrated solution drop by drop under stirring. After completion, filter out the fine aggregate and lightweight pottery sand, place them in an oven at 60°C and dry them to constant weight to obtain lightweight hydrophobic recycled fine aggregate.

[0046] (3) Take the following raw materials in the following proportions: 0.8 parts by weight of the lightweight hydrophobic recycled fine aggregate of this embodiment, 1.5 parts by weight of the red mud powder with a fineness of 300 mesh, 1.2 parts by weight of 42.5 ordinary Portland cement, 0.025 parts by weight of polypropylene fiber (diameter between 10 and 20 μm, length 8 mm), 0.04 parts by weight of sodium lignosulfonate water reducer, and 0.7 parts by weight of mixing water. Mix the above raw materials and mix them evenly to obtain ECC concrete slurry, pour it into a mold, demould it after hardening and forming, and naturally cure it until the 28th day to obtain a pretreated concrete structure.

[0047] (4) The pretreated concrete structure is immersed in the mixed system again (same as the above step (1) of this embodiment), and then an excess amount of the concentrated solution is added dropwise under stirring conditions, and a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is obtained after completion.

[0048] According to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 52.14MPa, contact angle = 141.7°.

[0049] Example 3

[0050] A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure comprises the following steps:

[0051] (1) Clean water and Bayer red mud (from Chalco Shandong Co., Ltd.) were mixed in a ratio of 1g:20ml and stirred for 2 hours for leaching treatment. Then, solid-liquid separation was performed by filtration, and the obtained solid was dried at 100°C to constant weight, and then the solid was ground to obtain 600-mesh red mud powder for use. Excess carbon dioxide (flow rate of 3L / min) was continuously introduced into the alkaline liquid phase obtained by filtration, and then the heating was stopped at 70°C until solids precipitated, and the obtained concentrated solution was used for use.

[0052] (2) Dissolve silane coupling agent KH570 in a saturated aqueous solution of calcium gluconate and magnesium sulfate to form a mixed system, wherein the mass fraction of the silane coupling agent is 1.5%. Soak recycled concrete fine aggregate and lightweight pottery sand in the mixed system in a ratio of 1g:2g:20ml, and then add an excess of the concentrated solution drop by drop under stirring. After completion, filter out the fine aggregate and lightweight pottery sand, place them in an oven and dry them at 40°C to constant weight to obtain lightweight hydrophobic recycled fine aggregate.

[0053] (3) Take the following raw materials in the following proportions: 1.0 weight part of the lightweight hydrophobic recycled fine aggregate of this embodiment, 1.8 weight parts of the red mud powder with a fineness of 600 mesh, 1.5 weight parts of 42.5 ordinary Portland cement, 0.035 weight parts of polyacrylonitrile fiber (diameter between 10 and 20 μm, length 16 mm), 0.06 weight parts of polycarboxylate water reducer, and 0.9 weight parts of mixing water. Mix the above raw materials and mix them evenly to obtain ECC concrete slurry, pour it into a mold, demould it after hardening and forming, and naturally cure it until the 21st day to obtain a pretreated concrete structure.

[0054] (4) The pretreated concrete structure is immersed in the mixed system again (same as the above step (1) of this embodiment), and then an excess amount of the concentrated solution is added dropwise under stirring conditions, and a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is obtained after completion.

[0055] According to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 47.36MPa, contact angle = 135.2°. In addition, the compressive strength and surface contact angle of the pretreated concrete structure prepared in step (3) of this embodiment were tested, and the results were: 28d compressive strength = 46.19MPa, contact angle = 127.5°. It is explained that the treatment process of step (4) further improves the strength and hydrophobicity of the ECC concrete structure.

[0056] Example 4

[0057] A method for preparing a lightweight, high-strength, super-hydrophobic recycled ECC concrete structure is the same as the above-mentioned embodiment 1, except that the lightweight hydrophobic recycled fine aggregate of this embodiment is prepared by the following method: dissolving silane coupling agent KH550 into a saturated aqueous solution of calcium chloride to form a mixed system, wherein the mass fraction of the silane coupling agent KH550 is 1.3%. Soaking recycled concrete fine aggregate and lightweight pottery sand in the mixed system at a ratio of 1g:1g:15ml, and then dripping an excess of the concentrated solution under stirring conditions, filtering out the fine aggregate and lightweight pottery sand after completion, and drying them in an oven at 50°C to constant weight to obtain lightweight hydrophobic recycled fine aggregate.

[0058] According to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 48.21MPa, contact angle = 116.8°.

[0059] Example 5

[0060] A method for preparing a lightweight, high-strength, super-hydrophobic recycled ECC concrete structure is the same as the above-mentioned embodiment 1, except that the lightweight hydrophobic recycled fine aggregate of this embodiment is prepared by the following method: dissolving silane coupling agent KH550 into a saturated aqueous solution of magnesium chloride to form a mixed system, wherein the mass fraction of the silane coupling agent KH550 is 1.3%. Recycled concrete fine aggregate and lightweight pottery sand are soaked in the mixed system at a ratio of 1g:1g:15ml, and then an excess of the concentrated solution is added dropwise under stirring. After completion, the fine aggregate and lightweight pottery sand are filtered out, placed in an oven and dried at 50°C to constant weight to obtain lightweight hydrophobic recycled fine aggregate.

[0061] According to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 46.87MPa, contact angle = 120.4°.

[0062] It can be seen that the compressive strength and contact angle of the ECC concrete structures prepared in Example 4 and this example are significantly lower than those in Example 1. This is because the single Ca 2+ Mg 2+ The reaction system cannot form Ca X Mg 1-X CO 3 Micro-nano crystals construct micro-nano sized protrusions on the surface of fine aggregate and ceramic sand, similar to the "lotus leaf surface structure", achieving super hydrophobic properties. 2+ Mg 2+ The CaCO formed by the reaction system 3 and MgCO 3 The crystals are larger in size, such as spheres and rods, which results in a wider average distance between the protrusions formed on the surface of fine aggregate and pottery sand. Water droplets can more easily penetrate into the gaps between these protrusions, and the macroscopic manifestation is a decrease in hydrophobicity.

[0063] Example 6

[0064] A method for preparing a lightweight, high-strength, super-hydrophobic recycled ECC concrete structure is the same as the above-mentioned embodiment 2, except that the lightweight hydrophobic recycled fine aggregate in this embodiment is prepared by the following method: the recycled concrete fine aggregate and lightweight pottery sand are soaked in a saturated aqueous solution of calcium nitrate and magnesium nitrate in a ratio of 1g:1.5g:10ml to form a mixed system, and then an excess of the concentrated solution is added dropwise under stirring conditions. After completion, the fine aggregate and lightweight pottery sand are filtered out, and placed in an oven to dry at 60°C to constant weight to obtain a lightweight hydrophobic recycled fine aggregate.

[0065] According to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 51.72MPa, contact angle = 113.8°.

[0066] Example 7

[0067] A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is the same as the above-mentioned Example 3, except that the concentrated solution of this embodiment is prepared by the following method: clean water and Bayer red mud (from Chalco Shandong Co., Ltd.) are mixed in a ratio of 1g:30ml and stirred for 2 hours for leaching treatment. Then filter and separate the solid and liquid, dry the obtained solid at 120°C to constant weight, and then grind the solid to obtain 500-mesh red mud powder for standby use. The alkaline liquid phase obtained by filtration is heated at 70°C until solids are precipitated and then stopped to obtain the concentrated solution.

[0068] According to the "Concrete Physical and Mechanical Properties Test Method Standard" (GBT 50081-2019), the compressive strength of the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure prepared in this embodiment was tested, and the surface contact angle of the ECC concrete structure was tested. The results are: 28d compressive strength = 33.56MPa, contact angle = 84.3°.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure, characterized in that: The steps include: (1) Leaching the red mud with clean water, then performing solid-liquid separation, grinding and drying the obtained solid to obtain red mud powder for later use; introducing excess carbon dioxide into the obtained alkaline liquid phase, then heating and concentrating it to form a concentrated liquid for later use; (2) soaking the recycled concrete fine aggregate and lightweight pottery sand in a silane coupling agent-water mixture system containing saturated calcium and magnesium ion sources, and then adding an excess of the concentrated solution dropwise under stirring conditions, separating the fine aggregate and lightweight pottery sand after the reaction is completed, and drying them to obtain lightweight hydrophobic recycled fine aggregate for later use; (3) uniformly mixing the lightweight hydrophobic recycled fine aggregate with the red mud powder, cement, organic fiber, water reducing agent and water to obtain an ECC concrete slurry, and curing the slurry after forming and hardening it to obtain a pretreated concrete structure; (4) The pretreated concrete structure is immersed again in a silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources, and then an excess of the concentrated solution is added dropwise under stirring conditions. After the reaction is completed, the lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure is obtained.

2. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (1), the ratio of red mud to clean water is 1g:20-40ml.

3. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (1), the drying temperature is 100-150° C., and the solid is dried to constant weight at this temperature, and then the solid is ground to obtain the red mud powder.

4. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (1), the fineness of the red mud powder is 300-600 mesh.

5. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (1), the flow rate of the carbon dioxide gas is 3-5 L / min.

6. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (1), heating is stopped when solid matter precipitates to obtain the concentrated solution.

7. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the calcium ion source includes at least one of calcium chloride and calcium nitrate.

8. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the magnesium ion source includes at least one of magnesium chloride, magnesium sulfate, and magnesium nitrate.

9. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the mass fraction of the silane coupling agent in the mixed system is 0.9-1.5%.

10. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the silane coupling agent includes at least one of KH550, KH560, and KH570.

11. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the ratio of the recycled concrete fine aggregate, lightweight pottery sand and mixed system is 1g: 1~2g: 10~20ml.

12. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the particle size of the fine aggregate is distributed between 0.1 and 1 mm.

13. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the particle size of the lightweight ceramic sand is distributed between 0.5 and 2 mm.

14. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (2), the drying temperature is 40-60° C., and the material is dried at this temperature to a constant weight, thereby obtaining the lightweight hydrophobic recycled fine aggregate.

15. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (3), the ratio of the lightweight hydrophobic recycled fine aggregate, red mud powder, cement, organic fiber, water reducing agent and water is 0.8-1 parts by weight: 1.5-1.8 parts by weight: 1.2-1.5 parts by weight: 0.025-0.035 parts by weight: 0.04-0.06 parts by weight: 0.7-0.9 parts by weight.

16. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (3), the curing time is not less than 21 days.

17. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (4), the silane coupling agent-water mixed system containing saturated calcium and magnesium ion sources is the same as that in step (2).

18. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to any one of claims 1 to 9, characterized in that: In step (3), the organic fiber includes at least one of polyvinyl alcohol fiber, polyethylene fiber, polypropylene fiber, and polyacrylonitrile fiber.

19. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (3), the diameter of the organic fiber is 10-20 μm and the length is 8-16 mm.

20. The method for preparing a lightweight, high-strength, super-hydrophobic regenerated ECC concrete structure according to claim 1, characterized in that: In step (3), the water reducer includes at least one of a polycarboxylate water reducer, a naphthalene-based water reducer, and a wood sulfonate water reducer.

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