Recycled aggregate concrete 3D printing wall material modification process

Abstract

The invention discloses a modification process of a recycled aggregate concrete 3D printing wall material, and relates to the technical field of building materials. The regenerated bone is subjected to pore filling through impregnation, so that the porosity is reduced; a composite modifier is further used for carrying out surface modification on the recycled aggregate, so that the recycled aggregate has hydrophobicity, and the water absorption rate of the recycled aggregate is reduced; finally, the recycled aggregate concrete 3D printing wall material is prepared by optimizing the dosage and proportion of the added composite cementing material and other auxiliaries, and the key performance such as the binding power and the compressive strength of the recycled aggregate concrete 3D printing wall material is improved.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and in particular to a modification process for recycled aggregate concrete 3D printing wall materials. Background Art

[0002] With the rapid development of the construction industry, a large amount of construction waste is being generated, placing a heavy burden on the environment. Recycled aggregate concrete, as a key area for the resourceful utilization of construction waste, is gradually gaining attention. Furthermore, the rise of 3D printing technology in the construction sector has brought significant innovations to the industry. Consequently, 3D-printed recycled aggregate concrete is receiving increasing research and attention. However, 3D printing technology places stringent demands on printing materials. It requires the material to have excellent fluidity to ensure smooth extrusion from the nozzle, to quickly solidify and harden after printing to support subsequent structures, and to have sufficient strength and stability to meet the requirements of structural mechanics. Traditional recycled aggregate concrete, however, suffers from numerous issues, such as high aggregate porosity, strong water absorption, and insufficient adhesion to cementitious materials. These issues make it difficult to directly meet the specific requirements of 3D printing, necessitating the development of targeted modification processes.

[0003] Chinese patent application publication number CN113480263A discloses a 3D-printed concrete made from recycled aggregate and its preparation method. The concrete comprises 110-140 parts cement, 70-90 parts sand and gravel, 150-170 parts recycled aggregate, 1-1.5 parts water reducer, 0-5-1 parts accelerator, 10-15 parts admixture, 5%-20% by weight of the admixture coated with a temperature-sensitive membrane, and 70-80 parts water. The 3D-printed concrete made from recycled aggregate in this application has the advantages of a low hydration heat temperature and high concrete strength. However, this application still does not fully address the many problems associated with recycled aggregate concrete, such as high aggregate porosity, strong water absorption, and insufficient adhesion to cementitious materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a process for modifying recycled aggregate concrete 3D printing wall materials. The process involves impregnating the regenerated aggregate to fill pores and reduce porosity. A composite modifier is then used to surface-modify the recycled aggregate, making it hydrophobic and reducing its water absorption. Finally, by optimizing the amount and ratio of the added composite cementitious material and other additives, a recycled aggregate concrete 3D printing wall material with even superior performance is produced.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] Mixing nano-silicon dioxide and ultrafine mineral powder, adding the mixture to the first sodium silicate solution, and stirring for a first preset time to form an impregnation solution;

[0007] adding the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnating the tank under a preset vacuum degree for a second preset time, then pressurizing the tank to a preset pressure and maintaining the pressure for a third preset time to obtain impregnated recycled aggregate;

[0008] The long-chain silane coupling agent is mixed with the FEVE fluorocarbon resin to obtain a composite modifier;

[0009] Adding the impregnated recycled aggregate to a high-speed mixer, starting stirring, and spraying the composite modifier into the mixer by atomization, and continuing stirring for a fourth preset time to obtain modified recycled aggregate;

[0010] Mixing fly ash, slag, plant ash, and a composite activator, and adding ultrafine calcium carbonate, basalt fiber, and PVA fiber, and mixing and stirring for a fifth preset time to obtain a composite gelling material;

[0011] The modified recycled aggregate, the composite cementitious material, water, the water reducer, the thixotropic agent and the retarder are mixed and stirred for a sixth preset time to obtain a recycled aggregate concrete 3D printing wall material.

[0012] Beneficial technical effects:

[0013] In the modification process provided in this application, the multi-dimensional performance improvement of the recycled aggregate concrete 3D printing wall material is achieved through the mechanism of impregnation filling-chemical modification-interface synergistic strengthening: nano-silica and ultrafine mineral powder are used to block the pores of the recycled aggregate under vacuum pressure impregnation, and combined with sodium silicate solution to generate CSH gel. The silicon oxygen chain (-Si-O-) in the CSH gel forms a chemical connection with the active silicon, aluminum oxide and subsequent composite cementitious material on the surface of the recycled aggregate, thereby strengthening the interface transition zone of each component and enhancing the bonding between the recycled aggregate and other components; through the chemical bond bridging of the silane coupling agent and the barrier of the FEVE fluorocarbon resin hydrophobic film, the performance of the recycled aggregate is further enhanced. Strengthen the interfacial bonding and hydrophobicity between recycled aggregate and cementitious materials; at the same time, the composite cementitious material quickly generates sodium aluminum silicate gel under the action of the composite activator, and its three-dimensional network structure is dense, and the early strength develops rapidly, which can meet the rapid setting requirements of 3D printing layer by layer; in addition, compared with traditional cement, the composite cementitious material is more resistant to chemical corrosion (such as sulfate and chloride ions) and has better long-term durability; finally, the composite cementitious material is supplemented by the shear thinning properties of the thixotropic agent, the three-dimensional support network formed by basalt fiber and PVA fiber, and the coagulation regulation of the retarder, which synergistically optimizes the compressive strength, bonding strength and extrudability of the recycled aggregate concrete 3D printing wall material. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a physical picture of the recycled aggregate concrete 3D printing wall material obtained through the modification process.

[0015] Figure 2 It is a schematic diagram of the preparation process of the modified process of recycled aggregate concrete 3D printing wall material. DETAILED DESCRIPTION

[0016] In order to make the technical problems, technical solutions, and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below with reference to the following examples. However, this should not be construed as limiting the scope of this application to the following examples. Without departing from the above-mentioned method concepts of this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0017] In this application, the terms used in this application are for the purpose of describing specific embodiments only and are not intended to be limiting of the application.

[0018] As used in this application, the singular forms "for," "a," "the," and "any" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0019] The present application provides a modified process for recycled aggregate concrete 3D printing wall material, and the physical object of recycled aggregate concrete 3D printing wall material is obtained by the modified process. Figure 1 shown.

[0020] The modification process comprises the following steps:

[0021] Mixing nano-silicon dioxide and ultrafine mineral powder, adding the mixture to the first sodium silicate solution, and stirring for a first preset time to form an impregnation solution;

[0022] adding the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnating the tank under a preset vacuum degree for a second preset time, then pressurizing the tank to a preset pressure and maintaining the pressure for a third preset time to obtain impregnated recycled aggregate;

[0023] The long-chain silane coupling agent is mixed with the FEVE fluorocarbon resin to obtain a composite modifier;

[0024] Adding the impregnated recycled aggregate to a high-speed mixer, starting stirring, and spraying the composite modifier into the mixer by atomization, and continuing stirring for a fourth preset time to obtain modified recycled aggregate;

[0025] Mixing fly ash, slag, plant ash, and a composite activator, and adding ultrafine calcium carbonate, basalt fiber, and PVA fiber, and mixing and stirring for a fifth preset time to obtain a composite gelling material;

[0026] The modified recycled aggregate, the composite cementitious material, water, the water reducer, the thixotropic agent and the retarder are mixed and stirred for a sixth preset time to obtain a recycled aggregate concrete 3D printing wall material.

[0027] In a feasible implementation scheme, the mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is (1.5-3): (8-12): (85-90); the modulus of the first sodium silicate solution is 1.2-1.8; and the mass ratio of the recycled aggregate to the impregnation solution is (25-45): (55-75).

[0028] In terms of a feasible implementation scheme, the compounding ratio of the long-chain silane coupling agent and the FEVE fluorocarbon resin is a mass ratio of 1:3; the long-chain silane coupling agent includes any one of n-decyltrimethoxysilane, n-decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane and hexadecyltriethoxysilane; the solid content of the FEVE fluorocarbon resin is 20% to 30%; the mass ratio of the impregnated recycled aggregate to the composite modifier is (95 to 99): (1 to 5).

[0029] In one feasible implementation scheme, the composite activator includes a second sodium silicate solution and a hydroxyethyltrimethylammonium hydroxide solution; the modulus of the second sodium silicate solution is 1.6; and the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is (60-70): (30-40).

[0030] In terms of a feasible implementation scheme, the mass ratio of the fly ash, slag, wood ash, composite activator, ultrafine calcium carbonate, basalt fiber and PVA fiber is (40-50): (20-30): (5-15): (20-30): (3-8): (0.2-0.5): (0.2-0.5).

[0031] In one feasible embodiment, the water reducer includes any one of a lignin sulfonate water reducer, an aminosulfonate water reducer and a polycarboxylate water reducer.

[0032] In one feasible embodiment, the thixotropic agent includes any one of water-based polyamide wax, hydroxyethyl cellulose and xanthan gum.

[0033] In one feasible embodiment, the retarder includes any one of a phosphate retarder, a polyol retarder and a hydroxycarboxylic acid retarder.

[0034] In a feasible implementation scheme, the mass ratio of the modified recycled aggregate, composite cementitious material, water, water reducer, thixotropic agent and retarder is (50-70): (20-35): (8-15): (0.5-1.5): (0.2-0.8): (0.1-0.3).

[0035] In terms of a feasible implementation scheme, the first preset time is 20 to 30 minutes, the second preset time is 5 to 8 hours, the third preset time is 2 to 4 hours, the fourth preset time is 5 to 10 minutes, the fifth preset time is 1 to 2 hours, and the sixth preset time is 40 to 60 minutes; the preset vacuum degree is 0.01 to 0.05 MPa; and the preset pressure is 1.0 to 1.5 MPa.

[0036] The following will describe in detail a modified process for 3D printing wall materials of recycled aggregate concrete provided by this application in combination with different embodiments.

[0037] Example 1

[0038] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0039] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 25 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 2.0:10.0:88.0;

[0040] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.03 MPa for 6 hours, then pressurize to 1.2 MPa and maintain for 3 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 35.0:65.0;

[0041] 3. n-decyltrimethoxysilane and FEVE fluorocarbon resin with a solid content of 25% are mixed and compounded to obtain a composite modifier; the mass ratio of n-decyltrimethoxysilane to FEVE fluorocarbon resin with a solid content of 25% is 1:3;

[0042] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 8 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 97.0:3.0.

[0043] 5. Fly ash, slag, plant ash, a composite activator (the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 65:35), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1.5 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 40.0:24.4:10.0:20.0:5.0:0.3:0.3;

[0044] 6. The modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder were mixed and stirred for 50 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder was 58.3:30.0:10.0:1.0:0.5:0.2.

[0045] Example 2

[0046] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0047] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 20 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 1.5:8.0:90.5;

[0048] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.01 MPa for 8 hours, then pressurize to 1.0 MPa and maintain for 4 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 25.0:75.0;

[0049] 3. Mixing dodecyltriethoxysilane with FEVE fluorocarbon resin having a solid content of 30% to obtain a composite modifier; the mass ratio of the dodecyltriethoxysilane to the FEVE fluorocarbon resin having a solid content of 30% is 1:3;

[0050] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 5 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 95.0:5.0.

[0051] 5. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 60:40), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1 hour to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 40.0:26.0:5.0:25.0:3.0:0.5:0.5;

[0052] 6. The modified recycled aggregate, composite cementitious material, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder were mixed and stirred for 40 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder was 50.0:35.0:12.5:1.5:0.8:0.2.

[0053] Example 3

[0054] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0055] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 30 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 3.0:12.0:85.0;

[0056] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.05 MPa for 5 hours, then pressurize to 1.5 MPa and maintain for 2 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 45.0:55.0;

[0057] 3. Hexadecyltrimethoxysilane and FEVE fluorocarbon resin with a solid content of 20% are mixed and compounded to obtain a composite modifier; the mass ratio of the hexadecyltrimethoxysilane to the FEVE fluorocarbon resin with a solid content of 20% is 1:3;

[0058] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 10 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 99.0:1.0.

[0059] 5. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 70:30), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 2 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 42.0:20.0:12.4:20.0:5.0:0.4:0.2;

[0060] 6. The modified recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder were mixed and stirred for 40 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder was 70.0:20.0:9.2:0.5:0.2:0.1.

[0061] Example 4

[0062] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0063] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 22 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 2.5:9.0:88.5;

[0064] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.02 MPa for 7 hours, then pressurize to 1.3 MPa and maintain for 3.5 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 33.0:67.0;

[0065] 3. n-decyltriethoxysilane and FEVE fluorocarbon resin with a solid content of 28% are mixed and compounded to obtain a composite modifier; the mass ratio of n-decyltriethoxysilane to FEVE fluorocarbon resin with a solid content of 28% is 1:3;

[0066] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 7 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 96.0:4.0.

[0067] 5. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 64:36), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1.2 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 42.0:21.2:8.0:22.0:6.0:0.4:0.4;

[0068] 6. The modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder were mixed and stirred for 45 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder was 64.2:25.0:9.0:1.0:0.6:0.2.

[0069] Example 5

[0070] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0071] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 28 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 1.8:11.0:87.2;

[0072] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.04 MPa for 6.5 hours, then pressurize to 1.4 MPa and maintain for 2.5 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 40.0:60.0;

[0073] 3. Mixing dodecyltrimethoxysilane with FEVE fluorocarbon resin having a solid content of 22% to obtain a composite modifier; the mass ratio of the dodecyltrimethoxysilane to the FEVE fluorocarbon resin having a solid content of 22% is 1:3;

[0074] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 9 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 98.0:2.0.

[0075] 5. Fly ash, slag, plant ash, a composite activator (the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 67:33), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1.8 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 43.3:21.0:7.0:21.0:7.0:0.3:0.4;

[0076] 6. The modified recycled aggregate, composite cementitious material, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder were mixed and stirred for 55 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder was 55.0:32.0:11.0:1.2:0.5:0.3.

[0077] Example 6

[0078] like Figure 2 As shown, a process for modifying recycled aggregate concrete 3D printing wall materials includes the following steps:

[0079] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 24 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 2.2:10.5:87.3;

[0080] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.03 MPa for 5 hours, then pressurize to 1.2 MPa and maintain for 3 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 38.0:62.0;

[0081] 3. Hexadecyltriethoxysilane and FEVE fluorocarbon resin with a solid content of 26% are mixed and compounded to obtain a composite modifier; the mass ratio of the hexadecyltriethoxysilane to the FEVE fluorocarbon resin with a solid content of 26% is 1:3;

[0082] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 6 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 97.5:2.5.

[0083] 5. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 70:30), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1.6 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 41.0:23.0:9.0:21.0:5.5:0.2:0.3;

[0084] 6. The modified recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder were mixed and stirred for 50 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder was 61.0:28.0:10.0:0.6:0.3:0.1.

[0085] Comparative Example 1

[0086] A process for modifying recycled aggregate concrete 3D printing wall materials comprises the following steps:

[0087] 1. n-Decyltrimethoxysilane and FEVE fluorocarbon resin with a solid content of 25% are mixed and compounded to obtain a composite modifier; the mass ratio of n-Decyltrimethoxysilane to FEVE fluorocarbon resin with a solid content of 25% is 1:3;

[0088] 2. Add the recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 8 minutes to obtain modified recycled aggregate. The mass ratio of the recycled aggregate to the composite modifier is 97.0:3.0.

[0089] 3. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 65:35), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 1.5 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 40.0:24.4:10.0:20.0:5.0:0.3:0.3;

[0090] 4. The modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder were mixed and stirred for 50 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate water reducer, hydroxyethyl cellulose and hydroxycarboxylate retarder was 58.3:30.0:10.0:1.0:0.5:0.2.

[0091] Comparative Example 2

[0092] A process for modifying recycled aggregate concrete 3D printing wall materials comprises the following steps:

[0093] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 30 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 3.0:12.0:85.0;

[0094] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.05 MPa for 5 hours, then pressurize to 1.5 MPa and maintain for 2 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 45.0:55.0;

[0095] 3. Fly ash, slag, plant ash, a composite activator (wherein the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is 70:30), ultrafine calcium carbonate, basalt fiber, and PVA fiber are mixed and stirred for 2 hours to obtain a composite cementitious material; the mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber, and PVA fiber is 42.0:20.0:12.4:20.0:5.0:0.4:0.2;

[0096] 4. The impregnated recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder were mixed and stirred for 40 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the impregnated recycled aggregate, composite cementitious material, water, lignin sulfonate water reducer, xanthan gum and polyol retarder was 70.0:20.0:9.2:0.5:0.2:0.1.

[0097] Comparative Example 3

[0098] A process for modifying recycled aggregate concrete 3D printing wall materials comprises the following steps:

[0099] 1. Mix nano-silicon dioxide and ultrafine mineral powder and add them to the first sodium silicate solution, stirring for 24 minutes to form an impregnation solution; the mass ratio of the nano-silicon dioxide, ultrafine mineral powder and the first sodium silicate solution is 2.2:10.5:87.3;

[0100] 2. Add the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnate at 0.03 MPa for 5 hours, then pressurize to 1.2 MPa and maintain for 3 hours to obtain impregnated recycled aggregate; the mass ratio of the recycled aggregate to the impregnation liquid is 38.0:62.0;

[0101] 3. Hexadecyltriethoxysilane and FEVE fluorocarbon resin with a solid content of 26% are mixed and compounded to obtain a composite modifier; the mass ratio of the hexadecyltriethoxysilane to the FEVE fluorocarbon resin with a solid content of 26% is 1:3;

[0102] 4. Add the impregnated recycled aggregate to a high-speed mixer, start stirring, and spray the composite modifier into the mixer by atomization. Continue stirring for 6 minutes to obtain modified recycled aggregate. The mass ratio of the impregnated recycled aggregate to the composite modifier is 97.5:2.5.

[0103] 5. The modified recycled aggregate, cement, water, lignin sulfonate water reducer, xanthan gum and polyol retarder were mixed and stirred for 50 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, cement, water, lignin sulfonate water reducer, xanthan gum and polyol retarder was 61.0:28.0:10.0:0.6:0.3:0.1.

[0104] Comparative Example 4

[0105] Recycled aggregate, cement, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder were mixed and stirred for 55 minutes to obtain a recycled aggregate concrete 3D printing wall material; the mass ratio of the recycled aggregate, cement, water, aminosulfonate water reducer, water-based polyamide wax and phosphate retarder was 55.0:32.0:11.0:1.2:0.5:0.3.

[0106] According to the "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T 50081-2019), the compressive strength, bond strength and water absorption of the prepared recycled aggregate concrete 3D printing wall material were tested.

[0107] Table 1 Test results of recycled aggregate concrete 3D printing wall materials prepared in Example and Comparative Example

[0108]

[0109]

[0110] As can be seen from Table 1, all test data of the recycled aggregate concrete 3D printing wall materials prepared in Examples 1 to 6 are better than those in Comparative Examples 1 to 3.

[0111] This is because, in the modification process of the recycled aggregate concrete 3D printing wall material prepared in Examples 1 to 6, the multi-dimensional performance improvement of the recycled aggregate concrete 3D printing wall material is achieved through the mechanism of impregnation filling-chemical modification-interface synergistic strengthening: nano-silica and ultrafine mineral powder are used to block the pores of the recycled aggregate under vacuum pressure impregnation, and sodium silicate solution is combined to generate CSH gel to strengthen the interface transition zone. The silicon oxygen chain (-Si-O-) in the CSH gel forms a chemical connection with the active silicon, aluminum oxide and subsequent composite cementitious material on the surface of the recycled aggregate, thereby enhancing the bonding of the recycled aggregate with other components; through the chemical bond bridging of the silane coupling agent and the hydrophobicity of the FEVE fluorocarbon resin The membrane barrier further enhances the interfacial bonding force and hydrophobicity of the recycled aggregate and cementitious material; at the same time, the composite cementitious material quickly generates sodium aluminum silicate gel under the action of the composite activator, and its three-dimensional network structure is dense, and the early strength develops rapidly, which can meet the rapid setting requirements of 3D printing layer by layer; in addition, compared with traditional cement, the composite cementitious material is more resistant to chemical corrosion (such as sulfate and chloride ions) and has better long-term durability; finally, the composite cementitious material is supplemented by the shear thinning properties of the thixotropic agent, the three-dimensional support network formed by basalt fiber and PVA fiber, and the coagulation regulation of the retarder, which synergistically optimizes the compressive strength, bonding strength and extrudability of the recycled aggregate concrete 3D printing wall material.

[0112] In Comparative Example 1, however, the recycled aggregate was not subjected to vacuum pressure impregnation, so the pores in the recycled aggregate could not be filled well. The presence of pores can form internal defects, leading to stress concentration. If cracks are generated when stressed, they are more likely to expand in the pores, reducing the compressive strength and bond strength of the concrete. In addition, the pores easily form interconnected seepage channels, making it easier for harmful substances (chloride ions, CO2, water, etc.) to invade the interior of the concrete, accelerating the erosion of the concrete and its steel bars.

[0113] In Comparative Example 2, the recycled aggregate was not chemically modified, so chemical bond bridging and the hydrophobic membrane barrier effect of FEVE fluorocarbon resin could not be generated between the recycled aggregate and the cementitious material. Ultimately, the resulting recycled aggregate concrete 3D printed wall material had poor compressive strength and bonding strength, and its hydrophobicity was not good enough.

[0114] In Comparative Example 3, no composite cementitious material is used but traditional cement is used, so sodium aluminum silicate gel cannot be generated, making it difficult to meet the rapid setting requirements of layer-by-layer stacking in 3D printing, and the thixotropic agent, basalt fiber, PVA fiber and retarder cannot be coordinated. Therefore, the compressive strength and bonding strength of the recycled aggregate concrete 3D printing wall material obtained are also poor, and other properties are also weakened.

[0115] For the same reasons as the above comparative examples, since comparative example 4 did not undergo vacuum pressure impregnation, chemical modification, or use of composite cementitious materials, the performance of the recycled aggregate concrete 3D printed wall material obtained was the worst.

[0116] The above results show and describe the basic principles and main features of this application as well as the advantages of this application.

[0117] Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and descriptions are merely illustrative of the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. Such changes and improvements are intended to fall within the scope of the present application. The scope of protection claimed in the present application is defined by the equivalents of the appended claims.

Claims

1. A modified process for recycled aggregate concrete 3D printing wall material, characterized in that: The following steps are involved: Mixing nano-silicon dioxide and ultrafine mineral powder, adding the mixture to the first sodium silicate solution, and stirring for a first preset time to form an impregnation solution; adding the recycled aggregate into a vacuum tank containing an impregnation liquid, impregnating the tank under a preset vacuum degree for a second preset time, then pressurizing the tank to a preset pressure and maintaining the pressure for a third preset time to obtain impregnated recycled aggregate; The long-chain silane coupling agent is mixed with the FEVE fluorocarbon resin to obtain a composite modifier; Adding the impregnated recycled aggregate to a high-speed mixer, starting stirring, and spraying the composite modifier into the mixer by atomization, and continuing stirring for a fourth preset time to obtain modified recycled aggregate; Mixing fly ash, slag, plant ash, and a composite activator, and adding ultrafine calcium carbonate, basalt fiber, and PVA fiber, and mixing and stirring for a fifth preset time to obtain a composite gelling material; The modified recycled aggregate, the composite cementitious material, water, the water reducer, the thixotropic agent and the retarder are mixed and stirred for a sixth preset time to obtain a recycled aggregate concrete 3D printing wall material.

2. A recycled aggregate concrete 3D printing wall material modification process according to claim 1, characterized in that: The mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is (1.5-3): (8-12): (85-90); the modulus of the first sodium silicate solution is 1.2-1.8; and the mass ratio of the recycled aggregate to the impregnation solution is (25-45): (55-75).

3. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The compounding ratio of the long-chain silane coupling agent to the FEVE fluorocarbon resin is 1:3 by mass; the long-chain silane coupling agent includes any one of n-decyltrimethoxysilane, n-decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane and hexadecyltriethoxysilane; the solid content of the FEVE fluorocarbon resin is 20% to 30%; the mass ratio of the impregnated recycled aggregate to the composite modifier is (95 to 99): (1 to 5).

4. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The composite activator includes a second sodium silicate solution and a hydroxyethyltrimethylammonium hydroxide solution; the modulus of the second sodium silicate solution is 1.6; and the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylammonium hydroxide solution is (60-70):(30-40).

5. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The mass ratio of the fly ash, slag, plant ash, composite activator, ultrafine calcium carbonate, basalt fiber and PVA fiber is (40-50): (20-30): (5-15): (20-30): (3-8): (0.2-0.5): (0.2-0.5).

6. A recycled aggregate concrete 3D printing wall material modification process according to claim 1, characterized in that: The water reducer includes any one of a lignin sulfonate water reducer, an aminosulfonate water reducer and a polycarboxylate water reducer.

7. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The thixotropic agent includes any one of water-based polyamide wax, hydroxyethyl cellulose and xanthan gum.

8. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The retarder includes any one of a phosphate retarder, a polyol retarder and a hydroxycarboxylic acid retarder.

9. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The mass ratio of the modified recycled aggregate, composite cementitious material, water, water reducer, thixotropic agent and retarder is (50-70): (20-35): (8-15): (0.5-1.5): (0.2-0.8): (0.1-0.3).

10. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that: The first preset time is 20 to 30 minutes, the second preset time is 5 to 8 hours, the third preset time is 2 to 4 hours, the fourth preset time is 5 to 10 minutes, the fifth preset time is 1 to 2 hours, and the sixth preset time is 40 to 60 minutes; the preset vacuum degree is 0.01 to 0.05 MPa; and the preset pressure is 1.0 to 1.5 MPa.

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