A modification process for 3D printed wall materials using recycled aggregate concrete

Abstract

This application discloses a modification process for 3D printed wall materials using recycled aggregate concrete, relating to the field of building materials technology. The process involves impregnating the recycled aggregate to fill pores and reduce porosity; further, a composite modifier is used to modify the surface of the recycled aggregate, making it hydrophobic and thus reducing its water absorption; finally, by optimizing the dosage and ratio of the added composite cementitious materials and other additives, a 3D printed wall material using recycled aggregate concrete is obtained, improving its key properties such as adhesion and compressive strength.

Description

Technical Field

[0001] This application relates to the field of building materials technology, and in particular to a modification process for 3D printed wall materials using recycled aggregate concrete. Background Technology

[0002] With the rapid development of the construction industry, a large amount of construction waste is generated, placing a heavy burden on the environment. Recycled aggregate concrete, as an important direction for the resource utilization of construction waste, has gradually attracted attention. Meanwhile, the rise of 3D printing technology in the construction field has brought significant innovation to the industry. Therefore, 3D-printed recycled aggregate concrete has received increasing research and attention. However, 3D printing technology has stringent requirements for printing materials. It requires materials with good flowability to ensure smooth extrusion from the nozzle, rapid setting and hardening after printing to support subsequent structures, and sufficient strength and stability to meet structural mechanical requirements. Traditional recycled aggregate concrete has many problems, such as high aggregate porosity, strong water absorption, and insufficient adhesion to cementitious materials, making it difficult to directly meet the characteristics required for 3D printing. Therefore, there is an urgent need to develop targeted modification processes.

[0003] Chinese patent application CN113480263A discloses a method for preparing 3D-printed concrete using recycled aggregates, comprising 110-140 parts cement, 70-90 parts sand and gravel, 150-170 parts recycled aggregates, 1-1.5 parts water-reducing agent, 0-5-1 parts quick-setting agent, 10-15 parts admixtures (5%-20% by weight of which are coated with a temperature-sensitive membrane), and 70-80 parts water. The 3D-printed concrete prepared using recycled aggregates in this application has the advantages of low heat of hydration and high concrete strength. However, this application still does not fully solve many problems associated with recycled aggregate concrete, such as high aggregate porosity, high water absorption, and insufficient adhesion to cementitious materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a modification process for recycled aggregate concrete 3D printing wall materials. The process involves impregnating the recycled aggregate to fill pores and reduce porosity; further, a composite modifier is used to modify the surface of the recycled aggregate, making it hydrophobic and thus reducing its water absorption; finally, by optimizing the dosage and ratio of the added composite cementitious materials and other additives, a recycled aggregate concrete 3D printing wall material with superior performance is obtained.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution, and stirred for a first preset time to form an impregnation solution;

[0007] The recycled aggregate is added to a vacuum tank containing impregnation liquid and impregnated for a second preset time under a preset vacuum degree. Then, it is pressurized to a preset pressure and maintained for a third preset time to obtain impregnated recycled aggregate.

[0008] A composite modifier is obtained by mixing and compounding a long-chain silane coupling agent with FEVE fluorocarbon resin.

[0009] Add the impregnated recycled aggregate to a high-speed mixer, start the mixer, and spray the composite modifier into it by atomization. Continue mixing for a fourth preset time to obtain modified recycled aggregate.

[0010] Fly ash, slag, wood ash, and composite activator are mixed, and ultrafine calcium carbonate, basalt fiber, and PVA fiber are added. The mixture is stirred for a fifth preset time to obtain a composite cementitious material.

[0011] Modified recycled aggregate, composite cementitious material, water, water-reducing agent, thixotropic agent and retarder are mixed and stirred for a sixth preset time to obtain recycled aggregate concrete 3D printed wall material.

[0012] Beneficial technical effects:

[0013] The modification process provided in this application achieves multi-dimensional performance enhancement of recycled aggregate concrete 3D printing wall materials through a mechanism of impregnation-filling-chemical modification-interface synergistic strengthening: Nano-silica and ultrafine mineral powder are used to block the pores of recycled aggregate under vacuum pressure impregnation, and combined with sodium silicate solution to generate CSH gel. The silica chains (-Si-O-) in the CSH gel form chemical bonds with the active silicon, aluminum oxide, and subsequent composite cementitious materials on the surface of the recycled aggregate, thereby strengthening the interfacial transition zone of each component and enhancing the bonding between the recycled aggregate and other components; further enhancement is achieved through chemical bond bridging by silane coupling agents and the barrier effect of the FEVE fluorocarbon resin hydrophobic film. The composite cementitious material exhibits strong interfacial bonding and hydrophobicity between the recycled aggregate and the cementitious material. Simultaneously, under the action of a composite activator, the composite cementitious material rapidly generates sodium aluminum silicate gel with a dense three-dimensional network structure, resulting in rapid early strength development and meeting the rapid setting requirements of layer-by-layer stacking in 3D printing. Furthermore, compared to traditional cement, the composite cementitious material demonstrates stronger resistance to chemical erosion (such as sulfates and chloride ions) and superior long-term durability. Finally, the composite cementitious material, combined with the shear-thinning properties of a thixotropic agent, the three-dimensional support network formed by basalt fibers and PVA fibers, and the setting regulation of a retarder, synergistically optimizes the compressive strength, bond strength, and extrudability of the recycled aggregate concrete 3D printed wall material. Attached Figure Description

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

[0015] Figure 2 This is a schematic diagram of the preparation process for the modification technology of recycled aggregate concrete 3D printing wall materials. Detailed Implementation

[0016] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0017] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0018] The singular forms “for,” “a,” “the,” and “any one” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0019] This application provides a modification process for recycled aggregate concrete 3D printing wall materials, through which physical samples of recycled aggregate concrete 3D printing wall materials are obtained, such as... Figure 1 As shown.

[0020] The modification process includes the following steps:

[0021] Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution, and stirred for a first preset time to form an impregnation solution;

[0022] The recycled aggregate is added to a vacuum tank containing impregnation liquid and impregnated for a second preset time under a preset vacuum degree. Then, it is pressurized to a preset pressure and maintained for a third preset time to obtain impregnated recycled aggregate.

[0023] A composite modifier is obtained by mixing and compounding a long-chain silane coupling agent with FEVE fluorocarbon resin.

[0024] Add the impregnated recycled aggregate to a high-speed mixer, start the mixer, and spray the composite modifier into it by atomization. Continue mixing for a fourth preset time to obtain modified recycled aggregate.

[0025] Fly ash, slag, wood ash, and composite activator are mixed, and ultrafine calcium carbonate, basalt fiber, and PVA fiber are added. The mixture is stirred for a fifth preset time to obtain a composite cementitious material.

[0026] Modified recycled aggregate, composite cementitious material, water, water-reducing agent, thixotropic agent and retarder are mixed and stirred for a sixth preset time to obtain recycled aggregate concrete 3D printed wall material.

[0027] In one feasible implementation, 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 liquid is (25-45):(55-75).

[0028] In one feasible implementation, 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%; and the mass ratio of the impregnated recycled aggregate to the composite modifier is (95 to 99):(1 to 5).

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

[0030] In one feasible implementation, the mass ratio of 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 implementation, the water-reducing agent includes any one of lignin sulfonate water-reducing agents, aminosulfonate water-reducing agents, and polycarboxylate water-reducing agents.

[0032] In one feasible implementation, the thixotropic agent comprises any one of aqueous polyamide wax, hydroxyethyl cellulose, and xanthan gum.

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

[0034] In one feasible implementation, the mass ratio of the modified recycled aggregate, composite cementitious material, water, water-reducing agent, 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 one feasible implementation, the first preset time is 20-30 min, the second preset time is 5-8 h, the third preset time is 2-4 h, the fourth preset time is 5-10 min, the fifth preset time is 1-2 h, and the sixth preset time is 40-60 min; the preset vacuum degree is 0.01-0.05 MPa; and the preset pressure is 1.0-1.5 MPa.

[0036] The following will describe in detail, with reference to different embodiments, a process for modifying recycled aggregate concrete 3D printing wall materials provided in this application.

[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. The nano-silica and ultrafine mineral powder are mixed and compounded, and then added to the first sodium silicate solution and stirred for 25 minutes to form an impregnation solution; the mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is 2.0:10.0:88.0;

[0040] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.03 MPa for 6 hours, then pressurize it to 1.2 MPa and maintain it 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. A composite modifier is obtained by mixing and compounding n-decyltrimethoxysilane with FEVE fluorocarbon resin with a solid content of 25%; 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 the stirring, and spray the composite modifier into it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder for 50 minutes to obtain the recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder is 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. The nano-silica and ultrafine mineral powder are mixed and compounded, and then added to the first sodium silicate solution and stirred for 20 minutes to form an impregnation solution; the mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is 1.5:8.0:90.5;

[0048] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.01 MPa for 8 hours, then pressurize it to 1.0 MPa and maintain it 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. Dodecyltriethoxysilane is mixed and compounded with FEVE fluorocarbon resin with a solid content of 30% to obtain a composite modifier; the mass ratio of dodecyltriethoxysilane to FEVE fluorocarbon resin with a solid content of 30% is 1:3;

[0050] 4. Add the impregnated recycled aggregate to a high-speed mixer, start the mixer, and spray the composite modifier into it by atomization. Continue mixing 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, aminosulfonate water-reducing agent, water-based polyamide wax and phosphate retarder for 40 minutes to obtain recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, aminosulfonate water-reducing agent, water-based polyamide wax and phosphate retarder is 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. The nano-silica and ultrafine mineral powder are mixed and compounded, and then added to the first sodium silicate solution and stirred for 30 minutes to form an impregnation solution; the mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is 3.0:12.0:85.0;

[0056] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.05 MPa for 5 hours, then pressurize it to 1.5 MPa and maintain it 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. A composite modifier is obtained by mixing and compounding hexadecyltrimethoxysilane with FEVE fluorocarbon resin with a solid content of 20%; the mass ratio of hexadecyltrimethoxysilane to 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 the stirring, and spray the composite modifier into it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder for 40 minutes to obtain the recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder is 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. Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution and stirred for 22 minutes to form an impregnation solution; the mass ratio of nano-silica, ultrafine mineral powder and first sodium silicate solution is 2.5:9.0:88.5;

[0064] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.02 MPa for 7 hours, then pressurize it to 1.3 MPa and maintain it 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. A composite modifier is obtained by mixing and compounding n-decyltriethoxysilane with FEVE fluorocarbon resin with a solid content of 28%; 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 the stirring, and spray the composite modifier into it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder for 45 minutes to obtain recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder is 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. Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution and stirred for 28 minutes to form an impregnation solution; the mass ratio of nano-silica, ultrafine mineral powder and first sodium silicate solution is 1.8:11.0:87.2.

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

[0073] 3. A composite modifier is obtained by mixing and compounding dodecyltrimethoxysilane with FEVE fluorocarbon resin with a solid content of 22%; the mass ratio of dodecyltrimethoxysilane to FEVE fluorocarbon resin with a solid content of 22% is 1:3.

[0074] 4. Add the impregnated recycled aggregate to a high-speed mixer, start the stirring, and spray the composite modifier into it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, aminosulfonate water-reducing agent, water-based polyamide wax and phosphate retarder for 55 minutes to obtain recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, aminosulfonate water-reducing agent, water-based polyamide wax and phosphate retarder is 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. Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution and stirred for 24 minutes to form an impregnation solution; the mass ratio of nano-silica, ultrafine mineral powder and first sodium silicate solution is 2.2:10.5:87.3;

[0080] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.03 MPa for 5 hours, then pressurize it to 1.2 MPa and maintain it 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. A composite modifier is obtained by mixing and compounding hexadecyltriethoxysilane with FEVE fluorocarbon resin with a solid content of 26%; the mass ratio of hexadecyltriethoxysilane to 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 the stirring, and spray the composite modifier into it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder for 50 minutes to obtain the recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder is 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 includes the following steps:

[0087] 1. A composite modifier is obtained by mixing and compounding n-decyltrimethoxysilane with FEVE fluorocarbon resin with a solid content of 25%; 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 the mixer, and spray the composite modifier into it by atomization. Continue mixing 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder for 50 minutes to obtain the recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, composite cementitious material, water, polycarboxylate superplasticizer, hydroxyethyl cellulose and hydroxycarboxylate retarder is 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 includes the following steps:

[0093] 1. The nano-silica and ultrafine mineral powder are mixed and compounded, and then added to the first sodium silicate solution and stirred for 30 minutes to form an impregnation solution; the mass ratio of the nano-silica, ultrafine mineral powder and the first sodium silicate solution is 3.0:12.0:85.0;

[0094] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.05 MPa for 5 hours, then pressurize it to 1.5 MPa and maintain it 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, wood ash, composite activator (where the mass ratio of sodium disilicate solution to hydroxyethyltrimethylamine 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 fly ash, slag, wood 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. Mix the impregnated recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder for 40 minutes to obtain recycled aggregate concrete 3D printing wall material; the mass ratio of the impregnated recycled aggregate, composite cementitious material, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder is 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 includes the following steps:

[0099] 1. Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution and stirred for 24 minutes to form an impregnation solution; the mass ratio of nano-silica, ultrafine mineral powder and first sodium silicate solution is 2.2:10.5:87.3;

[0100] 2. Add the recycled aggregate to a vacuum tank containing impregnation liquid and impregnate it at 0.03 MPa for 5 hours, then pressurize it to 1.2 MPa and maintain it 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. A composite modifier is obtained by mixing and compounding hexadecyltriethoxysilane with FEVE fluorocarbon resin with a solid content of 26%; the mass ratio of hexadecyltriethoxysilane to 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 the stirring, and spray the composite modifier into it 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. Mix the modified recycled aggregate, cement, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder for 50 minutes to obtain the recycled aggregate concrete 3D printing wall material; the mass ratio of the modified recycled aggregate, cement, water, lignosulfonate water-reducing agent, xanthan gum and polyol retarder is 61.0:28.0:10.0:0.6:0.3:0.1.

[0104] Comparative Example 4

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

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

[0107] Table 1. Test results of recycled aggregate concrete 3D printed wall materials prepared in the examples and comparative examples.

[0108]

[0109]

[0110] As shown in Table 1, the test data of the recycled aggregate concrete 3D printing wall materials prepared in Examples 1-6 are better than those of Comparative Examples 1-3.

[0111] This is because, in the modification process of the recycled aggregate concrete 3D printing wall material prepared in Examples 1-6, 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 combined with sodium silicate solution to generate CSH gel to strengthen the interfacial transition zone. The silica chains (-Si-O-) in the CSH gel form chemical connections with the active silicon, aluminum oxide, and subsequent composite cementitious materials on the surface of the recycled aggregate, thereby enhancing the bonding between the recycled aggregate and other components; the chemical bonding of the silane coupling agent and the hydrophobicity of the FEVE fluorocarbon resin further enhance the performance improvement. Membrane barrier further enhances the interfacial bonding and hydrophobicity between recycled aggregate and cementitious material. Simultaneously, under the action of the composite activator, the composite cementitious material rapidly generates sodium aluminum silicate gel with a dense three-dimensional network structure and rapid early strength development, meeting the rapid setting requirements of 3D printing's layer-by-layer stacking. Furthermore, compared to traditional cement, the composite cementitious material exhibits stronger resistance to chemical erosion (such as sulfates and chloride ions) and superior long-term durability. Finally, the composite cementitious material, supplemented by the shear-thinning properties of a thixotropic agent, the three-dimensional support network formed by basalt fibers and PVA fibers, and the setting regulation of a retarder, synergistically optimizes the compressive strength, bond strength, and extrudability of the recycled aggregate concrete 3D printed wall material.

[0112] In Comparative Example 1, the recycled aggregate was not vacuum-impregnated, resulting in inadequate filling of its pores. The presence of pores creates internal defects, leading to stress concentration. This makes it easier for cracks to propagate through these pores under stress, reducing the compressive and bond strength of the concrete. Furthermore, pores easily form interconnected drainage channels, allowing harmful substances (chloride ions, CO2, moisture, etc.) to penetrate the concrete more readily, accelerating the erosion of the concrete and its reinforcing steel.

[0113] In Comparative Example 2, no chemical modification was performed on the recycled aggregate, so it was impossible to generate chemical bond bridging between the recycled aggregate and the cementitious material and the hydrophobic film barrier effect of FEVE fluorocarbon resin. As a result, the compressive strength and bond strength of the recycled aggregate concrete 3D printed wall material were poor, and the hydrophobicity was also not good enough.

[0114] In Comparative Example 3, no composite cementitious material was used; instead, traditional cement was used. Therefore, sodium aluminum silicate gel could not be generated, making it difficult to meet the rapid setting requirements of 3D printing layer-by-layer stacking. Furthermore, it could not synergize with thixotropic agents, basalt fibers, PVA fibers, and retarders. Consequently, the compressive strength and bond strength of the recycled aggregate concrete 3D printed wall material were poor, and other properties were also weakened.

[0115] For the same reasons as the comparative examples above, since neither vacuum pressure impregnation nor chemical modification was carried out in Comparative Example 4, nor composite cementitious materials were used, the resulting recycled aggregate concrete 3D printed wall material had the worst performance.

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

[0117] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A modification process for 3D printed wall materials using recycled aggregate concrete, characterized in that, Includes the following steps: Nano-silica and ultrafine mineral powder are mixed and compounded, then added to a first sodium silicate solution, and stirred for a first preset time to form an impregnation solution; The recycled aggregate is added to a vacuum tank containing impregnation liquid and impregnated for a second preset time under a preset vacuum degree. Then, it is pressurized to a preset pressure and maintained for a third preset time to obtain impregnated recycled aggregate. A composite modifier is obtained by mixing and compounding a long-chain silane coupling agent with FEVE fluorocarbon resin. Add the impregnated recycled aggregate to a high-speed mixer, start the mixer, and spray the composite modifier into it by atomization. Continue mixing for a fourth preset time to obtain modified recycled aggregate. Fly ash, slag, wood ash, and composite activator are mixed, and ultrafine calcium carbonate, basalt fiber, and PVA fiber are added. The mixture is stirred for a fifth preset time to obtain a composite cementitious material. Modified recycled aggregate, composite cementitious material, water, water-reducing agent, thixotropic agent and retarder are mixed and stirred for a sixth preset time to obtain recycled aggregate concrete 3D printed wall material; The composite activator comprises a second sodium silicate solution and a hydroxyethyltrimethylamine hydroxide solution; the modulus of the second sodium silicate solution is 1.6; the mass ratio of the second sodium silicate solution to the hydroxyethyltrimethylamine hydroxide solution is (60~70):(30~40).

2. The process for modifying recycled aggregate concrete 3D printing wall materials 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; the mass ratio of the recycled aggregate to the impregnation liquid 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%~30%; the mass ratio of the impregnated recycled aggregate to the composite modifier is (95~99):(1~5).

4. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that, The mass ratio of 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).

5. The process for modifying recycled aggregate concrete 3D printing wall materials according to claim 1, characterized in that, The water-reducing agent includes any one of lignin sulfonate water-reducing agents, aminosulfonate water-reducing agents, and polycarboxylate water-reducing agents.

6. 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 waterborne polyamide wax, hydroxyethyl cellulose, and xanthan gum.

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

8. 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-reducing agent, thixotropic agent and retarder is (50~70):(20~35):(8~15):(0.5~1.5):(0.2~0.8):(0.1~0.3).

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

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