A dual-channel 3D printer and method for printing functionally graded concrete structures

Abstract

The present invention relates to a dual-channel 3D printer and a method for printing a functional gradient concrete structure. The dual-channel 3D printer includes: a feeding module, including a first filling chamber and a second filling chamber, the side walls of the first filling chamber and the second filling chamber are both provided with a concrete mixture inlet, and the concrete mixture inlet is connected to a concrete feeding pump; a mixing module, including a mixing chamber and a mixing unit; an extrusion module, including a print head and an extrusion unit; a robotic arm module, the robotic arm module is used to achieve three-dimensional movement of the 3D printer; the feeding module, the mixing module, and the extrusion module are arranged in sequence along the vertical direction and are all placed at the end of the robotic arm module; and a control module, the control module is respectively communicated with the feeding module, the mixing module, the extrusion module, and the robotic arm module. Compared with the existing technology, the present invention gives full play to the performance advantages of different building materials, improves the functionality and practicality of the building structure, and the construction process of the invention has a high degree of automation.

Description

Technical Field

[0001] The present invention relates to the technical field of building 3D printing and construction solid waste resource utilization, and in particular to a dual-channel 3D printer and a method for printing a functional gradient concrete structure. Background Art

[0002] With the advancement of society and technology, intelligent construction has become an inevitable trend in the future of the construction industry. 3D-printed concrete technology, with its high degree of automation, extensive design freedom, and formwork-free construction, presents unprecedented opportunities for development. In recent years, with in-depth research into the printability, mechanical properties, and structural reinforcement and toughening methods of 3D-printed concrete materials, the technology has been successfully applied in fields such as urban infrastructure and landscape architecture.

[0003] However, as we all know, building structures must not only meet structural safety requirements but also consider practicality. Practicality here includes structural advantages beyond basic mechanical properties, such as cost-effectiveness, functionality, and environmental friendliness. From a structural design perspective, building structures must be strong enough to withstand the maximum stresses experienced during their service life, which are typically concentrated in specific areas. However, traditional cast concrete is made from homogeneous materials, wasting most of the material's performance in areas with lower mechanical performance requirements, resulting in low cost-effectiveness. Furthermore, structures made from a single material are also limited in functionality and environmental friendliness by the material itself.

[0004] In this context, inspired by natural structures such as bone and bamboo, functional gradient design has been introduced into the field of architectural concrete structures. Functionally gradient concrete can optimize its material distribution based on the stress distribution of the structure, fully utilizing the material's advantages to achieve a lightweight and high-strength structure. However, the construction of gradient concrete structures using current construction technology still presents complex and tedious construction issues, making it difficult to carry out refined and automated gradient concrete structure construction. 3D printing concrete technology has significant advantages over traditional construction technology in terms of construction refinement and automation. Therefore, how to use 3D printing concrete technology to construct functionally gradient concrete structures is a key issue that needs to be addressed urgently and has a real need. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the prior art by providing a dual-channel 3D printer and method for printing functionally graded concrete structures. This approach aims to improve the current state of 3D-printed concrete structures, which suffer from low automation levels and a struggle to balance mechanical properties with structural functionality. Furthermore, the 3D-printed functionally graded concrete structures utilize recycled sand, facilitating the resourceful reuse of construction waste and offering significant environmental and economic benefits.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a dual-channel 3D printer, comprising:

[0008] The feeding module includes a first filling chamber and a second filling chamber. The side walls of the first filling chamber and the second filling chamber are both provided with concrete mixture inlets, which are connected to the concrete feeding pump; the tops of the first filling chamber and the second filling chamber are both provided with pressing pistons, and the bottoms of the first filling chamber and the second filling chamber are provided with control valves between the mixing chamber and the bottom; wherein the control valve is composed of two independent valves a and b, which respectively control the connection between the first filling chamber and the second filling chamber and the mixing chamber.

[0009] The stirring module includes a stirring chamber and a stirring unit. The top of the stirring chamber is connected to both filling chambers, with a control valve serving as a boundary between the filling chambers. The bottom of the stirring chamber is connected to the print head. The stirring unit includes a stirring rod and a plurality of first rotating blades.

[0010] An extrusion module includes a print head and an extrusion unit, wherein the top of the print head is connected to the stirring chamber, and the extrusion unit includes an extrusion rod and a plurality of second rotating blades;

[0011] The robotic arm module is used to achieve three-dimensional movement of the 3D printer. The robotic arm module includes connecting rods and joints and is driven by hydraulic drive. The feeding module, stirring module and extrusion module are arranged in sequence along the vertical direction and are all placed at the end of the robotic arm module.

[0012] The control module includes an electronic computer and a motor. The control module is respectively connected to the feeding module, the stirring module, the extrusion module and the mechanical arm module for communication.

[0013] The present invention proposes a modification of the existing 3D printer. By controlling the valve to separate the feeding system from the mixing system, the number of filling chambers is increased, and by mixing different materials in multiple proportions, multi-material printing and gradient printing of concrete can be achieved, thereby enhancing the functionality of 3D printed concrete structures.

[0014] The stirring rod and extrusion rod of the dual-channel 3D printer are independent of each other and can be controlled separately.

[0015] Furthermore, a plurality of first rotating blades are evenly distributed along the length direction and the rotation direction of the stirring rod, and the length of the stirring rod is consistent with the length of the stirring chamber; a plurality of second rotating blades are evenly distributed along the length direction and the rotation direction of the stirring rod, and the length of the extrusion rod is half of the length of the print nozzle, and is located at the upper part of the print nozzle.

[0016] Furthermore, the top of the printing nozzle is connected to the stirring chamber by bolts and can be disassembled and replaced.

[0017] Furthermore, the dual-channel 3D printer is capable of recognizing and running G-code codes.

[0018] Furthermore, the lengths of the first rotating blade and the second rotating blade of the dual-channel 3D printer are close to the radius of the corresponding chamber outer wall, ensuring sufficient stirring.

[0019] The present invention also provides a method for printing a functionally gradient concrete structure, comprising the following steps:

[0020] S1: Weigh cement, regenerated sand, water, cellulose, sodium gluconate, and nanoclay in appropriate proportions, mix them in proportion, and stir until uniform to obtain mixture 1; weigh cement, fine sand, fiber, water, cellulose, sodium gluconate, and nanoclay in appropriate proportions, mix them in proportion, and stir until uniform to obtain mixture 2;

[0021] S2: Add an appropriate amount of water reducer to mixture 1 and mixture 2 respectively and stir until uniform, thereby obtaining reclaimed sand-based and fiber-based printable concrete mixtures respectively;

[0022] S3: The reclaimed sand-based printable concrete mixture and the fiber-based printable concrete mixture are respectively delivered to the first filling chamber and the second filling chamber of the dual-pipe 3D printer through a concrete feed pump;

[0023] S4: starting the dual-channel 3D printer to print, and during the printing process, extruding concrete strips with gradient changes in recycled sand content and fiber content;

[0024] S5: During the printing process, the dual-channel 3D printer is continuously fed with materials, and attention is paid to the printable window of the supplied concrete mixture to ensure that the printed concrete strips are coherent and consistent; the dual-channel 3D printer continuously prints according to the preset 3D printing code to obtain a 3D printed functional gradient structure.

[0025] Furthermore, in S4, the pressing pistons at the top of the first filling chamber and the control valves at the bottom of the second filling chamber work in coordination to press the two concrete mixtures into the mixing chamber at different rates for mixing.

[0026] Furthermore, the filling chamber should be filled in time after each grouting is completed in S4 to ensure that the filling chamber has sufficient mixing material when the next grouting is pressed, so as to ensure the continuity of the printing process and the printing quality.

[0027] Furthermore, in S2, the printable concrete mixture based on reclaimed sand comprises the following components in parts by weight:

[0028] 1000 parts of cement, 1000 parts of regenerated sand, 420 parts of water, 1.28 parts of cellulose, 0.8 parts of water reducer, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay.

[0029] Furthermore, in S2, the fiber-based printable concrete mixture comprises the following components in parts by weight:

[0030] 1000 parts of cement, 1000 parts of fine sand, 40 parts of fiber, 300 parts of water, 1.28 parts of cellulose, 1.2 parts of water reducer, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay.

[0031] Preferably, the cement is ordinary Portland cement, grade 425;

[0032] Preferably, the fiber is polyethylene fiber with a length of 12 mm;

[0033] Preferably, the particle size of the regenerated sand is less than or equal to 1.18 mm;

[0034] Preferably, the fine sand is river sand with a particle size of 0.15 mm to 1.18 mm;

[0035] Preferably, the water reducer is a polycarboxylic acid high performance water reducer with a water reduction rate of 15% to 20%;

[0036] Preferably, the cellulose is hydroxypropyl methylcellulose;

[0037] Preferably, the water is tap water.

[0038] The fluidity of the 3D printed concrete mixture obtained in S2 was measured using the jumping table test specified in the GB / T 2419-2005 "Determination of fluidity of cement mortar" standard, and its expansion diameter was 80-120 mm.

[0039] The 3D printed functional gradient structure obtained by S5 has both good mechanical properties and practical functions, including sound insulation and heat insulation, energy saving and environmental protection, light weight and high strength.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] The present invention improves the structural form of a building 3D printer, upgrading the 3D printer from a single-material printing mode to a multi-material printing mode, thereby increasing the printing freedom of building 3D printing technology; the concrete structure constructed using the 3D printing concrete structure preparation method based on functional gradient design described in the present invention has more advantages in achieving structure-function integration than the existing technology; based on the construction idea of ​​printing suitable materials in suitable locations, this method can give full play to the performance advantages of different building materials and improve the functionality and practicality of the building structure; the construction process of the invention has a high degree of automation, which conforms to the intelligent characteristics of building 3D printing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of a dual-channel 3D printer;

[0043] Figure 2 Schematic diagram of the wall panel structure dimensions in Example 1;

[0044] Figure 3 This is a schematic diagram of the wall panel gradient design in Example 1;

[0045] Figure 4 This is a schematic diagram of the wall panel gradient design in Example 2;

[0046] Figure 5 Schematic diagram of beam structure dimensions in Example 3;

[0047] Figure 6 Schematic diagram of the beam structure gradient design in Example 3.

[0048] Reference numerals: 1 - first filling chamber; 2 - second filling chamber; 3 - concrete mixture inlet; 4 - control valve; 5 - mixing chamber; 6 - robotic arm module. DETAILED DESCRIPTION

[0049] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Component models, material names, connection structures, control methods, algorithms, and other features not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0050] Example 1

[0051] The present invention provides a dual-channel 3D printer, such as Figure 1 As shown, including:

[0052] The feeding module includes a first filling chamber 1 and a second filling chamber 2. A concrete mixture inlet 3 is provided on the side wall of the first filling chamber 1 and the second filling chamber 2, and the concrete mixture inlet 3 is connected to the concrete feeding pump; a pressing piston is provided on the top of the first filling chamber 1 and the second filling chamber 2, and a control valve 4 is provided between the bottom of the first filling chamber 1 and the second filling chamber 2 and the mixing chamber; wherein the control valve 4 is composed of two independent valves a and b, which respectively control the connection between the first filling chamber 1 and the second filling chamber 2 and the mixing chamber 5.

[0053] The stirring module includes a stirring chamber 5 and a stirring unit. The top of the stirring chamber is connected to both filling chambers, and the different filling chambers are separated by a control valve 4. The bottom of the stirring chamber 5 is connected to the print head. The stirring unit includes a stirring rod and a plurality of first rotating blades.

[0054] An extrusion module includes a print head and an extrusion unit, wherein the top of the print head is connected to the stirring chamber 5, and the extrusion unit includes an extrusion rod and a plurality of second rotating blades;

[0055] The robotic arm module 6 is used to achieve three-dimensional movement of the 3D printer. The robotic arm module 6 includes connecting rods and joints and is driven by hydraulic drive. The feeding module, stirring module, and extrusion module are arranged in sequence in a vertical direction and are all placed at the end of the robotic arm module 6.

[0056] The control module includes an electronic computer and a motor. The control module is respectively connected to the feeding module, the stirring module, the extrusion module, and the robotic arm module 6 in communication.

[0057] This embodiment also provides a method for printing a functionally gradient concrete structure to prepare a functionally gradient concrete wall panel.

[0058] like Figure 2 、 Figure 3 As shown, the center of the wall in the thickness direction is the main insulation layer, and the two sides in the thickness direction are the main load-bearing layers. The replacement rate of recycled fine aggregate decreases from the center to the two ends, which are 100% replacement rate, 50% replacement rate, and 0% replacement rate, respectively, while the fiber content increases from the center to the two ends, which are 0% content, 1% content, and 2% content, respectively. The size of the wall panel printed in this embodiment is 1480mm×1470mm×180mm, and the cross-sectional size of a single concrete strip printed by the selected printing nozzle is 30mm×15mm.

[0059] The following steps are involved:

[0060] S1: Writing the Printing Code: First, model the 3D-printed functionally gradient wallboard using AutoCAD software. This involves drawing a rectangular parallelepiped measuring 1480mm × 1470mm × 180mm, then dividing the rectangular parallelepiped into 30mm × 15mm strips. Based on the wallboard model, a single-layer printing route is designed, and then layers are stacked to create the overall wallboard printing route. Considering the potential for collapse when printing the wallboard vertically, this embodiment defines the printing route along the wall thickness as the height direction during printing. The model dimensions are expressed in a Cartesian coordinate system as follows: x = 1480mm, y = 1470mm, z = 180mm. Material composition information for different regions is then incorporated into the printing route based on the wallboard's gradient design. Based on this information, G-code is then written in a txt file.

[0061] S2: Preparation of 3D printing concrete mixture: Weigh 1000 parts of 425 ordinary Portland cement, 1000 parts of regenerated sand, 420 parts of water, 1.28 parts of cellulose, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay, pour them into a 50L concrete mixer and stir for 5 minutes, then pour 0.8 parts of water reducer into the concrete mixer and stir for 5 minutes to obtain a printable concrete mixture with a regenerated sand replacement rate of 100%; similarly, weigh 1000 parts of 425 ordinary Portland cement, 1000 parts of fine sand, 40 parts of fiber, 300 parts of water, 1.28 parts of cellulose, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay, pour them into a 50L concrete mixer and stir for 5 minutes, then pour 1.2 parts of water reducer into the concrete mixer and stir for 5 minutes to obtain a printable concrete mixture with a fiber content of 2%.

[0062] S3: Printing functional gradient wall panels: The printable concrete mixture with a recycled sand replacement rate of 100% and the printable concrete mixture with a fiber content of 2% are respectively delivered to the first filling chamber (1) and the second filling chamber (2) of the dual-pipe 3D printer through a concrete feed pump; the initial position of the printing nozzle is adjusted through the control module, and then the G-code written in S1 is run on the control computer of the 3D printer to start printing; during the printing process, attention is paid to ensuring that the concrete mixture in the filling chamber is sufficient to ensure that the quality of the concrete strips is consistent and continuous during the printing process.

[0063] S4: Functionally graded wall panel curing: The printed structure is cured at room temperature for 28 days to obtain a 3D printed functionally graded wall panel structure.

[0064] The compressive strength of the 3D-printed functionally gradient wall panel structure was tested with reference to the standard "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019), and its longitudinal compressive strength was measured to be 28.62 MPa. The thermal conductivity of the 3D-printed functionally gradient wall panel structure was measured using the steady-state hot plate method with reference to the standard "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials - Guarded Hot Plate Method" (GB / T 10294-2008), and its thermal conductivity was measured to be 0.62 W / (m·K).

[0065] Example 2

[0066] The present invention provides a dual-channel 3D printer, comprising:

[0067] The feeding module includes a first filling chamber 1 and a second filling chamber 2. A concrete mixture inlet 3 is provided on the side wall of the first filling chamber 1 and the second filling chamber 2, and the concrete mixture inlet 3 is connected to the concrete feeding pump; a pressing piston is provided on the top of the first filling chamber 1 and the second filling chamber 2, and a control valve 4 is provided between the bottom of the first filling chamber 1 and the second filling chamber 2 and the mixing chamber; wherein the control valve 4 is composed of two independent valves a and b, which respectively control the connection between the first filling chamber 1 and the second filling chamber 2 and the mixing chamber 5.

[0068] The stirring module includes a stirring chamber 5 and a stirring unit. The top of the stirring chamber is connected to both filling chambers, and the different filling chambers are separated by a control valve 4. The bottom of the stirring chamber 5 is connected to the print head. The stirring unit includes a stirring rod and a plurality of first rotating blades.

[0069] An extrusion module includes a print head and an extrusion unit, wherein the top of the print head is connected to the stirring chamber 5, and the extrusion unit includes an extrusion rod and a plurality of second rotating blades;

[0070] The robotic arm module 6 is used to achieve three-dimensional movement of the 3D printer. The robotic arm module 6 includes connecting rods and joints and is driven by hydraulic drive. The feeding module, stirring module, and extrusion module are arranged in sequence in a vertical direction and are all placed at the end of the robotic arm module 6.

[0071] The control module includes an electronic computer and a motor. The control module is respectively connected to the feeding module, the stirring module, the extrusion module, and the robotic arm module 6 in communication.

[0072] This embodiment also provides a method for printing a functionally gradient concrete structure to prepare a functionally gradient concrete wall panel.

[0073] like Figure 4As shown, the wall panel gradient design is as follows: with one side of the wall thickness as the primary insulation layer and the other side as the primary load-bearing layer, the recycled fine aggregate replacement rate increases from one end to the other, reaching 0%, 20%, 40%, 60%, 80%, and 100%, respectively. The fiber content decreases from one end to the other, reaching 2%, 1.6%, 1.2%, 0.8%, 0.4%, and 0%, respectively. Aside from the gradient design, this embodiment is identical to Example 1 in all other parameters, including the printed wall panel size, strip size, and printing steps.

[0074] The compressive strength of the 3D-printed functionally gradient wall panel structure was tested with reference to the standard "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019), and its longitudinal compressive strength was measured to be 27.43 MPa. The thermal conductivity of the 3D-printed functionally gradient wall panel structure was measured using the steady-state hot plate method with reference to the standard "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials - Guarded Hot Plate Method" (GB / T 10294-2008), and its thermal conductivity was measured to be 0.54 W / (m·K).

[0075] Example 3

[0076] The present invention provides a dual-channel 3D printer, comprising:

[0077] The feeding module includes a first filling chamber 1 and a second filling chamber 2. A concrete mixture inlet 3 is provided on the side wall of the first filling chamber 1 and the second filling chamber 2, and the concrete mixture inlet 3 is connected to the concrete feeding pump; a pressing piston is provided on the top of the first filling chamber 1 and the second filling chamber 2, and a control valve 4 is provided between the bottom of the first filling chamber 1 and the second filling chamber 2 and the mixing chamber; wherein the control valve 4 is composed of two independent valves a and b, which respectively control the connection between the first filling chamber 1 and the second filling chamber 2 and the mixing chamber 5.

[0078] The stirring module includes a stirring chamber 5 and a stirring unit. The top of the stirring chamber is connected to both filling chambers, and the different filling chambers are separated by a control valve 4. The bottom of the stirring chamber 5 is connected to the print head. The stirring unit includes a stirring rod and a plurality of first rotating blades.

[0079] An extrusion module includes a print head and an extrusion unit, wherein the top of the print head is connected to the stirring chamber 5, and the extrusion unit includes an extrusion rod and a plurality of second rotating blades;

[0080] The robotic arm module 6 is used to achieve three-dimensional movement of the 3D printer. The robotic arm module 6 includes connecting rods and joints and is driven by hydraulic drive. The feeding module, stirring module, and extrusion module are arranged in sequence in a vertical direction and are all placed at the end of the robotic arm module 6.

[0081] The control module includes an electronic computer and a motor. The control module is respectively connected to the feeding module, the stirring module, the extrusion module, and the robotic arm module 6 in communication.

[0082] like Figure 5 、 Figure 6 As shown, this embodiment also provides a method for printing a functional gradient concrete structure to prepare a functional gradient concrete beam structure. The size of the beam structure is 400mm×90mm×90mm, and the cross-sectional size of a single concrete strip printed by the selected printing nozzle is 15mm×15mm. The gradient design is as follows: the fiber content decreases from the bottom to the top of the beam structure, which are 2%, 1.6%, 1.2%, 0.8%, 0.4%, and 0% respectively. The replacement rate of regenerated sand increases from the bottom to the top of the beam structure, which are 0% replacement rate, 20% replacement rate, 40% replacement rate, 60% replacement rate, 80% replacement rate, and 100% replacement rate respectively. The printing steps of this embodiment are the same as those of Example 1.

[0083] The flexural strength of the 3D printed functionally graded beam structure was tested with reference to the standard "Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019), and the flexural strength was measured to be 6.12 MPa.

[0084] Comparative Example 1

[0085] This embodiment uses a 3D printing method for preparing functional gradient enclosure structures to prepare concrete wall panels. The wall panels have no gradient design and are homogeneous materials. The recycled fine aggregate replacement rate of the homogeneous material is 50%, and the fiber content is 1%. Except for the gradient design, the other parameters of this embodiment, such as the printed wall panel size, strip size, and printing steps, are the same as those in Example 1.

[0086] The compressive strength of the 3D-printed functionally gradient wall panel structure was tested with reference to the standard "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019), and its longitudinal compressive strength was measured to be 31.34 MPa. The thermal conductivity of the 3D-printed functionally gradient wall panel structure was measured using the steady-state hot plate method with reference to the standard "Determination of Steady-State Thermal Resistance and Related Properties of Insulating Materials - Guarded Hot Plate Method" (GB / T 10294-2008), and its thermal conductivity was measured to be 0.92 W / (m·K).

[0087] Comparative Example 2

[0088] This example uses a 3D-printed concrete structure fabrication method based on functional gradient design to produce a concrete beam structure. The beam structure has no gradient design and is made of a homogeneous material with a 50% recycled fine aggregate replacement ratio and a 1% fiber content. Aside from the gradient design, this example is identical to Example 3 in all other parameters, including beam structure dimensions, print strip size, and printing steps.

[0089] The flexural strength of the 3D printed functional gradient beam structure was tested with reference to the standard "Standard for Test Methods for Physical and Mechanical Properties of Concrete" (GB / T50081-2019), and its flexural strength was measured to be 4.32 MPa.

[0090] Components not described in detail in this embodiment are all existing components that can be purchased through public channels.

[0091] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A dual-channel 3D printer, characterized in that: include: A feeding module comprises a first filling chamber (1) and a second filling chamber (2), wherein a concrete mixture inlet (3) is provided on the side wall of the first filling chamber (1) and the second filling chamber (2), and the concrete mixture inlet (3) is connected to a concrete feeding pump; a pressing piston is provided on the top of the first filling chamber (1) and the second filling chamber (2), and a control valve (4) is provided between the bottom of the first filling chamber (1) and the second filling chamber (2) and the mixing chamber; wherein the control valve (4) is composed of two independent valves (a) and (b), which respectively control the connection between the first filling chamber (1) and the second filling chamber (2) and the mixing chamber (5); The stirring module includes a stirring chamber (5) and a stirring unit. The top of the stirring chamber is connected to two filling chambers at the same time. The control valve (4) is used as a boundary between different filling chambers. The bottom of the stirring chamber (5) is connected to the printing nozzle. The stirring unit includes a stirring rod and a plurality of first rotating blades. An extrusion module comprises a printing nozzle and an extrusion unit, wherein the top of the printing nozzle is connected to the stirring chamber (5), and the extrusion unit comprises an extrusion rod and a plurality of second rotating blades; A robotic arm module (6) is used to realize three-dimensional movement of the 3D printer. The robotic arm module (6) includes a connecting rod and a joint, and the driving mode is hydraulic drive. The feeding module, the stirring module and the extrusion module are arranged in sequence along the vertical direction and are all placed at the end of the robotic arm module (6); A control module, comprising an electronic computer and a motor, wherein the control module is respectively connected to the feeding module, the stirring module, the extrusion module, and the robotic arm module (6); The pressing pistons at the top of the first filling chamber (1) and the second filling chamber (2) and the control valves (4) at the bottom work in coordination to press the two concrete mixtures into the mixing chamber (5) at different rates for mixing and stirring; the dual-channel 3D printer is capable of recognizing and running G-code-format codes, and the dual-channel 3D printer continuously prints according to the preset 3D printing codes to obtain a 3D printed functional gradient structure.

2. A dual-channel 3D printer according to claim 1, characterized in that: A plurality of first rotating blades are evenly distributed along the length direction and the rotation direction of the stirring rod, and the length of the stirring rod is consistent with the length of the stirring chamber (5); a plurality of second rotating blades are evenly distributed along the length direction and the rotation direction of the stirring rod, and the length of the extrusion rod is half of the length of the printing nozzle, and is located at the upper part of the printing nozzle.

3. A dual-channel 3D printer according to claim 1, characterized in that: The top of the printing nozzle is connected to the stirring chamber (5) by bolts and can be disassembled and replaced.

4. A dual-channel 3D printer according to claim 1, characterized in that: The lengths of the first rotating blade and the second rotating blade of the dual-channel 3D printer are close to the radius of the corresponding chamber outer wall, ensuring sufficient stirring.

5. A method for printing a functionally graded concrete structure, characterized in that: The following steps are involved: S1: Weigh cement, regenerated sand, water, cellulose, sodium gluconate, and nanoclay, mix them in proportion, and stir until uniform to obtain mixture 1; weigh cement, fine sand, fiber, water, cellulose, sodium gluconate, and nanoclay, mix them in proportion, and stir until uniform to obtain mixture 2; S2: adding a water reducer to mixture 1 and mixture 2 respectively and stirring until uniform, thereby obtaining a reclaimed sand-based and a fiber-based printable concrete mixture respectively; S3: transporting the regenerated sand-based printable concrete mixture and the fiber-based printable concrete mixture respectively into the first filling chamber (1) and the second filling chamber (2) of the dual-channel 3D printer according to any one of claims 1 to 4 through a concrete feed pump; S4: starting the dual-channel 3D printer according to any one of claims 1 to 4 to perform printing, and during the printing process, extruding concrete strips having a gradient of regenerated sand content and fiber content; S5: The dual-channel 3D printer continuously prints according to the preset 3D printing code to obtain a 3D printed functional gradient structure.

6. The method for printing a functionally graded concrete structure according to claim 5, characterized in that: In S4, the filling chamber should be filled in time after each grouting is completed to ensure that the filling chamber has sufficient mixing material when the next grouting is pressed, so as to ensure the continuity of the printing process and the printing quality.

7. The method for printing a functionally graded concrete structure according to claim 5, characterized in that: In S2, the printable concrete mixture based on reclaimed sand comprises the following components in parts by weight: 1000 parts of cement, 1000 parts of regenerated sand, 420 parts of water, 1.28 parts of cellulose, 0.8 parts of water reducer, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay.

8. The method for printing a functionally graded concrete structure according to claim 5, wherein: In S2, the fiber-based printable concrete mixture comprises the following components in parts by weight: 1000 parts of cement, 1000 parts of fine sand, 40 parts of fiber, 300 parts of water, 1.28 parts of cellulose, 1.2 parts of water reducer, 0.7 parts of sodium gluconate, and 6.4 parts of nanoclay.

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