3D printing three-dimensional directional self-resetting fiber concrete, 3D printing device and preparation method of 3D printing three-dimensional directional self-resetting fiber concrete

Abstract

The invention discloses 3D printing three-dimensional directional self-resetting fiber concrete, a 3D printing device and a preparation method of the 3D printing three-dimensional directional self-resetting fiber concrete. The 3D printing three-dimensional directional self-resetting fiber concrete is prepared from 12 parts by mass of Portland cement, 12 parts by mass of sand, 3-6 parts by mass of water, 0.024-0.036 part by mass of a water reducing agent, SMA metal fibers with the volume fraction being 2%-3.5% of the weight of the Portland cement and a strong plasticizer with the doping amount being 1% of the mass fraction of the cement. The 3D printing three-dimensional directional self-resetting fiber concrete comprises a vertical fiber layer and a horizontal fiber layer. On the basis of the self-resetting fiber concrete, the 3D printing technology is used, SMA metal fibers with the corresponding length-diameter ratio and volume capacity are doped according to the printable performance of a cement-based material and the diameter of a printing nozzle, and the 3D printing self-resetting fiber concrete has good printable performance and mechanical performance; the practical engineering application of the 3D printing concrete is favorably promoted.

Description

Technical Field

[0001] The present invention relates to the field of concrete technology, and in particular to a 3D printed three-dimensional directional self-resetting fiber concrete, a 3D printing device and a preparation method thereof. Background Art

[0002] With the rapid development of the construction industry, concrete, as one of the main building materials, is facing increasing demands for performance and quality. Among the numerous concrete research topics, self-righting concrete has become a hot topic in recent years due to its unique properties and advantages. Self-righting concrete has excellent self-repair capabilities, automatically restoring its integrity after cracks or damage, thereby improving the durability and safety of concrete structures. Existing self-righting concrete is only proposed at the concrete structural level, which can cause significant impact on the structural joints during repair. The self-righting fiber concrete proposed in this invention provides a new solution for repairing damage to concrete structures. After cracks or damage occur, self-righting concrete can utilize its internal self-repair mechanism to automatically repair the damaged area and restore structural integrity. The emergence of self-righting concrete not only improves the durability and safety of concrete structures but also provides a new direction for the sustainable development of the construction industry. Incorporating fibers into ordinary concrete can effectively bridge cracks, reduce the risk of cracking, and significantly improve its mechanical properties. However, during use, the stress direction experienced by concrete structures is constant, and SMA metal fibers that are not parallel or perpendicular to the stress direction cannot play a reinforcing role, resulting in fiber waste. In order to improve the reinforcement efficiency of the fiber, the method of regulating the fiber direction is often adopted to make it parallel to the stress direction, thereby achieving fiber orientation. By arranging SMA metal fibers in a directional manner, the strength and toughness of concrete can be fully improved, and the overall performance of concrete can be improved. Oriented fiber concrete can have better mechanical properties such as tensile strength and bending resistance, and can bear loads more evenly when under stress. The current method of using 3D printing technology to cast concrete buildings is efficient and convenient, but when casting using ordinary 3D printing methods, the SMA metal fibers inside the extruded material are randomly distributed, resulting in low fiber reinforcement efficiency, which restricts the improvement of structural strength. Summary of the Invention

[0003] The purpose of the present invention is to provide a 3D printed three-dimensional directional self-resetting fiber concrete to address the technical defects in the prior art.

[0004] Another object of the present invention is to provide a 3D printing device for 3D printing three-dimensional directional self-resetting fiber concrete.

[0005] Another object of the present invention is to provide a method for preparing the 3D printed three-dimensional oriented self-centering fiber concrete.

[0006] The technical solution adopted to achieve the object of the present invention is as follows:

[0007] A 3D printed three-dimensional oriented self-centering fiber concrete includes 12 parts by mass of portland cement, 12 parts by mass of sand, 3 - 6 parts by mass of water, 0.024 - 0.036 parts by mass of water reducing agent, SMA metal fibers with a volume fraction of 2% - 3.5% of the weight of the portland cement, and a superplasticizer with a dosage of 1% of the cement mass fraction;

[0008] The 3D printed three-dimensional oriented self-centering fiber concrete contains a vertical fiber layer and a horizontal fiber layer.

[0009] In the above technical solution, the preparation method of the SMA metal fibers is as follows: subject the SMA bars to stress induction to generate a 2% pre-strain; use the wire cutting method to make the SMA bars into metal fibers with a required length of 20 - 60 mm and a diameter of 0.13 - 0.6 mm.

[0010] In the above technical solution, the SMA bars are SMA plain round bars, SMA ribbed bars or SMA strips; the shapes of the SMA fibers are straight SMA fibers, ribbed SMA fibers, corrugated SMA fibers or hooked SMA fibers;

[0011] The SMA metal fibers are iron-based shape memory alloys, nickel-titanium shape memory alloys or copper-based shape memory alloys.

[0012] On the other hand, the present invention provides a 3D printing device for preparing the 3D printed three-dimensional oriented self-centering fiber concrete, including a control unit, a universal walking mechanism, a material conveying unit and an SMA metal fiber orientation unit. The SMA metal fiber orientation unit is fixedly installed at the output end of the material conveying unit for fiber orientation of the material output by the material conveying unit;

[0013] The control unit is installed on the universal walking mechanism. The control unit is electrically connected to the universal walking mechanism and the SMA metal fiber orientation unit respectively, and is used to control the spatial position and printing speed of the material conveying unit and the direction of the fibers;

[0014] The material conveying unit includes a feed inlet and a material transmission channel. One end of the feed inlet is externally connected to a feeding system, and the other end of the feed inlet is connected to one end of the material transmission channel;

[0015] The SMA metal fiber orientation unit includes a fiber horizontal orientation unit and a fiber vertical orientation unit. The fiber horizontal orientation unit is responsible for horizontal orientation, and the fiber vertical orientation unit is responsible for vertical orientation. The feed port includes a vertical orientation feed port and a horizontal orientation feed port. The material conveying channel includes a vertical orientation material conveying channel and a horizontal orientation material conveying channel. The vertical orientation feed port is connected to the fiber vertical orientation unit through the vertical orientation material conveying channel, and the horizontal orientation feed port is connected to the fiber horizontal orientation unit through the horizontal orientation material conveying channel. The fiber horizontal orientation unit is connected with a horizontal orientation nozzle, and the fiber vertical orientation unit is connected with a vertical orientation nozzle. Preferably, the vertical material conveying channel is made of non-metallic material.

[0016] In the above technical solution, the fiber horizontal orientation unit includes a rotating sleeve, a horizontal oscillator and a permanent magnet. The rotating sleeve is sleeved on the outer wall of the other end of the horizontal orientation material transmission channel. The rotating sleeve can rotate relative to the horizontal orientation material transmission channel. There are multiple pairs of permanent magnets, and each pair of permanent magnets is fixedly arranged opposite to each other in the radial direction of the outer wall of the rotating sleeve. There is at least one pair of horizontal oscillators, and each pair of horizontal orientation exciters is fixedly arranged opposite to each other on the outer wall of the rotating sleeve. And each pair of permanent magnets and each pair of horizontal orientation exciters are arranged vertically in the radial direction and spaced axially on the outer wall of the rotating sleeve. Preferably, the rotating sleeve is made of non-metallic material.

[0017] In the above technical solution, the fiber vertical orientation unit includes a vertical orientation sleeve, a vertical oscillator and a coil. The vertical orientation sleeve is sleeved on the outer wall of the other end of the vertical orientation material transmission channel. There is at least one pair of vertical oscillators, and the vertical orientation exciters are fixedly arranged vertically opposite to each other on the upper and lower surfaces of the vertical orientation sleeve. The coil is wound around the outer wall of the vertical orientation sleeve. Preferably, the vertical orientation sleeve is made of non-metallic material.

[0018] On the other hand, the present invention provides a preparation method of 3D printing three-dimensional orientation self-resetting fiber concrete based on the above 3D printing device, including the following steps:

[0019] Step 1, obtain the three-dimensional model of the printed part, and plan the printing path in the control unit to make the printing path meet the principles of high printing efficiency, material saving and conforming to the structural stress characteristics. Then import the printing path information into the control system. The control panel is internally provided with a position locator to control the movement trajectory of the universal walking mechanism, and further control the spatial position and printing speed of the horizontal orientation nozzle and the vertical orientation nozzle during the printing process, and synchronously debug the rotation speed of the rotating sleeve and the magnitude of the current of the energized coil;

[0020] Step 2: According to the actual load-bearing performance and durability requirements of the structure, calculate the proportions of raw materials such as water, Portland cement, sand, SMA metal fibers, and water reducer. Weigh the raw materials according to the proportions and stir the raw materials evenly to prepare a ready-mixed mortar mixture. The ready-mixed mortar mixture enters the material transmission channel from the feed inlet. At this time, the SMA metal fibers in the ready-mixed mortar mixture in the material transmission channel are randomly distributed in a disorderly manner;

[0021] Step 3: Control the vertical orientation unit to vertically orient the SMA metal fibers in the ready-mixed mortar mixture respectively, and control the horizontal orientation unit to horizontally orient the SMA metal fibers in the ready-mixed mortar mixture;

[0022] Step 4: The oriented ready-mixed mortar mixture is extruded by the horizontal orientation nozzle and the vertical orientation nozzle to complete the printing;

[0023] Step 5: After waiting for the self-centering fiber concrete printed by 3D to reach final setting, perform high-temperature excitation on the self-centering fiber concrete, heat it to reach the austenite finish temperature, and generate a recovery stress.

[0024] In the above technical solution, the ready-mixed mortar mixture in Step 2 is prepared by the following method: First, dry-mix the sand and Portland cement, then add water and stir; then add SMA metal fibers and stir; then add water reducer and superplasticizer and stir to obtain the ready-mixed mortar mixture.

[0025] In the above technical solution, Step 3 further includes:

[0026] Step 3.1: After the power is turned on, the rotating sleeve rotates, and several pairs of permanent magnets rotate synchronously to form a rotating magnetic field. When the ready-mixed mortar mixture passes through the rotating sleeve, its rotating magnetic field will drive the SMA metal fibers in the ready-mixed mortar mixture to rotate to the horizontal direction. At the same time, each pair of horizontal orientation exciters adjusts the vibration frequency of the horizontal orientation exciter, the rotation speed of the rotating sleeve, and the fluidity of the ready-mixed mortar mixture again through the control unit. The horizontal orientation exciter generates high-frequency and micro-amplitude vibrations, and the vibrations cause the ready-mixed mortar mixture inside the rotating sleeve to liquefy and make the SMA metal fibers rotate, so that the SMA metal fibers are horizontally oriented;

[0027] Step 3.2, wind coils around the outer surface of the vertical orientation sleeve. After power is switched on, a vertical magnetic field is formed in the vertical orientation sleeve. The vertical magnetic field will drive the SMA metal fibers in the ready-mixed mortar mixture to rotate to the vertical direction. At the same time, each pair of the vertical orientation vibrators adjusts the vibration frequency of the vertical orientation vibrators, the rotation speed of the rotating sleeve, and the fluidity of the ready-mixed mortar mixture again through the control unit. The vertical orientation vibrators generate high-frequency and micro-amplitude vibrations, and the vibrations cause the ready-mixed mortar mixture inside the rotating sleeve to liquefy, enabling the SMA metal fibers to rotate, so that the SMA metal fibers are vertically oriented;

[0028] Preferably, the vibration frequencies of the horizontal orientation vibrators and the vertical orientation vibrators are 50 - 80 Hz, the rotation speed of the rotating sleeve is 100 - 150 r / min, and the current of the coil is 10 A.

[0029] In the above technical solution, step 4 further includes:

[0030] Step 4.1, conduct a preliminary experiment, and adjust the moving speeds of the horizontal orientation nozzle and the vertical orientation nozzle through the control unit so that the speeds of the ready-mixed mortar mixture extruded from the horizontal orientation nozzle and the vertical orientation nozzle meet the requirements of continuous printing performance;

[0031] Step 4.2, conduct a formal experiment, and start to prepare three-dimensional oriented SMA metal fiber concrete specimens through the control unit, the external feeding system, the universal walking mechanism, and the SMA metal fiber orientation unit.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] 1. The advantage of the 3D self-centering fiber concrete of the present invention is that the added SMA metal fiber is an innovative material with enhanced ductility, high strength and durability, reduced deformation, and minimized residual cracks. It shows better flexure and ductility during the process of preventing the development of microcracks and has the inherent property of self-healing. The present invention provides a new solution for the damage repair of concrete structures. After cracks or damage occur in the self-centering fiber concrete, it can utilize its internal self-healing mechanism to automatically repair the damaged part and restore the integrity of the structure. The emergence of self-centering fiber concrete not only improves the durability and safety of concrete structures, but also provides a new direction for the sustainable development of the construction industry. Based on the self-centering fiber concrete, using 3D printing technology, according to the printability of the cement-based material and the diameter of the printing nozzle, SMA metal fibers with corresponding aspect ratios and volume contents are incorporated, making the 3D printed self-centering fiber concrete have good printability and mechanical properties, which is conducive to promoting the practical engineering application of 3D printed concrete.

[0034] 2. The 3D printing device of the present invention can directly achieve horizontal orientation and vertical orientation of SMA fibers in the premixed mortar mixture.

[0035] 3. The self-centering fiber concrete member produced by the preparation method of the present invention conducts three-dimensional orientation of metal fibers in the premixed mortar mixture during the printing process, making the flexural strength and tensile strength of the printed concrete member higher, and effectively solving the problem of interlayer printing interface defects existing in three-dimensional printing, thereby prolonging the service life of the concrete member. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of a 3D printed three-dimensional fiber-oriented self-centering concrete test block;

[0037] Figure 2 Schematic diagram of SMA-Fe fiber;

[0038] Figure 3 Schematic structural diagram of the 3D printing device of the present invention;

[0039] Figure 4 For Figure 3 Partial enlarged schematic diagram at position A in

[0040] Figure 5 Schematic cross-sectional structural diagram of the rotating sleeve of the present invention;

[0041] Figure 6 Schematic cross-sectional structural diagram of the vertical orientation sleeve of the present invention.

[0042] In the figure: 1 - control unit, 2 - universal walking mechanism, 3a - fiber horizontal orientation unit, 3b - fiber vertical orientation unit, 4a - horizontal orientation feed port, 4b - vertical orientation feed port, 5a - horizontal orientation material transmission channel, 5b - vertical orientation material transmission channel, 6a - rotating sleeve, 6b - vertical orientation sleeve, 7a - horizontal orientation nozzle, 7b - vertical orientation nozzle, 8a - permanent magnet, 8b - coil, 9a - horizontal orientation vibrator, 9b - vertical orientation vibrator. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0044] Embodiment 1

[0045] A 3D printing device for preparing 3D printed three-dimensionally oriented self-centering fiber concrete, as Figures 3 - 6As shown in the figure, it includes a control unit 1, an omnidirectional walking mechanism 2, a material conveying unit, and an SMA metal fiber orientation unit. The SMA metal fiber orientation unit is fixedly installed at the output end of the material conveying unit and is used to orient the fibers of the material output by the material conveying unit.

[0046] The control unit 1 is installed on the omnidirectional walking mechanism 2. The control unit 1 is electrically connected to the omnidirectional walking mechanism 2 and the SMA metal fiber orientation unit respectively, and is used to control the spatial position and printing speed of the material conveying unit and the direction of the fibers.

[0047] The material conveying unit includes a feed inlet and a material transmission channel. One end of the feed inlet is externally connected to a feeding system, and the other end of the feed inlet is connected to one end of the material transmission channel.

[0048] The SMA metal fiber orientation unit includes a fiber horizontal orientation unit 3a and a fiber vertical orientation unit 3b. The fiber horizontal orientation unit 3a is responsible for horizontal orientation, and the fiber vertical orientation unit 3b is responsible for vertical orientation. The feed inlet includes a vertical orientation feed inlet 4b and a horizontal orientation feed inlet 4a. The material conveying channel includes a vertical orientation material conveying channel and a horizontal orientation material conveying channel. The vertical orientation feed inlet 4b is connected to the fiber vertical orientation unit 3b through the vertical orientation material conveying channel, and the horizontal orientation feed inlet 4a is connected to the fiber horizontal orientation unit 3a through the horizontal orientation material conveying channel. The fiber horizontal orientation unit 3a is connected with a horizontal orientation nozzle 7a, and the fiber vertical orientation unit 3b is connected with a vertical orientation nozzle 7b. Preferably, the vertical orientation material conveying channel and the horizontal orientation material conveying channel are made of non-metallic materials.

[0049] The fiber horizontal orientation unit 3a includes a rotating sleeve 6a, a horizontal oscillator, and a permanent magnet 8a. The rotating sleeve 6a is sleeved on the outer wall of the other end of the horizontal orientation material transmission channel 5a. The rotating sleeve 6a can rotate relative to the horizontal orientation material transmission channel 5a. A plurality of pairs of permanent magnets 8a are provided. Each pair of permanent magnets 8a is fixedly arranged opposite to each other in the radial direction of the outer wall of the rotating sleeve 6a. At least one pair of horizontal oscillators is provided. Each pair of horizontal orientation exciters 9a is fixedly arranged opposite to each other on the outer wall of the rotating sleeve 6a. And each pair of permanent magnets 8a and each pair of horizontal orientation exciters 9a are arranged perpendicular to each other in the radial direction and spaced apart axially on the outer wall of the rotating sleeve 6a. The rotating sleeve 6a is made of non-metallic material.

[0050] The fiber vertical orientation unit 3b includes a vertical orientation sleeve 6b, a vertical oscillator, and a coil 8b. The vertical orientation sleeve 6b is sleeved on the outer wall of the other end of the vertical orientation material transmission channel 5b. There is at least one pair of vertical oscillators. The vertical orientation exciters 9b are vertically fixed to the upper and lower surfaces of the vertical orientation sleeve 6b relatively. The coil 8b is wound around the outer wall of the vertical orientation sleeve 6b. Preferably, the vertical orientation sleeve 6b is made of a non-metallic material.

[0051] Example 2

[0052] Based on Example 1, a preparation method of 3D printed three-dimensional orientation self-resetting fiber concrete includes the following steps:

[0053] Step 1: Obtain the three-dimensional model of the printed part, and plan the printing path in the control unit 1 to make the printing path meet the principles of high printing efficiency, material saving, and conforming to the structural stress characteristics. Then import the printing path information into the control system. The control panel is built-in with a position locator to control the movement trajectory of the universal walking mechanism 2, and further control the spatial position and printing speed of the horizontal orientation nozzle 7a and the vertical orientation nozzle 7b during the printing process. Synchronously debug the rotation speed of the rotating sleeve 6a and the magnitude of the current of the energized coil 8b.

[0054] Step 2: Calculate the ratios of raw materials such as water, portland cement, sand, SMA metal fibers, and water reducer according to the actual load-bearing performance and durability requirements of the structure. Weigh the raw materials according to the ratios and stir the raw materials evenly to prepare a premixed mortar mixture. The premixed mortar mixture enters the material transmission channel from the feed inlet. At this time, the SMA metal fibers in the premixed mortar mixture in the material transmission channel are randomly distributed. Among them, the premixed mortar mixture is prepared by the following method: First, dry-mix the sand and portland cement, then add water and stir; then add the SMA metal fibers and stir; then add the water reducer and the strong plasticizer and stir to obtain the premixed mortar mixture.

[0055] Step 3: Control the vertical orientation unit to vertically orient the SMA metal fibers in the premixed mortar mixture respectively, and control the horizontal orientation unit to horizontally orient the SMA metal fibers in the premixed mortar mixture. Specifically, it includes:

[0056] Step 3.1: After the power is turned on, the rotating sleeve 6a rotates, and several pairs of permanent magnets 8a rotate synchronously to form a rotating magnetic field. When the premixed mortar mixture passes through the rotating sleeve 6a, the rotating magnetic field drives the SMA metal fibers in the premixed mortar mixture to rotate to the horizontal direction. At the same time, each pair of the horizontal orientation vibrators 9a adjusts the vibration frequency of the horizontal orientation vibrators 9a, the rotation speed of the rotating sleeve 6a, and the fluidity of the premixed mortar mixture again through the control unit 1. The horizontal orientation vibrators 9a generate high-frequency and micro-amplitude vibrations. The vibrations cause the premixed mortar mixture inside the rotating sleeve 6a to liquefy and the SMA metal fibers to rotate, so that the SMA metal fibers are horizontally oriented;

[0057] Step 3.2, The outer surface of the vertical orientation sleeve 6b is wound with a coil 8b. After the power is turned on, the vertical orientation sleeve 6b forms a vertical magnetic field, and its vertical magnetic field drives the SMA metal fibers in the premixed mortar mixture to rotate to the vertical direction. At the same time, each pair of the vertical orientation vibrators 9b adjusts the vibration frequency of the vertical orientation vibrators 9b, the rotation speed of the rotating sleeve 6a, and the fluidity of the premixed mortar mixture again through the control unit 1. The vertical orientation vibrators 9b generate high-frequency and micro-amplitude vibrations. The vibrations cause the premixed mortar mixture inside the rotating sleeve 6a to liquefy and the SMA metal fibers to rotate, so that the SMA metal fibers are vertically oriented; The vibration frequencies of the horizontal orientation vibrators 9a and the vertical orientation vibrators 9b are 80 Hz, the rotation speed of the rotating sleeve 6a is 150 r / min, and the current of the coil 8b is 10 A.

[0058] Step 4, The premixed mortar mixture after orientation is extruded by the horizontal orientation nozzle 7a and the vertical orientation nozzle 7b to complete printing. Specifically, it includes: Step 4.1, Conduct a preliminary experiment, set the moving speeds of the horizontal orientation nozzle 7a and the vertical orientation nozzle 7b to 50 mm / s, so that the speeds of the premixed mortar mixture extruded by the horizontal orientation nozzle 7a and the vertical orientation nozzle 7b meet the continuous printing performance requirements;

[0059] Step 4.2, Conduct a formal experiment. Through the control unit 1, start the external feeding system, the universal walking mechanism 2, and the SMA metal fiber orientation unit to output in layers, and complete the three-dimensional oriented SMA metal fiber concrete square plate component, increasing the bending and tensile strength of the component and reducing the interface defects caused by 3D printing.

[0060] Step 5, After waiting for the self-centering fiber concrete printed by 3D to reach final setting, heat the concrete to 160 °C by environmental excitation for high-temperature excitation, and heat it to reach the austenite completion temperature to generate recovery stress.

[0061] Example 3

[0062] Based on Embodiments 1-2, as Figures 1 - 2 shown, a 3D printed three-dimensional self-centering fiber concrete comprises 12 parts of ordinary Portland cement, 12 parts of sand, 6 parts of water, 0.028 part of water reducing agent, SMA metal fibers with a volume fraction of 2% of the weight of the cement, and a superplasticizer with a dosage of 1% of the weight of the cement. The SMA metal fibers with a diameter of 0.2 mm and a length of 13 mm are used as horizontal fibers, and the metal fibers with a diameter of 3.5 mm and a length of 35 mm are used as vertical fibers, with a total volume dosage of 2%, and the horizontal fibers and vertical fibers each account for 1% of the volume dosage. The SMA metal fibers added to the self-centering concrete are iron-based shape memory alloys (Fe-SMA). First, it is necessary to induce stress (pre-tension) on it using Fe-SMA plain round steel bars to generate a 2% pre-strain, and then cut the steel bars to make SMA metal fibers with a diameter of 0.2 mm and a length of 13 mm and a diameter of 3.5 mm and a length of 35 mm. Before cutting the steel wire, diamond-shaped pits are pressed on the steel wire with the pinch rolls for feeding the steel wire to increase the bonding strength between the fibers and the concrete. This concrete can be applied to important components such as nuclear power plant containments.

[0063] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A 3D printed three-dimensional oriented self-centering fiber concrete, characterized in that, It includes 12 parts by mass of portland cement, 12 parts by mass of sand, 3 - 6 parts by mass of water, 0.024 - 0.036 parts by mass of water reducer, SMA metal fibers with a volume fraction of 2% - 3.5% of the weight of the portland cement, and a superplasticizer with a dosage of 1% of the cement mass fraction; The 3D printed three - dimensional self - resetting fiber concrete contains a vertical fiber layer and a horizontal fiber layer.

2. The 3D printed three-dimensional self-centering fiber concrete according to claim 1, characterized in that, The preparation method of the SMA metal fibers is as follows: subject the SMA bars to stress induction to generate a 2% pre - strain; use the wire cutting method to make the SMA bars into metal fibers with a required length of 20 - 60 mm and a diameter of 0.13 - 0.6 mm.

3. The 3D printed three-dimensional self-centering fiber concrete according to claim 2, wherein The SMA bars are SMA plain round bars, SMA ribbed bars or SMA strips; the shapes of the SMA fibers are straight SMA fibers, ribbed SMA fibers, corrugated SMA fibers or hooked SMA fibers; The SMA metal fibers are iron - based shape memory alloys, nickel - titanium shape memory alloys or copper - based shape memory alloys.

4. A 3D printing device for preparing the 3D printed three-dimensional directionally self-centering fiber concrete according to any one of claims 1-3, characterized in that, It includes a control unit, an omnidirectional walking mechanism, a material conveying unit and an SMA metal fiber orientation unit. The SMA metal fiber orientation unit is fixedly installed at the output end of the material conveying unit and is used to orient the materials output by the material conveying unit; The control unit is installed on the omnidirectional walking mechanism. The control unit is electrically connected to the omnidirectional walking mechanism and the SMA metal fiber orientation unit respectively and is used to control the spatial position and printing speed of the material conveying unit and the direction of the fibers; The material conveying unit includes a feed inlet and a material transmission channel. One end of the feed inlet is externally connected to a feeding system, and the other end of the feed inlet is connected to one end of the material transmission channel; The SMA metal fiber orientation unit includes a fiber horizontal orientation unit and a fiber vertical orientation unit. The fiber horizontal orientation unit is responsible for horizontal orientation, and the fiber vertical orientation unit is responsible for vertical orientation. The feed inlet includes a vertical orientation feed inlet and a horizontal orientation feed inlet. The material transmission channel includes a vertical orientation material transmission channel and a horizontal orientation material transmission channel. The vertical orientation feed inlet is connected to the fiber vertical orientation unit through the vertical orientation material transmission channel, and the horizontal orientation feed inlet is connected to the fiber horizontal orientation unit through the horizontal orientation material transmission channel. The fiber horizontal orientation unit is connected with a horizontal orientation nozzle, and the fiber vertical orientation unit is connected with a vertical orientation nozzle. Preferably, the vertical material transmission channel is made of non - metal material.

5. The 3D printing device according to claim 4, characterized in that, The fiber horizontal orientation unit includes a rotating sleeve, a horizontal oscillator, and permanent magnets. The rotating sleeve is sleeved on the outer wall of the other end of the horizontal orientation material transmission channel. The rotating sleeve can rotate relative to the horizontal orientation material transmission channel. There are multiple pairs of permanent magnets, and each pair of permanent magnets is fixedly arranged opposite to each other in the radial direction on the outer wall of the rotating sleeve. There is at least one pair of horizontal oscillators, and each pair of horizontal orientation exciters is fixedly opposite to each other on the outer wall of the rotating sleeve. Moreover, each pair of permanent magnets and each pair of horizontal orientation exciters are arranged vertically in the radial direction and spaced axially on the outer wall of the rotating sleeve. Preferably, the rotating sleeve is made of a non-metallic material.

6. The 3D printing device according to claim 4, characterized in that, The fiber vertical orientation unit includes a vertical orientation sleeve, a vertical oscillator, and coils. The vertical orientation sleeve is sleeved on the outer wall of the other end of the vertical orientation material transmission channel. There is at least one pair of vertical oscillators, and the vertical orientation exciters are fixedly opposite to each other on the upper and lower surfaces of the vertical orientation sleeve. The coils are wound around the outer wall of the vertical orientation sleeve. Preferably, the vertical orientation sleeve is made of a non-metallic material.

7. A method for preparing 3D printed three-dimensional directionally self-resetting fiber concrete based on the 3D printing device according to any one of claims 4-6, characterized in that, It includes the following steps: Step 1: Obtain the three-dimensional model of the printed part, and plan the printing path in the control unit to make the printing path meet the principles of high printing efficiency, material saving, and conforming to the structural stress characteristics. Then import the printing path information into the control system. The control panel is built-in with a position locator to control the movement trajectory of the universal walking mechanism, and further control the spatial position and printing speed of the horizontal orientation nozzle and the vertical orientation nozzle during the printing process. Synchronously debug the rotation speed of the rotating sleeve and the magnitude of the current of the energized coil. Step 2: According to the actual load-bearing performance and durability requirements of the structure, calculate the ratios of raw materials such as water, Portland cement, sand, SMA metal fibers, and water reducer. Weigh the raw materials according to the ratios and stir the raw materials evenly to prepare a ready-mixed mortar mixture. The ready-mixed mortar mixture enters the material transmission channel from the feed port. At this time, the SMA metal fibers in the ready-mixed mortar mixture in the material transmission channel are randomly distributed. Step 3: Control the vertical orientation unit to vertically orient the SMA metal fibers in the ready-mixed mortar mixture respectively, and control the horizontal orientation unit to horizontally orient the SMA metal fibers in the ready-mixed mortar mixture. Step 4: The oriented ready-mixed mortar mixture is extruded by the horizontal orientation nozzle and the vertical orientation nozzle to complete the printing. Step 5: After waiting for the self-centering fiber concrete printed by 3D to reach final setting, perform high-temperature excitation on the self-centering fiber concrete to heat it to the austenite finish temperature to generate a recovery stress.

8. The preparation method according to claim 7, characterized in that, The ready-mixed mortar mixture in Step 2 is prepared by the following method: First, dry-mix the sand and Portland cement, then add water and stir; then add SMA metal fibers and stir; then add water reducer and superplasticizer and stir to obtain the ready-mixed mortar mixture.

9. The preparation method according to claim 7, characterized in that, Step 3 also includes: Step 3.1: After the power is turned on, the rotating sleeve rotates, and several pairs of permanent magnets rotate synchronously to form a rotating magnetic field. When the premixed mortar mixture passes through the rotating sleeve, the rotating magnetic field will drive the SMA metal fibers in the premixed mortar mixture to rotate to the horizontal direction. At the same time, each pair of the horizontal orientation vibrators adjusts the vibration frequency of the horizontal orientation vibrators, the rotation speed of the rotating sleeve, and the fluidity of the premixed mortar mixture again through the control unit. The horizontal orientation vibrators generate high-frequency and micro-amplitude vibrations, and the vibrations cause the premixed mortar mixture inside the rotating sleeve to liquefy and the SMA metal fibers to rotate, so that the SMA metal fibers are horizontally oriented; Step 3.2: The outer surface of the vertical orientation sleeve is wound with coils. After the power is turned on, the vertical orientation sleeve forms a vertical magnetic field, and its vertical magnetic field will drive the SMA metal fibers in the premixed mortar mixture to rotate to the vertical direction. At the same time, each pair of the vertical orientation vibrators adjusts the vibration frequency of the vertical orientation vibrators, the rotation speed of the rotating sleeve, and the fluidity of the premixed mortar mixture again through the control unit. The vertical orientation vibrators generate high-frequency and micro-amplitude vibrations, and the vibrations cause the premixed mortar mixture inside the rotating sleeve to liquefy and the SMA metal fibers to rotate, so that the SMA metal fibers are vertically oriented; Preferably, the vibration frequencies of the horizontal orientation vibrators and the vertical orientation vibrators are 50 - 80 Hz, the rotation speed of the rotating sleeve is 100 - 150 r / min, and the current of the coils is 10 A.

10. The preparation method according to claim 7, characterized in that, Step 4 further includes: Step 4.1: Conduct a preliminary experiment. Through the control unit, adjust the moving speeds of the horizontal orientation nozzle and the vertical orientation nozzle so that the speeds of the premixed mortar mixture extruded by the horizontal orientation nozzle and the vertical orientation nozzle meet the requirements of continuous printing performance; Step 4.2: Conduct a formal experiment. Through the control unit, start the external feeding system, the universal walking mechanism, and the SMA metal fiber orientation unit to start preparing three-dimensionally oriented SMA metal fiber concrete specimens.

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