Continuous 3D printing method for cement concrete

Abstract

The invention provides a cement concrete continuous 3D printing method which comprises the following steps: 1) before 3D printing of hydraulic concrete, arranging a steel bar or a steel wire mesh at the bottom of a printing area, connecting a zero-potential electrode, connecting a printing head of a 3D printer to a high-potential electrode, and connecting alternating current to form an alternating-current electric field of more than 50Hz in the printing area; (2) when the printed cement concrete reaches a certain height, steel bars or steel wire meshes are arranged on the surface of the cement concrete at the height, and an intermediate voltage electrode is connected; and 3) repeating the step 2) according to the change of the height of the printed cement concrete until the printing is finished. According to the method, the setting time of the cement concrete can be shortened by 70% or above, an initial setting agent does not need to be added into the cement concrete, the setting time of the cement concrete is remarkably shortened, 3D continuous printing of the cement concrete can be achieved, meanwhile, direct current can be effectively prevented from corroding an electrode under the action of alternating current, and the service life of the cement concrete is prolonged. Meanwhile, the hydration speed can be reduced, and the electrode service life is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of cement concrete preparation, and in particular to a method for continuous 3D printing of cement concrete Background Art

[0002] 3D printing is widely used in industrial design, aerospace, engineering and construction, and has brought an impact on traditional production technology. Meng Qingcheng and others used a full life cycle approach to evaluate concrete 3D printing technology. The results showed that compared with traditional construction methods, concrete 3D printing technology not only saves labor, but also reduces total carbon emissions by 15.97%.

[0003] Compared with traditional concrete construction methods, concrete 3D printing technology has many advantages: concrete 3D printing technology has extremely high design freedom. Traditional concrete construction requires the use of templates to constrain its shape, while concrete 3D printing technology does not require template constraints and directly piles up concrete according to the design model, and can build various complex geometric shapes. For parts with high precision requirements during construction, concrete 3D printing technology can reduce or even eliminate the use of manual labor, eliminate manual operation links, and directly control mechanical equipment by computer, which can well control dimensional errors.

[0004] However, 3D printing concrete requires low viscosity and high fluidity when pumping, and high viscosity and low fluidity to maintain shape stability after extrusion from the print port. These two stages require the material to have two opposite properties, which results in the complexity of 3D printing concrete batching and high difficulty in construction. Therefore, the maximum height of a conventional 3D concrete print is usually no more than 500mm, and the next print must wait for the bottom layer of printed concrete to harden and reach sufficient strength before implementing the next print. As a result, a large number of cold seams are created between the strips of 3D printed concrete, affecting the strength. Summary of the invention

[0005] Based on the problems existing in the prior art, the present invention provides a method for continuous 3D printing of cement concrete, which aims to achieve continuous 3D printing of hydraulic concrete by applying a suitable alternating electric field to the 3D printed cement concrete so that the printed cement concrete can solidify and harden quickly.

[0006] The present invention provides a method for continuous 3D printing of cement concrete, comprising the following steps:

[0007] 1) Before 3D printing hydraulic concrete, steel bars or steel mesh are set at the bottom of the printing area and connected to a zero potential electrode. The print head of the 3D printer is connected to a high potential electrode and AC power is turned on to form an AC electric field in the printing area.

[0008] 2) When the printed cement concrete reaches a certain height, steel bars or steel mesh are set on the surface of the cement concrete at that height and connected to the intermediate potential electrode;

[0009] 3) Repeat step 2) according to the change in the height of the printed cement concrete until the printing is completed.

[0010] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, the voltage of the high potential electrode is 40-60V.

[0011] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, in step 2), the cement concrete reaches a certain height of 500±50 mm, and the voltage of the intermediate potential electrode is 10-45V.

[0012] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, the step 2) is repeated in step 3) as follows: when the height of the upper cement concrete layer is the same as the height of the lower cement concrete layer, with the steel bar or steel wire mesh as the boundary, steel bars or steel wire mesh are arranged on the surface of the upper cement concrete layer, and electrodes are connected, the potential difference between the electrodes of the two adjacent layers of cement concrete is 10-15V, and the sum of the currents of the electrodes is not less than 2A.

[0013] As a preferred embodiment of a method for continuous 3D printing of cement concrete of the present invention, when the number of cement concrete layers reaches 4 or more, a voltage is applied to the surface steel bars or wire mesh access electrodes from the i-th to the i-3-th layers, where i is the current number of layers of the cement concrete.

[0014] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, the voltages of the electrodes to which the surface steel bars or steel meshes of the i-th to i-3-th layers are connected are successively reduced.

[0015] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, the frequency of the alternating current is above 50 Hz.

[0016] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, when the number of cement concrete layers reaches 4 or more, the position of the zero potential electrode is adjusted in the area where the cement concrete is completely solidified, as long as it is located below the aforementioned i-3th layer and the layer of cement concrete is completely solidified.

[0017] As a preferred embodiment of the method for continuous 3D printing of cement concrete of the present invention, in the step 1), an insulating layer is firstly provided at the bottom of the printing area, and then steel bars or steel mesh are provided on the insulating layer to improve safety.

[0018] It should be noted that the voltage referred to in the present invention is the effective voltage of alternating current known in the art.

[0019] The present invention creatively discovered that during the solidification process of cement concrete, the dissolved Ca 2+ Ions will gather on the surface of cement particles, hindering the development of hydration into the interior of cement particles. The above problem can be effectively solved by applying an electric field to cement concrete. This is because under the action of the electric field, Ca 2+ Migration will occur and then leave the particle surface, thereby promoting the occurrence of hydration reaction and ultimately improving the solidification efficiency of cement concrete. On this basis, the choice of electric field type is also very important. If a direct current electric field is used, the cations in the cement concrete are easy to crystallize at the negative electrode, which will corrode the negative electrode and reduce the life of the negative electrode. On the other hand, the aggregated cations will reduce the transmission capacity of the current, thereby affecting the continuation of the hydration reaction. The alternating current electric field used in the present invention will not cause the above problems, because the current direction of the alternating current will change rapidly, so it will not cause the enrichment of cations on the electrode surface.

[0020] Since the height of hydraulic concrete will change continuously during 3D printing, an appropriate electric field arrangement is required to effectively promote the hydration reaction. In the technical solution of the present invention, electrodes are introduced by arranging steel bars or wire mesh after the concrete reaches a certain height, thereby effectively avoiding the decrease of current in the electric field due to the increase of concrete printing height. At the same time, in order to ensure the uniformity of current distribution, the present invention proposes that the potential difference between the electrodes of two adjacent layers of cement concrete is 10-15V, and the sum of the currents of each electrode is not less than 2A.

[0021] According to the technical solution of the present invention, when the number of cement concrete layers reaches more than 5, except for the 4th layer which is still unsolidified, the solidification strength of the remaining layers has reached the support requirements. Therefore, it is only necessary to connect the steel bars or wire mesh on the surface of the i-th to i-3 layers to the electrodes and apply the corresponding voltage, where i is the current number of layers of the cement concrete. This can avoid the danger of using high voltage, and at the same time, only by adjusting the layout position of the electrodes, the voltage applied by each electrode does not need to be adjusted, thereby effectively ensuring the continuous printing of cement concrete.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. Compared with traditional concrete solidification technology, the method of the present invention can shorten the solidification time of cement concrete by more than 70%, and there is no need to add any strength-stimulating substances to the cement concrete.

[0024] 2. Compared with DC / DC pulse technology, the method of the present invention can avoid the corrosion of the negative electrode and the reduction of the hydration rate, thereby increasing the life of the electrode, significantly reducing the setting time of cement concrete, and preventing the precipitation of crystals in the concrete caused by the DC electric field to produce new cold joints.

[0025] 3. The solution of the present invention can realize 3D continuous printing of cement concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of continuous 3D printing of concrete according to the present invention.

[0027] Figure 2 Schematic diagram of electrode voltage control according to an embodiment of the present invention.

[0028] Figure 3 It is a comparison chart of the solidification change trends of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0029] Example 1

[0030] A method for continuous 3D printing of cement concrete, comprising the following steps:

[0031] 1) Before 3D printing cement concrete, set steel bars or steel mesh at the bottom of the printing area and connect to a zero potential electrode. Connect the print head of the 3D printer to a high potential electrode, set the voltage to 60V and the frequency to 50Hz, connect AC power to form an AC electric field in the printing area, and use cement concrete with a water-cement ratio of 0.28 for printing. The output current of the AC power is 5A.

[0032] 2) When the printing height reaches 500mm, a wire loop is set on the upper surface of the layer (i.e., the first layer), the size of which is consistent with the size of the surface of the cement concrete layer, and then connected to the first intermediate potential electrode, and the voltage is set to 15V;

[0033] 3) When the printing height reaches 1000mm, a wire loop is set on the surface of this layer (i.e., the second layer), the size of which is consistent with the size of the surface of this layer of cement concrete, and then connected to the second intermediate potential electrode, and the voltage is set to 30V;

[0034] 4) When the printing height reaches 1500mm, a wire loop is set on the surface of this layer (i.e., the third layer), the size of which is consistent with the size of the surface of this layer of cement concrete, and then connected to the third intermediate potential electrode, and the voltage is set to 45V;

[0035] 5) When the printing height reaches 2000mm, a wire loop is set on the surface of the layer (i.e., the 4th layer), and the size of the wire loop is consistent with the size of the surface of the cement concrete layer. Then, the electrodes in steps 2)-4) are moved up one layer, that is, the 2nd to 4th layers are connected to the first, second, third, and fourth intermediate potential electrodes respectively, and the voltage of each intermediate potential electrode is kept unchanged;

[0036] 6) When the printing height increases by 500mm, move the powered electrode up one layer until the printing is completed.

[0037] It has been determined that the solidification process of the first layer during the 3D printing process of this embodiment is as follows: Figure 2 As shown, it can be seen that under this working condition, the time for the first layer to reach 0.1MPa is 15 minutes, and this strength can support a print body of no less than 1000mm in height. The time for the first layer to reach 0.3MPa is 33 minutes, and this strength can support a print body of no less than 3000mm in height, which can well meet the requirements of existing 3D printing continuity (printing speed within 2000mm / 30min). At the same time, according to the temperature measurement results, during this period of time, the temperature of the first layer of cement concrete only increased by 4°C. And the final product has no cold seams, and the strength meets the requirements of continuous printing support strength.

[0038] Example 2

[0039] A method for continuous 3D printing of cement concrete, comprising the following steps:

[0040] 1) Before 3D printing hydraulic concrete, a steel bar or steel mesh is set at the bottom of the printing area and connected to a zero potential electrode. The print head of the 3D printer is connected to a high potential electrode, the voltage is set to 40V, the frequency is 20000Hz, and the alternating current is turned on to form an alternating electric field in the printing area. Cement concrete with a water-cement ratio of 0.26 is used for printing, and the output current of the alternating current is 5A;

[0041] 2) When the printing height reaches 400mm, a steel mesh is set on the surface of the layer (i.e., the first layer), the size of which is consistent with the size of the surface of the cement concrete layer, and then the first intermediate potential electrode is connected, and the voltage is set to 10V;

[0042] 3) When the printing height reaches 800mm, a steel mesh is set on the surface of the layer (i.e., the second layer), the size of which is consistent with the size of the surface of the cement concrete layer, and then the second intermediate potential electrode is connected, and the voltage is set to 20V;

[0043] 4) When the printing height reaches 1200mm, a steel mesh is set on the surface of this layer (i.e., the third layer), the size of which is consistent with the size of the surface of this layer of cement concrete, and then the third intermediate potential electrode is connected, and the voltage is set to 30V;

[0044] 5) When the printing height reaches 1600mm, a steel mesh is set on the surface of the layer (i.e., the 4th layer), the size of which is consistent with the size of the surface of the cement concrete layer, and then the electrodes in steps 2)-4) are moved up one layer, i.e., the 2nd to 4th layers are respectively connected to the first, second, third, and fourth intermediate potential electrodes, and the voltage of each intermediate potential electrode is kept unchanged;

[0045] 6) When the printing height increases by 400mm, move the powered electrode up one layer until the printing is completed.

[0046] According to the test, under this working condition, the first layer reaches 0.1MPa strength in 18 minutes, which can support a print body of no less than 1000mm in height, and the first layer reaches 0.3MPa in 35 minutes, which can support a print body of no less than 3000mm in height, which can well meet the requirements of existing 3D printing continuity (printing speed within 2000mm / 30min). At the same time, according to the temperature measurement results, the temperature of the first layer of cement concrete increased by 6°C during this period.

[0047] Comparative Example 1

[0048] A method for solidifying cement concrete comprises the following steps:

[0049] The same 3D printer as in Example 1 was used to print cement concrete with a water-cement ratio of 0.26, without applying any electric field.

[0050] It has been determined that under this working condition, the time for cement concrete to reach a strength of 0.1MPa is 75 minutes, and the time to reach 0.3MPa is 126 minutes. The concrete strength improvement speed after implementation of this scheme is completely unable to meet the requirements of current 3D continuous printing. It can be seen that compared with Comparative Example 1, Example 1 achieves continuous printing with unlimited height. The method of Example 1 shortens the time for cement concrete to reach a strength of 0.1MPa by 80% and the time to reach initial setting strength by 74%.

[0051] Comparative Example 2

[0052] A method for solidifying cement concrete comprises the following steps:

[0053] The same 3D printer as in Example 1 was used to print cement concrete with a water-binder ratio of 0.26, during which a DC electric field was applied.

[0054] It was determined that under this working condition, the time for the first layer (500mm high) of cement concrete to reach a strength of 0.1MPa was 14 minutes, slightly shorter than that of Example 1. However, due to the Ca 2+ , Fe 3+、Na + Plasma gathers and precipitates a large number of crystals, causing the current to drop. Therefore, it takes 42 minutes to reach 0.3MPa, which is 9 minutes longer than Example 1. Subsequently, the crystals on the bottom plate wire mesh become thicker and thicker, causing the current to drop rapidly. As the printing height increases, this situation occurs on each layer of newly added electrodes, resulting in a significant decrease in the accelerating effect of the electric field. The maximum height of continuous printing finally achieved is 3 layers, i.e., 1.5 meters. It can be seen that, relative to Comparative Example 2, the method of Example 1 shortens the time for cement concrete to reach an initial setting strength of 0.3MPa by 27%, and Example 1 can achieve continuous printing without height restrictions. In addition, it was found in the experiment that a large number of crystals were precipitated on the steel mesh of Example 2, and these crystals expanded when precipitated, resulting in a decrease in the bonding strength between the steel mesh and the concrete or even separation, which actually formed a cold seam and reduced the integrity of the concrete.

[0055] It should be noted that, according to the above embodiments of the present invention, those skilled in the art can fully realize the full scope of the independent claims and dependent rights of the present invention, and the implementation process and method are the same as the above embodiments; and the part not described in detail in the present invention belongs to the well-known technology in the field. However, the protection scope of the present invention is not limited to this, and any changes or substitutions that can be easily thought of by any person familiar with the field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for continuous 3D printing of cement concrete, characterized in that: The steps include: 1) Before 3D printing hydraulic concrete, steel bars or steel mesh are set at the bottom of the printing area and connected to a zero potential electrode. The print head of the 3D printer is connected to a high potential electrode and AC power is turned on to form an AC electric field in the printing area. 2) When the printed cement concrete reaches a certain height, steel bars or steel mesh are set on the surface of the cement concrete at that height and connected to the intermediate potential electrode; 3) Repeat step 2) according to the change in the height of the printed cement concrete until the printing is completed.

2. The method according to claim 1, characterized in that The voltage of the high potential electrode is 40-60V.

3. The method according to claim 1, characterized in that In step 2), the cement concrete reaches a certain height, specifically 500±50 mm, and the voltage of the intermediate potential electrode is 10-45V.

4. The method according to claim 1, characterized in that In step 3), the step 2) is specifically repeated as follows: when the height of the upper cement concrete layer is the same as the height of the lower cement concrete layer, with the steel bar or steel wire mesh as the boundary, steel bars or steel wire mesh are arranged on the surface of the upper cement concrete layer, and electrodes are connected, the potential difference between the electrodes of the two adjacent cement concrete layers is 10-20V, and the sum of the currents of the electrodes is not less than 2A.

5. The method according to claim 4, characterized in that When the number of cement concrete layers reaches 4 or more, voltage is applied to the surface steel bars or steel mesh access electrodes of the i-th to i-3-th layers, where i is the current number of cement concrete layers.

6. The method according to claim 5, characterized in that The voltages of the electrodes connected to the surface steel bars or steel wire mesh of the i-th to i-3-th layers decrease successively.

7. The method according to any one of claims 1 to 6, characterized in that: The frequency of the alternating current is above 50 Hz.

8. The method according to any one of claims 1 to 6, characterized in that: When the number of cement concrete layers reaches 4 or more, the position of the zero potential electrode is adjusted in the area where the cement concrete is completely solidified.

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