CN114895006A - Test method for testing constructability of 3D printed concrete - Google Patents
Test method for testing constructability of 3D printed concrete Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 148
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- 239000004576 sand Substances 0.000 claims abstract description 111
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- 238000007639 printing Methods 0.000 claims abstract description 35
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- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/36—Embedding or analogous mounting of samples
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Abstract
The invention relates to the technical field of intelligent manufacturing, in particular to a test method for testing the constructability of 3D printed concrete, which comprises the following steps: preparing a piece to be tested; adjusting the testing device; installing a test piece and regulating and controlling a test environment; and (3) testing: the sand grains in the sand storage tank fall onto the upper pressing plate, the load value of the accumulated printing layer simulation unit, the inclination angle value of the upper pressing plate and the transverse and vertical deformation values of the four side surfaces of the test piece are collected, the amount of the released sand grains is controlled according to the load value, and the gravity action of the accumulated printing layer simulation unit is simulated; and (3) judging test results: stopping the test when the inclination value reaches a set threshold value; using time-rate of inclinationθ t Time rate of measurement of test piece△D t Two indexes are used for evaluating the constructability of the 3D printing concrete mixture. The method can be used for 3D printing with different mix ratiosAnd accurately comparing and evaluating the constructability of the concrete mixture.
Description
Technical Field
The invention relates to the technical field of intelligent manufacturing, in particular to a testing method for testing the constructability of 3D printed concrete.
Background
At present, with the advance of the fourth industrial revolution towards artificial intelligence, the construction industry also meets the era of intelligent construction, and the economic and social benefits of the 3D printed concrete technology, such as intelligent, efficient and accurate construction, low manpower demand, low resource consumption, low environmental load and the like, make the concrete become a key component for developing intelligent construction of the construction industry. However, at present, both the 3D printing concrete preparation theory and the performance evaluation method are still imperfect and far away from the actual requirements, and the progress and development of the 3D printing concrete technology are severely restricted.
As an additive manufacturing process for layer-by-layer stacking, the 3D printing process not only requires that the freshly mixed material has enough fluidity to ensure smooth extrusion from a nozzle, but also has enough constructability to ensure that the bottom material can support the weight of the subsequent layer, and the subsequent layer cannot be inclined or collapsed due to excessive accumulated deformation. The constructability not only determines the printing efficiency, but also determines the appearance quality, mechanical property, durability and the like of the printed product. But the constructability breaks through the range of the performance requirements of the traditional concrete, and a suitable test method and evaluation indexes are not available at present. The existing method is mostly based on the traditional concrete rheology theory, and adopts yield stress, plastic viscosity and thixotropy indexes, but there is a controversial debate on whether the indexes, particularly the thixotropy, reflect the constructability of 3D printed concrete. In view of the fact that overturning and collapsing are visual expressions reflecting poor volume stability of 3D printed concrete mixture, it is necessary to develop a test method and an evaluation index capable of directly evaluating constructability aiming at the anti-overturning and anti-dimensional variation capabilities of 3D printed concrete fresh mixture.
Disclosure of Invention
The invention provides a test method for testing the constructability of 3D printed concrete, aiming at solving the test problem of the anti-overturning and anti-dimensional variation capabilities of fresh concrete mixtures of 3D printed concrete.
In order to realize the purpose, the technical scheme of the invention is as follows:
a test method for testing the constructability of 3D printed concrete,
step A: preparing a to-be-tested piece: preparing a square test mold, fixing the test mold on a bearing plate, and pouring a mixture into the test mold to prepare a test piece;
and B: adjusting the testing device: before pouring in the step A, respectively connecting a sand bag with a sand storage tank and an upper pressure plate in an environment box, wherein the sand storage tank is arranged above the inside of the environment box, the bottom of the sand storage tank is provided with a sand leakage nozzle, the sand leakage nozzle corresponds to the center of the sand bag, the upper pressure plate is arranged below the sand bag, and a space is reserved below the upper pressure plate for placing and demoulding of a test piece;
and C: installing a test piece, regulating and controlling a test environment: b, placing the test piece poured in the step A, the test mold and the bearing plate below the upper pressing plate, fixing the bearing plate, then removing the test mold, sealing the environment box, and controlling the temperature and humidity values in the environment box;
step D: and (3) testing: the sand grains in the sand storage tank fall onto the upper pressing plate, the load value of the accumulated printing layer simulation unit, the inclination angle value of the upper pressing plate and the transverse and vertical deformation values of the four side surfaces of the test piece are collected, the amount of the released sand grains is controlled according to the load value, and the gravity action of the accumulated printing layer simulation unit is simulated; the accumulated printing layer simulation unit comprises a sand storage tank, a sand bag, an upper pressing plate and a bearing plate;
step E: and (3) judging test results: stopping the test when the inclination value reaches a set threshold value; using the time-rate of inclination theta t Dimensional time-rate of change DeltaD of test piece t Two indexes are used for evaluating the constructability of the 3D printing concrete mixture.
Time rate of inclination angle theta of tested piece t The smaller, the better the constructability of the 3D printed concrete mix, the greater the height can be printed without tilt collapse with a smaller printing width; delta D t The smaller the value of (a), the more stable the volume of the test piece, representing the better the constructability of the 3D printed concrete mix.
Furthermore, in the step A, before pouring the mixture into the test mold, a release agent is used for brushing the inner side surface of the test mold and the bottom plate surface of the test mold formed by the bearing plate; and in the step B, the sand bag is respectively connected with the sand storage tank and the upper pressing plate through a sand bag snap ring.
Furthermore, after the test mold is removed, a data acquisition unit and an automatic control unit are arranged in the environment box, wherein the data acquisition unit comprises a load sensor, an inclinometer and a displacement sensor, the load sensor is arranged below the bearing plate, the inclinometer is arranged on the upper pressing plate, the number of the displacement sensors is multiple, and the displacement sensors are positioned on the side part of the test piece;
the automatic control unit comprises a controller, wherein the load sensor, the inclinometer and the displacement sensor are connected to the controller, the sand leakage nozzle is provided with a flow valve, and the controller is connected with the flow valve.
Furthermore, in step C, after the environmental chamber is closed, the automatic control unit is operated to return the load value of the load sensor to zero.
Furthermore, in the step D, before the sand grains in the sand storage tank fall, the upper pressure plate is contacted with the upper surface of the test piece, when the load sensor has a load value, the load indication value can be reset to zero again, and the flow valve is opened; or the upper pressure plate is contacted with the upper surface of the test piece before the environmental chamber is closed in the step C.
Furthermore, a load sensor, an inclinometer and a displacement sensor are used for respectively acquiring a load value of the cumulative printing layer simulation unit, an inclination angle value of the upper pressure plate and transverse and vertical deformation values of four side surfaces of the test piece, the load value, the inclination angle value and the transverse and vertical deformation values are stored in real time by the automatic control unit, and the controller controls the amount of sand grains released by the flow valve according to the load value.
Furthermore, the accumulation printing layer simulation unit further comprises a servo power source and a lifting column, the servo power source is arranged below the inside of the environment box, the servo power source is connected with the controller, the lifting column is arranged on the servo power source and connected with the servo power source, and the upper end of the lifting column is connected with the sand storage tank through a support.
Furthermore, the cumulative printing layer simulation unit further comprises an upright column, a winch and a lifting rope, wherein the upright column is arranged below the inside of the environment box, the upper end of the upright column is provided with the winch, the winch is connected with the controller, and the winch is connected with the sand storage tank through the lifting rope in a transmission mode.
Further, the automatic control unit further comprises an environment regulation and control unit, the environment regulation and control unit comprises a temperature sensor, a humidity sensor, a temperature transmitter, an evaporator, a heating device, a refrigerating device, an atomizer and a fan, the environment regulation and control unit is connected with the controller, and the environment regulation and control unit is used for detecting and controlling the temperature and the humidity in the environment box.
Further, the inclination angle time-varying rate theta t The calculation formula is the variation quantity delta theta (t) of the dip angle of the printing layer in unit time delta t and is as the following formula (1):
dimensional time-rate Δ D of the test piece t Calculating the size time-varying rate Delta D of a tested piece after printing for a certain time, wherein the calculation formula is as shown in formula (2):
△D t ＝abc/t (2)
in the formula, a, b and c are deformation ratios in three directions of the test piece x, y and z respectively: a ═ Δ x/x, b ═ Δ y/y, c ═ Δ z/z, t is the elapsed time, min.
Through the technical scheme, the invention has the beneficial effects that:
1. according to the invention, the one-time pouring test piece is adopted to replace the layer-by-layer accumulative printing test piece, so that the test error caused by the difference of printing conditions can be reduced, and the test method is more convenient to be connected with the traditional test method.
2. The test method of the invention provides two indexes for evaluating the constructability of 3D printed concrete: the dip angle time-rate theta t and the test piece size time-rate delta Dt; the constructability of 3D printing concrete mixtures with different mixing ratios can be accurately compared and evaluated through the testing device and the testing method.
Drawings
Fig. 1 is a flowchart of a testing method for testing a 3D printed concrete shearable model according to the present invention.
FIG. 2 is a schematic structural diagram of a testing apparatus for testing the constructability of 3D printed concrete according to a first embodiment of the invention;
FIG. 3 is a schematic view of a test mold and a support plate for molding a test piece;
FIG. 4 is a second schematic view of the test mold and the support plate for forming the test specimen;
fig. 5 is a schematic structural diagram of a test apparatus for testing the constructability of 3D-printed concrete according to the second embodiment.
Fig. 6 is a schematic structural diagram of a test apparatus for testing 3D printed concrete constructability according to the third embodiment.
The reference numbers in the figures are: the device comprises a sand storage tank 1, a support 2, a sand bag clamping ring 3, a lifting column 4, a sand leakage nozzle 5, a sand bag 6, sand 7, a servo power source 8, an upper pressure plate 9, a test piece 10, a bearing plate 11, a positioning plate 12, a load sensor 13, an environment regulating unit 14, an environment box 16, a flow valve 17, a controller 18, a computer 19, an inclinometer 20, a displacement sensor 21, a box door 22, a main machine seat 23, a test mold 24, a connecting bolt 25, a positioning bolt 26, a positioning limb 27, an upright column 28, a winch 29 and a lifting rope 30.
Detailed Description
The invention is further described with reference to the following figures and detailed description:
in the description of the present invention, it is to be understood that the terms "left", "right", "upper", "lower", "lateral", "vertical", etc. indicate orientations or positional relationships based on those shown in fig. 1 only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Example one
As shown in fig. 1, a test method for testing the constructability of the 3D-printed concrete according to the embodiment includes the following steps:
step A: preparing a to-be-tested piece: the test piece 10 needs to be prepared by adopting a square test mold 24 with specified size, as shown in fig. 3 and 4, the test mold is composed of four side plates, two side plates are fixedly connected at right angles to form a group, two groups of side plates are connected into a whole through connecting bolts 25 to form a square shape, a positioning limb 27 is arranged on the outer side of the short side of the side plate of the test mold 24, a screw hole for screwing a positioning bolt 26 is correspondingly arranged in a U-shaped clamping groove at the end part of the supporting piece plate 11 and the positioning limb 27, and the test mold 24 and the supporting piece plate 11 can be connected into a whole through the positioning bolt 26. The base area of the test piece 24 is smaller than the area of the support plate 11 to provide sufficient space for plastic deformation of the test piece 10. Brushing the inner side surface of a test mold 24 and the bottom plate surface of the test mold 24 formed by a bearing plate 11 with a release agent, pouring the mixed mixture into the test mold 24 in a plurality of times, properly inserting and tamping, properly compacting on a vibrating table after filling the test mold 24, and trowelling the surface;
and B: adjusting the test device to leave a placing space for the test piece 10 and the bearing plate 11: before pouring in the step A, respectively connecting a sand bag 6 with a sand storage tank 1 and an upper pressure plate 9 through a sand bag clamping ring 3, enabling the center of the sand bag 6 to correspond to the center of a sand leakage nozzle 5, and enabling a space to be reserved below the upper pressure plate 9 for placing and demolding operation of a test piece 10;
as shown in fig. 2 to 4, the apparatus for testing the constructability of 3D printed concrete used in the present embodiment includes an environment box 16, an accumulated print layer simulation unit, a data acquisition unit, and an automatic control unit.
Specifically, the environmental chamber 16 includes a chamber door 22, and a main housing 23 is disposed on a bottom plate inside the environmental chamber 16 to facilitate mounting and fixing of components. The environmental chamber 16 is a test site, including but not limited to a chamber, a laboratory.
The accumulation printing layer simulation unit is located in the environment box 16 and comprises a sand storage tank 1, a sand bag 6, an upper pressing plate 9 and a bearing plate 11, the sand storage tank 1 is arranged above the inside of the environment box 16, the sand storage tank 1 is used for placing sand, in the embodiment, the sand is a steel ball, the steel ball made of granular materials is used as a loading mode to facilitate the accumulation printing process of simulation materials layer by layer, errors caused by volatilization and the like of liquid materials can be avoided, the steel ball is regular and wear-resistant in particles, environmental pollution caused by natural sandy soil and the like can be avoided, and the using amount of the steel ball is large in density and can be reduced. The upper part of the sand storage tank 1 is cylindrical, the lower part of the sand storage tank is conical, a sand leakage nozzle 5 is arranged at the bottom of the sand storage tank 1, the sand leakage nozzle 5 is positioned at the center of the bottom of the conical structure of the sand storage tank 1, and a flow valve 17 is arranged on the sand leakage nozzle 5; the sand bag 6 is arranged at the lower end of the sand storage tank 1, the sand leakage nozzle 5 corresponds to the center of the sand bag 6, the sand bag 6 is in a foldable cylindrical shape, and the cylindrical sand bag is convenient for weight simulation of a subsequent printing layer and also reduces the influence on the inclination angle of a test piece; the upper pressing plate 9 is arranged below the sand bag 6.
In this embodiment, the upper and lower both ends of sand bag 6 are connected with sand storage tank 1 and top board 9 through sand bag snap ring 3 respectively, and sand bag snap ring 3 is a rigid ring, including inner ring and outer loop, and the upper and lower both ends of sand bag 6 set up the outer loop of sand bag snap ring 3 respectively with storing up sand tank 1 below relevant position, and the inner and outer loop passes through screw thread or spring buckle connection formation one width of cloth to the upper and lower both ends that make the sand bag are connected with sand storage tank 1 and top board 9 respectively. When the sand bag 6 is connected to the bottom of the sand storage tank 1, the center of the sand bag 6 corresponds to the sand leakage nozzle 5, sand 7 flows into the sand bag 6 through the control of the flow valve, the gravity center of the formed sand pile approximately coincides with the axis of the sand bag, and when the geometric center of the placed test piece coincides with the geometric center of the sand bag, the uniform gravity action on the test piece can be ensured.
In this embodiment, the sand bag is a flexible cylinder made of a polymer material, so that the weight is light, active restrictive influence on deformation of the test piece is not generated, and the load gravity center change rule formed by the sand bag and the accumulated printing layer gravity center change rule are closer to each other.
And C: installing a piece to be tested, and regulating and controlling the testing environment: and (3) arranging a load sensor 13 on a main machine base 23 at the bottom of the environment box, placing the test piece poured in the step A, the test die and the bearing plate 11 below the upper pressing plate 9 and above the load sensor 13, wherein the bearing plate 11 corresponds to the upper pressing plate 9, and placing the test piece 10 between the bearing plate 11 and the upper pressing plate 9. In order to facilitate the preparation and the placement of test piece 10, the support plate 11 of this embodiment is detachable, and is specific, be provided with locating plate 12 between load sensor 13 and the support plate 11, be provided with trapezoidal keyway structure between locating plate 12 and the support plate 11, trapezoidal keyway structure is including setting up at the trapezoidal key of support plate 11 below, seting up the dovetail groove in locating plate 12 top, and trapezoidal key and dovetail groove cooperate to fix a position and fix support plate 11.
Before the test mold is removed, the data acquisition unit and the automatic control unit are installed and connected, the test mold is removed, the environment box 16 is closed, the automatic control unit is operated, the load indication value of the load sensor 13 is enabled to return to zero, the temperature and humidity values inside the environment box 16 are set, and the environment adjusting and controlling machine set is started to control the environment in the environment box 16.
The data acquisition unit further comprises an inclinometer 20 and a displacement sensor 21 besides the load sensor 13, wherein the inclinometer 20 is arranged on the upper pressure plate 9, the number of the displacement sensors 21 is multiple, the displacement sensors 21 are located on the side portion of a test piece, in the embodiment, the test piece is square, and two displacement sensors are arranged on each side of the test piece.
The automatic control unit comprises a controller 18 and a computer 19, wherein the controller 18 is connected with a flow valve 17, and a load sensor 13, an inclinometer 20 and a displacement sensor 21 are connected to the controller 18. In this embodiment, the flow valve 17 is an electromagnetic valve, and the sand production amount can be accurately controlled by control software.
The load sensor 13 is mainly used for the gravity action formed by the upper test piece 10, the upper pressing plate 9, the inclinometer 20, the sand bag 6 and the sand grains 7, and transmitting the obtained load data signal to the controller through a cable. Two displacement sensors 21 are arranged on each side face of the square test piece 10, so that errors caused by the contact type displacement sensors to test results are avoided, the displacement sensors are high-precision non-contact type laser displacement meters, the transverse and vertical deformation of the test piece under the action of gravity can be accurately tested, and deformation signals are transmitted to the controller through data cables. The inclinometer 20 is fixed on the upper surface of the upper pressing plate 9, is a light flat plate and can be made of organic glass, and when the test piece is unevenly and vertically deformed, the inclinometer can be driven to move and can transmit the acquired space position change signal to the controller through a data cable. The controller converts the received load and deformation signals into data and transmits the data to the computer 19, and the data state is displayed on a computer screen in real time through control software and is stored.
The automatic control unit still includes environment regulation and control unit 14, environment regulation and control unit 14 includes temperature sensor, humidity transducer, temperature transmitter, evaporimeter, heating device, refrigerating plant, atomizer and fan, and temperature sensor is connected with temperature transmitter, and humidity sensor, temperature transmitter, evaporimeter, heating device, refrigerating plant, atomizer and fan all are connected with controller 18, and environment regulation and control unit is used for detecting and the humiture of control environment incasement. After the door 22 is closed, the temperature and humidity signals are collected by the temperature sensor and the humidity sensor and transmitted to the controller 18 and the computer 19, and the data are analyzed by software, and the instruction is transmitted to the environment machine external group and the environment machine internal group to realize the accurate regulation and control of the temperature and the humidity in the environment box 16.
The accumulation printing layer simulation unit further comprises a servo power source 8 and a lifting column 4, wherein the servo power source 8 is arranged below the inside of the environment box 16, the servo power source 8 is connected with the controller 18, the lifting column 4 is arranged on the servo power source 8 and is connected with the servo power source 8, and the upper end of the lifting column 4 is connected with the sand storage tank 1 through the support 2. The servo power source 8 is a power system controlled by a hydraulic servo or an electric servo, the lifting column 4 can be driven to finish lifting and descending motions according to a set program, the sand storage tank can be driven to do lifting motions in a test, sand grains are added into the sand bag through the control program, and the gravity action exerted on the bottommost layer by the accumulated and increased upper printing layer is simulated.
Step D: and (3) a testing stage: starting a servo power source 8 to drive the lifting column 4 to descend, enabling the upper pressure plate 9 to be in contact with the upper surface of the test piece, and enabling the load indication value to return to zero again when the automatic control unit displays the load value; opening a flow valve 17, enabling sand grains in a sand storage tank 1 to fall onto an upper pressing plate 9, respectively collecting a load value, an inclination angle value and transverse and vertical deformation values of four side surfaces of a test piece by a load sensor 13, an inclinometer 20 and a displacement sensor 21, storing the load values, the inclination angle value and the transverse and vertical deformation values in real time by a computer 19 of an automatic control unit, and controlling the quantity of the sand grains released by the flow valve 17 by a controller 18 according to a load feedback value to simulate the gravity action of an accumulated printing layer;
step E: and (3) judging test results: and stopping the test when the inclination angle value reaches a set threshold value. In the printing process, due to the difference of homogeneity and rheological property of the 3D printing concrete mixture, the deformation resistance of different parts of a printed product is different, and the inclination and collapse damage can occur along with the increase of the accumulated printing layer under the condition of no template support. Therefore, if the degree of inclination of the lowermost printed layer does not cause the upper printed layer to topple over within a prescribed time period, and at the same time, the lateral dimension variation is within an acceptable range, it can be considered that the constructability is satisfactory. Two indexes are adopted to evaluate the constructability of the 3D printing concrete mixture, wherein the first index is the inclination angle time-rate theta t I.e. the variation Δ θ (t) of the printing layer inclination angle per unit time Δ t, the calculation formula is as follows:
time rate of inclination angle theta of tested piece t The smaller, the better the constructability of the 3D printed concrete mix, the greater the height can be printed without tilt collapse with a smaller printing width;
the second index isDimensional time-rate of change DeltaD of test piece t Namely, the size time-varying rate DeltaD of the tested piece after printing for a certain time, and the calculation formula is as shown in formula (2):
△D t ＝abc/t (2)
in the formula, a, b and c are deformation ratios in three directions of the test piece x, y and z respectively: a ═ Δ x/x, b ═ Δ y/y, c ═ Δ z/z, t is the elapsed time, min. Delta D t The smaller the value of (a), the more stable the volume of the test piece, representing the better the constructability of the 3D printed concrete mix.
Example two
This embodiment is substantially the same as the first embodiment, and the same parts are not described again, except that:
as shown in fig. 5, in order to save the manufacturing cost of the testing device, the servo power source 8 and the lifting column 4 of the first embodiment may be replaced by a column 28. In step C of the test method, the upper platen 9 is manually brought into contact with the upper surface of the test piece by an operator before closing the environmental chamber.
EXAMPLE III
This embodiment is substantially the same as the first embodiment, and the same parts are not described again, except that:
as shown in fig. 6, the servo power source 8 and the lifting column 4 of the first embodiment can be replaced by a column 28, a hoist 29 and a lifting rope 30, wherein the column 28 is arranged below the inside of the environmental chamber 16, the hoist 29 is arranged at the upper end of the column 28, the hoist 29 is connected with the controller 18, and the hoist 29 is in transmission connection with the sand storage tank 1 through the lifting rope 30. The hoisting machine 29 and the lifting rope 30 are used for controlling the lifting of the sand storage tank to replace the function of the lifting column. In order to avoid the sand storage tank from horizontally deflecting and swinging, four lifting ropes are provided.
In step D of the test method, the hoist 29 is started to drive the lifting rope 30 and the sand storage tank to descend, so that the upper pressure plate contacts the upper surface of the test piece.
The above-described embodiments are merely preferred embodiments of the present invention, and not intended to limit the scope of the invention, so that equivalent changes or modifications in the structure, features and principles described in the present invention should be included in the claims of the present invention.
Claims (10)
1. A test method for testing the constructability of 3D printed concrete is characterized in that,
step A: preparing a to-be-tested piece: preparing a square test mold, fixing the test mold on a bearing plate (11), pouring a mixture into the test mold, and preparing a test piece;
and B: adjusting the testing device: before pouring in the step A, a sand bag (6) is respectively connected with a sand storage tank (1) and an upper pressing plate (9) in an environment box (16), the sand storage tank (1) is arranged above the inside of the environment box (16), a sand leakage nozzle (5) is arranged at the bottom of the sand storage tank (1), the sand leakage nozzle (5) corresponds to the center of the sand bag (6), the upper pressing plate (9) is arranged below the sand bag (6), and a space is reserved below the upper pressing plate (9) for placing and demolding of a test piece;
and C: installing a test piece, regulating and controlling a test environment: placing the test piece poured in the step A, the test mold and the bearing plate (11) below the upper pressing plate (9), fixing the bearing plate (11), then removing the test mold, sealing the environment box (16), and controlling the temperature and humidity value in the environment box (16);
step D: and (3) testing: the sand grains in the sand storage tank (1) fall onto an upper pressing plate (9), the load value of an accumulated printing layer simulation unit, the inclination angle value of the upper pressing plate (9) and the transverse and vertical deformation values of four side surfaces of the test piece are collected, the amount of the released sand grains is controlled according to the load value, and the gravity action of the accumulated printing layer simulation unit is simulated; the accumulated printing layer simulation unit comprises a sand storage tank (1), a sand bag (6), an upper pressing plate (9) and a bearing plate (11);
step E: and (3) judging test results: stopping the test when the inclination value reaches a set threshold value; using the time-rate of inclination theta t Dimensional time-rate of change DeltaD of test piece t Two indexes are used for evaluating the constructability of the 3D printing concrete mixture.
2. The method for testing the constructability of the 3D printed concrete according to the claim 1, wherein in the step A, before the mixture is poured into the test mold, the inner side surface of the test mold and the bottom plate surface of the test mold formed by the support plate are coated with a release agent; in the step B, the sand bag (6) is respectively connected with the sand storage tank (1) and the upper pressing plate (9) through the sand bag snap ring (3).
3. The test method for testing the constructability of 3D printed concrete according to claim 1, characterized in that after the test mold is removed, a data acquisition unit and an automatic control unit are arranged in the environment box (16), wherein the data acquisition unit comprises a load sensor (13), an inclinometer (20) and a displacement sensor (21), the load sensor (13) is arranged below the bearing plate (11), the inclinometer (20) is arranged on the upper pressing plate (9), the number of the displacement sensors (21) is multiple, and the displacement sensors (21) are positioned at the side part of the test piece;
the automatic control unit comprises a controller (18), wherein a load sensor (13), an inclinometer (20) and a displacement sensor (21) are connected to the controller (18), a flow valve (17) is arranged on the sand leakage nozzle (5), and the controller (18) is connected with the flow valve (17).
4. A test method for testing the constructability of 3D printed concrete according to claim 3, characterized in that in step C, after the environmental chamber (16) is closed, the automatic control unit is operated to zero the load value of the load cell (13).
5. The test method for testing the constructability of 3D printed concrete according to the claim 3, characterized in that, in the step D, before the sand grains in the sand storage tank (1) fall, the upper pressure plate (9) is contacted with the upper surface of the test piece, when the load sensor (13) has a load value, the load indication value can be reset to zero again, and the flow valve (17) is opened; or the upper pressing plate (9) is contacted with the upper surface of the test piece before the environmental box is closed in the step C.
6. A test method for testing the constructability of 3D printed concrete according to claim 3, characterized in that the load value of the cumulative printing layer simulation unit, the inclination angle value of the upper press plate (9) and the lateral and vertical deformation values of the four sides of the test piece are respectively collected by using the load sensor (13), the inclinometer (20) and the displacement sensor (21) and are stored in real time by the automatic control unit, and the controller (18) controls how much the flow valve (17) releases the sand grains according to the load values.
7. The test method for testing the constructability of 3D printed concrete according to claim 3, wherein the cumulative printing layer simulation unit further comprises a servo power source (8) and a lifting column (4), the servo power source (8) is arranged below the inside of the environment box (16), the servo power source (8) is connected with the controller (18), the lifting column (4) is arranged on the servo power source (8) and connected with the servo power source (8), and the upper end of the lifting column (4) is connected with the sand storage tank (1) through a bracket (2).
8. The test method for testing the constructability of the 3D printed concrete according to the claim 3, wherein the cumulative printing layer simulation unit further comprises a vertical column (28), a winch (29) and a lifting rope (30), the vertical column (28) is arranged below the inside of the environment box (16), the winch (29) is arranged at the upper end of the vertical column (28), the winch (29) is connected with the controller (18), and the winch (29) is in transmission connection with the sand storage tank (1) through the lifting rope (30).
9. The test method for testing the constructability of the 3D printed concrete according to the claim 3, characterized in that the automatic control unit further comprises an environment control unit (14), the environment control unit (14) comprises a temperature sensor, a humidity sensor, a temperature transmitter, an evaporator, a heating device, a refrigerating device, an atomizer and a fan, the environment control unit (14) is connected with the controller (18), and the environment control unit is used for detecting and controlling the temperature and the humidity in the environment box.
10. The test method for testing the constructability of 3D printed concrete according to claim 1,
the time rate of inclination angle theta t The calculation formula is the variation quantity delta theta (t) of the dip angle of the printing layer in unit time delta t and is as the following formula (1):
time rate of inclination angle theta of tested piece t The smaller, the better the constructability of the 3D printed concrete mix, the greater the height can be printed without tilt collapse with a smaller printing width;
dimensional time-rate Δ D of the test piece t Calculating the size time-varying rate Delta D of a tested piece after printing for a certain time, wherein the formula is as follows (2):
△D t ＝abc/t (2)
in the formula, a, b and c are deformation ratios in three directions of the test piece x, y and z respectively: a ═ Δ x/x, b ═ Δ y/y, c ═ Δ z/z, t is elapsed time, min;
△D t the smaller the value of (a), the more stable the volume of the test piece, representing the better the constructability of the 3D printed concrete mix.
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