A device and method for testing the unconfined compressive strength of 3D printed concrete green bodies

Abstract

The present application relates to a kind of 3D printing concrete wet body unconfined compressive strength testing device and method, belong to concrete compression test technical field, device includes a hollow cylindrical moulding cylinder and a hollow cylindrical positioning cylinder;Moulding cylinder outer wall is provided with at least two vertical track keys, and the top of outer wall is symmetrically provided with two grippers;Positioning cylinder is sleeved on the outside of moulding cylinder, and its inner wall is provided with track groove matched with track key, and the sliding fit of both constitutes guide rail system, ensure that moulding cylinder moves along strict vertical path when demoulding.Positioning cylinder is outwardly extended with at least three positioning legs with positioning scale at lower end, for cooperating with the centering mark on the loading plate of press, realize accurate positioning of entire device in the center of loading plate.The entire process greatly reduces human operation error and subjective judgment, makes test result more accurate, higher repeatability, easy to standardize promotion.

Description

Technical Field

[0001] This invention relates to a device and method for testing the unconfined compressive strength of 3D printed wet concrete blanks, belonging to the field of concrete compressive strength testing technology. Background Technology

[0002] 3D printing of concrete is a key component of industrialized building and intelligent construction, offering significant advantages such as high automation, high degree of freedom in molding, and high material utilization. The core of this technology lies in the layer-by-layer deposition of wet concrete material (i.e., "wet blanks") to construct a three-dimensional solid. During this process, the deposited layers must maintain sufficient stability under their own weight and the loads of subsequent layers, preventing excessive deformation or collapse. This is crucial for the geometric accuracy, structural integrity, and final mechanical properties of the printed component. The structural stability of the wet blank directly determines the feasibility of printing and the reliability of the component.

[0003] The stability of printed structures is highly dependent on the strength of the wet preform. Insufficient wet preform strength will cause a series of serious problems: during the layer-by-layer printing process, the lower layers of wet preform may undergo plastic deformation, crushing, or overall instability due to their inability to withstand the loads of the upper layers, leading to geometric deviations, interlayer misalignment, or even complete collapse of the printed structure. Simultaneously, excessively low wet preform strength also means weak interlayer bonding, directly affecting the integrity and load-bearing capacity of the final component. Therefore, accurately evaluating the unconfined compressive strength of 3D printed concrete wet preforms is crucial for predicting printing stability, optimizing material mix design, and developing reasonable printing process parameters (such as layer height, printing speed, and interlayer interval).

[0004] Currently, there is a lack of unified, mature, and applicable standard methods for testing the unconfined compressive strength of wet 3D-printed concrete blanks. Traditional methods for testing the compressive strength of concrete (such as testing standard cubic or cylindrical specimens) require the specimens to reach a certain hardening strength and undergo demolding and curing, which is completely unsuitable for wet blanks in the fluid to initial setting state. Existing testing methods for the workability (such as slump) or early strength development (such as the penetration resistance method) of fresh concrete also fail to directly and quantitatively reflect the actual compressive bearing capacity of wet blanks in the unconfined state. Therefore, there is an urgent need to develop a standardized testing method and supporting equipment that can effectively characterize the unconfined compressive strength of wet 3D-printed concrete blanks, providing a scientific and reliable evaluation tool for material design, process optimization, and engineering applications. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a simple and reliable method for testing the unconfined compressive strength of wet 3D printed concrete blanks, which is not suitable for evaluating the compressive strength of existing experimental evaluation methods. It also provides a simple, low-error, and easily implementable device for preparing wet 3D printed concrete blanks.

[0006] The technical solution of the present invention is as follows: A 3D-printed concrete wet blank unconfined compressive strength testing device includes a hollow cylindrical molding cylinder and a hollow cylindrical positioning cylinder. The outer wall of the formwork cylinder is provided with at least two vertical track keys, and two grippers are symmetrically arranged at the top of the outer wall; The positioning cylinder is fitted outside the forming cylinder, and its inner wall is provided with a track groove that matches the track key. The two slide together to form a guide track system, ensuring that the forming cylinder moves along a strictly vertical path during demolding. The lower end of the positioning cylinder extends outward with at least three positioning legs with positioning scales, which are used to cooperate with the centering marks on the loading plate of the press to achieve precise positioning of the entire device at the center of the loading plate.

[0007] Preferably, a miniature oscillating motor switch is encapsulated in the gripper of the molding cylinder, and an oscillating motor is installed inside the molding cylinder wall. The oscillating motor is connected to the oscillating motor switch through an internal cable of the molding cylinder. When the molding cylinder is lifted, the motor is activated to generate high-frequency micro-amplitude vibration, which helps to achieve non-adhesive demolding.

[0008] Preferably, the inner wall of the molding cylinder has a microscopic anisotropic surface texture, which consists of vertically distributed micron-sized grooves to guide moisture distribution and significantly reduce vertical demolding resistance.

[0009] Preferably, the positioning cylinder integrates a non-contact dimensional measurement system, including a vertical measurement array composed of multiple pairs of through-beam photoelectric sensors arranged vertically along the inner wall, a horizontal measurement array composed of multiple pairs of through-beam photoelectric sensors arranged horizontally at different heights on the inner wall of the positioning cylinder, and a microprocessor encapsulated within the positioning cylinder wall for controlling sensor array scanning, receiving on / off signals, identifying critical point positions, and automatically calculating the initial volume of the wet blank. V 0. The positioning cylinder is equipped with a data acquisition switch, which is used to trigger the measurement system and obtain the measurement results with one click.

[0010] The method for testing the unconfined compressive strength of early-age 3D-printed wet concrete blanks using the aforementioned 3D-printed concrete wet blank unconfined compressive strength testing device includes the following steps: S1. In-situ sample preparation and early diagnosis: 1-1. Apply Vaseline lubricant evenly to the lower loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film. Place the assembled device precisely in the center of the lower loading plate of the press by aligning the positioning legs with the positioning scale. 1-2. Apply oil-based concrete release agent to the inner wall of the formwork cylinder to minimize friction and moisture loss; 1-3. Control the laboratory temperature at 20±2℃ and the humidity at 40%RH. Use a shovel to load the freshly mixed 3D printing concrete into the molding cylinder and use a scraper to smooth the surface. S2. Disturbance-free demolding: After standing, start the micro oscillation motor and slowly lift the molding cylinder vertically upward through the guide rail system to complete the undisturbed in-situ demolding of the wet blank; S3. Initial Dimension Test of Wet Preform The positioning cylinder is equipped with a data acquisition switch, which is used to trigger the measurement system and obtain measurement results with one click; Keep the positioning cylinder in place and allow the wet billet to stand for 1 minute. Then, activate the data acquisition switch located inside the positioning cylinder to trigger the non-contact dimensional measurement system. The vertical and horizontal measurement arrays will automatically scan and acquire data, and the integrated microprocessor will record the initial height of the wet billet. h 0 and initial diameter / width b 0, and according to the formula V 0= h 0×π×( b 0 / 2)² Automatically calculates the initial volume of the wet blank. V 0; S4. Unconfined Compression Test: 4-1. Apply Vaseline lubricant evenly to the upper loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film to ensure frictionless boundary conditions as much as possible. 4-2. The wet billet is compressed using a displacement control method, and the load is continuously recorded until the height of the wet billet reaches 40%. F (t) and displacement h (t) data; S5. Overall Performance Evaluation: 5-1. Changes in wet billet deformation over time h (t) divided by the initial height of the wet blank h The strain of the 3D printed concrete wet blank as a function of loading time can be calculated from 0. ε (t); 5-2. Based on strain ε (t) can be calculated using the following formula to determine the real-time loading area of ​​the wet blank. A (t): A (t)= A 0 / [1-0.01 ε (t)]; 5-3. Based on the real-time loading area of ​​the wet blank A (t) can calculate the real-time stress of the wet billet. : = F / A (t); 5-4. Plot the stress-strain curve of the wet billet. The maximum value of the stress-strain curve within the test time range is the unconfined compressive strength of the wet billet. f c .

[0011] The beneficial effects of this invention are as follows: The 3D-printed concrete wet blank preparation device proposed in this invention is used in conjunction with the testing of early compressive strength. The hollow design in the middle of the mold cylinder and positioning cylinder ensures that the wet blank is placed directly on the nylon film on the lower loading plate, ensuring accurate test results. The combination of nylon film and Vaseline ensures that the boundary conditions of the test are frictionless. The guide rail system ensures that the cylindrical wet blank remains upright during demolding, preventing eccentric loading, and the positioning and centering system enables in-situ demolding loading.

[0012] The high-frequency, low-amplitude vibration generated by the "micro-oscillating motor" works in conjunction with the guide grooves of the "functionalized inner wall" to effectively break the adhesion and static friction between the wet blank and the mold, minimizing the demolding disturbance of the fluidized wet blank and ensuring the initial authenticity of the test sample.

[0013] The non-contact dimensional measurement system inside the positioning cylinder can quickly and accurately test the initial dimensions of the wet billet, which is then used to calculate the unconfined compressive strength of the wet billet. The entire process greatly reduces human error and subjective judgment, making the test results more accurate, more repeatable, and easier to standardize and promote. Attached Figure Description

[0014] Figure 1 Top view of a 3D-printed unconfined compressive strength testing device for wet concrete blanks; Figure 2 A side view of a 3D-printed unconfined compressive strength testing device for wet concrete blanks; Figure 3 Vertical cross-sectional view of the formwork cylinder; Figure 4 This is a cross-sectional view of the formwork cylinder; Figure 5 This is a typical stress-strain curve diagram; In the figure, 1 is the molding cylinder, 2 is the positioning cylinder, 3 is the track key, 4 is the gripper, 5 is the track groove, 6 is the positioning leg, 7 is the positioning scale, 8 is the oscillation motor switch, 9 is the horizontal measurement array of the through-beam photoelectric sensor, 10 is the vertical measurement array of the through-beam photoelectric sensor, 11 is the data acquisition switch, 12 is the internal cable of the molding cylinder, 13 is the oscillation motor, and 14 is the inner wall of the molding cylinder. Detailed Implementation

[0015] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0016] Example 1 See Figures 1-4 The present invention provides a 3D printed concrete wet blank unconfined compressive strength testing device, including a hollow cylindrical molding cylinder 1 and a hollow cylindrical positioning cylinder 2.

[0017] The outer wall of the molding cylinder has four vertical track keys 3, and two grippers 4 are symmetrically arranged at the top of the outer wall. A miniature oscillation motor switch 8 is encapsulated in the grippers of the molding cylinder. An oscillation motor 13 is installed inside the molding cylinder wall. The oscillation motor 13 is connected to the oscillation motor switch 8 via an internal cable 12. When the molding cylinder is lifted, the motor is activated, generating high-frequency micro-amplitude vibrations to assist in achieving non-adhesive demolding. The inner wall 14 of the molding cylinder has a microscopic anisotropic surface texture, consisting of vertically distributed micron-level grooves, which guide moisture distribution and significantly reduce vertical demolding resistance.

[0018] The positioning cylinder is fitted outside the mold-forming cylinder, and its inner wall is provided with a track groove 5 that matches the track key. The two slide together to form a guide track system, ensuring that the mold-forming cylinder moves along a strictly vertical path during demolding. This ensures that the side of the cylindrical wet blank remains upright during demolding, preventing eccentric loading. The lower end of the positioning cylinder extends outward with three positioning legs 6 with positioning scales 7, which are used to cooperate with the centering marks on the lower loading plate of the press to achieve precise positioning of the entire device at the center of the loading plate.

[0019] The positioning cylinder integrates a non-contact dimensional measurement system, including a vertical measurement array 10 composed of multiple pairs of through-beam photoelectric sensors arranged vertically along the inner wall, a horizontal measurement array 9 composed of multiple pairs of through-beam photoelectric sensors arranged horizontally at different heights on the inner wall of the positioning cylinder, and a microprocessor encapsulated within the positioning cylinder wall for controlling sensor array scanning, receiving on / off signals, identifying critical point positions, and automatically calculating the initial volume of the wet blank. V 0. The positioning cylinder is equipped with a data acquisition switch 11, which is used to trigger the measurement system with one key and obtain the measurement results.

[0020] Example 2 The method for testing the unconfined compressive strength of early-age 3D-printed wet concrete blanks using the apparatus described in Example 1 includes the following steps: S1. In-situ sample preparation and early diagnosis: 1-1. Apply Vaseline lubricant evenly to the lower loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film. Place the assembled device precisely in the center of the lower loading plate of the press by aligning the positioning legs with the positioning scale. 1-2. Apply oil-based concrete release agent to the inner wall of the formwork cylinder to minimize friction and moisture loss; 1-3. Control the laboratory temperature at 20±2℃ and the humidity at 40%RH. Use a shovel to load the freshly mixed 3D printing concrete into the molding cylinder and use a scraper to smooth the surface.

[0021] S2. Disturbance-free demolding: After settling, start the micro-oscillation motor and simultaneously lift the mold cylinder vertically upward slowly through the guide rail system to complete the undisturbed in-situ demolding of the wet blank.

[0022] S3. Initial Dimension Test of Wet Preform The positioning cylinder is equipped with a data acquisition switch, which is used to trigger the measurement system and obtain measurement results with one button.

[0023] Keep the positioning cylinder in place and allow the wet billet to stand for 1 minute. Then, activate the data acquisition switch located inside the positioning cylinder, triggering the non-contact dimensional measurement system. The vertical and horizontal measurement arrays will automatically scan and acquire data, and the integrated microprocessor will record the initial height of the wet billet. h 0 and initial diameter / width b 0, and according to the formula V 0= h 0×π×( b 0 / 2)² Automatically calculates the initial volume of the wet blank. V 0.

[0024] S4. Unconfined Compression Test: 4-1. Apply Vaseline lubricant evenly to the upper loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film to ensure frictionless boundary conditions as much as possible. 4-2. The wet billet is compressed using a displacement control method, and the load is continuously recorded until the height of the wet billet reaches 40%. F (t) and displacement h (t) data.

[0025] S5. Overall Performance Evaluation: 5-1. Changes in wet billet deformation over time h (t) divided by the initial height of the wet blank h The strain of the 3D printed concrete wet blank as a function of loading time can be calculated from 0. ε (t).

[0026] 5-2. Based on strain ε (t) can be calculated using the following formula to determine the real-time loading area of ​​the wet blank. A (t): A (t)= A 0 / [1-0.01 ε (t)]; 5-3. Based on the real-time loading area of ​​the wet blankA (t) can calculate the real-time stress of the wet billet. : = F / A (t); 5-4. Plot the stress-strain curve of the wet billet. The maximum value of the stress-strain curve within the test time range is the unconfined compressive strength of the wet billet. f c .

[0027] A 3D-printed concrete mix design (as shown in Table 1) was selected, and wet 3D-printed concrete specimens were prepared according to the method described above. Through a series of experiments, the load and deformation of the wet 3D-printed concrete specimens over time were obtained under a 10-minute gradient within 60 minutes, and the stress-strain curves were calculated, as shown below. Figure 5 As shown in the figure, the curve conforms to scientific principles and matches the range of early-stage unconfined compressive strength test values ​​for similar concrete, while significantly improving the test accuracy.

[0028] Table 1. Mix proportions for 3D printed concrete. <![CDATA[Cement (kg / m 3 )]]><![CDATA Sand-to-rubber ratio Water-to-glue ratio <![CDATA[Thickener (kg / m 3 )]]> 1140 2 / 3 0.3 0.83 Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, without departing from the spirit of the present invention, several modifications or improvements can still be made, and all such modifications or improvements fall within the scope of protection claimed by the present invention.

Claims

1. A device for testing the unconfined compressive strength of 3D-printed wet concrete blanks, characterized in that, It includes a hollow cylindrical molding cylinder and a hollow cylindrical positioning cylinder; The outer wall of the formwork cylinder is provided with at least two vertical track keys, and two grippers are symmetrically arranged on the outer wall; The positioning cylinder is sleeved outside the molding cylinder, and its inner wall is provided with a track groove that matches the track key. The two slide together to form a guide track system. The lower end of the positioning cylinder extends outward with at least three positioning legs with positioning scales, which are used to cooperate with the centering marks on the lower loading plate of the press. The gripper of the molding cylinder is equipped with an oscillating motor switch, and an oscillating motor is installed inside the molding cylinder wall. The oscillating motor is connected to the oscillating motor switch through an internal cable of the molding cylinder. The inner wall of the molding cylinder has a microscopic anisotropic surface texture, which is a vertically distributed micron-level groove. The positioning cylinder integrates a non-contact dimensional measurement system, including a vertical measurement array composed of multiple pairs of through-beam photoelectric sensors arranged vertically along the inner wall, a horizontal measurement array composed of multiple pairs of through-beam photoelectric sensors arranged horizontally at different heights on the inner wall of the positioning cylinder, and a microprocessor encapsulated within the positioning cylinder wall for controlling sensor array scanning, receiving on / off signals, identifying critical point positions, and calculating the initial volume of the wet blank. V 0. The positioning cylinder is equipped with a data acquisition switch, which is used to trigger the measurement system and obtain the measurement results with one click.

2. A method for testing the unconfined compressive strength of early-age 3D-printed wet concrete blanks using the unconfined compressive strength testing device for 3D-printed wet concrete blanks as described in claim 1, characterized in that, Includes the following steps: S1. In-situ sample preparation and early diagnosis: 1-1. Apply Vaseline lubricant evenly to the lower loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film. Place the assembled device in the center of the lower loading plate of the press by aligning the positioning legs with the positioning scale. 1-2. Apply oil-based concrete release agent to the inner wall of the formwork cylinder; 1-3. Control the laboratory temperature at 20±2℃ and the humidity at 40%RH. Fill the freshly mixed 3D printed concrete into the molding cylinder and smooth the surface. S2. Disturbance-free demolding: Start the oscillating motor and simultaneously lift the mold cylinder vertically upward through the guide rail system to complete the undisturbed in-situ demolding of the wet blank; S3. Initial Dimension Test of Wet Preform The positioning cylinder is equipped with a data acquisition switch, which is used to trigger the measurement system and obtain measurement results with one click; Keeping the positioning cylinder in place, allow the wet billet to stand for 1 minute. Then, activate the data acquisition switch located inside the positioning cylinder, triggering the non-contact dimensional measurement system. The vertical and horizontal measurement arrays will scan and acquire data, and the integrated microprocessor will record the initial height of the wet billet. h 0 and initial diameter / width b 0, and according to the formula V 0= h 0 × π × ( b 0 / 2)² Automatically calculates the initial volume of the wet blank. V 0; S4. Unconfined Compression Test: 4-1. Apply Vaseline lubricant evenly to the upper loading plate, then cover it with a layer of nylon film, and then apply Vaseline lubricant to the surface of the nylon film. 4-2. The wet billet is compressed using a displacement control method, and the load is continuously recorded until the height of the wet billet reaches 40%. F (t) and displacement h (t) data; S5. Overall Performance Evaluation: 5-1. Changes in wet billet deformation over time h (t) divided by the initial height of the wet blank h 0 represents the calculated strain of the 3D-printed wet concrete blank as a function of loading time. ε (t); 5-2. Based on strain ε (t) The real-time loading area of ​​the wet blank is calculated using the following formula. A (t): A (t)= A 0 / [1-0.01 ε (t)]; 5-3. Based on the real-time loading area of ​​the wet blank A (t) Calculate the real-time stress of the wet blank. ： = F / A (t); 5-4. Plot the stress-strain curve of the wet billet. The maximum value of the stress-strain curve within the test time range is the unconfined compressive strength of the wet billet. f c .

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