Method for testing plastic shrinkage of 3D printing cement-based material

Abstract

The invention relates to the technical field of building material testing, and discloses a 3D printing cement-based material plastic shrinkage testing method which comprises the following steps: filling a detachable mold with a to-be-tested cement-based material, and compacting the to-be-tested cement-based material; removing a side template of the detachable mold within 1-2 hours after the initial setting of the material; placing the sample in a dry hot air environment, and enabling the sample to generate a crack at the stress constraint device; observing and measuring the width of a crack generated at the stress constraint device; and calculating the plastic shrinkage strain according to the ratio of the sum of the crack widths of the plurality of observation points to the length of the sample. According to the invention, accurate quantification of the plastic shrinkage strain is realized through the detachable three-surface exposed mold, the stress constraint device induces the crack, and the crack width is measured at multiple observation points.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building material testing, in particular to a 3D printing cement-based material plastic shrinkage test method. BACKGROUND

[0002] In the traditional construction process, a large amount of formwork material and manual labor are required, carbon emissions are large, and the economic cost is high. The 3D printing technology brings a new solution. Concrete 3D printing can significantly simplify the construction process and maximize waste reduction. Due to the high plasticity and stability of the material, it has a significant advantage in building design and customized construction, solving many limitations and shortcomings of traditional construction.

[0003] Due to the formwork-free printing and layer-by-layer stacking construction method of concrete 3D printing, the surface area exposed to air increases, accelerating water evaporation. From material mixing, standing to a printable state, to extrusion and stacking, there is a long time span. During this period, a large amount of water continues to evaporate from the surface of the material and the printed component, and the high plastic viscosity characteristics of the material itself and the long contact with air will cause the printed component to produce a large plastic shrinkage in the early stage, thereby exacerbating the cracking risk. This problem will seriously damage the application durability, printing aesthetics, and structural stability of the 3D printing concrete component.

[0004] Plastic shrinkage is one of the main reasons for early cracking of concrete structures. It is of great significance to carry out relevant test analysis on the early plastic shrinkage behavior of 3D printing concrete components. Although advanced technologies such as non-contact full-field strain measurement systems and laser range finders have a broad prospect due to their high precision and ability to capture detailed deformation patterns, these methods require complex settings and powerful computing power, in addition, the test personnel also need to have certain operation basis, which further limits their wide application. In addition, compared with conventional cast concrete, 3D printing concrete components have a unique layered structure and irregular cell shape, making it difficult for traditional methods to accurately test the plastic shrinkage and cracking behavior of printed components, and the test mold cannot be reused.

[0005] Therefore, there is an urgent need for a 3D printing cement-based material plastic shrinkage test method to solve the above problems. SUMMARY

[0006] The purpose of the present application is to provide a 3D printing cement-based material plastic shrinkage test method to solve the above problems existing in the prior art.

[0007] To achieve the above purpose, the present application provides the following scheme: the present application provides a 3D printing cement-based material plastic shrinkage test method, comprising the following steps:

[0008] The cement-based material to be tested is filled into a removable mold and compacted.

[0009] Remove the side templates of the detachable mold within 1-2 hours after the material has initially set;

[0010] The specimen was placed in a dry, hot air environment to induce cracks at the stress restraint.

[0011] Observe and measure the width of the crack generated at the stress restraint;

[0012] The plastic shrinkage strain is calculated based on the ratio of the sum of the crack widths at multiple observation points to the specimen length.

[0013] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided. The detachable mold includes a base plate, and side constraint plates are detachably connected to both sides of the base plate. Constraint blocks are provided at both ends between the two side constraint plates, and stress constrainers are provided on the base plate.

[0014] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided, wherein the two side constraint plates are detachably connected by bolts.

[0015] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided. The stress constraint includes a large-size constraint and two small-size constraints. The large-size constraint is located in the middle of the substrate, and the two small-size constraints are located on both sides of the large-size constraint and are evenly arranged at four equal points on the mold.

[0016] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided, wherein the flow spread of the cement-based material to be tested is in the range of 150mm-250mm and the initial setting time is 1-2 hours.

[0017] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided, wherein the environment of the sample is dry hot air generated by a heater and a dehumidifier.

[0018] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided, wherein the cement-based material to be tested is filled by pouring through a wide-mouth funnel or by compacting in layers.

[0019] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided, wherein the formula for calculating the plastic shrinkage strain ε is as follows:

[0020] ε(%)=(A+B+C+a'+c') / L×100;

[0021] Where A and C are the crack widths at the observation points corresponding to the two small-sized constraint blocks, B is the crack width at the observation point corresponding to the large-sized constraint block, a' and c' are the crack widths at the corresponding observation points between the two constraint blocks and the specimen, and L is the specimen length. The units for crack width and specimen length are mm.

[0022] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials is provided. The crack width is measured using a scale with a graduation of 0.5 mm. At least three points are measured along the widest part of the crack, and the average value is taken as the representative width of the crack.

[0023] According to the present invention, a method for testing the plastic shrinkage of 3D printed cement-based materials involves placing the sample in a dry, hot air environment with the wind direction parallel to the length of the sample.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This invention provides a method for testing the plastic shrinkage of 3D-printed cement-based materials. In use, a substrate, double-sided constraint plates, and stress restraints are fixed with bolts and nuts. Dry powder and fine aggregate are mixed according to the mixing ratio for 3 minutes. Water and admixtures are added in two batches, and mixing continues until homogeneous, controlling the flowability to 150-250 mm. Depending on the material's flowability, the sample is filled into the mold using either pouring or layered compaction. The mold is gently tapped to remove air bubbles. One to two hours after initial setting, the side molds are removed. The sample is placed in a dry, hot air environment with the airflow parallel to the sample. The crack widths at points A, B, C, a', and c' are measured using a 0.5 mm graduated scale. The ratio of the total width to the sample length is calculated to obtain the plastic shrinkage strain. This invention achieves accurate quantification of plastic shrinkage strain through a detachable, three-sided exposed mold, stress restraints inducing cracks, and multi-point measurement of crack width. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Fig. 1 This is a front view of the overall structure of the present invention;

[0028] Fig. 2 This is a top view of the overall structure of the present invention;

[0029] Among them, 1. substrate; 2. side constraint plate; 3. stress constraint device; 4. constraint block. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] Reference Figs. 1-2 This invention provides a method for testing the plastic shrinkage of 3D printed cement-based materials, comprising the following steps:

[0033] The cement-based material to be tested is filled into a removable mold and compacted.

[0034] Remove the side templates of the detachable mold within 1-2 hours after the material has initially set;

[0035] The specimen was placed in a dry, hot air environment to induce cracks at the stress restraint.

[0036] Observe and measure the width of the crack generated at the stress restraint;

[0037] The plastic shrinkage strain is calculated based on the ratio of the sum of the crack widths at multiple observation points to the specimen length.

[0038] In one embodiment of the present invention, during use, a substrate, double-sided constraint plates, and stress restrainers are used and fixed with bolts and nuts. The dry powder and fine aggregate are mixed for 3 minutes according to the mixing ratio. Water and additives are added in two batches and the mixture is stirred until uniform. The flowability is controlled at 150-250 mm. Depending on the material flowability, the sample is filled into the mold by pouring or layered compaction. The mold is tapped lightly to remove air bubbles. The side molds are removed 1-2 hours after initial setting. The sample is placed in a dry hot air environment with the wind direction parallel to the sample. The crack widths at points A, B, C, a', and c' are measured using a 0.5 mm graduated scale. The ratio of the total width to the sample length is calculated to obtain the plastic shrinkage strain.

[0039] As an optional implementation, the detachable mold includes a base plate 1, with side constraint plates 2 detachably connected to both sides of the base plate 1, and constraint blocks 4 provided at both ends between the two side constraint plates 2, and stress constraint devices 3 provided on the base plate.

[0040] In one embodiment of the present invention, this structure constitutes an innovative "three-sided exposure" testing system. The substrate simulates the bottom support of the printed component, and the detachable constraint plates on both sides simulate the state of the component being exposed to air on both sides. This design increases accuracy by approximately 200% compared to traditional closed molds, accurately reproducing the multidirectional moisture evaporation scenario of 3D printed components during actual construction, making the testing conditions closer to actual engineering conditions, and the test results more representative.

[0041] As an optional implementation, the two side constraint plates 2 are detachably connected by bolts.

[0042] In one embodiment of the present invention, bolted connections enable rapid and non-destructive assembly and disassembly of the mold. This design overcomes the technical bottleneck of traditional test molds being disposable and wasteful, significantly reducing testing costs and improving testing efficiency. Simultaneously, the bolted connection ensures sufficient structural rigidity and stability of the mold during filling and compaction, while allowing for smooth loosening during demolding, avoiding disturbance or damage to cement samples with very low early strength.

[0043] As an optional implementation, the stress constraint 3 includes a large-size constraint and two small-size constraints. The large-size constraint is located in the middle of the substrate, and the two small-size constraints are located on both sides of the large-size constraint and are evenly arranged at the four division points of the mold.

[0044] In one embodiment of the present invention, a stress constraint device 3 is arranged in four equal parts. An adjustable bolt group forms a gradient stress field inside the specimen, precisely inducing cracks. This design concentrates crack initiation locations at preset observation points A, B, and C, improving crack detection rate. Combined with auxiliary monitoring points a' and c', a multi-dimensional shrinkage strain monitoring network is formed, resulting in more reliable test data compared to traditional random cracking modes.

[0045] This invention provides a systematic method for measuring crack width, enabling comprehensive monitoring of crack conditions at different locations. It establishes a weighted strain calculation formula based on multiple observation points a', A, B, C, and c', achieving distributed measurement of plastic shrinkage strain and significantly improving the accuracy and repeatability of the test. The standardized testing procedure ensures the comparability of test results under different conditions, providing a scientific basis for material performance evaluation and mix design optimization.

[0046] As an optional implementation method, the flow spread of the cement-based material to be tested ranges from 150mm to 250mm, and the initial setting time is 1-2 hours.

[0047] In one embodiment of the present invention, this limitation clarifies the scope of application of the test method, covering everything from self-leveling materials with good flowability to printable materials with high viscosity and high thixotropy. Correlating the initial setting time with the demolding time by 1-2 hours ensures that the test can be conducted during the critical stage when the material is most plastic, thereby accurately capturing the deformation and cracking behavior dominated by plastic shrinkage. This makes the method highly applicable and targeted to mainstream 3D printing cement-based materials.

[0048] As an alternative implementation, the environment of the sample is provided with dry, hot air generated using a heater and a dehumidifier.

[0049] In one embodiment of this invention, a standardized, dry-heat condition that accelerates moisture evaporation is created by actively controlling the ambient temperature and humidity. This not only shortens the testing cycle but, more importantly, ensures the comparability of test results for different batches and formulations of materials. This environmental control method follows internationally accepted standards (such as ASTM C1579), enhancing the scientific rigor and authority of the test data.

[0050] As an optional implementation method, the cement-based material to be tested can be filled by pouring through a wide-mouthed funnel or by compacting in layers.

[0051] In one embodiment of the present invention, two sample preparation processes adapted to different material properties are provided. For cement materials with high initial processability and thixotropic properties, pouring using a wide-mouth funnel can simulate the extrusion process during printing. For mixtures with limited flowability and higher stiffness, each layer is thoroughly compacted using a tamping rod, and the template is gently tapped with a hammer to enhance compaction. Layered compaction ensures sample density and reduces internal defects. This flexibility allows the present invention to accurately test a range of 3D printing materials from soft to hard, filling the technological gap of lacking effective testing methods for high plasticity and viscosity materials.

[0052] As an optional implementation method, the formula for calculating the plastic shrinkage strain ε is:

[0053] ε(%)=(A+B+C+a'+c') / L×100;

[0054] Where A and C are the crack widths at the observation points corresponding to the two small-sized constraint devices, B is the crack width at the observation point corresponding to the large-sized constraint device, a' and c' are the crack widths at the corresponding observation points between the two constraint blocks 4 and the specimen, and L is the specimen length. The units for crack width and specimen length are mm.

[0055] In one embodiment of the present invention, the formula establishes a distributed plastic shrinkage strain quantification model based on multiple observation points. By summing the crack widths of the main restraints A, B, C and auxiliary monitoring points a', c', and normalizing them relative to the specimen length, the model can comprehensively and holistically reflect the overall shrinkage deformation of the specimen, rather than just the local information of a single crack. This method significantly improves the accuracy of strain calculation and the ability to characterize the overall shrinkage behavior of the material.

[0056] As an optional implementation, the crack width is measured using a scale with a graduation of 0.5 mm. At least three points are measured along the widest part of the crack, and the average value is taken as the representative width of the crack.

[0057] In one embodiment of the present invention, a 0.5mm graduated scale is used to ensure basic measurement accuracy, while the method of "averaging at least three points" effectively reduces measurement errors caused by uneven crack widths, improving the representativeness and reliability of individual crack width data. This allows the method to be successfully implemented even in ordinary laboratories lacking expensive optical measurement equipment, facilitating the promotion of the technology.

[0058] As an optional implementation, the sample is placed in a dry, hot air environment with the airflow direction parallel to the length of the sample.

[0059] In one embodiment of the present invention, the sample is placed in a dry, hot air environment with the wind direction parallel to the sample's length. This ensures that the sample is uniformly exposed to dry air along its length, avoiding uneven moisture evaporation rates in different parts of the sample due to turbulent wind direction or wind perpendicular to the sample, which could lead to uneven shrinkage and additional disturbance stress. This control ensures that plastic shrinkage cracks are mainly caused by the material's inherent properties and its reaction under preset stress constraints, improving the repeatability and accuracy of the test results.

[0060] This invention employs a three-sided exposed, detachable mold structure to accurately simulate the multi-directional exposure state of 3D printed components during actual construction. Compared to traditional single-sided exposure testing methods, this device, through a combination structure of side constraint plates and a substrate, increases the test surface area by 200% compared to traditional closed molds, thus more accurately reflecting the actual exposure state of the printed components.

[0061] This invention proposes a four-part layout for the stress restraint device, which uses adjustable bolt groups to create a gradient stress field inside the specimen, precisely inducing cracks. This design concentrates crack initiation locations at preset observation points A, B, and C, improving crack detection rate. Combined with auxiliary monitoring points a' and c', it forms a multi-dimensional shrinkage strain monitoring network, resulting in more reliable test data compared to traditional random cracking modes.

[0062] This invention provides a systematic method for measuring crack width, enabling comprehensive monitoring of crack conditions at different locations. It establishes a weighted strain calculation formula based on multiple observation points a', A, B, C, and c', achieving distributed measurement of plastic shrinkage strain and significantly improving the accuracy and repeatability of the test. The standardized testing procedure ensures the comparability of test results under different conditions, providing a scientific basis for material performance evaluation and mix design optimization.

[0063] This invention proposes an integrated testing process of "casting-mold removal-monitoring," overcoming the technical bottleneck of traditional molds that cannot be reused. It also proposes a combined testing method of "layered compaction-directional airflow," simulating the interlayer moisture migration effect of printed components by controlling the timing of mold removal and aligning it parallel to the airflow direction. Furthermore, it develops a dual-mode sample preparation process combining layered compaction and integral casting, adaptable to most printing materials from self-leveling to high thixotropic materials, filling a gap in testing methods for high-plasticity, high-viscosity printing materials.

[0064] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0065] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method of testing the plastic shrinkage of a 3D printed cementitious material, characterized in that, The method comprises the following steps: The cement-based material to be tested is filled into a detachable mold and compacted; The side mold plate of the detachable mold is removed within 1-2 hours after the material is initially set; The sample is placed in a dry hot air environment to generate cracks at the stress restrictor; The crack width generated at the stress restrictor is observed and measured; The plastic shrinkage strain is calculated according to the ratio of the sum of crack widths of multiple observation points to the length of the sample.

2. A method of testing the plastic shrinkage of a 3D printing cementitious material according to claim 1, characterized in that: The detachable mold comprises a base plate (1), both sides of which are detachably connected with side constraint plates (2), both ends between the two side constraint plates (2) are provided with constraint blocks (4), and a stress restrictor (3) is arranged on the base plate.

3. A method of testing the plastic shrinkage of a 3D printing cementitious material according to claim 2, characterized in that: The two side constraint plates (2) are detachably connected through bolts.

4. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 2, wherein: The stress restrictor (3) comprises one large-size restrictor and two small-size restrictors, the large-size restrictor is located at the middle of the base plate, and the two small-size restrictors are respectively located on both sides of the large-size restrictor and are uniformly arranged at four equally divided points of the mold.

5. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein: The flow spread of the cement-based material to be tested ranges from 150 mm to 250 mm, and the initial setting time is 1-2 hours.

6. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein: The environment of the sample uses a heater and a dehumidifier to generate dry hot air.

7. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein: The cement-based material to be tested is filled into a detachable mold and compacted; 8. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein, The formula for calculating the plastic shrinkage strain ε is: ε (%) = (A+B+C+a'+c') / L×100; Wherein, A and C are the crack widths of the observation points corresponding to the two small-size restrictors, B is the crack width of the observation point corresponding to the large-size restrictor, a' and c' are the crack widths of the observation points between the two constraint blocks (4) and the sample, L is the length of the sample, and the units of crack width and sample length are mm.

9. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein: The crack width is measured using a scale with a division of 0.5 mm, at least three points along the widest part of the crack are measured, and the average value is taken as the representative width of the crack.

10. The method for testing plastic shrinkage of a 3D printing cementitious material according to claim 1, wherein: The sample is placed in a dry hot air environment, and the wind direction is parallel to the length direction of the sample.

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