Method for evaluating the properties of cement-based materials

Abstract

To provide a property assessing method for a cement-based material capable of assessing lamination stability of a cement-based material.SOLUTION: A property assessing method for a cement-based material forms a laminate, the method comprising: a measurement step of measuring vane shear strength of the cement-based material; a calculation step of calculating shear stress generated in the laminate; and a first assessment step of comparing the vane shear strength and the shear stress and when the vane shear strength value is larger, assessing the cement-based material as having excellent lamination stability.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] This invention relates to a method for evaluating the properties of cement-based materials. [Background technology]

[0002] In recent years, technological development in 3D printing, which forms structures by layering cement-based materials, has been progressing. Since the cement-based materials that form the structures are extremely important elements in this 3D printing process, various technologies have been proposed for evaluating the properties of these materials. For example, Patent Document 1 proposes an apparatus that applies a load to a cement-based test specimen using a weight, measures the amount of lateral displacement of the specimen, and evaluates the specimen based on the measured value. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-6767 [Overview of the project] [Problems that the invention aims to solve]

[0004] When forming structures using 3D printing, it is necessary to layer cement-based materials until a predetermined height is reached. Therefore, the ability of the cement-based material to maintain its shape while being layered (referred to as "buildability") is a very important parameter. Herein, the technology described in Patent Document 1 requires special equipment for evaluating cement-based materials, which means that the situations and contexts in which it can be used are very limited, and it can be said that it is a technology with poor versatility. Therefore, the inventors wanted to create a new, simple evaluation method for assessing lamination stability that does not require special equipment.

[0005] Therefore, an object of the present invention is to provide a method for evaluating the properties of a cementitious material that can easily evaluate the stacking stability of the cementitious material.

Means for Solving the Problems

[0006] The method for evaluating the properties of a cementitious material according to the present invention for solving the above problems is as follows. Lamination begins X minutes after mixing is complete, and t minutes after lamination have elapsed. The vane shear strength of the cementitious material τ (X,t) A measuring step of measuring; Lamination begins X minutes after mixing is complete, and t minutes after lamination have elapsed. The shear stress generated in the laminate τ G (X,t) A calculating step of calculating; and a first evaluation step of comparing the vane shear strength τ V (X,t) with the shear stress τ G (X,t) and evaluating that the cementitious material has excellent stacking stability when the value of the vane shear strength is larger. Furthermore, the shear stress τ G A method for evaluating the properties of cement-based materials, characterized in that (X,t) is calculated based on the following formula. τ G (X,t) = 1 / 2·K·ρgh·n (K: construction coefficient of cement-based material, ρ: density of cement-based material (kg / m³)) 3 ), g:9.8(m / s 2 (h: height of one layer (m), n: number of layers after t minutes have elapsed since stacking) According to the present invention, by comparing the vane shear strength measured in the measuring step with the shear stress calculated in the calculating step, it is possible to easily evaluate the stacking stability without using a special device. Therefore, according to the present invention, it is possible to confirm up to what height the cementitious material to be evaluated can be appropriately stacked (stacking height). In addition, according to the present invention, since it can be evaluated based on the result of a vane shear test (vane shear strength) that can be easily carried out and the calculation result (shear stress), it can be applied not only to pre-material evaluation but also to real-time evaluation of materials used on site, and it can be said that it is a highly versatile evaluation method.

[0007] In the method for evaluating the properties of a cement-based material according to the present invention, it is preferable that the cement-based material is a cement-based material for 3D printers. 。 Book According to the invention, the stacking stability can be evaluated more accurately by calculating the shear stress based on a predetermined formula.

[0008] The method for evaluating the properties of a cement-based material according to the present invention includes a second evaluation step in which the cement-based material is evaluated as having excellent flow retention properties if the vane shear strength of the cement-based material immediately after final stirring, as measured in the measurement step, is 1.0 kPa or less. According to the present invention, since a second evaluation step is included, not only the lamination stability but also the flow retention properties can be appropriately evaluated. [Effects of the Invention]

[0009] According to the method for evaluating the properties of cement-based materials of the present invention, the lamination stability of cement-based materials that form a laminate can be easily evaluated. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the results of the mortar flow test for each sample. [Figure 2A] This graph shows the results of vane shear strength measurement and shear stress calculation, specifically the results for a sample at 10°C. [Figure 2B] This graph shows the results of vane shear strength measurement and shear stress calculation, specifically the results for a sample at 20°C. [Figure 2C] This graph shows the results of vane shear strength measurement and shear stress calculation, specifically the results for a sample at 30°C. [Figure 3] This graph illustrates the correlation between the vane shear strength ratio and the flow value ratio. [Modes for carrying out the invention]

[0011] First, let's explain the "cement-based materials" that are the subject of this property evaluation. [Cement-based materials] Cement-based materials are materials used to form laminates and are materials (filaments) for 3D printers. Cement-based materials include (1) binders, (2) fine aggregates, (3) admixtures, and (4) water.

[0012] (1) Binding material The binder is not particularly limited, and one or more can be selected from ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, blast furnace cement (types A-C), fly ash cement (types A-C), silica cement (types A-C), eco-cement, etc. In addition to the above-mentioned cements, geopolymers and the like may also be used as binders. However, binders that have rapid hardening properties are preferred for use as materials for 3D printers. (2) Fine aggregate The fine aggregate (crushed sand, fine powder) is not particularly limited, and one or more types selected from mountain sand, river sand, sea sand, crushed sand, silica sand, lime sand, etc. can be used. However, since the cement-based material is pumped and discharged from a nozzle, it is preferable that the fine aggregate has a small maximum diameter. The mass ratio of fine aggregate to binder (fine aggregate / binder ratio) is preferably 120-240%, more preferably 150-200%. (3) Admixture The admixture can be any conventionally known material, such as separation reducing agents, water reducing agents, defoaming agents, setting retarders, setting accelerators, AE agents, AE water reducing agents, etc. The mass ratio of the admixture to the binder (admixture / binder ratio) is preferably 1 to 10%, more preferably 2 to 7%. (4)Water The water is not particularly limited, and tap water, sludge water, etc., can be used. The mass ratio of water to binder (water / binder ratio) is preferably 20-50%, more preferably 30-45%. (5) Others The cementitious material may also contain other commonly used substances, such as admixtures such as fly ash, silica fume, and fine powder of blast furnace slag. Note that "for 3D printers" of the cementitious material indicates the use for 3D printers (also referred to as three-dimensional modeling systems or 3D printing systems). A 3D printer is a device that includes a supply head for discharging a material from a nozzle and a pump for pumping the material to the supply head, and forms a three-dimensional object by laminating the material layer by layer.

[0013] Next, a method for evaluating the properties of the cementitious material according to this embodiment will be described. [Method for Evaluating the Properties of Cementitious Material] The method for evaluating the properties of the cementitious material according to this embodiment includes a measurement step, a calculation step, and a first evaluation step. Further, the method for evaluating the properties of the cementitious material according to this embodiment may include a second evaluation step after the measurement step.

[0014] (Measurement Step) The measurement step is a step of measuring the vane shear strength of the cementitious material. τ, which is the vane shear strength V can be measured by using a general vane tester in accordance with the method specified in the "In-situ Vane Shear Test Method" of the Geotechnical Society of Japan Geotechnical Investigation Standard and Guidelines Committee: Methods and Explanations of Geotechnical Investigations - Volume 1 of 2, pp404 - 419, March 2013, Geotechnical Society of Japan Standard (JGS 141l - 2012). When evaluating layer stacking stability, it is necessary to consider the 3D printing time. Therefore, in the measurement process, the vane shear strength of the cement-based material should be measured at predetermined time intervals (several minutes or tens of minutes) after the "final stirring" (when the mixture is mixed, or the last stirring if it has been stirred once or more after mixing). However, for example, if layer stacking starts 25 minutes after mixing, and the layer stacking stability is to be evaluated 30 minutes after the start of stacking, the vane shear strength of the cement-based material after it has been left to stand for 30 minutes from 25 minutes after mixing (i.e., the vane shear strength 55 minutes after mixing) may be measured precisely. On the other hand, when evaluating fluidity retention, in order to confirm the properties immediately after the final stirring, the measurement process should involve measuring the vane shear strength of the cement-based material immediately after the final stirring (for example, within 1 minute of the final stirring).

[0015] (calculation process) The calculation process involves calculating the shear stress generated in the laminate. τ is the shear stress that occurs in a laminate. G is, "τ G It can be calculated based on the formula "=1 / 2·K·ρgh·n". In the above formula, K is the construction coefficient (-) of the cement-based material, and ρ is the density (kg / m³) of the cement-based material. 3 ) and g is 9.8 (m / s 2 ) where h is the height of one layer (m) and n is the number of layers in the stack (-). In detail, the above formula was established assuming that the compressive stress generated in the existing filament layer (cement-based material in this embodiment) is caused by the self-weight of the filaments stacked on top of that layer, and taking into consideration that in the field of geotechnical material testing, half the value of the unconfined compressive strength is used as an estimate of the undrained shear strength (shear stress) of soft cohesive soil for short-term stability problems (Japanese Geotechnical Society, Geotechnical Investigation Standards and Criteria Committee: Methods and Commentary on Geotechnical Investigation - Part 1 of 2, pp. 404-419, March 2013). The construction coefficient K for cement-based materials in the above formula can be calculated from the actual stacking height achieved using cement-based materials and the theoretical height. For example, the value "0.64" derived by the inventors based on previous experimental results can be used. The density ρ of the cement-based material can be measured with a general density measuring device. The height h of one layer is determined based on the settings of the 3D printer used. The number of layers n is a variable that increases over time. For example, when stacking at 1 layer / min, the value after 5 minutes from the start of stacking is 5.

[0016] The construction coefficient K for cement-based materials may be calculated as follows. First, as mentioned above, based on the knowledge in the field of geotechnical material testing, shear stress τ G The relationship between this and the uniaxial compressive strength σ is given by "τ G We can derive "=1 / 2σ" (Equation 1), and the uniaxial compressive strength σ can be expressed as "σ=(ρ·S·h)·g·n / S=ρ·h·g·n" (Equation 2). From these Equations 1 and 2, "n=2τ G The formula " / ρgh" (Equation 3) can be calculated. Then, the shear stress τ measured using a vane shear tester for a given cement-based material can be calculated. G Substitute the given values ​​into Equation 3 to calculate n. In addition, perform a lamination test using the specified cement-based material and confirm the number of layers n' that can be laminated. Finally, calculate the construction coefficient K for the specified cement-based material using "K = n / n'".

[0017] (First evaluation process) The first evaluation step involves comparing the vane shear strength obtained in the measurement step with the shear stress obtained in the calculation step to evaluate the lamination stability of the cement-based material. Here, "buildability" refers to the property of a 3D printer where material (also called filament) can be layered repeatedly on top of the material extruded from the nozzle, maintaining a three-dimensional shape. By evaluating "buildability" in the first evaluation step, it is possible to determine the "layer limit height" by confirming how high the material can be layered while maintaining its three-dimensional shape. If buildability is poor, the material will not be able to maintain its three-dimensional shape when layered, resulting in problems such as tilting or falling over.

[0018] The vane shear strength of cement-based materials increases after the final mixing and the start of lamination (specifically, after being pumped (re-mixed) and extruded into the 3D printer's supply nozzle) because it remains in a stationary state without further mixing. Therefore, in the first evaluation step, it is necessary to take these factors into consideration and compare the vane shear strength with the shear stress. For example, if lamination is started X minutes after mixing is complete, and the vane shear strength after t minutes has elapsed since lamination is defined as "τ V Let (X,t) be the shear stress, and let τ be the shear stress. G If we define "(X,t)", then "τ V (X,t) > τ G When the condition is (X,t), it is evaluated as having excellent stacking stability (in other words, it can be stacked stably up to a height at least t minutes after stacking). Specifically, when lamination is started 20 minutes after mixing is complete, and the lamination stability is evaluated 10 minutes after lamination is complete, the vane shear strength "τ" at 30 minutes after mixing is complete is evaluated. V The measured value of (20,10) and the number of layers n after 10 minutes from the start of lamination are given by τ G The shear stress "τ" obtained by substituting into = 1 / 2·K·ρgh·n G The stacking stability will be determined by comparing the calculated values ​​of (20,10). The time intervals for measuring vane shear strength and calculating shear stress are not particularly limited and can be set appropriately, such as 5-minute intervals, 15-minute intervals, or 30-minute intervals, depending on the required level of accuracy. Similarly, the period for measuring vane shear strength and calculating shear stress are not particularly limited and can be set appropriately, such as until 30 minutes, 60 minutes, or 90 minutes have elapsed since the final mixing, depending on the operating time of the 3D printer. Furthermore, as mentioned above, in the first evaluation step, vane shear strength and shear stress are compared at a pinpoint value (for example, if lamination starts 30 minutes after mixing, τ at t minutes after lamination). V (30,t) and τ G (Only 30, t) may be compared. Alternatively, if you want to perform a simple preliminary evaluation, the above τ V Instead of (30,t), τ is the vane shear strength when the material is laminated immediately after mixing. V (0,t) may also be used.

[0019] (Second evaluation process) The second evaluation step is to evaluate the flow retention properties of the cement-based material based on the vane shear strength obtained in the measurement step. Here, "fluidity retention" refers to the property of a 3D printer to appropriately maintain the fluidity of the material for a predetermined period of time during steady-state pumping and nozzle extrusion. Therefore, if fluidity retention is poor, problems such as a reduced amount of material discharged during pumping or blockage of pipes and nozzles will occur. In the second evaluation step, the vane shear strength τ of the cement-based material immediately after the final stirring (for example, within 1 minute of the final stirring) is evaluated. V If it is 1.0 kPa or less (τ V If the value is ≤1.0, it is evaluated as having excellent flow retention properties.

[0020] (others) The measurement process and the calculation process can be performed in either order or simultaneously. However, if the vane shear strength is calculated in advance, the order should be calculation process → measurement process. If, in any evaluation process, the material properties are not deemed satisfactory, appropriate measures such as readjusting the material composition, re-mixing the material, or suspending construction may be taken. [Examples]

[0021] [Samples used in each test] Considering the various ambient temperatures for 3D printing in the field, three types of materials were prepared with the formulations shown in Table 1: a "10°C sample" intended for use in a 10°C environment, a "20°C sample" intended for use in a 20°C environment, and a "30°C sample" intended for use in a 30°C environment. The binder (P) used is a fast-setting cement with enhanced initial reactivity, and has a density of 3.08 g / cm³. 3 , specific surface area 3970cm 2 The density was / g. Crushed sand (S1) and fine powder (S2) were used as fine aggregate. The density of crushed sand (S1) was 2.71 g / cm³. 3 The maximum particle size was 2 mm, and the coarseness ratio was 2.86. The fine powder (S2) had a density of 2.71 g / cm³. 3 , specific surface area 8160cm 2 A sample with a concentration of 4.0% / g and a residue of 45μ was used. As an admixture, a water-soluble separation reducing agent (V) (density 1.32 g / cm³) was used. 3 ), a polycarboxylic acid-based high-performance water-reducing agent (SP), an antifoaming agent (De), and an oxycarboxylic acid-based setting retarder (Re) were used. Furthermore, 10°C and 30°C samples were prepared by fine-tuning the amount of setting retarder (Re) and fine powder (S2) used, based on the 20°C sample. For mixing each sample, a mixer as specified in JIS R5201:2015 was used. The powder was dry-mixed at low speed for 15 seconds, then water was added and mixed at low speed for 2 minutes. After scraping, it was mixed at low speed for another 2 minutes.

[0022] [Table 1]

[0023] [Preliminary test: Mortar flow test] (Contents of the mortar flow test) The mortar flow test was conducted in accordance with JIS R5201:2015 "Physical Testing Methods for Cement." For each sample (10°C sample, 20°C sample, 30°C sample), the flow value immediately after removing the flow cone (referred to as "0-strike flow value") and the flow value measured after 15 drops over 15 seconds (referred to as "15-strike flow value") were measured. In addition, to match the vane shear test case (a) described later, two flow values ​​were measured for each sample at the time of mixing, and at 25 minutes, 55 minutes, 85 minutes, and 115 minutes later. Furthermore, in the mortar flow test, except for the measurement immediately after mixing, each sample was mixed again at a low speed for 20 seconds using a Hobart mixer and then measured. The mortar flow tests were conducted in constant temperature and humidity chambers (70% RH) at 10°C, 20°C, and 30°C, respectively, depending on the sample. The vane shear tests described later followed the same procedure.

[0024] (Review of mortar flow test results) First, the inventors have previously confirmed in their studies that good 3D printing can be performed when the material's 0-strand flow value is in the range of 115±15mm and the 15-strand flow value is in the range of 170±20mm (Experimental study on the mix and extrudeability of short-fiber reinforced mortar suitable for 3D printing, Annual Proceedings of the Concrete Engineering Society, Vol.43, No.1, pp1373~1378, 2021). Figure 1 shows the results of the mortar flow test performed on each sample using the method described above. As shown in Figure 1, the flow values ​​for both the 10°C and 30°C samples fell within the acceptable range (the range in which good 3D printing can be confirmed) within 115 minutes of mixing completion. In particular, the results for the 30°C sample were found to be distributed almost entirely near the center of the acceptable range. On the other hand, the 20°C sample met the acceptable range within 85 minutes of mixing, but at 115 minutes, the 0-strand and 15-strand flow values ​​increased sharply, significantly exceeding the upper limit of the acceptable range. In actual testing, it was confirmed that the sample immediately lost its fluidity and began to solidify after the flow values ​​increased, suggesting that the effect of the setting retarder was lost. Therefore, the results of the vane shear test at 115 minutes after mixing for the 20°C sample, which will be described later, could not be obtained. In other words, the results in Figure 1 confirm that, with a few exceptions (115 minutes after mixing the 20°C sample), each sample was capable of good 3D printing and, naturally, also exhibited excellent fluidity retention.

[0025] [Examples] (Details of the vane shear test) The vane shear test was conducted in accordance with the method specified in the Japanese Geotechnical Society standard (JGS1411-012) "In-situ vane shear test method," using a push-type vane shear tester with a shear strength measurement limit of 16.2 kPa. To obtain stable results, the depth of the vane tip after insertion was set to four times the vane diameter from the sample surface, and the vane rotation speed was standardized to 15° per second. The vane shear strength was calculated from the average of three rotational resistance measurements taken when the blade was pushed in and rotated at different locations within the sample. Furthermore, in actual 3D printing, the material mixed in one batch is consumed gradually, so it is conceivable that the material may be left to stand for a predetermined time between mixing and the start of layering. Therefore, as shown below, vane shear tests were performed on each sample in four cases with different stirring timings. (a) Mixing complete → Stirring after 25 minutes → Stirring after 55 minutes → Stirring after 85 minutes → Stirring after 115 minutes (b) After mixing is complete, let it stand (continue to stand without stirring). (c) After mixing is complete, stir after 25 minutes (then leave to stand without stirring). (d) After mixing is complete, stir after 55 minutes (then leave to stand without stirring). Figures 2A to 2C are graphs showing the results of the vane shear test performed on each sample using the method described above. Figure 2A shows the results for the 10°C sample, Figure 2B shows the results for the 20°C sample, and Figure 2C shows the results for the 30°C sample. In Figure 2, the "×" marking indicates the measurement result at that point, but it also means that the measurement limit of 16.2 kPa was exceeded in the next measurement. Furthermore, in Figures 2A-2C, M1, M4, and M7 are line graphs connecting the measurement results for case (b), M2, M5, and M8 are line graphs connecting the measurement results for case (c), and M3, M6, and M9 are line graphs connecting the measurement results for case (d).

[0026] (Method for calculating shear stress) Shear stress τ G is, "τ G It was calculated based on "=1 / 2·K·ρgh·n". In the above formula, K is "0.64" as the construction coefficient for cement-based materials, and ρ is the density of each sample (kg / m³). 3 ), g is "9.8" (m / s 2 ), where h is the height of one layer "0.01" (m), n is the number of layers in the stack (-), and the stacking speed was assumed to be 1 layer / min. In Figures 2A-2C, lines L1, L4, and L7 are straight lines showing the calculated shear stress when lamination is started immediately after mixing; lines L2, L5, and L8 are straight lines showing the calculated shear stress when lamination is started 25 minutes after mixing; and lines L3, L6, and L9 are straight lines showing the calculated shear stress when lamination is started 55 minutes after mixing.

[0027] (Examination of results from the examples: fluidity retention) Focusing on the results for case (a) of each sample shown in Figures 2A to 2C, it was confirmed that, with the exception of the 20°C sample which could not be measured after 115 minutes, the vane shear strength of all samples was lower than 1.0 kPa and remained within a relatively small range. Furthermore, considering the results obtained in the mortar flow test (Figure 1) mentioned above (resulting in each sample exhibiting excellent flow retention), it was confirmed that the criterion of judging excellent flow retention as a vane shear strength of 1.0 kPa or less after stirring is appropriate.

[0028] Figure 3 is a graph showing the correlation between the flow value ratio and the vane shear strength ratio. For each sample, the ratio of the measured value immediately after final stirring to the measured flow value immediately after mixing is calculated based on the measured flow value immediately after mixing and the measured vane shear strength immediately after final stirring. Specifically, for example, the plot at 25 minutes after mixing is plotted based on the flow value ratio calculated by "flow value immediately after re-stirring 25 minutes after mixing / flow value immediately after mixing" and the vane shear strength ratio calculated by "vane shear strength immediately after re-stirring 25 minutes after mixing / vane shear strength immediately after mixing". Then, linear regression was performed on the zero-touch flow ratio Rf(0) and the vane shear strength ratio Rv, and on the 15-touch flow ratio Rf(15) and the vane shear strength ratio Rv, respectively, and the resulting regression equations are shown as equations (1) and (2) below. Formula (1): Rf(0)=-0.09Rv+108.67, R 2 =0.73 Formula (2): Rf(15)=-0.15Rv+113.39, R 2 =0.87 Although the amount of data obtained from this test was small, a correlation was observed between the vane shear strength ratio Rf(15) and the vane shear strength ratio, particularly in the range of 54 to 181. From these results, it was confirmed that the vane shear test, which is simpler than the mortar flow test, can appropriately evaluate the flow retention properties of the material.

[0029] (Examination of results from the examples: Lamination stability) In cases (b), (c), and (d) shown in Figures 2A to 2C, the vane shear strength of each sample increases as the standing time elapses after the final stirring. On the other hand, as the vane shear strength increases, the load on the upper layers also continues to increase due to repeated lamination, resulting in larger shear stresses as shown in L1 to L9. According to the results in Figures 2A-2C, in most cases (b), (c), and (d), the vane shear strength was greater than the shear stress generated by the upper layer load. In detail, each plot on the vane shear strength M1 in Figure 2A was greater than the shear stress L1, each plot on the vane shear strength M2 in Figure 2A was greater than the shear stress L2, and each plot on the vane shear strength M3 in Figure 2A was greater than the shear stress L3. Furthermore, each plot on the vane shear strength M4 in Figure 2B showed a value greater than the shear stress L4, and each plot on the vane shear strength M5 in Figure 2B showed a value greater than the shear stress L5. Furthermore, each plot on the vane shear strength M7 in Figure 2C was greater than the shear stress L7, each plot on the vane shear strength M8 in Figure 2C was greater than the shear stress L8, and each plot on the vane shear strength M9 in Figure 2C was greater than the shear stress L9. Based on the above, it was confirmed that the criterion of determining superior lamination stability when the vane shear strength is greater than the shear stress is appropriate.

Claims

1. A method for evaluating the properties of cement-based materials that form a laminate, A measurement step in which lamination is started X minutes after mixing is complete, and the vane shear strength τ V (X, t) of the cement-based material is measured after t minutes have elapsed since lamination, A calculation step in which lamination is started X minutes after mixing is complete, and the shear stress τG(X,t) generated in the laminate after t minutes has elapsed since lamination is calculated, A first evaluation step in which the vane shear strength τ V (X, t) and the shear stress τ G (X, t) are compared, and if the value of the vane shear strength is greater, the cement-based material is evaluated as having excellent lamination stability. Includes, A method for evaluating the properties of a cement-based material, characterized in that the shear stress τG(X,t) is calculated based on the following formula. τ G (X, t) = 1 / 2・K・ρgh・n (K: Construction coefficient for cement-based material, ρ: Density of cement-based material (kg / m³), g: 9.8 (m / s²), h: Height of one layer (m), n: Number of layers after t minutes have elapsed since lamination)

2. The method for evaluating the properties of a cement-based material according to claim 1, characterized in that the cement-based material is a cement-based material for 3D printers.

3. A method for evaluating the properties of a cement-based material according to claim 1 or 2, characterized in that it includes a second evaluation step in which the cement-based material is evaluated as having excellent flow retention properties if the vane shear strength of the cement-based material immediately after final stirring, as measured in the measurement step, is 1.0 kPa or less.

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