A method for quickly evaluating the printability of 3D printed concrete based on torque feedback

Abstract

The present invention belongs to the field of 3D printing concrete, and specifically relates to a method for quickly evaluating the printability of 3D printing concrete based on torque feedback. First, an actual printing unit, a small-scale simulation unit, and an effect detection unit are set up. Then, the actual printing unit and the small-scale simulation unit simultaneously perform printing and stirring operations on the same freshly mixed concrete material, record their respective torque-speed curves and print effect evaluations, and establish a database one by one corresponding to each other. The optimal printing range of torque characteristics is obtained based on the existing data. Then, the small-scale simulation unit prints the concrete material with unknown characteristics, and determines whether the torque characteristics of the material fall within the optimal printing range of torque characteristics, so as to quickly evaluate the printability of the concrete material, reduce the material consumption required for actual printing tests, and at the same time provide quick and accurate feedback for the design of concrete materials and the targeted optimization of printing performance; it only takes about 0.5 hours to complete a reliable evaluation of the printability of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing concrete, and particularly relates to a method for quickly evaluating the printability of 3D printing concrete based on torque feedback. Background Art

[0002] As a new building construction method, 3D printing concrete technology has received extensive attention in recent years. The concrete materials used in 3D printing concrete technology require the concrete to have pumpability for smooth transportation through pipes, extrudability for smooth extrusion through nozzles, stackability for smooth stacking after extrusion from nozzles, and volume stability for maintaining stability after stacking. These properties of concrete materials are mainly related to their rheology and setting time.

[0003] In 3D concrete printing operations, it is necessary to match printing parameters according to the characteristics of concrete materials. However, the evaluation of the printability of concrete materials has always been one of the main challenges in this field. The rheological properties of materials directly determine the quality and efficiency of 3D printing concrete. The traditional evaluation method for 3D printing concrete requires a large number of actual printing tests to determine the printing parameters of a certain concrete mix ratio that has not been printed before. This not only takes time and effort but also causes a large amount of material waste and high costs. In addition, due to the lack of a standardized and quantitative evaluation system, it is difficult to objectively compare the printability of different concrete mix ratios.

[0004] Therefore, it is necessary to provide an improved technical solution for the above-mentioned deficiencies of the prior art. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for quickly evaluating the printability of 3D printing concrete based on torque feedback, which can measure the torque characteristics of concrete materials through a small-scale simulation unit and quickly judge the printability of the concrete materials according to the results.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] A method for quickly evaluating the printability of 3D printing concrete based on torque feedback, comprising the following steps:

[0008] Step S1, Equipment preparation and basic configuration:

[0009] Set up an actual printing unit, a small-scale simulation unit, and an effect detection unit; the actual printing unit is a 3D printing device for carrying out actual 3D printing operations, and this stirring mechanism is internally equipped with a first sensor that can sense and record in real time the torque generated by the motor during the stirring process of the 3D printing device; the small-scale simulation unit has a stirring function and is internally equipped with a second sensor that records the torque generated by the motor during the material stirring process; the effect detection unit is used to evaluate the printing results of the actual printing unit.

[0010] Step S2. Basic test and data collection:

[0011] The actual printing unit and the small-scale simulation unit simultaneously carry out printing and stirring operations on the same freshly mixed concrete material, and record their respective torque-speed curves.

[0012] Step S3. Printing effect evaluation:

[0013] Use this freshly mixed concrete material to print a standard test model, and at the same time use the effect detection unit to score the printing effect of the actual printing unit; establish the corresponding relationship between the torque-speed curves of the actual printing unit and the small-scale simulation unit and the printing effect.

[0014] Step S4. Establish a database and determine the optimal parameters:

[0015] Prepare concretes with various different components, repeat steps S2 and S3, and construct a database in which the torque-speed curves of the actual printing unit, the torque-speed curves of the small-scale simulation unit, the printing effects, and the printing parameters of the actual printing unit correspond one by one.

[0016] Based on the numerical comparison of the printing effect results in the database, according to the optimal printing effect range, determine the optimal printing interval of the torque characteristics; the torque characteristics include the static torque growth rate and the dynamic torque growth rate.

[0017] Step S5. Printability evaluation of concrete material X:

[0018] For the concrete material X with unknown printing characteristics, use the small-scale simulation unit to obtain the torque characteristics of the concrete material X, and judge whether the torque characteristics of the unknown concrete material fall within the optimal printing interval of the torque characteristics; if it falls within the optimal printing interval of the torque characteristics, then the concrete material X has good printability and no proportion adjustment is required.

[0019] Further, the method for quickly evaluating the printability of 3D printed concrete based on torque feedback further includes step S6, determining printing parameters: for the concrete material whose torque characteristics fall within the optimal printing range of torque characteristics, multiple groups of printing parameter tests are carried out through the actual printing unit, and the optimal printing parameters are preferably selected according to the result values of the printing effect; the printing parameters include the traveling speed of the traveling mechanism and the extrusion speed of the stirring mechanism.

[0020] Further, in step S5, it further includes a database update step: the torque-speed curve, rheological parameters, printing effect score, and optimal printing parameters obtained by testing the concrete material X with unknown printing characteristics are entered into the database.

[0021] Further, the comprehensive printing effect score E is:

[0022] E = 50% × H + 25% × S + 25% × C ,

[0023] wherein, , , ;

[0024] In the formula, H is the height completion rate, H = h a / h 0, h a is the actual printing height, h 0 is the model preset height; F is the incidence rate of complete fracture of strips with a length exceeding 1 mm, N f is the number of layers with fractures, N t is the total number of layers; V is the void distribution rate on the strip surface, A v is the void area, A t is the total surface area; S is the integrity of the strip surface, C is the width overrun rate, C 0 is the number of measurement points with a width exceeding 120% of the preset width, C t is the total number of measurement points;

[0025] The printing effect score result is 0 - 100%; when the score ≥ 90%, it indicates that the material can be directly printed; when the score < 90%, it indicates that the material cannot be directly printed.

[0026] Furthermore, the optimal printing range of the torque characteristics is a static torque growth rate of 20 - 25 N·m / s and a dynamic torque growth rate of 15 - 20 N·m / (r / s).

[0027] Furthermore, the standard test models are a cylinder model and a single-layer wall model. The cylinder model has a single layer of 20×φ300 mm 2 ; the single-layer wall model has a single layer of 20×500 mm 2 ; the actual printing unit travels at a rate of 60 mm / s, the extrusion rate is 0.6 r / s; the small simulation unit rotates at a speed of 0.6 r / s.

[0028] Furthermore, based on the Bingham model, the static yield torque in the small simulation unit and the torque growth rate reflecting the elastic modulus over time are obtained by setting a low-speed constant shear mode; the dynamic yield torque and the torque growth rate reflecting the material viscosity over the rotational speed are obtained by setting a shear mode from high speed to low speed; the corresponding relationship between the torque-rotation speed curve and the printing effect is obtained through consistent tests of different concrete materials and recorded in the database.

[0029] Furthermore, the small simulation unit can perform rheological property tests based on the Bingham model; the shear force is applied in the rheological property test procedure using the small simulation unit to obtain the torque-time curve performance of the concrete material X corresponding to the unknown printing characteristics.

[0030] Furthermore, the actual printing unit is a 3D printing device for carrying out actual 3D printing operations. The actual printing unit includes a stirring mechanism and a traveling mechanism. The stirring mechanism has the function of adjusting the traveling rate of the nozzle and the material extrusion rate during printing; the stirring mechanism is internally provided with a first sensor for real-time sensing and recording the torque generated by the motor during the stirring process of the 3D printing device; the small simulation unit includes at least a second stirring mechanism, and the capacity of the second stirring mechanism is smaller than that of the first stirring mechanism of the actual printing unit; the second stirring mechanism is internally provided with a second sensor for real-time sensing and recording the torque and rotational speed generated by the motor during the stirring process;

[0031] The effect detection unit is configured as a high-speed camera system with continuous recording and image recognition functions, which can continuously record the height of the 3D printed structure and the distribution and ratio characteristics of appearance defects while the actual printing unit is working; the effect detection unit is internally provided with a fast analysis program system for evaluating the printing effect based on the height and integrity of the 3D printed structure.

[0032] Furthermore, the small simulation unit is a small stirring device or a rheometer with an internal torque-rotation speed sensor.

[0033] The beneficial effects of the present invention are:

[0034] The object of the present invention is to provide a method for quickly evaluating the printability of 3D printing concrete based on torque feedback. This method aims to establish a rapid and quantitative evaluation feedback system for the printability of concrete required for on-site printing. By using a miniaturized simulation device, the torque-rotation speed curve of an unknown concrete material is obtained, thereby obtaining the torque characteristics. Then, it is determined whether the torque characteristics fall within the optimal printing interval of the torque characteristics, so as to quickly evaluate the printability of the concrete material, reduce the material consumption required for actual printing tests, and at the same time provide rapid and accurate feedback for the design of concrete materials and the targeted optimization of printing performance;

[0035] Through the rapid evaluation method based on torque feedback of the present invention, the evaluation of the printability of the material and the optimization of printing parameters are completed in only about 0.5 hours. Compared with the traditional rheometer test method, the efficiency is greatly improved, and there is consistency with the printing effect, and the evaluation results are reliable. Description of the Drawings

[0036] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. Among them:

[0037] Figure 1 It is the dynamic shear result of the ZD-50 type stirring device in the embodiment of the present invention.

[0038] Figure 2 It is the static shear result of the ZD-50 type stirring device in the embodiment of the present invention.

[0039] Figure 3 It is the printing schematic diagram of the cylindrical standard test model in the embodiment of the present invention.

[0040] Figure 4 It is the printing schematic diagram of the single-layer wall standard test model in the embodiment of the present invention.

[0041] Figure 5 It is the fitting schematic diagram of the static yield torque growth rate in the embodiment of the present invention.

[0042] Figure 6 It is the fitting schematic diagram of the dynamic yield torque growth rate in the embodiment of the present invention.

[0043] Figure 7 It is the standard test model for the comprehensive scoring of different printing effects in the embodiment of the present invention.

[0044] Figure 8 It is the dynamic shear result of the rheometer in the embodiment of the present invention.

[0045] Figure 9Static shear results of the rheometer according to the embodiments of the present invention. Detailed implementation manners

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0047] The present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0048] A method for quickly evaluating the printability of 3D printed concrete based on torque feedback, characterized by comprising the following steps:

[0049] Step S1, equipment preparation and basic configuration:

[0050] Set up an actual printing unit, a small simulation unit, and an effect detection unit; the actual printing unit is a 3D printing device for carrying out actual 3D printing operations, and a first sensor for real-time sensing and recording the torque generated by the motor during the stirring process of the 3D printing device is built in the stirring mechanism; the small simulation unit can quickly detect the rheological properties of concrete materials, and a second sensor for recording the torque generated by the motor during the material stirring process is built in; the effect detection unit is used to evaluate the printing results of the actual printing unit.

[0051] Step S2, basic test and data collection:

[0052] The actual printing unit and the small simulation unit simultaneously carry out printing and stirring operations on the same fresh concrete material, and record their respective torque-speed curves.

[0053] Step S3, printing effect evaluation:

[0054] Use the fresh concrete material to print a standard test model, and at the same time use the effect detection unit to score the printing effect of the actual printing unit; establish the corresponding relationship between the torque-speed curves of the actual printing unit and the small simulation unit and the printing effect; as Figure 3 、 Figure 4 shows the printing state of the standard test model, Figure 7 is the standard test model for comprehensive scoring of different printing effects;

[0055] Step S4, establishing a database and determining optimal parameters:

[0056] Prepare concretes with multiple different components, repeat steps S2 and S3, and construct a database in which the torque - rotation speed curve of the actual printing unit, the torque - rotation speed curve of the small - scale simulation unit, the rheological properties of the concrete material represented by torque - related parameters, the printing effect, and the printing parameters of the actual printing unit correspond one by one;

[0057] Based on the numerical comparison of the printing effect results in the database, determine the optimal printing interval of the torque characteristics according to the optimal printing effect range; the torque characteristics include the static torque growth rate and the dynamic torque growth rate; according to the results of previous tests, the optimal printing interval of the present invention is a static torque growth rate of 20 - 25 N·m / s and a dynamic torque growth rate of 15 - 20 N·m / (r / s);

[0058] The torque characteristics, rheological properties, etc. of the materials involved in the present invention are all obtained based on the Bingham model;

[0059] Step S5, Printability evaluation of concrete material X:

[0060] For the concrete material X with unknown printing characteristics, obtain the torque characteristics of the concrete material X using the small - scale simulation unit, and determine whether the torque characteristics of the unknown concrete material fall within the optimal printing interval of the torque characteristics; if it falls within the optimal printing interval of the torque characteristics, then the concrete material X has good printability and no proportion adjustment is required; if not, then the concrete material X cannot be directly printed and its formula needs to be optimized before re - evaluation;

[0061] At the same time, input the torque - rotation speed curve, torque - time curve, rheological parameters, printing effect score, and optimal printing parameters obtained from testing the concrete material X with unknown printing characteristics into the database for database update;

[0062] Step S6, Determination of printing parameters:

[0063] For the concrete material whose torque characteristics fall within the optimal printing interval of the torque characteristics, conduct multiple groups of printing parameter tests through the actual printing unit, and select the optimal printing parameters according to the numerical results of the printing effect; the printing parameters include the traveling speed of the traveling mechanism and the extrusion speed of the stirring mechanism.

[0064] Furthermore, the comprehensive printing effect score E is:

[0065] E = 50%× H +25%× S +25%× C ,

[0066] wherein, , , ;

[0067] In the formula, H is the high completion rate, H = h a / h 0, h a is the actual printing height, h 0 is the preset height of the model; F is the complete fracture incidence rate of strips with a length exceeding 1 mm, N f is the number of layers with fractures, N t is the total number of layers; V is the void distribution rate on the strip surface, A v is the void area, A t is the total surface area; S is the integrity of the strip surface, C is the width overrun rate, C 0 is the number of measurement points with a width exceeding 120% of the preset width, C t is the total number of measurement points; The implementation method of the width overrun rate C uses an edge detection algorithm (such as Canny edge detection) to identify the edges of the strip, selects a pair of symmetric measurement points at equal intervals along the strip length direction (such as every 5 mm, 10 mm), calculates the distance between the two edges at each pair of measurement points as the width, compares the width of each measurement point with the preset width, and calculates the overrun rate by counting the number of overrun points and the total number of measurement points;

[0068] The printing effect scoring result is 0 - 100%; When the score ≥ 90%, it indicates that the material can be directly printed; When the score < 90%, it indicates that the material cannot be directly printed and needs to be optimized by adding admixtures through the feedback of torque data.

[0069] Furthermore, according to the different components of the concrete material, different optimization methods are selected. For example, for the water-binder ratio, the printing result optimization can analyze the yield stress and plastic viscosity of the material according to the Bingham fluid model; For aggregates, adjust the fineness modulus according to the aggregate gradation theory; For the case of adding fly ash, adjust according to the pozzolanic activity theory; For the case of adding nano-modified materials, adjust based on the nano-material dispersion theory. It is also possible to optimize the concrete formulation in the direction of good printing effect according to the existing similar concrete formulations with good printing effects in the database.

[0070] Furthermore, it is a small mixing device or rheometer with an in-built torque-rotation speed sensor. Figures 1 - 2 , Figures 8 - 9Shear result diagrams of the ZD-50 type stirring device and the rheometer, which are respectively small-scale simulation units. It can be seen from the comparison in the figure that the biggest difference between the simulation machine and the rheometer tests lies in the numerical magnitude - the growth rate of the dynamic / static torque measured by the simulation machine is approximately 2-10 times that of the rheometer. Under static conditions, the rheometer test shows that the optimal region can obtain the best number of layers when the torque growth rate is 3.0-3.5 N·m / s and the yield torque is 4.5-5.0 N·m; corresponding to the ZD-50 type stirring device, the optimal region appears at a static torque growth rate of 20-25 N·m / s and a static yield torque of 8-10 N·m. Under dynamic conditions, the rheometer test shows that the optimal interval is within a torque growth rate of 0.4-0.6 N·m / s (r / s) and a yield torque of 0.8-1.0 Mm, while for the ZD-50 type stirring device, the optimal region under dynamic conditions appears at a torque growth rate of 15-20 N m / (r / s) and a yield torque of about 2-3 Nm. Both tests show that the optimal parameters under dynamic conditions will decrease, indicating that this non-linear characteristic is an attribute of the material itself rather than caused by the test method. Considering that the simulation machine is closer to actual 3D concrete printing, it is therefore preferred to use small-scale stirring devices such as the ZD-50 type stirring device as small-scale simulation units, but the rheometer can be used for rapid screening.

[0071] Next, a specific example is used to illustrate the method of the present invention. Among them, the database has been preliminarily established according to the previous experimental results, so it is not shown in the following steps; at the same time, in order to illustrate the reliability of the evaluation results of the present invention, printing is carried out through an actual printing unit and the printing effect is evaluated.

[0072] A method for rapidly evaluating the printability of 3D printed concrete based on torque feedback, and the specific implementation steps are as follows:

[0073] Select a cement-based 3D printing material with a water-binder ratio of 0.30 and a mineral admixture replacement rate of 30%, and conduct a rapid evaluation of its printability.

[0074] (1) Equipment preparation and basic configuration

[0075] The actual printing unit uses a ZD-300 type 3D printing device, including a main mechanism and a traveling mechanism with a φ300mm stirring barrel, and a first sensor is built in. The first sensor can be a KH-T8 type torque sensor; the small-scale simulation unit uses a ZD-50 type stirring device with a stirring barrel capacity of 50L, and a second sensor is configured. The second sensor can be a KH-T5 type torque-rotation speed sensor; the effect detection unit uses a high-speed camera system with a frame rate of 1000fps and is equipped with an automatic image analysis program for evaluating the printing results of the actual printing unit.

[0076] (2) Basic test and data collection

[0077] Load the concrete material to be tested into the actual printing unit and the small-scale simulation unit simultaneously. Set the initial traveling speed of the actual printing unit to 60 mm / s and the extrusion speed to 0.6 r / s; set the stirring speed of the small-scale simulation unit to 0.6 r / s.

[0078] First, conduct a low-speed constant shear test with the rotation speed set to 0.025 r / s, record the obtained static yield torque as 3.2 N·m, and the torque-time growth rate as 22.5 N·m / s; then conduct a high-speed to low-speed shear test, record the dynamic yield torque as 2.6 N·m, and the torque-rotation speed growth rate as 17.8 N·m / (r / s). Figure 5 and Figure 6 shows the schematic diagram of obtaining the growth rates of static and dynamic yield torques, Figure 5 、 Figure 6 The slope of the fitted line in the scatter plot is the growth rate of static and dynamic yield torques.

[0079] (3)Printing effect evaluation

[0080] Use a standard test model for printing evaluation, including a cylinder (20×φ300 mm²) and a single-layer wall (20×500 mm²). The effect detection unit records the following parameters:

[0081] The actual printing height is 285 mm, the preset height is 300 mm, and the calculated height completion rate H = 95%;

[0082] The void distribution rate V on the strip surface is 3%, the fracture incidence rate F is 2%, and the comprehensive surface integrity S is 95%;

[0083] The total number of width measurement points is 200, the number of out-of-limit points is 16, and the calculated width out-of-limit rate C = 8%;

[0084] According to the comprehensive scoring formula for printing effect E = 50%H + 25%S + 25%C, the calculated comprehensive score is 94.5%.

[0085] (4)Parameter optimization and solution determination

[0086] Based on the comparison in the database, the torque characteristics of this material fall within the optimal printing range (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s), and no ratio adjustment is required. Through three groups of printing parameter tests, the optimal printing parameters are finally determined: traveling speed 65 mm / s, extrusion speed 0.65 r / s.

[0087] (5)Verification test

[0088] Perform verification printing with optimized printing parameters. Continuously print 5 groups of standard specimens. The height completion rate reaches over 98%, the surface integrity remains above 96%, the width overrun rate is controlled within 5%, and the comprehensive score is stable above 95%. This proves that the material has good printability and the printing parameter settings are reasonable.

[0089] (6)Database update

[0090] Enter the torque - speed curve, rheological parameters, printing effect score, and optimal printing parameters obtained from this test into the database for rapid evaluation reference of subsequent similar materials.

[0091] Through the rapid evaluation method based on torque feedback of the present invention, it only takes about 0.5 hours to complete the evaluation of the printability of the material and the optimization of the printing parameters. Compared with the traditional rheometer test method, the efficiency is increased by about 70%, and the printing effect is reliably guaranteed.

[0092] Next, the evaluation, verification, and optimization processes of 3D - printed concrete for 7 examples with different formulations are given. Among them, Examples 1 - 6 are optimized one or two times, and finally, concrete materials with good printability above 80% are obtained; Example 7 is the printed concrete designed according to the optimal interval parameters obtained in the previous research and directly has good printability.

[0093] Example 1

[0094] A method for rapidly evaluating the printability of 3D - printed concrete based on torque feedback, the specific steps are as follows.

[0095] Select 3D - printed concrete with a water - binder ratio of 0.42 and a mineral admixture replacement rate of 15% for evaluation. The initial test shows that the static yield torque is 1.8 N·m, and the torque - time growth rate is 12.3 N·m / s; the dynamic yield torque is 1.2 N·m, and the torque - speed growth rate is 8.5 N·m / (r / s). These parameters are all significantly lower than the requirements of the printable interval (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), indicating that the material has excessive fluidity due to too high a water - binder ratio and lacks sufficient support strength, and the raw material ratio should be adjusted.

[0096] Verification of printing effect: The actual printing height only reaches 195 mm (preset 300 mm), and the calculated height completion rate H = 65%; there are 8% void ratio and 6% fracture rate on the strip surface, and the surface integrity S = 72% is obtained; at the same time, the width overrun rate C = 28% is measured, reflecting poor self - standing ability of the material. According to the comprehensive printing effect scoring formula E = 50%H + 25%S + 25%C, the comprehensive score is only 67.5%, indicating that the material does not meet the 3D printing requirements under the existing ratio.

[0097] Based on the analysis of the Bingham fluid model, to increase the yield stress and plastic viscosity of the material, first, the water-binder ratio was reduced to 0.38 to enhance the cohesion of the paste. At the same time, to maintain appropriate fluidity, 0.3% of water reducer was added. The reduction of the water-binder ratio can directly increase the static yield strength, while the addition of the water reducer can regulate the dynamic rheological properties, enabling the material to have good pumpability while maintaining sufficient support strength.

[0098] The optimized test results show that: the static yield torque is increased to 2.8 N·m, and the torque-time growth rate reaches 19.5 N·m / s; the dynamic yield torque is increased to 2.2 N·m, and the torque-rotation speed growth rate reaches 16.8 N·m / (r / s). These parameters are all close to the optimal printing range, and the printing effect is significantly improved: the height completion rate is increased to 92%, the surface integrity is increased to 85%, and the width overrun rate is reduced to 15%. Calculated according to the same scoring equation, the comprehensive score of the material is increased to 86%, reaching the standard for optimized use.

[0099] Example 2

[0100] 3D printing concrete with a water-binder ratio of 0.32 and a mineral admixture replacement rate of 45% was selected for evaluation. The initial test shows that the static yield torque is 4.5 N·m, and the torque-time growth rate is 28.6 N·m / s; the dynamic yield torque is 3.8 N·m, and the torque-rotation speed growth rate is 22.4 N·m / (r / s). These parameters all exceed the upper limit of the optimal range (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), indicating that the material has too high viscosity and insufficient fluidity, and the raw material ratio should be adjusted.

[0101] This judgment was verified during the printing process: obvious resistance occurred during the extrusion of the material, resulting in an actual printing height of only 135 mm (preset 300 mm), and the calculated height completion rate H = 45%; there was a 15% porosity and a 12% fracture rate on the surface of the strip, and the surface integrity S = 65%; at the same time, the width overrun rate C = 35% was measured. Calculated according to the comprehensive printing effect scoring formula E = 50%H + 25%S + 25%C, the comprehensive score is only 55%, indicating that the material is completely unsuitable for 3D printing in its current state.

[0102] Based on the Bingham fluid model, to reduce the yield stress and plastic viscosity of the material, first, the water-binder ratio was increased to 0.35, and 0.2% of water reducer was introduced. This adjustment plan is based on the following considerations: appropriately increasing the water-binder ratio can reduce the static yield strength, and the introduction of the water reducer can improve the fluidity of the material, but the dosage needs to be controlled to avoid excessive reduction of the support capacity of the material.

[0103] The test results after the first optimization show that: the static yield torque drops to 3.5 N·m, and the torque-time growth rate drops to 23.2 N·m / s; the dynamic yield torque drops to 2.8 N·m, and the torque-rotation speed growth rate drops to 19.5 N·m / (r / s). The printing effect has been improved: the height completion rate is increased to 78%, the surface integrity is increased to 75%, and the width overrun rate is reduced to 25%. The comprehensive score is increased to 75%, but it still does not reach the optimal standard.

[0104] To further optimize the material properties, the dosage of water reducing agent is adjusted to 0.8%. This adjustment is based on the fact that the first optimization results show that there is still room for optimization of the material, and the torque parameters indicate that the printing performance can be optimized by further improving the fluidity. The final test results show that: the static yield torque is 3.1 N·m, and the torque-time growth rate is 21.5 N·m / s; the dynamic yield torque is 2.5 N·m, and the torque-rotation speed growth rate is 17.2 N·m / (r / s). These parameters all fall within the optimal printing range, and the printing effect is significantly improved: the height completion rate reaches 90%, the surface integrity is increased to 83%, and the width overrun rate is reduced to 18%. The final comprehensive score reaches 85%.

[0105] Example 3

[0106] 3D printing concrete with a water-binder ratio of 0.38, a mineral admixture replacement rate of 25%, and fine sand with a fineness modulus of 1.8 as aggregate is selected for evaluation. The initial test shows that: the static yield torque is 2.2 N·m, and the torque-time growth rate is 15.6 N·m / s; the dynamic yield torque is 1.5 N·m, and the torque-rotation speed growth rate is 11.2 N·m / (r / s). These parameters are lower than the lower limit of the optimal range (static torque growth rate of 20 - 25 N·m / s, dynamic torque growth rate of 15 - 20 N·m / (r / s)), and compared with the concrete with normal graded sand, its static shape retention ability is significantly insufficient, and the raw material ratio should be adjusted.

[0107] Verification of printing effect: In the printing test, the material shows poor interlayer bonding and large deformation: the actual printing height is 174 mm (preset 300 mm), and the calculated height completion rate H = 58%; due to unreasonable aggregate gradation, the surface has a porosity of 12% and a fracture rate of 8%, and the surface integrity S is only 68%; the width overrun rate C reaches 32%. According to the comprehensive score formula for printing effect E = 50%H + 25%S + 25%C, the comprehensive score is 62%, indicating that the material performance needs to be improved urgently.

[0108] Based on the aggregate gradation theory, first, the fineness modulus of sand was adjusted to 2.3 to optimize the void ratio between aggregates, and at the same time, 0.5% thickener was added to increase the viscosity of the paste. Increasing the fineness modulus of sand can improve the aggregate gradation and optimize the internal structure of hardened concrete; while the addition of thickener can increase the plastic viscosity and yield stress of the paste, enhancing the shape retention ability of the material.

[0109] The test results after the first optimization showed that: the static yield torque increased to 2.6 N·m, and the torque-time growth rate increased to 18.8 N·m / s; the dynamic yield torque increased to 2.0 N·m, and the torque-rotation speed growth rate increased to 15.5 N·m / (r / s). The printing effect was significantly improved: the height completion rate increased to 82%, the surface integrity increased to 78%, and the width overrun rate decreased to 22%. The comprehensive score increased to 78%, but there was still a gap from the optimal printing range.

[0110] To further optimize the material properties, the water-binder ratio was adjusted to 0.36, and at the same time, the binder dosage was increased by 5%. This adjustment was based on the analysis of the torque curve after the first optimization, and there was still room for improvement in the static shape retention ability of the material. The final test results showed that: the static yield torque was 2.9 N·m, and the torque-time growth rate was 20.8 N·m / s; the dynamic yield torque was 2.4 N·m, and the torque-rotation speed growth rate was 16.8 N·m / (r / s). The material properties were significantly improved: the height completion rate reached 90%, the surface integrity increased to 85%, and the width overrun rate decreased to 15%. The final comprehensive score reached 85%.

[0111] Example 4

[0112] A 3D printing concrete with a high fly ash content (replacement rate 50%) and a water-binder ratio of 0.36 was selected for evaluation. The initial test showed that the static yield torque was 2.1 N·m, and the torque-time growth rate was 13.2 N·m / s; the dynamic yield torque was 1.4 N·m, and the torque-rotation speed growth rate was 9.8 N·m / (r / s). These parameters were all lower than the optimal range (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), and the ratio of dynamic and static parameters was significantly low, indicating that the early strength development of the material was slow due to the replacement of high fly ash content, and the raw material ratio should be adjusted.

[0113] Verification of printing effect: Obvious interlayer deformation occurred during the printing test; the actual printing height was 156 mm (preset 300 mm), and the calculated height completion rate H = 52%; although the surface void ratio was only 6% and the fracture rate was 7%, the surface integrity S = 75% was obtained, but the width overrun rate C was as high as 38%, reflecting insufficient support performance of the material. According to the comprehensive scoring formula for printing effect E = 50%H + 25%S + 25%C, the comprehensive score was 61.8%.

[0114] Based on the pozzolanic activity theory, 5% silica fume was first added to supplement the early strength. Silica fume has a large specific surface area and high activity, which can quickly react with Ca(OH)2 to form C-S-H gel, making up for the slow early hydration reaction of fly ash. At the same time, the ultra-fine filling effect of silica fume also helps to increase the viscosity of the slurry.

[0115] After the first optimization, the test results showed that: the static yield torque increased to 2.4 N·m, and the torque-time growth rate increased to 16.5 N·m / s; the dynamic yield torque increased to 1.8 N·m, and the torque-rotation speed growth rate increased to 13.2 N·m / (r / s). The printing effect was improved: the height completion rate increased to 76%, the surface integrity increased to 80%, and the width overrun rate decreased to 28%. The comprehensive material score increased to 73%, but further optimization was still needed.

[0116] To achieve a better printing effect, a compound system of a quick-setting agent (0.8% by mass of the cementitious material) and a water-reducing agent (1.2%) was introduced. This adjustment was based on the results of the first optimization. The quick-setting agent quickly formed an early skeleton structure, while the water-reducing agent was used to control the fluidity. The final test results showed that: the static yield torque was 2.8 N·m, and the torque-time growth rate was 19.8 N·m / s; the dynamic yield torque was 2.3 N·m, and the torque-rotation speed growth rate was 16.5 N·m / (r / s). The printing performance was significantly improved: the height completion rate reached 88%, the surface integrity remained at 82%, and the width overrun rate decreased to 16%. The final comprehensive score reached 83%.

[0117] Example 5

[0118] A 3D printing concrete modified with 2% nano-silica and a water-binder ratio of 0.34 was selected for evaluation. The initial test showed that due to the high specific surface area characteristics of the nano-materials, the water demand of the material was large and the dispersibility was poor, resulting in significant fluctuations in the torque data: the static yield torque fluctuated in the range of 3.8 - 5.2 N·m, and the torque-time growth rate varied between 25.5 - 32.1 N·m / s; the dynamic yield torque fluctuated in the range of 3.2 - 4.1 N·m, and the torque-rotation speed growth rate varied between 20.8 - 24.5 N·m / (r / s). These unstable parameters seriously exceeded the optimal range (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), and the raw material ratio should be adjusted.

[0119] Printing effect verification: Obvious "intermittent material discharge" phenomenon occurred during printing; the actual printing height was only 144 mm (preset 300 mm), and the calculated height completion rate H = 48%; the surface void ratio of the strip was 18%, the fracture rate was 15%, and the surface integrity S was only 58%; the width overrun rate C reached 45%. According to the comprehensive scoring formula for printing effect E = 50%H + 25%S + 25%C, the comprehensive score was only 49.8%.

[0120] Based on the nanomaterial dispersion theory, first, the dosage of polycarboxylate superplasticizer was increased to 1.5%, and 0.3% dispersant was introduced to improve the dispersion of nano-silica. This adjustment plan was based on the following considerations: The steric hindrance effect of polycarboxylate superplasticizer can effectively disperse the cementitious material, and the introduction of a special dispersant can further enhance the dispersion stability of nanoparticles, so that the material can obtain stable rheological properties.

[0121] After the first optimization, the rheological properties of the material tended to be stable: the static yield torque was stable at 3.3 N·m, and the torque-time growth rate dropped to 22.8 N·m / s; the dynamic yield torque was stable at 2.7 N·m, and the torque-rotation speed growth rate dropped to 18.5 N·m / (r / s). The printing effect was significantly improved: the height completion rate increased to 78%, the surface integrity increased to 70%, and the width overrun rate decreased to 25%. The comprehensive score of the material increased to 72%, but there was still a gap from the optimal printing range.

[0122] Further optimization was achieved by adjusting the water-binder ratio to 0.36 and adopting a compound admixture system (superplasticizer 1.5% + dispersant 0.3% + stabilizer 0.2%). This adjustment was based on the results of the first optimization. On the basis of ensuring dispersion, the introduction of a stabilizer was used to control bleeding and segregation. The final test results showed that: the static yield torque was 3.0 N·m, and the torque-time growth rate was 21.2 N·m / s; the dynamic yield torque was 2.4 N·m, and the torque-rotation speed growth rate was 17.1 N·m / (r / s). The printing performance was significantly improved: the height completion rate reached 92%, the surface integrity increased to 85%, and the width overrun rate decreased to 14%. The final comprehensive score reached 87%.

[0123] Example 6

[0124] Select a 3D printing concrete using recycled concrete aggregates (replacement rate 40%) and a water-binder ratio of 0.37 for evaluation. Initial tests showed that due to the high water absorption characteristics of recycled aggregates, the workability of the material rapidly decayed: the static yield torque increased rapidly from an initial 2.5 N·m to 4.2 N·m, and the torque-time growth rate increased from 16.8 N·m / s to 27.5 N·m / s; the dynamic yield torque increased from 1.8 N·m to 3.5 N·m, and the torque-rotation speed growth rate increased from 12.5 N·m / (r / s) to 21.8 N·m / (r / s). This significant time-varying characteristic caused the parameters to quickly deviate from the optimal range (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), and the raw material mix ratio should be adjusted.

[0125] Verification of printing effect: During the printing process, the consistency of the material changed greatly. The actual printing height was 165 mm (preset 300 mm), and the calculated height completion rate H = 55%; the void ratio of the strip surface was 14%, the fracture rate was 11%, and the surface integrity S was 63%; the width overrun rate C reached 36%. According to the comprehensive scoring formula for printing effect E = 50%H + 25%S + 25%C, the comprehensive score was only 59.5%.

[0126] Based on the characteristics of recycled aggregates and their influence laws on the rheological properties of concrete, first adopt a two-stage mixing method, and pre-wet and surface-treat the recycled aggregates. Through pre-wetting treatment, the water absorption of recycled aggregates can be reduced, and surface treatment can improve the aggregate interface characteristics; the adoption of the two-stage mixing method helps to fully wet the aggregate surface and slow down the workability loss caused by aggregate water absorption.

[0127] After the first optimization, the rheological properties of the material tended to be stable: the static yield torque was stable at 2.8 N·m, and the torque-time growth rate was 19.2 N·m / s; the dynamic yield torque was stable at 2.2 N·m, and the torque-rotation speed growth rate was 15.8 N·m / (r / s). The printing effect was significantly improved: the height completion rate increased to 80%, the surface integrity increased to 75%, and the width overrun rate decreased to 22%. The comprehensive score of the material increased to 76%, but the duration of workability still needed to be improved.

[0128] To further improve the printing performance, 0.6% of the slump-retaining agent was added to control the workability attenuation. Meanwhile, the amount of binder was appropriately increased by 8% to compensate for the water absorption effect of recycled aggregates. This adjustment was based on the results of the first optimization. Chemical admixtures were used to delay the loss of workability, while ensuring sufficient binder content to meet the requirements of recycled aggregates. The final test results showed that the static yield torque was 2.9 N·m, and the torque-time growth rate was 20.5 N·m / s; the dynamic yield torque was 2.3 N·m, and the torque-rotation speed growth rate was 16.8 N·m / (r / s). The printing performance was significantly improved: the height completion rate reached 89%, the surface integrity was increased to 83%, and the width overrun rate was reduced to 15%. The final comprehensive score reached 84%.

[0129] Example 7

[0130] A 3D printing concrete with a composite binder system (cement: slag powder: fly ash = 6:2:2) and a water-binder ratio of 0.35 was selected for evaluation. This mix design was based on the optimal interval parameters obtained in previous studies, and continuously graded manufactured sand (fineness modulus 2.5) was used as the aggregate. The initial test showed that the static yield torque was 3.0 N·m, and the torque-time growth rate was 22.5 N·m / s; the dynamic yield torque was 2.4 N·m, and the torque-rotation speed growth rate was 16.8 N·m / (r / s). These parameters all fell within the optimal interval (static torque growth rate 20 - 25 N·m / s, dynamic torque growth rate 15 - 20 N·m / (r / s)), indicating that the material had a good rheological property balance and could be directly used as raw material for 3D concrete printing.

[0131] Verification of printing effect: Excellent performance was shown in the printing test; the actual printing height was 285 mm (preset 300 mm), and the calculated height completion rate H = 95%; there were only 3% void ratio and 2% fracture rate on the strip surface, and the surface integrity S reached 94%; the width overrun rate C was only 8%. According to the comprehensive scoring formula for printing effect E = 50%H + 25%S + 25%C, the comprehensive score reached 93.5%. The reasonable mix of the composite binder provided sufficient early strength while ensuring appropriate rheological properties; the controlled water-binder ratio and the use of continuously graded aggregates provided a stable internal structure for the material; finally, through the compound system of adding 0.8% polycarboxylate superplasticizer and 0.2% thickener, a good balance between fluidity and cohesion was achieved.

[0132] To verify the stability of this mix ratio, an intermittent printing test lasting for 4 hours was carried out. The fluctuation range of torque parameters was controlled within 5%, the printing quality remained stable, and the comprehensive score always remained above 90%.

[0133] For those skilled in the art, without departing from the core spirit and basic principles of the present invention, they can freely make various adjustments and equivalent replacements to the technical solutions. Therefore, all adjustments, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for rapidly evaluating the printability of 3D printed concrete based on torque feedback, characterized in that It includes the following steps: Step S1, equipment preparation and basic configuration: Set up an actual printing unit, a small simulation unit, and an effect detection unit; the actual printing unit is a 3D printing device for carrying out actual 3D printing operations, and the actual printing unit includes a stirring mechanism and a traveling mechanism. The stirring mechanism is internally provided with a first sensor that can sense and record in real time the torque generated by the motor during the stirring process of the 3D printing device; the small simulation unit includes at least a second stirring mechanism, and the capacity of the second stirring mechanism is smaller than that of the first stirring mechanism of the actual printing unit; the second stirring mechanism is internally provided with a second sensor that can sense and record in real time the torque and rotational speed generated by the motor during the stirring process; Step S3, basic testing and data collection: The actual printing unit and the small simulation unit simultaneously perform printing and stirring operations on the same freshly mixed concrete material, and record their respective torque-rotation scatter plots; Step S5, printing effect evaluation: Use the freshly mixed concrete material to print a standard test model, and at the same time use the effect detection unit to score the printing effect of the actual printing unit; establish the corresponding relationship between the torque-rotation scatter plots of the actual printing unit and the small simulation unit and the printing effect scores; Step S7, establish a database and determine the optimal parameters: Prepare concretes with multiple different components, repeat steps S2 and S3, and construct a database in which the torque-rotation scatter plots of the actual printing unit, the torque-rotation scatter plots of the small simulation unit, the printing effect scores, and the printing parameters of the actual printing unit correspond one by one; Based on the comparison of the printing effect scores in the database, according to the optimal printing effect score range, determine the optimal printing interval of the dynamic torque growth rate; the dynamic torque growth rate is the slope of the fitting line of the torque-rotation scatter plot; Step S10, printability evaluation of concrete material X: For the concrete material X with unknown printing characteristics, use the small simulation unit to obtain the dynamic torque growth rate of the concrete material X, and judge whether the dynamic torque growth rate of the unknown concrete material falls within the optimal printing interval of the dynamic torque growth rate; if it falls within the optimal printing interval of the dynamic torque growth rate, then the concrete material X has good printability and no proportion adjustment is required.

2. The method for rapidly evaluating the printability of 3D printed concrete based on torque feedback according to claim 1, wherein: It further includes step S12, determine the printing parameters: for the concrete material whose dynamic torque growth rate falls within the optimal printing interval of the dynamic torque growth rate, perform multiple groups of printing parameter tests through the actual printing unit, and select the optimal printing parameters according to the printing effect scores; The printing parameters include the traveling speed of the traveling mechanism and the extrusion speed of the stirring mechanism.

3. The method for quickly evaluating the printability of 3D printing concrete based on torque feedback according to claim 1, characterized in that: The printing effect score E is: E = 50%×H + 25%×S + 25%×C, Among them, ; Wherein, H is the height completion rate, and H = h a / h0, where h a is the actual printing height, and h0 is the preset height of the model; F is the complete fracture incidence rate of strips with a length exceeding 1 mm, N f is the number of layers with fractures, N t is the total number of layers; V is the void distribution rate on the strip surface, A v is the void area, A t is the total surface area; S is the strip surface integrity, C is the width overrun rate, C0 is the number of measurement points with a width exceeding 120% of the preset width, C t is the total number of measurement points; The printing effect score E ranges from 0 to 100%; when the printing effect score E ≥ 90%, it indicates that the material can be directly printed; when the printing effect score E < 90%, it indicates that the material cannot be directly printed.

4. The method for rapidly evaluating the printability of 3D printed concrete based on torque feedback according to claim 1, wherein: The standard test models are a cylinder model and a single-layer wall model. The cylinder model has a single layer of 20×φ300mm 2 ; the single-layer wall model has a single layer of 20×500mm 2 ; the actual printing unit travel speed is 60mm / s, the extrusion speed is 0.6r / s; the small simulation unit rotation speed is 0.6r / s.

5. The method for rapidly evaluating the printability of 3D printed concrete based on torque feedback according to claim 1, wherein: The stirring mechanism has the function of adjusting the traveling speed of the nozzle and the extrusion speed of the material during the printing process.

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