Printing parameter defining method for isotropic foam concrete

Abstract

The invention belongs to the field of 3D printing building material preparation, and particularly relates to a printing parameter defining method for isotropic foam concrete. Comprising the following steps: (1) preparing foam concrete meeting 3D printing; (2) determining a value range of a printing interval ti according to the following formula; (3) curing the printing sample, and preparing a water absorption test sample; (4) performing perspective imaging on the article in the dry state to obtain a dry sample image, performing a water absorption test on the corresponding dry sample, and performing perspective imaging on the sample after water absorption to obtain a water absorption sample image; and (5) subtracting the dry sample image and the water absorption sample image before and after water absorption to obtain a water content curve in the sample, and obtaining an optimal printing interval for preparing the isotropic foam concrete according to the water content curve. The problems that the lower layer structure of the 3D printing foam concrete is prone to collapse and the microstructure is inconsistent in all directions are solved, and the preparation technology of the 3D printing foam concrete is optimized.

Description

Technical Field

[0001] The invention belongs to the field of 3D printing building material preparation, and specifically relates to a method for defining printing parameters of isotropic foam concrete. Background Art

[0002] Today's progress in science and technology has promoted the development of new materials, among which 3D printed foam concrete has attracted widespread attention as a potential building material. Foam concrete has unique application advantages in construction engineering, protective engineering and explosion-proof engineering due to its light weight, heat insulation, wave absorption and other characteristics. However, despite the excellent performance of foam concrete in traditional applications, its development in the field of 3D printing is relatively lagging behind. Due to the complexity of the foam concrete preparation process, which includes the foaming process, it is difficult to maintain the uniform pore structure and stable performance of foam concrete using the 3D printing method in the existing printing process, and how to achieve uniform foam distribution between different layers and maintain a suitable air content has also become a challenge. Therefore, the use of 3D printing methods to prepare foam concrete has been little done. At the same time, from the current results, like ordinary 3D printed concrete, 3D printed foam concrete has a relatively fragile interface between adjacent printed strips due to inconsistent hydration and humidity between the upper and lower layers. During the printing process, the rapid accumulation of interlayer filling materials may cause the materials at the interface to fail to fully fuse or dry unevenly, which in turn affects the overall quality and strength of the foam concrete. It is difficult to achieve an interface bonding strength comparable to that of traditional processes, resulting in unsatisfactory interface performance of 3D printed foam concrete.

[0003] In order to solve the problem of improving the interfacial performance of 3D printed foam concrete, existing research has adopted methods such as optimizing material formulas and additives, using advanced printing equipment or adjusting printing parameters. The interfacial bonding performance of materials can be improved by optimizing material formulas and additives and adjusting the composition and proportion of foam concrete. This method needs to fully consider the compatibility and stability between different materials, as well as the rheological properties and curing process of concrete, which may increase production costs and complicate production processes. Although additives can improve interfacial bonding strength and tensile properties, excessive or inappropriate additives may also cause other properties of materials to decline, thereby affecting the lightweight performance and use characteristics of foam concrete. Advanced printing equipment, such as dual-nozzle or multi-nozzle printing technology, can achieve alternating printing and interlayer bonding of different materials, thereby improving the interface quality and consistency of foam concrete. However, the cost of advanced printing equipment is high. Compared with traditional single-nozzle equipment, the manufacturing and maintenance costs are significantly increased, and the use of advanced printing equipment may increase the complexity of the printing process. In addition, adjusting printing parameters can also optimize interlayer performance. It can directly affect the key factors in the printing process without changing the material formula and increasing the complexity of the equipment, thereby improving the overall performance of 3D printed foam concrete. However, at present, the methods for evaluating the interface performance of 3D printed concrete are still immature, lacking unified standards and accurate quantitative indicators. Existing technologies can evaluate the mechanical properties of the interface of 3D printed foam concrete through macroscopic mechanical tests, such as splitting tensile tests. However, since the shape of the sample interface directly affects the crack propagation path and stress distribution, specimens with different interface shapes may lead to differences in test results, which limits the comparability and versatility of the results. At the same time, the internal interface characteristics of 3D printed foam concrete can be observed by imaging scanning instruments and other means to analyze porosity, pore distribution and interface bonding. However, although imagers can provide important microstructural information, they also have some significant disadvantages and limitations. Since 3D printed foam concrete usually has a high degree of porosity and a fine pore structure, its low resolution limits its wide application in the study of 3D printed foam concrete. In addition, for the quantitative information of the internal interface characteristics of 3D printed foam concrete, the data obtained often require further interpretation and analysis. For example, how to link the pore structure observed by the microscope with the interface performance of 3D printed foam concrete is still a challenging problem. Summary of the invention

[0004] The purpose of the present invention is to provide a method for defining printing parameters of isotropic foam concrete.

[0005] The technical solution to achieve the purpose of the present invention is: a method for defining printing parameters of isotropic foam concrete, comprising the following steps:

[0006] Step (1): preparing foamed concrete suitable for 3D printing;

[0007] Step (2) Determine the printing interval t according to the following formula: i The value range of

[0008] t i =K 1 (t Final -t Initial )+T Initial ×K 2 / f T,H +f v,h

[0009] f T，H ={TT 阈值 , HH 阈值}

[0010] f v,h =h / v

[0011] In the formula, K 1 is the safety factor, K 2 is the humidity influence coefficient, t Initial is the initial setting time of foam concrete, t Final is the final setting time of foam concrete, f T : Temperature and humidity function, describing the impact of the environment on the condensation time, f T，H is the temperature and humidity function, T is the ambient temperature, unit is °C, H is the relative humidity of the lower printing strip, unit is %, h is the thickness of each layer, and v is the printing speed;

[0012] Step (3): curing the printed sample and preparing a water absorption test sample;

[0013] Step (4): performing perspective imaging on the dry product to obtain a dry sample image, performing a water absorption test on the corresponding dry sample, performing perspective imaging on the sample after water absorption to obtain a water absorption sample image;

[0014] Step (5): Subtract the dry sample image before and after water absorption from the water absorption sample image to obtain a water content curve inside the sample, and according to the water content curve, obtain the optimal printing interval for preparing isotropic foam concrete.

[0015] Furthermore, in step (2), T 阈值 The best printing temperature is 20±2℃, H 阈值 The best printing humidity is 50% to 60%; the safety factor K 1 Set to 0.1, humidity influence coefficient K 2 Set to 0.08.

[0016] Furthermore, the curing of the printed sample in step (3) is specifically as follows: after the sample is printed, it is placed at room temperature for 24±4 hours, and then transferred to a saturated calcium hydroxide solution at a temperature of 50±2° C. and cured for 24±4 hours.

[0017] Furthermore, after the curing in step (3) is completed, the sample is cut into a column, the main body of which includes the upper layer, the interlayer and the lower layer area; it is then dried in a vacuum oven at 80±10°C for 12±2 hours until the sample mass is constant, and the five sides of the sample are sealed with epoxy resin, leaving one surface for water absorption, thereby obtaining a water absorption test sample.

[0018] Furthermore, in the water absorption test of step (4), a contrast agent is added to water.

[0019] Furthermore, the contrast agent is potassium iodide or cesium chloride.

[0020] Furthermore, in step (4), the fluoroscopic imaging is performed using an X-ray, a neutron ray flaw detector, a gamma ray flaw detector, a resistivity meter, an ultrasonic flaw detector or an infrared thermal imager.

[0021] Furthermore, in step (5), "deriving the optimal printing interval for preparing isotropic foamed concrete according to the moisture content curve" is specifically:

[0022] For the moisture content curve, the average gray value differences between the upper layer, lower layer and interlayer of the 3D printed foam concrete sample are set to be W A , W B , W C , the average gray value difference of the three regions is μ, and the standard deviation of the average gray value difference of each region is calculated as follows:

[0023]

[0024] The standard deviation σ of the average gray value difference of each group of samples is compared. The smaller the standard deviation, the smaller the difference between different regions in the group. The printing time interval of the group of samples is selected as the optimal printing interval.

[0025] Compared with the prior art, the present invention has the following significant advantages:

[0026] (1) The general process often improves the performance of the interface between 3D printed concrete layers by shortening the printing interval. However, when the printing interval is too short, the lower printing strip has not yet hardened, so the printing strip covering it may cause the foam structure of the lower printing strip to collapse; while this patented technology does not need to compress the printing interval time, it can improve the interface performance while ensuring the isotropy of the foam concrete; at the same time, due to the long printing interval time, this method has lower requirements on the operating speed of the printing equipment, the process is simpler, and it has wide applicability.

[0027] (2) This patented technology uses a water absorption test to evaluate the structural differences of different parts of foam concrete. The experimental principle is simple and the results are highly accurate. In addition, the patent uses multiple projection images of the flaw detector for subtraction. Compared with single imaging, the water absorption image obtained has a higher signal-to-noise ratio, the water absorption information is easier to read, and the microstructure of 3D printed foam concrete is easier to evaluate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of cutting 3D printed foam concrete specimens;

[0029] Figure 2 Schematic diagram of the water absorption process of 3D printed foam concrete specimen;

[0030] Figure 3 The original X-ray image of the sample before water absorption with a printing interval of 15 minutes;

[0031] Figure 4 To print the original X-ray image of the sample after water absorption with an interval of 15 minutes;

[0032] Figure 5 To print the X-ray subtraction images of the sample before and after water absorption with an interval of 15 minutes;

[0033] Figure 6 It is the average gray value difference curve of the sample with a printing interval of 3 minutes;

[0034] Figure 7 This is the average gray value difference curve of the sample with a printing interval of 9 minutes;

[0035] Figure 8 It is the average gray value difference curve of the sample with a printing interval of 15 minutes;

[0036] Fig. 9 This is the average gray value difference curve of the sample with a printing interval of 21 minutes. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0038] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and implementation examples, but the scope of protection claimed by the present invention is not limited thereto.

[0039] The present invention discloses a method for defining printing parameters of isotropic foam concrete, specifically:

[0040] S1. First, cement, fly ash and silica fume are selected as cementitious materials. The cement is P·II 52.5 cement produced by Onoda Cement Plant in Nanjing, Jiangsu Province, the fly ash is F-type fly ash produced by Minghui Plant in Zhuhai, Guangdong Province, and the water reducer is a polycarboxylic acid water reducer provided by Jiangsu Bote New Materials Co., Ltd. The water reduction rate is 30%, and the water-cement ratio is 0.33. The slurry is prepared according to the mix ratio. The foaming agent is a solid powder foaming agent, which is foamed in the form of electric stirring. The experimental foam stabilizer is a modified silicone resin polyether emulsion. The prepared foam is added to the stirred slurry. When the wet density of the slurry reaches the designed wet density, the addition is stopped and the slurry is mixed evenly.

[0041] S2. Add the prepared foam slurry into the printing nozzle at a uniform speed for 3D printing, and determine the value range of the printing interval according to the following formula:

[0042] t i =K 1 (t Final -t Initial )+T Initial ×K 2 / f T,H +f v,h

[0043] f T，H ={TT 阈值 , HH 阈值}

[0044] f v,h =h / v

[0045] Further T 阈值 That is, the best printing temperature is 20℃, H 阈值 That is, the best printing humidity is 50%.

[0046] So we have f T,H =T-20+H-50%

[0047] The temperature T is 20℃, and the initial setting time of foam concrete is t Initial is 1800s, the final setting time of foam concrete is t Final The safety factor K is set according to the actual experience value. 1 The humidity influence coefficient K is set to 0.1 according to the actual experience value. 2 is 0.08, the printing temperature T is 20℃, the relative humidity of the lower printing strip is 100% (corresponding to 3min), 90% (corresponding to 9min), 70% (corresponding to 15min), 63.3% (corresponding to 21min); in this experiment, v: printing speed is 14mm / s, h: layer thickness is 20mm; T 1 =180s, T 2=541.428s≈540s, T 3 =900.428s≈900s, T 4 =1264.135s≈1260s;

[0048] A total of 4 groups of samples were printed, with three layers and eight columns in each group. The printing height of each layer was set to 20 mm and the length was set to 200 mm. After the sample was printed, it was placed at room temperature for 24 hours, and then transferred to a saturated calcium hydroxide solution at a temperature of 50°C for rapid curing for 24 hours.

[0049] S3. After curing, cut the sample into pieces with a size of 20×20×60mm. 3 The column (see Figure 1 ), which includes the upper layer, interlayer and lower layer areas. It was then dried in a vacuum oven at 80°C for 12 hours until the sample mass was constant.

[0050] S4. Use epoxy resin to seal the five sides of the sample, leaving one surface (20×20mm 2 ) is used to absorb water. Place it in a container and use an X-ray flaw detector to scan the sample in a dry state. The working voltage and current used are 100KeV and 0.3mA respectively, and then start the water absorption test (see Figure 2 ). A 3% CsCl contrast agent solution was added to the vessel. During the water absorption test, in order to ensure the consistency of the water absorption effect, each group of samples was immersed in the contrast agent to a depth of 2 mm, and the samples were kept in the same position. The timing started from the moment when the bottom surface of the sample came into contact with the contrast agent. The X-ray flaw detector was used to scan various parts of the sample multiple times after 24 hours of water absorption.

[0051] S5. Obtain a microstructure image of the sample, and obtain the average gray value difference of each area within each group of samples by subtracting the images before and after water absorption.

[0052] S6. According to the average gray value difference curve, the average gray value differences between the upper layer, the lower layer and the interlayer of the 3D printed foam concrete sample are set to be W A , W B , W C , the average gray value difference of the three regions is μ, and the standard deviation of the average gray value difference of each region is calculated:

[0053] W A，3min =40.689,W B，3min =26.125,W C，3min =24.722

[0054]

[0055] W A，9min=37.417,W B，9min =77.15,W C，9min =38.461

[0056]

[0057]

[0058] W A，15min =40.031,W B，15min =41.925,W C，15min =39.322

[0059]

[0060] W A，21min =40.094,W B，21min =24.5,W C，21min =37.567

[0061]

[0062] Compare the standard deviation σ of the average gray value difference of each group of samples:

[0063] σ 9min >σ 3min >σ 21min >σ 15min

[0064] The smaller the standard deviation, the smaller the difference between different regions in the group. Therefore, under the 15-min printing interval, the 3D printed foam concrete sample is isotropic, and 15 minutes is selected as the optimal printing interval for 3D printed foam concrete.

Claims

1. A method for defining printing parameters of isotropic foam concrete, characterized in that: The steps include: Step (1): preparing foamed concrete suitable for 3D printing; Step (2) Determine the printing interval t according to the following formula: i The value range of t i =K1(t Final -t Initial )+T Initial ×K2 / f T,H +f v,h f T，H ={T-T 阈值 ,H-H 阈值 } f v,h =h / v In the formula, K1 is the safety factor, K2 is the humidity influence factor, t Initial is the initial setting time of foam concrete, t Final is the final setting time of foam concrete, f T : Temperature and humidity function, describing the impact of the environment on the condensation time, f T，H is the temperature and humidity function, T is the ambient temperature, unit is °C, H is the relative humidity of the lower printing strip, unit is %, h is the thickness of each layer, and v is the printing speed; Step (3): curing the printed sample and preparing a water absorption test sample; Step (4): performing perspective imaging on the dry product to obtain a dry sample image, performing a water absorption test on the corresponding dry sample, performing perspective imaging on the sample after water absorption to obtain a water absorption sample image; Step (5): Subtract the dry sample image before and after water absorption from the water absorption sample image to obtain a water content curve inside the sample, and according to the water content curve, obtain the optimal printing interval for preparing isotropic foam concrete.

2. The method according to claim 1, characterized in that: In step (2), T 阈值 The best printing temperature is 20±2℃, H 阈值 The best printing humidity is 50% to 60%; the safety factor K1 is set to 0.1, and the humidity influence factor K2 is set to 0.

08.

3. The method according to claim 2, characterized in that The specific method of curing the printed sample in step (3) is as follows: after the sample is printed, it is placed at room temperature for 24±4 hours, and then transferred to a saturated calcium hydroxide solution at a temperature of 50±2° C. and cured for 24±4 hours.

4. The method according to claim 3, characterized in that After the curing in step (3) is completed, the sample is cut into a column, the main body of which includes the upper layer, the interlayer and the lower layer area; then it is dried in a vacuum oven at 80±10°C for 12±2 hours until the sample mass is constant, and the five sides of the sample are sealed with epoxy resin, leaving one surface for water absorption, thereby obtaining a water absorption test sample.

5. The method according to claim 4, characterized in that In the water absorption test of step (4), a contrast agent is added to water.

6. The method according to claim 5, characterized in that The contrast agent is potassium iodide or cesium chloride.

7. The method according to claim 6, characterized in that In step (4), the fluoroscopic imaging is performed using an X-ray, a neutron ray flaw detector, a gamma ray flaw detector, a resistivity meter, an ultrasonic flaw detector or an infrared thermal imager.

8. The method according to claim 7, characterized in that In step (5), "deriving the optimal printing interval for preparing isotropic foam concrete according to the moisture content curve" is specifically: For the moisture content curve, the average gray value differences between the upper layer, lower layer and interlayer of the 3D printed foam concrete sample are set to be W A , W B , W C , the average gray value difference of the three regions is μ, and the standard deviation of the average gray value difference of each region is calculated as follows: The standard deviation σ of the average gray value difference of each group of samples is compared. The smaller the standard deviation, the smaller the difference between different regions in the group. The printing time interval of the group of samples is selected as the optimal printing interval.

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