3D printing fiber cement-based material based on in-situ polymerization toughening as well as preparation method and application of 3D printing fiber cement-based material

Abstract

The invention discloses a 3D printing fiber cement-based material based on in-situ polymerization toughening as well as a preparation method and application of the 3D printing fiber cement-based material. The cement-based material is prepared from the following raw materials in parts by weight: 20-25 parts of Portland cement; 7-9 parts of quartz sand; 0.1 to 0.4 part of a polymer monomer; 0.003 to 0.009 part of an initiator; 0.002 to 0.008 part of a polyamino cross-linking agent; 0.12 to 0.18 part of fiber; 0.06 to 0.08 part of a water reducing agent; and 7-10 parts of water. According to the cement-based material, a multi-scale toughening method is adopted, the toughness of the 3D printing cement-based material is greatly improved through polymer monomer in-situ polymerization and fiber doping, and the 3D printing cement-based material has good printability by adjusting the water-cement ratio, the polymer / fiber content, the water reducer content and other parameters of the 3D printing cement-based material. The problem of balance between printability and mechanical properties of traditional 3D printing building materials is effectively solved, and further engineering application of the 3D printing technology can be promoted.

Description

Technical Field

[0001] The present invention relates to a cement-based material, in particular to a 3D printed fiber cement-based material based on in-situ polymerization toughening, and also to a preparation method and application of the cement-based material. Background Art

[0002] With the development of the construction industry, digital 3D printing technology is gradually becoming more popular. 3D printing concrete technology has the advantages of rapid construction, high quality and precision, and personalized design. The use of this technology can effectively improve the construction efficiency of the project, achieve efficient use of resources, and promote the sustainable development of the construction industry. Unlike traditional casting methods, 3D printing requires that the material has specific rheological properties (such as shear thinning and thixotropy) in the fresh state (unhardened stage) to ensure the extrudability, interlayer adhesion and shape stability of the material. At the same time, the hardened structure must meet the mechanical strength and toughness requirements to withstand loads and resist cracking.

[0003] At present, there is a significant contradiction between the printability and toughening of 3D printed cement-based materials. For example, although relying solely on polymer modification has little effect on printability, it has limited effect on improving the toughness and interlayer bonding properties of the material and enhancing crack resistance; and although relying solely on fiber reinforcement can significantly improve crack resistance, it is easy to cause the rheological properties of the material to deteriorate, and it is easy to cause entanglement and nozzle clogging during printing, affecting the continuity and stability of the printing process. A single modification method is often difficult to simultaneously meet the comprehensive requirements of the material in terms of rheology, printability and mechanical properties. Therefore, it is urgent to develop a 3D printing cement-based material with improved printability and toughness. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a 3D printed fiber cement-based material based on in-situ polymerization toughening, which achieves a synergistic improvement in the rheology and toughness of the material by optimizing the synergistic mechanism between polymer and fiber, and also provides a preparation method and application of the above-mentioned cement-based material.

[0005] Technical solution: The 3D printing fiber cement-based material based on in-situ polymerization toughening of the present invention is made of raw materials according to the following weight ratios: 20-25 parts of silicate cement; 7-9 parts of quartz sand; 0.1-0.4 parts of polymer monomer; 0.003-0.009 parts of initiator; 0.002-0.008 parts of polyamino crosslinking agent; 0.12-0.18 parts of fiber; 0.06-0.08 parts of water reducer; 7-10 parts of water.

[0006] Among them, preferably, there are 20 parts of portland cement, 7 parts of quartz sand, 0.2 part of polymer monomer, 0.0036 part of initiator, 0.0056 part of polyamino crosslinking agent, 0.12 - 0.18 part of polyethylene fiber, 0.06 - 0.08 part of polycarboxylate superplasticizer, and 7 parts of water.

[0007] Among them, the cement is PII·52.5 grade ordinary portland cement, with a specific surface area of 345.0 - 355.0 m 2 / kg and an average particle size of 17.50 - 18.00 μm; the fineness modulus of the quartz sand is 1.2 - 1.5, and the particle size is 0.1 - 0.25 mm.

[0008] Among them, the polymer monomer includes acrylamide (AM), 2 - acrylamido - 2 - methylpropanesulfonic acid (AMPS), vinyl acetate (VAc), or methyl methacrylate (MMA), the initiator includes ammonium persulfate (APS) or potassium persulfate (KPS), and the polyamino crosslinking agent is tetramethylethylenediamine (TEMED).

[0009] Preferably, the mass ratio of the polymer monomer to the initiator is 100:(0.1 - 5); the mass ratio of the polymer monomer to the crosslinking agent is 100:(0.2 - 5).

[0010] Among them, the fiber includes synthetic fibers such as polyethylene fiber (PE), polypropylene fiber (PP), polyvinyl alcohol fiber (PVA), polyester fiber (PET), and mineral fibers such as basalt fiber and glass fiber, and carbon fiber.

[0011] Preferably, the polyethylene fiber has a length of 9 - 15 mm, a diameter of 17 - 20 μm, a tensile strength ≥ 2820 MPa, and an elastic modulus ≥ 85 GPa;

[0012] Among them, the solid content of the superplasticizer is a polycarboxylate - based superplasticizer ≥ 30%, and the water - reducing rate ≥ 30%.

[0013] Among them, the water is tap water or drinking water, meeting the requirements of the "Standard for Water Used in Concrete" (JGJ63 - 2006).

[0014] The preparation method of the above - mentioned 3D - printed fiber cement - based material based on in - situ polymerization toughening includes the following steps:

[0015] (1) Dissolve the polymer monomer, initiator, and polyamino crosslinking agent in deionized water, and stir and mix evenly to obtain an acrylamide solution;

[0016] (2) Slowly stir and mix the portland cement and quartz sand evenly to obtain a dry mixture; then slowly add the mixing water and polycarboxylate - based superplasticizer to the dry mixture, and slowly stir and mix evenly to obtain a fresh slurry;

[0017] (3) Add the acrylamide solution to the freshly mixed slurry, and slowly stir and mix evenly to obtain a slurry mixture.

[0018] (4) Gradually add the pre-dispersed polyethylene fibers to the slurry mixture, and quickly stir and mix evenly to form a homogeneous cement mixture without fiber lumps, that is, the 3D printing fiber cement-based material toughened by in-situ polymerization is obtained.

[0019] Among them, the 3D printing fiber cement-based material toughened by in-situ polymerization is prepared by a concrete / mortar 3D printer.

[0020] Among them, in step (1), a magnetic stirrer is used for stirring and mixing, the stirring speed is 120 - 180 rpm, and the stirring and mixing time is 60 - 150 s.

[0021] Among them, in steps (2) and (3), when slowly stirring, the rotational speed of the mixer of the stirrer is 30 - 50 rpm, the rotational speed of the rotor is 130 - 170 rpm, the rotational directions of the mixer and the rotor are opposite, and the slow stirring and mixing time is 120 - 180 s; the stirrer is a JJ-5 type planetary cement mortar stirrer.

[0022] Among them, in step (2), the content of deionized water in the AM solution needs to be subtracted from the mixing water.

[0023] Among them, in step (4), the rotational speed of the mixer of the stirrer is 30 - 50 rpm, the rotational speed of the rotor is 280 - 320 rpm, the rotational directions of the mixer and the rotor are opposite, and the quick stirring and mixing time is 480 - 720 s.

[0024] The present invention also discloses the application of the above-mentioned 3D printing fiber cement-based material toughened by in-situ polymerization in the field of 3D printing construction.

[0025] Invention principle: For the 3D printing fiber cement-based material toughened by in-situ polymerization of the present invention, acrylamide and polyethylene fibers are added to the cement-based material, the performance of the cement-based material is improved through multi-scale modification, and through further optimization of the rheological properties of the material, a synergistic strengthening mechanism is generated between the polymer three-dimensional cross-linked network and the fiber reinforcement phase. The in-situ polymerization-generated organic-inorganic hybrid interface effectively improves the chemical bonding performance between the fiber and the matrix, and a high-toughness cement-based composite material suitable for 3D printing is designed and prepared.

[0026] Specifically, at the micro-nano scale, acrylamide undergoes in-situ polymerization in the cement matrix and jointly forms a three-dimensional interpenetrating network structure with the cement hydration products. The carboxyl groups at the ends of the polyacrylamide chains can form chemical bonds with the hydration products, further enhancing the bonding between the polymer and the hydration products. The cement-based materials can be effectively modified by in-situ polymerization of acrylamide, significantly improving their flexural strength. At the fine macro scale, the "bridging effect" of polyethylene fibers can inhibit the occurrence and expansion of cracks in the cement matrix, further enhancing the performance of the cement-based materials, especially the tensile strength and toughness. Polyacrylamide can also modify the surface of polyethylene fibers to enhance their adhesion to the cement matrix, and the modification measures at different scales have a synergistic effect. By controlling the water-cement ratio and the content of water-reducing agent, the extrudability and constructability of the cement-based composite material are optimized to meet the requirements of the 3D printing process.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: while meeting the requirements of the 3D printing process for the rheological properties of cement-based materials, the present invention realizes the synergistic optimization of the printability, structural strength and fracture toughness of the materials through in-situ polymerization of polymers and fiber toughening. Compared with ordinary cement-based materials, its flexural strength is increased by 185% (up to 21.29 MPa), the axial tensile strength is increased by 156% (up to 7.42 MPa), and the toughness is increased by 158%, effectively overcoming the balance problem between the printability and mechanical properties of traditional 3D printing building materials. Description of the Drawings

[0028] Figure 1 SEM image of the cement-based material prepared in Example 3;

[0029] Figure 2 SEM image of the cement-based material in Example 2;

[0030] Figure 3 Photo of the NELD-3D736 type truss concrete (mortar) 3D printer;

[0031] Figure 4 Photo of the formed state of the polymer-fiber synergistically toughened 3D printed cement-based material prepared in Example 2 during the constructability test;

[0032] Figure 5 Photo of the formed state of the 3D printed hollow cylinder prepared in Example 2;

[0033] Figure 6 Photo of the extrusion fracture and dislocation behavior of the cement-based material prepared in Comparative Example 1;

[0034] Figure 7 Stress-strain curve of the specimens prepared in the examples and comparative examples under uniaxial tensile load. Detailed Description of the Invention

[0035] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings.

[0036] The cement is PII·52.5 grade ordinary Portland cement;

[0037] The fly ash is Class I fly ash;

[0038] The fineness modulus of the quartz sand is 1.2 - 1.5, and the particle size is 0.1mm - 0.25mm;

[0039] The polyethylene fiber has a length of 12 - 15mm, a diameter of 17 - 20μm, an elongation at break of 2 - 3%, a tensile strength of ≥2820 Mpa, and a modulus of elasticity of ≥85 GPa;

[0040] The solid content of the polycarboxylate superplasticizer is ≥40%, and the water reduction rate is ≥30%;

[0041] The water is tap water or drinking water, meeting the requirements of the "Standard for Concrete Water" (JGJ63 - 2006);

[0042] The mixers used are a magnetic stirrer and a JJ - 5 type planetary cement mortar mixer.

[0043] Example 1

[0044] For the 3D printing fiber cement - based material based on in - situ polymerization toughening of the present invention, the following raw material components are taken by weight: 20 parts of cement, 7 parts of quartz sand, 0.2 part of acrylamide, 0.0036 part of ammonium persulfate, 0.0056 part of tetramethylethylenediamine, 0.12 part of polyethylene fiber, 7 parts of water, and 0.06 part of polycarboxylate superplasticizer.

[0045] The preparation method includes the following steps:

[0046] (1) Dissolve acrylamide monomer, ammonium persulfate, and tetramethylethylenediamine in 100 mL of deionized water, and stir and mix using a magnetic stirrer at a stirring speed of 150 rpm for 120 s to obtain an acrylamide solution.

[0047] (2) Add the pre - weighed PII52.5 Portland cement and quartz sand into the planetary cement mortar mixer in sequence, and slowly stir and mix evenly. The rotation speed of the mixer of the mixer is 45 rpm, the rotation speed of the rotor is 150 rpm, and the rotation directions of the mixer and the rotor are opposite. The slow stirring and mixing time is 120 s to obtain a dry mixture; slowly add mixing water and polycarboxylate superplasticizer to the dry mixture, and slowly stir and mix evenly. The rotation speed of the mixer of the mixer is 45 rpm, the rotation speed of the rotor is 150 rpm, and the rotation directions of the mixer and the rotor are opposite. The slow stirring and mixing time is 180 s to obtain a fresh slurry.

[0048] (3) Add the acrylamide solution to the freshly mixed slurry and slowly stir to mix evenly. The rotational speed of the mixer of the mixer is 45 rpm, the rotational speed of the rotor is 150 rpm, the rotational directions of the mixer and the rotor are opposite, and the time for slow stirring and mixing is 180 s to obtain a slurry mixture.

[0049] (4) Gradually add the pre-dispersed PE fibers to the slurry mixture and quickly stir to mix. The rotational speed of the mixer of the mixer is 45 rpm, the rotational speed of the rotor is 300 rpm, the rotational directions of the mixer and the rotor are opposite, and the time for quick stirring and mixing is 600 s to form a homogeneous mixture without fiber lumps.

[0050] Example 2

[0051] For the 3D printing fiber cement-based material based on in-situ polymerization toughening of the present invention, the following raw material components are taken by weight parts: 20 parts of cement, 7 parts of quartz sand, 0.2 part of acrylamide, 0.0036 part of ammonium persulfate, 0.0056 part of tetramethylethylenediamine, 0.18 part of polyethylene fiber, 7 parts of water, and 0.08 part of polycarboxylate superplasticizer.

[0052] The preparation method is the same as that of Example 1.

[0053] Example 3

[0054] A cement-based material, the following raw material components are taken by weight parts: 20 parts of cement, 7 parts of quartz sand, 0 part of acrylamide, 0 part of ammonium persulfate, 0 part of tetramethylethylenediamine, 0.18 part of polyethylene fiber, 7 parts of water, and 0.08 part of polycarboxylate superplasticizer.

[0055] The preparation method is the same as that of Example 1.

[0056] Comparative Example 1

[0057] A cement-based material, the following raw material components are taken by weight parts: 20 parts of cement, 7 parts of quartz sand, 0.6 part of acrylamide, 0.0108 part of ammonium persulfate, 0.0168 part of tetramethylethylenediamine, 0.18 part of polyethylene fiber, 7 parts of water, and 0.08 part of polycarboxylate superplasticizer.

[0058] The preparation method is the same as that of Example 1.

[0059] Comparative Example 2

[0060] A cement-based material, the following raw material components are taken by weight parts: 20 parts of cement, 7 parts of quartz sand, 0 part of acrylamide, 0 part of ammonium persulfate, 0 part of tetramethylethylenediamine, 0 part of polyethylene fiber, 7 parts of water, and 0 part of polycarboxylate superplasticizer;

[0061] The preparation method is the same as that of Example 1.

[0062] The materials prepared in the examples and comparative examples were tested:

[0063] (1) Flexural strength: Prismatic specimens with dimensions of 40×40×160 mm were used. For each example and comparative example, 3 specimens were molded and cured under standard conditions for 28 d. The curing temperature was 20±2 °C, and the relative humidity was ≥95%. The loading speed was 50 N / s, and the test index was flexural strength;

[0064] (2) Uniaxial tensile test: Dog-bone-shaped thin plate specimens with dimensions of 12 mm×40 mm×160 mm were used. For each example and comparative example, 3 specimens were molded and cured under standard conditions for 28 d. The curing temperature was 20±2 °C, and the relative humidity was ≥95%. The test indexes were tensile strength and toughness index (the ratio of the ultimate tensile strain to the initial crack strain of the specimen);

[0065] (3) Extrudability: The cement mortar was extruded immediately after mixing. A strip with a total length of 3000 mm and a width of 20 mm was continuously extruded at a constant speed along a specific path. The evaluation criteria were defined as follows: Good, no obvious fracture, blockage, jamming, etc. occurred during extrusion, the surface continuity of the paste was good, and there were no obvious cracks; General, no obvious fracture, blockage, jamming, etc. occurred during extrusion, but the surface continuity of the paste was not good, and there were obvious cracks; Poor, obvious fracture, blockage, jamming, etc. occurred during extrusion;

[0066] (4) Buildability: After the cement mortar was mixed, 20-layer hollow cylindrical specimens with a width of 20 mm and a height of 5 mm were cumulatively extruded. The vertical height was measured at four points on the ring of the specimen, and the vertical height change rate η (the ratio of the actual height to the theoretical height) was calculated, and the results were averaged. The evaluation criteria were defined as follows: Good (η < 5%); General (5% ≤ η ≤ 10%); Poor (η > 10%).

[0067] As Figure 3 shown, the printability test was carried out using an NELD-3D736 type truss concrete (mortar) 3D printer. This equipment consists of three core modules:

[0068] (1) Computer numerical control system, responsible for model parsing and instruction generation;

[0069] (2) Extrusion system, including a silo, a screw conveyor mechanism, and a replaceable-size conical nozzle;

[0070] (3) Three-axis rectangular coordinate moving platform, providing precise positioning in the X / Y / Z axes.

[0071] The test process follows the standardized operating procedures: First, draw a 3D model in Solidworks software, and import the STL format file of the 3D model into the numerical control system slicing software to complete the setting of process parameters such as layer thickness optimization, path planning, and basic rate; then, start the screw rod and slowly inject the freshly mixed slurry into the printing hopper. Stop the rotation immediately after the slurry is extruded and level the surface of the extrusion port; finally, start printing. A variable-diameter screw rod is used to achieve a stable extrusion volume, the extrusion rate is 0.6L / min, and the print head moves at a constant speed to complete the layer-by-layer stacking, with a moving rate of 40mm / s.

[0072] The test results are shown in Table 1

[0073] Table 1. Test Results

[0074] Number Flexural strength / MPa Tensile strength / MPa Toughness index Extrudability Buildability Example 1 15.09 5.95 1.79 Good Good Example 2 21.29 7.42 3.26 Good Good Example 3 17.64 5.65 1.97 Good Good Comparative example 1 15.77 6.17 2.78 Poor Poor Comparative example 2 7.47 2.89 1.26 Good Poor

[0075] The cement-based material of the present invention (Example 2) shows significant performance advantages compared with the ordinary OPC material (Comparative Example 2): its flexural strength is increased by 185% (reaching 21.29MPa), the axial tensile strength is increased by 156% (reaching 7.42MPa), and the toughness is increased by 158%, effectively overcoming the balance problem between printability and mechanical properties of traditional 3D printing building materials.

[0076] The polymer content will significantly affect the printability of 3D printed cement mortar. For example, in Comparative Example 1, acrylamide with a cement mass fraction of 3% is incorporated. Due to the self-cohesion of the polymer, the mortar is too thick and the material extrudability is poor; Comparative Example 2 is a blank group, and the mortar has a large fluidity and does not have constructability. When Example 2 incorporates acrylamide with a cement mass fraction of 1% and PE fiber with a specimen volume fraction of 1.5% at the same time, the material has both excellent printability and strong and tough properties.

[0077] As Figure 1 shown, in the single fiber toughening system, the fiber-cement matrix interface transition zone of Example 3 shows a smooth pull-out feature; as Figure 2 shown, when in-situ polymerization polymer modification is introduced, a significant mechanical interlocking structure is formed in the interface region of Example 2, and dense hydration products can be observed on the surface of the pulled-out fibers. This difference confirms the generation of a synergistic strengthening mechanism between the polymer three-dimensional cross-linked network and the fiber reinforcement phase, and the in-situ polymerization-generated organic-inorganic hybrid interface effectively improves the chemical bonding performance between the fiber and the matrix.

[0078] As Figure 4 、 Figure 5 shown, the extrudability, constructability, and structural stability of each example are good, and this polymer-fiber synergistically toughened cement-based material meets the requirements of 3D printing technology. As Figure 6 shown, in Comparative Example 1, due to the excessive addition of both polymer and fiber, obvious misalignment and fracture phenomena occur during the extrusion of the material.Figure 7 As shown, the stress–strain curves of the embodiments exhibit obvious strain hardening characteristics.

[0079] Therefore, for the 3D printed fiber cementitious material based on in-situ polymerization toughening of the present invention, due to the in-situ polymerization modification of acrylamide, a three-dimensional network structure is formed in the cement matrix, and the modification effect is better than direct incorporation. Due to the addition of polyethylene fibers, the cementitious material has stronger tensile strength and toughness, and a synergistic strengthening mechanism is generated between the polymer three-dimensional cross-linked network and the fiber reinforcement phase. The in-situ polymerization-generated organic-inorganic hybrid interface effectively improves the chemical bonding performance between the fiber and the matrix, and the material also has good printability. Under the condition of meeting the rheological property requirements of the 3D printing process for the cementitious material, the present invention effectively improves the strength and toughness of the 3D printed cementitious material.

Claims

1. A 3D printing fiber cement-based material toughened by in-situ polymerization and its preparation method, characterized in that, The cement-based material is made from raw materials in the following weight proportions: 20-25 parts of portland cement; 7-9 parts of quartz sand; 0.1-0.4 part of polymer monomer; 0.003-0.009 part of initiator; 0.002-0.008 part of polyamino crosslinking agent; 0.12-0.18 part of fiber; 0.06-0.08 part of water-reducing agent; 7-10 parts of water.

2. The 3D printing fiber cement-based material toughened by in-situ polymerization according to claim 1, wherein The cement is PII·52.5 ordinary Portland cement with a specific surface area of 345.0 - 355.0 m 2 / kg and an average particle size of 17.50 - 18.00 μm; the fineness modulus of the quartz sand is 1.2 - 1.5, and the particle size is 0.1 - 0.25 mm.

3. The 3D printing fiber cement-based material based on in-situ polymerization toughening according to claim 1, wherein The polymer monomer includes acrylamide AM, 2-acrylamido-2-methylpropanesulfonic acid AMPS, vinyl acetate VAc or methyl methacrylate MMA. The initiator includes ammonium persulfate APS or potassium persulfate KPS. The polyamino crosslinking agent is tetramethylethylenediamine TEMED.

4. The 3D printing fiber cement-based material toughened by in-situ polymerization according to claim 1, characterized in that, The fiber includes synthetic fibers such as polyethylene fiber PE, polypropylene fiber PP, polyvinyl alcohol fiber PVA, polyester fiber PET, and mineral fibers such as basalt fiber and glass fiber, and carbon fiber. The water-reducing agent is a polycarboxylate-based water-reducing agent.

5. The preparation method of the 3D printing fiber cement-based material toughened by in-situ polymerization as claimed in claim 1, characterized in that It includes the following steps: (1) Dissolve the polymer monomer, initiator and polyamino crosslinking agent in deionized water, and stir and mix evenly to obtain an acrylamide solution. (2) Slowly stir and mix the portland cement and quartz sand evenly to obtain a dry mixture. Subsequently, slowly add mixing water and polycarboxylate-based water-reducing agent to the dry mixture, and slowly stir and mix evenly to obtain a fresh paste. (3) Add the acrylamide solution to the fresh paste, and slowly stir and mix evenly to obtain a paste mixture. (4) Gradually add the pre-dispersed polyethylene fiber to the paste mixture, and quickly stir and mix evenly to form a uniform cement mixture without fiber lumps, that is, the 3D printing fiber cement-based material toughened by in-situ polymerization is obtained.

6. The preparation method according to claim 5, characterized in that, The 3D printing fiber cement-based material toughened by in-situ polymerization is obtained by a concrete / mortar 3D printer.

7. The preparation method according to claim 5, characterized in that, In step (1), use a magnetic stirrer to stir and mix, the stirring speed is 120-180 rpm, and the stirring and mixing time is 60-150 s.

8. The preparation method according to claim 5, wherein In steps (2) and (3), when slowly stirring, the rotation speed of the mixer of the stirrer is 30-50 rpm, the rotation speed of the rotor is 130-170 rpm, the rotation directions of the mixer and the rotor are opposite, and the slow stirring and mixing time is 120-180 s.

9. The preparation method according to claim 5, wherein In step (4), the rotation speed of the mixer of the stirrer is 30-50 rpm, the rotation speed of the rotor is 280-320 rpm, the rotation directions of the mixer and the rotor are opposite, and the quick stirring and mixing time is 480-720 s.

10. Application of the 3D printing fiber cement-based material toughened by in-situ polymerization according to claim 1 in the field of 3D printing construction.

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