CN113912374A

CN113912374A - Powder 3D printing high-strength high-toughness cement-based material and preparation method thereof

Info

Publication number: CN113912374A
Application number: CN202111238192.6A
Authority: CN
Inventors: 刘雄飞; 王楠; 李之建
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2021-10-25
Filing date: 2021-10-25
Publication date: 2022-01-11
Anticipated expiration: 2041-10-25
Also published as: CN113912374B

Abstract

The invention relates to a high-strength and high-toughness cement-based material for powder 3D printing and a preparation method thereof, belonging to the technical field of new materials. Aiming at the problems that interlayer interface bonding performance is reduced by layer-by-layer printing in the powder 3D printing process, the printing layer material is long in setting time and low in strength, constructability is reduced, shrinkage cracking is improved by die-free maintenance and the like, the method combines the advantages of high bonding performance and early strength of Magnesium Phosphate Cement (MPC) and the advantages of intelligence, flexibility and accuracy of a powder 3D printing process, utilizes components of reinforced toughening liquid and reinforced toughening powder to develop a high-strength high-toughness MPC cement-based material capable of being subjected to powder 3D printing, and solves the problems that the powder 3D printing technology has requirements on early-stage quick-hardening high-strength performance of the material, weakening of the printing interlayer interface and die-free maintenance. The pore structure of the powder 3D printed MPC material is optimized, the splitting strength and the breaking strength are obviously improved, and the powder 3D printed MPC material can be applied to structures with requirements on strength and toughness, such as thin walls, hollows, complex shapes and the like.

Description

Powder 3D printing high-strength high-toughness cement-based material and preparation method thereof

Technical Field

The invention belongs to the technical field of new materials, and particularly relates to a powder 3D printing high-strength high-toughness cement-based material and a preparation method thereof.

Background

Since the 21 st century, with the continuous and high-speed development of social economy in China, China continuously makes breakthroughs in the fields of aerospace, modern large-scale engineering and the like, the demand of infrastructure such as roads, bridges, ports and docks, civil airports, national defense engineering and the like is increasing day by day, and meanwhile, people also put higher requirements on materials used in engineering. Throughout the world civil engineering field, cement concrete materials become the most widely used building materials due to the advantages of abundant sources, simple construction, castable, fire resistance, economy, long service life and the like. However, with the continuous progress of social science and technology and the continuous forward progress of urbanization, the demand of the cement material is shifted from the traditional load bearing effect to the development of high performance, multifunction and green sustainable direction nowadays. However, cement materials often have a large number of cracks in engineering applications due to their high brittleness and poor toughness. Problems caused by the reduction of the structural load capacity due to such disadvantages cause a great loss to national economy.

Although compared with the traditional building construction process, the powder 3D printing has the advantages of free building shape, low cost, high efficiency, flexible design, high safety, high accuracy and the like, the innovation and development of the technology will have certain impact on the traditional building and construction method. Powder 3D printing technology is severely limited in its application due to the requirements of printable materials. Currently, only fast hardening portland cement, calcium aluminate cement, magnesium oxychloride cement, and small amounts of cement-based polymers can be used for powder 3D printing. However, these limited materials do not meet the diversity requirements of industrial applications and have no specific evaluation criteria, so the diversity of materials must be increased. The invention researches a powder 3D printing building cement-based material which has good performance, meets the requirements of energy conservation, emission reduction, environmental protection, low energy consumption, low pollution and the like, and plays a key role in the popularization and application of the current technology.

At present, concrete materials are gradually applied to more complex structures and more severe environments, and the problem caused by material failure is increasingly serious. The mechanical and durability properties of concrete are largely dependent on the properties of the cement matrix, and especially for high performance cement-based materials, the cracking strength and the durability of the micro-junction pair material are very important.

In order to overcome the above disadvantages, it has been conventionally practiced to improve the tensile strength and ductility of cement materials at millimeter or micrometer scale using microfibers such as carbon fibers, glass fibers, steel fibers, asbestos fibers, natural fibers, and synthetic fibers; however, each of the above fibers, although having its own unique reinforcing effect in terms of strength, ductility, crack control, etc., can only restrict the propagation of cracks within the material from the macroscopic scale, and cannot restrict the generation of microcracks or nanocractures.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a high-strength and high-toughness cement-based material for powder 3D printing and a preparation method thereof.

The technical scheme of the invention is as follows:

the high-strength and high-toughness cement-based material for powder 3D printing is characterized by comprising the following components in parts by weight:

magnesium phosphate powder: calcining MgO at 800-1600 ℃ for 45min, wherein the particle size is less than 150 mu m; the particle diameter of the fly ash is between 100 and 150 mu m, and the density is more than 2.8g/cm³(ii) a The particle size of the phosphate is less than 150 mu m; the particle sizes of the quartz sand and the PVA are less than 150 mu m; wherein, the molar ratio of magnesium oxide/phosphate is 4/1-5/1; the fly ash accounts for 10-20% of the total amount of the magnesium oxide and the phosphate; the quartz sand accounts for 15-20% of the total amount of the magnesium oxide and the phosphate; PVA accounts for 3-5% of the total amount of magnesium oxide and phosphate;

the components of the reinforcing and toughening liquid are as follows: distilled water, a surface binder, 1,2 propylene glycol and a Polyacrylate (PA) emulsion, wherein the surface tension of the components of the reinforcing and toughening liquid is 41.8-47.8 mN/m, and the viscosity is 1.22-1.67 mPa & s;

the components of the reinforcing and toughening powder are as follows: the magnesium phosphate powder toughening agent comprises a toughening active component and a dispersing agent, wherein the toughening active component is selected from at least one of nano oxides, multi-walled carbon nanotubes and nano fibers, and the doping amount of the toughening active component accounts for 0.1-0.5% of the mass of magnesium phosphate powder;

the magnesium phosphate powder and the reinforcing and toughening powder components form an MPC powder bed, and the porosity of the MPC powder bed is 15-55%.

The nano oxide has the appearance shape of sphere, the average particle size of 100-150 nm and the specific surface area of 10-20 m²A density of 5.88 to 5.91g/cm³The content is more than 99 percent; the multi-wall carbon nanotube has a length of 10-20 μm, an outer diameter of 30-50 nm, and a specific surface area of 60m²The purity is more than 95 percent; the diameter of the nanofiber is 40-60 nm, and the length of the nanofiber is 5-10 mu m; the nano oxide is selected from nano silicon dioxide, nano titanium dioxide, nano iron oxide, nano aluminum oxide and nano zirconium dioxide; the porosity of the MPC powder bed is 15-55%.

When the nano oxide is doped with cement, the nano oxide can react with the cement to reduce the porosity of the non-heavy metal oxide; the toughening active component and the dispersant are mixed according to the mass ratio of 1: 1 is added.

The 3d compressive strength of the printing test piece in three printing directions is above 15MPa, the 3d flexural strength in three printing directions is above 8MPa, the compressive strength difference in three directions is within 4MPa, and the flexural strength difference in three directions is within 42 MPa.

The preparation method of the powder 3D printing high-strength high-toughness cement-based material is characterized by comprising the following steps:

1) mixing and stirring magnesium oxide and phosphate for not less than 1min, then adding fly ash, quartz sand and PVA, stirring for not less than 3min, finally adding the components of a dispersing agent and a reinforcing and toughening powder, stirring for not less than 3min, and preparing uniform powder 3D printing MPC powder;

2) the method comprises the steps of putting a reinforcing and toughening liquid component into an ink box, carrying out ultrasonic treatment on the ink box for 2-5 minutes, opening software to carry out ink jet calibration, pouring mixed MPC powder into a storage cylinder, carrying out Z-axis calibration, setting the powder laying speed to be 30-45 mm/s and the vibration speed to be 20-40 mm/s, setting the printing thickness of each layer to be 0.15mm, automatically starting printing by a printer after the automatic introduction of a file is finished, finishing the printing, and removing the powder after standing for 5-10 minutes to obtain a test piece.

Compared with the prior art, the invention has the following beneficial effects:

1) the invention uses nano materials (the particle size is 1-100 nm) and the characteristics of high surface activity, strong activity, small size and the like of the nano materials are superior to those of conventional materials, so that the nano materials are applied to the modification of cement-based materials. The particles of the nano material can play a filling role in micropores of 20-150 nm in cement hardening so that the pore structure is more reasonable. The nano particles added into the cement can not only fill the gaps of the cement, optimize the particle size distribution of a particle system, but also improve the microstructure and improve the mechanical property. Because of the high surface activity and small size effect of the nano powder, the nano particles are used as the core, and the mechanical strength and permeability of cement hardening are greatly improved.

2) According to the invention, the magnesium phosphate powder is provided with specific magnesium oxide/phosphate (molar ratio) of 4/1-5/1 and a proper particle size, so that smooth powder printing can be ensured, rollers cannot be adhered, and the powder spreading effect can be ensured and the printability of powder printing can be ensured by adding quartz sand and PVA in the magnesium phosphate powder.

3) According to the invention, the components of the reinforcing and toughening powder are all made of nano materials, the porosity of the MPC powder bed is controlled to be below 55%, the gaps can be effectively filled, the porosity is lower, the powder bed is more compact, and the mechanical property of the powder bed is enhanced.

4) At present, with the continuous enhancement of environmental awareness of people, the requirement on green buildings is higher and higher, and the green building construction becomes a new direction of the future building industry. In a concrete structure, the durability is also one of important indexes for measuring the green standard, green high-performance concrete is produced at present, some high-performance concrete is adopted abroad at present, some key projects in China also make hard requirements on the aspect, and the concrete is gradually popularized to various engineering constructions later, but the concrete is not applied to 3D printing intelligent construction at present. In the process of preparing the green high-performance concrete, the addition of the ultrafine mineral admixtures (fly ash) plays a great role, the admixtures can replace the same amount of cement, the performance of the concrete is greatly improved compared with the common concrete after the admixtures are added, the cost investment is reduced, and the purposes of environmental protection and energy conservation can be achieved.

5) The main mechanism of the strengthening and toughening effects of the multi-walled carbon nanotubes, the nano-scale fibers and the nano-oxides on cement is as follows: the crystal nucleus effect is that the nano material can form crystal nucleus in the hydration product and promote the hydration process so as to improve the early strength and the filling effect, and the nano material which is dispersed uniformly in a proper amount can be effectively filled in the pores of the hydration product and improve the density of the material; the multi-wall carbon nano-tube and the nano-material can connect hydration products together and play a role in resisting cracking in the cracking process of the matrix. The spherical nano oxide particles are adopted, and the porosity of the composite particle cement-based material can be further improved, the compactness and uniformity of a system are increased, the stress concentration phenomenon in the system is reduced, the uniformity of the cement-based material is improved, and the tensile and fracture resistance of the composite cement-based material can be greatly improved through the interface structure between the spherical particles and the composite cement-based material.

6) The powder 3D printing technology and the high-toughness and high-strength cement-based material combination are utilized to form a complex structure with self-controlled size, so that the time and the cost are saved. The magnesium phosphate cement adopted by the invention has the characteristics of quick and controllable setting and hardening, high hour strength, good volume stability, high bonding strength, good durability, simple maintenance, environmental protection and the like, the characteristics of quick hardening, early strength and controllability can effectively solve the requirements of the powder 3D printing technology on the early quick hardening and high strength performance of materials, the high bonding characteristic can effectively solve the problems of interface weakening between printing layers and poor bonding property with concrete in powder 3D printing, and the characteristics of thinness and accurate controllability of the layer-by-layer 3D printing can solve the problem of difficult construction of a composite structure. The nano material can further improve the grain composition, increase the compactness of the system, react with phosphate, improve the uniformity of the cement-based material, improve the crystal orientation and control the grain size in the cement hydration process, and the micro material filling function is the main reason for improving the toughness resistance of cement mortar and improving the compactness of the cement-based material, and finally, the tensile strength also obviously shows that the toughness of the cement-based material is improved.

7) According to the invention, the high-strength and high-toughness cement-based material is prepared from magnesium oxide, the reinforcing and toughening liquid and the reinforcing and toughening powder, and the advantages of high cohesiveness, quick hardening and early strengthening of MPC and intelligence, flexibility and accuracy of the powder 3D printing process are combined to develop the high-strength and high-toughness cement-based material capable of being subjected to powder 3D printing. And evaluating the mechanical property index of the steel. The splitting strength and the anti-bending strength of the cement-based material are obviously improved, wherein the anti-pressing/anti-bending strength of the toughening component material in three directions is respectively improved by 44.8 percent and 59.7 percent, the nano material can be effectively dispersed into the cement matrix, the requirement of low porosity of a powder bed is ensured, and the mesh filling effect can be realized.

Drawings

Fig. 1 is a tensile stress-strain curve of powder 3D printed samples under different powder beds.

Fig. 2 is a tensile stress-strain curve of powder 3D printed samples under different liquid compositions.

Detailed Description

The present invention is further explained by the following examples, which should not be construed as limiting the scope of the present invention.

The invention relates to a powder 3D printing high-strength high-toughness cement-based material, which comprises the following components:

magnesium phosphate powder: calcining MgO at 800-1600 ℃ for 45min, wherein the particle size is less than 150 mu m; the particle diameter of the fly ash is between 100 and 150 mu m, and the density is more than 2.8g/cm³(ii) a The particle size of the phosphate is less than 150 mu m; the grain sizes of the quartz sand and the PVA are less than 150 mu m. Wherein, the molar ratio of magnesium oxide/phosphate is 4/1-5/1; fly ash accounts for the mass of the cementing material (magnesium oxide and phosphate)Total amount) of 10-20%; the quartz sand accounts for 15-20% of the mass of the cementing material; PVA accounts for 3-5% of the mass of the cementing material.

The components of the reinforcing and toughening liquid are as follows: the surface tension of the mixed liquid of distilled water, a surface adhesive, 1,2 propylene glycol, Polyacrylate (PA) emulsion and a reinforcing and toughening liquid component is 41.8-47.8 mN/m, the viscosity is 1.22-1.67 mPa.s, and the functions of adhesion, toughening and reinforcing can be achieved.

The components of the reinforcing and toughening powder are as follows: any one of nano oxide, multi-wall carbon nano tube and nano fiber, and dispersant IW.

The Polyacrylate (PA) emulsion is prepared by adding some functional monomers such as acrylic acid, methacrylic acid, hydroxyethyl acrylate and the like into monomers such as butyl acrylate, methyl methacrylate and the like, and performing emulsion polymerization under the action of an initiator.

The reinforcing and toughening powder component, wherein the nano oxide is selected from nano silicon dioxide, nano titanium dioxide, nano iron oxide, nano aluminum oxide and nano zirconium dioxide. Wherein the nano oxide has a spherical appearance, an average particle diameter of 100-150 nm and a specific surface area of 10-20 m²A density of 5.88 to 5.91g/cm³The content is more than 99 percent; the multi-wall carbon nanotube has a length of 10-20 μm, an outer diameter of 30-50 nm, and a specific surface area of 60m²The purity is more than 95 percent; the diameter of the nano fiber is 40-60 nm, the length of the nano fiber is 5-10 mu m, a finer structure can be printed, and the porosity of the MPC powder bed is 15-55%.

The nano-fiber is carbon nano-fiber, polypropylene fiber, aromatic polyamide fiber, Al2O3 nano-fiber, SiC nano-fiber and the like.

The preparation method of the powder 3D printing high-strength and high-toughness cement-based material comprises the following steps:

2) the method comprises the steps of putting a reinforcing and toughening liquid component into an ink box, carrying out ultrasonic treatment on the ink box for 2 minutes, opening software to carry out ink jet calibration, pouring mixed MPC powder into a storage cylinder, carrying out Z-axis calibration, setting the powder laying speed to be 30-45 mm/s and the vibration speed to be 20-40 mm/s, setting the printing thickness of each layer to be 0.15mm, automatically starting printing by a printer after the automatic introduction of a file is finished, finishing the printing, and removing the powder after standing for 5-10 minutes to obtain a test piece.

The control of each process parameter in the preparation method can ensure the powder printing and forming.

Example 1

The powder 3D printing high-strength and high-toughness cement-based material and the preparation method comprise the following steps:

phosphate powder: calcining MgO at 1200 deg.C for 45min to obtain 150 μm particle size; the particle diameter of the fly ash is 150 mu m, and the density is 3.0g/cm³(ii) a The particle size of the ammonium dihydrogen phosphate is 150 mu m; screening quartz sand and PVA with particle size of 100 μm; wherein, the molar ratio of magnesium oxide/ammonium dihydrogen phosphate is 5:1, the fly ash accounts for 20% of the mass of the cementing material (the total amount of magnesium oxide and phosphate), the quartz sand accounts for 20% of the mass of the cementing material, and the PVA accounts for 5% of the mass of the cementing material.

The components of the reinforcing and toughening liquid are as follows: distilled water, Surfynol465 surface binder, 1,2 propylene glycol and Polyacrylate (PA) emulsion, wherein the mass ratio of the distilled water to the Surfynol465 surface binder to the 1,2 propylene glycol to the Polyacrylate (PA) emulsion is as follows: distilled water: surface adhesive agent: 1,2 propylene glycol: PA-20: 0.2: 1: 0.2.

the components of the reinforcing and toughening powder are as follows: nano oxide (the addition amount accounts for 0.5 percent of the phosphate component), multi-wall carbon nano tubes or nano fibers (the addition amount accounts for 0.1 percent of the phosphate component), and a dispersing agent IW, wherein the addition amount of the dispersing agent is equal to the amount of the nano oxide or the nano fibers.

The preparation process comprises the following steps: firstly, mixing and stirring magnesium oxide and phosphate for not less than 1min, then adding fly ash, quartz sand and PVA, stirring for not less than 3min, finally adding a dispersing agent and a reinforcing and toughening powder component, stirring for not less than 3min, and preparing uniform powder 3D printing MPC powder.

The method comprises the steps of putting a reinforcing and toughening liquid component into an ink box, carrying out ultrasonic treatment on the ink box for 2 minutes, opening software to carry out ink jet calibration, pouring mixed powder materials into a storage barrel, carrying out Z-axis calibration, setting the powder laying speed to be 30-45 mm/s and the vibration speed to be 20-40 mm/s, setting the printing thickness of each layer to be 0.15mm, automatically starting printing by a printer after the automatic introduction of a file is finished, and removing powder and taking a test piece ten minutes after the printing is finished. Every layer in this application print thickness can control within 0.2mm, single layer thickness is little, it is high to print the precision, be particularly useful for printing the requirement of high precision, complicated shape, the matched stack that this application set up can print the object of higher accuracy, and this application does not need special maintenance condition when getting the test piece, also need not add the admixture, do not need early strength agent, just can realize the sclerosis in the short time (5-10min), can realize instant usefulness almost, low cost is a green prescription that does not have harm to the environment.

The surface tension of the mixed liquid is 41.8mN/m, and the viscosity is 1.22 mPa.

The reinforcing and toughening powder component, wherein the nano oxide is selected from nano silicon dioxide, nano titanium dioxide, nano iron oxide, nano aluminum oxide and nano zirconium dioxide. (in this example, nanosilica was selected for performance testing). Wherein the nano oxide has spherical appearance, average particle diameter of 120nm and specific surface area of 15m²G, density 5.89g/cm³And the content is more than 99 percent. The diameter of the nanofiber particles is 50nm, and the diameter is 5 μm (in this example, the carbon nanofiber is selected for performance test); the porosity of the MPC powder bed was 30.0/34.0%.

TABLE 1 composite powder Properties for different powder types

Table 1 shows the data of the composite properties without using the powder type, and tests show that the doping of the nanofibers and the nano oxides can significantly improve the powder laying performance of the composite powder, and the proper amount of doping can reduce the porosity of the powder bed and increase the compactness. As shown in table 1, the powder bed porosity reached a minimum of 0.30. The composite powder has achieved good powder laying effect. Actual printing finds that when the total amount of the nano-fibers and the metal oxides exceeds the amount determined by the invention, the printed test piece has difficulty in generating enough early strength, and the nano-materials with low reaction degree or no reaction have difficulty in forming enough cementing capacity to maintain the forming and subsequent processing of the model.

TABLE 2 Strength of powder type to different printing directions

(wherein X is the direction of roller laying powder; Y is the direction of adhesive jetting; Z is the vertical direction perpendicular to the printed layer)

As can be seen from Table 2, when the powder material is phosphate powder + nanofiber/phosphate powder + nano oxide, the compression resistance in the Y direction is the best compared with other powder materials, and the compression resistance in the Y direction can reach 17.48/17.35Mpa respectively; the anti-breaking strength reinforcing effect in the Y direction is also the best, and can respectively reach 14.67/14.85 Mpa. The 3d compressive strength of the printed sample in three printing directions is more than 15MPa, the 3d flexural strength of the printed sample in three printing directions is more than 10MPa, the compressive strength difference in three directions is within 3MPa, and the flexural strength difference in three directions is within 4MPa, so that the material is considered to be isotropic.

Example 2

The components and preparation process in this example are the same as example 1, except that in this example, 0.5% nano iron oxide is used as the reinforcing and toughening powder component, the porosity of MPC powder bed is 30.0-40.0%, and the influence of different binder types (liquid components) on the strength in different printing directions is examined, and the specific results are shown in Table 3.

Table 3 strength of binder type for different printing directions

Wherein X is the powder spreading direction of the roller; y is the direction of adhesive spray; z is the vertical direction perpendicular to the printed layers.

As can be seen from Table 3, when the binder is the reinforcing and toughening liquid component (No. 3) of the invention, the compressive strength and the flexural strength in the printing cost Y direction are better than those of other binder, the reinforcing effect is respectively 15.39 Mpa and 9.15Mpa, and the respective strength is 44.8% and 59.7% higher than that of common distilled water; therefore, the embodiment 1 and the embodiment 2 show that the material is more suitable for being applied to a powder 3D printing device, and the three-dimensional compressive strength and the flexural strength of a printing sample can be obviously enhanced under the same conditions.

The tensile stress-strain of the powder 3D-printed samples obtained in example 1 and example 2 are shown in fig. 1 and 2. The peak stress of a printing sample is increased from 3.04MPa in 3D printing ink to 5.04MPa in liquid toughening component, and the strain capacity is improved by 39.7%; the peak stress of the printed sample increased from 3.27MPa when 3D printed gypsum to 5.07MPa when the liquid toughening component was used, increasing the strain capacity by 35.5%. It can be seen that the present invention significantly improves tensile properties in terms of peak stress and strain capacity.

The experimental results can be obviously seen that: in the patent requirement range, the beneficial effects of the nano material can be fully exerted through the proper proportion of the raw materials and the nano material on the premise of not adding an additive, so that the toughness of the cement-based material is improved, and the porosity and the strength of the powder 3D printing magnesium phosphate cement are greatly improved. The invention combines powder 3D printing with magnesium phosphate cement-based powder and nano materials, compared with common energy-consuming materials and conventional construction technical methods, the method has the advantages of high strength, high toughness, intellectualization, high accuracy, high stability, simple and quick working procedure, easy operation, good stability and the like, the strength and toughness of the material are obviously improved, and the intelligent market requirement of powder 3D printing is met.

Nothing in this specification is said to apply to the prior art.

Claims

1. The high-strength and high-toughness cement-based material for powder 3D printing is characterized by comprising the following components in parts by weight:

2. The high-strength high-toughness cement-based material for powder 3D printing according to claim 1, wherein the shape of the nano-oxide is spherical, the average particle size of the nano-oxide is 100-150 nm, and the specific surface area of the nano-oxide is 10-20 m²A density of 5.88 to 5.91g/cm³The content is more than 99 percent; the multi-wall carbon nanotube has a length of 10-20 μm, an outer diameter of 30-50 nm, and a specific surface area of 60m²The purity is more than 95 percent; the diameter of the nanofiber is 40-60 nm, and the length of the nanofiber is 5-10 mu m; the nano oxide is selected from nano silicon dioxide, nano titanium dioxide, nano iron oxide, nano aluminum oxide and nano zirconium dioxide; the porosity of the MPC powder bed is 15-55%.

3. The powder 3D printing high-strength high-toughness cement-based material as claimed in claim 1, wherein the nano-oxide is a non-heavy metal oxide capable of reacting with cement to reduce porosity when doped with cement; the toughening active component and the dispersant are mixed according to the mass ratio of 1: 1 is added.

4. The powder 3D printed high-strength high-toughness cement-based material as claimed in claim 1, wherein 3D compressive strength of the printed test piece in three printing directions is above 15MPa, 3D flexural strength in three printing directions is above 8MPa, the compressive strength in three directions is within 4MPa, and the flexural strength in three directions is within 42 MPa.

5. A method for the preparation of a powder 3D printed high strength and high toughness cementitious material according to any of claims 1-4, characterised in that the method comprises the steps of: