3D printing ultra-high performance fiber concrete material containing coarse aggregate and preparation

Abstract

The application belongs to the technical field of building materials, and more particularly relates to a 3D printing ultra-high performance fiber reinforced concrete material containing coarse aggregate and a preparation method thereof. The concrete material comprises 180-500 parts of coarse aggregate, 600-700 parts of cement, 200-400 parts of silica fume, 300-450 parts of fine sand, 150-350 parts of medium sand, 10-15 parts of water reducing agent, 100-160 parts of water, 140-160 parts of steel fiber, and 0.5-2 parts of cellulose. The concrete material can be prepared by using the 3D printing technology. The formula improves the bonding strength between the printing layers by adding the coarse aggregate, and effectively reduces the amount of cement-based cementitious material, thereby reducing the preparation cost and achieving the high strength and high toughness mechanical properties equivalent to the conventional 3D printing UHPFRC without coarse aggregate. In particular, the formula can effectively ensure the formability of the UHPFRC containing coarse aggregate (CA) in the printing process.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and more specifically, relates to a 3D-printed ultra-high performance fiber concrete material containing coarse aggregate and its preparation. Background Technology

[0002] Ultra-high performance fiber reinforced concrete (UHPFRC), as a novel building material, significantly improves upon the shortcomings of traditional building materials such as ordinary concrete in terms of tensile strength and toughness. The maturity of 3D-printed concrete technology has driven the innovative development of intelligent building manufacturing. It is an emerging technology that does not require molds, and is more intelligent, flexible, and faster than traditional construction processes. Existing 3D building materials have varying degrees of mechanical performance defects and cost issues. On the one hand, due to the existence of weak areas between layers, 3D-printed ordinary concrete and fiber-reinforced concrete suffer from low tensile strength, easy interlayer cracking, and brittle fracture, which limits the large-scale application of 3D concrete printing technology. On the other hand, the amount of cementitious materials used in 3D-printed UHPFRC materials, especially the high cement content, increases material costs. Furthermore, the use of large-volume cementitious materials causes volume shrinkage after printing, weakening the interlayer interface mechanical properties and leading to severe anisotropy problems. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a 3D-printed ultra-high performance fiber reinforced concrete material (CA-UHPFRC) containing coarse aggregate and its preparation method. This invention solves the problems of low tensile strength, easy interlayer cracking and brittle fracture in existing 3D-printed UHPFRC materials due to the presence of weak interlayer regions, as well as the technical problems of volume shrinkage after printing due to the use of large-volume cementitious materials in 3D-printed UHPFRC materials, which weakens the interlayer interface mechanical properties and leads to severe anisotropy.

[0004] To achieve the above objectives, the present invention provides a high-performance fiber-reinforced concrete material containing coarse aggregate suitable for 3D printing. The raw material components, by weight, include 180-500 parts coarse aggregate, 600-700 parts silicate cement, 200-400 parts silica fume, 300-450 parts fine sand, 150-350 parts medium sand, 10-15 parts water-reducing agent, 100-160 parts water, 140-160 parts steel fiber, and 0.5-2 parts cellulose.

[0005] Preferably, the raw material components, by weight, include 300-500 parts coarse aggregate, 640-650 parts silicate cement, 350-360 parts silica fume, 380-400 parts fine sand, 300-320 parts medium sand, 13-15 parts water-reducing agent, 150-160 parts water, 140-150 parts steel fiber, and 1.1-1.5 parts cellulose.

[0006] Preferably, the coarse aggregate has a particle size of 5-8 mm, more preferably 4-6 mm, and a density of 1400-1630 kg / m³. 3 .

[0007] More preferably, the coarse aggregate is gravel.

[0008] According to another aspect of the present invention, a method for preparing the aforementioned coarse aggregate-containing ultra-high performance fiber-reinforced concrete material suitable for 3D printing is provided, comprising the following steps:

[0009] (1) According to the weight ratio, 600-700 parts of the silicate cement, 200-400 parts of silica fume, 300-400 parts of fine sand, 150-350 parts of medium sand and 180-500 parts of coarse aggregate are mixed and stirred to obtain a uniformly stirred powder.

[0010] (2) Mix 10-15 parts of the water-reducing agent and 70-120 parts of water to obtain a mixed solution;

[0011] (3) Mix the powder that was stirred evenly in step (1) with the mixed solution described in step (2) to obtain a mixed slurry;

[0012] (4) Mix the 0.5-2 parts of cellulose with the remaining water to obtain a cellulose solution;

[0013] (5) Mix and stir the mixed slurry obtained in step (3) with the cellulose solution obtained in step (4) until a slurry with obvious viscosity is obtained;

[0014] (6) Mix 140-160 parts of steel fiber with the slurry obtained in step (5) to make the steel fiber evenly distributed in the slurry, and obtain an ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing.

[0015] (7) The ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing described in step (6) is fed into the feeding chamber of the 3D printing equipment, and 3D printing is performed according to the set printing parameters to obtain ultra-high performance fiber-reinforced concrete components.

[0016] Preferably, the printing parameters in step (7) are: nozzle diameter of 30-40 mm and extrusion speed of 0.2-0.5 m / s. 3 / h, horizontal printing speed 20-50mm / s, printhead distance from the ground 25-30mm.

[0017] In summary, compared with the prior art, the above-described technical solutions conceived by this invention have the following advantages:

[0018] Beneficial effects:

[0019] (1) The present invention provides a 3D printing ultra-high performance fiber reinforced concrete material containing coarse aggregate. By adding coarse aggregate, the amount of cementitious material is effectively reduced, the cost is reduced, and the toughness of the composite material is improved. At the same time, the volume shrinkage rate can be effectively reduced, and the anisotropy problem in the X, Y and Z directions of 3D printing can be reduced. It has mechanical properties comparable to UHPFRC without coarse aggregate.

[0020] (2) This invention overcomes the problem of material interruption caused by the introduction of coarse aggregate into ultra-high performance fiber reinforced concrete, which easily clogs the extrusion nozzle, by adjusting the proportions of each component in the ultra-high performance fiber reinforced concrete material formula and controlling the printing speed during the extrusion process. This invention can achieve uniform distribution of coarse aggregate in ultra-high performance fiber reinforced concrete, without the need for mixing equipment or special speed and time limitations, only requiring a specific feeding sequence. This makes the concrete based on the proportions of this invention suitable not only for traditional casting methods but also for 3D printing technology.

[0021] (3) The present invention provides a 3D printing ultra-high performance fiber reinforced concrete material containing coarse aggregate. The addition of cellulose can effectively improve the bonding performance between cement slurry and steel fiber, ensure that the printed fiber has a high bonding force with the interface of the matrix concrete, and improve the synergistic stress performance of fiber and matrix material. Attached Figure Description

[0022] Figure 1 Load-mid-span deflection curves for the UHPFRC without coarse aggregate provided in Comparative Example 1 and the 3D-printed ultra-high performance fiber reinforced concrete (CA-UHPFRC) beam with coarse aggregate in Example 1.

[0023] Figure 2 The image shows the finished product of the 3D-printed ultra-high performance fiber-reinforced concrete beam containing coarse aggregate provided in Example 4.

[0024] Figure 3 A comparison of the load-mid-span deflection diagrams of ordinary cast-in-place and 3D-printed ultra-high performance fiber-reinforced concrete beams containing coarse aggregate provided in Example 1.

[0025] Figure 4The image provided is a CT scan of a cross section (XZ direction) of a 3D-printed ultra-high performance fiber-reinforced concrete beam containing coarse aggregate, provided for an embodiment.

[0026] Figure 5 This is a rendering of the 3D printing effect of concrete material in Example 2.

[0027] Figure 6 The images show the 3D printing effects of concrete materials in Comparative Example 1, Example 1, Example 4, Example 3, Comparative Example 2, and Comparative Example 3. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Unlike traditional ultra-high performance fiber concrete applicable to 3D printing, the printing slurry in this invention contains coarse aggregate. The raw material components, by weight, include 180-500 parts coarse aggregate, 600-700 parts silicate cement, 200-400 parts silica fume, 300-450 parts fine sand, 150-350 parts medium sand, 10-15 parts water-reducing agent, 100-160 parts water, 140-160 parts steel fiber, and 0.5-2 parts cellulose.

[0030] In a preferred embodiment, the raw material components, by weight, include 300-500 parts coarse aggregate, 640-650 parts silicate cement, 350-360 parts silica fume, 380-400 parts fine sand, 300-320 parts medium sand, 13-15 parts water-reducing agent, 150-160 parts water, 140-150 parts steel fiber, and 1.1-1.5 parts cellulose.

[0031] In some embodiments, the coarse aggregate has a particle size of 5-8 mm, more preferably 4-6 mm, and a density of 1400-1630 kg / m³. 3 In a preferred embodiment, the coarse aggregate is gravel.

[0032] This invention uses silicate cement with a strength grade of not less than 42.5 and adds a water-reducing agent. The selected water-reducing agent should meet the water reduction rate standard of polycarboxylate-based water-reducing agents, aiming to improve the fluidity and density of CA-UHPFRC under low water-cement ratio conditions. In some embodiments, the particle size of the silicate cement is 0.8-168 μm, the particle size of the silica fume is 0.4-18 μm, the particle size of the fine sand is between 75 μm and 425 μm, the particle size of the medium sand is between 425 μm and 2000 μm, and the median particle sizes of the fine sand and medium sand are 175 μm and 402 μm, respectively. The water-reducing agent is a high-performance polycarboxylate water-reducing agent with a water reduction rate greater than or equal to 30%. The fiber is steel fiber, selected from straight steel fibers, hooked steel fibers, or corrugated steel fibers, with a fiber length of 8–13 mm, a diameter of 0.14–0.2 mm, and a tensile strength of 2800–3100 MPa. Preferred steel fibers in this invention are commercially available copper-plated high-strength straight steel fibers and corrugated copper-plated high-strength steel fibers. Steel fibers can improve the tensile, bending, shear, and fatigue resistance of the matrix concrete material, enhancing its corresponding stiffness and toughness.

[0033] In some embodiments of the present invention, the viscosity of the hydroxypropyl methylcellulose ether material is 300,000. Cellulose has a high molecular chain structure, exhibits a complex adsorption effect on UHPFRC hydration products, and can dissolve in water through physical action. This product can improve the flowability of low water-to-binder ratio materials and increase the printability of low water-to-ash ratio materials without increasing the amount of water used in the material.

[0034] The present invention also provides a method for preparing the aforementioned coarse aggregate-containing ultra-high performance fiber-reinforced concrete material suitable for 3D printing, comprising the following steps:

[0035] (1) According to the weight ratio, 600-700 parts of the silicate cement, 200-400 parts of silica fume, 300-450 parts of fine sand, 150-350 parts of medium sand and 180-500 parts of coarse aggregate are mixed and stirred to obtain a uniformly stirred powder.

[0036] (2) Mix 10-15 parts of the water-reducing agent and 70-120 parts of water to obtain a mixed solution;

[0037] (3) Mix the powder that was stirred evenly in step (1) with the mixed solution described in step (2) to obtain a mixed slurry;

[0038] (4) Mix the 0.5-2 parts of cellulose with the remaining water to obtain a cellulose solution;

[0039] (5) Mix and stir the mixed slurry obtained in step (3) with the cellulose solution obtained in step (4) until a slurry with obvious viscosity is obtained;

[0040] (6) Mix 140-160 parts of fiber with the slurry obtained in step (5) to ensure that the steel fiber is evenly distributed in the slurry, and obtain an ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing.

[0041] (7) The ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing described in step (6) is fed into the feeding chamber of the 3D printing equipment, and 3D printing is performed according to the set printing parameters to obtain ultra-high performance fiber-reinforced concrete components.

[0042] In some embodiments, the printing parameters in step (7) are specifically: nozzle diameter of 30-40 mm and extrusion speed of 0.2-0.5 m / s. 3 / h, horizontal printing speed 20-50mm / s, printhead distance from the ground 25-30mm.

[0043] In a preferred embodiment, the printing parameters in step (7) are specifically: nozzle diameter of 30-35 mm and extrusion speed of 0.25-0.3 m / s. 3 / h, horizontal printing speed 45-50mm / s, printhead distance from the ground 23-27mm.

[0044] This invention involves mixing cellulose with water to obtain a cellulose solution. There are no particular limitations on the stirring rate and time in the preparation of the cellulose solution, as long as the components are mixed evenly. There are no particular limitations on the mixing method; any mixing method well-known to those skilled in the art can be used.

[0045] In this invention, the mixture, the slurry, and the cellulose solution are preferably mixed in a mixing tank. The mixing method includes pre-stirring the mixture, followed by sequentially adding the slurry and the cellulose solution. There is no particular limitation on the pre-stirring rate, but a preferred pre-stirring time is 90-150 seconds. The purpose of pre-stirring is to ensure that the components of the mixture are thoroughly and uniformly mixed.

[0046] The mixing method in this invention includes stirring all powders (cement, silica fume, fine sand, medium sand, and coarse aggregate), stirring a mixture of slurry and cellulose solution, and uniformly adding steel fibers to the mixture within 10 seconds. The stirring time is preferably 20 to 25 minutes. This invention does not impose special restrictions on the stirring operation; it is only necessary to ensure that the steel fibers are fully mixed with all components.

[0047] The preparation method provided by this invention involves mixing and stirring powdered materials and liquid slurry to achieve the dispersion and water-reducing effect of the water-reducing agent. Then, a cellulose solution is added to increase the binding force of the mixture and reduce the slump of the material, thereby improving the extrudability, flowability, and formability of the material. Finally, steel fibers are added, with raw materials gradually added during the mixing process to ensure uniform mixing and homogeneity.

[0048] This invention does not impose any special limitations on the 3D printing equipment; any 3D printing equipment well-known to those skilled in the art can be used. The mixing ratio and printing parameters provided by this invention are well-matched, and the above-described technical solution can be used to prepare ultra-high performance fiber-reinforced concrete materials containing coarse aggregate suitable for 3D printing.

[0049] To improve the homogeneity within and between layers, reduce the amount of cementitious materials (primarily cement) and thus lower manufacturing costs, and enhance the mechanical properties of 3D-printed ultra-high performance fiber-reinforced concrete (UHPFRC), this invention aims to reduce the amount of cementitious materials per unit volume by adding coarse aggregate, thus preparing coarse aggregate-containing UHPFRC material (CA-UHPFRC). Compared to ordinary concrete, UHPFRC exhibits significantly improved tensile strength and toughness. Existing technologies introduce coarse aggregate into ordinary concrete materials for 3D printing of ordinary concrete components, which can improve interlayer bond strength. However, while adding coarse aggregate can reduce costs for UHPFRC, the high cement powder content and large amount of steel fibers used to enhance strength in 3D printing make the steel fibers prone to clogging the nozzle during extrusion, leading to material breakage. Introducing coarse aggregate further increases this risk of breakage. Traditional 3D printing methods are prone to material strength reduction due to clogging and extrusion interruptions. Furthermore, coarse aggregates have a higher density than the concrete matrix, making them prone to settling during mixing and dispersion, thus hindering the production of a uniform concrete slurry. This invention addresses this by simultaneously adjusting the material mix proportions and printing parameters to regulate the bond strength between the coarse aggregate and the matrix, particularly the coarse aggregate, sand, cement, cellulose, and water-reducing agent. Adjusting printing parameters, including printing speed and extrusion speed, ensures smooth slurry extrusion. The resulting concrete component significantly reduces cement usage and costs compared to UHPFRC components without coarse aggregate, while exhibiting comparable flexural mechanical properties to UHPFRC components without coarse aggregate. Simultaneously, the compressive strength is significantly increased, meeting the requirement of over 100 MPa in the X, Y, and Z directions for ultra-high performance fiber-reinforced concrete.

[0050] The formulation of this invention solves the cracking problem of existing UHPFRCs, and the invented material possesses the extrudability, flowability, and moldability required for 3D printing. The resulting composite material exhibits high compressive strength, effectively improving the dynamic and static mechanical properties of the original UHPFRC sample.

[0051] The 3D-printed ultra-high performance fiber-reinforced concrete material containing coarse aggregate proposed in this invention is not only suitable for traditional casting methods but also for 3D printing technology. By adding coarse aggregate, the amount of cementitious materials can be effectively reduced, the cost can be lowered, and the toughness of the composite material can be improved. At the same time, the volume shrinkage rate can also be effectively reduced, and it has mechanical properties comparable to UHPFRC without coarse aggregate.

[0052] The technical solution of the present invention is briefly described below through embodiments. These embodiments are merely some examples of the present invention; other embodiments based on these embodiments are also within the scope of protection of the present invention.

[0053] Example 1

[0054] This embodiment provides an ultra-high performance fiber-reinforced concrete material containing coarse aggregate suitable for 3D printing. Unlike traditional ultra-high performance fiber-reinforced concrete applicable to 3D printing, the printing slurry in this invention contains coarse aggregate. The raw material components, by weight, include 300 parts of coarse aggregate (coarse aggregate consists of stones with an average diameter of 5mm and a density of 1500kg / m³). 3 The composition includes: 650 parts of silicate cement with a strength grade of not less than 42.5; 350 parts of silica fume (particle size 0.4-18μm); 400 parts of fine sand (particle size between 75μm and 425μm, median particle size 175μm); 300 parts of medium sand (particle size between 425μm and 2000μm, median particle size 402μm); 14 parts of water-reducing agent (polycarboxylate high-performance water-reducing agent with a water reduction rate ≥30%); 160 parts of water; 145 parts of fiber; and 1.3 parts of cellulose (abbreviated as HPMC).

[0055] 1) Weigh each material according to its mass percentage, including silicate cement, silica fume, fine quartz powder, medium sand, coarse aggregate, steel fiber, and polycarboxylate superplasticizer. Mix the polycarboxylate superplasticizer with water to prepare a mixed slurry; mix hydroxypropyl methylcellulose with water to prepare a cellulose solution.

[0056] 2) Put all the ingredients, 650 parts of cement of not less than 42.5, 350 parts of silica fume, 400 parts of fine sand, 300 parts of medium sand, and 300 parts of coarse aggregate into a mixer and mix to obtain a uniform powder.

[0057] 3) Mix 14 parts of water-reducing agent with 100 parts of water into mixed solution 1;

[0058] 4) Add the mixed solution 1 from 3) to the mixed powder obtained in 2) and continue stirring for 4 minutes until homogeneous to obtain a mixed slurry;

[0059] 5) Mix cellulose with 60 parts of water to obtain a cellulose solution;

[0060] 6) Mix the mixed slurry obtained in step 4) with the cellulose solution obtained in step 5) and continue stirring for 5 minutes until the mixture and the original slurry have fully interacted. At this point, the slurry exhibits obvious viscosity.

[0061] 7) Mix 145 parts of steel fiber with the mixture obtained in step 6) to ensure that the steel fiber is evenly distributed in the slurry material in 6), and obtain an ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing.

[0062] 8) During the printing process, the mixture obtained in 7) is added to the feeding hopper of the 3D printer, according to the set printing parameters (nozzle diameter 30mm, extrusion speed 0.3m). 3 The component is printed at a horizontal printing speed of 50mm / s and a nozzle-to-ground distance of 25mm.

[0063] Comparative Example 1

[0064] Comparative Example 1 had the same conditions and parameters as Example 1, except that no coarse aggregate was added and the cement content was 800 parts.

[0065] Figure 1 The load-mid-span deflection curves of the 3D-printed ultra-high performance fiber-reinforced concrete (3DCA-UHPFRC) with coarse aggregate provided in Example 1 and the 3D-printed ultra-high performance fiber-reinforced concrete (3DUHPFRC) without coarse aggregate in Comparative Example 1 are shown. It can be seen that Example 1, by adding coarse aggregate, can reduce the amount of cementitious materials, especially cement, and achieve flexural mechanical properties comparable to 3D-printed ultra-high performance concrete without coarse aggregate. The concrete material mentioned in this example can be prepared using 3D printing technology. This formulation improves the bond strength between printed layers by incorporating coarse aggregate and effectively reduces the amount of cement-based cementitious materials in 3D-CA-UHPFRC, achieving high strength and high toughness mechanical properties comparable to conventional 3D-printed UHPFRC without coarse aggregate while reducing preparation costs. In particular, this formulation effectively ensures the formability of UHPFRC with coarse aggregate during the printing process.

[0066] Figure 2The image shown in Example 4 illustrates the finished product of a 3D-printed ultra-high performance fiber-reinforced concrete beam containing coarse aggregate. It can be seen that due to the density difference and settlement effect, the coarse aggregate passes through the lower printed layer under the action of gravity and compresses the lower printed layer to a certain extent, causing each printed layer and the interlayer to present a convex and concave distribution. Due to the connection effect of the coarse aggregate between the printed layers, the interlayer bonding strength will be significantly improved, thereby improving the overall material mechanical properties, as well as the molding and printing performance.

[0067] Figure 3 The load-mid-span deflection diagrams for the 3D-printed and conventionally cast ultra-high performance fiber-reinforced concrete beams containing coarse aggregate provided in Example 1 are shown. It can be seen that the difference in flexural bearing capacity between the 3D-printed beam and the conventionally cast beam is reduced in the Z direction. Figure 3 The diagram shows the mid-span deflection curves of CA-UHPFRC beams prepared and printed in Example 1 and those cast in ordinary form. The peak loads can reach 33kN and 29kN, respectively. The comparison shows that UHFFRC material with added coarse aggregate can achieve bending mechanical properties comparable to conventional UHPFRC components without coarse aggregate while reducing the amount of cementitious material due to fiber orientation. It has the characteristics of high strength and high toughness.

[0068] Figure 4 The image shown is an XCT scan of a cross-section (XZ direction) of the 3D-printed ultra-high performance fiber-reinforced concrete beam provided in Example 1. It can be seen that aggregate passes through the lower layer before the upper and lower layers, which may be the reason why adding aggregate can improve the interlayer bond strength of the 3D-printed component.

[0069] Table 1 shows the mix proportions of 3D printed CA-UHPFRC for Examples 1 to 5, Comparative Examples 1, 2 and 3. Table 2 shows the 3D printing parameters of the concrete materials for each example and comparative example. Table 3 shows the compressive strength test results of the concrete materials for each example and comparative example after molding using a general testing press from the School of Civil Engineering and Architecture of Wuhan University, with a loading speed of 0.2 MPa / s.

[0070] Table 1. Mix proportions of concrete materials for each embodiment and comparative example (unit: kg)

[0071]

[0072] Table 2. 3D printing parameters of concrete materials used in the examples and comparative examples.

[0073] Material Printing speed <![CDATA[Extrusion speed (m 3 / h)]]> Nozzle diameter (mm) Nozzle distance from ground (mm) Example 1 50 0.3 30 25 Comparative Example 1 30 0.25 30 25 Example 2 50 0.3 30 25 Example 3 50 0.3 30 25 Example 4 50 0.3 30 25 Example 5 50 0.3 30 25 Comparative Example 2 25 0.25 40 30 Comparative Example 3 25 0.25 40 30

[0074] Table 3. Compressive strength and ordinary casting strength of 3D printed UHPFR-CA in various embodiments and comparative examples (unit: MPa)

[0075] Test Plan Ordinary casting X-direction Y-direction Z-direction Example 1 128 110 103 107 Comparative Example 1 162 145 132 135 Example 2 112 78 65 93 Example 3 137 106 101 104 Example 4 156 124 112 116 Example 5 152 125 112 115 Comparative Example 2 133 80 71 79 Comparative Example 3 139 86 83 85

[0076] As can be seen from Table 3, compared with Example 1, Example 2 kept the coarse aggregate diameter unchanged but changed the mix ratio. The compressive strength of the printed components in the X, Y, and Z directions was all lower than 100 MPa. Figure 5 The 3D printing effect diagram illustrates that the mix proportion of concrete materials has a significant impact on the strength of 3D printed components after the introduction of coarse aggregate.

[0077] Comparative Example 1 shows a typical composition of existing ultra-high performance concrete without coarse aggregate. It can be seen that it has high strength, but the high cement content increases material costs. Examples 3 and 4 are based on Example 1, with everything else remaining unchanged, except that the amount of coarse aggregate is increased from 300 parts to 500 parts and 400 parts respectively. It can be seen that the compressive strength of the printed concrete components in the X, Y, and Z directions are all higher than 100 MPa, meeting the strength requirements of ultra-high performance fiber-reinforced concrete. Furthermore, the cement content in Examples 1 to 3 is 18.8% lower than that in Comparative Example 1. In addition, Comparative Example 1, which does not introduce coarse aggregate, shows significant differences in printing strength in various directions. However, Examples 1 to 5, especially Examples 1, 3, 4, and 5, show significantly reduced strength differences in various directions. This to some extent solves the problem of volume shrinkage after printing in existing ultra-high performance fiber-reinforced concrete without coarse aggregate, which weakens the interlayer interface mechanical properties and leads to severe anisotropy due to the use of large-volume cementitious materials.

[0078] Compared to Example 1, Comparative Examples 2 and 3 maintained the same mix proportions. The only change was increasing the diameter of the coarse aggregate from 5 mm in Example 1 to 10 mm and 15 mm, respectively. It can be seen that although the ordinary casting strength is high, the compressive strength of the 3D printed components in the X, Y, and Z directions is significantly reduced, failing to meet the requirements of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC). This indicates that the size of the coarse aggregate should not be too large. Due to the increased coarse aggregate size in Comparative Examples 2 and 3, the extrusion speed needed to be reduced to 0.25 m / s during the printing process to achieve higher bond strength and component performance. 3 The printing speed was reduced to 25 mm / s. The 3D printing effect images of concrete materials in various embodiments and comparative examples are shown below. Figure 6 As shown in Table 3, after obtaining the 3D printed components with the best printing effect for different mixing ratios, their compressive strength was tested.

[0079] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A coarse aggregate-containing ultra-high performance fiber-reinforced concrete material suitable for 3D printing, characterized in that, Its raw material components, by weight, include 500 parts coarse aggregate, 650 parts silicate cement, 350 parts silica fume, 400 parts fine sand, 300 parts medium sand, 14 parts water-reducing agent, 160 parts water, 145 parts steel fiber and 1.3 parts cellulose. The coarse aggregate has a particle size of 4-6 mm and a density of 1400-1630 kg / m³. 3 ; The silicate cement has a particle size of 0.8-168 µm, the silica fume has a particle size of 0.4-18 µm, the fine sand has a particle size between 75 µm and 425 µm, and the medium sand has a particle size between 425 µm and 2000 µm. The cellulose is composed of hydroxypropyl methylcellulose ether with a viscosity of 300,000. The method for preparing the ultra-high performance fiber-reinforced concrete material containing coarse aggregate suitable for 3D printing includes the following steps: (1) According to the weight ratio, 650 parts of the silicate cement, 350 parts of silica fume, 400 parts of fine sand, 300 parts of medium sand and 500 parts of coarse aggregate are mixed and stirred to obtain a uniformly stirred powder. (2) Mix the 14 parts of water-reducing agent and 100 parts of water to obtain a mixed solution; (3) Mix the powder that was stirred evenly in step (1) with the mixed solution described in step (2) to obtain a mixed slurry; (4) Mix the 1.3 parts of cellulose with the remaining water to obtain a cellulose solution; (5) Mix the mixed slurry obtained in step (3) with the cellulose solution obtained in step (4) until a slurry with obvious viscosity is obtained; (6) Mix 145 parts of steel fiber with the slurry obtained in step (5) to make the steel fiber evenly distributed in the slurry, and obtain an ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing. (7) The ultra-high performance fiber-reinforced concrete slurry containing coarse aggregate, suitable for 3D printing, described in step (6) is fed into the feeding chamber of the 3D printing equipment. 3D printing is then performed according to the set printing parameters to obtain an ultra-high performance fiber-reinforced concrete component. Specifically, the printing parameters are: nozzle diameter 30 mm, extrusion speed 0.3 m / s². 3 / h, horizontal printing speed 50mm / s, printhead distance from the ground 25mm.

2. The concrete material as described in claim 1, characterized in that, The strength grade of the silicate cement is greater than or equal to 42.

5.

3. The concrete material as described in claim 1, characterized in that, The median particle sizes of the fine sand and medium sand are 175 µm and 402 µm, respectively.

4. The concrete material as described in claim 1, characterized in that, The water-reducing agent is a polycarboxylate high-performance water-reducing agent with a water reduction rate of ≥30%.

5. The concrete material as described in claim 1, characterized in that, The steel fibers are selected from straight steel fibers, hooked steel fibers, or corrugated steel fibers. The steel fibers have a length of 8 to 13 mm, a diameter of 0.14 to 0.2 mm, and a tensile strength of 2800 to 3100 MPa.

6. The method for preparing a coarse aggregate-containing ultra-high performance fiber-reinforced concrete material suitable for 3D printing as described in any one of claims 1 to 5, characterized in that, Includes the following steps: (1) According to the weight ratio, 650 parts of the silicate cement, 350 parts of silica fume, 400 parts of fine sand, 300 parts of medium sand and 500 parts of coarse aggregate are mixed and stirred to obtain a uniformly stirred powder. (2) Mix the 14 parts of water-reducing agent and 100 parts of water to obtain a mixed solution; (3) Mix the powder that was stirred evenly in step (1) with the mixed solution described in step (2) to obtain a mixed slurry; (4) Mix the 1.3 parts of cellulose with the remaining water to obtain a cellulose solution; (5) Mix the mixed slurry obtained in step (3) with the cellulose solution obtained in step (4) until a slurry with obvious viscosity is obtained; (6) Mix 145 parts of steel fiber with the slurry obtained in step (5) to make the steel fiber evenly distributed in the slurry, and obtain an ultra-high performance fiber-reinforced concrete material slurry containing coarse aggregate suitable for 3D printing. (7) The ultra-high performance fiber-reinforced concrete slurry containing coarse aggregate, suitable for 3D printing, described in step (6) is fed into the feeding chamber of the 3D printing equipment. 3D printing is performed according to the set printing parameters to obtain an ultra-high performance fiber-reinforced concrete component. The specific printing parameters are: nozzle diameter 30 mm, extrusion speed 0.3 m / s. 3 / h, horizontal printing speed 50mm / s, printhead distance from the ground 25mm.

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