Preparation method of low-cost 3D printing tire fiber reinforced green ultra-high performance concrete

Abstract

The invention discloses a preparation method of low-cost 3D printing tire fiber reinforced green ultra-high performance concrete, and belongs to the technical field of concrete. The regenerated tire steel fiber is adopted to replace traditional industrial steel fiber which is high in production cost and large in energy consumption, the material cost of the ultra-high-performance concrete is greatly reduced, and the mechanical property of the ultra-high-performance concrete is improved through the special-shaped characteristics of the regenerated tire steel fiber; meanwhile, the Portland cement, the silica fume, the quartz powder, the fine aggregate, the coarse aggregate, the water reducing agent and the nano calcium carbonate are added, and the dosage ratio of all the components is regulated and controlled, so that the technical problems of the traditional ultra-high performance concrete in the aspect of 3D printing forming and the printing difficulty caused by tire fiber profile are solved; finally, the low-cost 3D printing tire fiber reinforced green ultra-high performance concrete with good extrudability, constructability, printability, ultra-high strength and high toughness is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete, and in particular relates to a method for preparing low-cost 3D printed tire fiber reinforced green ultra-high performance concrete. Background Art

[0002] Concrete 3D printing technology is gradually revolutionizing the construction mode of the traditional construction industry with its significant advantages of intelligence, flexible operation, low labor demand and moldlessness. The development of 3D printed UHPC (ultra-high performance concrete) is particularly eye-catching. In pursuit of the ultra-high strength and high toughness characteristics of UHPC, the incorporation of a large amount of steel fiber becomes necessary. However, this not only increases the complexity of the material, but also significantly increases the overall cost in large-scale production due to the high cost of steel fiber, limiting the widespread application of 3D printed UHPC.

[0003] At the same time, with the vigorous development of my country's automobile industry, the number of waste tires has increased dramatically. In 2023, it has exceeded 330 million, with a total weight of about 14.5 million tons. This "black pollution" problem needs to be solved urgently. Traditionally, the steel wires in waste tires are mostly treated as scrap steel at a low price and used in the steelmaking process. This move not only fails to make efficient use of resources, but also increases the consumption of energy and resources. It is worth noting that these waste steel wires are similar to the steel fibers required for 3D printing in some forms and functions, which provides a new idea for reducing the cost of 3D printing UHPC-that is, the steel wires (tire steel fibers) in waste tires are introduced into the mortar matrix as reinforcing materials, which is expected to significantly reduce material costs.

[0004] Waste tire steel fiber is a steel wire obtained by processing waste tires. Steel wire needs to be added during the manufacturing process of tires to increase the strength and hardness of the tires. Therefore, steel fiber can be obtained after the waste tires are processed. Waste tire steel fiber has high tensile strength and elastic modulus. Adding it to concrete can improve the mechanical properties of concrete, such as compressive strength and flexural strength. However, the addition of waste tire steel wire will cause the working performance of concrete to decline, resulting in printing difficulties. Therefore, how to balance cost control and concrete performance has become a key challenge. In particular, how to reduce the cost of 3D printing UHPC while maintaining its good extrudability, buildability, printability, ultra-high strength and high toughness. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method for preparing low-cost 3D printed tire fiber reinforced green ultra-high performance concrete. The present invention uses steel fibers in waste tires as reinforcing materials, which reduces the production cost of high-performance concrete on the one hand, and realizes the efficient utilization of waste tires on the other hand; and the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete provided by the present invention not only maintains the superior performance of ultra-high strength and high toughness, but also has excellent 3D printing capabilities, solves the technical difficulties of traditional ultra-high performance concrete in 3D printing molding and the printing difficulties caused by the special shape of tire steel fibers, and opens up a new way for the sustainable development of the construction industry and the recycling of waste resources.

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

[0007] The invention provides a low-cost 3D printed tire fiber reinforced green ultra-high performance concrete, which comprises the following components by weight: 640-660 parts of silicate cement with a strength grade not less than 52.5, 265-285 parts of silica fume, 220-240 parts of quartz powder, 430-450 parts of fine aggregate, 710-730 parts of coarse aggregate, 39-157 parts of recycled tire steel fiber, 25-30 parts of water reducer and 22-27 parts of nano calcium carbonate.

[0008] Technical principle: The present invention adopts recycled tire steel fiber to replace the traditional industrial steel fiber with high production cost and high energy consumption, which not only greatly reduces the material cost of ultra-high performance concrete, but also improves the mechanical properties of ultra-high performance concrete due to the special-shaped characteristics of recycled tire steel fiber; at the same time, combined with the addition of silicate cement, silica fume, quartz powder, fine aggregate, coarse aggregate, water reducer and nano-calcium carbonate, and regulating the dosage ratio of each component, finally obtains low-cost 3D printed tire fiber reinforced green ultra-high performance concrete with good extrudability, buildability, printability, ultra-high strength and high toughness.

[0009] Preferably, the recycled tire steel fiber has a length of 5 to 30 mm, a diameter of 0.2 to 0.22 mm, and a tensile strength of 1500 to 2200 MPa.

[0010] Preferably, the particle size of the silicate cement with a strength grade not less than 52.5 is 0.38 to 83.8 μm.

[0011] Preferably, the particle size of the quartz powder is 3.45-365 μm; the particle size of the fine aggregate is 83.8-762 μm; the particle size of the coarse aggregate is 762-2600 μm; the Mohs hardness of the quartz powder, fine aggregate and coarse aggregate is 7.0, and the density is 2.65 g / cm 3 .

[0012] Preferably, the particle size of the silica fume is 0.14-107 μm.

[0013] Preferably, the water reducing agent has a water reducing rate of >25%, a dissolved solid content of 28.8%, and a bulk density of 758 kg / m 3 , a melamine-based BASF water reducer with a drying loss of 1.7% and a dissolving pH of 10.5.

[0014] Preferably, the particle size of the nano calcium carbonate is 10 to 100 nm.

[0015] The present invention provides a method for preparing low-cost 3D printed tire fiber reinforced green ultra-high performance concrete as described in the above technical solution, comprising the following steps:

[0016] (1) mixing silicate cement, silica fume, quartz powder, fine aggregate, coarse aggregate and nano calcium carbonate to obtain a mixed material; mixing a water reducer with water to obtain a mixed slurry;

[0017] (2) mixing the mixed material obtained in step (1) with the mixed slurry to obtain a mixture;

[0018] (3) Mixing the recycled tire steel fiber with the mixture obtained in step (2) to obtain the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete.

[0019] The present invention also provides a method for using the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete described in the above technical solution, comprising the following steps: 3D printing the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete; the parameters of the 3D printing include: a nozzle diameter of 10 to 40 mm, an extrusion speed of 40 to 80 rpm, and a horizontal printing speed of 30 to 60 mm / s.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete provided by the present invention adopts silicate cement of grade not less than 52.5 as a cementitious material, which can make the concrete have higher strength and durability; silica fume, as a fine filler in ultra-high performance concrete, can fill the gaps between cement particles, greatly improve the density and strength, durability and impermeability of concrete, and accelerate the cement hydration process to achieve the control of hydration rate; quartz powder and quartz sand are used as filling skeletons to further improve the compactness of concrete, thereby increasing the strength; water reducer, as a core additive in ultra-high performance concrete, can greatly reduce water consumption, while enhancing the fluidity and construction performance of concrete, providing an ideal printable operation time window for UHPC materials; nano calcium carbonate can fill the tiny gaps inside the concrete, improve the density and strength of the concrete, and also reduce the permeability of the concrete, improve its durability, and nano calcium carbonate can also effectively enhance the frost resistance, sulfate erosion resistance and crack resistance of the concrete, thereby extending the service life of the concrete. The synergistic effect of these components ensures the synchronous development of CSH gel and hydration products such as calcium aluminate, and constructs a UHPC printing material that is highly compatible with the printing process, has strong grip of recycled tire steel fibers, and has a dense microstructure. In addition, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete provided by the present invention has a good load-mid-span displacement curve after 3D printing, and the maximum bending load can reach 8162.7N, showing ultra-high strength and high toughness comparable to standard 3D printed UHPC, opening up a new path for the innovation of building materials and the development of 3D printing technology.

[0022] The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete provided by the present invention combines 3D printing technology and ultra-high performance concrete (UHPC). By adding a small amount of nano-calcium carbonate to enhance the matrix density, and using a water reducer to adjust the curing and fluidity of UHPC, it is adapted to the 3D printing process requirements. Recycled tire steel fiber is introduced as a reinforcing material, which is derived from waste tires, which not only greatly reduces the manufacturing cost of 3D printed UHPC, but also achieves a dual improvement in environmental protection and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 1;

[0025] Figure 2 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 2;

[0026] Figure 3 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 3;

[0027] Figure 4 The load-mid-span displacement curves of the ultra-high performance concrete 3D printed products prepared in Comparative Example 4, Example 1 and Comparative Example 1;

[0028] Figure 5 Load-mid-span displacement curves of the ultra-high performance concrete 3D printed products prepared in Comparative Example 4, Example 2 and Comparative Example 2. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The embodiment of the present invention provides a low-cost 3D printed tire fiber reinforced green ultra-high performance concrete, which includes the following components by weight: 640-660 parts of silicate cement with a strength grade not less than 52.5, 265-285 parts of silica fume, 220-240 parts of quartz powder, 430-450 parts of fine aggregate, 710-730 parts of coarse aggregate, 39-157 parts of recycled tire steel fiber, 25-30 parts of water reducer and 22-27 parts of nano calcium carbonate.

[0032] In a preferred embodiment, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 640-660 parts of silicate cement with a strength grade of not less than 52.5, preferably 645-655 parts, and more preferably 650-655 parts by weight; the silicate cement with a strength grade of not less than 52.5 is silicate cement with a strength grade of 52.5, and the silicate cement with a strength grade of 52.5 comes from Shandong Yangchun Shanshui Cement Co., Ltd. The present invention uses silicate cement with a strength grade of not less than 52.5 as a cementitious material, which mainly plays the role of wrapping aggregates, so that the concrete has higher strength and durability.

[0033] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade of not less than 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 265 to 285 parts of silica fume, preferably 270 to 280 parts, and more preferably 275 to 280 parts; the particle size of the silica fume is 0.14 to 107 μm, more preferably 0.18 to 66 μm, and more preferably 0.23 to 5.6 μm. The silica fume in the present invention can fill the gaps between cement particles and improve the viscosity of the printed substrate, thereby enhancing the interlayer bonding and buildability of the printed UHPC.

[0034] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade not less than 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 220 to 240 parts of quartz powder, preferably 225 to 235 parts, and more preferably 230 to 235 parts; the particle size of the quartz powder is 3.45 to 365 μm, and more preferably 31 to 136 μm; the Mohs hardness of the quartz powder is 7.0, and the density is 2.65 g / cm 3 ; The quartz powder is from Nanyang Chufeng Silicon Material Co., Ltd. The present invention controls the amount and particle size of the quartz powder within the above range, which is conducive to obtaining high-strength concrete; excessive amount of quartz powder will cause serious water shortage in the cement matrix, reduce fluidity, affect the printing effect, and even make printing impossible. Too little quartz powder cannot ensure the density and high strength of the matrix; too small a particle size of quartz powder will weaken the tight stacking effect, thereby reducing the overall strength.

[0035] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade of not less than 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 430 to 450 parts of fine aggregate, preferably 435 to 445 parts, and more preferably 440 to 445 parts; the particle size of the fine aggregate is 83.8 to 762 μm, more preferably 174.9 to 596.6 μm, and more preferably 285.8 to 596.6 μm; the Mohs hardness of the fine aggregate is 7.0 and the density is 2.65 g / cm 3 The present invention increases the amount of fine aggregate and cooperates with other materials in the matrix to form an ideal tightly packed structure, which can effectively improve the density and mechanical properties of the material and optimize the stability of the overall structure.

[0036] In a preferred embodiment, the fine aggregate is one or more of quartz sand and river sand, more preferably quartz sand; the quartz sand comes from Nanyang Chufeng Silicon Material Co., Ltd. The fine aggregate in the present invention plays a role of skeleton and filling in concrete.

[0037] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade not less than 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 710 to 730 parts of coarse aggregate, preferably 715 to 725 parts, and more preferably 720 to 725 parts; the particle size of the coarse aggregate is 762 to 2600 μm, more preferably 762 to 2034 μm, and more preferably 762 to 1591 μm; the Mohs hardness of the coarse aggregate is 7.0 and the density is 2.65 g / cm 3 The present invention increases the amount of coarse aggregate to enhance the skeleton support of the matrix, which can effectively improve the stability of the matrix and further improve the compressive and flexural strengths of the UHPC matrix.

[0038] In a preferred embodiment, the coarse aggregate is one or more of quartz sand and river sand, more preferably quartz sand; the quartz sand comes from Nanyang Chufeng Silicon Material Co., Ltd. The coarse aggregate in the present invention plays a role of skeleton or filling in concrete.

[0039] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade not less than grade 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 39 to 157 parts of recycled tire steel fiber, preferably 78 to 157 parts; the length of the recycled tire steel fiber is 5 to 30 mm, more preferably 10 to 25 mm, and more preferably 13 to 22 mm; the diameter of the recycled tire steel fiber is 0.2 to 0.22 mm; the tensile strength of the recycled tire steel fiber is 1500 to 2200 MPa, more preferably 1900 to 2100 MPa. The length of recycled tire steel fiber varies. In the present invention, the length of recycled tire steel fiber refers to the main body length of the fiber. The length of recycled tire steel fiber should not be too small. Too small length will lead to insufficient bridging effect of the fiber on the crack, which is not conducive to enhancing the mechanical properties such as strength and toughness of UHPC. The recycled tire steel fiber in the present invention is a byproduct steel wire produced by recycling waste tires; the recycled tire steel fiber comes from Shanxi Luqiao Renewable Resources Development Co., Ltd. The recycled tire steel fiber in the invention can improve the toughness, tensile strength, bending strength, shear strength and fatigue resistance of concrete.

[0040] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade not less than grade 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 25 to 30 parts of water reducer, preferably 26 to 28 parts, and more preferably 25 to 26 parts. In the present invention, the water reducer has a water reduction rate of >25%, a dissolved solid content of 28.8%, and a bulk density of 758 kg / m 3, a melamine-based BASF water reducer with a drying loss of 1.7% and a dissolving pH of 10.5. The water reducer in the present invention can reduce the amount of water used, thereby improving the density and hardness of ultra-high performance concrete, increasing its fluidity and printable time, and making the base material easier to extrude.

[0041] In a preferred embodiment, based on 640 to 660 parts by weight of silicate cement with a strength grade not less than 52.5, the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete includes 22 to 27 parts of nano calcium carbonate, preferably 24 to 26 parts; the particle size of the nano calcium carbonate is 10 to 100 nm, more preferably 20 to 60 nm, and more preferably 30 to 50 nm. The nano calcium carbonate in the present invention can improve the density and strength of concrete by filling the tiny gaps inside the concrete, while also reducing the permeability of the concrete and improving its durability. Nano calcium carbonate can also effectively enhance the frost resistance, sulfate erosion resistance and crack resistance of concrete, thereby extending the service life of concrete.

[0042] The present invention also provides a method for preparing the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to the above technical solution, comprising the following steps:

[0043] (1) mixing silicate cement, silica fume, quartz powder, fine aggregate, coarse aggregate and nano calcium carbonate to obtain a mixed material; mixing a water reducer with water to obtain a mixed slurry;

[0044] (2) mixing the mixed material obtained in step (1) with the mixed slurry to obtain a mixture;

[0045] (3) Mixing the recycled tire steel fiber with the mixture obtained in step (2) to obtain the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete.

[0046] In a preferred embodiment, in step (1), the mixing of the silicate cement, silica fume, quartz powder, fine aggregate, coarse aggregate and nano calcium carbonate is carried out under stirring conditions. The present invention has no particular limitation on the stirring rate and time, as long as the components are mixed evenly.

[0047] In a preferred embodiment, in step (1), the water reducing agent and water are mixed under stirring conditions. The present invention has no particular limitation on the stirring rate and time, as long as the components are mixed evenly.

[0048] In a preferred embodiment, in step (1), the ratio of the water reducing agent to water is (25-30): (207-212) by weight.

[0049] In a preferred embodiment, in step (2), the mixing of the mixed material and the mixed slurry is specifically as follows: pre-stirring the mixed material, then adding the mixed slurry and continuing to stir; the mixing of the mixed material and the mixed slurry is carried out in a stirring pot.

[0050] In a preferred embodiment, the pre-mixing time is 90 to 200 seconds, more preferably 100 to 180 seconds; there is no particular limitation on the pre-mixing rate. The pre-mixing in the present invention is to ensure that the components of the mixed material are mixed uniformly.

[0051] In a preferred embodiment, the mixed slurry is added to the pre-stirred mixed material at a uniform speed within 20 seconds for continued stirring; the continued stirring time is 420 to 850 seconds, and more preferably 510 to 750 seconds.

[0052] In a preferred embodiment, in step (3), the mixing of the recycled tire steel fiber and the mixture is specifically as follows: adding the recycled tire steel fiber to the mixture and stirring; the stirring time is 10 to 25 minutes, preferably 15 to 20 minutes, and more preferably 16 to 18 minutes. In the present invention, the recycled tire steel fiber is preferably added to the mixture at a uniform speed within 2 minutes and stirred. When adding, it is necessary to disperse the recycled tire steel fiber to avoid agglomeration and clogging the print head.

[0053] The present invention efficiently stirs the mixed material and the mixed slurry in an orderly manner to maximize the water reducing efficiency of the water reducing agent. Subsequently, the recycled tire steel fiber is gradually added during continuous stirring to ensure that all raw materials are evenly mixed during the step-by-step addition process, thereby giving the material good performance.

[0054] The present invention also provides a method for using the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete described in the above technical solution, comprising the following steps: 3D printing the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete; the parameters of the 3D printing include: a nozzle diameter of 10 to 40 mm, an extrusion speed of 40 to 80 rpm, and a horizontal printing speed of 30 to 60 mm / s; further preferably: a nozzle diameter of 30 mm, an extrusion speed of 60 rpm, and a horizontal printing speed of 45 mm / s.

[0055] The present invention has no special limitation on the 3D printing equipment, and any 3D printing equipment well known to those skilled in the art may be used.

[0056] The printing parameters of the method of use provided by the present invention can match the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete described in the above technical solution, thereby realizing 3D printing of low-cost 3D printed tire fiber reinforced ultra-high performance concrete.

[0057] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0058] Example 1

[0059] (1) According to the weight ratio, 651 parts of silicate cement with a strength grade of 52.5; 276 parts of silica fume with a particle size of 0.23 to 5.6 μm; and 276 parts of silica fume with a particle size of 31 to 136 μm, a Mohs hardness of 7.0, and a density of 2.65 g / cm 3 232 parts of quartz powder; particle size 285.8-596.6 μm, Mohs hardness 7.0, density 2.65 g / cm 3 441 parts of quartz sand (fine aggregate); particle size 762-1591 μm, Mohs hardness 7.0, density 2.65 g / cm 3 718 parts of quartz sand (coarse aggregate) and 24 parts of nano calcium carbonate with a particle size of 30 to 50 nm are mixed and stirred to obtain a mixed material; 27 parts of water reducer are mixed with 209 parts of water by weight and stirred to obtain a mixed slurry; the water reducer has a water reduction rate of more than 25%, a dissolved solid content of 28.8%, and a bulk density of 758 kg / m 3 , a melamine-based BASF water reducer with a drying loss of 1.7% and a dissolving pH of 10.5.

[0060] (2) The mixed material obtained in step (1) is pre-mixed in a stirring pot for 180 seconds; then the mixed slurry obtained in step (1) is uniformly added to the pre-mixed mixed material within 5 seconds and the mixture is continuously stirred for 600 seconds; finally, 39.25 parts (0.5% volume fraction) of recycled tire steel fibers with a length of 13 to 22 mm, a diameter of 0.2 mm, and a tensile strength of 2000 MPa are uniformly dispersed within 120 seconds and poured into the stirring pot and stirred for 600 seconds to obtain low-cost 3D printed tire fiber reinforced green ultra-high performance concrete.

[0061] (3) The low-cost 3D printed tire fiber reinforced ultra-high performance concrete obtained in step (2) is 3D printed, the print nozzle diameter is set to 30 mm, the extrusion speed is 60 rpm, and the horizontal printing speed is 45 mm / s, and then printing is performed to obtain an ultra-high performance concrete 3D printed product.

[0062] Example 2

[0063] The difference from Example 1 is that the amount of recycled tire steel fiber added in step (2) is replaced by "39.25 parts (0.5% volume fraction)" to "78.5 parts (1% volume fraction)", and the other steps are the same as Example 1.

[0064] Example 3

[0065] The difference from Example 1 is that the amount of recycled tire steel fiber added in step (2) is replaced by "39.25 parts (0.5% volume fraction)" to "157 parts (2% volume fraction)", and the other steps are the same as Example 1.

[0066] Figure 1 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 1. Figure 2 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 2. Figure 3 This is a physical picture of the ultra-high performance concrete 3D printed product obtained in Example 3. Figure 1-2 It can be seen that the present invention successfully realizes the preparation of low-cost 3D printed tire fiber reinforced green ultra-high performance concrete. However, it is worth noting that due to the different lengths of recycled tire steel fibers, some of which can reach 30 mm, excessive addition can easily cause the fibers to entangle the extrusion rod during printing, clogging the print head and thus affecting the printing effect (such as Figure 3 shown).

[0067] Comparative Example 1

[0068] (1) According to the weight ratio, 651 parts of silicate cement with a strength grade of 52.5; 276 parts of silica fume with a particle size of 0.23 to 5.6 μm; and 276 parts of silica fume with a particle size of 31 to 136 μm, a Mohs hardness of 7.0, and a density of 2.65 g / cm 3 232 parts of quartz powder; particle size 285.8-596.6 μm, Mohs hardness 7.0, density 2.65 g / cm 3 441 parts of quartz sand (fine aggregate); particle size 762-1591 μm, Mohs hardness 7.0, density 2.65 g / cm 3 718 parts of quartz sand (coarse aggregate) and nano calcium carbonate with a particle size of 30 to 50 nm are mixed to obtain a mixed material; 27 parts of a water reducer are mixed with 209 parts of water by weight to obtain a mixed slurry.

[0069] (2) The mixed material obtained in step (1) is pre-mixed in a stirring pot for 180 seconds; then the mixed slurry obtained in step (1) is uniformly added to the pre-mixed mixed material within 5 seconds and the mixture is continuously stirred for 600 seconds; finally, 39.25 parts (0.5% volume fraction) of copper-plated steel fibers with a length of 13 mm, a diameter of 0.2 mm, and a tensile strength of >2400 MPa are uniformly dispersed within 120 seconds and poured into the stirring pot and the mixture is continuously stirred for 600 seconds to obtain 3D printable concrete.

[0070] (3) The 3D printable concrete obtained in step (2) is 3D printed, the print nozzle diameter is set to 30 mm, the extrusion speed is set to 60 rpm, and the horizontal printing speed is set to 45 mm / s, and then printing is performed to obtain an ultra-high performance concrete 3D printed product.

[0071] Comparative Example 2

[0072] The difference from Comparative Example 1 is that the amount of copper-plated steel fiber added in step (2) is replaced by "39.25 parts (0.5% volume fraction)" to "78.5 parts (1% volume fraction)", and the other steps are the same as Comparative Example 1.

[0073] Comparative Example 3

[0074] The difference from Comparative Example 1 is that the amount of copper-plated steel fiber added in step (2) is replaced by "39.25 parts (0.5% volume fraction)" to "157 parts (2% volume fraction)", and the other steps are the same as Comparative Example 1.

[0075] Comparative Example 4

[0076] The difference from Comparative Example 1 is that the copper-plated steel fiber is omitted, and the other steps are the same as Comparative Example 1.

[0077] Figure 4 The load-mid-span displacement curves of the ultra-high performance concrete 3D printed products prepared in Comparative Example 4, Example 1, and Comparative Example 1. In the figure, 0% no steel fiber is Comparative Example 4, 0.5% tire fiber is Example 1, and 0.5% industrial fiber is Comparative Example 1. Figure 5 The load-mid-span displacement curves of the ultra-high performance concrete 3D printed products prepared in Comparative Example 4, Example 2 and Comparative Example 2 are shown in the figure. In the figure, 0% steel fiber is Comparative Example 4, 1% tire fiber is Example 2, and 1% industrial fiber is Comparative Example 2. Figure 4-5 It can be seen that the flexural strength of the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete provided by the present invention is higher than that of the 3D printed UHPC prepared with copper-plated steel fibers when the recycled tire steel fiber content is 0.5% and 1%, and its toughness is significantly higher than that of the specimen without steel fiber addition.

[0078] 52.5 The costs of Portland cement, silica fume, quartz sand aggregate and steel fiber are shown in Table 1.

[0079] Table 1

[0080] Material 52.5 Portland cement Silica Fume Quartz powder and quartz sand aggregate Steel Fiber total Dosage (portion) 651 276 1391 78.5 2200 Fee (Yuan) 385 429 990 39(Tire) 1843 Fee (Yuan) 385 429 990 858(Copper plating) 2662

[0081] As can be seen from Table 1, the present invention uses recycled tire steel fibers to replace traditional industrial steel fibers with high production costs and high energy consumption to prepare ultra-high performance concrete, which significantly reduces material costs (1% steel fiber content reduces costs by about 30%).

[0082] Comparative Examples 5-9

[0083] The preparation process of concrete is the same as that of Example 1, and the dosage ratio of each raw material is shown in Table 2.

[0084] Table 2

[0085]

[0086] The compressive peak load of the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete obtained in Example 2 and the 3D printable concrete obtained in Comparative Examples 5-9 was tested by displacement loading (loading rate 0.06 mm / min). The fluidity was tested by using an NLD-3 electric jumping table. The bottom diameter of the jumping table mold was 100 mm, the upper diameter was 70 mm, and the height was 60 mm. After jumping 25 times, the expansion diameter was measured in two directions perpendicular to each other on the bottom surface of the mortar and the average value was calculated. The fluidity test must be completed within 5 minutes. The results are shown in Table 3.

[0087] Table 3

[0088] Peak compressive load (KN) Fluidity(mm) Printability Constructive Comparative Example 5 —— 90 Poor —— Comparative Example 6 —— 103 Poor —— Comparative Example 7 480 130 generally good Comparative Example 8 570 126 generally good Comparative Example 9 500 134 generally good Example 2 625 150 good good

[0089] It can be seen from Table 3 that the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete prepared by using the raw material mix ratios provided by the present invention shows excellent performance in comprehensive printing performance and strength. The peak force of the compressive test piece obtained by pouring the concrete of Example 2 of the present invention is up to 625KN, which is higher than that of Comparative Examples 5-9.

[0090] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A low-cost 3D printed tire fiber reinforced green ultra-high performance concrete, characterized in that: Calculated by weight, the composition includes: 640-660 parts of silicate cement with a strength grade not less than 52.5, 265-285 parts of silica fume, 220-240 parts of quartz powder, 430-450 parts of fine aggregate, 710-730 parts of coarse aggregate, 39-157 parts of recycled tire steel fiber, 25-30 parts of water reducing agent and 22-27 parts of nano calcium carbonate.

2. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The length of the recycled tire steel fiber is 5 to 30 mm, the diameter is 0.2 to 0.22 mm, and the tensile strength is 1500 to 2200 MPa.

3. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The particle size of the silicate cement with a strength grade not less than 52.5 is 0.38 to 83.8 μm.

4. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The particle size of the quartz powder is 3.45-365 μm; the particle size of the fine aggregate is 83.8-762 μm; the particle size of the coarse aggregate is 762-2600 μm; the Mohs hardness of the quartz powder, fine aggregate and coarse aggregate is 7.0, and the density is 2.65 g / cm 3 .

5. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The particle size of the silica fume is 0.14-107 μm.

6. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The water reducing agent has a water reducing rate of >25%, a dissolved solid content of 28.8%, and a bulk density of 758 kg / m 3 , a melamine-based BASF water reducer with a drying loss of 1.7% and a dissolving pH of 10.

5.

7. The low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to claim 1, characterized in that: The particle size of the nano calcium carbonate is 10 to 100 nm.

8. A method for preparing low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) mixing silicate cement, silica fume, quartz powder, fine aggregate, coarse aggregate and nano calcium carbonate to obtain a mixed material; mixing a water reducer with water to obtain a mixed slurry; (2) mixing the mixed material obtained in step (1) with the mixed slurry to obtain a mixture; (3) Mixing the recycled tire steel fiber with the mixture obtained in step (2) to obtain the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete.

9. The method for using the low-cost 3D printed tire fiber reinforced green ultra-high performance concrete according to any one of claims 1 to 7, characterized in that: The following steps are involved: Low-cost 3D printed tire fiber reinforced green ultra-high performance concrete is 3D printed; the parameters of the 3D printing include: a nozzle diameter of 10 to 40 mm, an extrusion speed of 40 to 80 rpm, and a horizontal printing speed of 30 to 60 mm / s.

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