Prestressed fiber reinforced 3d printed concrete and method of making the same

Abstract

The present application relates to a kind of prestressed fiber reinforced 3D printing concrete and its preparation method, the present application is by double-end printing mode, printing heat-shrinkable fiber and concrete simultaneously, make heat-shrinkable fiber evenly and continuously distribute in concrete, avoid excessive addition or uneven distribution cause concrete uneven strength;The present application uses continuous heat-shrinkable fiber as prestressed tendon, and the process is simple, and the synchronous process of planting and printing;Compared with other contractile fibers, the shrinkage temperature of the heat-shrinkable fiber used in the present application is low, the energy consumption is low, and the operation is simple;After heat curing to concrete, heat-shrinkable fiber is heated and shrunk to drive concrete shrinkage, directional prestress is applied to concrete, the bending tensile load capacity and crack resistance of 3D printing concrete are improved, the cracking and embrittlement of concrete structure can be effectively reduced, thereby improving its durability and service life.

Description

Technical Field

[0001] This invention relates to the field of building materials construction, specifically to a prestressed fiber reinforced 3D printed concrete and its preparation method. Background Technology

[0002] In recent years, 3D printing technology has emerged rapidly and been applied to various fields. 3D printing technology uses digital models to generate printing paths, stacking materials layer by layer to form a predetermined shape and structure. It has advantages such as being green and environmentally friendly, low cost, highly designable, and fast. At present, 3D printing technology is also being used more and more in the field of construction.

[0003] 3D printed concrete is faster, cheaper, and requires fewer technicians than traditional concrete construction. It can also print various complex and intricate geometries more flexibly, reducing waste and carbon emissions during building construction, making it more environmentally friendly.

[0004] However, 3D printing of concrete buildings often uses only concrete as a single material. It is printed layer by layer by stacking. There are interfaces between adjacent layers, the interlayer bonding force is weak, and the mechanical properties are discontinuous. When subjected to impact, the interlayer is damaged first, which can easily lead to damage or collapse. It is difficult to guarantee the safety of the structure and there are safety hazards. This defect needs to be improved through research on concrete materials.

[0005] Prestressed concrete is constructed by applying compressive stress to pre-tensioned steel bars before the structure bears any load. When the concrete structure is subjected to bending and tensile loads, the prestress stored in the steel bars can offset or reduce the tensile stress generated by the external load, preventing cracks from forming or delaying cracking under normal use. Prestressing technology can effectively improve the tensile and crack resistance of concrete. However, applying prestress to 3D-printed concrete using tensioned steel bars not only increases costs but also makes the process difficult to control, making it hard to achieve the desired strengthening effect.

[0006] Heat-shrinkable fiber is an environmentally friendly reinforcing material that can replace steel bars, effectively reducing the amount of steel bars used in concrete structures, reducing environmental pollution, and making it easier to achieve the desired reinforcement effect. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a prestressed fiber reinforced 3D printed concrete and its preparation method.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0009] A method for preparing prestressed fiber reinforced 3D printed concrete includes the following steps:

[0010] Step 1: Weigh the raw materials according to the proportions, stir and mix them evenly to obtain concrete paste. The raw materials include the following components by weight: 100 parts cement, 0-30 parts mineral admixtures, 50-200 parts sand, 1-8 parts accelerator, 1-4 parts water-reducing agent, 1-4 parts defoamer, and a water-cement ratio of 0.18-0.30. First, dry mix the weighed cement, mineral admixtures, sand and accelerator evenly, then add water, water-reducing agent, defoamer, etc. and stir to form a uniform paste.

[0011] Step 2: Use dual-printer 3D printing technology. One printer prints concrete slurry using a layered printing and stacking method. The diameter of the concrete printer is 10-40mm. The other printer produces continuous heat-shrinkable fibers. The two printers are arranged side by side, one in front of the other. When moving, the fiber printer is in front and the concrete printer is behind. The concrete extruded by the concrete printer covers and wraps the continuous heat-shrinkable fibers produced by the fiber printer.

[0012] Step 3: After the concrete is printed, allow it to cure naturally at an ambient temperature of 5-40℃ and an ambient humidity of 50-80% until the concrete reaches its final set.

[0013] Step 4: Heat curing is carried out after the concrete is formed.

[0014] Furthermore, the method for preparing the heat-shrinkable fiber includes the following steps:

[0015] Step 1.1: Mix 100 parts by weight of high-shrinkage polyester chips with 0.1-20 parts by weight of modifier to obtain modified raw material, wherein the modifier is at least one of polymer whiskers, inorganic salt whiskers and fine inorganic powder.

[0016] Step 1.2: After vacuum drying the modified raw material and polyethylene chips obtained in Step 1.1 at 60-70℃, perform core-sheath composite spinning with polyethylene as the sheath and the modified raw material as the core layer. The composite ratio is 1:3-5 to obtain polyethylene / polyester core-sheath composite fiber. Set the polyethylene feed screw and melt pipe temperature to 130℃, the polyester feed screw and melt pipe temperature to 120-125℃, the spinning box temperature to 125-130℃, the side blowing speed to 0.2-0.4m / s, the spinning speed to 500-800m / min, the stretching speed to 50-80m / min, the stretching temperature to 110-120℃, and the stretching ratio to 3-5 times.

[0017] Step 1.3: Perform a second traction stretching on the composite fiber obtained in Step 1.2. Specifically, cool the composite fiber obtained by the composite spinning machine at a temperature of 25-40℃, perform a second traction stretching at a temperature of 120-130℃ with a stretching ratio of 2-3 times, and cool it at a temperature of 25-40℃ to obtain heat-shrinkable fiber.

[0018] Step 1.4: Indent the surface of the fiber obtained in step 1.3, and then wind it for later use.

[0019] Furthermore, the heat curing temperature is 60-80℃, and the heat curing temperature for concrete is not lower than the shrinkage temperature of the prestressed fiber reinforcement, and the heat curing time is 5-60 minutes.

[0020] Furthermore, the heat curing is applied between the final set of the concrete and 3 days of age.

[0021] Furthermore, the heat curing method can be any one of hot water curing, steam curing, high-temperature furnace curing, and pre-embedded resistance wire heating curing.

[0022] Furthermore, the fineness modulus of the sand is 2.8-1.5, and the mud content is <0.5%; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent or a melamine water-reducing agent; the defoamer is a nonionic silicone polyether defoamer or a dry powder organosiloxane defoamer; and the coagulant is one or a mixture of several of lithium carbonate, calcium formate, lithium chloride, calcium chloride, and sodium sulfate.

[0023] A prestressed fiber reinforced 3D printed concrete is prepared by the above method.

[0024] The beneficial effects of this invention are as follows:

[0025] This invention can control the distribution of prestressed fiber reinforcement, ensuring its uniform and continuous distribution in concrete, thus avoiding uneven concrete strength caused by excessive addition or uneven distribution. This invention uses continuous heat-shrinkable fibers as prestressed reinforcement, and the installation and printing are carried out simultaneously, making the process simple. Compared with other shrinkable fibers, the heat-shrinkable fibers used in this invention have a low shrinkage temperature, low energy consumption, and are easy to operate.

[0026] After heat curing, the heat-shrinkable fibers shrink due to heat, causing the concrete to shrink and applying prestress to the concrete in a directional manner. This improves the flexural and tensile bearing capacity and crack resistance of 3D printed concrete, effectively reducing cracking and embrittlement of concrete structures, thereby improving their durability and service life. Detailed Implementation

[0027] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0028] Example 1

[0029] First, prepare continuous heat-shrinkable fiber A according to the following steps:

[0030] 100 parts by weight of high-shrinkage polyester chips and 20 parts by weight of modifier were mixed to obtain modified raw materials. The obtained modified raw materials and polyethylene chips were vacuum dried at 60℃ for 10 hours. Polyethylene was used as the sheath layer and the modified raw materials were used as the core layer for sheath-core composite spinning with a composite ratio of 1:3 to obtain polyethylene / polyester sheath-core composite fibers. The temperatures of the polyethylene feed screw and melt pipe were set at 130℃, the polyester feed screw and melt pipe temperatures were set at 120-125℃, the spinning box temperature was set at 125-130℃, the side blowing speed was 0.2-0.4 m / s, the spinning speed was 500 m / min, the stretching speed was 60 m / min, the stretching temperature was 110-120℃, and the stretching ratio was 5 times. A second traction stretching process is performed: the composite fiber obtained by the composite spinning machine is cooled at 25-40℃, then subjected to a second traction stretching at 120-130℃, with a stretching ratio of 2 times, and cooled again at 25-40℃ to obtain heat-shrinkable fiber A. The fiber surface is then indented and wound for later use. This fiber has a diameter of 0.8 mm and begins to shrink at 60℃, with a shrinkage rate of 2.5%.

[0031] The obtained continuous heat-shrinkable fiber A was used as the prestressed fiber reinforcement for 3D printed concrete. The basic mix proportion of the 3D printed concrete is shown in Table 1. Dual-head 3D printing technology was used. One print head printed concrete slurry in a layered and stacked manner. The diameter of the concrete print head was 30 mm. The other print head produced 5 continuous heat-shrinkable fibers A. The two print heads were arranged side by side and one after the other. When moving, the fiber print head was in front and the concrete print head was behind. The concrete extruded by the concrete print head covered and wrapped the continuous heat-shrinkable fibers A produced by the fiber print head.

[0032] After the concrete is printed and formed, it is cured under standard curing conditions for 24 hours, then placed in a water bath and cured at a constant temperature of 65℃ for 60 minutes, and finally cured under standard curing conditions for 28 days.

[0033] Example 2

[0034] The continuous heat-shrinkable fiber A obtained in Example 1 was used as the prestressed fiber reinforcement for 3D printed concrete. The mix proportion, fiber content, and diameter of the concrete printing head were the same as in Example 1. After the concrete was poured and formed, it was cured under standard curing conditions for 24 hours, then placed in a steam curing chamber and cured at a constant temperature of 75°C for 50 minutes, and finally cured under standard curing conditions for 28 days.

[0035] Example 3

[0036] First, prepare continuous heat-shrinkable fiber B according to the following steps:

[0037] 100 parts by weight of high-shrinkage polyester chips and 10 parts by weight of modifier were mixed to obtain modified raw materials. The obtained modified raw materials and polyethylene chips were vacuum dried at 70℃ for 6 hours. Polyethylene was used as the sheath layer and the modified raw materials were used as the core layer for sheath-core composite spinning with a composite ratio of 1:4 to obtain polyethylene / polyester sheath-core composite fibers. The temperatures of the polyethylene feed screw and melt pipe were set at 130℃, the polyester feed screw and melt pipe temperatures were set at 120-125℃, the spinning box temperature was set at 125-130℃, the side blowing speed was 0.2-0.4 m / s, the spinning speed was 800 m / min, the stretching speed was 50 m / min, the stretching temperature was 110-120℃, and the stretching ratio was 3 times. A second traction stretching process is performed: the composite fibers from the composite spinning machine are cooled at 25-40℃, then subjected to a second traction stretching at 120-130℃, with a stretching ratio of 3 times. After cooling at 25-40℃, heat-shrinkable fiber B is obtained. The fiber surface is then indented and wound for later use. This fiber has a diameter of 0.3mm and begins to shrink at 70℃, with a shrinkage rate of 4%.

[0038] The obtained continuous heat-shrinkable fiber B was used as the prestressed fiber reinforcement in the 3D printed concrete. The basic mix proportions of the 3D printed concrete are shown in Table 1. A dual-printer head 3D printing technology was employed. One printer head printed concrete slurry using a layered printing and stacking method; the diameter of the concrete printer head was 40 mm. The other printer head produced 20 continuous heat-shrinkable fibers B. The two printers were arranged side-by-side, one in front of the other. During travel, the fiber printer head was in front, and the concrete printer head was behind. The concrete extruded from the concrete printer head covered and enveloped the continuous heat-shrinkable fibers B produced by the fiber printer head.

[0039] After the concrete is poured and formed, it is cured under standard curing conditions for 24 hours, then placed in a high-temperature furnace and cured at a constant temperature of 80℃ for 20 minutes, and finally cured under standard curing conditions for 28 days.

[0040] Example 4

[0041] The continuous heat-shrinkable fiber B from Example 3 was used as the prestressed fiber reinforcement in the 3D printed concrete. The mix proportions, fiber usage, and print head diameter of the 3D printed concrete were the same as in Example 3. After the concrete was poured and molded, it was cured under standard curing conditions for 24 hours, then placed in a steam curing chamber and cured at a constant temperature of 70°C for 40 minutes, and finally cured under standard curing conditions for 28 days.

[0042] Comparative Example 1

[0043] Comparative Example 1 uses continuous heat-shrinkable fiber A. The concrete mix proportion, fiber content, and concrete printing head diameter are the same as in Example 1. The difference is that Comparative Example 1 does not use heat curing and is placed in a standard curing environment for 28 days after molding.

[0044] Comparative Example 2

[0045] To compare the effects of heat-shrinkable and ordinary fibers on the mechanical properties of 3D-printed concrete, Comparative Example 2 was designed. Its concrete mix proportions and the amount of heat-shrinkable fiber A were the same as in Example 1, the difference being that non-shrinkable ordinary polyester fiber was used in Comparative Example 2. The curing method for Comparative Example 2 was the same as in Example 1.

[0046] Comparative Example 3

[0047] In this comparative example, ordinary 3D printed concrete without any fibers was prepared. The diameter of the concrete printing head and the curing method of Comparative Example 3 were the same as those of Example 1.

[0048] Table 1 Concrete mix proportions (kg / m³) 3

[0049] cement Mineral admixtures sand water Water reducing agent coagulant Defoamer 100 21 140 25 2 6 3

[0050] Table 2 Fiber Diameter and Heat Curing Methods

[0051] fiber Fiber diameter / mm Heat curing method Example 1 Continuous heat-shrinkable fiber A 0.8 65℃ water bath maintenance Example 2 Continuous heat-shrinkable fiber A 0.8 75℃ steam curing Example 3 Continuous heat-shrinkable fiber B 0.3 80℃ high temperature furnace curing Example 4 Continuous heat-shrinkable fiber B 0.3 70℃ steam curing Comparative Example 1 Continuous heat-shrinkable fiber A 0.8 No heat curing Comparative Example 2 ordinary polyester fiber 0.8 65℃ water bath maintenance Comparative Example 3 No fiber added 0 65℃ water bath maintenance

[0052] Table 3 Concrete setting time and mechanical properties

[0053]

[0054] As can be seen from the above examples and comparative examples, compared with 3D printed concrete without embedded fibers and 3D printed concrete with embedded ordinary synthetic fibers, 3D printed concrete with embedded continuous heat-shrinkable fibers and simultaneous heat curing exhibits significantly improved compressive strength, tensile strength, and flexural toughness. This is because prestressed fiber-reinforced concrete applies compressive stress to the concrete matrix through shrinking continuous fibers before the structure bears a load. When the 3D printed concrete structure is subjected to bending and tensile loads, the prestress stored in the fibers within the concrete can offset or reduce the tensile stress generated by the external load, preventing cracking or delaying cracking under normal use. The diameter of the continuous heat-shrinkable fibers also affects the mechanical properties of 3D printed concrete to some extent. The initial and final setting times of the concrete vary depending on the amount of accelerator used.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing prestressed fiber reinforced 3D printed concrete, characterized in that, Includes the following steps: Step 1: Weigh the raw materials according to the proportions, stir and mix them evenly to obtain concrete paste. The raw materials include the following components by weight: 100 parts cement, 0-30 parts mineral admixtures, 50-200 parts sand, 1-8 parts accelerator, 1-4 parts water-reducing agent, 1-4 parts defoamer, and a water-cement ratio of 0.18-0.

30. First, dry mix the weighed cement, mineral admixtures, sand and accelerator evenly, then add water, water-reducing agent and defoamer and stir to form a uniform paste. Step 2: Use dual-printer 3D printing technology. One printer prints concrete slurry using a layered printing and stacking method. The diameter of the concrete printer is 10-40mm. The other printer produces continuous heat-shrinkable fibers. The two printers are arranged side by side, one in front of the other. When moving, the fiber printer is in front and the concrete printer is behind. The concrete extruded by the concrete printer covers and wraps the continuous heat-shrinkable fibers produced by the fiber printer. The method for preparing the heat-shrinkable fiber includes the following steps: Step 1.1: Mix 100 parts by weight of high-shrinkage polyester chips with 0.1-20 parts by weight of modifier to obtain modified raw material, wherein the modifier is at least one of polymer whiskers, inorganic salt whiskers and fine inorganic powder. Step 1.2: After vacuum drying the modified raw material and polyethylene chips obtained in Step 1.1 at 60-70℃, perform core-sheath composite spinning with polyethylene as the sheath and the modified raw material as the core layer. The composite ratio is 1:3-5 to obtain polyethylene / polyester core-sheath composite fiber. Set the polyethylene feed screw and melt pipe temperature to 130℃, the polyester feed screw and melt pipe temperature to 120-125℃, the spinning box temperature to 125-130℃, the side blowing speed to 0.2-0.4m / s, the spinning speed to 500-800m / min, the stretching speed to 50-80m / min, the stretching temperature to 110-120℃, and the stretching ratio to 3-5 times. Step 1.3: Perform a second traction stretching on the composite fiber obtained in Step 1.

2. Specifically, cool the composite fiber obtained by the composite spinning machine at a temperature of 25-40℃, perform a second traction stretching at a temperature of 120-130℃ with a stretching ratio of 2-3 times, and cool it at a temperature of 25-40℃ to obtain heat-shrinkable fiber. Step 1.4: Indent the surface of the fiber obtained in Step 1.3, then wind it up for later use; Step 3: After the concrete is printed, allow it to cure naturally at an ambient temperature of 5-40℃ and an ambient humidity of 50-80% until the concrete reaches its final set. Step 4: Heat curing is carried out after the concrete is formed.

2. The method for preparing prestressed fiber reinforced 3D printed concrete according to claim 1, characterized in that, The heat curing temperature is 60-80℃, and the heat curing temperature for concrete is not lower than the shrinkage temperature of the prestressed fiber reinforcement. The heat curing time is 5-60 minutes.

3. The method for preparing prestressed fiber reinforced 3D printed concrete according to claim 1, characterized in that, In step 3, the heat curing is applied between the final set of the concrete and 3 days of age.

4. The method for preparing prestressed fiber reinforced 3D printed concrete according to claim 1, characterized in that, The heat curing method can be any one of hot water curing, steam curing, high-temperature furnace curing, and pre-embedded resistance wire heating curing.

5. The method for preparing prestressed fiber reinforced 3D printed concrete according to claim 1, characterized in that, The fineness modulus of the sand is 2.8-1.5, and the mud content is <0.5%; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent or a melamine water-reducing agent; the defoamer is a nonionic silicone polyether defoamer or a dry powder organosiloxane defoamer; the coagulant is one or a mixture of several of lithium carbonate, calcium formate, lithium chloride, calcium chloride and sodium sulfate.

6. A prestressed fiber reinforced 3D printed concrete, characterized in that, Prepared by the method described in any one of claims 1-5.

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