Thermally shrinkable fiber reinforced 3D printed concrete and method of making the same

Abstract

The present application relates to a kind of thermal shrinkage type fiber reinforced 3D printing concrete and its preparation method, the present application will be added to concrete thermal shrinkage type fiber, its length will change after heating, by the shrinkage stress of thermal shrinkage type fiber uniformly distributed in concrete to concrete prestressed, to improve the density of concrete, thermal shrinkage type fiber uniformly dispersed in concrete to the self-stress of three-dimensional tightness that concrete matrix is applied, can heal the gel hole and microcrack formed in early hydration, help to form more dense microstructure, realize the enhancement and toughening of concrete structure, to increase the bearing capacity and crack resistance of 3D printing concrete, compared with the 3D printing concrete without adding fiber and the 3D printing concrete mixed with ordinary synthetic fiber, the 3D printing concrete mixed with thermal shrinkage type fiber and simultaneously using heat curing, its compressive strength, flexural strength and flexural toughness significantly improve.

Description

Technical Field

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

[0002] Due to its high efficiency, low cost, minimal material usage, low pollution, and ability to create irregularly shaped structures, 3D printing technology is increasingly being used in the construction industry, leading to the emergence of various types of 3D-printed concrete buildings. Whether it's a one-piece 3D-printed concrete building or a prefabricated 3D-printed concrete building, both need to provide safe and reliable living and working spaces for humans, just like conventional reinforced concrete buildings.

[0003] However, due to the technical characteristics of 3D printing, 3D printed buildings often only use concrete as a single material, lacking the reinforcing steel found in conventional reinforced concrete structures. Therefore, their load-bearing capacity often relies solely on the concrete itself. 3D printed concrete is an additive manufacturing process; a flowing concrete slurry is extruded by a printer and stacked layer by layer to form a pre-defined shape. Although its rheological properties and setting time are optimized, the concrete slurry naturally flows after extrusion and tends to sag under gravity. Furthermore, this molding process cannot be compacted through vibration, resulting in numerous pores and microcracks within the material, leading to relatively poor density. This poses a potential threat to the mechanical properties and durability of 3D printed concrete. Especially under impact loads or earthquakes, 3D printed concrete structures lack sufficient toughness and crack resistance, often leading to structural collapse when cracks occur. Therefore, for 3D printed concrete structures in buildings, appropriate prestressing technology is needed to enhance the overall mechanical properties of the concrete, improve its flexural toughness and crack resistance, and ensure the safety and reliability of the building structure. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a heat-shrinkable fiber-reinforced 3D printed concrete and its preparation method.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for preparing heat-shrinkable fiber-reinforced 3D printed concrete includes the following steps:

[0007] Step 1: Weigh the raw materials according to the proportion, 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, 0.1-3 parts heat-shrinkable fiber, 1-8 parts accelerator, 1-5 parts water-reducing agent, and 1-4 parts defoamer; the water-cement ratio is 0.18-0.30.

[0008] Step 2: The above concrete slurry is fed into the print head of the 3D printer, and a concrete blank is printed using a layer-by-layer printing method.

[0009] Step 3: Allow the concrete blank to cure naturally at an ambient temperature of 5-40℃ and an ambient humidity of 50-80% until the concrete reaches its final set state. Then, perform heat curing to obtain heat-shrinkable fiber-reinforced 3D printed concrete.

[0010] Furthermore, the method for preparing the heat-shrinkable fiber includes the following steps:

[0011] 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;

[0012] 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 layer and the modified raw material as the core layer. The core-sheath material ratio is 1:3-9 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 500-1000m / min, the stretching speed to 50-100m / min, the stretching temperature to 110-120℃, and the stretching ratio to 5-10 times.

[0013] 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.

[0014] Step 1.4: Cut the heat-shrinkable fiber obtained in step 1.3 into short heat-shrinkable fibers with a length of 3-9 mm.

[0015] Furthermore, the heat curing temperature is 60-100℃, and the heat curing temperature of the concrete is not lower than the shrinkage temperature of the heat-shrinkable fiber, and the heat curing time is 5-60 minutes.

[0016] Furthermore, the heat curing begins between the final set of the concrete and 3 days of age.

[0017] 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.

[0018] Furthermore, the fineness modulus of the sand is 2.5-1.3, 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 more of lithium carbonate, calcium formate, lithium chloride, calcium chloride, and sodium sulfate.

[0019] A heat-shrinkable fiber-reinforced 3D printed concrete is prepared by the above method.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention incorporates heat-shrinkable fibers into concrete. Upon heating, the fibers change length, and the shrinkage stress of the uniformly distributed fibers applies prestress to the concrete, thereby improving its density. The uniformly dispersed heat-shrinkable fibers exert three-dimensional shrinkage self-stress on the concrete matrix, healing gel pores and microcracks formed in the early stages of hydration. This helps form a denser microstructure, enhancing and toughening the 3D-printed concrete structure, thus improving its load-bearing capacity and crack resistance. Compared to 3D-printed concrete without fibers and 3D-printed concrete with ordinary synthetic fibers, 3D-printed concrete with heat-shrinkable fibers and simultaneous heat curing exhibits significantly improved compressive strength, flexural strength, and flexural toughness. Detailed Implementation

[0022] 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.

[0023] Example 1

[0024] First, prepare heat-shrinkable fiber A according to the following steps:

[0025] 100 parts by weight of high-shrinkage polyester chips were mixed with 20 parts by weight of modifier to obtain modified raw material. The obtained modified raw material and polyethylene chips were vacuum dried at 60℃ for 12 hours. Polyethylene was used as the sheath layer and modified raw material as the core layer for sheath-core composite spinning, with a sheath-core material ratio of 1:5, to obtain polyethylene / polyester sheath-core composite fiber. The polyethylene feed screw and melt pipe temperature were set at 130℃, the polyester feed screw and melt pipe temperature at 120-125℃, the spinning box temperature at 125-130℃, the side blowing speed at 0.2-0.4 m / s, the spinning speed at 600 m / min, the stretching speed at 90 m / min, the stretching temperature at 110-120℃, and the stretching ratio at 5 times. The obtained composite fiber was subjected to a second traction stretching process: the composite fiber obtained by the composite spinning machine was cooled at 25-40℃, and 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 A was obtained, which was then cut into 5mm chopped heat-shrinkable fiber A with a fiber diameter of 200μm. This fiber begins to shrink at 60℃, with a shrinkage rate of 5%.

[0026] Concrete was prepared using the obtained heat-shrinkable fiber A. The basic mix proportion is shown in Table 1. Based on this, 2.5 parts by weight of heat-shrinkable fiber A were introduced. The above raw materials were stirred and mixed evenly to obtain concrete paste.

[0027] The concrete slurry was fed into the print head of a 3D printer and printed in layers to obtain a concrete blank. The concrete blank was then naturally cured at an ambient temperature of 20°C and an ambient humidity of 75%. After the concrete reached its final set, it was placed in a water bath and cured at a constant temperature of 80°C for 60 minutes. Finally, it was cured under standard curing conditions for 28 days.

[0028] Example 2

[0029] Concrete was prepared using the heat-shrinkable fiber A from Example 1. The concrete mix proportion and curing method were the same as in Example 1, except that the mass fraction of heat-shrinkable fiber A was 1.8.

[0030] Example 3

[0031] Concrete was prepared using the heat-shrinkable fiber A from Example 1, with the same mix proportions as in Example 1, but the mass fraction of heat-shrinkable fiber A was 2. The concrete slurry was layer-by-layer printed using a 3D printer to obtain concrete blanks. The concrete blanks were then naturally cured at an ambient temperature of 30°C and an ambient humidity of 80% for 48 hours. After curing, they were placed in a steam curing chamber and cured at a constant temperature of 100°C for 30 minutes. Finally, they were cured under standard curing conditions for 28 days.

[0032] Example 4

[0033] First, prepare heat-shrinkable fiber B according to the following steps:

[0034] 100 parts by weight of high-shrinkage polyester chips were mixed with 10 parts by weight of modifier to obtain modified raw material. The obtained modified raw material and polyethylene chips were vacuum dried at 70℃ for 6 hours. Polyethylene was used as the sheath layer and modified raw material as the core layer for sheath-core composite spinning, with a sheath-core material ratio of 1:8, to obtain polyethylene / polyester sheath-core composite fiber. The polyethylene feed screw and melt pipe temperature were set at 130℃, the polyester feed screw and melt pipe temperature at 120-125℃, the spinning box temperature at 125-130℃, the side blowing speed at 0.2-0.4 m / s, the spinning speed at 1000 m / min, the stretching speed at 80 m / min, the stretching temperature at 110-120℃, and the stretching ratio at 8 times. The obtained composite fiber was subjected to a second traction stretching process: the composite fiber obtained by the composite spinning machine was cooled at 25-40℃, and then subjected to a second traction stretching at 125-130℃, with a stretching ratio of 2 times. After cooling at 25-40℃, heat-shrinkable fiber B was obtained, which was then cut into 8mm chopped heat-shrinkable fibers with a diameter of 150μm. This fiber began to shrink at 70℃, with a shrinkage rate of 3%.

[0035] Concrete was prepared using the obtained heat-shrinkable fiber B. The basic mix proportion is shown in Table 1. Based on this, heat-shrinkable fiber B with a mass fraction of 0.9 was introduced.

[0036] The concrete slurry was printed in layers by a 3D printer to obtain a concrete blank. The concrete blank was naturally cured at an ambient temperature of 25℃ and an ambient humidity of 70% for 48 hours. After printing, it was cured in a standard curing environment for 24 hours, then placed in a high-temperature furnace and cured at a constant temperature of 100℃ for 20 minutes. Finally, it was cured in a standard curing environment for 28 days.

[0037] Example 5

[0038] Concrete was prepared using the heat-shrinkable fiber B from Example 4. The concrete mix proportions are shown in Table 1. Based on this, heat-shrinkable fiber B with a mass ratio of 1 was introduced. The concrete slurry was printed in layers by a 3D printer to obtain concrete blanks. The concrete blanks were naturally cured at an ambient temperature of 10°C and an ambient humidity of 60%. After curing for 1 day, they were placed in a steam curing chamber and cured at a constant temperature of 90°C for 40 minutes. Finally, they were cured under standard curing conditions for 28 days.

[0039] Comparative Example 1

[0040] The concrete mix proportion of Comparative Example 1 is the same as that of Example 1, and the natural curing method is also the same as that of Example 1. The difference is that Comparative Example 1 does not use heat curing, and after natural curing, it is placed in the standard curing environment for 28 days.

[0041] Comparative Example 2

[0042] To compare the effects of heat-shrinkable fibers and ordinary fibers on the mechanical properties of 3D-printed concrete, Comparative Example 2 was designed. Its concrete mix proportions and fiber content were the same as in Example 1, except that non-shrinkable ordinary polyester fibers were added in Comparative Example 2. The curing method for Comparative Example 2 was the same as in Example 1.

[0043] Comparative Example 3

[0044] In this comparative example, concrete without any added fibers was prepared, and the curing method of Comparative Example 3 was the same as that of Example 1.

[0045] Table 1. Mix proportions of 3D printed concrete (parts by weight)

[0046] cement Mineral admixtures sand water Water reducing agent coagulant Defoamer 100 25 160 30 1.5 8 4

[0047] Table 2 Fiber Content and Heat Curing Methods

[0048] fiber Fiber weight Heat curing method Example 1 Heat-shrinkable fiber A 2.5 80℃ water bath maintenance Example 2 Heat-shrinkable fiber A 1.8 80℃ water bath maintenance Example 3 Heat-shrinkable fiber A 2 100℃ steam curing Example 4 Heat-shrinkable fiber B 0.9 100℃ high temperature furnace curing Example 5 Heat-shrinkable fiber B 1 90℃ steam curing Comparative Example 1 Heat-shrinkable fiber A 2.5 No heat curing Comparative Example 2 ordinary polyester fiber 2.5 80℃ water bath maintenance Comparative Example 3 No fiber added 0 80℃ water bath maintenance

[0049] Table 3 Concrete setting time and mechanical properties

[0050]

[0051] As can be seen from the above embodiments and comparative examples, compared with 3D printed concrete without added fibers and 3D printed concrete with added ordinary synthetic fibers, 3D printed concrete with added heat-shrinkable fibers and simultaneously heat-cured exhibits significantly improved compressive strength, flexural strength, and flexural toughness. This is because heat-shrinkable fibers shrink and deform upon heating, generating shrinkage stress. When heat-shrinkable fibers are added to concrete, their length changes after heating. The shrinkage stress of the uniformly distributed heat-shrinkable fibers applies prestress to the concrete matrix, thereby improving the density of the 3D concrete and achieving reinforcement and toughening of the 3D concrete structure. The initial and final setting times of the concrete vary depending on the amount of accelerator used.

[0052] 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 the production of heat-shrinkable fiber-reinforced 3D-printed concrete, characterized in that, The method comprises the following steps: Step 1, proportionally weighing and stirring the raw materials to obtain a concrete slurry, wherein the raw materials comprise the following components by mass fraction: cement 100 parts, mineral admixture 0-30 parts, sand 50-200 parts, heat-shrinkable fiber 0.1-3 parts, coagulant 1-8 parts, water reducing agent 1-5 parts, and defoaming agent 1-4 parts; The water-cement ratio is 0.18-0.30; The preparation method of the heat-shrinkable fiber comprises the following steps: Step 1.1, mixing 100 parts of high-shrinkage polyester chips with 0.1-20 parts of a modifier to obtain modified raw materials, wherein the modifier is at least one of polymer whiskers, inorganic salt whiskers and micro-inorganic powder; Step 1.2, after vacuum drying the modified raw materials and polyethylene chips obtained in step 1.1 at 60-70℃, performing skin-core composite spinning with polyethylene as the skin layer and the modified raw materials as the core layer, and the skin-core material ratio is 1:3-9, to obtain polyethylene / polyester skin-core composite fibers; the polyethylene feeding screw and the melt pipe temperature are set to 130℃, the polyester feeding screw and the melt pipe temperature are set to 120-125℃, the spinning box temperature is 125-130℃, the side blowing speed is 0.2-0.4m / s, the spinning speed is 500-1000m / min, the stretching speed is 50-100m / min, the stretching temperature is 110-120℃, and the stretching multiple is 5-10 times; Step 1.3, performing second traction stretching on the composite fibers obtained in step 1.2, specifically: cooling the composite fibers prepared by the composite spinning machine at a temperature of 25-40℃, performing second traction stretching at a temperature of 120-130℃, the stretching multiple is 2-3 times, and cooling at a temperature of 25-40℃ to obtain heat-shrinkable fibers; Step 1.4, cutting the heat-shrinkable fibers obtained in step 1.3 to obtain short-cut heat-shrinkable fibers with a length of 3-9mm; Step 2, conveying the concrete slurry into the printing nozzle of a 3D printer, and printing the concrete slurry by a layering printing method to obtain a concrete green body; Step 3, naturally curing the concrete green body, the environmental temperature ranges from 5-40℃, the environmental humidity ranges from 50-80%, and after the concrete reaches the final setting state, performing heat curing to obtain heat-shrinkable fiber reinforced 3D printed concrete.

2. The method for preparing heat-shrinkable fiber-reinforced 3D printed concrete according to claim 1, characterized in that, The heat curing temperature is 60-100℃, and the heat curing temperature of the concrete is not lower than the shrinkage temperature of the heat-shrinkable fiber, and the heat curing time is 5-60min.

3. The method for preparing heat-shrinkable fiber-reinforced 3D printed concrete according to claim 1, characterized in that, The starting time of the heat curing in step 3 is between the final setting and 3d age of the concrete.

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

5. The method for preparing heat-shrinkable fiber-reinforced 3D printed concrete according to claim 1, characterized in that, The sand has a fineness modulus of 2.5-1.3 and a clay content of <0.5%; the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent or a melamine water reducing agent; the defoaming agent is a non-ionic silicon polyether defoaming agent or a dry powder type organosiloxane defoaming agent; and the coagulant is one or more of lithium carbonate, calcium formate, lithium chloride, calcium chloride and sodium sulfate.

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

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