Low-shrinkage 3D printing concrete material suitable for severe cold environment and preparation method

Abstract

The invention discloses a low-shrinkage 3D printing concrete material suitable for a severe cold environment and a preparation method thereof, and the material comprises the following components in parts by weight: 538-573 parts of cement, 577-810 parts of coarse aggregate, 256-270 parts of steel slag powder, 128-137 parts of regenerated brick powder, 403-430 parts of sand, 1-4 parts of a water reducing agent, 312-333 parts of water, 28-47 parts of a calcium oxide type expanding agent, 2.9-3.8 parts of super absorbent resin, and 39-78 parts of steel fiber. The volume of the steel fibers accounts for 0.5%-1% of the total volume of the concrete. According to the invention, by optimizing the particle size combination of the aggregate, adopting a proper admixture ratio, controlling the water-binder ratio and utilizing the excellent crack resistance enhancement effect of the steel fiber, the contractility of the concrete is remarkably reduced, and the cold resistance of the concrete is improved. The preparation method disclosed by the invention can be used for efficiently and economically preparing the concrete material suitable for 3D printing.

Description

Technical Field

[0001] The present invention relates to a concrete material for 3D printing and a preparation method thereof, and particularly to a low-shrinkage concrete material for 3D printing applicable to severe cold environments and a preparation method thereof. Background Art

[0002] With the continuous development of construction technology, 3D printing technology, as a new type of building construction method, has gradually become an important research direction in the construction field. 3D printing concrete technology, as an important branch in this field, has demonstrated great application potential in the construction industry with its flexible shaping ability, high construction efficiency, and low labor cost.

[0003] However, the existing 3D printing concrete materials still face many challenges in the application process. First of all, during the curing process of 3D printing concrete, the evaporation of moisture and the hydration reaction of cement will cause the concrete to shrink. Especially during the large-volume printing process, the shrinkage phenomenon is more obvious, prone to cracking, and affecting the durability and safety of the structure. Secondly, the performance of 3D printing concrete materials in cold environments is relatively fragile. The low-temperature environment in cold regions will affect the early strength development of concrete, and even freeze-thaw damage may occur under extremely low-temperature conditions. In order to enable 3D printing concrete to adapt to different climate conditions, especially in cold regions, improving its cold resistance and ensuring its structural stability and durability in low-temperature environments are one of the challenges that need to be solved urgently.

[0004] Therefore, the research and development of a new 3D printing concrete material that can effectively reduce its shrinkage, improve its cold resistance, and optimize the adaptability of coarse aggregates has important theoretical significance and practical application value. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to provide a low-shrinkage concrete material for 3D printing applicable to severe cold environments, which can effectively reduce shrinkage, improve cold resistance, and optimize the adaptability of coarse aggregates;

[0006] The second object of the present invention is to provide a preparation method for the above-mentioned low-shrinkage concrete material for 3D printing applicable to severe cold environments.

[0007] Technical Solution: The low-shrinkage concrete material for 3D printing applicable to severe cold environments described in the present invention comprises the following components by weight:

[0008]

[0009]

[0010] Among them, the volume of the steel fiber accounts for 0.5%-1% of the total volume of the concrete.

[0011] Among them, the cement is Portland cement, and the true density is 2800 - 3200 Kg / m 3 .

[0012] Among them, the superabsorbent resin is a pre-absorbed superabsorbent resin.

[0013] Among them, the coarse aggregate is continuously graded gravel, and its particle size range is 5 - 10 mm.

[0014] Among them, the particle size of the steel slag powder is 0.5 - 86.3 μm, and the true density is 3220 - 3290 Kg / m 3 .

[0015] Among them, the particle size of the recycled brick powder is 0.3 - 45.4 μm, and the true density is 2650 - 2740 Kg / m 3 .

[0016] Among them, the sand is continuously graded sand, and its particle size range is 0.15 - 0.5 mm.

[0017] Among them, the water reducing agent is a polycarboxylic acid type water reducing agent, its solid content is 30%, and the water reducing rate is greater than 20%.

[0018] Among them, the steel fiber is a copper-plated micro wire, with a hook-shaped end, a length of 12 - 13 mm, and a diameter of 0.2 - 0.25 mm.

[0019] The preparation method of the above-mentioned low-shrinkage 3D printing concrete material applicable to severe cold environments includes the following steps:

[0020] (1) Pre-absorb the superabsorbent resin at a ratio of 20 - 25;

[0021] (2) Mix the pre-absorbed superabsorbent resin in step (1) with cement, fly ash, coarse aggregate, steel slag powder, brick powder, expansive agent, and sand to obtain a mixture;

[0022] (3) Add the required water to the mixture and stir, then add steel fiber and 2 / 3 of the water reducing agent and stir again;

[0023] (4) Add the remaining 1 / 3 of the water reducing agent to the mixture obtained in step (3), continue to stir to make the steel fiber evenly distributed in the slurry, and obtain a concrete material component through 3D printing.

[0024] Among them, in step (3), the stirring time after adding water is 1.5 min, and the re-stirring time is 2.5 min.

[0025] Among them, in step (4), the stirring time is 1 min.

[0026] Among them, in step (4), the 3D printing parameters are specifically: nozzle diameter 40 mm, screw rotation speed 100 r / min, print head moving speed 6 mm / min, and single-layer strip height 25 mm.

[0027] Principle of the invention: Generally, air-entraining agents are added to ordinary concrete to improve frost resistance, but this will lead to a decrease in the strength of the concrete. And in some cases, excessive air bubbles may cause voids or pores on the surface of the concrete, affecting the appearance and surface quality. Moreover, the addition of air-entraining agents will also increase the cost of the concrete. The low-shrinkage and cold-resistant 3D printing concrete material provided by the present invention incorporates calcium oxide and SAP. Through the expansion effect of calcium oxide, the shrinkage of the concrete caused by water evaporation can be effectively reduced, preventing the generation of dry shrinkage cracks. The pre-absorbed SAP can store water and release it during freezing, alleviating the expansion pressure generated when water freezes and improving the frost resistance of the concrete. The simultaneous addition of the two can achieve the reduction of shrinkage while maintaining good frost resistance and without causing loss of strength. On the other hand, by adding steel fibers, the tensile strength of ordinary 3D printing coarse aggregate concrete materials is effectively improved, and the problem of too poor brittleness is improved.

[0028] Adding steel fibers and coarse aggregates to the concrete will greatly increase the yield stress of the material, resulting in difficult extrusion. The present invention effectively reduces the yield stress of the paste by compounding steel slag powder and brick powder, ensuring extrudability while maintaining good buildability. And to a certain extent, the dosage of portland cement is reduced, realizing environmental sustainability.

[0029] Through specific embodiments, the present invention explores that different aggregate particle sizes will affect the frost resistance and shrinkage of the concrete. Therefore, the present invention selects a suitable particle size combination to achieve the best performance. In addition, adding expansive agents, resins, steel fibers, and coarse aggregates will make it difficult to extrude the paste. The present invention adjusts by adding water reducers, and the corresponding water reducer content can achieve the smooth extrusion of the slurry.

[0030] Beneficial effects: Compared with the prior art, the present invention has achieved the following remarkable effects:

[0031] (1) By optimizing the particle size combination of the aggregates, adopting a suitable admixture ratio, and simultaneously utilizing the excellent crack resistance and strengthening effect of steel fibers, the present invention significantly reduces the shrinkage of the concrete and improves its cold resistance.

[0032] (2) By optimizing the concrete mix ratio, adjusting the particle size distribution of the aggregates, and improving the formulation design of the materials, the present invention can significantly improve the overall performance of 3D printing concrete and promote its wide application in the construction industry, especially in cold regions and large-scale structural engineering.

[0033] (3) The present invention provides a low-shrinkage and cold-resistant 3D printing concrete material containing coarse aggregate and a preparation method thereof, which solves the problems of existing 3D printing concrete materials in terms of shrinkage, cold resistance, and adaptability to coarse aggregate, thereby realizing the application of more efficient, durable, and reliable 3D printing concrete structures. Detailed implementation manners

[0034] The present invention will be further described in detail below.

[0035] Example 1

[0036] A 3D printing concrete material containing coarse aggregate, by weight, the concrete material comprises 538 parts of cement, 677 parts of coarse aggregate with a particle size of 5-10 mm, 270 parts of steel slag powder, 137 parts of recycled brick powder, 403 parts of sand, 4 parts of water reducing agent, 312 parts of water, 78 parts of steel fiber, 28 parts of calcium oxide type expansive agent, and 3.8 parts of superabsorbent resin. The water-binder ratio of each embodiment of the present invention is 0.33; the coarse aggregate is all crushed stone.

[0037] The preparation method of the above 3D printing coarse aggregate concrete material comprises the following steps:

[0038] (1) Before mixing and stirring, first soak the superabsorbent resin with water at a ratio of 25 and continuously stir. After absorption, let it stand for 30 minutes.

[0039] (2) Mix cement, coarse aggregate, steel slag powder, brick powder, expansive agent, pre-absorbed water superabsorbent resin, and sand according to the corresponding weight ratio to obtain a mixed material.

[0040] (3) Add the required water to the mixture according to the corresponding weight ratio, stir for 1.5 min, and then add steel fiber and 2 / 3 of the water reducing agent.

[0041] (4) Stir the obtained mixed material in a stirring pot for 2.5 min, then add the remaining 1 / 3 of the water reducing agent, and finally continue to stir for 1 min to obtain the required 3D printing concrete material.

[0042] (5) Feed the slurry of the coarse aggregate concrete material suitable for 3D printing described in step (4) into the storage box of the 3D printing equipment, and start layer-by-layer printing according to the pre-set printing parameters to obtain a 3D printing coarse aggregate concrete material component; wherein, the printing parameters are: nozzle diameter 40 mm, screw rotation speed 100 r / min, printing head moving speed 6 mm / min, and single-layer strip height 25 mm.

[0043] After testing, the 28-day shrinkage rate of the concrete is 0.0123%, and the frost resistance grade is F400.

[0044] Example 2

[0045] A 3D printing concrete material containing coarse aggregate, by weight, the concrete material comprises 573 parts of cement, 677 parts of coarse aggregate with a particle size of 5 - 8 mm, 256 parts of steel slag powder, 128 parts of recycled brick powder, 430 parts of sand, 2 parts of water reducing agent, 333 parts of water, 78 parts of steel fiber, 28 parts of calcium oxide type expansive agent, and 2.9 parts of superabsorbent resin.

[0046] The preparation method of the above 3D printed coarse aggregate concrete material comprises the following steps:

[0047] (1) Before mixing and stirring, first soak the superabsorbent resin with water at a ratio of 25, and keep stirring. After absorption, let it stand for 30 minutes.

[0048] (2) Mix cement, coarse aggregate, steel slag powder, brick powder, expansive agent, pre - absorbed superabsorbent resin, and sand according to the corresponding weight ratio to obtain a mixed material.

[0049] (3) Add the required water to the mixed material according to the corresponding weight ratio, stir for 1.5 min, then add steel fiber and 2 / 3 of the water reducing agent.

[0050] (4) Stir the obtained mixed material in a mixing pan for 2.5 min, then add the remaining 1 / 3 of the water reducing agent, and finally continue to stir for 1 min to obtain the required 3D printing concrete material.

[0051] (5) Feed the slurry of the coarse aggregate concrete material suitable for 3D printing described in step (4) into the storage bin of the 3D printing equipment, and start layer - by - layer printing according to the pre - set printing parameters to obtain a 3D printed coarse aggregate concrete material component; wherein, the printing parameters are: nozzle diameter 40 mm, screw rotation speed 100 r / min, printing head moving speed 6 mm / min, single - layer strip height 25 mm.

[0052] After testing, the 28 - day shrinkage rate of the concrete is 0.0141%, and the frost resistance grade is F350.

[0053] Example 3

[0054] A 3D printing concrete material containing coarse aggregate, by weight, the concrete material comprises 573 parts of cement, 577 parts of coarse aggregate with a particle size of 5 - 15 mm, 256 parts of steel slag powder, 128 parts of recycled brick powder, 430 parts of sand, 2 parts of water reducing agent, 333 parts of water, 78 parts of steel fiber, 28 parts of calcium oxide type expansive agent, and 2.9 parts of superabsorbent resin.

[0055] The preparation method of the above 3D printed coarse aggregate concrete material comprises the following steps:

[0056] (1) Before mixing and stirring, first soak the superabsorbent resin with water at a ratio of 25, and keep stirring. After absorption, let it stand for 30 minutes.

[0057] (2) Mix cement, coarse aggregate, steel slag powder, brick powder, expansive agent, pre-absorbed superabsorbent resin, and sand according to the corresponding weight ratios to obtain a mixed material;

[0058] (3) Add the required amount of water to the mixture according to the corresponding weight ratio, stir for 1.5 min, and then add steel fibers and 2 / 3 of the water reducer;

[0059] (4) Stir the obtained mixed material in a stirring pot for 2.5 min, then add the remaining 1 / 3 of the water reducer, and finally continue to stir for 1 min to obtain the desired 3D printing concrete material.

[0060] (5) Feed the coarse aggregate concrete material slurry suitable for 3D printing described in step (4) into the storage bin of the 3D printing equipment, and start layer-by-layer printing according to the pre-set printing parameters to obtain a 3D printed coarse aggregate concrete material component; wherein, the printing parameters are: nozzle diameter 40 mm, screw rotation speed 100 r / min, printing head moving speed 6 mm / min, single-layer strip height 25 mm.

[0061] After testing, the 28-day shrinkage rate of the concrete is 0.0118%, and the frost resistance grade is F400.

[0062] Example 4

[0063] A 3D printing concrete material containing coarse aggregate, by weight, the concrete material comprises 538 parts of cement, 677 parts of coarse aggregate with a particle size of 5-10 mm, 270 parts of steel slag powder, 137 parts of recycled brick powder, 403 parts of sand, 4 parts of water reducer, 312 parts of water, 78 parts of steel fibers, 47 parts of calcium oxide type expansive agent, and 2.9 parts of superabsorbent resin.

[0064] The preparation method of the above 3D printed coarse aggregate concrete material comprises the following steps:

[0065] (1) Before mixing and stirring, first absorb water with the superabsorbent resin at a ratio of 25, and continuously stir. After water absorption, let it stand for 30 minutes;

[0066] (2) Mix cement, coarse aggregate, steel slag powder, brick powder, expansive agent, pre-absorbed superabsorbent resin, and sand according to the corresponding weight ratios to obtain a mixed material;

[0067] (3) Add the required amount of water to the mixture according to the corresponding weight ratio, stir for 1.5 min, and then add steel fibers and 2 / 3 of the water reducer;

[0068] (4) Stir in a stirring pot for 2.5 min, then add the remaining 1 / 3 of the water reducer, and finally continue to stir for 1 min to obtain the desired 3D printing concrete material.

[0069] (5) Feed the steel fiber-containing coarse aggregate concrete material paste suitable for 3D printing described in step (3) into the storage bin of the 3D printing equipment, and start layer-by-layer printing according to the pre-set printing parameters to obtain a 3D printed coarse aggregate concrete material component; wherein, the printing parameters are: nozzle diameter 40 mm, screw rotation speed 100 r / min, printing head moving speed 6 mm / min, single-layer strip height 25 mm.

[0070] After testing, the 28-day shrinkage rate of the concrete is 0.0093%, and the frost resistance grade is F400.

[0071] Comparative Example 1

[0072] On the basis of Example 1, the difference from Example 1 is that the number of parts of coarse aggregate is 810 parts.

[0073] After testing, the printing head was blocked during the printing of the concrete, and normal printing could not be carried out.

[0074] Comparative Example 2

[0075] On the basis of Example 1, the difference from Example 1 is that the type of steel fiber is straight.

[0076] After testing, the strips were discontinuous during the printing of the concrete, and normal printing could not be carried out.

[0077] Comparative Example 3

[0078] On the basis of Example 1, the difference from Example 1 is that the number of parts of steel fiber is 39 parts.

[0079] After testing, the 28-day shrinkage rate of the concrete is 0.0193%, and the frost resistance grade is F350.

[0080] Comparative Example 4

[0081] On the basis of Example 1, the difference from Example 1 is that no steel fiber is added.

[0082] After testing, the 28-day shrinkage rate of the concrete is 0.0267%, and the frost resistance grade is F300.

[0083] Comparative Example 5

[0084] On the basis of Example 4, the difference from Example 4 is that the added superabsorbent resin is not pre-absorbed with water.

[0085] After testing, the 28-day shrinkage rate of the concrete is 0.0114%, and the frost resistance grade is F350.

[0086] Comparative Example 6

[0087] On the basis of Example 4, different from Example 4, no calcium oxide type expansive agent was added.

[0088] After testing, the 28-day shrinkage rate of the concrete was 0.0273%, and the frost resistance grade was F400.

[0089] The 3D printing concrete materials containing coarse aggregate in Examples 1-4 of the present invention all have a low shrinkage rate, and the frost resistance grade reaches F300, and can be applied to relatively cold regions. However, in Comparative Example 1 and Comparative Example 2, when the coarse aggregate content was increased or the steel fiber type was changed, printing failure occurred. In Comparative Example 3, when the number of steel fiber parts was reduced compared with Example 1, its shrinkage rate increased and its frost resistance decreased. This shows that in a system where steel fibers and coarse aggregates coexist, it is necessary to reasonably control the aggregate content and fiber dosage, otherwise printing failure will occur, and the printed components will have a high shrinkage rate and poor frost resistance. Comparative Example 4 is ordinary concrete without steel fibers, and its shrinkage rate is significantly larger and its frost resistance is lower. Compared with Example 4, in Comparative Example 5, the superabsorbent resin added was not pre-absorbed with water, and as a result, the frost resistance was significantly reduced and the shrinkage rate also increased. This is mainly because since the resin has absorbed water, they can form a more uniform water distribution inside the concrete. This uniformity helps to reduce the risk of uneven shrinkage, thereby effectively reducing the overall impact of drying shrinkage. At the same time, it can better release the stored water during freeze-thaw cycles, reduce the expansion pressure, and improve the frost resistance.

Claims

1. A low-shrinkage 3D printing concrete material suitable for severe cold environments, characterized in that: The following components are included by weight: The volume of the steel fiber accounts for 0.5%-1% of the total volume of the concrete.

2. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The coarse aggregate is continuously graded crushed stone with a particle size ranging from 5 to 10 mm.

3. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The super absorbent resin is a pre-absorbent super absorbent resin.

4. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The steel fiber is a copper-plated microfilament with a hook-end shape, a length of 12-13 mm, and a diameter of 0.2-0.25 mm.

5. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The cement is silicate cement with a true density of 2800-3200 Kg / m 3 .

6. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The particle size of the steel slag powder is 0.5-86.3 μm, and the true density is 3220-3290 Kg / m 3 .

7. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The particle size of the recycled brick powder is 0.3-45.4 μm, and the true density is 2650-2740 Kg / m 3 .

8. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The sand is continuously graded sand, and its particle size ranges from 0.15 to 0.5 mm.

9. The low-shrinkage 3D printing concrete material suitable for severe cold environments according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid type water reducing agent, and the water reducing rate is greater than 20%.

10. A method for preparing a low-shrinkage 3D printing concrete material suitable for severe cold environments as claimed in claim 1, characterized in that: The following steps are involved: (1) pre-absorb water by a super absorbent resin at a rate of 20-25; (2) mixing the super absorbent resin pre-absorbed with water in step (1) with cement, fly ash, coarse aggregate, steel slag powder, brick powder, expansion agent, and sand to obtain a mixture; (3) Add the required water to the mixture and stir, add steel fiber and 2 / 3 of the water reducing agent; (4) Add the remaining 1 / 3 of the water reducing agent to the mixture obtained in step (3), continue stirring to evenly distribute the steel fibers in the slurry, and obtain a concrete material component by 3D printing.

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