Ultra-high performance concrete based on waste bamboo fiber toughening and internal curing and its preparation method

Abstract

The present invention discloses a ultra-high performance concrete based on waste bamboo fiber toughening and internal curing, and the composition is as follows by weight percentage: 420 - 1250 parts of cement, 50 - 190 parts of silica fume, 130 - 280 parts of fly ash, 840 - 1650 parts of quartz sand, 0.3 - 20 parts of bamboo fiber, 135 - 352 parts of steel fiber, 8 - 32 parts of water reducing agent, and 183 - 324 parts of water; the preparation method includes soaking the bamboo fiber in part of water to ensure that its initial water absorption is 0.1 - 10 g water / g bamboo fiber; mixing cement, silica fume, fly ash, quartz sand, and water reducing agent, adding water and stirring to a homogeneous slurry state, adding the water-absorbed bamboo fiber and stirring for 1 - 3 min, adding steel fiber and continuing to stir for 5 - 8 min to obtain the ultra-high performance concrete based on waste bamboo fiber toughening and internal curing; the present invention can disperse and pre-absorb water for waste bamboo fiber bundles, which can be used as a toughening material to improve the toughness of ultra-high performance concrete, and at the same time as an internal curing agent to reduce shrinkage and improve the later strength.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and particularly relates to a ultra-high performance concrete based on waste bamboo fibers for toughening and internal curing and a preparation method thereof. Background Art

[0002] As a green material, bamboo fibers have natural antibacterial properties, good strength and durability. Therefore, they are mostly used as filling materials for sofas, mattresses, automotive interiors, home decoration boards and other household items. However, after the main body reaches the service life, bamboo fibers are buried, incinerated or microbially degraded as waste, not only with a low recovery rate, but also contrary to the original intention of using bamboo fiber materials in a natural, green, economical and environmentally friendly way. Therefore, there is an urgent need to seek an efficient and environmentally friendly way to recycle bamboo fibers.

[0003] Due to the excellent properties caused by the high content of steel fibers in the system, ultra-high performance concrete has been widely used in road and bridge structures to improve the stiffness and fatigue life of building structures. However, the brittleness of cement-based materials itself has always been one of the main obstacles to their practical application. At present, steel fibers are mostly used to strengthen and toughen the system, but a high content of steel fibers will significantly increase the material cost and produce negative economic benefits. Therefore, researchers mostly consider compounding other fibers in the ultra-high performance concrete system to reduce costs and toughen. CN115108785A discloses a ultra-high ductility double-doped fiber concrete and a preparation method thereof, which uses PVA fibers and PE fibers in combination to improve the ductility of concrete specimens and prevent cracking; CN113149552A discloses a polypropylene fiber concrete and its production process, which solves the defects of existing concrete such as low tensile strength, small ultimate elongation and brittleness. However, for polymer fibers, their production process will cause environmental pollution, and most polymer fibers themselves have high toughness, but have poor bonding with the cement matrix. Therefore, most polymer fibers need to be surface-modified before use to increase their interfacial affinity with the cement matrix, greatly increasing their use difficulty.

[0004] In addition, due to the high content of cementitious materials, ultra-high performance concrete undergoes rapid hydration, resulting in high early strength. However, precisely because of this rapid reaction, it is prone to early cracking and a decline in later strength. To avoid the above situations, the "internal curing" mechanism has been proposed in the industry. CN115974439A discloses a kind of microceramsite for internal curing of concrete and its preparation method, which prepares microceramsite with high water absorption and high strength through steps such as stirring and foaming, sintering, etc.; CN116041614A discloses an inorganic-organic framework material for internal curing of concrete and its preparation method, which uses a high water absorption resin monomer as the matrix and introduces a variety of substances such as nano-scale cement hydration product suspension, cross-linking agent, initiator, catalyst, etc. to prepare an inorganic-organic framework with high water absorption and slow release. Obviously, the above internal curing agents all require cumbersome steps to obtain, and it is very difficult to ensure their compatibility with the cement matrix. Summary of the Invention

[0005] The purpose of the present invention is to provide an ultra-high performance concrete based on waste bamboo fiber toughening and internal curing and its preparation method. After the waste bamboo fiber bundle is dispersed and pre-absorbed with water, it can be used as a toughening material to improve the toughness of ultra-high performance concrete, and at the same time as an internal curing agent to reduce shrinkage and improve later strength.

[0006] To achieve the above purpose, the technical solution is as follows:

[0007] An ultra-high performance concrete based on waste bamboo fiber toughening and internal curing, its composition is as follows by weight percentage:

[0008] 420 - 1250 parts of cement, 50 - 190 parts of silica fume, 130 - 280 parts of fly ash, 840 - 1650 parts of quartz sand, 0.3 - 20 parts of bamboo fiber, 135 - 352 parts of steel fiber, 8 - 32 parts of water reducer, 183 - 324 parts of water.

[0009] According to the above scheme, the cement is Portland cement or ordinary Portland cement with a strength grade of 42.5 or above.

[0010] According to the above scheme, the specific surface area of the silica fume ≥ 12500 m 2 / kg, and the SiO2 content in the silica fume ≥ 93%.

[0011] According to the above scheme, the specific surface area of the fly ash ≥ 2000 m 2 / kg, where the SiO2 content ≥ 43%, and the Al2O3 content ≥ 21%.

[0012] According to the above scheme, the particle size of the quartz sand is 30 - 80 mesh.

[0013] According to the above scheme, the steel fiber is a long straight steel fiber with a circular cross-section, a length of 10-25 mm, a diameter of 0.08-0.27 mm, and a tensile strength of ≥2500 MPa.

[0014] According to the above scheme, the water reducing agent is one of naphthalene-based or polycarboxylate-based high-performance water reducing agents.

[0015] According to the above scheme, the original bamboo fiber is obtained by recycling waste mattresses, sofa fillers, automotive interiors or home improvement boards.

[0016] According to the above scheme, the original bamboo fiber is processed by a fiber disperser to disperse the agglomerated original bamboo fiber bundles into single original bamboo fibers with a length of 6-15 mm and a diameter of 5-100 μm.

[0017] The above method for preparing ultra-high performance concrete with toughening and internal curing based on waste original bamboo fiber includes the following steps:

[0018] (1) Immerse the original bamboo fiber in part of the water to ensure that its initial water absorption is 0.1-10 g of water / g of original bamboo fiber;

[0019] (2) Mix cement, silica fume, fly ash, quartz sand, and water reducing agent, add water and stir until it becomes a homogeneous slurry state, add the water-absorbed original bamboo fiber and stir for 1-3 min, then add steel fiber and continue to stir for 5-8 min to obtain ultra-high performance concrete with toughening and internal curing based on waste original bamboo fiber.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] Compared with organic fibers such as PVA and PE, the original bamboo fiber has a higher specific surface area, microstructure and special functional groups. Therefore, it has a higher compatibility with the concrete matrix. Without additional modification, the interfacial bonding strength between the original bamboo fiber and the cement matrix is relatively high, and the toughness of the original bamboo fiber itself can be fully exerted. The original bamboo fiber is generally used as a filling material for products such as home improvement boards, mattresses and sofas. It is difficult to recycle and reuse in the same scenario. The common disposal method is microbial degradation, but this disposal method has a long cycle and high economic cost, resulting in a large amount of waste original bamboo fiber accumulation. And the ultra-high performance concrete material, as a system with relatively high tolerance, is suitable for disposing of a large number of waste materials. In addition, the conventional use method of the original bamboo fiber does not undergo any pretreatment, and the agglomerated original bamboo fiber bundles cannot perfectly exert their toughening characteristics. In the present invention, the original bamboo fiber bundles are dispersed to depolymerize them into single original bamboo fibers, which can not only increase the contact area between the original bamboo fiber and the concrete matrix to improve the toughening effect, but also increase the moisture content to improve the internal curing effect.

[0022] The porous structure of bamboo fiber results in its high water absorption rate. After losing water, it can maintain its original shape, have a good interfacial bond with the matrix, and optimize the interfacial transition zone. Therefore, it greatly avoids the autogenous shrinkage caused by the early rapid hydration of ultra-high performance concrete. In the later stage of hydration, the water in the bamboo fiber is slowly released, producing an "internal curing" effect, which solves the drawback of insufficient late strength development of ultra-high performance concrete.

[0023] When bamboo fiber is compounded with steel fiber, the toughness of ultra-high performance concrete is greatly improved and the service life is extended on the premise of reducing the system cost. Brief Description of the Drawings

[0024] Figure 1 : Electron Microscope of the Fracture Interface of Ultra-High Performance Concrete Based on Waste Bamboo Fiber for Toughness Enhancement and Internal Curing Figure 1 。

[0025] Figure 2 : Electron Microscope of the Fracture Interface of Ultra-High Performance Concrete Based on Waste Bamboo Fiber for Toughness Enhancement and Internal Curing Figure 2 。 Detailed Embodiments

[0026] The following embodiments further illustrate the technical solutions of the present invention, but do not limit the protection scope of the present invention.

[0027] The detailed embodiments provide an ultra-high performance concrete based on waste bamboo fiber for toughness enhancement and internal curing, and its composition is as follows by weight percentage:

[0028] 420 - 1250 parts of cement, 50 - 190 parts of silica fume, 130 - 280 parts of fly ash, 840 - 1650 parts of quartz sand, 0.3 - 20 parts of bamboo fiber, 135 - 352 parts of steel fiber, 8 - 32 parts of water reducing agent, 183 - 324 parts of water.

[0029] Specifically, the cement is Portland cement or ordinary Portland cement with a strength grade of 42.5 or above.

[0030] Specifically, the specific surface area of the silica fume ≥ 12500 m 2 / kg, and the SiO2 content in the silica fume ≥ 93%.

[0031] Specifically, the specific surface area of the fly ash ≥ 2000 m 2 / kg, where the SiO2 content ≥ 43% and the Al2O3 content ≥ 21%.

[0032] Specifically, the particle size of the quartz sand is 30 - 80 mesh.

[0033] Specifically, the steel fiber is a long straight steel fiber with a circular cross-section, a length of 10 - 25 mm, a diameter of 0.08 - 0.27 mm, and a tensile strength of ≥2500 MPa.

[0034] Specifically, the water reducing agent is one of naphthalene-based or polycarboxylic acid type high-performance water reducing agents.

[0035] Specifically, the original bamboo fiber is obtained by recycling waste mattresses, sofa fillers, automotive interiors or home improvement boards; after being processed by a fiber disperser, the agglomerated original bamboo fiber bundles are dispersed into single original bamboo fibers with a length of 6 - 15 mm and a diameter of 5 - 100 μm. Preferably, the original bamboo fiber is yellow bamboo fiber.

[0036] The specific implementation manner also provides the above-mentioned preparation method of ultra-high performance concrete based on waste original bamboo fiber toughening and internal curing:

[0037] (1) Immerse the original bamboo fiber in part of the water to ensure its initial water absorption is 0.1 - 10 g water / g original bamboo fiber;

[0038] (2) Mix cement, silica fume, fly ash, quartz sand, water reducing agent, add water and stir until it becomes a homogeneous slurry state, add the water-absorbed original bamboo fiber and stir for 1 - 3 min, then add steel fiber and continue to stir for 5 - 8 min to obtain ultra-high performance concrete based on waste original bamboo fiber toughening and internal curing.

[0039] Example 1

[0040] The ultra-high performance concrete based on waste original bamboo fiber toughening and internal curing in this example has components including cement, silica fume, fly ash, quartz sand, water reducing agent, water, steel fiber, and yellow bamboo fiber. A total of 8 groups of ultra-high performance concrete materials with different proportions are designed, numbered 1 - 1, 1 - 2, 1 - 3, 1 - 4, 1 - 5, 1 - 6, 1 - 7, 1 - 8. The mass fractions of each component are given in Table 1. Among them, the cement used is PO52.5 cement, the water reducing agent used is polycarboxylic acid type high-performance water reducing agent, the steel fiber used is long straight steel fiber with a size of Φ0.2 mm × 13 mm, and the yellow bamboo fiber used has a length of about 12 mm and a diameter of about 50 μm after being dispersed.

[0041] Table 1 Mix proportion of ultra-high performance concrete materials based on waste original bamboo fiber toughening and internal curing

[0042] Number Cement Silica fume Fly ash Quartz sand Water reducing agent Water Steel fiber Yellow bamboo fiber 1-1 1030 185 240 1375 17 260 200 0 1-2 1030 185 240 1375 17 260 200 1(S0) 1-3 1030 185 240 1375 17 259 200 1(S1) 1-4 1030 185 240 1375 17 258 200 1(S2) 1-5 1030 185 240 1375 17 256 200 1(S3) 1-6 1030 185 240 1375 17 256 200 2(S2) 1-7 1030 185 240 1375 17 252 200 4(S2) 1-8 1030 185 240 1375 17 244 200 8(S2)

[0043] Among them, S0 represents that the yellow bamboo fiber is not water-absorbed, S1 represents that the water absorption of the yellow bamboo fiber is 1 g water / g yellow bamboo fiber, S2 represents that the water absorption of the yellow bamboo fiber is 2 g water / g yellow bamboo fiber, and S3 represents that the water absorption of the yellow bamboo fiber is 4 g water / g yellow bamboo fiber. The water absorption of the yellow bamboo fiber is deducted from the total water consumption of the system.

[0044] In this embodiment, the specific forming process is as follows:

[0045] (1) Immerse the yellow bamboo fiber in part of the water and set its initial water absorption according to the aforementioned rules;

[0046] (2) Stir and mix cement, silica fume, fly ash, quartz sand, and water reducing agent evenly, add water and stir until it becomes a homogeneous slurry state, then add the water-absorbed yellow bamboo fiber. After stirring for 3 minutes, add steel fiber and continue to stir for 6 minutes to obtain ultra-high performance concrete based on waste bamboo original fiber toughening and internal curing.

[0047] Example 2

[0048] This example shows the performance test results of the ultra-high performance concrete based on waste bamboo original fiber toughening and internal curing prepared in Example 1 after 3d, 7d, and 28d standard curing. The size of the test piece is 40mm×40mm×160mm, and the compressive strength and flexural strength are tested in accordance with GB / T 17671-2021. The shrinkage rate test is carried out in accordance with the relevant regulations of GB / T 50082-2009.

[0049] The specific performance test results of the ultra-high performance concrete based on waste bamboo original fiber toughening and internal curing described in the present invention are shown in Table 2. Table 2

[0050]

[0051] Compare the mechanical properties of each coagulation period of No. 1-2 to No. 1-6 with No. 1-1. The incorporation of yellow bamboo fiber improves the flexural strength of the test piece to varying degrees. In addition, through pre-water absorption treatment of the yellow bamboo fiber, its compressive strength at different coagulation periods shows significant growth (No. 1-3 to No. 1-6). The increase in early strength may be due to the reduction of the overall water-binder ratio of the cementitious material by the water stored in the yellow bamboo fiber. The increase in later strength is due to the internal curing effect of the yellow bamboo fiber, which promotes the further hydration of the cementitious material in the later stage of curing. 1-7 and 1-8 show relatively poor mechanical properties, probably because the excessive content of yellow bamboo fiber leads to internal agglomeration, which not only fails to play the toughening role of yellow bamboo fiber but also increases the number of defects inside the system. Therefore, the improvement of early strength is limited. However, it is worth noting that with the progress of curing, the water in the yellow bamboo fiber is slowly released, inducing the hydration of the cementitious material to fill the internal pores of the system. Therefore, the 28d compressive strength is still better than the control group (1-1 and 1-2). By observing the shrinkage and expansion rate of each coagulation period of the test piece, it can be found that the shrinkage of the group incorporated with yellow bamboo fiber (No. 1-2 to No. 1-8) is generally lower than that of the control group (1-1). The highest shrinkage at 28d can be reduced by 120με, and the shrinkage rate is reduced by about 20%. This means that yellow bamboo fiber has significant advantages as an internal curing agent.

[0052] AppendixFigure 1 and attached Figure 2 Both are SEM images of the fracture interface of the concrete products obtained from Nos. 1 - 6. Figure 1 The single yellow bamboo fiber is within the red square in [Figure], and the steel fiber is on its left. It can be seen that after being processed by the fiber disperser, the yellow bamboo fiber bundle has been dispersed into single yellow bamboo fibers, avoiding the low fiber utilization efficiency caused by fiber bundle agglomeration. Attached Figure 2 shows the microscopic morphology of the bonding between the yellow bamboo fiber and the matrix. The cracks in the fiber and at the bonding between the fiber and the matrix in the figure indicate that the yellow bamboo fiber absorbs a large amount of energy when the concrete product is fractured under stress, which is also the main reason for the improvement of the flexural strength of the concrete product.

[0053] The above embodiments are only examples for illustration and do not impose any limitation on the implementation manners. For those skilled in the art, any equivalent modification and substitution made to the present invention are also within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ultra-high performance concrete based on toughening and internal curing of waste bamboo fibers, characterized in that The following steps are involved: (1) Soak the bamboo fiber in water to ensure that its initial water absorption is 0.1-10g water / g bamboo fiber; (2) Cement, silica fume, fly ash, quartz sand, and water reducer are mixed, water is added and stirred until a homogeneous slurry is obtained, bamboo fiber after water absorption is added and stirred for 1-3 minutes, steel fiber is added and stirred for 5-8 minutes, and ultra-high performance concrete toughened and internally cured based on waste bamboo fiber is obtained; The composition of the ultra-high performance concrete is as follows in percentage by weight: 420-1250 parts of cement, 50-190 parts of silica fume, 130-280 parts of fly ash, 840-1650 parts of quartz sand, 0.3-20 parts of bamboo fiber, 135-352 parts of steel fiber, 8-32 parts of water reducer, 183-324 parts of water; The bamboo fibers are recycled from discarded mattresses, sofa fillings, car interiors or home decoration panels; the bamboo fibers are processed by a fiber disintegrator to disperse the agglomerated bamboo fiber bundles into single bamboo fibers with a length of 6-15 mm and a diameter of 5-100 μm; The steel fiber is a long straight steel fiber with a circular cross section, a length of 10-25 mm, a diameter of 0.08-0.27 mm, and a tensile strength of ≥2500 MPa.

2. The method for preparing ultra-high performance concrete based on waste bamboo fiber toughening and internal curing as claimed in claim 1, characterized in that The cement is silicate cement or ordinary silicate cement with a strength grade of 42.5 or above.

3. The method for preparing ultra-high performance concrete based on toughening and internal curing of waste bamboo fibers as claimed in claim 1, characterized in that The specific surface area of the silica fume is ≥12500m 2 / kg, SiO2 content in silica fume ≥93%.

4. The method for preparing ultra-high performance concrete based on waste bamboo fiber toughening and internal curing as claimed in claim 1, characterized in that The fly ash specific surface area is ≥2000m 2 / kg, of which SiO2 content is ≥43%, Al2O3 content is ≥21%.

5. The method for preparing ultra-high performance concrete based on toughening and internal curing of waste bamboo fibers as claimed in claim 1, characterized in that The quartz sand particle size is 30-80 meshes.

6. The method for preparing ultra-high performance concrete based on toughening and internal curing of waste bamboo fibers as claimed in claim 1, characterized in that The water reducer is a naphthalene-based or polycarboxylic acid-based high-efficiency water reducer.

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